Vacuum melting. Melting induction furnace for metal, scheme, properties of types

A vacuum furnace is a sealed heating device, in the cavity of which a rarefaction is created with a value determined by the technological process. Vacuum (from the Latin “vacuus” – “empty”) furnace (from the Orthodox “pekty” – “bake, furnace”) is designed for melting or heating materials of high quality and cost in vacuum.

In this article, we will look at:

• vacuum resistance furnaces;
• vacuum hydrogen furnace;
• chamber vacuum furnaces;
• vacuum furnace chamber;
• vacuum three-chamber furnaces;
• laboratory vacuum furnaces;
• the principle of operation of a vacuum furnace;
• vacuum sintering furnaces;
• electric vacuum oven;
• Vega vacuum oven;
• NPF vacuum furnaces;
• vacuum compression furnace;
• vacuum melting furnaces;
• vacuum oven for soldering;
• vacuum induction melting furnace;
• vacuum annealing furnace;
• vacuum muffle furnace;
• vacuum induction furnace;
• vacuum furnace for heat treatment;
• vacuum hydrogen furnace;
• bell-type hydrogen furnace;
• hydrogen-filled furnaces;
• hydrogen sintering furnace;
• hydrogen furnace design.

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The history of the creation of vacuum furnaces with electric heating is interesting. Russian physicist Vasily Vladimirovich Petrov (1761 - 1834), conducting experiments to obtain a white flame between pieces of charcoal, in 1802 discovered the phenomenon of an electric arc. Having created the largest battery of galvanic cells for his time, Petrov set up experiments on the use of an electric arc for melting and welding metals, thereby laying the foundation for modern electrometallurgy.

For the first time, an electric furnace with rarefied air was made in 1839 by the English engineer R. Har. In his furnace, placed in a bell with a vacuum, the inventor decomposed the elements by evaporation due to the application of electricity from a galvanic battery.

The first chamber thermal electric furnace was patented in 1853 by the French chemist L.-A. Pichon. But practical application this furnace, like the previous ones, did not receive due to insufficient power sources of electricity. The prototype of modern steel-smelting electric furnaces is the melting furnace with vertical electrodes proposed in 1899 by the French metallurgist Paul Louis Toussaint Héroux (1863-1914). By the end of the 20th century, mass production of vacuum furnaces began in the advanced countries of the world.

Consider the device of a typical vacuum furnace. Its main unit is a sealed heat chamber connected to a vacuum pump that provides a vacuum of 5 to 10 -5 mmHg. By design, there are two types of vacuum electric furnaces:

• in the retort version, in which the heaters are placed outside the chamber;
• in a chamber version, when the heaters are installed inside the chamber.

The principle of operation of a vacuum furnace is as follows. Before the beginning heat treatment in a vacuum, the chamber of the vacuum furnace, together with the workpieces, is hermetically sealed, and the vacuum pump pumps air out of it to the required level. Workpieces in a refractory crucible using a high-frequency inductor are melted or heated to a predetermined temperature. After holding and completion of the technological process, the chamber is depressurized, opened, and the heat-treated parts are unloaded. The plant is ready for the next cycle of operation.

Vacuum arc furnace began to be used with the development of nuclear energy, rocket science, space research, when there was an urgent need to process ultrapure materials with special physical and mechanical properties.

The advantages of vacuum arc furnaces are as follows:

1. The ability to achieve the highest temperatures up to 2000 0 С and high pressures.
2. Homogeneity and high density of ingots due to directional crystallization of liquid metal in vacuum.
3. The possibility of non-oxidizing heating of workpieces, which significantly reduces the loss of metal for waste.
4. Obtaining special metals and alloys of high purity in the absence of air.
5. No oxidation of electrodes, heating elements and internal metal structures in the furnace.

Vacuum in furnaces allows you to effectively perform various technological processes associated with the heating of materials: melting, heating, sintering, heat treatment, drying, etc.

The following types of industrial vacuum furnaces are currently used:

• chamber vacuum furnaces;
• three-chamber vacuum furnaces;
• shaft vacuum furnaces;
• vacuum resistance furnaces;
• vacuum melting furnaces;
• vacuum furnaces for metal heat treatment;
• vacuum furnace for hardening parts;
• vacuum annealing furnace;
• vacuum hydrogen furnace;
• vacuum furnace for nitriding;
• vacuum carburizing furnace;
• vacuum oven for soldering;
• vacuum muffle furnace;
• vacuum compression furnace;
• vacuum sintering furnaces;
• laboratory vacuum furnaces.

