Metal casting process part 2

Unit –II
Casting
Part 2
Dr. L.K. Bhagi
Associate Professor
School of Mechanical Engineering
Lovely Professional University
MEC323: PRIMARY MANUFACTURING
(Dr. L K Bhagi)

Solidification
(Dr. L K Bhagi)

Solidification
Temperature as a function of time for
the solidification of pure metals. Note
that the freezing takes place at a
constant temperature.
 When the liquid metal is poured in to a
relatively cool mould, it initiates the process of
solidification.
 During this stage of solidification, the cast
develops cohesion and acquires structural
properties.
 Final properties of the cast are influenced be
casting:
1) Metallographic Structure
2) Soundness (true degree of continuity)
(Dr. L K Bhagi)

Solidification
 Metallographic structure determines inherent
properties of castings. Grain size / shape,
orientation of grains, distribution of alloying
elements, crystal structure & imperfections in
crystal structure…
 Solidification occurs in 2 stages: nucleation
& growth, and it is important to control both the
parameters…
Density as a function of time
Unit-2
Solidification animation
(Dr. L K Bhagi)

Solidification
Nucleation:
 Nucleation occurs when a particle of a stable solid forms within the molten liquid.
 Nucleation generally occurs at a temperature somewhat below equilibrium melting
point (temperature where the internal energies of the solid and liquid are equal).
 The difference between the melting point and the temperature of nucleation is known as
the amount to under cooling.
 Each nucleation event produces a crystal or grain in the final casting.
 In most cases the nucleation process utilizes existing surfaces where the solidification
can begin without the need to create full, surrounding interface. These surfaces are usually
present in the form of mould or container walls, or solid impurity particles within the
molten liquid. In some cases, additional impurities (called nucleating agents) are added to
promote nucleation, this process is called grain refinement or inoculation.
(Dr. L K Bhagi)

Solidification
Growth:
 When the evolved heat of fusion is continually extracted from the liquid material, than
growth of nucleated growth happens, promoting solidification.
 The direction , rate, and type of growth can be controlled, by the way heat is extracted.
 Directional solidification, assures sound castings.
 Faster rates of cooling generally produces products with finer grain size and superior
mechanical properties.
 The crystal growth can be accompanied by following stages:
o The formation of initial nucleus which does not have equilibrium shape,
o The transition of initial nucleus into more stable shapes: spheriodal or
ellipsoidal,
o After attaining critical radius, nuclei formation with equilibrium shape,
(Dr. L K Bhagi)

Solidification
Development of a preferred texture at a cool mold wall. Note that
only favorably oriented grains grow away from the surface of the mold
(Dr. L K Bhagi)

Solidification
Metals have well defined
melting (freezing) points, hence
they solidify at constant
temperature.
Ex:
Al – 660 oC,
Fe – 1537 oC,
W – 3410 oC
(Dr. L K Bhagi)

Solidification
Solidification of alloys
Dendrites solidification
(Dr. L K Bhagi)

(Dr. L K Bhagi)

Type of Gating system
3. Horizontal Gating System : This is used most widely. This type
is normally applied in ferrous metal's sand casting and gravity
die-casting of non-ferrous metals. They are used for flat casting,
which are filled under gravity.
(Dr. L K Bhagi)

Directional Solidification- Design Optimization
• In order to minimize the damaging effects of shrinkage, it is
desirable that the regions far from the riser (metal supply) should
solidify earlier than those near the riser in order to ensure metal
flow to distant regions to compensate shrinkage. This is achieved
by using Chvorinov’s rule.
• So, casting and mold design should be optimal: riser should be
kept far from the regions of casting having low V/A ratio.
MEC323: PRIMARY
MANUFACTURING (Dr. L K
Bhagi)

