Keyword：Continuous Casting Tundish, Nozzle, Magnesia carbon brick
The continuous casting tundish is one of the key equipment in the continuous casting process. It has the function of stabilizing and diverting the flow, and plays a very important role in the continuous casting operation and the quality of molten steel. The stable pouring of the tundish is beneficial to prolong the residence time of the molten steel in the tundish and to uniform the temperature and composition of the molten steel. However, the working layer near the impact zone of the tundish is eroded too quickly by molten steel, which restricts the service life of the tundish. By adding a flow stabilizer in the impact area of the molten steel in the tundish, the erosion of the molten steel on the working layer of the tundish near the impact area can be slowed down, thereby further increasing the life of the tundish. After installing the current stabilizer, the movement track of the molten steel in the tundish is changed, which reduces the additional circulation, basically eliminates the short-circuit flow, reduces slag entrainment, and promotes the floating of inclusions. However, there are still problems of severe erosion and high temperature at the corners on both sides of the tundish, block blocks, and the upper nozzle, which reduces the service life of the tundish, resulting in increased heat exchange billets, high consumption of steel materials, and increased cost of refractory materials. Therefore, it is necessary to improve and optimize the metallurgical process of the continuous casting tundish to increase the service life of the tundish, ensure the cleanliness of molten steel, improve the quality of casting slabs, and meet user requirements. By taking effective measures, better metallurgical effects have been achieved.
Process flow and existing problems
Process flow:
50t combined blowing converter → refining → continuous casting ladle rotary table → tundish → flow stabilizer → upper nozzle → crystallizer.
There is a problem:
1) The working layer of the tundish of the continuous casting machine in the old area of the steelmaking plant has undergone multiple expansions and transformations. The working lining is relatively thin, and the thickness of the working lining of the cladding wall is about 80mm. The cladding of the tundish has not been updated for many years, and the cladding is seriously deformed. Resulting in uneven wall thickness. The erosion thickness of the slag line of the working layer of the tundish is more than 40mm after being used for more than 48 hours recently, and the slag line and impact area of the tundish are seriously eroded. After the slag line of the tundish is corroded, the measured temperature of this part is more than 50 ℃ higher than that of other parts.
2) At present, in the production of stopper rod tundish of continuous casting machine, the head of stopper rod is washed unevenly and strongly by the molten steel in the tundish. After 12 hours of use, the tip of the stopper rod was uneven and eroded too quickly, which made the tundish of the stopper rod unable to control the flow stably. It is the key factor that limits the service life of the stopper rod tundish.
3) At the end of the service life of the sizing tundish, the upper nozzle of the tundish erodes too quickly, the zirconium core falls off, and the problems of nozzle blockage and continuous casting cut-off often occur, which seriously affect the efficient production of continuous casting. The above factors lead to more unplanned tundish replacements, seriously affecting the improvement of the life of the tundish, and bringing greater risks to the safe and stable production of the continuous casting machine.
Improvement measures:
Tundish slag line magnesia carbon brick composite repair technology
Tundish refractories are divided into two parts: permanent layer and working layer. The permanent layer is mainly used for heat preservation of the tundish and has poor erosion resistance; the working layer is mainly used to resist erosion of high-temperature molten steel and steel slag, and its heat preservation effect is relatively poor. Improving the anti-erosion performance of the tundish slag line is mainly improved by optimizing the working layer.
Through the development of a tundish slag line magnesia carbon brick masonry process. According to the erosion width of the tundish slag line and the thickness of the working layer of the tundish. Design a special magnesia carbon brick for the tundish slag line with a size of 300mm×300mm×30mm, and the material for the working layer of the tundish is magnesia dry material. According to the different erosion conditions in the tundish, the material of the dry magnesium material at the slag line of the tundish is improved, and the corrosion resistance of the dry magnesium material at the slag line is improved. Magnesium dry material is divided into two types: slag line magnesium dry material and bottom magnesium dry material. Below the slag line of the tundish and at the bottom of the tundish, dry magnesia material is used at the bottom of the tundish, and special dry magnesia material is used for the slag line of the tundish. When preparing the tundish, after the permanent layer of the tundish is knotted, the working layer of the tundish is knotted. First fill the tundish slag line below the magnesia dry material at the bottom of the tundish, and then place a circle of special magnesia carbon bricks for the tundish slag line along the inner wall of the permanent layer of the tundish. Finally, the slag-line magnesium dry material is filled, and it is formed after being baked in a medium-low fire for 1.5 to 2.0 hours.
Composite repair of magnesia plates in the impact zone of the tundish
Increasing the thickness of the working layer in the impact zone of the tundish is limited by the narrow space in the impact zone of the tundish. Reduce the thickness of the permanent layer in the impact zone of the tundish from 200-220mm to 150-170mm. The thickness of the working layer in the impact zone of the tundish is correspondingly increased from 80-100mm to 130-150mm. After increasing the thickness of the working layer in the impact zone of the tundish, the erosion resistance of the impact zone of the tundish can be significantly improved.
