The influence of contact stress distribution and specific film thickness on the wear of spur gears during pitting tests

Abstract

One of the main gear damage mechanisms is the formation of pitting and spalling on the tooth flank. Several factors have significant influence on the damage formation, such as: contact stress level; tooth profile type; relative contact speed; surface finish and lubrication conditions. This work comprehends the global observation of all such parameters and was carried out to explain the phenomena related to this wear mechanism. The wear test equipment uses the power recirculation principle and is commonly known as FZG test rig. The gears were made from AISI 8620 steel and had two types of surface finishing (by shaving or by milling). The wear experiments were performed with two torque stages: 135 N.m (running-in) and 302 N.m (steady-state), and two test temperatures: 60oC (running-in) and 90oC (steady-state). The wear level was determined by using image analysis. In order to calculate the specific film thickness and friction coefficient, the roughness of tooth flank was measured at each test stop. After the experiments were completed, it was possible to confirm that, for both manufacturing processes, the boundary lubrication regime was adopted at the tooth flank and the specific film thickness presents a different behavior when compared to addendum, pitch diameter and deddendum regions. The wear on the gear flanks depended on the lubricant film thickness and it was higher for the milled gears.