HDTV installations with frequency control. High frequency hardening technology. Furnace for melting metal on a welding inverter

The strength of elements in especially 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, resistance or viscosity, heat treatment operations are carried out. Strengthen the surface of parts by various methods. One of them is current hardening high frequency, i.e. HDTV. It belongs to the most common and very productive method during large-scale production of various structural elements.

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

Technology used to strengthen knots technological equipment and transport, as well as when hardening various tools.

Essence of technology

HDTV 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, exposing it to heat. The depth of penetration due to the magnetic field can be different. Simultaneously with surface heating and hardening, the core of the node may not be heated at all or only slightly increase its temperature. The surface layer of the workpiece forms the necessary thickness, sufficient for the passage of electric current. This layer represents the depth of penetration of the electric current.

Experiments have proven that an increase in the frequency of the current contributes to a decrease in the penetration depth. This fact opens up opportunities for regulation and production of parts with a minimum hardened layer.

HDTV heat treatment is carried out in special installations - generators, multipliers, frequency converters, allowing 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 was also revealed - the smaller the product and the simpler its shape, the better the hardening process goes. This also reduces the overall energy consumption of the installation.

copper inductor. On the inner surface there are often additional holes designed to supply water during cooling. In this case, the process is accompanied by primary heating and subsequent cooling without current supply. 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 hardening tank.

The main requirement for the process of HD hardening is to maintain a constant gap between the inductor and the workpiece. While maintaining the specified interval, the quality of hardening becomes the highest.

Strengthening can be done in one of the ways:

Continuous-series: the part is stationary, and the inductor moves along its axis.
Simultaneous: the product is moving, and the inductor is vice versa.
Sequential: Processing the various parts one by one.

Features of the induction installation

Installation for HDTV hardening is a high-frequency generator together with an inductor. The workpiece is located both in the inductor itself and next to it. It is 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 in 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 bulk hardening.

Induction heating - characteristics

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

The heating time is characterized by the total amount of heat expended and the developed temperature. Frequency, as mentioned above, determines the depth of penetration of currents and the formed hardenable layer. These characteristics are inversely related. As the frequency increases, the volumetric mass of the heated metal decreases.

It is these 3 parameters that make it possible to regulate the degree of hardness and layer depth, as well as the volume of heating, in a wide range.

Practice shows that the characteristics of the generator set (voltage, power and current values), as well as the heating time, are controlled. The degree of heating of the part can be controlled using a pyrometer. However, in general, continuous temperature monitoring is not required, as 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 analysis. The hardness, structure, depth and plane of the distributed hardened layer are studied.

Surface hardening HDTV accompanied by a lot of 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 to ensure the 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 the granular elements in the steel structure do not have time to grow in a minimum time. In addition, bulk hardening has a lower strength of up to 2-3 units. After HFC hardening, the part has greater wear resistance and hardness.

How is the temperature chosen?

Compliance with technology should 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 a value slightly higher than necessary to convert pearlite and ferrite to austenite. Range from 800 to 850 degrees. After that, the part is cooled at high speed. After rapid cooling, austenite transforms into martensite, which has high hardness and strength. With a short holding time, fine-grained austenite is obtained, as well as finely acicular martensite. Steel gets high hardness and little 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 preserve in the structure a certain volume of cementite, which has a higher hardness in comparison with martensite. Upon rapid cooling, austenite transforms into martensite. Cementite is preserved by small inclusions. The zone also retains fully dissolved carbon, which has turned into solid carbide.

Advantages of technology

Mode control;
Replacement of alloy steel with carbon steel;
Uniform heating process of the product;
Possibility not to heat the whole part completely. Reduced energy consumption;
High resulting strength of the processed workpiece;
There is no oxidation process, carbon is not burned;
No microcracks;
There are no warped points;
Heating and hardening of certain sections of products;
Reducing the time spent on the procedure;
Implementation in the manufacture of parts for high-frequency installations in production lines.

Flaws

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

Learn more about the operation and principle of operation of the installation on the presented videos.

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

In this case, non-hardened viscous layers of metal remain under the hardened solid outer surface of the workpiece. Such a structure reduces brittleness, increases the durability and reliability of the entire product, and also reduces energy consumption for heating the entire part.

