Although alloyed cast iron brake shoe feature low aggressiveness against wheels and high adhesion force, it doesnft have enough friction in high-speed range. To cope with further speed increase of rolling stock, cast iron composite brake shoe is developed, that guarantee stable adhesion force and braking power in high-speed range.
Cast iron composite brake shoe is the conventional alloyed cast iron type inserted with silicon carbide filters (Fig. 1). These take advantage of the fact that the friction coefficient increases when silicon carbide particles are present between the surfaces of the wheel and the brake shoe. In brake shoe manufacture, silicon carbide filters were used to filter oxide in molten cast iron. It was found by chance that these filters adhered to the alloyed cast iron brake shoe more strongly than with the method used to compound particles or to embed block of silicon carbide.
Since silicon carbide is substantially harder than alloyed cast iron, it would generate excessive friction or thermal cracks in quantity on the wheel tread. To prevent this problem, filter with improved roughness were appropriately arranged on the friction surface to make the ratio of the silicon carbide surface approximately 1% or less. As a result, the friction coefficient in high-speed range increased significantly while suppressing the aggressiveness against the wheels, even though the amount of wear is almost the same as that of conventional brake shoe (Fig. 2). The braking distance is cut to about 80% at an initial braking speed of approximately 130 km/h.
The manufacturing processes are almost the same as those for conventional brake shoe. Mass production is made possible by simple addition of minor processes to set filters and guide bars to fix their positions in the casting mold before molten iron is poured.
In a running test on a four-car train set in which one car was applied with the developed brake shoes, it is confirmed that the braking distance was shorter than that of a train only with conventional brake shoes, while the wheel temperature and amount of brake-shoe wear remained almost unchanged.