Intermittent rolling billet heating method and system

Abstract

The invention relates to the field of billet heating, in particular to a billet heating method and system for intermittent rolling, and the method comprises the steps: calculating the residual heating time of a current billet to an outlet of a current furnace section, and the residual heating time of the current billet to an outlet of each downstream furnace section; further obtaining the residual heating time of the current steel billet in the current furnace section and the residual heating time of the current steel billet in each downstream furnace section; according to the remaining heating time of the current steel billet in the current furnace section and the target outlet temperature of the current furnace section, the hearth temperature needed by the current furnace section is calculated; according to the residual heating time of the steel billet at each downstream furnace section and the target outlet temperature of the corresponding furnace section, calculating the hearth temperature required by the corresponding furnace section when the current steel billet reaches each downstream furnace section; and heating the steel billet according to the calculated hearth temperature required by each furnace section in combination with a preset target heating curve. By adopting the method, the heating effect of the steel billet can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of steel billet heating, and more particularly to a method and system for heating steel billets during intermittent rolling. Background Art

[0002] In the steel production process, heating furnaces heat steel billets to the target temperature for rolling. On continuous rolling lines, the billet discharge rhythm is relatively uniform, easily matching the mill's rhythm. However, on intermittent rolling lines, due to mill pauses between batches, the time intervals between billets discharged from the heating furnace vary, resulting in a non-uniform discharge rhythm.

[0003] Most existing methods for heating billets for intermittent rolling are based on fixed heating curves or empirical formulas for furnace temperature control, which only considers the target discharge temperature and ignores the dynamic position of different billets in the furnace, the remaining residence time, and the changes in the discharge rhythm. When using this billet heating method, due to the large differences in the residence time of each billet in the furnace, it is easy to cause individual billets to be underheated or overheated. In addition, since the remaining heating time of the billet in each furnace section cannot be accurately predicted, the furnace temperature setting deviation is large. When the rolling rhythm is adjusted, it is difficult for the existing method to correct the heating strategy in time, resulting in poor rolling quality and reduced production efficiency.

[0004] In summary, the existing intermittent rolling billet heating method has technical problems such as uneven heating, insufficient control accuracy, and deterioration of rolling quality and low production efficiency when the rolling rhythm changes. Summary of the Invention

[0005] In order to solve the technical problems of uneven heating, insufficient control accuracy, deterioration of rolling quality and low production efficiency in the existing intermittent rolling billet heating method, the present invention provides solutions in the following aspects.

[0006] In a first aspect, the present invention provides a method for heating a steel billet during intermittent rolling, comprising: Calculate the remaining heating time from the current billet to the current furnace section outlet, as well as the remaining heating time from the current billet to the outlet of each downstream furnace section, and then obtain the remaining heating time of the current billet in the current furnace section and the remaining heating time of the current billet in each downstream furnace section; The required furnace temperature of the current furnace section is calculated based on the remaining heating time of the current billet in the current furnace section and the target outlet temperature of the current furnace section; the required furnace temperature of each downstream furnace section when the current billet arrives at the corresponding furnace section is calculated based on the remaining heating time of the billet in each downstream furnace section and the target outlet temperature of the corresponding furnace section; The billet is heated based on the calculated furnace temperature required for each furnace section and the preset target heating curve. Calculating the remaining heating time from the current billet to the outlet of a furnace section includes: Obtain the distance L between the current billet and the furnace section exit, and obtain the number N of billets whose distance from the furnace outlet is less than or equal to L; calculate the remaining heating time from the current billet to the furnace section exit based on the number N of billets combined with the furnace exit rhythm. , the calculation expression is: ; Where, Indicates the remaining time for the billet to be discharged. It indicates the rhythm of the kth billet being discharged from the furnace, k indicates the serial number of the billet, the serial number of the billet about to be discharged is 1, and starting from the billet about to be discharged, the serial number of the billet increases in steps of 1 in the direction away from the heating furnace outlet.

[0007] Preferably, the calculation expression for the remaining time of the billet to be discharged is: ; Where, Indicates the scheduled time for the billet to be taken out of the furnace. Indicates the current moment.

[0008] Preferably, obtaining the remaining heating time of the current steel billet in the kth downstream furnace section includes: subtracting the remaining heating time of the current steel billet to the outlet of the k-1th downstream furnace section from the remaining heating time of the current steel billet to the outlet of the k-1th downstream furnace section, thereby obtaining the remaining heating time of the current steel billet in the kth downstream furnace section.

[0009] Preferably, the calculation of the furnace temperature required for the current furnace section includes: According to the specific heat capacity of the billet and mass m, calculate the heat Q1 that the billet needs to absorb in this section. The calculation expression is as follows: ; Calculate the heat transferred to the billet by the furnace in the current furnace section , the calculation expression is: ; make , thus obtaining the furnace temperature required for this section ; In the above formulas, Indicates the target outlet temperature of the current furnace section, Indicates the current temperature of the billet, is the average temperature of the steel billet in the current furnace section, K is the heat transfer coefficient, It is the remaining heating time of the current billet in the current furnace section.

