Derrick
A derrick is a crane that consists of a mast braced or braced at the top and an adjustable boom. The boom is articulated on the mast and is held in a certain position by a rope guided over the top of the mast. The load is lifted with a rope passed over the tip of the boom. The boom can also be swiveled around the vertical axis of the mast, usually the entire mast rotates with it. The name comes from the English executioner Thomas Derrick .
history
Because of its favorable properties, this construction principle of a hoist was used early on. Similar predecessor designs, in which the function of mast and boom coincided in an A-shaped frame and which allowed the load to move horizontally in at most one direction, were already used in ancient Greece. The use of Derrickkranen as haggard as a rule, construction cranes with hochangesetztem boom reached its peak in the mid-20th century, after which they were increasingly easier-to-use tower cranes and mobile cranes replaced.
construction
In the case of the so-called low-set boom with mounting on the mast base, the force introduction into the construction, which takes place exclusively at the ends of the components via ropes or joints, does not result in any bending moments : only compressive forces act in the mast and boom; when the mast is fixed with two struts, only tension acts on it - and pressure forces. Therefore, only the bending stiffness required for the buckling strength is necessary for all components , which allows a relatively slim and light construction. In order to be able to work over larger obstacles, however, a high-mounted boom is required, as a result of which bending moments occur in the mast, which accordingly requires more complex mast constructions.
Because of the favorable ratio between the cross-sectional dimensions of the mast and the boom and thus also the dead weight on the one hand and the load on the other hand, such derrick cranes are used as mobile cranes where these properties are required when there are no obstacles at the same time, such as the free front construction of bridges, where the weight of the Crane loads the cantilevered component and in the construction of high-rise buildings , where the derrick crane on the building may be used to dismantle other cranes that have climbed with it and can finally be lowered in parts without a crane, for example through elevator shafts. As stationary cranes, such derrick cranes are also often used in quarries where large blocks of natural stone are extracted because of their cost-effective construction.
Derricks in quarries
In natural stone quarries, derrick cranes usually lift stone blocks of 30 t and more. Examples are Belgian bluestone quarries and marble quarries in Carrara . Derricks have largely been replaced by wheel loaders in quarries today . Smaller specimens can still be found occasionally in stone or wood sawmills or in quarries with complicated terrain (steep slopes) or smaller mining volumes.
Technical details
The derrick cranes commonly used in quarries have a horizontal slewing range of up to 220 °. The boom has a vertically lowerable range of motion from 85 ° to 0 ° (or below). Its typical working range is between 85 ° and 30 °. The common cranes lift loads between 20 and 40 tons, in a steep jib position (85 °) even up to 80 tons. The boom has a length between 15 and 45 meters depending on the specific application. In the case of quarries on a slope, a longer extension arm is usually necessary. Broken shafts require longer rope lengths and a largely barrier-free maximum horizontal swiveling freedom.
A pulley block is attached to the boom , which ensures favorable payload conditions when transporting loads. The extension arm is operated via its own cable pull.
The vertical main mast is stabilized by means of lateral, inclined lattice mast arms or, in the case of smaller derrick cranes, by means of tensioned ropes that are also attached to a floor anchor. The latter principle allows a horizontal swivel range of 360 ° in individual cases and can occasionally be observed in this form in storage areas in quarries or stone processing plants.
Foreign language terms
- italian gru derrik
- french grue de derrick or derrick
- english guy derrick or stiffleg derrick
See also
literature
- Franco Cucchi, Santo Gerdol: I marmi del Carso triestino . Camera di Commercio Industria Artigianato e Agricoltura, Trieste 1985, pp. 59-60, 97 (Italian).
- Günther Mehling (Ed.): Natural stone lexicon . Material, tools and machines, economy and trade, design and techniques from antiquity to today 4th, completely revised and updated edition, Callwey, Munich 1993 (first edition 1973, 5th A. 2003), pp. 101-102, ISBN 3 -7667-1054-0 .
- Raymond Perrier: Les roches ornementales . Pro Roc, Ternay 2004, p. 66, ISBN 2-9508992-6-9 (French).
Individual evidence
- ↑ Cucchi, Gerdol, 1985, p. 59
- ↑ Perrier, 2004, p. 501
- ↑ Technical specification ( Memento of the original from August 20, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
Web links
- Image examples
- large cranes (PDF; 976 kB)
- Derrick crane adding chimneys to the Dresden thermal power station in 1949; Chimney as a crane mast: [1] , [2] , [3] , [4] , [5]