INDUCTION HEATINGSUBMITTED BY RAJ MOYAL ROLL NO.084022
CONTENTS
INDUCTION HEATING PRINCIPLE OF INDUCTION HEATING SKIN EFFECT INDUCTION HEATING SETUP INDUCTION HEATING CIRCUITS APPLICATIONS OF INDUCTION HEATING ADVANTAGES OF INDUCTION HEATING DISADVANTAGES OF INDUCTION HEATING
INDUCTION HEATING
Induction heating is a process which is used to bond, harden or soften metals or other conductive materials. For modern manufacturing processes, induction heating offers an attractive combination of speed, consistency and control.
The material to be heated is known as work piece and the coil wound around it is known as work coil.
INDUCTION HEATING PRINCIPLE
When a high frequency ac voltage is applied across the work coil, a magnetizing current flows through it. this will generate flux in the work piece and induce voltage into the work piece. since the work piece is closed onto itself, eddy current flows into it. the work piece will be heated up due to finite resistance offered by the work piece to the flow of the eddy currents. The heat loss in the work piece is normally confined to surface of the work piece (skin-effect). The skin effect increases the effective resistance of the metal to passage of the large current,hence increases the heating.
The fundamental theory of IH, however, is similar to that of a transformer. Figure shows the simplest form of a transformer, where the secondary current is in direct proportion to the primary current according to the turn ratio. The primary and secondary losses are caused by the resistance of windings.
SKIN EFFECT
The higher the frequency of the current administered to the coil, the more intensive is the induced current flowing around the surface of the load. The density of the induced current diminishes when flowing closer to the center . This is called the skin effect or kelvin effect. = 1/ f =penetration depth f=applied frequency =pearmeability of material =conductivity of material
Induction Heating Setup
INDUCTION HEATING CIRCUITS
VOLTAGE-SOURCE SERIES RESONANT INVERTER-
Here the output current is nearly sinusoidal at the switching freq slightly below the resonance. The power is controlled by a variable switchingAC LINE POWER FACTOR CORREC-TION UNCONTROLLED RECTIFIER
Cf
Voltage source inverter
Filter capacitor
Inductive coil+load
frequency control.
SERIES RESONANCE CIRCUIT
The work coil is made to resonate at the intended operating frequency by means of a capacitor placed in series with it.
The series resonance also magnifies the voltage across the work coil, far higher than the output voltage of the inverter alone.
The main drawbacks of the series resonant arrangement
the inverter must carry the same current that flows in the work coil.
In addition to this the voltage rise due to series resonance can become very pronounced if there is not a significantly sized workpiece present in the work coil to damp the circuit.
CURRENT SOURCE PARALLEL RESONANT INVERTER Here the output current source parallel resonant inverter, the output current is nearly sinusoidal at the switching freq slightly above the resonance
POWER FACTOR CORRECTION
CONTRO-LLED RECTIFIER
CURRENT SOURCE INVERTER
INDUCTIVE COIL+LOAD
Parallel resonance circuit
The work coil is made to resonate at the intended operating frequency by means of a capacitor placed in parallel with it. The parallel resonance also magnifies the current through the work coil, far higher than the output current capability of the inverter alone. Work coils using this technique often consist of only a few turns of a thick copper conductor but with large currents of many hundreds or thousands of amps flowing. (This is necessary to get the required Ampere turns to do the induction heating.)
IMPEDENCE MATCHING
This refers to the electronics that sits between the source of high frequency power and the work coil we are using for heating.
It is the job of the matching network and the work coil itself to transform the high-voltage/low-current from the inverter to the low-voltage/high-current required to heat the workpiece efficiently.
APPLICATIONS OF INDUCTION HEATINGINDUCTION COOKING: The circulating currents in the metal pan on the top of the induction coil directly heats the pan.
ANNEALING: process is used to soften metal for improved ductility and machinability, as well as to relieve residual stress.
BRAZING: is the process of joining two or more pieces of metal or ceramic material with a molten filler metal such as silver, aluminum alloy or copper.
SOLDERING: is a process in which
two or more metal items are joined together by melting and flowing a filler metal into the joint.
SURFACE
HARDENING: is the process of hardening the surface of a metal, often a low carbon steel, by infusing elements into the material's surface, forming a thin layer of a harder alloy.
ADVANTAGES OF INDUCTION HEATING
Heating speed linked to the possibility of obtaining very high power density.Exact location of the heating effect thanks to the inductor design and an operating frequency perfectly adapted to the part to be heated. The possibility to heat at very high temperatures with an efficiency practically independent of the temperature. A process perfectly adapted to industrial medium-sized and mass production requirements.
Easy automation of equipment. Absence of thermal inertia (rapid start-up). Repeatability of operations carried out. Often extremely high heating efficiency. Absence of pollution from the source of heating (cold source).
Good working conditions.
DISADVANTAGES OF INDUCTION HEATING
A high frequency power source is required ,which is costly and complex.thus,initial cost required is more. The running cost or cost of operation is high. Due to conversion of a.c supply into high frequency supply and low frequency of induction coil, this heating process is not efficient.
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