It is used to lift or lower the load. This is usually achieved by steel wire ropes being affixed to a crane hook or a grab hanging from the outer end of the jib. The rope is applied through some receiving arrangement and controlled and operated by a winch system.
The long horizontal jib is the part of the crane that carries the load. The counter-jib carries a counterweight, usually of concrete blocks, while the jib suspends the load to and from the center of the crane.
A level-luffing crane is a crane mechanism where the hook remains at the same level whilst luffing; moving the jib up and down, so as to move the hook inwards and outwards relative to the base.
Cranes combine simple machines to lift extremely heavy objects. In balance-style cranes, the crane beam is balanced at a point, called the fulcrum. This allows it to lift heavy objects with a relatively small force. In this way, the crane beam acts as a simple lever.
Derricking or Luffing motion:
It is imparted to the inclined member or the jib to move in a vertical plane so that the angle of the jib may be changed in order to bring the load line nearer to or further off from the centre of the crane.
It is imparted to the whole superstructure of the crane including the jib, so that it can turn about a central pivot shaft w.r.t. the non-revolving parts. This motion enables the crane to shift the load line to revolve round the crane.
Long Travel Motion:
It may be required when the whole crane structure has to be shifted to a distant place along a rail track or along a road.
Jib crane consists of an inclined member supported by a rope or any other type of structural member attached to a vertical mast or frame. The load is usually suspended from the outer end of this inclined mast. The outreach of the jib may be fixed or variable. The cranes as a whole may be either fixed or moveable. Various sub-classification of these cranes are possible.
Lifting capacity of such cranes may vary from 1/2 ton to 200 ton and outreach from a few meters to 50 meters. Such cranes find various applications in the port area, construction site, and other outdoor works.
For handling general cargo, lifting capacities are usually 1/2 ton to 5 ton with maximum outreach of 30 meters.Jib Cranes provided with grabbing facilities have usually a capacity ranging from 3 to 20 tons operating 50 to 100 cycles per hour. Lifting heights may be 30 meters or more.
Jib crane used in shipyards for lifting heavy machinery and equipment, weighing 100 to 300 tons, are usually mounted on pontoons. Frequently these cranes are provided with two main hoisting winches which can be employed singly or together to lift a load. For handling light loads these cranes may have auxiliary arrangement.
Types Of Jib Crane:
Depending on the use, jib cranes are classified into a number of varieties, primarily on the basis of their mountings.
Hand Operated Scotch Derrick Type
Wall Mounted Jib crane
Portal / Semi-portal cranes of different varieties-Wharf cranes
Mobile jib cranes consisting of truck mounted and crawler mounted cranes
Scotch Derrick Type / Wall Cranes:
Wall cranes are used in warehouses for handling light weight and when there is little or no wharf between them and the water front. Slewing or rotational motion of the crane is possible within restricted angle and the motion is slow. Hoisting and lifting speeds are comparable to those of wharf cranes. In some modified version these cranes can have travelling speed along the wall.
These are used in the shipyard and port for handling unit and bulk load. These are usually self propelled balanced level luffing type with full circle slewing motion facility. Wharf cranes may be of different types, depending on the type of structure on which it is mounted. The choice of structure for mounting depends on site condition.
The principal types of wharf cranes are:
Portal crane is a fixed or revolving type jib crane mounted on a portal frame fixed in location or arranged to travel along a fixed track of rails at the same level. The portal frame consists essentially of horizontal girders connected at both ends to vertical or inclined member’s having equal lengths.
Semi portal Crane:
Semi portal crane is a fixed or revolving type jib crane mounted on a semi portal frame fixed in location or arranged to travel along a fixed track or rails at different levels. The semi portal frame essentially consists of horizontal girders connected at both ends to vertical or inclined members which constitute a shorter side and a longer side. The shorter members may consist only of the trolley running along the elevated rail.
Mobile Crane (Power Driven) includes all types of travelling jib cranes, such as truck mounted, crawler mounted, locomotive crane on rails.
A jib crane usually sits on an existing building column or has its own integral support column as “free standing.” The jib cranes mounted on an existing column of a building were mostly constrained to about 180 degrees. In most independent jib crans, the power supply is maintained at a hoist at a rate of 360 degrees, or even continuously when provided with collector rings.
How to select the proper criteria of Jib crane
1. Foundation and base structure
We will need to determine whether the existing building slab is suitable or whether a separate poured footer is required when installing a free standing jib crane. In most buildings, height capacity exceeding a half tonne usually demands a dedicated footer.
2. Capacity loading
The rotation of the jib crane can be manual or powered. Powered rotation can help control higher loads and protect operator safety for capacity greater than two tonnes. Usually light loads can be handled manually.