Do-it-yourself induction crucible furnace. Induction crucible melting furnaces. Crucible induction furnaces

At present, stoves operating on inductive principle which are commonly used in industry. In order for induction furnaces to be used in domestic conditions, their design was significantly changed, only the principle of energy conversion remained unchanged. Such a device can be made with your own hands from available materials. The main thing is to understand the design and understand how this furnace works.

The principle of operation of the induction furnace

The operation of such a furnace is based on the principle of induction heating. In other words, thermal energy is obtained from the electric current generated by the electromagnetic field. Due to this feature, this device differs from ordinary electric heaters.

The design of the inductor is quite simple. Its center is graphite or metal an electrically conductive workpiece around which the wire is to be wound. With the help of the generator power, currents of different frequencies begin to run into the inductor, creating a powerful electromagnetic field around the inductor. Due to the effect of such a field on the workpiece and the creation of eddy currents in it, graphite or metal begins to heat up very strongly and give off heat to the surrounding air.

In everyday life, inductors began to be used relatively recently.

Types of induction devices

According to their purpose, such devices are household and industrial. However, this classification is considered incomplete. There is still several types of stoves:

Crucible. The most common type of aggregates used in metallurgy. This design does not contain a core. These devices are mainly used for the processing and smelting of any metals. They have performed admirably in other areas as well.
Channel. Their design is similar to a transformer.
Vacuum. They are used when it is necessary to remove impurities from the metal.

Domestic ovens are divided into two groups:

Units used for heating. They are small induction boiler plants that are mounted in autonomous heating systems.
Induction cookers for cooking food. The main difference from an ordinary electric stove is the economical use of electricity.

Is it possible to make an induction furnace designed for melting metals with your own hands? Although it is, on the one hand, complex equipment, on the other hand, due to the relative simplicity and clarity of the principle of operation, it becomes possible to make an induction heating device with your own hands. In addition, many professionals with necessary knowledge and skills, able to create high-quality aggregates from conventional materials. To make an induction furnace with your own hands, you will need a diagram and good knowledge physics.

Do-it-yourself induction furnaces in general used for space heating. Small crucible structures are best suited for small volume melting of metals, such as in the manufacture of costume jewelry or jewelry. Induction cookers are considered great solution for country houses. And in a city apartment they are used as an additional heater if there is any failure in the central heating system.

A diagram of such a simple induction heater will be needed to complete the work. You can work without it, but it is undesirable, since such a heater is complex electrical equipment. Its design and internal contents are developed in advance. The scheme combines all the ideas of the master into a single whole. If you need to design a stove, and not a simple heater, you won’t be able to do without a circuit at all.

The design of an induction furnace with your own hands is quite simple: a heating element, common housing, inductor. If the unit is required for the processing of materials, the melting chamber should be additionally designed. The heart of an induction furnace is a workpiece that conducts current and can be heated to high temperatures. A nichrome spiral or graphite brushes do a great job with this task. Choosing between them, you should focus on the tasks that the heater faces. For melting furnace the best option will use graphite brushes, for heater– nichrome spiral. The use of nichrome makes it possible to connect the unit to a conventional electrical network.

How to make an induction oven with your own hands

To create an efficient unit, it is necessary consider the following parameters:

generator frequency and power;
the rate at which heat is lost;
the amount of eddy current losses.

First you need to correctly select all the necessary details of the circuit to obtain sufficient conditions for melting in the workshop. If the unit is assembled by hand, the generator frequency should be 27.12 MHz. The coil should be made of wire or a thin copper tube, and there should not be more than 10 turns.

The power of electronic lamps must be large. The scheme provides for the installation of a neon lamp, which will be used as an indicator of the readiness of the device. The circuit also provides for the use of chokes and ceramic capacitors. The connection to the home socket is made through a rectifier.

A do-it-yourself induction furnace looks like this: a small stand on legs, to which a generator is attached with all the necessary details of the circuit. And already the inductor is connected to the generator.

Advantages and disadvantages of induction furnaces

Induction units can have different power and it depends on the design features. It is very difficult to assemble an industrial frequency device with your own hands, and even this is not necessary. It's better to buy them.

