METAL CASTING PROCESSES

ME8351 MANUFACTURING TECHNOLOGY 1
UNIT 1 METAL CASTING PROCESS
S.BALAMURUGAN
ASSISTANT PROFESSOR
MECHANICAL ENGINEERING
AAA COLLEGE OF ENGINEEERING & TECHNOLOGY

Steps in Casting Process
• Melting the metal
• Pouring it into a previously made mould which will give the shape for
the part
• Allowing the molten metal to cool & Solidify in the mould
• Removing the solidified component from the mould, cleaning it &
subjecting it to further treatment.
• The solidified piece of metal, which is taken out of the mould is called
Casting.
• A plant where the castings are made is called, Foundary. It is a
collection of necessary tools, materials & equipment to produce casting.
Foundry – Latin word – fundere – Melting & Pouring
CASTING PROCESS
ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET

CLASSIFICATION OF CASTING PROCESS
CASTING PROCESS
Expendable
Mould Casting
Permanent
Pattern, Sand
Casting
Expendable
Pattern,
Investment
Casting
Non Expendable
(Permanent) Mould casting
Die casting, Centrifugal casting,
Continuous casting
Permanent
Core (Metal
Core)
Semi-Permanent
Core (Sand Core)

SAND MOULD CASTING• This process accounts 80% of the total output of cast products.
• Single cast moulds – completely destroyed for taking out the casting – Knockout.
• Moulding material – Sand – To improve the cohesive strength & Mouldability,
Small amount of Binder, Additives & Water is added.
• To make mould, the moulding material will have to be consolidated & contained
around the pattern. The metallic container is called Flask.
• One flask design – Pit Moulding process, Full mould process (Evaporative pattern)
Types of Sand mould casting process
• Bench Moulding – For small work
• Floor moulding – Done on the foundary floor – Medium sized casting
• Pit Moulding – for Large size casting – Pit will be created in the floor(Drag) – Top flask is placed
over the pit – the walls of the pit, Brick lined & Plastered with Loam sand – Bottom of the pit is
rammed with a 50-80mm layer of coke to improve permeability – Vent pipes are run from this
layer to side surface – Coke is covered with Blacking sand

GATING SYSTEM
Pouring basin: A small funnel shaped cavity at the top of the mold into which
the molten metal is poured.
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.
Runner: The channel through which the molten metal is carried from the sprue
to the gate.
Gate: A channel through which the molten metal enters the mold cavity.
Riser: A column of molten metal placed in the mold to feed the castings as it
shrinks and solidifies. Also known as “feed head”.
Splash core: A ceramic splash core placed at the end of the sprue also reduces
the eroding force of the liquid metal stream.
Choke: The part having small cross sectional area, to control the rate of metal
flow to lower the flow velocity in the runner, to hold back slag & foreign material

Bars & Gaggers: With large cope flasks, added support is normally required to
keep the moulding sand from falling out when the cope is raised t remove the
pattern. This support is provided by this components.
Skim Bob: To prevent heavier and lighter impurities skim bob is used. Skin bob
does not allow to impurities to reach mould cavity.
Chaplets: Chaplets are used to support the cores inside the mold cavity to take
care of its own weight and overcome the metallostatic force.
Vent: Small opening in the mold to facilitate escape of air and gases.
Chills: Metal plates, with special
heat removing devices which are
used to remove the heat quickly at
places where harder structures are
required.

PATTERNS
• Element used for making cavities in the
mould.
• Not an exact replica, Slightly larger than
the desired casting, due to the various
allowances.
• Consists of projections or bosses called
core prints.(It is an open space provided
in the mould for locating, positioning and
supporting the core)
REQUIREMENTS
• Secure the desired shape & size of casting
• Cheap & readily repairable
• Having high strength & long life in order to
make as many moulds as required.
• Surface should be smooth & wear
resistant. Light in weight
Pattern Materials – Wood, Metal,
Plastic.
Piece & Short production – Wood,
10 – 500 parts per lot.
Mass production – Metal, Mostly
Continuos production, 1,00,000
parts per year, Standardized parts –
Nuts, Bolts, Washers
Batch Production – Plastics, 300
parts per lot, Annual production-
2500 to 1,00,000 parts

Pattern Materials
Wood
• It should be dried & seasoned.
• It should not contain more than 10% moisture to avoid warping.
• It should be straight grained & free from knots.
▪ White pine – Straight grain, soft , easy to work
▪ Mahogany – Harder & more durable than white pine.
▪ Maple, Birch & Cherry – Harder & heavier than white pine, used for
small patterns.
Advantages
• Light in weight, inexpensive, Workability
• Holds well vanishes & Paints
Disadvantages
• Absorbs & gives of moisture, it varies the volume of the part. This
drawback can be eliminated by drying, seasoning it & then gives coats of
water proof vanishes & paints.
• Poor wear & Abrasion resistance
• Can’t withstand rough handling

Pattern Materials
Metal – Prepared using master wood pattern or machining.
Advantages
• Durable, Accurate in size, Smooth surface
• Resistant to wear, abrasion & swelling
Disadvantges
• Ferrous pattern can get rusted
• Expensive, Heavier than wood
Materials
Cast iron – Heavier, difficult to work, Cheaper, More durable
Brass – Easily worked & built up by soldering or brazing – Expensive – Used
for small cast parts
Aluminium – light in weight, corrosion resistant, easily worked, best pattern
material – Shrinkage & wear by abrasive action

