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History
Practical induction heating has been used since the 1920's. Growth in
the induction heating industry expanded very rapidly during World
War II. Surface hardening, or case hardening, was one of the main
growth areas during WWII. Military vehicles and weaponry using case
hardening on axles and engine components could outlast those without
case hardening. After the war, the technology improvements moved
rapidly into the civilian sector as the demand for reliable
automobiles increased. Today induction heating is used in a wide
variety of industrial processes including: forging of metals,
melting and casting, surface coatings, "cap sealing" for food
products, metal surface hardening, bonding metal parts and the
manufacturing of semi-conductors.
What is Induction Heating?
Induction heating is the process of heating conductors, (usually
metals), by inducing an electric current to flow in the object to be
heated. Current is induced into the object in the same manner that
current is induced into the secondary of a transformer.
An
alternating current is applied to the primary of a transformer,
which creates an alternating magnetic field. The secondary of the
transformer is located within the magnetic field. Faraday's Law
shows that an electric current will be induced into the secondary of
the transformer. In induction heating, a coil of copper is wound
around an object to be heated. The coil of copper can be compared to
the transformer primary, and the object to be heated can be compared
to the secondary of the transformer.
The
object to be heated acts like a single turn secondary in a
transformer. Additionally, the object acts as if the single turn
secondary were short circuited. Thus, applying an alternating
current to the induction coil induces a current into the object to
be heated. Imagine how a short circuit secondary on a transformer
would heat up if you connected power to the primary!
Induction heating equipment must create alternating currents at
frequencies from 60 Hz to over 1 MHz. In the beginning, spark gap
oscillators, motor driven generators and vacuum tubes were used to
create the alternating current. Technology advanced and soon SCR,
(Silicon Controlled Rectifier), based power supplies were used to
replace older generators. Very large and powerful transistors are
now used in power supplies for induction heating.
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Components
An
induction heating system is comprised of several major components.
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Power Supply (generates the high frequency current)
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Load Matching Station (matches the impedance of the coil to the
power supply)
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Induction Coil (copper coil wrapped around object to be heated)
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Water Cooling (high power systems are water cooled to remove waste
heat)
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Applications
Induction heating is replacing many gas fired heaters
because of the efficiency of producing product, superior
quality of product, and zero pollution contribution by
induction heating.
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The following is a quick list of some applications where
induction heating is used. The list is by no means
complete since new induction heating applications are
created every day. Also, the descriptions are not
intended to be technically correct, but rather to
describe the industries in which induction heating is
used.
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FORGING : Metal is heated to near its melting
point, and then squeezed in a press into a new shape.
Some products are bicycle cranks and axles, piston rods
in automobile engines, axles, bearings, and high
pressure pipe fittings.
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MELTING AND CASTING : Metal is heated above its
melting point, and then poured into a casting mold. Some
products are art sculptures, engine blocks, and lamp
posts.
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COATINGS : Metal is heated and a coating is
sprayed onto the surface of the metal. The coating melts
and adheres to the metal. Some products include
reinforcing bar, (rebar), for concrete structures (for
corrosion resistance), and paint curing, (speeds up the
drying process for paints).
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FOOD PRODUCTS : This industry is known as "Cap
Sealing". The aluminum foil that you have to remove from
your vitamin bottles, ketchup bottles, and all others
has been melted into place, on the bottle cap, by
induction heating. This provides you with the tamper
evident bottles.
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SURFACE AND CASE HARDENING : Any product that
must be abrasion resistant is surface hardened during
manufacturing. All engine and drive train products in
automobiles are surface hardened. Pliers, scissors,
wrenches, lawn mower blades, fish hooks, surgical
instruments, fork truck forks, pulleys in elevators, and
all bearings. BONDING : Metals are bonded together using
a thermo set adhesive. Believe it or not, your
automobile is glued together now. In many locations
where spot welds once held body panels together, glue is
now used, and is stronger than the old spot weld. Other
applications are tool boxes, luggage, and cabinets.
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MANUFACTURE OF SEMI-CONDUCTORS : A curious
process called zone refinement may be used in the
manufacture of semi-conductors. Highly pure silicon for
semi-conductors is required for today's integrated
circuits. When silicon is melted, impurities are
attracted to the molten area. Therefore, induction
heating is used to melt portions of an ingot of silicon.
The coil is moved so that the molten zone of silicon
moves, and this carries the impurities along with the
molten zone. Several passes of an induction created
molten zone removes impurities from the ingot of
silicon.
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Providing Field Proven Induction Heating Products
Worldwide Since 1984 |
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