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Static rubber seals are common in bolted flange joints. These seals share the feature that, during assembly, the seal compresses until there is metal-to-metal contact. Examples include O-rings in grooves, metal carrier gaskets, or metal grommets at bolt holes. It is this “fixed compression” of the rubber that creates the optimum initial sealing stress within the rubber. However, a rubber seal will relax over time and, as the sealing stress decreases, leaks can develop. Since further compression of the rubber over time is prevented by metal-to-metal contact, there is no mechanical remedy for this type of failure. Rubber-edged composite seals have a rubber seal on the inner edge of a composite carrier. This is a completely new type of seal construction. The dynamics of joints using this sealing solution are different from the dynamics of joints using “fixed compression” sealing solutions.

A new flange sealing technology is described which meets industry standard durability and sealability testing. This technology was developed by first analyzing sealing mechanisms and failure modes of other current static sealing systems, and applying that knowledge to design a new sealing mechanism that may be less susceptible to common failure modes. The ability to choose the optimum polymer edge shape, polymer type, level of polymer surface adhesion, and structural carrier properties gives the design engineer a high degree of flexibility in designing flanged joints and effective static seals. The concept is validated by showing that gaskets can be designed for numerous applications which pass industry standard validation tests, including engine dynamometer, environmental chamber, and steam table testing.

In high-stress, dynamic sealing applications, new generation fiber gasket materials are solving problems where older style gaskets and various rubber/metal composite gaskets have failed. These applications include flywheel housing-to-block gaskets, gearcase-to-block gaskets, axle covers, cast aluminum oil pan gaskets, rear seal carrier gaskets, heavy duty valve cover gaskets, etc. What these applications have in common is a high degree of torsional or shear stress on the gasket which can lead to failure. Often, shear stress is a result of the heating and cooling of a joint which is made up of two different metals with dissimilar thermal expansion rates. Other applications carry torsional and shear loads due to their mounting and/or function in the vehicle. These applications require that the gasket be able to move with the flanges, maintain flexibility, strength, and bolt tightness, and continue sealing through the service life of the application.

An expert system called GMX: The Gasket Material Selection Expert was presented at the 1989 SAE Conference(1).* The capabilities of this program have since been increased tremendously by the development of a Mathematical Model which predicts physical flange distortion and gasket compression values for any bolted, gasketed flange configuration. The expert system contains the logic (Rules) and facts (Databases) needed to compare gasket material properties to application-specific requirements and to specify gasket materials that will perform best in the application. The Flange Distortion Model is used by the expert system to calculate certain quantities that are needed to compare materials for the application. This paper describes how material properties and gasket engineering are used to make a material recommendation, and how an expert system and mathematical model have been utilized to make this expertise available to the gasket specifiers.

An expert system has been designed to help transfer gasket engineering expertise from a Research and Development environment to the gasket specifying business. This paper will describe the complex requirements of today's gasket applications, how material properties and gasket engineering are used to make a material recommendation, and how an expert system has been utilized to bring this expertise to the gasket specifiers.