Effect of lubricant degradation on the tribological performance of a wheel-rail system

Abstract

Abstrac: In this work lubricant degradation and its relationship with tribological behavior was studied. Commercial grease (Sintono Terra HLK) and three versions of a newly developed product (Tribolub) for the Metro system of Medellín city were studied. A twin-disc testing machine was used to evaluate the effect of degradation caused by either radiation or mechanical action on the tribological properties of the greases; also, a number of tests were carried out to learn about the changes in rheological properties of the greases. The results showed that tribological testing of degraded greases using a twin-disc machine and a subsequent viscometric analysis can be considered as a viable option to study performance of degraded greases used for wheel-rail systems. All the greases studied showed a decrease in their tribological performance after mechanical degradation in twin-disc testing machine, being the degraded Tribolub-3 the one that allowed obtaining lower values of friction coefficient and mass loss of the samples. Both mechanical and radiation-induced degradation led to a significant increase in the viscosity of the greases studied, especially for low shear rates. FTIR analyses showed that such response was mainly caused by chemical changes in the structure of the greases. Viscosity-time curves showed a rheopectic behavior at low shear rates for Sintono Terra HLK and one of the versions of Tribolub, which was related to the particle contents and the effect of thickeners. Wetting tests showed better wettability for Tribolub than for Sintono Terra HLK, both before and after degradation