Do-it-yourself induction furnace for hardening metal. Do-it-yourself induction furnace: principle of operation, design and parameters, use for heating. Features of the use of induction furnaces

Induction furnaces are used for smelting metals and are distinguished by the fact that they are heated by means of electric current. The excitation of the current occurs in the inductor, or rather in a non-variable field.

In such constructions, energy is converted several times (in this sequence):

into the electromagnetic
electrical;
thermal.

Such stoves allow you to use heat with maximum efficiency, which is not surprising, because they are the most advanced of all existing models that run on electricity.

Note! Induction designs are of two types - with or without a core. In the first case, the metal is placed in a tubular chute, which is located around the inductor. The core is located in the inductor itself. The second option is called the crucible, because in it the metal with the crucible is already inside the indicator. Of course, there can be no talk of any core in this case.

In today's article, we will talk about how to make an induction furnace with your own hands.

Pros and cons of induction designs

Among the many benefits are the following:

environmental cleanliness and safety;
increased homogeneity of the melt due to the active movement of the metal;
speed - the oven can be used almost immediately after switching on;
zone and focused orientation of energy;
high melting rate;
lack of waste from alloying substances;
the ability to adjust the temperature;
numerous technical possibilities.

But there are also disadvantages.

The slag is heated by the metal, as a result of which it has a low temperature.
If the slag is cold, then it is very difficult to remove phosphorus and sulfur from the metal.
Between the coil and the melting metal, the magnetic field dissipates, so a reduction in lining thickness will be required. This will soon lead to the fact that the lining itself will fail.

Video - Induction furnace

Industrial Application

Both design options are used in the smelting of iron, aluminium, steel, magnesium, copper and precious metals. The useful volume of such structures can range from several kilograms to several hundred tons.

Furnaces for industrial use are divided into several types.

Medium frequency designs are commonly used in mechanical engineering and metallurgy. With their help, steel is melted, and when using graphite crucibles, non-ferrous metals are also melted.
Industrial frequency designs are used in iron smelting.
Resistance structures are intended for melting aluminum, aluminum alloys, zinc.

Note! It was induction technology that formed the basis of more popular devices - microwave ovens.

domestic use

For obvious reasons, the induction melting furnace is rarely used in the home. But the technology described in the article is found in almost all modern houses and apartments. These are the microwaves mentioned above, and induction cookers, and electric ovens.

Consider, for example, plates. They heat the dishes due to inductive eddy currents, as a result of which the heating occurs almost instantly. It is characteristic that it is impossible to turn on the burner on which there are no dishes.

The efficiency of induction cookers reaches 90%. For comparison: for electric stoves it is about 55-65%, and for gas stoves - no more than 30-50%. But in fairness, it is worth noting that the operation of the described stoves requires special dishes.

Homemade induction oven

Not so long ago, domestic radio amateurs clearly demonstrated that you can make an induction furnace yourself. Today, there are a lot of different schemes and manufacturing technologies, but we have given only the most popular of them, which means the most effective and easy to implement.

Induction furnace from high frequency generator

Below is an electrical circuit for making a homemade device from a high-frequency (27.22 megahertz) generator.

In addition to the generator, the assembly will require four high-power light bulbs and a heavy lamp for the ready-to-work indicator.

Note! The main difference between the furnace, made according to this scheme, is the condenser handle - in this case, it is located outside.

In addition, the metal in the coil (inductor) will melt in the device of the smallest power.

When manufacturing, it is necessary to remember some important points that affect the speed of metal boarding. This is:

power;
frequency;
eddy losses;
heat transfer intensity;
hysteresis loss.

The device will be powered by a standard 220 V network, but with a pre-installed rectifier. If the furnace is intended for heating a room, then it is recommended to use a nichrome spiral, and if for melting, then graphite brushes. Let's get acquainted with each of the structures in more detail.

Video - Welding inverter design

The essence of the design is as follows: a pair of graphite brushes is installed, and powdered granite is poured between them, after which a step-down transformer is connected. It is characteristic that when smelting, one can not be afraid of electric shock, since there is no need to use 220 V.

Assembly technology

Step 1. The base is assembled - a box of fireclay bricks measuring 10x10x18 cm, laid on a refractory tile.

Step 2. Boxing is finished with asbestos cardboard. After wetting with water, the material softens, which allows you to give it any shape. If desired, the structure can be wrapped with steel wire.

Note! The dimensions of the box may vary depending on the power of the transformer.

Step 3. The best option for a graphite furnace is a transformer from a 0.63 kW welding machine. If the transformer is designed for 380 V, then it can be rewound, although many experienced electricians say that you can leave everything as it is.

