MIIKA KOIVUNEN

DETERMINATION OF THE MECHANICAL DURABILITY OF

ORGANIC COIL COATINGS

Master of Science Thesis

Examiners: Asst. Prof Essi Sarlin & Project Manager Kati Valtonen Examiner and topic approved by the Faculty Council of Faculty of Engineering Sciences on 28th February 2018

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ABSTRACT

Miika Koivunen: DETERMINATION OF THE MECHANICAL DURABILITY OF ORGANIC COIL COATINGS Tampere University of technology Master of Science Thesis, 104 pages, 24 Appendix pages August 2018 Master’s Degree Program in Materials Science Major: Polymeric Materials Examiners: Asst. Prof. Essi Sarlin and Project Manager Kati Valtonen Keywords: coil coating, coil coated steel, organic coatings, mechanical durability, wear resistance, wear, scratch resistance, scratch hardness, scratching, friction.

The goal of the thesis was to measure mechanical durability of a variety of organic

coatings. The present measurement methods used at SSAB, Pencil Hardness and

resistance to scratching, were found insufficient and alternative measurement methods

were studied. Multiple standardized and a few novel scratch and wear methods were

implemented on the coatings. The measurement methods were chosen or modified to fit

measuring the properties of two layered organic coating.

The chosen coatings for the thesis represent eight different coating types and from each

coating type multiple colours were studied to decrease the scatter on results. The effect

of surface structure on durability was studied between smooth, wrinkled and particle

structured coatings. The surface structure is partially linked on gloss level of the coating

and different gloss levels were also compared. Effects of the coating colour were also

studied, because in different colours the amount and quality of pigments differs. The

coatings were chosen on the bases, that the same colours were represented in most of

the coatings and so, that from the same coating type low gloss and high gloss were

available.

With the test methods mostly critical levels were measured. The critical levels are when

the first scratch is visible (Lc1), when the coating is scratched down to primer (Lc2),

when the first pinholes through both organic coating layers are visible (Lc3) and when

the whole two layered coating is worn off (Lc4). In wear testing, also visual changes in

the coating were evaluated in scale of 0 to 5 and volume loss of coating was estimated

from mass changes during the test. In many cases the critical levels were only

applicable measure of wear and the evaluation was mainly done visually.

Twelve different scratching tests were implemented in the thesis. Three of the methods

were measuring Lc1 level, two of the methods measured Lc2 level, five of the methods

measured Lc3 level and one method measured level Lc4. In addition, scratch hardness

was measured from the width of the scratch implemented by Bruker Tribolab UMT-3

device. In principle, all four Lc levels are possible to measure from a progressive load

scratch and it was studied among multiple constant load scratches.

Six different wear devices were used in the thesis and sixteen different methods of

determining the durability were studied. With one device, it was typically possible to

estimate the amount of wear after certain amount of time and study the amount of time

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needed to wear the samples until certain Lc level. The wear tests were chosen to make it

possible to study abrasive wear, fatigue wear, adhesive wear and erosive wear

separately. Also, a novel method especially designed for measuring the wear event

inside coils was studied.

To help the comparison of test results and test methods, all the results were scaled

mathematically in the range of 0 to 5. With the uniform scale, it was possible to

determine average results for the durability of the coatings and estimate systematic and

statistical differences between methods and average results. Correlation coefficient

between measurement methods and average results were used to help the comparison of

different test methods. The average result from the coatings was estimated to describe

the mechanical durability of coatings so well, that the statistical analysis could be used

for ranking the measurement methods as well.

In the tests, polyurethane based coatings were most durable, polyvinylidene based

coatings were slightly less durable and polyester based coatings had the lowest

durability. The gloss level was noticed to influence on the durability of the coatings,

favouring higher gloss products. Also, the colour of the coating was noted to have some

influence on the durability of the coating, and black coloured coatings were more

durable in most coating types. The cause for the difference might have been either the

amount or the quality of the pigments. In black coatings, there is less pigment by the

volume and thus there is more binder to be worn. Also, the used pigment, carbon black,

may improve wear properties of polymer-based materials. The thickness of the coatings

had some impact on the mechanical durability of the coatings, but for example thin low

gloss polyurethane coatings were approximately on the same level of durability as

thicker polyester based coatings.

It was determined, that the best way to estimate mechanical durability of organic

coatings is to measure separately scratch resistance and wear resistance of the coating.

The scratch measurement device must have enough accuracy in the adjustment of load,

stabile load and stable scratching angle. Examples of suitable scratching devices are

Braive Instrument Multifunction Scratcher, Bruker UMT-3 Tribolab and Erichsen

Scratch Hardness tester 413. In wear testing, multiple different test methods can be used

and at least the tested abrasive and erosive methods gave rather uniform results. In

determination of mechanical wear resistance of coatings, for example Bruker UMT

Tribolab rotary wear, Taber Rotary Platform Abrasion Tester and Solid Particle Erosion

tester were found to be suitable.

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TIIVISTELMÄ

Miika Koivunen: Orgaanisten maalipinnoitteiden mekaanisen kestävyyden määrittäminen. Tampereen teknillinen yliopisto Diplomityö, 104 sivua, 24 liitesivua Elokuu 2018 Materiaalitekniikan diplomi-insinöörin tutkinto-ohjelma Pääaine: Polymeerimateriaalit Tarkastajat: Asst. Prof. Essi Sarlin ja Project Manager Kati Valtonen Avainsanat: Orgaaniset pinnoitteet, mekaaninen kestävyys, kulumiskestävyys, kuluminen, naarmuuntumiskestävyys, kynäkovuus, naarmu, kitka.

Diplomityön tavoitteena oli mitata orgaanisten pinnoitteiden mekaanista naarmutus- ja

kulumiskestävyyttä. Nykyisin SSAB:lla käytössä olevat menetelmät lyijykynäkovuus ja

neulanaarmutus Braive Instruments Multifunction scratcherilla on koettu

riittämättömiksi, joten mittauksiin valittiin useita standardoituja ja standardoimattomia

naarmutus- ja kulutustestilaitteilla. Mittausmenetelmät pyrittiin sovittamaan sopiviksi

kaksikerroksisen maalipinnoitteen tutkimiselle.

Mitatut pinnoitteet edustavat 8 eri pinnoitetyyppiä ja jokaisesta pinnoitetyypistä valittiin

useampi väri hajonnan selvittämiseksi. Samalla oli tarkoitus tutkia vaikuttaako

pinnoitteen erilainen strukturointi tai pigmenttien määrä sekä laatu, ja siten myös väri

pinnoitteiden ominaisuuksiin. Pinnoitetyypit oli valittu niin, että samankaltaisesta

pinnoitteesta oli vaihtoehtona sekä korkea- että matalakiiltoinen vaihtoehto, jotta

voitaisiin vertailla vaikuttaako pinnoitteen kiiltotaso mekaaniseen kestävyyteen.

Testimenetelmillä mitattiin pääasiassa kriittisiä arvoja, jonka jälkeen ensimmäinen

visuaalinen naarmu syntyy (Lc1), pinnoite naarmuuntuu läpi ensimmäisen

pinnoitekerroksen (Lc2), koko kaksikerrospinnoite läpäistään ensimmäisen kerran (Lc3)

tai kun naarmuuntuminen läpi koko pinnoitteen muuttuu vakavaksi (Lc4).

Kulutustestauksissa arvioitiin myös monessa tapauksessa visuaalista muutosta asteikolla

0-5 tai massahäviötä testin aikana. Monessa tapauksessa kriittisten arvojen

määrittäminen oli kuitenkin helpompi vaihtoehto. Mittaustulosten evaluointi tapahtui

pääosin silmämääräisesti kaikissa mittauksissa.

Naarmutustestejä suoritettiin yhteensä 12 kappaletta, joista kolme oli tarkoitettu

mittaamaan Lc1 tasoa, kaksi Lc2 tasoa, yksi Lc4 tasoa ja viisi Lc3 tasoa. Lisäksi

naarmutuskovuutta mitattiin syntyneen naarmun leveydestä UMT-3 Tribolab laitteella.

Periaatteellisesti nousevan voiman testissä pystyisi mittaamaan kaikkia Lc tasoja yhdellä

mittauksella, mutta testiparametrit eivät olleet tähän täysin sopivat.

Kulutustestauksia suoritettiin yhteensä 16 kappaletta kuudella eri laitteella. Samalla

laitteella usein arvioitiin kulumista visuaalisesti tietyssä pisteessä, massahäviötä tietyssä

pisteessä tai tiettyyn Lc tasoon vaadittavaa kulutuksen määrää. Kulutustestit oli valittu

niin, että sekä adhesiivinen, abrasiivinen, väsymis- ja eroosiokuluminen saataisiin

mitattua. Lisäksi kulumista mitattiin erityisesti kelapinnoitetulle materiaalille

suunnitellulla menetelmällä, jossa simuloitiin kelalla tapahtuvaa kulumista.

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Erilaisista mittauksista saadut tulokset skaalattiin asteikolle 0-5 erilaisilla

matemaattisilla operaattoreilla vertailun helpottamiseksi. Yhteisen asteikon avulla

saatiin määriteltyä tuloksille keskiarvo, johon tuloksia pystyi vertaamaan ja laskemaan

systemaattisen sekä satunnaisen eroavaisuuden. Tuloksien analysoinnin apuna käytettiin

myös testimenetelmien korrelaatiokertoimia toistensa, sekä kaikkien tulosten

keskiarvon kanssa. Keskiarvotulosten oletettiin kuvaavan pinnoitteiden todellista

mekaanista kestävyyttä niin hyvin, että tilastollisten analyysien avulla voidaan arvioida

myös sopiva mittausmenetelmä orgaanisen pinnoitteen mekaanisen kestävyyden

mittaamiseksi.

Testeissä PUR -pohjaiset pinnoitteet pärjäsivät parhaiten, PVDF -pohjaiset pinnoitteet

toisiksi parhaiten ja PES -pohjaiset pinnoitteet heikoiten. Kiiltotason havaittiin

vaikuttavan melko voimakkaasti pinnoitteen mekaaniseen kestävyyteen suosien

korkeampikiiltoisia pinnoitteita. Myös värin havaittiin vaikuttavan tuloksiin ja tulokset

mustilla pinnoitteilla olivat parempia kuin muilla mitatuilla väreillä. Syynä eri värien

suorituskykyjen eroavaisuudessa voi olla pigmenttien määrä tai laatu, sillä mustassa

värissä pigmenttiä on vähiten ja toisaalta hiilimustan on myös todettu vaikuttavan

materiaalien kulumisominaisuuksiin. Pinnoitteen paksuus vaikutti vain vähän

pinnoitteen mekaanisen kestävyyteen ja esimerkiksi ohuet matalakiiltoiset PUR -

pohjaiset pinnoitteet ovat samalla tasolla mekaanisessa kestävyydessä paksujen PES -

pohjaisten pinnoitteiden kanssa.

Parhaiten orgaanisten pinnoitteiden mekaanisen kestävyyttä saa arvioitua, kun mittaa

erikseen naarmunkestävyyttä ja kulutuskestävyyttä. Naarmutuslaitteeksi kelpaavat

tarpeeksi säätötarkkuutta omaavat naarmutusmenetelmät, joissa naarmutuskulma ja

voima ovat tasaiset. Esimerkkejä tällaisista laitteista ovat Braive Instrumentsin

Multifunction Scratcher, Erichsen Scratch Hardness tester 413 sekä Bruker UMT-3

Tribolab. Kulutustestaukseen sopii useanlaiset laitteet ja kulumistyypillä ei ole erityisen

paljon väliä, sillä ainakin abrasiiviset ja eroosiokulutuslaitteet antavat hyvin

samankaltaisia tuloksia. Esimerkkejä orgaanisen pinnoitteen mekaanisen kestävyyden

määrittämiseen soveltuvista kulutuslaitteistoista ovat Bruker UMT-3 Tribolab rotary

wear, Taber Rotary Platform Abrasion tester sekä Solid particle erosion tester -laitteet.

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PREFACE

The thesis was written in collaboration with Product development team of coil coatings

at SSAB Hämeenlinna. Besides support with the thesis, the team taught me a lot about

organic coatings in general and it is a pleasure to continue working with the team in

future as well.

Special gratitude for guiding me with the thesis goes to my supervisors Antti Markkula,

Essi Sarlin and Kati Valtonen. Antti as my supervisor at SSAB had planned the base of

the thesis well and he gave me good sparring with the problems that occurred. Essi and

Kati were a great help when guiding with theories and practical writing work and

without them the thesis would have been less scientific.

The measurements were done in collaboration with multiple partners. Thank you for the

friendly people in R&D laboratory of SSAB Hämeenlinna, HAMK, TUT, Celego,

YTM-Industrials, PTE Coatings and Bruker for helping with the measurements. Thank

you especially for Dr. Udo Volz for experienced advices on testing the coatings.

In my opinion, thesis and studies are not the most important part of being in University

and learning through hobbies and friends is even more important. The student life that

TUT offered me was more than I had expected and I enjoyed every moment I spent

there. Thank you especially NMKSV, YKI, MIK and TTYY for the magnificent time

and I hope I will be in contact with the people I met for the rest of my life.

Without my family I would have never got this far. Thank you for my mother and father

for raising me as I am and encouraging me to study since primary school. During the

thesis work, the greatest help has come from Vilma in a form of well-timed catering and

continuous support.

Thank you.

Tampere, 31.07.2018

Miika Koivunen

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CONTENTS

1. INTRODUCTION .................................................................................................... 1

2. ORGANIC COATINGS ON STEEL ....................................................................... 3

2.1 Typical organic coatings on coil coated steel................................................. 4

2.1.1 Binder systems ................................................................................. 5

2.1.2 Pigments and other compounds ....................................................... 6

3. DURABILITY OF ORGANIC COATINGS AGAINST MECHANICAL WEAR . 8

3.1 Determination of Wear ................................................................................... 8

3.2 Properties of organic coatings effecting on mechanical durability .............. 12

3.2.1 Binder driven wear properties ........................................................ 12

3.2.2 Particle driven wear properties ...................................................... 14

3.2.3 Environment driven wear properties .............................................. 15

3.3 Typical mechanical wear sources on coil coated steel ................................. 16

4. MATERIALS AND TEST METHODS ................................................................. 20

4.1 Tested coatings ............................................................................................. 20

4.2 Test methods ................................................................................................ 23

4.3 Evaluation methods for scratches and abraded area..................................... 25

5. TESTING OF THE COATINGS ............................................................................ 28

5.1 Hardness pencil test ...................................................................................... 29

5.2 Braive Instruments Multifunction Scratcher ................................................ 30

5.2.1 “Needle” scratch ............................................................................ 32

5.2.2 Coin scratch.................................................................................... 33

5.3 Elcometer 3092 Sclerometer Hardness Tester ............................................. 36

5.4 Erichsen scratch hardness tester 413 ............................................................ 39

5.5 UMT-3 Tribolab ........................................................................................... 44

5.5.1 Progressive load scratch ................................................................. 45

5.5.2 Constant load scratch ..................................................................... 48

5.5.3 Rotating Ball-on-disk wear ............................................................ 51

5.6 Taber Rotary Platform Abrasion Tester ....................................................... 56

5.7 Erosive wear tests ......................................................................................... 60

5.7.1 Solid particle erosion tester ............................................................ 60

5.7.2 High speed slurry pot ..................................................................... 64

5.8 Coil damage measurement device ................................................................ 67

5.9 Flat-to-flat friction ........................................................................................ 70

5.10 Sledge friction .............................................................................................. 73

5.11 Abrasion testing machine at SSAB .............................................................. 76

5.12 Other possible test methods.......................................................................... 77

6. ANALYSIS AND COMPARISON OF THE TEST RESULTS ............................ 78

6.1 Grading of coatings’ performance................................................................ 78

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6.2 Calculating statistical parameters to help comparison of test methods and

test results .............................................................................................................. 83

6.3 Comparison of test methods and results ....................................................... 87

6.4 Experience based grading of the test methods ............................................. 90

6.5 Defining weighting parameters .................................................................... 91

6.6 Determining the mechanical durability of the coatings ............................... 93

7. OUTCOME OF THE THESIS AND FURTHER INVESTIGATION ................... 96

7.1 Recommended methods for measuring mechanical durability .................... 98

7.2 Methods not suitable for measuring mechanical durability of coatings ....... 99

8. POSSIBLE ERROR SOURCES ........................................................................... 101

9. CONCLUSIONS ................................................................................................... 103

REFERENCES .............................................................................................................. 105

APPENDICES:

APPENDIX 1: Measurement parameters of the tests

APPENDIX 2: Results of Hardness pencil test

APPENDIX 3: Results with Braive Instrument Multifunction Scratcher

APPENDIX 4: Results with Elcometer 3092 Sclerometer Hardness Tester

APPENDIX 5: Results with Erichsen Scratch Hardness Tester 413

APPENDIX 6: Results with Bruker UMT Tribolab

APPENDIX 7: Results from Taber Rotary Platform Abrasion Tester

APPENDIX 8: Results from Solid particle erosion test

APPENDIX 9: Results from Slurry pot erosion test

APPENDIX 10: Results from Coil damage measurement device measurements

APPENDIX 11: Results from Flat-to-flat friction

APPENDIX 12: Results from Sledge friction test

APPENDIX 13: Visual presentation of all test results on each coating and coating type

APPENDIX 14: Correlation coefficients between the test methods

APPENDIX 15: Experience based grading of the tests

APPENDIX 16: Weighted average grades for each colour

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LIST OF SYMBOLS AND ABBREVIATIONS

B Black

G Grey

HAMK Hämeenlinna University of Applied Sciences

hBN Hexagonal boron nitride

M Matt

PES Polyester

PMMA Poly (methyl methacrylate)

PTFE Polytetrafluoroethylene

PUR Polyurethane

PVC Polyvinyl chloride

PVDF Polyvinylidene fluoride

R Red

TiO2 Titanium dioxide

TUT Tampere University of Technology

UV Ultraviolet light

W White

a result from a measurement for a single coating

AW Weighted average result for a coating, measure of mechanical

durability in the thesis

b volume loss of the coating in a single test

C Constant determined separately for each test method

CW Weighting parameter of the test method

Es Statistical error determined in chapter 6.2

GU Grade of usability of test method

GS Grade of suitability of test method to measure desired properties

HSp Scratch hardness value determined from the depth or width of

scratch

Lc1 Critical level or load when scratch or wear is barely visible

Lc2 Critical level or load when first coating layer is pierced

Lc3 Critical level or load when both coating layers are barely pierced

Lc4 Critical level or load when the scratch or wear is severely pierced

the whole coating

Lc Critical load or level of wear

P Load on calculating of HSp

ρX, Y Correlation coefficient of X and Y

w width

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1. INTRODUCTION

Using steel sheets is an easy way to cover large surfaces on construction applications,

but without any protection commonly used low carbon type of steel corrodes and rusts

easily. Coating the steel with zinc by hot dip galvanizing improves the corrosion

resistance by electrochemical means, but applying an organic coating prevents water to

come in contact with the steel or metal coating. Because of this the organic coating is

efficient way to protect steel from corrosion, but it is effective only when the coating is

uniform - even small scratches through the coating may result in corrosion of the steel.

Other main reason for using organic coatings is the ease of providing different colours

on the coating. Organic coatings can be considered multifunctional coatings which

improve the visual and corrosive properties of the steel.

SSAB is a global steel company with a base on Nordic countries and the US. SSAB has

steel production facilities in Finland, Sweden and North America, with a total of almost

15000 employees in over 50 countries. The annual production capacity is around 8.8

million metric tons of steel. SSAB is divided into five different sections with different

market segments: SSAB Special Steels, SSAB Europe, SSAB Americas, Tibnor and

Ruukki Construction. The company is listed on the Nasdaq OMX Stockholm and

Nasdaq OMX Helsinki. Coil coating lines SSAB has in Finland and in Sweden. [1]

It is common to coat the steel already on coil and form the final product afterwards. The

coating process is generally called coil coating and the product is called coil coated

steel. The forming of the products after coating means that the coating has to withstand

the possible scratch and wear sources from transportation of the coils, processing to end

product, transportation of sheet and profiles, installation and the end use. After

installation, the products are promised a warranty up to 25 years, depending on the

application, and the endurance is limited if the coating is damaged. Defected products

should never be installed without repairing the damage, but it is common that, for

example, smaller scratches are left unnoticed during installation work. Even if the

scratch is noticed and repainted it is not always an effective solution that provides full

life span for the product. [2]

Mechanical durability of the organic coatings has been a large concern for coil coated

products for a long time, and in this thesis the focus is on wear and scratching of

coatings. The difficulty in understanding scratch and wear properties of a coating is that

the scratch and wear resistance are not single material properties but a combination of

many different factors. The coating is so thin that the adhesion layers and also the core

material most probably influence on the scratch resistance properties. Also, material

2

properties of the coating like hardness and elasticity are important for the wear

resistance but the properties of the wear counterpart are known to have a high influence

at wear as well [3]. Typical paints used in coil coating contain fillers and pigments and

these embedded particles make the coating a composite material. In a composite

material, the particles partially bear the load and when getting detached the particles can

inflict on the wear properties. Because of all this, the durability properties must be

measured from a full coating system, not just for the polymers involved in the coating.

Main goal of the thesis is to measure the mechanical durability of coil coatings

produced at SSAB. The current methods, pencil hardness and needle scratch, used at the

company are insufficient to describe the complex scratch and wear resistance properties

of the product and thus a variety of available tests are chosen for the thesis. Some of the

test methods are acknowledged on coil coating industry by standards included in EN

13523 [4], but to increase the variety of tests also novel methods are inducted for

measuring properties of coil coatings, including Bruker UMT-3 Tribolab and Solid

particle erosion tester. The damage inflicted in the testing is evaluated and compared to

real damage typically occurred in the use of coil coating. After evaluation of damages

the measurement methods are ranked based on their suitability for testing the wanted

properties and the coatings are graded with numerical values of total performance. The

tests are conducted at different temperatures and conditions that coil coated steel could

face in outdoor applications, but the influence of chemical or thermal effects is not

being focused on the study. Test methods, where the core material is formed are

excluded or in minor role in the thesis.

When fulfilling the goals, the thesis will give extensive background information of

different types of scratch and wear mechanisms for organic coil coatings. Based on the

thesis, SSAB aims to provide the market with better understanding of mechanical

durability of coil coated steel and how the durability could be measured. It is also

possible that based on the thesis a new measurement method is implemented at SSAB

for determination of the mechanical durability of coil coatings.

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2. ORGANIC COATINGS ON STEEL

Coil coating refers to a method in which flat steel products are continuously coated with

an organic coating [5]. Coil coated steels are used in multiple different applications, for

example in construction industry at indoor and outdoor applications, automotive and

transport industries, cabinets for electronic goods and furniture. Coil coated steel can be

bent, roll formed or deep drawn without damaging the coating significantly. In this

chapter a short introduction of the coating process of steel, use of coil coated products

and the chemical and structural basis of paints used in coil coating is presented. [6]

The main benefits for using coil coated steel instead of painting the products in-situ are

cost of the method, stability of quality, speed of coating, repeatability, precision and

environmental issues. In SSAB’s coil coating line the speeds can exceed 100 m∙min-1

providing thousands of square meters of painted material per hour with a uniform coat.

If the material was painted after forming, it would be very slow and have probably

inaccurate painting coverage on demanding components. In coil coating line the

parameters and atmosphere can be kept constant, while for example painting roofing in

situ is weather dependent and curing of the paint can be time consuming. In coil coating

the volatile solvents can be gathered and no harmful substances are released in the

nature. These solvents can also be used as fuel for the curing ovens and at SSAB

Hämeenlinna for example the curing ovens run mostly without excess energy sources.

[6]

At SSAB Hämeenlinna the coil coated steel is almost always hot dip galvanized before

coating. The galvanization protects the steel against corrosion in cut edges of sheet and

in damaged areas of organic coating. Non-galvanized steel is used only in indoor

applications and some special products. Laminating the steel strips with prefabricated

polymer films is also possible, but most of the products are coated with wet paint using

roll coating. The coating line of Hämeenlinna is shown in figure 1.

4

Figure 1. Coil coating line of SSAB Hämeenlinna [7]

Coil coating process includes cleaning of the steel strip in the beginning of the line,

chemical pre-treatment and the application of the paint or film. Usually the coating

consists of a primer layer and one or more layers of top coating paint. After applying

each layer of paint, the strip goes to an oven where the paint dries and cures forming the

coating layer. Often the two sides of the steel strip are coated with different paints

because only other side is exposed to UV light. The weathering or visual properties of

backing coat does not need to be as good as in topcoat, but in some of the applications

backing coat needs special properties like excellent adhesion on glue [2].

Sometimes the coated steel is covered with temporary strippable film to avoid

scratching and abrasion during transportation and processing to end product [5]. The

temporary protective film is removed before the end use and it turns into an expensive

waste for the end customer.

2.1 Typical organic coatings on coil coated steel

Organic coatings consist of binder, solvents and fillers. Binder is the polymeric part

which forms the layer, solvents makes the binder applicable to a surface and fillers are

colour pigments or other organic and inorganic particles. [8]

Typical use for coil coated steel is construction materials, like steel roofs and claddings,

and indoor applications like domestic heaters and lighting covers. Many of the

applications urge excellent UV stability, chemical resistance, good formability and

resistance to wear [2]. UV light and imposing to chemicals may reduce the physical

properties of the product and also effect on the visual properties. Mechanical properties

depend highly on the polymer grade, but with additives and fillers different grades can

often be modified to fulfil the required properties.

The coating system can be based either on thermosetting resin or thermoplastic resin.

Thermosetting resin reacts during curing process and thermoplastic resin can be molten

or composed with solvent to form a uniform coating. In the curing process the solvent

either evaporates or reacts with the binder and becomes part of the thermosetting coat.

5

Typical polymers used in coil coated products for outdoor use are polyesters (PES),

polyurethanes (PUR), polyvinylidene fluoride (PVDF) and plasticised polyvinyl

chloride (PVC). Typically backing coats are not exposed to UV light and epoxy or

lower grade PES based coatings can be used. If both faces are left visible, higher quality

coatings are typically used at both sides. [2]

2.1.1 Binder systems

Polyester coatings are the most commonly used in coil coating because of relatively low

cost and good availability of polyester resins. PES is a generic abbreviation for a large

group of different kind of polyester resins and the properties can vary a lot with small

changes in the polymer structure [8]. PES is formed in condensation reaction of di- or

trifunctional alcohols and carboxylic acids, and later chemically reacted with melamine

as cross-linker in coil coating process. Polyesters have typically excellent adhesion to

metals [2].

PUR coatings are a special application of PES. In PUR coatings the crosslinking agent

is partially or wholly changed into isocyanate, which reacts by forming urethane bonds.

In many cases polyurethane binders consist of more durable aliphatic or cycloaliphatic

polyester polyol resin and thus they have typically higher UV resistance than

conventional aromatic polyester resins [2]. The wear properties of PUR based coatings

have also been recorded to be better than with PES. On coil coating applications

polyurethane is mostly applied as a heat curable “one-package” solution. In this case,

the polyurethane is blocked and when exposed to heat the isocyanate groups become

active to crosslink the resin. [9]

PVDF is a thermoplastic polymer, which is difficult to apply directly as a coating. It can

be fused with another thermoplastic, poly(methyl methacrylate) (PMMA), to ease the

processing. The PVDF based coatings have a low surface energy, which provides

excellent resistance to dirt. The coatings possess an ability to uphold its visual

appearance even in extreme conditions and are well resistant to chemicals. The fused

PMMA has a good weather resistance due to its resistance of hydrolysis and the lack of

absorption of ultraviolet light [10]. PVDF and PMMA together form a thermoplastic

coating, thus temperature is estimated to play larger role on the properties of the

coating.

All the backing coats used in the thesis are epoxy based. Backing coats are not focused

on the study, but they are used as a contact surface in one of the tests. Epoxy coatings

are designed for the less critical surfaces like backing coats due to its typically lower

UV and scratch resistance. In coil coating, mostly heat-cured epoxy resin coatings are

used [2].

6

2.1.2 Pigments and other compounds

Coating always is much more than the polymer material – it includes fillers, pigments,

and special additives. The additives are used to improve wettability on painting, UV

resistance and some rheological properties of wet paint. Some of the properties can be

extracted from the polymer chemistry but most of the properties are a sum of several

factors. The paints can be thought as a nano or micro composite of a kind due to having

particles inside polymeric matrix. The mechanical properties of different coatings most

likely depend on the properties and volume of pigments as well, because for example in

white coloured coatings the coating consists 60-70% of pigments by the volume and in

black colours only about 20% [2]. Also, the quality of pigments of one colour can have

significant differences depending on the manufacturing method, chemical structure,

shape et cetera [8]. In this thesis, different colours are considered in each binder system

to study if the pigments have a role in the wear properties of the coatings.

At SSAB, all the regular colour pigments used are inorganic compounds. Inorganic

pigments are hard solids with size varying between 0.02 and 5.0 µm. The shape of the

pigments can vary from needle like shape to flat discs and round spheres. Most used

pigments are titanium dioxide TiO2 for white colour, carbon black for black colour and

different ferrous oxides for red, black and brown colours. Blue, green, purple, orange

and yellow inorganic pigments exist, but organic pigments have to be used for more

intensive and brighter colours. Organic pigments are typically more sensitive to UV

radiation and ageing than inorganic pigments and thus they are only used in special

occasions at outdoor applications. No matter what the colour is, white or black pigments

are almost always present. Some pigments are used also as extenders for the paint to

obtain certain mechanical properties or to lower the price of the paint. [8]

Fillers can influence on the wear properties and friction of the material by modifying the

bulk properties or the interface of the polymer system [11]. Typically, multiple sized

fillers are used but the largest can be even from 20 µm to 30 µm in diameter. The fillers

bear part of the load and their functionality is based on modifying the stress distribution

of matrix. On the interface, the particles may adhere to the matrix firmly and modify the

surface properties or wear off and act as abrading or lubricating particles. Filler particles

on or near the surface are used to reduce the gloss or modify appearance of the coating,

but the rise of surface roughness also may influence on the mechanical properties. The

surface roughness and gloss level can be also modified by wrinkling the surface

chemically [2]. In the thesis term ‘particles’ is used when effects of colour pigments and

fillers are discussed in general.

The effect of additives can also be significant but most of the additives hold business

confidentialities and they cannot be considered in the thesis. The additives and used

amounts can also vary a lot between colours and paint suppliers, and thus their effect is

difficult to be taken into account. It also has to be taken into account that the paint

7

supplier typically only have certain limits for the mechanical, visual and aging

properties but they have multiple ways to reach the goals. This means that the effects of

pigments and fillers can be balanced with small modifications in the paint chemistry.

8

3. DURABILITY OF ORGANIC COATINGS

AGAINST MECHANICAL WEAR

The core material properties such as hardness, elasticity and strength, not to forget the

different core material thicknesses, influence on the properties of the coating [3]. The

coating consists of solvent, binder and multiple different fillers such as colour pigments.

The binder is the key element in the coating, which is being worn, and the material

properties of this polymer like strength, strain at brake, toughness and elasticity

determine the possibility to groove or detach material in stress [12]. Solvent is usually

evaporated during the painting process and should not influence on the properties of the

coating, but in many cases residues of solvent is left on the dried coating and usually

decrease the mechanical properties of the system. The shape, size, hardness, elasticity,

adhesion to binder and distribution of the fillers are all in key role to determine whether

the fillers increase or decrease the wear resistance of the system.

