The consumption of refractory bricks for steelmaking is particularly large, and it is directly related to the service life of the steelmaking furnace and the cost of steelmaking. Therefore, the corresponding refractory bricks must be selected for the steelmaking furnace. Refractory bricks for electric arc furnaces include several types, such as high alumina bricks or unformed refractories for furnace covers, magnesia bricks, magnesia chrome bricks, magnesia carbon bricks or furnace wall inserts.
Keywords: Electric Arc Furnace Steelmaking，electric arc furnace refractory lining
Electric arc furnace steelmaking is a complex high-temperature process with high humidity in the furnace (1700-1800°C). The atmosphere changes drastically and the smelting cycle is short. The electric arc furnace is divided into two parts: the furnace cover (top) and the furnace body. The furnace cover is movable, the outer ring is made of steel, mostly water-cooled, and the top is made of refractory materials except for the water-cooled ring. The furnace cover has three electrode holes, and three graphite electrodes are inserted into the furnace. The main body of the furnace body is composed of a furnace bottom, a furnace slope, and a furnace wall (furnace wall). It is made of refractory material and covered with a steel shell. There is a furnace door on one side of the furnace wall, and an outlet connected to the outlet slot on the other side.
The lining of the electric arc furnace is mainly affected by slag, molten steel, slag, dust erosion, mechanical shock when installing scrap steel, and thermal stress caused by high temperature and strong heat radiation.
The outer ring of the electric furnace roof (furnace cover) is called the main furnace roof, and the middle ring is called the small furnace roof, which is worn by dust erosion. During the melting and refining process, the temperature of the furnace roof becomes very high. When the steel is tapped, as soon as the furnace cover is removed, the temperature rises to room temperature, the temperature changes rapidly, and the thermal stress increases. During pyrolysis and purification, they are also affected by erosion and atmospheric changes caused by slag and dust droplets.
In the past, the furnace cover of the electric furnace was mainly made of silica bricks, but its fire resistance and heat resistance were low, and it was easily damaged by slag erosion, splashing, peeling, etc., and its service life was short. At present, high-alumina bricks and high-alumina overall fireproof materials have good performance, and their service life is two to three times that of silica bricks. In large super-high-power electric furnaces, fired or non-fired alkaline bricks are often used due to harsh working conditions, but refractory bricks have low high-temperature strength and heavy weight, and are mainly suspended structures. The direct combination of magnesia bricks and magnesia-chrome bricks is superior to ordinary magnesia bricks and magnesia-chrome bricks, which can significantly reduce spalling damage caused by structural collapse and thermal collapse.
The furnace wall is mainly eroded by high-temperature slag and molten steel, as well as impact and wear during charging. The vulnerable parts are the slag line area and the hot spot (the furnace wall is close to the electrode arc radiation). The furnace bottom and inclination form a molten pool, and the molten pool is mainly subjected to the mechanical impact of the charge and the erosion of slag and molten steel.
The wall of the electric arc furnace is close to the arc and the molten pool, emitting high-temperature heat, and the atmosphere and temperature in the furnace have undergone drastic changes, and are affected by the scrap and the melt. The furnace wall is affected by various functions and is easily damaged. Localized melt damage usually occurs near hot spots near the electrodes, where damage to the furnace wall is more severe. According to the characteristics of the electric furnace smelting process, the thermal system and properties of the slag, the basic refractory bricks are used for the furnace walls of almost all furnaces. Common furnace wall parts are mostly made of magnesia bricks and magnesia chrome bricks. In addition to the products of fired bricks and unburned bricks, the effect of unburned bricks is also good. Small electric furnaces in Japan mainly use tar pitch, tar impregnated with dolomite bricks and dolomite bricks, and tar pitch combined with magnesium and dolomite crushed materials. The slag area is a weak point of the electric arc furnace, and most of them are the direct combination of magnesia bricks and magnesia chrome bricks. Large-scale electric furnaces use fused-cast magnesia-chrome bricks or magnesia-chrome bricks.
electric arc furnace refractory lining Damage Factors
EAF lining fireproof materials are usually very hot. The working conditions are very harsh, with conditions of slag erosion and rapid cooling and rapid heating. During melting and oxidation in ironworks, the inner lining is not damaged by high temperature, but during the reduction period, the temperature of molten steel is very high, and direct arc radiation can easily damage the inner lining. In addition, after the steel is assembled, the temperature of the furnace lining drops sharply, and after the assembly is powered on, the temperature gradually rises. This rapid temperature change is often the direct cause of the peeling off of the furnace lining.
