A Comparison of Ratings for Plastic Gears

The failure mechanisms of plastic gears are examined and methods for calculating tooth bending and surface contact stresses for non-metallic gears are reviewed. The applications and limitations of the Lewis equation and Hertzian contact theory are considered and comparisons made between steel and plastic conditions, gear standards and various commercial rating practices for plastic gears. Special emphasis is laid on the British Standard BS 6168: 1987, the Polypenco rating method and ESDU 68001 for the design of non-metallic gears. A comparison is made between gears of different materials and material combinations, and for gears running under dry and oil-lubricated conditions. The effects of gear speed on ratings are briefly examined. As a result some shortcomings in the various rating methods are mentioned.