Liquid level fluctuation control method based on water gap insertion depth

Abstract

The invention relates to the technical field of metallurgical industry continuous casting, in particular to a nozzle insertion depth-based liquid level fluctuation control method, which comprises the following steps of: constructing a nozzle insertion depth-critical wave height mapping model; the water gap insertion depth is converted into a direct control variable, and the optimal depth is decided in real time by solving the minimum value point of the model; when the residual fluctuation standard deviation is larger than 2 mm, stopper rod amplitude limiting adjustment is triggered to be + / -80 mm, and cooperative control over a water gap stopper rod is achieved; the defects of an existing feedback control method based on a liquid level sensor in continuous casting production are overcome, a dynamic mathematical model of the water gap insertion depth and the liquid level fluctuation is established, a high-precision liquid level sensor is not needed, and the liquid level fluctuation control method actively optimizes the water gap insertion depth; therefore, the fluctuation of the liquid level of the molten steel in the crystallizer is accurately and efficiently inhibited, the slag entrapment risk is effectively reduced, and the casting blank quality and the stability and reliability of continuous casting production are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of continuous casting in the metallurgical industry, and in particular to a liquid level fluctuation control method based on nozzle insertion depth. BACKGROUND

[0002] In the process of steel continuous casting production, the stable control of the liquid level of molten steel in the crystallizer plays a decisive role in the quality of the casting blank. At present, the mainstream liquid level fluctuation control method in the industry relies on liquid level sensor feedback, detects the liquid level height in real time, adjusts the stopper or sliding nozzle opening degree by using PID control technology, and maintains the stability of the liquid level. However, this technical route has exposed significant defects in actual application. Due to the harsh environment of high-temperature molten steel in the continuous casting process, the liquid level sensor is prone to drift or even damage, resulting in inaccurate detection data; and there is a time lag from sensor detection to control action execution, which cannot respond to rapid changes in the liquid level in time. At the same time, the traditional control scheme regards the nozzle insertion depth as a fixed parameter or only adjusts it according to artificial experience, and fails to fully tap its potential for regulating and controlling the liquid level fluctuation, ignores the dynamic correlation between the nozzle insertion depth and the liquid level fluctuation, and lacks scientific mathematical model support, making it difficult for the control strategy to achieve optimal results.

[0003] In addition, under the complex and changeable working conditions of steel continuous casting, the anti-interference ability of the traditional control method is also a prominent problem. When the molten steel flow changes suddenly or the temperature fluctuates greatly, the traditional control method based on liquid level sensor feedback responds slowly and cannot make effective adjustments in time, which easily leads to problems such as slag entrapment that seriously affect the quality of the casting blank. With the continuous improvement of the quality requirements of the steel industry, the traditional control method has been difficult to meet the demand for high-quality production. Therefore, developing a control method that does not rely on high-precision liquid level sensors and can effectively suppress liquid level fluctuation by actively optimizing the nozzle insertion depth has become the key to solving the problems of continuous casting production and improving the quality of steel products, and has important significance for promoting the intelligentization and high-quality development of the steel industry. SUMMARY

[0004] The present application provides a liquid level fluctuation control method based on nozzle insertion depth, aiming to overcome the defects of the existing liquid level sensor feedback control method in continuous casting production. In view of the problems such as adverse effects of high-temperature molten steel on the sensor, control lag, ineffective use of nozzle insertion depth for regulation and control, and weak anti-interference ability, a dynamic mathematical model of nozzle insertion depth and liquid level fluctuation is established, and a liquid level fluctuation control method that actively optimizes the nozzle insertion depth without relying on high-precision liquid level sensors is developed, thereby realizing accurate and efficient suppression of the liquid level fluctuation of molten steel in the crystallizer, effectively reducing the risk of slag entrapment, and significantly improving the quality of the casting blank and the stability and reliability of continuous casting production.

[0005] In order to achieve the above object, the present application adopts the following technical solutions:

[0006] A liquid level fluctuation control method based on water gap insertion depth, comprising the following steps:

[0007] S1, constructing a water gap insertion depth-critical wave height mapping model;

[0008] S2, converting the water gap insertion depth into a direct control variable, and determining the optimal depth in real time by solving the minimum point of the model;

[0009] S3, triggering the stopper limit adjustment ±80mm when |residual fluctuation standard deviation|>2mm, realizing the collaborative control of the water gap stopper.

[0010] Further, the water gap insertion depth-critical wave height mapping model is the joint action of the jet decay term and the vortex effect term, resulting in the existence of the minimum wave height point, the critical depth D c , the liquid level wave height H ω and the water gap insertion depth D c There is a critical depth D ω to minimize the wave height:

[0011] H -αD =k·e v +β·Q -1

[0012] Where H ω is the liquid level wave height; D is the water gap insertion depth; k, α, β are steel grade characteristic coefficients, calibrated by experiment; Q v is the volume flow rate of molten steel.

