manufacturing tech.pptx

Pradnesh R. Padave
Subject In-charge

“Failure is an option here. If things are not failing,
you are not innovating enough.”

CASTING PROCESS?
In metalworking, casting means a process, in which liquid
metal is poured into a mold, that contains a hollow cavity
of the desired shape, and is then allowed to cool and solid
ify. The solidified part is also known as a casting, which i
s ejected or broken out of the mold to complete the process
.

WHAT IS PATTERN?
• In casting, a pattern is a replica of the object to be c
ast, used to prepare the cavity into which molten ma
terial will be poured during the casting process. Patte
rns used in sand casting may be made of wood, me
tal, plastics or other materials.

REQIREMENT OF GOOD PATTERN
Secure the desired shape and size of the casting.
Cheap and readily repairable.
Simple in design for ease of manufacture.
Light in mass and convenient to handle.
Have high strength and long life in order to make as many moulds
as required.
Retain its dimensions and rigidity during the definite service life.
Its surface should be smooth and wear resistant.
Able to withstand rough handling.

DIFFERENT TYPES OF PATTERN
Several types of patterns are used in foundries depending on the castin
g requirements the pattern may conform to one of the following types :
Solid piece pattern Segmental pattern
Split piece pattern Follow board pattern
Match plate pattern Lagged up pattern
Cope and drag pattern Multi piece pattern
Loose piece pattern
Gated patterns
Sweep patterns
Skelton pattern
Shell pattern

SOLID OR SINGLE PATTERN
It is the simplest of all patterns is made in one piece and carries no j
oints, partition or loose pieces. The pattern is cheap and it is best su
ited for limited production only. Since its moulding involves a large
number of manual operations like gate cutting, providing runner an
d risers. so, such patterns are used for producing a few large casti
ngs for example, stuffing box of steam engine.

SPLIT ORTWOPIECE PATTERN
These patterns are used for intricate casting of usual shapes. They are
made in two parts and these two parts of the pattern are joined togethe
r with the help of dowel pins. While molding one of the patterns is cont
ained by the drag and other by the cope. For a more complex casti
ng, the pattern may be split in more than two parts.

MATCH PLATE PATTERN
These are used for mass production these patterns find a great favor in machi
ne moulding. A match plate pattern is a split pattern having the cope and dra
gs portions mounted on opposite sides of a plate (usually metallic), called the
“match plate” that conforms to the contour of the parting surface. The gates a
nd runners are also mounted on the match plate, so that very little hand work
is required. This results in higher productivity.

COPE AND DRAG PATTERN
When very large casting are to be made, the complete pattern becomes
too heavy to be handled by a single operator. such pattern is made i
n two parts which are separately moulded in different moulding box
es. After completion of the moulds, the two boxes are assembled to f
rom the complete cavity. It is similar to two-piece pattern.

LOOSE PATTERN
Some patterns usually single piece are made to have loose pieces in orde
r to enable their easy with drawl from the mould. These pieces form and
integral part of the pattern during moulding. After the mould is complete
, the pattern is withdrawn leaving the pieces in the sand, which are late
r with drawn separately through the cavity formed by the pattern.

GATED PATTERN
They are used in mass production for such castings multi
–cavity moulds are prepared i.e., a single sand mould carries a num
ber of cavities patterns and these castings are connected to each othe
r by means of gate formers. Which provides suitable channels or gat
es in sand for feeding all the cavities. Gated patterns reduce the mo
ulding time somewhat. Because of their higher cost, these patterns ar
e used for producing small castings in mass production systems and
on moulding machines.

SWEEP PATTERN
Sweeps can be advantageously used for preparing moulds of large sym
metrical castings. This effects a large savingin time, labour and mat
erial. A sweep is a section or board (wooden) of proper contour that is
rotated about one edge to shape mould cavities having shapes of rotat
ionalsymmetry. This type of pattern is used when a casting of large si
ze is to be produced in a short time.

SKELETON PATTERN
For large castings having simple geometrical shapes, skeleton pattern
s are used. Just like sweep patterns, these are simple wooden frame
s that outline the shape of the part to be cast and are also used as gu
ides by the molder in the hand shaping of the mould. This type of pa
ttern is also used in pit or floor molding process.

FOLLOW BOARD PATTERN
A follow board is a wooden board used for support a pattern during
moulding. It acts as a seat for the pattern. In the former case, the fol
low board is provided with a cavity corresponding to the shape of the
pattern in which the pattern is seated for moulding.

Class Assignment
Sr. No. Type of Pattern Application
1 Solid or Single Pattern Eg. Carbonator, Stuffing box of ste
am engine etc.
2 Split or Two Piece Pattern
3 Match Plate Patten
4 Cope and Drag Pattern
5 Loose Pattern
6 Gated Pattern
7 Sweep Pattern
8 Skeleton Pattern
9 Follow Board Pattern
10 Shell Pattern

Reason for allowances:
Solidification Shrinkage
 Most metals undergo noticeable vo
lumetric contraction when cooled
 Three principle stages of shrinkage
 Shrinkage of liquid as it cools from
the solidification temperature
 Solidification shrinkage as the liquid
turns into solid
 Solid metal contraction as the solidified
metal cools to room temperature
Figure Dimensional changes experienced bya
metal column as the material cools froma
superheated liquid to a room-temperature solid.
Note the significant shrinkage that occursupon
solidification.

