Homemade induction furnaces. Induction furnace for metal melting. How to assemble an induction furnace - diagrams and instructions

Many people believe that the process of smelting metal requires huge facilities, practically factories with a large number of employees. But there is still such a profession as a jeweler and metals such as gold, silver, platinum and others used to make delicate and exquisite jewelry, some of which are rightfully considered real works of art. A jewelry workshop is an enterprise that does not tolerate excessive scale. And the melting process in them is simply necessary. Therefore, an induction furnace for melting metal is necessary here. It is not large, and very efficient, and easy to handle.

The principle of operation of an induction furnace is a wonderful example of how an undesirable phenomenon is used with increased efficiency. The so-called Foucault eddy currents, which usually interfere with any kind of electrical engineering, are only aimed at a positive result here.

In order for the structure of the metal to begin to heat up and then melt, it must be placed under these same Foucault currents, and they are formed in an induction coil, which, by and large, is a furnace.

Simply put, everyone knows that during operation, any electrical appliance starts to heat up. The metal melting induction furnace takes full advantage of this otherwise undesirable effect.

Advantages over other types of melting furnaces

Induction furnaces are not the only invention used to melt metals. There are also famous open-hearth, blast furnaces and other types. However, the furnace we are considering has a number of undeniable advantages over all the others.

• Induction ovens can be quite compact, and their placement will not cause any difficulties.
• High melting speed. If other metal melting furnaces require several hours just to heat up, induction copes with this several times faster.
• The efficiency is only slightly less than 100%.
• According to the purity of the melt, the induction furnace confidently takes the first place. In other devices, the workpiece prepared for the melt is in direct contact with the heating element, which often leads to contamination. Foucault currents heat the workpiece from the inside, affecting the molecular structure of the metal, and no side elements get into it.

The latter advantage is essential in jewelry, where the frequency of the material enhances its value and uniqueness.

Furnace placement

Compact induction furnace, depending on the size, it can be floor and desktop. Whichever option you choose, there are a few basic rules for choosing where to put it.

• Despite the ease of handling the oven, it is still an electrical appliance that requires safety measures. And the first thing to consider during installation is the availability of the correct power source corresponding to the model of the device.
• The ability to carry out high-quality grounding.
• Provision of installation with water supply.
• Table ovens require a stable base.
• But most importantly, nothing should interfere with work. Even if the melt is not too large in volume and mass, its temperature is more than 1000 degrees and accidentally splashing it out of the mold means inflicting very severe injury either on oneself or on what is nearby.

There is nothing to say about the fact that there should not be any combustible and, even more so, explosive materials near a working induction furnace. But a fire shield within walking distance is absolutely necessary.

Types of induction furnaces

Two types of induction furnaces are widely used: channel and crucible. They differ only in the way they work. In all other respects, including advantages, such melting furnaces are very similar. Let's consider each option separately:

• Channel oven. The main advantage of this type is a continuous cycle. You can load a new portion of raw materials and unload already molten metal directly during heating. The only difficulty may arise at startup. The channel through which the liquid metal will be removed from the furnace must be filled.
• Crucible furnace. Unlike the first option, each portion of the metal will have to be loaded separately. This is the point. The raw material is placed in a heat-resistant crucible and placed inside the inductor. After the metal melts, it is drained from the crucible and only then the next portion is loaded. Such a furnace is ideal for small workshops where large masses of molten raw materials are not required.

The main advantage of both options is the speed of production. However, the crucible furnace wins here too. In addition, it is quite possible to make it yourself at home.

A home-made induction furnace does not contain any difficulties so that an ordinary person who is at least a little familiar with electrical engineering cannot assemble it. It has only three main blocks:

• Generator.
• Inductor.
• Crucible.

The inductor is a copper winding that you can make yourself. You will have to look for the crucible either in the appropriate stores, or get it in other ways. And as a generator can be used: a welding inverter, a personally assembled transistor or lamp circuit.

Induction furnace on a welding inverter

The simplest and most widely used option. Efforts will have to be expended only on the construction of the inductor. A copper thin-walled tube 8-10 cm in diameter is taken and bent according to the desired pattern. The turns should be located at a distance of 5-8 mm, and their number depends on the characteristics and diameter of the inverter. The inductor is fixed in a textolite or graphite case, and a crucible is placed inside the installation.

transistor induction furnace

In this case, you will have to work not only with your hands, but also with your head. And run around the shops in search of the necessary spare parts. After all, you will need transistors of different capacities, a couple of diodes, resistors, film capacitors, two copper wires of different thicknesses and a couple of rings from chokes.

