JP2021164955A - Method for manufacturing seamless metal pipe - Google Patents

Abstract

To provide a method for manufacturing a seamless metal pipe capable of realizing a 3-roll type piercing milling machine.SOLUTION: A method for manufacturing a seamless metal pipe comprises: a step (#5) of providing a material to be rolled having an outer diameter Db larger than an outer diameter D; and a step (#15) of piercing-rolling the heated material to be rolled by a 3-roll type piercing milling machine. The step of piercing-rolling satisfies all of formulas (1) to (4): 0.95×Dp≤Dpg≤Dp (1); 0.95×Dp+2×t≤ROg≤Dp+2×t (2); 0≤L2/L1≤0.25 (3); 1.0<(Db-ROp)/Db×100 (4) [Dpg: plug diameter at gorge position, Dp: maximum plug diameter, ROg: degree of opening of inclined roll at position of gorge part, L1: length of rolling part of plug, L2: length of reeling part of plug, and ROp: degree of opening of inclined roll at tip position of plug.]SELECTED DRAWING: Figure 7

Description

The present invention relates to a method for manufacturing a seamless metal tube by the Mannesmann method.

Generally, a method for manufacturing a seamless metal tube by the Mannesmann method includes the following steps. The round billet is heated to a predetermined temperature. A raw pipe (seamless metal pipe) is manufactured by drilling and rolling a round billet. The raw pipe is further stretch-rolled and further constant-diameter rolled. A drilling and rolling machine (eg, piercer) is used in the drilling and rolling process. In the draw-rolling process, a draw-rolling machine (eg, mandrel mill, elongator) is used. In the constant diameter rolling process, a constant diameter rolling mill (eg, sizer, stretch reducer) is used.

Conventionally, a drilling and rolling mill includes a plug and two inclined rolls as a rolling tool (see, for example, International Publication No. 2009/119245 (Patent Document 1) and JP-A-7-275908 (Patent Document 2)). .. A drilling and rolling mill equipped with two inclined rolls is referred to as a two-roll type piercer or a two-roll type drilling and rolling mill. Each tilt roll is evenly spaced around the pass line. The central axis of each tilt roll is tilted with respect to the pass line. That is, each tilt roll is given a tilt angle. An additional crossover angle may be given to each tilt roll. The plugs are placed on the path line between the tilted rolls. In the case of a two-roll type piercer, a guide tool (eg, plate shoe, disc roll) is provided between the inclined rolls around the pass line. The guide tool plays a role of limiting the overhang of the material to be rolled during drilling and rolling.

The drilling and rolling is performed as follows. The material to be rolled is a solid round billet. The heated material to be rolled is placed on the pass line. The material to be rolled is sent between the rotating inclined rolls by the pusher and bites into the inclined rolls. Then, the material to be rolled advances while rotating around its own axis on the pass line, and is perforated and rolled by an inclined roll and a plug. As a result, a bare pipe (seamless metal pipe) having a predetermined wall thickness and outer diameter can be obtained. Hereinafter, the seamless metal pipe obtained by drilling and rolling is also referred to as a drilling material.

Here, in the drilling and rolling with a two-roll type piercer, Mannesmann fracture occurs in the material to be rolled. Specifically, during drilling and rolling, the compressive stress in the direction in which the inclined rolls face each other and the tensile stress in the direction in which the guide tools face each other act simultaneously on the central portion of the rotating material to be rolled. Such stress is repeated every time the material to be rolled makes a quarter turn. Mannesmann fracture occurs due to repeated stress loading. Mannesmann destruction facilitates perforation. On the other hand, when Mannesmann fracture becomes significant, internal defects occur in the obtained perforated material.

Further, in drilling and rolling with a two-roll type piercer, the guide tool slides with the material to be rolled during drilling and rolling. When this sliding becomes remarkable, an outer surface defect occurs in the obtained perforated material.

In recent years, in order to suppress inner and outer surface defects of a perforated material, practical application of a perforated rolling mill provided with three inclined rolls has been studied (for example, Japanese Patent Application Laid-Open No. 2008-543569 (Patent Document 3)). A drilling and rolling mill equipped with three inclined rolls is called a 3-roll type piercer or a 3-roll type drilling and rolling mill. Similar to the two-roll piercer, each tilted roll is evenly spaced around the pass line. However, no guide tool is provided.

Mannesmann fracture is less likely to occur in drilling and rolling with a 3-roll type piercer than in drilling and rolling with a 2-roll type piercer. This is because during drilling and rolling, only compressive stress acts on the central portion of the material to be rolled, and tensile stress does not act. Therefore, internal defects are unlikely to occur. Further, in the drilling and rolling with a 3-roll type piercer, since no guide tool is used, no external flaws occur. Therefore, in order to solve the quality problem inherent in drilling and rolling using a 2-roll type piercer, drilling and rolling using a 3-roll type piercer is extremely useful.

By the way, when a thick-walled drilling material is manufactured by a drilling and rolling mill, plug clogging is likely to occur. Plug clogging is a problem in which the maximum diameter of the plug stays at the rear end of the perforated material after drilling and rolling, and the plug cannot be completely removed from the perforated material. If the plug is clogged, the drilling and rolling mill must be stopped for a long time. This is because the plug and the perforated material are firmly engaged with each other as if they were shrink-fitted, and the two cannot be easily separated. Due to such measures, the production efficiency is significantly reduced.

On the other hand, when a thin-walled drilling material is manufactured by a drilling and rolling mill, experience shows that plug clogging does not occur. Although Patent Document 3 discloses drilling and rolling with a three-roll type piercer, it merely discloses a technique for producing a thin-walled drilling material. That is, Patent Document 3 does not pay any attention to the problem in producing a thick-walled perforated material.

Therefore, in order to put the 3-roll type piercer into practical use, it is desired to establish a technique capable of suppressing plug clogging when producing a thick-walled perforated material.

International Publication No. 2009/11924 Japanese Unexamined Patent Publication No. 7-275908 Japanese Patent Application Laid-Open No. 2008-543569

One object of the present invention is to provide a method for producing a seamless metal pipe, which can be put into practical use for a three-roll perforated rolling mill for producing a thick-walled seamless metal pipe.

