What is the disadvantage of induction heater?

Process of heating an electrically conducting object by electromagnetic induction

TY-induction Product Page

This article is about Induction heating. Not to be confused with Joule heating

Component of Stirling radioisotope generator is heated by induction during testing

Induction heating is the process of heating electrically conductive materials, namely metals or semi-conductors, by electromagnetic induction, through heat transfer passing through an inductor that creates an electromagnetic field within the coil to heat up and possibly melt steel, copper, brass, graphite, gold, silver, aluminum, or carbide.

An important feature of the induction heating process is that the heat is generated inside the object itself, instead of by an external heat source via heat conduction. Thus objects can be heated very rapidly. In addition, there need not be any external contact, which can be important where contamination is an issue. Induction heating is used in many industrial processes, such as heat treatment in metallurgy, Czochralski crystal growth and zone refining used in the semiconductor industry, and to melt refractory metals that require very high temperatures. It is also used in induction cooktops.

An induction heater consists of an electromagnet and an electronic oscillator that passes a high-frequency alternating current (AC) through the electromagnet. The rapidly alternating magnetic field penetrates the object, generating electric currents inside the conductor called eddy currents. The eddy currents flow through the resistance of the material, and heat it by Joule heating. In ferromagnetic and ferrimagnetic materials, such as iron, heat also is generated by magnetic hysteresis losses. The frequency of the electric current used for induction heating depends on the object size, material type, coupling (between the work coil and the object to be heated), and the penetration depth.

Applications

[

edit

]

Induction heating of 25 mm metal bar using 15 kW at 450 kHz. Keeping silicon in crucible molten at 2,650 °F (1,450 °C) for Czochralski crystal growth, .

Induction heating allows the targeted heating of an applicable item for applications including surface hardening, melting, brazing and soldering, and heating to fit. Due to their ferromagnetic nature, iron and its alloys respond best to induction heating. Eddy currents can, however, be generated in any conductor, and magnetic hysteresis can occur in any magnetic material. Induction heating has been used to heat liquid conductors (such as molten metals) and also gaseous conductors (such as a gas plasma&#;see Induction plasma technology). Induction heating is often used to heat graphite crucibles (containing other materials) and is used extensively in the semiconductor industry for the heating of silicon and other semiconductors. Utility frequency (50/60 Hz) induction heating is used for many lower-cost industrial applications as inverters are not required.

Furnace

[

edit

]

An induction furnace uses induction to heat 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. 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. Because it is a clean and non-contact process, it can be used in a vacuum or inert atmosphere. Vacuum furnaces use induction heating to produce specialty steels and other alloys that would oxidize if heated in the presence of air.

Welding

[

edit

]

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.

Seams of tubes can be welded this way. Currents induced in a tube run along the open seam and heat the edges resulting in a temperature high enough for welding. At this point, the seam edges are forced together and the seam is welded. The RF current can also be conveyed to the tube by brushes, but the result is still the same&#;the current flows along the open seam, heating it.

Manufacturing

[

edit

]

In the Rapid Induction Printing metal additive printing process, a conductive wire feedstock and shielding gas is fed through a coiled nozzle, subjecting the feedstock to induction heating and ejection from the nozzle as a liquid, in order to refuse under shielding to form three-dimensional metal structures. The core benefit of the use of induction heating in this process is significantly greater energy and material efficiency as well as a higher degree of safety when compared with other additive manufacturing methods, such as selective laser sintering, which deliver heat to the material using a powerful laser or electron beam.

Cooking

[

edit

]

In induction cooking, an induction coil inside the cooktop heats the iron base of cookware by magnetic induction. Using induction cookers produces safety, efficiency (the induction cooktop is not heated itself), and speed. Non-ferrous pans such as copper-bottomed pans and aluminium pans are generally unsuitable. By thermal conduction, the heat induced in the base is transferred to the food inside.[1]

Brazing

[

edit

]

Induction brazing is often used in higher production runs. It produces uniform results and is very repeatable. There are many types of industrial equipment where induction brazing is used. For instance, Induction is used for brazing carbide to a shaft.

