Concepts of metal casting

1. Metal Casting Technology (MEE2014)
Faculty: Dr. B.Venkateshwarlu, Associate Professor,
School of Mechanical Engineering
VIT University, Vellore

2. Metal casting process
Casting is one of oldest and popular manufacturing processes

3. Text Book
1. Heine, et. al (2003), Principles of Metal Casting, Tata-
McGraw-HiII Publication.
Reference Books
1. Campbell, J., Castings (2003), Butter Worth,
Heinemann Publishers.
2. Beeley P.R. (2001), Foundry Technology, Buttersworth.
3. Srinath Viswanathan (2008), Metal Casting ASME
Handbook.

4. Mode of Evaluation :
Digital Assignments /Surprise Test/
Seminars/CAT/FAT

7. Introduction to casting and foundry industry-Basic
principles of casting processes-Sequence in foundry
operations-Moulding sand and its properties-
Carbon dioxide moulding-Moulding Equipment,
Moulding technique, Patterns and Cores.
Module 1
Moulding practices-Production of Moulds and Cores

9. Terminology:

10. Cast Product is also called
as “ CASTING”

13. https://www.youtube.com/watch?v=l638qR0Y6YE

14. Step1: Preparation of
Drag Box

16. Sprinkle dry facing Sand after placing the pattern so that the
pattern does not stick to the moulding sand during withdrawal
of pattern

23. Step2: Preparation of
Cope Box
Sprinkle dry parting sand on the top of the drag box and
then keep the cope part of pattern on the drag and then
align them with dowel pins

24. Sprue pin and
Riser pin

32. View after placing one sprue pin

33. View after placing both sprue pins

36. Venting: The basic purpose of
vent creating vent holes in cope
is to permit the escape of gases
generated during pouring and
solidification of the casting.
Remove conical pins
by rapping

37. Top view after removing sprue pin and riser

71. Refractory: Resistance to heat
Ex: Silica is a very good refractory material (1,713 °C)
It is the ability of the moulding material to resist the
temperature of the liquid metal to be poured so that
it does not get fused with the metal. The
refractoriness of the Silica sand is highest.

72. Permeability tells us how well
the generated gases can pass
through the moulding sand
The moulding sand must be sufficiently porous to allow the
dissolved gases, which are evolved when the metal freezes or
moisture present or generated within the moulds to be
removed freely when the moulds are poured. This property of
sand is called porosity or permeability.

73. It is an important property of the moulding sand
as the sand particles must be capable of
adhering to another body, then only the sand
should be easily attached itself with the sides of
the moulding box and give easy of lifting and
turning the box when filled with the sand.

75. Green strength is the strength of sand in the
wet state and is required for making possible to
prepare and handle the mould.

76. • If the metal is poured into a green mould the
sand adjacent to the metal dries and in the
dry state it should have strength to resist
erosion and the pressure of metal.
• The strength of the sand that has been dried
is called dry strength

77. Dry strength of moulding sand

78. At the time of pouring molten metal, mould must
be able to withstand flow and pressure of the
molten metal at high temperature otherwise the
mould may enlarge, crack, get washed or break
Hot Strength

79. The sand adjacent to the metal is suddenly
heated and undergoes expansion. If the
mould wall is not dimensionally stable under
rapid heating, cracks, buckling and flacking
off sand may occur.
Thermal stability

82. Lecture 3
• Moulding Equipment
• Moulding Technique
• Carbon dioxide moulding

83. Carbon dioxide moulding (Co2) Moulding
Mould Material : Sand + Liquid form Sodium Silicate Binder (Na2Sio3)
((3-5% based on sand weight) )
The carbon dioxide gas is passed through
the vent holes for a few seconds.

84. Mould Material : Sand + Sodium Silicate Binder (Na2Sio3)
Sodium silicate reacts with carbon dioxide gas to form silica gel that binds the
sand particles together.
The chemical reaction is given by: Na 2 Si03 + C0 2 -> Na 2 C0 3 + Si02 (Sodium
Carbonate) (silica gel)

85. Advantages:
• Instantaneous strength development and moulds are strong
• Provides great dimensional accuracy in production
Disadvantages:
• Poor collapsibility of moulds
• Over gassing and under gassing adversely affects the properties of cured
sand
Applications:
• Can be where speed and flexibility is the prime requirement
• molds of a varied sizes and shapes can be moulded by this process.

