Disc Brake Noise Reduction Through Metallurgical Control of Rotor Resonances

The mechanical properties of a gray cast iron disc brake rotor are directly influenced by the amount and morphology of the graphite present throughout the rotor. Two of these properties, the modulus of elasticity and the damping capacity, can have a significant effect on the propensity for the disc brake rotor to produce noise. The noise propensity of a disc brake is in a large part determined by the relationship between the rotor resonances and the resonances of the other brake components such as the pads. In this paper, we are concerned only with the effect that modulus of elasticity has on disc brake noise through its influence on rotor resonances. The amount and morphology of the graphite in gray cast iron is determined by the carbon content and silicon content of the iron. The carbon and silicon content are measured by one parameter called the carbon equivalent. For gray cast iron the relationship between carbon equivalent and modulus of elasticity is almost linear for the grades used in disc brake rotors. This relationship allows the modulus of elasticity and, in turn, the rotor resonances and resulting brake noise to be influenced by the carbon equivalent of the rotor. A case study showing the effectiveness of controlling rotor resonances through carbon equivalent to reduce brake noise is presented. The subsequent effect of foundry process control on brake noise propensity is also evaluated.