Small square billet continuous casting arc-shaped crystallizer and optimization method and application of water gap position of small square billet continuous casting arc-shaped crystallizer

Abstract

The invention discloses an optimization technology for a nozzle position of a small square billet continuous casting arc-shaped crystallizer, and belongs to the technical field of metallurgical industry continuous casting. Aiming at the technical problems of non-uniform distribution of a flow field and a temperature field in a crystallizer and high casting blank corner longitudinal crack rate caused by the traditional nozzle centering design, the invention provides a nozzle position and incident angle optimization method through combination of numerical simulation and experimental verification, and the method comprises the following steps: establishing a three-dimensional geometric model based on an actual crystallizer structure; non-uniform grid division and multi-physical field coupling simulation are adopted, and optimized parameters of deviation or deflection of the water gap in the inner arc direction are determined; the position of the water gap is adjusted through a high-precision displacement and angle adjusting device, and field experiment verification is combined, so that the symmetry of inner and outer arc flow fields is improved, the temperature gradient is reduced, the temperature field tends to be uniform, and the longitudinal crack occurrence rate of the corners of the casting blank is reduced to be smaller than or equal to 1.0%. The method is easy and convenient to operate, low in cost and suitable for small square billet continuous casting, the rolling rejection rate is reduced compared with a traditional scheme, and the remarkable industrial application value is achieved.

Description

Technical Field

[0001] The present invention relates to the continuous casting technology in the metallurgical industry, especially an optimized method and application for the submerged entry nozzle (SEN) position of a small billet continuous casting curved mold. The aim is to adjust the position and angle of the SEN to improve the flow field and temperature field distribution of the molten steel in the mold, thereby effectively reducing the incidence of longitudinal cracks at the corners of the billet and improving the quality of the billet. Background Art

[0002] During the continuous casting process, the flow and temperature distribution of the molten steel in the mold have an important impact on the quality of the billet. Traditional SEN designs usually place the SEN at the center of the mold. However, due to the curved design of the mold, the SEN at the center position will cause an asymmetric flow field between the inner and outer arcs, which in turn leads to uneven temperature distribution. This is one of the main reasons for the generation of cracks on the surface of the billet. In the prior art, although there are some studies on the adjustment of the SEN position, there is a lack of a systematic optimization scheme. In particular, the optimization technology for the SEN position of a small billet continuous casting curved mold has not been fully developed. Summary of the Invention

[0003] The purpose of the present invention is to provide an optimized technology for the SEN position of a small billet continuous casting curved mold, and a simulation method is provided to systematically optimize the flow and temperature distribution of the molten steel in the mold. By adjusting the position and angle of the SEN, combined with on-site experiments, it is demonstrated that the present invention can improve the flow field and temperature field distribution of the molten steel in the mold, thereby effectively reducing the incidence of longitudinal cracks at the corners of the billet.

[0004] The technical solution of the present invention is as follows:

[0005] An optimized method for the SEN position of a small billet continuous casting curved mold, characterized by including the following steps:

[0006] S1. Based on the arc structure parameters of the actual small billet continuous casting mold, a three-dimensional geometric model including the SEN, copper mold, cooling water channel, and molten steel flow region is established;

[0007] S2. Perform non-uniform mesh division on the geometric model. Among them, the mesh size of the SEN area is an unstructured tetrahedral mesh of 1-2 mm, and other areas use a structured hexahedral mesh with a mesh size of 3-5 mm. At least three layers of boundary layer meshes are set on the inner wall of the SEN and the surface of the copper mold;

[0008] S3. Based on the ANSYS CFX software, perform coupled simulation of the flow field and temperature field. The simulation includes:

[0009] - Simulate the molten steel flow and the slag-metal interface fluctuation based on the Navier-Stokes equation, standard κ-ε turbulence model, and VOF interface tracking method;

[0010] - Calculate the temperature field distribution using the coupled heat conduction, convection and radiation heat transfer model;

[0011] S4. Adjust the nozzle position and / or the incident angle according to the simulation results, specifically:

[0012] - Horizontally offset the nozzle 3 - 7 mm along the inner arc direction, with an offset error ≤ 0.1 mm;

[0013] - Or deflect the incident angle 0.3° - 1.5° towards the inner arc direction, with an angle error ≤ 0.1°.

