Influence of Particle Size of Graphite on Performance Properties of Friction Composites

Non-Asbestos Organic (NAO) brake- material research has been significant in the last decade in an attempt to replace the conventional semi-metallic and asbestos based materials. Influence of ingredients in this multi-ingredient (generally 10-25 in different proportions) system on performance properties, however, is still not thoroughly researched area because of complexity involved and needs intensive efforts to understand this aspect. Graphite is one of the most important and almost inevitable ingredients in friction materials. A wide variety of graphite varying in origin, particle size, crystallinity, thermal conductivity etc. is used by the industry. An in-depth and systematic study on the influence of size of graphite on tribo-performance, however, is not available. Hence in this work, graphite of three different particle sizes (460, 130 and 20 μm) having same crystallinity range (≈75%) was used to develop three friction composites using other conventional ingredients and straight phenolic resin as a binder in identical proportion. The studies conducted on Krauss machine for their fade & recovery performance as per ECE R90 regulation indicated that all friction performance parameters showed strong dependence on the size of graphite. Moderate sized particles proved best performer from friction point of view but not from wear point of view.