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crane, in zoology
crane,large wading bird found in marshes in the Northern Hemisphere and in Africa. Although sometimes confused with heronsheron
, common name for members of the family Ardeidae, large wading birds including the bittern and the egret, found in most temperate regions but most numerous in tropical and subtropical areas.
..... Click the link for more information. , cranes are more closely related to railsrail,
common name for some members of the large family Rallidae, marsh and tropical forest birds that include the gallinule and the coot, two specialized rails. Rails are cosmopolitan in distribution, except in polar regions.
..... Click the link for more information. and limpkinslimpkin
, common terms for a long-legged, nonmigratory marsh bird, considered the connecting evolutionary link between the crane and the rail. They have a cranelike skeletal structure, but their digestive system, as well as their nesting habits and behavior,
..... Click the link for more information. . Cranes are known for their loud trumpeting call that can be heard for miles and for the rhythmic, jumping dances both males and females perform during mating season. They eat small animals, grain, and other vegetable matter. The North American whooping crane, a white bird almost 5 ft (1.5 m) tall, was nearly extinct by the 1940s. Many have since been raised in captivity and new populations in the wild have been fostered, although the bird is still endangered. Most migratory whooping cranes winter at Aransas Bay, Tex. The migratory populations of the sandhill crane, about 4 ft (1.2 m) tall with gray plumage, winter west of the Mississippi River; they are noted for their large congregations along the Platte River in Nebraska during migration. The crowned crane of Africa has bright, contrasting colors. At the beginning of the 21st cent. there were 15 species of crane in the world, 11 of them endangered. Cranes are classified in the phylum ChordataChordata
, phylum of animals having a notochord, or dorsal stiffening rod, as the chief internal skeletal support at some stage of their development. Most chordates are vertebrates (animals with backbones), but the phylum also includes some small marine invertebrate animals.
..... Click the link for more information. , subphylum Vertebrata, class Aves, order Gruiformes, family Gruidae.
See P. Matthiesen, The Birds of Heaven: Travels With Cranes (2001).
crane,hoisting machine for lifting heavy loads and transferring them from one place to another, ordinarily over distances of not more than 200 ft (60 m). Cranes have a long reach and can lift loads to great heights. Powered by manual or animal power, cranes have been in use from early times. Modern cranes are of varied types and sizes; they may be actuated by steam, electricity, diesel, or hydraulic power as well as by manual power, and they are indispensable in industries where heavy materials are handled constantly. The overhead traveling crane, a type of bridge crane, is used inside buildings or in outdoor storage yards. Two or more parallel girders span its working area. Another girder, called the bridge, stretches between them and rolls along them on wheels; this girder, in turn, supports a carriage from which a lifting attachment is lowered by pulleys. On a stacking crane the pulleys are replaced by a stiff, rotating column on which a pair of forks ride up and down. The gantry crane, another type of bridge crane, has a bridge supported by vertical structures that move along tracks. Gantries are used on piers or in shipyards. The jib crane has a horizontal load-supporting boom fastened to a rotating vertical column, either attached to a wall or extending from floor to ceiling; when the column is held only at the bottom it is called a pillar crane. The derrick is a crane equipped either with a vertical mast held by struts, as on barges, or with guy wires, as in building construction. The boom is attached to the bottom of the mast by a pivot and is raised and lowered by a cable reaching from the top of the mast to the end of the boom. A crawler crane is a self-propelled crane that moves on caterpillar treads.
a cyclical-operation hoisting machine with reciprocating movement of the hoisting gear; it is used to lift and move freight. The operating cycle of a crane consists of three steps; grasping the load, movement for shifting and releasing the load, and return of the empty hoisting gear to a pickup point for another load. A crane may also move in order to shift the position of the crane body or the boom. The main characteristic of a crane is its lifting capacity, which is defined as the greatest weight that can be lifted; in the case of the interchangeable hoisting gear, the weight of the gear is included in the total capacity.
History. Until the late 18th century the simplest cranes, like most hoisting machines, were made of wood and operated manually. In the early 19th century, metal came to be used for critical parts that wore out quickly, such as shafts, wheels, and gripping devices. The first all-metal cranes, which were manually operated, appeared in the 1820’s; mechanically driven cranes appeared in the 1830’s.
