JPH067824A - Method for controlling plate thickness in rolling mill - Google Patents

Abstract

PURPOSE:To improve yield and to reduce rolling trouble by improving the thickness accuracy especially in the tip part of a metal plate in a method for controlling the thickness of a material to be rolled by automatically setting the screw-down position of a rolling mill before rolling the metal plate. CONSTITUTION:In the method that the screw-down position of the rolling mill is determind from a rolling load and the target thickness that are beforehand determined before rolling the metal plate using a roll-gap calculating formula and automatically set, correction terms of the roll-gap calculating formula that the wear and thermal expansion of the roll of the rolling mill are taken into consideration are taken as the sum of a value that the roll wear and thermal crown of two diameters are multiplied by a correction factor (a) of less than 1.0 and the amount of parallel expansion of two diameters.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the plate thickness of a material to be rolled by automatically setting a rolling position of a rolling mill prior to rolling the material.

[0002]

2. Description of the Related Art Generally, in strip rolling, in particular, in order to obtain a target strip thickness at the tip of a material to be rolled until feedback control based on the strip thickness measurement result at the rolling mill exit side is implemented. Prior to rolling, it is necessary to properly set the rolling position of the rolling mill. The roll gap calculation formula (1) below, a so-called gauge meter formula, is used to set the rolling position.

H = S + P / M (1) where S is the distance between the upper and lower work roll chocks in the rolling mill (rolling position), M is the mill constant, P is the rolling load, h
Is the strip thickness at the delivery side of the rolling mill (roll gap at the center of the mill).

However, in practice, the roll diameter changes due to roll wear and thermal expansion, so that the plate thickness calculated using equation (1) has an error from the actual plate thickness. Figure 10
Indicates the transition of this error within the rolling cycle.
As shown in FIG. 10, since the thermal expansion of the roll is significantly increased in the first half of the cycle, the roll diameter becomes larger than in the initial state and the actual plate thickness becomes smaller than the calculated plate thickness. Also,
In the latter half of the cycle, since the thermal expansion of the roll is saturated, the roll diameter gradually becomes smaller than the initial state as the wear progresses, and as a result, the actual plate thickness becomes larger than the calculated plate thickness.

This error is generally called an offset, and in order to reduce the offset, it has been conventionally considered to add a correction term ΔS considering the thermal expansion and wear of the roll as shown in the following expression (2). There is. As the correction term ΔS, it is general to consider the amount of change in the roll diameter at the mill center due to thermal expansion and wear of the roll from the state in which the rolling mill is installed.

H = S + P / M + ΔS (2)

[0007]

However, in the conventional plate thickness control method for a rolling mill, a change in roll diameter under no load condition is considered as a change in roll gap, and a roll under a rolling load is considered. It does not always match the change in the gap. This is because when the roll profile changes from the initial state, the contact pressure distribution between the work roll (WR) and the backup roll (BUR) in the rolling mill is different, even if the same rolling load as that at the time of the initial profile acts. This is because the amount of elastic deformation of the roll system such as the flatness between the work roll and the backup roll and the bending of the backup roll is different.

Therefore, the reduction position calculated by using the equation (2) does not always become an appropriate set value, the yield is reduced by cutting off the portion where the target plate thickness is not obtained, and each stand in tandem rolling. It becomes a factor that causes the trouble of strip passing due to the loss of mass balance. The decrease in yield varies depending on the strip running speed, but the length until the start of the thickness gauge feedback control is about 10 m, and for example, the slab has a thickness of 230 mm.
mm x length 10000 mm and target thickness 3.2 mm, about 1.
It corresponds to 4%. Further, as the threading trouble, there is a case where the plate material is cut between the stands and cannot be rolled.

The present invention has been made to solve the above problems, and improves the plate thickness accuracy of the plate material, particularly at the tip portion thereof, thereby improving the yield and reducing rolling troubles. The purpose is to provide a control method.

[0010]

In order to achieve the above object, a method for controlling the plate thickness of a rolling mill according to the present invention is based on a roll gap obtained from a rolling load and a target plate thickness obtained in advance before rolling of a plate material. In what is automatically set by obtaining the rolling position of the rolling mill using the calculation formula, a correction term considering wear and thermal expansion of the roll of the rolling mill included in the roll gap calculation formula, prior to the rolling position setting calculation. It is characterized in that it is changed according to the change in the roll profile calculated or actually measured.

