JP2006239727A - Method for rolling hot-rolled steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an economical and high-productivity rolling method of a hot-rolled steel sheet by which the target sheet crown after finish rolling is secured as maintaining the steel sheet in a good shape when performing the hot rolling of the steel sheet, especially, schedule-free rolling by which the rolling is performed while successively arbitrarily changing the width or the like of each steel sheet in a rolling cycle. <P>SOLUTION: In this method, the setting an actuator for controlling the sheet crown and sheet shape of each rolling stand which is provided on one or more rolling stands and the setting of the thickness reduction schedule of each rolling stand are performed so that the sheet crown of the steel sheet after rolling does not come into a reverse crown profile. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for rolling a hot-rolled steel sheet, and more particularly to a method for rolling a hot-rolled steel sheet suitable for schedule-free rolling in which the width of each steel sheet in a rolling cycle is rolled while being arbitrarily changed. .

  In the rolling of hot-rolled steel sheets, the temperature of the material to be rolled is as high as about 800 to 1050 ° C. Therefore, as rolling progresses, a trapezoidal thermal expansion called a thermal crown occurs in a range in contact with the material to be rolled of the rolling roll. Arise. Moreover, in addition to the contact surface with the material to be rolled becoming high temperature, the surface pressure acting between the material to be rolled and the rolling roll and between the reinforcing rolls such as the rolling roll and the backup roll becomes very high. Roll wear also progresses sequentially.

  Therefore, in the rolling of hot-rolled steel sheets, in order to ensure the desired finishing dimensions that differ from coil to coil, in particular, the sheet crown and sheet shape, which are the sheet thickness profiles in the sheet width direction, Based on the predicted change, the setting of a plate crown / plate shape control actuator such as a work roll bender, a roll cloth, and a roll shift is performed (for example, see Patent Document 1).

  On the other hand, in the rolling of hot-rolled steel sheets, in recent years, so-called schedule-free rolling, in which the material and dimensions (particularly, the sheet width) of the material to be rolled are sequentially and arbitrarily changed, is aimed at from the viewpoint of productivity.

  In recent years, the introduction of rolling rolls with excellent wear resistance, such as high-speed rolls, has been advancing in the rolling of hot-rolled steel sheets. Countermeasures against these issues are becoming important. Hereinafter, the reason for this will be described with reference to FIGS.

  As shown in FIG. 6, when the narrow coil is continuously rolled, a trapezoidal thermal crown develops at the plate width position of the material to be rolled. In this state, when the next coil (j + 1 coil) wider than the previous coil (jth coil) is rolled, the thickness is steeply steep at the position outside the trapezoidal thermal crown within the plate width. As shown in FIG. 7, a plate thickness profile called reverse crown profile is obtained. Normally, the thickness profile of a hot-rolled steel sheet is a profile that gradually decreases from the center of the sheet width to the end of the sheet width, while the reverse crown profile has a thickness that gradually decreases from the center of the sheet width to the end of the sheet width. It is a plate thickness profile in which a plate thickness minimum value and a plate thickness maximum value are generated in the vicinity. When a reverse crown profile occurs, for example, the specifications from the customer cannot be satisfied, scratches occur at the edge of the plate in the cold rolling process, and extreme ear wave shapes occur, resulting in plate-through performance. It becomes a big problem, such as inhibiting.

  In order to solve the above-described problem, a roll surface profile control method has been proposed as a means for preventing the occurrence of a reverse crown profile (see, for example, Patent Document 2 and Patent Document 3).

  FIG. 8 shows a method for controlling the thermal crown profile disclosed in Patent Document 2, in which an induction heating device is provided in the vicinity of both ends of the rolling roll, and the plate widths of the coil and the next coil are compared. If the plate width of the next coil is wide, the position corresponding to the plate end of the next coil on the surface of the rolling roll is set at the time of passing the coil and the coil and the next coil so as not to deteriorate the plate crown and plate shape. In between, heating is performed so that necessary thermal expansion is obtained.

