JP2011224613A - Tube with inner surface groove, and method and device for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tube with an inner surface groove capable of stabilizing an orthogonal cross section to the axial direction of the tube in the tube axis direction, and a method and device for manufacturing the same.SOLUTION: In this method of manufacturing this tube with an inner surface groove, a connection rod 34 for connecting a floating plug 23 used in a diameter-reducing process to a grooved plug 32 used in a grooving work process is formed with a rigid body formed of a single constituent material continuing along a tube axis direction; the connection rod 34 is formed with a floating plug mounting part 34f allowing the floating plug 23 to be mounted thereto and formed with the grooved plug mounting part allowing the grooved plug to be mounted thereto; the diameter-reducing process is performed using the floating plug 23 directly mounted to the floating plug mounting part 34f; and the grooving work process is performed using the grooved plug 32 directly mounted to the grooved plug mounting part 34g.

Description

  The present invention relates to an internally grooved tube used as a heat transfer tube for a heat exchanger provided in an air conditioner such as a refrigeration device, a domestic air conditioner (air conditioner), a commercial air conditioner (package air conditioner), and a manufacturing method and a manufacturing apparatus thereof. About.

  A manufacturing apparatus and a manufacturing method of an internally grooved tube for manufacturing an internally grooved tube used as a heat transfer tube for a heat exchanger is disclosed in Patent Document 1.

  More specifically, in Patent Document 1, a diameter-reducing portion that pulls out a pipe between a die and a floating plug to reduce the diameter, and a rolling element that rolls along the pipe circumferential direction on the outer surface of the raw pipe (four balls). A manufacturing apparatus having a configuration including a groove processing portion that presses the inner surface of the raw tube against a grooved plug provided inside the tube while forming a plurality of grooves on the inner surface of the raw tube is disclosed. .

  Further, Patent Document 1 discloses a method of manufacturing an internally grooved tube in which the inner tube is grooved by a rolling element and a grooved plug after the raw tube is reduced in diameter by a die and a floating plug.

  In the manufacturing apparatus, a grooved plug and a floating plug are rotatably connected by a plug rod, and the grooved plug, the floating plug, and the plug rod are integrally formed as a cored bar and disposed inside the pipe. It is a configuration.

  However, when the cored bar is assembled, for example, if there is a mounting error of the plug rod or grooved plug with respect to the floating plug, an axial misalignment occurs between the plug rod and the grooved plug, and the cored bar is moved inside the pipe. There is a difficulty in that shaft runout occurs when rotated.

  When such a metal core having a large amount of shaft misalignment is used, the shaft runout is increased in the groove processing portion, so that the pressing force of the rolling elements is not stable, and the undulation of the outer surface of the tube tends to increase.

  Further, when such a metal core having a large amount of axial deviation is used, the groove processing on the inner surface of the tube by the grooved plug is not stable, and the groove shape such as the groove depth varies in the tube axis direction.

  Furthermore, when grooving is performed in a state where the shaft runout is large, the number of rotations of the rolling elements is increased, and the tube is twisted. To avoid this, it is necessary to reduce the number of rotations. It was necessary to reduce the processing speed, and there was a problem that the production efficiency was reduced.

  Also, if the tube cross-section is not stable in the tube axis direction due to large undulations on the tube outer surface, noise will increase and scratches (defects) will occur when performing a nondestructive flaw detection test at the time of shipment as an internally grooved tube. The detection accuracy is adversely affected and the product yield is low.

  Also, when a heat exchanger is manufactured using an internally grooved tube with a large undulation on the tube outer surface as a heat transfer tube, holes formed in advance in a plurality of heat dissipating fins arranged with a predetermined pitch are arranged. When the tube is inserted and expanded, there is also a difficulty that desired performance cannot be obtained due to variations in the close contact state with the radiating fins.

  Furthermore, if the groove depth on the inner surface of the tube is not stable in the tube axis direction, there arises a difficulty that desired excellent heat transfer performance cannot be obtained.

JP-A-5-50136

  An object of the present invention is to provide an internally grooved tube capable of stabilizing the cross section perpendicular to the axial direction of the tube in the axial direction of the tube, a manufacturing method thereof, and a manufacturing apparatus.

  The present invention relates to a diameter reduction step of drawing a base tube between a diameter reducing die and a floating plug to reduce the diameter, and an inner surface of the base tube while pressing the outer surface of the base tube with a rolling element that rolls around the tube axis. A grooved plug that is pressed against a grooved plug provided inside the tube to form a plurality of grooves on the inner surface of the raw tube, and a method of manufacturing an internally grooved tube, the floating plug and the grooved plug And a floating plug attachment portion that allows the floating plug to be directly attached to the connecting rod on the side of the reduced diameter die in the axial direction of the connecting rod. In addition, a grooved plug attaching portion that allows the grooved plug to be directly attached to the connecting rod is formed on the side of the rolling element in the axial direction of the connecting rod, and the floating plug is formed. It performs the reduced diameter step using the floating plug attached to the grayed mounting portion, and performing the grooving process using the grooved plug attached to the plug mounting portion with grooves.

  As an aspect of the present invention, in the manufacturing method, the connecting rod may be formed using a rigid body made of one constituent material from the floating plug mounting portion to the grooved plug mounting portion.

  As an aspect of the present invention, in the manufacturing method, the floating plug mounting portion includes a floating plug insertion allowing portion that allows the floating plug to be inserted, and the floating plug is slidable in the tube axis direction to the floating plug. A floating plug insertion portion to be inserted into the floating plug insertion allowance portion is configured, and the grooved plug mounting portion is configured with a grooved plug insertion allowance portion that allows insertion of the grooved plug, The grooved plug is configured to have a grooved plug insertion portion that is slidably inserted in the grooved plug insertion allowable portion so as to be slidable in the tube axis direction, and the floating rod and the grooved plug in the connecting rod An interval regulating tube that is inserted in the tube axis direction and regulates the floating plug and the grooved plug at a predetermined interval in the tube axis direction. It can be performed using one of the configuration including.

  Moreover, as an aspect of the present invention, the manufacturing method includes a reduced diameter portion configured by the reduced diameter die and the floating plug, a grooved processed portion configured by the rolling element and the grooved plug, and An intermediate drawing machine that draws the raw pipe between the pipe axis directions, and the raw pipe reduced in the diameter reducing step by the intermediate drawing machine while performing the diameter reducing step and the grooving step. An intermediate drawing process of drawing can be performed.

  Further, the present invention is an internal grooved tube manufactured by the above-described internal grooved tube manufacturing method, wherein the tube weight is measured every 10 mm in a predetermined section having a tube length of 1 m in the tube axis direction. The variation of the tube weight converted per 1 m is ± 1% or less.