Induction Furnaces can have both pros and cons:

Safety

When working with the oven, you should be wary of getting thermal burns. In addition, this device has a high fire hazard. Under no circumstances should these units be moved during operation. You need to be very careful when such stoves are installed in an apartment.

Variable electromagnetic field begins to warm up the room surrounding it, and this feature is directly dependent on the power and frequency of the radiation of the device. Powerful industrial furnaces can affect items in clothing pockets, nearby metal parts, and human tissue.

Conclusion

An induction furnace can be made independently, but this is not always advisable. It is better not to take on such work if there is absolutely no knowledge in the field of electrical equipment and physics. Before proceeding with the design of even the most simple device, it should be developed, designed and charted. If there is no experience in the manufacture of electrical appliances, it is best to purchase such a factory-made unit.

Developed over a century ago, induction stoves are firmly established in our everyday life. This became possible thanks to the development of electronics. The explosive growth in the power of controllers based on silicon semiconductors and the appearance on the market of transistors capable of providing high power (several kilowatts) in recent years has acquired the character of an avalanche. All this gave humanity incredibly great prospects for the development of miniature installations comparable in power to industrial devices of the recent past.

Use and structure of the device

The use of induction furnaces in household avoids the appearance of foci in the room open flame and is a fairly effective method of melting and controlled heating of metals and alloys. This is due to the fact that the metal is heated, heated and melted not under the influence of high-temperature burners, but by passing high-frequency currents through itself, stimulating the active movement of particles in the structure of the material.

It became possible to appear in everyday life:

In addition, electric induction stoves are becoming more widespread, which work not only with conductive material. Their device is slightly different from conventional induction furnaces, since it is based on heating by electric induction of a material that does not conduct current (they are also called dielectrics) between capacitor plates, that is, its conclusions of different polarity. At the same time, the temperatures reached are not very high (about 80-150 degrees Celsius), therefore, such installations are used for melting plastic or its heat treatment.

Design features and principle of operation

The induction furnace works on the basis of the formation of eddy electric currents in it. To do this, use an inductor consisting of turns of a thick wire, to which an alternating current source is supplied. It is the alternating current that forms a magnetic field that is constantly changing depending on the current frequency. It provokes the transfer of these currents to the substance placed inside the coil, along with a large amount of heat. In this case, even the most ordinary welding inverter can act as a generator.

There are two types of induction furnaces:

With a magnetic core, a feature of which is the location of the inductor inside the volume of metal that can be melted.
Without a magnetic circuit - when the inductor is outside.

The design with the presence of a magnetic circuit is used, for example, in channel furnaces. They use an open metal (most often steel) magnetic circuit, inside which there is a crucible for melting and an inductor that form the primary circuit of the winding. The crucible material can be graphite, heat-resistant clay, or any other non-conductive material with suitable heat resistance. It contains the metal that needs to be melted. These are, as a rule, all kinds of non-ferrous metal alloys, duralumin and cast iron.

The generator of such a furnace must provide AC frequency within 400 hertz. There are also options for using a conventional generator instead of a generator. electrical network and feed the furnace with a current with a frequency of 50 hertz, but in this case the heating temperature will be lower and such an installation will not work for more refractory alloys.

Crucible furnaces, which do not have a magnetic circuit in their design, have become much more widespread among enthusiasts. They use currents of much higher frequency to achieve higher field densities. This is due precisely to the absence of a magnetic circuit - too much of the field energy is dissipated in space. To counteract this, the furnace must be very finely tuned:

Ensure that the frequency of the induction circuit and the voltage from the generator are equal (when using an inverter, this is easiest to do).
Select the diameter of the melting crucible so that it is close to the wavelength of the received magnetic field radiation.

In this way, losses can be minimized up to 25% of the total power. In order to achieve the same best result it is recommended to set twice or even three times the frequency of the AC source than the resonant one. In this case, the diffusion of the metals that make up the alloy will be maximum, and its quality will be much better. If you increase the frequency further, you can achieve the effect of pushing the high-frequency field to the surface of the product and so harden it.