In the method for producing a seamless metal pipe according to the embodiment of the present invention, a seamless metal pipe is used, and the ratio t / D of the wall thickness t (mm) to the outer diameter D (mm) is 15% to 30%. Manufacture metal tubes. The drilling and rolling mill comprises a plug arranged on the pass line and three inclined rolls arranged around the pass line at equal intervals, each having an entry side surface and an exit side surface. The distance between the pass line and the entry side surface gradually decreases from the entry side to the exit side of the pass line, and the distance between the pass line and the exit side surface gradually increases from the entry side to the exit side of the pass line.

The manufacturing method includes a preparation step, a heating step, and a drilling and rolling step. In the preparatory step, a material to be rolled is prepared having an outer diameter Db (mm) larger than the outer diameter D of the seamless metal pipe. The heating step heats the material to be rolled. In the drilling and rolling step, the heated material to be rolled is drilled and rolled by a drilling and rolling machine. In the drilling and rolling step, various conditions of the plug and the inclined roll are set so as to satisfy all of the following formulas (1) to (4).

0.95 × Dp ≦ Dpg ≦ Dp (1)
0.95 × Dp + 2 × t ≦ ROg ≦ Dp + 2 × t (2)
0 ≦ L2 / L1 ≦ 0.25 (3)
1.0 <(Db-ROp) / Db × 100 (4)
The meanings of the symbols in equations (1) to (4) are as follows.
Dpg: Plug diameter (mm) at the position of the gorge of the tilted roll,
Dp: Maximum plug diameter (mm),
ROg: Opening degree (mm) of the tilted roll at the position of the gorge portion of the tilted roll,
L1: Length of rolled part of plug (mm),
L2: The length of the reeling portion of the plug (mm), and ROp: the opening degree of the inclined roll at the position of the tip of the plug (mm).

According to the manufacturing method according to the embodiment of the present invention, it is possible to suppress the occurrence of plug clogging in drilling and rolling when a thick-walled seamless metal pipe is manufactured by using a 3-roll drilling and rolling mill. Therefore, a 3-roll type drilling and rolling mill can be put into practical use for manufacturing a thick seamless metal pipe.

FIG. 1 is a perspective view of a 3-roll drilling and rolling mill. FIG. 2 is a front view of a 3-roll drilling and rolling mill. FIG. 3 is a top view of a 3-roll drilling and rolling mill. FIG. 4 is a side view of a 3-roll type drilling and rolling mill. FIG. 5 is a diagram showing an example of an inclined roll. FIG. 6 is a diagram showing an example of a plug. FIG. 7 is a flow chart showing a method for manufacturing a seamless metal tube according to the present embodiment. FIG. 8 is a schematic view showing an example of a situation during drilling and rolling. FIG. 9 is a cross-sectional view showing a situation during drilling and rolling by a 3-roll drilling and rolling mill. FIG. 10 is a cross-sectional view showing a situation during drilling and rolling by a two-roll type drilling and rolling mill. FIG. 11 is a diagram showing a locus of the center of gravity (central axis) of the plug during drilling and rolling. FIG. 12 is a diagram showing the wall thickness distribution of the perforated material obtained by perforating and rolling. FIG. 13 is a processing flow chart showing a general manufacturing method of product pipes. FIG. 14 is a processing flow diagram showing another manufacturing method of the product tube.

In order to solve the above problems, the present inventors have made extensive studies, and as a result, the following findings have been obtained.

[Basic configuration of 3-roll drilling and rolling mill]
1 to 4 are views showing the configuration of a 3-roll drilling and rolling mill. Of these figures, FIG. 1 shows a perspective view of the drilling and rolling mill as viewed from the exit side of the pass line PL. FIG. 2 shows a front view of the drilling and rolling mill when viewed from the entry side of the pass line PL along the pass line PL. FIG. 3 shows a top view of the drilling and rolling mill. FIG. 4 shows a side view of the drilling and rolling mill. In FIG. 1, the illustration of the plug 2 is omitted. In FIGS. 3 and 4, only one inclined roll 1 arranged vertically above the pass line PL is shown, and illustration of the two inclined rolls 1 arranged below is omitted. In FIG. 4, the material to be rolled WP is shown in a cross section including a pass line PL. The material to be rolled WP is a solid round billet. In the present specification, the 3-roll type drilling and rolling mill (3-roll type piercer) may be simply referred to as a drilling and rolling mill.

With reference to FIGS. 1 to 4, the drilling and rolling mill includes a plug 2 and three inclined rolls 1 as rolling tools. The three tilt rolls 1 are evenly spaced around the pass line PL. That is, the three inclined rolls 1 are arranged at intervals of 120 ° from each other. One of the three inclined rolls 1 is arranged directly above the pass line PL (upper in the vertical direction). However, the positions of the three inclined rolls 1 are not limited as long as the three inclined rolls 1 are arranged around the pass line PL at equal intervals. For example, one inclined roll 1 may be arranged directly below the pass line PL (downward in the vertical direction). The surface of each inclined roll 1 is divided into an entry side surface 1a and an exit side surface 1b along the pass line PL. The boundary between the entry side surface 1a and the exit side surface 1b is the gorge portion G.

The central axis 1c of each inclined roll 1 is inclined with respect to the pass line PL. That is, each inclined roll 1 is given an inclined angle FA (see FIG. 3). A crossover angle CA is given to each inclined roll (see FIG. 4). The tilt angle FA and the crossover angle CA are adjustable. Further, each inclined roll 1 is given an opening degree with respect to the pass line PL. This roll opening can also be adjusted.

The tilt angle FA means a swing angle of the central axis 1c of the tilt roll 1 in the circumferential direction centered on the pass line PL. The crossover angle CA means a runout angle of the central axis 1c of the inclined roll 1 in the radial direction about the pass line PL.

The distance between the pass line PL and the entry side surface 1a gradually decreases from the entry side to the exit side of the pass line PL. On the other hand, the distance between the pass line PL and the exit side surface 1b gradually increases from the entry side to the exit side of the pass line PL. Therefore, the distance between the pass line PL and the surface of the inclined roll 1 is the smallest at the position of the gorge portion G. The entry side surface 1a is, for example, a tapered surface having a constant gradient. The protruding side surface 1b is, for example, a tapered surface having a constant gradient.

The plug 2 is arranged on the path line PL between the inclined rolls 1. The plug 2 is held by a core metal 3 extending along the pass line PL.

