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The difference between box furnace direct heating and indirect heating

The difference between box furnace direct heating and indirect heating.

Joule heat generated by the current conductor as a heat source box furnace . Box furnaces are divided into two types, direct heating box furnaces and indirect heating box furnaces, 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 evenly, the conductive cross section and conductivity of each part of the material are required to be the same;
②The resistance of the material itself is quite small, and the working current is quite large to achieve the required electric heating power The power transmission electrode 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 benefit of resistance furnace is his shortcoming. 
box type resistance furnace
    Most box-type resistance furnaces are indirect heating resistance furnaces, which are equipped with a resistor body specially used to realize 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. Commonly used power supply voltage is 220 volts or 380 volts, and an intermediate transformer with adjustable voltage is configured if necessary.

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