A three-dimensional dynamic cooling water control method and system for the secondary cooling of a large round billet

Abstract

The present application relates to a kind of extra round billet secondary cooling water three-dimensional dynamic cold line control method and system, belong to steel metallurgy continuous casting process control field, to solve the problem that before straightening, extra round billet is easily into third brittle temperature interval, cause straightening crack, internal quality is not good etc..The present application adds independent spraying cooling section in the arc air cooling section before casting blank enters straightening machine, using three-dimensional transient temperature field solution model as the core of three-dimensional dynamic secondary cooling control model, integrates feedforward, feedback, adaptive composite control architecture, realizes whole process water amount decoupling and dynamic distribution, the surface temperature of casting blank before straightening is stably controlled at 600 ℃~700 ℃, completely avoids third brittle temperature interval.The present application can greatly reduce straightening crack rate, improve casting blank internal quality and equipment life, and the transformation cost is low, adaptability is strong, with significant industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of continuous casting process control in iron and steel metallurgy, and is particularly applicable to the continuous casting production of extra-large round billets with a nominal diameter ≥600mm and high crack sensitivity. It relates to a three-dimensional dynamic cooling control method and system for extra-large round billets with secondary cooling water. Background Technology

[0002] Extra-large round billets (nominal diameter ≥ 600 mm) are core raw materials for high-end equipment manufacturing such as seamless steel pipes, large forgings, wind turbine main shafts, and heavy gears. As the equipment manufacturing industry develops towards larger scale and higher performance, market demand for high-quality extra-large round billets made of high-carbon steel and alloy structural steel continues to rise. However, frequent straightening cracks during the continuous casting process of extra-large round billets lead to high scrap rates and limited production efficiency, becoming a common technical bottleneck restricting the development and large-scale production of high-end round billet products.

[0003] From a metallurgical perspective, steel exhibits a significant third brittle temperature range between 700℃ and 900℃. Within this range, a thin film of proeutectoid ferrite precipitates at austenite grain boundaries, causing a sharp decrease in grain boundary strength. Tensile stress during straightening concentrates strain at the grain boundaries, inducing intergranular cracks that propagate inward. Extra-large round billets, due to their large cross-sectional dimensions and high thermal inertia, experience significant internal and external temperature differences and uneven circumferential temperature distribution before straightening, further exacerbating stress concentration during straightening and significantly increasing the risk of crack formation.

[0004] Currently, the industry commonly employs a thermal control approach to address the cracking problem in extra-large round billets during straightening. This involves using processes such as weak cooling and heat preservation to maintain the surface temperature of the billet above 900℃ before straightening, attempting to passively avoid the third brittle temperature range. However, this approach has several inherent drawbacks: (1) Low temperature control precision and poor process stability: The temperature control deviation before billet straightening is large, and the casting speed is prone to accidentally falling into the brittle temperature range when the casting speed fluctuates, and the crack prevention effect lacks certainty. (2) Deterioration of the internal quality of the billet: The weak cooling throughout the process leads to excessively high temperature in the center of the billet and excessive temperature difference between the inside and outside, which can easily cause internal defects such as central porosity, shrinkage cavities, and segregation, and cannot meet the requirements for flaw detection and use of high-end products. (3) Uneven circumferential temperature causes shape defects: Differentiated cooling was not implemented for the structural characteristics of slow heat dissipation in the inner arc and fast heat dissipation in the outer arc of the extra-large round billet. The large circumferential temperature difference of the billet easily causes warping deformation, which affects the shape accuracy of the billet. (4) Increased equipment wear and production costs: High-temperature straightening causes excessive heat load on the straightening rollers, which exacerbates equipment wear and shortens service life; the heat preservation device increases equipment investment and maintenance costs, and the high-temperature residence time of the billet is long, resulting in a large amount of iron oxide scale that adheres firmly, significantly increasing subsequent cleaning costs. (5) Insufficient production flexibility and adaptability: Process parameters rely on manual experience to set, which cannot adapt to the flexible production needs of multiple steel types, variable drawing speed, and large specifications. The debugging cycle for new steel types and new specifications is long. (6) The control mode has inherent shortcomings: it only adopts feedback regulation, which has significant control lag and temperature is prone to runaway when the pulling speed changes abruptly; it does not realize asymmetric cooling in the spatial dimension and dynamic feedforward control in the time dimension, and cannot actively and accurately regulate the temperature before straightening.

[0005] For a long time, thermal control has been the inherent technical approach for solving straightening crack problems in this field, and research and development have always been limited to "increasing the temperature of the billet before straightening," forming a solidified technological inertia. Crack prevention under this approach is probabilistic and cannot definitively eliminate straightening cracks at their root. At the same time, the associated problems caused by thermal control, such as decreased internal quality of the billet, shortened equipment life, and increased production energy consumption, have not been effectively solved. The technical approach of "actively reducing the billet temperature below the third brittle temperature range" has never been included in the key research scope due to industry concerns about internal cracks caused by overcooling and increased straightening force, becoming a core barrier to technological breakthroughs.

[0006] To address the shortcomings of existing technologies and limitations in industry understanding, this invention aims to solve the following key technical problems: fundamentally eliminate straightening cracks at the metallurgical mechanism level, abandoning probabilistic control and eliminating the basic conditions for crack formation; achieve precise, dynamic, and closed-loop control of the temperature before straightening of extra-large round billets, adapting to actual production conditions of variable casting speed, multiple steel grades, and large diameters; achieve high-efficiency compatibility of the control method with existing continuous casting equipment under the premise of low cost and low modification intensity; and simultaneously consider comprehensive benefits from multiple dimensions, including billet internal quality, circumferential temperature uniformity, equipment service life, production energy consumption, and cost, while eliminating straightening cracks. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a three-dimensional dynamic cooling control method for the secondary cooling water in continuous casting of extra-large round billets. By subverting the traditional hot cooling control paradigm and adopting a cold cooling control approach, and combining three-dimensional dynamic secondary cooling control with precise spraying before straightening, the surface temperature of extra-large round billets before straightening is precisely controlled at 600℃~700℃, completely eliminating straightening cracks from the metallurgical root cause. At the same time, it improves the internal quality of the billet and the circumferential temperature uniformity, adapts to existing continuous casting equipment at low cost, and fundamentally solves the common industry bottleneck of high incidence of straightening cracks in continuous casting of extra-large round billets.

