Electric arc furnace(EAF) about the working principle

Electric arc furnace is a kind of arc discharge of gas. Gas arc discharge shows that the voltage between the electrodes is very low, but the current through the gas is very large, there is dazzling white light, and the arc zone temperature is very high (about 5000k). The huge current density comes from the thermionic emission of the cathode and the self-emission of electrons, that is, there is a layer of positive ions near the cathode to form a strong electric field, which makes the cathode automatically emit electrons.

 A large number of electrons collide with gaseous molecules between the electrodes to ionize them, generating a larger number of positive ions and secondary electrons. Under the action of an electric field, they impact the cathode and anode respectively, resulting in high temperature. The cathode uses part of the energy due to electron emission, so the temperature is lower than the anode. The interelectrode also generates high temperature due to the recombination of some positive ions and electrons. Electric arc furnaces are industrial furnaces that use this principle to smelt metals. Electric arc furnaces in a vacuum environment are vacuum arc furnaces. Vacuum arc smelting uses high current and low voltage, which is a short arc operation. Generally, the arc voltage is 22 ~ 65V, and the corresponding arc length is 20 ~ 50mm (the latter is a large ingot). 

Since the successful experiment of smelting platinum wire in 1839, people began to study the smelting of refractory metals for more than 100 years. The vacuum electric arc furnace was officially used in industry in 1953. Until 1956, the United States and many European countries were still using non-consumable furnaces to smelt titanium, and in 1955 they began to use consumable furnaces to make steel. Around 1960, the weight of ingots produced by consumable furnaces had reached more than 30 tons, and it began to take shape. The current development situation can be represented by the vacuum consumable furnace manufactured by the United States Consack Company. In order to improve productivity and equipment utilization, the two furnaces share a set of main power supply, vacuum system and automatic control system.