. Dimensional Allowances
 Typical allowances
 Cast iron
 Steel
 Aluminum
 Magnesium
0.8-1.0%
1.5-2.0%
1.0-1.3%
1.0-1.3%
 Brass 1.5%
 Shrinkage allowances are incorporated into the
pattern using shrink rules
 Thermal contraction might not be the only factor for
determining pattern size
 Surface finishing operations (machining, etc.)
should be taken into consideration

Types of Pattern Allowances:
PATTERNALLOWANCES ARE:
1. Shrinkage or contraction allowance.
2. Machining or finish allowance.
3. Draft of tapper allowances.
4. Distortion or chamber allowance.
5. Shake or rapping allowance.

1.ShrinkageAllowance:
• All most all cast metals shrink or contract volu
metrically on cooling.
1.Liquid Shrinkage:
• It refers to the reduction in volume when themetal cha
nges from liquid state to solid state at the solidus temperat
ure.To account for this shrinkage;riser,which feed the liquid
metal to the casting,are provided in the mold.
2.Solid Shrinkage:
• It refers to the reduction in volume caused when metal
loses temperature in solid state.To account for this, shrinkag
e allowance is provided on the patterns.

Almost all cast metals shrink orcontract
volumetrically after solidification and therefore the pattern to obtain a
particular sized casting ismade oversize by an amount equal to that of
shrinkage or contraction.
Different metals shrink at different ratesbecause shrinkage is the
property of the cast metal/alloy. The metal shrinkage dependsupon:
1. The cast metal oralloy.
2. Solidification temp.of the metal/alloy.
3. Casted dimensions(size).
4. Casting design aspects.
5. Molding conditions(i.e.,mould materials and molding met
hods employed)

Material Dimension Shrinkageallowance
(inch/ft)
Grey Cast Iron Up to 2 feet
2 feet to 4feet Over 4f
eet
0.125
0.105
0.083
CastSteel Upto2feet 2feetto6f
eet over6feet
0.251
0.191
0.155
Aluminum Upto4feet 4feetto6f
eet over6feet
0.155
0.143
0.125
Magnesium Upto4feet Over4f
eet
0.173
0.155
RATE OF CONTRACTION OF VARIOUS METALS :

. 2.MachiningAllowance:
A CASTING IS GIVENAN ALLOWANCE FOR MACHINING, BECAUSE:
•Castings get oxidized in the mold and during heat treatment;scales
etc.,thus formed need to be removed.
•It is the intended to remove surface roughness and other imperfectio
ns from the castings.
•It is required to achieve exact castingdimensions.
•Surface finish is required on thecasting.
HOW MUCH EXTRA METAL OR HOW MUCH MACHINING ALLOWANCE SHOULD BE
PROVIDED, DEPENDS ON THE FACTORS LISTED BELOW:
Nature of metals.
Size and shape of casting.
The type of machining operations to be employe

Metal Dimension(inch) Allowance(inch)
Castiron
Upto12 12to2
0 20to40
0.12
0.20
0.25
Caststeel
Upto6 6to20
20to40
0.12
0.25
0.30
Nonferrous
Upto8 8to12
12to40
0.09
0.12
0.16
MACHINING ALLOWANCES OF VARIOUS METALS:

3.Draft orTaperAllowance:
It is given to all surfaces perpendicular toparting line.
Draft allowance is given so that the patterncan be easily
removed from the molding material tightly packed aroun
d it with out damaging the mould cavity.
The amount of taper dependsupon:
i. Shape and size of pattern in the depth direction in contact
with the mouldcavity.
ii. Moulding methods.
iii. Mould materials.
iv. Draft allowance is imparted on internal as well as external s

Core
Full-scale model of interior surfaces of part
 It is inserted into the mold cavity prior to pouring
 The molten metal flows and solidifies between the mold cavity and th
e core to form the casting's external and internal surfaces
 May require supports to hold it in position in the mold cavit during pouri
ng, called chaplets
Figure (a) Core held in place in the mold cavity by chaplets,
(b) possible chaplet design, (c) casting with internal cavity.

©2007 John Wiley & Sons,
Inc. M P Groover,
Fundamentals of Modern
Manufacturing 3/e
Draft
 Minor changes in part design can reduce
need for coring
Figure Design change to eliminate the need for
using a core: (a) original design, and (b) redesign.

Pattern mat
erial
Heightofthe giv
ensurface
(inch)
Draft angle
(External sur
face)
Draft angle
(Internal su
rface)
Wood
1to2 2to4
4to8 8to3
2
3.00
1.50
1.00
0.75
0.50
3.00
2.50
1.50
1.00
1.00
Metal and plastic
1to2 2to4
4to8 8to3
2
1.50
1.00
0.75
0.50
0.50
3.00
2.00
1.00
1.00
0.75
Draft Allowancesof Various Metals:

4. Distortion or camberedAllowance:
A CASTING WILL DISTORT OR WRAP IF :
i. It is of irregular shape,
ii. All it parts do not shrink uniformly i.e.,some parts shrink
s while others are restrictedfrom during so,
iii. It is u or v-shape,
iv. The arms possess unequal thickness,
v. It has long,rangy arms as those of propeller strut for the sh
ip,
vi. It is a long flatcasting,

5.Shake allowance:
A patter is shaken or rapped by striking the same with a wooden
piece from side to side.This is done so that the pattern a little is l
oosened in the mold cavity and can be easilyremoved.
In turn,therefore,rapping enlarges the mould cavity which re
sults in a bigger sizedcasting.
Hence,a ve allowance is provided on thepattern i.e.,the pattern
dimensions are kept smaller in order to compensate the enlarg
ement of mould cavity due to rapping.
The magnitude of shake allowance canbe reduced by in
creasing the tapper.

