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S B S T , C E P T U n i .

K a s t u r b h a i L a l b h a i

C a m p u s ,

A h m e d a b a d .

Amit DubeyHatim Mithaseth

Steel, the maximum used metal in 21st Century,

has a very complex procedure of manufacturing,and processing, which makes the steel what we

know it like. Since all steel is not Stainless Steel,there arises the need of some kind of protection,which can prevent the corrosion, i.e. oxidation of

steel when it comes in contact with Oxygen. That

precisely is what is done at JSW Steel Limiteds

Boisar Plant, extending the life of such necessaryan alloy by many folds.

es eeLtd., Boisar

2009

2009

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The Boisar unit of JSW Steel Limited processes Hot Rolled Steelsheets, which includes Galvanizing and Colour Coating. This is thefinal processing of Rolled Sheets, preparing them as per theorders from different clients. The manufacturing is done at Bellaryin Karnataka.

An Overview of Steel Manufacturing:

After Concrete the maximum produced manmade material on thisplanet is steel. Today, steel is incorporated in each and everyaspect of our life weather we realize it or not.

Steel is basically an alloy of Iron with Carbon in varyingproportions ranging from 0.02% to 1.4%. Steel now-a-days isproduced by the basic Oxygen Steel Making Process.

The oxygen steelmaking process rapidly refines a charge ofmolten pig Iron and ambient scrap into steel of a desired carbonand temperature using high purity Oxygen. Steel is made indiscrete batches called heats.

The furnace or converter is a barrel shaped, open topped,refractory lined vessel that can rotate on a horizontal trunnionaxis. The basic operational steps are shown in the figure A.

The pig Iron used in the Oxygen Steel Furnaces is obtained from

blast furnaces. The basic materials used for the manufacture ofpig iron are iron ore, coke, and limestone. The coke is thereducing agent and is partly burnt as a fuel to heat the furnace;but to reduce consumption of this expensive commodity,additional fuels such as natural gas, fuel oil, and pulverized coalare added to the air blast injected near the bottom of the furnace.By doing this, coke consumption has been halved since the 1980sto an average 500 kg (1,100 lb) per tonne of metal produced. Theair reacts with the carbon in the coke to produce carbonmonoxide, which combines with the iron oxides in the ore,reducing them to metallic iron. This is the basic chemical reaction

in the blast furnace; it has the equation

Fe2O3 + 3CO = 3CO2 + 2Fe

The limestone in the furnace charge acts as a flux to combinewith the infusible silica present in the ore to form fusible calcium

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silicate slag. Without the limestone, iron silicate would be formed,with a resulting loss of metallic iron. Calcium silicate and otherimpurities form a slag that floats on top of the molten metal atthe bottom of the furnace. Ordinary pig iron as produced by blastfurnaces has the composition: iron, about 92 per cent; carbon, 3to 4 per cent; silicon, 0.5 to 3 per cent; manganese, 0.25 to 2.5

per cent; phosphorus, 0.04 to 2 per cent; with a trace of sulphur.

A typical blast furnace consists of a cylindrical steel shell linedwith a refractory, which is any non-metallic substance such asfirebrick. The shell is tapered at the top and at the bottom and iswidest at a point about one quarter of the distance from thebottom. The lower portion of the furnace, called the bosh, isequipped with several tubular openings or tuyres through whichthe air blast is forced. Near the bottom of the bosh is a holethrough which the molten pig iron flows when the furnace is

tapped, and above this hole, but below the tuyres, is anotherhole for draining the slag. The top of the furnace, which is about27 m (90 ft) in height, contains vents for the escaping gases,which are collected, de-dusted, and then blended with natural gasfor use as a fuel within the plant. The blast furnace top is fittedwith a charging device such as a pair of round hoppers closedwith bell-shaped valves through which the charge is introducedinto the furnace, or a movable chute that is continuously adjustedto direct the charge to the required spot in the top of the furnace.The materials are brought up to the top of the furnace by

conveyor or in small dump cars or skips that are hauled up aninclined external skip hoist.

Blast furnaces operate continuously. The raw material to be fedinto the furnace is divided into a number of small charges that areintroduced into the furnace at 10- to 15-minute intervals. Slag isdrawn off from the top of the melt about once every 2 hours, andthe iron itself is drawn off or tapped about five times a day.

