On Reciprocating Elastomeric Seals: Calculation of Film Thicknesses Using the Inverse Hydrodynamic Lubrication Theory

The elastohydrodynamic lubrication (EHL) problem of an axi-symmetric, elastomeric, reciprocating seal may be considered as one of a heavily loaded line contact with only small piezo-viscous effects. A method is presented to calculate the overall film thickness for the stationary, isothermal situation with sufficient lubricant supply and negligible surface roughness effects. It applies the inverse theory to the frictionless dry contact pressure distribution, considering the influence of the boosting action in the entry zone of the film. Its validity is shown for the isoviscous EHL of the Hertzian contact. The finite element method (FEM) may be used to calculate the contact situation of mounted and pressurized seals. Important aspects of such calculations are discussed. To calculate film thicknesses using such FEM results, a computer program PROGRES was written. Good correspondence between the predictions of PROGRES and experimental outstroke film thicknesses are obtained for a rectangular rod seal with rounded edges.