Gating System
• Mould is used for producing a casting. Molten metal is
conveyed into the mold cavity by using Gating system.
• In casting process, gating system plays an important role
to produce a high quality casting.
• A poorlydesigned gating system results in casting defect
s.
• A gating system controls mould filling process. The main
function of gating system is to lead molten metal from
ladle to the casting cavity ensuring smooth, uniform and
complete filling.

Elements of Gating System
• Pouring Cup
• Sprue
• Sprue well
• Cross-gate or Runner
• Ingate or Gates
41

Pouring Cup
It is the funnel-shaped opening, made at the top of the mold. The mainpurpose of the pouring
basin is to direct the flow of molten metal from ladle to the sprue.
Sprue
It is a vertical passage connects the pouring basin to the runner or ingate. It is generally made
tapered downward to avoid aspiration of air. The crosssection of the sprue may be square,
rectangular, or circular.
Sprue well
It is located at the base of the sprue. It arrests the free fall of moltenmetal through the
sprue and turns it by a right angle towards therunner.
Runner
It is a long horizontal channel which carries molten metal and distribute it to the ingates. It
will ensure proper supply of molten metal to the cavity so that proper filling of the cavity take
place.
Gates
These are small channels connecting the mould cavity and the runner.The gates used may
vary in number depends on size of the casting.

43
Functions of gating system
• A good gating system should help easy and complete filling of the
mould cavity.
• It should fill the mould cavity with molten metal with least amount
of turbulance.
• It should prevent mould erosion.
• It should establish proper temperature gradient in the casting.
• It should promote directional solidification.
• It should regulate the rate of flow of metal into the mould cavity.

44
Defects occurring due to improper design of
gating system
• Oxidation of metal
• Cold shuts
• Mould erosion
• Shrinkages
• Porosity
• Misruns
• Penetration of liquid metal into mould walls.
The freezing of the surface of liquid metal during the pouring of an
ingot or casting due to interrupted or improper pouring
The continued material loss at the mold surface due to the contact and
relative movement between the mold surface and the incoming melt

CLASSIFICATION OF CASTING DEFECTS
Casting Defects
Based on nature of
defects
Based on contributing
factors
Surface defects
Internal defects
Incorrect chemical compo.
Unsatisfactory mech.
properties
Defects caused by pattern M
aking & molding
Defects caused due to impr
oper
Gating & rise ring
Defects caused by
molten metal

Surface defects :may be visible on surface
incorrect shape & size, laps, flashes, poor surface
finish.
Internal defects :these are present in interior of
cast. Can be revealed through NDT techniques.
Incorrect chemical composition – formation of
undesirable microstructure.
Unsatisfactory mechanical properties – low
quality, poor percent of usage.
BASED ON NATURE OFDEFECTS

BASED ON CONTRIBUTING FACTORS
Defects caused by pattern making and moulds: r
esults in incorrect dimensions, poor surface finish,
flash, mismatch.
Defects – improper gating & risering
results in cold shut, misrun, inclusions, pulls, shrinkage
cavities.
Defects caused – molten metal
results in cold shut, metal penetration, porosity.

CAUSES FOR DEFECTS
Unsuitable and unsatisfactory raw materials.
Application of unsatisfactory casting principles.
Use of improper tools, equipment, appliances or
patterns.
Unprofessional management.
Unsatisfactory setting up of procedures, poor work
discipline, lack of training.

CASTING DEFECTS ,FACTORS RESPONSIBLE FOR THEM AND
REMEDIES
CORE SHIFT
WRAPED CASTING
SWELL
FIN
BLOW HOLES
PIN HOLES
GASHOLES
SHRINKAGE CAVITY
HOT TEAR
INCLUSIONS
MISRUN AND COLDSHUT
EXPANSION SCABS

CORE SHIFT
Results in mismatch of the section.
Usually easy to identify.
Can be repaired provided with in tolerable
limits.
Misalignment of flasks is a common cause.
Can be prevented by ensuring proper alignment
of pattern, die parts, molding boxes.

WARPED CASTING
Warpage - Undesirable deformation in a casting.
Large cross sections or intersections are
particularly prone to warping.
Can be reduced by proper casting design,
judicious use of ribs.
Cannot be eliminated but allowances can be
given along with machining allowance, to r
emove by machining.

SWELL
Swell-enlargement of the mould cavity by metal
pressures, results – localized or overall enlarge
ment of castings
Caused due to insufficient ramming of the sand.
Also due to rapid pouring of molten metal.
Also due to insufficient weighting of mould
Remedies – avoid rapid pouring, provide suf
ficient ram on sands , proper weighting of m
oulds.

FIN
Athin projection of metal – not a part of cast.
Usually occur at the parting of mould or core
sections.
Causes - Incorrect assembly of cores and mo
ulds, improper clamping, improper sealing.
Remedy is proper clamping of cores and mould.

BLOW HOLES
They are entrapped gases.
This is result of gases from mould, molten metal
and steam sand.
Remedy is to provide sufficient permeability,
making vent holes, use minimum quantity of
water.
Also use of dry sand moulds, use of no bake
sands.

SHRINKAGE CAVITY
It is a void or depression in the casting caused
mainly by uncontrolled solidification.
Remedy is apply principles of casting, provide
adequate risers, feeders, which supply the mo
lten metal to compensate the shrinkage.

