Technical Elastomers Chnical Elast Te

VERLAG MODERNE INDUSTRIE omers Technical Elastomers chnical Elast Te

The basis of high-tech sealing and vibration control technology solutions

Freudenberg Sealing Technologies verlag moderne industrie

Technical Elastomers

The basis of high-tech sealing and vibration control technology solutions

Meike Rinnbauer This book was produced with the technical collaboration of Freudenberg Sealing Technologies GmbH & Co. KG. Content

Elastomer development 4 Translation: Flanagan Language Services, Aingeal Flanagan, Köln From natural rubber to high-tech material ...... 4 Basic principles ...... 5

Elastomers and their properties 9 The viscoelastic behavior of elastomers...... 9 The correlation between frequency and temperature ...... 12 The systematization of elastomers ...... 13

Factors that influence material behavior 16 Compound ingredients ...... 16 The influence of the cross-link density ...... 19 Physical and chemical action ...... 22

Processing techniques 30 Mixing technology ...... 30 Molding processes...... 37 Optimizing elastomer processing procedures ...... 43

Testing elastomers 46 Testing during the production process...... 46 Estimating the working life ...... 48 Component simulation using FEM ...... 49 © 2007 All rights reserved with sv corporate media GmbH, D-80992 Munich, Germany High-tech products made of technical elastomers 52 www.sv-corporate-media.de Outlook 63 First published in Germany in the series Glossary 66 OriginalDie Biblio title:thek der Technik © 2006 by sv corporateTechnische media Elastomerwerkstof GmbH fe Bibliography67 Illustrations: Freudenberg Sealing Technologies GmbH & Co. KG, Weinheim Appendix 68 Typesetting: abavo GmbH, D-86807 Buchloe Printing and binding: Sellier Druck GmbH, D-85354 Freising The company behind this book 71 4 Basic principles 5

Fig. 1: The operating princi- Elastomer ple of a Simmerring® (cross-section) development featuring an additional dust lip to protect the seal From natural rubber to high-tech against dirt and dust material Humankind has been familiar with elastomer materials in the form of natural rubbers for Age-old centuries. Natives in Central and South Amer- Lubricant material ica used this material for seals and balls. The Dust lip Sealing edge term “caoutchouc” comes from the Mayan lan- Grease filling guage ( = tree and = tear) and is a col- cao ochu lective term for all non-cross-linked elastic Shaft surface polymers. The accidental discovery of vulcan- Discovery of ization (curing) by Charles Goodyear in 1839 ogy. The increasing multi-functionality of vulcanization paved the way for the manufacture of highly modern elastomeric components means that flexible cross-linked materials (elastomers), expertise and a wealth of experience are which in turn made it possible to use these ma- needed for targeted elastomeric development. terials for countless technical applications. To- day, elastomers are indispensable for seals and vibration-control applications. Were it not for Basic principles elastomers, there would be no such thing as Polymers are very large molecules that are cars or planes, and hydraulics and pneumatics formed by the linkage of a large number of would be unimaginable. Many of today’s elas- very small structural units (monomers). The High-tech tomer components are high-tech products that monomers are linked by means of functional, products meet even the most exacting requirements re- reactive groups, thereby creating composites garding temperature, chemical resistance, and that exhibit completely different properties to wear. A radial shaft seal (Simmerring®) is a the starting materials. The molecular structure perfect example of a highly developed elas- of polymers can be linear, branched, or cross- tomeric component. It works like a micro- linked. Depending on the orientation of the scopic pump that transports lubricants or gases molecule chains, a differentiation is made be- under the sealing edge and back into the oil tween polymers in an amorphous and a par- chamber, thereby ensuring adequate lubrica- tially crystalline state. The degree of poly- tion between the shaft and the seal (Fig. 1). In merization – i.e. the number of monomers in Degree of addition to performing a simple sealing func- a polymer chain – has a significant influence polymerization Additional tion, seals can also assume other functions on the mechanical properties of the polymers. functions when combined with modern sensor technol- As the crystallinity or density of the polymer 6Elastomer development Basic principles 7 increases, so too do the melting range, tensile Polymer materials are categorized according to strength, stiffness (elastic modulus), hard- their structure, their mechanical deformation ness, resistance to solvents, and impermeabil- behavior and, correspondingly, their properties ity to gases and vapors. and areas of application (Fig. 3). Polymers of high molecular weight such as are made up of long and linearThermoplas- or loosely Thermoplastics elastomers demonstrate a pronounced visco- branchedtics polymers that are not cross-linked. Viscoelastic elastic behavior compared to most other ma- At room temperature they are in a state that is behavior terials when subjected to mechanical loads. De- somewhere between glassy and ductile. Ther- pending on the load exerted, the deformation moplastics can have amorphous or partially that occurs is of an elastic or a viscous nature. crystalline structures. In amorphous thermo- The key to understanding the mechanical prop- plastics, the polymer chains are arranged in a erties at various temperatures is a knowledge of random manner both in the molten and in the the processes that take place in the transition solid state. Partially crystalline thermoplastics zone between the defined states, which is, are amorphous in the molten state. However, among other things, characterized by the so- when solid, there are areas in which the poly- Fig. 3: called “glass transition temperature” or Tg. The mer chains are arranged parallel to one an- Glass transition Schematic structure glass transition is a characteristic variable for other. The degree of crystallinity has a signifi- of polymers and temperature every polymer. Below the glass transition tem- cant influence on the mechanical properties of elastic modulus- temperature curves perature, the proper motion of the molecules – which is also known as Brownian motion – freezes. The material is in a hard, glassy state. Thermoplastic Thermoplastic Elastomer Thermoset elastomer When the glass transition is exceeded, the molecules become mobile once again and the polymer changes over to a soft, rubbery-elastic state (Fig. 2). If the temperature continues to rise, viscous flow occurs followed by decomposition of the polymer.

Glassy state

Elastic behavior Viscous flow Elastic modulus Elastic modulus Elastic modulus Elastic modulus

Elastic modulus Glass transition “rubbery-elastic Fig. 2: temperature plateau” The relationship Tg Temperature Temperature Temperature Temperature between the elastic modulus of polymer Temperature = Operative range and temperature 8Elastomer development 9 the material. Temperature increases and heavy shearing plasticize thermoplastics, at which point they can be formed or molded. Elastomers and their are created by the loose cross- Elastomers Elastomers properties linking of amorphous, often highly branched The ASTM standard D 1566 (ASTM: Ameri- polymers (e.g. natural rubber). This loose fix- can Society for Testing and Materials) defines ation of polymer chains by chemical bonds elastomers as high-polymeric, organic net- results in the highly elastic behavior above works that are capable of absorbing large de- High-polymeric the glass transition temperature Tg that is so formations in a reversible manner. This prop- organic typical of this polymer material (the so-called erty, coupled with the fact that elastomers are networks “rubbery-elastic plateau”). capable of absorbing mechanical energy, Unlike thermoplastics, the molding of elas- means that elastomers can be used to manu- tomers is associated with a chemical reaction facture products that accommodate toler- (cross-linking). In the case of higher degrees ances, allow for movement between different of cross-linking, the Tg is pushed upwards un- components, make it possible to create static til almost all molecular movements are pre- and mobile seals, diminish and damp vibra- vented by the rigid fixation of the polymer tions, and assume spring functions. chains (as is the case, for example, with ebonite). This means that only minimal displacements are possible when subjected to ex- The viscoelastic behavior of ternal loads. Close (three-dimensional) cross- linking or “hardening” leads to , elastomers Thermosets thermosets Unlike energy-elastic solids such as metals or which, like elastomers, are irreversibly de- Entropy- alloys, elastomers are entropy-elastic. The stroyed once the decomposition temperature is elasticity force behind this elasticity is entropy, i.e. the exceeded. Examples of thermosets include degree of disorder which is greater in the en- epoxide resins or phenol formaldehydes. tangled, disordered state of the polymer constitute a chains than in an arranged, extended, orderly TPE hybridThermoplastic class. Betweenelastomer Tgs (TPE) and the melting state. In entropy-elasticity, the distance be- Fig. 4: point and/or the softening point, they behave tween the atoms does not alter; the individual Entropy-elasticity like elastomers. They are, however, thermo- model formable at higher temperatures (i.e. >100°C). In many TPEs, a thermoreversible structure with elastic properties is formed during the cooling phase as a result of physical cross- linking across (partially) crystalline areas. This Force means that – as is the case with thermoplastics – exceeding the softening point to even the smallest degree can cause irreversible loss of component geometry in the application. 10 Elastomers and their properties The viscoelastic behavior of elastomers 11 chain segments are merely pushed towards to creep, stress relaxation, or cold flow. Vis- one another. If stress is applied to the elas- cous flow can be suppressed to a great degree tomer in this state, the entangled chains are by fixing the chains to one another (cross- transformed into an arranged and thus less linking). In other words, loose cross-linking plausible state (entropy decrease). When the ultimately causes typical rubbery-elastic (elas- Entropy stress is released, the original, more energy- tomeric) behavior. The viscoelasticity of elas- decrease … favorable entangled state is reassumed (en- tomers results in a pronounced time- and tem- tropy increase). The change in entropy is the perature-dependency for a large number of … and increase driving force behind the resilience of elas- physical and in particular mechanical proper- tomers in the rubbery-elastic range above the ties. In the case of steel, for example, there is glass transition temperature Tg (Fig. 4). a linear relationship between stress and strain, Viscoelastic behavior in elastomers means whereas with elastomer, there is a non-linear that both the elastic behavior of solids (re- relationship between the two. This non-linear versible) and the viscous behavior of fluids relationship is demonstrated among other (irreversible) can be observed. Depending on things by the elastomer’s dependency on the the load applied, one or other of the properties deformation speed (Fig. 6). is more pronounced (Fig. 5). At low tempera- The consequence of this dependency is that tures and high deformation speeds, the solid elastomers react with great sensitivity to Fig. 6: Fig. 5: material behavior dominates, while viscous changes in test conditions. This is why prob- Stress-strain Spring-damper behavior can be observed at high temperatures lems are frequently encountered in practical diagram model used to and low deformation speeds. The latter leads operation when correlating simple physical Left-hand diagram: illustrate elasticity test results with the actual prevailing loads ex- a comparison of steel, thermoplastic, erted on an elastomer component in the instal- and elastomer State Cause Working model lation space (the complex of loads acting on Right-hand diagram: the component). This means that it is ab- the behavior of elas- Energy Based on reversible changes Spring solutely essential for exact specifications to be tomers at different elasticity in the vibration and rotation deformation speeds conditions of atoms.

