Manufacturing technology process introduction and foundary
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Manufacturing Technology- I
ME-401
UNIT-I
Introduction to
Manufacturing Process and
Foundry
By Prof. Rajeev Khanduja
UNIT-I
Introduction to Manufacturing and Manufacturing Processes,
Classification of Manufacturing Processes, Metal Casting Processes:
Introduction, Basic steps in Casting Processes, Advantage and
limitations, sand mold making procedure, Patterns and Cores.
Pattern materials, pattern allowances, types of pattern, colour
coding,Moulding material, Moulding sand composition, and
preparation, sand properties and testing type of sand moulds. Types
of cores, core prints, chaplets, chills. Gating systems and Casting
Defects, Gates and gaiting systems risers, melting practice, Cupola,
charge calculations.
Casting cleaning and casting defects Fettling, defects in castings and
their remedies, methods of testing of castings for their soundness.
Special Casting Processes: Shell molding, precision investment
casting, permanent mold casting, die casting, centrifugal casting, and
continuous casting.
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Introduction to Manufacturing
Processes
Workshop Technology, and Production
Systems
Products manufactured by: fitting;
smithy; machining; mechanical working-
-forging, rolling, sheet metal working;
wood working, pattern making, foundry;
joining-- welding, brazing, soldering etc.
Workshop Technology-- theoretical and
practical knowledge of manufacturing
processes and materials
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Production is an art of converting raw
materials into finished goods with the
application of tools and manufacturing
processes. Three types of production
systems:-- (i) Jobbing; (ii) Batch;
(iii) Mass production.
Jobbing—Completion of one job at a time.
Tailor made; 10-15 parts in a lot. Quality-
very good. Per piece cost –Highest;
Investment lowest.
Batch—A number of identical item; then
next item; Regular or irregular; About 300
parts in a lot. Annual production: 2,500 –
1,00,000 parts. Quality; per piece cost;
investment—Intermediate;
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Mass Production --A large No. of identical items
continuously produced in different successive
operations; Production: more than 1 lac parts;
Quality lowest; Large investment on jigs, fixtures,
m/cs. Examples: Nuts; Bolts; Screws; Washers;
Sewing m/cs; bicycles etc
Manufacturing Pprocess --Production of desired
object from the raw material-- Important prodn
technology; Other technologies– Process; &
energy technology.
MP involves new techniques, replacement /
improvement of old processes, new and compact
design, better accuracy in dimensions, quicker
methods of production, better surface finishes,
tooling system, automatic and numerical control
system, higher mechanization for greater output.
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Item Jobbing Batch Mass Prodn
Method One job at
time.
one batch at
a time.
A large no. of
identical items.
Annual
prodn.
< 2500 parts 2500 to 1 lac
parts
> 1 lac parts
Lot size 10-50 parts < 300 parts > 300 parts
Quality Best Medium Lowest
Investmen
t
Lowest Medium Highest
Cost per
piece
Highest Medium Lowest
Typical
Examples
Tailor made
individual
shirts, pants;
Aeroplanes;
M/C Tools;
Rolling Mills
I.C. Engines;
Compressor
pumps
Nuts; Bolts;
Screws; Washers;
Sewing m/cs;
bicycles
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Types of Manufacturing Processes
There are three types of Mfg Procs.
These are used to convert ingots /
semi-finished into products.
1. Primary Shaping Processes
Most metals --from ores by reduction and
refining in molten form. Cast in moulds --
commercial castings or ingots or pigs.
Ingots/pigs are used to produce metal
products of different shapes and sizes
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(A) Primary Shaping Processes--(a)
Casting; (b) Forging; (c) Smithy; (d)
Drawing; (e) Rolling; (f) Bending; (g)
Extruding; (h) Squeezing; (i) Shearing; (j)
Crushing; (k) Spinning; (l) Piercing; (m)
Forming; (n) Embossing
Classification of Mfg Processes
2. Secondary Shaping Processes
• Machining processes;
• Joining processes;
• Surface Finishing processes)
3. Tertiary Processes –These processes
change the properties
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Joining Processes
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Casting is process of forming metallic products
in a shop—called foundry by (i) Melting the metal,
(ii) Pouring it into a cavity known as the mould and
(iii) Allowing it to solidify.
Almost all metals and all sizes can be cast in
sand molds. Sand molds-- Single use-- completely
destroyed after casting.
Permanent mold –Much less labour cost.
Special casting methods-- high initial cost, but
advantages of: Greater dimensional accuracy;
High production rates; Lower production cost ;
Better surface finish; fine grain structure ;
Greater dimensional accuracy; Less defects
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Melting, Pouring,
Cooling, Shake Out,
Finishing
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Basic Steps in Casting
Process
(1) Pattern making,
(2) Moulding and core-making,
(3) Melting and casting,
(4) Fettling, and
(5) Testing and inspection.
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1. Pattern making,
2. Selection & prep. of moulding sand
3. Making of mould with moulding sand and
by using pattern
4. Melting of metal
5. Pouring the molten metal in the mould.
6. Removing casting from mould after
solidification.
7. Fettling--Cleaning of casting & finishing
8. Testing & inspection of casting
9. Removing the defects, if any,
10. Again inspection.
11. Storage or shipping of casting
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Bottom Pouring Ladle
Large Lip Pouring Ladle
Tea Pot
Hand
Shake
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• Defined as a “model of the desired product”
• It is used for forming a mould (cavity) in damp
sand.
• Pattern is the “replica of the casting”.
Pattern Materials---Wood; cast iron; brass;
aluminum alloys; white metal; plaster; plastic
compound; wax
Material Selection for Pattern is based on –
(i) Design; (ii) No. of castings; (iii) quality &
shape (Intricacy) of casting; (iv) types of
moulding process & material ; (v) possibility of
design changes; (vi) repetition of same
castings again; (vii) moulding materials used
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ISE 316 - Manufacturing
Processes Engineering
The Pattern
A full-sized model of the part,
slightly enlarged to account for
shrinkage and machining
allowances in the casting
• Pattern materials:
– Wood - common material because it
is easy to work, but it warps
– Metal - more expensive to make, but
lasts much longer
– Plastic - compromise between wood
and metal
ISE 316 - Manufacturing
Processes Engineering
Pattern Material
• Wood :- Wood is the most common material used for
pattern because it satisfies the many of the desired
requirement. Wood used for pattern making should be
properly dried, straight grained, free from knots and
free from excessive sapwood. Common wood used for
patterns is teak, mahogany, shisham, pine, deodar etc.
• Advantages :-Cheap,Easily worked, Light in
weight,Easily available, Easy to join, Easy to obtain
good surface finish,Can be easily repaired ,Wooden
laminated patterns are strong and light in weight.
• Disadvantages :-Susceptible to moisture , Tends to
warp ,Wears out quickly due to sand abrasion,Weaker
than metallic patterns.
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ISE 316 - Manufacturing
Processes Engineering
Pattern Material
• Metals :-Metallic patterns are used where
repetitive production of casting is required in
large quantities. Different metals like cast Iron,
brass, Aluminum alloys and white metal etc. are
used for making patterns.
• Advantages :-Easy to file and fit, Strong, Good
resistance against sand abrasion, Good surface
finish.
• Disadvantages :-Heavy, Easily
broken,Rust,Brittleness, Machining Cost is very
High
ISE 316 - Manufacturing
Processes Engineering
Pattern Material
• Plaster :- Gypsum plaster (plaster of paris)
when mixed with a correct quantity of water
sets in a given time and forms a hard mass
having high compressive strength (up to 300
Kg/cm2).
• Advantages :- Cheap and easily available, Easily
workable , Good surface finish , Light in weight
• Disadvantages :- Expands on solidification ,
Strength is not so much as that of metals.
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ISE 316 - Manufacturing
Processes Engineering
Pattern Material
• Plastic compounds :- Both thermosetting and
thermoplastic materials are used for pattern work.
In the thermosetting epoxy and polyester resins
have found increasing used. In the thermoplastic
type, polystyrene has become popular.
• Advantages :- Easily castable, High strength to
weight ratio, Low cost of working, Good resistance
to wear and abrasion ,Low cost of material.
• Disadvantages :- Cannot withstand high
temperature,Not too much strong , Can not be
reused
ISE 316 - Manufacturing
Processes Engineering
Pattern Material
• Waxes :- The waxes commonly chosen are paraffin
wax, shellac wax, bees wax, and cerasin wax. Additives
which acts polymerizing agents and stabilizers are also
added.
• Their use helps in imparting a high degree of surface
finish and dimensional accuracy to castings.
• Wax patterns are prepared by pouring heated wax into
split moulds or a pair of dies. The dies after having
been cooled down are parted off. Now the wax pattern
is taken out and used for moulding.
• Wax pattern need not to be drawn out solid from the
mould. After the mould is ready, the wax is poured out
by heating the mould and keeping it upside down.
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Functions of a Pattern
• A pattern prepares a mould cavity for the purpose of
making a casting.
• To produce seats for cores in the moulds so need coreprints
on the pattern.
