| Abstrakt: |
Under the stimuli of reducing product weight and reducing cost through part consolidation, polymers have been replacing metals in many manufacturing operations. One of the newer polymer processes, reaction injection molding (RIM), has enjoyed a rapidly growing market, especially in automotive applications, for low strength appearance parts such as grill opening panels, styled bumper covers, and, more recently, “friendly” fenders. For many applications, RIM competes directly with compression molding processes such as sheet molding compound (SMC) and bulk molding compound (BMC). Generally, RP molding compounds require one or more steps prior to molding where resin, catalysts, fillers, and reinforcing fibers are combined and packaged. When these compounds are compression molded, they require high pressures, usually 500 to 1500 psi, and high strength, relatively expensive molds. In the RIM process, reactive feeds such as polyol and isocyanate or epoxy resin plus curative are instantaneously mixed while flowing into a mold, where they quickly polymerize to form the solid part. The advantage of the RIM process is the ease of handling liquids, reduced cost of low-pressure molding equipment, and the rapid cycle times. Without reinforcement, the properties of molded parts are generally inadequate for load-bearing structural applications; polyurethane formulations lack strength and rigidity, and epoxies are brittle. [ABSTRACT FROM PUBLISHER] |
