Tribochemical Wear of Rail Steels Lubricated with Synthetic Ester-Based Model Lubricants

Headchecks are a common type of damage in heavily loaded curved freight tracks. This paper deals with synthetic ester formulations' ability to prevent damage caused by headchecks through mild tribochemical wear. An experimental study pertaining to wear and friction of two rail steels lubricated by two synthetic ester base fluids, TMP-oleate and TMP-C₈-C₁₀, has been carried out. Six different free fatty acids were used in this study to act as performance additives. Three of the fatty acids were mono-acids with different, straight, carbon chain lengths (stearic acid C₁₈, decanoic acid C₁₀ and octanoic acid C₈), one was a mono-unsaturated straight-chain fatty acid (oleic acid C_18:1) while two were dibasic acids with intermediate carbon chain length (C₉ and C₁₀). Each fatty acid was blended with either ester, one at a time. The tests were carried out by using a high frequency reciprocating friction and wear test machine. In these tests, the gage face/wheel flange contact was simulated, and all tests were conducted in the boundary lubrication regime. An initial contact pressure of 316 MPa and a maximum sliding speed of 0.11 m/s were employed during the tests. The tests showed a wide range of wear rates, as well as different surface features depending on the interactions between synthetic esters, fatty acids and steel. The use of stearic and azaleic acid in lubricating rail steels results in very smooth surfaces with significant differences in their wear rates.