On the Flash Temperature Rise of the Tooth Surface of Surface-Hardened Gear : 1 st Report, Effect of Thermal Conductivity in the Surface Layers of Surface-Hardened Gears

Abstract

A number of surface-hardened gears are usually used for heavy load high speed gears in which scoring is a serious problem. When the scoring factor on these surface-hardened gears are to be determined, it is necessary to examine both the variation of the thermophysical properties in the surface layer due to surface-hardening and the effect of the variation of the thermophysical properties on the equation of the temperature rise of the surface.We have obtained the following results through both the calculation of the surface temperature rise caused by frictional heat of a surface-hardened gear and some measurements on the thermal conductivity in the surface layers of surface-hardened gear teeth.(1) The thickness of the surface layer of the surface-hardened gear, such as a high-frequency induction hardened gear and a carburized hardened gear, is usually greater than the width of Hertzian contact zone. Therefore, when the surface temperature rise of the surface-hardened gear tooth is calculated, the thermal conductivity in the surface layer of the surface-hardened gear is used for calculation.(2) After heat treatment of hardening or carburizing, the thermal conductivity of the material, such as S 45 C steel or SCM 22 H steel, falls remarkably.