1 introduction of casting

By
CH.PAVAN KUMAR
Assistant Professor
Mechanical Engineering Department
pavanME304@gmail.com
Introdcution to Casting
1

Manufacturing is the backbone of any industrialized nation.
Manufacturing and technical staff in industry must know the following;
Manufacturing processes
Materials being processed
Tools and equipments for manufacturing different components
Products with optimal process plan using proper precautions
Specified safety rules to avoid accidents
Introduction to Manufacturing Technology
3

Production or manufacturing can be simply defined as value addition
processes by which raw materials are converted into valued products.
Manufacturing Processes
4 Source for Fig 1.1 NPTL Manufacturing

This refers to science and technology of manufacturing products
effectively, efficiently, economically and environment-friendly through
Application of any existing manufacturing process and system
Proper selection of input materials, tools, machines and environments
Improvement of the existing materials and processes
Development of new materials, systems, processes and techniques
All such manufacturing processes, systems, techniques have to be
Technologically acceptable
Technically feasible
Economically viable
Eco-friendly
5

Broad classification of Manufacturing Processes
(a) Shaping or forming Manufacturing a solid product of definite
size and shape from a given material taken in three possible states:
• in solid state – e.g., forging rolling, extrusion, drawing etc.
• in liquid or semi-liquid state – e.g., casting, injection moulding etc.
• in powder form – e.g., powder metallurgical process.
(b) Joining process
Welding, brazing, soldering etc.
(c) Removal process
Machining (Traditional or Non-traditional), Grinding etc.
(d) Regenerative manufacturing Production of solid products in
layer by layer from raw materials in different form:
• liquid – e.g., stereo lithography
• powder – e.g., selective sintering
• sheet – e.g., LOM (laminated object manufacturing)
• wire – e.g., FDM. (Fused Deposition Modelling)6

Casting
It is a earliest metal shaping technique known to human being since 3500BC.
Simple and complicated shapes can be made from any metal that can be melted.
Example of cast parts: frames, structural parts, machine components, engine
blocks, valves, pipes, statues, ornamental artifacts.
Casting sizes range form few mm (teeth of a zipper) to 10 m (propellers of
ocean liners).
Casting processes basically involve the introduction of a
molten metal into refractory mold cavity, where upon
solidification, the metal takes on the shape of the mold cavity.
Refractory mold  pour liquid metal  solidify, remove  finish7

1. Pour the molten metal into sand mold
2. Allow time for metal to solidify
3. Break up the mold to remove casting
4. Clean and inspect casting
Separate gating and riser system
5. Heat treatment of casting is sometimes required to improve
metallurgical properties
Steps in Sand Casting
8

