Friction and wear performance of nickel and molybdenum-reduction cast iron composite brake blocks including ceramic foams

Abstract

High speed trains in the northern area of Japan use alloyed cast iron brake blocks including nickel (Ni) and molybdenum (Mo). Reducing the Ni and Mo contents of the alloyed cast iron brake blocks would be beneficial because they are rare metals with variable prices. Ni and Mo play important roles in increasing the friction coefficient and decreasing the wear of brake blocks at high speeds. Brake blocks with reduced contents of these metals must maintain a sufficient friction coefficient and wear characteristics at high speeds. Cast iron composite brake blocks with reduced Ni and Mo contents were prepared using two types of alumina: aluminum titanate and silicon carbide foams to maintain the friction coefficient and decrease the wear characteristics at high speeds. These blocks were tested on a full-scale dynamometer, and the friction and wear performance of one of the best performing blocks were tested under real operating conditions. The friction coefficients of all reduced Ni, Mo cast iron composite brake blocks were higher than those of conventional blocks at high speeds. The wear of the reduced Ni, Mo cast iron composite brake blocks containing alumina blended with aluminum phosphate (AlPO4) foam was significantly decreased as compared with that of conventional blocks. Under real operation, the friction coefficients of conventional and reduced Ni, Mo brake blocks were similar under normal braking conditions, but those of conventional brake blocks were lower than those of the reduced Ni, Mo blocks under emergency braking conditions. The lower friction coefficient of conventional brake blocks under emergency braking conditions is likely caused by the adhesion of wear particles to the wheel tread. While the wheel tread was not worn by conventional brake blocks, it was worn by the reduced Ni, Mo blocks under emergency braking conditions.