- Problem analysis:
1.1 The bottom of the ladle has poor corrosion resistance
The corrosion of refractory materials is divided into physical erosion and chemical erosion. Physical erosion refers to the erosion of refractory materials by impact and other mechanical effects; while chemical erosion refers to the resistance of refractory materials to changes in temperature and stress fields under high temperature load. Erosion of wood. The bottom of the ladle is mainly physical erosion. During the use of the ladle, the bottom working layer of the ladle has poor corrosion resistance and impact resistance. Under the impact and erosion of high temperature molten steel, a large area of refractory material will fall off, and the delamination thickness is 100 mm ~ 150 mm. The layers are mostly concentrated on the impact position of the molten steel (as shown in the figure below), which brings great hidden dangers to the safe use of the ladle.
1.2 The ladle air brick is not synchronized with the age of the ladle
Due to the advantages of wide adjustable range of air supply and good corrosion resistance, slit-type air-permeable bricks are widely used as bottom blowing components in the steelmaking process. However, the performance of bottom-blown air-permeable bricks directly affects the bottom-blowing effect and usage of the ladle. During the full-line bottom-blowing process of the ladle, the bottom-blowing, low air permeability, and poor air permeability often occur, causing the ladle to be forced down. Line, affect the age of the ladle, causing the breathable brick and the ladle life to be out of sync.
1.3 The ladle is not shut down in time
Since there is no equipment specifically used to measure the bottom of the bag, the erosion of the bag condition (the bottom of the bag, the wall of the bag, the ventilating brick, the nozzle block) is all judged by the experience of the hot repair skateboarder and the weight of the empty bag (with the cover). There are differences in the level of the hot repair workers, and the condition of each ladle is different, and when the ladle is hot, the hot repairer is in the hot state of the ladle, and it is not easy to observe, which often leads to misjudgment and thus appears The phenomenon that the ladle is out of service too early or too late. If the ladle is stopped too early, it will affect the life of the ladle; if the ladle is stopped too late, there will be hidden dangers of ladle accidents.
- Improvement measures
2.1 Improvement of the repairing process of the bottom of the ladle
Before the improvement, the bottom of the pouring material ladle was punched with a castable (high aluminum material) after vibrating or pouring, which was 100 mm higher than the bottom of the ladle, showing a slope-like shape. In the course of use, it will be eroded and eroded by molten steel for a long time, and it is very easy to have pits at the impact site, causing the bottom of the bag to be thin and burying hidden accidents.
After the improvement, the repair form of the prefabricated impact block at the impact zone of the cell bottom is replaced by the original slope-shaped high-alumina material. The prefabricated block is composed of magnesium and carbon, and the punching strength is 1700 N. Construction plan: After pouring 300 mm of castable at the bottom of the ladle, fix the prefabricated impact block and inlay it in the impact area of the bottom of the ladle, then pour 300 mm thick castable with vibrating rods around it. After construction, the prefabricated block in the impact area is 150 mm higher than the bottom of the bag. The effect comparison before and after the improvement of the ladle bottom repair process is shown in the figure below. (Picture two, picture three)
2.2 Improvements to breathable bricks
In view of the poor air permeability of the air-permeable bricks and the fact that the service life is not synchronized with the bottom of the ladle, the following measures should be taken: (1) Increase the number of air-permeable brick slits from the original 20 to 36;
(2) Increase the air-permeable brick slits The width of the brick is increased from 0.13 mm to 0.20 mm; (3) The material of the original ventilated brick core is changed from corundum to chrome corundum.
Improve the air permeability and service life of the air-permeable brick by improving the slit and material technology of the air-permeable brick.
Research, formulate the physical and chemical indexes of the ventilating brick core as the basis for regular inspection. The specific physical and chemical indexes are shown in the table below. (Picture 4)
2.3 Improving if the pouring bag is not stopped in time
Add a measuring ruler to measure the thickness of the bottom of the bag and the thickness of the air-permeable brick to reduce the error of judgment based on experience. Aiming at the phenomenon that the pouring material ladle is not stopped in time, a reasonable equipment for measuring the bottom of the ladle (fire shield and measuring scale) is set up to reduce or even eliminate the phenomenon of premature or late deactivation of the ladle, eliminate the impact on production, and make the ladle The deactivation of the ladle is safe and reasonable, and the best state of deactivation of the ladle is achieved. The inspection method of the ladle condition of the front and rear ladle is added as shown in the figure below. (Picture 5, Picture 6)
Technical scheme: For the pouring material bag with the bag age ≥ 70 furnaces or with special circumstances, the staff on duty must be organized to measure the bottom of the bag and the lowest point of the two breathable bricks at least once. Before measurement, a large oxygen pipe must be used to clean the scrap steel slag adhering to the bottom of the bag and the two breathable bricks (prohibited point), while the breathable bricks are purged, a nitrogen back blow is connected.
Reference standard: bag bottom ≥ 300 mm, breathable brick ≥ 250 mm, bag wall ≥ 130 mm, with cover (without rim) z46.5 t.
Measuring ruler size: The bottom of the measuring bag is designed according to the length of 2700 mm, and the measuring wall is designed according to the length of 2750 mm.
- Improve effect
(1) By adopting the measures of inlaying the impact block at the bottom of the ladle, the castable ladle is resistant to molten steel erosion and erosion during the process, and the phenomenon of pits in the impact area is slowed down.
(2) The corrosion resistance of the ventilating brick has been greatly improved, and the air permeability has reached the bottom blowing requirement of the converter, and the service life can reach the age of the bag.
(3) By comparing the residual thickness measurement data of the off-line ladle before and after using the measuring equipment, it can be seen that after using the measuring device, the residual thickness of the off-line ladle is more in line with the requirements of the down-line standard of the casting material (the bottom of the ladle). The thickness is 280+20 mm, and the thickness of the breathable brick is 160+20mm), which effectively reduces the frequency of premature or late deactivation of the ladle, eliminates the impact on production, makes the deactivation of the ladle safer and more reasonable, and achieves an optimal It is found that the data measured by the measuring ruler is more consistent with the specified residual thickness data through the measurement of the residual thickness data after unpacking.
(4) The overall ladle age of the castable ladle has increased from a low level of about 80 furnaces in the original to a higher level of over 100 furnaces. The maximum ladle age has reached 125 furnaces.