• Runner, gates and riser may form a part of the pattern
• Pattern establish the parting line and parting surfaces in
the mould.
• Patterns properly made and having finished and smooth
surface reduce casting defects.
• Properly constructed patterns minimize overall cost of he
casting.
ISE 316 - Manufacturing
Processes Engineering
Difference between Pattern and Casting
• The material of the pattern is not necessarily
same as that of the casting. Pattern may be
made from wood.
• The colour of the pattern may not be same as
that of the casting.
• Pattern carries an additional allowance to
compensate for metal shrinkage.
• It carries additional allowance for machining.
• It carries the necessary draft to enable its easy
removal from the sand mass.
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ISE 316 - Manufacturing
Processes Engineering
Difference between Pattern and Casting
• It carries distortions allowance. Due to distortion
allowance, the shape of casting is opposite to
pattern.
• Pattern may carry additional projections, called
core prints to produce seats for cores.
• Pattern may be in pieces (more than one piece)
where as casting is in one piece.
• Sharp changes are not provided on the patterns.
These are provided on the casting with the help of
machining.
• Surface finish may not be same as that of the
casting. ISE 316 - Manufacturing
Processes Engineering
Colour Coding for Patterns and Core Boxes
• The surfaces to be left unmachined are painted blue for
steel, red for Grey cast iron.
• Surfaces to be machined – Yellow
• Coreprints for unmachined opening and end prints.
• Periphery Black
• Ends Black
• Coreprints or machined opening.
• Periphery Yellow strips on black
• Ends Black.
• Seats for core prints (loose) – green
• Stop off – Diagonal block strips or clear varnish.
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1. Solid or single piece;
2. Split (Two piece);
3. Multi-piece;
4. Match plate;
5. Gated;
6. Skeleton;
7. Sweep;
8. Pattern with loose pieces;
9. Cope and drag;
10. Follow board;
11. Segmental.
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Solid or single piece pattern-- No joints, partings
or any loose pieces. Cheaper. Runners, gates &
risers to be cut—so more time. Used for simple
shaped large castings. Examples – Simple
shapes of castings; Gland of steam engines.
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Split (Two piece) pattern—Used
when single piece is difficult.
Two halves—upper and lower,
held by means of dowel-pins.
Examples: Spindles; cylinders;
steam valve bodies; water stop
cocks; and taps.
Multi-piece Pattern--For complex
shaped casting; Pattern has > 2
parts.
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Match plate pattern--one half on
one side of a plate (Match plate) &
other half directly opposite side of
plate. Used in machine moulding.
High cost.
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Gated patterns--Used to ensure flow
of full supply of molten metal into
every part of the mould, Cavities
are connected to each other by
means of gate formers.
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Gated Pattern
Skeleton pattern-- hollow
patterns made of frame
work filled with loam sand.
Saves material & cost of
pattern.
Examples --Turbine
castings, water pipes, L-
bends etc
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Cope and drag pattern--A form of split
pattern; each half moulded separately.
Each half fixed to a separate metal/wood
plate with a provision for moulding runner
and gates.
Two moulds of each half are finally
assembled.
Used for big castings-- inconvenient for one
moulder alone.
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Pattern with
loose pieces--
Made with loose
pieces
(attached with
dowel pins ) for
easy removal.
More labour &
cost.
Follow board pattern--Wooden board
forming parting line and supporting a
very thin and fragile pattern. Used
for casting master patterns.
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Segmental pattern--Sections of a
pattern arranged to form a complete
mould. Prepares the mould by parts. 70
•Needed due to met. and mech.
reasons,
•To get accurate casting.
Allowances needed for:
(i) Shrinkage or contraction;
(ii) Machining or finish;
(iii) Draft or taper ;
(iv) Distortion or camber ;
(v) Shake or rapping.
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1. Shrinkage or contraction
allowance.
2. Machining or finish allowance
3. Draft or taper allowance
4. Distortion or camber
allowance
5. Shake or rapping allowance.
6. Mould wall movement allowance
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To compensate for the
shrinkage during
solidification & cooling.
Value (mm/mm)
Gray C.I.-- 0.0105; White
C.I.-- 0.0160 to 0.0230; Al &
Mg--0.0130; Cu--0.0160; Pb--
0.0260; Brass--0.0155 74
(i) Machining or finish allowance--
In addition to shrinkage
allowance, it is provided to get
good surface finish after m/cning
Amount 1.6 to 12.5 mm
depending upon type of metal;
size, shape, method of casting
& machining and degree of
finish.
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(ii) Draft or inward
taper allowance
(in mm/m) or
in degrees (½ to
1½)—
To facilitate easy
removal of pattern
from mould.
Depends upon--
length of vertical
side; intricacy,
type, material of
pattern; method
of moulding.
No draft allowance
Draft allowance
provided
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(iii) Distortion or camber
allowance
To eliminate distortion in U
shaped product.
Legs may diverge.
Distortion or warping due to: (i)
irregular shape; (ii) non-uniform
shrinkage of all parts; (iii) long
flat surface; (iv) arms with
unequal thickness.
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(iv) Shake/ rapping allowance-
To compensate for increase of
cavity of mould during rapping
for withdrawing the pattern.
Can be reduced by increased
taper.
Rapping allowance is negative.
All other allowances are
positive
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• Mould wall moves due to pr. of liquid.
• Pressure may increase due to
graphitization in cast iron.
• If ramming is mould is less then wall
movement is more.
• If moisture in mould is more then also
wall movement is more.
• To compensate wall movement,
pattern is made slightly smaller.
• This allowance is negative allowance
• Place one-half of pattern on a mould
board, with drag section. Powder
pattern with lycopodium, talc, or
graphite.
• Sprinkle 15-20 mm layer of facing
sand on the pattern.
• Fill mould with layers of used green
sand mixture (70-100 mm thick),
compacting each layer with rammer.
• Ram top of mould with butt end of a
rammer. Scrape off excess sand by
strickle.
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•Vent the mould for escape of
gases by sticking it with a fine
stiff wire at numerous places.
• Sprinkle loose sand over mould, place
bottom board, roll over the drag.
Remove moulding board and sprinkle
upper surface with parting sand.
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•Assemble remaining half of pattern in
cope section and place tapered pegs for
sprue and riser in proper position and
make ready the cope as the drag
portion.
•Use a series of
cross-bars and
lifters or
gaggers to give
support to the
moulding sand
in the cope.
• Remove wooden pegs from cope &
scoop a funnel- shaped opening to form
pouring basin.
• Place cope on a board with the parting
line upward.
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• Draw out pattern and cut runner
and gate in the drag from pattern
to sprue.
• Set core in print left by pattern in
drag.
• Remove loose particles of sand by
a jet of air and dust the mould with
foundry blackings so as to give a
smooth surface.
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• Finally, assemble mould by placing
cope on drag so that the flask pins
fit into the bushes.
• Place sufficient load on
cope to prevent it from
floating up when metal is
poured.
• Now mould is ready for
pouring molten metal for
casting.
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Classification of Moulding Sand
(a) by Availability
1. Natural sand 2. Synthetic sand 3. Special
sand.
Natural Sand (Green sand )-- From river beds,
pits or by crushing and milling soft yellow
sand stones. Contains good amount of clay
(binder) & moisture. Low cost. Used for most
non ferrous castings.
Synthetic sand--By mixing relatively clay free
sand, binder and other materials as required.
Better moulding sand with control on
properties.
Classification of Moulding Sand
(b) by Use
1. Green sand
2. Dry sand
3. Loam sand
4. Facing sand
5. Backing sand
6. System sand
7. Parting sand
8. Core sand
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Classification of Moulding Sand
(b) by Use
Green sand --Natural or moist state; Silica
sand + (18-30%) clay + (6--8 %) water.; No
baking /heating; Used for simple, small
and medium size castings.
Dry sand —After drying/baking of green
sand moulds; More strength , rigidity &
thermal stability; Large & heavy
castings.
Loam sand -- Contains about 50% clay;
Sweep or skeleton patterns for loam
moulding; Used for large Grey iron
castings.
Classification of Moulding Sand by Use
Facing sand --Used 20-30 mm layer next
to surface of pattern ; Comes in contact
with molten metal; Unused fresh sand;
High strength & refractoriness.
Backing sand --Backs up facing sand;
Repeatedly used; Black colour due to
addition of coal dust & its burning; To be
cleaned off fins, nails etc.
System sand --Used in Mechanized
foundries; No facing sand is used; Used
sand is used after cleaning &
reactivation with waters, binders and
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special additives; Strength,
permeability and refractoriness
higher than backing sand.
Parting sand -- Clay free dried
silica sand, sea sand or burnt sand;
Used on pattern & at parting
surface of mould.
Core sand-- For making cores. Also
called oil sand; contains linseed oil
or other binder.
Moulding sand is used to
prepare moulds for casting of
metals.
The moulding sand consists of:
(i) Silica Sand
(ii) Binder
(iii) Additives
(iv) Water
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(i) Silica sand
• Silica sand is the major portion of
the moulding sand.
