casting notes mpya.pptx

MANUFACTURING
PROCESSES-
CASTING
Mr. S . Lucas

Mechanical engineering is a discipline
of engineering that applies the principles of
physics and materials science for analysis,
design, manufacturing, and maintenance of
mechanical systems.
Mechanical Engineering

Manufacturing
Manufacturing basically implies making of
goods or articles and providing services to meet
the needs of mankind.
Manufacturing process is that part of the production
process which is directly concerned with the change of
form or dimensions of the part being produced.

•Began about 5000 to 4000 B.C with the production of various
articles of wood, ceramic, stone and metal
• Derived from Latin word manu factus – meaning “made by hand”
• The word manufacture first appeared in 1567
• The word manufacturing appeared in 1683
• Production is also used interchangeably .
Evolution of Manufacturing

Traditional Manufacturing Processes
Casting
Forming
Sheet metal processing
Plastics processing
Joining
Lathe

Casting Process
• Casting process is one of the earliest metal
shaping techniques known to human being.
• It means pouring molten metal into a refractory
mold cavity and allows it to solidify.
• The solidified object is taken out from the mold
either by breaking or taking the mold apart.
• The solidified object is called casting and the
technique followed in method is known as casting
process.

Casting Terms:
1. Flask: A metal or wood
frame, without fixed
top or bottom, in
which the mold is
formed.
drag - lower molding
flask,
cope - upper molding
flask,
cheek - intermediate
molding flask used in
three piece molding.

Casting Terms:
2. Pattern: It is the
replica of the final
object to be made.
The mold cavity is
made with the help
of pattern.
3. Parting line: This is
the dividing line
between the two
molding flasks that
makes up the
mold.
Pattern

4.Pouring basin: A small funnel shaped cavity at
the top of the mold into which the molten metal
is poured.
5.Sprue: The passage through which the molten
metal, from the pouring basin, reaches the mold
cavity. In many cases it controls the flow of
metal into the mold.

4.Runner: The channel through which the molten
metal is carried from the sprue to the gate.
7.Riser: A column of molten metal placed in the
mold to feed the castings as it shrinks and
solidifies. Also known as feed head.
8. Gate: A channel through which the molten metal
enters the mold cavity.

9.Core: A separate part of the mold, made of sand and
generally baked, which is used to create openings
and various shaped cavities in the castings.
10.Chaplets: Chaplets are used to support the cores
inside the mold cavity to take care of its own weight
and overcome the metallostatic force.
11.Vent: Small opening in the mold to facilitate escape
of air and gases.

Steps involved in making a casting:
1. Make the pattern out of Wood , Metal or Plastic.
2. Prepare the necessary sand mixtures for mould
and core making.
3. Prepare the Mould and necessary Cores.
4. Melt the metal/alloy to be cast.
5. Pour the molten metal/alloy into mould and
remove the casting from the mould after the
metal solidifies.
6. Clean and finish the casting.
7. Test and inspect the casting.
8. Remove the defects, if any.
9. Relieve the casting stresses by Heat Treatment.
10. Again inspect the casting.
11. The casting is ready for shipping.

sand
runner
ın gate
bottom board
core
rıser
Gr:ıg
kent P‹»ıring hisin (cııp)
Blind
Sprue
Runner
Saı›J
Rurting

Drag
Gore Print
Ladle
Open Riser
Chapter
Gate Runner
d dheld
Malten Metal
Riser
PourinBCup
Sprue
Flask
Casting
Ladle
Molten metal

Aligning Pin
Sprue
Botto m board
Rise r Pin
Lug S prue
Aligning
Drag
Skim
bob
Po uring basin
Aligning P in
Drag
Drag Patte rn
(b)
Riser
Date
(
d
/
Rammed
MouIding Sand
Pa rling line

Advantages
• Product can be cast as one piece.
• Very heavy and bulky parts can be
manufactured
• Metals difficult to be shaped by other
manufacturing processes may be cast (eg: Cast
Iron)
• Best for mass production
• Complex shapes can be manufactured

Disadvantages of Casting
• Casting process is a labour intensive process
• Not possible for high melting point metals
• Dimensional accuracy, surface finish and the
amount of defects depends on the casting
process
• Allowances required.

Applications of Casting:
Transportation vehicles
Turbine vanes
Power generators
Railway crossings
Agricultural parts
Aircraft jet engine parts
Sanitary fittings
Communication, Construction and
Atomic Energy applications, etc..

Raw Materials for Foundry:
Metals and alloys
Fuels (For melting metals)
Fluxes

Metals and alloys commonly
used in Foundries:
1. Ferrous
2. Non-Ferrous
FERROUS:
a. Cast irons
b. Steels
NON-FERROUS:
a. Copper alloys
b. Aluminium alloys
c. Magnesium alloys
d. Zinc alloys
e. Nickel alloys

Pattern
•
•
•
•
Pattern is the principal tool during the casting
process.
A pattern is a model or the replica of the object (to
be casted)
It may be defined as a model or form around
which sand is packed to give rise to a cavity known
as mold cavity in which when molten metal is
poured, the result is the cast object.
A pattern prepares a mold cavity for the purpose
of making a casting.

OBJECTIVES OF A PATTERN
•
•
•
•
•
•
•
Pattern prepares a mould cavity for the purpose of making a
casting.
Pattern possesses core prints which produces seats in form of
extra recess for core placement in the mould.
It establishes the parting line and parting surfaces in the mould.
Runner, gates and riser may form a part of the pattern.
Properly constructed patterns minimize overall cost of the
casting.
Pattern may help in establishing locating pins on the mould and
therefore on the casting with a purpose to check the casting
dimensions.
Properly made pattern having finished and smooth surface
reduce casting defects.

