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BMCI Gains Advantage with AOC Resin

18 June 2006

Bulk Molding Compounds have used unsaturated polyester from AOC in the first commercial application of their Gas Evacuation Technology - a refrigerator handle.

The handle is injection moulded in BMC 310, an appliance grade, fibreglass-reinforced bulk moulding compound which meets Underwriters Laboratory 5-V standard at a 0.070-inch (1.8-centimetre) thickness. BMC 310 is pigmentable in a range of colours and can be injection, compression or transfer moulded.

“AOC supplies the base resin for our BMC 310 appliance grade product,” says Len Nunnery, BMCI’s Director of Sales and Marketing. “The AOC resin component is a very consistent, high quality product that we have noted as a ‘go to’ for more demanding, aesthetically critical molding applications. This resin allows our molding customers to achieve the gloss, food stain and heat resistance necessary to meet the difficult surface requirements imposed by major appliance OEMs.”

BMCI claim that the Gas Evacuation Technology (GET) process results in parts that use up to 40% less material and are moulded in up to 60% less time. The technology allows thermoset composites to regain a cost advantage that was temporarily lost to thermoplastic parts that were gas-assist injection moulded. Gas-assist moulding consumes less material by leaving a hollow cavity in elongated sections. The hollow core design results in stiffness properties that are equal to or greater than those of a solid part.

Len Nunnery and Fran Zappitelli, Executive Vice President Corporate for BMCI, felt they could regain the cost advantage for thermosets by developing a cavity-forming technology for that family of polymers, and developed GET which combines a special fibreglass-reinforced thermoset polyester bulk moulding compound (BMC) with pressurized gas.

With GET, the BMC is injected into the cavity or cavities of a heated mold and held under pressure until a “skin” of material has cured to produce the desired net shape of the part. Pressurized gas is then introduced into the centre of the material at the end of flow. The pressure forces the uncured BMC back through the part and runner/manifold, and into the barrel of the moulding machine. The gas-evacuated material is effectively reclaimed and positioned in front of the injection screw check ring as part of the next moulded shot. The recovery of uncured material for reuse is the key to making GET competitive with gas-assist injection moulded thermoplastics which, unlike thermosets, do not crosslink under heat.

In the commercial debut of GET, custom moulder Dickten & Masch, Nashotah, Wisconsin, uses AOC resin-based BMC 310 to injection mold a 42-inch (107-centimeter) long refrigerator handle. The handle is roughly 1.5-inches (3.8 centimeters) in diameter at its largest cross-section and weighs about 2 pounds (0.9 kilogram). “Gas assist processing with BMC is drawing the attention of the composite manufacturing community,” Nunnery states. “This is a solid advancement for thermosets.”