Metal smelting by induction is actively used in various industries, such as mechanical engineering, metallurgical and jewelry production. The material heats up under the influence electric current, which allows you to use heat with maximum efficiency. Large factories have special industrial units for this, while at home you can assemble a simple and small induction furnace with your own hands.

Such furnaces are popular in production

Self-assembly of the stove

There are many technologies and schematic descriptions of this process presented on the Internet and magazines, but when choosing, it is worth choosing one model that is most effective in operation, as well as affordable and easy to implement.

Homemade melting furnaces have a fairly simple design and usually consist of only three main parts housed in a sturdy casing. These include:

• element generating high frequency alternating current;
• a spiral-shaped part created from a copper tube or thick wire, called an inductor;
• crucible - a container in which calcination or melting will be carried out, made of refractory material.

Of course, such equipment is not often used in everyday life, because not all craftsmen need such units. But the technologies found in these devices are found in household appliances that many people deal with almost every day. This includes microwaves, electric ovens And induction cookers. You can make it yourself using the diagrams miscellaneous equipment, if available necessary knowledge and skills.

In this video you will learn what this oven consists of

Heating in this technique is carried out thanks to induction eddy currents. The temperature rise occurs instantly, unlike other devices of a similar purpose.

For example, induction cookers have an efficiency of 90%, but gas and electric cookers cannot boast of this value, it is only 30-40% and 55-65%, respectively. However, HDTV cookers have a drawback: to use them you will have to prepare special dishes.

Transistor design

There are many different schemes for assembling induction melters at home. A simple and proven oven made from field effect transistors It is quite easy to assemble; many craftsmen familiar with the basics of radio engineering can handle its manufacture according to the diagram shown in the figure. To create an installation need to prepare following materials and details:

• two IRFZ44V transistors;
• copper wires (for winding) in enamel insulation, 1.2 and 2 mm thick (one piece each);
• two rings from chokes, they can be removed from the power supply of an old computer;
• one 470 Ohm resistor per 1 W (you can connect two 0.5 W each in series);
• two UF4007 diodes (can easily be replaced with the UF4001 model);
• 250 W film capacitors - one piece with a capacity of 330 nF, four - 220 nF, three - 1 µF, 1 piece - 470 nF.

Before assembling such a stove, do not forget about the tools

Assembly takes place according to the schematic drawing; it is also recommended to check step by step instructions, this will protect you from errors and damage to elements. Creating an induction melting furnace with your own hands is carried out according to the following algorithm:

1. Transistors are placed on fairly large heatsinks. The fact is that circuits can get very hot during operation, which is why it is so important to select parts of the appropriate size. All transistors can be placed on one radiator, but in this case you will have to insulate them, preventing them from coming into contact with metal. Washers and gaskets made of plastic and rubber will help with this. The correct pinout of transistors is shown in the picture.
2. Then they start making chokes; you will need two of them. To do this, take copper wire 1.2 millimeters in diameter and wrap it around rings taken from the power supply. These elements contain ferromagnetic iron in powder form, so it is necessary to make at least 7-15 turns, leaving a small distance between them.
3. The resulting modules are assembled into one battery with a capacity of 4.6 μF, and the capacitors are connected in parallel.
4. Copper wire 2 mm thick is used to wind the inductor. It is wrapped 7-8 times around any object. cylindrical, its diameter must correspond to the size of the crucible. The excess wire is cut off, but rather long ends are left: they will be needed for connecting to other parts.
5. All elements are connected on the board, as shown in the figure.

If necessary, you can build a housing for the unit; for this purpose, only heat-resistant materials, such as textolite, are used. The power of the device can be adjusted, for which it is enough to change the number of turns of wire on the inductor and their diameter.

There are several variations of the induction furnace that can be assembled

With graphite brushes

The main element of this design is assembled from graphite brushes, the space between which is filled with granite, crushed to a powder state. Then the finished module is connected to a step-down transformer. When working with such equipment, you do not have to worry about electric shock, since it does not need to use 220 volts.

