In the automotive industry, the most widely used technique to predict the sealing capacity of an elastomeric gasket material is based on compression set data which is obtained after short term aging in air or reference fluids. Compression set measures the percentage of permanent deformation after the removal of the applied strain. This is an indirect measure of the sealing capacity and it can easily be misleading as a predictor of the sealing performance of gasket materials. Recent increases in service temperature requirements along with use of “SG” grade motor oils have created the need for a better means of assessing the high temperature, long term performance of elastomeric materials used in automobile engine gaskets. This paper reports Compression Stress Relaxation measurements on a variety of gasket materials using the Wykeham-Farrance Compression Stress Relaxation tester. This study also examines the effect of cycling heating and cooling on the retention of sealing force of gasket materials and includes the cumulative effect of exposure of the gasket material to motor oils and ASTM #2 oil at 125°C up to 1008 hours.

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