Classification of casting processes
9

Advantages
It is possible to cast any material be it ferrous or non-ferrous.
Tools required for casting moulds are very simple and inexpensive.
It is an ideal method for trail production or production of small lots.
Good directional properties.
Casting of any size and weight, even up to 200 tonnes can be made.
Limitations
Dimensional accuracy and surface finish achieved is some what less.
Traditional casting methods are labour intensive.
Difficult to remove the defects in some materials due to moisture in sand.
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Applications
Cylinder blocks
Liners
Machine tool beds
Pistons
Piston rings
Mill rolls
Wheels
Housings
Water supply pipes
Bells etc.,
air compressor frame
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Casting Terms
1. Flask (Cope & Drag)
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2. Pattern
It is a replica of the object to be made.
Mould cavity is made with the help of pattern
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3. Parting Line
It is a dividing line between cope, drag and also for split pattern.
4. Bottom Board
It is made of wood, the pattern is first kept on the bottom board
5. Facing Sand
Carbonaceous material is sprinkled on the inner surface of the
moulding cavity to give better castings
7. Moulding Sand
Mixture of silica sand with 18 to 30 percent clay, having moisture content
from 6 to 8%. It is used to make mould cavity.
8. Pouring Basin
It is a funnel shaped cavity at the top of the mould into which molten
material is poured.
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Steps involved in making a sand mould
1.Initially a suitable size of moulding box for suitable wall thickness is selected
for a two piece pattern.
2.Next, place the drag portion of the pattern with the parting surface down on
the bottom (ram-up) board as shown below;
3.The facing sand is then sprinkled carefully all around the pattern so that the
pattern does not stick with moulding sand during withdrawn of the pattern.
4.The drag is then filled with loose prepared moulding sand and ramming of
the moulding sand is done uniformly in the moulding box around the pattern.
Fill the moulding sand once again and then perform ramming. Repeat the
process three four times,
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5.The excess amount of sand is then removed using strike off bar to bring
moulding sand at the same level of the moulding flask height to completes the
drag.
6.The drag is then rolled over and the parting sand is sprinkled over on the top
of the drag
7.Now the cope pattern is placed on the drag pattern and alignment is done
using dowel pins.
8.Then cope (flask) is placed over the rammed drag and the parting sand is
sprinkled all around the cope pattern.
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13.Rap and remove both the cope and drag patterns and repair the mould
suitably if needed and dressing is applied
14.The gate is then cut connecting the lower base of sprue basin with runner
and then the mould cavity.
15.Apply mould coating with a swab and bake the mould in case of a dry sand
mould.
16.Set the cores in the mould, if needed and close the mould by inverting cope
over drag.
17. The cope is then clamped with drag and the mould is ready for pouring
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Patterns
Pattern is the replica of the casting and it is embedded in moulding sand. The
pattern is then withdrawn for generating cavity (known as mould) in moulding sand,
so it is a mould forming tool.
Objectives of a pattern
1.Pattern prepares a mould cavity for the purpose of making a casting.
2.Pattern possesses core prints which produces seats in form of extra recess for
core placement in the mould.
3.It establishes the parting line and parting surfaces in the mould.
4.Runner, gates and riser may form a part of the pattern.
5.Properly constructed patterns minimize overall cost of the casting.
6.Properly made pattern having finished and smooth surface reduce casting
defects.
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Types of Patterns
1. Single-piece or solid pattern
Solid pattern is made of single piece without
joints, partings lines or loose pieces. It is the
simplest form of the pattern.
2. Two-piece or split pattern
•When solid pattern is difficult for withdrawal from the mold cavity, then
solid pattern is splited in two parts.
• Split pattern is made in two pieces which are joined at the parting line by means
of dowel pins.
21• The splitting at the parting line is done to facilitate the withdrawal of the pattern.

Types of Patterns
3. Gated pattern
•In the mass production of casings,
multi cavity moulds are used.
•Such moulds are formed by
joining a number of patterns and gates and providing a common runner for the
molten metal.
•These patterns are made of metals, and metallic pieces to form gates and runners
are attached to the pattern.
4. Cope and drag pattern
•Cope and drag part of the mould are prepared separately.
•This is done when the complete mould is too heavy to be handled by one operator.
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•The pattern is made up of two halves, which are mounted on different plates.

Types of Patterns
5. Match plate pattern
Cope and drag patterns along with
Gating , risering are mounted on a single
matching plate on either side.
After removing match plate mould cavity along with gating will be formed.
Several patterns can be fixed to a single match plate if they are small in size.
Used for small castings with higher dimensional accuracy and & large production.
This pattern is used in machine molding.
6. Loose-piece Pattern
It is used when pattern is difficult for withdrawl from the mould.
Loose pieces are provided on the pattern and they are the part of pattern.
23First main pattern is removed finally the loose piece is withdrawal separately

Types of Patterns
7. Follow board pattern
Used for castings which are structurally
Weak.
Bottom board is modified as follow board
to follow the contour of weak pattern and give support during ramming
8. Sweep Pattern
Used for forming large circular moulds of
symmetric kind by revolving a sweep attached
to a spindle.
Sweep is a template of wood or metal and
is attached to the spindle at one edge and
the other edge has a contour depending upon the desired shape of the mould.
24The pivot end is attached to a stake of metal in the center of the mould.

