Process and advantages of electric arc furnace melting cast iron

At present, the domestic electric arc furnace smelting of high carbon wear-resistant steel castings has developed rapidly, but its application in smelting high-end cast iron refractory castings is less.

Electric arc furnace smelting process

1. Types and proportions of smelting raw materials

The raw materials of 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 smelting purpose is to digest the materials that cannot be processed by the intermediate frequency furnace. The quality of various furnaces directly affects the smelting cycle, smelting cost, and hot metal yield. Therefore, the following are the most basic requirements for various furnace materials:

(1) The chemical composition of various charges shall be clear and stable.

(2) All kinds of furnace materials shall not be mixed with sealed containers, flammable, explosive and wet dripping materials to ensure feeding safety and smelting safety.

(3) All kinds of furnace materials should be clean and free of rust and impurities, otherwise the conductivity of furnace materials will be reduced, the melting time will be prolonged, and even the electrode will be broken. Therefore, it is a key link in the aspect of proportioning and feeding.

(4) In terms of the overall dimensions of various scrap and slag steel, the cross-sectional area should not exceed 280cm * 280cm. If the cross-sectional area is too large, the feeding time and the difficulty of loading will be affected. Large irregular near circular scrap is easy to collapse and break the electrode during smelting.

(5) Batching is an indispensable part of electric arc furnace smelting. Whether the batching is reasonable and whether the operator can conduct smelting operation normally according to the process requirements. Reasonable burden can shorten smelting time. During batching, attention should be paid to: First, the size of furnace charge should be matched in proportion to achieve the purpose of easy loading and fast processing. Second, all kinds of furnace materials are used according to the quality requirements of molten iron and smelting methods. Third, the ingredients must meet the process requirements.

(6) The requirements for the materials to be mixed into the furnace are as follows: the lower part is dense, the upper part is loose, the middle part is high, the periphery is low, and there are no large pieces of materials at the furnace entrance, so that the well can be penetrated quickly without bridging during smelting.

2. Melting period:

In the electric arc furnace smelting process, the melting period is from the beginning of electricity to the time when the furnace burden is completely melted. The melting period takes up 3/4 of the time of the whole smelting process. The task of the melting period is to quickly melt and heat the furnace charge with the least power consumption on the premise of ensuring the furnace life. It is one of the necessary conditions to improve the service life of the electric arc furnace to select the slag in the melting period so as to stabilize the good submerged arc effect of the electric arc furnace. It is one of the necessary conditions to improve the service life of the furnace. Since molten iron is melted in the electric arc furnace under the alkaline melting atmosphere, even if lime is not added in the melting period, the formation effect of foam slag in the furnace is relatively good, and the slag is also slightly alkaline (the refractory characteristics of the electric arc furnace are also alkaline). Therefore, slagging without lime has little impact on the service life of the furnace. During the melting period, the arc melting material is mainly used in the arc furnace, and oxygen is used as an auxiliary to melt the materials in the cold zone around the furnace wall, so as to shorten the melting period.

3. Reduction period:

The period from the end of melting to tapping is the reduction period. In the reduction period, add an appropriate amount of silicon carbide (4% - 5% of raw materials) to stop blowing oxygen. The furnace door is sealed to form a good reduction atmosphere in the furnace. The long arc stirring is formed through low voltage and high current. The surface deoxidization reduces the oxides in the slag to improve the alloy yield. Generally, the reduction period is controlled within 10-15 minutes. Finally, the required temperature for slag discharge is controlled, That is, the whole smelting process is completed.

4. Smelting cost

The cost of molten iron smelting in the electric arc furnace directly affects the utilization rate of the electric arc furnace. Although the selection of raw materials for the electric arc furnace is wider than that for the intermediate frequency furnace, the low cost method must be selected based on its iron melting cost. Then, the price of the intermediate frequency furnace, the electric arc furnace and the raw materials should be analyzed; The total cost of electric arc furnace will be significantly lower than that of medium frequency furnace as long as the furnace burden ratio is properly matched. According to the current electricity price in Shandong Province, it is estimated that each ton of molten iron can be reduced by about 130 yuan.