Wear as a phenomenon is discussed in this chapter. The wear is not a single material

property and wear can occur in multiple different ways and even in more different

reasons [3]. The material properties influencing on the wear can be divided to be driven

by binder or filler and environmental conditions of wear event may increase or decrease

the amount of wear. The material properties and environmental properties that influence

on the wear are studied and typical wear sources are represented at the end of the

chapter.

3.1 Determination of Wear

Wear is defined as the damage to a solid surface due to relative motion between a

surface and a contacting material or materials. Defining the wear types varies depending

on the source. A modern approach for definition of wear is given by Varenberg [13],

who divides wear into two different surface states, five types of relative motion and four

mechanisms of surface disturbance. In definition of wear also standard ASTM G40 [14]

and multiple different sources are applied [3, 11, 12].

The surface states consider where the action of wear takes place. The surface states are

normal state, where self-regenerating secondary layer is removed and born again in

contact with environment, and pathological state, where deeper layers of material are

damaged and torn in multiple different ways. Relative motion types answer question

why the wear occurs, and the movement types are oscillating movement, sliding,

rolling, impact of surfaces or flow of liquids and particles. Surface disturbance is the

9

way how energy of the movement is absorbed: storage of defects, motion of defects and

generation of heat by chemical interaction or by physical interaction. [13]

Tribo-chemical wear is the only wear mechanism on the normal state. No matter of the

type of relative movement and mechanism of surface disturbance, a new surface layer is

born again by a chemical reaction. In pathological state there are 11 different wear

mechanisms shown in figure 2. [13]

Figure 2. Wear mechanisms on pathological wear determined by relative motion

and surface disturbance. [13]

The significance of each wear mechanism depends on the application. On the transfer,

forming, storing and using of coil coated products all of the relative motions may occur.

Wear by chemical interaction is not considered in this thesis and the focus is only in

mechanical interaction. Examples of typical wear on the coatings are given in chapter

3.3. All wear mechanisms presented in figure 2 are simplifications and in reality the

effects and definitions can overlap [13].

In adhesion wear the surfaces in contact adhere and may switch matter between surfaces

or detach matter from both surfaces. In abrasion, an asperity slides or rolls on the

surface pushing a groove or detaching debris by gouging. Solid particle crushing occurs

during abrasive wear. Fretting fatigue, fatigue wear and pitting are caused by alternating

stress on the surface, which leads into cracking on or under the surface and eventually

chipping it off. Fretting wear occurs when the surface is disturbed in merely vibrating

movement and it is similar with sliding wear. [3, 12, 13]

The actual wear process includes either adhesion or an asperity cutting or compressing

the material. Adhesion occurs always between surfaces in contact [3]. Adhesion itself

consists of multiple aspects including electron exchange, chemical bonding and

macromolecular diffusion. For polymer-based materials adhesion of the material to the

wear counterpart often lead into formation of transfer layers. This transfer film is

usually adhered or interlocked mechanically to either of the counterparts. [12]

10

In movement of two solid bodies, single asperities cause scratching to the worn surface.

These microscratches have different topographical shapes depending on the worn

material and they can be divided into microploughing, microcutting and microcracking.

Typically, microscratch types do not appear alone, but the most dominating one can be

distinguished from topography or with microscope. If another scratch partially overlaps

a previous scratch, the phenomenon can be called microfatigue. The interaction types in

abrasion are shown in figure 3. [3]

Figure 3. Physical interaction types under single asperities on the surface. [3]

In microploughing, the movement of a single asperity should not result any detachment

of material but only displaces the material to form a groove with side walls.

Microcutting removes material and in ideal case the volume of groove is equal to the

volume of material loss. The transition between microcutting and microploughing

depends on the material properties like friction coefficient and on the operating

conditions like the attack angle and penetration depth. Also, material properties such as

cohesion and elasticity influence on the transition between microcutting and

microploughing. [3]

Microcracking typically occurs on brittle materials. The coating itself can be brittle

enough for cracking, but more probable is that the hard fillers start to break. One other

possibility is that the adhesion between fillers and polymer matrix starts cracking and

propagates into detaching the fillers. Microcracking types are shown in figure 4. [3]

11

Figure 4. Microcracking at a) large filler, b) around fillers and c) in the matrix. [3]

Microfatigue occurs when repeating alternating load on the surface. The load can be

caused by sliding and/or rolling contact of solid or impact of solid or liquid.

Microfatigue causes wear by crack formation and flaking of material. [3]

Storage of defects typically can occur in adhesion layers between coating layers. This

leads into fatigue type of wear and the coating can be detached in an instance. The

internal layered damage might be unnoticed for a long time and is difficult to estimate.

The intensity of wear does not only depend on the type of the wear but also on the time

of being worn. Also, abrasive wear, adhesive wear and fatigue wear behave in different

manner as the wear time increases. In figure 5 wear intensities are shown as a function

of time.

Figure 5. Wear loss a) of dominant wear mechanisms and b) in general as a

function of operating time. [3]

The intensity of wear is usually linear only in case if the wear is purely induced by

motion of defects. If the energy is stored in defects during the wearing process the

intensity increases exponentially when the operating time increases, due propagation of

the defects. In case of physical interaction, such as adhesion wear, the wear intensity has

three different phases as wear loss in general. In physical interaction and at wear in

general the start phase (I) is intensive at the beginning but decreases into linear wear

state. The linear wear phase (II) lasts until the material is almost worn off and in the

third phase (III) the wear starts to increase exponentially until the material is completely

worn off. Practically the wear is always combination of multiple wear types. [3]

12

3.2 Properties of organic coatings effecting on mechanical

durability

Mechanical durability, as in scratch and wear resistance, of organic coating is a sum of

material properties. The ultimate origin for wear and friction are the same: losing energy

of relative motion by forming structural defects, storing it in elastic strains, emitting the

energy as acoustic waves, photons or electrons and transforming the energy into heat.

[13] Wave formation, sound formation and emitting of photons do not play a

remarkable role in energy loss when thinking about the wear of organic coating. Thus,

material properties that have connection to born of structural defect, elasticity and heat

absorption are of interest.

Addition of particles on the organic matrix influences on the material properties. Colour

pigments are used to obtain the colour of the coating and thus particles are always

present in coil coatings. The chemical and physical properties of the particles may

influence, for example, on the adhesion to the matrix and in this way also to the

macroscopic properties. In some occasions, the fillers improve the wear resistance and

decrease friction coefficient, but also degradation caused by fillers have been reported.

Both, the wear properties of pure polymer materials and polymer micro-composites are

studied in this chapter. [12]

3.2.1 Binder driven wear properties

Binder polymer defines a large amount of the mechanical properties and capabilities of

a coating. To cause wear to the coating, the binder has to be deformed plastically or

fillers have to be detached from it. For pure polymers tensile strength, elongation at

break, elasticity and adhesion properties are the most significant properties for

determination of the wear properties. Friction can be applied in some occasions as a

measure of wear and thus is also an important factor. [3, 12]

Friction of polymers can be divided roughly into two processes – adhesion and

deformation. The adhesion of polymer to the friction counterpart inflicts shear at the

surface junctions. Adhesion based friction is dependant to the real contact area and

shear stress required to form movement. If abrasion is present the deformation mode of

friction becomes more dominant than adhesion. In deformation driven friction the

harder counterface penetrates to the softer surface, in this case the binder polymer, and

ploughs a groove. The friction force is then dependent on the coatings yield pressure

and the area of grooved track. [12]

For polymer-based materials indentation hardness is much less significant factor in wear

behaviour and friction than for metals and ceramics. Ball indentation hardness and

coefficient of friction do not correlate well between different polymeric materials, but

depth of wear groove and coefficient of friction correlate quite well, especially with

13

thermoplastic polymers [3]. Scratch hardness describes the wear properties more

precisely because the coating can only be scratched if the stresses exceed tensile

strength of the coating [8]. Thus, the hardness of polymers should be measured as

scratch hardness instead of indentation hardness. Fillers in the binder also make the

indentation hardness very difficult due to uneven distribution of pigments and other

fillers in microscopic scale. There are multiple different ways to determine scratch

hardness of a system, but typically it is determined from the depth or width of the visual

scratch.

High crystallinity and molecular weight usually increase the hardness of a polymer. In

wear, crystallinity has shown an optimal value at certain test conditions. Also, the type

of the crystalline structure has been recorded to influence the wear properties and semi-

crystalline polymers without spherulitic structures have shown higher wear resistance.

In development of scratch resistant coatings, a balance between scratch resistance and

formability of coating must be found in terms of molecular weight. [3]

In moving contact between the counterface and coating, the polymer chains move in

relation to each other and straining may occur. Straining during contact may lead into

orientating the polymer molecules and into slight increase of strength in the direction of

sliding. This increase may improve the scratch and wear resistance temporarily, but in

case of brittle material, orientation may lead into high amount of microcracking and

premature breakage. [3]

Not only the crystallinity but the length of the polymer chain and crosslinking density

influence on the wear properties. High crosslink density typically means that the

polymer is very hard and has a very low elongation at fracture. Crosslink density is also

one of the key factors between brittle and ductile behaviour of polymer. In a study of

influence of crosslink density to scratch resistance it has been found that with PES and

PUR coatings the scratch resistance increased as crosslink density increased. However,

with epoxy coatings the correlation was shown to be the opposite in one case. [15]

Fatigue properties of polymers also effects on the wear. Under cyclic loading and heat

formation micro-cracks can be formed on the polymer surface or subsurface. Micro-

cracking can result in fatigue failure of the material. Low thermal conductivity and

viscoelastic behaviour lead into hysteresis behaviour which reinforces the damage of

cyclic stresses. The form of loading wave, frequency of load, stress ratio and molecular

weight of polymer can influence on the fatigue behaviour of polymers. [12]

In contact, polymers form a transfer film on the wear counterpart. The properties of

transfer film define if the coating can have a low wear rate or not. Tough and strongly

adhering, maybe even lubricating transfer film would reduce the wear whereas thick and

bulky transfer films tend to detach from the counterface leading to even higher wear

rates. [16]

14

3.2.2 Particle driven wear properties

The particles play also a high role in the wear properties of the coating. The size of the

pigments varies from 0.01 µm up to 5.0 µm meaning that 20% of the thickness of a

coating can be of a single pigment particle on some colours. The amount of colouring

pigments varies between 10% - 70% of volume for a good coverage, depending on the

colour [2]. Filler particles instead can be up to 30 µm of diameter, meaning that there

might be areas where only small amount of binder is on top and below the filler.

Smaller particle fillers are also used to modify the gloss level of the coating. In the

thesis term ‘particles’ is used when effects of colour pigments and fillers are discussed

in general.

The fillers and pigments may increase or decrease the wear properties depending on

each case. At the surface particles usually increase the surface roughness, but they can

be modified to act as lubricating agents. In the matrix, the particles act as load bearing

components increasing wear resistance. In common case the particles become detached

and they will become abrading or in some cases lubricating solids. [12]

The wear mechanism depends not only on the motion of surfaces but also on the

properties of surface asperities. Surface quality determines partially what wear

mechanisms are possible. [3] The relation of surface roughness on wear intensity and

wear modes on sliding is shown in figure 6.

Figure 6. Wear intensity, wear modes and wear mechanisms as a function of the

surface roughness of unlubricated sliding pairs. [3]

Dominant wear mechanism in rough surfaces is abrasive wear, and in smooth surfaces

adhesive wear or fatigue wear. Low gloss is obtained usually with a rough surface finish

obtained by adding suitable fillers or texturing the coating by chemical wrinkling. Thus,

matt coatings are most likely above the critical roughness and grooving wear is

15

dominant with any sliding pair roughness. High gloss products are typically less

structured and thus are expected to depend more on the sliding pair. Real and apparent

area at contact may vary a lot with rough coatings and even seemingly smooth coatings

and the ratio between real and apparent area of contact may be as low as 10-4

. Not only

surface roughness of the counterpart is influencing on the wear mode, but the shape of

asperities as well. Sharper asperities tend to inflict grooving wear when round asperities

favour fatigue behaviour. [3]

It is possible to modify the coatings with soft and lubricating solids to reduce their wear

and frictional heating. The filler has to be available at the interface in sufficient amount

to realize the positive effects. Often soft lubricating particles reduce the strength and

load-carrying capacity of the material so balance between reduction of friction and wear

while maintaining mechanical properties is crucial. Polytetrafluoroethylene (PTFE),

hexagonal boron nitride (hBN) and graphite particles have been in use as fillers of this

kind [17]. Carbon black, the pigment used in coatings, may have similar lubricative

nature as graphite. In development of mechanical durability of coatings, lubricating

particles could be one way to improve the properties.

In traditional composites the function of the filler material is to strengthen the polymer

matrix and improve the load-bearing properties of polymer bulk. Disadvantage of

particle fillers is the decrease in toughness that increases the wear by fatigue behaviour.

Fibrous fillers have shown improved load-bearing capacity and toughness compared to

particle fillers and they could be a way to improve wear resistance of the coatings [11].

Detached micro sized particles have been reported to groove material abrasively, and

nano sized material not. The small particles have also reduced friction by positive

rolling of wear debris on the surface. In a research of A. Abdelbary [12] with three

different micro sized fillers, the smaller the filler size was, the more effective the

reduction of friction was. It was implied in the study that with decreasing grooving wear

the transfer films were smoother, and the smoother transfer film was responsible for the

best wear resistance. With nanoparticles, the increase on wear resistance properties are

achieved with much smaller concentration than with micro sized particles but with

nanoparticles the uniform dispersion on the matrix becomes even more important. In

case of nanoscale particles, the properties can differ significantly depending on the

particle material, particle dispersion and amount of particles. [12]

3.2.3 Environment driven wear properties

Applied load, sliding speed, temperature, humidity etc. are not properties of the coating,

but their influence on wear can be high. The environmental circumstances have to be

considered when estimating the cause or intensity of wear. Many of the environmental

parameters influence on the properties of transfer film.

16

Sliding speed can influence the wear rate and friction of polymers in multiple different

ways. Sliding speed is connected to the amount of heat produced on the surface and to

transfer film stability and thickness. The overall temperature in wear tests may increase

but more interesting are localized flash temperatures. The effect is rather low in low

temperatures and sliding speed but when surface temperature of thermoplastic coating

gets near glass-transition temperature there has been noted to be a decrease at wear rate.

This localized flash temperature melts and softens the surface thermally and smooths

down the surface asperities of polymer. The overall temperature rise of polymer is small

irrespective of sliding speed, and the effect can only be seen in transfer film properties.

For thermosetting polymers, there is not yet sufficient data from localized flash

temperatures, but the impact of glass-transition is typically smaller in them. [12]

For wear and friction of polymers the applied load or the contact pressure is not

straightforward. Contact pressure is also responsible for the increase of temperature in

surfaces at contact and thus is connected to localized flash temperatures. In cyclic

loading the effect of temperature rise under pressure may increase fatigue behaviour.

The friction coefficients of thermoplastic polymers have been reported to be constant at

high loads from 10 N to 100 N but in the range of 0.02 N to 1 N the friction coefficient

increases as the load decreases. The increase at decreasing load is concluded to be

caused by transformation of plastic contact to elastic contact, where elastic deformation

stores more energy. [12]

Effects of water and humidity on the wear process can be significant. The effect can be

either positive or negative depending on the polymer and circumstance. Water reduces

coefficient of friction and works as a lubricant, but at the same time it flushes the

possible transfer film off from the counterface. Water also diffuses in the polymer and

results swelling, softening and plasticisation of polymer. The diffused water typically

reduces hardness and strength. The polymer chains forming bonds with water molecules

also reduces the attachment of polymer chains to each other and allows easier removal

of material during sliding. Water also may react chemically causing corrosion.

Typically, the main wear mechanisms under water lubricated conditions are mechanical

microploughing and abrasive wear. [12]

Intentional lubrication of surfaces in contact is a possible way to influence on the wear

of polymers. The effects of lubricants are not studied in the thesis, but they are

sometimes used in deep drawing and roll forming processes. Lubrication mainly

influences on the adhesion properties between counterfaces by decreasing the adhesion

[3].

3.3 Typical mechanical wear sources on coil coated steel

The coatings of coated steel have to withstand five different phases during their lives:

storage, transportation, processing, installation and end use. Some of the phases like

17

storage and transportation may occur several times during the manufacturing process. In

all the phases there are typical mechanical damage sources to the coating. In this

chapter, the typical damage types are discussed, and some examples of damaged areas

are evaluated. Some examples of damaged coatings are shown in figure 7.

Figure 7. Damages resulted in a) slipping at coil opening b) pressure marks at

transportation c) dragging and compression in roll forming and d) marring of

the coating because of fretting in transportation. [18]

After coating process, the product is stored and transported as a coil. Pressures inside

coils can be high because the coils typically weight between 3 and 12 tons and they

must be winded with pressure to obtain uniform coils. To cut or to start processing the

product the coil has to be opened or slit into narrower coils. If the coiling pressures are

not correct there may occur some slipping, which could cause scratches on the coating

(figure 6 a) [18]. The wear mechanism on slipping is mostly abrasive and adhesive

wear. In tight coils the pressure can decrease the surface roughness and gloss level of

the coating, but the original appearance is partially or wholly restored after a short time

from coil opening.

To prevent rolling of the coils during storing and transportation certain supporting

pallets are used. The localized pressure may leave pressure marks which typically

recover. Sometimes relative fretting movement occurs on the localized pressure areas

and actual wear can occur (figure 6 b) [18]. The possible wear is caused only by rubbing

of the front and backside coatings with each other, because typically no external

impurities are found inside coils. If the coated steel is cut into sheets before

transportation the pressures are lower but more relative movement may occur. Adhesive

wear can take place between top coat and backing coat and the coating can be marked.

18

In addition of adhesive marking there typically are some abrasive scratches caused by

fillers (figure 6 c) [18].

In roll forming the coil or sheets are deformed by several rotating rolls until the desired

profile of the sheet is achieved. The rolls expose the coating to cyclic rolling load and

both adhesive wear and fatigue wear can take place. It is also possible that some

slippage occurs between the rolls and coating if the friction is not at desired level or the

core material thickness is not suitable for the design. The slipping may cause scratching

of the coating (figure 6 d) [18].

In deep drawing a metal sheet is compressed in a forming die to take the shape of the

die. During the forming process the coating is dragged among the surface of the die,

causing a typical source of adhesive wear. Lubricating oils or temporary strippable films

are often used to protect the coating from excess wear in roll forming and deep drawing

of coated sheets.

Transportation and storage of formed sheets becomes more complicated. The products

may have gathered dust and other impurities between forming processes and

transportation. Also, the more complex shapes expose the coating to wear, especially

when loading and unloading the items. Deformed coating is thinner from place to place,

partially oriented and already exposed to some wear in the forming process. Scratching

and abrasive wear can take place at formed sheets.

Installation of the formed sheets differs by the end purpose and in some cases part of the

forming process is done in-situ. One common way to install a roof is done by tinsmiths,

where the preformed standing seams are tightened after overlapping the sheets (figure 8)

[19]. In bending of the standing seams, the wear mechanism is most likely combination

of abrasive wear, fatigue wear and adhesive wear. When forming sheets in-situ there is a

higher possibility for dirt or dust to end up on top of the coatings and act as an external

abrasive. During installation work any dragging, sliding or rolling of tools etc. can be a

cause for scratching or abrading the coating. There is always a risk of mechanical

damage when any relative movement occurs on the coated surface.

19

Figure 8. Installing of roof panels with preformed standing seams and the scratch

marks occurred at tightening of the seams.[19]

During end use common wear sources derive from the nature and use based wear is

small especially in roofing. Possible impurities on roof, for example pine cones,

needles, leaves or sticks have only a small wearing effect. The stress under these

impurities is low while rolling or sliding on the roof and thus the wear as well is

minimal. The wear becomes more severe when the impurities are trapped under heavy

snow layer or if somebody walks on top of them. In rain water systems, the impurities

flow with water and the severity of wear is also larger than with plain impurities. Also,

sandstorms or more likely dust storms can cause some erosive wear and falling tree

branches may cause scratching of coating or impact wear. Almost all excess wear

during use is avoidable with proper maintenance of roof, facades and surroundings but

it is not possible to be prepared for everything.

All wear mechanisms presented on figure 2 are possible during manufacturing and use.

For example, adhesive wear can occur while transporting coils and sheet; abrasive wear

can occur when the coils are slipping, and particles scratch the surface; fatigue wear can

occur during roll forming of the coils, and erosive wear occurs in the end use. In the

thesis, it is estimated that the most important causes of wear in coil coated steel are

fatigue wear, abrasive wear, adhesive wear and erosion.

20

4. MATERIALS AND TEST METHODS

Before the measurements, all material was transported to the product development

laboratory of SSAB to be cut and stored. In many occasions the tests were conducted

outside SSAB and the samples had to be transported again to somewhere for testing.

This means that some wear may already be induced to the test samples, but in such

cases the samples were replaced with intact ones.

The test methods were chosen so, that the circumstances were similar with real life

damages or the methods were otherwise standardized for coil coatings. Scratching was

implemented with devices with different loading systems and with different shaped and

sized scratching tips. In wear studies, different wear mechanisms were of interest and

connection to real damage was more important than in scratching. Friction was studied

with two different test systems to find out whether wear and friction are connected in

coil coated steel. In choosing of the test methods there were many interesting options

besides the ones chosen to the thesis.

Because almost all of the test methods give only qualitative data the evaluation methods

are as well considered in this chapter. Most of the methods only inflict a scratch or wear

on the coating without capability to evaluate the amount of damage, so the damage must

be evaluated visually in many cases to obtain comparable results. Also, some common

other evaluation methods are discussed.

4.1 Tested coatings

Three different PUR based coating systems, four different PES based coating systems

and three different PVDF based coating system were used at the measurements. In the

thesis, if thickness or gloss level changes the coating is counted as a different coating

system. Three different colours from each binder system are tested to study the effect of

colour pigments on wear. The samples represent common gloss levels, coating

thicknesses and binder systems at coil coating systems.

It must be also noted that the coatings are designed for different applications. PVDF is

only used at façade applications, PES2 is used at façade and roof applications and the

rest are used typically for roofing only. The coating types are designed with different

features and mechanical durability is not only parameter for choosing a coating for

certain application, and for example PVDF coatings are not recommended to be used at

roofing. The coatings and their abbreviations used in the thesis are shown in table 1.

21

Table 1. Tested coatings and their coating thicknesses and densities.

Abbreviation Coating type

Coating thickness (µm)

Density of the coating (mg/cm3)

PUR1 B Black structured polyurethane coating 48 1.16

PUR1 R Red structured polyurethane coating 47 1.31

PUR1 G Grey structured polyurethane coating 53 1.26

PUR1 M B Black textured low gloss polyurethane coating 46 1.18

PUR1 M R Red textured low gloss polyurethane coating 45 1.36

PUR1 M G Grey textured low gloss polyurethane coating 48 1.32

PUR2 M B Black low gloss structured polyurethane thin coating 26 1.15

PUR2 M R Red low gloss structured polyurethane thin coating 24 1.41

PES1 B Black polyester coating 36 1.18

PES1 R Red polyester coating 35 1.38

PES1 G Grey polyester coating 35 1.35

PES1 M B Black low gloss matt polyester coating 36 1.22

PES1 M R Red low gloss matt polyester coating 36 1.40

PES2 B Black polyester thin coating 26 1.21

PES2 R Red polyester thin coating 25 1.39

PES2 W White polyester thin coating 27 1.59

PES2 M B Black textured low gloss polyester thin coating 30 1.23

PES2 M R Red textured low gloss polyester thin coating 29 1.36

PES2 M G Grey textured low gloss polyester thin coating 30 1.26

PVDF B Black polyvinylidene fluoride coating 27 1.50

PVDF S Silver polyvinylidene fluoride coating 26 1.62

PVDF W White polyvinylidene fluoride coating 26 1.83

PVDF M S Silver low gloss polyvinylidene fluoride coating 29 1.80

PVDF MAX S Silver polyvinylidene fluoride thick coating 36 1.62

In table 1, the beginning part of abbreviations describe the binder system, number

indicates the coating thickness 1 being thicker and 2 thinner, M signifies low gloss level

(matt) and letter B, R, G, S and W mean black, red, grey, silver and white, respectively.

For example, PUR2 M B means that the referred coating is low gloss (M), black (B) and

thin (2) polyurethane coating.

The results in the thesis are discussed by the coating type. The results in most of the

tables are given as average value between colours of certain coating type, and the actual

measurement values are represented only in appendices. If only the coating type without

colour is presented, for example PUR2 M, the average value between the colours is

discussed. For PVDF it must be noted that the low gloss coating and thick PVDF are

counter in the average because of lack of samples. In certain cases, all colours could not

be measured for due to limited accessibility of the method. In these cases, it is indicated

clearly that only certain values are used for calculations. Results between colours may

22

vary a lot and because of this also the deviation between colours is presented with the

average values. The comparison between colours is done separately.

All studied PUR products are structured polyurethane coatings. The structure particles

are added to improve durability in the forming process. PUR1 is a high gloss coating

and PUR1 M is chemically wrinkled low gloss coating and the low gloss of PUR2 M is

obtained with additional structuring particles. PUR2 M is also thinner than PUR1 and

PUR1 M coatings. Structuring particles and good properties of PUR give reason to

expect that properties of PUR will be good even in thinner PUR2 M coating. Due to

very high surface roughness PUR1 M may have lower mechanical durability than high

gloss coatings but is still expected to exceed other low gloss products in performance.

PES based coatings differ between PES1 and PES2 products. PES1 and PES1 M are

slightly better grade of PES in overall performance than PES2 and PES2 M. PES1 and

PES1 M coatings are also coated with higher coating thicknesses and they have

structuring particles. PES1 M is also structured by organic particles to obtain lower

gloss. PES2 instead is smooth and PES2 M chemically wrinkled and both are free from

structural particles. Even that wear is expected to correlate highly on surface roughness

PES2 is expected to be poor in the durability because of its binder-based properties.

PES2 M has high surface roughness, similar to PUR1 M, but is however expected to

have one of the lowest mechanical durability due to less durable binder and lower

coating thickness.

PVDF coatings are mostly used in façade applications because of its unique UV-

durability, which mean that the scope with the coating is slightly different than with

other coatings. PVDF is mostly compared to PES2, and regular, matt and thick silver

PVDF are compared with each other. When comparing average results of coatings, it

has to be noted that PVDF contains a low gloss coating and a thick PVDF coating

among three normal gloss coatings in the average. The same colours are not used in

facades and roofs and thus the chosen colours are also different.

In addition of differences between coating types, the coatings can have quite significant

differences in chemical structure even within same coating type. Different paint

suppliers try to reach the given specifications by changing different variables in the

coating like crosslink density, chain length control, additives etc. Typically, one coating

type can have multiple paint suppliers and even the same supplier can have moderate

changes in chemistry between different colours.

The colours chosen represents three different pigment levels. In façade coatings and

roofing coatings different colours were chosen, because white coating was not available

from coatings designed for roofing. Black coatings contain typically only black

pigment; grey or white coatings contain white and black pigments; red coatings contain

black, white and red pigments, and silver coatings contain black, white and metallic

23

pigments. In black coatings the amount of pigments is clearly the lowest. The amount of

pigments may differ slightly between coating types, because the overall colour of the

coating is in focus on production.

The samples are taken directly from production line and thus the properties of the steel

in the core material and thickness of the core material vary among the samples. In

production, the coating thickness and the speed of coating line can vary slightly

between different batches which may cause minor changes in coating properties. Also,

the quality of the coating between the beginning of the coil and at the end of the coil as

well as in the sides of the sheet compared to the middle can have minor differences. In

the actual coating the composition of fillers, concentration of fillers and even paint

chemistry can deviate slightly between different batches of the same paint, not to

mention different colours. In this thesis, the used samples are collected from one

production batch and the material should be consistent.

The thicknesses are the actual measured thicknesses of the coatings and densities are

calculated densities for estimated curing level. The thickness of the coating might have

small variation among the length and width of the coil but the thickness presented is

considered to be accurate enough. Densities vary highly between coating colours and

especially red and white coloured coatings have higher density than black coatings.

Also, density of PVDF is significantly higher than the density of other coating types

studied.

In previous studies at SSAB and its predecessor Rautaruukki Oyj, elongation at break

and tensile strength for the materials has been determined in a tensile test. Not all the

coatings used in this study have been characterized in previous studies and since most

of coating systems have changed to bio-based technology. However, the comparison

between coating types should have stayed the same. The results state that PVDF

coatings were the strongest but they had almost none of elastic strain. PUR based

coatings had most elasticity on the measurements, but also PUR had higher tensile

strength than PES based coatings. The data was insufficient to determine whether

wrinkled low gloss coatings have more or less elastic strain compared to high gloss

coatings. [20]

4.2 Test methods

Many different scratch and wear tests were implied on the chosen coatings. Most of the

tests were conducted for all of the chosen coatings but due to lack of resources or other

difficulties some tests were only implied for black coatings from each coating type. The

scratch methods were selected so that there were methods from hand-held devices to

high tech load monitoring devices. In choosing of wear tests each wear type was

considered at least in one method. Also, a novel method designed for studying marring

24

effect on coil was conducted and friction was monitored with two different methods to

compare if the friction correlates with the mechanical durability.

Most of the test devices were used to test more than one measurement method and in

total 32 different test methods were measured for the thesis with 11 different devices.

The methods, the measurement device used, and wear mechanism of the method are

presented in table 2. The methods and devices are described in chapter 5 with test

results and a brief evaluation of the method itself. Some testing parameters are shown in

appendix 1.

Table 2. Table of all test methods and what they are expected to describe.

Test method Measurement device What the test measures

Lc3 Pencil Hardness Faber-Castell brand pencils Scratch

Lc2 with Braive instrument "needle" scratch

Braive instrument Multifunction scratcher

Scratch

Lc3 with Braive instrument "needle" scratch

Braive instrument Multifunction scratcher

Scratch

Lc2 with Braive instrument coin like scratcher

Braive instrument Multifunction scratcher

Single pass wear / wide scratch

Lc1 with Sclerometer Elcometer 3092 Sclerometer Hardness Tester

Scratch

Lc1 after 1 hour with Sclerometer Elcometer 3092 Sclerometer Hardness Tester

Scratch

Lc3 with Sclerometer Elcometer 3092 Sclerometer Hardness Tester

Scratch

Lc1 with spherical head in Erichsen scratch hardness tester

Erichsen scratch hardness tester 413

Scratch

Lc3 with conical head in Erichsen scratch hardness tester

Erichsen scratch hardness tester 413

Scratch

Lc3 in Erichsen scratch hardness tester wear test

Erichsen scratch hardness tester 413

Scratch / Fatigue wear

Lc3 with UMT Progressive load scratch

Bruker UMT-3 Tribolab Scratch

Lc4 with UMT Progressive load scratch

Bruker UMT-3 Tribolab Scratch

Scratch hardness HSp with 3 N load wit UMT

Bruker UMT-3 Tribolab Scratch hardness

Lc2 with UMT wear test Bruker UMT-3 Tribolab Fatigue wear

Lc4 with UMT wear test Bruker UMT-3 Tribolab Fatigue wear

Volume loss at 250 rounds with 1 kg weight at Taber test

Taber Rotary Platform Abrasion Tester

Abrasive wear

Volume loss per revolution at 250 rounds with 1 kg weight at Taber test

Taber Rotary Platform Abrasion Tester

Abrasive wear

Volume loss at primer at Lc2 test with Taber

Taber Rotary Platform Abrasion Tester

Abrasive wear

Lc2 test with Taber Taber Rotary Platform Abrasion Tester

Abrasive wear

Volume loss per round in Lc2 test with Taber

Taber Rotary Platform Abrasion Tester

Abrasive wear

Visual evaluation after 2 kg in Solid particle erosion test

Solid particle erosion tester at TUT

Erosive wear

Volume loss after 2 kg in Solid particle erosion test

Solid particle erosion tester at TUT

Erosive wear

25

Lc2 at Solid particle erosion test Solid particle erosion tester at TUT

Erosive wear

Lc3 at Solid particle erosion test Solid particle erosion tester at TUT

Erosive wear

Visual evaluation after 2 hours in Slurry pot

High speed slurry pot tester at TUT

Erosive wear

Volume loss after 2 hours in Slurry pot

High speed slurry pot tester at TUT

Erosive wear

Visual evaluation of appearance of top coat on Coil damage measurement device

Coil damage measurement device Adhesive/abrasive wear

Visual evaluation of appearance of backing coat on Coil damage measurement device

Coil damage measurement device Adhesive/abrasive wear

Kinetic friction coefficient at room temperature in flat-to-flat friction test

Zwick-Roell Z050 Allround-Line Table-Top tensile test device

Friction

Kinetic friction coefficient at -15 C in flat-to-flat friction test

Zwick-Roell Z050 Allround-Line Table-Top tensile test device

Friction

Static friction coefficient in Sledge friction test

Zwick-Roell Z005 TH Allround-Line Table-Top test device

Friction

Kinetic friction coefficient in Sledge friction test

Zwick-Roell Z005 TH Allround-Line Table-Top test device

Friction

At scratching tests, as can be seen from the appendix 1, the scratching angles and

scratching tip shapes and sizes vary among the test methods. Standard SFS-EN 13523

[21] states that spherical 1 mm scratching tips are most suitable for coil coatings but

other type of scratching tips were also studied for comparison. This means that the

results are not straightforward to be compared.

