JP6044589B2 - Metal strip rolling method - Google Patents

Description

  The present invention relates to a method of hot rolling a metal strip, and more specifically, between a plurality of rolled materials in a rolling cycle, between a predetermined folding position by a rolling mill having a shift mechanism for shifting a work roll in the axial direction. The present invention relates to a hot rolling method in which a work roll is shifted for each material to be rolled at a predetermined pitch while reciprocating.

  In rolling a metal strip, friction occurs at the contact portion between the work roll and the material to be rolled (hereinafter referred to as “plate path”), and the friction corresponding to the plate path of the work roll progresses. In particular, in hot rolling, since the material to be rolled becomes a high temperature of about 800 ° C. to 1100 ° C., thermal expansion occurs in a portion corresponding to the plate path of the work roll called a thermal crown.

For this reason, as the number of rolling rolls increases, the work roll profile changes due to the local friction and thermal expansion of the work rolls, so the width direction thickness distribution and shape of the material to be rolled deteriorate, and the product quality and threading There was a problem that the stability was lowered.
For example, since the local plate road wear progresses as in the case of rolling a narrow material continuously, an abnormality occurs in the thickness distribution of the wide material that is subsequently rolled to avoid this. In addition, process management (roll chance regulation) for restricting the sheet width in the rolling cycle, such as rolling in a stepwise manner from a wide material to a narrow material, has been forced.

In order to suppress these, as described in, for example, Patent Document 1 and Patent Document 2, each time the material to be rolled is rolled, the axial position of the work roll is called a constant pitch (hereinafter referred to as “shift pitch”). ), A cyclic shift method is widely used in which the shift is continued when the position of the work roll in the axial direction reaches the maximum or minimum, and the shift is continued.
Further, Patent Document 3 devised a rolling method for obtaining an error between a predicted calculation value and a target value of a work roll profile for all rolled materials in a rolling cycle and minimizing this error for all rolled materials using an evaluation function. Has been.

Patent Document 1 Japanese Patent Application Laid-Open No. 06-154823 Patent Document 2 Japanese Patent Application Laid-Open No. 11-254015 Patent Document 3 Japanese Patent Application Laid-Open No. 2013-111649

  However, in the above technique, in order to minimize an error from the target value in all materials, for example, after a material having a narrow width continues as a preceding material to be rolled, the width is 200 mm or more larger than this material, for example. In a special case where only one wide rolled material is rolled and then the narrow material is followed again, this wide rolled material cannot be filled with errors, As a result of flexibly shifting the shift position of the general material rolled before that, there was a risk that the profile of the general material was sacrificed, and it was not easy to obtain a metal band with a good profile.

In the present invention, in a cyclic shift rolling of a metal strip by a rolling mill equipped with a shift mechanism that shifts a work roll in the axial direction, the material to be rolled that follows the rolling of a narrow material is the rolling progress in the rolling cycle. When the material to be rolled is wider than the width dimension of the narrow material, in particular, the material to be rolled following the rolling of the narrow material is a material to be rolled having a width larger than the width dimension of the narrow material. When the material to be rolled subsequent to the material is rolled back to the material to be narrowed again (hereinafter referred to as “width-return rolling”), it is favorable in the width direction when rolling the material to be rolled wide. It aims at providing the rolling method which obtains the metal strip of a profile.
Here, “narrow” and “wide” in “narrow material” and “wide material” refer to a relative relationship in which the width of the wide material is larger than the width of the narrow material. It does not refer to absolute things below millimeters or above millimeters. Moreover, in said width return rolling, the narrow to-be-rolled materials before and behind a wide to-be-rolled material do not need to be the same width dimension.

  In addition, the rolling cycle starts rolling by a rolling mill in which a work roll is incorporated by roll exchange, rolls several (50 to 100 inside / outside) materials to be rolled, and then rolls the work roll by the next roll exchange. A group consisting of a group of the above-mentioned several pieces (50 to 100 inside and outside) of rolling materials until rolling is started by a rolling mill in which is incorporated is referred to as a constituent unit.