Directional Solidification- Use of Chills
• The chills increase the heat extraction.
• Internal and external chills can also be used for directional
cooling.
• For thick sections, small metal parts, with same material
as that of casting, are put inside the cavity. The metal
solidifies around these pieces as it is poured into cavity.
• For thin long sections, external chills are used. Vent holes
are made in the cavity walls or metal pieces are put in
cavity wall.
• If Chorinov’s rule can not be employed, use chills
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• A chill is an object used to promote solidification in a specific portion of
a metal casting mold.
• Normally the metal in the mold cools at a certain rate relative to thickness
of the casting.
• When the geometry of the molding cavity prevents directional
solidification from occurring naturally, a chill can be strategically placed to
help promote it.
• Internal chills are pieces of metal that are placed inside the molding cavity.
When the cavity is filled, part of the chill will melt and ultimately become
part of the casting, thus the chill must be the same material as the casting.
Note that internal chills will absorb both heat capacity and heat of
fusion energy.
• External chills are masses of material that have a high heat capacity
and thermal conductivity. They are placed on the edge of the molding cavity,
and effectively become part of the wall of the molding cavity. This type of
chill can be used to increase the feeding distance of a riser or reduce the
number of risers required.
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Chills
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• Chills can be made of many materials,
including iron, copper, bronze, aluminium,
graphite, and silicon carbide. Other sand
materials with higher densities, thermal
conductivity or thermal capacity can also be
used as a chill.
• For example, chromite sand or zircon sand can
be used when molding with silica sand
MEC323: PRIMARY
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Metal splashes during pouring and solid globules
form and become entrapped in casting
Some common defects in castings: (c) cold shot
General Defects in Casting: Cold Shot
Gating system should be improved
to avoid splashing

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Depression in surface or internal void
caused by solidification shrinkage
Some common defects in castings: (d) shrinkage cavity
General Defects: Shrinkage Cavity
Proper riser design can solve this issue

MEC323: PRIMARY MANUFACTURING (Dr. L K Bhagi)
Hot tearing/cracking in casting occurs when the
molten metal is not allowed to contract by an
underlying mold during cooling/ solidification.
Common defects in sand castings: (e) hot tearing
General Casting Defects: Hot Tearing
The collapsibility (ability to give way and allow
molten metal to shrink during solidification) of
mold should be improved

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Balloon-shaped gas cavity caused by
release of mold gases during pouring
Common defects in sand castings: (a) sand blow
Sand Blow or Blow Holes
Low permeability of mold, poor venting,
high moisture content in sand are major
reasons

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Formation of many small gas cavities at or
slightly below surface of casting
Common defects in sand castings: (b) pin holes
Sand Casting Defects: Pin Holes
Caused by release of gas during pouring
of molten metal.
To avoid, improve permeability &
venting in mold

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When fluidity of liquid metal is high, it may
penetrate into sand mold or core, causing casting
surface to consist of a mixture of sand grains and
metal
Common defects in sand castings: (e) penetration
Sand Casting Defects: Penetration
Harder packing of sand helps to alleviate this
problem
Reduce pouring temp if possible
Use better sand binders

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A step in cast product at parting line caused
by sidewise relative displacement of cope
and drag
Common defects in sand castings: (f) mold shift
Sand Casting Defects: Mold Shift
It is caused by buoyancy force of molten
metal.
Cope an drag must be aligned accurately
and fastened.
Use match plate patterns

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it is core that is displaced and the
displacement is usually vertical.
Common defects in sand castings: (g) core shift
Sand Casting Defects: Core Shift
It is caused by buoyancy force of molten
metal.
Core must be fastened with chaplet

MEC323: PRIMARY MANUFACTURING (Dr. L K Bhagi)
An irregularity in the casting surface
caused by erosion of sand mold
during pouring.
Common defects in sand castings: (h) sand wash
Sand Casting Defects: Sand Wash
Turbulence in metal flow during pouring
should be controlled. Also, very high pouring
temperature cause erosion of mold.

