The electric arc furnace is an electric furnace that uses electric arc energy to smelt metals. The electric arc furnaces used in industry can be divided into three categories: the first category is direct heating, where the arc occurs between the special electrode rod and the smelted charge, and the charge is directly subjected to the arc heat. It is mainly used for steelmaking, and secondly for smelting iron, copper, refractory materials, refined steel liquid, etc.
The second category is indirect heating, where the arc occurs between two special electrode rods, and the charge is subjected to the radiant heat of the arc, and is used for smelting copper, copper alloys, etc. This type of furnace has high noise and poor smelting quality, and has gradually been replaced by other types of furnaces.
The third category is called an electric arc furnace, which uses high-resistivity ore as raw material. During the working process, the lower part of the electrode is generally buried in the charge. Its heating principle is: it not only uses the heat generated by the charge resistance when the current passes through the charge, but also uses the heat generated by the arc between the electrode and the charge. So it is also called an arc resistance furnace.
The furnace wall of the electric arc furnace is divided into three parts according to the use conditions: the main furnace wall, the slag line and the hot spot
① In the main furnace wall of high-power and ultra-high-power electric furnaces, direct-bonded magnesia-chrome bricks, pre-reacted magnesia-chrome bricks, magnesia bricks, etc. are mainly used.
② The hot spot is close to the arc, subjected to high-temperature radiation and slag splashing, and the damage is particularly serious. Oil-immersed magnesia bricks, direct-bonded magnesia-chrome bricks, fused-cast magnesia-chrome bricks, magnesia-carbon bricks, etc. are mainly used.
③ The slag line is severely corroded by molten steel and slag, and the use conditions are harsh. High-quality refractory materials similar to the hot spot should be used. The lining of the electric furnace body is shown in Figure 14-4.
Due to the different working conditions of various parts of the furnace wall, few are built with a single material. Most of them use a variety of bricks for comprehensive masonry in order to balance the erosion. In the upper part of the furnace wall, the slag line and the hot spot are weak areas of the furnace wall due to uneven heat load, chemical erosion and mechanical action. The "hot spot" even restricts the service life of the furnace wall. In order to meet the needs of these harsh corrosion areas, magnesia-carbon bricks with corrosion resistance, thermal shock resistance and low linear expansion rate are increasingly used in high-corrosion areas of electric furnaces. It has become the preferred refractory material for UHP electric furnace walls at home and abroad.
What are the differences between the refractory materials used for the lining of electric furnace walls at home and abroad?
In the 1960s, the United States began to use high-temperature fired direct-bonded magnesia-chrome bricks for electric furnace walls. In the 1970s, in order to meet the needs of large electric furnaces and UHP electric furnace hot spots, fused-cast magnesia-chrome bricks and re-bonded magnesia-chrome bricks were tried for comprehensive masonry. In 1976, "Corhart" fused-cast magnesia-chrome bricks were widely used in UHP electric furnaces, 90%~95% of which were laid in hot spots and some were used in slag line areas. The fused-cast bricks have a high degree of direct bonding of magnesia-chrome spinel and a dense structure.
In the mid-1970s, electric furnace steel in the United States developed rapidly. A major development that effectively improved the productivity of electric furnace steel was the development and use of magnesia-carbon bricks with low raw material and process costs and good use effects in high-loss areas of electric furnace walls. The raw material is magnesia carbon brick produced by sintering magnesia with high purity and high density of CaO/SiO2=3, with carbon content of about 10%, apparent porosity of 3%, and volume density greater than 2.95g/cm3.
Most of the electric furnace walls in the former Soviet Union are made of magnesia materials. Recombined magnesia chrome bricks were once trial-produced with fused periclase and chromium ore sand, which were used in the upper part of the steel outlet of the 100t electric furnace where corrosion was serious. The brick has less low melting point mineral phase, good corrosion resistance, and better use effect.
For the walls of British electric furnaces, ordinary chrome magnesia bricks (70% chromium ore, 30% seawater magnesia) and fired magnesia chrome bricks (70% seawater magnesia, 30% chromium ore) are generally used, as well as ordinary magnesia bricks and high-quality magnesia bricks produced with seawater magnesia. High-temperature fired magnesia bricks prepared with seawater magnesia or fired magnesia bricks impregnated with asphalt and tar are used at hot spots and slag lines to obtain good use effects.
The furnace wall of Japan's electric furnace uses magnesia-chrome bricks and magnesia bricks, and the hot spots use magnesia bricks, magnesia-carbon bricks, fused magnesia-chrome bricks, carbon bricks, etc. In the 1980s, my country's electric furnace steelmaking has achieved rapid development, and has developed from ordinary power electric furnaces to ultra-high power electric furnaces. The progress of electric furnace steelmaking technology is closely related to the synchronous development of refractory technology, which has promoted the steady increase of electric furnace life and the gradual reduction of refractory unit consumption. my country's ordinary power electric furnace uses two types of linings. One is the overall lining of ramming material with low and medium temperature binders added to sintered magnesia sand and fused magnesia sand; the other is the lining of tar-bonded magnesia bricks and magnesia-carbon bricks of different standards. Alkaline carbon-containing products are the main materials for the lining of the furnace wall, and magnesia-carbon bricks play an important role in electric furnaces.
HOME