CN117787066B - Method for predicting roll shape of working roll based on thermal convexity of CVC rolling mill - Google Patents

Abstract

The present invention provides a method for predicting the roll shape of a working roll based on the thermal crown of a CVC rolling mill, comprising: collecting strip steel parameters, rolling process parameters, cooling water parameters, CVC rolling mill parameters and working roll temperature data; establishing a three-dimensional thermal crown finite element model of the CVC working roll according to the CVC rolling mill parameters; calculating the convective heat transfer coefficient between the working roll and the strip steel, air and cooling water during the rolling process, applying the convective heat transfer coefficient to the three-dimensional thermal crown finite element model, and performing a finite element simulation experiment; adjusting the temperature boundary conditions of the three-dimensional thermal crown finite element model so that the working roll temperature data curve of the finite element simulation experiment is consistent with the working roll temperature data curve measured on site; performing a finite element simulation experiment based on the adjusted three-dimensional thermal crown finite element model, extracting the lateral distribution data of the thermal expansion of the working roll surface at different time nodes, and fitting the data with the initial CVC working roll shape curve to obtain a new working roll shape curve.

Description

A method for predicting work roll shape based on thermal crown of CVC rolling mill

Technical Field

The invention belongs to the technical field of hot rolling and relates to a method for predicting the roll shape of a working roll based on the thermal crown of a CVC rolling mill.

Background technique

At present, obtaining the required roll gap convexity by axially shifting the working rolls of the rolling mill during hot strip rolling has become a major means of controlling strip shape. The representative rolling mill is the CVC rolling mill, which can achieve the purpose of controlling the flatness and convexity of the strip by axially shifting the working rolls. The roll shape of the working roll is the most direct and active factor affecting the strip shape control. Therefore, the original roll shape of the working roll of the axially shifting variable convexity rolling mill directly affects its strip shape control ability and effect. Taking the working roll of the CVC rolling mill as an example, the CVC working roll currently generally adopts a cubic curve design. The difference in cubic curve design will directly affect the roll shape of the working roll, and then affect the control effect of the CVC rolling mill on the strip shape. Therefore, it is of great significance to give a specific method for optimizing and designing the working roll roll curve in combination with the on-site process conditions.

In the production of hot rolled strip steel, the hot roll shape of the working roll is one of the important factors affecting the strip shape. In order to improve the quality of the strip steel, the hot roll crown of the working roll must be accurately calculated and predicted. During the hot rolling process, the temperature of the strip steel is continuously input into the working roll, resulting in uneven temperature in the middle and edge of the working roll. The expansion in the middle is greater than that in the edge, which changes the roll shape curve, and then the roll gap shape also changes. The strip thickness distribution along the lateral direction also changes, which affects the plate shape.

Domestic researchers have conducted many related studies on the hot roll shape problem in the hot rolling production process. The Chinese invention patent application "A method for analyzing the influence of thermal convexity on plate shape during cold rolling" with application number CN202210448408.X invented a method that combines the thermal convexity numerical simulation model with the rolling process numerical simulation model. This method can intuitively reflect the change of the thermal convexity of the working roll. The thermal expansion of the working roll will affect the plate shape, and further the plate shape under different thermal convexities can be obtained. The Chinese journal "Research on the Simulation of the Hot Roll Shape of the Working Roll of the Hot Continuous Rolling Mill" uses the differential method to establish a two-dimensional transient temperature field of the roll and a prediction model of the hot roll shape, and studies the change process of the hot roll shape of the working roll during the rolling process. It further analyzes the influence of the width of the rolled piece, the roll shifting system, etc. on the hot roll shape, providing a guiding basis for actual production and theoretical research. The Chinese journal paper "Research on the Roller Temperature Field and Thermal Convexity of the 1700 Hot Continuous Rolling Mill" calculates the working roll temperature field and thermal convexity of a certain rolling cycle by establishing a differential model of the working roll temperature field of the hot steel rolling mill. For CVC rolls, the surface temperature distribution and thermal crown of the rolls are affected by the roll lateral displacement. During the entire rolling process, the thermal deformation change of the roll surface is closely related to the rolling rhythm. The Chinese journal paper "Research on CVC Roller Thermal Crown Model" studied and analyzed the roll thermal crown model of the CVC rolling mill. By comparing it with the theoretical calculation value of the two-dimensional roll thermal crown model in the plate shape control system, the problems existing in the existing model were found. On this basis, the thermal crown model was improved, the calculation accuracy of the roll thermal crown model was improved, and the strip shape control accuracy was improved.

