JP2005046906A - Device and method for manufacturing inside grooved tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for manufacturing an inside grooved tube which is hardly broken during the working, and a method for manufacturing the inside grooved tube using the device. <P>SOLUTION: A holding plug 2, a plug shaft 4, and grooved plugs 5a and 5b with grooves formed in each outer surface thereof are disposed inside a stock tube 1. In the grooved plugs 5a and 5b, a first tapered part 22, a columnar part 21 and a second tapered part 23 are provided along the drawing direction of the stock tube 1, and the grooves are formed continuous to the columnar part 21 and the second tapered part 23. The rotational axes of work rolls 16a and 16b are disposed between the position on the upstream side by 3 mm and at the position on the downstream side by 2 mm in the tube drawing direction from a boundary surface 24b at the grooved plugs 5a and 5b. In addition, a sizing die 8a is disposed between the work roll 16a and the work roll 16b, and a sizing die 8b is disposed on the downstream side in the tube drawing direction of the work roll 16b. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a seamless inner grooved tube manufacturing apparatus suitable as a heat transfer tube incorporated in a heat exchanger used in a room air conditioner, a packaged air conditioner, a vending machine or the like, and an inner grooved tube manufacturing method using the apparatus. In particular, the present invention relates to an apparatus and a method for manufacturing an internally grooved tube using a grooved plug and a rolling roll.

  The internally grooved tube is used as a heat transfer tube incorporated in an air-cooled heat exchanger used in an air conditioner or the like. There are two types of internally grooved pipes: seamless internally grooved pipes manufactured by rolling and welded internally grooved pipes manufactured by high frequency induction welding or the like. The welded inner surface grooved tube is formed by once forming the ingot after melting into a plate material, then subjecting the plate material to groove processing with a groove roll, and then rolling the plate material into an arc shape by roll forming, and performing high frequency welding or TIG (Tungsten Inert Gas) manufactured by forming into a tube by welding. On the other hand, a seamless inner surface grooved tube is manufactured by directly forming a tube from a molten ingot and subjecting the tube to groove processing. For this reason, the seamless inner surface grooved tube requires fewer processes than the welded inner surface grooved tube and is superior to the welded inner surface grooved tube in productivity. In addition, in manufacturing a welded inner surface grooved tube, increasing the processing speed to improve productivity decreases the stability of the welding quality and causes a high current to flow through the heating coil. Life is shortened. In addition, the power consumption increases and the manufacturing cost increases.

  There are two methods for producing a seamless internally grooved tube: a ball rolling method and a roll machining method. First, a method for producing an internally grooved tube by ball rolling (hereinafter referred to as a ball rolling method) will be described. As the material, a raw tube made of an annealed material (O material) tempered by bright annealing or annealing by an induction heater is used. A grooved plug having a groove formed on the outer surface is inserted into the element tube, and a rolling ball that rotates in a planetary contact with the outer surface of the element tube is disposed at a position corresponding to the grooved plug. The planetary rotation of the rolling ball is performed by a magnetic levitation high-speed motor. Then, the rolled ball is pressed toward the grooved plug by the rolling ball, and the grooved plug rotates around the tube axis by drawing the raw tube, so that the entire inner surface of the raw tube is formed. The groove of the grooved plug is transferred to form a groove.

  However, the above-mentioned ball rolling method has the following problems. First, in the ball rolling method, it is necessary to use a magnetic levitation type high-speed motor to rotate the rolled ball at high speed. Since this magnetic levitation type high-speed motor is an extremely expensive device, there is a problem that the equipment cost is high.

  Further, in the ball rolling method, it is necessary to increase the drawing speed of the tube in order to improve the productivity of the seamless inner grooved tube and reduce the manufacturing cost. On the other hand, in the ball rolling method, one of the factors affecting the groove formability of the inner surface of the tube is the processing pitch (the length of the raw tube that advances while one ball revolves once). In order to increase the drawing speed while maintaining the groove formability by setting this processing pitch to the same level as before, it is necessary to increase the revolution speed of the rolled ball. However, in a normal magnetic levitation type high-speed motor, the upper limit of the rotational speed is about 30,000 revolutions / minute. For this reason, when the processing pitch of the pipe is 2 mm per rotation, the upper limit value of the drawing speed is about 60 m / min. Even in the current maximum speed magnetically levitated high-speed motor, the rotation speed is limited to about 45,000 rotations / minute, and therefore the drawing speed is limited to about 90 m / minute. For this reason, in the ball rolling method, the drawing speed of the tube cannot be increased so much, and the improvement in productivity is limited.

  Furthermore, in the ball rolling method, it is necessary to use an annealed material (O material) as a raw tube. This is because the ball rolling method deforms the pipe in the radial direction by the rolling ball that revolves. Therefore, if the pipe is not made of a soft material such as an annealed material, the pipe is sufficiently deformed. This is because the groove cannot be formed. For this reason, when a seamless inner grooved tube is manufactured by the ball rolling method, it is necessary to configure the base tube with an annealing material before performing ball rolling, which increases the manufacturing cost. In the case of welded pipes, grooves can be formed even with a material that has not been annealed (H material), but it is easy to cause defects in the groove roll, which in turn increases costs. The base tube is preferably made of an annealed material.

  As described above, the manufacture of seamless inner surface grooved pipes by the ball rolling method can reduce the manufacturing cost as compared with the manufacture of welded inner surface grooved pipes, but it is necessary to install a magnetically levitated high-speed motor in the manufacturing equipment. In addition, it is difficult to increase the drawing speed of the tube, and there is a limit to the reduction in manufacturing cost.

  Furthermore, in the ball rolling method, since the tube is pulled out while the material of the tube flows into the groove carved on the outer surface of the grooved plug, the grooved plug rotates as the tube is pulled out. This rotation causes the relative movement of the grooved plug relative to the tube to be lubricated. However, when the lead angle of the groove of the grooved plug, that is, the angle formed by the straight line parallel to the axial direction on the side surface of the grooved plug and the direction in which the groove extends is 0 ° (parallel to the tube drawing direction), the grooved The plug stops rotating and the tube breaks. For this reason, in the ball rolling method, it is difficult to form a groove parallel to the tube axis direction on the tube inner surface.

  Furthermore, even if a plurality of grooves having different lead angles are formed on the outer surface of the grooved plug, the grooved plug cannot be rotated. For this reason, a cross groove cannot be formed on the inner surface of the pipe by the ball rolling method. Furthermore, when grooves having the same lead angle but different pitches are formed on the outer surface of the grooved plug, the grooved plug can be rotated as the tube is pulled out. However, when the rolling ball revolves, the material of the tube moves in the circumferential direction along with the revolution and flows into the groove of the grooved plug to form a groove on the inner surface of the tube. When the groove moves from the dense area to the sparse area, the escape material for the tube material disappears. As a result, the shape of the groove formed on the inner surface of the tube becomes unstable, or the tube is broken due to fluctuations in the drawing load.