HOT TEAR
If the mould surface is rigid, it restrains solidifying
casting from contraction and resulting in develop
ment of cracks or tear, also called pulls.
Remedy is avoid excessive ramming.
Controlled ramming should be done.

Hot Tears
7
ME 6222: Manufacturing Processes and Systems
Prof. J.S. Colton

METAL PENETRATION
When molten metal penetrates in the spaces
between sand grains.
Result - sand willbe tightly held to the casting.
Remedy – good optimum mould hardness.

MISRUN & COLDSHUT
Misrun occurs particular section of casting is
solidified before filling .
when two streams of molten metal which are t
oo cold to meet and do not fuse then results in
coldshut.
Prevented by proper casting design.

Casting Defects
6
ME 6222: Manufacturing Processes and Systems
Prof. J.S. Colton

EXPANSION SCABS
This is due to expansion property of sand.
Due to high temperature sand will expand.
Low thermal stability of sand used.
This expansion isprevented bymould condition, results in cracks,
poor surface finish.
Remedy is to reduce use clay content.
Use of additives which reduce thermal expansion o
f sand.

Sr. No. Casting Defect Reason of
Defect
Remedies to avoid
defects

68
Class Assignment
Sr. No
.
Defects Causes Remedies to resolve defects
1 Oxidation of metal Excess Melting
Temperature
Material must heat upto
desired melting temperature only
2 Cold shuts
3 Mould erosion
4 Shrinkages
5 Porosity
6 Misruns
7 Penetration of liquid
metal into mould wall

69
Types of Gates
• Depending upon the orientation of the parting plane.
– Horizontal Gating System
– Vertical Gating System
• Depending upon the position of ingate(s), horizontal
gating system.
– Top Gating System
– Bottom Gating System
– Parting-line Gating System

71
Pouring Time
• Pouring rate is nothing but the time taken for filling the mould cavity by
a known quantity of metal i.e., Pouring time can be used as an index to
determine the pouring rate.
• When molten metal is being poured into the mould at a very fast rate,
mould erosion, rough surface, excessive shrinkage may takesplace.
• When the pouring rate is very low, the complete filling of the mould is
not assured and may result in excessive drop in the molten metal
temperature.
• This result in casting defects such as cold shut, misrun etc.,
• In order to avoid this, it is necessary to arrive at the correct rate of
pouring of metal into the mould cavity.
• The type of metal, size and shape of the casting decide the pouring rate.

72
Gating Ratio
Gating ratio refers to the relation between area of the choke to total area
of runner total area of Ingates. Mathematically, it can be written as Ac: Ar:Ag .
The gating system completely controls the molten metal flow. Gating
systems can be classified as Pressurised system and Unpressurised system.
Gating ratio depends on the nature of the molten metal.
• Pressurized system is used for reactive metals like magnesium alloy etc.
Unpressurised gating system is used for normal metals such as brass, steel,
aluminium alloy, etc.
• A Gating ratio such as 1:2:1 or 1:0.75:0.5 refers to pressured system; whereas
the gating ratio such as 1:2:2 or 1:3:3, 1:1:3, refers to unpressurised gating
system.

73
• Pressurized system is referred to as “Gate control System”, since
ingates controls the flow of metal.
• Unpressurised system is referred to as “Choke Control System”, since
the choke controls the flow of metal.
• In the pressurized system high metal velocity occurs and results in
turbulence. In the case of unpressurised system, turbulence is produced
and streamline flow is induced.
• Pressurized System Consumes less metal and yield is more.
Unpressurised system consumes more metal and the yield will be
slightly lowered
• In the case of pressurized system, the system will always be full of liqu
id metal . In the case of unpressurised system flow is not full.

Guidelines for Designing Gating System
• The size of the sprue fixes the flow rate. The amount of molten metal that can be
fed into the mold cavity in a given time period is limited by the size of the sprue.
• The sprue should be located at certain distance from the gates so as to minimize
velocity of molten metal at ingates.
• Sprue should be tapered by approximately 5% minimum to avoid aspiration of the
air and free fall of the metal.
• Ingates should be located in thick regions.
• Locate the gates so as to minimize the erosion of the sand mold by the metal stream
This may be achieved by orienting the gates in the direction of the natural flow
paths.
• Multiple gating is frequently desirable. This has the advantage of lower pouring
temperatures, which improves the metallurgical structure of the casting. In addition,
multiple gating helps to reduce the temperature gradients in the casting1.3

Solidification of Casting
• During solidification metal experience shrinkage which
results in void formation.
• This can be avoided by feeding hot spot during
solidification.
• Riser are used to feed casting during solidification.

Solidification of Iron & Carbon Steels
Figure 10.5 (a) Solidification patterns for gray cast iron in a 180-mm (7-in.) square casting. Note that aft
er 11 minutes of cooling, dendrites reach each other, but the casting is still mushy throughout. It takes ab
out two hours for this casting to solidify completely. (b) Solidification of carbon steels in sand and chill (
metal) molds. Note the difference in solidification patterns as the carbon content increases.

What Are Risers?
• Risers are added reservoirs designed to feed liquid m
etal to the solidifying casting as a means for compens
ating for solidification shrinkage.
• Riser must solidify after casting.
• Riser should be located so that directional solidificati
on occurs from the extremities of mold cavity back to
ward the riser.
• Thickest part of casting – last to freeze, Riser should
feed directly to these regions.

