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1、英文文献翻译 The Two LuCable CranesGeneral DescriptionThe 2 luffing cable cranes are destined for the construction of the Three Gorges Dam in the valley of the Yangtze River.The jobsite is situated near Sandouping, Yichang in the province Hubei in the Peoples Republic of China.The cable cranes, representi
2、ng the main transport facility of a dam construction jobsite, have been designed for the purpose of transporting concrete, formwork items, concrete pre-fabitems, reinforcing material, building machinery and machine components such as penstocks, generators, lock gates, etc. . The cable cranes that wi
3、ll be used on the jobsite are of the luffing type, i. e. it has been given that name because for moving the track rope, the towers or masts one have to luff to the upstream or downstream direction.Both the slewing masts of each single crane between which the track ropes are installed, are situated -
4、at an elevation of + 185 m on block 8 already concreted on the left bank and on the longitudinal coffer dam at the elevation of + 160 m.Each mast has a height of 125 + 25 = 150m, and is firmly anchored by rear stay ropes in longitudinal direction. On their sides, the masts are held respectively move
5、d by 6-strand luffing ropes actuated by winches.The spans are:Rear stay ropes on the left bank approx. 270mRear stay ropes on the right bank approx. 604.5m.Track ropes: approx. 1416mThe machine houses for the winches of the cranes are arranged on the foot of the masts.In the machine houses on the fo
6、ot of the head towers are arranged the winches for hoisting crab traversing and mast luffing.In the machine houses on the foot of the tail towers are only situated the winches for mast luffing . This machine houses are therefore called luffing winch house .The control electronics are each located in
7、 separate rooms, for thus avoiding any problems as might occur by dust or also temperature variations.There are three possibilities to control the winches.Normally the crane is controlled by the drivers cabin that is movable between the machine side and the counter side on a long cable.The second wa
8、y is to control the cable crane by a -wireless portable control unit. For each crane there is one mobile unit.The third possibility to control the winches is the local control device nearby the machines for the hoist, crab traversing and luffing systems . The local control device is for purpose of e
9、asy adjustment and repairing.Because of the local situation, there are certain areas of the working field with obstacles. These areas are locked by the programmable computer control system.For the control systems see also the Electrical documents of ABB Company.The crab traversing winch is driven by
10、 a DC-motor that allows for an infinitely variable speed regulation. For physics reasons he acceleration shouldnt be much beyond 0. 75 m/s2 .Thereof result acceleration and braking times of approx. 10 seconds (braking torque about 6000 Nm) ; respective path is approx. 37:5m. With commissioning opera
11、tions the mechanicalbrake shall be set in a way that the loaded crab will come to be stopped after at the latest 12 seconds (braking torque approx. 6000 Nm). Because of the varying loads will result otherwise with merely mechanical braking (emergency) shorter braking times. Normally the torque havin
12、g been generated by the motor is transmitted over a 2-groove drive pulley to the crab traversing rope. Here one has to check periodically for ensuring-an uniform running in the two grooves (see chapter Maintenance). Between the two grooves the crab traversing rope is led over the return pulley; at t
13、he shaft of which is also fitted :the screw-type limit switch and the position indicator, just also the tachometers for measuring the speed and for control of a possible over speed. Although the screw-type limit switch and the position indicator are driven by the non-driven return pulley, it is unav
14、oidable that after a duration of operation occurs a certain miss-indication, so that the correction will have to be made (see chapter Traversing Limit Switches and Position Indicators).For safety reasons have been installed, however, at the first and at the last rope carrier additional limit switche
15、s for monitoring the crab speed. Since these limit switches cannot shift out of their set position, the signal is absolute. Finally the crab traversing is then stopped by a lever limit switch attached at each end of the track rope.The tachometer for monitoring a possibly occurring over speed disconn
16、ects the crab traversing gear at 115% rated speed by emergency off.For providing the operation and maintenance team with information concerning the plant output, the crab traversing gear is equipped with an operation hour s counter and a cycle counter. Here the operation hours counter is detecting the time in which the crab traversing motor is working, and the cycle counter the number of traversing runs. Therefore the cycle count
