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INTRODUCTION
Continuous Casting Shop is a part of SMS-2 (steel melting shop-2).
Continuous Casting Shop consumes most of the production of SMS-2.SMS2 comprises of Converter Shop & Continuous Casting Shop. The
Converter Shop has 3 converter of 130T capacity each. Tap time of
converter is 60 min with an average heat of nearly 120 Tons. Tapping is a
process of pouring of hot metal into the ladle.
The operation cycle of the converter is as follows: -
Charging 5min
Oxygen blowing 20min
Sampling & temperature measurement 8min
Correction before tapping 5min
Tapping 5min
Nitrogen splashing, coating 7min
Total 50min
The converter shop has many sections as described below:
MIXTURE SECTION: The main function of mixture is to
supply hot metal (pig iron) to the converter at a fairly uniform temperature &
composition, in required quantity whenever demanded. The mixture acts as
buffer between Blast Furnace and Converters.
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There are two mixture of 1300 T capacity each. The pig iron reaches
mixture in ladle of 100 T capacities. Burners are provided in the mixture to
maintain the temperature of hot metal. Hot metal from mixture is supplied to
the converter as per demand.
SCRAP YARD:
Scrap yard receives the scraps generated from all over the plant
in wagons and truck. Two magnet cranes do the unloading / loading of
scraps. Scraps are supplied to the converters, which is melt with hot metal.
LADLE PREPARATION SECTION:
The steel-casting ladle, required for tapping of steel from converter is
prepared here. There are 26 ladles of 130 T capacities each. These entire
ladles are of bottom purging through porous plugs and fitted with slide gate
system for pouring of steel for casting. The ladles are lined with magnesia
carbon bricks to with stand the heat and erosion during treatment in the
VAD, LF, & RH units.
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SLAG POT HANDLING SECTION:
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The slag produced during steel making is poured out of the
converter into 16m3 slag pots. The tilting slag car are taken by locomotives
to slag yard where the slag cups are tilted and emptied.
BLUK MATERIAL HANDLING SECTION:
The following bulk material are handled in this section:
Lime Calcined dolomite Lime stone
Coke Raw material Iron ore
Lime and calcined dolomite are used as fluxes, iron ore and limestone
are used as coolants. Coke is used for preheating the converter and coating.
These materials are and charged into the converter. Very sophisticated
microprocessor based system, of weighing and then charging of bulk
material into converter, is installed in the main control pulpit.
GENERAL DESCIRPTION OF CONTINUOUS CASTING
PROCESS: -
Continuous Casting is a process of casting without interruption.
Liquid steel form the converter is taken to the Argon Rising Unit. Argon is
blown into the ladle. This homogenizes the temperature and composition of
the molten steel. Aluminum may be added to it to reduce oxygen content.
Ferro alloy are added are for trimming addition.
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The molten steel in the ladle is then delivered to a reservoir above the
continuous casting machine called a tundish. The flow of steel from the
tundish into one or more open-ended, water-cooled copper mould is
controlled by a stopper rod or a slide gate.
To initiate a cast, a dummy bar is inserted into the mould and sealed
so that the initial flow of steel is contained in the mould and a solid skin is
formed. After the mould has been filled to desired height, the dummy bar is
gradually withdrawn at the same rate at which casting is done.
The initial liquid steel solidifies on a suitable attachment of thedummy bar so that the cast stand can be withdrawn through the machine.
Solidification of a shell begins immediately at the surface of the copper
mould and the casting speed is such that the shell thickness is capable of
withstanding the pressure of the molten core upon exiting from the copper
mould.
To prevent sticking of the frozen shell to the copper mould, the
mould is oscillated during the casting operation and a lubricant is added to
the mould, the strand is mechanically supported by rolls below the mould
where secondary cooling is achieved by spraying cooling water or air mist
onto the strand surface to complete the solidification process. After the stand
has fully solidified, it is cut into desired length by cut off torch (normally an
oxy-acetylene torch), which moves along with the stand. This final portionfor disengagement and storage of the dummy bar.
