The material system, construction method and performance of hot patch, spray patch, grout and hand thrown material for the maintenance of different areas of the converter are summarized, the selection of refractory materials for the maintenance of the converter, the consumption ratio and its correlation with the working conditions of the converter are analyzed, and the development of refractory materials for the maintenance of the converter in the future is looked forward to.
Improving the life of the converter has always been the focus of steel mills and refractory plants. The lining of the converter is generally built with magnesium-carbon bricks with different functions and combined with slag sputtering and furnace protection technology. The requirements of domestic steel mills for the life of the converter are generally above 5000 furnaces, or even more than 10,000 furnaces, so it is necessary to be equipped with the corresponding refractory materials for maintenance. At present, it is common to use large-surface hot patching material to maintain the charging side, bottom and outlet side of the converter, spray patching material to maintain the molten pool, fillet and trunnion of the converter, grouting material for the caulking and maintenance of the outlet area of the converter when the outlet is replaced, and hand-throwing material for the maintenance of the converter’s furnace cap. In addition, the spatter guard technology also plays a role in prolonging the life of the converter, but with the clean steel smelting and the understanding of the concept of economic age of the converter, the proportion of the converter spatter guard will continue to decline, so the role of the refractory materials for maintenance will be more and more important.
The following is a review of the material system, construction method, performance and consumption ratio of refractory materials used for maintenance of different areas of the converter and their correlation with the converter operating conditions.
1.Converter large surface hot repair material
Converter large surface hot repair material is mainly used to maintain the charging side, furnace bottom and steel outlet side of the converter, and its material now mainly includes magnesium carbonaceous hot repair material combined with asphalt or resin, magnesium aqueous environmentally friendly hot repair material combined with SiO2 micropowder, and magnesium self-fluxing hot repair material combined with sodium metasilicate hydrate, etc. The material is mainly used to maintain the charging side, furnace bottom and steel outlet side of the converter.
（1）Comparison of construction methods
Magnesia carbonaceous hot repair material is mainly based on magnesia sand and asphalt or resin powder as the main raw material, with wetting agent, flow promoter and antioxidant added to the matrix. It is poured into the converter through the hopper, with the help of shaking furnace and liquefaction when the binding agent meets the heat, so that the large fabric flows rapidly to the area to be maintained and self-flowing dense, and the lining of the furnace is tightly combined together. Magnesium-silicon water-based environmentally friendly hot repair material is mainly based on magnesium sand and SiO2 micro-powder as the main raw material, the matrix is added with water-reducing agent, anti-sedimentation agent and explosion-proof agent, etc., which needs to be added to the mixer with water and stirred uniformly to achieve the self-flowing state, and then poured through the hopper into the converter with the help of shaking the furnace and the evaporation of moisture in the presence of heat to make the large surface material flow rapidly to the area in need of maintenance and self-flowing and compact, and the lining of the furnace to be tightly integrated together. Sodium metasilicate hydrate combined with magnesium hot repair material is mainly based on magnesium sand and sodium metasilicate hydrate as the main raw materials, the furnace repair method is the same as the carbon hot repair material, the difference is that it is through the above inorganic salts released when the heat of the water and the evaporation of the water so that the repair material boiled, flow and precipitation, and with the lining of the furnace combined together, so as to achieve the goal of maintenance.
The above three kinds of large fabrics are utilized to realize the furnace patching operation by using the residual heat of the converter after the steel is discharged from the converter and the timely shaking of the converter, and the dosage of each maintenance is 0.7~3.2t, so it is necessary to repair the converter in time when the residual temperature is higher after the steel is discharged from the converter and to ensure the sufficient sintering time. Magnesium carbon hot repair material in the sintering process there is asphalt / resin combustion and carbonization, accompanied by a lot of smoke out of the environment is not friendly, and the sintering time is generally in the 30 ~ 60min. magnesium-silicon water-based environmentally friendly hot repair material and sodium metasilicate hydrate combined with magnesium hot repair material in the sintering process is mainly the evaporation of water, the environment does not have a negative impact, and the sintering time is generally less than 20min, which has a significant impact on the It is of great significance to improve the production efficiency of converter.
