This document summarizes various metal casting processes and techniques. It discusses sand casting and the key components of sand molds like the flask, pouring basin, sprue, runners, and risers. It also covers cores, moulding sands, patterns, moulding machines, melting furnaces, and common defects in sand casting. Testing methods for moulding sands like moisture content, clay content, and permeability are also summarized.

1. Unit 1
Metal casting processes
Sand Casting : Sand Mould – Type of patterns - Pattern Materials
– Pattern allowances Moulding sand Properties and testing –
Cores –Types and applications – Moulding machines– Types
and applications; Melting furnaces : Blast and Cupola
Furnaces; Principle of special casting processes : Shell -
investment – Ceramic mould – Pressure die casting -
Centrifugal Casting - CO2 process – Stir casting; Defects in
Sand casting

2. • Casting: process of producing metal components
by pouring molten metal into the mould cavity of
the required shape and allowing the metal to
solidify. The solidified piece is called casting.
Casting is done in a foundry.
• Sand Casting : a metal casting process
characterized by using sand as the mould
material. Sand castings are produced in
specialized factories called foundries.
• Most widely used casting
• Production of quantities from one to million.
• Sand mould is used,

3. SAND MOULD FEATURES

4. Major components of sand molds:
Flask – supports the mold
Pouring basin – in which molten metal is poured in to
Sprue – through which molten metal flows downward
Runner system – channels that carry molten metal from the sprue
Risers - supply additional metal to the casting during shrinkage
Cores - Inserts made of sand
Used to make hollow regions
Vents – used to carry off gases that are produced and exhaust air from the mold
cavity as metal flows in to the mold

5. Sand Moulds
1. Green Sand Moulds
2. Dry Sand Moulds
3. Loam Sand Moulds
4. Cemented –Bonded Moulds
5. CO2 Moulds
6. Resin – Bonded Sand Moulds
7. Dry Sand Core Moulds
8. Composite Moulds

6. Green Sand Moulds
• Mixture of Silica sand, Clay (act as a Binder), water
• Green refers to wetness or freshness
• Cheapest and reclaimed
• Mould is weak in damp condition and cannot be stored for long time
• Used to make small and Medium size casting

7. 2. Dry Sand Moulds
• 1 to 2% cereal flour and 1 to 2 % pitch additives
• Baked in an oven 110 to 2600C for several hours
• Additives increases hot strength due to evaporation of water and oxidation and
polymerization of the pitch
• Used for large castings and better surface finish
• Reduces gas holes, porosity
• Possibility for tearing
3. Loam Sand Moulds
• Fine sand and finely ground refractories clay 50%, graphite and fibrous reinforcements
• Used in pit moulding – Large castings (Engine bodies, machine tool beds and frames)

8. 4. Cemented – Bonded Moulds
• 10 to 15% cement – binder, Stronger and harder, Pit moulding
• Develop strength by air drying, Large steel castings
• Poor Collapsability
5. CO2 Moulds
• Sodium Silicate (Na2O.xSiO2) used as a binder(2 to 6%)
• Sand Mixture hardens due to the following reaction
• Na2O.xSiO2 + nH2O + CO2 →Na2CO3 + x.Sio2.n . n(H2O) – Stiff gel
6. Resin – Bonded Sand Moulds
• Green sand mixture is mixed with thermosetting resins or linseed oil or soya bean oil
• Baking polymerizes and strength increases than dry sand mould
• No bake process – Furan resin
7. Dry sand Core moulds
• Moulds are made from assemblies of cores
• Baked at 1750C to 2300C for 4 to 24 hrs
8. Composite Moulds
• Moulds are made of two or more different materials – Shells, plaster, sand with
binder and graphite
Used in shell moulding – Complex shapes – Turbine impellers, Good surface finish
Dimensional accuracy

9. Patterns -Actual replica of the desired casting, used to prepare the cavity into which
molten material will be poured during the casting process. Patterns used in sand
casting may be made of wood, metal, plastics or other materials.
1. Solid or Single Piece Pattern
2. Split Pattern
3. Loose Piece Pattern
4. Gated Patterns
5. Match Plate Pattern
6. Cope and Drag Pattern
7. Sweep Pattern
8.Skeleton Pattern
9. Segmental Pattern
10. Build up Pattern
11. Shell pattern
12. Box up pattern
13. Lagged up pattern
14.Left and right hand pattern

