UNIT 1 - CASTING
BY
V.KAMALA
Assistant Professor,
DOIE, Anna University,
Chennai.
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A foundry is:
A factory that pours molten metal into molds,
producing cast metal objects.
Some
typical cast
metal
objects:
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Engine blocks,
axles
Turbine blades
in jet engines
Aluminum
pots
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CASTING
PATTERN
A copy of the shape you want to
produce, made of wood, plastic or
metal
SAND,
Mixed With Clay Binder &
Water (So It Will Hold Its
Shape) Plus Coal Dust To
Improve Surface Finish
Container of molten metal
(filled from furnace)
Top and bottom mold forms
(made of metal, open at top and bottom)
Rammer (tool to compact the sand;
often a pressing machine is used)
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A very basic summary of the sand casting process. . .
First of all,
Mix the sand.
THEN
MOLDING:
MOLDING:
Sand placed into
bottom mold
form &
compacted
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2 Pattern placed into mold
MOLDING: Add
the top mold
form
A tube or pipe provides
a path to pour the
metal in
Pattern is still inside!
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MOLDING: Fill top form
with compacted sand.
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In the middle of the
sand is a cavity shaped
like the pattern!
MOLDING: Take
the top mold off
and remove
pattern & pipe
or post
Pouring
hole
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MOLDING: Replace the
top mold and fasten
securely!
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CASTING:
Pour the metal (container is filled
from furnace immediately before
you are ready to pour)
Wait for the metal to cool
(minutes to days,
depending on the size of
the casting)
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A copy of the pattern
has now been made
in metal
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CLEANING. Sand is
cleaned off the part, the
tab where metal flowed
in must be removed.
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SHAKE OUT: Break apart the two
halves of the mold & take out the
partusually requires vibrating or
striking the mold to break apart the
sand
10 Mold forms are reused
Sand is broken up,
11 screened to remove debris
and clumps, and sent for
remixing
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It is the process of making metal
parts, by pouring molten metal in
to the cavity of the required
shape and allowing it to solidify !
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CASTING TERMINOLOGY
FLASK
The frame and support
COPE
The upper half of sand
mold
DRAG
The lower half of the sand
mold
PATTERN
Shape used to mold the
shape of the casting
POURING BASIN
Orifice where molten metal
is poured into the mold
SPRUE
Vertical channel through
which molten metal flows
downward into mold
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CASTING TERMINOLOGY
RUNNERS
Channels that carry molten
metal from sprue to mold
RISER
Reservoirs to supply the
molten metal needed to make
up shrinkage losses during
solidification.
GATE
Portion Of Runner Through
Which The Molten Metal
Enters The Mold Cavity, Used
To Trap Contaminants.
VENTS
Openings used to carry off
gases given off by the metal
and exhaust air.
CORES
Insets
used
to
produce
interior cavities.
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Patternmaking
Core making
Molding
Melting and pouring
Cleaning
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A pattern is made of wood or metal, is a replica of the final
product and is used for preparing mould cavity
Mould cavity should posses refractory characteristics and
with stand the pouring temperature.
When the mold is used for single casting, it made of sand and
known as expendable mold.
When the mold is used repeatedly for number of castings and
is made of metal or graphite are called permanent mould.
For making holes or hollow cavities inside a casting, cores
made of either sand or metal are used.
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Several types of furnaces are available for melting
metals and their selection depends on the type of
metal, the maximum temperature required and the
rate and the mode of molten metal delivery.
Before pouring provisions are made for the escape of
dissolved gases. The gating system should be designed
to minimize the turbulent flow and erosion of mould
cavity. The other important factors are the pouring
temperature and the pouring rate.
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The properties of the casting significantly
depends on the solidification time cooing rate.
Shrinkage of casting, during cooling of
solidified metal should not be restrained by the
mould material, otherwise internal stresses
may develop and form cracks in casting.
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After the casting is removed from the
mould it is thoroughly cleaned and the
excess material usually along the parting
line and the place where the molten
metal was poured, is removed using a
potable grinder.
White light inspection, pressure test,
magnetic
particle
inspection,
radiographic test, ultrasonic inspection
etc. are used
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It is a Replica Model of the final object
with some modifications.
Shape and size of the pattern is made
larger than the final casting to
compensate the volume reduction
occurred during the conversion of high to
low temperature.
It is made up of wood, metal and plastics.
