JPH11104712A - Making of tube with inner surface groove - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method to mold a groove stably by preventing partial fracture and abrasion of a grove molding roll. SOLUTION: A groove molding roll 11 has on the circumferential surface plural rings 1a and 1b with grooves 2a and 2b formed in the direction which tilts against the circumferential direction, and in respect of the adjoining ring 1a and 1b with the groove, the formation direction of the groove 2a and 2b is tilting towards the opposite direction against the circumferential direction. The radius of the groove molding roll 11 in the boundary between the ring 1a with the groove and the ring 1b with the groove is set at the small radius r1 and at the large radius r2 alternately. By rotating the groove molding roll 11 in a circumferential direction 8b, and the smooth roll 12 in a circumferential direction 8a, the grooves 2a and 2b are copied on one side of the metal plate 13. Then the metal plate is bento in the way that the plane with the groove molded comes inside, and the butted part is welded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an internally grooved tube by roll rolling and welding, and more particularly to a method of manufacturing an internally grooved tube for suppressing local breakage and wear of a groove forming roll.

[0002]

2. Description of the Related Art In a condenser of an air-cooled heat exchanger such as an air conditioner for home use or business use, a tube having an inner surface groove is used in which a spiral groove is formed on the inner surface of the tube to improve heat transfer efficiency. I have. A welded pipe formed by rounding a metal plate having a groove and welding the butt portion is used as the inner grooved pipe. The method of manufacturing this welded pipe is as follows. First, a metal plate having a fixed width is sandwiched between a roll having a groove on its surface and a roll having a smooth surface to be rolled to form a metal plate having a groove on one surface. Next, the metal plate is curved with the surface having the groove inside, and the butt portion is welded to form a welded tube. In order to improve the heat transfer performance of the inner grooved tube, there has been proposed a method of forming grooves having different groove pitches, lead angles and shapes on the inner surface of the tube (Japanese Patent Laid-Open No. 4-15).
No. 8193). In the method described in this publication, a groove forming roll is formed by coaxially coupling a plurality of grooved rings in which grooves having different groove pitches, lead angles or shapes are formed on the outer surface. I have. Then, the metal plate is sandwiched between the groove forming roll and the smooth roll having a smooth surface, and is continuously supplied and rolled in the longitudinal direction so that the groove pitch, the lead angle in the circumferential direction of the pipe are formed on one surface. Alternatively, a metal plate in which grooves having different shapes are formed is manufactured. Next, the metal plate having a groove formed on one side is curved with the groove inside, and the butted portion is welded to complete the inner grooved pipe. According to this conventional technique, since the groove pitch, lead angle, or shape of the groove formed on the inner surface changes in the circumferential direction, the flow of the refrigerant passing through the inner surface of the tube is easily disturbed, and the heat transfer performance is improved.

Further, a method for stabilizing the plate thickness of a butt portion where welding is performed has been proposed (Japanese Patent Laid-Open No. 4-29481).
No. 9). In the method described in this publication, the groove is reduced by reducing the diameter of the roll from 0.1 to 0.7% toward the ends from a portion 15 to 35% of the plate width away from both ends of the groove forming roll. A tapered surface is formed on the forming roll. Then, an inner grooved pipe is manufactured in the same manner as in the above-described conventional technique. According to this conventional technique, since the tapered surfaces are formed at both ends of the groove forming roll, both ends of the metal plate are prevented from being locally thinned. For this reason, when welding this part and manufacturing a welded pipe, a fall of intensity | strength can be prevented.

[0004]

However, these prior arts have the following problems. JP 4-
In the prior art described in 158193,
When grooved rings with different groove pitches are adjacent to each other,
The phase shift of the groove occurs at the connecting portion between the grooved rings. Then, stress concentrates on the end of the groove projection, and damage such as tooth spilling and local wear occur at this portion. For this reason, the production cost increases, and the shape of the groove on the inner surface of the pipe is not stable. FIG. 6 is a schematic view showing a conventional groove forming roll. When the grooved rings 21 in which the twist directions of the grooves 22 are different from each other are adjacent to each other, the adjacent grooved rings 21
A boundary 23a is formed in which the point of the V-shape formed by the groove 22 is oriented in the direction 28 opposite to the roll rotation direction during rolling. When the groove 22 is formed on the metal plate using the groove forming roll 24, the metal flow becomes the groove 22 of the groove forming roll 24.
Therefore, the metal flow is concentrated on the boundary 23a. For this reason, the rolling reduction increases at the boundary 23a, and tool wear and tool breakage occur. In order to prevent concentration of metal flow, a method of chamfering the end of the grooved ring is also performed, but a protrusion having a shape matching the chamfer is formed on the surface of the metal plate facing the chamfered portion. For this reason, if the chamfering is performed sufficiently to protect the tool, the protrusion in the manufactured inner grooved pipe impedes the flow of the refrigerant, resulting in a decrease in heat transfer performance.

