This paper describes the heat generation, power transmission efficiency, and life of plastic helical and worm wheels meshed with a steel worm. A machine for testing plastic worm gears was developed, in which the center distance and shaft angle are variable, and by which the transmission efficiency can be measured. Experiments were performed using plastic helical and worm wheels and steel worms under no-lubrication condition. Polyacetal homopolymer and copolymer were used as wheel materials. The tooth temperatures of the plastic helical and worm wheels and the torques of the worm and wheel shafts were measured. The failure mode for plastic helical and worm wheels; the temperature of the wheel teeth; the transmission efficiencies between meshing gear teeth; and the lives of plastic wheels were determined. The effects of backlash and shaft angle on the life of plastic wheels were also determined.
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