Heating process of medium frequency induction furnace
As we all know, medium frequency induction furnace is an induction heating equipment used to heat metal, which is commonly used in forging industry, casting industry and metal modulation heating. So, what is the heating process of medium frequency induction furnace? How to convert electric energy into heat energy to heat metal?
The first stage: the alternating current of frequency converter of medium frequency induction furnace produces alternating magnetic field.
When the alternating frequency current of medium frequency induction furnace passes through the spiral induction coil, a magnetic field is generated in the space and around the coil. The polarity and intensity of the magnetic field vary with the frequency of the alternating current, so it is an alternating magnetic field. One part of the magnetic line of alternating magnetic field penetrates through the metal charge and the other part penetrates through the lining material. The polarity, intensity and flux change rate of the alternating magnetic field, i.e. the direction of the magnetic field and the number and density of the magnetic lines of force, are determined by the current intensity and frequency passing through the induction coil, as well as the turns and geometric dimensions of the coil.
The second stage: the induction current is produced by the alternating magnetic field of the frequency converter of medium frequency induction furnace.
When the polarity and strength of the magnetic line of force change periodically, the magnetic line of force is cut by the metal charge, which is equivalent to the movement of the conductor cutting the magnetic line of force, so that the induced electromotive force E is generated in the closed circuit formed between the metal charges. Its size can be expressed as follows:
E=4.44f φ（ V）
Where φ—— The flux of alternating magnetic field, WB;
F — frequency of alternating current, Hz.
Under the action of induced electromotive force E of medium frequency induction furnace, induced current is produced in metal charge. The magnitude of induced current I obeys Ohm’s law and is expressed as follows:
Induced current I = u / R
Where r — effective resistance of metal charge, Ω。
The third stage: the induction current of medium frequency induction furnace is transformed into heat energy.
The induced current generated in the metal charge has to overcome a certain resistance in the process of flow, so that the electric energy is converted into heat energy. This heat energy is used to heat and melt the metal charge. The amount of heat produced by induced current obeys Joule Lenz law.
It can be seen that the energy conversion of the whole heating process of medium frequency induction furnace. First, the electric energy is transformed into magnetic energy, and then the magnetic energy is transformed into electric energy, most importantly, the electric energy is transformed into heat energy to heat the metal. It can be seen from this that the heating method of medium frequency induction furnace is different from that of electric arc furnace, plasma furnace and resistance furnace. It is inevitable that there will be loss in the multiple conversion of energy form, so it is called low thermal efficiency. This requires that measures be taken to compensate from the electrical circuit to reduce losses and improve efficiency, so as to make the medium frequency induction furnace equipment more energy-saving.