Effect of fused magnesia on properties of bauxite-based castables

Fused magnesia is one of the most widely used refractory raw materials for basic refractories. The melting process of fused aluminum chrome sand magnesia (MgO) from raw materials is the smelting process of fused magnesia. The raw materials for the production of fused magnesia in my country are mainly magnesite ore. These raw materials contain many impurities, mainly SiO2, CaO, Al2O3 and Fe2O3, etc. Since the melting points of different substances are different, this determines the melting point of fused magnesia. The sand method adopts the exclusion method. According to the different melting points of each impurity in the raw material, the impurities of different components will be melted at the temperature of their respective melting points in turn by the heat of the arc. As the temperature increases during the melting process, impurities with a low melting point will first melt and migrate outward. As the temperature continues to rise, the impurities will precipitate one after another, which will make the purity of the main magnesium oxide higher and higher.

Fused aluminum chrome sand

 Fused magnesia

 In the smelting process of fused magnesia, it undergoes melting, precipitation, purification and crystallization in sequence. If the raw material contains more impurities (especially SiO2), it will be limited in the purification process of magnesia, which will affect the physical and chemical properties of the frit to a certain extent. High magnesite ore is used as raw material for smelting. The melting rate is affected by the particle size of the raw material. In industrial production, the ore should be crushed before feeding. If the particle size is too large, the melting speed will be reduced, and the power consumption will increase accordingly. However, if the particle size is too small, the impurities will often melt in the middle of the material layer. And crusting, so that it becomes difficult for impurities to volatilize and escape, and the quality and purity of the frit will be greatly affected. Therefore, it is very critical to maintain a proper layer thickness during the smelting process of fused magnesia. If the material layer is thin, the feeding interval will be shortened, the power supply system will fluctuate easily during operation, and it will be easy to catch fire. Excessive thickness of the material layer will lead to crusting of the material, which is not conducive to the escape of impurities. Therefore, the selection of reasonable raw materials, high-level operation and suitable electric heating system are all important for smelting qualified fused magnesia products. step.

 Fused magnesia chrome sand. Fused chrome sand. Fused magnesia sand

 The process of producing fused magnesium crystals by electrofusion method can be divided into the following three stages: starting, melting and finishing. First, the start-up stage: a layer of magnesite is placed on the bottom of the furnace, and three electrodes are inserted. Then put a carbon block between the electrodes as the arc starting material, and adjust the position of the electrodes to start the arc. After the arc is started and the current is stable, the material can be fed near the electrode. The arc will directly melt a part of the material, forming a molten pool at the lower end of the electrode, and the other part of the material will fall into the molten pool to melt. With the input and melting of the raw materials, the height of the molten pool will increase. will keep rising. Therefore, during the melting process, the electrode should be continuously adjusted and raised as the molten pool rises. The previously melted melt will gradually condense and crystallize due to the continuous heat dissipation and cooling of the furnace body. At this time, the molten lump is formed in the molten pool. In the furnace body, the raw materials near the periphery of the furnace shell cannot be melted, which plays a role of heat preservation. As the melting time prolongs, the molten pool continues to rise until it reaches the surface of the upper mouth of the furnace shell, at which point the melting process ends. Power off. Then use a trolley to pull the melted crystal lump together with the furnace body out of the melting station, let it cool naturally, and then come out of the furnace for manual crushing and classification.

 Fused magnesia

 The smelting process of fused magnesia is a very complex process, which is affected by many factors. Different electric heating systems will produce products with different crystal grains and different purity. In the initial start-up stage of the fused magnesia furnace, since there is very little liquid charge with good conductivity at the bottom of the furnace, the resistance of the circuit is relatively large, and the melting current is relatively small, so if the operator cannot be careful at this time. Operation, once the furnace is extinguished, it is very difficult to restart the furnace. With the continuous increase of the conductive liquid charge at the bottom of the furnace, the resistance of the circuit will gradually decrease, and the smelting current will gradually increase accordingly. Generally, about 30 to 40 minutes after starting the furnace, the fused magnesia furnace will enter the normal smelting process. At this stage, with the continuous melting of the solid charge added, the bottom of the fused magnesia furnace will form a stable molten pool, and its current will gradually stabilize. During the smelting process, the operator needs to continuously add solid charge into the furnace. The continuous addition of cold charge will change the circuit resistance and thermal balance in the furnace, resulting in a sharp change in the smelting current. At the same time, during the smelting process, due to external interference, the current value may become abnormally high at a certain time. At this time, in order to prevent the transformer from tripping and ensure the continuity of smelting, emergency protection measures should be taken. When the fused magnesia furnace is in the cooling stage, or when it must stop working because of a trip, at this time, in order to ensure the safety of the smelting, we should not touch the electrode, that is to say, the electrode cannot have any action. As the smelting process progresses, more and more charge will cool down in the furnace. When the distance between the charge surface and the furnace mouth reaches about 20cm, the operator will generally stop all operations. At this point, the operator turned off the power and pulled the electrode out of the furnace.

 Fused magnesia

 The process of smelting fused magnesia is the densification and purification process of magnesia itself, and the key to the process is the formation of polycrystals and the establishment of melts. In the fused magnesia furnace, the high temperature generated by the arc causes the raw materials with high magnesium content to undergo physical and chemical processes such as dehydration and decarburization in the furnace and melt. The completely molten raw material starts a series of polycrystalline growth processes after the heating of the fused magnesia furnace is stopped, which is a conservative process. According to the aging effect proposed by stward, the aging effect is worth the gradual growth and analysis of large crystals, which is accomplished by consuming microcrystals or adsorbing thermally diffusive atoms from the mother liquor. At the beginning of the process, the crystalline feedstock is in a liquid state, and the solid begins to grow by solidifying at specific interfaces in a supercooled melt. When the temperature of a certain part of the melt drops to about the melting point, crystal nuclei will appear irregularly in that part. During this process the crystals grow. Therefore, in order to improve the multi-purity crystal, it is necessary to improve the purity of the melt first. In the process of melting the material, the impurity with low melting point is melted first, and the MgO crystal is not melted. At this time, MgO constitutes a porous layer, through which the low-melting material penetrates from the inside to the outside.