Used tower cranes
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Tower cranes are a modern form of balance crane that consist of the same basic parts. Fixed to the ground on a concrete slab (and sometimes attached to the sides of structures as well), tower cranes often give the best combination of height and lifting capacity and are used in the construction of tall buildings. The base is then attached to the mast which gives the crane its height. Further the mast is attached to the slewing unit (gear and motor) that allows the crane to rotate. On top of the slewing unit there are three main parts which are: the long horizontal jib (working arm), shorter counter-jib, and the operator’s cab.
Tower crane cabin
The long horizontal jib is the part of the crane that carries the load. The counter-jib carries a counterweight, usually of concrete blocks, while the jib suspends the load to and from the center of the crane. The crane operator either sits in a cab at the top of the tower or controls the crane by radio remote control from the ground. In the first case the operator’s cab is most usually located at the top of the tower attached to the turntable, but can be mounted on the jib, or partway down the tower. The lifting hook is operated by the crane operator using electric motors to manipulate wire rope cables through a system of sheaves. The hook is located on the long horizontal arm to lift the load which also contains its motor.
File:Rotating tower crane.ogv
A tower crane rotates on its axis before lowering the lifting hook.
In order to hook and unhook the loads, the operator usually works in conjunction with a signaller (known as a ‘dogger’, ‘rigger’ or ‘swamper’). They are most often in radio contact, and always use hand signals. The rigger or dogger directs the schedule of lifts for the crane, and is responsible for the safety of the rigging and loads.
Tower Cranes are used extensively in construction and other industry to hoist and move materials. There are many types of tower cranes. Although they are different in type, the main parts are the same, as follows:
Mast: the main supporting tower of the crane. It is made of steel trussed sections that are connected together during installation.
Slewing Unit: the slewing unit sits at the top of the mast. This is the engine that enables the crane to rotate.
Operating Cabin: the operating cabin sits just above the slewing unit. It contains the operating controls.
Jib: the jib, or operating arm, extends horizontally from the crane. A “luffing” jib is able to move up and down; a fixed jib has a rolling trolley that runs along the underside to move goods horizontally.
Hook: the hook (or hooks) is used to connect the material to the crane. It hangs at the end of thick steel cables that run along the jib to the motor.
Weights: Large concrete counterweights are mounted toward the rear of the mast, to compensate for the weight of the goods lifted.
A tower crane is usually assembled by a telescopic jib (mobile) crane of greater reach (also see “self-erecting crane” below) and in the case of tower cranes that have risen while constructing very tall skyscrapers, a smaller crane (or derrick) will often be lifted to the roof of the completed tower to dismantle the tower crane afterwards, which may be more difficult than the installation.
Four self-erecting tower cranes mounted on the roof of 1st observatory (height 375 m) of Tokyo Skytree (Tower tip and two crane operator as of 497 m)
Generally a type of tower crane, these cranes, also called self-assembling, jack-up, or “kangaroo” cranes, lift themselves from the ground or lift an upper, telescoping section using jacks, allowing the next section of the tower to be inserted at ground level or lifted into place by the partially erected crane itself. They can thus be assembled without outside help, and can grow together with the building or structure they are erecting.
For a video of a crane getting taller, see here :
For another animation of such a crane in use see this video : (Here, the crane is used to erect a scaffold which in turn contains a gantry to lift sections of a bridge spire.)
A telescopic crane has a boom that consists of a number of tubes fitted one inside the other. A hydraulic or other powered mechanism extends or retracts the tubes to increase or decrease the total length of the boom. These types of booms are often used for short term construction projects, rescue jobs, lifting boats in and out of the water, etc. The relative compactness of telescopic booms make them adaptable for many mobile applications.
Though not all telescopic cranes are mobile cranes, many of them are truck-mounted.
A telescopic tower crane has a telescopic mast and a superstructure (jib) on top so that it functions as a tower crane. Some telescopic tower cranes also have a telescopic jib.
The “hammerhead”, or giant cantilever, crane is a fixed-jib crane consisting of a steel-braced tower on which revolves a large, horizontal, double cantilever; the forward part of this cantilever or jib carries the lifting trolley, the jib is extended backwards in order to form a support for the machinery and counterbalancing weight. In addition to the motions of lifting and revolving, there is provided a so-called “racking” motion, by which the lifting trolley, with the load suspended, can be moved in and out along the jib without altering the level of the load. Such horizontal movement of the load is a marked feature of later crane design. These cranes are generally constructed in large sizes and can weigh up to 350 tons.
The design of hammerkran evolved first in Germany around the turn of the 19th century and was adopted and developed for use in British shipyards to support the battleship construction program from 1904 to 1914. The ability of the hammerhead crane to lift heavy weights was useful for installing large pieces of battleships such as armour plate and gun barrels. Giant cantilever cranes were also installed in naval shipyards in Japan and in the United States. The British government also installed a giant cantilever crane at the Singapore Naval Base (1938) and later a copy of the crane was installed at Garden Island Naval Dockyard in Sydney (1951). These cranes provided repair support for the battle fleet operating far from Great Britain.
In the British Empire, the engineering firm Sir William Arrol & Co Ltd was the principal manufacturer of giant cantilever cranes; the company built a total of fourteen. Among the sixty built in the world, few remain; seven in England and Scotland of about fifteen worldwide.
The Titan Clydebank is one of the 4 Scottish cranes on the Clydebank and preserved as a tourist attraction.