The properties of magnesium calcium iron sand: the mineral phases are Mgo, C2F, C4AF, C2S, C3S
Features: high C2F content, excellent sintering, good resistance to FeO erosion, strong resistance to slag penetration
Electric furnaces mainly use scrap steel as the main raw material for steelmaking. Scrap steel, lime, etc. are added to the furnace. When the electricity is turned on, an electric arc occurs between the electrode and the scrap steel to heat the charge and carry out a series of metallurgical chemical reactions to smelt the scrap steel into steel. Electric furnaces mainly include DC electric arc furnaces, AC electric arc furnaces and induction furnaces. The use of refractory materials for the furnace bottom depends on the size of the electric furnace. The refractory materials used for the furnace bottom include magnesia carbon bricks, Magnesite Bricks, magnesia dry ramming materials, etc.
The AC electric arc furnace has a long history of steelmaking, so its refractory materials (Magnesite Bricks)for the bottom of the furnace have also undergone changes. The bottom of the furnace is rammed with asphalt tar magnesia or brine magnesia. Because brine magnesia is eroded quickly at the bottom of the furnace, it cannot meet the requirements for use. Although asphalt tar magnesia has better durability, it is troublesome to construct and has environmental pollution. Therefore, more magnesite Bricks and low-grade magnesia-carbon bricks are used to build the bottom of the furnace. The durability of the brick-built furnace bottom is very good, but the masonry is labor-intensive and time-consuming.
By the 1990s, my country began to use the furnace bottom dry ramming material(Magnesite Bricks). It is simple and convenient to construct, and does not need to be baked. After the construction is completed, it can be directly used for steelmaking. The material is magnesium calcium iron (Magnesite Bricks) dry vibrating ramming material. Using the low melting point calcium ferrite it contains, when the temperature rises above 1200C, it can quickly sinter to produce strength. Under the hydraulic pressure of molten steel, it can rapidly sinter and shrink, the shrinkage reaches 4%~5%, and the bulk density increases to more than 3.0 g/cm3. Has particularly good corrosion resistance and good use results.
The consumption of steel per ton of refractory materials (Magnesite Bricks) is reduced from 4 to 8 kg of asphalt magnesite bricks to less than 2 kg. Some modern electric arc furnace bottom dry materials consume as low as 0.3 kg per ton of steel, which mainly corresponds to the steelmaking process technology; in the process of use, the material is sintered layer by layer, sintered and densified near the molten steel, and resists. The erosion and scouring of molten steel, the transition layer is under the sintered layer, and the loose non-sintered layer is under it. This loose layer has low density and low thermal conductivity, which play an important role in the insulation of the electric arc furnace. After years of promotion and development, the vast majority of electric furnace bottoms in my country use this kind of ramming material (Magnesite Bricks).
The construction and use of the furnace bottom dry material are the key factors affecting the use effect. The bottom material should be called dry vibratory castable more appropriately. Because the vibration densification density of the material is more than 0.2g/cm3 higher than that of ramming, the erosion resistance will be significantly improved. Kairuid kiln believes that the dry material should be vibrated for construction, especially for the DC electric arc furnace bottom that is not easy to be repaired. When repairing, the slag and scrap steel at the bottom of the furnace must be cleaned up, otherwise the steel slag under the repairing material may melt when used to a certain extent, and the furnace bottom material will float up under the impact of the steel block. When tapping, the floating bottom block may block the tapping hole and affect the tapping. In the process of use, the furnace bottom should be observed at any time. When there is a floating, it should be repaired in time (generally, the same kind of material can be filled to the pit) to prevent the floating from further expansion and prevent the occurrence of steel breakout.
The bottom of the electric furnace and the slope of the embankment together form the molten pool. The refractory material directly bears the high temperature heat load and the erosion of the molten slag. bottom, resulting in a thinning of the bottom of the furnace.
The structure of the ultra-high power electric furnace bottom is generally divided into 3 layers.
①The thermal insulation layer is the bottom layer of the furnace bottom. Its function is to reduce the heat loss of the electric furnace and ensure that the temperature difference between the top and bottom of the molten pool is reduced. Generally, a layer of asbestos board is first laid near the furnace shell, and then diatomite powder is laid on it. Flat lay insulating bricks.
②The permanent layer is above the thermal insulation layer, and its function is to ensure the firmness of the molten pool and to support the bottom of the pad. Generally, bricks are used, with about 3 layers of staggered joints, and fired magnesia bricks containing Mg095%~96%, asphalt combined magnesia bricks, magnesia dolomite bricks, etc. Firmly compact.
③ The working layer is above the permanent layer, which is in direct contact with molten steel, with high thermal load, serious chemical erosion, strong mechanical scouring effect, and easy corrosion and damage. High-quality refractory materials (Magnesite Bricks)should be selected. The bottom working layer of electric furnace in my country is made of asphalt combined, magnesia sintering or electric melting (Magnesite Bricks), ramming bottom of dolomite calcined block or calcined magnesite brick masonry.
At present, ultra-high power electric furnaces generally use a mixture of magnesia rich in 2CaOFe20 and magnesia dolomite rich in 2CaO·Fe2O (without any binder). The bottom of the furnace is rammed (actually the lower bed) into an integral structure, and its durability is high.
There are usually two types of ordinary power electric furnace bottoms.
① Knot the bottom of the furnace (or vibrate and compress the bottom of the furnace). The working layer uses magnesia (Magnesite Bricks), and its binder is tar and asphalt, and when making carbon-free furnace lining (Magnesite Bricks), brine or water glass is used as the binder.
② Brick bottom. Usually, asphalt is combined with magnesite bricks, and carbon-free furnace linings are combined with brine and magnesite bricks.