（2）Comparison of physical and chemical properties and applications
The density and strength of magnesium silicon environmentally friendly thermal repair material are the highest, followed by sodium metasilicate nonahydrate combined with magnesium thermal repair material, and magnesium carbon thermal repair material is the lowest. This difference is related to its chemical composition: the main components of magnesium silicon environmentally friendly thermal repair material are MgO and SiO2, which will form a high melting point phase M2S (melting point 1890℃) at high temperature; the main components of magnesium carbon thermal repair material are MgO and C, which will form a carbon bond at high temperature; the main components of sodium metasilicate nonahydrate combined with magnesium thermal repair material are MgO, SiO2 and Na2O, which will have more low melting point phases at high temperature.
Due to the difference in density and strength, magnesium-silicon environmentally friendly thermal repair material has the longest service life, but because it is restricted by the construction method and belongs to the emerging technology developed in recent years, its current scope of use ranks second; the service life of magnesium-carbon thermal repair material is second, but because it is easy to construct and is a mature technology that has been used for many years, its current scope of use is the widest; sodium metasilicate nonahydrate combined with magnesium thermal repair material has the shortest service life and its current scope of use is also the narrowest.
2.Gunning material for converter trunnion and fillet maintenance
The converter trunnion and the fillet area on the same side of the trunnion are repaired with magnesium or magnesium-carbon gunning materials. Both of these gunning materials use magnesia as the main raw material, phosphate as the binder, and introduce appropriate amounts of SiO2 micropowder, hardening agent and plasticizer into the matrix, and the repair effect is achieved through gunning equipment.
The maintenance of the converter trunnion and fillet with magnesium and magnesium-carbon gunning materials generally starts in the middle of the converter’s service life, and try to use the sintering time after the converter hot repair material maintenance. The amount used each time is generally 0.4~0.8t, the sintering time is within 10min, and the service life is generally 4~5 furnaces.
3.Magnesium grout for converter outlet replacement
Converter outlet life is generally 90~150 furnaces, replacement of magnesium grout to fill the gap between it and the outlet seat brick. Magnesium grout adopts magnesium sand as the main raw material, phosphate as the binding agent, and introduces appropriate amount of magnesite (or dolomite, limestone) fine powder, chromium oxide micro-powder, SiO2 micro-powder, clay powder, low-temperature sintering agent and hardening agent, etc. in the matrix.
The general construction process of magnesium grout is as follows: after the end of the steel outlet of the converter, the residual bricks of the outlet will be crushed and removed through the special drilling and crushing machine, and the assembled outlet replacement bricks will be inserted and fixed on the flange around the outlet holes; and then the converter will be swung to the platform behind the furnace, and the grout will be sprayed at high speed into the gap between the outlet replacement bricks and outlet seat bricks by spraying and filling equipment for the maintenance of the same trunnions and round corners to fill up the gap tightly, see Fig. 1(b). The gap is filled densely. The construction time of the grout is generally within 30 min, and the maintenance dosage is about 0.8 t. After the construction, the converter can be put into production immediately, and the life of the grout is synchronized with the outlet replacement bricks.
4.Magnesia carbonaceous hand-thrown material for converter caps
Converter cap near the outlet area there are frequent contact with high temperature steel and slag and other problems, compared with other areas of the cap melt loss rate is large, the area of large surface hot repair material maintenance can not be, some steel mills use magnesium carbonaceous hand casting material to maintain. Magnesium carbon hand-throwing material and large surface magnesium carbon hot repair material belongs to the same material system, the same principle of repair furnace, the difference is that the magnesium carbon hand-throwing material is generally magnesium peridotite as the aggregate, magnesium sand as fine powder, asphalt or resin powder to add less, in order to meet at lower temperatures and a shorter period of time to complete the sintering.
Magnesium carbonaceous hand feeding is generally carried out immediately after the completion of the converter steel, and the small-packed magnesium carbonaceous repair material is put into the furnace cap directly from the furnace mouth to the area to be repaired by hand. The maintenance dosage of converter cap hand feeding is 0.4~0.8t per time, and the service life is 100~200 furnaces.
