Frictional performance of semimetal brake lining for automobiles

Purpose - The purpose of this paper is to find the variations of brake lining's frictional performance with braking conditions, and their influence on the braking safety and reliability of automobiles. Design/methodology/approach - As the semimetal brake lining is widely used currently in automobiles, it was selected as the experimental material. By simulating the braking conditions and environment of automobiles, some tribological experiments of the brake lining were investigated on the X-DM friction tester, when it is paired with the friction disc made of gray cast iron. The influence of braking pressure, sliding velocity and surface temperature on the friction coefficient and its stability coefficient were studied in depth through experiments. Findings - The friction coefficient decreases gradually with the increasing of braking pressure and sliding velocity when the surface temperature is naturally rising. It rises first then falls with the surface temperature rising and the maximal value appears at nearly 200 degrees C. The stability of friction coefficient decreases obviously when the sliding velocity exceeds 30 m/s, the braking pressure exceeds 1.8 MPa and the surface temperature is over 200 degrees C. Based on the experimental results, the authors consider that it is not reliable to execute an emergency braking only by rising the braking pressure when the automobile is driving with a high velocity. In order to reduce the bad influence of high temperature on frictional performance, some effective actions should be taken for cooling the friction disc. What is more, special attention should be paid to the decreasing of frictional stability during the braking with high velocity, pressure and temperature. Originality/value - This paper studies the influence of braking conditions on friction coefficient and its stability of the semimetal brake lining for automobiles. It is believed that this research may have some actual guidance for enhancing the braking safety and reliability of automobiles.