As the demand for molten steel refining deepens, the residence time of molten steel in the ladle is extended, making the working conditions of the refractory materials of the ladle lining more demanding; in addition, the expansion of steel production scale and the increase in steel output have also further accelerated the turnover rate of the ladle. These factors have led to a significant reduction in the age of the ladle. In order to increase the life of the ladle and improve the safety of the ladle, Ma Steel’s First Steel Rolling Plant adopted a permanent layer integral casting process, and by further optimizing the ladle lining masonry mode, it ultimately improved the economic benefits of the company’s production.
The ladle used in the steel plant is a 120t ladle after expansion and transformation. The refractory materials and masonry processes of the permanent layer of the ladle have gone through three modes: integral T-4 clay brick masonry, slag line T-4 clay brick molten pool casting masonry, and lightweight castable integral casting masonry.
1.Analysis of the original process of permanent layer
The permanent layer is built with T-4 clay bricks, that is, a layer of T-4 clay bricks is built outside the insulation layer. It is gradually being eliminated because of its complicated construction process, easy drilling of steel in brick joints, and low lifespan. The slag line T-4 clay brick molten pool castable masonry, that is, a layer of T-4 clay bricks is built at the slag line, and the molten pool adopts the castable mode. This type of masonry mode is carried out in stages: first, install the mold of the nozzle seat brick and the air brick pad brick, and pour the permanent layer of the bottom of the bag; second, after the permanent layer of the bottom of the bag is hardened, place the air brick and the nozzle seat brick, lay a layer of T-4 clay bricks on the permanent layer of the bottom of the bag, and use corundum castables to pour the working layer of the bottom of the bag; third, after the bottom of the bag is cured for 8~12 hours, a layer of ceramic fiberboard, i.e., insulation layer, is laid along the steel shell; fourth, the permanent layer is built, and the masonry of the permanent layer is divided into two types, i.e., integral masonry of T-4 clay bricks and slag line T-4 clay brick melting pool castables; fifth, the working layer and the can sealing mouth are built. The advantages of this process are simple process, continuous construction, convenient maintenance and low cost; the disadvantages are that the brick seams at the slag line are easy to drill steel, and the steel shell is prone to redness and steel leakage, so it is gradually replaced by the integral casting process of castables.
2.Analysis of the integral casting process of lightweight castables
In order to solve the problem of reddening and steel leakage at the slag line of the ladle in production, Ma Steel First Steel Rolling Plant has summarized a set of integral casting process for the permanent layer of the ladle that is suitable for its own production characteristics by drawing on the experience of similar enterprises.
Integral casting process of the permanent layer of the ladle: First, install the mold of the water nozzle seat brick and the mold of the air brick part, and cast the permanent layer of the ladle bottom; second, paste a layer of hard ceramic fiberboard insulation board along the steel shell, that is, the insulation layer. Place the permanent layer telescopic casting membrane (its technical parameters are shown in Table 2), use a mixer to stir the lightweight casting material, and cast the permanent layer; third, after curing, demoulding and baking for 8 hours, lay the working layer, and use the shaped prefabricated blocks for the working layer molten pool, and the magnesia carbon bricks for the slag line; fourth, place the water nozzle seat brick, air brick pad brick and air brick, lay a layer of high-alumina bricks on the permanent layer of the ladle bottom, and cast the working layer of the ladle bottom; fifth, pour the tank mouth. The characteristics of this process are: first, the weakest part of the ladle is the brick joint. This process replaces the T-4 clay bricks of the original process. The castable is vibrated and compacted, which improves the safety of the ladle; second, the permanent layer is not easily damaged during the dismantling of the ladle, and its service life is stable at more than 3 laps; third, after the permanent layer is poured, the shape of the inner cavity is standardized, which is convenient for the close masonry of the working layer and the permanent layer, improving the masonry quality; fourth, the lightweight castable has the advantages of high porosity, low bulk density, and low thermal conductivity, and has a good insulation effect, which is beneficial to the insulation of the ladle.
3.Effects
The integral casting process of the permanent layer of the ladle has been put into practical operation for several years, and the effect is good. The steel leakage accident of the ladle, especially the steel leakage accident of the slag line brick part, has been curbed, and the safety of the ladle has been greatly improved; the thermal insulation performance of the ladle has been improved, and the average temperature of the ladle shell has dropped from about 270℃ at the slag line part and about 230℃ at the molten pool part of the original process to about 240℃ at the slag line part and about 210℃ at the molten pool part of the new process; the average service life of the permanent layer has also been increased from 65 times to 400 times. According to the annual output of 3.3 million tons of steel, the annual cost of refractory materials of the permanent layer of the ladle is saved by (0.53-0.25)×330=924,000 yuan; at the same time, the use of mechanized equipment instead of manual construction has reduced the labor intensity.
By using permanent layer castables with appropriate physical and chemical indicators and selecting a reasonable overall casting process, the service life of the permanent layer is prolonged, serious accidents such as steel leakage at the slag line are prevented, the safety of ladle use is improved, the thermal insulation function of the permanent layer of the ladle is enhanced, good economic results are achieved, and it is worth promoting and using in similar steel mills.
