At May’s SPE Annual Technical Conference in Milwaukee, researchers from the Institute of Plastics Processing (IKV) in Aachen, Germany, presented a progress report on a developmental physical-foaming process for standard injection machines.

At May’s SPE Annual Technical Conference in Milwaukee, researchers from the Institute of Plastics Processing (IKV) in Aachen, Germany, presented a progress report on a developmental physical-foaming process for standard injection machines. Called ProFoam, it feeds nitrogen or CO2 gas directly from the bottle to the machine throat under pressure of 450 to 725 psi. ProFoam was conceived to achieve lower cost than using chemical blowing agents and to eliminate any unwanted byproducts of decomposition. Unlike other physical foaming processes, ProFoam uses moderate pressure and no special screw or barrel nor costly gas-metering equipment. However, the back end of the screw does need a gas-tight seal, and the throat will require an air lock (still to be developed) able to withstand up to 725-psi pressure differential. Once fully developed, potential advantages of ProFoam are said to include a simple, stable process that is fast and easy to start up. In experiments with polystyrene, pellets were preloaded with enough CO2 to achieve 20% weight reduction in 5 min. Gas preloading is faster than with autoclave methods (see p. 45) because heat inside the barrel accelerates diffusion of gas into the melt, reportedly yielding a one-phase solution with no bubbles. In a test run of 40 plaques (54 g each), weight variation was less than 0.5%. Further work (which is being supported by several companies) is needed to test the process on a larger machine (a 200-ton press with a 30-mm barrel was used) and more complex part geometry. For more information, contact Thorsten Krumpholz at the IKV. +49 241 80-93806 • krumpholz@ikv.rwth-aachen.de

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