[0014] Furthermore, it further includes the following steps:

[0015] S5. Verify the optimization effect through on-site casting experiments. The experiments include a control group (nozzle centered) and an experimental group (nozzle offset or deflected), and determine the optimal parameters through the rolling scrap rate and thermal imaging data.

[0016] Furthermore, in step (4), the nozzle offset is realized by a high-precision displacement device driven by a servo motor. The adjustment range of the displacement device is ±10 mm, and the resolution ≤ 0.05 mm; the nozzle angle adjustment is realized by a gimbal mechanism with inclination feedback, and the resolution ≤ 0.02°.

[0017] On the other hand, the present invention also provides a small billet continuous casting arc mold, which is characterized in that the nozzle position and / or the incident angle are adjusted by the above optimization method, so that the flow velocity difference between the inner and outer arcs ≤ 10%, the temperature gradient difference ≤ 15%, and the incidence rate of longitudinal cracks at the corner ≤ 1.0%.

[0018] Furthermore, the nozzle fixing device includes:

[0019] - A displacement module with an adjustment range of ±10 mm and an accuracy of ±0.1 mm;

[0020] - An angle adjustment module with an adjustment range of ±2.0° and an accuracy of ±0.05°;

[0021] - A real-time calibration module integrated with a laser locator and an inclination sensor.

[0022] Thirdly, the present invention also provides a continuous casting production line, which is characterized in that it includes the above-mentioned arc mold, and at least one of the following devices:

[0023] - A molten steel flow closed-loop control system with an adjustment accuracy of ±0.1 m 3 / h;

[0024] - A cooling water temperature constant control system with a fluctuation range ≤ ±2°C;

[0025] - A data acquisition and analysis module that real-time feeds back the simulation results of the flow field and the temperature field.

[0026] The production line is applicable to the continuous casting of small square billets with cross-sectional dimensions of 120mm×120mm to 200mm×200mm, and the rolling rejection rate is reduced by 30% to 60% compared with the traditional middle nozzle scheme.

[0027] Compared with the prior art, the technical effects of the present invention are as follows:

[0028] 1) In the traditional nozzle design, the uneven temperature distribution caused by the asymmetric flow field in the arc-shaped mold leads to longitudinal cracks at the corners of the billet. By optimizing the parameters of offsetting the nozzle 5mm inward or deflecting it by 0.5° to 1.0° in the inner arc, the present invention combines numerical simulation (ANSYSCFX) with on-site experiments to solve the problems of flow field and temperature field distribution.

[0029] 2) Experiments show that the incidence of longitudinal cracks at the corners of the billet after optimization is significantly reduced. For example, the rejection rate of the 55SiCrA steel grade is reduced from 1.63% to 0.96%, and that of the ML40Cr steel grade is reduced from 0.69% to 0.57% (offset 5mm inward in the inner arc). Description of the Drawings

[0030] Figure 1 It is a schematic diagram of a small square billet continuous casting mold, where (a) is a geometric model diagram and (b) is a general grid division diagram;

[0031] Figure 2 It is a split diagram of the mold geometric model;

[0032] Figure 3 It is a boundary condition diagram of the mold model simulation;

[0033] Figure 4 It is a schematic diagram of the inner and outer arc orientations of the mold;

[0034] Figure 5 It is a flow field distribution diagram of the mid-plane after adjusting the nozzle position and angle;

[0035] Figure 6 It is a temperature field distribution diagram of the mid-plane after adjusting the nozzle position and angle;

[0036] Figure 7 It is a result comparison diagram of on-site experiments in a certain steel plant. Detailed Embodiments

[0037] The following details the specific embodiments of the present invention in conjunction with the drawings and embodiments to ensure that those skilled in the art can implement this technical solution based on this description, but this should not limit the protection scope of the present invention.