Types of Patterns
9. Skeleton pattern
Used for large castings having simple geometric shape.
These are simple wooden frames that outline the shape of the part to be cast.
Used in Pit or floor moulding process.
For round shape pattern is made into two halves.
Used for casting water pipe turbine castings etc.
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Pattern Materials
Wood, Metal, Plastic, Plaster, Wax, Etc…
Wood is most commonly used because of easily available, machinability and low
Weight.
Metal patterns are used for large scale casting productions, close tolerances,
Smooth, Surface finish. Aluminium and white metals are commonly used.
Plastics are used because of their low weight, easier formability, smooth surface.
Choice of pattern material depends on Size, No of Castings, Dimensional accuracy,
Expected life.
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Pattern Allowances



1. Shrinkage allowances
 Metal Shrinks on solidification and contracts further cooling at room temperature.
 Liquid Shrinkage refers to reduction in volume when metal changes from liquid to
solid state. Risers are used to compensate this.
Solid Shrinkage refers to reduction in volume when metal loses temperature in
solid state. Shrinkage allowance is used to overcome this.
Rate of contraction with temperature is dependent on the material.
Shrink rulers are used for different castings.
Final dimensions of casting are different from pattern because of various reasons
Cast Iron, Malleable iron 10mm/m
Brass, Cu, Al 13mm/m
Steel 21.0mm/m
Zinc, lead 25mm/m27

Pattern Allowances
2. Draft allowances
 continual contact with the sand and may damageVertical faces of pattern are
during withdrawal.


It is a positive allowance and is given on all the vertical surfaces of pattern so
that its withdrawal becomes easier.
Inner details of the pattern require higher draft than outer surfaces.
 More draft is needed for hand moulding
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Pattern Allowances
3. Machining allowance
 To get better surface finish for casting
 Depends on type of metal and finish
4. Shake allowance
 Pattern is rapped all around the faces to remove and it enlarges the final casting.
 So original dimensions should be reduced to overcome this.
 Purely depends on skill of labour
 It is negative allowance and one way to overcome is increase the draft.
5. Distortion allowance
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Moulding Types
Commonly used traditional methods of molding are bench molding, floor
molding, pit molding and machine molding.
1. Bench Molding
This type of molding is preferred for small jobs.
Whole molding operation is carried out on a bench of convenient height.
 In this process, a minimum of two flasks, namely cope and drag molding flasks
are necessary.
But in certain cases, the number of flasks may increase depending upon the
number of parting surfaces required.
2. Floor Molding
This type of molding is preferred for medium and large size jobs.
 In this method, only drag portion of molding flask is used to make the mold
The floor itself is utilized as drag
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It is usually performed with dry sand.