The air used to supply the blast in a blast furnace is preheated totemperatures between approximately 1350 and 1400 C (2450and 2550 F). The heating is performed in stoves, cylinderscontaining networks of firebrick. The bricks in the stoves areheated for several hours by burning blast-furnace gas, the wastegases from the top of the furnace. Then the flame is turned offand the air for the blast is blown through the stove. The weight of

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air used in the operation of a blast furnace exceeds the totalweight of the other raw materials employed.

An important development in blast-furnace technology, thepressurizing of furnaces, was introduced after World War II. By

throttling the flow of gas from the furnace vents, the pressurewithin the furnace may be built up to 1.7 atmosphere or more.The pressurizing technique makes possible better combustion ofthe coke and higher output of pig iron. The output of many blastfurnaces can be increased by 25 per cent in this way.Experimental installations have also shown that the output ofblast furnaces can be increased by enriching the air blast withoxygen, a level of 2.5 to 5 per cent being common.

The process of tapping consists of knocking out a clay plug fromthe iron hole near the bottom of the bosh and allowing the moltenmetal to flow into a clay-lined runner and then into a large, brick-lined metal container, which may be either a ladle or a rail carcapable of holding as much as 100 tonnes or more of metal. Anyslag that may flow from the furnace with the metal is skimmed offbefore it reaches the container. The molten pig iron is thentransported to the steel-making shop.

Modern blast furnaces are operated in conjunction with basicoxygen furnaces and occasionally an electric arc furnace, or in afew countries the older open-hearth furnaces, as part of a single

steel-producing plant. In such plants the molten pig iron is used tocharge the steel furnaces. The molten metal from several blastfurnaces may be mixed in a large mixer vessel before it isconverted to steel, to minimize any irregularities in thecomposition of the individual melts.

The Steel thus produced is Shaped in two different manners.

1. Continuous casting (right, red arrows) is a method ofworking steel that conveys the metal from its molten state toblooms, ingots, or slabs. The white-hot metal is poured into open-ended moulds and continues on through rollers cooled by water.A series of guide rollers further shapes the steel into the desiredform.

2. Hot rolling (left, blue arrows), the primary means of millingsteel. This process begins with pre-shaped steel slabs, which are

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reheated in a soaking pit. The steel passes through a series ofmills: the blooming mill, the roughing mill, and the finishing mill,which make it progressively thinner. Finally, the steel is woundinto coils and transported elsewhere for further processing.

Methods of Steel Shaping

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Figure A: Schematic figure of Operational Steps in Oxygen Steel Making Processes.

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Steel Processing:

The whole process is carried out in 5 different stages once theCoils are procured.

1. Hard Roll Slitting2. Pickling3. Rewinding4. Thinning5. Galvanizing/ Colour Coating

Slitting:

The Hard rolled sheets procured from JSWs Bellary unit, in

Karnataka, are of width and thickness as per the requirements oforders. Now, once these are brought here, the sheets are Slit,cut from the sides, decreasing called Slitting, and the portion ofthe Factory performing this exercise is known as the Hard RollSlitting Section. The factory has two such Slitting machines,placed adjacent to each other.

Pickling:

Once the Steel sheets are slit to proper width, they are cleaned to

remove the rust and dust, developed and adhered respectively ontheir surface, thus preparing the sheets for Galvanizing. This isdone by applying Hydrochloric Acid of about 4% to 6% initially,then 6% to 8%, and finally 8% to 16% concentration on the Strips,by submerging the strips in tanks filled with it. Once the acidwash is complete, the sheets are rinsed in Distilled water. Thiswhole process is carried out in the pickling line, which has threedifferent initial tanks having Hydrochloric Acid of the above statedconcentration and in the above stated order and finally a fourthtank having the Distilled water. There are two such Pickling linesin the Factory.

