The lubricant film developed in rotary lip seals is a vital element in achieving long-lasting seals with low friction. In this paper the basic principles controlling the development of a lubricant film in lip seals are studied using a micro-hydrodynamic model. This model takes into account the visco-elastic effects of the rubber on the development of the sealing pressure. Central to the model’s hypothesis is the assumption of the predominant action of the surface micro-geometry in the formation of the lubricant film. Optical observations of the contact area of a lip seal, using blue light induced fluorescence, supported this concept. Using this basic lubrication model, the minimum and average film thickness and shear stress are calculated for different loading conditions, material stiffnesses and statistical parameters characterizing the micro-geometry of the sealing surfaces. In the model the effect of the viscoelastic properties of the rubber on the dynamic response of the seal and resulting pressure is also considered. To support the predictions of the theory, a new experimental method for the determination of the film thickness in elastomeric contacts is applied. Comparison between experimental and theoretical results indicates the ability of the model to deal with effects previously excluded from the analysis. The correlation between measured film thicknesses and thicknesses predicted using the present model was found to be good for the full range of speeds tested.

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