The arc melting process is a method of melting charged material, typically metal ore or scrap metal, using an electric arc. It involves the application of alternating current to an electrode inside a melting furnace. The heat generated by the arcing causes the residues on the metal base to melt.
In an arc melting furnace, the main component is an electric welder, which acts as a large transformer to convert high voltage into a low voltage and high current. The electric welder triggers the arc by creating an instantaneous short circuit between the positive and negative poles. The arc is a self-sustaining discharge phenomenon that maintains a relatively long arc stable combustion without the need for high voltage.
The arc melting furnace operates at extremely high temperatures, with a maximum temperature of 3000℃. It utilizes the arc, which is a common thermal plasma, to generate the necessary heat for melting the material. The furnace ensures a consistent melt process by controlling factors such as pool geometry and melt rate.
During the arc melting process, the electrode to be melted is loaded into the furnace. For specialty steels and superalloys, the electrode is previously cast in air or vacuum. For primary reactive metals like titanium, the electrode is fabricated from compacted sponge and/or scrap, or from a hearth melt process like Plasma or Electron Beam.
The vacuum vessel in which melting occurs consists of two major mechanical assemblies - the movable furnace head and the fixed melt station. The movable furnace head is the upper section of the vessel and contains an integral ram assembly connected to a servo drive. This assembly supports and controls the movement of the electrode. The water-cooled ram extends through a vacuum seal in the head, and the electrode clamps to its lower extremity, becoming the cathode of the arc melting operation.
The fixed melt station forms the lower half of the vacuum vessel and consists of a removable copper crucible placed into a fixed stainless steel water jacket. Once the electrode is clamped to the ram assembly, the ram lifts the electrode while the furnace head is lowered to create a vacuum seal on top of the crucible.
With a vacuum established, the DC power supply is activated and the control system strikes a high current arc between the consumable electrode (cathode -) and the crucible base (anode +). This quickly forms a molten pool of metal. The arc gap between the melting electrode and the metal pool is precisely maintained, and a controlled melt rate is established. The metal droplets falling through the arc gap are exposed to the vacuum environment and the extreme temperatures of the arc zone, leading to the removal of dissolved gases, vaporization of tramp elements, and improvement in oxide cleanliness.
The water-cooled crucible allows for directional solidification of the molten pool, preventing macro segregation and reducing micro segregation. This enhances the material properties of the solidified ingot. Towards the end of the process, the power is gradually reduced to provide a controlled hot top, maximizing the yield of useful product.
Overall, the arc melting process in the electric arc melting furnace enables the melting of charged material through the application of an electric arc, resulting in a controlled and efficient method of melting metals.
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