DIY induction oven. Induction melting furnace

The induction furnace is no longer a new product - this invention has existed since the 19th century, but only in our time, with the development of technology and elemental base, is it finally beginning to enter everyday life everywhere. Previously, there were many questions about the intricacies of the operation of induction furnaces; not all physical processes were fully understood, and the units themselves had a lot of shortcomings and were used only in industry, mainly for melting metals.

Now, with the advent of powerful high-frequency transistors and cheap microcontrollers that have made breakthroughs in all areas of science and technology, truly effective induction stoves have appeared that can be freely used for household needs (cooking, heating water, heating) and even assembled with your own hands.

Physical basis and principle of operation of the furnace

Fig.1. Induction furnace diagram

Before choosing or making an induction heater, you should understand what it is. Recently, there has been a surge of interest in this topic, but few people have a complete understanding of the physics of magnetic waves. This has given rise to many misconceptions, myths and a lot of ineffective or unsafe homemade products. You can make an induction furnace with your own hands, but before that you should obtain at least basic knowledge.

The operating principle of an induction stove is based on the phenomenon of electromagnetic induction. The key element here is the inductor, which is a high-quality inductor. Induction furnaces are widely used for heating or melting electrically conductive materials, most often metals, due to the thermal effect of inducing an eddy electric current into them. The diagram presented above illustrates the structure of this furnace (Fig. 1).

Generator G produces a variable frequency voltage. Under the influence of its electromotive force, an alternating current I 1 flows in the inductor coil L. The inductor L together with the capacitor C represents an oscillatory circuit tuned to resonance with the frequency of the source G, due to which the efficiency of the furnace increases significantly.

In accordance with physical laws, an alternating magnetic field H appears in the space around the inductor L. This field can also exist in the air, but to improve the characteristics, special ferromagnetic cores that have better magnetic conductivity compared to air are sometimes used.

Magnetic field lines pass through an object W placed inside the inductor and induce a magnetic flux F in it. If the material from which the workpiece W is made is electrically conductive, an induced current I 2 appears in it, closing inside and forming vortex induction flows. In accordance with the law of the thermal effect of electricity, eddy currents heat up the object W.

Making an inductive heater

An induction furnace consists of two main functional blocks: an inductor (heating induction coil) and a generator (AC voltage source). The inductor is a bare copper tube, rolled into a spiral (Fig. 2).

To make a furnace with a power of no more than 3 kW with your own hands, the inductor must be made with the following parameters:

tube diameter – 10 mm;
spiral diameter – 8-15 cm;
number of coil turns – 8-10;
the distance between the turns is 5-7 mm;
The minimum clearance in the screen is 5 cm.

Do not allow adjacent turns of the coil to come into contact; maintain the specified distance. The inductor must not in any way come into contact with the protective screen of the furnace; the gap between them must be no less than specified.

Generator manufacturing

Fig.3. Lamp circuit

It is worth noting that an induction furnace for its manufacture requires at least average radio engineering skills and abilities. It is especially important to have them to create the second key element - a high-frequency current generator. You won’t be able to assemble or use a home-made stove without this knowledge. Moreover, it can be life-threatening.

For those who take on this task with knowledge and understanding of the process, there are various methods and schemes by which an induction furnace can be assembled. When choosing a suitable generator circuit, it is recommended to abandon options with a hard radiation spectrum. These include a widely used circuit using a thyristor switch. High-frequency radiation from such a generator can create powerful interference for all surrounding radio devices.

Since the mid-20th century, an induction furnace assembled with 4 lamps has enjoyed great success among radio amateurs. Its quality and efficiency are far from the best, and radio tubes are difficult to obtain nowadays, however, many continue to assemble generators according to this particular scheme, since it has big advantage: soft, narrow-band spectrum of the generated current, thanks to which such a furnace emits a minimum of interference and is as safe as possible (Fig. 3).

The operating mode of this generator is configured using variable capacitor C. The capacitor must have an air dielectric, the gap between its plates must be at least 3 mm. The diagram also contains a neon lamp L, which serves as an indicator.

Universal generator circuit

Modern induction furnaces operate on more advanced elements - microcircuits and transistors. The universal circuit of a push-pull generator, developing power up to 1 kW, has enjoyed great success. The operating principle is based on an independent excitation generator, with the inductor switched on in bridge mode (Fig. 4).

Advantages of a push-pull generator assembled according to this scheme:

Ability to work on the 2nd and 3rd modes in addition to the main one.
There is a surface heating mode.
Regulation range 10-10000 kHz.
Soft emission spectrum throughout the entire range.
Does not require additional protection.

Frequency adjustment is carried out using a variable resistor R2. The operating frequency range is set by capacitors C 1 and C 2. The interstage matching transformer must have a ring ferrite core with a cross-section of at least 2 sq.cm. The winding of the transformer is made of enameled wire with a cross section of 0.8-1.2 mm. Transistors must be placed on a common radiator with an area of 400 sq.cm.

Conclusion on the topic

The electromagnetic field (EMF) emitted by an inductor stove affects all conductors around it. This includes effects on the human body. Under the influence of EMF, the internal organs are evenly warmed up, and the overall body temperature rises throughout the entire volume.

Therefore, when working with the stove, it is important to take certain precautions to avoid negative consequences.

First of all, the generator housing must be shielded using a casing made of galvanized iron sheets or a mesh with small cells. This will reduce the radiation intensity by 30-50 times.

It should also be borne in mind that in the immediate vicinity of the inductor the energy flux density will be higher, especially along the winding axis. Therefore, the induction coil should be positioned vertically, and it is better to observe the heating from afar.

An induction furnace is a furnace apparatus that is used for melting non-ferrous (bronze, aluminum, copper, gold and others) and ferrous (cast iron, steel and others) metals due to the operation of an inductor. A current is produced in the field of its inductor, it heats the metal and brings it to a molten state.

Collapse

First, it will be affected by an electromagnetic field, then by an electric current, and then it will go through the thermal stage. Simple design Such a stove device can be assembled independently from various available materials.

Principle of operation

Such a furnace device is an electrical transformer with a secondary short-circuited winding. The operating principle of an induction furnace is as follows:

using a generator, an alternating current is created in the inductor;
an inductor with a capacitor creates an oscillatory circuit, it is tuned to the operating frequency;
in the case of using a self-oscillating generator, the capacitor is excluded from the device circuit and in this case the inductor’s own reserve capacitance is used;
the magnetic field created by the inductor can exist in free space or be closed using an individual ferromagnetic core;
the magnetic field acts on the metal workpiece or charge located in the inductor and forms a magnetic flux;
according to Maxwell's equations, it induces a secondary current in the workpiece;
with a solid and massive magnetic flux, the created current is closed in the workpiece and a Foucault current or eddy current is created;
after the formation of such a current, the Joule-Lenz law comes into effect, and the energy obtained using an inductor and a magnetic field heats the metal workpiece or charge.

Despite multi-stage operation, the induction furnace device can provide up to 100% efficiency in vacuum or air. If the medium has magnetic permeability, then this indicator will increase; in the case of a medium made of a non-ideal dielectric, it will fall.

Device

The furnace in question is a kind of transformer, but it does not have a secondary winding; it is replaced by a metal sample placed in the inductor. It will conduct current, but the dielectrics do not heat up in this process, they remain cold.

The design of induction crucible furnaces includes an inductor, which consists of several turns of a copper tube, coiled in the form of a coil, with coolant constantly moving inside it. The inductor also contains a crucible, which can be made of graphite, steel and other materials.

In addition to the inductor, the furnace has a magnetic core and a hearth stone, all of which are enclosed in the furnace body. It includes:

In high-power furnace models, the bath casing is usually made quite rigid, so there is no frame in such a device. The housing fastening must withstand strong loads when the entire oven is tilted. The frame is most often made of shaped beams made of steel.

A crucible induction furnace for melting metal is installed on a foundation into which supports are mounted; the axles of the tilting mechanism of the device rest on their bearings.

The bath casing is made of metal sheets, onto which stiffeners are welded for strength.

The induction unit casing is used as a connecting link between the furnace transformer and the hearth stone. To reduce current losses, it is made of two halves, between which there is an insulating gasket.

The halves are connected using bolts, washers and bushings. Such a casing is made cast or welded; when choosing a material for it, preference is given to non-magnetic alloys. The two-chamber induction steelmaking furnace comes with a common casing for both the bath and the induction unit.

In small ovens that do not have water cooling, there is a ventilation unit that helps remove excess heat from the unit. Even if you install a water-cooled inductor, you need to ventilate the opening near the hearth stone so that it does not overheat.

