JP7180477B2 - Method for manufacturing hot-rolled coil - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a coil by winding a hot-rolled steel sheet with a coiler in a hot-rolling process.

In the hot rolling process, the hot-rolled steel sheet after finish rolling is cooled to a predetermined temperature by a cooling device while being transported from the finishing mill to the coiler by the run-out table, and then wound on the coiler (mandrel). It is manufactured as a coil (hot rolled coil). After the coil is once wound at a predetermined winding temperature, the coil is transported to a coil yard, cooled to normal temperature, and then shipped to a user or transported to the next process.

So-called telescoping may occur in coils manufactured in this way. Telescopes include a bamboo telescope in which the hot-rolled steel sheet is wound in one direction in a bamboo-like shape when it is wound by a coiler, a bowl-shaped telescope in which the hot-rolled steel sheet is wound in a bowl shape, and a jagged telescope in which the steel is wound in a stepped manner. The telescope targeted this time is a jagged winding telescope phenomenon in which unevenness occurs in the width direction of the hot-rolled steel sheet H on the side surface of the coil C, as shown in FIGS. 1 and 2 . In particular, when the thickness of the hot-rolled steel sheet H is large, unevenness is repeated at a predetermined period, and a jagged telescope J (hereinafter sometimes referred to as a jagged winding telescope J) is likely to occur. If such a jagged telescope occurs, for example, when the coil is transported, there is a risk that the protruding portion on the side surface of the coil will be bent and damaged. In the next step, for example, when the coil is unwound to produce a pipe, the hot-rolled steel sheet cannot be properly welded, resulting in a decrease in yield. Therefore, it is important to reduce the jagged telescope.

In Patent Document 1, in a winding device of a hot rolling line, a pair of pinch rolls are provided as guide rolls for applying a bending moment in the same direction as a bending moment for bending a material to be rolled (hot-rolled steel sheet). It is disclosed that it is attached to. By applying a bending moment to the hot-rolled steel sheet in this way, the tension acting on the hot-rolled steel sheet is ensured, and the telescope is suppressed.

Patent Document 2 discloses controlling the leveling of pinch rolls in order to stabilize the winding shape of the coil in the coiler. Specifically, for the coil being wound, the entry side off-center amount at the entry side of the coiler is measured, and based on the measurement result, the pinch roll leveling is feedforward controlled. In addition, the telescopic amount of the coil during winding and/or the off-center amount before winding is measured, and the pinch roll leveling is feedback-controlled based on the measurement results.

Patent Literature 3 discloses a method of correcting winding unevenness formed on the side surface of a coil generated by a telescope. In this method, the uneven winding is corrected by pressing the suspended coil from both ends.

JP 2011-73036 A Japanese Patent Application Laid-Open No. 2001-179332 JP 2005-186073 A

However, when the inventors of the present invention investigated in detail the shape of the coil wound under various conditions, it was found that simply securing the tension acting on the hot-rolled steel sheet as disclosed in Patent Document 1 would not It turns out that the scope cannot be suppressed sufficiently. It has also been found that even when the pinch roll leveling is controlled as disclosed in Patent Document 2, the serrated telescope cannot be sufficiently suppressed. It should be noted that the specific reason why these jagged telescopes cannot be suppressed is clear from the mechanism of occurrence of jagged telescopes clarified by the present inventors, and will be described later.

Further, the method disclosed in Patent Document 3 does not suppress the generation of the jagged winding telescope itself, but corrects winding unevenness of the coil separately after winding the hot-rolled steel sheet. Therefore, it takes time and money to correct the winding irregularities.

As described above, conventionally, there is room for improvement in sufficiently suppressing the jagged telescope.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress generation of telescopes in a coil of hot-rolled steel sheet in a hot-rolling process.

In order to solve the above problems, the present inventors have made intensive studies, and as a result, have clarified the mechanism by which the jagged telescope is generated. Specifically, when wavy out-of-plane deformation called edge waves occurs at the edges of the hot-rolled steel sheet in the width direction after finish rolling, or when the hot-rolled steel sheet is in a flat state, jagged telescopes are likely to occur. became clear. Therefore, the present inventors have found that in order to suppress the generation of the jagged telescope, medium waves should be formed in the hot-rolled steel sheet after the finish rolling.

