A furnace Ladle is a large-scale tool for connecting converters, receiving molten steel, refining molten steel outside the ladle refining furnace and casting molten steel. With the continuous increase of special steel types and the continuous deepening of molten steel refining, the service environment of the ladle becomes worse. Improving the service life of ladles and reducing the consumption of refractory materials under the premise of ensuring safe use within the scope of meeting the requirements of cleanliness and carbon content of molten steel is still a major research topic in the field of refractory materials.
Increasing the furnace ladle age can effectively reduce the number of ladle turnover and the number of new ladles online, and at the same time, it can improve the tapping rate of the red ladles and the bottom blowing permeability of ladles. It is an effective method to ensure the cleanliness of molten steel and stabilize its composition of molten steel.
The cost of ladle refractory is the main cost of refractory in the refining area of the steelmaking department, accounting for more than 50%. Increasing the ladle age can effectively reduce the consumption of refractory and create considerable economic benefits for the steel plant.
The regular repair mode, masonry technology and baking system of ladle are improved, and the safety performance and service life of furnace ladle are studied.
1. Factors Affecting Furnace Ladle Service Life
1.1 Molten Steel Smelting
Master the correct and appropriate tapping temperature. If the tapping temperature is too high, the inner wall working layer will be seriously eroded. If the tapping temperature is too low, the refining time will be prolonged, and the molten steel stagnation time will be too long, which will also cause serious erosion and mechanical damage.
The content of iron oxide shall be appropriate. If the content of iron oxide is too high, it will have a strong chemical reaction with the refractory lining of the molten steel tank and cause corrosion. Keep proper basicity of molten slag. The smaller the basicity of molten slag, the more serious the erosion to the working lining of the molten steel tank. During tapping, the position of the molten steel truck shall be properly controlled to avoid the impact of molten steel flow on the ladle wall, resulting in serious erosion of the slag pouring bread wall.
1.2 Ladle Masonry Design
The cladding thickness and material shall be selected according to the erosion conditions of different parts; The position of the bottom blowing brick and nozzle shall be reasonably selected to avoid excessive erosion of molten steel to the local cladding wall.
1.3 Ladle Masonry Quality
Repair the damaged parts after the ladle is taken off the line, and clean the residual steel in the furnace ladle lining. The gaps and pits caused by molten steel scouring and mechanical damage shall be filled or coated. The baking method and baking time of ladle lining shall be reasonable.
2. Measures to Improve the Service Life of the Ladle
2.1 Improvement of Ladle Maintenance Mode
The bottom and wall working layers of the 300t ladle of Shougang Jingtang Company are made of corundum carbon-free bricks, and the working layers of the slag line are made of low-carbon magnesia-carbon bricks. The repair mode of the furnace ladle mainly considers the matching of ventilation bricks, nozzle block bricks, slag line bricks and wall-clad bricks. The stable repair mode can effectively reduce the safety hazards and abnormal offline of the ladle, speed up the turnover and use of the ladle, ensure the cleanliness of the molten steel and the stability of the molten steel composition, and also reduce the slow ladle turnover and abnormal offline on the steelmaking output. influences.
(1) Standardize the Brick Masonry of the Cladding Wall and the Working Layer of the Slag Line
The working layer of the cladding wall and slag line is built with flat bricks in a circular shape. The doors are stacked layer by layer. The door closing position must be at the ladle trunnion. There can only be one door on the first floor. In masonry, two or more types of bricks are used in combination. The inner wall of each layer should not be obviously misaligned, and the masonry surface of each layer of the working layer must be guaranteed to be level. The gap between the working layer and the permanent layer must be firm. If the gap is caused by the cladding, aluminum-magnesium fire clay or castable should be used to fill the gap and fill it. Brick masonry gaps ≤ 1mm, and the gaps are filled with mud. The fire mud should be applied evenly between the bricks, and the specifications of "full mud, close to the back, hammering the brick surface, and staggering the brick seams" should be strictly implemented during the masonry process.
