Foundry Lectures

FOUNDRY ENGINEERING
(Met 207)
•To Be Taught By : Dr Ather Ibrahim
•Books:
•Principles of Metal casting by Philip C Rosenthal
•Foundry Engineering by Beely
•Foundry Engineering by Campbell
•Foundry Technology by Peter Beely
•Metallurgical Principles
of Foundry Castings by Campbell J.

Traditional Manufacturing Processes
Casting
Forming
Sheet metal processing
Cutting
Joining
Powder- and Ceramics Processing
Plastics processing
Surface treatment

Casting
mold  pour liquid metal  solidify, remove  finish
Casting is a manufacturing process in which molten/liquid
material is poured into a mold containing a cavity of specific
shape, and then allowed to solidify. The solid casting is then
taken out and cleaned to complete the process

• VERSATILE:
•complex geometry, internal cavities/ external shapes, hollow
sections
•Wide range of Weight and size
•small (~10 grams)  very large parts (100 tones)
•Teeth Zipper (few mm) Ocean Liner Propeller (10 m)
•Net Shape, Near Net Shape
•Any Metal (that can be melt)
•Some metal can only be cast
•Simplified Construction
•Some Engineering properties are only possible in casting
•Isotropic
•Machinability
•Damping capacity
•Good Bearing qualities
•Strength and Lightness
• ECONOMICAL:
•little wastage (extra metal is re-used) Low cost
•Suitable for mass production
Advantages

Limitations Depend upon casting method
• Mechanical Properties
•Porosity
•Poor Dimensional Accuracy
•Surface Finish
•Safety Hazard

History
Casting is a 6000 year old process.
Earliest castings include the 11 cm high bronze dancing girl found at
Mohen-jo-daro(dated about 3000 BC).
The remains of the Harappan civilization contain kilns for smelting copper
ingots, casting tools, stone moulds, cast ornaments and other items of
copper, gold, silver and lead.
Iron pillars, arrows, hooks, nails, bowls dated 2000 BC
Another oldest casting is a copper frog dated 3200 BC discovered in
Mesopotamia
The Iron Pillar of Delhi, standing 23 feet, weighing 6 tonnes and
containing iron, is a remarkable example of metallurgical science in 5th century AD

Types of Foundries
•Based on material
• Ferrous , Non ferrous, gray Iron, Steel, Brass, Light metal
•Based on nature and Organisational Framework
•Jobbing foundry(A foundry that creates a wide variety of
castings, in small quantities for a range of customers)
•Production foundry
•Semi Production foundry
•Captive foundry(A foundry operation that is wholly
incorporated into a larger manufacturing operation)
•Independent foundry

Casting Process
• Preparing a mold cavity of the desired shape with
proper allowances and provided with means for
the escape of air or gases.
• Melting the metal with acceptable quality and
temperature.
• Pouring the metal into the cavity.
• Solidification process designed and controlled to
avoid defects.
• Casting removal.
• Finishing, cleaning and inspection operations.

Process Selection
Design and Specification
Determination of Casting Technique
Pattern MakingMoulding Material
Preparation
Furnace Charge
Preparation
Moulding & Core making Metal Melting
Casting
Fettling
Heat Treatment & Finishing
Inspection & Testing
Black Casting
Flow Diagram
for Casting
Production

Classification of Casting Processes

Different Casting Processes
Process Advantages Disadvantages Examples
Sand many metals, sizes, shapes, cheap poor finish & tolerance engine blocks,
cylinder heads
Shell mold better accuracy, finish, higher
production rate
limited part size connecting rods, gear
housings
Expendable
pattern
Wide range of metals, sizes,
shapes
patterns have low
strength
cylinder heads, brake
components
Plaster mold complex shapes, good surface
finish
non-ferrous metals, low
production rate
prototypes of
mechanical parts
Ceramic mold complex shapes, high accuracy,
good finish
small sizes impellers, injection
mold tooling
Investment complex shapes, excellent finish small parts, expensive jewellery
Permanent
mold
good finish, low porosity, high
production rate
Costly mold, simpler
shapes only
gears, gear housings
Die Excellent dimensional accuracy,
high production rate
costly dies, small parts,
non-ferrous metals
gears, camera bodies,
car wheels
Centrifugal Large cylindrical parts, good
quality
Expensive, few shapes pipes, boilers,
flywheels

Types of Mould
Open Mould Closed Mould

[ )]()( 0 mplfms
TTCHTTCVH −++−= ρ
Where
H = Total heat Required to raise the temperature of the metal to the pouring
temperature, J (Btu)
ρ = Density g/cm3
Cs= Weight Specific Heat for the Solid Metal J/g-o
C
Hf = Heat of Fusion J/g
Cl= Weight Specific Heat for the Liquid Metal J/g-o
C
Tm, Tp, To = Melting, pouring and ambient temperature respectively
V = Volume
A Good Approximation!
Why?
Heating of Metal

• Specific Heat and other Thermal Properties of a Solid Metal Vary with
Temperature Especially if the Metal Undergoes a Change of Phase During
Heating
• A Metal Specific Heat may be Different in the Solid and Liquid States
• Most Casting Metals are Alloys; Thus Heat of Fusion Cannot be Applied so
Simply
• The Property Values Required may not be Available for All Alloys
• There are Significant Heat Losses to the Environment During Heating

Factors Affecting the Pouring Operation
Pouring Temperature (Super Heat)
Pouring Rate (Slow excessive)
Turbulence
Re = Vd/v
V = mean velocity
d = Linear dimension of the mould channel section
v = kinematic viscosity of the liquid

2
2
22
21
2
12
1
22
F
g
vP
hF
g
vP
h +++=+++
ρρ
Where
h= Head cm
P = Pressure on the liquid N/cm2
ρ = Density g/cm3
v = Flow velocity cm/s
g = Gravitational Acceleration Constant
Bernoulli’s Theorem
Continuity Law
Q = V1A1=V2A2
Mould Filling Time
MFT = V/Q

Gl=Hl-TSl And Gs=Hs-TSs
Nucleation

Nucleation
• Homogeneous Nucleation (Self Nucleation)
•Heterogeneous Nucleation

Homogeneous Nucleation
2
3
23
3
16
2
0
)(
4
3
4
v
v
v
G
G
G
r
dr
Gd
rGrG
∆
=∆
∆
−=
=
∆
+∆=∆
∗
λγ
γ
γππ

Solidification
• During solidification process a series of events occur
which affect
– Size & shape of grains formed
– Influences overall properties
• In general casting results in reasonably uniform grain
structure
• Some difference between
– Pure metals
– alloys

Solidification – Pure Metals
• Solidifies at constant temperature
– Must give off latent heat of fusion before phase
change
• Rapid cooling at mold edge
– Skin/shell – fine grains
– Slower in the middle – columnar grains

Characteristics of Molten Metal
• Viscosity
– How runny is it when hot
• Surface Tension
– Development of film

Casting Parameters
• Mold Design
– Risers, runners, gates, etc.
• Mold Material
– Thermal conductivity
– Roughness of its surface
• Rate of Pouring
• Degree of superheating
– How far above melting point

Fluidity of Molten Metals
• Fluidity – capability of molten metal to fill
mold cavity
• Two basic factors
– Characteristics of molten metal
– Casting parameters

