Induction furnace crucible: principle of operation, scheme and reviews

Thanks to the appearance of available electronic and insulating components in modern production, the field of application of induction heating becomes more and more widespread. This technology is used not only in metalurgy, but also in the development of home appliances.

Induction heating principle

At the heart of the induction furnace is the transformer principle of energy exchange. The inductor is made from a copper tube, which is then wound into a multi-turn coil. An alternating current is applied to the primary circuit of the inductor, which leads to the formation of an alternating magnetic field around it. Under the influence of the magnetic field in the body placed inside the inductor, an electric field appears, which subsequently leads to a heating process. The power, and accordingly, the heat emitted by the induction crucible melting furnace, directly depend on the frequency of the alternating magnetic field. Consequently, for an efficient operation, the furnace requires high frequency currents.

Application of induction furnaces

Induction heating can be used to work with any material: metal, slag, gas, etc. The main advantage of its use is non-contact heat transfer. Also, induction heating makes it possible to achieve virtually any heating rate - it all depends on the power of the generator supplying the furnace. The heat losses at this heating are minimal. The maximum temperature to which the object can be heated in the oven is limited only by the resistance of the refractory material. The process of contactless heat transfer to the heated material makes it possible to produce heating in a vacuum environment.

According to the opinion of metallurgists, the scope of induction furnaces is somewhat limited in connection with the existing shortcomings. The minus crucible furnace includes:

• High price of electrical equipment;
• Cold slags complicating the refining process;
• Low stability of lining during temperature jumps between fuses.

Scheme of crucible induction furnace

The induction crucible furnace has the following structure.

The main element of the furnace is a crucible (7), covered with a lid (1). The crucible is located inside the heating inductor (3), manufactured in the form of a multi-turn coil. The coil is a copper tube, inside of which, for the purpose of cooling, water constantly circulates. The magnetic flux from the inductor passes along the magnetic cores (4), which are made of special transformer steel. The swivel assembly (2) is provided for tilting the furnace during spillage of the molten liquid. The furnace is installed on a masonry structure (5). Cooling is performed with water cooling hoses (6). An auxiliary platform (8) is used for servicing the furnace.

Also, the crucible furnace scheme includes a transformer, capacitors, a control unit and a gas pumping system. Power of the crucible electric furnace is produced by currents with a frequency of 50 Hz.

Features of internal structural elements

Most often the inductor is made of a tube of circular cross section. But there are situations in which a round copper tube is not applicable. In certain cases, for the construction of an induction crucible furnace, profiled elements are used, due to which the magnetic flux of dissipation decreases. The tubes of the inductor are insulated with a glass cloth impregnated with a special lacquer. Protected turns are compressed by blocks made of dielectric material. The inductor and the crucible placed inside the coil are installed on a pallet made of refractory bricks or heat-resistant concrete. In industrial conditions, the process of making the crucible occurs directly in the furnace. In this case, the inductor in the assembled state is installed on a pallet and insulated with asbestos. After that, the pallet is filled with refractory powder, which is compacted by pneumatic installation. The clearance between the template installed on the bottom and the inductor is filled with powders of refractory materials.

The lining of the zone above the inductor provides refractory brick. The collar and the drain chute are also lined with heat-resistant bricks. The work of the induction crucible furnace takes place under the most difficult conditions, therefore, the quality of the heat-resistant materials used is increased. The lining life is affected by the composition of the refractory mass, the operating mode and the applied frequency of the electric current. As a rule, the crucible can withstand up to 100 melts, and then it breaks down.

Design of external elements

The frame of the melting crucible furnace is the base to which all its elements are attached. On large industrial devices, the frame looks like a solid casing. All parts of the frame must have high strength, due to the influence of the electromagnetic field of the inductor on them. The shell under certain conditions can be heated in the same way as the material in the furnace. To reduce heat, the frame is rationally manufactured from non-conductive materials. However, since dielectric materials have a high price, the material for the carcass is usually steel. The steel structure is divided into several elements, which, in turn, are isolated from each other. To reduce the electromagnetic field near the frame used screens. A protective screen is installed between the inductor and the furnace body. The screen has the shape of a cylinder and is made of aluminum or copper.

The swivel unit is an important design element. The main requirement for a turning mechanism is to provide a slope for a complete drain of the metal. The rotation mechanisms can be used different. In small-volume furnaces, a manual or electric winch is used. Industrial furnaces are tilted with a crane beam. Large volume furnaces can be equipped with a hydraulic tilt drive.