86. Moulding Equipment
• Moulding Board
• Moulding Boxes or Moulding Flasks

87. • Strike off bar
• Shovel

88. • Rammers
• Trowels

89. • Vent wires
• Gate cutters

90. • Draw spike or draw screw
• Mallet

91. • Slick
• Riddle or sieve

92. • Sprue pins
• Swab

93. • Lifters

94. Furnace

95. Patterns and Cores

96. 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

97. Types of Patterns
Figure: Types of patterns used in sand casting:
(a) solid pattern
(b) split pattern
(c) match-plate pattern
(d) cope and drag pattern

98. Match Plate Pattern
https://www.youtube.com/watch?v=rf8n9J2CDV4

99. Characteristics of Match Plate Pattern
• It is a split pattern
• Cop and Drags on the opposite site of the metallic (generally) plate.
• The gates are runners are on the match plate.
• Can be used for large number of casting with very little hand work.
• A match plate can be single pattern or a combination of many small
patterns
• Example : IC engine piston rings can be produced by match plate
pattern

100. Cope and Drag Pattern
https://www.youtube.com/watch?v=m4qBETv7bX0

103. Gated Pattern

104. https://www.youtube.com/watch?v=Jk
2PC2o_XSg
• Gating and runner system are integral with the
pattern
• Eliminates the hand cutting of runners and
gates and helps in improving the productivity of
a moulder

105. https://www.youtube.com/watch?v=n
CoostMdU3c
Loose Piece Pattern

106. Follow Board Pattern
https://www.youtube.com/watch?v=o-FICSc39sY

107. Sweep Pattern
Used for producing large size symmetrical castings such as
bells

108. Skelton Pattern
Used for large castings
in small quantities
https://www.youtube.com/watch?v=WJb2KFt
CdGY

110. Fluidity: The physical property of a substance that enables
it to flow.

143. Moulding Sand Composition
Ingredients of Moulding Sand:
• Silica grains (SiO2)
• Clay (as binder)
• Moisture (to activate clay and
provide plasticity)

146. Refractory: Resistance to heat
Ex: Silica is a very good refractory material (1,713 °C)
It is the ability of the moulding material to resist the
temperature of the liquid metal to be poured so that
it does not get fused with the metal. The
refractoriness of the Silica sand is highest.

147. Permeability tells us how well
the generated gases can pass
through the moulding sand
The moulding sand must be sufficiently porous to allow the
dissolved gases, which are evolved when the metal freezes or
moisture present or generated within the moulds to be
removed freely when the moulds are poured. This property of
sand is called porosity or permeability.

148. It is the important property of the moulding
sand and it is defined as the sand particles must
be capable of adhering to another body, then
only the sand should be easily attach itself with
the sides of the moulding box and give easy of
lifting and turning the box when filled with the
sand.

150. Green strength is the strength of sand in the
wet state and is required for making possible to
prepare and handle the mould.

151. • If the metal is poured into a green mould the
sand adjacent to the metal dries and in the dry
state it should have strength to resist erosion
and the pressure of metal.
• The strength of the sand that has been dried
is called dry strength

153. At the time of pouring the molten metal the
mould must be able to withstand flow and
pressure of the metal at high temperature
otherwise the mould may enlarge, crack, get
washed or break
Hot Strength

154. The sand adjacent to the metal is suddenly
heated and undergoes expansion. If the
mould wall is not dimensionally stable under
rapid heating, cracks, buckling and flacking
off sand may occur.
Thermal stability

159. 3-D View

160. Ferrous (Cast Iron, steel)or
non-ferrous like
aluminium

162. Thermosetting resin
binder
2.5-4.0%

163. 175-370 0C

164. Coated with a heat resistant
lubricant (Silicone) to facilitate
removal

171. The heated pattern partially
cures the mixture

172. Curing of shell for 1 - 3
min at 250 0C – 450 0C

175. (Backing material)