[0010] Preferably, calculating the furnace temperature required for a corresponding downstream furnace section when the current billet arrives at the downstream furnace section includes: According to the specific heat capacity of the billet and mass m, calculate the heat Q3 that the billet needs to absorb in the downstream furnace section. The calculation expression is as follows: ; Calculate the heat transferred to the billet by the downstream furnace section , the calculation expression is: ; make , thus obtaining the furnace temperature required for this section ; In the above formulas, Indicates the outlet target temperature of the downstream furnace section, Indicates the target temperature at the outlet of the upstream furnace section of the downstream furnace section. Indicates the average temperature of the steel billet in the downstream furnace section, It is the remaining heating time of the current billet in the downstream furnace section.

[0011] Preferably, it also includes real-time feedback adjustment, including: real-time monitoring of the billet temperature through the temperature detection device in the furnace, adjusting the furnace temperature according to the target temperature of each section, when the temperature of the billet is lower than the target temperature, increasing the furnace temperature of the section, otherwise reducing the furnace temperature of the section.

[0012] Preferably, the method for generating the target heating curve includes: The heat flux density from the furnace gas to the billet surface in the heating section is calculated based on the temperature rise coefficient of the heating section, and the heat flux density from the furnace gas to the billet surface in the preheating section is calculated based on the temperature rise coefficient of the preheating section; A heat transfer equation is established, with initial conditions set as follows: the billet surface temperature upon exiting the furnace is equal to the target temperature, and the billet center temperature upon exiting the furnace is equal to the difference between the target temperature and the target uniformity. A termination condition is set as follows: the temperature difference between the billet center temperature and the billet surface temperature is greater than a preset temperature difference threshold. The heat transfer equation is reversely solved using the finite difference method to obtain the billet surface temperature and billet center temperature at each discrete time point corresponding to the uniformity section, as well as the surface temperature that the billet must reach upon entering the uniformity section. The reverse recursive formula for the billet surface temperature in the heating section is obtained based on the heat flux density from the furnace gas to the billet surface in the heating section. Combined with the surface temperature that the billet needs to reach when entering the soaking section, the billet surface temperature at each discrete time point in the heating section and the surface temperature that the billet needs to reach when entering the heating section are iteratively calculated. The reverse recursive formula for the billet surface temperature in the preheating section is obtained based on the heat flux density from the furnace gas to the billet surface in the preheating section. Combined with the surface temperature that the billet needs to reach when entering the heating section, the billet surface temperature at each discrete time point in the preheating section is iteratively calculated. The target billet temperature rise curve is generated based on the billet surface temperature at each discrete time point corresponding to the preheating section, heating section, and soaking section. The reverse recursive formula for the billet surface temperature in the i-th section of the heating furnace is calculated as follows: ; Where, represents the temperature of the Mth spatial node corresponding to the kth discrete time point, and They represent the temperature of the Mth spatial node and the temperature of the M-1th spatial node corresponding to the k+1th discrete time point, respectively. It represents the heat flux density from the furnace gas to the surface of the steel billet in the i-th section heating furnace.

[0013] Preferably, using the finite difference method to reversely solve the heat transfer equation includes: The billet is divided into M+1 equally spaced spatial nodes from the center to the surface. The sequence number of the spatial nodes increases from the center to the surface. The sequence number of the spatial node at the center is 0, and the sequence number of the spatial node at the surface is M. The time step between adjacent discrete time points is set to ; The spacing between spatial nodes is ; Obtaining a reverse recursive formula for the center temperature of the steel billet and a reverse recursive formula for the surface temperature of the steel billet in the soaking section based on the heat transfer equation; Based on the billet surface temperature at the time of discharge from the furnace and the reverse recursive formula for the billet surface temperature in the soaking section, the billet surface temperature at each discrete time point before the discharge from the furnace is iteratively calculated. Based on the billet center temperature at the time of discharge from the furnace and the reverse recursive formula for the billet center temperature, the billet center temperature at each discrete time point before the discharge from the furnace is iteratively calculated. The termination condition of the iteration is: the temperature difference between the billet center temperature and the billet surface temperature is greater than a preset temperature difference threshold. The reverse recursive formula for the center temperature of the billet is: ; The reverse recursive formula for the billet surface temperature in the soaking section is: ; In the above two formulas, 、 They represent the temperature of the 0th spatial node and the temperature of the Mth spatial node corresponding to the kth discrete time point, respectively. 、 、 as well as They represent the temperature of the 0th spatial node, the temperature of the 1st spatial node, the temperature of the Mth spatial node, and the temperature of the M-1th spatial node corresponding to the k+1th discrete time point; c represents the temperature value The specific heat capacity of the steel billet is Indicates that the temperature is and The average value of is the thermal conductivity of the steel billet.