Modern furnace installations not only have a water-cooled inductor, but also provide water cooling of the casings. Fans powered by a drive motor can be installed on the furnace frame. If such a device has a significant mass, the ventilation device is installed near the stove. If an induction furnace for steel production comes with a removable version of induction units, then each of them is provided with its own fan.

Separately, it is worth noting the tilt mechanism, which for small ovens comes with a manual drive, and for large ones it is equipped with a hydraulic drive located at the drain spout. Whatever the tilt mechanism is installed, it must ensure that the entire contents of the bathroom are completely drained.

Power calculation

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

The power of an 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 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 necessary to take into account the metal or alloy being melted: according to the condition, it is zinc. This is an important point, the heat balance of cast iron melting in an induction furnace, as well as other alloys, is different.

Useful power transferred to liquid metal:

Рpol = Wtheor×t×P,
Wtheor – specific energy consumption, it is theoretical, and shows the overheating of the metal by 1 0 C;
P – productivity of the furnace installation, t/h;
t is the overheating temperature of the alloy or metal billet in the furnace bath, 0 C
Rpol = 0.298×800×5.5 = 1430.4 kW.

Active power:

P = Ppol/Yuterm,
Rpol – taken from the previous formula, kW;
Yuterm is the efficiency of a foundry furnace, its limits are from 0.7 to 0.85, with an average of 0.76.
P = 1311.2/0.76 = 1892.1 kW, the value is rounded to 1900 kW.

At the final stage, the inductor power is calculated:

Rind = P/N,
P – active power of the furnace installation, kW;
N is the number of inductors provided on the furnace.
Rind =1900/2= 950 kW.

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

Species and subspecies

Induction furnaces are divided into two main types:

In addition to this division, induction furnaces are compressor, vacuum, open and gas-filled.

DIY induction furnaces

Among the available common methods for creating such units, you can find a step-by-step guide on how to make an induction furnace from a welding inverter, with a nichrome spiral or graphite brushes; we will give their features.

High frequency generator unit

It is performed taking into account the design power of the unit, eddy losses and hysteresis leaks. The structure will be powered from a regular 220 V network, but using a rectifier. This type of furnace can be equipped with graphite brushes or a nichrome spiral.

To create a furnace you will need:

two UF4007 diodes;
film capacitors;
field-effect transistors, two pieces;
470 Ohm resistor;
two throttle rings, they can be removed from an old computer system technician;
copper wire Ø section 2 mm.

The tools used are a soldering iron and pliers.

Here is a diagram for an induction furnace:

Induction portable melting furnaces of this type are created in the following sequence:

Transistors are located on radiators. Due to the fact that during the process of metal melting the device circuit heats up quickly, the radiator for it must be selected with large parameters. It is permissible to install several transistors on one generator, but in this case they need to be isolated from the metal using gaskets made of plastic and rubber.
Two chokes are manufactured. For them, two rings previously removed from the computer are taken, copper wire is wound around them, the number of turns is limited from 7 to 15.
The capacitors are combined into a battery to produce a capacitance of 4.7 μF at the output; they are connected in parallel.
A copper wire is wrapped around the inductor; its diameter should be 2 mm. The inner diameter of the winding must match the size of the crucible used for the furnace. A total of 7-8 turns are made and long ends are left so that they can be connected to the circuit.
A 12 V battery is connected to the assembled circuit as a source; it lasts for about 40 minutes of oven operation.

If necessary, the housing is made of a material with high heat resistance. If an induction melting furnace is made from a welding inverter, then a protective housing must be present, but it must be grounded.

Graphite brush design

Such a furnace is used for smelting any metal and alloys.

To create a device you need to prepare:

graphite brushes;
powdered granite;
transformer;
fireclay brick;
steel wire;
thin aluminum.

The technology for assembling the structure is as follows:

Device with nichrome spiral

Such a device is used for smelting large volumes of metal.

The following materials are used as consumables for setting up a homemade stove:

nichrome;
asbestos thread;
piece of ceramic pipe.

After connecting all the components of the furnace according to the diagram, its operation is as follows: after applying electric current to the nichrome spiral, it transfers heat to the metal and melts it.

The creation of such a furnace is carried out in the following sequence:

This design is characterized by high performance; it cools down for a long time and heats up quickly. But it is necessary to take into account that if the spiral is poorly insulated, it will quickly burn out.

Prices for ready-made induction furnaces

Homemade furnace designs will cost much less than purchased ones, but they cannot be created in large volumes, so you cannot do without ready-made options for mass production of the melt.

Prices for induction furnaces for metal melting depend on their capacity and configuration.

Model	Characteristics and Features	Price, rubles
INDUTHERM MU-200	The furnace supports 16 temperature programs, the maximum heating temperature is 1400 0C, the mode is controlled with an S-type thermocouple. The unit produces a power of 3.5 kW.	820 thousand
INDUTHERM MU-900	The furnace operates from a power supply of 380 V, temperature control occurs using an S-type thermocouple and can reach up to 1500 0C. Power – 15 kW.	1.7 million
UPI-60-2	This mini induction melting furnace can be used for melting non-ferrous and precious metals. The workpieces are loaded into a graphite crucible, and they are heated according to the transformer principle.	125 thousand
IST-1/0.8 M5	The furnace inductor is a basket in which a magnetic circuit is built together with a coil. Unit 1 ton.	1.7 million
UI-25P	The furnace device is designed for a load of 20 kg, it is equipped with a geared inclination of the melting unit. The stove comes with a block of capacitor batteries. Installation power – 25 kW. Maximum heating t is 1600 0C.	470 thousand
UI-0.50T-400	The unit is designed for a load of 500 kg, the most high power installation - 525 kW, the voltage for it must be at least 380V, maximum operating temperature - 1850 0C.	900 thousand
ST 10	The oven of the Italian company is equipped with a digital thermostat; SMD technology is built into the control panel, which is fast. The universal unit can work with different capacities from 1 to 3 kg, for this it does not need to be readjusted. It is intended for precious metals, its maximum temperature is 1250 0C.	1 million
ST 12	Static induction oven with digital thermostat. It can be supplemented with a vacuum casting chamber, which makes it possible to carry out casting right next to the installation. Control occurs using the touch panel. Maximum temperature – 1250 0С.	1050 thousand
IChT-10TN	The furnace is designed for a load of 10 tons, it is a rather voluminous unit, for its installation you need to allocate a closed workshop room.	8.9 million

Conclusion

Making an induction furnace yourself is exciting, but it comes with some limitations and unknown consequences, since you need to rely on the laws of physics and chemistry, and those who are not good at this will not be able to carry out the process safely. For frequent use of such a setup, it is better to choose suitable option from those presented above.

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The induction furnace was invented a long time ago, back in 1887, by S. Farranti. The first industrial installation started operating in 1890 at the Benedicks Bultfabrik company. For a long time Induction furnaces were exotic in the industry, but not because of the high cost of electricity; then it was no more expensive than now. There were still many unknowns in the processes occurring in induction furnaces, and the electronics element base did not allow creating effective schemes managing them.

In the induction furnace industry, a revolution has occurred literally before our eyes, thanks to the emergence, firstly, of microcontrollers, the computing power of which exceeds that of personal computers ten years ago. Secondly, thanks to... mobile communications. Its development required the availability of inexpensive transistors capable of delivering power of several kW at high frequencies. They, in turn, were created on the basis of semiconductor heterostructures, for the research of which Russian physicist Zhores Alferov received the Nobel Prize.

Ultimately, induction stoves not only completely transformed the industry, but also became widely used in everyday life. Interest in the subject gave rise to a lot of homemade products, which, in principle, could be useful. But most authors of designs and ideas (there are many more descriptions of which in the sources than functional products) have a poor understanding of both the basics of the physics of induction heating and the potential danger of poorly executed designs. This article is intended to clarify some of the more confusing points. The material is based on consideration of specific structures:

An industrial channel furnace for melting metal, and the possibility of creating it yourself.
Induction-type crucible furnaces, the simplest to use and the most popular among home-made furnaces.
Induction hot water boilers are rapidly replacing boilers with heating elements.
Household induction cooking appliances that compete with gas stoves and are superior to microwaves in a number of parameters.

Note: All devices under consideration are based on magnetic induction created by an inductor (inductor), and therefore are called induction. Only electrically conductive materials, metals, etc. can be melted/heated in them. There are also electric induction capacitive furnaces, based on electrical induction in the dielectric between the capacitor plates; they are used for “gentle” melting and electrical heat treatment of plastics. But they are much less common than inductor ones; consideration of them requires a separate discussion, so we’ll leave them for now.

