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　　Do you know how long a medium-frequency furnace can last?

　　At Medium-frequency furnace In operation, the lining of the furnace uses refractory materials with a thickness of only 70–110 mm. The inner side is in contact with high-temperature molten metal, while the outer side is in close contact with water-cooled coils. As a result, there is a significant temperature difference between the inner and outer surfaces of the refractory material. Given these operating conditions—characterized by a relatively thin cross-section and exposure to highly corrosive environments during numerous melting operations—the primary process parameters influencing furnace lining damage include melting temperature, degassing time, initial degassing volume, chemical composition of the slag, and the type of steel (or iron) being produced. The main factors contributing to furnace lining failure are chemical erosion by the slag, spalling of the refractory material’s microstructure, and thermal erosion.

　　 Medium-frequency furnace The furnace lining is typically composed of refractory materials of various particle sizes and specifications. (The commonly used refractory materials mainly include magnesia-based, quartz-based, alumina-based, and composite materials.) These materials feature direct bonding, resulting in high corrosion resistance, high mechanical strength, and excellent thermal shock resistance.

　　The failure mechanisms of magnesia-based lining materials—taking magnesia refractories as an example—are discussed herein. The primary failure modes of magnesia materials are thermal erosion caused by the flow of molten steel and chemical erosion resulting from the penetration of slag components into the material. The solutions dissolved in the slag permeate through the pores within the refractory matrix, infiltrating deep into the refractory body and eroding the lining. The components that penetrate into the refractory matrix include CaO, SiO2, and FeO from the slag, as well as Fe, Si, Al, Mn, and C from the molten steel; indeed, even metallic vapors and CO gas may be involved. These penetrating substances accumulate in the pores of the refractory material, leading to discontinuities in both the physicochemical properties of the working surface and the original refractory matrix itself. Sudden changes in operating temperature can induce cracking, spalling, and structural loosening. Strictly speaking, this degradation process is far more severe than the dissolution-induced failure mechanism.

　　The metallic materials fed into the medium-frequency furnace carry various oxides. Depending on the material composition and the furnace batch, the slag composition varies accordingly. The oxides, carbides, sulfides, and various complex compounds present in the slag almost all undergo chemical reactions with the lining, forming new compounds with different melting points. During these reactions, low-melting-point oxides such as FeO-SiO2 and MnO-SiO2 are typically generated within a temperature range of around 1200°C. Such low-melting-point slags exhibit excellent fluidity, creating a flux effect that can cause severe chemical erosion of the furnace lining and significantly reduce its service life.

　　The high-melting-point slag components formed during the reaction—such as mullite (3Al₂O₃·2SiO₂), forsterite (2MgO·SiO₂)—as well as certain high-melting-point metallic elements, can have melting points exceeding 1800°C. As the furnace capacity increases, the proportion of heat lost from the molten metal surface through suspended high-melting-point and low-melting-point slags decreases. Consequently, the slag temperature in larger furnaces is higher than in smaller ones, and the slag exhibits better fluidity. This leads to intensified erosion of the furnace lining. In large induction furnaces, steel is often tapped using a mixed steel-slag approach. To meet the requirements of this tapping process, the slag must possess excellent fluidity. As a result, the slag line area experiences severe erosion, which is another factor contributing to the shortened service life of the furnace lining. Based on the above considerations, the service life of large furnaces is shorter than that of medium- and small-sized furnaces. To improve... Medium-frequency furnace To extend the service life of the furnace lining, it is necessary to appropriately increase its thickness. However, as the lining wall thickness increases, the resistance value rises, reactive power losses increase, and thermal efficiency declines. Therefore, the thickness of the lining wall is limited within a certain range. Consequently, it is essential to select a reasonable wall thickness—this ensures high electrical efficiency and guarantees the longevity of the medium-frequency furnace lining.