Vacuum consumable electrode arc furnaces are a key technology in the production of high-purity alloys, especially for materials like titanium, active metals, and refractory metals. These furnaces operate under vacuum conditions, allowing for precise control over the melting process. Unlike non-consumable arc furnaces, which use electrodes that remain intact during operation, consumable electrode arc furnaces utilize an electrode that melts completely during the process. This method is widely used in industrial settings for smelting superalloys such as iron-based and nickel-based materials.
The system includes several essential components: the furnace body, power supply, vacuum system, control system, optical monitoring, and water-cooling units. The furnace itself consists of a shell, electrodes, electrode rods, lifting mechanisms, and a crucible. Power is typically provided through a direct current (DC) system. Historically, DC generators were used to supply power, but modern systems now often rely on thyristor rectifiers. Due to the low voltage (20–28 V), a step-down transformer is necessary before the rectifier to ensure safe and efficient operation.
This type of furnace offers numerous advantages in metal purification. It allows for the production of large ingots from high-melting-point metals at a lower cost compared to other methods like electron beam melting or high-vacuum sintering. During the process, impurities rise to the surface of the molten bath and can be removed. Additionally, the high temperature and vacuum environment help decompose oxides and nitrides, while volatile impurities are pumped out. As a result, the final ingot has excellent purity and a uniform microstructure. The gradual solidification from bottom to top minimizes element segregation and reduces shrinkage, leading to improved mechanical properties such as tensile strength, creep resistance, and fatigue performance. However, one drawback is the difficulty in precisely controlling the alloy composition.
Another type of vacuum furnace, the vacuum arc furnace, is commonly used for smelting copper and its alloys. This furnace features a spherical shape and uses the molten material itself as the crucible. The outer shell is cooled by water, forming a solidified shell known as a "citrus worm." The furnace includes a mold and a charging system, with the molten metal being poured into the mold. Its structure is shown in Figure 4-8.
Flame reverberatory furnaces, which traditionally used coke, coal gas, natural gas, or fuel oil as energy sources, have been largely replaced due to environmental concerns and technological advancements. These furnaces were once widely used for smelting aluminum and copper alloys, with capacities ranging from hundreds of kilograms to tens of tons. Today, they have been largely substituted by oxygen-fueled or gas-fired systems. For example, melting reverberatory furnaces are still used for processing aluminum ingots and scrap materials, often paired with static furnaces for further refining and degassing. The structure of a circular reverberatory furnace is illustrated in Figure 4-9.
Copper smelting reverberatory furnaces are primarily used for mixed smelting, processing materials such as electrolytic copper and wire scraps. To enhance purity, oxidation-reduction processes may be applied. The furnace lining must withstand harsh conditions, and special refractory materials are used for the bath, walls, and roof. Cooling systems are also implemented around the charging port to prevent damage to the lining. Exhaust gases are directed through flues, and waste heat recovery systems are often installed in larger furnaces.
Combustion boiler vortex furnaces are designed for small-batch smelting of various non-ferrous alloys. They have evolved from traditional coke or fuel-fired models to more advanced, environmentally friendly systems. These furnaces include fixed, tiltable, and holding types, each suited for different applications. Their development has focused on improving working conditions and reducing emissions, making them more suitable for modern foundries.
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