manufacturing tech i unit 1

8/11/2019 Manufacturing Tech I UNIT 1

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PATTERN ALLOWANCES


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Sand casting

Casting is one of the processes used for

making components of complicated shapes in

larger quantity


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It is the process of producing metal parts by

pouring moltern metal into the mould cavity of the

required shape and allowing the metal into

soliditfy

Refractory mold

pour liquid metal

solidify, remove

finish


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Moltern metal


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Cavity


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This solidified metal piece is called as casting

A plant where the casting are made is called a

foundry

Therefore it is a collection of necessary

materials, tools and equipments to produce

casting


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Sand moulds:

Mould is a cavity of required shape made in

moulding sand

Pattern is the model of required casting made in

wood, metal or plastics

It is primarily used to produce the mould cavity in

sand

The important process involved in foundry are

Pattern making

Mould making

Casting


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Pattern in wood, metal or plastics


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IN METAL


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IN PLASTICS


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PATTERN AND PATTERN MAKING

A Pattern is one of the important tools used

for making cavities in the mould whichmoltern metal is poured to produce a casting


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Projects or Core print


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Core prints


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Types of patterns

The following types of patterns are normallyuse in foundry

Solid or single piece pattern

Split pattern Loose piece pattern

Match plate pattern

Segmental pattern

Shell pattern


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Solid pattern or single piece

Made of single solid piece with out joints It is used for making a few large size simple

casting

Removal of pattern from the sand is easy


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Single piece pattern


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Split pattern

Split patterns is made of two parts

One part is used to produce the lower half of

the mould where as the other parts is used to

produce the upper half of the mould

These two parts are assembled together

position by pins called dowel pins


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Spilt piece pattern


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Loose piece patterns

When a one piece solid pattern has projections orback drafts which lie above or below the parting

plane, it is impossible to with draw it from the

mould. With such patterns, the projections aremade with the help of loose pieces.


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Match plate


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Sweep pattern

Sweep patterns are mainly used to generatesurfaces of revolution to generate surfaces like

cyliner,cone,sphere in large casting


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Pattern materials

The following factors to be considered for

selecting pattern materials

Design of casting

Number of castings to be produced

Degree of accuracy and surface finish required

Shape,complexity and size of the casting

Casting or moulding method adopted


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Commonly used pattern making

materials are given below

Wood-teak wood,mahogany,white pine

Metal-cast iron,brass, aluminum,white metals etc

Plaster

Plastics

wax


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Wood-teak wood,mahogany,white

pine


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mahogany


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White pine


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Plaster Casting V-belt pulleys
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PATTERN ALLOWANCES

Patterns are not made into extact size of the

castings to be produced

Patterns are made slighty larger than the

required castings

This extra size given on pattern is called

pattern allowances

If allowances not given on the pattern, the

casting will become smaller than the requiredsize

The various allowances normally


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The various allowances normallyprovided on the pattern are

Shrinkage allowances

Maching or finish allowance

Draft or taper allowance

Distortion or chamber allowance

Rapping or shake allowance


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Shrinkage allowances

The metals shrinks on solidification and

contracts further on cooling to room

temperature

To compensate this ,the pattern is made larger

than the required casting

This extra size provided on the pattern for

metal shrinkage is called shrinkage allowance


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Machining or finish allowance

All the casting are to be machined to get the

required surface finish on the metal

During machining some of the metal is

removed from the casting

For this purpose the pattern for machining is

made larger than the required shape

This extra size given on pattern is called

Machining or finish allowance

Draft allowance


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Draft allowance

When the pattern is to be removed from the

sand mold, there is a possibility that any leadingedges may break off, or get damaged in the

process.

To avoid this, a taper is provided on the pattern,

so as to facilitate easy removal of the pattern

from the mold, and hence reduce damage to

edges.

The taper angle provided is called the Draft

angle.

This slight taper provided on the vertical sides of

pattern is called draft allowances


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Distortion allowance

During cooling of the mold, stresses

developed in the solid metal may inducedistortions in the cast.

