Operating principle of induction furnaces. The principle of induction heating. How to make an induction furnace with your own hands Do-it-yourself induction crucible

Well-established metal and steel production technologies have already been formed in the world, which metallurgical enterprises still use today. These include: converter method of metal production, rolling, drawing, casting, stamping, forging, pressing, etc. However, the most common when modern conditions is the remelting of metal and steel in convectors, open-hearth furnaces and electric furnaces. Each of these technologies has a number of disadvantages and advantages. However, the most perfect and the latest technology today is the production of steel in electric furnaces. The main advantages of the latter over other technologies are high performance and environmental friendliness. Let's consider how to assemble a device where metal will be melted at home with your own hands.

Small-sized induction electric furnace for melting metals at home

Melting metals at home is possible if you have an electric furnace that you can make yourself. Let's consider the creation of an inductive small-sized electric oven to obtain homogeneous alloys (OS). Compared to analogues, the created installation will differ in the following features:

low cost (up to 10,000 rubles), while the cost of analogues is from 150,000 rubles;
possibility of regulation temperature regime;
the possibility of high-speed melting of metals in small volumes, which allows the installation to be used not only in the scientific field, but also, for example, in the jewelry, dental fields, etc.
uniformity and heating rate;
the possibility of placing the working body in a furnace in a vacuum;
relatively small dimensions;
low noise level, almost complete absence of smoke, which will increase labor productivity when working with the installation;
possibility of operation from both single-phase and three-phase networks.

Choosing a schema type

Most often, when building induction heaters, three main types of circuits are used: half bridge, asymmetric bridge and full bridge. When designing this installation, two types of circuits were used - a half-bridge and a full bridge with frequency regulation. This choice was driven by the need to regulate power factor. The problem arose of maintaining the resonance mode in the circuit, since it is with its help that the required power value can be adjusted. There are two ways to regulate resonance:

by changing the capacity;
by changing the frequency.

In our case, resonance is supported by adjusting the frequency. It was this feature that caused the choice of the type of frequency-controlled circuit.

Analysis of circuit components

Analyzing the operation of an induction furnace for melting metal at home (IP), we can distinguish its three main parts: a generator, a power supply unit, and a power unit. To provide the required frequency during operation of the installation, a generator is used, which, to avoid interference from other units of the installation, is connected to them through a galvanic solution in the form of a transformer. To provide the power voltage circuit, a power supply is required to ensure safe and reliable operation strength elements of the structure. Actually, it is the power unit that generates the necessary powerful signals to create the required power factor at the output of the circuit.

Figure 1 shows the general circuit diagram induction installation.

Creating a Wiring Diagram

Wiring diagram (wiring diagram) shows connections components products and identifies the wires and cables that make these connections, as well as their connection points.

For the convenience of further installation of the installation, a connection diagram was developed that reflects the main contacts between the functional blocks of the furnace (Fig. 2).

Frequency generator

The most complex IP block is the generator. It provides the required operating frequency of the installation and creates the initial conditions for obtaining a resonant circuit. A specialized electronic pulse controller of the KR1211EU1 type is used as a source of oscillations (Fig. 3). This choice was caused by the ability of this microcircuit to operate in a fairly wide frequency range (up to 5 MHz), which makes it possible to obtain high value power at the output of the power block of the circuit.

Figures 4 and 5 show a schematic diagram of the frequency generator and a diagram of the electrical board.

The KR1211EU1 microcircuit generates signals of a given frequency, which can be changed using a control resistor installed outside the microcircuit. Next, the signals go to transistors operating in switching mode. In our case, silicon field-effect transistors with an insulated gate of the KP727 type are used. Their advantages are as follows: the maximum permissible pulse current that they can withstand is 56 A; maximum voltage is 50 V. We are completely satisfied with the range of these indicators. But, in connection with this, the problem of significant overheating arose. It is to solve this issue that a key mode is needed, which will reduce the time the transistors are in working condition.

power unit

This block provides power supply to the executive units of the installation. Its main feature is the ability to operate from single-phase and three-phase networks. A 380V power supply is used to improve the power factor generated in the inductor.

The input voltage is supplied to a rectifying bridge, which converts 220V AC voltage into pulsating DC voltage. Storage capacitors are connected to the bridge outputs, which maintain a constant voltage level after removing the load from the installation. To ensure reliable operation of the installation, the unit is equipped with an automatic switch.