Operating principle

The operating principle of an induction furnace is illustrated in Fig. on right. In essence, it is an electrical transformer with a short-circuited secondary winding:

The alternating voltage generator G creates an alternating current I1 in the inductor L (heating coil).
Capacitor C together with L form an oscillatory circuit tuned to the operating frequency, this in most cases increases the technical parameters of the installation.
If the generator G is self-oscillating, then C is often excluded from the circuit, using the inductor’s own capacitance instead. For the high-frequency inductors described below, it is several tens of picofarads, which exactly corresponds to the operating frequency range.
In accordance with Maxwell's equations, the inductor creates an alternating magnetic field with intensity H in the surrounding space. The magnetic field of the inductor can either be closed through a separate ferromagnetic core or exist in free space.
The magnetic field, penetrating the workpiece (or melting charge) W placed in the inductor, creates a magnetic flux F in it.
F, if W is electrically conductive, induces a secondary current I2 in it, then the same Maxwell equations.
If Ф is sufficiently massive and solid, then I2 closes inside W, forming an eddy current, or Foucault current.
Eddy currents, according to the Joule-Lenz law, release the energy received through the inductor and the magnetic field from the generator, heating the workpiece (charge).

Electromagnetic interaction from the point of view of physics is quite strong and has a fairly high long-range effect. Therefore, despite the multi-stage energy conversion, an induction furnace is capable of showing an efficiency of up to 100% in air or vacuum.

Note: in a medium made of a non-ideal dielectric with a dielectric constant >1, the potentially achievable efficiency of induction furnaces drops, and in a medium with a magnetic permeability >1, it is easier to achieve high efficiency.

Channel furnace

The channel induction melting furnace is the first one used in industry. It is structurally similar to a transformer, see fig. on right:

The primary winding, powered by a current of industrial (50/60 Hz) or high (400 Hz) frequency, is made of a copper tube cooled from the inside by a liquid coolant;
Secondary short-circuited winding – melt;
A ring-shaped crucible made of heat-resistant dielectric in which the melt is placed;
Magnetic circuit assembled from transformer steel plates.

Channel furnaces are used for melting duralumin, non-ferrous special alloys, and producing high-quality cast iron. Industrial channel furnaces require priming with a melt, otherwise the “secondary” will not short-circuit and there will be no heating. Or arc discharges will appear between the crumbs of the charge, and the entire melt will simply explode. Therefore, before starting the furnace, a little melt is poured into the crucible, and the remelted portion is not poured completely. Metallurgists say that a channel furnace has residual capacity.

A channel furnace with a power of up to 2-3 kW can be made from an industrial frequency welding transformer yourself. In such a furnace you can melt up to 300-400 g of zinc, bronze, brass or copper. You can melt duralumin, but the casting needs to be allowed to age after cooling, from several hours to 2 weeks, depending on the composition of the alloy, so that it gains strength, toughness and elasticity.

Note: duralumin was actually invented by accident. The developers, angry that they could not alloy aluminum, abandoned another “nothing” sample in the laboratory and went on a spree out of grief. We sobered up, returned - and no one had changed color. They checked it - and it gained the strength of almost steel, while remaining as light as aluminum.

The “primary” of the transformer is left standard; it is already designed to operate in the short-circuit mode of the secondary with a welding arc. The “secondary” is removed (it can then be put back and the transformer can be used for its intended purpose), and a ring crucible is put in its place. But trying to convert an HF welding inverter into a channel furnace is dangerous! Its ferrite core will overheat and shatter into pieces due to the fact that the dielectric constant of ferrite is >>1, see above.

The problem of residual capacity in a low-power furnace disappears: a wire of the same metal, bent into a ring and with twisted ends, is placed in the seeding charge. Wire diameter – from 1 mm/kW furnace power.

But a problem arises with a ring crucible: the only material suitable for a small crucible is electroporcelain. It is impossible to process it yourself at home, but where can you get a suitable one? Other refractories are not suitable due to high dielectric losses in them or porosity and low mechanical strength. Therefore, although a channel furnace produces smelting of the highest quality, does not require electronics, and its efficiency already at a power of 1 kW exceeds 90%, they are not used by home-made people.

For a regular crucible

The residual capacity irritated metallurgists - the alloys they melted were expensive. Therefore, as soon as sufficiently powerful radio tubes appeared in the 20s of the last century, an idea was immediately born: throw a magnetic circuit onto (we will not repeat the professional idioms of tough men), and put an ordinary crucible directly into the inductor, see fig.

You can’t do this at an industrial frequency; a low-frequency magnetic field without a magnetic circuit concentrating it will spread out (this is the so-called stray field) and give off its energy anywhere, but not into the melt. The stray field can be compensated by increasing the frequency to a high one: if the diameter of the inductor is commensurate with the wavelength of the operating frequency, and the entire system is in electromagnetic resonance, then up to 75% or more of the energy of its electromagnetic field will be concentrated inside the “heartless” coil. The efficiency will be corresponding.

However, already in the laboratories it became clear that the authors of the idea overlooked an obvious circumstance: the melt in the inductor, although diamagnetic, is electrically conductive, due to its own magnetic field from eddy currents, it changes the inductance of the heating coil. The initial frequency had to be set under the cold charge and changed as it melted. Moreover, the range is greater, the larger the workpiece: if for 200 g of steel you can get by with a range of 2-30 MHz, then for a blank the size of a railway tank, the initial frequency will be about 30-40 Hz, and the operating frequency will be up to several kHz.

It is difficult to make suitable automation on lamps; to “pull” the frequency behind the blank requires a highly qualified operator. In addition, the stray field manifests itself most strongly at low frequencies. The melt, which in such a furnace is also the core of the coil, to some extent collects a magnetic field near it, but still, to obtain acceptable efficiency it was necessary to surround the entire furnace with a powerful ferromagnetic screen.

Nevertheless, due to their outstanding advantages and unique qualities (see below), crucible induction furnaces are widely used both in industry and by home-made people. Therefore, let’s take a closer look at how to properly make one with your own hands.

A little theory

When designing a homemade “induction”, you need to firmly remember: the minimum power consumption does not correspond to the maximum efficiency, and vice versa. The stove will take the minimum power from the network when operating at the main resonant frequency, Pos. 1 in Fig. In this case, the blank/charge (and at lower, pre-resonant frequencies) operates as one short-circuited turn, and only one convective cell is observed in the melt.

In the main resonance mode, up to 0.5 kg of steel can be melted in a 2-3 kW furnace, but heating the charge/workpiece will take up to an hour or more. Accordingly, the total electricity consumption from the network will be high, and the overall efficiency will be low. At pre-resonant frequencies it is even lower.

As a result, induction furnaces for melting metal most often operate at the 2nd, 3rd, and other higher harmonics (Pos. 2 in the figure). The power required for heating/melting increases; for the same half a kilo of steel, the 2nd one will need 7-8 kW, and the 3rd one 10-12 kW. But warming up occurs very quickly, in minutes or fractions of minutes. Therefore, the efficiency is high: the stove does not have time to “eat” much before the melt can be poured.

Furnaces using harmonics have the most important, even unique advantage: several convective cells appear in the melt, instantly and thoroughly mixing it. Therefore, it is possible to conduct melting in the so-called mode. rapid charge, producing alloys that are fundamentally impossible to smelt in any other melting furnaces.

If you “raise” the frequency 5-6 or more times higher than the main one, then the efficiency drops somewhat (not much), but another remarkable property of harmonic induction appears: surface heating due to the skin effect, displacing EMF to the surface of the workpiece, Pos. 3 in Fig. This mode is rarely used for melting, but for heating workpieces for surface cementation and hardening it is a nice thing. Modern technology would be simply impossible without this method of heat treatment.

About levitation in an inductor

Now let’s do a trick: wind the first 1-3 turns of the inductor, then bend the tube/bus 180 degrees, and wind the rest of the winding in the opposite direction (Pos. 4 in the figure). Connect it to the generator, insert a crucible in the charge into the inductor, and give current. Let's wait until it melts and remove the crucible. The melt in the inductor will gather into a sphere, which will remain hanging there until we turn off the generator. Then it will fall down.

The effect of electromagnetic levitation of the melt is used to purify metals by zone melting, to obtain high-precision metal balls and microspheres, etc. But for a proper result, melting must be carried out in a high vacuum, so here levitation in the inductor is mentioned only for information.

Why an inductor at home?

As you can see, even a low-power induction stove for apartment wiring and consumption limits is too powerful. Why is it worth doing it?

Firstly, for the purification and separation of precious, non-ferrous and rare metals. Take, for example, an old Soviet radio connector with gold-plated contacts; They did not spare gold/silver for plating back then. We put the contacts in a narrow, high crucible, put them into the inductor, and melt them at the main resonance (professionally speaking, at the zero mode). After melting, we gradually reduce the frequency and power, allowing the blank to harden for 15 minutes to half an hour.

