Dimples shape and distribution effect on characteristics of Stribeck curve

A purpose of this research is to study the influence of geometrical characteristics of the surface texture on the Stribeck curve in lubricating sliding. The tribosystem consists of the stationary block pressed at the required constant load 1800 N against the ring rotating at the defined speeds. Tests were conducted at increasing sliding speed of range 0.08-0.69 m/s. Every speed was maintained for 2 min. The test was carried out under conformal contact conditions. The sliding was unidirectional. The block was a part of a bearing sleeve hardened EN-GJS 400-15 cast iron with a hardness value of 50 HRC. The ring samples, 35 mm in diameter, were made from hardened 42CrMo4 steel of hardness 32 HRC. Some variants of specimen surfaces were created by burnishing technique. The area density of oil pockets S was in the range 7.5-20%. The dimples depth to length ratios were between 0.03 and 0.08. Ring surfaces with oil pockets of short drop, long drop and spherical shapes were tested. It was shown that with proper shape and dimensions as well as suitable area density of oil pockets the friction characteristic of the sliding pairs could be improved in comparison to non-textured surfaces. (C) 2009 Elsevier Ltd. All rights reserved.