Sealing

[

edit

]

Induction heating is used in cap sealing of containers in the food and pharmaceutical industries. A layer of aluminum foil is placed over the bottle or jar opening and heated by induction to fuse it to the container. This provides a tamper-resistant seal since altering the contents requires breaking the foil.[2]

Heating to fit

[

edit

]

Induction heating is often used to heat an item causing it to expand before fitting or assembly. Bearings are routinely heated in this way using utility frequency (50/60 Hz) and a laminated steel transformer-type core passing through the centre of the bearing.

Heat treatment

[

edit

]

Induction heating is often used in the heat treatment of metal items. The most common applications are induction hardening of steel parts, induction soldering/brazing as a means of joining metal components, and induction annealing to selectively soften an area of a steel part.

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 thermal 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 the choice of induction frequency, power density, and interaction time.

Limits to the flexibility of the process arise 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 specialized engineering and "copper-fitting."

Plastic processing

[

edit

If you want to learn more, please visit our website industrial induction heater.

]

Induction heating is used in plastic injection molding machines. Induction heating improves energy efficiency for injection and extrusion processes. Heat is directly generated in the barrel of the machine, reducing warm-up time and energy consumption. The induction coil can be placed outside thermal insulation, so it operates at low temperatures and has a long life. The frequency used ranges from 30 kHz down to 5 kHz, decreasing for thicker barrels. The reduction in the cost of inverter equipment has made induction heating increasingly popular. Induction heating can also be applied to molds, offering more even mold temperature and improved product quality.[3]

Pyrolysis

[

edit

]

Induction heating is used to obtain biochar in the pyrolysis of biomass. Heat is directly generated into shaker reactor walls, enabling the pyrolysis of the biomass with good mixing and temperature control.[4]

Bolt heating

[

edit

]

Induction heating is used by mechanics to remove rusted bolts. The heat helps remove the rust induced tension between the threads. [5]

Details

[

edit

]

The basic setup is an AC power supply that provides electricity with low voltage but very high current and high frequency. The workpiece to heat is placed inside an air coil driven by the power supply, usually in combination with a resonant tank capacitor to increase the reactive power. The alternating magnetic field induces eddy currents in the workpiece.

The frequency of the inductive current determines the depth that the induced eddy currents penetrate the workpiece. In the simplest case of a solid round bar, the induced current decreases exponentially from the surface. The penetration depth δ {\displaystyle \delta } in which 86% of power will be concentrated, can be derived as δ = 503 ρ μ f {\displaystyle \delta =503{\sqrt {\frac {\rho }{\mu f}}}} , where δ {\displaystyle \delta } is the depth in meters, ρ {\displaystyle \rho } is the resistivity of the workpiece in ohm-meters, μ {\displaystyle \mu } is the dimensionless relative magnetic permeability of the workpiece, and f {\displaystyle f} is the frequency of the AC field in Hz. The AC field can be calculated using the formula 1 T {\displaystyle {\frac {1}{T}}} .[6] The equivalent resistance of the workpiece and thus the efficiency is a function of the workpiece diameter a {\displaystyle a} over the reference depth d {\displaystyle d} , increasing rapidly up to about a / d = 4 {\displaystyle a/d=4} .[7] Since the workpiece diameter is fixed by the application, the value of a / d {\displaystyle a/d} is determined by the reference depth. Decreasing the reference depth requires increasing the frequency. Since the cost of induction power supplies increases with frequency, supplies are often optimized to achieve a critical frequency at which a / d = 4 {\displaystyle a/d=4} . If operated below the critical frequency, heating efficiency is reduced because eddy currents from either side of the workpiece impinge upon one another and cancel out. Increasing the frequency beyond the critical frequency creates minimal further improvement in heating efficiency, although it is used in applications that seek to heat treat only the surface of the workpiece.

Relative depth varies with temperature because resistivities and permeability vary with temperature. For steel, the relative permeability drops to 1 above the Curie temperature. Thus the reference depth can vary with temperature by a factor of 2&#;3 for nonmagnetic conductors and by as much as 20 for magnetic steels.[8]

Applications of frequency ranges Frequency (kHz) Workpiece type 5&#;30 Thick materials (e.g. steel at 815 °C with diameter 50 mm or greater). 100&#;400 Small workpieces or shallow penetration (e.g. steel at 815 °C with diameter of 5&#;10 mm or steel at 25 °C with a diameter around 0.1 mm). 480 Microscopic pieces

Magnetic materials improve the induction heat process because of hysteresis. Materials with high permeability (100&#;500) are easier to heat with induction heating. Hysteresis heating occurs below the Curie temperature, where materials retain their magnetic properties. High permeability below the Curie temperature in the workpiece is useful. Temperature difference, mass, and specific heat influence the workpiece heating.