Plastic patterns – Made by
• Injection moulding process
• Utilizing laminated construction by building successive layers of resin
& glass fibre
• By pouring glass material into a Plaster mould
Advantages
• Make it more economical in cost & labour
• Mouding sand sticks less to plastc than woood
• No moisture absorption
• Smooth surface of patterns
Finishing of Pattern
• Patterns should be finished by sanding, it erases the tool marks &
irregularities
• Then 2 to 3 coats of shellac, it fills up the pores & gives smooth finish
• Good quality enamel paint should be applied on the pattern
Pattern Materials

PATTERN
SINGLE PIECE PATTERN
• Job is very simple and does not create
any withdrawal problems.
• Small-scale production or in prototype
development.
• This type of pattern is expected to be
entirely in the drag and one of the
surface is expected to be flat which is
used as the parting plane.
• A gating system is made in the mold by
cutting sand with the help of sand tools.
• Most inexpensive of all types of patterns.
• It is often used for the generation of
large castings such as stuffing box of
steam engine and for creating simple
shapes, flat surfaces like simple
rectangular blocks

TWO PIECE PATTERN
It is split along the parting surface, One half of the pattern is molded
in drag and the other half in cope.
The two halves of the pattern must be aligned properly by making
use of the dowel pins, which are fitted, to the cope half of the
pattern.
These dowel pins match with the precisely made holes in the drag
half of the pattern.
Widely used type of pattern for intricate castings. It is used in
applications where it is very difficult to withdraw casting from the
mold.
Applications: It is used in AK-47. It is widely used in steam valves.
PATTERN

LOOSE PIECE PATTERN
• If solid pattern has projections or backdrafts which lie above
or below the parting line, it is impossible to with draw it from
the mould.
• For this, the projections are made with the help of loose
pieces
• A loose piece is attached to the main body of the pattern by
a pin or with a dovetail slide
• First, sand is rammed securely around the loose pieces,
then the pins are removed, again sand is packed & rammed
around the total pattern.
• First, Main pattern drawn, then loose piece drawn from the
mould.
GATED PATTERN
• Used to make multiple components inside the single mold.
• It is nothing but the pattern consisting one or more patterns.
• For joining different patterns gates are used. These are
loose patterns where gates and runners have already
attached.
• These patterns are very expensive. Due to their high cost
they are used for creating small castings.
PATTERN

MULTI PIECE PATTERN
• Sometimes castings have very difficult and
complicated designs.
• In such difficult situations multi piece types
of patterns are used. 3 or more patterns are
included in multi piece pattern.
• Three- piece pattern - Multi piece pattern.
• This three- piece pattern consists of top,
bottom and middle parts. The bottom part is
drag, top part is cope where the middle part
is termed as check box.
SWEEP PATTERN
• It consists of three parts spindle, base and
sweep which is wooden board.
• This wooden board of proper size is to be
rotated about one edge to shape the cavity as
circular or rotational symmetry.
• Requires less time.
• Spindle is directed in vertical direction and
base is attached with sand.
PATTERN

MATCH PLATE PATTERN
• A split pattern having the cope & drag portion mounted on
opposite sides of plate, called the Match plate.
• The gate & runners are mounted on the match plate, so very little
hand work is required.
• Higher productivity
• Used for large castings
• Several patterns can be mounted on the match plate, if the
casting is small.
• This will be done in a moulding machine.
• Applications – Piston rings if I.C engines
PATTERN

PATTERN
COPE & DRAG PATTERN
• It is a split pattern. This pattern has cope and drag on separate
plate.
• Cope and drag pattern has two parts which are separately molded
on molding box.
• After molding parts, these two separate parts are combined to
form the entire cavity. Cope and drag pattern is almost like two-
piece pattern.
• Used in production of large castings where the molds are very
heavy and unhandy for a user.

PATTERN
Follow Board Pattern
• In casting process some portions are structurally
weak. It is not supported properly and may be break
under the force of ramming. In this stage the special
pattern to allow the mold may be such as wooden
material.
Shell pattern
• It is specially used for obtaining hollow shaped
structure. Along the center the parting process is
done. The resultant halves produced after parting are
both doweled.
Segmental pattern
• It is used to prepare the mold of larger circular
casting to avoid the use of solid pattern of exact size
• The sweep pattern is give a continuous revolve
motion to generate the part, but the segmental
pattern itself and mold is prepared.
• In this segmental pattern construction should be
save the material for pattern make and easy carried.

REASONS FOR PROVIDING COLOURS
• To quickly identify the main pattern body & different pattern parts
• To identify the loose piece, core prints
• To visualize machined surface
RED – Cast surface to be machined
BLACK – Surface to be left unmachined
YELLOW – Core prints seats
RED STRIPS ON YELLOW BASE – Loose Piece & Seating
CLEAR OR NO COLOUR – Parting Surface
YELLOW STRIPS ON BLACK BACKGROUND – Core Prints for Machined
Castings
SUPPORTS – Black Strips on Yellow Base
PATTERN COLOURS

PATTERN ALLOWANCES
• The difference in the dimension of pattern & final product of
casting is known as Pattern Allowance.
• Factors – Composition of Alloy, Mold Material, Mold design,
Complexity of pattern, component size
Shrinkage Allowance
• Metal shrinks on solidification & contracts further on
cooling to room temperature.
• To compensate this problem, linear dimensions of the
patterns are increased.
Cast Iron, malleable iron = 10 mm/m, Steel = 20 mm/m
Aluminium, Copper, Brass = 15 mm/m
• Liquid Shrinkage – Reduction in volume of metal, when it
transforms from liquid to solid
• Phase transformation Shrinkage – During Phase Transition
• Solid shrinkage – Reduction in volume as the solid metal cool
down
• Liquid Shrinkage, Phase transformation Shrinkage are
compensated by feeding molten metal from the riser till metal
solidified.

