Load-Capacity Evaluation of Polyacetal (POM) internal gears according to JIS B 1759:2016 (Effect of number of teeth of pinion)

The present paper describes the load capacity of POM internal gears, which were evaluated from the results of running tests according to JIS B 1759. As a result, POM internal gears showed a higher load capacity than expected from the running tests performed against external ones. The tendency became marked, especially on internal gears mating with a relatively large number of teeth steel pinion. Two indexes were proposed to explain the higher load capacity, i.e., the ratio of contact ratio for loaded teeth to geometrical one and an integral value of the PV. The contact ratio plays a fundamental role in estimating a load on one tooth, and the PV value indicates the frictional work, i.e., the tooth temperature during meshing. At present, however, only these indexes are not enough to explain the higher load capacity. Furthermore, cracks due to tooth-bending stress were observed to examine the 60°-tangent method for determining the critical-section position of internal gears. The observation demonstrated that the 30°- or 45°-tangent could be more suitable for the determination.