JP5338116B2 - 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 manufacturing the thin plate has a large ratio of width to thickness 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).
JP-A 64-2707 JP-A-62-101336 JP 62-101335 A JP 9-327707 A

  However, the above-described prior art relating to the prevention of buckling of the width press has a fundamental problem particularly regarding the prevention of occurrence of buckling of the slab tip. In other words, in the study by the present inventors, in order to prevent buckling of the slab leading edge, which is the free end, it is necessary to appropriately set the vertical position of the buckling restraining roll considering the deformation of the slab by the width press. This is important because the prior art does not consider this point at all.

  For example, in the technique disclosed in Patent Document 1, although the load setting of the buckling restraint roll is optimized, the position setting of the buckling restraint roll is not mentioned at all, and the example thereof is used. As shown, since the same load is applied to the upper and lower buckling restraining rolls, when the buckling occurs, the suppressing effect is hardly obtained. In other words, even if buckling occurs in either the upward or downward direction, the restraining load necessary to suppress buckling is generated because the pressing force of the upper and lower buckling restraining rolls is balanced. This is because it cannot be done.

  Further, in the technique disclosed in Patent Document 2, as shown in the embodiment, the required pressing force is calculated based on the signal from the width press device to control the buckling restraint roll. However, in this case, unless the buckling occurrence behavior during width reduction is monitored by some means and the pressing force of the upper and lower buckling restraining rolls is individually controlled according to the buckling direction and the amount of buckling. Since the upper and lower pressing forces are balanced in the same manner as in Patent Document 1, a buckling suppressing effect cannot be expected.

  The technique disclosed in Patent Document 3 or 4 is effective by matching the position of the center of gravity and the buckling-restraining roll position of the width reduction load by the mold at the slab tip, steady part, and tail part. However, this technique does not mention anything about the setting of the vertical position of the buckling restraining roll, and has a fundamental problem.

  Furthermore, normally, when performing width press, the height position of the buckling restraint roll, the height position of the transport roll, etc. are the predicted values of the plate thickness increase (plate thickness increase amount) in the steady part of the slab. Since it was originally set and was originally a free end, there was a problem that it was unsuitable as a setting for a tip end or a tail end having a thickness-thickening behavior different from that of a steady portion.

  The present invention has been made in view of the circumstances as described above, and is capable of stably reducing the width by preventing buckling of the hot slab when the width of the hot slab is reduced by the width press device. An object of the present invention is to provide a buckling prevention method for an intermediate slab width press.

  In order to solve the above-mentioned problems, the present inventors have intensively studied the occurrence behavior of slab buckling in a width press, and in order to prevent buckling over the entire length of the slab, in particular, it serves as a trigger for buckling divergence. It is important to prevent buckling of the slab tip (the most advanced part), and for that purpose, setting the vertical position of the buckling-restraining roll taking into account deformation of the slab (thickness increase in thickness) due to width reduction is the most important. I found out. In other words, as will be described in detail later, the buckling phenomenon at the tip of the slab that triggers buckling divergence is that the increase in the thickness of the slab due to width reduction is constrained by improper positioning of the buckling restraining roll. I found out that it is also caused by.

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

[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, depending on the predicted value of the thickness thickening amount, and to adjust the height position of the buckling restraint roll, in each of the width reduction of the width reduction conducted intermittently, the lower surface side buckling restraint roll The height position is fixed at a position adjusted according to the predicted value of the thickness increase of the plate, and a restraining load determined based on a preset allowable buckling amount is applied to the buckling restraining roll on the upper surface side. A method for preventing buckling of a hot slab width press.

[ 2 ] The predicted value of the thickness increase is calculated from the steel type of the slab, the temperature of the slab, the dimension of the slab, the width reduction amount, and the contact length of the press die parallel part . hot buckling prevention method of the slab width press according to.

  According to the present invention, during the width reduction of the hot slab by the width press device, the buckling of the hot slab is prevented and stable width reduction is possible.

  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 according to the plate thickness increase behavior in the longitudinal direction of the slab, and as a result of repeated examinations of various setting methods in the width press from such a viewpoint, the present inventors have When the buckling phenomenon is likely to occur at the tip 10a due to the difference in the profile of the plate thickness cross section at the slab tip 10a and the steady pressure lower part 10b, and the tip 10a is buckled. As shown in FIG. 7, the buckling tendency in the same direction is inherited over the entire length of the slab 10, and the buckling diverges abruptly in the vicinity of the tail end portion (most end portion) 10c that becomes the free end. I found out.

  That is, in the conventional setting method, the height position of the buckling restraining roll on the lower surface side of the slab is set based on the predicted value of the plate thickness (thickness increase amount) in the vicinity of the center portion of the slab width at the steady pressure lower portion 10b. However, as shown in FIGS. 5 (a) and 5 (b), there is a large difference in the plate thickness (thickness increase amount) in the vicinity of the center portion of the slab width between the tip portion 10a and the steady portion 10b of the slab. Since the position in the height direction of the side surface of the slab during width reduction is fixed by the frictional force due to contact with the mold, the conventional setting method, as shown in FIG. It is inevitable that a large thickness increase in the central portion of the slab width at the portion 10a is restrained by the buckling restraining roll 12b on the lower surface side of the slab, resulting in a convex buckling shape upward. 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.