[0014] Preferably, calculating the surface temperature of the steel billet at each discrete time point corresponding to the i-th stage heating furnace includes: Based on the surface temperature that the steel billet needs to reach when entering the downstream section of the i-th heating furnace and the reverse recursive formula of the steel billet surface temperature of the i-th heating furnace, starting from the moment of entering the downstream section of the i-th heating furnace, the surface temperature of the steel billet at each discrete time point within a first preset time length before entering the downstream section of the i-th heating furnace is iteratively calculated; the first preset time length is equal to the total residence time of the steel billet in the i-th heating furnace.

[0015] In a second aspect, the present invention provides a system for heating intermittently rolled steel billets, the system comprising a processor and a memory, the memory storing computer program instructions, which implement the method for heating intermittently rolled steel billets of the present invention when executed by the processor.

[0016] The beneficial effects of the present invention are as follows: the intermittent rolling billet heating method of this embodiment calculates the distance between the billet and the outlet of each furnace section, and calculates the remaining heating time of the billet to the furnace section outlet in combination with the number of billets in the range and the furnace discharge rhythm, thereby achieving a relatively accurate prediction of the remaining heating time of the billet to the furnace section outlet, thereby making the prediction result of the remaining heating time of the billet in each furnace section more accurate, which helps to improve the accuracy of the furnace temperature setting. In addition, by dynamically correcting the heating process, underheating or overheating of the billet due to intermittent rolling is avoided, and the temperature uniformity of the cross section and longitudinal direction of the billet is improved. Furthermore, the method of this embodiment can adjust the heating scheme in real time according to the actual furnace discharge rhythm, so that the heating process adapts to the beat change of intermittent rolling, ensures the continuity and stability of the rolling process, and thus ensures that the billet has high rolling quality and production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the accompanying drawings, several embodiments of the present invention are shown in an illustrative and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein: Figure 1is a flow chart schematically illustrating a method for heating a steel billet during intermittent rolling according to an embodiment of the present invention; Figure 2 Schematic diagram showing the positions of various steel billets in a heating furnace according to an embodiment of the present invention; Figure 3 FIG1 is a schematic diagram showing the structure of a billet heating system for intermittent rolling according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0019] Example of a method for heating a steel billet during intermittent rolling: like Figure 1 As shown, the intermittent rolling steel billet heating method of the present invention comprises: S101. Obtaining the remaining heating time of the current billet in the current furnace section and each downstream furnace section, specifically: calculating the remaining heating time from the current billet to the current furnace section outlet, and the remaining heating time from the current billet to the outlet of each downstream furnace section, and then obtaining the remaining heating time of the current billet in the current furnace section and the remaining heating time of the current billet in each downstream furnace section; S102. Calculate the required furnace temperature of the current furnace section and each downstream furnace section, specifically: calculate the required furnace temperature of the current furnace section based on the remaining heating time of the current steel billet in the current furnace section and the target outlet temperature of the current furnace section; calculate the required furnace temperature of each downstream furnace section when the current steel billet arrives at the corresponding furnace section based on the remaining heating time of the steel billet in each downstream furnace section and the target outlet temperature of the corresponding furnace section; S103 , heating the steel billet according to the calculated furnace temperature required for each furnace section and a preset target heating curve.

[0020] In this embodiment, calculating the remaining heating time from the current billet to the outlet of a certain furnace section includes: Obtain the distance L between the current billet and the furnace section exit, and obtain the number N of billets whose distance from the furnace outlet is less than or equal to L; calculate the remaining heating time from the current billet to the furnace section exit based on the number N of billets combined with the furnace exit rhythm. , the calculation expression is: (1) Where, Indicates the remaining time for the billet to be discharged. It indicates the rhythm of the kth billet being discharged from the furnace, k indicates the serial number of the billet, the serial number of the billet about to be discharged is 1, and starting from the billet about to be discharged, the serial number of the billet increases in steps of 1 in the direction away from the heating furnace outlet.

[0021] like Figure 2 As shown in the figure, assuming that the remaining time for the billet to be discharged is 3 seconds, and the discharge rhythm of each billet is the same, 5 seconds. The current billet is numbered M3 in the preheating section. The distance from this billet to the preheating section exit is L2. As can be seen from the figure, the number of billets with a distance from the discharge port less than or equal to L2 is 4. Therefore, the remaining heating time for this billet to the discharge port of this section is 23 seconds. The distance from this billet to the discharge port of the heating section is L2 + L3. As can be seen from the figure, the number of billets with a distance from the discharge port less than or equal to L2 + L3 is 11. Therefore, the remaining heating time for this billet to the discharge port of the heating section is 3 + 11 × 5 = 58 seconds. The distance between the steel billet and the outlet of the heating furnace is L2+L3+L4. As can be seen from the figure, the number of steel billets whose distance from the outlet of the heating furnace is less than or equal to L2+L3+L4 is 17. The remaining heating time of the steel billet to the outlet of the heating furnace is 3+5×17=88 seconds.

[0022] In this embodiment, the furnace discharge rhythm refers to the time interval between two adjacent steel billets being pushed out from the heating furnace outlet.