High frequency hardening technology

HFC surface hardening is a heat treatment process to improve 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 unit. 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 passage of the hardening process, the correct selection of temperature is very important, which depends on the material used.

According to the carbon content, steels are divided into hypoeutectoid - less than 0.8% and hypereutectoid - more than 0.8%. Steel with less than 0.4% carbon is not hardened due to the resulting low hardness. Hypoeutectoid steels are heated slightly above the phase transformation temperature of pearlite and ferrite to austenite. This occurs in the range of 800-850°C. Then the workpiece is rapidly cooled. When cooled abruptly, austenite transforms into martensite, which has high hardness and strength. A short holding time makes it possible to obtain fine-grained austenite and fine-acicular 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 ones, 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 in the metal melt, a small amount of cementite remains undissolved, which has a higher hardness than that of martensite. After rapid cooling, austenite transforms into martensite, while 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 hardening of high-frequency current, the temperature is close to the transition one, and austenite is formed with residual ferrite. 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 improves in this zone, it becomes fine-grained and uniform.

Overheating of the workpiece surface promotes the growth of austenite crystals, which has a detrimental effect on brittleness. Underheating does not allow a completely ferritic-perritic structure to pass into austenite, and unquenched spots can form.

After cooling, high compressive stresses remain on the metal surface, which increase the operational 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 quenching and tempering.

It is also possible to carry out the so-called self-tempering - to cool the part not completely, but to a temperature of 200 ° C, while it will remain warm in its core. Further, the part should cool slowly. This will equalize the internal stresses.

induction plant

The HDTV induction heat treatment plant is a high-frequency generator and an inductor for HDTV hardening. The part to be hardened can be located in the inductor or near it. The inductor is made in the form of a coil, a copper tube is wound on it. It can have any shape depending on the shape and dimensions of the part. When an alternating current passes through the inductor, an alternating electromagnetic field appears in it, passing through the part. This electromagnetic field induces eddy currents in the workpiece, known as Foucault currents. Such eddy currents, passing through the metal layers, 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. So 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 HDTV. This makes it possible to harden only the surface of the workpiece, leaving the inner layer soft and viscous to avoid excessive brittleness. Moreover, it is possible to adjust the depth of the hardened layer by changing the current parameters.

The increased frequency of the current allows a large amount of heat to be concentrated 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 zone of higher temperature. In this case, the hardness increases by 2-4 units, up to 58-62 HRC, which cannot be achieved with bulk hardening.

For the correct course of the HDTV hardening process, it is necessary to ensure that the same clearance between the inductor and the workpiece is maintained over the entire hardening surface, it is necessary to exclude mutual touches. This is ensured, if possible, by rotating the workpiece in the centers, which makes it possible to ensure uniform heating, and, as a result, the same structure and hardness of the surface of the hardened workpiece.

The inductor for HDTV hardening has several versions:

single or multi-turn annular - for heating the outer or inner surface of parts in the form of bodies of revolution - 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 it is also simultaneously cooled;
continuous-sequential - one zone of the part is heated, then when the inductor or part is displaced, another zone is heated, while the previous one is cooled.

Simultaneous HDTV heating the entire surface requires a lot 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 poured with a stream of water.

Continuous-sequential hardening of high-frequency current makes it possible to harden large-sized parts, for example, gear rims, since this process heats up a small area of the part, which requires less power of the high-frequency generator.

Part cooling

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 takes place in coolant or splash tanks. For high-quality hardening, it is necessary to maintain a stable temperature of the coolant, to prevent its overheating. The holes in the sprayer must be of the same diameter and evenly spaced, so that the same structure of the metal on the surface is achieved.

To prevent the inductor from overheating during operation, water constantly circulates through the copper tube. Some inductors are made combined with the 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 parts using HDTV has both advantages and disadvantages. The advantages include the following:

After HFC hardening, the part retains a soft center, which significantly increases its resistance to plastic deformation.
The cost-effectiveness of the hardening process of 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.
In the mass production of parts, it is necessary to set up the process and then it will automatically repeat, 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.
The short heating and holding time at high temperature contributes to the absence of oxidation, decarburization of the upper layer and the formation of scale on the surface of the part.
Rapid heating and cooling reduces warpage and leash, which reduces the finishing allowance.

