Control method of plate discrepancy

Abstract

An embodiment of the present invention provides a method for controlling the plate discrepancy of medium and thick plates, which relates to the field of steel rolling technology. The method for controlling the plate discrepancy of medium and thick plates comprises: when the steel grade specification changes beyond a preset range, before the fourth-to-last rolling pass, pre-adjusting ZPC to obtain ZPC1; before the second-to-last rolling pass, correcting ZPC1 to obtain ZPC2; before the last rolling pass, correcting ZPC2 to obtain ZPC3. This method significantly reduces the plate discrepancy of rolled plates, significantly reduces the thickness fluctuation difference between the front and rear steel plates, significantly improves the thickness hit rate, and significantly reduces the spot and quality disputes caused by thickness, laying a technical foundation for rolling special small-tolerance steel plates and expanding the product categories.

Description

Technical Field

[0001] The present invention relates to the technical field of steel rolling, and in particular to a method for controlling plate deviations of medium and thick plates. Background Art

[0002] Existing rolling mills are generally four-roll reversible types, characterized by high rolling force and rigidity. The rolling process is completed using process automation and basic automation programs. During the rolling process, the mill's thickness adaptive model cannot automatically adjust in a timely and effective manner. Furthermore, many factors affect steel plate thickness, such as changes in steel grade, rolling temperature, rolling thickness, rolling width, mill setting parameters, and rolling reduction during production.

[0003] To improve yield, reduce metal consumption, and increase profitability, negative tolerance rolling is required in production, placing higher demands on the accuracy and stability of the thickness control system. During rolling, the allowable thickness fluctuation is relatively small. Excessively thick rolling thickness, exceeding the feedstock thickness, can result in a short finished product and produce spot goods. Excessively thin rolling thickness, combined with the influence of plate variations, can lead to the risk of localized thinning and may also result in spot goods. Therefore, proactive adjustments are necessary in planning, hot rolling, and parameter settings to maximize the probability of achieving the target thickness range.

[0004] There is no standardized control method, and the thickness of steel plates fluctuates greatly during production, and the steel plate thickness hit rate is poor, resulting in spot thickness sizes, reducing the yield rate of steel plates, and some inspection omissions flow into the market, causing quality disputes, which has a certain impact on the company's interests and image. Summary of the Invention

[0005] The purpose of the present invention includes providing a method for controlling the thickness difference of medium and thick plates, which can reduce the fluctuation of the thickness difference of steel plates, improve the thickness hit rate of steel plates, and improve the yield rate of steel plates.

[0006] The embodiments of the present invention can be implemented as follows:

[0007] The present invention provides a method for controlling the plate discrepancy of medium and thick plates, the method comprising:

[0008] When the steel grade specification changes beyond the preset range, ZPC is pre-adjusted before the fourth-to-last rolling pass to obtain ZPC1;

[0009] Before the penultimate rolling pass, ZPC1 is corrected to obtain ZPC2;

[0010] Before the last rolling pass, ZPC2 is corrected to obtain ZPC3.

[0011] In an optional embodiment, the preset range includes ΔW≦200 mm, ΔH≦5 mm and ΔQ≦100 MPa, wherein ΔW is the change in rolling width; ΔH is the change in rolling thickness; and ΔQ is the change in steel plate strength.

[0012] In an optional embodiment, before the fourth-to-last rolling pass, the ZPC is pre-adjusted to obtain the ZPC1, including the following steps:

[0013] When changing the steel grade during rolling, if the steel grade strength increases, the ZPC is pre-adjusted to -0.2~0; if the steel grade strength decreases, the ZPC is pre-adjusted to 0~0.2;

[0014] When changing the rolling specifications, if the rolling width increases, the ZPC is pre-adjusted to -0.2~0, and if the rolling width decreases, the ZPC is pre-adjusted to 0~0.2.

[0015] In an optional embodiment, before the fourth-to-last rolling pass, the ZPC is pre-adjusted to obtain the ZPC1, including the following steps:

[0016] When Hh≧0.15 or Hh≦-0.15, ZPC1=(Hh)*0.5, where H is the target thickness of the fourth-to-last rolling pass, and h is the thickness measured by the thickness gauge before the fourth-to-last rolling pass.

