Sealing technology manual for the process industry - Temperature and fat resistance

Seals are used in a broad variety of media, resulting in very specific operational conditions. Depending on the duration and nature of their exposure to these media, aging processes in the elastomer trigger changes that could lead to harden- ing or softening. This is reflected, for example, by swelling, cracking and brittleness or discoloration of the material. The higher the temperature, the faster aging proceeds. During contact with the media, there are always two differ- ent processes impacting the elastomer material which may affect physical swelling and chemical reaction. In contrast to pure swelling, the chemical processes are irreversible. In general, the chemical principle is “like dissolves like”. This means that polar elastomers swell in polar media and non-polar elastomers are only conditionally stable in non-polar media. No single elastomer can be used univer- sally. The requirements with respect to media resistance and the lower and upper temperature limits must be taken into account and then be used together with the specific application to select the most suitable material. Elastomeric materials Resistance to Polar media Non-polar media FFKM Fluoroprene® XP HNBR max. 325 200 100 Temperature in °C VMQ FKM NBR EPDM Elastic modulus Aging and viscous flow Diagram 1 Temperature application range threshold range glass condition Glass state Glass transition temperature Tg Elastic behavior Rubbery-elastic plateau Viscous flow TEMPERATURE AND FAT RESISTANCE APPENDIX PRODUCT PORTFOLIO MATERIALS RESISTANCE & PURITY ENGINEERING PLASTICS ELASTOMERIC MATERIALS TECHNICAL FUNDAMENTALS INTRODUCTION 55

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