When the induction coil is working, the alternating current forms an alternating magnetic field through the induction coil. According to Faraday's law of electromagnetic induction, the alternating magnetic field lines cut the metal inside the coil to form the induced current. Because the metal itself, there is resistance to heat, the current flow in the process of internal heat generated, so that the metal heating or melting. This is the basic principle of induction heating and induction melting.
Induction coil work has the following characteristics:
1. There is a high voltage and a high current in the coil.
2. The coil itself is in a high temperature working environment;
3. Between the coil and the coil must ensure good insulation performance, once the ignition or the formation of short circuit, electric furnace efficiency will be greatly reduced.
Because the coil itself is a conductor, the induction coil can not form any turn between the turns, so the induction coil insulation is very important, directly affect the efficiency of the induction furnace and the safety of the operating environment. However, unfortunately, the induction coil insulation in the industry and did not get enough attention, most of the production enterprises only in the coil after the completion of the production of a layer of conventional insulating paint spray as a means of insulation, most of such insulating paint Is the organic material, at room temperature with good insulation, but with the temperature rise, the performance of such insulating paint quickly deteriorated, and its itself has been gradually carbonized, when the temperature exceeds 100 ° C, the insulating paint will be completely carbonized Black, completely lost insulation capacity.
The main reason for the insulation damage caused by the induction coil surface is that the working environment of the induction furnace is mostly harsh, although there is a water-cooled system, it can not ensure that the insulating paint has been working in a lower temperature environment. This is mainly due to the following reasons:
1. The induced current through the coil has a skin effect, that is, the current is mainly concentrated in the surface of the copper tube, the higher the frequency of induced current, the greater the surface current density. So the induction coil copper tube heat concentrated in the surface, contact with the insulating paint surface temperature is much higher than the copper pipe and the contact with the cooling water temperature. Even under normal circulating water cooling conditions, the effluent temperature is controlled at 50-60 ° C and the temperature on the surface of the copper tube will exceed 80 ° C.
2. The heat transfer of molten steel in the furnace. The new furnace lining is thick, can effectively prevent the heat of molten steel in the furnace to the coil surface, but later with the rapid erosion of the lining, to the late lining thinning, molten steel conduction to the coil surface heat is much higher than the new lining. The temperature of the coil slurry layer has risen to approximately 200 ° C at the time of the lining (the thickness of about 5 cm) when the temperature of the coil slurry layer is 80 ° or more at the time of the new lining (the lining thickness is about 15 cm) Conventional insulating varnishes have been completely carbonized.
3. Cooling water cooling capacity decline, which is mainly due to the impact of water quality caused. High temperature cooling water is easy to scale, especially in the hard water of the north and west areas, cooling water scaling phenomenon, blocking the brass,Induction coil water pressure decreases, cooling capacity decreased significantly, in turn, accelerated fouling The Once this happens, the temperature of the surface of the copper tube will rise rapidly, conventional insulating paint in a very short period of time will be destroyed by carbonation. Once the coil surface of the insulating paint damage loss of insulation, this time easily lead to coil ignition, mainly because:
1. Water vapor, especially when the new lining is running, the moisture content of the lining material is suddenly heated and vaporized through the pores of the coil slurry, and the coil with relatively low temperature is immediately condensed into water droplets. , Immediately caused by ignition.
2. Brush the bristles. Because the circulating water in the brass may be caused by partial dripping.
3. Metal dust in the workshop in the coil surface accumulation, the formation of short-circuit ignition.
Once the ignition phenomenon occurs, the temperature rises rapidly, the first will completely destroy the part of the original residual insulation coating, to accelerate the ignition, until the formation of drawing arc, breakdown of copper, serious production accidents and property losses.
In addition, the electric furnace overload is also easy to cause the coil ignition is an important factor, because more than the rated power, the current through the coil voltage increases, the coil heat increased, this time the insulation layer is more susceptible to high temperature damage and loss of insulation The ability to fire at high voltage is more prone to occur.