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Scabs are rough areas on the surface of casting
due to un-necessary deposit of sand and metal.
Sand Casting Defects: Scabs
It is caused by portions of the mold surface
flaking off during solidification and becoming
embedded in the casting surface
Improve mold strength by reducing grain size
and changing binders

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Occurs when the strength of mold is not
sufficient to withstand high temperatures
Common defects in sand castings: (j) mold crack
Sand Casting Defects: Mold Crack
Improve mold strength by reducing grain size
and changing binders

Riser Design
(Dr. L K Bhagi)

Unit-2Riser Design
The function of riser is to feed the casting during solidification, to compensate
shrinkage cavities.
Various materials have different volumetric shrinkages, hence riser design depends
upon the type of metal poured and the complexity of the casting.
Grey cast iron: negative shrinkage, because of high C & Si contents, which leads to
graphitization…
For Al and Steel contraction will be higher…
Hence Riser is used to promote directional solidification aswell..
Medium C Steel – 2.5 – 3%,
1% C Steel - 4%
Pure Al – 6.6%
Pure Cu – 4.92%
White Cast Iron – 4 – 5.5%
(Dr. L K Bhagi)

Unit-2Riser Design
Type of Riser :
1. Top Riser,
2. Blind Riser
3. Side Riser,
Top Riser
 Most common & most efficient risers
provided on castings where hot-spots are
 accessible from the top directly…
 Easy to mould, easy to fettle & act
efficiently by gravitational force…
 They help in exhaust of mould gases &
indicate the filling
 They are always default chosen…
Blind Riser
 They are used to feed localized hot spots
which are below parting line and not
accessible for top or side risers.
 When castings have profile with different
heights… ex. Valves and intricate castings
 Blind risers help in reducing the excessive
feed material compared to top risers.
(Dr. L K Bhagi)

Unit-2Riser Design
Side Riser
 Side risers are provided on casting having
hot-spots not accessible for direct top risers.
 They help in reducing excess metal of
padding and reduce fettling cost.
Functions of a Riser
 The primary function of the riser is to feed metal to casting as it solidifies, so that no
shrinkage cavities are formed.
 A riser allows escape of air & gases as the mould cavity is being filled with molten metal.
 A riser should promote directional solidification.
 To indicate that a mould is full while pouring
 A casting solidifying under the liquid metal pressure of riser is sound.MEC323: PRIMARY MANUFACTURING
(Dr. L K Bhagi)

Unit-2Riser Design
Design of a Riser:
1. Riser Shape
2. Riser Size
3. Location of Riser
4. Grouping of castings
5. Riser connection to castings
6. Use of Chills
7. Insulations & exothermic compounds,
Riser Shape
 Casting loses its thermal energy by transferring it to its surroundings by radiation,
conduction & convection.
 Solidification time was expressed as: ts = V2
C / A2
C (metric units)
 According to the solidification time, riser shape is designed, the minimum riser shape is a
sphere…However voids are formed in spheres.
 Practice says that cylindrical shaped risers are ideal…
(Dr. L K Bhagi)

Riser Size
 Riser is similar to the casting in its solidification behavior, hence the riser characteristics
are also specified by the ratio of its surface area to volume.
 The shape of the riser should be designed such that it has minimum heat loss and is able
to maintain the molten metal in liquid state as long as possible.
i.e., volume of the riser should be minimum and cooling rate of molten metal is slower
 Optimum riser size for casting is obtained by following methods:
Unit-2Riser Design
Chvorinov’s Rule Freezing Ratio ‘X’
(Dr. L K Bhagi)

Unit-2Riser Design
Caine’s Method :
Riser Size :
(Dr. L K Bhagi)

Unit-2Riser Design
Modulus Method :Riser Size :
 This method of finding the optimum riser size is well documented by
Wlodawer. It is empirically established that if the modulus of the riser (Mr)
exceeds the modulus of casting (Mc) by factor of 1.2, the feeding during
solidification would be satisfactory.
 Modulus if the inverse of the cooling characteristic (surface area/volume).
 In castings, it is generally preferable to choose a riser with a height to diameter
ratio ~ 1…
Hence,
The bottom end of the riser is in the contact with casting, hence do not contribute
to surface area calculation…
Hence,
Considering the allowance of metal fed to counteract the contraction of casting:
(Dr. L K Bhagi)

Unit-2Riser Design
Modulus Method :
Riser Size :
(Dr. L K Bhagi)

Unit-2Riser Design
Naval Research Laboratory Method:Riser Size :
(Dr. L K Bhagi)