Research and develop a masonry process of magnesium plate combination in the impact area of the tundish, and design the special magnesium plate for the impact area of the tundish according to the shape and size of the tundish. The magnesium board is formed by knotting dry tundish materials, and is divided into three types: outer arc board, side arc board and side board. The thickness of the magnesium outer arc board and side arc board is 100mm, and the thickness of the magnesium side board is 50mm. The outer arc plate, side arc plate, and side plate of the magnesium plate in the impact area of the tundish are combined to protect the working layer in the impact area of the tundish. After the working layer of the tundish is knotted. Install a flow stabilizer in the impact zone of the tundish. The magnesium outer arc plate is installed above the current stabilizer. Two magnesium side arc plates are installed on the left and right sides of the current stabilizer. Two magnesium side panels are mounted on either side of the corner of the impact zone. After the installation is completed, it is bonded with a smear material, and it is formed after baking in a medium and low fire for 1.5 to 2.0 hours.
Continuous casting tundish long life upper nozzle
In order to solve the problem of rapid erosion of the upper nozzle of the tundish and the falling off of the zirconium core. Developed and used a new type of long-life upper nozzle. Increase the height of the inverted upper nozzle, increase the thickness of the magnesium carbon protective layer on the upper part of the zirconium core of the upper nozzle, and reduce the erosion of the molten steel on the zirconium core; increase the thickness of the zirconium core of the upper nozzle as a whole, and improve the corrosion resistance of the zirconium core of the upper nozzle.
1) Design of external dimensions. The height of the upper nozzle is increased from 95mm to 145mm. A magnesium-carbon protective refractory is added to the upper end of the zirconium core of the upper nozzle. The thickness of the magnesium-carbon protective refractory material is 20mm, which plays the role of isolating the zirconium core of the upper nozzle from the molten steel, and reduces the direct erosion of the molten steel on the upper end of the zirconium core.
2) Optimization of inner cavity zirconium material. The height of the upper nozzle zirconium core body is increased from 80mm to 125mm, and the overall thickness of the upper nozzle zirconium core body is increased by 2mm. The inner hole where the upper end of the upper nozzle zirconium core is in direct contact with the molten steel is designed as an R arc with a radius of 5mm to improve the strength of the upper nozzle zirconium core. And buffer the impact of molten steel on the zirconium core.
Stopper tundish combined cofferdam block
The quality of stopper rods, block bricks and upper nozzle refractory materials used in continuous casting tundish determines the service life of stopper rod tundish. The seat brick is used in conjunction with the upper nozzle of the tundish, the main function is to fix and protect the upper nozzle of the tundish, improve the installation accuracy and service life of the upper nozzle, and the stopper rod cooperates with the upper nozzle of the tundish to control the flow.
In order to solve the problem of uneven and fast erosion of the stopper rod head in the stopper rod tundish, a combined cofferdam seat brick for the stopper rod tundish was developed. The combined seat brick is divided into two parts: the lower seat brick is used for the positioning of the tundish seat brick and the upper nozzle. The upper seat brick is higher than the matching bowl of the upper nozzle of the tundish, which plays a role in protecting the bowl of the upper nozzle of the tundish and the head of the stopper. The combination of the upper nozzle of the stopper rod tundish, the stopper rod and the combined cofferdam seat brick solves the uneven and fast erosion of the stopper rod head by the molten steel in the tundish, and improves the service life of the stopper rod tundish.
Effect
1) The composite masonry process of the tundish working layer greatly improves the corrosion resistance of the tundish slag line. After the process was implemented, observe that the tundish was used for 48 hours, the erosion of the working layer at the slag line of the tundish disappeared, and the shape of the magnesia-carbon brick was intact; the magnesia-carbon brick was observed to be in good shape when the tundish was used for 70 hours, and some magnesia-carbon bricks remained at the slag line of the tundish. , check that the permanent layer is intact.
2) The combined masonry process of magnesia plates in the impact area of the tundish improves the corrosion resistance of the impact area of the tundish.
After the process is implemented, observe that the tundish is used for 48 hours, the shape of the magnesium carbon plate in the impact area of the tundish is obviously eroded, and the working layer is intact; the tundish is used for 70 hours, the magnesium carbon plate in the impact area of the tundish disappears, and the erosion thickness of the working layer is 100-150mm In 2019, the number of tundish offline due to severe erosion in the impact zone was reduced to zero.
3) The application of the combined cofferdam seat brick in the tundish of the stopper rod effectively solves the problem of uneven and fast erosion of the head of the stopper rod tundish, and greatly improves the anti-corrosion performance of the head of the stopper rod. After the process was implemented, it was observed that the tundish of the stopper rod was used for 11 hours, and the head of the tundish of the stopper rod was slightly eroded; it was observed that the head of the tundish of the stopper rod was eroded obviously after being used for 18 hours, but it was obviously lighter than before optimization, and it can continue to be used.
4) The application of the new long-life upper nozzle reduces the corrosion of the zirconium core by molten steel. After 72 hours of on-site use, the upper nozzle of the tundish has no cracking phenomenon, and the foreign matter in the nozzle is reduced to 1 time per month.
Through the application of tundish slag line magnesia-carbon brick composite repair technology, tundish impact zone magnesia board combined repair technology, continuous casting tundish long-life upper nozzle technology, stopper rod tundish combined cofferdam seat brick technology. The overall erosion resistance of the tundish in the steelmaking plant is improved, the refractory material in the impact zone is stable, the cleanliness of molten steel is guaranteed, and the metal yield is improved. The average life of the sizing tundish is increased from 48h/pack to 72h/pack.