  The present invention also provides a reduced diameter portion for reducing the diameter of the pipe by pulling the raw pipe between the reduced diameter die and the floating plug, and a rolling element that rolls the outer surface of the raw pipe along the circumferential direction of the pipe. An inner surface grooved pipe manufacturing apparatus comprising a groove processing portion that forms a plurality of grooves by pressing on a grooved plug provided inside the tube on the inner surface of the element pipe, wherein the reduced diameter portion and the groove A connecting rod arranged between the processing portion and connecting the floating plug and the grooved plug is provided inside the tube, and the floating plug is connected to the reduced diameter portion in the axial direction of the connecting rod. A floating plug attachment portion that allows attachment directly to the rod is formed, and the grooved plug is attached directly to the connection rod on the groove processing portion side in the axial direction of the connection rod. Slotted plastic that allows Characterized in that the formation of the mounting portion.

  Here, attaching the floating plug directly to the connecting rod or attaching the grooved plug directly to the connecting rod means that the floating plug or the grooved plug is connected to the connecting rod. It is the concept which attaches without interposing another member between.

  However, as long as the grooved plug does not swing as the connecting rod rotates about the axis during processing, for example, lubrication is performed between the floating plug and the connecting rod or between the grooved plug and the connecting rod. The interposition of oil or the like is included in the concept of attaching the floating plug directly to the connecting rod or attaching the grooved plug directly to the connecting rod.

  The above-mentioned rigid body made of one constituent material is, for example, a rigid body continuously formed with the same constituent member over the entire length in the tube axis direction, such as a single pin, and a midway portion in the tube axis direction is formed by a screw or the like. A member that does not have a discontinuous portion in the middle portion in the tube axis direction by being connected is included.

  The floating plug insertion allowing portion is formed in a concave shape or a convex shape, and the floating plug insertion portion is formed in a convex shape or a concave shape so as to be insertable into the floating plug insertion allowing portion. Can do.

  Similarly, the grooved plug insertion allowing portion is formed in a concave shape or a convex shape, and the grooved plug insertion allowing portion is convex so as to be insertable into the grooved plug insertion allowing portion, or , Can be formed in a concave shape.

  The element tube is not particularly limited as long as it is a metal having excellent thermal conductivity, such as copper, copper alloy, aluminum, or aluminum alloy.

  The rolling element is not limited to a rolled ball, for example, and can be configured by using a roller, and a combination of a rolled ball and a roller.

  According to the present invention, it is possible to provide an internally grooved tube capable of stabilizing the cross section orthogonal to the axial direction of the tube in the axial direction of the tube, a manufacturing method thereof, and a manufacturing apparatus thereof.

  With such an internally grooved tube, it is possible to improve the product yield by improving the reliability of the scratch detection accuracy at the time of shipment as a product, to stabilize the heat transfer performance, and to Sufficient adhesion can be obtained.

Sectional drawing which shows the manufacturing apparatus of the inner surface grooved pipe | tube of 1st Embodiment. The side view of the metal core with which the manufacturing apparatus of the inner surface grooved pipe of 1st Embodiment was equipped. AA line sectional view in FIG. The structure explanatory view which decomposed | disassembled the core metal with which the manufacturing apparatus of the inner surface grooved pipe of 1st Embodiment was decomposed | disassembled, and showed it with a partial cross section. Sectional drawing which shows the manufacturing apparatus of the inner surface grooved pipe of 2nd Embodiment. Explanatory drawing which shows a mode that the experiment 1 is performed. Explanatory drawing explaining the processing pitch of a rolling ball. Explanatory drawing for demonstrating the method to confirm the dispersion | variation in single unit change rate. The graph which shows the dispersion | variation in the single weight in the pipe-axis direction of the test tube processed using the metal core of the example of this invention. The graph which shows the dispersion | variation in the single weight change rate in the pipe-axis direction of the test tube processed using the metal core of the example of this invention. Sectional drawing which shows a part of orthogonal cross section with respect to a pipe-axis direction. The graph which shows the dispersion | variation in the cross-sectional shape in the pipe-axis direction of the test tube processed using the metal core of the example of this invention. The graph which shows the eddy current test result in the test tube processed using the metal core of the example of the present invention. The photograph which shows the external appearance of the internally grooved pipe processed using the cored bar of the example of the present invention. The graph which shows the eddy current test result in the internal grooved pipe processed using the core metal of the example of the present invention. The side view of the metal core with which the manufacturing apparatus of the conventional internal grooved pipe was equipped. AA sectional view taken on the line in FIG. The structure explanatory drawing which decomposed | disassembled the core metal with which the manufacturing apparatus of the conventional internal grooved pipe was shown, and showed it with a partial cross section. The graph which shows the single weight dispersion | variation in the pipe-axis direction of the test tube processed using the conventional metal core. The graph which shows the dispersion | variation in the single weight change rate in the pipe-axis direction of the test tube processed using the conventional metal core. The graph which shows the dispersion | variation in the cross-sectional shape in the pipe-axis direction of the test tube processed using the conventional metal core. The graph which shows the eddy current test result in the test tube processed using the conventional metal core. A photograph showing an internally grooved tube processed using a conventional cored bar. The graph which shows the eddy current test result in the internally grooved tube processed using the conventional metal core.

An embodiment of the present invention will be described below with reference to the drawings.
(First embodiment)
The inner surface grooved pipe manufacturing apparatus 10 of the first embodiment is configured as shown in FIG.
In addition, FIG. 1 is sectional drawing which shows a part of manufacturing apparatus 10 of the inner surface grooved pipe | tube in this embodiment.

  The said manufacturing apparatus 10 is the structure provided with the diameter reducing part 21, the groove process part 31, and the shaping die 15 which were arrange | positioned in order along the downstream from the upstream of the drawing direction X, and the raw pipe 1a is continuously processed by these structures. Thus, the inner grooved tube 1e is manufactured.

  The diameter-reducing portion 21 includes a cylindrical diameter-reducing die 22 for reducing the diameter of the passing raw pipe 1a, and the inner pipe 1a so that the inner periphery of the elemental tube 1a narrowed by the diameter-reducing die 22 is pressed. It is comprised with the floating plug 23 inserted in the inside.

  The diameter-reducing die 22 has a die hole 22a having an upstream portion opened. The die hole 22a opens in a truncated cone shape so as to have a large diameter toward the upstream side.

  Furthermore, the floating plug 23 has a frustoconical outer peripheral surface having a small diameter toward the downstream side at the downstream side portion in the drawing direction X.