  Furthermore, it is possible in principle to form cross grooves and grooves with different pitches on the inner surface of the pipe by performing the rolling process twice. In practice, however, the grooved plug is used in the second rolling process. The load applied to the surface becomes too large, and the grooved plug is likely to be lost. For this reason, it is extremely difficult in practice to form cross grooves or grooves having different pitches on the inner surface of the pipe by two rolling processes.

  Furthermore, in the ball rolling method, the inner surface of the tube is divided into a plurality of regions in the tube circumferential direction, and different types of grooves are formed in each region, or grooves are formed only in some regions, and the remaining regions are formed. It is impossible not to form a groove. Thus, the ball rolling method has a problem that only a simple spiral groove having a constant lead angle and pitch can be formed on the inner surface of the tube, and the degree of freedom of the groove pattern that can be formed on the inner surface of the tube is extremely small.

  As means for solving these problems, there is a method for producing a seamless internally grooved tube by roll processing (see, for example, Patent Documents 1 to 3). A method for producing a seamless internally grooved tube by roll processing (hereinafter referred to as roll rolling method) will be described below.

  FIG. 6 is a cross-sectional view showing a seamless inner grooved heat transfer tube manufacturing apparatus and manufacturing method by a conventional roll rolling method, and FIG. 7 is an enlarged cross-sectional view showing a rolling part of the manufacturing apparatus shown in FIG. 8 is a cross-sectional view taken along line AA shown in FIG. As shown in FIG. 6, a holding plug 2 is inserted into a base tube 1 made of copper or a copper alloy (hereinafter collectively referred to as copper). The shape of the holding plug 2 is such that the outer diameter on the tube supply side (upstream side) is slightly smaller than the inner diameter of the raw tube 1, and the outer diameter on the tube extraction side (downstream in the tube extraction direction) is smaller than the outer diameter on the tube supply side. It has become. A holding die 3 for reducing the diameter of the pipe 1 together with the holding plug 2 is disposed on the outer surface of the pipe 1 at a position aligned with the holding plug 2. A grooved plug 15 is connected to the holding plug 2 via a plug shaft 4. A groove having a shape to be formed on the inner peripheral surface of the raw tube 1 is processed on the outer peripheral surface of the grooved plug 15. The grooved plug 15 can freely rotate about the plug shaft 4 as an axis.

  Further, as shown in FIG. 7, the grooved plug 15 includes a cylindrical portion 11 and tapered portions 12 formed at both ends of the cylindrical portion 11. The tapered portion 12 is a chamfered portion to prevent the tube from breaking when the tube contacts the corner of the grooved plug 15. Generally, the tapered portion 12 has a side edge of the cylindrical portion 11 and the tapered portion 12. The angle φ formed with the side edge is about 45 °. The axial length of the grooved plug 15 is about 5 to 30 mm, and a groove is formed on the side surface of the cylindrical portion 11. The lead angle β of this groove, that is, the angle formed by the straight line parallel to the axial direction on the side surface of the cylinder 11 and the direction in which the groove extends is 0 to 10 °. And in the cylindrical part 11 of the grooved plug 15, the space between the grooves is a fin, and the depth of the groove, that is, the height of the fin is 0.05 to 0.15 mm. In the cross section orthogonal to the axis of the grooved plug 15, the radius of curvature of the groove bottom is 0.04 to 0.06 mm, the radius of curvature of the top of the fin is about 0.05 mm, and the peak angle of the fin 14 is It is 80 to 120 °.

  Further, a pair of rolling rolls 6 are disposed so as to be in rolling contact with the outer surface of the raw tube 1 at a position aligned with the grooved plug 15 on the outer side of the raw tube 1. Each rolling roll 6 can rotate, and the direction of the rotation axis thereof is orthogonal to the tube axis direction of the raw tube 1. The grooved plug 15 and the rolling roll 6 constitute a rolling part 17. In addition, a sizing die 8 is provided on the downstream side of the rolling portion 17 in the tube drawing direction to reduce the outer diameter of the raw tube 1 having a groove formed on the inner surface to a predetermined size.

  As shown in FIG. 7, the rotation axis of the rolling roll 6 is located near the longitudinal center of the grooved plug 15 in the tube drawing direction. And as shown in FIG. 8, the shape of the rolling roll 6 is a drum shape in which the diameter of a roll center part is smaller than the diameter of a roll both ends, In the cross section containing the rotating shaft of this rolling roll 6, the shape of a side edge Is substantially matched to the outer surface shape of the raw tube 1. That is, the curvature radius of the side surface of the rolling roll 6 is substantially equal to the curvature radius of the outer surface of the raw tube 1.

  Next, a conventional method for manufacturing an internally grooved tube will be described. As shown in FIG. 6, first, the drawing oil 10 is filled on the upstream side of the holding plug 2 inside the base tube 1. The base tube 1 is reduced in diameter by the holding plug 2 and the holding die 3. Next, the outer surface of the diameter-reduced raw tube 1 is reduced in diameter by being pressed by a rolling roll 6 that rolls in contact with the outer surface and rotates, and is pressed toward the grooved plug 15. Thereby, the groove of the grooved plug 15 is transferred to the inner surface of the raw tube 1. At this time, the grooved plug 15 is connected to the holding plug 2 via the plug shaft 4, and the holding plug 2 is aligned with the holding die 3 by the frictional force caused by the drawing of the raw tube 1 and the drag from the holding die 3. Since it is locked at the position, the grooved plug 15 is also stopped at a position aligned with the rolling roll 6. Next, the raw tube 1 in which the groove is formed on the inner surface that has passed through the rolling portion 17 is further reduced in diameter by the sizing die 8 and shaped so that the cross section of the tube axis is a perfect circle. The inner grooved tube 9 has an outer diameter.

  Thus, in the roll rolling method, since no rolling ball is used, a magnetic levitation type high-speed motor for rotating the rolling ball is unnecessary. For this reason, equipment cost can be held down. Further, since no rolling ball is used, the drawing speed of the tube is not determined by the revolution speed of the rolling ball. For this reason, the drawing speed of a pipe can be improved and productivity can be improved.

Japanese Patent Publication No. 3-5882 (Page 2-4, Fig. 1) JP-A-1-99713 (page 2-5, FIG. 1) JP-A-4-302999 (page 3-4, Fig. 1-2)

  However, the conventional techniques described above have the following problems. That is, when the internally grooved tube 9 is manufactured by the manufacturing apparatus shown in FIGS. 5 to 8, depending on the manufacturing conditions such as the shape of the groove formed on the inner surface of the raw tube 1 or the drawing speed, the rolling roll 6 and the sizing die 8 are used. Or on the exit side of the sizing die, the base tube 1 may break.

  The present invention has been made in view of such a problem, and provides a manufacturing apparatus for an internally grooved tube and a manufacturing method for an internally grooved pipe using the manufacturing apparatus, in which the tube is not easily broken during processing. Objective.