Riser Location
 Casting of big bars or plates without risers show that ends of casting are sound, because
of directional solidification starts at ends…
 The fall in the temperature at the ends is more rapid as compared to rest of casting.
 If the casting have variety of section thickness, the riser must be placed at the thickest
portion…
Unit-2Riser Design
Grouping of Castings
 Grouping of several castings around a single riser helps in increasing the casting
yield, since the same riser will be able to feed to more than one casting.
 Also by a small variation in the moulding practice, it is possible to reduce risering
requirements…
(Dr. L K Bhagi)

Riser Connection to the Casting
 The way that a riser is attached to the casting is important because it determines:
o How well the riser can feed the casting,
o How readily the riser can be removed from the casting.
 It may also control to some extent the depth of shrinkage cavity by solidifying just
before the riser freezes, thereby preventing the cavity from extending into casting.
Unit-2Riser Design
(Dr. L K Bhagi)

Chills:
 Chills are provided in the mould so as to increase the heat extraction capability of the
sand mould. A chill normally provides a steeper temperature gradient so that directional
solidification as required in a casting be obtained. The chills are metallic objects having
higher heat absorbing capability than the sand mould. The chills are two types:
o External Chills,
o Internal Chills.
Unit-2Riser Design
(Dr. L K Bhagi)

Use of Insulators and Exothermic Compounds:
 A riser can be made more efficient by employing some artificial means to keep the top of
the riser from freezing over so that the molten metal beneath can be exposed to
exothermic pressure.
 This can be done by use of certain additions made to the surface of the molten metal in
the riser, preferably asap after the metal enters the riser…
 Ex: Graphite, Charcoal , rice or oat hulls, and refractory powders (insulators)
Unit-2Riser Design
(Dr. L K Bhagi)

Feeding Distances:
 Once the optimum riser diameter is decided, no. of feeders and distances between each
feeders have to be established. (to avoid micro/macro/centre-line shrinkages).
 By thumb rule, a single riser is adequate if feeding length is less than 4.5 times the
thickness of plate for 12-100 mm thick plates…
Unit-2Riser Design
(Dr. L K Bhagi)

Unit-2Casting Design Considerations
Casting Design Considerations:
 To produce the best quality product at the lowest possible cost, it is important
that the designer of castings give careful attention to several process requirements
and, if possible, work closely with the producing foundry.
 Following are some of the important design considerations:
 Selection of Alloy
 Casting Process Parameters:
 Dimensional Tolerances,
 Surface finish,
 Size of the castings,
 Quality,
 Quantity.
 Casting Geometry consideration,
 Reducing casting process cost…
(Dr. L K Bhagi)

Casting Processes
(Dr. L K Bhagi)

Unit-2Centrifugal casting
Process:
 This process uses the centrifugal forces caused by rotation to distribute the
molten metal into the mould cavities…
 In this process mould is rotated rapidly about its central axis as the metal is
poured into it. Because of the centrifugal force, a continuous pressure will be
acting on the metal surface as it solidifies.
 The lighter slag, oxides and other inclusions being lighter, gets separated from
the metal and segregates towards the centre.
 Three types of Centrifugal casting:
o True Centrifugal Casting,
o Semi- Centrifugal Casting,
o Centrifuging.
(Dr. L K Bhagi)

True Centrifugal Casting:
 Mould materials include: Dry-sand, Graphite or even Metals…
 Either horizontal or vertical axis (with 300 – 3000 rpm)…
 Hallow castings with cylindrical, hexagonal or other symmetrical shapes (ex.
pipes, gun barrels e.t.c)
 No core or mould is needed to shape interior, it always has a round profile,
because molten metal is uniformly distributed by centrifugal forces…
 In Horizontal axis castings, the inner surface is cylindrical, whereas, in vertical
castings, gravitational forces cause the inner surface to become a section little
parabola profiled…
(Dr. L K Bhagi)

