HDTV installations with frequency regulator. High frequency hardening technology. Furnace for melting metal using a welding inverter

The strength of elements in particularly critical steel structures largely depends on the condition of the nodes. The surface of the parts plays an important role. To give it the necessary hardness, durability or viscosity, heat treatment operations are carried out. The surface of parts is hardened using various methods. One of them is current hardening high frequency, that is, HDTV. It is one of the most common and very productive methods during large-scale production of various structural elements.

Such heat treatment is applied both to entire parts and to individual sections. In this case, the goal is to achieve certain levels of strength, thereby increasing service life and performance.

Technology is used to strengthen nodes technological equipment and transport, as well as during hardening of various tools.

The essence of technology

High-frequency hardening is an improvement in the strength characteristics of a part due to the ability of an electric current (with variable amplitude) to penetrate the surface of the part, subjecting it to heating. The penetration depth due to the magnetic field can be different. Simultaneously with surface heating and hardening, the core of the assembly may not be heated at all or may only slightly increase its temperature. The surface layer of the workpiece forms the required thickness, sufficient for the passage of electric current. This layer represents the depth of penetration of the electric current.

Experiments have proven that increasing the frequency of the current helps to reduce the depth of penetration. This fact opens up opportunities for regulation and production of parts with a minimal hardened layer.

Heat treatment of HDTV is carried out in special installations - generators, multipliers, frequency converters, which allow adjustment in the required range. In addition to the frequency characteristics, the final hardening is influenced by the dimensions and shape of the part, the material of manufacture and the inductor used.

The following pattern has also been revealed - the smaller the product and the simpler its shape, the better the hardening process. This also reduces the overall energy consumption of the installation.

The inductor is copper. There are often additional holes on the inner surface designed to supply water during cooling. In this case, the process is accompanied by primary heating and subsequent cooling without current supply. The inductor configurations are different. The selected device directly depends on the workpiece being processed. Some devices do not have holes. In such a situation, the part is cooled in a special quenching tank.

The main requirement for the high-frequency hardening process is to maintain a constant gap between the inductor and the product. When maintaining a given interval, the quality of hardening becomes the highest.

Hardening can be done in one of the following ways::

Continuous-sequential: the part is stationary, and the inductor moves along its axis.
Simultaneous: the product moves, and the inductor moves vice versa.
Sequential: different parts are processed one after the other.

Features of the induction installation

The installation for high-frequency hardening is a high-frequency generator together with an inductor. The workpiece is located both in the inductor itself and next to it. It consists of a coil on which a copper tube is wound.

Variable electricity when passing through the inductor, it creates an electromagnetic field that penetrates the workpiece. It provokes the development of eddy currents (Foucault currents), which pass into the structure of the part and increase its temperature.

The main feature of the technology– penetration of eddy current into the surface structure of the metal.

Increasing the frequency opens up the possibility of concentrating heat on a small area of the part. This increases the rate of temperature rise and can reach up to 100 – 200 degrees/sec. The degree of hardness increases to 4 units, which is excluded during volumetric hardening.

Induction heating - characteristics

The degree of induction heating depends on three parameters - specific power, heating time, frequency of electric current. Power determines the time spent heating the part. Accordingly, with a larger value, less time is spent.

The heating time is characterized by the total volume of heat expended and the temperature developed. Frequency, as mentioned above, determines the depth of penetration of currents and the hardened layer formed. These characteristics have an inverse relationship. As the frequency increases, the volumetric mass of the heated metal decreases.

It is these 3 parameters that allow you to adjust the degree of hardness and layer depth, as well as the heating volume, over a wide range.

Practice shows that the characteristics of the generator set (voltage, power and current values), as well as the heating time, are monitored. The degree of heating of the part can be controlled using a pyrometer. However, in general, continuous temperature monitoring is not required because There are optimal HDTV heating modes that ensure stable quality. The appropriate mode is selected taking into account the changed electrical characteristics.

After hardening, the product is sent to the laboratory for testing. The hardness, structure, depth and plane of the distributed hardening layer are studied.

Surface hardening HDTV accompanied by high heat compared to the conventional process. This is explained as follows. First of all, a high rate of temperature increase contributes to an increase in critical points. Secondly, it is necessary to short term ensure completion of the transformation of pearlite into austenite.