[0011]

In the plate thickness control method for a rolling mill of the present invention described above,
In the roll gap calculation formula used for the initial setting of the rolling position,
A change in elastic deformation of the roll system due to a change in roll profile can be taken into consideration, and thus an appropriate reduction position can be set.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A sheet thickness control method for a rolling mill as an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a flow chart for explaining the procedure, and FIG. 2 is a diagram showing rolling in a rolling cycle. Fig. 3 is a graph showing changes in load cell load when tightened to the same rolling position in the absence of pressure, Fig. 3 is a graph showing a comparison between the plate thickness correction amount calculation value and the roll profile calculation value, and Fig. 4 (a) is the roll profile. 4 (b) is a graph showing the relationship between the depth of the concave portion and the elastic deformation reduction amount of the roll system when the roll profile shown in FIG. 4 (a) is assumed, and FIG. 6A and 6B are graphs showing the relationship between the width of the unevenness of the roll profile and the correction coefficient of the plate thickness correction term. FIGS. 6A and 6B are for explaining the change amount of the roll diameter at the center of the mill from the time of incorporating the roll. Figures and 7 show the actual work roll wear profile. FIG. 8 is a graph showing a comparison between measured values and calculated values, FIG. 8 is a graph showing a thermal expansion amount at the start of the n-th rolling, and FIG. 9 is a graph showing comparison between measured values and calculated values of the thermal profile.

First, the principle of the method of the present invention will be described with reference to FIGS. FIG. 2 shows the experimental results by the present inventors. In the hot-finishing rolling mill of 7 stands (F1 to F7), the rolling was performed immediately after the work roll was incorporated and in the middle of the rolling cycle. It shows the transition of the load applied to the load cell when the work rolls are brought into contact with each other and tightened to the same rolling position. As shown in FIG. 2, in each stand, the load cell load increases at the beginning of the rolling cycle. After that, until the end of the cycle, the former stand (for example, the stand F1,
In F3), it slightly increases or saturates, and the latter stand (for example, Fig. 2
In stand F6) it decreases. The increase or decrease of the load cell load is due to the change of the roll diameter, and it can be considered that the load increases when the roll diameter becomes larger than the initial state and decreases when the roll diameter becomes smaller than the initial state. It is qualitatively consistent with the well-known wear and thermal expansion behavior of the work rolls of each stand.

FIG. 3 shows the above-mentioned (2) based on this result.
The sheet thickness correction term ΔS obtained by using the formula, that is, the roll gap change amount, and the roll profile change amount at the mill center obtained by a separate calculation, that is, roll wear and thermal expansion 2
It is shown by comparing with the diameter. As shown in FIG. 3, in any case, the absolute value of the roll gap change amount obtained from the load change tends to be smaller than the roll diameter change amount 2 diameters at the mill center. Further, there is almost the same difference in the former stand (for example, the stand F1 in FIG. 3) regardless of the measurement chance, and the latter stand (for example, in FIG. 3).
Among them, in the stand F6), the coincidences are relatively good in the second and third measurement opportunities, but the difference between the two is large in the fourth and fifth measurement opportunities. That is, referring to FIG. 2, it can be understood that the error increases as the load on the load cell changes and the uneven shape of the roll profile increases. It is considered that this is because the elastic deformation of the central portion of the roll increases when the roll profile has a convex shape and decreases when the roll profile has a concave shape as compared with the initial state.

FIG. 4 (b) shows the elastic deformation of the roll system when the work rolls are in contact with the depth δ of the recess, assuming the concave roll profile shown in FIG. 4 (a). It shows the result of calculating the relationship with the amount of decrease. As shown in FIG. 4B, in the calculation, the elastic deformation in each part of the roll system decreases in proportion to the recess depth δ. Fig. 4 shows the case where the roll profile is concave, but the relationship between the height of the convex portion and the amount of increase in elastic deformation when the roll profile is convex is also shown in Fig. 4 (b).
Will be similar to. As a result of correcting the roll profile change amount in FIG. 3 based on this result, as shown by the arrow in FIG. 3, the error with the plate thickness correction term ΔS is significantly reduced.