  That is, in this embodiment, when the width of the hot slab 10 is intermittently reduced by the width press device provided with the buckling restraining roll 12a on the upper surface side of the slab and the buckling restraining roll 12b on the lower surface side of the slab, The height positions of the buckling-restraining rolls 12a and 12b are adjusted in accordance with the predicted values of the thickness increase of the tip portion 10a and the steady portion 10b of the hot slab due to the 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. 1 (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. 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. 1 (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. 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 it is conceivable, the buckling phenomenon at the tip portion 10a of the slab is supposed to occur due to asymmetrical deformation or non-uniformity of the slab C warpage caused by asymmetrical deformation due to slab heat deviation or asymmetrical cooling up and down. Therefore, in order to reliably prevent buckling at the slab tip 10a, the position of the buckling restraining roll 10b on the lower surface side of the slab is appropriately set according to the plate thickness increase behavior of the slab tip 10a due to the width reduction. It is preferable to set and apply a predetermined buckling restraint 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 Since the temperature, slab size, width reduction amount, and slab tip 10a also depend on the contact length with the parallel part of the mold 11, the plate thickness increase by these parameters in advance through experiments and numerical calculations You should investigate and formulate the effect on quantity.

  Further, the buckling restraining load applied to the restraining roll 10a on the upper surface side of the slab can be calculated by the following equation (1) 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. 2, the horizontal component Px of the force P acting in the slab width direction by 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 (1) is derived from the geometrical relationship of Py / Px = Z ^* / ((W−ΔW) / 2).

  And, the width reduction load Px is the slab width reduction condition (slab steel grade, slab temperature, slab size, width reduction amount, contact length with the parallel part of the mold 11) as in the above-described thickness increase of the plate thickness. The allowable buckling amount Z * is a parameter for determining the buckling constraint load F in the equation (1).

According to the equation (1), when there is no asymmetry in the slab shape, the smaller the allowable buckling amount 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.

  Examples of the present invention will be described below.

  FIG. 3 shows a slab that has been cooled by large buckling with respect to the total rolling amount in each elapsed month when the present invention is applied in a hot rolling factory having a width press device on the upstream side of the rough rolling line. It is a figure which shows transition of the ratio of the number, the ratio of the number of slabs in which a mild to moderate buckling shape has occurred, and the ratio of the number of slabs in which a surface defect has occurred although the cooling treatment has not been performed.

  As shown by the symbol Δ in FIG. 3, before the application of the present invention (elapsed 0 months), a large average buckling / cooling treatment slab of 2 to 3 (average ratio of 0.037%) occurred monthly. However, immediately after the application of the present invention (adjustment of the height position of the buckling restraint roll) was started (elapsed one month), no large buckling slabs were generated. Further, as indicated by the symbol “◯” in FIG. 3, the mild to moderate buckling occurring about 0.37% was reduced to about １ ／.

  Then, while observing the width reduction conditions such as slab steel type, slab temperature, slab size, width reduction amount and buckling occurrence in operation, adjustment of the height position of the buckling restraint roll, that is, the slab tip and steady pressure After adjusting the buckling restraint load by observing the surface unevenness after the width press caused by the buckling restraining roll and adjusting the prediction of the thickness increase in the lower part, the mild to medium level after 6 months No surface defects due to buckling and buckling restraining rolls.

  Conventionally, the maximum width reduction amount was restricted to 300 mm in order to prevent buckling problems, but stable width reduction is possible even when the maximum width reduction amount is increased to 350 mm by applying the present invention. It was.

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 buckling prevention effect in the Example 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.

Explanation of symbols

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 (2)

When the width of the hot slab is intermittently reduced by the width press with the buckling-restraining rolls on the upper and lower sides of the hot slab, the center of the slab width of the hot slab tip and the steady portion by the width reduction The height position of the buckling-restraining roll is adjusted according to the predicted value of the thickness increase in the thickness of the part, and during each width reduction performed intermittently, the buckling restriction on the lower surface side is performed. By fixing the height position of the roll for use at the position adjusted according to the predicted value of the thickness increase of the plate thickness , the width of the tip of the hot slab is being reduced while the width of the steady portion of the hot slab is being reduced. Compared to the estimated value of the thickness increase in the central portion of the slab width of the tip portion and the predicted value of the thickness increase in the central portion of the slab width of the stationary portion, the lower side of with fixing the height position of the buckling-restrained roll, the buckling restraint roll on the upper surface side, a preset Hot buckling prevention method of the slab width press, characterized in that loading the buckling restraint load determined by the following equation (1) based on contents seat屈量.

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.   2. The heat according to claim 1, wherein the predicted thickness increase amount is calculated based on a slab steel type, a slab temperature, a slab size, a width reduction amount, and a press die parallel part contact length. How to prevent buckling of intermediate slab width press.

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