Step 4. The transformer is wrapped with thin aluminum - so the structure will not get very hot during operation.

Step 5. Graphite brushes are installed, a clay substrate is installed on the bottom of the box - so the molten metal will not spread.

The main advantage of such a furnace is the high temperature, which is suitable even for melting platinum or palladium. But among the minuses is the rapid heating of the transformer, a small volume (no more than 10 g can be smelted at a time). For this reason, a different design will be required for melting large volumes.

So, for the smelting of large volumes of metal, a furnace with nichrome wire is required. The principle of operation of the design is quite simple: an electric current is applied to a nichrome spiral, which heats up and melts the metal. There are a lot of different formulas on the Web for calculating the length of the wire, but they are all, in principle, the same.

Step 1. For the spiral, nichrome o0.3 mm is used, about 11 m long.

Step 2. The wire must be wound. To do this, you need a straight copper tube o5 mm - a spiral is wound on it.

Step 3. A small ceramic pipe o1.6 cm and 15 cm long is used as a crucible. One end of the pipe is plugged with asbestos thread - so the molten metal will not flow out.

Step 4. After checking the performance, the spiral is laid around the pipe. At the same time, the same asbestos thread is placed between the turns - it will prevent a short circuit and limit the access of oxygen.

Step 5. The finished coil is placed in a cartridge from a high power lamp. Such cartridges are usually ceramic and have the required size.

The advantages of such a design:

high productivity (up to 30 g per run);
fast heating (about five minutes) and long cooling;
ease of use - it is convenient to pour metal into molds;
prompt replacement of the spiral in case of burnout.

But there are, of course, downsides:

nichrome burns out, especially if the spiral is poorly insulated;
insecurity - the device is connected to the mains 220 V.

Note! You can not add metal to the stove if the previous portion is already melted there. Otherwise, all the material will scatter around the room, moreover, it may injure the eyes.

As a conclusion

As you can see, you can still make an induction furnace on your own. But to be frank, the described design (like everything available on the Internet) is not quite a furnace, but a Kukhtetsky laboratory inverter. It is simply impossible to assemble a full-fledged induction structure at home.

The induction furnace was invented long ago, back in 1887, by S. Farranti. The first industrial plant was put into operation in 1890 by Benedicks Bultfabrik. 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 was still a lot of incomprehensibility in the processes taking place in induction furnaces, and the element base of electronics did not allow creating effective control circuits for them.

In the induction-furnace sphere, a revolution took place literally before our eyes today, thanks to the appearance, 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 appearance on sale of inexpensive transistors capable of delivering several kW of power at high frequencies. They, in turn, were created on the basis of semiconductor heterostructures, for the research of which the Russian physicist Zhores Alferov received the Nobel Prize.

Ultimately, induction stoves not only completely changed in industry, but also widely entered into 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 in the sources than workable products) have a poor idea of both the basics of the physics of induction heating and the potential danger of illiterate designs. This article aims to clarify some of the most confusing points. The material is built on the consideration of specific structures:

An industrial channel furnace for melting metal, and the possibility of creating it yourself.
Crucible furnaces of the induction type, the easiest to perform and the most popular among homemade people.
Induction hot water boilers, rapidly replacing boilers with heating elements.
Household cooking induction appliances that compete with gas stoves and surpass microwaves in a number of parameters.

Note: all the devices under consideration are based on the magnetic induction created by the 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 electric 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, their consideration requires a separate discussion, so let's leave it for now.

Operating principle

The principle of operation of the 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 just corresponds to the operating frequency range.
The inductor, in accordance with Maxwell's equations, creates an alternating magnetic field with strength 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.
Ф, 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, gives off the energy received by it through the inductor and the magnetic field from the generator, heating the workpiece (charge).

From the point of view of physics, the electromagnetic interaction is quite strong and has a rather high long-range action. Therefore, despite the multi-stage energy conversion, the induction furnace is able to show an efficiency of up to 100% in air or vacuum.

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

channel furnace

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

The primary winding, fed with industrial (50/60 Hz) or increased (400 Hz) frequency current, is made of a copper tube cooled from the inside by a liquid heat carrier;
Secondary short-circuited winding - melt;
An annular crucible made of a heat-resistant dielectric in which the melt is placed;
Type-setting of plates of transformer steel magnetic core.

Channel furnaces are used for remelting duralumin, non-ferrous special alloys, and producing high-quality cast iron. Industrial channel furnaces require melt seeding, otherwise the "secondary" will not short-circuit and there will be no heating. Or arc discharges will occur 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 completely poured. Metallurgists say that the channel furnace has a residual capacity.

