Study of the Formulation Mechanism for Metal Pick-up on the Frictional Surface of a Disc Brake Pad

The authors have conducted a study on the mechanism of how metal pick-up occurs on the NAO disc brake pad. The study is conducted in four separate steps. First, a vehicle test is conducted to generate metal pick-up. The resulting metal pick-up on the surface of the disc brake pad is analyzed and results show it to be a lump of iron. Through the observation and element analysis, an iron oxide layer exists between friction material and metal pick-up. Second, using a disc brake pad of a simple formulation and a test piece friction tester, the iron is quantitatively analyzed on the friction surface of the disc brake pad. The quantitative analysis will reveal the amount of the transferred iron depends on the rotor temperature and the void volume of the friction material. Third, on the basis of the first two analyses, a formation model for metal pick-up is created. Fourth, using a brake dynamometer and a disc brake pad, the distribution of iron over the friction surface is observed during the heat cycle and cooling process by controlling brake frequency. This four step process proved the validity of our formation model of metal pick-up.