production Engineering

1. Metal Casting
By S K Mondal

2. Sand casting
 Sand casting uses ordinary sand as the primary
mould material.
 The sand grains are mixed with small amounts of
other materials, such as clay and water, to improve
mouldability and cohesive strength, and are then
packed around a pattern that has the shape of the
desired casting.
 The pattern must be removed before pouring, the
mold is usually made in two or more pieces.
 An opening called a sprue hole is cut from the top of
the mold through the sand and connected to a
system of channels called runners. Contd….

3.  The molten metal is poured into the sprue hole, flows
through the runners, and enters the mold cavity
through an opening called a gate.
 Gravity flow is the most common means of
introducing the metal into the mold.
 After solidification, the mold is broken and the
finished casting is removed.
 The casting is then “fettled” by cutting off the ingate
and the feeder head.
 Because the mold is destroyed, a new mold must be
made for each casting.
Contd…

5. Sequential steps in making a sand casting
 A pattern board is placed between the bottom (drag)
and top (cope) halves of a flask, with the bottom side up.
 Sand is then packed into the drag half of the mold.
 A bottom board is positioned on top of the packed sand,
and the mold is turned over, showing the top (cope) half
of pattern with sprue and riser pins in place.
 The cope half of the mold is then packed with sand.
Contd…

6.  The mold is opened, the pattern board is drawn
(removed), and the runner and gate are cut into the
surface of the sand.
 The mold is reassembled with the pattern board
removed, and molten metal is poured through the
sprue.
 The contents are shaken from the flask and the metal
segment is separated from the sand, ready for further
processing.

10. Casting Terms
 Flask: A moulding flask is one which holds the sand
mould intact. It is made up of wood for temporary
applications or metal for long-term use.
 Drag: Lower moulding flask.
 Cope: Upper moulding flask.
 Cheek: Intermediate moulding flask used in three-
piece moulding.
Contd…

11. Three flask mould

12.  Pattern: Pattern is a replica of the final object to be
made with some modifications.
 Parting line: This is the dividing line between the two
moulding flasks that makes up the sand mould.
 Bottom board: This is a board normally made of wood,
which is used at the start of the mould making.
Contd…

13.  Moulding sand: The freshly prepared refractory
material used for making the mould cavity. It is a
mixture of silica, clay and moisture in appropriate
proportions.
 Backing sand: This is made up of used and burnt
sand.
 Core: Used for making hollow cavities in castings.

14.  Pouring basin: A small funnel-shaped cavity at the top
of the mould into which the molten metal is poured.
 Sprue: The passage through which the molten metal
from the pouring basin reaches the mould cavity.
 Runner: The passage ways in the parting plane through
which molten metal flow is regulated before they reach
the mould cavity.
 Gate: The actual entry point through which molten
metal enters the mould cavity in a controlled rate. Contd…

15.  Chaplet: Chaplets are used to support cores inside the
mould cavity.
 Chill: Chills are metallic objects, which are placed in
the mould to increase the cooling rate of castings.
 Riser: It is a reservoir of molten metal provided in the
casting so that hot metal can flow back into the mould
cavity when there is a reduction in volume of metal due
to solidification
Contd…

16. Padding
 Tapering of thinner section towards thicker section
is known as 'padding'.
 This will require extra material.
 If padding is not provided, centre line shrinkage or
porosity will result in the thinner section.

17. IES-1996
Which of the following methods are used for
obtaining directional solidification for riser design
1. Suitable placement of chills
2. Suitable placement of chaplets
3. Employing padding
Select the correct answer.
(a) 1 and 2 (b) 1 and 3 (c) 2 and 3 (d) 1, 2 and 3

18. Pattern
A pattern is a replica of the object to be made by the
casting process, with some modifications.
The main modifications are
 The addition of pattern allowances,
 The provision of core prints, and
 Elimination of fine details, which cannot be obtained
by casting and hence are to be obtained by further
processing

19. Pattern Allowances
1. Shrinkage or contraction allowance
2. Draft or taper allowance
3. Machining or finish allowance
4. Distortion or camber allowance
5. Rapping allowance

20. Shrinkage allowance
 All metals shrink when cooling except perhaps
bismuth.
 This is because of the inter-atomic vibrations which
are amplified by an increase in temperature.
 The shrinkage allowance is always to be added to the
linear dimensions. Even in case of internal dimensions.
Contd…

21. Liquid shrinkage and solid shrinkage
 Liquid shrinkage refers to the reduction in volume
when the metal changes temperature from pouring to
solidus temperature in liquid state. To account for this,
risers are provided in the moulds.
 Solidification shrinkage refers to the reduction in
volume when metal changes from liquid to solid state
at the solidus temperature. To account for this, risers
are provided in the moulds.
 Solid shrinkage is the reduction in volume caused,
when a metal loses temperature in the solid state. The
shrinkage allowance is provided to take care of this
reduction.

22.  Gray CI with a carbon equivalent of 4.3% has
negative shrinkage, that is, it actually expands
upto 2.5% because of graphite precipitation. So,
for this, no riser is needed.

