Surface Cleaning Engineering

7/30/2019 Surface Cleaning Engineering

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MFSA Qualit Metal Finishing Guides

Chemical Surface Preparation For Electroplated and Metallic Coatings

INTRODUCTION

This Quality Metal Finishing Guide deals with pretreatment of surfaces for metallic

coatings. In this context, pretreatment is defined as the process of substrate preparation

specific metallic coating.

Generally, the objective of applying a metallic coating is to provide one or several new pbasis metal. Coatings include decorative finishes such as copper or brass on zinc diecast,

coatings such as hard chrome or electroless nickel on aluminum, or corrosion resistant zi

steel.

Regardless of the function, these coatings all must adhere completely to the basis metal

provide the decorative or functional properties required. Plate adhesion must exceed the

strength of either the substrate or the electroplate. In other words, an attempt to peel t

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caig f he bae hd ee a ae f he bai ea ih eaai

f he bae a he bda. I aig, hi ee f adhei i ibe beee

he bae ad he aed ea.

Whaee he echai, adhei deed he cdii f he face beig aed

heefe, ci f he ciica e ed i he ea f a deiabe caia

iefee ih he ie-aic adhei. Tica caia ae i ch a i, ge

ide ad cae.

Peeae a affec he caig eie. Ee if adhei i eced iiia, b

ig , e i dei, ad faie de hdge ebiee ccig a a

be eaed face eaai.

Peae faie eig f ci ca be aided b efec face ea

cee ceage b he ecified caig. Aie ad he idie e he

aed ce i idig g-e dc-eface aaie.

The ia eeci f a gie eeae ce i dicaed b fac.

1. THE METAL BEING PROCESSED AND THE CLEANING SOLUTION

Geea, ee ad ce ca ihad g aaie ceae (H 10-14), ad aci

50% hdchic acid, ih ie aac f he bai ea. Be ad ba ei

(H 9-13) ad e eeae ee he eecie ea f he ic f he

(deicificai). Zic ad ai eie e ide ihibied aai (H 9-12) ad

Piea fai ae aaiabe ee hee eed.

2. THE TYPE OF SOILS TO BE REMOVED

Si i a bace he face f he ea ha i iefee ih he ea-fiihi

efed. Si a be he e f ieia aicai he ea f a aeia h

ea ig, hadig, ad ee high eeae he ahee.

Geea eaig, he e f i ca be be d i bad caegie: g

igaic.

a. Oganic

OSP Fia Fiih VeificaiPga

Ehe Ai DeieFcci, Maage f e-

Maeig Cicai

Ne Achie

Safe Hab CiaceREACh

C G

C Eecic

Aha

Seicdc

Pacagig

EheA.c


3/31

Saifiabe aia ad egeabe i.

Uaifiabe iea i ad ae.

Miceae caia eihe fed i i (eaic a fed i he b

ihibi f ceai acid icig i edeiig he ea.

b. Inoganic

Scae ad , ide ad eaic eide.Pihig cd, abaie, gidig ad ihig eide gi.

Miceae h d ad deig fe.

Thee ae a fe f he i eceed. Se f he he icde ai, ceai

a ae-i-i ei, figei, ad igaic caig ch a hhae, ch

eeaie.

Ma f he bica, ca ad ci eeie ed da ae be e

i ae be ceaed i a id, -caic-da-caiig aaie ceae a efac, a ae-be bica ca be eed aia b a a ae e-ie,

edcig ceae caiai ad iiiig ceaig be. Paicae ae i

eadi eed b id, -eeae ceaig.

MECHANISMS OF SOIL REMOVAL

M ceaig ad i ea i accihed b e e f he fig echai

1. WETTING

The ce b hich he ceae, hgh he e f face-acie age, e hebd b he diacee f i ad he eig f face ad iefacia ei. We

i he fi eiee f ceaig ied ea.

2. EMULSIFICATION

Oce eig ae ace, he ce f eificai ca cc. Thi i he diei

iicibe iid. Eificai i deede he i eceed ad he chice f

ecdai fac ch a H, eeae ad agiai.


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3.SAPONIFICATION

The eaci f fa acid ih h aai dce be eifiabe a. Ea

aificai f bffig cd ad eaae daig cd.

4. SOLUBILIATION

The ce b hich he bii f a bace (i) i iceaed i a ceai edi,

he e eeci f face acie age. Ma i ed da ae, i fac, ae

5. DEFLOCCULATION

The ce heeb he i i be i e fie aice ad dieed i he cea

i i he aiaied a a diei ad eeed f aggeaig ad eeig

beig ceaed.

6. SEQUESTRATION

The ce i hich deiabe i ch a Ca++ Mg++ ad hea ea ae "ie

deaciaed, heeb eeig he f eacig ih aeia ha a d f

dc. The caic eae i he had ae c fed he a heic de

ed. The c fed i he eaci beee a ad he Ca++ Mg++ i i hahe ae i feed, he Ca++ ad Mg++ i ae "ied " eeeed, eeig

eacig.

