提升系统和安全装置毕业论文外文翻译.doc

英语原文Hoisting System And Safety DevicesThomas D.BarkandSenior Member,IEEEMine Safety And Health AdministrationPittsburgh,Pennsylvania 15236Abstract As noted,there are two main operating malfunctions which can occur in a hoist system that can kill men and damage equipment. 1. Overtravel at the shaft extremity.2.Overspeed during the duty cycle .What is required in the case just illustrated is a device that would check hoist speed far enough down the shaft so that if the conveyance were traveling too fast at that point,the hoist would “E”stop soon enough to bring the skip to a stop before it overtraveled its stopping point and did damage.This paper discusses the application of a suspension rope brake to a single rope mine hoist. Technical challenges associated with accelerated rope brake lining wear and suspension rope lubrication are addressed.HOISTING SYSTEMThe hoist together with its associated plant for an underground mine is the single most important and expensive lement of the mine plant.The hoist plant consists of all those components of mine plant that are necessary to elevate ore,coal,stone,or waste and to raise and lower personnel and materiel in the mine.It is with the hoisting system itself-these components of the hoist plant located in the hoist room-that engineering design is mainly needed.These key factors govern hoist selection:1. Production rate,or tonnage to be hoisted per unit of time2. Depth of shaft3. Number of levels to be accessedThere are basically only two hoisting methods,plus some modifications,in use today:drum and friction.The drum hoist stores the rope not extended in the shaft.The friction-sheave hoist passes the rope (or the ropes) over the drive wheel but does not store it.A minor method that has fallen into disuse is reel hoisting,in which a single width of rope is wrapped in many layers.A new method devised in South Africa for very deep shafts is multidrum hoisting using multiple ropes.DESIGN OF HOISTING SYSTEMThe design process for a mine hotsting stytem should be understood by the mining engineer,enen though the design and installation are contracted to an engineer-constructor firm and the equipment bid to a hoist manufacturer.Typically,the mining company developing the mine assigns its own engineering department to monitor the entire process,including both the planning and construction of the surface hoist plant.The design process will now be examined in detail and illustrated by a numerial example.1. Balanced hoisting.All mine hoisting systems are operated in balance to reduce moments,torque,and power demand on the hoist.Generally,two conveyances are suspended from one hoist;sometimes,when more than one level is to be serviced,a counterweight replaces one conveyance.It is designed with a weight equal to the dead load ot the skip or cage plus one half the live load.To further balance the loads,a tail rope can be installed.2. Slippage in friction sheave hoisting.Slippage occurs in a friction-sheave hoist if the ratio of the rope tensions exteeds a theoretical limit.3. Wire rope size.Wire rope has a complex structure.In designing a hoisting system,the two properties of wire rope that are most important are weight per unit length and breaking strength.Note that properties for two qualities of steel are included for round-strand and flattened-strand rope.4. Sheave and drum diameter.To minimize flexing and stressing of the wire rope as it is wound over a sheave or drum,a recommended minimum ratio of drum or sheave diameter to rope diameter should be 80100.Since the cost of wire rope is modest,there may be occasions,espcially in shallow shafts,where it is more coat-effective to select a smaller drum diameter and replace the hoist rope oftener.5. Rope fleet angle.This is the angle subtended by the hoist rope and the centerline from the idler sheave to the drum.To reduce rope abrasion in the sheave groove,the fleet angle is restricted to 11.5°.The principal effect of such a limit is to restrict the width of the drum.6. Skip size vs.hoisting velocity.To achieve a desired production rate in a shaft,the design engineer seeks a balance between skip size and hoisting velocity.The ultimate limit on skip size is rope strength,and on hoisting velocity it is energy consumption.As a compromise it is generally advantageous to hoist the large skip load possible at the lowest possible rope velocity.7. Hoisting cycle.The relationship of time to distance in hoisting is referred to as the hoisting cycle.Calculation of time and distance elements is accomplished with the following formulas:a. Acceleration time b. Acceleration distance c. Constant-velocity distance d. Constant-velocity time e. Cycle time 8. Duty cycle.The relationship between hoist motor torque requirements and hoisting cycle times is called the duty cycle.The sloping section of the drum hoist reflects the unbalanced