High deformation speed Steel Based on the largely reversible Spring Damper Entropy Thermoplastic elasticity displacement of molecule Low deformation speed segments while retaining the Elastomer center of gravity of the molecule Pseudo-static (micro-Brownian motion). Stress Stress behavior

Viscous Based on the irreversible dis- Damper flow placement of entire molecules towards one another (macro-Brownian motion). Strain Strain 12 Elastomers and their properties The systematization of elastomers 13 prepared for an elastomer component in order

to ensure that the most important properties of 500 500

° a] a] the product can be reproduced in tests. T = –10 °C f = 1 Hz T = 0 C f = 10 Hz [MP 400 ° 400 T = 10 °C f = 100 Hz T = 20 C f = 1000 Hz The correlation between frequency 300 300 and temperature In practice, a leap in the mechanical proper- 200 200

ties of elastomer are noticeable both at low 100 100 Dynamic modulus [MP temperatures and at high frequencies. This Dynamic modulus leap is caused by the viscoelastic behavior of 0 0 –2 0246810 –50 –25 02550 elastomers. If a load generated by pressure or ° tensile force is exerted on the elastomer for Frequency [lgHz] Temperature [ C] varying periods of time, there is a correlation premature hardening of the material (increase between the frequency of the load and the Fig. 7: in the dynamic modulus). thermal behavior. Because of the viscous pro- The time-tempera- This influence of relaxation, which depends ture correspondence portion in elastomer, the stress that occurs on temperature and frequency, must therefore principle: depen- during deformation is partially reduced by dency of the dynamic be taken into account when designing compo- chain displacements (micro-Brownian mo- modulus on fre- nents, especially dynamic seals. quency (left) and on tion). The time required for this is known as temperature (right) . As the temperature decreases, the Relaxation relaxation chain movements in the polymer slowly stop The systematization of elastomers and the length of time needed to decrease ASTM D 1418 defines a systematization for Table 1: stress increases. The elastomer hardens and elastomers and a set of abbreviations. The ab - The systematization becomes glassy. If the load frequency in- of elastomer types creases, the chain mobility no longer suffices for absorption of the deformation. The mate- Last letter in Meaning Example rial appears to be “frozen”. This effect is the abbreviation known as This means that M Rubbers with saturated chains EPDM, ACM, EVM, Dynamic dynamic hardening. of carbon atoms, no double FKM, FFKM an increase in frequency has the exact same bonds hardening effect as a drop in temperature (Fig. 7). R Rubbers with double bonds NR, CR, SR, SBR, in the carbon chain IIR, NBR, HNBR Accordingly, the glass transition temperature (unsaturated) Tg depends not only on the method of deter- O Rubbers with oxygen CO, ECO mination, but also on the test frequency, and in the polymer chain increases by approximately 7 Kelvin per fre- Q Rubbers with silicon and VMQ, FVMQ Time-tempera- quency decade. This effect is known as the oxygen in the polymer chain ture correspon- time-temperature correspondence principle. T Rubbers with sulfur in Polysulfide elastomer the polymer chain dence principle The result of this principle is that an increase U Rubbers with carbon, oxygen, AU, EU in frequency at low temperatures leads to a and nitrogen in the polymer chain 14 Elastomers and their properties The systematization of elastomers 15 breviations are made up of a combination of Polysiloxanes differ from organic rubbers in between two and four letters (Table 1). The that the main chain is not made of carbon Fig. 8: first letters describe the base polymer, the last bonds, but alternating silicon and oxygen Usable temperature range for elas- letter indicates the chemical structure of the atoms. These elastomers are known as elastomers. For example, all elastomers with These compounds are also known Q-as tomers: the shaded types. Silicone rubber areas indicate the main chains containing only carbon atoms silicone rubbers. usable temperature and no double bonds (reactive areas) are re- Figure 8 provides an overview of the thermal ranges to which ferred to as . If the main chain con- application ranges for the various types of standard types can M-types be exposed for brief tains double bonds, these elastomers are re- elastomers (for properties and areas of appli- periods only or ferred to as elastomers. These are also cation, please refer to the appendix on pages which are covered referred to asR-type unsaturated or diene rubbers. 68 and 69). by special types

FFKM

PVMQ

FVMQ

VMQ

FKM

AEM

bers ACM

Rub HNBR

ECO

IIR/CIIR

NBR

EPDM

SBR

±100 ±50 050100 150 200 250 300 ° Temperature [ C] 16 Compound ingredients 17 The basic properties of an elastomeric compound are determined by the polymer and are Factors that influence decisive for the performance of the seal. For example, although it is the polymer that de- material behavior termines the elastomer’s low-temperature Elastomers are sensitive to light, ozone, high properties, plasticizers can improve these temperatures, a large number of fluids and properties within certain limits. However, chemicals, and wear. This means that not when adding plasticizers, it is important to Plasticizers only the usable temperature range, but fre- take into consideration that they can be ex- quently also the elastomer’s chemical resis- tracted from the elastomer through contact tance and swelling behavior is of major sig- with lubricating oils and can evaporate at nificance when selecting a suitable sealing high temperatures. This is why it is important material. It also explains why information at the development stage to take account of Knowledge of about the range of application – e.g. the fluid the operating conditions (e.g. temperatures) the range of or gaseous media with which the material to which a seal will be exposed. application will come in contact – plays a decisive role in So-called reinforcing fillers such as carbon determining the functional capability of an blacks or silicas also have a significant influ- Reinforcing elastomeric material. However, when devel- ence on the material properties of the elas- fillers oping the elastomeric compound, not only tomer. By varying the type and amount of must the chemical and physical factors of en- fillers used, the physical properties of the vironmental influences be taken into account, elastomer can be adapted to suit the intended but also the processes of interaction that are application. The specific surface, the struc- created by the polymer and the compound in- ture, and the surface activity of the fillers gredients and which determine the overall largely determine the reinforcement effect. physical properties of the elastomer. To- The principle is based on the interaction of gether, all of these factors have a significant the filler with the polymer matrix or – if the influence on the life of the final component. filler content is sufficiently high – on the formation of filler networks that are superim- posed on the chemical polymer network. Re- Compound ingredients inforcing fillers – in other words active fillers Elastomers are multi-component systems in – have a particle diameter of between 10 and which each component has a very specific 100 nm (nano particles); inactive fillers, on role to play. When developing the compound, the other hand, have a particle diameter of be- four main effects must be achieved: the rein- tween 500 and 1,000 nm. Carbon blacks are Four main forcement of the elastomer by fillers, the im- classified using an ASTM code that charac- effects provement of processability, the cross-linking terizes the activity of the carbon blacks. The of rubber using curing agents, and the protec- smaller the number, the greater the reinforc- tion of the elastomeric component against ing effect of the carbon black. Because active damaging external influences. carbon blacks have a much greater influence Active carbon blacks 18 Factors that influence material behavior The influence of the cross-link density 19 on the properties of elastomers than inactive quality elastomeric product. This is why car- fillers, a dependency of mechanical proper- bon blacks that ensure good dispersibility and ties such as tensile strength, abrasion resis- high processing reliability are now used in tance, or tear strength on the structure and the production of engineering elastomeric surface of the carbon blacks and the filler materials. content can be observed (Fig. 9). A homoge- White fillers such as silicas exhibit similar re- neous dispersion (distribution) of fillers in the inforcement potential to carbon blacks. How- Silicas Homogeneous polymer matrix is the prerequisite for a high- ever, silicas have a marked tendency to ag- dispersion glomerate. They create strong filler networks

28 that are responsible for the reinforcement effect in the polymer matrix. This is why compounds with active silicas are much more dif- N 220 ficult to process than compounds with the 21 a] N 330 same amount of carbon black fillers. More- over, because of their polarity, silicas disrupt N 550 the cross-linking with sulfur accelerator sys- 14 tems, which in turn slows down the cross- N 770 linking process. Consequently, when replac- ing carbon blacks with silicas, the cross-link- nsile strength [MP N 990

Te 7 ing chemistry must be adapted accordingly.

The influence of the cross-link 0 0 20 40 60 80 100 120 density Proportion of carbon black [phr] Curing or cross-linking is the name given to the production stage during which an elas- Cross-linking 200 as the formation N 220 tomeric component is molded. During this Fig. 9: procedure, chemical bonds are made that stage The effect of active (N 220, N 330), 150 transform the rubber compound into an elas- semi-active (N 550), tomer with tailored properties. Curing gener- and inactive carbon ally takes place under pressure and at in- N 330 blacks (N 770, N 990) 100 on compound creased temperatures (T >140°C) in specially properties such as N 550 constructed tools. N 770 N 990 tensile strength and 50 The cross-linking system determines the pro- viscosity is largely y viscosity [ML (1+4)/100 ° C] cessing qualities, the chemical structure of determined by the type and proportion the network, and the physical properties of 0 of the selected Moone 0 20 40 60 80 100 120 the elastomers. This is why the cross-linking c arbon black Proportion of carbon black [phr] system chosen during the development of the (phr = parts per elastomer compound plays a decisive role in hundred rubber). 20 Factors that influence material behavior The influence of the cross-link density 21

obtaining the desired material properties. The Fig. 10: two most frequent types of cross-linking are: Tear strength The influence and Fatigue of cross-link density Sulfur and sulfur cross-linking peroxide cross-link- Resilience . The sulfur cross-linking process consists Hardness on the elastomer peroxide ingnot only of the addition of free sulfur, but properties cross-linking also the combination of different substances Tensile that ensures the required cross-linking char- ties of the cure strength acteristics. In practice, this means developing Damping

