1. A machine for hoisting and lowering heavy weights.
It consists of a vertical post or frame, which is rotatable on its axis, and a jib or projecting arm over which the chain or rope passes on its way from the winch at the foot of the post to the load to be lifted.
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Old Dutch crane. |
The
corvus of the Romans, which has been translated
crane, was a boarding device, consisting of a ladder attached to a vertical spar and so pivoted as to bring the outer end over the deck of the ship to be boarded.
A grappling-hook was suspended from the end of the staging.
By this means of approach the Romans boarded the Carthaginian vessels, and achieved success in several naval engagements.
A
corvus was also used as a true crane for picking off soldiers garrisoning a city wall, and setting them down outside.
It is described by
Tacitus:—
“The stones of the pyramids were raised by making mounds of earth; cranes and other engines not being known at that time.” — Diodorus Siculus (60 B. C.).
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Cranes. |
The old
Dutch crane, which was also in use in
England till the early part of the present century, was operated by a tread-wheel, around which the rope was wound; the rope then passed over guiderollers to the jib of the crane, which projected over the hatchway of the ship and turned upon a pivot, so that it could move round about three fourths of a circle, and so deliver the goods upon the quay.
In order to lower the goods the men walked backward; but as it sometimes happened that they were overbalanced by the descending weight, a bar or pole of wood was suspended from the axle, so that in such case they might lay hold of it, and save themselves from being whirled round in the wheel.
The great wheel and the framing which supported
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it were contained in a wooden building, to the corner of which the jib was attached.
The essential features of a crane may be combined in a machine of simple construction (
Fig. 1505), the central pillar being sustained by a frame of timber
a, by a planted pillar
b, or by guys
c, as in the three examples of cranes of simple construction.
The operation is sufficiently plain without entering into detail.
The ordinary warehouse or foundry crane (
d, Fig. 1505) is usually stepped in the floor, and has its upper bearing in a joist or beam.
Its size, proportions, and to some extent its construction, depend upon its place and application.
The application of iron in the construction of the crane causes some change in the appearance
e, apparent lightness and compactness being gained.
The double crane (
f,
Fig. 1505) has two jibs; one of which is employed in raising a load, while the other is depositing its load in position.
The crane is mounted on a carriage traversing on rails or rollers, and in the illustration is shown as applied to laying stones on a breakwater.
Each jib has a sliding carriage over which the chain passes, so that the stones may be deposited either near to or farther from the shaft of the crane.
This carriage is worked by a sheave and rope which passes over the point of the jib and down by the side of the spindle.
The crane rotates horizontally on an axis, to bring the jibs over the places for receiving and depositing the stones respectively.
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Cranes. |
Peronnet's crane,
French, (
g,
Fig. 1506,) was used by him in constructing the bridge of Neuilly.
It was constructed of wood, and worked by two large wheels which had hand-pins whereby they were turned.
The spindle or vertical shaft was journaled and stepped in a movable frame, and the hoistingwheels formed a partial counterpoise for the load suspended from the end of the jib.
Fairbairn's tubular crane (lower figure
g) is made of wrought-iron plates riveted together, and arranged so as to give the convex back and upper sides a sufficient degree of strength to resist tension, while the concave side has a cellular structure to resist compression.
Cranes were worked by hydraulic pressure as early as 1846, at
Newcastle, England; subsequently the lock-gates and cranes of the
Albert Dock,
Liverpool, and those of the
Grimsby Dock, were worked by water, derived either from the town-reservoirs or from elevated reservoirs into which it was pumped for that special purpose.
These sources, being fluctuating or expensive, gave rise to the adaptation of machinery for the purpose.
Armstrong's hydraulic crane,
English, 1854 (
h,
Fig. 1506), consists of one or more hydraulic presses, with a set of sheaves used in the inverted order of blocks and pulleys, for the purpose of obtaining an extended motion of the chain from a comparatively short stroke of the piston.
In the illustration, the motion is multiplied threefold, each block having two sheaves.
Swinging the jib is effected by means of a rack or chain operating on the base of the movable part of the crane, and connected either with the cylinder and piston, having alternate motion like that of a steam-engine, or with two presses applied to produce the same effect by alternate action.
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Cranes. |
Armstrong's accumulator is intended to store the power exerted by the engine in charging it, and consists of a reservoir giving pressure by load instead of by elevation.
It is a large, cast-iron cylinder fitted with a plunger, from which a heavy load-case is suspended.
Water is injected by the engine, raising the plunger and the load, the effective weight of which is utilized in ejecting the water as it may be occasionally called for.
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The power thus exerted in the ejection of water from the engine is usually equal to a column of water 1,500 feet high.
See accumulator.
A form of crane (
i,
Fig. 1507) traveling upon a wide-gage railroad, and bearing its load suspended from a beam above, has been adopted in some yards where heavy timber, stone, or iron require to be moved, loaded, and unloaded.
The hoisting-chains are worked by winches on each section, and pass over a truck above, which has traverses on the beam, so as to bring the hook over a load nearer to or farther from the rails.
By means of the traveling motion of the machine on the rails and the traversing motion of the truck above, the hook of the chain may be brought over any part of the space within the rails.
If both windlasses be turned at once, the load rises.
If one be unwound while the other is winding, the hook does not rise, but the truck traverses.
Fairbairn's traveling crane (
j,
Fig. 1507) is adapted for a wrecking-crane for railroad use. A crane adapted for lifting fifteen tons will have a counterweight of ten tons in the rear.
In the example from which the illustration is derived, the jib swept over a circle of 25 feet diameter, and was capable of lifting the load 18 feet above the rails on the beam above, towards the winding side.
By turning or unturning the respective windlasses at the necessary speeds relatively, a compound motion may be attained, towards or from either rail upward or downward.
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Foundry-crane. |
One form of
traversing-crane consists of a
crab upon a carriage traveling upon rails on the beams overhead in a foundry.
By the rotation of the roller of the crab, the chain or rope is wound on and the load lifted, and by the motion of the carriage is transported to any place within the range of the rails.
It is known as an
overhead crane.
The foundry-crane has a traversing carriage on the jib, which permits the point of suspension to be moved out or in from the central post; the range being from the outer end to the mid-length of the jib. The traversing-carriage is moved by an endless chain descending to the floor of the foundry.
In
Morrison's steam-crane, the crane-post forms the steam-cylinder, and is fitted with a piston having a flexible piston-rod of wire rope, which works steam-tight through a stuffing-box at the top, and passes over two pulleys, itself forming the chain for lifting the load.
The downward stroke only of the piston is utilized in lifting, and the steam induction and eduction are governed by slide-valves operated by hand-levers.
In
Evans's steam-crane, a vertical boiler forms the crane-post and revolves with it. The cast-iron top of the boiler has lugs for the attachment of the tension-rods.
An oscillating cylinder is attached and furnishes the power.
The projecting arm or beam of a crane is the
jib.
The
post and
jib collectively are sometimes known as the
gibbet.
The diagonal is the
stay.
2. (
Nautical.)
a. A forked post to support a boom or spare spar on deck.
b. A projecting bracket to support spars, etc.
3. An overhanging tube for supplying a tender with water.
A water-crane.
4. A contrivance to hold a stone, and present it to the slicer of the lapidary.
It consists of a clamp which moves horizontally, having its bearings on a vertical post rising from the bench of the lapidary.
A weighted string is attached to the lever-arm, and keeps the stone constantly pressed up against the slicer.
See slicer.