The pattern material should be:
1. Easily worked, shaped and joined.
2. Light in weight.
3. Strong, hard and durable.
4. Resistant to wear and abrasion .
5. Resistant to corrosion, and to chemical
reactions.
6. Dimensionally stable and unaffected by
variations in temperature and humidity.
7. Available at low cost.

Materials for making patterns:
WOOD
METAL
PLASTIC
PLASTER
WAX

Pattern Materials
•
•
•
•
•
•
Wood: Inexpensive, Easily available, Light weight, easy to
shape, good surface finish, Poor wear resistance, absorb
moisture, less strength, not suitable for machine moulding,
easily repaired, warping, weaker than metallic patterns.
Eg. Shisam, kail, deodar, Teak wood, maogani.
Metal: less wear and tear, not affected by moisture, metal is
easier to shape the pattern with good precision, surface finish
and intricacy in shapes, withstand against corrosion and
handling for longer, excellent strength to weight ratio,
metallic patterns are higher cost, higher weight and tendency
of rusting.
preferred for production of castings in large quantities with
same pattern.
Eg.: cast iron, brass and bronzes and aluminum alloys

• Plastic:-Plastics are getting more popularity
because the patterns made of these materials
now a days
are lighter,
•
stronger, moisture and wear resistant, non sticky to molding
sand, durable and they are not affected by the moisture of the
molding sand.
fragile, less resistant to sudden loading and their section may
need metal reinforcement.
Eg.:phenolic resin, foam plastic
•
• Plaster: Intricate shapes can be
made,
good compressive
strength, expands while solidifying, less dimensionally
accurate.
• •Wax: Good surface finish, high accuracy, no need to remove
from the mould, less strength.

FACTORS EFFECTING SELECTION OF
PATTERN MATERIAL
1. Number of castings to be produced. Metal pattern are preferred
when castings arerequired large in number.
2. Type of mould material used.
3. Kind of molding process.
4. Method of molding (hand or machine).
5. Degree of dimensional accuracy and surface finish required.
6. Minimum thickness required.
7. Shape, complexity and size of casting.
8. Cost of pattern and chances of repeat orders of the pattern

Types of Patterns:
Single piece pattern.
Split pattern
Loose piece pattern
Match plate pattern
Sweep pattern
Gated pattern
Skeleton pattern
Follow board pattern
Cope and Drag pattern

(a)Split pattern
(b)Follow-board
(c) Match Plate
(d) Loose-piece
(e) Sweep
(f)Skeleton
pattern

TYPES OF PATTERN
• 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.
Typical single piece pattern is shown in Fig.
Simplest type, inexpensive used for limited production

• 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.
• The splitting at the parting line is done to facilitate the withdrawal of the
pattern.
• A typical example is shown in Fig.

• Cope and drag pattern
• In this case, 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.
• The pattern is made up of two halves, which are mounted on different
plates. A typical example of match plate pattern is shown in Fig.

COPE SECTION
DRAG SECTION
COPE AND DRAG PATTERN

• Loose-piece Pattern
• used when pattern is difficult for withdrawal from the mould.
• Loose pieces are provided on the pattern and they are the part of pattern.
• The main pattern is removed first leaving the loose piece portion of the
pattern in the mould.
• Finally the loose piece is withdrawal separately leaving the intricate mould.

• Match plate pattern
• This pattern is made in two halves and is on mounted on the opposite sides
of a wooden or metallic plate, known as match plate.
• The gates and runners are also attached to the plate.
• This pattern is used in machine molding. A typical example of match plate
pattern is shown in Fig.

Follnrv board
PaLfé rft Al ale
Copo half
Fi9 ure: Three types of patterns used fnproduce a water pump casting in various
quantities. (s) Woo b pattern on a follow bna rd, good for 20 in 30 castings.
(b) Match plate paaern for up to 50,000 castings depending on material.
(c) Cope and drag plastic (up to 20,000 castings) or metal (10il,000 or more
castings) pattern.

• Follow board pattern
• When the use of solid or split patterns becomes difficult, a contour
corresponding to the exact shape of one half of the pattern is made in a
wooden board, which is called a follow board and it acts as a molding
board for the first molding operation as shown in Fig.

• 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, as shown in Fig.
• These patterns are made of metals, and metallic pieces to form gates and
runners are attached to the pattern.

castings
Gating system
GATED PATTRN

• Sweep pattern
•
• Sweep patterns are used for forming large circular moulds of symmetric
kind by revolving a sweep attached to a spindle as shown in Fig.
• 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.
The pivot end is attached to a stake of metal in the center of the mould.

• Segmental pattern
• Patterns of this type are generally used for circular castings, for example
wheel rim, gear blank etc.
• Such patterns are sections of a pattern so arranged as to form a complete
• mould by being moved to form each section of the mould.
• The movement of segmental pattern is guided by the use of a central pivot.
A segment pattern for a wheel rim is shown in Fig.

• Shell pattern
• Shell patterns are used mostly for piping work or for
producing drainage fittings. This pattern consists of a thin
cylindrical or curved metal piece parted along the center line.
• The two halves of the pattern are held in alignment by dowels.
• The outside surface of the pattern is used to make the mould
for the fitting required while the inside can serve as a core box.

Shell-Maklng Bhall Mold Casting CasMng

Types of Pattern Allowances:
The various pattern
allowances are:
1. Shrinkage or contraction
allowance.
2. Machining or finish allowance.
3. Draft of tapper allowances.
4. Distortion or chamber allowance.
5. Shake or rapping allowance.

1.Shrinkage Allowance:
All most all cast metals shrink or contract
volumetrically on cooling.
The metal shrinkage
is of two
types:
1. Liquid Shrinkage:
2. Solid Shrinkage:

2. Machining Allowance:
A Casting is given an allowance for
machining, because:
i. Castings get oxidized in the mold and during
heat treatment; scales etc., thus formed need
to be removed.
ii. It is the intended to remove surface
roughness and other imperfections from the
castings.
iii. It is required to achieve exact casting
dimensions.
iv. Surface finish is required on the casting.