In wear tests as many different methods were chosen as possible. Two different test

assemblies for abrasive wear, fatigue wear, adhesive wear and erosive wear were

planned, but at trialling an adhesive wear method and second abrasive method with

Taber Rotary Platform Abrasion tester were found to be unsuitable for the coatings

considered. Other of the erosion tests chosen was applied in dry environment while the

other was done in wet conditions. Coil damage measurement system is designed to

simulate conditions on the coil. The method has not been studied before and it simulates

damage on transportation and storing, but the capability to measure the properties

wanted is a question. The friction methods were chosen to study if the friction and wear

properties have a connection. Friction measurements are also used for evaluating

surface slipperiness in profiling or in end use when people are walking on it.

4.3 Evaluation methods for scratches and abraded area

The wear measurement devices often do not give any data directly and the damage

inflicted must be evaluated separately. Common evaluation methods include weight,

gloss or colour change measurements but they are often subjective and difficult to

attribute to the performance of coatings. In many occasions wear is defined as a loss of

dominant characteristics [3]. The most important properties of the coating in coil coated

steel are corrosion resistance and visual characteristics and thus the evaluation mainly

have to consider them.

26

Gloss and colour can be measured with gloss tester and colorimeter. There are several

difficulties in applying of colour and gloss measurements on estimation of wear.

Typically, the colour measurement area is so large that the wear tracks from the tests

cannot even be measured with the devices. Human eye is capable to distinguish

comparably low changes in colour and visual evaluation is also much faster than colour

measurements. In visual grading standard SFS-EN ISO 4628 [22] is applied on gloss,

colour and damage changes.

The amount of gloss reduction differs between different materials and comparison of

results between hard, soft, high gloss and low gloss coatings is difficult. Surface

roughness determines mostly the gloss level of the coating and roughness of wear

counterpart typically inflicts certain roughness to the tested sample [15]. Some of the

studied low gloss coatings are reported to have increase of gloss at wear but at most of

the coatings the gloss decreases during wear [23]. Also, the amount of change in gloss is

dependent from the brittleness of the coating. Gloss of brittle materials decreases more

from small scratches because multiple reflective surfaces are created [15]. On ductile

materials, the scratches tend to be rounder and the light reflects on the same manner as

before. Gloss is compared only visually to an unworn sample because of the complexity

of gloss reduction and goal is to evaluate if the gloss has increased or decreased. PVDF

is assumed to have partially brittle behaviour and PES and PUR to have ductile

behaviour due to previous tensile tests [20].

Corrosion resistance of coating can be estimated with electrochemical resistance

measurements. It has been noted, that chemical corrosion of the coated metal can occur

even when scratches do not penetrate the organic coating completely. Value 106 Ω cm

2

has been defined as a threshold value for electron change to sufficiently start corrosion

of steel [24] but often the damage is visually detected before even close to this limit. No

electrochemical measurements are implemented in this study, because it is estimated

that the visual evaluation gives enough data for comparison of the performance of the

coatings.

The most common methods in determination of wear are volumetric and mass changes

during wear. Volumetric change and mass change are easy to measure and can be used

to estimate how severe the wear is. The disadvantage of these methods is that the data is

not directly comparable if the densities vary, and the visual defects are not in most cases

linearly connected to mass or volume loss. Therefore, a visual evaluation was also

conducted in the thesis for the samples measured with mass loss or volume loss. [3]

In this thesis, the most used evaluation method is to determine if scratch or wear has

passed or failed at certain threshold level. The evaluation is done visually and four

different critical levels or loads (Lc1, Lc2 Lc3 and Lc4) can be determined. The critical

levels are defined in table 3. In some tests, the defined Lc levels cannot be applied

directly and the exceptions are described within the measurement method.

27

Table 3. Definitions of critical levels of wear or critical loads (Lc) where damage occurs.

Critical level Definition

Lc1 Lowest load or level of wear where a visible mark is noticed

Lc2 Lowest level where primer is revealed even at small amounts or pinholes

Lc3 Lowest level where zinc is revealed even at small amounts or pinholes

Lc4 Level when the zinc has been revealed from large areas or adhesion

between primer and zinc is lost

The amount of damage counted as certain Lc level differs between measurement

methods, but altered definition is noted within the test method. Examples of each

critical level of wear are shown in figure 9.

Figure 9. Examples of Lc1 in scratching, Lc2 in erosion test and Lc3 and Lc4 in

progressive load scratch.

More about the evaluation of Lc1, Lc2, Lc3 and Lc4 is discussed within each testing

method. The critical levels can be extracted to reality as Lc1 can be referred as unwanted

visual change, Lc2 a severe visual damage, Lc3 as a level when corrosion of core

material may initiate because of the damage and at Lc4 corrosion protection is

completely lost. At practical purposes Lc3 is more important to be measured than Lc4,

because water needs only pinholes to zinc for corrosion to start. For estimation of

amount of wear Lc4 limit can still be valuable. Not all the Lc levels can be tested with

the same equipment, for example Lc2 cannot be recognized in many tests with the

available load range of the test method and only Lc3 is reasonable to be measured. The

definition of critical load Lc is often referred as the load at which the material starts to

fracture [25].

28

5. TESTING OF THE COATINGS

With only one measurement method it is not possible to describe the wear and scratch

resistance properly for any material. In choosing of suitable test methods there are

several constants to be considered: the material pair, possible lubricant, loading

conditions, contact area, time of contact, shape of both faces, surface finishing, velocity,

vibration level, temperature, humidity etc. [3] The tribological system, as in the test

equipment affects significantly on the results. The amount of wear and even the ranking

order of different materials may vary between different measurement devices. There are

no applicable simulation models of wear that could be used on estimating the wear

properties of coatings correctly. Also, the simulations typically need material properties,

which are almost as difficult to measure as the wear itself. For identification of the most

important factors influencing on wear, the mechanisms presented in chapter 3.1 can be

used for help. [3, 12]

In sample preparation, the surface must be kept clean at all times. Any additional grease

from fingers or from machines may lubricate the scratching event, and so influence on

the wear properties. Also, cutting debris has to be avoided to prevent excess,

unpredictable wear it may cause. Degree of cure can slightly increase during time, but

all samples were gathered in two months window making them comparable. In some

tests, extra cleaning of wear counterpart or samples was done with ethanol which should

not influence on the results, but the cleaning is mentioned in the testing method. In

some occasions coatings could be grinded for smooth surface roughness to gain more

information about the material tested [26] but this kind of methods are excluded because

the scope is to compare the coatings as systems.

In scratching methods, there are few limitations on adapting the test results. For soft

coatings and structured coatings, the accuracy of the test decreases due to potential

snagging of the needle. Accuracy with steel substrates under 0.4 mm can also be

discussed, because it is possible that the substrate deforms rather than the coating is

scratched [21]. The steel substrates in the thesis exceed this limit with the thinnest

substrate of 0.50 mm but the possible effect has to be considered.

Determination of the mechanical durability with almost all of the devices needs visual

evaluation. For example, in scratching certain parameters can be adjusted and the

coating is afterwards visually approved as passed or failed under the circumstances. In

many tests, visual evaluation is the only measurable value, but in some wear tests also

mass loss after the test can be measured. Mass loss itself describes the amount of

material lost, but volume loss in this case is more interesting to estimate how much

29

coating is left. Volume loss is calculated from the mass losses in the thesis. For

scientific purposes a quantitative method for determination of the severity of the

damage would be preferable, but due to difficult nature of the layered material it is

difficult to find. Viscoelastic behaviour of the coatings also set limitation for the

properties on the evaluation methods and the evaluations should be done immediately or

at a certain time after testing.

In this chapter, various tests are run on selected samples. The analysis of results is

difficult especially for non-standardized methods, but the methods mostly follow ISO,

ASTM or SFS standards for paints or coil coatings. The results are given in the thesis as

average values between colours of desired coating type, but the actual measurement

data is shown in appendices 2-12.

5.1 Hardness pencil test

Hardness pencil test is the most widely used measurement method for determination of

mechanical durability of coil coated steel. Pencil hardness test follows standard SFS-EN

13523-4 [27]. In the test a pencil with specific lead dimension, shape and hardness is

drawn on top of the coated surface. The angle between coated surface and the pencil has

to be stabile 45° ± 1° and horizontal load 7.5 N ± 0.1 N during testing. The hardness of

the coating is determined as the hardness of the hardest pencil lead, which without

braking, scratches the coating for a minimum of 3 mm length. [27]

Accuracy of the test is higher for smooth surfaces, but the test is also applicable for

structured surfaces. Accuracy also depends highly on the experience of the person, and

if applied with a different test device, batch of pencil or manufacturer of pencil the

absolute result of the test may vary. Thus, only tests applied by the same tester with the

same test pencils at the same conditions can be compared in approvable rates. Because

of this the testing is accurate only in internal use. It is possible to use a pencil holding

apparatus for more consistent results, but this only gives limited improvements in force

and angle and makes sharpening of the pencil more difficult. Pencil hardness in many

cases does not correlate with the actual wear or scratching properties of a coating.

Another problem of the method is that the results do not have enough separating

capacity.

The pencils are Faber-Castell brand and the measurements were done at product

development laboratories of SSAB. The pencils are sharpened before each scratch and

their width is 2.0 mm. The Scratch hardness value is determined as the hardest pencil

which does not pierce the coating, as in Lc3 described before. The scale of the test is

from softest to hardest: 6B-5B-4B-3B-2B-B-HB-F-H-2H-3H-4H-5H-6H, but the

coatings only performed at the scale from 2B to H. In the thesis, the pencil hardness

values are given numerical values between 1 and 5 where 2B is 1 and H is 5. The results

for different coating types and their deviation between different colours are shown in

30

table 4. The complete test results, which the table 4 is based on, are shown in appendix

2.

Table 4. Average results of pencil test for different coating types and deviation between

coating colours.

Coating type

Lc3 Pencil Hardness (0-5)

Standard deviation between colours (0-5)

Standard deviation between colours (%)

PUR1 2.7 0.5 18

PUR1 M 1.7 0.5 28

PUR2 2.0 1.0 50

PES1 3.0 0.0 0

PES1 M 2.0 0.0 0

PES2 3.0 0.0 0

PES2 M 1.3 0.5 35

PVDF 2.6 1.5 58

In the test, all of the coatings had low results in average. The scatter between colours

was significant and difference between high gloss and low gloss products was large.

The test favours smooth surfaced coatings and in wrinkled coatings the decrease in

results is severe.

The test itself does not actually measure the properties of the coating, but properties of

the scratcher. The load and angle of scratching are as steady as a person can have and

only the hardness of the scratching lead is changing. The comparison to real life damage

is difficult to justify, because the scratches are typically inflicted by other metal sheets.

5.2 Braive Instruments Multifunction Scratcher

Braive Instruments Multifunction Scratcher is a pressure driven scratch test device. It

differs slightly from device described in SFS-EN 13523 [21], because it does not use

electrical current in detection of the scratch, and it does not have a sloping ramp in

approaching of the needle to the sample. The scratching head in the device can be

changed, but usually the device is used with needle like scratching head and a coin

shaped scratching head. Sample is attached with electrical magnet to the table, but when

scratching with the coin geometry an additional stopper must be used to prevent sliding

of the sample. The specimen holder where sample is attached is moved vertically by a

mechanical system. The length of the scratch can be adjusted by setting the distance

how much the specimen holder moves. The scratching pressure can be adjusted in

accuracy of 0.1 bars and the minimum air pressure used for accurate testing is 0.2 bars.

Problem with Multifunction Scratcher has been the rather rough adjustment of the

pressure. The device is shown in figure 10.

31

Figure 10. Braive instrument multifunction scratcher with a sample attached.

Single scratches do not often describe the real situation of wear, but it gives a way to

understand what may happen under a single asperity [12]. When testing scratch

resistance, multiple parallel scratches have to be performed. There is a suggestion that 4

mm gaps have to be used between scratches in one sample [28].

This method is typically used in determination of Lc2 and Lc3 limits with visual

evaluation. 15 mm of both ends of the scratch are not considered in the evaluation due

the device always shows a mark where the scratching head has landed and lifted off. For

needle like scratching tip, it is possible to determine the strength through top coat and

strength through the whole coating. Coin geometry can be used only through top coat

due the coin does not withstand the pressure needed to scrape the both coating layers.

The needle and coin geometry scratching heads are shown in figure 11.

32

Figure 11. Needle scratch and coin scratch scratching heads.

Curvature of the samples typically may cause some error in testing of sheet samples. In

Multifunction scratcher, the curvature should have no effect, because the samples are

attached to a magnetic table capable to flatten all the samples tested. The scratching tips

are non-magnetic, so that the magnetic table does not cause error.

5.2.1 “Needle” scratch

Needle like scratching tip is used for determination of scratching resistance. With the

device, it is typically measured the critical loads of Lc2 and Lc3 presented in chapter 4.3.

The head of the tip was hemispherical hard-metal with diameter of 1 mm according to

ISO 13523 [21] and is set in 90° angle to the studied surface. The tip was cleaned with

ethanol between the tests. The average results between colours are shown in table 5 and

the results where the calculation is based is shown in appendix 3.

33

Table 5. Results of Multifunction scratcher with spherical scratching tip and standard

deviation between coating colours.

Coating type

Average Lc2 with needle like scratcher (bar)

Standard deviation between colours (bar)

Standard deviation between colours (%)

Average Lc3 with needle like scratcher (bar)

Standard deviation between colours (bar)

Standard deviation between colours (%)

PUR1 0.33 0.05 14 0.60 0.00 0

PUR1 M 0.30 0.14 47 0.60 0.00 0

PUR2 M 0.20 0.00 0 0.55 0.05 9

PES1 0.30 0.08 27 0.50 0.00 0

PES1 M 0.40 0.00 0 0.40 0.00 0

PES2 0.23 0.05 20 0.40 0.00 0

PES2 M < 0.20 - - 0.33 0.05 14

PVDF < 0.20 - - 0.64 0.08 12

With the device, only pressures of 0.2 bar and over can be measured accurately and thus

Lc2 could not be measured for all of the coatings. The separation ability in the

measurements is relatively low, and even the results showed to be mostly consistent, the

standard deviations between colours was high.

High gloss coatings were expected to perform slightly better than low gloss coatings

because of possible snagging of the needle. Only significant exception to this was Lc2

test between PES1 and PES1 M where the result showed the opposite. PES1 M had the

best overall performance and PUR1 M B had the highest single result with 0.5 bars. For

rest of the coatings the single measurement values were between 0.2 bars and 0.4 bars.

At determination of Lc3 all coatings exceeded the 0.2 bar accuracy limit and could be

measured. At Lc3 test assumption of high gloss having better performance was realized,

except with PUR1 and PUR1 M where the results are the same.

Notable is that PVDF has the lowest possible Lc2 value, but at Lc3 test it has the highest

performance of all the coatings. The increase is notable, and it happens with every

colour, with both gloss levels and with thin and thick PVDF. The difference between

results in Lc2 and Lc3 tests are also large in other coatings, except in PES1 M. The

performance of PES1 M is very high at Lc2 test and with a more precise load control the

Lc2 and Lc3 results most likely would have had difference. The coatings’ mechanical

durability is designed for Lc3 type of scratching with the standard needle and thus the

results are in expected order.

5.2.2 Coin scratch

Coin scratching is used to measure single pass wear caused by sharp edges. For

example, dragging sheets on top of each other could be described with this kind of

34

method. Because of the large contact area, the pressures used are higher and scratching

down to the substrate is not recommended due excess wear of the scratching coin. The

scratching coin is 20 mm in diameter, 1.0 mm in thickness and slightly concave. It is

made of hard metal and the edges are not rounded. The coin is dragged 8 cm in an angle

of 40° as seen in figure 11. The average results are shown in table 6, while results for

each coating are shown in appendix 3.

Table 6. Average results for coatings in coin scratch test.

Average Lc2 with coin like scratcher (bar)

Standard deviation in coin scratch (bar)

Standard deviation (%)

PUR1 0.53 0.05 9

PUR1 M 0.80 0.00 0

PUR2 M 0.55 0.15 27

PES1 0.53 0.05 9

PES1 M 0.60 0.10 17

PES2 0.33 0.05 14

PES2 M 0.43 0.05 11

PVDF 0.90 0.25 28

The result did not follow the results of needle scratch of Lc2 and surprisingly almost all

the low gloss coatings managed well in the test compared to high gloss coatings. This

may be because the larger scratching tip decreases the effects of small scale surface

roughness. Low gloss and high gloss coatings are typically designed for high scratch

resistances with standard 1.0 mm needle. This may lead into improving of the scratch

behaviour of binder system used in the low gloss coatings. When the contact area is

increased, and surface roughness becomes less significant, the low gloss coatings might

get an advantage.

It was notable, that most of the coatings had different scratching behaviour in the test.

With all coatings, the coin glided on top of the coating at low pressures and maybe

detached some particles leaving only small scratching mark at structured coatings and a

compression mark at coatings without structuring particles. For PVDF, PUR1 M and

PES2 M coatings the severity of scratch increased almost linearly and at some point, the

Lc2 limit was reached. The rest of the coatings had a certain threshold load where the

scratching became more severe and Lc2 was in PUR1 and PES1 M R reached before and

in PES1, PES1 M B and PES2 at the threshold. Interesting was that PES1 M B and

PES1 M R, despite being from same binder, were acting in different manners. With

higher measurement accuracy, the behaviour of the scratches could have been studied

more. PUR2 M type coatings were the only ones reaching Lc2 after the increase to

severe wear.

35

In most of the coatings, the wear debris was mostly round or needle like dust but in

PUR1 M, PUR2 M and PVDF coatings the residue was continuous from start to the end.

The continuous residue was irregular at PUR1 M and PUR2 M coatings, most likely due

to their rough surface and at PVDF coatings the residue was smooth with uniform

thickness. The difference in the residue of PVDF most likely has something to do with

the thermoplastic nature of PVDF. In PES1 M and PUR2 M the low gloss is achieved

with structuring particles and thus they were expected to act in the same manner, which

was not the case. The same occurred with the wrinkled PUR1 M and PES2 M and no

explanation could be given to these different behaviours. Also notable is that at some

coatings, for example PES2 R, there was no wear debris at low loads. Wear debris from

PES1 M R, PVDF S, PUR1 M R and PES2 R are shown as an example of different

debris in figure 12.

Figure 12. Wear residue from PES1 M R, PVDF S, PUR1 M R and PUR1 M B.

The test plates are 10 cm in height and 15 cm in width

The coin scratch test itself is simple and efficient, but the scratching coin wears a lot. At

start the coin has a sharp edge but it quickly becomes blunt and the test results seem to

improve. Because of this the coin should be rotated after each test but because of lack of

coins the rotation was done only before the test series and once in the middle of the

series. This may have increased the possibility of error between results but in uncertain

situations the coating was tested again with both rotated, intact surface and with a more

used blunt coin.

36

The coin scratch describes more of a scratch possible in real life than a scratch with

spherical 1 mm head. Some tools like seam folders have shown some correlation in this

kind of testing [19]. With a more accurate load control system the method would be

more interesting to be studied. Peeling of the coating layer of PVDF S shown in figure

12 would not be accepted at customer, even the coating layer is not close to Lc2 or Lc3

limit and thus other test method should be applied. The first scratch to leave pressure

marks (as in Lc1) and the point where scratching becomes more severe would be of

interest, especially with PVDF coatings.

5.3 Elcometer 3092 Sclerometer Hardness Tester

Elcometer 3092 Sclerometer hardness tester is a handheld device with application area

between 0 N and 30 N. The device is provided with three springs with different load

ranges. The load is controlled by springs with different spring forces. The spring is set

to certain load with a collar, and when the tip is pushed in about 2 mm the wanted load

is applied. The tip oscillates slightly during scratching and this has to be considered as a

source of error. The measurement angle is suggested to be perpendicular to the studied

surface and scratch length must be at least 10 mm long. The test is used to study Lc1 and

Lc3 levels of the coating. Measurement of Lc2 is not possible to measure with the device,

because the tip pierces through the both coating layers when the load is raised. The

scratching head is spherical 0.75 mm diameter tungsten carbide tip. The device and

springs are shown in figure 13.

Figure 13. Elcometer 3092 Sclerometer in its case with the provided springs

and ø 0.75 mm scratching head.

Elcometer Sclerometer has a guaranty to operate many years reliably when operated and

stored at normal conditions. This means that there are no other possibilities for

37

maintenance and calibration than changing the spring and tip whenever the user finds it

necessary.

In the instructions Sclerometer was recommended to be used to find out the first force

level in which a scratch can be noticed, as in Lc1 described in chapter 4.3. The device is

accurate even at low loads, which makes the device suitable for a test like this. The test

was performed with making three at least 10 mm scratches with each load in steps of

0.2 N and the scratches were evaluated visually at multiple angles from 90° to 180 °

against a natural light. To estimate the elastic-plastic properties of the samples the

scratches were evaluated again after 1 hour and compared to the previous results. The

result is given as the load value, which inflicted the noticeable scratch. The results for

coating types and the deviation between colours are shown in table 7 and the full results

in appendix 4.

Table 7. Elcometer results for Lc1 immediately after scratching and 1 hour after

scratching with standard deviations between different colours.

Lc1 straight after scratching (N)

Standard deviation between colours (N)

Standard deviation between colours (%)

Lc1 one hour after scratching (N)

Standard deviation between colours (N)

Standard deviation between colours (%)

PUR1 1.5 0.2 12 2.3 0.1 4

PUR1 M 0.3 0.2 57 0.9 0.9 96

PUR2 M 1.0 0.6 60 1.8 0.8 44

PES1 1.3 0.2 14 1.8 0.6 33

PES1 M 1.0 0.4 40 1.2 0.2 17

PES2 0.4 0.0 0 0.9 0.6 66

PES2 M 0.7 0.1 13 3.8 0.2 6

PVDF 1.5 0.6 41 1.5 0.5 35

The standard deviation was very high at testing the first scratch noticed between colours

of the same type. The test itself is very subjective for determination whether one sees a

scratch or not, and there is a large difference in noticing the scratches in different

coloured coatings with different surface roughness’s.

From the Lc1 results there cannot be drawn many conclusions. As estimated at SFS-EN

13523-12, the measurement results were more consistent for higher gloss products. The

significance of high and low gloss in the coatings is uncertain. In PUR coatings higher

gloss PUR1 samples lasted significantly larger load than PUR1 M samples, and PVDF

M S was scratched even with the smallest load of the device while PVDF S had the

highest Lc1. The difference between PES1 and PES1 M was only small favouring the

higher gloss, but for PES and PES2 M the difference was the opposite. Interesting was

that PUR1 M had the lowest Lc1 based on this measurement.

38

At evaluating the Lc1 after 1 hour it was supposed to study how much small scratch is

recovered after short period by viscoelastic flow. With some coatings, this creeping

effect was noticed to be almost non-existent, but for example in PES2 M the recovery

was significant. PES2 M coatings had low Lc1 values when evaluated immediately, but

after 1 hour the same scratches were not visible and Lc1 after 1 hour the values were the

highest of all coatings. The recovery effect also varied a lot between colours without

larger trend. For example, PES2 R did not have any recovery as for PES2 W the Lc1

after 1 hour was 1.8 N when immediately evaluated it was only 0.4 N. The

measurement was even more dependent on the instructor because searching for a scratch

is much more difficult after it is not inflicted at sight. Based on the measurement small

scratches do visually recover slightly on all coatings except PVDF, and with PES2 M

the visual recovery can be significant. In other coatings, the results differed so much

that no conclusions can be made.

At Lc3 measurement the Sclerometer was evaluated with four different technicians to

see how much variance between measurers there is. It was noticeable that three

technicians provided mostly the same values, but fourth evaluator almost always had

higher Lc3 values. Some of the samples were double checked because of a high variance

but the secondary results had the same amount of variance, or even more. Sometimes

better results were gained when repeating the test multiple times and sometimes rotating

the pen 90° helped as well. This implies that there might be some wear in the tip of the

pencil and when scratched parallel to the wear paths of the tip the results are better. To

prevent this, a direction to how to use the pen has to be agreed. For a handheld device,

the Sclerometer performed rather well on the testing: the separation capacity of the

measurement was good but random error with some coatings was quite high. For each

coating type, the average Lc3 results from all testers and colours with their deviation are

shown in table 8 and complete results in appendix 4.

Table 8. Elcometer Sclerometer Lc3 results and deviation between different colours

among all testers.

Coating type

Lc3 measured with Elcometer Sclerometer (N)

Standard deviation between colours (N)

Standard deviation between colours (%)

PUR1 19.9 0.3 1

PUR1 M 17.6 2.7 15

PUR2 M 17.0 2.3 13

PES1 17.3 2.2 13

PES1 M 19.1 0.8 4

PES2 15.3 1.8 12

PES2 M 7.5 1.2 17

PVDF 15.1 3.3 22

39

PUR1 outperformed all the other coatings due the measurement limits of the device

were reached with all of the colours. PES1 M was the second best and PUR1 M, PES1

and PUR2 M followed right behind. PVDF performed much worse in this test compared

to other scratching tests, by having the second lowest Lc3 level with PES2. PES2 M had

the lowest performance and a less stiff spring was used to increase accuracy. The results

had less variance than in many other tests and the standard deviation between different

persons was mostly under 10% and at largest 21% (3 N) in a sample. The large

deviation in PVDF is between the colours and thicknesses: white PVDF had the lowest

performance, while thick silver PVDF was almost in the same level as PUR1.

The results are in slightly different order than in other scratching tests. Partially this is

caused by reaching the limit of 20N with many of the coatings but partially it may be

caused by different radius of the spherical part of the needle. Low gloss achieved by

structuring particles seems to increase the scratch resistance in the test.

5.4 Erichsen scratch hardness tester 413

Erichsen scratch hardness tester 413 is a rotary scratching device with a capability to

scratch single or multiple scratches on same path. This means it can be used as a wear

test apparatus as well as a scratch tester. The device is provided with two different

scratching tips – a ball shaped tip with diameter of 0.7 mm and a conical Vickers

scratching tip. The load is adjusted with weights and the load range is from 0.01 N to

1.00 N with the smaller weight and from 1.0 to 10.0 N with the larger weight. The

rotating speed is fixed to 5 rpm but the radius of the scratch and thus the scratching

speed could be adjusted slightly. The test device was property of Oy Celego AB, and it

was trialled in product development laboratory of SSAB in Hämeenlinna. The

scratching device is shown in figure 14.

Figure 14. Erichsen scratch hardness tester model 413.

40

At standard 13523-12 [21] tells that scratching tip used should be spherical when

scratching a pigmented or structured coating. In the scratch hardness tester 413 the

largest possible load is too low for testing Lc2 or Lc3 limits so conical tip had to be used

in determination of Lc3 limit. With the spherical scratching tip, it was possible to

determine Lc1 limit and it was also more suitable for wear testing to Lc3 limit with the

device. The scratching speed differs when altering the scratching radius. Maximum

radius in the tester is 9.5 cm and minimum 5.0 cm so the speed varies between 7.9 mm

s-1

and 4.2 mm s-1

. The significance of scratching speed is assumed to be non-existent,

but this is an issue that should be studied separately.

The test device is developed for determining the first visible scratch on the surface. The

test is not optimal for structured coatings, like the ones studied, because the visual

evaluation between different coatings is difficult. The benefit of Erichsen model 413

compared to Elcometer Sclerometer is that the load is transmitted by a weight and

movement is stabile compared to hand driven device. Difficulty in Erichsen scratch

tester was that the evaluation of the sample between tests is slower because the sample

needs to be detached for visual evaluation.

The Lc1 test was implemented with accuracy of 0.2 N when value was over 1.0 N and

with 0.1 N if the value was under 1.0 N. The test is implemented as a pass or fail test,

where highest passing value is taken as a result. The difficulty in visual evaluation of

first noticeable scratch is the viewing angle and tendency to elastically recover from

such low stresses. The colour of the coating, surface roughness and illumination of the

sample all influence on the visual evaluation especially in the case of barely visible

scratches. This makes the test highly dependent of the operator. The results are shown

in appendix 5 and averages based on the results in table 9.

Table 9. Results of Lc1 scratch test with Erichsen scratch hardness tester model 413 and

standard deviation between colours.

Coating

type

Average

result in

Lc1 with

spherical

head (N)

Standard

deviation

between

colours

(N)

Standard

deviation

between

colours

(%)

PUR1 1.80 0.33 18

PUR1 M 0.40 0.42 106

PUR2 M 0.70 0.30 43

PES1 1.20 0.16 14

PES1 M 0.70 0.20 29

PES2 0.30 0.08 27

PES2 M 0.73 0.19 26

PVDF 0.58 0.31 53

41

In most coatings, low gloss decreased the Lc1 limit, but no trends could be found for

structured, smooth and wrinkled coatings. PUR1 outperformed other coatings and had a

relatively low deviation in the test and PES1 followed on second place with even lower

deviation. Non-structured PES2 coatings had low Lc1 scratch resistance but with smooth

PVDF coatings and wrinkled PUR1 M coatings the results varied. PUR1 M B had an

Lc1 value of 1.0 N but the two other colours of PUR1 M B had the lowest performance

of all coatings with 0.1 N. For PVDF, silver PVDF had higher Lc1 of 1.0 N but other

colours decreased the average below 0.6 N. The rest of the coatings PUR2 M, PES1 M

and PES2 M are almost at the same level of performance and deviation.

The high deviation between colours could be reasoned with different ability to detect

tiny scratches in the coatings. The difference in detection of scratches most likely is

reason also for the difference in the results between the coatings. There should not be

made larger conclusions from the test results, because the test is so much depended on

the person evaluating the samples, colour of the sample and structure of the sample.

An example of difficulty of the evaluation can be seen in figure 15. Also, samples from

Lc3 scratch test and rotation Lc3 test can be seen in the same figure.

Figure 15. Tested PES2 samples from a) Lc1 scratch test with spherical tip, b)

Lc3 scratch test with conical tip and c) Lc3 wear test with spherical tip with

Erichsen model 413.

