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Gasket materials, whether manufactured by the beater addition or the compressed sheet process, are inherently porous composites. The quantity and morphology of the pores existing in the structure will depend on the manufacturing specifics, the formulation and other variables. Since the primary function of the gasket is to prevent the flow of fluid, having an understanding of the type and nature of its pore structure aids in the tailoring of a material for a specific application as well as making formulation changes which will further enhance performance. Furthermore, knowledge of the pore structure as it exists in the actual flange environment should provide additional insight into gasket performance. The purpose of this paper is to discuss how pore structure of gasket materials influence their performance.

The subject of fluid permeation through porous media has been invoked as a basis for the study of gas and liquid leakage through fibrous gasket materials. The study has encompassed a variety of annular specimen sizes, specimen porosities and structures, fluid viscosities, and fluid pressure. To provide some control of material properties, the ASTM F37 Method B test method was modified to incorporate shims in the fixture. This modification prevents material creep during the test and provides a known porosity for each leakage measurement. The resulting data is highly reproducible and can be related to the intrinsic pore structure of the tested material. The technique can be utilized as a means to study the pore structure for purposes of optimizing gasket formulations; conversely, from a knowledge of the structure the leakage rate can be predicted as a function of sample geometry, state of compression, fluid viscosity, and fluid pressure.

The room temperature and elevated temperature (300°F) compression behavior for a select series of fibrous/elastomeric composites has been studied at stress levels up to 200,000 psi. Fiber reinforcement consisted of both asbestos and non-asbestos. It was found that the strain at room temperature could be largely explained in terms of the composite's pore volume fraction and that material failure was not observed in the materials formulated for this study. At elevated temperature, the binder volume fraction for these materials can be used to predict the material response. Test methods and data analyses are discussed.