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©2012 Civil-Comp Ltd |
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F. Abate, V. D'Agostino and R. Di Giuda
Department of Industrial Engineering, University of Salerno, Fisciano (SA), Italy
Keywords: parallel thrust bearing, surface texturing, friction coefficient.
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The aim of the work described in this paper is to provide an effective numerical tool to examine through a parametric analysis how texture might influence tribological characteristics in a mixed lubrication regime.
A simplified geometrical model of a single pad in the form of a rectangular parallel slider is considered in this paper. It is well known, in fact, that each pad, when properly textured, develops the same hydrodynamic force. Hence, in order to evaluate the load carrying capacity of the complete parallel thrust bearing it is sufficient to determine the hydrodynamic pressure distribution over a single pad. The Reynolds equation in two-dimensional form, that governs the problem studied is applied to problems in finite geometry, does not permit exact analyticalsolution but requires a resolution of the numerical type. Moreover, obtaining the solution is further complicated by the equation of balance of the loads arising from both the fluid and the multi asperity contacts. Furthermore, the discretization with a fixed grid has led to large numbers of nodes, in order to reconstruct with accuracy the pressure distribution inside the cavities.
Therefore a numerical study of a thrust bearing with a series of dimples created on the stationary surface was carried out in order to evaluate the influence of the texture parameters. Simulations were performed varying the parameters of, width, depth and density of the dimples. The results obtained are presented in terms of pressure distribution, friction coefficient, minimum film thickness and load carrying capacity.
The main conclusions that can be drawn are:
- the partial laser texturing seems to be much more suitable than the full laser texturing to the formation of a pressure that can support external loads
- the existence of dimples on the steel surface was observed to reduce the friction coefficient substantially, when compared with un-textured surfaces
- the positive effect of the dimples does not depend linearly by their number; the dimple influence is affected by working conditions and the width of the dimples
- one of the key parameters appears to be the aspect ratio, it is not possible to uniquely identify an optimum value as this depends on the mutual distance between the dimples
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