The addition of continuous casting slag protection
Release time:
2022-01-01
In actual production, the quality of slag protection is closely related to the slag operation. The continuous casting production practices of steel mills at home and abroad have proved that even if the selected mold flux is correct, if it is not used correctly, there will be problems with the quality of the billet. When adding mold flux to the mold, the mold flux must be evenly distributed on the surface of the molten steel in the mold. When fluctuations, deviations, stoppages, or other failures occur on the molten steel surface during casting, corresponding measures should be taken. Let's learn more about this below. Continuous Casting Flux addition operation.
I. Continuous Casting Flux Input Operation
1. Steps for Adding Flux
(1) Preparation of slag adding tools, as follows.
Slag removal rod: The main function of the slag removal rod is to remove large slag rings in the mold. When bonding, it also has the function of exploring the shell and confirming the operation of the shell. Metal oxygen-burning tubes and wooden strips can be used. For the level monitoring system of the eddy current system, a wooden slag-removing rod is needed; for the level monitoring system of other systems, an oxygen-burning tube can be used, which is very practical.
Flux spoon: Used for loading and replacing the flux in the mold and removing the flux when removing slag.
Slag rake: A tool for adding protective slag to the mold. For the liquid level monitoring system of the eddy current system, in order not to interfere with the signal, a wooden rake is also used.
Winnowing basket: Used for changing the slag in the mold and putting in the slag removed when removing slag.
2) Precautions for Continuous Casting Flux
1) When the liquid level in the mold changes abnormally, add mold flux after the liquid level stabilizes.
2) Do not directly press the mold powder into the corners of the mold.
3) When removing slag blocks or slag rings, pick them up slowly to prevent molten steel from wrapping around the slag.
4) When opening the tundish, the protective slag must be immersed in the molten steel surface and then put in after being immersed in the distributor nozzle.
5) If any abnormality is found during the addition of mold flux, and the consumption is too low, the slag must be replaced.
6) It is better to carefully add or thinly add the flux to ensure that the molten flux layer is always covered with new flux material.
II. "Black" Slag Operation
The so-called "black" slag operation refers to continuously adding sufficient protective slag to the surface of the molten steel in the mold to prevent "red leakage" on the surface of the protective slag. Generally speaking, the surface of the residual slag should be gray (surface temperature about 400) instead of red (surface temperature about 800), and the escaping flame is not high, about 20 mm. Generally, the liquid slag layer thickness is 7-15 mm, and the original slag layer thickness is preferably 15-20 mm. The protective slag should not be stirred frequently, which will only affect the three-layer structure of the protective slag and is not conducive to the protective slag's function.
At present, most continuous casting in China uses manual slag addition, but it is necessary to add frequently, add less, and add evenly. The interval between each slag addition should not be too long. For carbon steel and other crack-sensitive steel grades cast during casting, when using protective slag with a solidification temperature exceeding 1100, special attention should be paid to adding protective slag. When the casting speed is low, due to the low heat of the molten steel, the surface layer of the protective slag will solidify prematurely. To provide more effective heat insulation, it is best to use protective slag with a low solidification temperature. The thickness is 40-50 mm.
III. Slag Protection Operation During Casting
When the continuous casting machine is put into operation, the size of the molten steel flow from the tundish must be appropriate. This is to avoid damaging the ingot and not to overturn the ingot to damage the blocking material. In addition, attention must be paid during operation to ensure the teeming time required by the technical requirements.
1) During the process of the molten steel level rising in the mold, it is customary to close the stopper 1-2 times to ensure that the teeming time is between 30-90s.
2) When the molten steel in the mold reaches the specified height (usually 70-100 mm from the top), under the condition of ensuring the teeming time, the casting machine starts the billet and vibration device. The starting speed is implemented according to the process regulations, usually 0.3-0.6 m/min.
3) Add protective slag immediately after the submerged nozzle outlet is submerged by the molten steel.
When the continuous casting flux is just poured out, the molten steel in the mold dissipates heat quickly. After adding the mold flux, it will also absorb a large amount of heat, and a shell may be formed on the surface of the molten steel. At this time, gently stir with a slag screwdriver. If it is clear that no shell has been formed, the mold flux can be added using the usual method. Please note that there will be slag when the molten steel submerges the side holes of the submerged nozzle.
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