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In the use of electric furnaces, the life of our linings is mostly determined by the degree of erosion of the bottom of the lining and the integrity of the lining to determine whether to continue to use. Electric furnace spray
Erosion of the bottom of the furnace
In the normal use of the lining, the thickness of the lining and the thickness of the bottom of the furnace will gradually become thinner due to the cyclic erosion of the molten iron in the long-term use. The most intuitive situation is the increase of the furnace capacity, and the general lining is eroded 30--50. When it is %, it will be destroyed again, and then a new furnace building work will be carried out. From the whole lining analysis, the most obvious place for erosion is the slope position where the bottom of the furnace is combined with the lining. Generally, after the long-term use of the furnace, the thick lining of the original slope has been eroded to be similar to the lining. And the furnace lining on a circular arc surface, even in the soil combined with the furnace bottom material and the furnace lining material, there is a slight depression. As the furnace age increases, the depression of this position becomes deeper and deeper. The closer to the electric furnace coil, which affects the safety of use, the need to rebuild the furnace. The cause of the lining depression is related to the chemical corrosion during melting of the additive in use and the mechanical erosion during operation, in addition to the density of the quartz sand during furnace formation.
(1) Chemical attack
The so-called chemical erosion is the reflection of the lining material formed by the composition of the charge and alloy components and the composition of the lining material that we add in the production. As mentioned above, the C and Si ratios of the composition of the molten iron and the composition of the lining in the oven lining should be considered. In the production process, we also need to add a recarburizer to supplement the required If the C component of the molten iron is added too early to the recarburizing agent, there will be an excessive C content in the small amount of molten iron in the furnace. At this time, the Si required for the balance of C and Si ratio is required. In turn, a large amount of Si is taken from the lining, causing premature erosion of the slope. The pig iron in the dissolved material should not be added because of its high C low SI composition. The characteristics of scrap steel that is almost free of C and Si and the oxides that tend to erode the lining should also avoid its addition. In view of the above reasons, our feeding sequence should be added to the pig iron after adding some of the recycled materials, and then add the recarburizer to the other alloys when the molten iron in the furnace is melted by 1/3 or 1/2. Join and then melt the molten iron.
(2) Mechanical erosion
Regarding the mechanical erosion, it is mainly related to the operation of our personnel. Generally, when we dissolve, we often encounter the problem of the furnace material bridge in the furnace. That is to say, the molten iron has been dissolved in the slope of the bottom of the furnace, and the charge added above is The card is not in contact with the molten iron in the middle of the electric furnace. Since this kind of situation cannot be seen visually, the input power is not reduced. When the temperature of the bottom of the furnace rises above 1600 °C, the erosion rate of the lining will be normal. The erosion rate is several times higher, and the higher the temperature, the faster the erosion rate. If the temperature of the molten iron continues to rise to the temperature of the lining limit (1725 degrees), the sintering layer of the lining material will overheat. The furnace lining after overheating is more easily eroded. Another similar situation is that we will encounter a small amount of molten iron for long-term insulation during the production process. If the insulation power given is unstable or too high, it will cause the same phenomenon as above. Therefore, for our operators. Careful control of the melting process and continuous temperature measurement is necessary.
2. The integrity of the lining
The integrity of the lining refers to the osmosis and cracking that often occurs in the lining. In our production, there will often be a weekend rest and shutdown. When the electric furnace is emptied and stopped to melt, the lining will slowly cool. Since the sinter material after sintering is brittle, the sintered layer is inevitable under the action of thermal expansion and contraction. The occurrence of cracks, the crack is very harmful, which will cause the molten iron to penetrate into the furnace lining and cause the furnace to leak. From the aspect of protecting the lining, the crack is finer and denser and evenly distributed, because only in this way can the crack be bridged when the furnace is cold-drawn, and a complete sintered layer is lining. In order to reduce the crack propagation, we should pay attention to several problems in production.