  An apparatus for manufacturing an internally grooved tube according to the first invention of the present application includes a holding die that contacts an outer surface of a metal tube, and the metal tube that is disposed inside the metal tube and is engaged with the holding die, together with the holding die. A holding plug for reducing the diameter, a grooved plug that is rotatably supported on the plug shaft of the holding plug and has a groove formed on the outer surface, and a rotating shaft that is parallel to the outer surface of the metal tube and A pair of rolling rolls arranged so as to be orthogonal to the tube axis direction and rollingly contacting the outer surface of the metal tube to press the metal tube toward the grooved plug to form a groove on the inner surface of the metal tube; A sizing die that is disposed downstream of the pair of rolling rolls in the drawing direction of the metal tube and contacts the outer surface of the metal tube to reduce the diameter of the metal tube, and the grooved plug is the metal tube A first taper along the pulling direction of The cylindrical portion and the second tapered portion are provided, the first tapered portion has a truncated cone shape whose diameter increases toward the cylindrical portion, and the second tapered portion moves away from the cylindrical portion. And the groove is formed continuously with the cylindrical portion and the second tapered portion, and in the cross section including the central axis of the grooved plug, the cylindrical portion The length in the axial direction is 3 mm or less, and the downstream end portion in the metal tube extraction direction of the portion where the groove of the second taper portion is formed and the downstream end surface in the metal tube extraction direction of the column portion The distance between the side edge of the cylindrical portion and the side edge of the first tapered portion is 120 to 150 °, and the side edge of the cylindrical portion and the second tapered portion The angle formed by the side edge of is larger than 150 ° , And less than 180 °.

  The inventors of the present invention conducted intensive experimental studies to find out the cause of the above-described breakage of the tube, and obtained the following knowledge. In the roll rolling method, in order to form a uniform groove on the inner surface of the metal tube, the shape of the rolling roll is a drum shape, and the side surface of the rolling roll is in uniform contact with the outer surface of the metal tube. For this reason, the metal tube material that has flowed into the groove formed in the grooved plug does not spring back, and is kept in contact with the grooved plug. Thus, when the metal tube is pulled out with a large contact area between the grooved plug and the metal tube, a large frictional force is generated. Therefore, in order to pull out the metal tube, it is necessary to apply a large pulling force exceeding the large frictional force to the metal tube. When the pulling force exceeds the tensile breaking load of the metal tube, the metal tube is broken. Therefore, in the present invention, the length of the cylindrical portion is made shorter than the grooved plug used in the conventional manufacturing apparatus, and the cylindrical portion is formed on the tapered portion provided on the downstream end surface of the cylindrical portion in the tube drawing direction. Since the groove continuous from the groove of the portion is formed, the contact area between the grooved plug and the metal tube is reduced, and the frictional force generated between the metal tube and the grooved plug is reduced. Thereby, the drawing force applied to the metal tube can be reduced, and the metal tube can be prevented from breaking.

  For example, on the outer peripheral surface of the grooved plug, an angle formed by a straight line parallel to the axial direction of the grooved plug and a direction in which the groove extends is 0 to 20 °, and the depth of the groove is 0.05 to 0.15 mm, the angle formed by the inclined surface of the groove in the cross-axis orthogonal section of the grooved plug is 60 to 120 °, and the radius of curvature of the bottom of the groove and the top of the fin is 0.04 to 0.00. 06 mm.

  Further, the rotation axis of the pair of rolling rolls is located at a position 3 mm upstream and downstream from the boundary surface between the cylindrical portion of the grooved plug and the second taper portion with respect to the drawing direction of the metal tube. It is preferable to arrange | position between 2 mm positions. Thereby, the drawing force applied to the metal tube can be reduced, the metal tube can be prevented from breaking, and a uniform groove can be formed on the inner surface of the metal tube.

  Furthermore, the rolling part consisting of the grooved plug and the rolling roll pair and the sizing die may be arranged in a plurality of stages along the drawing direction of the metal tube. Thereby, a groove | channel can be formed more uniformly in a metal pipe inner surface. Also, multiple types of grooves can be formed on the inner surface of the metal tube.

  The rolling part composed of the grooved plug and the rolling roll pair may be arranged in two stages in the drawing direction of the metal tube, and the opposing directions of the rolling roll pair in each rolling part are orthogonal to each other, and at least one of them The pair of rolling rolls can change the facing direction by an angle θ from the orthogonal basic position. This angle θ is, for example, in the range of 0 to 90 °. Thereby, a groove | channel can be formed more uniformly in a metal pipe inner surface.

  A pair of backup rolls having a diameter larger than that of the rolling roll and pressing the rolling roll in the direction of the metal tube may be in rolling contact with the rolling roll pair. Thereby, the force with which the rolling roll presses the metal tube is made uniform.

  According to a second aspect of the present invention, there is provided a method of manufacturing an internally grooved tube. A diameter reduction process, a grooved plug that is rotatably supported by the plug shaft of the holding plug and has a groove formed on the outer surface, and a tube shaft of the metal tube that has a rotation axis parallel to the outer surface of the metal tube Forming a groove on the inner surface of the metal tube by pressing the metal tube against the grooved plug by a pair of rolling rolls arranged so as to be orthogonal to the direction, and reducing the diameter of the metal tube by a sizing die The grooved plug is provided with a first taper portion, a columnar portion and a second taper portion along the drawing direction of the metal tube, and the first taper portion is A truncated cone whose diameter increases toward the cylindrical part And the second tapered portion has a frustoconical shape whose diameter decreases with increasing distance from the cylindrical portion, the groove is formed continuously with the cylindrical portion and the second tapered portion, and the grooved plug In the cross section including the central axis, the length of the cylindrical portion in the axial direction is 3 mm or less, and the downstream end portion of the cylindrical portion in the drawing direction of the metal tube in the portion where the groove of the second tapered portion is formed. The distance from the downstream end surface of the metal pipe in the drawing direction is 2 to 5 mm, the angle formed by the side edge of the cylindrical portion and the side edge of the first tapered portion is 120 to 150 °, and the side edge of the cylindrical portion And the side edge of the second taper portion is greater than 150 ° and less than 180 °.

  In the present invention, the length of the cylindrical portion is shorter than that of the conventional grooved plug, and a continuous groove from the groove of the cylindrical portion is formed in the tapered portion provided on the downstream end surface of the cylindrical portion in the tube drawing direction. Since the grooved plug is used, the contact area between the grooved plug and the metal tube is reduced, and the frictional force generated between the metal tube and the grooved plug is reduced. Thereby, since the drawing force applied to the metal tube can be reduced, the groove can be formed on the inner surface without breaking the metal tube.

  According to the present invention, the length of the cylindrical portion in which the groove of the grooved plug is formed is shortened, and the groove is also formed in a part of the tapered portion provided at the downstream end portion of the cylindrical portion in the tube drawing direction. As a result, the contact area between the grooved plug and the metal tube is reduced, and the frictional force generated between the metal tube and the grooved plug can be reduced, thereby reducing the pulling force applied to the metal tube. It is possible to prevent the metal tube from breaking.

