The progress of fluorine-containing sintering technology is generally divided into four stages: the early stage starts from the cold strength of sintered ore, improves the sintering productivity and solves the problem of normal production of sintering; the second stage improves the softening temperature of sintered ore, controls the nodulation of blast furnace, and solves the problem of eating sinter in blast furnace. The third stage is to optimize the chemical composition of the sintered ore and improve the comprehensive performance of the sintered ore under low fluorine conditions. In recent years, it is aimed at improving the particle size of the low-fluorine sintered ore and the poor permeability of the soft melt. sintering, iron smelting comprehensive economic indicators, the establishment of a new generation of high-quality sinter blast furnace reasonable charge structure for the purpose of development. The fluorine-containing ore sintering series of problems cold strength, yield, productivity and metallurgical properties, and in the sinter mineral composition and chemical composition and structure of the root of the iron ore concentrate containing a high fluoride, potassium, sodium, and complex Mineral composition. More than 30 years of experience have shown that these problems can only be solved by optimizing the ratio of raw materials, adjusting the chemical composition, and changing the composition and structure of the sinter minerals. The optimization process is a process of continuous understanding and deepening. It is a process of improving the quality of iron concentrates and sintering. The optimization process is aimed at meeting the needs of blast furnaces, taking into account the quality, productivity, cost and reasonable composition of the blast furnace. The comprehensive problem of the charge structure.
(1) Production of self-fluxing sintered ore and study on sinter strength
1. Self-fluxing sinter production brief introduction In the first ten years of the sintering and production of Baotou Steel, the self-fluxing sinter with a basicity of 1.0 was designed. The production index is very backward. In the past ten years, the production of sintered ore is 4 million tons, the solid fuel consumption is up to 150kg/t, and the utilization coefficient of the sintering machine is only 50% of the design value. The quality of the sintered ore is inferior, the strength is low, and the powder is high. The blast furnace is equipped with 50% of the sintered ore, and the smelting index is not as good as the fluorine-containing lump ore. In the early 1970s, the fluorine content of iron concentrates increased sharply, and various contradictions were sharper. Sintering seriously hindered iron production. During this period, although Pangjiabao powder ore with slaked lime and high silicon in sintering was used, the sintered ore silica was as high as 12% to 13%, and it still failed to reverse the sintering and ironmaking passive.
The most prominent problem of self-fluxing sinter is low strength, which is characterized by high return rate in the production process, low yield, low productivity, and high solid fuel consumption. The reaction is produced in a blast furnace where there is a large amount of sinter ore powder. When sinter is used, the ratio of gray iron blown out by the blast furnace is multiplied. The first problem with fluorine-containing sintering is the strength of the sintered ore.
2. Study on the strength of self-fluxing sinter In the early 1970s, Baotou Steel and Beijing Iron and Steel Institute and Steel Research Institute jointly studied the strength of self-fluxing sinter. The results are as follows.
The effect of silica on the strength of different fluorine content sinter is shown in Figure 1. Under the two conditions of carbon blending, the sinter drum index decreases with the increase of fluorine content, and increases with the increase of silica content. high. Another set of tests is a sintering test in which calcium fluoride is added to different WISCO concentrates and Benxi steel concentrates. The results are shown in Fig. 2. The low silicon WISCO concentrate increases with the increase of fluorine content and sintering. The mine drum index and drop strength are significantly worse. For high-silicon Benxi concentrate, the influence of fluorine is the same, but the impact is much smaller. Both results indicate that fluorine has a great destructive effect on sinter, while silica has an inhibitory effect on fluorine. [next]
Macroscopic structure observations show that the prominent feature of fluorine-containing self-fluxing sintered ore is “thin-wall porousâ€. Under the microscope, a large number of micropores can be seen between magnetite grains. This structural feature is low in direct strength. the reason.
