The object is heated at a high temperature generated by an electric arc. The arc is a gas discharge phenomenon between the two electrodes. The voltage of the arc is not high but the current is large, and its strong current is maintained by a large amount of ions evaporated on the electrode, so the arc is susceptible to the surrounding magnetic field. When an arc is formed between the electrodes, the temperature of the arc column can reach 3000 to 6000 K, which is suitable for high temperature melting of metals.
Arc heating has both direct and indirect arc heating. The arc current heated by the direct arc passes directly through the object to be heated, and the object to be heated must be an electrode or medium of the arc. The arc current heated by the indirect arc does not pass through the object to be heated, but is mainly heated by the heat radiated by the arc. The characteristics of arc heating are: high arc temperature and concentrated energy, and the surface power of the steelmaking arc furnace can reach 560-1200 kW/m2. However, the noise of the arc is large, and its volt-ampere characteristic is a negative resistance characteristic (falling characteristic). In order to keep the arc stable during arc heating, the instantaneous value of the circuit voltage is greater than the arcing voltage value when the arc current instantaneously crosses zero, and in order to limit the short circuit current, a resistor of a certain value must be connected in series in the power supply circuit.
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