The present invention has been made based on such findings, and is a method of manufacturing a coil by winding a hot-rolled steel sheet having a ratio of finished thickness to width of 0.0083 or more with a coiler in a hot rolling process. At least the final stand of the finishing mill so that medium waves are formed on the hot-rolled steel sheet from the time the tip of the hot-rolled steel sheet exits the final stand of the finishing mill to the time it winds around the coiler is characterized by controlling the crown of the hot-rolled steel sheet. In addition, the medium wave in the present invention indicates a wave shape formed so that the wave height varies periodically in the rolling direction at least in the central portion in the width direction of the hot-rolled steel sheet.

In the hot-rolled coil manufacturing method, the coiler may wind the hot-rolled steel sheet with a winding tension of 7 MPa or more.

In the hot-rolled coil manufacturing method, the hot-rolled steel sheet is wound by the coiler in a state in which the distance between the pair of pinch rolls in the coiler is 0.5 mm or more larger than the thickness of the hot-rolled steel sheet. good too.

According to the present invention, medium waves are formed in the hot-rolled steel sheet from the time when the tip of the hot-rolled steel sheet leaves the final stand of the finishing mill until it winds around the coiler, so that telescope generation is suppressed. can be done.

FIG. 4 is an explanatory diagram showing a state in which a jagged winding telescope is generated in a hot-rolled coil; FIG. 4 is an explanatory diagram showing a state in which a jagged winding telescope is generated in a hot-rolled coil; It is explanatory drawing which shows the outline of the structure after a finishing mill of a hot-rolling equipment. It is explanatory drawing which shows the outline of a structure of a coiler. FIG. 10 is an explanatory diagram showing a mechanism by which a jagged telescope is generated; FIG. 3 is an explanatory diagram showing a state in which a serration is formed on a hot-rolled steel sheet; FIG. 3 is an explanatory diagram showing a state in which medium waves are formed on a hot-rolled steel sheet; FIG. 2 is an explanatory diagram showing the relationship between the tension acting on a hot-rolled steel sheet and the shape of the hot-rolled steel sheet; 7 is a graph showing the relationship between the rate of occurrence of jagged telescopes and the winding tension. It is explanatory drawing which shows the relationship between a pinch roll and a hot-rolled steel plate. 4 is a graph showing the relationship between the rate of occurrence of notched telescopes and the pinch roll gap.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

<Hot rolling equipment>
First, the configuration of the hot rolling equipment according to the present invention will be described. FIG. 3 is an explanatory view showing the outline of the configuration after the finishing mill 2 of the hot rolling mill 1. As shown in FIG.

The hot rolling equipment 1 includes a finishing rolling mill 2 for continuously rolling a steel plate H discharged from a heating furnace (not shown) and rolled by a rough rolling mill (not shown) to a predetermined thickness, and a steel plate after finish rolling. A cooling device 3 for cooling H (hereinafter referred to as a hot-rolled steel sheet H) to a predetermined temperature and a coiler 4 for winding the cooled hot-rolled steel sheet H are provided in the conveying direction of the hot-rolled steel sheet H in this order. A run-out table 5 for conveying the hot-rolled steel sheet H is provided between the finishing mill 2 and the coiler 4 . The hot-rolled steel sheet H rolled by the finishing mill 2 is cooled by the cooling device 3 while being transported on the run-out table 5, and then wound around the coiler 4 to be manufactured as a coil C.

The finishing rolling mill 2 is composed of a plurality of finishing rolling stands, for example, seven finishing rolling stands of first stand F1 to seventh stand F7 as shown in FIG. In this embodiment, the seventh stand F7 is the final stand. Each rolling stand is provided with a pair of upper and lower rolling rolls (work rolls), a backup roll, and the like. Since the construction of each rolling stand and the like is well known, detailed description thereof will be omitted.

FIG. 4 is an explanatory diagram showing the outline of the configuration of the coiler 4. As shown in FIG. Note that the example of FIG. 4 shows a state in which the coiler 4 starts the winding operation. The coiler 4 has a pinch roll 10, a chute 11, a mandrel 12 and a wrapper roll 13.

