Surface analysis of the elastomer in lip seals run against shafts manufactured with micro-cavity patterns

Abstract

Radial lip seals are used to retain lubricants and to prevent external contamination. When running against a plain stainless steel shaft, it is generally accepted that the micro-asperities that are developed on the lip seal elastomer by the shaft surface characteristics are responsible for the sealing mechanism in the form of reverse pumping. In this study, lip seals are tested against conventional stainless steel shafts and shafts manufactured with deterministic triangular micro-cavities of different orientations. Comprehensive surface characterization and wear ana-lysis are done using a scanning electron microscope and an optical profilometer to investigate the elastomer micro-asperities and shaft micro-cavities. Surface parameters are computed from the lip seal wear track of both the initial (before testing) and final (after testing) shaft surface. The lip seal elastomer surface wears away depending on the surface characteristics of the shaft. Previous work has concluded that incorporating surface textures on the shaft surface allows for control of the pumping direction through the seal but that the magnitude of that pumping rate has a large variability even for identical shaft surface textures. This study finds that this large variability may be due to the large variability in the elastomer sealing zone surface characteristics that develop due to wear over time. This study also confirms the previous results showing that the deterministic surface textures manufactured on the shaft surface dominate the lip seal pumping direction in spite of the large variation in the elastomer surface. Finally and most interestingly, this study finds a correlation between the axial location of the smoothest portion of the lip seal elastomer and the pumping rate of the lip seals.