IN modern technology Vacuum resistance furnaces are the most common.

Induction oven

Vacuum induction melting furnace contains a high-frequency inductor placed inside the chamber, from which the air is pumped out. It is used for melting and pouring heat-resistant and corrosion-resistant materials, growing single crystals and zone cleaning. Unlike an electric arc furnace, it has the ability to load and melt lumpy blanks (scrap, scrap, lumpy waste, defective blanks). The most common type is the vacuum induction furnace with a tilting refractory crucible mounted inside a stationary shell.

If you are interested in the price of vacuum induction furnaces, then it depends on the type of furnace, the manufacturer, the level of vacuum created, the temperature, the power consumption and the performance of the installation. Contact us, we will help you figure it out and choose a reliable, but inexpensive stove.

Thermal Vacuum Furnace

The thermal vacuum furnace can perform vacuum quenching, tempering, annealing, sintering, brazing, nitriding and carburizing. The advantage is the performance of heat treatment in an oxygen-free environment and, as a result, the absence of traces of oxides and decarburization on the surface of products. After the workpieces are taken out of the vacuum heat chamber, there are no traces of corrosion on them, and the mechanical characteristics, resistance to corrosion and wear increase.

Thermal vacuum furnaces are produced with different volumes of one, two or three working cavities, different technical parameters and characteristics, in horizontal or vertical execution. If you are going to buy a vacuum furnace for metal heat treatment, then it can be manufactured according to a standard scheme and a regular price, or according to an improved scheme, taking into account the individual wishes of the customer, but the price will be slightly higher. Come, come, we will think together and choose what suits you the most.

Vacuum hydrogen furnace allows sintering and heat treatment of parts in a vacuum or reducing hydrogen environment. Here, the method of indirect heating by high-frequency currents is used at high voltage and low current this saves energy. The design of the hydrogen furnace is different explosion-proof design corps and special device thermal insulation, which increases the reliability of equipment maintenance. Heating of sintered products from refractory metals (titanium, tungsten, molybdenum) and their alloys is carried out by radiation by placing a crucible made of heat-resistant material inside the inductor.

Distinguish the following constructions hydrogen-filled furnaces:

• bell-type hydrogen furnace;
• chamber hydrogen furnace;
• shaft hydrogen furnace;
• pusher hydrogen furnace.

In order to select and buy a conventional hydrogen furnace or a hydrogen sintering furnace, call us. We'll try to help. In the absence of suitable equipment in stock, we will order the model you like from the manufacturer.

Conclusion

From our point of view, brand models of vacuum furnaces of the following companies are of interest:

• vacuum ovens SECO/WARWICK;
• vacuum furnaces SCHMETZ;
• IPSEN vacuum furnaces;
• vacuum furnaces ALD;
• vacuum furnaces NPF;
• vacuum furnace SGV;
• vacuum furnace Vega-5;
• vacuum furnace SEV;
• vacuum furnace SNVE;
• vacuum furnace A2318;
• pusher hydrogen furnace PVT-6.

See, choose, contact and consult with us. Let's help everyone.

Technological processes of production and processing various materials often include the stage of thermal exposure. In this way, hardening, drying at high temperatures, soldering and other procedures are performed. It is not always possible to implement such measures in conventional furnaces, even for industrial purposes. Restrictions may be associated with the inadmissibility of contact with air environment. Therefore, to solve such problems, a vacuum furnace is used, the processing in which also eliminates the processes of excessive deformation and warping of the workpieces.

Purpose and scope of vacuum furnaces

Vacuum thermal roasting operations are used in machine and instrument making, in the construction industry, in various industries, etc. For example, in instrument making, using such a unit, the operation of degassing elements is performed, which later become components of various equipment. Within the framework of the same direction, a vacuum furnace allows high-quality soldering and final sealing of individual sections on electrical circuit boards.

The operation of sintering is also widespread. With its help in construction and production, the necessary operational qualities are given. ceramic products, hard alloys, refractory metal powders, etc. Separately, it is worth noting the metallurgical industry, which is also interested in heat treatment operations. For example, a vacuum furnace makes it possible to carry out quenching, aging, and tempering of alloys. Various steels, bronze and magnesium can be subjected to such treatments.

