Vacuum consumable arc furnace of the working principle

An arc is an arc discharge of gas.  Gas arc discharge is characterized by a very low voltage between poles, but a very large current through the gas, with dazzling white light and a very high temperature in the arc region (about 5000K).  The huge current density comes from the emission of hot electrons from the cathode, as well as the self-emission of electrons, that is, there is a layer of positive ions near the cathode, forming a strong electric field, so that the cathode automatically emits electrons.  A large number of electrons collide with gaseous molecules between the poles to ionize them, producing more positive ions and secondary electrons. Under the action of electric field, they collide with cathode and anode respectively, and the result is high temperature.  The temperature of the cathode is lower than that of the anode because some energy is used in electron emission.  The high temperature also occurs between the poles due to the exothermic combination of some positive ions and electrons.  Electric arc furnace is the industrial furnace that smelts metal with this principle.  Electric arc furnace in vacuum environment is vacuum arc furnace.  Vacuum arc melting adopts high current and low voltage, which belongs to short arc operation.  The general arc voltage is 22 ~ 65V, and the corresponding arc length is 20 ~ 50mm (the latter is large ingot).  Since the success of the platinum wire smelting experiment in 1839, people began to study the smelting of refractory metals for more than one hundred years.  The vacuum arc furnace was officially used in industry in 1953.  Until 1956, titanium was smelted in non-consumable furnaces in the United States and many countries in Europe, and steel was smelted in consumable furnaces in 1955.  Around 1960, the weight of ingot produced by self-consumption furnace has reached more than 30 tons, and began to take shape.  The current development can be represented by the vacuum self-consumption furnace manufactured by the American company Kangsac.  In order to increase productivity and equipment utilization, the two furnaces share a main power supply, vacuum system and automatic control system.  

1. Operating principle of vacuum consumable arc furnace  

In the process of forming droplet and droplet falling at the lower end of the electrode, a certain physical and chemical reaction is generated, which can remove part of the gas impurities.  The process characteristic of vacuum consumable arc furnace is smelting in water-cooled copper crystallizer, so as to overcome the disadvantage of contamination of metal due to the interaction between metal and refractory materials.  At the same time, under the condition of high water cooling, the steel ingot with uniform arrangement, no shrinkage cavity and compact can be obtained by condensation and crystallization of molten steel.  The melting process of vacuum consumable arc furnace is carried out under the action of DC low voltage and high current arc.  

First of all, the lower end of the consumption electrode with the crystallizer between the arc, the lower end of the consumption electrode with the molten pool form an arc plasma area, the area has a very high temperature, can make the consumption of extreme part of the first here is melted down.  With some non-metallic inclusions in the consumable electrode, such as oxides and nitrous compounds, they disintegrate or are removed by carbon reduction under vacuum and high temperature conditions, reaching the intention of further purification.  Because the vacuum consumable arc furnace process can remove gas and non-metallic inclusions, as well as some harmful impurities with low melting point, the cold and hot processing functions, plasticity and mechanical functions, and physical functions have been significantly improved.  In particular, the difference between vertical and horizontal functions has been improved, which is extremely important to ensure the stability, consistency and reliability of data functions.  

2. Electrical equipment of vacuum consumable arc furnace  

In order to obtain high quality spindle, the smelting power is required to be stable, and the DC current with constant current characteristics is required for the power supply.  

(1) It has the characteristic of constant current within the operating voltage scale of 20-40V, and the no-load voltage is about 70V.  

(2) The current conditioning scale is 1:10.  

(3) When 10% of the silicon elements in each rectifier arm are damaged, the system will give a signal, but it can continue to operate at the rated current.  

(4) Allow 10% overload, operation for 1 minute.  

To sum up, vacuum arc furnace has the following characteristics:  

(1) In the vacuum state, there is no slag or other data between the consumable electrode and the spindle, so the data smelted during remelting will not be polluted.  

(2) vacuum arc furnace smelting, the smelted metal is directly exposed to vacuum, so the degassing effect is very good, can effectively remove hydrogen, nitrogen, oxygen and other gases.  

(3) In the vacuum arc furnace smelting, the non-metallic inclusions in the smelted metal have a light proportion and always float on the top of the molten metal, which leads to the very pure internal structure of the spindle.  

(4) Because the spindle is cooled in water-cooled copper crucible, the cooling speed is very fast, which leads to the uniform internal structure of the spindle and no segregation.  

(5) In the vacuum state, a large amount of alloying agent can be added, so high grade alloy steel can be smelted.  

(6) the short time from the steel to the steel, so improve the productivity of the equipment and reduce the production cost.