[0013] Further, the steel grade characteristic coefficients are classified according to steel grade: low carbon steel: k=12.5, α=0.22, β=0.028, peritectic steel: k=15.2, α=0.25, β=0.032, high strength steel: k=18.3, α=0.31, β=0.035.

[0014] Further, the volume flow rate of molten steel is determined by the withdrawal rate and the cross-sectional area of the casting blank, according to the law of conservation of mass:

[0015] Q v =A×V c

[0016] Where V c is the withdrawal rate, m / min; A is the cross-sectional area of the casting blank, m 2 .

[0017] Further, the step S2 is specifically: obtaining the steel grade type, the withdrawal rate V c, the actual water gap depth D, according to the steel grade to retrieve the corresponding coefficient k, alpha, beta, real-time calculation of the optimal depth D opt :

[0018] D opt = argm D in

[0019] Drive the water gap lifting mechanism to dynamically adjust D to D opt , real-time output depth setting value D opt , directly guide the actuator action.

[0020] Compared with the prior art, the beneficial effects of the present application are:

[0021] 1) Through the quantitative physical relationship between the water gap insertion depth and the liquid level fluctuation to realize control. The optimal depth calculation module driven by the mechanism model, the high-precision water gap lifting and the stopper collaborative fine adjustment are constructed to realize the source inhibition and self-adaptive stabilization of the continuous casting tundish liquid level fluctuation;

[0022] 2) For the first time, the water gap depth is taken as the main control variable, and the fluctuation source, i.e. the turbulent energy distribution, is directly inhibited through the physical model;

[0023] 3) The anti-interference performance is improved, and when the pulling speed changes, the depth adjustment response speed is faster than the traditional liquid level;

[0024] 4) The precise and efficient inhibition of the molten steel liquid level fluctuation in the crystallizer is realized, the risk of slag entrapment is effectively reduced, the quality of the cast slab and the stability and reliability of the continuous casting production are significantly improved, the slag entrapment rate is reduced, the product quality is improved, and the production cost is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is the system structure schematic diagram of the present application.

[0026] Figure 2 is the water gap depth-wave height characteristic curve described in the present application.

[0027] Figure 3 is the flow chart of the method described in the present application.

[0028] Figure 4 is the comparison experiment graph of the embodiment of the present application. DETAILED DESCRIPTION

[0029] The specific embodiments of the present application will be further described below in combination with the drawings:

[0030] See Figure 1It is the system structure schematic diagram of the present application. The water surface fluctuation control method based on the water gap insertion depth, the system used includes displacement sensor, controller, water gap lifting mechanism, electromagnetic liquid level detector and invasive water gap, the signal line of the displacement sensor is connected to the analog quantity input output port of the controller, the digital quantity input output port of the controller is connected to the signal line of the water gap lifting mechanism, the communication port of the controller is connected to the electromagnetic liquid level detector, and the water gap lifting mechanism is connected to the invasive water gap.

[0031] The water surface fluctuation control method based on the water gap insertion depth, the water gap insertion depth and the quantitative physical relation of liquid surface fluctuation are used to realize control, the mechanism model driven optimal depth calculation, high-precision water gap lifting and stopper collaborative fine adjustment are constructed, and the source inhibition and adaptive stability of the liquid surface fluctuation in continuous casting tundish are realized. The core innovation points are as follows: 1) the display physical equation of the liquid surface fluctuation height and the water gap depth is established, the jet attenuation effect and the vortex dominant effect are established; 2) the water gap insertion depth D is converted into a direct control variable, the optimal depth is decided in real time by solving the minimum point of the model, and the traditional liquid level sensor feedback mechanism is replaced; 3) the master-slave control strategy is proposed, the stopper limiting fine adjustment is triggered when | residual fluctuation standard deviation | > 2mm, and the collaborative control of the water gap stopper is realized, as shown in Figure 3 , and specifically includes the following steps:

[0032] S1, a water gap insertion depth-critical wave height mapping model is constructed;

[0033] The jet attenuation term, according to fluid dynamics, when the molten steel is jetted out from the water gap at high speed, a submerged jet is formed, the turbulent kinetic energy E of the jet core area k Increases exponentially with the increase of insertion depth D; the liquid surface fluctuation energy is directly dependent on the residual kinetic energy of the jet reaching the liquid surface, so the wave height decreases exponentially with the increase of depth, and the deep water area is dominated;

[0034] The vortex effect term, when the water gap is inserted too shallowly, i.e. D < 100mm, the Taylor vortex is formed near the liquid surface by the molten steel flow, the low pressure area of the vortex core causes the liquid surface to be concave, and the surface vortex intensity increases in inverse proportion with the decrease of depth, and the shallow water area is dominated;