7. MECHANICAL ACTION

Thi i a eee ia fac i ea ceaig, ice i ca gea iceae he

efficiec f i ea. Mechaica aci ca be accihed b i ee

he ief. Se e f i agiai ae ai, echaica, aic, a a

f eecic ceaig. Ai agiai i a efficie a he he ehd.

CLASSES OF CLEANERS

Ceae fi i hee g - e, ei-ae ad ae.

1. SOLVENT-BASED CLEANERS

Bh a degeaig ad e iei ae beig haed eiced a a e

cce ad eiea egai.


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2. SEMI-AQUEOUS OR DIPHASE CLEANERS

Thee ae ei f ae, gaic e ad eifie. The hae iied aic

ie, ice he eie ecda ae ceaig e.

3. AQUEOUS CLEANERS

Cie he age g ad ca heee be fi i hee caegie: acid, e

ceae:

a. Acid Cleane

Baed cceai f gaic igaic acid ch a ciic ad hhic.

he igh ea ide ae ee. The e f acid ad addiie acage ed deed

ea, e f i ad bee ceig. Aicai f acid ceae icde bff

ba hee ii aac f he face i eaed.

b. Neal cleane (alo called deegen cleane)

Neihe acid aaie baed. The a ci f eeeig age, diea

age ad eig age. High cceai ad eeae ae hei e iie

c. Alkaline cleane

The he f he id. The ae ea e, eaie afe ad ea c.

e feibe ad hae bade eaig ii ha he ceae. Aaie ceae a

cheica ha ide aaie cdiiig, aificai f fa i ad i e

Geneal chemiie ed in alkaline cleane:

Caic alkali - ide he highe ee f aaii, ih eaab c. The

ad he de f aac ie. The ide ecee aaii he ed i e

Cabonae - ide bffeig, ie e ad fe ae b eciiai. Deedig

ide a ide age f aaii. Cabae ca cae caig i had ae aea if

ied ih he ae-feig age.

Silicae - ae ce he caic aai i e f aaii. The ae gd bffe, e

eifie ad he i i edig. Siicae be e ied i acid di

ee ibe i icic acid ge f fig.


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Phophae - ide ae feig, id aaii ad e bffeig. The ae

eig age, ehacig he ea ceaig effec.

ETTING AGENTS (SURFACTANTS)

Weig age ae ciica he fci f ceae. Thee gaic aeia

e f haig ae eeig (hdhbic) ad ae aacig (hdhiic)

ece. Thi aagiic effec a f he eeai f hee aeia a he caia-ea face), ieface, heeb faciiaig ea ad biiai f

C faca ed i ceae ae:

Anionic - hich ide gd deegec. The ae a gd cig age f he

Sa i a eae f a aa deied aiic faca. Aiic faca ae ge

fae.

Nonionic - ae heic aeia ad ae gd eifie. I addii, he ae ed

eed ceae ad f fa c i a ceae. The bii f iic fa

ceaig i deceae ih iceaig eeae ad cceai. Thi i caei. Whe a aaie ceae caiig iic faca i eaed abe he e

eeae ad cceai, he faca bece ae ibe ad begi ac

iei ceae hi i deiea ad ca cae he f he faca hgh

I a a ceae, -cd-i iic faca ae fe ed a defae.

Amphoeic - ae iia aiic faca he ed i aaie ceae. The

abii i g aaie iid. Aheic faca be e ied i

acid, hich i ce he caiic fi fe.

Caionic - faca ae fi fe ad ae ed i ecia aaie ceae ad a i

acid.

ALKALINE DESCALING

Aaie decaig i a ecia e f ceaig ha i deiged ee igh ide a

fe bae. The ceae ae baed high aaii i cbiai ih ce


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chelating agents. Used at 168.8-185F, alkaline descalers are capable of dissolving light

by immersion.

One or more additional cleaning actions as described under Mechanism of Soil Removal

involved in soak cleaning applications. Removal of buffing compounds, for instance, requ

saponification, emulsification and deflocculation. On the other hand, if the emphasis is o

skimming of oils from cleaners, displacement, rather than emulsifying type cleaners are

with chemicals that provide good wetting characteristics.

METHODS OF SURFACE PREPARATION

A total surface preparation process consists of one or several operations. They are carrie

sequence designed to produce an optimum condition for the application of the intended c

steps are typically classified in accordance with their particular cleaning mechanism,

as follows:

1. MECHANICAL CLEANING (spra and ultrasonic)

2. SOAK CLEANING3. ELECTROCLEANING

4. ACID ACTIVATION

While some pretreatment processes call for soak cleaning followed by acid activation, oth

all or most of the above operations.