23.  Pattern Allowances
Cast Iron 10 mm/m
Brass, Copper, Aluminium 15 mm/m
Steel 20 mm/m
Zinc, Lead 25 mm/m

24. GATE-2004
Gray cast iron blocks 200 x 100 x 10 mm are to be
cast in sand moulds. Shrinkage allowance for
pattern making is 1%. The ratio of the volume of
pattern to that of the casting will be
(a) 0.97 (b) 0.99 (c) 1.01 (d) 1.03

25. GATE-2016
Gray cast iron blocks of size 100 mm x 50 mm x
10 mm with a central spherical cavity of
diameter 4 mm are sand cast. The shrinkage
allowance for the pattern is 3%. The ratio of
the volume of the pattern to volume of the
casting is ____________

26. GATE 2011
A cubic casting of 50 mm side undergoes volumetric
solidification shrinkage and volumetric solid
contraction of 4% and 6% respectively. No riser is
used. Assume uniform cooling in all directions. The
side of the cube after solidification and contraction is
(a) 48.32 mm
(b) 49.90 mm
(c) 49.94 mm
(d) 49.96 mm

27. Draft
 To reduce the chances of the damage of the mould
cavity at the time of pattern removal, the vertical faces
of the pattern are always tapered from the parting line.
This provision is called draft allowance.
 Inner surfaces of the pattern require higher draft than
outer surfaces.
 Draft is always provided as an extra metal.

28. DRAFT ALLOWANCE

29. Shake Allowance
 At the time of pattern removal, the pattern is rapped
all around the vertical faces to enlarge the mould
cavity slightly to facilitates its removal.
 It is a negative allowance and is to be applied only to
those dimensions, which are parallel to the parting
plane.

30. Distortion Allowance
 A metal when it has just solidified is very weak and
therefore is likely to be distortion prone.
 This is particularly so for weaker sections such as long
flat portions, V, U sections or in a complicated casting
which may have thin and long sections which are
connected to thick sections.
 The foundry practice should be to make extra
material provision for reducing the distortion.

31. Pattern Materials
 Wood patterns are relatively easy to make. Wood is not
very dimensionally stable. Commonly used teak, white
pine and mahogany wood.
 Metal patterns are more expensive but are more
dimensionally stable and more durable. Commonly used
CI, Brass, aluminium and white metal.
 Hard plastics, such as urethanes, and are often preferred
with processes that use strong, organically bonded sands
that tend to stick to other pattern materials.
 In the full-mold process, expanded polystyrene (EPS) is
used.
 Investment casting uses wax patterns.

32. The pattern material should be
 Easily worked, shaped and joined
 Light in weight
 Strong, hard and durable
 Resistant to wear and abrasion
 Resistant to corrosion, and to chemical reactions
 Dimensionally stable and unaffected by variations in
temperature and humidity.
 Available at low cost.

33. IES-1994
Which of the following materials can be used for
making patterns?
1. Aluminium 2. Wax 3. Mercury 4. Lead
Select the correct answer using the codes given below:
Codes:
(a) 1,3 and 4 (b) 2,3 and 4 (c) 1, 2 and 4 (d) 1, 2 and 3

34. Types of Pattern
Single Piece Pattern
These are inexpensive and the simplest type of
patterns. As the name indicates, they are made of a
single piece.
Gated Pattern
Gating and runner system are integral with the
pattern. This would eliminate the hand cutting of
the runners and gates and help in improving the
productivity of a moulding.

35. Types of Pattern
Split Pattern or Two Piece Pattern
This is the most widely used type of pattern for intricate
castings. When the contour of the casting makes its
withdrawal from the mould difficult, or when the depth
of the casting is too high, then the pattern is split into two
parts so that one part is in the drag and the other in the
cope.

36. Types of Pattern
 Cope and Drag Pattern
These are similar to split patterns. In addition to
splitting the pattern, the cope and drag halves of
the pattern along with the gating and riser systems
are attached separately to the metal or wooden
plates along with the alignment pins. They are
called the cope and drag patterns.

37. Types of Pattern
 Match Plate Pattern
The cope and drag patterns along with the
gating and the risering are mounted on a single
matching metal or wooden plate on either side.

38. Types of Pattern
 Loose Piece Pattern
This type of pattern is also used when the
contour of the part is such that withdrawing the
pattern from the mould is not possible.

39. Types of Pattern
 Follow Board Pattern
This type of pattern is adopted for those
castings where there are some portions, which
are structurally weak and if not supported
properly are likely to break under the force of
ramming.

40. Types of Pattern
 Sweep Pattern
It is used to sweep the complete casting by means
of a plane sweep. These are used for generating
large shapes, which are axi-symmetrical or
prismatic in nature such as bell-shaped or
cylindrical.

41. Types of Pattern
 Skeleton Pattern
A skeleton of the pattern made of strips of wood
is used for building the final pattern by packing
sand around the skeleton. After packing the
sand, the desired form is obtained with the help
of a strickle. This type of pattern is useful
generally for very large castings, required in
small quantities where large expense on
complete wooden pattern is not justified.

42. Cooling Curve

43. GATE-2016
Heat is removed from a molten metal of mass 2 kg at a
constant rate of 10 kW till it is completely solidified. The
cooling curve is shown in the figure.
Assuming uniform
temperature
throughout the
volume of the metal
during solidification,
the latent heat of
fusion of the metal
(in KJ/kg) is
__________

44. Fluidity
The ability of a metal to flow and fill a mold is known
as fluidity.
Pouring Temperature
 The most important controlling factor of fluidity is the
pouring temperature or the amount of superheat.
 Higher the pouring temperature, the higher the fluidity.
 Excessive temperatures should be avoided, however. At
high pouring temperatures, metal-mold reactions are
accelerated and the fluidity may be so great as to permit
penetration.
 Penetration is a defect where the metal not only fills the
mold cavity but also fills the small voids between the sand
particles in a sand mold.