  Hereinafter, an internal grooved pipe manufacturing apparatus according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing a manufacturing apparatus and a manufacturing method of an internally grooved tube according to an embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view showing a rolled part of the manufacturing apparatus shown in FIG. FIG. 3 is a partial cross-sectional view showing a grooved plug of the inner surface grooved pipe manufacturing apparatus of the present embodiment. 1 to 3, the same components as those of the conventional apparatus shown in FIGS. 6 to 8 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 1, the inner surface grooved pipe manufacturing apparatus of the present embodiment includes a holding plug 2, a grooved plug 5a via a plug shaft 4, and a grooved plug 5b having a smaller diameter than the grooved plug 5a. Are connected. These grooved plugs 5a and 5b are attached so as to be rotatable relative to each other. As shown in FIG. 2, the grooved plugs 5 a and 5 b are provided with a first tapered portion 22, a cylindrical portion 21, and a second tapered portion 23 along the drawing direction of the raw tube 1. .

  The length of the grooved plugs 5a and 5b in the axial direction is, for example, 10 to 25 mm, and the outer diameter of the cylindrical portion 21 is, for example, 5 to 10 mm. The cylindrical portion 21 has a cylindrical shape with a length x in the axial direction of 3 mm or less, and the side surface has a shape necessary to be formed on the inner peripheral surface of the raw tube 1 such as a spiral shape or a straight shape. Grooves are formed. FIG. 4 is a cross-sectional view showing the grooved plug when the length x in the axial direction of the cylindrical portion 21 is 0 mm. As shown in FIG. 4, the grooved plug in the inner surface grooved tube manufacturing apparatus of the present embodiment is not provided with the cylindrical portion 21, and is configured only by the first tapered portion 22 and the second tapered portion 23. Also good. Further, the lead angle β of the groove, that is, the angle formed by the straight line parallel to the axial direction of the cylindrical portion 21 on the side surface of the cylindrical portion 21 and the direction in which the groove extends is, for example, 0 to 20 °. When the lead angle β is 0 °, the groove is a straight line parallel to the axial direction.

As shown in FIG. 3, fins 14 are provided between the grooves 13 in the cylindrical portion 21 of the grooved plugs 5 a and 5 b. The depth h of the groove 13 is, for example, 0.05 to 0.15 mm. The depth h of the groove 13 is equal to the height of the fin 14, the central axis is the same as the central axis of the grooved plugs 5 a and 5 b, and the virtual cylindrical surface 20 a connecting the bottoms of the fins 14 and the central axis are It is the same as the central axis of the grooved plugs 5a and 5b and is the distance from the virtual cylindrical surface 20b connecting the tops of the fins 14. Further, in the cross section shown in FIG. 3, that is, the cross section orthogonal to the axis of the cylindrical portion 21, the curvature radius r _{1 at} the bottom of the groove 13 and the curvature radius r _{2 at} the top of the fin 14 are, for example, 0.04 to 0.00. 06 mm. Furthermore, the peak angle α of the fin 14, that is, the angle formed by both sides of the fin 14 is, for example, 60 to 120 °. The grooved plugs 5a and 5b are preferably made of an ultrafine particle superalloy, and more preferably an ultrafine particle alloy containing fine particles of tungsten carbide (WC) having an average particle size of 0.5 μm or less. . Moreover, the lifetime can be extended by vapor-depositing TiC or TiN etc. on the surface of the grooved plugs 5a and 5b.

On the other hand, as shown in FIG. 2, the shape of the first tapered portion 22 and the second tapered portion 23 is a truncated cone shape whose side surfaces are tapered, and is separated from the boundary surfaces 24 a and 24 b with the cylindrical portion 21. The diameter is getting smaller. In addition, a groove is formed in a part of the outer surface of the second tapered portion 23, following the cylindrical portion 21. The groove lead angle β formed in the second taper portion 23 is the same as that of the cylindrical portion 21, and the groove depth h becomes smaller toward the downstream side in the tube drawing direction. Further, in the cross section including the central axis of the grooved plugs 5a and 5b, the length L of the portion where the groove is formed, that is, the end 24c and the boundary surface on the downstream side in the tube drawing direction of the portion where the groove is formed. The distance from 24b is 2 to 5 mm. Note that no groove is formed in the first tapered portion 22. Further, in the cross section including the central axis of the grooved plug 5a and 5b, the side edges and the angle phi ₁ formed between the first tapered portion 22 of the cylindrical portion 21 is, for example, from 120 to 0.99 °, the cylindrical portion 21 angle phi ₂ forming the side edge and the second tapered portion 23 is, for example, exceed 0.99 °, less than 180 °. In addition, the boundary part of the 1st taper part 22 and the 2nd taper part 23, and the cylindrical part 21 is comprised by the curved surface.

  In addition, a pair of work rolls (rolling rolls) 16a having rotating shafts parallel to each other are positioned at a position aligned with the grooved plug 5a on the outer side of the raw tube 1, and at a position aligned with the grooved plug 5b. A pair of work rolls 16b having parallel rotation axes are arranged so as to make rolling contact with the outer surface of the raw tube 1 respectively. In the work roll pairs 16a and 16b, the direction in which their rotation axes extend is perpendicular to the tube axis direction of the raw tube 1, and the opposing direction of the work roll pair 16a and the opposing direction of the work roll pair 16b are mutually orthogonal. (This position is hereinafter referred to as a basic position). For example, when processing a metal tube having an outer diameter of 6 to 12 mm and a wall thickness of 0.25 to 0.40 mm, the maximum diameter D of the work rolls 16a and 16b, i.e., the cross section, in a cross section parallel to the tube drawing direction. The diameter in the cross section where the area is maximum may be 40 to 80 mm, and the minimum radius d, that is, the diameter in the cross section where the cross sectional area is minimum may be 20 to 60 mm. In addition, since the work rolls 16a and 16b are small, and a large force is applied during rolling, in order to stably manufacture the inner surface grooved tube for a long period of time, as with the grooved plugs 5a and 5b described above, It is preferable that it is composed of an ultrafine particle superalloy. In particular, in order to prevent chipping and ensure fatigue strength, for example, it is preferably made of an ultrafine particle alloy containing tungsten carbide (WC) fine particles having an average particle diameter of 0.5 μm or less.

  In this manufacturing apparatus, the facing direction of at least one of the work roll pairs 16a and 16b can be changed by the angle θ from the basic position described above. This angle θ is, for example, in the range of 0 to 90 °. Further, the work rolls 16a and 16b can rotate, and the shape thereof is a drum shape whose both end portions are thick and whose central portion is thin. In this manufacturing apparatus, in the cross section including the rotation axis, the radius of curvature of the central portion is substantially equal to the radius of the outer surface of the raw tube 1, and the side edge shape of the central portion is substantially the same as the outer surface shape of the raw tube 1. The work rolls 16a and 16b are in line contact with the base tube 1 substantially evenly.