• Before assembly, it must be borne in mind that the resulting circuit will become very hot during operation. Therefore, fairly large heatsinks must be used.
• Capacitors are collected in parallel in a battery.
• Copper wire with a diameter of 1.2 mm is wound on the throttle rings. Depending on the power, the turns should be from 7 to 15.
• On a cylindrical object, suitable in diameter to the size of the crucible, 7-8 turns of copper wire with a diameter of 2 mm are wound. The ends of the wire are left long enough for connection.
• According to a special scheme, everything is mounted on the board.
• The power source can be a 12-volt battery.
• If necessary, you can make a textolite or graphite case.
• The power of the device is regulated by increasing or decreasing the turns of the inductor winding.

It is not easy to assemble such a device on your own. And you can take on this work only when there is confidence in the correctness of your actions.

Lamp induction oven

Unlike a transistor one, a lamp furnace will turn out to be much more powerful, which means that you will have to be more careful with both it and the circuit.

• 4 ray lamps connected in parallel will generate high frequency currents.
• Copper wire is bent into a spiral. The distance between the turns is 5 mm or more. The turns themselves are 8-16 cm in diameter. The inductor must be of such a size that the crucible can easily fit inside.
• The inductor is placed in a housing made of a non-conductive material (textolite, graphite).
• You can put a neon indicator lamp on the case.
• You can also include a tuning capacitor in the circuit.

The manufacture of both circuits requires the possession of some knowledge, which can be obtained, but it is better if a real specialist does this.

Cooling

This question is probably the most difficult of all those that are put before a person who decides to independently assemble a melting apparatus based on the induction principle. The fact is that it is not recommended to put the fan directly near the oven. The metal and electrical parts of the cooling unit may adversely affect the operation of the stove. A fan located far away may not provide the necessary cooling, which will lead to overheating.

The second option is to carry out water cooling. However, it is not only difficult to perform it at home qualitatively and correctly, but it is also not financially profitable. In this case, it is worth considering: would it not be more economical to purchase an industrial version of an induction furnace, produced at the factory, in compliance with all the necessary technologies?

Safety precautions when smelting metal in an induction furnace

There is no need to expand on this topic, since almost everyone knows the basic safety regulations. It is necessary to dwell only on those issues that are unique to this type of equipment.

• Let's start with personal safety. When working with an induction furnace, it should be well understood that the temperatures here are very high, and this is a risk of burns. Also, the device is electrical and requires increased attention.
• If you bought a finished oven, you should pay attention to the radius of influence of the electromagnetic field. Otherwise, watches, phones, camcorders and other electronic gadgets may start to fail or even break down.
• Work clothes should be selected with non-metallic fasteners. Their presence, on the contrary, will affect the operation of the furnace.
• Particular attention in this respect should be given to the lamp oven. All elements with high voltage must be hidden in the case.

Of course, such equipment is unlikely to come in handy in a city apartment, but radio amateurs who are constantly engaged in tinning and jewelry craftsmen cannot do without an induction furnace. For them, this thing is very useful, one might say irreplaceable, and how it helps in their work, it is better to ask them themselves.

Induction furnaces were invented as early as 1887. And three years later, the first industrial development appeared, with the help of which various metals were smelted. I would like to note that in those distant years these furnaces were a curiosity. The thing is that scientists of that time did not quite understand what processes were taking place in it. Got it figured out today. 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?

Principle of operation

It is necessary to start the assembly, having understood the principle of operation and the device device. Let's start with this. Pay attention to the picture above, we will understand it.

The device includes:

• Generator G, which creates an alternating current.
• Capacitor C, together with coil L, creates an oscillatory circuit, which provides the installation with a 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 mixture (W), in which it creates a magnetic flux (F). By the way, instead of the charge, some workpiece 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 act inside it. It is of the vortex type.
• In this case, eddy currents transfer thermal energy from the generator through a magnetic field, thereby heating the workpiece.

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

crucible furnace

Varieties

There are two main designs of induction furnaces:

• Channel.
• Crucible.

We will not describe all their distinctive features here. 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 did not work. The second option is an advanced scheme that uses technology without residual melt. That is, the crucible is simply installed directly into the inductor.

How it works

Why do you need such an oven 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 a variety of 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 the help of this home-made unit, various processes with metals can be carried out. For example, you can harden or leave.

