Development of Joint Sheet Gasket with Reduced Amount of Aramid Fibers

摘要

Gaskets made of joint sheet are widely used for mating surfaces in engines and transmissions. Before the regulation was issued for restrictions of asbestos usage as a hazardous substance, Honda had already developed non-asbestos joint sheets using aramid fibers substituting for asbestos and started applying them to the products sold worldwide. However, aramid fiber is significantly expensive but, on the other hand, the amount of aramid fiber mixed in a joint sheet will largely influence the sealing performance. Thus, when aramid fiber is applied, cost increase becomes a concern. With this background, a gasket material was designed for reducing the cost without sacrificing the required reliability as a joint sheet assuming the actual applications. The cost was reduced mainly by reducing the amount of aramid fibers used. Based on the required properties for joint sheets, the constituent materials of the middle layer were optimized by combining glass fibers, mixed with coarse-grained silica as a reinforcement substance, with a base material of highly-fibrillated aramid fibers. The material structure was also optimized by adding a skin layer to get an excellent surface-fitting performance and adhesion to the part to be fastened. By combining these measures, the amount of aramid fibers was successfully reduced while satisfying the required properties. Furthermore, by constructing a dynamic evaluation method that considers the operating environment of the engine, it was made possible to evaluate the performances, as a unit component, of a joint sheet with high accuracy. As a consequence, the established material enabled the development of joint sheets using less aramid fiber, producing superior sealing performance with long-lasting durability at a lower cost.