Conveyor Runs Better With Acetal

When Rapistan Demag Corp. (Grand Rapids, MI) unveiled its Model 1728 conveyor, customers were impressed. Not only did the new model run faster than comparable accumulation conveyors, it also ran with only half the noise. The credit for toning down what is typically a noisy moving belt goes to the material chosen for an air-powered actuator mechanism that controls contact between the rubber drive belt and the rollers. Eight parts within the assembly--a pneumatic manifold, air actuator, support bracket, belt-contact shoe, and four belt guides--are injection molded from acetal resin (Delrin from DuPont).

"The acetal parts operate more quietly than equivalent metal ones," says Ricardo Schiesser, engineering manager for Rapistan Demag. "Consistently close molding tolerances prevent rattling, and the natural lubricity of the resin produces smooth, squeak-free movement without added lubrication." The shoe assembly's belt guides, in contact with the belt edges, needed low friction and wear resistance because the moving belt rides on them. According to Schiesser, designers chose Delrin AF, a grade that contains Teflon fibers. Other parts of the mechanism used Delrin 100P.

Actuator parts were also designed for easy assembly and disassembly. The air actuator and manifold snap fit into the bracket, and molded-in spring hooks hold the bracket in the conveyor side rails.

The concurrent design team included Rapistan engineers, members from molder Lakeshore Diversified Products (Spring Lake, MI), and materials support from DuPont. Using the team approach allowed Rapistan to develop the new model from concept through production in less than two years. Schiesser notes, "DuPont provided FEA results that proved the bracket would meet our strength requirements with thinner walls than expected. We saved material and got shorter molding cycles as well."