5.Refractory consumption for converter maintenance and correlation with converter operating conditions
Three top and bottom double-blown converters from three large domestic steel mills were selected, numbered Z1, Z2 and Z3, and their working layer magnesium carbon brick configurations and smelting conditions were analyzed in detail. The consumption of maintenance refractory materials was listed. From the analysis of the data, it can be seen that the configurations of the working layer magnesium carbon bricks of the three converters are basically the same, but the working conditions are different. The working conditions of Z1 are the most demanding, followed by Z2, and Z3 is the best. The consumption of maintenance refractory materials per ton of steel of the three converters varies greatly, which are 0.75kg (Z1), 0.62kg (Z2) and 0.51kg (Z3) respectively. Combined with the working conditions of the three converters, the overall selection of maintenance refractory materials and the consumption per ton of steel vary greatly.
(1) The steel plant where Z1 is located has only two converters. Magnesium-silicon environmentally friendly hot repair materials are selected to meet the working conditions of high steel-making frequency and short maintenance time of its converters. The steel plants where Z2 and Z3 are located have three converters. The use of magnesium-carbon hot repair materials can adapt to the current steel-making frequency and maintenance mode. From the perspective of the entire furnace campaign, the consumption of magnesium-silicon environmentally friendly hot repair materials per ton of steel is close to that of magnesium-carbon hot repair materials, but magnesium-silicon materials have a short sintering time and a long service life, which can greatly improve the turnover efficiency of the converter. Comparing Z1, Z2 and Z3, Z1 had a total of 211 maintenances and took 4220 minutes, while Z2 had a total of 417 maintenances and took 25020 minutes, and Z3 had a total of 740 maintenances and took 22200 minutes. Calculated based on the 40-minute smelting turnover time of one furnace, if Z2 and Z3 were maintained with magnesium-silicon materials, they would be able to smelt 93825 and 64750 tons of molten steel respectively.
(2) The requirement of bottom blowing of tuyere determines the consumption of magnesium gunning material. The Z1 tuyere is exposed throughout the whole furnace service, the number of tuyere bricks is large, and the argon blowing tube adopts a single-tube cluster structure, which causes frequent and severe scouring of the fillet area, so the consumption of magnesium gunning material increases sharply; Z2 is the same as Z1, but because it does not require the whole furnace service to be exposed, its consumption of gunning material per ton of steel has dropped significantly; Z3 has a small number of tuyere bricks, adopts a capillary structure, and does not require the whole furnace service to be exposed, so its consumption of gunning material per ton of steel is the least.
6.Technology Outlook for Refractories for Converter Maintenance
At present, large-surface hot repair materials, gunning materials for trunnion and fillet maintenance, grouting materials for tapping port replacement, and manual feeding materials for furnace cap maintenance are still the main materials for converter maintenance. With the strengthening of national control over magnesium resources, the improvement of efficiency and environmental protection requirements of steel mills, and the requirements of high-end steel grades in steel mills for slag splashing furnace protection and blowing ratio, there will be some new changes in the refractory technology for converter maintenance in the future:
(1) The trend of tight magnesium resources will force refractory manufacturers to look for more alternative resources, such as forsterite, magnesium dolomite, various alkaline recycled waste bricks, etc., which will become popular raw materials for maintaining refractory materials.
(2) Magnesium-silica environmentally friendly hot repair materials for large-surface maintenance of converters are superior to traditional magnesium-carbon hot repair materials in terms of environmental protection and improving converter turnover efficiency, and their scope of use will become wider and wider.
(3) The automation and intelligence of equipment for converter trunnions, fillet maintenance gunning materials, and taphole grouting materials will gradually be promoted. It can automatically adjust the water-to-material ratio and gunning speed, greatly improving the adhesion effect of maintenance materials, thereby greatly reducing the consumption of refractory materials per ton of steel.
(4) Due to the increasing demand for high-end steel grades, steel mills will gradually reduce the proportion of slag splashing furnace protection and pursue a suitable economic furnace age. In addition to the development of high-grade furnace lining bricks, high-performance converter maintenance materials, especially new gunning materials with long life, are also in urgent need of development.