But it is economically feasible to use induction installations only in mass production, and for a single production, the purchase or manufacture of an inductor is unprofitable. For some parts of complex shape, the production of an induction installation is very difficult or impossible to obtain a uniform hardened layer. In such cases, other types of surface hardening are used, for example, flame or bulk hardening.

In hydromechanical systems, devices and assemblies, parts that work on friction, compression, twisting 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 by high frequency current (HF).

In the process of application, HDTV hardening has proven 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 items.

Heating by high-frequency 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 a metal part, which cause heating of the hardened product. Being exclusively on the surface of the part, they allow you to heat it to a certain adjustable depth.

HDTV 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 turns into austenite), the temperature level of the critical points rises. And the second - the faster the temperature transition passes, the faster the transformation of the metal surface takes place, because it must occur in the 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 happen. 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 hardening by HDTV 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 provides an increase in 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 action of such stresses manifests itself to the highest extent at a small depth of the hardened layer.

Installations, materials and auxiliary means used for HDTV hardening

A fully automatic high-frequency hardening complex includes a hardening machine and high-frequency equipment (mechanical-type fastening systems, components for turning a part around its axis, movement of the inductor in the direction of the workpiece, pumps that supply and pump out liquid or gas for cooling, electromagnetic valves for switching working liquids or gases (water/emulsion/gas)).

The HDTV machine allows you to move the inductor along 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.

A schematic diagram of an HDTV induction installation for self-assembly was given.

High-frequency induction hardening can be characterized by two main parameters: the degree of hardness and the depth of hardening of the surface. The technical parameters of induction installations produced in the 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 frequencies of 20-40 kilohertz or 40-70 kilohertz. If it is necessary to harden layers that are deeper, it is worth using frequency indicators from 6 to 20 kilohertz.

The frequency range is selected based on the range of steel grades, as well as the depth level 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 particular 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 tons, up to 1 ton, up to 2 tons). Complexes for hardening, 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. Water, inert gases, or polymer compositions with thermal conductivity properties close to oil are usually chosen as the quenching medium. The hardening medium is selected depending on the required parameters of the finished product.

HDTV hardening technology

For parts or surfaces flat shape small diameter, stationary type high-frequency quenching 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 such a case, either the heating device moves towards the workpiece, or the workpiece moves under the heating apparatus.

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

The structure of the metal of the gear tooth, after hardening by the HDTV method

After high-frequency heating of the product, its low tempering is performed at a temperature of 160-200°C. This allows to increase the wear resistance of the surface of the product. Holidays are made in electric furnaces. Another option is to take a break. To do this, it is necessary to turn off the device that supplies water a little earlier, which contributes to incomplete cooling. Detail 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 an RF installation. To achieve the desired result, heating is carried out at a lower rate and more deeply than with surface hardening. The required heating mode can be determined by the selection method.

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.

Scope of hardening HDTV

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

shafts, axles and pins;
gears, gear wheels and rims;
teeth or cavities;
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 at a higher percentage, cracks are likely to occur when cooling with a water shower.

In most situations, quenching with high-frequency currents makes it possible to replace alloyed steels with more inexpensive carbon steels. 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. In the same way as 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 high-frequency currents:

fully automatic process;
work with products of any form;
lack of soot;
minimum deformation;
variability of the depth level 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 overlaying the levels of heating and cooling;
high cost of equipment.

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

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.

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

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;
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 the correct installation of the chimney.
you will find recommendations for choosing a solid fuel boiler, and in the following you will get acquainted with the types and rules:

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 operation is about 10 A, the battery capacity in this case is enough for about 40 minutes. If necessary, the furnace body is made of 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.

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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 during operation is the 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 put on clothes without metal elements, remove complex devices from the coverage area: phones, digital cameras.

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

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 operation of the presented installations can be adjusted to a specific task by changing the parameters of the inductor and the output signal of the generator sets - this way you can achieve their maximum efficiency.