Drilling and rolling using such a drilling and rolling machine is performed as follows. The material to be rolled WP, which is a round billet, is heated. The heated material WP to be rolled is arranged on the pass line PL. The material to be rolled WP is sent between the rotating inclined rolls 1 by the pusher and bites into the inclined roll 1. Then, the material to be rolled WP advances while rotating around its own axis on the pass line PL, and is perforated and rolled by the inclined roll 1 and the plug 2. As a result, a perforated material (bare pipe, seamless metal pipe) having a predetermined wall thickness and outer diameter can be obtained.

[Study on practical application of 3-roll drilling and rolling mill]
Consider the case where a thick-walled perforated material is produced by a perforated rolling mill. The thick perforated material means a perforated material in which the ratio t / D of the wall thickness t (mm) of the perforated material to the outer diameter D (mm) of the perforated material is in the range of 15% to 30%. In the present specification, the ratio t / D may be referred to as a wall thickness outer diameter ratio t / D.

As described above, when a thick-walled drilling material is produced by a drilling and rolling mill, plug clogging is likely to occur regardless of whether the number of inclined rolls is two or three. This is considered to be due to the following reasons. In the case of producing a thick-walled perforated material, the amount of wall thickness reduction of the material to be rolled by the inclined roll and the plug during drilling and rolling is smaller than in the case of producing a thin-walled perforated material. Therefore, the elongation in the circumferential direction of the material to be rolled (circumferential strain = -strain in the wall thickness direction-strain in the longitudinal direction) becomes small, and the peripheral length of the material to be rolled becomes insufficient. This reduces the clearance between the inner surface of the material to be rolled and the plug at the maximum diameter of the plug. If this clearance is too small, plug clogging will occur. In the present specification, the clearance may be referred to as a plug final clearance.

In particular, in the drilling and rolling with the 3-roll type piercer, the wall thickness reduction amount borne by one inclined roll is 2/3 of the wall thickness reduction amount borne by one inclined roll in the piercing and rolling with the 2-roll type piercer. Therefore, in the perforated rolling with the 3-roll type piercer, the peripheral length of the material to be rolled tends to be more insufficient than in the perforated rolling with the 2-roll type piercer. As a result, the final plug clearance becomes too small, and there is more concern about the occurrence of plug clogging.

Therefore, the present inventors have studied a method of increasing the final plug clearance in order to suppress the occurrence of plug clogging. As a result of diligent examination, it was found that the final plug clearance can be effectively expanded if the following conditions are met.

The amount of wall thickness rolling of the material to be rolled by the inclined roll and the plug is substantially increased. Due to this increase in the wall thickness reduction amount, the peripheral length of the material to be rolled increases during drilling and rolling, and the final plug clearance is expanded.

In order to realize an increase in the wall thickness reduction amount, as a first condition, the plug is arranged closer to the entry side of the inclined roll. As the second condition, the wall thickness processing of the material to be rolled is completed in the region (including the gorge portion) of the entrance side surface of the inclined roll. That is, in the region of the entrance side surface of the inclined roll, the wall thickness reduction amount of the material to be rolled is secured at a high level, and the wall thickness of the material to be rolled is processed to the wall thickness of the perforated material (target wall thickness). In this case, the outer diameter D of the perforated material is smaller than the outer diameter Db of the material to be rolled. As a third condition, the wall thickness rolling reduction amount of the material to be rolled is secured at a high position at the position of the gorge portion of the inclined roll.

However, if the first condition is simply satisfied, poor biting of the material to be rolled may occur. Poor biting of the material to be rolled is a trouble that the material to be rolled and the inclined roll are relatively idle in the initial stage of drilling and rolling, which makes drilling and rolling impossible. If the plug is excessively moved toward the entry side in an attempt to satisfy the first condition, the material to be rolled hits the tip of the plug before the material to be rolled is sufficiently engaged with the inclined roll. In this case, poor biting of the material to be rolled occurs.

As a fourth condition, a draft rate PD at the tip of the plug is secured in order to suppress the occurrence of poor biting of the material to be rolled. The plug tip draft rate PD is represented by the following formula (a), and its unit is%.
PD = (Db-ROp) / Db × 100 (a)
The meaning of each symbol in the formula (a) is as follows.
ROP: Opening degree (mm) of the inclined roll at the position of the tip of the plug, and Db: Outer diameter (mm) of the material to be rolled (round billet).

In the present specification, the opening ROp of the inclined roll at the position of the tip of the plug may be referred to as the opening ROp of the plug tip roll.

If the plug tip roll opening ROp is sufficiently small with respect to the outer diameter Db of the material to be rolled, the material to be rolled is sufficiently provided by the inclined roll from the time when the material to be rolled bites into the inclined roll until it reaches the tip of the plug. It is pressed down and fully bites into the inclined roll. In this case, it is possible to suppress poor biting of the material to be rolled. In this respect, as is clear from the equation (a), the smaller the plug tip roll opening ROp, the larger the plug tip draft rate PD. Therefore, if the plug tip draft ratio PD is large, the plug tip roll opening ROp is small, and as a result, poor biting of the material to be rolled can be suppressed.

The method for manufacturing a seamless metal tube of the present invention has been completed based on the above findings.

In the method for producing a seamless metal pipe according to the embodiment of the present invention, a seamless metal pipe is used, and the ratio t / D of the wall thickness t (mm) to the outer diameter D (mm) is 15% to 30%. Manufacture metal tubes. The drilling and rolling mill comprises a plug and three tilted rolls. The plug is placed on the path line. The three tilted rolls are evenly spaced around the pass line, each with an entry side and an exit side. The distance between the pass line and the entry side surface gradually decreases from the entry side to the exit side of the pass line. The distance between the pass line and the exit side surface gradually increases from the entry side to the exit side of the pass line.

The manufacturing method includes a preparation step, a heating step, and a drilling and rolling step. In the preparatory step, a material to be rolled is prepared having an outer diameter Db (mm) larger than the outer diameter D of the seamless metal pipe. The heating step heats the material to be rolled. In the drilling and rolling step, the heated material to be rolled is drilled and rolled by a drilling and rolling machine. In the drilling and rolling step, various conditions of the plug and the inclined roll are set so as to satisfy all of the following formulas (1) to (4).

