JP5338265B2 - Buckling prevention method for width reduction press - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a buckling prevention method for a width reduction press that enables stable width reduction by preventing the buckling of a hot slab in the width reduction (width reduction press) of a hot slab by a width press apparatus. It 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 molds installed facing each other in the plate width direction of the hot slab. In the width reduction (width reduction press) by this width press apparatus, a width reduction of about 300 to 350 mm at maximum is usually performed on a hot slab having a width of about 900 to 2000 mm, and the same width is obtained by continuous casting. It is possible to manufacture steel plate products with different widths than cast slabs. 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 plate 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, particularly under conditions where the width reduction amount is about 250 mm or more, a plastic unstable state due to width reduction, That is, an upward or downward buckling phenomenon is likely to occur. 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 tends to be manifested when there is some initial irregularity such as an asymmetry of the shape and width reduction operation. And once buckling occurs during slab pressure, the amount of buckling increases from there to the tail end, especially at the tail end, which is the free end, diverges greatly and the bending height is as large as several hundred mm. It may be buckled. In such a case, in the subsequent hot rolling, the buckling portion collides with equipment such as a descaling device and is damaged, or causes a biting failure in rolling. For this reason, when a large buckling occurs in the slab with the width reduction press, the rolling operation is stopped, and the crane is taken out of the line as it is and cooled, etc. Is one factor that reduces productivity. In addition, even if the buckling height is within the rollable range, the buckling part is deformed by an upward convex shape or a downward convex shape due to the deformation caused by the width reduction. The amount is not secured. For this reason, the buckled portion is deformed in the direction of a large width return in the plate width direction by horizontal rolling, and a large plate width variation is caused in the longitudinal direction due to the difference in the width return amount between the buckled portion and the steady width reduced portion. It will be. And, since the buckling phenomenon is more likely to occur under the condition that the width reduction amount is larger, the operation is controlled with the width reduction amount in actual operation, and the buckling trouble in the width reduction press is from the viewpoint of productivity and yield. It has become a big problem.

  In general, the width press device is provided with a pair of upper and lower buckling restraining rolls for the purpose of suppressing the occurrence of buckling, but an excessive pressing force is required to suppress buckling. When a load is applied, the roll bites into the surface of the slab and surface defects occur near the roll edge, or buckling is expanded from the viewpoint of protecting equipment such as a hydraulic cylinder that exerts pressing force on the buckling restraint roll. When an excessive pressing force is applied, measures are taken to release the hydraulic pressure, and it is difficult to reliably restrain buckling.

  As described above, since buckling troubles at the time of the width reduction press generate a large economic loss, various proposals have been conventionally made.

  For example, as a condition for preventing the occurrence of both buckling and surface depression due to the pressing roll, the force applied to the pressing roll is about 10% of the width reduction force (for example, Patent Document 1) and the force applied to the pressing roll is the width. A buckling restraint technique by optimizing the pressing force such as adjustment by the amount of reduction (for example, Patent Document 2) has been proposed.

  Moreover, the technique which changes a pressing roll position in a line 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, 4).

In addition, a technique has been proposed in which a mold or a buckling restraining roll is set so that the slab is intentionally bent upward or downward (for example, Patent Document 5).
JP-A 64-2707 JP-A-62-101336 JP 62-101335 A JP 9-327707 A JP-A-62-8201

  However, the conventional techniques (Patent Documents 1 to 5) relating to the buckling prevention described above have their respective problems and cannot reliably prevent buckling.

  For example, in the technology disclosed in Patent Document 1, although the buckling restraint load setting is optimized, the setting position is not mentioned at all, and as shown in the embodiment, 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 any buckling occurs, the restraining load necessary to suppress buckling cannot be generated because the vertical pressing force is balanced. Moreover, in the technique currently disclosed by patent document 2, as shown in the Example, the required pressing force is calculated based on the signal from a reduction device, and a control roll is controlled. However, in this case, as long as the buckling occurrence behavior during the reduction is monitored by some means and the pressing force of the upper and lower pressing rolls is individually controlled according to the buckling direction and the buckling amount, the same as in Patent Document 1. Since the upper and lower pressing forces are balanced, the buckling suppression effect cannot be expected.

  In the technique disclosed in Patent Document 3 or 4, an effective buckling suppressing action is achieved by matching the position of the center of gravity of the pressing load applied by the mold with the position of the pressing roll at the slab tip, the steady part, and the tail end. However, even in this technique, there is no mention of the setting of the vertical position of the presser roll, which has a fundamental problem.

  In the technique disclosed in Patent Document 5, the slab is forcibly bent by inclining the mold in the reduction direction. However, according to the knowledge of the present inventors, there is a slight deviation in the inclination angle of the mold. In such a case, there is a problem that the slab is easily twisted due to the width reduction.