A duct furnace with a power of up to 2-3 kW can also be made from an industrial frequency welding transformer. In such a furnace, up to 300-400 g of zinc, bronze, brass or copper can be melted. It is possible to melt duralumin, only the casting must be allowed to grow old after cooling, from several hours to 2 weeks, depending on the composition of the alloy, in order to gain strength, toughness and elasticity.

Note: duralumin was generally invented by accident. The developers, angry that it was impossible to alloy aluminum, threw another “no” sample in the laboratory and went on a spree out of grief. Sobered up, returned - but none changed color. Checked - and he gained strength almost steel, remaining light as aluminum.

The “primary” of the transformer is left as standard, it is already designed to work 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 an annular crucible is put on instead. But trying to convert a welding RF inverter into a channel furnace is dangerous! Its ferrite core will overheat and break into pieces due to the fact that the dielectric constant of the ferrite >> 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 charge for seeding. Wire diameter – from 1 mm/kW furnace power.

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

Under the usual crucible

The residual capacity irritated metallurgists - expensive alloys melted. 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 harsh 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 (this is the so-called stray field) and give up 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. Efficiency will be corresponding.

However, already in the laboratories it turned out that the authors of the idea overlooked the obvious circumstance: the melt in the inductor, although diamagnetic, but electrically conductive, due to its own magnetic field from eddy currents, changes the inductance of the heating coil. The initial frequency had to be set under the cold charge and changed as it melted. Moreover, within the larger limits, 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 with a railway tank, the initial frequency will be about 30-40 Hz, and the working frequency will be up to several kHz.

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

Nevertheless, due to their outstanding advantages and unique qualities (see below), crucible induction furnaces are widely used both in industry and by DIYers. Therefore, we will dwell in more detail on how to properly do this with your own hands.

A bit of theory

When designing a home-made "induction", you must 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) works as one short-circuited coil, and only one convective cell is observed in the melt.

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

As a result, induction furnaces for metal melting 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 pound of steel on the 2nd, 7-8 kW will be needed, on the 3rd 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” a lot, as the melt can already be poured.

Furnaces on 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. fast charge, obtaining alloys that are fundamentally impossible to smelt in any other melting furnaces.

If, however, the frequency is “lifted up” 5-6 or more times higher than the main one, then the efficiency drops somewhat (slightly) but another remarkable property of harmonic induction appears: surface heating due to the skin effect, which displaces the EMF to the surface of the workpiece, Pos. 3 in fig. For melting, this mode is rarely used, but for heating blanks for surface carburizing and hardening, it is a nice thing. Modern technology without such a method of heat treatment would be simply impossible.

About levitation in the inductor

And now let's do the trick: wind the first 1-3 turns of the inductor, then bend the tube / bus by 180 degrees, and wind the rest of the winding in the opposite direction (Pos 4 in the figure). Connect it to the generator, insert the crucible into the inductor in the charge, give current. Let's wait for the melting, remove the crucible. The melt in the inductor will collect 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 the 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 residential wiring and consumption limits is rather 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; gold / silver for plating was not spared then. We put the contacts in a narrow tall crucible, put them in an inductor, melt at the main resonance (professional speaking, at the zero mode). Upon melting, we gradually reduce the frequency and power, allowing the blank to solidify for 15 minutes - half an hour.

After cooling, we break the crucible, and what do we see? Brass bollard with a clearly visible gold tip that only needs to be cut off. Without mercury, cyanides and other deadly reagents. This cannot be achieved by heating the melt from the outside in any way, convection in it will not work.

Well, gold is gold, and now black scrap metal is not lying on the road. But here the need for uniform, or accurately dosed over the surface / volume / temperature of heating of metal parts for high-quality hardening from a do-it-yourselfer or an individual entrepreneur will always be found. And here again the inductor stove will help out, and the consumption of electricity will be feasible for the family budget: after all, the main share of the heating energy falls on the latent heat of metal fusion. 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 in the right place, without breaking the carburization with hardening at the end / ends. Then, where necessary, we bend, spit, and the rest remains solid, viscous, elastic. At the end, you can heat it up again, where it was released, and harden it again.

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

The 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, foreman or operator, you need to clearly understand the essence of the following concepts:

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

Note: The United States stands apart, they have an allowable PES of 1000 mW (!) per sq. km. m. body. In fact, the Americans consider its external manifestations to be the beginning of the physiological impact, when a person already becomes ill, and the long-term consequences of exposure to EMF are completely ignored.