Manufacturing technology of an induction furnace from graphite brushes:

1. First, the body is assembled; for this, fire-resistant (fireclay) bricks measuring 10 × 10 × 18 cm are laid on tiles that can withstand high temperatures. The finished box is wrapped in asbestos cardboard. To give this material the desired shape, it is enough to moisten it with a small amount of water. The size of the base directly depends on the power of the transformer used in the design. If desired, the box can be covered with steel wire.
2. An excellent option for graphite furnaces would be a transformer with a power of 0.063 kW, taken from welding machine. If it is designed for 380 V, then for safety reasons it can be subjected to winding, although many experienced radio technicians believe that this procedure can be abandoned without any risk. However, it is recommended to wrap the transformer with thin aluminum so that the finished device does not heat up during operation.
3. A clay substrate is placed at the bottom of the box so that the liquid metal does not spread, after which graphite brushes and granite sand are placed in the box.

The main advantage of such devices is considered to be the high melting point, which can change the state of aggregation of even palladium and platinum. The disadvantages include too rapid heating of the transformer, as well as small area a furnace that will not allow smelting more than 10 g of metal at a time. Therefore, every master should understand that if the device is assembled to process large volumes, then it is better to make a furnace of a different design.

Lamp-based device

A powerful melting stove can be assembled from electronic light bulbs. As can be seen in the diagram, to obtain high-frequency current, beam lamps must be connected in parallel. Instead of an inductor, this device uses a copper tube with a diameter of 10 mm. The design is also equipped with a tuning capacitor in order to be able to regulate the power of the furnace. For assembly you need to prepare:

• four lamps (tetrodes) L6, 6P3 or G807;
• trimmer capacitor;
• 4 chokes at 100-1000 µH;
• neon indicator light;
• four 0.01 µF capacitors.

To begin with, the copper tube is shaped into a spiral - this will be the inductor of the device. In this case, a distance of at least 5 mm is left between the turns, and their diameter should be 8-15 cm. The ends of the spiral are processed for attachment to the circuit. The thickness of the resulting inductor should be 10 mm greater than that of the crucible (it is placed inside).

The finished part is placed in the housing. For its manufacture, you should use a material that will provide electrical and thermal insulation for the filling of the device. Then a cascade is assembled from lamps, chokes and capacitors, as shown in the figure, the latter being connected in a straight line.

It's time to connect the neon indicator: it is needed so that the master can find out when the device is ready for work. This light bulb is connected to the furnace body along with the handle of the variable capacitor.

Cooling system equipment

Industrial units for melting metal are equipped with special cooling systems using antifreeze or water. To equip these important installations in homemade HDTV stoves, you will need additional expenses, because of which the assembly can significantly hit the wallet. Therefore, it is better to provide a household unit with a cheaper system consisting of fans.

Air cooling with these devices is possible when they are located remotely from the furnace. Otherwise, the metal windings and fan parts can serve as a loop for short-circuiting eddy currents, which will significantly reduce the efficiency of the equipment.

Lamp and electronic circuits also tend to actively heat up during operation of the unit. Heat sinks are usually used to cool them.

Terms of use

For experienced radio technicians, assembling an induction furnace according to the diagrams with your own hands may seem like an easy task, so the device will be ready quite quickly, and the master will want to try his creation in action. It is worth remembering that when working with a homemade installation, it is important to follow safety precautions and not forget about the main threats that may arise during operation of an inertial furnace:

1. Liquid metal and heating elements of the device can cause severe burns.
2. Tube circuits consist of parts with high voltage, therefore, during assembly of the unit, they must be placed in a closed box, thus eliminating the possibility of accidentally touching these elements.
3. The electromagnetic field can influence even those things that are outside the installation box. Therefore, before turning on the device, you need to remove all complex technical devices, such as Cell phones, digital cameras, MP3 players, and remove all metal jewelry. People with pacemakers are also at risk: they should never use such equipment.

