By Bill Bregar
PLASTICS NEW STAFF
April 7, 2003
Nashville, Tenn. — An injection-molded, polycarbonate windshield for jet fighters — a major plastics-in-aviation breakthrough that finally is nearing production after 20 years of work — took the top design award at the Society of the Plastics Industry Inc.’s Structural Plastics Division conference.
SPD gave two awards to EnviroTech Molded Products Inc. of Salt Lake City. Designed for use on an F-16, the 78-pound canopy took home top honors with the Conference Award. The clear, bubble-free canopy also won for the Industrial & Military category in the 53-entry design contest.
“It’s a very critical program for us. It’s a very exciting program,” said Forrest Day, EnviroTech’s director of marketing and product development. He outlined the long history of the injection molded windshield April 1 at the conference in Nashville.
Bob Pinnell, a project manager at Wright-Patterson Air Force Base in Dayton, Ohio, dreamed up the idea of injection molding jet canopies. He now is retired.
The traditional method — bending and drape-forming heated, extruded and laminated plastic sheet — takes several days or even weeks, and costs $20,000 – $40,000 for a single F-16 windshield.
“That’s a pretty good amount for a piece of plastic,” Day quipped. The sandwich constructions of polycarbonate and acrylic can delaminate, causing problems, he said. An injection molded version costs a few thousand dollars.
Pinnell applied for a patent in 1983. In the late 1980s he linked up with EnviroTech, a company known for molding massive parts such as T-joints for pipe and filter plates that can weigh hundreds of pounds. Delta Tooling Co. of Auburn Hills, Mich., built a giant mold.
EnviroTech specializes in a low-pressure molding process the company developed called bulk injection molding. Day would not provide many details, but he said the two-stage process first extrudes resin, then injects itself into a mold.
EnviroTech molded about 160 of the F-16 windshields in 1993, and they passed Air Force impact tests. Ten years later, they’re still not in production.
But at the SPD conference, Day reported some good news. EnviroTech probably will begin production molding a 46-pound canopy for a T-38 training jet later this year. And in mid-2004, the company hopes to start molding a full-size PC canopy weighing about 200 pounds for the F/A-22 Raptor.
Compared with standard injection molding, cycle times are long, at about an hour. But much of that involves slowly removing the part and carefully cleaning the mold between each shot, Day said.
“A canopy even every six hours vs. every six months, it’s kind of impressive,” he said.
EnviroTech also has injection molded PC sheet stock, which then can be formed into a canopy using traditional methods. The single-layer sheet holds up better than a laminate made of layers of extruded sheet, he said.
Fifty-three parts were on display at the SPD conference, held March 30 –
April 1. Mike Springer, chairman of the parts competition, said about half the winners were made by gas-assisted injection molding.
The reaction injection molding process was used to mold about a dozen parts, and the rest were made by structural foam, coinjection, multimaterial molding and regular injection molding.
Springer was impressed by the colorful array of parts, everything from a bright yellow portable barricade to glossy body parts for a motorcycle and a personal watercraft.
“Nobody wants to paint, so when you can mold-in color, you do it,” said
Springer, sales manager of Horizon Plastics Co. Ltd. of Cobourg, Ontario.