In the coiler 4, the hot-rolled steel sheet H is bent in the direction of the mandrel 12 by a pair of pinch rolls 10a and 10b, and passed through the chute 11. As shown in FIG. Here, before the tip of the hot-rolled steel sheet H reaches the mandrel 12, the wrapper roll 13 is closed (in contact with the mandrel 12), and waits while rotating at a speed several percent faster than the steel sheet speed. is doing. When the hot-rolled steel sheet H reaches the mandrel 12 and the wrapper roll 13, the hot-rolled steel sheet H is sandwiched between the mandrel 12 and the wrapper roll 13 and wound.

<Mechanism of generation of notched telescope>
In this embodiment, in the coil C manufactured by the hot rolling mill 1 configured as above, the generation of the jagged telescope shown in FIGS. 1 and 2 is suppressed. First, the present inventors elucidated the mechanism by which the serrated telescope is generated.

FIG. 5 is an explanatory diagram showing the mechanism by which the jagged telescope is generated. In FIG. 5 , the hot-rolled steel sheet H illustrated at a position away from the mandrel 12 shows the state of the hot-rolled steel sheet H immediately before being wound around the mandrel 12 .

The hot-rolled steel sheet H meanders on the delivery side of the seventh stand F7 of the finishing mill 2, and camber (lateral bending) occurs when the tip of the hot-rolled steel sheet H reaches the mandrel 12 as shown in FIG. 5(a). may occur. That is, off-center occurs at the start of winding of the hot-rolled steel sheet H, and the center Hc of the tip of the hot-rolled steel sheet H is shifted from the center Rc of the rolling line. In such a case, the hot-rolled steel sheet H is subjected to tension T (hatched area in FIG. 5). For example, when the hot-rolled steel sheet H bends to the left, the tension T acting on the right end in the width direction becomes greater than the tension T acting on the left end, creating a tension difference between the left and right ends. Then, the restoring force of the tension T, the so-called pincushion effect, returns the hot-rolled steel sheet H to the neutral position as shown in FIG. 5(b). The neutral position is a position that is not off-center, and is a position where the center Hc of the tip of the hot-rolled steel sheet H and the center Rc of the rolling line coincide.

However, if the hot-rolled steel sheet H bends to the left as described above while the hot-rolled steel sheet H is displaced from the neutral position as shown in FIG. The tension T increases, and the right side of the hot-rolled steel sheet H is stretched. That is, the cross-sectional tension T in the direction of travel where the hot-rolled steel sheet H is displaced increases and stretches. As a result, the winding of the right side of the hot-rolled steel plate H is delayed, and even when the hot-rolled steel plate H is in the neutral position as shown in FIG. don't go back to Therefore, the tension difference in the sheet width direction is not eliminated even at the neutral position, and the hot-rolled steel sheet H moves to the opposite side from the neutral position as indicated by the arrow in FIG. 5(b). Then, as shown in FIG. 5(c), when the geometrical neutral point in the width direction of the hot-rolled steel sheet H, that is, when the contact state of the left and right ends becomes the same position, the tension difference in the width direction disappears, and winding misalignment occurs. Stop.

When the hot-rolled steel sheet H is piled up as shown in FIG. 5(d) in a state where the winding misalignment has stopped, the surface pressure on the lower surface of the coil decreases due to the winding misalignment up to that point, and the surface pressure on the opposite side increases. Therefore, a difference in tension in the width direction begins to appear. As a result, the hot-rolled steel sheet H moves toward the opposite side as indicated by the arrow in FIG. In this manner, the states of FIGS. 5(a) to 5(d) are periodically repeated, the hot-rolled steel sheet H vibrates, and a jagged winding telescope is generated.

Alternatively, the mechanism of the jagged telescope can be explained by the pincushion effect alone.
(1) At the start of winding, an off-center occurs due to bending, etc., and the hot-rolled steel sheet is perpendicular to the mandrel due to the spool effect (geometrically neutral point, that is, the plate position in the width direction is macroscopically between the pinch roll and the mandrel). matching state). However, even if the hot-rolled steel sheet is wound on the mandrel at an apparent right angle, further miswinding occurs due to the influence of the winding misalignment from the hot-rolled steel sheet one turn before, and geometrically, it is 3 in the direction of travel. This is because the sheet is curved dimensionally (thickness and width directions) and does not come in contact with the left and right sides equally for winding.
(2) In the jagged winding telescope phenomenon, the walk of the hot-rolled steel sheet does not stop at the neutral position and goes too far. The reason for this is that while the hot-rolled steel sheet is displaced from the neutral position, the sheet tension on the shifted side increases. That is, as the sheet tension increases, the hot-rolled steel sheet on the side closer to the mandrel stretches on the mandrel entry side, so the winding around the mandrel is delayed. Since the angle does not return to a right angle, it goes too far and becomes a vibration phenomenon.