These furnaces can be used not only for smelting, but also for quickly heating metal objects during forming and tinning. By changing the output signal of the installation and the parameters of the inductor, you can configure the device for a specific task.

For melting small volumes of iron they will be used homemade stoves, these efficient devices can operate from regular outlets. The device does not take up much space, it can be placed on a desktop in a workshop or garage. If a person knows how to read simple electrical diagrams, then he does not need to purchase such equipment in a store, because he can assemble a small stove with his own hands in just a few hours.

Radio amateurs have long discovered that they can make induction furnaces for melting metal with their own hands. These simple diagrams will help you make a HDTV installation for home use. However, it would be more correct to call all the described designs “Kukhtetsky’s laboratory inverters,” since it is simply impossible to independently assemble a full-fledged stove of this type.

Induction heaters can be divided into industrial and household. One of the main methods of generating heat for melting metal in the metallurgical industry is induction furnaces. Devices operating on the induction principle are complex electrical equipment and are sold in a wide range.

Induction technology is the basis of such devices from our everyday life as microwaves, electric ovens, induction cookers, hot water boilers, furnace heating system. Kitchen stoves With inductive principle the work is convenient, practical and economical, but require the use of special utensils.

The most common stoves in everyday life are those using the induction principle of operation for heating rooms. Options for such heating are boiler installations or autonomous units. In jewelry making and small workshops, small induction furnaces are indispensable for melting metal.

Advantages of Melting

Induction heating is direct, non-contact and its principle allows the generated heat to be used with maximum efficiency. The efficiency factor (efficiency) when using this method tends to 90%. During the melting process, thermal and electrodynamic movement of the liquid metal occurs, which contributes to uniform temperature throughout the entire volume of the homogeneous material.

Technological potential of such devices creates advantages:

• performance – can be used immediately after switching on;
• high speed of the melting process;
• possibility of adjusting the melt temperature;
• zonal and focused energy orientation;
• uniformity of molten metal;
• no waste from alloying elements;
• environmental cleanliness and safety.

Benefits of heating

Scheme

It is quite possible for a craftsman who knows how to read electrical diagrams to make a heating furnace or induction melting furnace with his own hands. Feasibility of installation homemade unit Each master must determine for himself. It is also necessary to have a good understanding of the potential danger from poorly executed such structures.

To create a working furnace without ready-made scheme must have understanding of the basics of physics induction heating. Without certain knowledge, it is not possible to design and install such an electrical device. Device design consists of development, design, and diagramming.

For those smart owners who need a safe induction furnace, the circuit is especially important, as it combines all the best practices of a home craftsman. Such popular devices as induction furnaces have a variety of assembly schemes, where craftsmen have the opportunity to choose:

• oven containers;
• operating frequency;
• lining method.

Characteristics

When creating an induction melting furnace with your own hands, you need to consider certain technical characteristics, affecting the melting rate of the metal:

• generator power;
• pulse frequency;
• losses due to eddy flows;
• hysteresis losses;
• heat transfer intensity (cooling).

Principle of operation

The basis of the induction furnace is to obtain heat from the electricity generated variable electrical magnetic field (EMF) inductor (inductor). That is, electromagnetic energy is converted into vortex electrical energy, and then into thermal energy.

Eddy currents closed inside bodies release thermal energy, which heats the metal from the inside. Multi-stage energy conversion does not reduce the efficiency of the furnace. Because of simple principle jobs and opportunities self-assembly schemes increase the profitability of using such devices.

These efficient devices, in a simplified version and with reduced dimensions, operate from a standard 220V network, but require a rectifier. In such devices, only electrically conductive materials can be heated and melted.

Design

An induction device is a kind of transformer in which powered from a source alternating current inductor - primary winding, the heated body is the secondary winding.

The simplest low-frequency heating inductor can be considered an insulated conductor (straight core or spiral) located on the surface or inside a metal pipe.

Main components of the device, working on the principle of induction, consider:

Power from the generator launches powerful currents of varying frequencies into an inductor, which creates an electromagnetic field. This field is a source of eddy currents, which are absorbed by the metal and melt it.