a processable compound that guarantees not Proper Permanent set Coefficient only reliable molding, but also economical of friction production. The wide spectrum of available Elongation at break accelerators, sulfur donors, and retarding Cross-link density agents creates an almost endless number of possible combinations. Sulfur cross-linking is As the cross-link density increases, the Cross-link used primarily for the cross-linking of diene elastic modulus, hardness, and elasticity in- density rubbers such as NR, SBR, BR, NBR, or CR. crease, the elongation at break, damping, and The importance of peroxide cross-linking has permanent set decrease, while the tear increased with the development of saturated strength and tensile strength peak before de- synthetic rubber types. This type of cross- creasing significantly again. Consequently, linking paved the way for the cross-linking of an optimum cannot be reached for all mater- rubbers without double bonds in the main ial properties with any one cross-link density. chain. Moreover, peroxide cross-linking can As a rule, the cross-link density is selected in be used to improve thermal resistance. This is such a way as to optimize only those physi- particularly true of NBR. However, a variety cal properties that are important for a spe- of factors such as hot-air heating, fillers con- cific application. taining acid groups, or peroxide decomposi- Because it is very difficult to determine the tion products that form during the cross-linkcross-link density chemically, a mechanical ing process can prevent smooth cross-linking. variable that is almost directly proportional to The extent of the chemical bonds created be- the cross-link density – namely torque – is tween the polymer chains during curing for recorded at a constant temperature during the both types of cross-linking depends not only cross-linking reaction. An increase in cross-link on the rubber type, but also primarily on the density is indicated by an increase in torque. type and amount of the selected cross-linking The machine that is used for this purpose, the Measuring system. This is referred to as the degree of so-called rheometer, comprises a temperature- the torque cross-linking or the cross-link density. controlled measurement chamber and a flat, The cross-link density exerts a decisive in- cylindrical shearing disk (rotor) that moves at a fluence on material properties such as fa- constant speed. When the rubber sample is in- tigue, hardness, tensile strength, permanent serted, a torque is generated at the rotor shaft. set, friction, and elongation at break (Fig. 10). This torque is registered over the course of 22 Factors that influence material behavior Physical and chemical action 23 the loss of strength. These changes can take Fig. 11: 1.0 Cross-linking char- the form of swelling, cracking, embrittle- acteristics of elas- ment, or discoloration of the elastomer. An tomers determined 0.8 Flow Cross-linking increase in temperature accelerates the ageing by measurement of period period the torque 0.6 processes considerably. The following rule of thumb applies: for every 10°C increase in rque [Nm] 0.4

To Cross-link temperature, ageing accelerates by a factor density The life of the component of between 2 and 4. 0.2 is shortened accordingly by the same factor. No cross-link 0 0123456 Damage caused by oxygen Time [min] Seals are exposed to a large number of envi- ronmental influences such as oxygen, ozone, time and is used to estimate the cross-link den- UV light, or changing climatic conditions. sity. The vulcanization curve also sheds light The combination of oxygen in the air and in- on the viscosity of the compound at curing creased temperatures damages the elastomer temperature. One differentiates between three matrix. This damage can either lead to an ad- Damage to the characteristic periods (Fig. 11): ditional cross-linking of polymer chains or a elastomer matrix •The covers the interval be- degradation of cross-linking points. These in Flow period tweenflow the startperiod of the measurement to the turn lead to a loss of strength, hardening, or start of cross-linking, i.e. the point at which characteristic cracking, all of which can ulti- the torque starts to increase. It characterizes mately lead to the failure of the component. the period of viscous flow, which is used to Diene rubbers such as NR, SBR, and NBR fill the mold in the tool. During this period, which still contain double bonds in the poly- the torque initially decreases. mer chain are more sensitive to oxygen and, •The provides informa- most particularly, ozone, than saturated rub- Cross-linking tion cronoss-linking the interv periodal between the start of bers such as EPDM, ACM, ECO, etc. period cross-linking to the point when the material In order to retard or to halt the ageing process is transformed into a dimensionally stable altogether, antioxidants that have been se- state. lected to suit the elastomer type in question •The is completed when all possi- are added to elastomer compounds (espe- Cross-linking ble cross-linkcross-link points have been developed. cially diene rubbers). These antioxidants completed The torque stabilizes at this point. chemically neutralize the oxygen in the air so that oxidation of the polymer chains is reliably prevented. Appropriate anti-ozonants Physical and chemical action and waxes are used to prevent ozone-related Anti-ozonants Depending on the action involved, ageing damage. In the event of permanent deforma- and waxes processes in the elastomer network trigger tion – especially in the case of increased tem- changes that lead to hardening, softening, or peratures – chemical processes (chain degra- Elastomers age 24 Factors that influence material behavior Physical and chemical action 25

Fig. 12: Damage to the 180 3.0 e lastomer caused ε = 0.25 % by exposure to 160 2.9 ozone: (a) with anti- 140 ozonant, (b) without 2.8 anti-ozonant, (c) ess [%] 120 EA = 122 kJ/mol ] compared with an -1 2.7 elastomer that has not aged 100 2.6 80 e tensile str a) b) c) 1000/T [K 2.5 60 ° 100 C cont. air Relativ ° dation, reduction in the number of cross-link 2.4 40 110 °C cont. air points, or rearrangements) that lead to a per- 120 °C cont. air 100 C discont. air manent change in the material can be super- 20 ° 2.3 100 C cont. nitrogen imposed on the physical processes. Ozone- 0 2.2 -2 -1 0 1 2 3 4 related damage to elastomer components is 10 10 10 10 10 10 10 considerably accelerated if the component in Time [h] question is subject to tensile stress. In this case, characteristic cracks perpendicular to The best protection against ageing for an Fig. 13: the direction of stress appear. In unfavorable elastomer component depends largely on the Estimated working conditions, these cracks can lead to compo- operating conditions for which the compo- life extrapolated nent failure (Fig. 12). nent is intended. Only in the most favorable from the measured tensile stress relax- An exact assessment of ageing characteristics of cases will a single antioxidant suffice. As a ation values (mater- and a more detailed insight into ageing mech- rule, a combination of different antioxidants ial: peroxide-cured anisms allows chemical stress relaxation to is used. NBR) measured at Measuring be measured at different temperatures. In or- different temperatures in air and chemical stress der to evaluate a variety of chemical influ- relaxation The influence of the medium nitrogen ences better, measurements are also made by Whenever media such as oils and greases act ε = elongation comparing them in nitrogen or in fluid media. upon a material, two different processes oc- EA = activation An Arrhenius plot of the results makes it pos- cur: and energy of the ageing physical swelling chemical reaction. process sible to extrapolate the values for long expo- These processes can impair both the elas- sure times at lower temperatures (Fig. 13). In tomer and its sealing function. The difference the event of thicker test specimens, the between the two processes is that in the latter, slower diffusion of oxygen in the elastomer is the influence of the media causes a chemical the limiting factor for the destruction of the reaction that irreversibly changes the chemi- elastomer matrix and the associated ageing cal structure of the material. processes. This explains why in practice, In order to find out whether an elastomeric thicker elastomer components age much more material is suitable for use in conjunction slowly than thin elastomer components. with a specific medium, it is stored in the 26 Factors that influence material behavior Physical and chemical action 27

Fig. 14: perature. This is why test runs under operat- Immersion tests of ing conditions are an indispensable step elastomeric samples when evaluating a component. If the layout of the sealing environment is suitable, minor volume swelling does not pose a threat to the function of the elastomer seal. Volume shrinkage, on the other hand, can impair the Volume shrink- sealing function in that it can result in leakage impairs age. Permeation occurs when the medium sealing function (gaseous or fluid) migrates through the material without penetrating the pores or cracks. This leads to micro leakage in the seal. The action of the media influences many ma- fluid of the test medium for the duration of a terial properties such as hardness, density, short-term test (Fig. 14). The medium is ab- tear strength, and elongation as well as elec- sorbed into the elastomer matrix by means of trical and optical properties such as color and diffusion. In the process, the medium can ac- surface structure. Consequently, the causes of cumulate on the polymer chains. What is ini- damage are not necessarily exclusively attrib- tially a purely physical process of swelling utable to errors in seal production, but also to Swelling and and volume change can be overlaid by si- external influences such as the action of oils, volume change multaneous extraction processes. In this greases, or gases which can change the elas- case, elastomeric material ingredients such tomer both chemically and physically. In par- Damage caused as plasticizers, antioxidants, or other addi- ticular, the high proportion of additives in by lubricant tives migrate into the surrounding fluid new, fully synthetic oils can attack the sealing additives medium (chemical action). As a consequence material chemically and destroy it. This is the actual changes in volume and weight ob- why seal manufacturers must have a compre- served represent the balance of fluid that has hensive database of information that can be diffused into the material and the extracted used to predict the performance and life span constituent parts of the elastomeric material of the seal as accurately as possible based on that have leached into the fluid. The swelling interpretation of the interaction of the lubri- processes alone are completed after a few cant with the elastomer. days and provide information about the suit- There is no one elastomer that meets all ability of the material for use in the medium requirements of oil resistance, thermal rein question. However, short-term tests such sistance, and low-temperature flexibility as this (< 3 days) cannot provide a realistic equally. Consequently, it is essential to take impression of the long-term changes that can into account both the surrounding medium be expected, because the chemical action de- and the temperature conditions in the in- pends to varying degrees on time and tem- tended application when selecting a suitable 28 Factors that influence material behavior Physical and chemical action 29 tigue behavior of an elastomeric sealing mate- 275 rial is of little use because both the shape of PTFE the test specimen and the test conditions exert 250 FFKM ° C] a significant influence. For this reason, fin- 225 ished parts are generally tested on test FKM

ature [ benches under conditions that are very similar 200 VMQ PVMQ to those in the intended application (Fig. 16). 175 FVMQ ACM AEM Fig. 16: 150 EPDM ating temper HNBR Test field for testing IIR 125 ECO the function of radial TPE-E CR shaft seals (Simmer-

um oper 100 NBR AU SBR rings)

75 NR Maxim

50 020406080100 120 140 160 Swelling in the reference oil IRM 903 [%]

Fig. 15: sealing material. The following chemical The chemical resis- principle applies: “Similia similibus solvun- tance of elastomers tur” (Latin: “Like dissolves like”). This in the reference oil means that polar elastomers (e.g. NBR) swell IRM 903 considerably in polar media (e.g. glycol), while nonpolar elastomers (e.g. EPDM) are “Like dissolves not stable in nonpolar media (e.g. mineral like” External frictional load often causes material oil) (Fig. 15). For more details about the suit- abrasion or changes the material surface. This ability of elastomeric materials for use in se- type of depends not only on the elas- lected media, please refer to the appendix in tomeric material,wear but also on the shaft surface, Wear this book (see p. 70). the lubrication thereof, the sliding speed, and other parameters. It is only when exact and Dynamic load relevant material and fatigue data from field The constant recurrence of deformation trials are available that it is possible to use causes inner friction, which damages elas- modern calculation and simulation methods tomeric materials. Over time, this leads to the to predict the component’s properties and to internal heating of the elastomer and therefore make statements about the function over time. to the formation of cracks and the destruction of the material. This process is also known as . An investigation of the material’s Fatigue characteristicsfatigue in an attempt to predict the fa- 30 Mixing technology 31

Processing techniques Proportion model: Prerequisites for the production of compo- Carbon spaghetti nents made of high-performance elastomer Polymer black Zinc oxide materials include the reliability of the raw tangle aggregate particle (segment) material quality, exact raw material weight content, a controlled mixing process, and optimized molding processes.

