CN117900263A - A roll shape design method for an intermediate roll of a 20-roll rolling mill - Google Patents

Abstract

The invention discloses a method for designing a roll shape of an intermediate roll of a 20-roll mill, which belongs to the field of sheet metal rolling, wherein the designed roll shape comprises a straight section and a conical section, and the conical section comprises a transition section and a conical section; the transition section is used for smoothly connecting the conical section and the flat section so as to ensure the continuity of the roll shape; the method comprises the following steps: designing a roll curve function of the conical region; determining the relation between the roll shape curve function coefficient of the conical region and the roll shape parameter of the conical region; determining the value of a roll shape parameter of the conical region; determining the value of the curve function coefficient of the conical region roll shape according to the determined value of the conical region roll shape parameter; and determining the final roll shape according to the determined curve function coefficient of the roll shape of the conical region and the determined value of the roll shape parameter of the conical region. By adopting the scheme of the invention, the occurrence risk of the high-order wave shape of the plate belt can be reduced while the convexity regulation capability of the plate belt is ensured, so that the comprehensive control capability of the convexity and the high-order wave shape of the plate belt is improved.

Description

A roll shape design method for an intermediate roll of a 20-roll rolling mill

Technical Field

The present invention relates to the technical field of plate and strip metal rolling, and in particular to a roll shape design method for a 20-roller mill-intermediate roll that takes into account both the convexity and high-order wave shape control of the plate and strip.

Background technique

The tapered roller profile is widely used in cold rolling mills. Reference 1 (Ma Jiaji, Liu Haichao, You Xuechang, etc. A method for controlling the edge drop of silicon steel produced by Sendzimir mill [P]. Hebei Province: CN109158429B, 2020-03-20.) designed a 20-roll mill intermediate roller profile that can effectively control the edge thickness of silicon steel. Reference 2 (Hara K, Yamada T, Takagi K. Shape Controllability for Quarter Buckles of Strip in 20-high Sendzimir Mills [J]. Transactions of the Iron & Steel Institute of Japan, 1991, 31 (6): 607-613.) HARA proposed a solution for designing an intermediate roller profile with a concave roller profile at the corresponding high-order wave position for the high-order wave shape problem of the 20-roll mill. In reference 3 (Kim J T, Yi JJ, Han SY. Shape control of alloy steel rolled by Sendzimir mill [J]. Journal of Mechanical Science & Technology, 1996, 10 (3): 277-285.), KIM proposed a three-cone segment cone scheme to solve the problem that the roller shape scheme proposed by HARA is difficult to process. Industrial tests have shown that it can alleviate high-order wave defects.

However, multi-cone segment rolls are also difficult to process, and multiple transition zone taper angles need to be smoothed to avoid peaks in contact pressure between rolls. Therefore, the current 20-roll rolling in industrial production is still dominated by single-cone segment rolls. The existing single-cone segment roll shape consists of a straight section and a tapered section. For this roll shape, when the overlap length between the tapered section and the working roll increases, the edge deflection of the working roll will be significantly weakened, and the working roll will be in a high-order deflection state, resulting in excessive local thickness reduction of the plate and strip, which in turn causes high-order wave defects.

Summary of the invention

The present invention provides a method for designing the roll shape of an intermediate roll of a 20-roll rolling mill to solve the technical problem that the roll shape designed by the existing method for designing the roll shape of an intermediate roll of a 20-roll rolling mill is that when the overlapping length of the tapered section and the working roll increases, the edge deflection of the working roll will be significantly weakened, and the working roll will appear in a high-order deflection state, thereby causing excessive local thickness thinning of the plate and strip, and further causing high-order wave defects.

In order to solve the above technical problems, the present invention provides the following technical solutions:

A method for designing a roll shape of an intermediate roll of a 20-roll rolling mill, wherein the roll shape of the intermediate roll of the 20-roll rolling mill comprises a straight section and a tapered area, wherein the tapered area comprises a transition section and a tapered section; wherein the transition section is used to smoothly connect the tapered section and the straight section to ensure the continuity of the roll shape;

The roll shape design method of the intermediate roll of the 20-roller rolling mill comprises:

Design the roller curve function of the tapered area;

Determine the relationship between the cone zone roller curve function coefficient and the cone zone roller parameter;

Determine the value of the roller shape parameter of the tapered area;

According to the determined value of the tapered zone roller shape parameter, combined with the determined relationship between the tapered zone roller shape curve function coefficient and the tapered zone roller shape parameter, the value of the tapered zone roller shape curve function coefficient is determined;

According to the determined values of the tapered zone roll curve function coefficients and tapered zone roll curve parameters, combined with the designed tapered zone roll curve function, the roll shape of the middle roll of the 20-roll mill is determined.

