The fundamental requirements for alloy smelting can be summarized into five aspects: high quality, high yield, low consumption, long service life, and operational convenience. Its core task is to meet technical specifications such as molten metal temperature and composition. In modern metallurgical production, molten metal pretreatment and secondary refining are widely adopted smelting technologies for producing high-quality castings.
(1) Cast Iron Smelting
Cupola furnaces are traditional cast iron smelting equipment, known for their high production efficiency and low cost. However, cupola smelting generates significant exhaust emissions, which can easily pollute the surrounding atmosphere. Additionally, the composition of molten iron tends to fluctuate and is difficult to control precisely, making it unsuitable for smelting alloy cast iron. The technological development direction of cupola smelting is toward larger scale, intelligence, and continuous smelting, with computer control and monitoring to improve the stability of molten iron composition.
Induction furnaces, on the other hand, produce fewer exhaust emissions and have a smaller environmental impact. They allow for easier adjustment and control of molten iron temperature and chemical composition. Currently, induction furnaces for cast iron smelting include power frequency induction furnaces, medium frequency induction furnaces, and variable frequency induction furnaces. Power frequency induction furnaces are increasingly less used due to their low efficiency and operational complexity. Variable frequency induction furnaces, with their energy-saving, low-consumption, and high productivity advantages, are gaining wider application in cast iron production.
The cupola-induction furnace duplex smelting process is an ideal method for cast iron smelting. The cupola furnace supplies molten iron to the induction furnace, which then heats and adjusts the chemical composition of the molten iron. This approach improves the metallurgical quality of the molten iron while reducing costs. Additionally, the duplex process helps balance the supply and demand of molten iron, maximizes the melting capacity of the cupola furnace, and facilitates production organization.
(2) Cast Steel Smelting
Cast steel is typically smelted using electric arc furnaces and medium frequency induction furnaces. Electric arc furnaces generally employ oxidation-reduction methods for cast steel smelting. Medium frequency induction furnaces are simple to operate and can be used to smelt carbon steel, low-alloy steel, various high-alloy steels, and nickel-based alloys. Regardless of whether an electric arc furnace or a medium frequency induction furnace is used, deoxidation is an essential final step in cast steel smelting. Final deoxidation is typically performed in the ladle during tapping, with aluminum being the widely used final deoxidizer. Aluminum-calcium composite deoxidation can also be employed to enhance deoxidation effectiveness.
As quality requirements for cast steel components continue to rise, an increasing number of high-end castings are produced using secondary refining technologies. These include vacuum decarburization, oxygen blowing decarburization, powder injection desulfurization, and argon blowing. Refining technologies such as electroslag melting, argon stirring, argon-oxygen decarburization (AOD), and vacuum oxygen decarburization (VOD) can reduce alloy addition requirements, improve the purity of molten steel, enhance the strength and toughness of castings, and lower casting rejection rates.
(3) Aluminum Alloy Smelting
If the aluminum alloy smelting process is not strictly controlled, casting defects such as pinholes, oxide inclusions, and shrinkage porosity are likely to occur. Energy-saving technologies and methods for aluminum alloy smelting include furnace structure design, permanent magnet stirring technology, high-temperature air combustion technology, oxygen-enriched combustion technology, isothermal smelting technology, as well as the use of new energy-saving lining materials, waste heat recovery, and utilization.
In aluminum alloy smelting, traditional chloride-based refining processes using chlorides such as chlorine salts and hexachloroethane are gradually being phased out due to their environmental pollution and harmful effects on human health. Currently, inert gases such as argon and nitrogen are mainly used for refining.
