One-piece linkages based on Hytrel thermoplastic polyester in the 35 to 72 Shore D range have been developed to serve in a variety of suspension applications - snowmobiles, all terrain vehicles, machinery, even automobiles.
A conventional linked grommet assembly gets its strength from a rigid metal link, its elasticity from a soft rubber grommet, and its overall stiffness from both materials working together. It seems like a nice combination-until you consider the weight of the metal.
A single-piece, injection-molded, moderate-stiffness elastomer provides a lighter way to achieve a balance between stiffness and strength. The grades used would typically have a flexural modulus of roughly 80,000 psi and tensile strength around 7,000 psi-both far lower than the steel or aluminum used in metal designs. Yet with a cross-sectional area that typically exceeds that of the metal linkage by a factor of three, the plastic design can still provide an effective strength that allows it to compete with the stronger metals. At the same time, the plastic design would typically weigh two to four times less than the metal-based version, thanks to plastics' specific gravity advantage.
Molded plastics also offer opportunities to optimize stiffness through geometry changes. Instead of the mostly fixed geometry of the metal-based design, in which the choice of rubber dictates the spring rate of the grommet, the molded plastic version derives its stiffness characteristics from the geometry of the entire component.
Mark Schuchardt, DuPont Engineering Polymers, Box 7013, Troy, MI 48007-7013; Tel: (800) 441-0575; E-mail: [email protected]. For more information, Enter 509
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