46. Core
 Used for making cavities and hollow projections.
 All sides of core are surrounded by the molten metal
and are therefore subjected to much more severe
thermal and mechanical conditions and as a result the
core sand should be of higher strength than the
moulding sand.

47. Desired characteristics of a core
 Green Strength: A core made of green sand should
be strong enough to retain the shape till it goes for
baking.
 Dry Strength: It should have adequate dry strength
so that when the core is placed in the mould, it
should be able to resist the metal pressure acting on
it.
 Refractoriness: Since in most cases, the core is
surrounded all around it is desirable that the core
material should have higher refractoriness.
Contd…

48.  Permeability: Gases evolving from the molten metal
and generated from the mould may have to go
through the core to escape out of the mould. Hence
cores are required to have higher permeability.
 Permeability Number: The rate of flow of air passing
through a standard specimen under a standard pressure is
termed as permeability number.
 The standard permeability test is to measure time
taken by a 2000 cu cm of air at a pressure typically of
980 Pa (10 g/cm2), to pass through a standard sand
specimen confined in a specimen tube. The standard
specimen size is 50.8 mm in diameter and a length of
50.8 mm.

49.  Then, the permeability number, R is obtained by
Where V= volume of air = 2000 cm3
H = height of the sand specimen = 5.08 cm
p = air pressure, g/cm2
A = cross sectional area of sand specimen = 20.268 cm2
T = time in minutes for the complete air to pass through
Inserting the above standard values into the
expression, we get
VH
R
pAT

501.28
.
R
pT


50.  Calculate the permeability number of sand if it takes 1 min
25 s to pass 2000 cm3 of air at a pressure of5 g/cm2 through
the standard sample.
2
5.0 /
1min 25 1.417min
501.28
70.75
5 1.417
p g cm
T s
R

 
 


51. IES 2007
What is permeability? Permeability is more important
in the basic process of sand casting than porosity. Give
one important reason for this feature.
[2 marks]

52.  Collapsibility: At the time of cooling, casting shrinks, and
unless the core has good collapsibility (ability to decrease
in size) it is likely to provide resistance against shrinkage
and thus can cause hot tears.

53.  Friability: The ability to crumble should be a very
important consideration at the time of removal.
 Smoothness: Surface of the core should be smooth
for good finish to the casting.
 Low Gas Emission

54. Core Sands
 Used clay free silica sand.
 Binders used are linseed oil, core oil, resins, dextrin,
molasses, etc.
 Core oils are mixtures of linseed, soy, fish and
petroleum oils and coal tar.
 The general composition of a core sand mixture could
be core oil (1%) and water (2.5 to 6%).

55. Carbon Dioxide Moulding
 Sodium silicate (water glass, SiO2:Na2O) is used as a binder.
This is essentially a quick process of core or mould
preparation.
 The mould is prepared with a mixture of sodium silicate and
sand and then treated with carbon dioxide for two to three
minutes such that a dry compressive strength of over 1.4
MPa is arrived.
 The carbon dioxide is expected to form a weak acid, which
hydrolyses the sodium silicate resulting in amorphous silica,
which forms the bond.
 The introduction of CO2 gas starts the reaction by forming
hydrated sodium carbonate (Na2CO3 + H2O).
Contd…

56.  The compressive strength of the bond increases with
standing time due to dehydration.
 Because of the high strength of the bond, the core need not
be provided with any other reinforcements.
 It does not involve any distortions due to baking and also
better dimensional accuracies are achieved.
 The sand mixture does not have good shelf life and
therefore should be used immediately after preparation.

57. GATE – 2008 (PI)
In sand casting of a hollow part of lead, a cylindrical core
of diameter 120 mm and height 180 mm is placed inside
the mould cavity. The densities of core material and lead
are 1600 kg/m3 and 11,300 kg/m3 respectively. The net
force (in N) that tends to lift the core during pouring of
molten metal will be
(a) 19.7 (b) 64.5 (c) 193.7 (d) 257.6

58. GATE-2014
An aluminium alloy (density 2600 ) casting is to be
produced. A cylindrical hole of 100 mm diameter and
100 mm length is made in the casting using sand core
(density 1600 ). The net buoyancy force (in Newton)
acting on the core is ……………..

59. Moulding Sand Composition
 Sand: Ordinary silica Sand (SiO2), zircon, or olivine
sands.
 Clay: Acts as binding agents mixed to the moulding
sands
Kaolinite or fire clay (Al2O3 2SiO2 2H2O), and
Bentonite (Al2O3 4SiO2 H2O nH2O).
 Water: Clay is activated by water.

60. Other Additives
 Cereal binder up to 2% increases the strength.
 Pitch if used up to 3% would improve the hot
strength.
 Saw dust up to 2% may improve the collapsibility by
slowly burning, and increase the permeability.
 Other materials: sea coal, asphalt, fuel oil, graphite,
molasses, iron oxide, etc.

61. Moulding Sand Properties
 Porosity or Permeability: Permeability or porosity of
the moulding sand is the measure of its ability to
permit air to flow through it.
 Strength: It is defined as the property of holding
together of sand grains. A moulding sand should have
ample strength so that the mould does not collapse or
get partially destroyed during conveying, turning over
or closing.
 Refractoriness: It is the ability of the moulding sand
mixture to withstand the heat of melt without showing
any signs of softening or fusion.
Contd…

62.  Plasticity: It is the measure of the moulding sand to flow
around and over a pattern during ramming and to uniformly
fill the flask.
 Collapsibility: This is the ability of the moulding sand to
decrease in volume to some extent under the compressive
forces developed by the shrinkage of metal during freezing
and subsequent cooling.
 Adhesiveness: This is the property of sand mixture to
adhere to another body (here, the moulding flasks). The
moulding sand should cling to the sides of the moulding
boxes so that it does not fall out when the flasks are lifted
and turned over. This property depends on the type and
amount of binder used in the sand mix.