42

Interesting is that at the Lc1 sample in figure 15a there were no visible scratches left at

the moment of taking the photo, but the scratches became visible only after adjusting

the brightness and contrast of the photo. Image modifying or any magnification lenses

were not used in scientific purposes at the thesis.

At Lc3 scratch test with a conical scratch tip the loads were very low as assumed. The

test was more repeatable than what was expected. When some of the samples were

tested later with the same parameters the results had only a small scatter of 0.1 N, and

when using steps of 0.2 N the error could be minimized. The test results can be seen in

appendix 5 and the averages between colours in table 10.

Table 10. Results of Lc3 scratch test with Erichsen model 413 and deviation between

coating colours.

Coating type

Average result in Lc3 with conical head (N)

Standard deviation between colours (N)

Standard deviation between colours (%)

PUR1 3.9 0.34 9

PUR1 M 3.1 0.74 24

PUR2 M 2.3 0.30 13

PES1 2.9 0.47 16

PES1 M 2.9 0.10 3

PES2 2.5 0.09 4

PES2 M 1.3 0.09 7

PVDF 3.5 1.71 49

The results with conical tip of Erichsen model 413 had unexpectedly low deviation

between the colours. With PUR1 M the deviation was 24% and with PVDF 49% but at

other coatings the deviation was at acceptable rates. The conical head is not

recommended for structured coil coatings and most likely it is seen as a decrease in

performance of low gloss coatings. The pronounced effect of surface roughness can be

seen when PES2 had better results than PUR2 M, which was not typical on other Lc3

scratching tests. Otherwise the results were quite typical compared to other Lc3 scratch

tests: PUR1, PVDF and PUR1 M performed the best and PES2 M had the lowest

results.

At Lc3 wear test the load was set at start on 9.0 N with the spherical scratching head, and

the revolutions were counted while determining live if the Lc3 limit has been reached.

No parallel samples with the same load were run. Because results on some coatings

were difficult to determine, the test was applied again with 7.0 N load and again with

5.0 N load for the low performing coatings. The rotations were calculated manually,

which may have caused some error on the longer runs. This problem could have been

excluded if there was an automatic revolution calculator on the device or if wear time

43

was recorded instead of revolutions. The results are shown in appendix 5 and average

results in table 11. The test was stopped at 40 revolutions if the Lc3 was not yet reached.

Table 11. Results of Lc3 wear test with 9 N, 7 N and 5 N loads with Erichsen model 413

and deviation between colours. *The test was stopped at 40 rounds, but the

coatings were intact. **PES1 B was not measured.

Coating type

Revolutions to Lc3 with 9 N load (rounds)

Standard deviation between colours (%)

Revolutions to Lc3 with 7 N load (rounds)

Standard deviation between colours (%)

Revolutions to Lc3 with 5 N load (rounds)

Standard deviation between colours (%)

PUR1 28.7 20 *≥40.0 0 - -

PUR1 M 12.3 3 *≥40.0 0 - -

PUR2 M 3.5 4 10.5 43 44.5 12

PES1 4.0 21 9.7 68 **13.5 11

PES1 M 8.0 4 20.0 10 - -

PES2 1.0 0 2.0 41 10.0 36

PES2 M 0.0 0 0.3 141 3.0 0

PVDF 1.6 2 3.4 24 7.4 39

Test with 9 N load was first tested because it was estimated that all coatings would last

it, but the test times would be lower. The results were clear on the first test: PUR1 was a

magnitude better than the rest, while the results of PUR1 M and PES1 M followed

respectively. Because of small difference in rest of the results, and because PES2 M did

not have a result, the test was applied again with a force of 7 N.

All PUR1 and PUR1 M coatings lasted over 40 rounds in 7 N test and it was worthless

to measure more revolution than that. The order remained otherwise the same as in 9 N

test, except with PUR2 M and PES1. PES1 B increased the average of PES1 coatings

but the less the load was, the clearer was that more consistent PUR2 M coatings were

performing better. PES2 M R was the only coating from PES2 M coatings to get a result

and so the test was applied again with load of 5 N.

In 5 N load measurement PUR1, PUR1 M, PES1 M coatings and PES1 B were not

measured due they lasted too long to be convenient to measure. The order of the

coatings again changed slightly due PVDF did not improve its result compared to the

previous loads but with PES2 the increase was almost exponential and especially with

PES2 W.

The results of Lc3 wear tests with different loads are not easily comparable. Interesting

was that with so small changes in the testing parameters the order of the coatings in

durability can be changed.

44

5.5 UMT-3 Tribolab

CETR UMT-3 Tribolab is a multifunction testing device designed for wear, indentation

and scratching. It is a modular device which with it is possible to use different wearing

counterparts, contact geometries and different relative motions. It is possible to attach

multiple add-ons to the device, but heating chambers, lubricants and acoustic emission

measurements were not found to be suitable for coatings used at coil coated steel. The

device with scratching assembly is shown in figure 16 from inside the protective casing.

The measurements were done at Bruker GmbH laboratories in Karlsruhe.

Figure 16. UMT Tribolab from inside with scratching assembly with linear

drive module and microscope module attached. [29]

For coil coatings, scratching with progressive load, scratching with constant load and

wear with pin-on-disk geometry were found the most suitable to be measured.

Reciprocating motion was considered and tested with the same wear counterpart and

forces as rotating test, but it was found to be too harsh for most of the samples.

One of the largest difficulties faced was to attach the sample plates properly to the

moving platform. For such a fine-tuned height measurement, it is crucial that the sample

45

lies flat, and in case of coiled steel sheets the small samples tend to curve. This was

solved with a specific sample holder in the linear platform but in rotating platform such

a holder was not available. The error from this source is small in scratching but in

rotating wear the curvature may have caused some external error. It was only possible to

measure a small number of samples with UMT device and for the most comparability

black samples from PUR 1, PUR 1 M, PES 1, PES 1 M, PES 2 and PES 2 M coatings

were chosen.

5.5.1 Progressive load scratch

Progressive load scratch testing was implemented with 200 µm Rockwell head attached

to a load sensor. The scratching started from a static state after the load had been

stabilized on 0.25 N. The scratch speed was 0.2 mm s-1

, scratch length was 5 mm and

the load increased 1 N s-1

ending up to 19.5 N. The load was found to be suitable

because the coating could be damaged in every sample type. Longer scratches were not

possible, while it had to be possible to move the sample below the microscope.

Before and after test the scratch path was profiled with the Rockwell head and force of

0.02 N. During the pre-scan a height sensor records the height of the needle and marks

it as the zero level. During scratching the depth of the scratch and thus total deformation

is recorded and in post-scan depth of the scratch path is measured to map the permanent,

plastic deformation. Post-scan can be very helpful tool in evaluation of damage

occurred. Also, the friction against the movement direction was recorded. Pre-scan

profile, depth curves and friction curves as function of scratch length for PES1 B are

shown in figure 17. In polymer-based material always some viscoelastic deformation

occurs, and the post-scan must be implied at the same time to prevent error caused by

viscoelasticity.

Lc3 and Lc4 values are determined based on microscope figures with the help of depth

and friction curves obtained in pre- and post-scanning. Determination of Lc1 was found

to be too difficult because the scratch was too short on the low load area. Determination

of Lc2 was also not possible from the photos due to reflections and lack of contrast in the

scratch path. For evaluation, the microscope figure and depth curves had to be set on a

correct spot. This is difficult to do manually, because the landing point of the needle is

barely visible due to low load, and the lift off point is difficult to recognize in the

middle of deformed material. Visual evaluation of the scratches with bare eye was

unnecessary because the accurate value cannot be determined without scale next to the

specimen. With the addition of coefficient of friction to the load curve it was rather easy

to determine the points where the scratching starts and where the first pinholes start to

show. With a wider or spherical scratching head the effect of surface roughness would

have likely been less significant.

46

Figure 17. Pre-scan profile, depth curves and friction curve as function of

scratch length for PES1 B in progressive load scratch. Pre-scan of depth is the

surface roughness which has been removed from scratch depth and post-scan.

[29]

The scratch data presented in figure 17 from PES1 B showed typical behaviour and

other coatings are evaluated as such. Because the applied normal load is plotted, the Lc3

and Lc4 load values can be quite easily read from the curves. The scratch depths were in

all samples deeper than the thicknesses of the coatings. This can be caused either by

curvature of the samples or by deformation of the zinc coating layer under the needle. In

the samples, the Lc3 level was reached seen before the scratch depth surpassed the

coating thickness. Another clear change near Lc3 and Lc4 limits can be seen in the

friction curve and depth curve of post-scan. Changes in scratch depth or in friction

coefficient during scratch are not abrupt enough close the Lc limits to show a clear

47

connection. Average results from at least 2 measurements are shown in table 12 and the

results are shown in appendix 6.

Table 12. Average Lc3 and Lc4 results from progressive load scratch. *Three parallel

samples measured.

Coating

Lc3 from progressive load scratch (mm)

Lc3 from progressive load scratch (N)

Lc4 from progressive load scratch (mm)

Lc4 from progressive load scratch (N)

PUR1 B* 3.22 12.7 > 5.00 > 19.5

PUR1 M B 1.79 7.1 3.53 13.8

PES1 B 2.42 9.6 3.52 13.8

PES1 M B 3.18 12.5 3.62 14.2

PES2 B 2.58 10.1 3.58 14.0

PES2 M B 1.26 5.1 1.80 7.2

Progressive load scratch gave more consistent results than was expected. It was

expected that the pinholes to zinc as in Lc3 limit would have had a lot of scatter, because

they are most likely holes caused by detached particles. In addition, the Lc4 limits were

very consistent but as can be seen from the table 12 that almost all of the coatings had

the same Lc4 value. The Lc4 limit is quite subjective due there already are pinholes and

holes to the zinc beforehand and the continuous scratches to zinc are very short due

short scratching length. Standard deviations between measurements were under 12% in

both Lc3 and Lc4 tests.

PUR1 B and PES1 M B were almost as durable in Lc3 test with 3.2 mm result. PES2 B

and PES1 B were almost on same level with each other with results of 2.58 mm and

2.42 mm, respectively. PUR1 M B and PES2 M B were less durable than other coatings.

PUR2 M and PVDF were not measured. At Lc3 tests the wrinkled coatings had way

lower durability compared to other coatings, while PES2 B for example had untypically

high ranking in the test. Interesting is how PES1 M B had higher durability than PES1

B, if increased surface roughness was the reason for decreased results in other coatings.

Also, the thickness of the coatings seems not to have influenced on the results a lot.

In Lc4 measurement almost all of the coatings had the same result. PES2 M B had the

lowest performance with 1.8 N, PUR1 B endured the maximum 19.5 N at the test and

other coatings had Lc4 values around 14 N. Especially, good result in PES2 B may

indicate that smoothness of the coating is in advance with the used test parameters. In

determination of Lc4 also the effects of pile-up push pads in front of the sliding indenter

was seen in every coating. This can be seen as jumping in the scratching and post-scan

depth because the material resists the motion [17]. The results in both tests indicate that

the pinholes in wrinkled coatings are born only in the bottoms of the wrinkles, because

the Lc4 durability of wrinkled coatings is so good in comparison.

48

The different behaviour in Tribolab UMT scratch tests compared to other scratching

could be resulted due smaller scratching head with different geometry and the

controlling of load. The used 0.2 mm Rockwell indenter might have been too sharp

compared to spherical 1.0 mm tip recommended for the coil coatings. The smaller

radius of the tip allows the scratcher to follow the surface structure of the coatings more

and get attached to steep shapes. The load controlling system keeps the load steady with

very short response time when an obstacle is ahead. Typical scratching devices are

controlled with pressurized air, spring or a floating weight and the load stabilization

may interfere with the results. Especially good property at the device is that the time

between scratching and evaluation is exactly the same due the automated microscope

pictures.

5.5.2 Constant load scratch

Constant load scratches were measured with the same 200 µm Rockwell head as in

progressive load scratch and the load was determined to be 3 N to not to break the top

coats. The length of the scratch was 5 mm and the scratch path was pre- and post-

scanned as in progressive load scratch test. The measurement of constant load was

chosen to calculate a scratch hardness value (HSp) based on the width of the scratch

profile. Also, depth of the scratch could have been used in the calculation of HSp.

Scratch path of PUR1 B in constant load scratch with the friction and depth curves is

shown in figure 18.

49

Figure 18. Scratch profile, depth curves and friction curves as function of

scratch length for PUR1 B in 3N constant load scratch tests. [29]

The width of the scratch was measured from three spots and the HSp is calculated from

their mean. The equation is [30]

𝐻𝑆𝑝 =8𝑃

𝜋𝑤2,

where HSp is the scratch hardness number, P the load and w the width of the scratch. In

principle, the same HSp value could be measured with the depth of the scratch with

geometrical calculations. Plastic and elastic deformation value was measured from the

most representing spot of the curve in figure 18. The average data of scratch width,

50

scratch hardness, depth of plastic deformation and depth of elastic deformation is shown

in table 13. The friction coefficient curve is of low value in constant load scratch.

Table 13. Width of the scratch, scratch hardness values and plastic and elastic

deformations in direction of loading with constant load of 3 N.

Coating

Scratch width with 3 N (µm)

Scratch hardness HSp (MPa)

Depth of plastic deformation (µm)

Depth of elastic deformation (µm)

PUR1 B 187.7 217 7.3 22.5

PUR1 M B 159.4 302 6.6 25.8

PES1 B 178.5 240 6.2 14.3

PES1 M B 161.5 293 6.0 14.2

PES2 B 169.3 267 5.1 13.0

PES2 M B 133.2 440 4.9 15.3

The widths and thus the HSp values after measurement were not in predicted order but

the opposite. The hardest behaviour was seen with PES2 M B while PUR1 B was the

softest. The low gloss products had higher hardness value in all three coating types as

well. This finding is in correlation to the fact that scratch resistance and hardness is not

the same thing, as typically assumed. Based on the measurement, it seems the harder the

coating the worse the scratch resistance is. It must be taken into account that most likely

the coating thickness is reflecting to the HSp values in the measurement.

The amount of plastic deformation is in the direct order from top to bottom in the table

13. Order in elastic deformation is almost the same, with exception of wrinkled coatings

having slightly higher elastic deformations than rest of the coatings. It is uncertain

whether the method is applicable for measuring the hardness or durability of coatings

with different thicknesses. The scratching depths vary between 56% and 70% and the

difference between thinnest and thickest coating is considerable. Therefore, the scratch

depth, plastic deformation and elastic deformation are plotted as a function of coating

thickness in figure 19.

51

Figure 19. Scratch depth, plastic deformation and elastic deformation in

constant load scratching with 3 N load as a function of coating thickness

In figure 19 the scratch and residual depths are highly correlated only to the coating

thicknesses. For plastic deformation the correlation is linear, but in elastic deformation

the differences between binder materials can slightly be seen. The wrinkled low gloss

coatings seem to have slightly more elasticity and less plastic deformation than their

smoother high gloss versions, but the same cannot be seen with PES1 and PES1 M. This

would mean that wrinkled coatings are more elastic but also have higher scratch

hardness than smooth coatings. Because the difference in results is too small and the

scatter is too high compared to number of samples, no conclusions can be made from

the measurements.

The correlation of coating hardness and mechanical durability of the coatings would be

important to be studied, if the measurement is applied with more suitable parameters

and wider sampling. Based on this measurement, Rockwell type scratching tip with load

of 3 N is found unsuitable for comparing HSp of coatings with different coating

thicknesses.

5.5.3 Rotating Ball-on-disk wear

With spherical objects the load distribution is easier to maintain than with flat objects.

Rotating movement was chosen instead of reciprocating movement because then all the

passes are at the same direction and describe more real conditions in roll forming of a

product. Rotating movement is not optimal for the testing, but the modifications needed

for block on ring wear test were too difficult to apply with the schedule. The test was

performed with ceramic ball of 6 mm in diameter, speed of 20 rounds per minute,

constant load of 20 N and with a route diameter of 10 mm and 20 mm. The device kept

0

5

10

15

20

25

30

35

25 30 35 40 45 50

De

form

atio

n in

Z d

ire

ctio

n (

µm

)

Coating thickness (µm)

Elastic deformation

Plastic deformation

Scratch depth

PUR1 M PES1 & PES1 M PES2 M PES2 PUR1

52

the load stabile (± 0.1 N) and the height of the tip was again surveyed with load sensor.

The assembly of rotating ball on disk wear test can be seen in figure 20.

Figure 20. Ball-on-disk wear test assembly. [31]

A floating periodic average of the depth has to be drawn for a readable data, because of

difficulties at clamping the samples. The wear resistance of coatings is in completely

different magnitudes and logarithmic scale of rotations is used to provide readable data.

Floating average of the wear and friction coefficient is shown in figure 21 as a function

of rotation cycles.

53

Figure 21. Penetration depths (top) and friction coefficients (bottom) as a

function of logarithm of rotating cycles for all coatings. The figure could not be

re-modified. [31]

The order of the coatings performance can be easily seen from the figure 21 but

interesting is that the two measurements from same sample differ from each other so

much. Only different in the two parallel measurements was the diameter on the wear

path. PES2 M B did not perform well in the test and PUR1 B exceeded the other

coatings again in durability. The coatings did not wear off with a constant rate but each

of the wear curves had one or two jumps. The most probable reason is that the

continuous moving stress on the coating makes the adhesion of the layers loose and at

the steep slopes the whole layer is detached. This stage is repeated for the topcoat and

for the primer. The friction curves support the theory by starting to show a local

maximum in the middle of the slope, which indicates that the surface roughness is

changing. With the same amount of rotations for example at PES1 B it can be clearly

seen that the “depth” is actually negative. This indicates that the adhesion has been

partially lost and the delaminated coating is waving [31].

54

Based on the theory of adhesion loss Lc2, Lc3 and Lc4 could be read from the data for

most of the tested coatings. Part of the samples was not run long enough to show all of

their characters and most coatings do not show the Lc2. Probably the separate Lc2 is

missing because the adhesion of all layers is broken at the same time. Estimated average

results of Lc3 and Lc4 are represented in table 14 and complete results are shown in

appendix 6.

Table 14. Time needed to reach Lc3 and Lc4 read from friction and depth curves of ball-on-

disc wear test with ceramic ball. *Tests were stopped at 600 seconds or too

early.

Coating Lc3 with UMT wear test (s)

Lc4 with UMT wear test (s)

PUR1 B > 600* > 600*

PUR1 M B > 500* > 600*

PES1 B 25 70

PES1 M B 70 180

PES2 B 5 > 20*

PES2 M B 0 25

Many of the tests were stopped because of high noise level started when the ceramic

ball touched the metal for the first time. Because of this some of the Lc levels were not

reached in all tests. Also, the single tests were stopped after 10 minutes to decrease the

complete measurement time. The data thus is highly insufficient but still gives a hint of

what could be measured with the device. PUR based coatings perform clearly better

than PES coatings and PES1 B and PES1 M B coating clearly outperform PES2 and

PES2 M. The wrinkled surface on PUR1 M B and PES2 M B most likely makes the

coatings less durable than their higher gloss versions but PES1 M B outperformed PES1

B.

After the test PUR1 M B sample and PES2 B samples were profiled with Bruker

ContourGT-I 3D Optical Microscope at Bruker laboratories. In the figures 22 and 23 the

difference in the surface roughness’s of these two coatings can be easily noticed. In

PUR1 M B the transition from top coat to primer is clearly visible while in PES2 B

there is no transition visible in the correct wear depth. With PES2 B it is more clearly

visible how the material is ploughed on the sides of the wear path.

55

Figure 22. PUR1 M B topography of wear path after rotating wear test with

Bruker Tribolab. [31]

Figure 23. PES2 B topography of wear path after rotating wear test with

Bruker Tribolab. [31]

56

The ceramic ball was measured with profilometer as well after the measurements and

some residue seemed to be attached to the centre of the contact area. The unknown

material was adhered really well and it could not be detached with rubbing with a tissue.

After cleaning the ceramic ball, it was profiled again, and the wear of the ball was found

to be almost none existent after all of the tests.

5.6 Taber Rotary Platform Abrasion Tester

Taber wear tester is a common wear measurement device for different coatings. In the

test, a sample is attached to a rotating plate and abrasive rolls are resting on top of the

sample. The rotating movement of the plate makes the resting rolls rotate as well. There

are multiple different commercial abrasive wheels on the market and the pressure level

can be adjusted with adding weight on the rolls. The arrangement of the freely rolling

wheels and the rotating specimen causes a crosswise abrasive wear in a ring-shaped

zone in the standard test [32]. The test can be used to determine the amount of

revolutions to wear the topcoat (Lc2) or the whole coating off (Lc3) or to measure the

volume loss during wear.

Possible wear systems are limitless, and the manufacturer of the device provides a good

variety of different abrasive wheels for the device. For example, there are resilient or

non-resilient wheels with abrasive particles, rubber wheels without additional particles,

wool felt and aluminium wheel with or without sandpaper strip on top [33]. There are

also some modified methods of Taber test to determine the corrosion resistance

efficiency of the coating during the measurement [34], but their application is difficult.

In the measurements, resilient CS-10 wheels with mild-medium wear effect were used.

The rolls are sold by Taber Industries and the abrasive effect is caused by abrasive

particles embedded in the substrate. The manufacturer does not provide information

about the grit size of the particles and only states that the particles are either aluminium

oxide or silicon carbide. Also, non-resilient H-18 wheels and aluminium wheels from

Taber were examined for studying two body abrasion resistance and adhesive wear

respectively, but their use was not suitable with the coatings. It is also possible to use

the abrasion test device to study three-body abrasion by using rubber rolls with addition

of loose particles, but only two-body wear was studied in the thesis. The Taber

measurements were done in HAMK Sheet metal centres laboratory in Hämeenlinna.

With aluminium rolls, it was meant to study transfer film properties of the coatings, but

the rolls got scratched almost immediately when used with low gloss products. After the

rolls were scratched and high gloss products were measured the coatings got scratched

after a few rounds almost down to the zinc. The tendency of the freely rotating rolls to

inflict wear on the side area was emphasized with aluminium rolls. Thus, the

measurement with aluminium rolls had to be discarded due it did not measure the

desired properties.

57

The test method for the coatings was to measure the weight loss after 250 rounds of

rotation. The abrading wheels were resurfaced before each measurement to prevent

blocking of the rolls caused by paint. In figure 24 is represented a blocked and

resurfaced Taber wheel. The blocking effect was changing between samples and no

applicable trend could be easily found in measurements. Before and after measurement

the sample is wiped with woven cloth and ethanol to remove dirt and wear debris. For

black coatings, the test was continued after weight measurement at 250 rounds until Lc2.

If the Lc2 test had to be driven over 1000 rounds the wheels were resurfaced to reduce

the effect of blocking the abrasive surface. The samples were cleaned and weighted at

Lc2 and at 1000 rounds as well if applicable.

Figure 24. Taber roll after 1000 rounds on PUR1 and after resurfacing.

At wear to Lc2 the consumed time increased significantly compared to 250 round

testing. Because the speed of the wheel was 60 revolutions per minute it made the

longest wear test of 1907 revolution for PUR1 B to last over half an hour. The long test

time makes the visual in-situ evaluation difficult and increases the error from the

method. The point when Lc2 is reached was visually evaluated on the run and in long

runs the changes are difficult to notice. Stopping the test after every 50 rounds cycle and

evaluating the damage may help the tester but it makes the test last longer and

additional stops may interfere on the results. Also, if the test is stopped for too long time

the warmed rolls may inflict marks to the coating. The most applicable way to make the

test was to brush possible wear debris off with a soft paint brush during the test. If there

still was left something visually divergent, the test was paused and sample evaluated

while still.

The test results for volume loss after 250 revolutions and rounds until Lc2 is reached are

shown in table 15 for each coating type. No parallel tests are made for other colours

than black in 250 rounds test and the Lc2 tests are only applied for black coatings, so the

results are only indicative. The colour specific results for 250 rounds test can be seen in

58

the appendix 7. The low number of parallel samples was found suitable because of

consistent results in testing with black coatings. Three parallel samples were run for

black coatings, but for PUR1 B and PUR1 M B only one sample was taken into account

at Lc2 tests because the tests were overrun. Calculated volume loss is compared instead

of mass loss, because of large differences in densities of the coating colours and binder

materials.

Table 15. Taber abrasion results for calculated volume loss after 250 rounds and its

standard deviation. Rounds until Lc2 and volume loss per revolution tests are

measured only for black coatings. *no parallel samples are measured.

Coating type

Average volume loss at 250 rounds (cm

3)

Standard deviation between colours (cm

3)

Standard deviation between colours (%)

Rounds until Lc2 for black coatings

Volume loss per revolution at Lc2 test (cm

3)

PUR1 8.4 1.9 22 *1907 0.022

PUR1 M 13.9 1.5 11 *1900 0.017

PUR2 M 11.7 0.9 7 711 0.031

PES1 13.6 0.4 3 694 0.046

PES1 M 16.7 0.2 1 709 0.052

PES2 11.2 1.3 12 577 0.040

PES2 M 16.4 1.7 10 353 0.057

PVDF 8.0 2.7 34 1651 0.013

The test results differ highly at volume loss test at 250 rounds compared to Lc2 and

volume loss at Lc2 tests. At 250 rounds the volume loss is lowest at PVDF and PUR1

and highest at PES1 M, PES2 M and PUR1 M. PUR2 M is the most durable matt

coating being slightly more durable than PES1. The higher surface roughness is most

likely reason for PES2 to be slightly more durable than PES1 or PUR1 M. No trends

can be found for surface roughness or binder material, and most likely both have high

effect in volume loss in the test.

Between the different colours the deviation is rather large at 250 round tests. Parallel

samples are only measured in black coatings, which may increase the possibility of

errors. Though, the deviation in parallel samples on 250 rounds test was under 6% at

most coatings and should not affect that much on the results. For PUR1 B and PUR2 M

B the deviation was higher with 30% and 9% respectively, but the error does not alter

the order of the coatings. Even though the differences between the results are so high,

the coatings can be put in order based on their abrasion resistance. The same applies for

Lc2 tests that the error is rather small compared to the differences between different

coatings.

59

In Lc2 Taber test only black coatings were measured. PUR1 B and PUR1 M B are by far

the most durable and PVDF B the third. More durable binder material is most likely the

cause that PUR2 M B is as durable as thicker PES1 B and PES1 M B coating. The

decreasing effect of surface roughness is only seen between PES2 B and PES2 M B and

the difference in other high gloss and low gloss coatings is surprisingly small. In

volume loss per revolution at Lc2 the PVDF B is the most durable coating with PUR1 M

B. Otherwise the test favours more the smoother coatings and probably because of very

smooth surface PES2 B is better than PES1 B or PES1 M B.

When comparing the measurement data of 250 round tests black coatings show better

wear resistance. This may give proofs to the point that the colour pigments act as

abrasive particles while detached and the carbon black has the least abrasive effect.

Between red and grey colour, the effect cannot be seen, and this possibly can be caused

either by the lubricative effect of carbon black or the absence of titanium oxide

pigments on black coatings. The blocking should not be dominant at 250 round tests,

but the smaller particles of carbon black may be blocking more efficiently the abrasive

rolls. Some of the tested samples are represented in figure 25.

Figure 25. Taber samples PES1 B down to primer and PUR1 R, PES2 M G

and PVDF S after 250 rounds. Size of each sample is 10 cm x 10cm.

Visually the samples abraded almost the same level at the 250 round tests and at Lc2

tests. The colour of the abraded area is in all samples visually almost same as in non-

abraded area, but the gloss of high gloss coatings is decreased and with low gloss

products the gloss is increased in visual evaluation. Only exception in the colour

changes during the test are silver PVDF coatings. PVDF S, PVDF M S and PVDF

60

MAX S have all become darker and thus the gloss level evaluation visually is difficult.

In figure 25 is shown the gloss reduction in high gloss products and slight gloss increase

in low gloss products. Also, the colour change of PVDF S can be seen in the figure.

5.7 Erosive wear tests

With erosive wear, it is possible to estimate the behaviour of the coatings under flow of

loose material, for example street dust or pine cones. For the study, two different types

of erosive wear tests were chosen: solid particle erosion test for dry atmosphere and

slurry pot erosion test in wet conditions.

Erosive wear can be studied by using a certain amount of eroding matter with certain

speeds. It is difficult to know the exact eroding conditions due unstable flow of particles

but by repeating the same test for all the samples and comparing the results, a modelling

of flow is not necessary.

5.7.1 Solid particle erosion tester

In solid particle erosion tester, the eroding matter is fed from the middle and by

spinning the propellers the particles hit the tested samples with a determined speed. The

sample holders can be rotated to change the contact angle of the particles between 15°

and 90°. For metals and polymers an angle of 30° has shown to be the most compatible

for testing in the device at TUT. 30° contact angle also correlates to the real situation

where wind blows dust and possibly sand against the roof. Speed of the rotating plate

was set to 2002 ± 5 rounds per minute, so the particle speed was approximately 5 m s-1

.

The used sand was quartzite sand from Silicon Oy and the particle size was 50-200 µm.

The measurement was done at Tampere Wear Center, Tampere University of

Technology and the test configuration is shown in figure 26.

61

Figure 26. Solid particle erosion tester with samples attached

The tested samples were attached by wedging the 20 mm x 15 mm samples to sample

holders. It is possible to measure 15 samples simultaneously, which makes the testing

very efficient. Two test methods were run simultaneously: constant rate of erosion and

erosion until the coating is worn off. Three parallels of each sample were attached at the

start of the test and run with 2 kg of sand. After the tester stopped spinning, two of the

parallel samples were detached for weight measurements and visual comparison. The

sand was swiped off with a soft paint brush. The samples are also evaluated visually on

2 kg in a scale of 0-5. The visual grading in 2kg solid particle erosion test is explained

in table 16.

Table 16. Visual grading in solid particle erosion test

Visual grade Explanation

5 Looks like no test has been applied

4 Small changes in colour or gloss but no other visual flaws

3 Severe colour or gloss changes appear or few pinholes to primer

2 A lot of pinholes to primer or larger areas to primer. No zinc revealed

1 Primer can be seen easily and few pinholes to zinc

0 Zinc is revealed or multiple pinholes to zinc

Based on the grading in table 16 the coatings are evaluated at appendix 8 in addition

with volume losses. The average results of visual differences and volume losses

calculated from mass differences are shown in table 17.

62

Table 17. Average visual evaluation and volume loss after 2 kg of sand is used at Solid

particle erosion test

Coating type

Visual evaluation after 2 kg (0-5)

Standard deviation between colours

Standard deviation between colours (%)

Volume loss after 2 kg (cm

3)

Standard deviation between colours (cm

3)

Standard deviation between colours (%)

PUR1 3.3 0.12 4 0.53 0.08 16

PUR1 M 3.4 0.31 9 0.65 0.07 11

PUR2 M 1.0 0.00 0 0.73 0.08 11

PES1 3.0 0.00 0 0.74 0.11 15

PES1 M 1.0 0.00 0 1.35 0.12 9

PES2 2.3 0.47 20 0.70 0.22 31

PES2 M 1.0 0.00 0 0.74 0.07 9

PVDF 3.9 0.49 13 0.55 0.22 41

In the results, it is notable that PVDF coatings are the best at visual evaluation after 2 kg

test, but PUR1 is in fact the best performing coating based on the volume loss. Also, all

the matt coatings except PUR1 M are visually very poor while PUR1 M is the second

best in comparison. Volume loss test has quite large standard variation between the

colours and PVDF even more so, because of different kind of coatings under one name.

At volume loss test the losses are otherwise on the same level, except PES1 M has lost

almost double the volume loss as the other coatings. The reason for this large exception

is not known thus the surface roughness is at the same level as in PUR2 M and chemical

competence at similar level as in PES1. It might be that two parallel samples may have

been not enough to exclude single errors, but the results still should be considered

comparable.