Why Risers?
• The shrinkage occurs in three stages,
1. When temperature of liquid metal drops from Pouring to Freezi
ng temperature
2. When the metal changes from liquid to solid state,
and
3. When the temperature of solid phase drops from
freezing to room temperature
• The shrinkage for stage 3 is compensated by providing shrinkage
allowance on pattern, while the shrinkage during stages 1 and 2 a
re compensated by providing risers.

Optimum Riser Design
The role of the methods engineer in designing risers can be stated simply as making
sure that risers will provide the feed metal:
· In the right amount
· At the right place
· At the right time
To this list can be added several other considerations:
·The riser/casting junction should be designed to minimize riser removal costs
· The number and size of risers should be minimized to increase mold yield and to
reduce production costs
· Riser placement must be chosen so as not to exaggerate potential problems in a
particular casting design (for example, tendencies toward hot tearing or distortion)

Solidification Time For Casting
• Solidification of casting occurs by loosing heat from the surfaces
and amount of heat is given by volume of casting .
• Cooling characteristics of a casting is the ratio of
surface area to volume.
• Higher the value of cooling characteristics faster is the cooling of
casting.
Chvorinov rule state that solidification time is inversely proportion
al to cooling characteristics. Where;
Solidification time Ts = Solidification time
V = Volume of casting
K = mould constant
SA = Surface area

• The total solidification time is the time from pouring to the completion
of solidification; V is the volume of the casting; A is the surface area; an
d B is the mould constant, which depends on the characteristics of the m
etal being cast (its density, heat capacity, and heat of fusion), the mould
material (its density, thermal conductivity, and heat capacity), the mould t
hickness, and the amount of superheat. Test specimens can be cast to de
termine B for a given mould material, metal, and condition of casting.
This value can then be used to compute the solidification times for other
castings made under the same conditions. Since a riser and a casting are
both within the same mould and fill with the same metal under the
same conditions, Chvorinov's rule can be used to ensure that the
casting will solidify before the riser. This is necessary if the liquid
within the riser is to effectively feed the casting to compensate for
solidification shrinkage.
Prediction of Solidification Time: Chvorinov's Rule.

• Different cooling rates and solidification times
can produce substantial variation in the resulti
ng structure and properties. For instance, die
casting, which uses metal moulds, has faster
cooling and produces higher strength castings
than sand casting, which uses a more insulating
mould material. The various types of sands can
produce different cooling rates. Sands with high
moisture contents extract heat faster than sands
with low moisture.
Prediction of Solidification Time: Chvorinov's Rule.

Mould?
A mould is a hollowed-out block that is filled with a liqu
id like plastic, glass, metal, or ceramic raw materials .The li
quid hardens or sets inside the mould, adopting its shape.
A mould is the counterpart to a cast.
• Mould or Mould cavity contains molten metal and is essentially a
negative of the final product.
• Mould is obtained by pattern in moulding material (sand).
• Mould material should posses refractory characteristics and with
stand the pouring temperature.

Types of moulding:
1. Hand moulding- are used for odd castings generally less than 50 no. a
nd ramming is done by hands which takes more time.
2. Machine moulding- are used for simple castings to be produced in larg
e numbers. Ramming is done by machine so require less time.
3. Bench moulding- moulding is done on a bench of convenient height
to the moulder and is used for small castings.
4. Floor moulding-moulding is done on the foundry floor and is used for
all medium and large castings.
5. Pit moulding- moulding is done in a pit which act as drag and is used f
or very large castings

Characteristics
1. Should have the desired shape and size.
2. Must be produced with due allowances for shrinkage of the solidifying material.
3. Any geometrical feature desired in the finished casting must exist in the cavity. Consequently, t
he mould material must be able to reproduce the desired detail.
4. Should have are refractory character so that it will not contaminate the molten material.
5. The mould must be made from a material that can with stand repeated use.
Types of Moulds
Basically moulds are two types:
1. Expendable moulds- are made of sand and is used for single casting which break upon solidi
fication.
2. Permanent moulds- are made of metal or graphite (costly) and used repeatedly for large num
ber of castings which do not break upon solidification.

Class Assignment
Sr. No. Type of Cores Application
1
2
3
4
5
6
7
8
9
10

What is Furnace???
• Heating media or device.
• Used for heating and melting.
• For providing heat to chemical reactions for
processes like cracking.
• The furnace may be heated by fuel as in many f
urnaces coke is used as a fuel.
• some are operated by electrical energy e.g.
electric arc furnace.

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

Cupola Furnace
• Cupola was made by Rene-Antoine around 1720.
• Cupola is a melting device.
• Used in foundries for production of cast iron.
• Used for making bronzes.
• Its charge is Coke , Metal , Flux.
• Scrap of blast furnace is re melted in cupola.
• Large cupolas may produce up to 100 tons/hour of hot
iron.

Construction
• Cupola is a cylindrical in shape and placed vertical.
• Its shell is made of steel.
• Its size is expressed in diameters and can range
from 0.5 to 4.0 m.
• It supported by four legs.
• Internal walls are lined with refectory bricks.
• Its lining is temporary.

Parts of Cupola
• Spark arrester.
• Charging door.
• Air box.
• Tuyeres.
• Tap hole.
• Slag hole.

Charging of Cupola Furnace
• Before the blower is started, the furnace is uniformly pre
-heated and the metal, flux and coke charges, lying in alt
ernate layers, are sufficiently heated up.
• The cover plates are positioned suitably and the blower i
s started.
• The height of coke charge in the cupola in each layer v
aries generally from 10 to 15 cm . The requirement of flu
x to the metal charge depends upon the quality of the ch
arged metal and scarp, the composition of the coke and t
he amount of ash content present in the coke.