When grooved rings 21 having mutually different torsion directions of the grooves 22 are adjacent to each other, the point of the V-shape formed by the grooves 22 of the adjacent grooved rings 21 indicates the direction of roll rotation during rolling. Is formed.
At the boundary 23b, the metal flow is dispersed, whereby the thickness of the metal plate is reduced, so that a concave portion is easily formed on the outer surface of the pipe during the outer diameter reduction in the welding pipe forming process.

On the other hand, according to the prior art described in Japanese Patent Application Laid-Open No. 4-294819, the effect is exhibited if the grooves formed on the surface of the roll are uniform. When the groove pitch or the like changes along the circumferential direction of the tube in order to improve the thermal performance, damage to the groove and local wear at the connection between the grooved rings cannot be prevented. Further, the reduction ratio at both ends of the groove forming roll is defined by the tube diameter, but the magnitude of the stress concentration varies depending on the difference between the reduction ratio of the portion where the groove is formed and the reduction ratio of the portion where the groove is not formed. Therefore, the specified numerical values are not appropriate, and the groove forming roll has tooth dents or the like.

Further, in the case of forming a groove forming roll by adjoining conventional grooved rings in which the groove twist directions are different from each other, a connecting portion between adjacent grooved rings to suppress breakage and local wear. Preferably, adjacent grooves are brought into contact with each other, but when forming a groove forming roll by combining a plurality of grooved rings in which hundreds to thousands of grooves are formed in the circumferential direction, adjacent grooves are formed. Since it is difficult to make contact, the groove forming roll is expensive and not economical.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a method of manufacturing a grooved tube having an inner surface capable of preventing local breakage and wear of a groove forming roll and stably forming a groove. The purpose is to provide.

[0009]

The method of manufacturing an inner grooved pipe according to the present invention is characterized in that a metal plate is rolled by a groove forming roll having a groove formed on an outer peripheral surface and a smooth roll having a smooth outer peripheral surface. A groove forming step of forming a groove on one side of a metal plate, a tube forming step of forming the metal plate into a tube shape by bending the surface with the groove formed inside, and forming the tube-shaped metal plate. A method of manufacturing an inner grooved pipe having a welding step of welding and joining butt portions, wherein an outer peripheral surface of the groove forming roll is divided into a plurality of regions in the roll axis direction, and the grooves are formed in adjacent regions. The forming direction is inclined in a direction opposite to the circumferential direction, and the roll radius at the boundary of the region is alternately set to a small diameter r ₁ and a larger diameter r ₂ larger than this, and in the groove forming step, Is the large-diameter groove forming roll. tip of the V formed by the grooves of adjacent regions at the boundary of r _2, characterized in that the rotating to face the direction of rotation.

In the present invention, the radius of the groove forming region is defined to be appropriate, and the groove is formed in the metal plate by rotating the groove forming roll in a predetermined direction. And dispersion can be prevented. Thereby, while preventing the local breakage of the groove forming roll and the like,
The thickness of the inner grooved pipe can be prevented, and the groove can be formed stably in the metal plate.

[0011] When the depth of the groove is h, the difference between the large diameter r ₂ and the small diameter r ₁ is preferably (0.05 × h) to (0.5 × h). . By forming the groove in the metal plate with the difference between the large diameter r ₂ and the small diameter r ₁ being appropriate, the formability can be further improved and the wear of the tool can be further suppressed.