  Further, a pair of backup rolls 18a having a diameter larger than that of the work roll 16a and pressing the work roll 16a in the direction of the raw tube 1 are arranged so as to be in rolling contact with the work roll 16a. Similarly, a pair of backup rolls 18b that are larger in diameter than the work roll 16b and press the work roll 16b in the direction of the raw tube 1 are disposed so as to be in rolling contact with the work roll 16b. Thus, a large force can be uniformly applied to the raw tube 1 by pressing the work roll with the backup roll. The backup rolls 18a and 18b can be made of cemented carbide or bearing steel such as SUJ-2, for example. The rolled portion 7a is formed by the grooved plug 5a, the work roll pair 16a, and the backup roll pair 18a, and the rolled portion 7b is formed by the grooved plug 5b, the work roll pair 16b, and the backup roll pair 18b.

  Then, the rotation shafts of the work roll pairs 16a and 16b translated the boundary surface 24b between the cylindrical portion 21 and the second taper portion of the grooved plugs 5a and 5b by 3 mm from the boundary surface 24b to the upstream side in the tube drawing direction. It is located between the surface and a surface translated 2 mm downstream in the tube drawing direction.

  In the inner grooved pipe manufacturing apparatus of the present embodiment, a sizing die 8a for forming the raw pipe 1 is provided between the first-stage rolled portion 7a and the second-stage rolled portion 7b. A sizing die 8b is provided on the downstream side of the second-stage rolled portion 7b in the tube drawing direction to process the outer diameter of the raw tube 1 having a groove on the inner surface into a predetermined dimension. That is, the manufacturing apparatus of the internally grooved tube of the present embodiment is a dandem rolling manufacturing apparatus in which two rolling rolls are provided.

  Hereinafter, the reason for the numerical limitation in each constituent requirement of the present invention will be described.

Groove lead angle β of grooved plug: 0 to 20 °
When the groove is formed on the inner surface of the raw tube by the grooved plug, the groove of the grooved plug and the fin on the inner surface of the raw tube formed by transferring the groove to the inner surface of the raw tube are engaged with each other. It becomes. If the groove is spiral, that is, if the lead angle β of the groove is greater than 0 °, the element tube is drawn, so that the element tube rotates the grooved plug along the groove formed on the inner surface. Try to let them. The base tube receives a reaction force from the grooved plug and tries to rotate in the direction opposite to that of the grooved plug. On the other hand, since the rolling roll has a large contact area with the raw pipe, the raw roll is constrained in the pipe circumferential direction to prevent rotation. As a result, a large force is applied to the raw tube along the tube circumferential direction, and this force is added to the pulling force along the tube axis direction. When the lead angle β of the groove of the grooved plug exceeds 20 °, this force increases and the base tube is easily broken. Therefore, the groove lead angle β of the grooved plug is preferably 0 to 20 °.

Groove depth h of the grooved plug: 0.05 to 0.15 mm
If the groove depth h of the grooved plug is less than 0.05 mm, the height of the fin formed by transferring the groove to the inner surface of the base tube is lowered, and the heat transfer performance of the inner surface grooved tube is lowered. To do. On the other hand, if the depth h of the groove of the grooved plug exceeds 0.15 mm, the raw tube is easily broken and cannot be processed. Therefore, the groove depth h of the grooved plug is preferably 0.05 to 0.15 mm.

Radius of curvature r _{1 at} the bottom of the groove of the grooved plug : 0.04 to 0.06 mm
If the radius of curvature r _{1 at} the bottom of the groove is less than 0.04 mm, the groove shape becomes too sharp and the groove cannot be processed. On the other hand, if the radius of curvature r ₁ exceeds 0.06 mm, the fins formed on the inner surface of the inner grooved tube become thicker, the heat transfer performance of the inner grooved tube decreases, and the inner grooved tube has a single weight. Become heavier. Therefore, it is preferable that the radius of curvature r _{1 at} the bottom of the groove of the grooved plug is 0.04 to 0.06 mm.

The radius of curvature r ₂ of the top of the fin between the grooves of the grooved plug : 0.04 to 0.06 mm
The radius of curvature r ₂ of the top of the fin grooved plug is less than 0.04 mm, the shape of the fin becomes a sharp wedge-shaped, blank tube tends to break as a starting point the top of the fin. On the other hand, the radius of curvature r ₂ exceeds 0.06 mm, too thick the shape of the fins, the metal flow of the material forming the blank tube is deteriorated, the moldability of the fins is deteriorated. Thus, the radius of curvature _{r 2} of the top of the fin between the grooves of the grooved plug is 0.04 to 0.06 mm.

Top angle α of grooved plug fin: 60 to 120 °
When the peak angle α of the fin is less than 60 °, a fin having a height, that is, a groove depth of 0.05 mm or more cannot be formed. On the other hand, when the crest angle α of the fin exceeds 120 °, the width of the groove formed on the inner surface of the raw tube becomes wide, and the heat transfer performance of the inner grooved tube decreases. Therefore, the peak angle α of the fin of the grooved plug is preferably 60 to 120 °.

Angle φ ₁ formed between the side edge of the cylindrical portion and the side edge of the first taper portion : 120 to 150 °
The first taper portion is provided in order to prevent a stress concentration portion from being generated in the raw tube at the contact portion between the end portion of the grooved plug on the upstream side in the tube pulling direction and the raw tube, thereby breaking the raw tube. . In the cross section including the central axis of the cylindrical portion, if the angle φ ₁ formed between the side edge of the cylindrical portion and the side edge of the tapered portion exceeds 150 °, the tapered portion needs to be lengthened in order to obtain the effect of the tapered portion described above. Occurs. As a result, since the contact length between the taper portion and the raw pipe is increased, the frictional force generated between the grooved plug and the raw pipe is increased, the pulling force is increased, and the raw pipe is easily broken. On the other hand, in the angle phi ₁ is less than 120 °, becomes sharp shape of the upstream end of the grooved plug, reduces the effect due to the provision of the tapered portion, mother pipe is easily broken. Further, the inner surface of the raw tube is cut by the grooved plug, and powder is generated on the inner surface of the raw tube. Therefore, the angle phi ₁ the side edges of the side edge and the tapered portion of the cylindrical portion is preferably set to 120 to 150 °.

Angle phi ₂ formed by the side edges of the side edge and the second tapered portion of the cylindrical _portion: side edge of 180 ° less than the cylindrical portion larger than 150 ° and the angle phi ₂ is 150 formed between the side edge of the second tapered portion If it is less than 0 °, it is difficult to adjust the contact position between the roll and the grooved plug. The contact surface of the grooved plug is adjusted by changing the distance between the holding plug and the grooved plug. That is, the washer before and after the grooved plug is inserted and removed. As described above, the contact position between the roll and the grooved plug is adjusted by a 1 mm washer. Therefore, if the inclination angle is small, the contact surface of the grooved plug changes greatly, making adjustment difficult. On the other hand, when the angle phi ₂ is 180 °, i.e., when the second tapered portion is not formed, since the inner surface groove formed in the base pipe is in contact with the grooved plug, is broken to increase the drawing force It tends to occur. Therefore, the angle phi ₂ is greater than 0.99 °, and is less than 180 °. Thereby, position adjustment with a roll and a grooved plug becomes easy, and groove formability becomes favorable.

