Slag entrapment evaluation method for continuous casting crystallizer

Abstract

The invention relates to the technical field of clean steel smelting, in particular to a continuous casting crystallizer slag entrapment evaluation method which comprises the following steps: constructing a crystallizer three-dimensional model, taking a pipeline section at a crystallizer nozzle outlet, and calculating the molten steel flow at the nozzle side outlet; selecting an impact area formed after the fluid impacts the narrow surface of the crystallizer, and calculating the coordinates of an impact point; calculating the included angle between the jet flow of the nozzle side outlet and the horizontal plane according to the impact point coordinates, and obtaining the molten steel flow of the impact slag-metal interface according to the molten steel flow of the nozzle side outlet; the molten steel impact force is calculated according to the molten steel flow of the impact slag-metal interface; and the ratio of the impact force of the molten steel to the tension of the half slag-metal interface serves as a slag entrapment evaluation index and is used for judging whether slag entrapment occurs or not. According to the method, the slag entrapment phenomenon is judged through objective quantitative indexes, the stability of the casting quality can be effectively improved by accurately evaluating the slag entrapment risk, and the production cost of cast steel is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of clean steel smelting, and in particular to a method for evaluating slag entrainment in a continuous casting mold. Background Art

[0002] With the rapid development of social economy, the demand for high-quality steel is increasing. At present, most steel products are produced by continuous casting, and the level of continuous casting technology is directly related to the quality and output of steel products.

[0003] In the modern iron and steel continuous casting production process, as the core equipment, the operating state of the mold directly affects the quality of the cast slab. The phenomenon of slag entrainment in the mold is one of the key factors affecting the quality of the cast slab. The turning of the molten steel surface in the mold and the entrainment of slag will deteriorate the surface quality of the continuous casting slab, bring inclusion defects to the cast slab, and even lead to the occurrence of breakout accidents, seriously affecting the smooth progress of casting.

[0004] The existing methods for evaluating slag entrainment obtain a video data set of slag entrainment and use a deep learning model to evaluate the slag entrainment phenomenon. This method requires collecting and annotating a large amount of data for model training, has high computational resource requirements for the model, high training costs, poor interpretability, and is difficult to apply to actual production.

[0005] Therefore, how to find an objective and easily obtainable parameter based on the key physical quantities in the slag entrainment process as an index for evaluating slag entrainment to guide the determination of the quality of the cast slab is the focus of attention in the metallurgical industry at present. Summary of the Invention

[0006] For this reason, the technical problem to be solved by the present invention is to overcome the problem in the prior art that the lack of an objective and easily obtainable index for evaluating slag entrainment makes it difficult to improve the quality of the cast slab in continuous casting of steel.

[0007] To solve the above technical problem, the present invention provides a method for evaluating slag entrainment in a continuous casting mold, including: Constructing a three-dimensional model of the mold, taking a pipe cross-section at the outlet of the mold nozzle, where the pipe cross-section is within the nozzle outlet pipe wall and includes all the fluid flowing out of the nozzle, and calculating the molten steel flow rate at the outlet on the nozzle side according to the pipe cross-section with a pipe flow model; Selecting the impact zone formed after the fluid impacts the narrow face of the mold, and taking the average value of the vertical coordinates of each fluid particle in the impact zone as the coordinate of the impact point; Calculating the angle between the jet flow at the outlet on the nozzle side and the horizontal plane according to the coordinate of the impact point, and then obtaining the molten steel flow rate impacting the slag-metal interface according to the molten steel flow rate at the outlet on the nozzle side; Calculating the molten steel impact force according to the molten steel flow rate impacting the slag-metal interface; The ratio of the impact force of molten steel to half of the interfacial tension between slag and metal is used as the slag entrainment evaluation index; when the value of the slag entrainment evaluation index is greater than or equal to 1, slag entrainment occurs; when the value of the slag entrainment evaluation index is less than 1, slag entrainment does not occur; and the greater the value of the slag entrainment evaluation index, the more times of slag entrainment occur.

[0008] Preferably, a three-dimensional model of the mold is constructed, including: Using Solidworks to draw a three-dimensional model of the mold; Using the large eddy simulation model in FLUENT software to simulate the fluid motion in the mold; Using the DMP model to track the movement of bubbles, so that the tracking stops after the bubbles enter the free liquid surface of the fluid, and the bubbles are removed to simulate the condition of blowing gas; Using the VOF model to calculate the fluctuation of the slag-metal interface.

[0009] Preferably, the conditions for selecting the pipe cross-section include: the angle between the velocity direction of more than 90% of the fluid passing through the pipe cross-section and the pipe cross-section is 40°-90°.

[0010] Preferably, under the condition of no gas blowing, the molten steel flow rate at the nozzle side outlet is calculated according to the pipe cross-section by the pipe flow model, and the formula is: , where A is the area of the pipe cross-section, v is the velocity component of the fluid perpendicular to the pipe cross-section and in the same direction as the molten steel outflow direction, is the molten steel flow rate at the nozzle side outlet under the condition of no gas blowing.

[0011] Preferably, under the condition of no gas blowing, according to the molten steel flow rate at the nozzle side outlet, the molten steel flow rate impacting the slag-metal interface is obtained, and the formula is: ; Among them, is the molten steel flow rate impacting the slag-metal interface, is the angle between the jet at the nozzle side outlet and the horizontal plane, is the molten steel flow rate at the nozzle side outlet under the condition of no gas blowing.