Once it cools down, we break the crucible and what do we see? A brass post with a clearly visible gold tip that just needs to be cut off. Without mercury, cyanide and other deadly reagents. This cannot be achieved by heating the melt from the outside in any way; convection in it will not do so.

Well, gold is gold, and now there is no black scrap metal lying on the road. But the need for uniform or precisely dosed heating of metal parts over the surface/volume/temperature for high-quality hardening will always be found by a homemaker or individual entrepreneur. And here again an inductor stove will help out, and the electricity consumption will be feasible for the family budget: after all, the main share of heating energy comes from the latent heat of metal melting. And by changing the power, frequency and location of the part in the inductor, you can heat exactly the right place exactly as it should, see fig. higher.

Finally, by making a specially shaped inductor (see figure on the left), you can release the hardened part into in the right place, on breaking carburization with hardening at the end/ends. Then, where necessary, use bending, ivy, and the rest remains hard, viscous, elastic. At the end, you can reheat it again where it was released and harden it again.

Let's get to the stove: what you need to know

An electromagnetic field (EMF) affects the human body, at least warming it up in its entirety, like meat in a microwave. Therefore, when working with an induction furnace as a designer, craftsman or operator, you need to clearly understand the essence of the following concepts:

PES – electromagnetic field energy flux density. Determines the general physiological impact of EMF on the body, regardless of the frequency of radiation, because The PES of an EMF of the same intensity increases with increasing radiation frequency. According to sanitary standards of different countries permissible value PES from 1 to 30 mW per 1 sq. m. of body surface with constant (more than 1 hour per day) exposure and three to five times more with a single short-term, up to 20 minutes.

Note: The USA stands apart; its permissible power consumption is 1000 mW (!) per square meter. m. body. In fact, Americans consider the beginning of physiological effects to be external manifestations, when a person already becomes ill, and the long-term consequences of EMF exposure are completely ignored.

The PES decreases with distance from a point source of radiation by the square of the distance. Single-layer shielding with galvanized or fine-mesh galvanized mesh reduces the PES by 30-50 times. Near the coil along its axis, the PES will be 2-3 times higher than at the side.

Let's explain with an example. There is a 2 kW and 30 MHz inductor with an efficiency of 75%. Therefore, 0.5 kW or 500 W will go out of it. At a distance of 1 m from it (the area of a sphere with a radius of 1 m is 12.57 sq. m.) per 1 sq. m. will have 500/12.57 = 39.77 W, and per person - about 15 W, this is a lot. The inductor must be positioned vertically, before turning on the furnace, put a grounded shielding cap on it, monitor the process from a distance, and immediately turn off the furnace when it is completed. At a frequency of 1 MHz, the PES will drop by a factor of 900, and a shielded inductor can be operated without special precautions.

Microwave – ultra high frequencies. In radio electronics, microwave frequencies are considered to be so-called. Q-band, but according to microwave physiology it starts at about 120 MHz. The reason is electrical induction heating of cell plasma and resonance phenomena in organic molecules. Microwave has a specifically targeted biological effect with long-term consequences. It is enough to receive 10-30 mW for half an hour to undermine health and/or reproductive capacity. Individual susceptibility to microwaves is extremely variable; When working with him, you need to regularly undergo a special medical examination.

It is very difficult to suppress microwave radiation; as the pros say, it “siphons” through the slightest crack in the screen or with the slightest violation of the grounding quality. Effective combating of microwave radiation from equipment is possible only at the level of its design by highly qualified specialists.

Furnace components

Inductor

The most important part of an induction furnace is its heating coil, the inductor. For homemade stoves For a power of up to 3 kW, an inductor made of a bare copper tube with a diameter of 10 mm or a bare copper bus with a cross-section of at least 10 square meters will be used. mm. The internal diameter of the inductor is 80-150 mm, the number of turns is 8-10. The turns should not touch, the distance between them is 5-7 mm. Also, no part of the inductor should touch its shield; the minimum gap is 50 mm. Therefore, in order to pass the coil leads to the generator, it is necessary to provide a window in the screen that does not interfere with its removal/installation.

The inductors of industrial furnaces are cooled with water or antifreeze, but at a power of up to 3 kW, the inductor described above does not require forced cooling when operating for up to 20-30 minutes. However, it itself becomes very hot, and scale on copper sharply reduces the efficiency of the furnace until it loses its functionality. It is impossible to make a liquid-cooled inductor yourself, so it will have to be changed from time to time. You cannot use forced air cooling: the plastic or metal fan housing near the coil will “attract” EMFs to itself, overheat, and the efficiency of the furnace will drop.

Note: for comparison, an inductor for a melting furnace for 150 kg of steel is bent from a copper pipe with an outer diameter of 40 mm and an inner diameter of 30 mm. The number of turns is 7, the inside diameter of the coil is 400 mm, and the height is also 400 mm. To power it up in zero mode, you need 15-20 kW in the presence of a closed cooling circuit with distilled water.

Generator

The second main part of the furnace is the alternator. It’s not worth even trying to make an induction furnace without knowing the basics of radio electronics at least at the level of an average radio amateur. Operating is the same, because if the stove is not under computer control, you can set it to mode only by feeling the circuit.

When choosing a generator circuit, you should in every possible way avoid solutions that give a hard current spectrum. As an anti-example, we present a fairly common circuit using a thyristor switch, see Fig. higher. A calculation available to a specialist based on the oscillogram attached to it by the author shows that the PES at frequencies above 120 MHz from an inductor powered in this way exceeds 1 W/sq. m at a distance of 2.5 m from the installation. Deadly simplicity, to say the least.

As a nostalgic curiosity, we also present a diagram of an ancient tube generator, see fig. on right. These were made by Soviet radio amateurs back in the 50s, Fig. on right. Setting to mode - with an air capacitor of variable capacitance C, with a gap between the plates of at least 3 mm. Works only on zero mode. The setting indicator is a neon light bulb L. The peculiarity of the circuit is a very soft, “lamp” radiation spectrum, so this generator can be used without special precautions. But - alas! – you can’t find lamps for it now, and with a power in the inductor of about 500 W, the power consumption from the network is more than 2 kW.

Note: The frequency of 27.12 MHz indicated in the diagram is not optimal; it was chosen for reasons of electromagnetic compatibility. In the USSR, it was a free (“junk”) frequency, for which permission was not required to operate, as long as the device did not interfere with anyone. In general, C the generator can be tuned in a fairly wide range.

In the next fig. on the left is a simple self-excited generator. L2 – inductor; L1 – feedback coil, 2 turns of enameled wire with a diameter of 1.2-1.5 mm; L3 – blank or charge. The inductor's own capacitance is used as a loop capacitance, so this circuit does not require adjustment, it automatically enters the zero mode mode. The spectrum is soft, but if the phasing of L1 is incorrect, the transistor instantly burns out, because it turns out to be in active mode from short circuit to DC in the collector circuit.

Also, the transistor can burn out simply from a change in the external temperature or self-heating of the crystal - no measures are provided to stabilize its mode. In general, if you have old KT825 or similar ones lying around somewhere, then you can start experiments on induction heating with this circuit. The transistor must be installed on a radiator with an area of at least 400 square meters. see with blowing from a computer or similar fan. Adjustment of the capacity in the inductor, up to 0.3 kW, by changing the supply voltage within 6-24 V. Its source must provide a current of at least 25 A. The power dissipation of the resistors of the basic voltage divider is at least 5 W.

The diagram follows. rice. on the right is a multivibrator with an inductive load using powerful field-effect transistors (450 V Uk, at least 25 A Ik). Thanks to the use of capacitance in the oscillatory circuit circuit, it produces a rather soft spectrum, but out-of-mode, therefore suitable for heating parts up to 1 kg for quenching/tempering. The main disadvantage of the circuit is the high cost of components, powerful field switches and high-speed (cutoff frequency of at least 200 kHz) high-voltage diodes in their base circuits. Bipolar power transistors in this circuit do not work, overheat and burn out. The radiator here is the same as in the previous case, but airflow is no longer needed.

The following scheme already claims to be universal, with a power of up to 1 kW. This is a push-pull generator with independent excitation and bridge-connected inductor. Allows you to work in mode 2-3 or in surface heating mode; the frequency is regulated by a variable resistor R2, and the frequency ranges are switched by capacitors C1 and C2, from 10 kHz to 10 MHz. For the first range (10-30 kHz), the capacitance of capacitors C4-C7 should be increased to 6.8 μF.