Factor Affecting Fluidity
Pouring Temperature
Metal Composition
Viscosity
Heat Transfer to Surroundings
Volume Specific Heat
Latent Heat Of Fusion
Thermal Conductivity of the Alloy

a = Crucible
b= Electric resistance furnace
c= Fluidity test channel
d= Pressure reservoir
e= Manometer
f= Cartesian manostat
Vacuum Fluidity Test Apparatus

Influence of Superheat on fluidity
• Super heat
• Duration of flow depends upon the
amount of heat to be removed before
onset of solidification

Composition and Fluidity
• Pure Metal High fluidity
• Alloys
• Solid solution with long freezing range poor fluidity
• Eutectic High fluidity

Model of Solidification
in flow channel

• A pure metal
solidifies at a
constant
temperature
equal to its
freezing point
(same as
melting point)

Cooling and Solidification
Pure metal

Critical Radius Vs Under cooling

Solidification - Alloys
• Solidify with a temperature range
– Produces a mushy or pasty state
• Cooling rate effects
– Slow – coarse structures/grains
– Fast – fine structures/grains
• In general as grain size decreases
– Strength and ductility increase
– Shrinkage voids decrease
– Cracking during solidification decreases

Solidification of Alloys
• Most alloys freeze over a temperature range
• Phase diagram for a Cu Ni alloy system and‑
cooling curve for a 50%Ni 50%Cu composition‑

Development of columnar grain structure

Schematic representation of temperature distribution in plane front solidification
Thermal conditions suitable for
production of columnar structure
Positive thermal gradient at the
solid liquid interface
Interface advancing as the TG
(growth) is reached
Flat plane is formed when
cooling rate is slow and temp
gradient is steep
Latent heat is insufficient

Thermal conditions with reversal of temperature gradient in liquid adjoining interface
Latent heat is sufficient to
reverse the temperature
gradient at the interface
in such lowest temperature in
the liquid is no longer adjacent
to the interface therefore
growth mode changes from
plane front advancement to
deposition in regions of greater
undercooling and thus
microscopic heat flow becomes
important

Thermal equilibrium diagram for two metals forming a continuous
range of solid solutions

Equilibrium distribution of solute
between solid and liquid phases at
successive stages of unidirectional
freezing

Concentration of solute in liquid ahead
of advancing interface- non equilibrium
conditions
a)Solute distribution CL
b)Equilibrium liquidus temperature TE
corresponding to solute content at
distance D from solidification interface

Relation of temperature gradient in liquid to equilibrium freezing temperature profile
Constitutional undercooling
Temperature and compositional
gradients in the liquid are the
important influencing factors on
both grain and substructure of
casting

Dendritic growth
cored structure Cellular substructure formed by undercooling

Independent nucleation
Influence of temperature gradient in liquid on crystallization,
TE= eq freezing temp
TN= nucleation temp depending upon heterogeneous nuclei
T1-3= temperature gradients producing increasing undercooling and
associated changes in morphology planar-cellular-dendritic-independently
nucleated

The Structure of Casting
Three major influences
•Alloy constitution
• mode of crystallization, single/ multiphase eutectic or both
• Level of constitutional undercooling
•Thermal conditions
• Temperature distribution, rate of cooling are determined
based on initial temperature and thermal properties of
metal and mold
•Inherent nucleation and growth conditions in the liquid
• Homogeneous and heterogeneous nucleation stimulation
in liquid metal

Interaction of temperature and compositional gradients in determining structure
(a)Influence of a temperature gradient (T)
(b)Influence of a liquidus temperature profile (TE) (i) conditions favoring plane front
solidification, (ii) conditions producing undercooling

Influence of undercooling on interface morphology and mode of growth.
(a)Planar interface
(b)Cellular interface
(c)Dendritic growth
(d)Independent nucleation

Influence of temperature gradient G and freezing rate R on solidification morphology

Influence of solute concentration,
temperature gradient and freezing rate
on solidification phenomena in
unidirectional cooling
(a)Formation of cellular interface
(b)Cellular-dendritic transition in Sn-Pb
alloys
(c)Onset of equiaxed growth in Al-Mg
alloys

Thermal explanation of mixed structures in castings (a)
columnar growth stage (b) central equiaxed region

• Characteristic grain
structure in a
casting of a pure
metal, showing
randomly oriented
grains of small size
near the mold wall,
and large columnar
grains oriented
toward the center
of the casting
Solidification of Pure Metals

©2010 John Wiley & Sons, Inc. M P
Groover, Fundamentals of Modern
Manufacturing 4/e
• Characteristic
grain structure in
an alloy casting,
showing
segregation of
alloying
components in
center of casting
Solidification of Alloys

Three Cast Structures of Solidified Metals
•FIGURE 5.8
Schematic
illustration of three
cast structures of
metals solidified in a
square mold:
•(a) pure metals;
•(b) solid-solution
alloys; and
•(c) the structure
obtained by
heterogeneous
nucleation of grains,
using nucleating
agents.

Ken Youssefi Mechanical Engineering Dept., SJSU 63
Solidification Time
Solidification time = C(volume/surface area)2
Where C is a constant that depends on mold material and
thickness, metal characteristics and temperature.

The mold constant C depends on the properties of the metal, such as
Density, Heat Capacity, Heat of Fusion and superheat, and the mold,
such as initial temperature, density, Thermal conductivity, heat capacity
and wall thickness.
The metric units of the mold constant C are min/ cm2
According to Askeland, the constant n is usually 2, however Degarmo claims
it is between 1.5 and 2. The mold constant of Chvorinov's rule, C, can be
calculated using the following formula:
Where
Tm
= melting or freezing temperature of the liquid (in Kelvin)
To
= initial temperature of the mold (in Kelvin)
ΔTs
= Tpour
− Tm
= superheat (in Kelvin)
L = latent heat of fusion (in [J.Kg-1
])
k = thermal conductivity of the mold (in [W.m-1
.K-1
)])
ρ = density of the mold (in [Kg.m-3
])
c = specific heat of the mold (in [J.Kg-1
.k-1
])
ρm
= density of the metal (in [Kg.m-3
])
cm
= specific heat of the metal (in [J.Kg-1
.k-1
])
C

Ken Youssefi Mechanical Engineering Dept., SJSU 65
Solidification Time
Sphere, cube and a cylinder with the same volume

• Cooling rate depends on casting material and configuration. It also
depends on volume and surface area of the casting.
• The pouring rate should be such that solidification does not start and
the cavity is completely filled without eroding mould surface and
undue turbulence.
• On the basis of experience following empirical relations are
developed for pouring time
K: Fluidity factor
W: Weight In kg
Tp: Poring time in sec
Pouring Rate

Mould Fcators in Metal Flow
• Fluidity is the property of metal alone
• The flow of metal under given pressure head is also
strongly influenced by the nature of mould
• Metal flow is arrested through solidification, mould condition
can effect flow duration directly (thermal properties) or
indirectly (velocity)
• Reduction in velocity-> increased time for heat loss/length
of passage wall -> final arrest in shorter distance

Thermal properties
D = (kcρ) ½
K = thermal conductivity
c= Specific heat
ρ = density
• Rate of cooling depends upon the heat diffusivity on mould material
• Rapid cooling result from the use of high heat diffusivity mould
materials, chills etc
• Cooling is accelerated by water in green sand moulds, this effect
retards metal flow in thin sections
Mould Surface Effect
• Roughness of mould surface (grain size dependent) slows down the flow
• Moud coatings are used to increase flow characteristics
• e.g. hexachloroethane in aluminum alloy casting

Air Pressure Effect
• Inadequate vents and channels for the escape of rapidly expanding
air/gases can result in loss of fluidity due to reduced flow as result of
back pressure
• Mould conditions affecting flow are inherent in the moulding
process and material
• Successful filling of mould depends primarily on the use of
suitable gating techniques

The path of molten metal during casting process comprises mainly four
parts:
1. Pouring of molten metal from ladle to the cup in the mould
2. Flow within the gating channels, from pouring basin to ingate
3. Jet of molten metal emerging from ingate and entering the mould cavity
4. Filling of mould cavity by liquid movements in the bulk as well as near
the surface.