There are three main deficiencies in the above research: (1) The thermal crown model of the traditional working roll is set as a two-dimensional ideal model. However, there is a complex heat transfer process in the actual rolling process. If the ideal two-dimensional ideal model is used in the simulation process, it will inevitably be inconsistent with the actual rolling process. The two-dimensional ideal model ignores the temperature transfer and thermal expansion in the circumferential direction of the roll, and the error with the actual production process is large, which makes the thermal crown simulation model have certain limitations; (2) The differential model and mathematical model do not consider the heat conduction in the axial direction of the roll, and the calculation process is complicated. (3) The heat transfer of the working roll in the hot rolling process is more complicated than that in the cold rolling process, and the change of the hot roll shape is more drastic. Some schemes only consider the problem of cold rolling plate shape prediction, and do not consider the influence of hot roll shape, so they are not suitable for application in hot rolling.

Summary of the invention

In order to solve the above technical problems, the present invention provides a method for predicting the roll shape of a working roll based on the thermal crown of a CVC rolling mill.

The present invention provides a method for predicting the roll shape of a working roll based on the thermal crown of a CVC rolling mill, comprising:

Step 1: Collect the strip parameters, rolling process parameters, cooling water parameters, CVC mill parameters and work roll temperature data measured on site;

Step 2: Establish a three-dimensional thermal crown finite element model of the CVC work roll according to the CVC rolling mill parameters collected in step 1;

Step 3: Calculate the convective heat transfer coefficients between the working roll and the strip, the working roll and the air, and the working roll and the cooling water during the rolling process according to the strip parameters, rolling process parameters, and cooling water parameters collected in step 1, apply the convective heat transfer coefficients to the three-dimensional thermal crown finite element model, and conduct a finite element simulation experiment;

Step 4: Adjust the temperature boundary conditions of the three-dimensional thermal crown finite element model so that the work roll temperature data curve of the finite element simulation experiment is consistent with the work roll temperature data curve measured on site;

Step 5: Perform a finite element simulation experiment based on the adjusted three-dimensional thermal crown finite element model, extract the lateral distribution data of the thermal expansion of the work roll surface at different time nodes in the finite element simulation experiment, and fit it with the initial CVC work roll shape curve to obtain a new work roll shape curve;

Step 6: Based on the new work roll shape curve obtained in step 5, analyze the influence of the change of the working roll thermal crown at different time nodes on the CVC work roll shape curve.

Furthermore, the step 1 specifically includes: obtaining strip parameters, rolling process parameters, cooling water parameters, CVC rolling mill parameters and working roll temperature field data from the hot rolling production line;

The strip steel parameters include: strip steel grade, strip steel width, strip steel thickness and strip steel temperature;

The rolling process parameters include: rolling speed, friction coefficient, rolling gap time and working roll lateral displacement;

The cooling water parameters include: cooling water temperature, cooling water flow rate and cooling water injection pressure;

The CVC rolling mill parameters include: work roll diameter, work roll barrel length, work roll density, work roll elastic modulus, work roll Poisson's ratio, work roll thermal expansion coefficient, work roll specific heat capacity, work roll thermal conductivity and initial CVC work roll roll shape curve;

The working roll temperature field data is obtained by attaching reflective tape to the working roll along the axial direction after the work roll is taken off the machine, and using a thermal imager to take a picture of the temperature field cloud map of the working roll.

Furthermore, the initial CVC work roll shape curve equation is a cubic polynomial function, specifically:

;

;

In the formula, RU ( x ) is the upper roll shape function of the working roll, RL ₍ x ) is the _lower roll shape function of the working roll, x is the transverse coordinate of the roll; R0 is the nominal radius of the working roll, in mm; a1 _, a2 and a3 _{are the} roll shape coefficients to be determined; LREF is _the design length of the _working roll, in mm.

Furthermore, the step 2 is specifically as follows:

Step 2.1: Establishing modeling dimension parameters of the three-dimensional thermal crown finite element model of the CVC work roll according to the CVC rolling mill parameters collected in step 1;

Step 2.2: Establish material parameters of the three-dimensional thermal crown finite element model of the CVC work roll according to the CVC rolling mill parameters collected in step 1;

Step 2.3: Establish a three-dimensional thermal crown finite element model of the CVC work roll. To shorten the calculation time, take 1/30 of the circumferential direction of the work roll for modeling;

Step 2.4: Simplify boundary conditions.

Furthermore, the step 2.3 is specifically as follows: select SOLID164 eight-node hexahedral unit for modeling, define the thermophysical parameters of the working roll material, and draw the roll shape curve of the working roll using a high-order B-spline curve based on the CVC rolling mill parameters collected in step 1; perform mesh refinement on the surface of the working roll to ensure calculation accuracy, gradually thin out from the outside to the inside to shorten the calculation time, and the surface mesh size is 10 mm in the length direction, 2 mm in the width direction, and 3 mm in the depth direction.

Furthermore, the specific assumptions and simplified contents of step 2.4 are as follows:

(1) The temperature of any node during the rolling process changes periodically. Assuming that the work roll does not rotate, the boundary conditions are rotated in the opposite direction to simulate the rotation of the work roll.

