Study of the Correlation Between Theoretical and Actual Gear Fatigue Test Data on a Polyamide

摘要

DSM Engineering Plastics is a producer of nylon plastic materials used for gears. In the past two years, they have been running fatigue tests on actual molded gears in order to provide design data. This experiment used spur gears that are fully lubricated and temperature controlled. Testing for the materials has been done at DSM Research, while the gear tests are being conducted at the University of Berlin. The purpose of the testing is to see if there is a good correlation between fatigue data, generated on test bars, versus the actual fatigue performance in a gear. In order to do this, the theories of gear calculations to get root stresses also had to be examined. Advanced FEA showed that there are corrections needed to account for high loading or high temperatures in plastic gears. This corroborates other work within the industry. With proper corrections to get accurate root stresses, there can be shown good correlation between tensile bar fatigue and actual spur gear fatigue. The chemistry of various nylons used in gears is explained. A high crystalline nylon has been found which is an excellent material for gears in demanding applications and can withstand high torques and operating temperatures. The material has a crystallinity of 70%, which results in very good wear properties and excellent retention of mechanical properties (strength, stiffness, and fatigue) especially at elevated temperatures. Several commercial gear applications are currently utilizing these properties. These will be shown to demonstrate the benefits and manufacturability of this material.