Gating of Castings
• The rate and direction of metal flow must be such as to ensure complete
filling of the mould before freezing
• Flow should be smooth and uniform with minimum turbulence,
entrapment of air, metal oxidation and mould erosion
• It should promote ideal temperature distribution within the completely
filled mould cavity so that the pattern of subsequent cooling is
favourable to feeding
• The systems should have traps and filters for the separation of
inclusions
Gating system should be designed as per the
•Weight and shape of each casting
•Fluidity of metal
•Metal susceptibility to oxidation
• and ensure Minimum cost, molding time, fettling time, metal consumption
The main objective of a gating system is to lead clean molten metal
poured from ladle to the casting cavity, ensuring smooth, uniform
and complete filling.

(a) Bush/basin
(b) Sprue or down runner
(c) Runner
(d) Ingates
Separators/filters

Top Gating Bottom Gating Side Gating
Top Gating Open pour, edge gate, pencil gates

Normal horn gate reverse horn gate

Multiple ingate systems
(a),(b) parallel finger ingates
(c) Circumferentially placed ingates

Flow behavior in horizontal gating systems
(a) Central spure
(b) End sprue

Multiple finger ingate systems designed to induce uniform flow
(a)Pool in system
(b)Backswept runner
(c)Tapered runner

Horizontal gating systems
(a)Streamlined system with progressively
diminishing cross-sectional area of passages
(b)System using parallel runner with angled ingates

Step gating system
(a)Simple system
(b)Inclined Steps with common junction
(c)Reversed down runner

Some Devices for
separation of non metallic
inclusions
(a)Trap in gate member
(b)Underslung gates
(c)Baffle core
(d)Ball plug

Strainer cores and screens
(a)Strainer core
(b)System with metal screen

Shrinkage
• Most metals shrink during solidification & cooling
process
• Causes dimension changes and sometimes cracking
– Molten metal contracts as it cools prior to solidification
– Metal contracts during solidification process
– Metal contracts further as it cools to room temperature

Shrinkage
Metal Percent Contraction (-)
Expansion(+)
Aluminum
Zinc
Gold
Copper
Brass
Carbon Steel
Lead
Gray Cast Iron
-7.1%
-6.5%
-5.5%
-4.9%
-4.5%
-2.5-4%
-3.2%
+2.5%

©2010 John Wiley & Sons, Inc.
M P Groover, Fundamentals of
Modern Manufacturing 4/e
Shrinkage during Solidification and Cooling
• (0) starting level of molten metal immediately
after pouring; (1) reduction in level caused by
liquid contraction during cooling

Shrinkage during Solidification and Cooling
• (2) reduction in height and formation of
shrinkage cavity caused by solidification; (3)
further reduction in volume due to thermal
contraction during cooling of solid metal

Solidification Shrinkage
• Occurs in nearly all metals because the solid
phase has a higher density than the liquid
phase
• Thus, solidification causes a reduction in
volume per unit weight of metal
• Exception: cast iron with high C content
– Graphitization during final stages of freezing causes
expansion that counteracts volumetric decrease
associated with phase change

Shrinkage Allowance
• Patternmakers correct for solidification
shrinkage and thermal contraction by making
the mold cavity oversized
• Amount by which mold is made larger relative
to final casting size is called pattern shrinkage
allowance
• Casting dimensions are expressed linearly, so
allowances are applied accordingly

Directional Solidification
• To minimize effects of shrinkage, it is desirable
for regions of the casting most distant from
the liquid metal supply to freeze first and for
solidification to progress from these regions
toward the riser(s)
– Thus, molten metal is continually available from risers to
prevent shrinkage voids
– The term directional solidification describes this aspect
of freezing and methods by which it is controlled

Achieving Directional Solidification
• Directional solidification is achieved using
Chvorinov's Rule to design the casting, its
orientation in the mold, and the riser system
that feeds it
– Locate sections of the casting with lower V/A
ratios away from riser, so freezing occurs first in
these regions, and the liquid metal supply for the
rest of the casting remains open
– Chills internal or external heat sinks that cause‑
rapid freezing in certain regions of the casting

External Chills
• (a) External chill to encourage rapid freezing
of the molten metal in a thin section of the
casting; and (b) the likely result if the external
chill were not used

Riser Design
• Riser is waste metal that is separated from the
casting and re-melted to make more castings
• To minimize waste in the unit operation, it is
desirable for the volume of metal in the riser to
be a minimum
• Since the shape of the riser is normally designed
to maximize the V/A ratio, this allows riser
volume to be reduced to the minimum possible
value

Pattern allowances
• Shrinkage allowance
• Draft allowance
• Machining allowance
• Distortion allowance

MANUFACTURING MATERIAL
PATTERN WORKING DRAWING

DRAFT ANGLES

CAST PART WORKING DRAWING

Challenges with Casting
• Several defects can develop in castings
• Most can be avoided with proper design and
processing techniques

• Metallic Projections - fins, flash, rough surface
– Too high pressure
– Improper mating mold pieces
• Cavities - pockets caused by shrinkage or gases
– Can be controlled by adding flux
• Discontinuities – includes cracks, cold/hot tearing,
and cold shunts
– Constrained cooling
– Molten metal too low temperature

• Defective Surface – scars(marks), adhering sand
layers, oxide scale
– Design of gate may improve
• Incomplete Casting – premature solidification
– Insufficient volume of metal poured
• Incorrect Dimensions/Shape – improper shrinkage
allowance, warped( benting) casting, etc.
• Inclusions – form during melting, solidification,
and molding
– Usually a result of chemical reactions
– Reduce strength of casting
– Can/should be filtered out

Sand Casting
• Most prevalent form of casting
• 15 million tons of metal cast by this method
annually in the US
• Typical sand casting applications
– Machine bases
– Large turbine impellers
– Propellers
– Plumbing fixtures
– Agricultural and railroad equipment components

Sand Casting
• Utilizes gravity to feed molten metal into a non-
reuseable mold
• Sand contains binding materials
• Requires a reuseable mold pattern
• Produces a parting line on the work piece
• Requires drafts and fillets on pattern
• Produces rough textured(roughness) surfaces
• Sprues, risers, and runners must be removed

Green Sand Casting
Pouring Basin
Sprue
Runner
Gate
Mold Cavity
Riser
Drag
Cope

Green Sand Casting
• Wall Thickness
– Typical 0.25 - 1.0 in.
– Feasible 0.30 - 3.0 in.
• Casting Weight
– Typical 1 – 50 lb.
– Feasible few oz. – several hundred lb.