• It contains 80 - 82% silica sand.
• Purity of silica sand is 80- 90%.
• Its softening temperature is high.
• It has high thermal stability.
• It is produced from quartz rocks.
• The silica sand is found in rivers or
lakes.
• Silica sand impart refractoriness.
• It gives permeability to the sand.
(ii) Binder
•Binder is added to the moulding sand to
impart strength and cohesiveness.
•Binder reduces permeability of the sand
mould.
•Two types of binders are used.
•These are organic and inorganic type.
•Examples of organic binders are:
Linseed oil; Molasses; Pitch; Cereal
binders.
•Examples of inorganic binders are: Clay,
Sodium silicate; Portland cement.
•Common types of clays are : Bentonite;
Kaolinite or fire clay; Limonite
•Bentonite is widely used.
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ISE 316 - Manufacturing
Processes Engineering
Binders for Foundry Sands
• Sand is held together by a mixture of
water and bonding clay
– Typical mix: 90% sand, 3% water, and 7%
clay
• Other bonding agents also used in
sand molds:
– Organic resins (e g , phenolic resins)
– Inorganic binders (e g , sodium silicate
and phosphate)
• Additives are sometimes combined
with the mixture to enhance strength
and/or permeability
(iii) Additives
• Additives are added to improve
properties of moulding sand.
• Examples of commonly used
additives are: Sea coal; Pitch;
Asphalt; Silica flour; Graphite;
Wood flour; Corn flour
(iv) Water
• A suitable quantity of water (2 to
8%) is added to get required
strength and bond.
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1. Porosity or Permeability
2. Adequate Flowability (Plasticity)
3. Refractoriness
4. Adhesiveness
5. Fineness
6. Bench life
7. Coefficient of expansion
8. Chemically neutral
9. Reusable, cheap, easy availability
10. Cohesiveness
11. Collapsibility
12. Durability
1. Porosity or Permeability –to be enough
for dissolved gases in metal & steam to
come out, other wise porosity defect.
2. Adequate Flowability (Plasticity) for
better & uniform compaction. Increases
with clay & moisture content.
3. Refractoriness to withstand high temp.
without fusion, cracking, or buckling.
Increases quartz content and roughness
of grains.
4. Adhesiveness for clinging or bonding of
particles with one another.
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5. Fineness--To be adjusted to have good
balance between permeability &
smoothness of mould surface.
6. Bench life---To retain its properties
during storage or while standing (i.e. in
case of any delay).
7. Coefficient of expansion —Should be
low.
8. Moulding sand should be chemically
neutral.
9. Moulding sand should be reusable,
cheap and easily available.
10. Cohesiveness --sand particles to
stick together. Measured as Green
strength, Dry strength after baking; Hot
strength after moisture is evaporated.
11. Collapsibility—needed for sand mould
to break (collapse) automatically after
solidification of casting occurs to allow
free contraction of solidifying metal.
12. Durability---Capacity to withstand
repeated cycles of heating & cooling
during casting operations.
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ISE 316 - Manufacturing
Processes Engineering
Types of Sand Mold
• Green-sand molds - mixture of sand,
clay, and water;
– “Green" means mold contains moisture
at time of pouring”
• Dry-sand mold - organic binders
rather than clay and mold is baked
to improve strength
• Skin-dried mold - drying mold cavity
surface of a green-sand mold to a
depth of 10 to 25 mm, using torches
or heating lamps
Sand Preparation
1. Mixing 2. Tempering 3. Conditioning
1. Mixing of sand --Generally clay, lime,
magnesia, potash, soda etc. are mixed to
artificially make up such characteristics
of sand in which it lacks.
2. Tempering of sand is the process of
addition of adequate moisture to make it
workable. Moisture activates clay binder
by making a film around clay particles.
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3. Sand conditioning-- means uniform
distribution of binder around the sand
grains for free flow around to take up
details of the pattern. Done manually
or by machines. Mullers are used to
mix sand properly.
Testing of Moulding Sand
• Mould and core hardness test
• Moisture content test.
• Grain size of fineness test
• Strength test
• Clay content test;
• Permeability test
• Refractoriness Test
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Gating system includes:
(a) Pouring basin
(b) Sprue
(c) Runner
(d) Gate
(e) Riser
First molten metal is poured into pouring basin.
• Below the pouring basin there is a sprue.
• The metal travels down through sprue.
• Then the metal travels along horizontal
channel.
• This channel is called runner.
• Finally molten metal enters the gates,
• Then it reaches to mould cavity.
• Gating system has been shown in Fig. below.
Molten metal is poured into the mould from the
ladle. The passage way used for this purpose is
called the gating system.
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Runner
extension
Following points are important for design of
gating system.
1. The metal should enter the mould cavity
without turbulence.
2. The metal should enter the mould cavity at
optimum flow rate.
High flow rate causes erosion of gating
system.
Low flow rate leads to misrun and cold shut.
3. Proper thermal gradient should be maintained.
4. Molten metal should not absorb gases.
5. Slag should not enter the mould cavity.
6. The gating system should be economical,
7. It should be easy to operate and remove after
solidification.
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• It is a small funnel shaped cavity
at the top of the mould.
• It receives molten metal from the
ladle.
• It acts as reservoir for molten
metal.
• From here, metal moves smoothly
into sprue
• Pouring basin prevents the
erosion of mould.
• It holds back the slag and dirt
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• Sprue is the vertical portion
of gating system,
• From here molten metal
enters the parting plane.
• At parting plane molten metal
enters the runners.
• Sprue is gradually tapered
downwards.
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• It is the channel for flow of
metal from metal pool /
furnace to mould.
• Located in horiz. plane
(parting),
• Connects sprue to in-gates.
• Runner extension to trap
slag from metal.
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Top gate -- molten metal enters mould from
top. More mould erosion because metal falls
from a height.
Openings for molten metal to enter
mould cavity. 4 types
Bottom gate--- molten metal enters the
mould at or near its bottom.
Smooth flow metal-- less erosion of mould.
Problems in directional solidification, since
hottest metal remains at the bottom, while
coolest remains at the top.
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Step Gate-- molten metal enters from
number of in-gates arranged in vertical
steps.
Gradual filling of mould without erosion;
sound casting.
Parting Gate-- molten metal enters
cavity at plane. Compromise bet.
top and bottom gate-- more
common.
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• Most of the foundry alloys shrink during
solidification.
• Due to volumetric shrinkage during
solidification, voids may form in the
castings.
• To fill these voids, additional molten
metal is needed.
• Hence a reservoir of molten metal is to
be maintained.
• This reservoir is called riser.
• From riser, molten metal flows readily
into the casting when metal shrinks.
Risers are of two types namely:
(i) An open riser; (ii) The blind
riser.
Open Riser :-
•Here riser is exposed to atm.
•Commonly employed on topmost portion
of the casting.
Blind Riser :-
•It is on top or on side of a casting.
•It is surrounded from all sides by
moulding sand.
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ISE 316 - Manufacturing
Processes Engineering
Core
Cores are a body of sand used to form
hollow interior of casting .
It is inserted into the mold cavity prior
to pouring
• The molten metal flows and
solidifies between the mold cavity
and the core to form the casting's
external and internal surfaces
• May require supports to hold it in
position in the mold cavity during
pouring, called chaplets
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Core Sands and Core Making
Cores are a body of sand used to
form hollow interior of casting or a
hole through the casting. Core are
prepared separately in a core box.
Held and located in moulds in seats
formed by core prints provided on
patterns.
Provision is made to support cores
inside mould cavity on core print on
pattern.
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Properties of core or Core
must possess:
• High permeability for gases;
• High refractoriness;
• Smooth surface;
• High collapsibility;
• Sufficient strength to
support itself.
Main ingredients --sand (with < 5% clay )
and binder. Usually silica, but zircon,
olivine and chamotte sands' are also
used. More clay -- less permeability &
less collapsibility
Size, shape, and distribution of sand
grains & mineralogical composition --
Important. Sand with rounded grains is
more satisfactory for cores than with
angular grains for higher values of
permeability.
Core Sand
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Binders are used for almost pure sand
before and after cores are baked. They
impart strength, sufficient collapsibility
& good permeability, ample
refractoriness and other qualities that
cores should possess.
General types of binders: (a) Those that
harden at R.T. (b) Those that require
baking to harden, and (c) clays.
Commercial binders-- consist mainly of
oils, cereals, dextrine, resins, sulphite-
liquor, molasses and protein.
Core Sand
Core oils (linseed oil and corn oil), more
popular as they are very economical &
produce better cores. Sometimes,
specially processed mineral oils are also
added to achieve special properties.
Typical composition of Oil sands for
sand casting application.
Sand (by weight) 95.8 %
Cereal flour 1.0 %
Core oil 1 .2 %
Water 1 .9 %
Bentonite 0.1 %
Core Sands
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Oil sands are very popular for core
making because:
• Easy to use;
• Core sand is more collapsible than
clay bonded sand;
•Green & dry strength is better
controlled with variation of dextrine
& oil;
• Baked cores are very hard and not
easily damaged in handling or
during use.