Power block

This block provides direct signal amplification and the creation of a resonant circuit by changing the capacitance of the circle. Signals from the generator go to transistors, which operate in amplification mode. Thus, they, opening at different times, excite the corresponding electrical circuits passing through the step-up transformer and pass power current through it in different directions. As a result, at the output of the transformer (Tr1) we receive an increased signal with a given frequency. This signal is supplied to the installation with an inductor. An installation with an inductor (Tr2 in the diagram) consists of an inductor and a set of capacitors (C13 - Sp). Capacitors have a specially selected capacitance and create an oscillating circuit that allows you to adjust the level of inductance. This circuit must operate in resonance mode, which causes a rapid increase in the frequency of the signal in the inductor, and an increase in induction currents, due to which heating actually occurs. Figure 7 shows the electrical diagram of the power unit of an induction furnace.

Inductor and features of its operation

An inductor is a special device for transferring energy from a power source to a product; it heats up. Inductors are usually made from copper tubes. During operation, it is cooled by running water.

Melting non-ferrous metals at home using an induction furnace involves the penetration of induction currents into the middle of the metals, which arise due to the high frequency of voltage changes applied to the inductor terminals. The power of the installation depends on the magnitude of the applied voltage and its frequency. Frequency affects the intensity of induction currents and, accordingly, the temperature in the middle of the inductor. The greater the frequency and operating time of the installation, the better the metals are mixed. The inductor itself and the directions of flow of induction currents are shown in Figure 8.

To ensure uniform mixing and avoid contamination of the alloy with foreign elements, for example, electrodes from a tank with an alloy, an inductor with a reverse turn is used as shown in Figure 9. It is thanks to this turn that an electromagnetic field is created that holds the metal in the air, exceeding the force of gravity of the Earth.

Final installation of the installation

Each of the blocks is attached to the body of the induction furnace using special racks. This is done in order to avoid unwanted contacts of live parts with metal coating the body itself (Fig. 10).

For safe operation of the installation, it is completely covered with a durable casing (Fig. 11), thus creating a barrier between dangerous structural elements and the body of the person working with it.

For the convenience of setting up the induction installation as a whole, an indication panel was made to accommodate metrological devices, with the help of which all parameters of the installation are monitored. Such metrological devices include: an ammeter that shows the current in the inductor, a voltmeter connected to the output of the inductor, a temperature indicator, and a signal generation frequency controller. All of the above parameters make it possible to regulate the operating modes of the induction unit. The design is also equipped with a manual activation system and an indication system for heating processes. With the help of displays on devices, the operation of the installation as a whole is actually monitored.

Designing a small-sized induction installation is quite complex technological process, since it must ensure compliance with a large number of criteria, such as: ease of design, small size, portability, etc. This installation It works on the principle of contactless transfer of energy into an object and heats up. As a result of the targeted movement of induction currents in the inductor, the melting process itself occurs directly, the duration of which is several minutes.

The creation of this installation is quite profitable, since its scope of application is limitless, starting with use for ordinary laboratory work and ending with the production of complex homogeneous alloys from refractory metals.

Heating and melting of metals in induction furnaces occurs due to internal heating and changes in crystalline...

How to assemble an induction furnace for melting metal with your own hands at home

Metal smelting by induction is widely used in various industries: metallurgy, mechanical engineering, jewelry. You can assemble a simple induction furnace for melting metal at home with your own hands.

Operating principle

Heating and melting of metals in induction furnaces occurs due to internal heating and change crystal lattice metal when high-frequency eddy currents pass through them. This process is based on the phenomenon of resonance, in which eddy currents have a maximum value.

To cause eddy currents to flow through the molten metal, it is placed in the area of electricity. magnetic field inductor - coil. It can be in the shape of a spiral, figure eight or trefoil. The shape of the inductor depends on the size and shape of the heated workpiece.

The inductor coil is connected to an alternating current source. In industrial melting furnaces, industrial frequency currents of 50 Hz are used; for melting small volumes of metals in jewelry, high-frequency generators are used as they are more efficient.

Species

Eddy currents are closed along a circuit limited by the magnetic field of the inductor. Therefore, heating of the conductive elements is possible both inside the coil and on its outside.

channel, in which the container for melting metals is channels located around the inductor, and a core is located inside it;
crucible, they use a special container - a crucible made of heat-resistant material, usually removable.

