Optimized selection of metallic fillers for best combination of performance properties of friction materials: A comprehensive study

Metallic fillers are considered as very important and almost indispensible in non-asbestos organic (NAO) friction materials as they contribute to the performance properties in various ways. In spite of the awareness of the fact that their type, size, shape, amount, and combination control the performance of friction materials, hardly any systematic efforts are devoted in this direction. Authors in their earlier studies have highlighted some of the aspects in this area. The present paper has focused on very systematic and in depth investigations on these aspects by investigating the role of three different metallic fillers with variation in amount, shape, and size on the performance properties of NAO brake-pad materials. Two series of composites named P (powdery) and F (fibrous) were developed in such a way that the variation in metallic fillers was managed as; three types (copper, brass and iron) and three amounts (0, 10 and 20 wt%). Composites were characterized for physical, thermal, mechanical and tribological properties (on brake inertia dynamometer) as per the standard industrial practice. It is observed that the inclusion of metallic fillers enhanced the performance properties of composites significantly. Improved thermo-physical properties especially thermal conductivity of composites played an important role in the performance properties as copper powder based composites showed best tribo-behavior followed by brass and iron powder. In some properties 10% filler loading proved most promising while for others 20% proved beneficial. From shape point of view, powdery fillers had a clear edge over fibrous. Overall, 10% loading of copper powder proved promising in most of the properties, while composite without metallic fillers proved poorest.