[0017] In an optional embodiment, before the penultimate rolling pass, the step of correcting ZPC1 to obtain ZPC2 includes:

[0018] Determine whether -0.1≦H1-h1≦0.1, where H1 is the target thickness after the fourth-to-last rolling pass, and h1 is the thickness measured by the thickness gauge after the fourth-to-last rolling pass;

[0019] If -0.1≦H1-h1≦0.1, then ZPC2 is not corrected, i.e. ZPC2=ZPC1;

[0020] If H1-h1<-0.1 or H1-h1>0.1, then ZPC2=(H1-h1)*K, where K is the correction coefficient.

[0021] In an optional embodiment, before the final rolling pass, the step of correcting ZPC2 to obtain ZPC3 includes:

[0022] Determine whether -0.05≦H2-h2≦0.05, where H2 is the target thickness after the penultimate rolling pass and h2 is the thickness measured by the thickness gauge after the penultimate rolling pass;

[0023] If -0.05≦H2-h2≦0.05, then ZPC3 does not need to be corrected, that is, ZPC3=ZPC2;

[0024] If H2-h2<-0.05 or H2-h2>0.05, then ZPC3=(H2-h2)*K, where K is the correction coefficient.

[0025] In an optional embodiment, the correction coefficient K is between 0.3 and 1.0.

[0026] In an optional embodiment, the method for controlling plate discrepancies further includes:

[0027] When the steel grade specification changes do not exceed the preset range, no pre-adjustment is performed on ZPC, that is, ZPC1 is equal to the initial ZPC.

[0028] In an optional embodiment, the method for controlling plate discrepancies further includes:

[0029] The following restrictions are added to the rolling plan arrangement: smooth transition of rolling thickness, width and strength, and the frequency of rolling mode changes does not exceed the threshold; controlled rolling and uncontrolled rolling are not cross-arranged, and different steel grades are not cross-arranged; thickness transition ≤15mm, width ≤500mm, and steel grade strength transition <150Mpa.

[0030] In an optional embodiment, the method for controlling plate discrepancies further includes:

[0031] The following restrictions are added to the set rolling procedures: the difference in the number of finishing passes for the same section, steel grade and specification is controlled within 2 passes; the number of finishing passes of steel plates before and after cross rolling is kept consistent; the same reduction rate, torque and rolling force limit values ​​are used in the rolling process of steel plates of the same specification; an additional empty pass is added in cross rolling to keep the number of finishing passes unchanged; the reduction rate of the last pass is 6% to 13%; the final rolling temperature is implemented according to the upper limit of the process requirements.

[0032] The beneficial effects of the method for controlling plate discrepancies provided by the embodiment of the present invention include:

[0033] The difference between rolled plates has been greatly reduced, the thickness fluctuation difference between the front and rear steel plates has been significantly reduced, the thickness hit rate has been greatly improved, and the spot and quality disputes caused by thickness have been greatly reduced, laying a technical foundation for rolling special small tolerance steel plates and expanding the product categories. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1This is a flow chart of a method for controlling plate discrepancies provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0037] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0038] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0039] In the description of the present invention, it should be noted that if the terms "upper", "lower", "inside", "outside", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, or is the orientation or position relationship in which the product of the invention is usually placed when in use. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be understood as a limitation on the present invention.

[0040] In addition, the terms "first", "second", etc., if used, are merely used to distinguish and describe, and should not be understood as indicating or implying relative importance.

[0041] It should be noted that, in the absence of conflict, the features in the embodiments of the present invention may be combined with each other.

[0042] During the rolling production process of wide and thick plate production lines, the methods generally used for thickness control are: automatic correction of ZPC by calculation of the rolling mill secondary system, manual thickness deviation modification, and ZPC modification. When the steel plate is rolled to the penultimate pass, the thickness of the steel plate at this time is measured with a thickness gauge and compared with the set thickness of the rolling procedure for that pass. The difference between the two is used to estimate the thickness deviation modification value and modify it, or the difference between the two is estimated and the ZPC is modified to change the rolling roll gap of the last pass to achieve the purpose of correcting the thickness of the finished product. When the rolling procedure is adjusted, changes in the reduction of the last pass and the rolling temperature will have a significant impact on the thickness of the finished product. Due to the large deviation from the target thickness, this method has low accuracy and thickness hit rate in thickness deviation modification and ZPC modification during rolling. The poor stability cannot meet some production needs. In addition, these methods have a certain hysteresis, which will affect the execution of other processes and thus affect performance.

