Electric arc furnace melting process
1. Type ratio of smelting raw materials
The raw materials of the electric arc furnace can be blast furnace molten iron, iron slag, magnetic separation iron slag, slag steel, steel washing sand, scrap steel, pig iron, etc. The main purpose of smelting is to digest the materials that the induction melting furnace cannot process. The quality of various furnaces is good or bad. It directly affects the smelting cycle, smelting cost, and the yield of molten iron. Therefore, there are the following most basic requirements for various charge materials:
(1) The chemical composition of various charge materials should be clear and stable.
(2) All kinds of furnace materials must not be mixed with sealed containers, flammable, explosive and wet dripping materials to ensure the safety of feeding and melting.
(3) All kinds of charge should be clean, less rust, and free of debris, otherwise it will reduce the conductivity of the charge, prolong the melting time, or even break the electrode. Therefore, there is a very critical link in the proportion and addition of materials.
(4) In terms of the overall dimensions of various scrap steel and slag steel, the cross-sectional area should not exceed 280cm*280cm. It will affect the feeding time and the difficulty of feeding. Large irregular and nearly circular scraps will easily collapse and break during smelting. electrode.
(5) Batching is an indispensable important part of electric arc furnace smelting. Whether the batching is reasonable enough that the operator can perform the smelting operation normally in accordance with the process requirements. Reasonable ingredients can shorten the smelting time. Pay attention to the ingredients: First, the size of the charge must be matched in proportion to achieve the purpose of good installation and quickening. Second, all kinds of charge are used in combination according to the quality requirements of molten iron and the smelting method. The third is that the ingredients must meet the process requirements.
(6) Regarding the requirements of the material matching into the column furnace: the bottom is dense, the top is loose, the middle is high, the surrounding is low, and there is no large block at the furnace door, so that the well can be penetrated quickly during smelting and no bridges are built.
2. Melting period
In the electric arc furnace smelting process, the period from the start of electricity until the charge is completely melted is called the melting period. The melting period accounts for 3/4 of the entire smelting process. The task of the melting period is to quickly melt and heat up the charge with the least power consumption while ensuring the life of the furnace. And choose the slag in the melting period in order to stabilize the good submerged arc effect of the electric arc furnace, which is one of the necessary conditions for improving the service life of the furnace. It is one of the necessary conditions to increase the service life of the furnace. Because the original molten iron is smelted in an electric arc furnace, it is in an alkaline smelting atmosphere. Even if no lime is added during the melting period, the foam slag formation effect in the furnace is better, and the slag is also slightly alkaline (electric arc furnace refractories). The characteristics are also alkaline). Therefore, slagging without lime has little effect on the service life of the furnace. During the melting period, the arc furnace uses arcing materials as the main material, and oxygen is used as an auxiliary to boost the material in the cold zone around the furnace wall to shorten the melting period.
3. Recovery period
The period from the end of melting to tapping is the reduction period. During the reduction period, add an appropriate amount of silicon carbide (raw material 4%-5%) to stop blowing oxygen, and the furnace door is sealed, so that a good reducing atmosphere is formed in the furnace through low voltage and high current. Long-arc stirring is formed to deoxidize and reduce the oxides in the slag on the surface to increase the yield of the alloy. Generally, the reduction period is controlled between 10-15 minutes, and finally the required temperature is controlled to release the slag, and the entire smelting process is completed.
4. Melting cost
The cost of smelting raw molten iron in electric arc furnaces directly affects the utilization rate of electric arc furnaces. Although the selection of raw materials for electric arc furnaces is wider than that of induction melting furnaces, the cost of iron smelting must be integrated with low-cost methods. Price analysis of induction melting furnace and electric arc furnace, and raw materials; as long as the electric arc furnace is properly matched with the charge ratio, the total cost will be significantly lower than that of induction melting furnace. According to the current electricity price in Shandong Province, it is estimated that each ton of molten iron can be reduced by 130 yuan about.
From the above table, it can be seen that the comprehensive power consumption of duplex smelting can save 230Kwh of electricity, reaching 37% compared with the induction melting furnace smelting ton of molten iron. The green energy-saving effect of this process is very outstanding.
5. Lining service life
According to the characteristics of electric arc furnace smelting, the furnace age can reach long furnace age. The specific analysis is as follows:
(1) The effect of high-temperature heat: the furnace lining is generally at a high temperature and thermal state above 1600℃, and it has to withstand the rapid cooling and heat that will cause great damage to the furnace lining; while the electric arc furnace smelting molten iron, the temperature is generally controlled at about 1500℃, so The damage of high temperature to the furnace lining is basically negligible. Due to the continuous matching of molten iron to form a continuous smelting and at the same time to reach 1550 degrees of oxidation oxygen blowing temperature out of the furnace, the service life of the furnace lining can be greatly improved.
(2) The influence of chemical composition erosion: The electric arc furnace refractories are alkaline refractory materials. The ratio of raw materials is that the slag steel is accompanied by a large amount of alkaline slag, which makes the overall charge of the furnace weakly alkaline. The wall erosion is also small. The alkaline smelting environment is the basic condition for improving the furnace life, but the slag is too thick, which will locally form a high temperature zone, which will reduce the service life of the furnace lining.
(3) The radiation of the arc is reflected by the influence of the foam slag submerged arc during smelting, which can shorten the smelting cycle of the electric furnace. At the same time, the good submerged arc effect can reduce the heat radiation to the furnace lining, thereby increasing the furnace life.
(4) Mechanical collision and vibration will also affect the service life of the furnace. Reasonable feeding methods will also increase the service life of the furnace. The charging and distributing are unreasonable, or the material tank is raised too high, and the furnace bottom slope may bear large and heavy materials. Collision, vibration and impact form potholes, all of which reduce the life of the furnace lining. In addition, according to the electric arc furnace wall is a hot zone, the charging can spread the material to these three points, which will also increase the service life of the furnace lining.
(5) The oxygen blowing method will also affect the service life of the furnace. Oxygen acts as an auxiliary arc-assisted fuel in the electric furnace smelting. Generally, the two sides of the furnace wall and the furnace door are the cold zone, and the electrode is used to send the chemical material. Lengthened and reasonable oxygen blowing techniques can shorten the smelting cycle and increase the furnace life (according to different material conditions, large blocks of materials are selected for blowing, and the oxygen flame is not blown against the furnace bottom and furnace wall as much as possible), and blow at the same point The oxygen time should not be too long to avoid high local temperature near the furnace wall and erosion of the furnace wall.