63. Other Sands
 Facing sand: The small amount of carbonaceous
material sprinkled on the inner surface of the mold
cavity to give a better surface finish to the castings.
 Backing sand: It is what constitutes most of the
refractory material found in the mould. This is made
up of used and burnt sand.
 Green Sand: The molding sand that contains
moisture is termed as green sand. The green sand
should have enough strength so that the constructed
mould retains its shape.
 Dry sand: When the moisture in the moulding sand is
completely expelled, it is called dry sand.

64. Grain size number
 ASTM (American Society for Testing and Materials)
grain size number, defined as
N
 Where N is the number of grains per square inch
visible in a prepared specimen at 100X and n is the
ASTM grain-size number.
 Low ASTM numbers mean a few massive grains; high
numbers refer to many small grains.
-n 1
2

65. Sand Slinger

67. Casting Yield
The casting yield is the proportion of the actual
casting mass, w, to the mass of metal poured into the
mould, W, expressed as a percentage.
 Casting yield 100
w
W

68. Gating System
Contd…

69. Gating System
 Pouring basin: A small funnel shaped cavity at the
top of the mould into which the molten metal is
poured.
 Sprue: The passage through which the molten metal,
from the pouring basin, reaches the mould cavity. In
many cases it controls the flow of metal into the
mould.
Contd…

70.  Runner: A runner is commonly a horizontal channel
which connects the sprue with gates, thus allowing the
molten metal to enter the mould cavity. The runners
are of larger cross-section and often streamlined to
slow down and smooth out the flow, and are designed
to provide approximately uniform flow rates to the
various parts of the mould cavity. Runners are
commonly made trapezoidal in cross-section.
Contd…

71.  Ingate: A channel through which the molten metal
enters the mould cavity.
 Vent: Small opening in the mould to facilitate escape
of air and gases.

72. Types of Gate or In-gate
Top gate: Causes turbulence in the mould cavity, it is prone
to form dross, favourable temperature gradient towards the
gate, only for ferrous alloys.
Bottom gate: No mould erosion, used for very deep moulds,
higher pouring time, Causes unfavourable temperature
gradients.
Parting Gate: most widely used gate, easiest and most
economical in preparation.
Step Gate: Used for heavy and large castings, size of ingates
are normally increased from top to bottom.

73. IES 2011
In light metal casting, runner should be so designed
that:
1. It avoids aspiration
2. It avoids turbulence
3. The path of runner is reduced in area so that
unequal volume of flow through each gate
takes place
(a) 1 and 2 only (b) 1 and 3 only
(c) 2 and 3 only (d) 1, 2 and 3

74. The goals for the gating system
 To minimize turbulence to avoid trapping gasses into
the mold
 To get enough metal into the mold cavity before the
metal starts to solidify
 To avoid shrinkage
 Establish the best possible temperature gradient in the
solidifying casting so that the shrinkage if occurs must
be in the gating system not in the required cast part.
 Incorporates a system for trapping the non-metallic
inclusions.

75. Types of Gating Systems
The gating systems are of two types:
 Pressurized gating system
 Un-pressurized gating system

76. Pressurized Gating System
 The total cross sectional area decreases towards the
mold cavity
 Back pressure is maintained by the restrictions in the
metal flow
 Flow of liquid (volume) is almost equal from all gates
 Back pressure helps in reducing the aspiration as the
sprue always runs full
 Because of the restrictions the metal flows at high
velocity leading to more turbulence and chances of
mold erosion.

77. Un-Pressurized Gating System
 The total cross sectional area increases towards the
mold cavity
 Restriction only at the bottom of sprue
 Flow of liquid (volume) is different from all gates
 Aspiration in the gating system as the system never
runs full
 Less turbulence.

78. Sprue Design
 Sprue: Sprue is the channel through which the molten
metal is brought into the parting plane where it enters the
runners and gates to ultimately reach the mould cavity.
 The molten metal when moving from the top of the cope to
the parting plane gains in velocity and some low-pressure
area would be created around the metal in the sprue.
 Since the sand mould is permeable, atmospheric air would
be breathed into this low-pressure area which would then
be carried to the mould cavity.
 To eliminate this problem of air aspiration, the sprue is
tapered to gradually reduce the cross section as it moves
away from the top of the cope as shown in Figure below (b).
Contd…

79. The exact tapering can be obtained by the equation of
continuity. Denoting the top and choke sections of The sprue by
the subscripts’t’ and 'c' respectively, we get
t t c cA V A V  c
t c
t
V
A A
V
Contd…

80. Since the velocities are proportional to the square of
the potential heads, as can be derived from
Bernoulli's equation,
 c
t c
t
h
A A
h
Where H = actual
sprue height
and ht = h + H

81. GATE-2007
A 200 mm long down sprue has an area of cross
section of 650 mm2 where the pouring basin meets the
down sprue (i.e. at the beginning of the down sprue).
A constant head of molten metal is maintained by the
pouring basin. The Molten metal flow rate is 6.5 × 105
mm3/s. Considering the end of down sprue to be open
to atmosphere and an acceleration due to gravity of
104mm/s2, the area of the down sprue in mm2 at its end
(avoiding aspiration effect) should be
(a)650.0 (b)350.0 (c)290.7 (d)190.0
Contd…

83. Gating ratio
 Gating ratio is defined as: Sprue area: Runner area:
Ingate area.
 For high quality steel castings, a gating ratio of 1: 2: 2 or
1: 2: 1.5 will produce castings nearly free from erosion,
will minimize oxidation, and will produce uniform
flow.
 A gating ratio of 1: 4: 4 might favour the formation of
oxidation defects.