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

Let's explain with an example. There is an inductor for 2 kW and 30 MHz 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 \u003d 39.77 W, and about 15 W per person, this is a lot. The inductor must be placed vertically, before turning on the furnace, put a grounded shielding cap on it, monitor the process from afar, and immediately turn off the furnace after 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.

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

It is very difficult to stop microwave radiation, as the pros say, it “siphons” through the slightest crack in the screen or at the slightest violation of the quality of the ground. An effective fight against microwave radiation of 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 home-made stoves, 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 go to a power of up to 3 kW. mm. The inner 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 screen; the minimum clearance 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 it is operated for up to 20-30 minutes. However, at the same time, he himself becomes very hot, and scale on copper sharply reduces the efficiency of the furnace, up to the loss of its efficiency. It is impossible to make a liquid-cooled inductor yourself, so it will have to be changed from time to time. Forced air cooling cannot be used: the plastic or metal case of the fan 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 diameter of the coil inside is 400 mm, the height is also 400 mm. For its buildup in the zero mode, 15-20 kW are needed in the presence of a closed cooling circuit with distilled water.

Generator

The second main part of the furnace is the alternator. It is not worth trying to make an induction furnace without knowing the basics of radio electronics at least at the level of a medium-skilled radio amateur. Operate - too, because if the stove is not under computer control, you can set it to the mode only by feeling the circuit.

When choosing a generator circuit, solutions that give a hard current spectrum should be avoided in every possible way. As an anti-example, we present a fairly common circuit based on a thyristor key, see fig. higher. The calculation available to a specialist according to 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. Killer simplicity, you will not say anything.

As a nostalgic curiosity, we also give a diagram of an ancient lamp generator, see fig. on right. These were made by Soviet radio amateurs back in the 50s, fig. on right. Setting to the mode - by an air capacitor of variable capacity C, with a gap between the plates of at least 3 mm. Works only on zero mode. The tuning indicator is a neon light bulb L. A feature of the circuit is a very soft, “tube” radiation spectrum, so you can use this generator without any special precautions. But - alas! - you won’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 (“garbage”) frequency, for which permission was not required, as long as the device did not give interference to anyone. In general, C can rebuild the generator in a fairly wide range.

On the next fig. on the left - the simplest generator with self-excitation. 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 the loop capacitance, so this circuit does not require tuning, it automatically enters the zero mode mode. The spectrum is soft, but if the phasing of L1 is incorrect, the transistor burns out instantly, because. it is in active mode with a DC short circuit in the collector circuit.

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

Scheme next. rice. on the right - a multivibrator with an inductive load on powerful field-effect transistors (450 V Uk, at least 25 A Ik). Due to the use of capacitance in the circuit of the oscillatory circuit, it gives a rather soft spectrum, but out-of-mode, therefore it is suitable for heating parts up to 1 kg for quenching / tempering. The main drawback of the circuit is the high cost of components, powerful field devices 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 a bridged inductor. Allows you to work on 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 uF.

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

Video: homemade induction heater at work

Induction boilers

Induction 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 mass of homemade products, from which a specialist sometimes literally makes his hair stand on end.

Let's say this design: an inductor surrounds a propylene pipe with running water, and it is powered by a 15-25 A welding RF inverter. Option - a hollow donut (torus) is made of heat-resistant plastic, water is passed through the pipes through it, and wrapped around for heating bus, forming a coiled inductor.

The EMF will transfer its energy to the water well; it has a good electrical conductivity and an anomalously high (80) dielectric constant. Remember how the droplets of moisture remaining on the dishes are shot in the microwave.

But, firstly, for a full-fledged heating of an apartment or in winter, at least 20 kW of heat is needed, with careful insulation from the outside. 25 A at 220 V gives only 5.5 kW (and how much does this electricity cost according to our tariffs?) At 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 you have to pay for the bust at an increased rate. And the apartment wiring will not withstand 20 kW, you need to pull a separate feeder from the substation. What would such a job cost? If the electricians are still far from overpowering the district and they will allow it.

Then, the heat exchanger itself. It must be either massive metal, then only induction heating of the metal will operate, 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 gives off heat to water.