14. Pattern Materials
Requirements of a good Pattern
• Secure the desired shape and size of the casting
• Cheap and readily available
• Simple in design for ease of manufacture
• Light in mass and convenient to handle
• High strength and long life in order to make as many moulds
• Retain its dimensions and rigidity during the definite service life
• Surface should be smooth and wear resistant
• Able to withstand rough handling
Wood
• Properly dried and seasoned
• Should not contain moisture more than 10% to avoid warping and distortion
Advantages
• Light weight, Inexpensive, Good workability, Easy to glue and join, Holds paints
• Easy to repair
Limitation
• Non uniform in structure
• Poor wear and abrasion resistance
• Cannot withstand rough handling
• Absorbs moisture

15. Metal
Advantages
• More durable and accurate in size than wooden patterns
• Smooth surface
• Do not deform in storage
• Are resistance to wear, abrasion, corrosion and swelling
• Can withstand rough handling
Limitation
• Expensive, Not easily repaired, Heavier than wooden pattern
• Ferrous pattern rusted
Common metals are C.I., Brass, Aluminium, White metal
Plastics
• More economical, Highly resistant to corrosion, lighter and stronger than wood
• Less sticking, No moisture absorption
• Smooth surface, Strong and dimensionally stable

16. Core and core making
• A body made of sand used to make a hole or
cavity in a casting
• Similar to the shape of the cavity in casting

17. Essential qualities
• Permeability
• Refractoriness
• Strength
• Collapsibility
• Stability

18. Core making materials
• Core sand – refractories Si, zircon
• Binders – oils, core flour
• Additives – wood flour, coal powder, graphite,
cow dung.
• All are weighed and put in the muller. Dry binders are
put. Muller is started and water is added to the dry
mixture after a few min. Then oil is added. Total mixing
time is 3 to 6 min.

19. Core boxes and core ovens
Core box Core ovens
• Half core
• Dump or slap
• Split core
• Strickle
• Gang core
• Batch type
• Continuous
• Dielectric

25. Core types
• According to the state of core • According to the position of core
• Green sand core
• Dry sand core
• Horizontal
• Vertical
• Balanced
• Hanging
• Drop core

29. Methods of testing Mould sands
• Moisture content test
• Clay content test
• Grain fineness test
• Permeability test
• Strength test
• Deformation and toughness test
• Hot strength test
• Refractoriness test
• Mould hardness test

30. Moisture content
Moisture content = W1-W2

31. Clay content test
• Sand sample + distilled water + 1% NaOH
• Mixed and stirred for 5 min. The dirty water at
the top is removed. Again 1% NaOH and
distilled water is added. Dried again till the
water become clean. The water is then
drained completely and sand is dried
completely and weighed. The loss of weight
denotes the clay content.
• Clay content W1-W2

32. Grain fineness test
• Set of known values of graded sieves, one on
other. Decreasing order of sieve sizes from top to
bottom. Top is the coarsest and bottom most
finest.
• Sand is put in sieve and shaken for 15 min. then
amount in each sieve is measured and the % dist.
is obtained.
AFS = total products /total sand retained in
sieve and pan
AFS=(American Foundry men Society)

34. Permeability test
• Weighed quantity of moulding sand is taken.
• Both clay content and moisture are added and
mixed well.
• Specimen dimension =50.8x50.8 mm2
• Permeability Number = VH/APT.
• Volume V= 2000 CC
• H – height of specimen
• A- area of specimen
• P- air pressure measured by manometer
• T- Time taken by 2000 cc of air to pass through the sand
specimen (in min)

36. Strength test
• Holding power and bonding power of green or
dry sand.
• Compressive
• Shear
• Tensile
• Bending
Carried out in a UTM
Specimen 50.8mmx50.8mm

38. Deformation and toughness
• Deformation – testing the plasticity of sand by
applying compressive strength.
• Toughness – ability of the sand to withstand
rough handling.(when pattern is drawn)
• Toughness Number = deformation x (green
compressive strength

39. Refractoriness test
• Cylindrical specimens are made from the
mould sand as per dim.
• Heated in fire for up to 1550 ̊C for 2 hrs.
• Change in shape and appearance is noted. Up
to 7% change in dimension indicates good
refractoriness.