0.95 × Dp ≦ Dpg ≦ Dp (1)
0.95 × Dp + 2 × t ≦ ROg ≦ Dp + 2 × t (2)
0 ≦ L2 / L1 ≦ 0.25 (3)
1.0 <(Db-ROp) / Db × 100 (4)
The meanings of the symbols in equations (1) to (4) are as follows.
Dpg: Plug diameter (mm) at the position of the gorge of the tilted roll,
Dp: Maximum plug diameter (mm),
ROg: Opening degree (mm) of the tilted roll at the position of the gorge portion of the tilted roll,
L1: Length of rolled part of plug (mm),
L2: The length of the reeling portion of the plug (mm), and ROp: the opening degree of the inclined roll at the position of the tip of the plug (mm).

The manufacturing method of the present embodiment manufactures a thick perforated material (seamless metal tube) having a wall thickness outer diameter ratio t / D of 15% to 30%. In the manufacturing method of the present embodiment, the outer diameter Db of the material to be rolled is larger than the outer diameter D of the perforated material. In other words, the outer diameter D of the perforated material is smaller than the outer diameter Db of the material to be rolled. From another viewpoint, the ratio D / Db of the outer diameter D of the perforated material to the outer diameter Db of the material to be rolled is smaller than 1.0. Therefore, this condition corresponds to the second condition.

Equation (1) represents the range of the diameter Dpg of the plug at the position of the gorge portion of the inclined roll, using the maximum diameter Dp of the plug as an index. In the present specification, this diameter Dpg may be referred to as gorge position plug diameter Dpg. If the gorge position plug diameter Dpg is the same as or close to the maximum diameter Dp of the plug as in the condition represented by the equation (1), the plug is arranged closer to the entrance side of the inclined roll. .. Therefore, the condition represented by the equation (1) corresponds to the first condition.

Equation (2) expresses the range of the opening ROg of the inclined roll at the position of the gorge portion of the inclined roll, using the maximum diameter Dp of the plug and the wall thickness t of the perforated material as indexes. In the present specification, the opening ROg of the inclined roll at the position of the gorge portion of the inclined roll may be referred to as the gorge portion roll opening ROg. As in the condition represented by the formula (2), the gorge portion roll opening ROg is a value obtained by adding twice the wall thickness t of the drilling material to the maximum diameter Dp of the plug, or a value close to it. For example, in the region of the entry side surface of the inclined roll, the wall thickness reduction amount of the material to be rolled is secured at a high level. Therefore, the condition represented by the equation (2) corresponds to the second condition while satisfying the first condition.

Equation (3) represents the range of the ratio L2 / L1 of the length L2 of the reeling portion of the plug to the length L1 of the rolled portion of the plug. In the present specification, this ratio L2 / L1 may be referred to as a reeling length ratio L2 / L1. If the reeling length ratio L2 / L1 is 0 (zero) or a value close to it as in the condition represented by the equation (3), the reeling portion of the plug does not exist or the plug is plugged. The reeling part of the plug is shorter than the rolled part of. In this case, the thickness reduction amount of the material to be rolled is secured at a high position at the position of the gorge portion of the inclined roll. Therefore, the condition represented by the equation (3) corresponds to the third condition while satisfying the first and second conditions.

In short, the formula (4) represents the range of the plug tip draft rate PD represented by the above formula (a). If the plug tip draft rate PD exceeds 1.0% as in the condition represented by the equation (4), the plug tip roll opening ROp is sufficiently small. In this case, the material to be rolled is sufficiently compressed by the inclined roll and sufficiently engaged with the inclined roll from the time when the material to be rolled is bitten into the inclined roll until it reaches the tip of the plug. Therefore, the condition represented by the equation (4) corresponds to the fourth condition while satisfying the first condition.

The upper limit of the plug tip draft rate PD is not particularly limited. This is due to the following reasons. If the plug tip draft rate PD becomes excessive, the plug tip roll opening ROp becomes too small. In this case, the amount of rolling material to be rolled by the inclined roll becomes excessive. If the amount of rolling down is excessive, Mannesmann fracture will occur excessively in drilling and rolling with a two-roll type piercer. However, Mannesmann fracture does not occur in drilling and rolling with a 3-roll type piercer. Therefore, there is no upper limit to the plug tip draft rate PD. However, in order to avoid interference between the inclined rolls, the upper limit of the plug tip draft rate PD is about 50%.

According to the manufacturing method of the present embodiment, in the perforated rolling in the case of producing a thick perforated material using a 3-roll type perforated rolling mill, the outer diameter of the material to be rolled is outside the perforated material (seamless metal pipe). The conditions of the plug and the inclined roll are set so as to be larger than the diameter and satisfy all of the equations (1) to (4). As a result, in order to satisfy the first to third conditions, the amount of thickness reduction of the material to be rolled by the inclined roll and the plug is substantially increased. Due to this increase in the wall thickness reduction amount, the peripheral length of the material to be rolled increases during drilling and rolling, and the final plug clearance is expanded. As a result, the occurrence of plug clogging can be suppressed. Moreover, since the above-mentioned fourth condition is satisfied, it is possible to suppress poor biting of the material to be rolled. Therefore, a 3-roll type drilling and rolling mill can be put into practical use for manufacturing a thick seamless metal pipe.

The wall thickness is the target wall thickness after drilling and rolling, and may be slightly different from the value of the actual wall thickness of the drilled material after actually drilling and rolling.

The shape of the entry side surface of the inclined roll is not particularly limited as long as the distance between the pass line and the entry side surface gradually decreases from the entry side to the exit side of the pass line. In a typical example, the entry surface is a tapered surface with a constant slope. The entrance surface may be a convex curved surface. The shape of the protruding side surface of the inclined roll is not particularly limited as long as the distance between the pass line and the protruding side surface gradually increases from the entry side to the exit side of the pass line. In a typical example, the protruding surface is a tapered surface with a constant gradient.

In the case of the 3-roll type piercer, the gorge portion roll opening ROg is a value twice the shortest distance between the gorge portion of the inclined roll and the pass line. The plug tip roll opening ROp is a value twice the shortest distance between the surface of the inclined roll (for example, the entry side surface) and the pass line on the surface perpendicular to the pass line at the position of the plug tip. The lead of the plug means the distance from the gorge portion to the tip of the plug on the path line.