Main technical characteristics

The performance of the furnace design often becomes the main criterion for choosing a model. In this case, the installations have a potential of 3 to 20 kW. Moreover, this indicator affects the quality and efficiency to a minimum extent when providing thermal exposure. As a rule, power increases as the load volume increases, which already depends on the dimensions of the structure. So, in standard industrial models of this type, you can load from 15 to 40 kg of material on average. But there are also units that allow you to serve up to 100 kg at a time. The induction melting furnace endowed with medium characteristics is capable of serving up to 9000 kg in one shift. As for the quality and effectiveness of the impact inside the chamber, the temperature range should be taken into account directly. It ranges from 1800 to 2000 °C.

Smelting process

The technology in traditional units is based on the action of an arc discharge. There is a contact electric current and gas mixture. Further, the resulting arc, due to its high concentration in vacuum, provides an increased thermal effect. Even at low power, the vacuum arc furnace is capable of melting steel billets.

In this case, there are two principles of heat transfer in relation to the material. This is a direct and indirect impact. In the first case, the arc generates energy between the electrode and the workpiece, which in this configuration receives maximum heat. Indirect heating involves working with two electrodes that act on the object at some distance. Obviously, a direct heat transfer vacuum furnace is more efficient, but it tolerates a higher percentage of negative heat treatment factors.

Types of furnaces

The basic model of a vacuum furnace structure is the arc structure described above. With the help of such equipment, it is possible to service most varieties of a complex metal alloy, including refractory products. Another variation is the induction melting furnace, which has an inclined crucible. It is in the crucible that the process of remelting the material loaded into the working chamber is realized. Induction principle work is considered the most expensive to maintain, so it is used less often and only when it is necessary to work with complex metals. Electron-beam unit belongs to special types of vacuum furnaces. Such a device produces refined alloys and metal ingots at the output. Structurally, the equipment is a thermal gun, which, through a directed action, implements beam firing of the product.

Advantages and disadvantages of vacuum furnaces

Compared to conventional heat treatment furnaces, vacuum allows highly efficient heat treatment of workpieces. At the same time, the operator has the possibility of flexible adjustment of the heating parameters, which, for example, is provided by a vacuum induction furnace with a crucible. The advantages of such structures include the possibility of obtaining a relatively pure metal material. That is, the technology itself excludes excessive contamination of the array with foreign particles - heat treatment products.

As for the shortcomings, they are associated with a low resource of the parts that form the structure. It's not even about the flaws in the material of the constituent elements, but in the harsh conditions that are required to ensure productive heat treatment and that affect the structure of the working surfaces. In addition, a vacuum furnace, the average price of which is 500-700 thousand rubles, is available to a few enterprises. Nevertheless, the high quality of sintering and melting is an expensive method that limits its use.

Manufacturers

Only large enterprises cooperating with design and development institutes are engaged in the supply of vacuum furnaces industrial equipment. Today, high-quality units of this type are supplied to the domestic market by foreign manufacturers SCHMETZ and XERION. These products are oriented both for typical thermal operations and for specialized tasks such as diffuse annealing. The Moscow plant of industrial equipment, which specializes in the production of vacuum electric furnaces, also offers units that are worthy in terms of characteristics. With this equipment, the owner can carry out metal tempering, sintering and standard thermal processes. Automatic models are offered by Spetszhelezobeton Plant, which develops high-vacuum units with volumetric loading chambers.

Conclusion

An example of vacuum annealing technology shows that new solutions do not always justify themselves during operation. Although the same Moscow plant of industrial equipment seeks to optimize the units for the needs of a wide range of consumer enterprises, the high cost of vacuum heat treatment for many potential customers makes this method inaccessible. The refusal of such furnaces is due not only to their cost, but the lack of the need to obtain a high-quality product. However, advanced companies operating in high-tech industries can no longer do without the use of such heat treatment tools.

Collapse

An induction furnace is a furnace apparatus that is used to melt non-ferrous (bronze, aluminum, copper, gold, and others) and ferrous (cast iron, steel, and others) metals due to the operation of an inductor. A current is produced in the field of its inductor, it heats the metal and brings it to a molten state.

First, an electromagnetic field will act on it, then an electric current, and then it will pass through the thermal stage. simple design such a furnace device can be assembled independently from various improvised means.