This is more evident when the mold is thinner

in width as compared to its length. This can be eliminated by initially distorting

the pattern in the opposite direction


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Moulding sand

Moulding sand

The special type of sand is used for making

mould

Moulding stands essentially contains thefollowing three constituents

Refractory sand

Binder Additive

These types of sand are used in


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These types of sand are used in

moulding for the following reasons

It maintans shape at very high temperature

It can be used again and again

It is inexpensive

d


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Sand

Silica sand is widely used as moulding sand

Silica has 80 to 90 % silicon dioxide

Silica gives refractoriness to the sand

d


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Advantage

It is cheap and easily available

It has high thermal stability

According to the clay content,the moulding

sand is classified into

Silica sand 2% clay

Lean or weak sand 2 to 10%

Moderately Strong sand 10 to 20 % Strong sand upto 30% clay

Loam sand upto 50 % clay

T ere are t ree ma n types o


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T ere are t ree ma n types osand

Natural sand

Synthetic sand

Special sand

N l d


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Natural sand

It is available from natural deposits

It needs only 5-8% water

These sand are available at riverbeds and

it contains 80-90% OF silica,5 to 10% alumina

or clay and small % of lime and magnesia

This sand is generally used for making light

casting in ferrous and nonferrous


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S i l d


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Special sands

Special sand is prepared for abating specific

Properties such asrefractories,high heat

conductivity and low expansion ratio


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Some special sands are

Zircon sand

It is mainly used for making cores of brass

and bronze casting

Is is used as facing sand

Chromite sand

It may be used as facing sand in steel casting

Bi d


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Binder

Binders are used to bring the property of

cohesiveness to the sand

They bind the sand grains together and give

strength to the moulding sand

There are basically two types of blinders

used

Organic binders

Inorganic binder


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Organic binders

Resins,drying oil

I i bi d


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Inorganic binders

Clay is formed by weathering and

decomposition of rock

Kaolinite

Bentonite

ADDITIVES


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ADDITIVES

Additives are added to the moulding sand to

improve the properties like

strength,refractoriness and permeability

S l


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Sea coal


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Saw dust


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Saw dust


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Pitch coal tar


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Pitch coal tar

Silica flour


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Silica flour


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Types of moulding sand


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Types of moulding sand

Green sand

It is sand used in the wet condition for making themould. It is mixture of silica sand with 15-25 per

cent clay and 6-8 per cent water

As explained earlier green sand moulds are notdried and metal is poured in them in the wet

condition

Being damp the sand can be easily worked withhand to give it any desired shape

This sand is used for producing small to medium

sized moulds which are not very complex


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Dry sand

Dry sand is the green sand that has been dried

or baked after preparing the mould.

Drying sand gives strength to the mould so

that it can be used for larger castings


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Parting sand This sand is used during making of the mould to

ensure that green sand does not stick to the pattern

and the cope and drug parts can be easily separated

for removing the pattern without causing any

damage to the mould.

Parting sand consists of fine grained clay free dried

silica sand, sea sand or burnt sand with some

parting compounds. The parting compounds used include charcoal,

ground bone and limestone, groundnut shells, talc

and calcium phosphate.


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Facing sand

Facing sand is the sand which covers the pattern

all around it. The remaining box is filled with

ordinary floor sand.

Facing sand forms the face of the mould andcomes in direct contact with the molten metal

when it is poured.

High strength and refractoriness are required forthis sand.


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It is made of silica sand and clay without the

addition of any used sand.