(2) It is assumed that the temperature fields of the upper and lower working rolls are consistent, and the working rolls are in the 0 roll position;

(3) The heat exchange between the working roll and the strip, the working roll and the cooling water, and the working roll and the air is equivalent to convection heat exchange;

(4) Ignore the frictional heat between the working roll and the support roll;

(5) According to the contact arc length between the strip and the working roll, the working roll is divided into 30 equal parts along the axial direction, each part is 12°, and the part where the strip is in contact with the working roll is one part.

Furthermore, the step 3 is specifically as follows:

Step 3.1: The contact heat transfer and deformation heat between the working roll and the strip and the radiation heat transfer between the working roll and the air during the rolling process are equivalent to convection heat transfer;

Step 3.2: Determine the convection heat transfer coefficients between the strip and the working roll, between the working roll and the cooling water, and between the working roll and the air according to the convection heat transfer formula and empirical values;

Step 3.3: Generate a time-heat transfer coefficient cycle curve through the K file using the convective heat transfer coefficient calculated in step 3.2;

Step 3.4: Create SEGM on the surface of the three-dimensional thermal crown finite element model of the CVC work roll, apply the time-heat transfer coefficient curve to the SEGM, and realize the heating and cooling process of the work roll.

Furthermore, the step 3.2 is specifically as follows:

The expression of heat transfer coefficient in the contact arc between the working roll and the strip is as follows:

;

Where: hcon _is the convection heat transfer coefficient between the strip and the working roll; is the average unit rolling force, in N; v is the rolling speed, in m/s;

The heat transfer coefficient between the working roll and cooling water is expressed as follows:

(1) The working roll surface temperature T r is less than 100 ° C:

;

(2) The working roll surface temperature T r is greater than 200 ° C:

;

Wherein: h _cw is the convection heat transfer coefficient between the working roll and the cooling water; γ ₁ and γ ₂ are the cooling heat transfer correction coefficients; E is the elastic modulus of the working roll; Q is the water flow _density , Q = V _SP / A _SP ; P _SP is the injection pressure, unit MPa; TC is the cooling water temperature, unit ℃; V _SP is the cooling water volume, unit l/s ; A _SP is the injection area, unit, m ² ; when Q ＜10000 ( l /s/m ² ), B =(T _c /16) ^-0.17 ; when Q ≥10000 ( l /s/m ² ), B =1.0;

The heat exchange coefficient between the working roll and the air is expressed as follows:

;

Where: h _air is the convection heat transfer coefficient between the working roll and the air; Δ T is the temperature difference between the working roll and the surrounding air, unit: °C.

Furthermore, the step 5 is specifically as follows:

Step 5.1: Extract the lateral distribution data of the thermal expansion of the working roll surface at different time nodes of the finite element simulation experiment;

Step 5.2: Add the thermal expansion of the work roll surface to the initial CVC work roll shape curve to obtain multiple thermal crown work roll shape curves under different thermal crowns; normalize the work roll width data of the multiple thermal crown work roll shape curves under different thermal crowns, and fit the normalized thermal crown work roll shape curves using a cubic polynomial to obtain a cubic fitting polynomial as follows:

;

Wherein, y is the new working roll shape curve; x is the dimensionless coordinate after normalization in the width direction of the working roll, x ∈ [-1, 1]; A ₁ is the first-order fitting coefficient, A ₂ is the second-order fitting coefficient, A ₃ is the third-order fitting coefficient; e ( x ) is the fitting error;

Step 5.3: Based on A ₁ , A ₂ , and A ₃ , draw a new working roll profile curve and calculate the partial thermal crown c _p and overall thermal crown c _t indicators of the working roll:

;

;

Among them, h _c is the working roll diameter at the center point of the working roll, h _i is the working roll diameter at the operating side of the working roll, h _i ^' is the working roll diameter at the driving side of the working roll, h _j is the working roll diameter corresponding to the strip operating side, and h _j ^' is the working roll diameter corresponding to the strip driving side.

Furthermore, the influence of the thermal crown described in step 6 on the roll curve and the strip shape is:

At different rolling time nodes, the CVC working roll roll shape curve is distributed in an S shape, but with the increase of rolling time, the CVC working roll middle roll shape curve increases upward, which is equivalent to adding quadratic terms, linear terms and constant term coefficients on the basis of the initial CVC working roll roll shape curve.