Furthermore, the expression of the cone zone roller curve function is:

Among them, y _contour is the roller shape; x is the coordinate of the roller body of an intermediate roller; a ₆ and a ₂ are the roller curve function coefficients of the tapered area; l ₁ is the length of the transition section; l ₂ is the length of the tapered section; and k is the taper of the tapered section.

Further, the tapered zone roller parameters include: tapered section taper, transition section length, tapered section length, transition section height and overall tapered height;

The relationship between the cone zone roller curve function coefficient and the cone zone roller parameter is expressed as:

Among them, _h1 is the transition section height; _h2 is the overall cone height.

Further, the determining of the value of the tapered zone roller shape parameter includes:

Will Denote it as the transition section cone height coefficient η, and determine the conditions that η must satisfy to ensure that the transition section curve is monotonically increasing; where the conditions that η must satisfy are expressed as:

And/>

Determine the values of the transition section length l ₁ and the tapered section length l ₂ ;

According to the values of the transition section length l ₁ and the tapered section length l ₂ , the minimum value that satisfies the conditions is taken as the value of η;

According to the plate strip convexity control threshold, determine the value of the overall cone height _h2 ;

According to the values of _h2 and η, the value of the transition section height _h1 is determined.

Furthermore, the transition section length l ₁ has a value range of 100≤l ₁ ≤300.

Furthermore, the length of the tapered section _l2 is determined according to the maximum overlapping length between the tapered area and the strip, the length of the working roll, the width of the strip and the length of an intermediate roll, and the formula is:

Among them, ξ is the maximum overlapping length between the tapered area and the strip; _lw is the length of the working roll; B is the width of the strip; _lf is the length of an intermediate roll.

Furthermore, the value of the transition section length l ₁ is the same as the value of the tapered section length l ₂ .

Furthermore, according to the plate strip crown control threshold, the value of the overall cone height _h2 is determined, including:

The overall cone height _h2 is calculated by numerical calculation method to obtain the value of the overall cone height h2, which can meet the requirements of the plate strip crown control threshold under the preset overlapping length of the cone section and the plate strip.

The beneficial effects brought about by the technical solution provided by the present invention include at least:

The scheme of the present invention introduces a gentle transition section between the tapered section and the straight section of the single-taper-segment roller. The transition section roller has a special geometric shape, which can smoothly connect the tapered section and the straight section to ensure the continuity of the roller shape, and alleviate the high-order deflection problem caused by the difference in the ability of the tapered section and the straight section to affect the deflection of the working roller, while taking into account the convexity control ability of the plate and strip at the same time. It can reduce the risk of high-order wave shape and improve rolling stability, further improve the yield rate of the plate and strip, thereby improving production efficiency and reducing the plate shape defect rate.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

FIG1 is a schematic diagram of the roller structure of a 20-roll mill;

FIG2 is a schematic diagram of the roller shape of an intermediate roller of a 20-roll rolling mill provided by an embodiment of the present invention;

3 is a flow chart of a method for designing a roll shape of an intermediate roll of a 20-roll mill provided by an embodiment of the present invention;

FIG4 is a diagram of the roller shape and the single cone segment roller shape of the present invention;

FIG5 is a comparison diagram of the plastic strain in the rolling direction of the roll shape of the present invention and the single cone section roll shape.

Detailed ways

To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

First of all, it should be noted that in the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "exemplary" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "exemplarily" is intended to present the concept in a concrete way. In addition, in the embodiments of the present invention, the meaning expressed by "and/or" can be both, or it can be either of the two.

In addition, in the embodiments of the present invention, sometimes a subscript (such as W ₁ ) may be mistakenly written as a non-subscript form (such as W1 ). When the difference is not emphasized, the meanings to be expressed are consistent.

In order to solve the problem of high-order deflection caused by the difference in the ability of the tapered section and the straight section to influence the deflection of the working roll and take into account the ability to control the crown of the plate and strip at the same time, this embodiment adds a smooth transition section between the tapered section and the straight section, and based on this, provides a 20-roll mill intermediate roll shape design method that takes into account both the crown of the plate and strip and the control of high-order wave shape, so as to reduce the risk of high-order wave shape and take into account the ability to control the crown of the plate and strip.