Coil with battery (generator)

Stove components

In the "Operating principle" section, we have already mentioned all parts of the induction furnace. And if everything is clear with the generator, then the inductor (coil) should be dealt with. 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 coils of the copper tube must not touch each other. The optimal distance between them is 5-7 mm. The coil itself must 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 unit with a power of 3 kW, work up to half an hour does not threaten anything. True, over time, copper scale will form on the tube, which reduces the efficiency of the device. So periodically the coil will have to be changed.

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 there is no such knowledge, then forget about the induction stove. The most important thing is that you also need to be able to operate this device skillfully.

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 is at stake, we offer the simplest generator circuit for an induction furnace in the photo below.

Generator circuit

Required knowledge

The electromagnetic field acts on all living things. An example is meat in the microwave. Therefore, it is worth taking care of security. And it doesn't matter if you assemble the stove and test it or work on it. There is such an indicator as the energy flux density. So it depends on the electromagnetic field. And the higher the frequency of radiation, the worse the human body.

Many countries have adopted safety measures that take energy density into account. There are developed tolerance 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 a day. By the way, the installed galvanized screen reduces the density of the ceiling by 50 times.

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Ancient potters who fired pottery in kilns sometimes found shiny hard pieces with unusual properties at the bottom of the kilns. From the very moment when they began to think about what these wonderful substances were, how they appeared there, and also where they can be used with benefit, metallurgy was born - the craft and art of metal processing.

And the main tool for extracting new extremely useful materials from ore was thermosmelting forges. Their designs have come a long way of development: from primitive disposable clay domes heated by firewood to modern electric furnaces with automatic control of the melting process.

Metal-smelting units are needed not only by the giants of ferrous metallurgy, which use cupolas, blast furnaces, open-hearth furnaces and regenerator converters with a production of several hundred tons per cycle.
Such values ​​are typical for the smelting of iron and steel, which account for up to 90% of the industrial production of all metals.
In non-ferrous metallurgy and secondary processing, the volumes are much smaller. And the world turnover of production of rare earth metals is generally estimated at several kilograms per year.

But the need for smelting of metal products arises not only in its mass production. A significant sector of the metalworking market is occupied by foundry production, where metal-smelting units of relatively small output are required - from several tons to tens of kilograms. And for piece handicraft and arts and crafts production and jewelry, melting machines with a yield of several kilograms are used.

All types of metal-smelting devices can be divided according to the type of energy source for them:

1. Thermal. The heat carrier is flue gas or strongly heated air.
2. Electrical. Various thermal effects of electric current are used:
   • Muffle. Heating of materials placed in a heat-insulated housing with a spiral heating element.
   • resistance. Heating a sample by passing a large current through it.
   • Arc. The high temperature of the electric arc is used.
   • Induction. Melting of metal raw materials by internal heat from the action of eddy currents.
3. Streaming. Exotic plasma and cathode-ray devices.

In-Line Electron Beam Melting Furnace Thermal Open Hearth Furnace Electric Arc Furnace

With small volumes of generation, the most appropriate and economical is the use of electric, in particular, induction melting furnaces(IPP).

The device of induction electric furnaces

In short, their action is based on the phenomenon of Foucault currents - eddy induced currents in a conductor. In most cases, electrical engineers deal with them as a harmful phenomenon.
For example, it is precisely because of them that the cores of transformers are made of steel plates or tape: in a solid piece of metal, these currents can reach significant values, leading to useless energy losses for heating it.

In the induction melting furnace, this phenomenon is put to good use. In fact, it is a kind of transformer, in which the role of a short-circuited secondary winding, and in some cases the core, is played by a melted metal sample. It is metallic - only materials that conduct electricity can be heated in it, while dielectrics will remain cold. The role of the inductor - the primary winding of the transformer is performed by several turns of a thick copper tube rolled into a coil, through which the coolant circulates.

By the way, the extremely popular kitchen hobs with high-frequency induction heating operate on the same principle. A piece of ice placed on them will not even melt, and the set metal utensils will heat up almost instantly.

Design features of induction thermal furnaces

There are two main types of PPIs:

For both types of metal-smelting units, there are no fundamental differences in the type of working raw materials: they successfully melt both ferrous and non-ferrous metals. It is only necessary to select the appropriate operating mode and type of crucible.

Selection Options

Thus, the main criteria for choosing one or another type of thermal furnace are the volume and continuity of production. For a small foundry, for example, in most cases, a crucible electric furnace is suitable, and a channel furnace is suitable for a recycling company.

