Do-it-yourself induction furnace scheme. Melting metal at home in an induction electric furnace. Furnace for melting metal on a welding inverter

The principle of induction heating is to convert the energy of an electromagnetic field absorbed by an electrically conductive heated object into thermal energy.

In induction heating installations, an electromagnetic field is created by an inductor, which is a multi-turn cylindrical coil (solenoid). An alternating electric current is passed through the inductor, as a result of which a time-varying alternating magnetic field arises around the inductor. This is the first transformation of the energy of an electromagnetic field, described by Maxwell's first equation.

The object to be heated is placed inside or near the inductor. The changing (in time) flux of the magnetic induction vector created by the inductor penetrates the heated object and induces an electric field. The electric lines of this field are located in a plane perpendicular to the direction of the magnetic flux and are closed, i.e., the electric field in the heated object has a vortex character. Under the action of an electric field, according to Ohm's law, conduction currents (eddy currents) arise. This is the second transformation of the energy of the electromagnetic field, described by the second Maxwell equation.

In a heated object, the energy of the induced alternating electric field irreversibly transforms into heat. Such thermal dissipation of energy, resulting in heating of the object, is determined by the existence of conduction currents (eddy currents). This is the third transformation of the energy of the electromagnetic field, and the energy ratio of this transformation is described by the Lenz-Joule law.

The described transformations of the energy of the electromagnetic field make it possible:
1) transfer the electrical energy of the inductor to the heated object without resorting to contacts (unlike resistance furnaces)
2) release heat directly in the heated object (the so-called "furnace with an internal heating source" in the terminology of Prof. N.V. Okorokov), as a result of which the use of thermal energy is the most perfect and the heating rate increases significantly (compared to the so-called " ovens with an external heating source).

The magnitude of the electric field strength in a heated object is influenced by two factors: the magnitude of the magnetic flux, i.e., the number of magnetic field lines penetrating the object (or coupled to the heated object), and the frequency of the supply current, i.e., the frequency of changes (in time ) of the magnetic flux coupled to the heated object.

This makes it possible to perform two types of induction heating installations, which differ both in design and in operational properties: induction installations with a core and without a core.

According to the technological purpose, induction heating installations are divided into melting furnaces for melting metals and heating installations for heat treatment (hardening, tempering), for through heating of workpieces before plastic deformation (forging, stamping), for welding, soldering and surfacing, for chemical and thermal treatment products, etc.

According to the frequency of the change in the current supplying the induction heating installation, there are:
1) installations of industrial frequency (50 Hz), powered by the mains directly or through step-down transformers;
2) installations of increased frequency (500-10000 Hz), powered by electric or semiconductor frequency converters;
3) high-frequency installations (66,000-440,000 Hz and above), powered by tube electronic generators.

Core induction heating plants

In the melting furnace (Fig. 1), a cylindrical multi-turn inductor made of a copper profiled tube is mounted on a closed core made of sheet electrical steel (sheet thickness 0.5 mm). A refractory ceramic lining is placed around the inductor with a narrow annular channel (horizontal or vertical) where the liquid metal is located. A necessary condition for operation is a closed electrically conductive ring. Therefore, it is impossible to melt individual pieces of solid metal in such a furnace. To start the furnace, it is necessary to pour a portion of liquid metal from another furnace into the channel or leave part of the liquid metal from the previous melt (the residual capacity of the furnace).

Fig.1. Scheme of the device of the induction channel furnace: 1 - indicator; 2 - metal; 3 - channel; 4 - magnetic circuit; Ф - main magnetic flux; Ф 1р and Ф 2р - magnetic fluxes of scattering; U 1 and I 1 - voltage and current in the inductor circuit; I 2 - conduction current in the metal

In the steel magnetic circuit of the induction channel furnace, a large working magnetic flux is closed, and only a small part of the total magnetic flux created by the inductor is closed through the air in the form of a scattering flux. Therefore, such furnaces successfully operate at industrial frequency (50 Hz).

Currently, there are a large number of types and designs of such furnaces developed at VNIIETO (single-phase and multi-phase with one and several channels, with vertical and horizontal closed channels of various shapes). These furnaces are used for melting non-ferrous metals and alloys with a relatively low melting point, as well as for producing high-quality cast iron. When melting cast iron, the furnace is used either as a hoarder (mixer) or as a melting unit. The designs and technical characteristics of modern induction duct furnaces are given in special literature.

Coreless induction heating units

In a melting furnace (Fig. 2), the melted metal is in a ceramic crucible placed inside a cylindrical multi-turn inductor. made of a copper profiled tube through which cooling water is passed. You can learn more about the design of the inductor.

The absence of a steel core leads to a sharp increase in the leakage magnetic flux; the number of magnetic lines of force linked to the metal in the crucible will be extremely small. This circumstance requires a corresponding increase in the frequency of change (in time) of the electromagnetic field. Therefore, for the efficient operation of induction crucible furnaces, it is necessary to feed them with currents of increased, and in some cases, high frequency from appropriate current converters. Such furnaces have a very low natural power factor (cos φ=0.03-0.10). Therefore, it is necessary to use capacitors to compensate for reactive (inductive) power.

Currently, there are several types of induction crucible furnaces developed at VNIIETO in the form of appropriate size ranges (in terms of capacity) of high, high and industrial frequency, for steel melting (IST type).

Rice. 2. Scheme of the device of the induction crucible furnace: 1 - inductor; 2 - metal; 3 - crucible (arrows show the trajectory of liquid metal circulation as a result of electrodynamic phenomena)

The advantages of crucible furnaces are the following: heat released directly in the metal, high metal uniformity in chemical composition and temperature, no sources of metal contamination (other than the crucible lining), ease of control and regulation of the melting process, hygienic working conditions. In addition, induction crucible furnaces are characterized by: higher productivity due to high specific (per unit capacity) heating power; the ability to melt a solid charge without leaving metal from the previous melt (unlike channel furnaces); low mass of the lining compared to the mass of metal, which reduces the accumulation of thermal energy in the lining of the crucible, reduces the thermal inertia of the furnace and makes melting furnaces of this type extremely convenient for periodic operation with breaks between melts, in particular for shaped and foundry shops of machine-building plants; the compactness of the furnace, which makes it possible to simply isolate the working space from the environment and carry out melting in a vacuum or in a gaseous medium of a given composition. Therefore, vacuum induction crucible furnaces (ISV type) are widely used in metallurgy.

Along with the advantages, induction crucible furnaces have the following disadvantages: the presence of relatively cold slags (the slag temperature is lower than the metal temperature), which make it difficult to carry out refining processes when smelting high-quality steels; complex and expensive electrical equipment; low durability of the lining at sharp temperature fluctuations due to the small thermal inertia of the crucible lining and the eroding effect of liquid metal during electrodynamic phenomena. Therefore, such furnaces are used for remelting alloyed waste in order to reduce the waste of elements.

References:
1. Egorov A.V., Morzhin A.F. Electric furnaces (for steel production). M.: "Metallurgy", 1975, 352 p.

The induction furnace can be used for melting a small amount of metal, separating and refining precious metals, and heating metal products for quenching or tempering.

In addition, such stoves are proposed to be used for heating the home. Induction furnaces are commercially available, but it is more interesting and cheaper to make such an oven with your own hands.

The principle of operation of an induction furnace is based on heating the material using eddy currents.

To obtain such currents, a so-called inductor is used, which is an inductor containing only a few turns of thick wire.

The inductor is powered by a 50 Hz AC network (sometimes through a step-down transformer) or from a high frequency generator.

The alternating current flowing through the inductor generates an alternating magnetic field that permeates the space. If any material is found in this space, then currents will be induced in it, which will begin to heat this material. If this material is water, then its temperature will rise, and if it is a metal, then after a while it will begin to melt.

Induction furnaces are of two types:

• furnaces with a magnetic core;
• furnaces without a magnetic circuit.

The fundamental difference between these two types of furnaces is that in the first case, the inductor is located inside the melting metal, and in the second - outside. The presence of a magnetic circuit increases the density of the magnetic field penetrating the metal placed in the crucible, which facilitates its heating.

An example of an induction furnace with a magnetic core is a channel induction furnace. The scheme of such a furnace includes a closed magnetic circuit made of transformer steel, on which the primary winding is located - an inductor and an annular crucible, in which the material for melting is located. The crucible is made of heat-resistant dielectric. The power supply of such an installation is carried out from an alternating current network with a frequency of 50 Hz or a generator with an increased frequency of 400 Hz.

Such furnaces are used for melting duralumin, non-ferrous metals or producing high-quality cast iron.

Crucible furnaces that do not have a magnetic circuit are more common. The absence of a magnetic circuit in the furnace leads to the fact that the magnetic field created by industrial frequency currents is strongly dissipated in the surrounding space. And in order to increase the magnetic field density in the dielectric crucible with the melting material, it is necessary to use higher frequencies. It is considered that if the inductor circuit is tuned to resonance with the frequency of the supply voltage, and the diameter of the crucible is commensurate with the resonance wavelength, then up to 75% of the energy of the electromagnetic field can be concentrated in the region of the crucible.

Scheme of manufacturing an induction furnace

Studies have shown that in order to ensure efficient melting of metals in a crucible furnace, it is desirable that the frequency of the voltage supplying the inductor exceed the resonant frequency by 2-3 times. That is, such a furnace operates on the second or third frequency harmonic. In addition, when operating at such higher frequencies, better mixing of the alloy occurs, which improves its quality. The mode using even higher frequencies (fifth or sixth harmonics) can be used for surface carburizing or metal hardening, which is associated with the appearance of a skin effect, that is, the displacement of a high-frequency electromagnetic field to the surface of the workpiece.

Conclusions for the section:

1. There are two versions of the induction furnace - with a magnetic circuit and without a magnetic circuit.
2. The channel furnace, which belongs to the first version of the furnaces, is more complex in design, but can be powered directly from a 50 Hz network or a 400 Hz increased frequency network.
3. The crucible furnace, which belongs to the furnaces of the second type, is simpler in design, but requires a high-frequency generator to power the inductor.