[0043] This embodiment provides a method for controlling plate deviations of medium and thick plates. This method is to make relatively accurate corrections by correcting a series of key control points in advance before and during the rolling of the steel plates, and then comparing the measurement data of the thickness gauge to obtain a thickness within the target range (the actual thickness H is considered to be within the target thickness h±0.15), while not reducing the production efficiency of the rolling mill and ensuring the execution of other processes.

[0044] This embodiment provides a method for controlling plate discrepancies. The method has the following requirements for rolling plan arrangement:

[0045] 1. The rolling thickness, width and strength must be smoothly transitioned, and the rolling mode (including high temperature uncontrolled and controlled rolling) should not change too frequently;

[0046] 2. The process requires that controlled rolling and uncontrolled rolling are not allowed to be cross-arranged, and different steel grades are not allowed to be cross-arranged;

[0047] 3.Thickness transition ≤15mm, width transition ≤500mm, steel strength transition <150Mpa.

[0048] Requirements for setting rolling procedures include:

[0049] 1. The difference in the number of finishing passes for the same cross-section, steel grade and specification should be controlled within 2 passes;

[0050] 2. The number of passes for finishing rolling of steel plates before and after cross rolling remains the same;

[0051] 3. The same reduction rate, torque and rolling force limit values ​​should be used during the rolling process of steel plates of the same or similar specifications;

[0052] 4. In the second stage of cross rolling, an additional empty pass is added to ensure that the number of loaded passes in finishing rolling remains unchanged;

[0053] 5. The final reduction rate is 6% to 13%, which should be adjusted appropriately according to the rolling crown and wave shape to ensure a slight rolling crown (less than 0.1mm) and slight medium waves;

[0054] 6. The final rolling temperature shall be implemented according to the upper limit of the process requirements.

[0055] According to the thickness of the steel plate, the ZPC (zero position correction coefficient of the finishing mill) of the rolling mill is adjusted. The calculation formula of the target rolling thickness h is as follows:

[0056]

[0057]

[0058] In the formula, h is the target thickness, So is the no-load roll gap after pre-compression deformation, P is the rolling force, Po is the pre-pressure, and Km is the rolling mill stiffness.

[0059] See also Figure 1 After meeting the above requirements for rolling plan arrangement and setting rolling procedures, the method for controlling plate discrepancies provided in this embodiment further includes the following steps, wherein the unit of thickness is mm:

[0060] S1: Determine whether the steel grade specification change exceeds the preset range.

[0061] Specifically, the preset ranges include ΔW≦200mm, ΔH≦5mm and ΔQ≦100Mpa, where ΔW is the change in rolling width; ΔH is the change in rolling thickness; and ΔQ is the change in steel plate strength.

[0062] When the steel grade specification changes beyond the preset range, proceed to S2.

[0063] S2: Before the fourth-to-last rolling pass, ZPC is pre-adjusted to obtain ZPC1.

[0064] Specifically, S2 includes the following two cases:

[0065] Case 1: When changing steel grades for rolling, pre-adjust the ZPC in advance. Because changes in steel grade strength affect changes in rolling force and mill stiffness during rolling, if the steel grade strength increases, pre-adjust the ZPC by -0.2 to 0. If the steel grade strength decreases, pre-adjust the ZPC by 0 to 0.2. Pre-adjusting the ZPC by -0.2 to 0 means decreasing the ZPC by 0 to 0.2, while pre-adjusting the ZPC by 0 to 0.2 means increasing the ZPC by 0 to 0.2.

[0066] Case 2: When changing rolling specifications, if the rolling width increases, the ZPC is pre-adjusted to -0.2 to 0. If the rolling width decreases, the ZPC is pre-adjusted to 0 to 0.2. The specific ZPC value can be determined based on the change in rolling width. The purpose of pre-adjusting ZPC is to minimize the impact of rolling changes on thickness and improve the accuracy of subsequent thickness adjustments.

