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 furnace for melting metal with electric heater, namely induction. Due to the peculiarities of its structure, it can be effectively used in blacksmithing and become an indispensable tool in the forge.
The oven consists of 3 elements:
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, it is enough to place a piece of iron in the internal space of the primary winding L1.
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 high-frequency ceramic and designed for high voltage 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.
A smelter is a large or portable structure in which a quantity of non-ferrous metal can be melted. The induction melting furnace is widely known. In production conditions, large quantities of induction melting furnaces are installed in special rooms to melt metal in large quantities. They melt metal from which many parts for motorcycles, cars, and tractors are cast. To melt up to 5 kg of aluminum. you can build your own induction melting furnaces, solid fuel and gas installations. They all work great. How and from what can you make a home melting pot?
The installation for melting metal (Fig. 1) is assembled from bricks. It must be fireproof. Fireclay clay is used as a binder. To fire the device with coal, forced air is needed. For this, a special channel must be left in the lower half of the unit for air access. A grate is located under this channel. This is special cast iron grate, on which coal or coke is laid out. The grate can be used from an old stove or purchased at the market or at a hardware store. For strength, some scald finished building metal belt. The brick can be laid on its edge.
A smelting furnace cannot do without a crucible. You can use a cast iron cauldron instead. You can look for it on the farm. It will be good if it turns out to be enameled. The crucible is installed closer to the burning coke. All that remains is to install a fan as forced air, light the coke and start smelting. The oven is ready with your own hands. It can be used for melting cast iron, copper, bronze, aluminum.
From simple materials it is possible to build gas or electrical devices, which fit perfectly on a table or workbench. To work you will need:
Asbestos in last years prohibited for home use, so it can be replaced with tiles made of tiles or cement. The sizes depend on the wishes of the owner. The power of the electrical network and the output voltage of the transformer play a big role here. It is enough to apply a voltage of 25 V to the electrodes. For an industrial transformer used in welding work, this voltage is usually 50-60 V. In this case, the distance between the electrodes must be increased. Much is done by experience. As a result, melting 60-80 g of metal is a good result.
It is better to make electrodes from brushes from a fairly powerful electric motor. They have a very convenient current supply wire. You can grind them yourself. Big problems there should be no problem with searching for material. IN homemade product you need to drill holes on the side with a diameter of 5-6 mm, insert a copper stranded wire about 5 mm thick into them, and carefully hammer in a nail to secure the wire. All that remains is to make a notch with a file, it will help improve contact with the graphite in powder form. The inside of the oven is lined with mica. This is an excellent heat insulator. The outside walls of the oven are reinforced with tiles.
To power the furnace, you can take a transformer that lowers the mains voltage to 52 V. The mains winding is wound with 620 turns of wire Ø1 mm. The step-down winding is wound with a 4.2x2.8 mm wire having fiberglass insulation. Number of turns #8212; 70. The furnace is connected to the transformer with wires with a cross section of 7-8 mm² in good insulation. The finished installation must be turned on for a while so that all organic inclusions burn out. The oven was assembled by hand.
You cannot melt magnesium, zinc, cadmium, or silver contacts in such furnaces.
Cadmium burns out when melted, producing toxic yellow smoke.
When working with the installation, you must follow safety precautions:
If desired, you can make gas installations. They are well suited for melting small batches of non-ferrous metal. Induction melting furnaces are capable of melting any metal. They can be used as normal settings for working with color and precious metals, like melting and holding furnaces in production. They are suitable for various needs: for heating metals, for making alloys of several metals, for melting cast iron.
You can melt a small piece of iron in a self-assembled induction furnace. Exactly this efficient device, which operates from a 220V home socket. The stove is useful in a garage or workshop, where it can simply be placed on a desktop. There is no point in buying it, since an induction furnace can be assembled with your own hands in a couple of hours, if a person knows how to read electrical diagrams. It is not advisable to do without a diagram, because it gives a complete picture of the device and allows you to avoid errors when connecting.
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Main elements and components of the stove: heating element E1 (in the first burner), E2 (in the second burner), E3-E5 (in the oven), switching unit consisting of switches S1-S4, thermal relay F type T-300, indicators HL1 and HL (gas discharge for indicating the operation of the heating element), HL3 (incandescent type for illuminating the oven). The power of each heating element is about 1 kW
To adjust the power and degree of heating of the heating element of the oven, a 4-position switch S1 is used. When its handle is set to the first position, contacts P1-2 and P2-3 are closed. In this case, the following will be connected to the network using a plug: heating element E3 in series with parallel-connected heating elements E2 and E3. The current will flow along the path: lower contact of the plug XP, F, P1-2, E4 and E5, E3, P2-3, upper XP plug contact. Since heating element E3 is connected to heating element E4 and E5 in series, the circuit resistance will be maximum, and the power and degree of heating will be minimal. In addition, the neon indicator HL1 will light up due to the passage of current through the circuit: the lower contact of the XP plug, F, P1-2, E4 and E5, R1, HL1, the upper contact of XP.