If a stove is a heating device for practical needs, then a fireplace is needed for decor and comfort. , as well as an example of ordering a fireplace with an arch.

Read about how to choose the right electric heating boiler.

And here you will learn how automation works for gas heating boilers. Boilers by installation method and types of volatile systems.

Designs and parameters of induction furnaces

Drier

One of the options for making an induction furnace with your own hands is a channel.

For its manufacture, you can use a conventional welding transformer operating at a frequency of 50 Hz.

In this case, the secondary winding of the transformer must be replaced with an annular crucible.

In such a furnace, up to 300-400 g of non-ferrous metals can be melted, and it will consume 2-3 kW of power. Such a furnace will have high efficiency and will make it possible to smelt high quality metal.

The main difficulty in making a channel induction furnace with your own hands is the acquisition of a suitable crucible.

For the manufacture of the crucible, a material with high dielectric properties and high strength should be used. Such as electroporcelain. But such material is not easy to find, but even more difficult to process at home.

crucible

The most important elements of the induction type crucible furnace are:

• inductor;
• supply voltage generator.

As an inductor for crucible furnaces up to 3 kW, you can use a copper tube or wire with a diameter of 10 mm or a copper bus with a cross section of 10 mm². The diameter of the inductor can be about 100 mm. The number of turns is from 8 to 10.

In this case, there are many modifications of the inductor. For example, it can be made in the form of a figure eight, shamrock or other shape.

During operation, the inductor usually gets very hot. In industrial samples for the inductor, water cooling of the turns is used.

At home, using this method is difficult, but the inductor can work normally for 20-30 minutes, which is quite enough for homework.

However, this mode of operation of the inductor causes the appearance of scale on its surface, which sharply reduces the efficiency of the furnace. Therefore, from time to time the inductor has to be replaced with a new one. Some experts suggest covering the inductor with a heat-resistant material to protect against overheating.

The high frequency alternator is another important element of the induction type crucible furnace. Several types of such generators can be considered:

• transistor generator;
• thyristor generator;
• MOSFET generator.

The simplest alternator for powering the inductor is a self-excited generator, the circuit of which has one KT825 type transistor, two resistors and a feedback coil. Such a generator can generate power up to 300 W, and the generator power is adjusted by changing the constant voltage of the power source. The power supply must provide up to 25 A.

The thyristor-based generator proposed for the crucible furnace includes a T122-10-12 type thyristor, a KN102E dinistor, a number of diodes and a pulse transformer in the circuit. The thyristor operates in a pulsed mode.

DIY Induction Furnace

Such microwave radiation can adversely affect human health. In accordance with Russian safety standards, it is allowed to work with high-frequency vibrations at an electromagnetic energy flux density of no more than 1-30 mW / m². For this generator, as shown by calculations, this radiation at a distance of 2.5 m from the source reaches 1.5 W / m². This value is unacceptable.

The MOSFET oscillator circuit includes four MOSFETs of the IRF520 and IRFP450 types and is a push-pull oscillator with independent excitation and an inductor included in the bridge circuit. An IR2153 chip is used as a master oscillator. To cool the transistors, a radiator of at least 400 cm² and airflow are required.
This generator can supply power up to 1 kW and change the oscillation frequency from 10 kHz to 10 MHz. Due to this, a furnace using a generator of this type can operate both in the melting mode and surface heating.

A long-burning stove can work on one tab from 10 to 20 hours. In the manufacture, it is necessary to take into account the design features so that it gives out maximum heat with minimal energy consumption. For information on how to properly assemble the oven, read on our website.

You might be interested in learning about gas-fired garage heaters. What it should be in order to ensure warmth and safety, read the material.

Heating use

To heat a home, stoves of this type are usually used in conjunction with a hot water boiler.

One of the options for a home-made induction-type hot water boiler is a design that heats a pipe with flowing water using an inductor that is powered from the mains using an RF welding inverter.

However, as the analysis of such systems shows, due to the large energy losses of the electromagnetic field in the dielectric tube, the efficiency of such systems is extremely low. In addition, a very large amount of electricity is required to heat a home, which makes such heating economically unprofitable.

From this section we can conclude:

1. The most acceptable option for a do-it-yourself induction furnace is a crucible version with a MOS transistor power generator.
2. Using a do-it-yourself induction furnace to heat your home is not economically viable. In this case, it is better to purchase a factory system.

Operation features

An important issue in the use of an induction type oven is safety.

As mentioned above, crucible-type furnaces use high-frequency power supplies.

Therefore, when operating an induction furnace, the inductor must be placed vertically; before turning on the furnace, a grounded shield must be put on the inductor. When the furnace is turned on, it is necessary to observe the processes occurring in the crucible at a distance, and immediately turn it off after work is done.

When operating a self-made induction furnace, you must:

1. Take steps to protect the user of the oven from possible high frequency radiation.
2. Take into account the possibility of burns by the inductor.

Thermal hazards must also be taken into account when working with the oven. Touching the hot inductor to the skin can cause severe burns.

Induction heating is not possible without the use of three main elements:

• inductor;
• generator;
• heating element.

An inductor is a coil, usually made of copper wire, that generates a magnetic field. An alternator is used to produce a high frequency stream from a standard 50 Hz household power stream. A metal object is used as a heating element, capable of absorbing thermal energy under the influence of a magnetic field.

If you connect these elements correctly, you can get a high-performance device that is perfect for heating a liquid coolant and heating a house. With the help of a generator, an electric current with the necessary characteristics is supplied to the inductor, i.e. on a copper coil. When passing through it, the flow of charged particles forms a magnetic field.

The principle of operation of induction heaters is based on the occurrence of electric currents inside conductors that appear under the influence of magnetic fields.

The peculiarity of the field is that it has the ability to change the direction of electromagnetic waves at high frequencies. If any metal object is placed in this field, it will begin to heat up without direct contact with the inductor under the influence of the created eddy currents.

The high-frequency electric current flowing from the inverter to the induction coil creates a magnetic field with a constantly changing vector of magnetic waves. The metal placed in this field heats up quickly

The lack of contact makes it possible to make energy losses during the transition from one type to another negligible, which explains the increased efficiency of induction boilers.

To heat water for the heating circuit, it is enough to ensure its contact with a metal heater. Often, a metal pipe is used as a heating element, through which a stream of water is simply passed. Water simultaneously cools the heater, which significantly increases its service life.

The electromagnet of an induction device is obtained by winding a wire around a core of a ferromagnet. The resulting induction coil heats up and transfers heat to the heated body or to the coolant flowing nearby through the heat exchanger

Literature

• Babat G. I., Svenchansky A. D. Electrical industrial ovens. - M. : Gosenergoizdat, 1948. - 332 p.
• Burak Ya. I., Ogirko I. V. Optimal Heating of a Cylindrical Shell with Temperature-Dependent Characteristics of the Material // Mat. methods and fiz.-mekh. fields. - 1977. - Issue. 5 . - S. 26-30.
• Vasiliev A.S. Lamp generators for high-frequency heating. - L.: Mashinostroenie, 1990. - 80 p. - (Library of high-frequency thermist; Issue 15). - 5300 copies. - ISBN 5-217-00923-3.
• Vlasov V.F. Radio engineering course. - M. : Gosenergoizdat, 1962. - 928 p.
• Izyumov N. M., Linde D. P. Fundamentals of radio engineering. - M. : Gosenergoizdat, 1959. - 512 p.
• Lozinsky M. G. Industrial application of induction heating. - M.: Publishing House of the Academy of Sciences of the USSR, 1948. - 471 p.
• The use of high-frequency currents in electrothermy / Ed. A. E. Slukhotsky. - L.: Mashinostroenie, 1968. - 340 p.
• Slukhotsky A. E. Inductors. - L.: Mashinostroenie, 1989. - 69 p. - (Library of high-frequency thermist; Issue 12). - 10,000 copies. - ISBN 5-217-00571-8.
• Vogel A. A. Induction Method for Holding Liquid Metals in Suspension / Ed. A. N. Shamova. - 2nd ed., corrected. - L.: Mashinostroenie, 1989. - 79 p. - (Library of high-frequency thermist; Issue 11). - 2950 copies. - .

Operating principle

The latter option, most commonly used in heating boilers, has become in demand due to the simplicity of its implementation. The principle of operation of the induction heating unit is based on the transfer of magnetic field energy to the coolant (water). The magnetic field is formed in the inductor. Alternating current, passing through the coil, creates eddy currents that transform energy into heat.

The principle of operation of the installation of induction heating

The water supplied through the lower pipe to the boiler is heated by energy transfer, and exits through the upper pipe, getting further into the heating system. A built-in pump is used to create pressure. Constantly circulating water in the boiler does not allow the elements to overheat. In addition, during operation, the heat carrier vibrates (at a low noise level), due to which scale deposits on the inner walls of the boiler are impossible.

Induction heaters can be implemented in various ways.

Power calculation

Since the induction method of steel melting is less expensive than similar methods based on the use of fuel oil, coal and other energy carriers, the calculation of an induction furnace begins with the calculation of the power of the unit.

The power of the induction furnace is divided into active and useful, each of them has its own formula.

As initial data you need to know:

• the capacity of the furnace, in the case considered for example, it is equal to 8 tons;
• unit power (its maximum value is taken) - 1300 kW;
• current frequency - 50 Hz;
• the productivity of the furnace plant is 6 tons per hour.

It is also required to take into account the melted metal or alloy: by condition it is zinc. This is an important point, the heat balance of melting cast iron in an induction furnace, as well as other alloys.

Useful power, which is transferred to the liquid metal:

• Рpol \u003d Wtheor × t × P,
• Wtheor - specific energy consumption, it is theoretical, and shows the overheating of the metal by 10C;
• P - productivity of the furnace plant, t/h;
• t - overheating temperature of an alloy or a metal billet in a bath furnace, 0С
• Рpol \u003d 0.298 × 800 × 5.5 \u003d 1430.4 kW.