High-frequency hardening, in comparison with the conventional process, is accompanied by higher heating. However, the metal does not overheat. This is explained by the fact that granular elements in the steel structure do not have time to grow in a minimum time. In addition, volumetric hardening has a lower strength of up to 2-3 units. After high-frequency hardening, the part has greater wear resistance and hardness.

How is the temperature selected?

Compliance with technology must be accompanied the right choice temperature range. Basically, everything will depend on the metal being processed.

Steel is classified into several types:

Hypoeutectoid – carbon content up to 0.8%;
Hypereutectoid – more than 0.8%.

Hypoeutectoid steel is heated to just above that required to convert pearlite and ferrite to austenite. Range from 800 to 850 degrees. After this, the part is cooled at high speed. After rapid cooling, austenite is transformed into martensite, which has high hardness and strength. With a short holding time, austenite with a fine-grained structure, as well as fine-needle martensite, is obtained. Steel gains high hardness and low brittleness.

Hypereutectoid steel heats up less. Range from 750 to 800 degrees. In this case, incomplete hardening is performed. This is explained by the fact that such a temperature makes it possible to retain in the structure a certain volume of cementite, which has a higher hardness compared to martensite. Upon rapid cooling, austenite is transformed into martensite. Cementite is preserved by small inclusions. The zone also retains carbon that has not fully dissolved and has turned into solid carbide.

Advantages of technology

Controlling modes;
Replacing alloy steel with carbon steel;
Uniform heating process of the product;
The ability not to heat the entire part completely. Reduced energy consumption;
High resulting strength of the processed workpiece;
There is no oxidation process, no carbon is burned;
No microcracks;
There are no warped points;
Heating and hardening of certain areas of products;
Reducing the time spent on the procedure;
Introduction of high-frequency installations into production lines during the manufacture of parts.

Flaws

The main disadvantage of the technology under consideration is the significant installation price. It is for this reason that the feasibility of use is justified only in large-scale production and excludes the possibility of doing the work yourself at home.

Study the operation and principle of operation of the installation in more detail in the presented videos.

Hardening of steels with high frequency currents (HFC) is one of the most common methods of surface heat treatment, which allows increasing the hardness of the surface of workpieces. Used for parts made of carbon and structural steels or cast iron. Induction hardening HDTV is one of the most economical and technologically advanced methods of hardening. It makes it possible to harden the entire surface of a part or its individual elements or zones that experience the main load.

In this case, under the hardened hard outer surface of the workpiece, unhardened viscous layers of metal remain. This structure reduces fragility, increases the durability and reliability of the entire product, and also reduces energy consumption for heating the entire part.

High frequency hardening technology

HDTV surface hardening is a heat treatment process to increase the strength characteristics and hardness of the workpiece.

The main stages of surface hardening of HDTV are induction heating to a high temperature, holding at it, then rapid cooling. Heating during hardening of HDTV is carried out using a special induction installation. Cooling is carried out in a bath with a coolant (water, oil or emulsion) or by spraying it onto the part from special shower installations.

Temperature selection

For the correct completion of the hardening process, the correct selection of temperature, which depends on the material used, is very important.

Steels based on carbon content are divided into hypoeutectoid - less than 0.8% and hypereutectoid - more than 0.8%. Steel with carbon less than 0.4% is not hardened due to the resulting low hardness. Hypoeutectoid steels are heated slightly above the temperature of the phase transformation of pearlite and ferrite to austenite. This occurs in the range of 800-850°C. Then the workpiece is quickly cooled. When cooled sharply, austenite transforms into martensite, which has high hardness and strength. A short holding time makes it possible to obtain fine-grained austenite and fine-needle martensite; the grains do not have time to grow and remain small. This steel structure has high hardness and at the same time low brittleness.

Hypereutectoid steels are heated slightly lower than hypoeutectoid steels, to a temperature of 750-800°C, that is, incomplete hardening is performed. This is due to the fact that when heated to this temperature, in addition to the formation of austenite, a small amount of cementite, which has a higher hardness than martensite, remains undissolved in the metal melt. After rapid cooling, austenite transforms into martensite, and cementite remains in the form of small inclusions. Also in this zone, carbon that has not had time to completely dissolve forms solid carbides.

In the transition zone during high-frequency quenching, the temperature is close to the transition temperature, and austenite with ferrite residues is formed. But, since the transition zone does not cool down as quickly as the surface, but cools down slowly, as during normalization. At the same time, the structure in this zone improves, it becomes fine-grained and uniform.