Vacuum melting furnaces

This type of installation can hardly be called domestic, but it is worth considering because vacuum melting has a number of technological advantages compared to other types. By its design, it resembles a crucible, with the difference that the furnace itself is located in a vacuum chamber. This makes it possible to achieve greater purity of the metal melting process, reduce its oxidizability during processing and speed up the process, achieving significant energy savings.

In addition, the limited and closed space helps to avoid the release of harmful fumes of melting metals into the surrounding space and maintain the cleanliness of their processing. The ability to control the composition and processing process is also one of the advantages of this type of ovens.

Channel induction units

Another type of industrial oven that has a wider application than others. They can be used not only as smelters, but also as distributors of prepared material and mixers of several types of raw materials. Typical designs such devices include:

The slightest opening of the circuit, which is formed by liquid metal, a magnetic circuit and a coil, leads to an increase in its own resistance and an instantaneous ejection of the entire mass of raw materials from the channel. To counteract this phenomenon, a "swamp" is left inside the channel - a small mass of metal, which is maintained in liquid form.

Advantages of channel-type induction furnaces:

Low installation cost.
Efficiency - to maintain the temperature inside the bath, which does not dissipate heat well, you need a small amount of electricity.
The efficiency of the inductor during operation is very high.

Flaws:

The main elements of the furnace scheme

In order to assemble the installation and perform work on it, it is necessary to find a suitable scheme of the induction furnace and parts for it. To find the latter, it is very useful to have one or more unnecessary power supplies from the computer, since most of the details can be found in them. Typical scheme the simplest furnace with a homemade inverter will include items such as:

The inverter for the installation is assembled according to the scheme proposed by S. V. Kukhtetsky for laboratory tests. It can be easily found on the Internet. The power of the inverter, which is powered by a voltage in the range of 12-35 volts, will be 6 kilowatts, and its operating frequency will be 40-80 kilohertz, this will be more than enough for home projects.

Work safety

Since working with an induction furnace involves close contact with molten metal and currents of high frequency and strength, it is worth taking care of the quality grounding of the installation and reliable means protection. In this case, clothing must strictly comply with all requirements:

Do not forget about the good ventilation of the room in which they will work. Molten metal releases chemicals into the air that are not good for your lungs.

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

Now, with the advent of powerful high-frequency transistors and cheap microcontrollers that have made a breakthrough in all areas of science and technology, truly efficient induction furnaces have appeared that can be freely used for domestic needs (cooking, heating water, heating) and even assemble hands.

Physical basis and principle of operation of the furnace

Fig.1. Scheme of the induction furnace

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

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

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

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

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

Making an inductive heater

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

To make a do-it-yourself furnace with a power of not more than 3 kW, the inductor must be made with the following parameters:

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

Adjacent turns of the coil must not be allowed to touch, keep the specified distance. The inductor must not come into contact with protective screen ovens, the gap between them must not be less than the specified.

Generator manufacturing

Fig.3. Scheme on lamps

It is worth noting that an induction furnace for its manufacture requires at least average radio engineering skills and abilities. It is especially important to have them to create the second key element - a high-frequency current generator. Neither assembling nor using a do-it-yourself oven will work without this knowledge. Moreover, it can be life-threatening.

For those who take up this business with knowledge and understanding of the process, there are various ways and schemes by which an induction furnace can be assembled. When choosing a suitable generator circuit, it is recommended to abandon options with a hard emission spectrum. These include the widespread scheme using a thyristor key. High-frequency radiation from such a generator is capable of creating powerful interference for all surrounding radio devices.

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

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

Scheme of a universal generator

Modern induction furnaces operate on more advanced elements - microcircuits and transistors. The universal scheme of a push-pull generator, which develops power up to 1 kW, is enjoying great success. The principle of operation is based on an independent excitation generator, while the inductor is switched on in the bridge mode (Fig. 4).

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

The ability to work on the 2nd and 3rd mode in addition to the main one.
There is a surface heating mode.
Control range 10-10000 kHz.
Soft spectrum of radiation in the entire range.
Does not need additional protection.