True Centrifugal Casting:
 Metal is forced on the outer walls and solidification begins there.
 Lighter impurities (dross, refractory mtl, mould coating …) is collected in inner
surface, & these impurities can be removed by slight machining of inner surface
 Continuous feed of metal exists, because of centrifugal force, hence shrinkage
allowances need not be considered and does not even need risers, runners e.t.c
 Common metals that are cast are Fe, Steel, Stainless Steel, Al alloys, Cu, Ni…
(Dr. L K Bhagi)

True Centrifugal Casting: Advantages:
 Wide range of cylindrical parts can be casted (13 mm – 3 m ϕ & 16m length & 6
– 125 mm in thickness). (bearings, bushes, rolls etc.)
 Castings of dimensional accuracy and good quality & surface detail are obtained.
 No needs of Cores for making concentric cavities…
 There is no need of runners, gates, risers (increases casting yield ~100%).
 No Porosity, No slag / dirt/ oxides. Hence mechanical properties of centrifugal
castings are better compared to conventional methods…
True Centrifugal Casting: Limitations:
 Only castings with cylindrical or some axis-symmetric and having concentric
cavities are suitable…
 Equipment is expensive, hence it is suitable only for mass/ large quantity
production… MEC323: PRIMARY MANUFACTURING
(Dr. L K Bhagi)

Semi Centrifugal Casting:
 Castings with more complicated structures (but axis symmetric) are carried…
 In this process, centrifugal force assists the flow of metal from a central
reservoir to the extremities of a rotating symmetrical mould,
 The rotating speeds are lower compared
to that of true process,
 Central reservoir acts as riser and is the
last to freeze.
 Lighter impurities concentrate towards
the centre, hence it is best for castings with
hollow centers. (Disk shape parts, wheels,
rollers, pulleys, flywheel, etc)
(Dr. L K Bhagi)

Centrifuging:
 Centrifugal action is used to force the metal from a central reservoir into
separate mould cavities that are placed at a certain distance form the axis of
rotation …
 Relatively low rotational speeds are required to produce sound castings with
thin walls and intricate shapes.
 Properties with in the casting vary by the
distance from the axis of rotation.
 This process is generally used in order to
obtain higher metal pressures during
solidification, & when casting shapes are
not axissymmetrical.
(Dr. L K Bhagi)

Unit-2Permanent Mould Casting
Permanent Mould Casting:
 The permanent mould casting process uses, a reusable mould machined from
materials that maintain their strength at high temperatures like grey cast iron,
steel, bronze, graphite e.t.c.
 Both the cope & drag are made of metal, and sprue, runners, gates, riser all are
machined into the metal mould. There is a possibility of using cores.
 Both the halves are heated and clamped and metal is poured using gravity
action. Hence, it is even called gravity die casting.
 The mould is than reclosed and next batch of molten material is poured.
 In steel based moulds, Al, Mg, Cu based alloys are casted, whereas to cast steel,
iron e.t.c, graphite based permanent moulds are used.
 Inner surfaces of the moulds are coated with refractory slurry or sprayed with
graphite to increase the life of permanent mould.
(Dr. L K Bhagi)

Unit-2Permanent Mould Casting
Permanent Mould Casting: Advantages:
 The mould is reusable (~25000 times) & good surface finish is obtained,
 Higher dimensional accuracy (from ~ ± 0.25 mm),
 Defective free castings can be obtained by chilling or heating various thicker
sections separately,
 Faster cooling rates are possible (hence, better castings),
 Very small amount of sand is needed.
Permanent Mould Casting: Limitations:
 High initial cost, hence suitable only for mass production,
 Intricate shapes cannot be casted, since they can not removed from the mould.
 Generally limited to metals/ alloys with lower melting points.
 Has size restrictions (Because of metal mould, it is hard to handle huge sizes).
(Dr. L K Bhagi)