LengthDiameter Particle Length Diameter Mixing technology μ 1±3 m 0.15 nm Rubber molecule 10±30 m 15 mm Elastomers are multi-component systems. 50 nm 50 nm Polymer tangle 0.5 m 0.5 m The different raw materials with their varying 190 nm 50 nm Carbon black aggregate N330 1.9 m 0.5 m weight contents and consistencies must be 320 nm 180 nm Carbon black aggregate N990 3.2 m 1.8 m Objective: 4 nm 2 nm Plasticizer 40 mm 20 mm processed in such a way as to create a homo- μ μ creating a geneous compound. Rubber, for example, 5 m 5 m Zinc oxide 50 m 50 m 0.8 nm 0.8 nm Sulfur/accelerator 8 mm 8 mm homogeneous is delivered as a plastic polymer in bale or compound chip form and decreases in viscosity once it reaches processing temperature. Plasticizers, celerators). This so-called “spaghetti model” Fig. 17: on the other hand, are generally delivered in also highlights the demands that are made on Using the so-called oil form. the mixing process. The art of mixing rubber “spaghetti model” to lies in the breaking up of the various compo- illustrate the different sizes of the com- nents and agglomerates and their even distrib- pound ingredients The mixing process ution throughout the polymer matrix in order The objective of the mixing process is to dis- to ensure the homogeneous quality of the tribute all necessary raw materials evenly compound. (distributive mixing) and to break up any ag- As a rule, the various components glomerates (dispersive mixing) in order to . This iscannot particu- be Several achieve an optimum connection between the larlymerge trued in of a singlecompounds operation that use fine-particle operations filler particles and the polymer. This is partic- carbon blacks or natural rubber as their poly- ularly important because the interaction of mer base. The mixing process is generally di- the filler particles with the polymer matrix vided into four stages: determines several properties, among them the reinforcement of the elastomer. To illus- • The cold raw polymer, which is fed into the trate the different sizes of the compound in- mixing chamber in bale form, must be bro- Differently sized gredients, figure 17 uses a strand of spaghetti ken up in order to create sufficiently large compound to illustrate the length and diameter of a rub- surfaces for the incorporation of the fillers. ingredients ber molecule and the dimensions of its com- Two contradirectional rotors inside the mix - ponents (carbon blacks, plasticizers, and ac- ing chamber are used for this purpose. 32 Processing techniques Mixing technology 33 The shear forces generated by the rotors of the thermal processes) and, therefore, the heat up the polymer, making it less vis- flow characteristics of the materials being cous. mixed. This is why the timing of the energy • The added fillers and plasticizers must be input is considered to be the “finger print” of incorporated so that a coherent mass is cre- the compound (Fig. 18). Continuous docu- Continuous ated. During this stage, the polymer pene- mentation of the most important process para- documentation trates the gaps in the filler agglomerates meters – such as temperature, speed, time, and and displaces the air. This part of the pro- energy – are therefore used to monitor and en- cess is known as . sure the quality of the compound. Internal Incorporation incorporation • The fillers, especially the carbon blacks, mixers with intermeshing rotors are preferable are available in the form of agglomerates for the production of high-quality technical that are broken up by the shear forces. This elastomer components because they generally part of the process is known as . ensure a better quality of dispersion and allow Dispersion dispersion • The broken-up fillers are then evenly distri- for faster heat dissipation. This makes low- buted throughout the polymer matrix. This temperature mixing processes possible. part of the process is known as . From the provision of the raw materials to the Distribution distribution delivery of the finished and tested compound, Fig. 19: Fig. 18: At every stage of the mixing process, changes the production of a batch comprises a large Material flow in Time history of the occur in the surface properties, size, and de- production process parameters gree of distribution of the additives as well as during the mixing in the flowability of the polymer (as a result process White Carbon Bale fillers black cleaver Rubber Oil Oil bale Temperature Speed Plunger path Energy ameters Internal mixer par Process

Roller mill Roller mill Batch-off plant Time [min] 34 Processing techniques Mixing technology 35 number of different process stages. In order to break up filler agglomerates completely. In ensure the steady flow of material, a variety of such cases, the compound moves through a aggregates – from weighing equipment, bale very narrow roller gap (< 1 mm) with a si- cleavers, internal mixer, and roller mill to the multaneously high level of friction in an extra batch-off plant – are needed (Fig. 19). roller mill. This improves the quality of the compound and is essential for compounds that require a high level of dispersion. This is Using roller mills for homogenization Roller mills generally have two rollers that are the case for safety components, pressure arranged one behind the other and run at dif- seals, and lip seals. ferent speeds. The temperature at both rollers can be controlled. The friction between the Quality aspects and process control roller and the materials being mixed ensures The functional property and quality require- that the flattened mixture (compound sheets) ments for parts delivered to companies in the generally sticks to the slower front roller. automotive and general industries have al- The roller’s first task is to cool down the ready increased significantly in recent years compound, the temperature of which can be and are set to increase even more in the fu- as high as 150°C at the end of the mixing ture. Legal guidelines and the fact that cus- process in the internal mixer. The roller also tomers are demanding higher quality mean Cooling and further homogenizes the compound. The that continuous monitoring and documenta- homogenization mixing effect of the roller is based on several tion of the raw material quality, compounds, factors including the dispersion that occurs in and processes is a necessity. Systematic ad- Advance quality the roller gap as a result of the different roller vance quality planning ensures that all stages planning speeds. The distribution of the compound of the process – from the design phase to the ingredients is reinforced by cutting the development and production of the com- compound sheets and using auxiliary rollers, pound that is ready for series production – are which are also known as stock blenders. The carefully initiated and completed. During the sheeting-out of the compound is influenced development phase, for example, an FMEA by the width of the roller gap, the friction, ( ailure ode and ffects nalysis) is con- and the temperature. If the formulation r e - ductedF inM order to EevaluateA the compounds quires it, temperature-sensitive curing agents and any risks involved in their production. and a ccelerators are added to the rolling In view of the fact that elastomer compounds mill after the cool-down phase. If the mixing are “customized materials”, the manufactur- line has two roller mills, there is more time ers of technical elastomer products have to for rolling during the internal mixer c ycle. manufacture and manage a large number of In order to ensure that processes can be repro- different compounds (up to 1,000). A corre- duced and repeated, the roller process is auto- spondingly large number of raw materials is matically monitored and documented. also required for the production of the com- In exceptional cases, the compounds are sub- pounds. In order to ensure high-quality com- jected to very high shear forces in order to pounds, only raw materials from accepted High raw- material quality 36 Processing techniques Molding processes 37 Optimization of the mixing processes and plants ensures reliable and stable mixing ERP (Enterprise resource planning) processes. ial

k s) ) Molding processes bad Mater

h-off Rubber processing technology is a wide field edbac eight eight master data that covers numerous processes from the pro- Batc (w good/ Fe (w cessing of fluid latex to extrusion and molding procedures in self-contained tools and ials manually applied tank linings. The most ance

lation widely used molding and curing methods for mater eighing mu

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er Compression molding

age is one of the oldest Compression molding rehouse methods of manufacturing technical elastomer Stor w mat Wa components. This process requires a preform Ra that is large enough to fill the mold for the component that is to be manufactured. The Fig. 20: and certified suppliers are used. In the pro- Barwell procedure has proven most effective Computer-assisted duction process, computer-controlled systems for the manufacture of this type of preform. In process for planning handle orders, manage raw materials, and this procedure, the rubber mass is pressed resources control processes and quality (Fig. 20). In a through a die and cut into very uniform pieces Fig. 21: large mixing plant with several mixing lines, of the same weight by a rotating cutting appa- The principle of every formulation is allocated to a particular compression molding mixing line in order to make the most of aggregate-specific strengths and to avoid fre- Upper heating platen quent compound changes, associated set-up F and cleaning times, and the risk of contamination. The order in which compounds are Organizing dealt with is arranged in such a way as to mixing orders Preform ensure: •the largest possible batch sizes •that formulations with similar raw materials are handled in succession •that color changes can be avoided. Lower heating platen 38 Processing techniques Molding processes 39 ratus. The preform is subsequently inserted into the component mold in the tool (mold cavity) Upper heating platen and the press is closed. The heat generated by the heated platen is transferred to the molding F compound, thereby triggering the curing process (Fig. 21). Compression molding re- Long heating quires relatively long heating times. The reason Preform times for this is that the preform must be heated from ambient temperature to the curing temperature, which is somewhere between 150 and 180°C. In view of the fact that elastomers are poor conductors of heat, this process can take several minutes, especially in the case of thick- walled components. In order to avoid air en- trapments, the mold must be deventilated regu- Lower heating platen larly by carefully opening the press several times during the curing process. Any excess pressing the elastomer compound into the Fig. 22: material must also escape. The excess material mold cavity. Pressing the compound through The principle of forms a rubber skin (flash) in the mold parting the narrow channels ensures an intense ex- transfer molding surface of the two tool halves. This flash must change of heat between the compound and be removed from the molded part in a separate the wall of the tool. The flow speed also gen- finishing process after vulcanization. erates high frictional heat. This must be taken into account when developing the compound Transfer molding formulation, because additional frictional The transfer molding procedure is a refined heat can lead to premature curing of the com- version of compression molding and can es- pound. The heating times for transfer mold- sentially be performed using existing com- ing are much shorter than those required for Shorter heating pression molding presses. Here, the upper compression molding. Flash also forms in the times half of the tool contains a cavity known as a transfer molding procedure. However, it is “pot” into which the uncured compound is generally thinner than the flash created by inserted in the form of a simple preform compression molding. The transfer molding (Fig. 22). The pot in the upper half of the tool procedure allows molded parts to be manu- Molding using is connected to the mold cavity below by a se - factured within tight tolerance limits, which channels ries of narrow channels. The most important means that it is particularly good for the pro- difference between compression and transfer duction of complex small parts. molding is that in transfer molding, the mold cavity is already closed when the press Injection molding process begins. When the press is closed, the was used successfully in tool pushes against an integral piston, thereby Injectthe plasticsion molding industry for several years before 40 Processing techniques Molding processes 41 curing time in the injection molding process is shorter than that in all of the other processes mentioned here. However, as a re- Injection sult of the comparatively high investment plunger For larger Screw costs associated with this process, injection pre-plasticization production molding is only suitable for larger production series series.

