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          The current position: NEWS > Products Information > Advantages of using nano heat insulation board as heat insulation layer in steel ladle

          Advantages of using nano heat insulation board as heat insulation layer in steel ladle

          Date:2016-9-5 source:www.rodrigojames.com Number of visits:851

          Iron and steel production process is a typical high temperature metallurgical process, effective control of molten steel temperature is one of the key factors to ensure smooth production and casting quality. The heat transfer of ladle in the process of production turnover has a direct impact on the temperature change of molten steel in the process of steel filling and casting. Different ladle conditions will affect the tapping temperature drop, the heating and cooling rate of molten steel in the refining station and the superheat of molten steel in continuous casting tundish. In recent ten years, many domestic steel mills pay more and more attention to the heat loss of ladle and the temperature drop in the process of ladle thermal cycle.
          Reasonable control system of molten steel temperature is an effective means to improve the quality of molten steel and reduce production costs. This paper focuses on the analysis and research of the technological practice effect of 100t ladle with nano heat insulation board as the heat insulation layer in Angang No.1 rolling mill.

          1. Mechanism analysis of ladle heat transfer process
          In steel-making production, molten steel from tapping to the end of casting to the next furnace tapping, known as a thermal cycle. The ladle thermal cycle process can generally be divided into several main stages as shown in fig. 1: the heat transfer of the ladle can be divided into five stages: tapping stage, transporting stage, refining argon blowing stage, casting stage and baking stage. The main heat transfer modes of steel ladle are different in different processes, but each process has heat dissipation inside the molten steel through the lining contacting the molten steel in a heat conduction mode. The heat transfer process in ladle transportation stage is analyzed as an example.

          圖1 鋼包熱循環過程示意圖

          The heat loss during ladle transportation is mainly as follows: the surface of the composite insulation layer is radiated to the space above the surface of the composite insulation layer through heat conduction and heat dissipation of the clad wall and the clad bottom in contact with the molten steel.
          In the above five heat transfer processes, heat transfer is carried out by convection, radiation and conduction. In the normal production process, the larger the heat storage capacity of ladle lining is, the more favorable it is to reduce the heat loss of molten steel. According to production practice, the change of ladle lining temperature has nothing to do with the refining method after three continuous turnover processes. in addition, during the whole turnover process, the heat storage of ladle lining is mainly concentrated in the stage from tapping to refining, and the heat dissipation is mainly concentrated in the stage from casting to waiting tapping. at this time, without the heat transfer of molten steel, the heat dissipation loss of ladle itself increases sharply, and the temperature drop of ladle is very obvious. The solution is mainly to increase the thickness of the insulation material and reduce the heat transfer coefficient of the refractory material, but increasing the thickness of the insulation material will reduce the capacity of the steel ladle, and reducing the heat transfer coefficient of the refractory material can directly affect the heat dissipation of the steel ladle in the five heat transfer processes. Based on the mechanism analysis of ladle heat storage, heat transfer and heat dissipation, 100t ladle heat insulation layer was replaced by nano-material heat insulation board instead of the original high aluminum injection felt.
          2 main physical and chemical indexes of steel ladle structure and new material nano heat insulation board

          2.1 ladle structure
          Fig. 2 is a structural diagram of 100t refining ladle of Angang. Wherein that inn side of the permanent layer of the steel ladle is in contact with the high-temperature work layer, the outer side of the permanent layer is close to the nano heat insulation board ( heat insulation lay ) and the cladding wall, the thickness of the durable material of the permanent layer is 70 - 100 mm, and the thickness of the working layer is 230 - 300 mm, and the steel ladle sequentially comprises a cladding, a heat insulation layer, a permanent layer and a working layer from the outside to the inside. Ladle shell thickness of 30 mm, the thickness of the bottom shell 60 mm, thermal insulation layer is now using nano thermal insulation plate. The permanent layer is made of clay brick with good insulation, low thermal conductivity and high porosity. The working layer is made of magnesia carbon brick.
          Fig. 2 structural diagram of 100t refining ladle of Angang
          2.2 the main physical and chemical indicators of new material nano heat insulation board
          See table 1 for the main physical and chemical indexes of the new material nano heat insulation board.

