The magnetic controller converts 220V/380V, 50/60Hz AC into DC through a rectifier circuit, and then converts the DC into voltages of different frequencies through a control circuit. When current flows through the coil, it generates a changing alternating magnetic field. When the alternating magnetic field lines pass through ferromagnetic metal materials (iron, cobalt, nickel), countless small eddy currents are generated inside the metal, causing the metal material itself to heat up rapidly, thereby achieving the purpose of heating the metal material.
The working principle of the electromagnetic heater is: convert 220V or 380V AC into DC after rectification, then filter the DC, use IGBT or thyristor to convert DC back to AC, generate high-frequency magnetic field lines in the induction coil, causing eddy currents on the surface of the conductor workpiece inside the induction coil, which generates heat through its own internal resistance.
Electromagnetic induction heating is mainly divided into four frequency types: low frequency, medium frequency, super audio frequency, and high frequency.
Among them, low-frequency heating has several notable characteristics: the heat penetrates deeply into the workpiece, and the temperature difference along the radial direction of the workpiece is relatively small. Therefore, under low-frequency heating conditions, the thermal deformation of the workpiece is not obvious, and the thermal stress value is small. It is more suitable for heat preservation and smelting in relatively large-capacity furnaces, and also suitable for overall through-heating of large workpieces. Currently, most traditional power frequency induction furnaces are made using the principle of low-frequency induction heating. Abroad, devices made with power frequency induction heating can achieve power up to several hundred watts, and large-scale steel water temperature protection and through-heating of dozens of tons of workpieces mostly use power frequency induction heating devices. There are also some other low-frequency induction heating power supplies on the market, which are composed of solid-state devices, but they cannot compete with power frequency induction furnaces in terms of price, reliability, and power.
Medium frequency refers to frequencies between 150Hz and 10KHz. Within this frequency range, there are traditional electromagnetic frequency multipliers and medium-frequency generators, but these two devices have been replaced by another medium-frequency induction heating device—the thyristor induction heating device. Abroad, the capacity of this device has reached tens of megawatts, such as the 42MW induction furnace developed by Geneva Steel Company in the United States.
Super audio frequency refers to frequencies between 10KHz and 100KHz. Within this frequency range, machines from earlier years basically did not exist. Super audio frequency induction heating devices gradually developed after the emergence of semiconductor components such as thyristors. In the early days, technicians made super audio frequency power supplies using silicon-controlled rectifiers with frequency doubling circuits and time division circuits. By the 1980s, with the rapid development of technology, new semiconductor power devices (IGBT, GTO) appeared on the market. Super audio frequency induction heating power supplies composed of these components gradually occupied the market. Due to the different characteristics of different components, the super audio frequency induction heating power supply composed of IGBT is most accepted by the market because IGBT is more convenient to use.
High frequency refers to frequencies above 100KHz. Above this frequency, foreign countries are currently in a transitional stage. The electron tube high-frequency oscillator developed in Japan has a power range from several kilowatts to several thousand kilowatts, with a frequency range of 100KHz to 500KHz. Another high-frequency induction power supply, developed using SIT, has higher power and frequency, with power up to 400 kilowatts and frequency up to 400KHz. In 1987, a power supply with a power of 1200 kilowatts and a frequency of 200KHz also began development. At the same time, countries in Europe and America were also developing high-frequency induction heating power supplies based on transistors. For example, Spain's current-type induction heating power supply using MOSFET has a manufacturing level of 600KW/200KHz, Germany's electron tube high-frequency power supply level is about 110KW, and its current-type MOSFET induction heating power supply developed in 1989 has a capacity of 480KW/50-200KHz.
The heating method of the electric heating ring is to transfer heat to the barrel through contact conduction.
The heat is transferred to the barrel only from the inner side close to the barrel surface, so most of the heat on the outer side is dissipated into the air, resulting in heat conduction loss and causing the ambient temperature to rise. Another disadvantage of resistance wire heating is low power density, which cannot adapt to some heating occasions requiring higher temperatures. Electromagnetic heating technology uses the principle of electromagnetic induction to make the metal barrel itself generate heat, and can wrap a certain thickness of thermal insulation material outside the barrel according to specific conditions, thus greatly reducing heat loss and improving thermal efficiency. Therefore, the power-saving effect is very significant, reaching 30% to 75%. Because the electromagnetic heating coil itself does not generate heat and is made of insulating materials and high-temperature cables, it does not have the problem of the resistance wire of the original electric heating ring oxidizing at high temperatures and shortening its service life. It has the advantages of long service life, fast heating rate, and no need for maintenance, reducing maintenance time and costs. It has been widely used by plastic product enterprises, greatly reducing their production costs.