Graphite, mollases, plumbago etc. may be

added to the facing sand. Thickness of thesand layer varies from 20 to 30 mm


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Moulding tools


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Moulding tools

shovel


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Riddle


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TROWEL


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Srike off bar


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Swab


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Swab

Bellows


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Bellows

ld b


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Moulding boxes


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Core and core making

A core is a body made of sandWhich is used to make a cavity or a hole in a

casting

It is also used to make projections, undercuts andinternal cavities


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Essential qualities of a core


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Permeability

The property of a core which allows the steam andgases to pass out

Refractoriness

The property of core in withstanding the hightemperature

Strength

The core should be sufficiently strong and should not

break when it is handled

Collapsibility

stability

C ki i l


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Core making materials

Core is made of cores sand, binders, additiveCore sand-silica sand and zircon which have

refractoriness properties

Binders-vegetable oil or mineral oil,resins,bentoniteetc

Additives-wood flour, coal powder, cow dung etc

Core boxes


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Core boxes

Half core box- used to make one half of the

symmetrical core piece


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Dump or slap core box- used for


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making a full core

Split core box- this box has two similarh lf b


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half boxes

Strickle core box- used for irregular


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g

shape

Gang core box- used for producingf


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many no of cores

Core ovens


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Core ovens are used for heating the cores to

obtain required hardness

1.batch type ovens-small and medium cores

are baked in batch type ovens

2.continous type ovens-heating is done

continuously, core are loaded in conveyor

3.dielectric baking ovens-quickest methods of

heating here two electrodes are used


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Batch type oven


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Batch type oven

2 continous type ovens


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2.continous type ovens


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3 dielectric baking ovens


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3.dielectric baking ovens

Core making methods 1 hand core making method


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1.hand core making method

core sand preparation

Moulding a green sand core

Mixed with binders,additive and water

Baking or curing

Cores are heated in ovens,

Moisture is removed

Core becomes strong

Finishing

After baking cores are cleaned and sized and involves in 3 process

1.Triming

2.Brushing3.sizing

Coating

Coating will prevent the metal leaking into core

Types of cores


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(a)according to the state of core

1.green sand core

2.dry sand core

(b)According to the position of the cores

1.Horizontal core

2.Vertical core

3.Balanced core

4.Hanging core

5.Drop core

Methods of sand testing


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1.testing of moulding sand

2.testing of core

Various methods of testing core sand


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Various methods of testing core sand

1.Green strength test

tension,compression test carried out

2.Permeability test

Same like green strength test

3.Baked strength test

First the core is baked in oven at a particularTensile test in utm machine


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Moisture test


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Moisture test


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Clay content test


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Clay content test


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Types Moulding machines


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Molding machines will do the following

operations

1.Ramming the mould sand

2.Pattern easy removal

The following types of moulding machines are

used

1.jolting machine2.Squeezing machine

3.Sand slinger

Jolting machine


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Jolting Load - 700kgs

Pattern Draw - 350 mm

Table Size - 1254 X 1000mm

Table Height (from floor) - 760mm Net. Weight (approx) 2200 kgs

Jolt capacity is calculated at 90 PSI air pressure.


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Sand slinger


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Sand slinger

slinger


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upola Furnace

Group No 1


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Muhammad Zubair MME-12-29

M. Faisal Maqsood MME-12-20

Gulfam Hussain MME-12-30

Arif Ali MME-12-01

Muhammad Ahmad MME-12-14

Group No 1

What is Furnace???


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Heating media or device.

Used for heating and melting.

For providing heat to chemical reactions for

processes like cracking.

The furnace may be heated by fuel as in many

furnaces coke is used as a fuel.

some are operated by electrical energy e.g.

electric arc furnace.

What is

Furnace???

Cupola Furnace


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Cupola was made by Rene-Antoine around 1720.

Cupola is a melting device.

Used in foundries for production of cast iron.

Used for making bronzes.

Its charge is Coke , Metal , Flux.

Scrap of blast furnace is re melted in cupola.

Large cupolas may produce up to 100 tons/hourof hot iron.

Cupola Furnace

Construction


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Cupola is a cylindrical in shape and placedvertical.

Its shell is made of steel.

Its size is expressed in diameters and can rangefrom 0.5 to 4.0 m.

It supported by four legs.

Internal walls are lined with refectory bricks.

Its lining is temporary.

Construction

Parts of Cupola


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Spark arrester.

Charging door. Air box.

Tuyeres.

Tap hole.

Slag hole.