Moulding Types
3. Pit Molding
Usually large castings are made in pits instead of drag flasks because of their
huge size.
In pit molding, the sand under the pattern is rammed by bedding-in process.
The walls and the bottom of the pit are usually reinforced with concrete and a
layer of coke is laid on the bottom of the pit to enable easy escape of gas.
The coke bed is connected to atmosphere through vent pipes which provide an
outlet to the gases.
One box is generally required to complete the mold, runner, sprue, pouring basin
and gates are cut in it.
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Moulding Types
4. Machine Molding
For mass production of the casting
The main advantage of machine molding, besides the saving of labor and
working time, is the accuracy and uniformity of the castings which can otherwise be
only obtained with much time and labor.
Cost of machining on the casting can be reduced drastically because it is
possible to maintain the tolerances within narrow limits.
Molding machines thus prepare the moulds at a faster rate and also eliminate the
need of employing skilled molders.
The main operations performed by molding machines are ramming of the
molding sand, roll over the mold, form gate, rapping the pattern and its withdrawal.
Loam Molding and Carbon-Dioxide Gas Molding
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Moulding Sand
•It is used to prepare mold cavities
•Molding sands may be of two types namely natural or synthetic.
The common sources of molding sands available in India are as follows:
1 Batala sand ( Punjab)
2Ganges sand (Uttar Pradesh)
3 Oyaria sand (Bihar)
4 Damodar and Barakar sands (Bengal- Bihar Border)
5 Londha sand (Bombay)
6 Gigatamannu sand (Andhra Pradesh) and
7 Avadi and Veeriyambakam sand (Madras)
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Constituents of molding sand
Silica sand
It is the main constituent of moulding sand having enough refractoriness which
can impart strength, stability and permeability to moulding and core sand.
Binder
It can be either inorganic or organic substance.
Inorganic group includes Kaolonite, Ball Clay, Fire Clay, Limonite,
Fuller’s earth and Bentonite (mostly used).
Organic group includes dextrin, molasses, cereal binders, linseed oil and
resins like phenol formaldehyde, urea formaldehyde etc.
Moisture
Moisture content in the molding sand varies between 2 to 8 percent.
Amount of water is held rigidly by the clay and is mainly responsible for
Developing the strength in the sand.
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Additives
Generally added to the moulding and core sand mixture to develop some
special property in the sand.
Some commonly used additives;
Coal Dust
Corn flour
Dextrin
Sea coal
Pitch
Wood flour
Silica flour
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Properties of moulding sand
Refractoriness
Permeability
Cohesiveness
Green strength
Dry strength
Flowability or plasticity
Adhesiveness
Collapsibility
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Types of moulding sand
1. Green sand
Silica sand + Clay 18 to 30% + Moisture 6 to 8%
It is fine, soft, light, and porous.
Green sand is damp, when squeezed in the hand and it retains the shape
and the impression to give to it under pressure.
Moulds prepared by this sand are not requiring backing and hence are
known as green sand moulds.
This sand is easily available and it possesses low cost.
 It is commonly employed for production of ferrous and non-ferrous
castings.
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2. Dry sand
Green sand that has been baked in suitable oven after the making mould
and cores
It possesses more strength, rigidity and thermal stability.
It is mainly suitable for larger castings.
3. Facing sand
surface of the moulding cavity to give betterIt is sprinkled on the inner
castings
It is directly next to the surface of the pattern and it comes into contact
molten metal when the mould is poured.
It is made of silica sand and clay, without the use of used sand.
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4. Backing sand
It is used to back up the facing sand and is used to fill the whole volume of
the moulding flask.
Used moulding sand is mainly employed for this purpose.
Black in colour due to addition of coal dust and burning on coming in
contact with the molten metal.
5. Parting sand
This is clean clay-free silica sand which serves the same purpose as
parting dust.
To keep the green sand not to stick to the pattern and also to allow the
sand on the parting surface the cope and drag to separate without clinging.
6. Core sand
Core sand is used for making cores and it is sometimes also known as oil sand
This is highly rich silica sand mixed with oil binders such as core oil which
composed of linseed oil, resin, light mineral oil and other bind materials.
39 Pitch or flours and water may also be used in large cores for the sake of
economy.

Cores
Cores are made of sand which are used to make cavities and hallow
projections.
40

Characteristics of Core
Green strength – sufficient strength to hold up its shape till it is baked.
Dry strength – sufficient strength to resist bending forces due to hydrostatic
pressure from the liquid (molten metal), when core is placed inside the mould
Refractoriness – core is surrounded on all sides by molten metal and should
have high refractoriness.
Permeability – gases evolved may pass through the core to escape and
should posses sufficient permeability.
Collapsibility – should shrink as molten metal shrinks during solidification
Friability – should get dismantled easily once the casting is completely cooled.
Smoothness – surface of core should be smooth to have better surface finish.
Low gas emission – emission of gases from core should be as low as
possible to avoid voids formed inside core
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Core Sand
Core sand must be stronger than moulding sand
Core sand = Sand grains + Binders + Additives
Sand grains
Sand containing more than 5% clay is not used to make core
Excessive clay reduces the permeability and collapsibility of the core.
Coarse silica used for making steels and finer one for cast iron an
non- ferrous alloys
Binders
Organic binders tend to burn away under the heat of molten metal
and hence increases the collapsibility of the core.
Organic binder develop strength by polymerisation and cross-linking
and hence cores are baked.
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Some of the binders are linseed oil, dextrin, molasses, resins etc.

