foundry note

7/30/2019 Foundry Note

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INTRODUCTIONThere are several manufacturing methods for production of

metallic components these include:-

1. Mechanical Forming: (Solid state deformation methods)

These methods can further be classified into Hot Working

and Cold Working processes.

(a) Hot Working : This is the mechanical shaping of a metal

at a temperature in excess of its recrystallization

temperature. Hot working processes include hot rolling,extrusion, forging, etc

(b) Cold Working: This is the mechanical shaping of a metal

at a temperature below its recrystallisation temperature.

Cold working processes include cold rolling, drawing,

stretch forming, coining and embossing, etc.

2. Welding (Coalescence by localized melting)

Welding is the process of joining together pieces of metal

or metallic parts by bringing them into intimate proximity

and heating the places of contact to a state of fusion or

plasticity. This leads to interpenetration of the atoms of

the metals in weld zone and a strong inseparable joint is

formed after the metals have cooled. The commonly used

welding methods are:

(a) Gas welding (Oxy acetylene)


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(b) Are welding with consumable and non-consumable

electrodes

(c) Thermit welding

(d) Forge welding(e) Resistance welding (spot, seam and butt welding

methods)

(f) Cold welding

3. Machining (Removal of excess metal)

The term machining refers to the forming or generating of

shapes by means of a material removal process. The

range of machining processes includes drilling, milling,

turning, grinding, etc

4. Metallurgy (Sintering of metallic grains)

This is the production of shaped parts by die pressing and

sintering of metal powders. Powder metallurgy is a usefulprocess for the manufacture of parts in metals that

possess very high melting points. It is both difficult and

expensive to melt these metals. Another useful

application of powder metallurgy is in the production of

the so called hard metals. Hard metals are used for the

manufacture of cutting tool tips, precision tools and die

inserts.

5. Casting processes (Involving flowability in the molten

state)


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The main casting methods available are:

(a) Sand casting in which liquid metal is poured into a

shaped cavity moulded in a sand.

(b) Pressure die Casting(c) Centrifugal Casting

(d) Investment Casting (lost wax process)

(e) Gravity Casting

(f) Continuous Casting

Of all these processes, casting accounts for about 80%

of manufactured shapes ...... evaluation. This is so as a

result of the several advantages that it has over the

other manufacturing methods.

1. Very complex shapes can be cast in a single step by

casting. In this many way other finishing operations like

Machining, Welding, etc are minimized ..... eliminated.

2. Hard to machine parts which could have, been difficult

to produce by other means can easily be done by

casting.

3. Weight range: Casting process has no limitation as far

as weight is concerned. Castings ranging from as little

as 0.5g to several tons can be successfully cast. The

engine block which would have been difficult,

uneconomical to make by other methods is done in a

single step by casting .


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4. Casting also offers us the opportunity of improving

mechanical properties (at least in some parts of the

casting) by altering the structure of the metal.

5. It is less capital intensive.6. Adapts easily to mass production

Other processes are required before a metallic

component can be cast shape, and these processes are

integrated together to form the operation of a typical foundry.

Foundry processes include making of moulds, preparation and

melting of metals, pouring the molten metal into the mould

cast extraction and cleaning of casting etc.

Disadvantages:

1. The pattern is destroyed in the process.

2. The patterns are more delicate to handle.

3. It offers little opportunity to inspect the mould cavity

for possible corrections.

4. The process cant be used with mechanical moulding

equipment.

General Properties of Pattern Materials

The pattern determines to a large extent the degree of

smoothness and soundness of casting obtained and that is

the reason why some special consideration must be taken in

the selection of pattern materials. These include:


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1. A good pattern material should be resistant to sand

abrasion. During moulding, the pattern comes into

contact with the sharp silica sand grains and there is the

tendency of the pattern to wear during ramming.Therefore, patterns should be able to resist wear during

ramming so as to retain their features. Patterns made of

materials like brass, cast iron and steel exhibit this

properly.

2. A good pattern material should be resistant to the

influence of moisture. Wooden patterns tend to warp

when they come into prolonged contact with moisture

from the environment and also from the silica sand. Also

pattern materials like iron steel chemically react with

oxygen contained in the water of the green sand mould

and corrode. Therefore, a pattern must have high

resistance to moisture if it has to be used repeatedly.

Brass patterns tend to exhibit good behaviour when in

contact with green sand mould.

