At the beginning of the 20th Century theonly elastic material available was NaturalRubber. Today, designers can choose frommore than twenty different synthetic elas-tomers. This great variety offers outstandingflexibility to solve the sealing problems arisingfrom the numerous and multifaceted require-ments in modern applications. A very specialelastomer is fluoro rubber. In many fields, theproperties of this specialty rubber are superiorto those of other elastic materials. ZrunekGummiwaren GmbH specializes in the formu-lation and mixture of elastomer compoundsand focusses in particular on fluoroelastomer-based compound development. This class ofmaterials made by Zrunek is referred to asZruElast FPM.

What does ZruElast standfor?

ZruElast is a registered trade mark ofZrunek Gummiwaren GmbH. The nameZruElast represents all tested, specifiedand proven elastic materials made byZrunek. For more than 50 years, our in-house laboratory has provided completecompound development and testing serv-ices. The laboratory is supervised by Dr.Ulrich Zrunek himself who is a doctoratechemist.

Unlike plastics technology, where the ready-to-process raw materials have to be purchaseddirectly from the chemicals groups, rubbermaterials first have to be compounded basedon a formulation. For this process, fillers, plas-ticizers and various other chemicals are addedto and mixed with the base polymer (rubber).Only the proper combination of these rawmaterials results in the desired propertieswhich are expected of the developed elas-

tomer. Rubber formulation and compounddevelopment not only requires extensiveexpertise and experience, but also appropriatelaboratory facilities and equipment. Figure 1shows the first steps of the rubber formulatingprocedure. This begins with mixing of the suit-able raw materials in the laboratory mill. Sub-sequently, test pieces are vulcanized and later

measured using our advanced test-ing and laboratory equipment.Only after the desired results

and values are achieved,will the formulation be

released for pro-duction and mix-

ing-plant out-put.

The Difference betweenFPM, FKM and Viton®

The terms FPM, FKM and Viton® very oftencause confusion and lead to incorrect interpre-

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Fig.1: In-house compound development

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tations. All of these designations actually standfor one single base material:fluoro rubber.

FPM is the international abbreviationaccording to DIN/ISO, whereas FKM is theshort form for the fluoroelastomer categoryaccording to the American standard ASTM.Viton® is the registered trade mark of DuPontDow- Elastomers. Zrunek uses the designationFPM for all of its fluoro-elastomer materials.

Designing with Elastomers

Elastomers are not usually materials design-ers are overly familiar with, nor do they dealwith them day-to-day. In general, metals andtheir individual specifications are the materialswhich designers have in mind when designingand these influence their thinking at a basiclevel. Therefore, parts often are designed with-out considering that the material-specific prop-erties of metals can meet other requirementsthan those of elastomers. This difference maycompromise the correct selection of a suitableelastomer.

In order to select a proper elastomer it isnecessary to define the specific demands ofan application. This includes a full descriptionof the conditions in use and full details con-cerning exposure to any chemical media, ther-mal resistance requirements, compressionload, mechanical stresses as well as informa-tion about time-related factors.

Particular attention should be turned to themedia with which the elastomer is in contact.These media should not affect the sealingmaterial, nor should the media be affected bythe seal. Furthermore, the lifetime and durabili-ty of a seal can be very critical factors. Thesevery often are directly linked to temperature

and exposure to chemical media. In addition,parameters such as specific mechanicalrequirements for static and dynamic applica-tions, electrical properties, hardness, coloursor flammability should be taken into considera-tion.

As a result of the complexity and great num-ber of factors there is a simple rule for design-ers derived from practical experience:

Advantages of ZruElast FPMZruElast FPM are materials based on flu-

oroelastomers. These materials offer one ofthe highest resistances to heat and chemicalmedia of all elastomers ever developed. Theywithstand hundreds of fluids, from ordinary tomost aggressive, over a wide temperaturerange. Additionally, they retain reliable andleakage free sealing force in situations whereordinary elastomers would long have failed

Fluoroelastomers do not come cheap. Thisis why they primarily were used only for smallparts in environments where in contact with hotand corrosive fluids. Today, however, as aresult of higher energy costs, stringent envi-ronmental regulations, extended warrantiesand increasing maintenance costs, manyusers have reconsidered and now think ofZruElast FPM as a cost-effective material,especially when taking into regard the com-plete lifetime of a product.

