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, as well as in injection moulding and

transfer moulding Transfer molding (BrE: transfer moulding) is a manufacturing process in which casting material is forced into a mold. Transfer molding is different from compression molding in that the mold is enclosed rather than open to the fill plunger resul ...

. 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 inventi ...

s, styrene, an initiator, 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 r ...

, vinyl ester resin or epoxy resin). 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