Improving the service life of the tundish of the continuous casting machine is of great significance for reducing the consumption of refractory materials for continuous casting, reducing the tundish pouring and cutting off the ends and tails of the cast slab, and improving the quality of the molten steel. Due to the low life of the stopper rod, the improvement of the life of the tundish is restricted, and the structure of the tundish is not optimized, and the impact zone of the working layer is seriously eroded, resulting in a low life of the tundish and a high cost of refractory materials, and the life of the tundish is closely related to the quality of the steel. The refractory material consumed by corrosion will enter the molten steel, which is very detrimental to the purity of the molten steel. Therefore, improving the service life of the tundish is particularly important to reduce the cost of refractory materials and improve the quality of molten steel.
After the continuous casting of the steel plant increased production, the pulling speed increased accordingly. The upper nozzle of the tundish (the nozzle under the ladle pouring area) was not resistant to erosion. The upper nozzle expanded, and the molten steel eroded the lower nozzle (slider), causing the lower nozzle to turn red. According to the accident situation, in order to avoid larger production accidents, the on-site method was to block the flow and pull the tundish in advance, which seriously affected the service life of the tundish and restricted the increase in output.
After the production of the continuous casting tundish was increased, the refractory materials in the tundish have changed significantly. Compared with similar tundishes, a comparison was made from the aspects of tundish design, flow field analysis and nozzle layout. There are three tundish types, namely “T” There are three types of bags, namely “straight bag” for pairs and “knife handle” bags for pairs. The molten steel directly impacts the 4th and 5th flow nozzles in the nearest opposite ladle through the impact plate in the middle ladle, causing the flushing intensity and time of the 4th and 5th flow nozzles to be greater than those of other ladle types. After the output is increased, the nozzle damage is more obvious. The other two bag types do not have such problems in use and can be produced according to the designed output. The refractory materials are relatively stable in use and the service life can meet the requirements.
2.Analysis of causes
At the scene, the technicians analyzed the main reasons for the following two points.
(1) The aluminum carbon material outside the zirconium core of the upper nozzle of the tundish has poor resistance to the impact of molten steel. After the continuous casting speed is increased (the diameters of the upper and lower nozzles are simultaneously expanded), the zirconium core of the upper nozzle and the aluminum carbon refractory material outside the zirconium core are affected by the increase in the flow rate of the molten steel, and the corrosion resistance decreases.
(2) The upper nozzle of the tundish uses a zirconium core with a diameter of Φ20~21mm, and the lower slide uses a zirconium core with a diameter of 17~19mm. During the operation of the molten steel, it will stop at the bottom of the upper nozzle and the top of the lower nozzle (slider), and The continuous backflow directly impacts and erodes the aluminum carbon material on the outside of the zirconium core of the lower slider, causing serious erosion of the aluminum carbon material on the edges of the zirconium core (outer diameter 45mm) of the upper and lower drains (slider) and preventing normal production.
The nozzle part of the on-site off-line tundish was dismantled. Judging from the demolition situation, there is cold steel between the upper and lower nozzles. This is mainly caused by the back and forth circulation of molten steel through the upper and lower nozzles (but it does not cause steel accumulation). This will be The principle of molten steel erosion nozzle is simulated.
By comparing the current situation of use on the site and the photos of the wreckage at the outlet, the technicians took the following measures.
(1) According to the existing continuous casting conditions, the tundish manufacturer improves the aluminum carbon material outside the zirconium core of the upper nozzle of the tundish, mainly to improve the material, increase the compressive strength, and increase the aluminum carbon material outside the zirconium core nozzle. Impact resistance of carbon materials.
(2) The zirconium core inside the nozzle was modified, and the outer diameter of the zirconium core inside the upper and lower nozzles was expanded by 10 to 20 mm.
(3) Organize the corresponding relationship between the casting speed and the nozzle, and at the same time require the personnel in the continuous casting operation area to reasonably match the corresponding relationship between the casting speed and the nozzle, and use the corresponding upper nozzle.
(4) Routine maintenance measures for tundish. The technical department conducts on-site inspections from time to time, mainly for the on-site tundish contractor construction and the on-site operation of the steelmaking and continuous casting operation area. It communicates the contents of the inspection in a timely manner, and immediately corrects and rectifies those that do not follow the regulations.
(5) The tundish manufacturer’s subsequent research and design of the flow stabilizer in the impact zone requires it to have its own slag retaining wall, and the openings in the slag retaining wall should avoid the 4th and 5th streams that are most susceptible to impact.
4.Tundish structure optimization
The material of the tundish is magnesium dry material, and there is no problem with the mature technology of dry material, but the overall toe cap has been used in the impact area of the tundish. The overall toe cap is large in size, which seriously affects the volume of the impact area, which is not conducive to the flow field of the tundish and causes impact The area is severely eroded and eroded, and there is a risk of bag leakage, and affected by the climate in winter, cracks and defects often appear on the overall Baotou, which increases the risk of use.
To this end, the overall head of the impact area is removed. The impact area is constructed with dry materials. A circular flow stabilizer is installed at the impact point. The flow stabilizer is fixed with dry materials. Two slag retaining dams are installed opposite the impact area to improve the flow field in the middle package and reduce Molten steel scours the third and fourth streams.
The optimized tundish structure can not only meet safety needs but also increase tundish capacity. Through data calculation, this solution can be used to greatly increase the volume of the impact zone and increase the molten steel capacity of the tundish by about 4 tons. The volume of the impact zone of the tundish is increased, which improves the flow field of the tundish. The dead zone is reduced by 10%, the plug flow increases by 11%, and the residence time of the molten steel is 57 seconds longer than that of the original tundish. The velocity of the molten steel in the impact zone slows down, reducing the erosion of the third and fourth flow stopper rods. The tundish flow field is optimized, which is conducive to uniforming the temperature of the molten steel in the tundish, promoting the floating of inclusions, and reducing the erosion of the impact zone.
Regarding the above measures, the factory responded immediately and used a week to improve the nozzle, especially the first and second items. After it was put into use, we jointly paid attention to the use effect. The improved use time of the middle package nozzle was 47h20min (pulled down in advance, Maintenance of steelmaking converter, no molten iron), no major erosion or diameter expansion was seen around the zirconium core at the nozzle, thus achieving the expected use effect. The use time exceeded the design time by 45 hours, and the effect was good.
Through the improvement of the nozzle of the continuous casting tundish in the steelmaking plant and the management of all aspects, the output has been increased, the cost of refractory materials has been reduced, and the heat exchange time of the tundish has been saved.
Continuous casting tundish in the speed increase in production, constraints on the yield of the weak links are gradually manifested, for the tundish nozzles transformation, the benefits achieved are very obvious, the follow-up in order to improve the purity of steel, improve the service life of tundish, there are still a lot of work to be done, such as the need to impact the region of the addition of the tundish slag wall, etc., which requires the technicians for the constraints of the link to continue to research and transformation.
More details about tundish nozzles:
What is a tundish nozzle?
Tundish Nozzles are an integral part of Continuous Steel Casting process. These products are instrumental in controlling the flow of Molten Steel from Tundish to Continuous Casting. Long casting sequence time. Controlled casting speed. Excellent resistance to oxidation.
What material is a tundish nozzle made of?
Design and construction: Tundish nozzles are typically made from high-quality refractory materials, such as alumina, magnesia, zirconia, or a combination of these materials, depending on the specific application requirements.
What are the different types of tundish Nozzles?
Different kind of tundish nozzles include, Alumina, Alumina Carbon, Zirconia Alumina Nozzles, which are manufactured for single to multiple casting application.