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The difference between direct heating and indirect heating of box furnace electric furnace

     An electric furnace that uses Joule heat generated by current passing through a conductor as the heat source. Box furnace manufacturers divide resistance furnaces into direct heating and indirect heating according to the electric heat generation method.
    In the direct heating resistance furnace, the current passes directly through the material. Because the electric heating power of the industrial resistance furnace is concentrated on the material itself, the material heats up quickly and 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°C. 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 using this kind of furnace for heating, you should pay attention to:
①In order to make the material heated uniformly, the conductive cross section and conductivity of each part of the material are required to be consistent;

②The 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 should be in good contact with the material to avoid arcing to burn the material, and the resistance of the power transmission bus should be small to reduce circuit loss; 

③When supplying AC power, a short network should be reasonably configured to avoid excessive inductance and power factor Too low. The low thermal efficiency of the resistance furnace is one of his shortcomings. 

    Most of the resistance furnaces are indirect heating resistance furnaces, which are equipped with a resistor 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 furnace is lined with refractory materials such as ceramic fiber, and the materials are placed inside. Commonly used electric heaters are iron-chromium-aluminum electric heaters, nickel-chromium electric heaters, silicon carbide rods and molybdenum disilicide rods, silicon carbide rods, and zirconium diboride ceramic composite heaters. 

    According to needs, the atmosphere in the furnace can be ordinary atmosphere, protective atmosphere or vacuum. The general power supply voltage is 220 volts or 380 volts, and an adjustable voltage intermediate transformer should be equipped if necessary.

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