Avaliação do desempenho tribológico de graxas e modificadores de atrito a base de água utilizados no contato roda-trilho em um ensaio disco sobre disco

Abstract

The tribological phenomena on the wheel-rail interface is complex. This interface performance regarding friction and wear impacts fuel consumption, wheels’ and rails’ lifespan, which are among the highest operating costs on a railway. The total friction management aims to apply greases and water-based friction modifiers to this interface to improve performance. Comparing performance between different greases and between different friction modifiers in the field is costly and challenging due to the variety of uncontrollable parameters, time to obtain results, operating difficulties. Besides this, there is a gap in correlations between these products datasheet properties and their field performance. Therefore, in this work, greases and friction modifiers were analyzed in exploratory laboratory tests to find properties that might represent these products’ performance in the field and analyzed in a twin disk test rig, reproducing the rolling and sliding conditions of the wheel-rail contact. The methodology consisted of verifying the effect of grease formulations (base oil viscosity and type of thickener) concerning friction; wear by RCF crack propagation, and retentivity. While the friction modifier formulations (the composition of the solid film formed after water evaporation) only for friction and retentiveness. The conclusions for greases analyzed were: i) for low values of specific film thickness (Λ), the friction coefficient and crack propagation wear are highly dependent on the thickener type, both of which increase for Calcium thickener and decrease for the Lithium thickener; ii) for high values of specific film thickness (Λ), the friction coefficient and crack propagation wear are controlled by the base oil viscosity; iii) retentivity is controlled by the viscosity of the base oil regardless of the value of the specific film thickness or the type of thickener. The friction modifiers’ conclusions pointed out that friction and retentivity were similar regardless of the formed solid film’s composition.