Other technologies The problem of deflashing – or the avoidance of the formation of flashes in the first place – has led to the development of new processes Distribution and tools. The surface of the tool can, for ex- channels ample, be modified in such a way that air, but not elastomer, can escape from the mold cavity. This method is known as ready molding, or the flash-less process, and is particularly suitable for the manufacture of high-precision molded parts. Fig. 23: being introduced into the rubber industry. The The combination of various molding The principle of structure of the tool used for injection mold- processes has also resulted in the develop- injection molding ing is similar to that used for transfer molding ment of other processes. As the name sug- with the exception that the individual mold gests, the process, for Injection ready cavities in the latter are connected to the gate example, injecticombineson re theady featuresmolding of injection molding (injection point) by means of channels. The and ready molding. molding process starts when the tool is is used to manufInjectionacture compr small,ession flat Injection closed. The pre-plasticized compound is then moldedmolding parts, especially O-rings. This compression injected at high pressure through the injection process is based on the fact that a very tiny molding nozzle into the distribution channels and on gap remains open when the tool is closed. to the mold cavities (Fig. 23). The preferred The required pre-plasticized compound is type of injection molding used in the rubber then injected into this gap and the press is industry features screw pre-plasticization and closed. Flat, high-precision molded parts that plunger injection. Here, the plasticization and are largely flash-free can be manufactured us- injection procedures are kept separate, ing this process. Separate units thereby ensuring that the full potential of For the every part of the plant can be exploited. As a process, thecold injection runner channels injecti areon kemoldingpt ther- Cold runner in- result of pre-plasticization, the compound is mally separate from the tool. Thanks to the jection molding almost at curing temperature when it enters optimized design of the channel system and the mold cavity. This means that the actual the fact that the temperature is kept at the 42 Processing techniques Optimizing elastomer processing procedures 43 processes such as the conventional injection molding or the injection ready molding process, and allows for a high level of au- tomation. Screw Injection pre-plasticization plunger Optimizing elastomer processing procedures Regardless of the curing process in question, it is vitally important to know the rheological properties of the compounds in order to be able to adjust process parameters to suit Cooling the material. Rheology concerns itself with Insulation the flow characteristics (viscosity) and shear Upper heating platen behavior of materials. When it comes to optimizing production processes and saving costs in the rubber-processing industry, rheology and process simulation are inextrica- bly linked. A knowledge of cross-linking reactions and their speeds helps the person developing the compound to determine the Lower heating platen reaction kinetics and the chemical engineer to determine the ideal heating time. It also Fig. 24: right level, there is no loss of material as a re- facilitates quality assurance in production. The principle of sult of previously cured sprues (Fig. 24). This Rheological data is used for flow or injec- cold runner injection saves huge amounts of material, which is par- tion simulations in injection molding in or- Flow or injec- molding ticularly valuable when it comes to high- der to determine the dependency of the shear tion simulations quality compounds. By cleverly designing the rate on viscosity and to use the results to channels, larger molded parts with small calculate the elastic proportion of the elas- cross-sections can be manufactured. Com- tomer stress. The simulation of injection pounds with very high free-flowing charac- processes is, therefore, an important aid teristics are required for this process. One when it comes to manufacturing defect-free positive side effect of these good free-flowing components. For example, the flow front characteristics is the fact that they allow for progression and the position of flow lines or an increase in injection speed. Not only does the pressure required for selecting a suitable Time and this save time, it also means that channels no injection molding unit can all be calculated material savings longer have to be demolded and removed mathematically. This allows potential sources from the molded part. Cold runner injection of error, such as entrapped air, to be iden - molding can be combined with all molding tified and eliminated at an early stage. 44 Processing techniques Optimizing elastomer processing procedures 45 By supplementing universal flow simulation Simulation of the compression molding programs with optimized material models process poses a particular challenge. In con- that describe cure kinetics, both the trast to injection molding simulation, where Calculating the (flow period, i.e. the time that elapsesscorch the time-varying flow front within a rigid scorch index beforeindex the elastomer starts to cross-link) and area (fixed walls of the mold cavity) needs to the cross-link density during the injection be calculated, not only does the flow front – molding of elastomer parts can be calcu- and consequently the parameters – change in lated. the case of compression molding, but the two An elastomer particle experiences fluctuating halves of the tool also move towards each shear and elongation deformation between other. the time it is filled into the cylinder of the in- The advantage of all process simulations is jection molding machine and the time it that the parameters can be reliably altered, reaches its final position in the tool. The optimized, and checked on computer within strong speed gradients at the side walls of the days or hours. The findings can be channeled Early injection channel and the narrow temperature into the product and process design at an optimization boundary layers must be taken into account early stage of development. Simulation for the simulation. Both special software makes physical contexts and processes more packages and considerable computing power transparent, thereby allowing the user to im- Considerable are needed to describe the complex, three- prove his/her understanding of the product or computing dimensional flow processes (Fig. 25). process – something that is not the case with power exclusively experimental examinations. This means that optimization processes can be used in a targeted manner in places where the greatest potential is visible. It also means that maximum development results can be achieved at minimum expense and effort.

Fig. 25: Injection simulation of a conical spring illustrates complex flow processes. 46 Testing during the production process 47

Ageing characteristics Testing elastomers in the air in fluid media The main objectives of an elastomer test are Stress relaxation, Component design creep Material characteristics to characterize the material, check that it Based on the optimized Light and UV resistance Tensile test material model functions as intended, and control the quality. Ozone resistance Hardness FEM calculations Elasticity Design optimizations In view of the fact that most elastomer prop- Density Dynamic properties Simulation of static and Strength erties depend on time and deformation, tests Modulus, damping dynamic states of stress cannot cover all of the complex interrelation- Durability (life) Compression set Complex inter- Friction, wear Abrasion ships between elastomer properties. In many relationships cases, only limited statements can be made Thermal properties Low-temperature about the suitability of a product for the given performance Process simulation Crystallinity Rheological and thermal operation. Consequently, in order to deter- Processing characteristics Softening characteristics tool design Reactivity Flow characteristics mine whether an elastomer is suitable for a Rheological data Demolding Electrical properties PVT diagram specific application, it is vital not only to characteristics Electrical conductivity Heat-conducting Contamination properties gather material data, but also to test the com- Surface resistance properties ponent in field trials. Dielectric characteristics Other properties Diffusion Permeation Testing during the production process information gleaned on the suitability of the Fig. 26: An exact knowledge of the interrelationship material for dynamic and static applications Overview of the test- between the formulation, the physical proper- on the basis of the compression set. In addi- ing methods applied ties, and the way they change as a result of tion to mechanical/technological properties at various stages of the production the effects of ageing is a prerequisite when it such as density, hardness, tensile strength, process comes to improving the quality of the end and elongation at break, the physical inter- product. In order to characterize elastomeric action with contact media and chemical materials comprehensively, a large number of changes to the material caused by environ- material properties are tested (Fig. 26). Deter- mental influences are particularly relevant. mining the compression set, for example, However, data regarding the material’s char- Calculating the provides information on the extent to which acteristics are not suitable for deciding compression set the elastic properties of elastomers are re- whether a material is serviceable. Field trials tained after long-term, consistent compres- regarding the influences of temperature and Field trials sive deformation at a given temperature. In media over different periods of time are gen- short, the compression set is one of the most erally simulated in laboratory conditions. important material characteristics that the Modern component design procedures that product developer must know before his/her are based on the FEM ( inite lement seal goes into operation. The quality of the ethod) and laboratory test runsF underE oper- elastomer compound can be determined and atingM conditions allow for a comprehensive 48 Testing elastomers Component simulation using FEM 49 assessment of the function of components. 3 Fig. 27: Ideally, unambiguous statements about the A comparison of serviceability of a material are based on the Experimental data different material Neo-Hooke models and experi- results of field trials featuring component Mooney-Rivlin prototypes. 2 Optimized material model mental data regarding

a] stress-strain behavior Estimating the working life 1 Mechanical, thermal, and dynamic character- Stress [MP

istic values are the basis for the development 0 of material models, where not only the influences of the compound and the environment,

