Aue customer order 50tons aluminum-magnesium castable.
Discussion on application of aluminum-magnesium castable in ladle
Aluminum-magnesium refractory castable is a refractory material mainly composed of alumina and magnesia.
a Problems in the application range of ladles
The use of aluminum-magnesium castables in the overall lining of small and medium-capacity ladles has been completely successful. On large-capacity ladles, due to the different steel quality requirements and steelmaking processes, the composition and alkalinity of ladle slag are also different. Different types of ladles should use different refractory linings. When choosing pure aluminum-magnesium castable lining for large-capacity ladles, the suitable type should be selected according to the service conditions of different types of ladles or different parts of the same ladle.
For large-capacity continuous casting ladles, the use of pure aluminum-magnesium castable as an integral lining should be considered technically mature. However, special attention should be paid to the selection of pure Al2O3-MgO castables that can meet the requirements of corrosion resistance, slag permeability and permanent line change rate at the slag line. For the refining ladle that mainly refines clean steel, the use conditions are more severe , Only pure aluminum-magnesium can be used in the molten pool (wall and bottom) in the low corrosion area. It has been reported in the literature that pure Al2O3-MgO castables and MgO-C bricks are mixed in medium alkaline slag (CaO35%, MgO5%, SiO210%, Al2O315%, Fe2O325%, MnO10%, CaO/SiO2=3.5, (C+M )/(S+A)=1.6), the results show that due to the in-situ formation of SP, its erosion resistance is equivalent to the level of MgO-C bricks. Based on this, it can be considered that pure Al2O3-MgO can be used in the slag line of low-alkaline slag or even medium-alkaline slag ladle. However, when it comes into contact with highly alkaline slag (CaO63%, MgO1%, SiO212%, Al2O310%, Fe2O314%, CaO/SiO2=5.3, (C+M)/(S+A)=2.9), the anti-slag performance is poor. It is difficult to reach the level of MgO-C bricks, because when SP encounters slag with high CaO content, it will react according to CaO+SP→MgO+L to form MgO and liquid phase, and SP will be eroded by CaO slag, and its refractory performance will decrease. Therefore, at present, pure aluminum-magnesium castables are only used in the low corrosion area (melt pool) of the refining ladle
b. Development and application of castables for refining ladle slag line
Over the years, the practice of brick ladles has proved that although the service life and safety of use are completely reliable, the cumbersome manual labor of masonry operations has never been relieved. The successful promotion and application of the overall lining of the ladle has made people see that the mechanized construction Prospects. The improvement of the overall lining penetration rate is a major trend. At present, only the overall lining of the slag line of the refining ladle has not been fully successful and popularized. At home and abroad, a lot of research and development work is being done on alkaline castables for the slag line of the refining ladle, but none of them have reached the level of use of MgO-C bricks. The research and development of MgO-C castables for ladle slag line, due to the fluidity and C oxidation resistance, etc. have not been perfectly resolved, and its use effect is still not up to the level of MgO-C bricks. However, the whole inner lining of the refining ladle, It is the direction of mechanized construction of ladle lining, and it is believed that this goal will be fully realized.
c. Choice of type
The selection of pure Al2O3-SP and pure Al2O3-MgO castables in pure aluminum-magnesium castables for ladles should be considered in terms of the characteristics of each type, research and development history, and use effects. First of all, it is necessary to understand the advantages and disadvantages of pure Al2O3-SP and pure Al2O3-MgO, so that they can be reasonably selected in different ladles and different parts of the same ladle. Of course, in order to maintain the advantages of pure Al2O3-SP and pure Al2O3-MgO and overcome their respective shortcomings, according to the principle of matrix matching, Al2O3-SP-MgO system is selected for the matrix composition and the SP/MgO ratio is appropriate. The pure Al2O3-SP-MgO castable has the advantages of each type and overcomes its own shortcomings, and has better overall performance. It will get better results in the low corrosion area of the ladle. Secondly, according to the sequence of development and application, the pure Al2O3-SP material is prior to the pure Al2O3-MgO material, indicating that the latter has more advantages than the former, and the latter has wider applicability. From the perspective of the applicability of pure Al2O3-MgO, pure Al2O3-MgO with different compositions and characteristics can be used in any part of the low corrosion area of the refining ladle (the cladding wall, cladding bottom and impact zone of the molten pool). Especially when pure Al2O3-MgO is used for a large amount of cladding, the in-situ SP generated by the reaction of MgO and Al2O3 during use is accompanied by controllable and adjustable volume expansion, which is beneficial to reducing or limiting slag penetration.
What’s more, the pure Al2O3-MgO material used for cladding, due to the radial expansion characteristics of the annular cast body and the limitation of the circular steel shell, the so-called “free expansion” of the annular cast body will not occur. Third, the research on the corrosion mechanism of pure aluminum-magnesium ladles indicates that a protective layer zone is formed after the working lining of the cast body reacts with the slag, and most of the iron oxide and manganese oxide in the slag are embedded in the lattice structure to form spinel. The expansion caused by the reaction of iron oxide Al2O3 in the slag to FeO·Al2O3 is not large; the reaction of CaO in the slag with Al2O3 to form CA6 produces a large expansion, but it is caused by the reaction of CaO and SiO2 in the slag with Al2O3 to form calcium aluminum yellow. Minerals whose melting point temperature is lower than 1600°C (ladle operating temperature) such as anorthite and (or) anorthite (depending on the SiO2 content in the slag) are balanced. This combination of pure aluminum-magnesium castable ladle working lining reacting with slag to generate high and low melting point minerals provides a hot surface protective layer for the ladle working lining, minimizing further erosion of the working lining. The final performance is that the difference of different slag compositions on the service life of the two types of pure aluminum-magnesium ladle linings is not very obvious. In this way, the pure Al2O3-MgO material (especially condensed and combined) with relatively simple manufacturing process and low wood-forming value has more popularization value.