Channel furnace too large and designed for industrial volumes of metal smelting. It is used in the smelting of cast iron, aluminum and other non-ferrous metals.

Crucible furnace It is quite compact, it is used by jewelers and radio amateurs; such a stove can be assembled with your own hands and used at home.

Device

high frequency alternating current generator;
inductor - a spiral winding made of copper wire or tube, made by hand;
crucible.

The crucible is placed in an inductor, the ends of the winding are connected to a current source. When current flows through the winding, an electromagnetic field with a variable vector appears around it. In a magnetic field, eddy currents arise, directed perpendicular to its vector and passing along a closed loop inside the winding. They pass through the metal placed in the crucible, heating it to the melting point.

Advantages of an induction furnace:

fast and uniform heating of the metal immediately after turning on the installation;
direction of heating - only the metal is heated, and not the entire installation;
high melting speed and melt homogeneity;
there is no evaporation of metal alloying components;
The installation is environmentally friendly and safe.

A welding inverter can be used as a generator for an induction furnace for melting metal. You can also assemble a generator using the diagrams below with your own hands.

Furnace for melting metal using a welding inverter

This design is simple and safe, since all inverters are equipped with internal overload protection. The entire assembly of the furnace in this case comes down to making an inductor with your own hands.

It is usually performed in the form of a spiral from a thin-walled copper tube with a diameter of 8-10 mm. It is bent according to a template of the required diameter, placing the turns at a distance of 5-8 mm. The number of turns is from 7 to 12, depending on the diameter and characteristics of the inverter. The total resistance of the inductor must be such as not to cause overcurrent in the inverter, otherwise it will be turned off by the internal protection.

The inductor can be fixed in a housing made of graphite or textolite and a crucible can be installed inside. You can simply place the inductor on a heat-resistant surface. The housing must not conduct current, otherwise eddy currents will pass through it and the power of the installation will decrease. For the same reason, it is not recommended to place foreign objects in the melting zone.

When working from welding inverter its body must be grounded! The outlet and wiring must be rated for the current drawn by the inverter.

The heating system of a private home is based on the operation of a stove or boiler, the high performance and long uninterrupted service life of which depends on both the brand and installation itself heating devices, and from correct installation chimney.

Induction furnace with transistors: diagram

There are many different ways to assemble an induction heater yourself. A fairly simple and proven diagram of a furnace for melting metal is shown in the figure:

two field-effect transistors type IRFZ44V;
two UF4007 diodes (UF4001 can also be used);
resistor 470 Ohm, 1 W (you can take two 0.5 W connected in series);
film capacitors for 250 V: 3 pieces with a capacity of 1 μF; 4 pieces - 220 nF; 1 piece - 470 nF; 1 piece - 330 nF;
copper winding wire in enamel insulation Ø1.2 mm;
copper winding wire in enamel insulation Ø2 mm;
two rings from chokes removed from computer unit nutrition.

DIY assembly sequence:

Field effect transistors are installed on radiators. Since the circuit gets very hot during operation, the radiator must be large enough. You can install them on one radiator, but then you need to isolate the transistors from the metal using gaskets and washers made of rubber and plastic. The pinout of field-effect transistors is shown in the figure.

It is necessary to make two chokes. To make them, copper wire with a diameter of 1.2 mm is wound around rings removed from the power supply of any computer. These rings are made of powdered ferromagnetic iron. It is necessary to wind from 7 to 15 turns of wire on them, trying to maintain the distance between the turns.

The capacitors listed above are assembled into a battery with a total capacity of 4.7 μF. The connection of capacitors is parallel.

The inductor winding is made of copper wire with a diameter of 2 mm. Wrap 7-8 turns of winding around a cylindrical object suitable for the diameter of the crucible, leaving the ends long enough to connect to the circuit.
Connect the elements on the board in accordance with the diagram. A 12 V, 7.2 A/h battery is used as a power source. The current consumption in operating mode is about 10 A, the battery capacity in this case will last for about 40 minutes. If necessary, the furnace body is made from a heat-resistant material, for example, textolite. The power of the device can be changed by changing the number of turns of the inductor winding and their diameter.

During prolonged operation, the heater elements may overheat! You can use a fan to cool them.