Core Prints
Core prints are extra projections provided on the pattern that form
a seat in the mould. Core prints support the core in the mould cavity.
Core shifts and chaplets
Chaplets are used to support the cores
which tend to sag without adequate supports.
Chaplets are made of the same material as
that of the casting.
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Types of Cores
Horizontal cores –
Itis held horizontally along the parting line of the mould.
Ends of core rests in the seats provided by core prints on the pattern.
Vertical cores –
Twoends of the mould sits on the cope and drag portion of the mould.
Amount of taper on the top is more than the taper at the bottom of the core.
Balanced cores –
Whenopenings are required at only one end, balanced cores are used.
Coreprints are available at one end of the pattern.
Core prints need to be sufficiently longer to support the core in case of longer
44
holes.

Types of Cores
45
Hanging cores –
They are used when the casting is made in drag.
Core is supported from above and hangs into the mould.
Fastening wires or rods are used and hole is made in the upper part of the core
so that molten metal reaches the mould cavity.
Cover cores –
In cover core, core hangs from the cope portion and is supported by the drag.
Core acts as a cover and hence termed as cover core.
Wing cores –
A wing core is used when hole or recess is to be obtained in casting.
Core print is given sufficient amount of taper so that core is placed
readily in the mould.

Gating system in mold
Pouring basin
Sprue
Sprue Base
Runner
Gate
Riser
46

Functions of Gating system
47
To provide continuous, uniform feed of molten metal in to mould
cavity and to reduce the turbulence flow.
Proper directional solidification
To fill the mould cavity in a less time to avoid thermal gradient
To provide minimum excess metal
To prevent erosion of mould walls
To prevent the foreign materials to enter in mould cavity

Elements of Gating system
48
1. Pouring basin
It is the conical hollow element or tapered hollow vertical portion of
the gating system
It makes easier for the ladle operator to direct the flow of molten
metal from crucible to pouring basin and sprue.
It helps in maintaining the required rate of liquid metal flow.
It reduces turbulence and vortexing at the sprue entrance.
It also helps in separating dross, slag and foreign element etc.
Skim core plays very important role in removing slag.

2. Sprue
It is channel in cope side connected at bottom
of pouring basin which will carry molten metal to
the parting plane.
In straight sprue due to vortex flow air bubbles may enter in to the
cavity this can be compensated by providing taper to it.
It is tapered with its bigger end at to receive the molten metal the
smaller end is connected to the runner.
It some times possesses skim bob at its lower end.
49

50
the rate of solidification.
3. Sprue Base Well
It acts as a reservoir for metal at the bottom of sprue in order to
reduce moment of molten metal.
4. Runner
It will be in trapezoidal cross section which will connect the sprue to
ingates of mould cavity.
For ferrous metals runner will be in cope side
Metal flow rate from runner should be more than flow rate in ingates
then only slag will be trapped.
5. Gate
It is a small passage or channel being cut by gate cutter which
connect runner with the mould cavity.
 It feeds the liquid metal to the casting at the rate consistent with

51
6. Riser
It is a passage in molding sand made in the cope portion of the mold.
Molten metal rises in it after filling the mould cavity completely.
It compensates the shrinkage during solidification of the casting
thus avoiding the shrinkage defect in the casting.
It also permits the escape of air and mould gases.
It promotes directional solidification too and helps in bringing the
soundness in the casting.
Types of Gates
Top Gate
Bottom Gate
Parting Gate
Step Gate

Chills
In some casting, it is required to produce a hard surface at a particular place
in the casting.
 At that particular position, the special mould surface for fast extraction of
heat is to be made.
The fast heat extracting metallic materials known as chills will be
incorporated separately along with sand mould surface during molding.
The main function of chill is to provide a hard surface at a localized place in
52 the casting by way of special and fast solidification.