Frequency tuning is carried out using a variable resistor R 2 . The operating frequency range is set by capacitors C 1 and C 2 . The interstage matching transformer must be with a ring ferrite core with a cross section of at least 2 sq.cm. The winding of the transformer is made of enameled wire with a cross section of 0.8-1.2 mm. The transistors need to be seated on common radiator area from 400 sq.cm.

Conclusion on the topic

The electromagnetic field (EMF) emitted by the induction furnace affects all the conductors around. It also affects the human body. The internal organs under the action of EMF are evenly warmed up, the overall body temperature rises throughout the entire volume.

Therefore, when working with the oven, it is important to observe certain precautions in order to avoid negative consequences.

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

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

Induction melting is a process widely used in ferrous and non-ferrous metallurgy. Melting in induction heating devices is often superior to fuel-fired melting in terms of energy efficiency, product quality and production flexibility. These pre-

modern electrical technologies

properties are due to the specific physical characteristics of induction furnaces.

During induction melting, a solid material is transferred to a liquid phase under the influence of an electromagnetic field. As in the case of induction heating, heat is generated in the melted material due to the Joule effect from the induced eddy currents. The primary current passing through the inductor creates an electromagnetic field. Regardless of whether the electromagnetic field is concentrated by magnetic circuits or not, the coupled inductor-load system can be represented as a transformer with a magnetic circuit or as an air transformer. The electrical efficiency of the system is highly dependent on the field-influencing characteristics of the ferromagnetic structural elements.

Along with electromagnetic and thermal phenomena, electrodynamic forces play an important role in the process of induction melting. These forces must be taken into account, especially in the case of melting in powerful induction furnaces. The interaction of induced electric currents in the melt with the resulting magnetic field causes a mechanical force (Lorentz force)

Pressure Melt flows

Rice. 7.21. The action of electromagnetic forces

For example, the turbulent motion of the melt caused by forces has a very great importance both for good heat transfer and for mixing and adhesion of non-conductive particles in the melt.

There are two main types of induction furnaces: induction crucible furnaces (ITF) and induction channel furnaces (IKP). In ITP, the melted material is usually loaded in pieces into the crucible (Fig. 7.22). The inductor covers the crucible and the melted material. Due to the absence of a concentrating field of the magnetic circuit, the electromagnetic connection between

modern electrical technologies

inductor and loading strongly depends on the wall thickness of the ceramic crucible. To ensure high electrical efficiency, the insulation should be as thin as possible. On the other hand, the lining must be thick enough to withstand thermal stresses and

metal movement. Therefore, a compromise should be sought between the electrical and strength criteria.

Important characteristics of induction melting in IHF are the movement of the melt and the meniscus as a result of the action of electromagnetic forces. The movement of the melt provides both a uniform temperature distribution and a homogeneous chemical composition. The mixing effect at the melt surface reduces material losses during reloading of small batches and additives. Despite the use of cheap material, the reproduction of a melt of constant composition ensures high casting quality.

Depending on the size, the type of material to be melted and the field of application, ITPs operate at an industrial frequency (50 Hz) or medium

modern electrical technologies

them at frequencies up to 1000 Hz. The latter are becoming increasingly important due to their high efficiency in the smelting of cast iron and aluminium. Since the movement of the melt at constant power is attenuated with increasing frequency, higher specific powers become available at higher frequencies and, as a result, greater productivity. Due to the higher power, the melting time is shortened, which leads to an increase in the efficiency of the process (compared to furnaces operating at industrial frequency). In view of other technological advantages, such as flexibility in changing smelted materials, medium frequency IHFs are designed as powerful melting plants that currently dominate the iron foundry. Modern high-power medium-frequency ITPs for iron smelting have a capacity of up to 12 tons and a power of up to 10 MW. Industrial frequency ITPs are designed for larger capacities than medium-frequency ones, up to 150 tons for iron smelting. The intensive stirring of the bath has special meaning in the smelting of homogeneous alloys, such as brass, therefore, ITPs of industrial frequency are widely used in this area. Along with the use of crucible furnaces for melting, they are also currently used for holding liquid metal before pouring.