1. MECHANICAL CLEANING

Mechanical cleaning in the context of surface preparation for metal coating encompasses

ultrasonic cleaning. Mass finishing is also used, but is described in detail in a separate Q

Mechanical cleaning relies in great part on mechanical energy in physically removing soilsurface. To assist the removal process, detergents, alkalis or acids, deflocculants and so

Heat also helps, although low to moderate solution temperatures are the norm.

a. Spra Cleaning

This is a very common cleaning technique, often used in dedicated spray machines, or b

within a plating line. Primps deliver cleaning solutions through spray nozzles at pressure

20 to 200 psi. Some high-pressure systems can produce 800 psi or more. The cleaning s


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recirculated through a reservoir, which is usually fitted with heaters, oil skimmers, and l

Spray-cleaning solutions are formulated with low or non-foaming detergents. Since the

relies mostly on the spray-impact energy, the solution concentration is kept relatively lo

temperature. Spray cleaners are designed for specific applications, taking into account th

being processed and types of soils to be removed.

Mild acid or alkaline cleaners are used on nonferrous and highly finished metals, e.g., bu

aluminum. Stronger cleaners, incorporating rust inhibitors, are used on ferrous metals, i

alloys. Typical soils removed by spray cleaners are buffing compounds, heavy oils, drawi

compounds. Parts that benefit from spray cleaning include cabinets and other geometric

deep corners and recesses. For superior cleaning, turbojet nozzles are used inside an im

Parts may be cleaned in stationary positions or on conveyors moving across banks of spr

positioned to reach all areas to be cleaned. Spray cleaning may be single or multiple stat

rinsing, inhibiting and drying or other surface-preparation steps.

b. Ulaonic CleaningUltrasonic cleaning takes place when small vacuum cavities caused by high-frequency so

traveling in a liquid implode against surfaces submerged in the liquid. Transducers attac

or bottoms of cleaning tanks supply the ultrasonic waves to the cleaning solution. Tempe

140-160F should be avoided, as they tend to reduce the ultrasonic efficiency.

When this technique is used with a water-detergent solution, the scrubbing action that r

surface is effective in removing various contaminants, especially insoluble particles, smu

that are difficult to remove by conventional wetting or emulsification. It does not, howev

remove oils, which is why it is used after degreasing.

2. SOAK CLEANING

Cleaning by immersion is intended to remove the bulk of the soils, particularly those tha

mechanically deposited on the surface. Examples of such soils are cutting fluids, grease,

buffing compounds. There are various types of soak cleaners designed for different clean

By saponification of fatty acids such as those encountered in buffing compounds,

and drawing compounds. Saponification relies on the level of alkalinity available i


9/31

ad i ed b high eeae.

B eificai f i, geae, fa acid ad hei deiaie. Thi i acc

he e f ecia faca bed ad ceai aai ch a iicae.

B diacee f i ad geae, hgh he e f ecia faca. Di

he i be eai ied he faca a he ea face, hee he

eeaed a he face f he i. Effecie ie be ed ih c

ee dag f eeaed i he . Thee ceae a eie e

ice he ae eai aaed ih i.

3. ELECROCLEANING

Eecceaig i a ia e i ea-face eaai. I i a eecic

chaaceied b he e f diec ce ad a ecia faed eece. The

ceed a be eecica ceced a he ade, cahde, bh (aeae), de

aicai.

Ahgh eecceaig i a diffee ad diic ehd f face ceaig, i hd

iega a f he eae cce.

Eecceae a decibed hee ae aaie, ad i geea f aaie a ce

ecede acid aciai i he eae cce. Thei baic fci i ee i ha

eed b ie a ceaig degeaig. Eae f ch i ae a f:

Figei, daig cd, ad i die i face i aied

Fie diided aice ch a ihig abaie, eaic fie f gidig

eai, cab ad he aig eee. Ofe hee fie aicae a

efeed a , a be hed he face b ie echaica fce, eec

i a hi i geae ai.Mea idai dc, he e f ee he ahee, a he

a hea eae, fgig, edig, ec.

Ahgh eecceaig a a ee a aica e f i, i cdii

i f eaie ea i he bee e i he cce. F iace, a adhee i

eed egh be ifed i he fig ie a. Sface ide a be edced

e be f be eai died i he acid a.


10/31

a. Electrolsis of Electrocleaners

A ce i aied a eecceae, he fig eeccheica eaci ae

eecig ae. The aai ee a he cdcie edi.

A he Ade: 4[OH]- --> 2H20 + 02 + 4e

A he Cahde: 4H20 + 4e --> 4[OH] + 2H2

A ca be ee, ice a ch hdge i ibeaed a he cahde a ge a he a

b. Tpes of Electrocleaners

Eecceae ae caified he bai f ai ieeaed cieia:

Pai f he i he a.

Te f bae beig eaed.

