JP5625356B2 - How to prevent buckling of hot slab width press - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a buckling prevention method for a hot slab width press that enables stable width reduction by preventing buckling of a hot slab during width reduction (width press) of a hot slab by a width press device. Is.

  As a means for changing the width of the hot slab, the temperature of the slab manufactured by the continuous casting process is not lowered, or after the temperature is once lowered, the slab is heated to a predetermined temperature in a heating furnace. A width press apparatus is used in which a hot slab is intermittently rolled down in the plate width direction by a pair of press dies installed so as to face each other in the plate width direction of the hot slab.

  In the width reduction by this width press apparatus, the width reduction of about 300 to 350 mm is usually performed on the hot slab having a width of about 900 to 2000 mm. From the slab cast to the same width by continuous casting. This makes it possible to manufacture steel sheets with different widths. This has greatly contributed to the productivity improvement and rationalization of the steel sheet manufacturing process, such as reducing the number of width changes in the continuous casting process, expanding schedule-free rolling in the hot rolling process, and increasing the coil weight. The merit increases as the width reduction capability of the width press device increases.

  However, since the shape of the hot slab used for thin plate manufacturing has a large width-to-thickness ratio of about 3 to 10, the width reduction (width pressing amount) is about 250 mm or more. The plastic unstable state due to the width press), that is, as shown in FIG. 7 as an example, the slab 10 is likely to buckle upward or downward. The buckling phenomenon is a phenomenon in which a slight bending stress caused by a slight imbalance resulting from inhomogeneity leads to an unstable state of the system. Asymmetry of the initial slab shape, slab temperature, or mold It is likely to be manifested when there is some initial irregularity such as a shape or width press asymmetry. And once buckling occurs during the width press of the slab, the buckling amount expands from there to the tail end, especially at the end of the free end which diverges greatly and the bending height is several hundred mm. It can be a large buckling shape. In such a case, in the subsequent hot rolling, the buckled portion collides with equipment such as a descaling device and is damaged, or causes a biting failure in rolling and the like. From this, when large buckling occurs in the slab with the width press, the rolling operation is stopped, and the crane is discharged out of the line as it is and cooled, etc., and the productivity of the hot rolling line is increased. It is one factor to drop. In addition, even if the buckling height is within a rollable range, the buckling portion has a deformation due to the width reduction, which is an upward convex shape or a downward convex shape deformation. Is not secured. From this, the buckling part is deformed in the direction of a large width return in the sheet width direction by horizontal rolling, and a large sheet width fluctuation occurs in the longitudinal direction due to the difference in the width return amount between the buckling part and the normal width compression lower part. It will be. And, since the buckling phenomenon is more likely to occur in the condition where the width reduction amount is larger, the operation is unavoidably restricted in the width reduction amount in actual operation, and the buckling trouble in the width press is from the viewpoint of productivity and yield. It has become a big problem.

  In order to suppress the occurrence of this buckling, the width press device is usually provided with one or more pairs of buckling restraining rolls (pressing rolls), and the hot slab is moved up and down by these buckling restraining rolls. However, if an excessive pressing force is applied to suppress buckling, the roll may bite into the slab surface and surface defects may occur near the roll edge. From the point of protection of equipment such as hydraulic cylinders that give pressure to the cylinder, when the buckling expands and excessive pressure is applied, measures are taken to release the hydraulic pressure of the hydraulic cylinder. It is difficult to reliably restrain buckling.

  Therefore, as described above, a buckling trouble at the time of the width press causes a large economic loss, and thus various proposals have been made so far to prevent buckling at the time of the width press. For example, as a condition for preventing both the occurrence of buckling and the generation of surface dents due to the buckling restraint roll, the force (load) applied to the buckling restraint roll is about 10% of the width reduction force (for example, Patent Document 1). Also, a buckling restraint technique by optimizing the pressing force of the buckling restraint roll has been proposed, such as one in which the force (load) applied to the buckling restraint roll is adjusted by the width reduction amount (for example, Patent Document 2). Yes. Moreover, the technique which changes the position of a buckling restraining roll in a line direction (slab longitudinal direction) in the front-end | tip part of a slab, a stationary part, and a tail end part is proposed (for example, patent documents 3 and 4).

  However, these prior arts have a problem particularly in setting the vertical position of the buckling restraining roll at the slab leading edge. This is because the peculiarity of deformation of the slab tip was not taken into consideration.

  Therefore, the applicant previously proposed to adjust the height position of the buckling-restraining roll according to the predicted value of the thickness increase of the thickness of the tip portion and the steady portion of the hot slab due to the width reduction. (Patent Document 5).