Principle of operation

Such a furnace device is an electrical transformer with a secondary short-circuited winding. The principle of operation of the induction furnace is as follows:

• using a generator, an alternating current is created in the inductor;
• an inductor with a capacitor creates an oscillatory circuit, it is tuned to the operating frequency;
• in the case of using a self-oscillating generator, the capacitor is excluded from the device circuit and in this case, the inductor's own capacitance reserve is used;
• the magnetic field created by the inductor can exist in free space or be closed using an individual ferromagnetic core;
• the magnetic field acts on the metal workpiece or charge located in the inductor and forms a magnetic flux;
• according to Maxwell's equations, it induces a secondary current in the workpiece;
• with a solid and massive magnetic flux, the generated current closes in the workpiece and the Foucault current or eddy current is created;
• after the formation of such a current, the Joule-Lenz law comes into effect, and obtained with the help of an inductor and magnetic field energy heats the metal billet or charge.

Despite the multi-stage operation, the induction furnace device can give up to 100% efficiency in vacuum or air. If the medium has a magnetic permeability, then this indicator will increase, in the case of a medium from a non-ideal dielectric, it will fall.

Device

The furnace in question is a kind of transformer, but only it does not have a secondary winding, it is replaced by a metal sample placed in the inductor. It will conduct current, but dielectrics do not heat up in this process, they remain cold.

The design of induction crucible furnaces includes an inductor, which consists of several turns of a copper tube rolled up in the form of a coil, coolant is constantly moving inside it. The inductor also contains a crucible, which can be made of graphite, steel and other materials.

In addition to the inductor, a magnetic core and a hearth stone are installed in the furnace, all this is enclosed in the furnace body. It includes:

In models of high-power furnaces, the casing of the bath is usually made quite rigid, so there is no frame in such a device. The body fastening must withstand heavy loads when the entire oven is tilted. The frame is most often made of shaped beams made of steel.

The crucible induction furnace for melting metal is installed on a foundation in which the supports are mounted, the trunnions of the device tilt mechanism rest on their bearings.

Bath shell is made of metal sheets on which stiffeners are welded for strength.

The casing for the induction unit is used as a connecting link between the furnace transformer and the hearth stone. To reduce current losses, it is made of two halves, between which an insulating gasket is provided.

The screed of the halves occurs due to bolts, washers and bushings. Such a casing is made cast or welded; when choosing a material for it, preference is given to non-magnetic alloys. The double chamber induction steel furnace comes with a common casing for the bath and for the induction unit.

In small ovens that do not have water cooling, there is a ventilation unit, it helps to remove excess heat from the unit. Even if you install a water-cooled inductor, it is necessary to ventilate the opening, near the hearth stone, so that it does not overheat.

In modern furnace installations, there is not only a water-cooled inductor, but also water cooling of the casings is provided. Fans powered by a drive motor can be installed on the furnace frame. With a significant mass of such a device, the ventilation device is installed near the furnace. If an induction furnace for steelmaking comes with a removable version of the induction units, then each of them is provided with its own fan.

Separately, it is worth noting the tilt mechanism, which for small furnaces comes with a manual drive, and for large ones it is equipped with a hydraulic drive located at the drain spout. Whatever tilt mechanism is installed, it must ensure that all contents of the bathroom are completely drained.

Power calculation

Since the induction method of steel melting is less expensive than similar methods based on the use of fuel oil, coal and other energy carriers, the calculation of an induction furnace begins with the calculation of the power of the unit.

The power of the induction furnace is divided into active and useful, each of them has its own formula.

As initial data you need to know:

• the capacity of the furnace, in the case considered for example, it is equal to 8 tons;
• unit power (its maximum value is taken) - 1300 kW;
• current frequency - 50 Hz;
• the productivity of the furnace plant is 6 tons per hour.

It is also required to take into account the melted metal or alloy: by condition it is zinc. This important point, the heat balance of melting cast iron in an induction furnace, as well as other alloys.

Useful power, which is transferred to the liquid metal:

• Рpol \u003d Wtheor × t × P,
• Wtheor - specific energy consumption, it is theoretical, and shows the overheating of the metal by 1 0 C;
• P - productivity of the furnace plant, t/h;
• t is the overheating temperature of the alloy or metal billet in the bath furnace, 0 С
• Рpol \u003d 0.298 × 800 × 5.5 \u003d 1430.4 kW.