FIG. 9 shows a control method of the thermal crown profile disclosed in Patent Document 3, in which the cooling water amount distribution increases from the center in the coil plate width direction toward the plate end, and It is intended to eliminate the steep gradient of the thermal crown profile that develops in a trapezoidal shape by shutting off the roll cooling water in a portion that is not in contact with the material to be rolled or by extremely reducing the flow rate.
JP-A-7-75812 Japanese Patent Laid-Open No. 2004-98068 Japanese Patent Laid-Open No. 11-129010

  However, each of the prior arts described above has the following problems.

  In the method for setting the plate crown and plate shape actuators disclosed in Patent Document 1, the crown profile control by these actuators has a substantially parabolic shape in the plate width direction with the plate width center as the maximum point, that is, the roll surface There is a problem that the profile has a convex shape, and these actuators alone cannot compensate for a change in roll surface profile due to a sharp thermal crown around the sheet width end portion of the material to be rolled or roll wear. Moreover, as shown in FIG. 7, when the position A in the vicinity of the plate width end is selected as the quality evaluation point, and the position B of 50 to 200 mm from the plate end is selected as the plate shape evaluation point, the actual plate thickness profile is indicated by a solid line. Even if it is a reverse crown profile, since the false profile as shown by the broken line can be estimated from the quality evaluation point A and the plate shape evaluation point B, the actual plate thickness profile cannot be accurately determined. was there.

  In the method disclosed in Patent Document 2, the effect of changing the roll surface profile is recognized, but when introduced into only one stand of a continuous rolling mill composed of a plurality of stands, there is a concern that the plate shape may be suddenly disturbed. For this reason, it is presumed that it is desirable to apply it to a plurality of consecutive stands. In addition, if water adheres to the induction heating device due to splashing of roll cooling water, etc., the device will be destroyed due to an electrical short-circuit accident, so perfect waterproofing measures are inevitable, and it may be a very expensive facility. Inevitable. Moreover, since induction heating is surface high-density heating, there are concerns about dangers such as a decrease in roll surface hardness, roll cracks due to thermal stress, and occurrence of a spalling accident.

  In the method disclosed in Patent Document 3, although the effect of changing the roll surface profile is recognized, the effect is very slight, and it is estimated that it is difficult to cope with an arbitrary rolling schedule in the schedule-free rolling. The

  The present invention has been made in view of the above-described circumstances, and in performing hot rolling of a steel sheet, in particular, schedule-free rolling in which the width of each steel sheet in a rolling cycle is rolled while being arbitrarily changed. An object of the present invention is to provide an economical and highly productive rolling method for hot-rolled steel sheets that can secure a target sheet crown after finish rolling while maintaining the steel sheet in a good plate shape. .

  In order to solve the above-mentioned problems, the present inventors have conducted extensive studies on optimization of the sheet thickness reduction schedule and its setting method in addition to the evaluation position of the sheet crown and sheet shape in hot rolling. It has been found that by optimizing the sheet shape evaluation points and the sheet thickness reduction schedule, rolling of hot-rolled steel sheets of arbitrary finishing dimensions is performed sequentially, that is, schedule-free rolling can be appropriately handled.

  Hereinafter, means for solving the above problems will be described in detail by taking n-pass rolling as an example.

  The sheet crown in hot rolling is generally calculated by the equation (1).

  Here, Cr is a plate crown, Crm is a mechanical crown, i is a pass No. , Α is a transfer rate, and β is a parameter called a genetic coefficient. In general, a plate crown is a difference between a plate thickness at the center of the plate width and a plate thickness at a quality evaluation point set within 50 mm from the plate end. The target crown on the final rolling stand delivery side gives a target to the crown at this position. The mechanical crown Crm is a plate crown when a uniform load is applied to the rolling roll in the plate width direction. The rolling load, the operation amount of the plate crown / plate shape actuator, the initial crown of the rolling roll, the roll wear, Using a thermal crown, for example, it can be obtained by applying a method of finding a roll deformation called numerical model by numerical calculation. In addition, a method is also used in which the influence of various rolling conditions on roll deformation is obtained in advance, and a formula for calculating the mechanical crown Crm from the rolling conditions is created.

  Next, the plate shape is evaluated based on whether or not the amount of change in the crown ratio (plate crown Cr / plate thickness H) before and after each rolling stand falls within a predetermined range, as represented by equation (2). Is done.