In order to explore the cause of "thin-walled porous", the sinter of different fluorine and silica contents were ground and magnetically separated, and the cemented phase was separated for viscosity measurement. The results are shown in Fig. 3. The viscosity of the cemented phase increases with the increase of fluorine content. Significantly reduced, the increase in silica can increase the viscosity, but the effect is much smaller than fluorine. According to the analysis, the viscosity reduction reduces the liquid phase resistance of the sintering process in the high-temperature semi-molten state, and forms many passages under the action of the gas flow, and forms a "thin-wall porous" structure after cooling. According to the data, the replacement of divalent oxygen ions by a similarly priced monovalent fluoride ion destroys the electricity price balance of the original silicon oxytetrahedron, which divides the bulk silicon siloxane tetrahedron into small volumes, thus reducing the viscosity.
Comparing the fluorine-containing self-fluxing sintered ore with the mineral composition of the domestic alkalinity sinter, the most characteristic of the fluorine-containing sinter mineral composition is that the gunite (3CaO•2SiO 2 •CaF) accounts for a considerable amount in the cemented phase. Proportion, on the contrary, calcium fayaite and calcium ferrite are lower.
Compressive and anti-wear tests were carried out on synthetic gunite and calcium fayaite. The compressive strengths were 19.06 N/mm 2 and 65.93 N/mm 2 , respectively. The wear resistance of the former was also significantly lower than that of the latter. It is another reason for the low strength of fluorine-containing sinter. The conclusion is that fluorine reduces the viscosity of the cemented phase and makes the sintered ore form a "thin-walled porous" structure. In addition, the strength of the gun spar, which is the main part of the cement phase, is low, which is the main reason for the low strength of the fluorine-containing sinter. Silica can alleviate the effects of fluorine, but it does not solve the problem at all, and the improvement of sinter SiO 2 also reduces the reduction of sinter.
(II) Research and production of high alkalinity sinter In the series of tests aimed at improving the properties of sinter melt and improving the strength of sinter, high alkalinity sintering showed good results. From 1976 to 1977, Baotou Steel cooperated with the Steel Research Institute and other departments to carry out systematic research on high alkalinity sintering.
1. High alkalinity sintering test The initial test work was carried out in a small sintered cup using an iron concentrate with a fluorine content of up to 3.0% to 3.5%. When the alkalinity is increased from 1.5 to 2.0, the sinter drum index (+5mm) is increased from 70.1% to 81.1%, and the Taiwanese production is increased from 46.2t to 57.6t. When the material layer is increased from 220mm to 280mm, the time is increased. The increase in production was 74.4 tons, which was a very obvious effect at the time. A more systematic test was then carried out with the same effect as the original test. The suitable alkalinity was selected to be about 2.0. Compared with the self-fluxing sintering, the sintering yield, utilization factor and sinter drum index were significantly improved.
The industrial test conducted after the initial test, although the equipment was in poor condition at the time, still achieved significant results. Compared with the self-fluxing sintering, the strength of the sintered ore was greatly improved, the content of ferrous oxide was reduced by 10%, and the utilization coefficient of the sintering machine was used. Significant improvement. The No. 3 blast furnace smelting test synchronized with the industrial test of the knot achieved a good result of reducing the coke ratio by 17% and increasing the output by 39.4%. [next]
2. Characteristics of high alkalinity sinter ore The Steel Research Institute has conducted in-depth research on the characteristics of fluorinated high alkalinity sinter. As the alkalinity increases, the initial content of the gunite increases, the vitreous material decreases, and the alkalinity of the gunstone remains unchanged after 1.5, and calcium ferrite is rapidly increased. The alkalinity is 1.8 or more and the total slag amount is doubled. The inventors measured the strength of the cemented phase separated by different alkalinity sinter. The results show that the compressive strength of the cemented phase and the sinter drum index are good, and the inflection point occurs when the alkalinity is 1.5. The analysis considers that 1.5 is the free alkalinity of the gunite, and calcium oxide can only form a large amount of calcium ferrite after satisfying the formation of the gun spar.