Active power:

• P \u003d Rpol / Yuterm,
• Rpol - taken from the previous formula, kW;
• Yuterm - the efficiency of the foundry furnace, its limits are from 0.7 to 0.85, on average they take 0.76.
• P \u003d 1311.2 / 0.76 \u003d 1892.1 kW, the value is rounded up to 1900 kW.

At the final stage, the power of the inductor is calculated:

• Rind \u003d P / N,
• P is the active power of the furnace plant, kW;
• N is the number of inductors provided on the furnace.
• Rind \u003d 1900 / 2 \u003d 950 kW.

The power consumption of an induction furnace when melting steel depends on its performance and the type of inductor.

Furnace components

So, if you are interested in a do-it-yourself induction mini-oven, then it is important to know that its main element is a heating coil. In the case of a homemade version, it is enough to use an inductor made of a bare copper tube with a diameter of 10 mm

For the inductor, an inner diameter of 80-150 mm is used, and the number of turns is 8-10. It is important that the turns do not touch, and the distance between them is 5-7 mm. Parts of the inductor must not come into contact with its screen, the minimum clearance must be 50 mm.

If you are going to do-it-yourself induction furnace, then you should know that water or antifreeze is cooling the inductors on an industrial scale. In the case of low power and short operation of the created device, it is possible to do without cooling. But during operation, the inductor becomes very hot, and scale on copper can not only drastically reduce the efficiency of the device, but also lead to a complete loss of its performance. It is impossible to make an inductor with cooling on your own, so it will need to be replaced regularly. Forced air cooling should not be used, as the case of a fan placed close to the coil will “attract” EMF to itself, which will lead to overheating and a decrease in the efficiency of the furnace.

The problem of induction heating of workpieces made of magnetic materials

If the inverter for induction heating is not a self-oscillator, does not have a self-tuning circuit (PLL) and operates from an external master oscillator (at a frequency close to the resonant frequency of the "inductor - compensating capacitor bank" oscillatory circuit). At the moment a workpiece made of magnetic material is introduced into the inductor (if the workpiece dimensions are large enough and commensurate with the dimensions of the inductor), the inductance of the inductor increases sharply, which leads to an abrupt decrease in the natural resonant frequency of the oscillatory circuit and its deviation from the frequency of the master oscillator. The circuit goes out of resonance with the master oscillator, which leads to an increase in its resistance and an abrupt decrease in the power transmitted to the workpiece. If the power of the unit is controlled by an external power supply, then the natural reaction of the operator is to increase the supply voltage of the unit. When the workpiece is heated to the Curie point, its magnetic properties disappear, the natural frequency of the oscillatory circuit returns back to the frequency of the master oscillator. The resistance of the circuit decreases sharply, the current consumption increases sharply. If the operator does not have time to remove the increased supply voltage, the unit overheats and fails.
If the installation is equipped with an automatic control system, then the control system should monitor the transition through the Curie point and automatically reduce the frequency of the master oscillator, adjusting it to resonance with the oscillatory circuit (or reduce the supplied power if the frequency change is unacceptable).

If non-magnetic materials are being heated, then the above does not matter. The introduction of a workpiece made of non-magnetic material into the inductor practically does not change the inductance of the inductor and does not shift the resonant frequency of the working oscillatory circuit, and there is no need for a control system.

If the dimensions of the workpiece are much smaller than the dimensions of the inductor, then it also does not greatly shift the resonance of the working circuit.

induction cookers

Main article: Induction cooker

Induction cooker- an electric kitchen stove that heats up metal utensils with induced eddy currents generated by a high-frequency magnetic field, with a frequency of 20-100 kHz.

Such a stove has a high efficiency compared to heating elements of electric stoves, since less heat is spent on heating the case, and besides, there is no acceleration and cooling period (when the energy generated, but not absorbed by the dishes, is wasted).

Induction Melting Furnaces

Main article: Induction crucible furnace

Induction (non-contact) melting furnaces - electric furnaces for melting and overheating metals, in which heating occurs due to eddy currents that occur in a metal crucible (and metal), or only in metal (if the crucible is not made of metal; this method of heating is more efficient if the crucible is poorly insulated).

It is used in foundry shops of factories, as well as in precision casting shops and repair shops of machine-building plants to obtain high quality steel castings. It is possible to melt non-ferrous metals (bronze, brass, aluminum) and their alloys in a graphite crucible. The induction furnace works on the principle of a transformer, in which the primary winding is a water-cooled inductor, the secondary and at the same time load is the metal in the crucible. The heating and melting of the metal occur due to the currents flowing in it, which arise under the influence of the electromagnetic field created by the inductor.

History of induction heating

The discovery of electromagnetic induction in 1831 belongs to Michael Faraday. When a conductor moves in the field of a magnet, an EMF is induced in it, just as when a magnet moves, the lines of force of which intersect the conducting circuit. The current in the circuit is called inductive. The inventions of many devices are based on the law of electromagnetic induction, including the determining ones - generators and transformers that generate and distribute electrical energy, which is the fundamental basis of the entire electrical industry.

In 1841, James Joule (and, independently of him, Emil Lenz) formulated a quantitative estimate of the thermal effect of electric current: “The power of heat released per unit volume of the medium during the flow of electric current is proportional to the product of the density of the electric current and the magnitude of the electric field strength” (Joule’s law - Lenz). The thermal effect of the induced current gave rise to the search for devices for non-contact heating of metals. The first experiments on heating steel using inductive current were made by E. Colby in the USA.

The first successfully operating so-called. The channel induction furnace for steel melting was built in 1900 by Benedicks Bultfabrik in Gysing, Sweden. In the respectable magazine of that time "THE ENGINEER" on July 8, 1904, the famous appeared, where the Swedish inventor engineer F. A. Kjellin talks about his development. The furnace was powered by a single-phase transformer. Melting was carried out in a crucible in the form of a ring, the metal in it represented the secondary winding of a transformer powered by a current of 50-60 Hz.

The first 78 kW furnace was put into operation on March 18, 1900 and proved to be very uneconomical, since the melting capacity was only 270 kg of steel per day. The next furnace was manufactured in November of the same year with a capacity of 58 kW and a capacity of 100 kg for steel. The furnace showed high profitability, the melting capacity was from 600 to 700 kg of steel per day. However, wear due to thermal fluctuations was at an unacceptable level, frequent lining changes reduced the resulting efficiency.

The inventor came to the conclusion that for maximum melting performance, it is necessary to leave a significant part of the melt during discharge, which avoids many problems, including lining wear. This method of smelting steel with a residue, which began to be called "bog", has survived to this day in some industries where large-capacity furnaces are used.

In May 1902, a significantly improved furnace with a capacity of 1800 kg was put into operation, the discharge was 1000-1100 kg, the balance was 700-800 kg, the power was 165 kW, the steel melting capacity could reach up to 4100 kg per day! Such an energy consumption result of 970 kWh/t impresses with its efficiency, which is not much inferior to the modern productivity of about 650 kWh/t. According to the inventor's calculations, out of a power consumption of 165 kW, 87.5 kW went into losses, the useful thermal power was 77.5 kW, and a very high overall efficiency of 47% was obtained. Profitability is explained by the ring design of the crucible, which made it possible to make a multi-turn inductor with low current and high voltage - 3000 V. Modern furnaces with a cylindrical crucible are much more compact, require less capital investment, are easier to operate, equipped with many improvements over a hundred years of their development, but the efficiency is increased insignificant. True, the inventor in his publication ignored the fact that electricity is paid not for active power, but for full power, which at a frequency of 50-60 Hz is approximately twice as high as active power. And in modern furnaces, reactive power is compensated by a capacitor bank.

With his invention, the engineer F. A. Kjellin laid the foundation for the development of industrial channel furnaces for melting non-ferrous metals and steel in the industrial countries of Europe and America. The transition from 50-60 Hz channel furnaces to modern high-frequency crucible furnaces lasted from 1900 to 1940.

Heating system

In order to make an induction heater, knowledgeable craftsmen use a simple welding inverter that converts direct voltage to alternating voltage. For such cases, a cable with a cross section of 6-8 mm is used, but not standard for welding machines of 2.5 mm.

Such heating systems must necessarily be of a closed type, and control is automatic. For other safety, you need a pump that will circulate through the system, as well as an air bleed valve. Such a heater must be protected from wooden furniture, as well as from the floor and ceiling at least 1 meter.

Implementation at home

Induction heating has not yet sufficiently conquered the market due to the high cost of the heating system itself. So, for example, for industrial enterprises, such a system will cost 100,000 rubles, for domestic use - from 25,000 rubles. and higher. Therefore, the interest in circuits that allow you to create a home-made induction heater with your own hands is quite understandable.

heating induction boiler

Transformer based

The main element of the induction heating system with a transformer will be the device itself, which has a primary and secondary windings. Vortex flows will form in the primary winding and create an electromagnetic induction field. This field will affect the secondary, which is, in fact, an induction heater, physically implemented in the form of a heating boiler body. It is the secondary short-circuited winding that transfers energy to the coolant.

Secondary short-circuited winding of the transformer

The main elements of the induction heating installation are:

• core;
• winding;
• two types of insulation - thermal and electrical insulation.

The core is two ferrimagnetic tubes of different diameters with a wall thickness of at least 10 mm, welded into each other. A toroidal winding of copper wire is made along the outer tube. It is necessary to impose from 85 to 100 turns with an equal distance between the turns. Alternating current, changing in time, creates vortex flows in a closed circuit, which heat the core, and hence the coolant, by induction heating.

Using high frequency welding inverter

An induction heater can be created using a welding inverter, where the main components of the circuit are an alternator, an inductor and a heating element.

The generator is used to convert the standard 50 Hz mains frequency into a higher frequency current. This modulated current is applied to a cylindrical inductor, where copper wire is used as a winding.