JP-A 64-2707 JP-A-62-101336 JP 62-101335 A JP 9-327707 A JP 2009-248186 A

  However, applicant's subsequent work has shown that there is room for further improvement.

  The present invention has been made in view of the circumstances as described above, and in the width reduction of the hot slab by the width press device, the buckling of the hot slab and the occurrence of surface defects are prevented to stably reduce the width reduction. An object of the present invention is to provide a method for preventing buckling of a hot slab width press that can be performed.

  That is, the present invention is as follows.

[1] When the width of the hot slab is intermittently reduced by the width press device provided with the buckling-restraining rolls on the upper surface side and the lower surface side of the hot slab, A method for preventing buckling of a hot slab width press that adjusts the height position of the buckling-restraining roll according to a predicted value of the thickness increase of the plate thickness. A method for preventing buckling of a hot slab width press characterized by predicting the amount of meat.

Where ΔH is the thickness increase of the hot slab after width reduction (width center portion), W0 is the width of the hot slab before width reduction, ΔW is the width reduction amount, and H0 is the hot thickness before width reduction. This is the thickness of the slab.

  [2] During each width reduction under the width reduction performed intermittently, while fixing the height position of the buckling restraining roll on the lower surface side to a position adjusted according to the predicted value of the plate thickness increase amount, The method for preventing buckling of a hot slab width press according to [1], wherein a predetermined restraining load is applied to the buckling restraining roll on the upper surface side.

  [3] The hot value according to [1] or [2], wherein the predicted value of the thickness increase is calculated based on a steel type of the slab, a temperature of the slab, and a contact length of the press die parallel part. Buckling prevention method for slab width press.

  [4] A method for producing a hot-rolled metal plate using the method for preventing buckling of a width press in hot rolling according to any one of [1] to [3].

  According to the present invention, when the width of the hot slab is reduced by the width press device, the buckling of the hot slab and the occurrence of surface defects can be prevented and stable width reduction can be achieved.

It is a figure for demonstrating the result of the research leading to this invention. It is a figure which shows the height position of the buckling restraint roll in one Embodiment of this invention. It is explanatory drawing of the calculation method of the buckling restraint load in one Embodiment of this invention. It is a figure which shows the deformation | transformation area | region of the slab at the time of width reduction. It is a figure which shows the plate | board thickness thickening behavior of the slab at the time of width reduction. It is a figure which shows the example of the buckling shape by the conventional setting method. It is a figure which shows the buckling of the slab by width reduction.

  Hereinafter, an embodiment of the present invention will be described.

  When the width of the hot slab is reduced by the width press device, as shown in FIG. 4 (a), the slab tip 10a is a free end in which there is no deformation restraint in front of the deformation region indicated by the oblique lines. On the other hand, as shown in FIG. 4 (b), in the slab longitudinal steady-state lower portion (steady portion) 10b, there are portions that are restrained by deformation before and after the reduction region, and in both cases, the plate thickness caused by width reduction The thickening behavior is very different. In particular, under the condition that the slab width is narrow and the width reduction amount is large, the distortion due to the width reduction easily reaches the inside of the plate width at the slab tip portion 10a, and the plate thickness profile becomes thick at the center portion of the plate width as shown in FIG. It tends to be convex. On the other hand, in the steady pressure lower portion 10b in the longitudinal direction of the slab, the distortion due to the width reduction does not reach the inside of the plate width due to the presence of the non-deformation region before and after the deformation region, and the deformation concentrates in the vicinity of the plate width edge. As shown in (b), it tends to be a dogbone shape in which the plate thickness near the plate width edge increases.

  Normally, the barrel length of the buckling restraining roll is about 300 to 400 mm, and the buckling is suppressed by pressing the central part of the slab width from above and below in the vicinity of the mold reduction position. The slab width center thickness and maximum dogbone height are predicted, and the settings such as the conveyance table height, pinch roll height, and buckling restraint roll height are set according to the predicted values.

  However, as described above, the plate thickness cross-sectional profiles at the slab tip 10a and the steady pressure lower portion 10b are greatly different, and the difference in plate thickness between the slab tip 10a and the steady portion 10b near the center of the slab width ( The difference in plate thickness increase amount may reach 30 mm or more depending on the width reduction condition.

  Therefore, it is desirable to make various settings in accordance with the plate thickness increase behavior in the longitudinal direction of the slab, and the present inventors have repeatedly studied various setting methods in the width press from such a viewpoint. In the conventional setting method as described in Document 4, a buckling phenomenon is likely to occur at the tip portion 10a due to the difference in the plate thickness cross-sectional profile between the slab tip portion 10a and the steady pressure lower portion 10b, and the tip portion. When a buckling shape is obtained at 10a, the buckling tendency in the same direction is inherited over the entire length of the slab 10, as shown in FIG. We found that buckling diverges suddenly in the vicinity.