Generally, a thick seamless metal pipe (perforated material) obtained by drilling and rolling has an outer diameter and a wall thickness adjusted by undergoing a drawing rolling step and a constant diameter rolling step. The constant diameter rolling step is also a step of shrinking the outer diameter caused by irregularity by stretching rolling to bring it closer to a perfect circle. The seamless metal pipe whose outer diameter and wall thickness have been adjusted may be a product pipe having a desired inner diameter and outer diameter by undergoing a machining process for cutting the inner surface and the outer surface. If necessary, the metal tube may be cut to a predetermined length before the machining process. The product pipe is, for example, a metal pipe for coupling or a metal pipe for supporting a large structure. The product tube is processed as necessary to become the final product. For example, in the case of a raw pipe for coupling, cutting processing, thread cutting processing, etc. are performed.

Here, eccentric uneven thickness occurs in the seamless metal pipe obtained by drilling and rolling with a two-roll type piercer. Eccentric wall thickness means a non-uniform wall thickness caused by the deviation between the center of the outer circumference (center of gravity) and the center of the inner circumference (center of gravity) in the cross section of the metal tube. In the present specification, the eccentric uneven thickness is also simply referred to as an eccentric thickness. The amount of eccentric eccentric wall thickness can be reduced by stretching rolling and constant diameter rolling. Therefore, when machining a metal pipe obtained by drilling and rolling with a two-roll type piercer, it is indispensable to reduce the amount of uneven thickness in each step of draw rolling and constant diameter rolling. If stretch rolling and constant diameter rolling are not performed, a portion having an excessively large wall thickness and a portion having a small wall thickness are mixed in the cross section. In this case, the variation in the machining allowance in the machining process becomes large, and the center of gravity of the metal tube is not stable when performing rotary machining with a lathe or the like. As a result, machining becomes unstable.

On the other hand, when a 3-roll type piercer is used as in the manufacturing method of the present embodiment, the eccentric uneven thickness of the seamless metal pipe obtained by drilling and rolling is small. In this case, even if stretch rolling and constant diameter rolling are not performed, the portion having an excessively large wall thickness and the portion having a small wall thickness do not coexist, so that the variation in the machining allowance in the machining process can be reduced, and the center of gravity of the metal pipe can be reduced. Is also stable. Therefore, draw rolling and constant diameter rolling are not always necessary. Therefore, in manufacturing the product pipe, the draw rolling step and the constant diameter rolling step may be omitted.

Therefore, the method for manufacturing the product pipe of the present embodiment includes a machining step of cutting at least one of the inner surface and the outer surface of the seamless metal pipe obtained by the drilling and rolling step of the above manufacturing method. Machining may be applied only to the inner surface of the metal tube, only to the outer surface of the metal tube, or to both the inner and outer surfaces of the metal tube. In this case, after the material to be rolled is perforated and rolled, the obtained thick perforated material (seamless metal pipe) is machined. That is, the usual stretching rolling and constant diameter rolling are omitted. Therefore, the man-hours required to obtain the product tube can be reduced. As a result, the production efficiency of the product tube is improved. The seamless metal pipe obtained by the drilling and rolling process can be used as a product pipe without going through the machining process.

However, the method for manufacturing the product pipe is a drawing rolling step of stretching and rolling the seamless metal pipe obtained by the perforation rolling step of the above manufacturing method, and a fixed diameter rolling step of rolling the stretched seamless metal pipe with a constant diameter. May be included. In this case, the above machining is performed on the seamless metal pipe obtained by the constant diameter rolling step.

A specific example of the manufacturing method of the present embodiment will be described below with reference to the drawings. FIG. 5 is a diagram showing an example of an inclined roll 1 in a 3-roll type piercer used in the method for manufacturing a seamless metal tube of the present embodiment. FIG. 6 is a diagram showing an example of a plug 2 in a 3-roll type piercer used in the method for manufacturing a seamless metal tube of the present embodiment.

With reference to FIG. 5, the boundary between the entry side surface 1a and the exit side surface 1b is the gorge portion G. The entry side surface 1a of the inclined roll 1 is a tapered surface having a constant gradient. The entry side surface 1a has an entry side surface angle θa. The entry side surface angle θa is the maximum angle formed by the entry side surface 1a in the range of contact with the material to be rolled and the pass line in the cross section including the pass line. The protruding side surface 1b of the inclined roll 1 is a tapered surface having a constant gradient. The protruding side surface 1b has an protruding side surface angle θb. The protruding side surface angle θb is the maximum angle formed by the protruding side surface 1b and the pass line in the range of contact with the material to be rolled in the cross section including the pass line.

With reference to FIG. 6, the shape of the plug 2 is a general shell shape. The plug 2 includes a rolling portion 2a, a reeling portion 2b, and a relief portion 2c in this order from the tip end side of the plug 2. The rolling portion 2a and the reeling portion 2b contribute to drilling and rolling. The rolled portion 2a is responsible for most of the wall thickness reduction applied to the material to be rolled. The reeling portion 2b finishes the wall thickness of the material to be rolled to the wall thickness of the perforated material.

The surface of the reeling portion 2b is a tapered surface having a constant gradient with respect to the central axis Pc of the plug 2. That is, the line that appears when the reeling portion 2b is cut along the central axis Pc is a straight line. The angle θ formed by this straight line and the central axis Pc corresponds to the gradient of the tapered surface. In the present specification, this angle θ may be referred to as the surface angle θ of the reeling portion 2b.

The surface of the rolled portion 2a is a convex curved surface. The line that appears when the rolled portion 2a is cut along the central axis Pc of the plug 2 is a convex curve. Of this convex curve, the convex curve of the portion corresponding to the tip portion 2aa of the rolled portion 2a is, for example, an arc. The convex curve of the remaining portion (hereinafter referred to as the main body portion 2ab) is an arc that smoothly connects the arc of the tip portion 2aa of the rolling portion 2a and the straight line of the reeling portion 2b. Since the arc of the main body 2ab is smoothly connected to the straight line of the reeling portion 2b, its radius of curvature RLP is larger than the radius of curvature of the arc of the tip 2aa of the rolled portion 2a. The straight line connecting the rear end of the rolled portion 2a and the center of the arc of the main body portion 2ab forms a predetermined angle θR with the straight line perpendicular to the central axis Pc of the plug 2. Hereinafter, this angle θR may be referred to as a rolling portion reference angle θR.

