ABSTRACT
Injection molding was originally developed for thermoplastics using simple plunger type machines. Even if longer fibers are added into the compound, they are broken up during the plasticization and molding operations. Fibrous fillers increase the melt viscosity of the compound to a greater extent than particulate fillers; hence, fiber reinforced compounds are often more difficult to process than simple particulate filled materials. Until comparatively, it was considered that thermosets were not suitable for injection molding because of the risk of the material curing in the screw or plunger mechanism. Bulk Molding Compounds (BMCs) are fiber reinforced thermoset compounds based on thickened liquid resins such as unsaturated polyester, vinyl ester, and epoxide resins and their derivatives. They are amenable to injection molding subjected to similar principles as for the conventional thermoset compounds. Conventionally, particulate fillers are used, but for high-performance compounds a proportion of chopped or milled glass fiber may be included.