The structure observation of the sinter showed that when the alkalinity is 1.5 or more, the macroscopic structure of the sinter is changed from "thin-walled porous" to "thick-walled large pore". According to the microstructure observation, the magnetite becomes a crystal with a smaller particle size, and forms an interlaced and molten structure with calcium ferrite. The calcium ferrite also forms an interlaced strip structure with the gun spar. According to the analysis, due to the increase of calcium oxide content, the viscosity of the cemented phase increases greatly at high temperatures, thus forming a "thick-walled large pore" structure. The research results reveal the mechanism of high alkalinity to improve the strength of fluorine-containing sinter, indicating that high alkalinity is the most effective way to solve the problem of fluorine-containing sinter strength.
Determination of metallurgical properties of fluorine-containing sinter with different alkalinity. Compared with self-fluxing, the reduction of high alkalinity sinter is obviously improved, the low-temperature powdering index is improved, and the softening temperature is also improved. It is a kind of sinter with better metallurgical properties.
3. Production and significance of high alkalinity sinter After thorough test work, the 1977 high alkalinity sinter was officially used for production. Considering the blast furnace alkalinity balance, the sinter alkalinity is selected to be 1.8 to 2.0. This alkalinity has been maintained until the past two years. The research and production of high alkalinity sinter is of great significance:
(1) The high alkalinity sintering process not only solves the problem of sinter strength, but also basically solves the "bottleneck" problem that has plagued Baotou Steel's ten years of sintering and restricts the development of ironmaking production, and has made a turning point in the development of Baotou Steel's production. Promote.
(2) High alkalinity sinter is not only low in cold strength, but also high in productivity, low in fuel consumption, and can also significantly improve metallurgical properties such as reducing and low-temperature pulverization. It is a kind of blast furnace charge with good comprehensive performance. These superiorities have universal significance and have played a catalytic role in China.
(3) Baotou Steel took the lead in using the charge structure of high alkalinity sinter and acid pellets in China, and achieved good results. It has a great influence in China, and it has demonstrated and researched the rational charge structure. Promote. [next]
(III) Development and application of high alkalinity high-magnesium sinter ore Before the 1980s, blast furnace nodulation has been a difficult problem in the development of ironmaking production. The result of the furnace tumor research believes that excessive potassium and sodium in the furnace charge circulation in the blast furnace is an important reason for the formation of the furnace, and the low temperature of the soft or molten sinter is the direct cause of the nodulation. In the early 1980s, a proposal was made to improve the remelting of high- magnesium sinter.
1. Metallurgical properties of high alkalinity high magnesium sinter
The following are the results of several groups of high alkalinity high-magnesium sinter metallurgical properties test: Figure 5 is about 2% of sinter ore, the relationship between magnesium oxide content and sinter metallurgical properties; Figure 6 is 1.35% of sinter ore The results of the soft-melt properties obtained under conditions of 0.75%; Figure 7 is the softening temperature measured after soaking alkali in a sintered ore containing 0.75% fluorine, which is equivalent to 8-10 times of enrichment of potassium and sodium in the blast furnace. T 10 . and the differential pressure steep rise temperature T s . Although the two test times in the figure are different by ten years, the equipment and method are not the same, but the law is generally the same. In the reduction test at different temperatures, the reduction of ordinary sinter at high temperature is hindered, and the reduction of high alkalinity and high magnesium sinter at high temperature increases. The softening temperature T 10 of both groups increased with the increase of magnesium oxide content, and the magnesium oxide content was the highest value of 3%, which was about 30-60 °C higher than that of low-magnesium sintered ore. 7 and FIG. 6, the sinter after alkalizing also follows the above rule, but the temperature level is lowered by about 30 ° C. The differential pressure rise and the drop start temperatures T s and T 10 both increase slowly with the increase of magnesium oxide. The softening interval (T 40 to T 4 ) and the droplet interval (T D to T s ) exhibit a small value between 2.7% and 3.4% of the magnesium oxide content. According to the research, the suitable magnesium oxide content of the fluorine-containing sinter should be about 3%, which can be appropriately reduced under low fluorine conditions.
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