A Pin-on-Disc Study Focusing on How Different Load Levels Affect the Concentration and Size Distribution of Airborne Wear Particles from the Disc Brake Materials

Airborne wear particles originating from disc brakes are one important contributor to the concentration of airborne particles in urban environments. It is therefore of interest to improve the knowledge of these particles. The purpose of this article is to investigate the concentration and size distribution of the airborne wear particles generated from the contact between a low-metallic pad material and a grey cast iron disc at different load levels. This is done on model level with a pin-on-disc machine that allows the cleanliness of the air surrounding the test specimens to be controlled, and thus the airborne portion of the wear particles to be studied separately. The concentration and size of airborne wear particles were measured online during testing with four particle instruments. In addition, airborne wear particles were collected on filters during the tests and afterward analysed using SEM. Trimodal size distributions with peaks around 280, 350 and 550 nm were registered during running-in for all load levels. After running-in bimodal size distributions with peaks around 350 and 550 nm were registered for all load levels with the exception of the highest load level where multimodal size distributions were registered. At the two highest load levels the concentration of ultrafine/fine particles showed an increase up to a factor hundred indicating a change in wear mechanism. SEM images show ultrafine, fine and coarse airborne wear particles.