The method for predicting the roll shape of a working roll based on the thermal crown of a CVC rolling mill of the present invention has the following beneficial effects:

The method of the present invention establishes a three-dimensional thermal convexity simulation model of the CVC working roll according to the measured temperature boundary conditions, so that the change of the thermal convexity is closer to reality, and puts forward suggestions with practical production significance for the process arrangement, grinding roll system, and roll shifting strategy of hot rolling production; by fitting the thermal convexity with the original roll shape curve, the change of the CVC working roll roll shape can be predicted more intuitively and accurately, and the thermal convexity is taken into account when grinding the roll shape to ensure that the actual roll roll convexity is consistent with the target convexity, and at the same time, different plate shape actuators can be combined in actual production to better regulate the strip shape, which can help improve the plate shape quality of the strip, further improve product quality, and enhance enterprise benefits; the present invention adopts a simulation experiment method based on three-dimensional finite element simulation, which can reduce equipment, time and cost losses caused by actual experiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of a method for predicting the roll shape of a work roll based on the thermal crown of a CVC rolling mill according to the present invention;

Figure 2 is the initial CVC work roll profile curve;

Figure 3 shows the boundary condition area division of the working roll surface;

FIG4 is a comparison diagram of the working roll temperature data curve of the finite element simulation experiment and the working roll temperature data curve measured on site;

FIG5 is a comparison diagram of the measured thermal expansion of the middle part of the working roll and the simulation result;

FIG6 is a graph showing the thermal expansion of the working roll surface at different time points;

FIG7 is a distribution curve diagram of the overall thermal crown and partial thermal crown of the working roll;

FIG8 is a graph showing the new work roll shape curve and the initial CVC work roll shape curve under different thermal expansion amounts.

Detailed ways

In this embodiment, a 1780mm CVC four-roller hot rolling mill of a certain factory is taken as an example to conduct numerical simulation research and analysis. The working roll of the rolling mill is a CVC roll shape, and the support roll is a flat roll.

As shown in FIG1 , a method for predicting the roll shape of a work roll based on the thermal crown of a CVC rolling mill includes:

Step 1: Collect the strip parameters, rolling process parameters, cooling water parameters, CVC mill parameters and work roll temperature data measured on site;

During specific implementation, strip parameters, rolling process parameters, cooling water parameters, CVC rolling mill parameters, and working roll temperature field data are obtained from the hot rolling production line.

The strip steel parameters include: strip steel type, strip steel width, strip steel thickness, and strip steel temperature.

The rolling process parameters include: rolling speed, friction coefficient, rolling gap time, and lateral displacement of the working rolls.

The CVC rolling mill parameters include: work roll diameter, work roll barrel length, work roll density, work roll elastic modulus, work roll Poisson's ratio, work roll thermal expansion coefficient, work roll specific heat capacity, work roll thermal conductivity and initial CVC work roll roll shape curve.

The cooling water parameters include: cooling water temperature, cooling water flow rate, and cooling water injection pressure.

The working roll temperature field data is obtained by attaching reflective tape along the axial direction on the working roll after it is unloaded from the machine, and using a thermal imager to take a picture of the temperature field cloud map of the working roll.

In this example, the obtained strip steel parameters are shown in Table 1. The obtained rolling process parameters are shown in Table 2. The obtained CVC rolling mill parameters are shown in Table 3. The obtained cooling water parameters are shown in Table 4.

Table 1 Strip steel parameters.

Strip parameters Parameter Value Strip steel grade DD11-MD Strip width 1260mm Strip thickness 10.7mm Strip temperature 952.03℃

Table 2 Rolling process parameters.

Rolling process parameters Numeric Rolling speed 3.42m/s Friction coefficient 0.35 Rolling interval time 60s Working roll lateral displacement range -120~120mm

Table 3 CVC mill parameters.

parameter Numeric Working roll diameter 778mm Working roll barrel length 2080mm Working roll density 7850kg/ ^m3 Working roll elastic modulus 210GPa Poisson's ratio of working roll 0.3 Thermal expansion coefficient of working roll 1.2e ^-5 Specific heat capacity of working roll 590 J·(kg·℃) ^-1 Thermal conductivity of working roll 60 W·(m·K) ^-1

Table 4 Cooling water parameters.

parameter Numeric Cooling water temperature 30℃ Cooling water flow 2500 l /min Cooling water injection pressure 1.47MPa

In this embodiment, the working rolls of the CVC rolling mill are CVC roll-shaped, and the initial CVC working roll roll shape curve equation is a cubic polynomial function.

The upper roll and the lower roll of the working roll are placed in a plane rectangular coordinate system, as shown in Figure 2, and their roll curve functions are:

;

;

Wherein, RU ( x ) is the upper roll shape function of the working roll, RL ₍ x ) is the _lower roll shape function of the working roll, x is the transverse coordinate of the roll; R0 is the nominal radius of the working roll, in mm; a1 , a2 _{and a3} are the roll shape coefficients to be determined; LREF is _the design length of the working roll, in mm. The parameters of the roll shape curve _{of the} working roll in this example are shown in Table 5.

Table 5 CVC work roll profile parameters.