3. A good pattern materials must be available at a

reasonable cost. Worn out patterns which are very

expensive would need extensive patching and machining

before it can be used again.

4. A good pattern material must have the ability to take a

good surface finish.

5. It must lend itself to easy working, shaping and joining.


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6. It must be light in weight to facilitate handling and

working.

7. It must be strong, hard and durable.

Choice of Removable Pattern materialsThe characteristic properties of some removable patterns

influence to a large extent their selection for use in the

moulding operation. Some of these characteristics are here

under enumerated according to their merits and de-merits.

1.WOOD

Advantages

(a) It is cheap and easily worked.

(b) It is light in weight.

(c) Hardwood, like mahogany is durable and can be

used repeatedly.

Disadvantages

(a) Its resistance to moisture is poor (it tends to warp).

(b) Its wear resistance is also poor.

2. Cast Iron

Advantages(a) It is resistant to abrasion.

(b) It is cheap.

(c) It gives good surface finish.

Disadvantages

(a) Cast iron patterns are heavy and fracture easily

because of its brittle nature.


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3. Brass

Advantages

(a) It is resistant to the abrasive action of sand.

(b) It is resistant to the influence of moisture. It doesnot rust.

(c) It gives very good surface finish, even better than

that of cast iron.

(d) It is easily repaired.

Disadvantages

(a) Brass patterns are very heavy.

(b) They are expensive.

Aluminium

Advantages

(a) It is light in weight.

(b) Resists the influence of moisture.

(c) Resists sand abrasion.

(d) It is easy to cast.

(e) It is easy to machine to shape.

Disadvantages

(a) They dent easily.

(b) They are expensive.

Types of Pattern

There are three major types of pattern

(1) Loose patterns

(2) Match plates


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(3) Cope and drag patterns

The materials from which the pattern is formed does not in

any way determine the pattern type. The type is determined

by the physical appearance of the pattern.Loose patterns

Loose patterns can be

(a) Solid (one piece) pattern

(b) Split pattern

(c) Gated pattern

Solid pattern

These patterns usually have one flat surface and relatively

simple features appearing on the other side. The flat surface

coincides with the parting plane of the mould.

Solid patterns can be divided into.

(a) Regular parting solid pattern

(b) Irregular parting solid pattern

The regular parting solid pattern has one flat surface which

coincides with the parting plane of the mould.

Bottom board

Pattern

PL (Parting Line)

Regular parting solid

pattern pattern


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Irregular Parting Solid Pattern The irregular parting solid

pattern differs from the regular parting solid pattern in the

sense that the parting line is shifted from the standard positionto a hand-formed position. This is done to facilitate removal of

the pattern without destroying the mould.

The irregular parting solid appears to be the forerunner to the

split pattern. By introducing hand made PL we have been able

to do what would have been done easily using a split pattern.

Advantages of Irregular Parting Solid

(1) It provides an opportunity to cast objects that would have

been impossible by using solid pattern.

2. It is cheaper and easier to construct a solid pattern

than a split pattern

Disadvantages

(1) . It requires great skill to construct the parting line.

Match Plates

A match plate is a flat plate placed between the cope and the

drag to which patterns are securely mounted.

Crop

Head mace

parting line

Drop

Pattern

Bottom

Board


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Cope & Drag Patterns

One pattern plate has the drag pattern on it and the other the

cope pattern. Cope and drag patterns overcomes the weight

problem associated with match plates, and it also increase

productivity as it allow two different operators to work

simultaneously one in the cope part and the other in the drag

part.

Split patterns

These are used to cast complex shapes which do not have a

flat surface. The pattern is made to part or split along a plane

which coincides with the parting plane of the mould. In this

way, a part is made in the cope and the other in the drag.

Gated Patterns

Can be a solid pattern or split pattern to which gate have

been added. The addition of the gate eliminates the handcutting of the gating system.

Advantages

(1) Eliminates likely errors during hand cutting of gates


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(2) Reduces the skill required of the moulder.

(3). Rapid moulding.

Pattern Allowance

Pattern allowance is a vital feature in pattern design as it

affects the dimensional accuracy of the casting. Thus, when a

wooden pattern is produced, certain allowances must be given

on the sizes specified in the finished component drawing so

that the casting with the desired specifications can be

produced.The allowances usually considered in parting are :

(i) Shrinkage allowance

(ii) Draft or taper allowance

(iii) Machining allowance

Shrinkage Allowance

This allowance requires that the pattern be made slightly

larger than the would be casting to compensate for shrinkage

as the metal solidifies and cools. Total contraction is actually

volumetric but the correction for it is expressed linearly.