Parts of Cupola

Zones


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Well

The space between the bottomof the Tuyeres and the sandbed.

Molten metal collected in thisportion.

Combustion zone

Also known as oxidizing zone .

Combustion take place in thiszone.

It is located between well andmelting zone.

Height of this zone is normally15cm to 30cm.

Zones

Zones


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Zones

In this zone the temperatureis 1540C to 1870C.

The exothermic reactions

takes place in this zonethese are following .

C + O2 CO2 + Heat

Si + O2 SiO2 + Heat

2Mn + O2 2MnO + Heat

Reducing zone Locate between upper level

of combustion zone andupper level of coke bed.


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Zones


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Preheating zone This zone is starts from the upper

end of the melting zone and

continues up to the bottom level of

the charging door . Objective of this zone is preheat the

charges from room temperature to

about 1090C before entering the

metal charge to the melting zone.

Stack The empty portion of cupola above

the preheating zone is called as

stack. It provides the passage to hot

gases to go to atmosphere from the

cupola furnace.

Charging of Cupola Furnace


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Before the blower is started, the furnace is uniformly

pre-heated and the metal, flux and coke charges, lyingin alternate layers, are sufficiently heated up.

The cover plates are positioned suitably and the bloweris started.

The height of coke charge in the cupola in each layervaries generally from 10 to 15 cm . The requirement offlux to the metal charge depends upon the quality of

the charged metal and scarp, the composition of thecoke and the amount of ash content present in thecoke.

g g p

Working of Cupola Furnace


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Its charge consist ofscrap, coke and flux.

The charge is placed layer

by layer. The first layer is coke,

second is flux and thirdmetal.

Air enter through the

bottom tuyeres. This increases the energy

efficiency of the furnace.

Coke is consumed.

g p

Working of Cupola Furnace


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g p

The hot exhaust gases rise up

through the charge, preheating it.

The charge is melted.

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.

The slag is removed from slag hole.

The molten metal achieved by tap

hole.

Operation of Cupola


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Preparation of cupola.

Firing the cupola.

Soaking of iron.

Opening of air blast.

Pouring the molten metal.

Closing the cupola.

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Preparation of cupola


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Slag and metal adhere to the cupola liningfrom the previous run is removed and lining of

cupola is re made.

The bottom plates are swung to closingposition supported by prob.

The sand bed is then prepared with molding

sand such that its slopes to towards the taphole.

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Firing the Cupola


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The cupola is fired by kindling wood at thebottom.

This should be done 2.5 to 3 hours before themolten metal is required.

On the top of the kindling wood a bed of coke isbuilt.

The height of the coke bed is may be vary from

50cm to 125cm according to the size of cupola.

Firing the Cupola

Soaking of Iron


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When the furnace is charged fully it ismaintain for about 45 minutes.

The charge is slowly heated.

During the stage the air blast is shut off andiron is soaked.

g

Opening of blast air


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At the end of the soaking period the air blastis opened.

The taping hole is closed by a plug when the

melting proceeds and molten metal is collectat the bottom.

p g

Pouring of molten metal


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When the sufficient amount of metal hascollected in the hearth the slag hole is opened

and the slag is removed.

Then taping hole is opened and molten metalis flows out in the table.

The same procedure is repeated until the

charge is melted and the operation is over.

g

Closing the cupola


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When the operation is over the air blast isshut off .

The bottom of furnace is opened by removing

the prop.

Advantages


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It is simple and economical to operate .

Cupolas can refine the metal charge, removingimpurities out of the slag.

High melt rates .

Ease of operation .

Adequate temperature control . Chemical composition control .

Efficiency of cupola varies from 30 to 50%.

Less floor space requirements.


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SOME IMPORTANT TERMS-


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NOTE-

Minerals: A solid element or compound which occursnaturallyin the Earth's crust is called a mineral.

Ore: A mineral from which metals can be extracted

profitably is called a metal ore. Profitable extraction means

that the cost of getting the metal out of the ore is sufficientlyless than the amount of money made by selling the metal.