That is, the crown ratio Cr _i-1 / H _i-1 of the i-pass rolling before (after the i-1-pass rolling), the difference between the i-th crown ratio after pass rolling Cr _i / H _i is, delta ( Cr / H) _i min~Δ (if within the range of Cr / H) _i max, but a plate shape of the rolled material is _{good, Δ (Cr / H) i} min smaller when extends shaped medium is Thus, when it is larger than Δ (Cr / H) _i max, it becomes an ear wave shape. Incidentally, Δ (Cr / H) _i min and Δ (Cr / H) _i max are influenced by the plate width and thickness of the material to be rolled, and generally empirical formulas are used. Unless otherwise specified, H represents the plate thickness at the plate width center position.

The conventional method for setting the plate crown / plate shape control actuator is the plate crown value Cr _A at the point A (quality evaluation point) in the vicinity of the plate width end after the final rolling pass calculated by the equation (1). Is set to a desired value Cr _Aref, and the plate shape at each rolling stand is evaluated using the formula (2) at a point B (plate shape evaluation point) 50 to 200 mm from the end of the plate width. The actuator is set. For example, the operation amount Ei of the actuator at each rolling stand is set by means such as optimization calculation that minimizes the evaluation function J as shown in equation (3).

Here, u and v _i are weighting factors.

  However, as described above, when the shape evaluation point is one of the B points, a false profile such as a broken line can be estimated from the quality evaluation point A and the plate shape evaluation point B as shown in FIG. Therefore, since the actual reverse crown profile indicated by the solid line cannot be accurately determined, it has been difficult to prevent the reverse crown profile with the evaluation function J in the equation (3).

  Therefore, as shown in FIG. 2, the present inventors can accurately evaluate the reverse crown profile by setting the plate shape evaluation point to two or more positions in the range of 50 to 200 mm from the end of the plate width. Inspired to be. Here, the shape evaluation point was set in the region of 50 to 200 mm from the edge of the plate, which was found as a result of evaluating the plate crown profile under various conditions. As the plate shape evaluation point, the plate thickness minimum point and the plate thickness maximum point exist in the region of 50 to 200 mm from the plate end, and the plate thickness change in the plate width direction is small in the range exceeding 200 mm from the plate width end. Is not suitable.

In the initial conditions, point B shown in FIG. 2 is 50 to 100 mm from the end of the plate where the maximum point of thickness is likely to be located, and point C is 150 to 200 mm from the end of the plate where the minimum point of thickness is likely to be located. Desirably, when it is estimated by calculation that an inverse crown profile is obtained, point B is a position where the plate thickness is maximized in the vicinity of the plate width end, and point C is a plate thickness from point B to the center of the plate width. For example, the control amount E _i of the actuator at each rolling stand may be set by a technique such as optimization calculation that minimizes the evaluation function J ′ as shown in Equation (4).

Here, w _i is a weight function.

  However, as shown in FIG. 6, the reverse crown profile is generated by a thermal crown that has developed into a trapezoidal shape, and even if the operation amount of each actuator is optimized using equation (4), Due to the limitations, the reverse crown profile cannot be avoided. As described above, the crown control by the plate crown and plate shape control actuators such as the roll bender and the roll cloth is substantially parabolic in the plate width direction with the plate width center as the maximum point, that is, the roll surface profile is changed. This is because it is impossible to compensate for the thermal crown profile that is also trapezoidal in the convex direction because it is convex. Further, in the case of a plate crown / plate shape control actuator that can control the roll surface profile to a convex shape or a concave shape by changing the shift direction in the plate width direction of the upper and lower rolling rolls like a CVC roll, 4) By optimizing the amount of operation of the actuator using the formula, it is possible to cope with the reverse crown profile, but because there are restrictions on the work roll shift amount and roll surface unevenness amount, there is a limit to dealing with schedule-free rolling. There is.