As shown in Figure 1, it is a roller structure diagram of a 20-roll rolling mill. The method of this embodiment is to design the roller shape of one of the intermediate rollers. As shown in Figure 2, the designed roller shape includes a straight section and a tapered area, and the tapered area includes a transition section and a tapered section; wherein the transition section is used to smoothly connect the tapered section and the straight section to ensure the continuity of the roller shape. The overall design idea of the method in this embodiment is: obtain the distribution function of the roller curve in the tapered area, and determine the roller curve coefficients _α6 , _α2 and k to be determined; the roller curve coefficients _α6 , _α2 and k can be represented by _l1 , _l2 , _h1 and _h2 , and in this embodiment, _h1 / _h2 is recorded as the transition section cone height coefficient η; according to the smooth transition condition of the roller curve, the slope values of the roller curves of each section of the curve at the connection point should be the same; the relationship between the cone height coefficients η and _l1 , _l2 is determined according to the positive and negative values of the parameter _α6 and the monotonically increasing transition section; the transition section length l1 and the tapered section length _l2 are determined according to the maximum overlapping length ξ of the tapered area and the strip, the working roll length _lw , the strip width _B and the length of an intermediate roll lf; the transition section cone height coefficient η and the overall cone height _h2 are determined according to the strip crown control threshold, _and the final curve coefficient can be determined based on this.

Based on the above, the execution flow of the method in this embodiment is shown in FIG3 , which mainly includes the following steps:

S1, design the roller curve function of the tapered area;

The transition section curve uses sixth-order and second-order polynomials to ensure the smoothness of the transition section. The conical section is a first-order curve, that is, the ratio of the cone height to the cone length is a constant. Specifically, the function expression of the cone zone roller curve is:

Among them, y _contour is the roller shape quantity, in mm; x is the coordinate of the roller body of an intermediate roller, in mm; a ₆ and a ₂ are the roller shape curve function coefficients of the tapered area; l ₁ is the transition section length, in mm; l ₂ is the tapered section length, in mm; k is the tapering of the tapered section.

S2, determining the relationship between the cone-shaped area roller curve function coefficient and the cone-shaped area roller parameter;

The tapered zone roller parameters include: tapered section taper, transition section length, tapered section length, transition section height and overall tapered height; according to the smooth transition condition of the roller curve, the slope of the roller curve of each section curve at the connection point should be the same. Based on this, the tapered zone roller curve function coefficients α ₆ , α ₂ and the tapered section taper k can be expressed by the following boundary conditions:

The relationship between the cone zone roller curve function coefficient and the cone zone roller parameter can be solved by formula (2):

Among them, _h1 is the transition section height, in mm; _h2 is the overall cone height, in mm.

S3, determining the value of the roller shape parameter of the tapered area;

Specifically, in this embodiment, the method for determining the roller shape parameter value of each tapered area is as follows:

S31, record h ₁ /h ₂ as the transition section cone height coefficient η, and determine the conditions that η needs to meet to ensure that the transition section curve is monotonically increasing; wherein, to ensure that the transition section curve is monotonically increasing, the following conditions need to be met:

6a ₆ x ⁵ +2a ₂ x≥0 x∈[0,l ₁ ] (4)

When a ₆ > 0, we can get According to the value range of x, it should satisfy/> By replacing α ₆ and α ₂ with l ₁ , l ₂ and η, we can deduce:

When a ₆ <0, we can get According to the value range of x, it should satisfy/> By replacing α ₆ and α ₂ with l ₁ , l ₂ , and η, we can deduce:

Therefore, the relationship between the transition section cone height coefficient η and l ₁ and l ₂ can be determined according to the positive and negative values of α ₆ and the monotonically increasing transition section: And/> When , the transition curve can be guaranteed to increase monotonically.

S32, determining the values of the transition section length _l1 and the tapered section length _l2 ;

The transition section length l ₁ ranges from 100 ≤ _{l 1} ≤ 300, and is generally the same as l _2. The tapered section length l ₂ is determined based on the maximum overlap length ξ between the tapered area and the strip, the working roll length l _w , the strip width B mm, and the length of an intermediate roll l _f , and the calculation formula is as follows:

Specifically, in this embodiment, the maximum overlapping length ξ between the tapered zone and the strip is 148 mm, the working roll length l _w is 1414 mm, the strip width B is 1250 mm, and the length of an intermediate roll l _f is 1580 mm, so l ₂ = 230 mm. For ease of memory, l ₁ = l ₂ = 230 mm is taken. It can be determined that when η ≥ 1/7 and η ≠ 1/3, the transition section curve can be guaranteed to be monotonically increasing.

S33, determining the value of η according to the values of the transition section length _l1 and the tapered section length _l2 ;

Among them, this embodiment determines η based on the relationship between the transition section cone height coefficient η, the transition section length l ₁ and the tapered section length l ₂ , in accordance with the principle of smooth transition and the requirement of meeting the value range of the transition section cone height coefficient η.

