1、附 录 英文文献 A Comparison of Soft Start Mechanisms for Mining Belt Conveyors Michael L. Nave, P.E. CONSOL Inc. 1800 Washington RoadPittsburgh, PA15241 Belt Conveyors are an important method for transportation of bulk materials in the mining industry. The control of the application of the starting torque
2、 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 drive pulley via friction between the drive pulley and the belt fabric must t
3、ransmit the force required to move a belt conveyor. 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 static calc
4、ulations 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 prevent exc
5、essive tension in the belt fabric and forces in the belt drive system (Surtees, 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 conveyor
6、system performance problems with vertical curves, 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 enough to start
7、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 EVALUATION CRITERION
8、 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 (Llewellyn and Sudarshan, 1978). Belt Drive System For the purposes of this p
9、aper 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 coupling, the spe
10、ed reducer, the low speed coupling, the belt drive pulley, and the pulley brake or hold back (Zur, 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 system compo
11、nents 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 Attributes Size. Certain drive components are available and practical in different size ranges. F
12、or 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. Division of
13、sizes into these groups is entirely arbitrary. Care must be taken to resist the 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 result in destruct
14、ive over speeding on regeneration, or overheating with shortened motor life (Lodi, etal., 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 the limit of rat
15、ing 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 increments that would
16、 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 to accelerate t
17、he 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, the conveyor its
18、elf 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 horizontal sim
19、ple belt arrangement, to a 10/1 range 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 brak
20、ing system. The thermal load of each start Is dependent on the amount of belt load and the duration of the start. The designer must fulfill the application requirements for repeated starts after running the conveyor at full load. Typical mining belt starting duties vary from 3 to 10 starts per hour
21、equally spaced, or 2 to 4 starts in succession. Repeated starting may require the debating or over sizing of system components. There is a direct relationship between thermal rating for repeated starts and costs. Variable Speed. Some belt drive systems are suitable for controlling the starting torqu
22、e and speed, but only run at constant speed. Some belt applications would require a drive system capable of running for extended periods at less than full speed. This is useful when the drive load must be shared with other drives, the belt is used as a process feeder for rate control of the conveyed
23、 material, the belt speed is optimized for the haulage rate, the belt is used at slower speeds to transport men or materials, or the belt is run a slow inspection or inching speed for maintenance purposes (Hager, 1991). The variable speed belt drive will require a control system based on some algorithm to