The transformer between the stages is on a ferrite ring with a cross-sectional area of the magnetic core of 2 square meters. see Windings - made of enameled wire 0.8-1.2 mm. Transistor radiator – 400 sq. see for four with airflow. The current in the inductor is almost sinusoidal, so the radiation spectrum is soft and no additional protective measures are required at all operating frequencies, provided that it works for up to 30 minutes a day after 2 days on the 3rd.

Video: homemade induction heater in action

Induction boilers

Induction hot water boilers will undoubtedly replace boilers with heating elements wherever electricity is cheaper than other types of fuel. But their undeniable advantages have also given rise to a lot of homemade products, which sometimes literally make a specialist’s hair stand on end.

Let's say this design: a propylene pipe with running water is surrounded by an inductor, and it is powered by a 15-25 A HF welding inverter. An option is to make a hollow donut (torus) from heat-resistant plastic, pass water through the pipes, and wrap it around it for heating bus, forming an inductor rolled into a ring.

EMF will transfer its energy to water well; It has good electrical conductivity and an abnormally high (80) dielectric constant. Remember how the remaining droplets of moisture on the dishes shoot out in the microwave.

But, firstly, to fully heat an apartment in winter, you need at least 20 kW of heat, with careful insulation from the outside. 25 A at 220 V provide only 5.5 kW (how much does this electricity cost according to our tariffs?) with 100% efficiency. Okay, let's say we're in Finland, where electricity is cheaper than gas. But the consumption limit for housing is still 10 kW, and for excess you have to pay at an increased tariff. And the apartment wiring will not withstand 20 kW; you need to pull a separate feeder from the substation. How much will such work cost? If the electricians are still far from overpowering the area, they will allow it.

Then, the heat exchanger itself. It should either be massive metal, then only induction heating of the metal will work, or made of plastic with low dielectric losses (propylene, by the way, is not one of these, only expensive fluoroplastic is suitable), then the water will directly absorb the EMF energy. But in any case, it turns out that the inductor heats the entire volume of the heat exchanger, and only its inner surface transfers heat to the water.

As a result, at the cost of a lot of work and risk to health, we get a boiler with the efficiency of a cave fire.

An industrial induction heating boiler is designed in a completely different way: simple, but impossible to do at home, see fig. on right:

The massive copper inductor is connected directly to the network.
Its EMF also heats a massive metal labyrinth-heat exchanger made of ferromagnetic metal.
The labyrinth simultaneously isolates the inductor from water.

Such a boiler costs several times more than a conventional one with a heating element, and is suitable only for installation on plastic pipes, but in return it provides a lot of benefits:

It never burns out - there is no hot electric coil in it.
The massive labyrinth reliably shields the inductor: PES in the immediate vicinity of the 30 kW induction boiler is zero.
Efficiency – more than 99.5%
Absolutely safe: the intrinsic time constant of the highly inductive coil is more than 0.5 s, which is 10-30 times longer than the response time of the RCD or machine. It is further accelerated by the “recoil” from the transient process when the inductance breaks down on the housing.
The breakdown itself, due to the “oakiness” of the structure, is extremely unlikely.
Does not require separate grounding.
Indifferent to lightning strikes; It cannot burn a massive coil.
The large surface of the labyrinth ensures effective heat exchange with a minimum temperature gradient, which almost eliminates the formation of scale.
Enormous durability and ease of use: the induction boiler, together with a hydromagnetic system (HMS) and a sediment filter, operates without maintenance for at least 30 years.

About homemade boilers for hot water supply

Here in Fig. A diagram of a low-power induction heater for hot water systems with a storage tank is shown. It is based on any power transformer of 0.5-1.5 kW with a primary winding of 220 V. Dual transformers from old tube color TVs - “coffins” on a two-rod magnetic core of the PL type - are very suitable.

The secondary winding is removed from such windings, the primary is rewound onto one rod, increasing the number of its turns to operate in a mode close to a short circuit (short circuit) in the secondary. The secondary winding itself is water in a U-shaped pipe bend surrounding another rod. Plastic pipe or metal – it makes no difference at industrial frequency, but the metal pipe must be isolated from the rest of the system with dielectric inserts, as shown in the figure, so that the secondary current is closed only through water.

In any case, such a water heater is dangerous: a possible leak is adjacent to the winding under mains voltage. If you are going to take such a risk, then you need to drill a hole in the magnetic circuit for the grounding bolt, and first of all, tightly ground the transformer and the tank with a steel busbar of at least 1.5 square meters. cm (not sq. mm!).

Next, the transformer (it should be located directly under the tank), with a double-insulated power cable connected to it, a ground electrode and a water-heating coil, is poured into one “doll” with silicone sealant, like an aquarium filter pump motor. Finally, it is highly advisable to connect the entire unit to the network via a high-speed electronic RCD.

Video: “induction” boiler based on household tiles

Inductor in the kitchen

Induction hobs have become commonplace in the kitchen, see fig. According to the principle of operation, this is the same induction stove, only the bottom of any metal cooking vessel acts as a short-circuited secondary winding, see fig. on the right, and not just from ferromagnetic material, as the ignorant often write. Just aluminum cookware goes out of use; doctors have proven that free aluminum is a carcinogen, and copper and tin have long been out of use due to toxicity.

Household induction cookers are a product of the age of high technology, although the idea arose simultaneously with induction melting furnaces. Firstly, to isolate the inductor from the cooking, a durable, resistant, hygienic and EMF-free dielectric was needed. Suitable glass-ceramic composites have come into production relatively recently, and the top plate of the slab accounts for a significant portion of its cost.

Then, all cooking vessels are different, and their contents change their electrical parameters, and the cooking modes are also different. A specialist will not be able to do this by carefully tightening the knobs to the desired fashion; you need a high-performance microcontroller. Finally, according to sanitary requirements, the current in the inductor must be a pure sinusoid, and its magnitude and frequency must vary in a complex way according to the degree of readiness of the dish. That is, the generator must have digital generation of the output current, controlled by the same microcontroller.

There is no point in making a kitchen induction hob yourself: more money will be spent on electronic components alone at retail prices than on ready-made good tiles. And it’s still quite difficult to control these devices: anyone who has one knows how many buttons or sensors there are with the inscriptions: “Stew”, “Roast”, etc. The author of this article saw a tile that separately listed “Navy Borscht” and “Pretanier Soup.”

However, induction cookers have many advantages over others:

Almost zero, unlike microwave ovens, PPE, even if you sit on this tile yourself.
Possibility of programming for preparing the most complex dishes.
Melting chocolate, rendering fish and poultry fat, preparing caramel without the slightest sign of burning.
High efficiency as a result of fast heating and almost complete concentration of heat in the cooking vessel.

To the last point: take a look at fig. on the right, there are schedules for heating up cooking on an induction stove and a gas burner. Anyone who is familiar with integration will immediately understand that an inductor is 15-20% more economical, and there is no need to compare it with a cast-iron “pancake”. The cost of money on energy when preparing most dishes for an induction cooker is comparable to that of a gas cooker, and even less for stewing and cooking thick soups. The inductor is so far inferior to gas only during baking, when uniform heating is required on all sides.

Video: failed induction heater from a kitchen stove

Finally

So, it’s better to buy induction electrical appliances for heating water and cooking ready-made; they’ll be cheaper and easier. But it won’t hurt to have a homemade induction crucible furnace in your home workshop: subtle methods of melting and heat treating metals will become available. You just need to remember about PES with microwaves and strictly follow the rules of design, manufacturing and operation.

For melting metal on a small scale, some kind of device is sometimes necessary. This is especially acute in a workshop or in small-scale production. The most efficient furnace at the moment is a metal melting furnace with an electric heater, namely an induction furnace. Due to the peculiarities of its structure, it can be effectively used in blacksmithing and become an indispensable tool in the forge.

Induction furnace structure

The oven consists of 3 elements:

1. Electronic and electrical part.
2. Inductor and crucible.
3. inductor cooling system.

In order to assemble a working furnace for melting metal, it is enough to assemble a working electrical circuit and an inductor cooling system. The simplest version of metal melting is shown in the video below. Melting is carried out in the counter electromagnetic field of the inductor, which interacts with induced electro-eddy currents in the metal, which holds a piece of aluminum in the space of the inductor.

In order to effectively melt metal, large currents and high frequencies of the order of 400-600 Hz are required. The voltage from a regular 220V home socket is sufficient to melt metals. It is only necessary to turn 50 Hz into 400-600 Hz.
Any circuit for creating a Tesla coil is suitable for this. I liked the following 2 circuits on the GU 80, GU 81(M) lamp the most. And the lamp is powered by an MOT transformer from a microwave oven.

These circuits are intended for a tesla coil, but they make an excellent induction furnace; instead of the secondary coil L2, just place it in inner space primary winding L1 is a piece of iron.