Green Sand Casting
• Tolerances
– Typical ±0.125 in.
– Feasible ±0.0625 in.
• Surface Finish
– Typical 300-600 μin.
– Feasible 200-1000 μin.

Factors Affecting Tolerance and
Surface Finish
• Accuracy of pattern
• Dimensional stability of pattern
• Casting shrinkage
• Pattern smoothness
• Pattern wear
• Sand compaction
• Dimensional stability of casting alloy
• Gating and rising system

Four Main Components For Making A Sand
Casting Mold:
• Base Sand
• Binder
• Additives
• Parting Compound
SAND MOLD

MOLDING SAND CHARACTERSTICS
• Chemical inertness
• Refractoriness
• Permeability
• Cohesiveness (or bond)
• Surface finish
• Collapsibility
• Flowability
• Availability/cost

GENERAL PROPERTIES OF
MOLDING SANDS
• Molding sand must be readily moldable and produce
defect-free castings.
• AFS – sets forth the standard condition of testing the sand
properties.
1. GREEN STRENGTH:
• Adequate strength and toughness for making and handling
the mold.
2. DRY STRENGTH:
• Dry sand must have strength to resist erosion and also the
metallostatic pressure of the molten metal or else the mold
may enlarge.

3. HOT STRENGTH:
• Hot molten metal
• Metallostatic pressure of the liquid metal bearing
against the mold walls may cause mold
enlargement, or if the metal is still flowing,
erosion, cracks, or breakages may occur unless the
sand posses adequate hot strength.
4. PERMEABILITY:
• Steam and other gases
• The mold must be permeable, i.e. , porous to
permit the gases to escape.

5. THERMAL STABILITY:
• Heat from the casting causes rapid expansion of
the sand surface at the mold-metal interface.
• The mold surface may crack, buckle(twisted), or
flake off (scab) unless the molding sand is
relatively stable dimensionally under rapid heating.
6. REFRACTORINESS:
• The absence of melting, softening, or adherence of
the sand to the casting makes for better casting
surface and easier cleaning of the casting.
• Ferrous alloys ---- sand with high refractoriness.

7. FLOWABILITY:
• The sand should pack well/flow under load.
• Sands of low flowability may result in non-
uniform hardness.
• Soft molds --- enlargement of the casting or
roughness of the casting surfaces.
8. PRODUCE GOOD CASTING FINISH:
• Finer sands ----- a smoother casting surface.

9. COLLAPSIBILITY:
• Heated sands -------- hard and rocklike.
• Difficult to remove from the casting
• May cause the contracting metal to tear or crack.
10. THE SAND SHOULD BE REUSABLE.
11. EASE OF SAND PREPARATION AND
CONTROL.
** Economic production of good casting.

SAND DEFINATIONS
Silica Sand: White, washed and dried, silica sand grains of
high purity, 99.8+ percent SiO2.
Bank Sand: Sand from glacial or sedimentary deposits
occurring in banks or pits usually containing less
than 5 % clay.
Lake Sand: A sub-angular sand, from lake areas.
System Sand: employed in a mechanical sand preparation
and handling system.
Heap Sand: Sand thought of as being heaped on the floor
when it is prepared for use.
Facing Sand: A specially prepared sand used next to the
pattern and backed up with heap or system sand.

Backing Sand: Molding sand used to back up facing sand
and not used next to the pattern.
Bonding Sand: Sand high in clay content used to add clay to
a molding sand.
Sharp Sand: A sand substantially free of bond. Lake sands
Sand Additive: Any material added to molding sands for a
special effect.
Loam: A mixture of sand, silt and clayey particles in such a
proportions as to exhibit about 50 % sand grains
and 50 % silt and clay.

Types of Sands
SILICA (Sio2) Sand
Olivine Sand
Chromite Sand
Zircon Sand
Chamotte Sand

 Grain Shape is defined in terms of
• Angularity and
• Sphericity
 Sand Grains Vary from
• Well Rounded to Rounded
• Sub rounded
• Sub Angular
• Angular
• Very Angular
 With in each angularity band
grains may have
• High
• Medium
• Low Sphericity
Angularity is estimated through low power microscope
examination and comparison with published charts
The Best foundry sand
grains are
Rounded with medium to
high Sphericity giving rise
to Good Flowability and
Permeability with high
strength at low binder
additions
More Angular and low
sphericity sand require
higher binder additions
have lower packing density
and poor flowability
Grain Shape

Binders
• Clay and water
• Oil
• Resin
• Sodium silicate

Additives
To improve surface finish, dry strength, refractoriness,
and "cushioning(mechanical damping) properties of
the casting following: additives may be added upto
•Reducing Agents (5%) Coal Powder, Creosote,
Pitch, Fuel Oil
•Cushioning Material (3%) Wood Flour, Saw Dust
Powdered Husks(shell), Peat, And Straw
• Cereal Binders (2%) Starch, Dextrin, Molasses
Sulphite Lye(strong solution of sodium or potassium
hydroxide),
•2% Iron Oxide Powder
Disadvantage they greatly reduce permeability

Parting Compounds
Common Powders include
•Talc
•Graphite
•Dry Silica
Common Liquids include
•Mineral Oil
•Water-Based Silicon Solutions

Requirements of molding sand are:
(a) Refractoriness
(b) Cohesiveness
(c) Permeability
(d) Collapsibility
The performance of mould depends on
following factors:
(a) Permeability
(b) Green strength
(c) Dry strength

Effect of moisture, grain size and shape on
mould quality

Patterns
• Variety of patterns are used in casting and the choice
depends on the configuration of casting and number
of casting required
– Single-piece pattern
– Split pattern
– Follow board pattern
– Cope and drag pattern
– Match plate pattern
– Loose-piece pattern
– Sweep pattern
– Skeleton pattern

Pattern geometry
Solid
Split Match plate‑
Cope and Drag pattern

(a)Split pattern
(b) Follow-board
(c) Match Plate
(d) Loose-piece
(e) Sweep
(f) Skeleton
pattern

TABLE 11.3
Ratinga
Characteristic Wood Aluminum Steel Plastic Cast iron
Machinability E G F G G
Wear resistance P G E F E
Strength F G E G G
Weightb E G P G P
Repairability E P G F G
Resistance to:
Corrosionc E E P E P
Swellingc P E E E E
aE, Excellent; G, good; F, fair; P, poor.
bAs a factor in operator fatigue.
cBy water.
Source : D.C. Ekey and W.R. Winter, Introduction to Foundry Technology. New York.
McGraw-Hill, 1958.
Pattern Material Characteristics

145
Pattern Design suggestions

Use of chaplets to avoid shifting of cores
Possible chaplet design
and casting with core

147
More Pattern
Design
suggestions

148
And more…
Figure 7.2.32
Omit outside
bosses and the
need for cores.
(Courtesy of
Meehanite Metal
Corp.)
Figure 7.2.35
Avoid using ribs
which meet at
acute angles.
(Courtesy of
Meehanite Metal
Corp.)

