A method for evaluating a submerged nozzle of a high-pull speed slab continuous casting mold

Abstract

The application provides a high-pulling-speed slab continuous casting mold submerged nozzle evaluation method and relates to the technical field of steelmaking-continuous casting. The application carries out reasonable analysis on the design parameters of the outlet shape, outlet hole number, outlet angle and bottom shape of the continuous casting mold submerged nozzle, and proposes the continuous casting mold submerged nozzle evaluation method in combination with corresponding liquid surface fluctuation evaluation indexes. The application matches the nozzle and the pulling speed, considers the matching relationship between the nozzle structure and the casting blank section, is suitable for multi-steel-grade multi-section continuous casting blanks, and the result is more intuitive and accurate. The application can predict and analyze the adaptability of various continuous casting blank nozzles, casting blank sections and continuous casting processes, improves the production efficiency and increases the economic benefits.

Description

Technical Field

[0001] This invention relates to the field of steelmaking-continuous casting technology, and in particular to an evaluation method for submerged entry nozzles in high-speed slab continuous casting crystallizers. Background Technology

[0002] The increasing efficiency of next-generation continuous casting places higher demands on the stability of the continuous casting process, especially the control of molten steel flow and surface stability within the continuous casting mold under high casting speeds. The submerged entry nozzle, as the molten steel guiding device connecting the tundish and the mold, has a significant impact on the molten steel flow behavior within the mold. Furthermore, due to its advantages such as simple structural design, low production cost, and strong adaptability, the optimization design of the submerged entry nozzle has always been a research focus. However, currently, the submerged entry nozzles used in molds at steel plants both domestically and internationally are provided by the equipment manufacturers. Steel plants must study the characteristics of the specified nozzle and match it by changing continuous casting process parameters. This iterative industrial testing and debugging is extremely costly and seriously affects the economic benefits of enterprises. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides an evaluation method for submerged entry nozzles in high-speed slab continuous casting molds. The method rationally analyzes the design parameters of the submerged entry nozzle, such as its outlet shape, number of outlet holes, outlet angle, and bottom shape, and combines these with relevant liquid level fluctuation evaluation indicators to propose an evaluation method for submerged entry nozzles in continuous casting molds.

[0004] A method for evaluating the submersible nozzle in a high-speed slab continuous casting crystallizer includes the following steps:

[0005] Step 1: Obtain eight variable parameters that directly affect the molten steel flow field inside the crystallizer, specifically including the immersion depth L and groove depth L of the molten steel flow field and nozzle morphology inside the crystallizer. a Side hole area S a Side hole angle θ, impact point location D, flow velocity V at 1 / 4 of the meniscus e 1. Dimension of the wide side of the cast billet L d and the inner diameter d of the water inlet;

[0006] Furthermore, the immersion depth L of the sprue is the length from the upper edge of the sprue to the meniscus of the crystallizer.

[0007] Furthermore, the groove depth L a The length of the turbulent kinetic energy suppressor below the water inlet.

[0008] Furthermore, the area S of the side hole a This represents the maximum cross-sectional area of ​​the molten steel flowing out of the side hole of the nozzle.

[0009] Furthermore, the side hole angle θ is the angle between the angle of the molten steel flowing out of the side hole of the nozzle and the horizontal line of the crystallizer.

[0010] Furthermore, the impact point position D is the distance from the impact point of the molten steel flowing out of the nozzle to the meniscus of the crystallizer when the molten steel moves to the narrow face of the crystallizer.

[0011] Step 2: Combining the variable parameters from Step 1, and based on the actual cross-sectional dimensions of the casting machine's crystallizer and the cooling water supply method, establish a numerical simulation model of the steel-slag interface in the crystallizer.

[0012] The process of establishing the numerical simulation model of the slag interface of the crystallizer is as follows: based on the CAD drawings, a model fluid domain model is established using simulation modeling software; the fluid domain model is refined using a mesh generator; the established continuous casting crystallizer fluid domain model is imported into finite element analysis software, and boundary conditions and operating conditions are applied; calculation and visualization processing are performed.

[0013] Step 3: Analyze the numerical simulation model of the steel slag interface in the crystallizer, observe and record the eight variable parameters in Step 1, perform nonlinear fitting analysis on the eight variables, establish the sprue evaluation index formula by regressing each parameter index, and determine the reasonable range of the sprue evaluation index S index. It is determined that when the S index is between 5 and 8, the steel liquid flow field in the crystallizer is most reasonable, thus realizing the evaluation of the immersion sprue in the crystallizer.