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

An industrial induction heating boiler is arranged in a completely different way: simple, but not feasible at home, see fig. on right:

A massive copper inductor is connected directly to the network.
Its EMF is also heated by 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 for installation only on plastic pipes, but in return it gives 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%
It is absolutely safe: its own time constant of a coil with a large inductance is more than 0.5 s, which is 10-30 times longer than the tripping time of the RCD or machine. It is also accelerated by the "recoil" from the transient during the breakdown of the inductance on the case.
The breakdown itself due to the “oakness” of the structure is extremely unlikely.
Does not require separate grounding.
Indifferent to lightning strike; she can't burn a massive coil.
The large surface of the labyrinth ensures efficient heat exchange with a minimum temperature gradient, which almost eliminates the formation of scale.
Great durability and ease of use: an induction boiler, together with a hydromagnetic system (HMS) and a sump filter, has been operating 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 well suited.

The secondary winding is removed from such, 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 elbow from a pipe covering another rod. Plastic pipe or metal - it doesn't matter at the 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 closes only through water.

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

Next, the transformer (it should be located directly under the tank), with a double-insulated mains wire 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 desirable to connect the entire unit to the network through a high-speed electronic RCD.

Video: “induction” boiler based on household tiles

Inductor in the kitchen

Induction hobs for the kitchen have become familiar, 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 only from a ferromagnetic material, as often people who don’t know write. It's just that aluminum utensils are falling into disuse; 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 high-tech age, although the idea of its origin was born at the same time as induction melting furnaces. Firstly, to isolate the inductor from the cooking, a strong, resistant, hygienic and EMF-free dielectric was needed. Suitable glass-ceramic composites are relatively new to the industry, and the top plate of the cooker accounts for a significant portion of its cost.

Then, all cooking vessels are different, and their contents change their electrical parameters, and cooking modes are also different. Careful twisting of the handles to the desired fashion here and the specialist will not do, you need a high-performance microcontroller. Finally, the current in the inductor must be, according to sanitary requirements, 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 be with digital output current generation, controlled by the same microcontroller.

It makes no sense to make a kitchen induction cooker yourself: it will take more money for electronic components alone at retail prices than for a ready-made good tile. And it’s still difficult to manage these devices: whoever has one knows how many buttons or sensors are there with the inscriptions: “Stew”, “Roast”, etc. The author of this article saw a tile with the words “Navy Borscht” and “Pretanière Soup” listed separately.

However, induction cookers have a lot of advantages over others:

Almost zero, unlike microwaves, PES, even sit on this tile yourself.
Possibility of programming for the preparation of the most complex dishes.
Melting chocolate, melting fish and bird fat, making caramel without the slightest sign of burning.
High economic efficiency as a result of rapid heating and almost complete concentration of heat in the cookware.

To the last point: look at fig. on the right, there are graphs for heating up cooking on an induction cooker and a gas burner. Those who are familiar with integration will immediately understand that the inductor is 15-20% more economical, and it can not be compared with a cast-iron “pancake”. The cost of money for energy when cooking most dishes for an induction cooker is comparable to a gas stove, and even less for stewing and cooking thick soups. The inductor is still inferior to gas only during baking, when uniform heating is required from all sides.

Video: failed induction cooker heater

Finally

So, it is better to buy ready-made induction electrical appliances for heating water and cooking, it will be cheaper and easier. But it won’t hurt to start a home-made induction crucible furnace in a home workshop: subtle methods of melting and heat treatment of metals will become available. You just need to remember about PES with microwave and strictly follow the rules of design, manufacture and operation.

Induction heaters work on the principle of “getting current from magnetism”. In a special coil, a high-power alternating magnetic field is generated, which generates eddy electric currents in a closed conductor.

A closed conductor in induction cookers is metal utensils, which are heated by eddy electric currents. In general, the principle of operation of such devices is not complicated, and with little knowledge in physics and electrical engineering, it will not be difficult to assemble an induction heater with your own hands.

The following devices can be made independently:

Devices for heating in a heating boiler.
Mini ovens for melting metals.
Plates for cooking food.

Do-it-yourself induction cooker must be made in compliance with all norms and rules for the operation of these devices. If electromagnetic radiation dangerous for humans is emitted outside the case in the lateral directions, then it is strictly forbidden to use such a device.

In addition, a great difficulty in the design of the stove lies in the selection of material for the base of the hob, which must meet the following requirements:

Ideal for conducting electromagnetic radiation.
Not conductive.
Withstand high temperature stress.

In household induction hobs, expensive ceramics are used; in the manufacture of an induction cooker at home, it is rather difficult to find a worthy alternative to such material. Therefore, to begin with, you should design something simpler, for example, an induction furnace for hardening metals.

Manufacturing instructions

Blueprints

Figure 1. Electrical diagram of the induction heater

Figure 2. Device.