Connecting Dream 8 nodes:
In the second position, contacts P1-1, P2-3 are switched on. In this case, the current will flow through the circuit: the lower contact of the XP plug, F, P1-1, E3, P2-3, the upper contact of XP. In this situation, only one E3 heating element will work and the power will be greater due to a decrease in the total resistance at a constant mains voltage of 220V.
In the third position of switch S1, contacts P1-1, P2-2 will close, which will lead to connection to the network only of parallel-connected heating elements E4 and E5. Switch S4 is used to turn on the oven lighting lamp HL3.
5.Electra 1002
H1, H2 - tubular burners, H3 - cast iron burner 200mm, H4 - cast iron burner 145mm, P1, P2 - stepless power regulators, P3, P4 - seven-position power switches, PSh - three-stage oven switch, P5 - blocking switch, L1.... L4 - signal lamps for turning on the burners, L5 - signal lamp for turning on the oven or grill heaters, L6 - signal lamp for reaching the set temperature in the oven, H5, H6 - oven heaters, H7 - grill, T - temperature regulator, B - key switch, L7 – oven lighting lamp, M – gear motor.
6. BURNER SWITCHES Combustion, Нansa, Electra, Lysva:
Table of contents:
You can melt a small piece of iron in a self-assembled induction furnace.
This is the most efficient device that operates from a 220V home outlet. The stove is useful in a garage or workshop, where it can simply be placed on a desktop. There is no point in buying it, since an induction furnace can be assembled with your own hands in a couple of hours, if a person knows how to read electrical diagrams. It is not advisable to do without a diagram, because it gives a complete picture of the device and allows you to avoid errors when connecting.
A homemade induction furnace for melting a small amount of metal does not require large dimensions or such a complex device as industrial units. Its operation is based on the generation of alternating current magnetic field. The metal is melted in a special piece called a crucible and placed in an inductor. It is a spiral with a small number of turns of a conductor, for example, a copper tube. If the device is used for a short time, the conductor will not overheat. In such cases, it is sufficient to use copper wire.
A special generator launches powerful currents into this spiral (inductor), and an electromagnetic field is created around it. This field in the crucible and in the metal placed in it creates eddy currents. It is they who heat the crucible and melt the metal due to the fact that it absorbs them. It should be noted that the processes occur very quickly if you use a crucible made of non-metal, for example, fireclay, graphite, quartzite. A homemade furnace for melting provides a removable crucible design, that is, metal is placed in it, and after heating or melting it is pulled out of the inductor.
The high-frequency generator is assembled from 4 electronic tubes (tetrodes), which are connected to each other in parallel. The heating rate of the inductor is controlled by a variable capacitor. Its handle extends outward and allows you to adjust the capacitance of the capacitor. The maximum value will ensure that the piece of metal in the coil is heated to red in just a few seconds.
The effective operation of this device depends on the following parameters:
How to select the component parts of the circuit in order to obtain sufficient conditions for melting in the workshop? The generator frequency is preset: it should be 27.12 MHz if the device is assembled with your own hands for use in a home workshop. The coil is made of a thin copper tube or wire, PEV 0.8. It is enough to make no more than 10 turns.
Electronic lamps should be used with high power, for example, 6p3s brand. The scheme also provides for the installation of an additional neon lamp. It will serve as an indicator that the device is ready. The circuit also provides for the use of ceramic capacitors (from 1500V) and chokes. Connection to a home outlet is made through a rectifier.
Externally, a homemade induction furnace looks like this: a generator with all the details of the circuit is attached to a small stand on legs. An inductor (spiral) is connected to it. It should be noted that this option for assembling a homemade melting device is applicable for working with a small volume of metal. An inductor in the form of a spiral is the easiest to make, so for a homemade device it is used in this form.
However, there are many different modifications of the inductor. For example, it can be made in the shape of a figure eight, a trefoil, or any other shape. It should be convenient for placing the material for heat treatment. For example, a flat surface is most easily heated by coils arranged in a snake shape.
In addition, it tends to burn out, and in order to extend the service life of the inductor, it can be insulated with heat-resistant material. For example, pouring a refractory mixture is used. It should be noted that this device is not limited to copper wire material. You can also use steel wire or michrome. When working with an induction furnace, be aware of its thermal hazards. If accidentally touched, the skin gets severely burned.
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So, a furnace for melting metal. Here I didn’t invent anything much, but simply tried to make a device, if possible from ready-made components and, if possible, without leaving any slack in the manufacturing process.
At the stove top part Let's call it a melting pot, the bottom one is the control unit.
Don't let the white box on the right scare you - this is, in general, an ordinary transformer.
Main parameters of the furnace:
— oven power - 1000 W
- crucible volume - 62 cm3
— maximum temperature - 1200 °C
Since my goal was not to waste time on experiments with corundum-phosphate binders, but to save time by using ready-made components, I used a ready-made heater from YASAM, as well as a ceramic muffle working in tandem with it.