Roller curve parameters Numeric Roller shape factor a ₁ -1.850745×10 ^-3 Roller shape factor a ₂ 1.830577×10 ^-6 Roller shape factor a ₃ -5.260278×10 ^-10 Nominal roller radius R ₀ 389mm Roller design length L _REF 2080mm

Step 2: Establish a three-dimensional thermal crown finite element model of the CVC working roll according to the CVC rolling mill parameters collected in step 1. Step 2 is specifically as follows:

Step 2.1: Establishing modeling dimension parameters of the three-dimensional thermal crown finite element model of the CVC work roll according to the CVC rolling mill parameters collected in step 1;

Step 2.2: Establish material parameters of the three-dimensional thermal crown finite element model of the CVC work roll according to the CVC rolling mill parameters collected in step 1;

Step 2.3: Establish a three-dimensional thermal crown finite element model of the CVC work roll. To shorten the calculation time, take 1/30 of the circumferential direction of the work roll for modeling. The specific steps of step 2.3 are as follows:

Select SOLID164 eight-node hexahedral unit for modeling, define the thermophysical parameters of the working roll material, and use high-order B-spline curves to draw the roll shape curve of the working roll based on the CVC rolling mill parameters collected in step 1; refine the mesh on the surface of the working roll to ensure the calculation accuracy, and gradually thin it out from the outside to the inside to shorten the calculation time. The surface mesh size is 10 mm in length, 2 mm in width, and 3 mm in depth.

Step 2.4: Simplify the boundary conditions. The specific assumptions and simplifications are as follows:

(1) The temperature of any node during the rolling process changes periodically. Assuming that the work roll does not rotate, the boundary conditions are rotated in the opposite direction to simulate the rotation of the work roll.

(2) It is assumed that the temperature fields of the upper and lower working rolls are consistent, and the working rolls are in the 0 roll position;

(3) The heat exchange between the working roll and the strip, the working roll and the cooling water, and the working roll and the air is equivalent to convection heat exchange;

(4) The frictional heat generated between the working roll and the support roll is very small, so the frictional heat generated between the working roll and the support roll is ignored;

(5) According to the contact arc length between the strip and the working roll, the working roll is divided into thirty equal parts along the axial direction, each part is 12°, and the contact between the strip and the working roll is one part. As shown in Figure 3, the surface of the working roll is divided into 10 boundary areas. Area 2 is the heat exchange area where the working roll contacts the strip and is the direct source of heat for the working roll; areas 3, 6, 8, and 1 are the areas where the working roll contacts the air and undergoes convective heat exchange with the air; area 7 is the direct contact area between the working roll and the support roll; areas 5 and 9 are the forced convective heat exchange areas between the cooling water and the working roll; areas 4 and 10 are the convective heat exchange between the accumulated water between the water retaining plates and the working roll.

Step 3: Calculate the convective heat transfer coefficients between the working roll and the strip, the working roll and the air, and the working roll and the cooling water during the rolling process according to the strip parameters, rolling process parameters, and cooling water parameters collected in step 1, apply the convective heat transfer coefficients to the three-dimensional thermal crown finite element model of the CVC working roll, and perform a finite element simulation experiment. Step 3 is specifically as follows:

Step 3.1: The contact heat transfer and deformation heat between the working roll and the strip and the radiation heat transfer between the working roll and the air during the rolling process are equivalent to convection heat transfer;

Step 3.2: Determine the convection heat transfer coefficients between the strip and the working roll, between the working roll and the cooling water, and between the working roll and the air according to the convection heat transfer formula and empirical values. Step 3.2 is specifically as follows:

The expression of heat transfer coefficient in the contact arc between the working roll and the strip is as follows:

;

Where: hcon _is the convection heat transfer coefficient between the strip and the working roll; is the average unit rolling force, unit is N; v is the rolling speed, unit is m/s.

The heat transfer coefficient between the working roll and cooling water is expressed as follows:

(1) The working roll surface temperature T r is less than 100 ° C:

;

(2) The working roll surface temperature T r is greater than 200 ° C:

;

In the formula: h _cw is the convection heat transfer coefficient between the working roll and cooling water; γ ₁ and γ ₂ are cooling heat transfer correction coefficients; E is the elastic modulus of the working roll; Q is the water flow _density , Q = V _SP / A _SP ; P _SP is the injection pressure, unit MPa; TC is the cooling water temperature, unit ℃; V _SP is the cooling water volume, unit l/s ; A _SP is the injection area, unit, m ² ; when Q ＜10000 ( l /s/m ² ), B =(T _c /16) ^-0.17 ; when Q ≥10000 ( l /s/m ² ), B =1.0.

The heat exchange coefficient between the working roll and the air is expressed as follows:

;

Where: h _air is the convection heat transfer coefficient between the working roll and the air; Δ T is the temperature difference between the working roll and the surrounding air, unit: °C.

Step 3.3: Generate a time-heat transfer coefficient cycle curve through the K file using the convective heat transfer coefficient calculated in step 3.2;

Step 3.4: Create SEGM on the surface of the three-dimensional thermal crown finite element model of the CVC work roll, and apply the time-heat transfer coefficient curve to the SEGM to realize the heating and cooling process of the work roll.