DRAFT / TAPER ALLOWANCE
It is hard to remove casted object from pattern if it has vertical faces
as shown in fig.
Vertical faces causes a continuous contact or friction when object is
removing from the pattern.
The leading edge may break off during removal of cast, To avoid this,
vertical faces of the pattern are tapered in small known as draft angle.
Outer surface – 1 to 3 degree, Inner surface – 5 to 8 degree
Draft allowance, Hand moulding > Machine Moulding
Smaller vertical surfaces, needs more draft angle.
PATTERN ALLOWANCES

Machining Allowance
• Dimensional accuracy obtained by a casting
product are poor.
• The ferrous material would have scales on the
skin when it solidifies.
• To get dimensional accurate, a subsequent
finishing operation is required.
• It depends on the material, complexity of
surface details, type of moulding & required
surface finish.
• To reduce machining allowance, entire cast
inside the drag flask such that reducing defect
due to parting line.
Shake Allowance - Rapping Allowance
• The pattern when withdrawn from the mould it
distort the sides and shape of the cavity.
• To avoid this, the pattern is shaked to create a
small void or gap between the mould and
pattern surface for easy removal.
• This increases the size of cavity and hence to
compensate this, the size of the pattern is
slightly smaller than castings. Shake allowance
is considered as negative allowance
PATTERN ALLOWANCES

Distortion Allowances
Castings get distorted during solidification, due to their shape. U,V or L
shape, it will tend to contract at the closed end causing the vertical legs to
look slightly inclined.
This can be prevented by making the legs of the shaped pattern converge
slightly, so that distortion will have its sides vertical.
It may occur due to internal stresses, this stresses are due to unequal
cooling of different sections of the casting. To prevent this
• Modification of casting design
• Providing sufficient machining allowance to cover the distortion affect
• Providing suitable allowance on the pattern, called camber or distortion
allowance (inverse reflection)
PATTERN ALLOWANCES

MOULDING MATERIALS
Basic Moulding Material – Silica Sand, various Binders
Auxiliary Group – Additives
Constituents of Moulding Sand
Silica sand Cheap, Thermal Stability, Highly Refractory, Easily Moulded,
Reusable
Binder (Clay) • Combined with water act as a bonding agent, coating with
moist clay, the strength of the sand mix in increased.
• It imparts cohesiveness & Plasticity to the moulding sand in
the moist state & increases the strength after drying.
Additives It imparts strength, thermal stability, permeability,
refractiveness, thermal expansion to the moulding sand
Water Proper amount of water added to give a high strength with
sufficient plasticity after tempering the mould.

PROPERTIES OF MOULDING SAND
PERMEABILITY • Permeability or Porosity of the moulding sand is the
measure of its ability to permit air to flow through it.
STRENGTH OR
COHESIVENESS
• It is defined as the property of holding together of sand
grains. Moulding sand should have ample strength so
that the mould does not collapse.
REFRACTIVENESS • It is the ability of the moulding sand mixture to
withstand the heat of melt without showing any sign of
softening or fusion
PLASTICITY or
FLOWABILITY
• It is the measure of moulding sand to flow around &
over a pattern during ramming & to uniformly fill the
flask.
COLLAPSIBILITY • It permits the Moulding sand & Core to collapse easily
during shake out.
• Lack of collapsibility leads to formation of cracks in the
casting. It depends on the amount of binder.
ADHESIVENESS • It is the property of sand mixture to adhere to another
body (Moulding flask). The mould does not fall when
the flask are lifted or turned over
CO-EFFICIENT OF
EXPANSION
• Sand should have low coefficient of expansion
• How the size of an object changes with change in temp.

Sand • Natural sand – from Natural Deposits, Clay content is
higher than desired
• Synthetic Sand – Prepared by mixing a relatively clay free
with specified type of binder, water & Additives. Based on
metal to be cast, sand grains selected.
• Chemically coated sand – Clean silica sand coated with
hydrocarbon resin, which act as a binder, clay also added.
Excellent refractiveness – Clean surface can obtained
Binders Inorganic Binder – Clay – Formed by the weathering &
decomposition of rocks. Fire-Clay, Kaolinite, Bentonite,
Portland cement, Sodium Silicate
Organic Binder – Used for Core Making
Obtained from Wheat, Corn & Resins (Drying oils, linseed oil,
Soyabean oil, Pitch & Molasses)
Additives To enhance the existing Properties – Better Surface finish - To
eliminate defects.
Cereals(Corn), Saw dust, Wood Flour, Silica flour, Iron oxide
Facing Materials To obtain the smooth surface – Easy peeling of sand from
casting – Asphalt, Graphite, Pitch(distilled from soft coal)
Cushion
Materials
While pouring the molten metal, mould will expand. For getting
this kind space, Wood flour, Cereals & Cellulose added.
MOULDING MATERIALS

SAND PREPARATION & CONDITIONING
• Hand Mulling – Natural Sand
• Remove all the impurities
• Mixing of sand ingredients in dry state by Muller
• Temper the moulding sand ingredients & continue
mulling action till the uniform distribution of the
ingredients
• Aeration process – Power operated screening,
beating the sand or by passing the sand stream
over toothed belt.
• This process separates sand grains into individual
particles
• To avoid difficulties in mould making, sand is
cooled below 37°C
• Wheel is either rest on sand or 5-10mm above the
base
• Plows stir the sand & bring it under the wheels,
Wheels mix the sand with a squeezing action.