The energy transfer of induction heating is affected by the distance between the coil and the workpiece. Energy losses occur through heat conduction from workpiece to fixture, natural convection, and thermal radiation.

The induction coil is usually made of copper tubing and fluid coolant. Diameter, shape, and number of turns influence the efficiency and field pattern.

Core type furnace

[

edit

]

The furnace consists of a circular hearth that contains the charge to be melted in the form of a ring. The metal ring is large in diameter and is magnetically interlinked with an electrical winding energized by an AC source. It is essentially a transformer where the charge to be heated forms a single-turn short circuit secondary and is magnetically coupled to the primary by an iron core.

References

[

edit

]

• Brown, George Harold, Cyril N. Hoyler, and Rudolph A. Bierwirth, Theory and application of radio-frequency heating. New York, D. Van Nostrand Company, Inc., . LCCN
• Hartshorn, Leslie, Radio-frequency heating. London, G. Allen & Unwin, . LCCN
• Langton, L. L., Radio-frequency heating equipment, with particular reference to the theory and design of self-excited power oscillators. London, Pitman, . LCCN
• Shields, John Potter, Abc's of radio-frequency heating. 1st ed., Indianapolis, H. W. Sams, . LCCN
• 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 . NASA technical note. D-; Prepared at Lewis Research Center.

See also

[

edit

]

-01-05 From: Local  Views

Many people want to know what is advantage and disadvantage of induction heating, induction hardening,induction brazing,induction forging,induction melting or induction quenching.

High frequency induction machines and induction heating technology is currently the highest heating efficiency of the metallic materials, the fastest speed, and low power consumption of environmental protection. It has been widely used in various industries on the thermal processing of the metal material, heat treatment, hot assembly and welding, melting process. It can not only heating the workpiece as a whole, but also on the relevance of the workpiece local heating; deep through the heat of the workpiece can be realized, to focus only on its surface, the surface heating; not only the direct heating of the metal material, but also on non-metallic material indirect heating. And so on. Thus, induction heating technology is more widely used in all walks of life.

    Local heating of the surface of the workpiece with the induced current heat treatment process. This heat treatment process commonly used in the surface hardening, but also can be used for partial annealing or tempering, and sometimes also used for the overall quenching and tempering. The early s, the United States, the Soviet Union has applied to the induction heating method for surface hardening of parts. With industrial development, induction heating, heat treatment technology continue to improve, continue to expand the range of applications.

Basic principles: the workpiece into the inductor (coil), and when the sensors pass into the alternating current of a certain frequency, alternating magnetic field is generated around. The electromagnetic induction effect of the alternating magnetic field so that the induction current the workpiece generated within a closed &#; &#; vortex. Induced currents are very unevenly distributed in the cross section of the workpiece, a high current density of the workpiece surface, the inwardly gradually decreases, this phenomenon is called the skin effect. The high current density of the workpiece surface energy into thermal energy, so that the temperature of the surface layer is increased, i.e. the surface heating. The current frequency is higher, the current density of the workpiece surface and the internal differential is the greater, the heating layer is thinner. Rapid cooling, the temperature of the heating layer over the temperature of the critical point of steel surface hardening can be achieved.