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Size and complexity of the shape
Number of components produced
Method of castings to be used
Dimensional Accuracy
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Made of single solid piece without joints
most inexpensive of all types of patterns
Low quantity production
Made up of wood
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Made into two parts
One part is used to produce the lower half of
the mould, Other part is used to produce the
upper half of the mould
Two parts are assembled together in correct
position by pins
Line separating the two parts is called parting
line
Used for making symmetrical shaped castings
Eg. Cylinders , Bearings, Pulleys
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Pattern is made into two halves mounted
on both sides of a plate.
Match plate is accurately placed between
the cope and drag.
Many patterns can be mounted on the
same plate.
Little hard work
Eg. Piston rings of I.C Engine
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Patterns are made larger then the
required castings
Purpose of compensating the metal
shrinkage,
to provide extra metal which is to be
removed during machining,
for easy with drawl of pattern from the
mould.
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Shrinkage allowance
Machining or finish allowance
Draft or taper allowance
Distortion or camber allowance
Rapping or shake allowance
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1. SHRINKAGE ALLOWANCE
All most all cast metals shrink or contract
volumetrically on cooling. The metal shrinkage is of
two types:
Liquid Shrinkage: it refers to the reduction in
volume when the metal changes from liquid state
to solid state at the solidus temperature. To
account for this shrinkage; riser, which feed the
liquid metal to the casting, are provided in the
mold.
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Material
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Dimension
Shrinkage allowance
(inch/ft)
Grey Cast Iron
Up to 2 feet
2 feet to 4 feet
over 4 feet
0.125
0.105
0.083
Cast Steel
Up to 2 feet
2 feet to 6 feet
over 6 feet
0.251
0.191
0.155
Aluminum
Up to 4 feet
4 feet to 6 feet
over 6 feet
0.155
0.143
0.125
Magnesium
Up to 4 feet
Over 4 feet
0.173
0.155
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The casting shown is to be made in cast
iron using a wooden pattern. Assuming
only shrinkage allowance, calculate the
dimension of the pattern. All Dimensions
are in Inches
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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.
Pattern material
Height of the
given surface
(inch)
Draft angle
(External
surface)
Draft angle
(Internal
surface)
1
1 to 2
2 to 4
4 to 8
8 to 32
3.00
1.50
1.00
0.75
0.50
3.00
2.50
1.50
1.00
1.00
1
1 to 2
Metal and plastic 2 to 4
4 to 8
8 to 32
1.50
1.00
0.75
0.50
0.50
3.00
2.00
1.00
1.00
0.75
Wood
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During machining some of the metal is removed from
the casting, for this purpose the pattern is made larger
than the required casting.
The amount of finish allowance depends on the
material of the casting, its size ,volume of production,
method of moulding etc.
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Metal
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Dimension (inch)
Allowance (inch)
Cast iron
Up to 12
12 to 20
20 to 40
0.12
0.20
0.25
Cast steel
Up to 6
6 to 20
20 to 40
0.12
0.25
0.30
Non ferrous
Up to 8
8 to 12
12 to 40
0.09
0.12
0.16
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The casting shown is to be made in cast
iron using a wooden pattern. Assuming
only machining allowance, calculate the
dimension of the pattern. All Dimensions
are in Inches.
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The casting will distort or wrap during cooling
if it has irregular shape, flat long casting
surface or V shape and also all the parts do
not shrink uniformly.
Due to distortion ,the casting will not get the
required shape.
To avoid this ,the shape of the pattern is
slightly bent into the opposite direction.
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To take the pattern out of mould cavity it is
slightly rapped or shaked to detach it from
the mould cavity.
To avoid this the pattern is made slightly
smaller.
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Design of casting
Number of castings to be produced
Degree of accuracy and surface finish
required
Shape, complexity and size of the
castings
Castings or moulding methods adopted
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Advantages:
Inexpensive
Easily available in large quantities
Easy to fabricate
Light in weight
They can be repaired easily
Easy to obtain good surface finish
Limitations:
Susceptible to shrinkage and swelling
Possess poor wear resistance
Abraded easily by sand action
Absorb moisture, consequently get wraped
Cannot withstand rough handling
These are used where the no. of castings to be
produced is small and pattern size is large.
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Advantages:
Do not absorb moisture
More stronger
Possess much longer life
Do not wrap, retain their shape
Greater resistance to abrasion
Accurate and smooth surface finish
Good machinability
Limitations:
Expensive
Not easily repaired
Ferrous patterns get rusted
Heavy weight
These are employed where large no. of
castings have to be produced from same patterns.
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Advantages:
Durable
Provides a smooth surface
Moisture resistant
Does not involve any appreciable change in size or
shape
Light weight
Good strength
Wear and corrosion resistance
Easy to make
Abrasion resistance
Good resistance to chemical attack
Limitations:
Plastic patterns are Fragile
Advantages:
It can be easily worked by using wood
working tools.