Heater: fechral, wire diameter 1.5 mm, rods with a diameter of 3 mm are welded to the terminals. Resistance 5 ohms. The presence of a muffle is mandatory, since the wires inside the heater are bare. Heater size Ф60/50х124 mm. Muffle dimensions Ф54.5/34х130 mm. We make a hole in the bottom of the muffle for the elevator rod.
The body of the melter is made of standard stainless steel. pipe 220/200, machined to an acceptable wall thickness. The height was also taken for a reason. Since our lining will be fireclay brick, the height is taken taking into account the three thicknesses of the brick. It's time to post it Assembly drawing. In order not to clutter up the page, I will not publish here, but will give links: Part 1, Part 2.
The first drawing does not show the lightweight fireclay washer on which the crucible stands; the height of the washer depends on the crucible used. In the center of the washer there is a hole for the rod. The rod is pointed and in the lower position does not reach the crucible.
As I already wrote, the furnace lining is made of lightweight fireclay bricks ШЛ 0.4 or ШЛ 0.6, standard size No. 5. Its dimensions are 230x115x65 mm. Brick is easy to process with saws and sandpaper. The saw, however, won’t last long :) Processing fireclay bricks. On the right is the original brick :)
Straight cuts - a hacksaw for wood, for curved cuts - a homemade saw made of hacksaw blade with large teeth, with a reduced (ground) width of the blade.
When manufacturing the lining, one should observe simple rules:
- do not use any mortar to fasten the parts. Everything is dry. It'll break anyway
— parts of the lining should not rest anywhere. There must be slack, gaps
— if you make large parts of the lining from another material, it is better to divide it into smaller parts. It will still split. Therefore, you better do it.
For the thermocouple, we make a hole in the third layer, and in the second and first layers we make a gap between the heater and the lining. The gap is such that the thermocouple is pushed in tightly, as close to the heater as possible. You can use a purchased thermocouple at YASAM, but I use homemade ones. It’s not that I’m sorry for the money (although they are quite expensive there), I just basically leave the junction bare for better thermal contact. Although there is a risk of burning the input circuits of the regulator.
In the control unit, the lower and upper covers are equipped with grilles for cooling the heater terminals. Still, the diameter of the leads is 3 mm. In addition, heat radiation through the bottom of the melting pot is also present. There is no need to cool the regulator - 10 watts in total. At the same time, let’s cool the cold ends of the thermocouple. Control unit with temperature controller Termodat-10K2. At the top right is the power switch. At the top left is the crucible lift lever with the lift rod (stainless steel electrode Ф3mm).
Why did I choose Termodat as the regulator? I dealt with Aries, but after one winter in an unheated room, its firmware crashed. The thermodata has already withstood several winters and retained not only the firmware, but also the settings.
In addition, the body is metal, indestructible. (We should at least take a bottle from Perm residents for advertising :)
In addition, you can also get a power element from them - Triac Control Unit BUS1-B01. This block is designed to work specifically with Thermodats.
The instructions for Termodat-10K2 are here.
Scheme electric oven. The thick line shows high-current circuits. They use a wire of at least 6 mm2.
I'll tell you about the transformer later. Now about the control unit. It is turned on by the T1 toggle switch and is protected by a 0.25 A fuse. In addition, a surge filter is provided to power the regulator, which is located in the transformer housing. A TS142-80 triac is used as a power element (1420 volts, 80 amperes, written in CHIP and DIP). I placed the triac on the radiator, but as practice has shown, it hardly heats up. Don't forget to isolate the triac from the case. Either mica or ceramics. Either the triac itself, or assembled with a radiator.
In the photo behind the Thermodat there is a fan power supply. I then added it for the fan, which I placed on the bottom grille. The power supply is the simplest - trans, bridge and capacitor, produces 12 volts. Computer fan.
Heater output. Through the grille there is an outlet in a ceramic tube. To connect to the terminal, I used a cross-drilled bolt.
Inserting a thermocouple into the control unit. If you do not have such a ceramic straw, spit out the required amount in YASAM.
Please note - the installation is made with a regular installation wire, high-current circuits are multi-core of at least 6 mm2, thermocouple ends are directly into the terminal block. The BUS in its factory form does not fit, I had to remove the cover (and who has it easy now? ;). The rest can be seen in the photo.
Despite such a formidable appearance, this device is a regular 1 kW transformer. He just changed several professions before (graphite smelter, welder, etc.) and acquired a housing, an automatic switch, an indicator of the current consumed from the network and other wonderful things.
Of course, you don’t have to fence all this, a simple kilowatt trance under the table is enough. The basis of everything is a transformer made of U-shaped iron. Depending on the need, I rewind it without disassembling or changing the primary.
Why do you need a transformer anyway? The fact is that in order for the heater to work for an acceptable amount of time, the diameter of the wire must be as thick as possible. After analyzing this table, we can draw a disappointing conclusion - the wire should be as thick as possible. And this is no longer 220 volts.
Therefore, you will not find heaters designed for 220 volts in serious devices. Directly, if you connect this heater to the network, the power consumption will be around 9 kW. You will plant a network throughout the house, and such a blow will be fatal for the heater. That's why voltage limiting circuits are used. For me, the most convenient way is to use a transformer.
