Dynamic Tracking of Angular Misalignment in Liquid-Lubricated End-Face Seals

Abstract

End-face seals sometimes fail because the flexibly mounted face is unable to track the inevitable angular misalignment (relative to the shaft axis) of the fixed face, resulting in rubbing contact. It is important, then, that the critical amount of misalignment just to cause contact in a fully liquid-lubricated seal should be known so allowances can be made in the manufacturing and assembly tolerances. An analysis of dynamic tracking is presented for both common end-face seal arrangements. Expressions for critical misalignment are derived in terms of inertia, elastomer stiffness and damping, and fluid-film hydrostatic and hydrodynamic moment effects in the diametral tilt mode. Fluid-film effects are found to promote tracking, elastomer effects to resist. Tilt inertia resists tracking only for the flexibly mounted stator arrangement. However, as the inertia term is generally insignificant, this arrangement is preferred because, in practice, it is much easier to achieve good alignment of a rotating face fixed to the shaft than a stationary face fixed in a housing.