In addition, although the above-described mechanism causes a notched winding telescope, when securing the tension acting on the hot-rolled steel sheet as disclosed in the above-mentioned Patent Document 1, or when pinch rolls are disclosed as disclosed in Patent Document 2 In the case of controlling by elastically deforming the plate by the leveling of (1), vibration of the hot-rolled steel plate cannot be suppressed. Therefore, the conventional method cannot sufficiently suppress the jagged telescope.

<Relationship between notched telescope and hot-rolled steel plate width and finished plate thickness>
Next, the relationship between the serrated telescope and the width and finished thickness of the hot-rolled steel sheet will be described. The inventors performed a simulation by varying the width and finished thickness of the hot-rolled steel sheet. In this simulation, it was investigated whether or not the jagged winding telescope occurred with respect to the strip width and the finished strip thickness. Note that, here, when the height of the notch winding shown in FIG. In general, if the height of the serrated winding is less than 2 mm, the protruding portion of the side surface of the coil will not break when the coil is transported, and the hot-rolled steel sheet can be used even when the coil is unwound and pipe-manufactured. can be properly welded.
Table 1 shows the simulation results. Referring to Table 1, it was found that when the finished plate thickness t with respect to the plate width w is large, the jagged winding telescope is likely to occur. This is presumably because when the finished thickness t relative to the width w is large, the tension acting on the hot-rolled steel sheet increases, and the vibration of the hot-rolled steel sheet described above tends to continue. Specifically, when the ratio t/w of the finished plate thickness t to the plate width w was 0.0083 or more (t/w≧10/1200), the jagged winding telescope occurred. Therefore, the present embodiment targets a hot-rolled steel sheet having a t/w of 0.0083 or more.

<Relationship between notched telescope and shape of hot-rolled steel sheet>
Next, the relationship between the notched telescope and the shape of the hot-rolled steel sheet will be described. Here, examples of the shape of the hot-rolled steel sheet after finish rolling include a flat shape, a shape with serrations, and a shape with medium undulations.

The edge wave is a wave-shaped out-of-plane deformation that is formed such that the wave height periodically fluctuates in the rolling direction at the width direction end portion of the hot-rolled steel sheet. 6(a) is a plan view of the hot-rolled steel sheet H shown very simply for easy understanding, and FIG. 6(b) shows the profile of the AA section of the hot-rolled steel sheet H. FIG. The hot-rolled steel sheet H has an edge portion (shaded portion in FIG. 6(a)) in the width direction, and a flat portion F is formed in the center portion in the width direction. In the hot-rolled steel sheet H, the rigidity of the edge wave portion We against bending deformation in the direction of the arrow in FIG. .

A medium wave is a wave-shaped out-of-plane deformation that is formed such that the wave height periodically varies in the rolling direction at the central portion in the width direction of the hot-rolled steel sheet. FIG. 7(a) is a plan view of the hot-rolled steel sheet H, and FIG. 7(b) shows profiles of the BB section and the CC section of the hot-rolled steel sheet H. FIG. A medium wave portion Wm having medium waves is formed in the width direction central portion (shaded portion in FIG. 7(a)) of the hot-rolled steel sheet H, and a flat portion F is formed at the width direction end portion. In the hot-rolled steel sheet H, the rigidity of the medium-wave portion Wm against bending deformation in the direction of the arrow in FIG. Become. Compared to the edge wave, the medium wave has high bending rigidity because the rigidity is high at the edge part away from the center of rotation at the center of the width.

As shown in FIG. 5 described above, tension T acts on the hot-rolled steel sheet H when camber occurs when the tip of the hot-rolled steel sheet H reaches the mandrel 12 . FIG. 8 shows the relationship between this tension T and the shape of the hot-rolled steel sheet H. As shown in FIG.