  As a result of intensive studies on this point, the present inventors have optimized the sheet crown / plate shape control actuator and changed the sheet thickness reduction schedule (reduction ratio distribution of each rolling stand) in each rolling stand. Thus, it was found that the generation of a reverse crown profile can be suppressed. That is, while the thermal crown becomes a trapezoidal profile in the convex direction (expansion direction), the flat deformation between the material to be rolled and the roll due to the rolling load becomes a trapezoidal profile in the concave direction (dent direction). If the sheet crown after the final rolling pass has a reverse crown profile, it is effective to review the sheet thickness reduction schedule to reduce the rolling load at the front stage stand and increase the rolling load at the rear stage stand. I found out. This is because the temperature of the material to be rolled decreases as the latter stand generally decreases, so the amount of thermal crown is small, and the effect of pushing back the thermal crown is greater by increasing the rolling load at the latter stand and giving large flat deformation. Presumed to be.

  The setting of such a plate thickness reduction schedule (plate thickness at each stand) is formulated by, for example, formulating the plate crown Cr and the crown ratio Δ (Cr / H) as a function of the plate thickness on the entry / exit side of each stand, It has been found that it is possible to obtain an evaluation function J ″ by substituting it into the evaluation function J ′ and to obtain the evaluation function J ″ by a technique such as optimization calculation that minimizes the evaluation function J ″.

  The present invention has been made based on these findings and has the following characteristics.

  [1] A method of rolling a hot-rolled steel sheet by a continuous rolling mill comprising a plurality of rolling stands, each of which is provided in one or more rolling stands so that the crown of the steel sheet after rolling does not become a reverse crown profile. A method for rolling a hot-rolled steel sheet, comprising setting a plate crown / plate shape control actuator of a rolling stand and setting a sheet thickness reduction schedule of each rolling stand.

  [2] The setting of the plate crown / plate shape control actuator and the plate thickness reduction schedule are set so that a predetermined evaluation function defined by the target plate crown and the crown ratio becomes an optimum value. The method for rolling a hot-rolled steel sheet according to [1].

  [3] Sheet width end of the hot rolled steel sheet using the predicted value of the thermal crown of the rolling roll, the predicted value of wear of the rolling roll, the finished dimension of the hot rolled steel sheet, and the predicted value of the rolling load The crown ratio at two or more points in the region of 50 to 200 mm is obtained, and the crown ratio is substantially constant for all rolling stands, and the desired plate crown is obtained on the final rolling stand exit side. The method for rolling a hot-rolled steel sheet according to the above [1] or [2], wherein the setting of a crown / plate shape control actuator and a plate thickness reduction schedule are performed.

  [4] Using the predicted value of the thermal roll of the rolling roll, the predicted value of wear of the rolling roll, the finished dimension of the hot rolled steel sheet, and the predicted value of the rolling load, the width end of the hot rolled steel sheet The crown ratio at two or more points in the region of 50 to 200 mm is obtained, and the crown ratio is substantially constant for all rolling stands, and the desired plate crown is obtained on the final rolling stand exit side. [1] The calculation of the setting of the crown / plate shape control actuator is performed, and if it is determined that it is difficult to realize the desired crown profile, the setting calculation of the sheet thickness reduction schedule is performed. Thru | or the rolling method of the hot-rolled steel plate in any one of [3].

  [5] The position where the plate thickness is maximized in the vicinity of the plate width end in the region of 50 to 200 mm from the plate width end of the hot-rolled steel plate, and the plate thickness is minimized from that point to the center of the plate width. The method for rolling a hot-rolled steel sheet according to [3] or [4], wherein the crown ratio is evaluated at a position.

  According to the present invention, even for schedule-free rolling in which hot rolling of a steel plate, in particular, rolling of a hot-rolled steel plate having an arbitrary finishing dimension is sequentially performed, no new equipment is added, and an existing plate crown / plate shape is added. The software measures of optimizing the setting of the actuator for control and the setting of the sheet thickness reduction schedule can secure the target plate crown after finish rolling while maintaining the steel plate in good shape. It is possible to provide a method for rolling hot-rolled steel sheets that is efficient and productive.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2.

  FIG. 1 shows a setting procedure of a plate crown / plate shape control actuator and a plate thickness reduction schedule in an embodiment of the present invention.

  As shown in FIG. 1, the setting procedure of the plate crown / plate shape control actuator and the plate thickness reduction schedule in this embodiment is as follows.