load of the hoist rope.Integrating the area under the curve provides the energy consumption for the hoisting-duty cycles.Safety Devices-like all mechanical devices with large heavy moving parts,such as gears,drums,conveyances and motors,a mine hoist must bu protected from traveling too far in any given direction and traveling too fast.Protective devices are incorporated into a mine hoist for two reasons.The first is to protect life and limb of persons riding the cage and working in the vicinity of the shaft.The second is to protect the hoist headframe and,most important,the shaft.As noted,there are two main operating malfunctions which can occur in a hoist system that can kill men and damage equipment.These are:1. Overtravel at the shaft extremity.2. Overspeed during the duty cycle.Overtravel is defined as travel of a conveyance past the planned or programmed stopping point.This stopping point can be the dump bin in the headframe or a shaft loading pocket or cage landing. Overspeed is defined as speed in excess of that required or programmed for any particular point in the travel in the shaft.It can easily be seen why this is important by considering the case when the skip is traveling at full speed while entering the dump scrolls. Given:Travel distance in dump scrolls 20ft(6.1m) Full hoist speed 30fps(9.14m/s) Emergency-stop retard rate 7.5(2.3m/) This means that the skip would overshoot the dump bin by some 60 ft.In all likelihood it would be pulled though the top of the headframe and thus damage structural work at the shaft collar.What is required in the case just illustrated is a device that would check hoist speed far enough down the shaft so that if the conveyance were traveling too fast at that point,the hoist would “E”stop soon enough to bring the skip to a stop before it overtraveled its stopping point and did damage.There are a mumber of such devices available around the world that,when geared and driven from the hoist drum(or wheel),will provide accurate and sensitive protection of the hoist and conveyance from damage due to overtravel and overspeed.The best known and most widely used is the “Lilly Controller”,manufactured by the Logan Actuator Co.,Inc.,Chicago.INTRODUCTIONMine elevators and personnel hoists provide a lifeline for miners at more than 360 mines nationwide l. The hoisting system transports mine personnel through an isolated corridor during routine operations or life threatening emergencies. The potential risk of injury is great if the hoisting system fails. Therefore, a safe, reliable hoisting system is essential to the well being of the miners. In mining history there have been two well documented investigations of mine hoisting systems crashing in the upward direction 2, 3. These accidents occurred on counterweighted hoisting systems when the mechanical brake failed while the cage was empty. This allowed the counterweight to fall to the bottom of the shaft, causing the car to overspeed and crash into the overhead structure. The accidents were initially believed to be isolated incidents. However, research covering a 5-year period, showed there were over eighteen documented cases of ascending elevators striking the overhead structure 4.Rules and regulations applying to elevator safety have come under review in response to these accidents. The Canadian Elevator Safety Code and the Pennsylvania Bureau of Deep Mine Safety have recently revised their regulations and policies to require supplemental ascending car overspeed protection. As a result of this initiative, a new generation of braking systems has been developed and applied to mine elevators and hoists.Several supplemental emergency braking systems can be applied to mine hoisting systems. Some of the proven systems are counterweight safeties, electrical dynamicbraking, and a pneumatic rope brake system. The application of these braking systems to multiple rope hoisting systems is discussed in other literature 5, 6. The purpose of this paper is to discuss the application of these systems to single rope mine hoists. The electrical dynamic braking system is inherently unaffected by the number of suspension ropes and has been successfully applied to a single rope mine hoist 7. However, the application of the rope brake on a single rope hoist has presented technical challenges. This paper will discuss the control, design, and testing of the world's first application of a suspension rope brake to a single rope mine hoist. Problems with accelerated rope brake lining wear and excessive suspension rope lubrication will be addressed. The dynamic performance will be compared to rope brake installations on multiple rope hoisting systems.CASE STUDY: SINGLE ROPE MINE HOISTThe first installation of a Bode rope brake' on a single rope mine hoist was evaluated January 30-31, 1992. The pneumatic rope brake was installed on a ground mounted hoist which