JIB CRANE

Jib crane have the following motions:

1. Hoisting motion
2. Derricking or luffing motion
3. Slewing motion
4. Long travel motion

Hoisting motion:

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.

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.

Slewing motion:

It is imparted to the whole super structure 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. 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 meter to 50 meter. Such cranes find various applications in port area, construction site, and other outdoor works.

For handling general cargo, lifting capacities are usually 1  1/2 ton to  5 ton with maximum outreach of 30 meter. 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 ship yards 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.

These are:

1. Hand Operated Scotch Derrick Type
2. Wall Mounted Jib crane
3. Portal / Semi-portal cranes of different varieties-Wharf cranes
4. Mobile jib cranes consisting of truck mounted and crawler mounted cranes

Scotch Derrick Type / Wall Cranes:

Wall cranes are used in ware houses 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.

Wharf Cranes:

These are used in 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:

• High pedestal
• Full Portal
• Semi-portal

Portal Cranes:

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:

Mobile Crane ( Power Driven ) includes all type of travelling jib cranes, such as truck mounted, crawler mounted, locomotive crane on rails.

 

CASTING

Methods are:

1. Pressing
2. Centrifugal Casting
3. Slip Casting
4. Extruding
5. Gravity Casting
6. Rolling
7. Iso-static Moulding
8. Explosive Compacting
9. Fibre Metal processes

Pressing:

The function principles of the mechanic press machines differ in how to ensure the upper punch main movement by cams, spindles and friction drives, eccentric, knuckle-joints or by the round table principle, independent if the die or lower punch movement is realized by cams  or eccentric systems or other mechanically or hydraulically combined systems. The executions of auxiliary movements are also not decisive for a term-classification. These auxiliary movements can also base on pneumatic and hydraulic principles. In comparison to hydraulic press machines the maximum compaction forces of mechanical powder presses are limited and are placed in the range </= 5000 kN. For the requirements of wet and dry pressing techniques in the field of Technical Ceramics cams, eccentric, knuckle joint as well as round table presses have proved and tested, whereas cam presses especially used for wet-press-techniques of pourable materials. The range of compaction force of mechanical presses for products of the Technical Ceramics is < 2500 kN, what is caused from the less density of the ceramic materials. Normally the upper punch, lower punch and die systems of mechanical presses don’t work on base of multi subdivided punches.

Centrifugal Casting:

It employed for compacting heavy metal powders such as Tungsten Carbide. The powder is twirled in a mould and packed uniformly with pressures up to 3 MPa. The uniform density is obtained as a result of centrifugal force, acting on each particle of powder.

Slip Casting:

Green compact of metal powder may be obtained by slip casting. The slurry, consisting of metal powder is poured in to porous mould. the free liquid in a slurry is absorbed by the mould tearing the solid layer of material on the surface of mould. The mould may be vibrated to increase the density of component. The Components are dried and sintered to provide sufficient strength.

Extruding:

It employed to produce the components with high density and excellent mechanical properties.

Both hot and cold extrusion processes are used for compacting special materials. In cold extrusion the powder is mixed with binder and the mixture is often compressed into billet before being extruded. The binder must be removed before or during sintering. In hot extrusion the powder is compacted in to billet and is then heated to extruding temperature in non oxidizing atmosphere.

Gravity Casting:

It used for making sheets having controlled porosity, the powder is poured on a ceramic tray to form a uniform layer and then sintered up to 48 hrs in Ammonia Gas at high temperature. The sheets are then rolled to desired thickness and to obtain a better surface finish. Porous sheets of stainless steel, made by this process are used for filters.

Rolling:

It employed for making continuous strips and rods having controlled porosity with uniform mechanical properties. In this method the metal powder is feed in to two rolls, which compress and interlock the powder particles to form a sheet of sufficient strength. It is then sintered, re-rolled and heat treated if necessary. Metal powders which can be compacted in to strips include Copper, Brass, Bronze, Nickel, Monel and Stainless Steel.

Iso Static Moulding:

It used to obtain the products having uniform density and uniform strength in all directions. metal powder is placed in elastic mould (Deformable Mould) which is subjected to Gas pressure (65 to 650 MPa). After pressing the compact is removed.

Explosive Compacting:

It employed for pressing hard particles. The metal powder are placed in water proof bags which are immersed in water. It contained in a cylinder having wall thickness. Due to sudden deformation of change at the end of cylinder the pressure in the cylinder increases. The pressure used to press the metal powders to form green compact.

Fibre Metal Processes:

In this process, the metal fibers (Fine wires of Convenient length) are mixed with a liquid slurry and poured over a porous bottom. The liquid is drawed off leaving the green mat of fibre. The mat in which the fibers are randomly distributed is pressed and sintered. The products are mainly used for Filters, Battery Plates and Damping’s.

 

BELT DRIVES

Types and Selection of Drives:

• Single Unsnubbed Bare / Lagged pulley Drive
• Snubbed Bare / Lagged Pulley Drive
• Tandem Drive
• Special Drives

Single Unsnubbed Bare / Lagged Pulley Drive:

This is the simplest drive arrangement consisting of a steel pulley connected to a motor and the belt wrapped round it on an arc of 180°. This can be used for low capacity short center conveyors handling non-abrasive material. The pulley may be lagged to increase the coefficient of friction.

Snubbed Bare / Lagged Pulley Drive:

Here the angle of wrap is increased from 180° to 210° or even up to 230°, by providing a snub pulley to the driving pulley. In majority of medium to large capacity belt conveyors, handling mild abrasive to fairly abrasive materials, 210° snub pulley drive with load pulley lagged with hard rubber is adopted.

Tandem drive:

Here belt tension estimated to be high; the angle of wrap is increased by adopting tandem drives. Both of tandem pulleys are driven. The tandem drive with arc of contact from 300° to 480° or more can operate with one or two motors. The location of such drive is usually determined by the physical requirements of the plant and structural constraints.

Special Drive:

Special drives with snub pulleys and pressure belts used in heavy and long conveyors.