Induction heater for metal melting: video

Induction furnace with lamps

You can assemble a more powerful induction furnace for melting metals with your own hands using electronic tubes. The device diagram is shown in the figure.

To generate high-frequency current, 4 beam lamps connected in parallel are used. A copper tube with a diameter of 10 mm is used as an inductor. The installation is equipped with a tuning capacitor to regulate power. The issued frequency is 27.12 MHz.

To assemble the circuit you need:

4 electron tubes - tetrodes, you can use 6L6, 6P3 or G807;
4 chokes at 100...1000 µH;
4 capacitors at 0.01 µF;
neon indicator lamp;
trimmer capacitor.

Assembling the device yourself:

An inductor is made from a copper tube by bending it into a spiral shape. The diameter of the turns is 8-15 cm, the distance between the turns is at least 5 mm. The ends are tinned for soldering to the circuit. The diameter of the inductor should be 10 mm larger than the diameter of the crucible placed inside.
The inductor is placed in the housing. It can be made from a heat-resistant, non-conducting material, or from metal, providing thermal and electrical insulation from the circuit elements.
Cascades of lamps are assembled according to a circuit with capacitors and chokes. The cascades are connected in parallel.
Connect a neon indicator lamp - it will signal that the circuit is ready for operation. The lamp is brought out to the installation body.
The circuit includes a tuning capacitor variable capacity, its handle is also brought out onto the body.

For all lovers of delicacies prepared using the cold smoking method, we suggest you learn here how to quickly and easily make a smokehouse with your own hands, and here you can get acquainted with photos and video instructions for making a smoke generator for cold smoking.

Circuit cooling

Industrial smelting plants are equipped with a forced cooling system using water or antifreeze. Performing water cooling at home will require additional costs, comparable in price to the cost of the metal melting installation itself.

Air cooling using a fan is possible, provided the fan is located far enough away. Otherwise, the metal winding and other elements of the fan will serve as an additional circuit for closing eddy currents, which will reduce the efficiency of the installation.

Elements of electronic and lamp circuits can also actively heat up. To cool them, heat sinks are provided.

Safety precautions when working

The main danger when working with homemade installation- danger of burns from heated elements of the installation and molten metal.
The lamp circuit includes high-voltage elements, so it must be placed in a closed housing to prevent accidental contact with the elements.
The electromagnetic field can affect objects located outside the device body. Therefore, before work, it is better to put on clothes without metal elements, remove complex devices from the coverage area: phones, digital cameras.

A furnace for melting metals at home can also be used to quickly heat metal elements, for example, when tinning or forming them. The operating characteristics of the presented installations can be adjusted to a specific task by changing the parameters of the inductor and the output signal generator sets- this is how you can achieve their maximum efficiency.

Induction furnaces are used for smelting metals and are distinguished by the fact that heating in them occurs through electric current. The current is excited in the inductor, or more precisely in a constant field.

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

into 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.

Pay attention! Induction designs come in two types - with or without a core. In the first case, the metal is placed in a tubular trough, which is located around the inductor. The core is located in the inductor itself. The second option is called crucible, because in it the metal and the crucible are 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 makeDIY induction oven.

Pros and cons of induction designs

Among the many advantages, the following are worth highlighting:

environmental cleanliness and safety;
increased homogeneity of the melt due to active movement of metal;
speed – the oven can be used almost immediately after switching on;
zonal and focused energy orientation;
high melting rate;
no fumes from alloying substances;
possibility of temperature adjustment;
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.
The magnetic field is dissipated between the coil and the melting metal, so a reduction in the thickness of the lining will be required. This will soon lead to the lining itself failing.

Video – Induction oven

Industrial Application

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

Furnaces industrial purposes 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 melted.
Industrial frequency designs are used in iron smelting.
Resistance structures are intended for melting aluminum, aluminum alloys, and zinc.

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

Household use

Due to obvious reasons, an induction furnace for melting is not often used in everyday life. But the technology described in the article is found in almost all modern houses and apartments. These include the above-mentioned microwave ovens, induction cookers, and electric ovens.

Consider, for example, slabs. They heat the dishes due to induction eddy currents, as a result of which heating occurs almost instantly. It is typical that it is impossible to turn on a burner that has no cookware on it.

