The relevance of brake emission measurements and control aiming the years to come is increasing, as the efforts to reduce particle emissions from automotive friction systems. Removing copper from friction materials due to environmental legislation brought, also, an impact on brake emission and now friction material industry works with a challenge to develop copper-free and low-brake emission materials. This work presents a comparison of airborne particle emissions originated from three different commercial brake pad formulations and relates them to each tribological behavior and raw materials applied. The objective of this work was to verify if abrasive and lubricants elements, in some defined contents and sizes, have a clear and defined role on brake emission of copper-free materials and compare them to a copper-based one to understand different emission behaviors, also correlating bench tests with inertial dynamometer tests. A Pin-on-Disc investigation was done in an enclosured tribometer, considering a copper-based (Cu-Full) and two copper-free (Cu-free) friction material formulations. A TSI® Optical Particle Sizer (OPS) model measured the particle number concentration and a Dekati® PM10 impactor connected to the chamber measured the two size ranges from 10 to 2.5 μm (PM2.5) and from 2.5 to 1 μm (PM1). SEM micrographs and EDXS maps of the materials under study were obtained to properly characterize the pad and disc surfaces and collected airbornes as well. The Cu-full formulation showed intermediate values of friction coefficient, pin wear and emissions but disc wear was higher than the other two materials. When a Cu-free made of long metallic fibers and coarser lubricants was analyzed, higher friction coefficient, higher pin wear and higher emissions were identified. When analyzing a Cu-free made of a mix of metallic fiber and powders, as finer lubricants, the lowest friction coefficient, lower pin and disc wear and lower emissions were identified. These results corroborate with results from wear tests in commercial dynamometer, where the second Cu-free formulation shows an outstanding rotor durability. A correlation between higher disc wear and higher brake emissions is likely to happen, which indicates that different metallic shapes, abrasive particles and lubricant species, depending on the sizes and contents, act directly on promoting lessen airborne emissions.
Mr. Willian Ferreira de Camargo, Research Chemist, Fras-le SA; Dr. Eng. Ana Paula Gomes Nogueira, Engineer, Università di Trento; Ms. Natalia Pagnoncelli Lorandi, Chemical Engineer, Fras-le SA; Mr. Ricardo Gilberto Lamb, Sr. Chemical Engineer, Fras-le SA; Prof. Dr. Giovanni Straffelini, Professor, Università di Trento