Figure 3. Scheme of a simple induction heater

For the manufacture of the furnace you will need the following materials and tools:

solder;
textolite board.
mini drill.
radioelements.
thermal paste.
chemical reagents for board etching.

Additional materials and their features:

To make a coil, which will emit an alternating magnetic field necessary for heating, it is necessary to prepare a piece of copper tube with a diameter of 8 mm and a length of 800 mm.
Powerful power transistors are the most expensive part of a homemade induction installation. To mount the frequency generator circuit, it is necessary to prepare 2 such elements. For these purposes, transistors of brands are suitable: IRFP-150; IRFP-260; IRFP-460. In the manufacture of the circuit, 2 identical of the listed field-effect transistors are used.
For the manufacture of an oscillatory circuit you will need ceramic capacitors with a capacity of 0.1 mF and an operating voltage of 1600 V. In order for a high power alternating current to form in the coil, 7 such capacitors are required.
During the operation of such an induction device, field-effect transistors will get very hot and if aluminum alloy radiators are not attached to them, then after a few seconds of operation at maximum power, these elements will fail. Putting transistors on heat sinks should be through a thin layer of thermal paste, otherwise the efficiency of such cooling will be minimal.
Diodes, which are used in an induction heater, must be of ultra-fast action. The most suitable for this circuit, diodes: MUR-460; UV-4007; HER-307.
Resistors used in circuit 3: 10 kOhm with a power of 0.25 W - 2 pcs. and 440 ohm power - 2 watts. Zener diodes: 2 pcs. with an operating voltage of 15 V. The power of the zener diodes must be at least 2 watts. A choke for connecting to the power outputs of the coil is used with induction.
To power the entire device, you will need a power supply unit with a capacity of up to 500. W. and voltage 12 - 40 V. You can power this device from a car battery, but you will not be able to get the highest power readings at this voltage.

The very process of manufacturing an electronic generator and coil takes a little time and is carried out in the following sequence:

From a copper pipe a spiral with a diameter of 4 cm is made. To make a spiral, a copper tube should be wound onto a rod with a flat surface with a diameter of 4 cm. The spiral should have 7 turns that should not touch. Mounting rings are soldered to the 2 ends of the tube for connection to the transistor radiators.
The printed circuit board is made according to the scheme. If it is possible to supply polypropylene capacitors, then due to the fact that such elements have minimal losses and stable operation at large amplitudes of voltage fluctuations, the device will work much more stable. The capacitors in the circuit are installed in parallel, forming an oscillatory circuit with a copper coil.
Metal heating occurs inside the coil, after the circuit is connected to a power supply or battery. When heating the metal, it is necessary to ensure that there is no short circuit of the spring windings. If you touch the heated metal 2 turns of the coil at the same time, then the transistors fail instantly.

Nuances

When conducting experiments on heating and hardening metals, inside the induction coil the temperature can be significant and amounts to 100 degrees Celsius. This heating effect can be used to heat domestic water or to heat a house.
Scheme of the heater discussed above (Figure 3), at maximum load it is able to provide the radiation of magnetic energy inside the coil equal to 500 watts. Such power is not enough to heat a large volume of water, and the construction of a high power induction coil will require the manufacture of a circuit in which it will be necessary to use very expensive radio elements.
A budget solution for organizing induction heating of a liquid, is the use of several devices described above, arranged in series. In this case, the spirals must be on the same line and not have a common metal conductor.
Asa stainless steel pipe with a diameter of 20 mm is used. Several induction spirals are “strung” onto the pipe, so that the heat exchanger is in the middle of the spiral and does not come into contact with its turns. With the simultaneous inclusion of 4 such devices, the heating power will be about 2 kW, which is already enough for the flow heating of the liquid with a small circulation of water, to values \u200b\u200ballowing the use of this design in supplying warm water to a small house.
If you connect such a heating element to a well-insulated tank, which will be located above the heater, the result will be a boiler system in which the heating of the liquid will be carried out inside the stainless pipe, the heated water will rise up, and a colder liquid will take its place.
If the area of the house is significant, the number of induction coils can be increased up to 10 pieces.
The power of such a boiler can be easily adjusted by turning off or on the spirals. The more sections that are simultaneously turned on, the greater the power of the heating device operating in this way will be.
To power such a module, you need a powerful power supply. If a DC inverter welding machine is available, then a voltage converter of the required power can be made from it.
Due to the fact that the system operates on direct electric current, which does not exceed 40 V, the operation of such a device is relatively safe, the main thing is to provide a fuse block in the generator power circuit, which, in the event of a short circuit, will de-energize the system, thereby eliminating the possibility of a fire.
It is possible to organize “free” heating of the house in this way, provided that batteries are installed to power induction devices, which will be charged using solar and wind energy.
Batteries should be combined in sections of 2, connected in series. As a result, the supply voltage with such a connection will be at least 24 V., which will ensure the operation of the boiler at high power. In addition, series connection will reduce the current in the circuit and increase the battery life.