[0012] Preferably, under the condition of gas blowing, the molten steel flow rate at the nozzle side outlet is calculated according to the pipe cross-section by the pipe flow model, including: Calculating the molten steel flow rate at the nozzle side outlet under the condition of gas blowing according to the pipe cross-section by the pipe flow model ; Calculating the flow rate of the part of the molten steel that floats up due to bubbles through the pipe cross-section and directly impacts the slag-metal interface ; Then the molten steel flow rate that can impact the narrow face to form an upward backflow at the nozzle side outlet under the condition of gas blowing is .

[0013] Preferably, under the condition of blowing gas, the molten steel flow rate impacting the slag-metal interface is obtained based on the molten steel flow rate at the outlet on the tundish nozzle side, including: Based on the molten steel flow rate that can impact the narrow face to form an upward backflow at the outlet on the tundish nozzle side under the condition of blowing gas Calculate the upward backflow rate: ; Wherein, is the upward backflow rate, is the angle between the jet flow at the outlet on the tundish nozzle side and the horizontal plane, is the molten steel flow rate that can impact the narrow face to form an upward backflow at the outlet on the tundish nozzle side under the condition of blowing gas; Adding the upward backflow rate and the molten steel flow rate of the part that floats upward due to bubbles through the pipe cross-section , to obtain the molten steel flow rate impacting the slag-metal interface .

[0014] Preferably, the mathematical description of the impact zone is a continuous area at a preset distance from the narrow face, and the velocity component of the fluid perpendicular to the narrow face in this area is greater than the preset velocity.

[0015] Preferably, the value range of the preset distance is 4 - 5 cm; the value range of the preset velocity is 0.1 m / s - 0.15 m / s, and its magnitude increases with the increase of the casting speed.

[0016] Preferably, the angle between the jet flow at the outlet on the tundish nozzle side and the horizontal plane is calculated according to the coordinates of the impact point, and the formula is: ; Wherein, is the angle between the jet flow at the outlet on the tundish nozzle side and the horizontal plane, and are the z coordinates of the impact point and the slag-metal interface respectively, is the length of the wide face of the mold.

[0017] Preferably, the molten steel impact force is calculated according to the molten steel flow rate impacting the slag-metal interface, and the formula is: ; Wherein, is the molten steel impact force, is the molten steel density, is the molten steel flow rate impacting the slag-metal interface, is the fluid velocity at the impact point.

[0018] Preferably, the calculation formula for half of the slag-metal interfacial tension is: ; Wherein, is half of the slag-metal interfacial tension; is the equivalent diameter of the slag-metal interface, and W and B are the lengths of the wide face and the narrow face of the mold respectively, is the interfacial tension coefficient of the slag-metal.

[0019] The above technical solution of the present invention has the following beneficial effects compared with the prior art: The method for evaluating slag entrainment in a continuous casting mold of the present invention takes a pipe cross-section at the outlet of the mold nozzle. By using the pipe flow model, the molten steel flow rate at the outlet on the nozzle side of the mold can be accurately calculated; by selecting the impact zone formed after the molten steel impacts the narrow face of the mold and simplifying the impact zone into an impact point, the angle between the jet flow at the outlet on the nozzle side and the horizontal plane can be obtained by calculating the coordinates of the impact point, and further the molten steel flow rate and the molten steel impact force on the slag-metal interface can be obtained; finally, the ratio of the molten steel impact force to the interfacial tension of the slag-metal is used as the slag entrainment evaluation index. According to the slag entrainment evaluation index, it can be judged whether slag entrainment occurs on the liquid surface, and the degree of slag entrainment can be reflected by the magnitude of the slag entrainment evaluation index value. The present invention judges the slag entrainment phenomenon with objective quantitative indexes. By accurately evaluating the slag entrainment risk, it can effectively improve the stability of the casting quality and reduce the production cost of cast steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in conjunction with the drawings, where: Figure 1 is a flow chart of the method for evaluating slag entrainment in a continuous casting mold of the present invention; Figure 2 is an example diagram of the pipe cross-section of the embodiment of the present invention; Figure 3 is a vector diagram of the pipe cross-section at the outlet on the nozzle side under the condition of gas blowing; Figure 4 is a schematic diagram of the impact zone of the embodiment of the present invention; Figure 5 is a flow rate contour map of the outlet on the nozzle side of the embodiment of the present invention; Figure 6 is a schematic diagram of the mold without gas blowing; Figure 7 is a schematic diagram of the mold with gas blowing. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The following further illustrates the present invention in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments given are not intended to limit the present invention.

[0022] After the molten steel flows out of the nozzle, an upper backflow and a lower circulation are formed after impacting the narrow face. The upper backflow will impact the slag-metal interface, causing liquid level fluctuations. Therefore, the slag entrainment process is mainly related to the upper backflow. The main influence of the lower circulation on slag entrainment is that after the slag droplets are entrained, it drives the slag droplets to flow deep into the billet, but it has little influence on the initial formation of the slag droplets. The slag entrainment evaluation index should focus on reflecting the impact of the upward flow on the slag-metal interface.

