Bulk moulding compound (BMC), bulk moulding composite, or dough moulding compound (DMC), is a ready-to-mold, glass-fiber reinforced thermoset polymer material primarily used in

compression moulding Compression molding is a method of molding in which the molding material, generally preheated, is first placed in an open, heated mold cavity. The mold is closed with a top force or plug member, pressure is applied to force the material int ...

, as well as in

injection moulding Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for ...

and transfer moulding. Typical applications include demanding electrical applications, corrosion resistant needs, appliance, automotive, and transit.

Manufacturing

BMC is manufactured by mixing strands (Greater than 1/8” and less than 2") of chopped

glass fiber Glass fiber ( or glass fibre) is a material consisting of numerous extremely fine fibers of glass. Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the inventio ...

styrene Styrene () is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concen ...

, an

initiator An initiator can refer to: * A person who instigates something. * Modulated neutron initiator, a neutron source used in some nuclear weapons ** Initiator, an Explosive booster ** Initiator, the first Nuclear chain reaction * Pyrotechnic initiato ...

, and filler in a mixer with an unsaturated thermoset resin (commonly

polyester resin Polyester resins are synthetic resins formed by the reaction of dibasic organic acids and polyhydric alcohols. Maleic anhydride is a commonly used raw material with diacid functionality in unsaturated polyester resins. Unsaturated polyester resins ...

vinyl ester resin Vinyl ester resin, or often just vinyl ester, is a resin produced by the esterification of an epoxy resin with acrylic or methacrylic acids. The "vinyl" groups refer to these ester substituents, which are prone to polymerize and thus an inhibitor is ...

epoxy resin Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also coll ...

). The mixing is done at room temperature and stored at low temperatures to slow down curing prior to molding. The concentration of the mixture can vary depending on application, but is typically 30% glass fibers, 25% filler, and 45% resin, styrene, and initiator. The material is provided in bulk or in logs approximately 4" in diameter. The glass fibers in BMC increase the strength properties of the product to be higher than standard thermoplastic products. The machine required to mixng this BMC Compound i
Sigma Mixer
The

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

of BMC dictates how effectively it can fill a mold. When at high viscosity, the pressure applied to the BMC is not enough for it to flow, and when at low viscosity, the fibers will stay in one place while the rest of the material flows without them. The viscosity constrains the amount of each component that can be used when mixing BMC. Having a large amount of fibers or longer fibers improves mechanical properties but makes the BMC more viscous. Adding fillers can lower the cost of the BMC or improve a certain property, but causes the BMC to become more viscous. Adding more styrene lowers viscosity but causes the moulded BMC to become brittle. When at an optimal viscosity to allow flow, components made using BMC can be up to 16" in their longest dimension before the components of the mixture begin to separate.

References

Composite materials Fibre-reinforced polymers {{material-stub

Manufacturing

See also

References