Smelting methods for silicon calcium alloy
Silicon calcium alloy is a binary alloy of silicon and calcium containing little iron and is mainly used for deoxidation of high temperature alloys. With the development of continuous casting and ladle refining outside the furnace, the consumption of silicon-calcium alloys is rapidly increasing. There are two production methods for silicon calcium alloy: one-step and two-step. One-step method is in an electric furnace, with carbon reduction of silica and lime to produce calcium silicon alloy; two-step method is first in an electric furnace to produce calcium carbide (or high-carbon ferrosilicon), and then with calcium carbide plus silica and coke (or with high-carbon ferrosilicon plus lime) in another electric furnace to produce calcium silicon alloy.
The one-step method is subdivided into the mixed charging method and the layered charging method.
The mixed charging method involves adding silica, lime and coke together to the reduction furnace. Carbon is used to reduce CaO and SiO2 simultaneously to the calcium silica alloy, the reaction is: CaO + 3SiO + 7c = CaSi2 + Si + 7CO
The disadvantage of this method is that the contact between calcium oxide and silica produces a low melting point silicate, and it is difficult to reduce silicon and calcium from the silicate, based on this situation the layered charging method was created. The aim is to reduce the contact between calcium oxide and silica in order to reduce the Cao-SiO2 formation reaction.
The layered charging method involves first adding lime and coke (the amount added is based on the reaction to produce calcium carbide) near the electrode, melting it to allow the CaO to produce as much CaC2 as possible then mixing the silica with the remaining carbon and adding it to the furnace to produce a calcium-silica alloy.
There are two methods, one is to produce lime and calcium carbide from lime and coke in one furnace and then crush the calcium carbide with coke and silica in another furnace to produce a calcium silicon alloy, the other is to produce high ferrosilicon silica in one furnace and then use the high ferrosilicon silica as a reducing agent to reduce calcium oxide in the furnace to produce a calcium silicon alloy. The calcium content of the alloy produced by this method is generally less than 20%, but calcium silicon alloy containing 30-32% calcium can also be produced.
