High-frequency induction heating. Calculation of induction heating

In induction furnaces and devices, the heat in the heated device is emitted by currents arising in an alternating electromagnetic field inside the unit. They are called induction. As a result of their action, the temperature rises. Induction heating of metals is based on two main physical laws:

• Faraday-Maxwell;
• Joule-Lentz.

In metallic bodies, when they are placed in an alternating field, vortex electric fields begin to appear.

Induction heating device

Everything happens as follows. Under the action of a variable magnetic flux , the electromotive force (EMF) of induction is changed. The EMF acts in such a way that vortex currents flow inside the bodies , which produce heat in full accordance with the Joule-Lenz law. Also, the EMF generates an alternating current in the metal. This generates heat energy, which leads to an increase in the temperature of the metal.

This type of heating is the simplest, since it is non-contact. It allows to reach very high temperatures, at which the most refractory metals can be processed .

To provide induction heating, it is required to create a certain voltage and frequency in electromagnetic fields. You can do it in a special device - inductor. Its power is supplied from the industrial network in 50 Hz. You can use for this purpose individual power supplies - converters and generators.

The simplest device of a small frequency inductor is a spiral (conductor insulated), which can be placed inside a metal tube or wound on it. Passing currents heat the pipe, which, in turn, transfers heat to the environment.

The use of induction heating at low frequencies is quite rare. More common processing of metals at medium and high frequency. Such devices are distinguished by the fact that a magnetic wave hits the surface, where its damping occurs. The body converts the energy of this wave into heat. To achieve maximum effect, both components should be close in shape.

Where

The use of induction heating in the modern world is widespread. Area of use:

• Melting of metals, their soldering in a non-contact way;
• Obtaining new metal alloys;
• Machine building;
• Jewelry business;
• The manufacture of small parts that can be damaged by other methods;
• Hardening of surfaces (the parts can be the most complex configuration);
• Heat treatment (machining of parts for machines, hardened surfaces);
• Medicine (disinfection of instruments and instruments).

Induction heating: positive characteristics

This method has many advantages:

• With it, you can quickly heat and melt any current-carrying material.
• Allows to produce heating in any environment: in a vacuum, atmosphere, a liquid that does not conduct current.
• Due to the fact that only the conductive material is heated, the walls, weakly absorbing waves, remain cold.
• In the specialized fields of metallurgy, obtaining ultra-pure alloys. This is an entertaining process, because the metals are mixed in a suspended state, in a shell of protective gas.

• In comparison with other types, induction does not pollute the environment. If contamination is present in the case of gas burners, as well as in arc heating, then induction eliminates this, due to "pure" electromagnetic radiation.
• Small dimensions of the inductor device.
• The possibility of making an inductor of any shape, this will not lead to local heating, but will contribute to an even distribution of heat.
• It is irreplaceable if it is necessary to heat only a certain area of the surface.
• It is not difficult to set up such equipment for the desired mode and adjust it.

disadvantages

The system has such disadvantages:

• Independently to establish and adjust the type of heating (induction) and its equipment is rather difficult. It is better to consult specialists.
• The need to accurately compare the inductor and the workpiece, otherwise induction heating will be inadequate, its power can reach small values.

Heating by induction equipment

To arrange individual heating it is possible to consider such an option as induction heating. As the unit will go a transformer, consisting of windings of two types: primary and secondary (which, in turn, is short-circuited).

How does it work

The principle of operation of an ordinary inductor: the vortex flows pass inside and direct the electric field to the second body.

To allow water to pass through such a boiler, two nozzles are fed to it: for a cold one, which comes in, and at the outlet of warm water, a second branch pipe. Due to the pressure, water constantly circulates, which excludes the possibility of heating the inductor element. The presence of scale is excluded, since constant vibrations occur in the inductor.

Such an element in the maintenance will be inexpensive. The main advantage is that the device operates silently. You can install it in any room.

Manufacture of equipment yourself

Installation of induction heating of great complexity will not be. Even those who do not have experience, after careful study will cope with the task. Before you start, you need to stock up with the following necessary elements:

• Inverter. It can be used from a welding machine, it is inexpensive and will be necessary high frequency. You can make it yourself. But this is a time consuming occupation.
• The heater body (for this purpose a piece of plastic pipe, induction heating of the pipe in this case will be the most effective).
• Material (a wire with a diameter of not more than seven millimeters will fit).
• Devices for connecting the inductor to the heating network.
• Grid for holding the wire inside the inductor.
• The induction coil can be made of copper wire (it must be enameled).
• Pump (for water to be fed into the inductor).

Rules for manufacturing equipment yourself

In order for the induction heating unit to work correctly, the current for such a product must correspond to the power (it should be at least 15 amperes, if it is required, it can be more).

• The wire should be cut into pieces no more than five centimeters. This is necessary for efficient heating in a high-frequency field.
• The body must be at least as large as the prepared wire, and have thick walls.
• For fixing to the heating network, a special adapter is attached to one side of the structure.
• At the bottom of the pipe, you need to put a wire to prevent the wire from falling out.
• The latter is needed in such a quantity that it fills the entire interior space.
• The construction is closed, an adapter is placed.
• Then a coil is constructed from this tube. To do this, wrap it with the already harvested wire. The number of turns must be observed: a minimum of 80, a maximum of 90.
• After connecting to the heating system, the device is filled with water. The coil is connected to the harvested inverter.
• The water supply pump is installed.
• The temperature regulator is mounted.

Thus, the calculation of induction heating will depend on the following parameters: length, diameter, temperature and processing time. Pay attention to the inductance of the tires leading to the inductor, which can be much larger than the indices of the inductor itself.

About cooking surfaces

Another application in the home, except for the heating system, this type of heating found in the hob panels. Such a surface looks like a conventional transformer. Its coil is hidden under the surface of the panel, which can be glass or ceramic. A current passes through it. This is the first part of the coil. But the second is the dishes in which cooking will take place. At the bottom of the dishes vortex currents are created. They heat the dishes first, and then the products in it.

Heat will be released only when the surface of the panel put dishes. If it is absent, no action occurs. The induction heating zone will correspond to the diameter of the dishes placed on it.

Special plates are needed for such plates. Most ferromagnetic metals can interact with an induction field: aluminum, stainless and enamelled steel, cast iron. Not suitable for such surfaces only: copper, ceramic, glassware and non-ferrous metal ware.

Naturally, the induction cooker will switch on only when a suitable dish is installed on it.
Modern plates are equipped with an electronic control unit, which allows you to recognize empty and unusable dishes. The main advantages of cooking induction panels are: safety, ease of cleaning, quickness, efficiency, economy. The surface of the panel must never be burned.

So, we found out where this type of heating (induction) is used.