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Reducing the amount of slag in the converter tapping process is an important aspect of improving the quality of the molten steel. One of the necessary means to produce pure steel is to tap with less slag or slag block. Its purpose is the precise control of the composition of the steel melt, effective reduction of re-phosphorisation of steel melt, Improve alloying element absorption, and reduce alloy consumption. A reduction in the amount of inclusions in steel is beneficial, to improve the refining effect of the ladle and to reduce the corrosion of the refractory materials of the ladle and to extend the service life of the ladle. At the same time, it also improves the life of the converter tapping port. At present, the refining outside the furnace requires the thickness of the ladle slag layer to be less than 50m and the slag per ton of steel to be less than 3kg/t.
Slag blocking technology continues to improve. At present, there are more than a dozen slag blocking methods, such as using the slag blocking cap method to block the first slag; blocking the second slag using the slag blocking ball method, slag blocking plug method, slag blocking rod method, slag avoidance hood method, electromagnetic slag blocking method, pneumatic slag blocking device method, pneumatic slag blowing method, etc. As shown in the figure.
1.Slag blocking cap
A conical slag blocking cap made of steel plate is used to block the first molten slag at the beginning of tapping.
2.Slag ball
The density of the slag ball is between that of molten steel and slag (generally 4.2~4.5g/cm3). It is put into the furnace near the tapping port near the end of steel tapping. As the molten steel level drops, the slag ball sinks and blocks the tapping port to prevent the slag from entering the ladle. Considering that the tapping port becomes larger due to erosion, the diameter of the slag ball should be slightly larger than the tapping port diameter to play the role of slag blocking.
3.Slag plug
The slag plug can effectively prevent slag from entering the steel flow. The structure of the slag plug consists of a plug rod and a plug head. Its material is the same as that of the slag ball, and its density can be the same as or slightly lower than that of the slag ball. The upper part of the plug rod is a steel rod used for clamping and positioning, and the lower part is wrapped with refractory material. When the tapping is about to end, according to the tapping angle of the converter, the plug rod is strictly aligned and inserted into the tapping port with mechanical loading. When the tapping is finished, the plug head seals the tapping port. There are grooves on the plug head, and the remaining molten steel in the furnace can flow out through the grooves, while the slag is blocked in the furnace. The slag stopper has the dual functions of stopping slag and suppressing eddy current. It has a better slag stopping effect than the slag stopper ball and is currently widely used.
4.Slag avoidance hood
The slag avoidance hood is built at the tapping port. When tapping, the molten steel flows into the tapping port through the side holes of the slag avoidance hood made of refractory materials. Since the top of the slag avoidance hood is closed, the conditions for the formation of eddy currents above the tapping port are blocked, which can effectively prevent the eddy currents from entraining slag.
5.Pneumatic slag stopper
When tapping is almost over, a mechanical device uses a slag stopper nozzle from the outside of the converter to blow air into the tapping port to prevent the slag from flowing out. This method has strict requirements on the shape and position of the tapping port, and requires the nozzle to be aligned with the center line of the tapping port.
6.Pneumatic slag blowing method
It is most difficult to block the eddy current under slag in the late stage of tapping. Once the eddy current is generated, slag and steel are easily mixed. Therefore, in order to prevent the generation of eddy currents in the late stage of tapping, or even if eddy currents are generated, the method of blocking the slag on the surface of the eddy current molten steel is also the most effective method, which is the pneumatic slag blowing method. High-pressure gas is used to blow away the slag on the molten steel surface above the tapping port to achieve the purpose of slag removal. This method can make the ladle slag layer thickness reach 15~55mm.