MODIFIED SLAB CASTING MACHINE
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Different Sections:-
Continuous Casting consist of following sections:
Argon rinsing Bay Tundish preparation Bay
Casting Bay
VAD (Vacuum Arc Degassing Unit)
Ladle Furnace
RH Degasser
Discharge Bay
Slab & Bloom Storage Yard (SBS)
Mould Repair Shop
Casting Powder Plant
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DIFFRENT PARTS IN CONTINEOUS CASTING MACHINE: -
Ladle with slide gate opening
Lift and turn mechanism Hydraulic cylinder for opening slide gate
Tundish car
Stroud holding and adjusting mechanism
Stroud
Tundish nozzle with tundish block integral
Stopper
Stopper mechanism
Nozzle (submersed)
Mould
Mould supporting & oscillating frame
Foot roll integral with mould
Five roll set
Pinch roll set
Dummy bar
Roll table
Oxyacetylene gas cutting system
Roll cooling system
Hydraulic system
Roll bearing lubrication system
Roll drive system and reducer
Transfer car and cranes
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BREAKDOWN MAINTENACE: -
Break own maintenance is a process of maintaining the machine component
and equipment as soon as it is detected. It is done so because due to failure
of that machine component or equipment caster operation will be directly
affected and even it may bring it to rest immediately. In it as soon as fault or
failure is detected operation is brought to rest and that component is change
by spare one if available.
Before going for maintenance following steps are taken:
Machine is switched off and operation is stopped
Machine is allowed to cool down. It takes about 3 hours for
cooling. It is cooled through secondary equipment and cooling water
It may be the case that cooling of machine is not require for
maintaining that part bur for starting the process if it is essential
Then the water supply is stopped and takes full shut down of the
machine. For this shut down form is filled up.
Next step in integral inspection of machine. All pinch roll are kept in
lifted position. Inspector goes inside the machine and check for bearings and
rollers and breakdown & minor defect list is prepared
Defective rollers and other broken or failed components are changed
by spare one.
Local alignment is checked.
Full machine alignment is checked and correction is made for that.
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Top sets are fixed and roll gap is fixed.
Secondary cooling system is checked.
A SAMPLELIST OF BREAKDOWN MAINTENANCE : -1. Tundish car (Hoist drive) : -
Limit switch was by passed thereby damaging the locking nut of bolts
reducer.
2. Pinch rolls (Pinch roll stand) : -
Pinch roll no 03 roller broken.
3. Dummy bar unit (dummy bar unit) : -
Dummy bar link (first) broken.
4. Receiving roll table (Drive for roller rotation): -
Bearing broken thereby damaging gear teeth.
CONDITION BASED MAINTENANCE (CBM)(PROTECTIVE MAINTENANCE)
Condition based maintenance is a type of preventive maintenance. During
break down maintenance and after certain no of heats machine in brought to
rest and all the components and equipments are checked and checklist is
prepared about the defect and its extent. It is also mentioned that how long a
defective component may work properly without breakage. According to
that schedule of preventive maintenance is prepared. A sample checklist of
component is as follows:
(For slab caster at BSP Bhilai)
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EQUIPMENT JOB
PARENT EQUIPMENT: Lift & turn stand
GENERAL:
Check for smoothness of
operations during rotation
DRIVE FOR TURNINIG:
Check brakes and regulation
Check main gear auxiliary reducer bull gear reducer
Check lubrication of bull gear
FRAME STRUCTURE OF BODY:
Check condition of plate form and rolling
PARENT EQUIPMENT: Tundish car
GENERAL:
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SECONDARY COOLING BUNKER:
Check bunker plate and structure
PARENT EQUIPMENT: Pinch Roll
GENERAL:
Check condition of plate form & rolling
DRIVE FOR PINCH ROLL:
Check the condition of PR brakes
Check lubrication spindle pusher
PINCH ROLL STAND: Check top frame fixing firm locking, condition of spindle locking &
slide blocks
Check the condition of buffer spring side pins
Check the condition of rollers bearing & uprooting rollers
SECONDARY COOLING SYSETM: Check rollers cooling outlet flow of water from rolls
TIME BASED MAINTENANCE
(CAPITAL MAINTENANCE)
From experience and experiments it is decided that a machine will operate
satisfactorily for certain no of heats after that machine is maintained
completely over all machine is dismantled and goes for repair in different
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shops. There in hops they see what are minor and major problem in the
component or equipment & then they rectify all. The problem and
equipment is prepared completely to work in machine. In this maintenance
process check list of defects and maintenance is prepared.
MAINTANANCE OF DIFFERENT PARTS OF MACHINE:
These are mainly set of rollers and there failure criterion is different thus
maintenance procedure is different.
A) MAINTENANCE OF FIVE ROLL & EIGHT ROLL SET:
FAILURE CRITERION: Following are the main failure criterion for five
& eight roll set:
1. Roller bending
2.
Bearing failure3. Misalignment
POSSIBLE CAUSES:
1. Bearing failure may be due to improper greasing and improper
secondary cooling may also lead to bearing failure.
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2. Low temperature of metal from ladle and stoppage of strand in the
rollers and low bending strength of the rollers may lead to the permanent
bending of rollers.