Shrinkage allowance depends on the type of metal to be cast.

The following allowances are commonly used.

Ferrous cast iron 0.8-1%

Steel 1.5-2%


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Non-ferrous Aluminium 10.-1.3%

Magnesium 1.0-1.3%

Brass 1.5%

These allowances are incorporated into the pattern by usingspecial shrink rules which are larger than a standard rule by

the desired shrinkage allowances.

Sometimes double shrinkage allowances are provided in the

wooden pattern if it is to be used to cast metal pattern which

in turn would be used to cast other castings. Thus, the total

shrinkage allowance on a wooden pattern to be used to cast

an aluminium pattern which in turn would be sued to cast iron

casting is 2.3%.

Wooden pattern Aluminium Pattern cast

iron castings

2.3% 1.3% + 1%

Draft (Taper) AllowanceDraft is the angular difference between the sides of the

pattern and an imaginary straight line to the parting line. It is

usually expressed in degrees.

Draft PL

PL


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Functions of DraftDraft allows the pattern to be drawn from the moulding

medium easily, without rupturing it. The main features that

determine the mount of draft are.

(i) Depth of the draw face

(ii) Type of moulding medium (type of foundry sand used)

(iii) Texture of the pattern material

(iv) Complexity of design

Draft may be external or internalExternal Draft-Draft provided on the external of a pattern, it

may be two-sided or one-sided.

Two sided

It is always desirable to reduce the amount of draft as this

means extra metal and extra clean-up to be done.

Interior draft -this is used when the draw face is in the interior

of the pattern when the interior area of the hole is large

enough for the sand to support itself.

One sided


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Allowance for Machining: This is an extra allowanceprovided on surfaces to be machined.

Pattern colours:Colour makings have been recommended for wooden patternsas an aid for the best use in the foundry. These are as follow:(1) Black : Black shows the body of a casting which remain in

this condition resulting from the cleaning operations

(surfaces needing no further work apart from the cleaning

operations)

(ii) Red: Surfaces to be machined

(iii) Yellow: This shows the pattern of core prints and seals for

loose core prints.

(iv) Red strips: Red strips marked on a yellow background

show core seats and loose pieces from the pattern.

Internal DraftFig


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CHAPTER 2

PROPERTIES OF SILICA SAND

A major factor in the production of casting (sand casting) is the

use of sand mould and the amount of sand used is usually

large and must be controlled to make good casting. Actually

the sand mould is the tool which forms the casting. Therefore

a great deal of attention must be paid to the detailed sand

operations of preparing of preparing, controlling, handling and

using of the moulding sand. From the general point of view thesand must be readily mouldable and capable of producing

defects free castings.

If silica sand mould is of quality as a good one it must have the

following properties

(i) Ample strength (Green strength, Dry strength and Hot

strength).(ii) Good gas permeability

(iii) Flowability (plasticity)

(iv) Refractoriness

(v) Collapsibility

Strength

Green Strength: A green sand is that sand for which water is

added and mixed for develop strength. Green strength is

needed of a green sand to enable it withstand handling during

the making of the mould.


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Dry Strength: As molten metal is poured into the mould

cavity the sand layer adjacent to the molten metal quickly

dries up loosing is water. The dry sand must possess dry

strength to enable it withstand mould erosion and

metallostatic pressure of the molten metal. Other wise the

mould would enlarge.

Hot Strength: After the sand has lost most of its water and is

now dry, it is still in contact with the dry hot molten metal and

is required to possess hot strength at elevated temperature(above 100oc). If the sand does not develop hot strength, the

molten metal may cause enlargement of the mould, or while

still flowing may cause erosion.

Gas permeability: Molten metal always contain some

dissolved gas which are upon solidification and cooling. As

heat from the casting causes the moulding sand to evolve a

great deal of gases (green sand). If these evolved gases do not

have the opportunity to escape through the mould they

remain trapped in the molten metal causing gas defects (pin

holes, blowholes, etc.)

