Analysis of the working condition of induction furnace
The theory of mutual inductance of the transformer, the secondary winding (both charge) the effective value of the induced potential within (represented by E 2) and the maximum frequency with two alternating magnetic flux related parameters in the induced potential E 2 of under the action, and the charge of the formed closed loop, the eddy current there through, the value of the size of eddy current, and is proportional to the induced potential E 2, the impedance is inversely proportional to the charge circuit, in the case where the impedance of the charge has been determined, the heat generation Proportional to the induced potential. Since there is no magnetically conductive object in the coreless induction furnace , the magnetic flux must be closed by the air , but the magnetic reluctance of the air is large , which reduces the effective magnetic flux . In order to obtain the necessary induced potential , it is required to increase the cutting speed of the magnetic line. , which requires increasing the frequency of the current through induction coil, to achieve the purpose of heating effect is remarkable. But the charge induced in the flow of current in an actual case, the magnetic field will be formed, but the direction is opposite to the magnetic field of the inductor, together with the results of two superimposed magnetic field will weaken the entire action. As the continuously weakened magnetic field continues to distribute deep into the interior of the charge and continuously generates current , the demagnetization of the current causes the electric field strength and current density induced in the charge to decrease sharplyfrom the surface to the center , and the higher the frequency of the current , This phenomenon is also more pronounced , which is the result of the so-called skin effect effect. In order to increase the calorific value of the charge , if the frequency is increased without limit, one is limited by the complexity of the power supply device . More importantly, due to the above-mentioned skin effect , the eddy current heat increases with the current frequency, and only the charge is now The surrounding surface layer , while the heat in the center of the charge is conducted from the surface , so the heating time will be lengthened and the electrical efficiency will no longer rise. The relationship between the frequency of the power source and the electrical efficiency can be described as follows . In the case where thediameter of the induction furnace charge is fixed and the physical properties of the charge are constant , the electrical efficiency will rise significantly as the current frequency increases , but as the frequency continues to increase At this time , the electrical efficiency will no longer be close to the saturation phase as the frequency changes. Therefore , we can make an assertion that for a certain size induction furnace , and under the same physical conditions of the material of the charge and the sensor material , there must be a critical frequency. It is for these reasons that the electric furnace manufacturer will select the frequency according to the size of the furnace. Taking into account the electrical and thermal efficiency of the furnace, select the appropriate frequency. When the furnace capacity is small, the frequency is higher , and when the capacity is larger, the lower one is selected , generally in the range of 200 Hz--8000 Hz .
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