The efficiency of induction cookers reaches 90%. For comparison: for electric stoves it is approximately 55-65%, and for gas stoves it is no more than 30-50%. But in fairness, it is worth noting that special utensils are required to operate the described stoves.

Homemade induction furnace

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

Induction furnace made from high frequency generator

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

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

Pay attention! The main difference between a stove made according to this scheme is the condenser handle - in this case it is located outside.

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

When making it is necessary to remember some important points, affecting the speed of metal control. This:

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

The device will be powered from 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 take a closer look at each of the designs.

Video - Construction of a welding inverter

The essence of the design is as follows: a pair of graphite brushes is installed, and granite powder is poured between them, after which the connection is made to the step-down transformer. It is characteristic that during smelting there is no need to fear electric shock, since there is no need to use 220 V.

Assembly technology

Step 1. The base is assembled - a box made of fireclay bricks measuring 10x10x18 cm, laid on fire-resistant tiles.

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

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

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

Step 4. The transformer is wrapped thin aluminum– this way the structure will not get too hot during operation.

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

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

So, to smelt large volumes of metal you will need a furnace with nichrome wire. The operating principle of the design is quite simple: electric current is supplied to a nichrome spiral, which heats up and melts the metal. There are a lot of different formulas on the Internet for calculating the length of a wire, but they are all, in principle, the same.

Step 1. For the spiral, nichrome ø0.3 mm with a length of about 11 m is used.

Step 2. The wire must be wound. To do this, you will need a straight copper tube ø5 mm - the spiral is wound on it.

Step 3. A small ceramic pipe ø1.6 cm and 15 cm long is used as a crucible. One end of the pipe is plugged with asbestos thread - this way the molten metal will not flow out.

Step 4. After checking the functionality, the spiral is laid around the pipe. In this case, the same asbestos thread is placed between the turns - it will prevent short circuits and limit the access of oxygen.

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

Advantages of this design:

high productivity (up to 30 g per pass);
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, disadvantages:

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

Pay attention! You cannot add metal to the stove if the previous portion has already been melted there. Otherwise, all the material will scatter throughout the room, moreover, it can injure your eyes.

As a conclusion

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

editor-in-chief

How to make an induction heater with your own hands?

Electric heaters

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

The closed conductor in induction cookers is metal utensils, 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:

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

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:

Ideally conduct electromagnetic radiation.
Not a conductive material.
Withstand high temperature load.

Expensive ceramics are used in household induction hobs; when manufactured 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.

Manufacturing instructions

Figure 1. Electrical diagram induction heater

Figure 2. Device.

Figure 3. Schematic of a simple induction heater

To make a furnace you will need following materials and tools:

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

Additional materials and their features:

For making a coil, which will emit the 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 install the frequency generator circuit, you need to prepare 2 such elements. Transistors of the following brands are suitable for these purposes: IRFP-150; IRFP-260; IRFP-460. When manufacturing 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 high-power alternating current to form in the coil, 7 such capacitors will be required.
When working like this induction device , field-effect transistors will get very hot and if radiators from aluminum alloy, then after just a few seconds of working on maximum power, these elements will fail. Transistors should be placed on heat sinks through thin layer thermal paste, otherwise the effectiveness of such cooling will be minimal.
Diodes, which are used in an induction heater, must be ultra-fast acting. The most suitable diodes for this circuit are: MUR-460; UF-4007; HER – 307.
Resistors used in circuit 3: 10 kOhm power 0.25 W – 2 pcs. and 440 Ohm power - 2 W. Zener diodes: 2 pcs. with an operating voltage of 15 V. The power of the zener diodes must be at least 2 W. A choke for connecting to the power terminals of the coil is used with induction.
To power the entire device you will need a power supply with a power of up to 500 W. and voltage 12 - 40 V. This device can be powered from car battery, but it will not be possible to obtain the highest power readings at this voltage.

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

From copper pipe a spiral with a diameter of 4 cm is made. To make a spiral, you should copper tube screw onto the rod with flat surface 4 cm in diameter. The spiral must have 7 turns, which should not touch. Fastening 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 diagram. 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 operate much more stable. The capacitors in the circuit are installed in parallel to form an oscillating circuit with a copper coil.
Heating the metal occurs inside the coil after the circuit is connected to the power supply or battery. When heating metal, care must be taken not to short circuit spring windings. If you touch 2 turns of the coil at the same time with heated metal, the transistors will fail instantly.