• Mixing of sand manually or with
machines --paddle mixers or
mullers.
• Ramming of core sand in Core
box manually or with machines.
• Venting of core by wires to
increase permeability.
• Reinforcing of core with metal
wires to increase strength.
• Baking in radiant bakers at 150-
400 C.
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• Finishing by rubbing or filing
& coating with a refractory or
protective material.
• Joining (more than 1 piece)
by pasting, bolting or leading;
Setting of cores in mould.
Wood is common for making
core boxes, but metal core
boxes for mass production.
Core Making
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Strickle Core Box
Classification of Cores
1. Horizontal core
2. Vertical core
3. Balanced core
4. Hanging or cover core
5. Drop core or stop off core
6. Ram up core;
7. Kiss core.
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1. Horizontal core -- placed / assembled
horizontally at parting line of the mould
such that one half remains in the cope
and the other half in the drag.
Core Assembly-1
2. Vertical core is placed/assembled in
vertical position both in cope and drag
halves of the mould. Amount of taper on
the top is > that at the bottom.
Core Assembly-1
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3. Hanging or cover core -- is hung from
cope and no support at bottom of drag.
Cover core covers the mould and rests on
a seat made in the drag. Fastened with
the help of wires etc.
Core Assembly-1
Core Assembly-1
4. Balanced core --is assembled/
supported and balanced from its one
end only. Used when casting does not
need a through hole or cavity.
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5. Ram-up core -- placed with
pattern before ramming. Used when
cavity is not accessible.
Core Assembly-2
6. Kiss core -- does not require core
seats. Held in position due to pr.
exerted by cope on drag. No. of
holes by using No. of kiss cores.
Core Assembly-1
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7. Drop core, stop off core or wing core -
- used when a hole, recess or cavity
required in a casting is not in line with
parting surface i.e. it is above or below
parting line. Also known as tail core,
saddle core or chair core
Core Assembly-1
To keep core in its place during casting
some form of chaplets are required.
Chaplets are supporters of cores. These
are rods with flat or curved plates riveted
to them. Various types of chaplets are
used to different types of cores.
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If a casting have different thickness at different sections
than thin section tend to solidify more quickly as
compared to thick section so chills are inserting on the
thick sections in order to accelerate the cooling rate so
that no internal stress is developed due to different
cooling rate.
Sometimes some surfaces of the castings are more
exposed to atmosphere in that case also chills are used to
obtain the proper directional solidification. The chills are
broadly of two types external and internal. External
chills are placed in the mould walls (i.e. external to the
casting) while internal chills are placed in the mould
cavity (i.e. a part of the casting).
Green sand moulds :-
The sand mould prepared from natural moulding sand in its
green state is called green sand mould.
In a green sand mould, molten metal is poured while it is in
green state i.e. the undried condition.
A green sand mould possesses lower strength and lower
permeability
Green sand mould offers less resistance to the solid
shrinkage of castings and thus the castings don’t crack or
tear while solidifying.
Green sand moulds are suitable for producing small and
medium sized castings.
Green sand moulds contain moisture, therefore certain
defects like blow holes may occur in casting. The surface
finish is also not good.
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Dry sand moulds :-
Dry sand moulds are prepared from fine grained
sand mixed with suitable binder and baking in an
over (at temperature 300 to 6500F) before the
molten metal is poured in them.
Dry sand moulds possess higher strengths as
compared to green sand moulds.
They are more expensive and consume more time in
making as compared to green sand moulds.
Castings are more susceptible to tears.
Casting produced are dimensionally accurate,
better surface finish.
Skin dried moulds :-
The mold is made with the moulding sand in the
green (moisture) condition and then the skin of
the mould cavity is dried with the help of gas
torches or heat lumps. Thus it is the compromise
between green sand and dry sand moulds.
Skin dried moulds are dried only upto a depth
varying form 8 mm to 25 mm.
If a skin dried mould is not poured immediately
after drying, moisture from green backing sand
penetrate the dried skin and make the skin dried
sand ineffective.
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Air dried moulds :-
These moulds are similar to skin dried moulds in the sense
that their skin is dried, but they are not artificially heated.
Skin hardness is obtained by exposing them (moulds) to
air for a certain length of time. Large pit moulds get dried
in this manner because they are exposed to air for a
considerable time during making.
Loam moulds :-
They are used for extremely large castings. They are first
built up with bricks and often reinforced with Iron plates.
A loam mortar is prepared and plastered on the backing
made from bricks and Iron then they are finished by
sweeps or stickles, given a refractory coating and finally
baked. Construction of these moulds reduce the pattern
cost.
Cement Bonded Sand Moulds :-
Cement bonded sand mould material consists of 85.5% pure
silica sand, 10% Portland cement and 4.5% water.
Cement bonded sand moulds develop strength and hardness
because of the setting action of the Portland cement. Drying
and setting of cement takes about 72 hours. Casting made in
them are accurate, smooth surfaced, need no further
machining, having clean surface.
Plaster moulds :-
Plaster mould is prepared in the following way.
Use a pattern of metallic or some other moisture resistant
material.
Make a slurry of the mixtures of gypsum or plaster of Paris
(CaSo4 .½ H2O) and additives such as talc, silica flour,
asbestos fibre etc. with water.
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The slurry is poured over the pattern and is allowed to
preset.
Pattern is taken out and the preset mould is heated in an
oven at about 6000f for several hours. It removes moisture
from the plaster mould.
Cope and drag are made separately by the method described
above and are assembled for pouring.
Plaster moulds are used for non-ferrous castings.
Plaster moulds imparts good surface finish and dimensional
accuracy to the casting but mould possess poor permeability
which causes several defects.
The rate of cooling of the metal is slow giving rise to the
growth of large grains of metal.
Low strength and heat conductivity of the mould limits the
size of the castings.
Carbon-di-oxide moulds :-
These moulds are made from a mixture of clean
and dry silica sand and sodium base binder.
Carbon dioxide gas is passed through this mould
to obtain the desired hardness.
Shell moulds :-
Shell moulds are produced with the help of
heated Iron or steel patterns.
A mixture of fine sand and phenolic resin is used
to produce shells.
Shells are assembled to form the mould in which
liquid metal is poured.
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Metallic Moulds :-
Metal moulds are also known as permanent moulds they
are generally made up of Grey cast Iron or steel. Metal
moulds are employed in the following casting processes.
Permanent mould casting.
Pressure die casting.
Centrifugal casting.
Core sand moulds :-
Core sand mould is made by assembling a number of
cores made individually in separate core boxes and
baked. Core sand moulds are more expensive (because of
the cost of binders etc.) as compared to green and dry
sand moulds.
1. Bench Moulding
2. Floor Moulding
3. Pit Moulding
4. M/C Moulding
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1. Bench Moulding —On bench for small
& light, green moulds; For small
production, moulds are prepared in 2-3
boxes with use of moulding boards &
then removed from bench for pouring. For
mass production a match plate is used in
conjunction with the bench.
2. Floor Moulding --done on floor, which
acts as a drag. Covered by a cope open
casting—Used for medium & large
castings.
3. Pit Moulding —done in pit. Used for very
large castings. Drag part in pit. Separate
cope is rammed & used above pit. Sides of
pit lined with bricks and bottom is covered
with moulding sand. Gates, runner, pouring
basis, sprue etc. are made in the cope.
4. M/C Moulding --done by a m/c. Ramming of
sand, rolling the mould over, forming gate
and drawing out of pattern can be done by
machines much better & more efficiently
than by hand. Identical & consistent
castings. Preferred for mass production
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175
• Machine Moulding
Following are three methods commonly used for green sand
moulding.
Open sand method :-
This is the simplest form of green sand moulding particularly
suitable for solid patterns.
It uses no moulding box. The sand on the foundry floor is
leveled and the pattern impression is formed in it.
Upper surface of the mould is open to air.
Pouring basin is made at one end of the mould, and the
overflow channel cut at the sides of the cavity.
The upper surface of the casting made by this method is
rough.
This method is used for the casting of railing and gates,
moulding boxes, grills, floor plates, weights etc.
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Bedded in method :-
This method is used if the upper surface of the casting is
required to be smooth or the upper surface of the casting
is not flat but has some other shape. That is why these is
the need of cope which is not employed in open sand
method. The pattern is placed on the sand bed. Sand is
rammed properly around the pattern.
The top of drag is smoothened and the parting sand is
spreaded.
Cope flask is placed on the drag (including the pattern)
and is rammed.
Runner, gates etc. are cut after removing the cope.
Pattern is withdrawn and the cope and drag are
assembled for pouring.
Turn over method :-
Place the flat side of one half of the split pattern on a
moulding board (with the help of dowel pins).
Place drag flask (bottom part of the moulding box) over
the pattern and ram the sand.
Invert the drag and remove the moulding board
Fix (with dowels) the second half of the pattern over the
first half.
