INVESTIGATION OF WEAR CHARACTERISTICS OF CONICAL DELRIN THRUST BEARINGS
Mirbagheri, Seyed Ehsan
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This study focuses on the wear rate in conical thrust bearings, which is responsible for field failures of stepper motors in optical disk drives (ODD). These bearings support the stepper motor worm shaft and consist of a steel ball supported in a polymer conical bearing cup. The tribological behaviors of polymers used in bearing application has been addressed by using Archard's wear model, a well known classical model for fretting wear in the literature. However, these studies were for planar bearing surfaces and other geometries, not for the conical geometry addressed in this study. Tests were designed and implemented to study the wear rate of the conical bearing cups at with different load levels. The tribological behavior of Delrin in conical thrust bearing applications has been characterized, by quantifying the wear factors used in the modified Archard's model. Distinct reduction of wear rate is observed due to formation of a polymer transfer film on the steel ball. The variability of the wear properties is explored through replication of the test conditions. Destructive physical analysis is conducted to gain insight into the fundamental wear mechanisms as a part of this study. The results of the wear tests are used to develop a life model of the stepper motor as a case study, to demonstrate an application of this approach. The life model is used to study the effect of variability in the initial axial bearing preload (due to manufacturing tolerances), on the wear rate and life of the stepper motor.