  Thereby, the diameter reducing die 22 and the floating plug 23 are engaged with each other so as to sandwich the element tube 1a therebetween.

  The groove processing section 31 includes a grooved plug 32 having a plurality of spiral grooves 32 a formed on the outer periphery and a plurality of rolling balls 33.

  The grooved plug 32 is inserted into the raw tube 1 b and is connected to the floating plug 23 via a connecting rod 34 so as to be relatively rotatable. The plurality of rolling balls 33 roll while rotating and revolving around an axis, and in the tube circumferential direction so as to press the tube 1b toward the grooved plug 32 side on the tube outer side of the tube 1b. It is arranged at equal intervals.

  The shaping die 15 performs a process of smoothly shaping, for example, distortion of the pipe surface caused by the pressing of the rolling ball 33 in the grooved portion 31 when the inner grooved tube 1d passes through.

In addition, a single metal core 60 is disposed along the tube axis direction inside the raw tube 1b between the reduced diameter portion 21 and the groove processing portion 31.
The tube axis direction indicates a direction that coincides with the drawing direction X in FIG.

  The core metal 60 includes the grooved plug 32, the floating plug 23, and the connecting rod 34 as a part of its constituent parts.

The configuration of the metal core 60 will be described with reference to FIGS. 2, 3, and 4.
2 is a side view of the metal core 60 of the first embodiment, FIG. 3 is a cross-sectional view taken along the line AA in FIG. 2, and FIG. 4 is an exploded cross-section of the metal core 60 disassembled for each part. FIG.

  The metal core 60 includes a gap regulating pipe 61, a clasp 62, and a spacer 63 in addition to the grooved plug 32, the floating plug 23, and the connecting rod 34.

  The grooved plug 32 is formed of a cylindrical member, and has a grooved plug insertion through hole 32H penetrating along the central axis so as to allow insertion of the connecting rod 34 (see FIG. 4).

  The floating plug 23 is formed with a floating plug insertion through hole 23H penetrating along the central axis so as to allow insertion of the connecting rod 34 (see FIG. 4).

  The connecting rod 34 is formed in the shape of an elongated round bar having a length corresponding to that between the reduced diameter portion 21 and the groove processing portion 31, and the grooved plug insertion through hole 32H and the floating plug insertion through hole 23H. It is formed with an outer diameter that allows insertion into.

  Further, the connecting rod 34 is a pin formed of a single rigid body made of a steel material without having a joint portion over the entire length in the tube axis direction. A hook-shaped head portion 34a is formed on one end side (right side in FIG. 4) of the connecting rod 34 in the length direction, and a screw portion 34b is formed on the other end portion (left side in FIG. 4) in the length direction. It is composed of a bolt-shaped pin formed.

  Furthermore, the connecting rod 34 forms the outer peripheral surface between the head portion 34a and the screw portion 34b as a smooth smooth outer peripheral surface 34A. The end of the smooth outer peripheral surface 34A on the head 34a side is set to a grooved plug insertion portion 34g for inserting the grooved plug 32, and the screw portion 34b side portion of the smooth outer peripheral surface 34A is set to the floating plug 23. Is set to the floating plug insertion portion 34f to which is inserted.

  The interval regulating pipe 61 has a length corresponding to that between the reduced diameter portion 21 and the groove processing portion 31, and is formed with an insertion through hole 61H penetrating along the central axis so as to allow the insertion of the connecting rod 34. This is a circular tubular member (see FIG. 4).

  The clasp 62 is a cylindrical member that has an insertion hole 62H that allows insertion of the connecting rod 34 and that is closed at one end, and has a female member that can be screwed onto the screw portion 34b of the connecting rod 34 on its inner peripheral surface. A screw portion 62a is formed (see FIG. 4). In addition, the closed one end side of the clasp 62 is formed in an arcuate tapered shape so that it is difficult to be caught when the outer surface of the base tube 1a is recessed.

  The spacer 63 is a circular tubular member interposed between the clasp 62 and the floating plug 23, and can be provided with a plurality of types according to the tube length. Depending on whether one of them is attached, the floating plug 23, The insertion positions of the grooved plug 32 and the interval regulating pipe 61 with respect to the connecting rod 34 can be kept constant.

A method for assembling the cored bar 60 using the above-described members will be described.
The grooved plug 32, the spacing regulating tube 61, the floating plug 23, and the spacer 63 are inserted in this order from the end on the head 34a side in the axial direction of the connecting rod 34 to the end on the male screw 34b side, and the clasp 62 is attached. As shown in FIG. 2 and FIG. 3, the core bar 60 is inserted into the connecting rod 34 and screwed into the female screw portion 62 a of the clasp 62 and the male screw portion 34 b of the connecting rod 34. It can be configured integrally.

  At this time, the grooved plug 32 is rotatable around the axis by abutting the end portions between the head portion 34a of the connecting rod 34 and the interval regulating tube 61, and is positioned in the tube axis direction so as to float. The plug 23 is rotatable about its axis and positioned in the tube axis direction by bringing these end portions into contact with each other between the clasp 62 and the interval regulating tube 61 via the spacer 63.

The manufacturing method in this embodiment using the manufacturing apparatus 10 provided with the core metal 60 mentioned above is demonstrated.
The manufacturing method of this embodiment is a manufacturing method provided with a diameter reducing process and a groove processing process.

  Specifically, the diameter reducing step is a step of reducing the diameter of the element pipe 1b by narrowing the element pipe 1a with the diameter reducing die 22 and pressing the inner surface of the pipe against the floating plug 23.

  In the grooving step, the diameter of the raw tube 1b is reduced by the grooved plug 32 and the plurality of rolling balls 33, and the plurality of rolling balls 33 rolls around the pipe to the grooved plug 32. This is a step of pressing a surface to form a plurality of spiral grooves 5 (see FIG. 1) having a predetermined lead angle and height on the inner surface of the tube.

The following various actions and effects can be obtained by the manufacturing apparatus 10 and the manufacturing method described above.
The manufacturing method described above is a method of manufacturing the internally grooved tube 1e with the manufacturing apparatus 10 provided with the core metal 60 described above. Specifically, the diameter reducing step is performed using the floating plug 23 attached directly to the floating plug insertion portion 34f, and the grooved plug 32 attached directly to the grooved plug insertion portion 34g is used. It is a manufacturing method of the inner surface grooved pipe 1e which performs the grooved processing.

  For this reason, the metal core 60 is not configured to attach the floating plug 23 and the grooved plug 32 to the connecting rod 34 with another member interposed therebetween (see FIG. 3). The shaft misalignment of the cored bar 60 can be prevented without being affected by the processing error of the member.