In accordance with the energy balance of ITP (Fig. 7.23), the level of electrical efficiency for almost all types of furnaces is about 0.8. Approximately 20% of the original energy is lost in the inductor in the form of Joe - heat. The ratio of heat losses through the walls of the crucible to that induced in the melt electrical energy reaches 10%, so the total efficiency of the furnace is about 0.7.

The second widespread type of induction furnaces are ICP. They are used for casting, holding and, especially, melting in ferrous and non-ferrous metallurgy. The ICP generally consists of a ceramic bath and one or more induction units (Fig. 7.24). IN

principle, the induction unit can be represented as a transform-

The operating principle of the ICP requires a permanently closed secondary loop, so these furnaces operate with the liquid residue of the melt. Useful heat is generated mainly in the channel having a small cross section. The circulation of the melt under the action of electromagnetic and thermal forces ensures sufficient heat transfer to the bulk of the melt in the bath. Until now, ICPs have been designed for industrial frequency, but research work is also being carried out for higher frequencies. Thanks to the compact design of the furnace and the very good electromagnetic coupling, its electrical efficiency reaches 95%, and the overall efficiency reaches 80% and even 90%, depending on the material being melted.

In accordance with the technological conditions in different areas of application, ICPs are required various designs induction channels. Single-channel furnaces are mainly used for holding and casting,

modern electrical technologies

rarer steel melting at installed capacities up to 3 MW. For melting and holding non-ferrous metals, two-channel designs are preferable, providing best use energy. In aluminum smelters, the channels are straight for easy cleaning.

The production of aluminium, copper, brass and their alloys is the main field of application of the ICP. Today, the most powerful ICPs with a capacity of

up to 70 tons and power up to 3 MW are used for aluminum smelting. Along with high electrical efficiency in aluminum production, low melt losses are very important, which predetermines the choice of ICP.

Promising applications of induction melting technology are the production of high purity metals such as titanium and its alloys in cold crucible induction furnaces and the melting of ceramics such as zirconium silicate and zirconium oxide.

When melting in induction furnaces, the advantages of induction heating are clearly manifested, such as high density energy and productivity, homogenization of the melt due to mixing, precise

modern electrical technologies

energy and temperature control, as well as ease of automatic process control, ease of manual control and great flexibility. High electrical and thermal efficiencies, combined with low melt losses and therefore savings in raw materials, result in low specific energy consumption and environmental competitiveness.

The superiority of induction melting devices over fuel ones is constantly increasing due to practical research, supported by numerical methods for solving electromagnetic and hydrodynamic problems. As an example, we can note the internal coating with copper strips of the steel casing of the ICP for copper melting. The reduction of losses from eddy currents increased the efficiency of the furnace by 8%, and it reached 92%.

Further improvement economic indicators induction melting is possible through the use of modern technologies controls such as tandem or dual power control. Two tandem ITPs have one power source, and while melting is in progress in one, the molten metal is held in the other for pouring. Switching the power source from one oven to another increases its utilization. A further development of this principle is dual power management (Fig. 7.25), which provides continuous simultaneous work furnaces without switching using special process control automation. It should also be noted that an integral part of the smelting economics is the compensation of the total reactive power.

In conclusion, to demonstrate the advantages of energy- and material-saving induction technology, fuel and electrothermal methods of aluminum smelting can be compared. Rice. 7.26 shows a significant reduction in energy consumption per ton of aluminum when smelting in

Chapter 7

□ loss of metal; Shch melting

modern electrical technologies

induction channel furnace with a capacity of 50 tons. The final energy consumed is reduced by about 60%, and the primary energy by 20%. At the same time, CO2 emissions are significantly reduced. (All calculations are based on typical German energy conversion and CO2 emissions from mixed power plants). The results obtained emphasize the special effect of metal losses during melting associated with its oxidation. Their compensation requires a large additional expenditure of energy. It is noteworthy that in the production of copper, metal losses during melting are also large and should be taken into account when choosing one or another melting technology.

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

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

Melting metal by induction is widely used in various industries: metallurgy, engineering, jewelry. A simple induction type furnace for melting metal at home can be assembled with your own hands.