[0014] The formula for the water outlet evaluation index is as follows:

[0015]

[0016] In the formula, S is the sprue evaluation index; ρ is the density of molten steel, kg / m³. 3 S a The area of ​​the side orifice of the water inlet is m. 2 θ is the angle of the side orifice of the sprue; D is the distance from the impact point to the meniscus, in meters; V e The velocity at 1 / 4 of the meniscus is m / s; L is the immersion depth of the nozzle, m; L a L is the length of the concave bottom of the sprue, in meters. d d is the width dimension of the billet, in meters; d is the inner diameter of the sprue, in meters.

[0017] The beneficial effects of adopting the above technical solution are as follows:

[0018] This invention provides a method for evaluating the submerged entry nozzle of a high-speed slab continuous casting crystallizer. Traditional methods evaluate crystallizer nozzles by detecting fluctuations in the molten steel level during each heat in continuous casting. Severe fluctuations can lead to slag entrapment and steel leakage, resulting in slab quality loss and severely impacting steel plant production. The submerged entry nozzle evaluation method of this invention uses simulation technology to visualize the molten steel inside the crystallizer. The simulation results are accurately matched to the slab. By monitoring the nozzle and the outflowing molten steel, a nozzle evaluation index (S-index) is fitted, reducing finished product quality losses caused by industrial trials. This method is applicable to multi-steel grade and multi-section continuous casting slabs, and can predict and analyze the adaptability of various continuous casting nozzles, slab cross-sections, and continuous casting processes, providing more intuitive and accurate results. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the water inlet evaluation parameters in an embodiment of the present invention;

[0020] Figure 2 The side hole area S in this embodiment of the invention a The effect on the flow field inside the crystallizer;

[0021] Figure 3 This illustrates the effect of the side hole angle θ on the flow field inside the crystallizer in an embodiment of the present invention.

[0022] Figure 4 The groove depth L in this embodiment of the invention a The effect on the flow field inside the crystallizer;

[0023] Figure 5 This illustrates the effect of the billet cross-sectional dimensions on the flow field inside the crystallizer in this embodiment of the invention.

[0024] Figure 6 In this embodiment of the invention, the fluctuation range of the liquid level at the crystallizer nozzle in a steel plant where the S number was not within the range of 5 to 8 is described.

[0025] Figure 7 In this embodiment of the invention, the S number is used to represent the fluctuation range of the liquid level at the crystallizer nozzle within the range of 5 to 8. Detailed Implementation

[0026] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0027] A method for evaluating the submersible nozzle in a high-speed slab continuous casting crystallizer includes the following steps:

[0028] Step 1: Obtain eight variable parameters that directly affect the molten steel flow field within the crystallizer, such as... Figure 1As shown, this specifically includes the immersion depth L and groove depth L of the molten steel flow field and nozzle morphology within the crystallizer. a Side hole area S a Side hole angle θ, impact point location D, flow velocity V at 1 / 4 of the meniscus e 1. Dimension of the wide side of the cast billet L d and the inner diameter d of the water inlet;

[0029] Furthermore, the immersion depth L of the sprue is the length from the upper edge of the sprue to the meniscus of the crystallizer.

[0030] Furthermore, the groove depth L a The length of the turbulent kinetic energy suppressor below the water inlet.

[0031] Furthermore, the area S of the side hole a This represents the maximum cross-sectional area of ​​the molten steel flowing out of the side hole of the nozzle.

[0032] Furthermore, the side hole angle θ is the angle between the angle of the molten steel flowing out of the side hole of the nozzle and the horizontal line of the crystallizer.

[0033] Furthermore, the impact point position D is the distance from the impact point of the molten steel flowing out of the nozzle to the meniscus of the crystallizer when the molten steel moves to the narrow face of the crystallizer.

[0034] Step 2: Combining the variable parameters from Step 1, and based on the actual cross-sectional dimensions of the casting machine's crystallizer and the cooling water supply method, establish a numerical simulation model of the steel-slag interface in the crystallizer.

[0035] The process of establishing the numerical simulation model of the slag interface of the crystallizer is as follows: Based on the CAD drawings, the fluid domain model is established using the simulation modeling software SolidWorks; the fluid domain model is refined using the mesh generator; the established fluid domain model of the continuous casting crystallizer is imported into the finite element analysis software ANSYS, and boundary conditions and working conditions are applied; calculation and visualization are performed.

[0036] Step 3: Analyze the numerical simulation model of the steel slag interface in the crystallizer, observe and record the eight variable parameters in Step 1, perform nonlinear fitting analysis on the eight variables, establish the sprue evaluation index formula by regressing each parameter index, and determine the reasonable range of the sprue evaluation index S index. It is determined that when the S index is between 5 and 8, the steel liquid flow field in the crystallizer is most reasonable, thus realizing the evaluation of the immersion sprue in the crystallizer.

