A method for controlling the slag line deviation of a bloom submerged entry nozzle

Abstract

This invention discloses a method for controlling slag line deviation in a submerged entry nozzle for large billets, belonging to the field of continuous casting technology, and overcoming the problem of abnormal slag line deviation in existing technologies. The slag line deviation control method of this invention includes the following steps: Step 1. Measure the alignment of the submerged entry nozzle and control the nozzle deviation angle to ≤1.8°; Step 2. Adjust the electromagnetic stirring intensity of the crystallizer so that the maximum magnetic induction intensity 33≤mT. This invention simultaneously considers the influence of the nozzle's own installation angle and the rotation state of the molten steel on the slag line state. Using the formula: Nozzle deviation angle = arcsin(distance between steel ball and nozzle / length of bottom nozzle in tundish) / π * 180°, the slag line deviation height is effectively controlled to ≤5mm.

Description

Technical Field

[0001] This invention relates to a method for controlling the slag line deviation of a large billet submerged nozzle, belonging to the field of steelmaking technology. Background Technology

[0002] As one of the three major components of continuous casting, the submerged entry nozzle is a crucial refractory sleeve used for casting during the continuous casting process. Installed at the bottom of the tundish and inserted below the molten steel surface in the mold, it serves to prevent oxidation and splashing of the molten steel, regulate the flow of the molten steel within the mold, and prevent slag entrapment. Because it is inserted below the molten steel surface, the submerged entry nozzle is subjected to alternating scouring and erosion by the molten steel and protective slag, causing the refractory material to continuously dissolve and peel off, gradually forming a slag line.

[0003] The phenomenon of slag line deviation at the nozzle frequently occurs during production, reflecting the instability of molten steel flow in the mold. This can easily lead to uneven billet shell growth and slag entrapment within the mold, severely impacting the quality of continuously cast billets. How to effectively improve the slag line deviation at the nozzle is a topic that continuous casting workers need to explore and refine.

[0004] Patent application CN203556867U provides an immersion nozzle fixing and adjusting device that adjusts the actual length of the hanging mechanism according to the actual site conditions, solving the problem of immersion nozzle skew caused by interference factors during the casting process. Although this patent application corrects the installation angle of the nozzle, it can still cause slag line skew when the molten steel surface is unstable. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the problem of abnormal slag line deviation in the prior art, thereby providing a method for controlling the slag line deviation of the submerged nozzle for large billets.

[0006] To this end, the present invention provides the following technical solution, including the following steps: Step 1. Measure the alignment of the immersion nozzle, suspend a steel ball by the lower end of a thin line, and tie the upper end of the thin line to the junction of the nozzle and the bottom of the sprue, keeping the steel ball flush with the lower end of the nozzle; adjust the nozzle so that the distance between the steel ball and the nozzle wall is ≤20mm, and control the nozzle deflection angle to ≤1.8° using the formula: nozzle deflection angle = arcsin(distance between steel ball and nozzle / length of nozzle at the bottom of sprue) / π * 180°, ensuring the nozzle alignment.

[0007] Step 2. Adjust the intensity of the electromagnetic stirring in the crystallizer, control the electromagnetic stirring current of the crystallizer to 400~500A and the frequency to 1~2Hz, so that the maximum magnetic induction intensity is 33≤mT, and ensure the stability of the molten steel surface.

[0008] Furthermore, the tundish seat groove is made of refractory material. When turning the tundish over, mechanical impact should be reduced. Before building the tundish, foreign objects at the bottom of the tundish seat groove should be cleaned and the installation angle of the tundish seat should be corrected. The tundish seat groove is made of general refractory material. If it is subjected to mechanical impact or there are foreign objects at the bottom of the tundish seat groove when turning the tundish over, the bottom of the tundish seat groove will be unstable, and the installation angle of the tundish seat will be unstable, resulting in the skewing angle of the water nozzle.

[0009] Furthermore, the diameter of the thin wire should be controlled within 0.5 mm, and the diameter of the steel ball should be controlled between 5 and 10 mm. During measurement, first fix a section of the thin wire at the junction of the sprue and the bottom of the inlet, then place the steel ball as close as possible to the side wall of the sprue, and release the steel ball to reduce its swing amplitude. When the steel ball is relatively stationary, measure the distance between the center of the steel ball and the sprue wall.

[0010] Furthermore, the overall length of the sprue is 110~120cm, the outer diameter is 9~10cm, the inner cavity diameter is 3.5~4cm, and the length from the bottom of the intermediate package to the lower end of the sprue after installation is 60~70cm.