40. Mould hardness
• Specimen is made and indentation is made on
it. Dimension of specimen and indentation is
noted.
•Indicates the ramming density of molding sand
Mould hardness number = P
------------------------------
D-√ D2 – d2

42. Moulding Machines
• Used for mass production
• Reduces labour and increases mould quality.
• Operations involved
– Ramming the sand
– rapping the pattern for easy removal
– removing pattern from sand
• Types
– Jolting machines
– Squeezing machines
– Sand slingers

43. Jolting machines
• Pattern placed in a flask on table.
• Mold sand is filled.
• The flask is then raised to 80 mm and dropped
suddenly. This makes even distribution of sand
in the flask.
• Table is operated hydraulically/ pneumatically.
• Operation is noisy.

45. Squeezing machine
• Top squeezing
• Bottom squeezing
Moulding sand squeezed between m/c table and
squeezer head.
Top squeezing
• Mould board on table. Flask on mould board. Pattern
in flask. Sand filled in flask. Table raised against
squeezer mechanism. Sand is packed tightly.
Table is set to original position after packing is done.
• Sand at top is rammed more densely than the bottom

46. Bottom squeezing
• Pattern on table
• Table is clamped on ram. Flask is placed on a
frame and is filled with sand.
• Table with pattern is raised against squeezer
head, thus flask is with pattern is squeezed
b/w sq. head and table. Table then returns to
original position.

47. Squeezing machines

48. Sand slingers
• Here the pattern is placed on a board.
• Flask is placed over it. Slinger contains an impeller
which can be rotated at different speeds. When
impeller rotates it throws a stream of sand at high
velocity into the flask, by which the sand gets packed
well.
• The slinger can be moved to pack the sand uniformly.
Density of sand is controlled by speed of impeller.
• Appropriate for medium and large sized molds.
• Ramming is uniform with good strength.

49. Sand slinger

50. Cupola Furnace
Used to melt cast iron due to its cost of construction, installation and operation
Principle:
• Metallic charge – Pig iron and scrap is melted
• Coke and oxygen in air as fuel
• Lime stone works as flux to separate impurities in the form of slag from liquid metal
• Charging of material is Continuous
Description:
• Long cylindrical shell made of mild steel – lined with fire clay refractory bricks
• Door for charging and a spark arrester to prevent sparks and unburnt fuel particles
from flowing into the atmosphere.
• Bottom has a circular door hinges for emptying the contents of the furnace
• Air is supplied by blower through a wind box for uniform pressure and number of
rectangular openings – tuyers
• Metal tap hole and slag hole is kept above the tap hole
Operation:
• Lime stone – 2 to 4% by weight of metal charge
• Coke - 8 to 12% of the metal charge
• Should be thoroughly dried before firing
• Layer of sand 150mm ht is placed over the doors and sloped towards tap hole
• Wood is kindled with fire and coke is added slightly above the tuyers

51. Various zones of cupola:
1. Well or crucible
2. Tuyer zone
3. Combustion Zone
4. Reducing Zone
5. Melting Zone
6. Preheating Zone
Advantages
• Low cost, continuous operation, easy to operate
Drawbacks
•Difficult to control temp. and composition

54. Blast furnace
• A blast furnace is a type of metallurgical furnace used for smelting
to produce industrial metals, generally iron, but also others such as
lead or copper.
• In a blast furnace, fuel, ore, and flux (limestone) are continuously
supplied through the top of the furnace, while a hot blast of air
(sometimes with oxygen enrichment) is blown into the lower
section of the furnace through a series of pipes called tuyers, so
that the chemical reactions take place throughout the furnace as
the material moves downward. The end products are usually
molten metal and slag phases tapped from the bottom, and flue
gases exiting from the top of the furnace. The downward flow of
the ore and flux in contact with an upflow of hot, carbon monoxide-
rich combustion gases is a countercurrent exchange process.

