Medium frequency furnace use process, the thickness of the refractory material used for the furnace lining is only 70-110mm, the inner side of the contact with the high temperature metal liquid, the outer side of the water-cooled coils close to the refractory material inside and outside temperature difference is very large, in the use of the relatively thin section and many melting operation of the strong erosive environment under the use of the conditions. The main process conditions affecting the destruction of the furnace lining include: melting temperature, degassing time, the amount of primary degassing, the chemical composition of the slag and the type of steel (iron) produced. The main factors affecting the destruction of the furnace lining are: chemical erosion of the slag, structural spalling of the refractory material and thermal erosion.
1.Medium frequency furnace lining
Medium frequency furnace lining is usually made of various specifications of particle size composition of refractory materials knotted (commonly used refractory materials are mainly magnesium, quartz, aluminum and composite materials of four categories).
Its characteristics are: direct bonding. As a result, it has high erosion resistance, high mechanical strength and good thermal shock resistance.
2.Damage mechanism of magnesium furnace lining materials
Magnesium refractory materials as an example, to explain the destruction mechanism of magnesium materials:
Magnesium material damage is mainly manifested in the following ways: thermal erosion caused by flowing steel and chemical erosion caused by slag component penetration into the material.
During the melting process, the solution will penetrate into the refractory matrix through the capillary channels in the refractory matrix to erode the furnace lining. The components that penetrate into the refractory matrix include; CaO, SiO2, FeO in the slag; Fe, Si, Ai, Mn, C in the molten steel, and even metal vapors, CO gas and so on. These infiltration components deposited in the refractory capillary pore channel, resulting in the physical and chemical properties of the refractory work surface and the original refractory matrix discontinuity, in the operation of the temperature of the rapid change will appear cracks, flaking and structural loosening, strictly speaking, this damage process is much more serious than the process of dissolution of the damage.
Metal materials added to the furnace will bring a variety of different oxides, different materials, different furnace slag composition is not the same. Slag in the presence of a variety of oxides, carbides, sulfides and a variety of forms of composite compounds, most of which will be and the lining of the chemical reaction to generate new compounds with different melting points. Some low melting point oxides generated in the reaction, such as iron olivine (FeOSiO2), manganese olivine (MnOSiO2) and other melting points are generally in the range of about 1200 ℃. The low melting point slag has excellent mobility and may form a flux effect, which produces violent chemical erosion of the furnace lining, thus reducing the service life of the furnace lining.
High melting point slag generated in the reaction, such as mullite (3Al2O3-2SiO2), magnesium olivine (2MgO-SiO2), and some high melting point of the metal elements melting point of up to 1800 ℃ or more, suspended in the metal solution of the high melting point of the slag and low melting point slag and the interspersed intermixing effect, the slag is very easy to adhere to the furnace wall and the formation of the cumulative, resulting in a serious slag, affecting the power, melting speed and capacity until the impact of furnace lining life. Furnace power, melting speed and capacity, until the lining life.
With the increase in furnace capacity, the proportion of heat dissipated from the surface of the liquid steel decreases, the slag temperature is higher than the small capacity furnace, the mobility of slag is also better than the small capacity furnace, thus increasing the erosion of the furnace lining. Large induction furnace more steel, slag mixed out of the method of steel, slag is required to have good mobility, in order to adapt to the conditions of steel. Therefore, the slag line part of the erosion is serious, which is caused by the service life of the furnace lining down another reason. Due to the above reasons, the service life of large induction furnace lining is lower than that of small and medium-sized induction furnace, and the thickness of the lining should be increased appropriately in terms of improving the service life of the lining. However, as the thickness of the lining wall increases, the resistance value increases, the reactive power loss increases, and the electrical efficiency decreases. Therefore, the thickness of the furnace lining wall is limited to a certain range. Therefore, it is necessary to select a reasonable wall thickness, that is, to ensure high electrical efficiency and ensure the service life of the furnace lining.
