Manufacturing Processes

Mr. ANSAR A. MULLA
AUTOMOBILE ENGG DEPARTMENT
R.I.T. ISLAMPUR
R.I.T. ISLAMPUR
1
AE 2091 – Manufacturing Processes
Chapter 02- Melting Pouring and Fettling of Casting

Contents
1. Types of melting furnaces,
2. Metal pouring equipments
3. Casting defects, remedies, Safety pollution,
4. Control and mechanization in foundries
5. Applications of Ferrous and non ferrous casting in
automobiles
2

01 Types of melting furnaces,
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Furnace?
Furnace is used for carrying out not only the basic ore refining process but
mainly utilized…
to melt the metal.
Blast Furnace-Basic Melting of iron ore to get pig iron.
Cupola Furnace – CI
Electric arc Furnace – re melting steel.

4
Factors for selection of furnace
1. Initial & Operational cost.
2. Cost of repair & Maintenance.
3. Various Fuels used.
4. Melting Efficiency in melting speed.
5. Composition and melting temp of metal
6. Quality degree in composition , purification of refining.
7. Cleanliness and noise level in operation
8. Personnel choice or sales influence.

5
Types of MF for melting Different Materials
Grey Cast Iron
(a) Cupola
(b) Air furnace (or Reverberatory Furnace)
(c) Rotary furnace
(d) Electric arc furnace
Steel
(a) Electric furnaces
(b) Open hearth furnace

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Types of MF for melting Different Materials
Non-ferrous Metals
(a) Reverberatory furnaces (fuel fired) (Al, Cu)
(i) Stationary
(ii) Tilting
(b) Rotary furnaces
(i) Fuel fired
(ii) Electrically heated
(c) Induction furnace (Cu, Al)
(i) Low frequency
(ii) High frequency.
(d) Electric Arc furnaces (Cu)
(e) Crucible furnaces (AI, Cu)
(i) Pit type
(ii) Tilting type
(iii) Non-tilting or bale-out type
(iv) Electric resistance type (Cu)
(f) Pot furnaces (fuel fired) (Mg and AI)
(i) Stationary
(ii) Tilting

CUPOLA FURNACE
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Cupola furnace is employed for melting scrap metal or pig iron for production of various
cast irons.

CUPOLA FURNACE
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Production process of market form of steel
supply of different shapes or sections

CUPOLA FURNACE
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Production Malleable CI
Varying sizes
Selection Considerations
melting capacity,
diameter of shell without lining or with lining,
spark arrester.

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CUPOLA FURNACE
Construction
1. Well
2. Combustion zone
3. Reduction zone
4. Melting zone
5. Preheating zone
6. Stack
Charging
Working

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CUPOLA FURNACE
Construction
Well
Combustion zone
C + O2 ——→ CO2 + Heat
Si + O2 ——→ SiO2 + Heat
2Mn + O2 ——→ 2MnO + Heat
Reduction zone
CO2 + C (coke) ——→ 2CO + Heat
Melting zone
3Fe + 2CO ——→ Fe3C + CO2
Preheating zone
Stack
Charging
Working

PIT FURNACE
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•Pit furnace is a type of a furnace
bath which is installed in the form of
a pit.
•Melting small quantities of ferrous
and non ferrous metals.
•It is provided with refractory inside
and chimney at the top.
•Generally coke is used as fuel.
•Natural and artificial draught can
be used for increasing the capability
towards smooth operation of the
furnace.

AIR FURNACE
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This furnace is also
known as puddling or
reverberatory furnace.
It is used for making
wrought iron.

CORELESS TYPE INDUCTION FURNACE
14
It is also called high frequency induction furnace.
It consists of refractory crucible placed centrally inside a water cooled copper coil.

