Two horizontal bevel gears and the assembled washing-machine transmission are shown. Each bevel gear has roughly a 15-in. diameter. As the last stage in the gear train, they are used to impart washing action in the machine.

Two horizontal bevel gears and the assembled washing-machine transmission are shown. Each bevel gear has roughly a 15-in. diameter. As the last stage in the gear train, they are used to impart washing action in the machine.


Published polymer data sheets are a good starting point for selecting gear materials. But designers must test candidate resins for wear, fatigue, and noise under conditions that simulate the environment of working gears. One system that helps designers narrow the field of resins, prior to full-scale field testing, is the Plastic Gear Evaluation and Research (P-Gear) unit.

P-Gear is a precision dynamometer that evaluates gear sets at loads having a maximum torque of 100 lb-in. at speeds to 4,000 rpm. It accommodates parallel-axis gears with center distances to 5 in., as well as worm gears and other cross-axis drives. The tester measures temperature, acoustic emissions, backlash, and transmission error. The data gives designers a feel for overall gear quality and performance. It lets them compare fatigue strengths, contact stresses, wear, average tooth temperatures, mesh stiffness, and tooth breakage of candidate resins.

P-Gear works with unlubricated gears, as well as those that are initially greased or run in oil. It measures temperatures from 40 to 392°F (40 to 200°C) using noncontact, infrared sensors for unlubricated gears and fluid-temperature sensors for lubricated gears. Thermal data is taken at different loads and speeds to predict how gears will function at corresponding end-use temperatures.

Encoders monitor the relative position of meshing gears under programmed loads to quantify backlash and indicate tooth stiffness, wear, and transmission error. Wear is determined at set loading rates and speeds. The tester also defines gear material fatigue strength by recording the number of cycles until teeth break at various torques and temperatures.

P-Gear also records the sounds created by meshing gears. Gear noise is from transmission and alignment errors, gear inaccuracies, and tooth stiffness. At low speed without lubrication there is squeaking as materials slide over each other. The tester evaluates noise and documents how well different material combinations and resin formulations reduce noise.

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