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Liquid Injection Molded silicone elastomers represent a processing alternative to heat-cured silicone elastomers used in traditional compression molding processes. Higher injection speeds, cure speeds, and complex mold filling by Liquid Injection Molded materials offer rubber fabricators productivity gains that more than offset higher initial material and investment costs. However, the wide-spread acceptance of Liquid Injection Molded products in the automotive industry has been limited from a performance standpoint; up until now, Liquid Injection Molded products have not reached the level of underhood performance of heat-cured silicone elastomers in terms of heat age, compression set, and oil stability. We describe 2 breakthroughs in Liquid Injection Molded technology that will lead to much wider industry acceptance.

The drive to control airborne automobile emissions will soon encompass sealed systems for onboard capture and reuse of fuel vapors resulting from refueling. In contrast to current systems that are based in the fuel dispensing pump, onboard refueling vapor recovery (ORVR) systems are intended to capture fuel vapor in a filler-neck sealing system, feed it to a holding canister, and bleed it off into the fuel injection system for combustion in the engine. For these systems to be effective, specialized elastomers will be required for collars, seals, and valve components. Not only must these materials resist degradation caused by fuel and fuel vapors, including those of methanol-containing fuels, they must also function over a wide temperature range. This paper discusses performance characteristics of fluorosilicone and fluorocarbon materials in an ORVR environment.

This paper describes the development of elastomeric barrier coatings which can be applied to the surface of molded silicone rubber gaskets to reduce oil permeation and weepage while retaining the advantages of silicone rubber in automotive sealing applications. The paper will also include discussion of test methodology for measuring weepage as well as gasket design and compounding considerations to minimize oil permeability of silicone gaskets.

A compression stress relaxation test method consistent with ISO 3384 is being used for the evaluation of sealant materials. The test measures important material performance characteristics not measured by traditional test methods. This paper provides a brief introduction to compression stress relaxation. This is followed by a discussion of the effects on gasketing materials, particularly when the gasket is confined to a groove, of engine oil contaminated with gasoline. The paper concludes with a discussion of using compression stress relaxation to design improved materials for automatic transmission fluid gaskets. In all cases silicone rubber is the primary material being studied.