Anodic ElectrocleaningThe i ceced he iie (ade) ide f he ecifie. Thi ce i a

eecceaig, ice he ai i ie ha i eecaig. A decibed de

ge i ibeaed a he face f he (he ade) he ce i aied. A h

, i ceae a echaica cbbig aci ha e ad if he i.

T he heea a ae ace. A ge bbbe ae fed he face, he

g befe he ie i ci ae. I i beieed ha he aic chage hdig fi

he face i eeaed hgh he ae f bbbe, faciiaig i ea hgh h

aci. Thi hee a aie he he de f eecceaig.

Cheica effec, idai ad d i H a ae ace a he ade face. If ece

idai ca be ee ch ea a ba, ic ad ie, a he dic, ai

ihibied adic eecceae ae aaiabe f ba ad ic.

Whe ice i adica eaed, i i ic aiae ad ee aig i f

eaciaed.


11/31

A iia effec i eeieced ih aie ee. Rega ee ae adee affe

eecceaig, heea high-cab ee ae e eiie ad eie deai.

ice ad ie ae aaced aihed b adic eecceaig.

A ge i ibeaed a he ade, he e H ae ed iceae a he ieface.

be iced ee if a eecceae' aaii i b deig a a e f

aieace. The ee i e aid idied, ad eciiaed i hdide f

Pa eiig he a i hae a eched aeaace, eecia i high-ce-

The iai ca be eadi ecified b iceaig he aaii f he bah b edci

dei be a eaig ee.

Cathodic Electrocleaning

The i ceced he egaie eia (cahde) ide f he ecifie. Thi i a

diec eecceaig. I hi cae, hdge i ibeaed a he cahde. Tice a ch

ge i geeaed. Cee, e cbbig aci ad ceaig abii ae ee

eecceaig, hee, ha fd a ideead e i id f ea:

ab hdge ebiee a a e f ci hdge eeae a he face; aae f chaged iiie f he i he cahdic face. The ae

eceibe he caa bee a he a ei he a, b ead adhei

eecdei. Caia eadig ch adhei faie ae eaic fie, ceai

faca, cid, eaic a ad dagged-i heaae che.

Cahdic ceae, he e cea ad e aiaied, ae ed f ceig bffed

hie ea, ih aihig, ad f eecceaig ice ad high ice ee i

aiai. Whe ed ee ad ce ae adaage f hei ei cb-c

ecda adic eecceae hd f, if ee f a fe ecd. Thi eiiie ha a hae deied he b cahdic aci.

Periodic-Reerse Electrocleaning

Thi ehd f eecceaig f fe ea e a cbiai f bh adic ad

ceaig. A eidic-eee i ( a P.R.) i iaed he ecifie' . Th

ichig echai ha eee he ai a ced ad ied iea. The

ae aeaig adic ad cahdic aiie f he ecified ceaig ie.


12/31

A ica eig i 10 ec. cahdic - 10 ec. adic. B chagig he eig, e cah

a be ed effec ai ceaig. The i ca be gaed ha he a

adic befe he ie eig h ff he ecifie. Thi ee ea f a chage

a hae aed he dig cahdic ceaig.

The ci idai ad edci a he face ce he ide ad cae

be f ha ae iced b caide cheaig age bi i he ceae f

PR ceae eea bece aaed ih died i ide ad be eace

acica, he ca be egeeaed b aig he i cahdica. PR. ceaig i e

decaig ad deig high egh ad ig ee ih he e f decaig acid

heeb cig hdge ebiee. (ASTM B242 dea ecifica ih he a

eceded f he eaai f high cab ee f eecaig iiie hd

ebiee).

c. Operating Parameters and Process Considerations

A eaied eaie, eeci i he ai diig ce i eecceae. The a

eibe f he cbbig aci a he eecde i a fci f he a f chgh he ce. Theefe, hee aaee cig ce hd be cideed:

Solution Conductivit

Thi i i a fci f ceae cceai ad eeae a a gie age. T

cceai ad eeae, a acica ee, he highe he cdcii ad

gaig ad cbbig aci.

Vage Aied-Ce iceae ih age, ahgh he ae i e ai

V. Highe ae ae cae "big" ghe a.

Surface Area Being Cleaned

The face aea beig ceaed eecica ad he a f ce aied e i

ce dei (CD). I i eaed i aee e ae f (af). Ce dei a

efficiec.

Adeae eceded CD age f diffee bai ea ae aied i Tabe I.

ae dce igh agia eecceaig. Highe ae geea ead echi


13/31

f he face.

Ade cahde aea ai f 1:1 ae adeae f aicai. The ai i

he ecified ce deiie ae aiaied.

TABLE I: Recommended Electrocleaning Current Densit-Rack Applications

A/f2 Pai

(A=Adic, C=Ca

See, -cab 47-93 A,C

See high egh 28-47 A

Saie ee 47-74 C

Ce 47-74 A, C

Ba 19-37 A, C (adic ihib

Zic dieca 19-37 A, C (adic ihib

Nice ad i a 19-28 C

Lead ad i a 47-74 C

Sie ad i a 19-28 C

*In barrel applications, a fraction of the above C.D. values should be epected.