Further, the depth of the groove is h, and the width of the tip of the convex portion of the groove in the direction of the roll axis in the groove forming region is w.
In the groove forming roll, the radius is (r ₁ ) to (r ₁ −0.5 × h), the thickness is (w) to (5 × w) at the boundary of the small diameter r ₁ , and the smoothness is obtained. First having a smooth outer peripheral surface
It has a non-groove area, and has a radius of (r ₂ ) to (r ₂ −0.5 × h) and a thickness of (w) to (5 × w) at the boundary of the large diameter r _2.
It is desirable to have a second grooveless region having a smooth outer peripheral surface. By forming a groove on the metal plate by providing a groove-free region of an appropriate shape on the groove forming roll, local concentration and dispersion of the metal flow can be further prevented, and wear and the like of the groove forming roll can be prevented. It will be easier.

The radius of the smooth roll at a position facing the boundary of the small diameter r ₁ may be smaller than the radius at a position facing the boundary of the large diameter r ₂ .
The radius at the boundary position opposed to the small diameter r ₁ of the smoothing roll, to be smaller than radius at the boundary position opposed to the large diameter r _2, it is possible to further prevent the local concentration of the metal flow .

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, a plurality of grooved rings are used as groove forming regions in the groove forming roll. FIG. 1 is a schematic front view showing a grooved ring used in the method of the embodiment of the present invention. The grooved ring 1a used in the method of this embodiment is provided with a roll shaft hole in a direction perpendicular to the circumferential direction (hereinafter, referred to as a ring axis direction). A groove 2a having a depth h and a width w in the ring axis direction at the tip of the projection is formed on the outer peripheral surface in a direction inclined with respect to the ring axis direction. Moreover, the radius of the 1-way end 3a is r _1, the radius of the other end portion 3b is r _2. The radius of the grooved ring 1a is the end 3b.
Are reduced toward the end portion 3a of the radius r ₁ of the end portion 3a is provided smaller than the radius r ₂ of the end portion 3b.

FIG. 2 is a schematic view showing a groove forming apparatus to which the grooved ring shown in FIG. 1 is applied. In the groove forming roll 11 to which the grooved ring shown in FIG. 1 is applied, the grooved ring 1a shown in FIG. 1 and the groove 2b of the grooved ring 1a are formed in a direction opposite to the ring axis direction. Grooved ring 1
b and the end portions 3a and the end portions 3b are connected alternately with each other in the same ring axis direction, and the roll shaft 4 having a radius equal to the diameter of the hole is inserted into the roll shaft holes, thereby forming the ring shaft. It is arranged in series in the direction. The grooved ring 1
Also in b, the radius of the end portion 3a is r _1, the radius of the end portion 3b is r _2, the radius of the grooved ring 1b is reduced toward the end portion 3a from the end 3b. Therefore, the end 3a
Is set smaller than the radius of the end 3b.
Further, at the outer ends of the grooved rings located at both ends of the grooved ring portion composed of a plurality of grooved rings 1a and 1b, a smooth ring 6 having a smooth outer peripheral surface is rolled into its roll shaft hole. The shaft 4 is fitted and connected.

In the groove forming roll 11 configured as described above, a connecting portion 5a which is a boundary between the ends 3a and a connecting portion 5b which is a boundary between the ends 3b are formed.
The radius of the small diameter r ₁ next to the groove forming roll 11 in the connecting portion 5a, the radius of the large diameter r ₂ becomes in the connection portion 5b, it is smaller than the radius of the radius connecting portion 5b of the connecting portion 5a.

Further, a groove forming apparatus is constructed by arranging a smoothing roll 12 having substantially the same shape as the groove forming roll 11 except that the outer peripheral surface is a smooth cylindrical surface in parallel with the groove forming roll 11. . Groove forming roll 11 and smoothing roll 1
The thickness of the inner grooved tube manufactured can be changed by adjusting the distance from the inner grooved tube 2.