Thinning:

The orders from Clients have many specifications, which alsoincludes that of the thickness. Now the required thickness is

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mostly such that cannot be attained simply by Galvanizing thePickled sheets as the Coating itself has its thickness, which isadded up into the thickness of the sheet finally. So, the thicknessof the sheet is reduced up to the extent from where thecumulative thickness of the sheet and the provided coating totalsto the thickness required by the Client. This process is called

thinning and is carried out in Horizontally Inserted Cold RollingMills. In these mills, loading the sheets with Hydraulic Pressurebetween two working rolls thins them.

Rewinding:

The rewinding unit is an assembly of an uncoiler and a recoilerunit, with a cutting and waste collection system attached inbetween. In these machines, the sheets once pickled and thinned,are again slit from the sides, decreasing their width, accurately,to that needed by the clients. This ensures minimum wastage andmost efficient use of the coating material, be it Zinc, or anyColour Coat.

Coating:

Once the sheet exits the Rewinding Machine, it is fully preparedto undergo the final and the most important process ofGalvanizing.

The above stated is the most important process carried out in thewhole of the Factory and also the continuous one going on 24 x 7,round the year, without any stop, until inevitable.

The galvanizing takes place in the assembly known as theGalvanizing line, in the Factory or the CSDs, i.e. Coated StripDivisions.

The Galvanizing line consists of an assembly or series of manybasic component machineries such as Pinch Rolls, Bridles, TheAnnealing Furnace, Melting Pot, Welders, Uncoilers, Coolers,

Degreasing Unit, Accumulator, Coating Equipment, Steering Rolls,Quench Tank, Dryer etc. of which, the Furnace and the MeltingPot can be considered the core Setups, the others being thenecessary Accessories and Utilities, which also include the manycranes.

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The Roll from the rewinding machine is installed on the Uncoilerand here from begins the process of Galvanizing.

The Sheet from the Uncoiler passes into the pinch Roll, whichpulls the sheet forward into the Welders. These welders arebasically Plate welders, which are used to weld the beginning of

one sheet to the tail of the previous one, so that the new sheet isset on the line properly. If this is not done, it becomes very muchtime consuming and challenging to put a sheet properly on theline such that it passes from each and every component in themanner it is supposed to, which eventually means a loss of ahuge amount of money.

From the welder, the sheet passes on into the Bridle, which, pullsthe sheet and also applies tension to it. From here, the Sheet ispassed on into the Entry Accumulator. There is anotheraccumulator at the exit end of the line also. Both theseaccumulators collectively act when a roll is about to complete, insuch a manner so as to provide enough time for welding thebeginning end of the new roll to the tail of the one which is aboutto finish, carrying with it the new sheet across each component ofthe line.

From the entry accumulator the sheet passes into the DegreasingSection. Here, oil and other organic matter, if adhered on thesheet, are removed by the help of solvents.

From the Degreasing unit, the sheet goes into the Annealingfurnace, passing through an intermediate dryer, which dries thesheet of any solvent adhering on its surface from the degreasingsection.

In the Annealing Furnace, the strip is heated to a temperature ofabout 1400 C in the initial Non Oxidation and RTF (Radium TubeFurnace) zones. The whole of the furnace has an inertatmosphere to prevent the Oxidation of Steel. In the furnace, careis taken to ensure no direct contact of the strip and the firingflame. From the RTF section the strip passes into the Soaking

section of the furnace where its temperature is reduced to about700 C 750 C. Then comes the Cooler section consisting of fourJet coolers, which cool down the strips further to about 440 C to460 C, which is the same temperature as that of the zinc meltingpot.

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When the strip exits the Jet coolers, it is submerged into the ZincMelting Pot. Here the Zinc adheres on the surface of the strip. TheThickness of the coat on either side of the strip is maintained bythe help of two Nitrogen Jets one on each face of the strip,covering it with the needed amount of Zinc.

The temperature of the molten Zinc and the Steel strip both beingthe same, once the Steel with the coating is cooled down, thedifferent layers merge into one and this is what prevents the zincfrom just getting peeled off the surface of the steel sheet.

Once exiting the melting pot and the coat thickness maintainer,the strip is cooled with the help of a series of coolers and finallyby quenching in a tank filled with water.

Then again the Strip oases from the many accessories such asbridles and pinch rolls, then the exit accumulator and finally isrewound on the Recoiler.

From the Re-coiler, the coil is uninstalled and with the help of acrane is removed and stacked for Packaging.