When conducting experiments on heating and hardening of metals, inside the induction coil the temperature can be significant and amounts to 100 degrees Celsius. This thermal heating effect can be used to heat water for household needs or for heating a house.
Diagram of the heater discussed above (Figure 3), at maximum load is capable of providing radiation of magnetic energy inside the coil equal to 500 W. This 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.
Budget solution for organizing induction heating of liquids, is the use of several devices described above, located in series. In this case, the spirals must be on the same line and not have a common metal conductor.
As a heat exchangera pipe from stainless steel with a diameter of 20 mm. 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. When 4 such devices are turned on simultaneously, the heating power will be about 2 kW, which is already sufficient for flow-through heating of liquid with a small circulation of water, to values allowing the use of this design in supply warm water small house.
If you connect this heating element with well insulated tank, which will be located above the heater, the result will be a boiler system in which the liquid will be heated inside stainless pipe, heated water will rise upward, and colder liquid will take its place.
If the area of the house is significant, then the number of induction coils can be increased to 10 pieces.
The power of such a boiler can be easily adjusted by turning off or turning on the spirals. The more sections that are turned on at the same time, the greater the power of the heating device operating in this way.
To power such a module you will need a powerful power supply. If inverter is available welding machine DC, then a voltage converter of the required power can be made from it.
Due to the fact that the system operates on constant 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.
You can organize “free” home heating in this way., subject to the installation of rechargeable batteries to power the induction devices, the charging of which will be carried out using solar and wind energy.
The batteries should be combined into 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 boiler operates at high power. Besides this, serial connection will reduce the current in the circuit and increase the service life of the batteries.

Operation homemade devices induction heating, does not always eliminate the spread of harmful to humans electromagnetic radiation, 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 can be made hob for cooking according to the scheme specified in the article, but it is not recommended to use this device constantly due to imperfections self-made shielding of this device, because of this, the human body may be exposed to harmful electromagnetic radiation that can adversely affect health.

Induction furnaces were invented back in 1887. And just three years later, the first industrial development appeared, with the help of which they smelted various metals. I would like to note that in those distant years these stoves were a novelty. The thing is that scientists of that time did not quite understand what processes were occurring in it. Today we figured it out. In this article we will be interested in the topic - do-it-yourself induction furnace. How simple is its design, is it possible to assemble this unit at home?

Operating principle

You need to start assembling by understanding the principle of operation and structure of the device. Let's start with this. Pay attention to the figure above, we will understand it according to it.

The device includes:

Generator G, which produces alternating current.
Capacitor C, together with coil L, creates an oscillating circuit, which provides the installation with high temperature.

Attention! Some designs use a so-called self-oscillating generator. This makes it possible to remove the capacitor from the circuit.
The coil in the surrounding space forms a magnetic field in which there is a voltage, indicated in our figure by the letter “H”. The magnetic field itself exists in free space, and can be closed through a ferromagnetic core.
It also acts on the charge (W), in which it creates a magnetic flux (F). By the way, instead of the charge, some kind of blank can be installed.
The magnetic flux induces a secondary voltage of 12 V. But this only happens if W is an electrically conductive element.
If the heated workpiece is large and solid, then the so-called Foucault current begins to operate inside it. It is of the vortex type.
In this case, eddy currents are transmitted from the generator through a magnetic field thermal energy, thereby heating the workpiece.

The electromagnetic field is quite wide. And even the multi-stage energy conversion, which is present in homemade induction furnaces, has maximum efficiency - up to 100%.

Crucible furnace

Varieties

There are two main designs induction furnaces:

Duct.
Crucible.

We won’t describe them all here. distinctive features. Just note that the channel version is a design that is similar to a welding machine. In addition, in order to melt metal in such furnaces, it was necessary to leave a little melt, without which the process simply would not work. The second option is an improved scheme that uses technology without residual melt. That is, the crucible is simply installed directly into the inductor.

How does this work

Why do you need such a stove at home?

In general, the question is quite interesting. Let's look at this situation. There is a fairly large number of Soviet electrical and electronic devices that used gold or silver contacts. These metals can be removed in different ways. One of them is an induction stove.

That is, you take the contacts, put them in a narrow and long crucible, which you install in the inductor. After 15-20 minutes, reducing the power, cooling the apparatus and breaking the crucible, you will get a rod, at the end of which you will find a gold or silver tip. Cut it off and take it to a pawnshop.

