Safe melting method and characteristics of cast iron

The methods of melting cast iron are divided into cupola melting, induction furnace melting, electric arc furnace melting, reverberatory furnace melting and the combination of some methods, such as cupola-electric arc furnace, cupola-induction furnace double method and so on.

1. Cupola melting method

(1) dome structure

The basic structure of cupola is shown in figure 1. The furnace body, bellows and flue are welded with steel plates. Refractory bricks are usually built inside the furnace shaft to resist the high temperature caused by coke combustion. In order to store molten iron, most furnace tops are equipped with forehearth.

② cupola melting principle

In the process of smelting, the lower part of the furnace shaft is filled with coke, which is called bottom coke. At the top of the bottom coke, lots of iron (pig iron, scrap steel, recycled materials, ferroalloys, etc. ), coke and flux (limestone, fluorite, etc. ) installed alternately. Through injection, the coke at the bottom burns strongly, and the generated high-temperature furnace gas rises along the height direction of the furnace body, so that the upper iron material is melted.

(3) Advantages and disadvantages of cupola melting and its application.

Cupola is the most widely used cast iron smelting equipment. It uses coke as fuel, and the heat generated by coke combustion is directly used to melt the burden and raise the temperature of molten iron, saving energy compared with electric arc furnaces and other furnaces. Moreover, the equipment is relatively simple and can be used by large and small factories. However, cupola also has some disadvantages, mainly because molten iron is in direct contact with coke, so the process of increasing carbon and sulfur in molten iron will occur during smelting.

Cupola-electric arc furnace duplex melting method or cupola-induction furnace duplex melting method is adopted to make full use of the advantages of high melting efficiency of cupola, strong overheating ability of electric arc furnace and induction furnace and easy control of chemical composition.

2. Induction furnace smelting

Structure and working principle of (1) induction furnace

Induction furnace is a furnace that uses the heat generated by current induction to heat and melt iron. The structure of the furnace can be divided into two types: cored and coreless. In the coreless induction furnace, the iron material in the crucible generates induced current under the action of alternating magnetic field, and thus generates heat, which melts itself and heats the molten iron process. In the cored induction furnace, molten iron melted by other furnaces (such as cupola) needs to be added. The alternating magnetic field generated in the annular iron core keeps the molten iron in the groove, and the molten iron in the groove and the molten pool above it is used to heat all the molten iron. Coreless induction furnace has the ability to melt solid charge, while cored induction furnace can only overheat molten iron, but in terms of electric energy consumption of overheated molten iron, cored induction furnace is more economical.

1-induction coil 2-yoke 3-refractory 4-molten iron 5-slag

(2) Advantages and disadvantages of induction furnace melting and its application.

Compared with cupola melting, induction furnace melting has the advantages of not increasing carbon and sulfur during melting, and covering molten iron with slag during melting, which can prevent the oxidation of silicon, manganese and alloy elements in molten iron to some extent and reduce the absorption of gas from furnace gas, thus making molten iron more pure. The disadvantage of this smelting method is that it consumes a lot of electric energy.

The induction furnace is suitable for melting high-quality gray cast iron, alloy cast iron, nodular cast iron and vermicular cast iron. Coreless induction furnace can directly melt solid burden, which is convenient to start and stop, and is suitable for intermittent production conditions. The cored induction furnace is inconvenient to start and stop, and is suitable for continuous production. This furnace has low thermal efficiency of melting solid charge and high thermal efficiency of superheated molten iron, and is suitable for cupola. At present, these two kinds of induction furnaces have been applied in cast iron production.

3. Electric arc furnace smelting

Structure and working principle of 1 electric arc furnace

Electric arc furnace smelting is to use the heat generated by the arc between graphite electrode and molten iron to melt molten iron and overheat it. Three-phase arc furnace is widely used in production. In the process of electric arc furnace smelting, after the iron material is melted, the smelting operation of further heating and adjusting the chemical composition is carried out under the condition that the slag covers the molten iron. According to the properties of slag and lining refractories, EAF can be divided into two types: acidic and alkaline. Alkaline arc furnace has the ability of desulfurization and dephosphorization.

(2) Advantages and disadvantages of EAF smelting and its application.

The advantage of electric arc furnace smelting is its strong ability to melt solid charge, which can overheat molten iron and adjust its chemical composition under the condition of slag coverage, so it can avoid the inhalation of molten iron and the oxidation of elements to some extent. This creates favorable conditions for melting low-carbon cast iron and alloy cast iron. The disadvantage of electric arc furnace is that it consumes a lot of energy and is not as economical as cupola from the melting point of view, so the double melting method of foaming at the mouth and electric arc furnace is often used in cast iron production. Because of the poor quenching and heating resistance of the lining of alkaline electric arc furnace, the lining life is short under intermittent smelting conditions, which leads to high smelting cost, so acid electric arc furnace is often used in combination with cupola.