(Step S1) Finished target crown Cr _{nA at} point A in the vicinity of the end of the plate width, initial values of input and output side plate thicknesses H _i-1 and H _i at each rolling stand, and operation amount of the plate crown / plate shape control actuator The initial value of E _i , the predicted value of the thermal crown, the predicted value of wear of the rolling roll, and other various rolling conditions are input. Note that the point A is usually selected as a quality evaluation point within 50 mm from the end of the plate width as shown in FIG.

Here, the target crown value Cr _nA is determined in consideration of designation from a customer or plate passing property in the next process, and is usually about 20 to 70 μm.

In addition, the sheet thickness reduction schedule, that is, the initial values of the input and output side sheet thicknesses H _i-1 and H _i of each stand are determined in consideration of the rolling load ratio and the reduction ratio balance at each rolling stand. For example, it is set by managing by a table according to the steel type of the material to be rolled and the finishing dimensions, or is set by the experience of the operator.

The initial value of the operation amount E _i of the plate crown / plate shape control actuator is a parameter that optimizes the operation amount E _i of the plate crown / plate shape control actuator itself. Although there is a slight influence on the convergence behavior of, it does not become a big problem, so an arbitrary value may be set within the range of equipment specifications. In addition, in the optimization calculation to be performed below, if an equipment specification is added as a constraint condition for the operation amount E _i of the actuator, an unrealistic solution can be avoided.

  Further, the other various rolling conditions are, for example, rolling roll dimensions, rolling speed, rolling temperature, etc., and the rolling roll dimensions may be entered by inputting actual roll dimensions, such as rolling speed, rolling temperature, etc. The value is separately set and calculated so as to obtain a desired finishing temperature and productivity.

  (Step S2) Based on the input initial conditions, the rolling temperature and rolling load at each rolling stand are calculated.

(Step S3) The crown Cr _n at the quality evaluation point A becomes the target crown Cr _nA , and the crown ratio (Cr / H) _i at the shape evaluation points B and C in each rolling stand is constant in all rolling stands. Then, the operation amount E _i of the actuator for controlling the plate crown and plate shape of each rolling stand is calculated. Here, as shown in FIG. 2, the shape evaluation points B and C are two points selected within an area of 50 to 200 mm from the end portion of the plate width. However, in this initial condition, it is preferable that the point B is a position 50 to 100 mm from the end of the plate and the point C is a position 150 to 200 mm from the end of the plate.

Then, the calculated actuator - based on the operation amount of data E _i, a crown ratio (Cr _i / H _{i) B} of a shape evaluation point B, the crown ratio in the shape evaluation point _{C (Cr i / H i)} C Then, the crown Cr _n at the quality evaluation point A is calculated, and the evaluation function J ′ of the equation (4) is calculated using the calculated value.

(Step S4) The calculation in step S3 is repeated several times, and the operation amount E _i of the plate crown / plate shape control actuator having the smallest evaluation function J ′ is output as a temporary solution.

  In the above optimization calculation, for example, if nonlinear programming or the like is used, an optimum value can be obtained by several iterations. However, the number of iterations can be taken into account the time that can be spent on the set calculation time. What is necessary is just to set.

(Step S5) In the above procedure, the plate crown profile is calculated using the operation amount E _i of the plate crown / plate shape control actuator output as a provisional solution. Judging.

  That is, on the final rolling stand delivery side, if the plate thickness gradually decreases from the plate width center to the plate end, the setting calculation is terminated, and the process proceeds to step S6.

In addition, even when the above relationship is not satisfied and the plate thickness profile is such that a plate thickness minimum value and a plate thickness maximum value are generated in the vicinity of the plate width end, the plate of the plate thickness minimum value and the plate thickness maximum value is obtained. thickness difference ΔH is the case [Delta] C _ref smaller exit configuration calculated as inverted crown profiles within an allowable range, the process proceeds to step S6. The determination value ΔC _ref is set in consideration of designation from a customer or plate passing property in the next process, and is usually a value of about 0 to 15 μm.

In other cases, that is, when the plate thickness difference ΔH between the plate thickness minimum value and the plate thickness maximum value is larger than ΔC _ref , the process proceeds to step S7 as an unacceptable reverse crown profile.

(Step S6) The provisional solution of the operation amount E _i of the plate crown / plate shape control actuator obtained in step S4 is determined as the final solution.

