Bulk molding compound BMC

Bulk molding compound BMC is also called dough molding compound (DMC). It is a molding compound (extruded log form) that is not produced in sheet form. It consists... 

Bulk molding compounds (BMCs), 30 Bulk polymerization, 166 Bulk polysulfonylation, 331... 

Sheet molding compounds (SMCs) and bulk molding compounds (BMCs) are the dominant materials used in automotive applications. These composites of unsaturated polyester resin, fillers and fiberglass have advantages of high stiffness, heat resistance and low coefficient of expansion. Coupled with low creep resistance, which is a distinct advantage over thermoplastic competition, and low-profile additives, which can yield Class A surfaces, these materials are well suited for applications from exterior body panels to under the hood components. 

The matrix can be either a thermoset or thermoplastic. The oldest and still widest used material for compression molded products is phenolic. The thermoset materials used to manufacture fiber reinforced compression molded articles is unsaturated polyester sheet or bulk, reinforced with glass fibers, known as sheet molding compound (SMC) or bulk molding compound (BMC). In SMC, the 25 mm long reinforcing fibers are randomly oriented in the plane of the sheet and make up for 20-30% of the molding compound s volume fraction. 

Bulk Molding Compound (BMC). Liquid resin,in. long glass fiber, and simple filler (typically calcium carbonate or clay) are mixed in a dough mixer or cold extruder. Group II metal oxide is added to gel the liquid resin (Table 15.26). This doughy mix ( premix ) is placed in a hot mold, pressed to flow and fill the mold cavity, and held until cured. 

Prepregs, in the strict sense of the term, are therefore limited to certain resin systems and are usually employed in higher-performance materials. An alternative form, which has been used very widely for almost a half century, is sheet molding compound (SMC) and bulk molding compound (BMC), which are fully-formulated materials ready for molding by compression or injection, mainly based on TS polyesters and glass fibers (Table 4.1). 

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