TESTING OF MOULDING SAND
Moisture
Content
Test
• Test sample is weighed 50 gm of moulding sand.
Heated for 2 hours at 110°C
• Allowed to cool to room temperature. Then
reweighing the sample.
Moisture Content=
𝑰𝒏𝒊𝒕𝒊𝒂𝒍 𝒘𝒆𝒊𝒈𝒉𝒕 −𝒇𝒊𝒏𝒂𝒍 𝒘𝒆𝒊𝒈𝒉𝒕
𝑰𝒏𝒊𝒕𝒊𝒂𝒍 𝒘𝒆𝒊𝒈𝒉𝒕
× 100
Clay
Content
Test
• Take the standard dried sand sample (50 gm)
• Mixed with distilled water & 1% NaOH solution,
stirring for 5 minutes, then allowed to settle down
10 minutes.
• This step repeated until, the water above the sand
is clean. Now the sand is dried & weighed. The
loss of weight gives the clay content.
Clay Content=
𝑰𝒏𝒊𝒕𝒊𝒂𝒍 𝒘𝒆𝒊𝒈𝒉𝒕 −𝒇𝒊𝒏𝒂𝒍 𝒘𝒆𝒊𝒈𝒉𝒕
𝑰𝒏𝒊𝒕𝒊𝒂𝒍 𝒘𝒆𝒊𝒈𝒉𝒕
× 100
Strength
Test
• UTM machine. Compressive, Shear, Tensile &
Bending Strength
• Test Specimen – 5.08cm dia × 5.08 long

TESTING OF MOULDING SAND
Permeability
Test
• Ability to permit air to flow through it.
• Test Specimen – 5.08cm dia × 5.08 long(h) ,
Volume of air(V) – 2000cm3, A – Area
• Air pressure(p) – 10gm/cm2, t - Time
• Permeability Number =
𝑽× 𝒉
𝒑 ×𝑨× 𝒕
Fineness
Test
• With the help of sieve with different size,
the size of the grains will be determined.
Completely dry & Clay free sand. 15
minutes by electric motor.
• Top – Coarse sieve, Bottom – Finest Sieve
Hardness
Test
• To check the ramming density of the sand,
prepared mould surface is tested.
• 40 – Lightly Rammed Sand, 50 – Medium,
70 – Hard Rammed Sand.

Moulding is the process of making a cavity similar to the product required in
sand.
• Selection of a mould is governed by the type of metal to be cast, size of
casting, accuracy & the surface finish of the casting.
MOULDING PROCESS
GREEN SAND MOULD • Green sand contains Silica sand,
Clay, Water & Additives.
• 10 - 15% Clay, 4 - 6% Water &
remaining Silica sand.
• Small & Medium Sized Castings
• Non ferrous metals & Alloys
ADVANTAGES
• Less time(No drying) & cost
DISADVANTAGES
• Less surface finish, Low mould
strength
• Blow hole defect

DRY SAND MOULD
• Green sand mould is dried after making the mould.
• Mixture of silica sand, coal dust, clay & molasses
DRYING
• Large size moulds – Oxy acetylene flame
• Small moulds – Oven
ADVANTAGES – Stronger than green sand mould, Long life, Permeability more
DISADVANTAGES – Time consuming, Cost high, Subjected to Hot Tear
LOAM MOULDING
• Very large castings – moulding box & Pattern can not be used due to cost
• Loam sand is a mixture of Silica sand, Graphite powder & more amount of clay.
• Initially rough frame work made by Bricks. Then loam sand is applied over the
brickwork. Plates & Bars used to reinforce the brick.
• A sweep pattern is used to get the required shape
ADVANTAGES - Large casting with less cost, good surface finish
DISADVANTAGES – Time consuming, Skilled labours
MOULDING PROCESS

BENCH MOULDING – For small work
FLOOR MOULDING – Done on the foundary floor – Medium sized casting
PIT MOULDING – For Large size casting – Pit will be created in the
floor(Drag) – Top flask is placed over the pit – the walls of the pit, Brick lined
& Plastered with Loam sand – Bottom of the pit is rammed with a 50-80mm
layer of coke to improve permeability – Vent pipes are run from this layer to
side surface – Coke is covered with Blacking sand.
SWEEP MOULDING
• Part is symmetrical about vertical axis
• Used for large & medium sized casting
• Drag on the floor, A sweep board having a shape required
MOULDING METHODS

MOULDING MACHINE
JOLTING MACHINE SAND SLINGER
Mass production – Reduce labors, increase the quality of the mould
OPERATION – 1) Ramming the moulding sand 2) Shake the pattern for easy removal
3) Removing the pattern from the sand
• Pattern is placed in the flask
• Filling of sand
• Raising the table with mouding box to
80mm & sudden drop
• Operated by pneumatic or Hydraulic
• Used for ramming horizontal surfaces
on the mould
• Noisy operation
• Pattern is placed in the flask
• Slinger is operated
• Slinger has an impeller which can be
rotated with different speeds.
• Due to rotation, impeller throws a
stream of sand at greater velocity into
the flask.
• The density of sand is controlled by the
speed of the impeller.