3. Draft or Taper Allowance:
 It is given to all surfaces perpendicular
to parting line.
 Draft allowance is given so that the
pattern can be easily removed from the
molding material tightly packed around
it with out damaging the mould cavity.

4. Distortion or cambered allowance:
A casting will distort or wrap if :
iii.
i. It is of irregular shape,
ii. All it parts do not shrink uniformly i.e., some
parts shrinks while others are restricted from
during so,
It is u or v-shape

Distortion Allowance
• This allowance is applied to the castings which have the tendency to distort
during cooling due to thermal stresses developed.
• For example a casting in the form of U shape will contract at the closed
end on cooling, while the open end will remain fixed in position.
• Therefore, to avoid the distortion, the legs of U pattern must converge
slightly so that the sides will remain parallel after cooling.

5. Shake allowance:
A pattern is shaken or rapped by striking the
same with a wooden piece from side to side.
This is done so that the pattern a little is
loosened in the mold cavity and can be easily
removed.
In turn, therefore, rapping enlarges the mould
cavity which results in a bigger sized casting.
Hence, a –ve allowance is provided on the
pattern i.e., the pattern dimensions are kept
smaller in order to compensate the
enlargement of mould cavity due to rapping.

Pattern Layout:
Steps involved:
 Get the working drawing of the part for which the
pattern is to be made.
 Make two views of the part drawing on a sheet,
using a shrink rule. A shrink rule is modified form
of an ordinary scale which has already taken
care of shrinkage allowance for a particular metal
to be cast.
 Add machining allowances as per the
requirements.
 Depending upon the method of molding, provide
the draft allowance.

Pattern Construction:
 Study the pattern layout carefully and establish,
a. Location of parting surface.
b. No. of parts in which the pattern will be made.
 Using the various hand tools and pattern making
machines fabricate the different parts of the pattern.
 Inspect the pattern as regards the alignment of
different portions of the pattern and its dimensional
accuracy.
 Fill wax in all the fillets in order to remove sharp
corners.
 Give a shellac coatings(3 coats) to pattern.
 impart suitable colors to the pattern for identification
purposes and for other informations.

The Mold in Casting
• Mould is a container with cavity
whose geometry determines part
shape
– Actual size and shape of cavity must be slightly
oversized to allow for shrinkage of metal during
solidification and cooling
– Molds are made of a variety of materials,
including sand, plaster, ceramic, and metal
Foundry Technology- EPE - CET - MUST

Open Moulds and Closed Moulds
Two forms of mould: (a) open mould, simply a container in the shape of the
desired part; and (b) closed mould, in which the mould geometry is
more complex and requires a gating system (passageway) leading into
the cavity.
Cavity is open to atmosphere
Cavity is closed

Two Categories of Casting Processes
1. Expendable mould processes –mould is sacrificed to remove part
/uses an expendable mould which must be destroyed to remove
casting
– Mold materials: sand, plaster, and similar materials, plus binders
– Advantage: more complex shapes possible
– Disadvantage: production rates often limited by time to make mould rather than
casting itself
2. Permanent mould processes –mould is made of metal and can be
used to make many castings / uses a permanent mould which can
be used over and over to produce many castings
– Made of metal (or, less commonly, a ceramic refractory material)
– Advantage: higher production rates
– Disadvantage: geometries limited by need to open mould

Mould
•
•
•
•
•
This is suitable and workable material possessing high
refractoriness in nature
material can be metallic or non-metallic
For metallic category, the common materials are cast iron,
mild steel and alloy steels.
non-metallic group molding sands, plaster of paris, graphite,
silicon carbide and ceramics
molding sand is the most common utilized non-metallic
molding material because of its certain inherent properties
namely refractoriness, chemical and thermal stability at higher
temperature, high permeability and workability along with
good strength.

•
•
•
•
•
•
•
molding sand is the most common utilized non-metallic
molding material
because of its certain inherent properties namely,
refractoriness,
chemical and thermal stability at higher temperature,
high permeability and
workability along with good strength.
highly cheap and easily available.

MOLDING SAND
• Sources of receiving molding sands
• beds of sea,
• rivers,
• lakes,
• granulular elements of rocks,
and deserts.

Natural Molding sand:
• known as green sand
• having appreciable amount of clay which acts as a
binder between sand grains
• obtained by crushing and milling of soft yellow sand
stone, carboniferrous etc
• Ease of availability
• Low cost
• High flexibility
• Mostly used for ferrous and non ferrous metal casting

Synthetic sand
• known as silica sand
• not having binder(clay) in natural form
• desired strength and properties developed by separate addition
of binder like bentonite, water and other materials.
• More expensive than natural sand

Cont…..
Silica (SiO2) or silica mixed with other minerals
can have;
• Good refractory properties - capacity to endure
high temperatures
• Small grain size yields better surface finish on
the cast part
• Large grain size is more permeable, allowing
gases to escape during pouring
• Irregular grain shapes strengthen molds due to
interlocking, compared to round grains
– Disadvantage: interlocking tends to reduce
permeability

Special sands
• Zicron-cores of brass and bronze casting
• Olivine-for non ferrous casting
• Chromite-for heavy steel casting
• Chrome-magnesite-used as facing materials in steel casting.

Types of moulding sand
(According to use)
Green sand
Dry sand
Facing sand
Backing sand
System sand
Parting sand
Loam sand
Core sand

Green sand
• Green sand is also known as tempered or natural sand
• mixture of silica sand with 18 to 30 percent clay, having moisture content from 6 to
8%.
• The clay and water furnish the bond for green sand. 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.
• Molds prepared by this sand are not requiring backing and hence are known as
green sand molds.
Green-sand molds - mixture of sand, clay, and water;
“Green" means mould contains moisture at time of pouring

Dry sand
• Green sand that has been dried or baked in suitable oven after the making mold and
cores, is called dry sand.
• more strength,
• rigidity and
• thermal stability.
• mainly suitable for larger castings.
• mold prepared in this sand are known as dry sand molds.

