scope:

In several applications like hoisting equipment, cranes, open gears are used to transmit power at rather low speeds (tangential velocity < 1m/s) with lubrication by grease. In consequence those applications have particularities in term of lubricating conditions and friction involved, pairing of material between pinion and gear wheel, lubricant supply, loading cycles and behavior of materials with significant contact pressure due to lower number of cycles.

The comparison of proven old rating methods [2] with ISO 6336 has shown that ISO is very conservative for through hardened steel gear wheels running with case hardened pinions, specifically in the range of limited life.

In order to clarify the situation, an experimental test methodology and a test bench has been developed with representative conditions.

To assess new values of allowable contact-pressure stress numbers, the authors present the concept and the realization of this new test bench in order to satisfy those requirements with the associated procedures of calibration and testing: low-speed tangential velocity and grease lubrication.

Analysis of experimental results and metallurgical analysis of cold work hardening of material on the tooth flank surfaces are analyzed and given on a 42CrMo4 steels.

Fatigue SN curves resulting from tests are then compared and discussed with values given in ISO and AGMA gear rating standards.