55. • The tuyers are used to implement a hot blast, which is
used to increase the efficiency of the blast furnace. The
hot blast is directed into the furnace through water-
cooled copper nozzles called tuyers near the base.
• The hot blast temperature can be from 900 °C to
1300 °C (1600 °F to 2300 °F) depending on the stove
design and condition. The temperatures they deal with
may be 2000 °C to 2300 °C (3600 °F to 4200 °F).
• Blast furnaces operate on the principle of chemical
reduction whereby carbon monoxide reduces the iron
to its elemental form

56. Blast furnace
1. Melting zone (bosh)
2. Reduction zone of
ferrous oxide (barrel)
3. Reduction zone of
ferric oxide (stack)
4. Pre-heating zone
(throat)
4
3
2
1

57. Crucible furnace
- crucible placed underground

58. Coke fired stationary furnace
Above ground level.
Steel shell lined with firebricks.

59. Oil fired tilting furnace

60. Direct Arc Electric Furnace
Principle:
•Heat is generated when resistance is offered to the flow electricity.
•Furnace electrode carries 25000 A, 3 Graphite or Carbon electrodes
•750 mm Diameter electrode, 1.5 to 2.5m in length.
•Length can be adjusted depends on amount of charge & wear of electrodes
•3 phase supply, 600 to 850KWh of electric energy to produce 1 tonne of steel.
•Temp 19250C, Can melt Chromium, Tungsten, Molybdenum
Indirect Arc Electric Furnace
•Arc is struck between two electrodes
•To melt copper base alloys
•2 Carbon or graphite electrodes
•Capacity 1000Kg
Advantages
• High thermal efficiency
• Most alloying elements Cr, Tungsten, Nickel can be recovered from scrap
• Quicker readiness for use, longer hearth life and ease of repair
Disadvantages
•High power consumption

63. Induction Furnace (alloy steels)
• All the heat is generated in the charge itself instead of arc
• Furnace contains a refractory lined crucible surrounded by a water cooled Cu coil
• Works on the principle of transformer. Water cooled coil is Primary and secondary is
• The charge. When a .c is passed through the Cu tubing, a magnetic field is set up.
• The magnetic field induces eddy current in the crucible charge which melts metal
Charge:
Steel : 40 to 60%
Pig Iron: 4 to 7%
Capacity : 50 kg to 10 tonnes
1. Core –less or high frequency Induction furnace
Water cooled Cu coil completely surrounds the crucible.
High frequency current (10,000 cps to 5,00,000 cps) is passed through the coil
Heavier current is induced in the charge
2. Core or Channel furnace or Low frequency induction furnace
Coil surrounds only a small portion of the crucible and low freq. (50 to 60 cps)
Melt Steel, iron, bronze, brass and Al base alloys
Advantages
• Readily started or stopped, High rate of melting and deliver at regular intervals
• Very high temp, Automatic stirring due to strong electromagnetic forces
•Uniform composition

65. Special casting process
• Shell casting (expendable moulds)
• Investment or lost wax method (expendable
moulds)
• Ceramic casting
• Pressure die casting
• Centrifugal casting
• CO2 casting
• Stir casting

66. 1. Heated metal pattern ready for shell formation
from resin-binded sand.
2. Box inversion for shell formation.
3. Partial cured shell layer hardened; box re-
inverted to allow the loose sand particles to be
separated.
Shell Mold

67. 4. Sand shell is heated to complete the curing.
5. Sand shell removed from the pattern
6. Two halves of the sand shell are assembled and
ready for pouring.
7. Finished shell casting with sprue removed.
Shell Mold

68. Shell Mold
Pros:
– Smoother surface finish than sans casting.
– Surface finish of 2.5 m can be obtained.
– Good dimensional accuracy  0.25 mm on small to
medium size parts.
– No further machining is needed.
– Capability for automation lowers the cost for larger
quantities.
Cons:
– More expensive metal pattern, especially for small
batch.

69. Investment Casting
1. Wax Pattern made.
2. Patterns attached to wax sprue.
3. Pattern tree coated with thin layer of refractory
material.
4. Pattern tree coated with sufficient refractory
material.