[0023] The intermittent rolling billet heating method of this embodiment calculates the distance between the billet and the outlet of each furnace section, and calculates the remaining heating time of the billet to the furnace section outlet in combination with the number of billets in the range and the furnace discharge rhythm, thereby achieving a relatively accurate prediction of the remaining heating time of the billet to the furnace section outlet, thereby making the prediction result of the remaining heating time of the billet in each furnace section more accurate, which helps to improve the accuracy of the furnace temperature setting. In addition, by dynamically correcting the heating process, the underheating or overheating of the billet caused by intermittent rolling is avoided, and the temperature uniformity of the cross section and longitudinal direction of the billet is improved. Furthermore, the method of this embodiment can adjust the heating scheme in real time according to the actual furnace discharge rhythm, so that the heating process adapts to the beat change of intermittent rolling, ensures the continuity and stability of the rolling process, and thus ensures that the billet has high rolling quality and production efficiency.

[0024] In one embodiment, the remaining time for a billet to be discharged is calculated as follows: ; Where, Indicates the scheduled time for the billet to be taken out of the furnace. Indicates the current moment.

[0025] In one embodiment, obtaining the remaining heating time of the current steel billet in the kth downstream furnace section includes: subtracting the remaining heating time of the current steel billet to the outlet of the kth downstream furnace section from the remaining heating time of the current steel billet to the outlet of the k-1th downstream furnace section, thereby obtaining the remaining heating time of the current steel billet in the kth downstream furnace section.

[0026] In one embodiment, calculating the furnace temperature required for the current furnace section includes: According to the specific heat capacity of the billet and mass m, calculate the heat Q1 that the billet needs to absorb in this section. The calculation expression is as follows: (2) Calculate the heat transferred to the billet by the furnace in the current furnace section , the calculation expression is: (3) make , thus obtaining the furnace temperature required for this section ; In the above formulas, Indicates the target outlet temperature of the current furnace section, Indicates the current temperature of the billet, is the average temperature of the steel billet in the current furnace section, K is the heat transfer coefficient, It is the remaining heating time of the current billet in the current furnace section.

[0027] In one embodiment, calculating the furnace temperature required for a certain downstream furnace section when the current steel billet arrives at the corresponding furnace section includes: According to the specific heat capacity of the billet and mass m, calculate the heat Q3 that the billet needs to absorb in the downstream furnace section. The calculation expression is as follows: (4) Calculate the heat transferred to the billet by the downstream furnace section , the calculation expression is: (5) make , thus obtaining the furnace temperature required for this section ; In the above formulas, Indicates the outlet target temperature of the downstream furnace section, Indicates the target temperature at the outlet of the upstream furnace section of the downstream furnace section. Indicates the average temperature of the steel billet in the downstream furnace section, It is the remaining heating time of the current billet in the downstream furnace section.

[0028] In one embodiment, real-time feedback adjustment is also included, including: real-time monitoring of the billet temperature through the temperature detection device in the furnace, adjusting the furnace temperature according to the target temperature of each section, when the temperature of the billet is lower than the target temperature, increasing the furnace temperature of the section, otherwise reducing the furnace temperature of the section.

[0029] By adjusting the furnace temperature in real time, the temperature of the steel billet in the heating furnace can be kept as close as possible to the target temperature of the corresponding furnace section, thereby further ensuring the quality of steel billet rolling.

[0030] In one embodiment, the method for generating the target heating curve includes: S201. Calculating the heat flux density from the furnace gas to the surface of the steel billet in the heating section based on the temperature rise coefficient of the heating section, and calculating the heat flux density from the furnace gas to the surface of the steel billet in the preheating section based on the temperature rise coefficient of the preheating section; S202. Establish a heat transfer equation, set the initial conditions as follows: the billet surface temperature upon exiting the furnace is equal to the target temperature upon exiting the furnace, and the billet center temperature upon exiting the furnace is equal to the difference between the target temperature upon exiting the furnace and the target uniformity; set the termination condition as follows: the temperature difference between the billet center temperature and the billet surface temperature is greater than a preset temperature difference threshold; and use the finite difference method to reversely solve the heat transfer equation to obtain the billet surface temperature and billet center temperature at each discrete time point corresponding to the uniformity section, as well as the billet surface temperature that needs to be reached upon entering the uniformity section. S203, obtaining a reverse recursive formula for the billet surface temperature in the heating section based on the heat flux density from the furnace gas to the billet surface in the heating section, and iteratively calculating the billet surface temperature at each discrete time point corresponding to the heating section, as well as the billet surface temperature that needs to be reached when entering the soaking section, in combination with the billet surface temperature that needs to be reached when entering the soaking section; S204, obtaining a reverse recursive formula for the billet surface temperature in the preheating section based on the heat flux density from the furnace gas to the billet surface in the preheating section, and iteratively calculating the billet surface temperature at each discrete time point corresponding to the preheating section in combination with the surface temperature that the billet needs to reach when entering the heating section; S205. Generate a target billet temperature rise curve based on the billet surface temperature at each discrete time point corresponding to the preheating section, the heating section, and the soaking section. The calculation expression of the reverse recursive formula for the billet surface temperature in the i-th section of the heating furnace is: (6) Where, represents the temperature of the Mth spatial node corresponding to the kth discrete time point, and They represent the temperature of the Mth spatial node and the temperature of the M-1th spatial node corresponding to the k+1th discrete time point, respectively. It represents the heat flux density from the furnace gas to the surface of the steel billet in the i-th section heating furnace.

