Load-Carrying Capacity of HB≃340 (Hardened and Tempered) Gears : 5th Report, Influences of Gear Ratio and Surface Roughness on Surface Durability

Abstract

The surface durability of hardened and tempered gears (HB<sime>340) having a gear ratio of u≠1 was investigated by using a power circulating-type gear testing machine. The test results reveal that the gear ratio has a great influence on surface durability in the case of gears with rough tooth surfaces, such as hobbed gears. The endurance limit of medium-hardness gears is summarized as follows : Under the condition of rough initial tooth surface, (i) P_max<sime>0.1 HB kgf/mm² in the case where the gear ratio u is not unity, (ii) P_max<sime>0.2 HB kgf/mm² in the case that u equals unity. But, if the initial tooth surface is very smooth, (iii) P_max<sime>0.3 HB kgf/mm² regardless of the gear ratio. In conclusion, the tooth surface should be finished as smoothly as possible in order to obtain a high load-carrying capacity because the influence of roughness is more remarkable in conventional gears having a gear ratio of u≠1.