Full-Scale Dynamometer Tests of Composite Railway Brake Shoes: Effect of the Resin-Rubber Ratio on Friction Performance and Wear

Designing a friction material for a brake system entails considering the effects of each constituent and the interactions that they may present between them. In the present work, a characterization of the influence of the resin-rubber ratio in a brake block material is carried out. Railway brake shoes were produced and tested in a full-scale railway dynamometer in demanding conditions. The brake blocks had also their physical and mechanical properties tested. The progressive addition of resin was proven to heavily affect the friction level in dry and wet conditions. Interestingly, the use of 5% of resin showed significantly higher friction in wet conditions. This composition also presented a more severe metal pick-up. The nature of the binder also affected wear-rates (which were lower for lower resin contents) and the wear mechanism. The sample using only rubber presented thermal cracks and heavier delamination as specific failure modes. Differences in the microstructure of the friction materials were observed depending on the binder. About 5% of resin appears as a very interesting choice to avoid friction loss in wet environments without incurring high wear-rates, as long as metal pick-up is diminished by different means. Otherwise, 100% of rubber as a binder grants the instantaneous friction stability that is often threatened by thermal fade.