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 addi- tional 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 mol- ecules become mobile once again and the poly- mer changes over to a soft, rubbery-elastic state (Fig. 2). If the temperature continues to rise, viscous flow occurs followed by decomposi- tion 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 dis- placements 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