Working Principle and Characteristics of Vacuum Arc Furnace

Working Principle and Characteristics of Vacuum Arc Furnace

Vacuum Arc Furnace is a type of vacuum metallurgical smelting equipment. The furnace body is a closed container, which is evacuated or filled with inert gas. After the electrodes introduced from the top of the furnace and the water-cooled crystallizer at the bottom of the furnace are energized and arc is generated, the metal or alloy is melted by the heat of the arc, and solidified in the crystallizer.

 The electrode is made of the smelted metal, which is called a "consumable electrode vacuum arc furnace". If the electrode is made of non-melting material, it is called a "non-consumable electrode vacuum arc furnace". The product has few impurities, low gas content, good ingot structure, and excellent mechanical and physical properties. It is suitable for smelting high melting point metals, active metals, special steels and metals.

The world's first vacuum arc furnace was born in the United States in 1950. The vacuum consumable arc furnace is an electric furnace that uses the energy of the arc to melt metal in a vacuum chamber. The vacuum consumable arc furnace is mainly used to melt active metals and refractory metals such as titanium, zirconium, and molybdenum. It is also used to melt heat-resistant steel, stainless steel, tool steel, and bearing steel. In the early 1950s, it was used to remelt high-temperature alloys and showed good superiority. It is considered to be one of the important methods for remelting high-temperature alloys and special steels.



1. Working Principle of Vacuum Consumable Arc Furnace



During the formation of molten droplets at the lower end of the electrode and the process of molten droplets falling, certain physical and chemical reactions occur, which can remove part of the gas impurities. The process feature of the vacuum consumable arc furnace is that the smelting is carried out in a water-cooled copper crystallizer, which overcomes the harm of metal contamination caused by the interaction between metal and refractory materials. At the same time, under a highly water-cooled state, the molten steel is condensed and crystallized to obtain a uniformly arranged, shrinkage-free and dense ingot. The smelting process of the vacuum consumable arc furnace is carried out under the arc effect of DC low voltage and high current.



First, an arc is ignited between the lower end of the consumable electrode and the crystallizer, and an arc plasma zone is formed between the lower end of the consumable electrode and the molten pool. This zone has a high temperature, which can make the consumable electrode part melted here first. Then some non-metallic inclusions in the consumable electrode, such as oxides and nitrides, are dissociated or reduced by carbon under vacuum and high temperature conditions and removed to achieve the purpose of further purification. Since the vacuum consumable arc furnace process can remove gas and non-metallic inclusions, as well as some harmful impurities with low melting points, the cold and hot processing functions, plasticity and mechanical functions, and physical functions are significantly improved. In particular, the difference in longitudinal and transverse functions is improved, which is of great significance to ensure the stability, consistency and reliability of material functions.



2. Electrical Equipment of Vacuum Consumable Arc Furnace

In order to obtain high-quality ingots, the smelting power is required to be stable during the smelting process, and the power supply requires a DC current with constant current characteristics.



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

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

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

(4) It allows overload of 10% and operation for 1 minute.



In summary, the vacuum arc furnace has the following characteristics:

(1) Under vacuum conditions, there is no slag or other materials between the consumable electrode and the ingot, so the smelted material is not contaminated during remelting.

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

(3) When the vacuum arc furnace is smelting, the non-metallic inclusions in the smelted metal have a light specific gravity and always float on the Z of the molten metal, which makes the internal structure of the ingot very pure.

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

(5) Under vacuum conditions, a large amount of alloying agent can be added, so high-grade alloy steel can be smelted.

(6) Short tapping time to tapping time, thus improving equipment productivity and reducing production costs.



Currently, the capacity of vacuum arc furnaces ranges from 15 to 200 t. The processes of heating, degassing, slag treatment and alloy adjustment are all carried out continuously under vacuum conditions. The fully enclosed processing station combined with a steam ejection vacuum pump provides clean smelting equipment that does not pollute the surrounding environment.