Refractory for continuous casting function series
November 23, 2020
The nozzle series is divided into long nozzle, constant diameter nozzle, immersion nozzle and separation ring.
(1) Long nozzle
The long nozzle is under the ladle and above the tundish, the upper part is connected with the lower nozzle under the ladle, and the lower part is buried into the molten steel of the tundish. It separates the flow of molten steel from ladle to tunic from the air, preventing the flow of molten steel, reducing the entry of inclusions and protecting the molten steel from oxidation. The long nozzle is not only eroded by strong thermal shock and molten steel, but also eroded by tundish coating agent. With the development of metallurgical technology and the intensification of market competition, the requirement of steel quality is higher and higher, in order to meet this development, the proportion of protective pouring is higher and higher. Therefore, the use of long nozzle proportion is also increasing. Not only high quality steel needs protective casting, but also the proportion of ordinary steel protective casting is increasing.
The long nozzle began in the 1960s with the use of molten quartz. It is all amorphous phase, its outstanding characteristics is extremely low linear expansion coefficient, close to zero, its thermal shock resistance is very good, in the use of the process does not burst to ensure the safety of continuous casting. But the disadvantage is the lack of corrosion resistance, especially for high manganese steel and other special steel casting service life is shorter. For the continuous casting level requirements are not high still in use.
With the improvement of continuous casting level, especially the casting of special steel, not only the erosion resistance of quartz long nozzle is not enough to meet the requirements of the service life of continuous casting, but also has a bad effect on the quality of steel. This requires the development of new materials of the long nozzle, after the study of aluminum - carbon long nozzle appeared. It significantly improves service life. However, at that time, the aluminum-carbon long nozzle was mainly composed of composite materials made of corundum, mullite, graphite and fused quartz, which were mixed with carbon binder in a certain proportion, and then isostatic pressing, firing and machining. The inclusion of mullite and quartz significantly improves the thermal shock resistance and avoids the fracture during use. However, the quartz composition of Mullite is still insufficient to resist the erosion of special steel such as high manganese steel, which restricts the further improvement of the service life of continuous casting. In order to solve this problem, the development of composite long nozzle, namely slag line magnesium carbon material, zirconium carbon material, the main body with aluminum zirconium carbon material, in order to adapt to the casting of low carbon steel, the inner layer with aluminum and magnesium, Sialon ceramics and other carbon-free materials. For casting aluminum-killed steel, the nozzle is often nodulated and blocked. In this case, good results have been obtained by blowing argon with a vent ring at the top of a long nozzle and by using non-carbon refractory and calcium zirconate materials for the inner layer. In order to meet the urgent needs of steel plants, the need for non-baking can be used by the long nozzle, that is, high thermal shock resistance of the long nozzle should also be developed to meet the requirements of users. In short, the development of long nozzle to meet the requirements of users, different types of steel casting and long life.
At present, the service life of China's long shuikou is not high, generally within 10h. This is caused by many reasons, that is, the material is not good, durability is not enough, and China's conservative use and steel supply is insufficient, so that even the water supply can not go up, resulting in the disconnect, and Japan's long nozzle service life some reach more than 20h, we have a lot of gaps. Therefore, innovation should be implemented in material and technology should be further improved in order to improve the quality and use level of China's long shuikou.
It is worth mentioning here that the development of the amorphous long nozzle has made progress in recent years. By casting instead of isostatic forming, it is different from the previous quartz nozzle casting. At present, it USES the method of castable vibration molding to grow the nozzle. At present, it mainly focuses on the aluminum-carbon and quartz composite nozzle. Aluminum-magnesium casting molding is also used, and certain use effect has been obtained. In the manufacturing method also has the new creativity, namely the machine presses the product and the vibration casts the combination, the vibration casts and the centrifugal casts the combination, the firing and does not burn the combination. These advances will promote the improvement of the performance of the long nozzle and the reduction of the cost.
(2) Sizing nozzle
The sizing nozzle is mainly used in billet continuous casting and is installed at the bottom of tundish.
It is required that the sizing nozzle should not be enlarged or eroded under the condition of strong scouring and erosion of molten steel, so as to stabilize the steel flow and play the role of controlling the stability of continuous casting. There are three types of traditional sizing nozzle structure, namely, inlay type, compound type and integral type. The so-called inlaid type fixed diameter nozzle is the part of the inner contact with molten steel with extremely excellent zirconia ceramic refractory, the outer layer with low price of ordinary high aluminum refractory, the inner and outer refractory with binder or fireclay bonded together, that is, the inner layer of extremely excellent refractory inlaid in the coat. This sizing nozzle has the highest cost performance, so it has been widely used. The so-called composite sizing nozzle means that the inner and outer refractory materials of sizing nozzle are different, which are directly compounded and sintered together in the production process. Due to the different expansibility of the two materials, it is easy to produce great thermal stress in the process of use, which will lead to the explosion of the sizing nozzle and the occurrence of steel leakage accident, making the continuous casting unable to proceed. Therefore, the sizing nozzle is rarely used. The integral sizing nozzle is the entire nozzle which is a material. This material generally does not reach the excellent level of the inner layer of the water inlet with fixed diameter, mainly because the cost is too high, so its use effect is poor, and the cost performance is not as high as that of the Mosaic type. It is worth pointing out that at present, many steel mills use brick and fixed diameter nozzle inlaid together, forming a whole, which has brought a lot of convenience to the construction, security is also significantly improved.
(3) In order to control the steel flow and stabilize the continuous casting, a plug rod is installed above the nozzle of tundish. By adjusting the gap between it and the nozzle, the purpose of controlling the velocity of molten steel is achieved. The sleeve brick of the plug rod is high aluminum or clay, and the plug head is made of aluminum carbon. They are installed in combination with steel structure controls for later use.
