Experimental characterization of the tribological behaviour of railway brake shoes with a scaled twin-disc rig

European regulations are thrusting the replacement of traditional cast iron brake shoes with new composite materials, aiming to reduce rolling noise. Nonetheless, composite materials exhibit different tribological and thermal properties with respect to cast iron shoes. This paper aims to investigate and map the wear and frictional behaviour of a K-type composite shoe and compare it with a traditional cast iron shoe. Experimental tests are performed with a dedicated scaled twin-disc rig, which follows Pascal's similitude rule. Tests are run under drag braking conditions exploring a wide range of real-word speed and contact pressure conditions. The collected data is used to tune a power-law analytical model for the calculation of a proportionality coefficient, depending on speed and contact pressure, that relates the amount of worn material to the dissipated energy. The results of the experimental campaign show that the volume rate of the K-type material is approximately 10.5 times lower when compared to cast iron, hence improving the lifetime span of composite shoes. For both materials, the wear rate increases with increasing contact pressure, while an opposite behaviour is obtained with respect to speed: with increasing speed, wear of the cast iron shoe tends to decrease, while wear of the composite material becomes higher. Concerning friction, it is found that the composite material has a more stable behaviour with low dependency on speed and pressure, while the coefficient of friction of the cast iron shoe has a wider variation range.