[0008] To achieve the above objectives, this invention provides a three-dimensional dynamic cooling control method for the secondary cooling system of an extra-large round billet continuous casting machine. The method is applied to the secondary cooling system of an extra-large round billet continuous casting machine. The secondary cooling system, along the billet straightening direction, sequentially includes a crystallizer, a foot roller zone, multiple arc-shaped cooling zones, a straightener, and a subsequent air cooling section. The method comprises the following steps: Step 1: Set up an independent spray cooling section in the arc-shaped air cooling section before the billet enters the straightening machine; Step 2: A three-dimensional dynamic secondary cooling control model is adopted, with the three-dimensional transient numerical model of solidification heat transfer of the billet as the core. The steel composition, nominal diameter of the billet, casting speed, casting temperature, measured temperature of each cooling zone, and measured pressure / flow rate of each cooling zone are used as input parameters to calculate and output the instantaneous target water volume of each secondary cooling zone and the independent spray cooling zone. The three-dimensional dynamic secondary cooling control model adopts a composite control architecture that integrates feedforward control, feedback control and adaptive control. Step 3: The flow regulating valves of each cooling zone are controlled in a closed loop by the PLC system. The water volume of all secondary cooling zones is precisely decoupled and dynamically distributed to keep the surface temperature of the billet before straightening at 600℃~700℃, avoiding the third brittle temperature range.

[0009] Optionally, the length of the independent spray cooling section is set according to the nominal diameter of the billet: the length L of the spray section and the nominal diameter D of the billet satisfy: L=k·D, where k=0.005~0.008.

[0010] Preferably, when the nominal diameter of the billet is ≥600mm, the length of the independent spray cooling section is 3~5m; when the nominal diameter of the billet is ≥800mm, the length of the independent spray cooling section is 4~6m; the independent spray cooling section is uniformly arranged with several sets of atomizing nozzles along the circumference of the billet, and the nozzles on the inner arc side and the outer arc side are independently controlled in separate zones. The water volume on the inner arc side is set to 1.2~2.5 times that on the outer arc side, so as to achieve asymmetric circumferential cooling of the billet.

[0011] Optionally, the three-dimensional dynamic secondary cooling control model is established using the finite difference method or the finite element method to solve the three-dimensional transient temperature field of the billet length, width, and radial direction. The boundary conditions of the three-dimensional transient temperature field solution model include: the cooling heat flux density of the crystallizer, the convective heat transfer coefficients of each secondary cooling zone related to water flow / pressure / billet surface temperature and nozzle type, radiative heat dissipation, and the forced convective heat transfer boundary of the spray section before straightening. The convective heat transfer coefficient h is related to the water flow rate Q and the billet surface temperature T. s satisfy: h = a·Q^b·exp(-c·T) s ) In the formula, a, b, and c are empirical coefficients related to nozzle type, calibrated through offline spraying experiments; the core of the three-dimensional dynamic secondary cooling control model is embedded with a database of high-temperature thermophysical parameters of steel grades and the logic for determining the third brittle temperature range.

[0012] Optionally, the three-dimensional dynamic secondary cooling control model is a composite control architecture integrating feedforward control, feedback control, and adaptive control: feedforward control pre-calculates the reference water volume for each zone based on the target casting speed and target casting temperature; feedback control corrects water volume deviation in real time based on infrared temperature measurement before straightening and outlet temperature measurement of each zone; adaptive control optimizes the heat transfer coefficient and model parameters online based on historical production data to achieve self-learning; the dynamic water volume algorithm includes constraint condition verification to ensure that the water volume does not exceed the threshold range, the temperature drop rate does not exceed the limit, and the overcooling alarm is not triggered.

[0013] Optionally, the adaptive control is based on the production data of the most recent N furnaces, and uses the recursive least squares method to correct the heat transfer coefficient of each cooling zone online, with a correction cycle of ≤1 furnace.

[0014] Optionally, the target temperature range of the billet before straightening can be set to 650℃~700℃; for high crack-sensitive steel grades, the target temperature range of the billet before straightening can be set to 600℃~650℃, and the water volume of each cooling section can be automatically adapted by the three-dimensional dynamic secondary cooling control model.

[0015] Optionally, the billet in the independent spray cooling section is sprayed using an air-water atomization cooling method. The atomizing gas pressure is set to 0.1~0.4MPa, the air-water ratio is set to 3:1~6:1, and the nozzle outlet pressure is set to 0.1~0.7MPa. The spray angle on the inner arc side is controlled to 30°~50°, the spray angle on the outer arc side is controlled to 40°~60°, and the nozzle density on the inner arc side is controlled to be 1.2~1.5 times that on the outer arc side.

[0016] Optionally, multiple sets of infrared thermometers are arranged circumferentially between the outlet of the pre-straightening spray section and the inlet of the straightening machine, with the inner and outer arcs symmetrically distributed; the detection frequency of the infrared thermometers is set to ≥2Hz and the detection accuracy is set to ±5℃; the temperature measurement data is input in real time into the three-dimensional dynamic secondary cooling control model as a feedback correction benchmark.

[0017] This invention also provides a three-dimensional dynamic cooling control system for continuous casting of extra-large round billets with secondary cooling water, characterized in that it includes: An independent spray cooling section is set in the arc-shaped air cooling section before the billet enters the straightening machine, and is equipped with atomizing nozzles arranged circumferentially and with independent zone control of the inner and outer arcs. The three-dimensional dynamic secondary cooling control model, with the three-dimensional transient numerical model of solidification heat transfer of billet as the core, is used to calculate the instantaneous target water volume of each secondary cooling section and independent spray cooling section. The PLC control system, which embeds the three-dimensional dynamic secondary cooling control model, is electrically connected to the flow regulating valves, pressure detection units, infrared temperature measurement units, casting speed detection units, and casting temperature detection units of each cooling zone. It realizes the fully automated closed-loop control of data acquisition, model calculation, water distribution, and valve position adjustment, and controls the surface temperature of the billet before straightening at 600℃~700℃.