  That is, in the conventional setting methods such as Patent Document 1 to Patent Document 4, the buckling constraint on the lower surface side of the slab is determined based on the predicted value of the plate thickness (plate thickness increase amount) in the vicinity of the center portion of the slab width at the steady pressure lower portion 10b. Although the height position of the roll is set, as shown in FIGS. 5A and 5B, the slab tip portion 10a and the steady portion 10b have a plate thickness (plate thickness) near the slab width center portion. From the fact that there is a large difference in the (thickening amount) and the position of the side surface of the slab during width reduction is fixed by the frictional force due to contact with the mold, as in Patent Documents 1 to 4 In this conventional setting method, as shown in FIG. 6 (a), a large plate thickness increase in the slab width center portion is restrained by the buckling restraining roll 12b on the lower surface side of the slab, as shown in FIG. Therefore, it was inevitable to have a convex buckling shape. When a convex buckling shape is generated at the slab tip 10a, the tail end 10c tends to have a large buckling shape as shown in FIG. 6B.

  Therefore, in the slab tip 10a and the stationary part 10b, it is possible to appropriately change the height position of the buckling-restraining roll in accordance with the plate thickness difference (plate thickness increase amount difference) ΔS in the vicinity of the center portion of the slab width. Importantly, at the tip portion 10a of the slab, it is necessary to lower the height position of the buckling restraining roll 12b on the lower surface side of the slab by 1/2 of the plate thickness difference ΔS compared to the steady portion 10b. For example, when it is predicted that the plate thickness near the center of the slab width of the slab tip 10a will be about 30 mm thicker than the plate thickness near the center of the slab width of the steady pressure lower portion 10b (ΔS≈30 mm). In the tip portion 10a of the slab, it is necessary to lower the height position of the buckling restraining roll 12b on the lower surface side of the slab by about 15 mm compared to the steady portion 10b.

  Therefore, in Patent Document 5, the applicant intermittently reduces the width of the hot slab 10 by a width press device including a buckling restraining roll 12a on the slab upper surface side and a buckling restraining roll 12b on the slab lower surface side. At this time, the height positions of the buckling-restraining rolls 12a and 12b are adjusted according to the predicted values of the thickness increase in the thickness of the tip portion 10a and the steady portion 10b of the hot slab due to the width reduction.

  That is, when the width of the tip portion 10a of the slab is reduced, the plate thickness increase behavior (plate thickness cross-sectional profile) predicted when not restrained by the buckling restraining rolls 12a and 12b as shown in FIG. 2 (a), the height positions of the buckling restraining rolls 12a and 12b so that the buckling restraining rolls 12a and 12b are in contact with the center portion of the slab width after the thickness increase, as shown in FIG. Was set. On the other hand, when the width of the steady portion 10b of the slab is reduced, the plate thickness increase behavior (plate thickness cross-sectional profile) predicted when not restrained by the buckling restraining rolls 12a and 12b as shown in FIG. 5B. 2 (b), the height positions of the buckling restraining rolls 12a and 12b so that the buckling restraining rolls 12a and 12b are in contact with the center portion of the slab width after the thickness increase, as shown in FIG. Was set.

  In order to prevent the buckling caused by the mechanism as described above, it is effective to retract the buckling restraining rolls 12a and 12b in the vertical direction of the slab when the width of the tip portion 10a of the slab is reduced. Although the inventors have considered, after the research, the slab tip portion 10a and the slab steady portion 10b have, as shown in FIG. I found that there is a relationship. When this is replaced with an equation, the following equation (1) is obtained.

Where ΔH is the thickness increase [mm] of the hot slab (width center) after width reduction, W0 is the width [mm] of the hot slab before width reduction, and ΔW is the width reduction [mm]. , H0 is the plate thickness [mm] of the hot slab before width reduction.

  The relationship between the width reduction ratio and the plate thickness increase rate can be expressed only by changing the coefficient using the same formula for the slab tip 10a and the slab steady part 10b, and the hot slab is intermittent. When the width is reduced, the height position of the buckling-restraining roll can be adjusted according to the predicted value of the thickness increase in the thickness of the front end portion and the steady portion of the hot slab due to the width reduction. Become. When analyzed from the results of FIG. 1, α is α = 1.85 at the tip of the hot slab and α = 0.93 at the stationary portion.