Loam sand
• Loam is mixture of sand and clay with water to a thin plastic paste.
• sand possesses high clay as much as 30-50% and 18% water.
• Patterns are not used for loam molding and shape is given to mold by
sweeps.
• particularly employed for loam molding used for large grey iron castings.
• This sand is used for loam sand moulds for making very heavy castings
usually with the help of sweeps and skeleton patterns.

Facing sand
•
• Facing sand is just prepared and forms the face of the mould.
• It is directly next to the surface of the pattern and it comes into contact
molten metal when the mould is poured.
• high strength refractoriness.
• made of silica sand and clay, without the use of used sand.
• Different forms of carbon are used to prevent the metal burning into the
sand.
• A facing sand mixture for green sand of cast iron may consist of 25% fresh
and specially prepared and 5% sea coal.
sometimes mixed with 6-15 times as much fine molding sand to make
facings.
• The layer of facing sand in a mold usually ranges from 22-28 mm. From
10 to 15% of the whole amount of molding sand is the facing sand.

Backing sand
• Backing sand or floor sand is used to back up the facing sand
and is used to fill the whole volume of the molding flask.
• Used molding sand is mainly employed for this purpose.
• The backing sand is sometimes called black sand because that
old

System sand
• In mechanized foundries where machine molding is employed.
• A so-called system sand is used to fill the whole molding flask.
• The used sand is cleaned and re-activated by the addition of water and special
additives. This is known as system sand.
• Since the whole mold is made of this system sand, the properties such as
strength, permeability and refractoriness of the molding sand must be higher
than those of backing sand.

Parting sand
• without binder and moisture to keep the green sand not to stick
to the pattern
• to allow the sand on the parting surface the cope and drag to
separate without clinging.
• This is clean clay-free silica sand which serves the same
purpose as parting dust.

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.
• Pitch or flours and water may also be used in large cores for
the sake of economy.

Properties of Moulding Sand
• Refractoriness
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Refractoriness is defined as the ability of molding sand to withstand high
temperatures without breaking down or fusing thus facilitating to get sound
casting.
poor refractoriness
burn on to the casting surface and
no smooth casting surface can be obtained.
degree of refractoriness depends on the SiO2 i.e. quartz content, and the
shape and grain size of the particle.
higher the SiO2 content higher is the refractoriness of the molding
Refractoriness is measured by the sinter point of the sand rather than its
melting point.

• Permeability
•
•
•
•
It is also termed as porosity of the molding sand in order to allow the
escape of any air, gases or moisture present or generated in the mould
when the molten metal is poured into it.
All these gaseous generated during pouring and solidification process must
escape otherwise the casting becomes defective.
Permeability is a function of grain size, grain shape, and moisture and clay
contents in the molding sand.
The extent of ramming of the sand directly affects the permeability.

• Cohesiveness
•
•
It is property by virtue of which the sand grain particles interact and attract
each other within the molding sand.
Thus, the binding capability of the molding sand gets enhanced to increase
the green, dry and hot strength property of molding and core sand.

• Green strength
•
•
•
By virtue of this property, the pattern can be taken out from the mould
without breaking the mould and also the erosion of mould wall surfaces
does not occur during the flow of molten metal.
The green sand after water has been mixed into it, must have sufficient
strength and toughness to permit the making and handling of the mould.
For this, the sand grains must be adhesive, i.e. they must be capable of
attaching themselves to another body and therefore, and sand grains having
high adhesiveness will cling to the sides of the molding box.

• Dry strength
• As soon as the molten metal is poured into the mould, the moisture in the
sand layer adjacent to the hot metal gets evaporated and this dry sand layer
must have sufficient strength to its shape in order to avoid erosion of mould
wall during the flow of molten metal.
• The dry strength also prevents the enlargement of mould cavity cause by
the metallostatic pressure of the liquid metal.

• Strength of the moulding sand depends on:
• 1. Grain size and shape
• 2. Moisture content
• 3. Density of sand after ramming
• ·The strength of the mould increases with a decrease of grain size and an increase
of clay content and density after ramming. The strength also goes down if moisture
content is higher than an optimum value.

• Flowability or plasticity
• It is the ability of the sand to get compacted and behave like a fluid. It will
flow uniformly to all portions of pattern when rammed and distribute the
ramming pressure evenly all around in all directions.
• Generally sand particles resist moving around corners or projections.
• In general, flowability increases with decrease in green strength, an,
decrease in grain size.
• The flowability also varies with moisture and clay content.

• Adhesiveness
• · It is the important property of the moulding sand and it is defined as the
sand particles must be capable of adhering to another body, then only the
sand should be easily attach itself with the sides of the moulding box and
give easy of lifting and turning the box when filled with the stand.

• Collapsibility
• After the molten metal in the mould gets solidified, the sand mould must be
collapsible so that free contraction of the metal occurs and this would
naturally avoid the tearing or cracking of the contracting metal.
• In absence of this property the contraction of the metal is hindered by the
mold and thus results in tears and cracks in the casting.
• This property is highly desired in cores.

CONSTITUENTS OF MOLDING SAND
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•
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•
•
The main constituents of molding sand involve
silica sand,
binder,
moisture content and
additives.

• Silica sand
•
•
•
•
•
•
•
Silica sand in form of granular quarts is the main constituent of molding
sand
having enough refractoriness
which can impart strength,
stability and permeability to
molding and core sand.
along with silica small amounts of iron oxide, alumina, lime stone,
magnesia, soda and potash are present as impurities.
The silica sand can be specified according to the size (small, medium and
large silica sand grain) and
the shape (angular, sub-angular and rounded).