(2) Masonry of Tank Bricks within the Specified Scope
The surrounding part of the tank is built with flat masonry and 4 layers of masonry. During masonry, the doors are stacked layer by layer, and the bricks on the same layer, the upper and lower layers, and the bricks are required to be tightly squeezed before the door is closed, which can be squeezed with a jack as appropriate. When the door is closed, the size of the bricks is not suitable for cutting bricks with a brick cutter, and the thickness of the bricks is ≥60mm. Each layer is built with 7 to 10 standard bricks and 1 to 2 reflexive bricks or adjustment bricks. The positions of the closing doors on the adjacent upper and lower floors must be staggered by more than 800mm, and do not overlap with the closing doors of the same layer. Between the brick and the working layer of the cladding wall, the aluminum-magnesium castable shall be used for pouring and firming.
2.3 Strengthen the Operation Control during the Use of Ladle
The stable operation of the furnace ladle during use can effectively avoid the peeling of the refractory lining of the ladle due to rapid cooling and heating. Strengthening the control of the ladle use process can effectively improve the service life of the ladle. The specific measures are as follows.
(1) Regulate the Blowing Operation of Bottom Blowing Bricks
A special bottom blowing brick blowing test device is used to determine the blowing condition of the bottom blowing brick through the flow of the argon press of the bottom blowing brick of the ladle, so as to avoid the abnormal offline of the ladle caused by the excessive erosion of the bottom blowing brick and reduce the service life of the ladle.
(2) Standardized Treatment of Ladle Edge Operation
In order to avoid the influence of large furnace ladle edge on steel making, refining and ladle baking, and avoid the abnormal offline of ladle due to the damage of ladle edge bricks caused by excessive post-treatment of ladle edge, the ladle edge must be handled in time. Specific requirements: when the extension width of the inner ladle edge of the ladle mouth to the ladle is ≥ 200mm, and the slag sticking outside the ladle mouth is ≥ 100mm higher than the height of the ladle mouth, it must be handled in time; After the operation of rubbing the edge of the bag, observe whether the bricks along the bag are loose and fall off. If any problem is found, timely notify the contractor to carry out a key inspection.
2.4 Improvement of Furnace Ladle Baking System
Molten steel temperature is an important index for smelting steel. Ladle baking is an important method to reduce the tapping temperature drop and a transportation temperature drop of molten steel. A reasonable ladle baking temperature can reduce the heat dissipation of the ladle and reduce the impact on the tapping temperature of molten steel. But too much baking not only wastes gas, but also has a great impact on the life of refractory materials.
(1) Baking System of the Ladle to Be Put into Operation
Preheating and baking of furnace ladle to be put into service: after the ladle masonry drying and baking is completed and stopped, the preheating and baking operation shall be carried out before putting it into service. The ladle dispatcher shall record the baking start and end time on the record sheet.
(2) Stop Ladle Baking System
Stop baking before the furnace ladle is put into service: since there is too many ladles off-line in turnover, preheating and baking shall be carried out before it is put into service again (the ladle parking time is calculated from the casting machine stopping time).
It is strictly prohibited to use the off-line ladle for more than 2h, and off-line baking must be carried out; The parking time shall be 2-4h, and the baking time shall be controlled above 2H before online; The storage time of the offline ladle is 4-8h, and the baking time before the online ladle is controlled to be more than 4H; The storage time of the offline ladle is 8-24h, and the baking time before the online ladle is controlled to be more than 5h; The storage time of the offline ladle is more than 24h, and the baking time before the online ladle is controlled to be more than 7h.
3. Improved Ladle Service Life
After adjusting the regular repair mode, and improving the ladle masonry process and baking system, the online safety performance of the ladle has been significantly improved, the number of abnormal downlines has been significantly reduced, and the number of production affected by the ladle safety hazards and abnormal downlines has been significantly reduced, and the ladle age has been further improved.
Stable regular repair mode, reasonable masonry technology and the baking system can effectively ensure the safety performance of the ladle and improve its service life of ladle. The improvement of the safety performance and service life of the ladle has reduced the accident rate caused by the potential safety problems of the furnace ladle, and reduced the consumption of refractory materials and production cost. It is estimated that the production cost can be reduced by more than 1 million yuan per year.
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