Compressibility And Friction Performance Of Automotive Brake Friction Materials

Safe, comfort and clean are three important requirements which brake pad should meet according to modern automotive industry in nowadays. Safe is always justified by friction and wear performance, while compressibility has been a new important parameter to estimate comfort performance recently.In this experiment, based on one kind of semi-metallic formulation, the effect of acrylonitrile butadiene rubber (NBR)/phenolic resin (PF), binder, steel wools and potassium titanate whiskers(PTW) on compressibility and tribological properties of brake material were investigated by means of constant-speed friction test machine,1620 model compressibility test machine and SEM. The results are included as follows:Cold compressibility was remarkably improved by NBR/PF and PTW. Adding every 1% of NBR and PTW, the compression deflections of samples (17 mm in thickness) were decreased by 10.4μm and 2.5μm respectively. However, the content of binders and steel wools showed no significant effects on cold compressibility. Hot compressibility was significantly increased as the NBR/PF ratio (≤1), the content of binder and PWT increasing. When the content of NBR, PTW and binder were increased by 1%, the compression deflections were decreased by 17.0μm, 4.9μm and 16.6μm respectively. But the influence of steel wool content is minor.The NBR/PF ratio, binder content, steel wool and PTW content played different roles in frictional properties improvement. Below 200℃, with NBR/PF ratio increasing, the friction coefficient (μ) of pads increased first and then decreased; at higher temperature, heir thermal fading performance were improved first and then got worse. The wear rate of composites declined first and then increased when temperature was in the range of 100℃to 350℃. Good friction and wear properties of composites were obtained when the ratio of NBR is between 1/5 and 1/2. Given NBR/PF ratio were 1/2, the friction coefficient of composites showed an increasing trend first and then a declined as the binder content increased. A maximum friction coefficient was found at 12%. When the binder content did not surpass 16%, pads had stableμand good heat fading properties. When binder content increased to 20%, pads faded severely and the initial fading temperature decreased to 250℃. The lowest wear ratio was found when binder content was 12%. With the steel fibre content increasing, heat fading decreased a little first and increased then. Excellent friction properties could be reached when the content is in the range of 10% to 15%. With the addition of PTW, the fading and wear properties gradually decreased and only increased when the PTW content increased to 16%. It was found that adding 8%-12% of PTW could improve friction properties at high temperature effectively.