[0037] The area of ​​the nozzle side orifice primarily affects the outlet velocity. When the nozzle side orifice area is too small, the molten steel outlet velocity is high, easily causing violent fluctuations at the steel-slag interface and resulting in slag entrapment. When the nozzle side orifice area is too large, the upper reflux zone area of ​​the molten steel is small, the steel-slag interface activity is insufficient, and slag formation is difficult. The nozzle side orifice outlet angle mainly affects the ratio of the upper and lower reflux zones within the crystallizer. If the outlet angle is too small, the upper reflux zone area is small, the distance for the molten steel to reach the meniscus is shorter, the flow velocity increases, and it will cause violent fluctuations at the steel-slag interface. If the outlet angle is too large, the molten steel impacts the primary billet shell more concentratedly, easily causing uneven growth of the primary billet shell, and in severe cases, causing steel leakage. Under the same casting speed, when the nozzle inner diameter is small, the area of ​​the high-velocity region of the instantaneous molten steel outlet is larger, while when the nozzle inner diameter is larger, the high-velocity region is weakened. Only when the casting speed and nozzle inner diameter are matched can the molten steel flow field distribution within the crystallizer be more reasonable.

[0038] The formula for the water outlet evaluation index is as follows:

[0039]

[0040] In the formula, S is the sprue evaluation index; ρ is the density of molten steel, kg / m³. 3 S a The area of ​​the side orifice of the water inlet is m. 2 θ is the angle of the side orifice of the sprue; D is the distance from the impact point to the meniscus, in meters; V e The velocity at 1 / 4 of the meniscus is m / s; L is the immersion depth of the nozzle, m; L a L is the length of the concave bottom of the sprue, in meters. d d is the width dimension of the billet, in meters; d is the inner diameter of the sprue, in meters.

[0041] Based on the range of the S-index proposed in step 3, the fluctuation range of the liquid level at the crystallizer nozzle was detected when the S-index was not within the range of 5 to 8 and when the S-index was within the range of 5 to 8; this verified the accuracy of the formula in step 3.

[0042] Figure 2 The figure shows the area S of different water inlet side holes. a Flow field cloud diagram inside the lower crystallizer. Comparing Figures (a) and (b), it can be seen that under a constant casting speed, when the side orifice area of ​​the nozzle is 42mm × 30mm, the flow rate of molten steel through the side orifice per unit time increases, resulting in a higher velocity of the molten steel flowing out of the nozzle. However, when the side orifice area increases to 42mm × 40mm, the outflow velocity from the nozzle decreases from 1.5m / s to 0.8m / s. The molten steel velocity here simultaneously affects both the upper and lower reflux zones of the crystallizer. When the molten steel velocity here is controlled within a reasonable range, it will help stabilize the meniscus slag formation and the steel-slag interface, and also allow for more uniform and stable growth of the initial billet shell in the crystallizer.

[0043] Figure 3 The figure shows the effect of different nozzle side outlet angles θ on the flow field inside the mold. As can be seen from the figure, with the continuous increase of the nozzle side outlet angle, the distance from the impact point of the molten steel reaching the narrow face of the mold to the meniscus continuously increases. The nozzle side outlet angle directly affects the area ratio of the upper and lower recirculation zones inside the mold.

[0044] Figure 4 For different groove depths L a The influence of the flow field inside the lower crystallizer. As the groove depth increases, the turbulent kinetic energy inside the crystallizer decreases significantly, indicating that the groove depth has an inhibitory effect on turbulent kinetic energy. However, a larger groove depth is not always better. An excessively long depth will hinder the activity of the steel-slag interface and affect the melting of the protective slag. This is one of the reasons why the nozzle is replaced periodically.

[0045] Figure 5 The diagram illustrates the influence of different billet cross-sectional dimensions on the flow field within the mold. ① At location ①, as the billet cross-sectional size increases, the flow path of the molten steel exiting the nozzle in the upper recirculation zone increases, resulting in a higher turbulent kinetic energy dissipation rate, which contributes to the stability of the steel-slag interface. ② At location ②, as the billet cross-sectional size increases, the distance from the nozzle exiting the nozzle to the narrow face of the mold continuously decreases, causing the high-temperature region within the mold to shift downwards. Simultaneously, the velocity of the molten steel reaching the narrow face of the mold decreases from 1.8 m / s to 0.6 m / s, significantly reducing the scouring effect on the primary billet shell. ③ At location ③, as the billet cross-sectional size continuously increases, the lower recirculation vortex center continuously shifts downwards.

