Abstract
The tribological behavior and the related airborne particles emission of three copper-free automotive friction materials are investigated. The tests were conducted using a pin-on-disc tribometer equipped with a specifically designed clean-enclosure chamber for the emission measurement. Particle number concentration from particle size 0.3 µm up to 10 µm and the mass of emitted particles between 1 µm to 10 µm were measured. Particular emphasis was given to the chemical composition of the bulk materials, the friction layers and the emissions, in order to explain the acting wear mechanisms, and the recorded emission of airborne particles. The results indicate that the recorded emissions do not correlate with the friction coefficient and the wear rates, since the wear mechanisms exert a different influence on the tribological and emission behavior of the materials under study.
Highlights
The growing interest for environmentally friendly friction materials to be used for vehicular brake systems has sparked research efforts aiming at developing new material compositions, which might effectively respond both to performance and low pollution requirements
Copper has been a fundamental constituent of friction materials not exclusively because of its thermal properties [1] and for its ability to form compact secondary plateaus [1,2], which contribute to a lower thermal fade and lower wear of the braking system, respectively
The tribological and the associated emission behavior of friction materials are related to the characteristics of the friction layers that form on the pin surfaces during PoD sliding tests [25,31,37]
Summary
The growing interest for environmentally friendly friction materials to be used for vehicular brake systems has sparked research efforts aiming at developing new material compositions, which might effectively respond both to performance and low pollution requirements. Airborne particles related to brake pads wear pose as an environmental [1,4,5] and health hazard due to their metallic content, in particular due to their copper content, by prominently damaging the human respiratory system [6,7,8,9,10,11]. For this reason, the amount of copper allowed in friction materials is undergoing increasingly restrictive legislative regulations
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