Copper wire for winding

The coil creates an alternating magnetic field, the vector of which changes with the frequency set by the generator. The created eddy currents, induced by the magnetic field, heat the metal element, which transfers energy to the coolant. Thus, another do-it-yourself induction heating scheme is implemented.

A heating element can also be created with your own hands from a cut metal wire about 5 mm long and a piece of a polymer pipe into which the metal is placed. When installing valves at the top and bottom of the pipe, check the filling density - there should be no free space. According to the scheme, about 100 turns of copper wiring are superimposed on top of the pipe, which is the inductor connected to the generator terminals. Induction heating of copper wire occurs due to eddy currents generated by an alternating magnetic field.

Note: Do-it-yourself induction heaters can be made according to any scheme, the main thing to remember is that it is important to carry out reliable thermal insulation, otherwise the efficiency of the heating system will drop significantly. .

Advantages and disadvantages of the device

The “pluses” of the vortex induction heater are numerous. This is a simple circuit for self-production, increased reliability, high efficiency, relatively low energy costs, long service life, low probability of breakdowns, etc.

The performance of the device can be significant; units of this type are successfully used in the metallurgical industry. In terms of the rate of heating of the coolant, devices of this type confidently compete with traditional electric boilers, the water temperature in the system quickly reaches the required level.

During the operation of the induction boiler, the heater vibrates slightly. This vibration shakes off limescale and other possible contaminants from the walls of the metal pipe, so such a device rarely needs to be cleaned. Of course, the heating system must be protected from these contaminants with a mechanical filter.

The induction coil heats the metal (pipe or pieces of wire) placed inside it using high frequency eddy currents, contact is not necessary

Constant contact with water also minimizes the likelihood of heater burnout, which is a fairly common problem for traditional boilers with heating elements. Despite the vibration, the boiler operates exceptionally quietly; additional noise insulation at the installation site of the device is not required.

Induction boilers are also good because they almost never leak, if only the installation of the system is done correctly. The absence of leaks is due to the non-contact method of transferring thermal energy to the heater. The coolant using the technology described above can be heated almost to a vapor state.

This provides sufficient thermal convection to stimulate efficient movement of the coolant through the pipes. In most cases, the heating system will not have to be equipped with a circulation pump, although it all depends on the features and layout of a particular heating system.

Sometimes a circulation pump is needed. Installing the device is relatively easy. Although this will require some skills in the installation of electrical appliances and heating pipes.

But this convenient and reliable device has a number of shortcomings, which should also be considered. For example, the boiler heats not only the coolant, but also the entire workspace surrounding it. It is necessary to allocate a separate room for such a unit and remove all foreign objects from it. For a person, a long stay in the immediate vicinity of a working boiler can also be unsafe.

Induction heaters require electricity to operate. Both homemade and factory-made equipment are connected to a household AC mains.

The device requires electricity to operate. In areas where there is no free access to this benefit of civilization, the induction boiler will be useless. Yes, and where there are frequent power outages, it will demonstrate low efficiency.

An explosion may occur if the instrument is not handled with care.

If the coolant is overheated, it will turn into steam. As a result, the pressure in the system will increase dramatically, which the pipes simply cannot withstand, they will burst. Therefore, for the normal operation of the system, the device should be equipped with at least a pressure gauge, and even better - an emergency shutdown device, a thermostat, etc.

All this can significantly increase the cost of a homemade induction boiler. Although the device is considered to be practically silent, this is not always the case. Some models, for various reasons, may still make some noise. For a self-made device, the likelihood of such an outcome increases.

In the design of both factory-made and home-made induction heaters, there are practically no wearing components. They last a long time and work flawlessly.

Homemade induction boilers

The simplest scheme of the device, which is assembled, consists of a piece of plastic pipe, into the cavity of which various metal elements are laid in order to create a core. It can be a thin stainless wire rolled into balls, chopped into small pieces of wire - wire rod with a diameter of 6-8 mm, or even a drill with a diameter corresponding to the internal size of the pipe. Outside, fiberglass sticks are glued to it, and a wire 1.5-1.7 mm thick is wound on them in glass insulation. The length of the wire is about 11 m. The manufacturing technology can be studied by watching the video:

Then a home-made induction heater was tested by filling it with water and connecting it to a factory-made ORION induction hob with a power of 2 kW instead of a standard inductor. The test results are shown in the following video:

Other masters recommend taking a low-power welding inverter as a source by connecting the terminals of the secondary winding to the coil terminals. If you carefully study the work done by the author, then the following conclusions arise:

• The author did a good job and his product, of course, works.
• No calculations were made for the thickness of the wire, the number and diameter of the turns of the coil. The winding parameters were taken by analogy with the hob, respectively, the induction water heater will turn out to be no higher than 2 kW.
• In the best case, a home-made unit will be able to heat water for two heating radiators of 1 kW each, this is enough to heat one room. In the worst case, the heating will be weak or disappear altogether, because the tests were carried out without a coolant flow.

It is difficult to draw more accurate conclusions due to the lack of information about further tests of the device. Another way to independently organize induction water heating for heating is shown in the following video:

A radiator welded from several metal pipes acts as an external core for eddy currents created by the coil of the same induction hob. The conclusions are as follows:

• The thermal power of the resulting heater does not exceed the electrical power of the panel.
• The number and size of the tubes were chosen at random, but provided sufficient surface for the transfer of heat generated from the eddy currents.
• This scheme of the induction heater proved to be successful for the specific case when the apartment is surrounded by the premises of other heated apartments. In addition, the author did not show the operation of the installation in the cold season with fixing the air temperature in the rooms.

To confirm the conclusions made, it is proposed to watch a video where the author tried to use a similar heater in a separate insulated building:

Operating principle

Induction heating is the heating of materials by electric currents that are induced by an alternating magnetic field. Therefore, this is the heating of products made of conductive materials (conductors) by the magnetic field of inductors (sources of an alternating magnetic field).

Induction heating is carried out as follows. An electrically conductive (metal, graphite) workpiece is placed in the so-called inductor, which is one or more turns of wire (most often copper). Powerful currents of various frequencies (from tens of Hz to several MHz) are induced in the inductor with the help of a special generator, as a result of which an electromagnetic field arises around the inductor. The electromagnetic field induces eddy currents in the workpiece. Eddy currents heat the workpiece under the action of Joule heat.

The inductor-blank system is a coreless transformer in which the inductor is the primary winding. The workpiece is, as it were, a secondary winding, short-circuited. The magnetic flux between the windings closes in air.

At a high frequency, eddy currents are displaced by the magnetic field formed by them into thin surface layers of the workpiece Δ ​​(skin effect), as a result of which their density increases sharply and the workpiece is heated. The underlying layers of the metal are heated due to thermal conductivity. It is not the current that is important, but the high current density. In the skin layer Δ, the current density increases in e times relative to the current density in the workpiece, while 86.4% of the heat from the total heat release is released in the skin layer. The depth of the skin layer depends on the radiation frequency: the higher the frequency, the thinner the skin layer. It also depends on the relative magnetic permeability μ of the workpiece material.

For iron, cobalt, nickel and magnetic alloys at temperatures below the  Curie point, μ has a value from several hundreds to tens of thousands. For other materials (melts, non-ferrous metals, liquid low-melting eutectics, graphite, electrically conductive ceramics, etc.), μ is approximately equal to one.

Formula for calculating skin depth in mm:

Δ=103ρμπf(\displaystyle \Delta =10^(3)(\sqrt (\frac (\rho )(\mu \pi f)))),

where ρ - specific electrical resistance of the workpiece material at the processing temperature, Ohm m, f- frequency of the electromagnetic field generated by the inductor, Hz.

For example, at a frequency of 2 MHz, the skin depth for copper is about 0.047 mm, for iron ≈ 0.0001 mm.

The inductor gets very hot during operation, as it absorbs its own radiation. In addition, it absorbs heat radiation from a hot workpiece. They make inductors from copper tubes cooled by water. Water is supplied by suction - this ensures safety in case of a burn or other depressurization of the inductor.

Operating principle

The melting unit of the induction furnace is used to heat a wide variety of metals and alloys. The classic design consists of the following elements:

1. Drain pump.
2. Water cooled inductor.
3. Frame in stainless steel or aluminium.
4. Contact area.
5. Hearth made of heat-resistant concrete.
6. Support with hydraulic cylinder and bearing unit.

The principle of operation is based on the creation of eddy induced Foucault currents. As a rule, during the operation of household appliances, such currents cause failures, but in this case they are used to heat the charge to the required temperature. Almost all electronics start to heat up during operation. This negative factor in the use of electricity is used to its full potential.

Device advantages

The induction melting furnace has been used relatively recently. Famous open-hearth furnaces, blast furnaces and other types of equipment are installed at production sites. Such a metal melting furnace has the following advantages:

1. The application of the principle of induction allows you to make the equipment compact. That is why there are no problems with their placement in small rooms. An example is blast furnaces, which can only be installed in prepared premises.
2. The results of the conducted studies indicate that the efficiency is almost 100%.
3. High melting speed. The high efficiency index determines that it takes much less time to heat up the metal when compared with other furnaces.
4. Some furnaces during melting can lead to a change in the chemical composition of the metal. Induction takes first place in terms of melt purity. The generated Foucault currents heat the workpiece from the inside, which eliminates the possibility of getting into the composition of various impurities.

It is the latter advantage that determines the spread of the induction furnace in jewelry, since even a small concentration of foreign impurities can adversely affect the result.

Due to the fact that M. Faraday discovered the phenomenon of electromagnetic induction back in 1831, the world saw a large number of devices that heat water and other media.

Because this discovery was realized, people use it daily in everyday life:

• Electric kettle with disc heater for water heating;
• Multicooker oven;
• induction hob;
• Microwaves (stove);
• Heater;
• Heating column.

Also, the opening is applied to the extruder (not mechanical). Previously, it was widely used in metallurgy and other industries related to metal processing. The factory inductive boiler operates on the principle of the action of eddy currents on a special core located in the inside of the coil. Foucault eddy currents are superficial, so it is better to take a hollow metal pipe as a core, through which the coolant element passes.