Classification: according to the frequency of the alternating current, the induction heating and heat treatment is divided into UHF, HF, RF, MF, working frequency.
(1) ultra-high frequency induction heating treatment used in the current frequency up to 27 MHz, the heating layer is extremely thin, only about 0.15 mm, can be used for complex shapes such as circular saws and workpiece thin surface hardening.
&#; high-frequency induction heating heat treatment is usually used in current frequency of 200 to 300 kHz, the depth of the heating layer is 0.5 to 2 mm can be used for the gear, cylinder sleeve, cam, shaft and other parts of the surface quenching.
&#;The  radio induction heating heat treatment with the current frequency of 20 to 30 kHz, with a super audio induced current small modulus gear heating, the heating layer roughly along the tooth profile distribution, the pure fire better performance.
4 MF (Medium Frequency) induction heating of the heat treatment using the current frequency is generally from 2.5 to 10 kHz, the depth of the heating layer is 2 to 8 mm, and more for large modulus gear, having a larger diameter shaft and cold roll the workpiece such as surface hardening.
&#; power frequency induction heating heat treatment used in the current frequency of 50 to 60 Hz, the depth of the heating layer is 10 to 15 mm, can be used for the surface hardening of large workpieces.

Characteristics and application: The main advantage of induction heating: &#; having overall heating workpiece deformation is small, small power consumption. The &#; pollution. &#; heating speed, the workpiece surface oxidation and decarbonization lighter. &#; surface hardened layer can be adjusted as needed, easy to control. (5) heating equipment can be installed in the mechanical processing production line, easy to realize mechanization and automation, easy to manage, and can reduce the transportation, saving manpower, improve production efficiency. &#; hardened layer martensite smaller, hardness, strength, toughness, are higher. &#; surface hardening of the workpiece surface greater compression internal stress, higher workpiece anti-fatigue breaking ability.

The induction heating heat treatment also has some drawbacks or disadvantages. Compared with flame hardening, induction heating equipment is more complex, and adaptability to poor, difficult to guarantee the quality of some of the complex shape of the workpiece.
The induction heater is more complex, once the cost of inputs is relatively high, interchangeability and adaptability of the induction coil(inductor) is poor, can not be used for some complex shape of the workpiece. 

But obviously,the advantages outweighed the disadvantages. 
Therefore, the induction heating is a better choice of metalworking for replacing coal heating, oil heating, gas heating, electric cooker, electric oven heating and other heating methods.

Applications: Induction heating is widely used for the surface hardening of the gears, shafts, crankshafts, cams, rollers, etc. of the workpiece, the purpose is to improve the abrasion resistance and anti-fatigue breaking capability of these artifacts. Automobile rear axle using induction heating surface hardening, fatigue design load cycles increases by about 10 times more than the quenched and tempered. Induction heating surface hardening of the workpiece material is generally in the carbon steel. In order to meet the special needs of some of the workpiece has been developed for induction heating surface hardening dedicated low hardenability steel. High-carbon steel and cast iron workpiece can also be used induction heating surface hardening. The quenching medium commonly Water or polymer solution.

Equipment: Induction Heat Treatment Equipment power equipment, quenching machine and sensor. The main role of the power supply apparatus is suitable output frequency of the alternating current. The high-frequency current power supply tube high-frequency generator and two SCR inverter. IF current power supply generator sets. General power supply can only output a frequency current, some equipment can change the current frequency, directly with the 50 Hz power frequency current induction heating.

Selection: the depth of the induction heating device selection and the workpiece requires heating layer. Heating the deep layer of the workpiece, using the current low frequency power supply apparatus; the heating layer shallow workpiece, the current high frequency power supply apparatus should be used. Select other conditions of the power supply is the power of the device. Heating surface area increases, the electrical power required by the corresponding increase. When the heating surface area is too large, or when insufficient power supply, the method may be continuously heated, so that the relative movement of workpiece and the sensor, the front heating, behind cooling. But the best, or the entire heating surface heating. This can use the the workpiece core section waste heat so that the hardened surface layer tempering so that the process is simplified, and also saving energy.

The main role of the induction heating machine is the workpiece positioning and necessary movement. It should also be accompanied by the quenching media device. Quenching machine can be divided into standard machine tools and special machine tools, the former applies to the general workpiece, which is suitable for mass production of complex workpieces.

Inductive heating of heat treatment, in order to ensure the quality of the heat treatment and to improve thermal efficiency, it is necessary according to the shape of the workpiece and requirements, design and manufacturing structure appropriate sensors. Common sensor heating the outer surface of the sensor, inner hole heating sensor plane heat sensor, universal heating sensor, a special type of heating sensor, a single type of heating sensors, the composite heated sensor, smelting furnace .

For more information, please visit induction heating machines.