When and how to add mold flux for continuous casting is the most beneficial? -Continuous casting technology

Description: In the actual production process, the performance of slag powder is closely related to the operation of adding slag. Even if the mold powder is selected correctly, it will cause no quality problems for the cast slab if it is not used correctly. When adding flux powder to the mold, the mold powder must be evenly distributed on the molten steel surface in the mold. When the molten steel level fluctuates, drifts, stops casting and other failures occur during the pouring process, corresponding measures must be taken. In the actual operation process, the following items should be paid attention to when adding flux powder.
Title: When and how to add flux powder for continuous casting is the most beneficial? -Continuous casting technology
Keyword: continuous casting technology, continuous casting slag powder, flux powder
Related product: Copper tube crystallizer, copper mould tube

Crystallizer adding slag operation

  1. The sequence of adding slag

    (1) Prepare slagging tools: the slagging tools are as follows:

Slag removal rod: The slag removal rod is mainly used to remove the large slag circle in the crystallizer. It also has the function of testing the shell to confirm the operation of the shell during bonding. Metallic oxygen tubes or wooden rods can be used. For eddy current level monitoring systems, wooden slag rods must be used. For other types of level monitoring systems, oxygen-burning pipes can be used, which is convenient and practical.

Slag removal spoon: used to hold the removed slag when changing and removing slag in the crystallizer.

Slag pushing rake: a tool for adding protective slag to the crystallizer. For eddy current liquid level monitoring systems, wooden wooden speculative rake should also be used to avoid interfering with the signal. Slag removal dustpan: used to hold the removed slag when changing and removing slag in the crystallizer.

            (2) Matters needing attention
1) When the liquid level of the crystallizer fluctuates abnormally, the flux powder should be added after the liquid level is stable.

2) slag powder must not be directly pushed into the corner of the mold.

3) When removing the slag lump or slag ring, pick it up gently to prevent the molten steel from entraining the slag.

4) When the tundish is pouring, the protective slag must be added after the steel surface is immersed in the submerged nozzle.

5) Abnormality of protective slag is found during the pouring process. If the consumption is too low, the slag must be replaced.

6) It is advisable to add slag frequently and thinly to ensure that a layer of new slag is always covered on the molten slag layer.

  1. “Black” slag operation

The so-called “black” slag operation is to continuously add enough flux powder to the molten steel surface in the mold to keep the slag powder surface from “leaking red”. Generally, the surface of the slag is required to be gray (surface temperature is about 400°C) instead of red (surface temperature is about 800°C), and the escaping flame is not required to be too high, about 20mm. Generally, the thickness of the liquid slag layer is 7-15mm, and the thickness of the original slag layer is more appropriate to be 15-20mm. It is not suitable to stir the slag powder frequently. This will only have a three-layer structure of the slag powder, which is not conducive to the function of the slag powder.

At present, most of continuous casting adopts manual slag adding method to add slag powder. It should be added frequently, less frequently, and evenly, and the interval between each addition of slag powder should not be too long. When casting medium carbon steel and other crack-sensitive steels and using mold powder with a solidification temperature higher than 1100℃, special attention should be paid to the addition of mold powder. When the casting speed is low, the surface of the slag powder will condense prematurely due to the low heat from molten steel. It is best to use mold powder with a low solidification temperature with a thickness of 40-50mm to provide more effective heat insulation.

  1. The slag powder operation during pouring

When the continuous casting machine starts pouring, the size of the steel flow in the tundish must be appropriate to ensure that the starter head and the material blocked by the starter head are not damaged. In addition, the emergence time required by the process must be ensured. Pay attention to the operation:

(1) It is customary to try to close the stopper rod 1-2 times to prevent the electric rod during the process of rising the liquid level of the mold steel. Ensure that the emergence time is between 30-90s.

(2) When the molten steel in the mold reaches the specified height (generally 70-100mm from the upper mouth), under the condition of ensuring the emergence time, the caster starts the billet drawing and vibration device. The starting speed is implemented in accordance with the process regulations, generally 0.3-0.6m/min.

(3) Immediately add protective slag after the immersion nozzle outlet is submerged by molten steel.

When continuous casting is just started, the molten steel in the mold dissipates quickly, and a large amount of heat is absorbed after the mold slag is added, and the molten steel surface may crust. At this time, the slag surface should be gently stirred with a slag removal rod. When crusting, the protective slag can be added in the normal way. Note that the protective slag can only be added when the side hole of the immersion nozzle is submerged by molten steel.

  1. Normal pouring of protective slag operation

The slag powder should maintain a certain thickness in the mold, and the thick slab is usually controlled within the range of 40-50mm. In order to ensure the uniform melting of the slag powder in the mold, the liquid slag layer remains stable and at the same time plays the role of heat preservation.

