|All X-cess bike racks can hold either two or four bikes. The clamps permit access to any individual bike on the rack without disturbing the others.|
Thermoplastic vulcanizate plays a key role in both the function and aesthetics of the All X-cess bicycle rack built by Stromberg Carlson Products Inc., Traverse City, Mich. The racks sport molded polymer clamps outfitted with soft TPV pads that protect bike frames and cables from abrasion during transport.
The UV-stabilized plastic, NexPrene 1064A UV/LCOF from Solvay Engineered Polymers, Auburn Hills, Mich. (www.solvayengineeredpolymers.com), is a fully crosslinked ethylene-propylene-diene-monomer/polypropylene compound that provides the performance of thermoset rubber with the processing ease of thermoplastics. It sports a 64 Shore-A hardness, low surface friction, and rebounds well, thanks to high compression-set resistance.
These attributes are key, says Stromberg President Bob Brammer. The TPV's low-friction surface protects the painted frame and bike components from abrasion while its resistance to compression set ensures the clamp delivers a secure grip. "The pad acts like a lockwasher," says Brammer, "as you turn the handle to tighten the clamp, the pad compresses, putting back pressure on the threads to keep the clamp from coming loose."
Color was also important in selecting NexPrene. Stromberg Carlson wanted the pads to be highly visible bright yellow to warn drivers that the vehicle in front has a rack extending beyond its bumper. NexPrene is precolored to match Stromberg Carlson's yellow specification.
According to, spokesperson Jim Schramski for the Traverse City firm ACRA Engineered Plastic Solutions Inc. (www.acrinc.com), that molds the clamps, the low coefficient of friction grade was selected instead of a standard 64 Shore A grade based on its mold-release performance. The pad has a severe undercut about a quarter inch around its perimeter, which holds the hard plastic body of the clamp. Standard grades did not eject from the mold. "NexPrene LCOF gave faster mold fills as well as easier release, dropping cycle times by 10 sec." Schramski adds, while LCOF grade is more costly than the standard grade, faster cycle times more than offset the cost difference between the two.
-- Jean Hoffman