Solidification
• Solidification mechanism is essential for preventing defects due to
shrinkage.
• As soon as the molten metal is poured in a sand mold, the process of
solidification starts.
• During solidification, cast forms develops cohesion and acquires structural
characteristics.
• The mode of solidification affects the properties of the casting acquires a
metallographic structure which is determined during solidification. The
metallographic structure consists of:
 Grain size, shape and orientation
 Distribution of alloying elements
 Underlying crystal structure and its imperfections
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• A metal in molten condition possesses high energy
• As the molten metal cools, it loses energy to form crystals
• Since heat loss is more rapid near the mold walls than any other place, the
first metal crystallites called ‘nuclei’ formhere.
• Nuclei formed as above tend to grow at the second stage of solidification.
• The crystal growth occurs in a dendrite manner.
• Dendrite growth takes place by the evolution of small arms on the original
branches of individual dendrites:
 Slow cooling makes the dendrites to grow long whereas fast cooling causes
short dendrite growth.
 Since eventually dendrites become grains, slow cooling results in large
grain structure and fast cooling in small grain structure in the solidified
metal.
Solidification on Casting
55

• As solidification proceeds, more and more arms grow on an existing
dendrite and also more and more dendrites form until the whole melt is
crystallized.
Figure showing formation of dendrites
56

Solidification of Pure Metals
Pure metals generally posses
 Excellent thermal and electrical conductivity(e.g. Cu andAl).
 Higher ductility, higher melting point, lower yield point and tensile
strength, and
 Better corrosion resistance, as compared to alloys.
As metals posses high melting points, they exhibit certain difficulties in
casting,
 Difficulties during pouring
 Occurrence of several metal-mold reactions
 Greater tendency toward cracking
 Their mode of solidification, which may produce defective castings.
Above freezing point the metal is liquid and below freezing point, it is in solid.
57

Solidification curve for metals58

From the above curve the following observations can bemade:
 Liquid metals cools from A toB
 From B to C, the melt liberates latent heat of fusion; temperature remains
constant.
 The liquid metal starts solidifying at B and it is partly solid at any point
between B and C and at C metal is purely solid.
 From C to D, the solid metal cools and tends to reach room temperature.
 The slopes of AB and CD depend upon the specific heats of liquidand solid
metals respectively.
59

Solidification of Alloys
Alloyed metals possess:
 Higher tensile strengths
 Better high temperature strengths
 Better corrosion resistance
 Improved machinability and workability
 Lower melting points
Improved castability
Main types of alloys:
 Solid solution alloys
 Eutectic alloys
 Peritectic alloys
60

Solidification curve for alloys
The above curve shows the cooling curve of a binary-solid solution alloy
 From Ato B, the alloy is in liquid state
 Solidification starts at B and completes at point C.
 Unlike pure metals, solidification occurs throughout the temperature
range(i.e., from Tb to Tc).
 Latent heat of fusion is liberated gradually from B to C and it tendsto
increase the time required for the solidification61

• If two metals of a binary solid solution system are mixed in different
proportions and a cooling curve is constructed for each composition,
resulting diagram will be one which is known as PHASE DIAGRAM for
the alloy system.
• A phase diagram shows two different and distinct phases; one isliquid
metal solution and the other is solid solution.
• Within these two phases i.e., liquidus and solidus, the two phases – the
liquid and solid exist together.
• Liquidus is that line (a) above which the alloy is in liquid state,and
• Solidus is that line (a) below which the alloy is in solid state, and (b) where
solidification completes.
• If in a phase diagram, for each change of phase, adequate time is allowed
for the change to complete so that phase change takes place under
equilibrium conditions, the phase diagram will be known as Equilibrium
diagram.
63

