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.Lining of medium frequency furnace
The lining of the medium frequency furnace is usually made of refractory materials of various specifications and sizes (commonly used refractory materials are mainly magnesium, quartz, aluminum and composite materials).
Its characteristics are: direct bonding. Therefore, it has high corrosion resistance, high mechanical strength and good thermal shock resistance.
2.Damage mechanism of magnesia furnace lining materials
Magnesium refractory materials as an example, to explain the destruction mechanism of magnesium materials:
Magnesium material damage is mainly manifested in: flow of liquid steel caused by thermal erosion and slag composition penetration into the material caused by chemical erosion.
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, etc. These penetrating components are deposited in the refractory capillary pore channels, causing the furnace lining to erode. 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, spalling and structural loosening, strictly speaking, this damage process than the dissolution of the damage process is much more serious.
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 ℃. Low melting point slag has excellent mobility, may form a flux effect on the furnace lining to produce intense chemical erosion, 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), etc., and some high melting point of the melting point of the metal elements up to 1800 ℃ or more, suspended in the metal liquid high melting point of slag and low melting point slag and there is a more complex interspersed intermixing effect, these slag is very easy to adhere to the furnace wall and the formation of the cumulative, resulting in a serious slag, affecting the power of the furnace, melting rate and melting speed, and thus reduce the service life of the furnace lining. Furnace power, melting speed and capacity, until the impact of furnace lining life.
With the increase in furnace capacity, the proportion of heat dissipated from the surface of the liquid steel decreases, the temperature of the slag is higher than the small-capacity furnace, and the mobility of the slag is better than that of the small-capacity furnace, thus aggravating 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.Solution Design
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. 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 the 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.
4.Effective Measures
(1) The furnace lining material should be characterized by high thermal strength, low permeability and low porosity.
(2) The initial damage to the lining is due to front-end erosion caused by dissolution of the sintered layer of the lining refractory in the slag, and cracking due to cyclic changes in temperature. Another factor causing crack expansion in the overall lining is the stress caused by the different coefficients of expansion between the “three zones” due to heating to excessively high temperatures.
(3) The life of the lining depends on proper operation, including inspection of the lining and the application of “patching compounds” to repair any cracks that occur in a timely manner and to avoid the penetration of molten steel and slag into the lining matrix.
(4) Slagging of the furnace lining can be effectively solved by SlagR.