[0023] Since the flow rate of the mold powder is relatively slow, far less than that of the molten steel, a large velocity gradient will be generated near the slag-metal interface. When the velocity gradient at the interface exceeds a certain critical value, slag entrainment will occur. Conduct a force analysis on the entire slag-metal interface. The forces acting on the interface include buoyancy, gravity, interfacial tension, and shear force. As long as the interface fluctuations are maintained constant, it can basically be considered that gravity and buoyancy cancel each other out, and the shear force can also be ignored. Only the interfacial tension and the impact force of the molten steel remain. When the impact force is greater than the interfacial tension, the slag-metal interface will be torn, resulting in slag entrainment. Therefore, in the present invention, through numerical calculation, a slag entrainment evaluation index is constructed based on the impact force of the molten steel on the narrow face to reflect the degree of slag entrainment and guide engineering practice.

[0024] Refer to Figure 1 As shown, Embodiment 1 of the present application provides a method for evaluating slag entrainment in a continuous casting mold, including: S1: Construct a three-dimensional model of the mold. Take a pipe cross-section at the outlet of the mold nozzle. This pipe cross-section is within the nozzle outlet pipe wall and includes all the fluid flowing out of the nozzle. Calculate the molten steel flow rate at the nozzle side outlet according to the pipe cross-section using the pipe flow model.

[0025] Preferably, in this embodiment, the large eddy simulation model is used to simulate the fluid in the mold in the FLUENT software, and the DMP model is used to track the bubble movement; UDF self-programming is used to stop tracking the bubbles after they enter the free liquid surface of the fluid and remove the bubbles; the VOF model is used to calculate the slag-metal interface fluctuations to describe the phenomenon of mold powder being entrained into the molten steel.

[0026] The flow of the molten steel in the mold nozzle belongs to the characteristics of pipe flow and becomes a jet after the outlet. Although the molten steel at the nozzle outlet is a jet, it is in the initial stage of the jet, and the flow rate change is very small, conforming to the nature of pipe flow. To simplify the calculation, the pipe flow model method can be used to calculate the nozzle flow rate. The pipe flow model means that the volume of fluid flowing through any complete cross-section in the nozzle pipe is equal per unit time, that is, the flow rate is conserved.

[0027] Therefore, in the present invention, the pipe cross-section is taken near the outlet on the tundish side, and the pipe cross-section is within the tundish pipe wall and includes all the fluid flowing out of the tundish side outlet, so as to ensure that the fluid passing through the pipe cross-section is still in the initial stage of the jet. If part of the pipe cross-section extends beyond the tundish, the flow rate of this cross-section enters the main stage of the jet, and its fluid flow rate increases rapidly, which does not conform to the calculation criterion of the tundish flow rate in the present invention.

[0028] In this embodiment, the horizontal coordinate value range of the pipe cross-section is 0 - 3 cm inward from the edge of the outlet on the tundish side.

[0029] To simplify the calculation, under ideal conditions, the cross-section perpendicular to the fluid velocity direction is selected as the pipe cross-section. And to eliminate the influence of backflow, the velocity direction of the fluid within the selected pipe cross-section should be kept consistent without sudden changes, which is conducive to reducing the integration error and minimizing the calculated flow rate error. However, in actual calculations, there is no pipe cross-section under ideal conditions. Through experimental verification, the conditions for selecting the pipe cross-section in this embodiment are: the angle between the velocity direction of more than 90% of the fluid passing through the pipe cross-section and the pipe cross-section is 40° - 90°, so as to ensure that the velocity directions of most of the fluid passing through the pipe cross-section are consistent and reduce the error in calculating the molten steel flow rate at the tundish.

[0030] Exemplarily, Figure 2 is a schematic diagram of the pipe cross-section. In this example, the ZY cross-section is selected as the pipe cross-section, and the vertical vector of this cross-section is the X-direction vector. Then, the boundary condition Velocity u>0 is added to the pipe cross-section. Figure 3 is the vector diagram of the pipe cross-section at the outlet on the tundish side under the condition of gas blowing.

[0031] If the pipe cross-section is an inclined cross-section, the magnitudes of the fluid velocities in the horizontal and vertical directions of the inclined interface are measured respectively, and the calculation is carried out by projecting onto the vertical cross-section vector.

[0032] Specifically, under the condition of no gas blowing, according to the pipe cross-section, the molten steel flow rate at the outlet on the tundish side is calculated by the pipe flow model, and the formula is: , where A is the area of the pipe cross-section, v is the velocity component of the fluid perpendicular to the pipe cross-section and in the same direction as the molten steel outflow direction, is the molten steel flow rate at the outlet on the tundish side under the condition of no gas blowing. is a tiny component of the cross-section. All the tiny interfaces together form a continuous interface, so it satisfies the continuous function and is convenient for integration.

[0033] Specifically, under the condition of gas blowing, according to the pipe cross-section, the molten steel flow rate at the outlet on the tundish side is calculated by the pipe flow model, including: Calculating the molten steel flow rate at the outlet on the tundish side under the condition of gas blowing according to the pipe cross-section by the pipe flow model ;The molten steel flowing through the pipe cross-section and floating upward due to bubbles directly impacts the slag-metal interface, and the flow rate of this part of the molten steel is calculated. ;Then, the flow rate of the molten steel that can impact the narrow face and form an upward backflow at the outlet on the nozzle side under the blowing condition is .