[0018] Optionally, the inner and outer arc sides of the independent spray cooling section are respectively equipped with independent flow regulating valves and pressure detection units, and the length of the spray section and the nozzle parameters are matched with the nominal diameter of the billet.

[0019] Optionally, the PLC control system is also connected to an alarm device, which triggers an alarm and performs protective adjustments when the billet temperature is lower than a set threshold, the detection unit fails, or the actuator malfunctions.

[0020] The beneficial effects of this invention are as follows: 1. This invention precisely controls the surface temperature of the billet before straightening to 600℃~700℃, completely avoiding the third brittle temperature range. Cracks lose their metallurgical basis, and the incidence rate is reduced from 3%~8% in traditional methods to below 0.2%; the reduction is ≥95%, and the control is stable and unaffected by casting speed fluctuations.

[0021] 2. This invention uses pre-straightening forced cooling to shrink the surface of the billet and mechanically compress the central liquid phase; the liquid phase fills the dendrite gaps, reducing the central porosity rating from 2.0~2.5 to ≤1.0; V-shaped segregation and central shrinkage cavity are improved simultaneously, meeting the flaw detection requirements of high-end forgings and significantly improving the internal density of the billet.

[0022] 3. This invention adopts an asymmetrical cooling method with inner and outer arcs. The enhanced cooling on the inner arc side offsets the natural disadvantage of slow heat dissipation of the inner arc of the extra-large round billet. The temperature difference between the inner and outer arcs is controlled from the traditional 80℃~100℃ to ≤30℃, which precisely balances the circumferential temperature distribution of the billet, eliminates the warping deformation of the billet, and makes the straightening stress evenly distributed.

[0023] 4. This invention enables stable continuous casting of highly crack-sensitive steel grades and large-diameter extra-large round billets, breaking through the limitations of traditional processes and broadening the product range. For φ800mm 45# steel: the traditional crack rate is >5%, while that of this invention is ≤0.2%; for φ700mm 40Cr: the traditional crack rate is 6%~8%, while that of this invention is ≤0.15%.

[0024] 5. This invention achieves fully automated closed-loop control through a three-dimensional dynamic model, replacing manual water allocation based on experience. The commissioning cycle for new steel grades is reduced from 3 months to 1 week. Furthermore, the self-learning function of the fully automated closed-loop control in this invention improves production management accuracy as production batches increase.

[0025] 6. This invention requires no modification to existing continuous casting equipment, only the addition of a pre-straightening spray section and an upgrade to PLC control software; it requires no alteration to the secondary cooling main structure, nor changes to the crystallizer, arc section, or straightener; the single-flow modification cost is ≤300,000 RMB, and the investment payback period is <3 months; it is compatible with all arc-shaped continuous casting machines, and can be quickly deployed on both new and old production lines with only simple installation and software upgrades required. It has low modification costs, strong adaptability, and good industrial applicability.

[0026] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 A simplified flowchart of a three-dimensional dynamic cooling control method for a large round billet under secondary cooling water provided by the present invention; Figure 2 The detailed step diagram of step 3 of the three-dimensional dynamic cooling control method for a large round billet under secondary cooling water provided by the present invention is shown below; Figure 3 The architecture diagram of the three-dimensional dynamic secondary cooling control model provided by the present invention; Figure 4 This is a bar chart comparing the crack rate of the present invention with that of traditional methods. Figure 5 This invention provides a comparison of the internal porosity rating of the cast billet using the present invention and traditional methods. Figure 6 This is a comparison curve of the circumferential temperature difference between the present invention and the traditional method. Detailed Implementation

[0028] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0029] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0030] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0031] This invention addresses a common industry-wide technical problem in the continuous casting of extra-large round billets: the billets easily enter the third brittle temperature range before straightening, leading to straightening cracks. By adding an independent spray cooling section to the arc-shaped air-cooling section before the billet enters the straightener, and combining a three-dimensional dynamic secondary cooling control model with PLC automated closed-loop control, precise decoupling and dynamic distribution of water volume throughout the secondary cooling section are achieved. This stabilizes the billet surface temperature at 600℃~700℃ before straightening, completely avoiding the third brittle temperature range. This eliminates the conditions for straightening crack formation from a metallurgical perspective, while simultaneously optimizing the internal quality of the billet, improving equipment lifespan, and enhancing production economy. Please refer to [link to relevant documentation]. Figures 1-6 The following is a detailed explanation.

[0032] This invention provides a three-dimensional dynamic cooling control method for the secondary cooling system of an extra-large round billet continuous casting machine. The method is applied to the secondary cooling system of an extra-large round billet continuous casting machine. The secondary cooling system, along the billet straightening direction, sequentially includes a crystallizer, a foot roller zone, multiple arc-shaped cooling zones, a straightener, and a subsequent air cooling section. The specific implementation method is as follows: Step 1: Set up an independent spray cooling section in the arc-shaped air cooling section before the billet enters the straightening machine.

[0033] The length of the independent spray cooling section is set according to the nominal diameter of the billet, and the length L of the spray section and the nominal diameter D of the billet satisfy: L = k·D, where k = 0.005~0.008. Preferably, when the nominal diameter of the billet is ≥600mm, the length of the independent spray cooling section is 3~5m, and when the nominal diameter of the billet is ≥800mm, the length of the independent spray cooling section is 4~6m. The independent spray cooling section is uniformly arranged with 8~16 sets of atomizing nozzles along the circumference of the billet. The nozzles on the inner arc side and the outer arc side are independently controlled. Preferably, the water volume on the inner arc side is set to 1.2~2.5 times that on the outer arc side, so as to achieve asymmetrical circumferential cooling of the billet, compensate for the inherent characteristic of slow heat dissipation of the inner arc of extra-large round billets, and ensure uniform circumferential temperature of the billet.

