There are various processes for finishing the friction surfaces of a brake disc, which affect the braking effectiveness of a vehicle in the early stages of use in some cases. To examine the interaction between the disc surface texture, rotational direction, and friction material, a series of experiments on a tribotester using small-scale specimens was conducted.
In a previous paper (2013-01-2056), the results from the first series of experiments, which involved of thirty disc surface textures and a less aggressive non-asbestos organic (NAO) friction material in on-brake-drag conditions combining constant speed and normal-load, was reported. Disc surfaces were finished by the following finishing processes in two rotational directions: turning under four cutting conditions, roller burnishing after turning, turning with a wiper insert, and grinding with two stones. Contact-pressure dependency of friction and wear was confirmed. Roller-burnished and wiper-turned discs exhibited different friction and wear at a certain contact pressure between rotational directions in the turning process.
In the present study, four discs finished by grinding in a different cross-hatch pattern from that in the previous study and two friction materials (aggressive NAO and low-steel friction materials) were additionally tested. The findings from the test results on friction, wear, and transfer-layer build-up are presented. The directional difference in friction and wear was confirmed to depend on the combinations of disc surface texture, friction material, contact pressure, and test period. Even a grinding-finished disc and low-steel friction material exhibited a directional effect in some cases.
