Extended Wear Lifetime Calculation for Grease Lubricated Gears in Consideration of Surface Hardness and Roughness

Abstract

Greases have a variety of advantages when special operating conditions apply for gear lubrication, e. g. improved properties against continuous (or slow speed) wear. Often, gears with different surface hardness are combined, in order to reduce costs during manufacturing and heat treatment. However, this has detrimental effect on the wear lifetime. Consequently, the calculation of the wear service life within the gear design process is essential. One common way of wear lifetime prediction is the calculation method acc. to Plewe that is typically combined with a standardized wear test with case carburized gears. It allows to calculate the wear carrying capacity for different gear-lubricant-systems, but a conversion between gear stages of different gear materials is not possible so far. Based on theoretical studies, influences from different surface hardness and surface roughness values as well as lubricating conditions were investigated on FZG back-to-back test rig. The results prove that hard-soft gear pairings have a higher risk for strong wear compared to case hardened gear stages, but basically follow the same trends and mechanisms. Furthermore, surface roughness of the harder gear has an effect on the wear life time of the softer gear. Based on these results the existing calculation method for the wear lifetime of gears was extended.