Unit-2Die Casting
Die Casting:
 Was developed early ~1900, where components were produced by injecting molten
metal at a high pressure ~ 0.7 to 700 Mpa. (also called as pressure die casting)
 Most castings are made of nonferrous metals & alloys.
 Because of combination of high pressure, metal moulds & dies, fine sections &
excellent details can be achieved.
 There will be two die’s where one is stationary and other is movable.
Process is done in following steps :
o Two dies are separated and lubricant is applied,
o Dies are closed and clamped and required amount of metal is injected,
Once casting is solidified, movable die is opened and casting is removed.
Two types of die castings exist:
o Hot-chamber Die casting,
o Cold-chamber Die casting.
(Dr. L K Bhagi)

Unit-2Die Casting
Hot-Chamber Die Casting:
 Pressures range up to 35 Mpa,
 Suitable for low melting point alloys such as Zn, Sn, Pb e.t.c
(Dr. L K Bhagi)

Unit-2Die Casting
Cold-Chamber Die Casting:
 Pressures range up to ~150 Mpa.
 Shot chamber is not heated, hence the name Cold-chamber casting.
(Dr. L K Bhagi)

Unit-2Die Casting
Die Casting: Advantages:
 Extremely smooth surface finish (~ 1 µm),
 Excellent Dimensional tolerances ( ± 0.08 mm),
 Possible to produce complex castings because of movable cores,
 High production rates can be achieved,
 Components with better mechanical properties can be achieved, because of the
fine grained skin formed during solidification (compared to sand casting)
Die Casting: Limitations:
 Equipment (dies & machine) is expensive, hence it is suitable only for mass/
large quantity production…
 Limited only to high fluidity non ferrous metals & alloys
 Since air gets trapped between dies, there would be porosity problem,
Limited to small castings (~15 Kg), Scrap in sprues, runners & flash is produced.MEC323: PRIMARY MANUFACTURING
(Dr. L K Bhagi)

Applications
• Piston
• Stators
• Connecting rods
• Oil pump bodies
• Carburetors
• Decorative parts
• Sharpener
• Rotor fan
• Brake shoe
• Game equipments
• Mechanical parts etc
(Dr. L K Bhagi)

Unit-2Investment Casting
Investment Casting:
 Also called as lost wax process
 Was used first during 4000 – 3000 BC. Famous among jewelers & dentists.
 Process :
(Dr. L K Bhagi)

• Procedure:
1. Making of die for making wax pattern
2. Making of wax pattern ( injected at 4 bar)
3. Assembly of wax pattern to a wax gating system
4. Investing wax pattern: a) dipped into a slurry of refractory coating
material. (Fine silica with ethyl silicate solution or gypsum, mix with
plaster to bond the mold shape
5. B) final investment is carried out by inverting wax assembly.
6. Removal of wax pattern: by heating in furnace or oven (100-
120)
7. Pouring : firstly heated upto 900
8. Shake out casting and remove gating system
9. Cleaning and inspection
(Dr. L K Bhagi)

Unit-2Investment Casting
Investment Casting: Advantages:
 Excellent surface finish, can be use readily used (may need minor machining),
 Suitable for producing intricate shapes from a wide variety of ferrous & non
ferrous metals & alloys,
 High dimensional accuracy ( 0.125 mm/mm),
Extremely complex shapes can be casted in a single piece.
Very thin sections ~ 0.4 mm can be produced.
Investment Casting: Limitations:
 The labor & material involved makes investment casting very costly,
 The process is limited by size of castings (upper limit ~ 5Kg).
(Dr. L K Bhagi)

Unit-2Shell Mould Casting
Shell Mould Casting:
 It is an semi precise method for producing many types of castings with close
tolerances and good surface finish at low cost. (lead, bronze and tin alloy, plaster)
 Process :
(Dr. L K Bhagi)

Unit-2Shell Mould Casting
Shell Mould Casting: Advantages:
 Faster production rate than sand moulding,
 Higher dimensional accuracy (from ~ ± 0.03 - 0.25 mm) with smooth surfaces,
 Complex shapes can be produced with less labor, & process can be automated,
 Permeability of shell is high, hence no gas inclusions can happen,
 Very small amount of sand is needed.
Shell Mould Casting: Limitations:
 Requires expensive metal patters (hard to handle aswell), Hence suitable for
mass production, Cost of plastic has to be considered.
 Needs sophisticated handling equipment to heat metal plates.
 Has size restrictions (max of ~ 450 Kgs).
(Dr. L K Bhagi)