Operation of homemade induction heating devices, does not always make it possible to exclude the spread of electromagnetic radiation harmful to humans, therefore the induction boiler should be installed in a non-residential area and shielded with galvanized steel.
Mandatory when working with electricity safety regulations must be followed and, especially for 220 V AC networks.
As an experiment you can make a hob for cooking according to the scheme indicated in the article, but it is not recommended to constantly operate this device due to the imperfection of self-manufacturing of the shielding of this device, because of this, the human body may be exposed to harmful electromagnetic radiation that can adversely affect health.

Collapse

An induction furnace is a furnace apparatus that is used to melt 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.

First, an electromagnetic field will act on it, then an electric current, and then it will pass through the thermal stage. The simple design of such a furnace device can be assembled independently from various improvised means.

Principle of operation

Such a furnace device is an electrical transformer with a secondary short-circuited winding. The principle of operation of the 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 capacitance reserve 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 generated current closes in the workpiece and the Foucault current or eddy current is created;
after the formation of such a current, the Joule-Lenz law comes into play, and the energy obtained with the help of an inductor and a magnetic field heats the metal billet or charge.

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

Device

The furnace in question is a kind of transformer, but only it does not have a secondary winding, it is replaced by a metal sample placed in the inductor. It will conduct current, but 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 rolled up in the form of a coil, coolant is 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, a magnetic core and a hearth stone are installed in the furnace, all this is enclosed in the furnace body. It includes:

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

The crucible induction furnace for melting metal is installed on a foundation in which the supports are mounted, the trunnions of the device tilt mechanism rest on their bearings.

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

The casing for the induction unit 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 an insulating gasket is provided.

The screed of the halves occurs due to 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 double chamber induction steel furnace comes with a common casing for the bath and for the induction unit.

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

In modern furnace installations, there is not only a water-cooled inductor, but also water cooling of the casings is provided. Fans powered by a drive motor can be installed on the furnace frame. With a significant mass of such a device, the ventilation device is installed near the furnace. If the induction furnace for steelmaking comes with a removable version of the induction units, then each of them is provided with its own fan.

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

Power calculation

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

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

As initial data you need to know:

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

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

Useful power, which is transferred to the liquid metal:

Рpol \u003d Wtheor × t × P,
Wtheor - specific energy consumption, it is theoretical, and shows the overheating of the metal by 1 0 С;
P - productivity of the furnace plant, t/h;
t is the overheating temperature of the alloy or metal billet in the bath furnace, 0 С
Рpol \u003d 0.298 × 800 × 5.5 \u003d 1430.4 kW.

Active power:

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

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

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

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

Species and subspecies

Induction furnaces are divided into two main types:

In addition to this separation, 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.

The unit from the high-frequency generator

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

To create an oven you will need:

two diodes UF4007;
film capacitors;
field-effect transistors in the amount of two pieces;
470 ohm resistor;
two throttle rings, they can be removed from the old computer system engineer;
copper wire section Ø 2 mm.

As a tool, a soldering iron and pliers are used.

Here is a diagram for an induction furnace:

Induction portable melting furnaces of such a plan are created in the following sequence:

Transistors are located on radiators. Due to the fact that during the process of melting the metal, the circuit of the device 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 must be isolated from the metal with gaskets made of plastic and rubber.
Two throttles are made. For them, two rings previously removed from the computer are taken, copper wire is wrapped 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 microfarads at the output, their connection is carried out in parallel.
A copper wire is wrapped around the inductor, its diameter should be 2 mm. The internal diameter of the winding must match the size of the crucible used for the furnace. In total, 7-8 turns are made and long ends are left so that they can be connected to the circuit.
As a source, a 12 V battery is connected to the assembled circuit, it is enough for about 40 minutes of the furnace operation.

If necessary, the case is made of a material with high thermal stability. If an induction melting furnace is made from a welding inverter, then a protective case must be required, but it must be grounded.

Graphite brush design

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

To create a device, you need to prepare:

graphite brushes;
powder granite;
transformer;
fireclay brick;
steel wire;
thin aluminium.

The assembly technology of the structure is as follows:

Device with nichrome spiral

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

The following are used as consumables for arranging a homemade oven:

nichrome;
asbestos thread;
piece of ceramic pipe.