The test was continued for one sample of each coating until Lc2 and Lc3 were reached.

First addition of sand was 1 kg, which was followed by several 0.5 kg steps until all of

the samples showed damage to Lc3, or until total of 5.5 kg of sand was consumed. The

amount of sand used before Lc2 or Lc3 is reached is recorded as the result. The Lc2 and

Lc3 definitions had to be determined separately for the erosion test, because the erosion

area was more severe on the other side of the samples. In solid particle erosion test Lc2

and Lc3 are reached when there are multiple pinholes of primer or zinc visible, or the

area is spread slightly instead of localized single pinholes to the lower layer. The

uneven distribution of erosion area can be seen in the figure 27. Results from the Lc2

and Lc3 tests are shown in appendix 8 and the average between colours in table 18.

63

Table 18. Average amounts of sand the coating lasts until Lc2 and Lc3 are reached. The

definitions in the Lc2 and Lc3 differ slightly on the test.

Coating type

Lc2 at erosion test (kg)

Standard deviation between colours (kg)

Standard deviation between colours (%)

Lc3 at erosion test (kg)

Standard deviation between colours (kg)

Standard deviation between colours (%)

PUR1 4.2 0.47 11 5.2 0.24 5

PUR1 M 4.0 0.71 18 5.2 0.47 9

PUR2 M < 2.0 0.00 0 2.5 0.00 0

PES1 2.8 0.24 8 3.7 0.24 6

PES1 M 2.5 0.00 0 2.5 0.00 0

PES2 2.5 0.00 0 2.8 0.47 17

PES2 M < 2.0 0.00 0 2.5 0.00 0

PVDF 3.8 0.40 11 4.2 0.51 12

In Lc2 and Lc3 tests the matt coatings were consistently less durable than high gloss

coatings. The sand particles possibly got stuck in surface shapes and eroded the coating

more efficiently than in smoother surfaces. For thin matt coatings PUR2 M and PES2 M

the erosion atmosphere seems to be slightly too rough after 2 kg and the Lc2 level cannot

be measured precisely. The order of the coating types can still be measured accurate

enough and PUR1, PUR1 M and PVDF were the most durable nearly at the same

performance and PES1, PES1 M and PES2 reached their Lc2 after around 2.5 kg of

sand.

At Lc3 test PUR2 M, PES1 M and PES2 M got almost the same low results, while the

higher gloss versions PES1 and PES2 M had their results in completely different level.

With PUR1 the difference between low gloss and higher gloss was non-existent, which

is interesting because at other coatings the difference is so distinct. PUR1 and PUR1 M

are clearly more durable than other coatings and PVDF coatings follow with PES1

being in the middle. PES2 is only slightly more durable than the low gloss coatings. In

figure 27 PUR1 M and PES2 M samples can be seen after the tests compared to a

reference.

64

Figure 27. PUR1 M samples (left) and PES2 M samples (right) in solid

particle erosion test. The uppermost row is reference, two rows in the middle are

after 2 kg of sand and the lowest row is after 5.5 kg of sand. Sample size 20 mm

x 15 mm.

Not all the sample sets were run with 5.5 kg of sand because the samples had already

abraded through. The area where sand particles hit was changing slightly during the test,

due to eroding of the sample holders and the tubes where the speed of sand was

accelerated.

5.7.2 High speed slurry pot

High speed slurry pot can be used to determine erosive properties of particles in a

liquid. The liquid can be determined for the application to have acidic or basic condition

and the particle size and material can be chosen freely. The presence of water makes the

test conditions different from solid particle erosion due cavitation and other properties

of flow. The test was picked due the possibility to describe wear conditions such as dirt

running down the roof during rain. The slurry pot tester at Tampere Wear Center can be

seen in figure 28.

65

Figure 28. Slurry pot erosion tester with samples after a 30 min cycle.

The test parameters were set to be mild enough to be relevant for coatings on roof. The

used slurry contained 19% of 50-200 µm quartz sand on water and the samples were

well under water level during the testing. Speed of the rotation was 500 ± 4 rpm, which

means around 4.5 m∙s-1

velocity on the outer edge of the samples. The sample size was

35 mm x 35 mm and the samples were edge protected as shown in figure 28. Because

the flow properties are slightly different in each sample holder height, the test was

stopped after every 30 minutes, and the samples were switched between sample holders.

Four 30-minute cycles were repeated and the whole testing time was 2 hours for each

sample. The slurry was also changed after each 30-minute step to provide homogenous

conditions.

The wear was evaluated visually and with volume loss calculated from the mass

difference. Due polymers tendency to absorb water the samples were dried for 60

minutes in an oven at 40 °C before each weighting. The coating thicknesses are so low

that the samples should have dried enough even in such conditions without influencing

on other properties of the coating. The samples were cleaned with a paint brush by

sweeping 10 times in one direction just before weighting. Visual evaluation was

implemented in the same manner as with solid particle erosion test (table 16). The

average results of visual evaluation and volume loss are shown in table 19 and the full

results in appendix 9 with their standard deviations.

66

Table 19. Average visual grading and volume loss of coatings and the deviation between

samples at Slurry pot testing.

Coating type

Visual evaluation (0-5)

Standard deviation between colours

Standard deviation between colours (%)

Volume loss (cm

3)

Standard deviation between colours (cm

3)

Standard deviation between colours (%)

PUR1 4.0 0.0 0 6.9 1.5 21

PUR1 M 3.7 0.5 13 11.3 1.0 9

PUR2 M 1.5 0.5 33 10.5 1.0 9

PES1 2.5 0.7 28 11.6 1.7 15

PES1 M 1.8 0.3 14 16.7 1.5 9

PES2 1.8 1.3 72 11.8 3.1 26

PES2 M 0.8 0.5 57 13.6 0.6 4

PVDF 4.2 0.4 10 5.2 1.5 29

Visually the test samples were consistent in two parallel samples, but the deviation

between colours was moderate. The differences between coating types was larger than

deviation between colours of a coating and thus the order of performance can be made.

PUR1, PUR1 M and PVDF performed again well at visual test and low gloss coatings

had lower performance than their higher gloss versions, except for PVDF M S. The

difference in results between PUR2 M, PES1 M and PES2 was so small that they can be

considered to perform at the same level but PES1 is slightly better than these coatings

while PES2 M could be considered the poorest coating in the visual test. Some visual

samples are shown in figure 29.

67

Figure 29. PUR1 (left), PES1 (right) and PES2 M (down) after Slurry pot test.

The sample size is 35 mm x 35 mm and the top row in each photo is a reference

sample.

At volume loss test PES1 M had the largest volume loss in a large marginal, even the

visual grade was at the same level with many of the coatings. Its higher gloss version

PES1 was considerably on a higher level of performance, though still being less durable

than any of the PUR based coatings and only slightly more durable than PES2 and PES2

M. PUR1 and PVDF had the lowest volume losses in the test. The gloss level in PUR1

and PES1 coatings had very high difference in favour of higher gloss, but the difference

between PES2 and PES2 M was slightly lower. It has to be noted that all samples of

PES1 M, PES2 M and some occasional colours in other coatings were completely

eroded through topcoats. This means that in these samples also primer started eroding

and may have inflicted on the mass losses. Interesting is that at high gloss coatings the

standard deviation between coating colours was a lot higher than in matt coatings.

5.8 Coil damage measurement device

Coil damage measurement device is a self-build method at PTE Coatings AB Gamleby.

In the test, flat sheets of coated metal are compressed against each other and rotated 33°.

Typically, the coating is rotated against its own backing coating to give information

about the marring effect and possible transfer film formation when the product is on

coil. The speed of the rotation is set at 0.5 rpm and the pressure can be adjusted between

the runs.

68

The test samples are not attached to the test device but are just bent from the edges to

prevent slipping of the samples during the test. This brought out a problem because the

friction with testing at 6.3 bars was too high for the substrate and the core metal started

to form instead of marring the coating. With most of the samples the forming effect of

the steel was so small that the test could be carried out with 6.3 bars but additional test

at 5.0 bars was implemented for the highly formed samples. The 5 bar test was only

applied for black coatings. The test assembly can be seen in figure 30.

Figure 30. Test assembly of coil damage measurement test, starting position at

left and end position at right. The contact area of samples is 100 mm x 160 mm.

The evaluation of the samples was made only visually. The visual evaluation does not

follow any standard, because about half of the samples were scratched to zinc. The

grading system of the coatings is represented in table 20.

Table 20. Description of grades resulted with Coil damage measurement device

Grade Description

5 Sample looks like no test has been applied

4 Tiny scratches or thin trails with transfer film or colour change can be noticed

3 Small areas of transfer film

2 Large areas of transfer film

1 The coating severely scratched or zinc visible in pinholes

0 Adhesion between primer and zinc completely lost in medium areas

Examples of each value in visual evaluation of Coil damage measurement device is

shown in figure 31.

69

Figure 31. Visual samples of grading from 5 to 0. The arrows indicate barely

visible wear or marring. The contact areas of the samples seen in figure are 100

mm x 160 mm.

The coating and backing coat were evaluated to estimate the overall wear during the

test. Average values from each coating type are shown in table 21 and complete results

in appendix 10.

Table 21. Visual evaluation of the samples after Coil damage measurement test. *Only

black colour on 5 bars is tested

Coating

Average

top coat

Standard

deviation

(%)

Average

back

coat

Standard

deviation

(%)

PUR1 4.0 20 3.3 14

PUR1 M 3.3 14 3.0 0

*PUR2 M 3.0 - 2.0 -

PES1 2.3 53 2.0 71

PES1 M 1.5 33 0.5 100

*PES2 0.0 - 0.0 -

*PES2 M 2.0 - 1.0 -

PVDF 0.2 200 0.2 200

70

PUR1 was the most durable coating in the test and PES2 with PVDF the least durable.

PUR1 M and PUR2 M were almost as durable, but it has to be noted that PUR2 M was

measured with lower pressure. PES based coatings were almost at the same level of

durability with each other, except PES2 which had a 0 result even in the testing with

lower pressure. PVDF coatings except PVDF S had also a 0 result in testing with the

original 6.3 bar pressure. The significance of gloss level cannot be directly concluded

from the measurement but interesting is that the coatings with smoothest surface had the

ultimate lowest durability. This may be caused by higher real contact area in PES2 and

PVDF coatings during the test, since they are the only coatings without structuring

particles or wrinkling.

Evaluation of the coatings was difficult because the visual difference might not be very

large, and no parallel samples were measured. The standard deviation between colours

is rather high but the back coat seems to correlate well with the top coat. Due to

differences in the wear counterpart material the test gives more correlation to real life,

but the data is only for comparison. More suitable way to use the test equipment would

be to use a certain pressure as a threshold, which at there should be no visible damage

over value 3.

5.9 Flat-to-flat friction

Flat to flat friction measures friction of coating and a friction counterpart at higher

pressures. The tests were made with Zwick-Roell Z050 Allround-Line Table-Top

tensile test device with a self-made pressure clamps perpendicular to the direction of

movement. The used 15 mm x 15 mm friction counterparts of through-hardened K600

steel are clamped with wanted pressure and the metal sheet or sheets are pulled and the

device measures the pulling force needed. The clamping pressure used was 100 bars,

area of the friction counterparts 225 mm2, speed of the test 10 mm/s and the

measurement distance 150 mm. Because the topcoat and backing coat are not the same

material, two samples of each material was put their back coatings against each other.

So, the friction counterparts located on both sides of the sample are touching only

topcoat. The samples and friction counterparts were wiped with ethanol and nonwoven

cloth before measurements to remove grease and dirt. The test assembly can be seen in

figure 32.

71

Figure 32. Test assembly of flat-to-flat friction test with Zwick-Roell Z050

Allround-Line Table-Top tensile test device at temperature closet. Two sample

sheets are set backing coats against each other for one measurement.

In coil, the stresses can be rather high as in flat to flat friction. With this method, it may

be possible to see differences at transfer film formation. There have also been problems

with opening of coils and the friction is in interest outside of the thesis area as well. The

method simulates partially the processing of the sheets and with different material pairs

the test could simulate the effects of walking on the roof.

Calculated contact force between the clamps in the test with 100 bars is 1880 N. The

friction coefficient is calculated from the average pulling load from three parallel

measurements by dividing them with contact force. Load cell of 50 kN is used with

precise measurement range starting from 500 N. The results are shown in appendix 11

and average results with standard deviations between colours are shown in table 22.

72

Table 22. Average friction coefficients for coating types at room temperature with 100

bars clamping force in flat-to-flat friction test.

Coating type

Friction coefficient

Standard deviation between colours

Standard deviation between colours (%)

PUR1 0.38 0.11 28

PUR1 M 0.62 0.16 25

PUR2 M 0.32 0.03 9

PES1 0.38 0.05 13

PES1 M 0.38 0.03 9

PES2 0.50 0.02 5

PES2 M 0.39 0.02 5

PVDF 0.46 0.08 17

It is interesting that the surface roughness of matt coatings did not show correlation to

the friction coefficient results in either direction. The parallel samples in the same

colour had deviations under 10%, but between colours the deviation raises up to 28% in

some coatings. The friction coefficients were between 0.30 and 0.60 for most coatings

but for PUR1 G the friction was only 0.25 and for PUR1 M R the coefficient was even

0.83. The exceptional values still did not influence on the order of the average results

for the coatings and the friction levels can be considered comparable. PVDF M S

increases the average for PVDF coatings and the average of higher gloss PVDF coatings

would be at same level with most of the other coatings. It is not certain whether the

increased friction coefficient of PUR1 M and PES2 or slightly lower value of PUR2 M

are significant or not.

The results become more interesting when compared to the results from the same test at

-15.0 °C. Friction behaviour of polymers in general is difficult to estimate. The device

has built-in cooling unit working with liquid nitrogen. The deviation of the temperature

was around ± 0.3 °C. The test was only measured for black coatings and for few random

coloured coatings. Two parallel samples are measured from most of the coatings, if

marked otherwise only one measurement is fulfilled. The average results for the coating

types are shown in table 23 and full testing results in appendix 11.

73

Table 23. Average friction coefficients for chosen coatings at -15 °C with 100 bars

clamping force in flat-to-flat friction test. *No parallel samples measured

Coating type

Friction coefficient at -15 °C

Friction coefficient at room temperature

Increase of friction coefficient

Increase of friction coefficient (%)

PUR1 B* 0.65 0.51 0.14 28

PUR1 M B 0.61 0.45 0.16 35

PUR1 M R* 0.89 0.83 0.06 7

PUR2 M B 0.36 0.29 0.07 26

PES1 B 0.61 0.33 0.27 82

PES1 M B 0.61 0.34 0.27 77

PES2 B 0.64 0.50 0.14 27

PES2 M B 0.73 0.37 0.36 98

PES2 M G* 0.74 0.41 0.33 81

PVDF B 0.38 0.37 0.02 5

With all coatings, the friction coefficient had increased at sub-zero temperatures. The

increase of friction coefficient is largest with PES2 M B, PES2 M G, PES1 B and PES 1

M B. PES2 B was the only PES based coating where the increase in friction coefficient

was not extremely high. The lowest friction values and smallest increases in friction at

cold circumstances were with PUR2 M B and PVDF B. PUR1 M R showed

extraordinarily high friction coefficient already at room temperature, but the coefficient

of friction still increased in cold conditions.

Friction behaviour of polymers in different temperatures is very complex [35] and the

thesis does not try to answer on questions based on it. In many cases the friction

coefficient increases while temperature decreases, and this can be seen also in the

measurements. External humidity in the testing chamber could have influenced on the

friction properties at sub-zero temperatures and even some snow formation was seen

when the cooling cycle was on. The samples were wiped clean with ethanol right before

testing so no water and ice should have been between samples and friction counterparts.

5.10 Sledge friction

Another friction measurement, the sledge friction test was performed with Zwick-Roell

Z005 TH Allround-Line Table-Top Machine at HAMK. At this measurement, the

contact pressure is adjusted by adding weights on a sliding sledge. A power sell of 100

N is used on pulling the sledge and the measurement is repeated nine times on the same

sample: three times with three different sledge weights. The length of the pulling

distance is 15 cm. The material pair is a rubber sheet of 60 mm x 50 mm. The goal of

the measurement is not to directly estimate the mechanical durability but to measure

which coating is the most slippery compared to a shoe bottom. The properties of the

74

rubber sheet were not measured and most likely differed from shoe bottom partially.

The test assembly is shown in figure 33.

Figure 33. Test configuration of sledge friction where sledge with rubber sheet

attached is dragged on top of the sample (PUR1 G in this case).

The friction coefficients were calculated from the pulling force and weight of the

sledge. The static friction was calculated from the peak values of pulling forces at the

start of the tests and kinetic friction coefficient is received from the average pulling

forces. The total weights of the sledges are 210 g, 511 g and 1014 g. Average results for

coating types are shown in table 24 and for each colour in appendix 12.

Table 24. Static and kinetic friction coefficients for and their deviation between coating

colours.

Coating type

Average static friction coefficient

Standard deviation between colours

Standard deviation (%)

Average kinetic friction coefficient

Standard deviation between colours

Standard deviation (%)

PUR1 1.2 0.45 38 0.8 0.12 15

PUR1 M 0.6 0.06 10 0.5 0.02 5

PUR2 M 1.0 0.01 1 0.6 0.02 4

PES1 0.9 0.08 9 0.6 0.03 5

PES1 M 0.6 0.02 4 0.5 0.01 2

PES2 1.6 0.19 12 1.0 0.11 11

PES2 M 0.7 0.10 15 0.5 0.07 13

PVDF 1.0 0.26 27 0.6 0.12 19

75

High gloss coatings had higher static friction coefficients than low gloss coatings at the

Sledge friction test. Many of the high gloss coatings exceeded value of 1.0 meaning that

the pulling force had to be higher than what is the total weight of the sledge. Highest

static friction coefficients were with PUR1 R, PES2 B and PES2 W with ratios of 1.80,

1.79 and 1.70 respectively. The standard deviation between different colours is rather

small for most of the coatings but PUR1 and PVDF coatings make an exception. For

PUR1 coatings the PUR1 R increases the standard deviation extremely while PUR1 B

and PUR1 G have static friction coefficients of 0.90 and 0.81 respectively. In PVDF

coatings black and white have friction coefficient values well above 1.0 but silver

coatings PVDF S, PVDF M S and PVDF MAX S are only 0.86, 0.73 and 0.72

respectively.

At kinetic friction measurements, the frictions were lower than the static friction

coefficients. Otherwise the results were almost in the same order but the magnitude of

the difference between coatings decreased. Low gloss products had slightly smaller

friction coefficients, but it cannot be said whether the differences are significant. Also,

the deviations between colours are slightly smaller in the tests.

Only one rubber sheet was used, and its wear was followed. After every measurement,

the rubber surface showed some dark stripes, but they could be cleaned with wiping the

surface with ethanol and nonwoven cloth. The rubber sheet attached to the sledge can be

seen before and after cleaning in figure 34.

Figure 34. Cleaned rubber surface at left and the surface after testing at right.

Size of the contact area was 50mm x 60mm.

76

Standard deviations within colours are good, under 10% in most coatings which makes

the friction measurement itself very comparable. The error from using the same sample

in all measurements can be considered almost non-existent. It is just not clear how much

and how the friction coefficient values could help in estimation of mechanical durability

of the product, but the measurement was merely applied for roof safety matters.

5.11 Abrasion testing machine at SSAB

SSAB has built its own abrasion testing machine where sandpaper or scouring pads

reciprocates and wears the surface of the samples, but the test method was not

considered in the thesis because a previous study of the equipment has been made [23]

and the results were not promising. The testing equipment consists of an upright drill

with rotating crank handle, reciprocating plate and a sample holder. In the reciprocating

plate there, are holes for blocks in which the abrasive paper can be attached. It is

possible to attach additional weight to the blocks for more severe abrasion. The blocks

are reshaped if any deformation is noticed and the wearing counterpart is changed after

every test. [23]

In scouring pad testing the sample is scrubbed with a procrastinating movement for one

minute with speed of 56 min-1

. The total weight of the block is 600 g. The scrubbed area

is evaluated visually and graded numerically from 0 to 3 by comparison of standard

samples. The test is known to produce better results for white coloured coatings and

structured surfaces due to visual evaluation and easier detection of wear on dark or

smooth coatings. Metallic colours especially are sensitive for gloss change in different

angles in visual evaluation. Gloss and colour measurement devices can be used in

addition, but it has to be noted that the gloss value for high gloss products lowers and

for low gloss products it rises. Possible error sources are the deviation in the wearing

material, wear of the counterpart and the attachment of the sample. [23]

Abrasion test is used to determine the maximum load a coating withstands without

wearing down to zinc. A silicon carbide abrasive paper from Würth with grit size of 120

is used. The speed of the drill is the same 56 min-1

the testing time is 2 times 60

seconds. In the middle of the test the samples are cleaned with compressed air and

switched to other position to reduce the error from the test method. The coatings are

evaluated as passed if there are 0 or 1 uniform scratches down to zinc with length of 10

mm. The result of the test is given as a mass the coating withstands in the test. [23]

One possible way to use the testing machine is to use a constant load with abrasive

paper to determine the mass change during the test. Difficulty in this testing is that the

change in the mass is rather low and the testing time has to be low to not to wear the

zinc or metal substrate.

77

5.12 Other possible test methods

The used methods are only a variety of methods which were found suitable and were

available. There also exist multiple different test methods for determination of

mechanical durability of a coating. Popular methods in coating industry and interesting

possible methods, which were not measured, are briefly described in this chapter.

Connection between hardness and wear is typically linked in metallic and ceramic

materials [3] and the connection in coatings would be interesting to be studied. It was

concluded that with scratch hardness the scatter in indentation hardness would be

decreased. Hardness measurements as pendulum hardness or micro indentation were

considered to be tested but because lack of resources they had to be discarded.

Pendulum hardness testing is a common possible way to measure hardness for non-

structured materials. Substrate must not deform or vibrate under load of pendulum and

film thickness over 30 µm is recommended to minimize the influences of substrate.

Coatings must be plane and clean: coarse fillers and dust causes false measurements.

Due to high filler contents in the samples pendulum hardness was discarded. [36]

Stone chip resistance testing is especially used in car industry. It is used to determine

impact wear [37] and it was not used in the measurements because the chips usually are

too large to simulate any damage that is common to happen at a roof or façade. Similar

and more reasonable impact properties were achieved with the used solid particle

erosion tester.

Taber rotating platform test would be very interesting to be determined in slurry. It does

not completely correlate on the environment on roof, but electric resistance of a coating

has been in a high interest on recent research [38]. By moderating the test to be in

milder wear environment, for example with small bearing balls it would be possible to

simulate icy snow rolling on a roof.

78

6. ANALYSIS AND COMPARISON OF THE TEST

RESULTS

Comparison of different results was found to be difficult between scratch methods and

wear methods. Different scratching tips were used at scratch tests and different wear

equipment measured different wear types, so the results were typically in different

magnitudes or units. In chapter 6 the results are analysed and compared with few

different ways.

By grading the test results with same scale, the comparison of results gets easier.

Common scale makes it also possible to calculate an overall average of the durability of

the coatings. From the graded results it is easier to imply statistical analysis, which is

used to help to compare the results and test methods.

All of the tests give valuable data about how the coating lasts in certain test

environment but some of the used methods did not describe the real-life damage as well

as expected. Also, some of the methods had low accuracy, some methods had scatter in

parallel samples and some methods correlated only on the thickness of the coating.

Because of this, the methods are graded by experience and then weighted so that the

methods with higher usability have higher influence on the final grade of the

mechanical durability of the coating. The mechanical durability of a coating is thus

defined as the wear and scratch resistance of the coating from weighted average of

chosen measurement methods.

6.1 Grading of coatings’ performance

All of the measurement results can be converted into a numerical value, but the results

are not easily comparable. To make comparison easier, each of the result is given a

grade between 0 and 5. For measurements where detection of damage is considered,

standard ISO 4628-1 [22] is applied and in other tests the standard is adapted on suitable

parts. Not all of the measurements are found to be gradable, for example it is not known

which level of friction is acceptable in the friction tests or how the elastic-plastic

dependency in UMT could help on estimation of durability of the coatings. Thus, these

methods are not given grades and are excluded from the numerical comparison.

Correlation of the ungradable methods to other methods is still studied.

The fitting of grades to a scale of 0 to 5 is made by different mathematical operations

presented below. The scale is chosen because visual grading is already done in similar

79

scale according to standard SFS-EN ISO 4628-1 [22], where 0 is the most severe

damage and 5 significates that no visual damage can be seen. Some of the results are

already in the scale of 0-5, for example in Lc4 progressive load test with Tribolab is run

into 5 mm and so the grade can be interpreted directly from the distance of where Lc4

starts. Transition from numerical result to a grade directly is marked as “equation” 0.

In most cases the grading is not as straightforward. One way for determining the grade

is to give the highest single measurement point a value 5 and the ratio of the grade and

absolute measurement value can be used as a multiplier. The equation gets a form

𝐺𝑟𝑎𝑑𝑒 =𝑎 ∙ 5

𝑎𝑚𝑎𝑥, (1)

where a is the result for the coating and amax the highest value obtained from any of the

measured coatings. This is the most used formula in the thesis for determination of the

grade.

The wear test results do not always fall on a linear scale of grades when using the

formula 1. At least in wear tests with Erichsen scratch hardness tester and with Tribolab

UMT a logarithmic scale gives more comparable results and the formula 1 is put in

form

𝐺𝑟𝑎𝑑𝑒 =log(𝑎) ∙ 5

log (𝑎max ). (2a)

Logarithmic scale can be

Other wear tests, such as Taber Lc2 revolution test, do not fit properly on the linear or

the logarithmic scale but is somewhere in the middle. Thus, function 2b with square

root is established

𝐺𝑟𝑎𝑑𝑒 =√𝑎 ∙ 5

√𝑎max . (2b)

Square root of value a is found to give the best comparison between results and is thus

used in grading of how many revolutions a coating last in Taber Lc2 test.

At volume loss tests the more the coating loses weight, the less it resists the mechanical

damage. Thus, the equation has to be modified into a form

𝐺𝑟𝑎𝑑𝑒 = 𝐶 −𝑏 ∙ 5

𝑏𝑚𝑎𝑥, (3)

where C is a measurement related constant, b is the volume loss of the coating and bmax

the maximum average volume loss of all coatings. Constant C is determined so that the

highest grade for any of the coatings gets the value 5.0. The graded values are shown in

80

table 25. Number in the end of the name of the test tells which equation has been used

as determined previously.

Table 25. Applicable graded results from single pass scratch type of tests. Numbers in

parenthesis indicate the equation of how the grade is calculated.

Coating Co

ati

ng

th

ickn

es

s (

µm

)

Pen

cil

Ha

rdn

ess

Lc3 (

0)

Bra

ive in

str

um

en

t L

c2 w

ith

need

le s

cra

tch

(1)

Bra

ive in

str

um

en

t L

c3 w

ith

need

le s

cra

tch

(1)

Bra

ive in

str

um

en

t L

c2 w

ith

co

in lik

e s

cra

tch

er

(1)

Lc1 w

ith

Scle

rom

ete

r (1

)

Lc1 a

fter

1 h

ou

r w

ith

Scle

rom

ete

r (1

)

Lc3 w

ith

Scle

rom

ete

r (1

)

Lc1 w

ith

sp

heri

cal h

ead

in

Eri

ch

sen

scra

tch

ha

rdn

ess t

este

r (1

)

Lc3 w

ith

co

nic

al h

ead

in

Eri

ch

sen

sc

ratc

h h

ard

nes

s t

este

r (1

)

Lc3 w

ith

UM

T P

rog

ressiv

e lo

ad

sc

ratc

h (

1)

Lc4 w

ith

UM

T P

rog

ressiv

e lo

ad

sc

ratc

h (

0)

Scra

tch

ha

rdn

ess

HS

p w

ith

3 N

lo

ad

wit

UM

T (

1)

Avera

ge o

f s

cra

tch

ing

ty

pe o

f te

sti

ng

PUR1 B 48 2.0 3.0 4.3 1.9 3.5 2.8 5.0 3.2 4.1 5.0 5.0 2.5 3.5

PUR1 R 47 3.0 3.0 4.3 1.9 3.5 2.8 5.0 4.1 5.0 - - - 3.6

PUR1 G 53 3.0 4.0 4.3 2.3 4.5 3.0 5.0 5.0 4.3 - - - 3.9

PUR1 M B 46 1.0 5.0 4.3 3.1 1.5 2.8 4.7 2.3 4.5 2.8 3.5 3.4 3.2

PUR1 M R 45 2.0 2.0 4.3 3.1 0.5 0.3 4.8 0.2 2.5 - - - 2.2

PUR1 M G 48 2.0 2.0 4.3 3.1 0.5 0.5 3.7 0.2 3.4 - - - 2.2

PUR2 B 26 3.0 2.0 4.3 1.5 1.0 1.3 4.8 0.9 3.0 - - - 2.4

PUR2 R 24 1.0 2.0 3.6 2.7 4.0 3.3 3.9 2.3 2.3 - - - 2.8

PES1 B 36 3.0 4.0 3.6 2.3 4.0 3.3 5.0 2.7 4.1 3.8 3.5 2.7 3.5

PES1 R 35 3.0 3.0 3.6 1.9 3.0 2.0 3.8 2.3 3.0 - - - 2.8

PES1 G 35 3.0 2.0 3.6 1.9 3.0 1.5 4.2 3.2 3.0 - - - 2.8

PES1 M B 36 2.0 4.0 2.9 2.7 3.5 1.8 4.8 2.0 3.4 4.9 3.6 3.3 3.2

PES1 M R 36 2.0 4.0 2.9 1.9 1.5 1.3 4.8 1.1 3.2 - - - 2.5

PES2 B 26 3.0 2.0 2.9 1.5 1.0 0.8 3.9 0.7 3.0 4.0 3.6 3.0 2.4

PES2 R 25 3.0 2.0 2.9 1.2 1.0 0.5 3.7 0.9 2.7 - - - 2.0

PES2 W 27 3.0 3.0 2.9 1.2 1.0 2.3 3.9 0.5 3.0 - - - 2.3

PES2 M B 30 1.0 1.0 2.1 1.5 2.0 5.0 2.0 1.4 1.6 2.0 1.8 5.0 2.2

PES2 M R 29 2.0 1.0 2.9 1.9 2.0 5.0 1.7 2.3 1.4 - - - 2.2

PES2 M G 30 1.0 1.0 2.1 1.5 1.5 4.4 1.9 1.4 1.4 - - - 1.8

PVDF B 27 5.0 1.0 3.6 3.5 3.0 1.5 3.8 1.1 2.0 - - - 2.7

PVDF S 26 1.0 1.0 5.0 5.0 5.0 2.5 4.3 2.3 5.0 - - - 3.5

PVDF W 26 3.0 2.0 5.0 1.9 1.5 1.0 2.8 1.1 2.3 - - - 2.3

PVDF M S 29 3.0 1.0 4.3 3.5 0.5 0.3 3.0 0.2 3.2 - - - 2.1

PVDF MAX S 36 1.0 1.0 5.0 3.5 5.0 2.5 4.8 1.8 5.0 - - - 3.3

81

Table 26. Applicable graded results from different wear and erosion tests. Numbers in

parenthesis indicate the equation of how the grade is calculated.