Overheating the surface of the workpiece promotes the growth of austenite crystals, which has a detrimental effect on brittleness. Underheating prevents the complete ferrite-perrite structure from transforming into austenite, and unhardened spots may form.

After cooling, high compressive stresses remain on the metal surface, which increase the performance properties of the part. Internal stresses between the surface layer and the middle must be eliminated. This is done using low-temperature tempering - holding at a temperature of about 200°C in an oven. To avoid the appearance of microcracks on the surface, it is necessary to minimize the time between hardening and tempering.

You can also carry out the so-called self-tempering - cool the part not completely, but to a temperature of 200 ° C, while heat will remain in its core. Then the part should cool slowly. This will equalize internal stresses.

Induction installation

The HDTV induction heat treatment unit is a high-frequency generator and inductor for HDTV hardening. The part to be hardened can be located in or near the inductor. The inductor is made in the form of a coil, with a copper tube wound on it. It can have any shape depending on the shape and size of the part. When alternating current passes through the inductor, an alternating electromagnetic field appears in it, passing through the part. This electromagnetic field causes eddy currents known as Foucault currents to occur in the workpiece. Such eddy currents, passing through layers of metal, heat it to a high temperature.

A distinctive feature of induction heating using HDTV is the passage of eddy currents on the surface of the heated part. This way, only the outer layer of the metal is heated, and the higher the frequency of the current, the smaller the depth of heating, and, accordingly, the depth of hardening of the high-frequency frequency. This makes it possible to harden only the surface of the workpiece, leaving the inner layer soft and tough to avoid excessive brittleness. Moreover, you can adjust the depth of the hardened layer by changing the current parameters.

The increased frequency of the current allows you to concentrate a large amount of heat in a small area, which increases the heating rate to several hundred degrees per second. Such a high heating rate moves the phase transition to a higher temperature zone. In this case, the hardness increases by 2-4 units, up to 58-62 HRC, which cannot be achieved with volumetric hardening.

For the correct implementation of the HDTV hardening process, it is necessary to ensure that the same clearance is maintained between the inductor and the workpiece over the entire hardening surface, and mutual touching must be avoided. This is ensured, if possible, by rotating the workpiece in the centers, which allows for uniform heating, and, as a consequence, the same structure and hardness of the surface of the hardened workpiece.

The inductor for hardening HDTV has several versions:

single- or multi-turn annular - for heating the outer or inner surface of parts in the form of bodies of rotation - shafts, wheels or holes in them;
loop - for heating the working plane of the product, for example, the surface of the bed or the working edge of the tool;
shaped - for heating parts of complex or irregular shape, for example, gear teeth.

Depending on the shape, size and depth of the hardening layer, the following HDTV hardening modes are used:

simultaneous - the entire surface of the workpiece or a certain zone is heated at once, then also cooled simultaneously;
continuous-sequential - one zone of a part is heated, then when the inductor or part is displaced, another zone is heated, while the previous one is cooled.

Simultaneous high-frequency heating of the entire surface requires large amounts of power, so it is more profitable to use it for hardening small parts - rolls, bushings, pins, as well as part elements - holes, necks, etc. After heating, the part is completely lowered into a tank with coolant or sprayed with a stream of water.

Continuous-sequential hardening of high-frequency frequencies allows you to harden large-sized parts, for example, the crowns of gear wheels, since during this process a small zone of the part is heated, which requires less power of the high-frequency generator.

Cooling parts

Cooling is the second important stage of the hardening process; the quality and hardness of the entire surface depends on its speed and uniformity. Cooling occurs in coolant tanks or by spray. For high-quality hardening, it is necessary to maintain a stable temperature of the coolant and prevent it from overheating. The holes in the sprayer must be of the same diameter and spaced evenly, this way the same metal structure on the surface is achieved.

To prevent the inductor from overheating during operation, water is constantly circulated through the copper tube. Some inductors are made combined with a workpiece cooling system. Holes are cut in the inductor tube through which cold water enters the hot part and cools it.