The occurrence of electric currents occurs due to the supply of an alternating voltage to the winding, causing the appearance of an alternating electric magnetic field, which changes the potentials 50 times / sec. at standard industrial frequency of 50 Hz.

At the same time, the Ruhmkorff induction coil is designed in such a way that it can be connected directly to the AC mains. In production, high-frequency electric currents are used for such heating - up to 1 MHz, so it is quite difficult to achieve the operation of the device at 50 Hz. The thickness of the wire and the number of winding turns used by the device are calculated separately for each unit according to a special method for the required heat output. A home-made, powerful unit must function efficiently, quickly heat the water flowing through the pipe and not heat up.

Organizations invest heavily in the development and implementation of such products, so:

• All tasks are solved successfully;
• The efficiency of the heating device is 98%;
• Functions without interruption.

In addition to the highest efficiency, one cannot but attract the speed with which the heating of the medium passing through the core takes place. On fig. a scheme of functioning of an induction water heater created at the plant is proposed. Such a scheme has a VIN brand unit, which is produced by the Izhevsk plant.

How long the unit will work depends solely on how tight the case is and the insulation of the turns of the wire is not damaged, and this is a rather significant period, according to the manufacturer - up to 30 years.

For all these advantages, which the device has 100%, you need to pay a lot of money, an inductor, magnetic water heater is the most expensive of all types of heating installations. Therefore, many craftsmen prefer to assemble an ultra-economical unit for heating on their own.

Rules for the manufacture of equipment independently

In order for the induction heating installation to work correctly, the current for such a product must correspond to the power (it must be at least 15 amperes, if required, it can be more).

• The wire should be cut into pieces no more than five centimeters. This is necessary for efficient heating in a high-frequency field.
• The body must be no smaller in diameter than the prepared wire, and have thick walls.
• For attachment to the heating network, a special adapter is attached to one side of the structure.
• A net should be placed at the bottom of the pipe to prevent the wire from falling out.
• The latter is needed in such quantity that it fills the entire internal space.
• The design is closed, an adapter is placed.
• Then a coil is constructed from this pipe. To do this, wrap it with already prepared wire. The number of turns must be observed: minimum 80, maximum 90.
• After connecting to the heating system, water is poured into the apparatus. The coil is connected to the prepared inverter.
• A water pump is installed.
• The temperature controller is installed.

Thus, the calculation of induction heating will depend on the following parameters: length, diameter, temperature and processing time

Pay attention to the inductance of the tires leading to the inductor, which can be much higher than the inductor itself.

High precision induction heating

Such heating has the simplest principle, since it is non-contact. High-frequency pulsed heating makes it possible to achieve the highest temperature conditions, at which it is possible to process the most difficult metals in melting. To perform induction heating, it is necessary to create the required voltage of 12V (volts) and the frequency of the inductance in electromagnetic fields.

This can be done in a special device - an inductor. It is powered by electricity from an industrial power supply at 50 Hz.

It is possible to use individual power supplies for this - converters / generators. The simplest device for a low-frequency device is a spiral (insulated conductor), which can be placed in the inside of a metal pipe or wound around it. The going currents heat the tube, which, in the future, gives heat to the living room.

The use of induction heating at minimum frequencies is not a frequent phenomenon. The most common processing of metals at a higher or medium frequency. Such devices are distinguished by the fact that the magnetic wave goes to the surface, where it decays. Energy is converted into heat. For the effect to be better, both components must have a similar shape. Where is heat applied?

Today, the use of high-frequency heating is widespread:

• For melting metals, and their soldering by a non-contact method;
• Engineering industry;
• Jewelry business;
• Creation of small elements (boards) that can be damaged when using other techniques;
• Hardening of surfaces of parts, different configurations;
• Heat treatment of parts;
• Medical practice (disinfection of devices/instruments).

Heating can solve many problems.

What is induction heating

How an induction water heater works.

The induction device works on the energy generated by the electromagnetic field. It is absorbed by the heat carrier, then giving it to the premises:

1. An inductor creates an electromagnetic field in such a water heater. This is a multi-turn cylindrical wire coil.
2. Flowing through it, an alternating electric current around the coil generates a magnetic field.
3. Its lines are placed perpendicular to the electromagnetic flux vector. When moved, they recreate a closed circle.
4. The eddy currents created by alternating current convert the energy of electricity into heat.

Thermal energy during induction heating is spent sparingly and at a low heating rate. Thanks to this, the induction device brings the water for the heating system to a high temperature in a short time period.

Device Features

The electric current is connected to the primary winding.

Induction heating is carried out using a transformer. It consists of a pair of windings:

• external (primary);
• short-circuited internal (secondary).

Eddy currents occur in the deep part of the transformer. They redirect the emerging electromagnetic field to the secondary circuit. He simultaneously performs the function of the body and acts as a heating element for water.

With an increase in the density of vortex flows directed to the core, it first heats up itself, then the entire thermal element.

To supply cool water and remove the prepared coolant to the heating system, the induction heater is equipped with a pair of pipes:

1. The lower one is installed on the inlet of the water supply.
2. The upper branch pipe - to the supply section of the heating system.

What elements does the device consist of, and how does it work

The induction water heater consists of the following structural elements:

A photo	Structural node
	Inductor. It consists of many coils of copper wire. They generate an electromagnetic field.
	A heating element. This is a pipe made of metal or steel wire trimmings placed inside the inductor.
	Generator. It transforms household electricity into high-frequency electric current. The role of the generator can be played by an inverter from the welding machine.

The scheme of operation of the heating system with an induction water heater.

When all components of the device interact, heat energy is generated and transferred to water. The scheme of operation of the unit is as follows:

1. The generator produces a high-frequency electric current. He then passes it on to an induction coil.
2. She, having perceived the current, transforms it into an electric magnetic field.
3. The heater, located inside the coil, is heated by the action of vortex flows that appear due to a change in the magnetic field vector.
4. The water circulating inside the element is heated by it. Then it enters the heating system.

Advantages and disadvantages of the induction heating method

The unit is compact and takes up little space.

Induction heaters are endowed with such advantages:

• high level of efficiency;
• do not need frequent maintenance;
• they take up little free space;
• due to vibrations of the magnetic field, scale does not settle inside them;
• devices are silent;
• they are safe;
• due to the tightness of the housing, there are no leaks;
• the operation of the heater is fully automated;
• the unit is environmentally friendly, does not emit soot, soot, carbon monoxide, etc.

In the photo - a factory water-heating induction boiler.

The main disadvantage of the device is the high cost of its factory models..

However, this disadvantage can be leveled if you assemble an induction heater with your own hands. The unit is mounted from easily accessible elements, their price is low.

Benefits of using all types of induction heaters

The induction heater has undoubted advantages and is the leader among all types of devices. This advantage consists of the following:

• It consumes less electricity and does not pollute the environment.
• Easy to operate, it provides high quality work and allows you to control the process.
• Heating through the walls of the chamber provides a special purity and the ability to obtain ultra-pure alloys, while melting can be carried out in different atmospheres, including inert gases and in vacuum.
• With its help uniform heating of details of any form or selective heating is possible.
• Finally, induction heaters are universal, which allows them to be used everywhere, replacing outdated energy-consuming and inefficient installations.

When making an induction heater with your own hands, you need to worry about the safety of the device. To do this, it is necessary to be guided by the following rules that increase the level of reliability of the overall system:

1. A safety valve should be inserted into the upper tee to relieve excess pressure. Otherwise, if the circulation pump fails, the core will simply burst under the influence of steam. As a rule, the scheme of a simple induction heater provides for such moments.
2. The inverter is connected to the network only through the RCD. This device works in critical situations and will help to avoid a short circuit.
3. The welding inverter must be grounded by leading the cable to a special metal circuit mounted in the ground behind the walls of the structure.
4. The body of the induction heater must be placed at a height of 80 cm above the floor. Moreover, the distance to the ceiling should be at least 70 cm, and to other pieces of furniture - more than 30 cm.
5. An induction heater is a source of a very strong electromagnetic field, so this installation should be kept away from living quarters and enclosures with pets.

Diagram of an induction heater

Thanks to the discovery by M. Faraday in 1831 of the phenomenon of electromagnetic induction, many devices have appeared in our modern life that heat water and other media. Every day we use an electric kettle with a disc heater, a multicooker, an induction hob, since we managed to realize this discovery for everyday life only in our time. Previously, it was used in the metallurgical and other branches of the metalworking industry.

The factory induction boiler uses in its work the principle of the action of eddy currents on a metal core placed inside the coil. Foucault eddy currents are of a surface nature, so it makes sense to use a hollow metal pipe as a core, through which a heated coolant flows.

The principle of operation of the induction heater

The occurrence of currents is due to the supply of an alternating electrical voltage to the winding, causing the appearance of an alternating electromagnetic field that changes potentials 50 times per second at a normal industrial frequency of 50 Hz. At the same time, the induction coil is designed in such a way that it can be connected directly to the AC mains. In industry, high-frequency currents are used for such heating - up to 1 MHz, so it is not easy to achieve device operation at a frequency of 50 Hz.

The thickness of the copper wire and the number of winding turns used by induction water heaters are calculated separately for each unit using a special method for the required heat output. The product must work efficiently, quickly heat the water flowing through the pipe and at the same time not overheat. Enterprises invest a lot of money in the development and implementation of such products, so all tasks are solved successfully, and the heater efficiency indicator is 98%.

In addition to high efficiency, the speed at which the medium flowing through the core is heated is especially attractive. The figure shows a diagram of the operation of an induction heater made in the factory. Such a scheme is used in units of the well-known trademark "VIN", produced by the Izhevsk plant.

Heater operation diagram

The durability of the heat generator depends only on the tightness of the case and the integrity of the insulation of the turns of the wire, and this turns out to be a rather long period, the manufacturers declare - up to 30 years. For all these advantages that these devices actually possess, you have to pay a lot of money, an induction water heater is the most expensive of all types of heating electrical installations. For this reason, some craftsmen took up the manufacture of a home-made device in order to use it in heating the house.