Place a cope flask (upper part of he molding box) over
the drag.
Ram up the sand in the cope
Remove the cope and cut gates etc.
Remove the split pattern.
Invert the cope over drag
The mould is ready for pouring
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This process in basically a hardening process for moulds
and cores.
Principal :-
The principal of working of the CO2 process is based on
the fact that if Co2 gas is passed through a sand mix
containing sodium silicate,the sand immediately becomes
extremely strong bonded as the sodium silicate becomes
a stiff gel. This gel is responsible for giving the necessary
strength to the mould. The reaction is :
Na2SiO3 × H2O + Co2 - Na2Co3 + SiO2 × H2O
(Sodium silicate) (Carbon di-oxide) (sodiumcarbonate) (silica gel)
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Operation :-
The mould material consists of pure dry silica
sand (free from clay) and 3 to 5% sodium silicate
liquid (water) base binder and moisture is
generally less than 3%. Small amount of starch
may be added to improve the green strength.
Sugar may be added to improve the collapsibility.
After sand preparation, it is rammed around the
pattern in the mould boxes or core boxes.
Carbon dioxide gas is forced into the mould or
core at about 1.4 to 1.5 kg/cm2.
Additional hardening may be done by baking.
Over-gassing should be avoided as it reduces core strength.
After gassing, cores etc. may be given a suitable refractory
coating and the system is ready for pouring.
Both wooden and metal pattern can be employed .
In case the pattern has not got passages for Co2 to flow in to
sand rammed around it , gassing may be done after
withdrawing the pattern..
Pattern withdrawal can be eased by rubbing the pattern with
graphite before ramming the sand around it and gassing.
Wood pattern or wood boxes are attacked by sodium silicate
and may be protected by an application of a varnish or
silicon lacquer that is resistant to the effect of the binder.
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Advantages :-
Speedy operation & No baking is required (Generally)
Cores and moulds can be stored for long times.
Less floor space is required.
Same sand is used for the production of both cores and
moulds
Process can be easily mechanized.
Permeability and flow ability of sand are improved.
It can be used for both ferrous and non ferrous casting.
Good surface finish, good dimensional accuracy.
Disadvantages :
Sand mixture is costly, Collapsibility is poor
It is difficult to reclaim the used sand.
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Introduction :-
It is a process in which, the sand mixed with
a thermosetting resin is allowed to come into
contact with a heated metallic pattern plate,
so that a thin and strong shell of mould is
formed around the pattern. Then the shell is
removed from the pattern and the cope and
drag are removed together and kept in a
flask with the necessary back up material
and the molten metal is poured into this
mould.
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Procedure :-
A metal pattern, heated to about 1750c to 3500c, is
clamped over a box containing sand mixed with
thermosetting resin such as phenol formaldehyde, urea
formaldehyde or polyesters.
The box and pattern are inverted for a short time. The
mixture when comes in contact with hot pattern, it
causes an initial set and builds up a coherent sand shell
next to the pattern. The thickness of this shell is about 6
mm to 18 mm and is dependent on the pattern
temperature and the sand mixture. This takes 5 to 20
seconds only.
The box and pattern are brought in its original position.
The shell of resin bonded sand is retained on the pattern
surface, while the unaffected sand falls into box.
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The shell, still on the pattern is cured by heating
it in an oven from 2500C to 3500C for 1 to 3
minutes.
The assembly is removed from the oven and the
shell is stripped from the pattern by ejector pins.
In order to obtain clean stripping ,a silicon
parting agent may be sprayed on the pattern.
The shell halves are assembled with clamps and
supported in a flask with backing material. The
shell mould is now ready for pouring.
Advantages of shell moulding :-
Suitable for thin sections.
Surface finish obtained is excellent.
Good dimensional accuracy (Tolerance = .002 to
.003mm per mm)
Less floor space.
Machining and cleaning cost is negligible.
The total sand used is only 5 to 10% that of green
sand mould
The molds can be stored until required
Less skilled labour is required.
Cooling rate of cast metal is slow so larger gain size.
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Disadvantages of shell moulding :-
Initial cost of pattern and sand is high
Special equipments are to be used.
Reuse of sand is difficult.
Maximum size is limited.
Minimum thickness of the section that can be cast
is 4mm.
Melting (Cupola) and Pouring
Advantages of Cupola for melting C.I.: Low cost;
Better control of chemical comp.; Easier temp.
control; Tapping at regular intervals; Easily
available and less expensive fuels.
Main disadvantage-- not possible to produce iron
with < 2.8% C for certain white C.I. For this
duplex process is employed.
Description of a cupola
Shell-- Steel sheet 6-12 mm thick and lined
inside with acid refractory bricks [((SiO2) and
Alumina (Al2O3)]and clay. Dia.: 1-2 m. Height: 3 to
5 times the diameter.
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Foundation/Support--- Brick works or steel
columns. Drop bottom door for discharging
debris of coke, slag at end of a melting.
Tuyers – for providing air for combustion at
a ht. of 0.6 - 1.2 m.
Wind belt—to deliver air to tuyeres on outer
shell.
Blower ---a high pressure fan to supply the
air to wind belt.
Slag hole --at 250 mm below centres of
tuyeres to remove slag.
Charging hole – at 3-6 m above tuyeres for
feeding charge.
Chimney or stack --- 4.5-6 m above the
charging hole
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Combustion or Oxidising Zone
Reducing Zone
Melting Zone
3 Fe + 2 CO= Fe3C + CO2
Zones in a Cupola
Crucible Zone/Well :- Between top of sand
bed and bottom of tuyeres to accummulate
molten metal.
Combustion or Oxidizing Zone :- 150 -300
mm above top of tuyers. Heat by following
reactions.
C + O2 CO2 + Heat
Si + O2 SiO2 + Heat
2Mn + O2 2MnO + Heat
Fe + O FeO + Heat
Temperature in this zone: 1540 – 18700C
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Zones in a Cupola
Reducing zone :-From top of combustion zone
upto top of coke bed. Temp. drops to about
12000C
CO2 + C(coke) 2CO – Heat
Melting zone :- From top of coke bed upto a
ht. of 900 mm. Temp. here is >12000C;
Melting point of cast iron = 11470C
3Fe + 2CO Fe3C + CO2 + Heat
Preheating zone or charging zone :- From top
of melting zone upto charging door.
Stack zone :- From charging zone upto top of
cupola.
Cupola Operation
Preparation of Cupola :- Clean out slag.
Repair damaged lining with mixture of fire
clay and silica sand. Raise bottom doors.
Introduce bottom sand. Form slag hole.
Firing the cupola :- Kindle wood at the
bottom. Add coke to a level slightly above
tuyers. Start air blast at a slower rate. After
red spots, add extra coke.
Charging the cupola :- After proper burning,
charge alternate layers of Pig Iron
(including steel scrap), coke and flux
(limestone @ 2-3% of metal charge) up to full
height.
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Cupola Operation
Opening of air blast :- Open air blast. Keep
tap hole closed to accummulate hot metal in
hearth. Maintain rate of charging equal to
rate of melting so that the furnace remains
full.
Pouring the molten Iron :- After sufficient
metal collects in well, open slag hole to
remove slag. Then open tap hole to collect
molten metal.
Closing the cupola :- At end of operation,
shut off blast. Swing open bottom plates to
take out remains inside cupola.
• Efficiency of Cupola (η = 30-50%)
Thermal η= Heat utilized /Potential heat in
coke, air blast & oxidation of Fe, Si, Mn
Pouring of Liquid Metal
• Tap metal in large receiving ladle lined
with fire clay refractory. Distribute to
small pouring ladles. There are various
types of ladles. Common ladle—15-30 kg
hand type.
• Shank/bull ladle --30-150 kg is also used.
• Large castings are poured with bottom
pouring ladle.
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• For small and medium sized mould, tea
pot ladle is used. The tea pot ladle and
bottom pouring ladle have built in spout
to pour metal free of slag.
• Pouring to be done continuously and at a
uniform rate until the mould, gates and
risers are full. If temperature too high,
blow holes due to hot gases. If too cold,
the metal will solidify prematurely.
• Temperature of metal is checked by
optical pyrometer. Skim back floating
slag with a skimming bar to avoid
forming slag pockets in casting.
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Operation of cutting off unwanted parts
such as sprue, gates, riser etc, removal
of sand attached to the casting by
cleaning and finishing of casting is
know as fettling.
1. Rough Cleaning of Casting —
•Removal of: cores; gates and risers;
unwanted metal projections, fins, nails;
adhering sand and oxide scale.
•Repair of casting, wherever possible or
required.
•Heat treatment of casting.
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2. Surface Cleaning of Casting
by:
1. Wire brushing.
2.Tumbling- of castings inside large
steel barrels, together with a
number of small cast Iron pieces
called stars. Efficient method.
3.Sand blasting by a stream of high
velocity air carrying large size
sand particles.
4. Shot blasting -- Similar to sand
blasting but metallic abrasives are
used.
5. Hydro-blasting — using high velocity
stream consisting of water and sand.
