Working Principle of Vacuum Degassing in Vacuum Electric Arc Furnaces

A vacuum electric arc furnace is an industrial furnace that leverages the principles of vacuum arc smelting to refine metals. Operating within a vacuum environment, this furnace utilizes a high-current, low-voltage short arc for its smelting process.

Fundamentals of Vacuum Arc Discharge

The vacuum arc furnace operates on the principle of gas arc discharge. In this setup, the voltage between electrodes is notably low, yet the current passing through the gas is substantial, resulting in an extremely high temperature within the arc zone, approximately 5000K. This large current density originates from thermionic emission and self-emission of electrons. Specifically, a layer of positive ions forms around the negative electrode, creating a strong electric field that prompts the cathode to automatically emit electrons. These electrons collide with gas molecules between the electrodes, ionizing them and generating additional positive ions and secondary electrons. Under the influence of the electric field, these charged particles collide with the cathode and anode, respectively, producing intense heat. The cathode's temperature remains lower than the anode's because a portion of the energy is expended in electron emission. Additionally, the recombination of some positive ions and electrons contributes to the high temperatures observed.

Operational Parameters of Vacuum Arc Smelting

Vacuum arc smelting typically employs an arc voltage ranging from 22 to 65 volts, with a corresponding arc length of 20 to 50 millimeters (the latter applicable for larger ingots). This short arc operation is characteristic of vacuum electric arc furnaces, ensuring efficient and controlled smelting processes.

Historical Development and Industrial Applications

Since the successful platinum wire smelting experiment in 1839, it took over a century for researchers to begin exploring the smelting of refractory metals. In 1953, vacuum electric arc furnaces were introduced into industrial production. By 1956, the United States and several European countries were still utilizing non-expendable furnaces for titanium smelting, while 1955 marked the advent of expendable furnaces for steel production. Around 1960, the weight of steel ingots produced by consumable furnaces exceeded 30 tons, signaling a significant advancement in the field. Presently, the vacuum consumable furnaces manufactured by Kangsai Company exemplify this developmental trajectory, featuring shared main power supplies, vacuum systems, and automatic control systems between two furnaces to enhance production efficiency and equipment utilization.

Vacuum Heat Treatment Benefits

Heat treating workpieces or materials in a vacuum environment offers numerous advantages. It extends the service life of tools and molds by preventing oxidation and decarburization, resulting in a bright surface finish, minimal deformation, energy savings, and pollution-free operations. Furthermore, vacuum heat treatment can alter the mechanical and metallurgical properties of materials, enhancing their overall performance.

Advantages of Vacuum Melting Furnaces

Vacuum melting furnaces are primarily employed for smelting reactive and insoluble metals, hard alloys, magnetic materials, and stainless steel. Operating under low pressure (decompression) conditions, these furnaces offer several benefits:

1. Gas Removal: Vacuum environments facilitate the removal of adsorbed gases and promote significant shrinkage during the later stages of smelting.
2. Impurity Purification: Vacuum helps eliminate impurities such as silicon, aluminum, magnesium, calcium, and their oxides, purifying the material.
3. Enhanced Wettability: Vacuum improves the wettability of liquid phase smelting, aiding in shrinkage during the smelting process and refining the alloy's structure.
4. Inert Environment: When other primary or inert gases are unsuitable, or when materials are prone to decarburization and carburization, a vacuum melting furnace provides an ideal solution.
5. Reduced Pollution: Vacuum smelting minimizes product contamination by harmful atmospheric components like water, oxygen, and nitrogen. For instance, achieving a dew point of -40°C in electrolytic hydrogen is challenging, whereas vacuum smelting at a few hundred Pa equivalently achieves this level of purity.

In summary, vacuum electric arc furnaces offer a sophisticated and efficient means of smelting metals, leveraging vacuum arc discharge principles to achieve superior material properties and production outcomes.

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