The first steam-driven crane was built in Great Britain in 1830, and the first hydraulic crane in 1847. An internal-combustion engine was used in a crane in 1895, and in the period 1880–85 electric motors came into use almost simultaneously in the USA and Germany in bridge cranes with single-motor drives. In 1890 cranes with multimotor individual drives were introduced.
The production of modern types of cranes began in Russia in the late 19th century at the Putilov, Briansk, Kramatorsk, and Nikolaev plants. After the October Revolution of 1917 the construction of cranes in the USSR became an important branch of heavy machine building, and specialized plants were set up.
General information. A crane may be rotary or fixed, depending on its design and the method of operation. Rotary cranes may be mounted on rails (locomotive cranes and cranes on tracks); they may travel without rails (trailer-mounted cranes, crane trucks, and crawler cranes); they may be mounted on the walls and roofs of buildings (wall-bracket and roof cranes); or they may be on pontoons and ships (floating and ship cranes). There are also rotary cranes, called walking cranes, that move along two rails at different levels (above and below). Locomotive, truck, and crawler rotary cranes are often classified as self-propelled rotary-jib cranes.
The slewing portion of a crane is supported on a fixed or rotating pillar or on a swivel plate with wheels, rollers, or balls. The slewing portion may be in the form of a high tower (column cranes) or a mast (guyed or rigidly mounted mast-jib cranes). It may be mounted on a gantry (gantry cranes). Rotary cranes may have a fixed or variable radius (the distance between the load and the axis of rotation of the crane), which is changed by swinging the jib (boom) or moving the hoisting gear.
The fixed cranes include those of the span type, such as bridge and transporter cranes, and also wall-bracket cantilever cranes. Bridge cranes have a traveling bridge that moves along rails laid on the walls of a building or on special piers outside the building. A hoist trolley with a winch moves along the bridge, and in some designs the trolley is equipped with a rotary jib. Wall-bracket cantilever cranes consist of a wall-mounted cantilever beam and a hoist trolley with a winch that moves along the beam. Transporter cranes are similar to bridge cranes, but their bridge has high supports (legs) that move along ground tracks. If the spans are long, the cranes are called bridge transporters or transporter bridges, and if the spans are short they are called gantry cranes. However, there is no clear-cut division. The bridges of transporters can have fixed or extensible cantilevers; a hoist trolley or a rotary crane can travel along the bridge. Cantilever transporters designed for loading and unloading ships are called harbor cantilever transporters and can also be mounted on ships (ship transporter cranes). A special type of transporter is the cable crane, in which the hoist trolley is moved by a traction cable along a fixed cable that is stretched between two traveling towers or stationary pillars. Bridge cable cranes, in which the fixed cable is attached to the ends of the bridge truss, are a variety of cable crane. Monorails with trolleys equipped hoisting mechanisms are similar in design to cranes.
Helicopter cranes with load-gripping devices are also used in modern construction to perform operations in areas that are difficult of access.
Fields of application. Bridge cranes are standard equipment in industrial shops, electric power plants, warehouses, and storage yards. Their lifting capacity is up to 500–600 tons, and their span (the distance between the axes of the rails under the cranes) is up to 50-60 m. Loads may be lifted to heights of 40–50 m, and in special cases up to 500 m; the travel speed of the bridge is 30–160 m/min, and that of the hoist trolley is 10-60 m/min; the rate of lift is up to 60 m/min. Two hoist trolleys may be mounted on one or two tracks (adjoining or at different levels) on a single bridge. General-purpose bridge cranes include hook, magnetic, grab-bucket, and combined magnetic and grab bucket types. In the simplest single-rail hook cranes, both top-running and underhung, the hoist trolley is a self-propelled electric pulley block. A special group is made up by the metallurgical bridge cranes (foundry, changing, soaking-pit, ingot-stripping, and other types), which are equipped with special load-gripping devices and control mechanisms. A variety of bridge crane is the stacker crane, which has a hoist trolley fitted with a rotary mast along which a fork-lift attachment moves, so that package loads on pallets can be carried, stacked, and sorted.
Fixed, cantilever wall-bracket cranes are used mainly in shops to reduce the work load of bridge cranes. Such cranes usually have a lifting capacity of 3-10 tons, a span of 5-10 m, and a travel speed of 90–200 m/min.
