You must have seen a crane lifting and moving heavy loads at construction sites and other places. The machine got its name from its resemblance to the crane bird which has a long neck!
Although cranes have been in use .since ancient times, their widespread use only began in the 19th century with the development of steam engines, internal combustion engines and electric motors.
Basically, cranes are of two types: fixed and mobile. The mobile cranes are more common. Some have a jib or boom that can move up and down and can swing around in a circle. Some others form a bridge and can lift a load up and down, move it along a track and move it from side to side above the construction site.
A common mobile crane is the crawler. It is mounted on a vehicle with wheels. These cranes are mainly used for civil engineering and construction work. They can lift heavy loads upto around 72 tons and can have a boom length of 30 m (100 ft) or more.
Another type of crane is the hammer head or cantilever crane. It is used in the construction and erection of tall buildings. It has a long horizontal jib that is cantilevered and mounted on a tower. The tower can be raised by jacking it up, floor by floor, as the building becomes taller. The load is suspended from a trolley that moves along the jib.
Bridge cranes comprise another important class of cranes in which the hoisting apparatus moves on tracks along a horizontal beam. In most cases, the ends of the beam move along a pair of parallel rails, so that the crane can serve as a large rectangular area.
The forklift truck, widely used for moving goods between warehouse storage shipping vehicles, is a highly maneuverable crane adapted to handling drums, crates or loaded skids or pallets. Gantry cranes, with long booms, are used for unloading ships while overhead cranes are used in factories.
The world’s most powerful crane is owned by Heerema Engineering Service of Netherlands. It weighs 53,000 tons and is 178 m long. It can lift upto 3000 tons.