In the present embodiment, the reeling length ratio L2 / L1, that is, the ratio L2 / L1 of the length L2 of the reeling portion 2b to the length L1 of the rolled portion 2a satisfies the condition represented by the above formula (3). do. Specifically, the reeling length ratio L2 / L1 is 0 (zero) or more and 0.25 or less. That is, the reeling length ratio L2 / L1 is 0 or a value close to it. In this case, in the plug 2, the rolling portion 2a is present but the reeling portion 2b is not present, or the reeling portion 2b is shorter than the rolling portion 2a. The maximum diameter Dp of the plug 2 is the diameter at the rear end of the reeling portion 2b, that is, at the boundary between the reeling portion 2b and the relief portion 2c. In the absence of the reeling portion 2b, the maximum diameter Dp of the plug 2 is the diameter at the rear end of the rolled portion 2a.

FIG. 7 is a flow chart showing a method for manufacturing a seamless metal tube according to the present embodiment. FIG. 8 is a schematic view showing an example of a situation during drilling and rolling. FIG. 8 shows a state when the drilling and rolling mill is viewed from the side. In FIG. 8, the material to be rolled WP is shown in a cross section including the pass line PL, and the core metal 3 is not shown.

As shown in FIG. 7, the manufacturing method of the present embodiment includes a preparation step (# 5), a heating step (# 10), and a drilling and rolling step (# 15). In the manufacturing method of this embodiment, the three-roll piercers shown in FIGS. 1 to 6 are used. By this manufacturing method, a thick perforated material (seamless metal tube) SP having a wall thickness outer diameter ratio t / D of 15% to 30% is manufactured. Hereinafter, description will be made with reference to FIGS. 7 and 8.

[Preparation process (# 5)]
In the preparation step (# 5), the material to be rolled WP having an outer diameter Db (mm) larger than the outer diameter D of the drilling material SP is prepared. The material to be rolled WP is a round billet. The dimensions and material of the material to be rolled WP are determined according to the specifications required for the seamless metal pipe (perforated material) SP to be manufactured. The material of the material to be rolled WP is not particularly limited. For example, the material of the material to be rolled WP is carbon steel or alloy steel.

[Heating step (# 10)]
The heating step (# 10) heats the material to be rolled WP. At that time, the material to be rolled WP is heated to a predetermined temperature by a heating furnace. The heating temperature of the material to be rolled WP is, for example, in the range of 1100 to 1250 ° C.

[Punching and rolling process (# 15)]
In the drilling and rolling step (# 15), the heated material WP to be rolled is punched and rolled using a 3-roll type piercer. As a result, a thick seamless metal pipe (perforated material) SP having a wall thickness outer diameter ratio t / D of 15% to 30% is manufactured. At that time, the conditions of the plug 2 and the inclined roll 1 are set in advance so as to satisfy all of the above equations (1) to (4). Under these setting conditions, drilling and rolling is performed.

With reference to FIG. 8, the outer diameter D of the perforated material is smaller than the outer diameter Db of the material to be rolled. This condition corresponds to the second condition described above.

The gorge position plug diameter Dpg satisfies the condition represented by the equation (1). That is, the gorge position plug diameter Dpg is the same as or close to the maximum diameter Dp of the plug 2. In this case, the plug 2 is arranged closer to the entrance side of the inclined roll 1. This condition corresponds to the first condition.

The gorge roll opening ROg satisfies the condition represented by the equation (2). That is, the gorge portion roll opening ROg is a value obtained by adding twice the wall thickness t of the drilling material SP to the maximum diameter Dp of the plug 2, or a value close to it. In this case, the wall thickness reduction amount of the material to be rolled WP is secured at a high level in the region of the entry side surface 1a of the inclined roll 1. This condition corresponds to the second condition while satisfying the first condition.

The reeling length ratio L2 / L1 (see FIG. 6) satisfies the condition represented by the equation (3). That is, the reeling length ratio L2 / L1 is 0 or a value close to it. From another point of view, the reeling portion 2b of the plug 2 does not exist, or the reeling portion 2b of the plug 2 is shorter than the rolled portion 2a of the plug 2. In this case, the wall thickness reduction amount of the material to be rolled WP is secured at a high position at the position of the gorge portion G of the inclined roll 1. This condition corresponds to the third condition while satisfying the first and second conditions.

The plug tip draft rate PD (= (Db-ROp) / Db × 100) satisfies the condition represented by the equation (4). That is, the plug tip draft rate PD is a value exceeding 1.0%. From another point of view, the plug tip roll opening ROp is sufficiently small. In this case, the material WP to be rolled is sufficiently compressed by the inclined roll 1 and sufficiently engaged with the inclined roll 1 from the time when the material WP to be rolled is bitten into the inclined roll 1 until it reaches the tip of the plug 2. This condition corresponds to the fourth condition while satisfying the first condition.

As described above, in the perforated rolling in the case of producing the thick-walled perforated material SP using the 3-roll type piercer, the outer diameter Db of the material to be rolled WP is larger than the outer diameter D of the perforated material SP, and the formula (1) )-The conditions of the plug 2 and the inclined roll 1 are set so as to satisfy all of the equations (4). As a result, in order to satisfy the first to third conditions, the amount of thickness reduction of the material to be rolled by the inclined roll 1 and the plug 2 is substantially increased. Due to this increase in the wall thickness reduction amount, the peripheral length of the material to be rolled WP increases during drilling and rolling, and the final plug clearance is expanded. As a result, the occurrence of plug clogging can be suppressed. Moreover, since the above-mentioned fourth condition is satisfied, it is possible to suppress poor biting of the material to be rolled WP.

Subsequently, with reference to FIGS. 9 to 12, the wall thickness of the perforated material (seamless metal pipe) SP obtained by perforating and rolling the material to be rolled WP is verified. More specifically, the uneven thickness state of the perforated material SP will be verified. In order to confirm the uneven thickness state of the perforated material SP obtained by the manufacturing method according to the present embodiment, an analysis model having substantially the same shape as the 3-roll type piercer shown in FIG. 8 was created, and elasto-plastic 3D-FEM. The analysis was performed. For comparison, the same analysis was performed when a 2-roll piercer was used instead of the 3-roll piercer.

FIG. 9 is a cross-sectional view showing a situation during drilling and rolling with a 3-roll type piercer. FIG. 9 shows a cross section perpendicular to the path line PL. The arrows in FIG. 9 indicate the rotation directions of the inclined roll 1 and the plug 2. With reference to FIG. 9, the plug 2 is arranged on the path line PL. The three tilt rolls 1 are evenly spaced around the plug 2. One of the three inclined rolls is arranged directly above the plug 2 (upper in the vertical direction).

