Gas Assist Smooths Out Compression Molding.

A new patent-pending technique adapts the gas-assist approach used for injection molding to compression molding of thermoset and thermoplastic composites. The technology was jointly developed by Composite Technologies Co. (CTC), L.L.C. of Dayton, Ohio, and Alliance Gas Systems, Inc. of Chesterfield Township, Mich. Alliance supplies the hardware components for controlled injection of nitrogen gas into the mold cavity in order to hollow out selective areas of the part. This approach can be used to reduce part weight by up to 15-20%, save material, and speed curing or cooling of thick part sections. It also helps pack out the part, reduce stresses, and provide more uniform shrinkage.

However, up to now, gas-assist has been used in compression molding mainly to reduce sinks, especially over deep ribs. CTC, which has proprietary technology for compression molding thermoplastics with long-glass reinforcements, has used gas assist on two PP/long-glass parts--a cargo carrier for Reese Products (shown here) and basketball backboards for Huffy Sports. Among several other products in development is a large PP table, where gas assist could help ensure flatness.

So far, gas assist has been applied only to sample parts of thermoset SMC or BMC, hut it reportedly has shown potential to improve packing and reduce sinks. Alliance Gas Systems plans to try external gas molding, where the gas is injected between the mold and one side of the part in order to improve surface quality on the opposite side. Molders interested in the process should contact either CTC or Alliance Gas Systems.