A study on fundamental water lubrication characteristics of flat thrust bearing with partial water-repellent regions

Abstract

The water lubrication characteristic of partial water-repellent (slip) type flat thrust bearings was examined. In this bearing, water-repellent (slip) regions and hydrophilic (non-slip) regions were alternately arranged in the slip direction, and the pressure to support the load was generated by discontinuity of shear flow rate in both regions. The measured pressure in slip direction increases in the water-repellent region and then decreases in the hydrophilic region, and it increases in proportion to the load. The fundamental lubrication characteristics of this bearing were considered based on the infinite-width bearing approximation theory that can explain the experimental tendency. On bearing surfaces with large slip length, the shear flow rate increases and a high pressure is generated, resulting in a large load capacity. However, the influence of pressure flow that suppresses the slip of shear flow increases, and the degree of increase in load capacity with increase of the slip length becomes low, under the condition of large slip length and thin film. On the other hand, the film thickness increases and the velocity gradient on the slip surface decreases under the same load for large slip length bearing, so the frictional force tends to decrease. However, the difference in friction force due to the difference in slip length is not remarkable. Since the degree of increase in frictional force is lower than that in load capacity in case of decreasing film thickness, the friction coefficient decreases with decreasing film thickness. Especially, a sudden decrease of friction coefficient is shown in the thin film region. Since the effect of slip on frictional force is also small, the difference in friction coefficient due to the difference in slip length decreases as the film thickness becomes thinner. The slip effect in this bearing acts to improve the bearing characteristics.

Keywords

• slip flow
• water-repellent
• thrust bearing
• pressure distribution
• water lubrication