Processing and performance advantages led the largest remaining U.S. roller-skate manufacturer to choose a specialty olefinic TPE over other materials for the cushions of its skate trucks. The injection molded cushions mount on the bolt that attaches the truck to the shoe. Originally, the cushions were molded of thermoset natural rubber. But rubber is costly and complicated to process. So several years ago, Sure-Grip International in South Gate, Calif., switched to TPU for the cushions. "Urethane was fine and it lasts forever," says Clay Stadler, president of C-Tech Tool & Molding, Englewood, Colo., which produces the parts for Sure-Grip. But continuing cost pressure from Asian skate makers forced Sure-Grip and C-Tech to consider "less expensive and more molding-friendly options," according to Stadler. In particular, he notes, "TPU cycle times are too long." After testing other materials, Sure-Grip chose Alcryn Melt-Processible Rubber from Advanced Polymer Alloys (APA), Wilmington, Del. Alcryn MPR is a partially crosslinked, chlorinated polyolefin. C-Tech found it much easier to process. Stadler says the skate cushions are thick and Alcryn makes them easier to pack and eject than does TPU. In addition, Alcryn sets up faster so cycle times are now 15% to 20% shorter in the 24-cavity, cold-runner mold. Shot size is about half a pound. "Our reject rate is almost zero," says Stadler. "On top of that, the Alcryn product looks better and even performs closer to the rubber standard." C-Tech now molds more than a million Alcryn cushions a year.
Advanced Polymer Alloys
Quillen Building 2E
3521 Silverside Rd. Wilmington, DE 19810