[0034] In this embodiment, in the CFD-POST software, the nozzle flow rate is calculated using the areaInt(Velocity a)@Iso Clip A function. Among them, areaInt() is a custom function in the software, which is used to integrate a certain parameter in the selected area over this area; Velocity a is the velocity component of the fluid perpendicular to the pipe cross-section and in the same direction as the outflow direction of the molten steel. Iso Clip is a built-in function of the software, and Iso Clip A is the pipe cross-section at the outlet of the mold nozzle. The selection of the Iso Clip A boundary condition is to determine Iso Clip A inside the nozzle by selecting the coordinate range according to different nozzle sizes, and at the same time add boundary conditions to exclude the influence of the backflow. It is detected in the Chart that the velocity values of the fluid fluctuate at different times, resulting in fluctuations in the fluid flow rate at different times. In this embodiment, the average value of the flow rate within a period of time after the flow field reaches a steady state is used as the nozzle flow rate.

[0035] S2: Select the impact zone formed after the fluid impacts the narrow face of the mold, and use the average value of the vertical coordinates of each fluid particle in the impact zone as the coordinates of the impact point.

[0036] Preferably, the average value of the coordinates of the impact point within the steady-state time is used as the coordinates of the target impact point.

[0037] After the molten steel is ejected from the outlet on the nozzle side, it impacts the narrow face of the mold to form an impact zone, and an upward backflow and a downward circulation are formed respectively upward and downward.

[0038] Preferably, the mathematical description of the impact zone is a continuous area at a preset distance from the narrow face, and the velocity component of the fluid perpendicular to the pipe cross-section within this area is greater than the preset velocity.

[0039] The selection of the impact point should be more than 1 grid distance away from the narrow face to avoid the influence of the boundary layer effect close to the narrow face. Preferably, the value range of the preset distance is 4-5 cm. The value range of the preset velocity is 0.1 m / s - 0.15 m / s, and its magnitude increases with the increase of the drawing speed.

[0040] Since the impact point can only be formed when the jet at the nozzle side outlet hits the narrow face, there is almost no horizontal direction vector of the backflow near the narrow face. Only in the impact zone, due to the influence of the jet, there is a horizontal direction vector, and the vertical direction vector cannot reflect the impact zone. Therefore, the boundary condition of the impact zone is set as the velocity component of the fluid perpendicular to the narrow face being greater than the preset velocity, so as to exclude the influence of the backflow and accurately find the range of the impact zone.

[0041] Figure 4 Schematic diagram of the impact zone selected for this embodiment. Figure 5 Flow rate contour map of the nozzle side outlet for this embodiment. Compare Figure 4 and Figure 5 , it can be seen that the impact zone selected for this embodiment conforms to the actual situation.

[0042] In this embodiment, in the CFD-POST software, the coordinates of the side impact point are calculated by the areaAve(Z)@Iso Clip b function. Among them, Z represents the z coordinate of each fluid particle in the impact zone, and the positive direction of the z-axis is the direction of gravity; areaAve() is used to calculate the weighted average of a certain parameter on the selected area on the surface, and Iso Clip b is the selected impact zone. It is detected in the Chart that the velocity values of the fluid at different times fluctuate, resulting in fluctuations in the impact points at different times. In this embodiment, the average value of the impact point coordinates within a period of time after the flow field reaches a steady state is used as the target impact point coordinates.

[0043] S3: Calculate the angle between the jet at the nozzle side outlet and the horizontal plane according to the coordinates of the impact point, and then obtain the molten steel flow rate at the impact slag-metal interface according to the molten steel flow rate at the nozzle side outlet.

[0044] Referring to Figure 6 shown, calculate the angle between the jet at the nozzle side outlet and the horizontal plane according to the coordinates of the impact point. The formula is: ; Among them, is the angle between the jet at the nozzle side outlet and the horizontal plane, and are the z coordinates of the impact point and the slag-metal interface respectively, is the length of the wide face of the mold.

[0045] After the molten steel impacts the narrow face, an upper backflow and a lower circulation are formed. According to the law of conservation of mass, the flow rate of the molten steel should satisfy the equation: ; Among them, is the upper backflow flow rate, is the lower circulation flow rate, is the flow rate at the nozzle side outlet.

[0046] According to the momentum conservation theory in fluid mechanics, the upward backflow and the downward circulation are regarded as two branches of fluid, and a pipe flow model of the molten steel flow in the mold is established. In order to derive the equations, the model must first meet the following assumptions: The density of the molten steel changes little with temperature and can be regarded as an incompressible fluid; The flow in the mold is regarded as two-dimensional incompressible steady flow, and the flow field velocity takes the average value; Neglect the viscosity of the molten steel inside the flow tube, and regard the molten steel in the flow tube as an ideal fluid.

[0047] Meeting the above conditions, a set of Bernoulli equations can be listed for the main flow at the outlet on the tundish side and the two branches of the upward backflow and the downward circulation: ; Among them, , and are the velocities of the upward backflow, the downward circulation and the impact point respectively, , and D are the heights of the upward backflow, the downward circulation and the main flow at the outlet on the tundish side respectively, , and are the pressures of the upward backflow, the downward circulation and the main flow at the outlet on the tundish side respectively, is the density of the molten steel, and g represents the acceleration of gravity.