COOLING EFFECTS ON MOLD CAVITIES
FILLED WITH MOLTEN METAL

General design rules
• Casting soundness-feeder heads can be placed to offset liquid
shrinkage
• Fillet or round all sharp angles
• Bring the minimum number of adjoining sections together
• Design all sections as nearly uniform in thickness as possible
• Avoid abrupt section changes-eliminate sharp corners at
adjoining sections: not exceed a 2:1 ratio
• Design ribs for maximum effectiveness-increase stiffness and
reduce mass
• Avoid bosses & pads unless absolutely necessary

General design rules continued
• Use curved spokes-less likely to crack
• Use an odd number of spokes-more resilient to casting
stresses
• Consider wall thicknesses
– Gray-iron & aluminum: .16 in minimum
– Malleable iron & steel: .18 in minimum
– Bronze,brass,magnesium: .10 minimum
 Parting lines: a line along which the pattern is divided for
molding or along which sections of the mold separate
(consider shape of casting, elimination of machining on
draft surfaces, methods of supporting cores, location of
gates & feeders)
 Drill holes in castings: small holes are drilled and not
cored

DESIGN MEMBERS SO THAT ALL PARTS INCREASE
PROGRESSIVELY TO FEEDER RISERS

FILLET ALL SHARP ANGLES

Other Considerations
• Draft angle
– Facilitate the removal of the part from the mold
– Typically 1º-5º
• Shrinkage Allowance
– Added to the pattern size so the desired
tolerances can be maintained on the part

Production steps in sand casting including pattern
making and mold making

Squeeze Heads
Figure 11.9 Various
designs of squeeze heads for
mold making: (a)
conventional flat head; (b)
profile head; (c) equalizing
squeeze pistons; and (d)
flexible diaphragm. Source:
© Institute of British
Foundrymen. Used with
permission.

Vertical Flaskless Molding
Figure 11.10 Vertical flaskless molding. (a) Sand is squeezed between two halves of the pattern.
(b) Assembled molds pass along an assembly line for pouring.

• A core is a preformed baked sand or green sand aggregate inserted in a
mold to shape the interior part of a casting which cannot be shaped by
the pattern.
• A core box is a wood or metal structure, the cavity of which has the
shape of the desired core which is made therein.
• A core box, like a pattern is made by the pattern maker.
• Cores run from extremely simple to extremely complicated.
• A core could be a simple round cylinder form needed to core a hole
through a hub of a wheel or it could be a very complicated core used to
core out the water cooling channels in a cast iron engine block along
with the inside of the cylinders.
• Dry sand cores are for the most part made of sharp, clay-free, dry silica
sand mixed with a binder and baked until cured; the binder cements the
sand together.
• When the metal is poured the core holds together long enough for the
metal to solidify, then the binder is finely cooked, from the heat of the
casting, until its bonding power is lost or burned out. If the core mix is
correct for the job, it can be readily removed from the castings interior by
simply pouring it out as burnt core sand. This characteristic of a core mix
is called its collapsibility.
Cores

• The size and pouring temperature of a casting determines how well and
how long the core will stay together.
• The gases generated within the core during pouring must be vented to
the outside of the mold preventing gas porosity and a defect known as a
core blow. Also, a core must have sufficient hot strength to be handled
and used properly.
• The hot strength refers to its strength while being heated by the casting
operation. Because of the shape and size of some cores they must be
further strengthened with rods and wires.
• A long span core for a length of cast iron pipe would require rodding to
prevent the core from sagging or bending upward when the mold is
poured because of the liquid metal exerting a strong pressure during
pouring.

BINDERS
•There are many types of binders to mix with core sand. A binder should be
selected on the basis of the characteristics that are most suitable for
particular use.
•Some binders require no baking becoming firm at room temperature such as
rubber cement, Portland cement and sodium silicate or water glass.
• In large foundry operations and in some small foundries, sodium silicate is a
popular binder as it can be hardened almost instantly by blowing carbon
dioxide gas through the mixture.
•The sodium silicate/CO2 process hardens through reaction. The silica gel
that is formed binds individual sand grains together.
•Oil binders require heating or baking before they develop sufficient strength
to withstand the molten metal.
• Sulfite binders also require heating. The most popular of the sulfite binders
is a product of the wood pulp industry.
• There are many liquid binders made from starches, cereals and sugars.
They are available under a countless number of trade names.

A good binder will have the following properties;
•Strength
•Collapse rapidly when metal starts to shrink.
•Will not distort core during baking.
•Maintain strength during storage time.
•Absorb a minimum of moisture when in the mould or in storage.
•Withstand normal handling.
•Disperse properly and evenly throughout the sand mix.
•Should produce a mixture that can be easily formed
MANUFACTURING OF CORE
•Core sand mixes can be mixed in a Muller or paddle type
mixer and in small amounts on the bench by hand.
•The core is made by ramming the sand into the core box
and placing the core on a core plate to bake.

Core Making: Cores are made of foundry sand with addition
of some resin for strength by means of core boxes
Core box, two core
halves ready for baking,
and the complete core
made by gluing the two
halves together

Balance Core
This is when the core is
supported on one end
only and the other
unsupported end
extends a good way into
the mold cavity.
CHAPLETS
• Chaplets consist of metallic supports or
spacers used in a mold to maintain cores,
which are not self-supporting, in their
correct position during the casting
process.
• They are not required when a pattern
has a core print or prints which will serve
the same purpose.
• The pattern is drilled, wherever a
chaplet is needed.

CORE BAKING AND CORE OVENS
•The cores are baked in order to set the binder.
•The usual temperature range for oil bonded cores is from 300 to 450 degrees
Fahrenheit. The time required varies with the bulk of the core.
•A large core might take several days to bake or a small core might bake out
in an hour or less.
•When an oil core is completely baked the outside is a rich dark brown not
black or burned. The core must be cured completely through with no soft
centres.
•Another factor which relates to the time and temperature required to properly
dry a core, is the type and amount of binder used. Oil binders require hotter
and quicker baking.
•The core oven, which is usually a gas fired oven with temperature controls, is
equipped with shelves on which to set the core plates and cores for baking.
•The core oven can consist of a square or rectangular brick oven with doors.
The bottom of the oven is floor level. The ores are placed on racks which,
when full, are rolled into the oven, the oven closed and the cores baked.

Types of Permanent Pattern Casting
TechniquesGreen Sand Molds The most common type consisting of
forming the mold from damp molding sand (silica, clay and
moisture)
Skin-dried Molds It is done in two ways; (1) The sand around
the pattern to a depth of about 1/2 in(10 mm) is mixed with a
binder so that when it is dried it will leave a hard surface on
the mold. (2) Entire mold is made from green sand, but a
spray or wash, which hardens when heat is applied, is used.
(3) The surface is then dried upto a depth of 12-25 mm by
means of hot air, infrared lamp etc.
Dry Sand Molds These molds are made entirely from fairly
coarse molding sand mixed with binders (linseed oil or
gelatinized starch). They baked before being used. A dry sand
mold holds its shape when poured and is free from gas
troubles due to moisture.

Floor and Pit Mold
Loam sand Mold
High Pressure Mold

Resin Bond : Shell Molding
Casting process in which the mold is a thin shell of
sand held together by thermosetting resin binder
Steps in shell molding: (1) a match plate or cope and drag metal‑ ‑ ‑ ‑
pattern is heated and placed over a box containing sand mixed with
thermosetting resin.