Selection and Use of Electrocleaners - Thee ae geea cideai i he eeci

e f eecceae:

Formulation - Seea iea fai ae aaiabe, ceig a ide age f

Thee fai hd ide he fig eie:

A iabe degee f aaii f he ea ceed, e.g., high aaii f e

ad ba.

A e ai f hdide iicae ee ibe iicae fi f adhe


14/31

and affecting plate adhesion.

TABLE II: Tpical Operating Conditions for Electrocleaners

Steel and Copper Brass Zinc Ni

Alkalinity, g/L

(as NaOH)

50-100 15-20 15-20 30-

Temperature F 140-195 120-160 120-160 120

Time, seconds 1-5 1-3 1-3 1-5

The above are typical average operating conditions. Suppliers of proprietary electroclean

specify optimum operating parameters for specific applications. Alkalinity expressed as N

represent from 20 to 80% of the total product formulation.

Equipment Maintenance and Operation-Corrugated or mesh steel can be used as anodes

provide optimum surface area and solution circulation. Periodic cleaning of the anode/canecessary to remove plated-on smut, oxides and other charged particles. Using the tank

cathode is not recommended, as it leads to uneven current distribution and provides a s

current. Many electrocleaning problems, such as under- and over-cleaning, have been tr

such a practice.

Solid polypropylene or plastic-lined steel tanks are recommended for alkaline electroclea

should be fitted with steel, stainless steel or Teflon heaters. Recirculating pumps are rec

provide solution recirculation, overall homogeneity, and to prevent stratification. It shou

solution inlets and outlets must be located at two opposite diagonal top and bottom corn

for efficient solution movement.

TABLE III: Most Common Electrocleaning Problems

Problem Probable Causes

Etching, tarnishing


15/31

Too high C.D.

Cleane non-inhibied fo nonfeo

Wong polai

Tempeae oo high fo nonfeo

Eceie oil in olion

Roghne Cleane oo eak, caing bn o

C.D.

In anodic cleaning: plling alloing

face

In cahodic cleaning: depoiing ch

and m on face

Incomplee ining of elecocleane

Hae nde plaeCleane empeae oo high, ca

film.

Cleane oo eak

Incomplee ining afe cleaning

Inefficien oak o pecleaning pioelecocleaning

Heaalen chome conaminaion

Poo adheion, blie, piing of plaeCleane oo eak

C.D. oo lo o oo high


16/31

Cleaning ime oo lo o oo high

Reee of inended polai

Heaalen chome conaminaion

Infficien ining afe cleaning

Eceie oil, geae in cleane

4. ACID ACTIATION

Acid aciaion i ed o aciae he face of a meal afe alkaline pa, oak, o el

ch, he acid nealie eidal alkalini a ell a objecionable oide, and epoe

eadil plaeable face.

Thi poce i ed o emoe chemicall fomed oil fom he meal face. Tpicallmeal oide and hei al. The fom a a el of epoe o high empeae, o

amophee. Eample ae hea-eaing oide and cale, foging and caing cale,

oidaion.

Alhogh ome of hee oide ae plaeable, he lead o poo plae adheion and coo

Oide emoal i geneall caied o b acid eamen.

The acid ae eleced accoding o he meal being poceed, o ha limied o no aa

meal occ.

Thee ae hee majo pe of acid aciao:

Oganic and Mild Mineal Acid- Eample ae glconic, phophoic, and ciic acid.picall ed o aciae highl polihed o eniie meal ch a alminm, ba an

diecaing, and ome polihed eel.

Sfacan and eing agen ma be ed o edce he face enion and impoe


17/31

Mineal Acid - Hdchic ad fic acid ae eae f g iea acid. Th

geea ed decae ad aciae ee ad e aie ee.

Niic acid b ief i cbiai ih fic ad hdfic i ed de a

ai ad i a.

Fbic ad hdchic ae ed eaded ee ad eaded ba. Cbiai f

ad hdchic ae eie ed i decaig ad bigh diig ce ad ba, a

geeae hea ige ide fe ad be haded ih eee cae. Secia

ad ihibi a be ed ih hee acid diee i geae eide, ie

face aciai, ad f iiiig aac f he bai ea.

Acid Sal - Acid a ae ica f he fae e, baed aia eaied

eaiig hdge i i he a ide fficie acidi aciae ea face.

Adaage f acid a icde afe hadig ad he feibii cd he ih

faca ad ihibi dce a ide age f ecia acia.

Cd acid a a, f eae, icde fide ad ihibi ha ae e effe

ad ea f fe ea, e ihibi aac f bai ea. The ae gee

ad e cie a eie.

