What is the standard for electric furnace tapping?

Metallurgical arc furnace that uses electric heating effect to supply heat

Electric furnace equipment is usually a complete set, including electric furnace body, power equipment (electric furnace transformer, rectifier, frequency converter, etc.), switches, auxiliary auxiliary appliances (resistors, compensation capacitors, etc.), vacuum equipment, detection and control instruments (electrician Instrumentation, thermal instrumentation, etc.), automatic adjustment system, furnace mechanical equipment (inlet and discharge machinery, furnace body tilting device, etc.). The electrical equipment and detection and control instruments of large electric furnaces are generally concentrated in the electric furnace power supply room. Compared with fuel furnaces, electric furnaces have the following advantages: the atmosphere in the furnace is easy to control, and can even be vacuumed; the material is heated quickly, the heating temperature is high, and the temperature is easy to control; the production process is easier to achieve mechanization and automation; good labor and hygiene conditions; high thermal efficiency ; Good product quality, etc. 

Electric furnaces in the metallurgical industry are mainly used for smelting, heating and heat treatment of iron and steel, ferroalloys, and non-ferrous metals. Industrial-scale electric furnaces appeared at the end of the 19th century. Since the 1950s, due to the increase in demand for advanced metallurgical products and the decline in electricity costs with the development of the power industry, the proportion of electric furnaces in metallurgical furnace equipment has increased year by year. Electric furnaces can be divided into resistance furnaces, induction furnaces, electric arc furnaces, plasma furnaces, electron beam furnaces, etc.

Resistance electric heat furnace

An electric furnace that uses Joule heat generated by current passing through a conductor as the heat source. According to the method of electric heat generation, resistance furnaces are divided into direct heating and indirect heating. In the direct heating resistance furnace, the current passes directly through the material. Because the electric heating power is concentrated on the material itself, the material is heated quickly, which is suitable for processes that require rapid heating, such as the heating of forging blanks. This kind of resistance furnace can heat the material to a very high temperature. For example, the carbon material graphitization electric furnace can heat the material to more than 2500. The direct heating resistance furnace can be made into a vacuum resistance heating furnace or a protective gas resistance heating furnace. In powder metallurgy, it is often used for sintering tungsten, tantalum, niobium and other products. 

When heating with this kind of furnace, attention should be paid to: In order to make the material heated evenly, the conductive cross section and conductivity of each part of the material are required to be consistent; The resistance of the material itself is quite small, in order to achieve the required electric heating power, the working current is quite large, so The power transmission electrode should be in good contact with the material to avoid arcing and burn the material, and the resistance of the power transmission bus should be small to reduce circuit loss; When supplying AC power, a short network should be reasonably configured to avoid excessive inductance and power factor Too low.

   Most of the resistance furnaces are indirect heating resistance furnaces, which are equipped with a resistance body specially used to realize the electric-heat conversion, called an electric heating body, which transfers heat energy to the materials in the furnace. The shell of this electric furnace is made of steel plate, the hearth is lined with refractory materials, and materials are 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. According to needs, the atmosphere in the furnace can be ordinary atmosphere, protective atmosphere or vacuum. Generally, the power supply voltage is 220 volts or 380 volts, and an adjustable voltage intermediate transformer should be equipped if necessary. Single-phase power supply for small furnaces (<10 kW) and three-phase power supply for large furnaces. For materials with single varieties and large batches, continuous furnace heating should be used. Most resistance furnaces with furnace temperature lower than 700 are equipped with blowers to strengthen heat transfer in the furnace and ensure uniform heating. The resistance furnace used to melt fusible metals (lead, lead-bismuth alloys, aluminum, magnesium and their alloys, etc.) can be made into a crucible furnace; or into a reverberatory furnace with a molten pool, with an electric heating element installed on the top of the furnace. Electroslag furnace is a resistance furnace that realizes electrothermal transformation from molten slag.