84. Risers and Riser Design
 Risers are added reservoirs designed to feed liquid
metal to the solidifying casting as a means of
compensating for solidification shrinkage.
 To perform this function, the risers must solidify after
the casting.
 According to Chvorinov's rule, a good shape for a riser
would be one that has a long freezing time (i.e., a small
surface area per unit volume).
 Live risers (also known as hot risers) receive the last
hot metal that enters the mold and generally do so at a
time when the metal in the mold cavity has already
begun to cool and solidify.

85. Chvorinov’s rule
 Total solidification time (ts) = B (V/A) n
where n = 1.5 to 2.0
[Where, B = mould constant and is a function of (mould
material, casting material, and condition of casting]
n = 2 and triser = 1.25 tcasting
   
   
   
2 2
riser casting
V V
1.25
A A
 
 
  
2
2
V D H / 4
DA DH 2
4
For cylinder
of diameter D
and height H
or

86. Types of Risers

87. IES 2011
The relationship between total freezing time t,
volume of the casting V and its surface area A,
according to Chvorinov’s rule is :
Where K is a constant
2
2
( )
( )
( )
( )
V
a t k
A
A
b t k
V
A
c t k
V
V
d t k
A
 
  
 
 
  
 
 
  
 
 
  
 

88. IES-1998
A spherical drop of molten metal of radius 2 mm
was found to solidify in 10 seconds. A similar drop of
radius 4 mm would solidify in
(a) 14.14 seconds
(b) 20 seconds
(c) 28.30 seconds
(d) 40 seconds

89. GATE-2013 Same Question (PI)
A cube shaped casting solidifies in 5 min. The
solidification time in min for a cube of the same
material, which is 8 times heavier than the original
casting, will be
(a) 10 (b) 20 (c) 24 (d) 40

90. GATE-2014 (PI)
For a given volume of a riser, if the solidification
time of the molten metal in riser needs to be
quadrupled, the surface area of the riser should be
made
(a) one-fourth (b) half
(c) double (d) four times

91. GATE-2014
A cylindrical riser of 6 cm diameter and 6 cm height has
to be designed for a sand casting mould for producing a
steel rectangular plate casting of 7 cm × 10 cm × 2 cm
dimensions having the total solidification time of 1.36
minute. The total solidification time (in minute) of the
riser is ……..

92. GATE-2003
With a solidification factor of 0.97 x 106 s/m2, the
solidification time (in seconds) for a spherical
casting of 200 mm diameter is
(a) 539 (b) 1078 (c) 4311 (d) 3233

93. IES-2006
According to Chvorinov's equation, the
solidification time of a casting is proportional to:
(a) v2
(b) v
(c) 1/v
(d) 1/v2
Where, v = volume of casting

94. GATE-2015
The solidification time of a casting is
proportional to (V/A)2 , where V is the volume of
casting and A is the total casting surface area
losing heat. Two cubes of same material and size
are cast using sand casting process. The top face
of one of the cube is completely insulated. The
ratio of the solidification time for the cube with
top face insulated to that of the other cube is
(a) 25/36 (b) 36/25 (c) 1 (d) 6/5

95. GATE-2016 (PI)
Two cast iron blocks P and Q, each of 500 mm length, have
the same cross-sectional area. Block P has rectangular cross-
section of 100 mm × 200 mm. Block Q is of square cross-
section. Both P and Q were cast under the same conditions
with all their surfaces enclosed within the mould. The
solidification time of a casting is proportional to the square
of the ratio of its volume to its surface area. The ratio of
solidification time of the block P to that of the block Q is
______

96. GATE – 2010 (PI)
Solidification time of a metallic alloy casting is
(a) Directly proportional to its surface area
(b) Directly proportional to the specific heat of the
cast material
(c) Directly proportional to the thermal diffusivity of
the molten metal
(d)Inversely proportional to the pouring
temperature.

97. GATE-2016
Equal amount of a liquid metal at the same temperature
are poured into three moulds made of steel, copper and
aluminium. The shape of the cavity is a cylinder with 15
mm diameter. The size of the moulds are such that the
outside temperature of the moulds do not increase
appreciably beyond the atmospheric temperature during
solidification. The sequence of solidification in the
mould from the fastest to slowest is
(Thermal conductivities of steel, copper and aluminium
are 60.5, 401 and 237 W/m-K, respectively.
Specific heats of steel, copper and aluminium are 434,
385 and 903 J/kg-K, respectively.
Densities of steel, copper and aluminium are 7854, 8933
and 2700 kg/m3, respectively.)