The e f acid acia f caef cideai. The eeced acid

aac he ea beig ceaed, a hi a gie ie fai, iig ad g

bee caig.

The e f acid ed a be caibe ih he aig ce. Hdchic acid

be ed i acid ce aig. Chide caiai ca ei affecha aig bah. Lieie, fic acid i eceded f ead eaded a, a

ibe ead fae he face f a.

Ue f g iea, ihibied acid hd be eiced ig- ad high-cab

eaci ih ch acid ead hdge ebiee.

Acid acia i eae cce a be ed b ie di iei, eecic


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he ea beig eaed. Geea eecic acid aciai i ed fe ad

a. The a ae a ceced cahdica (egaie chaged) i he a. Le

ade ae ed. Ceai ea ch a aie ee ae adica (iie) chag

aciaed ide ei adhei f he aed caig.

Nice ad ice aed a ae acid aciaed eecica ee he aie fi

fhe aig. I hi cae, he ice i ceced cahdica. The aie fi, ice

edced a he cahde.

Seciaied bicai ad ecedai f ie ae gd ce f ifa

ad efficie e f acid acia.

SURFACE PREPARATION OF ALUMINUM AND ITS ALLOS

Sface eaai f ai f aig i diffee f ha f fe ad he

diffeece i caed b he high degee f ai eacii. O ee ai, a

aid ad ce he face f ai. Thi ae ee diec bdig ih he

Ahe be i he diffeece i icce beee diffee ai a a

bgh ab b hea eae f he ae a. The e i a age f eec

eie eiig diffee eeae ad aciai echie. A ih he e

face i ch a i, geae, bffig cd, figei, ec. a a be ee

eed. A geea cce a fed eea ai i a f:

1. DEGREASING

2. OIDE REMOVAL

3. SURFACE CONDITIONING TO PREVENT REOIDATION

4. PLATE

1. DEGREASING

The e f degeaig i ee echaica deied i he face, e.g.

bffig cd, figei, ec.

Geea, a aac f he face a hi i d be ee, eig i a bch


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cdii. The degeaig e, heefe, hd be deiged ee hee i ih

bai ea. Mid aai, deege, ad e aied ih ih aic ae

e.

Aaie -ech ceae ae ide ed i hi e. Thee ceae a a

a a f hei cii. Siicae ae ecee degeaig age, b a high cce

eeae i f ibe ai iicae fi he face. T be eed e

fi eie he e f fide addiie i bee acid dee.

Siicae-fee -ech ceae e gd faca ad defccaig age deg

ih eaig ihibiig fi.

Se ece deee hae ade i ibe cbie a high degee f deegec

iae echig eie. Thee fai ae iied ea f igh i,

caef ied, ice he ech ae a be affeced b i adig i he i.

2. OIDE REMOVAL

A eaied eaie, a ide ae i ee ee ai face. The ae' hhade deed aig eee, afacig echie ad hea eae.

ide ae i a ciica e i he eae cce. Oide ea ca be achieed b ai

aaie eae.

High aaie i caiig di hdide ffe a high ae f aac f ai

e effecie i ide ea.

Died ai eai i i a aiae a g a fficie fee aaii

he bah. A be f addiie ae ed c ech ae, ech ae gai ie,

he fai f hdaed ai ide cae ad heae ad a a.

Rea f ide b aaie echig, hee, eae behid a eide f aig di

eee ha ae aaie be. Thi eide, decibed a , a cai iic

agei, ec. deedig he a cii. Theefe a deig e f

echig.

Acid echa ae a aaiabe. The ae ed hee aggeie aaie echig i


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. A .

D ,

. T IV . T

. A ( , , )

.

E , ,

, , . H- , , " " . T

,

. R

), -

3. FACE CONDIIONING

A ,

. A

. T , , .., , , , , .

T , . A

,

. N

. T

. T

. T .

T , , . T

.

A . D

. T

, .


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Addiional ncleaion ie deelop, eling in a moe nifom, een and adheen inc

lae peen eoidaion of he face, making anfe ime pio o plaing le cii

Anohe feae of allo incae i hei capabili o poec edge and hap cone of

in bael o blk fom being on, a common poblem leading o blie in bael plain

TABLE IV: Tpical Desmutting and Acid-Deoidiing Solution

For 1XXX and 2XXX Allos

Niic acid 30-70% /

Wae Balance

For 2XXX and 4XXX Containing Silicon and Most Castings

Niic acid 30-50% /

Floide 60-100 g/L

Wae Balance

For 5XXX Containing Magnesium (Ma also be used as all-purpose desmutter)

Niic acid 30-50% /

Slfic acid 20-30%

Floide 60-100 g/L

Wae Balance

For Copper Magnesium Allos (Fluoride ma be added for silicon-containing allo


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Sulfuric 5-10% v/v

Hdrogen Peroide 3-5%

Water Balance

Proprietar, nonfuming, stable-acid desmutters are also available for most applications.