[0067] If the steel grade specification changes do not exceed the preset range, ZPC does not need to be pre-adjusted, and subsequent adjustments can be made to correct it, that is, if ZPC1 is equal to the initial ZPC, then S3 is performed.

[0068] In addition, for feedback corrections of the same specification and steel grade, when rolling the same specification and steel grade, the rolling procedure is kept stable. In abnormal situations, such as Hh≧0.15 or Hh≦-0.15, ZPC1 is directly pre-corrected, and ZPC1=(Hh)*0.5 is used to reduce subsequent corrections, where H is the target thickness of the fourth-to-last rolling pass, and h is the thickness measured by the thickness gauge before the fourth-to-last rolling pass.

[0069] S3: Before the penultimate rolling pass, ZPC1 is corrected to obtain ZPC2.

[0070] Specifically, during the fourth-to-last rolling pass, a thickness gauge at the mill exit measures the actual thickness. ZPC2 is calculated based on the comparison between the target thickness H1 after the fourth-to-last rolling pass and the thickness h1 measured by the thickness gauge after the fourth-to-last rolling pass.

[0071] The calculation process of ZPC2 is as follows:

[0072] First, determine whether -0.1≦H1-h1≦0.1.

[0073] If -0.1≦H1-h1≦0.1, then ZPC2 will not be corrected, but it can be corrected through subsequent adjustments, i.e., ZPC2=ZPC1.

[0074] If H1-h1<-0.1 or H1-h1>0.1, then ZPC2=(H1-h1)*K, where K is the correction coefficient. K is obtained through continuous summary in long-term production and takes a value between 0.3 and 1.0, corresponding to the size of the change.

[0075] Since there is only a thickness gauge at the rolling mill outlet, the steel plate is measured by the thickness gauge after the fourth to last pass is completed or during the rolling process. The third to last pass is rolled from the outlet to the inlet, and there is no thickness gauge at the rolling mill inlet. The second to last pass is the same as the fourth to last pass.

[0076] S4: Before the final rolling pass, ZPC2 is corrected to obtain ZPC3.

[0077] Specifically, in the penultimate rolling pass, the steel plate is rolled from the inlet to the outlet of the rolling mill, and the actual thickness of the steel plate measured by the thickness gauge is compared with the target thickness H2 after the penultimate rolling pass and the thickness h2 measured by the thickness gauge after the penultimate rolling pass to calculate ZPC3.

[0078] The calculation process of ZPC3 is as follows:

[0079] First, determine whether -0.05≦H2-h2≦0.05.

[0080] If -0.05≦H2-h2≦0.05, due to the first two thickness corrections, the target thickness of the penultimate rolling pass is very close to the thickness measured by the thickness gauge, which can greatly improve the hit rate of the third correction ZPC. In this case, ZPC3 does not need to be corrected, and the rolling thickness is already within the target thickness, that is, ZPC3=ZPC2.

[0081] If H2-h2<-0.05 or H2-h2>0.05, then ZPC3=(H2-h2)*K.

[0082] Through three ZPC corrections, under normal circumstances, the rolling thickness fluctuation can be guaranteed to be between -0.15 and 0.15, greatly improving the rolling thickness hit rate. The rolling thickness fluctuation of steel plates with a thickness of less than 25mm can be achieved within the range of -0.1 to 0.1.

[0083] Example

[0084] 1. The method for controlling the difference in plate thickness is implemented on a 4300mm single-stand wide and heavy plate rolling line, with the following production planning requirements:

[0085] In principle (assuming sufficient blanks), the production plan should meet the following conditions:

[0086] 1.1 Steel plate rolling process requirements: controlled rolling and uncontrolled rolling are not allowed to be cross-arranged, and different steel grades are not allowed to be cross-arranged;

[0087] 1.2 The thickness of the steel plate transition is ≤15mm. The transition of steel plates with specifications above 30mm can be relaxed to 40mm. The width transition is ≤500mm. The strength transition of steel grades is <150Mpa. The focus is on ensuring that the width and steel grade transition are smooth as required;

[0088] 1.3 Before maintenance or changing rolls and starting rolling, try to arrange the two steel plates to the specified length;

[0089] 1.4 The eccentricity of the rolling mill roll is less than 0.2 after calibration.

