An accelerated multilevel test and design procedure for polymer gears

Abstract This paper presents a new accelerated testing procedure for plastic gears that is based on several different levels of testing. The iterative testing procedure fulfils requests from the product development process. The following criteria are considered for testing: reduced number of tests, shorter test time and reliable results for different applications. The proposed method was applied over the full range on a gear pair made from polyacetal (POM) and polyamide 6 (PA6). Different rotational speeds and torque loads, and therefore different transferred powers, were used for testing. During testing, gear temperature and cycles to failure were monitored. The paper also includes a comparison between the measured and theoretically calculated gear temperatures. A prediction of the life span on the basis of statistical methods is a part of the proposed test procedure. The presented procedure enables testing within acceptable cost and time consumption limits. The testing method can be reproduced and applied to plastic gears from different materials. Testing has shown that polymer gears fail in two typical ways: by fatigue and by sudden melting. The wear fail mode can be avoided by using an appropriate material pair. Fatigue can be measured by life span tests and is predictable. However, the melting of gears, which is a consequence of high gear temperatures, is not easily predictable. In most cases, melting failure mode occurs during the first few hours of gear testing. For reliable and optimal gear design, gear testing cannot be avoided because the tribological interaction between gears is specific for each combination of materials.