Gas-assist with a twist

Incoe Corporation debuted a new external gas molding (EGM) process to the North American market at this year’s NPE show in Chicago. EGM was used on a Sandretto injection molding machine to mold a non-commercial panel for a Xerox copy machine in a demonstration of the process’s capability.

While the part was non-commercial, it was typical of the kind of part suppliers to Xerox have found challenging using conventional gas-assist molding methods, according to Incoe’s John Blundy.

EGM was invented in the 1980s by Dr. Robert Carroll. Called the “injection compression process” at the time, it was the first patented use of gas as a packing technique in injection molding; however it was never brought to commercial status. Asahi Chemical of Japan purchased the patent portfolio of the process. In 1999 Incoe obtained licensed rights to use and sell the technology in North and South America.

With EGM, gas is injected at low pressure (typically less than 1000 psi) through the core side of the mold. Gas is not injected into the plastic material, but onto the surface or selected surfaces creating a layer of gas across the entire area, which is sealed at the parting line to prevent escape.

According to Blundy one main advantage of EGM is that the gas injection point can be remote from the material gate. Also, most significantly, EGM eliminates some of the problems commonly associated with conventional gas-assisted injection molding, such weld lines and penetration of gas into thin wall sections, so-called fingering.

Blundy says running EGM requires a nitrogen source and a very simple gas delivery device. He believes the process has potential for wide applications.

“Many parts, such as cell phones and laptop computer housings are becoming thinner. With EGM it may be a simple matter to apply gas externally across the surface instead of putting high processing demands on the machine itself.”