November 1, 2025
Operating Principles and Features of the Vacuum Consumable Arc Furnace (VAR)
The world’s first Vacuum Consumable Arc Furnace (VAR) was introduced in the United States in 1950. This type of electric furnace utilizes electric arc energy to melt metals within a vacuum chamber. It is primarily employed for melting reactive and refractory metals such as titanium, zirconium, and molybdenum, as well as for producing heat-resistant steels, stainless steels, tool steels, and bearing steels. Since its early application in the 1950s for remelting superalloys, the VAR process has demonstrated outstanding performance, establishing itself as a critical method for remelting high-temperature alloys and specialty steels.
1. Operating Principle of the VAR Furnace
During operation, molten droplets form at the lower end of a consumable electrode and fall into a molten pool. Throughout this droplet formation and transfer process, specific physical and chemical reactions occur, enabling the removal of certain gaseous impurities. A key feature of VAR is that melting takes place within a water-cooled copper crucible (crystallizer). This design eliminates contamination that can arise from interactions between the molten metal and refractory linings. Simultaneously, the molten metal solidifies under intense water cooling, resulting in a uniform, dense ingot free from shrinkage porosity.
The VAR process is conducted using a direct current (DC) arc operating at low voltage and high current. An arc is initially struck between the tip of the consumable electrode and the base of the crucible, creating a high-temperature arc plasma zone between the electrode and the molten pool. This extreme heat melts the electrode tip. Non-metallic inclusions within the electrode, such as oxides and nitrides, are either dissociated or reduced under the combined effect of vacuum and high temperature, achieving further purification.
Since the VAR process effectively removes gases, non-metallic inclusions, and certain low-melting-point harmful impurities, the resulting materials exhibit significantly improved hot and cold workability, plasticity, mechanical properties, and physical characteristics. Notably, the anisotropy (difference between longitudinal and transverse properties) is reduced, which is crucial for ensuring the stability, consistency, and reliability of material performance.
2. Key Characteristics of the VAR Process
In summary, the Vacuum Consumable Arc Furnace offers the following advantages:
(1) High-Purity Melting: The process occurs under vacuum with no slag or foreign materials between the electrode and the solidifying ingot, preventing contamination during remelting.
(2) Effective Degassing: The molten metal is directly exposed to vacuum, enabling excellent removal of gases such as hydrogen, nitrogen, and oxygen.
(3) Inclusion Control: Non-metallic inclusions, due to their lower density, tend to float to the top of the molten pool, contributing to a very pure internal ingot structure.
(4) Rapid Solidification: The use of a water-cooled copper crucible ensures very fast cooling rates, leading to a uniform ingot structure with minimal segregation.
(5) Alloying Flexibility: The vacuum environment allows for the addition of significant amounts of alloying elements, facilitating the production of high-grade alloy steels.
(6) Enhanced Productivity: Short tapping times contribute to higher equipment productivity and reduced production costs.
Currently, VAR furnaces are available with capacities ranging from 15 to 200 tonnes. Processes such as heating, degassing, and alloy adjustment are conducted continuously under vacuum. The fully enclosed design, often coupled with steam ejector vacuum pumps, provides a clean melting operation with no environmental pollution.
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