  Therefore, it is possible to prevent the grooved plug 32 from axially swinging with respect to the core metal 60, that is, the floating plug 23 during processing, and to manufacture the internally grooved tube 1e with small variations in cross-sectional shape dimensions in the tube axis direction. Can do.

Specifically, the conventional cored bar 100 used in the manufacturing method of the inner surface grooved tube has a grooved plug 32, a floating plug 23, a connecting rod 101, and a grooved, as shown in FIGS. A plug insertion bolt 102, a floating plug insertion bolt 103, and two spacers 104, 104 are included.
The connecting rod 101 is a columnar member, and screw holes 101H and 101H are formed along the tube axis direction at the center of both end portions in the length direction. The inner peripheral surfaces of the screw holes 101H and 101H are respectively Female screw portions 101a and 101a are formed (see FIG. 18).

The grooved plug insertion bolt 102 and the floating plug insertion bolt 103 both have hook-shaped heads 102a and 103a on one end side in the length direction, and male screw portions 102b and 103b on the other end side. It is formed by a bolt-shaped pin formed by the formed elongated cylindrical member.
Note that the grooved plug 32, the floating plug 23, and the spacer 104 (63) are the same as those in the present embodiment, and thus the description thereof is omitted.

A method for assembling the conventional cored bar 100 composed of such components will be described.
First, the grooved plug 32 and the spacer 104 are arranged in the tube axis direction on one end side of the connecting rod 101, the grooved plug 32 and the spacer 104 are inserted into the grooved plug insertion bolt 102, and the grooved plug is inserted in this state. The spacer 104, the grooved plug 32, and the connecting rod 101 are attached in this order by screwing the male screw portion 102b and the female screw portion 101a of the connecting rod 101 while inserting the wearing bolt 102 into the screw hole 101H.

  Similarly, the floating plug 23 and the spacer 104 are arranged in the tube axis direction on the other end side of the connecting rod 101, and the spacer 104 and the floating plug 23 are inserted into the floating plug insertion bolt 103. In this state, the floating plug insertion bolt is inserted. By inserting the male screw portion 103b and the female screw portion 101a of the connecting rod 101 while inserting the screw 103 into the screw hole 101H, the spacer 104, the floating plug 23, and the connecting rod 101 are attached in this order, and the cored bar 100 is integrated. Can be assembled.

  Thus, since the grooved plug 32 in the conventional core metal 100 is configured to be attached to the connecting rod 101 with the grooved plug insertion bolt 102 interposed therebetween (see FIG. 17), the grooved plug insertion bolt 102 is provided. In addition, the processing error of the female screw portion 101a also affects the mounting accuracy of the grooved plug 32 with respect to the connecting rod 101.

  In particular, the male screw portion 102b of the grooved plug insertion bolt 102 and the female screw portion 101a of the connecting rod 101 are screwed together. Variations are likely to occur, and the shaft misalignment in the assembled core metal 100 may increase.

  Since the floating plug 23 is also attached to the connecting rod 101 with the floating plug insertion bolt 103 interposed, as in the case of the grooved plug 32, the axial displacement of the assembled core metal 100 becomes large. Sometimes.

  When grooving is performed using the conventional cored bar 100 having a large axial deviation in this way, the shaft runout of the cored bar 100 being processed increases, so that the internally grooved tube after passing through the grooved portion 31. If the shape of the groove 5 (see FIG. 1) is not stable and the shape of the groove 5 (see FIG. 1) is not stable, an internally grooved tube whose cross section is not stable in the tube axis direction will be manufactured.

  Further, when the grooving process is performed using the conventional metal core 100 with a large axial deviation, the rotational speed of the rolling ball 33 is increased in order to increase the processing speed, and the rolling ball 33 is rotated at a predetermined speed. When the number is reached, a so-called twist phenomenon occurs in which the raw tube that has passed through the grooved portion 31 is twisted.

  Since the groove 5 is not appropriately formed on the inner surface of the pipe in which the twist phenomenon has occurred in this way, the rotational speed of the rolling ball 33 must be lowered to a rotational speed at which the twist phenomenon does not occur. Further, the core metal 100 having a large shaft runout has a problem that the grooving speed cannot be increased because the twisting phenomenon tends to occur even if the rotational speed of the rolling ball 33 is low.

  In addition, if the cross section of the manufactured inner grooved tube is not stable in the tube axis direction, noise will increase when performing a nondestructive flaw detection test at the time of shipment as a product, which will adversely affect the detection accuracy of scratches (defects). Even if it is a non-defective product, it is erroneously detected as a defective product, resulting in a problem that the product yield is lowered.

  Furthermore, when manufacturing the heat exchanger by incorporating the inner grooved tube 1e as a heat transfer tube, the heat transfer tube is inserted into a hole formed in advance in the heat radiating fin, and when the tube is expanded, the heat radiating fin comes into close contact with the heat radiating fin. There also arises a difficulty that desired performance cannot be obtained due to variations.

  Furthermore, if the groove depth on the inner surface of the tube is not stable in the tube axis direction, there arises a problem that desired excellent heat transfer performance cannot be obtained.

  In response to such a problem, the manufacturing method of the present embodiment performs the diameter reducing step using the floating plug 23 attached directly to the floating plug insertion portion 34f as described above, and the grooved plug Since it is a manufacturing method of an internally grooved tube that performs the groove processing step using the grooved plug 32 attached directly to the insertion portion 34g, the core metal 60 is not misaligned. It is possible to prevent the shaft 60 from swinging.

  Accordingly, it is possible to manufacture the internally grooved tube 1e having a small variation in the tube axis direction of the cross-sectional shape dimension orthogonal to the tube axis direction such as the tube outer surface and groove shape in the tube axis direction.

  Further, the connecting rod 34 is formed of a rigid body made of one steel material over the entire length including the floating plug insertion portion 34f and the grooved plug insertion portion 34g in the tube axis direction. In addition, for example, there is no connection portion by screwing or the like between the length direction of the floating plug insertion portion 34f and the grooved plug insertion portion 34g in the connection rod 34.

  Accordingly, no shaft misalignment occurs, and the amount of shaft runout in which the grooved plug 32 shakes as the connecting rod 34 rotates around the shaft during machining can be greatly reduced.

  Furthermore, as described above, the cored bar 60 has a configuration in which the interval regulating pipe 61 is inserted between the floating plug 23 and the grooved plug 32 in the connecting rod 34 as shown in FIGS. Therefore, in the axial direction of the connecting rod 34, the slidable floating plug 23 and the grooved plug 32 can be regulated (positioned) so as to be maintained at a predetermined interval.