Active power:

• P \u003d Rpol / Yuterm,
• Rpol - taken from the previous formula, kW;
• Yuterm - the efficiency of the foundry furnace, its limits are from 0.7 to 0.85, on average they take 0.76.
• P \u003d 1311.2 / 0.76 \u003d 1892.1 kW, the value is rounded up to 1900 kW.

At the final stage, the power of the inductor is calculated:

• Rind \u003d P / N,
• R - active power furnace installation, kW;
• N is the number of inductors provided on the furnace.
• Rind \u003d 1900 / 2 \u003d 950 kW.

The power consumption of an induction furnace when melting steel depends on its performance and the type of inductor.

Species and subspecies

Induction furnaces are divided into two main types:

In addition to this separation, induction furnaces are compressor, vacuum, open and gas-filled.

DIY induction furnaces

Among the available common methods for creating such aggregates, one can find step by step guide how to make an induction oven welding inverter, with a nichrome spiral or graphite brushes, we will give their features.

The unit from the high-frequency generator

It is carried out taking into account the rated power of the unit, eddy losses and hysteresis leaks. The structure will be powered from a conventional 220 V network, but using a rectifier. This type of furnace can come with graphite brushes or a nichrome spiral.

To create an oven you will need:

• two diodes UF4007;
• film capacitors;
• field-effect transistors in the amount of two pieces;
• 470 ohm resistor;
• two throttle rings, they can be removed from the old computer system engineer;
• copper wire section Ø 2 mm.

As a tool, a soldering iron and pliers are used.

Here is a diagram for an induction furnace:

Induction portable melting furnaces of such a plan are created in the following sequence:

1. Transistors are located on radiators. Due to the fact that during the process of melting the metal, the circuit of the device heats up quickly, the radiator for it must be selected with large parameters. It is permissible to install several transistors on one generator, but in this case they must be isolated from the metal using gaskets made of plastic and rubber.
2. Two throttles are made. For them, two rings previously removed from the computer are taken, copper wire is wrapped around them, the number of turns is limited from 7 to 15.
3. The capacitors are combined into a battery to produce a capacitance of 4.7 microfarads at the output, their connection is carried out in parallel.
4. A copper wire is wrapped around the inductor, its diameter should be 2 mm. Inner diameter winding must match the size of the crucible used for the furnace. In total, 7-8 turns are made and long ends are left so that they can be connected to the circuit.
5. As a source, a 12 V battery is connected to the assembled circuit, it is enough for about 40 minutes of the furnace operation.

If necessary, the case is made of a material with high thermal stability. If an induction melting furnace is made from a welding inverter, then a protective case must be required, but it must be grounded.

Graphite brush design

Such a furnace is used for the smelting of any metal and alloys.

To create a device, you need to prepare:

• graphite brushes;
• powder granite;
• transformer;
• fireclay brick;
• steel wire;
• thin aluminium.

The assembly technology of the structure is as follows:

Device with nichrome spiral

Such a device is used for smelting large volumes of metal.

As Supplies for arranging a homemade oven is used:

• nichrome;
• asbestos thread;
• piece of ceramic pipe.

After connecting all the components of the furnace according to the scheme, its work is as follows: after applying electric current to the nichrome spiral, it transfers heat to the metal and melts it.

The creation of such a furnace is carried out in the following sequence:

This design is characterized by high performance, it cools down for a long time and heats up quickly. But it must be taken into account that if the spiral is poorly insulated, it will quickly burn out.

Prices for finished induction furnaces

Home-made furnace designs will cost much cheaper than purchased ones, but they cannot be created in large volumes, therefore, without ready-made options for mass production of the melt is indispensable.

Prices for induction furnaces for melting metal depend on their capacity and configuration.