Step 4: Adjust the temperature boundary conditions of the three-dimensional thermal crown finite element model so that the working roll temperature data curve of the finite element simulation experiment is consistent with the working roll temperature field data curve measured on site. The specific steps of step 4 are:

The temperature field data of the working roll along the axial distribution in the finite element simulation experiment was extracted and compared with the temperature field data measured on site. The accuracy of the three-dimensional thermal convexity finite element model was made consistent with the accuracy of the on-site measurement by adjusting the boundary conditions and the convection heat transfer coefficient. The working roll temperature data curve of the finite element simulation experiment is consistent with the working roll temperature field data curve measured on site, and the absolute error between the simulation result and the measured value is less than 0.5℃. According to the PFC work log collected from the site, the real-time change data of the thermal expansion amount in a roll change cycle of the F4 frame was selected. The comparison with the simulation result is shown in Figure 5. It can be seen that the thermal expansion amount of the working roll increases with time and then gradually stabilizes, and finally remains stable at about 250μm. Because there is an idle period during rolling, the temperature of the working roll body decreases and the thermal expansion decreases, so some points fluctuate greatly. Figure 4 is a pair of the working roll temperature data curve of the finite element simulation experiment and the working roll temperature data curve measured on site. Figure 5 is a comparison chart of the measured thermal expansion amount in the middle of the working roll and the simulation result.

Step 5: Based on the adjusted three-dimensional thermal crown finite element model, a finite element experiment is performed to extract the lateral distribution data of the thermal expansion of the work roll surface at different time nodes in the finite element experiment, and the new work roll shape curve is obtained by fitting with the initial CVC work roll shape curve. The specific steps of step 5 are:

Step 5.1: Extract the lateral distribution data of the thermal expansion of the working roll surface at different time nodes of the finite element simulation experiment;

In the specific implementation, the post-processing software is used to extract the thermal expansion of the working roll along the axial direction at different time nodes. As shown in Figure 6, it is a curve diagram of the thermal expansion of the working roll surface at different time nodes.

Step 5.2: Add the thermal expansion of the work roll surface to the initial CVC work roll shape curve to obtain multiple thermal crown work roll shape curves at different time nodes, that is, different thermal crowns; normalize the work roll width data of the multiple thermal crown work roll shape curves at different thermal crowns, and fit the normalized thermal crown work roll shape curves using a cubic polynomial to obtain a cubic fitting polynomial as follows:

;

Among them, y is the new working roll shape distribution curve; x is the normalized dimensionless coordinate _in the width direction of the working roll, x ∈ [-1,1]; A1 is the _linear fitting coefficient, A2 is the quadratic fitting coefficient, A3 is the cubic fitting coefficient; e ( x ) is _the fitting error.

Step 5.3: Based on A ₁ , A ₂ , and A ₃ , draw a new working roll profile curve and calculate the partial thermal crown c _p and overall thermal crown c _t indicators of the working roll:

;

;

Wherein, h _c is the diameter of the work roll at the center point of the work roll, h _i is the diameter of the work roll at the operating side of the work roll, h _i ^' is the diameter of the work roll at the driving side of the work roll, h _j is the diameter of the work roll corresponding to the strip operating side, and h _j ^' is the diameter of the work roll corresponding to the strip driving side. In this example, data extraction is performed according to the above formula to draw Figures 7 and 8. Figure 7 is a distribution curve of the overall thermal crown and partial thermal crown of the work roll. Figure 8 is a new work roll roll shape curve and an initial CVC work roll roll shape curve under different thermal expansion amounts.

Step 6: Based on the new work roll shape curve data obtained in step 5, analyze the influence of the change of the work roll thermal crown at different time nodes on the CVC work roll shape curve.

At the beginning of rolling, the working roll contacts the strip, the temperature increases rapidly, and the expansion also increases rapidly. When the rolling time increases from 1000s to 5000s, the diameter of the middle part of the working roll increases by 139.23μm. After 5000s, the diameter of the middle part of the working roll increases slowly, increasing by 3.59μm, and then tends to be gentle. The thermal expansion of the edge of the working roll increases with the rolling time, from 1.24μm to 26.88μm. The thermal expansion change of the working roll forms the thermal crown of the working roll. When the rolling time increases from 1000s to 5000s, the overall thermal crown and local thermal crown of the working roll increase rapidly before 5000s, increasing by 472.28μm and 170.01μm respectively. After 5000s, it increases slowly, and the thermal crown of the working roll tends to be stable. When the rolling time increases from 1000s to 5000s, the roll shape curve in the middle of the CVC working roll increases upward with the increase of rolling time, which is equivalent to adding quadratic terms, linear terms and constant term coefficients on the basis of the original roll shape curve, but all roll shape curves still present an S-shaped distribution. After 5000s, as time increases, the thermal convexity no longer changes, and the roll shape curve no longer changes, reaching stability.