Working of Cupola Furnace
• Its charge consist of scrap, cok
e and flux.
• The charge is placed layer by la
yer.
• The first layer is coke, second i
s flux and third metal.
• Air enter through the bottom tuy
eres.
• This increases the energy effici
ency of the furnace.
• Coke is consumed.

Working of Cupola Furnace
• The hot exhaust gases rise up throug
h the charge, preheating it.
• The charge is melted.
• As the material is consumed, additio
nal charges can be added to the furn
ace.
• A continuous flow of iron emerges fro
m the bottom of the furnace.
• The slag is removed from slag hole.
• The molten metal achieved by tap hol
e.

Operation of Cupola
• Preparation of cupola.
• Firing the cupola.
• Soaking of iron.
• Opening of air blast.
• Pouring the molten metal.
• Closing the cupola.

Preparation of cupola
• Slag and metal adhere to the cupola lining from
the previous run is removed and lining of cupola
is re made.
• The bottom plates are swung to closing positio
n supported by prob.
• The sand bed is then prepared with molding san
d such that its slopes to towards the tap hole.

Firing the Cupola
• The cupola is fired by kindling wood at the bottom
.
• This should be done 2.5 to 3 hours before the mol
ten metal is required.
• On the top of the kindling wood a bed of coke is b
uilt.
• The height of the coke bed is may be vary from 5
0cm to 125cm according to the size of cupola.

Soaking of Iron
• When the furnace is charged fully it i
s maintain for about 45 minutes.
• The charge is slowly heated.
• Duringthe stagethe air blast is shut off
and iron is soaked.

Opening of blast air
• At the end of the soaking period the air bla
st is opened.
• The taping hole is closed by a plug when t
he melting proceeds and molten metal is c
ollect at the bottom.

Pouring of molten metal
• When the sufficient amount of metal has c
ollected in the hearth the slag hole is open
ed and the slag is removed.
• Then taping hole is opened and molten me
tal is flows out in the table.
• The same procedure is repeated until the
charge is melted and the operation is over.

Closing the cupola
• When the operation is over the air blast i
s shut off .
• The bottom of furnace is opened by removi
ng the prop.

Advantages
• It is simple and economical to operate .
• Cupolas can refine the metal charge, rem
oving impurities out of the slag.
• High melt rates .
• Ease of operation .
• Adequate temperature control .
• Chemical composition control .

Disadvantages
• Since molten iron and coke are in contact
with each other, certain elements like si ,
Mn are lost and others like sulphur are pic
ked up. This changes the final analysis of
molten metal.
• Close temperature control is difficult to ma
intain

Cupolas
Vertical cylindrical furnace equipped with tappin
g spout near base
• Used only for cast irons
– Although other furnaces are also used, the largest t
onnage
of cast iron is melted in cupolas
• The "charge," consisting of iron, coke, flux, and p
ossible alloying elements, is loaded through a ch
arging door located less than halfway up height o
f cupola

Direct Fuel-Fired Furnaces
Small open-hearth in which charge is heated by natural g
as fuel burners located on side of furnace
• Furnace roof assists heating action by reflecti
ng flame down against charge
• At bottom of hearth is a tap hole to release molten m
etal
• 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-temperat
ure steel alloy
• Used for nonferrous metals such as bronze, brass, and alloys of zinc a
nd aluminum
• Three types used in foundries: (a) lift-out type, (b) stationary, (c) tilti
ng

Crucible Furnaces
Figure Three types of crucible furnaces: (a) lift-out crucible, (b) stationa
ry pot, from which molten metal must be ladled, and (c) tilting-pot fur
nace.

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

Introduction:
 Electric Arc Furnace is a furnace that heats the charged mat
erial by mean of an electric arc.
 Arc Furnace range in size from small units of approxi
mately one ton capacity up to 400 tons. industrial arc
furnace can be heat up to 1800°C.
 Arc Furnace is different from induction furnace because char
ge material is directly exposed to an electric arc furnace, an
d the current in the furnace terminals passes through the ch
arged material.

Construction:
 The furnace consists of a spherical hearth (bottom), cylindrical shell and a
swinging water-cooled dome-shaped roof.
 The roof has three holes for consumable graphite electrodes held by a cla
mping mechanism.
 Thismechanism provides independent lifting and lowering of each ectrode

 Furnace is split into three sections
 The “shell”, which consist of the sidewalls and lower steel bowl.
 The “Hearth”, Which consist of the refractory that lines the low
er bowl.
 The “roof”, which may be refractory lined or water cooled, and
can be shaped as a section of sphere, or as a conicalsection.

Operation:
The electric arc furnace operates as a batch melting
process.
 Furnace Charging
 Melting
 Tapping
 Furnace turn-around

Furnace Charging:
 The first step is “charging”. The roof and electrode are raised and are swung
to the side of the furnace to allow the material to be charged.
 When the charging is complete the roof and electrodes swing back into place
over the furnace. The roof is lowered and then the electrodes are lowered t
o strike an arc on the charged material.
 The heat produce by electrode is primarily dependent on volume and density
of
charge.