If possible, try to cut down the designrequirements to those 'absolute neces-sary' and try to avoid demands such as

'would like to have' or other arbitrarydemands.

The Exceptional Strengthsof ZruElast FPM

Temperature Resistance

Fluoropolymers in general feature excellentheat resistance. ZruElast FPM retains itselastic properties even at a continuous operat-ing temperature of 200° C. When talking abouttemperature resistance, it has to be consideredfor how long materials are exposed to heat orelevated temperatures. Figure 2 shows therelation between operating temperature andhours of use. Besides the ability to withstandshort blasts of more than 300° C, laboratorytests have confirmed that products made ofZruElast FPM still remained soft and elasticeven after ageing in a heat cabinet over a peri-od of three years at a temperature of 190° C. Ifyou compare these values with the perform-ance of other elastomers they seem even moresignificant. Nitrile rubber (NBR), for example,usefully serves only up to a continuous maxi-mum temperature of 120° C.

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Fig. 2: Heat resistance of ZruElast FPM in air

Abb. 3: Swell resistance of ZruElast FPMExamples (Compound “7575” und “7009”)

Similar in temperature performance are thematerials chloroprene (CR) and chlorosulfonat-ed polyethylene. Aged at a temperature of 200°C, products made of these materials wouldbecome brittle only after a few hours.

Swell Resistance

The excellent swell behaviour of fluoroelas-tomers has already been tested in a number ofimportant media, for example mineral oils,fuels, acids, bases, solvents, and numerouschemicals. Figure 3 on the previous pagegives you a short overview of the outstandingvolume swell resistance of ZruElast FPM. .Zrunek has compiled a chemical resistanceguide which will give you extensive informationabout the swell behaviour of ZruElast FPMFPM in a number of chemical media. You alsowill find additional technical data demonstrat-

ing the relation between temperature and vol-ume swell in several examples.

In sealing technology, in particular in engineconstruction and hydraulics, oil resistancecombined with exposure to heat plays a funda-mental role. Figure 4 shows the resistance toheat and volume swell of ZruElast FPM incomparison with other common elastomers. Asyou can easily see, only Kalrez®, an extremelyexpensive perfluoroelastomer, delivers betterperformance. All other commercially processedelastomers neither achieve the thermal stabili-ty of ZruElast FPM nor feature the same lowvolume swell characteristics.

This outstanding resistance to swell com-bined with exposure to heat makes ZruElastFPM the most universal sealing material of allcommercial elastomers.

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Fig.4: Heat and oil resistance of ZruElast FPM in comparison with other elastomers

Long-Term Retention ofSealing Force

Resistance to compression set is anothervery important physical property in sealingtechnology. The lower the compression setvalues, the better the sealing force and abilityto recover from applied deformation. In combi-nation with exposure to high temperatures,ZruElast FPM further shows its superiorcompression set properties. Without any prob-lems values of 8% at 200° C can be achieved.

ZruElast FPM is also unbeatable when itcomes to sealing force over a longer period.As illustrated in figure 5, all other commonelastomers fail long before. After 100 hours ofuse in static application in air at 150° C Zru-Elast FPM retains 91% of its original sealingforce, while silicone, acrylate and nitrile rubberwith 69%, 56% and 38% show values wellbelow. After 10,000 hours of service time atlast only FPM provides sufficient sealing force(70%) These characteristics are of special

importance when designing long-life, high-quality machines, where absolute product reli-ability is demanded, when high guarantees arerequired or when the risks of causing environ-mental damage due to seal failure or leakagebecome incalculable

Low Temperature Resistance

Experience has shown that seals made ofFPM in dynamic applications usefully serve attemperatures down to approx. -20° C. In staticuse they even can work at temperatures downto -40° C. Furthermore, experience has shownthat the more thin-walled parts are, the lowerthe operating temperature at which they canwork. The same effect occurs when the seal iscontinuously in contact with a medium thatcauses slight swell. This improves the low tem-perature flexibility and allows use at even low-er temperatures.