In order to achieve the above object, the present invention employs the following means.
[1] For each material to be rolled in a rolling cycle, the material is rolled at a constant pitch while reciprocating between predetermined folding positions by a rolling mill having a shift mechanism for shifting the work roll in the axial direction. In the rolling method of the metal strip for shifting the work roll, when rolling a material to be rolled that is wider than the preceding material to be rolled, the following formula (1) is used between the predetermined roll-back positions of the work roll shift. A method of hot rolling a metal strip, wherein rolling is performed while changing a work roll shift position so as to minimize an obtained evaluation function J _ΔCR .
[2] The width of the wide rolled material is 10% or more larger than the width of the preceding rolled material, and when the wide rolled material is rolled, the preceding rolled material continues. rolling method for metal strip according to [1], which is to 5km or more in the rolling on the total rolling length Te.
[3] The metal according to [1] or [2], wherein a rolling mill having a shift mechanism for shifting the work roll in the axial direction is provided on one or more stands of a tandem rolling mill. Strip hot rolling method.
[4] The hot work of the metal strip according to any one of [1] to [3], wherein the work roll of a rolling mill provided with a shift mechanism for shifting the work roll in the axial direction is a high-speed roll. Rolling method.

  In the cyclic shift rolling method using a rolling mill equipped with a shift mechanism that shifts the work roll in the axial direction by the metal strip rolling method of the present invention, the width of the material to be rolled is larger than that of the preceding material to be rolled. The profile can be improved, which makes it possible to relax the roll chance regulation and facilitate the process management of the rolling operation.

The simulation conditions of the material to be rolled in the rolling cycle are shown. The profile (crown distribution of the width direction) after the rolling of the wide material in width return rolling is shown. The relationship between the number of rolling narrow materials and the amount of high spot (maximum crown difference ΔCR) is shown. The mechanical board crown of the board width direction formed in the work roll of F7 stand is shown. The wear profile of the board width direction formed in the work roll of F7 stand is shown. The mechanical board crown of the board width direction of each stand of F5-F7 stand after rolling a narrow material is shown. The thermal crown of the board width direction of each stand of F5-F7 stand after rolling a narrow material is shown. In cyclic shift rolling with a constant shift pitch, simulation conditions for shift change at the time of rolling a wide material in width return rolling are shown. The profile (crown distribution of the width direction) after the rolling of the wide material in width return rolling is shown about five cases from which the shift position of a work roll differs. The thermal crown maximum amount of the work roll of F5 stand is shown. The relationship between the plate | board width direction distribution of a thermal crown and the plate | board width of a to-be-rolled material (narrow material and wide material) is shown. 2 shows an algorithm of the present invention. The calculation method of the evaluation function is shown. The simulation conditions to which the logic of the present invention is applied are shown. FIG. 14 shows the evaluation function (a) at the shift position of the work roll during width return rolling and the plate thickness distribution (b) at the end in the width direction under the conditions shown in FIG. The rolling cycle of an Example is shown. The shift position of the work roll of F5 stand is shown about each to-be-rolled material. The thickness distribution of the edge part of the width direction in the F7 stand exit side is shown. The width direction profile of the to-be-rolled material in which edge buildup is formed is shown.

First, using a simulator, in the rolling cycle, the mechanism of the profile failure that occurs when rolling a wide material that is 200 mm or more than the width step of the narrow material preceded by the amount of expansion of the width dimension in the width return rolling is discussed below. To do.
A simulation was performed for hot rolling with a 7-stand tandem rolling mill composed of F1 to F7 stands.
Here, the work rolls (hereinafter may be referred to as “WR”) for each material to be rolled were cyclic-shift rolled in the roll axis direction at a constant pitch using F5 to F7 stands.
As a work roll material, a high-speed roll was used in each of the stands F1 to F6, and a nickel grain roll was used in the F7 stand. High-speed rolls have high surface hardness and wear resistance, but are generally not used in the final F7 stand because of their high coefficient of thermal expansion. This is because the plate profile is not stable when a work roll having a high thermal expansion coefficient is used in the final stand.

