BMC Thermoset Molding
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BMC, or Bulk Molding Compound, is a common type of moldable thermoset material or composite. BMCs are unsaturated polyesters or vinyl esters, and may be injection or compression molded with thermoset molding machines. The properties of BMC molded parts exhibit exceptional dielectric strength, electrical insulation, heat resistance, and chemical resistance. These beneficial material properties lend BMC materials to be molded in a variety of safety-critical applications and component assemblies within the Electrical, Automotive, and Industrial markets. In its raw state, BMC resembles a play-dough like form usually filled with glass fibers and or minerals dispersed within the resin system. Molding wise, BMCs are more commonly injection molded, but can also be compression or transfer molded. Injection molding BMCs require the use of a molding machine stuffer or ram to help inject material into the screw and barrel to preheat and plasticize prior to injecting into the molds. (more…)
Why are thermosets commonly used as a molding material for electrical parts and component assemblies? Thermosets are implemented in electrical applications due to the materials’ exceptional electrical stability, high dielectric strength, and resistance to arc and track which protect internal components from electrical charge and risk of fire or product failure. Parts including circuit breakers, terminal blocks, and electrical connectors are molded from thermoset materials to ensure product safety. Whereas a thermoplastic can degrade, disfigure, or ignite; thermosets such as unsaturated polyester BMC and phenolic molding compounds remain durable and strong when exposed to such electrical elements. From a cost comparison, thermosets are a commercial option available at a low cost per lb. compared to engineered thermoplastics with similar type of electrical and heat resistant properties. Common thermoset materials used in electrical applications include both phenolic and bulk molding compounds (BMC). 