Next, the procedure of the plate thickness control method of this embodiment will be described with reference to FIG. First, when the plate material to be rolled from now on is the n-th plate material counted from the roll-in, the roll profile immediately before the n-th rolling is calculated (or measured) (step S1). Here, in the calculation, the roll wear and thermal expansion are obtained by using the rolling record data from the first roll to the (n-1) th roll, and the initial profile (grinding profile) at the time of incorporating the roll is added to this.
An online roll profilometer or the like is used for the actual measurement.

Here, the means for calculating the roll profile will be described in more detail with reference to FIGS. Basically,
The work roll wear profile and thermal profile are calculated, and the sum of these is used as the roll profile.

First, the work roll (WR) wear profile calculation is performed. Work roll wear amount W at the center of strip width
_c is expressed as a function of the rolling pressure, the number of contact between the plate and the work roll, and the sliding distance due to the advance of the plate in the roll bite, as shown in the following equation (3).

[0019]

[Equation 1]

Here, P is rolling load, B is plate width, l _d is contact arc length, L is rolling length, D _w is work roll diameter, and f
Is the advanced rate, and k, α, and β are constants.

The work roll wear profile W (x) is the roll axis direction by the product of the profile determined from the results of continuous rolling experiment work roll wear amount W _c the same width as the plate material of the plate width central portion function w (x) It is obtained by calculating the amount of wear at each position and superimposing this on each rolling. Therefore, the wear profile W _n (x) at the start of the n-th rolling
Is expressed by the following equation (4). FIG. 7 shows the comparison result between the calculated value and the measured value by the equation (4). As shown in this Figure 7, (4)
It can be seen that the calculated value by the formula agrees well with the measured value.

[0022]

[Equation 2]

For the thermal profile calculation, a two-dimensional simple model considering temperature distributions in the work roll radial direction and the axial direction is used. In this method, the averaged temperature rise in the radial direction θ _m obtained from the approximate solution of the heat conduction equation in the radial direction in the central portion of the strip width for each rolled material and the profile function V (x ) And the average temperature increase in the radial direction at each position in the axial direction are calculated, and as shown in FIG. 8, they are superposed each time rolling is performed. The thermal expansion U _n (x) at the start of the n-th rolling is
It is represented by (5). In the equation (5), γ is a linear expansion coefficient, V
_i (x), θ _mi is a function of time.

Here, the minimum value of U _n (x) in the axial direction is called a parallel expansion amount, and this is expressed as U _n (x ₀ ) when the position where the minimum value is taken is x ₀ . Although x ₀ is usually the roll barrel end, especially in the case of a mill that moves the roll in the axial direction, it is the barrel barrel end on the side where the distance from the plate is long. The thermal profile is U
_It is expressed as the difference between _n (x) and U _n (x ₀ ). FIG. 9 shows a comparison result between the calculated value of the thermal profile using the equation (5) and the actually measured value. As shown in FIG. 9, it can be seen that the calculated value of the thermal profile using the equation (5) agrees well with the measured value.

[0025]

[Equation 3]

The work roll wear profile W _n (x) and the thermal profile U _n (x) -U calculated as described above.
_The roll profile is calculated as the sum of _n (x ₀ ).

Next, similarly to the conventional rolling position initial setting calculation, the pass schedule (each pass exit side plate thickness) determination (step S2), temperature prediction calculation (step S3), and load prediction calculation (step S4) are sequentially executed. To do.

Thereafter, the correction coefficient a is calculated by the predetermined function f (step S5). This function f is the shape of the unevenness,
It is a function such as the roll diameter, and the shape of the function is determined in advance based on an offline analysis. In this embodiment, the roll profile is approximated by a trapezoid from the measured results of wear and thermal profile shown in FIGS. FIG. 5 is a result of calculating the elastic deformation amount of the roll central portion in a rolling state when the roll profile is approximated by a trapezoid and the unevenness amount and the uneven width of the roll central portion are changed. Is changing. And the following formula (6)
Then, the set rolling position S is obtained (step S6). In addition,
In the formula (6) below, W _n (0) and U _n (0) are values at the mill center.

