Which refractories are suitable for medium frequency furnace lining
Refractories with melting points higher than 1700 ℃ are roughly classified into six categories according to chemical composition: oxides, carbides, nitrides, sulfides, boride and chemical elements.
Among them, chemical elements and carbides work in high temperature and oxidizing atmosphere and are easily oxidized or dissolved in molten iron. Silicon carbide can be used to repair the tapping trough or charging trough of the furnace, but it cannot be used as the lining material of induction furnace due to its electrical conductivity. Sulfide, boride, etc. can be dissolved in or react with molten iron and reduced by iron and carbon, and are not suitable as lining materials. Silicon nitride (Si 3N4) and aluminum nitride in nitride have the advantages of good oxidation resistance, peeling resistance and not easy to be eroded by molten metal, but they are expensive and cannot be used in industry.
Therefore, at present, the refractory used as induction furnace lining is mainly oxides. Of the 17056 kinds of oxides in nature, there are only more than 50 kinds of oxide materials with melting points higher than 1700 ℃. Some of them have poor chemical stability and low decomposition pressure at high temperature, and are often reduced by components in metal molten solution. In addition, some oxides are easy to hydrate at low temperatures, so they cannot be used as lining refractories. Some oxide resources are scarce and expensive, such as Y3O4, HFO2, CeO2, etc., which are rarely used as furnace lining materials. Some oxides are radioactive (ThO2) or toxic (BeO), and cannot be used as lining materials. In actual production, the three oxides are most widely used, namely silicon oxide, alumina and magnesium oxide and their mixtures.