Quality Check:

The quality check of the finished materials, i.e. the galvanizedsheets is done for each and every single roll. The Zinc coating persquare metre is measured. Respective to the thickness of thesheet, the hardness is also checked. Moreover bending test isdone on the coated sheet to assure that the Zinc coat doesntchip off the surface of the steel when bent to the maximumpossible extent.

If the product fails in any of the above tests, the whole roll, about20 metric tonnes of steel, is put for auction.

Moreover, the Yield Strength, the Tensile Strength and theElongation of the sheet are also checked.

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Apart from these, the various materials used for processing atdifferent stages are also checked at regular intervals to ensuretheir quality. The Oil in Water emulsion, used in thinning Mills ascoolant and lubricant, is checked for its emulsificationparameters. The composition of the zinc pot is checked whenever

a new batch is switched on to ensure the needed quality ofcoating. The melting pot has the following elements in the givenrespective traces, which are the safe limits for these elements.

Element Permissible limitAlluminium 0.15% to 0.2%Iron 0.3% to 0.4%Antimony 0.1%Tin 0.1%

And the rest is to be Zinc. Lead is also present in traces and thesize of the spangles is directly proportionate to the quantity ofthat.

Packing:

There are two types of packing done here, one is the ImportPacking and the other is Domestic Packing.

Import Packing has three Layers for Corrugated Sheets. The

innermost layer is of Paper. Above the paper is a layer of HighDensity Polyethylene (HDPE), and finally, all this is packed intosteel sheets, leaving no polyethylene exposed.

For Rolled Coils too, the layers are the same as that for thecorrugated sheet bundles.

Domestic packing, on the other hand has steel covered on justone side of the bundle, leaving the other exposed. In case ofRolls, the Steel covering is not done, instead the HDPE covering isconsidered sufficient.

The packaging is done this way because the consignments forImport take a very long time, actually months to get delivered tothe clients from the time of packing. Hence, it becomes verynecessary to ensure that no degradation of the goods takes placeduring transport and the goods are delivered in a Factory Fresh

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Condition. Whereas the domestic deliveries are met with withinvery short period of time, hence no need for too much protectionarises.

Safety:

Like any other large scale industry, JSW also has a very massivestationary and non-stationary infrastructure, with a very largeman-power working at the factory, which obviously gives rise to avery important issue of SAFETY.

At the factory, in any of the massive sheds, there are manyBridge Cranes, moving at the height of about 7 to 8 metres. Fromthis height, even if a small bolt falls down on a human, itll causeenough damage to put the person in a critical situation. Apart

from this, there are many blowers, many rolling mills, allproducing sound of very high intensity, enough to deafen onesyears. Then there is the Zinc melting pot on the Galvanizing line,where splashes of Zinc are experienced when solid ingots areadded into the molten mass. These droplets, being about 450Celsius hot, are enough to give serious burns and if they comeinto contact with the eye, can also depart them of Vision.

Hence, many safety equipments such as helmets, protectivecoverings for the face, earplugs, Safety shoes, etc are verynecessary for ensuring self safety. The company does maintain a

safety code and takes care that every employee abides to it butfinally it is a matter of how concerned is an individual about his orher own safety. Many employees, mostly the engineers an theother educated officers, who do understand the effectiveness ofthe safety equipments do use them, but those who arentsufficiently educated dont understand the worth of the PersonalProtection Equipments and mostly dont use them either, simplyexposing themselves to fatal injuries.

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Acknowledgements:

We both are highly grateful to Mr. Nitin Tekade, HOD, HR, andMiss Shweta Bhalekar for giving us such a wonderful opportunityto expand our practical knowledge, by permitting us for oursummer training, and guiding us when the need evolved, and fortheir very appreciable understanding.

We are also thankful to our Institute, which encourages us to goout into the field and have an experience of the real workingpatterns in the industry rather than just providing us with textualtheoretical knowledge.

We consider it our good luck to have met and learned from Mr.Paresh Shah, Mr. Deepak Sharma and Mr. Dilip Pawar all of whomencouraged us to go and explore the plant and learn things to ourhearts content, and helped us out when we got entangledsomewhere.