c a s t i r o n Report

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C A S T I R O N

(CUPOLA REMELTING

FURNACE)

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Table of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

The Cupola Furnace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

The Appearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

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INTRODUCTION

A ageold metal melting device, the cupola furnace is use to melt cast iron, bronze

and ni-resist iron. A Cupola or Cupola furnace is a melting device used in foundries that

can be used to melt cast iron, ni-resist iron and bronzes. It is widely used because the

operating methods are simple, economical and eco-friendly.

The use of cupola furnaces is one of the oldest process for making cast iron and

is still among the dominant technologies in the world. In Queensland, most of the larger

foundries have replaced their cupola furnaces with more efficient electric furnaces.

Some of these foundries still maintain a cupola furnace for specific melts or for reserve

capacity.

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The Cupola Furnace

A Cupola or Cupola furnace is a melting device used in foundries that can be used to

melt cast iron, ni-resist iron and some bronzes. The cupola can be made almost any

practical size. The size of a cupola is expressed in diameters and can range from 1.5 to

13 feet (0.5 to 4.0 m).[1]The overall shape is cylindrical and the equipment is arranged

vertically, usually supported by four legs. The overall look is similar to a

large smokestack.

Old print- IRON CASTING MACHINERY CUPOLA FURNACE MOULDING

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The bottom of the cylinder is fitted with doors which swing down and out to 'drop

bottom'. The top where gases escape can be open or fitted with a cap to prevent rain

from entering the cupola. Tocontrol emissions a cupola may be fitted with a cap that is

designed to pull the gases into a device to cool the gasses and remove particulate

matter.

Cupola furnace - An earlytype of cupola.

The shell of the cupola, being usually made of steel, has refractory

brick and refractory patching material lining it. The bottom is lined in a similar manner

but often a clay and sand mixture ("bod") may be used, as this lining is temporary.

Finely divided coal ("sea coal") can be mixed with the clay lining so when heated the

coal decomposes and the bod becomes slightly friable, easing the opening up of the tap

holes.[2]The bottom lining is compressed or 'rammed' against the bottom doors. Some

cupolas are fitted with cooling jackets to keep the sides cool and with oxygen injection

to make the coke fire burn hotter.

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The cupola furnace has several unique characteristics which are responsible for its

widespread use as a melting unit for cast iron.

1. The cupolas is one of the only methods of melting which is continuous in its

operation

2. High melt rates

3. Relatively low operating costs

4. Ease of operation

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HISTORY

Ren-Antoine Ferchault deRaumur

Cupola furnace is a very old and still a widely used method for making cast iron.

In some place cupola furnae has been replace by the less fussy electric furnace cupola

furnace is still used for melting some special metals. Though the cupola furnace is said

to have been used for the 3rd Century B.C. by the Chinese, the first cupola furance was

officially known to have been made by Ren-Antoine Ferchault de Raumur around

1720 AD.

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The Appearance

Cupola furnace is cylindrically shaped and place on a four legged structure for a

support. The shell of the cupola, being usually made of steel, has refractory brick and

refractory patching material lining it. The bottom is lining in a similar manner but often a

clay and sand mixture may be used, as this lining is temporary. The bottom lining is

compressed or 'rammed' against the bottom doors. Some cupolas are fitted with cooling

jackets to keep the sides cool and with oxygen injection to make the coke fire burn

hotter. The other equipment are arranged around the cylinder and the bottom of the

cylinder has a door thrugh which the molten metals can be dropped down. The top of

the cylinder is usually open for the gas to escape. A typical cupola melting furnace

consists of a water-cooled vertical cylinder which is lined with refractory material. The

metal and the fuel ingredients like coke and limestone are fed into the cylinder. Air

which contins air goes in through the bottom. The coke is heated and the metal gets

melted. In some cases this process is preferred to electric furnace because mos the

impurities are removed while the iron is melted.

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OPERATION

To begin a production run, called a 'cupola campaign', the furnace is filled with

layers of coke and ignited with torches. Some smaller cupolas may be ignited with wood

to start the coke burning. When the coke is ignited, air is introduced to the coke bed

through ports in the sides called tuyeres.

When the coke is very hot, solid pieces of metal are charged into the furnace through an

opening in the top. The metal is alternated with additional layers of fresh

coke. Limestone is added to act as a flux. As the heat rises within the stack the metal is

melted. It drips down through the coke bed to collect in a pool at the bottom, just above

the bottom doors. During the melting proses a thermodynamic reaction takes place

between the fuel and the blast air. The carbon in the coke combines with the oxygen in

the air to form carbon monoxide. The carbon monoxide further burns to form carbon

dioxide. Some of the carbon is picked up by the falling droplets of molten metal which

raises the carbon content of the iron. Silicon carbide and ferromanganese briquettes

may also be added to the charge materials. The silicon carbide dissociates and carbon

and silicon enters into the molten metal. Likewise the ferromanganese melts and is

combined into the pool of liquid iron in the 'well' at the bottom of the cupola. Additions to

the molten iron such as ferromanganese, ferrosilicon, Silicon carbide and other alloying

agents are used to alter the molten iron to conform to the needs of the castings at hand.