  Further, since the buckling phenomenon at the slab tip 10a is considered to be caused by asymmetric deformation due to uneven heat of the slab, asymmetry or non-uniformity of the slab C warp shape caused by vertical asymmetric cooling, etc., the slab tip In order to reliably prevent buckling in the portion 10a, the position of the buckling restraining roll 10b on the lower surface side of the slab is appropriately set according to the thickness increase behavior of the tip portion 10a of the slab due to width reduction, and It is preferable to apply a predetermined buckling restraining load without fixing the position of the restraining roll 10a on the upper surface side of the slab.

  That is, in this embodiment, during each width reduction performed intermittently, the position where the height position of the buckling restraining roll 12b on the lower surface side is adjusted according to the predicted value of the plate thickness increase amount. And a predetermined restraining load is applied to the buckling restraining roll 12a on the upper surface side (in other words, the height position of the buckling restraining roll 12a on the upper surface side receives a predetermined amount of reaction force). To be adjusted).

  At that time, it is important to accurately predict the thickness increase due to the width reduction at the tip portion 10a and the steady pressure lower portion 10b of the slab, but the thickness increase due to the width reduction depends on the steel type of the slab, the slab The temperature of the slab and the contact length of the slab tip 10a with the parallel part of the mold 11 depend on the influence of these parameters on the plate thickness increase by experiments and numerical calculations in advance. It is also preferable to formulate.

  The buckling restraint load applied to the restraining roll 10a on the upper surface side of the slab can be calculated by the following equation (2) from the relationship shown in FIG.

  Here, F is a buckling restraint load, Px is a width reduction load, Z * is an allowable buckling amount, W is a slab width before width reduction, and ΔW is a width reduction amount.

  As shown in FIG. 3, the horizontal component Px of the force P acting in the slab width direction due to the width reduction of the slab 10 is the width reduction load, and the vertical component Py is the reaction force acting on the restraining roll 10a on the slab upper surface side. It becomes. That is, the buckling restraint load F = 2 × reaction force Py, and the equation (2) is derived from the geometrical relationship of Py / Px = Z * / ((W−ΔW) / 2).

  And the width reduction load Px can be calculated by the slab width reduction conditions (slab steel type, slab temperature, contact length with the parallel part of the mold 11), similarly to the above-described plate thickness increase amount, In equation (2), the allowable buckling amount Z * is a parameter for determining the buckling restraint load F.

  According to the equation (2), when there is no asymmetry in the slab shape, the smaller the buckling allowance Z *, the smaller the required buckling restraint load F. In other words, the buckling restraint load F may be zero. It will be. However, in actuality, slab C warpage may have occurred due to uneven vertical cooling at the slab yard, etc., and surface wrinkles may be caused by investigating the amount of C warpage in actual operation or pressing the buckling restraining roll 12a. The allowable buckling amount Z *, which is an adjustment coefficient, may be set by investigating a buckling restraint load condition for preventing the occurrence of the buckling.

DESCRIPTION OF SYMBOLS 10 Hot slab 10a Tip part of hot slab 10b Steady part of hot slab (steady part pressure lower part)
10c Tail end portion of hot slab 11 Press die 12a Buckling constraining roll on slab upper surface side 12b Buckling constraining roll on slab lower surface side

Claims (4)

When the width of the hot slab is intermittently reduced by the width press machine equipped with buckling-restraining rolls on the upper and lower sides of the hot slab, the thickness of the tip and steady parts of the hot slab is increased by the width reduction. A method for preventing buckling of a hot slab width press that adjusts the height position of the buckling-restraining roll according to the predicted value of the amount of wall, wherein the thickness increase by the following equation (1) A method for preventing buckling of a hot slab width press characterized by predicting.

Where ΔH is the thickness increase of the hot slab after width reduction (width center portion), W0 is the width of the hot slab before width reduction, ΔW is the width reduction amount, and H0 is the hot thickness before width reduction. The plate thickness , α, of the slab is a coefficient obtained from the relational expression obtained in advance from the relationship between the width reduction rate (ΔW / W0) and the plate thickness increase rate (ΔH / H0) at the center of the width.   During each width reduction under the width reduction performed intermittently, the height position of the buckling restraining roll on the lower surface side is fixed to a position adjusted according to the predicted value of the plate thickness increase amount, and The method for preventing buckling of a hot slab width press according to claim 1, wherein a predetermined restraining load is applied to the buckling restraining roll.   3. The hot slab width press seat according to claim 1 or 2, wherein the predicted value of the thickness increase is calculated from the steel type of the slab, the temperature of the slab, and the contact length of the press die parallel part. Bending prevention method.   A method for producing a hot-rolled metal sheet using the method for preventing buckling of a width press in hot rolling according to any one of claims 1 to 3.