  In addition, by providing the gap regulating tube 61 between the floating plug 23 and the grooved plug 32, the connecting rod 34 can be formed when the connecting rod 34 is formed in a long shape or a small diameter. Even if it becomes easy to bend, it also functions as a reinforcing member for preventing the connecting rod 34 from being bent during processing, and the amount of axial deflection can be kept to a minimum.

  By manufacturing the inner grooved tube 1e by the manufacturing apparatus 10 using the above-described cored bar 60, the tube weight measured at intervals of 10 mm in a predetermined section having a tube length of 1 m in the tube axis direction per 1 m. It is possible to manufacture the internally grooved tube 1e having a stable cross section in the tube axis direction in which the variation of the respective tube weights converted into と い う is ± 1% or less.

  As a result, the shape of the outer surface of the tube in the tube axis direction can be stabilized, so that the occurrence of noise in the detection signal can be suppressed when a nondestructive flaw detection test is performed at the time of shipment using the inner grooved tube 1e as a product.

  Therefore, scratches (defects) can be detected reliably, and the product yield can be improved.

  Furthermore, when the heat exchanger tube is manufactured by incorporating the inner grooved tube 1e as a heat transfer tube, the heat transfer tube is inserted into a hole previously formed in the heat radiating fin, and when the tube is expanded, sufficient adhesion with the heat radiating fin is achieved. A state can be obtained and a desired performance can be obtained.

  Further, since the shape such as the depth of the groove 5 on the inner surface of the tube is stabilized in the tube axis direction, desired excellent heat transfer performance can be obtained.

(Second Embodiment)
As shown in FIG. 5, the manufacturing apparatus 20 according to the second embodiment includes the intermediate drawing machine 17 between the reduced diameter portion 21 and the groove processing portion 31 in the tube axis direction. Is supporting the drawing by a drawing device (not shown) provided on the downstream side by drawing the raw tube 1a in the drawing direction X. That is, the grooving by the grooving section 31 becomes resistance when the raw pipe 1a is drawn, and the drawing load at the time of grooving increases, but the drawing load applied to the raw pipe 1a by the intermediate drawing machine 17 is increased. Can be dispersed.

  The intermediate drawing machine 17 includes a pair of belts 42a and 42b disposed on the upper and lower sides or the left and right sides with respect to the cross section orthogonal to the tube axis direction of the raw tube 1a. Each belt 42a, 42b is formed in a loop shape (endless shape), and is stretched around a pulley 43 so as to be rotatable by a rotational drive of a motor. The belts 42a and 42b are configured in a caterpillar type in which a plurality of pads 44 are continuously provided along the length direction on the outer peripheral surface.

  A wiper 51 is provided on the upstream side of the intermediate drawing machine 17 to remove an oil film and foreign matter adhering to the outer surface of the raw tube 1b, and an intermediate shaping die 52 is provided on the downstream side.

  The reduced diameter portion 21 and the groove processing portion 31 in the tube axis direction are arranged at a wider interval by the amount of the intermediate drawing machine 17 disposed therebetween.

  The connecting rod 34L is formed to have a longer length than the length of the connecting rod 34 of the first embodiment because the distance between the reduced diameter portion 21 and the groove processing portion 31 is increased.

  Since the manufacturing apparatus 20 of the second embodiment includes the intermediate drawing machine 17, even if the connecting rod 34 </ b> L is long, the shaft bar of the core bar 60 does not occur during processing. Variation in shape such as the depth of the groove 5 to be formed can be greatly suppressed.

  In the case of the conventional manufacturing method, by providing the intermediate drawing machine 17, the interval between the reduced diameter portion 21 and the groove processing portion 31 in the tube axis direction is widened, and processing is performed using the cored bar 100 having a long connecting rod. Therefore, the influence of the shaft runout of the cored bar 100 appears remarkably during processing. Furthermore, if the shaft runout of the core metal 100 is large, the drawing force fluctuates, and the intermediate drawing machine 17 tries to positively control the drawing force during the grooving process, resulting in a large variation in load. There has been a problem that a variation in the depth of the formed groove falls into a vicious circle that becomes more prominent.

  On the other hand, since the manufacturing apparatus 20 of the second embodiment includes the intermediate drawing machine 17, even if the connecting rod 34 becomes long, no shaft runout occurs during processing. The drawing force by the machine 17 is also stable, and the variation in the depth of the groove formed on the inner surface of the pipe can be greatly suppressed.

  Hereinafter, an effect confirmation experiment performed to confirm the effect of the cored bar 60 will be described.

(Experiment 1)
In Experiment 1, the axial runout amounts of the core metal 60 of the first embodiment and the conventional metal core 100 were measured and compared for verification.
Further, in Experiment 1, as shown in FIGS. 2 and 3, the metal core 60 described in the first and second embodiments is assembled with the grooved plug 32 removed, and the product No. 1 to 5 cores were used.
Specifically, as shown in FIG. The other end of the metal core 60 in the axial direction is placed with the dial gauge probe placed on the surface of the grooved plug insertion portion 34g on one end side in the axial direction. The shaft runout amount of the cored bar 60 in the grooved plug insertion portion 34g was measured in order by rotating the side around the axis.

  Similarly, the conventional core No. 100 in which the conventional cored bar 100 as shown in FIGS. 1 to 5 cores were used.

Specifically, as shown in FIG. The core metal 100 from 1 to 5 is placed on the V block in order, and the other end in the axial direction of the core metal 100 with the dial gauge probe placed on the surface of the grooved plug insertion bolt 102 on one axial end side. The shaft runout amount of the cored bar 100 in the grooved plug insertion bolt 102 was measured in order by rotating the side around the axis.
The measurement results are shown in [Experiment 1] in Table 1 below.

As shown in Table 1, the conventional product No. The shaft runout amounts of the cores 100 of 1 to 5 were all as large as 0.100 mm or more, and the variation from lot to lot was also large.
In contrast, the product No. The core bars 60 of 1 to 5 all have small shaft runouts of 0.010 mm or less, and it has been proved that the variation from lot to lot is also small.

(Experiment 2)
In Experiment 2, the product No. 1 of the present invention used in Experiment 1 was used. 1 to 5 cores 60 and conventional product No. A grooved plug 32 is attached to each of the core bars 100 from 1 to 5, and the core bars 60 and 100 are used for actual diameter reduction processing and grooving processing. The occurrence of the phenomenon was verified.