Cover, which covers the crucible furnace for melting, serves to maintain the temperature inside the unit at a higher level. However, considering that it is possible to cover the oven only after the melting of the charge has completely melted, the use of a cover is not mandatory.

Making a stove with your own hands

Induction furnaces have found wide application not only in industry, but also in everyday life. You can find schemes of a large number of self-made devices, but some of them at best will not work, and at worst - will damage the health of its creator. Many such amateurs warn of such consequences. In everyday life, the method of induction heating is used in such devices:

• Channel furnace for melting metal;
• Crucible induction furnace - the most simple in design, and in this regard, the most popular among enthusiasts, judging by the reviews;
• Water heating boiler, whose work is based on the method of induction;
• Induction cooking surfaces, which compete with popular gas stoves.

Duct Furnace

This type of furnace is used to produce high quality cast iron, as well as melting duralumin and colored special alloys. A duct furnace with a capacity of up to 3 kW is manufactured independently from a welding transformer whose frequency corresponds to an industrial one. Such an oven makes it possible to melt a bronze or copper billet weighing up to half a kilogram. The duct furnace also allows the melting of the duralumin, but it is necessary to take into account that the smelting process must be followed by the "aging" process. The time of this process can be up to 2 weeks and depends on the composition of the alloy.

For the manufacture of the furnace, the primary winding of the welding transformer is left unchanged, and a crucible type crucible is placed in place of the secondary winding. The best material for the crucible of a small channel furnace is the electro-porcelain. Other options are not suitable because of low strength and dielectric losses. According to the reviews of amateur metallurgists, the problem is that it is not possible to process the electrophorphone by itself, and it is very unlikely to find a suitable element for sale. It is because of the scarce crucible that the channel kiln was not widely used by enthusiasts, although this type of furnace has an efficiency of more than 90%.

Induction crucible furnace

The crucible furnace, produced by hand, is used primarily for the purification of precious metals. For example, having a radio connector made in the Soviet Union, you can get a certain amount of gold from his contacts. Using external heating, such a result can not be achieved.

In addition to gold mining, such a furnace is often used to evenly heat the metal, which is required for quality hardening. By changing the position of the part in the inductor and adjusting its power, it is possible to achieve a given temperature at a particular section of the metal. It is important that the use of such a furnace will be quite budgetary, because virtually all energy is directed to the process of heating the part.

Induction boilers

Induction hot water boilers have all chances in the future to displace conventional boilers. The disadvantage of this heater is that users consider a high price, but at the same time, by systematizing numerous reviews, there are several advantages:

• Reliability. The boiler does not have an electric spiral, which is a weak link in a conventional boiler.
• Coefficient of efficiency is almost 100%.
• Security. Electricity access to the boiler body is impossible due to design features.
• The device does not need special grounding.
• Resistant to a power surge in the electrical network.
• Does not form scale.
• Durability. The boiler is able to work without service for about 30 years.

Homemade water heating boiler

The basis of such a water heater is a power transformer with a power of up to 1.5 kW, the primary winding of which is designed for 220 V. The transformer from a tube color TV is a perfect choice. The secondary winding should be removed, and the number of primary turns must be increased.

The cadets advise and caution: the use of such a homemade device is unsafe, so the transformer should be grounded, and the device itself must be connected via a high-speed RCD.

Inductor in the kitchen

Induction cooking hobs no longer cause surprise and are widely used in everyday life. At the heart of the device are the same principles as the induction furnace, with the only difference being that the secondary winding is the metal bottom of the dish.

The use of such plates became possible due to the appearance in the manufacture of a dielectric, which, in addition to carrying out the task of isolating the inductor, must also have strength and hygienic characteristics. Satisfying all the requirements the material appeared relatively recently, and its cost is a significant part of the total price of the slab.

Users in one voice say: the independent manufacture of an induction cooker does not make sense for two reasons. The first - the preparation of dishes on such a hob requires fine-tuning for each type of food. For the necessary adjustment of all electrical parameters during the preparation, a microcontroller is required. The second reason is the price of electronic parts, of which the plate consists. In sum, all elements will cost much more than the cost of a ready-made device.

Induction cooking stove has such positive qualities:

• The absence, in contrast to microwave ovens, of outside radiation;
• The possibility of programming the cooker under your own manner of cooking;
• Preparation of such dishes as caramel, without overheating and burning;
• Efficiency, thanks to the rational use of heating energy.