FIG. 10 is a cross-sectional view showing a situation during drilling and rolling with a two-roll type piercer. FIG. 10 shows a cross section perpendicular to the path line PL, as in FIG. The arrows in FIG. 10 indicate the rotation directions of the inclined roll 1 and the plug 2 as in FIG. 9. With reference to FIG. 10, the plug 2 is arranged on the path line PL. The two inclined rolls 1 are arranged right beside the plug 2 (both sides in the horizontal direction). Disc rolls 4 are arranged as guide tools directly above and below the plug 2 (both sides in the vertical direction). The disc roll 4 plays a role of suppressing the material WP to be rolled from protruding in the vertical direction during drilling and rolling.

With reference to FIG. 10, when a two-roll piercer is used, the material to be rolled WP is rolled down by two inclined rolls 1 arranged around the pass line PL at intervals of 180 ° from each other. In this case, the plug 2 is restricted from moving in the direction (horizontal direction (right direction and left direction)) toward each of the two inclined rolls 1 via the material to be rolled WP. On the other hand, the material to be rolled WP is not rolled down in the region where the inclined roll 1 does not exist. Therefore, the plug 2 is allowed to move toward the adjacent inclined rolls 1. That is, the plug 2 is allowed to move in the direction in which the disc rolls 4 face each other (vertical direction (upward and downward)). This is because the movement of the plug 2 is only restricted from two directions by the two inclined rolls 1.

Therefore, when a 2-roll type piercer is used, it is expected that the plug 2 is largely displaced in the vertical direction during drilling and rolling. If the displacement of the plug 2 during drilling and rolling is large, eccentric thickness deviation occurs in the drilling material SP. This is because the wall thickness of the perforated material SP is determined by rolling with the inclined roll 1 and the plug 2.

On the other hand, referring to FIG. 9, when a 3-roll type piercer is used, the material to be rolled WP is rolled down by three inclined rolls 1 arranged around the pass line PL at intervals of 120 °. NS. In this case, the plug 2 is restricted from moving in the directions (upward, lower right, and lower left) toward each of the three inclined rolls 1 via the material to be rolled WP. Further, in this case, although the plug 2 is allowed to move toward the adjacent inclined rolls 1, the movement allowance is small. This is because the movement of the plug 2 is restricted from three directions by the three inclined rolls 1.

Therefore, when a 3-roll type piercer is used, the displacement of the plug 2 during drilling and rolling is expected to be small. When the displacement of the plug 2 during drilling and rolling is small, the drilling material SP has less eccentricity and uneven thickness.

The results of the FEM analysis will be described with reference to FIGS. 11 and 12. FIG. 11 is a diagram showing a locus of the center of gravity (central axis) of the plug 2 during drilling and rolling. In FIG. 11, the vertical axis shows the displacement of the center of gravity position of the plug 2 in the vertical direction, and the horizontal axis shows the displacement of the center of gravity position of the plug 2 in the horizontal direction. FIG. 12 is a diagram showing the wall thickness distribution of the drilling material SP obtained by drilling and rolling. In FIG. 12, the vertical axis indicates the wall thickness of the perforated material SP, and the horizontal axis indicates the angle around the central axis of the perforated material SP.

When drilling and rolling is performed using a two-roll type piercer with reference to FIG. 11, the displacement of the plug 2 during drilling and rolling is large as a whole. In particular, the displacement in the vertical direction is remarkable. On the other hand, when drilling and rolling is performed using a 3-roll type piercer, the displacement of the plug 2 during drilling and rolling is small.

With reference to FIG. 12, when a 3-roll type piercer is used, the wall thickness of the perforated material SP is constant at about 5.5 mm over the entire circumferential direction. That is, the uneven thickness is very small. On the other hand, when a 2-roll type piercer is used, the wall thickness of the perforated material SP varies greatly depending on the angle, the maximum wall thickness is about 6.1 mm, and the minimum wall thickness is about 4.9 mm. .. That is, the uneven thickness is large.

From FIGS. 11 and 12, the degree of uneven thickness of the drilling material SP depends on the magnitude of displacement of the plug 2 during drilling and rolling. If a 2-roll type piercer is used, the uneven thickness of the perforated material SP is large, and if a 3-roll type piercer is used, the uneven thickness of the perforated material SP is small.

As described above, when the drilling and rolling is performed using the 3-roll type piercer, the uneven thickness of the drilling material SP obtained in the drilling and rolling step (# 15) shown in FIG. 7 is small. Therefore, in manufacturing a product pipe from the perforated material SP, a step of reducing the uneven thickness amount with respect to the perforated material SP is not always necessary.

FIG. 13 is a processing flow chart showing a general manufacturing method of product pipes. The method for manufacturing the product pipe shown in FIG. 13 can be applied to the punching material SP obtained in the drilling and rolling step of the manufacturing method of the present embodiment. FIG. 13 shows a process from obtaining the drilling material SP in the drilling and rolling step (# 15) shown in FIG. 7 to obtaining a product pipe.

As shown in FIG. 13, the method for manufacturing the product pipe is as follows: the drilling rolling step (# 15), the stretching rolling step (# 20), the constant diameter rolling step (# 25), and the machining step (# 30). including. In the draw-rolling step (# 20), the perforated material SP obtained in the perforated rolling step (# 15) is stretch-rolled. In the constant diameter rolling step (# 25), the stretch-rolled seamless metal pipe is constant-diameter rolled. The outer diameter and wall thickness are adjusted by stretch rolling and constant diameter rolling. After that, in the machining step (# 30), the inner surface and the outer surface of the seamless metal pipe after constant diameter rolling are cut. The machining process (# 30) may be performed only on the inner surface of the metal tube, only on the outer surface of the metal tube, or on both the inner and outer surfaces of the metal tube. good. As a result, a product tube having a desired inner and outer diameters can be obtained. In the draw rolling step (# 20), for example, a mandrel mill is used, and in the constant diameter rolling step (# 25), for example, a sizer is used. If necessary, the method for manufacturing the product tube may include a step of cutting the metal tube to a predetermined length before the machining step (# 30).

FIG. 14 is a processing flow diagram showing another manufacturing method of the product tube. The product tube manufacturing method shown in FIG. 14 can be applied to the punching material SP obtained in the drilling and rolling step of the manufacturing method of the present embodiment. FIG. 14 shows a process from obtaining the drilling material SP in the drilling and rolling step (# 15) shown in FIG. 7 to obtaining a product pipe.

