Working principle and characteristics of VAR (Vacuum Consumable Arc Furnace)

The first vacuum consumable arc furnace in the world was born in the United States in 1950. Vacuum consumable electric arc furnace is a kind of electric arc furnace which uses the energy of electric arc to smelt metal in vacuum chamber. Vacuum consumable arc furnace is mainly used for smelting active metals and refractory metals such as titanium, zirconium and molybdenum, as well as heat-resistant steel, stainless steel, tool steel and bearing steel.

1. Working Principle of Vacuum Consumable Arc Furnace

In the process of forming and dropping droplets at the lower end of the electrode, there is a certain physical and chemical reaction, which can remove some gas impurities. The process characteristic of vacuum consumable arc furnace is melting in water-cooled copper mold, which overcomes the problem of metal contamination caused by the interaction between metal and refractory. At the same time, under the condition of high water cooling, the ingot with uniform structure, no shrinkage cavity and compact structure can be obtained by solidification crystallization. The melting process of vacuum consumable arc furnace is carried out under the action of DC low voltage and large current arc.

First of all, an arc is ignited between the lower end of the consumable electrode and the mold, and an arc plasma region is formed between the lower end of the consumable electrode and the molten pool. This region has a very high temperature, which can make the end of the consumable electrode melt down here first. Some non-metallic inclusions, such as oxides and nitrides, in the consumable electrode are dissociated or removed by carbon reduction under vacuum and high temperature conditions, so as to achieve the purpose 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 working properties, plastic and mechanical properties, and physical properties are significantly improved. In particular, the difference between the longitudinal and transverse properties is improved, which is of great significance to ensure the stability, consistency and reliability of material properties.

2. Electrical equipment of vacuum consumable arc furnace

In order to obtain high quality spindles, the smelting power is required to be stable in the smelting process, and the DC current with constant current characteristic is required for the power supply.

Vacuum arc furnace has the following characteristics:

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

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

(3) When smelting in vacuum arc furnace, the proportion of non-metallic inclusions in the melted metal is light, which always floats on the top of the molten metal, which leads to the very pure internal structure of spindle.

(4) As the spindle is cooled in a water-cooled copper crucible, its cooling speed is very fast, which leads to the uniform internal structure of the spindle without segregation. 

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

(6) The short time from tapping to tapping improves the equipment productivity and reduces the production cost.

At present, the capacity range of vacuum arc furnace is between 15-200 t. The processes of heating, degassing, slag treatment and alloy adjustment are carried out continuously in vacuum. The fully enclosed treatment station combined with the steam jet vacuum pump provides clean smelting equipment without pollution to the surrounding environment.