JPH07256336A - Production of inner surface grooved tube - Google Patents

Abstract

PURPOSE:To produce a inner surface grooved tube for heat exchanger to deep groove in high speed and high quality. CONSTITUTION:A grooved plug 2 is inserted in a metal tube 1 free to rotate and is arrayed along a tapered inner peripheral surface of a rotary die 5 on an outer peripheral surface of the plug 2 inserted position of the metal tube 1, while pressing a taper roller 5 to rotate around the axis of and on its axis, by rotating force of the rotary die 5, the inner surface of metal tube is subjected to grooving by drawing the metal tube 1. The tapered inner peripheral surface of the rotary die 5 is formed to diverged shape, an end part of more tip side than a tapered surface 7 of a taper roller 3 is formed to the prescribed shape and is pressed on an outer peripheral surface of inserted position of the plug 2 of the metal tube 1, the taper roller 3 is arrayed with an angle of 10 deg. between the taper surface 7 and outer peripheral surface of the metal tube 1. By this method, a deep groove is worked because the pressing area is small pressing area. Pressed marks is smoothly worked by the tapered surface 7. Directions of the centrifugal force F1 and thrust force F2 applied on the taper roller 3 is turned to same, the surface quality is improved due to no axis misalignment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an inner grooved tube used as a heat transfer tube for heat exchangers such as refrigeration equipment and air conditioning equipment.

[0002]

2. Description of the Related Art Inner grooved pipes are used in heat exchangers, which are the main members of refrigeration and air conditioning equipment, and greatly contribute to the improvement of heat transfer characteristics of these equipment. In the manufacture of such an inner grooved tube, conventionally, a plug having a groove on its peripheral surface is rotatably inserted into the metal tube, and a fixed die is arranged on the outer periphery of the plug insertion position of the metal tube to It was carried out by a method of forming a groove on the inner surface while reducing the diameter. In the manufacturing method using this fixed die, the resistance due to the diameter reduction processing and the resistance due to the groove processing are polymerized and a high drawing force is required, so that the amount of heat generation is large and the productivity is poor. Figure from this
As shown in 10, a method of pressing the ball 8 in the rotary die 5 with a stopper 11 and causing the ball 8 to rotate and revolve by the rotational force of the rotary die 5 to press the plug 2 insertion position of the metal tube 1 from the outside. (Japanese Patent Laid-Open No. 55-103215) or, as shown in FIG. 12, the taper roller 3 is rotated and revolved by the rotating force of the rotary die 5, and the taper surface 7 is pressed to the plug 2 insertion position of the metal tube 1. Method (JP-A-63-17)
7906), a method of reducing resistance due to diameter reduction processing has been proposed.

[0003]

By the way, in recent years, there has been a demand for energy saving of refrigerating and air-conditioning equipment as a part of the environmental damage prevention movement, and in connection therewith, the inner surface groove of the metal pipe is deepened to enhance the heat exchange efficiency. It was raised. However, in order to make the groove deep by the above-mentioned ball pressing method, it is necessary to reduce the diameter of the ball 8 to increase the pressing force per unit area, but when the ball 8 has a small diameter, the surface of the metal tube as shown in FIG. The pressure mark 19 of the ball remains clearly, and further the metal tube 1
There was a problem of breaking. Further, in the method using the taper roller, the taper surface is severely worn due to a large pressing force at the time of groove processing, and when the drawing speed is increased, the taper surface 7 and the metal tube 1 slip and the surface quality of the metal tube 1 is deteriorated. Further, since the tapered inner peripheral surface of the conventional rotary die 5 is narrowed in the drawing direction, the direction F _{1 of the} centrifugal force applied to the taper roller 3 and the direction of the thrust force (force acting in the axial direction) F ₂ are opposite, As a result, the taper roller 3 caused axial deviation in the rotary die 5 and a defect was generated on the surface of the metal tube 1. As described above, according to the conventional method, it is difficult to manufacture a deep grooved grooved tube.

[0004]

The present invention has been earnestly studied in such a situation. The purpose of the present invention is to obtain a deep groove inner surface grooved pipe with high surface quality. It is to provide a method of manufacturing at high speed. That is, according to the invention of claim 1, a plug having a large number of grooves on its peripheral surface is rotatably inserted into the metal pipe, and the tapered inner peripheral surface of the rotary die is attached to the outer peripheral surface of the metal pipe at the plug insertion position. The inner surface of the metal tube is grooved on the inner surface of the metal tube while pressing the plurality of taper rollers that are arranged along In the method of manufacturing a pipe, a tapered inner peripheral surface of the rotary die is formed so as to widen in the drawing direction, and an end portion of a tip end of the taper roller is formed into a predetermined shape to form an outer periphery of a plug insertion position of a metal tube. The taper roller is arranged so that the taper surface is pressed against a surface and the taper surface makes an angle of 10 degrees or less with the outer peripheral surface of the metal tube after the inner surface groove is processed.

The invention of claim 1 will be described below in detail with reference to the drawings. FIG. 1 is an explanatory view showing an embodiment of the invention of claim 1. A plug 2 having a large number of grooves on its peripheral surface is rotatably inserted into the metal tube 1, and one end of a plurality of taper rollers 3 is pressed against the outer peripheral surface of the metal tube 1 at the plug 2 insertion position. It is arranged in a closed state. The taper roller 3 is arranged along the tapered inner peripheral surface 6 of the rotary die 5, and is frictionally driven by the rotating force of the rotary die 5 to revolve while rotating on the outer peripheral surface of the metal tube 1 at the plug 2 insertion position. To do. And while rotating the rotary die 5,
When the metal tube 1 is pulled out and the diameter thereof is reduced, a groove is formed on the inner surface of the metal tube 1. Tapered inner peripheral surface 6 of the rotary die 5
Is wide in the pulling direction. Further, the taper surface 7 of the taper roller 3 arranged along the taper-shaped inner peripheral surface 6 of the rotary die 5 is flared in the drawing direction.