  FIG. 1 shows a rolling cycle in which 100 materials are rolled 5 times (width circled in FIG. 1), that is, a narrow material (steel strip) with a plate width of 1000 mm is rolled. Later, a simulation condition is shown in which a wide material having a width of 1200 mm whose width is expanded by 200 mm is rolled, and then a narrow material whose width is returned again is subsequently rolled.

FIG. 2 shows a profile (crown distribution in the plate width direction) on the F7 stand exit side of the wide material in the width return rolling as a result of the simulation.
In “1” indicated by a mark, a narrow material having a width of 1000 mm is rolled in advance immediately before rolling a wide material having a width of 1200 mm. In the case of “15” indicated by the mark (1), 14 narrow materials are rolled in advance immediately before the wide rolling, and the 15th material to be rolled is counted from the “1” wide material. It is. “30” indicated by the ▲ mark is also rolled with 17 narrow materials immediately before the rolling of the wide material, and the 34th is counted from the “1” wide material. “50” indicated by ● is also rolled with 19 narrow materials in advance, just before the wide rolling, and the 54th is counted from the “1” wide material.

  FIG. 3 shows the high spot amount (maximum crown difference ΔCR) based on the simulation result of FIG. “♦”, “■”, “▲”, and “●” in the figure correspond to “1”, “15”, “30”, and “50”, respectively.

As can be seen from FIG. 2 and FIG. 3, when the wide material is rolled after continuously rolling the narrow material, that is, when performing the width return rolling, “15” except for “1”, “30” In the case of “50”, a local protrusion (high spot) having a large ΔCR is formed in the vicinity of the width end portion of the wide material, and the ΔCR increases as the number of rolling increases.
In this way, when the wide material is rolled after continuing the narrow material, the profile of the work roll is transferred to the wide material, and the edge build is locally thickened at the plate width end. It is thought that a protrusion called “up” is generated and the plate profile is deteriorated (refer to FIG. 19 for edge buildup).

In order to investigate the formation mechanism of this high spot, the mechanical plate crown and the wear profile formed by the upper and lower work rolls on the F7 stand were obtained, and these are shown in FIGS. 4 and 5, respectively.
Here, the “mechanical plate crown” is a work roll crown obtained by adding the thermal expansion amount and the wear amount of the work roll to the initial value of the work roll radius.
The amount of thermal expansion and wear of the work roll can be predicted and calculated based on the rolling history under the simulation conditions described above.

4 and 5, it can be seen that the wear of the work rolls increases as the number of rolled narrow materials increases. This is the cause of the mechanical plate crown swinging to the negative side. The mechanical plate crown in the F7 stand is dominated by roll wear, and as shown in FIG. It does not sway, and there is almost no element of edge buildup formation.

On the other hand, FIG. 6 shows the mechanical plate crowns for each stand of the F5 to F7 stands when the number of rolling is “50”, and the mechanical plate crowns of the F5 and F6 stands increase toward the edge.
FIG. 7 shows a thermal crown which is one of the constituent elements. FIG. 7 shows that the thermal crown of the F5 and F6 stand work rolls is larger than that of the F7 stand work roll (FIG. 7). F5 and F6 curves almost overlap).
This is because a nickel grain roll is used as a work roll in the F7 stand as the final stand, whereas a high-speed roll having a relatively high thermal expansion coefficient is used in the F5 and F6 stands.

