3. cupola and blast furnace

8/11/2019 3. Cupola and Blast Furnace

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Oxygen in the air reacts with coke to give carbondioxide:

C(s)

+ O2(g)CO2(g)

The limestone breaks down to form carbondioxide:

CaCO3(s)CO2(g)+ CaO(s)

Carbon dioxide produced in 1 + 2 react with more

coke to produce carbon monoxide:

CO2(g)+ C(s)2CO(g)

Several reactions take place before the iron is

finally produced.


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The carbon monoxide reduces the iron in the ore to give

molten iron:

3CO(g)+ Fe2O3(s)2Fe(l)+ 3CO2(g)

The limestone from 2, reacts with the sand to form slag(calcium silicate):

CaO(s)+ SiO(s)CaSiO3(l)


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Both the slag and iron are drained from the bottom of thefurnace.

The slag is mainly used to build roads.

The iron whilst molten is poured into moulds and left to

solidify - this is called cast iron and is used to make railings

and storage tanks.

The rest of the iron is used to make steel.


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A cupola furnace is a

vertical cylindrical

furnace used for

melting only cast

iron. Although otherfurnaces are capable

of melting cast iron,

the largest tonnage of

cast iron is melted inCupola furnace.

Cupola Furnace

The cupola showing the general inputs and outputs.


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Construction of Cupola Furnace

* The cupola furnace consists of a cylindrical steel shell lined with a refractory material like

firebrick and clay.

* The height of the Cupola Furnace may range from 20 - 35 feet.* The Cupola Furnace is open at the both its top and bottom.

* At the bottom of the Cupola Furnace, hinged insulated doors are provided, so that after

melting is completed, the contents left inside the cupola furnace can be dropped down by

opening the hinged doors.

* A coarse refractory sand and clay are rammed slightly on the bottom doors of cupola

furnace. The sand is rammed in a tapered manner to allow the flow of molten metal easilythrough the tapping spout.

* Opposite to the tapping spout and little higher is a slag hole through which the slag is

removed.

*Slightly above the slag hole is the wind box and tuyeres. The tuyeres are small

openings (covered by wind box) through which air under pressure is forced into the furnace

from the wind box, via a pipe from the blowing equipment.

* At the top end of the shell, a charging door is provided through which the charge is fed into

the Cupola Furnace.
http://www.themetalmachine.com/index.html


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http://www.themetalmachine.com/index.html


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Working of Cupola Furnace

1. Starting The Cupola Furnace

Initially, soft and dry wooden pieces are placed on the sand bottom after which coke is

charged up to the tuyeres lever. The wooden pieces are ignited through the tap hole and

sufficient air is passed through the tuyeres for proper combustion of coke.

2. Charging Cupola Furnace

The charge used in cupola furnace consists of alternate layers of coke, flux and metal

(iron). These three components are continuously built into the cupola furnace. The most

commonly used iron - to - coke ratio is 8:1. The flux may be limestone (CaCO3),

fluorspar, sodium carbonate or calcium carbide. Limestone is the commonly employedflux. The total weight of the flux will be approximately 1/5th the weight of the coke

charge.


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3.Melting in Cupola Furnace

Cupola furnace works on the counter current principle. As the combustion takes place,the charge materials (coke, flux and metal) will be descending downwards, while the

hot gases due to combustion will be ascending upwards. Heat exchange takes placebetween the rising hot gases and the descending charge thereby melting the metal. Theliquid metal drops down, while the coke floats up on top of it.

The flux also melts and reacts with the impurities of the molten metal forming a slag.The slag floats on the surface of the molten metal thereby preventing oxidation of themetal.

4. Tapping slag and molten metal in Cupola Furnace

When sufficient liquid metal is collected in the reservoir, the slag door is opened andthe slag floating on the surface of the molten metal is tapped and disposed off.

Immediately the tapping spout which was closed with a bott ( a clay plug ) is openedand the liquid metal is tapped into ladles. The tapping spout is again closed with thebott. The liquid metal from the ladle is poured into the moulds.


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5. Dropping Down The Bottom in Cupola Furnace

When melting is complete and no more liquid is required, the charging of cupola

furnace is stopped. The prop under the bottom door is knocked down and the bottom

door is swung out of the way allowing the contents in the cupola to drop down. The

un-melted charge is collected and used during the next melting.

Note:- The operation of dropping down the bottom is very dangerous and has to bedone by a trained person.


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Zones Of Cupola Furnace

1. Well zone in Cupola Furnace

2. Combustion Zone in Cupola Furnace

3. Reducing Zone in Cupola Furnace

4. Melting Zone in Cupola Furnace

5. Preheating zone in Cupola Furnace


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1. Well zone in Cupola Furnace:-

Well zone in the portion situated between the rammed sand bottom

and just below the bottom edge of the tuyeres. The molten metal is

occupied in this zone.


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2. Combustion Zone in Cupola Furnace

The combustion zone or oxidizing zone is situated normally 15-30 cm

from the bottom edge of the tuyeres. It is in this zone where rapid

combustion of coke takes place due to which a lot of heat is generated in

the furnace. The combustion is rapid due to the supply of blast air

through the tuyeres.

Oxidation of manganese and silicon evolve still more heat. The reactions

which take place in this zone are:

C+O2 (from air) CO2+heat

2Mn+O2 2 MnO + heat

Si+O2 SiO2 + heat

The temperature in this zone varies from 1550C - 1850C.


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3. Reducing Zone in Cupola Furnace

Reducing zone or protection zone is the portion located from the top of thecombustion zone to the top of the coke bed. In this zone, some of the hot CO2

gas moving upward through the hot coke gets reduced to CO. In other words,

reduction of CO2to CO occurs in this zone. Due to the reducing atmosphere,

the charge is protected from oxidation. The reaction taking place in this zone

is given by.

CO2+C (coke) = 2CO - Heat

Due to the reduction, the temperature reduces to around 1200 C in this zone.


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5. Preheating zone in Cupola Furnace

The portion occupied from the top surface of the melting zone to the

charging door is called Preheating zone. The hot gases rising upwards

from the combustion and reducing zone gives its heat to the charge

before passing out of the furnace. Thus, the charge is preheated beforedescending downwards


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3. STEEL MANUFACTURING


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Steel productsSemi-finished products(continuous cast steel)

Finished products (rolled steel)


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Steel Making Plant

Electric Arc Furnace Ladle Furnace Continuous Casting Machine


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What is Steel used for - IStructures, canned food, oil platforms,

catalytic converters, paper clips, mounts

for electronic chips...are all made of steel.

1. In the construction of bridges

or buildings...2. In the automobile sector...


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What is Steel used for-II3. For everyday uses:

cans,pots,containers,etc...4. At the heart of food

preservation...

5. In communications... 6. In energy... 7. In health...

3. cupola and blast furnace

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