Gantry cranes are used mainly in open storage yards (less frequently in warehouses) for piece goods, containers, and timber. They are also used in the assembly of prefabricated industrial and public buildings, to serve hydroelectric power plants, and to assemble sections in shipbuilding. They are constructed with hooks or special load-gripping devices. General-purpose cranes usually have a span of 4–40 m; for servicing shipbuilding slips, up to 170 m. The lifting capacity of such cranes is 3-50 tons, but in cranes serving hydroelectric power plants and building slips it may be 400–800 tons (in certain cases, 1,600 tons, using two trolleys of 800 tons each). The travel of such cranes, at a rate of 20-100 m/min, is frequently the working movement; for small lifting capacities self-propelled electric tackle blocks are used as hoist trolleys. Cranes with two hoist trollies are used in the assembly of large objects, as in the case of shipbuilding; this makes it possible to tilt the load while it is suspended. Construction cranes, whose site of operation changes, are designed to be self-erecting. Gantry cranes on pneumatic tires, with spans of 6-15 m, lifting capacities of 15-30 tons, and travel speeds of up to 8 km/hr, are often used in open yards where piece goods are stored.
Bridge transporters, or transporter bridges, are usually made with grab buckets; they are used mainly in open storage yards for coal and ores and in industrial enterprises, electric power plants, and ports. The lifting capacity of transporters with grab buckets is 15–30 tons, the speed of movement of the hoist trolley is 160–360 m/min, the lifting speed is 60-70 m/min, and the capacity is 500–1,000 tons/hr. To increase the area served by a crane, the hoist trolleys can be equipped with a rotary jib having a rate of rotation of 2–4 rpm and a span of 3-6 m. Transporters with a rotary crane have a lifting capacity of 10-20 tons and a boom span of 10-20 m, and the speed of the crane’s movement along the upper part of the bridge is 120–180 m/min. They are sometimes equipped with a belt conveyor that is loaded by the crane, thus reducing its travel and increasing the efficiency of the transporter.
Hook-type transporters for piece loads have a lifting capacity of up to 300 tons. To serve circular storage yards, radial bridges in which one of the supports is fixed by swiveling and the other moves along a circular track are used. The bridges have a span of up to 120 m, with a cantilever length of up to 50 m. The lifting time of the cantilever is 5-10 min. The travel speed of the bridge when changing position is 10-30 m/min.
Self-propelled jib cranes—locomotive cranes, crane trucks, and all-purpose crawler cranes (on a twin caterpillar track, and also on a tractor base)—are designed for loading-unloading and assembly operations in construction, industrial enterprises, and transportation. The cranes are equipped with interchangeable booms of various lengths and configurations, such as straight, curved, and telescoping types, depending on the operating conditions. The length of the booms on crane trucks and crawler cranes for lifting loads to great heights can reach 60–100 m. Outrigger supports are used to improve stability. The speed of the movements varies with the lifting capacity of the crane and the radius of the boom and is usually 5-25 m/min for lifting and 1-4 rpm for slewing; the time to raise the boom from its lowest position to its highest is 1-3 min. During operation, the crane travels at 1–10 km/hr.
Jib cranes are made with hooks and grab buckets, and diesel-electric cranes are also equipped with an electromagnet. They have a variable lifting capacity, which is greatest when the radius is the least and outriggers are used: for locomotive cranes it is up to 40 tons (special emergency and assembly cranes have a capacity of up to 300 tons); for truck cranes, 16–40 tons; for pneumatic-tired trailer-mounted cranes, up to 200 tons (for special assembly cranes, up to 600 tons); and for crawler cranes, up to 300 tons. High-capacity pneumatic-tired cranes are mounted on trailers with tractors.
Tower cranes are used mainly for civil, industrial, and hydraulic-engineering construction (building cranes) and also for serving open shipbuilding berths and outfitting operations in shipbuilding (shipbuilding cranes). The design of tower construction cranes is such that they can be quickly assembled and disassembled and transported by a motor vehicle. They are usually of the hook type with rotary and fixed towers that telescope or can be extended at the top or bottom for greater height. Construction cranes usually move along rails, but where considerable heights are involved they may also be of the attachable type, which rests on the ground and on the frame of the building under construction, or the self-raising type (sometimes called climbing cranes), which are supported by the building and travel vertically as the structure being erected gains in height. Tower cranes on trucks, special rubber-tired chassis, and crawler tracks are based on ordinary jib cranes; they have derrick gear in the form of lifting (swinging) booms or cantilever booms along which a hoist trolley is moved by a traction cable. The radius of construction cranes is up to 40 m, the lift height is up to 150 m, the lifting speed is 10-100 m/min, the rate of rotation is 0.2-1.0 rpm, and the travel speed when moving into position is 10–30 m/min. The lifting capacity is variable, ranging up to 75 tons at minimum radius. Shipbuilding tower cranes have a radius of up to 50 m and are designed to travel on the ground or on trestles. Berth cranes have a lifting capacity of up to 100 tons. Stationary outfitting cranes have a capacity of up to 400 tons.
