Iron-manganese and iron alloy, and used as a deoxidizer in steelmaking alloying additions, is the largest amount of iron alloy. The manganese ore used for smelting ferromanganese is generally required to contain 40% to 50% of manganese, the ratio of manganese to iron is greater than 7, and the ratio of phosphorus to manganese is less than 0.003. Before smelting, the manganese carbonate ore should be calcined first, and the fine ore should be sintered to form a block. Ore with high iron content and high phosphorus can only be used together, or can be reduced by low-iron and low-phosphorus manganese-rich slag. Using coke as a reducing agent, some plants are also equipped with a die in a prison or anthracite coal smelting. The auxiliary raw material is mainly lime, and silica is generally added when smelting manganese-silicon alloy.
Manganese iron products are classified into carbon, medium carbon and low carbon according to different carbon content. Manganese-silicon alloys, mirror irons and manganese metal are commonly used in the name of manganese-based ferroalloys. The general standard for carbon ferromanganese is 75%-80%. In order to meet the low raw material conditions of manganese ore, China has a lower grade containing manganese (electric furnace ferromanganese containing more than 65% manganese, blast furnace manganese iron containing manganese 50 %the above). In the past, smelting carbon ferromanganese mainly used blast furnaces. With the development of the power industry, the number of electric furnaces has gradually increased. At present, blast furnaces are mainly used in Western Europe and China, and electric furnaces are used in Norway and Japan. Electric kiln is also used in new manganese-iron plants in the former Soviet Union, Australia, Brazil and other countries.
First, blast furnace smelting
Generally, a blast furnace of 1000 m 3 or less is used, and the equipment and production process are generally the same as those of the ironmaking blast furnace. In the process of manganese ore falling in the top of the electric furnace, high-priced manganese oxide (MnO 2 , Mn 2 O 3 , Mn 3 O 4 ) is gradually reduced to MnO by CO as the temperature increases. However, MnO can only be directly reduced to metal by carbon at high temperature, so smelting ferromanganese requires a higher furnace temperature. For this reason, the blast furnace for smelting ferromanganese uses a higher coke ratio (1600 kg/t) and a wind temperature (1000 Â°C). the above). In order to reduce manganese loss, the slag should maintain a high alkalinity (CaO / SiO 2 is greater than 1:3). Due to the high coke ratio and low indirect reduction rate, the gas yield and CO content of the ferromanganese blast furnace are higher than that of the ironmaking blast furnace, and the furnace top temperature is also higher (above 350 Â° C). The rich air blast can increase the temperature of the hearth, reduce the coke ratio, increase the output, and reduce the temperature of the top of the furnace due to the reduction of the amount of gas, which has a significant improvement effect on the smelting of ferromanganese.
Second, electric furnace smelting
The reduction and smelting of ferromanganese has two kinds of flux method (also called low manganese slag method) and no flux method (high manganese slag method). The principle of the flux method is the same as that of the blast furnace smelting, except that the coke for heating is replaced by electric energy. The high alkalinity slag (CaO/SiO 2 is 1.3 to 1.6) is formed by adding lime to reduce the loss of manganese. No fluxing method is used to smelt without lime, and low-iron low-phosphorus manganese-rich slag with low alkalinity (CaO/SiO 2 <1.0) and high manganese content is formed. The amount of slag is small, the power consumption can be reduced, and the evaporation loss of manganese can be alleviated because the slag temperature is low, and the manganese-rich slag of the by-product (25% to 40% of manganese) can be used as a raw material for smelting manganese-silicon alloy. The comprehensive recovery rate of manganese (more than 90%). Most of the modern industrial production uses the non-flux method to smelt carbon ferromanganese, and combines the production process with the smelting of manganese silicon alloy and medium and low carbon manganese silver .
The modern large-scale ferromanganese reduction electric furnace has a capacity of 40,000 to 75,000 kVÂ·A, which is generally fixed and closed. The smelting power consumption of the flux method is generally (2.5 to 3.5) Ã— 3.6 GJ/t, and the power consumption of the fluxless method is (2 to 3) Ã— 3.6 GJ/t.
The manganese silicon alloy is smelted in a closed or semi-closed reduction electric furnace. Generally, manganese ore with high silica content and low phosphorus content or additional silica is used as raw material. The manganese-rich slag has low phosphorus content and high silica content, which is a good raw material for smelting manganese-silicon alloy. The smelting power consumption is generally about (3.5 ~ 5) Ã— 3.6GJ / t. The raw materials for the furnace are pretreated, including whole grain, preheating, pre-reduction and powder sintering, which significantly improve the operation of the furnace and technical and economic indicators.
Third, electric furnace refining
Medium and low carbon ferromanganese is generally desiliconized and refined with 1500ï½ž6000KvÂ·A electric furnace. The manganese silicon, manganese rich ore and lime are used as raw materials, and the reaction is:
The use of high alkalinity slag can reduce the manganese content of the slag and reduce the manganese loss caused by the waste residue. In the joint production, the lower slag basicity (CaO/SiO 2 <1.3) is used, and the slag containing higher manganese (20% to 30%) is used for smelting the manganese-silicon alloy. The preheating of the charge or the filling of the liquid manganese-silicon alloy helps to shorten the smelting time and reduce the power consumption. The refining power consumption is generally around 3.6GJ. The medium and low carbon ferromanganese is also produced by the heat exchange method of the liquid manganese-silicon alloy and the manganese ore and the lime melt.
Fourth, oxygen blowing refining
The liquid carbon ferromanganese or manganese silicon alloy is blown with pure oxygen to obtain medium and low carbon ferromanganese. After years of experimental research, this method entered industrial scale production in 1976.
It should be noted that according to statistics, in the 1970s, manganese used in the steel industry accounted for more than 95% of the world's total manganese ore production (about 98% of which was used for steelmaking), half of which was used for non-ferrous metal alloys, and half for batteries, chemical industries, etc. . Regarding the processing and utilization of manganese in other aspects, such as the production of manganese dioxide for batteries and some manganese chemical products, please refer to the related monographs.
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