Next, a description will be given of a method of manufacturing an inner grooved pipe using the groove forming apparatus configured as described above. First, after adjusting the interval between the groove forming roll 11 and the smoothing roll 12 according to the thickness of the inner surface grooved pipe to be manufactured, the groove forming roll 11 is rotated in the circumferential direction 8b opposite to the circumferential direction 8a,
The smooth roll 12 is rotated in the circumferential direction 8a. When the metal plate 13 is supplied between the groove forming roll 11 and the smoothing roll 12 in a direction orthogonal to the roll axis 4, the metal plate 13 is sandwiched between the groove forming roll 11 and the smoothing roll 12, and Rolled along with rotation and discharged to the discharge side. At this time, the metal plate 13 is rolled by the groove forming roll 11 and the smoothing roll 12, and
The grooves 2a and 2b formed on the outer peripheral surface are transferred to one surface thereof. Next, the metal plate 13 having a groove formed on one side is curved with the grooved surface facing inward, and the butted portions are joined by welding to produce an inner grooved pipe.

The groove forming roll 1 used in the method of the present embodiment.
1, the radius of the connecting portion 5a where the metal flow is concentrated when forming the groove in the metal plate 13 is smaller than the radius of the connecting portion 5b where the metal flow is dispersed.
Between the connecting portion 5b and the connecting portion 5a
It gradually spreads toward. Therefore, the rolling reduction of the metal plate 13 by the groove forming device gradually decreases from the connecting portion 5b toward the connecting portion 5a. Thereby, this connecting part 5a
The concentration of the metal flow on the metal plate 13 at the position facing the metal plate 13 is suppressed. Further, even when the metal flow is concentrated, the metal flow is absorbed by the space between the wide groove forming roll 11 and the smooth roll 12, so that the local increase in the rolling reduction is suppressed. Wear and breakage are reduced. Further, the metal plate 1 facing the connecting portion 5b
At the position 3, since the amount of metal flow generated is reduced, the thinning phenomenon of the metal plate 13 at this position is reduced.

The difference between the large diameter r ₂ and the small diameter r ₁ is represented by Δr (=
r ₂ −r ₁ ), the radius difference Δr is (0.05 × h) to (0.5 × h) with respect to the depth h of the grooves 2 a and 2 b.
It is desirable that Radius difference Δr is (0.05 × h)
If it is less than the radius, the radius difference with respect to the amount of generated metal flow becomes small, and it is difficult to suppress a local increase in the rolling reduction due to the concentration of the metal flow. On the other hand, the radius difference Δr
Exceeds (0.5 × h), the radius difference with respect to the amount of generated metal flow becomes excessive, and it becomes difficult to form a groove in the metal plate 13 in the connecting portion 3a. In addition, a thicker portion may be formed at the bottom of the groove, which may increase the weight of the inner grooved tube and increase the price. Therefore, it is desirable that the radius difference Δr is (0.05 × h) to (0.5 × h).

Further, a grooveless ring having no groove formed on the outer peripheral surface may be disposed between the grooved rings 1a and 1b as a grooveless region. FIG. 3 is a schematic view showing a groove forming apparatus provided with a grooveless ring, and FIG. 4 is a schematic front view showing a connecting portion between the grooved ring and the grooveless ring. The grooved ring 1a is provided on the first grooveless ring 7a and the second grooveless ring 7b.
Similarly to FIGS. 1 and 1b, a roll shaft hole is provided in the ring shaft direction, and the roll shaft 4 is inserted through the roll shaft hole and disposed between the grooved rings 1a and 1b. The radius of the first grooveless ring 7a disposed between the ends 3a is _defined as r _0a
, The small diameter r ₁ of the end 3a and the grooves 2a and 2b
The radius r _0a is (r ₁ −h) to r ₁ with respect to the depth h. If the radius r _0a is less than (r ₁ -h), the interval between the first grooveless ring 7a and the smooth roll becomes excessively large, and the metal plate is insufficiently filled in this portion, and the smooth surface after rolling is formed. A recess is formed in the substrate. This concave portion is amplified in the tube reduction in the welding pipe forming process, and the edge of the cross section of the manufactured internally grooved tube does not become a perfect circle. In such an internally grooved tube, the pressure loss increases, and when the tube is incorporated in a plate fin coil heat exchanger, a gap is formed between the tube and the fins, which hinders heat transfer and deteriorates performance. on the other hand,
If the radius r _0a exceeds r ₁ , the rolling force on the first grooveless ring 7a increases, and the wear thereof is remarkably caused. Therefore, the radius r _0a is (r ₁ −h) to r ₁ . Moreover, the radius of the second groove-free ring 7b disposed between the ends 3b when the r _{0 b} is the same reason, the radius r _0b is the (r ₂ -h) to r _2.

