Bulk molding compounds

A BMC is a molding compound that is not produced in sheet form. It basically consists of the mixture used in an SMC, except that it contains only short fibers. 

---

SMC = sheet molding compound BMC = bulk molding compound. 

The usual process for processing TP-short glass fiber RPs is IM consuming about 55wt % of all RPs. Specially designed IMMs process TS-RPs with materials such as BMCs (bulk molding compounds). The other processes primarily use TS plastic matrices. 

Entries on new materials, including re-cyclate plastics, fullerenes, hard-surfaced polymers, dendrimers, transflective materials, rapid prototyping materials, silicone nitride, supercritical fluids, bulk molding compounds, conversion coatings, folic acid, replacements for chloro-fluorocarbons ... 

BMC bulk molding compound CPVC chlorinated polyvinyl chloride... 

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

Transportation Bulk molding compound Propylene glycol/dipropylene... 

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. 

Acrylonitrile-butadiene-styrene copolymer USA grade phenolic microspheres Bulk molding compound USSR grade phenolic microspheres Dough molding compound Dinitrosopentamethylenetetramine... 

Sheet and Bulk Molding Compounds. The activity with SMC and and BMC is based on resin technology which was known more than 20 years ago (3). The key concept involves increasing the viscosity of the unsaturated polyester resin. The polyester resin with an initial viscosity of several thousand centipoise is advanced chemically to a viscosity of several million centipoise. 

Again, as in many other fields covered in the book, modified epoxies are the most studied systems (toughened epoxies for adhesive coatings and composites). But also rubber-modified phenolics and low-profile unsaturated polyesters for sheet and bulk molding compounds have been extensively studied. 

Compression molding involves the use of preforms (bulk molding compounds, sheets of glass fibers impregnated with the thermoset precursors, etc.) that are placed in a heated mold. When the mold is closed, the plastified preform flows to fill the mold and cure takes place in about 1-2 min. Then, the mold is opened and the final part ejected. 

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. 

---