The sealing mechanism of rotary shaft seals with reference to the elastomer deformation in the contact zone

In order that elastomer rotary shaft seals function correctly many conditions must be satisfied, especially in the zone defined as the contact band. The conditions are achieved by using the correct lip geometry, an appropriately formulated elastomer compound. and a suitable shaft surface structure. Various theories have been put forward to explain the sealing - or pumping - phenomenon and in some cases they have been shown feasible from experimental rig tests or computer simulations. There still, however, remains the question of whether a chosen model accurately defines the behavior of a rotary lip seal. Whatever theory is postulated it should account for the practical observations and accommodate the characteristics of the materials. Of relevance to the study presented in this paper is that existing theory which attributes sealing to the formation of a geometrical structure on the elastomer contact area. However, in contrast to the usual premise that the pumping structure is an inherent part of the contact surface created by the bedding-in process, it is proposed that the structure is transient, being created and destroyed solely due to the forces in the sealing area. In the analysis, instead of treating the elastomer as a bulk, the surface representing the contact band is considered to be a membrane. When this is subject to shear along the circumferential edges it undergoes deformation perpendicular to its original surface, and in particular produces waves. The waves are orientated depending on the direction of the applied shear forces and can thus provide effective pumping channels for both directions of shaft rotation, if certain conditions are met.