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1.0 Area of use
Central Mechanical Workshop
Central Electrical Repair shop
Turbine House
Compressor House
Power Plant
Foundry and heavy machine shop
Stores
Port / Ware house
2.0 EOT cranes are of two types
(a) EOT Cranes with Operator Cabin: EOT cranes with operator cabin are generally of high capacity or where operation is to be done with clear view of the shop floor area of use. In this type, the operator stands (or sits) in the cabin, in which control gear for operation are housed. In machine shops, foundries etc. where the load is very heavy and the use is on continuous basis, such cranes are used.
(b) EOT cranes operated from floor level: This type has relatively less capacity and the use is less. Here, the operator operates a crane by the pendent in his hand. He is on the same floor and can see the job. Such cranes are used in the power plants, workshops, compressor houses. Use is more during shut down or for short time during misc. purposes.
3.0 Main Components/Parts
Main Rails (Two horizontal rails)
Bridge girder (on which the trolley travels) & wheels
Trolley (on which gearbox, rope drum, motors, Panels etc. are mounted)
Cables for transmitting power/control
Hook (hanging from the drum) on which load is hanged
Electrical Panel (contains power/control components)
Main switch (mounted at operating height)
Pendent (by which the crane is operated)
Ladder
4.0 Types of movements
Long Travel : The main structure of the crane travels along the main rails.
Sometimes, this movement is achieved by mechanical means instead of
electrical.
Cross Travel : This movement is perpendicular to the long travel. The trolley has four wheels, which move across the length.
Hoist : This is vertical movement of the load. The rope is wound or unwound on the drum driven by the gearbox coupled with motors. In many cases, along with main hoist, Creep hoist is also given for the jobs of lower weight.
5.0 Cranes in Hazardous Area
In petrochemicals, refining and fertilizers industries, there are mixtures of
flammable gases and air present in the plant. Hence the crane should be of such
type that, during operation. No unsafe conditions arise.
Wheels of such crane are of phosphorous bronze, so that there will not by any spark generation.
Open wire bus running along the crane, are not allowed due to explosive mixture in the atmosphere.
All the power/ control circuit components are installed in the FLP panel. Brakes are
also of flameproof type.
Control circuit is of Intrinsically safe design if pendent is of non FLP enclosure.
6.0 Electrical Components
Motor: High torque (double cage rotor or deep bar rotor) having good cooling. Suitable for inching duty. It has six terminals (for rotation in both directions)
Contactors: Suitably sized for frequent high starting current. Forward & Reverse operations. Suitable duty-
Power Fuses: Special characteristics (Delayed action) to take care of high starting current & frequent operation.
Brakes: Operated by solenoid. Change in adjustment will cause slipping of load.
Cables : Flexible copper, spiral armored
Open Bus wires: Copper wires mounted on the insulators. Collector on the crane, remains in contact with these wires.
Limit switches : To prevent the over-travel of the crane in all directions and to limit
the movements of the load hook, limit switches are provided, which cut off the power whenever get pressed.
Pendent: It has got push buttons for all operations. ON, OFF, UP, DOWN, North, South, East, West, main & creep.
Main Switch: Cable from substation is terminated in this switch. This switch is kept OFF when the crane is not in use.
7.0 Interlocks
At a time, movement only in one direction is possible – long travel, cross travel or hoist.
As soon as hoist PB is switched off (released), brake is applied automatically. As soon as this PB is pressed, brake gets released.
During long travel, cross travel as well as hoist, there are limits fixed by limit switches. These limit switches are adjustable.
8.0 Sample data of crane
Designed as per IS 800, IS 807 & IS 3177
Class of duty – Class-II (Medium duty) as per IS 3177- 807
(There are four class – I, II, III & IV)
Height – 11 Mt. Span -12.5 Mt.
Wheels –double flanged type- made of phosphorus bronze. (for hazardous area crane)
Speed – Hoist – 3.5 to 5 Mt per minute
Cross travel – 10 Mt per minute
Long travel – 10 to 15 Mt per minute
Wire rope – 6 X 37
Main hoist capacity – 20 T Micro hoist capacity – 5 T
Maximum deflection on 125 % test load – 1/900 times the span
9.0 Problems & Rectification
Hoist not operating –
(a) Power/control fuse blown
(b) Bimetal relay operated
(c) Contactor coil burnt
(d) Limit switch operated
(e) Power supply not available
(f) Fault in the pendent PB
(g) Brake solenoid coil burnt
Load slipping –
(a) Brake adjustment disturbed
(b) Brake liners worn out
Operation continues even after releasing inching PB
(a) Power contactor stuck up, hence power continues
(b) Inching PB problem
10.0 Some safety hints
There should be ladder provided on any one side, to reach to the trolley for
maintenance.
The main switch shall be normally be normally kept in switched off condition, when crane is not in use.
For the crane with bare bus arrangement, necessary safety precautions will be taken to avoid accident.
Limit switches should never be bypassed.
If there are two motors for hoist operation, after maintenance, check the rotation of both. They should rotate in the same direction. Opposite rotations will blow off the power fuses.
While testing the control circuit, limit switch operation should also be simulated for maximum travel.
Never try to lift the load of weight more than the rated capacity of the crane.
