Development of a Dynamometer to Study the Performance of Plastic Gears

Abstract

A testing facility has been developed to explore the failure modes of plastic gears. The overall goal is the prediction of gear tooth failure for a given set of operating conditions and to classify failure modes of plastic gears. The initial investigation is centered on the testing of plastic spur gears placed on a parallel-shaft drive train between a variable-speed, reversible DC motor and an eddy current dynamometer. The testing apparatus has been designed, fabricated, and refined to deliver consistent results. The dynamometer places two plastic spur gears in mesh, one being the drive gear and the other the driven. Most of the test gear pairs were injection molded, 40-tooth, 0.8 module gears. These gears were molded using Delrin™ 311DP, a polyoxymethylene polymer which is made by the DuPont Company. Optical encoders were attached to the input and output shafts to sense the shaft position providing a measurement of the deflection and wear of the gear teeth. In addition, an infrared temperature sensor was retrofitted to the dynamometer apparatus to measure the tooth-flank surface temperature. All of the tests where the gear flank temperature reached 250°F resulted in a catastrophic failure. The apparatus was also fitted with a high-speed digital camera system capable of sampling 1000 frames per second. The camera recorded the failure of the plastic gears.