98. GATE-2016 contd....
Densities of steel, copper and aluminium are 7854, 8933
and 2700 kg/m3, respectively.)
(a) Copper – Steel – Aluminium
(b) Aluminium – Steel – Copper
(c) Copper – aluminium – Steel
(d) Steel – Copper – Aluminium

99. GATE-2007
Volume of a cube of side 'l' and volume of a sphere of
radius ‘r’ are equal. Both the cube and the sphere are solid
and of same material. They are being cast. The ratio of the
solidification time of the cube to the same of the sphere is:
       
3 6 2 2 3 2 4
4 r 4 r 4 r 4 r
a b c d
6 l 6 l 6 l 6 l
                 
              
              

100. A cube and sphere made of cast iron (each of volume
1000 cm3 ) were cast under identical conditions . The
time taken for solidifying the cube was 4 s. The
solidification time (in s) for the sphere is _______
GATE-2015

101. GATE -2011 (PI)
In a sand casting process, a sphere and a cylinder of
equal volumes are separately cast from the same molten
metal under identical conditions. The height and
diameter of the cylinder are equal. The ratio of the
solidification time of the sphere to that of the cylinder is
(a) 1.14 (b) 0.87
(c) 1.31 (d) 0.76

102. GATE-2009 (PI)
A solid cylinder of diameter D and height equal to D, and a solid
cube of side L are being sand cast by using the same material.
Assuming there is no superheat in both the cases, the ratio of
solidification time of the cylinder to the solidification time of the
cube is
(a) (L/D)2
(b) (2L/D)2
(c) (2D/L)2
(d) (D/L)2

103. Ratio of solidification time of a cylindrical
casting ( height = radius) to that of a cubic
casting of side two times the height of
cylindrical casting is ____
GATE-2015

105. IES - 2012
The ratio of surface area of volume for a unit volume of
riser is minimum in case of
(a) Cylindrical riser
(b) Spherical riser
(c) Hemispherical riser
(d) Cuboids riser

106. IES 2011 Conventional
 A round casting is 20 mm in diameter and 50 mm in
length. Another casting of the same metal is elliptical in
cross section, with a major to minor axis ratio of 2, and
has the same length and cross-sectional area as the
round casting. Both pieces are cast under the same
conditions. What is the difference in the solidification
times of the two castings ? [10 – Marks]
    
 2 2
Area of ellipse
Circumference 3 3 3
2 / 2 (approx.)
ab
a b a b a b
a b




     
 
 

107. Conventional Question ESE 2003
Compare the solidification time of two optimum side –
risers of the same volume with one has cylindrical shape
and other is parallopiped. [30 Marks]

108. Mold cavity
Riser
d
h
Sprue basin
GATE-2014
A cylindrical blind riser with diameter d and height h, is
placed on the top of the mold cavity of a closed type
sand mold as shown in the figure. If the riser is of
constant volume, then the rate of solidification in the
riser is the least when the ratio h : d is
(a) 1 : 2 (b) 2 : 1
(c) 1 : 4 (d) 4 : 1

109. Modulus Method
 It has been empirically established that if the modulus
of the riser exceeds the modulus of the casting by a
factor of 1.2, the feeding during solidification would be
satisfactory.
MR = 1.2 Mc
 Modulus = volume/Surface area
 In steel castings, it is generally preferable to choose a
riser with a height-to-diameter ratio of 1.
Contd…

110. 2
2
4
D
D



111. Conventional Question IES-2008
 Calculate the size of a cylindrical riser (height and diameter
equal) necessary to feed a steel slab casting of dimensions
30 x 30 x 6 cm with a side riser, casting poured horizontally
into the mould.
[Use Modulus Method]
[10 - Marks]

112. GATE-2016
A cylindrical job with diameter of 200 mm and
height of 100 mm is to be cast using modulus
method of riser design. Assume that the bottom
surface of cylindrical riser does not contribute as
cooling surface. If the diameter of the riser is equal
to its height, then the height of the riser (in mm) is
(a) 150 (b) 200 (c) 100 (d) 125

113. Caine’s Method
Freezing ratio = ratio of cooling characteristics of casting to
the riser.
The riser should solidify last so x > 1
According to Caine X =
Y = and a, b, c are constant.
a
c
Y b


riser
casting
V
V
 
 
Casting
Riser
A
V
X
A
V


115. Table: Constants in Caine’s Method

116. Conventional Question IES-2007
 Calculate the size of a cylindrical riser (height and
diameter equal) necessary to feed a steel slab
casting of dimensions 25 x 25 x 5 cm with a side
riser, casting poured horizontally into the mould.
[Use Caine’s Method]
[ For steel a = 0.10, b = 0.03 and c = 1.00 ]

117. This method is a simplification of Caine's
method. In this method, freezing ratio is replaced
by Shape Factor.
The shape factor is defined as
Shape Factor= (Length+Width)/Thickness
The underlying argument is that calculating
volumes and surface areas is too complicated and
therefore simplification would be desirable. The
length, width and thicknesses are computed from
the maximum dimensions of the casting section.
Naval Research Laboratory Method

119. Procedure for getting riser size is as follows:
1. Calculate the shape factor for the given casting.
2. Obtain riser volume to casting volume ratio from the
graph . (or the table provided in questions)
3. Calculate riser volume Vr .
4. For cylindrical riser (h=D), Vr = (Π.D3 )/4
5. Obtain the diameter.
•For circular plates, the length and width are same as that
of the diameter.
•But for cylinders, the width and thickness are same as the
diameter for calculating the shape factor.
But for calculating the riser volume actual casting volume
is to be used.

