Cutting sharper edges at the roller derby

July 27, 2006
Sure-Grip International (formerly Sure-Grip Skate Co.), South Gate, Calif., is the last of the large skate manufacturers to produce its products entirely in the U.S.

Reportedly, rebound is the most important attribute of melt-processible rubber-based cushions used in conventional and inline skates from Snyder Skate Co., Rock Skates, and Nova. The cushions fit on the bolt that attaches the truck to the shoe. The cushions need to rebound close to their original size after each turn or manipulation of the skate.

Sure-Grip International (formerly Sure-Grip Skate Co.), South Gate, Calif., is the last of the large skate manufacturers to produce its products entirely in the U.S. "We are reluctant to take our business to Asia, but it becomes more difficult every year," says Jim Ball, owner and president of Sure-Grip. "So we are constantly looking for ways to improve our products while reducing costs."

Several years ago the company switched from natural rubber to thermoplastic urethane (TPU) for the cushion component in its "Double-Action" skate trucks. First introduced in 1945, the Double-Action feature uses large, rubber cushions and a rubber pivot insert in the skate trucks. The cushions made skates more maneuverable and easier to turn.

The move to TPUs proved to be only a temporary solution because TPUs are hard to mold and their molding cycle and curing times are long. "TPUs virtually last forever," says Clay Stadler, president of C-Tech Tool & Molding, the Englewood, Colo., molding house that has produced Sure-Grip skate components for 20 years. "But with the crucial need to reduce costs, another less-expensive and more molding-friendly option had to be found."

Stadler's molding experience helped C-Tech identify better material options that included TPVs, elastomers, and various durometer TPUs along with a melt-processible rubber (MPR) from Advanced Polymer Alloys, Wilmington, Del. "All the materials under evaluation performed relatively well, but Alcryn MPR came out on top. It outperforms the rubber standard," says Stadler. "It also processes easier and retains physical properties that closely match those of the ideal (thermoset rubber), but at a lower cost."

"Alcryn MPR has improved skate quality and reined in production costs while dropping rejection rate to almost zero," Stadler says. There were, however, some initial production challenges such as eliminating side shrinkage, as well as producing flat and parallel parts.

Sure-Grip road tested the finished product to compare various elastomer cushion components by putting them on rental skates at a few local roller rinks. The TPV cushions broke down much quicker than those made from Alcryn MPR 2300, says Ball.

Advanced Polymer Alloys,
(888) 663-6005,
C-Tech Tool & Molding,
(303) 761-3505, e-mail: [email protected]
Sure-Grip International,
(562) 923-0724,

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