o TYPES OF CRANES
o PARTS OF EOT CRANES
o SINTERING PROSSES IN BRIEF
CRANE AVAILABILTY IN SINTER PLANT
To find out the availability and utilization of cranes in sinter plant and to find the probable solution to maximize the availability of crane.
Types of cranes
Electric Overhead Traveling (EOT) Cranes:
EOT cranes travel on a pair of gantry rails mounted on gantry girders, which in turn are supported on columns on two sides of bay. The crane consists of bridge girders, end carriages, platforms, trolley assemble and long travel machinery. Machineries for hoisting motion and trolley travel (traverse motion) are mounted on trolley. The trolley moves on rails fixed on the top of bridge girders.
These cranes find their application in wide range of industry. Depending upon the need specified by the customer inquiry, the cranes are supplied with special features such as-
? 2 or 3 trolleys running on common pair of bridge girders (paper industry)
? 2 trolleys running on 2 separate pair of bridge girders (4 girder ladle cranes in steel plant)
? creep/inching speed for various motion
? planetary gear box with 2 motor drive for hoist motion (ladle cranes)
? Thyristor/variable voltage variable frequency controls for various drives.
? Hoist arrangement in 4 independent rope suspension (ladle crane)
? trolley running on the top of the bridge girder (Mono box cranes)
? permanent/detachable attachments such as, grab bucket, magnet, lifting beam, rotating beam, slab/coil tong, sheet pack lifter, ‘C’ hook, etc.
? two part trolley with rotation drive for upper trolley part (rotating trolley cranes)
? flame-proof design
? insulated hook block
? remote control either radio or infra red
? traveling type operators cabin
? PLC operation
These cranes are used in places where adequate space is not available between top of gantry and bottom of roof truss. These cranes run on the inner flanges on gantry girder I beams.
Unlike EOT cranes, Goliath cranes run on gantry rails mounted on floor level. The bridge girders are supported on e pair of legs which are supported on end carriages.
Semi Goliath cranes operate on rails mounted on shop gantry girder on one side end on shop floor on the other side.
Goliath cranes can be supplied with bridges extending beyond the centerline of rail mounted on ground to facilitate loading and unloading of material beyond crane span.
Moving Type Cantilever Crane:
These cranes commonly find their application in large steel plants. These cranes run only on gantry rail. Reaction rollers are provided to balance the moment arising out of cantilever loads. These cranes are mainly used for maintenance operation in steel plants.
Rail mounted Jib cranes:
These types of cranes have hoisting, slewing and machinery at a fixed rotating frame.
These cranes generally find their application in ports. Depending on customer’s needs, the jib luffing and hoisting drive can be designed to ensure fixed level of load during luffing operation (level luffing cranes).
Major Parts Of EOT Crane:
? Trolley Assembly
? Bridge Girders
? End Carriages
? Long travel drive mechanism
? Trolley power supply arrangement
? Operator’s cabin
The trolley assembly consists of hoist drive mechanism, trolley travel mechanism and the trolley frame. Typically the trolley frame is supported by 4 wheels which runs on rails mounted on bridge girder. For the safety of maintenance personnel the following is provided on the trolley.
? The top of trolley frame is covered with chequered
? Toe guards/kick plates are provided around opening
? Hand rails and access ladder are provided.
The trolley frame also houses rail sweep plate, derailment guard and jacking pads.
The bridge girders are fabricated using tested weldable quality steel. The bridge girders are stiffened with the help of vertical/longitudinal stiffeners according to the design requirement. The girders are cambered upwards.
The bridge girder transmits the lifted load and the load arising out of weight of trolley, LT drive mechanism, platforms, electrical panels, operator’s cabin and its self weight to the gantry girder through end carriages and long travel wheels.
The end carriages are fabricated from tested weldable quality plates/rolled members. The end carriages are rigidly connected to the girders through machined bolts/high tensile friction grip bolts. The end carriages along with bridge girders from rigid frame which resists skewing forces. The end carriages houses long travel wheels, rail sweep plates, derailment guard and jacking pads.
Long travel Drive Mechanism:
Depending on crane span, duty classification and long travel speed, either single, twin or four units of long travel drives are provided on each crane.
Long travel consists of sq. cage/slipring motor, reduction gear box, brake, couplings, floating/line shafts and long travel wheels.
The selection of type of motors, gear boxes and brake is governed by design requirements and the specifications of the customer.
Access platforms are provided for easy access to operator’s cabin, electrical panels and for maintenance of long travel machinery.
