塔式起重机的英文简介.doc

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1、Tower crane (塔式起重机)1.Introduction to How Tower Cranes Work Tower cranes are a common fixture at any major construction site. Theyre pretty hard to miss - they often rise hundreds of feet into the air, and can reach out just as far. The construction crew uses the tower crane to lift steel, concrete,

2、large tools like acetylene torches and generators, and a wide variety of other building materials.When you look at one of these cranes, what it can do seems nearly impossible: Why doesnt it tip over? How can such a long boom lift so much weight? How is it able to grow taller as the building grows ta

3、ller? If you have ever wondered about how tower cranes work, then this article is for you. In this article, youll find out the answers to all of these questions and more! 2.Parts of a Tower CraneAll tower cranes consist of the same basic parts: The base is bolted to a large concrete pad that support

4、s the crane. The base connects to the mast (or tower), which gives the tower crane its height. Attached to the top of the mast is the slewing unit - the gear and motor - that allows the crane to rotate: On top of the slewing unit are three parts: The long horizontal jib (or working arm), which is th

5、e portion of the crane that carries the load. A trolley runs along the jib to move the load in and out from the cranes center: The shorter horizontal machinery arm, which contains the cranes motors and electronics as well as the large concrete counter weights: The operators cabThe machinery arm cont

6、ains the motor that lifts the load, along with the control electronics that drive it and the cable drum, as shown here:The motors that drive the slewing unit are located above the units large gearNow lets find out how much weight this equipment can handle.3.How Much Weight Can They Lift?A typical to

7、wer crane has the following specifications: Maximum unsupported height - 265 feet (80 meters) The crane can have a total height much greater than 265 feet if it is tied into the building as the building rises around the crane. Maximum reach - 230 feet (70 meters) Maximum lifting power - 19.8 tons (1

8、8 metric tons), 300 tonne-meters (metric ton = tonne) Counterweights - 20 tons (16.3 metric tons) The maximum load that the crane can lift is 18 metric tons (39,690 pounds), but the crane cannot lift that much weight if the load is positioned at the end of the jib. The closer the load is positioned

9、to the mast, the more weight the crane can lift safely. The 300 tonne-meter rating tells you the relationship. For example, if the operator positions the load 30 meters (100 feet) from the mast, the crane can lift a maximum of 10.1 tonnes. The crane uses two limit switches to make sure that the oper

10、ator does not overload the crane: The maximum load switch monitors the pull on the cable and makes sure that the load does not exceed 18 tonnes. The load moment switch makes sure that the operator does not exceed the tonne-meter rating of the crane as the load moves out on the jib. A cat head assemb

11、ly in the slewing unit can measure the amount of collapse in the jib and sense when an overload condition occurs. Now, it would be a pretty big problem if one of these things fell over on a job site. Lets find out what keeps these massive structures standing upright. 4.Why Dont They Fall Over?When y

12、ou look at a tall tower crane, the whole thing seems outrageous - why dont these structures fall over, especially since they have no support wires of any kind? The first element of the tower cranes stability is a large concrete pad that the construction company pours several weeks before the crane a

13、rrives. This pad typically measures 30 feet by 30 feet by 4 feet (10 x 10 x 1.3 meters) and weighs 400,000 pounds (182,000 kg) - these are the pad measurements for the crane shown here. Large anchor bolts embedded deep into this pad support the base of the crane: So these cranes are essentially bolt

14、ed to the ground to ensure their stability. In the next section, youll learn how tower cranes grow. 5.How Do They Grow?Tower cranes arrive at the construction site on 10 to 12 tractor-trailer rigs. The crew uses a mobile crane to assemble the jib and the machinery section, and places these horizonta

15、l members on a 40-foot (12-m) mast that consists of two mast sections. The mobile crane then adds the counterweights. The mast rises from this firm foundation. The mast is a large, triangulated lattice structure, typically 10 feet (3.2 meters) square. The triangulated structure gives the mast the st

16、rength to remain upright. 6.To rise to its maximum height, the crane grows itself one mast section at a time! The crew uses a top climber or climbing frame that fits between the slewing unit and the top of the mast. Heres the process: The crew hangs a weight on the jib to balance the counterweight. The crew detaches the slewing unit from the top of the ma

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