3. Misalignment is cause by both bearing failure & roll bending.
REPARE PROCESS:
1. Roller set is brought from the shop is dismantled completely.
2. All the rollers are removed form the strand and are fully opened.
3. There are two bearing in each side of roller, which is removed by
removing outer covering from the shaft.
4. Bearings are checked if any problem is found bearing is removed &
spar bearing is placed.
5. Spar rollers are placed on the frame & tighten through bolts.
6. In case of five roll set bottom set is bigger radius this set is first
maintained.
7. First and last row of rollers are maintained at a height of 310mm
from reference plane using plate below the shaft.
8. Above the reference plane plate of different thickness based on cross
section required9. Then upper or smaller radius at the op is placed & is locked with
bottom with by studs and bolts.
10. Now rollers gap is maintained using tiller gauge & taking correction
factor for shrinkage of slab.
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ROLL GAP FROM TOP TO BOTTOM
FOR FIVE ROLL SET GAP (mm)
1 201.70
2 201.58
3 201.45
4 201.33
5 201.20
FOR EIGHT ROLL SET GAP (mm)
1 201.20
2 201.13
3 201.06
4 200.99
5 200.92
6 200.85
7 200.77
8 200.70
11. Only different fire roll & eight roll repair is that in eight roll set is small radius
bottom set is larger set.
MAINTENANCE OF PINCH ROLL:
CRITERION OF FAILURE: Following are the main criterion for rejecting
the roll.
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Roller bending Max allowable 2mm
Bearing failure
Fire cracks Max allowable depth is 30 to 40 mm.
Roller breakage
Bearing surface failure of roller.
POSSIBLE CAUSEC:
1. Bearing failure may be due to improper lubrication bending of roll bulging of strand etc.
2. Roller bending may be due to improper cooling of rolls bulged strand
and stoppage of standing the roll due to stoppage of process.
3. Fire cracks due to composition of roller material & was not detect
earlier.
REPAIR PROCESS:
To make the blended rollers concentric rollers are turned on lathe to
make concentric.
Bearing failure is maintained by replacing break bearing by spare one &
damaged one is sent for repair.
Roller rejected.
From pinch rolls is used in roll table set where cutting by oxyacetylene
is done if it is not totally breaked.
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Breaked rolls con not be repaired thus they become scrap.
If bearing surface is wearied due to breaked bearing or due to lack of
lubrication it is sent to reclamation and is machined there to bring it to the
proper size.
.
MAINTENANCE OF ROLL TABLE:
Failure criterion:
Following are the failure criterion of roll table
a) Breakage of rolls.
b) Excessive wear of rolls due to molten metal facing and cutting
flame during cutting process of slab.
Maintenance of mould: maintenance of mould is done in mould repair shop.
Criterion of mould failure:
Leakage of cooling water from the copper wall gap. There should be no leakage
normal working pressure is 7kgf/cm 2 during the operation.
Improper gap between two walls at corner. This cause bursting of skin formedduring primary cooling and can lead to breakout also. Max allowable gap for satisfactory
operation is 0.2mm but normal practice is 0.1mm(safer side).
Sticking of metal on walls due to break out of skin and all.
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In case of capital it is preferred to repair because it is to bring the initial position,
although it is capable of working satisfactorily for some more heats to secure no
interruption in process for long time.
Primary cooling water may not be soft thus it may case rusting in the passage and
may create problem in proper distribution of water through out the mould walls.
Repair process:
Repair process of mould consist of following steps be followed:
Dismantling of mould
Machining copper walls
Assembly of mould
Check the comer gap rectify if required
Put abestor mills board fix up sheets
Check alignment of mould.
Blast Furnace
Blast furnace department consists of 7 blast furnace three of them are of 1033m 3 useful volume and production is of about 2000T/day, three of themare 1719m 3 useful volume and production of about 2500T/day, and blastfurnace no.7 is of 2000cum useful volume and produce 3500T of hotmetal/day. The annual revised rated capacity for hot metal is 4.5MT withonly five-blast operation in operation.
There are 3 main section of the department:
1. Raw material section
2. Furnace section
3. Auxiliary section
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Raw material section:
The raw materials used for the production of pig iron are:
Coke (fuel), Iron Ore, Sinter (Fe-bearing material), Limestone (Flux) & Mn-
Ore and Quartzite (additives).
1. Fine ore : 85,000 tones
2. Iron ore (lumps) : 1,80,000 tones
3. Limestone : 40,000 tones
4. Mn.Ore : 11,000 tones
5. Quartzite : 3,000 tones
Furnace Section:
Blast Furnace is a vertical shaft furnace, enclose in a welded shell, lined with
fire-clay bricks of high alumina content. The hearth bottom, hearth, bosh and
the cylinder part of the bosh are cooled by means of plate coolers. In the
shaft, there are cantilever cooler. The walls of the furnace top are protected
by steel refractory lined plates. In BF#7 for cooling the shaft, there are
inverted L shapes cooler.
