Direct measurements of grease film thickness in a rolling bearing using a novel sapphire bearing rig with optical interferometry
Author(s)
Kadiric, Amir
Liang, He
Lugt, Piet M
Type
Journal Article
Abstract
This paper reports direct measurements of lubricant film thickness in a radially-loaded grease-lubricated model rolling bearing. These measurements are performed on a recently developed set-up, termed the Sapphire Bearing Rig, which allows for direct observation and measurement of film thickness in a single ball-outer ring contact in a rotating bearing using optical interferometry. Measurements are made with a selection of greases covering different base oils and thickener types. The results show that starvation occurs as the bearing speed increases. This is confirmed by observations of the inlet meniscus. The bearing speed at which starvation occurs is determined by grease properties, particularly the base oil viscosity. When the bearing operates for a prolonged time at a constant speed, as is usually the case in practice, the initial film thickness is seen to decay in the first few hours of operation, to eventually reach a steady state value that is lower than that predicted by elastohydrodynamic lubrication (EHL) theory. For conditions tested here, this steady-state film thickness was largely independent of bearing speed, which suggests that it is mainly governed by the level of lubricant supply in the inlet. Such film behavior clearly cannot be predicted using the standard EHL theory. Stopping the bearing for a sufficiently long time leads to a temporary recovery of the film thickness upon restart. These measurements provide new insights into grease lubrication mechanisms of rolling bearings and can aid the development of new tools for improved prediction of grease film thickness in rolling bearings.
Date Issued
2025-01-02
Date Acceptance
2024-11-26
Citation
Tribology Transactions, 2025, 68 (1), pp.194-205
ISSN
1040-2004
Publisher
Taylor and Francis Group
Start Page
194
End Page
205
Journal / Book Title
Tribology Transactions
Volume
68
Issue
1
Copyright Statement
© 2025 The Author(s). Published with license by Taylor & Francis Group, LLC. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way. The terms on which this article has been published allow the posting of the Accepted Manuscript in a repository by the author(s) or with their consent.
Identifier
10.1080/10402004.2024.2436097
Subjects
BEHAVIOR
CONTACTS
ELASTOHYDRODYNAMIC LUBRICATION
elastohydrodynamic lubrication (EHL)
Engineering
Engineering, Mechanical
grease
Rolling bearings
Science & Technology
Technology
Publication Status
Published
Date Publish Online
2025-01-08