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1 - Melt
2 - water-cooled coil
3 - yokes
4 - crucible
INDUCTION FURNACE
alternating current
magnetic field
eddy currents, circular electric currents, inside
the metal, by electromagnetic induction.
The eddy currents, flowing through
the electrical resistance of the bulk metal, heat
it by
Joule heating
Advantage - the heat is generated within the
furnace's charge itself rather than burning fuel,
Applications - where contamination is an issue

16
An induction furnace consists of a nonconductive crucible holding the charge of metal to be melted, surrounded
by a coil of copper wire. A powerful alternating current flows through the wire. The coil creates a rapidly
reversing magnetic field that penetrates the metal. The magnetic field induces eddy currents, circular electric
currents, inside the metal, by electromagnetic induction. The eddy currents, flowing through the electrical
resistance of the bulk metal, heat it by Joule heating. In ferromagnetic materials like iron, the material may also
be heated by magnetic hysteresis, the reversal of the molecular magnetic dipoles in the metal. Once melted, the
eddy currents cause vigorous stirring of the melt, assuring good mixing. An advantage of induction heating is that
the heat is generated within the furnace's charge itself rather than applied by a burning fuel or other external heat
source, which can be important in applications where contamination is an issue.
Operating frequencies range from utility frequency (50 or 60 Hz) to 400 kHz or higher, usually depending on the
material being melted, the capacity (volume) of the furnace and the melting speed required. Generally, the smaller
the volume of the melts, the higher the frequency of the furnace used; this is due to the skin depth which is a
measure of the distance an alternating current can penetrate beneath the surface of a conductor. For the same
conductivity, the higher frequencies have a shallow skin depth—that is less penetration into the melt. Lower
frequencies can generate stirring or turbulence in the metal.
A preheated, one-tonne furnace melting iron can melt cold charge to tapping readiness within an hour. Power
supplies range from 10 kW to 42 MW, with melt sizes of 20 kg to 65 tonnes of metal respectively.
An operating induction furnace usually emits a hum or whine (due to fluctuating magnetic forces
and magnetostriction), the pitch of which can be used by operators to identify whether the furnace is operating
correctly or at what power level.
INDUCTION FURNACE

02 Metal pouring equipments
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Ladle
inside of ladle bowl is lined with fire clay, generally 25mm thick.
Types of ladles depending upon method of carrying them.
Types of ladle used for pouring is determined by size and number of castings to
be poured.
Handle ladle
Shank
Tea-Pot
Crane or Bull
Bottom Pouring
Ladle Handler

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Handle ladle
Handled by one man
15-30 kg
Shank ladle
Larger quantity of molten metal.
two persons.
30-150 kg
Tea-Pot
Small & Medium sized mould.
Have built in spout-allows metal
to be taken from bottom.

19
Crane or Bull
Large Capacity – Crane or
monorail.
Bottom Pouring
Wide appl in steel foundries.
Ladle Handler
Enables one man to handle and
pour with large ladles.
Hung to monorail.
Rapidly raising or lowering the
ladle.

03 Casting defects, remedies, Safety pollution
20
Casting defects may be defined – Those characteristics that create a deficiency or
imperfection to quality specifications imposed by design and service requirements.
Reduces total output, increases the cost of production.
Even in modern foundries the rejection rate as high up to 20% of the number of casting
produced.
• Since reclamation of defective castings is often costly and sometimes outright impossible,
care should be taken to avoid the occurrence of the defects in the first instance.
• It is therefore necessary to understand the various defects that occur in sand castings and
the main factors that are responsible for their occurrence

21
CLASSIFICATION OF CASTING DEFECTS
Casting Defects
Surface defects Internal defects
Incorrect chemical composition.
Unsatisfactory mech.
properties

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 Surface defects : May be visible on surface, including incorrect shape & size,
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 – These are due to low quality, poor
percent of usage.

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Some of the common defects are described below.
1. Open Blows and Blow Holes
2. Pin Hole Porosity
3. Entrapped Air and other gases
4. Cracked Casting
5. Bent or Twisted Casting
6. Dropped Mould
7. Fusion
8. Swell
9. Run out
10. Mismatch
11. Mis-run and Cold Shut
12. Shrinkage-Faults
13. Rat Tail and Buckles
14. Core Shift
15. Inclusions
16. Cuts and Washes
17. Metal penetration
18. Hard Spots
19. Scabs
20. Hot tears

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Probable Causes and Suggested Remedies of Various Casting Defects.