The thickness of the non-grooved rings 7a and 7b is t
In this case, the thickness t is set to w to (5 × w) with respect to the width w of the tip of the groove convex portion. When the thickness t is less than w, the strength against the force in the ring axial direction applied from the metal flow is insufficient, and the grooveless rings 7a and 7b are selectively worn. On the other hand, if the thickness t exceeds (5 × w), the interval between adjacent grooved rings becomes excessively large, and underfilling of the metal plate occurs at the time of rolling, and concavities are formed on the smooth surface side after rolling. Is done. Also in this case, the edge of the cross section of the manufactured inner grooved tube does not become a perfect circle. Therefore, the thickness t ranges from w to (5 × w).

The smooth roll which is rolled with the metal plate together with the groove forming roll at the time of forming the groove is not limited to a roll having a smooth cylindrical outer peripheral surface. For example, the outer peripheral surface may be a smooth surface on which no groove is formed, and the radius of the roll may vary similarly to the groove forming rolls arranged in parallel. FIG. 5 is a schematic view showing a groove forming apparatus to which a smooth roll having an inclined outer peripheral surface is applied. In this embodiment, the shape other than the shape of the smoothing roll is the same as that of the embodiment shown in FIG. Therefore, in the embodiment shown in FIG. 5, the same components as those in the embodiment shown in FIG. 2 are denoted by the same reference numerals, and the detailed description thereof will be omitted. In this embodiment, the radius of the position facing the connecting portion 5a of smaller diameter r ₁ of the groove forming roll 11 smooth roll 12a is a r _1, connecting portion 5b of the larger diameter r ₂ of the groove forming roll 11 and the counter The radius of the position where the movement is performed is r ₂ . By making the shape of the smoothing rolls like this, local concentration and dispersion of the metal flow can be more easily prevented.

Furthermore, it is desirable to appropriately chamfer the ends of the grooved ring and the grooveless ring. By performing chamfering, it is possible to suppress wear at the ends of the grooved ring and the grooveless ring.

It should be noted that the present invention is not limited to the case where the groove forming rolls are formed of different members. The groove forming region and the non-groove region may be made of the same member.

[0026]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples that fall outside the scope of the claims.

First, using a smoothing roll and groove forming rolls having various shapes, the sheet thickness is 0.5 mm and the sheet width is 2 mm.
A groove was formed on one surface of a copper plate of a soft material measuring 6.0 mm.
In the case of a groove forming roll, the circumferential direction is 2 mm.
0 ° inclined, depth 0.2 mm, groove pitch in the ring axis direction 0.4 mm, width of the tip of the projection in the ring axis direction 0.2
mm and six grooved rings in which grooves having the ring radii shown in Table 1 below are formed. The torsional directions of the grooves of adjacent grooved rings are opposite to each other with respect to the circumferential direction. It is suitable. A grooveless ring having a ring radius shown in Table 2 below is interposed between the grooved rings. Further, smooth rings having smooth outer peripheral surfaces are arranged at outer ends of the grooved rings located at both ends. By rolling a copper plate using the groove forming roll configured as described above, a portion having a width of about 25 mm is divided into six portions at the center in the plate width direction, and two types of grooved bands are provided alternately. The part was a flat part.

[0028]

[Table 1]

[0029]

[Table 2]

Next, in each of Examples and Comparative Examples, a grooved tube having an outer diameter of about 7 mm was manufactured by bending the surface with the groove formed inside and welding the butted portion with high frequency.

Then, the formability at the time of forming the groove, the wear of the tool, and the presence or absence of deformation after welding pipe formation were evaluated. The results are shown in Table 3 below. In Table 3, ○ indicates good, Δ indicates slightly good, and × indicates bad.

[0032]

[Table 3]

As shown in Table 3 above, Examples 1 to 10
In the above, since the radius of the grooved ring is appropriate, the formability at the time of groove formation is good, damage such as wear of the grooved ring and the ring without groove is suppressed, and the quality after welding pipe forming is good. there were. In Examples 1, 3 and 4, since the radius difference Δr of the grooved ring and the radius and thickness of the grooveless ring were appropriate, the evaluation results were particularly excellent.

