Research Papers: Lubricants

Free Surface Thin Layer Flow on Bearing Raceways

[+] Author and Article Information
M. T. van Zoelen, C. H. Venner

Department of Engineering Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands

P. M. Lugt

 SKF ERC, P.O. Box 2350, 3430 DT Nieuwegein, The Netherlands

J. Tribol 130(2), 021802 (Apr 07, 2008) (10 pages) doi:10.1115/1.2805433 History: Received June 21, 2007; Revised September 19, 2007; Published April 07, 2008

In this paper, the effects of rotation on the distribution of a layer of oil on a bearing raceway are analyzed in relation to the geometry of the raceway. The research is motivated by the need to understand the behavior of grease lubricated bearings. Some specific aspects of grease lubrication can be understood by approximating the contact as a starved lubricated elastohydrodynamic lubrication contact. In such a contact, the shape and thickness of the inlet layer of oil, supplied to the contact on the running track, are of crucial importance to the film formation and contact performance. Small changes in the distribution of lubricant on the rolling track, as a result of reflow or redistribution, may have a large (local) effect on the film thickness inside the contact. Starting from the Navier–Stokes equations, the free surface thin layer flow equation for axisymmetric rotating surfaces is derived. For the case of bearing applications, it is shown that a simple quasilinear equation can be derived for the layer thickness, as a function of location and time, which can be solved analytically. Experiments have been carried out, measuring the changes of a layer of oil on rotating raceways in time in relation to the rotational speed and the raceway geometry. It is shown that the simplified model accurately predicts the thin layer flow, except in a region near the outflow boundary, where the effect of the boundary condition on the layer shape is crucial. This is further illustrated by results of numerical simulations.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Typical configuration of a thin layer with free surface on a surface of revolution and a suitable coordinate system for its description

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Figure 2

Parametrization of the inner raceway of a taper roller bearing

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Figure 3

Solution for the film thickness h on a tapered raceway, starting with a uniform liquid layer, b=0.6

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Figure 4

Parametrization of the inner raceway of a spherical roller bearing

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Figure 5

Solution for the film thickness h on a spherical raceway, starting with a uniform liquid layer, L∕R=0.2 and β=0.5

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Figure 6

Tapered bearing inner raceway mounted on a rotating shaft. The markers indicate locations where layer thickness is measured using the surface profiler.

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Figure 7

Results of the oil layer thickness for different rotation speeds on a tapered surface Type I: 500rpm, 1000rpm, and 2000rpm, respectively. The colored striped lines are measured values. Black lines are calculated by the model. Kinematic viscosity of the oil: ν=1367×10−6m2∕s.

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Figure 8

Results of the oil layer thickness on the tapered raceway Type II, which rotates with 1000rpm. Kinematic viscosity of the oil: ν=1556×10−6m2∕s.

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Figure 9

Results of the oil layer thickness on the spherical raceway rotating at 1000rpm. Kinematic viscosity of the oil: ν=1620×10−6m2∕s.

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Figure 10

Numerical (solid) and analytical (dashed) solutions of thin layer flow of a spherical raceway

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Figure 11

Solution of the layer thickness calculated on various grid and time step sizes



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