Operating principle

Heating and melting of metals in induction furnaces occur due to internal heating and changes in the crystal lattice of the 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 the flow of eddy currents through the melted metal, it is placed in the zone of action of the electromagnetic field of the inductor - the coil. It can be in the form 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.

Kinds

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

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

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

crucible furnace quite compact, it is used by jewelers, radio amateurs, such an oven can be assembled with your own hands and used at home.

Device

simple design

high frequency alternator;
inductor - do-it-yourself spiral winding of copper wire or tube;
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 arises around it. In a magnetic field, eddy currents arise, directed perpendicular to its vector and passing through a closed loop inside the winding. They pass through the metal placed in the crucible, while heating it to the melting point.

Advantages of the induction furnace:

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

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

Furnace for melting metal on a welding inverter

This design is simple and safe as 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 copper thin-walled tube with a diameter of 8-10 mm. It is bent according to a template of the desired 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 that it does not cause an overcurrent in the inverter, otherwise it will be tripped by the internal protection.

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

When working from a welding inverter, its housing must be grounded! The socket and wiring must be rated for the current drawn by the inverter.

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

Transistor induction furnace: circuit

There are many various ways assemble an induction heater with your own hands. A fairly simple and proven scheme of a furnace for melting metal is shown in the figure:

two field-effect transistors of the IRFZ44V type;
two diodes UF4007 (you can also use UF4001);
resistor 470 Ohm, 1 W (you can take two series-connected 0.5 W each);
film capacitors for 250 V: 3 pieces with a capacity of 1 microfarad; 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 taken from a computer power supply.

Do-it-yourself assembly sequence:

Field-effect transistors are mounted on radiators. Since the circuit gets very hot during operation, the radiator must be large enough. You can also 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. For their manufacture, copper wire with a diameter of 1.2 mm is wound around rings taken from the power supply of any computer. These rings are made of powdered ferromagnetic iron. They need to be wound from 7 to 15 turns of wire, trying to maintain the distance between the turns.

The capacitors listed above are assembled into a battery with a total capacity of 4.7 microfarads. Connection of capacitors - parallel.

The inductor winding is made of copper wire with a diameter of 2 mm. 7-8 turns of winding are wound on a cylindrical object suitable for the diameter of the crucible, leaving long enough ends 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 consumed in the operating mode is about 10 A, the battery capacity in this case is enough for about 40 minutes. If necessary, the furnace body is made of 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 melting metal: video

Lamp induction oven

A more powerful induction furnace for melting metals can be assembled by hand on vacuum tubes. The diagram of the device 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 unit is equipped with a trimmer capacitor for power adjustment. The output frequency is 27.12 MHz.

To assemble the circuit you need:

4 vacuum tubes - tetrodes, you can use 6L6, 6P3 or G807;
4 chokes for 100 ... 1000 μH;
4 capacitors at 0.01 uF;
neon indicator lamp;
tuning capacitor.

Assembling the device with your own hands:

An inductor is made from a copper tube, bending it in the form of a spiral. 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 must be 10 mm larger than the diameter of the crucible placed inside.
Place the inductor in the housing. It can be made from a heat-resistant non-conductive material, or from metal, providing thermal and electrical insulation from the circuit elements.
Cascades of lamps are assembled according to the scheme with capacitors and chokes. Cascades are connected in parallel.
Connect a neon indicator lamp - it will signal the readiness of the circuit for operation. The lamp is brought to the installation housing.
A tuning capacitor of variable capacitance is included in the circuit, its handle is also displayed on the case.

For all lovers of cold-smoked delicacies, we offer you to learn here how to quickly and easily make a smokehouse with your own hands, and here you can get acquainted with the photo and video instructions for making a cold-smoked smoke generator.

Circuit cooling

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

Air-cooling with a fan is possible provided that the fan is sufficiently remote. 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 the electronic and lamp circuits are also able to actively heat up. For their cooling, heat-removing radiators are provided.