operates with a cage in balance with a counterweight in a vertical shaft. The drum is designed to wind an "under" and "over" 1-lj2 inch flattened strand hoist rope in a single layer. The drum is helically grooved to wind 20.4 live turns, 6 dead and 6 cutting turns, plus 4 turns between ropes. The drive is arranged for SCR controlled single D.C. motor drive through a double reduction reducer. The controls are either semi-automatic or manual by operation from the control panel. This hoist was commissioned by the federal and state regulatory agencies on April 12-13, 1984.Hoist Mechanical and Electrical Specifications Hoist Distance : 571 Ft. - Personnel/MaterialsD.C. Motor : 300 Horsepower, 500 Volts DC,Drum : 110 Diameter x 58" FaceHoist Ropes : Two - 1-1/2 Flattened Strand 6 x 30 Fiber Core, Galvanized,Preformed, Lang Lay,Breaking Strength 235,000 lb.490 Amperes, 400 rpmPersonnel Load : 7,875 lb.Material Load : 10,750 lb.Weight of Cage : 13,000 lb.Weight ofCounterweight : 17,250 lb.Weight of Rope : 4,700 lb. - 3.95 lb./feetSpeed of Hoist : 600 fpmSpeed of Motor : 467 rpm 600 fpmSpeed of Drum : 20.55 rpm 600 fpmWR2 of Hoist ：1，098，340lb.-ft2Drum Brakes : Four - Disc Brake Units, Spring Applied Pressure Released, Two Discs, Two Units Per Disc Lilly One - Model "C' Lilly ControllerController : Man SafetySafety Catches : Instantaneous Type, Activated by Slack or Broken RopeRope Brake DesignThe rope brake grips the suspension ropes and stops the hoist when an overspeed of 15% is detected or the cage moves away from the landing when it is not under control of the hoist motor. The pneumatic design is identical to the model 580 described in the literature 6. When the rope brake is activated, a set of magnetic valves direct pressurized air from the compressor tank into the rope brake cylinder. The air pushes the piston inside the rope brake cylinder and forces a movable brake pad toward a stationary brake pad. The suspension rope is clamped between the two brake pads. The rope brake is released by energizing the magnetic valves, which vent the pressurized rope brake cylinder to the atmosphere through a blowout silencer. The brake pads are forced open by six coil springs.The force exerted on the suspension rope equals the air pressure multiplied by the surface area of the piston. The rope brake model number 580 designates the inner diameter of the brake cylinder in millimeters. This translates into 409.36 in2 of surface area. The working air pressure varies from 90 to 120 1bf/in2. The corresponding range of force applied to the suspension rope is 36,842 to 49,123 lb. The static force experienced by the suspension rope on the cage sheave, under fully loaded conditions is 26,OOO lb. Therefore, the ropes experience up to 89% greater force during application of the rope brake under emergency conditions, than normally encountered during full load operation. Rope Brake Installation The rope brake was installed in a control room constructed in the hoist. headframe directly below the cage suspension rope sheave as shown in Fig. 1. The control room contains the complete rope brake system, including the rope brake, control logic, and air compressor. The rope brake safety relay contacts were wired into the hoist control below through conduit. Heaters were installed in the rope brake control room to regulate the temperature during cold weather operation. Fig. 1: Rope Brake InstallationRope Brake ModificationsThe mechanical design of the rope brake was modified for this application to a single hoist rope in addition to the modifications previously presented 6. The rope pulse tachometer wheel was increased to approximately 5 inches in diameter which is more than double the original diameter. Consequently, the number of screws on the wheel was increased to maintain the original sensitivity of the speed and position sensing logic. The pulse tachometer wheel diameter was increased to provide a smoother operation on the relatively rough surface of the hoist rope, compared to a typical elevator rope.Rope Brake Tests and ResultsThe integrity of the existing hoist safety system was, verified prior to performing any rope brake tests. The hoist emergency stopping, safety catches, overspeed and overtravel protection were dynamically tested. This procedure was essential to assure the safe completion of the rope brake test agenda.A series of tests were then conducted to evaluate the performance of the rope brake under extreme loading conditions and multiple control system faults. The compound braking effect on the deceleration rate was also evaluated. Compound braking occurs when the rope brake and the hoist brake operate simultaneously.Average Hoist Deceleration Rates: The rope brake and the compound braking deceleration rates are shown in Table I. The four test conditions represent the extreme hoist loading conditions for all possible directions of tra