1、- 1 - 附录 A Comparison of Soft Start Mechanisms for Mining Belt Conveyors Michael L. Nave, P.E. CONSOL Inc. 1800 Washington Road Pittsburgh, PA 15241Belt Conveyors are an important method for transportation of bulk materials in the mining industry. The control of the application of the starting torqu
2、e from the belt drive system to the belt fabric affects the performance, life cost, and reliability of the conveyor. This paper examines applications of each starting method within the coal mining industry. INTRODUCTION The force required to move a belt conveyor must be transmitted by the drive pull
3、ey via friction between the drive pulley and the belt fabric. In order to transmit power there must be a difference in the belt tension as it approaches and leaves the drive pulley. These conditions are true for steady state running, starting, and stopping. Traditionally, belt designs are based on s
4、tatic calculations of running forces. Since starting and stopping are not examined in detail, safety factors are applied to static loadings (Harrison, 1987). This paper will primarily address the starting or acceleration duty of the conveyor. The belt designer must control starting acceleration to p
5、revent excessive tension in the belt fabric and forces in the belt drive system (Suttees, 1986). High acceleration forces can adversely affect the belt fabric, belt splices, drive pulleys, idler pulleys, shafts, bearings, speed reducers, and couplings. Uncontrolled acceleration forces can cause belt
6、 conveyor system performance problems with vertical curves, - 2 - excessive belt take-up movement, loss of drive pulley friction, spillage of materials, and festooning of the belt fabric. The belt designer is confronted with two problems, The belt drive system must produce a minimum torque powerful
7、enough to start the conveyor, and controlled such that the acceleration forces are within safe limits. Smooth starting of the conveyor can be accomplished by the use of drive torque control equipment, either mechanical or electrical, or a combination of the two (CEM, 1979). SOFT START MECHANISM EVAL
8、UATION CRITERION What is the best belt conveyor drive system? The answer depends on many variables. The best system is one that provides acceptable control for starting, running, and stopping at a reasonable cost and with high reliability (Lewdly and Sugarcane, 1978).Belt Drive SystemFor the purpose
9、s of this paper we will assume that belt conveyors are almost always driven by electrical prime movers (Goodyear Tire and Rubber, 1982). The belt drive system shall consist of multiple components including the electrical prime mover, the electrical motor starter with control system, the motor coupli
10、ng, the speed reducer, the low speed coupling, the belt drive pulley, and the pulley brake or hold back (Cur, 1986). It is important that the belt designer examine the applicability of each system component to the particular application. For the purpose of this paper, we will assume that all drive s
11、ystem components are located in the fresh air, non-permissible, areas of the mine, or in non-hazardous, National Electrical Code, Article 500 explosion-proof, areas of the surface of the mine. Belt Drive Component AttributesSize. Certain drive components are available and practical in different size
12、 ranges. For this discussion, we will assume that belt drive systems range from fractional horsepower to multiples of thousands of horsepower. Small drive systems are often below 50 horsepower. Medium systems range from 50 to 1000 horsepower. Large systems can be considered above 1000 horsepower. Di
13、vision of sizes into these groups is entirely arbitrary. Care must be taken to resist the - 3 - temptation to over motor or under motor a belt flight to enhance standardization. An over motored drive results in poor efficiency and the potential for high torques, while an under motored drive could re
14、sult in destructive overspending on regeneration, or overheating with shortened motor life (Lords, et al., 1978). Torque Control. Belt designers try to limit the starting torque to no more than 150% of the running torque(CEMA, 1979； Goodyear, 1982). The limit on the applied starting torque is often
15、the limitof rating of the belt carcass, belt splice, pulley lagging, or shaft deflections. On larger belts and belts with optimized sized components, torque limits of 110% through 125% are common (Elberton, 1986). In addition to a torque limit, the belt starter may be required to limit torque increm
16、ents that would stretch belting and cause traveling waves. An ideal starting control system would apply a pretension torque to the belt at rest up to the point of breakaway, or movement of the entire belt, then a torque equal to the movement requirements of the belt with load plus a constant torque
17、to accelerate the inertia of the system components from rest to final running speed. This would minimize system transient forces and belt stretch (Shultz, 1992). Different drive systems exhibit varying ability to control the application of torques to the belt at rest and at different speeds. Also, t
18、he conveyor itself exhibits two extremes of loading. An empty belt normally presents the smallest required torque for breakaway and acceleration, while a fully loaded belt presents the highest required torque. A mining drive system must be capable of scaling the applied torque from a 2/1 ratio for a
19、 horizontal simple belt arrangement, to a 10/1 ranges for an inclined or complex belt profile. Thermal Rating. During starting and running, each drive system may dissipate waste heat. The waste heat may be liberated in the electrical motor, the electrical controls, the couplings, the speed reducer, or the belt braking system. The thermal load of each start Is dependent on the amount of belt load and the duration of the start.