  The present invention has been made in view of the above circumstances, and in the width reduction of a hot slab by a width press apparatus (width reduction press), the buckling of the hot slab is prevented and the width reduction is stably performed. It is an object of the present invention to provide a method for preventing buckling of a width reduction press that enables the above.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies on the occurrence of slab buckling in a width reduction press, and as a result, completely suppressed the upward or downward slab buckling phenomenon, and the slab surface In order to prevent the occurrence of pressing by the buckling restraining roll, the gap (gap) setting between the upper and lower buckling restraining rolls and the buckling restraining force should be optimized in accordance with the width reduction press conditions. It was found that, as in the prior art, constantly holding the slab from the vertical direction itself contributes to the divergence of buckling.

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

  [1] When the hot slab is intermittently reduced in width by the width press device, the hot slab is formed by a pair or a plurality of pairs of buckling restraining rolls arranged in the vertical direction near the center of the plate width of the hot slab. In the buckling prevention method of the width reduction press for preventing buckling, the gap setting value between the upper and lower buckling restraining rolls is set to a value equal to or greater than the initial slab thickness plus the amount of increase in thickness caused by width reduction. The buckling prevention method of the width reduction press.

  [2] A buckling prevention method for a width reduction press according to [1], wherein a mechanism is provided to prevent the distance between the upper and lower buckling restraining rolls during width reduction from being equal to or less than an initial gap setting value. .

  [3] The buckling prevention of the width reduction press according to [1] or [2], wherein the amount of increase in thickness that occurs under width reduction is calculated from the steel type, slab thickness, slab width, and width reduction amount. Method.

  [4] Any one of the above [1] to [3], wherein a force applied to the upper and lower buckling restraining rolls is calculated from a steel type, a slab thickness, a slab width, a width reduction amount, and an allowable buckling amount. The buckling prevention method of the width reduction press as described in 2.

  According to the present invention, in the width reduction (width reduction press) of a hot slab by a width press apparatus, buckling of the hot slab is prevented and stable width reduction is possible.

  Hereinafter, embodiments of the present invention will be described.

  In order to establish a buckling prevention technology for hot slabs, the present inventors have conducted intensive studies on the optimum restraining force necessary to suppress the buckling phenomenon with a buckling restraining roll, as shown in FIG. Thus, when the slab 2 is restrained by the upper and lower buckling restraining rolls 3 and 4 and the width is reduced by the left and right molds 1a and 1b, the balance of force when the slab 2 is buckled is simply modeled. The following equation (1) was derived.

In Equation (1), F is a buckling restraint load, Px is a width reduction load, Z ^* is an allowable buckling amount, W is a slab width, and ΔW is a width reduction amount. The actual buckling shape is a parabola whose maximum displacement is the center of the plate width of the slab or a shape close to an arc shape, but in FIG. 3, the buckling shape is approximated as a simple one-step bent shape. Is overestimated in the upward force, and is multiplied by a coefficient β to correct this. In the study by the present inventors, when about 0.5 is used as the coefficient β, the results agree well with the results of experiments, FEM analysis, and the like. In addition, the expression (1) indicates that the buckling restraint load F can be calculated by multiplying the width reduction load Px by a coefficient α, which is the same as the knowledge in the prior art (for example, Patent Document 1). . By the way, according to the study by the present inventors, it is considered that about 0.05 to 0.10 is appropriate for α. The coefficient α in the equation (1) is determined by the allowable buckling amount Z * under the same width reduction condition. According to the equation (1), if there is no asymmetry in the slab shape, the buckling is allowed. The smaller the capacity Z ^* is, the smaller the required buckling restraint load F is. As a matter of course, the buckling restraint load F may be zero. However, in actuality, slab C warpage may have occurred due to uneven cooling in the slab yard, etc., and surface wrinkles may be caused by investigating the amount of C warpage in actual operations and pressing the restraining rolls 3 and 4. A constraint load condition Z ^* that is an adjustment amount may be set by investigating a constraint load condition for preventing the generation of the constraint.

  Now, the necessary buckling restraint load F can be calculated by the equation (1), but the present inventors have conducted extensive studies on the optimum method of using the upper and lower restraint rolls for buckling restraint. Problems with the prior art have been clarified. The problem will be described below based on a few examples.

FIG. 4 shows an example of the prior art, in which the upper and lower buckling restraining rolls 3 and 4 are movable in the vertical direction and the buckling restraining force is the same in the vertical direction (the buckling restraining force of the upper buckling restraining roll 3). P _U = the buckling restraining force P _{L of the} lower buckling restraining roll 4). In this case, (1) since it is also set buckling restraint load F added to the same load and below the buckling restraint roll 3,4 _(P U ₌ P _L) in formula, shown in FIG. 4, for example When upward buckling occurs, no restraining load can be generated to balance the upper and lower pressing forces P _U and P _L and suppress buckling. As shown in FIG. It continues to expand toward the edge. When the buckling restraining load F is set excessively, the upper and lower restraining rolls 3 and 4 are greatly bited into the slab 2 as shown in FIG.