120. •The other shape of interest is hollow cylindrical shape. In
these the heat removal is restricted , a correction factor k,
needs to be applied to get the effective plate thickness. If T
is the true wall thickness
Core
diameter
0.5T T 2T 4T
Correction
factor
1.17 1.14 1.02 1.00
Shape Factor = (Length+ width)/(k.T)

121. Calculate the height of cylindrical riser(height=diameter)
necessary to feed the steel slab casting 25 x 25 x 5 with a
side riser, casting poured horizontally into the mold.
Solution:
Shape Factor = (25+25)/5 = 10
From graph-1 at shape factor 10 (riser volume/casting volume)
is 0.47.
Riser Volume(Vr ) = (riser volume/casting volume) x casting
volume
Riser Volume = 0.47 x 25 x 25x 5 =1468.75 cm3
For cylindrical riser of height = diameter
Vr = (Π.D3 )/4
1468.75= (Π.D3 )/4
D = 12.32 cm
Example

122. The dimensions of a cylindrical side
riser(height = diameter) for a 25 cm x 15 cm x 5
cm steel casting are to be determined. For the
tabulated shape factor values given below, the
diameter of the riser (in cm)________
Shape Factor 2 4 6 8 10 12
Riser volume /
Casting Volume
1.0 0.70 0.55 0.50 0.40 0.35
GATE-2015

123. Normally the risers are located at the heaviest sections and they themselves act as
feeders for thin sections. But when smaller sections are connected to thicker
sections, the riser should have larger volume to cater this appendage.
The total volume of the casting is taken as the volume of the main section plus
the effective percentage of the appendage volume, called the parasitic volume.
GRAPH-2

124. Calculate the risering requirement for the casting
shown in fig.
Example

125. First neglect the branch and calculate shape factor for main
plate ;
Shape Factor = (25+12.5)/5 = 7.5
From graph-1 at shape factor 7.5 (riser volume/casting
volume) is 0.47.
Riser Volume(Vr ) = (riser volume/casting volume) x casting
volume
Riser Volume = 0.575 x 25 x 12.5x 5 =898.437 cm3
The branch Volume=2.5 x 2.5 x 10 =62.5cm3
This is plate feeding the bar with thickness ratio (2.5/5) of 0.5.
From the graph-2 we get parasitic volume of 30%
Hence, riser volume = 0.3 x 62.5 + 898.437=917.185cm3
Vr = (Π.D3 )/4 or 917.185= (Π.D3 )/4 or D = 10.53 cm

126. Chills
 External chills are masses of high-heat-capacity, high-thermal-
conductivity material that are placed in the mould (adjacent to
the casting) to accelerate the cooling of various regions.
Chills can effectively promote directional solidification or
increase the effective feeding distance of a riser. They can often
be used to reduce the number of risers required for a casting.
 Internal chills are pieces of metal that are placed within the
mould cavity to absorb heat and promote more rapid
solidification. Since some of this metal will melt during the
operation, it will absorb not only the heat-capacity energy, but
also some heat of fusion. Since they ultimately become part of
the final casting, internal chills must be made from the same
alloy as that being cast.

127. Cupola
 Cupola has been the most widely used furnace for
melting cast iron.
 In hot blast cupola, the flue gases are used to preheat the
air blast to the cupola so that the temperature in the
furnace is considerably higher than that in a
conventional cupola. Coke is fuel and Lime stone
(CaCO3) is mostly used flux.
 Cost of melting low.
 Main disadvantages of cupola is that it is not possible to
produce iron below 2.8% carbon.
 Steel can be also prepared in cupola by employing
duplexing and triplexing operations.

128. IES - 2012
Statement (I): Cupola furnace is not employed for
melting steel in foundry
Statement (II): The temperatures generated within a
cupola are not adequate for melting Steel
(a) Both Statement (I) and Statement (II) are
individually true and Statement (II) is the correct
explanation of Statement (I)
(b) Both Statement (I) and Statement (II) are
individually true but Statement (II) is not the correct
explanation of Statement (I)
(c) Statement (I) is true but Statement (II) is false
(d) Statement (I) is false but Statement (II) is true

129. Electric Arc Furnace
 For heavy steel castings, the
open-hearth type of furnaces
with electric arc or oil fired
would be generally suitable in
view of the large heat required
for melting.
 Electric arc furnaces are more
suitable for ferrous materials and
are larger in capacity.

130. Crucible Furnace or Pot Furnace
 Smaller foundries generally prefer the crucible furnace.
 The crucible is generally heated by electric resistance
or gas flame.

131. Induction Furnace
 The induction furnaces are used for all types of
materials, the chief advantage being that the heat
source is isolated from the charge and the slag and flux
get the necessary heat directly from the charge instead
of the heat source.

132. Ladles
 Two types of ladles used in the pouring of castings.

133. Casting Cleaning (fettling)
Impurities in the molten metal are prevented from reaching
the mould cavity by providing a
(i) Strainer
(ii) Bottom well
(iii) Skim bob

134. Pouring time
Time taken to fill the mould with top gate
Where A = Area of mould
H = Height of mould
Ag = Area of Gate
Hm = Gate height
Time taken to fill the mould with bottom gate
A
g m
A.H
t
A 2gh

 B m m
g
2A
t h h H
A 2g
  

135. GATE-2012 (PI)
A mould having dimensions 100 mm × 90 mm × 20 mm is filled
with molten metal through a gate as shown in the figure. For
height h and cross-sectional area A, the mould filling time is t1.
The height is now quadrupled and the cross-sectional area is
halved. The corresponding filling time is t2. The ratio t2/t1 is
1
( )
2
( )1
( ) 2
( )2
a
b
c
d