Binder
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•
•
•
•
•
In general, the binders can be either inorganic or organic substance.
The inorganic group includes clay sodium silicate and port land cement
etc.
In foundry shop, the clay acts as binder which may be Kaolonite, Ball
Clay, Fire Clay, Limonite, Fuller’s earth and Bentonite.
Binders included in the organic group are dextrin, molasses, cereal
binders, linseed oil and resins like phenol formaldehyde, urea
formaldehyde etc.
Organic binders are mostly used for core making.
Among all the above binders, the bentonite variety of clay is the most
common. However, this clay alone can not develop bonds among sand
grains without the presence of moisture in molding sand and core sand.

Moisture
•
•
•
•
•
•
•
The amount of moisture content in the molding sand varies generally
between 2 to 8 percent.
This amount is added to the mixture of clay and silica sand for developing
bonds.
This is the amount of water required to fill the pores between the particles of
clay without separating them.
This amount of water is held rigidly by the clay and is mainly responsible for
developing the strength in the sand.
The effect of clay and water decreases permeability with increasing clay and
moisture content.
The green compressive strength first increases with the increase in clay
content, but after a certain value, it starts decreasing.
For increasing the molding sand characteristics some other additional
materials beside basic constituents are added which are known as additives.

Additives
• Dextrin
• carbohydrates
• increases dry strength of the molds.
• Corn flour
• It belongs to the starch family of carbohydrates
• is used to increase the collapsibility of the molding and core sand.
• Coal dust
• To avoid oxidation of pouring metal
• For production of grey iron and malleable cast iron castings.
• Sea coal
• sand grains become restricted and cannot move into a dense packing pattern.
• Pitch
• form of soft coal (0.02 % to 2%)
• Wood flour:0.05 % to 2%
• To avoid expansion defects.
• increases collapsibility of both of mold and core.
• Silica flour
• added up to 3% which increases the
• hot strength and finish on the surfaces of the molds and cores.
• It also reduces metal penetration in the walls of the molds and cores.

Other Expendable Mold Processes
• Shell Moulding
• Vacuum Moulding
• Expanded Polystyrene Process
• Investment Casting
• Plaster Mould and Ceramic Mold
Casting

Shell Moulding
Casting process in which the cavity (& gating
system) is a thin shell of sand held
together by thermosetting resin binder
Steps in shell-molding: (1) a match-plate or cope-and-drag metal
pattern is heated and placed over a box containing sand mixed
with thermosetting resin.
part

Shell Moulding
Steps in shell-molding: (2) box is inverted so that sand and resin fall onto the
hot pattern, causing a layer of the mixture to partially cure on the surface
to form a hard shell; (3) box is repositioned so that loose uncured particles
drop away;

Shell Moulding
Steps in shell-molding: (4) sand shell is heated in oven for several minutes to
complete curing; (5) shell mould is stripped from the pattern;

Shell Molding
Steps in shell-molding: (6) two halves of the shell mould are assembled,
supported by sand or metal shot in a box, and pouring is accomplished;
(7) the finished casting with sprue removed.

Advantages and Disadvantages
• Advantages of shell molding:
– Smoother cavity surface permits easier flow of
molten metal and better surface finish
– Good dimensional accuracy - machining often not
required
– Mold collapsibility minimizes cracks in casting
– Can be mechanized for mass production
• Disadvantages:
– More expensive metal pattern
– Difficult to justify for small quantities

Vacuum Moulding

Vacuum Molding

Expanded Polystyrene Process or
lost-foam process
Uses a mould of sand packed around a polystyrene
foam pattern which vaporizes when molten
metal is poured into mould
• Other names: lost-foam process, lost pattern
process, evaporative-foam process, and full-mold
process
• Polystyrene foam pattern includes sprue, risers,
gating system, and internal cores (if needed)
• Mold does not have to be opened into cope and
drag sections

Expanded Polystyrene Process
Expanded polystyrene casting process: (1) pattern of polystyrene is coated
with refractory compound;

Expanded polystyrene casting process: (2) foam pattern is placed in mould
box, and sand is compacted around the pattern;

Expanded polystyrene casting process: (3) molten metal is
poured into the portion of the pattern that forms the pouring
cup and sprue. As the metal enters the mould, the
polystyrene foam is vaporized ahead of the advancing liquid,
thus the resulting mould cavity is filled.

• Advantages of expanded polystyrene process:
– Pattern need not be removed from the mould
– Simplifies and speeds mold-making, because two mould
halves are not required as in a conventional green-sand
mould
• Disadvantages:
– A new pattern is needed for every casting
– Economic justification of the process is highly dependent
on cost of producing patterns

• Applications:
– Mass production of castings for automobile
engines
– Automated and integrated manufacturing
systems are used to
1. Mold the polystyrene foam patterns and
then
2. Feed them to the downstream casting
operation

Investment Casting (Lost Wax Process)
A pattern made of wax is coated with a refractory
material to make mould, after which wax is
melted away prior to pouring molten metal
• "Investment" comes from a less familiar
definition of "invest" - "to cover completely,"
which refers to coating of refractory material
around wax pattern
• It is a precision casting process - capable of
producing castings of high accuracy and intricate
detail

Investment Casting
Steps in investment casting: (1) wax patterns are produced, (2) several
patterns are attached to a sprue to form a pattern tree

Investment Casting
Steps in investment casting: (3) the pattern tree is coated with a thin layer of
refractory material, (4) the full mould is formed by covering the coated
tree with sufficient refractory material to make it rigid

Investment Casting
Steps in investment casting: (5) the mould is held in an inverted position and
heated to melt the wax and permit it to drip out of the cavity, (6) the
mould is preheated to a high temperature, the molten metal is poured,
and it solidifies

Investment Casting
Steps in investment casting: (7) the mould is broken away from
the finished casting and the parts are separated from the
sprue