[0090] 2. Preparation before rolling and setting of rolling procedures

[0091] Reading the production plan and calculating the procedures: After taking over the shift, the production plan of the shift must be carefully read. If there are changes in rolling specifications (thickness, width), changes in steel grades, controlled rolling and non-controlled rolling, and special deviation requirements for steel plates, they must be marked on the task list. During the rolling process, the assistant operator must remind the main operator. Before rolling, the operator must perform the procedure calculation in advance and adjust and control according to the following requirements:

[0092] 2.1 Control of the number of finishing passes: Under normal circumstances, when the number of finishing passes of the same steel grade and specification is changed between the front and back rolling, the plate difference will fluctuate greatly, so the finishing passes need to be stabilized. Under abnormal circumstances, the number of finishing passes of the same steel grade and specification is allowed to differ by ≤4 passes;

[0093] 2.2 Control of the rolling force of the last loaded pass: When the specifications or steel grades change or there are abnormal conditions (such as large fluctuations in the temperature of the rolled steel plate), the rolling force difference of the last loaded pass of the changed steel plates is adjusted to less than 20MN by adjusting the reduction rate and rolling passes, thereby reducing the fluctuation of the steel plate difference caused by the model thickness compensation;

[0094] 3. Thickness control

[0095] The thickness control process is the same as S1 to S4 above.

[0096] 1) For rolling of the same specification, the finishing passes, rolling temperature, final pass reduction rate and mill parameter settings must be the same. Specifically, the difference between different plates of the same specification shown in Table 1 must be met.

[0097] Table 1 Difference between different boards of the same specification

[0098] Target thickness / mm Rolling width / mm Number of finishing passes Final pass reduction rate ZPC Finish rolling temperature / ℃ Thickness gauge 24.65 2575 6 8.2％ 0.13 835 24.66 24.65 2575 6 8.3％ 0.13 827 24.61 24.65 2575 6 8.3％ 0.13 833 24.63 24.65 2575 6 8.1％ 0.18 816 24.64

[0099] 2) When the specifications and steel grades change, adjust the rolling procedures, make the reduction rate consistent, and reduce variables. Specifically, the requirements for the different specifications and plate differences shown in Table 2 are met.

[0100] Table 2 Differences between different specifications

[0101] Steel Type Target thickness / mm Rolling width / mm Final pass reduction rate ZPC Finish rolling temperature / ℃ Thickness gauge Q355B 24.65 2575 8.6％ 0.21 832 24.67 Q390C 29.65 2275 9.3％ 0.15 838 29.62 Q345GJC 32.2 2475 10.1％ 0.11 855 32.12 Q345R 32.2 2075 9.8％ 0.24 844 32.21

[0102] 3) When the specifications and steel grades vary greatly (e.g. width span > 1000mm, thickness span > 20mm, steel plate strength span > 200Mpa), due to the weak adaptive strength of the model, it is necessary to make a prejudgment in advance and manually modify the ZPC roughly before rolling. For example, when the width increases, the ZPC value should be appropriately reduced; when the width decreases, the ZPC value should be appropriately increased; when the thickness increases or decreases, the ZPC value should be appropriately reduced or increased; when the reduction rate increases or decreases, the ZPC value should be appropriately increased or decreased. Then, during the rolling process, the above-mentioned S1 to S4 methods should be used for precise adjustment.

[0103] The beneficial effects of the method for controlling plate discrepancies provided in this embodiment include:

[0104] 1. In the old production process method, there were no requirements for production planning; there were no clear requirements for the control of the number of steel plate passes; thickness adjustment was limited to modifying the thickness deviation and could not be adjusted quantitatively. The method provided in this embodiment adds production planning requirements; it explicitly requires the number of steel plate passes to be ≤ 2; the thickness adjustment operation adds pre-adjustment and advance correction of the rolling mill ZPC, and can be adjusted quantitatively;

[0105] 2. After the method provided in this embodiment is implemented on a 4300mm wide and thick plate rolling line, the same-plate difference of the rolled plates is greatly reduced, and the thickness fluctuation difference between the front and rear steel plates is reduced from the previous ±0.5mm to within ±0.15mm. The thickness hit rate is greatly improved, and the spot and quality disputes caused by thickness are greatly reduced, which lays a technical foundation for rolling special small-tolerance steel plates and expands the product categories.