Metal Melting
(Dr. L K Bhagi)

Unit-2Melting Methods
Melting Methods:
 Melting of an alloy or metal is an important aspect of casting operation because:
o It has direct bearing on the quality of the casting,
o Liquid metal of required composition, temperature, quantity, desired rate,
o Almost 50% of the capital investment of foundry is dedicated to melting and its
associated equipment ,
o Out of total production rate of castings, 50% is contributed towards melting
process…
 Basic requirements of Melting depend upon:
o The compositional range of the material and super heat needed,
o Form & size of the material,
o Fuel or energy used to melt the charge,
o The degree of refining and control of the process
o The type & size of melting unit,
o Other economical factors (time, cost & labor).
(Dr. L K Bhagi)

Unit-2Melting Methods
Melting Methods:
 Number of melting methods are availabe and they depend upon:
o Temperature needed to melt and superheat the material,
o The alloy being melted and the form of the available charge metal,
o The desired melting rate or quantity of metal,
o The desired quality of the metal,
o The availability and cost of various fuels,
o Variety of various metals & alloys suitable for furnace,
o The various capital & operating costs…
(Dr. L K Bhagi)

Unit-2Cupola furnace
Cupola Furnace:
 The cupola is a shaft furnace employed for melting and reining pig iron or grey cast iron
along with scrap in foundries due to its cost of construction , installation and operation.
 It can not be used to melt any metal apart from cast iron,
 Charge materials are Metal, flux (lime stone) & coke,
 The important function is absorbing of heat by the charge from ascending gases, i.e.,
ascending hot gases heat the descending metal charge.
 Cupola operation Process:
o Preparation of cupola,
o Charging,
o Melting,
o Tapping and slagging,
o Dropping the bottom.
(Dr. L K Bhagi)

Unit-2Crucible furnace
Crucible Furnace:
 Crucible furnaces are indirect fuel-fired furnaces (fuel oil, LPG, fossil fuel or
electricity), used to melt small batches of non-ferrous metal,
 The combustion products do not come in contact to fuels (so there is no contamination),
 The low thermal efficiency of the process limits melting of material in small batches,
 Because of low investment costs it is preferred (materials with low melting points),
 Crucible furnaces can be classified into following categories:
o Lift out Furnaces,
o Bale out Furnaces,
o Tilting Furnaces,
o Immersed Crucible firing Furnace.
(Dr. L K Bhagi)

Unit-2
Crucible Furnace : Advantages:
 Reduced metal losses,
 Reduced danger of crucible damage on charging,
 More uniform distribution of temperature,
 Very cheap as investment is the lowest.
Crucible Furnace : Limitations:
 Pollution due to dust and fumes,
 Low thermal efficiency,
 Long cycle time,
 Not for high quality alloys,
 Not suitable of metals with very high melting points.
Crucible furnace
(Dr. L K Bhagi)

Unit-2Steel Making Process
The Bessemer Process
 The Bessemer process consists of blowing air through molten pig iron contained in an
egg shaped vessel, known as converter, of 15-25 tones capacity…
 The convertor is made of steel plates and refractory lining inside,
 The furnace is mounted in such a way that it can be tilted and charged with raw material,
 The air is blasted about ~ 2 – 2.5 atm through a number of holes in the base called
tuyeres… Temperatures ~ 1300 – 1700 oC
(Dr. L K Bhagi)

The L-D Process
 It is a latest process of steel making, where a jet of pure O2 is blown at high pressure and
travelling at supersonic speed through water cooled lance, on the surface of iron.
 Blowing of O2 at supersonic speeds produces intense heat (~ 2000- 3000 oC) and
reduces blowing time.
 ~ 100 tones of steel is produced per heat, (world wide 20 million tones is produced by
this process)
(Dr. L K Bhagi)

The L-D Process
(Dr. L K Bhagi)

Casting Defects
(Dr. L K Bhagi)

Unit-2Casting Defects
(Dr. L K Bhagi)

Metal casting process part 2

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