ANALYSIS OF CRACKS IN LADLE NOZZLE SEAT BRICKS AND SOLUTIONS

The role of the ladle in the steelmaking plant is to transport the molten steel smelted in the converter to the continuous casting. On the continuous casting ladle turntable, the 1500°C high-temperature molten steel flows out into the tundish through the nozzle and slide plate at the bottom of the ladle, and the transfer of the billet is suspended. Finally, it flows out from the tundish nozzle to the continuous casting and straightening to complete the billet forming. For the nozzle that high-temperature molten steel flows out of the ladle, it needs to be placed inside the nozzle seat brick. During the use of the ladle, the nozzle can be replaced online 20-25 times. The nozzle seat brick must be replaced when the ladle is repaired for minor repairs. Replace the nozzle block. The quality of the nozzle block brick and the quality of the construction directly affect whether the ladle can operate normally. The quality problems of ladle nozzle block bricks during operation usually include unstable material, problems in the control of the knotting process, inadequate baking, and defects in on-site construction and installation. This paper sorts out and solves the problems of the nozzle block bricks on site, and finally achieves satisfactory results, ensuring the normal operation of the ladle.
1. On-site conditions of ladle use
A steelmaking plant of an enterprise uses a 150-ton ladle with double nozzles. The nozzles are directly inlaid inside the seat brick. The seat brick is installed at the bottom of the bag when building magnesia-carbon bricks with the bottom of the bag. The life is synchronized with the bottom of the bag, and the service life is 70-80 furnaces Between times, the entire service life is between 130-150 furnaces. The ladle nozzle is installed before the ladle is baked and goes online. The sealant is applied to the outside of the nozzle, and the nozzle is artificially inlaid into the inside of the block by strong pressure, so that the block , cement and nozzle are closely connected as a whole, which increases the overall strength. During the use of the block, the uppermost part of the block directly contacts the initial impact of the molten steel, the continuous erosion and erosion during the outflow of the molten steel, and the length of the block is constantly shortened. The impact of high temperature molten steel, friction and temperature difference in the production process, the connection with the seat brick is sealed by the sealing glue between them. From July to September 2019, the phenomenon of cracks in the bricks of the nozzle block appeared one after another. It was found that the offline treatment was carried out in time, and it was found that the steel piercing through the cement channel between the nozzle and the block was not timely, which seriously restricted the on-site production. The rhythm increases the cost of the ladle, and the production is in a passive situation.
Aiming at the steel leakage accident between the channel and the nozzle caused by the crack of the seat brick, analyze and track one by one from the quality of the nozzle, composition, quality of the seat brick, construction, etc., the nozzle is intact, and the cause can be ruled out; Found cracks, the analysis is mainly due to cracks in the block, the integrity is incomplete, the strength decreases, and the gap between the block and the nozzle increases, the molten steel seeps into the gap of the cement, and the block, the cement and the nozzle are connected together. The overall strength is destroyed, and the sealant can not withstand the high temperature and hot molten steel, and it is gradually eroded, resulting in the occurrence of steel leakage and steel leakage accidents.
2. Plans and measures for steel leakage
For the steel breakout accident caused by cracks in the block bricks, the personnel of the steelmaking plant and the technical center combined with the manufacturer to analyze the reasons. The products of companies with good reputation are tried out, the situation is as follows:
1) The seat brick of manufacturer A was used on site, and in the later period (about 60 times), micro-cracks were found, and the upper part of the seat brick had obvious diameter expansion;
2) The seat brick of manufacturer B went offline, and it was found that there were also many longitudinal micro-cracks, and the cracks were distributed 90 degrees in the middle of the seat brick (the personnel from the ladle hot repair platform faced the seat brick as a horizontal reference, and the cracks were not in the seat brick. the four corners).
3) The ladle contractor analyzed the material of the seat bricks, selected high-quality raw materials for formula operation step by step, and adjusted the formula and composition of internal aggregates and powders, and summarized them in use. The probability of cracks gradually occurred. reduce;
The measures taken for the installation and operation of the seat block are as follows:
The seat bricks are built together with the bottom of the package during installation. Before the seat bricks are installed and positioned, the steel structure at the bottom of the seat bricks is cleaned and filled with impurities, and the surrounding area is vibrated and filled with castables, and baked after construction is completed , go online, the specific schematic diagram is shown in the following figure:
1) The water-cement ratio of the castable around the base brick is strictly controlled, and the moisture is controlled between 6-8%.
2) Castable construction: For the gap (30-100mm) between the seat brick and the bottom of the bag, the vibrating process should be manually operated, and the vibrating rod should not be used to vibrate, so as to avoid excessive vibration force and aggregate sinking.
3) When replacing the nozzle online, check the crack and erosion of the seat brick.
4) Contact scheduling frequently. If the time for the ladle to go off the assembly line exceeds 30 minutes, secondary baking should be performed.
5) Strictly monitor the temperature during ladle baking, designate a special record book, mainly record the temperature of each part (bottom of ladle, ladle wall, slag line, ladle mouth), and pay close attention to the exhaust at the ladle nozzle and the ladle wall during baking situation.
6) The manufacturer, in conjunction with the company’s technical center personnel, issues a complete plan for on-site ladle construction, and conducts regular training.
3. The effect after transformation
Through the public relations of several aspects of the seat bricks for nearly two months, the cracks of the seat bricks gradually decreased and disappeared, and the service life was also within the controllable range. The direction and effect of the renovation were better, which prevented production accidents and saved the cost of refractory materials. .
4 Conclusion
The steel-making ladle is an important tool for the transfer of the steel-making liquid. The quality of the internal refractory and construction quality are directly related to the production and safety. The daily management and deployment of the ladle requires the technical personnel of each steel plant according to their own requirements. To explore and summarize the working conditions, the above experience can be worthy of reference and promotion.