The primary coil L1 or inductor consists of a copper tube rolled into 5-6 turns, the ends of which are threaded to connect the cooling system. For levitation melting, the last turn should be done in the opposite direction.
Capacitor C2 in the first circuit and an identical one in the second sets the frequency of the generator. At a value of 1000 picoFarads, the frequency is about 400 kHz. This capacitor must be a high-frequency ceramic capacitor and designed for high voltage of about 10 kV (KVI-2, KVI-3, K15U-1), other types are not suitable! It's better to use K15U. Capacitors can be connected in parallel. It is also worth taking into account the power for which the capacitors are designed (this is written on their case), take it with a reserve. the other two capacitors KVI-3 and KVI-2 heat up at long work. All other capacitors are also taken from the KVI-2, KVI-3, K15U-1 series; only the capacitance changes in the characteristics of the capacitors.
Here is a schematic diagram of what should happen. I circled 3 blocks in frames.

The cooling system is made of a pump with a flow of 60 l/min, a radiator from any VAZ car, and I placed a regular home cooling fan opposite the radiator.

Induction heating is impossible 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 current from the standard 50 Hz household electrical current. A metal object capable of absorbing thermal energy under the influence of a magnetic field is used as a heating element.

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

The operating principle 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 direction at high frequencies electromagnetic waves. 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 supplied from the inverter to the induction coil creates a magnetic field with a constantly changing vector of magnetic waves. Metal placed in this field heats up quickly

The absence 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. The water simultaneously cools the heater, which significantly increases its service life.

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

Literature

Babat G. I., Svenchansky A. D. Electric industrial furnaces. - M.: Gosenergoizdat, 1948. - 332 p.
Burak Ya. I., Ogirko I. V. Optimal heating of a cylindrical shell with temperature-dependent material characteristics // Mat. methods and physical-mechanical fields. - 1977. - Issue. 5 . - pp. 26-30.
Vasiliev A. S. Tube generators for high-frequency heating. - L.: Mechanical Engineering, 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. Basics of radio engineering. - M.: Gosenergoizdat, 1959. - 512 p.
Lozinsky M. G. Industrial application of induction heating. - M.: Publishing House of the USSR Academy of Sciences, 1948. - 471 p.
Application of high frequency currents in electrothermy / Ed. A. E. Slukhotsky. - L.: Mechanical Engineering, 1968. - 340 p.
Slukhotsky A. E. Inductors. - L.: Mechanical Engineering, 1989. - 69 p. - (Library of high-frequency thermist; Issue 12). - 10,000 copies. - ISBN 5-217-00571-8.
Fogel A. A. Induction method for keeping liquid metals in suspension / Ed. A. N. Shamova. - 2nd ed., rev. - L.: Mechanical Engineering, 1989. - 79 p. - (Library of high-frequency thermist; Issue 11). - 2950 copies. - .

Operating principle

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

Operating principle of induction heating installation

The water supplied through the lower pipe to the boiler is heated by energy transfer and exits through the upper pipe, entering the heating system. A built-in pump is used to create pressure. Constantly circulating water in the boiler prevents the elements from overheating. In addition, during operation the coolant vibrates (at a low noise level), due to which scale deposits on the internal 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 sources, the calculation of an induction furnace begins with calculating the power of the unit.

The power of an 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 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.

Useful power transferred to liquid metal:

Рpol = Wtheor×t×P,
Wtheor – specific energy consumption, it is theoretical, and shows the overheating of the metal by 10C;
P – productivity of the furnace installation, t/h;
t - overheating temperature of the alloy or metal billet in the furnace bath, 0C
Rpol = 0.298×800×5.5 = 1430.4 kW.

Active power:

P = Ppol/Yuterm,
Rpol – taken from the previous formula, kW;
Yuterm is the efficiency of a foundry furnace, its limits are from 0.7 to 0.85, with an average of 0.76.
P = 1311.2/0.76 = 1892.1 kW, the value is rounded to 1900 kW.

At the final stage, the inductor power is calculated:

Rind = P/N,
P – active power of the furnace installation, kW;
N is the number of inductors provided on the furnace.
Rind =1900/2= 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 making a mini induction oven with your own hands, then it is important to know that its main element is the heating coil. In the case of a homemade version, it is enough to use an inductor made of a bare copper tube, the diameter of which is 10 mm

For the inductor, an internal 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 should not come into contact with its screen; the minimum gap should be 50 mm.

If you are planning to make an induction furnace with your own hands, then you should know that on an industrial scale, water or antifreeze is used to cool the inductors. In the case of low power and short-term operation of the device being created, you can do without cooling. But during operation, the inductor gets very hot, and scale on copper can not only sharply reduce the efficiency of the device, but also lead to a complete loss of its performance. It is impossible to make a cooled inductor on your own, so it will need to be replaced regularly. You cannot use forced air cooling, since the fan housing placed close to the coil will “attract” EMF, 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 an automatic frequency control circuit (PLL) and operates from an external master oscillator (at a frequency close to the resonant frequency of the oscillatory circuit “inductor - compensating capacitor bank”). At the moment a workpiece made of magnetic material is introduced into the inductor (if the dimensions of the workpiece are large enough and commensurate with the dimensions of the inductor), the inductance of the inductor increases sharply, which leads to a sudden 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 a sudden decrease in the power transmitted to the workpiece. If the power of the installation is regulated by an external power source, then the natural reaction of the operator is to increase the supply voltage of the installation. When the workpiece is heated to the Curie point, it magnetic properties disappear, the natural frequency of the oscillatory circuit returns back to the frequency of the master oscillator. The circuit resistance decreases sharply, and the current consumption increases sharply. If the operator does not have time to remove the increased supply voltage, the installation will overheat and fail.
If the installation is equipped with an automatic control system, then the control system must 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 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 there are many workpiece sizes smaller sizes inductor, then it also does not greatly shift the resonance of the operating circuit.

Induction cookers

Main article: Induction cooker

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

Such a stove has a higher efficiency compared to electric heating elements, since less heat is spent on heating the body, and in addition there is no acceleration and cooling period (when the energy generated, but not absorbed by the cookware, is wasted).

Induction melting furnaces

Main article: Induction crucible furnace

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

It is used in foundries of factories, as well as in precision casting shops and repair shops of machine-building plants to produce high-quality steel castings. It is possible to melt non-ferrous metals (bronze, brass, aluminum) and their alloys in a graphite crucible. An induction furnace operates on the principle of a transformer, in which the primary winding is a water-cooled inductor, and the secondary and at the same time load is the metal located in the crucible. Heating and melting of the metal occurs 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, power lines which the conductive circuit is crossed. The current in the circuit is called induction. The law of electromagnetic induction is the basis for the invention of many devices, including the defining 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 Emil Lenz) formulated a quantitative assessment of the thermal effect of electric current: “The power of heat released per unit volume of a medium during the flow of electric current is proportional to the product of the electric current density and the magnitude of the electric field strength” (Joule’s law - Lenz). The thermal effect of induced current gave rise to the search for devices for non-contact heating of metals. The first experiments on heating steel using induction current were made by E. Colby in the USA.

The first successfully operating so-called. The channel induction furnace for melting steel was built in 1900 by Benedicks Bultfabrik in Gysing, Sweden. In the respectable magazine of that time “THE ENGINEER” on July 8, 1904, a famous one 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 furnace with a capacity of 78 kW was put into operation on March 18, 1900 and turned out 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 power of 58 kW and a steel capacity of 100 kg. The furnace showed high efficiency; the melting capacity was from 600 to 700 kg of steel per day. However, wear from thermal fluctuations turned out to be at an unacceptable level, and frequent lining replacements reduced the final efficiency.

The inventor came to the conclusion that for maximum melting performance it is necessary to leave a significant part of the melt when draining, which avoids many problems, including wear of the lining. This method of smelting steel with a residue, which came to be called “swamp,” is still preserved in some industries that use large-capacity furnaces.

In May 1902, a significantly improved furnace with a capacity of 1800 kg was put into operation, the discharge was 1000-1100 kg, the remainder 700-800 kg, power 165 kW, steel melting capacity could reach 4100 kg per day! This result in energy consumption of 970 kWh/t is impressive in its efficiency, which is not much inferior to modern productivity of about 650 kWh/t. According to the inventor's calculations, out of a power consumption of 165 kW, 87.5 kW was lost, the useful thermal power was 77.5 kW, and a very high total efficiency of 47% was obtained. The cost-effectiveness is explained by the annular 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, are equipped with many improvements over a hundred years of their development, but the efficiency is increased immaterial. True, the inventor in his publication ignored the fact that electricity is paid not for active power, but for total 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, 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, which converts direct voltage into alternating voltage. For such cases, a cable with a cross-section of 6-8 mm is used, but not the standard 2.5 mm for welding machines.