Melting:
 The melting period is a heart of Electric arc furnace. The EAF has evolved in
to a highly efficient melting apparatus and modern design are focused on m
aximizing is accomplished by supplying energy to the furnace interior. This e
nergy can be electrical or chemical.
 Electrical energy is supplied via graphite electrodes and is usually the larges
t contributor in melting operations. Initially, an intermediate voltage tap is s
elected until the electrodes bore into the scrap. usually light scrap is placed
on top of the charge to accelerate bore-in. approximately 15% of scrap is m
elted during the initial bore-in period.

 after a few minutes, the electrodes will have penetrated the material sufficien
tly so that a long arc tap can be used without fear of radiation damage to the r
oof.
 The long arc maximizing the transfer of power to the material and a liquid pool
of a metal will form in the furnace hearth. At the start of melting the arc is uns
table. As the atmosphere of furnace is heated up the arc stabilizes and once th
e molten pool is formed, the arc become stable and the average power input in
creases.
 Chemical energy is supplied via several sources including oxy-fuel burners and o
xygen lances. Oxy-fuel burners burn natural gas using oxygen or a blend of oxyg
en and air.

 Heat is transferred to charge material by flame radiation and convection by
the hot products of combustion. Heat is transferred within the charged mate
rial by conduction.
 Large pieces of scrap take longer time to melt into the bath than smaller pie
ces. In some operations oxygen is injected via a consumable pipe lance to “c
ut” the charged material and burns iron to produce intense heat.
 This oxygen will react with several components in the bath including, alumin
um , silicon , manganese , phosphorous , carbon , and iron all these reaction
s are exothermic.

Tapping:
 Once the charged material has been melted, the tap hole of furnace is
opened, the furnace is tilted, and molten metal is pours into a ladle.
Furnace turned around:
 It is the period after completion of tapping until the furnace is recharged fo
r the next heat.
 During this period the electrodes and roof are raised and furnace lining is i
nspected for refractory damage.

Advantage:
 Electric arc furnace can be used as heat treatment furnac
e.
 It can be used for melting.
 EAF is used for production of steel making by pig iron
 Electric arc furnace provides flexibility, EAFs can be rapidl
y started and stopped.
Disadvantages:
 A lot of electricity consumption.

Definition.
 Electric induction furnace is type of melting furnace that
uses electric current to melt the metal.
 Once molten, the high frequency magnetic field can also
be used to stir the hot metal, which is useful in ensuring t
hat alloying additions are fully mixed into the melt.
 Induction furnaces are used in most modern foundries as
a cleaner method of melting metals than a reverberatory f
urnace or a cupola.
 Sizes ranges from kilogram of capacity to a hundred tonn
es capacity.

 Metals which are melted in an induction furnace in
clude iron and steel, copper, aluminum, and precio
us metals because it is a clean and non- contact pr
ocess it can be used in a vacuum or inert atmosph
ere.
 Vacuum furnaces make use of induction heating for
production of specialty steels and other alloys that
would oxidize if heated in the presence of air.
 The basic principle of induction furnace is the indu
ction heating.

Induction heating
 Induction heating is a form of non contact heating for c
onductive materials.it is process of heating an electric
ally conducting object by electromagnetic induction wh
ere eddy currents are generated within the metal and r
esistant leads to joule heating of the metal.
 Principle of induction heating is mainly based on two w
ell known physical phenomena.
1. Electro-magnetic Induction
2. The Joule Effect

Electro-magnetic induction
 The energy transfer to the object to be heated occu
rs by means of electromagnetic induction.
 Any electrically conductive material placed in a
variable magnetic field is the site of induced electric
currents, called eddy current which will eventually l
ead to joule heating.

Features of induction furnace
 An electric induction furnace requires an electric coil to produ
ce the charge. This heating coil is eventually replaced
 The crucible in which the metal is placed is made of stronger
materials that can resist the required heat and the electric coil
itself cooled by a water system so that it does not overheat or
melt.
 The advantage of the induction furnace is a clean energy effic
ient and well controllable melting process compared to most
other means of metal melting.

 The induction furnace can ranges in size from a small furna
ce used for very precise alloys only about a kilogram in wei
ght to a much larger furnaces made to mass produce clean
metal for many different applications.
 Foundries use this type of furnace and now also more iron f
oundries are replacing cupolas with induction furnaces to m
elt cast iron as the former emit lots of dust and other polluta
nts.

Construction of induction furnace.
 There are many different design for the electric induction furnace but th
ey are center around basic idea.
 The electrical coil is placed around or inside of crucible, which holds th
e metal to be melted often this crucible is divided into two different part
s.
 The lower section holds the melt in its purest form
,the metal as the manufacturers desire it , while the higher section is us
ed to remove the slag, the contaminants that rise to the surface of the
melt.
 Crucibles may also be equipped with strong lids to lessen how much ai
r has access to the melting metal until it is poured out making a purer
melt.

Advantages
 Higher Yield. The absence of combustion sources reduces oxidation losses that
can be significant in production economics.
 Faster Startup. Full power from power supply is available instantaneously; thus
reducing the time to reach working temperature.
 Flexibility. No molten metal is necessary to start medium frequency coreless
induction melting equipment.
 Natural Stirring. Medium frequency units can give a strong stirring action resulting
in a homogeneous melt.
 Cleaner Melting. No bi-product are produced due to cleaner melting environment.
 Compact Installation. High malting rates can be obtained from small furnaces
.
 Energy Conservation. Overall energy efficiency in induction melting ranges
from 55 to 75 percent, and is significantly better than combustion processes.

Disadvantages
 The one major drawback to induction furnace usage
in a foundry is the lack of refining capacity; charge
materials must be clean of oxidation products and of
known composition, and some alloying elements may
be lost due to oxidation.
 Removal of S & P is limited, so selection of charges
with less impurity is required.