MOULDING MACHINE
The moulding sand in the flask is squeezed between the machine table & a squeezer head
• Mould is clamped on the table
• The flask is placed on the mouding board
• Placing of pattern in the flask
• Filling of sand in the flask
• The table is raised by the table lift
mechanism against squeezer head.
• The plate enter the sand frame & packs the
sand.
• Then the table comes down to starting point
• Pattern is placed on the mound table
• Mound table is clamped on the Ram
• The flask is placed on the frame & filled with
sand
• The table with pattern is raised up against
the squeezer head
• The flask with pattern is squeezed between
squeezer head & table
• Then the table returns to starting point

CORES
It is used to provide internal cavities, recesses, or projections in
the casting. It is usually positioned into a mould after the removal
of the pattern. It is a body of refractory material (Sand or Metal)
It is subjected to severe thermal & mechanical effects than mould, they surrounded
all side except end.
Requirements
• Strength – Based on the sand & Binder
• High Refractiveness – Increased by Thin coating of Graphite to the surface.
• Good permeability – Based on grain size & distribution of grains in the core
sand mix.
• Collapsibility – Enhanced by Oil Binders

TYPES OF CORE
BASED ON THE STATE OF CORE
GREEN SAND CORE
• It is formed by the pattern itself when it is rammed.
• It is made up of same sand as the moulding sand.
• Cores are weak, for Light Castings
DRY SAND CORE
• This core made sepeartely & then positioned in the
mould, after the pattern is taken out & before the
mould is closed.
BASED ON THE POSITION OF THE CORE
HORIZONTAL CORE
• Placed horizontally in the mould, positioned along
the parting line of the mould.
• The ends of the core rest in the seats provided by
the core prints on the pattern
VERTICAL CORE
• Positioned vertically, the two ends of the core rest
on core seats in the Cope & Drag.
• Maximum position of the core supported in drag.

BALANCED CORE
• Used for blind holes along the horizontal axis.
• Core supported at one end, this support should be
sufficient length to prevent its falling into the mould.
HANGING CORE
• This will be used, When a cored casting is to be
completely moulded in the drag, with the help of a
single piece solid pattern.
• Core is supported above & hangs into the mould
DROP CORE
• A hole which is not in line with the parting surface is
to be produced at a lower level.
KISSING CORE
• Used when a number of holes of less dimensional
accuracy is required. No core prints are provided,
No seat is available for the core.
• The core is held in position approximately between
the cope and drag and hence referred as kiss core.
TYPES OF CORE

MELTING FURNACE
• To pour the metal into the mould, the metal to be in liquid state.
• Furnace is used to melt the metal.
• Heat source – Fuel combustion, Electric Arc, Electric Resistance
• It contains a high temperature zone surrounded by a refractory wall structure
which withstands high temperature.
• Blast furnace – Basic Melting operation
• Electric Arc Furnace, Foundary Furnace – Remelting operation
SELECTION OF FURNACE
• Initial furnace cost
• Type of metal melted
• Melting & Pouring Temperature required
• Quantity & Quality of metal to be melted
According to the melting method:
Furnace for Batch Melting – Crucible Furnace, Electric Furnace, Air Furnace
Operated by Coal, Coke, Oil, Gas or Electricity
Furnace for Continuous Melting – Cupola Furnace

CRUCIBLE FURNACE
• Simplest of all furnaces, used in small foundries.
• Melting is not continuous & Large variety of metals
can be melted in small quantities.
• Melting of metal takes place inside a melting pot,
called Crucible
• Crucible is made up of Clay & Graphite

COKE FIRED FURNACES OIL FIRED FURNACES
• Installed in Pit form, Pit Furnaces
• Used for melting small quantity of
ferrous & Non-Ferrous metals
• It consists of Refractory lining
inside & Chimney at the top
• Fuel – Coke
• Natural & Artificial draught used
• Metal pieces are placed inside the
crucible.
• Crucible is placed on the coke
bed, Coke is placed around the
crucible
• Crucible is placed on a pad
• Fuel – Oil or Gas
• A mixture of Oil & Air or Gas & Air is
fed into the furnace, which burns
inside to produce the required
temperature
• While burning, the mixture enters
tangentially & encircles the crucible
• To prevent heat loss, a cover is
provided at the top
Applications – Cast iron & Non-
Ferrous Alloys in small quantity
Applications – Cast iron & Non-
Ferrous Alloys in small quantity

ELECTRIC FURNACE
APPLICATIONS – High quality Carbon
steels & Alloy steels
• First, the furnace is preheated
• Charging of Steel scraps
• The electrodes are lowered down & a
gap between the electrode & metal
charge is maintained by Automatic
control.
• Electrode are consumable
APPLICATIONS – To melt cast iron,
steel, copper & its alloys.
HEAT SOURCE
Heat radiation from arc
Hot Refractory walls of the furnace
Conduction from the hot linings when
the furnace rocks
• Used for High quality castings – Oxidation loss eliminated, Alloying elements can be added
without loss, Composition & its temperature can be controlled accurately.

CUPOLA FURNACE – CONTINUOUS MELTING
• Used for Grey Cast iron,
Nodular Cast Iron,
Copper based alloys &
Pig Iron products
• Fuel – Low suplhur
coke, Anthratic coal,
Carbon Briquettes
• Cylindrical shell, Boiler
Plate, 6-10mm thick,
Cast Iron Legs
• Tuyeres are the opening
through which
pressurized air is
forced into cupola
• Air from blower, comes
through Blast pipe &
enters a chamber called
Wind Box

PREPARATION OF CUPOLA
• The bottom door is dropped to open, to remove
the slag, coke & iron, which is left in the previous
melting operation.
• Repairing the damaged fire bricks, Refractory
lining with refractory patching mixture.
• Then bottom door is closed, tempered sand
bottom of 10cm thick slope will created to the Tap
hole.
LIGHTING THE FIRE
• To start the cupola, dry & soft wooden pieces are
placed on the rammed sand
• Coke is placed over the wooden pieces & the
wooden pieces are ignited
• Air required for combustion of coke enters from
the tuyeres
• After the well burning of initial coke, additional
coke is added to the desired height

