A Comparative Study by Vehicle Testing of Copper Alloy and Gray Iron Brake Discs

Automotive friction materials are composites containing three kinds of components: an organic binder, fiber for reinforcement, and property modifiers. At low braking temperatures, the wear rate of the friction materials is controlled primarily by abrasive and adhesive mechanisms. At higher braking temperatures, the wear rate increases exponentially with increasing temperature due to thermal degradation of the binder and other components, and the exponential wear rate is frequently accompanied by brake fade. Thus, one method of reducing thermal wear and fade tendency is to lower the temperature at the rotor/friction material interface. Since the rate of heat transfer from the interface is mostly dependent upon the conductive and convective modes, a rotor of high thermal conductivity will have a significant advantage over a rotor of low conductivity, if the heat capacity remains the same. Therefore, brake discs made of chromium copper (99 Cu-1 Cr) were evaluated and compared with gray cast-iron discs. The thermal conductivity of chromium copper is six times greater than that of gray cast iron. The evaluation methods were dynamometer and vehicle (24,500 lb gvw) tests. In all cases, the copper alloy brakes were found to run substantially cooler than gray cast-iron brakes. The copper alloy brakes were more effective in terms of torque or deceleration at high temperatures, and showed substantially lower wear of the friction material as well as of the disc when compared with gray cast-iron brakes. The copper alloy discs used did not have any coatings on the surface.