DIY manufacturing process

The following tools will be useful for work:

• welding inverter;
• welding generating current with a power of 15 amperes.

You will also need copper wire, which is wound around the core body. The device will act as an inductor. The wire contacts are connected to the inverter terminals so that no twists are formed. The piece of material needed to assemble the core must be the correct length. On average, the number of turns is 50, the diameter of the wire is 3 millimeters.

Copper wire of different diameters for winding

Now let's move on to the core. In his role will be a polymer pipe made of polyethylene. This type of plastic can withstand quite high temperatures. Core diameter - 50 millimeters, wall thickness - at least 3 mm. This part is used as a gauge on which a copper wire is wound, forming an inductor. Almost anyone can assemble the simplest induction water heater.

On the video you will see a way - how to independently organize induction heating of water for heating:

First option

The wire is cut into 50 mm segments, a plastic tube is filled with it. To prevent it from spilling out of the pipe, plug the ends with wire mesh. At the ends, adapters are placed from the pipe, in the place where the heater is connected.

A winding is wound on the body of the latter with copper wire. For this purpose, you need about 17 meters of wire: you need to make 90 turns, the pipe diameter is 60 millimeters. 3.14×60×90=17 m.

It is important to know! When checking the operation of the device, make sure that there is water (coolant) in it. Otherwise, the body of the device will quickly melt.
. The pipe crashes into the pipeline

The heater is connected to the inverter. It remains to fill the device with water and turn it on. Everything is ready!

The pipe crashes into the pipeline. The heater is connected to the inverter. It remains to fill the device with water and turn it on. Everything is ready!

Second option

This option is much easier. A straight section of a meter size is selected on the vertical part of the pipe. It should be carefully cleaned of paint using sandpaper. Further, this section of the pipe is covered with three layers of electrical fabric. An induction coil is wound with copper wire. The entire connection system is well insulated. Now you can connect the welding inverter and the assembly process is complete.

Induction coil wrapped with copper wire

Before you start making a water heater with your own hands, it is advisable to familiarize yourself with the characteristics of factory products and study their drawings. This will help to understand the initial data of home-made equipment and avoid possible errors.

Third option

To make the heater in this more complicated way, you need to use welding. To work, you still need a three-phase transformer. Two pipes must be welded into each other, which will act as a heater and a core. A winding is wound onto the body of the inductor. This increases the performance of the device, which has a compact size, which is very convenient for its use at home.

Winding on the body of the inductor

For water supply and drainage, 2 branch pipes are welded into the body of the inductor. In order not to lose heat and prevent possible current leakage, insulation must be made. It will eliminate the problems described above, and completely eliminate the appearance of noise during the operation of the boiler.

Depending on the design features, floor and desktop induction furnaces are distinguished. Regardless of which option was chosen, there are several basic rules for installation:

1. When the equipment is in operation, the power grid is subjected to a high load. In order to exclude the possibility of a short circuit due to wear of the insulation, high-quality grounding must be carried out during installation.
2. The design has a water cooling circuit, which eliminates the possibility of overheating of the main elements. That is why it is necessary to ensure a reliable rise in water.
3. If a desktop oven is being installed, then attention should be paid to the stability of the base used.
4. The metal melting furnace is a complex electrical appliance, the installation of which must follow all the manufacturer's recommendations. Particular attention is paid to the parameters of the power source, which must match the model of the device.
5. Do not forget that there should be quite a lot of free space around the stove. During operation, even a small melt in terms of volume and mass can accidentally splash out of the mold. At temperatures above 1000 degrees Celsius, it will cause irreparable damage to various materials, and may also cause a fire.

The device may become very hot during operation. That is why there should not be any flammable or explosive substances nearby. In addition, according to fire safety regulations, nearby should be installed fire shield.

Safety regulations

for heating systems that use induction heating, it is important to follow a few rules to avoid leaks, loss of efficiency, energy consumption, accidents. . Induction heating systems require a safety valve to release water and steam in case the pump fails.


To prevent failures in the operation of the electrical network, it is recommended to connect a do-it-yourself boiler with induction heating according to the proposed schemes to a separate supply line, the cable cross section of which will be at least 5 mm2

Ordinary wiring may not be able to withstand the required power consumption.

1. Induction heating systems require a safety valve to release water and steam in case the pump fails.
2. A manometer and an RCD are required for the safe operation of a do-it-yourself heating system.
3. The presence of grounding and electrical insulation of the entire induction heating system will prevent electric shock.
4. In order to avoid the harmful effects of the electromagnetic field on the human body, it is better to take such systems outside the residential area, where installation rules should be observed, according to which the induction heating device should be placed at a distance of 80 cm from horizontal (floor and ceiling) and 30 cm from vertical surfaces.
5. Before turning on the system, be sure to check the presence of the coolant.
6. To prevent malfunctions in the electrical network, it is recommended to connect a do-it-yourself induction heating boiler according to the proposed schemes to a separate supply line, the cable cross section of which will be at least 5 mm2. Ordinary wiring may not be able to withstand the required power consumption.

Creating sophisticated fixtures

It is more difficult to make an HDTV heating installation with your own hands, but it is subject to radio amateurs, because to collect it you will need a multivibrator circuit. The principle of operation is similar - eddy currents arising from the interaction of the metal filler in the center of the coil and its own highly magnetic field heat the surface.

Design of HDTV installations

Since even small coils produce a current of about 100 A, a resonating capacitance will need to be connected with them to balance the induction thrust. There are 2 types of working circuits for heating HDTV at 12 V:

• connected to mains power.

• targeted electrical;
• connected to mains power.

In the first case, a mini HDTV installation can be assembled in an hour. Even in the absence of a 220 V network, you can use such a generator anywhere, but if you have car batteries as power sources. Of course, it is not powerful enough to melt metal, but it is able to heat up to the high temperatures needed for fine work, such as heating knives and screwdrivers to blue. To create it, you need to purchase:

• field effect transistors BUZ11, IRFP460, IRFP240;
• car battery from 70 A / h;
• high voltage capacitors.

The current of the 11 A power supply is reduced to 6 A during the heating process due to the resistance of the metal, but the need for thick wires that can withstand a current of 11-12 A remains to avoid overheating.

The second circuit for an induction heating installation in a plastic case is more complex, based on the IR2153 driver, but it is more convenient to build a 100k resonance over the regulator using it. It is necessary to control the circuit through a network adapter with a voltage of 12 V or more. The power unit can be connected directly to the main network of 220 V using a diode bridge. The resonance frequency is 30 kHz. The following items will be required:

• ferrite core 10 mm and choke 20 turns;
• copper tube as an HDTV coil of 25 turns per mandrel 5–8 cm;
• capacitors 250 V.

Vortex heaters

A more powerful installation, capable of heating the bolts to yellow, can be assembled according to a simple scheme. But during operation, the heat generation will be quite large, so it is recommended to install radiators on transistors. You will also need a choke, which you can borrow from the power supply of any computer, and the following auxiliary materials:

• steel ferromagnetic wire;
• copper wire 1.5 mm;
• field-effect transistors and diodes for reverse voltage from 500 V;
• zener diodes with a power of 2-3 W with a calculation of 15 V;
• simple resistors.

Depending on the desired result, the winding of the wire on the copper base is from 10 to 30 turns. Next comes the assembly of the circuit and the preparation of the base coil of the heater from about 7 turns of 1.5 mm copper wire. It connects to the circuit and then to electricity.

Craftsmen familiar with welding and operating a three-phase transformer can further increase the efficiency of the device while reducing weight and size. To do this, it is necessary to weld the bases of two pipes, which will serve as both a core and a heater, and after winding, weld two pipes into the body to supply and remove the coolant.

Advantages and disadvantages

Having dealt with the principle of operation of the induction heater, you can consider its positive and negative sides. Given the high popularity of this type of heat generators, it can be assumed that it has much more advantages than disadvantages. Among the most significant advantages are:

• Simplicity of design.
• High rate of efficiency.
• Long service life.
• Small risk of damage to the device.
• Significant energy savings.

Since the performance indicator of an induction boiler is in a wide range, it is possible to choose a unit for a specific building heating system without any problems. These devices are able to quickly heat the coolant to a predetermined temperature, which has made them a worthy competitor to traditional boilers.

During operation of the induction heater, a slight vibration is observed, due to which scale is shaken off the pipes. As a result, the unit can be cleaned less frequently. Since the coolant is in constant contact with the heating element, the risks of its failure are relatively small.

Part 1. DIY INDUCTION BOILER - it's easy. Attachment for induction hob.

If no mistakes were made during the installation of the induction boiler, then leakage is practically excluded. This is due to the contactless transfer of heat energy to the heater. Using induction water heating technology allows you to bring it almost to a gaseous state. Thus, an efficient movement of water through the pipes is achieved, and in some situations it is even possible to dispense with the use of circulation pumping units.

Unfortunately, ideal devices do not exist today. Along with a large number of advantages, induction heaters also have a number of disadvantages. Since the unit requires electricity to operate, it will not be able to operate at maximum efficiency in regions with frequent power outages. When the coolant overheats, the pressure in the system increases sharply and the pipes can break. To avoid this, the induction heater must be equipped with an emergency shutdown device.

DIY induction heater

Working principle of induction heating

In the work of the induction heater, the energy of the electromagnetic field is used, which the heated object absorbs and converts into heat. To generate a magnetic field, an inductor is used, that is, a multi-turn cylindrical coil. Passing through this inductor, an alternating electric current creates an alternating magnetic field around the coil.

A homemade inverter heater allows you to heat up quickly and to very high temperatures. With the help of such devices, you can not only heat water, but even melt various metals.

If a heated object is placed inside or near the inductor, it will be pierced by the flux of the magnetic induction vector, which is constantly changing in time. In this case, an electric field arises, the lines of which are located perpendicular to the direction of the magnetic flux and move in a vicious circle. Thanks to these vortex flows, electrical energy is transformed into thermal energy and the object heats up.