Although it should be noted that with this homemade unit can be carried out various processes with metals. For example, you can harden or temper.

Coil with battery (generator)

Stove components

In the Working Principle section, we have already mentioned all the parts of an induction furnace. And if everything is clear with the generator, then the inductor (coil) needs to be sorted out. A copper tube is suitable for it. If you are assembling a device with a power of 3 kW, then you will need a tube with a diameter of 10 mm. The coil itself is twisted with a diameter of 80-150 mm, with a number of turns from 8 to 10.

Please note that the turns of the copper tube should not touch each other. The optimal distance between them is 5-7 mm. The coil itself should not touch the screen. The distance between them is 50 mm.

Typically, industrial induction furnaces have a cooling unit. It is impossible to do this at home. But for a 3 kW unit, working for up to half an hour is not dangerous. True, over time, copper scale will form on the tube, which reduces the efficiency of the device. So the coil will have to be changed periodically.

Generator

In principle, making a generator with your own hands is not a problem. But this is only possible if you have sufficient knowledge in radio electronics at the level of an average radio amateur. If you don’t have such knowledge, then forget about the induction stove. The most important thing is that you also need to skillfully operate this device.

If you are faced with the dilemma of choosing a generator circuit, then take one piece of advice - it should not have a hard current spectrum. In order to make it clearer what we are talking about, we offer the most simple diagram generator for an induction furnace in the photo below.

Generator circuit

Required knowledge

The electromagnetic field affects all living things. An example is microwaved meat. Therefore, it is worth taking care of safety. And it doesn’t matter whether you are assembling the stove and testing it or working on it. There is such an indicator as energy flux density. So it depends on exactly electromagnetic field. And the higher the frequency of radiation, the worse it is for the human body.

Many countries have adopted safety measures that take into account energy flux density. There are developed acceptable limits. This is 1-30 mW per 1 m² of the human body. These indicators are valid if exposure occurs no more than one hour per day. By the way, the installed galvanized screen reduces the density of the ceiling by 50 times.

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The closed conductor in induction cookers is a metal pan, 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:

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

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:

Ideally conduct electromagnetic radiation.
Not a conductive material.
Withstand high temperature load.

Household induction cooking surfaces use expensive ceramics; when making an induction cooker at home, it is quite difficult to find a worthy alternative to such material. Therefore, first you should design something simpler, for example, an induction furnace for hardening metals.

Manufacturing instructions

Drawings

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:

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

Additional materials and their features:

For making a coil, which will emit the 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 install the frequency generator circuit, you need to prepare 2 such elements. Transistors of the following brands are suitable for these purposes: IRFP-150; IRFP-260; IRFP-460. When manufacturing 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 high-power alternating current to form in the coil, 7 such capacitors will be required.
When operating such an induction device, field-effect transistors will get very hot and if aluminum alloy radiators are not attached to them, then after just a few seconds of operation at maximum power, these elements will fail. Transistors should be placed on heat sinks through a thin layer of thermal paste, otherwise the effectiveness of such cooling will be minimal.
Diodes, which are used in an induction heater, must be ultra-fast acting. The most suitable diodes for this circuit are: MUR-460; UF-4007; HER – 307.
Resistors used in circuit 3: 10 kOhm power 0.25 W – 2 pcs. and 440 Ohm power - 2 W. Zener diodes: 2 pcs. with an operating voltage of 15 V. The power of the zener diodes must be at least 2 W. A choke for connecting to the power terminals of the coil is used with induction.
To power the entire device you will need a power supply with a power of up to 500 W. and voltage 12 - 40 V. You can power this device from a car battery, but you won’t be able to get the highest power readings at this voltage.

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

From copper pipe a spiral with a diameter of 4 cm is made. To make a spiral, a copper tube should be screwed onto a rod with a flat surface with a diameter of 4 cm. The spiral should have 7 turns, which should not touch. Fastening 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 diagram. If it is possible to install 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 operate much more stable. The capacitors in the circuit are installed in parallel to form an oscillating circuit with a copper coil.
Heating the metal occurs inside the coil after the circuit is connected to the power supply or battery. When heating the metal, it is necessary to ensure that there is no short circuit in the spring windings. If you touch 2 turns of the coil at the same time with heated metal, the transistors will fail instantly.