[0034] Furthermore, the billet in the independent spray cooling section is cooled by air-water atomization. The atomizing gas pressure is set to 0.1~0.4MPa, the air-water ratio is set to 3:1~6:1, and the nozzle outlet pressure is set to 0.1~0.7MPa. At the same time, the spray angle on the inner arc side is controlled to 30°~50°, the spray angle on the outer arc side is controlled to 40°~60°, and the nozzle density on the inner arc side is controlled to be 1.2~1.5 times that on the outer arc side, thereby improving the cooling accuracy and heat exchange efficiency.

[0035] Step 2: A three-dimensional dynamic secondary cooling control model is adopted, with the three-dimensional transient numerical model of solidification heat transfer of the billet as the core. The steel composition, nominal diameter of the billet, casting speed, casting temperature, measured temperature of each cooling zone, and measured pressure / flow rate of each cooling zone are used as input parameters of the three-dimensional dynamic secondary cooling control model. After real-time calculation by the model, the instantaneous target water volume of each secondary cooling zone and independent spray cooling zone is output.

[0036] Optionally, the three-dimensional dynamic secondary cooling control model employs the finite difference method or the finite element method to establish a three-dimensional transient temperature field solution model for the length, width, and radial direction of the billet. The boundary conditions of the three-dimensional transient temperature field solution model include the cooling heat flux density of the crystallizer, the convective heat transfer coefficients of each secondary cooling zone related to water flow / pressure / billet surface temperature, radiative heat dissipation, and the forced convective heat transfer boundary of the spray section before straightening. The convective heat transfer coefficient h satisfies the following relationship with the water flow rate Q and the billet surface temperature Ts: h = a·Q^b·exp(-c·Ts). a, b, and c are empirical coefficients related to nozzle type, calibrated through offline spray experiments. Furthermore, the core of the three-dimensional dynamic secondary cooling control model embeds a database of high-temperature thermophysical parameters for steel grades and logic for determining the third brittle temperature range, providing accurate data and logical support for water volume calculation.

[0037] Furthermore, the three-dimensional dynamic secondary cooling control model is a composite control architecture integrating feedforward control, feedback control, and adaptive control. Feedforward control pre-calculates the reference water volume for each zone based on the target casting speed and target casting temperature, achieving proactive water volume regulation. Feedback control corrects water volume deviations in real time based on infrared temperature measurement before straightening and outlet temperature measurement of each zone, ensuring temperature control accuracy. Adaptive control optimizes the heat transfer coefficient and model parameters online based on historical production data, achieving model self-learning and continuously improving control stability and accuracy. Preferably, the adaptive control uses recursive least squares method to correct the heat transfer coefficient of each cooling zone online based on the production data of the most recent N furnaces, with a correction cycle ≤ 1 furnace.

[0038] Furthermore, the target temperature range for the billet before straightening is conventionally set to 650℃~700℃. For steels with high crack sensitivity, the target temperature range for the billet before straightening is lowered to 600℃~650℃. The three-dimensional dynamic secondary cooling control model automatically adapts the water volume of each cooling section to suit the high-temperature plasticity characteristics of different steels.

[0039] Preferably, 6 to 10 sets of infrared thermometers are arranged circumferentially between the outlet of the pre-straightening spray section and the inlet of the straightening machine, with the inner and outer arcs symmetrically distributed; the detection frequency of the infrared thermometers is set to ≥2Hz and the detection accuracy is set to ±5℃, and the temperature measurement data is input in real time into the three-dimensional dynamic secondary cooling control model as a feedback correction benchmark to realize real-time closed-loop control of the surface temperature of the billet.

[0040] Step 3: The flow regulating valves of each cooling zone are controlled in a closed loop by the PLC system. The water volume of all secondary cooling zones is precisely decoupled and dynamically distributed, so that the surface temperature of the billet before entering the straightening zone is stably controlled at 600℃~700℃, completely avoiding the third brittle temperature range and eliminating straightening cracks from the root.

[0041] Furthermore, the closed-loop control and water allocation process described in step 3 is specifically executed according to the following steps S1 to S7: S1: System initialization, input the steel grade to be cast, nominal diameter of the billet, target casting speed and casting temperature, the three-dimensional dynamic secondary cooling control model loads the high-temperature thermophysical parameters and historical optimization parameters of the corresponding steel grade, pre-calculates the initial water volume of each cooling section and the independent spray cooling section and writes it into the PLC system; S2: Casting start-up and conventional cooling control. After the billet exits the crystallizer, it enters the foot roller area and each arc section cooling area in sequence. The PLC system controls the flow regulating valve of each area according to the initial water volume pre-calculated by the model. The outlet temperature measurement data of each area is fed back to the model in real time and closed-loop correction is performed. S3: Activation and cold running control of the pre-straightening spray section. When the billet head reaches the inlet of the independent spray cooling section, the model activates the partition control of the inner arc side and outer arc side of the section. The target temperature before straightening is 650℃~700℃. For steels with high crack sensitivity, the target temperature is adjusted to 600℃~650℃. The water volume on the inner arc side is executed according to the model calculation value. If necessary, it can reach 1.5~2.5 times the water volume on the outer arc side. S4: Closed-loop temperature fine-tuning before straightening. A circumferential infrared thermometer collects the surface temperature of the billet at a frequency of ≥2Hz. When the deviation between the measured temperature and the target temperature is greater than 10℃, the model prioritizes adjusting the water volume of the independent spray cooling section. When the deviation is greater than 20℃ and adjusting the independent spray cooling section is ineffective, the cooling water volume of the upstream arc section is gradually adjusted back. When the temperature difference between the inner and outer arcs is greater than 30℃, the water volume of the inner and outer arc zones of the independent spray cooling section is adjusted differentially. S5: Pulling speed linkage and dynamic adaptation, the pulling speed change signal is input into the model in real time, the model recalculates the water distribution of the whole process and performs feedforward adjustment, the water volume of the independent spray cooling section is positively correlated with the pulling speed after model optimization; S6: Heat preservation in the straightening section and weak cooling after straightening. When the billet enters the straightening machine, the cooling water in the straightening section is automatically shut off and the heat preservation cover is opened. After the billet is straightened, it enters the subsequent air cooling section. The subsequent air cooling section adopts a weak cooling mode. The water volume is 20%~40% of that in the independent spray cooling section, and the temperature drop rate does not exceed 5℃ / min. S7: Abnormal handling. When the temperature before straightening is detected to be below 600℃ (below 550℃ for high crack-sensitive steel), the system will alarm and automatically shut off 50%~80% of the water flow in the independent spray cooling section. When nozzle blockage, abnormal pressure, or temperature measurement failure is detected, the system will alarm and switch to the backup circuit. The model will continue to run until the casting is completed.

