Influence of amount and modification of resin on fade and recovery behavior of non-asbestos organic (NAO) friction materials

Phenol formaldehyde resin is one of the most important ingredients in friction materials that binds the other multiple ingredients firmly. The type and amount of resin in the friction material is very critical for structural integrity of the composite. Present work focuses on the influence of resin percentage and modification of straight phenolic resin by cashew nut shell liquid (CNSL) on fade and recovery behavior of friction composites developed in the laboratory. These composites were based on variation in amount of CNSL modified resin (10, 12.5, and 15 wt.%) keeping other ingredients same. Fade and recovery studies on these composites were done according to ECE R-90 regulation. The friction coefficient (mu) (all types viz. performance, fade, and recovery), extent of fade and recovery, increase in counterface temperature, wear and mechanical properties were significantly influenced by the variation in amount of resin. It was observed that with increase in amount of resin all types of mu decreased and extent of fade increased. Most of the mechanical properties and wear, however, improved with increase in percentage of resin. Since mu is more important for friction materials rather than wear, it was concluded that 10 wt.% CNSL resin was an optimum amount for best friction performance in severe operating conditions. The performance properties of these composites when compared with similar composites based on unmodified resin in earlier work, it was revealed that the modification of phenolic resin by CNSL deteriorated the fade and recovery performance.