billets process

7/26/2019 Billets Process

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1. THE SCRAP TO STEEL BILLET PROCESS

The scrap is then loaded by a grab crane into baskets. Each heat is created from three basket

loads of Scrap. The baskets are loaded from a recipe sheet. The first basket will hold the most scrap

20 tonnes plus and then basket two and three will progressiely hold less. The target is !0

tonnes of scrap per heat.

The first basket is lowered oer the electric arc furnace and the scrap is dropped in. "n electrica

current is combined with chemical energy to heat the scrap to a near molten state. "t this point the

second basket is added and once this is also molten# the third and final basket is added. This

progressie basket process is re$uired in order to fit all the scrap in one heat

%e then in&ect o'ygen and carbon and the process takes the molten metal to a base leel# this also

enables us to form slag on the top of molten steel.

The slag (which contains the impurities we don)t want* the steel effectiely bubbles off the top of the

heat and is collected in a slag pit below. %e process this slag and is reused as high grade roading

material all around +ew ,ealand recycling at its best-

%hen the steel temperature is around /20 degrees elsius the molten steel is then poured into a

ladle1 this is called tapping. uring the tapping process we add lime# manganese# silicon# carbon and

if necessary depending on what type of steel is being made# anadium.


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The ladle is then transported by crane to the refining station# where more carbon# manganese# silicon

and anadium are added to achiee the specification of the grade of steel being made. "rgon gas

bubbles through the ladle to help remoe any remaining impurities.

3nce the specification of the steel is confirmed the ladle is transported again by crane to the

continuous casting area. 4ere the ladle gate is opened and the molten steel is allowed flow in acontrolled matter into a tundish. This steel flows into three billet moulds. The steel billets are formed

and then cut to the desired length for further processing.

The billet is normally consumed by our rolling mill# where it is further processed into rolled products

like reinforcing bar or wire rod. 5acific Steel also e'ports billet a globally traded commodity.


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STEEL MAKING BY INDUCTION FURNACE - PROCESS

The greatest adantage of the 6nduction 7urnace is its low capital cost compared with other types of 8elting 9nits. 6tsinstallation is relatiely easier and its operation simpler. "mong other adantages# there is ery little heat loss from thefurnace as he bath is constantly coered and there is practically no noise during its operation. The molten metal in an6nduction 7urnace is circulated automatically by electromagnetic action so that when alloy additions are made# ahomogeneous product is ensured in minimum time. The time between tap and charge# the charging time# power delaysetc. are items of utmost importance are meeting the ob&ectie of ma'imum output in tones:hour at a low operational cost.The process for manufacturing steel may be broadly diided into the following stages;

Melting the h!"ge #i$e% &' (teel ) I"&n ("!*.

L!%le tee#ing *"!tie '&" C!(ting +OR,

Di"et tee#ing *"!tie '&" Ing&t C!(ting nl&!%!le tee#ing #!hine.

+I, Melting The Ch!"ge

The furnace is switched on# current starts flowing at a high rate and a comparatiely low oltage through the inductioncoils of the furnace# producing an induced magnetic field inside the central space of the coils where the crucible is locatedThe induced magnetic flu'es thus generated out through the packed charge in the crucible# which is placed centrallyinside the induction coil.

"s the magnetic flu'es generated out through the scraps and complete the circuit# they generate and induce eddy currentin the scrap. This induced eddy current# as it flows through the highly resistie bath of scrap# generates tremendous heatand melting starts. 6t is thus apparent that the melting rate depends primarily on two things (* the density of magneticflu'es and (2* compactness of the charge. The charge mi'ed arrangement has already been described. The magneticflu'es can be controlled by arying input of power to the furnace# especially the current and fre$uency.

6n a medium fre$uency furnace# the fre$uency range normally aries between !010< cycles:second. This heat isdeeloped mainly in the outer rim of the metal in the charge but is carried $uickly to the center by conduction. Soon a poolof molten metal forms in the bottom causing the charge to sink. "t this point any remaining charge mi'ed is addedgradually. The eddy current# which is generated in the charge# has other uses. 6t imparts a molten effect on the li$uid steelwhich is thereby stirred and mi'ed and heated more homogeneously. This stirring effect is inersely proportional to thefre$uency of the furnace and so that furnace fre$uency is selected in accordance with the purpose for which the furnacewill be utili=ed.

