Neutral linings for induction furnaces are usually made of acidic (silicon dioxide) or basic (magnesium oxide) compounds. It is very important to select the right refractory material for a given melting or holding application. The choice of refractory lining depends on many factors, such as melting temperature, holding time, volume, induction stirring, additives and alloying agents, etc. Considering that magnesium oxide has poor thermal shock resistance and silica-based linings are rapidly corroded. Therefore, the new energy concept is neutral ramming mass (NRM). It mainly consists of Al2O3, with the addition of MgO in the matrix, which forms in-situ spinel (MgO·Al2O3) at the melting temperature of steel. The in-situ spinel formation is associated with a significant volume expansion and provides a rigid structure. It also provides a hard sintered refractory surface layer for the metal bath, resulting in good corrosion resistance. The inner refractory layer will remain powdery. If the hot face erodes, the next inner layer is exposed to a higher temperature and is sintered in turn by in-situ spinel formation.
Slag Hanging on Medium Frequency Furnace Lining
Analysis of Slag Hanging Phenomenon of Medium Frequency Furnace Ramming Material
Mechanism of formation of slag sticking on furnace lining: Slag formation in the melting process of medium frequency furnace is inevitable. The slag sticking on medium frequency induction furnace usually accumulates at the working induction coil position in the upper section of the furnace wall. The composition of slag is related to the composition of the charge added, and the cleanliness of the charge has a great influence on the formation of slag. Because the oxides and non-metallic impurities in it are difficult to dissolve in the molten metal, they are usually suspended in the form of emulsion. When the induction furnace is working, the induced current will form a great stirring force on the molten metal, and the slag particles suspended in it will gradually grow under such a strong stirring action, and the buoyancy they are subjected to will gradually increase. When the buoyancy is greater than the stirring force, the grown slag particles will float up into the slag layer on the surface of the molten metal. At this point, it can be removed mechanically, such as: using a slag remover to pick it out.
So how is the slag sticking on the furnace lining formed? It turns out that when the grown slag particles are floating up, due to the strong stirring, these slag particles will gradually approach the furnace wall under the action of centrifugal force. When the hot slag comes into contact with the furnace lining, due to the relatively low temperature of the lining and the relatively high melting point of the slag, when the lining temperature is lower than the solidification temperature of the slag, the slag will adhere to the lining and condense into a solid state, which is the slag sticking to the furnace wall. Understanding the formation mechanism of this sticky slag helps us understand why sticky slag usually appears in the working coil area above the lining. At the same time, we also realize that the higher the melting point, that is, the solidification temperature of the slag, the easier it is to be cooled by the lining and form sticky slag. If measures are not taken to avoid the formation of sticky slag on the lining, the furnace wall will become thicker and thicker, and the effective furnace capacity will gradually decrease. At the same time, the smelting efficiency will also be greatly reduced, resulting in a significant reduction in the overall generation efficiency.
Dry Ramming Mix Materials from RS Refractory Factory
Methods for Removing Sticky Slag from Furnace Lining
Mechanical removal method
The so-called mechanical removal method is to use mechanical means, such as shovels, iron rods, etc. to scrape off the sticky slag on the furnace lining after the sticky slag appears. The mechanical removal method will cause the following problems:
In order to make it easier to scrape off the sticky slag on the furnace lining, the smelting temperature is often increased to make the sticky slag softer and easier to remove. This operation not only increases additional power consumption, but also causes damage to the furnace lining due to high temperature, affecting the service life. When workers scrape off the slag, in order to ensure safe operation, they will reduce the power of the electric furnace. The reduction in the power of the electric furnace will lead to a decrease in electrical efficiency, which actually leads to an increase in smelting power consumption.
Moreover, the mechanical removal method will cause varying degrees of damage to the surface of the furnace lining.
Chemical removal method
The so-called chemical removal method is completely different from the mechanical removal method. According to the principle of slag formation, the slag formation mechanism is changed to fundamentally eliminate the possibility of slag sticking to the lining. Analysis of the formation mechanism of slag sticking to the lining shows that if the solidification temperature of the slag is lower than the lining temperature, even if the slag contacts the lining during the floating process, the lining temperature will not lower the slag temperature below its solidification temperature, thereby preventing the slag from solidifying on the furnace wall to form sticky slag. The chemical removal method uses this principle to change the physical and chemical properties of the slag and reduce its melting point by adding some additives. In the past, fluorite (the main component is CaF2) was often used as a solvent to reduce the melting point of slag, but the effect of using fluorite alone is not obvious, and it will cause lining erosion. Improper use will aggravate the reduction of lining life.
Through in-depth research on the characteristics of slag, SlagR can effectively improve the performance of slag, reduce the melting point, reduce the viscosity of slag, and improve the fluidity of slag. Moreover, it does not contain substances harmful to the human body and is the most effective chemical flux for removing sticky slag from the lining.
In short, three points: clean charge, diligent operation and appropriate temperature can effectively reduce the slag phenomenon of ramming charge in medium frequency furnace.
Ramming Material for Long-Life Medium Frequency Furnace Working Lining
The quality of the medium frequency induction furnace lining directly determines its service life and production efficiency. Compared with other smelting processes, medium frequency furnace smelting has the characteristics of short process and convenient production adjustment. However, the structure of the medium frequency furnace is complex, and the induction coil is cooled by water, which requires high quality of the medium frequency furnace ramming material. If the quality of the dry ramming material is not good, it is very easy to cause safety accidents such as steel leakage and explosion. With the rapid development of short-process steelmaking and stainless steel smelting, the demand for high-quality medium frequency furnace dry ramming material is increasing. Corundum has a high melting point, a small thermal expansion coefficient, good thermal volume stability, and excellent corrosion resistance. Because corundum reacts with magnesia at high temperature to form spinel, it produces volume expansion, which can effectively inhibit the cracking of the corundum-based lining. Aluminum-magnesium ramming material uses electric fused corundum as the main raw material, and adds an appropriate amount of magnesia and additives. Using corundum-magnesia ramming material as the lining material, the cracking of the hot surface of the lining is significantly controlled, and the microcracks are significantly reduced. At present, aluminum-magnesium ramming mass with fused corundum as the main raw material has gradually become the preferred lining material for medium frequency furnace steelmaking.
