After a certain period of use, the main trench of the blast furnace iron-making yard is forced to be shut down for maintenance due to the thinning of the working lining. The main trench working lining is mainly eroded and washed by molten iron and slag, oxidized by the material itself, thermal shock of intermittent iron-making in the blast furnace, and construction, which causes the main trench to be periodically overhauled.
Main trench maintenance of the blast furnace iron-making yard
1. Residual iron release in the main trench: The main trench is used for a certain period of thinning of the working lining for maintenance, and the residual iron and slag in the main trench need to be released. The residual iron eye is opened by burning oxygen, electric drilling, etc., and it takes 0.5 to 1 hour to release the residual iron. Some sites use high-grade materials to block the residual iron eyes, and the high strength makes it relatively difficult to poke the residual iron eyes and takes a long time. The use of siliceous materials has a relatively good effect. Siliceous materials expand at high temperatures and can completely block the residual iron eyes. In addition, the strength of siliceous materials is relatively low, which is convenient to poke, saving time and reducing labor intensity.
2. Removal of the main trench: After the residual iron is released, the surface of the main trench is sprayed with water to cool it down, and a hook machine is used for removal. The surface oxide layer and sintered layer of the main trench lining are completely removed, the slag in the trench is cleaned, and the slag in the trench is blown away with high-pressure air to reveal the overall outline of the main trench. The removal of the main trench takes about 10 hours.
3. Mold placement: The main trench mold is placed in the middle of the main trench, the front section corresponds to the iron outlet, and the rear section is placed in the middle with the support iron trench as a reference, and the front and back are in a straight line. The mold is welded firmly. It takes about 2 hours to place and fix the mold.
4. Pouring: A forced mixer is used, and a water adding device is set. The water addition amount of the main trench castable is generally about 4.5%. The water addition amount can be appropriately increased for 2-3 plates before the hot trench repair. Stir for 2-3 minutes to ensure that the castable is evenly stirred. Use a φ70mm vibrating rod to vibrate evenly to prevent segregation and leakage. Continuous pouring is required, and the time takes 2~3 hours.
5. Curing and baking: The main trench hot repair is generally cured for 2 hours before demoulding and baking. The curing time can be appropriately increased or decreased according to the actual situation of each manufacturer. The temperature control is relatively stable when the iron ditch is baked with coke. In China, wood is generally used for baking, and the baking time is 4-6 hours. The temperature range of the iron ditch castable is easy to oxidize at 400~1000℃, so the baking temperature can be up to 600℃. The ditch can be repaired once, and the personnel, equipment, materials, etc. are fully prepared, and the smooth progress can be controlled within 24 hours.
Materials for the second blast furnace iron-making yard
The materials for the blast furnace iron-making ditch are castables based on aluminum-silicon carbide-carbon. The main raw materials are special alumina, corundum, silicon carbide, ball pitch, carbon black, alumina powder, binder, antioxidant, explosion-proof agent, water reducer, etc.
Brown corundum and dense corundum have good strength, anti-scouring and wear resistance, but the thermal shock stability is relatively poor. Generally, some special alumina and plate-shaped corundum are matched to improve the thermal shock stability of the castable. Special alumina and plate-shaped corundum have advantages over brown corundum and dense corundum in price.
Silicon carbide has good chemical stability and good resistance to slag erosion and permeability. The general addition amount is 15~20%. There are literature reports that the addition amount of main trench slag line castables in Europe, the United States, Japan and other countries exceeds 30%.
Carbon has good slag resistance and is mainly added in the form of spherical asphalt. Carbon is a hydrophobic material and is not easy to wet with water. In addition, carbon has a low density and is easy to float. Currently, popular carbon black, carbon resin powder, modified graphite, etc. can be added to iron trench castables, but the addition amount is relatively small.
The binder is mainly cement, pure calcium aluminate CA-70, CA-80, etc., and hydrated alumina (ρ aluminum), with an addition amount of 1-3%.
The antioxidants used in main trench castables are commonly used. Silicon metal, boron carbide, calcium boride, titanium boride, etc., and the addition amount is relatively small.
The explosion-proof agent mainly includes explosion-proof fiber and metal aluminum powder. Metal aluminum reacts with water to generate hydrogen, so that the castable forms through pores, which is conducive to the discharge of water vapor during the baking process. The explosion-proof fiber melts at about 100°C. Countless explosion-proof fibers are irregularly distributed in the castable and can be connected to each other to form through pores, which are conducive to the discharge of water vapor during the baking process.
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