Influence of increasing amount of attapulgite on the performance properties of Cu-free brake-pads

Copper is almost inevitable functional filler in the brake-material and efforts to replace it are continuing since it is now known as a hazard to the aquatic life. It is always desirable to search for ingredients for Cu-free brake-pads, which will be beneficial for friction-related properties and especially fade resistance. Attapulgite, is a mineral which was proven to be an excellent substitute for asbestos in brake-pads long back. However, hardly anything in details is reported on its exact role in controlling tribo-properties of friction materials (FMs). It was of interest, if it can be helpful in enhancing the performance of Cu-free FMs. Hence, in this work a series of brake-pads (five types) was formulated and developed with increasing amount of attapulgite (0, 5, 10 and 15 wt. %) by compensating with inert barite particles in Cu-free FMs. The parent composition was fixed and instead of Cu powder, 10 wt.% stainless steel powder was used. One more type of pads was also developed containing Cu and attapulgite (10 wt. % each) just to compare its performance with that containing 10 % stainless steel powder and attapulgite, (10 wt. % each) keeping every other ingredients in parent composition as constant. The pads were characterised for physical, chemical and mechanical properties. The tribological characteristics were evaluated using full-scale inertia dynamometer as per JASO-C-406 standards under dry condition. The results revealed that the attapulgite exhibited slightly lubricating properties by reducing average μ with increasing amount. However, it helped to increase the wear resistance to small extent, but at the cost of deterioration in some beneficial properties such as fade resistance, fluctuations in μ. Overall, its inclusion in Cu-free brake-pads did not prove beneficial as expected.