That is, the cause of the deterioration of the sheet profile of the wide material in the width return rolling is a mechanism in which the edge buildup generated on the exit side of the F5 stand or F6 stand is rolled by the work roll worn on the box shape of the F7 stand and becomes an ear shape. This is thought to have occurred in
Therefore, based on the above-described mechanism at the time of rollback rolling, the following simulation was performed to search for means for reducing the influence of the thermal crown of the work rolls of the F5 and F6 stands.

Also in the rolling conditions shown in FIG. 8, similarly to the one shown in FIG. 1, the work rolls of the subsequent stands of F5 to F7 are shifted to the upper limit value +150 mm, the lower limit value −150 mm, and the shift pitch 30 mm. Then, the rolling of the narrow material having a width of 1000 mm was performed 50 times, and then the wide material having a width of 1200 mm was rolled (at the 67th number).
As shown in FIG. 8, in the rolling of the 67th wide material having a width of 1200 mm, as shown in FIG. 8, the shift of the work rolls of the F5 and F6 stands was continued at a constant pitch, and “0 (current setting value)” (▲ mark) Rolling) and shifting the shift position to +150 mm (displayed with ◆), +60 mm (displayed with ■), −40 mm (displayed with ● mark), −150 mm (displayed with ● mark), Simulation was performed for five cases of rolling by changing the shift position.

FIG. 9 shows the profiles on the F7 stand exit side for the above five cases with different work roll shift positions. FIG. 10 shows the thermal crown maximum value of the work roll of the F5 stand for these five cases.
As can be seen from FIG. 9, the profile is most improved in the case where the cycle shift position is -150 mm. This is because the thermal crown of F5 at this shift position is minimized as shown in FIG.

The reason is as follows based on FIG.
FIG. 11 shows the thermal crown of the work roll and its maximum value (peak point) together with the material to be rolled (strip) in the case assumed in rolling of the F5 stand.
FIG. 11A shows a case where a peak point at which the thermal crown is maximum exists near the center of the plate reference and a narrow material (plate width 800 mm) is rolled. FIG. 11 (b) shows a case where a wide material (plate width 1000 mm) is shifted by one cyclic shift from there and rolled, and FIG. 11 (c) is shown in FIG. 11 (b). ) Shows the case where the work roll shift position is shifted to the maximum shift amount.

  In the case of FIG. 11 (a), the peak point at which the thermal crown is maximized is at the center of the plate reference (a half of the plate width), but when rolling a narrow material, the crown amount by the thermal crown is Almost does not affect the board profile. However, in the case of FIG. 11B in which a wide material having a wide width is rolled, the position of the peak point is not substantially changed, and the thermal crown is transferred as it is to the end portion of the wide material as the thermal crown grows. Then it becomes edge buildup.

On the other hand, in the case of FIG. 11 (c) in which the shift position of the work roll is moved to the portion of the maximum shift amount instead of the cyclic shift scheduled position of FIG. 11 (b) when rolling the wide material, the peak point is rolled. It can sometimes be moved from the center of the plate to the vicinity of the end of the plate, and as a result, it is considered that the transfer of the thermal crown can be minimized.
When the shift is set to +150 mm in FIG. 9, the edge buildup is not improved, but this is because the last work roll shift operation is + 150⇒ + 120⇒ + 90⇒ + 60⇒ + 30. In comparison, the effect was weakened by the presence of a larger thermal crown in the positive side region of the shift position.