Nuances

When conducting experiments on heating and hardening of metals, inside the induction coil the temperature can be significant and amounts to 100 degrees Celsius. This thermal heating effect can be used to heat water for domestic use or for heating a home.
Diagram of the heater discussed above (Figure 3), at maximum load is capable of providing radiation of magnetic energy inside the coil equal to 500 W. This 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.
Budget solution for organizing induction heating of liquids, is the use of several devices described above, located 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. When 4 such devices are turned on simultaneously, the heating power will be about 2 kW, which is already sufficient for flow-through heating of liquid with a small circulation of water, to values that allow this design to be used 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 liquid will be heated inside a stainless pipe, the heated water will rise upward, and a colder liquid will take its place.
If the area of the house is significant, then the number of induction coils can be increased to 10 pieces.
The power of such a boiler can be easily adjusted by turning off or turning on the spirals. The more sections that are turned on at the same time, the greater the power of the heating device operating in this way.
To power such a module you will need a powerful power supply. If you have a DC inverter welding machine, you can use it to make a voltage converter of the required power.
Due to the fact that the system operates on constant 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.
You can organize “free” home heating in this way., subject to the installation of rechargeable batteries to power the induction devices, the charging of which will be carried out using solar and wind energy.
The batteries should be combined into 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 boiler operates at high power. In addition, a series connection will reduce the current in the circuit and increase the service life of the batteries.

Operation of homemade induction heating devices, does not always eliminate the spread of electromagnetic radiation harmful to humans, so 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 specified in the article, but it is not recommended to constantly operate this device due to the imperfection of the self-manufactured shielding of this device; because of this, the human body may be exposed to harmful electromagnetic radiation that can negatively affect health.

Heating of bodies using an electromagnetic field arising from exposure to an induced current is called induction heating. Electrothermal equipment, or induction furnace, has different models, designed to perform tasks for various purposes.

Design and principle of operation

By technical specifications The device is part of a plant used in the metallurgical industry. The working principle of induction furnace depends on alternating current, the power of the installation is determined by the purpose of the device, the design of which includes:

inductor;
frame;
melting chamber;
vacuum system;
mechanisms for moving the heating object and other devices.

Modern consumer market has a large number of models of devices operating according to the scheme of formation of eddy currents. The operating principle and design features of an industrial induction furnace make it possible to perform a number of specific operations related to the melting of non-ferrous metals, heat treatment metal products, sintering synthetic materials, cleaning precious and semi-precious stones. Household appliances used for disinfection of household items and heating of premises.

The work of an induction furnace is to heat objects placed in the chamber with eddy currents emitted by an inductor, which is an inductor coil made in the shape of a spiral, figure eight or trefoil with a winding of large cross-section wire. An inductor operating from alternating current creates a pulsed magnetic field, the power of which varies in accordance with the frequency of the current. An object placed in a magnetic field is heated to the point of boiling (liquid) or melting (metal).

Installations operating using a magnetic field are produced in two types: with a magnetic conductor and without a magnetic conductor. The first type of device has an inductor in its design, enclosed in a metal case, which ensures a rapid increase in temperature inside the object being processed. In furnaces of the second type, the magnetotron is located outside the installation.

Features of induction devices

The master also requires skills in the design and installation of electrical appliances. The safety of a custom-assembled device lies in a number of features:

equipment capacity;
operating pulse frequency;
generator power;
eddy losses;
hysteresis losses;
heat output intensity;
lining method.

Channel furnaces got their name from the presence in the space of the unit of two holes with a channel forming a closed loop. By design features the device cannot work without a circuit, thanks to which the liquid aluminum is in continuous movement. If the manufacturer's recommendations are not followed, the equipment switches off spontaneously, interrupting the melting process.

According to the location of the channels, induction melting units can be vertical or horizontal with a drum or cylindrical chamber shape. The drum furnace in which cast iron can be melted is made of sheet steel. The turning mechanism is equipped with drive rollers, a two-speed electric motor and a chain drive.

Liquid bronze is poured through a siphon located on the end wall, additives and slags are loaded and removed through special holes. Issue finished products carried out through a V-shaped drain channel made in the lining according to a template, which melts during the working process. Cooling of the winding and core is carried out by air mass, the temperature of the housing is regulated using water.