Specifically, in this embodiment, it is known that l ₁ =l ₂ =230 mm, then η≥1/7 and η≠1/3, thereby determining the minimum transition section cone height coefficient η=0.15 with two decimal places retained.

S34, determining the value of the overall cone height _h2 according to the plate strip convexity control threshold;

In this embodiment, the overall cone height h ₂ is calculated by a numerical calculation method to meet the requirement that the convexity of the plate strip reaches a threshold value ρ under the overlapping length of a certain cone section and the plate strip.

Specifically, in this embodiment, in order to ensure that the crown control capability of the roller shape of the present invention can reach the crown control capability of the strip of a single-cone section roller shape (cone length 230 mm and taper 0.85%), the strip crown control threshold ρ is set to the strip crown value of the single-cone section roller shape (cone length 230 mm and taper 0.85%) when the overlapping length of the cone section and the strip is 100 mm, that is, ρ = -6 μm. By using the numerical simulation method, it can be determined that the threshold requirement can be met when the overall cone height h ₂ = 0.725.

S35, determining the value of the transition section height _h1 according to the values of _h2 and η.

S4, determining the value of the tapered zone roller curve function coefficient according to the determined value of the tapered zone roller shape parameter and the determined relationship between the tapered zone roller shape curve function coefficient and the tapered zone roller shape parameter;

Specifically, in this embodiment, the values of α ₆ , α ₂ , and k are determined according to η, l ₁ , l ₂ , and h ₂ as follows:

S5, determining the roll shape of an intermediate roll of a 20-roll mill according to the determined values of the tapered zone roll shape curve function coefficients and tapered zone roll shape parameters and in combination with the designed tapered zone roll shape curve function.

The roller shape of the intermediate roller of the 20-roll mill provided in this embodiment that takes into account both the strip crown and the high-order corrugation control is simulated by finite element software. The roller shape of the present invention and the single-cone section roller shape are shown in FIG4 , and the distribution of the plastic strain in the rolling direction of the two roller shapes when the overlapping length of the tapered section and the strip is 100 mm and the strip crown reaches the threshold value of -6 μm is shown in FIG5 . It can be seen that when the strip crown control capability is the same, the local convex peak value of the rolling direction plastic strain of the roller shape of the present invention is only 59.53% of that of the single-cone section roller shape under the same strip crown control capability, indicating that the roller shape of the present invention can effectively reduce the risk of high-order corrugation and take into account the strip crown control.

In summary, this embodiment provides a method for designing the roll shape of an intermediate roll of a 20-roll mill, introduces a gentle transition section between the tapered section and the straight section of the single-taper section roll shape, and by designing a suitable roll shape curve form and roll shape parameters of the tapered area of the intermediate roll of the 20-roll mill, the problem of high-order deflection caused by the difference in the ability of the tapered section and the straight section to affect the deflection of the working roll is alleviated while taking into account the convexity control ability of the plate and strip. This can reduce the risk of high-order wave shapes, improve rolling stability, and further improve the yield rate of the plate and strip.

In addition, it should be noted that the present invention can be provided as a method, an apparatus or a computer program product. Therefore, the embodiment of the present invention can be in the form of a full or partial hardware embodiment, a full or partial software embodiment or an embodiment combining software and hardware. Moreover, when implemented using software, the embodiment of the present invention can be in the form of a computer program product implemented on one or more computer-usable storage media containing computer-usable program codes. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, the process or function described in the embodiment of the present invention is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium, for example, the computer instructions can be transmitted from one website, computer, server or data center to another website, computer, server or data center by wired (e.g., infrared, wireless, microwave, etc.). The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device such as a server, data center, etc. that contains one or more available media sets. The available medium can be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium. The semiconductor medium may be a solid state drive.

The embodiments of the present invention are described with reference to the flowcharts and/or block diagrams of the methods, terminal devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and/or box in the flowchart and/or block diagram, as well as the combination of the processes and/or boxes in the flowchart and/or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, an embedded processor, or other programmable data processing terminal device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing terminal device generate a device for implementing the functions specified in one process or multiple processes in the flowchart and/or one box or multiple boxes in the block diagram.

These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing terminal device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce a product including an instruction device that implements the functions specified in one or more processes of the flowchart and/or one or more blocks of the block diagram. These computer program instructions may also be loaded onto a computer or other programmable data processing terminal device, so that a series of operation steps are performed on the computer or other programmable terminal device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable terminal device provide steps for implementing the functions specified in one or more processes of the flowchart and/or one or more blocks of the block diagram.

It should also be noted that, in this article, the terms "include", "comprises" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or terminal device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or terminal device. In the absence of further restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, article or terminal device including the elements.