Flame Retardance

ZruElast FPM is based upon fluorocarbonelastomers. The chemical bond of fluorine tocarbon is extremely strong. Thus, under condi-

tions of fire, its resistance tobreaking and damageexceeds that of all otherhydrocarbon elastomers.

Use in Vacuum

ZruElast FPM containsno plasticizers and thusexhibits very low outgassingin use under extreme vacu-um conditions. Loss ofweight of only 2-3 % in vacu-um applications is typical forthis material. Therefore Zru-Elast FPM is the ideally

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Fig. 5: Long-term sealing force of ZruElastFPM in comparison with other elastomers

suited material for seals requiring absolutepureness, lowest outgassing rates and minimalvolume changes in extreme vacuums.

Weathering and Ozone Resis-tance

The combination of atmospheric oxygenwith sunlight and ozone (weathering) is a veryaggressive and corrosive effect. But in thisrespect ZruElast FPM also offers highestresistance. In fact, even after 20 years of dailyexposure to direct sunlight no cracking or split-ting was observed. Even direct exposure to

ozone has no effect on ZruElast FPM. Forexample, after 300 hours of continuous ageingat a temperature of 60° C in an environmentcontaining 150 ppm ozone no cracks could beobserved. In comparison, parts produced fromnatural rubber would end up with cracked andsplit surfaces and become useless after just 10minutes in the same conditions.

The extremely good weathering and ozoneresistance of ZruElast FPM also is shownby the fact that UV-radiation does not have anyeffect on colored parts made of FPM.

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Table 1: Comparison of ZruElast FPM compounds

Gas Permeability

Products made of ZruElast FPM havevery low gas permeability.

ZruElast FPM Compounds

Zrunek mixes all its compounds in-house.As demonstrated before, all formulations arefirst developed and then get tested in our ownlaboratory. Over the years, a standard programof different compound types has been devel-oped, which in the meantime has proved itselfmany times over. Characteristics and proper-ties of these compounds are shown in table 1.Zrunek's standard program differentiates 3 cat-egories of compounds: The first categoryincludes the standard compound types usedfor the manufacturing of black all-purposeparts, eg. cords, hoses, tubes or molded parts.These materials cover a durometer range from60-90 Shore A. Compounds of the second cat-egory are used for colored parts. The third cat-egory shows compounds which have to meetspecific requirements in demanding applica-tions. The common durometer range for FPMparts is 60 to 90 Shore A.

If you need softer sealswith a lower hardness butwant to retain favourable com-pression set values, technicalrealization could become diffi-cult. Especially to meet theserequirements Zrunek devel-oped compound #7245.

If the volume swell of ourstandard compounds causedby some specific media is toohigh for your applications, wealso can provide special for-

mulations to better meet your needs. A typicalexample is the exposure to methanol. Thevarying swell behaviour of different types ofZruElast FPM compounds is shown in fig-ure 6. If, for example, your applicationrequires higher resistance to swell in methanolor toluene, compound #7003 or #7010 woulddeliver better performance and be the com-pound of choice.

Table 1 shows a small selection of theextensive range of formulations provided byZrunek. All of the compounds shown here arefield-proven and currently used in industry.However, if your application demands addition-al requirements, Zrunek can help you, eitherby using one of the variety of formulationsalready available or by developing a new for-mulation in-house in order to meet your needs.If you have specific requirements, please firsthave a look at our guidelines listed on page 3 -''Designing with fluoroelastomers''.

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Fig. 6: Swell resistance - Comparison of vari-ous ZruElast FPM compounds

ZruElast FPM is More Expen-sive, but it's Worth it !

Due to the base elastomers used and theirspecific manufacturing process, fluoroelas-tomers rank among the costlier elastomers.However, this does not mean that the use ofZruElast FPM comes at a high price.Instead, considering the total costs over serv-ice time, ZruElast FPM very often is themore cost-effective solution compared withless expensive elastomers due to its extendedlifetime - and this effect comes with additionalsafety.