Length x in the axial direction of the cylindrical portion : 3 mm or less If the length x of the cylindrical portion exceeds 3 mm, it becomes longer than the length required for groove formation, so the frictional force between the blank tube and the grooved plug increases. As a result, the pulling force is increased and the base tube is easily broken. In addition, even if the length x of the cylindrical portion is 0 mm, that is, the cylindrical portion is not provided, groove processing is possible.

Length L of the second taper portion in which the groove in the cross section including the central axis of the grooved plug is formed: 2 to 5 mm
In the second taper portion, the length L of the portion where the groove is formed in the cross section including the central axis of the grooved plug, that is, the downstream end portion and the boundary surface of the portion where the groove is formed in the tube drawing direction If the distance is less than 2 mm, effective groove formation cannot be performed. On the other hand, when the length L of the portion where the groove is formed exceeds 5 mm, the contact area between the inner surface of the raw tube and the grooved plug increases, and the raw tube is easily broken.

Position a of the rotation axis of the work roll pair: The rotation axis of the work roll pair is between the 3 mm upstream side and the 2 mm downstream side with respect to the tube drawing direction from the boundary surface between the cylindrical portion and the second taper portion. When the distance between the plane 25 including the rotation axis of the work roll pair and the boundary surface exceeds 3 mm when located on the upstream side in the tube drawing direction, fins and grooved plugs formed on the inner surface of the raw tube Since the contact area with the groove increases and the frictional force between the pipe and the grooved plug increases, the pipe tends to break. On the other hand, when the rotation axis of the rolling roll pair is located downstream of the boundary surface in the tube drawing direction, if the distance between the plane including the rotation axis of the rolling roll pair and the boundary surface exceeds 2 mm, the grooved Since the material of the raw tube does not enter the depth of the groove formed in the plug, the groove depth h becomes shallow and a predetermined groove cannot be formed. Therefore, the position of the rotation axis of the rolling roll is between the 3 mm upstream side and the 2 mm downstream side with respect to the tube drawing direction from the boundary surface between the cylindrical portion and the tapered portion.

  Next, the operation of the inner grooved pipe manufacturing apparatus configured as described above, that is, the inner grooved pipe manufacturing method according to the present embodiment will be described. In the method for manufacturing an internally grooved tube of the present embodiment, as shown in FIG. 1, first, the raw tube 1 is installed at a predetermined position of the manufacturing apparatus configured as described above. Any material can be used for forming the raw tube 1 as long as it can be rolled. For example, copper such as C1101, C1201, and C1220 defined by JIS H 3300, Cu—Zn alloy, Cu—Fe—P, and the like. It can be applied to a system alloy or an aluminum alloy. For example, the outer diameter is 6 to 12 mm and the wall thickness is 0.25 to 0.40 mm. In addition, when forming the groove on the inner surface of the raw tube by pressing the inner surface of the raw tube against the grooved plug by rolling, the linear portion of the cross section of the raw tube is simultaneously grooved at the portion that contacts the rolling roll. The stress applied to the pipe during processing is larger than that in the case of ball rolling. Furthermore, when using the manufacturing apparatus for inner surface grooved pipes of the present embodiment, the processed part has a smaller spring back than the conventional manufacturing apparatus, so that while the pipe is pulled out, Since it is pulled out in a contact state, the frictional force increases and the pulling force increases. For this reason, when an annealed soft base tube is used, the tube is likely to break due to stress or drawing force during processing. Therefore, in the manufacturing method of the internally grooved tube of the present embodiment, a material harder than (1/2) H is used for the raw tube 1.

  Next, the drawing oil 10 is filled on the upstream side of the holding plug 2 inside the base tube 1. Then, a pulling force toward the central direction is applied to the raw tube 1 to pull out the raw tube 1. Thereby, after the diameter of the base tube 1 is reduced by the holding plug 2 and the holding die 3, a groove is formed on the inner surface by the grooved plug 5a and the work roll 16a in the first-stage rolled portion 17a. At this time, the rotation axis of the work roll pair 16a is positioned between 3 mm upstream and 2 mm downstream from the boundary surface 24b between the cylindrical portion 21 and the second taper portion 23 with respect to the tube drawing direction. The machining is performed while adjusting the position of the work roll pair 16a. Thereby, the fracture | rupture of a pipe | tube is suppressed and the internally grooved pipe | tube excellent in groove formability can be manufactured.

  In addition, the raw tube 1 grooved by the rolled portion 7a is twisted somewhat by the rotation of the fluted plug 5a provided in the rolled portion 7a. Generally, the second-stage rolled portion 7b is installed to form a groove in a region where the groove is not formed in the rolled portion 7a. For example, when groove processing is performed on the upper and lower halves of the raw tube 1 at the rolling portion 7a, if the raw tube 1 is not twisted, the rotation axis of the work roll 16a and the rotation axis of the work roll 16b May have an angle of 90 ° in the cross section perpendicular to the tube drawing direction. However, in actuality, as described above, when the raw tube 1 that has been grooved by the rolled portion 7a reaches the position of the rolled portion 7b, the region in which no groove is formed is displaced due to twisting. . Therefore, in the manufacturing apparatus used in the manufacturing method of the inner surface grooved tube of the present embodiment, the work roll is formed so that the groove is formed in a region where the groove is not formed in the rolled portion 7a in the rolled portion 7b. The facing direction of at least one of the pair of work rolls 16a and 16b is changed by the angle θ from the basic position described above. This angle θ can be appropriately set within the range of 0 to 90 ° in consideration of the shape of the groove to be formed, processing conditions, and the like.

  Thereafter, the raw tube 1 is formed by a sizing die 8a so that the cross section perpendicular to the tube axis becomes a true circle. Next, in the rolled portion 7b, the raw tube 1 is reduced in diameter by a grooved plug 5b and a pair of work rolls 16b and a groove is formed on the inner surface, and further reduced in diameter by a sizing die 8b and molded. The inner grooved tube 19 is obtained. At this time, the grooved plugs 5 a and 5 b are connected to the holding plug 2 via the plug shaft 4, and the holding plug 2 is caused by the frictional force caused by pulling out the raw tube 1 and the drag from the holding die 3. Therefore, the grooved plugs 5a and 5b are also stopped at a position aligned with the work rolls 16a and 16b.

  In the manufacturing method of an internally grooved tube of the present embodiment, a cylindrical portion 21 in which a groove is formed, and a first taper portion that is formed at the upstream end of the cylindrical portion 21 in the tube drawing direction to prevent the tube from being broken. 22 and a grooved plug 5a formed by a second taper portion 23 formed at an end portion of the cylindrical portion 21 on the downstream side in the tube drawing direction, and a groove is formed in a part of the cylindrical portion 21 continuously from the cylindrical portion 21; Since 5b is used, the contact area between the inner surface of the raw tube 1 and the grooved plugs 5a and 5b is smaller than in the conventional manufacturing method shown in FIG. As a result, the frictional force between the inner surface of the raw tube 1 and the grooved plugs 5a and 5b can be reduced, and the raw tube 1 can be prevented from breaking. Furthermore, since the pulling force is reduced, it is possible to reduce the peak angle α of the groove formed on the inner surface of the raw tube 1 or increase the lead angle β.