[0048] To solve this system of equations, the equations need to be appropriately simplified. The two branches are very close, and it can be considered that ; Secondly, without considering the flow loss, the hydrostatic pressure . By simplifying the system of equations through the above theory, the relationship between the magnitudes of the velocities of the upward backflow, the downward circulation and the impact point can be obtained as , that is, the flow velocities of the molten steel in the upward backflow, the downward circulation and the main flow area are equal. Therefore, it can be obtained that: ; According to the flow rate at the outlet on the tundish side, the upward backflow rate is obtained, and the formula is: ; According to the flow rate at the outlet on the tundish side, the downward circulation rate is obtained, and the formula is: ; Among them, is the upward backflow rate, is the downward circulation rate, is the included angle between the upward backflow and the outlet on the tundish side, is the flow rate at the outlet on the tundish side.

[0049] Under the condition of no gas blowing, the upward backflow rate is the flow rate of the molten steel impacting the slag-metal interface. Therefore, according to the flow rate of the molten steel at the outlet on the tundish side The molten steel flow rate at the impact slag-metal interface is obtained by the formula: ; Wherein, is the molten steel flow rate at the impact slag-metal interface, is the angle between the jet at the nozzle side outlet and the horizontal plane, is the molten steel flow rate at the nozzle side outlet under the condition of no gas blowing.

[0050] Under the condition of gas blowing, as shown in Figure 7 , the molten steel flow rate at the impact slag-metal interface is obtained according to the molten steel flow rate at the nozzle side outlet, including: Calculating the upward reflux flow rate according to the molten steel flow rate that can impact the narrow face to form an upward reflux at the nozzle side outlet under the condition of gas blowing: ; Wherein, is the upward reflux flow rate, is the angle between the jet at the nozzle side outlet and the horizontal plane, is the molten steel flow rate that can impact the narrow face to form an upward reflux at the nozzle side outlet under the condition of gas blowing; Adding the upward reflux flow rate to the part of the molten steel flow rate that passes through the pipe cross-section and floats due to bubbles , the molten steel flow rate at the impact slag-metal interface is obtained.

[0051] S4: Calculating the molten steel impact force according to the molten steel flow rate at the impact slag-metal interface.

[0052] Ignoring the flow loss of the molten steel, according to the fluid momentum equation, the magnitude of the molten steel impact force is: ; Wherein, is the molten steel impact force, is the molten steel density, is the molten steel flow rate at the impact slag-metal interface, is the fluid velocity at the impact point.

[0053] According to the Young-Laplace equation, the calculation formula for half of the slag-metal interfacial tension is: ; Wherein, is half of the slag-metal interfacial tension; is the equivalent diameter of the slag-metal interface, W and B are the lengths of the wide face and the narrow face of the mold respectively, is the slag-metal interfacial tension coefficient.

[0054] S5: Take the ratio of the molten steel impact force to half of the slag-metal interfacial tension as the slag entrainment evaluation index. When the value of the slag entrainment evaluation index is greater than or equal to 1, slag entrainment occurs; when the value of the slag entrainment evaluation index is less than 1, slag entrainment does not occur; and the greater the value of the slag entrainment evaluation index, the more times slag entrainment occurs.

[0055] The formula for the slag entrainment evaluation index is: .

[0056] Under the condition of no gas blowing, the formula for the slag entrainment evaluation index is: .

[0057] In summary, for the slag entrainment evaluation method of the continuous casting mold described in the present invention, by taking the pipe cross-section at the outlet of the mold nozzle, the molten steel flow rate at the outlet on the nozzle side of the mold can be accurately calculated using the pipe flow model; by selecting the impact zone formed after the molten steel impacts the narrow surface of the mold and simplifying this impact zone into an impact point, the angle between the jet flow of the molten steel at the outlet on the nozzle side and the horizontal plane is obtained by calculating the coordinates of the impact point, and further the molten steel flow rate and the molten steel impact force on the slag-metal interface are obtained; finally, the ratio of the molten steel impact force to the slag-metal interfacial tension is used as the slag entrainment evaluation index. According to the slag entrainment evaluation index, it can be judged whether slag entrainment occurs on the liquid surface, and the degree of slag entrainment can be reflected by the value of the slag entrainment evaluation index. The present invention judges the slag entrainment phenomenon with objective quantitative indicators. By accurately evaluating the slag entrainment risk, it can effectively improve the stability of the casting quality and reduce the production cost of cast steel.

[0058] In the second embodiment provided in the present application, an advanced large eddy model is used in the FLUENT software to simulate fluid flow. The size of the mold is 170×1570mm, including the left outlet of the nozzle, the right outlet of the nozzle, and the bottom outlet of the nozzle.

[0059] In this experiment, the drawing speed is set to 1.2m / min, the time step is 0.05s, the total duration is 100s, and there is no gas blowing condition.

