Induction furnaces are one of the most challenging of all refractory applications. The successful assembly of large-scale induction steelmaking equipment urgently needs to improve the performance of refractory materials, and as a result, it promotes the continuous improvement of the performance of refractory materials for induction steelmaking.
Refractory materials for induction furnaces need to be selected based on the furnace type, furnace structure, type of steel being smelted, smelting process and operating conditions. At the same time, the phase and physical properties of the refractory material from room temperature to working temperature should also be considered. The change process and mechanism, as well as the application conditions of refractory materials, etc.
1. When melting cast iron and non-ferrous metals in a coreless induction furnace, SiO2, ZrO2·SiO2 and complex phase refractory materials composed of them are generally selected. Because ZrO2·SiO2 decomposes at high temperatures to form ZrO2 and fSiO2, which are evenly distributed in the material, thus imparting high-temperature plasticity and corrosion resistance to the material, indicating that ZrO2 can extend the service life of SiO2-based refractory materials.
2. Coreless induction furnaces can use acidic steelmaking methods or alkaline steelmaking methods. The refractory materials used in acid steelmaking are the same as those used in smelting cast iron, while neutral or alkaline refractory materials are used in alkaline steelmaking.
3. When making steel in small coreless induction furnaces, magnesia refractory materials are usually used for lining. However, this kind of refractory material has poor thermal shock resistance and is easily penetrated by slag, resulting in structural peeling and premature damage, so it is difficult to adapt. High-capacity, intermittent operation usage environment.
4. When making steel in a medium-sized coreless induction furnace in normal operation, refractory materials made of MgO-Al2O3 or MgO-Spinal mixtures are used, both of which belong to the MgO-spind series refractory materials.
5. Medium-sized coreless induction furnaces that use a variety of scrap steel as raw materials to make steel use Al2O3-MgO (about 10% MgO) refractory materials to achieve a long service life.
6. Medium-sized induction furnaces that use direct reduced iron balls as additives should use MgO-Al2O3-Cr2O3 (added chromium ore) refractory materials. Since MgO, Al2O3, Cr2O3, etc. react to form composite spinel when heated at high temperatures, it has high fire resistance and strong corrosion resistance. As a result, its adaptability to high-erosion iron/manganese slag is improved, so its service life is improved. long.
7. Large coreless induction furnaces use spinel refractory materials made of pre-synthesized Spinel granules, or a mixture composed of MgO (coarse particles, fine powder), Spinel (medium particles, fine powder) and Al2O3 particles. It is a MgO-Spine refractory material made by carefully balancing the ratio of pre-synthesized Spinel and in-situ Spinel. Both types of refractory materials can adapt to the operating conditions of large coreless induction furnaces.
8. The operating temperature of cored induction furnace for smelting gray iron and cast iron is 1450~1550℃, which is not very high. Although the temperature at the inductor molten trench and water jacket is as high as 1600~1700°C, the selection of refractory materials is not very difficult because water cooling is implemented.
9. Coreless induction furnaces mainly use knotting methods to build linings, while cored induction furnaces mainly use pouring methods to build linings. Knotted lined refractory materials form a sintered layer during the sintering process. In order to obtain high adaptability, it is expected that the expansion of the sintered layer and the increase in strength proceed slowly. Therefore, the formula design and raw material selection of refractory materials should ensure that the working surface in contact with the high-temperature melt during the lining operation can be sintered to form a sintered layer with a certain strength, while the non-working layer should maintain the scattered structure before sintering. This kind of The structure has the function of preventing the migration of cracks in the working layer and absorbing cracks, thereby laying a good foundation for extending the service life of the lining.