Milacron, Apex, and Premix teamed to develop a new thermoset injection process for fuel-cell plates.

Machinery makers Ferromatik Milacron North America and Apex Plastic Technologies, and ma-terial-supplier Premix/Quantum have collaborated on an injection-molding process that cuts the cost and production time for a key component used in fuel cells — what some experts believe is the most promising clean power source currently under development. The thermoset injection process replaces the costly and time-consuming compression-molding process for making bi-polar fuel-cell plates, while cutting cycle time significantly. According to Apex President Taras Konowal, the breakthrough gives injection molders new opportunities in a market projected to consume approximately 0.9 billion kg (2 billion lb) per year by the year 2003.

Widely used in military and space-exploration applications, fuel cells are being aggressively developed by automotive and consumer power companies around the world. Protoype buses are in service in Chicago, and all the major automotive companies have development initiatives in advanced stages, such as Toyota's Fuel-Cell Electric Vehicle (FCEV) and Mercedes-Benz's NECAR. Fuel cells are energy-efficient, producing electricity from propane, natural gas, or hydrogen, with water and heat (which can be recycled) as the only emissions.

A typical proton exchange membrane (PEM) fuel cell can utilize up to 200 plates that are bolted together in a "stack" similar to a conventional battery. Plate dimensions and weights can vary depending on the design of the fuel cell. Critical specifications for the plates include flatness, strength, and electrical conductivity. Available materials and molding technology have limited the manufacture of these plates to compression molding, a relatively slow process requiring load/unload automation.

Apex, Premix, and Milacron began a cooperative development project in 1999 to create the material and molding technology to "capture" this market for injection molding. Quantum Composites, a division of Premix, created a proprietary, injection-grade, fuel-cell molding compound called Pemtex. According Konowal, the material was initially very difficult to injection mold and required technological advancements throughout the injection system and mold, as well as in the machine and control software. Konowal said plates molded with the new injection process have been tested and found to be stronger than compression-molded parts, with all the necessary dimensional precision and conductivity.

The new line of BMC thermoset injection-molding machines from Milacron and Apex are rated at 990 to 770-t (100 to 850-ton) clamp force. They are based on a variety of Milacron machine platforms, and use screw, barrel, and stuffer technology from Apex. The Apex/Milacron team has delivered more than 15 machines since its creation in 1999, moving to a leading U.S. market position in thermoset molding in less than a year.

The new line of machines processes the full range of granular, sheet, hulk, vinyl ester, and thick molding compounds. Apex's new servoelectric Revolution stuffer allows continuous processing with the full range of vinyl ester, BMC, TMC, and SMC viscosities.

Standard machine features include screw torque limiter and reverse lock, high heat-exchanger capacity, heat-resistant platen bushings, air-blast flash removal, four electric mold heaters, closed-loop temperature control units for the plasticizing barrel, and mold venting/breath cycle. The new-design Apex injection barrel features a removable water jacket for easier cleaning. The water channel is a double-helix groove, which eliminates hot spots. The swiveling injection unit allows easy screw removal and access to the nozzle. A full range of options is available, including gate cutting, core pull sequences, accumulator-boosted injection speeds, injection compression, and extended temperature-controlled nozzles.

Injection units feature new screw and barrel technology from Apex. A wide variety of sizes, matched to clamp tonnage, provide phenolic shot capability at the high-pressure end of 40 g/230 MPa (1.4 oz/33,400 psi) and 1270 g/290 MPa (44.7 oz/42,000 psi), down to 225 g/118 MPa (8 oz/1 7,065 psi) and 4280 g/190 MPa (151 oz/27,500 psi) at the low pressure end. Capacities with polyester material range from a high-pressure end of 180 g/230 MPa (6.32 oz/33,400 psi) and 3056 g/290 MPa (107.8 oz/42,000 psi), to 490 g/90 MPa (17.3 oz/13,000 psi) and 12,230 g/97 MPa (431.5 oz/l4,000 psi) at the low pressure end.

The Apex electric stuffer allows overlap of plasticating and clamp operations for continuous processing. Stuffer storage capacities range from 45 to 180 kg (100 to 400 lb). The unit is designed for easy removal from the barrel inlet to aid switching from bulk to granular material. It processes material on a first-in/first-out basis, without dead spots or edges to trap material, and with very low shear to avoid degrading fiber length. Parts exposed to the material are corrosion resistant. The stuffer is designed for easy cleaning and loading from near floor level. It easily handles fluffy bulk material through compacted, extruded material.

Jean L. Broge

AEI October 2000