Coating Lc3 in

Eri

ch

sen

sc

ratc

h h

ard

nes

s t

este

r w

ea

r te

st

(2)

Lc2 w

ith

UM

T w

ea

r te

st

(2)

Lc4 w

ith

UM

T w

ea

r te

st

(2)

250 r

ou

nd

s T

ab

er

test

wit

h 1

kg

weig

ht

(1)

Vo

lum

e lo

ss a

t p

rim

er

at

Lc2 t

est

wit

h T

ab

er

(3)

Lc2 t

est

wit

h T

ab

er

(2.2

)

Vis

ua

l ev

alu

ati

on

aft

er

2 k

g in

So

lid

part

icle

ero

sio

n t

est

(0)

Vo

lum

e lo

ss a

fte

r 2 k

g in

So

lid

pa

rtic

le e

rosio

n t

est

(3)

Lc2 a

t S

olid

part

icle

ero

sio

n t

est

(1)

Lc3 a

t S

olid

part

icle

ero

sio

n t

est

(1)

Vis

ua

l ev

alu

ati

on

aft

er

2 h

ou

rs in

Slu

rry p

ot

(0)

Vo

lum

e lo

ss a

fte

r 2 h

ou

rs in

Slu

rry p

ot

(3)

Vis

ua

l ev

alu

ati

on

of

ap

pe

ara

nc

e o

f to

p c

oat

aft

er

Co

il d

am

ag

e

measu

rem

en

t te

st

(0)

Avera

ge o

f w

ea

r an

d e

ros

ion

testi

ng

PUR1 B 4.9 5.0 5.0 4.5 4.6 5.0 3.5 4.1 5.0 5.0 4.0 4.5 5.0 4.6

PUR1 R 5.0 - - 3.3 - - 3.3 3.7 3.9 4.5 4.0 3.8 3.0 3.8

PUR1 G 4.8 - - 3.5 - - 3.3 3.4 5.0 4.5 4.0 3.6 4.0 4.0

PUR1 M B 4.7 4.9 5.0 2.7 5.0 5.0 3.0 3.1 3.3 4.1 3.0 2.9 4.0 3.9

PUR1 M R 4.5 - - 2.2 - - 3.8 3.7 5.0 5.0 4.0 3.0 3.0 3.8

PUR1 M G 4.4 - - 1.7 - - 3.5 3.2 5.0 5.0 4.0 2.4 3.0 3.6

PUR2 B 3.7 - - 3.1 3.9 1.9 1.0 3.3 2.2 2.3 2.0 3.2 3.0 2.7

PUR2 R 2.7 - - 2.6 - - 1.0 2.8 2.2 2.3 1.0 2.7 - 2.2

PES1 B 4.0 2.5 3.3 2.3 2.5 1.8 3.0 3.1 3.3 3.6 3.5 3.3 4.0 3.1

PES1 R 2.2 - - 2.4 - - 3.0 3.5 3.3 3.2 2.0 2.3 2.0 2.7

PES1 G 2.1 - - 2.2 - - 3.0 2.5 2.8 3.2 2.0 2.4 1.0 2.4

PES1 M B 4.1 3.3 4.1 1.4 1.9 1.9 1.0 1.4 2.8 2.3 2.0 1.7 2.0 2.3

PES1 M R 3.9 - - 1.5 - - 1.0 0.6 2.8 2.3 1.5 0.9 1.0 1.7

PES2 B 0.8 1.3 2.5 3.4 3.0 1.5 2.0 2.2 2.8 2.3 3.0 3.4 0.0 2.2

PES2 R 1.2 - - 3.0 - - 3.0 4.0 2.8 2.3 2.5 3.0 - 2.7

PES2 W 1.7 - - 2.5 - - 2.0 3.4 2.8 3.2 0.0 1.4 - 2.1

PES2 M B 0.5 0.0 2.5 2.2 1.4 0.9 1.0 3.3 2.2 2.3 1.5 2.3 2.0 1.7

PES2 M R 0.5 - - 1.1 - - 1.0 2.8 2.2 2.3 0.5 2.0 - 1.5

PES2 M G 0.5 - - 1.2 - - 1.0 3.0 2.2 2.3 0.5 2.1 - 1.6

PVDF B 1.1 - - 5.0 5.0 4.3 4.0 5.0 5.0 4.1 4.0 5.0 0.0 3.9

PVDF S 1.5 - - 4.1 - - 4.0 3.2 3.9 3.6 4.0 4.6 1.0 3.3

PVDF W 1.3 - - 3.2 - - 4.5 3.6 3.9 3.6 4.0 4.0 0.0 3.1

PVDF M S 1.4 - - 2.9 - - 4.0 2.7 3.9 3.2 5.0 3.9 0.0 3.0

PVDF MAX S 2.3 - - 4.2 - - 3.0 3.9 4.4 4.5 4.0 4.6 0.0 3.4

The results can be visualised with column charts. Average values from scratch tests,

wear tests and all tests together are shown in figure 35. The results from each test

method can be distracting and thus they are only shown in appendix 13. Only notable

82

observation from appendix 13 is that the grading of the coating varies a lot between

measurement methods.

Figure 35. Average grading for a) all coatings b) coating types from scratch

methods, wear methods and all methods combined

From the visualisations in figure 35 it is easy to note that low gloss coatings have

slightly lower durability than higher gloss coatings, especially at wear tests. The

difference between wear and scratch resistance is also notable at multiple coatings.

0

1

2

3

4

5

PU

R1

B

PU

R1

R

PU

R1

G

PU

R1

M B

PU

R1

M R

PU

R1

M G

PU

R2

M B

PU

R2

M R

PES

1 B

PES

1 R

PES

1 G

PES

1 M

B

PES

1 M

R

PES

2 B

PES

2 R

PES

2 W

PES

2 M

B

PES

2 M

R

PES

2 M

G

PV

DF

B

PV

DF

S

PV

DF

W

PV

DF

M S

PV

DF

MA

X S

Ave

rage

gra

de

s

Coating

Scratch only Wear only Average

a)

0

1

2

3

4

5

PUR1 PUR1 M PUR2 M PES1 PES1 M PES2 PES2 M PVDF

Ave

rage

gra

de

s

Coating type

Scratch only Wear only Averageb)

83

6.2 Calculating statistical parameters to help comparison of

test methods and test results

In comparison of test results it has to be noted that mild wear, scratches and severe wear

describe different properties of the coating. Numerical values of the tests are compared

in the following chapters, but when making conclusions, the test event has to be

considered as well. In statistical analysis three different methods are used:

1. The capability of test method to estimate separation ability of the method can be

estimated with average value and standard deviation. Average value of test

method describes the typical result from the test method. Standard deviation

between the results on one method describes the separating capacity of the test

method.

2. Difference of test method from all tests’ average is estimated in two different

ways. First the difference of a single measurement value of a coating is

calculated from the average result of all measurements on the coating. The

average of these single measurement value differences is estimated to be

systematic difference of the method. Standard deviation of single measurement

values’ difference describes the average statistical difference of the method from

overall average. The values can be considered as systematic and statistical

errors, if the average result is considered as the true result.

3. Correlation coefficients help on comparing results of tests with each other or to

coating thickness and averages of the results. The correlation coefficient tells

how well the measurement results follow the increases and decreases on the

other method. It does not consider the amount of the increases.

The results of statistical analyses do not tell the whole truth and the statistics also have

to be analysed with caution. Especially it has to be noted that many of the methods were

not capable to measure accurately the lowest or the highest values and this also may

distort the statistics. In part of the tests all of the coatings were not measured, and in

statistical analyses the methods where fewer samples are measured may seem more

favourable. For example, correlation with fewer samples is more likely having a higher

correlation coefficient, even without larger trend of correlation. The statistics are used to

make the comparison of tests and test methods easier and to determine weighting

parameters for the coatings. The results of statistical analyses are shown in table 27 and

29.

84

Table 27. Statistical analysis of average values and standard deviation of the test method,

and systematic difference and statistical difference of the method from overall

average. If statistical error is 40 or over, it is highlighted in red, and if 25 or

under it is highlighted in green.

Test method

Average value of the test method

Standard deviation within test method

Systematic difference of method from the overall average

Statistical difference of method from the overall average

Lc3 Pencil Hardness (0) 2.3 1.0 -14 36

Lc2 with Braive instrument "needle" scratch (1) 2.3 1.2 -16 40

Lc3 with Braive instrument "needle" scratch (1) 3.7 0.8 33 22

Lc2 with Braive instrument coin like scratcher (1)

2.4 0.9 -16 26

Lc1 with Sclerometer (1) 2.4 1.4 -17 43

Lc1 after 1 hour with Sclerometer (1) 2.2 1.4 -16 72

Lc3 with Sclerometer (1) 4.0 1.0 42 31

Lc1 with spherical head in Erichsen scratch hardness tester (1)

1.8 1.2 -37 35

Lc3 with conical head in Erichsen scratch hardness tester (1)

3.2 1.1 12 25

Lc3 with UMT Progressive load scratch (1) 2.7 1.6 -10 48

Lc4 with UMT Progressive load scratch (0) 3.7 1.1 28 37

Scratch hardness HSp with 3 N load wit UMT (1)

3.5 0.9 18 22

Lc3 in Erichsen scratch hardness tester wear test (2a)

3.3 0.8 25 64

Lc2 with UMT wear test (2a) 2.8 1.8 -15 47

Lc4 with UMT wear test (2a) 3.7 1.0 25 16

250 rounds Taber test with 1 kg weight (1) 2.8 1.0 -3 28

Volume loss at primer at Lc2 test with Taber (3) 3.4 1.3 12 33

Lc2 test with Taber (2b) 2.8 1.6 -13 34

Visual evaluation after 2 kg in Solid particle erosion test (0)

2.6 1.2 -9 36

Volume loss after 2 kg in Solid particle erosion test (3)

3.1 0.9 15 36

Lc2 at Solid particle erosion test (1) 3.4 1.0 23 22

Lc3 at Solid particle erosion test (1) 3.4 1.0 19 21

Visual evaluation after 2 hours in Slurry pot (0) 2.8 1.4 -6 43

Volume loss after 2 hours in Slurry pot (3) 3.0 1.1 8 30

Visual evaluation of appearance of top coat after Coil damage measurement (0)

2.0 1.6 -36 46

85

Most of the tests give average results in a reasonable scale and separation of poor and

good result, as in standard deviation, is large enough in the tests. Probably Sclerometer

gets higher average result because the power of the load spring was insufficient and at

Coil damage measurement device the load might have been set too high to give lower

result than most of the other methods. Nevertheless no method can be completely

discarded because of these reasons.

None of the test methods by themselves give the same grading as the overall average

grade. Thus the systematic difference and statistical difference values vary highly.

Systematic difference tells how much the average of a single measurement point is and

thus is a multiplier to get the average result if only the single method was used. The

statistical difference tells how much difference there would be, if the grade was given

by the single method and not with the average result. No method is identical with the

average and statistical differences are rather high, from 16% to 71%. Statistical

differences under 25% can be considered to follow the average grade rather well and if

the difference is over 40% the method can be considered to follow the average poorly.

The analyses presented in table 27 only considers the differences in single measurement

points, but with correlation coefficients of data strings it is possible to estimate if the

data sets correlate with each other. The data set is so large that colour coding is used in

analysis of the correlation coefficient table and the colour coding is shown in table 28.

Table 28. Colour coding in correlation analysis

Colour

coding Type of correlation

Correlation

coefficient

Red fill Highly negative correlation C < -0.55

Light red fill Negative correlation -0.55 < C ≤ -0.05

Grey text Small positive correlation -0.05 < C < 0.35

No fill Moderate positive correlation 0.35 ≤ C < 0.65

Green fill High positive correlation C ≥ 0.65

Correlation coefficients of test methods with coating thicknesses and average results are

shown in table 29. The correlation coefficients between the test methods are shown in

appendix 14. The table is divided into segments by coating thickness, scratch methods,

wear methods, friction methods and averages to help the reading of the table. The

correlation coefficients are determined with a Microsoft Excel function “CORREL

(array1, array2)”. When evaluating the correlation table, it has to be noted that in

Tribolab testing and Lc2 Taber testing there were less samples than in other tests. Also,

some tests like Sclerometer could not be used properly and this causes some error on the

correlation as well.

86

Table 29. Correlation of the tests to average results. Meaning of colour coding is

described in table 28. Rest of the table is shown in appendix 14.

Test method Scra

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Coating thickness 0.5 0.6 0.7 0.6

Lc3 Pencil Hardness (0) 0.0 0.2 0.1 0.1

Lc2 with Braive instrument "needle" scratch (1) 0.5 0.2 0.4 0.3

Lc3 with Braive instrument "needle" scratch (1) 0.5 0.8 0.7 0.8

Lc2 with Braive instrument coin like scratcher (1) 0.3 0.5 0.5 0.5

Lc1 with Sclerometer (1) 0.8 0.3 0.6 0.5

Lc1 after 1 hour with Sclerometer (1) 0.2 -0.3 -0.1 -0.2

Lc3 with Sclerometer (1) 0.7 0.6 0.7 0.7

Lc1 with spherical head in Erichsen scratch hardness tester (1) 0.8 0.3 0.6 0.5

Lc3 with conical head in Erichsen scratch hardness tester (1) 0.8 0.6 0.8 0.8

Lc3 with UMT Progressive load scratch (1) 0.6 0.4 0.5 0.4

Lc4 with UMT Progressive load scratch (0) 0.7 0.8 0.8 0.8

Scratch hardness HSp with 3 N load wit UMT (1) -0.8 -0.7 -0.7 -0.7

Lc3 in Erichsen scratch hardness tester wear test (2a) 0.6 0.6 0.7 0.7

Lc2 with UMT wear test (2a) 0.8 0.9 0.9 0.9

Lc4 with UMT wear test (2a) 0.8 0.9 0.9 0.8

250 rounds Taber test with 1 kg weight (1) 0.4 0.7 0.7 0.7

Volume loss at primer at Lc2 test with Taber (3) 0.2 0.9 0.7 0.7

Lc2 test with Taber (2b) 0.5 0.9 0.9 0.8

Visual evaluation after 2 kg in Solid particle erosion test (0) 0.3 0.8 0.6 0.7

Volume loss after 2 kg in Solid particle erosion test (3) 0.1 0.6 0.4 0.4

Lc2 at Solid particle erosion test (1) 0.4 0.9 0.8 0.8

Lc3 at Solid particle erosion test (1) 0.5 0.9 0.8 0.8

Visual evaluation after 2 hours in Slurry pot (0) 0.4 0.8 0.7 0.8

Volume loss after 2 hours in Slurry pot (3) 0.4 0.7 0.7 0.7

Visual evaluation of appearance of top coat after Coil damage measurement (0)

0.5 0.5 0.5 0.5

Kinetic friction coefficient at room temperature in flat-to-flat friction test

-0.4 0.2 -0.1 0.0

Kinetic friction coefficient at -15 C in flat-to-flat friction test -0.3 -0.1 -0.2 -0.2

Static friction coefficient in Sledge friction test 0.0 0.0 0.0 0.0

Kinetic friction coefficient in Sledge friction test 0.0 0.1 0.1 0.0

Scratch resistance average 1.0 0.6 0.8 0.8

Wear test average 0.6 1.0 0.9 0.9

Overall average 0.8 0.9 1.0 1.0

87

Notable is that in traditional methods, Pencil Hardness Lc3 has no correlation with any

average results and with Lc3 Braive instrument with “needle” scratch the correlation

with scratch average is low. Also, the correlation with friction and scratch or wear is

very low because the suitable parameters are not known.

6.3 Comparison of test methods and results

With the statistics and visualisation, the results can be compared with a more objective

view. Each test method and typical results is analysed in this chapter with the help of

statistical analyses. Also, scratching resistance and wear resistance is compared with

each other.

The different scratch methods had less connection in results than what was expected.

The correlation coefficient was small between Lc1, Lc2 and Lc3 methods but within

similar scratching methods the connection was also small. For example, Lc3 Pencil

hardness had small or slightly negative correlation on almost all of other test methods,

while only Lc4 scratch of Tribolab and Lc3 of Sclerometer had higher correlations with

several other methods.

Within Lc1 tests evaluated immediately after scratching, the correlation was on a good

level. When comparing the results alone there are some exceptions, like that Lc1 of

PVDF was mediocre when tested with Erichsen Scratch Hardness Tester and most of

PVDF coatings were very good when tested with Elcometer Sclerometer. When

compared to the damage after 1 hour of scratching event, the results have very low

correlation. The largest error source in the tests was the difficulty of evaluation. Also

applying a stabile load was difficult with Sclerometer.

A perfect example of how much the wear conditions can alter when changing contact

geometry is Lc2 tests with spherical scratching head and coin scratching head. The

correlation coefficient with the methods was slightly negative and the reason is most

likely that at scratching with spherical head the surface structure has more significant

result than when scratching with a wider contact area. Also, the wear mechanism on the

scratch is most likely different in many methods and the change could be seen even with

different loads on Lc2 coin scratch.

Lc3 and Lc4 scratch tests were expected to have highest correlation of all methods, which

was not the case in the measurements. The correlation with Lc3 scratches in Braive

instrument scratcher, in Sclerometer and in Erichsen scratcher were on moderate level,

but only Lc4 with Tribolab was having higher correlation with all three different Lc3

methods. The problem with the correlation coefficients of Tribolab and other methods is

that only 6 of the 24 coatings were measured. Thus, the correlation coefficient is not as

trustable as in other methods, but the correlation of Tribolab Lc4 scratch most likely was

at moderate level as well with Lc3 test methods. It also has to be noted that with

88

Sclerometer the measurements had to be stopped at 20 N, because the stiffest load

spring was not available. The lowest correlation between the Lc3 methods was with

Pencil hardness test, which was not a surprise. The test measures merely the hardness of

the pencil lead capable to pierce the coating than properties of the coating. The method

though can be used at comparison of coating with itself but in scientific matters with

coatings with different surface roughness and coating thickness the method is of low

value.

Interesting notice is that HSp values based on the width of scratch had medium to high

negative correlation on the scratch and wear resistance of the coating. Lc1 limit after 1

hour was the only measurement to have a positive correlation on the HSp value. Neither

of the two tests was found very suitable method for estimating the properties of the

coating but their correlation to each other is fascinating. If a conclusion was to be made

solely based on the two measurements, the overall mechanical durability is poor if

scratch mark is difficult to notice after a while. This is the opposite of what is expected,

and this result cannot be trusted without further investigation.

Surprisingly almost all different wear tests correlated on moderate to high level with

each other. It was supposed that especially in different wear methods with different

wear mechanisms the results would be completely different. The high difference can be

seen when compared fatigue wear of Lc3 wear test with Erichsen model 413 and Coil

damage measurement method with other devices. With abrasive and erosive test

methods the correlation is high and thus they are having the highest influence on the

average wear grade. The low number of tested samples may influence on the correlation

results of Taber Lc2 tests and Tribolab wear tests but they give similar results that most

of the methods.

Between each other, wear tests and scratch tests have small correlations besides some

exceptions. Abrasive and erosive wear tests were assumed to have connection with

scratching with low loads as in Lc1 test methods and Lc3 scratches were assumed to have

connection with fatigue wear. Lc1 tests had really low correlation coefficient with all of

the wear test methods but Lc2 “Needle” Scratch with Multifunction scratcher, Lc3

scratch with Sclerometer and Tribolab Lc4 scratches had rather good correlation with

wear tests on Tribolab and Erichsen model 413. The fatigue wear will need some

additional testing with larger wear/scratching counterparts but based on the

measurements the scratching is at least partially connected with fatigue wear.

Surprisingly Lc3 scratch with Braive instrument scratcher and Lc4 scratch with Tribolab

had high correlation with multiple abrasive and erosive test methods as well. Why the

results seem to be connected is unclear but the coatings are as durable in the different

tests. At least in Lc3 with Braive scratcher the correlation to thickness is low and it thus

is not the connecting factor. Tribolab wear tests are the only other tests that had higher

89

correlation coefficients with scratch test methods, but the correlation has to be doubted

because of lack of samples.

Comparison of the test results and the statistics with average results give knowledge of

which methods could give the same results as the wide study applied in the thesis. Many

of the test methods had high correlation on some of the average values but only three

test methods applied with Tribolab had high correlation with all averages. Most likely

the fewer samples measured with Tribolab interferes with the correlation and measuring

the scratch and wear separately is suggested. Lc1 and Lc3 scratches applied with

Sclerometer or Erichsen scratcher are the only methods to have high correlation with

scratch resistances. It has to be considered that scratch average takes also Pencil

hardness and Scratch hardness HSp into account within multiple Lc1 and Lc3 scratches,

which may slightly increase or decrease correlation with some methods. At wear tests,

only solid particle erosion after 2 kg and visual evaluation after Coil damage

measurements have low correlation with the wear average and thus almost any of the

wear tests could be used to approximate wear.

The correlation between scratch test average and wear test average is only moderate and

it is another reason why scratch and wear resistance should be measured separately. The

thickness of the coatings had only moderate correlation with average of scratching

methods and slightly more correlation with average of wear methods and overall

average.

As expected, friction coefficients from either of the tests do not have direct correlation

to the wear or scratching of the coatings. Also, the correlation with the two different

friction methods is slightly negative or near zero. Only Lc1 test methods with different

devices had higher negative correlation to the flat-to-flat friction at room temperature.

At -15°C the correlation to Pencil test, Scratch Hardness HSp, Lc2 wear with Tribolab

and volume loss at 250 rounds had highly negative correlation and Lc3 wear in Erichsen

rotating test even highly positive correlation. Most likely all of them are statistical

anomalies but still mentionable. Conclusion that temperature can have significant effect

on wear can still though be made, but the temperature correlation of wear has to be

studied separately.

By picking the tests, where both statistical differences and correlation with overall

averages is on good level, only four different test methods are left for comparison. The

methods are Lc3 scratch with Braive instrument multifunction scratcher, Lc4 wear with

UMT Tribolab, Lc2 with solid particle erosion tester and Lc3 with solid particle erosion

tester. The statistics do not show the whole picture, because Braive instrument Lc3 might

have had a low statistical error because it had such low separating capacity. Also, the

correlation of UMT Tribolab is only based on the six measurement points instead of 24

samples. Many of the wear tests had a very good correlation on the average results, and

90

in choosing of single test method it is possible to choose between separating capacity

and statistical error of the method.

6.4 Experience based grading of the test methods

Each of the methods is also given grade for their suitability for testing. The usability of

the method is estimated by its workload, difficulty of evaluation and other method

relating usability, for example if highest load were not possible to measure. Suitability

is also estimated by how well the test describes something that really could happen to

the coatings during use. The grading is done in scale of 0 to 5 and the grades are shown

in table 30. The grades are explained verbally in appendix 15. Friction measurement

methods and the methods, which were not graded earlier, are not considered in

experience-based grading.

The most usable methods on the grading were Lc2 Coin scratch with Braive Instruments

Multifunction Scratcher and Volume loss at 250 rounds with Taber Rotary Platform

Abrasion tester. Both test methods were easy and fast to use, and the visual evaluation

was easy to apply. Correlation with Coin scratch and real wear has been found and mild

abrasive wear like at Taber test is estimated to occur during transportation and end use.

Other usable methods are Lc3 scratches with Multifunction scratcher, Sclerometer and

Erichsen model 413; Lc4 scratch with Tribolab and Lc4 wear test with Tribolab.

The least usable method in experience-based grading was Lc2 wear test with Tribolab.

The method is rather slow, and the evaluation is really subjective and difficult. The Lc2

limit was also not visible in multiple coatings. From scratch methods only Lc3 Pencil

Hardness and Scratch hardness HSp with Tribolab were found unsuitable methods for

determination of wear at organic coatings. At Lc3 Pencil hardness test the problem is

that the measurement itself is difficult to apply as an unexperienced tester, and it was

not found to describe the properties of the coatings. Scratch Hardness HSp on the other

hand was easy method to apply, but the results, at least with these parameters, were not

trusted.

From wear methods multiple tests scored low in usability. These methods were Lc3 wear

test with Erichsen scratch hardness tester 413, and volume loss tests with Taber at Lc2

limit, Solid particle erosion tester after 2 kg of sand and Slurry Pot erosion tester after 2

hours of testing. Problem in wear test with Erichsen scratch hardness tester is that the

wear is difficult to evaluate and is time consuming because continuous observation is

needed. Also 0.75 mm scratching tip is found to be uncertain to estimate wear occurring

at profiling of the sheets, for example. At Taber volume loss test at Lc2 the rolls are

likely to be blocked, and it can have large effects at estimating volume loss per

revolution. Because Lc2 limit has to be measured at the same time, it is also found

unnecessary. The usability of erosion testers is low, because their using needs handling

91

of sand and the sand dust may cause a health risk. Also, the samples were difficult to

clean completely from the sand dust which can cause error at mass measurements.

6.5 Defining weighting parameters

Not all the measurement methods copy real life damage and for example friction is not

directly correlating with wear or scratch resistance as could have been the case. The

suitability and large deviation in some tests makes the reliability of the results

questionable and this why each of the method is given a specific weighting factor for

the final grading.

The weighting parameters (CW) are defined from calculated statistic error (Es),

correlation of the results of method to the average results from all methods (ρi, Aw) and

from the user experience-based grades of usability (GU) and suitability (GS). The

calculation is done with an equation

𝐶𝑊 = 𝜌𝑖,𝐴𝑤 ∙ 5 +100

𝐸𝑠+ 𝐺𝑈 + 𝐺𝑆. (4)

The coefficients in equation 4 are defined so that each term is scaled on the same level.

The Cw, Es, ρi, Aw, GU and GS values are represented in table 30. The high value of the

experience-based grading is reasoned, because there are so many possible errors also in

the calculated errors and correlations as well. For example, tests where fewer samples

have been measured are able to have higher correlation.

92

Table 30. Experience based grading of the test methods and the defined weighing

parameters. Green highlight is used if CW is over 14.0 and red highlight if CW is

under 10.0. *Only black coatings measured. **Not used at final weighted

average.

Test method

Usability of the test method

How well the test describes wanted properties

Correlation based grade

Statistical difference based grade

Calculated weighting parameter

Lc3 Pencil Hardness (0) 3 1 0.7 2.8 7.5

Lc2 with Braive instrument "needle" scratch (1)

4 2 1.9 2.5 10.5

Lc3 with Braive instrument "needle" scratch (1)

4 3 3.6 4.6 15.2

Lc2 with Braive instrument coin like scratcher (1)

4 5 2.3 3.8 15.2

Lc1 with Sclerometer (1) 2 4 2.8 2.3 11.1

Lc1 after 1 hour with Sclerometer (1) 1 4 -0.4 1.4 5.9

Lc3 with Sclerometer (1) 4 3 3.5 3.3 13.8

Lc1 with spherical head in Erichsen scratch hardness tester (1)

2 4 2.9 2.8 11.7

Lc3 with conical head in Erichsen scratch hardness tester (1)

4 3 3.9 4.1 15.0

Lc3 with UMT Progressive load scratch (1)

3 3 2.3 2.1 10.4**

Lc4 with UMT Progressive load scratch (0)

5 2 4.1 2.7 13.8**

Scratch hardness HSp with 3 N load wit UMT (1)

4 0 -3.6 4.6 5.0**

Lc3 in Erichsen scratch hardness tester wear test (2a)

2 2 3.3 1.6 8.9

Lc2 with UMT wear test (2a) 1 1 4.6 2.1 8.7**

Lc4 with UMT wear test (2a) 5 2 4.4 6.2 17.6**

250 rounds Taber test with 1 kg weight (1)

5 4 3.3 3.6 15.9

Volume loss at primer at Lc2 test with Taber (3)

3 1 3.6 3.0 10.6**

Lc2 test with Taber (2b) 3 3 4.4 2.9 13.3**

Visual evaluation after 2 kg in Solid particle erosion test (0)

2 4 3.2 2.8 12.0

Volume loss after 2 kg in Solid particle erosion test (3)

1 3 2.2 2.8 9.0

Lc2 at Solid particle erosion test (1) 2 3 3.8 4.5 13.3

Lc3 at Solid particle erosion test (1) 3 3 4.1 4.7 14.7

Visual evaluation after 2 hours in Slurry pot (0)

2 4 3.6 2.4 12.0

Volume loss after 2 hours in Slurry pot (3)

1 3 3.3 3.4 10.7

Visual evaluation of appearance of top coat after Coil damage measurement (0)

2 4 2.6 2.2 10.8

93

Calculated weighting parameters are used to make a new, weighted average grading of

the performance of the coatings. The weighted average (AW) for each coating is

calculated with equation

𝐴𝑊,𝑖 =∑ (𝐶𝑊,𝑖∙𝐺𝑟𝑎𝑑𝑒𝑖)𝑖=𝑀𝑒𝑡ℎ𝑜𝑑

∑ (𝐶𝑊,𝑖)𝑖=𝑚𝑒𝑡ℎ𝑜𝑑. (4)

The methods, where only part of the coatings is measured, have to be excluded from the

weighted average results. The lack of measurements on some colours distorts the

weighted average results so much that they different colours are not comparable any

more. Also, as PUR2 M B and PVDF B are not measured at Tribolab tests the

comparison between coatings would be questionable. The calculated weighted graded

results are shown in appendix 16.

The weighting parameters can be used for further comparison of the test methods. In

comparison, the actual numerical values are only suggestive, but the size level is more

important. Boundary value 10 and 14 are set so, that suitable amount of methods are

ruled in three different categories. The methods with Cw values over 14 can be

considered the most preferred test method for testing the mechanical durability of the

coil coatings. On the other hand, test methods with Cw value under 10 can be considered

non-suitable methods due to lack of usability, lack of correlation and high statistical

error in measurement. The rest of the methods can be considered to be partially suitable

or suitable with some modifications. When comparing the CW values, it has to be noted

that Tribolab and Lc2 based Taber test were not run for all of the samples, which reduces

the reliability of their CW values.

6.6 Determining the mechanical durability of the coatings

The mechanical durability of coatings is determined from the average results of all tests.

Both, weighted average and average grade have their limitations. In average grade from

all tests, the non-suitable methods determined in the evaluation are overcompensated.

They have the same value on overall average formation as the methods, which are

estimated to describe the properties well. On the other hand, weighted average result is

based on the average grade, and some of the well performing test methods have to be

discarded due not all samples were measured.

The average results of coating types and deviation between coating colours are shown in

table 31. The results for each coating is presented appendix 16.

94

Table 31. Average graded result from applicable tests and weighted graded results for

each coating type. *Coating thickness and gloss level are not constant. **Tests

where only part of the samples was measured are excluded.

Coating Coating type

Coating thickness (µm)

Average grade of all tests

Standard deviation between colours (%)

Weighted average grade of all tests

Standard deviation between colours (%)

PUR1 Structured polyurethane coating

49 3.9 4 3.9 3

PUR1 M Textured low gloss polyurethane coating

46 3.1 10 3.2 5

PUR2 M Structured low gloss polyurethane thin coating

25 2.5 2 2.5 4

PES1 Structured polyester coating

35 2.9 11 3.0 12

PES1 M Structured low gloss matt polyester coating

36 2.4 13 2.4 8

PES2 Polyester thin coating 26 2.3 2 2.2 3

PES2 M Textured low gloss polyester thin coating

30 1.9 6 1.7 8

PVDF Polyvinylidene fluoride coating*

29 3.1 12 3.2 12

The order of the coatings remains exactly the same in average results and in weighted

average. Only differences are that at PUR1 M, PES1 and PVDF the grade increases by

0.1 grades and the grade of PES2 and PES2 M decreases slightly. Standard deviation

between colours in both averages is also on same magnitude, though varies slightly

depending on the coating. Thus, the average from all methods would have been as

suitable on determination of the coatings as weighted average is. The statistical analysis

done, while determining weighting parameters, though can be used in valuable tools to

compare the coatings and test methods.