Heating system

When installing homemade induction heaters in the heating system, craftsmen often use inexpensive models welding inverters (DC to AC voltage converters). The energy consumption of the inverter is large, so for continuous operation of such systems you need a cable with a cross section of 4–6 mm2 instead of the usual 2.5 mm2.

Such heating systems must be closed and automatically controlled. Also, for operational safety, a pump is required for forced circulation of the coolant, devices for removing air trapped in the system, and a pressure gauge. The heater must be located at least 1 m from the ceiling and floor, and at least 30 cm from walls and furniture.

Generator

The inductors receive power from the industrial frequency setting of 50 Hz in the factory. And from generators and converters of high, medium and low frequencies(individual power supplies) inductors also work in everyday life. The most effective way to involve in assembly high frequency generators. Can be used in mini induction ovens currents of different frequencies.

The alternator should not produce a hard current spectrum. According to one of the most popular schemes for assembling induction furnaces in domestic conditions, a generator frequency of 27.12 MHz is recommended. One of these generators is assembled from the following parts:

• 4 tetrodes (electronic tubes) of high power (6p3s brand), with parallel connection;
• 1 additional neon light - indicator that the device is ready for operation.

Inductor

Various modifications of the inductor can be presented in the shape of a trefoil, a figure of eight, and other options. The center of the assembly is an electrically conductive graphite or metal blank, around which the conductor is wound.

Good up to high temperatures graphite brushes heat up(melting furnaces) and nichrome spiral(heating device). The easiest way to make an inductor is in the form of a spiral, the internal diameter of which is 80–150 mm. The material for the heating coil of the conductor is also often copper tube or PEV wire 0.8.

The number of turns of the heating coil must be at least 8–10. The required distance between turns is 5–7 mm, and the diameter of the copper tube is usually 10 mm. Minimum clearance There must be at least 50 mm between the inductor and other parts of the device.

Kinds

Distinguish types of induction furnaces with your own hands:

• channel - the molten metal is located in a groove around the inductor core;
• crucible - the metal is located in a removable crucible inside the inductor.

On large productions Channel furnaces operate from industrial frequency devices, and crucible furnaces operate at industrial, medium and high frequencies. In the metallurgical industry, crucible type furnaces are used for smelting:

• cast iron;
• become;
• copper;
• magnesium;
• aluminum;
• precious metals.

Channel type induction furnaces are used in smelting:

• cast iron;
• various non-ferrous metals and their alloys.

Duct

A channel-type induction furnace must have, when heated, electrically conductive body in the heat generation zone. During the initial startup of such a furnace, molten metal is poured into the melting zone or a prepared metal template is inserted. Upon completion of metal smelting, the raw materials are not completely drained, leaving a “swamp” for the next smelting.

Crucible

Crucible induction furnaces are the most popular among craftsmen because they are easy to use. A crucible is a special removable container placed in an inductor along with metal for subsequent heating or melting. The crucible can be made of ceramics, steel, graphite and many other materials. It differs from the channel type in the absence of a core.

Cooling

Increases the efficiency of the melting furnace in industrial environments and in domestic small factory-made appliances cooling. In case of short-term work and low power homemade device You can do without this function.

Perform the cooling task yourself home handyman does not seem possible. Scale on copper may lead to loss of functionality of the device, so regular replacement of the inductor will be required.

In industrial conditions, water cooling is used, using antifreeze, and is also combined with air cooling. Forced air cooling in home-made household appliances is unacceptable, since the fan can draw EMF onto itself, which will lead to overheating of the fan housing and a decrease in the efficiency of the stove.

Safety

When working with the oven, you should beware of thermal burns and take into account the high fire danger device. While the devices are operating, they must not be moved. You need to be especially prudent when installing heating stoves in residential areas.

EMF affects and heats the entire surrounding space, and this feature is closely related to the power and frequency of the device’s radiation. Powerful industrial devices can affect metal parts near them, human tissue, and objects in clothing pockets.

