Optimization of a semimetallic friction material formulation

A semimetallic friction material formulation consisting of Al2O3, B2O3, brass chips, graphite, NBR (nitrile rubber), steel wool, and benzoxazine (a ring-opening polymerized phenolic) with high friction coefficient (mu) and low wear was developed using the Golden Section approach to search the optimal volume fraction of each ingredient in the formulations. All raw materials used were divided into three groups: fibers, filters, and binder. The volume fraction of each ingredient in the formulations was calculated by means of V-i=0.618 in phase 1, V-j=V-i+/-V-i x r(m)/V-F and V-j=V-i+/-V-i x r(m)/V-f in phase 2 and V-j=V-i+/-V-i x r(m)/(V-F=V-f) in phase 3. Two exponent equations, w=k(0)V(1)(k 1)V(2)(k 2)...V-p(k p) and mu=m(0)V(1)(m 1)V(2)(m 2)...V-p(p)m, were proposed to correlate the compositional dependence of wear and mu. The least-squares error method was utilized to calculate the effect of each ingredient on mu and wear. Experimental and calculated results proved that both brass chips and B2O3 play important roles in enhancing mu. After doing 18 formulation experiments that preformed using Friction Assessment and Screening Test (FAST), an optimized formulation (BB-17) with high mu (average mu=0.701) and low wear (w=4.74%) was obtained.