So, primary: - 1.1 Volts per turn
— Idle current 450 mA
Secondary: - for a load of 5 ohms and a power of 1000 W, the voltage will be 70 Volts
— secondary current 14 A, wire 6 mm2, wire length 28 m.
Of course, this heater will not last forever. But I can replace it by finding a suitable wire and quickly rewinding the secondary.
If you read the instructions for Thermodat, then there is the possibility of limiting the maximum power. But this will not suit us, because we are talking about the average power per heater. In the distributed pulse mode, like ours, the pulses will be all 9 kW and we risk getting a pandemonium with light and music. And on the neighbors too, because the machines in the entrance are also designed for medium power.
For those who don’t like to read instructions for a long time, I’m posting a cheat sheet with coefficients and settings for a specific oven. After setting up the Thermodat, turn on the trance and go ahead.
Due to the inertia of the pointer, the indicator of the current consumed from the network also shows the average power. While the heater is cold, the current will be closer to 5 amperes, as it warms up slightly lower (due to the increase in heater resistance). As it approaches the setpoint, it will drop almost to zero (PID controller operation).
Load the crucible full with a bronze crowbar and close the lid. The inside of the lid is lined with lightweight fireclay on mortar for fireplaces and stoves. For those who are especially curious (I am one myself), there is a window in the lid covered with mica.
The temperature is over 1000, but the surface of the melting pot has not yet heated up. This indicates the quality of the lining. After 30-40 minutes, the contents of the crucible melted.
After finishing the melting, we press the elevator lever, after which we can already pick up the crucible with a grip. The photo shows a notch in the upper part of the crucible just for a secure grip.
P.S. About the crucibles. YASAM equips its furnaces with graphite crucibles that work with these heaters. If you work with gold and silver, it makes sense to buy them. But I am against these bourgeois excesses. The fact is that the F32/28 stainless steel pipe miraculously matches the diameter of the graphite crucible. You can draw your own conclusion 😉
We insulate the heater leads from the body with ceramic tubes. Ceramic tubes - from fuses, maybe from resistors.
The top row of bricks is flush with the edge of the body. Don't forget the hole for the elevator rod.
Third layer of lining. In this layer we make holes for the heater leads and for the thermocouple (pictured).
Second layer of lining. Cut for the top outlet of the heater.
In induction furnaces, the metal is heated by currents excited in the unalternating field of the inductor. Essentially, induction furnaces are also resistance furnaces, but differ from them in the way they transfer energy to the heated metal. Unlike resistance furnaces Electric Energy in induction furnaces it turns first into electromagnetic, then again into electric and, finally, into heat.
With induction heating, heat is released directly in the heated metal, so the use of heat is the most complete. From this point of view, these ovens are the most advanced type of electric ovens.
There are two types of induction furnaces: coreless and coreless crucible. In core furnaces, the metal is contained in an annular groove around the inductor, within which the core passes. In crucible furnaces, a crucible with metal is located inside the inductor. It is impossible to use a closed core in this case.
Due to a number of electrodynamic effects occurring in the metal ring around the inductor, power density Channel furnaces are limited to certain limits. Therefore, these furnaces are used primarily for melting low-melting non-ferrous metals and only in some cases are used for melting and overheating cast iron in foundries. 
The specific power of induction crucible furnaces can be quite high, and the forces arising from the interaction of magnetic furnaces of metal and inductor have a positive effect on the process in these furnaces, promoting metal mixing.
Coreless induction furnaces are used for smelting special, especially low-carbon steels and alloys based on nickel, chromium, iron, and cobalt.
An important advantage of crucible furnaces is their simplicity of design and small dimensions. Thanks to this, they can be completely placed in a vacuum chamber and it is possible to process the metal with vacuum during the melting process. As vacuum steelmaking units, induction crucible furnaces are becoming increasingly widespread in the metallurgy of high-quality steels.
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Figure 3. Schematic representation of an induction channel furnace (a) and transformer (b)
INDUCTION CROUCHABLE FURNACES.
Alloys of ferrous and non-ferrous metals and pure metals (cast iron, steel, bronze, brass, copper, aluminum) are smelted in these furnaces. By current frequency: 1) Furnaces with industrial frequency 50 Hz. 2) Medium frequency up to 600 Hz. (up to 2400 Hz also included). 3) High frequency up to 18000 Hz.
Often ind. furnaces operate in pairs (duplex process). In the first furnace the charge is melted, in the second the Me is brought to the desired chemical level. composition or maintain Me at the required temperature until casting. Transfer of Chalk from furnace to furnace can be carried out continuously along a chute using crane buckets or buckets on an electric car. In induction furnaces, the composition of the charge changes; instead of pig iron, lightweight, low-quality materials are used (chips, lightweight scrap metal, waste from own production, i.e. trimmings).