The possible impact of such devices on people with implanted pacemakers during operation must be taken into account. When purchasing devices with an induction operating principle, you must carefully read the operating instructions.

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

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properties are determined by the specific physical characteristics of induction furnaces.

During induction melting, a transfer occurs hard material into the liquid phase under the influence of an electromagnetic field. As in the case of induction heating, heat is released in the melted material due to the Joule effect from induced eddy currents. The primary current passing through the inductor creates an electromagnetic field. Regardless of whether the electromagnetic field is concentrated by magnetic cores or not, connected system inductor - loading can be represented as a transformer with a magnetic core or as an air transformer. The electrical efficiency of the system is highly dependent on the field-influencing characteristics of the ferromagnetic components.

Along with electromagnetic and thermal phenomena in the process induction melting Electrodynamic forces play an important role. 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. Action of electromagnetic forces

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

There are two main types of induction furnaces: induction crucible furnaces (IFC) and induction channel furnaces (ICF). In ITP, the molten material is usually loaded in pieces into a 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

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inductor and loading strongly depends on the wall thickness of the ceramic crucible. To ensure high electrical efficiency, the insulation must 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 electrical and strength criteria.

Important characteristics of induction melting in ITP are the movement of the melt and the meniscus as a result of the influence of electromagnetic forces. The movement of the melt ensures both uniform temperature distribution and homogeneous chemical composition. The mixing effect at the surface of the melt reduces material losses during additional loading of small-sized charge and additives. Despite the use of cheap material, the reproduction of a melt of constant composition ensures high quality casting

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

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at frequencies up to 1000 Hz. The latter are becoming increasingly important due to their high efficiency in melting cast iron and aluminum. Since the movement of the melt at constant power weakens with increasing frequency, by more high frequencies ah, higher power densities and, as a consequence, greater productivity become available. Due to the higher power, the melting time is reduced, which leads to an increase in the efficiency of the process (compared to furnaces operating at industrial frequency). Taking into account other technological advantages, such as flexibility in changing melted materials, mid-frequency ITPs are designed as the high-power melting plants that currently dominate the iron foundry industry. Modern powerful mid-frequency ITS for cast iron melting have a capacity of up to 12 tons and a power of up to 10 MW. Industrial frequency ITPs are developed for large containers than mid-frequency ones, up to 150 tons for cast iron melting. Intensive mixing of the bath is of particular importance when smelting homogeneous alloys, such as brass, therefore, industrial frequency ITPs are widely used in this area. Along with the use of crucible furnaces for smelting, they are currently also used for holding liquid metal before casting.

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

The second widely used type of induction furnace is the IKP. They are used for casting, aging 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

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

The operating principle of the IKP requires the presence of a constantly closed secondary loop, so these furnaces operate with a liquid residue of the melt. Useful heat is generated mainly in the channel, which has a small cross-section. The circulation of the melt under the influence of electromagnetic and thermal forces ensures sufficient heat transfer into the bulk of the melt located in the bath. Until now, ICPs have been designed for industrial frequency, however research papers are also carried out for higher frequencies. Thanks to the furnace's compact design and very good electromagnetic coupling, its electrical efficiency reaches 95%, and its overall efficiency reaches 80% and even 90%, depending on the material being melted.

According to the technological conditions in different fields of application, ICPs are required various designs induction channels. Single-channel furnaces are mainly used for aging and casting,

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less often melting steel 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 melting plants, the channels are made straight for ease of cleaning.

The production of aluminum, copper, brass and their alloys is the main area of ​​application of IKP. Today, the most powerful ICPs with a capacity

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

Promising applications of induction melting technology include 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, melt homogenization due to stirring, precise

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

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

Further improvement in the economics of induction melting is possible through the use of modern control technologies such as tandem or dual feed control. Two tandem ITPs have one power source, and while melting is underway in one, the molten metal is held in the other for casting. Switching the power source from one furnace to another increases its utilization. Further development This principle is dual power control (Fig. 7.25), which ensures long-term simultaneous operation of furnaces without switching using special automatic process control. It should also be noted that an integral part of the economics of smelting is the compensation of total reactive power.