Thus, the electrical energy of the inductor is transferred to the object without the use of contacts, as happens in resistance furnaces. As a result, thermal energy is spent more efficiently, and the heating rate increases markedly. This principle is widely used in the field of metal processing: its melting, forging, brazing, etc. With no less success, a vortex induction heater can be used to heat water.

High frequency induction heaters

The widest range of applications is for high-frequency induction heaters. The heaters are characterized by a high frequency of 30-100 kHz and a wide power range of 15-160 kW. The high-frequency type provides a small depth of heating, but this is enough to improve the chemical properties of the metal.

High frequency induction heaters are easy to operate and economical, while their efficiency can reach 95%. All types work continuously for a long time, and the two-block version (when the high-frequency transformer is placed in a separate block) allows round-the-clock operation. The heater has 28 types of protections, each of which is responsible for its own function. Example: control of water pressure in the cooling system.

• Induction heater 60 kW Perm
• Induction heater 65 kW Novosibirsk
• Induction heater 60 kW Krasnoyarsk
• Induction heater 60 kW Kaluga
• Induction heater 100 kW Novosibirsk
• Induction heater 120 kW Ekaterinburg
• Induction heater 160 kW Samara

Application:

• surface hardened gear
• shaft hardening
• crane wheel hardening
• heating parts before bending
• soldering of cutters, cutters, drill bits
• heating the workpiece during hot stamping
• bolt landing
• welding and surfacing of metals
• restoration of details.

Induction melting is a process widely used in ferrous and non-ferrous metallurgy. Melting in induction heating devices is often superior to fuel-fired melting in terms of energy efficiency, product quality and production flexibility. These pre-

modern electrical technologies

properties are due to the specific physical characteristics of induction furnaces.

During induction melting, a solid material is transferred to a liquid phase under the influence of an electromagnetic field. As in the case of induction heating, heat is generated in the melted material due to the Joule effect from the induced eddy currents. The primary current passing through the inductor creates an electromagnetic field. Regardless of whether the electromagnetic field is concentrated by magnetic circuits or not, the coupled inductor-load system can be represented as a transformer with a magnetic circuit or as an air transformer. The electrical efficiency of the system is highly dependent on the field-influencing characteristics of the ferromagnetic structural elements.

Along with electromagnetic and thermal phenomena, electrodynamic forces play an important role in the process of induction melting. These forces must be taken into account, especially in the case of melting in powerful induction furnaces. The interaction of induced electric currents in the melt with the resulting magnetic field causes a mechanical force (Lorentz force)

Pressure Melt flows

Rice. 7.21. The action of electromagnetic forces

For example, the force-induced turbulent motion of the melt is of great importance both for good heat transfer and for the mixing and adhesion of non-conductive particles in the melt.

There are two main types of induction furnaces: induction crucible furnaces (ITF) and induction channel furnaces (IKP). In ITP, the melted material is usually loaded in pieces into the crucible (Fig. 7.22). The inductor covers the crucible and the melted material. Due to the absence of a concentrating field of the magnetic circuit, the electromagnetic connection between

modern electrical technologies

inductor and loading strongly depends on the wall thickness of the ceramic crucible. To ensure high electrical efficiency, the insulation should be as thin as possible. On the other hand, the lining must be thick enough to withstand thermal stresses and

metal movement. Therefore, a compromise should be sought between the electrical and strength criteria.

Important characteristics of induction melting in IHF are the movement of the melt and the meniscus as a result of the action of electromagnetic forces. The movement of the melt provides both a uniform temperature distribution and a homogeneous chemical composition. The mixing effect at the melt surface reduces material losses during reloading of small batches and additives. Despite the use of cheap material, the reproduction of a melt of constant composition ensures high casting quality.

Depending on the size, the type of material to be melted and the field of application, ITPs operate at an industrial frequency (50 Hz) or medium

modern electrical technologies

them at frequencies up to 1000 Hz. The latter are becoming increasingly important due to their high efficiency in the smelting of cast iron and aluminium. Since the movement of the melt at constant power is attenuated with increasing frequency, higher specific powers become available at higher frequencies and, as a result, greater productivity. Due to the higher power, the melting time is shortened, which leads to an increase in the efficiency of the process (compared to furnaces operating at industrial frequency). Taking into account other technological advantages, such as flexibility in changing the materials being smelted, medium frequency IHFs are designed as the powerful melting units that currently dominate the iron foundry. Modern high-power medium-frequency ITPs for iron smelting have a capacity of up to 12 tons and a power of up to 10 MW. Industrial frequency ITPs are designed for larger capacities than medium-frequency ones, up to 150 tons for iron smelting. Intensive mixing of the bath is of particular importance in the smelting of homogeneous alloys, such as brass, so industrial frequency ITPs are widely used in this area. Along with the use of crucible furnaces for melting, they are also currently used for holding liquid metal before pouring.

In accordance with the energy balance of ITP (Fig. 7.23), the level of electrical efficiency for almost all types of furnaces is about 0.8. Approximately 20% of the original energy is lost in the inductor in the form of Joe - heat. The ratio of heat losses through the walls of the crucible to the electrical energy induced in the melt reaches 10%, so the total efficiency of the furnace is about 0.7.

The second widespread type of induction furnaces are ICP. They are used for casting, holding and, especially, melting in ferrous and non-ferrous metallurgy. The ICP generally consists of a ceramic bath and one or more induction units (Fig. 7.24). AT

principle, the induction unit can be represented as a transform-

The operating principle of the ICP requires a permanently closed secondary loop, so these furnaces operate with the liquid residue of the melt. Useful heat is generated mainly in the channel having a small cross section. The circulation of the melt under the action of electromagnetic and thermal forces ensures sufficient heat transfer to the bulk of the melt in the bath. Until now, ICPs have been designed for industrial frequency, but research work is also being carried out for higher frequencies. Thanks to the compact design of the furnace and the very good electromagnetic coupling, its electrical efficiency reaches 95%, and the overall efficiency reaches 80% and even 90%, depending on the material being melted.

In accordance with the technological conditions in different areas of application of ICP, different designs of induction channels are required. Single-channel furnaces are mainly used for holding and casting,

modern electrical technologies

rarer steel melting at installed capacities up to 3 MW. For melting and soaking non-ferrous metals, two-channel designs are preferred for better energy utilization. In aluminum smelters, the channels are straight for easy cleaning.

The production of aluminium, copper, brass and their alloys is the main field of application of the ICP. Today, the most powerful ICPs with a capacity of

up to 70 tons and power up to 3 MW are used for aluminum smelting. Along with high electrical efficiency in aluminum production, low melt losses are very important, which predetermines the choice of ICP.

Promising applications of induction melting technology are the production of high purity metals such as titanium and its alloys in cold crucible induction furnaces and the melting of ceramics such as zirconium silicate and zirconium oxide.

When melting in induction furnaces, the advantages of induction heating are clearly manifested, such as high energy density and productivity, homogenization of the melt due to stirring, accurate

modern electrical technologies

energy and temperature control, as well as ease of automatic process control, ease of manual control and great flexibility. High electrical and thermal efficiencies, combined with low melt losses and therefore savings in raw materials, result in low specific energy consumption and environmental competitiveness.

The superiority of induction melting devices over fuel ones is constantly increasing due to practical research, supported by numerical methods for solving electromagnetic and hydrodynamic problems. As an example, we can note the internal coating with copper strips of the steel casing of the ICP for copper melting. The reduction of losses from eddy currents increased the efficiency of the furnace by 8%, and it reached 92%.

Further improvement in the economics of induction melting is possible through the application of modern control technologies such as tandem or dual feed control. Two tandem ITPs have one power source, and while melting is in progress in one, the molten metal is held in the other for pouring. Switching the power source from one oven to another increases its utilization. A further development of this principle is dual feed control (Fig. 7.25), which ensures continuous simultaneous operation of furnaces without switching using special process control automation. It should also be noted that an integral part of the smelting economics is the compensation of the total reactive power.

In conclusion, to demonstrate the advantages of energy- and material-saving induction technology, fuel and electrothermal methods of aluminum smelting can be compared. Rice. 7.26 shows a significant reduction in energy consumption per ton of aluminum when smelting in

Chapter 7

□ loss of metal; Shch melting

modern electrical technologies

induction channel furnace with a capacity of 50 tons. The final energy consumed is reduced by about 60%, and the primary energy by 20%. At the same time, CO2 emissions are significantly reduced. (All calculations are based on typical German energy conversion and CO2 emissions from mixed power plants). The results obtained emphasize the special effect of metal losses during melting associated with its oxidation. Their compensation requires a large additional expenditure of energy. It is noteworthy that in the production of copper, metal losses during melting are also large and should be taken into account when choosing one or another melting technology.

Induction furnaces are widely used in the metallurgical industry. Such ovens are often made independently. To do this, you need to know their principle of operation and design features. The principle of operation of such furnaces was known two centuries ago.

Induction furnaces are capable of solving the following tasks:

• Metal melting.
• Heat treatment of metal parts.
• Purification of precious metals.

Such functions are available in industrial furnaces. For domestic conditions and space heating, there are stoves of a special design.

Operating principle

The work of an induction furnace is to heat materials by using the properties of eddy currents. To create such currents, a special inductor is used, which consists of an inductor with several turns of wire of a large cross section.

The AC power supply is connected to the inductor. In the inductor, alternating current creates a magnetic field that changes with the frequency of the network, and permeates the interior of the inductor. When a material is placed in this space, eddy currents arise in it, heating it.

The water in the working inductor heats up and boils, and the metal begins to melt when the appropriate temperature is reached. It is conditionally possible to divide induction furnaces into types:

• Furnaces with a magnetic core.
• Without magnetic circuit.

The first type of furnace contains an inductor enclosed in metal, which creates a special effect that increases the magnetic field density, so heating is carried out efficiently and quickly. In furnaces without a magnetic circuit, the inductor is located outside.

