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swings guards against the collision technology, the field bus, the carrier-current communication and the control, the non- contact power supply and the three dimensional barcode technology and so on widely obtains the application. Enable the hoist crane to have a higher flexibility, suits many raids of few batches the flexible production pattern, raises the single plane synthesis automation level. The key development take the microprocessor as the core high performance electricity transmission device, enable the hoist crane to have the fine velocity action and the static dynamic characteristic, may carry on the operation the automatic control, the automatic demonstration and the record, the hoist crane movement automatic protection and the automatic detection, the special occasion long-distance range remote control and so on, meets the automated production need Introduction Vast quantities of materials,parts and products have to be moved in road and bridge construction.Loads are handled in construction and erection jobs, in loading materials excavated from quarries or delivered by railway and water transport onto trucks and other vehicles,and in storehouses servicing the construction site.Factories producing concrete,mortars and prefabricated reinforced-concrete products widely utilize all kinds of materials bandling equipment,as do various depots. All materials hangdling equipment is either intermittent or continuous-action.Depending on its purpose,it consists of the following two main groups: a、Hoisting machinery:winches,jacks,hoists and cranks for intermittent operation. b、Conveyingmachinery:conveyors(belt,bucket,screw,cableways,air-operated equipment)and loading equipment (fork-life,single-bucket loader). 1.Main Parameters of Cranes （1）Lifting Capacity:The maximum load under specified condition for which the crane may be used. （2）Height of Lift:The vertical distance between the ground level or datum level,and the lowest point of the throat of the hook when the hook is in the highest working position. （3）Radius:The horizontal distance measured between the centerline of the hook and a perpendicular projected through the center of rotation. （4）Track center:The horizontal distance between the centers of each pair of track rails. （5）Working speeds:The working speeds of different mechanisms(hoisting,traveling,derricking slewing)for crane. （6）Overall Dimensions and Weight. （7）Stability:The anchoring and/or ballasting of the crane shall be such as to ensure that with the jib in any position the righting moment imposed under service conditions.Under storm conditions the crane shall be stable. If the crane is rail mounted,the devices for anchoring the crane to the rails shall not be taken into account when determining the stability of the crane. 2.Specific Parts for Cranes Hooks They are used to lift loads,There are single hooks and solid or built-up dual hooks. To handling small loads(upto 3 tons)a hook may be attached directly to the free end of the rope,although the usual practice is to suspend the hook in a casing with a moving rope sheave.A bearing seating ring supporing the hook nut allows the load and the hook to turn freely around the vertical axis.For loads exceeding 40 tons,hooks of the ramshorn type,B.S3017,or of the triangular type,B.S3317,are preferable.If required,a locking device shall be fitted to prevent rotation of the hook. Steel wire Ropes Steel wire ropes are used as flexible appliances to lift loads and transmit motion and forces.such ropes are wound from steel wire from 0.5 mm to 2 mm in diameter and have 共 15 页 第 5 页
an ultimate strength of 1400-2000Nmm2.Steel wire ropes are available in a great variety of designs. Machines used in amterials handling, construction and road making are provided mostly with round double lay (cross or regular lay)ropes from 11 mm to 32 mm in dismeter. Double lay ropes are manufactured from preliminarily twisted spiral wire strands.In a parallel(Long)lay rope the direction of twist of the direction of twist of the wires in the strand is the same as that of the atrands in the rope,while regular lay ropes are so constructed that the direction of twist of the wires in the strand is opposite to that strands in the rope.To make the ropes more flexible and provde proper lubrication of wires of the strands are laid on a hemp core impregnated with oil.Special locked-coil steel wire ropes find application in cable cranes and cable ways.These ropes,used to carry trolleys,have the cross section.The outer specially shaped wires form a smooth surface.These ropes have a low flexibility and high resistance to wear and keep out moisture. Lleys and Drums Ropes are supported and guided by means of cast iron pulleys. The groove on the pulley rim is shaped so as not to pinch the rope. The nominal diameter of the pulley D is the diameter of the circle described by the exis of the rope.The pulley diameter appreciably affects the magnitude of the bending stresses and the rope servive life and for this reason the existing norms should be taken into account in selecting a pulley diameter. During lifting or other displacement of the load the rope may be wound around drums drums in the form of cylinders with a smooth or grooved surface. A rope resting in a groove ensures,besides the proper direction,a smaller pressure on separate wires in the rop which increase the rop service life. Brakes One of the most important components crane is the brake on the hoisting motion.Electric cranes are invariably fitted with an automatic electric-mechanical brake actuated by solenoid or on alternating current by a thrustor which applies itself immediately current is cut off from the motor.Centrifugal brakes are occasionally fitted to prevent excessive acceleration when lowering,but it is preferable to use some system of electric braking such as dynamic with potentiometer control on direct current,and one of the systems of creating an opposing torque with alternating current.Slow speeds for accurate movement can be obtained by a manual brake applied to create a torque and so load up the motor to make it sensitive to resistance control.On large power installations the Word Leonard system is frequently used as it provides for a large range of speeds with simple control gear but the cost of the motor generator set offsets the saving in cost of main current controllers.Brake drums are preferably made of a high tensile iron which maintains a smooth rubbing surface without tearing. 共 15 页 第 6 页
指 导 教 师 评 语 外文翻译成绩： 指导教师签字： 年 月 日 注：1. 指导教师对译文进行评阅时应注意以下几个方面：①翻译的外文文献与毕业设计（论文）的主题是
否高度相关，并作为外文参考文献列入毕业设计（论文）的参考文献；②翻译的外文文献字数是否
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达到规定数量（3 000字以上）；③译文语言是否准确、通顺、具有参考价值。 外文原文应以附件的方式置于译文之后。
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2.