but also the behavior of the material under -1 dynamic load are taken into consideration. -50 050100 150 200 Unlike other materials such as metals and ce- Strain [%] ramics, there is no linear relationship between tests enhance numerical material models, stress and strain in elastomers. In addition to thereby providing a comprehensive idea of this non-linear behavior, the stiffness of the the durability and, consequently, the working material as a function of the deformation life of the elastomer seal. speed must be taken into account. Optimized material models – so-called Hyperelastic – demonstrate hypergood elasticorrelationc ma- material models terial models Component simulation using FEM between the experimental data and remain The finite element method is used in indus- valid (Fig. 27) even in the event of consider- trial product development as a calculation able material deformation (>150%). procedure for solving complex problems Evaluation of the ageing stability of elas- relating to statics, strength, dynamics, and Evaluating tomers is a particularly important criterion thermodynamics. In order to ensure the best ageing stability when it comes to assessing the durability of possible design, the shortest possible devel- seals. The tests generally take the form of opment times, and top product quality when tensile tests on aged samples. In this regard, it developing a technical elastomeric compo- is important to note that short-term and sin- nent, it is necessary to apply optimized meth- gle-point determinations can always lead to ods of calculating the non-linear behavior and misinterpretations. Observing ageing phe- thus to illustrate the behavior of the material nomena at different temperature and time in- in the most accurate way possible. tervals, on the other hand, can provide signif- Non-linear FEM calculation models are indis- icantly more meaningful results and allow the pensable when it comes to describing impor- Non-linear long-term behavior of the elastomer to be es- tant phenomena such as the operating perfor- FEM model timated. Additional information that is ob- mance of elastomeric components, the process tained from component analyses and ageing simulation in forming technology, or the cal- 50 Testing elastomers Component simulation using FEM 51 culated simulation of impact processes. On have long working lives. The loads applied to the one hand, simulation makes physical inter- the axially symmetrical component are not relationships more transparent for the user. On themselves axially symmetrical. This is why the other hand, taking account of non-lineari- a combination of axial and transverse loads ties in the design process at an early stage al- must be taken into account during the calcu- lows the functions of the component to be re- lation. The simulation reveals stress peaks in Safeguarding liably secured. Simulations based on FEM the component. These stress peaks can be re- the component models, which describe the behavior of the duced by adapting the design of the compo- function material in exact terms, can make an impor- nent accordingly or, to a certain extent, by tant contribution in this regard and are gaining optimizing the material. Changes in the com- in importance. For example, the topology and ponent design have an enormous effect on the form of components that will be subjected to size of tensile and compressive stresses. In mechanical loads can be optimized by taking the case of bellows, this means that the maxi- minor stresses and strains into account. mum stress in the elastomer can be illustrated and subsequently reduced using simulations, Result: Fig. 28: which in turn means that the working life FEM calculation for of the component can be extended by up to extended an axle boot; the red 10 percent compared with the conventional working life areas indicate areas of extreme stress in design (Fig. 28). the material

Bellows are a perfect example of how FEM Example: calculations can be used with great success. bellows Bellows that must be capable of accommo- dating large angular movements are used to seal the lubricant at axle joints. In addition to meeting elasticity requirements, it is vital that the components used in these applications 52 High-tech products made of technical elastomers 53 This contact pressure force is also supported by the pressure of the media. As long as the O- High-tech products ring is installed correctly and the right mate - rial is chosen for the application, pressures of made of technical up to 1,000 bar and more can be sealed. Mod- elastomers ern calculation methods can be used to simu- late the deformation behavior of the O-ring Despite progress made in the various material during operation, thereby making it possible to groups, the special chemical, thermal, and enhance durability and optimize design. In ad- mechanical properties of elastomers mean dition to classic O-rings, various special ver- Special parts for that they continue to be the basis of technical sions that are capable of sealing complex com- complex compo- sealing solutions. Secure bonds between elas- ponent geometries are also available. O-rings nent geometries Combinations tomers and metals, plastics, fabrics, or other that come into contact with hot water or steam with other materials mean that the material-specific during operation, e.g. in fittings, control materials properties of the various materials can be valves, steam generators, feed pumps, sole- used to great advantage. Such bonds create noid valves, or in solar technology, are gener- multi-functional elements in the form of sta- ally made of EPDM or HNBR (Fig. 29). tic or dynamic seals, molded parts, elastomeric composite parts, and much more. Fig. 29: Whether used in a static or a dynamic appli- O-ring made of cation, elastomer is always of decisive impor- EPDM destined for use in solar tance for the function, durability, and eco- technology nomic efficiency of the seal. Depending on the range of application, other special demands are made on the materials. The spectrum of available seals is broad and ranges from classic cord O-rings and radial shaft seals to components that simultaneously seal and provide vibration control. Some of these products are described below. are predominantly used to provide a O-rings staticO-rings seal between stationary machine parts O-rings made of special EPDM compounds and fluid or gaseous media. The sealing effect are characterized by improved long-time sta- of the O-ring is based on the axial or radial de- bility especially at high temperatures (up to formation of its cross-section when it is in- 180°C in steam). In order to be able to use stalled. This deformation is achieved by de- these O-ring materials in conjunction with signing the installation area accordingly. The drinking water, special approvals, which can resulting restoring force provides the contact vary from country to country, are required in pressure force necessary for the seal function. addition. 54 High-tech products made of technical elastomers High-tech products made of technical elastomers 55

Fig. 30: industry must also be highly resistant to steam Butterfly valve and aggressive detergents. In other words they must be suitable for use in CIP (cleaning in place) and SIP (sterilization in place) procedures. By virtue of the fact that they come into contact with foods, only harmless compound ingredients may be used in the elastomeric compounds for these applications. Moreover, these compound ingredients must comply with relevant legal guidelines (e.g. the recom- mendations of the BfR and FDA CFR 21 § 177.2600). New developments in this area include high-performance materials that are New, high- based on EPDM, HNBR, FKM, and in special performance cases, on FFKM. HNBR compounds, for materials Thousands upon thousands of example, combine very good mechanical Butterfly valves or mechanically actuated shut-ofbutterflyf valv valveses for strength values with good frictional character- flow control are used in drinks, dairy, and istics. In view of the fact that HNBR is highly bottling technology (Fig. 30). Simple and ro- resistant to fats, waxes, and oils, these com- bust in design, they rarely malfunction. But- pounds are widely used in plants where these terfly valves must be capable of reliably with- media have to be blocked or controlled. The standing pressures of up to 10 bar and flow operating temperature range for HNBR butter- speeds of up to 2.5 meters per second. The fly valve seals is –20°C to +140°C. service life of seals is a decisive factor when are always used in applications it comes to the efficiency of butterfly valves. Diaphrwhere componentsagms must be linked in a flexi- Diaphragms As long as the right material is selected, the ble way, spaces between components sepa- seal will last for many thousands of switching rated, and at the same time a tight separating cycles. In order to meet increasing technical wall ensured between them. In view of the requirements, the materials used must allow wide range of possible diaphragm functions for low frictional torque when the valve is ac- (transporting, adjusting, controlling, sealing, tuated and exhibit very good sealing behavior separating, storing), diaphragms can be used over the broadest possible operative range. in applications in the fields of mechanical Long-term Low elastomer relaxation also ensures that engineering, automotive technology, space tightness the valve seals exhibit high elastic resilience travel, and medical technology. In the major- and therefore remain tight even after long cy- ity of cases, customized solutions are needed cles during which they are exposed to pres- to meet varying requirements with regard to Customized sure (closed state). mechanical, thermal, and chemical loads. Di- solutions In addition to being resistant to the medium aphragms are used, for example, in pumps being sealed, seals for the food and beverage that transport fuel or lubricating media, or as 56 High-tech products made of technical elastomers High-tech products made of technical elastomers 57 control and sealing elements in valves for system channels hot exhaust emissions past bottling plants. In addition to high media re- the turbocharger during cold starts and full- sistance, diaphragms must exhibit high abra- load operation. The twin-chamber system sion resistance and good dynamic properties. comprises two chambers working in the same The combination of tear strength (e.g. by us- direction that are separated by diaphragms. ing special fabrics) and flexibility allows di- This system accelerates the light-off perfor- aphragms to achieve high to extremely high mance of the catalytic converter appreciably. compressive strength and creep strength. In view of the fact that spark-ignition and Modern diaphragms that are used in actuators diesel engines have different operating tem- situated close to the engine translate even the perature ranges, different elastomer com- tiniest pressure differentials into control and pounds must be used for the diaphragms. switching operations. Even under critical op- such as radial shaft seals Dynamic seals erating conditions – e.g. close to turbocharg- Dynamic(Simmerrings) seals are used to seal moving parts ers or in blow-by gas flows that occur in the (e.g. rotating shafts). Among other things, engine combustion process – diaphragms en- they are used to seal crankshafts and sure long service lives and consistently reli- camshafts in engines or in the drive train of able switching precision. One example of passenger cars, commercial vehicles, agricul- Example: the where diaphragms are used in actuators is the tural machinery, and construction machinery, twin-chamber twin-chamber system, where they are used as as well as in industrial gears, hydraulic power system a waste gate valve in vehicles (Fig. 31). This units, and washing machines. Dynamic seals used in industrial applications must last for up to 40,000 hours. Despite the use of fric- Service life up tion-optimized materials, high shaft speeds to 40,000 hours and the resulting high circumferential speeds often cause extreme temperature increases at the sealing lip. In adverse conditions, this can lead to charring of the oil. The build up of charred oil residue at the sealing edge can ultimately result in leakage. This is why the elastomer used for radial shaft seals must be capable of withstanding such high temperatures. As a result of the increased use of modern synthetic lubricants in engines and gears, elastomers are also exposed to completely different chemical loads than is the case with conventional mineral oils. In short, the elas- Fig. 31: tomers selected for these applications must Twin-chamber exhibit a high resistance to this new genera- system acting as a tion of oil. waste gate valve 58 High-tech products made of technical elastomers High-tech products made of technical elastomers 59

Fig. 32: Fig. 33: Simmerring® with Sealing solutions leakage sensor with integral sensor, plug, and flexible printed circuit board can be manufactured for almost any kind of installation area.