Steps in shell molding: (2) box is inverted so that sand and‑
resin fall onto the hot pattern, causing a layer of the mixture
to partially cure on the surface to form a hard shell; (3) box
is repositioned so that loose uncured particles drop away;

Steps in shell molding: (4) sand shell is heated in oven for‑
several minutes to complete curing; (5) shell mold is stripped
from the pattern;

Steps in shell molding: (6) two halves of the shell mold are‑
assembled, supported by sand or metal shot in a box, and
pouring is accomplished; (7) the finished casting with sprue
removed.
From www.janfa.com

Advantages and Disadvantages
• Advantages of shell molding:
– Smoother cavity surface permits easier flow of
molten metal and better surface finish
– Good dimensional accuracy - machining often not
required
– Mold collapsibility minimizes cracks in casting
– Can be mechanized for mass production
• Disadvantages:
– More expensive metal pattern
– Difficult to justify for small quantities

Resin Bond
Cold Box
– synthetic liquid resin mixed with sand.
– Cold-setting process- bonding of mold takes
place without heat
Hot Box
organic and inorganic binders added.
greater dimensional accuracy.
greater cost.

Schematic of the V-process or vacuum molding. A) A vacuum is pulled on a pattern, drawing a heated
shrink-wrap plastic sheet tightly against it. b) A vacuum flask is placed over the pattern and filled with
dry unbonded sand, a pouring basin and sprue are formed; the remaining sand is leveled; a second
heated plastic sheet is placed on top; and a mold vacuum is drawn to compact the sand and hold the
shape. c) With the mold vacuum being maintained, the pattern vacuum is then broken and the pattern
is withdrawn. The cope and drag segments are assembled, and the molten metal is poured.
V Process- No Bond

Advantages and Disadvantages of the V-Process
• Advantages
– Absence of moisture-related defects
– Binder cost is eliminated
– Sand is completely reusable
– Finer sands can be used
– Better surface finish
– No fumes generated during the pouring operation
– Exceptional shakeout characteristics
• Disadvantages
– Relatively slow process
– Used primarily for production of prototypes
– Low to medium volume parts
– More than 10 but less than 50,000

Plaster Mold Casting
Similar to sand casting except mold is made of
plaster of Paris (gypsum CaSO‑ 4 2H‑ 2O)
• In mold-making, plaster and water mixture is
poured over plastic or metal pattern and
allowed to set
– Wood patterns not generally used due to extended
contact with water
• Plaster mixture readily flows around pattern,
capturing its fine details and good surface
finish

Engr 241 181
Plaster–mold casting(cont.)
• Mold dried in oven
• Poured in vacuum or under pressure due to
low permeability
• Low permeability (gas cannot escape)

Plaster-Mold Casting
Antioch Process
• Plaster of paris with talc and silica flour.
• Mixed with water
• Poured over pattern
• Plaster sets – pattern removed
Engr 241 182

• Advantages of plaster mold casting:
– Good accuracy and surface finish
– Capability to make thin cross sections‑
• Disadvantages:
– Mold must be baked to remove moisture,
which can cause problems in casting
– Mold strength is lost if over-baked
– Plaster molds cannot stand high
temperatures, so limited to lower melting
point alloys (Mg, A, Zn)

Ceramic Mold Casting
Similar to plaster mold casting except that mold
is made of refractory ceramic material zircon,
aluminum oxide and fused silica that can
withstand higher temperatures than plaster
• Can be used to cast steels, cast irons, and
other high temperature alloys‑
• Applications similar to those of plaster mold
casting except for the metals cast
• Advantages (good accuracy and finish) also
similar but expansive

Unicast and Shaw Process
a mixture of refractory aggregate, hydrolyzed ethyl
silicate, alcohol, and a gelling agent to create a mold. The
slurry hardens almost immediately to a rubbery state . The
flask and pattern is then removed. Then a torch is used to
ignite the mold, which causes most of the volatiles to burn-off
and the formation of ceramic microcrazes (microscopic
cracks). These cracks are important, because they allow
gases to escape while preventing the metal from flowing
through; they also ease thermal expansion and contraction
during solidification and shrinkage. After the burn-off, the
mold is baked at 1,800 °F (980 °C) to remove any remaining
volatiles. Prior to pouring metal, the mold is pre-warmed to
control shrinkage

A typical ceramic mold (Shaw process) for casting steel dies used in hot forging. Source: Metals
Handbook, vol. 5, 8th ed.

Expanded Polystyrene Process
Expanded polystyrene casting process: pattern of polystyrene is
coated with refractory compound;
Uses a mold of sand packed around a polystyrene foam pattern
which vaporizes when molten metal is poured into mold
 Other names: lost foam process, lost pattern process,‑
evaporative foam process, and full mold process‑ ‑
 Polystyrene foam pattern includes sprue, risers, gating system,
and internal cores (if needed)
 Mold does not have to be opened into cope and drag sections
From www.wtec.org/loyola/casting/fh05_20.jpg

Foam pattern is placed in mold box,
and sand is compacted around the
pattern;
Molten metal is poured into the portion of
the pattern that forms the pouring cup
and sprue. As the metal enters the mold,
the polystyrene foam is vaporized ahead
of the advancing liquid, thus the resulting
mold cavity is filled.

• Advantages of expanded polystyrene process:
– Pattern need not be removed from the mold
– Simplifies and speeds mold making, because two mold‑
halves are not required as in a conventional green sand‑
mold
• Disadvantages:
– A new pattern is needed for every casting
– Economic justification of the process is highly dependent
on cost of producing patterns

• Applications:
– Mass production of castings for automobile engines
– Automated and integrated manufacturing systems are
used to
1. Mold the polystyrene foam patterns and then
2. Feed them to the downstream casting operation

Investment Casting (Lost Wax Process)
A pattern made of wax (plastic) is coated with a
refractory material to make mold, after which
wax is melted away prior to pouring molten
metal
• "Investment" comes from a less familiar
definition of "invest" - "to cover completely,"
which refers to coating of refractory material
around wax pattern
• It is a precision casting process - capable of
producing castings of high accuracy and
intricate detail

Investment Casting
Figure 11.8 Steps in investment casting: (1) wax patterns are
produced, (2) several patterns are attached to a sprue to form a
pattern tree

Investment Casting
Figure 11.8 Steps in investment casting: (3) the pattern tree is coated with
a thin layer of refractory material, (4) the full mold is formed by covering
the coated tree with sufficient refractory material to make it rigid

Investment Casting
Figure 11.8 Steps in investment casting: (5) the mold is held in an inverted
position and heated to melt the wax and permit it to drip out of the
cavity, (6) the mold is preheated to a high temperature, the molten metal
is poured, and it solidifies

Investment Casting
Figure 11.8 Steps in investment casting: (7) the mold is broken
away from the finished casting and the parts are separated
from the sprue

Investment Casting
Figure 11 9 A one piece compressor stator with 108 separate‑
airfoils made by investment casting (photo courtesy of
Howmet Corp.).

