Derrick

A derrick is a crane, the guyed at the top of a mast or abgestrebten and an adjustable boom there. The jib is articulated to the mast and is held and guided by the top of the mast rope in a specific position. The load is lifted with a guided over the tip of the boom cable. The boom can also be pivoted about the vertical axis of the mast, normally rotates with the entire mast.

The so-called low-set boom with storage at the foot of the mast to pass through, which takes place exclusively at the ends of the components by means of cables or joints of force to the construction, no bending moments: in mast and boom are only effective compressive forces acting at fixing the mast with two struts in these only train - and pressure forces. Therefore, only those required for the buckling resistance bending stiffness is necessary for all components, which allows a relatively slim and light design. To be effective over large obstacles, however, a high set boom is required, which occur in the mast bending moments, which requires correspondingly more complex poles and towers.

Due to the low in tiefangesetztem arm ratio between the cross -sectional dimensions of the mast and boom, and thus self-weight on the one hand and payload on the other hand those derricks used as transportable crane, where these properties are required at the same lack of obstructions, such as the free front end of bridges, where the weight of the crane loads the convex part and the construction of high-rise buildings where the derrick on the building if necessary serves to reduce mitgekletterter other cranes and finally can be drained in part, without the crane, for example through elevator shafts. As such stationary cranes derricks are also frequently used because of their cost structure in the same quarries where large stone blocks are obtained.

Thanks to its favorable properties of this construction principle of a hoist has been used early. The name comes from the English executioner Thomas Derrick. Similar precursor structures in which function of mast and boom in an A-shaped coincided framework and the allowable horizontal movement of the load in more than one direction have already been used in Ancient Greece. The application of Derrickkranen than usually haggard construction site cranes with hochangesetztem boom reached in the mid-20th century, culminating, after which they were increasingly replaced by easier -to-use tower cranes and mobile cranes.

• 4.1 Notes and references

Derricks in quarries

In natural stone quarries lift derricks stone blocks of usually 30 tons or more. Examples are Belgian bluestone quarries and marble quarries in Carrara. Derricks have been replaced in quarries today largely by the wheel loader. Smaller specimens are occasionally found even in stone or wood sawmills and quarries with complicated terrain position ( steep slopes ) or smaller volume reduction. He is also referred to as a three gantry crane.

Foreign language names

• Italian gru derrik
• French grue de derrick or derrick
• English guy derrick or derrick stiffleg

Technical details

The major quarries derricks have a horizontal swivel range of up to 220 °. The bracket has a vertical range of movement can be lowered from 85 ° to 0 ° ( or less). Its typical working range is between 85 ° and 30 °. The common cranes lift loads between 20 and 40 tons, in a steep boom position ( 85 ° ) up to 80 tons. The boom has depending on the specific application requires a length between 15 and 45 meters. In quarries on the hillside usually a longer extension arm is necessary. Shaft fractures require larger cable lengths and a largely barrier-free maximum horizontal pivot freedom.

On boom a pulley is attached, which provides load handling for the lowest load conditions. The boom is operated by a separate cable.

The stabilization of the main vertical mast is done via lateral, oblique lattice mast arms or with smaller derricks means of tensioned cables that are as attached to a ground anchor. The latter principle is in the individual case into a horizontal swivel range of 360 ° and is occasionally observed in this form of storage locations of the quarries and stone processing plants.