[0042] On the other hand, the present invention also provides a three-dimensional dynamic cooling control system for secondary cooling water in continuous casting of extra-large round billets, including an independent spray cooling section, a three-dimensional dynamic secondary cooling control model, and a PLC control system.

[0043] An independent spray cooling section is set in the arc-shaped air cooling section before the billet enters the straightening machine. It is equipped with atomizing nozzles arranged circumferentially and with independent zone control for the inner and outer arcs. Independent flow regulating valves and pressure detection units are respectively configured on the inner and outer arc sides. The length of the spray section and the nozzle parameters are matched with the nominal diameter of the billet.

[0044] The three-dimensional dynamic secondary cooling control model, based on the three-dimensional transient numerical model of solidification heat transfer in the billet, is used to calculate the instantaneous target water volume in each secondary cooling section and the independent spray cooling section. Specifically, the three-dimensional dynamic secondary cooling control model, based on the three-dimensional transient numerical model of solidification heat transfer in the billet, uses the finite difference method or the finite element method to establish the three-dimensional unsteady heat conduction equations for the length, width, and thickness (radial) of the billet:

[0045] Wherein, S is the latent heat source term for solidification, which is processed using the equivalent specific heat method or the enthalpy method; the model boundary conditions include the cooling heat flux density of the crystallizer, the convective heat transfer coefficient of each zone of the secondary cooling, the radiative heat dissipation, and the forced convective heat transfer boundary of the spray section before straightening; the relationship model between the convective heat transfer coefficient and the water volume, the surface temperature of the billet, and the nozzle type is embedded into the model after being calibrated through industrial experiments.

[0046] The input parameters of the model are divided into three categories: Static parameters: steel composition, liquidus temperature, solidus temperature, high-temperature thermophysical parameters (thermal conductivity, specific heat, density, latent heat); Dynamic parameters: current casting speed, casting temperature, measured water volume / pressure in each cooling zone, and temperature at each measuring point; Target parameter: Target temperature before straightening (set according to steel grade).

[0047] The model executes a dynamic water volume algorithm in each control cycle (≤1s): pre-calculates the reference water volume of each cooling zone based on the current casting speed, target casting temperature, and target pre-straightening temperature; adjusts the water volume of the added spray section and upstream zones according to the optimization algorithm based on the deviation between the measured temperature before straightening and the target temperature; and differentially adjusts the water volume of the added spray section in the inner and outer arc zones based on the measured temperature difference between the inner and outer arcs. At the same time, it performs constraint condition verification to ensure that the water volume does not exceed the threshold range, the temperature drop rate does not exceed the limit, and the overcooling alarm is not triggered.

[0048] The model has three types of adaptive capabilities: first, online correction of heat transfer coefficient, which identifies the actual heat transfer coefficient of each cooling zone based on historical production data, and the model is automatically optimized for each heat; second, expansion of the steel property library, which automatically generates recommended water distribution parameters for a new steel grade after 3 to 5 heats of production; and third, self-learning function, which continuously accumulates production data and improves control accuracy as the production frequency increases.

[0049] The PLC control system has an embedded three-dimensional dynamic secondary cooling control model, which is electrically connected to the flow regulating valves, pressure detection units, infrared temperature measurement units, casting speed detection units, and casting temperature detection units of each cooling zone. This enables fully automated closed-loop control of the entire process, including data acquisition, model calculation, water distribution, and valve position adjustment. The PLC control system is also connected to an alarm device. When the billet temperature is lower than the set threshold, the detection unit fails, or the actuator malfunctions, an alarm is triggered and protective adjustments are performed to ensure continuous and stable production.

[0050] It is worth noting that for older PLC systems lacking online 3D calculation capabilities, a lightweight model deployment approach can be adopted. Through offline training combined with lookup table interpolation, the calculation results of the 3D dynamic model can be pre-generated into a dynamic water distribution table, achieving quasi-dynamic control and adapting to the upgrading and transformation needs of older production lines. For extra-large round billets with a nominal diameter >900mm, the circumferential spray section before straightening can be divided into 4-6 independent control zones: inner arc left, inner arc middle, inner arc right, outer arc left, outer arc middle, and outer arc right, further improving the circumferential temperature uniformity of the billet. The 3D dynamic secondary cooling control model can be integrated into the factory's MES intelligent scheduling system, automatically pre-loading steel grades and billet specification parameters according to the production plan, achieving zero-wait switching between furnace cycles and improving the level of production intelligence. The core technologies of this invention—cold flow control, 3D dynamic model regulation, and enhanced cooling before straightening—can be extended to continuous casting straightening crack control for large-section square billets, rectangular billets, and irregular-shaped billets after adaptive structural and parameter modifications, with a wide range of applications.

