How to Decrease Impurities in Molten Steels of Casting
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How to decrease the impurities in molten steels of continuous casting? The following are three method to realize this goal.
First. To adopt suitable casting powders.
As an important assistant material, the casting powder can preserve heat and realize lubrication during casting manufacture. It can also prevent molten steels from oxidation. What’s more, it can absorb floating impurity and improve thermal conditions of crystallizers. Therefore, making sure the correct elements of casting powders are critical for absorbing floating impurities.
In general situation, elements like ferric oxide would be decreased to reduce the extent of oxidation. If Al203 were the element that needed to be absorbed, then content of Al2O3 within casting powders should be decreased as much as possible.
Second. To utilize high-quality fire-proofing materials.
Molten steels that contain over 1% manganese will seriously erode the fire-proofing materials used for casting. Thus, manufacturers should utilize high-quality fire-proofing materials for pouring process. Fire-proofing materials with few free silica can decrease corrosion to some extent. As to ladles and tundish, they should be made from high alumina instead of acid clay bricks. When continuously casting high-quality steels, the tunish should adopt magnesia insulating board or bricks packing coated with magnesia to prevent fire-proofing materials from peeling and improving its corrosion resistant ability. In this way, cleanliness of molten steels can be improved.
Third. To employ properly shaped submersed nozzles.
There are four kinds of submersed nozzles: straight opening type, side opening up type, side opening down type and box type. Manufacturers should select from them according to their pouring speeds and section sizes of cystallizers. The materials, shapes and insertion depth of submersed nozzles should in favor of buoyancy of impurities. What’s more, filters have to be used here. When molten steels flowing through the porous filters, the filters will make impurities stay and let liquids go. Therefore, more than 50lm impurities can be eliminated and molten steels can be purified further. At present, ceramic filters are the most widely used filters.
Conclusion.
The basic solution to control impurities contains decreasing contents, sizes and distribution pattern of impurities. The various safeguard procedures adopted during tapping or teeming process aim at reducing the secondary oxidation of molten steels. At present, to reduce impurities, especially those large impurities, is the major imperative when controlling content of impurities.
