tailieunhanh - Clutches and brakes design and selection P8

Brake and clutch design or selection from a manufacturer’s catalog both require that we design or select a brake or clutch which has the torque capability necessary to stop or start either a machine or a mechanical component in a specified amount of time and also has the ability to dissipate the heat generated. Torque capability depends, as we have found, on the particular brake or clutch design. The heat to be dissipated does not; it depends only on the machinery being stopped and is, therefore, independent of the brake or clutch used. In this chapter we are concerned with. | 8 Acceleration Time and Heat Dissipation Calculations Brake and clutch design or selection from a manufacturer s catalog both require that we design or select a brake or clutch which has the torque capability necessary to stop or start either a machine or a mechanical component in a specified amount of time and also has the ability to dissipate the heat generated. Torque capability depends as we have found on the particular brake or clutch design. The heat to be dissipated does not it depends only on the machinery being stopped and is therefore independent of the brake or clutch used. In this chapter we are concerned with the related problems of estimating stop or startup times and the amount of heat generated. Both problems may be analyzed in terms of the energy supplied by the driving unit the energy transmitted to the driven unit and the energy dissipated as heat by either the brake or clutch. Although the energy considerations are independent of the particular brake clutch design involved the resulting formulas may be used to compare various brake clutch design suitability for any mechanical system. Calculation of heat dissipation by a mechanical system involving a clutch or brake may be divided into two parts the mechanical energy converted to heat in the clutch or brake and the rate of transfer of this heat to the surroundings. In the remainder of this chapter we shall be concerned only with the first of these two problems. Those readers who may be concerned with the second problem as well are referred to existing books devoted to the calculation of heat transfer by conduction convection and radiation along Copyright 2004 Marcel Dekker Inc. with the specific heats for common cooling fluids including air the methods for determining the coefficients involved and the numerical techniques required for solving practical heat transfer problems. I. ENERGY DISSIPATED IN BRAKING The heat dissipated in any mechanical system is equal to the energy withdrawn from the .