Intricate shapes can be cast without any
difficulty.
It has high compressive strength.
Advantages:
Provide very good surface finish.
Impart high accuracy to castings.
After being molded, the wax pattern is not
taken out of the mould like other patterns;
rather the mould is inverted and heated; the
molten wax comes out and/or is evaporated.
Thus there is no chance of the mould cavity
getting damaged while removing the pattern.
It maintains shape at very high
temperature
It makes a mould porous
It is inexpensive
It mainly consist of
Refractory sand
Binder
Additives
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Silica sand is most commonly used base
sand.
Other base sands that are also used for
making mold are zircon sand, Chromite
sand, and olivine sand.
Silica sand is cheapest among all types of
base sand and it is easily available.
GREEN SAND
DRY SAND
LEAN SAND
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CO2 sand
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Binders are of many types such as:
1. Clay binders,
2. Organic binders and
3. Inorganic binders
Clay binders are most commonly used binding agents
mixed with the molding sands to provide the strength.
1. The most popular clay types are:
2. Kaolinite or fire clay (Al2O3 2 SiO2 2 H2O) and
Bentonite (Al2O3 4 SiO2 nH2O)
3. Of the two the Bentonite can absorb more water
which increases its bonding power.
4. To bring the property of cohesiveness
To improve the properties like strength,
refractoriness and permeability.
To give a good surface finish.
Sea Coal
Silica flour
sawdust
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REFRACTORINESS
POROSITY or PERMEABILITY
STRENGTH or COHESIVINESS
PLASTICITY or FLOWABILITY
FINENESS
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It is the ability of the molding material to
with
stand
high
temperatures
(experienced during pouring) with out
1. Fusion,
2. Cracking, buckling or scabbing,
3. Experiencing any major physical
change.
Silica sand have high refractoriness.
During pouring and subsequent solidification of a
casting, a large amount of gases and steam is
generated.
These gases are those that have been absorbed by the
metal during melting, air absorbed from the
atmosphere and the steam generated by the molding
and core sand.
If these gases are not allowed to escape from the
mold, they would be entrapped inside the casting and
cause casting defects.
To overcome this problem the molding material must
be porous.
Proper venting of the mold also helps in escaping the
gases that are generated inside the mold cavity.
The molding sand that contains moisture is
termed as green sand.
The green sand particles must have the
ability to cling to each other to impart
sufficient strength to the mold.
The green sand must have enough strength
so that the constructed mold retains its
shape.
Green strength helps in making and handling
the moulds.
It is the ability of the molding sand to get
compacted to a uniform density.
Flowability assists molding sand to flow
and pack all-around the pattern and take
up the required shape.
Flowability increases as clay and water
contents increase.
Finer sand mould resist metal penetration
and produce smooth casting surfaces.
Fineness and permeability are in conflict with
each other and hence they must be balanced
for optimum results.
MIXING OF SAND Mixing of sand ,
Binder and moisture
TEMPERING OF SAND Spraying of
water
CONDITIONING OF SAND - controlling
the moisture
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1. Moisture content test
2. Clay content test
3. Grain finenss test
4. Permeability test
5. Refractoriness test
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1. A Measured Quantity 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.
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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
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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 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 = (W1W2)/(W1) * 100
Where, W1Weight of the sand before drying,
W2Weight of the sand after drying
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
Grain fineness test:
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
bottommost sieve is the finest
of all the sieves. In between sieve
are placed in order of fineness
from top to bottom.
AFS grain Fineness number
= Wi Fi/ Fi
Wi =Multiplication factor
Fi = Retained sample
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
An inverted bell jar, which floats in a water.
Specimen tube, for the purpose of hold the equipment
A manometer (measure the air pressure)
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)
The refractoriness is used to measure the ability of to sand to
with stand 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
MOULDING TOOLS
SHOVEL
RIDDLE
RAMMER
TROWEL
SLICK
STRIKE OFF BAR
LIFTER
VENT WIRE
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SPRUCE PIN
RISER PIN
GATE CUTTER
DRAW SPIKE
SWAP
MALLET
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Ramming the moulding sand
Rapping the pattern fro easy removal
Removing the pattern from the sand
JOLTING MACHINE
SQUEEZING MACHINE
SAND SLINGER
JOLTING MACHINE
Pattern is placed in
the flask on the
table
The table with flask
is raised about
80mm and
suddenly dropped
It is mainly used
for horizontal
surface
Operations is noisy
because of jolting
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SQUEEZING MACHINE
Moulding sand in the flask
is squeezed between the
machine table and
squeezer head
The mould board is
clamped on the table
The flask is placed on the
mould board
The pattern is placed
inside the disk
The table is raised by table
left mechanism against the
squeezer head
After the squeezing is over,
the table comes down to
the starting position
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SAND SLINGER
Pattern is placed on a
board
Flask is placed on it
The slinger has an
impeller rotates at
different speeds
It throws a stream of
sand at great velocity
into the flask
Slinger can be moved to
pack the sand uniformly
around the pattern.
