The electric resistance furnace is an electric furnace in which Joule heat generated by current passing through a conductor is used as a heat source. The electric resistance furnace uses electricity as a heat source to convert electrical energy into heat energy through an electric heating element, and heats the metal in the furnace. Resistance furnace and flame ratio, high thermal efficiency, up to 50-80c / o, thermal system is easy to control, labor conditions are good, furnace life is long, suitable for the heating of more demanding workpieces, but the power consumption is high.
According to the heat transfer method, the resistance furnace is divided into a radiant resistance furnace and a convection resistance furnace. The radiant resistance furnace is mainly radiative heat transfer, and the convection heat transfer effect is small; the convection resistance furnace is mainly convective heat transfer, usually called air circulation resistance furnace, which is heated by hot air, and the furnace temperature is lower than 650 °C. .
According to the electric heating method, the electric resistance furnace is divided into direct heating and indirect heating.
In the direct heating resistance furnace, the current directly passes through the material, and since the electric heating power is concentrated on the material itself, the material is heated quickly, and is suitable for a process requiring rapid heating, such as heating of a forged billet. This electric resistance furnace can heat the material to a very high temperature, such as a carbon material graphitization electric furnace, which can heat the material to more than 2500 â–¡. The direct heating resistance furnace can be used as a vacuum resistance heating furnace or a protective gas resistance heating furnace. In powder metallurgy, it is commonly used for sintering tungsten, tantalum, niobium and other products.
When using this kind of furnace heating, it should be noted that: 1 is to make the material heating evenly, and the conductive cross section and electrical conductivity of each part of the material are required to be consistent; 2 because the material itself has relatively small resistance, in order to achieve the required electric heating power, the working current is quite large, so The contact between the power transmitting electrode and the material should be good, so as to avoid the arc burning material, and the resistance of the power transmitting busbar should be small to reduce the circuit loss; 3 when the alternating current is supplied, the short net should be properly arranged to avoid the overvoltage and the power factor. Too low.
Most of the resistance furnaces are indirect heating resistance furnaces, in which a resistor body dedicated to electro-thermal transformation is called, which is called an electric heating body, which transfers heat energy to the materials in the furnace. The electric furnace shell is made of steel plate, the furnace is lined with refractory material, and the material is placed inside. The most commonly used electric heaters are iron chromium aluminum electric heaters, nickel chromium electric heaters, silicon carbide rods and molybdenum disilicide rods. The atmosphere in the furnace may be a normal atmosphere, a protective atmosphere or a vacuum, as needed. The general power supply voltage is 220 volts or 380 volts, and an intermediate transformer with adjustable voltage can be configured if necessary. Small furnace (<10 kW) single-phase power supply, large furnace three-phase power supply. For materials with a single variety and large batch volume, continuous furnace heating should be used. Resistance furnaces with furnace temperatures below 700 â–¡, most of which are equipped with blowers to enhance heat transfer in the furnace to ensure uniform heating. The electric resistance furnace for melting fusible metals (lead, lead-bismuth alloy, aluminum and magnesium, alloys, etc.) can be made into a crucible furnace; or a reverberatory furnace having a molten pool, and an electric heating body is installed on the top of the furnace.