136. Expression for choke area
Where m = mass of the casting, kg
= Density of metal, kg / m3
t = pouring time
c = Efficiency factor and is the function of gate
system used
H = Effective head of liquid metal
= h for top gate
 2m
CA mm
cρt 2gH
ρ
Contd…

137. H=h- for bottom gate
=h- for parting line gate
top gate parting line gate bottom gate
mh
2
2
c
m
h
2h
Top gale
m
h
Parting line gate
mh
C
h
Parting line gate
mh

138. GATE-2016
The part of a gating system which regulates
the rate of pouring of molten metal is
(a) Pouring basin (b) runner
(c) Choke (d) ingate

139. IES 2009
 2 marks

140. Casting Defects
The following are the major defects, which are likely to
occur in sand castings:
 Gas defects
 Shrinkage cavities
 Molding material defects
 Pouring metal defects
 Mold shift.

141. Gas Defects
 A condition existing in a casting caused by the
trapping of gas in the molten metal or by mold gases
evolved during the pouring of the casting.
 The defects in this category can be classified into
blowholes and pinhole porosity.
 Blowholes are spherical or elongated cavities present
in the casting on the surface or inside the casting.
 Pinhole porosity occurs due to the dissolution of
hydrogen gas, which gets entrapped during heating of
molten metal.

142. Shrinkage Cavities
 These are caused by liquid shrinkage occurring during the
solidification of the casting.
 To compensate for this, proper feeding of liquid metal is
required. For this reason risers are placed at the
appropriate places in the mold.
 Sprues may be too thin, too long or not attached in the
proper location, causing shrinkage cavities.
 It is recommended to use thick sprues to avoid shrinkage
cavities.

143. Molding Material Defects
 Cuts and washes,
 Scab
 Metal penetration,
 Fusion, and
 Swell

144. Cut and washes
 These appear as rough spots and areas of excess metal, and
are caused by erosion of molding sand by the flowing
metal.
 This is caused by the molding sand not having enough
strength and the molten metal flowing at high velocity.
 The former can be taken care of by the proper choice of
molding sand and the latter can be overcome by the
proper design of the gating system.

145. Scab
 This defect occurs when a portion of the face of a mould
lifts or breaks down and the recess thus made is filled by
metal.
 When the metal is poured into the cavity, gas may be
disengaged with such violence as to break up the sand,
which is then washed away and the resulting cavity filled
with metal.
 The reasons can be: - too fine sand, low permeability of
sand, high moisture content of sand and uneven mould
ramming.

146. Metal penetration
 When molten metal enters into the gaps between sand
grains, the result is a rough casting surface.
 This occurs because the sand is coarse or no mold wash was
applied on the surface of the mold. The coarser the sand
grains more the metal penetration.

147. Fusion
 This is caused by the fusion of the sand grains with
the molten metal, giving a brittle, glassy appearance
on the casting surface.
 The main reason for this is that the clay or the sand
particles are of lower refractoriness or that the
pouring temperature is too high.

148. Swell
Under the influence of metallostatic forces, the mold
wall may move back causing a swell in the dimension
of the casting. A proper ramming of the mold will
correct this defect.
Inclusions
Particles of slag, refractory materials sand or
deoxidation products are trapped in the casting during
pouring solidification. The provision of choke in the
gating system and the pouring basin at the top of the
mold can prevent this defect

149. Pouring Metal Defects
The likely defects in this category are
 Mis-runs and
 Cold shuts
 A mis-run is caused when the metal is unable to fill
the mold cavity completely and thus leaves unfilled
cavities.
 A cold shut is caused when two streams while meeting
in the mold cavity, do not fuse together properly thus
forming a discontinuity in the casting.
Contd…

150.  The mis-run and cold shut defects are caused either by
a lower fluidity of the mold or when the section
thickness of the casting is very small. Fluidity can be
improved by changing the composition of the metal
and by increasing the pouring temperature of the
metal.

151. Mold Shift
The mold shift defect occurs when cope and drag
or molding boxes have not been properly aligned.

152. Metallurgical defects
 Hot tears or hot cracking, cause of this defect is that
stresses and strains built up during solidification are too
high compared to the actual strength of the semisolid
material. This type of defects occurs in the lower part of
the solidification range, close to the solidus, when the
alloy has a wide solidification temperature range and a
small amount of liquid, when the solid fraction is more
than 0.9, the hot tearing is easy to occur. Proper mould
design prevents this type of defect.
 Hot spots are areas on the surface of casting that
become very hard because they cooled more quickly
than the surrounding material.

153. Cast Aluminium Code
 Four digit identification system
 First digit indicates alloy group
1 – Aluminium, 99% or more
2 – copper
3 – Silicon, with copper and/or magnesium
4 – silicon
5 – magnesium
6 – not used
7 – zinc
8 – tin
9 – other elements

154. Cast Aluminium Code Contd..
 Second two digits identify the aluminium alloy or
indicate the aluminium purity.
 The last digit is separating from the other three by a
decimal point and indicates the product form; that is,
castings or ingots
 A modification of the original alloy is indicated by a
serial letter before the numerical designation.
 Alloy A514.0 indicates an aluminium alloy casting with
magnesium as the principal alloy. One modification to
the original alloy has made, as indicated by the letter A.

155. IES 2011
In the designation of Aluminium casting A514.0
indicates :
(a) Aluminium purity
(b) Aluminium content
(c) Percentage of alloy element
(d) Magnesium Content
Ans. (d)