CHARGING OF CUPOLA
• After igniting the coke bed properly, the cupola is
charged from the charging door, by using alternate
layers of limestone, iron & Coke upto the level of
charging door
• Ratio of Metal to Fuel – 4 : 1 to 12 : 1 By weight
• Metal Charge – Pig Iron 30%, Cast iron Scrap 30%, 10%
Steel Scrap & 30% Returns(Sprue, Gates, Risers)
• Charging should be completed 45 minutes to 1 hour,
before the air blast is turned on.
MELTING
• The charge is heated up with natural draft for 20-50 min
• Soaking period, Blowers are not started
• At the end soaking period, the blast is turned on & the
coke becomes fairly hot to melt the metal charge
• 10 minutes after the start of blast, Melting will start.
• By using the moulding sand bolt, the tap & slag holes
are closed
• 5 minutes for collecting the molten metal

SLAGGING & METAL TAPPING
• After the collection of Molten metal, slag hole is opened & it is removed
• The bolt inserted in the Tap hole is Knocked out & molten metal is taken out
• Air blast still continues, melting progresses & the molten iron is tapped
• The Tap hole is sealed with conical clay plug when the slag appears in the
tap hole.
• Repeating the Slagging & Tapping till metal is tapped
• Then heating finished, charging stopped & Blast is off.
• Bottom door are dropped, allow all the materials from the cupola to floor
COMBUSTION ZONE – LOT OF HEAT IS LIBERATED
C + O2 CO2 + Heat, 2Mn + O2 2MnO2 + Heat, Si + O2 SiO2+Heat
REDUCTION ZONE – REDUCES THE HEAT UPTO 1200°C
Protects the metal from oxidation, CO2 + C 2CO – Heat
MELTING ZONE - 1600°C – First Layer of Coke Bed
3Fe + 2CO Fe3C + CO2
PREHEATING ZONE – Gases CO2, CO & N2 rising upwards, 1150°C

SPECIAL CASTING PROCESS
SHELL MOULDING CASTING
Pattern creation - A two-piece metal pattern is created in the shape of the desired part,
Pattern material - Copper Alloys, Aluminum Alloy(Low Volume) or graphite for casting
reactive materials.
Mold creation - First, each pattern half is heated to 175-370°C and coated with a
lubricant to facilitate removal.
Next, the heated pattern is clamped to a dump box, which contains a mixture of sand
and a resin binder.
The dump box is inverted, allowing this sand-resin mixture to coat the pattern. The
heated pattern partially cures the mixture, which now forms a shell around the pattern.
Each pattern half and surrounding shell is cured to completion in an oven and then the
shell is ejected from the pattern.

SPECIAL CASTING PROCESS
Mold assembly - The two shell halves are joined together and securely clamped to
form the complete shell mold. If any cores are required, they are inserted prior to
closing the mold. The shell mold is then placed into a flask and supported by a backing
material.
Pouring - The mold is securely clamped together while the molten metal is poured from
a ladle into the gating system and fills the mold cavity.
Cooling - After the mold has been filled, the molten metal is allowed to cool and solidify
into the shape of the final casting.
Casting removal - After the molten metal has cooled, the mold can be broken and the
casting removed. Trimming and cleaning processes are required to remove any excess
metal from the feed system and any sand from the mold.

• CASTING MATERIALS - Alloy Steel, Carbon Steel, Cast Iron,
Stainless Steel, Aluminum, Copper, Nickel
ADVANTAGES
• Can form complex shapes and fine details
• Very good surface finish
• High production rate
• Low labor cost, Low tooling cost, Little scrap generated
DISADVANTAGES
• High equipment cost
APPLICATIONS
• Cylinder heads, connecting rods

INVESTMENT CASTING or LOST WAX PROCESS
Pattern creation - The wax patterns are typically injection molded into a metal die and
are formed as one piece. Cores may be used to form any internal features on the
pattern. Several of these patterns are attached to a central wax gating system (sprue,
runners, and risers), to form a tree-like assembly. The gating system forms the channels
through which the molten metal will flow to the mold cavity.
Mold creation - This "pattern tree" is dipped into a slurry of fine ceramic particles,
coated with more coarse particles, and then dried to form a ceramic shell around the
patterns and gating system. This process is repeated until the shell is thick enough
to withstand the molten metal it will encounter. The shell is then placed into an oven
and the wax is melted out leaving a hollow ceramic shell that acts as a one-piece mold,
hence the name "lost wax" casting.

Pouring - The mold is preheated in a furnace to approximately 1000°C and the molten
metal is poured from a ladle into the gating system of the mold, filling the mold cavity.
Cooling - After the mold has been filled, the molten metal is allowed to cool and solidify
into the shape of the final casting.
Casting removal - After the molten metal has cooled, the mold can be broken and the
casting removed. The ceramic mold is typically broken using water jets, Once removed,
the parts are separated from the gating system by either sawing or cold breaking (using
liquid nitrogen).
Finishing - Often times, finishing operations such as grinding or sandblasting are used
to smooth the part at the gates. Heat treatment is also sometimes used to harden the
final part.