TABLE V: Tpical Preparation Ccles

1. For Simple Allos and Castings:

Non-etch soak

Etch

Desmut

Zincate

Plate

2. For Heat Treated Allos:

Non-etch soak

Deoidie

Etch clean

Desmut

Zincate

Plate

3. For Magnesium and Heat Treated Allos:

Non-etch soak

Etch

Desmut

Zincate

Strip (50% nitric acid)


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Zincate

Plate

Rining

The chemistries of the different steps could vary substantially from tank to tank in a giv

preparation process. Types and degrees of alkalinity or acidity, surfactants, etc. may not

among the different solutions. Such cross contamination can create a general drop in cle

and cause objectionable residues to form on the surface being prepared. Sil icate residue,

contact with acids will precipitate insoluble silica acid on the metal surface, leading to ha

loss of adhesion when parts are plated. Rinsing is therefore considered an important and

the surface-preparation process.

Adequate rinsing should provide a flow rate adequate to remove residues from the previ

the given rinse time, taking into account the extent that a maximum level of that residu

Flow controllers, conductivity meters and counter-current-flow rinse techniques are tool

optimize quantity and quality of water used.

Rinse-water temperature is a factor often ignored in preplate cycles. Temperatures beloinadequate in rinsing off alkalis and surfactant residues. This is a problem often encount

weather, with incoming rinse water at 40-50F. Optimum temperature for efficient solub

cleaners and salts is 70-90F. Higher temperatures are effective but may induce flash ru

Air agitation and spray rinsing greatly improve rinsing efficiency and are often used whe

Reclaimed water for reuse in rinsing is generally acceptable in preplate cycles as long as

are compatible with the different chemistries used in the process. A fraction of fresh wat

used to prevent an increase in residual content.

Poce ConolControl of cleaners is usually done by titration of the acid or alkali contents. Maintenanc

replenish the basic constituents as well as surfactants and other components included in

Suppliers of proprietary cleaners provide complete control procedures and kits that allow

means to control and maintain the solutions at optimum operating conditions.

Although the essential components can be maintained, contaminants build up and event

O


24/31

. O ,

,

G . I .

- . H

T .

S , ,

H , -

. C .

,

. T ,

.

Cleanline Cieia

T . M, ,

. T UV ,

UV- , , , .

T W B T. T

. T

. T -

, -- . T

, -

- . S

ASTM B320-60, ,

. T

C . H

. ASTM B-3

W B T. A 30

, .

Adheion Teing

Since surface preparation has a direct impact on adhesion of the plate adhesion testing i


25/31

Since surface preparation has a direct impact on adhesion of the plate, adhesion testing i

performed to measure the adequacy of the preplate process. There are several adhesion

as a form of production control. The choice of a particular test is limited by the type of p

intended use.

For example, if a part is expected to be exposed to high temperature, a heat-and-quench

relevant. Bending would be an adequate test for post-plate forming operations. ASTM B-

the following tests in detail. One or more may be specified for a particular application. In

coating is expected to remain intact, with no signs of peeling or flaking off the substrate.

a. Bend Test

Bending of parts at a 90 angle around a mandrel, or back and forth through 180 until

basis metal occurs. Cracks in the metal without lifting of the deposit do not constitute a

b. Chisel-Knife Test

An attempt is made to undercut and lift the coating with a sharp chisel or knife. Not reco

soft or thin deposits.

c. Burnish Test

Rubbing and applying pressure on the plate with a smooth-ended tool, producing a burni

no peeling or blistering. Not satisfactory for thick deposits.

d. File Test

The cross section of the part is filed with a coarse file at a 45 angle so that the substrat

leaving the edge of the plate protruding. The plate should not lift or peel when pulled.

e. Grind-Sa Test

Grind or saw the plated article in the direction that favors separation of the plate.

f. Heat-Quench Test

Articles are heated in an inert or reducing atmosphere, then quenched in water. The tem

different basis and plated metals are specified in ASTM B57. Appearance of blisters may

deposit cannot be peeled off the substrate in areas around the blisters, it is not an adhes

g. Impact Test

A hammer or an impact device is used to strike and deform the plated part


26/31

A hammer or an impact device is used to strike and deform the plated part.

h. Peel Test

A strip of steel or brass is soldered or secured by a heat cured adhesive to the plate. The

90 to the surface.

i. Push Test

A blind hold is drilled through the substrate on one side of the part, short of reaching th

other side. A punch is pushed through the hole against the supported part until a buttonNo exfoliation or peeling in the punched area should occur.

j. Scribe-Grid Test

This is a commonly used test in which the surface is scribed with a sharp blade in a grid

special adhesive tape is applied to the scribed area, then pulled off rapidly. No peeling sh