The chart in figure 7 shows how servicecosts can accumulate over a time period ofthree years using low cost sealing materials incomparison to ZruElast FPM.

As you easily can see, the price of an FPMseal is rather higher than that of a conventionalseal (EUR 16,00 instead of EUR 2,00). How-ever, even after three years of service the FPMseal remains sufficiently leakproof and its life-time even exceeds that length of time. Withinthe same period conventional seals wouldhave to be replaced at least twice. This notonly causes additional costs for the sealsthemselves, but it also has of the disadvantageof considerable replacement and downtimecosts. Therefore, the use of ZruElast FPMhelps you save costs and reduces lifetimecosts. After three years of use, finally, you cansee a clear result: The conventional sealshave caused costs of EUR 96, whereas thecosts of ZruElast FPM seals add up to EUR26,00.

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Fig. 7: Total cost over a service time period of 3 years - Seals made of low cost materials in comparisonwith sealings made of ZruElast FPM

The example and calculation in table 2shows why ZruElast FPM might be the morecost-effective alternative (Figure 7).

Beware of Low-Cost Fluoro-elastomer Blends!

ZruElast FPM guarantees that you willget 100% virgin fluoroelastomers. Unfortunate-ly, there are numerous low cost fluoroelas-tomer blends on the market, which at firstglance seem to be a good deal because oftheir lower price. These prices can only beoffered because the materials are blends ofFPM and hydrocarbon elastomers, such asEPDM, nitrile or acrylate rubbers. This 'fillingand stretching' can of course result in largerisks for the end-user. Ordinary rubbers areoften blended with other elastomers in order tospecifically upgrade certain properties andgain better performance. FPM, however, can-

not be blended without significantly degradingjust these properties, such as excellent resist-ance to heat, chemicals or compression set.As a result you would only end up with unnec-cessarily expensive blends of hydrocarbonrubbers.

It may be the case that some rubbers showgood resistance to certain media, for example,acrylate rubber exhibits low swell in mineraloils. But compared to vulcanizates based on100% FPM, blends of FPM can in no wayachieve the same excellent performance, inparticular when regarding resistance to swellat elevated temperatures, resistance to othercommon chemical media or long-term func-tionality and sealing performance.

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Table 2: Service costs of an ordinary seal made oflow-cost material in comparison with costs for thesame seal made of ZruElast FPM for a time peri-od of 3 years

This very clearly is illustrated in both chartsbelow (figures 8 and 9). In each case the dif-ferent blends perform much more poorly thanZruElast FPM. With regard to resistance tocompression set the superior performance ofZruElast FPM becomes even more signifi-cant.

It may be true that blends of FPM arecheaper considering the price/kg. But com-pared to ZruElast FPM which is based on

100% fluoroelastomers they are definitely themore costly alternative with respect to total life-time costs.

What is Viton®?

Since 1957 fluoroelastomers have occupiedan important position in industry. Many peoplewould think of Viton® the registered trade markof DuPont Dow Elastomers, which was the firstcompany to develop a fluoroelastomer andintroduce it to the market. Just like the brandname Perbunan® has become a well-estab-lished term for nitrile rubber, Viton® has turnedout to be a well-known brand name for fluoro-elastomers. However, there are also othercompanies which have been successfullymanufacturing and supplying fluoroelastomersfor several decades, such as Dyneon withDyneon®, Solvay with Tecnoflon® and DaikinIndustries with Dai-El®. All these companieshave in common that they invest high amountsin research and development and offer aremarkable selection of high-performance fluo-roelastomers.

The end-user has to be aware of the factthat the brand name Viton® (like other brandnames, too) does not stand for a certain mate-rial specification, but rather is a name for alltypes of fluoro rubbers which are made byDuPont Dow Elastomers. The various types offluoroelastomers differ in fluorine content,swell behaviour, resistance to compression setor processing. It is the task of the manufactur-er to specify the correct type of rubber to meetthe operating requirements of your applicationand to develop and formulate an appropriatetype of fluoroelastomer compound.