[0035] The two terms together cause the existence of a minimum wave height point, the critical depth D c ; the water gap depth-wave height characteristic curve is shown in Figure 2 ;

[0036] It is found that there is a critical depth D c between the liquid surface wave height H ω and the water gap insertion depth D, which makes the wave height minimum:

[0037] H ω = k·e -αD + β·Q v·D -1

[0038] where H ω is the wave height; D is the nozzle insertion depth; k, α, β are the steel grade characteristic coefficients, calibrated by experiments; Q v is the volume flow rate of the molten steel;

[0039] The steel grade characteristic coefficients are classified according to the steel grade, and the low-carbon steel: k = 12.5, α = 0.22, β = 0.028, the peritectic steel: k = 15.2, α = 0.25, β = 0.032, the high-strength steel: k = 18.3, α = 0.31, β = 0.035;

[0040] The molten steel flow rate Q v (m 3 / min) is determined by the withdrawal speed V c (m / min) and the cross-sectional area A (m 2 ) of the casting blank, and according to the law of conservation of mass:

[0041] Q v = A × V c

[0042] Because the density ρ steel of the molten steel is constant during the continuous casting process, the volume flow rate can be directly used for model calculation;

[0043] When D < D c , the vortex effect is dominant, and deepening the nozzle can significantly reduce the wave height; when D > D c , the jet decay effect is saturated, and because the disturbance of the molten steel backflow is enhanced, the wave height is slightly increased by over-deepening.

[0044] S2, depth-driven closed-loop control logic;

[0045] Obtain the steel grade type, the withdrawal speed V c , the actual nozzle depth D, retrieve the corresponding coefficients k, α, β according to the steel grade, and calculate the optimal depth D opt in real time:

[0046] D opt = argm D in

[0047] The formula means: find the depth parameter D that makes the function H ω = ke -αD + βQ v D -1 take the minimum value;

[0048] The formula converts the fluid mechanics mechanism into a calculable optimization problem, drives the nozzle lifting mechanism to dynamically adjust D to D opt , and outputs the depth setting value D in real timeopt directly instructs the actuator to act;

[0049] When D is less than 50mm, the vortex effect dominates, and the wave height increases; when D is greater than 150mm, the jet decay saturates, the wave height rises, and there is only one "wave valley point" D opt .

[0050] S3, a coordinated stopper micro compensation mechanism;

[0051] When | residual fluctuation standard deviation | > 2mm, trigger the stopper limit adjustment ±80mm, realize the coordinated control of the stopper, that is, when the depth of the water gap reaches D opt After that, use low gain PID control stopper opening to compensate for the remaining small fluctuations.

[0052] The following examples are implemented on the premise of the technical scheme of the application, and detailed implementation modes and specific operation processes are given, but the protection scope of the application is not limited to the following examples. The methods used in the following examples are all conventional methods unless otherwise specified.

[0053] Example:

[0054] The application is a liquid level fluctuation control method based on the depth of the water gap, which is theoretically based on the turbulent energy dissipation free surface wave theory of fluid dynamics, and is specifically constructed through two physical processes of jet decay law and surface vortex generation mechanism. The implementation steps are as follows:

[0055] S1, constructing a water gap insertion depth-critical wave height mapping model;

[0056] H ω =k·e -αD +β·Q v ·D -1

[0057] Wherein, k, alpha, beta are steel grade characteristic coefficients, k represents the initial turbulent intensity of jet, alpha represents the turbulent kinetic energy decay rate, beta represents the surface vortex generation efficiency, which is calibrated by experiment; Q v is the volume flow rate of molten steel;

[0058] The steel grade characteristic coefficients are classified according to the steel grade, and the low carbon steel: k=12.5, alpha=0.22, beta=0.028, the peritectic steel: k=15.2, alpha=0.25, beta=0.032, the high strength steel: k=18.3, alpha=0.31, beta=0.035;

[0059] The first term k·e -αD describes the exponential decay of jet impact energy with increasing depth (dominant in deep water area);

[0060] The second term beta·Q v·D -1 , the reaction surface vortex intensity is inversely proportional to the decrease of depth (dominant shallow water area);

[0061] There is a critical depth D c , two common causes lead to the existence of the minimum wave height, see the table, the minimum wave height is 4.0mm;

[0062] Experimental verification:

[0063] Shroud depth D (mm) Observed wave height H ω (mm) Model calculated H ω (mm) 80 8.5 8.7 100 5.2 5.1 120 4.3 4.0 150 5.8 5.6

[0064] The molten steel flow Q v (m 3 / min) is determined by the pulling speed V c (m / min) and the cross-sectional area A (m 2 ) of the billet, according to the law of conservation of mass:

[0065] Q v =A×V c

[0066] S2, depth-driven closed-loop control logic;

[0067] The steel type is obtained from the production planning system, the pulling speed V c is obtained from the caster PLC in real time, and the actual nozzle depth D is read from the database. According to the steel type, the corresponding coefficients k, α, β are called, and the optimal depth D opt is calculated in real time:

[0068]

[0069] The formula converts the fluid mechanics mechanism into a calculable optimization problem, drives the nozzle lifting mechanism to dynamically adjust D to D opt , and outputs the depth setting value D opt in real time, directly guiding the actuator action.