[0051] This invention has been operating stably for over 18 months in actual industrial production on the No. 3 arc-shaped continuous casting machine (radius 16m, suitable for billet specifications φ600mm~φ1000mm) of a special steel plant, producing a total of 126,000 tons of extra-large round billets of high-carbon steel, alloy structural steel, and bearing steel series, including 45#, 40Cr, 42CrMo, GCr15, and Q345E. Actual production statistics show significant improvements in various indicators: the straightening crack rate decreased from 4.8% to 0.14%, a reduction of 97%; the proportion of internal porosity ≤1.0 grade increased from 32% to 96%, an increase of 200%; the proportion of circumferential temperature difference ≤30℃ increased from 5% to 91%; the average lifespan of the straightening rolls increased from 9.2 months to 13.8 months, an increase of 50%; and the water consumption per ton of steel decreased from 1.42m³ / h. 3 / t dropped to 1.18m 3 / t, reduced by 17%, iron oxide scale thickness reduced from 2.1mm to 1.4mm, a reduction of 33%, and the commissioning cycle for new steel grades shortened from 3-6 months to 5-10 days, significantly improving commissioning efficiency.

[0052] The technical solution of this invention is complete, clear, and repeatable. Equipment modification only requires the addition of an independent spray cooling section and an upgrade of the PLC control software. There is no need to modify the main equipment such as the crystallizer, arc section, and straightening machine. The modification cost is low, the construction period is short, and the adaptability is strong. The control method is stable in operation and easy to maintain. No special professional training is required to operate it. During the production process, the crack rate is greatly reduced, energy and water consumption are reduced, and the added value of the product is increased. The economic benefits are significant and the investment recovery period is short. This fully verifies the technical advancement, industrial reliability, outstanding industrial practicality, and promotional value of this invention.

[0053] Example 1: Continuous casting of extra-large round billets of φ800mm 45# steel This embodiment uses an arc-shaped continuous casting machine with a radius of 16m, a nominal billet diameter of φ800mm, and 45# steel with a carbon content of 0.45% and a manganese content of 1.6%, which is a high crack-sensitive steel. The target casting speed is set at 0.30m / min, and the target temperature range before billet straightening is 650℃~700℃.

[0054] The independent spray cooling section before straightening is 4.5m long, with 12 sets of atomizing nozzles evenly arranged along the circumference of the billet, 6 sets on the inner arc side and 6 sets on the outer arc side. The cooling method is air-water atomization, with an air-water ratio of 5:1, an atomizing gas pressure of 0.9MPa, and a nozzle outlet pressure of 1.2MPa. The spray angle on the inner arc side is 35°, and the spray angle on the outer arc side is 45°. The nozzle flow coefficient on the inner arc side is 1.4 times that on the outer arc side. Eight sets of infrared thermometers are arranged at the outlet of the spray section before straightening, 4 sets on the inner arc and 4 sets on the outer arc, symmetrically distributed to achieve comprehensive circumferential temperature detection.

[0055] The three-dimensional dynamic secondary cooling control model was meshed with 1m / unit in the length direction, 20 nodes in the radial direction, and 32 nodes in the circumferential direction. The model time step was 0.5s. The model was loaded with the high-temperature physical properties of 45# steel: liquidus temperature 1495℃, solidus temperature 1440℃, latent heat 270kJ / kg, and the target temperature in the model was set to 680℃.

[0056] During the casting process, the casting speed remained stable at 0.30 m / min from 0 to 30 minutes. The model output the reference water volume through feedforward control, and the billet temperature remained stable at 680℃±12℃ before straightening. At 30 minutes, the casting speed increased to 0.35 m / min, and the model completed the full-process water volume redistribution within two control cycles. The water volume of the inner arc in the independent spray cooling section was increased by 18%, and the water volume of the outer arc was increased by 9%, with the billet temperature fluctuation less than 15℃. At 45 minutes, the casting speed dropped to 0.28 m / min, and the model automatically reduced the water volume in each section, maintaining a stable billet temperature. The temperature difference between the inner and outer arcs did not exceed 25℃ throughout the entire production process, and the system had no abnormal alarms, achieving stable control without manual intervention.

[0057] According to the production statistics of 208 furnaces in this embodiment, the straightening crack rate of the billet is only 0.13%; the central porosity rating reaches 0.5~1.0, and the internal density is significantly improved; the iron oxide scale thickness is reduced by 32% compared with the traditional process, and the metal burning loss is reduced; the service life of the straightening roller is extended by 41%, and the equipment operation and maintenance cost is reduced; the water consumption per ton of steel is reduced by 16%, and the production energy consumption and water consumption are effectively optimized.

[0058] To further illustrate the technical effects of this embodiment, the following two comparative examples are provided in this embodiment: Comparative Example 1: Traditional Thermal Control Process The production conditions for this comparative example are the same as those for the example. φ800mm 45# steel is used. The secondary cooling system adopts the traditional weak cooling and arc-shaped heat insulation cover thermal control process. The target temperature of the billet before straightening is controlled at 900℃~950℃. No independent spray cooling section is set up, and no three-dimensional dynamic secondary cooling control model is used.

[0059] Production verification showed that the straightening crack rate of the billet under this process was 4.2%~6.5%, and the crack rate worsened further when the casting speed fluctuated; the central porosity rating was 2.0~2.5, indicating poor internal quality; the temperature difference between the inner and outer arcs reached 80℃~110℃, and some furnaces showed billet warping and deformation; the service life of the straightening rollers was only 8 months, far less than the 14 months of the present invention; the iron oxide scale was thick and firmly attached, requiring additional shot blasting cleaning, which increased production costs and process complexity.

[0060] Comparative Example 2 only adds a spray section and lacks a three-dimensional dynamic secondary cooling control model. The hardware configuration of this comparative example is exactly the same as that of Example 1, except that an independent spray cooling section is added to the arc-shaped air-cooling section before straightening. However, the secondary cooling water volume is still controlled by the traditional empirical formula, and the water volume of the independent spray cooling section is set to a fixed value manually. A three-dimensional dynamic secondary cooling control model is not installed.