[0038] An optimization method for the nozzle position of an arc-shaped mold for small square billet continuous casting includes the following steps:

[0039] 1. Optimization of nozzle position: Through numerical simulation and experimental verification, the optimization scheme of the nozzle shifting 5mm to the inner arc or deflecting 0.5° to 1.0° to the inner arc is determined. This scheme can significantly improve the symmetry of the inner and outer arc flow fields and reduce the unevenness of temperature distribution.

[0040] 2. Flow field and temperature field simulation: ANSYS CFX software is used to establish a three-dimensional mathematical model to simulate the flow of molten steel, cooling water flow and slag interface fluctuations in the crystallizer. Through steady-state and unsteady-state calculations, the effects of different nozzle positions and incident angles on the flow field and temperature field are analyzed.

[0041] 3. Field experiment verification: The nozzle position adjustment experiment was carried out on site, and the pouring was carried out using the normal centering, 5mm inward and 5mm outward schemes, and the optimization effect was evaluated by the rolling scrap rate. The field experiment results showed that the 5mm inward scheme could significantly reduce the incidence of longitudinal cracks in the corners of the ingot.

[0042] The temperature field and flow field model simulation is based on the finite element method (FEM) and computational fluid dynamics (CFD). A mathematical model is established to describe the flow of molten steel, cooling water flow and slag interface fluctuations in the crystallizer, and the temperature field distribution is analyzed in combination with the heat transfer model.

[0043] Embodiment 1:

[0044] 1. Model construction:

[0045] According to the actual size of the billet continuous casting mold (such as Figure 1 As shown in the figure, use 3D modeling software to build the geometric model of the billet crystallizer, including key components such as nozzle, copper mold, cooling water channel, and molten steel flow area. The model must accurately reflect the arc structure characteristics of the crystallizer, and the curvature radius of the inner and outer arcs must be consistent with the actual production line parameters.

[0046] ANSYS Meshing or ICEM CFD software is used for meshing. Unstructured tetrahedral meshes are used for complex areas (such as near the nozzle and the slag interface), and structured hexahedral meshes are used for simple areas (such as cooling water channels). This ensures calculation accuracy.

[0047] 2. Flow field and temperature field calculation: The model calculation was performed on the laboratory's self-built server, using 40 cores for parallel computing. The steady-state task calculation time was 2 hours, and the unsteady-state task calculation time was 26 hours. Through the coupled calculation of the flow field and temperature field, the thermal stress on the surface of the ingot and the static pressure distribution of the molten steel were obtained.

[0048] 3. On-site experiment: Conduct an on-site experiment on adjusting the nozzle position. Pouring is carried out using the schemes of normal centering, 5 mm inward deviation, and 5 mm outward deviation respectively. The optimization effect is evaluated through the rolling scrap rate. The experimental and on-site results consistently show that the scheme of 5 mm inward deviation can significantly reduce the incidence of longitudinal cracks at the corners of the billet.

[0049] Example 1: On the small billet continuous casting production line of Xiangtan Steel Plant in China, experiments are carried out using three experimental schemes of normal centering, 5 mm inward deviation, and 5 mm outward deviation. Judging from the scrap rate, the obtained results are as follows: The scrap rate of the 55SiCrA steel grade drops from 1.63% under normal centering to 0.96% with 5 mm inward deviation; the scrap rate of the ML40Cr steel grade drops from 0.69% under normal centering to 0.57% with 5 mm inward deviation, and rises to 1.52% with 5 mm outward deviation, and the flow field and temperature field distributions are more uniform.

[0050] Example 2: On the same production line, deflect the nozzle 0.5° towards the inner arc for an on-site experiment. The experimental results show that the incidence of longitudinal cracks at the corners of the billet is further reduced, and the flow field and temperature field distributions are more symmetrical.