          表1 納米隔熱板的主要理化指標

          3 test methods and test results
          3.1 test methods
          Nano - insulation panels of new materials were tested in 3, 4, 8, 19 and 21 steel ladle insulation layers respectively. two layers were laid on the bottom of the ladle and three layers were laid on the wall of the ladle, each layer was 10 mm thick, and the whole ladle was spread to 500 mm of the ladle opening. a total of 130 m2 of new insulation panels were used, with an average of about 40 m2 of each layer.
          In order to test the thermal insulation performance of the new materials, strict temperature measurement procedures were formulated during the test. The temperature measurement time is selected before continuous casting at the end of refining, the heat sensitive part on the surface of the steel ladle is marked, and the temperature measurement is carried out on - line, synchronous and steel grade comparison with the 13 ( ordinary heat insulation material steel ladle on - line, and the influence of the novel steel ladle on refining power consumption and superheat degree of molten steel in continuous casting is analyzed at the same time.
          3.2 test results
          Table 2 shows the temperature comparison of the ladle shell before the steel is put on the test ladle and the ordinary ladle.

          表2 試驗鋼包和普通鋼包上鋼前的包殼溫度對比

          As can be seen from table 2, under the normal production conditions, the heat transfer of the steel ladle and the thermal conductivity of the insulation layer is larger, the use of nano heat insulation layer can greatly reduce the heat dissipation of the steel ladle, so as to reduce the temperature drop of molten steel in the process of transportation and casting, reduce due to the large fluctuation of molten steel temperature to the production of various adverse effects.
          Table 3 shows the comparison of refining power consumption between test ladle and ordinary ladle lf furnace

          表3 試驗鋼包和普通鋼包對LF 爐精煉電耗的影響

          The data in table 3 show that the refining power consumption of different steel grades is reduced by 2 ~ 8.41 kw h / t due to the slow heat dissipation of the new steel ladle and the increase of refining heating rate. According to the product outline of Angang No.1 rolling mill, the current steel production is 1.2 million tons / year, which is expected to reduce the power consumption cost by about 3 million yuan.
          Table 4 shows the effect of test ladle and ordinary ladle on the temperature of molten steel in continuous casting.

           表4 試驗鋼包和普通鋼包對連鑄中包鋼水溫度的影響

          The data in table 4 show that the average temperature drop of molten steel from ladle to tundish is reduced by 5.16 ℃ under the same temperature of upper steel, while the fluctuation of molten steel temperature in tundish is reduced from the original average temperature of 12 ℃ to 6 ℃, which reduces the quality drop of casting billet caused by unqualified molten steel temperature, and the qualified rate of molten steel temperature in tundish is increased from the original 85 % to 97 %. Agreement material ( refers to the composition, performance qualified, but the surface defects such as scarring, does not affect the use, agreement sales of steel ) ratio from the original 0.96 % to 0.8 %. Especially for 82b, c72da and other steel grades with low drawing speed and narrow control range of superheat degree of medium-sized steel, the improvement effect is more obvious, and the rate of revision is reduced from 6.8 % to 4.5 %. The application of nano heat insulation board in ladle heat insulation layer has created conditions for continuous casting with low superheat degree, and the internal quality of casting billet has been improved obviously.
          Conclusion
          The steel-making plant adopts the nano heat insulation board as the heat insulation layer of the steel ladle, because the material has low heat conductivity and good heat insulation performance, the heat dissipation of the steel ladle is greatly reduced, the production is stable, the production cost is reduced, the process control of the temperature of the molten steel is optimized, and the physical quality of the continuous casting billet is improved. Meanwhile, that temperature difference between the cold and hot surface of the refractory material can be reduced, and the ladle age can be improve. The temperature of that out wall of the ladle can be greatly reduced, the thermal stress of the clad can be reduced, the strength and creep resistance of the clad can be improved, and the working environment temperature can be reduce.

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