As a result, the operation amount E _{i of} the plate crown / plate shape control actuator and the input / output side plate thicknesses H _i-1 and H _{i of} each rolling stand can be determined. The setting of the thickness reduction schedule can be completed.

(Step S7) On the other hand, if it is determined in Step S5 that the reverse crown profile is unacceptable, the shape evaluation points B and C are set to the position B ′ where the plate thickness maximum value is near the plate width end and the plate thickness minimum. The value C is changed to the position C ′, the crown Cr _n at the quality evaluation point A becomes the target crown Cr _nA , and the crown ratio (Cr / H) _i at the points B ′ and C ′ in each rolling stand is The input and output side plate thicknesses H _i-1 and H _i of each rolling stand and the operation amount E _i of the plate crown / plate shape control actuator of each rolling stand are calculated so as to be constant for all rolling stands.

Then, based on the calculated input / output side plate thicknesses H _i-1 and H _{i of} each rolling stand and the operation amount E _i of the actuator, the evaluation function J ″ derived from the evaluation function J ′ of the equation (4) Calculate

  At the same time, as shown in step S5, it is determined whether or not it is a reverse crown profile.

(Step S8) The calculation in Step S7 is repeated several times, the crown profile is satisfactory, and the evaluation function J ″ is minimized. When the evaluation function J ″ is minimized, the optimization calculation is terminated. Then, the exit side plate thickness H _i of each rolling stand and the operation amount E _i of the actuator are output as final solutions, and the process proceeds to step S10.

Here, at the time of the optimization calculation of the evaluation function J ″, the actuator operation amount E _i obtained by the optimization calculation of the evaluation function J ″ may be used as a fixed value. The optimization calculation may be performed using the actuator operation amount E _i as a variable together with the side plate thicknesses H _i and H _i−1 .

  Further, in the optimization calculation of the evaluation function J ″, if the rolling load range at each rolling stand is added as a constraint, it is possible to avoid an unrealistic solution.

  For the optimization calculation of the evaluation function J ″, as in the optimization calculation of the evaluation function J ′, for example, if nonlinear programming or the like is used, an optimum value can be obtained by several iterations. The number of calculations may be arbitrarily set in consideration of time that can be spent on the set calculation time.

When the calculation in step S7 is repeated, the rolling temperature and the rolling load at each rolling stand change due to the change of the entry and exit side thicknesses H _i and H _i-1 of each rolling stand. Then, the rolling temperature and rolling load are recalculated (step S9).

(Step S10) Based on the final solution obtained in Step S8, the exit side plate thickness H _i of each rolling stand and the operation amount E _i of the actuator are determined.

  Thereby, the setting of the plate crown / plate shape control actuator and the plate thickness reduction schedule can be completed.

  In the above setting procedure, when each rolling stand is provided with a plurality of plate crown / plate shape control actuators, the operation amount of each actuator can be used as a variable.

  Further, when there is a rolling stand not provided with a plate crown / plate shape control actuator, the operation amount of the actuator at the rolling stand may be set to zero.

  Furthermore, the rolling method of the hot rolled steel sheet of the present invention can be applied to a general rolling cycle, that is, a rolling cycle assembled so that the sheet width of the material to be rolled is gradually reduced. It is particularly effective when applied to schedule-free rolling, which tends to occur.

  Examples of the present invention will be described below.

  By using a 7-stand continuous rolling mill having only a work roll bender as a plate crown / plate shape control actuator for each rolling stand, the heat according to the present invention is applied to 78 rolling cycles as the plate width schedule shown in FIG. The rolled steel sheet rolling method was carried out and the sheet crown profile was investigated.

  For the quality evaluation point, a position 25 mm from the edge of the plate width is selected, the target plate crown is set to 50 μm, and two positions of 75 mm and 200 mm from the plate end of the plate width end are used as initial plate shape evaluation points. Selected. The evaluation of the reverse crown profile was that the finish plate width was 270 mm wider than the front coil (1270 mm width) and the 66th coil (1540 mm width) and the finish dimensions (2.8 mm thickness x 1540 mm width) were exactly the same 67 It implemented in the coil eyes (1540mm width).