[0060] The boundary conditions of the pipe cross-section are: 0.17m ≤ Z ≤ 0.27m, -0.02m ≤ Y ≤ 0.02m, Velocity u ≥ 0. Calculate the magnitude of the molten steel flow rate at the outlet on the nozzle side at each moment, and take the average value of the last 80S to obtain the flow rate of the left outlet of the nozzle as 0.001970m 3 / s. Similarly, the flow rate of the right outlet of the nozzle is calculated as 0.001969m 3 / s, and the flow rate of the bottom outlet of the nozzle is 0.001438m 3 / s. The inlet velocity is 1.208 m / s. Define a concept fit degree, which is the ratio of the sum of the flow rates at the nozzle outlets to the inlet flow rate, used to measure whether the flow rate is conserved, and further measure the feasibility and rationality of the flow rate distribution theory. Considering the error, the fit degree should be between 0.97 and 1.03. The calculated fit degree of this embodiment is 1.00757, which can prove that the difference between the calculated outlet flow rate and the inlet flow rate is very small, indicating that the nozzle flow rate calculated by the present invention is very accurate.

[0061] The mathematical description of the impact zone is a coherent area near the narrow face, and the velocity component of the fluid perpendicular to the pipe cross-section in this area is greater than the preset velocity. In this embodiment, the value range of the preset velocity is 0.1 - 0.15 m / s. The calculated Z coordinate of the impact point is 0.5565 m. Then, the angle θ between the jet at the outlet on the nozzle side and the horizontal plane can be calculated as 28.75°. Therefore, the molten steel flow rate impacting the slag-metal interface is further calculated as 0.000511 m 3 / s, and the lower circulation flow rate is 0.001459 m 3 / s.

[0062] Half of the slag-metal interfacial tension is 1.2×0.5 = 0.6, and this value is the fixed interfacial tension set in FLUENT.

[0063] Impact point velocity is 0.217 m / s. The impact force of the molten steel is 7100×0.000511×0.217 = 0.787. The slag entrainment evaluation index J = 1.311 > 1, indicating that slag entrainment occurs, which is consistent with the actual results.

[0064] In Embodiment 3 provided in the present application, the model parameters and settings are the same as those in Embodiment 2, and the casting speed is changed to 1.4 m / min without the blowing condition.

[0065] Calculate the molten steel flow rate magnitude at the outlet on the nozzle side at each moment. Taking the average value of the last 80 s, the flow rate at the left outlet of the nozzle is obtained as 0.002269 m 3 / s. Similarly, the flow rate at the right outlet of the nozzle is calculated as 0.002277 m 3 / s, and the flow rate at the bottom outlet of the nozzle is 0.001681 m 3 / s. The inlet velocity is 1.41 m / s. The calculated fit degree of this embodiment is 0.99968, which can prove that the error between the calculated outlet flow rate and the inlet flow rate is very small, and once again proves the accuracy of the present invention in calculating the nozzle flow rate.

[0066] In this embodiment, the calculated Z coordinate of the impact point is 0.5817 m, and the angle θ between the jet at the outlet on the nozzle side and the horizontal plane is 30.29°. Therefore, the molten steel flow rate impacting the slag-metal interface is further calculated as 0.000562 m3 / s, the downward circulation flow rate is 0.001707 m 3 / s.

[0067] Impact point velocity is 0.256 m / s, the molten steel impact force is 7100×0.000562×0.256 = 1.02, and the slag entrainment evaluation index J = 1.702 > 1, so slag entrainment occurs, which is consistent with the actual result.

[0068] In Embodiment 4 provided by the present application, the model parameters and settings are the same as those in Embodiment 2, and the blowing condition is added. It is set that Ar gas flows into the mold nozzle, and the flow rate is 4 L / min.

[0069] Calculate the molten steel flow rate at the nozzle side outlet at each moment, and take the average value of the last 80 s to obtain the flow rate at the left side outlet of the nozzle as 0.001915 m 3 / s. Similarly, the flow rate at the right side outlet of the nozzle is calculated as 0.001868 m 3 / s, and the flow rate at the bottom outlet of the nozzle is 0.001676 m 3 / s. The inlet velocity is 1.208 m / s. The fitting degree of this embodiment is calculated to be 1.01025, which can prove that the error between the calculated outlet flow rate and the inlet flow rate is very small, indicating that the method for calculating the nozzle flow rate of the present invention is also applicable to the blowing condition.

[0070] In this embodiment, the calculated impact point Z coordinate is 0.4611 m, the angle θ between the jet flow at the nozzle side outlet and the horizontal plane is 22.47°, and calculate the molten steel flow rate passing through the pipe cross-section and floating upward due to bubbles is 0.00011 m 3 / s, and the molten steel flow rate that can impact the narrow face and form an upward reverse flow at the nozzle side outlet is 0.001805 m 3 / s. Therefore, it is further calculated that the molten steel flow rate impacting the slag-metal interface is 0.000668 m 3 / s, and the downward circulation flow rate is 0.001247 m 3 / s.

[0071] Impact point velocity is 0.192 m / s, the molten steel impact force is 7100×0.000647×0.192 = 0.882, and the slag entrainment evaluation index J = 1.47 > 1, so slag entrainment occurs, which is consistent with the actual result.

[0072] In Embodiment 5 provided by the present application, the model parameters and settings are the same as those in Embodiment 2, the blowing condition is added, it is set that Ar gas flows into the mold nozzle, the flow rate is 4 L / min, and the drawing speed is increased to 1.4 m / min.