The weighted average grade is determined as the measure of mechanical durability in

the thesis. The grading is done by the coating type because it is estimated that the three

chosen colours represent well enough all of the coating colours. It was expected that

between the colours there might be some scatter on the results and that certain colour

can manage well on some tests and worse on others. The samples were collected from

production, so they also should represent actual coatings rather well.

From the data it is also possible to determine whether a certain colour or a gloss level

has a better mechanical durability than the other. Because it was not possible to gather

all colours from all coating types, only PUR1, PUR1 M, PES1 and PES2 M are

considered in the comparison of black, grey and red coatings. In comparison of gloss

levels only those colours were considered which were available in both gloss levels of

the coating. The results are shown in table 32.

95

Table 32. Comparison of results in scratch resistance test, wear resistance tests and in

general by colour and gloss level.

Colour or

gloss level

Scratch

resistance

Wear

resistance

Mechanical

durability

Black 3.1 3.3 3.2

Red 2.8 2.9 2.9

Grey 2.8 2.9 2.8

High gloss 3.2 3.3 3.3

Low gloss 2.6 2.6 2.6

In the comparison it can be seen that black coloured coatings have a higher mechanical

durability than red or grey. The difference is slightly higher in wear resistance than in

scratch resistance, but still noticeable in both the average results. Interesting is that red

and grey have exactly the same value with each other in both scratch and wear. All of

the colours have the same paint specification and should have the same properties, but

this difference may be caused by many different reasons. Most likely the difference can

be explained by the amount and size of the pigment in the coating. Black coloured

coatings have the lowest volume of pigments in them and there is more binder to be

worn. Black pigment, carbon black, can also act as a lubricative agent as graphite has

been reported to.

Gloss level has an effect on the mechanical durability as expected. The effect was seen

in almost all of the measurements and with almost all of the coatings. Gloss level is

typically influencing on the surface roughness and the connection of surface roughness

and wear resistance are almost always connected. The durability of low gloss coatings is

rather significantly lower than in higher gloss in both scratch and wear. This has to be

considered when choosing a coating for specific application.

96

7. OUTCOME OF THE THESIS AND FURTHER

INVESTIGATION

As an outcome of the thesis, the durability of the chosen coatings could be determined

and multiple different test methods were studied. Based on the thesis, multiple different

test methods can be used to determine scratch or wear resistance of the coating, but they

should be studied separately. Also it was concluded that Pencil Hardness test widely

used in coil coating industry is of low value in determination of durability and if it is

used in quality control, other test methods should be applied before making additional

conclusions. Also more knowledge about scratching and wear mechanisms of organic

two-layered coatings was gained.

By applying multiple scratch and wear tests and scaling the results on a scale of 0 to 5 it

was possible to estimate the mechanical durability of the coatings. Mechanical

durability was first estimated to be the average grade of all tests, but many of the

methods were found to be unsuitable to accurately measure scratch or wear resistance.

Significance of less suitable methods on the average was as high as with more suitable

methods, and thus weighted average was proposed. The weighting parameters were

determined with statistical analysis and the weighted average is determined as the

measure of mechanical durability of the coatings. The result in weighted average and

average grade is very similar. The statistical analyses were also used for easier

comparison of the test methods and test results.

The best mechanical durability from coatings designed for roofing are on polyurethane

based coatings. On façade coatings the mechanical durability of PVDF is outstanding

compared to PES based coatings. The mechanical durability of low gloss coatings was

found to be consistently lower than in normal gloss coatings. In choosing of a coating it

seems that mechanical durability has to be considered while choosing the appearance. It

was also found out that thicker coating is not always better. This can be seen when thin

polyurethane-based coatings were on the same level of durability as thick polyester-

based coatings, at least in low gloss coatings. Thin high gloss polyurethane coatings

were not studied and the durability of it can differ from low gloss version. The thickness

of the coatings was significant factor when comparing coatings of same binder material.

During the thesis, more information about the behaviour of coatings was found.

Necking properties and recovering of the coating were found to be more profound than

expected. Typically, though the coating did not cover the revealed zinc layer completely

97

and corrosion resistance is lost with even small scratches. The studied coatings cannot

be considered as self-healing coatings at any measure.

Based on the literature studies and the measurements, it is also clear that the scratching

resistance does not equal to hardness. Scratch resistance is often referred scratch

hardness in the coil coating industry, most likely because of the Pencil hardness test. In

the case of the pencil test it is partially true because of the hardness values of the pens

are compared. More likely the coatings reflect to scratching as an adhesion-related

failure by delamination [39] than is connected to the hardness of the coating. The

delamination can occur between the organic coating layers or between the organic

coating and the metal coating.

Abrasive wear, adhesive wear, fatigue wear and erosive wear were studied separately.

Abrasive wear could be studied with Taber abrasive wear test methods and erosive wear

with Solid particle erosion tester or with Slurry pot erosion tester. Mostly adhesive wear

can be estimated to occur in Coil damage measurement device and in friction tests,

where the wear was so low that it was not practical to be measured. On Rotating Ball-

on-disk wear with Tribolab and with Erichsen scratch hardness tester 413 rotary wear

test, the wear mechanism most probably was almost completely based on storage of the

defects and thus in fatigue wear.

In the test set there were more erosion tests than wear mechanism based tests. The

results in abrasion resistance and erosion tests were really similar but there was not

sufficient data to compare adhesive wear or fatigue wear to other mechanisms.

Nevertheless, the results were otherwise more or less consistent but the results with

PES2 and PVDF were moderate and excellent in erosion tests respectively, but in

Erichsen wear test the durability of these coatings were very poor. In Coil damage

measurement the wear could be more of adhesive type and on the results PES2 and

PVDF were again less durable. Thus, it is clear that with different wear mechanisms the

performance of the coatings is different.

It was found out that in many wear methods the wear can be put on linear scale in

comparison of coatings. This most likely indicates that the wear is a combination of

motion of defects or physical interaction, based on the curves presented in figure 5.

Thus the dominant wear mechanisms are abrasive or erosive. In rotating ball-on-disk

wear tests with Erichsen model 413 and Tribolab the wear is not linear, but logarithmic.

This must be a result of repetitive loading of the coating where fatigue behaviour of the

binder and adhesion layer, in addition of particle crushing plays a large role. Thus the

dominant wear mechanism is most likely fatigue wear. Taber Lc2 test results did not fit

on linear scale or on the logarithmic scale. Most likely the wear in the method is a

combination of motion of defects, physical interaction and storage of defects and thus

the scale is difficult to determine. The blocking effect of the rolls most likely changes

the wear type partially and perhaps more suitable would be to apply the method without

98

cleaning the rotating rolls in the middle. The best estimation of a scale for Taber Lc2 test

is to fit the results with a square root.

In future studies, wear mechanisms occurring on profiling or deep drawing are of

interest. Also, the studying of wear mechanisms occurring on the tests should be studied

more to know what exactly is being measured. With the connection between

mechanisms on real wear and test are known, the wear cause can be studied in

laboratory and the development of more durable coatings for the special case would

become easier. In addition of wear mechanisms, also the cutting debris in coin scratch

and physical interaction under scratching will be of interest in determination of

properties of the coating material itself.

7.1 Recommended methods for measuring mechanical

durability

Based on the studies, recommendable is that scratching is measured separately with

wear. Depending on what properties are desired at the end use, Lc1 and Lc3 scratches can

be considered separately, and in studying of wear, different wear mechanisms have to

be considered.

If visual damage is the most important property of the coating, Lc1 scratch testing can be

applied with caution. Measuring of Lc1 scratch is not recommended directly, because the

evaluation of the first visible scratch is very difficult and subjective. Also, special care

has to be considered in loading and when choosing acceptable level of scratching. Lc1

scratch test could be recommended if certain load level with certain testing equipment is

applied and the result is only compared to a certain border level. If a certain reason for

Lc1 is found, the measurement is not recommended.

With Lc3 scratch methods, it is possible to determine which coatings last the highest

load on scratching, before corrosion starts. The load needed depends on the geometry of

the scratcher, but the order of the coatings remains mostly the same between different

testers. The Lc3 level is very easy to measure and it most likely has some correlation

with profiling of coatings. The geometry of scratching tip can be altered to find suitable

correlation with real life damage, but 1mm spherical scratching tip [21] is a

standardized and thus recommended scratching geometry. With larger scratching tips

the loads have to be higher and scratching down to primer (Lc2) is recommended in that

case. For example, with coin like scratching head a connection to wear occurred in

installation of roof with standing seams has been found.

In choosing of wear test method, the most common and critical wear mechanisms have

to be determined before testing. If determination of wear during end use or

transportation is needed, abrasion or erosive wear testing is recommended. For studying

wear or marring occurring inside coil, adhesive wear test methods are recommended.

99

During processing of the sheets, profiling or deep forming, the coating most likely is

worn because of fatigue properties at adhesion layer between coatings. Thus, fatigue

wear methods are recommended. Suitable testing parameters or device for adhesive and

fatigue wear were not found in the thesis.

The most suitable devices for studying mechanical durability of the coatings on the

thesis are Braive Instruments Multifunction Scratcher, Erichsen Scratch Hardness tester

413, Bruker UMT Tribolab, Taber Rotary Platform Abrasion tester and Solid particle

erosion test. Also, Elcometer Sclerometer was found suitable for fast testing. All of the

test devices had one or more test methods and typically one or two of them were found

to be suitable for testing.

7.2 Methods not suitable for measuring mechanical durability

of coatings

The least suitable methods on testing mechanical durability were Pencil Hardness test,

Lc1 after 1 hour with Elcometer Sclerometer, Scratch Hardness HSp with UMT

Tribolab, Lc2 test in Tribolab wear and Volume loss on Solid particle erosion test. The

low suitability is justified with low weighting parameters calculated in chapter 6.4.

Some of the methods had low accuracy of repeating the overall grade, some of the tests

had difficulties in measurements and some of the methods were not found to measure

relevant properties.

In Lc1 measurements the subjective nature of the evaluation is the largest problem. After

1 hour of recovering the positions where the scratches are, are very difficult to notice.

Also, the stability of scratching angle and load were questionable when scratching with

Sclerometer. Bruker Tribolab is as a measurement device flexible and accurate but the

testing parameters in HSp were not proper and the determination of Lc2 from wear

curves was difficult. In volume loss measurement with Solid particle erosion test the

cleaning of the samples is difficult and the mass difference is so low that high risk of

weighting error exists.

Alarming is that one of the most used methods of coil coating industry, Pencil hardness

test, is one of the methods with lowest value in determination of mechanical durability.

Based on the study, pencil hardness test should not be compared with scratch or wear

tests. The pencil hardness test did not find correlation with any other method

represented in the thesis. The pencil hardness test is fast method, but if a coating has a

low result in the test it may still have completely normal mechanical durability. The

complete opposite did not occur in the measurements, and coatings with higher result in

scratch hardness test had at least mediocre result in mechanical durability. Thus, the

method may still be suitable for quality control, but in research use the value of pencil

hardness method is low. The test method is standardized, but in the standard it is also

stated that the method is not repeatable, if the measurer does not have practical

100

experience. Also, the scientific background for the test is also slightly questionable,

because in real life the hardness of the scratcher does not vary, but the scratching load

or shape does.

101

8. POSSIBLE ERROR SOURCES

Possible error sources can occur in any time of the measurement procedure. In planning

of the measurements, the error is minimized by picking representative samples. During

the measurements the possible errors are monitored and in analysis of the measurements

the previous knowledge has to be considered before making assumptions.

Errors between coatings were minimized by using the same 3 colours for different

coatings. With three colours it is possible to estimate the differences between different

coatings and the average result most likely represents the averages of all colours

decently. All of the coatings are from production and have passed regular quality

control before collecting. Thus, they should represent the coating types rather well. For

all coating types the same colours were not available, so this can be considered as an

error source, but the effect of the colour is also studied.

It is always possible, that some of the samples have been damaged internally before

testing or have minor flaws in manufacturing. The samples were all prepared in SSAB

Hämeenlinna R&D laboratory but in many cases the measurements were done

elsewhere. During the transportation of cut sample sheets there is always a risk of

damage. Many times the tested area is very small so even small mistakes in the surface

may influence on the results. For example, scratches in crossing direction may increase

the probability of pinholes through from that spot. The possibly damaged samples were

tried to replace with intact ones, but even flaws that are not visible may have some

influence on the results. The age of the samples was approximately the same for all

samples, and no degradation should have occurred for any sample.

Densities of the coatings were estimations at volume loss tests, and it may have caused

some error. Mass loss itself is not the desired property to be measured but by calculating

volume loss the possible visual or corrosion resistance losses are easier to estimate.

Curing level or particle distribution can slightly vary on the coating, but the error should

be minimal. More error can be caused if primer has also been worn at volume loss tests.

Most of the possible error sources during the measurements were discussed within each

measurement method. Typically errors during the measurement can be estimated to be

small but errors in the measurement procedure itself can cause higher errors. Most

notable errors in the test procedures were that in Elcometer Sclerometer, Erichsen tester

413 and in Tribolab the load was too low for scratching all of the coatings. Also, in

Tribolab wear test the samples were not run sufficient times and in Coil damage

102

measurement device all of the samples could not be measured because the steel was

formed.

In evaluation of the samples the time should be set because of viscoelastic nature of the

coating. Even though the coatings do not have self-healing properties, the creeping of

the scratches may make the evaluation more difficult. Pinholes down to zinc have not

been reported to disappear afterwards on these types of coatings but the severity of the

scratches may seem slightly different after time. On wear tests the worn area is always

so large that creeping of the coating should not cause error on visual evaluation.

Room temperature or humidity was not followed during the measurements, and neither

the temperature of the samples. Temperature behaviour of polymers is difficult to

forecast, and the amount of change differs between polymer grades. The room

temperature is estimated to stay between 21°C and 25°C, except in cold testing of

friction. The temperature difference is so low that the effect on wear should be minimal

compared to other error sources. The atmospheric humidity level can have changed

quite radically, due part of the methods was measured in February when humidity is

really low, and part were measured during spring rains. The effect of humidity in air

though is still estimated to be minimal.

The errors in statistical analyses are complex. First of all, the measurement data is not

completely trusted and thus this has to be kept in mind, second the choosing of the

statistical operators can influence on how the results can be read and third the reading of

the statistics is very risky and making conclusions based only on the statistics can lead

into completely wrong direction. No separate error estimation is done for the statistical

analyses and this is kept in mind when using the statistics in comparison.

103

9. CONCLUSIONS

Determining mechanical durability of coil coatings is not an easy task. The results are

typically qualitative and have to be in most cases evaluated visually for quantitative

results. The amount of different test methods in the thesis was large, and in comparison

of methods the exact test procedure has to be taken into account. The mechanical

durability of the coatings was determined in the thesis as mechanical wear and

scratching resistance, and the durability is estimated with the weighted average of

applicable tests.

The most durable coatings were polyurethane based coatings. The coating was the most

durable in many of the tests and it ranked low in only HSp scratch hardness test, where

the width of scratch marks was compared. Slightly less durable and most durable matt

coating was polyurethane based, chemically wrinkled matt coating. Its durability was

highly above average in most of the tests, but especially when first visual scratch was

tested, its performance was one of the lowest. Polyvinylidene fluoride coatings designed

for façade applications was the third best performing coating and its durability varied a

lot in the tests. Polyvinylidene based coatings were the most durable in many of the

tests but on the other hand it had really low performance in many tests as well. Thin

polyurethane based matt coatings, polyester based coatings and polyester based matt

coatings were almost as durable with each other and their performance was during all

the tests from mediocre to good. The lower coating thickness of thin polyurethane-based

coatings decreased its performance from time to time, but the better grade of binder

compensated its durability in part of the tests. Thin polyester-based coating and its

wrinkled matt version were the least durable coatings, most likely because of their

lowest binder grade and coating thickness.

Gloss level had impact on the durability at all coating types. Low gloss is obtained with

structuring particles or with chemical wrinkling and in both ways the surface roughness

increases. In all matt coatings, no matter wrinkled or structured, the mechanical

durability decreases compared to normal gloss version of product. The method how the

low gloss is obtained does not seem to have large effect on reduction of the properties,

or the effect depends too much on other factors as well. The decrease of the durability is

noticeable, but in the measured samples the matt finish was typically less significant

than the difference between coating types.

Between colours there also is difference between durability. The durability of red and

grey coatings on the comparable samples was the same, but in black coatings the

durability was slightly increased. This most likely is because in black coatings there is

104

less pigments by the volume. Carbon black might also increase wear resistance because

of its small particle size [12] and possible lubricating effect [17].

In measurement of durability of two layered organic coating it is recommended to

measure scratch resistance and wear resistance separately, based on the thesis. There are

multiple suitable ways to measure both, but in scratch resistance it is important that the

method has stabile load and stabile angle. With sharper or smaller scratching tips, the

surface roughness has more pronounced effect but based on the measurements all

different scratching tips give still comparable results. For example, the scratch

resistance can be measured with Braive Instruments Multifunction scratcher, Erichsen

Scratch Hardness tester 413 and Bruker UMT Tribolab. Test method, where scratch

pierces both coating layers is most recommended.

On wear tests, abrasive and erosive wear methods gave similar results. Erosive test

results were slightly more dependent on the thickness of the coating, but with both wear

types it is possible to study wear occurring on use. Because not enough measurements

were done with adhesive or fatigue wear methods, it is not sure if erosive wear and

abrasive wear correlated well with it. More measurements of adhesive and fatigue wear

are needed to determine whether wear with the used test methods could correlate with

wear caused in forming of the sheets.

More studies of wear mechanisms and physical interactions on scratching in two

layered organic coatings would make the comparison of real damage and testing of

durability easier. Also, the effect of colour pigments and other particles on wear can be

significant and the effects should be studied more, when developing durable coatings.

105

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106

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määrittäminen hankaustestilaitteella, Tampere University of Technology, 2010.

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108

APPENDIX 1: MEASUREMENT PARAMETERS OF THE TESTS

Test method Scratching / Contact velocity

Contact type Contact material

Lc3 Pencil Hardness ~ 50 mm/s Cylindrical on 40°-50° angle

Pencil lead, hardness varies

Lc2 with Braive instrument "needle" scratch

~ 100 mm/s ø 1,0 mm spherical on 90° angle

Hard metal

Lc3 with Braive instrument "needle" scratch

~ 100 mm/s ø 1,0 mm spherical on 90° angle

Hard metal

Lc2 with Braive instrument coin like scratcher

~ 100 mm/s ø 1,0 mm spherical on 90° angle

Hard metal

Lc1 with Sclerometer ~ 50 mm/s ø 0.75 mm spherical on 85°-95° angle

Hard metal

Lc1 after 1 hour with Sclerometer ~ 50 mm/s ø 0.75 mm spherical on 85°-95° angle

Hard metal

Lc3 with Sclerometer ~ 50 mm/s ø 0.75 mm spherical on 90°-100° angle

Hard metal

Lc1 with spherical head in Erichsen scratch hardness tester

4.2 mm/s - 7.9 mm/s

ø 0.75 mm spherical tip on 90° angle

Hard metal

Lc3 with conical head in Erichsen scratch hardness tester

4.2 mm/s - 7.9 mm/s

Conical on 90° angle Diamond

Lc3 with 7 N load in Erichsen scratch hardness tester

4.2 mm/s - 7.9 mm/s

ø 0.75 mm spherical tip on 90° angle

Hard metal

Lc3 with UMT Progressive load scratch

0.2 mm/s Rockwell on 90° angle Hard metal

Lc4 with UMT Progressive load scratch

0.2 mm/s Rockwell on 90° angle Hard metal

Scratch hardness HSp with 3 N load wit UMT

0.2 mm/s Rockwell on 90° angle Hard metal

Lc2 with UMT wear test 3.3 mm/s and 6.6 mm/s

ø 6 mm spherical on 90° angle

Ceramic

Lc4 with UMT wear test 3.3 mm/s and 6.6 mm/s

ø 6 mm spherical on 90° angle

Ceramic

Volume loss at 250 rounds with 1 kg weight at Taber test

60 rpm 10 mm wide freely rotating roll

Resilient rubber roll with abrasive particles

Volume loss per revolution at 250 rounds with 1 kg weight at Taber test

60 rpm 10 mm wide freely rotating roll

Resilient rubber roll with abrasive particles

Volume loss at primer at Lc2 test with Taber

60 rpm 10 mm wide freely rotating roll

Resilient rubber roll with abrasive particles

Lc2 test with Taber 60 rpm 10 mm wide freely rotating roll

Resilient rubber roll with abrasive particles

Volume loss per round in Lc2 test with Taber

60 rpm 10 mm wide freely rotating roll

Resilient rubber roll with abrasive particles

Visual evaluation after 2 kg in Solid particle erosion test

5 m/s 50-200 µm quartz sand

Quartz from Sibelcon Oy

109

Volume loss after 2 kg in Solid particle erosion test

5 m/s 50-200 µm quartz sand

Quartz from Sibelcon Oy

Lc2 at Solid particle erosion test 5 m/s 50-200 µm quartz sand

Quartz from Sibelcon Oy

Lc3 at Solid particle erosion test 5 m/s 50-200 µm quartz sand

Quartz from Sibelcon Oy

Visual evaluation after 2 hours in Slurry pot

3.7 m/s 50-200 µm quartz sand in water

Quartz from Sibelcon Oy

Volume loss after 2 hours in Slurry pot

3.7 m/s 50-200 µm quartz sand in water

Quartz from Sibelcon Oy

Visual evaluation of appearance of top coat on Coil damage measurement device

0.5 rpm 160 cm

2 of top coat

against backing coat Top coat against backing coat

Visual evaluation of appearance of backing coat on Coil damage measurement device

0.5 rpm 160 cm

2of top coat

against backing coat Top coat against backing coat

Kinetic friction coefficient at room temperature in flat-to-flat friction test

10 mm/s 2.25 cm

2 flat on 90°

angle Through-hardened K600 steel

Kinetic friction coefficient at -15 C in flat-to-flat friction test

10 mm/s 2.25 cm

2 flat on 90°

angle Through-hardened K600 steel

Static friction coefficient in Sledge friction test

1.67 mm/s 30 cm2 of rubber sheet Unknown rubber

Kinetic friction coefficient in Sledge friction test

1.67 mm/s 30 cm2 of rubber sheet Unknown rubber

110

APPENDIX 2: RESULTS OF HARDNESS PENCIL TEST

Coating

Pencil Hardness (Lc3)

Pencil hardness grading

PUR1 B B 2

PUR1 R HB 3

PUR1 G HB 3

PUR1 M B 2B 1

PUR1 M R B 2

PUR1 M G B 2

PUR2 M B HB 3

PUR2 M R 2B 1

PES1 B HB 3

PES1 R HB 3

PES1 G HB 3

PES1 M B B 2

PES1 M R B 2

PES2 B HB 3

PES2 R HB 3

PES2 W HB 3

PES2 M B 2B 1

PES2 M R B 2

PES2 M G 2B 1

PVDF B H 5

PVDF S 2B 1

PVDF W HB 3

PVDF M S HB 3

PVDF MAX S 2B 1

111

APPENDIX 3: RESULTS WITH BRAIVE INSTRUMENT

MULTIFUNCTION SCRATCHER

Coating

Lc2 with needle scratch (bar)

Lc3 with needle scratch (bar)

Lc2 with coin like scratcher (bar)

PUR1 B 0.3 0.6 0.5

PUR1 R 0.3 0.6 0.5

PUR1 G 0.4 0.6 0.6

PUR1 M B 0.5 0.6 0.8

PUR1 M R 0.2 0.6 0.8

PUR1 M G 0.2 0.6 0.8

PUR2 M B 0.2 0.6 0.4

PUR2 M R 0.2 0.5 0.7

PES1 B 0.4 0.5 0.6

PES1 R 0.3 0.5 0.5

PES1 G 0.2 0.5 0.5

PES1 M B 0.4 0.4 0.7

PES1 M R 0.4 0.4 0.5

PES2 B 0.2 0.4 0.4

PES2 R 0.2 0.4 0.3

PES2 W 0.3 0.4 0.3

PES2 M B < 0.2 0.3 0.4

PES2 M R < 0.2 0.4 0.5

PES2 M G < 0.2 0.3 0.4

PVDF B < 0.2 0.5 0.9

PVDF S < 0.2 0.7 1.3

PVDF W 0.2 0.7 0.5

PVDF M S < 0.2 0.6 0.9

PVDF MAX S < 0.2 0.7 0.9

112

APPENDIX 4: RESULTS WITH ELCOMETER 3092

SCLEROMETER HARDNESS TESTER

Lc1 with Elcometer 3092 Sclerometer Hardness tester (N)

Coating Lc1 with Sclerometer (bar)

Lc1 after 1 hour with Sclerometer (N)

PUR1 B 1.4 2.2

PUR1 R 1.4 2.2

PUR1 G 1.8 2.4

PUR1 M B 0.6 2.2

PUR1 M R 0.2 0.2

PUR1 M G 0.2 0.4

PUR2 M B 0.4 1.0

PUR2 M R 1.6 2.6

PES1 B 1.6 2.6

PES1 R 1.2 1.6

PES1 G 1.2 1.2

PES1 M B 1.4 1.4

PES1 M R 0.6 1.0

PES2 B 0.4 0.6

PES2 R 0.4 0.4

PES2 W 0.4 1.8

PES2 M B 0.8 4.0

PES2 M R 0.8 4.0

PES2 M G 0.6 3.5

PVDF B 1.2 1.2

PVDF S 2.0 2.0

PVDF W 0.6 0.8

PVDF M S 0.2* 0.2*

PVDF MAX S 2.0 2.0

*Seen only in viewing angle of 180°

113

Lc3 with Elcometer 3092 Sclerometer Hardness tester (N)

Coating Person 1 Person 2 Person 3 Person 4 Average

PUR1 B 20** 20** 20** 19 20

PUR1 R 20** 20** 20** 20** 20

PUR1 G 20** 20** 20** 20** 20

PUR1 M B 20** 16 20** 19 19

PUR1 M R 19 20** 19 19 19

PUR1 M G 15 11 18 15 15

PUR2 M B 18 - 20 19 19

PUR2 M R 16 15 18 13 16

PES1 B 19 20** 20** 20** 20

PES1 R 13 15 18 15 15

PES1 G 16 17 18 16 17

PES1 M B 19 20** 20** 18 19

PES1 M R 19 19 20** 18 19

PES2 B 15 14 18 15 16

PES2 R 14 13 19 13 15

PES2 W 16 17 16 14 16

PES2 M B 8 7 10 6.5 8

PES2 M R 7 7 - 6.5 7

PES2 M G 7 7 10 6.5 8

PVDF B 13 14 19 15 15

PVDF S 15 18 18 16 17

PVDF W 11 12 12 10 11

PVDF M S 11 - 16 12 13

PVDF MAX S 20** - 20** 19 20

**Only loads up to 20 N were able to be measured

114

APPENDIX 5: RESULTS WITH ERICHSEN SCRATCH

HARDNESS TESTER 413

Coating

Lc3 with conical head in Erichsen scratch hardness tester (N)

Lc1 with spherical head in Erichsen scratch hardness tester (N)

Through entire system with 9 N (rounds)

Lc3 with 7 N load in Erichsen scratch hardness tester (rounds)

Through entire system with 5 N (rounds)

PUR1 B 3.6 1.4 29 40 -

PUR1 R 4.4 1.8 33 40 -

PUR1 G 3.8 2.2 24 40 -

PUR1 M B 4 1.0 17 40 -

PUR1 M R 2.2 0.1 11 40 -

PUR1 M G 3 0.1 9 40 -

PUR2 M B 2.6 0.4 5 15 50

PUR2 M R 2 1.0 2 6 39

PES1 B 3.6 1.2 8 19 -

PES1 R 2.6 1.0 2 5 15

PES1 G 2.6 1.4 2 5 12

PES1 M B 3 0.9 9 22 -

PES1 M R 2.8 0.5 7 18 -

PES2 B 2.6 0.3 1 1 7

PES2 R 2.4 0.4 1 2 8

PES2 W 2.6 0.2 1 3 15

PES2 M B 1.4 0.6 0 0 3

PES2 M R 1.2 1.0 0 1 3

PES2 M G 1.2 0.6 0 0 3

PVDF B 1.8 0.5 1 3 4

PVDF S 4.8 1.0 2 3 5

PVDF W 2 0.5 1 3 7

PVDF M S 2.8 0.1 1 3 9

PVDF MAX S 6.2 0.8 3 5 12

115

APPENDIX 6: RESULTS WITH BRUKER UMT TRIBOLAB

Constant load scratch

Coating

Scratch width with 3 N (um)

Hardness (MPa)

Average scratch depth (um)

Average post-scan depth / plastic deformation (um)

Elastic deformation depth (um)

PUR1 B 187.7 217 29.7 7.3 22.5

PUR1 M B 159.4 302 32.4 6.6 25.8

PES1 B 178.5 240 20.5 6.2 14.3

PES1 M B 161.5 293 20.2 6.0 14.2

PES2 B 169.3 267 18.2 5.1 13.0

PES2 M B 133.2 440 20.2 4.9 15.3

Progressive load scratch

Coating

Compression level during scratching

Lc3 from progressive load scratch (mm)

Lc3 from progressive load scratch (N)

Lc4 from progressive load scratch (mm)

Lc4 from progressive load scratch (N)

PUR1 B 62 3.22 12.7 - 20.0

PUR1 M B 70 1.79 7.1 3.53 13.8

PES1 B 57 2.42 9.6 3.52 13.8

PES1 M B 56 3.18 12.5 3.62 14.2

PES2 B 70 2.58 10.1 3.58 14.0

PES2 M B 67 1.26 5.1 1.80 7.2

116

APPENDIX 7: RESULTS FROM TABER ROTARY PLATFORM

ABRASION TESTER

Sample 1 Sample 2

Coating

Volume loss at 250 rounds (mg)

Volume loss at primer (cm

3)

Rounds until primer

Volume loss at 250 rounds (mg)

Volume loss at primer (cm

3)

Rounds until primer

PUR1 B 9.5 41.3 1907 4.7 & 5.9 - -

PUR1 R 13.2 - - - - -

PUR1 G 11.7 - - - - -

PUR1 M B 13.2 32.4 1900 - - -

PUR1 M R 19.0 - - - - -

PUR1 M G 20.8 - - - - -

PUR2 B 13.6 23.0 722 13.6 20.8 700.0

PUR2 R 17.7 - - - - -

PES1 B 16.0 36.2 787 16.1 28.3 600.0

PES1 R 18.1 - - - - -

PES1 G 19.0 - - - - -

PES1 M B 21.0 35.7 672 20.2 37.6 745.0

PES1 M R 23.0 - - - - -

PES2 B 12.1 23.5 578 11.4 22.2 575.0

PES2 R 15.3 - - - - -

PES2 W 20.6 - - - - -

PES2 M B 18.4 20.6 355 16.2 19.4 350.0

PES2 M R 24.2 - - - - -

PES2 M G 22.1 - - - - -

PVDF B 5.9 22.8 1801 6.0 21.3 1500.0

PVDF S 11.4 - - - - -

PVDF W 19.2 - - - - -

PVDF M S 20.7 - - - - -

PVDF MAX S 11.3 - - - - -

117

APPENDIX 8: RESULTS FROM SOLID PARTICLE EROSION

TEST

Coating

Average of two samples

Lc2 at erosion test (kg)

Lc3 at erosion test (kg)

Average visual evaluation after 2 kg in Solid particle erosion test (0-5)

Average volume loss after 2 kg in Solid particle erosion test (cm

3)