  In order to see the effect of setting the sheet thickness reduction schedule according to the present invention, the optimization of the sheet thickness reduction schedule and the work roll bender based on the minimization of the evaluation function J ″ is performed at the 66th coil. Then, a conventional reduction schedule based on the experience of the operator was adopted, and the operation amount set by the optimization calculation of the 66th coil was used as it was as the operation amount of the work roll bender.

  Usually, the thermal crown grows rapidly from the start of the rolling cycle, and the amount of thermal expansion is almost saturated after rolling of about 30 to 50 coils. Therefore, it is possible to investigate the influence of the sheet thickness reduction schedule on the crown profile.

  The sheet thickness reduction schedule used in this example is shown in FIG. In the 66th coil adopting the plate thickness reduction schedule according to the present invention, the amount of reduction at the front stage stand is smaller and the amount of reduction at the rear stage stand is larger than the conventional plate thickness reduction schedule.

  FIG. 5 is a comparison of the crown profile of the 66th coil according to the present invention and the 67th coil according to the conventional example. In the conventional example, the reverse crown profile is about 15 μm. In the example of the invention, the edge peak portion is reduced, and the crown at the 25 mm position from the end of the plate as the quality evaluation point is 44 μm, which is an error of about 10% from the target value of 50 μm, and has a good crown profile. Was confirmed.

It is a figure which shows the setting procedure of the actuator for board crown and board shape control and board thickness reduction schedule in one Embodiment of this invention. It is a figure which shows the quality evaluation point and shape evaluation point in one Embodiment of this invention. It is a figure which shows the rolling cycle (plate width) in the Example of this invention. It is a figure which shows the board thickness reduction schedule in the Example of this invention. It is a figure which shows the crown profile improvement effect in the Example of this invention. It is a figure which shows 1 generation | occurrence | production mechanism of a reverse crown profile. It is a figure which shows the false crown profile which can be estimated from the quality evaluation point and shape evaluation point in a prior art. It is explanatory drawing of a prior art. It is explanatory drawing of another prior art.

Claims (5)

A rolling method for hot-rolled steel sheets by a continuous rolling mill comprising a plurality of rolling stands,
Set the plate crown and plate shape control actuators of each rolling stand and the plate thickness reduction schedule of each rolling stand so that the rolled crown of the steel plate does not have a reverse crown profile. A method for rolling a hot-rolled steel sheet, characterized by comprising:   The setting of the plate crown / plate shape control actuator and the setting of the plate thickness reduction schedule are set so that a predetermined evaluation function defined by the target plate crown and the crown ratio becomes an optimum value. The rolling method of the hot-rolled steel sheet as described.   Using the predicted value of the thermal crown of the rolling roll, the predicted value of the wear of the rolling roll, the finished dimension of the hot-rolled steel sheet, and the predicted value of the rolling load, 50 to 50 mm from the plate width end of the hot-rolled steel sheet. Obtain the crown ratio at two or more points in the 200 mm area, and ensure that the crown ratio is substantially constant for all rolling stands and that the desired crown is obtained on the final rolling stand exit side. The method for rolling a hot-rolled steel sheet according to claim 1 or 2, wherein a setting of an actuator for shape control and a setting of a sheet thickness reduction schedule are performed.   Using the predicted value of the thermal crown of the rolling roll, the predicted value of the wear of the rolling roll, the finished dimension of the hot-rolled steel sheet, and the predicted value of the rolling load, 50 to 50 mm from the plate width end of the hot-rolled steel sheet. Obtain the crown ratio at two or more points in the 200 mm area, and ensure that the crown ratio is substantially constant for all rolling stands and that the desired crown is obtained on the final rolling stand exit side. 4. The shape calculation actuator setting calculation is performed, and as a result, when it is determined that it is difficult to realize a desired crown profile, the sheet thickness reduction schedule setting calculation is performed. A method for rolling a hot-rolled steel sheet according to claim 1.   At the position where the plate thickness is maximized in the vicinity of the plate width end in the region of 50 to 200 mm from the plate width end of the hot-rolled steel plate, and at the position where the plate thickness is minimum from that point to the center of the plate width. The method for rolling a hot-rolled steel sheet according to claim 3 or 4, wherein a crown ratio is evaluated.

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