[0031] The target heating curve generation method of this embodiment uses the final product quality indicators "heat uniformity" and "furnace target temperature" as the initial input of the algorithm. Through reverse deduction, it ensures that the generated heating curve must theoretically meet the most critical metallurgical process requirements, fundamentally solving the problem of disconnection between the goals and results of traditional methods.

[0032] Secondly, this method can generate a unique optimal heating curve in real time for billets of different sizes, steel grades, and initial temperatures, achieving refined heating with a "one strategy for one billet" approach, significantly improving the process's flexibility and adaptability to changing operating conditions. By introducing the "temperature rise coefficient for each furnace section," this method can accurately utilize the heating characteristics of different furnace sections and rationally allocate heating tasks to each section. For example, the temperature is rapidly increased in the efficient heating section, while the uniform temperature is focused in the uniform heating section, thereby achieving overall optimization of heating time and energy consumption while ensuring quality.

[0033] Furthermore, the present invention provides a set of clear and automatically executable algorithm processes, which converts the complex heating process into a solvable mathematical model, gets rid of the dependence on manual experience, and provides core technical support for realizing unmanned and intelligent operation of the heating furnace.

[0034] In one embodiment, it further includes: S901. Compare the calculated billet surface temperature at the earliest discrete time point in the preheating section with the actual billet entering the furnace temperature. If the deviation between the two is greater than a preset deviation threshold, adjust the furnace gas temperature in the preheating section and the heating section, and re-obtain the reverse recursive formula for the billet surface temperature in the heating section and the reverse recursive formula for the billet surface temperature in the preheating section, thereby regenerating a target billet heating curve. S902 , iteratively regenerate a target temperature rise curve for the steel billet until the deviation between the calculated steel billet surface temperature at the earliest discrete time point in the preheating section and the actual temperature of the steel billet entering the furnace is less than a preset deviation threshold.

[0035] In this embodiment, the deviation threshold can be set to 0.5 degrees Celsius.

[0036] The method of this embodiment compares the calculated billet surface temperature at the earliest discrete time point in the preheating section with the actual billet entry temperature, and adjusts the furnace gas temperature in the preheating section and the heating section, iteratively regenerates the target temperature rise curve, thereby avoiding cold charging and hot charging of the billet when entering the furnace as much as possible.

[0037] In one embodiment, using a finite difference method to reversely solve the heat transfer equation includes: S301. Divide the steel billet into M+1 equally spaced spatial nodes from the center to the surface. The sequence number of the spatial nodes increases from the center to the surface. The sequence number of the spatial node at the center is 0, and the sequence number of the spatial node at the surface is M. Set the time step between adjacent discrete time points to ; The spacing between spatial nodes is ; S302, obtaining a reverse recursive formula for the center temperature of the steel billet and a reverse recursive formula for the surface temperature of the steel billet in the soaking section according to the heat transfer equation; S303. Based on the surface temperature of the steel billet at the time of being taken out of the furnace and the reverse recursive formula of the steel billet surface temperature in the soaking section, iteratively calculate the surface temperature of the steel billet at each discrete time point before the time of being taken out of the furnace; based on the center temperature of the steel billet at the time of being taken out of the furnace and the reverse recursive formula of the steel billet center temperature, iteratively calculate the center temperature of the steel billet at each discrete time point before the time of being taken out of the furnace; the termination condition of the iteration is: the temperature difference between the center temperature of the steel billet and the surface temperature of the steel billet is greater than the preset temperature difference threshold.

[0038] The reverse recursive formula for the center temperature of the billet is: (7) The reverse recursive formula for the billet surface temperature in the soaking section is: (8) Because the temperature distribution through the thickness is approximately parabolic in steady state or near steady state, the temperature of the intermediate nodes at the time of leaving the furnace can be obtained by quadratic function interpolation. The intermediate nodes refer to the spatial nodes between the 0th spatial node and the Mth spatial node.

