Luoyang Judian Metal Hot Processing Equipment Co., LTD is mainly engaged in the manufacture of complete sets of equipment in the metal thermal processing industry and the integration of the entire production line.
The main advantage of this system is that it does not require frequency conversion. Since no rotating mechanism is required and no complex electronic equipment is required, power loss is reduced, the system is greatly simplified, the operation is simple, and the switch device, power factor compensation capacitor, control circuit, etc. can be selected from the standard range. Secondly, radiation losses, scattered magnetic field heating and useless high-frequency induction current can be ignored. The investment cost of the basic equipment is usually lower than that of medium frequency or radio frequency devices.
vacuum induction melting
From the application point of view, power frequency heating, or mainly 50/60 Hz frequency heating, is mainly used for penetration heating. Since most penetration heating requires maximum temperature uniformity, it is more appropriate to use power frequency than higher frequencies.
The lowest frequency can achieve the maximum current penetration layer depth, so power frequency heating is widely used in melting furnaces.
The basic disadvantage of low-frequency heating (especially 50/60 Hz heating) is that for a certain workpiece shape and inductor magnetic field strength, its input power decreases. Formula (1.2) shows that the input power varies directly with the frequency. This disadvantage is often fully compensated by the factor of temperature uniformity, since it takes only a short time to uniformize the temperature by absorbing heat from the surface. Despite the low surface power density values, the workpiece sizes are large, with bar diameters often reaching 250-350 mm, sheet sections up to 2 m x 30 mm, and lengths up to 10 m. Therefore, high inductor power and system power are required.
melting furnace for steel
A single inductor can have a power of several megawatts and the installed power of the system can reach more than 200 megawatts. Due to the high power, balanced three-phase systems are almost always used. The inductors can be designed as three-phase inductors or as multiples of three single-phase inductors with equal load. Generally speaking, most non-ferrous metals are heated through the entire body with a single induction coil heater as shown in Figure 6.3. When the inductor is filled with the workpiece, the load of these three-phase inductors is quite balanced. If the inductor is only partially filled with the workpiece, one phase will become unbalanced. Therefore, it is best to have a neutral conductor in the supply line. This neutral conductor can draw excess current. Another alternative is the phase-balanced system discussed in Section 6.2.
Most systems use the method of passing the workpiece continuously through one or more inductor coils, but integral heating systems are still used. Medium frequency heating is sometimes used to achieve the higher temperatures above the Curie point required for heating steel, and in such a dual-frequency system, the number of 50/60 Hz inductors is such that each inductor can be single-phase, so that the three-phase load of the power supply can be well balanced. Three single-phase low-power systems can be loaded onto the three-phase power supply.
represents the main part of a typical power frequency system. In order to match the low-impedance, low-voltage inductor with the high-voltage power supply, a transformer is generally configured. To match the changes in inductor operation and power control, the primary coil of the transformer generally has several taps. These taps are in an open circuit state.
In addition to changing the speed of the workpiece or turning the power on and off (or pulsating the power) with the help of temperature/contactors for control, the tap method is a typical matching and control method. This method is generally used for heating non-ferrous metals one by one, during which the load changes significantly. Because there is current and voltage when there is load, the tap must be changed after the load is removed. Sometimes the inductor is operated with a low voltage (such as 230/440 volts), so the transformer can be omitted. On these devices, the only control method is to control the heating time, that is, to control the speed of the workpiece passing. Although limited power control is a disadvantage of the power frequency heating system, this is not as important as in the high frequency heating system. Because at low frequencies, the heating time is usually much longer.