70. Investment Casting
5. Invert tree and melt wax by heat.
6. Preheat mold to high temperature to induce flow
and remove contaminants.
7. Mold broken and parts remove.

71. Investment Casting
Pros:
– Capability to cast parts with great complexity and
intricacy.
– Close dimensional control ( 0.076 m tolerance).
– Good surface finish.
– Wax can be recovered and reuse.
– Additional machining normally not required.
Cons:
– Normally cater for smaller parts.
– Relatively expensive.

72. CO2 casting
• Used to make good quality castings in large numbers.
• Pure dry Si sand with Sodium silicate liquid is used as
binder.
• Moisture 3% , additives sawdust 1.5 % , asbestos
powder 5% makes the core more deformable and
collapsible.
• Sand mix is filled in core box and rammed. CO2 gas is
passed for 30 sec. at Pr. 140 KN/m2.
• CO2 reacts with Sodium silicate and forms sodium
carbonate and silica gel. The Silica gel binds the sand
tightly and provides strength and hardness to the core.

74. Permanent Mold Casting -
Die Casting
Molten metal is injected at high pressure (7 to 350
MPa) into the mold cavity. Pressure is maintained at
solidification and part is removed after mold opening.

75. Permanent Mold Casting - Die Casting
Hot-chamber die casting :
Metal furnace is an integral part of the mould. Typical
injection pressures are 7 to 35 MPa. The piston is
made to force the molten metal into the die. Finished
parts are ejected out after solidification. The process is
often used for low melting point metals such as zinc,
tin, lead or magnesium alloys.

76. Permanent Mold Casting - Die Casting
Hot chamber
casting

77. Cold-chamber die casting
Molten metal is poured into an unheated
chamber from an external furnace. Typical
injection pressures are 14 to 140 MPa. Often
used for high melting point metal such as
aluminum, brass, and magnesium alloys

78. Permanent Mold Casting -
Die Casting
Cold
chamber
casting

79. Permanent Mold Casting -
Die Casting
• Mold made of tool steel.
• Mold opening mechanism to be
synchronized with ejector pins.
• Venting is needed for air and gas typically at
the parting surface.
• Flash formation is common.

80. Permanent Mold Casting -
Die Casting
Pros:
– High production rates are possible.
– Economical for large quantities.
– Close tolerances are possible ( 0.076 mm).
– Good surface finish.
– Thin sections are possible (down to 0.5 mm).
– Rapid cooling, fine grain, high strength.
Cons:
– melting point of metals.
– shape restriction.

81. Permanent Mold Casting -
Centrifugal Casting
Used for making hollow castings like tubes,drums,
gun barrels. Molten metal is poured into a rotating
tube to generate a tubular part. High density part
produced. Shrinkage compensated by centrifugal
force. Impurities on the outer wall only.

82. LIST OF DEFECTS
01. Shrinkage
02. Cold Shut
03. Mismatch
04. Blow holes
05. Pin Holes
06. Fin
07. Drop
08. Swell
09. Metal Penetration
10. Hot Tears
11. Porosity
12. Scabs
13. Hard Spots
14. BucklesRat Tails
15. Misrun

83. Shrinkage

84. Cold shut
When two streams of molten metal approach each other in the mould cavity from
opposite directions but fail to fuse properly, with the result of discontinuity between
them, it is called a cold shut

85. Mismatch
• It is a shift /misalignment between two
mating surfaces or the top and bottom parts
of the casting at the mould joint.

86. Blow holes
• Balloon-shaped gas cavities caused by release
of mould gases during pouring are known as
blow holes.

87. Pin holes
• Pin holes are tiny blow holes appearing just
below the casting surface.

88. Fins
• Fins are excessive amounts of metal created
by solidification into the parting line of the
mold

89. Drop
• Drop is an irregularly-shaped projection on
the cope surface caused by dropping of sand.

90. Swell
• Swells are excessive amounts of metal in the
vicinity of gates or beneath the sprue

91. Penetration
• Penetration occurs when the molten metal
flows between the sand particles in the
mould. These defects are due to inadequate
strength of the mold and high temperature of
the molten metal adds on it.