The erosion of the lining by slag determines its composition and fluidity. The higher the SiO2 content in the slag, the more serious the erosion of the foundation lining. In addition to SiO2, Al2O3.Fe2O3.CaF2, etc. will also corrode the lining. The fluidity of the slag can also affect the lining. The inner lining is not well washed, and the arc reflection ability is strong, which increases the heat load of the inner lining fireproof material. The viscosity of the molten slag makes it difficult to heat the molten pool, worsens the physical and chemical reaction conditions, and increases the high temperature time of the furnace lining (that is, the melting time). These accelerate damage to the furnace lining.
The damage of the furnace lining is usually caused by the influence of mechanical force such as unreasonable fabric. The bottom of the furnace is not protected from small debris. Loaded material canister is too high. In this case, a large amount of waste material will accumulate at the bottom of the furnace. Mechanical vibrations caused by tilting furnace steel are also responsible for lining damage. In addition, improper filling rates and improper melting operations such as hot oxygen flow in direct contact with the lining during oxygen injection can damage the lining.
Therefore, the fireproof materials for masonry electric arc furnaces must have high refractoriness and load softening point. Excellent thermal stability and slag resistance, sufficient high temperature mechanical strength, low thermal conductivity. Silica bricks are commonly used for masonry acid electric arc furnaces, and magnesia bricks are used for basic electric arc furnaces, but the top of the furnace is mostly high alumina bricks. Silica brick stove tops are rarely used.
Traditionally, the furnace cover of electric arc furnaces is mainly made of silica bricks, but their refractoriness and heat resistance are low, they are easily damaged by slag erosion, splashing, peeling, etc., and their service life is short. Since then, the properties of high-alumina bricks and high-alumina integral fireproof materials have been widely used, and their service life is twice and three times that of silica bricks. With the development of ultra-high-power electric furnaces, the use conditions of electric arc furnace covers have further deteriorated due to the acceleration of ironmaking rhythm. Add high alumina bricks or sillimanite mineral materials to the ingredients, and add micropowder. Spinel, silicon carbide, etc. improve the slag resistance of bricks. High-temperature volume stability and thermal shock stability meet the development needs of ultra-high-power electric furnaces. Due to the harsh working conditions, corundum is often used in the triangular area of the furnace cover electrode. The injection and prefabrication of chromium core and core Dan spinel simplifies the structure and prolongs the service life of the furnace cover.
The preforms are poured using the electric arc furnace lid.
Due to the development and innovation of electric arc furnace technology, refractory materials are gradually used in the furnace cover of electric arc furnace. Corundum-infused corundum and chrome prefabricated parts replaced the original high-alumina bricks and many high-alumina brick materials. The life of injected prefabricated components is obviously longer than that of high alumina brick structure, and the structure is simple, fast and labor intensive. It reduces strength, saves energy, and reduces drag.
Working environment of electric arc furnace hood
Its main function is to keep warm, reduce heat loss, prevent chemical gases and dust particles from overflowing, and pollute the environment. The central part of the electric arc furnace cover has a hole, which is convenient for inserting electrodes and adding metallurgical additives. Although it is not in direct contact with steel or water, it is often opened and generates strong thermal shock stress. The thermal oxide powder forms a liquid phase with the refractory material of the furnace cover, which promotes the sintering of the surface material of the electric arc furnace cover. The spun layer and the non-sheathed layer are subjected to thermal stress due to temperature fluctuations caused by the opening of the furnace cover, resulting in increased cracking and material shedding at the interface. Especially when the arc radiation and the electrodes are pulled out and inserted above 2000 degrees, the thermal stress and corrosion generated by the triangular part of the electric arc furnace cover will cause the furnace cover to peel off and crack, shortening its service life. This is the main cause of damage to the electric arc furnace cover.
The electric arc furnace hood injection prefabricated brick is mainly made of high alumina aggregate with an aluminum content of more than 85%, multi-particle gradation, pure calcium aluminate cement as a compounding agent, kyanite, polycrystalline stone, explosion-proof fiber, etc. Low cement grouting material made with chemicals. The mold is customized by the injection molding material manufacturer, the injection molding material sample is checked, the injection molding material is stirred and injected. It has the advantages of high temperature resistance, high temperature resistance to solid particles and dust erosion. It is chemically resistant and perfectly adapted to the working environment above the electric arc furnace.