Performance of environmentally sustainable NAO Cu-free brake pads containing nitrile rubbers and recycled friction material

Abstract

"As the automotive industry tends towards development of sustainable and environmentally friendly friction material, studies on potentially recycling and re-using friction material have become increasingly important. In this research, two brake pads, made of sustainable recycled friction material (ACI Industries, Ltd.), identical in formulation except the type of rubber (Zeon Chemicals L.P.), were developed in the laboratory. Rubbers are a key component in brake friction material and impact dampening the friction level and stability, wear, vibration, and noise, by contributing to formation of friction layers and influencing mechanical and thermal and corrosion properties of brake pads. These aspects become even more relevant when electric vehicles are considered since they are almost noise-free. The laboratory-developed samples were tested by adopting the scaled-down SAE J2522 brake effectiveness procedure [1, 2, 3] against surface treated commercially available pearlitic gray cast iron rotors (Waupaca Foundry Inc.), [4, 5]. Universal Mechanical Tester (UMT, Tribolab by Bruker) was used to perform the test. Vibrational response was characterized by using a triaxial ICP accelerometer (PCB Electronics, Model = 356A45), sound pressure levels were monitored by a ¼” free-field prepolarized microphone (PCB Electronics, Model = 377C01) and data from them were collected using a high-performance oscilloscope (Agilent Technologies, Model = MSOX2024A) and DAQ (NI USB - 6218). Wear debris and the friction surfaces of tested samples were analyzed using Scanning Electron Microscopy (FEI, Model: Quanta FEG450) and Energy Dispersive X-ray spectroscopy (EDX, Oxford Instruments). Mechanical properties, density and porosity were measured using CV Shore D durometer (ASTM D2240) and AWS ALX – 310 precision balance. The developed lightweight samples exhibited extremely low open porosity (< 3.5 %) and optimal (with respect to compressibility) hardness (~ 55). The newly developed pads when tested against coated rotors developed optimal friction layer responsible for very stable and relatively high friction levels, very low wear of pads and rotors, and a extremely ""quiet"" operating conditions. This performance was ascribed to a combined effect of the i) appropriate friction layer, ii) hardness and compressibility, and iii) the low porosity. [1] Rohith Redda Boyna, “Impact of Friction Test Scale on Brake Friction Performance”, Master’s thesis, Southern Illinois University Carbondale, December 2016 [2] Vishal Reddy, et al., ""Impact of Acrylic Fiber on the Performance of Newly Developed Friction Materials for Vehicles with Regenerative Braking,"" 38th Annual SAE Brake Colloquium (Online and on-demand), Oct. 2020 [oral presentation only] [3] Vishal Reddy, et al., “On Scaled-down Bench Testing to Accelerate Development of Novel Friction Brake Materials” (to be published) [4] Filip, Peter, and Nathan K. Meckel. ""Wear resistant braking systems."" U.S. Patent 10,895,295, issued January 19, 2021. [5] Filip, Peter, and Nathan K. Meckel. ""Wear resistant braking systems."" U.S. Patent 10,197,121, issued February 5, 2019. "