Wear-coefficient analyses for polymer-gear life-time predictions: A critical appraisal of methodologies

Abstract

Polymer gears are used in many devices due to their advantages, among other, dry-running possibilities. As part of their design, the life-time predictions for fatigue and wear are among the most critical and necessary for any application. In a wear life-time prediction, the wear coefficient is the key parameter. The VDI 2736 guideline considers the wear coefficients obtained from pin-on-disc tests. Due to the obvious possible differences in wear coefficients from pin-on-disc tests and actual gear tests, these data can vary considerably. Moreover, the methodology for determining wear coefficients in a real-scale gear test has several possible variations that can lead to significant differences. This study evaluates several methods of determining the wear coefficient, i.e., pin-on-disc, as well as seven methodologies based on real-scale gear tests. Two different polyacetal (POM) materials (Delrin 500P and Hostaform C9091), typical for polymer gears, were used for the pin-on-disc analyses and a re-evaluation from the literature. The Delrin 500P was additionally used in real-scale gear tests to provide a direct comparison of the wear coefficients with the selected methods. The overall conclusion is that the wear coefficient of polymers used in gear-design calculations should be obtained from real-scale gear tests. This can be concluded from empirical wear coefficient results, as well as from surface wear mechanisms analyses.