  Next, a modification of this embodiment will be described. FIG. 5 is a cross-sectional view showing the grooved plug in the present modification. In the manufacturing apparatus for an internally grooved tube according to this modification, grooved plugs 5c and 5d having the shape shown in FIG. 5 are provided instead of the grooved plugs 5a and 5b. The configuration other than the above in the present modification is the same as that of the above-described embodiment.

  As shown in FIG. 5, the grooved plugs 5c and 5d are coupled to the upstream end surface of the first cylindrical portion 21 in the tube pulling direction to form a first tapered portion 22, and this first tapered portion. A second cylindrical portion 30 having a diameter equal to the diameter of the end surface is formed by being coupled to the upstream end surface of the tube 22 in the tube drawing direction. In addition, a second taper portion 23 is formed by being coupled to the downstream end surface of the first cylindrical portion 21 in the tube extraction direction, and is coupled to the downstream end surface of the second taper portion 23 in the tube extraction direction. A third cylindrical portion 31 having the same diameter as that of the end face is formed. By providing the second cylindrical portion 30 and the third cylindrical portion 31, vibration during processing can be suppressed. In the present modification, if at least one of the second cylindrical portion 30 and the third cylindrical portion 31 is provided, a vibration suppressing effect can be obtained. Other effects and operations in this modification are the same as those in the above-described embodiment. Hereinafter, the reason for limiting the numerical values will be described.

Hereinafter, the effect of the Example of this invention is demonstrated compared with the comparative example which remove | deviates from the scope of the present invention. First, the length x of the cylindrical portion in the grooved plug having the shape shown in FIG. 3, the length L of the groove forming portion in the second taper portion, the angle φ ₁ of the first taper portion, and the angle φ ₂ of the second taper portion. In addition, the inner grooved pipes of Examples 1 to 9 and Comparative Examples 1 to 7 were manufactured by a single rolling type manufacturing apparatus having one rolling section and changing the position a of the rotation axis of the work roll pair. Next, the length x of the cylindrical portion in the grooved plug having the shape shown in FIG. 3, the length L of the groove forming portion in the second taper portion, the angle φ ₁ of the _first taper portion, the angle φ of the second taper portion ₂ and the position a of the rotation axis of the work roll pair were changed, and the internally grooved pipes of Examples 10 and 11 were manufactured by the manufacturing apparatus of the tandem rolling method shown in FIG. Moreover, the internal grooved pipe of Comparative Examples 8 and 9 was manufactured by the apparatus of the single rolling system and the tandem rolling system using the conventional grooved plug shown in FIG. The processing conditions at that time are shown in Table 1 below, and the grooved plug shapes are shown in Tables 2 and 3 below. In addition, the work roll rotating shaft position a shown in the following Table 2 shows 0 as the boundary surface between the tapered portion and the cylindrical portion, and + as the upstream side in the tube drawing direction from the boundary surface and − as the downstream side.

  Next, the groove shapes of the internally grooved tubes manufactured under the conditions of Examples 1 to 11 and Comparative Examples 1 to 11 shown in Tables 1 to 3 were examined. The results are shown in Table 4.

As shown in Table 4 above, the shape of the groove formed on the inner surface of the internally grooved tube of Comparative Example 1, Comparative Examples 3 to 6, Comparative Example 8 and Comparative Example 10 is the groove formed on the grooved plug. It was equivalent. However, Comparative Example 1 in which the length x of the cylindrical portion is longer than the range of the present invention and Comparative Example 3 in which the grooved portion length L is longer than the range of the present invention and Comparative Example 3 are used. angle phi ₂ is 180 ° in Comparative example angle phi ₁ of the tapered portion is use a small grooved plug from the scope of the present invention 4 and a second tapered portion, i.e., grooved second tapered portion is not formed In Comparative Example 6 using a plug, since the contact area between the raw tube and the grooved plug was large, the coefficient of friction acting between them was high, and the tube broke during processing. Moreover, the range is greater than Comparative Example 5 of the aforementioned angle phi ₁ is the present invention is a tube in the boundary portion between the first tapered portion and the cylindrical portion of the grooved plug (edge portion) is broken. Further, in Comparative Examples 8 and 9 using the conventional grooved plug, the tube broke during processing in both the single method and the tandem method. Furthermore, in Comparative Example 2 using the grooved plug whose groove forming portion length L is shorter than the range of the present invention, the groove depth becomes shallow, and the predetermined groove was not formed. Further, in the inner grooved tube of Comparative Example 7 in which the angle φ2 of the _second taper portion is smaller than the range of the present invention, the predetermined groove was not formed due to poor adjustment of the contact position between the grooved plug and the roll. . On the other hand, in Examples 1 to 13, which are within the scope of the present invention, the pipe has no target breakage and has a length of 2000 m with a desired groove shape, regardless of whether a single type or a tandem type manufacturing apparatus is used. An internally grooved tube could be manufactured. However, the inner surface grooved tube of Example 10 in which the rotation axis of the work roll pair is arranged 4.0 mm upstream from the boundary surface between the taper portion and the cylindrical portion in the pipe drawing direction is the rotation axis of the work roll pair as the taper portion. The pulling load increased by about 5 to 10% compared to the inner grooved tube of Example 6 manufactured under the same conditions except that the tube was arranged 2.5 mm upstream from the boundary surface with the cylindrical portion.

It is sectional drawing which shows the manufacturing apparatus and manufacturing method of an internal grooved pipe of embodiment of this invention. It is sectional drawing which shows the rolling part of the manufacturing apparatus of this embodiment. It is a fragmentary sectional view showing the slotted plug in this embodiment. It is sectional drawing which shows the case where the length x in the axial direction of a cylindrical part is 0 mm in the grooved plug used with the manufacturing apparatus of this embodiment. It is sectional drawing which shows the grooved plug in the modification of this embodiment. It is sectional drawing which shows the manufacturing apparatus and manufacturing method of a seamless inner surface grooved pipe by the conventional roll rolling method. It is an expanded sectional view which shows the rolling part of the manufacturing apparatus shown in FIG. It is sectional drawing by the AA line shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Element pipe 2; Holding plug 3; Holding die 4; Plug shaft 5a, 5b, 5c, 5d, 15; Slotted plug 6; Rolling roll 7a, 7b, 17; Rolling part 8, 8a, 8b; 9, 19; Internal grooved tube 10; Drawing oil 11, 21, 30, 31; Cylindrical part 12; Tapered part 13; Groove 14; Fins 16, 16a, 16b; Work rolls 18a, 18b; Backup roll 22; Taper portion 23; second taper portion 24; boundary surface 25; plane including rotation axis of work roll pair a; position of rotation axis of work roll pair h; groove depth r ₁ ; radius of curvature r ₂ of groove bottom portion ; Curvature radius of fin top part x; length of cylindrical part L; groove forming part length α; peak angle of fin β; groove lead angle θ; tilt angle of rotation axis of work roll pair φ ₁ , φ ₂ ; Edge and side edge of taper Nasu angle