Advantages and disadvantages

Hardening of parts using HDTV has both advantages and disadvantages. The advantages include the following:

After high-frequency quenching, the part retains a soft center, which significantly increases its resistance to plastic deformation.
The cost-effectiveness of the process of hardening HDTV parts is due to the fact that only the surface or zone that needs to be hardened is heated, and not the entire part.
During mass production of parts, it is necessary to set up the process and then it will be automatically repeated, ensuring required quality hardening
The ability to accurately calculate and adjust the depth of the hardened layer.
The continuous-sequential hardening method allows the use of low-power equipment.
A short heating and holding time at high temperature contributes to the absence of oxidation, decarburization of the top layer and the formation of scale on the surface of the part.
Rapid heating and cooling does not result in large warpage and distortion, which allows for a reduction in finishing allowance.

But it is economically feasible to use induction installations only for mass production, and for single production, purchasing or manufacturing an inductor is unprofitable. For some parts with complex shapes, induction production is very difficult or impossible to obtain a uniform hardened layer. In such cases, other types of surface hardening are used, for example, gas-flame or volumetric hardening.

In hydromechanical systems, devices and assemblies, parts that operate on friction, compression, and torsion are most often used. That is why the main requirement for them is sufficient hardness of their surface. To obtain the required characteristics of the part, the surface is hardened with high frequency current (HFC).

In the process of application, high-frequency hardening has shown itself to be an economical and highly effective method of heat treatment of the surface of metal parts, which gives additional wear resistance and high quality processed elements.

Heating with HF currents is based on the phenomenon in which, due to the passage of an alternating high-frequency current through an inductor (a spiral element made of copper tubes), a magnetic field is formed around it, creating eddy currents in the metal part, which cause heating of the hardened product. Being located exclusively on the surface of the part, they allow it to be heated to a certain adjustable depth.

High-frequency hardening of metal surfaces differs from standard full hardening, which consists in an increased heating temperature. This is due to two factors. The first of them is at high speed heating (when pearlite transforms into austenite), the temperature level of critical points increases. And the second is that the faster the temperature transition occurs, the faster the transformation of the metal surface occurs, because it must occur in a minimum time.

It is worth saying that, despite the fact that when using high-frequency hardening, heating is caused more than usual, overheating of the metal does not occur. This phenomenon is explained by the fact that the grain in the steel part does not have time to increase due to the minimum time of high-frequency heating. In addition, due to the fact that the heating level is higher and the cooling is more intense, the hardness of the workpiece after its high-frequency quenching increases by approximately 2-3 HRC. And this guarantees the highest strength and reliability of the surface of the part.

At the same time, there is an additional important factor that increases the wear resistance of parts during operation. Due to the creation of a martensitic structure, compressive stresses are formed on the upper part of the part. The effect of such stresses is most pronounced at a small depth of the hardened layer.

High-frequency installations, materials and auxiliaries used for hardening

A fully automatic high-frequency hardening complex includes a hardening machine and high-frequency installations (mechanical fastening systems, units for rotating the part around its axis, movement of the inductor in the direction of the workpiece, pumps supplying and pumping out liquid or gas for cooling, electromagnetic valves for switching working liquids or gases (water/emulsion/gas)).

The high-frequency machine allows you to move the inductor over the entire height of the workpiece, as well as rotate the workpiece at different speed levels, adjust the output current on the inductor, and this makes it possible to select the correct mode of the hardening process and obtain a uniformly hard surface of the workpiece.

Schematic diagram of induction HDTV installations for self-assembly was given.

Induction high-frequency hardening can be characterized by two main parameters: the degree of hardness and the depth of surface hardening. The technical parameters of induction units produced in production are determined by the power and frequency of operation. To create a hardened layer, induction heating devices with a power of 40-300 kVA are used at a frequency of 20-40 kilohertz or 40-70 kilohertz. If it is necessary to harden layers that are deeper, it is worth using frequency values from 6 to 20 kilohertz.

The frequency range is selected based on the range of steel grades, as well as the level of depth of the hardened surface of the product. There is a huge range of complete sets of induction installations, which helps to choose a rational option for a specific technological process.

The technical parameters of automatic hardening machines are determined by the overall dimensions of the parts used for hardening in height (from 50 to 250 centimeters), in diameter (from 1 to 50 centimeters) and weight (up to 0.5 t, up to 1 t, up to 2 t). Hardening complexes, the height of which is 1500 mm or more, are equipped with an electronic-mechanical system for clamping the part with a certain force.

High-frequency hardening of parts is carried out in two modes. In the first, each device is individually connected by the operator, and in the second, it occurs without his intervention. The quenching medium is usually water, inert gases or polymer compounds that have thermal conductivity properties similar to oil. The hardening medium is selected depending on the required parameters of the finished product.