Ramming will be uniform
with good strength
Used for large and
medium size moulds
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A core is a body made of refractory
material which is set in to the prepared
mould before closing and pouring it, for
forming through holes, projections and
internal cavities.
CORE MAKING MATERIALS
Core Sand
Refractories like silica
sand ,zircon, liven etc
Binders
Vegetable oil, core
flour, resins water, fire
clay, urea.
Additives
Wood flour, coal
powder, seal coal,
graphite etc.,
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Sand core is usually made of river sand mixed
with a binder.
Sand is weighed and put into the Muller.
Dry binders are filled in the Muller.
Muller is started and allowed to work for a
little time.
Weight quantity of water is added to dry
mixture.
After some time , the binder is added.
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CORE BOXES
HALF CORE BOX
DUMP OR SLAB CORE BOX
SPLIT CORE BOX
STRICKLE CORE BOX
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HALF CORE BOX
Used to make one half
of the symmetrical core
pieces
After baking, two core
pieces will be pasted to
form the full core
DUMP OR SLAB CORE
BOX
Used for making a full
core
Used for making slab or
rectangular cores
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CORE BOXES
SPLIT CORE BOX
Two similar half boxes
Box is assembled in correct
position by dowel pins before
filling the sand
Boxes are separated after
ramming the sand
STRICKLE CORE BOX
Dump core box is filled up
with core sand
Strickle board is pressed and
swiped to form the profile
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Ovens Are Used For Heating The Cores To
Obtain The Hardness
BATCH TYPE OVENS
CONTINUOUS TYPE OVENS
DIELECTRIC BAKING OVENS
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BATH TYPE OVENS
Small and medium
cores are baked
These are fired with
coal or oil
It has several drawers
Each drawer is loaded
with batch of cores
Cores are heated batch
by batch
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CONTINUOUS TYPE OVEN
Heating is done continuously
Cores are loaded on a conveyor
at one side of the oven and it
moves slowly inside the oven
Cores are heated ,after that
unloaded from the other side
Heating time is controlled by
conveyor speed
It is suited for mass production
The temperature of the oven
varies from 2500 c to 2700c
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DIELECTRIC BAKING OVEN
Two parallel electrodes
Cores are placed in
between electrodes
High frequency current
is supplied to the
electrodes to heat the
electrodes uniformly
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According to the state of core
Green sand core
Dry sand core
According to the position of the core
Horizontal core
Vertical core
Balanced core
Hanging core
Drop core
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GREEN SAND CORE
It is formed by pattern itself
Green sand core is made out of
the same sand from which the
rest of the mould has been made
DRY SAND CORE
It is made separately
positioned in the mould
and
HORIZONTAL CORE
Placed horizontally in the mould
It may have any shape depending
on the design
It is supported in the core seats at
the ends
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VERTICAL CORE
It is positioned vertically in
the mould
Ends of the cores rest on
core seats in core and drag
HANGING CORE
These are supported above
and hang into the mould
No support from the
bottom
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BALANCING CORE
Core is supported and
balanced from its end
It requires a long core seat
so that core does not sag or
fall into the mould
It is used when the blind
holes along a horizontal
axis are to be produced
DROP CORE
This core is used when a
hole is not in line with the
parting surface is to be
produced at a lower surface
Hole may be above or
below the parting line of
the mould
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Melting is an equally important parameter for
obtaining a quality castings. A number of furnaces can
be used for melting the metal, to be used, to make a
metal casting. The choice of furnace depends on the
type of metal to be melted. Some of the furnaces used
in metal casting are as following:.
Crucible furnaces
Cupola
Induction furnace
Rotatory
Reverberatory furnace
ADVANTAGES OF CUPOLA
Simple design and easier construction
Low initial cost as compared to other furnaces of same
capacity
Simple to operate and maintain in good condition
Less floor space requirements as compared to those of
other furnaces of capacity
Cupola can be continuously operated for many hours.
Electric Power is not required.
Offer very high melting rate ( 1 to 35 tons per hour)
High Power Consumption
High installation costs
Shell casting
Investment casting
Ceramic mould
Lost Wax process
Pressure die casting
Centrifugal casting
CO2process