Gantry cranes are used for loading and unloading operations in ports and storage yards, for construction work (mainly in hydraulic engineering), for assembly operations in shipbuilding, and for ship repairs from the shore and from floating docks. They are subdivided into loading cranes (hook-type, grab-bucket, and less frequently, magnetic) and assembly cranes, depending on the nature of the work. A special type of gantry crane is the high-performance bucket-bin loading crane which is designed for unloading ships. In this type of crane with programmed control, the bucket fills a bin located on the gantry. The rotary portion of the cranes can be mounted on semigantries (single rails on the wall of a building) or on triangular supports on sloping embankments. The derrick gear usually permits horizontal movement of the load by changing the radius. The lifting capacity of bucket cranes is fixed, but that of the hook type is more often variable. The lifting capacity of loading-unloading cranes is 5–40 tons, and that of assembly cranes 100-300 tons; the radius is usually 25-35 m but may reach 50–100 m for shipbuilding cranes. The lifting speed is 60–90 m/min, the rate of rotation is 1.5–2 rpm, and the travel speed when moving into position is 30 m/min; the figures for assembly cranes are substantially lower than for loading-unloading cranes.
Wall-bracket, cantilever rotary cranes are usually stationary, and less frequently mobile. Stationary cranes are used to serve work areas in shops and warehouses, whereas mobile cranes are used mainly to perform internal operations in large machine shops. The lifting capacity of stationary cranes is 0.25-3.2 tons, and the radius is 3-6 m.
Floating cranes, which are designed to operate while afloat, consist of a superstructure (the crane) and a self-propelled (10–15 km/hr) or a non-self-propelled pontoon. They are subdivided into rotary (general-purpose) types and fixed (pillar and gantry) types, according to the design of the superstructure. Fixed floating cranes have a lifting capacity of up to 1,500–2,500 tons and a radius (from the edge of the pontoon) of up to 25 m. They are used to lift particularly heavy loads and to perform special operations. The rotary portion of floating cranes is similar to that of gantry cranes.
Cranes used for bulk large-scale loading and unloading operations are usually non-self-propelled and have a lifting capacity of up to 25 tons and a radius of up to 35 m; rotary cranes for loading operations on heavy-cargo vessels, and also for assembly and installation operations, for shipbuilding, and for emergency and salvage operations, have a lifting capacity of up to 350 tons with a radius of up to 60 m (they are usually self-propelled).
Ship cranes are usually of the stationary rotary type, but some are mobile (bridge or gantry cranes). The lifting capacity of stationary cranes is 1-16 tons at a radius of up to 16 m.
Main subassemblies. The principal mechanism in a crane is the hoist, and there are usually one to three (in some cases up to six) other mechanisms in various types of cranes—for example, mechanisms for moving hoist trolleys, for revolving the rotary portion or the derrick gear of hoist trolleys, for changing the radius of the boom, or for raising or extending the cantilever of the bridge. Mobile cranes also have drive mechanisms. In addition to the mechanism for the principal hoist, high-capacity cranes often have one or two independently operated auxiliary hoisting mechanisms for the speedy movement of loads of lesser weight.
A hoisting mechanism consists of a flexible hoisting member, usually a steel-wire rope, and a single-drum or double-drum winch. Attached to the lower end of the rope, either directly or through a ring on the pulley block, is a load hook or one of various load-gripping devices, which may be automatic—for example, lifting electromagnets, pneumatic suckers, gripping tongs, and grab buckets (such cranes are correspondingly called hook, bucket, magnet, tong, and container cranes). If several hoisting speeds are required—for example, speed for setting loads down and a faster speed for loads of low weight—a multi-speed winch is used. In cases where particularly high accuracy is required, as in the performance of technological operations (for example, in certain metallurgical bridge cranes) or when stacking loads, a “rigid” suspension is used. In such cases the load-gripping device is attached to a rod that moves vertically in a guide shaft. The rigid suspension completely eliminates rocking of the load but substantially increases the weight of the crane. To ensure safe operation, the hoisting mechanisms are equipped with stops for the load-gripping device and limiters of the lifting capacity or the load moment. Some cranes have automatic scales for determining the weight of the load being lifted. The mechanisms for moving cranes and hoist trolleys along tracks usually use drive wheels; traction cables are sometimes used, but usually only for the hoist trolleys. The wheels may have a common drive or individual drive. In the case of a common drive, the wheels are turned by a single motor through a driveshaft. With individual drives, each wheel or truck of the traveling trolley has its own motor.
