Download Dielectric and Arc Heating

DIELECTRIC HEATING
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DIELECTRIC HEATING
Dielectric heating, also known as electronic
heating, RF heating, high-frequency
heating and diathermy.
Dielectric heating is a special way of transforming
electric current into heat.
By the method of dielectric heating, generally, foils,
plates and profiles with a thickness of 0,1-2,0 mm is
are welded.
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DIELECTRIC HEATING
We understand dielectric heating as the generation of
thermal energy (heat) in a non-conducting material by the
application of an electromagnetic force or field t it. This is
the way a microwave oven heats things placed in it.
Wasted energy appears as heat called dielectric loss.
The non metallic material with poor thermal conductivity
can be very effectively heated by dielectric heating.
Dielectric loss is proportional to frequency and square of
the supply voltage.
Frequency can be selected between 10 to 30kHz and
voltage about 20kV
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When
a
solid
dielectric
material
(Insulating)
.
is subjected to an alternating electric field ,
it is not supposed to carry any current.
However, in practice some leakage current
passes through it and power loss is takes
place. This loss is called as dielectric loss
and result into heating of dielectric
material.
APPLICATION OF DIELECTRIC
HEATING
 Plywood Industry
 Sand Core Baking
 Plastic Industry
 Tobacco Industry
 Bakeries
 Electronic Sawing
 Dehydration of food
 Electro medical application
 Book Binding
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Advantages of Dielectric heating
1) Heating is very quick
2) The efficiency is higher
3) Heating is uniform
4) Being free from smoke, dust, process is
very clean
5) There are no flue gases, no risk of
pollution
6) Heat is produced due to dielectric loss
occurs in the material itself
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ARC HEATING
• One of the popular method of heating.
• Principle:- When voltage is applied between the two electrodes
separated by small distance in air is increased, a stage is reached when
the air gets ionized and air act like conductingmedium. Hence, current
flows between the electrodes in the form of continuous spark called
ARC. This self sustained discharge of electricity between 2 electrodes
through air is known as “Electric ARC”.
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ARC Heating Types:1) Direct ARC heating
2) Indirect ARC heating
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Direct ARC Furnance
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The power is controlled by adjusting the ARC
length by moving the electrodes manually or
automatically.
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during refining process.
Direct ARC operates at 0.8 p.f. Lagging
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INDIRECT ARC:
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have to provide rocking motion through
a motor to distribute heat uniformly.
USE:- melting non-ferrous metals.
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two metallic pieces to be joined principle behind ARC welding
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SUBMERGED ARC FURNACE
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USE:Manufacturing of ferro-chrome and ferromanganese
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Principle of transformers
In the transformer, supply is utilized by secondary.
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•Induction method is based on Principle of “Electromagnetic
Induction”
•When alternating Current flows in a conductor it produces
alternating flux.
•If any other conducting material is placed in this magnetic flux
emf gets induced in it
•This induced emf drives eddy current in that piece and power
loss due to eddy current appears as heat.
or number of turns.
3) Heating effect can be increased by
employing high frequency supply.
DIRECT INDUCTION HEATING
In this, currents are induced in the charge itself. This is usually used
in furnaces for smelting (extraction of metal from ore), melting of
metals etc.
This requires very high frequency supply.
They are classified as core and coreless type induction furnaces.
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INDIRECT INDUCTION HEATING
(Example :- Oven)
In this, eddy currents are induced in the heating element.
Thus heat produced by heating element is then transferred to
the charge by radiation or convection.
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Secondary winding is metal
container.
Below part is situated in the oven
chamber which is made up of
special alloy which losses its
magnetic property and regain when
they cooled.
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Operation
When the primary winding is connected to the supply , the
eddy currents gets induced in the metal container forming th
walls of the oven.
Due to eddy currents, metal container gets heated and then i
transferred to the charge by radiation.
ACTION OF SPECIAL ALLOY:Oven reaches its critical temperature . Magnetic circuit looses its
magnetic property. Due to this reluctance of the magnetic circuit
becomes very high and inductive effect corrosponding decreases.
Applications:-
1) Simple and foolproof method of temperature control
2) No external temperature control equipments required
1) Poor Power factor
2) Complicated Construction
It is used for general heat treatment of metallic and other charges.
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