After connecting all the components of the furnace according to the scheme, its work 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 must be taken into account that if the spiral is poorly insulated, it will quickly burn out.

Prices for finished induction furnaces

Home-made designs of furnaces will cost much cheaper 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 melting metal 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 0С, 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 is powered by a 380 V power supply, the temperature is controlled 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 to melt non-ferrous and precious metals. Billets are loaded into a graphite crucible, their heating is carried out according to the principle of a transformer.	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 reduction inclination of the melting unit. Included with the furnace is a block of capacitor banks. Installation power - 25 kW. The maximum heating t is 1600 0С.	470 thousand
UI-0.50T-400	The unit is designed for a load of 500 kg, the largest power of the installation is 525 kW, the voltage for it must be at least 380V, the maximum operating t is 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 designed for precious metals, its maximum temperature is 1250 0С.	1 million
ST 12	Static induction oven with digital thermostat. It can be supplemented with a vacuum casting chamber, which makes it possible to produce castings right next to the machine. Management takes place using the touch panel. The maximum temperature is 1250 0С.	1050 thousand
IChT-10TN	The furnace is designed for a load of 10 tons, a rather voluminous unit, for its installation it is necessary to allocate a closed workshop room.	8.9 million

An induction furnace is a heating device where the induction method is used to melt steel, copper and other metals (the metal is heated by currents excited by a non-alternating inductor field). Some consider it one of the types of resistance heaters, but the difference is energy transfer method heated metal. First, electrical energy becomes electromagnetic, then again electrical, and only at the very end it turns into heat. Induction stoves are considered the most perfect from all gas and electric (, steelmaking, mini stoves), thanks to its heating method. With induction, heat is generated within the metal itself, and the use of thermal energy is most efficient.

Induction furnaces are divided into two types:

with a core (channel);
without core (crucible).

The latter are considered more modern and useful (heaters with a core, due to their design, are limited in power). The transition from channel to crucible furnaces began in early 1900s. At the moment, they are widely used in industry.

Such types of electrical appliances as muffle melting furnace, steel melting furnace and arc steel melting furnace are quite popular. The former are very effective and safe to use. On the shelves there is a large assortment of muffle furnaces of this type. A very important role for metallurgy was played by such an invention as a steel furnace. With its help, it became possible to heat any materials.

However, at the moment, steel smelting is more often carried out using such a heating structure as, it uses the thermal effect for melting, and it is more convenient and practical.
With your own hands, you can make many simple heating structures. For example, very popular. If you decide to build a mini heating structure with your own hands, you need to know its device. There are many types of induction furnaces, but we will describe only a few of them. If necessary, you can use the necessary diagrams, drawings and video recordings.

Induction Furnace Components

For the simplest designs, there are only two main parts: an inductor and a generator. However, you can add something of your own, improve the unit, using the necessary schemes.
Inductor
The heating coil is the most important component. Absolutely the entire operation of the heating structure depends on it. For homemade stoves with low power, it is acceptable to use an inductor from a bare copper tube. with a diameter of 10 mm. The inner diameter of the inductor must be not less than 80 mm. and not more than 150 mm., the number of turns - 8-10. It must be taken into account that the turns should not touch, so the distance between them should be 5-7 mm. Also, no part of the inductor should touch its screen.
Generator
The second most important component of the furnace is the alternator. When choosing a generator circuit, you should in every possible way avoid blueprints, giving a hard current spectrum. As something that you DO NOT need to choose, we present a popular circuit on a thyristor key.

Crucible furnace device

Inside there is a melting crucible with a drain sock (“ collar“). On the outer sides of the structure, an inductor is located in a vertical position. Next comes a layer of thermal insulation, and at the top is a cover. One of the outer sides may have a supply current and cooling water. Below is a device for signaling the wear of the crucible.

The melting crucible is one of the most important components of the unit, it largely determines its operational reliability. Therefore, very stringent requirements are imposed on the crucible and other materials used.

How to make an induction oven

First you need to assemble the generator for the inductor. Here you will need the K174XA11 circuit. The transformer should be wound on a mini-ring with a diameter of 2 centimeters. The entire winding is carried out with a wire with a diameter of 0.4 centimeters and should be 30 turns. The primary winding is characterized by the presence exactly 22 turns of wire with a diameter of 1 millimeter, and the secondary should contain only 2-3 turns the same wire, but already folded four times. The inductor must be made of 3 mm. wire with a diameter of 11 mm. There should be exactly 6 turns. To adjust the resonance, it is best to set the normal or mini led.

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