Safety devices for the movement mechanisms include travel limiters (limit switches and stops) and anticreep devices (to protect against wind effects). The boom devices are for nonhorizontal and horizontal movement of the load when raising and lowering the boom (changing the radius). The devices for non-horizontal load movements are used in cranes where a change in the radius is an adjustment movement and is performed when the boom is not loaded (for example, on locomotive cranes). The devices for horizontal load movements, including hinged-joint jibs, substantially reduce the drive power; they are used on cranes for which a change in the radius is an operating movement—for example, tower, bridge, floating, and rotary ship cranes.
The mechanisms for changing the radius are in the form of a boom pulley block with a winch, a rectilinearly moving screw rod or rack with a drive, a hydraulic cylinder, a drive gear quadrant, or crank gear mechanism. These mechanisms act directly on the boom or on a system of levers linked to it. The safety devices for the boom are limit switches that restrict the angle of swing of the boom.
The metal structures of cranes are usually welded. In the interests of weight reduction they are made of high-strength low-alloy steels, as well as aluminum alloys.
Electric motors (mainly of the AC type), internal-combustion engines (usually diesels), hydraulic and compressed-air motors, and hand-operated gears are used in the drive mechanisms of cranes. If smooth speed adjustment over a wide range is required, DC electric motors are used. Internal-combustion engines are installed on cranes that must operate independently of an electric power system (floating, locomotive, truck, and crawler cranes). To avoid the complications and control difficulties of a distributive drive from a single motor to a number of mechanisms (single-motor drive), a combination diesel-electric or diesel-hydraulic drive is used in which each mechanism has a separate electric or hydraulic motor (hydraulic cylinder), thus making up a multimotor drive in which the diesel engine operates an electric generator or pumps. The hydraulic drive is compact and can provide infinitely variable control over a wide range of speeds, but its efficiency is low. Pneumatic drives with piston engines and cylinders are used on small hoisting cranes that operate in locations where there is a danger of explosion. A manual drive is used on cranes that are intended for occasional shifting of loads over small distances. The speed of movement in this case is low because of the limited power.
The crane mechanisms are controlled by a single operator from a cab that may be located on the rotary portion, the hoist trolley, or the bridge. Low-speed and infrequently used cranes can be controlled by workers on the ground by means of pushbutton apparatus. Remote control through wire or radio is also possible. When working on a definite schedule, programmed control that automatically handles most of the operations is also feasible; radiotelephone and television communication between the crane operator and the work location is used in some cases. The mechanisms are slowed or stopped by automatic or operator-controlled mechanical brakes. If electric motors are used, electrical braking is also possible.
Prospects for development. The prospects for development in crane design correspond to the growing needs of the sectors of the national economy in which cranes are used. Two major problems are to increase the lifting capacity and the principal parameters, such as the spans, the radius of booms, and the lifting height, and to improve the maneuverability of mobile cranes. These improvements are directed toward broadening the sphere of application of cranes. An increase in efficiency is also important; to this end an increase in the speed of the working movements, the use of automatic load-gripping devices, and the introduction of automatic control systems are envisioned. Another important problem is improvement of the precision of crane operations, which will require development of automatic systems for damping oscillations of the load and an increase in the range of speed regulation. Dynamic loading and the empty weight of cranes should also be reduced.
REFERENCESSpravochnik po kranam, 2nd ed., vols. 1-2. Edited by A. I. Dukel’skii. Leningrad, 1971-73. (Contains a bibliography.)
Gruzopod”emnye mashiny. Edited by M. P. Aleksandrov. Moscow, 1973.
Scheffler, M., G. Pajer, and F. Kurth. Grundlagen der Fordertechnik, 4th ed. Berlin, 1971.
Broughton, H. H. Electric Cranes, 3rd ed. London, 1958.
A. I. DUKEL’SKII