Mechanical face seals. Hydrodynamic and mixed lubrication

The article [BM 5 421] recalls the wide variety of arrangements and industrial applications of seals (the technical aspects of which are developed in articles [ [BM 5 425] and [BM 5 426] ) and presents the study of fluid flow between aligned surfaces separated by a stationary distance (hydrostatic lubrication). The fluid forces developing in the sealing interface and the leakage rate are determined in this case.

This article focuses on the lubrication regimes established between the surfaces of a mechanical seal when they are in relative motion, which is the normal operating mode of a dynamic seal. The hydrodynamic lubrication regime corresponding to the case where the surfaces are completely separated by a fluid film is first studied. The second part deals with the case where the fluid film is not thick enough to prevent contact between asperities. This is the mixed lubrication regime.

In some cases, approximations can be used to establish theoretical models with analytical or semi-analytical solutions that the design engineer can implement. In this article, we focus on these approaches, highlighting certain mechanisms and providing numerous examples.

This article also shows that in other cases, the previous approximations lead to imprecise or erroneous results. In such cases, a more in-depth theoretical approach is required, with the implementation of more complex dedicated calculation codes. The basic principles of these studies are briefly explained and their bibliographical references cited.