Claims (14)

A holding die that contacts the outer surface of the metal tube, a holding plug that is disposed inside the metal tube and engages with the holding die and reduces the diameter of the metal tube together with the holding die, and a plug shaft of the holding plug A grooved plug that is rotatably supported and has grooves formed on the outer surface thereof, and an outer surface of the metal tube that is disposed on the outer surface of the metal tube so that the rotation axes are parallel to each other and perpendicular to the tube axis direction of the metal tube. And a pair of rolling rolls that press the metal tube toward the grooved plug to form grooves on the inner surface of the metal tube, and are arranged downstream of the rolling roll pair in the drawing direction of the metal tube. And a sizing die for reducing the diameter of the metal tube in contact with the outer surface of the metal tube, and the grooved plug includes a first taper portion, a cylindrical portion, and a cylindrical portion along the drawing direction of the metal tube. A second taper is provided The first tapered portion has a truncated cone shape whose diameter increases toward the cylindrical portion, and the second tapered portion has a truncated cone shape whose diameter decreases as the distance from the cylindrical portion increases, The groove is formed continuously with the cylindrical portion and the second tapered portion, and in a cross section including a central axis of the grooved plug, a length in the axial direction of the cylindrical portion is 3 mm or less, and the first The distance between the downstream end of the metal tube pull-out direction of the portion where the groove of the taper portion of 2 is formed and the downstream end surface of the cylindrical portion in the metal tube pull-out direction is 2 to 5 mm, The angle formed by the edge and the side edge of the first tapered portion is 120 to 150 °, and the angle formed by the side edge of the cylindrical portion and the side edge of the second tapered portion is greater than 150 °, and 180 Inner surface characterized by less than ° Apparatus for manufacturing with tube. On the outer peripheral surface of the grooved plug, an angle formed by a straight line parallel to the axial direction of the grooved plug and the direction in which the groove extends is 0 to 20 °, and the depth of the groove is 0.05 to 0. 0. The angle formed by the inclined surface of the groove is 60 to 120 °, and the radius of curvature of the bottom of the groove and the top of the fin is 0.04 to 0.06 mm. The apparatus for producing an internally grooved tube according to claim 1, wherein: The rotation axis of the pair of rolling rolls is 3 mm upstream and 2 mm downstream from the boundary surface between the cylindrical portion of the grooved plug and the second tapered portion. The apparatus for manufacturing an internally grooved tube according to claim 1 or 2, wherein 4. The rolling part comprising the grooved plug and the rolling roll pair and the sizing die are arranged in a plurality of stages along the drawing direction of the metal tube. 5. An apparatus for producing an internally grooved tube according to claim 1. The rolling part comprising the grooved plug and the rolling roll pair is arranged in two stages in the drawing direction of the metal tube, and the opposing directions of the rolling roll pair in each rolling part are orthogonal to each other, and at least one of the rolling roll pairs The apparatus for manufacturing an internally grooved tube according to claim 4, wherein the opposing direction can be changed by an angle θ from the orthogonal basic position. 6. The inner grooved tube manufacturing apparatus according to claim 5, wherein the angle [theta] is in the range of 0 to 90 [deg.]. The pair of backup rolls having a larger diameter than the rolling roll and a pair of backup rolls that press the rolling roll in the direction of the metal tube are in rolling contact with the rolling roll pair. An apparatus for producing an internally grooved tube according to Item. A process of reducing the diameter of the metal tube by a holding die arranged outside the tube of the metal tube drawn in the axial direction and a holding plug arranged inside the tube and engaging with the holding die, and rotating to the plug shaft of the holding plug A grooved plug that is pivotally supported and has grooves formed on the outer surface, and a pair of rolling rolls that are arranged on the outer surface of the metal tube so that the rotation axes are parallel to each other and perpendicular to the tube axis direction of the metal tube. The grooved plug includes a step of pressing the metal tube against the grooved plug to form a groove on the inner surface of the metal tube, and a step of reducing the diameter of the metal tube with a sizing die. The first tapered portion, the cylindrical portion and the second tapered portion are provided along the drawing direction of the metal tube, and the first tapered portion has a truncated cone shape whose diameter increases toward the cylindrical portion, Whether the second taper part is the cylindrical part In the cross section including the central axis of the grooved plug, the groove is formed in a truncated cone shape whose diameter decreases as the distance increases, and the groove is formed in the axial direction of the cylinder portion. The length is 3 mm or less, and the distance between the downstream end portion in the metal tube extraction direction of the portion where the groove of the second taper portion is formed and the downstream end surface in the metal tube extraction direction of the cylindrical portion is 2 to 2 5 mm, the angle formed between the side edge of the cylindrical portion and the side edge of the first tapered portion is 120 to 150 °, and the angle formed between the side edge of the cylindrical portion and the side edge of the second tapered portion Is greater than 150 ° and less than 180 °. On the outer peripheral surface of the grooved plug, an angle formed by a straight line parallel to the axial direction of the grooved plug and a direction in which the groove extends is 0 to 20 °, and the depth of the groove is 0.05 to 0.15 mm. The angle formed by the inclined surface of the groove in the cross-axis orthogonal section of the grooved plug is 60 to 120 °, and the curvature radius of the bottom of the groove and the top of the fin is 0.04 to 0.06 mm. A method for producing an internally grooved tube according to claim 8. The rotation axis of the pair of rolling rolls is positioned 3 mm upstream and 2 mm downstream of the metal tube with respect to the drawing direction of the metal tube with respect to the boundary surface between the cylindrical portion and the second tapered portion of the grooved plug. The method for producing an internally grooved tube according to claim 9, wherein: The sizing die and the rolled part composed of the grooved plug and the rolling roll pair are arranged in a plurality of stages along the drawing direction of the metal tube, and the diameter is reduced by the step of forming the groove and the sizing die. The method for producing an internally grooved tube according to any one of claims 8 to 10, wherein the step is performed a plurality of times. The rolling part comprising the grooved plug and the rolling roll pair is arranged in two stages in the drawing direction of the metal tube, and the opposing directions of the rolling roll pair in each rolling part are orthogonal to each other, and at least one of the rolling roll pairs 12. The method for manufacturing an internally grooved tube according to claim 11, wherein the opposing direction can be changed by an angle θ from the orthogonal basic position. 13. The method for manufacturing an internally grooved tube according to claim 12, wherein the angle [theta] is in the range of 0 to 90 [deg.]. The pair of rolling rolls is in contact with a pair of backup rolls having a diameter larger than that of the rolling rolls, and the rolling rolls are pressed in the direction of the metal tube by the backup rolls. 14. A method for manufacturing an internally grooved tube according to any one of items 1 to 13.

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