INSPECTION OF CASTING
PROCESS INSPECTION
VISUAL INSPECTION
DIMENSIONAL INSPECTION

PROCESS INSPECTION
Inspection done while parts are being processed.
This is helpful to detect defects at the start and
allow the corrections.
This is an preventive act.

VISUAL INSPECTION
Simplest and most fastest inspectional methods.
Most commonly employed.
Usually good to check surface defects.
Fails to identify internal defects.

DIMENSIONAL INSPECTIION
Before casting are to be machined dimensional
inspection is done.
Castings are placed on surface plate or surface
table with angle - measuring instruments.
Various measuring instruments are employed for
a first set of castings, so as to standardize subseq
uent castings.

TESTING METHODS
PRESSURE TESTING
DESTRUCTIVE TESTING
NON DESTRUCTIVETESTING

PRESSURE TESTING
Casting that is used for containing or conveying
liquids, gases, such type are subjected to
pressure testing.
It is tested for any leaks through their walls.
Leaks may be detected by submerging the com
plete casting under water for gas pressures.
Or by visual inspection by liquid pressures.

DESTRUCTIVE TESTING
This test is done causing harm to the casting i.e.
by destroying it.
Various tests include fatigue tests, compression
tests, creep tests etc.

NON DESTRUCTIVE TESTING
Here parts to be tested are inspected for internal defects
and surface defects without destroying the component.
Various methods available are:
Liquid penetrate test LPI
Magnetic particle inspection MPI
X – Ray radiography XRR
Ultrasonic testing UT
Eddy current test ECT
Gamma ray radiography GRR

Liquid penetrant test
Surface preparation
Penetrant application
Penetrant dwell
Excess Penetrant removal
Developer application
Indication development
Inspection
Clean surface.

Magnetic Particle Inspection - MPI
Most satisfactory method Used to find surface
and sub surface defects.
It is quick, cheap, very sensitive
Can only be applied to ferrous metals like steel,
cast iron etc

Principle - MPI
When a metal placed in magnetic field, magnetic
flux are intersected by the defect – magnetic pol
es are induced on either side of discontinuity.
Abrupt change in path of flux – local leakage
This can detected when magnetic particles are
attracted towards defective region.
Magnetic particles piles up in defective region.

Procedure
Preparation of specimen
Surface should be cleaned thoroughly, free from
rust, grease, oil, paint etc.
Cleaning of surface can be done using wire steel
brushes, shot blasting technique or by using sol
vents.

Magnetization
To induce magnetic lines – two methods –
permanent magnet – electromagnet.
Electromagnet is proffered as it has capability to
produce stronger magnetic field.
Magnetization – two types – longitudinal or for
parallel defects – circular or for perpendicular
defects.
For a defect to be detected flux lined should
pass perpendicular line.

Application of magnetic particles
Magnetic particles are applied uniformly so that they
move on the surface freely.
The particles must be as fine as possible.
Generally pulverized iron oxide, carbonyl iron powd
er are used.
Powder can be of
Powder suspended in liquid petroleum
Dry powder
Fluorescent powder – can be viewed in UV light.

Inspection of defect
Generally carried out in good light.
If no defects then regular pattern, if presence of defects then flu
x lines distorted.
Magnetic particles spreads out at the point of defects indicati
ng presence of defect.

X – ray radiography
X – Raysare produced when high energyelectrons collide with the n
ucleus of an atom .
The x– rayequipment ---which produces incandescent light, placed
near ahighlycharged cathode, causing the electrons to flow from th
e cathode which isattributed bythe anode or target.
The intensity of x– raysproduced isdirectly proportional to the numb
er of electrons produced at the filament.
The pattern of the x– rayso produced depends on the shape of the
target.

X – ray radiography
Aradiographic film isplaced next to the part to be tested and xraysare directed against
the part.
The x– rayswillpass through the part to be tested proportional to the den
sity and thickness of the part.
The absorption of x– raysisdirectly proportional to the density of and thicknes
s of the part. If the part has no defects, the x- rayswillpass uniformly through t
he part.
However if there are anydefects such as porosity which leads to lesser density, the penet
ration of x– rayswillbe move through them which shows as darker areas on the film.
X – Raystechnique iseffective in locating cracks, slay inclusions, porosity, blo
w holes, pin holes etc.
X- Rayscan be used for inspection of casting in alltype of metals, likesteel, aluminu
m, magnesium etc.

Ultrasonic Testing
Ultrasonic Testing (UT) uses high frequency sound energy to condu
ct examinations and make measurements.
Ultrasonic testing is based on piezoelectric effect which converts
electrical energy to mechanical energy thus generating ultrasonic
waves
Ultrasonic waves are generated when a high frequency alternating c
urrent of about a million times per second is impressed across the f
orces of piezoelectric materials like quartz crystal.
The crystal expands in full half of the cycleand contracts when the
electric field is increased, thus producing mechanical vibrations.

Ultrasonic Testing
When there is a discontinuity (such as a crack) in the wave path, part o
f the energy willbe reflected back from the flaw surface
The reflected wavesignalis transformed into an electrical signal by t
he transducer and is displayed on a screen
In the applet below, the reflected signal strength is displayed versus th
e time from signalgeneration to when an echo was received. Signaltra
vel time can be directly related to the distance that the signal traveled
From the signal, information about the reflector location, size, orie
ntation and other features can sometimes be

Referance
• Slideshare.com
• Youtube.com
• P N Rao
• Hajra Chaudhary V1

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