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Compressive Stress Relaxation (CSR) testing is challenging due to the different sample geometries, fixtures, aeration, and temperature cycles. Ageing environments such as hot air, static fluids, and aerated fluids contribute significantly to this challenge. ASTM and Original Equipment Manufacturer (OEM) standards allow a fixture two hours to equilibrate after immersion in ageing medium before testing. Experience has shown that the sample may not be at room temperature thus leading to possible errors in force readings. The focus of this paper is to conduct thermal cycle testing on typical rubber gasket compounds in order to determine their properties in such environments. Various thermal cycling methods were performed in order to determine the influence on the compound properties.

The current method for testing and evaluating sealing material candidates is plagued with concerns, issues and problems. Compressive Stress Relaxation (CSR) testing is challenging to operate. There are at least four different intermittent fixture types (Jamak, Jones-Odem, Wallace and Wykeham-Farrance) and one continuous compressive stress relaxation, CCSR fixture (Elastocon). Complicating this are four different sample geometry types and the potential use of aeration. The focus of this paper is to address these issues and offer some comparisons of the new ACM (polyacrylate) polymers that have been developed for the increasing temperature requirements in an engine compartment.

Recent developments in polyacrylate elastomers (ACM) technology now offer potential solutions to the current weepage and noise transmission problems associated with silicone (VMQ) reported in the USA. The Non Oil Weepage (NOW) ideals have been in place in Europe and Japan. In Europe and Japan ACM have been used for more than 20 years as the sealing material of choice for rocker cover and oil pan gaskets. In the USA special design techniques have allowed easy to process VMQs to be used. Illustrative dynamic test data are shown for ACM. In addition, data from recent laboratory work using compressive stress relaxation techniques is given. A laboratory method that shows weepage-type problems is evaluated. The comparative testing includes air oven aging, engine oil aging, and compression set testing. Finally, new polyacrylic elastomer systems are described that offer cure characteristics more similar to VMQ-type polymers.