Toe guards/kick plates and hand rails are provided on the platform for safety of operating personnel. The platform also supports fixtures for under bright lights. Generally, separate platforms are provided for supporting foot mounted long travel drive mechanism to minimize transmission of vibration of LT mechanism to main platforms. Access ladders are provided for safe access to different levels of platform and from girder/end carriage to platform.
SINTERING PROCESS IN BRIEF:
Sintering is essentially a process of heating of mass of fine particles to the stage of incipient fusion (temperature till below the melting point of or softening point) for the purpose of agglomerating them into lumps.
Metal powder compacts ore are sintered to obtain desired solid shapes. In iron ore sintering the aim is to produce a strong but porous agglomerate from a sandy (incompact) mass. Sintering is therefore carried out layer by layer in a mass of charge.
Iron ore sintering, in essence, is carried out by putting mixture of iron-bearing fines mixed with solid fuel on permeable grate. Since coke breeze is normally available as an otherwise wasteful product in integrated steel plants, it is universally incorporated as solid fuel in sinter mix.
The top layer of sinter bed is heated to the sintering temperature (1050-1220°C) by a gas or oil burner and air is drawn downwards, through the grate, with the help of exhaust blowers connected from underneath, to the grate.
The cold blast drawn through the bed cools the already sintered layer and thereby gets itself heated. The heat contained in the blast is utilized in drying and preheating the lower layers in the bed. In advance of combustion therefore each layer gets dried and preheated by the heat transferred from the upper combustion zones. Much of the heat in the gases is absorbed by the lower portion of the bed.
RAW MATERIALS OF SINTERING PROCESS :
Iron Ore : Fines purchased from various sources (Donimalai,
Specific consumption: 918 kg/ton of sinter.
Coke : Undersized generated at BF is crushed to -3mm
Specific consumption: 47 kg/ton of sinter.
Limestone : Purchased from outside sources and crushed to –
Specific consumption : 81 kg/ton of sinter
Dolomite : Purchased from outside sources and crushed to –
Specific consumption : 75kg/ton of sinter.
Calcined Lime: Purchased from outside sources and crushed to –
Specific consumption : 42kg/ton of sinter.
Moisture : Industrial water obtained through the water
network and steam generated from waste heat
recovery system of sinter.
Specific consumption : 0.165 m3/ton of sinter.
Furnace Fuel: BF gas enriched with propane gas.
Specific Consumption: 0.08GJ/ton of sinter.
Plant waste materials:
SINTER PROCESS REACTIONS:
Thermal Dissociation of Hematite
3Fe2O3 + CO 2Fe3O4 + CO2
Reduction of Hematite
3Fe2O3 + CO = 2Fe3 O4 + CO2
Reduction of Fe3O4 and FeO
Fe3 O4 +CO = 3FeO + CO2
FeO + CO = Fe + CO2
Cranes Availability in sinter plant:
Sl no Crane Location Capacity Make
1 Sinter M/C building 35/5T Mukund
2 Fun house 35/5T Mukund
3 Sinter screen 1 20/5T Mukund
4 Sinter screen 2 20/5T Mukund
5 Fine Crushing house 16/5T Mukund
6 Discharge end ESP fan house 12T Mukund
7 Fuel & Flux Crushing building 5T SG swift
8 Sampling house 2T SG swift
The cranes available in the sinter plant are not production cranes. They are used only for maintenance purpose, so the availability of cranes is round the clock. The non-availability of crane is due to technical failures.
The crane should not be loaded beyond the maximum safe working load specified on the crane name plate. For cranes having more than one hoisting mechanisms with single or multiple trolleys, special attention should be paid to ensure that the total lifted load by all the mechanisms does not exceed the safe working load of the individual hoisting mechanism.
It must be ensured that the trolley and hoisting mechanism are loaded only in the vertical direction for the safe operation of the crane. Side pulling of the loads, shunting of rail cars or other vehicles by means of crane hook is prohibited.
It is also prohibited to use the crane for tearing of jammed loads. Sharp or jerky starting, stopping and lowering of loads is not allowed.
The wire rope should not be allowed to uncoil from the rope drum completely. Atleast two dead turns of the wire rope should be left on the rope drum when hook block is at the bottom most position.
Creep speeds are meant for spotting the loads at exact location. Creep speed should be used only for a short duration for this purpose. The crane should not be operated for long period with creep speed.
By following the above suggestions we can be able to avoid the technical failures occurring in the cranes, so that the availability of crane for maintenance work is ensured.
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