In addition, among the main parameters of a crucible thermal furnace is the volume of one heat, on the basis of which a specific model should be chosen. Important characteristics are also the maximum operating power and the type of current: single-phase or three-phase.

Choice of mounting location

The placement of the induction furnace in a workshop or workshop should provide a free approach to it for the safe performance of all technological operations during the melting process:

• loading of raw materials;
• manipulations during the working cycle;
• unloading of the finished melt.

The installation site must be provided with the necessary electrical networks with the required operating voltage and number of phases, protective earthing with the possibility of a quick emergency shutdown of the unit. Also, the installation must be provided with a supply of water for cooling.

Desktop structures of small dimensions must, however, be installed on strong and reliable individual bases that are not intended for other operations. Floor units also need to provide a solid reinforced foundation.

It is forbidden to place flammable and explosive materials in the melt discharge area. A fire shield with extinguishing agents must be hung near the location of the stove.

Installation instructions

Industrial thermomelting units are devices with high power consumption. Their installation and wiring must be carried out by qualified specialists. The connection of small units with a load of up to 150 kg can be carried out by a qualified electrician, following the usual rules for electrical installations.

For example, an IPP-35 furnace with a power of 35 kW with a production volume of ferrous metals of 12 kg, and non-ferrous metals - up to 40 has a mass of 140 kg. Accordingly, its installation will consist of the following steps:

1. Selection of a suitable location with a solid base for the hot melt unit and the water-cooled high voltage induction unit with capacitor bank. The location of the unit must comply with all operational requirements and regulations for electrical and fire safety.
2. Providing installation with a water cooling line. The described electric melting furnace does not come with cooling equipment, which must be purchased separately. The best solution for this would be a double circuit closed circuit cooling tower.
3. Protective earth connection.
   

   The operation of any electric melting furnace without grounding is strictly prohibited.

4. Connecting a separate electrical line with a cable, the cross section of which provides the appropriate load. The power shield must also provide the required load with a power margin

For small workshops and home use, mini-furnaces are produced, for example, UPI-60-2, with a power of 2 kW with a crucible volume of 60 cm³ for melting non-ferrous metals: copper, brass, bronze ~ 0.6 kg, silver ~ 0.9 kg, gold ~ 1.2 kg. The weight of the installation itself is 11 kg, dimensions - 40x25x25 cm. Its installation consists in placing it on a metal workbench, connecting flowing water cooling and plugging it into a power outlet.

Technology of use

Before starting work with a crucible electric furnace, it is imperative to check the condition of the crucibles and lining - internal protective thermal insulation. If it is designed for the use of two types of crucibles: ceramic and graphite, it is necessary to choose the appropriate loaded material according to the instructions.

Usually ceramic crucibles are used for ferrous metals, graphite - for non-ferrous.

Operating procedure:

• Insert the crucible inside the inductor and, having loaded the working material, cover it with a heat-insulating cover.
• Turn on water cooling. Many models of electric melting units will not start if there is not the necessary water pressure.

• The melting process in the crucible IPP begins with its inclusion and access to the operating mode. If there is a power regulator, set it to the minimum position before turning it on.
• Slowly raise the power to the working power corresponding to the loaded material.
• After melting the metal, reduce the power to a quarter of the working one to maintain the material in a molten state.
• Before pouring, turn the regulator to a minimum.
• At the end of melting - de-energize the installation. Turn off water cooling after it cools down.

All the time of melting the unit must be under supervision. Any manipulations with the crucibles should be done with tongs and in protective gloves. In the event of a fire, the installation should be immediately de-energized and the flames should be extinguished with a tarpaulin or extinguished with any fire extinguisher other than acid. Filling with water is strictly prohibited.

Advantages of induction furnaces

• High purity of the resulting melt. In other types of metal-melting thermal furnaces, there is usually direct contact of the heat carrier with the material, and, as a result, contamination of the latter. In IPP, heating is produced by absorption of the electromagnetic field of the inductor by the internal structure of the conductive materials. Therefore, such furnaces are ideal for jewelry production.
  

  For thermal furnaces, the main problem is to reduce the content of phosphorus and sulfur in the melts of ferrous metals, which worsen their quality.

• High efficiency of induction-melting devices, reaching up to 98%.
• High melting speed due to the heating of the sample from the inside and, as a result, high productivity of the IPP, especially for small working volumes up to 200 kg.
  