[0073] Calculate the molten steel flow rate at the nozzle side outlet at each moment, and take the average value of the last 80 s to obtain the flow rate of the left side outlet of the nozzle as 0.002185 m 3 / s. Similarly, calculate the flow rate of the right side outlet of the nozzle as 0.002187 m 3 / s, and the flow rate of the bottom outlet of the nozzle as 0.001946 m 3 / s. The inlet velocity is 1.41 m / s. The fit degree of this embodiment is calculated to be 1.00349, which can prove that the error between the required outlet flow rate and the inlet flow rate is very small.

[0074] Similarly, calculate the Z coordinate of the impact point as 0.4875 m, the angle θ between the jet flow at the nozzle side outlet and the horizontal plane as 30.29°, and calculate the molten steel flow rate of the part that passes through the pipe cross-section and floats up due to bubbles as 0.000115 m 3 / s, and the molten steel flow rate that the nozzle side outlet can impact the narrow face to form an upward backflow is 0.002070 m 3 / s. Therefore, further calculate the molten steel flow rate impacting the slag-metal interface as 0.000701 m 3 / s, and the lower circulation flow rate as 0.001484 m 3 / s.

[0075] Impact point velocity is 0.225 m / s, the molten steel impact force is 7100×0.000701×0.225 = 1.12, and the slag entrainment evaluation index J = 1.867 > 1, indicating that slag entrainment occurs, which is consistent with the actual results.

[0076] It can be seen from Embodiment 2 and Embodiment 3 that the error between the nozzle flow rate calculated by the present invention and the inlet flow rate is very small, and it can accurately reflect the magnitude of the flow rate. The impact point moves downward with the increase of the drawing speed, which is in line with the production reality. At the same time, the molten steel flow rate impacting the slag-metal interface in Embodiment 3 is greater than that in Embodiment 2, the slag entrainment evaluation index value in Embodiment 3 is also greater than that in Embodiment 2, and the observed slag entrainment in Embodiment 3 is also significantly more than that in Embodiment 2. This shows that the slag entrainment evaluation index proposed by the present invention can not only judge whether there is a slag entrainment phenomenon, but also reflect the degree of slag entrainment by the magnitude of the slag entrainment evaluation index value under different drawing speeds without blowing conditions.

[0077] As can be seen from Example 2 and Example 4, the error between the nozzle flow rate calculated by the present invention and the inlet flow rate is very small, which can accurately reflect the magnitude of the flow rate. The impact point moves upward with the increase of the blowing gas volume, which is in line with the actual production. At the same time, the molten steel flow rate at the impact slag-metal interface in Example 4 is greater than that in Example 2, and the slag entrainment evaluation index value in Example 4 is also greater than that in Example 2. The observed slag entrainment in Example 4 is also significantly more than that in Example 2. This shows that the slag entrainment evaluation index proposed by the present invention can not only judge whether there is a slag entrainment phenomenon, but also reflect the degree of slag entrainment by the magnitude of the slag entrainment evaluation index value under the conditions of the same casting speed and with or without blowing gas.

[0078] As can be seen from Example 4 and Example 5, the error between the nozzle flow rate calculated by the present invention and the inlet flow rate is very small, which can accurately reflect the magnitude of the flow rate. The impact point moves downward with the increase of the casting speed, which is in line with the actual production. And slag entrainment occurs in both Example 4 and Example 5, indicating that the slag entrainment evaluation index proposed by the present invention can judge whether there is a slag entrainment phenomenon under the condition of blowing gas.

[0079] In summary, a method for evaluating slag entrainment in a continuous casting mold proposed by the present invention can accurately reflect whether slag entrainment occurs under various conditions to guide actual production.

[0080] Those skilled in the art should understand that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0081] The present application is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowcharts and / or block diagrams, and the combination of processes and / or blocks in the flowcharts and / or block diagrams, can be realized by computer program instructions. These computer program instructions can be provided to the processors of general-purpose computers, special-purpose computers, embedded processors, or other programmable data processing devices to generate a machine, so that the instructions executed by the processors of the computer or other programmable data processing devices generate means for realizing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0082] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to work in a particular manner, such that the instructions stored in the computer-readable memory produce a manufacture including an instruction device that implements the functions specified in one or more of the processes and / or blocks Figure 1 one or more processes and / or blocks Figure 1 specified in the block or blocks.

[0083] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus, such that a series of operational steps are performed on the computer or other programmable apparatus to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable apparatus provide steps for implementing the functions specified in one or more of the processes and / or blocks Figure 1 one or more processes and / or blocks Figure 1 specified in the block or blocks.

[0084] Obviously, the above embodiments are only examples for clear illustration and are not limitations on the implementation. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for evaluating slag entrainment in a continuous casting mold, characterized in that, Including: Construct a three-dimensional model of the mold. Take a pipe cross-section at the outlet of the mold nozzle. The pipe cross-section is within the nozzle outlet pipe wall and includes all the fluid flowing out of the nozzle. Calculate the molten steel flow rate at the nozzle side outlet according to the pipe cross-section using the pipe flow model. Select the impact zone formed after the fluid impacts the narrow face of the mold. Take the average value of the vertical coordinates of each fluid particle in the impact zone as the coordinates of the impact point. Calculate the angle between the jet at the nozzle side outlet and the horizontal plane according to the coordinates of the impact point, and then obtain the molten steel flow rate impacting the slag-metal interface according to the molten steel flow rate at the nozzle side outlet. Calculate the molten steel impact force according to the molten steel flow rate impacting the slag-metal interface. Take the ratio of the molten steel impact force to half of the slag-metal interface tension as the slag entrainment evaluation index. When the value of the slag entrainment evaluation index is greater than or equal to 1, slag entrainment occurs. When the value of the slag entrainment evaluation index is less than 1, slag entrainment does not occur. And the greater the value of the slag entrainment evaluation index, the more times slag entrainment occurs.