Work Safety Measures

The main danger when working with homemade installation- risk of burns from the heated elements of the installation and molten metal.
The lamp circuit includes elements with high voltage, so it must be placed in a closed case, eliminating accidental contact with the elements.
The electromagnetic field can affect objects that are outside the device case. Therefore, before work, it is better to wear clothes without metal elements, remove from the area of action complex devices: telephones, digital cameras.

A domestic metal melting furnace can also be used to quickly heat up metal elements, for example, when they are tinned or shaped. The characteristics of the presented installations can be adjusted to specific task, changing the parameters of the inductor and the output signal generating sets- so you can achieve their maximum efficiency.

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

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

into the electromagnetic
electrical;
thermal.

Such ovens allow the use of heat from maximum efficiency, which is not surprising, because they are the most advanced of all existing models powered by electricity.

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

In today's article we will talk about how to makeDIY induction oven.

Pros and cons of induction designs

Among the many benefits are the following:

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

But there are also disadvantages.

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

Video - Induction furnace

Industrial Application

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

Furnaces for industrial use are divided into several types.

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

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

domestic use

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

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

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

Homemade induction oven

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

Induction furnace from high frequency generator

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

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

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

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

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

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

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

Video - Welding inverter design

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

Assembly technology

Step 1. The base is going to - boxing from fireclay bricks size 10x10x18 cm, laid on a refractory tile.

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

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

Step 3 The best option for a graphite furnace - 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 say that you can leave everything as it is.

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

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

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

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

Step 1. For the spiral, nichrome ø0.3 mm is used, about 11 m long.

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

Step 3 Use a small crucible ceramic pipeø1.6 cm and 15 cm long. One end of the pipe is plugged with asbestos thread - so the molten metal will not flow out.

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

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

The advantages of such a design:

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

But there are, of course, downsides:

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

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

As a conclusion

As you can see, you can still make an induction furnace on your own. But to be frank, the described design (like everything available on the Internet) is not quite a furnace, but a Kukhtetsky laboratory inverter. Collect a complete induction construction at home is simply not possible.

Chief Editor

How to make an induction heater with your own hands?

Electric heaters

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

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

The following devices can be made independently:

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

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

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

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

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

Manufacturing instructions

Figure 1. Electrical diagram of the induction heater

Figure 2. Device.

Figure 3. Scheme of a simple induction heater

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

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

Additional materials and their features:

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

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

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

When conducting experiments on heating and hardening metals, inside the induction coil the temperature can be significant and amounts to 100 degrees Celsius. This heating effect can be used to heat domestic water or to heat a house.
Scheme of the heater discussed above (Figure 3), at maximum load it is able to provide the radiation of magnetic energy inside the coil equal to 500 watts. Such power is not enough to heat a large volume of water, and the construction of a high power induction coil will require the manufacture of a circuit in which it will be necessary to use very expensive radio elements.
A budget solution for organizing induction heating of a liquid, is the use of several devices described above, arranged in series. In this case, the spirals must be on the same line and not have a common metal conductor.
as a heat exchangera 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 flow heating of the liquid with a small circulation of water, to values allowing the use of this design in the supply warm water small house.
If you connect such a heating element to a well-insulated tank, which will be located above the heater, the result will be a boiler system in which the heating of the liquid will be carried out inside the stainless pipe, the heated water will rise up, and a colder liquid will take its place.
If the area of the house is significant, the number of induction coils can be increased up to 10 pieces.
The power of such a boiler can be easily adjusted by turning off or on the spirals. The more sections that are simultaneously turned on, the greater the power of the heating device operating in this way will be.
To power such a module, you need a powerful power supply. If there is an inverter welding machine direct current, then it is possible to make a voltage converter of the required power from it.
Due to the fact that the system works at a 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 box in the generator power circuit, which, in the event of a short circuit, will de-energize the system, thereby eliminating the possibility of a fire.
It is possible to organize “free” heating of the house in this way, provided that batteries are installed to power induction devices, which will be charged using solar and wind energy.
Batteries should be combined in sections of 2, connected in series. As a result, the supply voltage with such a connection will be at least 24 V., which will ensure the operation of the boiler at high power. Besides, serial connection will reduce the current in the circuit and increase the life of the batteries.

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