[0061] During production, temperature control was acceptable when the casting speed was stable, but when the casting speed fluctuated, the billet temperature deviation exceeded 50°C, and the temperature control accuracy dropped significantly. Frequent overcooling alarms occurred on the inner arc side, requiring manual intervention by reducing the spray water volume. The billet straightening crack rate was 0.8%~1.5%, which, while better than traditional thermal control, was far inferior to the technical solution of this invention. This comparative example demonstrates that the independent spray cooling section is only the foundation for technical implementation; the three-dimensional dynamic secondary cooling control model is the core for achieving precise cooling control and realizing all technical effects.

[0062] Example 2: Continuous casting of extra-large round billets of φ700mm 40Cr alloy steel In this embodiment, the nominal diameter of the billet is φ700mm, and the steel used is 40Cr alloy steel with a carbon content of 0.40% and a chromium content of 1.0%. It belongs to the medium crack-sensitive steel. Because the brittle range of alloy steel is lowered, the target temperature range before straightening the billet is set to 600℃~650℃, and the target casting speed is 0.35m / min.

[0063] The length of the independent spray cooling section before straightening is set to 4.0m, with 10 sets of atomizing nozzles evenly arranged along the circumference of the billet; the atomizing gas pressure is set to 0.25MPa, the gas-to-water ratio is 4:1, and the nozzle outlet pressure is 0.5MPa; the spray angle on the inner arc side is 30°, and the spray angle on the outer arc side is 50°. The three-dimensional dynamic secondary cooling control model adjusts the target temperature to 630℃ based on the steel grade characteristics. During the control process, the water volume of the inner arc of the independent spray cooling section is set to 1.8 times that of the outer arc side. Through asymmetric cooling to balance the circumferential temperature, the billet temperature before straightening is stabilized at 615℃~645℃, and the temperature difference between the inner and outer arcs does not exceed 28℃.

[0064] The straightening crack rate of the billet produced in this embodiment is only 0.09%, and the center segregation index is ≤1.05, indicating excellent internal quality. This billet is used as a forging billet for wind turbine main shafts, and the non-destructive testing pass rate reaches 99.6%, which can meet the stringent requirements of high-end equipment manufacturing.

[0065] Example 3: Continuous casting of extra-large round billets with a diameter of 800mm and a diameter of 45# steel (equipped with a three-dimensional dynamic secondary cooling control model, eliminating asymmetric differential cooling process). 1. Test-equivalent reference conditions The experimental conditions in this embodiment are completely consistent with those in Embodiment 1: φ800 mm 45# steel extra-large round billets are used; the continuous casting speed is set to 0.30 m / min; the effective length of the independent spray cooling section is 4.5 m; and all process parameters related to air-water atomization and the operating conditions of the spray equipment are kept synchronized and unified. The same three-dimensional dynamic secondary cooling control model is used, along with a feedforward-feedback-adaptive composite control logic. During production, the target process temperature range before billet straightening is uniformly limited to 650–700 ℃, ensuring no deviation from the experimental baseline conditions in all dimensions.

[0066] This embodiment sets only a single variable for differentiation: canceling the independent control of cooling configuration of the inner and outer arc sides of the independent spray cooling section, uniformly adjusting the spray cooling water ratio of the inner and outer arc sides of the cooling section to a 1:1 equal symmetrical water supply, without applying any asymmetric differentiated cooling control measures, and keeping the other continuous casting process parameters and equipment operating status consistent with Embodiment 1, without any additional changes to the operating conditions.

[0067] 2. Synchronous benchmarking and testing results throughout the entire process Under the aforementioned unified benchmark conditions, only the cooling water volume was retained as a single variable with symmetrical distribution. Simultaneously, online monitoring of the billet temperature, verification of external deformation, and internal metallurgical quality physicochemical testing were conducted. Parallel comparisons were performed using the corresponding indicators from Example 1. The specific experimental results are as follows: (1) The temperature detection results of the cross section before straightening of the billet show that: under the working conditions of this embodiment, the actual temperature of the inner arc side of the billet is 695 ℃ and the actual temperature of the outer arc side is 620 ℃, and the actual temperature difference between the inner and outer arcs reaches 75 ℃; while under the same temperature measurement cross section, the temperature difference between the inner and outer arcs in Embodiment 1 of the present invention can be controlled within 25 ℃. The temperature field uniformity of this embodiment is significantly worse, and the problem of uneven heat dissipation in the circumferential direction is prominent.

[0068] (2) The dimensional tracking test of the billet shows that the billet body has obvious warping deformation due to the thermal stress caused by uneven heat dissipation in the circumferential direction. The measured warping deformation per unit length is in the range of 8 to 12 mm / m. The overall flatness of the billet has obvious deviation, and the billet forming regularity does not meet the requirements of conventional production.

[0069] (3) Batch flaw detection statistics show that the overall crack detection rate of the billet straightening area in this embodiment is 0.65% to 0.95%, which is significantly higher than the crack rate of 0.13% in Embodiment 1 of this invention; at the same time, shallow microcracks were detected in the outer arc side area of ​​the billet, and the actual microcrack detection rate was 12%, and the number of defects on the billet surface increased significantly.

[0070] (4) The metallographic rating results of the low magnification structure inside the billet show that the porosity rating of the center of the billet in this embodiment is 1.5 to 2.0, and the internal density is generally average; while in Example 1, the porosity of the center can be stably controlled at 1.0 or below. The internal metallurgical quality of this embodiment has not been effectively optimized and improved.