• Advantages of investment casting:
– Parts of great complexity and intricacy can be cast
– Close dimensional control and good surface finish
– Wax can usually be recovered for reuse
– Additional machining is not normally required this is a‑
net shape process
• Disadvantages
– Many processing steps are required
– Relatively expensive process

Permanent Mold Casting Processes
• Economic disadvantage of expendable mold
casting: a new mold is required for every casting
• In permanent mold casting, the mold is reused
many times
• The processes include:
– Basic permanent mold casting
– Die casting
– Centrifugal casting

The Basic Permanent Mold Process
Uses a metal mold constructed of two sections
designed for easy, precise opening and closing
•Molds used for casting lower melting point
alloys are commonly made of steel or cast iron
•Molds used for casting steel must be made of
refractory material, due to the very high pouring
temperatures

Permanent Mold Casting
Figure 11.10 Steps in permanent mold casting: (1) mold is preheated and
coated

Permanent Mold Casting
Figure 11.10 Steps in permanent mold casting: (2) cores (if used) are
inserted and mold is closed, (3) molten metal is poured into the mold,
where it solidifies.

Advantages and Limitations
• Advantages of permanent mold
casting:
– Good dimensional control and surface finish
– More rapid solidification caused by the cold
metal mold results in a finer grain structure, so
castings are stronger
• Limitations:
– Generally limited to metals of lower melting
point
– Simpler part geometries compared to sand
casting because of need to open the mold
– High cost of mold

Applications of Permanent Mold
Casting
• Due to high mold cost, process is best suited
to high volume production and can be
automated accordingly
• Typical parts: automotive pistons, pump
bodies, and certain castings for aircraft and
missiles
• Metals commonly cast: aluminum,
magnesium, copper base alloys, and cast iron‑

Die Casting
A permanent mold casting process in which molten
metal is injected into mold cavity under high
pressure
•Pressure is maintained during solidification, then
mold is opened and part is removed
•Molds in this casting operation are called dies;
hence the name die casting
•Use of high pressure to force metal into die cavity
is what distinguishes this from other permanent
mold processes

Die Casting Machines
• Designed to hold and accurately close two
mold halves and keep them closed while
liquid metal is forced into cavity

Process Capabilities and Machine SelectionProcess Capabilities and Machine Selection
– Dies are rated according to their clamping force that is needed
– Factors involved in selection of die cast machines are
• Die size
• Piston stroke
• Shot pressure
• Cost
– Die-casting dies
• Single cavity
• Multiple-cavity
• Combination-cavity
• Unit dies
– Ratio of Die weight to part weight is 1000 to 1
– Surface cracking is a problem with dies due to the hot metal that is
poured in to them
– Has ability to produce strong high- quality parts with complex shapes
– Good dimensional accuracy and surface details

Various types of cavities in a die casting die.Various types of cavities in a die casting die.
a) Single – cavity die
b) Multiple – cavity die
c) Combination die
d) Unit die

Die CastingDie Casting
• Molten metal is forced into the die cavity at pressures ranging
from .7MPa – 700MPa
• Parts made from here range from:
– Hand tools
– Toys
– Appliance components
• There are two basic types of die casting machines
– Hot-chamber - involves the use of a piston to push molten
metal in to the die cavity
– Cold-chamber – molten metal is poured in to the injection
chamber & the shot chamber is not heated

Hot-Chamber Die Casting
Metal is melted in a container, and a piston injects
liquid metal under high pressure into the die
•High production rates - 500 parts per hour not
uncommon
•Applications limited to low melting point metals
that do not chemically attack plunger and other
mechanical components
•Casting metals: zinc, tin, lead, and magnesium

Hot-Chamber Die Casting
Cycle in hot chamber casting: (1) with die closed and plunger‑
withdrawn, molten metal flows into the chamber (2) plunger forces
metal in chamber to flow into die, maintaining pressure during cooling
and solidification.

Die Casting in Hot-Chamber Process
• FIGURE 5.28 Sequence of steps in die casting of a part in the hot-chamber
process. Source: Courtesy of Foundry Management and Technology.

Hot chamber Die-casting processHot chamber Die-casting process
• 1. The die is closed and the
piston rises, opening the
port and allowing molten
metal to fill the cylinder.
• 2. The plunger moves
down and seals the port
pushing the molten metal
through the gooseneck and
nozzle into the die cavity,
where it is held under
pressure until it solidifies.

• 3. The die opens and the
cores, if any, retract. The
casting remains in only one
die, the ejector side. The
plunger returns, allowing
residual molten metal to flow
back through the nozzle and
gooseneck.
• 4. Ejector pins push the
casting out of the ejector die.
As the plunger uncovers the
filling hole, molten metal flows
through the inlet to refill the
gooseneck, as in step (1).

Cold Chamber Die Casting Machine‑
Molten metal is poured into unheated chamber
from external melting container, and a piston
injects metal under high pressure into die cavity
•High production but not usually as fast as
hot chamber machines because of pouring step‑
•Casting metals: aluminum, brass, and magnesium
alloys
•Advantages of hot chamber process favor its use‑
on low melting point alloys (zinc, tin, lead)‑

Cold Chamber Die Casting‑
Cycle in cold chamber casting: (1) with die closed and ram‑
withdrawn, molten metal is poured into the chamber

Cold Chamber Die Casting‑
Cycle in cold chamber casting: (2) ram forces metal to flow into die,‑
maintaining pressure during cooling and solidification.

Cold-Die casting processCold-Die casting process
• 1. The die is closed and the
molten metal is ladled into the
cold-chamber shot sleeve.
• 2. The plunger pushes the molten
metal into the die cavity where it
is held under pressure until
solidification.

• 3. The die opens and the plunger
advances, to ensure that the
casting remains in the ejector die.
Cores, if any, retract.
• 4. Ejector pins push the casting
out of the ejector die and the
plunger returns to its original
position.

Molds for Die Casting
• Usually made of tool steel, mold steel, or
maraging steel
• Tungsten and molybdenum (good refractory
qualities) used to die cast steel and cast iron
• Ejector pins required to remove part from die
when it opens
• Lubricants must be sprayed into cavities to
prevent sticking

Advantages and Limitations
• Advantages of die casting:
– Economical for large production quantities
– Good accuracy and surface finish
– Thin sections are possible
– Rapid cooling provides small grain size and good
strength to casting
• Disadvantages:
– Generally limited to metals with low metal
points
– Part geometry must allow removal from die

Low Pressure Die Casting Process

Pressure-Casting Process
• FIGURE 5.27 The pressure-casting process uses graphite molds for the
production of steel railroad wheels. Source: Griffin Wheel Division of
Amsted Industries Incorporated.

(a) The bottom-pressure casting process utilizes graphite molds for the productin of
steel railroad wheels. (b) Gravity pouring method of casting a railroad wheel. Note
that the pouring basin also serves as a riser.
Pressure CastingPressure Casting

Slush CastingSlush Casting
• Molten metal is poured into the metal mold
• A desired thickness of the solidified skin is obtained
• The remaining metal is poured out
• The mold halves are then opened and the casting is removed
• Used a graphite or metal mold
• Molten metal is forced into the mold by gas pressure
• The pressure is maintained until the metal solidifies in the mold
• Used for high-quality castings
Pressure CastingPressure Casting

Centrifugal Casting
A family of casting processes in which the mold
is rotated at high speed so centrifugal force
distributes molten metal to outer regions of die
cavity
•The group includes:
– True centrifugal casting
– Semi centrifugal casting
– Centrifuge casting

True Centrifugal Casting
Molten metal is poured into rotating mold to
produce a tubular part
•In some operations, mold rotation commences
after pouring rather than before
•Parts: pipes, tubes, bushings, and rings
•Outside shape of casting can be round,
octagonal, hexagonal, etc , but inside shape is
(theoretically) perfectly round, due to radially
symmetric forces

Centrifugal Casting Process
FIGURE 5.30 Schematic illustration of the centrifugal casting process.
Pipes, cylinder liners, and similarly shaped parts can be cast by this
process.

