Influence of novolac phenolic resins and butadiene rubbers on airborne wear particles emission from train brake friction materials against steel brake discs with roughness of Ra2.5

Three train brake materials based on straight or resorcinol-modified novolac phenolic resin and nitrile or styrene-butadiene rubber were tested during pin-on-disc tribological tests. Each material was tested and retested at 9 different friction regimes with various contact pressure values (0.33, 0.66 and 1 MPa) and various sliding velocity values (0.6, 1.2 and 1.8 m/s). Each friction regime lasted 2 hours and was performed with a new pair of samples under constant contact pressure and constant sliding velocity. The decision to use a brake disc with a surface roughness of Ra2.5 was made on the basis of the previously obtained test results, where the emission of airborne wear particles increased with increasing surface roughness of the brake disc. The temperature near the sliding surface was measured using the Graphtec GL7000/GL7-HSV data logger. The concentration of airborne wear particles was measured using the  TSI Optical Particle Sizer 3330 and the TSI NanoScan SMPS Nanoparticle Sizer 3910 for particles of size 0.3–10 μm and 0.01–0.42 μm respectively.