In the Gartsherrie machine of Messrs Baird, the earliest of the flexible chain cutter type, the chain of cutters works round a fixed frame or jib projecting at right angles from the engine carriage, an arrangement which makes it necessary to cut from the end of the block of coal to the full depth, instead of holing into it from the face.
This type is usually fitted with a very high jib, so as to lift goods in and out of high-sided vessels.
Where the face of the warehouse is sufficiently close to the water to permit of the crane rope plumbing the hatches without requiring a jib of excessive radius, it is a very convenient plan to place the whole crane on the warehouse roof.
On arriving at a certain height the lift ceases and the jenny is released, and by the continued pull of the rope, it runs up the jib; on arriving at an adjustable stop, the jenny is again locked, and the load can be lowered out; the hook can then be raised, when the jenny is automatically unlocked, and on paying out the rope the jenny gravitates to its first position, when the load is lowered and the cycle repeated.
This class is the ordinary jib crane.
Jib cranes can be subdivided into fixed cranes and portable cranes; in the former the central post or pivot is firmly fixed in a permanent position, while in the latter the whole crane is mounted on wheels, so that it may be transported from place to place.
For dock-side jib cranes the use of electric power is making rapid strides.
The limit of speed of lift of hand cranes has already been mentioned; for steam jib cranes average practice is represented by the.
4 is a diagram of a fixed hand revolving jib crane, of moderate size, as used in railway goods yards Fixed and similar places.
Load is suspended from the crane jib; this jib is attached at the lower end to the side frames, and the upper end is supported by tierods, connected to the framework, the whole revolving together.
This simple form of crane thus embodies the essential elements of foundation, post, framework, jib, tie-rods and gearing.
The derrick crane introduces a problem for which many solutions have been sought, that of preventing the load from being lifted or lowered when the jib is pivoted up or down to alter the radius.
Here the place of the jib is taken by two inclined legs joined together at the top and pivoted at the bottom; a third back-leg is connected at the top to the other two, and at the bottom is coupled to a nut which runs on a long horizontal screw.
Here the jib, superstructure and post are all united in one piece, which revolves in a foundation well, being supported at the bottom by a toe-step and near the ground level by horizontal FIG.
This type of crane used to be in great favour, in consequence of the great clearance it gives under the jib, but it is expensive and requires very heavy foundations.
9) consists of a steel braced tower, on which revolves a large horizontal double cantilever; the forward part of this cantilever or jib carries the lifting crab, and the jib is extended backwards in order to form a support for the machinery and counter-balance.
Dock-side jib cranes for working general cargo are almost always made portable, in order to enable them to be placed in correct position in regard to the hatchways of the vessels which they serve.
12 shows an ordinary hydraulic dock-side jib crane.
GIBEONITES, the inhabitants of Gibeon, an Amorite or Hivite stronghold, the modern El-Jib, 5 m.
The present name is El-Jib; this is a small village about 5 m.
18 shows a modern design of crane intended to command the maximum of yard space, and having some of the characteristics both of the Goliath and of the revolving jib crane, and fig.
19 depicts a combination of a traveller and a hanging jib crane.