On the Normal Stress Effect in Grease-Lubricated Bearing Seals

Abstract

The film formation in lip seals, due to the non-Newtonian rheology of the lubricant, has been a topic of speculation. Earlier work suggests that normal stresses in grease would be favorable for the film buildup between the seal lip and shaft or bearing ring. In the current article, we evaluate this earlier work and our earlier theoretical seal lip model with a series of experiments. We use a modified concentric cylinder geometry and a model fluid to study the fluid pressure distribution in the seal-type geometry. The results are then related to grease-lubricated seals and our earlier theoretical predictions. The present analysis shows that this earlier work and our earlier predictions are not correct and indicate that normal stresses in the grease pull the seal lip toward the shaft, increasing the contact pressure. However, normal stresses also ensure the presence of grease on the shaft or bearing inner ring, which enhances replenishment of the sealing contact.

KEY WORDS:

• Non-Newtonian Behavior
• Lip Seals
• Grease
• Normal Stress

This article is related to:

Non-Newtonian Effects on Film Formation in Grease-Lubricated Radial Lip Seals

ACKNOWLEDGMENT

The authors thank Professor R. F. Salant for bringing to our attention the error in our earlier work and for his contribution in revising the theory. The authors also thank Alexander de Vries, Director SKF Group Product Development, for his kind permission to publish this article.