Do-it-yourself induction furnace for melting metal. Characteristics and design of induction furnaces Homemade induction furnace for melting

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

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property are due to specific physical characteristics induction furnaces.

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

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

Pressure Melt flows

Rice. 7.21. The action of electromagnetic forces

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Chapter 7

□ loss of metal; Shch melting

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

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

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

The following devices can be made independently:

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

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

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

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

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

Manufacturing instructions

Blueprints

Picture 1. Wiring diagram induction heater

Figure 2. Device.

Figure 3. Scheme of a simple induction heater

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

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

Additional materials and their features:

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

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

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

Nuances

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

Exploitation homemade devices induction heating, does not always make it possible to exclude the spread of electromagnetic radiation harmful to humans, therefore the induction boiler should be installed in non-residential premises and shielded with galvanized steel.
Mandatory when working with electricity safety regulations must be followed and especially for networks alternating current voltage 220 V.
As an experiment can be made hob for cooking food according to the scheme indicated in the article, but it is not recommended to constantly operate this device due to imperfections self-manufacturing shielding of this device, because of this, exposure to the human body of harmful electromagnetic radiation that can adversely affect health is possible.

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

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

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

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

Advantages over other types of melting furnaces

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

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

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

Furnace placement

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

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

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

Types of induction furnaces

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

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

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

A homemade induction furnace does not contain any difficulties so that it cannot be assembled a common person at least a little familiar with electrical engineering. It has only three main blocks:

Generator.
Inductor.
Crucible.

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

Induction furnace on a welding inverter

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

transistor induction furnace

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

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

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

Lamp induction oven

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

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

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

Cooling

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

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

Safety precautions when smelting metal in an induction furnace

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

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

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

An induction furnace is a heating device where the induction method is used to melt steel, copper and other metals (the metal is heated by currents excited by a non-alternating inductor field). Some consider it one of the types of resistance heaters, but the difference is energy transfer method heated metal. First Electric Energy becomes electromagnetic, then again electrical, and only at the very end it turns into heat. Induction stoves are considered the most perfect from all gas and electric (, steelmaking, mini stoves), thanks to its heating method. With induction, heat is generated within the metal itself, and the use of thermal energy is most efficient.

Induction furnaces are divided into two types:

with a core (channel);
without core (crucible).

The latter are considered more modern and useful ( heating appliances with a core, due to their device, are limited in power). The transition from channel to crucible furnaces began in early 1900s. On the this moment they are widely used in industry.

These types are quite popular. electrical appliances like muffle melting furnace, steel melting furnace and arc steel melting furnace. The former are very effective and safe to use. On the shelves there is a wide range of muffle furnaces of this kind. A very important role for metallurgy was played by such an invention as a steel furnace. With its help, it became possible to heat any materials.

However, at the moment, steel smelting is more often carried out using such a heating structure as, it uses the thermal effect for melting, and it is more convenient and practical.
With your own hands, you can make many simple heating structures. For example, very popular. If you decide to build a mini heating structure with your own hands, you need to know its device. There are many types of induction furnaces, but we will describe only a few of them. If necessary, you can use necessary schemes, drawings and video recordings.

Induction Furnace Components

For the simplest designs, there are only two main parts: an inductor and a generator. However, you can add something of your own, improve the unit, using the necessary schemes.
Inductor
The heating coil is the most important component. Absolutely the entire operation of the heating structure depends on it. For homemade stoves with low power, it is acceptable to use an inductor from a bare copper tube. with a diameter of 10 mm. The inner diameter of the inductor must be not less than 80 mm. and not more than 150 mm., the number of turns - 8-10. It must be taken into account that the turns should not touch, so the distance between them should be 5-7 mm. Also, no part of the inductor should touch its screen.
Generator
The second most important component of the furnace is the alternator. When choosing a generator circuit, you should in every possible way avoid blueprints, giving a hard current spectrum. As something that you DO NOT need to choose, we present a popular circuit on a thyristor key.

Crucible furnace device

Inside there is a melting crucible with a drain sock (“ collar“). On the outer sides of the structure, an inductor is located in a vertical position. Next comes a layer of thermal insulation, and at the top is a cover. One of the outer sides may have a supply current and cooling water. Below is a device for signaling the wear of the crucible.

The melting crucible is one of the most important components of the unit, it largely determines its operational reliability. Therefore, very stringent requirements are imposed on the crucible and other materials used.

How to make an induction oven

First you need to assemble the generator for the inductor. Here you will need the K174XA11 circuit. The transformer should be wound on a mini-ring with a diameter of 2 centimeters. The entire winding is carried out with a wire with a diameter of 0.4 centimeters and should be 30 turns. The primary winding is characterized by the presence exactly 22 turns of wire with a diameter of 1 millimeter, and the secondary should contain only 2-3 turns the same wire, but already folded four times. The inductor must be made of 3 mm. wire with a diameter of 11 mm. There should be exactly 6 turns. To adjust the resonance, it is best to set the normal or mini led.