Operating principle The charge, alternating electric current, is loaded into the crucible. the current passing through the inductor (coil) creates a magnetic field, which induces an electromotive force in the metal cage, which causes induced currents, which cause the heating and melting of the chalk. Inside the coil is a crucible made of fireproof material, which protects the inductor from the effects of liquid chalk. The primary winding is an inductor. The secondary winding and at the same time the load is Chalk in a crucible.
The efficiency of the furnace depends on the electrical resistance of Mel and on the frequency of the current. For high efficiency, it is necessary that the diameter of the charge (d crucible) be at least 3.5-7 depths of current penetration into Me-l. Approximate relationships between the crucible capacity and the current frequency for steel and cast iron. The productivity of furnaces is usually 30-40 t/hour for cast iron and steel. With an energy consumption of 500-1000 kWh/ton. For bronze, copper 15-22 t/hour, for aluminum 8-9 t/hour. Most often a cylindrical crucible is used. The magnetic flux created by the inductor passes through closed lines both inside and outside the inductor.
Depending on the way the magnetic flux passes through outside distinguish: 1) open; 2) shielded; 3) closed oven design
With an open structure, the magnetic flux passes through the air, so the structural elements (for example, the frame) are made of non-metallic or placed at a great distance from the inductor. When shielding, the magnetic flux from steel structures is separated by a copper screen. When closed, the magnetic flux passes through radially arranged packages of transformer steel - magnetic cores.
Diagram of an electric induction furnace: 1 - cover, 2 rotation unit, 3 - inductor, 4 - magnetic circuits, 5 - metal structure, 6 - water cooling inlets, 7 - crucible, 8 - platform
The oven turns on. nodes:Inductor, Lining, Frame, Magnetic cores, Cover, Pad, Tilt mechanisms.
In addition to its main purpose, the inductor also performs the function of an electrical device that receives the fur. And thermal load from the crucible side. In addition, cooling the inductor ensures the removal of heat that arises due to electrical losses, so inductors are made either in the form of a cylindrical single-layer coil, where all turns are arranged in the form of a spiral with a constant angle of inclination, or in the form of a coil in which all turns are laid in a horizontal plane , and the transitions between them are in the form of short inclined sections.
Depending on the brand of Mel and the t-p level, 3 types of lining are used:
1. Sour(contains > 90% SiO2) withstands 80-100 heats
2. Main(up to 85% MgO) withstands 40-50 heats for small furnaces and up to 20 heats for furnaces with a capacity >1 ton
3. Neutral(based on Al2O3 or CrO2 oxides)
Diagrams of induction melting furnaces: a - crucible, b - channel; 1 - inductor; 2 - molten metal; 3 - crucible; 4 - magnetic core; 5 - hearth stone with a heat release channel.
The padina is made of fireclay bricks for large ovens or aspocement for small ones. Cover made of structural steel and lined from the inside. Advantages of crucible furnaces:1) Intensive circulation of the melt in the crucible; 2) The ability to create an atmosphere of any type (oxidizing, reducing, neutral) at any pressure; 3) High performance; 4) Possibility of completely draining the chalk from the furnace; 5) Ease of maintenance, possibility of mechanization and automation. Flaws: 1) Relatively low temperature of slags directed at the Mel mirror; 2) Relatively low durability of the lining at high temperatures of the melt and in the presence of thermal shifts.
INDUCTION CHANNEL OVEN.
The principle of operation is that an alternating magnetic flux penetrates a closed circuit formed by liquid Chalk and excites a current in this circuit.
The liquid chalk circuit is surrounded by fireproof material, which is baked into a steel body. The space that is filled with liquid chalk has the shape of a curved channel. Working space The stove (bath) is connected to the channel with 2 holes, due to which a closed circuit is formed. During operation of the furnace, liquid Chalk moves in the channel and at the junction with the bath. The movement is caused by overheating of the Mel (in the channel it is 50-100 ºС higher than in the bath), as well as by the influence of the magnetic field.
When all the Chalk is drained from the furnace, the electrical circuit breaks, which is created by the liquid Chalk in the channel. Therefore, in channel furnaces produce partial drainage of liquid chalk. The mass of the “swamp” is determined based on the fact that the mass of the column of liquid Chalk above the channel exceeds the electrodynamic force pushing the Chalk out of the channel.
Channel furnaces are used as a mixer for holding and melting furnaces. The mixer is designed to accumulate a certain mass of Mel and hold Mel at a certain temperature. The mixer capacity is taken to be equal to at least twice the hourly productivity of the melting furnace. Holding ovens are used to pour liquid chalk directly into molds.
Compared to crucible furnaces, channel furnaces have lower capital investments (50-70% of the crucible furnace), low specific energy consumption (higher efficiency). Flaw: Lack of flexibility in regulating the chemical composition.
The main nodes include: Furnace frame; Lining; Inductor; Fur-zm tilt; Electrical equipment; Water cooling system.
Induction heaters work on the principle of “derived current from magnetism”. An alternating magnetic field is generated in a special coil high power, which generates eddy electric currents in a closed conductor.