Types and features of furnaces

Induction furnaces can be divided into types that have their own characteristics of work and distinctive features. Some are used for work in industry, others are used in everyday life, for cooking.

Vacuum induction furnaces

This furnace is designed for melting and casting alloys by induction. It consists of a hermetically sealed chamber containing a crucible induction furnace with a mold.

In a vacuum, perfect metallurgical processes can be ensured and high-quality castings can be obtained. Currently, vacuum production has switched to new technological processes from continuous chains in a vacuum environment, which makes it possible to create new products and reduce production costs.

Advantages of vacuum melting

• Liquid metal can be kept in vacuum for a long time.
• Increased degassing of metals.
• During the melting process, it is possible to reload the furnace and influence the refining and deoxidation process at any time.
• Possibility of continuous monitoring and adjustment of the temperature of the alloy and its chemical composition during operation.
• High purity castings.
• Fast heating and melting speed.
• Increased homogeneity of the alloy due to high-quality mixing.
• Any form of raw material.
• Ecological cleanliness and economy.

The principle of operation of a vacuum furnace is that in a crucible in a vacuum, a high-frequency inductor is used to melt a solid charge and purify the liquid metal. The vacuum is created by pumping air out with pumps. Vacuum melting achieves a large reduction in hydrogen and nitrogen.

Channel induction furnaces

Electromagnetic core furnaces (channel) are widely used in foundries for non-ferrous and ferrous metals as holding furnaces, mixers.

1 - Bath
2 - Channel
3 - Magnetic core
4 - Primary coil

An alternating magnetic flux passes through the magnetic circuit, the contour of the channel in the form of a ring of liquid metal. An electric current is excited in the ring, which heats up the liquid metal. The magnetic flux is generated by the primary winding, powered by alternating current.

To enhance the magnetic flux, a closed magnetic circuit is used, which is made of transformer steel. The space of the furnace is connected by two holes to the channel, therefore, when filling the furnace with liquid metal, a closed circuit is created. The furnace will not be able to work without a closed circuit. In such cases, the resistance of the circuit is large, and a small current flows in it, which is called the no-load current.

Due to overheating of the metal and the action of the magnetic field, which tends to push the metal out of the channel, the liquid metal in the channel is constantly moving. Since the metal in the channel is heated higher than in the furnace bath, the metal constantly rises into the bath, from which metal with a lower temperature enters.

If the metal is drained below the permissible norm, then the liquid metal will be ejected from the channel by electrodynamic force. As a result, the oven will spontaneously turn off and the electrical circuit will break. To avoid such cases, the furnaces leave a certain amount of metal in liquid form. They call it the swamp.

Channel furnaces are divided into:

• Melting furnaces.
• Mixers.
• Distribution ovens.

To accumulate a certain amount of liquid metal, averaging its chemical composition and exposure, use mixers. The volume of the mixer is calculated equal to at least twice the hourly output of the furnace.

Channel furnaces are divided into classes according to the location of the channels:

• Vertical.
• Horizontal.

According to the shape of the working chamber:

• Drum induction furnaces.
• Cylindrical induction furnaces.

The drum furnace is made in the form of a steel welded cylinder with two walls at the ends. Drive rollers are used to rotate the furnace. In order to rotate the furnace, it is necessary to turn on the electric motor drive with two speeds and a chain drive. The engine has plate brakes.

On the end walls there is a siphon for pouring metal. There are openings for loading additives and removing slags. There is also a channel for issuing metal. The channel block consists of a furnace inductor with V-shaped channels made in the lining using templates. At the first heat, these templates are melted. The winding and the core are cooled by air, the body of the block is cooled by water.

If the channel furnace has a different shape, then the metal is dispensed by tilting the bath with hydraulic cylinders. Sometimes the metal is squeezed out by excess gas pressure.

Advantages of channel ovens

• Low power consumption due to low heat loss of the bath.
• Increased electrical efficiency of the inductor.
• Low cost.

Disadvantages of channel ovens

• The difficulty of adjusting the chemical composition of the metal, since the presence of liquid metal left in the furnace creates difficulties in the transition from one composition to another.
• The low speed of movement of the metal in the furnace reduces the possibility of melting technology.

Design features

The frame of the furnace is made of low carbon steel sheet with a thickness of 30 to 70 mm. At the bottom of the frame there are windows with attached inductors. The inductor is made in the form of a steel case, a primary coil, a magnetic circuit and a lining. Its body is made detachable, and the parts are insulated with gaskets so that the parts of the body do not create a closed loop. Otherwise, eddy current will be generated.

The magnetic circuit is made of plates of special electrical steel 0.5 mm. The plates are isolated from each other to reduce losses from eddy currents.

The coil is made of a copper conductor with a cross section depending on the load current and the cooling method. With air cooling, the allowable current is 4 amperes per mm 2, with water cooling, the allowable current is 20 amperes per mm 2. A screen is mounted between the lining and the coil, which is cooled by water. The screen is made of magnetic steel or copper. To remove heat from the coil, a fan is mounted. To obtain the exact dimensions of the channel, a template is used. It is made in the form of a hollow steel casting. The template is placed in the inductor until it is filled with a refractory mass. It is in the inductor during heating and drying of the lining.

Wet and dry refractory masses are used for lining. Wet masses are used in the form of stuffing or filling materials. Pouring concrete is used for complex inductor shapes, if it is impossible to compact the mass throughout the entire volume of the inductor.

The inductor is filled with such a mass and compacted with vibrators. Dry masses are compacted with high-frequency vibrators, ramming masses are compacted with pneumatic rammers. If cast iron is smelted in the furnace, then the lining is made of magnesium oxide. The quality of the lining is determined by the temperature of the cooling water. The most effective method of checking the lining is to check the value of inductive and active resistance. These measurements are carried out using control devices.

The electrical equipment of the furnace includes:

• Transformer.
• Capacitor bank to compensate for electrical energy losses.
• Choke for connecting a 1-phase inductor to a 3-phase network.
• Control boards.
• Power cables.

In order for the furnace to function normally, it is connected to a 10 kilovolt power supply, which has 10 voltage steps on the secondary winding to adjust the power of the furnace.

Lining stuffing materials contain:

• 48% dry quartz.
• 1.8% boric acid, sifted through a fine sieve with 0.5 mm cells.

The mass for lining is prepared in dry form using a mixer, and then sieved through a sieve. The prepared mixture should not be stored for more than 15 hours after preparation.

The lining of the crucible is produced by sealing with vibrators. Electric vibrators are used for lining large furnaces. The vibrators are immersed in the template space and the mass is compacted through the walls. During compaction, the vibrator is moved by a crane and rotated vertically.

Crucible induction furnaces

The main components of a crucible furnace are an inductor and a generator. For the manufacture of the inductor, a copper tube is used in the form of wound 8-10 turns. Forms of inductors can be of various types.

This type of oven is the most common. There is no core in the design of the furnace. A common form of the furnace is a cylinder made of fire-resistant material. The crucible is located in the cavity of the inductor. AC power is supplied to it.

Advantages of crucible furnaces

• Energy is released when material is loaded into the oven, so auxiliary heating elements are not needed.
• High homogeneity of multicomponent alloys is achieved.
• In the furnace, it is possible to create a reduction, oxidation reaction, regardless of the pressure.
• High performance furnaces due to increased power density at any frequency.
• Breaks in the melting of the metal do not affect the efficiency of work, since a lot of electricity is not required for heating.
• The possibility of any settings and simple operation with the possibility of automation.
• There are no local overheating, the temperature is equalized throughout the volume of the bath.
• Rapid melting to create quality alloys with good uniformity.
• Environmental Safety. The external environment is not exposed to any harmful effects of the furnace. Melting also does not harm nature.

Disadvantages of crucible furnaces

• Low temperature of slag used for processing the melt mirror.
• Low resistance of the lining under sudden temperature changes.

Despite the existing shortcomings, crucible induction furnaces have gained great popularity in manufacturing and other areas.

Induction furnaces for space heating

Most often, such an oven is installed in the kitchen. In its design, the main part is a welding inverter. The design of the furnace is usually combined with a water heating boiler, which makes it possible to heat all rooms in the building. It is also possible to connect the hot water supply to the building.

The efficiency of such a device is small, however, often such equipment is still used for heating a house.

The design of the heating part of an induction boiler is similar to a transformer. The outer circuit is the windings of a kind of transformer that are connected to the network. The second internal circuit is a heat exchange device. It circulates the coolant. When the power is connected, the coil creates a variable. As a result, currents are induced inside the heat exchanger, which carry out its heating. The metal heats the coolant, which usually consists of water.

The operation of household induction cookers is based on the same principle, in which dishes made of a special material act as a secondary circuit. Such a stove is much more economical than conventional stoves due to the absence of heat loss.

The water heater of the boiler is equipped with control devices that make it possible to maintain the temperature of the heat carrier at a certain level.

Heating with electricity is an expensive pleasure. It cannot compete with solid fuels and gas, diesel fuel and liquefied gas. One of the methods to reduce costs is to install a heat accumulator, as well as connect the boiler at night, since at night there is most often a preferential charge for electricity.

In order to decide on the installation of an induction boiler for the home, it is necessary to get advice from professional specialists in heat engineering. An induction boiler has practically no advantages over a conventional boiler. The disadvantage is the high cost of the equipment. Ordinary boilers with heating elements are sold ready for installation, and an induction heater requires additional equipment and settings. Therefore, before purchasing such an induction boiler, it is necessary to make a careful economic calculation and planning.

Lining of induction furnaces

The lining process is necessary to ensure that the furnace body is protected from elevated temperatures. It makes it possible to significantly reduce heat loss, increase the efficiency of metal melting or material heating.

For lining, quartzite is used, which is a modification of silica. There are some requirements for lining materials.

Such a material should provide 3 zones of material states:

• Monolithic.
• Buffer.
• Intermediate.

Only the presence of three layers in the coating is able to protect the furnace casing. The lining is adversely affected by improper material placement, poor material quality and harsh furnace operating conditions.