6. Mechanical Impact cleaning -- Using
metallic abrasives by means of
centrifugal force.
7. Pickling by use of an acid.
3. Finishing — by machining, chemical
treatment, polishing, buffing, and
painting etc
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Inspection of Castings
Destructive & non-destructive methods
Destructive
Cutting sample castings into pieces and
examining for defects and mechanical
properties.
Non destructive methods
1. Visual Inspection for cracks, dirt, blow
holes, metal penetration, shifts, run-outs
2. Dimensional Inspection for dimensions
and tolerances using height and depth
gauges, dividing heads, go and not gauges,
snap and plug gauges.
3. Pr. Testing --to locate leaks in a casting.
4. Radiographic Inspection ( X- ray or
Gamma ray) –is used for internal defects.
Intensity of transmitted rays is recorded
on a photographic film. Defects appear as
darker areas.
5. Magnetic Particle Inspection-- used on
ferrous castings for surface or slightly sub-
surface defects. Casting surface or areas
are magnetized by magnetic field; fine
ferromagnetic particles are applied on it.
ferromagnetic particles concentrate
around the defect.
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Fluorescent Dye Penetrant Test
used for pores and cracks on
surface.
A fluorescent penetrating oil mixed
with whiting powder is applied to
the surface by dipping, spraying or
brushing.
After wiping, oil creeps out of
cracks or other defects to show
crack.6.
Casting Defects and Remedies
Reasons
1. Improper design of casting.
2. Improper design of pattern.
3. Inadequate care during molding and
core making
4. Improper mould and core material
5. Improper design of gating & risering
6. Inadequate care during melting &
pouring
7. Unsuitable metal composition
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Types of Defects-
1. Blow holes; Porosity;
2. Shrinkage ; Misruns and Cold Shuts;
3. Hot tears; Cuts and Washes;
4. Metal Penetration; Drop;
5. Fusion; Shot Metal;
6. Shift; Rat tails or buckles;
7. Swells; Hard spots;
8. Run outs; Crushes;
9. Warpage; Inclusions
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ISE 316 - Manufacturing
Processes Engineering
Misrun
A casting that has solidified before
completely filling mold cavity
ISE 316 - Manufacturing
Processes Engineering
Cold Shut
Two portions of metal flow together but
there is a lack of fusion due to
premature freezing
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ISE 316 - Manufacturing
Processes Engineering
Cold Shot
Metal splatters during pouring and solid
globules form and become entrapped in
casting
ISE 316 - Manufacturing
Processes Engineering
Shrinkage Cavity
Depression in surface or internal void
caused by solidification shrinkage that
restricts amount of molten metal
available in last region to freeze
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ISE 316 - Manufacturing
Processes Engineering
Sand Blow
Balloon-shaped gas cavity caused by
release of mold gases during pouring
ISE 316 - Manufacturing
Processes Engineering
Pin Holes
Formation of many small gas cavities at
or slightly below surface of casting
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ISE 316 - Manufacturing
Processes Engineering
Penetration
When fluidity of liquid metal is high, it may
penetrate into sand mold or sand core,
causing casting surface to consist of a
mixture of sand grains and metal
ISE 316 - Manufacturing
Processes Engineering
Mold Shift
A step in cast product at parting line caused by
sidewise relative displacement of cope and drag
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Blow Holes--as cavities (Holes). Visible--
open blow holes. Non visible --blow holes.
Causes & Remedies
• Excessive moisture in sand. Control
moisture.
• Low permeability and excessive fine grain
sands. Control permeability.
• Cores, neither properly baked not
adequately vented. Control.
• Extra hard rammed sand. Control
• Rusted and damp chills, chaplets and
inserts. Control
• Excessive use of organic binders. Control.
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Porosity --pin hole porosity or gas porosity
due to H2 trapped during solidification.
Causes Remedies
• High pouring temperature. Adjust·
• Gas dissolved in metal. Degas·
• High moisture & low permeability in mould.
Control
Warpage-- deformation due to internal
stresses developed by differential
solidification in different sections.
Causes & Remedies
• Not proper directional solidification.
Facilitate.
• Continuous large flat surfaces. Modify
casting design
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Misruns— metal not enough to fill
mould and Cold Shuts—Two metal
streams do not fuse.
Causes & Remedies
• Lack of fluidity. Adjust temp.
• Faulty design. Modify
• Faulty gating. Modify
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Porosity --pin hole porosity or gas porosity
due to H2 trapped during solidification.
Causes Remedies
• High pouring temperature. Adjust·
• Gas dissolved in metal. Degas·
• High moisture & low permeability in mould.
Control
Warpage-- deformation due to internal
stresses developed by differential
solidification in different sections.
Causes & Remedies
• Not proper directional solidification.
Facilitate.
• Continuous large flat surfaces. Modify
casting design
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Misruns— metal not enough to fill
mould and Cold Shuts—Two metal
streams do not fuse.
Causes & Remedies
• Lack of fluidity. Adjust temp.
• Faulty design. Modify
• Faulty gating. Modify
234
Shrinkage –due to vol. shrinkage
during solidification.
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Shrinkage –due to vol. shrinkage
during solidification.
Causes & Remedies
•Faulty gating and risering.
•Improper chilling.
Ensure proper directional
solidification by modifying gating,
risering and chilling.
Inclusions--sulphides, oxides,
phosphates, other impurities.
Causes & Remedies
•Faulty gating and faulty pouring.
Modify
•Inferior moulding or core sand. Use
superior sand.
•Soft ramming. Provide hard
ramming.
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Hot tears –due to cooling stresses.
Causes & Remedies
Lack of collapsibility of core and
mould. Improve
Faulty design. Modify
Hard ramming. Provide soft ramming.
Cuts and Washes—due to erosion of
sand from mould or core.
Causes & Remedies
• Low strength of mould and core. Adust
• Lack of binders in facing and core sand.
Adjust
• Faulty gating. Modify design
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Metal Penetration— due to loose
sand mould
Causes & Remedies
• Large grain size of sand. Use fine
size.
• Soft ramming. Provide harder
ramming
• Moulding sand or core has low
strength. Adjust.
• Pouring temperature of metal two
high. Adjust.
Drop-- a portion of sand from mould in molten
metal.
Causes & Remedies
• Low green strength of sand and core. Modify
composition.
• Too soft ramming. Provide harder ramming.
• Inadequate reinforcement of sand. Provide
adequate.
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Fusion—of sand grains with molten
metal.
Causes & Remedies
• Low refractoriness. Improve.
• Faulty gating. Modify.
• Too high pouring temp. Use lower
temp.
• Poor facing sand. Improve quality.
Shot Metal --improper fusion bet. main
stream and already solidified particles.
Causes & Remedies
• Too low pouring temp. Adjust..
• Excess S content in the metal. Reduce S.
• Faulty gating. Modify.
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Shift-- misalignment between two
mating surfaces. Mould shift or core
shift.
Causes & Remedies
Misalignment. Repair or replace the pins.
Improper support & location of core.
Improve.
Faulty core boxes. Repair or Replace.
Hard spots--on Iron castings rich in
Si due to local chilling.
Causes & Remedies
• Faulty metal composition. Adjust.
• Faulty casting design. Modify.
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Swells – due to
increase in cavity
by movement of
mould wall due to
liquid metal
pressure.
Causes & Remedies
•Soft ramming of
mould. Provide
harder.
•Low strength of
mould and core.
Increase strength.
•Mould not properly
supported. Provide
Rat tails or buckles-- an irregular
line on the surface of casting due to
expansion of sand by heat of metal.
Causes & Remedies
Excessive mould hardness. Reduce.
Large flat surface of casting. Provide
grooves or depressions.
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Run outs —due to leakage of molten
metal. incomplete casting.
Causes & Remedies
•Faulty moulding. Improve.
•Defective moulding boxes. Replace.
Crushes--deformation of mould
due to pressing or scrapping of
sand during setting of core or
assembly.
Causes & Remedies
•Careless assembly of cores in the
mould. Take care.
•Worn out core prints on patterns.
Repair core prints.
•Defective core boxes. Replace.
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Gravity Die or Permanent Mold Casting :-
This casting is called gravity die casting because
molten metal is poured into the mold under
gravity only; no external pressure is applied to
force the liquid metal into the mold cavity
(opposite to die casting)
This casting is called permanent mold casting
because it uses the mold which is permanent i.e.
the mold can be reused many times before it is
discarded or rebuilt.
Permanent Molds :-
Permanent molds are made of Grey cast iron (having high
resistance to thermal shocks), alloy or non ferrous alloys.
Inner surface of the moulds are coated first with a refractory.
This is done in order to reduce the chilling effect on the cast
metal and to facilitate the removal of casting and prevent the
adherence of the molten metal to the mould.
A permanent mold is made in two halves in order to facilitate
the removal of casting from the mould.
Pouring cups, sprue, gates and riser are built in the mold
halves itself.
