Film Thickness Model for Grease-Lubricated Bearing Seals with an Axial Contacting Lip

A theoretical model is presented to predict the oil film thickness in an axial sealing contact based on grease properties and operating conditions. It is assumed that a small amount of grease will form an oil reservoir on the rotating part and slowly supply oil to the sealing contact. The oil bleed model from a previous study is implemented and oil loss due to centrifugal forces and the seal pumping action are taken into account. The results show that, depending on the operating conditions, an oil film is present in the sealing contact for a certain period of time. The oil film thickness decreases in time due to the decreasing oil supply from the grease reservoir and oil loss from the contact due to centrifugal forces. Seal pumping has only a small effect and the seal material and geometry are therefore not important for the predicted time until the mixed lubrication regime is reached. This time depends on the oil viscosity, rotational speed, and seal contact radius and scales with the η /(n2·ds) parameter. The volumetric size of the grease reservoir also has a large impact on maintaining the film thickness in time.