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

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. •Evaluation of different methods to calculate the gear wear coefficient required in polymer gear design.•Pin-on-disc and real-scale gear tests performed and compared to literature and existing guidelines.•Two different polyacetal (POM) materials considered in analyses.•Overall conclusion is that long-term real-scale gear tests are definitely needed for prediction of gear wear coefficient.