Here, the relationship between the notched winding telescope and the shape of the hot-rolled steel sheet H is explained based on the tension T from the following two indices. The first index is the apparent strip width on which the tension T acts. As shown in Table 1 above, when the apparent width of the plate on which the tension T acts is large, the jagged winding telescope is less likely to occur. On the other hand, if the plate width is small, jagged winding telescopes tend to occur. The second index is the frictional force due to the tension T. When the tension T acting on the hot-rolled steel sheet H is small, the surface pressure between the steel sheets caused by the tension during winding becomes small, and the frictional force that acts to suppress the slippage of winding is reduced. As a result, the jagged winding telescope. becomes more likely to occur. On the other hand, when the tension T is large, the surface pressure becomes large, the frictional force becomes large, and the jagged winding telescope becomes difficult to occur.

As shown in FIG. 8(a), when the selvage portion We is formed at the end portion in the width direction of the hot-rolled steel sheet H, a tension T acts on the selvage portion We because the rigidity of the selvage portion We is small. do not do. On the other hand, since the rigidity of the flat portion F is high, a tension T acts on the flat portion F. In such a case, since the apparent width of the plate on which the tension T acts, which is the first index, becomes smaller, the jagged winding telescope is more likely to occur.

When the entire width direction of the hot-rolled steel sheet H becomes a flat portion F as shown in FIG. 8B, the tension T acts on the flat portion F. In such a case, an average frictional force due to the tension T, which is the second index, is generated, and the jagged telescope is likely to occur.

On the other hand, when the medium wave portion Wm is formed in the center portion in the width direction of the hot-rolled steel sheet H as shown in FIG. does not work. On the other hand, since the rigidity of the flat portion F is high, a tension T acts on the flat portion F. In this case, the apparent plate width acting on the tension T, which is the first index, is larger than when the selvage portion We shown in FIG. unlikely to occur. In addition, the frictional force due to the tension T, which is the second index, is greater in surface pressure and frictional force than in the case where the entire width direction is the flat portion F shown in FIG. A winding telescope is less likely to occur. Then, the frictional force increases with the ratio of the flat portion F to the plate width. Rigidity) makes it difficult for the jagged telescope to occur overall.

As described above, when the corrugated portion We is formed in the hot-rolled steel sheet H after the finish rolling, or when the entire width direction of the hot-rolled steel sheet H becomes the flat portion F, the jagged telescope is likely to occur. . On the other hand, when the medium wave portion Wm is formed in the hot-rolled steel sheet H, although the rigidity is slightly reduced, the contact area is reduced, so the surface pressure is increased, and the frictional force is increased. unlikely to occur.

<Method for Suppressing Knurled Telescope>
Based on the above findings, the present inventors found that medium waves should be formed in the hot-rolled steel sheet after finish rolling in order to suppress the generation of the jagged telescope. As described above, the hot-rolled steel sheet is a steel sheet having a ratio of finished thickness to width of 0.0083 or more.

The range in which medium waves are formed in the hot-rolled steel sheet after finish rolling is until the tip of the hot-rolled steel sheet winds around the mandrel, for example, in the range of 150 m to 200 m from the tip. In the following description, this area of the hot-rolled steel sheet may be referred to as the front end. In the range after the tip of the hot-rolled steel sheet, tension is generated in the hot-rolled steel sheet in the seventh stand after finish rolling, so medium waves are less likely to occur. Also, it occurs depending on the amount of lateral bending including the camber at the tip, so if it does not occur at the tip, the jagged telescope is unlikely to occur.

In the hot rolling plant 1 shown in FIG. 3, any method may be used to form medium waves in the hot-rolled steel sheet H in the finishing mill 2 in order to suppress the jagged telescope. For example, there is a method of controlling the crown of the hot-rolled steel sheet H in the seventh stand F7 of the finishing mill 2 . Specifically, a moment is applied to the work roll by a bender (not shown) to protrude the central portion of the work roll in the width direction. Then, the work roll presses the center portion of the hot-rolled steel sheet H in the width direction, so that the hot-rolled steel sheet H is formed with medium waves. Note that medium waves may be formed on the hot-rolled steel sheet H in the other finishing rolling stands F1 to F6 of the finishing rolling mill 2 as well. It is also possible to form medium waves in the hot-rolled steel sheet H by varying the rolling load in the finishing mill 2 .

