Induction heating
From Wikipedia, the free encyclopedia
Induction heating is the process of heating a metal object by electromagnetic induction, where eddy currents are generated within the metal and resistance leads to Joule heating of the metal. An induction heater (for any process) consists of an electromagnet, through which a high-frequency Alternating current (AC) is passed. Heat may also be generated by magnetic hysteresis losses.
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[edit] Applications of induction heating
Induction heating allows the precision heating of an applicable item, for applications from surface hardening to melting. Often, iron and its alloys respond best to induction heating, due to their ferromagnetic nature. Eddy currents can, however, be generated in any conductor, and magnetic hysteresis can occur in any magnetic material.
[edit] Induction furnace
An induction furnace uses induction to heat a metal to its melting point. Once molten, the high-frequency magnetic field can also be used to stir the hot metal, which is useful in ensuring that alloying additions are fully mixed into the melt. Most induction furnaces consist of a tube of water-cooled copper rings, surrounding a container of refractory material. Induction furnaces are used in most modern foundries, as a cleaner method of melting metals than a reverberatory furnace or a cupola. Sizes range from a kilogram of capacity, to a hundred tonnes capacity. Induction furnaces often emit a high-pitched whine or hum when they are running, depending on their operating frequency. Metals melted include iron and steel, copper, aluminium, and precious metals.
[edit] Induction welding
A similar, smaller-scale process is used for induction welding. Plastics may also be welded by induction, if they are either doped with ferromagnetic ceramics (where magnetic hysteresis of the particles provides the heat required) or by metallic particles.
[edit] Induction cooking
In induction cooking, an induction coil in the cook-top heats the iron base of cookware. Copper bottomed pans, aluminium pans and most stainless steel pans are not suitable.
The heat induced in the base is transferred to the food via conduction. Benefits of induction cookers include efficiency, safety (the induction cook-top is not heated itself) and speed. Drawbacks include the fact that non-ferrous cookware such as copper, aluminium and glass cannot be used on an induction cook-top. Both installed and portable induction cookers are available.
[edit] Induction sealing
Induction heating is often used in Induction sealing or "cap sealing".
[edit] Heat treatment
Induction heating is often used in the heat treatment of metal items. The most common applications are induction hardening of steel parts and induction soldering/brazing as a means of joining metal components. Induction heating can produce high power densities which allow short interaction times to reach the required temperature. This gives tight control of the heating 'pattern' with the pattern following the applied magnetic field quite closely and allows reduced themal distortion and damage. This ability can be used in hardening to produce parts with varying properties. The most common hardening process is to produce a localised surface hardening of an area that needs wear-resistance, while retaining the toughness of the original structure as needed elsewhere. The depth of induction hardened patterns can be controlled through choice of induction-frequency, power-density and interaction time. There are limits to the flexibility of the process - mainly arising from the need to produce dedicated inductors for many applications. This is quite expensive and requires the marshalling of high current-densities in small copper inductors, which can require specialist engineering and 'copper-fitting'.
[edit] Further reading
- Shields, John Potter, Abc's of radio-frequency heating. 1st ed., Indianapolis, H. W. Sams, 1969. LCCN 76098943
- Hartshorn, Leslie, Radio-frequency heating. London, G. Allen & Unwin, 1949. LCCN 50002705
- Langton, L. L., Radio-frequency heating equipment, with particular reference to the theory and design of self-excited power oscillators. London, Pitman, 1949. LCCN 50001900
- Sovie, Ronald J., and George R. Seikel, Radio-frequency induction heating of low-pressure plasmas. Washington, D.C. : National Aeronautics and Space Administration ; Springfield, Va. : Clearinghouse for Federal Scientific and Technical Information, October 1967. NASA technical note. D-4206; Prepared at Lewis Research Center.
- Brown, George Harold, Cyril N. Hoyler, and Rudolph A. Bierwirth, Theory and application of radio-frequency heating. New York, D. Van Nostrand Company, Inc., 1947. LCCN 47003544
[edit] External links
- Metro Electric Company - Induction melting and Vacuum casting furnace manufacturer for precious metals industries
- Plustherm - Induction heater manufacturer and more information about induction heating (with calculations)
- Inductotherm - One of the largest induction furnace and heating manufacturers
- The Thermosafe Induction Drum Heater Site - information on induction heating of industrial drums and containers with 50/60Hz supply
- Induction Heating by R. Burnett - homemade equipment with circuits and photos
- Turnkey Induction Heating Solutions - site includes extensive information about induction heating and various applications
- Ameritherm Over 200 application notes covering over 20 processes using induction heating
- Inductelec Theoretical analysis of ideal heating systems as a lecture series, also general company website
- Fluxtrol, Inc.- Advanced induction heating solutions and Fluxtrol materials for magnetic flux control
- EFD Induction group- Largest European base induction heating solutions manufacturers
