Improve the life of the middle pack of continuous casting machine is of great significance to reduce the consumption of refractory materials for tundish, reduce the casting surplus of middle pack and billet cutting head and tailing, and improve the quality of liquid steel. Due to the low life of the plug rod, restricting the middle pack life to improve, and the middle pack structure is not optimized, the working layer impact zone erosion is serious, resulting in low life of the middle pack, refractory cost is higher, and the life of the middle pack and the quality of steel is closely related to the erosion of the refractory consumed will be into the steel water on the steel purity is very unfavorable. Therefore, it is especially important to improve the tundish life to reduce the cost of refractory and improve the quality of steel.
Tundish continuous casting in the increase in production, the pulling speed of the corresponding increase in the tundish upper nozzle (ladle pouring area below nozzle) is not erosion-resistant, the emergence of the ladle upper nozzle dilatation, steel erosion of the lower nozzle (slider), resulting in the lower nozzle of the red, nuisance steel and other accidents, in order to avoid a greater production accidents, the site used to block the flow, the intermediate packet pulled off early in the form of a serious impact on the intermediate packet service life, constraints on the improvement of production.
Analysis of current situation
Tundish continuous casting in the package to raise production, the tundish in the resistant material appeared obvious changes, compared with similar intermediate package, from the package design, flow field analysis and nozzle arrangement and other aspects of the comparison, there are three kinds of packages, respectively, “T” type package, the package “straight package”, the package “knife handle type” package. Three types of packages are “T” type package, “straight type package”, “knife handle type” package, and three types of packages. The tundish belongs to the package “knife handle type” package, compare the three package types, from the flow field analysis, the package “knife handle type” package, steel through the tundish within the tundish impact plate directly impact on the recent nozzle of the package, resulting in the nozzle scouring intensity and time is greater than the other packages nozzle. The damage to the tundish nozzle is more obvious after the production is increased. The other two package types do not have such problems in use, and can be produced according to the designed output, the refractory material is more stable in use, and the service life can meet the requirements.
At the scene, technicians and manufacturers jointly analyzed that the main reasons are the following two points.
(1) The aluminum-carbon material outside the zirconium core of tundish upper nozzle has poor anti-steel impact performance. After continuous casting to enhance the pulling speed (upper and lower nozzle caliber at the same time to expand), the upper nozzle zirconium core and zirconium core outside the aluminum and carbon resistant material by the liquid steel flow rate increased, erosion resistance decreased.
(2) The tundish uses Φ20-21mm caliber zirconium core for the upper nozzle and Φ17-19mm caliber zirconium core for the lower slider. In the process of liquid steel operation, the zirconium core will stay at the bottom of the upper nozzle and at the top of the lower nozzle (slider) and will continuously flow back, and the flow back will directly impact and erode the aluminum and carbon material outside of the lower slider zirconium core, which results in serious aluminum and carbon erosion of the aluminum and carbon material at the edge of the zirconium cores (OD45mm) of the upper and lower nozzle (sliders), preventing normal production. This caused serious erosion of the aluminum and carbon material on the sides of the zirconium cores (45mm OD) of the upper and lower nozzle (sliders) and prevented normal production.
On the site of the downline ladle nozzle part of the demolition, from the demolition of the situation, the upper and lower nozzle between the cold steel, mainly through the upper and lower nozzle of the liquid steel circulation back and forth (but not to the extent of causing the nuisance steel) caused by the principle of the liquid steel erosion water mouth simulation.
By comparing the current situation of using the site and the photos of the remains of tundish nozzle offline, the technicians study together and take the following measures.
(1) The tundish manufacturer improved the aluminum and carbon material outside the zirconium core of the upper nozzle of the middle pack according to the existing continuous casting working conditions, mainly improving the material, improving the pressure resistance strength, and improving the impact resistance of the aluminum and carbon material outside the zirconium core nozzle.
(2) The zirconium core inside the nozzle port was modified, and the outer diameter of the zirconium core inside the upper and lower nozzle ports was enlarged by 10-20mm.
(3) Combined with the literature, the corresponding relationship between pulling speed and nozzle was organized, and at the same time, the personnel in the on-site continuous casting operation area were requested to reasonably match the corresponding relationship between pulling speed and nozzle, and to use the corresponding upper nozzle.
(4) The daily maintenance measures of tundish. Technology Department combined with the supply company, from time to time to carry out on-site inspections, mainly for the site in the contracting contractor construction and steelmaking continuous casting operation area on-site operation, for the inspection of the content of timely communication, not in accordance with the provisions of the implementation of the immediate rectification and rectification, repeated offenders to be punished.
(5) Tundish manufacturers follow-up research and design impact area of the flow stabilizer, requires its own slag wall, slag wall openings to avoid the most vulnerable to the impact of the region.
Tundish structure optimization
The tundish material for magnesium dry material, dry material technology is mature there is no problem, but the tundish impact zone parts have been using the whole head, the whole head is large, seriously affecting tundish impact zone volume, is not conducive to the tundish flow field, resulting in the impact zone scour erosion is serious, there is a risk of leakage package, and winter by the influence of the climate, the whole head is often cracked defects, increasing the risk of use.
For this reason, the whole header of the tundish impact zone is removed, the impact zone is constructed with dry material, a round flow stabilizer is installed at the impact point, the flow stabilizer is fixed with dry material, and two slag dams are installed opposite to the impact zone, which improves the flow field of the middle ladle and reduced steel washout.
The optimized tundish structure can meet the safety needs and increase the tundish capacity. Through the data calculation, the use of this scheme significantly increase the impact zone volume, so that the tundish steel capacity increased by about 4t. Tundish impact zone volume increased, improve the tundish flow field, dead zone reduced by 10%, the piston flow increased by 11%, the molten steel retention time than the original tundish to extend the 57 s. Impact zone slowed down the flow rate of molten steel to reduce the scouring of the three or four flow plug bar. Optimization of the tundish flow field is conducive to uniform tundish steel temperature, promote the uplift of inclusions, reduce the scouring of the impact zone.
For the above measures, the contracted manufacturers of tundish contract immediately responded, using a week’s time to improve the mouth of nozzle, especially the first item, the second item, after being put into use to jointly focus on the use of the effect of the improved tundish contracted mouth of the water to use the time of 47h20min (pulled down in advance, the steelmaking converter overhaul, no iron), under the mouth of the zirconium core around the no major erosion and expansion, so as to achieve the expected effect of the use of the use of the time of more than the design time of 45h, the effect of a good.
Through the improvement of tundish continuous casting nozzle outlet and management in all aspects of the steel plant, it has improved the output, reduced the cost of refractory materials, and saved the time of heat exchange of tundish at the same time. Specific benefits are as follows:
① daily savings of a tundish, the cost of about 80,000 RMB;
② hot pack time savings of 10min, efficiency: 40t steel × 4,500 RMB / t steel = 180,000 RMB;
③ production enhancement of about 1000t / shift, the daily efficiency of 2 × 1,000 × 100 = 200,000 RMB; total daily efficiency: ① + ② + ③ = 460,000 RMB.
Steelmaking continuous casting tundish in the speed increase in production, constraints on the yield of the weak links are gradually manifested, for the tundish nozzle transformation, the benefits achieved are very obvious, and then 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 for the impact of the region of the addition of the slag wall, etc., which requires the technicians for the constraints of the link to continue to research and transformation.