Resistance furnace is a current through a conductor joule heat generated by the electric furnace for the heat source. In electric resistance furnace as heat source, through the electric heating elements convert electrical energy into heat energy, in the furnace for heating metal. Resistance furnace and flame ratio, high thermal efficiency, can reach 50-80 ℅, easy to control the thermal system, good working conditions, the furnace life is long, suitable for relatively strict heating of artifacts, but the high cost of electricity.
By way of heat transfer and resistance furnace is divided into resistance furnace radiant and convection type resistance furnace. Radiation type resistance furnace is given priority to with radiation heat transfer, convection heat transfer effect is small; Convection type resistance furnace with convection heat transfer is given priority to, often referred to as air circulation resistance furnace, heating by hot air, furnace temperature is below 650 ℃.
According to the electric heating way, resistance furnace is divided into two directly heating and indirectly heating. In direct heating resistance furnace, current directly through the material, because of electric power concentrated in the material itself, so the material heat quickly, is suitable for the requirements of rapid heating process, such as forging billet heating.
The resistance furnace can be heated to very high temperatures, the supplies graphitizing furnace carbon materials, for example, can put the material is heated to more than 2500. Directly is made vacuum resistance furnace heat resistance or protective gas resistance furnace, heating furnace in powder metallurgy, commonly used in sintering tungsten, tantalum, niobium and other products. Using this stove heating should be paid attention to: (1) to make the material is heated evenly, for each part of the material conductive section and conductivity is consistent; (2) due to the resistance material itself is fairly small, to achieve the required heating power, working current is quite big, therefore power electrode and material contact is better, so as to avoid the arc burning material, and the resistance of the power bus, to reduce the circuit loss; (3) when used for alternating current (ac), to reasonably allocate short_net, in order to avoid excessive impedance and make the power factor is low.
Most of the resistance furnace is indirect heating resistance furnace, which is equipped with dedicated to the realization of electrical and thermal transition resistance, called the electric heating body, by its pass in the furnace the heat material (FIG. 1 indirect heating resistance furnace). This kind of electric furnace shell made of steel plate, build by laying bricks or stones of the chamber of a stove or furnace lining refractories, put inside the material. The most commonly used electric heating body is iron chromium aluminum electric heating body, nickel chromium electric heating body, silicon carbide rods and molybdenum disilicide bar. According to need, furnace atmosphere, protective atmosphere or vacuum can be a normal atmosphere. The general power supply voltage 220 v or 380 v, the middle of the configuration of adjustable voltage transformer when necessary. Small furnace (< 10 kw) single-phase power supply, three-phase power supply large furnace. For varieties of a single, large batch of shoes materials, appropriate USES continuous heating furnace. Temperature is below 700 - resistance furnace, most device blower, with enhancing heat transfer in furnace, ensure uniform heating. Used to melt fusible metal (lead, lead, bismuth alloys, aluminum and magnesium and its alloys, etc.) of the resistance furnace, can make a crucible furnace; Or make it have a reverberatory furnace of molten pool, installing electric heating body on top. Electroslag furnace consists of slag change electric resistance furnace.