  Here, the processing conditions in the diameter reduction processing and the grooving processing in Experiment 2 are as shown in Table 2.

Specifically, in Experiment 2, the rolling ball 33 in the grooving part 31 is started to be grooved at a low rotational speed, and the rotational speed of the rolling ball 33 in the grooving part 31 is increased in order to increase the processing speed. Then, we verified the occurrence of twisting phenomenon of the tube that occurred in the process.

  Furthermore, since the maximum rotation speed that is a limit on the performance of the rolling ball 33 of the groove processing portion 31 used in Experiment 2 is 30,000 rpm, the rolling ball 33 in the groove processing portion 31 may be twisted. The target maximum number of rotations at which grooving can be performed without setting was set to 30,000 rpm.

As a result, the measurement results shown in [Experiment 2] in Table 1 were obtained.
Conventional product No. In all of Nos. 1 to 5, the twisting phenomenon occurred before the rotational speed of the rolling ball 33 reached 30,000 rpm.
Specifically, the twisting phenomenon occurred when the rotational speed shown in Table 1 was reached. As is apparent from this result, the conventional product No. Among the core bars 100 of 1 to 5, the higher the shaft runout in Experiment 1, the lower the number of rotations at which the twisting phenomenon occurs, and the highest number of rotations of the rolling ball 33 But it was 25,000 rpm.

  In contrast, the product No. In any of the first to fifth core bars 60, no twisting phenomenon occurred even when the number of rotations of the rolling ball 33 was increased to 30,000 rpm.

In general, the grooving speed (drawing speed) during machining of the internally grooved tube 1e is V (m / min), the revolution speed of the rolling ball 33 is R (rpm), and the processing pitch of the rolling ball 33 Is P (mm), and the number of rolling balls 33 is N (pieces), the groove processing speed V (m / min) is
V = (R × P × N) / 1000 (1)
Can be represented.

  Here, the processing pitch P (mm) means that the rolling ball 33 is divided into the raw tube 1b by an angle equally distributed on the outer periphery of the raw tube 1b by the number of the rolling balls 33 arranged on the outer periphery as shown in FIG. It shows the distance that the raw tube 1b travels in the drawing direction X while revolving around.

  FIG. 7 is an explanatory diagram for explaining the processing pitch P schematically shown by omitting part of the vicinity of the groove processing portion 31. Moreover, L shown with the virtual line in FIG. 7 shows the locus | trajectory in which each of the some rolling ball 33 arrange | positioned at the outer periphery of the raw tube 1b pressed the outer surface of the raw tube 1b.

From this equation (1), it can be seen that in order to increase the grooving speed, it is necessary to increase the rotational speed of the rolling ball 33. Therefore, if the number of rotations of the rolling ball 33 can be increased without causing a twisting phenomenon, the grooving speed can be increased accordingly.
Therefore, the product No. of the present invention that can increase the number of rotations of the rolling ball 33. It was proved that the productivity of the inner grooved tube 1e can be greatly improved if the inner grooved tube 1e is manufactured by using the core bars 60 of 1 to 5.

(Experiment 3)
In Experiment 3, the product No. 1 to 5 of the core metal 60 and the conventional product No. Grooving was performed using the cores 100 of 1 to 5, and the test piece (inner grooved tube) produced in Experiment 2 was verified for variation in unit weight and unit weight change rate.

A procedure for calculating the unit weight and the unit weight change rate will be described. First, as shown in FIG. 8, 1 m (1000 mm) is taken out from the test tube as a measurement sample, the measurement sample is cut in 10 mm increments, and the exact length (mm) and weight (g ).
The unit weight (g / m) can be calculated by converting the weight of each sample piece into the weight per meter.
Furthermore, the unit weight change rate can be calculated using the following formula (2) based on the calculated unit weight.
ΔW = (Wn−Wa) / Wa × 100 (2)
However, ΔW: Unit weight change rate (%), Wn: Unit weight for each sample piece (g / m), Wa: Sample measurement point is the average unit weight (g / m) of 100 sample pieces. be able to.

  Invention product No. 1 to 5 of the core metal 60 and the conventional product No. The measurement results of the unit weight change rate of the test tubes prepared using each of the core bars 100 of 1 to 5 are shown in [Experiment 3] in Table 1.

  When the rate of change in unit weight was confirmed to be within ± 1.0%, it was confirmed that the conventional product No. The rate of change in unit weight of the test tubes prepared using the cores 100 of 1 to 5 was ± 1.7% or more and larger than ± 1.0%, and the degree of variation was large.

  In contrast, the product No. The rate of change in unit weight of the test tubes prepared using the core bars 60 of 1 to 5 was ± 0.5% or less, and was well within ± 1.0%.

  Specifically, the conventional product No. FIG. 19 shows the measurement result of the unit weight as an experimental result when the core metal 100 of 3 is used, and FIG. 20 shows the measurement result of the unit weight change rate.

  As shown in FIG. 19 and FIG. When the core metal 100 of 3 was used, the degree of variation was large in both the single weight and the single weight change rate. For example, as shown in FIG. The test tube produced using the No. 3 cored bar 100 was confirmed based on whether the unit weight change rate was within ± 1.0%, but it was not within ± 1.0%.

  In contrast, the invention product No. FIG. 9 shows the measurement result of the unit weight as an experimental result when using the No. 4 cored bar 60, and FIG. 10 shows the measurement result of the unit weight change rate.

  As shown in FIG. 9 and FIG. No. 4 core bar 60 is used, the conventional product No. Compared with the case where the core metal 100 of 3 was used, variation in both the unit weight and the unit weight change rate could be greatly reduced. For example, as shown in FIG. The test tube manufactured using the core metal 60 of No. 4 can keep the unit weight change rate within ± 0.5%. As compared with the case of using the No. 3 cored bar 100, the variation was greatly reduced.

  Further, in Experiment 3, along with the verification of the variation in the single weight change rate described above, the product No. No. 4 core metal 60 and the conventional product No. The thickness dimension of the cross-sectional shape was also verified for each of the test tubes produced by grooving in Experiment 2 using the No. 3 cored bar 100.

In the verification of the thickness dimension of the cross-sectional shape, as shown in FIG. 8, similarly to the verification of the unit weight and the unit weight change rate, each measurement sample was taken out from the test tube for 1000 mm, and the measurement sample was cut in 10 mm increments. . Furthermore, in the verification of the thickness dimension of the cross-sectional shape, as shown in FIG. 11, the total thickness (T), bottom wall thickness (t), groove depth (H ) Was measured and graphed for verification.
Conventional product No. 3 shows the measurement results of the total wall thickness (T), bottom wall thickness (t), and groove depth (H) of the cross-section of the tube when the core metal 100 of No. 3 is used. FIG. 12 shows the measurement results of the total wall thickness (T), bottom wall thickness (t), and groove depth (H) of the cross section perpendicular to the tube when the 4 cored bar 60 is used.