Semicentrifugal Casting
Centrifugal force is used to produce solid
castings rather than tubular parts
• Molds are designed with risers at center to
supply feed metal
• Density of metal in final casting is greater in
outer sections than at center of rotation
• Often used on parts in which center of casting
is machined away, thus eliminating the
portion where quality is lowest
• Examples: wheels and pulleys

Semicentrifugal Casting
Process
•FIGURE 5.31 (a) Schematic illustration of the semicentrifugal casting process. (b)
Schematic illustration of casting by centrifuging. The molds are placed at the periphery
of the machine, and the molten metal is forced into the molds by centrifugal forces.

Centrifuge Casting
Mold is designed with part cavities located away
from axis of rotation, so that molten metal
poured into mold is distributed to these cavities
by centrifugal force
•Used for smaller parts
•Radial symmetry of part is not required as in
other centrifugal casting methods

Vacuum CastingVacuum Casting1. Mixture of fine sand
and urethane is
molded over metal
dies a cured with
amine vapor
2. The mold is partially
immersed into molten
metal held in an
induction furnace
3. The metal is melted in
air or in a vacuum
4. The molten metal is
usually 55 C above
the liquidus
temperature – begins
to solidify within a
fraction of a second
5. Alternative to investment, shell-
mold, and green-sand casting
6. Relatively low cost

Squeeze-Casting Process
• FIGURE 5.32 Sequence of operations in the squeeze-casting process.
This process combines the advantages of casting and forging.

Plaster Molds Plaster or plaster-bonded molds are used for casting
certain aluminum or copper base alloys. Dimensional accuracy and
excellent surface finish make this a useful process for making rubber
tire molds, match plates, etc.
A variation of this method of molding is the Antioch process, using
mixtures of 50 percent silica sand, 40 percent gypsum cement, 8 percent
talc, and small amounts of sodium silicate, portland cement, and
magnesium oxide. These dry ingredients are mixed with water and
poured over the pattern. After the mixture is poured, the mold is steamtreated
in an autoclave and then allowed to set in air before drying in an
oven. When the mold has cooled it is ready for pouring. Tolerances of
0.005 in (0.13 mm) on small castings and 0.015 in (0.38 mm)
on large castings are obtained by this process.
A problem presented by plaster molds lies in inadequate permeability
in the mold material consistent with the desired smooth mold cavity
surface. A closely related process, the Shaw process, provides a solution

In this process, a refractory aggregate is mixed with a gelling agent and then poured
over the pattern. Initial set of the mixture results in a rubbery consistency which allows it
to be stripped from the pattern but which is sufficiently strong to return to the shape it
had when on the pattern. The mold is then ignited to burn off the volatile content in the
set gel and baked at very high heat. This last step results in a hard, rigid mold containing
microscopic cracks. The permeability of the completed mold is enhanced by the
presence of the so-called microcrazes, while the mold retains the high-quality definition
of the mold surface.
Two facts are inherent in the nature of sand molds: First, there may be one or few
castings required of a given piece, yet even then an expensive wood pattern is required.
Second, the requirement of removal of the pattern from the mold may involve some very
intricate pattern construction. These conditions may be alleviated entirely by the use of
the full mold process, wherein a foamed polystyrene pattern is used. Indeed,
the foamed pattern may be made complete with a gating and runner system,
and it can incorporate the elimination of draft allowance. In actual practice, the pattern is
left in place in the mold and is instantly vaporized when hot metal is poured. The hot
metal which vaporized the foam fills the mold cavity to the shape occupied previously by
the foam pattern. This process is ideal for casting runs of one or a few pieces, but it
can be applied to production quantities by mass-producing the foam patterns. There is
extra expense for the equipment to make the destructible foam patterns, but often the
economics of the total casting process is quite favorable when compared with resorting
to a reusable pattern. There are particular instances when the extreme complexity of a
casting can make a hand-carved foam pattern financially attractive.

True Centrifugal Casting
Setup for true centrifugal casting.

Die casting
- a type of permanent mold casting
- common uses: components for
rice cookers, stoves, fans, washing-, drying machines,
fridges, motors, toys, hand-tools, car wheels, …
HOT CHAMBER: (low mp e.g. Zn, Pb; non-alloying)
(i) die is closed, gooseneck cylinder is filled with molten metal
(ii) plunger pushes molten metal through gooseneck into cavity
(iii) metal is held under pressure until it solidifies
(iv) die opens, cores retracted; plunger returns
(v) ejector pins push casting out of ejector die
COLD CHAMBER: (high mp e.g. Cu, Al)
(i) die closed, molten metal is ladled into cylinder
(ii) plunger pushes molten metal into die cavity
(iii) metal is held under high pressure until it solidifies
(iv) die opens, plunger pushes solidified slug from the cylinder
(v) cores retracted
(iv) ejector pins push casting off ejector die

Furnaces for Casting Processes
• Furnaces most commonly used in foundries:
– Cupolas
– Direct fuel fired furnaces‑
– Crucible furnaces
– Electric arc furnaces‑
– Induction furnaces

Cupolas
Vertical cylindrical furnace equipped with
tapping spout near base
• Used only for cast irons
– Although other furnaces are also used, the largest tonnage
of cast iron is melted in cupolas
• The "charge," consisting of iron, coke, flux,
and possible alloying elements, is loaded
through a charging door located less than
halfway up height of cupola

Direct Fuel Fired Furnaces‑
Small open hearth in which charge is heated by‑
natural gas fuel burners located on side of
furnace
• Furnace roof assists heating action by
reflecting flame down against charge
• At bottom of hearth is a tap hole to release
molten metal
• Generally used for nonferrous metals such as
copper base alloys and aluminum‑

Crucible Furnaces
Metal is melted without direct contact with
burning fuel mixture
• Sometimes called indirect fuel fired furnaces‑
• Container (crucible) is made of refractory
material or high temperature steel alloy‑
• Used for nonferrous metals such as bronze,
brass, and alloys of zinc and aluminum
• Three types used in foundries: (a) lift out‑
type, (b) stationary, (c) tilting

Crucible Furnaces
Figure 11.19 Three types of crucible furnaces: (a) lift out crucible, (b)‑
stationary pot, from which molten metal must be ladled, and (c) tilting-
pot furnace.

Electric Arc Furnaces‑
Charge is melted by heat generated from an electric arc
• High power consumption, but electric arc furnaces can be designed‑
for high melting capacity
• Used primarily for melting steel

Induction Furnaces
Uses alternating current passing through a coil to develop magnetic field in
metal
• Induced current causes rapid heating and melting
• Electromagnetic force field also causes mixing action in liquid metal
• Since metal does not contact heating elements, environment can be
closely controlled to produce molten metals of high quality and purity
• Melting steel, cast iron, and aluminum alloys are common applications in
foundry work

Ladles
• Moving molten metal from melting
furnace to mold is sometimes done
using crucibles
• More often, transfer is accomplished
by ladles

Die Casting in Cold-Chamber Process
• FIGURE 5.29 Sequence of operations in die casting of a part in the cold-
chamber process.

Foundry Lectures

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