ADVANTAGES
• Can form complex shapes and fine details
• Many material options
• High strength parts
• Very good surface finish and accuracy
• Little need for secondary machining
DISADVANTAGES
• Time-consuming process
• High labor cost
• High tooling cost
• Long lead time possible
APPLICATION - Turbine blades, armament parts, pipe fittings, lock parts,
jewelry

PRESSURE DIE CASTING
Die casting is a manufacturing process that can produce geometrically
complex metal parts through the use of reusable molds, called dies.
HOT CHAMBER DIE CASTING – LOW MELTING TEMP. – ZINC, TIN, LEAD
COLD CHAMBER DIE CASTING – HIGH MELTING TEMP. - ALUMINUM
TOTAL CYCLE TIME 2 SEC TO 1 MIN
CLAMPING
• Time required for close & clamp the die depends upon the machine
• Lubrication in die halves – after 3 cycles
INJECTION
•Injection time depends on materials, wall thickness of casting
•Injection pressure 68 bar to 1350 bar
•This pressure holds the molten metal in the die during solidification
COOLING
• High wall thickness requires long cooling time
• Complex geometry also requires long time – additional resistance to the
flow of heat
EJECTION - During cooling, the part shrinks & adheres to the die
TRIMMING - During cooling, the material in the channels of the die will
solidify attached to the casting. This excess material, along with any flash
that has occurred, must be trimmed from the casting.

PRESSURE DIE CASTING - HOT CHAMBER DIE CASTING
• Low melting temperatures, such as
zinc, tin, and lead.
• High temperature would damage
the pump, which is in direct
contact with the molten metal.
• The molten metal then flows into
a shot chamber through an inlet
and a plunger, powered by
hydraulic pressure, forces the
molten metal through a gooseneck
channel and into the die.
• Typical injection pressures for a
hot chamber die casting machine
are between 68 and 340 bar.
• After the molten metal has been
injected into the die cavity, the
plunger remains down, holding the
pressure while the casting
solidifies.
• After solidification, the hydraulic
system retracts the plunger and
the part can be ejected by the
clamping unit.

PRESSURE DIE CASTING – COLD CHAMBER DIE CASTING
• Used for alloys with high melting
temperatures. Aluminum, Brass,
Magnesium
• Melting of metal takes place in open
holding pot. Using ladles, molten metal
poured in the pouring hole. this holding pot
is kept separate from the die casting
machine
• The metal is poured from the ladle into the
shot chamber through a pouring hole.
Injection is usually oriented horizontally
and does not include a gooseneck channel.
• A plunger, powered by hydraulic pressure,
forces the molten metal through the shot
chamber and into the injection sleeve in the
die. Injection pressure between 135 and
1350 bar.
• After the molten metal has been injected
into the die cavity, the plunger remains
forward, holding the pressure while the
casting solidifies.
• After solidification, the hydraulic system
retracts the plunger and the part can be
ejected by the clamping unit.

GRAVITY CASTING• Permanent Mould Casting – Nonferrous metals Zinc, Copper, Aluminum, Lead, Magnesium,
Tin Alloys
• APPLICATION – Carburetor bodies, Oil pump bodies, Pistons
• Used for large number of casting
• Permanent mould is made up of heat resisting Cast Iron, Alloy Steel, Graphite.
• Pouring cup, Sprue, Riser are made in this molud itself
• First, the mould is preheated
• Refractory coating By Spraying or Brushing – Protects from Erosion & Sticking
• Molten metal is fed into the mould by Gravitational force

CONTINUOUS CASTING
• Long vertical mould, made of copper, Brass or Graphite
• Water cooled mould – molten immediately solidified
• Saw or Oxy-Acetylene flame is used to cut the casting of required length
• X-Ray unit controls the pouring rate of molten metal from ladle
• Lubricating oil is applied between casting & mould wall to reduce friction
• Argon gas applied on the top of the mould to prevent the atmospheric reaction
• The guide rolls at the bottom keep on pulling the casting to match with the cooling
rate.
• By controlling the cooling rate, the grain size & structure of metal can be regulated.
Application – Rods, Pipes, Slabs, Bars

CARBON DIOXIDE CO2 PROCESS
• In this process the sand molding mixture is
hardened by blowing gas over over the
mould.
• Carbon di oxide molding deliver great
accuracy in production.
• Suitable proportions of Silica sand &
Sodium silicate binder(3-5%) are mixed
• Addition of additives (Aluminum oxide,
Molasses)
• Placing of pattern in the drag box, Parting
sand sprinkled on the pattern surface
• Filling the sand mixture & Ramming,
Placing Sprue, Riser pin
• Passing the CO2 gas through vent holes
• Sodium silicate reacts with carbon dioxide
gas to form silica gel that binds the sand
particles together.
• Removal of Sprue, Riser & the Pattern
Na2SiO3 + CO2 Na2CO3 + SiO2
ADVANTAGES
• Good Surface Finish
• High Production runs
DISADVANTAGES
• Poor collapsibility
• Over gassing affect the
property of sand

CENTRIFUGAL CASTING
• Centrifugal casting, sometimes called rotocasting, is a metal casting process that
uses centrifugal force to form cylindrical parts.
• This differs from most metal casting processes, which use gravity or pressure to fill
the mold.
• In centrifugal casting, a permanent mold made from steel, cast iron, or graphite is
typically used. Use of expendable sand molds is also possible.

CENTRIFUGAL CASTING
1.Mold preparation - The walls of a cylindrical mold are first coated with a refractory
ceramic coating, which involves a few steps (application, rotation, drying, and baking).
Once prepared and secured, the mold is rotated about its axis at high speeds (300-3000
RPM), typically around 1000 RPM.
2.Pouring - Molten metal is poured directly into the rotating mold, without the use of
runners or a gating system. The centrifugal force drives the material towards the mold
walls as the mold fills.
3.Cooling - With all of the molten metal in the mold, the mold remains spinning as the
metal cools. Cooling begins quickly at the mold walls and proceeds inwards.
4.Casting removal - After the casting has cooled and solidified, the rotation is stopped
and the casting can be removed.
5.Finishing - While the centrifugal force drives the dense metal to the mold walls, any
less dense impurities or bubbles flow to the inner surface of the casting. As a result,
secondary processes such as machining, grinding, or sand-blasting, are required to
clean and smooth the inner diameter of the part.