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

Chapter 7. Energy-saving capabilities of modern electrical technologies

□ metal loss; Shch melting

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induction channel furnace with a capacity of 50 tons. The final energy consumption is reduced by approximately 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 emission coefficients for mixed power plants). The results obtained highlight the special influence of metal losses during melting associated with its oxidation. Their compensation requires a large additional expenditure of energy. It is noteworthy that in copper production, metal losses during smelting are also large and must be taken into account when choosing a particular smelting technology.

The article discusses the designs of industrial induction melting furnaces (channel and crucible) and induction hardening plants powered by machine and static frequency converters.

Diagram of an induction channel furnace

Almost all industrial duct induction furnace designs are made with detachable induction units. The induction unit is an electric furnace transformer with a lined channel to accommodate the molten metal. The induction unit consists of the following elements: casing, magnetic core, lining, inductor.

Induction units are made as single-phase or two-phase (dual) with one or two channels per inductor. The induction unit is connected to the secondary side (LV side) of the electric furnace transformer using contactors having arc suppression devices. Sometimes two contactors with parallel operating power contacts in the main circuit are switched on.

In Fig. Figure 1 shows the power supply diagram for a single-phase induction unit of a channel furnace. Maximum current relays PM1 and PM2 are used to control and turn off the furnace in case of overloads and short circuits.

Three-phase transformers are used to power three-phase or two-phase furnaces that have either a common three-phase magnetic core or two or three separate core-type magnetic cores.

To power the furnace during the period of metal refining and to maintain the regime idle move autotransformers serve for more precise power control during the period of finishing the metal to the desired level chemical composition(with a calm, without seething, melting mode), as well as for the initial starts of the furnace during the first melts, which are carried out with a small volume of metal in the bath to ensure gradual drying and sintering of the lining. The power of the autotransformer is chosen within 25-30% of the power of the main transformer.

To control the temperature of water and air cooling the inductor and the casing of the induction unit, electric contact thermometers are installed that issue a signal when the temperature exceeds the permissible limit. The power to the furnace is automatically turned off when the furnace is turned to drain the metal. To control the position of the furnace, limit switches are used, interlocked with the electric furnace drive. For continuous furnaces and mixers, the induction units are not switched off when draining metal and loading new portions of the charge.

Rice. 1. Schematic diagram power supply of the induction unit of a channel furnace: VM - power switch, CL - contactor, Tr - transformer, C - capacitor battery, I - inductor, TN1, TN2 - voltage transformers, 777, TT2 - current transformers, R - disconnector, PR - fuses, RM1, RM2 - maximum current relay.

To ensure reliable power supply during operation and in emergency cases, the drive motors of the tilting mechanisms of the induction furnace, fan, drive of loading and unloading devices and control systems are powered from a separate auxiliary transformer.

Diagram of an induction crucible furnace

Industrial induction crucible furnaces with a capacity of more than 2 tons and a power of over 1000 kW are powered by three-phase step-down transformers with secondary voltage regulation under load, connected to a high-voltage industrial frequency network.

The furnaces are single-phase, and to ensure uniform load of the network phases, a balun device is connected to the secondary voltage circuit, consisting of a reactor L with inductance regulation by changing air gap in a magnetic circuit and a capacitor bank Cc connected with an inductor according to a delta circuit (see ARIS in Fig. 2). Power transformers with a capacity of 1000, 2500 and 6300 kV-A have 9 - 23 stages of secondary voltage with automatic power control at the desired level.

Furnaces of smaller capacity and power are powered by single-phase transformers with a power of 400 - 2500 kV-A; with a power consumption of over 1000 kW, balun devices are also installed, but on the HV side of the power transformer. With a lower furnace power and power supply from a high-voltage network of 6 or 10 kV, you can dispense with the balun device if the voltage fluctuations when turning the furnace on and off are within acceptable limits.

