Friction and wear properties of the composite brake material for mine hoister under different initial velocities

The initial velocity determines the energy input of a braking which affects the tribological performance of brake materials seriously. Aiming at emergency braking conditions of mine hoisters, some tribological experiments and scanning electron microscopy analysis was carried out to reveal its influence on the composite brake materials. It is found that when the initial velocity is increasing, the mean coefficient of friction and its stability coefficient all decreases first then rises and decreases again while the wear rate rises continually. By contrast, it rises slowly at a low velocity, fast at a middle velocity and slowly again at a high velocity. It is concluded that some tribological related films generated by braking load and heat oxidization weaken the friction at the beginning of braking. Its friction weakening influence appears more obviously under a braking with a lower initial velocity. However, the films may also help to reduce braking wear. As the impacting frequency and velocity between surface asperities are all affected by the initial velocity, a bigger initial velocity will cause a worse wear. For short braking time, only a thin material on the surface is destroyed. The main wear modality of the pairs may be mechanical wear: cutting wear on the brake disc, fatigue and grooving wear on the brake shoe.