Based on the above analysis, in the present invention, when rolling a wide material subsequent to the rolling of a narrow material in width return rolling or the like, the evaluation function J _ΔCR is calculated by algorithms (1) to (8) shown in FIG. Calculate and determine the optimum work roll shift position that can minimize the influence of the thermal crown. This algorithm will be described below.
(1) Calculation of work roll shift limit The work roll shift limit value is calculated in consideration of the sheet width and equipment limit of the material to be rolled in the rolling cycle.
(2) Determination of work roll shift pitch Determine the shift pitch of the work roll cyclic shift and the change limit from the cyclic swft in the rolling cycle.
(3) Change the work roll shift position (shift lower limit to shift upper limit)
The shift position of the work roll is determined between the shift lower limit and the shift upper limit.
The lower limit value and upper limit value of the shift are determined in consideration of the following values.
Shift upper limit = MIN (cycle shift upper limit, preceding material position + upper and lower limit values)
Shift lower limit = MAX (cyclic shift lower limit, preceding material position-upper and lower limit)
(4) Calculation of predicted mechanical plate crown of wide material Based on the rolling history of the rolling cycle, predicted value CR of mechanical plate crown is calculated from the thermal expansion amount and wear amount of the work roll.
(5) Calculation of target value of mechanical plate crown of wide material Based on rolling history of rolling cycle, a predetermined formula is set to calculate target value CR ^* of mechanical plate crown.
(6) _{Calculate the} evaluation function J _ΔCR (error from the target) The evaluation function J _ΔCR is the number of edge _portions of the plate width based on the predicted value and the target value of the mechanical plate crown obtained in the above (4) and (5). A location (for example, three points of 25 mm, 75 mm, and 150 mm from the edge of the plate width) is obtained from the following formula.
Note that the target value CR _i ^* of the mechanical plate crown can be calculated and set to be a quadratic function in the width direction, for example (see FIG. 13). In FIG. 13, CR ₀ is a value that varies depending on the work roll shift position, and Wid is the plate width.
(7) Calculate evaluation functions _JΔCR at all shift positions. Calculate evaluation functions at all shift positions. The shift position is calculated with a pitch width (for example, 5 mm) smaller than the pitch width of cyclic shift rolling.
Note that “No” in “Calculate at all shift positions” in FIG. 12 _indicates that there is a part where J _ΔCR is not calculated within the possible range of the work roll shift stroke, and “Yes” similarly indicates the work roll shift stroke. This _indicates the case where all J _ΔCR are calculated within the possible range.
(8) The evaluation function J _ΔCR is set to the minimum shift position → End (End)
When the cyclic shift stroke is set to be less than ± 150 mm, the shift position is determined within the setting range.

In this way, it is possible to determine the work roll shift position where the evaluation function J _ΔCR is minimized, that is, the position where the edge buildup is minimized.
FIG. 14 and FIG. 15 show simulation results of calculating the work roll shift shift optimum position using this logic.
As shown in FIG. 14, the simulation conditions are as follows. In the schedule for rolling 35 rolled materials by a cyclic shift method with a shift amount of 30 mm, 19 materials with a plate width of 1000 mm are rolled continuously, In rolling the material, a plate material having a plate width of 1200 mm, that is, a wide material having a plate width increased by 200 mm was rolled, and then 15 materials having a plate width of 1000 mm were continuously rolled.

FIG. _15A shows the simulation result of the evaluation function J _ΔCR at the shift position (−150 mm to +150 mm) in the rolling of the 20th material.
As can be seen from FIG. _15A , J _ΔCR is minimized at the plus shift position ₊₁₃₀ mm.
FIG. 15B shows a result of applying a cyclic shift rolling method that does not change the sheet thickness profile of the sheet width end portion on the F7 stand exit side after rolling and the conventional shift pitch based on the simulation result of applying the logic of the present invention to FIG. Based on the thickness profile.
It can be seen that the edge buildup is improved in the plate profile in the width direction of the wide material to be rolled to which the logic of the present invention is applied, compared with the case where the conventional rolling method is applied (actual result).

As for the roll type of the work roll, it is most effective to apply the present invention to a roll which has a dominant thermal crown which is a problem when rolling a wide material and has little roll wear.
Therefore, it is most effective to use a high-speed roll stand with a high coefficient of thermal expansion and low wear characteristics, and a work roll using a nickel grain roll, which is often used in the final stand of a finishing mill. The amount of wear is large and the above effect is reduced.

  In the above simulation, 19 narrow materials were continuously rolled in a rolling cycle, and then a wide material having a sheet width of 200 mm was rolled, and the logic of the present invention was applied to the wide material.

