Shaft surface texture plays a very important role in rotary oil seal system performance. Functionally, the shaft surface has to prevent oil leakage via pumping between the shaft and seal. The shaft surface texture must also provide adequate contact with the seal lip, while maintaining a lubricant film. Furthermore, the initial surface texture of the shaft plays a vital role in the process of oil seal lip break-in. The shaft surface finish specification is typically Ra, 10 to 20 μ″ with a 0° ± 0.05°lead angle.
The paper will describe a new surface measurement method based on interference microscopy, which generates a visual representation of a significant portion of the shaft surface texture to allow direct lead angle detection. Using this new technique, this paper will demonstrate the heredity of lead generation.
The shaft 3D surface texture measurement also provides a measure of the surface volume available for lubricant retention. The surface volume is expressed as the Normalized Oil Volume (NOV) in units of ‘billions of cubic microns per inch squared (BCM)”. Qualitatively, NOV is the amount of volume the surface provides per unit area for lubricant retention. We found that for the seal systems presented here, a NOV of about 0.5 BCM is required for adequate life performance.