[0039] The derivation process of the reverse recursive formula for the center temperature of the billet and the reverse recursive formula for the surface temperature of the billet in the soaking section is as follows: A. Simplify the above heat transfer equation as follows: (9) B. Write it in explicit difference form: (10) C. After sorting out, we get the temperature recursive formula for the forward solution: (11) D. Rearrange the terms of formula (11): (12) E. Due to the time step between adjacent discrete time points is small enough, the right side of Equation (12) can be use Approximate replacement, use Approximate replacement, use Approximate substitution, thus obtaining the core recursive formula for the reverse solution: (13) F. The reverse recursive formula for obtaining the center temperature of the billet based on the center boundary condition: Due to symmetry, there is no heat flow through the center of the billet (j=0). In the differential format, by setting a virtual node To achieve this. Substitute it into the core recursive formula to obtain the reverse recursive formula for the center temperature of the billet: (14) G. Obtain the reverse recursive formula of the billet surface temperature in the soaking section based on the surface boundary conditions: In the soaking section, the furnace gas temperature is very close to the billet surface temperature, and the main thing that occurs is internal heat balance. Therefore, it can be approximately considered that the heat exchange between the surface and the outside world is very weak, that is, the surface is approximately adiabatic. , the reverse solution formula can be obtained as: (15) In formulas (7) to (15), 、 They represent the temperature of the 0th spatial node and the temperature of the Mth spatial node corresponding to the kth discrete time point, respectively. 、 、 as well as They represent the temperature of the 0th spatial node, the temperature of the 1st spatial node, the temperature of the Mth spatial node, and the temperature of the M-1th spatial node corresponding to the k+1th discrete time point; c represents the temperature value The specific heat capacity of the steel billet is Indicates that the temperature is and The average value of is the thermal conductivity of the billet; T represents the billet temperature, x represents the distance from the center of the billet, 、 、 They represent the temperature of the j-1th spatial node, the temperature of the jth spatial node, and the temperature of the j+1th spatial node corresponding to the kth discrete time point, respectively. Represents the temperature of the jth spatial node corresponding to the k+1th discrete time point.

[0040] In one embodiment, calculating the surface temperature of the steel billet at each discrete time point corresponding to the i-section heating furnace includes: starting from the moment of entering the downstream section of the i-section heating furnace based on the surface temperature that the steel billet needs to reach when entering the downstream section of the i-section heating furnace and the reverse recursive formula of the steel billet surface temperature of the i-section heating furnace, iteratively calculating the surface temperature of the steel billet at each discrete time point within a first preset time length before entering the downstream section of the i-section heating furnace; the first preset time length is equal to the total residence time of the steel billet in the i-section heating furnace.

[0041] After obtaining the surface temperature that the steel billet needs to reach when entering the heating section, the surface temperature that the steel billet needs to reach when entering the heating section can be used as the initial condition, and the reverse recursive formula of the steel billet surface temperature in the preheating section can be used to iteratively calculate the steel billet surface temperature at discrete time points within a second preset time length before the moment the steel billet enters the heating section. The second preset time length is equal to the total residence time of the steel billet in the preheating section.

[0042] In one embodiment, the heat flux density from the furnace gas to the surface of the steel billet in the i-th stage heating furnace is The calculation expression is: (16) Where, represents the temperature rise coefficient of the i-th section heating furnace, represents the fourth power of the furnace gas temperature of the i-th heating furnace, Represents the temperature of the Mth spatial node corresponding to the k+1th discrete time point.

[0043] The derivation process of the reverse recursive formula for the billet surface temperature in the i-th section heating furnace is as follows: 1. Establishing the Control Volume For an internal node j, its control volume is centered at node j and has a thickness of A thin slice, the area of ​​the slice is unit area. For the central node, its control volume is from the center line to x= The thickness is A thin slice of; for the surface node M, its control volume is from to the surface , the thickness is also The surface control volume has two sides, the inner side and the outer side.

[0044] The inner side is located The outer surface is the physical surface of the billet, located at , in direct contact with the furnace gas environment.

[0045] 2. Apply the law of conservation of energy.

[0046] In a small time period Δt, its energy change follows the following law: the increase in the internal energy of the control volume = the heat entering the control volume - the heat leaving the control volume.

[0047] 2.1 Calculate the increase in internal energy: The change in the internal energy of the control volume is manifested as a change in its temperature.

[0048] The volume of the control volume is: (17) Control the quality of the container to (18) During the time Δt, the temperature of the control volume changes from becomes , the increase in internal energy is: (19) 2.2 Calculate the difference between the heat entering the control volume and the heat leaving the control volume.

[0049] Calculate the heat entering through the outer side (physical surface): This part of the heat comes from the radiation of the furnace gas. The heat flux density per unit time through a unit area is equal to the heat flux density from the furnace gas to the billet surface In the time Δt, the heat entering through the outer side is: (20) Calculate the heat entering through the inner surface: This part of the heat comes from the heat conduction of the subsurface layer inside the billet (the area where the node M-1 is located). According to Fourier's law, the heat flux density conducted through the inner surface is (twenty one) Using the difference to approximate this derivative, at the inner side x=(M-1 / 2)Δx, at the k+1th discrete time point, the temperature gradient can be approximated as: (twenty two) Therefore, the heat flux density expression conducted through the inner surface can be transformed into (twenty three) During the time Δt, the heat conducted into the inner surface is: (twenty four) The total net flow inflow rate P is: (25) 2.3 Let the rate of change of internal energy be equal to the rate of net heat inflow, and we can obtain: (26) Equation (26) is an implicit equation for forward solution. To obtain an explicit reverse solution, we transform and approximate it. All terms at time k are moved to the left, all terms at time k+1 are moved to the right, and the temperature at time k+1 is used to approximate the heat flow term: (27) After sorting out, the reverse recursive formula of the billet surface temperature in the heating section can be obtained as shown in formula (6).