From the logic of the present invention, it is clear that the present invention can be applied not only to the rolling of wide materials in reversing rolling, but also to the rolling in which rolling following the rolling of narrow materials is a wide material. It is more effective when the material is continuously rolled many times and the width of the wide material is somewhat larger than the width of the narrow material.
When the material to be rolled is a steel strip, the width of the wide material is 10 to 20% or more, preferably 20% or more larger than the width of the preceding narrow material. It is more effective when the extension is carried out for 5 to 10 km or more, preferably 10 km or more. The rolling length here is the length in the longitudinal direction (rolling direction) of the material to be rolled.
In the above simulation, the F5 and F6 stands of the tandem rolling mill including the F1 to F7 stands are applied. However, the tandem rolling mill having any number of stands, and further, the single stand rolling mill including one unit. It is clear that can also be applied.
The embodiment of the present invention was applied to an actual tandem rolling mill as follows, and the effect was confirmed.

The present invention was carried out in a hot rolling line having a tandem type finish rolling mill composed of F1 to F7 stands. The work roll shift mechanism is provided in F5 to F7. Table 1 shows equipment specifications of each rolling mill of F5 to F7 stands.
A high-speed roll was used for the work rolls of the F5 and F6 stands, and a nickel grain roll was used for the final F7 stand. Further, in the rolling mills of F1 to F4 stands, normal crown control is performed.

In three stands of F5 to F7, cyclic shift rolling was performed in which the work roll was shifted at a constant shift pitch of 30 mm for each material to be rolled.
And the work roll shift position change of this invention was implemented in F5 and F6 stand. The work roll of the F7 stand is set according to the cyclic shift because of large wear.

The material to be rolled was a medium-carbon steel strip, and the thickness and width of the material to be rolled in the rolling cycle are shown in FIG.
The above-mentioned work roll shift position change of the present invention was carried out on the 139th material to be rolled (indicated by circles in FIG. 16), that is, a wide material whose width dimension is 240 mm larger than the preceding material.
Before the material to be rolled, rolling of 30 narrow materials is continuously performed.
FIG. 17 shows the shift amount of the work roll of the F5 stand.

FIG. 18 shows the plate thickness profile on the F7 stand exit side, together with the results of the conventional example, for the example to which the present invention is applied.
In the conventional example, the work rolls of the F5 to F7 stands are set according to the cyclic shift.
Regarding the plate material after rolling, ΔCR at the edge portion was about 30 μm exceeding 25 μm in the conventional example, whereas it was about 10 μm lower than 25 μm in the example of the present invention.
As described above, according to the present invention, the build-up amount generated at the edge portion of the plate material after rolling can be reduced.

Claims (4)

About a material to be rolled in a rolling cycle, a work roll is provided for each material to be rolled at a constant pitch while reciprocating between predetermined folding positions by a rolling mill having a shift mechanism for shifting the work roll in the axial direction. In the rolling method of the metal strip to be shifted, when rolling a material to be rolled wider than the preceding material to be rolled, an evaluation function obtained by the following equation (1) between the turn-back positions of a predetermined work roll shift A method of hot rolling a metal strip, wherein the work roll shift position is changed and rolled so as to minimize J _ΔCR .
The width of the wide rolled material is 10% or more larger than the width of the preceding rolled material, and when rolling the wide rolled material, the preceding rolled material is continuously subjected to the total pressure. The metal strip rolling method according to claim 1, wherein the metal strip is rolled by 5 km or more as an extension.   The hot rolling of a metal strip according to claim 1 or 2, wherein a rolling mill having a shift mechanism for shifting the work roll in the axial direction is provided on one or more stands of a tandem rolling mill. Method.   The hot rolling method for a metal strip according to any one of claims 1 to 3, wherein the work roll of a rolling mill provided with a shift mechanism for shifting the work roll in the axial direction is a high-speed roll.