The process of vacuum arc remelting (VAR) is a secondary melting process used to produce metal ingots with high chemical and mechanical homogeneity for demanding applications. It is a refining process that is used when cleanliness and homogeneity requirements are beyond the capability of conventional production and casting processes.
The VAR process begins with a starting electrode, which is cast from a prior production process. The electrode is gradually remelted under vacuum conditions with heat supplied via an electric arc. The bottom of the electrode gradually melts and drips down to a molten pool, which then solidifies to form the final ingot.
The VAR process has three main parts: start-up, steady state, and hot top. During start-up, the electrode is gradually melted. In the steady state, the remelting process continues with a stable arc and a constant melt rate. The hot top refers to the top portion of the ingot, which is kept molten to prevent solidification and ensure a uniform ingot structure.
The VAR process offers several advantages. Smelting under vacuum eliminates contamination by outside air and reduces gas and low-melting point harmful metal impurities in the steel and alloys, resulting in improved purity. It can also effectively reduce the content of hydrogen, lead, bismuth, silver, and other impurities in the metal. The process allows for stable chemical composition control of the alloy, and the low oxygen partial pressure in the smelting chamber prevents burning of active elements such as aluminum and titanium.
Additionally, VAR allows for the remelting of refractory metals and their alloys due to the high temperature in the arc zone. The slag-free and water-cooled copper mold operation eliminates or reduces contamination of the alloy by external inclusions. The sequential solidification and rapid cooling during the process can remove non-metallic inclusions and improve the purity of the remelted metal. By controlling the solidification and crystallization process, the VAR process can produce high-quality ingots with low segregation and high density.
It is worth noting that the surface of the remelted ingot may be rough and porous, and it requires peeling before further processing. The remelting process does not include desulfurization, so a low sulfur content is required in the consumable electrode. Additionally, the atmosphere and pressure in the melting chamber can be controlled during the VAR process.
Overall, vacuum arc remelting is a critical process used to refine and purify metals and alloys, enhancing their strength, fatigue resistance, and overall quality. It is widely used in industries such as aerospace, energy, and nuclear, where high-performance materials are required.
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