Gas Assist Molding Technology
November 2002
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Formerly, gas assist molding technology was dominated by the processors of thermoplastics, according to the company. Its new Gas Evacuation Technique (GET), however, is said to offer molders of bulk molding compounds (BMCs) similar cycle and weight savings benefits. The company has developed a method of evacuating the center of thick, cross-sectioned injection molded designs. Unlike standard thermoplastic GAIM methods, the company uses a new technique made possible by the unique processing characteristics of the composite. By filling a die completely (as processors would do in standard molding operations), the pressure and heat associated with thermoset molding begins to cure the part from the outside in. By maintaining standard molding conditions for a pre-set amount of time, the BMC component's surface hardens, while remaining soft on the inside. Based on a study of time and temperature, the thickness of this “hardened” shell can reportedly be controlled. When the desired wall thickness has been obtained, a gas port mounted in the mold cavity is pressurized. This results in the uncured BMC being forced out through the center of the gate, runner, and sprue. The material is reclaimed in the press nozzle and mixed with virgin material as the next charge is plasticized. The result is said to be a hollow BMC component that requires 40 percent less material and 70 percent less clamp time.

Bulk Molding Compounds, Inc.

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