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1
Induction heating is a contact-free heating process which uses high-frequency
electricity to generate heat. When an alternating current (AC) flows through the coil
while a workpiece is positioned inside, an electromagnetic field is generated. Once
the current alternates (i.e., changes) direction, the direction of the electromagnetic
field also changes. Because this new electromagnetic field contradicts the initial
magnetic field, this process produces an eddy current (sometimes referred to as
Foucault’s current). Based on Joule’s first law,
1
Joule heating is then generated. As
time passes, the density of the workpiece increases, leading to growing resistance,
2
which in turn generates more Joule heating, causing the workpiece to get
incrementally hotter.
1
Joule's first law:
RT
I
Q
2
Q: Joule heating
I: Eddy current
R: resistance
T: time
2
Resistance:
S
L
R
ρ
R: resistance
ρ: resistivity of the metal
L: length
S: cross-section
I. Operating Principles