Such heating systems must be of a closed type and controlled automatically. For other safety, you need a pump that will provide circulation 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 by at least 1 meter.

Implementation in domestic conditions

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 homemade induction heater with your own hands is quite understandable.

induction heating boiler

Transformer based

The main element of an induction heating system with a transformer will be the device itself, which has a primary and secondary winding. 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, implemented physically 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 an 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. The toroidal winding of copper wire is made along the outer tube. It is necessary to apply from 85 to 100 turns with an equal distance between the turns. Alternating current, changing over time, creates eddy currents in closed loop, which heat the core, and therefore the coolant, carrying out 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 power supply frequency of 50 Hz to a current with a higher frequency. This modulated current is supplied to a cylindrical inductor coil, 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 a frequency specified by the generator. The created eddy currents induced by the magnetic field produce heating of the metal element, which transfers energy to the coolant. In this way, another do-it-yourself induction heating scheme is implemented.

The heating element can also be created with your own hands from cut metal wire about 5 mm long and a piece of 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 left. According to the diagram, about 100 turns of copper wiring are placed 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 provide reliable thermal insulation, otherwise the efficiency of the heating system will drop significantly. .

Advantages and disadvantages of the device

There are a lot of “advantages” of a vortex induction heater. It's easy for self-made circuit, increased reliability, high efficiency, relatively low energy costs, long term operation, low probability of breakdowns, etc.

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

During 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 should be protected from these contaminants using a mechanical filter.

An induction coil heats the metal (pipe or pieces of wire) placed inside it using high frequency eddy currents, no contact required

Constant contact with water minimizes the likelihood of the heater burning out, which is a fairly common problem for traditional boilers with heating elements. Despite the vibration, the boiler operates extremely quietly; additional sound insulation at the installation site is not required.

Another good thing about induction boilers is that they almost never leak, unless the system is installed correctly. The absence of leaks is due to the non-contact method of transferring thermal energy to the heater. Using the technology described above, the coolant can be heated almost to a vapor state.

This provides sufficient thermal convection to encourage efficient movement of 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 design of the specific heating system.

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

But this convenient and reliable device has a number of disadvantages that should also be taken into account. For example, a boiler heats not only the coolant, but also the entire working space surrounding it. It is necessary to allocate a separate room for such a unit and remove all foreign objects from it. For a person, staying in close proximity to a working boiler for a long time can also be unsafe.

Induction heaters require electric current to operate. Both homemade and factory-made equipment are connected to a household AC network

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

If the device is handled carelessly, an explosion may occur.

If you overheat the coolant, it will turn into steam. As a result, the pressure in the system will increase sharply, which the pipes simply cannot withstand and will burst. Therefore for normal operation 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 virtually silent, this is not always the case. Some models may still produce some noise for various reasons. For a device made independently, the likelihood of such an outcome increases.

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

Homemade induction boilers

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

The homemade induction heater was then tested by filling it with water and connecting it to a factory-made ORION 2 kW induction cooktop instead of the stock inductor. The test results are shown in the following video:

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

The author did a good job and his product undoubtedly works.
No calculations were made on the thickness of the wire, the number and diameter of the coil turns. The winding parameters were adopted by analogy with the hob; accordingly, the induction water heater will have a power of no more than 2 kW.
IN best case scenario a homemade 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 coolant flow.

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

The radiator, welded from several metal pipes, acts as an external core for the 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 electrical power panels.
The number and size of the pipes were chosen randomly but provided sufficient surface area to transfer the heat generated by the eddy currents.
This induction heater circuit turned out to be successful for a specific case where 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 recording of the air temperature in the rooms.

To confirm the conclusions drawn, it is proposed to watch a video where the author tried to use a similar heater in a free-standing, insulated building:

Operating principle

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

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

The inductor-blank system is a coreless transformer in which the inductor is the primary winding. The workpiece is like a secondary winding, short-circuited. The magnetic flux between the windings is closed through the air.

At high frequencies, eddy currents are displaced by the magnetic field they themselves generate into thin surface layers of the workpiece Δ (skin effect), as a result of which their density increases sharply and the workpiece heats up. The underlying layers of 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 by e times relative to the current density in the workpiece, while 86.4% of the heat of 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 hundred 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 unity.

Formula for calculating skin depth in mm:

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

Where ρ - electrical resistivity of the workpiece material at 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 becomes very hot during operation, as it absorbs its own radiation. In addition, it absorbs thermal radiation from the hot workpiece. Inductors are made from copper tubes cooled by water. Water is supplied by suction - this ensures safety in case of burnout or other depressurization of the inductor.

Operating principle

The melting unit of an induction furnace is used to heat the most various metals and alloys. The classic design consists of the following elements:

Drain pump.
Water cooled inductor.
Frame made of stainless steel or aluminum.
Contact area.
The hearth is made of heat-resistant concrete.
Support with hydraulic cylinder and bearing unit.

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

Advantages of the device

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

The use of the induction principle makes it possible to make the equipment compact. That is why there are no problems with their placement in small spaces. An example is blast furnaces, which can be installed exclusively in prepared rooms.
The results of the studies indicate that the efficiency is almost 100%.
High melting speed. The high efficiency rate determines that it takes much less time to heat the metal when compared with other furnaces.
Some furnaces may cause changes when melting chemical composition metal Induction takes first place in terms of melt purity. The created Foucault currents heat the workpiece from the inside, thereby eliminating the possibility of various impurities entering the composition.

It is this last advantage that determines the spread of induction furnaces in jewelry, since even a small concentration of foreign impurities can negatively affect the result obtained.

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 in everyday life:

Electric kettle with disk heater for heating water;
Multicooker oven;
Induction hob;
Microwaves (stove);
Heater;
Heating column.

The opening is also used for an extruder (not mechanical). Previously, it was widely used in metallurgy and other industries related to metal processing. A factory inductive boiler operates on the principle of the action of eddy currents on a special core located in the internal part 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 alternating electrical voltage to the winding, causing the appearance of an alternating electric magnetic field, which changes potentials 50 times/sec. at a standard industrial frequency of 50 Hz.

In this case, the Ruhmkorff induction coil is designed in such a way that it can be connected directly to an AC power supply. 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 that the device uses are calculated separately for each unit using a special method for the required heat power. A homemade, powerful unit must function efficiently, quickly heat the water flowing through the pipe and not heat up.

Organizations invest serious funds in the development and implementation of such products, therefore:

All problems are resolved successfully;
The efficiency of the heating device is 98%;
Functions without interruption.

In addition to the highest efficiency, one cannot help but be attracted by the speed at which the medium passing through the core is heated. In Fig. A diagram of the functioning of an induction water heater created at the plant is proposed. Such a scheme has a unit of the “VIN” brand, which is produced by the Izhevsk plant.

How long the unit will operate depends solely on how sealed the housing is and how the insulation of the wire turns is not damaged, and this is quite a significant period, according to the manufacturer - up to 30 years.

For all these advantages, which the device 100% has, you need to shell out a lot of money; an induction, magnetic water heater is the most expensive of all types of heating installations. Therefore, many craftsmen prefer to assemble an ultra-economical heating unit themselves.

Rules for making equipment yourself

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, more).

The wire should be cut into pieces no larger 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 mesh 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 structure is closed and the adapter is installed.
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 device. The coil is connected to the prepared inverter.
A water supply pump is installed.
A temperature regulator is installed.

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

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

High precision induction heating

This heating has the simplest principle, since it is non-contact. High-frequency pulse heating makes it possible to achieve the highest temperature conditions, at which it is possible to process the most difficult metals to melt. To perform induction heating, you need to create the required voltage of 12V (volts) and inductance frequency 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 flowing currents heat the tube, which subsequently supplies heat to the living space.

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

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

For melting metals and soldering them using a non-contact method;
Mechanical engineering industry;
Jewelry;
Creation small elements(boards) that may be damaged when using other methods;
Hardening of surfaces of parts of various configurations;
Heat treatment of parts;
Medical practice (disinfection of devices/instruments).

Heating can solve many problems.

What is induction heating

The principle on which an induction water heater works.

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

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

Features of the device

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 arise in the deep part of the transformer. They redirect the emerging electromagnetic field to the secondary circuit. It simultaneously functions as a housing and acts as a heating element for water.

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

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

The lower one is installed on the inlet part of the water supply system.
The upper pipe goes to the supply section of the heating system.

