1. Department of Technical Education
Andhra Pradesh
Name : V. Narsimha Reddy
Designation : Lecturer in EEE
Branch : D.E.C.E.
Institute : GMR. Polytechnic Gajwel
Semester : VI Semester
Subject : Electrical Utilization & Automation
Subject Code : EE605A
Topic : Electric Heating
Duration : 100 Minutes
Sub topic : Principle and Operation of Induction Furnace
Teaching Aids : PPT, Diagrams, Animation
Revised By : K. Chandra Sekhar, L/EEE, GPT, HYD
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2. Recap 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. Objectives On completion of this topic you would be able to know
Operation of Induction Heating
Core type and Coreless Induction Heating
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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
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5. Induction Heating
Heat transfer by high frequency heating is as much as ,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
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6. Induction Heating Induction furnaces are further classified as
i) Core type induction furnace
ii) Coreless induction furnace
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7. Core Type Induction Heating
Fig.1
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8. Core Type Induction Heating
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. Core Type Induction Heating
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
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10. Core Type Induction Heating
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
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11. Core Type Induction Heating
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
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12. Core Type Induction Heating
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
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13. Core Type Induction Heating
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
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14. Ajax Wyatt Vertical Core Furnace
Fig.2
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15. Ajax Wyatt Vertical Core Furnace
Fig 2 shows Ajax Wyatt 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
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16. Ajax Wyatt Vertical Core Furnace
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
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17. Ajax Wyatt Vertical Core Furnace
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. Indirect Core Type Induction Furnace
Fig.3
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19. Indirect Core Type Induction Furnace
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
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20. Indirect Core Type Induction Furnace
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
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21. Indirect Core Type Induction Furnace
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
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22. Indirect Core Type Induction Furnace
Critical temperature varying 4000c to 10000c can be employed for heating different materials
The furnace operates at a PF of around 0.8
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23. Coreless Induction Heating
PRIMARY WINDING
REFRACTORY CRUCIBLE
CHARGE
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24. Coreless Induction Heating
PRIMARY WINDING
REFRACTORY CRUCIBLE
CHARGE
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
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25. Coreless Induction Heating
PRIMARY WINDING
REFRACTORY CRUCIBLE
CHARGE
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
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26. Coreless Induction Heating
PRIMARY WINDING
REFRACTORY CRUCIBLE
CHARGE
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
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27. Coreless Induction Heating
PRIMARY WINDING
REFRACTORY CRUCIBLE
CHARGE
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
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28. Coreless Induction Furnace
Advantages
High speed of heating
Well suited for intermittent operation
High quality of product
Low operating cost
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29. Core type Induction Furnace
Industrial applications
Used in foundries for melting and refining brass, zinc and other non-ferrous metals
Used for heat treatment of metals
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30. Coreless Induction Furnace
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
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31. Comparison Between High Frequency And Power Frequency Furnaces
S. No.
High Frequency
Power frequency 1
Frequency converter is necessary
Not required. 2
More energy required i.e, 20% to 30% for same rating.
Less energy required. 3
Maintenance cost is more
Less 4
Less turbulence and stirring effect
More 5
Large scrap melts with more oxidation loss.
Large scrap melts with less oxidation loss. 6
No special starting procedure is required
Special starting procedure is required.
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32. Comparison Between High Frequency And Power Frequency Furnaces
Contd.. 7
Low capacity (few kgs. To 15 tons) furnaces are used
Large capacity (above 1 tone)
Less cost 8
Initial cost is more 9
High frequency (500 to 1000 Hz)
Only 50Hz. 10
Well suited for intermittent operation of different alloys.
Well suited for long production schedules of one alloy.
Negligible. 11
Care should be taken against stray field 12
Overall efficiency is low.
Overall efficient is more.
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33. Summary In this class we have discussed about
Principle and operation of induction heating
Core type induction heating
Core less induction heating
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34. Quiz 1.Coreless induction furnace operate on the principle of
Transformer
Induction motor
Generator
Motor
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35. Frequently Asked Questions
What is induction heating ?
Describe briefly with a neat sketch the core type induction furnace
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
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36. THANK YOU
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