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Last Updated: Sep 2009
Last Updated: Sep 2009
A hook is suspended from the top of the boom by cables and pulleys. The cables are operated by whatever prime movers the designers have available, operating through a variety of transmissions. Steam engines, electric motors and internal combustion engines (IC) have all been used. Older cranes' transmissions tended to be clutches. This was later modified when using IC engines to match the steam engines "max torque at zero speed" characteristic by the addition of a hydrokinetic element culminating in controlled torque converters.
The operational advantages of this arrangement can now be achieved by electronic control of hydrostatic drives, which for size and other considerations is becoming standard. Some examples of this type of crane can be converted to a demolition crane by adding a demolition ball, or to an earthmover by adding a clamshell bucket or a dragline and scoop, although design details can limit their effectiveness.
The operational advantages of this arrangement can now be achieved by electronic control of hydrostatic drives, which for size and other considerations is becoming standard. Some examples of this type of crane can be converted to a demolition crane by adding a demolition ball, or to an earthmover by adding a clamshell bucket or a dragline and scoop, although design details can limit their effectiveness.
crane is a tower or derrick equipped with cables and pulleys that can be used both to lift and lower materials and to shift them horizontally. Cranes are commonly employed in the construction industry and in manufacturing heavy equipment.
Construction cranes are usually temporary structures, either fixed to the ground or mounted on a purpose-built vehicle. Cranes may either be controlled from an operator in a cab that travels with the crane, by a pushbutton pendant control station, or by infrared or radio control. Where a cab operator is employed, workers on the ground will communicate with the operator through a system of standardised hand-signals or, in larger installations, radio systems; an experienced crew can position loads with great precision using only these signals.
The most basic type of crane consists of a steel truss or telescopic boom mounted on a mobile platform, which may be rail, wheeled or caterpillar tracks. The boom is hinged at the bottom, and can be raised and lowered by cables or by hydraulic cylinders.
Construction cranes are usually temporary structures, either fixed to the ground or mounted on a purpose-built vehicle. Cranes may either be controlled from an operator in a cab that travels with the crane, by a pushbutton pendant control station, or by infrared or radio control. Where a cab operator is employed, workers on the ground will communicate with the operator through a system of standardised hand-signals or, in larger installations, radio systems; an experienced crew can position loads with great precision using only these signals.
The most basic type of crane consists of a steel truss or telescopic boom mounted on a mobile platform, which may be rail, wheeled or caterpillar tracks. The boom is hinged at the bottom, and can be raised and lowered by cables or by hydraulic cylinders.
