Development of non-asbestos organic based composite brake lining compositions for railway vehicles

In this study, it is aimed to develop new K-type composite brake lining (pad) compositions with and without hexagonal boron nitride (h-BN) for railway vehicles with a bottom-up approach. In this context, tribological tests were performed in two stages. In the first stage, the samples were subjected to intermittent and continuous braking tests according to NF F 11-291 standard with using a pad-on-disk type brake pad material testing system. First of all, fiber (rock wool), friction modifier (CNSL), resin and steel fiber content optimization has been made on the starting brake pad material composition and an optimum brake pad composition without hexagonal boron nitride (h-BN) has been developed in terms of property outputs. The effect of different amount of h-BN on this composition was investigated with the same approach. In general, increasing the amount of rock fiber in the matrix decreased the average coefficient of friction of the samples, while improved the stability of the friction coefficient. The subsequently added cashew nut shell liquid (CNSL) improved the wear resistance of the sample and decreased the friction coefficient value. Decreasing the content of phenolic resin in the matrix structure increased the friction coefficient while it affected the mechanical properties of the samples adversely. On the other hand, adding the steel fiber to the structure increased the thermal conductivity and friction coefficient of the sample and decreased its hardness and compressive strength. The 1.5 % h-BN ingredient (BN-2) that was added on this developed composition (SF-3) was determined as the best composition giving the optimum properties. At the final stage of the study, full-size brake linings were produced from these optimum compositions and the samples extracted from them were subjected to low-scale (1/10) dynamometer tests to verify the results obtained from pad-on-disk based studies.