Optimum Carburized and Hardened Case Depth
The optimum carburized and hardened case depth for each gear failure mode is different and must be defined at different locations on the gear tooth. Current gear rating standards do not fully explain the different failure modes and do not clearly define the different locations that must be considered. Furthermore, they use different hardness values to define effective case depth and provide different values for recommended case depth. This paper explains why case hardening is beneficial; the risks involved and compares the methods for calculating and specifying case depth per the ISO 6336-5 and ANSI/AGMA 2101-D04 gear rating standards, and guidelines presented in the MAAG Gear Handbook. The paper shows the three locations that the case depth needs to be specified and presents separate calculation methods to determine the optimum case depth to avoid the failure modes of macropitting, subcase fatigue, bending fatigue, and case/core separation. For each failure mode there is a minimum case depth below which the load capacity drops off. On the other hand, an excessively deep case decreases load capacity, increases cost, and has other detrimental effects that are explained.
Authors: Robert Errichello and Andrew Milburn
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