FIGS. 5 and 6 show another example, in which the movable direction of the lower restraint roll 4 is set only in the downward direction, and the load of the lower restraint roll 4 is set larger than the load of the upper buckling restraint roll 3 ( buckling restraint P _U of the upper seat buckling restraint roll 3 _<buckling restraint P _L of the lower seat buckling restraint roll _4). Normally, the buckling restraint load is set by the hydraulic cylinder pressure. When an excessive force is applied to the lower restraint roll 4 from the viewpoint of equipment protection, the hydraulic pressure is relieved and lowered, and the buckling force is set restraint. lower restraint roll 4 is increased to a set position when it becomes smaller than the load P _L. FIG. 5 shows the case where the set force of the upper restraining roll 4 is defeated by the buckling force and the upper buckling expands, and the relationship of the force in this case is expressed by the following equation (2).

As a countermeasure, it increases the upper seat restraint effect by increasing the upper restraining roll force P _U, generation of surface flaws become by pushing the upper constraining rolls 3 and slab coercive state as shown in FIG. 8 is concerned Therefore, normally, the force P _U of the upper restraining roll is set to the minimum necessary force based on experience. For this reason, the upper buckling restraining action is limited, and it is difficult to completely prevent the upper buckling.

  FIG. 6 is a diagram showing the relationship of force when the lower buckling is expanded by the buckling restraint method, and the relationship of force in this case is expressed by the following equation (3).

In this case, since the upper restraining roll force P _U becomes force for promoting bending lower seat, (3) under the force difference restraining roll force P _L and the upper restraining roll force P _U as shown in the formula Only becomes effective force for buckling restraint. As a countermeasure, the lower seat restraint effect by decreasing the upper restraining roll force P _U increases, but will be weakened restraining action on upper seat bending simultaneously. Thus, the upper for a restraining roll force P _U, conflicting set as a measure of the lower seat bends the upper seat flexion since it is necessary, the determination of the effective upper restraining roll force P _U in both very difficult It was difficult to prevent perfect buckling.

Based on the above considerations, the present inventors have conducted an intensive study on a method that has an effect on both upward and downward buckling and prevents excessive buckling of the buckling-restraining roll on the slab surface. As a result, the upper restraint roll force P _U and the lower restraint roll force P _L are configured not to interfere with each other, and each of the restraint rolls 3 and 4 can be set with a sufficient force for buckling restraint. I found it effective. Specifically, as shown in FIGS. 1 and 2, the upper restraining roll 3 has a movable range only in a range above the set position, and the lower restraining roll 4 has a movable range only in a range below the set position. As shown in equation (4), the setting gap G between the two is set to be larger than the center thickness of the plate width after the slab thickening due to the width reduction.

  In equation (4), H is the slab thickness before width reduction, ΔH is the amount of increase in thickness at the center of the slab width by width reduction, and δ is the gap margin. At this time, it is important to accurately predict the thickness increase due to width reduction, but the thickness increase ΔH due to width reduction depends on the slab steel type, slab temperature, slab dimensions (slab width W, slab thickness). H), the width reduction amount ΔW, and the slab's most advanced part depends on the contact length of the mold parallel part, etc. You should investigate and formulate. Further, by appropriately setting the gap margin allowance δ, it is possible to ideally prevent the buckling restraining rolls 3 and 4 and the slab 2 from coming into strong contact with each other. The generation of surface flaws due to contact with the surface is greatly reduced.

In the present invention, the movable range of the upper and lower buckling restraining rolls 3 and 4 is set to a range in a direction away from the slab 2 from the initial setting position, and the buckling restraining rolls 3 and 4 are not actively pushed into the slab 2. Is the basic idea. That is, when either one of the upper and lower buckling starts to occur, only one of the upper and lower restraint rolls comes into contact, and the forces (P _U and P _L ) of the upper and lower restraint rolls do not interfere with each other. In an extreme case, if the vertical movement of the upper and lower buckling restraining rolls 3 and 4 is fixed, the buckling should not progress in any direction. However, since the mechanism for relieving the hydraulic pressure applied to the buckling restraining rolls 3 and 4 is important from the viewpoint of equipment protection, the forces P _U and P _L applied to the upper and lower restraining rolls 3 and 4 are, for example, ( 1) Based on the formula, calculated from steel type, slab thickness H, slab width W, width reduction amount ΔW, allowable buckling amount Z ^*, and the upper and lower restraint forces considering the weight of buckling restraining rolls 3 and 4 Should be set so as to be approximately the same (P _U ≈P _L ). According to the equation (1), the necessary buckling restraint load F is smaller as the allowable buckling amount Z ^* is smaller. Therefore, if the load applied to the buckling restraining rolls 3 and 4 is constant, the gap margin allowance The smaller δ is, the larger the buckling restraining effect is, and the strong contact between the slab 2 and the buckling restraining rolls 3 and 4 can be prevented. Ideally, the upper and lower restraining rolls 3 and 4 are set so as to lightly contact the slab 2 in the thickened state after the width reduction from the relationship of the expression (1), that is, by setting δ = 0. The bending restraint force may be almost zero, but if the gap margin allowance δ is set in consideration of the C warpage shape of the initial slab and the prediction error of the increase in thickness due to the error of the initial slab width, etc. Good.

