Deterministic Modeling of a Rotary Lip Seal with Microasperities on the Shaft Surface
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The rotary lip seal is the most widely used dynamic seal. It is used extensively in the automotive and appliance industries. Experimentally, it is well known that the microasperities on the shaft surface can significantly affect the performance of a lip seal, even though the shaft roughness, after run-in, is much smaller than the lip roughness. In the present study, several deterministic numerical models are developed to investigate the effect of shaft surface finish on rotary lip seal behavior, through an understanding of the basic physics of lip seal operation. This project is performed in a step by step manner with gradually increasing complexity. Four models are included in this study: hydrodynamic analysis, elastohydrodynamic analysis for full film lubrication, mixed-EHL model for mixed lubrication with asperity contact, and transient dynamic mixed-EHL model for startup and shutdown processes. Those analyses allow the examination of some important seal characteristics, such as the load support sharing between hydrodynamic and contact pressure, contact and cavitation area ratio, reverse pumping rate, liftoff speed for tracing the liftoff process and average film thickness. The development of fluid, contact and cavitation areas as a result of the changing operation condition is also examined. The results of the present deterministic modeling indicate that shaft surface roughness can produce significant desirable effects on lip seal behavior. An appropriate shaft surface profile could improve the sealing ability and prevent seal failure.