In the case of normal pouring, it is forbidden to frequently agitate the crystal liquid level, which will easily damage the melting of the protective slag, so that the performance changes of the protective slag can be grasped at any time. There are two situations of slag entrapment: one is that the liquid level fluctuates greatly. When the liquid level drops, a slag ring appears on the wall of the crystallizer and falls toward the center of the crystallizer. If the slag ring is not removed in time, the liquid level may rise. Involve the slag ring to cool the surface unevenly, which may cause steel leakage; the second is that the liquid slag layer of mold slag is too thick and solidifies quickly near the mold wall, and a thicker solid layer is concentrated and sticks to the surface of the cast slab. Affect the quality of the cast slab or slow down the heat transfer rate, affect the thickness of the slab shell, and also have the risk of breakout.

  1. The protective slag operation when quickly replacing the tundish

(1) After the ladle stops pouring, turn it out of the tundish pouring position.

(2) When the tundish steel liquid level still has a certain depth, appropriately reduce the drawing speed. In addition, the replacement ladle is located at the correct pouring position. At this time, gradually remove the slag from the crystallizer to facilitate the successful docking.

(3) When the liquid level of the tundish drops to about 400mm (be careful not to let the slag enter the crystallizer), stop pouring immediately, drive away the tundish car quickly, and appropriately reduce the amount of secondary cooling water.

(4) For small and medium section continuous casting slabs, control the liquid level at 1/3 of the upper mouth of the mold, and immediately insert the connecting piece into the molten steel in the mold, half of the connecting piece is immersed in the molten steel, and the other half is left outside. Used as a joint. If the climbing is inserted, the climbing is lowered and hooked with a hook to make it fixed to ensure that half of the climbing is exposed to the molten steel surface of the mold, and half is fixed in the new casting billet, and at the same time, the pull straightening is started to reduce the molten steel. Set at 2/3 away from the upper mouth of the crystallizer.

(5) The new tundish is quickly installed and centered. If a connector is used, the tundish nozzle shall not collide with the connector when it is lowered.

(6) After confirming that the new tundish is properly seated, open the ladle nozzle, pour molten steel into the tundish, and then follow the pouring operation regulations.

flux powder operation at the end of pouring (capping)

The purpose of capping operation in continuous casting production is to solidify and crust the molten steel at the end of the tail billet, so as to avoid accidents caused by leakage of molten steel at the end when the mold is pulled out. The order of capping and closing in production is:

(1) When the molten steel in the ladle is almost finished, no more slag powder is added. The pouring speed is carried out normally until the height of the molten steel in the tundish decreases and the outflow of molten steel becomes slower. At this time, the pouring speed is reduced accordingly.

(2) When the molten steel in the tundish is about 1/2 finished, the pouring speed should be reduced to about 1/2 of the normal pouring speed.

(3) When the height of the molten steel in the tundish is about 400mm, the mold flux must be removed from the molten steel surface.

(4) The continuous casting machine is switched to the lowest drawing speed and the tundish car is driven away.

(5) After all the slag is removed, only use a thin steel rod or argon blowing tube to gently agitate the molten steel. This operation must be uniform and sufficient, and then spray water on the mold copper plate around the end of the casting billet Accelerate the solidification of the top surface to form a steel shell.

Precautions for using flux powder

(1) Store the place of origin to be moisture-proof, and for steel grades with higher quality requirements, use pre-melted protective slag.

(2) When using protective slag that has been stored for more than half a year, it should be dried and tested for moisture content before use.

(3) On-site production personnel should be familiar with the technical parameters of the protective slag used on duty and be consistent with the type of steel poured.

(4) The production team shall designate a person to regularly calculate the slag consumption and measure the thickness of the liquid surface layer during the continuous casting process. An abnormality is found so that measures can be taken.

(5) In the continuous casting production process, the slag must be added frequently and less frequently when adding slag to the mold, and the slag powder must be evenly spread in the mold to ensure the black slag operation, and the surface slag must not be reddened. Bright.

(6) On-site personnel should carefully observe the slag condition in the crystallizer. If slag agglomeration is found, adjust it according to specific conditions. If there is a serious slagging circle phenomenon in the meniscus area, use a special tool to gently tap it. fish out.

Parameters that should be measured in the process of using flux powder

(1) Measure the total heat flow value in the crystallizer.

(2) The relationship between the temperature change of the mold copper plate and its position and time.

(3) The relationship between mold flux consumption and pulling speed.

(4) The accumulation of slag powder in the meniscus area.

(5) Measure the vibration marks of the casting billet in the meniscus area.

(6) The relationship between the friction force between the mold and the slab and the pulling speed.

(7) The surface temperature of the cast slab and its changes in the entire length and width directions.

If pouring high-quality cast slabs, the following parameters should also be measured:

(1) The type, frequency and severity of cracks.

(2) The frequency of visible oxide defects.

The relationship between the type, frequency, size, and severity of subcutaneous inclusions and the operating variables of the continuous casting machine during operation.

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