[0050] In formulas (17) to (27), A numerical value indicating the thickness of the sheet, is the density of the billet, c represents the temperature The specific heat capacity of the steel billet is Indicates that the temperature is and The thermal conductivity of the steel billet is the average value of 、 、 They respectively represent the temperature of the Mth spatial node corresponding to the k+1th discrete time point, the temperature of the Mth spatial node corresponding to the kth discrete time point, and the temperature of the M-1th spatial node corresponding to the k+1th discrete time point.

[0051] The reverse recursive formula for the surface temperature of the steel billet in the preheating section is constructed in the same manner as the reverse recursive formula for the surface temperature of the steel billet in the heating section, and will not be repeated here.

[0052] Example of a billet heating system for intermittent rolling: The present invention also provides a billet heating system for intermittent rolling. Figure 3 As shown, the intermittently rolled steel billet heating system includes a processor and a memory, wherein the memory stores computer program instructions. When the computer program instructions are executed by the processor, a method for heating a steel billet for intermittent rolling according to the present invention is implemented.

[0053] The intermittently rolled steel billet heating system also includes other components well known to those skilled in the art, such as a communication bus and a communication interface. The configuration and functions of these components are known in the art and will not be described in detail here.

[0054] While several embodiments of the present invention have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Numerous modifications, variations, and alternatives will occur to those skilled in the art without departing from the concept and spirit of the present invention. It should be understood that various alternatives to the embodiments of the present invention described herein may be employed in practicing the present invention.

Claims

1. A method for heating a steel billet during intermittent rolling, characterized in that: include: Calculate the remaining heating time from the current billet to the current furnace section outlet, as well as the remaining heating time from the current billet to the outlet of each downstream furnace section, and then obtain the remaining heating time of the current billet in the current furnace section and the remaining heating time of the current billet in each downstream furnace section; The required furnace temperature of the current furnace section is calculated based on the remaining heating time of the current billet in the current furnace section and the target outlet temperature of the current furnace section; the required furnace temperature of each downstream furnace section when the current billet arrives at the corresponding furnace section is calculated based on the remaining heating time of the billet in each downstream furnace section and the target outlet temperature of the corresponding furnace section; The billet is heated based on the calculated furnace temperature required for each furnace section and the preset target heating curve. Calculating the remaining heating time from the current billet to the outlet of a furnace section includes: Obtain the distance L between the current billet and the furnace section exit, and obtain the number N of billets whose distance from the furnace outlet is less than or equal to L; calculate the remaining heating time from the current billet to the furnace section exit based on the number N of billets combined with the furnace exit rhythm. , the calculation expression is: ； Where, Indicates the remaining time for the billet to be discharged. It indicates the rhythm of the kth billet being discharged from the furnace, k indicates the serial number of the billet, the serial number of the billet about to be discharged is 1, and starting from the billet about to be discharged, the serial number of the billet increases in steps of 1 in the direction away from the heating furnace outlet.

2. The method for heating a steel slab for intermittent rolling according to claim 1, wherein: The calculation expression for the remaining time of the billet to be discharged is: ； Where, Indicates the scheduled time for the billet to be taken out of the furnace. Indicates the current moment.

3. The method for heating a steel slab for intermittent rolling according to claim 1, wherein: Obtaining the remaining heating time of the current steel billet in the kth downstream furnace section includes: subtracting the remaining heating time from the current steel billet to the outlet of the kth downstream furnace section from the remaining heating time from the current steel billet to the outlet of the k-1th downstream furnace section, thereby obtaining the remaining heating time of the current steel billet in the kth downstream furnace section.

4. The method for heating a steel slab for intermittent rolling according to claim 1, wherein: The calculation of the furnace temperature required for the current furnace section includes: According to the specific heat capacity of the billet and mass m, calculate the heat Q1 that the billet needs to absorb in this section. The calculation expression is as follows: ； Calculate the heat transferred to the billet by the furnace in the current furnace section , the calculation expression is: ； make , thus obtaining the furnace temperature required for this section ; In the above formulas, Indicates the target outlet temperature of the current furnace section, Indicates the current temperature of the billet, is the average temperature of the steel billet in the current furnace section, K is the heat transfer coefficient, It is the remaining heating time of the current billet in the current furnace section.

5. The method for heating a steel slab for intermittent rolling according to claim 1, wherein: Calculating the furnace temperature required for a certain downstream furnace section when the current billet arrives at the corresponding furnace section includes: According to the specific heat capacity of the billet and mass m, calculate the heat Q3 that the billet needs to absorb in the downstream furnace section. The calculation expression is as follows: ； Calculate the heat transferred to the billet by the downstream furnace section , the calculation expression is: ； make , thus obtaining the furnace temperature required for this section ; In the above formulas, Indicates the outlet target temperature of the downstream furnace section, Indicates the target temperature at the outlet of the upstream furnace section of the downstream furnace section. Indicates the average temperature of the steel billet in the downstream furnace section, It is the remaining heating time of the current billet in the downstream furnace section.