184. Figure: Shell Moulding Process

185. Figure: Shell Moulding Process

186. Advantages :
-High precision and accurate castings with smooth surface finish can be
produced economically.
-complex parts having intricate shapes, and cleaning of casting is reduced or
completely eliminated.
-size of casting is 10 - 13.5 kg and minimum wall thickness 2 - 2.5mm is
possible.
Examples: Brake drum, bushing, cam/cam shaft, piston, piston rings, pinions,
pipe bends, air compressor crank cases, etc.,

188. https://www.youtube.com/watch?v=Xa
r5r9Jm04g

192. https://www.youtube.com/watch?v
=UrUsaGussfc
Animated Movie of Investment Casting Process

195. WAX or Plastic
(polystyrene)

202. Binder: Water, Ethyl Silicate, etc.

203. WAX
drains off
Temperature of 90-175 0C

205. Temperature of 650-1050 0C

217. Ex: Aluminium, Magnesium, Zinc and copper based alloys

219. Patterns also can be made of
aluminium alloys, thermosetting
plastics, Zinc alloys, etc.

222. Plaster of Paris + Water +
Silica flour

226. Temperature of 120-2600C

229. Gears, Valves, Fittings, tools and
Ornaments, etc.

235. (ZrSiO4)
(Al2O3)

240. Die Casting Process

244. Hot Chamber Die Casting process

245. Cold Chamber Die Casting Process

251. Centrifugal Casting Process

252. Rotational speed: 1000 rpm
(250-3600 rpm)

261. • Core may or may not be used
• Mostly used for making hollow objects
like pipes, tubes and bushes

262. The forces generated by the rotation of the mould ensure the distribution of
molten material to all the regions of the casting

263. Semi centrifugal casting technique is a variation of
true centrifugal casting and uses vertical axis with
less rotational speeds.
The main difference is that in semi
centrifugal casting the mold is filled completely
with molten metal, which is supplied to
the casting through a central sprue.
Castings manufactured by this process will
possess rotational symmetry.
If a central bore is required in the casting, a dry
sand core is best suited.

272. Gating system and its purpose
Gating system: Refers to all the passageways through
which the molten metal travels to enter the mould cavity
Typical Gating System

273. Components of A Gating System
• Pouring Basin
• Sprue
• Sprue base well
• Runner
• Runner extension
• Ingate
• Riser
Elements of a typical gating system:

274. Functions of Gating System Elements
Pouring Basin
Molten metal is not directly poured in to the mould cavity

275. Functions of Gating System Elements
Sprue
To avoid air aspiration problem the sprue is gradually tapered to reduce the cross section

276. Functions of Gating System Elements
Sprue base well
Acts as reservoir of molten metal at bottom of sprue to reduce momentum
and thereby mould erosion is reduced

277. Functions of Gating System Elements
Sprue base well
Acts as reservoir of molten metal at bottom of sprue to reduce momentum
and thereby mould erosion is reduced

278. Functions of Gating System Elements
Runner
Partially filled runner causes slag to enter the mould cavity

279. Functions of Gating System Elements
Runner Extension
Runner is extended a little further to trap the slag in the molten metal

280. Functions of Gating System Elements
Top gate
May cause mould erosion

281. Functions of Gating System Elements
Bottom gate
Mould erosion would not cause

282. (a) Top pouring system, (b) Bottom pouring system, (c)Side pouring system
Top pouring vs. Bottom pouring systems

283. Gating System Design
Molten metal obeys Bernouli’s theorem which states that the total energy head
remains constant at any section

284. Gating System Design
Law of Continuity
Law of continuity is also useful in understanding the gating system behaviour which
states that the volume of the molten metal flowing at any section in the mould is
constant
The same in the equation form can be written as
Q= A1V1= A2V2
Where Q= rate of flow.m3/s
A= area of cross section, m2
V= velocity of metal flow, m/s

285. Gating Ratio
Gating ratio refers to the proportion of the cross
sectional areas between the sprue, runner and
ingates and it is generally denoted as
sprue area: runner area: ingate area