25
Sand Blow
Balloon-shaped gas cavity caused by release of
mould gases during pouring

26
• Shrinkage faults are faults caused by improper directional solidifications, poor gating and riser
design and inadequate feeding.
• Solidification leads to volumetric contraction which must be compensated by feeding. If this
compensation is inadequate either surface shrinkage or internal shrinkage defects are produced
making the casting weaker.
Shrinkage faults can be reduced by providing proper gating system, pouring at correct
temperature and taking care of directional solidification.

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28
A casting that before completely filling mould cavity.
• A misrun is caused when the section thickness of a casting is so small or the
pouring temperature so low that the entire section is not filled before the metal
solidifies.

29
• Hot tears are ragged irregular internal or external cracks occurring immediately after the metal
have solidified.
• Hot tears occur on poorly designed castings having abrupt section changes or having no proper
fillets or corner radii. Wrongly placed chills.
• Improper placement of gates and risers or incorrect pouring temperatures can also produce hot
tears
• Hot tears are also caused by poor collapsibility of cores.
• If the core does not collapse when the casting is contracting
over it stresses will be set up in the casting leading to its failure.
• Hot tears can be eliminated by improved design, proper
directional solidification, and uniform rate of cooling, correct
pouring temperature and control of mould hardness.

30
• Hot tears
Description and reasons:
• hot tears are intercrystalline discontinuity
• cracks run along the grain boundaries
• the risk of cracks at alloys with a high freezing range is higher than with a small freezing range
• the reason are stresses during solidification because of hindered contraction (residual stress)
• the main reason for formation of hot tears are the geometry of casting
• if melt can flow into the crack - partial or completely annealed hot tears are possible
Prevention:
• design appropriate to casting, prevention of residual stresses, wide difference in the wall
thickness and hot spots)
• prevention of hot sand effects

31

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Metal penetration
When fluidity of liquid metal is high, it may
penetrate into sand mould or sand core, causing
casting surface to consist of a mixture of sand
grains and metal.

33
Cold Shut
Two portions of metal flow together but there is a
lack of fusion due to premature freezing.
It can be minimized by proper design of casting,
providing suitable gating and risering and using
correct temperature of the melt

34
Cuts and washes
• Cuts and washes are caused by
erosion of mould and core surfaces by
the metal flowing in the mould cavity.
• These defects are avoided by proper
ramming, having sand of required
strength and controlling the turbulence
during pouring.

35

36

37

38

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Rat Tail and Buckles:
• Rat tails and buckle are caused by the expansion of a thin outer layer of
moulding sand on the surface of the mould cavity due to metal heat.
• A rat tail is caused by depression of a part of the mould under compression
which appears as an irregular line on the surface of the casting.
• A buckle is a more severe failure of the sand surface under compression.
• The mould must provide for proper expansion instead of forming compressed
layers to avoid this defect.

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41

04 Control and mechanization in foundries
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Mechanization in Foundry
Act of replacement of manual work.
Foundries where machines are used to replace manual work are called mechanized
foundries.
Complete Mechanization is very expensive.
Small part of few varieties in large quantities – economical.
auto components, sewing m/c fans, electric motors. Repetitive jobs.
Decision of mechanization-size shape quantity required.
Production line.

43
Mechanization in Foundry
Advantages
•Increase Production.
•Higher degree of accuracy, closer tolerance and better surface finish.
•Saving of Time & labour.
•Minimize casting defects.
•Improve casting quality.
•Clean work area in comparison..
•Increase Earnings.
Limitations/Disadvantages
•Not for small jobbing.
•Non repetitive types
•Due to human replacement – art of founding will slowly disappear.

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Layout of Typical Mechanization

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Layout of Typical Mechanization
Practical Example
Labour
Sand slingers ensure uniform packing the moulding
sand.
Drawbacks – difficulty of drawing the patterns.

46
Mechanized Foundry
Figure
A typical mechanized foundry and flow sheet of sand circulation.

05 Applications of Ferrous and non ferrous casting
in automobiles
47
Applications
Students to do on their own.
Question Answering
Assignment

48
Ansar Allauddin Mulla
ansarmulla212@gmail.com

Manufacturing Processes

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