Consumable electrode arc melting, specifically referred to as Vacuum Arc Remelting (VAR), is a process that involves the use of a direct current (DC) power supply to generate an arc in a vacuum environment.
This arc is created between a consumable electrode and a water-cooled copper crucible, which serves as the anode.
The intense heat from the arc melts the electrode, forming a molten pool in the crucible.
This molten metal is then rapidly solidified and crystallized to form an ingot.
5 Key Steps Explained
1. Setup and Electrode Preparation
Before the process begins, the electrode to be melted is loaded into the furnace.
The electrode material varies depending on the type of metal being processed.
For specialty steels and superalloys, the electrode is typically cast in air or vacuum.
For reactive metals like titanium, the electrode is made from compacted sponge and/or scrap, or through a hearth melt process such as Plasma or Electron Beam.
2. Electrode Types
The electrodes used in the arc melting furnace are primarily of three types: carbon electrodes, graphite electrodes, and self-baking electrodes.
The choice of material (carbon or graphite) is based on their electrical conductivity, insolubility, infusibility, chemical inertness, mechanical strength, and resistance to thermal shock.
These electrodes can range from 18 cm to 27 cm in diameter, and the arc temperature can reach between 3,000 °C and 3,500 °C.
3. Furnace Configuration
The furnace consists of two major mechanical assemblies: the movable furnace head and the fixed melt station.
The movable furnace head supports the electrode through a ram assembly, which is controlled by a servo drive.
The electrode, acting as the cathode, is clamped to the lower extremity of the water-cooled ram.
The fixed melt station includes a removable copper crucible placed within a fixed stainless steel water jacket.
4. Melting Process
Once the electrode is secured and the furnace head is sealed, a vacuum is created inside the vessel.
The DC power supply is then activated, and the control system initiates a high-current arc between the consumable electrode (cathode) and the crucible base (anode).
This arc rapidly melts the electrode, forming a molten pool.
The continuous melting of the electrode feeds the pool, ensuring a steady supply of molten metal.
5. Solidification and Crystallization
The molten metal in the crucible is rapidly cooled and solidified due to the water-cooled copper crucible.
This rapid solidification helps in achieving a uniform crystalline structure and minimizes the possibility of impurities or defects in the final ingot.
This process is crucial for producing high-quality, pure metals and alloys, particularly for applications requiring high strength and resistance to corrosion or extreme temperatures.
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