The operator of the cupola is known as the 'Cupola Tender' or "Furnace Master". During

the operation of a tapped cupola (cupolas may vary in this regard)the tender observes

the amount of iron rising in the well of the cupola. When the metal level is sufficiently

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high, the cupola tender opens the "tap hole" to let the metal flow into a ladle or other

container to hold the molten metal. When enough metal is drawn off the "tap hole" is

plugged with a refractory plug made of clay.[6]

The cupola tender observes the furnace through the sight glass or peep sight in the

tuyeres. Slag will rise to the top of the pool of iron being formed. A slag hole, located

higher up on the cylinder of the furnace, and usually to the rear or side of the tap hole, is

opened to let the slag flow out. The viscosity is low (with proper fluxing) and the red hot

molten slag will flow easily. Sometimes the slag which runs out the slag hole is collected

in a small cup shaped tool, allowed to cool and harden. It is fractured and visually

examined. With acid refractory lined cupolas a greenish colored slag means the fluxing

is proper and adequate. In basic refractory lined cupolas the slag is brown.

After the cupola has produced enough metal to supply the foundry with its needs, the

bottom is opened, or 'dropped' and the remaining materials fall to the floor between the

legs. This material is allowed to cool and subsequently removed. The cupola can be

used over and over. A 'campaign' may last a few hours, a day, weeks or even months.

When the operation is over, the blast is shut off and the prop under the bottom door is

knocked down so that the bottom plates swing open. This enables the cupola remains

to drop to the floor or into a bucket. They are then quenched and removed from

underneath the cupola.

A typical cupola melting furnace consists of a water-cooled vertical cylinder which is

lined with refractory material. The process is as follows:

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The charge, consisting of metal, alloying ingredients, limestone, and coal coke for

fuel and carbonisation (8-16% of the metal charge), is fed in alternating layers

through an opening in the cylinder.

Air enters the bottom through tuyeres extending a short distance into the interior of

the cylinder. The air inflow often contains enhanced oxygen levels.

Coke is consumed. The hot exhaust gases rise up through the charge, preheating it.

This increases the energy efficiency of the furnace. The charge drops and is melted.

Although air is fed into the furnace, the environment is a reducing one. Burning of

coke under reducing conditions raises the carbon content of the metal charge to the

casting specifications.

As the material is consumed, additional charges can be added to the furnace.

A continuous flow of iron emerges from the bottom of the furnace.

Depending on the size of the furnace, the flow rate can be as high as 100 tonnes per

hour. At the metal melts it is refined to some extent, which removes contaminants.

This makes this process more suitable than electric furnaces for dirty charges.

A hole higher than the tap allows slag to be drawn off.

The exhaust gases emerge from the top of the cupola. Emission control technology is

used to treat the emissions to meet environmental standards.

Hinged doors at the bottom allow the furnace to be emptied when not in use.

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QUALITY CONTROL

During the production, samples may be taken from the metal and poured into

small molds. A chill wedge is often poured to monitor the iron quality. These small,

approx 18 mm (3/4") wide x 38 mm (1-12") tall triangular shaped pieces are allowed to

cool until the metal has solidified. They are then extracted from the sand mold and

quenched in water, wide end first. After cooling in the manned the wedges are fractured

and the metal coloration is assessed. A typical fracture will have a whitish color towards

the thin area of the wedge and grayish color towards the wide end. The width of the

wedge at the point of demarcation between the white and gray areas is measured and

compared to normal results for particular iron tensile strengths. This visual method

serves as a control measurement.

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Advantages of Cupola Furnace

The cupola furnace has received a lot of negative publicity in recent years. However,

the system does have a number of inherent advantages over electric furnaces:

It is simple and economical to operate.

A cupola is capable of accepting a wide range of materials without reducing melt

quality. Dirty, oily scrap can be melted as well as a wide range of steel and iron. They

therefore play an important role in the metal recycling industry

Cupolas can refine the metal charge, removing impurities out of the slag.

From a life-cycle perspective, cupolas are more efficient and less harmful to the

environment than electric furnaces. This is because they derive energy directly from

coke rather than from electricity that first has to be generated.

The continuous rather than batch process suits the demands of a repetition foundry.

Cupolas can be used to reuse foundry by-products and to destroy other pollutants

such as VOC from the core-making area.

Most of the impurities in the charges are removed while the ore is melted. The process

which is simple and economical can be used to melt a wide rang eof metals. An above

all cupola furnaces are eco-friendly since they take the heating energy from the coke in

the furnace. electricity that first has to be generated.

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REFERENCES

http://www.atlasfdry.com/cupolafurnace.htm

en.wikipedia.org/wiki/Cupola_furnace

www.localhistory.scit.wlv.ac.uk

www.igg.org.uk