The ladle has the function of receiving molten steel and performing refining outside the furnace. The service life of the ladle directly affects the ladle turnover rate and the consumption of refractory materials, thus affecting the smelting cost of the steel plant. The service life of a certain unit’s 75t carbon steel ladle is currently 135 furnaces. On average, the air-permeable bricks and nozzle seat bricks are replaced after 55 and 105 furnaces, and the slag line bricks are replaced after the 105th furnace. By analyzing the factors affecting the service life of the ladle, this unit has taken corresponding measures in terms of smelting conditions, ladle baking quality, and ladle maintenance technology, and the service life of the ladle has been increased to 150 furnaces.
Factors affecting the service life of ladle
1) Smelting conditions. The longer the steel-filling time of the ladle, the higher the refining temperature, the larger the amount of slag, the lower the slag basicity, and the stronger the slag oxidation, the faster the lining material of the ladle will be corroded.
2) Ladle baking quality. Before the ladle is put into use, the ladle needs to be baked, and the refractory of the ladle is fully sintered to prevent the refractory from falling off due to excessive heating after the new ladle is filled with molten steel. During the ladle turnover process, it should be avoided that the ladle turnover speed is slow, the temperature drop is large, and the refractory temperature is overheated or overcooled, which affects the life of the ladle.
3) Ladle lining. The ladle lining material is in direct contact with the molten steel. Its material is adapted to the smelting conditions and can greatly reduce the erosion of the refractory material by the molten steel and slag. In addition, improving the performance indicators of the refractory material can reduce the scouring and penetration of the refractory material by the molten steel and slag, and increase the life of the refractory material. The use of lining oxidation coating can greatly avoid the oxidation of the ladle during the baking process, thereby increasing the service life of the ladle.
4) Masonry method and quality.
① The ladle masonry must reduce defects such as triangular seams and misalignment to reduce the serious erosion of local refractory materials by molten steel or steel slag, which affects the overall life of the ladle.
② Ensure that the filler at the back seam of the ladle bricks is compacted to avoid the movement of the filler during the ladle inversion process, which may cause accidents such as brick extraction and steel seepage.
③ The ladle mouth must be compacted with a steel plate to avoid the bricks expanding and lifting during use and inversion, resulting in brick falling.
④ The appearance size of the ladle bricks is the guarantee of the quality of the ladle masonry, and must be strictly inspected in accordance with quality standards.
Measures to increase the service life of ladle
- Improve smelting conditions
1) Reduce heat loss of molten steel by keeping the ladle warm, thereby reducing refining temperature and time and extending the service life of refractory materials.
2) Reduce the amount of slag from the converter, thereby reducing the amount of magnesia carbon bricks dissolved in the slag, thereby increasing the service life of refractory materials.
3) Appropriately increase the amount of lime, increase the alkalinity and viscosity of the slag, reduce the penetration and melting loss of slag into refractory materials, thereby increasing the service life of refractory materials. - Improve the baking quality of ladle
1) The baking time before the ladle goes online is increased from 36h to 48h, and the temperature is raised strictly according to the baking curve, and the insulation time is ensured to meet the process requirements. The temperature reaches 900℃ when the ladle goes online.
2) Reduce the turnover ladles from 5 to 4, improve the turnover efficiency of the ladle, reduce the ladle processing time, reduce the time interval between pouring the ladle and re-injecting molten steel after pouring, and prevent the temperature of the ladle from fluctuating rapidly. - Strengthen the lining material
1) The characteristics of converter slag are strong oxygenation, low alkalinity, and strong penetration and erosion ability. It is necessary to enhance its anti-erosion ability by increasing the density of ladle bricks.
2) Alternation of hot and cold is an important factor that makes the ladle lining easy to be damaged. Improving the thermal shock resistance of ladle magnesia carbon bricks is conducive to improving the service life of the ladle.
3) Due to the high carbon content, magnesia carbon bricks are easily oxidized during the baking process of the ladle, and the longer the baking time, the more serious the oxidation degree. Applying an anti-oxidation coating on the working surface of magnesia carbon bricks can greatly avoid the oxidation of the ladle during the baking process, thereby increasing the service life of the ladle. - Improve the masonry method of the ladle
1) The bottom of the ladle is changed to a pouring mode. On the one hand, the bottom of the ladle has good integrity and no brick joints appear. On the other hand, the bottom of the ladle can be poured and maintained during the use of the ladle and when it is offline, avoiding the dismantling of the bottom of the ladle, so that the bottom of the ladle can be used unlimitedly and the consumption of refractory materials is reduced.
2) The area of the ladle body that is easily eroded by molten steel is a weak link and needs to be strengthened. Two aspects can be considered: strengthening the material to improve the density and anti-erosion performance of the brick; increasing the thickness of the brick to increase the life without changing the erosion rate. Or consider the above two points comprehensively to synchronize the life of the weak area with the refractory material in the ordinary position, thereby improving the overall service life of the ladle. - Maintenance method
1) Ladle bottom sleeve pouring repair. Clean the ladle bottom slag, and then use corundum material for pouring and repairing. The thickness can be repaired to the original ladle bottom thickness. Be careful not to pour too thick (no more than 50mm) to avoid separation and bulging of the pouring material from the ladle bottom during use.
2) Ladle body excavation and repair. Excavating and repairing the severely eroded area can greatly increase the service life of the ladle lining.
3) Applying repair material to the ladle wall. Generally, one set of ladle wall needs to be used with multiple sets of slag lines, which is easy to cause the ladle wall bricks to have a lower residual thickness than the slag line bricks, affecting the service life. A coating material for the cladding wall is used. This coating material has micro-expansion at high temperature, is not easy to crack, has good integrity, and can greatly increase the service life of the cladding wall. The service life of the coating material is generally more than 20 furnaces. Its usage method: Mix the coating material with an appropriate amount of water in proportion, and stir evenly into a plastic state that is easy to apply. Clean the slag pouring surface of the ladle and other places where the slag is too thick, and apply the coating material on the cladding wall from bottom to top in small amounts and multiple times, until the thickness of the original cladding wall bricks is about 50mm, and it is ready after solidification.
