外文翻译
英文原文
Belt Conveying Systems Development of driving system
Among the methods of material conveying employed，belt conveyors play a very important part in the reliable carrying of material over long distances at competitive cost．Conveyor systems have become larger and more complex and drive systems have also been going through a process of evolution and will continue to do so．Nowadays，bigger belts require more power and have brought the need for larger individual drives as well as multiple drives such as 3 drives of 750 kW for one belt(this is the ca for the conveyor drives in Chengzhuang Mine)．The ability to control drive acceleration torque is critical to belt conveyors’ performance．童话作文大全An efficient drive system should be able to provide smooth，soft starts while maintaining belt tensions within the specified safe limits．For load sharing 腹泻能吃什么水果on multiple drives．torque and speed control are also important considerations in the drive system’s design. Due to the advances in conveyor drive control technology，at prent ma
ny more reliable．Cost-effective and performance-driven conveyor drive systems covering a wide range of power are available for customers’ choices[1].
1 Analysis on conveyor drive technologies
1．1 Direct drives
Full-voltage starters．With a full-voltage starter design，the conveyor head shaft is direct-coupled to the motor through the gear drive．Direct full-voltage starters are adequate for relatively low-power, simple-profile conveyors．With direct fu11-voltage starters．no control is provided for various conveyor loads and．depending on the ratio between fu11- and no-1oad power requirements，empty starting times can be three or four times faster than full load．The maintenance-free starting system is simple，low-cost and very游玩的近义词 reliable．However, they cannot control starting torque and maximum stall torque；therefore．they are limited to the low-power, simple-profile conveyor belt drives．
Reduced-voltage starters．As conveyor power requirements increa，controlling the applied motor torque during the acceleration period becomes increasingly important．Becau motor torque 1s a function of voltage，motor voltage must be controlled．This can be achieved through reduced-voltage starters by employing a silicon controlled rectifier(SCR)．A common starting method with SCR reduced-voltage starters is to apply low voltage initially to take up conveyor belt slack．and then to apply a timed linear ramp up to full voltage and belt speed．However, this starting method will not produce constant conveyor belt acceleration．When acceleration is complete．the SCRs, which control the applied voltage to the electric motor． are locked in full conduction, providing fu11-line voltage to the motor．Motors with higher torque and pull—up torque，can provide better starting torque when combined with the SCR starters, which are available in sizes up to 750 KW．
Wound rotor induction motors．Wound rotor induction motors are connected directly to the drive system reducer and are a modified configuration of a standard AC induction motor．By inrting resistance in ries with the motor’s rotor windings．the modified mo
tor control system controls motor torque．For conveyor starting，resistance is placed in ries with the rotor for low initial torque．As the conveyor accelerates，the resistance is reduced slowly to maintain a constant acceleration torque．On 法定节假日multiple-drive systems．an external slip resistor may be left in ries with the rotor windings to aid in load sharing．The motor systems have a relatively simple design．However, the control systems for the can be highly complex，becau they are bad on computer control of the resistance switching．Today，the majority of control systems are custom designed to meet a conveyor 一片天system’s particular specifications．Wound rotor motors are appropriate for systems requiring more than 400 kW ．
DC motor．DC motors．available from a fraction微信声音小怎么调大声 of thousands of kW ，are designed to deliver constant torque below ba speed and constant kW above ba speed to the maximum allowable revolutions per minute(r/min)．with the majority of conveyor drives, a DC shunt wound motor is ud．Wherein the motor’s rotating armature is connected externally．The most common technology for controlling DC drives is a SCR device． which allows for continual variable-speed operation．The DC drive system is mechanicall
y simple, but can include complex custom-designed electronics to monitor and control the complete system．This system option is expensive in comparison to other soft-start systems．but it is a reliable, cost-effective drive in applications in which torque,1oad sharing and variable speed are primary considerations．思想教育DC motors generally are ud with higher-power conveyors，including complex profile conveyors with multiple-drive systems，booster tripper systems needing belt tension control and conveyors requiring a wide variable-speed range．
1．2 Hydrokinetic coupling
Hydrokinetic couplings，commonly referred to as fluid couplings．are compod of three basic elements; the driven impeller, which acts as a centrifugal pump；the driving hydraulic turbine known as the runner and a casing that enclos the two power components．Hydraulic fluid is pumped from the driven impeller to the driving runner, producing torque at the driven shaft．Becau circulating hydraulic fluid produces the torque and speed，no mechanical connection is required between the driving and driven
shafts．解构主义建筑The power produced by this coupling is bad on the circulated fluid’s amount and density and the torque in proportion to input speed．Becau the pumping action within the fluid coupling depends on centrifugal forces．the output speed is less than the input speed．Referred to as slip．this normally is between l% and 3%．Basic hydrokinetic couplings are available in configurations from fractional to veral thousand kW ．