• Advantages of investment casting:
– Parts of great complexity and intricacy can be cast
– Close dimensional control and good surface finish
– Wax can usually be recovered for reuse
– Additional machining is not normally required - this is a net
shape process
• Disadvantages
– Many processing steps are required
– Relatively expensive process

Plaster Mold Casting
Similar to sand casting except mould is made of
plaster of Paris (gypsum - CaSO4-2H2O)
• In mold-making, plaster and water mixture is
poured over plastic or metal pattern and allowed
to set
– Wood patterns not generally used due to extended contact with
water
• Plaster mixture readily flows around pattern,
capturing its fine details and good surface finish

• Advantages of plaster mould casting:
– Good accuracy and surface finish
– Capability to make thin cross-sections
• Disadvantages:
– Mold must be baked to remove moisture,
which can cause problems in casting
– Mold strength is lost if over-baked
– Plaster molds cannot stand high
temperatures, so limited to lower melting
point alloys can be casted

Ceramic Mold Casting
Similar to Plaster Mold Casting except the
material of mould is refractory ceramic
material instead of plaster.
The ceramic mould can withstand temperature
of metals having high melting points.
Surface quality is same as that in plaster mould
casting.

Permanent Mold Casting Processes
• Economic disadvantage of expendable mould
casting: a new mould is required for every
casting
• In permanent mould casting, the mould is
reused many times
• The processes include:
– Basic permanent mould casting
– Die casting
– Centrifugal casting

The Basic Permanent Mold Process
Uses a metal mould constructed of two
sections designed for easy, precise
opening and closing
• Molds used for casting lower melting-
point alloys (Al, Cu, Brass) are commonly
made of steel or cast iron
• Molds used for casting steel must be
made of refractory material, due to the
very high pouring temperatures
Permanent Mold Processes

Permanent Mold Casting
Steps in permanent mould casting: (1) mould is preheated and coated

Permanent Mold Casting
Steps in permanent mould casting: (2) cores (if used) are inserted and
mould is closed, (3) molten metal is poured into the mould, where it
solidifies.

Advantages and Limitations
• Advantages of permanent mould casting:
– Good dimensional control and surface finish
– Very economical for mass production
– More rapid solidification caused by the cold metal
mould results in a finer grain structure, so castings
are stronger
• Limitations:
– Generally limited to metals of lower melting point
– Complex part geometries can not be made because
of need to open the mould
– High cost of mould
– Not suitable for low-volume production

Variations of Permanent Mold
Casting:
a. Slush Casting
• The basic procedure the same as used
in Basic Permanent Mold Casting
• After partial solidification of metal, the
molten metal inside the mould is
drained out, leaving the part hollow
from inside.
• Statues, Lamp bases, Pedestals and
toys are usually made through this
process
• Metal with low melting point are
used: Zinc, Lead and Tin

Casting:
b. Low-pressure Casting
• The basic process is shown in Fig.
- In basic permanent and slush casting processes, metal in cavity is poured
under gravity. However, in low-pressure casting, the metal is forced into
cavity under low pressure (0.1 MPa) of air.

Casting:
b. Low-pressure Casting
• Advantages:
- Clean molten metal from the center of ladle
(cup) is introduced into the cavity.
- Reduced- gas porosity, oxidation defects,
improvement in mechanical properties

Casting:
C.Vacuum Permanent-Mold Casting
• This is a variation of low-pressure
permanent casting
• Instead of rising molten into the cavity
through air pressure, vacuum in cavity is
created which caused the molten metal
to rise in the cavity from metal pool.

Die Casting
A permanent mould casting process in which
molten metal is injected into mould cavity under
high pressure
• Pressure is maintained during solidification, then
mould is opened and part is removed
• Molds in this casting operation are called dies;
hence the name die casting
• Use of high pressure (7-35MPa) to force metal
into die cavity is what distinguishes this from
other permanent mould processes

Die Casting Machines
• Designed to hold and accurately close two
mould halves and keep them closed while
liquid metal is forced into cavity
• Two main types:
1. Hot-chamber machine
2. Cold-chamber machine

Hot-Chamber Die Casting
Metal is melted in a container, and a piston injects liquid
metal under high pressure into the die
• High production rates - 500 parts per hour not
uncommon
• Injection pressure: 7-35MPa
• Applications limited to low melting-point metals that
do not chemically attack plunger and other
mechanical components
• Casting metals: zinc, tin, lead, and magnesium

Cycle in hot-chamber casting: (1) with die closed and plunger
withdrawn, molten metal flows into the chamber

Cycle in hot-chamber casting: (2) plunger forces metal in
chamber to flow into die, maintaining pressure during cooling
and solidification.
Because the die material does not
have natural permeability (like sand
has), vent holes at die cavity needs
to be made

Cold-Chamber Die Casting
Molten metal is poured into unheated
chamber from external melting container,
and a piston injects metal under high
pressure (14-140MPa) into die cavity
• High production but not usually as fast as
hot-chamber machines because of pouring
step
• Casting metals: aluminum, brass, and
magnesium alloys
• Advantage of cold chamber is that high
melting point metals can be casted: Why???

Cycle in cold-chamber casting: (1) with die closed and ram
withdrawn, molten metal is poured into the chamber

Cycle in cold-chamber casting: (2) ram forces metal to flow into die,
maintaining pressure during cooling and solidification.