The melting continues till all the charge is melted and the bath deelops a cone' surface. 4oweer as the cone'

surface is not faorable to slag treatment# the power input is then naturally decreased to flatten the cone'ity and toreduce the circulation rate when refining under a reducing slag. The reduced flow of the li$uid metal accelerates thepurification reactions by constantly bringing new metal into close contact with the slag. >efore the actual reduction of steelis done# the li$uid steel which might contain some trapped o'ygen is first treated with some suitable deo'idi=er. %hen nopurification is attempted# the chief metallurgical adantages of the process attributable to the stirring action are uniformityof the product# control oer the super heat temperature and the opportunity afforded by the conditions of the melt tocontrol de1o'idation through proper addition.

"s soon as the charge has melted and de1o'idising ions hae ceased# any ob&ectionable slag is skimmed off# and thenecessary alloying elements are added. %hen these addities hae melted and diffused through the bath of the powerinput may be increased to bring the temperature of metal up to the point most desirable for pouring. The current is thenturned off and the furnace is tilted for pouring into a ladle. "s soon as pouring has ceased# any slag adhering to the wall ofthe crucible is crapped out and the furnace is readied for charging again.

"s the furnace is e$uipped with a higher coer oer the crucible ery little o'idation occurs during melting. Such a coeralso seres to preent cooling by radiation from the surface heat loss and protecting the metal is unnecessary# thoughslags are used in special cases. "nother adantage of the induction furnace is that there is hardly any melting losscompared with the arc furnace.

+ii, L!%le Tee#ing P"!tie

The molten metal from crucible taken out in a ladle by tilting the crucible and crucible is made free for further charge ofne't batch.

+iii, Di"et Tee#ing P"!tie


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6n addition to the bottom pouring ?adle Teeming process# irect Teeming process can also be used as and when re$uired.irect teeming of li$uid metal from induction furnace to mould assemble is another process of the >illet casting practice.6n this process the mould assemble comprising bottom plate@ >illet mould and trumpet properly lined with refractories areplaced on top of a rail bound transfer trolley moing across in front of the crucible which is supported properly from thefurnace structure.

%hile teeming the mould bogie transfer car is so positioned that the trumpet of the mould assembly is properly alignedwith the outlet no==le of the tundish. The li$uid metal from the spout is directed through the tundish to the trumpet forcasting of >illets. "fter the teeming is oer# the car is moed aside for stripping and remoal of >illets. +ormally two (2*such transfer cars are proided. %hile one is engaged for casting purposes the other is kept ready for ne't melt. irectteeming practice obiates the use of stopper sleee# stopper head and ladle refractory and re$uires only a nominal$uantity of refractory for lining the tundish and thus affects substantial saings in refractory costs.

B, CONTINUOUS CASTING MACHINE

The molten steel from the 67 or the ladle metallurgical facility is cast in a continuous casting machine (/: 2 stand >illetaster* to produce cast shapes including billets. 6n some processes# the cast shape is torch cut to length and transportedhot tothe hotrollingmill forfurther

processing. 3ther steel mills hae reheat furnaces. Steel billets are allowed to cool# and then be reheated in a furnaceprior to rolling the billets into bars or other shapes.

C!(ting( &*e"!ti&n( &n(i(t &' '&ll&/ing0 -

1.The process is continuous because li$uid steel is continuously poured into a AbottomlessA mould at the same rate asa continuous steel casting is e'tracted.

.>efore casting begins a dummy bar is used to close the bottom of the mould.

2." ladle of molten steel is lifted aboe the casting machine and a hole in the bottom of the ladle is opened# allowing the li$uid steel to pour into the mould to form the re$uired shape.

3."s the steelAs outer surface solidifies in the mould# the dummy bar is slowly withdrawn through the machine# pulling the steel with it.

4.%ater sprays along the machine to cool:solidify the steel.

5."t the end of the machine# the steel is cut to the re$uired length by gas torches.

P"e*!"!ti&n.

M!th Pl!te( +P!tte"n(,

P"e*!"!ti&n &' M&l%(

P&"ing &' #&lten (teel int& *"e*!"e% #&l%(

S&li%i'i!ti&n &' #&lten (teel

Kn&6ing &' #&l%(Re#&7!l &' "nne"( ) "i(e"(.

Fini(hing &' !(ting(8Ing&t(


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billets process

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