  Examples of the present invention will be described below.

  In this example, in a hot rolling factory having a width press device in front of the rough rolling line, in each case as shown in Table 1 (Invention Examples 1 to 4, Comparative Examples 1 to 3), each slab Rolling about 1000 pieces, buckling occurred and the number of slabs that were cooled, and although the cooling treatment was not done, a mild to moderate buckling shape occurred according to the visual judgment of the operator The total number of slabs determined as slabs was summarized as the percentage of occurrence of buckling relative to the total number of rolled slabs. In addition, in the surface defect meter installed in the cooling table after finish rolling, the ratio of the number of cracks found in the buckling-restrained roll contact area in the vicinity of the center part of either plate width on the front or back side Was also evaluated. In addition, in order to be able to judge the result in each case fairly, the test was carried out by selecting cycles in which the ratios of the steel type, the slab width, and the width reduction amount were substantially the same. In each case, the width reduction was performed up to 350 mm as required.

  As a result, as shown in Table 1, in the conventional technique as a comparative example, even if the buckling restraining force is increased, the buckling suppressing effect is hardly seen, and the occurrence rate of surface defects is increased. On the other hand, in the example of the present invention, the buckling suppressing effect and the surface defect suppressing effect are obvious as compared with the comparative example (prior art), and particularly as shown in the present invention example 4, it is sufficient for the buckling restraining roll. It was confirmed that buckling and surface defects can be completely prevented by applying a force and appropriately setting the gap allowance δ.

  Conventionally, the maximum width reduction amount has been regulated to 300 mm in order to prevent buckling troubles, but by applying the present invention, stable width reduction is possible even when the width is increased to 350 mm or more.

It is a figure which shows the state before the width reduction start which shows the movable range and Gap setting of the buckling restraint roll by this invention. It is a figure which shows the state in the bottom dead center under the width pressure which shows the movable range and Gap setting of the buckling restraint roll by this invention. It is a figure which shows the simple view of the balance of force at the time of buckling generation | occurrence | production. It is a figure which shows the example of the generation | occurrence | production situation of the upper buckling by the conventional setting. It is a figure which shows the example of another generation situation of the upper buckling by the conventional setting. It is a figure which shows the example of the generation | occurrence | production situation of the lower buckling by the conventional setting. It is a figure which shows the example of generation | occurrence | production of an upper buckling. It is a figure which shows the example of a condition where the up-and-down restraining roll has bite into the slab.

Explanation of symbols

1a mold 1b mold 2 slab 3 upper buckling restraint roll 4 lower buckling restraint roll

Claims (4)

When the hot slab is intermittently reduced in width by a width press, the hot slab is buckled by one or more pairs of buckling restraining rolls arranged in the vertical direction near the center of the plate width of the hot slab. In the buckling prevention method of the width reduction press to prevent, the gap setting value between the upper and lower buckling restraint rolls is set to be equal to or more than the value obtained by adding the amount of increase in wall thickness generated in the width reduction to the initial slab thickness ,
The upper restraint roll has a movable range only in the range above the set position, and the lower restraint roll has only the range below the set position as a movable range. As shown in the following equation, the gap set value G between the upper and lower buckling restraint rolls. Is set to be larger than the center thickness of the plate width after the slab is thickened by the width reduction.
G = H + ΔH + δ
Here, H is the slab thickness before width reduction, ΔH is the amount of increase in thickness at the center of the slab width due to width reduction, and δ is the gap margin.   The method of preventing buckling of a width reduction press according to claim 1, wherein a mechanism is provided to prevent the distance between the upper and lower buckling restraining rolls during width reduction from being equal to or less than an initial gap setting value.   The method for preventing buckling of a width reduction press according to claim 1 or 2, wherein the amount of increase in thickness generated by width reduction is calculated from the steel type, slab thickness, slab width, and width reduction amount.   The force applied to the upper and lower buckling restraining rolls is calculated from the steel type, slab thickness, slab width, width reduction amount, and allowable buckling amount. How to prevent buckling.

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