The present invention provides a method for predicting the plate shape based on the thermal crown of a CVC rolling mill. The method uses the measured parameters of the hot rolling production line and the finite element platform to establish a CVC rolling mill thermal crown simulation model to analyze the influence of the thermal crown on the mill roll curve. A scientific and reasonable verification plan is formulated to ensure the stability and accuracy of the model. Based on the on-site process parameters, after determining the lateral displacement of the working roll, the influence law is analyzed according to the obtained post-processing data.

The above description is only a preferred embodiment of the present invention and is not intended to limit the concept of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (5)

1. A method for predicting the roll shape of a work roll based on the thermal crown of a CVC rolling mill, characterized by comprising: Step 1: Collect the strip parameters, rolling process parameters, cooling water parameters, CVC mill parameters and work roll temperature field data measured on site; Step 2: Establish a three-dimensional thermal crown finite element model of the CVC work roll according to the CVC rolling mill parameters collected in step 1; Step 3: Calculate the convective heat transfer coefficients between the working roll and the strip, the working roll and the air, and the working roll and the cooling water during the rolling process according to the strip parameters, rolling process parameters, and cooling water parameters collected in step 1, apply the convective heat transfer coefficients to the three-dimensional thermal crown finite element model, and conduct a finite element simulation experiment; Step 4: Adjust the temperature boundary conditions of the three-dimensional thermal crown finite element model so that the work roll temperature data curve of the finite element simulation experiment is consistent with the work roll temperature data curve measured on site; Step 5: Perform a finite element simulation experiment based on the adjusted three-dimensional thermal crown finite element model, extract the lateral distribution data of the thermal expansion of the work roll surface at different time nodes in the finite element simulation experiment, and fit it with the initial CVC work roll shape curve to obtain a new work roll shape curve; Step 6: According to the new work roll shape curve obtained in step 5, the influence of the change of the work roll thermal crown at different time nodes on the CVC work roll shape curve is analyzed; The step 2 is specifically as follows: Step 2.1: Establishing modeling dimension parameters of the three-dimensional thermal crown finite element model of the CVC work roll according to the CVC rolling mill parameters collected in step 1; Step 2.2: Establish material parameters of the three-dimensional thermal crown finite element model of the CVC work roll according to the CVC rolling mill parameters collected in step 1; Step 2.3: Establish a three-dimensional thermal crown finite element model of the CVC work roll. To shorten the calculation time, take 1/30 of the circumferential direction of the work roll for modeling; Step 2.4: Simplify boundary conditions; The step 2.3 is specifically as follows: select SOLID164 eight-node hexahedral unit for modeling, define the thermophysical property parameters of the working roll material, and use a high-order B-spline curve to draw the roll shape curve of the working roll based on the CVC rolling mill parameters collected in step 1; refine the mesh on the surface of the working roll to ensure the calculation accuracy, gradually sparse from the outside to the inside to shorten the calculation time, and the surface mesh size is 10 mm in the length direction, 2 mm in the width direction, and 3 mm in the depth direction; The specific assumptions and simplifications of step 2.4 are as follows: (1) The temperature of any node during the rolling process changes periodically. Assuming that the work roll does not rotate, the boundary conditions are rotated in the opposite direction to simulate the rotation of the work roll. (2) It is assumed that the temperature fields of the upper and lower working rolls are consistent, and the working rolls are in the zero roll position; (3) The heat exchange between the working roll and the strip, the working roll and the cooling water, and the working roll and the air is equivalent to convection heat exchange; (4) Ignore the frictional heat between the working roll and the support roll; (5) According to the contact arc length between the strip and the working roll, the working roll is divided into 30 equal parts along the axial direction, each part is 12°, and the part where the strip is in contact with the working roll is one part; The step 5 is specifically as follows: Step 5.1: Extract the lateral distribution data of the thermal expansion of the working roll surface at different time nodes of the finite element simulation experiment; Step 5.2: Add the thermal expansion of the work roll surface to the initial CVC work roll shape curve to obtain multiple thermal crown work roll shape curves under different thermal crowns; normalize the work roll width data of the multiple thermal crown work roll shape curves under different thermal crowns, and fit the normalized thermal crown work roll shape curves using a cubic polynomial to obtain a cubic fitting polynomial as follows: y＝A ₁ x+A ₂ x ² +A ₃ x ³ +e(x); Wherein, y is the new working roll shape curve; x is the dimensionless coordinate after normalization in the width direction of the working roll, x∈[-1,1]; _A1 is the first-order fitting coefficient, _A2 