So All Ores Are Minerals But All Minerals Are Not Ores.

The most common metal ores are oxides and sulphides.

Metals are obtained from their ores by reduction.

What is a Blast furnace??


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It is a tall cylindrical furnace

made of steel.

It is lined inside with fire

bricks.

It is narrow at the top and

has an arrangement for the

introduction of ore and outletfor waste gases.

Heated with help of Hot

Gases.

What are the functions of a Blast Furnace???


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The function of a blastfurnace is to reduce and

convert iron oxides into liquidiron called "hot metal".

The blast furnace is a huge,steel stack lined withrefractory brick.

Iron ore, coke and limestoneare put into the top, andpreheated air is blown into thebottom.

Steps involved in Blast furnace --


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Your own footer Ahan M R ,10-B

\

.


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10-B Ahan M R

Step 1-Insert iron ore, limestone, and cokeinto blast furnace.

Step 2-Coke reacts with oxygen and formscarbon dioxide- C(s)+O2(g) --> CO2(g).

Step 3-Limestone decomposes and forms

another carbon dioxide- CaCO3(s) -->CO2(g)+CaO(s).


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10-B Ahan M R

Step 4-Carbon dioxide produced in thefirst 2 reactions reacts with excess

coke and forms carbon monoxide-CO2(g)+C(s) --> 2CO(g).

Step 5-Carbonmonoxide reduces iron

ore and produces molten iron-3CO(g)+Fe2O3(s) --> 2Fe(l)+3CO2(g).


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10-B Ahan M R

Step 6-The excess limestone from thesecond reaction reacts with the sand(coming from minerals in iron ore) and

forms calcium silicate (slag) -CaO(s)+SiO(s) --> CaSiO3(l).

Step 7-Slag and molten iron are drained

from the bottom of the furnace and gasproduced exits through holes in the top ofthe furnace


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Why does Iron have to be extracted in

a Blast Furnace???

Iron has to be extracted by the blastfurnace because it contains mud ,clay

,minerals , mixture of other metals andsome unwanted materials.

In the furnace ,the iron is be displaced by

carbon.This is more efficient method thanelectrolysis because it is more cost

effective


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The Method


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Three substances are needed to enable to extraction of iron from its ore.

The combined mixture is called the charge:

Iron ore, haematite- often contains sand with iron oxide, Fe2O3.

Limestone(calcium carbonate).

Coke- mainly carbon

The charge is placed a giant chimney called ablast furnace. The blast

furnace is around 30 metres high and lined with fireproof bricks. Hot air is

blasted through the bottom.

Several reactions take place before the ironis finally produced...


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Oxygen in the air reacts with coke to give carbon dioxide:

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

The limestone breaks down to form carbon dioxide:

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)

Casting Quality


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There are numerous opportunities for thingsto go wrong in a casting operation, resulting in

quality defects in the product

The defects can be classified as follows: Defects common to all casting processes

Defects related to sand casting process

Misrunh h l d f d b f l l


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A casting that has solidified before completely

filling mold cavity

Figure 11.22 - Some common defects in castings: (a) misrun


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Cold Shotl l d i i d lid l b l


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Metal splatters during pouring and solid globules

form and become entrapped in casting

Figure 11.22 - Some common defects in castings: (c) cold shot

Shrinkage CavityD i i f i t l id d b


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Depression in surface or internal void caused bysolidification shrinkage that restricts amount ofmolten metal available in last region to freeze

Figure 11.22 - Some common defects in castings: (d) shrinkage cavity

Sand BlowB ll h d i d b l f


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Balloon-shaped gas cavity caused by release of

mold gases during pouring

Figure 11.23 - Common defects in sand castings: (a) sand blow

Pin HolesF ti f ll iti t


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Formation of many small gas cavities at or

slightly below surface of casting

Figure 11.23 - Common defects in sand castings: (b) pin holes


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Mold Shift


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A step in cast product at parting line caused by

sidewise relative displacement of cope and drag

manufacturing tech i unit 1

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