The moulds also have the facilities of setting cores, ejector
pins for ejecting out casting from the mould and clamps for
clamping etc.For faster cooling, fins or projections may be
provided on the outside of the permanent mould.
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Advantages :-
Closer dimensional tolerance and accuracy.
Smoother surface and better appearances.
Fine grained metal structure (because of chilling effect)
Mass production is more economical
Less labour work and time.Require less skilled labour.
Good quality of casting (High density, less porosity etc.)
Requires less space.
Disadvantages :
A permanent mould costs much more than a sand mould.
It is suitable for small and medium sized non ferrous casting
only.
Casting have poor elongation.
Several defects like stress and surface hardness may be
produces due to surface chilling effect.
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Since the gating system is cut in the mould halves,
once machined, it cannot be changed.
The extremely high temp of the molten steel make
this method unsuitable for steel castings.
Applications :-
Carburetor bodies
Refrigeration castings.
Oil pump bodies
Connecting rods and automotive pistons.
Die Casting (Pressure die casting):-
Unlike gravity die casting, in this molten metal is forced into
permanent mold (die) cavity under pressure.
The pressure varies from 20 to 2000 kgf/cm2 and is
maintained till solidification stage was reached. The pressure
is generally obtained by compressed air or hydraulically.
Die casting machines :-
Die casting machines performs the following functions :
Holding two die halves firmly together.
Closing the die
Injecting molten metal into die.
Opening the die
Ejecting the casting out of the die.
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Die casing machines are of two types :
Hot chamber die-casing machines.
Cold chamber die-casting machines.
Hot chamber die casting :-
In hot chamber die casting machine, the melting unit is
in the machine itself that is why it is called hot chamber
die casting machine.
The molten metal possess normal amount of superheat
and therefore less pressure is needed to force the liquid
metal into die.
It has further two types of arrangements.
* Goose neck or air injection type (or direct air pressure)
* Submerged plunger type.
Good neck or Air injection type :-
In this machine, the goose neck container is
operated by a lifting mechanism. Initially it is
submerged in the molten metal and is filled by
gravity. Then it is raised so as to bring the nozzle
in contact with the die opening and is locked in
that position. Compressed air then forces the
metal into the die and pressure is maintained till
solidification. When solidification is complete, the
gooseneck is lowered down and casting is
removed by ejector pins after opening the dies.
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Submerged plunger type :-
In this machine, the goose neck type container
always remains immersed in the metal pot. The
molten metal from the metal container is forced
inside the die with the help of a plunger submerged
in the molten metal and operated hydraulically.
When the plunger moves up, the molten comes up
and fills the cylinder and when the plunger moves
down, the metals is forced into the die. The
movable die platen are synchronized such that
when plunger is moving up, the movable die
platen moves away and the casting is removed.
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Cold chamber die casting :-
In these machines, the metal is melted separately
in a furnace and transferred to these by means of
small hand ladle. After closing the die, the molten
metal is forced into the die cavity by a
hydraulically operated plunger and pressure is
maintained till solidification. These machines can
either have vertical plunger or horizontal plunger
for forcing molten metal into die. These machines
are widely used for casting a good number of
aluminum alloys and brasses.
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Advantages of die casting :-
It requires less floor space.
Thin sections of the complex shape are possible.
(0.4mm)
High production rate.
Greater surface finish.
Die castings are less defective than sand casting.
The labour cost involved is less.
A number of non-ferrous alloys can be die cast.
The die has a long life. It is possible to produce
1,00,000 castings in case of zinc base alloys 75,000
castings in case of copper base alloys.
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Limitations of die casting :-
The cost of die and equipment in high
The life of die decreases rapidly if metal temperature is
high.
Ferrous alloys are not cast and moreover a limited
number of non-ferrous alloys can be economically die-
cast.
The size of the casting is limited.
The air in the die cavity gets trapped inside the casting
and creates porosity.
Special skill is required for maintenance and supervision of die.
Die casting technique requires comparatively a longer
period of time for going into production (set up time,
preparation time)
Applications of die casting :-
Die casting process has been used for many non-ferrous
metals and alloys such as zinc, aluminum, copper,
magnesium ,lead and tin.
Automobile parts.
Marine uses.
Domestic appliances.
Instruments.
Parts of the refrigerators, washing machines, television,
typewriters, projectors, radio, Binocular, camera.
Lead base alloys castings are used in Radiation shielding,
battery parts, light duty bearings etc.
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Slush Casing :-
This method is a special application of permanent mould casting in
which hollow castings are produced without the use of cores. The
casting produced by this method are not desired for engineering use
because wall thickness of the castings are not uniform. External
shape is important in these castings.
In this method, molten metal is poured into the metallic mould and
allowed to solidify upto the required thickness. The mould is then
turned over so that the remaining liquid metal falls out and castings
of desired thickness can be obtained.
Normally small thickness casting of lead, zinc and low melting
alloys are obtained by slush casting methods.
The thickness of the casting depend upon the time for which the
metal is allowed to solidify into the permanent mould.
In order to facilitate the removal of casting the moulds are made in
two halves. Ornaments, statues, toys and other novelties are the
examples of die castings.
Centrifugal Casting :-
In centrifugal casting, centrifugal force plays a major role in
shaping and feeding of the casting. In this process mould is
rotated rapidly about its central axis as the metal is poured
into it.
The centrifugal force is utilized in two ways.
It is utilised to distribute liquid metal over the outer surface
of a mould. Hollow cylinders and other annular shapes are
formed in this way.
Centrifugal force tends the poured metal and the freezing
metal to fly outward, away from the axis of rotation, and this
tendency creates high pressure on the metal or casting while
it is freezing the lighter slag, oxides and other inclusions
being lighter, gets separated from the metal and segregates
towards the centre.
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True centrifugal casting :-
In this process, the casting are made in a hollow,
cylindrical mould rotated about an axis common to both
casting and mould.
The axis may be horizontal, vertical or inclined.
The castings have more or less a symmetrical
configuration (around, square, hexagonal etc.) on their
outer contour and don’t need any centre core
Castings cools and solidifies from outside towards the
axis of rotation so good directional solidification hence
castings free from shrinkage.
True centrifugal casting may be produced in metal or
sand lined mold, depending largely upon the quantity
desired.
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Advantages of true centrifugal casting :-
There is no need of core to make a pipe or tube.
No gates or risers are used so no material is wasted.
Proper directional solidification is obtained.
Fine grained metal casting.
It is a quick and economical method.
The impurities segregates towards the centre from where they can be
easily machined.
Disadvantages of true centrifugal casting :-
It is limited to symmetrical shaped objects such as pipes, rolls,
cylinder etc.
Equipment costs are high
Skilled workers are required.
Applications :-
Liners for I.C. engines
Pipes, rolls, cylinder sleeves, piston ring stock, bearings, bushing etc.
Semi Centrifugal casting :-
Unlike true centrifugal casting, a (sand) core is used to form
the central cavity (as in the hub of the wheel). So internal
shapes are controlled which is not possible in true centrifugal
casting.
Semi-centrifugal casting are normally made in vertical
machines the mold axis is concentric with the axis of rotation.
Directional solidification can be obtained by proper gating of
the casting, and selective chilling.
Casting shapes, more complicated than those possible for true
centrifugal casting can be made. A number of molds stacked
together, one over the other can be fed by a common central
sprue in order to produce more than one casing at a time.
Parts produced are gears, flywheels and track wheels etc.
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Centrifuge Casting :
In this casting, the axis of the mould and that of the rotation
don’t coincide with each other.
Parts are not symmetrical about any axis of rotation and cast
in a group of moulds arranged in a circle. The setup is
revolved around the centre of the circle to induce pressure on
the metal in the mould.
Mould cavities are fed by a central sprue under the action of
the centrifugal force. The metal is introduced at the centre
and fed into the mould through radial in gates.
Centrifuging is possible only in vertical direction.
Parts produced are valve bodies, valve bonnets, plugs, yokes,
pillow blocks etc.
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Advantages of centrifuge casting methods :-
Produce casting more economically.
Better quality
It can cast parts which cannot be satisfactorily
produced by other methods.
Casting shapes imposes no special limitation in
this process and an almost unlimited variety of
smaller shapes can be cast.
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Investment Mold Casting or Lost Wax
Process(Lost wax process) :-
This process uses wax pattern which is subsequently melted
from the mould, leaving a cavity having all the details of the
original pattern (required casting).
Procedure :-
Producing a die for making wax pattern :-
Dies may be made either by machining cavities in two or
more matching blocks of steels or by casting a low melting
point alloy around a (metal) master pattern
Dies halves are then sent for necessary machining and
drilling the gate through which wax is to be injected for
preparing expendable patterns (wax, plastic, tin, frozen
mercury in this process but wax is more commonly used).
Making wax patterns :-
The die halves are closed and properly clamped.
Molten wax is then forced into die, under pressure, by
means of a wax injection machine.
Allow cooling and solidification.
