Molding of Rubber for High Performance Applications

Abstract

Abstract This paper broadly considers rubbers (elastomers), molding methods, and some problems associated with molding for high-performance (HP) applications. Molding procedures are then reviewed for several products used in HP applications. The elastomers mainly discussed are NR, SBR, CR, NBR, chloro-sulfonylpolyethylene rubber, silicone rubber, hydrofluoroelastomer and perfluorelastomer. NR is used in HP applications because it possesses desirable properties such as excellent fatigue resistance and high strength. Other rubbers or elastomers, such as silicone or perfluoroelastomer, are used in HP applications because they resist high temperatures and aggressive fluids. When molding these elastomers by compression, transfer, and injection, special procedures are sometimes necessary. These are discussed along with factors that affect molding behavior and the quality of molded products. These factors include: rheology, rubber shrinkage, inserts in moldings, mold fouling, mold materials, and design factors for molds. A special design is used for a compression mold for O-rings made from perfluoroelastomer. These are used to seal against aggressive fluids like dinitrogen tetroxide. In other HP sealing applications, NBR lip seals are used; molding factors are discussed which significantly affect their sealing capability. Also discussed are laminates, where NR is bonded to metal. These are used as bridge bearings and the steel plates in them cause nonuniform shrinkage. A nozzle bearing for the space shuttle is another HP application for an NR laminate; over 100 thermocouples were used to monitor temperature during molding. This paper concludes with a brief discussion of molding silicone rubber for spark plug boots and electrical connectors.