With the widespread application of induction furnaces in the foundry industry, the use of lining materials has also been severely tested. In the process of use, induction furnace lining materials often have problems such as cracks, peeling, local or overall severe erosion, and liquid metal infiltration, which affect the normal use of the lining. In severe cases, safety accidents may even occur. For this reason, several common problems of induction furnace linings are analyzed for their causes.
Common Problems, Cause Analysis and Solutions
Whether it is acidic, alkaline or neutral lining, cracks are the most common problems of induction furnaces. There are three forms of cracks in induction furnace linings: longitudinal, transverse and irregular. When the high-temperature lining is rapidly cooled, cracks may occur due to thermal expansion and contraction. This type of crack is generally longitudinal. Longitudinal cracks less than 2mm can be healed by adopting the correct cold furnace startup process. If the crack exceeds 2mm, it needs to be repaired with corresponding repair materials.
There are many reasons for transverse cracks in the furnace lining. It may be due to incorrect furnace construction methods, resulting in material stratification; or because there is no cooling water for the back lining at the furnace mouth, it sintered during use, resulting in shrinkage and strain of the furnace lining after cooling, resulting in transverse cracks. In addition, the temperature difference between the upper and lower parts of the furnace is too large, and the alloy liquid is not poured out after the furnace is stopped, which can also cause transverse cracks. Transverse cracks are difficult to heal by cold furnace start-up and need to be repaired. During induction furnace smelting, mechanical impact on the lining during charging may cause irregular cracks in the impacted parts. In addition, if impurities are brought into the lining material during the furnace construction process, it will also cause irregular cracks after use. This type of crack is very dangerous. In severe cases, it may even cause liquid metal leakage and damage the furnace body.
Spalling
In the early stage of sintering of the new lining, the sintering layer is very thin. If it is hit by a large piece of charge, the lining is easy to peel off. This situation is especially serious during the first furnace baking. In the middle and late stages of the use of the furnace lining, if the sintered layer of the furnace lining is infiltrated by liquid metal and deteriorates, the difference in thermal expansion coefficients inside and outside is too large, and it will also peel off when heated.
Liquid metal infiltration
The furnace lining is infiltrated by liquid metal mainly because the furnace lining is not dense enough, which is related to the construction quality. For the acidic furnace lining, the heating rate is too fast before 870℃ for the first furnace baking, and the α-quartz phase has not been fully converted to α-tridymite in time. During the smelting process, the generation of liquid metal is accompanied by the volume expansion caused by the transformation of the α-quartz phase to α-cristobalite, and the structure is loose, which is very easy to infiltrate the refractory material of the furnace lining. When melting non-ferrous metals with low melting points, this situation may occur: the furnace lining has melted before the sintering metal, which will also directly cause the furnace lining to be infiltrated by liquid metal. The use of reasonable construction and furnace baking technology will avoid such situations to the greatest extent.
Erosion of the middle and lower part of the furnace lining
During the use of the induction furnace, the unreasonable order of adding the charge and the charge scaffolding during the smelting process will cause the temperature in the middle and lower part of the furnace to be too high, resulting in the appearance of liquid phase in the lining material, which will be severely eroded by the scouring of high-temperature liquid metal. In addition, if the bottom lining is not tightly knotted during the furnace construction process and the lining strength is insufficient, this situation may also occur.
Overall erosion of the lining
The overall erosion of the induction furnace lining is composed of three main factors: the normal wear of the lining material caused by the friction generated by the electromagnetic stirring of the internal liquid metal, the reaction between certain alloy components and refractory materials, and the erosion of the refractory materials caused by the slag during the smelting process. For the acidic lining used in ironmaking: SiO2+C→SiO(g)+CO(g) This reaction is the sum of a series of complex redox reactions. At standard pressure, the initial reaction temperature is 1481℃. When the temperature in the furnace exceeds this temperature, this reaction is one of the main factors for the consumption of the lining. The reaction between slag and refractory materials is very complex, and it is also an important factor in shortening the life of the furnace lining during the smelting of some special alloys. Acidic lining materials are suitable for the smelting of iron, copper and other metals with acidic or neutral slags; alkaline lining materials are used for the smelting of metals with alkaline slags such as manganese steel; neutral lining materials are suitable for large furnaces for smelting special steel grades. Only by selecting suitable refractory materials according to different furnace charges can a relatively long lining life be obtained.
Conclusion
During the use of induction furnace linings, most problems are caused by improper operation during furnace construction or use. If suitable materials are selected, reasonable furnace construction technology is adopted, and reasonable smelting technology is used, quality problems of the lining during use can be avoided and the service life of the lining can be improved.