Molds for Die Casting
• Usually made of tool steel, mould steel, or
maraging steel
• Tungsten and molybdenum (good refractory
qualities) are used to make die for casting
steel and cast iron
• Ejector pins are required to remove part from
die when it opens
• Lubricants must be sprayed into cavities to
prevent sticking

Advantages and Limitations
• Advantages of die casting:
– Economical for large production quantities
– Good accuracy (±0.076mm)and surface finish
– Thin sections are possible
– Rapid cooling provides small grain size and good
strength to casting
• Disadvantages:
– Generally limited to metals with low metal points
– Part geometry must allow removal from die, so very
complex parts can not be casted
– Flash and metal in vent holes need to be cleaned after
ejection of part

Centrifugal Casting
A family of casting processes in which the mould
is rotated at high speed so centrifugal force
distributes molten metal to outer regions of
die cavity
• The group includes:
– True centrifugal casting
– Semicentrifugal casting
– Centrifuge casting

(a) True Centrifugal Casting
Molten metal is poured into a rotating mould to produce a tubular part
• In some operations, mould rotation commences after pouring rather
than before
• Rotational axes can be either horizontal or vertical
• Parts: pipes, tubes, bushings, and rings
• Outside shape of casting can be round, octagonal, hexagonal, etc , but
inside shape is (theoretically) perfectly round, due to radially
symmetric forces
Shrinkage allowance is
not considerable factor

(b) Semicentrifugal Casting
Centrifugal force is used to produce solid castings rather than tubular
parts
• Molds are designed with risers at center to supply feed metal
• Density of metal in final casting is greater in outer sections than at
center of rotation
Axes of parts and rotational axis does
not match exactly
Often used on parts in which center
of casting is machined away, thus
eliminating the portion where
quality is lowest
Examples: wheels and pulleys
G factor keeps from 10-15

 Casting defects may be defined – Those
characteristics that create a deficiency or
imperfection to quality specifications
imposed by design and service
requirements.
 Reduces total output, increases the cost of
production.
 Even in modern foundries the rejection rate as
high up to 20% of the number of casting produced.

Surface defects Internal defects
Incorrect chemical compo. Unsatisfactory mech.
properties

 Sur face defects : May be visible on surface,
including incorrect shape & size, flashes, poor
surface finish.
 Internal defects : These are present in interior of
cast. Can be revealed through NDT techniques.
 Incorrect chemical composit ion – Formation of
undesirable microstructure.
 Unsatisfactory mechanical properties – These
are due to low quality, poor percent of usage.

 SWELL
 FIN
 Gas HOLES
 SHRINKAGE CAVITY
 HOT TEAR
 MISRUN AND COLD SHUT

 Swell - enlargement of the mould cavity by metal
pressures, results – localized or overall enlargement of
castings
Causes






Insufficient ramming of the sand.
Rapid pouring of molten metal.
Also due to insufficient weighting of mould.
Remedies –
Avoid rapid pouring.
provide sufficient ram on sands.
proper weighting of moulds.

 A thin projection of metal – not a part of cast.
Usually occur at the parting of mould or core
sections.
Causes –
 Incorrect assembly of cores and moulds,
 Improper clamping.
 Improper sealing.
Remedy –
 Reduces by proper clamping of cores and mould.

Gas Holes
Clean, smooth walled rounded holes of varying size
from pin heads to full section thickness, often
exposed during machining.
Causes
 Low pouring temperature.
 Gases blowing from the mould.
 Excessive turbulence during pouring.
 Moisture condensed on densors and chills.
Remedies
 Use correct pouring temperature and check with
pyrometer.

Continue…
 Increase permeability of sand and check grinding.
 Warm densors and chills.
 Modify gating to reduce turbulence, use sivex
filter.

It is a void or depression in the casting caused
mainly by uncontrolled solidification.
Causes:
1. Pouring temperature is too high causing liquid
shrinkage.
2. Failure to supply liquid feed metal.
3. Pre mature solidification.
Remedies :
Apply principles of casting, reduce the
pouring temperature and provide adequate
risers, feeders, which supply the molten metal to
compensate the shrinkage.

 One of the main defects is hot tearing or hot
cracking, or hot shortness. Irrespective of the name,
this phenomenon represents the formation of an
“irreversible failure (crack) in the still
semisolid casting.”
 Cause:
The inadequate compensation of solidification
shrinkage by melt flow in the presence of thermal
stresses.
 Remedy
 Avoid excessive ramming.
 Controlled ramming should be done.

Hot Tears
ME 6222: Manufacturing Processes and Systems 7
Prof. J.S. Colton

Castings not fully form heaving lines or seam of
discontinuity or holes with rounded edges through
casting walls.
Causes:
 Incomplete fusion where two streams of metal
meat.
 Metal freezes before mold is filled.
 Die too cold.
Remedies:
 Increase pouring temperature.
 Increase die temperature or improve venting.
 Increase permeability of sand.

Casting Defects
ME 6222: Manufacturing Processes and Systems 6
Prof. J.S. Colton

Sand Testing
•
•
•
•
•
Molding sand and core sand depend upon shape, size composition and distribution
of sand grains, amount of clay, moisture and additives.
The increase in demand for good surface finish and higher accuracy in castings
necessitates certainty in the quality of mold and core sands.
Sand testing often allows the use of less expensive local sands. It also ensures
reliable sand mixing and enables a utilization of the inherent properties of molding
sand.
Sand testing on delivery will immediately detect any variation from the standard
quality, and adjustment of the sand mixture to specific requirements so that the
casting defects can be minimized.
It allows the choice of sand mixtures to give a desired surface finish. Thus sand
testing is one of the dominating factors in foundry and pays for itself by obtaining
lower per unit cost and.

