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Problems and improvements in the application of refractory materials in converter sliding plate slag retaining technology

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Abstract: At present, the main problem of the refractory material of the sliding plate slag retaining system is to achieve matching of the service life of the refractory components on the basis of reasonably increasing the service life of the respective components, and to minimize the number of replacements of the refractory materials and the impact on the overall steelmaking process time. It is particularly important to take effective improvement measures to address this problem.

Keywords: slide gate plate; converter slag retaining technology; refractory materials; problem; improvement

Composition of refractory materials in slide gate plate slag retaining system

The use of sliding plates to retain slag in converter tapping is one of the most advanced methods in the world today, and it is also the most difficult slag retaining technology. Using the converter slide plate slag-stopping technology, the system’s refractory materials are mainly composed of five major refractory components, including taphole bricks, inner nozzle bricks, upper slide plates, lower slide plates, and outer nozzle bricks. The converter slide plate is one of the most critical components in the application of slide plate slag-stopping technology. .The tapping channel is formed by the tapping port, the inner nozzle, the sliding plate brick and the inner hole of the outer nozzle brick, and the slag blocking function is realized by the moving opening and closing of the lower sliding plate. The conventional refractory material structure of the sliding plate slag retaining system is shown in Figure 1.

Figure 1 Structural diagram of refractory material of slide gate plate slag retaining system

Main problems in the application of refractory materials

Domestic converter slag blocking technology is still in its infancy in general, and the relevant applied refractory materials, equipment, and replacement operation technology need to be continuously improved and optimized. Currently, the main refractory material issues and shortcomings that restrict the development of this technology are as follows.

The life of skateboards is relatively low

At present, the material of converter slide plates in China is mostly aluminum-zirconium carbon. As a ladle slide material, it has high strength, good thermal shock resistance, and excellent erosion and erosion resistance. However, as for the converter slide plate slag-blocking technology, the service life of the slide plate is relatively low and can only be stabilized between 10 and 14 furnaces, which is basically replaced once per shift. The mechanism is replaced relatively frequently, which to a certain extent cannot meet the needs of the fast-paced steelmaking production of the converter. It also increases the labor intensity of workers.

The life of the tap hole needs to be further improved

The life of the tap port is one of the important indicators of the converter slide plate slag-retaining technology. Due to frequent direct erosion and severe erosion from high-temperature molten steel and highly oxidizing slag, coupled with the effects of rapid cooling and rapid heating, the tap port is easily damaged. The length of its life directly affects the converter smelting cycle, steelmaking productivity and slag-retaining effect, thereby affecting the quality of steel. The integrity of the taphole directly controls the amount of slag discharged from the converter, and has a direct impact on the alloy yield and subsequent refining processes (LF, RH, etc.). At present, the service life can be stabilized between 90 and 110 furnaces, but it is difficult to break through the bottleneck of a higher service life. The core problem is mainly that the joint between the taphole and the inner nozzle brick is a flat surface or a sub-mouth contact form bonded by fire mud. . The contact parts are face-to-face contact, and the probability of air penetrating into the contact surface during use is high. Due to the oxidation, looseness and peeling of the contact surface caused by multiple replacements, especially the contact area between the taphole and the inner nozzle (end C brick) needs to be used with multiple sets of inner nozzle bricks, the impact of oxidation and loosening of the contact surface is more obvious , the service time of the C brick at the tap port end has become the key that directly determines the longevity of the tap port.

Improvement measures for refractory material application problems

Improve and optimize the material and structure of slide gate plates to greatly increase the service life

In view of the common problems in the material of the converter slide plate at present, our company is based on the actual production conditions of the steel plant and continuously optimizes the material of the slide plate. To improve the comprehensive performance of slide gate plates such as oxidation resistance, wear resistance, thermal shock stability, and corrosion resistance, magnesium carbon, aluminum carbon, aluminum zirconium carbon, and aluminum zirconium carbon inlaid zirconium materials have been developed. Finally, the aluminum-zirconium carbon body composite zirconium inlaid ring technology is adopted, which greatly improves the overall service life of the slide gate plate, and the average service life is steadily increased from the original 10 to 16 furnaces to 23 to 25 furnaces. The maximum service life reaches 27 furnaces, which is at the leading level in China (specific data are listed in Table 1). The goal of replacing the sliding plate once a day in the steelmaking plant was achieved, which greatly reduced the labor intensity of workers and provided a strong guarantee for the implementation of the fast-paced steelmaking process in the converter of the steelmaking plant.