According to the method for manufacturing a seamless metal pipe of the present embodiment, since a 3-roll type piercer is used for drilling and rolling, the uneven thickness of the drilling material SP obtained in the drilling and rolling step (# 15) is small. That is, the wall thickness of the perforated material SP is almost uniform, and there is little variation in the processing allowance in the machining process (# 30). Therefore, when manufacturing the product pipe from the perforated material SP, it is not necessary to adjust the outer diameter and the wall thickness with respect to the perforated material SP.

Therefore, as shown in FIG. 14, the product pipe manufacturing method includes a machining step (# 30) after the drilling and rolling step (# 15). That is, the stretching rolling step (# 20) and the constant diameter rolling step (# 25) shown in FIG. 13 are omitted. In this case, in the machining step (# 30), the drilling material SP obtained in the drilling and rolling step (# 15) is machined. That is, the inner and outer surfaces of the perforated and rolled seamless metal pipe are cut. The machining process (# 30) may be performed only on the inner surface of the metal tube, only on the outer surface of the metal tube, or on both the inner and outer surfaces of the metal tube. good. As a result, a product tube having a desired inner and outer diameters can be obtained. If necessary, the method for manufacturing the product tube may include a step of cutting the metal tube to a predetermined length before the machining step (# 30).

In the product tube manufacturing method shown in FIG. 14, since the draw rolling step (# 20) and the constant diameter rolling step (# 25) are omitted, the man-hours required to obtain the product tube can be reduced. As a result, the production efficiency of the product tube is improved as compared with the method for manufacturing the product tube shown in FIG.

A drilling and rolling test was carried out to investigate the presence or absence of plug clogging and poor biting of the material to be rolled. In this drilling and rolling test, a round billet (material to be rolled) was perforated and rolled using a 3-roll type piercer to produce a thick-walled raw pipe (seamless metal pipe, perforated material). Tables 1 and 2 below show the test conditions and test results.

The common test conditions were as follows. The material of the round billet was carbon steel (JIS standard S45C). The material of the plug was a molybdenum alloy having high strength in a high temperature range. The heating temperature of the round billet was 1250 ° C. The entry side surface angle θa of the inclined roll was 3.5 °.

Test No. The condition 1 was a condition in which the gorge position plug diameter Dpg deviated from the lower limit of the equation (1). That is, regarding the arrangement of the plug with respect to the inclined roll, it was insufficient to move the plug toward the entrance side. Furthermore, the test No. The condition 1 was a condition in which the gorge portion roll opening ROg deviates from the lower limit of the equation (2). That is, it was insufficient to secure the wall thickness reduction amount of the material to be rolled in the region of the entry side surface of the inclined roll. Therefore, plug clogging occurred.

Test No. The condition 2 was a condition in which the draft rate PD at the tip of the plug deviated from the lower limit of the equation (4). That is, the plug tip roll opening ROp was excessive with respect to the outer diameter Db of the material to be rolled. For this reason, poor biting of the material to be rolled occurred.

Test No. The condition of 4 was a condition in which the reeling length ratio L2 / L1 deviated from the upper limit of the equation (3). That is, at the position of the gorge portion of the inclined roll, it was insufficient to secure the thickness reduction amount of the material to be rolled. Therefore, plug clogging occurred.

For these, the test No. Each of the conditions 3 and 5 to 8 was a condition that satisfied all of the formulas (1) to (4). Therefore, it was possible to manufacture a thick-walled perforated material without causing any plug clogging or poor biting of the material to be rolled. In particular, Test No. It was also confirmed that a thick perforated material having a wall thickness outer diameter ratio t / D of 25.5% could be produced as in No. 8.

In addition, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

The manufacturing method of the present invention can be effectively used for manufacturing a seamless metal tube by the Mannesmann method.

1: Inclined roll G: Gorge part ROg: Opening of the inclined roll at the position of the gorge part ROp: Opening of the inclined roll at the position of the tip of the plug 2: Plug 2a: Rolling part 2b: Reeling part L1: Of the rolling part Length L2: Length of reeling part Dp: Maximum diameter of plug Dpg: Diameter of plug at position of gorge part PL: Pass line WP: Material to be rolled Db: Outer diameter of material to be rolled SP: Seamless metal tube ( Drilling material)
D: Outer diameter of seamless metal tube t: Thickness of seamless metal tube

Claims (2)

A method for manufacturing a seamless metal pipe, which uses a drilling and rolling mill to manufacture a seamless metal pipe having a ratio t / D of a wall thickness t (mm) to an outer diameter D (mm) of 15% to 30%. hand,
The drilling and rolling mill
With the plug placed on the path line,
Three inclined rolls arranged around the pass line at equal intervals, each having an entry side surface and an exit side surface, and the distance between the pass line and the entrance side surface is from the entry side to the exit side of the pass line. The inclined roll, which gradually decreases toward and gradually increases the distance between the pass line and the exit side surface from the entry side to the exit side of the pass line, is provided.
The manufacturing method is
A preparatory step for preparing a material to be rolled having an outer diameter Db (mm) larger than the outer diameter D of the seamless metal pipe, and
The heating process for heating the material to be rolled and
A drilling and rolling step of drilling and rolling the heated material to be rolled by the drilling and rolling machine, and various conditions of the plug and the inclined roll so as to satisfy all of the following formulas (1) to (4). A method for manufacturing a seamless metal pipe, including the drilling and rolling step of setting.
0.95 × Dp ≦ Dpg ≦ Dp (1)
0.95 × Dp + 2 × t ≦ ROg ≦ Dp + 2 × t (2)
0 ≦ L2 / L1 ≦ 0.25 (3)
1.0 <(Db-ROp) / Db × 100 (4)
The meanings of the symbols in equations (1) to (4) are as follows.
Dpg: Diameter (mm) of the plug at the position of the gorge portion of the inclined roll,
Dp: Maximum diameter (mm) of the plug,
ROg: Opening degree (mm) of the tilted roll at the position of the gorge portion of the tilted roll,
L1: Length (mm) of the rolled portion of the plug,
L2: The length of the reeling portion of the plug (mm), and ROp: the opening degree of the inclined roll at the position of the tip of the plug (mm). A method for manufacturing a product pipe, which comprises a machining step of cutting at least one of an inner surface and an outer surface of the seamless metal pipe obtained by the drilling and rolling step of the manufacturing method according to claim 1.

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