• 1. Moisture content test
• 2. Clay content test
• 3. Grain fitness test
• 4. Permeability test
• 5. Strength test
• 6. Refractoriness test
• 7. Mould hardness test

Moisture Content Test
•
•
•
•
•
•
•
•
•
•
Moisture is the property of the moulding sand it is defined as the amount of water present in
the moulding sand. Low moisture content in the moulding sand does not develop strength
properties. High moisture content decreases permeability.
Procedures are:
1.20 to 50 gms of prepared sand is placed in the pan and is heated by an infrared heater bulb
for 2 to 3 minutes.
2. The moisture in the moulding sand is thus evaporated.
3. Moulding sand is taken out of the pan and reweighed.
4.The percentage of moisture can be calculated from the difference in the weights, of the
original moist and the consequently dried sand samples.
Percentage of moisture content = (W1-W2)/(W1) %
Where, W1-Weight of the sand before drying,
W2-Weight of the sand after drying

• Clay Content Test
• Clay influences strength, permeability and other moulding properties. It is
responsible for bonding sand particles together.
• Procedures are:
• 1. Small quantity of prepared moulding sand was dried
• 2. Separate 50 gms of dry moulding sand and transfer wash bottle.
• 3. Add 475cc of distilled water + 25cc of a 3% NaOH.
• 4. Agitate this mixture about 10 minutes with the help of sand stirrer.
• 5. Fill the wash bottle with water up to the marker.
• 6. After the sand etc., has settled for about 10 minutes, Siphon out the water from
the wash bottle.
• 7. Dry the settled down sand.
• 8. The clay content can be determined from the difference in weights of the initial
and final sand samples.
• Percentage of clay content = (W1-W2)/(W1) * 100
• Where, W1-Weight of the sand before drying,
• W2-Weight of the sand after drying.

• Grain fitness test:
• The grain size, distribution, grain fitness are determined with the help of the fitness
testing of moulding sands. The apparatus consists of a number of standard sieves
mounted one above the other, on a power driven shaker.
• The shaker vibrates the sieves and the sand placed on the top sieve gets screened
and collects on different sieves depending upon the various sizes of grains present
in the moulding sand.
• The top sieve is coarsest and the bottom-most sieve is the finest of all the sieves. In
between sieve are placed in order of fineness from top to bottom.
• Procedures are:
• 1. Sample of dry sand (clay removed sand) placed in the upper sieve
• 2. Sand is vibrated for definite period
• 3. The amount of same retained on each sieve is weighted.
• 4. Percentage distribution of grain is computed.

• Flowability Test
• Flowability of the molding and core sand usually determined
by the movement of the rammer plunger between the fourth
and fifth drops and is indicated in percentages.
• This reading can directly be taken on the dial of the flow
indicator.
• Then the stem of this indicator rests again top of the plunger of
the rammer and it records the actual movement of the plunger
between the fourth and fifth drops.

• Permeability Test
• Permeability test:
• The quantity of air that will pass through a standard specimen of the sand at a
particular pressure condition is called the permeability of the sand.
• Following are the major parts of the permeability test equipment:
• 1. An inverted bell jar, which floats in a water.
• 2. Specimen tube, for the purpose of hold the equipment
• 3. A manometer (measure the air pressure)

• Steps involved are:
• 1. The air (2000cc volume) held in the bell jar is forced to pass through the sand
specimen.
• 2. At this time air entering the specimen equal to the air escaped through the
specimen
• 3. Take the pressure reading in the manometer.
• 4. Note the time required for 2000cc of air to pass the sand
• 5. Calculate the permeability number
• 6. Permeability number (N) = ((V x H) / (A x P x T))
• Where,
• V-Volume of air (cc)
• H-Height of the specimen (mm)
• A-Area of the specimen (mm2)
• P-Air pressure (gm / cm2)
• T-Time taken by the air to pass through the sand (seconds)

• Refractoriness Test
• The refractoriness of the molding sand is judged by heating the American Foundry
Society (A.F.S) standard sand specimen to very high temperatures ranges
depending upon the type of sand.
• The heated sand test pieces are cooled to room temperature and examined under a
microscope for surface characteristics or by scratching it with a steel needle.
• If the silica sand grains remain sharply defined and easily give way to the needle.
Sintering has not yet set in.
• In the actual experiment the sand specimen in a porcelain boat is p1aced into an
e1ectric furnace.
• It is usual practice to start the test from l000°C and raise the temperature in steps of
100°C to 1300°C and in steps of 50° above 1300°C till sintering of the silica sand
grains takes place.
• At each temperature level, it is kept for at least three minutes and then taken out
from the oven for examination under a microscope for evaluating surface
characteristics or by scratching it with a steel needle.

• The refractoriness is used to measure the ability of the sand to withstand the higher
temperature.
• Steps involved are:
• 1. Prepare a cylindrical specimen of sand
• 2. Heating the specimen at 1500 C for 2 hours
• 3. Observe the changes in dimension and appearance
• 4. If the sand is good, it retains specimen share and shows very little expansion. If
the sand is poor, specimen will shrink and distort.

• Strength Test
• Green strength and dry strength is the holding power of the various bonding
materials.
• Generally green compression strength test is performed on the specimen of green
sand (wet condition).
• The sample specimen may of green sand or dry sand which is placed in lugs and
compressive force is applied slowly by hand wheel until the specimen breaks.
• The reading of the needle of high pressure and low pressure manometer indicates
the compressive strength of the specimen in kgf/cm2.
• The most commonly test performed is compression test which is carried out in a
compression sand testing machine

• Measurements of strength of moulding sands can be carried out on the universal
sand strength testing machine. The strength can be measured in compression, shear
and tension.
• The sands that could be tested are green sand, dry sand or core sand. The
compression and shear test involve the standard cylindrical specimen that was used
for the permeability test.

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• Mould hardness test:
• Hardness of the mould surface can be tested with the help of an “indentation
hardness tester”. It consists of indicator, spring loaded spherical indenter.
• The spherical indenter is penetrates into the mould surface at the time of testing.
The depth of penetration w.r.t. the flat reference surface of the tester.
• Mould hardness number = ((P) / (D – (D2-d2))
• Where,
• P- Applied Force (N)
• D- Diameter of the indenter (mm)
• d- Diameter of the indentation (mm)

Inspection of Casting
• Visual Inspection
• Dimensional inspection
• Sound test
• Impact test
• Pressure test
• Magnetic particle testing
• Penetrant test
• Ultrasonic test

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