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CHICAGO — In a technology advancement, GE Plastics has applied existing sequential-valve-gating technology to mold parts with a thickness of less than 0.04 inch, or 1 millimeter. A big advantage: no weld lines. A proprietary GE Plastics tool demonstrates a new melt delivery system for thin-wall applications in NPE Booth S2311 in Chicago.

The process applies mostly to computer and telecommunication enclosures and housings. As recently as 1995, a laptop housing with a wall thickness of 0.08 inch was considered thin. Today, housing walls are barely half that thick.

``People capable of high-end molding have a chance to go thinner,'' said Kevin Andrews, technical manager for computer devices with GE Plastics in Pittsfield, Mass.

An example of the consumer product potential in thin-wall will appear this summer in the polycarbonate/ABS, 0.06-inch-thick walls of Black & Decker's new upscale Pro-Finish clothing iron. Most irons use less-expensive polypropylene. This application is the first using thin-wall in a nonbusiness electronics product, although it is not using sequential valve gating.

The iron is ``the first application where we've validated the process in something beyond computers,'' Andrews said.

Development engineers tested various gating techniques and processes to mold a part less than 0.04-inch thick. GE Plastics' Lexan SP7602 PC resin was time-released through five gates to fill the mold cavity in an optimal manner. The goal for the finished product was avoiding any lines where the melt fronts came together.

``We can make [thin-wall] parts in a standard injection molding process while reducing pressures by greater than 20 percent,'' Andrews said.

The engineers applied injection pressure of 19,200 pounds per square inch and used a fill time of 1.08 seconds.

Through the tests, ``we continue to gain information to provide more assistance'' to original equipment manufacturers, Andrews said.

The team looked beyond use of multiple direct gates through a hot runner because ``this produced undesirable weld lines, which caused aesthetic surface defects and created areas with poor impact strength,'' GE Plastics processing engineer Greg Tremblay said.

Thinness raises questions about painting of parts, particularly for notebook computers. This technology will offer particular benefits to filled materials that are more susceptible to the visual and mechanical limitations of weld lines, Andrews said. Often, customers paint or texture parts to enhance surface quality but at an additional cost.

The sequential-valve-gating tech- nology allows manufacturers to use less material, achieve faster cycle times and use fewer machines, the firm said.

While the engineering thermoplastic resin may cost more, the thin-wall molding process should produce a net cost savings for processors.