On the other hand, in Comparative Example 11, the tool was worn because the radius of the grooved ring was different from that specified in the present invention.

[0035]

As described in detail above, according to the present invention,
Since the radius of the groove forming region is defined as appropriate and the groove forming roll is rotated in a predetermined direction to form the groove in the metal plate, local concentration and dispersion of the metal flow can be prevented. . Accordingly, it is possible to prevent the groove forming roll from being locally damaged or the like, to prevent the inner grooved tube from being thinned, and to stably form the groove in the metal plate. Further, the cost can be reduced by reducing the frequency of replacing the groove forming rolls. Further, by performing the groove forming a metal plate the difference between the diameter r ₂ and the small diameter r ₁ as appropriate, together with further improve the moldability, it is possible to suppress the wear of the tool. Furthermore, by forming a groove in the metal plate by providing a groove-free region of an appropriate shape on the groove forming roll, local concentration and dispersion of the metal flow can be further prevented, and wear and the like of the groove forming roll can be reduced. It is easier to prevent. Further, by making the radius at the position facing the small diameter r _{1 of the} smooth roll smaller than the radius at the position facing the large diameter r ₂ , local concentration of the metal flow can be further prevented.

[Brief description of the drawings]

FIG. 1 is a schematic front view showing a grooved ring used in a method of an embodiment of the present invention.

FIG. 2 is a schematic view showing a groove forming apparatus to which the grooved ring shown in FIG. 1 is applied.

FIG. 3 is a schematic view showing a groove forming apparatus in which a grooveless ring is arranged.

FIG. 4 is a schematic front view showing a connection portion between a grooved ring and a grooveless ring.

FIG. 5 is a schematic view showing a groove forming apparatus to which a smooth roll having an inclined outer peripheral surface is applied.

FIG. 6 is a schematic view showing a conventional groove forming roll.

[Explanation of symbols]

 1a, 1b, 21; grooved ring 2a, 2b, 22; groove 3a, 3b; end portion 4; roll shaft 5a, 5b, 23a, 23b; connecting portion 6; smooth ring 7a, 7b; grooveless ring 8a, 8b Circumferential direction 11, 24; groove forming rolls 12, 12a; smoothing roll 13, metal plate 28;

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI F28F 1/40 F28F 1/40 E

Claims (4)

[Claims] A groove forming step of rolling a metal plate with a groove forming roll having a groove formed on an outer peripheral surface thereof and a smoothing roll having a smooth outer peripheral surface to form a groove on one surface of the metal plate; Pipe forming step of forming a pipe by bending the surface with the groove formed inside, and welding step of welding and joining butt portions of the metal plates formed into the pipe shape In the manufacturing method, the outer peripheral surface of the groove forming roll is divided into a plurality of regions in the roll axis direction, the forming direction of the groove in an adjacent region is inclined in a direction opposite to the circumferential direction, The roll radius at the boundary of the region is alternately set to a small diameter r ₁ and a large diameter r ₂ larger than this, and in the groove forming step, the groove forming rolls are adjacent at the boundary of the large diameter r _2. V-shaped point formed by the groove of the region A method for manufacturing an inner surface grooved tube, wherein the tube is rotated so that an end faces a rotation direction. 2. When the depth of the groove is h, the difference between the large diameter r ₂ and the small diameter r ₁ is (0.05 × h) to (0.
5 × h). The method according to claim 1, wherein 3. When the depth of the groove is h and the width of the tip of the convex portion of the groove in the roll axis direction of the groove forming region is w, the groove forming roll is located at the boundary of the small diameter r ₁ . A first groove-free region having a radius of (r ₁ ) to (r ₁ −0.5 × h), a thickness of (w) to (5 × w), and a smooth outer peripheral surface; radius at the boundary of r ₂ is (r ₂₎ to (r ₂
The inner groove according to claim 1 or 2, wherein the inner groove has a second grooveless region having a thickness of (w) to (5xw) and a smooth outer peripheral surface. A method of manufacturing a tube. 4. The smooth roll according to claim 1, wherein a radius of the smooth roll at a position facing the boundary of the small diameter r ₁ is smaller than a radius of the smooth roll at a position facing the boundary of the large diameter r ₂ . The method for producing an inner surface grooved pipe according to any one of the preceding claims.