[0051] By optimizing the nozzle position and incident angle of the arc-shaped mold for small billet continuous casting, the present invention significantly improves the uniformity of the flow field and temperature field, and effectively reduces the incidence of longitudinal cracks at the corners of the billet. This technology is simple to operate and has remarkable effects, aiming to reduce industrial costs and improve process efficiency. It is applicable to various small billet continuous casting production lines and has important industrial application value and application prospects.

Claims

1. An optimization method for the position of the submerged entry nozzle in the arc-type mold of small billet continuous casting, characterized in that, It includes the following steps: S1. Based on the arc structure parameters of the actual billet continuous casting mold, establish a three-dimensional geometric model including the nozzle, copper mold, cooling water channel and molten steel flow region; S2. Conduct non-uniform mesh division on the geometric model. Among them, the mesh size in the nozzle area is an unstructured tetrahedral mesh of 1-2 mm, and the other areas adopt a structured hexahedral mesh with a mesh size of 3-5 mm, and at least three layers of boundary layer meshes are set on the inner wall of the nozzle and the surface of the copper mold; S3. Conduct coupled simulation of the flow field and temperature field based on the ANSYS CFX software. The simulation includes: - Simulate the molten steel flow and the interface fluctuation of the molten steel and slag based on the Navier-Stokes equation, the standard κ-ε turbulence model and the VOF interface tracking method; - Couple the heat conduction, convection and radiation heat transfer models to calculate the temperature field distribution; S4. Adjust the position and / or incident angle of the nozzle according to the simulation results. Specifically: - Horizontally offset the nozzle 3-7 mm along the inner arc direction, and the offset error ≤ 0.1 mm; - Or deflect the incident angle 0.3°-1.5° towards the inner arc direction, and the angle error ≤ 0.1°.

2. The optimization method for the submerged nozzle position of the small billet continuous casting curved mold according to claim 1, characterized in that It also includes the following steps: S5. Verify the optimization effect through on-site casting experiments. The experiments include a control group (the nozzle is centered) and an experimental group (the nozzle is offset or deflected), and determine the optimal parameters through the rolling rejection rate and thermal imaging data.

3. The optimization method according to claim 1, characterized in that, In the step (4), the nozzle offset is realized by a high-precision displacement device driven by a servo motor. The adjustment range of the displacement device is ±10 mm, and the resolution ≤ 0.05 mm; the nozzle angle adjustment is realized by a universal joint mechanism with inclination feedback, and the resolution ≤ 0.02°.

4. A small billet continuous casting arc mold, characterized in that, Adopt the optimization method described in any one of claims 1-3 to adjust the position and / or incident angle of the nozzle, so that the flow velocity difference between the inner and outer arcs ≤ 10%, the temperature gradient difference ≤ 15%, and the incidence rate of longitudinal cracks at the corners ≤ 1.0%.

5. The arc-shaped mold according to claim 4, wherein The nozzle fixing device includes: - A displacement module with an adjustment range of ±10 mm and an accuracy of ±0.1 mm; - An angle adjustment module with an adjustment range of ±2.0° and an accuracy of ±0.05°; - A real-time calibration module integrating a laser locator and an inclination sensor.

6. A continuous casting production line, characterized in that, It includes the arc-shaped mold described in claim 5 or 6, and at least one of the following devices: - Closed-loop control system for molten steel flow rate, with an adjustment accuracy of ±0.1 m 3 / h; - A cooling water temperature constant control system with a fluctuation range ≤ ±2°C; - A data acquisition and analysis module that real-time feedbacks the simulation results of the flow field and temperature field.

7. The continuous casting production line according to claim 7, characterized in that, The production line is applicable to the continuous casting of small square billets with a cross-sectional size of 120 mm × 120 mm to 200 mm × 200 mm, and the rolling rejection rate is reduced by 30%-60% compared with the traditional centered nozzle scheme.

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