d. Promotion of overall lining of large-capacity ladles and “sleeve casting”
After the successful application of the overall lining of small and medium-capacity ladles and some large-capacity ladles in my country, the “sleeve pouring” technology was adopted: the overall lining was partially corroded to a certain thickness, cooled and manually or mechanically removed residues and working lining permeable layers, and the mold was installed The new overall lining is poured, and it is put into use after being baked and heated. It can also be “sleeved” many times, avoiding the waste of residual lining, and significantly reducing the unit consumption of refractory materials. Only when the overall lining and casing are used together can the superiority of ladle castables be shown. Most foreign large-capacity ladles use integral lining and casing pouring, and few large-capacity ladles in my country use integral lining and casing pouring, which can create conditions to promote these technologies.
The overall inner lining of large-capacity ladles must be technically and constructionally guaranteed to prevent high-temperature molten steel leakage accidents. To this end, security measures are taken in various aspects. For example, the permanent lining that used to be close to the cladding (or heat insulation layer) is now called a safety lining, which is defined as “the leak-proof refractory brick masonry or refractory integral lining between the furnace shell and the working lining. When the working lining is exposed to high temperature When the melt and slag are eroded and thinned, the safety lining should be able to resist penetration and erosion.” In the past, after the high-alumina castable safety lining was used for brick ladles, not only the service life was extended (the safety lining could go through several contracts without changing the safety lining), but also the accident of steel leakage was eliminated, indicating that the overall safety lining without joints is also safe and reliable. And then switch to ordinary aluminum-magnesium integral safety lining without joints and pure aluminum-magnesium castable integral working lining, and steel breakout accidents should not occur. Pure aluminum-magnesium research and development technology and application technology have long been proven to be very mature, and have long been proven to be safe and reliable. The reasons why the overall lining of pure aluminum-magnesium castables have not been fully promoted on large-capacity ladles at this stage may be:
(1) After the refractory bricks used in brick ladles pass the quality inspection in the refractory material manufacturing plant, they are transported to the steel mill and the furnace builders visually select the waste products. For many years, the quality of the bricks is considered to be the most reliable. The masonry quality can be checked according to the specifications to see whether it is qualified. However, the inspection of pouring quality is not easy to reflect the construction quality of pouring body in a comprehensive and timely manner, regardless of representativeness or timeliness.
(2) Who will complete the pouring construction of the overall inner lining of the ladle. The ladle brickwork is completed by a special construction (repair) furnace team. Over the years, steel mills and kiln companies have established professional furnace building (repair) teams. In recent years, some refractory factories have also organized professional furnace building teams. With a professional furnace building team, the quality of the masonry of the ladle brick lining is guaranteed. The pouring construction of the overall inner lining of the ladle is a project that requires high technical requirements, ensures the construction quality, and must be completed by a professional team with skilled operations. The pouring construction of the overall inner lining of the ladle should be completed by the castable manufacturer from the test to the promotion (especially the test stage). Only in this way, the manufacturing unit of castables can understand the problems in manufacturing, construction and use through on-site pouring construction and research on the use of ladles, and continuously improve performance, operating performance and use effects. Of course, after the test of the overall lining of the ladle is successful, it can be transferred to the team of a professional furnace building (repair) unit to undertake the construction of the overall lining of the ladle, but it must go through strict training and be able to undertake it and complete it with high quality and proficiency according to the construction standards. Task.
(3) The pouring construction site occupies a certain plane in the steel plant to store pouring machines and castables. Especially in the test stage, the pouring site and the brick ladle are on the same plane that interferes with each other. When the area of this site is not enough, the test is difficult.
(4) The curing, drying and heating time of the overall lining of the ladle is much longer than that of the brick ladle.
Steel mills that have the construction conditions for the overall lining of ladles should actively test and promote them, and continuously extend their service life. For steel mills that do not have the construction conditions for the overall lining in the near future, the use of prefabricated parts is also a good transitional solution. In fact, prefabricated parts are refractory products carefully manufactured (qualified by quality inspection) in the refractory material factory, but the pressure is not used. Brick machine and firing equipment (but the maintenance and drying are completed in the manufacturing plant). Steel mills can treat prefabricated parts as unfired bricks. The masonry project and drying heating are basically the same as brick ladles, as long as the unit consumption of refractory materials and The cost is not increased, and the service life is extended. This is a solution that is beneficial to both the refractory material factory and the steel factory. The shape and size of the prefabricated steel ladle can be kept the same as the original refractory bricks, or slightly larger. If conditions permit, the steel ladle can be realized The hoisting of the inner lining is mechanized, and large-size prefabricated blocks can be used. The unit weight of these prefabricated blocks should exceed 100kg (it cannot be lifted manually), and the pouring, curing, drying, pre-masonry and numbering are completed in the refractory factory. These prefabricated The transportation, loading and unloading and masonry of the prefabricated blocks that have been laid and numbered have all been mechanized. If the crane in the steel factory is tight, small lifting equipment can be used, which is easy to do.