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Cranes are construction machines used for lifting and lowering material needed on any construction projects. They are commonly used in the freight industry for loading and unloading heavy items as well as in the construction industry and in manufacturing for assembly purposes. Tower cranes are a common sight in any important construction site. They're quite hard to miss -- they often rise hundreds of feet high, and can reach out just as far. The construction crew uses the tower crane to lift steel, concrete, large tools such as generators, and other building materials.
Cranes are one of the first instruments used in construction and seems to have first been used in ancient Greece. While powered by men or animals at the time, they developed over the centuries to become what it is now. Cranes had a long wooden beam called arrow and was connected to a rotating base. The wheel turned thanks to a cord wrapped around a drum. The cable attached to a pulley above the arrow, a hook that had lifted the weight.
During the middle Ages, cranes were used to build European cathedrals and to load and unload ships at ports. A horizontal handle was added to the arrow. This handle is called the jib. This addition has improved the deflection of the crane, adding the ability to rotate. The streets were narrow in Europe, having high jib crane with the worker sitting on top was therefore a great advantage. In 1908, Julius Wolff Maschinenfabrik & Co. produced the first tower crane. About 10,000 units were sold. In 1949, Hans Liebherr realized that there were no cranes on the market. Liebherr was thus able to revolutionize the field of tower cranes with the conception of the TK-10.
The first mechanical crane powered by steam engine appeared in the 19th century and remained in use for many years, some are still in use to this day. Modern cranes have a combination of hydraulic and internal combustion systems that enable an increase in weight lifting.
The hydraulic system is based on a simple concept but is extremely efficient -- the transmission of forces from point to point is made through a fluid. Most hydraulic machines use some sort of incompressible fluid meaning that it is at its maximum density.
There are 2 main aspects to take into consideration when designing a crane: lifting capacity and stability.
Lifting capacity depends greatly upon the strength of the leveler, the pulley and the hydraulic system which are the main component to a crane. There are two limit switches the operator can use to make sure that he does not overload the crane: The maximum load switch and the “load moment” switch to make sure that he does not exceed the tone-meter rating of the crane while the load moves out on the jib.
There are different types of cranes each tailored to a specific use:
Tower cranes are the first thing we think about when talking about cranes. They do not generally have a moveable base. These are usually used in the construction of high buildings as they are the tallest cranes. They have to be assembled piece by piece. The base looks like a high ladder, and the arm is perpendicular to the base. In the case of skyscrapers, the crane is often assembled and set up inside the building itself during construction.
Overhead cranes: often used in factories they are used to carry heavy pieces of metal or material on a rail mounted cable.
A fairly simple type of crane is the mobile crane with just a telescopic arm or steel truss mounted on a movable platform. Either pulleys or levers raise the boom. Generally a hook suspends from the boom. Mobile cranes can also be truck-mounted.
From being simple machines used to carry up and down materials, cranes have become more sophisticated simplifying processes in manufacturing and construction industries. They have made it safer and easier to move large, heavy loads, reduced human effort and also enabled for better timing, thereby increasing the output.