SHORT FREEZING RANGE ALLOYS
1. The solidification front is planar. Solidification is from the outside walls in
towards the centre as the metal proceeds along the mould.
2. The flow of metal stops when the two freezing fronts meet Short Freezing
Range Alloys.
3. We will now consider the fluidity of short freezing range metals and alloys
This shows the mode of solidification from the outside walls in towards the
centre as the metal proceeds along the mould.
4. A point to notice is the remelting of the part of the frozen solid nearest the
source of hot metal. For this reason the solidified zone migrates
progressively along the mould, trailing behind the liquid tip
64

LONG FREEZING RANGE ALLOYS
1. We will now move onto the fluidity of long freezing range alloys. The
solidification of such alloys in a rapidly flowing stream is somewhat
different.
2. The solidification front is now, of course, no longer planar but dendrite, and
because freezing is occurring in a moving liquid, the bulk turbulence in the
liquid causes turbulent eddies to sweep through the dendrites, carrying
pockets of hot liquid into these cooler regions, and thus remelting dendrite
arms and other fragments, to build up a slurry of dendrite debris.
3. As heat is lost from the slurry, the slurry thickens, gradually becoming so
thick that it is too viscous to flow.
4. This occurs at different fractions of solid in different alloys, and also seems
to be influenced by the metallostatic head driving the flow. In general,
however, the flow of liquid is arrested when the volume fraction of solid is
somewhere between 25 and 50 %.
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Basic of Casting Process
71
Shell Casting
Investment Casting
Die casting
Centrifugal Casting

Shell Casting
It is a process in which, sand with thermosetting resin is poured on
heated metallic pattern to form a thin shells which act as a mould
cavity.
72

1. In this process a pattern is placed on a metal plate and it is then coated
with a mixture of fine sand and Phenol-resin (20:1).
2. In order to get thermosetting characteristics resign is mixed with hexa-
methylene-tetramine (hexa) up to 14-16%.
3. Sand, hexa and additives which are all dry are mixed in mueller for 1min.
4. The pattern is heated first and silicon grease is then sprayed on the
heated metal pattern ( grey cast Iron) for easy separation.
5. The pattern is heated to 205 to 230°C and covered with resin bounded
sand. After 30 seconds, a hard layer of sand is formed over pattern.
6. Pattern and shell are heated and treated in an oven at 315°C for 60 secs.,
7. Layer of about 4 to 10 mm in thickness is stuck on the pattern and the
loose material is then removed from the pattern.
8. Then mold is ready for pouring.
73
Process

Advantages
Very suitable for thin sections like petrol engine cylinder.
Excellent surface finish.
Good dimensional accuracy of order of 0.002 to 0.003 mm.
Negligible machining and cleaning cost.
Occupies less floor space.
Skillness required is less.
Molds can be stored until required.
Mass production.
Disadvantages
(i) Initial cost is high.
(ii) Specialized equipment is required.
(iii) Resin binder is an expensive material.
(iv) Limited for small size.
74

Applications
Suitable for production of Al, Cu and ferrous metals
Cylinder heads for air cooled IC engines
Automobile transmission parts
Cast tooth bevel gears
Break beam
Rollers for crawler tractors
Chain seat bracket
Refrigerator valve plate etc.
75

Investment Casting (lost wax casting)
(b) Multiple patterns assembled to wax sprue
(a) Wax pattern (injection molding)
76
In this process mould is prepared around expandable pattern.
Pattern is made of wax and same shape die has to be prepared first

(c) Shell built  immerse into ceramic
slurry  immerse into fine sand (few
layers)
(d) dry ceramic melt out the wax fire
ceramic (burn wax). Hot vapor solvent
trichloro-ethylene is used to remove
remained wax.
(e) Mould is preheated before pouring the melt. Pour
molten metal (gravity)  cool, solidify [Hollow casting:
pouring excess metal before solidification
77

(f) Break ceramic shell (vibration or water blasting)
(g) Cut off parts (high-speed friction saw)
 finishing (polish)
78

Advantages
Complex shapes can be produced
Very thin sections can be produced
Because of using fine grain sand products with good surface finish can be
produced
Little or no machining is required
Controlled mechanical properties
Disadvantages
(i) Limited to size and mass of casting
(ii) More expensive
Application
Jewellery, surgical instruments, vanes and blades of a gas turbine
 Fire arms, Steel valve bodies and impellers for turbo chargers, etc.
80

6
81
PERMANENT MOLD OR GRAVITY DIE CASTING
Used in;
Carburetor bodies
Oil pump bodies
Connecting rods
Pistons etc.