is the second-order fitting coefficient, and _A3 is the third-order fitting coefficient; e(x) is the fitting error; Step 5.3: Based on A ₁ , A ₂ , and A ₃ , draw a new working roll profile curve and calculate the partial thermal crown c _p and overall thermal crown c _t indicators of the working roll: Wherein, h _c is the working roll diameter at the center point of the working roll, _hi is the working roll diameter at the operating side of the working roll, _hi ' is the working roll diameter at the driving side of the working roll, h _j is the working roll diameter corresponding to the strip operating side, and h _j ' is the working roll diameter corresponding to the strip driving side; The influence of the thermal crown described in step 6 on the roll curve and the strip shape is: At different rolling time nodes, the CVC working roll roll shape curve is distributed in an S shape, but with the increase of rolling time, the CVC working roll middle roll shape curve increases upward, which is equivalent to adding quadratic terms, linear terms and constant term coefficients on the basis of the initial CVC working roll roll shape curve. 2. The method for predicting the work roll shape based on the thermal crown of a CVC rolling mill according to claim 1, characterized in that the step 1 specifically comprises: obtaining strip parameters, rolling process parameters, cooling water parameters, CVC rolling mill parameters and work roll temperature field data from the hot rolling production line; The strip steel parameters include: strip steel grade, strip steel width, strip steel thickness and strip steel temperature; The rolling process parameters include: rolling speed, friction coefficient, rolling gap time and working roll lateral displacement; The cooling water parameters include: cooling water temperature, cooling water flow rate and cooling water injection pressure; The CVC rolling mill parameters include: work roll diameter, work roll barrel length, work roll density, work roll elastic modulus, work roll Poisson's ratio, work roll thermal expansion coefficient, work roll specific heat capacity, work roll thermal conductivity and initial CVC work roll roll shape curve; The working roll temperature field data is obtained by attaching reflective tape to the working roll along the axial direction after the work roll is taken off the machine, and using a thermal imager to take a picture of the temperature field cloud map of the working roll. 3. The method for predicting the work roll profile based on the thermal crown of a CVC rolling mill according to claim 2, characterized in that the initial CVC work roll profile curve equation is a cubic polynomial function, specifically: R _U (x) = R ₀ + a ₁ ·x + a ₂ ·x ² + a ₃ ·x ³ ; RL ₍ x)＝ _R0 + _a1 ·( _LREF -x)+ _a2 ·( _LREF -x) ² + _a3 ·( _LREF -x) ³ ; Wherein, _RU (x) is the upper roll shape function of the working roll, _RL (x) is the lower roll shape function of the working roll, x is the transverse coordinate of the roll; _R0 is the nominal radius of the working roll, in mm; _a1 , _a2 and _a3 are the roll shape coefficients to be determined; _LREF is the design length of the working roll, in mm. 4. The method for predicting the work roll shape based on the thermal crown of a CVC rolling mill according to claim 1, characterized in that the step 3 specifically comprises: Step 3.1: The contact heat transfer and deformation heat between the working roll and the strip and the radiation heat transfer between the working roll and the air during the rolling process are equivalent to convection heat transfer; Step 3.2: Determine the convection heat transfer coefficients between the strip and the working roll, between the working roll and the cooling water, and between the working roll and the air according to the convection heat transfer formula; Step 3.3: Generate a time-heat transfer coefficient cycle curve through the K file using the convective heat transfer coefficient calculated in step 3.2; Step 3.4: Create SEGM on the surface of the three-dimensional thermal crown finite element model of the CVC work roll, apply the time-heat transfer coefficient curve to the SEGM, and realize the heating and cooling process of the work roll. 5. The method for predicting the work roll shape based on the thermal crown of a CVC rolling mill according to claim 4, characterized in that the step 3.2 is specifically: The expression of heat transfer coefficient in the contact arc between the working roll and the strip is as follows: Where: _hcon is the convection heat transfer coefficient between the strip and the working roll; is the average unit rolling force, in N; v is the rolling speed, in m/s; The heat transfer coefficient between the working roll and cooling water is expressed as follows: (1) The working roll surface temperature Tr is less than 100°C: (2) The working roll surface temperature Tr is greater than 200°C: Wherein: h _cw is the convection heat transfer coefficient between the working roll and the cooling water; γ ₁ and γ ₂ are the cooling heat transfer correction coefficients; E is the elastic modulus of the working roll; Q is the water flow density, Q=V _SP /A _SP ; PS _P is the injection pressure, in MPa; _TC is the cooling water temperature, in °C; V _SP is the cooling water volume, in l/s; A _SP is the injection area, in m ² ; when Q<10000 (l/s/m ² ), B=(T _c /16) ^-0.17 ; when Q≥10000 (l/s/m ² ), B=1.0; The heat exchange coefficient between the working roll and the air is expressed as follows: h _air =1.465ΔT ^1/3 ; Where: h _air is the convection heat transfer coefficient between the working roll and the air; ΔT is the temperature difference between the working roll and the surrounding air, unit: °C.