Model	Characteristics and features	Price, rubles
INDUTHERM MU-200	The furnace supports 16 temperature programs, the maximum heating temperature is 1400 0С, the mode is controlled with an S-type thermocouple. The unit produces a power of 3.5 kW.	820 thousand
INDUTHERM MU-900	The furnace is powered by a 380 W power supply, the temperature is controlled using an S-type thermocouple and can reach up to 1500 0C. Power - 15 kW.	1.7 million
UPI-60-2	This mini induction melting furnace can be used to melt non-ferrous and precious metals. Billets are loaded into a graphite crucible, their heating is carried out according to the principle of a transformer.	125 thousand
IST-1/0.8 M5	The furnace inductor is a basket in which a magnetic circuit is built together with a coil. Unit 1 ton.	1.7 million
UI-25P	The furnace device is designed for a load of 20 kg, it is equipped with a reduction inclination of the melting unit. Included with the furnace is a block of capacitor banks. Installation power - 25 kW. The maximum heating t is 1600 0С.	470 thousand
UI-0.50T-400	The unit is designed for a load of 500 kg, the largest power of the installation is 525 kW, the voltage for it must be at least 380 W, the maximum operating t is 1850 0С.	900 thousand
ST 10	The oven of the Italian company is equipped with a digital thermostat, SMD technology is built into the control panel, which is fast. The universal unit can work with different capacities from 1 to 3 kg, for this it does not need to be readjusted. It is designed for precious metals, its maximum temperature is 1250 0С.	1 million
ST 12	Static induction oven with digital thermostat. It can be supplemented with a vacuum casting chamber, which makes it possible to produce castings right next to the machine. Management takes place using the touch panel. Maximum temperature- 1250 0С.	1050 thousand
IChT-10TN	The furnace is designed for a load of 10 tons, a rather voluminous unit, for its installation it is necessary to allocate a closed workshop room.	8.9 million

Smelting in a vacuum induction furnace solves several problems in the production of complex alloys. Firstly, when melting in vacuum, by deoxidizing with carbon and raising the temperature, it is possible to destroy the oxide film on the bath surface and to melt and cast alloys with a pure mirror. Secondly, it provides stability chemical composition alloys from heat to heat and therefore a constant level of mechanical properties. So, for example, the content of aluminum and titanium can be controlled with an accuracy of ± 0.12%, while in open melting - with an accuracy of 1%.

Thirdly, after melting in a vacuum, the degree of purity of the alloys is significantly increased. So, for example, in a heat-resistant nickel alloy R235 (0.15% C; 15.5% Cr; 5.3% Mo; 10% Fe; 2.0% Ti; 3.0% Al) on a nickel base compared to melting, in air the oxygen content decreased from 0.017 to 0.0025%, nitrogen from 0.004 to 0.002%, hydrogen from 0.0006 to 0.00005%. In the Wespalloy alloy (0.07% C; 0.4% Si; 0.7% Mn; 19% Cr; 14% Co; 4.3% Mo; 3.0% Ti; 1.3% Al; Ni - rest.) the oxygen content after melting in vacuum decreased to 0.0012%; nitrogen up to 0.012%, hydrogen up to 0.00025%.

On fig. 113 shows the effect of nitrogen on the properties of the heat-resistant alloy ZhS6K- As can be seen from fig. FROM, for this alloy it is necessary to obtain some optimal nitrogen content. Nitrogen obviously has a modifying effect on the structure of the alloy. Oxygen in heat-resistant alloys has a negative effect on heat-resistant properties, which is clearly seen from Fig. 114, which shows the dependence of the destruction time of the Udimet-500 alloy under load on the oxygen concentration.

On the properties of Kh20N80 and Kh15N60 alloys smelted in VIP, big influence renders REM additive. In a vacuum, the amount of REM can be significantly reduced. The highest results were obtained when alloying the alloy with 0.10-0.15% cerium and 1.4% silicon or 0.05-0.08% cerium and 0.05-0.08% lanthanum. Due to the increase in the purity of the metal, the nitrogen content was 0.007%; oxygen 0.001%.

After HPT, the lifetime of the Kh20N80 alloy increased from 40 to 70 hours, and due to additional alloying of REM in vacuum from 70 to 150-250 hours (96% of all melts). The durability of the Kh15N60 alloy less alloyed than Kh20N80 exceeded 100 hours. The electrical properties also improved. Thus, for the Kh20N80 alloy, the electrical resistivity increased on average from 1.1 to 1.18 Ω mm2/m. When heated in a vacuum material, a change in electrical resistance by 3-8% occurs in 200-400 hours, while in a conventional alloy it takes 40-60 hours.

According to the authors of this work, the positive effect of the use of cerium in VIP is its effect on the formation of sulfides. Cerium contributes to the removal of sulfides by the formation of strong refractory sulfides that float up to crystallization or on it. early stage.. In the presence of cerium, the probability of formation of sulfides of other elements, such as titanium, if the latter is contained in the metal, is reduced. Magnesium has a similar effect on sulfur.

