Bulk molding

In bulk molding processes, curing is achieved under elevated temperature and applied pressure. There are several possibilities. 

The mix containing benzoyl peroxide as initiator can be molded between 120 - ISO C under pressure for 10 to 20 minutes depending on the thickness of the item to be produced. A pressure around IS MPa is satisfactory for most applications. Preforming of the cake may help to ease molding. 

A large variety of objects can be produced by this technique. Since UP resins have good electrical prtqterties, dough moldmg products find different applications in electrical field. 

This technique is also known as resin transfer molding and is especially suitable to produce complex shapes without high-cost tooling. It also provides mass production without size limitation. 

The preform thus produced is transferred to the lower part of a pair of heated matehed metal dies, and a measured quantity of resin containing initiator and accelerator is poured or pumped on top. The press is then closed and compressed to a pressure of about 1.5MPa causing the resin to flow and wet out the preform. The molding time is about 1-5 min at 140°C. 

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SMC = sheet molding compound BMC = bulk molding compound. 

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... 

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. 

Processors Some companies manufacture their own polymeric materials for subsequent processing, but the majority purchases the necessary polymeric materials from other companies. Processors may specialize in the use of selected polymers, such as nylons and polycarbonates, or focus on particular techniques of processing, such as coatings, films, sheets, laminates, and bulk molded and reinforced plastics. 

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. 

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