5. Service life of furnace lining

According to the smelting characteristics of electric arc furnace, the furnace life can reach long furnace life. The specific analysis is as follows:

(1) The influence of high temperature thermal action: the furnace lining is generally above 1600 ℃ when it is in a high temperature thermal state, and it is also subject to rapid cooling and heating, which will cause great damage to the furnace lining; The temperature of molten iron smelting in electric arc furnace is generally controlled at about 1500 ℃, so the damage of high temperature to furnace lining can be ignored. The service life of furnace lining can be greatly improved by continuously matching molten iron to form continuous smelting and discharging at the same time to reach 1550 ℃ oxidation and oxygen blowing temperature.

(2) Impact of chemical composition corrosion: the refractory of electric arc furnace belongs to alkaline refractory. The raw material ratio is, the slag steel is accompanied by a large amount of alkaline slag, which makes the furnace charge weakly alkaline as a whole. Therefore, the raw materials have less corrosion on the furnace wall during the smelting process. The alkaline smelting environment is the basic condition for improving the furnace life, but the slag is too thick, forming a local high temperature zone, which will reduce the service life of the furnace lining.

(3) The radiation of arc light has a reflection effect. Choosing foam slag submerged arc during smelting can shorten the smelting cycle of the electric furnace, and good submerged arc effect can reduce the heat radiation to the furnace lining, thus improving the furnace life.

(4) Mechanical collision and vibration will also affect the service life of the furnace. A reasonable charging method will also improve the service life of the furnace. If the charging and distribution are unreasonable, or the charging tank is lifted too high, the furnace bottom slope may bear the collision of large heavy materials, and the vibration and impact will form pits, which will reduce the service life of the furnace lining. In addition, according to the fact that the electric arc furnace wall is a hot area, the charging can pave materials at these three points, which will also improve the service life of the furnace lining.

(5) The oxygen blowing method will also affect the service life of the furnace. The oxygen plays a role in assisting the arc combustion supporting chemical materials in the electric furnace smelting. Generally, the two sides of the furnace wall and the furnace door are cold areas, and the electrode is used to feed the electric chemical materials. The cycle will be longer. A reasonable oxygen blowing method can shorten the smelting cycle and improve the furnace life (according to different material ratio, large materials are selected to be purged, and the oxygen flame is not blown against the furnace bottom and furnace wall as far as possible), The blowing time at the same point should not be too long to avoid local high temperature near the furnace wall eroding the furnace wall.

Advantages of EAF iron melting

1. When molten iron is smelted in the electric arc furnace, the tapping temperature is controlled below 1500 ℃. Compared with the requirements for steelmaking, when tapping temperature is above 1600 ℃, the power consumption can be greatly reduced. As the electric arc furnace is used to smelt molten iron, the temperature is low and the time is short, the smoke and dust generated is far lower than the dust and smoke generated when smelting molten steel; Moreover, the smoke and dust discharged from the electric arc furnace is almost the whole process of closed smelting, which is more than 90% less than the whole process of medium frequency smelting. Therefore, it is very environmentally friendly to melt molten iron in a fully enclosed dedusting electric arc furnace.

2. Low cost raw materials can be selected for smelting basic molten iron with electric arc furnace, the smelting process shall be strictly controlled, and the metallurgical characteristics such as dephosphorization and desulfurization of electric arc furnace shall be well utilized. Under the condition of smelting high-quality basic molten iron at the same temperature, each ton of molten iron can be up to 40% more than that of medium frequency furnace alone

3. It is coupled with the intermediate frequency furnace and uses high-quality low-cost basic molten iron to modify and fine tune the composition in the intermediate frequency furnace, so as to produce various brands of small batch products with strong mobility, wide adaptability and high quality, which is suitable for continuous production as well as intermittent production. It can also be compatible with both production methods.