TABLE VI: Tpical Cleaning Ccles

Substrate Alkalinitgm/l of

NaOH

Tpical Cleaner Condition

COLD ROLLED STEEL

Soak clean high 80-100

Electroclean 50-100 20-100 ASF Anodic or Cathodic followed by An

Rinse

Acid Activate n/a no current or 15-25 ASF Cathodic

Rinse

Electroclean 50-100 20-100 ASF Anodic


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Rinse

Mild acid dip plate n/a 3-5% HCI

STAINLESS STEEL

Compound remover 5-15 used if parts are polished soak or Ultrasonic

Soak clean 20-100 8 oz/gal, 4 min, 160F


Rinse

Acid activate or

Plate

50%Hcl 15-25 ASF Anodic

INC DIE CAST

Compound remover 5-15 Soak or Ultrasonic

Soak clean

moderate

low, 5-15


Rinse

Acid dip plate n/a

COPPER



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Soak clean high 20 100

Electroclean 20-100 20-50 Anodic

Rinse

Acid actiate n/a

BRASS

Soak clean

moderate

5-15

Electroclean 10-20 10-15 ASF Anodic or Anodic

Rinse

Acid dip n/a

TUNGSTEN


Acid dip n/a

Rinse

Anodic etch plate 20-100 100-300 ASF Anodic

anodic

TPICAL ALKALINIT RANGE

High 20-100


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High 20 100

Moderate 10-20

Low 5-15 (May not contain free Hydroxides)

Temperature and time vary depending on supplier recommendations and process used.

1. LIQID CLEANERS

Traditional cleaning products were dry powdered materials. Though liquid cleaners were

early as the 1970s, they were not accepted, for a variety of reasons. The most commonl

were that liquid cleaners were not concentrated, as were powders, had narrower operati

that the user was "paying to ship water." Advances in surfactant technology and the wid

potassium salts have enabled chemical manufacturers to overcome these perceived probl

another way, liquid cleaners are not powdered cleaners pre-dissolved in water. Liquid cle

chemically different than powders in the use of potassium salts, safe solvents, surfactant

carbonates and other fillers. A final factor in the acceptance of liquid cleaners is the inhe

they imply to the user, some of which are:

Improved safety, no risk of splashback.

Automatic control and replenishment-hands-off operation, consistent bath chemis

fewer defects. They are more suitable for SPC.

Less down time for make up - less sludge generated, less demand on the waste-tr

Effective and economical cleaning.

Cleaner filtration is gaining in popularity, with the aim of prolonging the bath life betwee

Several filtration techniques have been proposed, ranging from simple bag filtration to cof soil skimmers, coalescers and ultrafiltration. Since the cost of such systems varies app

feasibility study must be undertaken before adopting a particular system. In general, ho

been reported that any type of filtration does increase the bath life by at least 20%, and

or more.

Recent developments in preplate products promote the use of environmentally acceptabl

Substituting effective biodegradable surfactants for hard chelates and use of safer solven


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g g

emulsifiers in place of chlorinated solvents are examples.

Emphasis on simplified water treatment is another aspect of newer cleaning technologies

developments allow oil separation from process cleaner. While water treatment is made

cleaner solution life is extended and its performance maintained at optimum longer. Sep

reclaimed and reused.

SAFET AND HANDLINGThe majority of people who operate cleaner and acid tanks pay only minor attention to t

important subject. Many serious accidents, such as chemical burns, respiratory problems

can be avoided. This information is given to the user by the suppliers, including specific i

handling process chemicals. The following safety tips should help inexperienced personn

injuries.

When making up acid-dip tanks, never add water to the concentrated acid, always

the water, with constant stirring to avoid spattering. Sulfuric acid is a good exam

react violently if not handled properly.Never add dry cleaner (alkaline) directly to a hot tank above 120F. Violent erupt

large quantities of dry cleaner are added directly to the tank. Instead, add dry pro

continuous agitation.

Avoid breathing fumes from acids and cleaners. Otherwise respiratory problems c

Avoid skin and eye contract when handling chemicals. Wear protective clothes, gl

goggles and other protective equipment. A fume hood should be used when an an

involves the liberation of hazardous fumes.

In case of injury, contact a physician immediately. Give first aid and see MSDS sh

If a spill occurs, clean up the spill as soon as possible and prevent the spill from a

other chemicals, to prevent reaction. Maintain your own safety first, secure the ar

Do not allow personnel to work over hot solution without adequate precautions. N

in an area where chemicals are in use.

Provide professional training to those involved in handling chemicals.

Check appropriate MSDS sheets prior to the handling or use of all chemicals.

Good laboratory safety practice requires that incompatible chemicals be stored, transpor

of in ways that will prevent their coming together in the event of an accident. Tanks sho


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y p g g

labeled and identified by type of chemical used, hazard classification and safety informati

The preceding material has been reproduced

from the MFSA Qualit Metal Finishing Guide,

Volume 1, No. 1-P

"Chemical Surface Preparation for Electroplated Metallic Coatings"

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