Optimization of steel wool contents in non-asbestos organic (NAO) friction composites for best combination of thermal conductivity and tribo-performance

Abstract

Thermal conductivity (TC) of friction composites plays a vital role in the performance of the composites. Low TC renders the tribo-surface vulnerable for degradation of organic ingredients and affecting the braking capability adversely. Too high TC, on the other hand, results in adverse effect on brake-fluid. The optimum TC as a result of tailoring the composite with right contents of metallic fillers is hence desired. However, hardly any in depth efforts are placed in this direction. Hence, in this work, three friction composites were developed using same ingredients in same proportion except steel wool and barite which were added in a complementary manner. The compositions containing 4, 8 and 12 wt.% of steel wool (and inert filler barite in 31, 27, and 23 wt.%) were developed as brake-pads and designated as S 1, S 2 and S 3, respectively. The brake-pads were tested for their friction and wear behavior on a Krauss type RWDC 100, 450 V/50 Hz machine in simulated braking condition against a cast iron commercial disc and evaluated as per ECR 90 test schedule. It was observed that with increasing metal contents, mechanical properties decreased, TC increased slowly and other important friction properties including fade resistance improved. Wear properties however, did not show any correlation with amount of steel wool, TC or mechanical properties. Overall, composite S 3 proved to be the best performer. SEM studies proved helpful in understanding the wear mechanism.