Flowability: Flowability is also referred to as plasticity. High

plasticity is required of a moulding sand to obtain a good

impression of the pattern in the mould. Flowability of a

moulding sand refer to its ability to acquire a predetermined


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shape under pressure and to retain this shape when the

pressure is removed.

Collapsibility: Some degree of collapsibility is required of a

good moulding sand. That is its ability to decrease in

volume to an extent under the compressive forces

exerted by the solidifying and cooling metal. Poor

collapsibility may lead to cracking of the casting

Effects of Clay and Other Binders to Moulding Sand

When greater mechanical properties are required of a

moulding sand, binding agents are usually added. Sometimes

the binder is provided by nature with sand. A binder is any

material that imparts cohesiveness to the sand grains. In this

way much properties are improved.

Binders can be classified into 3 broad groups: (i) Organic and

(ii) inorganic binders (iii) clay-type binders.

1. Clay-type binders

Clays originate in three ways: (i) some are formed by the

decomposition of rocks and are called residual clays.

(ii) Others are formed by the alteration of rock of igneous

origin by underground waters.

(iii) Others are deposited as sediments and are called

sedimentary clays


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The commonly used clay binders are fireclays (kaolinite),

bentonites, illites montmorillonite, etc.

2. Organic Binders

Organ binders are those binding agents that contain carbon as

the major constituent element. The commonly used organic

binders are:

(1) Cereal binders

(2) Resins and Gums

(3) Proteins

(4) Pitch

(5) Drying oils

Cereal binders: These are derived from the common cereal,

e.g corn. They are frequently produced as flourlike dry

materials and occasionally as fluid materials such as molasses.

Many of the cereal binders are susceptible to souring in use

and may develop odours. They have been used in foundries for

thousands of years to give green strength to cores in the

green state .Cereal binders are also used in moulding sands,

iron and steel foundries to give a rubbery state to the foundry

sand to enable the molten metal move over the sand and not

burn in or penetrate the mould itself. Most cereal binders burn


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out at approximately 400oC, but then they would have fulfilled

their functions.

Resins and Gums:Natural resins are called gums while synthetic resins are

simply called resins. Gums are not usually used as primary

binders while synthetic resins are used as primary binders.

Thermoset Binders:

When phenolic resin comes in contact with heat for the first

time, they go through 3 stages.

First the resin melts into a liquid, then it changes into a

rubbery state and finally, the rubbery solid changes into a hard

strong almost insoluble material. This procedure is often

referred to as the shell process and is commonly used in the

foundry.

Shell Process:

A heated match plate (metal pattern) is damped to a dump

box containing a mixture of foundry sand and phenolic resin.

The box is inverted and the mixture is dumped on the match

plate. The phenolic resin now goes through the three stages

earlier mentioned. Thereafter the dump box is returned to its

original position and is further treated by baking it in an oven

to produce the shell of the pattern.


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Euran Binders

________________________________

3. Inorganic Binders

(i) Cement bonded mould

(ii) The CO2 process

Special sands

Silica sand has found extensive application in the foundry

industry because it is readily available and inexpensive.

- - - --- - --

- - -

- - - - -- - - - -

- -


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However the so-called specially sands are also used commonly

for certain reasons:

(i) Better stability at elevated temperatures hence better

cast surfaces are obtained.(ii) Strength

Commonly used special sands are olivine,zirconite and

chromite.

Because they are expensive they are commonly used as facing

sand, and sometimes as total mould.

Silica sand is much less expensive than specially sands. In

fact, olivine is about 10 times the cost of silica sand, while

chromite and zirconite cost twice as much as olivine.

Additives to Moulding Sand

Sand additives are those materials added to sand which do not

act as binders but impact certain important properties.

The commonly used additives are

(i) pulverised coal (ii) graphite (iii) peat (iv) wood flow and

other organic matter.

Upon contact with the molten metal these additives burn and

form gases which do not allow intimate contact between the

metal and the mould. This gas jacket do not only prevent

intimate contact between the mould materials and the metal


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but also makes the mould more collapsible as the metal

shrinks.

Pulverised coal, graphite and charcoal are used as additives to

prevent burn-on and metal penetration. They are finely grindand applied in the mould surface in the form of dust coating

(blacking).

Peat and wood flow are added to mould and to improve their

plasticity and collapsibility.

Dry sand moulds are coated with whitening which has high

refractoriness. Whitening eliminates the possibility of burn- on

and enables castings with smooth surfaces to be obtained.

