Performance of NAO Cu-free Brake Pads Containing Nitrile Butadiene Rubber

"Performance of NAO Cu-free Brake Pads Containing Nitrile Butadiene Rubber Vishal Singireddy Reddy, Peter Filip, Kim Stefanisin, Trevor Elliott School of Mechanical, Aerospace and Materials Engineering, Southern Illinois University Carbondale Brake pads represent an important element of friction brake and their development is often typified by trial and error. As every friction process braking using friction brakes is always accompanied by vibration and related noise generation as well as wear. Automotive industry is changing considerably and the relevance of friction brake is discussed widely. Less wear and release of pollutants, better corrosion resistance, capacity to absorb and dissipate heat generated by friction brake, proper blending with regenerative braking systems and mitigation of vibration and noise are the most frequently discussed aspects of modern brake materials. The use of a scientific approach (instead of trial and error approach) when developing new friction brake materials, more effective testing incorporating the role of regenerative brake and mitigating the pollutants and vibration are in focus of this paper. Scaled-down SAE J2522 brake performance test (UMT Tribolab by Bruker) equipped with triaxial ICP accelerometer (PCB electronics, Model 356A45), prepolarized microphone (PCB electronics, Model 377C01) were conducted with laboratory formulated and optimized NAO Cu-free brake pads and gray cast iron rotors (Waupaca, Inc). Sample were analyzed by SEM/EDX (FEI, Quanta FEG450, Oxford systems) Brake pads contained significant amounts of ?bubbly? nitrile butadiene rubber (NBR Nipol1411 and Nipol 1411C by Zeon Chemicals). The obtained friction testing results revealed high level and and extremely good stability of the coefficient of friction (average 0.4, delta mu=0.02) and a very low wear of pads (between 0.01 and 0.02 g) and rotors (0 .01to 0.04 g). This was ascribed to low porosity (3%) measured by Archimedes principle and distilled water. Despite the low porosity, the pads did not cause excessive vibration and noise with the the highest sound pressure levels always below 70dBA. The typical 7-10% porosity necessary for damping vibration was, however, provided by bubbly NBR, providing additional 7% but not measurable by applied method. NBR also contributed to formation of a stable friction layer over the surfaces of pads and rotors. "