Induction heating is the process of heating an object that performs electrically (usually metal) with electromagnetic induction, through the heat generated in the object by eddy currents. Induction heating consists of electromagnets, and electronic oscillators passing high-frequency back-and-forth (AC) currents through an electromagnet. The magnetic field rapidly changes through the object, generating an electric current inside a conductor called an eddy current. Eddy current flows through the resistance of the hot material with Joule heating. In ferromagnetic (and ferrimagnetic) materials such as iron, heat can also be generated by magnetic hysteresis losses. The current frequency used depends on the size of the object, the material type, the coupling (between the coil work and the object to be heated) and the penetration depth.
An important feature of the induction heating process is that heat is generated within the object itself, not by an external heat source through heat conduction. Thus objects can be heated very quickly. Additionally there is no need for external contact, which can be important where contamination is a problem. Induction heating is used in many industrial processes, such as heat treatment in metallurgy, Czochralski crystal growth and refining zones used in the semiconductor industry, and for liquefying refractory metals that require extremely high temperatures. It is also used in induction cookers for heating food containers; this is called induction cooking.
Video Induction heating
Apps
Induction heating allows targeted heating of applicable items for applications including surface hardening, melting, soldering and soldering and heating to fit. Iron and its alloys provide the best response to induction heating, due to its ferromagnetic properties. Eddy currents can, however, be generated in conductors, and magnetic hysteresis can occur in any magnetic material. Induction heating has been used to heat liquid conductors (such as liquid metals) and also gas conductors (such as gas plasma - see induction plasma technology). Induction heating is often used to heat the graphite crucibles (containing other ingredients) and is used extensively in the semiconductor industry for silicon heating and other semiconductors. Frequency heating (50/60 Hz) induction heating is used for many low cost industrial applications because inverters are not required.
Furnace
An induction furnace uses induction to heat the metal to its melting point. After melting, a high frequency magnetic field can also be used to stir the hot metal, which is useful to ensure that the addition of the alloy is fully mixed into the melt. Most induction furnaces consist of a water-cooled copper ring tube that surrounds the refractory container. Induction furnaces are used in most modern casting as a cleaner metal melting method than reverberatory or cupola stoves. Sizes range from one kilogram capacity to a capacity of one hundred tons. Induction furnaces often emit high-pitched whine or hum as they walk, depending on the frequency of their operation. Melt metals include iron and steel, copper, aluminum, and precious metals. Because it is a clean and non-contact process can be used in a vacuum or inert. The vacuum furnace utilizes induction heating for special steel production and other alloys that will oxidize if heated in the presence of air.
Welding
A similar small-scale process is used for induction welding. Plastics can also be welded by induction, if they are doped with ferromagnetic ceramics (where the magnetic hysteresis of the particles provides the required heat) or by metal particles.
The suture of the tube can be welded in this way. The induced current in the tube flows along the open layer and heats the edges which produce a sufficiently high temperature for welding. At this point the edges of the stitches are coerced together and the coating is welded. RF currents can also be delivered to the tube with a brush, but the result is still the same - current flows along the open layer, heating it up.
Cooking
In induction cooking, induction coil in cook-top heats the iron base of cookware with magnetic induction. Copper-grained pots, aluminum pans and other non-iron pans are generally unsuitable. The heat induced at the base is transferred to the food through conduction. The benefits of an induction cook include efficiency, safety (induction cooker not heated itself) and speed. Both permanently installed and portable induction cookers are available.
Mematri
Induction brazing is often used in higher production processes. This produces uniform and highly repeatable results. There are many industrial equipment where induction brazing is used. For example Induction is used for brazing carbides into shafts.
Sealing
Induction heating is used in cap sealing containers in the food and pharmaceutical industries. The aluminum foil layer is placed on top of a bottle or jar that is opened and heated by induction to combine it into a container. It provides a damage-proof seal, because changing its contents requires breaking the foil.
Warm up to fit
Induction heating is often used to heat an object that causes it to expand before it is installed or assembled. Bearings are heated regularly in this way using utility frequencies (50/60 Hz) and laminated steel core transformer types that pass through center bearing.
Heat treatment
Induction heating is often used in heat treatment of metal goods. The most common application is the induction hardening of steel parts, soldering induction as a way of combining metal components and induction smelting to selectively soften an area of ​​the steel section.
Induction heating can produce high power densities that allow short interaction time to reach the required temperature. It provides tight control of the heating pattern with a pattern following the applied magnetic field quite closely and enables reduced distortion and thermal damage.
This ability can be used in hardening to produce parts with varying properties. The most common hardening process is to produce local surface hardening of an area requiring wear resistance, while maintaining the original structure's toughness as required elsewhere. The depth of the induction hardening pattern can be controlled through the choice of induction frequency, power density and interaction time.
Limitations for process flexibility arise from the need to generate special inductors for many applications. It's quite expensive and requires marshalling high current densities in small copper inductors, which can require special techniques and 'copper fitting'.
Plastic processing
Induction heating is used in plastic injection molding machines. Induction heating increases energy efficiency for injection and extrusion processes. Direct heat is generated in machine barrel, reduces heating time and energy consumption. The induction coils can be placed outside the thermal insulation, so they operate at low temperatures and have long life. The frequency used ranges from 30 kHz to 5 kHz, decreasing for thick barrel. Reduced cost of inverter equipment has made induction heating more and more popular. Induction heating can also be applied to molds, offering more mold temperatures and improving product quality.
Maps Induction heating
Details
The basic setting is the AC power supply which provides electricity with low voltage but very high current and high frequency. The workpiece for heat is placed inside the power-driven air coil, usually in combination with the resonant tank capacitor to increase the reactive power. The alternating magnetic field induces the eddy current in the workpiece.
Relative depth varies with temperature because resistivity and permeability vary with temperature. For steel, the relative permeability drops to 1 above the Curie temperature. Thus the reference depth may vary with temperature by a factor of 2-3 for a nonmagnetic conductor, and as much as 20 for magnetic steel.
The magnetic material improves the induction heat process due to hysteresis. Materials with high permeability (100-500) are more easily heated by induction heating. Hysteresis heating occurs below the Curie temperature where the material retains its magnetic properties. High permeability below the Curie temperature in the workpiece is useful. Specific temperature, mass, and heat differences affect the heating of the workpiece.
Transfer of induction heating energy is affected by the distance between the coil and the workpiece. Loss of energy takes place through the heat conduction from the workpiece to the equipment, natural convection, and thermal radiation.
Induction coils are usually made of copper pipe and the liquid is cooled. The diameter, shape, and number of turns affect field efficiency and pattern.
Core type furnace
The furnace consists of a circular furnace containing the charge to be melted in the form of a ring. Metal rings are large diameter and are magnetically interconnected with electric coils energized by an AC source. It is essentially a transformer in which the charge to be heated forms a secondary short rotation curve and is magnetically coupled to the primer by an iron core.
References
- 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
- Hartshorn, Leslie, Radio frequency heating . London, G. Allen & amp; Unwin, 1949. LCCN 50002705
- Langton, L. L., Radio frequency heating equipment, with special reference to the theory and design of self-powered oscillator power . London, Pitman, 1949. LCCN 50001900
- Shields, John Potter, Abc radio frequency heating . 1st ed., Indianapolis, H. W. Sams, 1969. LCCN 76098943
- Sovie, Ronald J., and George R. Seikel, Heating induction of low pressure plasma radio frequency . 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.
Source of the article : Wikipedia
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