Whitening for grey cast iron consists chiefly of graphite, while

silica flow is used for steel castings.


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CHAPTER 3

MOULDING PROCESSES

Moulding machines or hands are used for the production of moulds. The hand

moulding is used for small work while the machine moulding is preferred formass production work.

Moulding Procedures: The most extensively used types of hand

moulding procedures are:

(1) Floor moulding flasks

(2) Pit moulding

(3) Sweep moulding

Pit moulding

In pit moulding, all the work in making the mould is done on

the foundry floor pit moulds may be either open or covered.

In open pit moulding, the upper part of the mould in pit is

open, in the covered pit moulding the top is finished off withcores or with sand rammed in a open flask.


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Pit moulding requires that the earth floor at the moulding site behorizontal and sufficiently permeable to gases. Therefore, theplace must be properly prepared before hand. This is called bedmaking the mould.

Preparation of the mould bed.This involves covering the rammed bottom of the pit with a 50

to 80mm layer of coke to improve the gas permeability of the

mould. This is particularly done for large castings. A bed of

sand is sufficient for smaller castings.

Vent pipes are then run from the coke layer to the surface (at

the dives) and the coke is covered with backing metal.

Open pit moulding

This method is used to cast simple shapes in which the upper

surface is flat (plates, grald, bars, pards, etc

Pattern 1 is placed face downwards on the sand bed and then

sunk gently into the bed with the help of gently hammer blows


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administered through a board placed on the pattern. The

horizontal position of the pattern is checked using the spirit

level (4). Next the pattern is covered at the sides with facing

sand and then consolidated and then backing sand is added.After this the pattern is checked again with the spirit level, and

then excess sand is removed. The sand around the pattern is

smoothed with trowel and vent holes (3) are provided.

Runners 6 and 7 are cut- to admit and drain excess metal.

After all the preceding operations, the pattern is withdrawn

with the help of the draw spike. The impression of the pattern,

i.e. the mould cavity, remains in the sand. Parts of the sand

mould damaged during pattern withdrawal are repaired and

smoothed down. The mould surfaces are then coated with

graphite dust and the molten metal poured in. Immediately

after pouring the surface of the molten metal is covered with

charcoal and a layer of dry sand to ensure uniform cooling of

the casting and to prevent oxidation of the metal.

Covered Pit moulding:

In covered pit moulding, parts of intricate shapes are made. An

example of covered pit moulding is illustrated in the fig. below.

Here the lower part of the pattern is placed in a previously

prepared pit and bedded into it to a certain depth. Next, all the

processes listed in the preparation of the open pit moulding

are followed and then the upper part (cope part) of the pattern


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is aligned with the drag part and the cope placed over it.

Pattern for runners and risers are located and the cope part is

filled and rammed. Next, the cope is separated from the drag

followed by withdrawal of pattern and subsequent assemblage(including the core made separately).

The mould is then ready for pouring.

Pit moulding is practiced in place or job production

Flask moulding:

This is the most widely employed process both in hand and

machine moulding procedures. Various flask moulding

procedures are employed depending on the shape size and

complexity of the casting be made. These are:


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(1) Two- part moulding with an unsplit pattern

(2) Two-part moulding with a split pattern

(3) Multiple part moulding

(4) Moulding with pattern having loose pieces(5) Stack moulding

(6) Snap or removable flask moulding etc.

Two-part moulding with unsplit and split patterns-refer to my

handout (national diploma)

Multiple part moulding

The shape of a casting may be so complex. It mould be

difficult to make it using two flasks. In such cases three or

more flasks may be required (each flask housing a part of the

casting). Where three flasks are used, the middle part is called

the check.

Stack moulding:

Stack moulding is used to make small light casting. One

advantage of this process is that it requires much loss floor

space in the foundry.

Two types of stack moulding procedures are employed in the

foundry

(i) The upright and

(ii) The stepped procedures


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In upright stack moulding from 10 to 12 flask sections are

arranged one above another; having a common down sprue

through which all of them are fed with molten metal.

In stepped stacking, the flask sections are arranged in steps

with each flask section having is own sprue. Each successive

mould is offset from the other by the width of the pouring

basin. Thus each mould is poured separately.


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Snap flask moulding

Snap flask moulding utilizes matched plates. The match plates

are designed to have an offset parting plane to avoid shifting

of the cope and drag and to prevent molten metal frombreaking out through the parting plane during pouring.

