When an alternating current flows in a conductor, it produces reversing magnetic magnetic field. EMF will be induced in any conducting material placed in this reversing magnetic field just as the emf is induced in the secondary of the transformer. The only difference in both the process is that in transformer, electrical energy transferred from primary, by electromagnetic induction is utilized outside the secondary winding where as in induction heating, this energy is utilized in the secondary winding.
Some of the points associated with induction heating are:
For a given magnetizing force, resistivity and frequency, heat input per unit volume is proportional to the square root of the relative permeability. Thus heating produced in magnetic material is more than in non magnetic materials which have relative permeability of one.
Apart from the increased amount of heating produced by the eddy currents in magnetic materials, there is substantial contribution to heating by hysteresis. But at higher frequencies, the heating contributed by the hysteresis becomes very small as compared to that contributed by the eddy currents. Steel cases to be magnetic above curie temperature. Therefore its permeability above this temperature reduces to one. In the absence of magnetic molecules above curie temperature, heat contribution by hysteresis is nill.
Depth of penetration for given material is inversely proportional to the frequency supplied. This fact is of special significance in connection with surface hardening operation
For a given material and frequency of supply, the heating effect varies square of the magnetizing force. Heating effect therefore can be varied by either varying the magnetizing current or number of turns in the inductor.
For a given material and magnetizing force, heating effect can be increased by employing the higher frequency supply but at higher frequencies skin effect cause significantly reduce the heating.
Specially at higher frequencies penetration of flux into the work piece is small due to shielding effect of eddy currents, flux densities varies exponentially, droping rapidly from the surface to interior. Hysteresis and eddy current losses are therefore, small due to small depth
Advantages of Induction Heating:
- Rate of heat generated Induction heating within the workpiece will be much faster compared to normal rate of heat generated by conventional heating and radiation process that occur in the furnace
- One of the advantage of Induction heating is that, it is very economical. Induction heaters can be switched off when and restarting is quicker.
- As the induction heating being faster, it helps in increase in productivity and reduced labor costs
- Induction heating reduces the material scale losses (steel) because of the rapid heating compared to slow gas fired furnace.
Applications of Induction Heating:
Induction heating are employed in industries for heat treatment and melting of metals.Induction heating employed in furnaces. Induction brazing and induction soldering is one of the applications. Induction heating to prior deformation of metals, Induction shrink fitting. Other applications includes crystal growth, plasma generation, levitation, carbon vapor deposition and sintering etc..