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

An induction water heater consists of the following structural elements:

Photo	Structural unit
	Inductor. It consists of many turns of copper wire. It is in them that the electromagnetic field is generated.
	A heating element. This is a metal pipe or pieces of steel wire placed inside the inductor.
	Generator. It transforms household electricity into high-frequency electric current. The role of a generator can be played by an inverter from a welding machine.

Diagram of operation of a heating system with an induction water heater.

When all components of the device interact, thermal energy is generated and transferred to water. The operating diagram of the unit is as follows:

The generator produces high-frequency electric current. It then transmits it to the induction coil.
It receives the current and transforms it into an electric magnetic field.
The heater located inside the coil heats up from the action of vortex flows that appear due to a change in the magnetic field vector.
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 require frequent maintenance;
they take up little free space;
due to vibrations of the magnetic field, scale does not settle inside them;
the 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 or soot carbon monoxide etc.

The photo shows a factory water heating induction boiler.

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

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

Benefits of using all types of induction heaters

An induction heater has undoubted advantages and is a leader among all types of devices. This advantage is as follows:

It consumes less electricity and does not pollute the surrounding space.
Easy to use, it provides high quality work and allows you to control the process.
Heating through the walls of the chamber ensures special purity and the ability to obtain ultra-pure alloys, while melting can be carried out in different atmospheres, including inert gases and vacuum.
With its help, it is possible to uniformly heat parts of any shape or selective heating
Finally, induction heaters are universal, which allows them to be used everywhere, displacing 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, you must follow the following rules that increase the level of reliability of the overall system:

A safety valve should be inserted into the upper tee to relieve excess pressure. Otherwise, if it fails circulation pump the core will simply burst under the influence of steam. As a rule, the circuit of a simple induction heater provides for such moments.
The inverter is connected to the network only through an RCD. This device works in critical situations and will help avoid short circuit.
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.
The induction heater body must be placed at a height of 80 cm above the floor level. Moreover, the distance to the ceiling should be at least 70 cm, and to other pieces of furniture - more than 30 cm.
An induction heater produces a very strong electromagnetic field, so such an installation should be kept away from living quarters and enclosures with pets.

Induction heater circuit

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

A factory induction boiler uses in its operation 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.

Operating principle of an induction heater

The occurrence of currents is due to the supply of 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. In this case, the induction coil is designed in such a way that it can be connected to the AC mains directly. In industry, high-frequency currents are used for such heating - up to 1 MHz, so it is quite difficult to achieve operation of the device at a frequency of 50 Hz.

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

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

Heater operation diagram

The longevity of the heat generator depends only on the tightness of the housing and the integrity of the insulation of the wire turns, and this turns out to be a fairly long period; manufacturers declare up to 30 years. For all these advantages that these devices actually have, you have to pay a lot of money; an induction water heater is the most expensive of all types of electrical heating installations. For this reason, some craftsmen have taken to making a homemade device with the goal of using it to heat a house.

DIY process

The following tools will be useful for the job:

welding inverter;
welding generating current from 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 of the required length. On average, the number of turns is 50, the wire diameter is 3 millimeters.

Copper wire of different diameters for winding

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

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

First option

The wire is cut into 50 mm sections and a plastic tube is filled with it. To prevent it from spilling out of the pipe, you should seal the ends with wire mesh. Adapters from the pipe are placed at the ends, in the place where the heater is connected.

A winding is wound onto the body of the latter using copper wire. For this purpose, you need approximately 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, you should carefully make sure that there is water (coolant) in it. Otherwise, the device body will quickly melt.
. Pipe crashes into pipeline

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

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

Second option

This option is much simpler. A straight meter-sized section is selected on the vertical part of the pipe. It should be thoroughly cleaned of paint using sandpaper. Next, 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 completely completed.

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 you understand the source data homemade equipment and avoid possible mistakes.

Third option

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

Winding on the inductor body

To supply and drain water, 2 pipes are welded into the body of the induction unit. In order not to lose heat and prevent possible current leaks, you need to make insulation. It will eliminate the problems described above and completely eliminate noise during boiler operation.

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

When the equipment is operating, there is a high load on the electrical network. In order to eliminate the possibility of a short circuit due to insulation wear, high-quality grounding must be carried out during installation.
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 reliable water rise.
If you are installing a tabletop stove, you should pay attention to the stability of the base used.
A furnace for melting metal is a complex electrical device, when installing which you must follow all the manufacturer’s recommendations. Particular attention is paid to the parameters of the power source, which must correspond to the device model.
Do not forget that there should be quite a lot of free space around the stove. During operation, even a small melt in 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 be no flammable or explosive substances nearby. In addition, according to fire safety precautions in the vicinity, a fire shield must be installed.

Safety regulations

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

To prevent disruptions in the operation of the electrical network, it is recommended to connect a boiler with induction heating, made by hand according to the proposed diagrams, to a separate supply line, the cable cross-section of which will be at least 5 mm2

Conventional wiring may not be able to handle the required power consumption.

Induction heating systems require a safety valve to release water and steam in case the pump fails.
A pressure gauge and an RCD are required for the safe operation of a heating system assembled by yourself.
Having the entire induction heating system grounded and electrically insulated will prevent electric shock.
To avoid the harmful effects of the electromagnetic field on the human body, it is better to move such systems outside the residential area, where installation rules must be followed, according to which the induction heating device must be placed at a distance of 80 cm from horizontal (floor and ceiling) and 30 cm from vertical surfaces.
Before turning on the system, be sure to check the presence of coolant.
To prevent failures in the operation of the electrical network, it is recommended to connect a boiler with induction heating, made by hand according to the proposed schemes, to a separate supply line, the cable cross-section of which will be at least 5 mm2. Conventional wiring may not be able to handle the required power consumption.

Creation of sophisticated devices

Make a heating HDTV installation It’s more difficult to do it yourself, but radio amateurs can do it, because to assemble 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 draft. 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, as long as you have car batteries as power sources. Of course, it is not powerful enough to melt metal, but it can reach the high temperatures necessary for small jobs, such as heating knives and screwdrivers 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 decreases to 6 A during heating due to metal resistance, 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 use it to build a resonance of 100k through the regulator. The circuit must be controlled via a network adapter with a voltage of 12 V or more. The power section 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:

10 mm ferrite core and 20 turns inductor;
copper tube as a HDTV coil of 25 turns on a 5-8 cm mandrel;
capacitors 250 V.

Vortex heaters

A more powerful installation, capable of heating bolts until they turn yellow, can be assembled using 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, rated at 15 V;
simple resistors.

Depending on the desired result, winding the wire on a copper base ranges from 10 to 30 turns. Next comes the assembly of the circuit and the preparation of the base coil of the heater from approximately 7 turns of 1.5 mm copper wire. It is connected 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, you need to weld the bases of two pipes, which will serve as both a core and a heater, and weld two pipes into the housing after the winding to supply and remove coolant.

Advantages and disadvantages

Having understood the operating principle of an induction heater, you can consider its positive and negative aspects. Considering the high popularity of heat generators of this type, it can be assumed that it has much more advantages than disadvantages. Among the most significant advantages are:

Simplicity of design.
High efficiency rate.
Long service life.
Slight risk of device damage.
Significant energy savings.

Since the performance indicator of an induction boiler is in a wide range, you can easily select the unit for specific system heating the building. These devices are capable of quickly heating the coolant to a given temperature, which 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 often. Since the coolant is in constant contact with heating element, then the risks of its failure are relatively small.

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

If no mistakes were made during the installation of the induction boiler, then leaks are 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. In this way, efficient movement of water through the pipes is achieved, and in some situations it is even possible to do without 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, in regions with frequent power outages it will not be able to operate with maximum efficiency. When the coolant overheats, the pressure in the system increases sharply and the pipes can burst. To avoid this, the induction heater must be equipped with an emergency shutdown device.

DIY induction heater

Working principle of induction heating

An induction heater uses the energy of an electromagnetic field, which the heated object absorbs and converts into heat. To generate a magnetic field, an inductor is used, i.e. 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 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 penetrated by the flux of the magnetic induction vector, which constantly changes over time. In this case, an electric field arises, the lines of which are perpendicular to the direction of the magnetic flux and move in a closed 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 noticeably. This principle is widely used in the field of metal processing: melting, forging, soldering, surfacing, 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 shallow heating, but this is enough to improve Chemical properties metal

High-frequency induction heaters are easy to operate and economical, and their efficiency can reach 95%. All types operate 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 protection, each of which is responsible for its own function. Example: monitoring water pressure in a 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 hardening of gear
hardening of shafts
hardening of crane wheels
heating parts before bending
soldering of cutters, milling cutters, drill bits
heating the workpiece during hot stamping
landing bolts
welding and surfacing of metals
restoration of parts.