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TECHNICAL PAPERS

A Low Friction Bearing Based on Liquid Slip at the Wall

[+] Author and Article Information
J. H. Choo

Mechanical Engineering Department, Imperial College London, London SW7 2BX, UKjianhuei.choo@imperial.ac.uk

R. P. Glovnea

School of Engineering and Design, Brunel University, Uxbridge, Middlesex UB8 3PH, UK

A. K. Forrest, H. A. Spikes

Mechanical Engineering Department, Imperial College London, London SW7 2BX, UK

J. Tribol 129(3), 611-620 (Jan 08, 2007) (10 pages) doi:10.1115/1.2736704 History: Received May 25, 2006; Revised January 08, 2007

In recent years it has been shown experimentally by a number of workers that simple, Newtonian liquids can slip against solid surfaces when the latter are both very smooth and lyophobic. It has also been shown theoretically how, based on a half-wetted bearing principle, this phenomenon may be used to significantly reduce friction in lubricated sliding contacts and thus make possible the hydrodynamic lubrication of very low load contacts. This paper describes the experimental validation of this concept. A low load bearing is constructed and the influence of surface roughness and the wetting properties of the surfaces on friction are investigated over a wide range of sliding speeds. It is shown that liquid slip can be used to considerably reduce friction in full film, hydrodynamic conditions.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of tribometer

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Figure 2

Closeup of contact between a Pyrex glass roller and upper stationary flat sapphire

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Figure 3

Measured friction force versus sliding speed for hexadecane with smooth, uncoated sapphire flat.

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Figure 4

Stribeck curves for hexadecane with smooth, uncoated sapphire flat (u1=sliding speed, η=dynamic viscosity, WL=applied load per unit length)

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Figure 5

Hydrodynamic regime chart for line contact showing range of conditions used in current work (for u1=0.5–2.5m∕s) as a shaded rectangle

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Figure 6

Calculated minimum hydrodynamic film thickness for hexadecane

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Figure 7

Calculated Poiseuille and Couette shear stress profiles across midline of contact from inlet (left) to exit, for u1=1m∕s, W=0.1N

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Figure 8

Comparison of measured and calculated hydrodynamic friction coefficient for hexadecane with smooth, lyophilic sapphire

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Figure 9

Influence of inlet meniscus distance on friction coefficient for hexadecane with smooth, lyophilic sapphire

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Figure 10

(a) Influence of lyophobicity and roughness of sapphire on friction coefficient for hexadecane, 0.1N load; (b) influence of lyophobicity and roughness of sapphire on friction coefficient for hexadecane, 0.2N load; and (c) influence of lyophobicity and roughness of sapphire on friction coefficient for hexadecane, 0.3N load

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Figure 11

Schematic diagram showing thin film of fluid between two, parallel solid surfaces

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Figure 12

Comparison of measured results for smooth, coated sapphire with half-wetted bearing slip theory with τco=30N∕m2, b=4μm

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Figure 13

Influence of slip (τco=30N∕m2, b=4μm) on calculated minimum film thickness

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Figure 14

Influence of slip (τco=30N∕m2, b=4μm) on calculated Poiseuille shear stress

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Figure 15

Influence of slip (τco=30N∕m2, b=4μm) on calculated Couette shear stress

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Figure 16

Influence of slip (τco=30N∕m2, b=4μm) on calculated velocity profile. The moving surface is at z=0, and the stationary one at z=1 (the two no-slip cases are superimposed)

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