[0071] 3. Core conclusions of the benchmarking experiment Based on the parallel comparative test data above, we can draw the objective conclusion that, under the premise of using the three-dimensional dynamic secondary cooling control model in normal operation, simply canceling the asymmetric cooling control method for the inner and outer arcs cannot effectively improve the fundamental problem of uneven circumferential heat dissipation during the production of extra-large round billets. A series of quality problems will still occur during billet production, including large temperature differences between the inner and outer arcs, body warping and deformation, high straightening crack rate, and high internal porosity. Therefore, it is evident that under this process system, the asymmetric cooling control method and the three-dimensional dynamic secondary cooling control model need to be used in conjunction with each other; they are complementary and cannot be used separately or as replacements.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A three-dimensional dynamic cooling control method for secondary cooling water in continuous casting of extra-large round billets, applied to the secondary cooling system of an extra-large round billet continuous casting machine, wherein the secondary cooling system is sequentially arranged along the billet straightening direction as a crystallizer, a foot roller zone, multiple arc-shaped cooling zones, a straightener, and a subsequent air cooling section, characterized in that, Includes the following steps: Step 1: Set up an independent spray cooling section in the arc-shaped air cooling section before the billet enters the straightening machine; Step 2: A three-dimensional dynamic secondary cooling control model is adopted, with the three-dimensional transient numerical model of solidification heat transfer of the billet as the core. The steel composition, nominal diameter of the billet, casting speed, casting temperature, measured temperature of each cooling zone, and measured pressure / flow rate of each cooling zone are used as input parameters to calculate and output the instantaneous target water volume of each secondary cooling zone and the independent spray cooling zone. The three-dimensional dynamic secondary cooling control model adopts a composite control architecture that integrates feedforward control, feedback control and adaptive control. Step 3: The flow regulating valves of each cooling zone are controlled in a closed loop by the PLC system. The water volume of all secondary cooling zones is precisely decoupled and dynamically distributed to keep the surface temperature of the billet before straightening at 600℃~700℃, avoiding the third brittle temperature range.

2. The control method according to claim 1, characterized in that, The length of the independent spray cooling section is set according to the nominal diameter of the billet: the length L of the spray section and the nominal diameter D of the billet satisfy: L = k·D, where k = 0.005~0.008; The independent spray cooling section is uniformly arranged with several sets of atomizing nozzles along the circumference of the billet. The nozzles on the inner arc side and the outer arc side are independently controlled in separate zones. The water volume on the inner arc side is set to 1.2 to 2.5 times that on the outer arc side, so as to achieve asymmetric circumferential cooling of the billet.

3. The control method according to claim 1, characterized in that, The three-dimensional dynamic secondary cooling control model is established by using the finite difference method or the finite element method to solve the three-dimensional transient temperature field of the billet length, width and radial direction. The boundary conditions of the three-dimensional transient temperature field solution model include: the cooling heat flux density of the crystallizer, the convective heat transfer coefficient of each zone of the secondary cooling system related to water volume / pressure / slab surface temperature and nozzle type, radiative heat dissipation, and the forced convective heat transfer boundary of the spray section before straightening. Among them, the convective heat transfer coefficient h is related to the water volume Q and the surface temperature T of the billet. s satisfy: h= a·Q^b·exp(-c·T s ) In the formula, a, b, and c are empirical coefficients related to nozzle type, which are calibrated through offline spraying experiments; The core of the three-dimensional dynamic secondary cooling control model is embedded with a database of high-temperature thermophysical parameters of steel grades and a logic for determining the third brittle temperature range.

4. The control method according to claim 1, characterized in that, The three-dimensional dynamic secondary cooling control model is a composite control architecture that integrates feedforward control, feedback control and adaptive control: the feedforward control pre-calculates the reference water volume of each zone based on the target casting speed and target casting temperature; Feedback control is based on real-time correction of water volume deviations using infrared temperature measurement before straightening and outlet temperature measurement of each zone; Adaptive control optimizes heat transfer coefficients and model parameters online based on historical production data, achieving self-learning; The dynamic water volume algorithm includes constraint verification to ensure that the water volume does not exceed the threshold range, the temperature drop rate does not exceed the limit, and the overcooling alarm is not triggered.

5. The method according to claim 4, characterized in that, The adaptive control is based on the production data of the most recent N furnaces and uses the recursive least squares method to correct the heat transfer coefficient of each cooling zone online, with a correction cycle of ≤1 furnace.

6. The control method according to claim 1, characterized in that, The target temperature range before the billet enters the straightening process is set to 650℃~700℃; for steels with high crack sensitivity, the target temperature range before the billet enters the straightening process is set to 600℃~650℃, and the water volume of each cooling section is automatically adapted by the three-dimensional dynamic secondary cooling control model.

7. The control method according to claim 1, characterized in that, Multiple sets of infrared thermometers are arranged circumferentially between the outlet of the pre-straightening spray section and the inlet of the straightening machine, with the inner and outer arcs symmetrically distributed; the detection frequency of the infrared thermometers is set to ≥2Hz and the detection accuracy is set to ±5℃; the temperature measurement data is input in real time into the three-dimensional dynamic secondary cooling control model as a feedback correction benchmark.

8. A three-dimensional dynamic cooling control system for continuous casting of extra-large round billets, characterized in that, include: An independent spray cooling section is set in the arc-shaped air cooling section before the billet enters the straightening machine, and is equipped with atomizing nozzles arranged circumferentially and with independent zone control of the inner and outer arcs. The three-dimensional dynamic secondary cooling control model, with the three-dimensional transient numerical model of solidification heat transfer of billet as the core, is used to calculate the instantaneous target water volume of each secondary cooling section and independent spray cooling section. The PLC control system, which embeds the three-dimensional dynamic secondary cooling control model, is electrically connected to the flow regulating valves, pressure detection units, infrared temperature measurement units, casting speed detection units, and casting temperature detection units of each cooling zone. It realizes the fully automated closed-loop control of data acquisition, model calculation, water distribution, and valve position adjustment, and controls the surface temperature of the billet before straightening at 600℃~700℃.

9. The control system according to claim 8, characterized in that, The inner and outer arc sides of the independent spray cooling section are respectively equipped with independent flow regulating valves and pressure detection units, and the length of the spray section and the nozzle parameters are matched with the nominal diameter of the billet.

10. The control system according to claim 8, characterized in that, The PLC control system is also connected to an alarm device. When the billet temperature is lower than the set threshold, the detection unit fails, or the actuator is abnormal, an alarm is triggered and protective adjustments are performed.

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