PUR1 B 3.5 0.4 4.5 5.5

PUR1 R 3.3 0.5 3.5 5.0

PUR1 G 3.3 0.6 4.5 5.0

PUR1 M B 3.0 0.7 3.0 4.5

PUR1 M R 3.8 0.6 4.5 5.5

PUR1 M G 3.5 0.7 4.5 5.5

PUR2 M B 1.0 0.7 < 2.0 2.5

PUR2 M R 1.0 0.8 < 2.0 2.5

PES1 B 3.0 0.7 3.0 4.0

PES1 R 3.0 0.6 3.0 3.5

PES1 G 3.0 0.9 2.5 3.5

PES1 M B 1.0 1.2 2.5 2.5

PES1 M R 1.0 1.5 2.5 2.5

PES2 B 2.0 1.0 2.5 2.5

PES2 R 3.0 0.5 2.5 2.5

PES2 W 2.0 0.6 2.5 3.5

PES2 M B 1.0 0.7 < 2.0 2.5

PES2 M R 1.0 0.8 < 2.0 2.5

PES2 M G 1.0 0.8 < 2.0 2.5

PVDF B 4.0 0.2 4.5 4.5

PVDF S 4.0 0.7 3.5 4.0

PVDF W 4.5 0.6 3.5 4.0

PVDF M S 4.0 0.8 3.5 3.5

PVDF MAX S 3.0 0.5 4.0 5.0

118

APPENDIX 9: RESULTS FROM SLURRY POT EROSION TEST

Average of two samples

Coating

Visual evaluation after 2 hours in Slurry pot (0-5)

Volume loss after 2 hours in Slurry pot (cm3)

PUR1 B 4 4.8

PUR1 R 4 7.6

PUR1 G 4 8.2

PUR1 M B 3 10.7

PUR1 M R 4 10.6

PUR1 M G 4 12.7

PUR2 M B 2 9.5

PUR2 M R 1 11.5

PES1 B 3.5 9.2

PES1 R 2 13.0

PES1 G 2 12.4

PES1 M B 2 15.1

PES1 M R 1.5 18.2

PES2 B 3 8.8

PES2 R 2.5 10.5

PES2 W 0 16.1

PES2 M B 1.5 12.8

PES2 M R 0.5 14.2

PES2 M G 0.5 13.7

PVDF B 4 3.1

PVDF S 4 4.5

PVDF W 4 6.8

PVDF M S 5 7.0

PVDF MAX S 4 4.4

119

APPENDIX 10: RESULTS FROM COIL DAMAGE

MEASUREMENT DEVICE MEASUREMENTS

Coating

Visual evaluation of top coat after Coil damage measurement test

Visual evaluation of backing coat after Coil damage measurement test

PUR1 B 5 3

PUR1 R 3 3

PUR1 G 4 4

PUR1 M B 4 3

PUR1 M R 3 3

PUR1 M G 3 3

PUR2 M B 3* 2*

PUR2 M R - -

PES1 B 4 3

PES1 R 2 3

PES1 G 1 0

PES1 M B 2 1

PES1 M R 1 0

PES2 B 0* 0*

PES2 R - -

PES2 G - -

PES2 M B 2* 1*

PES2 M R - -

PES2 M G - -

PVDF B 0 0

PVDF S 1 1

PVDF W 0 0

PVDF M S 0 0

PVDF MAX S 0 0

*Core metal did not last the test with original 6.3 bars and material was tested with 5 bars

120

APPENDIX 11: RESULTS FROM FLAT-TO-FLAT FRICTION

Coating

Average kinetic friction coefficient at room temperature

Average kinetic friction coefficient at -15 C

PUR1 B 0.51 0.65

PUR1 R 0.38

PUR1 G 0.25

PUR1 M B 0.45 0.61

PUR1 M R 0.83 0.89

PUR1 M G 0.58

PUR2 M B 0.29 0.36

PUR2 M R 0.35

PES1 B 0.33 0.61

PES1 R 0.45

PES1 G 0.36

PES1 M B 0.34 0.61

PES1 M R 0.41

PES2 B 0.50 0.64

PES2 R 0.47

PES2 W 0.53

PES2 M B 0.37 0.73

PES2 M R 0.41

PES2 M G 0.41 0.74

PVDF B 0.37 0.38

PVDF S 0.45

PVDF W 0.44

PVDF M S 0.60

PVDF MAX S 0.42

121

APPENDIX 12: RESULTS FROM SLEDGE FRICTION TEST

Coating

Average static friction coefficient in Sledge friction test

Average kinetic friction coefficient in Sledge friction test

PUR1 B 0.90 0.74

PUR1R 1.80 0.97

PUR1 G 0.81 0.70

PUR1 M B 0.72 0.54

PUR1 M R 0.58 0.49

PUR1 M G** 0.59 0.49

PUR2 M B 1.00 0.60

PUR2 M R 1.03 0.55

PES1 B 0.78 0.59

PES1 R 0.94 0.53

PES1 G 0.95 0.60

PES1 M B 0.61 0.49

PES1 M R 0.65 0.48

PES2 B 1.79 1.15

PES2 R 1.35 1.03

PES2 W* 1.70 0.87

PES2 M B 0.57 0.46

PES2 M R 0.70 0.49

PES2 M G 0.82 0.61

PVDF B 1.16 0.76

PVDF S 0.86 0.54

PVDF W 1.38 0.76

PVDF M S 0.73 0.49

PVDF MAX S 0.72 0.52

*Measurements with 1 kg weight could not be applied

** Whole test procedure was duplicated

122

APPENDIX 13: VISUAL PRESENTATION OF ALL TEST

RESULTS ON EACH COATING AND COATING TYPE

0

1

2

3

4

5

PU

R1

B

PU

R1

R

PU

R1

G

PU

R1

M B

PU

R1

M R

PU

R1

M G

PU

R2

M B

PU

R2

M R

PES

1 B

PES

1 R

PES

1 G

PES

1 M

B

PES

1 M

R

PES

2 B

PES

2 R

PES

2 W

PES

2 M

B

PES

2 M

R

PES

2 M

G

PV

DF

B

PV

DF

S

PV

DF

W

PV

DF

M S

PV

DF

MA

X S

Gra

de

fo

r e

ach

me

tho

d

Coating Lc3 Pencil Hardness (0)Lc2 with Braive instrument "needle" scratch (1)Lc3 with Braive instrument "needle" scratch (1)Lc2 with Braive instrument coin like scratcher (1)Lc1 with Sclerometer (1)Lc1 after 1 hour with Sclerometer (1)Lc3 with sclerometer (1)Lc1 with spherical head in Erichsen scratch hardness tester (1)Lc3 with conical head in Erichsen scratch hardness tester (1)Lc3 in Erichsen scratch hardness tester wear test (2a)Lc3 with UMT Progressive load scratch (1)Lc4 with UMT Progressive load scratch (0)Scratch hardness HSp with 3 N load wit UMT (1)Lc2 with UMT wear test (2a)Lc4 with UMT wear test (2a)250 rounds Taber test with 1 kg weight (1)

123

0

1

2

3

4

5

PUR1 PUR1 M PUR2 M PES1 PES1 M PES2 PES2 M PVDF

Gra

de

fo

r e

ach

me

tho

d

Coating type

Lc3 Pencil Hardness (0) Lc2 with Braive instrument "needle" scratch (1)

Lc3 with Braive instrument "needle" scratch (1) Lc2 with Braive instrument coin like scratcher (1)

Lc1 with Sclerometer (1) Lc1 after 1 hour with Sclerometer (1)

Lc3 with sclerometer (1) Lc1 with spherical head in Erichsen scratch hardness tester (1)

Lc3 with conical head in Erichsen scratch hardness tester (1) Lc3 in Erichsen scratch hardness tester wear test (2a)

Lc3 with UMT Progressive load scratch (1) Lc4 with UMT Progressive load scratch (0)

Scratch hardness HSp with 3 N load wit UMT (1) Lc2 with UMT wear test (2a)

Lc4 with UMT wear test (2a) 250 rounds Taber test with 1 kg weight (1)

Mass loss at primer at Lc2 test with Taber (3) Lc2 test with Taber (2b)

Visual evaluation after 2 kg in Solid particle erosion test (0) Mass loss after 2 kg in Solid particle erosion test (3)

Lc2 at Solid particle erosion test (1) Lc3 at Solid particle erosion test (1)

Visual evaluation after 2 hours in Slurry pot (0) Mass loss after 2 hours in Slurry pot (3)

Visual evaluation of appearance of top coat after Coil damage measurement (0)

124

APPENDIX 14: CORRELATION COEFFICIENTS BETWEEN THE

TEST METHODS

Correlation coefficients of scratch tests with coating thicknesses and scratch tests

Test method Lc

3 P

en

cil

Ha

rdn

es

s (

0)

Lc

2 w

ith

Bra

ive

in

str

um

en

t "n

ee

dle

" s

cra

tch

(1

)

Lc

3 w

ith

Bra

ive

in

str

um

en

t "n

ee

dle

" s

cra

tch

(1

)

Lc

2 w

ith

Bra

ive

in

str

um

en

t co

in l

ike

sc

ratc

he

r (1

)

Lc

1 w

ith

Sc

lero

me

ter

(1)

Lc

1 a

fte

r 1

ho

ur

wit

h S

cle

rom

ete

r (1

)

Lc

3 w

ith

Sc

lero

me

ter

(1)

Lc

1 w

ith

sp

he

ric

al

he

ad

in

Eri

ch

se

n s

cra

tch

ha

rdn

es

s

tes

ter

(1)

Lc

3 w

ith

co

nic

al h

ead

in

Eri

ch

se

n s

cra

tch

ha

rdn

es

s

tes

ter

(1)

Lc

3 w

ith

UM

T P

rog

ress

ive l

oa

d s

cra

tch

(1

)

Lc

4 w

ith

UM

T P

rog

ress

ive l

oa

d s

cra

tch

(0

)

Sc

ratc

h h

ard

ne

ss

HS

p w

ith

3 N

lo

ad

wit

UM

T (

1)

Coating thickness -0.1 0.5 0.3 0.1 0.2 0.0 0.5 0.5 0.5 0.3 0.6 -0.4

Lc3 Pencil Hardness (0) 1.0 0.0 0.0 -0.2 -0.2 -0.5 0.1 0.0 -0.1 0.6 0.4 -0.7

Lc2 with Braive instrument "needle" scratch (1)

0.0 1.0 0.0 -0.2 0.1 0.0 0.6 0.4 0.5 0.3 0.5 -0.5

Lc3 with Braive instrument "needle" scratch (1)

0.0 0.0 1.0 0.6 0.3 -0.3 0.5 0.2 0.6 0.3 0.8 -0.7

Lc2 with Braive instrument coin like scratcher (1)

-0.2 -0.2 0.6 1.0 0.4 -0.2 0.2 0.0 0.4 0.1 0.2 -0.2

Lc1 with Sclerometer (1) -0.2 0.1 0.3 0.4 1.0 0.4 0.4 0.7 0.5 0.5 0.4 -0.4

Lc1 after 1 hour with Sclerometer (1)

-0.5 0.0 -0.3 -0.2 0.4 1.0 -0.4 0.5 -0.1 -0.7 -0.6 0.6

Lc3 with Sclerometer (1) 0.1 0.6 0.5 0.2 0.4 -0.4 1.0 0.4 0.8 0.7 0.8 -0.9

Lc1 with spherical head in Erichsen scratch hardness tester (1)

0.0 0.4 0.2 0.0 0.7 0.5 0.4 1.0 0.5 0.4 0.6 -0.5

Lc3 with conical head in Erichsen scratch hardness tester (1)

-0.1 0.5 0.6 0.4 0.5 -0.1 0.8 0.5 1.0 0.5 0.8 -0.8

Lc3 with UMT Progressive load scratch (1)

0.6 0.3 0.3 0.1 0.5 -0.7 0.7 0.4 0.5 1.0 0.8 -0.8

Lc4 with UMT Progressive load scratch (0)

0.4 0.5 0.8 0.2 0.4 -0.6 0.8 0.6 0.8 0.8 1.0 -0.9

Scratch hardness HSp with 3 N load wit UMT (1)

-0.7 -0.5 -0.7 -0.2 -0.4 0.6 -0.9 -0.5 -0.8 -0.8 -0.9 1.0

125

Correlation coefficients of scratch tests with wear tests

Test method Lc3 in

Eri

ch

sen

sc

ratc

h h

ard

nes

s t

este

r w

ea

r te

st

(2a)

Lc2 w

ith

UM

T w

ea

r te

st

(2a)

Lc4 w

ith

UM

T w

ea

r te

st

(2a)

250 r

ou

nd

s T

ab

er

test

wit

h 1

kg

weig

ht

(1)

Vo

lum

e lo

ss a

t p

rim

er

at

Lc2 t

est

wit

h T

ab

er

(3)

Lc2 t

est

wit

h T

ab

er

(2b

)

Vis

ua

l ev

alu

ati

on

aft

er

2 k

g in

So

lid

part

icle

ero

sio

n

test

(0)

Vo

lum

e lo

ss a

fte

r 2 k

g in

So

lid

pa

rtic

le e

rosio

n t

est

(3)

Lc2 a

t S

olid

part

icle

ero

sio

n t

est

(1)

Lc3 a

t S

olid

part

icle

ero

sio

n t

est

(1)

Vis

ua

l ev

alu

ati

on

aft

er

2 h

ou

rs in

Slu

rry p

ot

(0)

Vo

lum

e lo

ss a

fte

r 2 h

ou

rs i

n S

lurr

y p

ot

(3)

Vis

ua

l ev

alu

ati

on

of

ap

pe

ara

nc

e o

f to

p c

oat

aft

er

Co

il

dam

ag

e m

easu

rem

en

t (0

)

Coating thickness 0.8 0.9 1.0 0.0 0.3 0.7 0.3 0.1 0.6 0.7 0.4 0.0 0.7

Lc3 Pencil Hardness (0) 0.0 -0.1 -0.3 0.3 0.3 0.1 0.4 0.3 0.2 0.1 0.2 0.2 -0.2

Lc2 with Braive instrument "needle" scratch (1)

0.7 0.8 0.7 -0.2 0.1 0.3 -0.1 -0.3 0.0 0.2 0.0 -0.3 0.6

Lc3 with Braive instrument "needle" scratch (1)

0.4 0.9 0.9 0.6 0.8 0.7 0.7 0.4 0.7 0.7 0.8 0.7 0.1

Lc2 with Braive instrument coin like scratcher (1)

0.1 0.7 0.7 0.3 0.5 0.6 0.5 0.1 0.5 0.4 0.6 0.5 -0.2

Lc1 with Sclerometer (1) 0.2 0.3 0.3 0.4 -0.1 0.2 0.1 0.1 0.2 0.2 0.2 0.4 0.1

Lc1 after 1 hour with Sclerometer (1)

-0.2 -0.3 -0.1 -0.2 -0.4 -0.1 -0.5 0.0 -0.4 -0.2 -0.5 -0.1 0.4

Lc3 with Sclerometer (1) 0.8 0.8 0.7 0.4 0.4 0.4 0.3 0.0 0.4 0.5 0.4 0.2 0.5

Lc1 with spherical head in Erichsen scratch hardness tester (1)

0.4 0.8 0.8 0.2 0.1 0.5 0.1 0.1 0.1 0.3 0.1 0.2 0.5

Lc3 with conical head in Erichsen scratch hardness tester (1)

0.6 0.9 0.8 0.4 0.3 0.5 0.4 0.0 0.5 0.6 0.6 0.4 0.3

Lc3 with UMT Progressive load scratch (1)

0.5 0.5 0.4 0.3 0.2 0.2 0.2 -0.3 0.6 0.2 0.5 0.3 0.1

Lc4 with UMT Progressive load scratch (0)

0.7 0.8 0.7 0.6 0.7 0.7 0.7 0.2 0.9 0.7 0.8 0.7 0.5

Scratch hardness HSp with 3 N load wit UMT (1)

-0.6 -0.6 -0.5 -0.5 -0.5 -0.5 -0.7 0.0 -0.7 -0.6 -0.9 -0.6 -0.4

126

Correlation coefficients of scratch tests with friction tests and average results

Test method Kin

eti

c f

ricti

on

co

eff

icie

nt

at

roo

m t

em

pe

ratu

re in

fla

t-to

-

flat

fric

tio

n t

est

Kin

eti

c f

ricti

on

co

eff

icie

nt

at

-15 C

in

fla

t-to

-fla

t fr

icti

on

test

Sta

tic f

ricti

on

co

eff

icie

nt

in S

led

ge f

ricti

on

test

Kin

eti

c f

ricti

on

co

eff

icie

nt

in S

led

ge f

ricti

on

te

st

Scra

tch

resis

tan

ce a

ve

rag

e

Wea

r te

st

ave

rag

e

Overa

ll a

vera

ge

Coating thickness 0.1 0.5 -0.3 -0.2 0.5 0.7 0.7

Lc3 Pencil Hardness -0.1 -0.7 0.5 0.5 0.0 0.2 0.1

Lc2 with Braive instrument “needle” scratch

-0.2 0.0 0.0 0.0 0.5 0.3 0.4

Lc3 with Braive instrument “needle” scratch

0.2 -0.2 0.0 -0.1 0.5 0.7 0.7

Lc2 with Braive instrument coin like scratcher

0.2 -0.1 -0.4 -0.4 0.3 0.4 0.4

Lc1 with Sclerometer -0.5 -0.3 -0.1 -0.1 0.8 0.3 0.6

Lc1 after 1 hour with Sclerometer -0.5 0.2 -0.2 -0.2 0.2 -0.2 -0.1

Lc3 with Sclerometer 0.0 -0.2 0.1 0.1 0.7 0.6 0.7

Lc1 with spherical head in Erichsen scratch hardness tester

-0.6 -0.1 0.0 0.0 0.8 0.3 0.6

Lc3 with conical head in Erichsen scratch hardness tester

-0.1 -0.2 0.0 0.1 0.8 0.6 0.8

Lc3 with UMT Progressive load scratch 0.2 -0.5 0.2 0.3 0.6 0.4 0.5

Lc4 with UMT Progressive load scratch 0.5 -0.6 0.3 0.4 0.7 0.8 0.8

Scratch hardness HSp with 3 N load wit UMT

-0.4 0.7 -0.4 -0.4 -0.8 -0.7 -0.7

127

Correlation coefficients of wear tests with wear tests

Test method Lc3 in

Eri

ch

sen

sc

ratc

h h

ard

nes

s t

este

r w

ea

r te

st

(2a)

Lc2 w

ith

UM

T w

ea

r te

st

(2a)

Lc4 w

ith

UM

T w

ea

r te

st

(2a)

250 r

ou

nd

s T

ab

er

test

wit

h 1

kg

weig

ht

(1)

Vo

lum

e lo

ss a

t p

rim

er

at

Lc2 t

est

wit

h T

ab

er

(3)

Lc2 t

est

wit

h T

ab

er

(2b

)

Vis

ua

l ev

alu

ati

on

aft

er

2 k

g in

So

lid

part

icle

ero

sio

n t

est

(0)

Vo

lum

e lo

ss a

fte

r 2 k

g in

So

lid

pa

rtic

le e

rosio

n t

es

t (3

)

Lc2 a

t S

olid

part

icle

ero

sio

n t

est

(1)

Lc3 a

t S

olid

part

icle

ero

sio

n t

est

(1)

Vis

ua

l ev

alu

ati

on

aft

er

2 h

ou

rs in

Slu

rry p

ot

(0)

Vo

lum

e lo

ss a

fte

r 2 h

ou

rs in

Slu

rry p

ot

(3)

Vis

ua

l ev

alu

ati

on

of

ap

pe

ara

nc

e o

f to

p c

oat

aft

er

Co

il

dam

ag

e m

easu

rem

en

t (0

)

Lc3 in Erichsen scratch hardness tester wear test (2a)

1.0 0.9 0.9 0.0 0.3 0.5 0.2 -0.1 0.4 0.6 0.4 0.0 0.8

Lc2 with UMT wear test (2a) 0.9 1.0 1.0 0.4 0.8 0.9 0.7 0.2 0.8 0.8 0.6 0.4 0.7

Lc4 with UMT wear test (2a) 0.9 1.0 1.0 0.3 0.8 0.9 0.6 0.3 0.7 0.8 0.5 0.3 0.8

250 rounds Taber test with 1 kg weight (1)

0.0 0.4 0.3 1.0 0.8 0.6 0.6 0.6 0.6 0.5 0.6 0.9 -0.1

Volume loss at primer at Lc2 test with Taber (3)

0.3 0.8 0.8 0.8 1.0 0.9 0.7 0.6 0.7 0.7 0.7 0.7 0.2

Lc2 test with Taber (2b) 0.5 0.9 0.9 0.6 0.9 1.0 0.8 0.6 0.8 0.9 0.7 0.6 0.4

Visual evaluation after 2 kg in Solid particle erosion test (0)

0.2 0.7 0.6 0.6 0.7 0.8 1.0 0.6 0.8 0.8 0.8 0.7 -0.1

Volume loss after 2 kg in Solid particle erosion test (3)

-0.1 0.2 0.3 0.6 0.6 0.6 0.6 1.0 0.5 0.5 0.4 0.7 0.2

Lc2 at Solid particle erosion test (1)

0.4 0.8 0.7 0.6 0.7 0.8 0.8 0.5 1.0 0.9 0.8 0.6 0.2

Lc3 at Solid particle erosion test (1)

0.6 0.8 0.8 0.5 0.7 0.9 0.8 0.5 0.9 1.0 0.7 0.5 0.4

Visual evaluation after 2 hours in Slurry pot (0)

0.4 0.6 0.5 0.6 0.7 0.7 0.8 0.4 0.8 0.7 1.0 0.8 0.0

Volume loss after 2 hours in Slurry pot (3)

0.0 0.4 0.3 0.9 0.7 0.6 0.7 0.7 0.6 0.5 0.8 1.0 -0.1

Visual evaluation of appearance of top coat after Coil damage measurement (0)

0.8 0.7 0.8 -0.1 0.2 0.4 -0.1 0.2 0.2 0.4 0.0 -0.1 1.0

128

Correlation coefficients of wear tests with friction tests and average results

Test method Kin

eti

c f

ricti

on

co

eff

icie

nt

at

roo

m t

em

pe

ratu

re in

flat-

to-f

lat

fric

tio

n t

est

Kin

eti

c f

ricti

on

co

eff

icie

nt

at

-15 C

in

fla

t-to

-fla

t

fric

tio

n t

es

t

Sta

tic f

ricti

on

co

eff

icie

nt

in S

led

ge f

ricti

on

test

Kin

eti

c f

ricti

on

co

eff

icie

nt

in S

led

ge f

ricti

on

te

st

Scra

tch

resis

tan

ce a

ve

rag

e

Wea

r te

st

ave

rag

e

Overa

ll a

vera

ge

Weig

hte

d a

ve

rag

e

Lc3 in Erichsen scratch hardness tester wear test (2a)

0.0 0.0 -0.2 -0.1 0.6 0.6 0.7 0.7

Lc2 with UMT wear test (2a) 0.3 -0.6 -0.2 -0.1 0.8 0.9 0.9 0.9

Lc4 with UMT wear test (2a) 0.3 -0.5 -0.4 -0.3 0.8 0.9 0.9 0.8

250 rounds Taber test with 1 kg weight (1)

-0.1 -0.5 0.4 0.4 0.4 0.7 0.7 0.7

Volume loss at primer at Lc2 test with Taber (3)

0.3 -0.5 0.3 0.2 0.2 0.9 0.7 0.7

Lc2 test with Taber (2b) 0.5 -0.2 0.0 0.0 0.5 0.9 0.9 0.8

Visual evaluation after 2 kg in Solid particle erosion test (0)

0.4 0.0 0.1 0.2 0.3 0.8 0.6 0.7

Volume loss after 2 kg in Solid particle erosion test (3)

0.1 -0.2 0.2 0.3 0.1 0.6 0.4 0.4

Lc2 at Solid particle erosion test (1) 0.4 0.1 -0.1 0.0 0.4 0.9 0.8 0.8

Lc3 at Solid particle erosion test (1) 0.4 0.2 -0.1 0.0 0.5 0.9 0.8 0.8

Visual evaluation after 2 hours in Slurry pot (0)

0.3 -0.1 0.0 0.1 0.4 0.8 0.7 0.8

Volume loss after 2 hours in Slurry pot (3)

0.0 -0.5 0.2 0.2 0.4 0.7 0.7 0.7

Visual evaluation of appearance of top coat after Coil damage measurement (0)

-0.1 0.2 -0.3 -0.1 0.5 0.5 0.5 0.5

129

APPENDIX 15: EXPERIENCE BASED GRADING OF THE TESTS

Test method Usability of the test method How well the test describes wanted properties

Pencil Hardness Lc3

3

Very easy and very fast to use. Very simple method but difficult to keep force and angle constant.

1 Measures the hardness of scratcher capable to pierce the coating, not directly coating itself.

Braive instrument Lc2 with needle scratch

4 Easy and rather fast method. Stabile angle and load.

2

Measures the lowest load for severe visual damage under single asperity. "Stone on shoe bottom damage", unlikely but plausible.

Braive instrument Lc3 with needle scratch

4 Easy and rather fast method. Stabile angle and load.

3

Measures the lowest load of scratch with single asperity, which after corrosion can start. "Stone on shoe bottom damage", unlikely but plausible.

Braive instrument Lc2 with coin like scratcher

4 Easy and rather fast method. Stabile angle and load.

5

Measures the lowest load for severe visual damage under larger scratcher. A connection to certain damage has been found

Lc1 with Sclerometer

2 Very difficult to evaluate. Easy and rather stabile scratching

4 Measures the lowest load which under a single asperity inflicts visual damage.

Lc1 after 1 hour with Sclerometer

1 Extremely difficult to evaluate. Easy and rather stabile scratching

4 Measures the lowest load which under a single asperity inflicts visual damage that is visible after 1 hour.

Lc3 with Sclerometer

4

Easy and rather fast to use. Very simple method but some difficulties in keeping the angle constant.

3

Measures the lowest load of scratch with single asperity, which after corrosion can start. "Stone on shoe bottom damage", unlikely but plausible.

Lc1 with spherical head in Erichsen scratch hardness tester

2 Very difficult to evaluate. Easy and stabile scratching

4 Measures the lowest load which under a single asperity inflicts visual damage

Lc3 with conical head in Erichsen scratch hardness tester

4 Easy and rather fast method. Stabile angle and load.

3

Measures the lowest load of scratch with single sharp asperity, which after corrosion can start. "Stone on shoe bottom damage", unlikely but plausible.

Lc3 with UMT Progressive load scratch

3

Automatic but slow method. Lc3 rather difficult to evaluate and has lot of scatter on parallel samples.

3

Measures the lowest load of scratch with single small asperity, which after corrosion can start. "Stone on shoe bottom damage", unlikely but plausible.

Lc4 with UMT Progressive load scratch

5 Automatic but slow method. Lc4 rather easy to evaluate.

2

Measures when the scratching becomes severe under single small asperity. "Stone on shoe bottom damage", unlikely but plausible.

Scratch hardness HSp with 3 N load wit UMT

4

Semi-automatic but slow method. Widths of the scratch easy to measure from figure.

0 Could be used with proper parameters in estimation of coating properties. Not relevant with current parameters.

130

Lc3 in Erichsen scratch hardness tester wear test

2 Rather slow method and evaluation on the run rather difficult.

2

Measures when the several scratches become severe under single small asperity. Not likely to happen but with larger scratching tip would have connection to wear on profiling.

Lc2 with UMT wear test

1

Slow method and evaluation of Lc2 not possible on all coatings and difficult on the rest.

1

Measures how long it takes from multiple passes with higher friction contact to break adhesion of top coat and primer. Not measurable for all coatings.

Lc4 with UMT wear test

5 Automatic but slow method. 2

Measures how long it takes from multiple passes with higher friction contact to break adhesion of coating and zinc. With different scratching tip the test would have connection to wear on profiling.

Volume loss at 250 rounds with 1 kg weight in Taber test

5 Semi-automatic and rather fast wear method.

4

Measures the loss of material under milder abrasive wear. Describes situation when snow and ice or dirt on transportation wears the coating.

Volume loss at primer at Lc2 test with Taber

3 Difficult to evaluate the Lc2 limit on the run and very slow method.

1

Measures the loss of coating material after abrasive wear. Time of wear differs, and abrasive surface can be blocked. More connected to material property than coating property.

Rounds until Lc2

test with Taber 3

Difficult to evaluate the Lc2 limit on the run and very slow method.

3

Measures the amount of abrasive wear the coating can last before severe visual damage. Time of wear differs, and abrasive surface can be blocked. Describes situation when snow and ice or dirt on transportation wears the coating.

Visual evaluation after 2 kg in Solid particle erosion test

2

Semi-automatic and rather fast method but rather difficult to evaluate. Health risk on the dust

4

Measures the visual properties of coatings after certain amount of erosive wear. Connected to erosive wear caused by dust, needles, and pine cones for example.

Volume loss after 2 kg in Solid particle erosion test

1

Semi-automatic and rather fast method but difficult to clean the samples from the dust. Health risk on the dust.

3

Measures the loss of coating material after certain amount of erosive wear. More connected on material property than coating property.

Lc2 at Solid particle erosion test

2

Semi-automatic and easy method but rather difficult to evaluate. Health risk on the dust

3

Measures the amount of erosive wear the coating can last before severe visual damage. Connected to erosive wear caused by dust, needles, and pine cones for example.

Lc3 at Solid particle erosion test

3 Semi-automatic and easy method to apply. Health risk on the dust

3

Measures the amount of erosive wear the coating can last before corrosion to start. Connected to erosive wear caused by dust, needles, and pine cones for example.

131

Visual evaluation after 2 hours in Slurry pot

2

Semi-automatic but very slow method and rather difficult to evaluate. Health risk on the dust

4

Measures the visual properties of coatings after certain amount of wet erosive wear. Describes situation when dirt on water, for example in rain water systems.

Volume loss after 2 hours in Slurry pot

1

Semi-automatic but very slow method and difficult to clean the samples from the dust. Health risk on the dust.

3

Measures the loss of coating material after certain amount of erosive wear. Describes situation when dirt on water, for example in rain water systems.

Visual evaluation of appearance of top coat after Coil damage measurement test

2

Fast method but the sample must be formed before attaching to the device. Core metal inflicts on the results and difficult to evaluate results

4 Measures visual difference on coatings if material is sliding, for example in coil.

132

APPENDIX 16: WEIGHTED AVERAGE GRADES FOR EACH

COLOUR

Coating type Weig

hte

d a

ve

rag

e s

cra

tch

test

gra

de

s

Weig

hte

d a

ve

rag

e w

ear

test

gra

des

Weig

hte

d a

ve

rag

e g

rad

es

PUR1 B 3.4 4.5 4.0

PUR1 R 3.7 3.8 3.8

PUR1 G 4.0 4.0 4.0

PUR1 M B 3.4 3.4 3.4

PUR1 M R 2.5 3.8 3.1

PUR1 M G 2.5 3.6 3.0

PUR2 B 2.6 2.6 2.6

PUR2 R 2.8 1.9 2.4

PES1 B 3.6 3.3 3.4

PES1 R 2.9 2.7 2.8

PES1 G 2.9 2.4 2.6

PES1 M B 3.1 2.0 2.6

PES1 M R 2.6 1.7 2.2

PES2 B 2.2 2.3 2.2

PES2 R 2.1 2.4 2.3

PES2 W 2.3 1.9 2.1

PES3 M B 1.8 1.9 1.9

PES3 M R 2.1 1.4 1.7

PES3 M G 1.7 1.4 1.6

PVDF B 2.8 3.8 3.3

PVDF S 3.8 3.4 3.6

PVDF W 2.4 3.2 2.8

PVDF M S 2.4 3.1 2.7

PVDF MAX S 3.6 3.5 3.6