[0106] 3. After the method provided in this embodiment is implemented, the thickness difference of steel plates is reduced to less than 0.1mm. After the thickness hit rate is improved, the negative deviation of the thickness of steel plates with a thickness of ≤40mm can be reduced by 0.05mm year-on-year, and the comprehensive yield rate can be increased by 0.1%. For a factory with an annual output of 1.5 million tons, about 1,400 tons of steel plates can be produced more each year.

[0107] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for controlling plate discrepancy, characterized in that: The method for controlling the difference in plate thickness includes: When the steel grade specification changes beyond the preset range, ZPC is pre-adjusted before the fourth-to-last rolling pass to obtain ZPC1, including: When changing the steel grade during rolling, if the steel grade strength increases, the ZPC is pre-adjusted to -0.2~0; if the steel grade strength decreases, the ZPC is pre-adjusted to 0~0.2; When changing the rolling specifications, if the rolling width increases, the ZPC is pre-adjusted to -0.2~0; if the rolling width decreases, the ZPC is pre-adjusted to 0~0.2; when Hh≧0.15 or Hh≦-0.15, ZPC1=(Hh)*0.5, where H is the target thickness of the fourth-to-last rolling pass, and h is the thickness measured by the thickness gauge before the fourth-to-last rolling pass; Before the penultimate rolling pass, ZPC1 is corrected to obtain ZPC2, including: Determine whether -0.1≦H1-h1≦0.1, where H1 is the target thickness after the fourth-to-last rolling pass, and h1 is the thickness measured by the thickness gauge after the fourth-to-last rolling pass; If -0.1≦H1-h1≦0.1, then ZPC2 is not corrected, that is, ZPC2=ZPC1; if H1-h1<-0.1 or H1-h1>0.1, then ZPC2=(H1-h1)*K, where K is the correction coefficient; Before the final rolling pass, ZPC2 is corrected to obtain ZPC3, including: Determine whether -0.05≦H2-h2≦0.05, where H2 is the target thickness after the penultimate rolling pass and h2 is the thickness measured by the thickness gauge after the penultimate rolling pass; If -0.05≦H2-h2≦0.05, then ZPC3 does not need to be corrected, that is, ZPC3=ZPC2; If H2-h2<-0.05 or H2-h2>0.05, then ZPC3=(H2-h2)*K, where K is the correction coefficient; The correction coefficient K is between 0.3 and 1.

0.

2. The method for controlling plate discrepancy according to claim 1, characterized in that: The preset range includes ΔW≦200mm, ΔH≦5mm and ΔQ≦100Mpa, wherein ΔW is the change in rolling width; ΔH is the change in rolling thickness; and ΔQ is the change in steel plate strength.

3. The method for controlling plate discrepancy according to claim 1, characterized in that: The method for controlling the difference between medium and thick plates further includes: When the steel grade specification changes do not exceed the preset range, no pre-adjustment is performed on ZPC, that is, ZPC1 is equal to the initial ZPC.

4. The method for controlling plate discrepancy according to claim 1, characterized in that: The method for controlling the difference between medium and thick plates further includes: The following restrictions are added to the rolling plan arrangement: smooth transition of rolling thickness, width and strength, and the frequency of rolling mode changes does not exceed the threshold; controlled rolling and uncontrolled rolling are not cross-arranged, and different steel grades are not cross-arranged; thickness transition ≤15mm, width transition ≤500mm, and steel grade strength transition <150Mpa.

5. The method for controlling plate discrepancy according to claim 1, characterized in that: The method for controlling the difference between medium and thick plates further includes: The following restrictions are added to the set rolling procedures: the difference in the number of finishing passes for the same section, steel grade and specification is controlled within 2 passes; the number of finishing passes of steel plates before and after cross rolling is kept consistent; the same reduction rate, torque and rolling force limit values ​​are used in the rolling process of steel plates of the same specification; an additional empty pass is added in cross rolling to keep the number of finishing passes unchanged; the reduction rate of the last pass is 6%~13%; the final rolling temperature is implemented according to the upper limit of the process requirements.

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