The die is then opened and the pattern removed. A
lubricant is then sprayed on to the die surfaces and the
same closed for casting the next wax pattern {therefore
one wax pattern is used for one piece only)
Assembling the wax patterns :-
Assemble a number of small wax patterns to a common
wax gating system so that they can be placed together in
one mould (to increase the production).
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Pre-coating the pattern assembly :-
The wax pattern assembly is dipped into a slurry
of a refractory coating material.
A typical slurry consist of 325-mesh silica flour
suspended in a ethyl silicate solution.
Wax pattern assembly is next, sprinkled with 40
to 50 AFS (American foundary society) silica sand
and is permitted to dry.
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Investing the wax pattern assembly for the production of
moulds:
This is done by inverting the wax assembly on the bottom board,
surrounding it with a paper lined steel flask and pouring the
investment moulding mixture around the pattern. The mould
material settles by gravity and complete surrounds the pattern as
the work table is vibrated.
The moulds are then allowed to dry in air for 2 to 3 hours.
Removal of wax pattern :-
The wax pattern can be removed from the mould by two methods
:
Place the mould in a furnace in an inverted position i.e. the sprue
down wards. The wax is melted out due to heat and collected for
reuse.
In other method, mould is placed in a bath of trichloromethylene
vapour which also enables the recovery of wax for reuse.
Pouring and casting :-
The mould is again heated at he rate of 400c to 700c per hour from
about 1500c to 10000c for ferrous alloys and 6500C aluminum
alloys.
Preheating is done :
To remove the wax if any
It help the metal to flow easily and fill up properly
It causes expansion of he mould.
After preheating, the metal is poured into the investment mould
under simple gravitational force or under the force of applied air
pressure or by centrifugal force.
Cleaning, finishing and inspection :-
Each casting is separated from the assembly and the gates etc are
removed.
Finishing and inspection of casting is done.
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Advantages of Investment Casting :-
High dimensional accuracy of the order of +_0.08 mm
can be attained.
A very smooth surface without parting line.
Machining can be eliminated.
Very thin sections can be cast easily (0.76mm).
Complex contours and intricate shapes can be easily
cast .
Castings are sound and have large grains as the rate of
cooling is slow.
Complex shapes are possible because pattern is
withdrawn by melting it.
Disadvantages of Investment Casting :-
The process is suitable for small size parts.
This is a more expensive process.
Process is relatively slow
One wax pattern is required to make one
investment casting.
The use of cores makes the process more
difficult.
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Application of Investment casting :-
Parts for sewing machines, locks, rifles, burner
nozzle, milling cutters and other type of tools,
jewelry and art casting.
In dentistry and surgical implants.
Parts of gas turbines
Corrosion resistant and wear resistant alloy
parts used in diesel engine, picture projectors and
chemical industry equipments.
Continuous Casting :-
In this process the molten metal is continuously poured into a
mould around which there are facilities for rapidly chilling the
metal to the point of solidification.
The solidified metal is then continuously removed from the
mould at the calculated rate.
Asarco process :-
In this the metal is fed by gravity into the mould and
withdrawn by the rolls below.
The die is water cooled and self lubricating.
The upper end of die is in molten metal and thus serves the
function of riser.
A saw is provided below the rolls to cut the product to desired
length or oxy-acetylene cutting is done.
Argon is added with molten metal to avoid atmospheric
contamination.
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Reciprocating process :-
In this process molten metal is poured into a holding
furnace.
At the bottom of this furnace, there is a valve by which
the quantity of flow can be changed.
The molten metal is poured into the mould at a uniform
speed.
The water cooled mould is reciprocated up and down.
The solidified portion of the casting is withdrawn by the
rolls at a constant speed.
The movement of the rolls and the reciprocating motion
of the mould are properly controlled by means of cams.
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Advantages of continuous casting :-
The process is cheaper than rolling.
Casting surfaces are better.
Grain size and structure of the casting can be easily
controlled.
The process can be easily mechanised and thus unit
labour cost is less.
Applications of continuous casting :-
Materials such as Brass, zinc, copper, aluminum and its
alloys, magnesium, carbon and alloys etc.
Production of blooms, billets, slabs, sheets, copper bar
etc.
It can produce any shape of uniform cross section such as
rectangular, square, hexagonal, fluted or gear toothed etc.
288
MP &Casting Process Important Questions
Define Manufacturing Process & Explain
the classification of Manufacturing
Process.
Discuss various machine moulding
processes.
Explain in brief, the various types of
moulding processes.
Discuss basic steps in a casting process.
Explain different types of casting
methods. Also explain the steps involved
in making a casting.
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Casting Process
1. (a) What is casting? Describe basic steps
in casting process.
(b) Discuss various machine moulding
processes.
(c) Explain in brief, the various types of
moulding processes.
(d) Name the types of moulding boxes?
Describe and sketch a snap moulding
box.
(e) Discuss any three methods of sand
mould casting process.
(f) Discuss the various types of sand
moulding methods.
2. (a) Explain the functions of the following. (i) Master
pattern (ii) Riser (iii) Runner (iv) Gate
(b) What are the different types of patterns?
Explain.
(c) Describe types of Patterns along with sketches
(d) Discuss pattern allowances.
(e) What are the various pattern allowances?
Explain
(f) Describe various types of patterns. Discuss
pattern materials and pattern allowances.
(g) What are different types of pattern allowances?
(h) What are the different types of patterns used in
foundry.
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(i) What is pattern? What are pattern
allowances? Why various allowances are
necessary for pattern making?
(j) Explain pattern allowances with its types
by gving neat sketches
(k) Give the types of patterns along with neat
sketches.
(l) What is pattern? Describe various types of
patterns.
(m) Why allowances are provided on pattern?
Explain various types of allowances with
neat sketches.
(n) Define pattern and name different types
of patterns. Explain any two types of
(o) Patterns with neat diagrams. 292
MP-Unit-I Foundry
Patterns & Pattern Allowances
What is pattern? With neat sketches, explain
different types of patterns.
Write short note on (i) Cope and Drag pattern (ii)
Follow up Board Pattern (iii) Shrinkage & draft
allowances.
What is a pattern? How does it differ from the
actual product to be made from it?
Explain the common allowances provided on
pattern.
What materials are used for making pattern.
Explain different types of patterns.
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293
MP-Unit-I-Foundry
Describe types of Patterns along with sketches
Discuss various pattern allowances.
What are the various pattern allowances? Explain
Describe various types of patterns. Discuss
pattern materials and pattern allowances.
What are different types of pattern allowances?
What are the different types of patterns used in
foundry.
Define pattern and name different types of
patterns. Explain any two types of Patterns with
neat diagrams.
Patterns & Pattern Allowances
294
MP-Unit-I-Foundry
Moulding Sand and Core sand
What is moulding sand and explain the properties
of moulding sand?
What are the different properties required for a
moulding sand?
What are the main constituents of moulding
sand? Explain in brief.
What are the properties of moulding sand?
Explain each property in detail.
Explain various Sand testing Techniques with
neat diagram.
Discuss the characteristics, which good moulding
sand should possess.
Explain various Types of mould.
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299
MP-Unit-I-Foundry
Gating System
Explain the terms: Riser, Runner, Core, Facing
sand, Backing sand
What are essential characteristics of Mould?
Sketch and name the principal parts of a mould.
With a neat sketch, explain different types of
gates and risers
Also discuss the functions of risers, runners and
gates.
Explain with the help of neat sketch the following
elements of gating system (i) Runner (ii) Riser
(iii) Gates (iv) Pouring basin
300
Make a neat sketch of Cupola and explain the following-- (i)
Construction of cupola (ii) Cupola zones (iii) Cupola
charging / operation (iv) Advantages of using Cupola
Write a brief note on Cupola and describe its working.
With the help of a diagram, explain the working of Cupola
Draw a neat sketch of cupola. Label different zones and
important parts. Explain its operation with reactions in
each zone. What are the advantages and disadvantages of
cupola?
With neat sketch, Describe the operation of cupola furnace
for melting cast iron.
Discuss the functioning of Cupola furnace using a diagram.
Write short notes on Cupola
Also describe the working of a Cupola. .
MP-Unit-I-Foundry
Cupola
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303
MP-Unit-I-Foundry
Casting Defects
Explain casting defects and their remedies.
Discuss various casting defects and remedies
observed in castings produced
What are the different casting defects? What are their
remedies?
Explain various casting defects with causes and their
remedies.
Sate various defects in sand castings and also
mention their main causes and remedies.
Write short notes on (i) Hot tears (ii) Pin hole porosity
Describe various defects in casting process..
7. (a) Explain Gravity die casting Process with neat
diagram.
(b) How the tubes or pipes are casted with the
True centrifugal casting process.
(c) Explain the Semi Centrifugal and Centrifuging
casting process.
(d). Explain Continous casting process with neat
diagram.
(e) Explain the various steps involved in the lost
was casting process.
(f) What is pressure Die Casting. Explain the Hot
Chamber and Cold Chamber Die Casting Machine
with neat diagram.
(g) Write Short note on 1. Chills 2. Chaplets 3. Core
Print 4. Pattern Colour code