  As shown in FIGS. 12 and 21, the product No. of the present invention is the same as in the case of the experimental results with the single weight and the single weight change rate described above. No. 4 core bar 60 is a conventional product no. It was proved that the degree of variation in cross-sectional shape in the tube axis direction was significantly reduced as compared with the case of using the No. 3 cored bar 100.

  In addition, it is clear from the measurement results of the unit weight, the unit weight change rate, and the cross-sectional shape described above that the unit weight and the cross-sectional shape dimensions are closely related. It was found that there was no problem in experimental accuracy even if the quality of the test tube was judged. Furthermore, since it takes time to measure the cross-sectional shape dimensions, it can be said that it is preferable to judge the quality of the test tube based on the unit weight change rate.

(Experiment 4)
In Experiment 4, the product No. of the present invention used in Experiments 1 to 3 was used. 1 to 5 different from the present invention product No. A grooving process is performed using the core metal 60 of 6 to 11, and each test tube is manufactured. Conventional product No. 1 different from 1 to 5 A grooving process was performed using 6 to 8 metal cores 100 to prepare test tubes, respectively, and the accuracy of detection of flaws on the outer surface of the tube in the eddy current test was verified.

  In the eddy current testing, the signal value detected by the detection coil provided in the eddy current testing device is used as a reference signal value for the artificial defect that was first drilled on the outer surface of the test material with a drill or the like. When the signal value detected from the location where the detection coil in the test material is subsequently passed is higher than the reference signal value, it is known that the location has a large scratch that causes a problem in use. This is a flaw detection test.

Further, the flaw detection performance in the eddy current flaw detection test verified in Experiment 4 is the S / N ratio of the signal detected in the eddy current flaw detection test, which is said to be closely related to the flaw detection performance (S: reference signal for artificial defects) Value, N: signal value of base of test material).
Note that the signal value (N) of the base of the test material indicates a signal value detected as noise at a place where there is no scratch in the test material.

  At the same time, as will be described later, in addition to the S / N ratio, the rate of change in unit weight is closely related to the flaw search performance, and by reducing the variation in unit rate of change (unit weight), the S The / N ratio can be increased, and as a result, the flaw detection accuracy on the outer surface of the tube in the eddy current flaw detection test can be improved.

  Therefore, in this Experiment 4, the product No. 6 to 11 cored bar 60 and conventional product No. The test tube produced using each of the 6 to 8 metal cores 100 was measured by verifying the single weight change rate and the S / N ratio of the detection signal in the eddy current testing. The results are as shown in Table 3.

As shown in Table 3, the conventional product No. When the 6 to 8 cored bar 100 was used, the unit weight change rate was larger than ± 1.0, and the S / N ratio was smaller than 2.0.

  In contrast, the product No. When the 6 to 11 cored bar 60 was used, the unit weight change rate was ± 1.0 or less, and the S / N ratio was 2.0 or more.

  In general, when the number of scratches on the outer surface of the inner grooved tube is inspected by an eddy current flaw detection test, it has been empirically revealed that scratches can be reliably detected when the S / N ratio is 2.0 or more. .

  As described above, the product No. It was revealed that scratches could be reliably detected when the 6 to 11 cored bar 60 was used.

  At the same time, it was also found that the rate of change in unit weight must be kept within ± 1% in order to reliably detect scratches (defects).

  The same result was obtained even when the shape of the groove formed on the inner surface and the size to be processed were different.

  Hereinafter, the relationship between the flaw exploration performance, the single weight change rate (single weight), and the S / N ratio in the above-described eddy current flaw detection test, and the product S. No. 9 test tube manufactured using the cored bar 60 and conventional product No. Description will be made by paying attention to a test tube manufactured using the No. 6 cored bar 100. At the same time, the product No. No. 9 test tube manufactured using the cored bar 60 and conventional product No. The more detailed measurement result about the flaw search performance in the eddy current flaw test performed about the test tube produced using the metal core 100 of 6 is demonstrated.

  Conventional product No. The results of the eddy current test of the test tube produced using the core metal 100 of No. 6 are as shown in the graph of FIG. FIG. 13 shows the results of the eddy current flaw detection test of the test tube produced using the No. 9 cored bar 60.

As shown in FIG. 22 and FIG. The test tube with the core metal 60 of No. 9 has an S / N ratio of 2.50. Since it is higher than the S / N ratio (1.30) of the test tube with the core metal 100 of No. 6, the conventional product no. It was revealed that scratches could be reliably detected by the eddy current flaw detection test rather than the test tube with the core metal 100 of 6.
Furthermore, as shown in FIG. 22 and FIG. The test tube with the cored bar 60 of No. 9 is the conventional product No. As in the test tube with the core metal 100 of No. 6, the reference signal value (S value) of the artificial defect was 1.50V. Furthermore, the present invention product No. 9 has a base signal value (N value) of 0.60 V. It was lower than the signal value (1.15 V) of the base of the test tube with the core metal 100 of 6.

  This shows that it is effective to keep the base signal value low in order to increase the S / N ratio.

  Furthermore, in order to keep the base signal value low, it is necessary to reduce the longitudinal variation of the cross-sectional shape dimensions, that is, to reduce the unit change rate.

  For details, please refer to the conventional product no. When a material having a particularly high base signal value during the eddy current test was examined, such as the inner grooved tube 1e manufactured using the core metal 100 of No. 6, the pitch of the unevenness formed on the outer surface of the tube was uniform. However, in the tube immediately after grooving (the tube before being reduced to the final outer diameter), undulation (see FIG. 23) that can be clearly confirmed visually occurred.

  Further, when the unit weight was verified for the material having a particularly high base signal value during the eddy current flaw detection test as described above, the variation in unit weight was large as shown in the result of Experiment 3 described above (see FIG. 19). The variation in the cross-sectional shape (total thickness) in the direction was also large (see FIG. 21).

  In contrast, the product No. As for the inner grooved tube 1e manufactured using the No. 9 metal core 60, no swell was confirmed for a material having a low base signal value in the eddy current flaw detection test (see FIG. 11). Furthermore, when the unit weight was verified for a material with a low base signal value during the eddy current testing, as shown in the result of Experiment 3 described above, the variation in unit weight was small (see FIG. 9) and the cross-sectional shape in the tube axis direction ( The variation in total thickness was also small (see FIG. 12).