The closed conductor in induction cookers is a metal cookware, which is heated by eddy electric currents. In general, the operating principle of such devices is not complicated, and if you have a little knowledge of physics and electrical engineering, assembling an induction heater with your own hands will not be difficult.
The following devices can be made independently:
A do-it-yourself induction cooker must be manufactured in compliance with all standards and regulations for the operation of these devices. If electromagnetic radiation dangerous to humans is emitted outside the housing in lateral directions, then the use of such a device is strictly prohibited.
In addition, the great difficulty in designing a stove lies in the selection of material for the base of the hob, which must meet the following requirements:
In household cookers induction surfaces Expensive ceramics are used when made at home induction cooker, finding a worthy alternative to such material is quite difficult. Therefore, first you should design something simpler, for example, an induction furnace for hardening metals.
Figure 1. Electrical circuit of an induction heater 
Figure 2. Device. 
Figure 3. Schematic of a simple induction heater To make a stove you will need the following materials and tools:
Additional materials and their features:
The process of manufacturing an electronic generator and coil takes a little time and is carried out in the following sequence:
1. Theory.
Heating occurs due to the magnetization reversal of the ferromagnet, and not the Foucault/Eddy/eddy currents in the frying pan, because when using only Foucault currents, it will be released in the stove itself large quantity heat or the design will be very complex with copper tubes. Everything written below is taken from pdf onsemiconductor, holtek and fairchild. I haven’t tested it in practice, so I could be mistaken. Simplified diagram of an induction cooker.
Cbus - capacitor for stabilizing the supply voltage during one period of the oscillatory process, 4...8 μF;
Cr - resonant capacitor, 0.2...0.3 µF;
Lr - inductor, 100 μH;
T1/D1 - IGBT type IHW20N120R2, FGA15N120ANTD, IRGP20B120UD (Vces=1200V/Ic=15A/Toff+Tf=400nC/Vsat=1.6 V).
I have shown what processes are taking place on this graph. 
The operating cycle consists of two large stages: charging the inductor with a linearly increasing current through an open transistor/diode and a damped oscillatory process with a closed transistor. Which can be divided into several small cycles.
2. Power circuit.
Purpose of elements:
Li - a ferrite torus, placed on a network wire, serves to suppress common-mode interference. In most cases there is none;
FUSE - fuse;
C1 is a pulse noise filtering capacitor, in most cases it is not present;
R1 - resistor for discharging C1 after power off;
D1, D2 - rectifier for SMPS and network voltage control (for calculating power and overvoltage protection);
RJ - shunt in the form of a piece of thick wire;
L1 - impulse noise filter, most often there is none;
C2 - capacitor for the possibility of returning the energy of the oscillatory circuit with the inductor to the intermediate circuit of direct current Ubas;
C3 is a resonant capacitor, needed to ensure continuous current after the transistor is turned off;
Lr1 - inductor, serves to transfer energy to the dishes;
T1 - IGBT transistor, needed to convert direct current to alternating current;
R2 is a resistor designed to ensure that the transistor is in a locked state after switching on;
R3 is a resistor designed to suppress high-frequency current at the gate;
Uoutlet - rectified voltage in the network;
Ush - current control for overload protection;
Uce - voltage control on the IGBT collector, serves as overvoltage protection and, together with Ubas, determines the moment the IGBT is turned on;
Ubus - used to determine when the IGBT is turned on.
I described the theory of work earlier, so I won’t repeat it.
3. Driver.
Purpose of elements:
D2 - does not allow 18V to sag when decreasing 18V at the output of the SMPS; instead of a diode there may be a 51 Ohm resistor or nothing at all;
C2 - driver supply voltage stabilization, may not exist;
R3, T4, R2, T3 - two amplification stages with a common emitter;
T1 and T2 - emitter follower;
D1 - prevents the output voltage from rising above 18V;
R1 - limits the IGBT gate charge current;
R5 - increases the driver input resistance, necessary to protect the controller output;
R4 - serves to channel leakage current T4;
C1 - speeds up the switching process T4.
4. Pulse Power Source 5 and 18 Volts.
They are made according to two schemes: a flyback converter and a forward converter. In both cases, the same components are used: PWM chip (PWM/PWM with a built-in switch, most often Viper12A), 78L05, transformer, resistors and capacitors.
In both schemes, S1 is a thermal fuse resting on the heat-resistant tile cover. Often it does not exist; R1 - serves for filtering (judging by the diagram in the Samsung datasheet: instead of a resistor there is a 300 µH inductor) or as a fuse (as written by stm).
4.1. Flyback converter. 
4.2 Double Output Buck Converter based on the same elements.
The circuit is copied from STM (AN1514, page 3), and is used in Alaska ic1800 up to the nominal values. . 
Several circuits from AN1514. 
5. Voltage control on the inductor.
Despite the fact that the IGBT must be opened when the collector voltage (Uce) is slightly below zero (when the freewheeling diode built into it is open), this point in time is determined not by this voltage crossing zero, but by comparing it with the DC intermediate circuit voltage (Ubus), followed by a delay. The voltages are compared in a comparator built into the control chip.