[0011] The installation position of the electromagnetic stirrer in the crystallizer affects the stirring intensity of the molten steel surface. The stirring intensity is greatest at the center of the electromagnetic stirrer; therefore, the closer the center is to the molten steel surface, the greater the stirring intensity.

[0012] Furthermore, the crystallizer is 78-82cm high, the electromagnetic stirrer is 58-60cm high, and the bottom of the electromagnetic stirrer is 1-3cm lower than the bottom of the crystallizer.

[0013] Furthermore, the cross-section of the crystallizer is (290~310)mm×(380~400)mm.

[0014] Furthermore, during normal casting, the submerged nozzle is inserted into the molten steel to a depth of 18-22 cm.

[0015] Furthermore, the crystallizer uses a protective slag, and the total slag layer thickness is controlled at 40~60mm; preferably, the protective slag is a high-carbon steel protective slag, and its composition by mass percentage includes: SiO2: 20~24%, CaO: 28~32%, Al2O3: 3-5%, Na2O: 10~12%, TC: 16~20%, H2O≤0.4%, basicity 1.2~1.6, and the rest are unavoidable impurity components.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] The suspended ball method employed in this invention, based on the distance between the steel ball and the nozzle, helps workshop construction personnel determine the nozzle's deviation and thus correct its installation angle. Compared to visual inspection and vertical measurement methods, it offers advantages such as simple operation and accurate measurement results. This invention simultaneously considers the influence of the nozzle installation angle and the intensity of electromagnetic stirring on slag line deviation, avoiding turbulence in the molten steel flow field and slag line deviation caused by nozzle installation deviation, and preventing excessive electromagnetic stirring intensity from exacerbating flow field turbulence, effectively controlling the nozzle slag line deviation height to ≤5mm. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention.

[0019] In the diagram: 1. Intermediate package; 2. Crystallizer; 3. Immersion nozzle. Detailed Implementation

[0020] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0021] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Example

[0022] Example 1

[0023] (1) Turn the middle package over and clean the foreign objects at the bottom of the seat brick groove to keep the bottom of the seat brick groove flat. Install the seat brick, fit the immersion water inlet, and measure the outlet deflection angle to be 0.8°; spray and bake the middle package to prepare for online use.

[0024] (2) The overall length of the sprue is 115cm, the outer diameter is 9.5cm, the inner diameter is 3.6cm, and the length from the bottom of the tundish to the lower end of the sprue after installation is 65cm. During normal pouring, the immersion sprue 3 is inserted into the molten steel to a depth of 20cm.

[0025] (3) The crystallizer 2 is 80cm high, the electromagnetic stirrer is 58cm high, and the bottom of the electromagnetic stirrer is 2cm lower than the bottom of the crystallizer. The electromagnetic stirring current of the crystallizer is 450A, the frequency is 1.5Hz, and the maximum magnetic induction intensity in the crystallizer is 30mT.

[0026] (4) When the molten steel in the tundish is 35t, the casting is carried out. The steel grade is C82DA, the temperature of the molten steel is 1495℃, the cross section of the continuous casting billet is 300mm×390mm, and the continuous casting speed is 0.66m / min.

[0027] (5) 15 furnaces were cast in the tundish, the slag line deflection height was 1 mm, and the erosion rate in the wall thickness direction of the slag line position was 0.55 mm / h.

[0028] Comparative Example 1

[0029] (1) Turn the middle package over and clean the bottom of the seat brick groove to ensure that the bottom of the seat brick groove is flat. Install the seat brick, fit the immersion water inlet, and measure the outlet deflection angle to be 3.5°. Spray and bake the middle package to prepare it for online use.

[0030] (2) The overall length of the sprue is 115cm, the outer diameter is 9.5cm, the inner diameter is 3.6cm, and the length from the bottom of the tundish to the bottom of the sprue after installation is 65cm. During normal pouring, the immersion sprue 3 is inserted to a depth of 20cm into the molten steel.

[0031] (3) The crystallizer 2 is 80cm high, the electromagnetic stirrer is 58cm high, and the bottom of the electromagnetic stirrer is 2cm lower than the bottom of the crystallizer. The electromagnetic stirring current of the crystallizer is 750A, the frequency is 1.5Hz, and the maximum magnetic induction intensity in the crystallizer is 53mT.