During vacuum smelting in an induction furnace of heat-resistant alloys, significant evaporation of non-ferrous metal impurities occurs. This method provides one of the most low levels the contents of these impurities compared with other methods. So, for high-strength steel, according to Chuprin, the content of non-ferrous metal impurities, depending on the smelting method, is characterized by the data given in Table. 37.

Table 37 IMPURITY CONTENT OF NON-FERROUS METALS IN HIGH-STRENGTH STEEL

	air melting

With an increase in the holding time of liquid metal in vacuum, the content of non-ferrous metal impurities decreases, and the mechanical properties of the alloys increase, as can be seen in Fig. 115.

But simple refining of metal from impurities does not always improve its properties.

So, according to K. Ya. Shpunt, for heat-resistant alloys, in addition to refining in vacuum, the residual content of the modifying elements magnesium and cerium is of great importance.

As a result of smelting in vacuum, the mechanical properties of heat-resistant alloys are significantly increased. An example is the improvement of the properties of a superalloy melted in a vacuum induction furnace.

Melting in a vacuum induction furnace increases the malleability of cobalt alloys and makes it possible to process normally non-deformable alloys. The properties of cast alloys, precision castings, such as blades, valves, turbine rotor disks, guides and other parts of jet engines are improved.

Melting in a vacuum makes it possible to improve the mechanical properties of heat-resistant alloys due to the complication of the composition, i.e., the introduction of new alloying components, an increase in the content of strengthening components. In conventional melting in air, an increase in the content of titanium, aluminum, molybdenum or a more complex composition leads to a decrease in heat-resistant properties.

Vacuum melting furnaces are used to obtain metals and alloys of the highest quality. The low pressure in the space of the working chamber makes it possible to drastically reduce the content of gases in the ingot without the use of protective media.

Scope of induction furnaces

Vacuum furnaces are used in many technological processes:

melting of metals and alloys: refractory, heat-resistant, highly alloyed;

sintering of products from easily oxidizing metals;

degassing of liquid metals and other materials;

heat treatment of metals (hardening, tempering, annealing);

coating by deposition of evaporated metals, etc.

Main types of vacuum furnaces

The most common types of vacuum furnaces are:

arc: used for smelting stainless, electrical and other high-quality steels, refractory metals (titanium, zirconium, tantalum, etc.);

plasma: designed for melting highly reactive and refractory metals;

induction: they can be attributed to the equipment of wide application. The most widespread vacuum melting induction furnaces with tilting crucible. They are used at large metallurgical plants for melting high-quality and high-alloy steels and pouring them into molds.

Standard sizes of melting furnaces

By dimensions, vacuum melting furnaces are divided into laboratory (with a capacity of up to 50-100 kg) and industrial. However, such a classification is very conditional: there are many models industrial value with a working volume of only 10-20 kg.

The principle of operation of induction industrial furnaces

In spite of design features different types vacuum melting furnaces, they work according to a single principle: in a refractory crucible placed in a vacuum chamber, with the help of a heating element, the metal is melted (or liquid is heated), refined and alloyed. The process ends with the casting of shaped products or simple ingots.

According to the principle of operation, vacuum melting furnaces are divided into three groups:

semi-continuous action;

continuous action;

periodical action.

Melting industrial semi-continuous furnaces do not require systematic depressurization. In them, molds are changed with the help of chambers separated from the main one by gates. The same sluice devices are also used to load the furnace. Semi-continuous devices are used in industry. Due to their design features:

the refractory lining of the crucibles is in favorable conditions, since it is not subjected to temperature changes;

there is no need to pump out air before starting a new melt, which has a very positive effect on the performance of the furnace;

in the chamber, the formation of metal oxides is minimized, and, consequently, the contamination of the subsequent melt is reduced.

In smelters industrial furnaces intermittent locks are not provided. In order to take out the mold or load the mixture, it is necessary to depressurize the case each time and open the vacuum chamber. This is how laboratory ovens work.

The main advantages of vacuum furnaces are:

economic benefit: instead of expensive inert gases, low pressure in the chamber is used;

high degree of metal purification;

the ability to exercise strict control of the chemical composition and temperature of the melt at any stage of the technological process;

protection of heating elements from oxidation, which allows to increase the operating temperature.

The cost of vacuum melting induction furnaces and other models is quite high, but the costs quickly pay off during their operation.