In order to identify functional difficulties in form a sub-assembly. Without the need for Integral leakage good time, radial shaft seals can also be man- boreholes, seals, and ducts, this multi-func- sensor ufactured with additional functions such as a tional sealing system allows electrical signals leakage sensor. to be sent into or out of an area filled with a If the seal’s sealing function diminishes once medium and/or subject to pressure. Given the the product has reached a certain age, a leak- significant design freedom allowed by this age collector absorbs any fluid that escapes. system, it can be used in a wide range of ap- An integral sensor identifies the leakage and plications in the automotive and consumer sends a signal that indicates when the system goods industries as well as for medical and will need to be serviced and the seal replaced telecommunications technology. The minia- (Fig. 32). This helps avoid unscheduled ma- turization of this sealing system and the fact chine downtime. that the flexible printed circuit board can be Space-saving New ground is also being broken in the fields folded mean that this is a space-saving com- solutions of control and sensor technology in order to ponent that can be installed in even the small- meet the requirements of low leakage rates est installation areas. (in the ppm range), reliability, and cost opti- are both used in the Bellows and mization. The combination of flexible printed automotiBellows veand, construction dust boots machinery, and food dust boots … circuit board technology and elastomers in industries as well as for electrotechnical ap- the form of multi-functional sealing systems plications and medical technology. In cars, Multi-functional forms the basis of products that are capable they are used to protect axles, transmission sealing systems of simultaneously sealing and transferring in- systems, shock absorbers, and steering sys- … protect sensi- terference-free electric signals without the tems. Drive shafts, propshafts, ball joints in tive components need for conventional cables (Fig. 33). This tie rods, and stabilizers are all protected system consists of a static seal with integrated against the infiltration of dirt and moisture by sensor, a plug, and a flexible printed circuit special elastomeric bellows. Elastomeric bel- board that connects all the components to lows used in drive shafts also prevent the loss 60 High-tech products made of technical elastomers High-tech products made of technical elastomers 61 of lubricants. Moreover, the bellows must be wipers, U-packings, guide strips, back-up able to withstand excursions of up to 45° as rings, and rod seals. Sealing elements in the well as exposure to high temperatures, media, hydraulic cylinders of excavators, wheel and high local loads. The bellows have a flex- bearings, and earth movers are exposed to ible center part and two connectors. Appro- particularly high loads. They must be capable priate connecting elements ensure that the of withstanding both heavy soiling from mud component sits securely in place and guaran- and dust, as well as major temperature fluctu- tees the required tightness. The design of the ations. In addition, the sealing system must bellows depends on the type of joint in ques- not be damaged by high system pressures and tion and the customers’ specific requirements. pressure peaks in particular, or by the lateral As a result of the different loads applied to forces exerted on the hydraulic cylinder. The fixed and slip joints (inboard and outboard latest generation of hydraulic seals exhibits mounted), different elastomeric materials are high resilience even at extremely low temper- needed to seal them. Joint shaft bellows for atures, thereby allowing mobile hydraulic High resilience fixed joints are preferably made of thermo- systems to perform fully without any note- plastic elastomers (TPEs), while joint shaft worthy leakages in all climatic zones, even in bellows for slip joints are generally made of the depths of winter (Fig. 35). chloroprene rubbers (Fig. 34). Another area of application in which techni- In view of the increased power density of cal elastomeric materials are used is vibration Area of Sealing systems , the need for high-perfor-hy- control technology. Vibrations occur in appli- application: for hydraulic drmance,aulic leakage-freeaggregates components can only be cations where starting torque, imbalances, or vibration control aggregates met by special sealing systems with long ser- the influence of external forces and torque technology vice lives. The sealing systems used in these peaks play a role. The vibrations that are gen- applications generally comprise a combina- erated in this way not only create noise, they tion of sealing elements that have been care- also subject components in the drive train to fully selected to suit each other such as stress, thereby potentially shortening its ser-

Fig. 34: Elastic protective Fig. 35: bellows for drive Sealing system for shafts hydraulic cylinders 62 High-tech products made of technical elastomers 63 vice life. Engines, gears, drive shafts, and couplings connected to downstream machines all affect each other mutually. In vehicles, vi- Outlook brations can also be transmitted to the chassis In view of the continuously increasing de- and therefore to the entire vehicle body, mands made on sealing materials with regard which can lead to a reduction in ride comfort to durability, friction, wear, and chemical and and even instability. The frequency range of temperature resistance, as well as the in- the vibrations in the vehicle extends from ap- creasingly strict specifications, it is vitally proximately 1 Hz to over 1,000 Hz. In the important for seal manufacturers to look stress field between insulation and damping, closely at materials and the factors that influ- elastomeric components ensure that engines ence their durability. This is the only way to and the shafts in the drive trains run smoothly ensure the development of modern elas- and with very little vibration and noise. When tomeric materials that can meet even the Toughest used as elastomeric decoupling elements with toughest functional requirements. As far as functional hydraulic damping properties, engines and gears are concerned, the trend is requirements Hydro mounts can, as a result of their special hydrdesign,o mounts damp towards a broader usable temperature range as damping both low-frequency vibrations and isolate (from –40°C to +175°C) and the use of fully elements high-frequency excitation. Hydro mounts synthetic lubricants. In addition to these requirements, both engines and gears have to Fig. 36: meet stricter legal regulations. An example Engine mount with of such a regulation is the one relating to the Strict laws integral hydraulic damping (hydro “zero-emission vehicle”, which stipulates mount) that motor vehicles will in future no longer be permitted to emit any volatile hydrocar- bon compounds. The manufacture of customized polymers for specific applications allows for a considerable extension of the range of applications in which elastomer compounds can be used. For example, tailored ACM polymers were developed for the latest generation of shaft seals. Tailor-made The usable temperature range of these poly- elastomers mers (–40°C to +175°C) is 15°C wider than (Fig. 36) that are used as cab bearings in agri- that of materials previously used in such ap- cultural and construction machinery improve plications, so that they consequently already user comfort and simultaneously create the meet the aforementioned requirements of the conditions needed to meet legal guidelines on automotive industry. Special formulations al- noise and vibrations as well as occupational low for the development of new materials safety guidelines. with improved wear resistance and ageing 64 Outlook Outlook 65 stability, which enhance the durability of the about a significant reduction in energy con- component. sumption and the emission of carbon dioxides As a result of the growing importance of in the field of transport and energy supply. electronics in general and the increased use of However, the requirements for seals used in electric drives, new sealing concepts into fuel cell systems are completely different to Fuel cell Integration which additional functions are integrated are those for seals used in conventional combus- of additional being developed. These new designs render tion engines. Here, for example, gas perme- functions individual components superfluous, thereby ation or very tough requirements regarding reducing the required installation space, cut- chemical purity play a very important role. ting weight, and ultimately simplifying instal- Accordingly, the seals used in these systems lation for the user. For example, radial shaft must be impermeable to gas and exhibit high seals with elastomeric encoder elements and chemical resistance to the reaction products active sensors for measuring vehicle speeds, generated in the fuel cell. especially in ABS systems, are already avail- The trend towards multi-functional sealing able. These seals feature a magnetizable elas- modules combined with modern processing tomer layer with encoded sectors (see cover technology makes it possible to produce com- photo) that is attached either axially or radi- ponents that are both delicate and complex. ally to the outer side of the seal. A field sen- An in-depth understanding and knowledge of sor registers the varying intensities along the materials and the use of ultra-modern calcula- Key to success: magnetic field and uses this data to provide a tion processes such as FEM, and high-perfor- materials signal that gives information about the speed. mance drawing and construction programs expertise In future, more consideration must be given such as CAD will further accelerate the de- to another aspect, namely electromagnetic velopment of innovative elastomeric materi- shielding. The increase in the number of elec- als that meet the high requirements of quality, tric systems used in vehicles causes electro- performance, and durability. magnetic interference, which in turn can cause components to malfunction. The development of elastomers with increased electri- Electrically cal conductivity prevents electrostatic charge conductive and interference caused by the mutual inter- elastomers action of electrical components. Seals made of such electrically conductive elastomeric materials will in future be used in the field of sensor technology or electronic communica- tions technology. The development of hydrogen and fuel cell technology is considered to be an important pillar of future development. It is fervently hoped that these technologies will bring 66 Glossary/Bibliography 67

The branch of science that deals with the deformation and flow Rheology behavior of materials. Glossary (Mayan language: = tree and = tear) A collective term for Condensed particles comprising a multitude of individual Rubber cao ochu Agglomerates non-cross-linked, elastic polymers. particles and measuring between approximately 50 and 100 nanometers (nm) The flow period, i.e. the time that elapses prior to cross-link- in diameter. Scorch index ing of the elastomer. The adjective describes materials in which the atoms do not Amorphous Radial shaft seal, a trademark registered by Freudenberg. exhibit an arranged structure, but instead adhere to an irregular pattern. The Simmerring® The decrease in stress over time under constant deforma- adjective ‘crystalline’, on the other hand, is used to describe materials with a Stress relaxation regular structure. tion and temperature. Situated downstream of the mixing process, this plant is Plastics that can be plastically deformed under the influence Batch-off plant Thermoplastics used to cool the sheeted-out elastomer compound. of heat. Thermoplastics generally comprise polymers with linear or slightly branched chain molecules. The phenomenon that describes the thermally driven Brownian motion Plastics that can no longer be molded once they have been proper motion of molecules. Thermosets cured. The temperature- and time-dependent deformation of materials ex- Creep The product of an applied force and the distance between the point posed to constant, long-term mechanical load. Torque of application and the fulcrum. Chemical reaction that is initiated by heat and/or pressure in Cross-linking The time-, temperature-, and speed-dependent elasticity of which the polymer chains are linked to one another to obtain elastic properties. Viscoelasticity polymers, molten materials, or solids (plastics). Process whereby rubber is transformed into a rubbery-elastic state as Curing a result of a change in its chemical structure; also known as vulcanization. The equalization of differences in concentration between gaseous Diffusion or dissolved substances in which particles move dependant on temperature from the area of higher concentration to the area of lower concentration. The tensile modulus of elasticity is an expression of the re- Elastic modulus lationship between tensile stress and elongation. It describes the stiffness of the elastomer. Bibliography Polymeric networks that are capable of absorbing large defor- Freudenberg Forschungsdienste KG, (2001). Elastomers Elastomere Werkstoffe mations in a reversible manner; cured rubber. Hirsch, V., Schneider, E., and Weiß, R., “Numerische Berechnungen für Dich- A thermodynamic quantity that describes the molecular mobility tungen und Bauteile”, , Vol. 65, 10/2004, p. 812. Entropy MTZ (disorder) of a system. Kaczmarek, M., Rieg, F., , Hanser und Taschenbuch der Maschinenelemente A protruding edge of elastomer that forms during the molding proce- Fachbuchverlag (Leipzig, 2006). Flash dure. Krompf, W., “Membrantechnik für motornahe Aktuatoren”, , Vol. 66, MTZ Abbreviation of ; a numerical mathematical 4/2005, p. 288. FEM Finite Element Method method. Mars, W.V., “Factors that affect the fatigue life of rubber: a literature survey”, Abbreviation of . The FMEA is an , Vol. 77, Issue 3, 2004, p. 391. FMEA Failure Mode and Effects Analysis Rubber Chemistry and Technology analytical method of identifying potential weak points. Priebe, N., “Kontinuierliches Mischen von Kautschukmischungen”, KGK – The temperature at which polymers change , Vol. 58, 03/2005, p. 102–108. Glass transition temperature Kautschuk, Gummi, Kunststoffe from being flexible (the rubbery-elastic state) to being brittle (the energy-elas- Röthemeyer, F. and Sommer, F., (Hanser Verlag, 2001). Kautschuktechnologie tic state). This temperature varies from one polymer to another. von Arndt, E. and Bußmann, M., “Gleiche Mischungsqualität von verschiede- A macromolecule made of similar units (monomers). A polymer nen Produktionsstandorten – Qualitätssystem eines multinationalen Gum- Polymer can be made of linear or branched molecules. miverarbeiters”, (2000). VDI-Jahrestagung Mischen Extrudieren Spritzgießen 68 Appendix 69

