Optimal Design Of Surface Texture Based On Hydrodynamic Lubrication

Friction, to a great extent, affects the mechanical reliability, durability and the energy efficiency.Reducing friction in mechanical systems plays a very important role in changing lubrication state,saving energy source, and increasing repair circle and working life, which can also significantlyincrease economic benefit. In recent years, the surface texturing has been proven as a viable means toenhance the tribological performance of friction pairs. The optimum tribological performance can beobtained by choosing suitable textural parameters. In order to enrich the research on design of surfacetexture, the textural parameters, dimple shapes and dimple arrangements were systematically studied.At first, an analytical model was developed in hydrodynamic lubrication region based onRenolds equation to investigate the effect of surface textural parameters, dimple shapes and dimplearrangements on hydrodynamic pressure generation. Then, the textured surfaces were designedaccording to the analytical results. And the friction tests were carried out using a reciprocating frictiontest rig. The friction pair which the upper specimen face-to-face contacting with the lower specimenwas selected as the research object. The texturing method used in the study was the photoelectrolyticetching.The results obtained from the research about surface textural parameters showed that both thedimple depth to diameter ratio and the dimple area ratio are the factors affecting hydrodynamicpressure generation. The optimum dimple depth to diameter ratio and the optimum dimple area ratioare affected by minimum film thickness. The test results showed a good correlation with thoseobtained from the analytical model. In the research, the specimen with a dimple diameter of200μm，adimple depth of8~10μm, and a dimple area ratio of10.4%presents optimum friction reductioncompared with untextured specimen.The results obtained from the research about dimple shapes showed that dimple shapes alsoaffect the hydrodynamic pressure generation. Under the condition of having the same dimple area,same depth, and same area ratio, dimple shapes have an obvious influence on film load carryingcapacity. Among the dimple shapes of circular, square, and elliptical selected in the experimentalstudy, elliptical dimples that the major axis is perpendicular to the flow direction of the lubricantalways showed the best friction reduction compared with untextured specimen. The square dimplesperformed the second best, and the circular dimples showed the worst results. Under the condition oftest load200N and crank rotational speed400r/min, the biggest friction reduction ratio is26.7%for elliptical dimple,21.8%for square dimple, and18.3%for circular dimple.The results obtained from the research about dimple arrangements showed that changing therelative location between dimples also affects the hydrodynamic pressure generation. Suitable dimplearrangement can improve the friction reduction once again compared with the textured surfaces whichthe dimples were located at the four corners of a square. In the extent of the research, The dimplearrangement which the transverse interval between dimples to longitudinal interval ratio of1/3givesthe best increasing rate of friction reduction22.14%when the test load was200N and the crankrotational speed was400r/min.As a special form in dimple arrangements, partial surface texture was also studied. The resultsshowed that the tribological performance of partial surface texture is affected by the dimpleparameters, dimples location, and partial texture ratio. Only if the dimple area ratio is bigger than10%,the partial surface texture owns the better friction reduction than full surface texture. Of the inletpartial surface texture, outlet partial surface texture, middle partial surface texture, and the two-sidepartial surface texture, the inlet partial surface texture presents the best friction reduction effect. Underthe optimum partial texture ratio of70%, an increasing rate of friction reduction18.8%can beobtained when test load was200N and crank rotational speed was400r/min.The results obtained in the research provide a reference for the further research and applicationof surface texture.