1. DIELECTRIC HEATING
• Dielectric heating is also known as radio frequency heating or
electronic heating.
• When a non-metallic material such as wood, plastic, bone or
ceramic is subjected to an alternating electrostatic field, then
dielectric loss occurs in it. This loss appears in the form of
heat. It is known as dielectric heating.
2. • When an atom is not under any electric field, then the centers of the
positive and negative charges coincide and atom acts as a neutral
particle.
• When the atom is subjected to an electric field, then centers of the
positive and negative charges gets shifted in opposite directions. The
atom in this state is said to be polarized.
PRINCIPLE OF DIELECTRIC HEATING
POLARISED ATOM
UNPOLARISED ATOM
3. • When an insulating material is subjected to an alternating
electric field, then atoms of that material gets repeatedly
polarized.
• The inter-atomic friction caused by repeated polarization
causes heat to be produced inside the insulating material. This
heating process is known as dielectric heating (or dielectric
loss).
• The amount of heat generated is directly proportionalto
1. Square of the Supply Voltage
2. Frequency of supply voltage
3. Area of the electrode plates
4. Relative permittivity of dielectric
4. ADVANTAGES
1. Heat is produced throughout the whole mass of material so,
we get uniform heating.
2. Short time is required to complete the process as compared
to another method.
3. Dielectric heating is suitable for non-conducting materials
like wood, plastics and synthetic compoundsetc.
5. DISADVANTAGES
1. Only those materials can be heated which have the
high dielectric loss.
2. The cost of equipment required for dielectric heating
is very high.
3. The overall efficiency of dielectric heating is very low
(about 50%).
4. High frequencies may cause radio interference.
6. APPLICATIONS
• This method is used in plastic and wood industries.
• This method is also employed in the textile, rubber, chemical
and food industries.
• It is used in Sterilization(killing germs) of food and medical
supplies.
• Plastic sheets are joined together by the technique involving a
combination of heat and pressure.
• This technique is very useful for manufacturing plastic products
such as raincoats and waterproofproducts etc.
8. • Induction heating is the process of heating an electrically conducting object
by electromagnetic induction(EMI). Heat is generated in the object by eddy
currents.
• An induction heater consists of an electromagnet, and an electronic
oscillator which passes a high-frequency alternating current (AC) through the
electromagnet.
•The rapidly alternating magnetic field penetrates(passes through) the object.
Due to this an electric current is produced inside the conductor called eddy
currents.
•The eddy currents flowing through the resistance of the material heat it by
Joule heating.
•The frequency of current used depends on the object size, material type,
coupling (between the work coil and the object to be heated) and the
penetration depth.
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12. Advantages:
• Selective areas can be heat treated.
• Very short surface heat-up time.
• Very low surface decarburization and oxidation.
• Slight deformation (bending); this can occur due to internal residual machining
stresses.
• Low operating costs.
Disadvantages:
• Only certain steels can be induction hardened.
• The method is restricted to components having a shape that is suitable for induction
hardening.
13.
14. DIFFERENCE BETWEEN INDUCTION HEATING AND
DIELECTRIC HEATING
• Induction heating is caused by eddy currents in imperfect
dielectrics and Dielectric heating is caused by the electrostatic
effect.
• The operating frequencies are in range of 200 to 500 kHz in
induction heating and from 1 to 50 MHz in dielectric heating.
• Induction heating is termed surface heating. Dielectric heating is
termed volume heating.
• The cost of equipment required in induction heating is low
compared to the cost of equipment required in dielectric heating.