Table 1 Service life of converter slide plates made of different materials

MaterialMagnesium carbonAluminum carbonAluminum zirconium carbonAluminum zirconium carbon inlaid zirconium
Life/furnace10~ 1313~ 1612~ 1523~ 25

Measures to improve the overall life of the tap hole

During the tapping process of the converter, the molten steel passes through the taphole to the ladle. The refractory material at the taphole is gradually melted and damaged under the erosion of high-temperature flowing molten steel. The inner hole of the tap hole is expanded into an “inverted trumpet (the upper opening is small and the lower opening is large)”. Since the tapping port is integrally assembled by the sleeve brick and the end brick (C brick), the C brick of the tapping port cannot be replaced separately during actual use. After using furnaces 90~110, even if the inner nozzle brick is replaced, the “expansion” of the taphole C brick is too large to ensure a safe combination area with the inner nozzle brick. There will be a very high risk of leakage of molten steel at the joint surface. At this time, the entire tap hole must be replaced immediately, while other sets of bricks in the tap hole of the converter wall can continue to be used. The resulting problem is that the comprehensive life of the taphole is greatly reduced, which not only increases the frequency of taphole replacement, affects the normal production organization and production capacity, but also increases the cost of using the taphole refractory materials.

The new design changes the C bricks of the overall structure into a combinable structure, and uses replacement bodies (bowl bricks) that can be replaced individually in the “expansion area”. The taphole C brick with a new structure is used. When the “expansion” of the taphole C brick is too large to ensure a safe combination area with the inner nozzle brick, a bowl brick is used to replace the taphole C brick separately. This ensures the safe combination area of the taphole C brick and the inner nozzle brick, and achieves a continuous improvement in the life of the taphole, with an increase of 20% to 40%. This move effectively increases the online service life of the taphole from about 90 to 110 furnaces to 120 to 140 furnaces, and greatly improves the safety factor of steel pouring in this part. The specific design description of taphole C brick is shown in Figure 2.

Figure 2 Description of the design structure of the new and old tapholes

Conclusion

1) Through continuous innovation in the key technologies of converter slag-stopping slides, the company’s slide gate plate slag-stopping technology has continued to enhance its competitiveness in the domestic and foreign markets. It has successfully entered the key application markets of slag-stopping technology for large and medium-sized converters of more than 200 tons at home and abroad, such as SLAZGITTER.A.G in Germany and Shougang (Qian’an). The use effect is good, the tapping time is stable at 6 ~ 8 minutes, the average service life reaches more than 23 furnaces, and the maximum service life reaches 27 furnaces, which is at the leading level in the country.

2) Optimize the structural design of the end C brick at the joint between the taphole and the inner nozzle brick. The C brick at the end of the tap opening has been changed from the original single overall design to a combined design of replaceable bowl bricks, which effectively improves the online service life of the tap opening from about 90 to 110 furnaces to 120 to 140 furnaces. It reduces the frequency of workers replacing the taphole, reduces labor intensity, greatly improves the safety factor of steel pouring in this part, reduces the amount of slag, and reduces the comprehensive consumption of steelmaking refractory materials.

LMM YOTAI established in 2007. Our production technology comes from Japanese Yotai. As an experienced and international player in the refractories industry. We have succeeded in expanding both the breadth of its product range and the depth of its services. From raw material selection, refractory portofio & optimization, installation & services & recycle of used refractories on site to further reduce client’s Opex & Capex in refractory consumption per ton steel output, meanwhile improve product quality of client.

Our Product have been supplied to world’s top steel manufacturer Arcelormittal, TATA Steel, EZZ steel etc. We do OEM for Concast and Danieli for a long time

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