TOP CHARGING EQUIPMENT
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The bell type chaging device (exhisting in BF 1,2 & 3) has a big bell, small bell with hoppers, gas seal, and receiving hopper; and receives raw materialfrom an oval shaped receiving hopper. In BF-3 RCU (Rotating ChargingUnit) is provided, by means of which charging can be distributed in desiredsector inside the furnace BFs. #4,5,6 & 7 are equipped with paul gate, upper sealing valve, lower material gate and lower sealing valve. This system alsohas a gearbox to operate a rotating chute. The latter distributes the materialinside the furnace peripherally in different rings. This facilities better distribution of charge inside the furnace.
CHARGING PROGRAMME
To facilitate smooth working of furnaces, the following charging programme is normally practiced.
A. Programme COC / COOCC / CCOOC
B. Programme CCOO
Each charging cycle consist of 3 programmes of A & B exclusively or in
combination depending on peripheral conditions. Generally in Bell-less Top
Furnace the programme selected is B i.e. CCOO, C=COKE; O=NON-
COKE i.e. ore, sinter, Mn ore, lime atone or quartzite.
STOVES
Form bottom of the furnace the hot blast is blown into the furnace
through tuyers with the help of turbo-blowers & hot blast stove.
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There are 3-4 stoves for each furnace. Each stove consists of a
combustion chamber and a regenerative chamber. Stoves are kept on blast
for 2 hrs. the following are the provision in a stove : cold blast valves (1) ,
Hot blast valve (2) , Chimney valve (2) , By-pass chimney valve (3) , gas butter fly valve (1) , Gas burner (1) , Air fan (1).
Blast of Air reaches as follows:
Cold blast CB Main Stoves HB Main Bustle pipeGooseneck pipe Tuyer stock Furnace
The liquid product of smelting namely pig iron and accumulator in the
hearth. Slag floats on the Pig Iron because of difference in density.
FLUSHING OF SLAG: TAPPING AND DISPOSAL OF HOT METAL
The furnace is provided with a tap hole, which is enclosed in a steel cast
frame and is cooled by two Tap hole coolers, which have their own supply
of water.
The hot metal is tapped out at an interval of 1-2 hrs depending upon the
furnace condition. The usual way of opening the tap hole is to drill the tap
hole until the skull is reached. Oxygen lancing is carried out melt the skull.
The hot metal continues to flow down the bend runner form, which it is
diverted into individual metal ladles. At the end of tapping the tap hole is
closed with mudgun, which is electrically or hydraulically operated.
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The hot metal ladle is a refractory lined 100 T capacity containers. It
transport hot metal form Blast Furnace to SMSs, PCM and Foundry. The
distribution of hot metal is 90% to SMS, 3% to foundry and rest to Pig
Casting Machines.
Fleets of 78-iron ladles car are available, out of which normally 48 are incirculation in cases all seven furnace are in operation.
SPECIFICATION OF RAW MATERIALS
Material Chemical Analysis Specification Size
Iron Ore Fe 64.2% min 10-40 mm
SiO 2 2.5+-0.5%
P 0.1 % max
Al2O 3 / SiO 2 0.88 % max
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Limestone CaO 39.5 % 0.1 % 6-50 mm
SiO 2 6.5 +- 0.25 %
MgO 8.5 +- 0.5 %
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_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
_ _ _ _
Mn. Ore Mn 30 %min 25-80 mm
SiO 2 30 % min
Al2O 3 5 % min
P 0.30 % max
Source of Raw Materials:
1. Iron Ore . Dalli, Rajahara Mines
2. Lime Stone . Nandini Mines
3. Manganese . Balaghat Mines
4. Sinter . Sintering Plants (SP-2, SP-3)
5. Coke . Coke Ovens (Coke sorting plants)
6. Converter Slag . SMS l l
Requirements for producing of one ton of Hot Metal
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(Specific Consumption)
Iron Ore . 459 Kg
Lime Stone . 850 Kg(Depending on Sinter Usage)
Manganese . 800 Kg(50% in burden)
Sinter . 35 Kg
Coke . 08 Kg
Converter Slag . 30 Kg
Services / By-Product per ton of Hot Metal
Steam . 120 Kg
Compressed Air . 25 M3
Air Blast . 2600 M 3
Electricity . 33.7 Kwh
Water . 40 M 3
Slag . 435 Kg
Flue Dust . 25 Kg
BF Gas . 1830 Kg(CV-800Kcal / M3)