Tribological Performance And Its Catastrophe Behaviors Of Mine Hoister's Brake Shoe During Emergency Braking

Disc brake is a key safeguard of mine hoister, whose braking performance is directly connected with the running safety of hoisting system. By the action of the friction force produced by the brake shoes sliding on the friction disc, the mine hoister is quickly stopped. The emergency braking is a process of transforming the dynamic energy of hoisting system into friction heat energy. So the tribological performance of brake shoe has decisive effects on the braking reliability of mine hoister. When a braking especially an emergency braking is occurring, for the action of high velocity friction, a great deal of friction heat may be produced on the surface of brake shoe. But for short braking time, the heat can not be transferred timely, which often causes a high surface temperature of the brake shoe. As a high temperature can easily cause a qualitative change of the brake shoe material, so the tribological performance may change quite differently as normal. When a catastrophe behavior of friction is occurring, an accident is then induced. So, for ensuring the hoisting safety, improving the economical and social benefit, it is helpful both theoretically and practically, to carry out some investigations on the tribological performance and its catastrophe behaviors of mine hoister′s brake shoe during its emergency braking.The dissertation was financially supported by the Natural Science Funds of China and the Natural Science Foundation of Jiangsu Province, which takes the disc brake of mine hoister as its study object, and aims at avoiding harmful accidents. Some investigations about the tribological performance and its catastrophe behaviors of mine hoister′s non-asbestos brake shoe during emergency braking were carried out in the dissertation, by methods of academic studies, tribological experiments and finite element simulations, also by combining of catastrophe theory and tribology.Firstly, by the simulating of single and repetitious emergency braking conditions of mine hoister, some tribological experiments were investigated, to find the rules that the initial braking velocity, braking pressure and braking frequency affecting on the brake shoe′s friction coefficient and its stability, wear rate and surface temperature. According to the catastrophe phenomena of the brake shoe′s friction coefficient observed in repetitious braking experiments, the friction catastrophe is pointed out to name it. Some experiments were then studied to find the influence of initial braking velocity and braking pressure on the intensity and starting time of friction catastrophe.Secondly, based on the basic tribologial principles and experimental results, the generating mechanism of the braking friction heat and its distributing mechanism between the friction pair were discussed in the dissertation. The dynamical thermo-mechanical property of the brake shoe was studied by some heat analysis experiments. The three-dimensional temperature field model of the brake shoe during emergency braking was founded and simulated, based on the heat exchange theory and finite element method. According to the actual hoisting conditions of mine hoister, a simple calculating model for estimating the maximal surface temperature of the brake shoe during emergency braking was established in the dissertation, by ignoring of some unimportant factors.Thirdly, based on the basic principles of tribology, the generating mechanism and changing rules of the braking force were discussed. According to the tribological experiments and temperature field simulation results, combining with the micro modality analysis of wearing surface, the wear mechanism of the non-asbestos brake shoe was discussed deeply in the dissertation. Based on the studies above, the mechanism of friction catastrophe was also discussed, combining with the DSC-TG heat analysis results of the brake shoe material.Finally, based on the investigations of braking friction heat and basic principle of catastrophe theory, a critical equation was founded, to describe the critical status when the catastrophe behavior of friction coefficient is occurring. The uppermost tribological index of the brake shoe, that is the friction coefficient was taken as the status variable. Two patulous variables which containing some actual braking conditions such as initial braking velocity, braking frequency, pressure and time, were taken as the control variables. A cusp catastrophe model was then established, to describe the friction catastrophe behaviors of the brake shoe during mine hoister′s repetitious emergency braking conditions. According to the friction catastrophe model, the catastrophe characters of the brake shoe′s tribological performance were analyzed, the necessary condition and critical status of the friction catastrophe were discussed, and the friction catastrophe was also qualitatively analyzed and forecasted.