Molten metal is poured into the mold under gravity only and no
external pressure is applied to force the liquid metal into the mold
cavity.
The metallic mold can be reused many times before it is discarded or
rebuilt.
These molds are made of dense, fine grained, heat resistant cast
iron, steel, bronze, anodized aluminum, graphite or other suitable
refractoriness.
The mold is made in two halves in order to facilitate the removal of
casting from the mold.
The mold walls of a permanent mold have thickness from 15 mm to
50 mm.
For faster cooling, fins or projections may be provided on the outside
of the permanent mold which provides the desirable chilling effect.
82

DIE CASTING or Pressure Die-Casting
83
It is a process of injecting the molten metal with high pressure in metallic die.
The pressure is generally created by compressed air or hydraulically means
The pressure varies from 70 to 5000 kg/cm2 and is maintained while the
casting solidifies.
Any narrow sections, complex shapes can be easily produced.
1. It consists of stationary die or cover die which is fixed to the die casting machine.
2. Second one is ejector die is moved out for the extraction of casting.
3. First lubricant is sprayed on the die cavity manually or automatic system.
4. Two dies are closed using the clamp.
5. Required amount of metal is injected in to the die cavity and is allowed to solidified
HOT CHAMBER and COLD CHAMBER DIE CASTING MACHINES

HOT CHAMBER
84
Dieis closed, gooseneck cylinder is filled
with molten metal
Plunger pushes molten metal through
gooseneck into cavity
Metalis held under pressure until it
solidifies
Die opens, cores retracted; plungerreturns
Ejector pins push casting out of ejector die

COLD CHAMBER:
•Die closed, molten metal is ladled into
cylinder
•Plunger pushes molten metal into die cavity
•Metal is held under high pressure until it
solidifies
•Die opens, plunger pushes solidified slug
from the cylinder
•Cores retracted
•Ejector pins push casting off ejector die
85

Centrifugal Casting
In this casting process, molten metal is
poured into a revolving mold and allowed
to solidify molten metal by pressure of
centrifugal force.
3 -Types
1. True centrifugal casting
2. Semi-centrifugal casting
3. Centrifuging
87

True Centrifugal Casting
 The process setup contains an accurately machined metal mold or die
surrounded by cooling water.
The machine is mounted on wheels and it can be move lengthwise on a
straight on a slightly inclined track.
At one end of the track there is a ladle containing proper quantities of
molten metal
As pouring proceeds mould is rotated and moved slowly down the track so
that the metal is laid progressively along the length of the mould wall.
After completion of pouring the machine will be at the lower end of its track
88 with the mold that rotating continuously till the molten metal has solidified in
form of a pipe.

89
Advantages
Good mechanical properties can be achieved
In order to make holes cores are not required
No need for gates and runners.
Limitations
Castings which are axi-symmetric and having concentric holes are suitable.
Equipment is expensive.

Semi - Centrifugal Casting
Used for articles which are more complicated than those possible in true
centrifugal casting, but are axi-symmetric in nature.
A particular shape of the casting is produced by mold and core and not by
centrifugal force.
 The centrifugal force aids proper feeding and helps in producing the
castings free from porosity.
90For larger production rates moulds are stacked one over the other.

Centrifuging Casting
To obtain high metal pressures during
solidification When the shapes are not axi-
symmetrical the centrifuging is used.
Suitable for only small jobs.
Radial runners are used to combine all the
jobs
Similar to Semi-centrifugal casting.
91

1 introduction of casting

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