ECO Epichloro- •Good resistance to fuels, Hydrin®, Diaphragms, molded hydrin mineral oils, and greases Herclor®, parts, engine mounts in Appendix rubber •Impermeable to gas Epichlomer® automobiles •Resistant to low temperatures Chemical nomenclature and sample applications HNBR Hydrated •Good oil and gasoline Therban®, Radial shaft seals, nitrile resistance like NBR, but Zetpol® dampers, absorbers, dia- Abbre- Chemical Properties Trade Application rubber with higher heat resistance phragms, hydraulic and viation nomen- name •Good ageing resistance pneumatic components, clature •Good abrasion and wear high-precision parts, O- properties rings for drive and electri- NR Natural •High static and dynamic – Vibration dampers, ab- cal technology, also used rubber strength sorbers, engine mounts, in sanitary and drinking •Very low damping machine mounts, and water applications (= high elasticity) couplings in automobiles, ® •Very good low-temperature mechanical engineering, ACM Poly- •Excellent heat, ozone, and Nipol AR , Radial shaft seals, acrylate ageing resistance Hytemp®, O-rings, flat gaskets, performance and shipping ® •Low ageing, ozone, and oil rubber •Very good oil resistance Noxtite molded parts for gears resistance •High damping in the automotive industry, also used in SBR Styrene- •Moderate elasticity Buna SL®, Molded parts, O-rings, ® oil and coolant circuits butadiene •Very good abrasion and Europrene , diaphragms, absorbers, ® ® AEM Ethylene- •Excellent heat and weathe- Dampers, absorbers, flat rubber wear resistance Solprene , also used in automobile Vamac ® acrylate ring resistance gaskets for gears in the •Moderate ageing Dunatex tires, conveyor belts, resistance hoses, and floor cover- rubber •High ozone resistance automotive industry, also •No ozone/oil resistance ings •High damping used in oil and coolant ® •Moderate oil resistance circuits CR Chloro- •Good heat, weathering, Neoprene , Bellows, dust boots, ® ® FKM Fluoro- •Very good oil and chemical Viton , Radial shaft seals, prene and ozone resistance Baypren brake hoses, dampers ® rubber •Moderate oil resistance in automobiles, applica- rubber resistance Fluorel , O-rings, diaphragms, •Extreme heat and weathe- Tecnoflon®, molded parts, high- (polychloro- •Tendency to crystallization tions in the general and ® prene) at T < 0 °C construction industries ring resistance Dai-El , precision parts for ® engine applications, ® •Poor low-temperature Noxtite EPDM Ethylene- •Very good heat and Dutral , O-rings, molded parts, hydraulics, chemical ® properties below –20°C propylene- weathering behavior Nordel , bearing elements in the and process engineering, ® (exception: special types) diene rubber •High ozone resistance Buna EP , food and beverage aviation ® (ethylene- •Very good abrasion and Keltan , industry, also used to ® ® FFKM Perfluoro- •Excellent chemical resi- Kalrez , Radial shaft seals, propylene wear resistance Vistalon seal brake fluids in ® copolymer) •Very good low-temperature automobiles elastomer stance Simriz O-rings, diaphragms, performance •Extreme heat and weathe- molded parts, high- •High hot water and steam ring resistance precision parts for resistance •Special types resistant to – chemical and process •Not oil resistant 20°C engineering, aerospace applications, also used NBR Nitrile •Good oil resistance Perbunan®, Radial shaft seals, to seal against aggres- rubber •Good damping (as the Nipol®, dampers, absorbers, sive media and steam ® acry lonitrile content Europrene , diaphragms, hydraulic ® ® VMQ Vinyl methyl •Extreme heat resistance Silopren , High-precision parts, increases) and pneumatic compo- ® Buna N polysilo- •Excellent low-temperature Silastic , O-rings, flat gaskets, •Good abrasion and wear nents, high-precision ® xane performance to –60°C Elastosil diaphragms for medical properties parts, O-rings for drive •Low strength applications •Poor ozone resistance and electrical techno- ® •Moderate ageing resistance logy, in the food indu- FVMQ Fluoro - •High heat, ageing, ozone, Silastic , Molded parts, dia- ® •Moderate low-temperature stry, also used to insu- silicone and weathering resistance FluorSilicon phragms, etc., mainly properties (depends on late against the cold rubber used in the aviation the acrylonitrile content) industry ® IIR Butyl •Excellent heat, ozone, Esso Butyl®, Diaphragms, O-rings PVMQ Phenyl- •Very good low-temperature GE-Sil , Molded parts, O-rings, vinyl- resistance, ozone-, UV- Silastic®, diaphragms rubber and weathering resistance Polysar for hot water and steam ® ® methyl- and weathering-resistant Silopren , •Chemical resistance to Butyl applications ® acids, hot water, and polysiloxane Elastosil glycols AU Polyester •Good ageing and ozone Adiprene®, Pneumatic and hydraulic •Impermeable to gas urethane resistance Pellethan® seals for general mecha- •Good low-temperature rubber •High tear strength and nical engineering appli- resistance wear resistance cations, agricultural and • High damping, heavy de- construction machinery, pendency on temperature conveyor technology 70 Appendix

Using elastomeric materials in a variety of sealing media The company behind this book 0 – – 0 0 – – + + –30 AU +90 Freudenberg Sealing Technologies –– –– –– –– +0 +0 +0 +– +0 +0 ++ +– +0 +– GmbH & Co. KG ++ –60 +175

FVMQ Höhnerweg 2–4 –+ 00 00 0+ 0– 0– 0+ –+ ++ ++ 69465 Weinheim, Germany +) (+) (+) (+) (+) (+) –60 Internet: www.FST.com VMQ +200 +( +– +– +– +– +– +– +– ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ –15 +230 FFKM Freudenberg Sealing Technologies is part of Freudenberg, the broadly –+ –+ –+ –+ ++ ++ ++ ++ +) ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ (+)

–20 diversified, internationally active and family-owned company. The tech- FKM +210 e nology specialist develops and manufactures a broad range of sealing –( –– ++ ++ ++ ++ ++ ++ technology solutions for its customers in the automotive, ancillary, and –40 AEM +150 general industries. This range includes both customized solutions that 00 –– –0 –– –– –– –– –– –– –– –– –– ++ ++ ++ are developed in close cooperation with the customer and globally stand- ++ ++ ++ ++ ++ ++ –30 ACM +160 ardized complete sealing packages. All of the world’s major carmakers, their most important suppliers, and over 15,000 customers in general in- –– +– +) +) +) +) +) ++ (+)

–30 dustry buy seals from Freudenberg. +150 HNBR 0+ –( –+ –( –+ –+ 0( 0( –– 00 ++ ++ ++ ++ ++ ++ ++ ++ +( Freudenberg has held a stake in the Japanese company NOK since 1960. (+) –40 ECO +130 The partners work closely and successfully within a global network on –– +0 ++ sealing technology solutions. They have founded a large number of joint +) +) +) +) (+) (+) (+) (+) (+) –30 ventures around the world and have adapted their company structures to NBR +120 complement one another. Milestones in the company’s globalization in- –( –0 –+ –– –( –( 0( –+ 00 ++ +– ++ ++ ++ (+) (+) clude the establishment of Freudenberg-NOK General Partnership, –40 +140 EPDM which is based in Plymouth, USA, in 1989 and the NOK Freudenberg –– –– –– ––+ ––+ ––+ ––+ ++ +) +) Asia Holding in 1996. Together, Freudenberg and NOK have over (+) –40 IIR

+130 50 production plants worldwide. 0– –– –– –( –– 0– –– –– –– –– –– –– –( ++

+) ® (+) (+) (+) (+) (+) (+) (+) (+) The Simmerring , which was developed at Freudenberg by Prof. CR –40 +120 Walther Simmer in 1929, was the starting point for a range that today includes over 80,000 different sealing technology products. Down –50 SBR +100 through the years, many of these products have been ground-breaking –– –( –– –– –– –– –– –– –– –– –– –– 00 –– 00 –– –– –– –– 00 –– –– 00 innovations. Today, seals assume additional functions, e.g. the transfer –60 +80 NR of signals to the brake or engine management system. , 0 moderate, – not suitable; special types may deviate from the information provided her art 2 art 3

s It is not possible to innovate in the field of sealing technology without [°C] .

ting oil an in-depth knowledge of elastomers. Freudenberg employs approxi- AG) AO)

ils mately 250 experts in its materials development units around the world. pe seed oil ] The company uses more than 1,600 different compounds and more than ne o alkylene [°C ter A group F oils ly-alpha- ly VP in accordance 850 different raw materials. State-of-the-art analysis methods and mod- Engi Gear oils Hypoid oils (EP oils) AT Greases glycols (P Po olefins (P HLP in accordance with DIN 51524 P HL with DIN 51524 P HETG ra synthetic ester HEPG polyglycol HF HFB group HFC group HFD group EL and L hea brake fluid Gasoline Wa Suds CIP/SIP Air Po HEES DOT3 /DOT4 ture els developed within the company for calculating and simulating the be- e pera s s havior of materials are used to continuously enhance and refine

tem Freudenberg’s sealing products. rmissible minimum temp Max. Mineral lubricant Synthetic lubricant Mineral hydraulic fluids Bio- degradabl hydraulic fluids Flame- resistant hydraulic fluids Other media Pe ++ very good, + (+) satisfactory