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Fig. 9: Compression set of ZruElast FPM incomparison with blends of FPM

Fig. 8: Swell resistance of ZruElast FPM incomparison with blends of FPM

Are other FluoroelastomersInferior?

No, because all fluoroelastomers producedby the above mentioned manufacturers arespecified in accordance with the globallyaccepted ASTM D 2000 standard and HK clas-sification. In this standard, elastomers areclassified according to their heat and oil resist-ance. 'H' designates that after thermal stressof 70 hours at 250° C changes of the mechani-cal parameters of the elastomer range withinthe following values:

maximum tensile strength change: ±± 30%elongation at break decreases less than 50%maximum hardness change : ±± 15

'K' stands for best swell resistance in test oil#3 according to ASTM D 471 after 70 hours(volume swell less than 10%), achieved byFPM. Table 3 demonstrates the special impor-tance of classification according to 'HK'.

This outstanding performance can only beexceeded by that of perfluoroelastomers.

Looking at the properties and parametersdemonstrated above you can easily recognizethat fluoroelastomers are materials which arebased on defined specifications and that ofcourse these are followed by all manufactur-ers.

DuPont Dow Elastomers was actually thefirst company to introduce fluoroelastomersunder the trade name Viton® However, fluoro-elastomers manufactured by other companies,such as Dyneon, Solvay or Daikin Industries,perform just as well. In fact, the opposite maybe true - competition has pushed these com-panies forward to develop and introduce somerather interesting and perhaps even higherquality products. Additionally, when regardingstandard products, considerable price differ-ences can be observed for the same productperformance. When already buying a high-priced material why spend extra money for abrand name?

Why is FPM Important forZrunek?

Zrunek has fundamental experience andexpertise in elastomer materials which goesback more than 50 years. The company wasfounded in 1947 by Dipl.Ing. Eduard Zrunek,the former managing director of the 'Matador'Semperit Company. Today the company is runby the third generation, Dr. Ulrich Zrunek. Nat-urally, over the years, we have been continu-ously engaged in new developments in thefield of elastomer technology. And this is par-ticularly true with a view towards ever higherperforming materials, such as fluoroelas-tomers. Especially the manufacture of fluoro-elastomers suits the production capabilities ofZrunek. Our production line is ideally suited forsmall and medium runs, as well as customized

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Table 3: Classification according to ASTM D2000 standard

solutions to your specific needs. Our capabili-ties extend from custom compound develop-ment in our own laboratory and in-house mix-ing-plant facilities, which guarantee flexibilityand consistent product quality, to advancedmachinery including presses, injection mould-ing machines and extruders to ensure a broadspectrum of manufacturing options.

A major part of our budget for research anddevelopment is spent on tasks concerning theextrusion and processing of FPM. As a resultof these activities, Zrunek has become theleading expert in the field of fluoroelastomerextrusion, as well as the largest processingmanufacturer of fluoro rubber in Austria.

Certified Accordingto ISO 9001

Nowadays it goes without say-ing that a company which manufactures suchbasic and high-quality components throughoutindustry has established a quality control sys-tem that is in compliance with the ISO 9001standard.

In addition to the technical competencebased on the company's long standing expert-ise and experience, we can also provide ourcustomers with high levels of security and reli-ability through our advanced quality controlsystem.

Satisfaction makes customers

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All general information, specifications and proposals contained in this brochure are intended to give our customers and other interested parties some basic information about the product ZruElast FPM andits applications. All technical data given here is based on characteristic output values and these do not replace agreements of specific quality characteristics made on orders of ZruElast products. Zrunek the-refore does not guarantee that special orders correspond with the general information and specifications listed in this brochure. This brochure also makes no statement about possible trademarkrights of any third party whatsoever. Only Zrunek's conditions of sale and delivery shall be valid in respect of all products supplied by us.

Zrunek Gummiwaren GmbHObkirchergasse 3A-1190 ViennaAustriaPhone: xx43-1-36 91 639Fax: xx43-1-36 91 639-70e-mail: office@zrunek.atinternet: www.zrunek.at ©

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