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The advantage of vacuum smelting

The advantage of vacuum smelting

Vacuum smelting is carried out under ambient conditions of less than 1.01 x 105 Pa, and is generally smelted in an environment of 1000 to 0.1 Pa. In this environment, the gas molecules are scarce, it is difficult to dissolve the gas into the metal, the molten metal casting does not produce pores; in the vacuum state, the oxidation is also rare, the molten high-temperature metal does not oxidize; under vacuum, the metal is produced. The melting and boiling temperature is lowered, which is conducive to energy saving and degassing. The characteristics of vacuum smelting can be summarized as follows.
(1) The low gas pressure in a vacuum environment changes the physical process of smelting and facilitates the escape
gas
Under vacuum conditions, the physical properties of the material change and the boiling point decreases. For example, water has a boiling point of 100 ° C at a normal pressure of 1.01 X 105 Pa) and only 97 ° C at a condition of 7.8 X 104 Pa, which varies with the degree of vacuum. The same is true for metals. Zinc boils at 906*0 under normal pressure and boils at more than 800 degrees under vacuum; lead has a boiling point of 1740 ° C at atmospheric pressure and evaporates at 1000 ° C in a vacuum. That is to say, under vacuum conditions, the boiling point of the metal is lowered, which is favorable for vaporization, evaporation and degassing of the metal. Under vacuum conditions, when the metal is melted, the gas originally contained in the metal is released, and the molten metal is quickly separated. Pumped away by a vacuum pump.
The metal is refined under vacuum without forming pores or intermediate inclusions. The vapor formed by a metal or an oxide under vacuum has a small molecular diameter and good dispersibility. In a vacuum, a polyatomic molecule tends to have a smaller atomic molecule, and the formed gas molecule is small, and the particle size is generally 10-. 10m, will not affect the quality of the metal.
(2) In a vacuum environment, the gas is thin, so that the chemical reaction in the smelting process changes, and few gases participate in the reaction.
The chemical reaction of metals in vacuum smelting is complicated. There is a redox reaction, the metal oxide is reduced to a solid or liquid metal, and may also be reduced to a gaseous metal; there is a decomposition reaction, the metal compound is thermally decomposed, and the gas is evolved; there is a synthesis reaction, and the vacuum slag remelting slag reacts with the metal inclusions. A new compound is formed to remove impurities such as sulfur and phosphorus from the metal.
Oxidation does not occur when the metal is heated to a very high temperature in a vacuum, and it is rarely oxidized whether the metal is solid or liquid.
Vacuum conditions can speed up the chemical reaction in the smelting process; reduce the reaction temperature, promote the development of the smelting process, and improve the quality of metallurgical products.
(3) Smelting in a vacuum environment to reduce environmental pollution
The vacuum smelting process basically has no waste water, waste gas and waste residue, and it has little pollution to the environment. Moreover, the vacuum smelting process is short, the land occupation is small, the consumption is small, the benefit is good, and the metal recovery rate is high, which can solve some problems that cannot be solved by atmospheric pressure metallurgy.

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Post time: May-15-2019