Due to the high centrifugal forces, these parts have a very fine grain on the
outer surface and possess mechanical properties approximately 30% greater
than parts formed with static casting methods
ADVANTAGES
• Can form very large parts
• Good mechanical properties
• Good surface finish and accuracy
• Low equipment cost
• Low labor cost
• Little scrap generated
DISADVANTAGES
• Limited to cylindrical parts
• Secondary machining is often required for inner diameter
• Long lead time possible
APPLICATIONS - Pipes, wheels, pulleys, nozzles
CENTRIFUGAL CASTING

STIR CASTING
• It is a liquid state method of composite
materials fabrication in which a
dispersed phase(ceramic, particles,
short fibers) is mixed with a molten
matrix metal by means of mechanical
stirring.
• Metal Matrix Composite (MMC)
• First matrix material is melted
• Next reinforcement material added to
the melt.
• Finally we obtain the MMC mixture
(suitable dispersion) through stirring.
• Pouring of molten metal into the desire
cavity
ADVANTAGES
• Low cost, simple & flexible operation
• High productivity
• Very large size parts can be made

DIFFICULTIES INVOLVED IN CASTING
STEELS OVER CAST IRON
• Steel contains 2% carbon –forge by hammering without breaking
• Cast iron 2.4 – 4% carbon – more brittle – difficult to forge by hammering
• Steel
• High Melting point
• Greater shrinkage rate – Require Proper mould design – More capacity of
Risers required
• Thinner areas will cool quicker than Thicker areas leads to internal stress
points – Fracture
• Molten steel is less fluid than molten iron – Pouring & filling of mould is
difficult
• Molten steel can react with moulding sand – Unpredictable results

CASTING DEFECTS
BLOW HOLES – Appears as cavities in Casting – Due to gases & Steam formed
• Excess moisture in the mouding sand
• Core are not sufficiently Baked, Rust & Moisture on Chills, Chaplets
• Moulds are not adequately vented
POROSITY – Occurs in casting in the form of pinhole porosity
• High temperature of pouring
• Gas dissolved in metal charge
• Less amount of flux, Slow solidification
SHRINKAGE – Volumetric Shrinkage – Depression on the casting surface
• Faulty gating & riser system, Improper Chilling

CASTING DEFECTS
HOT TEARS or HOT CRACKS – It is the crack in the casting by high residual
stress. An oxidized surface showing an irregular & Ragged Appearance on the
Fracture
• Lack of Mould, Core collapsability
• Faulty mould design
• Hard Ramming of Mould
MIS RUN or COLD SHUTS -
• Lack of fluidity in molten metal (Proper Pouring Temperature)
• Faulty Design & Gating
HARD SPOTS
• In iron casting, this spots developed in casting surface, Rich in Silicon Content,
due to local chilling of those spots in Moulding sand.
• Faulty Metal Composition, Faulty Design of Casting

CASTING DEFECTS
SCABS (CUT & WASHES) - The Cavities formed on the Mould & Core surfaces due
to erosion are filled by molten metal
• Low strength of Mould & Core, Faulty Gating
• Lack of Binders in Facing & Core sand
MISMATCH & CORE SHIFT – Misalignment between two mating surfaces & Changing
their location
• Worn out or Bent clamping pins, Faulty core boxes
• Misalignment of two halves of pattern
• Improper location & support of core
SCAR - Due to improper permeability or venting.
• Scars are shallow blows that appear on a flat surface
• Blisters are scars covered with a thin layer of metal.

CASTING DEFECTS
METAL PENETRATION
Metal penetration occurs when liquid metal penetrates gaps in the molding sand. The
penetration is visible to the naked eye as a rough and uneven surface finish of the
casting.
• Use of sand with low strength and high permeability
• Use of large or coarse sand grain: the coarser the sand grains, the more severe the
metal penetration
• Lack of mold wash
• Soft ramming of sand
SWELLS - Swells are an enlargement of the casting. Swells typically take on the
shape of a slight, smooth bulge on the vertical face of castings.
• Soft ramming of the mold
• Low strength mold.
https://www.intouch-quality.com/blog/21-casting-defects-and-how-to-prevent-them-in-
your-products

DESIGN CONSIDERATION OF CASTNG PROCESS
Designs showing the importance of
maintaining uniform cross-sections in
castings to avoid hot spots and shrinkage
cavities.

The use of metal padding (chills) to
increase the rate of cooling in thick
regions in a casting to avoid
shrinkage cavities
design modifications to avoid
shrinkage cavities in castings.

Redesign of a casting by making the parting line straight to avoid defects
PLACEMENT OF PARTING LINE SHOULD BE EVEN

USE OF GOOD RIBS DESIGN TO OBTAIN IMPROVED STIFFNESS &
REDUCE WEIGHT OF CASTING

Sharp corners, edges and rapid changes
in cross section should be avoided in cast
parts. Fillets should be added to sharp
corners and edges.
Uniform Wall Thickness
Wall thickness should be kept uniform as
it helps to create high quality cast parts.
Sudden variations and geometry changes
and in wall thickness affects metal flow,
resulting in air enclosures and poor
surface finish of parts.
Draft is the taper given to core and cavity
for easy removal of casting (or pattern).
Adding proper drafts on the cast parts
improves cycle time and quality of
surfaces. The sidewalls of the castings
and other features perpendicular to the
parting line must be drafted as much as
possible.

METAL CASTING PROCESSES

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METAL CASTING PROCESSES