In Fig. Figure 2 shows the power supply diagram for an industrial frequency induction furnace. The furnaces are equipped with ARIR electrical mode regulators, which, within specified limits, ensure the maintenance of voltage, power Рп and cosphi by changing the number of voltage steps of the power transformer and connecting additional sections of the capacitor bank. Regulators and measuring equipment are located in control cabinets.

Rice. 2. Power supply circuit for an induction crucible furnace from a power transformer with a balun device and furnace mode regulators: PSN - voltage step switch, C - balun capacitance, L - reactor of the balun device, S-St - compensating capacitor bank, I - furnace inductor, ARIS - balun regulator, ARIR - mode regulator, 1K-NK - battery capacity control contactors, TT1, TT2 - current transformers.

In Fig. Figure 3 shows a schematic diagram of power supply for induction crucible furnaces from a medium frequency machine converter. The furnaces are equipped with automatic electrical mode regulators, a crucible “eating” alarm system (for high-temperature furnaces), as well as an alarm for cooling failure in the water-cooled elements of the installation.

Rice. 3. Power supply circuit for an induction crucible furnace from a medium frequency machine converter with a block diagram automatic regulation melting mode: M - drive motor, G - medium frequency generator, 1K-NK - magnetic starters, TI - voltage transformer, TT - current transformer, IP - induction furnace, C - capacitors, DF - phase sensor, PU - switching device, UFR - amplifier-phase regulator, 1KL, 2KL - linear contactors, BS - comparison unit, BZ - protection unit, OV - excitation winding, RN - voltage regulator.

Scheme of induction hardening installation

In Fig. 4 shows the fundamental electrical diagram power supply of the induction hardening machine from a machine frequency converter. Besides the source power supply M-G the circuit includes a power contactor K, a hardening transformer TrZ, on the secondary winding of which an inductor I is connected, a compensating capacitor bank Sk, voltage and current transformers TN and 1TT, 2TT, measuring instruments(voltmeter V, wattmeter W, phase meter) and ammeters of the generator current and excitation current, as well as a maximum current relay 1РМ, 2РМ to protect the power source from short circuits and overloads.

Rice. 4. Schematic electrical diagram of an induction hardening installation: M - drive motor, G - generator, TN, TT - voltage and current transformers, K - contactor, 1PM, 2RM, ZRM - current relay, Rk - arrester, A, V, W - measuring instruments, TRZ - hardening transformer, OVG - generator excitation winding, RR - discharge resistor, PB - excitation relay contacts, PC - adjustable resistance.

To power old induction installations for heat treatment of parts, electric machine frequency converters are used - a drive motor of a synchronous or asynchronous type and a medium-frequency generator of an inductor type; in new induction installations - static frequency converters.

The circuit of an industrial thyristor frequency converter for powering an induction hardening installation is shown in Fig. 5. The thyristor frequency converter circuit consists of a rectifier, a block of chokes, a converter (inverter), control circuits and auxiliary components (reactors, heat exchangers, etc.). According to the method of excitation, inverters are made with independent excitation (from the master oscillator) and with self-excitation.

Thyristor converters can operate stably both with a change in frequency over a wide range (with a self-adjusting oscillatory circuit in accordance with changing load parameters), and at a constant frequency with wide range changes in load parameters due to changes in the active resistance of the heated metal and its magnetic properties (for ferromagnetic parts).

Rice. 5. Schematic diagram of the power circuits of a thyristor converter type TPC-800-1: L - smoothing reactor, BP - starting unit, VA - automatic switch.

The advantages of thyristor converters are the absence of rotating masses, low loads on the foundation and the small influence of the power utilization factor on the reduction in efficiency; the efficiency is 92 - 94% at full load, and at 0.25 it decreases by only 1 - 2%. In addition, since the frequency can be easily changed within a certain range, there is no need to adjust the capacitance to compensate for the reactive power of the oscillating circuit.