This comparator is also used to determine the presence of a frying pan: once every 2 seconds the IGBT opens for 1 mS, and then the oscillations are counted until they are completely attenuated; if there are more than 3...24 of them, then there is no frying pan on the tile. Therefore, two dividers are used here, which bring input voltages of about 1200V to values less than 5V (supply voltage of the control chip).
Additionally, the voltage on the collector is supplied to the analog input of the control ms for overvoltage protection. Therefore, this voltage is divided by another 1.5-3 times. Although this additional divisor may not exist.
Since a voltage of 1200V will break through any single resistor, in the upper arms of the divider they use 2 or 3 series-connected resistors of 1-2 W, but since Ubas cannot be much more than 300V, then in the upper arm of the divider there is Ubus with one or two resistors they bet less. At the output of the dividers, in series with the ic inputs there can be a 100-39000 Ohm resistor, they are probably needed for additional filtration interference. The result is the following diagram. 
6. Network voltage control.
In principle, this is the same as Ubus, but measured before the rectifier. Used for power metering and overvoltage protection. For both purposes, different voltage dividers are used: the output of one divider goes to the input of the ADC, and the other to the input of the comparator. The divider circuits are similar to the previous ones. Only the voltage at the ADC input is strongly averaged by a large capacitor. 
To save one large resistor, they can supply a constant voltage to the divider connected to the comporator, supply it from the divider connected to the ADC through a small resistor (these voltages are obviously less than 5V), and supply alternating voltage through a capacitor. 
7. Current control.
To control the current, an operational amplifier built into the control chip is used. That is, this circuit requires two outputs: the input of the op-amp and its output. Some tiles also use a built-in comparator for current protection. The diagram is clear without explanation. 
8. Igbt temperature control.
Under the igbt, using an elastic band, the thermistor is pressed tightly. It is needed to control the temperature of the igbt. 
The circuit is a regular voltage divider, in one arm of which there is an NTC thermistor of type 3950-100k. 
Recommended Samsung control logic:
-temperature above 85° - reduce power;
- temperature above 90° - turn off the stove.
9. Surface temperature control.
The circuit is identical to the previous one, only the thermistor is pressed to the surface of the stove. Where is the thermistor located? 
10. Tweeter and fan.
They can be controlled from separate outputs of the control microcircuit, but recently they are connected to one output, but the tweeter is via a capacitor. Moreover, the other output of the tweeter can be connected to any voltage: 0V, 5V or 18V. 
11. Other design options.
1. Circuit based on a thyristor with voltage resonance. Although it is simpler than this one, it is more reliable (no need to worry about the moment the thyristor turns off), more expensive (the resonant capacitor has a capacity 10 times larger) and heavier (the capacitors will be heavier). Now it cannot be implemented, because the industry has stopped producing inverter thyristors en masse. 
2. Half-bridge resonant inverter, offered by STM. 
The article discusses the designs of industrial induction melting furnaces (channel and crucible) and induction hardening plants powered by machine and static frequency converters.
Diagram of an induction channel furnace
Almost all industrial duct induction furnace designs are made with detachable induction units. The induction unit is an electric furnace transformer with a lined channel to accommodate the molten metal. The induction unit consists of the following elements: casing, magnetic core, lining, inductor.
Induction units are made as single-phase or two-phase (dual) with one or two channels per inductor. The induction unit is connected to the secondary side (LV side) of the electric furnace transformer using contactors having arc suppression devices. Sometimes two contactors with parallel operating power contacts in the main circuit are switched on.
In Fig. Figure 1 shows the power supply diagram for a single-phase induction unit of a channel furnace. Maximum current relays PM1 and PM2 are used to control and turn off the furnace in case of overloads and short circuits.
Three-phase transformers are used to power three-phase or two-phase furnaces that have either a common three-phase magnetic core or two or three separate core-type magnetic cores.
To power the furnace during the period of refining the metal and to maintain the idle mode, autotransformers are used to more accurately regulate power during the period of finishing the metal to the desired level chemical composition(with a calm, without seething, melting mode), as well as for the initial starts of the furnace during the first melts, which are carried out with a small volume of metal in the bath to ensure gradual drying and sintering of the lining. The power of the autotransformer is chosen within 25-30% of the power of the main transformer.
To control the temperature of water and air cooling the inductor and the casing of the induction unit, electric contact thermometers are installed that issue a signal when the temperature exceeds the permissible one. The power to the furnace is automatically turned off when the furnace is turned to drain the metal. To control the position of the furnace, limit switches are used, interlocked with the electric furnace drive. For continuous furnaces and mixers, the induction units are not switched off when draining metal and loading new portions of the charge.
Rice. 1. Schematic diagram of the power supply of the induction unit of a channel furnace: VM - power switch, CL - contactor, Tr - transformer, C - capacitor battery, I - inductor, TN1, TN2 - voltage transformers, 777, TT2 - current transformers, P - disconnector, PR - fuses, PM1, PM2 - maximum current relay.