As described above, by forming medium waves in the hot-rolled steel sheet after finish rolling, it is possible to suppress the occurrence of the jagged winding telescope. The steepness of the medium waves formed on the hot-rolled steel sheet is not particularly limited, but is, for example, greater than 0% and 4% or less. If it is more than 4%, the unwound flatness of the coil is poor and the shape must be corrected.

<Relationship between notched winding telescope and winding tension>
Next, the relationship between the notched winding telescope and the winding tension of the hot-rolled steel sheet will be described. In order to suppress the jagged telescope as described above, the inventors of the present invention should form medium waves in the hot-rolled steel sheet after finish rolling. The inventors have found that the coiler (mandrel) should be used to increase the winding tension when winding the hot-rolled steel sheet.

The inventors performed simulations by varying the winding tension. Then, the rate of occurrence of serrated telescope with respect to the winding tension was investigated. The results of the simulation are shown in FIG. Referring to FIG. 9, it was found that if the winding tension is less than 7 MPa, jagged winding telescope may occur. In other words, it was found that when the winding tension is 7 MPa or more, the generation of the jagged winding telescope can be suppressed.

<Relationship between notched telescope and pinch roll interval>
Next, the relationship between the notched telescope and the pinch roll spacing will be described. In order to suppress the jagged telescope as described above, the inventors of the present invention should form medium waves in the hot-rolled steel sheet after finish rolling. It has been found that the interval between the pinch rolls should be larger than the thickness of the hot-rolled steel sheet. That is, the gap L1 between the pair of pinch rolls 10a and 10b is larger than the plate thickness L2 of the hot-rolled steel plate H, as shown in FIG.

The inventors performed simulations by varying the distance between the pinch rolls. Then, the rate of occurrence of jagged telescope with respect to pinch roll spacing was investigated. FIG. 11 shows the results of the simulation. FIG. 11 shows the difference (=L1-L2) between the gap L1 between the pinch rolls 10a and 10b and the thickness L2 of the hot-rolled steel sheet H as the pinch roll gap. Referring to FIG. 11, it was found that if the pinch roll gap is greater than 0.5 mm, jagged telescoping may occur. In other words, it was found that when the pinch roll gap was 0.5 mm or more, the generation of the jagged telescope could be suppressed.

The original action of the pinch rolls is to bend the hot-rolled steel sheet, but even if the pinch roll gap is increased as described above, there is no problem with the bending action of the hot-rolled steel sheet.

Although the embodiments of the present invention have been described above, the present invention is not limited to such examples. It is obvious that a person skilled in the art can conceive various modifications or modifications within the scope of the technical idea described in the claims, and these are also within the technical scope of the present invention. be understood to belong to

INDUSTRIAL APPLICABILITY The present invention is useful when manufacturing a coil by winding a hot-rolled steel sheet with a coiler in a hot-rolling process.

1 hot rolling equipment 2 finishing rolling mill 3 cooling device 4 coiler 5 runout table 10 (10a, 10b) pinch roll 11 chute 12 mandrel 13 wrapper rolls F1 to F7 finishing rolling stand C coil H hot rolled steel sheet

Claims (3)

A method of manufacturing a coil by winding a hot-rolled steel sheet having a ratio of finished thickness to width of 0.0083 or more with a coiler in a hot rolling process,
From the time the tip of the hot-rolled steel sheet leaves the final stand of the finishing mill to the time it winds around the coiler, the hot-rolled steel sheet is hot-rolled at least at the final stand of the finishing mill so that medium waves are formed on the hot-rolled steel sheet. A method for producing a hot-rolled coil, characterized by controlling the crown of a steel plate. 2. The method for producing a hot-rolled coil according to claim 1, wherein the coiler winds the hot-rolled steel sheet with a winding tension of 7 MPa or more. 3. The coiler winds the hot-rolled steel sheet with the distance between the pair of pinch rolls in the coiler set to 0.5 mm or more larger than the thickness of the hot-rolled steel sheet. The method for manufacturing the hot-rolled coil according to .

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