In this procedure the drag (2) is placed on the metal match

plate (4) which is placed on an overturned cope and filled with

sand and rammed in the usual manner.

A bottom board (3) is then placed on the drag and the whole

mould is then turned over and then the cope is filled and

rammed as usual. Then the cope is lifted off and the match

plate pattern. Both cope and drag moulds are repaired and

then assembled. After this the cope and drag sections of the

flask are removed simultaneously from the mould. This of

course presents no difficulty because of the tapered nature ofthe flask. The mould is then taken to the pouring section,

where a steel jacket is worn over to provide rigidity.

Snap flask mould is extensively used for producing small

casting on a large scale. Knock-out is much easier in this

method and significant economy is attained in the cost of

flasks. Moulding sand consumption, however, is somewhat

higher.

Sweep moulding:


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This procedure is resorted to when the part to be cast is of

large size and the casting has to be done in a short time. In-

other words, the cast of pattern and the time required to make

it has been greatly reduced. Sweep moulding excludes the useof expensive pattern, and therefore reduces cost about 11/2

times.

Sweep moulding may be performed by 2 methods.

(1) By using a turning sweep (template) rotating either about

a vertical or horizontal axis to form surfaces of revolution(in moulding cylinders, bowls, etc).

(2) By using a drawing sweep pushed along a guide frame.

Moulding Machines

The commonly used ones are

(i) Jolting machine(ii) Squeezers

(iii)Jolt squeeze

(iv) Sand slingers

These machine not only ran and consolidate the sand they

also draw the pattern from the mould.

The use of moulding machines enables labour productivity

to be sharply increased, more accurate castings to be


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produced, costs to be reduced and a higher quality of

products to be maintained.

Moulding machines pack the sand and draw the patternfrom the mould. According to the method by which sand

compaction is achieved moulding machines are classified as

above.

Squeeze Moulding Machines

These are operated by compressed air at a pressure from 5

to 7 atmospheres.

A schematic diagram of a top squeeze machine is shown in

figure below.

Fig. 3. Top Squeeze Machine

The pattern plate with pattern is clamped on work table and

flask is placed on the plate. The sand frame is placed on the


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flask and the machine. Next the table lift mechanism is

switched on and the flask together with the sand frame and

pattern is lifted up against platen of the stationery squeeze

head, the platen enters the sand frame and compacts thesand down to the upper edge of the flask (shown by dash

line). After the squeeze, the work table returns to the

original position.

The principle of a bottom squeeze machine is shown in fig.4.

The pattern plate 2 with the pattern is clamped on work

table 1. Flask 3 is placed on frame 4 of the machine and is

filled with sand from a hopper. Next, the squeeze head 5

is brought against the top of the flask and the lift

mechanism is switched on. Table 1 and 2 and the pattern

are pushed up to the lower edge of the flask (shown by

the dash line). After this the table returns to the initial

position.

In squeeze moulding machines, maximum hardness is

achieved in areas around the squeeze head.


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Fig.4 Bottom squeeze machine

Jolt Moulding Machines

The schematic diagram in fig. 5 illustrates the principle ofa plain schockless jolt moulding machine.

In the operation of the jolt moulding machine, table 1with

pattern plate and pattern 2and 3, filled with moulding

sand lifted by plunge 4 to a definite height when

compressed air is admitted through hose 5 and channel 6.

Next, the table drops since compressed air is released

through hole 7.

While falling, the table strikes the stationary cylinder guide

8 and this impact packs the sand around the pattern in

the moulding flask. Spring 9 by cushioning the table

blows, reduce noise and prevent damage to the

mechanism and foundation.

In jolting, maximum mould hardness is achieved towards

the bottom, against the pattern surfaces.


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Fig 5 Jolt Moulding Machine

Jolt-Squeeze Machines

These machines utilise the advantages of the jolt and

squeeze moulding techniques.

The Sand Slinger

The sand slinger impels moulding sand into the flask with

sufficient force to pack it around the pattern to the

desired hardness.

The essential element of the sand slinger head shown in

fig.6.

The slinger head consists of housing 1, which is blade

2 rotates rapidly. Moulding sand is fed by a belt conveyor

through opening 3 into the head where it is picked up by

the rapidly rotating blade 2and thrown in separate

portions at a very high speed through outlet 4 into the

flask beneath.