2. The method for evaluating slag entrainment in a continuous casting mold according to claim 1, characterized in that, Construct a three-dimensional model of the mold, including: Use Solidworks to draw a three-dimensional model of the mold. Use the large eddy simulation model in FLUENT software to simulate the fluid motion in the mold. Use the DMP model to track the bubble motion, so that the tracking stops after the bubble enters the free liquid surface of the fluid, and the bubble is removed to simulate the condition with gas blowing. Use the VOF model to calculate the fluctuation of the slag-metal interface.

3. The method for evaluating slag entrainment in a continuous casting mold according to claim 1, characterized in that, The conditions for selecting the pipe cross-section include: the angle between the velocity direction of more than 90% of the fluid passing through the pipe cross-section and the pipe cross-section is 40° - 90°.

4. The method for evaluating slag entrainment in a continuous casting mold according to claim 1, characterized in that, Under the condition of no gas blowing, the molten steel flow rate at the nozzle side outlet is calculated according to the pipe flow model based on the pipe cross-section. The formula is as follows: , where A is the area of the pipe cross-section, v is the velocity component of the fluid perpendicular to the pipe cross-section and in the same direction as the molten steel outflow direction, is the molten steel flow rate at the nozzle side outlet under the condition of no gas blowing.

5. The method for evaluating slag entrainment in a continuous casting mold according to claim 4, characterized in that, Under the condition of no gas blowing, according to the molten steel flow rate at the outlet on the tundish nozzle side The molten steel flow rate impacting the slag-metal interface is obtained, and the formula is: ； Among them, is the molten steel flow rate at the impact slag-metal interface, is the angle between the jet at the nozzle side outlet and the horizontal plane, is the molten steel flow rate at the nozzle side outlet under the condition of no gas blowing.

6. The method for evaluating slag entrainment in a continuous casting mold according to claim 4, characterized in that, Under the condition with gas blowing, calculate the molten steel flow rate at the nozzle side outlet according to the pipe cross-section using the pipe flow model, including: Calculate the molten steel flow rate at the nozzle side outlet under the condition of gas blowing according to the pipe cross-section with a pipe flow model ; Calculate the molten steel flow rate of the part of the molten steel that passes through the pipe cross-section and floats upward due to bubbles and directly impacts the slag-metal interface ; Then the molten steel flow rate that can impact the narrow face and form an upward backflow at the nozzle side outlet under the condition of gas blowing is .

7. The method for evaluating slag entrainment in a continuous casting mold according to claim 6, characterized in that, Under the condition with gas blowing, obtain the molten steel flow rate impacting the slag-metal interface according to the molten steel flow rate at the nozzle side outlet, including: According to the molten steel flow rate at the nozzle side outlet under the condition of blowing gas, which can impact the narrow face to form an upward backflow Calculate the upward backflow rate: ； wherein, is the upward backflow rate, is the angle between the jet flow at the nozzle side outlet and the horizontal plane, is the molten steel flow rate that can impact the narrow face to form upward backflow at the nozzle side outlet under the condition of gas blowing; The above backflow rate plus the rate of molten steel flowing through the pipe cross-section and floating upward due to bubbles , gives the rate of molten steel impacting the slag-metal interface .

8. The method for evaluating slag entrainment in a continuous casting mold according to claim 1, characterized in that, The mathematical description of the impact zone is a continuous area at a preset distance from the narrow face, and the vertical velocity component of the fluid in this area is greater than the preset velocity.

9. The method for evaluating slag entrainment in a continuous casting mold according to claim 8, characterized in that, The value range of the preset distance is 4 - 5 cm; the value range of the preset velocity is 0.1 m / s - 0.15 m / s, and its magnitude increases with the increase of the casting speed.

10. The method for evaluating slag entrainment in a continuous casting mold according to claim 1, characterized in that, Calculate the angle between the jet at the nozzle side outlet and the horizontal plane according to the coordinates of the impact point. The formula is: ； Among them, is the angle between the jet flow at the nozzle side outlet and the horizontal plane, and are the z coordinates of the impact point and the slag-metal interface respectively, is the length of the wide face of the mold.

11. A method for evaluating slag entrainment in a continuous casting mold according to claim 1, characterized in that, Calculate the molten steel impact force according to the molten steel flow rate impacting the slag-metal interface. The formula is: ； Among them, is the impact force of the molten steel, is the density of the molten steel, is the flow rate of the molten steel impacting the slag-metal interface, is the fluid velocity at the impact point.

12. A method for evaluating slag entrainment in a continuous casting mold according to claim 1, characterized in that, The calculation formula for half of the slag-metal interface tension is: ； Among them, is the interfacial tension of the slag-metal semi-molten state; is the equivalent diameter of the slag-metal interface, where W and B are the lengths of the wide and narrow faces of the mold respectively, is the interfacial tension coefficient of the slag-metal interface.

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