[0046] This embodiment compares the liquid level fluctuations of the water inlet provided by the actual manufacturer on site with those of the water inlet designed after applying the S-number calculation formula of this invention. Figure 6 The following data describes the actual fluctuation range of the slurry level at the casting speeds of 1.4 m / min, 1.7 m / min, 1.9 m / min, and 2.2 m / min, provided by the manufacturer. Excessive fluctuation in the slurry level in the crystallizer directly affects the inflow of the protective slag into the billet-copper plate channel, impacting the normal lubrication and heat transfer control functions of the protective slag, increasing the incidence of adhesion and longitudinal cracks, and causing deep and disordered vibration marks. This makes the billet prone to subcutaneous inclusions and longitudinal cracks, posing a significant threat to production safety and billet quality. To produce high-quality billets, the slurry level fluctuation must be controlled within a reasonable range. Generally, the slurry level fluctuation range in the crystallizer should be controlled within ±5 mm, and for steel grades with strict quality requirements, it may even be required to be controlled within ±3 mm. Figure 6 As can be seen, when using the water inlet provided by the manufacturer, the fluctuation range of the liquid level is all beyond ±5mm, which is obviously difficult to meet the liquid level control standard. Figure 7The surface fluctuation amplitude of the sprue was designed using the S-number calculation formula of this invention at sprue speeds of 1.4 m / min, 1.7 m / min, 1.9 m / min, and 2.2 m / min. After the improvement, the surface fluctuation amplitude can be basically controlled within ±3 mm at sprue speeds of 1.4 m / min to 2.2 m / min. When the sprue speed continues to increase to 2.4 m / min, the surface fluctuation amplitude can still be basically controlled within ±3 mm. Using sprues with an S-number outside the range of 5 to 8, the surface fluctuation amplitude is always beyond ±5 mm under high sprue speed conditions, clearly making it difficult to meet the surface control standard. When the S-number is within the range of 5 to 8, the surface fluctuation amplitude can also be basically controlled within ±3 mm when the sprue speed continues to increase to 2.4 m / min. This verifies the effectiveness of the S-number range.

[0047] The above description is merely a preferred embodiment of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in the embodiments of this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in the embodiments of this disclosure.

Claims

1. A method for evaluating the submersible nozzle of a high-speed slab continuous casting crystallizer, characterized in that, Includes the following steps: Step 1: Obtain the variable parameters that directly affect the flow field of molten steel in the crystallizer; The specific variable parameters include the immersion depth L of the nozzle and the groove depth L of the molten steel flow field and nozzle morphology within the crystallizer. a Side hole area S a Side hole angle θ, impact point location D, flow velocity V at 1 / 4 of the meniscus e 1. Dimension of the wide side of the cast billet L d and the inner diameter d of the water inlet; The immersion depth L of the sprue is the length from the upper edge of the sprue to the meniscus of the crystallizer; the groove depth L a The length of the turbulent kinetic energy suppressor below the water inlet; the area of ​​the side hole S a The maximum cross-sectional area of ​​the molten steel flowing out of the side hole of the nozzle; the side hole angle θ is the angle between the angle of the molten steel flowing out of the side hole of the nozzle and the horizontal line of the crystallizer; the impact point position D is the length of the impact point from the meniscus of the crystallizer when the molten steel flowing out of the nozzle moves to the narrow face of the crystallizer. Step 2: Combining the variable parameters from Step 1, and based on the actual cross-sectional dimensions of the casting machine's crystallizer and the cooling water supply method, establish a numerical simulation model of the steel-slag interface in the crystallizer. Step 3: Analyze the numerical simulation model of the steel slag interface in the crystallizer, observe and record the variable parameters in Step 1, and perform nonlinear fitting analysis on the variable parameters to achieve evaluation of the submerged nozzle of the crystallizer. The nonlinear fitting analysis involves establishing a formula for the water outlet evaluation index and determining the rational range of the water outlet evaluation index S-index by regressing various parameter indicators. The rationalization range is 5 to 8; The formula for the water outlet evaluation index is as follows: ； In the formula, S is the sprue evaluation index, ρ is the density of molten steel, and S a Let V be the area of ​​the side hole, θ be the angle of the side hole, D be the location of the impact point, and V be the area of ​​the side hole. e The velocity at 1 / 4 of the meniscus is L, and the immersion depth of the nozzle is L. a L represents the groove depth. d d represents the width dimension of the billet, and d represents the inner diameter of the sprue.

2. The method for evaluating the submersible nozzle of a high-speed slab continuous casting crystallizer according to claim 1, characterized in that, The process of establishing the numerical simulation model of the slag interface in the crystallizer described in step 2 is as follows: Based on the CAD drawings, a fluid domain model is established using simulation modeling software; the fluid domain model is refined using a mesh generator to establish a continuous casting crystallizer fluid domain model; the continuous casting crystallizer fluid domain model is imported into finite element analysis software, and boundary conditions and operating conditions are applied to form a numerical simulation model of the slag interface in the crystallizer.

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