To ensure reliable power supply during operation and in emergency situations, the drive motors of the tilting mechanisms of the induction furnace, fan, drive of loading and unloading devices and control systems are powered from a separate auxiliary transformer.
Diagram of an induction crucible furnace
Industrial induction crucible furnaces with a capacity of more than 2 tons and a power of over 1000 kW are powered by three-phase step-down transformers with secondary voltage regulation under load, connected to a high-voltage industrial frequency network.
The furnaces are single-phase, and to ensure uniform load of the network phases, a balun device is connected to the secondary voltage circuit, consisting of a reactor L with inductance regulation by changing the air gap in the magnetic circuit and a capacitor bank Cc, connected with an inductor according to a triangle diagram (see ARIS in Fig. .2). Power transformers with a capacity of 1000, 2500 and 6300 kV-A have 9 - 23 stages of secondary voltage with automatic power control at the desired level.
Furnaces of smaller capacity and power are powered by single-phase transformers with a power of 400 - 2500 kV-A; with a power consumption of over 1000 kW, balun devices are also installed, but on the HV side of the power transformer. With a lower furnace power and power supply from a high-voltage network of 6 or 10 kV, you can dispense with the balun device if the voltage fluctuations when turning the furnace on and off are within acceptable limits.
In Fig. Figure 2 shows the power supply diagram for an industrial frequency induction furnace. The furnaces are equipped with ARIR electrical mode regulators, which, within specified limits, ensure the maintenance of voltage, power Рп and cosphi by changing the number of voltage steps of the power transformer and connecting additional sections of the capacitor bank. Regulators and measuring equipment are located in control cabinets.
Rice. 2. Power supply circuit for an induction crucible furnace from a power transformer with a balun device and furnace mode regulators: PSN - voltage step switch, C - balun capacitance, L - reactor of the balun device, S-St - compensating capacitor bank, I - furnace inductor, ARIS - balun regulator, ARIR - mode regulator, 1K-NK - battery capacity control contactors, TT1, TT2 - current transformers.
In Fig. Figure 3 shows a schematic diagram of power supply for induction crucible furnaces from a medium frequency machine converter. The ovens are equipped automatic regulators electric mode, crucible “eating” alarm system (for high temperature furnaces), as well as an alarm about cooling failure in the water-cooled elements of the installation.
Rice. 3. Power supply circuit for an induction crucible furnace from a medium frequency machine converter with a block diagram of automatic control of the melting mode: M - drive motor, G - medium frequency generator, 1K-NK - magnetic starters, TI - voltage transformer, TT - current transformer, IP - induction furnace, C - capacitors, DF - phase sensor, PU - switching device, UFR - amplifier-phase regulator, 1KL, 2KL - linear contactors, BS - comparison unit, BZ - protection unit, OV - excitation winding, RN - voltage regulator.
Scheme of induction hardening installation
In Fig. Figure 4 shows a schematic diagram of the power supply of an induction hardening machine from a machine frequency converter. Besides the source power supply M-G the circuit includes a power contactor K, a hardening transformer TrZ, on the secondary winding of which an inductor I is connected, a compensating capacitor bank Sk, voltage and current transformers TN and 1TT, 2TT, measuring instruments (voltmeter V, wattmeter W, phase meter) and generator current ammeters and excitation current, as well as a maximum current relay 1РМ, 2РМ to protect the power source from short circuits and overloads.
Rice. 4. Schematic electrical diagram of an induction hardening installation: M - drive motor, G - generator, TN, TT - voltage and current transformers, K - contactor, 1PM, 2RM, ZRM - current relay, Rk - arrester, A, V, W - measuring instruments, TRZ - hardening transformer, OVG - generator excitation winding, RR - discharge resistor, PB - excitation relay contacts, PC - adjustable resistance.
To power old induction installations for heat treatment of parts, electric machine frequency converters are used - a drive motor of a synchronous or asynchronous type and a medium-frequency generator of an inductor type; in new ones induction installations- static frequency converters.
The circuit of an industrial thyristor frequency converter for powering an induction hardening installation is shown in Fig. 5. The thyristor frequency converter circuit consists of a rectifier, a block of chokes, a converter (inverter), control circuits and auxiliary components (reactors, heat exchangers, etc.). According to the method of excitation, inverters are made with independent excitation (from the master oscillator) and with self-excitation.
Thyristor converters can operate stably both with frequency changes over a wide range (with self-adjusting oscillatory circuit in accordance with changing load parameters), and at a constant frequency with wide range changes in load parameters due to changes in the active resistance of the heated metal and its magnetic properties(for ferromagnetic parts).
Rice. 5. Schematic diagram of the power circuits of a thyristor converter type TPC-800-1: L - smoothing reactor, BP - starting unit, VA - automatic switch.
The advantages of thyristor converters are the absence of rotating masses, low loads on the foundation and the small influence of the power utilization factor on the reduction in efficiency; the efficiency is 92 - 94% at full load, and at 0.25 it decreases by only 1 - 2%. In addition, since the frequency can be easily changed within a certain range, there is no need to adjust the capacitance to compensate reactive power oscillatory circuit.
