The ef®ciency and friction of plastic cylindrical gears Part 1: In¯uence of materials

Abstract: Little has been published on the ef®ciency of plastic gears despite the fact that plastic gears are used in large quantities in a variety of machines. Among the many applications where plastic gears are used, one is where any form of lubrication must be avoided, such as in of®ce printing and food-processing equipment, but dry running can lead to high friction and associated high temperatures. As more is understood about plastic gears, the trend is towards high-power applications where inef®ciencies become even more important. As high temperatures must be avoided with plastics, knowledge of ef®ciencies and friction is essential in the rating of plastic gears. This paper looks at the ef®ciencies of plastic spur gears made from a range of polymers and polymer composites used in plastic gear manufacture. Tests were conducted in like±like and dissimilar material con®gurations for plastic gears as well as plastic±steel combinations. Tests were also carried out to assess the effect of grease lubrication. A test rig was developed to measure gear tooth meshing losses accurately and this facility is reported in the paper. Ef®ciencies were shown to be both load and speed dependent. U sing equations developed for calculating ef®ciencies, average coef®cients of friction for tooth meshing were determined for particular materials and operating conditions from measured ef®ciencies. These coef®cients were compared with values obtained from classical tribological tests such as thrust washer and roll/slide apparatus