Load-carrying capacity of surface-hardened gears. Influence of surface roughness on surface durability.

Abstract

The influences of material, heat treatment, tooth profile and surface roughness on the surface durability of surface-hardened gears were investigated. First, the effect of surface roughness on rolling/sliding contact fatigue was studied in detail by using a 2-roller-type contact fatigue testing machine. The results show that the initial surface roughness has a remarkable influence on the surface durability of surface-hardened steels, and that the decrease in surface roughness with running time does not always have an advantageous effect. Secondly, the load-carrying capacities of case-carburized gears and induction -hardened gears were investigated by using a power circulating-type gear testing machine. The phenomenon of grey-staining, which consists of many micro-cracks and micro-pits, appears on the ground tooth surface under a heavy load. In these tests, it is clear that the surface failure grey-staining, which causes degradation of the tooth profile and spalling, is most influenced by the initial tooth surface roughness. Furthermore, the effect of initial surface roughness on the surface durability of surface-hardened gears can be estimated quantitatively.