Some steel mills are still in use. The service life of the combined plug rod is not high, generally within 6h. The main reason for the damage is that the internal steel structure softeners and control failure under high temperature for a long time, and the sleeve brick erosion too fast. In order to solve this problem, the high temperature resistance of the steel control rod, the corrosion resistance of the sleeve brick and the match between the plug head and the nozzle bowl should be solved. Now slag line sleeve brick has used magnesium carbon brick, aluminum carbon brick, with aluminum zirconium carbon and other higher quality plug head.
An important way to solve the problem of low service life of composite plug is to adopt integral plug. That is, aluminum-carbon integral plug rod. It is made by isostatic forming, curing, machining and carbonization without metal rods. Therefore, there is no problem of softening. Its service life has been significantly increased to 10h. However, the plug head and the nozzle bowl are not smooth due to the flushing of steel, resulting in the flow control difficulties, or even shut. This is an important factor that restricts the service life and is worth researching and developing. For steel mills in which the converter is supplied with sufficient molten steel for the production of ordinary building steel, the service life of the plug rod is particularly required and the longer the better. Therefore, longevity plugs should be developed. For special steel plant, different types of steel to the refractory erosion is not the same. Plugs that are resistant to erosion of different types of steel are required. In this respect, magnesium carbon appeared in slag line, aluminum zirconium carbon appeared in plug head, etc. There has been some progress, but there is still room for improvement.
(4) Immersion nozzle
The upper end of the immersion nozzle is connected to the bottom of the tundish and the lower end is inserted into the mold. Ensure that the molten steel from the tunic is not exposed to the air, prevent the molten steel from escaping, reduce the entry of inclusions and protect the molten steel from oxidation. The immersion nozzle is not only eroded by strong thermal shock and molten steel, but also eroded by the protective slag in the crystallizer. Because the protective slag is a highly corrosive material with low melting point and low viscosity containing fluorite, potassium and sodium oxides, its erosion to the immersion nozzle is much more serious than that of the long nozzle, so the requirement for the immersion nozzle is much higher than that of the long nozzle. With the development of metallurgical technology and the intensification of market competition, the requirement of steel quality is higher and higher, and the proportion of protective pouring is higher and higher. Therefore, the proportion of immersion nozzle is also increasing. Not only high quality steel needs protective casting, but also the proportion of ordinary steel protective casting is increasing.
Immersion ports began in the 1960s with the use of molten quartz. The properties and characteristics of molten quartz immersion nozzle are basically the same as those of molten quartz long nozzle. Because the working conditions of the immersion nozzle are much worse than that of the long nozzle, the erosion rate of the molten quartz immersion nozzle is faster, which cannot meet the requirements of the high continuous casting level and special steel continuous casting except for the steel mills with very low continuous casting furnace.
With the improvement of continuous casting level, especially the pouring of special steel, not only the quartz immersion nozzle can not meet the requirements of the service life of continuous casting, but also have a bad effect on the quality of steel. This requires the development of new materials of the submerged nozzle, after the study of aluminum-carbon submerged nozzle appeared, it significantly increased the service life. In order to meet the requirement of thermal shock resistance, a certain amount of mullite and fused quartz is added to the aluminum-carbon immersion nozzle. However, the corrosion resistance of mullite and quartz components to special steel such as high manganese steel is still insufficient, especially the erosion resistance of protective slag becomes more significant, which restricts the further improvement of the service life of continuous casting. In order to solve this problem, the development of composite submerged nozzle, namely slag line zirconium carbon material, zirconium boride carbon material, the main body with aluminum-zirconium carbon or aluminum-carbon material, in order to adapt to the casting of low carbon steel, the inner layer with aluminum-magnesium, Sialon ceramics and other carbon-free materials. For casting aluminum-killed steel, the nozzle is often nodulated and blocked. In this case, good results have been obtained by blowing argon with a permeable ring at the submerged nozzle and by using non-carbon refractory and calcium zirconate materials in the inner layer. In order to meet the urgent needs of steel mills, the immersion nozzle that can be used without baking, namely the immersion nozzle with high thermal shock resistance, should also be developed to meet the requirements of users. By designing a trapezoidal immersion nozzle and placing a impeller in the nozzle, the flow field is changed so that inclusions in the molten steel float upward and nodules are prevented. The improvement of the structure of submerged nozzle is also an important content in the development of submerged nozzle. Another important problem of the immersion nozzle is the oxidation on the surface of the nozzle during the casting process, which makes the nozzle lose strength and destroy. Therefore, a layer of anti-oxidation layer is brushed on the surface and good results are obtained. A good anti-oxidation coating is often oxidized and burned without causing oxidation and decarburization at the nozzle. Another problem is that the thermal conductivity of carbon-containing refractory materials is too high, resulting in a high surface temperature of the nozzle, which will lead to a bad operating environment, and also lead to a drop in the temperature of the molten steel, which will aggravate the nodular formation. The solution is a layer of refractory felt on the surface of submerged nozzle, and good results have been obtained. In short, immersion ports are being developed to meet user requirements, different types of steel casting and long life.
At present, the service life of immersion nozzle in China is not high, generally within 10h. This is caused by many reasons, that is, the material is not good, durability is not enough, product quality is not stable, conservative use and steel supply is insufficient, so that even the water supply can not go up, resulting in a disconnect. And the service life of Japanese immersion nozzle can reach more than 15h, we have a lot of gaps. Therefore, innovation should be carried out in the aspect of material and its use level should be improved to improve the quality and use level of immersion nozzle in China.