Type of Cranes
Cranes can be classified into four kinds, namely, (a) overhead traveling crane; (b) jib crane; (c) bridge or gantry crane; and (d) cantilever crane.
Overhead traveling crane. Consists of a girder and a trolley. The girder is supported at each end on trucks capable of traveling on elevated fixed tracks. The trolley is equipped with hoisting and other mechanism, capable of traversing from end to end of such girder. The girder and associated end carriages are known as the bridge.
Such cranes vary in lifting capacity from about 2 tons to 400 tons, and in span from 20 ft to 150 ft,or more. Depending on the purpo for which it is to be ud, the crane can be operated either from a cabin fixed to the bridge or the trolley, or from the ground. When two troll乳鸽的营养价值及功效
eys are furnished, the may run on a common tracksarranged side-by-side or one above the other so that each trolley can traver the entire span.
Jib crane
Consists of an inclined member, or jib, capable of suspending a load at its outer end. The jib is supported by a rope or other member attached to a vertical mast of frame. The out reach of
the jib can be constant or variable, and the crane as a whole may be either fixed or movable.
Included in this kind are: mobile and caterpillar cranes, builders tower cranes, wharf cranes, and movable cranes mounted on high pedestals, gantries, pontoons and barges.
Lifting capacities vary from 1/2 ton to 300 tons or more, and outreaches from a few feet to 150 ft. Cranes required for handling heavy machinery and equipment in shipyards and at ports are frequently mounted on pontoons.
Bridge or gantry crane
Bridge or gantry crane. Consists of a bridge girder, connected at near both ends to upright members, which may be fixed or arranged to travel on a fixed track, and the load i
s suspended from a trolley or crane, capable or traversing from end to end of the bridge.
Cranes of this kind have lifting capacities varying 显示器大小
from end to end of the bridge. When ud in general and bulk-storage yards, the tracks may be of broad or narrow gauge. The tipping moment of the loaded crane is kept within proper limits by a counterweight which is moved along an independent track on the bridge above the trolley.
Cantilever crane.
Cantilever crane. Consists of horizontal and vertical members the former, known as the cantilever, being fixed to or totating in a horizontal plane about the axis of the vertical member. On the cantilever is formed a track which supports a movable trolley fromwhich the load is suspended.
The mechanism for hoisting and traversing is usually mounted on a rear extension of the cantilever. Although such cranes may be金字开头的成语
fixed ormovable, tho of large capacity are usually fixed. Lifting capacities, height of lift and outreach vary between wide limits. When
ud for the fitting out of ships, light loads are handled by an auxiliary hoist which may be mounted on a jib crane arranged to travel on track. The main lifting mechanism usually consists of two winches which can be operated independently or in concert. A typical fitting-out crane may be of 250 tons capacity with a total outreach of 180 ft and a lifting height of 200 ft.
Wharf Cranes
A wharf crane is any crane located on a wharf or pier, and particularly adapted to the transfer of cargo between the wharf or pier and the hold ofthe vesl alongside; it is also called a cargo crane, although the latter term is more general, as it 倒膜
compris also parts of the cargo-handling gear of a vesl. Owing to the varying spacing of vesl hatchways, the wharf crane in most cas must股市市值
be capable of movement along the wharf, and hence is generally mounted on a runway. Other requirements are sufficient horizontal reach to cover thehatchway,sufficient length of host to rai the load from the bottom of the hold to a point entirely clear of the vesl, and rapidity and每日健康
economy on operation.
Types much ud as wharf cranes are single or double portal gantries or traveling bridges on the wharf shed roof, carrying rotating bridges on cantilever gantries with folding extensions over the hatchways; gantries with inclined cantilever jibs; also of the derrick type.
In the handling of general cargo, as contrasted to bulk cargo, a broader view in analyzing the situation has to be taken. Diversity of shape, size and weight precludes the possibility of using elevators or conveyors to any great extent, while the necessity of sorting and piling in allotted places on the wharf
makes thetransporter, with its rather limited area of discharge, unsuitable.
The traveling portal crane, having a boom capable of being luffed as well swung, is much ud as a wharf crane. One of the chief disadvantages, however, which the ordinary luffing crane works under is that when the boom is luffed-in the loadsuspended from the top of the boom is simultaneously raid; converly, as the boom is lowered, the load falls by a corresponding amount. This, obviously,is a loss of work and means an unneces
sarily large motor to work the luffing gear.