For many years people have been smelting metal. Each material has its own melting point, which can only be achieved using special equipment. The first furnaces for melting metal were quite large and were installed exclusively in the workshops of large organizations. Today, a modern induction furnace can be installed in small workshops when setting up jewelry production. It is small, easy to use and highly effective.

Operating principle

The melting unit of an induction furnace is used to heat the most various metals and alloys. The classic design consists of the following elements:

1. Drain pump.
2. Water cooled inductor.
3. Frame made of stainless steel or aluminum.
4. Contact area.
5. The hearth is made of heat-resistant concrete.
6. Support with hydraulic cylinder and bearing unit.

The operating principle is based on the creation of Foucault eddy induction currents. As a rule, such currents cause malfunctions when operating household appliances, but in this case they are used to heat the charge to the required temperature. Almost all electronics begin to heat up during operation. This negative factor in the use of electricity is used to its full capacity.

Advantages of the device

The induction melting furnace began to be used relatively recently. The famous open-hearth furnaces, blast furnaces and other types of equipment are installed at production sites. Such a furnace for melting metal has the following advantages:

It is this last advantage that determines the spread of induction furnaces in jewelry, since even a small concentration of foreign impurities can negatively affect the result obtained.

Depending on the design features, floor-standing and tabletop induction furnaces are distinguished. Regardless of which option was chosen, there are several basic rules for installation:

The device may become very hot during operation. That is why there should be no flammable or explosive substances nearby. In addition, according to fire safety precautions in the vicinity, a fire shield must be installed.

Only two types of furnaces are widely used: crucible and channel. They have similar advantages and disadvantages, the differences lie only in the method of operation used:

The most popular type of induction furnace is the crucible type. This is due to their high performance and ease of operation. In addition, if necessary, such a design can be made independently.

Homemade versions are quite common. To create them you need:

1. Generator.
2. Crucible.
3. Inductor.

An experienced electrician, if necessary, can make an inductor with his own hands. This structural element is represented by a winding of copper wire. The crucible can be purchased at the store, but a lamp circuit, a self-assembled battery of transistors, or a welding inverter are used as a generator.

Using a welding inverter

An induction furnace for melting metal with your own hands can be created using welding inverter as a generator. This option is the most widely used since the efforts made concern only the manufacture of the inductor:

1. Thin-walled copper tube is used as the main material. The recommended diameter is 8-10 cm.
2. The tube is bent according to the desired pattern, which depends on the characteristics of the housing used.
3. There should be a distance of no more than 8 mm between the turns.
4. The inductor is placed in a textolite or graphite housing.

After creating the inductor and placing it in the housing, all that remains is to install the purchased crucible in its place.

Such a circuit is quite complex to implement and involves the use of resistors, several diodes, and transistors various capacities, film capacitor, copper wire with two different diameters and throttle rings. Assembly recommendations are as follows:

The created circuit is placed in a textolite or graphite case, which are dielectrics. Scheme, involving the use of transistors, quite difficult to implement. Therefore, you should undertake the manufacture of such a stove only if you have certain work skills.

Lamp stove

IN Lately stoves using lamps are being created less and less often, as they require care when handling. The circuit used is simpler compared to the case of using transistors. Assembly can be carried out in several stages:

The llamas used must be protected from mechanical impact.

Equipment cooling

When creating an induction furnace with your own hands, the biggest problem that arises is cooling. This is due to the following points:

1. During operation, not only the molten metal is heated, but also some elements of the equipment. That is why effective cooling is required for long-term operation.
2. The method based on the use of air flow is characterized by low efficiency. In addition, it is not recommended to install fans near the stove. This is due to the fact that metal elements can influence the eddy currents generated.

Typically, cooling is carried out by supplying water. Creating a water cooling circuit at home is not only difficult, but also economically unprofitable. Industrial versions of the furnace already have a built-in circuit, to which it is enough to connect cold water.

Safety precautions

When using an induction furnace, certain safety precautions must be followed. Basic recommendations:

When installing equipment, you should consider how the charge will be loaded and the molten metal will be extracted. It is recommended to set aside a separate prepared room for installing an induction furnace.