  From this, it is clear that the change in cross-sectional shape dimension is the main factor that increased the signal value of the base during the eddy current flaw detection test, and in order to keep the base signal value low, the unit weight change rate must be reduced. It can be said that it is effective.

  From the above, the base signal value can be kept low by reducing the variation in the unit weight change rate (unit weight), and as a result, the S / N ratio can be increased. The accuracy of flaw detection on the outer surface of the tube can be improved.

  In addition, as described in Experiment 4 above, the product No. It has been clarified that scratches can be reliably detected when the core bar 60 of 6 to 11 is used. Thus, by detecting the scratches accurately, it is possible to prevent erroneous detection of good or defective products, The production yield can be improved.

  Specifically, the inner grooved tube 1e is usually delivered to the user in the form of a coil or a straight line, and before delivery, as a nondestructive inspection for the presence of scratches on the outer surface of the tube over the entire length of the inner grooved tube 1e. A step of performing an eddy current test is performed.

  For example, when the inner grooved tube 1e is in the form of a coil, the upper limit of the number of scratches (defects) in the entire length of the coil portion is determined. If the upper limit is exceeded, the product cannot be shipped as a defective product. Are treated as

  A coil part with many defects was taken out for a predetermined number of turns, and the eddy current flaw detection test was performed again around the point where it was determined that there was a scratch. As shown in FIG. When the signal value shows a high value, it is difficult to find a difference in the value between the signal value detected at the place where it is judged to be flawed and the base signal value, so that many are judged to be flawed. It was. In other words, there were many cases where it was erroneously determined that there was a scratch even though there was no large scratch that would actually be a problem.

  On the other hand, as shown in FIG. 15, when the signal value of the base of the coil portion (the signal value indicated by the portion having no scratch on the test material) is generally low, such a coil portion is scratched. Since the signal value detected at the location determined to be a significant value with respect to the base signal value, a large scratch can be surely found.

  The test tube manufactured using the cored bar 60 of the present invention can suppress the signal value of the base in the eddy current flaw test, that is, the S / N ratio can be increased. Can be detected accurately, and the manufacturing yield can be improved.

In the correspondence between the configuration of the present invention and the above-described embodiment,
The grooved plug, the floating plug and the connecting rod, or the grooved plug, the floating plug, the connecting rod and the interval regulating tube correspond to the cored bar 100,
The floating plug insertion portion corresponds to the floating plug insertion through hole 23H,
The grooved plug insertion portion corresponds to the grooved plug insertion through hole 32H,
The rolling elements correspond to the rolling balls 33.

DESCRIPTION OF SYMBOLS 10 ... Manufacturing apparatus 17 ... Intermediate drawing machine 21 ... Reduced diameter part 22 ... Reduced diameter die 23 ... Floating plug 23H ... Floating plug insertion through hole 31 ... Grooved processing part 32 ... Grooved plug 32H ... Grooved plug insertion through hole 33 ... Rolled balls 34, 34L ... Connecting rod 34g ... Slotted plug insertion portion 34f ... Floating plug insertion portion 61 ... Spacing regulating tube 1a to 1c ... Elementary tube 1e ... Internal grooved tube

Claims (6)

The diameter reduction process of pulling out the raw tube between the diameter reducing die and the floating plug to reduce the diameter, and pressing the outer surface of the raw tube with a rolling element that rolls around the tube axis, And a grooved processing step of forming a plurality of grooves on the inner surface of the raw tube by pressing against the grooved plug provided in
A connecting rod for connecting the floating plug and the grooved plug is provided inside the pipe,
A floating plug mounting portion that allows the floating plug to be directly attached to the connecting rod is formed on the diameter-reducing die side in the axial direction of the connecting rod, and the rolling plug in the axial direction of the connecting rod is formed. On the side of the moving body, a grooved plug attachment portion that allows the grooved plug to be directly attached to the connecting rod is formed,
Performing the diameter reducing step using the floating plug attached to the floating plug attachment portion,
A method for manufacturing an internally grooved tube, wherein the grooved processing step is performed using the grooved plug attached to the grooved plug attachment portion. The method for manufacturing an internally grooved tube according to claim 1, wherein the connecting rod is formed of a rigid body made of one constituent material from the floating plug mounting portion to the grooved plug mounting portion. The floating plug mounting portion is configured with a floating plug insertion allowing portion that allows insertion of the floating plug,
The floating plug is configured to be inserted into the floating plug insertion allowing portion so as to be slidable in the tube axis direction.
The grooved plug mounting portion is configured with a grooved plug insertion allowing portion that allows insertion of the grooved plug,
The grooved plug is configured to have a grooved plug insertion portion that is slidably inserted in the grooved plug insertion allowable portion in a tube axis direction,
The connecting rod includes an interval regulating tube that is inserted between the floating plug and the grooved plug in the tube axis direction and regulates the floating plug and the grooved plug at a predetermined interval in the tube axis direction. The manufacturing method of the internally grooved pipe | tube of Claim 1 or 2. The raw tube is drawn between the reduced diameter portion constituted by the reduced diameter die and the floating plug, and the grooved portion constituted by the rolling element and the grooved plug. Equipped with an intermediate drawing machine,
4. The intermediate drawing step according to claim 1, wherein an intermediate drawing step of drawing the raw pipe reduced in the diameter reduction step is performed by the intermediate drawing machine while the diameter reduction step and the grooving step are performed. Manufacturing method of internally grooved tube. 5. The tube weight variation obtained by converting the tube weight measured every 10 mm in increments of 10 mm in a predetermined section having a tube length of 1 m in the tube axis direction to 1 m or less is ± 1% or less. An internally grooved tube manufactured by the method for manufacturing an internally grooved tube according to 1. A diameter-reducing portion that pulls out the pipe between the diameter-reducing die and the floating plug to reduce the diameter of the pipe, and a rolling element that rolls along the circumferential direction of the pipe while pressing the outer surface of the pipe. An inner surface grooved pipe manufacturing apparatus comprising a groove processing portion that forms a plurality of grooves by pressing an inner surface against a grooved plug provided inside the pipe,
A connecting rod that is arranged between the reduced diameter portion and the groove processing portion and connects the floating plug and the grooved plug is provided inside the pipe,
On the side of the reduced diameter portion in the axial direction of the connecting rod, a floating plug attaching portion that allows the floating plug to be attached directly to the connecting rod is formed.
An apparatus for manufacturing an internally grooved tube, in which a grooved plug attachment portion that allows the grooved plug to be directly attached to the connection rod is formed on the groove processing portion side in the axial direction of the connection rod.