(1) Avoid the lining of the lining
When the impurities, oxides, and raw materials in the charge are dissolved at high temperature, they become a kind of viscous material that often adheres to the upper part of the lining and the furnace mouth, because these slags will affect the temperature of the lining. The gradient will cause the lining to overheat and reduce the life of the lining. It can also cause the heat loss of the lining to decrease, and the thickness of the sintered layer will be thicker. The thickening of the sintered layer will affect the thickness of the loose layer, and the loose layer will be stopped when the furnace is stopped. The cracks generated will inevitably penetrate the lining, which will affect the safe operation of the furnace. Because the difference between the shrinkage expansion coefficient of the lining slag and the lining material also affects the size and depth of the crack, for example, when the lining of the lining is cooled and contracted, the lining inside the slag has not reached the shrinkage temperature, and The fact that the lining without the slag in the furnace substrate portion has also begun to shrink will cause the upper half of the lining to be "suspended", resulting in a large crack. Therefore, it is necessary to keep a smooth and clean sintered layer in the furnace during production and before stopping the furnace.
(2) The effect of excessive temperature on the lining
Occasionally, in the case of storage, the power given to the electric furnace by the operator during dissolution or temperature rise is not lowered in time, and the temperature of the molten iron exceeds 1600 ° C. Although the temperature of the molten iron does not reach the limit temperature of the quartz sand, the lining is also applied. Has caused a certain impact. In addition to the excessive temperature of the molten iron, the erosion of the lining is accelerated, the normal service life of the lining is reduced, and the thickness of the sintered layer is increased due to the excessive temperature of the strontium iron, which reduces the thickness of the loose layer. The storage of the loose layer can not only be The after-effect reduces the smallness and depth of cracks occurring in the cold furnace, and also because the loose layer does not have the property of cracks, which can effectively block the safety of the coil of the molten iron protection furnace penetrated by the crack, if there is no iron infiltrated by the loose layer It is possible for the liquid to directly contact the coil through the crack to form a leak furnace. It must be used in the dissolution process to grasp the temperature of the molten iron in the furnace to prevent the occurrence of such conditions.
(3) Cooling of the lining
When the furnace is shut down, we generally use the natural cooling of the furnace lining, but the crack generated by natural cooling is obviously larger than the crack generated by the method of using the furnace lining. The quick cooling method is the auxiliary cooling method, and the airflow by the compressed air or the fan is timely. Taking away the heat of the lining and letting the surface of the lining shrink in time to form many small cracks, which can better and timely close the furnace to reduce the probability of lining iron in the furnace operation. At the time of rapid cooling, attention should be paid to the uniformity of heat dissipation. The moisture in the compressed gas should also be avoided. The moisture can cause local chilling of the lining, which causes partial flaking of the lining.
(4) Problems to be noticed when cold-heating
In continuous production, the lining is always in a high temperature state, and the surface of the sintered layer of the lining has good thermal shock stability and certain mechanical strength. When the additive is dissolved, the lining can effectively absorb the impact force of the charging material, so that it is not added during feeding. It will cause great harm to the lining, but we should pay special attention to this problem when it is cold. The refractory material of the lining is the phenomenon that the brittle material will crack or peel off if it is subjected to strong impact at normal temperature. Therefore, we should pay special attention to this when feeding the cold furnace, and try to make it smaller and smaller when adding the furnace. The material is added, which can effectively avoid the artificial damage caused to the furnace lining.
Since the crack formed when the furnace lining is in the cold furnace can be fully closed after a certain preheating, we must ensure that the preheating time of the lining is sufficient, and it is necessary to prevent the molten iron from being melted before the lining crack is completely completely closed, thereby causing the phenomenon of iron lining. When the furnace is cooled, we should raise the temperature of the furnace material to 100 ° C below the melting point of the furnace material and then keep it for less than two hours before the melting operation can begin.
(5) Regular inspection of the lining
The place where iron seepage often occurs in production is the place where the nozzle and the lining material are combined. Since it is two different materials, there must be a certain gap at the joint point, and this gap creates an opportunity for the osmosis. The position of the coil is also under the mouth of the furnace, so it is very important to carry out regular inspection and repair of this position. If iron seepage is found, it should be cleaned and repaired in time to avoid damage to the coil. In addition to the attention to the nozzle, we should also strengthen the inspection of the entire lining, and provide a comprehensive understanding and timely feedback on the safety of the entire lining.