6. The method for heating a steel slab for intermittent rolling according to claim 1, wherein: It also includes real-time feedback adjustment, including: real-time monitoring of the billet temperature through the temperature detection device in the furnace, adjusting the furnace temperature according to the target temperature of each section, when the temperature of the billet is lower than the target temperature, increasing the furnace temperature of the section, otherwise reducing the furnace temperature of the section.

7. The method for heating a steel slab for intermittent rolling according to any one of claims 1 to 6, wherein: The method for generating the target heating curve includes: The heat flux density from the furnace gas to the billet surface in the heating section is calculated based on the temperature rise coefficient of the heating section, and the heat flux density from the furnace gas to the billet surface in the preheating section is calculated based on the temperature rise coefficient of the preheating section; A heat transfer equation is established, with initial conditions set as follows: the billet surface temperature upon exiting the furnace is equal to the target temperature, and the billet center temperature upon exiting the furnace is equal to the difference between the target temperature and the target uniformity. A termination condition is set as follows: the temperature difference between the billet center temperature and the billet surface temperature is greater than a preset temperature difference threshold. The heat transfer equation is reversely solved using the finite difference method to obtain the billet surface temperature and billet center temperature at each discrete time point corresponding to the uniformity section, as well as the surface temperature that the billet must reach upon entering the uniformity section. The reverse recursive formula for the billet surface temperature in the heating section is obtained based on the heat flux density from the furnace gas to the billet surface in the heating section. Combined with the surface temperature that the billet needs to reach when entering the soaking section, the billet surface temperature at each discrete time point in the heating section and the surface temperature that the billet needs to reach when entering the heating section are iteratively calculated. The reverse recursive formula for the billet surface temperature in the preheating section is obtained based on the heat flux density from the furnace gas to the billet surface in the preheating section. Combined with the surface temperature that the billet needs to reach when entering the heating section, the billet surface temperature at each discrete time point in the preheating section is iteratively calculated. The target billet temperature rise curve is generated based on the billet surface temperature at each discrete time point corresponding to the preheating section, heating section, and soaking section. The reverse recursive formula for the billet surface temperature in the i-th section of the heating furnace is calculated as follows: ； Where, represents the temperature of the Mth spatial node corresponding to the kth discrete time point, and They represent the temperature of the Mth spatial node and the temperature of the M-1th spatial node corresponding to the k+1th discrete time point, respectively. It represents the heat flux density from the furnace gas to the surface of the steel billet in the i-th section heating furnace.

8. The method for heating a steel slab for intermittent rolling according to claim 7, wherein: The reverse solution of the heat transfer equation using the finite difference method includes: The billet is divided into M+1 equally spaced spatial nodes from the center to the surface. The sequence number of the spatial nodes increases from the center to the surface. The sequence number of the spatial node at the center is 0, and the sequence number of the spatial node at the surface is M. The time step between adjacent discrete time points is set to ; The spacing between spatial nodes is ; Obtaining a reverse recursive formula for the center temperature of the steel billet and a reverse recursive formula for the surface temperature of the steel billet in the soaking section based on the heat transfer equation; Based on the billet surface temperature at the time of discharge from the furnace and the reverse recursive formula for the billet surface temperature in the soaking section, the billet surface temperature at each discrete time point before the discharge from the furnace is iteratively calculated. Based on the billet center temperature at the time of discharge from the furnace and the reverse recursive formula for the billet center temperature, the billet center temperature at each discrete time point before the discharge from the furnace is iteratively calculated. The termination condition of the iteration is: the temperature difference between the billet center temperature and the billet surface temperature is greater than a preset temperature difference threshold. The reverse recursive formula for the center temperature of the billet is: ； The reverse recursive formula for the billet surface temperature in the soaking section is: ； In the above two formulas, 、 They represent the temperature of the 0th spatial node and the temperature of the Mth spatial node corresponding to the kth discrete time point, respectively. 、 、 as well as They represent the temperature of the 0th spatial node, the temperature of the 1st spatial node, the temperature of the Mth spatial node, and the temperature of the M-1th spatial node corresponding to the k+1th discrete time point; c represents the temperature value The specific heat capacity of the steel billet is Indicates that the temperature is and The average value of is the thermal conductivity of the steel billet.

9. The method for heating a steel slab for intermittent rolling according to claim 8, wherein: Calculating the billet surface temperature at each discrete time point corresponding to the i-th section heating furnace includes: Based on the surface temperature that the steel billet needs to reach when entering the downstream section of the i-th heating furnace and the reverse recursive formula of the steel billet surface temperature of the i-th heating furnace, starting from the moment of entering the downstream section of the i-th heating furnace, the surface temperature of the steel billet at each discrete time point within a first preset time length before entering the downstream section of the i-th heating furnace is iteratively calculated; the first preset time length is equal to the total residence time of the steel billet in the i-th heating furnace.

10. A billet heating system for intermittent rolling, comprising a processor and a memory, wherein the memory stores computer program instructions, characterized in that: When the computer program instructions are executed by the processor, the method for heating a steel billet by intermittent rolling according to any one of claims 1 to 9 is implemented.

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