In addition, it can be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

In several embodiments provided by the present invention, it should be understood that the disclosed equipment, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of functional modules/units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another device, or some features can be ignored or not executed. Another point, the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms. The unit described as a separate component may or may not be physically separated, and the component displayed as a unit may or may not be a physical unit, that is, it may be located in one place, or it may be distributed on multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the scheme of this embodiment. In addition, each functional unit in each embodiment of the present invention can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit.

If the method is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

Finally, it should be noted that the above is a preferred embodiment of the present invention. It should be pointed out that although the preferred embodiment of the present invention has been described, once the basic creative concept of the present invention is known, a number of improvements and modifications can be made by those skilled in the art without departing from the principles of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention. Therefore, the attached claims are intended to be interpreted as including the preferred embodiment and all changes and modifications that fall within the scope of the embodiments of the present invention.

Claims (8)

1. A method for designing the roll shape of an intermediate roll of a 20-high rolling mill, characterized in that the roll shape of the intermediate roll of the 20-high rolling mill comprises a straight section and a tapered area, and the tapered area comprises a transition section and a tapered section; wherein the transition section is used to smoothly connect the tapered section and the straight section to ensure the continuity of the roll shape; The roll shape design method of the intermediate roll of the 20-roller rolling mill comprises: Design the roller curve function of the tapered area; Determine the relationship between the cone zone roller curve function coefficient and the cone zone roller parameter; Determine the value of the roller shape parameter of the tapered area; According to the determined value of the tapered zone roller shape parameter, combined with the determined relationship between the tapered zone roller shape curve function coefficient and the tapered zone roller shape parameter, the value of the tapered zone roller shape curve function coefficient is determined; According to the determined values of the tapered zone roll curve function coefficients and tapered zone roll curve parameters, combined with the designed tapered zone roll curve function, the roll shape of the middle roll of the 20-roll mill is determined. 2. The roll profile design method for an intermediate roll of a 20-high rolling mill according to claim 1, wherein the expression of the roll profile curve function of the tapered area is: Among them, y _contour is the roller shape; x is the coordinate of the roller body of an intermediate roller; a ₆ and a ₂ are the roller curve function coefficients of the tapered area; l ₁ is the length of the transition section; l ₂ is the length of the tapered section; and k is the taper of the tapered section. 3. The roll shape design method of a 20-roll mill intermediate roll according to claim 2, characterized in that the roll shape parameters of the tapered area include: tapering of the tapered section, transition section length, tapered section length, transition section height and overall tapered height; The relationship between the cone zone roller curve function coefficient and the cone zone roller parameter is expressed as: Among them, _h1 is the transition section height; _h2 is the overall cone height. 4. The method for designing the profile of an intermediate roll of a 20-high rolling mill according to claim 3, wherein the step of determining the value of the roll profile parameter of the tapered zone comprises: Will Denote it as the transition section cone height coefficient η, and determine the conditions that η must satisfy to ensure that the transition section curve is monotonically increasing; among them, the conditions that η must satisfy are expressed as: And/> Determine the values of the transition section length l ₁ and the tapered section length l ₂ ; According to the values of the transition section length l ₁ and the tapered section length l ₂ , the minimum value that satisfies the conditions is taken as the value of η; According to the plate strip convexity control threshold, determine the value of the overall cone height _h2 ; According to the values of _h2 and η, the value of the transition section height _h1 is determined. 5 . The method for designing the profile of an intermediate roll of a 20-high rolling mill according to claim 4 , wherein the transition section length l ₁ has a value in the range of 100≤l ₁ ≤300. 6. The method for designing the profile of an intermediate roll of a 20-high rolling mill according to claim 5, characterized in that the length of the tapered section _l2 is determined according to the maximum overlapping length of the tapered area and the strip, the length of the working roll, the width of the strip and the length of an intermediate roll, and the formula is: Among them, ξ is the maximum overlapping length between the tapered area and the strip; _lw is the length of the working roll; B is the width of the strip; _lf is the length of an intermediate roll. 7. The method for designing the roll shape of an intermediate roll of a 20-roll rolling mill as described in claim 6, characterized in that the value of the transition section length _l1 is the same as the value of the tapered section length _l2 . 8. The method for designing the profile of an intermediate roll of a 20-high rolling mill according to claim 4, characterized in that the step of determining the value of the overall cone height _h2 according to the strip crown control threshold comprises: The overall cone height _h2 is calculated by numerical calculation method to obtain the value of the overall cone height h2, which can meet the requirements of the plate strip crown control threshold under the preset overlapping length of the cone section and the plate strip.