3.Design of solutions
The above erosion leads to so-called structural spalling under cyclic fluctuations in temperature. During the production process, the slag penetrates into the pores of the refractory matrix, thus forming a large thickened layer of refractory. The physical and chemical properties of the part of the refractory material saturated with slag are changed. Due to the different coefficients of thermal expansion between the infiltrated layer and the residual undisturbed layer, when the temperature changes, significant stresses occur at the junction of the two layers, which leads to cracking parallel to the working surface and ultimately spalling of the furnace lining body. The slag penetrating into the refractory matrix dissolves the particles of the refractory and weakens the bonding between the particles, which leads to a decrease in the refractoriness and resistance to high temperatures of the material. As a result, it leads to faster destruction of the refractory material in the slag penetration layer by the erosion of flowing steel.
The alkalinity of the slag should be compatible with the furnace lining material. Magnesium furnace lining material can be eroded by high CaO slag and SiO2 slag. The amount of CaF in the slag should be controlled. Excessive CaF will erode the alkaline furnace lining and cause premature melting in the slag line area. When the slag of fluoride ions, metal manganese ions and other high or melting pool temperature to 1700 ℃ or more, the viscosity of the solution will also be a sharp decline in the destruction of the furnace lining to accelerate the speed of the lining life will be greatly reduced. Under vacuum for slag-free melting, the service life of the furnace lining is greater than the life of non-vacuum melting.
Infiltration of higher iron oxide content in the furnace lining destroys the microstructure of the original lining, reduces the refractoriness, and reduces the viscosity of the CaO-Ai2O3-SiO2 slag, which allows the slag to penetrate into the deeper layers of the material. However, a certain amount of iron oxide in the original lining facilitates rapid sintering of the lining and reduces the open porosity and permeability of the material. In particular, a certain amount of iron oxide in the molding material, the rapid sintering of the material, the elimination of sand washout and sand entrapment is very prominent.
Improve the magnesium oxide content and slag viscosity, both favorable to reduce the slag erosion of the furnace lining, but also conducive to improve the effect of slag collection. When the slag alkalinity is low, the magnesium lining erosion is more serious, and the life of the lining is reduced; on the contrary, when the slag alkalinity is high, the erosion of the lining is slight, and the life of the lining is relatively improved. Improve the slag alkalinity and slag in the MgO content, reduce the slag in the FeO content, favorable to reduce the slag on the refractory erosion. Therefore, the use of slagging agent should focus on the selection of high magnesium oxide materials. Reasonable configuration of slag structure, speed up the slagging speed, shorten the smelting time, reduce the iron oxide content in the slag.
Suitable slag should be selected according to the material of furnace lining. Alkaline slag is suitable for magnesium furnace lining, but it can be eroded by high CaO slag and SiO2 slag, and excessive CaF2 will also erode the alkaline furnace lining and make the slag line area melt prematurely. Acidic slag is suitable for quartz furnace lining, magnesium-alumina furnace lining can only be applied to weakly alkaline or neutral slag. Alumina furnace lining at high temperatures in different pH will show the typical amphoteric, which can be adapted to different pH slag, but compared to acidic furnace lining and alkaline furnace lining is slightly worse. For this reason, some in the selection of materials using high-purity magnesium sand and add a certain amount of spinel to change the matrix properties of pure magnesium furnace lining materials, but experiments have shown that high-purity corundum material erosion resistance is also significantly less than the purity of the sintered magnesium sand is not very high. Acidic slag is suitable for quartz furnace lining, magnesium-alumina furnace lining can only be applied to weakly alkaline or neutral slag. Alumina lining shows typical amphoteric properties at high temperatures in different pH, and it can be adapted to slags with different pH, but it is slightly inferior compared to acidic and alkaline lining.
In conclusion, considering the main damage mechanism of magnesium furnace lining, after continuous summarization and exploration, the slag penetration resistance of the material can be improved by restricting the open porosity and permeability, and the high temperature erosion and spalling resistance of the furnace lining matrix can be improved by increasing the high temperature flexural strength and the caustic softening temperature.
The performance of the furnace lining depends on a variety of factors, such as the particle size distribution of the material, the physical and chemical properties of the material and the sintering temperature of the lining.
