The efficiency and friction of plastic cylindrical gears Part 1: Influence of materials

Little has been published on the efficiency 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 office 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 inefficiencies become even more important. As high temperatures must be avoided with plastics, knowledge of efficiencies and friction is essential in the rating of plastic gears. This paper looks at the efficiencies 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 configurations 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. Efficiencies were shown to be both load and speed dependent. Using equations developed for calculating efficiencies, average coefficients of friction for tooth meshing were determined for particular materials and operating conditions from measured efficiencies. These coefficients were compared with values obtained from classical tribological tests such as thrust washer and roll/slide apparatus.