HDTV hardening technology

For parts or surfaces flat shape for small diameters, stationary type high-frequency hardening is used. For successful work the location of the heater and the part does not change.

When using continuous-sequential high-frequency hardening, which is most often used when processing flat or cylindrical parts and surfaces, one of the components of the system must move. In this case, either the heating device moves towards the part, or the part moves under the heating device.

To heat exclusively small cylindrical parts that rotate once, continuous-sequential high-frequency hardening of the tangential type is used.

Metal structure of a gear tooth after hardening by the high-frequency method

After high-frequency heating of the product, it is subjected to low tempering at a temperature of 160-200°C. This allows you to increase the wear resistance of the product surface. Temperings are carried out in electric furnaces. Another option is to take a self-vacation. To do this, you need to turn off the water supply device a little earlier, which contributes to incomplete cooling. Item saves high temperature, which heats the hardened layer to a low tempering temperature.

After hardening, electric tempering is also used, in which heating is carried out using a high-frequency installation. To achieve the desired result, heating is carried out at a lower speed and more deeply than with surface hardening. The required heating mode can be determined by selection.

To improve the mechanical parameters of the core and the overall wear resistance of the workpiece, it is necessary to carry out normalization and volumetric hardening with high tempering immediately before surface hardening HDTV.

Areas of application of HDTV hardening

HDTV hardening is used in a number of technological processes manufacturing of the following parts:

shafts, axles and pins;
gears, cogwheels and rims;
teeth or grooves;
cracks and internal parts of parts;
crane wheels and pulleys.

Most often, high-frequency hardening is used for parts that consist of carbon steel containing half a percent carbon. Such products acquire high hardness after hardening. If the presence of carbon is less than the above, such hardness is no longer achievable, and with a higher percentage, cracks are likely to occur when cooled with a water shower.

In most situations, hardening with high-frequency currents makes it possible to replace alloyed steels with more inexpensive ones - carbon ones. This can be explained by the fact that such advantages of steels with alloying additives, such as deep hardenability and less distortion of the surface layer, lose their significance for some products. With high-frequency hardening, the metal becomes stronger and its wear resistance increases. Just like carbon steels, chromium, chromium-nickel, chromium-silicon and many other types of steels with a low percentage of alloying additives are used.

Advantages and disadvantages of the method

Advantages of hardening with HF currents:

fully automatic process;
work with products of any shape;
no soot;
minimal deformation;
variability in the level of depth of the hardened surface;
individually determined parameters of the hardened layer.

Among the disadvantages are:

the need to create a special inductor for different shapes of parts;
difficulties in adjusting heating and cooling levels;
high cost of equipment.

The possibility of using hardening with high-frequency currents in individual production is unlikely, but in a mass flow, for example, in the manufacture of crankshafts, gears, bushings, spindles, cold rolling shafts, etc., hardening of high-frequency currents is becoming increasingly used.

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

Heating and melting of metals in induction furnaces occurs 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 molten metal, it is placed in the zone of action of the electromagnetic field of the inductor - the coil. It can be in the shape of a spiral, figure eight or trefoil. The shape of the inductor depends on the size and shape of the heated workpiece.

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

Kinds

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

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

Channel furnace too large and designed for industrial volumes of metal smelting. It is used in the smelting of cast iron, aluminum and other non-ferrous metals.
Crucible furnace It is quite compact, it is used by jewelers and radio amateurs; such a stove can be assembled with your own hands and used at home.

Device

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

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

Advantages of an induction furnace:

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

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

Furnace for melting metal using a welding inverter

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

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

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

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

The heating system of a private home is based on the operation of a stove or boiler, the high performance and long uninterrupted service life of which depends both on the brand and installation of the heating devices themselves, and on the correct installation of the chimney.
You will find recommendations for choosing a solid fuel boiler, and in the next section you will get acquainted with the types and rules:

Induction furnace with transistors: diagram

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

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

DIY assembly sequence:

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

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

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

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

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

Induction heater for metal melting: video

Induction furnace with lamps

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

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

To assemble the circuit you need:

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

Assembling the device yourself:

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

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

Circuit cooling

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

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

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

Safety precautions when working

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

It is not recommended to use the device for people with implanted pacemakers!

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