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2. In the last class you have learnt about
 Electric Arc Heating
 Types of Arc Furnaces
▪ Direct
▪ Indirect
 Applications of Direct and Indirect Arc Furnaces
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3. 3
Objectives
On completion of this topic you would be able to know
• Operation of Induction Heating
• Core type and Coreless Induction Heating

4. 4
Induction Heating
• Induction heating is also known as high frequency heating
• Induction heating process makes use of currents. induced by
electromagnetic action in the material to be heated
• It uses transformer principle
• Conversion of electromagnetic energy into heat energy takes
place in the material, it self

5. 5
Induction Heating
• Heat transfer by high frequency heating is as much as
10,000 W/cm2
• The high frequency heating can be applied mainly to two
classes of materials firstly, conducting materials &
secondary insulating materials
• Heating of first type of materials is called induction
heating and heating of Second type of materials is
dielectric heating

6. Induction furnaces are further classified as
6
i) Core type induction furnace
ii) Coreless induction furnace

7. 9EE605A.17to18 7
Core Type Induction Heating
Fig.1

8.  Fig 1 shows a core type
induction surface
 The Core type furnace is
essentially a transformer
 Primary side is connected
to supply
 Secondary side contains
charge (materials) in iron
core annular hearth
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9.  The charge is magnetically
coupled to the primary by
an iron core
 The magnetic coupling
between primary and
secondary is very poor
resulting in high leakage
current and a low power
factor. For this reason the
furnace is operated at low
frequencies of the order of
10Hz or so
9

10.  Hence it is called low
frequency furnace i.e.,
10Hz
 The low frequency
necessiates an additional
MG set or frequency
converter
 To start the furnace Molten
metal is poured in the
annular hearth before start
10

11.  Otherwise there is no
material and the secondary
side is open and no current
will be induced
 Hence no heating will take
place
 This is convenient where
the furnace is to be used
for melting different types
of charges
11

12.  If the current density
exceeds about 5A/mm2
the
pinch effect due to electro
magnetic forces, may
cause a complete
interruption of the
secondary circuit
12

13. Disadvantages
 A crucible of inconvenient shape is required
 Low power factor due to poor magnetic
 A M.G. or frequency converter is required
 It is bulky due to the presence of core
13

14. 14
Ajax Wyatt Vertical Core Furnace
Fig.2

15.  Fig 2 shows AjaxWyatt
Vertical Core Furnace
 It is an improvement over the
core type induction furnace
 The magnetic coupling in this
furnace is better than core
type furnace
 Leakage reactance is
comparatively low and
frequency is high, hence it is
high frequency furnace
15

16.  It employs vertical crucible
instead of horizontal
 The system avoids the
pinch effect due to the
weight of the charge in the
main body of the crucible
 The circulation of Molten
metal takes place round
the ‘V’ portion by
convection currents
16

17.  Inside the furnace is lined
depending upon the charge
 The top of the furnace is
covered with an insulated
cover which can be
removed for charging
 Hydraulic arrangements
are usually made for tilting
the furnace to remove the
molten metal
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18. 18
Indirect Core Type Induction Furnace
Fig.3

19.  This type of furnace is used
for heat treatment of
metals
 The wall of the container
forms the secondary
winding
 Iron core links the primary
as well as secondary
9EE605A.17to18 19

20.  Heat produced in the
secondary due to induced
current is transmitted to
the charge by radiation
 A detachable magnetic
circuit made of a special
alloy is kept inside the
chamber
9EE605A.17to18 20

21.  The alloy will loose
magnetic properties at a
particular temperature and
are regained when it cools
down
 On reaching the critical
temperature the reluctance
of the alloy increases and
here by decreasing
induction effect
9EE605A.17to18 21

22.  Critical temperature
varying 4000c to 10000c
can be employed for
heating different materials
 The furnace operates at a
PF of around 0.8
9EE605A.17to18 22

23. 9EE605A.17to18 23
Coreless Induction Heating
PRIMARY
WINDING
REFRACTORY
CRUCIBLE
CHARGE

24.  The coreless induction
furnace operates on
the principle of an
electric transformer
 If there is no core, the
flux density will be low
 For compensating the
low flux density, the
primary supply should
have high frequency
9EE605A.17to18 24
PRIMARY
WINDING
REFRACTORY
CRUCIBLE
CHARGE

25.  The furnace consists of a
refractory or ceramic
crucible cylindrical in shape
enclosed with in a coil
which forms the primary of
a transformer
 The furnace also may have
a conducting or non-
conducting container
9EE605A.17to18 25
PRIMARY
WINDING
REFRACTORY
CRUCIBLE
CHARGE

26.  When high frequency of
500 of 1000 Hz supply is
given to primary windings
 The eddy currents are set
up in charge or container
by transformer action
9EE605A.17to18 26
PRIMARY
WINDING
REFRACTORY
CRUCIBLE
CHARGE

27.  There currents heat the
charge to melting point
and they also set up the
electromagnetic force
which produce a stirring
action to the charge
 The furnace becomes
relatively light in weight
and can be easily tilted for
pouring the metal
9EE605A.17to18 27
PRIMARY
WINDING
REFRACTORY
CRUCIBLE
CHARGE

28. Advantages
 High speed of heating
 Well suited for intermittent operation
 High quality of product
 Low operating cost
9EE605A.17to18 28

29. Industrial applications
▪ Used in foundries for melting and refining brass, zinc
and other non-ferrous metals
▪ Used for heat treatment of metals
9EE605A.17to18 29

30. Industrial applications
 These are used for steel production
 These are used for melting of non-ferrous metals like brass ,
copper, aluminium along with various alloys of these
elements
 The production of carbon from ferrous alloys
9EE605A.17to18 30

31. 9EE605A.17to18 31
Comparison Between High Frequency And
Power Frequency Furnaces
Special starting procedure is
required.
No special starting procedure is
required
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Large scrap melts with less
oxidation loss.
Large scrap melts with more
oxidation loss.
5
MoreLess turbulence and stirring
effect
4
LessMaintenance cost is more3
Less energy required.More energy required i.e, 20%
to 30% for same rating.
2
Not required.Frequency converter is
necessary
1
Power frequencyHigh FrequencyS.
No.

32. 9EE605A.17to18 32
Overall efficient is more.Overall efficiency is low.12
Negligible.Care should be taken against
stray field
11
Well suited for long
production schedules of one
alloy.
Well suited for intermittent
operation of different alloys.
10
Only 50Hz.High frequency (500 to 1000 Hz)9
Less costInitial cost is more8
Large capacity (above 1
tone)
Low capacity (few kgs. To 15
tons) furnaces are used
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Contd..
Comparison Between High Frequency And Power
Frequency Furnaces

33. In this class we have discussed about
 Principle and operation of induction heating
 Core type induction heating
 Core less induction heating
9EE605A.17to18 33

34. 1.Coreless induction furnace operate on the principle of
a. Transformer
b. Induction motor
c. Generator
d. Motor
9EE605A.17to18 34

35. 9EE605A.17to18 35
Frequently Asked Questions
1) What is induction heating ?
2) Describe briefly with a neat sketch the core type induction
furnace
3) Explain the vertical core type of furnace (Ajax Wyatt
furnace) with a neat diagram
4) Explain the construction and operation of coreless induction
furnace
5) Explain the indirect core type induction furnace with sketch

36. THANK YOU
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