Proper film thickness key to bearing survival

Document Type

Article

Publication Date

12-14-2006

Abstract

The various factors affecting the design of oil and grease-lubricated bearings are discussed. The design of oil and grease-lubricated bearings depend on lubricant film thickness for smooth and trouble-free operation. For full-film lubrication of journal and thrust bearings, the composite surface roughness parameter, A is above the range of 3 to 10. Misalignment, thermal, and elastic distortions can increase that to about 10 to 20. For lubricating precision-finish journal bearings with a low-viscosity fluid the value of A should be greater than 3. Shaft journals in industrial electric motors typically have an initial surface finish of 32 μin. surface. For journal bearings, a minimum film thickness can be estimated for small fluid-film thickness in the range of 0.5 to 20 % of the radial internal clearance. Load in ball and roller bearings is distributed on extremely small contact areas, while contact stresses elastically deform the surfaces to accommodate formation of an oil film.

Publication Source (Journal or Book title)

Machine Design

First Page

100

Last Page

105

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