What is Induction Heating?
Induction Heating is a method of heating electrically conductive materials in an electromagnetic field.
When an alternating current flows through an induction heating coil a varying magnetic field is set up around and within the coil. If a metal part is placed in the heating coil, the magnetic field penetrates the part, inducing a voltage in it. This results in a current flow (eddy currents) that causes the part to heat. How efficiently the part heats depends on several factors including the resistivity of the metal, permeabilty, thermal conductivity, applied frequency, part geometry and mass, and the distance between the induction heating coil and the part. Magnetic materials such as steel and nickel also heat by hysteresis, which improves the heating effect. Hysteresis is basically the friction between the molecules of the metal as they oscillate back and forth due to the application of the high frequency alternating magnetic field.
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Induction heating is particularly useful when precise, repeatable heating is required. Heating is flameless and non-contact and can be focused on specific areas of a part by modifying the design of the induction coil. The heating occurs beneath the surface of the part. Surface conditions, such as oxidation or scale, do not affect the heating as may occur when contact with the heating element is required. Because only conductive metallic parts heat, nearby plastic or rubber components are not affected.
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Magnetic
Field
Metal Part
(Workpiece)
Induction
Coil
A basic Magneforce Heat Station induction heating system typically consists of a HS2500R2 or HS5000R2 induction power supply, a matching transformer connected to the power supply with a 6' long power cable and a custom heating coil. The induction power supply converts AC line power to a high frequency, high amperage sinusoidal output. The matching transformer further increases the amperage and provides the inductance needed to match the heating coil to the power supply so that it operates in the specified range of voltage, frequency and current. The heating coil is made to fit the part and generates the magnetic field that results in focused, controllable heating.
Typical HS2500R2 Heating System.
Induction power supply
generates high frequency
sinusoidal output
Heating coil focuses
magnetic field on part
Power cable connects
power supply to transformer
Matching transformer increases amperage
and inductance
The efficiency of the heating is optimized by the turns ratio of the matching transformer, the number of turns and geometry of the heating coil and the "coupling" or fit of the heating coil to the part. If the gap between the ID of the coil and the ID of the part is big, as illustrated below, efficiency and focus of the magnetic field will be reduced.
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Not all systems require the use of a matching transformer. When the part to be heated is large, the inductance of the heating coil will be greater and it is possible to design a coil with more turns to eliminate
the requirement for the matching transformer. Coils of this type are referred to as Inductors.
Coil Coupling
The "coupling" or fit of the coil around the part is closer, providing more efficient heating.
The "coupling" is greater, reducing the effect of the magnetic field on the part.