Core-Making

Through holes,


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Coros are made manually or with machine. Coro makingconsists of the following sequence of operation of

_________________ holding, ______ and cracking if a coro is made

of two of several

Reinforcement of coro

Vonting of coro

Provision of vent holes, to improved gas permeability vent

holes may be made by plorcing the cores with stiff winewere possible. Other methods are the ins----- of wax gardaduring core making (for slender cores) and the cutting ofgates and griming them after (heavy cores).

Coro Making machines(i) dieoxtrusion(ii) Squeeze and jott machines(iii) Sand slinger

(iv) Coro bloworn, etc


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CHAPTER 4

MOLTING INMETALLUGICAL FURANCES

Operation of the Cupola furnace.

The operation of the cupola involves several steps .first rags,

wood, coal, coke and other combustible materials are placed

on the sand floor and lit then an initai charge of coke is placed

top of the fuel .


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When the initial charge of hot alternating layers of metal, coke

The cupola furnace is widely used because of its simplicity.

However, there are so many difficulties connected with itsoperation. The chemical action within the furnace is very

difficult to control. A proper balance must be maintained

between metal, coko and limestone if the ouput is to have the

desired chemical and physical properties.

Electric furnace

Electric melting is one of the major methods of melting in iron

and steel foundrie. Electric furnace have proved a big asset in

the production of high quality metal as they attain high

melting efficiency with minimum loss.

Unlike cupola furnace Electric furnace posses greater

adaptability and flexibility and provide precise control over the

temperature ofter molten metal. The high cost of the electric

power is a limitation but this is outweighed by several

overwhelming advantages its types had been mentioned

above.

Direct are furnace

This furnace works on the principle that heal is produced when

resistance is offered to the flow of electricity. In the case, it is

the metal in the charge that provides the resistance of the


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flow of current. When the metal is molten. The slag offers

resistance to the flow of current. Thus to maintain proper

heating even when the metal is molten, the electrode must be

raised so that they just fou- the slag layer .

A typical direct are furnace is shown below with a refractory

lined steel shell, it has roof which can be rotate to open the

furnace for loading. Three adjustable carbon electrodes

extend through the roof.

The operation of eh furnace includes

Raising the electrodes

Rotating the roof to the open position

Loading the furnace(could be molten pig iron and steel

scrap or only steel scrap)

Rotating the roof to the closed position.

Lowering the electrodes to their arcing position

Turning on the power

Arcing between the electrodes and the charge creates theheat necessary for melting the metal.

Indirect are furnace


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The indirect are furnace may be used to melt all types of

metals, but it is specially designed for non-ferrous metals.

The furnace is made up of a barnel shaped drum, mountedhorizontally and so goarod that it can be rotated back and forth

through an angle of 180% the shall is lined with insulating and

refractory material.

Two electrodes are used, each are entering the furnace from

either end and coinciding with the horizontal axis of the

cylinders. As the electrodes are brought near each other, an are

is struck between the two ends and tremendous heat is

generated. The heat of the are is radiated and reflected in all

directions. Thus a part of the heat is directly absorbed by the

metal and the remainder byteh lining. As the shall rotates and

forth, metal flows over the heated surface and absorbs the heat

energy from the walls by conduction.

Induction furnaces

Melting of metal in an electric induction furnace differs from

that in the are furnace in that instead of the bulk of the heat


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being generated in an are and radiated to the charge, all the

heat is generated in the charge itself.

Two basic types of induction furnaces are in use. They are highfrequency crucible type and the low frequency core or channel

type. Both types operate by inducing current into the metal

charge.

Basic advantages of induction furnace over the are furnace are

There is precise control over temperature

Good quality of metal

It adapts easily to vacuuming

High frequency crucible induction furnace

Crucible type has a coil of copper tubing wrapped around it.

This coil carries a high frequency (up to 30.000 HZ) alternating

current. As the alternating current is applied to the an

alternating magnetic field is induced around the coil. This

magnetic field in turn success a high alternating current in the

charge.

The low frequency (channel of core) furnace


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The low frequency crucible works on the principle of the step

down transformer but the number of turns in the primary coil is

always greater than that the secondary. That of the secondary

is always a loop. The current come into channel through theprimary coil and the coil step down the vollage as it passes into

the secondary coil.


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foundry note

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