Electric furnace is a kind of heating furnace to convert the electric energy in the furnace into heat for heating the workpiece. Compared with the fuel furnace, the advantages of electric furnace are: the atmosphere in the furnace is easy to control, and even can be pumped into a vacuum; Material heating fast, heating temperature is high, temperature is easy to control.
Electric furnace is a kind of heating furnace to convert the electric energy in the furnace into heat for heating the workpiece. Compared with the fuel furnace, the advantages of electric furnace are: the atmosphere in the furnace is easy to control, and even can be pumped into a vacuum; Material heating fast, heating temperature is high, temperature is easy to control; The production process is easy to achieve mechanization and automation; Good labor hygiene conditions; High thermal efficiency; Good product quality; And more environmental protection with the increasingly serious environmental problems and is regarded as a good product and so on. The electric furnace in metallurgical industry is mainly used for smelting, heating and heat treatment of iron and steel, ferro alloy and non-ferrous metals. The end of the 19th century saw the emergence of industrial scale electric furnaces. Since the 1950s, the proportion of electric furnaces in metallurgical equipment has been increasing year by year due to the growth of the demand for advanced metallurgical products and the decline of electricity charges along with the development of the power industry. Electric furnace can be divided into resistance furnace, induction furnace, arc furnace, plasma furnace, electron beam furnace.
An electric furnace whose heat source is the joule heat produced by the passage of an electric current through a conductor. According to electric heating generation, resistance furnace is divided into direct heating and indirect heating. In the direct heating resistance furnace, the current passes through the material directly. Because the electric heat power is concentrated in the material itself, the material is heated quickly, which is suitable for the process requiring rapid heating, such as the heating of forging billet. This resistance furnace can heat materials to very high temperatures, such as carbon graphitization furnace, can heat materials to more than 2500℃. Direct heating resistance furnace can be made into vacuum resistance furnace or protective gas resistance furnace. In powder metallurgy, it is often used for sintering tungsten, tantalum, niobium and other products.
(1) in order to make the material heating uniform, the material parts of the conductive section and conductivity should be consistent;
Industrial resistance furnace
(2) due to the material resistance is quite small, in order to achieve the required thermal power, the working current is quite large, so the electrode and the material should contact well, so as not to burn the material from the arc, and the resistance of the power bus in order to reduce the circuit loss; Most resistance furnaces are indirect heating resistance furnaces, which are equipped with resistance bodies specially used to realize electric-thermal transformation, called electrothermal bodies, from which heat energy is transferred to the materials in the furnace.
This kind of electric furnace shell is made of steel plate, furnace lining refractory material such as ceramic fiber, inner material.
The most commonly used heating elements are ferrochrome aluminum heating element, nickel-chromium heating element, silicon carbide rod and molybdenum disilicate rod, silicon carbon rod and zirconium diboride ceramic composite heating element. The atmosphere inside the furnace can be general atmosphere, protective atmosphere or vacuum as required. General supply voltage 220 v or 380 v, if necessary with adjustable voltage of the intermediate transformer. Small furnace (<10 kw) single-phase power supply, large furnace three-phase power supply. For single variety, large batch of materials, should be used continuous furnace heating. Furnace temperature less than 700□ resistance furnace, most device blower, to strengthen heat transfer in the furnace, ensure uniform heating. Resistance furnace for melting fusible metals (lead, lead bismuth alloy, aluminum and magnesium alloy, etc.), which can be made into crucible furnace; Or make a reflective furnace with molten pool and install an electric heater on the top of the furnace. Electroslag furnace is a resistance furnace which realizes electrothermal transformation from dissolved slag (see electroslag remelting).
Induction furnace an electric furnace in which materials are heated or melted by the effect of induction heating. The basic part of induction furnace is an induction coil made of copper pipe. Alternating voltage is added at both ends of the induction coil to generate alternating electromagnetic field. Conductive materials are placed in the induction coil. Due to the eddy current generated by electromagnetic induction in the material, electric energy is converted into heat energy by resistance to heat the material. Therefore, induction heating can also be considered as a direct heating resistance heating.
The characteristic of induction heating is that the electric heating power (current distribution) transformed in the heated material is very uneven, with the largest surface and the smallest center, which is called skin effect. In order to improve the heating efficiency of induction heating, the power supply frequency should be appropriate. Small melting furnace or high frequency electricity should be used for surface heating of materials, large melting furnace or medium frequency or power frequency electricity should be used for deep penetration heating of materials. Induction coil is a load with considerable inductance and its power factor is usually very low. To improve the power factor, the induction coil is usually in parallel with if or hf capacitors, called resonant capacitors. The gap between the induction coil and the material should be small, the induction coil should be made of square red copper tube, water cooling inside the tube, the gap between the induction coil should be as small as possible, insulation is good. Induction heating device, mainly used for steel, copper, aluminum and zinc heating and melting casting, heating fast, less burning loss, high degree of mechanization and automation, suitable for automatic operation line.