Generally speaking, good quality refractory materials have good effects and long service life when used in furnaces and kilns, but the conditions of use cannot be ignored. For example, if the same refractories material is used on the same thermal equipment, the results of use are often very different due to changes in the conditions of use. There are many reasons for the failure of the furnace lining, such as furnace penetration and lining spalling. The following mainly introduces the analysis of the causes of furnace penetration and lining spalling in induction furnaces.
The furnace penetration phenomenon is manifested as: a large amount of metal penetrates into the cracks of the refractory material. Furnace penetration will lead to: metal penetration around the furnace penetration; the life of the refractories material of the furnace lining is significantly reduced; early grounding alarm; potential risk of metal liquid drilling into the coil; overall sintering of dry vibration materials without loose layers; the furnace lining is continuously expanding from the furnace mouth; oxidation of the furnace penetration part will cause local refractory erosion, etc. Figure 1 The reason for the metal penetration around the furnace penetration is mainly cracks formed by hot and cold cycles, including horizontal cracks, vertical cracks and cracks in any direction.
The main reasons for the formation of horizontal cracks are: ① Delamination: incorrect furnace construction method, resulting in the furnace lining not forming a dense lining knot layer; ② Furnace lining attachment: often occurs at the junction of the liquid outlet and the working furnace lining, which can be solved by changing the construction method of the furnace nozzle. Vertical cracks are caused by hot and cold shocks, mainly caused by incorrect cooling process and re-melting process. Cracks in any direction are generally caused by mechanical collision or demolding. Furnace lining peeling Furnace lining peeling is a phenomenon in which refractory materials fall off from the sintering furnace wall in blocks or sheets.
The reasons for lining peeling are:
(1) Improper furnace construction or sintering causes the furnace lining to fail to form a good sintering layer, causing lining peeling. (2) Water vapor: The lining is sintered too fast, and the moisture in the refractories material cannot be discharged in time. At high temperatures, H2O decomposes into H2 and O2. According to the ideal gas equation: PV=nRT, it can be seen that the temperature of the gas rises rapidly, the product of the pressure and volume of the gas will expand rapidly, and the volume will expand rapidly. The gas with rapidly increasing pressure will cause the unsintered furnace lining to peel off.
(3) Mechanical peeling: The repeated impact of the charging on the furnace lining, especially the furnace bottom, is the main cause of mechanical peeling.
(4) Expansion peeling: After the molten metal erodes the furnace lining, the thermal expansion rate of the eroded part is inconsistent with the thermal expansion rate of the uneroded part, which makes it easy to generate irregular stress at the interface between the two and cause the furnace lining to fall off.
(5) Extrusion peeling: It often occurs at the furnace bottom, caused by the impact of the charging on the furnace bottom and the long-term pressure of the molten metal's own weight on the furnace bottom.
(6) Thermal peeling: The temperature changes rapidly, and the fluctuation is too fast and too large in a short period of time, causing large internal stress in the refractory material, resulting in cracking, peeling and damage.