  Heating muffle electric furnace with a load of 5 kg occurs within a few hours, IPP - no more than an hour.

• Devices with a load of up to 200 kg are easy to place, install and operate.

The main disadvantage of electric melting devices, and induction devices are no exception, is the relative high cost of electricity as a coolant. But despite this, the high efficiency and good performance of the IPP largely pay for them during operation.

The video shows an induction furnace during operation.

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

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

The following devices can be made independently:

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

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

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

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

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

Manufacturing instructions

Blueprints

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

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

Additional materials and their features:

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

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

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

Nuances

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

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

The world has already formed well-established technologies for the production of metal and steel, which are used by metallurgical enterprises today. These include: a converter method for producing metal, rolling, drawing, casting, stamping, forging, pressing, etc. However, the most common under 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 advanced and latest technology today is the production of steel in electric furnaces. The main advantages of the latter over other technologies are high productivity and environmental friendliness. 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 do yourself. Consider the creation of an inductive small-sized electric furnace for the production of homogeneous alloys (OS). Compared with 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;
• the possibility of temperature control;
• 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 speed of heating;
• the possibility of placing the working body in the 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;
• the ability to work both from a single-phase and from a three-phase network.

Schematic type selection

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 for power factor control. 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 control resonance:

• by changing the capacitance;
• by changing the frequency.

In our case, resonance is maintained by adjusting the frequency. It was this feature that caused the choice of the type of circuit with frequency regulation.

Analysis of the components of the circuit

Analyzing the operation of an induction furnace for melting metal at home (IP), three main parts can be distinguished: a generator, a power supply unit, and a power unit. To provide the necessary frequency during the operation of the installation, a generator is used, which, in order 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 unit is required, which ensures the safe and reliable operation of the power elements of the structure. Actually, it is the power unit that generates the necessary powerful signals to create the desired power factor at the output of the circuit.

Figure 1 shows a general schematic diagram of an induction installation.

Create a wiring diagram

The connection diagram (installation) shows the connections of the component parts of the product and determines the wires, cables that make these connections, as well as the places of their connection.

For the convenience of further installation of the installation, a connection diagram was developed, reflecting 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 desired frequency of operation of the installation and creates the initial conditions for obtaining a resonant circuit. As a source of oscillations, a specialized controller of electronic impulses of the KR1211EU1 type is used (Fig. 3). This choice was due to the ability of this microcircuit to operate in a fairly wide frequency range (up to 5 MHz), which makes it possible to obtain a high power value at the output of the power block of the circuit.

Figures 4.5 show a schematic diagram of a frequency generator and a diagram of an electrical board.

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

Power Supply

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

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

Power block

This block provides direct amplification of the signal and the creation of a resonant circuit by changing the capacitance of the circle. The signals from the generator go to transistors that 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 get an increased signal with a given frequency. This signal is applied 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 the actual heating occurs. Figure 7 shows the electrical circuit of the power unit of the induction furnace.

Inductor and features of its work

Inductor - 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 of non-ferrous metals at home with the help of an induction furnace consists in the penetration of induction currents into the middle of the metals, which arise due to the high frequency of the voltage change applied to the inductor terminals. The power of the installation depends on the magnitude of the applied voltage and on 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 the flow of induction currents are shown in Figure 8.

For homogeneous mixing and to avoid contamination of the alloy by foreign elements, such as electrodes from an alloy tank, a reverse coil inductor is used as shown in Figure 9. It is thanks to this coil that an electromagnetic field is created that keeps the metal in the air, surpassing the force of gravity of the Earth.

Final assembly of the plant

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 current-carrying parts with the metal coating of the case itself (Fig. 10).

For safe work with the installation, it is completely closed by a strong case (Fig. 11), in order to create a barrier between dangerous structural elements and the body of a 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 controlled. 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 regulator. All the above parameters make it possible to regulate the operating modes of the induction installation. Also, the design is equipped with a manual activation system, and a system for indicating heating processes. With the help of impressions on devices, the operation of the installation as a whole is actually monitored.

The design of a small-sized induction installation is a rather complicated technological process, since it must ensure that a large number of criteria are met, such as: convenience of design, small size, portability, etc. This installation works on the principle of non-contact energy transfer to an object that heats up. As a result of the purposeful movement of induction currents in the inductor, the melting process itself takes place directly, the duration of which is several minutes.

The creation of this installation is quite profitable, since its scope is unlimited, from use for routine laboratory work to the production of complex homogeneous alloys from refractory metals.