[0070] S3, collaborative stopper micro compensation mechanism;

[0071] When the residual fluctuation standard deviation is greater than 2mm, the stopper limit adjustment ±80mm is triggered, realizing the collaborative control of the nozzle stopper, that is, when the nozzle depth reaches D opt , the low gain PID control is used to control the stopper opening, and the remaining small fluctuation is compensated.

[0072] A certain steel plant 6# slab caster, section 1530mm×230mm, steel grade Q235B;

[0073] Model coefficients: k=15.2, α=0.25mm -1 , β=0.032mm·s / L;

[0074] The water gap depth adjustment range is 80-150 mm; the drawing speed change range is 1.0 m / min-1.2 m / min;

[0075] The implementation process is as follows:

[0076] 1. Flow calculation

[0077] A=WxT=1.53 m x 0.23 m=0.3519 m 2

[0078] Before the speed increases: Q v1 =AxC v1 =0.3519 x 1.0=0.3519 m 3 / min

[0079] After the speed increases: Q v2 =AxC v2 =0.3519 x 1.2=0.4223 m 3 / min

[0080] 2. Optimal depth dynamic calculation;

[0081] Drawing speed: V c =1.0 m / min

[0082]

[0083] Drawing speed: V c =1.2 m / min

[0084]

[0085] 3. Water gap depth execution (drawing speed 1.0-1.2 m / min)

[0086]

[0087]

[0088] 4. Stopper coordination fine adjustment;

[0089] When the laser range finder detects that the fluctuation standard deviation σ>2 mm, trigger the stopper coordination fine adjustment;

[0090] The execution record is as follows:

[0091]

[0092] See Figure 4Compared with the traditional PID control method, the stable fluctuation is ±2.6 mm, the maximum fluctuation when the drawing speed changes is ±4.8 mm, and the adjustment time is 12.4 s; after the control method is used, the stable fluctuation is ±1.4 mm, the maximum fluctuation when the drawing speed changes is ±2.3 mm, and the adjustment time is 6.8 s.

Claims

1. A liquid level fluctuation control method based on a nozzle insertion depth, characterized by, Comprising the following steps: S1, constructing a water gap insertion depth-critical wave height mapping model; S2, converting the water gap insertion depth into a direct control variable, and deciding the optimal depth in real time by solving the minimum point of the model; S3, triggering the stopper limit adjustment ±80mm when |residual fluctuation standard deviation|>2mm, realizing the collaborative control of the water gap stopper.

2. The liquid level fluctuation control method based on the depth of the nozzle insertion according to claim 1, wherein The water gap insertion depth-critical wave height mapping model is a jet decay term and a vortex effect term jointly acting, resulting in the existence of a minimum wave height point, a critical depth D c , a liquid surface wave height H ω , and a water gap insertion depth D c Minimize the wave height: H ω = k e -αD + β Q v · D -1 where H ω is the liquid level wave height; D is the water gap insertion depth; k, a, b are steel type characteristic coefficients, calibrated by experiments; Q v is the molten steel volume flow rate.

3. The liquid level fluctuation control method based on the depth of the nozzle insertion according to claim 2, wherein The steel type characteristic coefficient is classified according to the steel type, and the low-carbon steel is k=12.5, alpha=0.22, beta=0.028, the peritectic steel is k=15.2, alpha=0.25, beta=0.032, and the high-strength steel is k=18.3, alpha=0.31, beta=0.

035.

4. The liquid level fluctuation control method based on the depth of the nozzle insertion according to claim 2, wherein The molten steel volume flow rate is determined by the withdrawal rate and the cross-sectional area of the casting blank, and according to the law of conservation of mass: Q v = A x V c wherein V c is the casting speed, m / min; A is the cross-sectional area of the strand, m 2 .

5. The liquid level fluctuation control method based on the depth of the nozzle insertion according to claim 3, wherein The step S2 is specifically: acquiring the steel type, the pulling speed V c , the actual nozzle depth D, calling the corresponding coefficients k, a, b according to the steel type, and calculating the optimal depth D opt in real time: D opt = argm D in Drive the nozzle lifting mechanism to dynamically adjust D to D opt , output the depth setting value D in real time opt , directly guide the actuator to act.

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