New insights into reducing airborne particle emissions from brake materials: Grooved textures on brake disc surface

Airborne particles from brake systems have been widely recognised as a great contributor of particulate matter (PM) in railway environments, such as micro- and nano-size airborne particles. Increasing attention is being paid to airborne particles due to their potential for adverse health effects. In the brake system, particulate matter and wear debris mostly come from the wear of brake pair materials. Reducing-friction and anti-wear effect can be achieved by means of a reasonable grooved texture. In this paper, evaluation of friction, wear and particle emission behaviour of commercial brake pads for high-speed trains were studied using a pin-on-disc tribometer. Effect of grooved textures on the characteristics of airborne particles and deposited debris particles, as well as the wear behaviour of brake materials, was investigated on the basis of the brake discs with different numbers and angles of grooved textures. Results show that the grooved texture on the brake disc can effectively restrain airborne brake particulate emissions, particularly particles in the size range of 1.0 µm ≤ d ≤ 5.0 µm. Compared with the brake discs with the grooved texture, the size of the abrasive particles generated in the non-textured test group become smaller, irregular agglomerates of wear debris are more easily formed, and the debris particles are mostly lamellar with smooth surfaces and sharp edges. The wear rate of the pins against the brake disc with the grooved texture slightly increases, but the surface wear of the brake discs is effectively mitigated. In comparison with the number of grooves, the angle of the grooved texture has a more significant effect on the particle emission and wear behaviour of the brake disc. Additionally, the brake disc with 6 grooves, as well as the angle of the grooves face the friction direction, exhibits the best comprehensive performance.