[0032] (4) When the molten steel in the tundish is 35t, the casting is carried out. The steel grade is C82DA, the temperature of the molten steel is 1496℃, the cross section of the continuous casting billet is 300mm×390mm, and the continuous casting speed is 0.66m / min.

[0033] (5) 13 furnaces were cast in the middle ladle. The slag line deflection height was 6 mm, and the erosion rate in the wall thickness direction of the slag line position was 0.7 mm / h.

[0034] A comparison of the two embodiments shows that in Embodiment 1, the technical means employed by the present invention control the nozzle deflection angle to 0.8°, the maximum magnetic induction intensity in the crystallizer to 30mT, and ultimately effectively control the nozzle slag line deflection height to 1mm≤5mm. In contrast, in Embodiment 1, the nozzle deflection angle was 3.5°, the maximum magnetic induction intensity in the crystallizer was 53mT, resulting in a slag line deflection height of 6mm, which failed to be controlled within 5mm.

[0035] The technical means disclosed in this invention are not limited to those disclosed above, but also include technical solutions composed of any combination of the above technical features.

[0036] Based on the above-described preferred embodiments of the present invention, and through the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of the present invention.

Claims

1. A method of controlling the slag line deviation of a bloom submerged entry nozzle, characterized by, Includes the following steps: Step 1. Measure the alignment of the submerged nozzle. Suspend a steel ball using the lower end of a thin line, with the upper end of the line tied at the junction of the nozzle and the bottom of the tundish, keeping the steel ball flush with the lower end of the nozzle. Adjust the nozzle so that the distance between the steel ball and the nozzle wall is ≤20mm. Using the formula: Nozzle deflection angle = arcsin(distance between steel ball and nozzle / length of nozzle at the bottom of tundish) / π * 180°, control the nozzle deflection angle to ≤1.8° to ensure proper nozzle alignment. The diameter of the thin line should be controlled within 0.5mm, and the diameter of the steel ball should be controlled between 5 and 10mm. During measurement, first fix a section of the thin line at the junction of the nozzle and the bottom of the tundish, then bring the steel ball as close as possible to the side wall of the nozzle and release it to reduce the swing amplitude. When the steel ball is relatively stationary, measure the distance between the center of the steel ball and the nozzle wall. During normal pouring, the submerged nozzle should be inserted into the molten steel to a depth of 18-22cm. Step 2. Adjust the intensity of the electromagnetic stirring in the crystallizer, control the electromagnetic stirring current of the crystallizer to 400~500A and the frequency to 1~2Hz, so that the maximum magnetic induction intensity is ≤33mT, and ensure the stability of the molten steel surface. The crystallizer uses protective slag, and the total thickness of the protective slag layer is controlled at 40~60mm. The protective slag is made of high-carbon steel and its composition, by mass percentage, includes: SiO2: 20-24%, CaO: 28-32%, Al2O3: 3-5%, Na2O: 10-12%, TC: 16-20%, H2O ≤ 0.4%, alkalinity 1.2-1.6, and other components are unavoidable impurities.

2. The method of controlling the slag line deviation of a bloom sub-merged entry nozzle according to claim 1, characterized by, Before proceeding to step 1, it is necessary to flip the intermediate package, clean the foreign objects at the bottom of the seat brick groove, keep the bottom of the seat brick groove flat, install the seat brick, fit the immersion nozzle, measure the outlet deflection angle, spray and bake the intermediate package, and then put it into use.

3. The method of controlling the slag line deviation of a bloom sub-merged entry nozzle according to claim 2, characterized by, The brick seat groove is made of refractory material. When turning over the bale, mechanical impact should be reduced. Before laying the bale, foreign objects at the bottom of the brick seat groove should be cleaned and the installation angle of the brick seat should be corrected.

4. The method of controlling the slag line deviation of a bloom submerged entry nozzle according to claim 1, characterized by, In step 1, the overall length of the sprue is 110~120cm, the outer diameter is 9~10cm, the inner diameter is 3.5~4cm, and the length from the bottom of the middle package to the lower end of the sprue after installation is 60~65cm.

5. The method of controlling the slag line deviation of a bloom submerged entry nozzle according to claim 1, characterized by, In step 2, the crystallizer is 78-82cm high, the crystallizer cross-section is (29-31)cm×(38-40)cm, the electromagnetic stirrer is 58-60cm high, and the lower opening of the electromagnetic stirrer is 1-3cm lower than the lower opening of the crystallizer.

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