S = h−P / M−2 [a {W _n (0) + U _n (0) -U _n (x ₀ )} + U _n (x ₀ )] (6) Therefore, (2) As the correction term ΔS in the formula, the initial profile due to roll wear and thermal crown (known in the profile after grinding, that is, immediately after roll incorporation)
Correction coefficient a less than 1.0 for 2 diameters, which is the amount of change from
The sum of the value obtained by multiplying by and the parallel expansion amount of 2 diameters will be used.

Here, as shown in FIGS. 6 (a) and 6 (b), since the plate thickness of the plate material 1 is determined by the gap between the work rolls 2 and 2, the elastic deformation of the roll system is not changed by the roll profile. Then, the amount of change from the initial profile due to wear and thermal expansion of the roll is geometrically 2 diameters. As shown in FIG. 6B, the plate thickness variation δ at the mill center is δ ₁ + δ ₂ + δ ₃ + δ ₄ . In FIG. 6, reference numeral 3 indicates a backup roll (BUR).

When the shape of the roll profile changes, the contact pressure between the work roll and the backup roll at the center of the mill changes even if the same rolling load as that at the initial profile is applied, and the flatness between the work roll and the backup roll changes. And backup roll deflection (roller elastic deformation)
Changes. Therefore, changes in the roll gap result in wear,
Since the elastic deformation change amount is subtracted from the change of two diameters due to thermal expansion, in the present embodiment, wear and the thermal crown of two diameters are multiplied by the correction coefficient a of less than 1.0, and the roll profile. The sum of two parallel expansions that do not affect the change in shape and two diameters is defined as the correction term ΔS.

As a result of applying the method of the present embodiment to the online roll gap calculation formula, the variation in the error of the calculated plate thickness with respect to the measured plate thickness was reduced from 38 μm of the related art to 30 μm.

As described above, according to the strip thickness control method for the rolling mill of the present embodiment, the change in elastic deformation of the roll system due to the change in roll profile is considered in the roll gap calculation formula used for the initial setting of the rolling position. Therefore, since the appropriate reduction position can be set, the plate thickness accuracy of the plate material, particularly at the tip portion, can be greatly improved, which can contribute to the improvement of yield and the reduction of rolling trouble.

[0034]

As described in detail above, according to the plate thickness control method for a rolling mill of the present invention, the elastic deformation of the roll system due to the change of the roll profile is included in the roll gap calculation formula used for the initial setting of the rolling position. In consideration of the change in temperature, it is possible to set the appropriate rolling position.Therefore, the plate thickness accuracy, especially at the tip of the plate, can be greatly improved, and the yield can be improved and rolling trouble can be reduced. is there.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining a procedure of a plate thickness control method for a rolling mill as an embodiment of the present invention.

FIG. 2 is a graph showing changes in load cell load when tightened to the same rolling position in a rolling cycle without rolling.

FIG. 3 is a graph showing a plate thickness correction amount calculation value and a roll profile calculation value in comparison.

FIG. 4A is a diagram for explaining an example of a roll profile, and FIG. 4B shows a relationship between the depth of the recess and the elastic deformation reduction amount of the roll system assuming the roll profile shown in FIG. It is a graph shown.

FIG. 5 is a graph showing the relationship between the width of the unevenness of the roll profile and the correction coefficient of the plate thickness correction term.

6 (a) and 6 (b) are views for explaining the roll diameter change amount at the center of the mill after the roll is incorporated.

FIG. 7 is a graph showing a comparison between an actually measured value and a calculated value of a work roll wear profile.

FIG. 8 is a graph showing the amount of thermal expansion at the start of the n-th rolling.

FIG. 9 is a graph showing a comparison between an actual measurement value and a calculated value of a thermal profile.

FIG. 10 is a graph showing a transition of sheet thickness calculation error when a change in roll profile within a rolling cycle is not considered.

[Explanation of symbols]

 1 Plate material 2 Work roll (WR) 3 Backup roll (BUR)

Claims (1)

[Claims] 1. A sheet thickness control method for automatically setting a rolling position of a rolling mill using a roll gap calculation formula from a rolling load and a target sheet thickness obtained in advance before rolling a sheet material, wherein the roll is used. A correction term in consideration of wear and thermal expansion of rolls of the rolling mill included in the gap calculation formula, which is changed according to a change in the roll profile calculated or actually measured prior to the rolling position setting calculation. Thickness control method for machine.