Usually, 3 to 6 taper rollers 3 are used. The taper roller is held in the rotary die by the stopper 11. The distance between the taper rollers 3 is kept constant by disposing a retainer (not shown) between the taper rollers 3. The taper roller 3 revolves in close contact with the inner peripheral surface of the rotary die 5 by the centrifugal force generated by the rotation of the rotary die 5. Therefore, the taper surface 7 of the taper roller 3 and the outer peripheral surface 10 of the metal tube after the inner surface groove is processed.
And the taper angle of the tapered inner peripheral surface 6 of the rotary die 5 and the taper angle of the taper surface 7 of the taper roller 3 are determined.

In the present invention, as the plug 2, a plug having a large number of grooves parallel to the axial direction or spirally parallel to each other is provided on the peripheral surface. As shown in FIGS. 2A to 2D, at the end of the taper roller that presses against the metal tube, the longitudinal section of the end 4 is semicircular (FIG. 2A), or the diameter is reduced halfway. , With a flat tip (Fig.
D), etc., as long as it has a shape that allows the metal tube to be uniformly pressed against the grooved plug, the shape is arbitrary, and the shape is the material, diameter, diameter reduction rate, processing conditions, etc. of the metal tube forming the inner surface groove. It is appropriately selected according to. The shape of the other end of the taper roller in contact with the stopper is arbitrary as long as it slides well with the stopper.

In the present invention, the reason why the angle α formed by the taper surface 7 of the taper roller 3 and the metal tube 1 is limited to 10 degrees or less is that when the taper surface 7 and the metal tube 1 are brought close to each other, both This is because, immediately after pressing, the trace of pressing at the end of the hemispherical portion is processed smoothly by the tapered surface 7 by contact. When α exceeds 10 degrees, pressing marks 9 as shown in FIG. 9 remain.

In the present invention, as shown in FIG. 1, since the tapered inner peripheral surface 6 of the rotary die 5 spreads in the drawing direction, the centrifugal force F ₁ and the thrust force F ₂ applied to the taper roller 3 by the rotation of the rotary die 5 are increased. The same direction, so there is no axial wobbling of the taper roller 3 during high-speed drawing,
Stable groove processing is possible.

According to a second aspect of the present invention, a plug having a large number of grooves on its peripheral surface is rotatably inserted into a metal pipe, and the tapered inner periphery of a rotary die is attached to the outer peripheral surface of the metal pipe at the plug insertion position. While being arranged along the surface, while pressing a plurality of taper rollers that rotate and revolve by the rotational force of the rotary die,
In the method of manufacturing an inner grooved tube in which the metal tube is drawn out in a predetermined direction to reduce its diameter, and the inner surface of the metal tube is grooved, a tapered inner peripheral surface of the rotary die is formed to be wide in the drawing direction, Hold the taper rollers in the retainer at equal intervals, place a stopper that receives the thrust force applied to the taper roller in the rotary die, and insert the metal pipe plug by forming the end part of the taper roller tip to the specified shape. Press the outer peripheral surface of the position, the taper roller,
The taper surface is arranged so as to form an angle of 10 degrees or less with the outer surface of the metal tube after the inner surface groove is formed, and the length L of the taper roller is set.
And the ratio L / D of the maximum diameter D of the end portion pressed against the outer peripheral surface of the metal pipe at the tip of the taper surface of the taper roller to 0.5 or more and 3 or less. Is.

According to the second aspect of the present invention, as shown in FIG. 3, the taper rollers 3 are arranged such that the angle α between the taper surface 7 and the outer peripheral surface of the metal tube 1 after the inner surface groove is formed is 10 degrees or less. , The length L of the taper roller 3 and the taper roller 3
The ratio L / D to the maximum diameter D of the end portion 4 pressed against the outer peripheral surface of the metal pipe at the tip of the tapered surface 7 is limited to 0.5 or more and 3 or less. When the angle α exceeds 10 degrees, the pressing trace by the end portion of the taper roller 3 will remain on the outer peripheral surface of the metal tube 1. When the L / D ratio is less than 0.5 or exceeds 3, the balance of the force applied to the taper roller is lost,
The stability of the taper roller is reduced and the shaft shake occurs. In the figure, 12 is a retainer.

According to a third aspect of the present invention, the taper roller is provided in the retainer, and the clearance between the taper roller and the retainer is
This is a manufacturing method in which the taper roller is prevented from axial deviation by holding it to 0.2 mm or less. FIG. 4 is a cross-sectional view showing a state in which the taper roller 3 is arranged inside the retainer 12. With the taper roller 3 pressing the outer peripheral surface of the metal tube 1, the clearance C between the taper roller 3 and the retainer 12 is maintained at 0.2 mm or less.

According to a fourth aspect of the present invention, as shown in FIG. 3, the stopper 11 receives the thrust force applied to the taper roller 3.
In the manufacturing method, the angle γ formed by the surface of the taper roller 3 that contacts the taper roller 3 and the center axis of rotation of the taper roller 3 is limited to 60 degrees to 85 degrees to prevent the axial deviation of the taper roller 3. When the angle γ is less than 60 degrees, the taper roller 3 bites between the rotary die 5 and the stopper 11 as shown in FIG.
If it exceeds 85 degrees, as shown in FIG. 8B, slippage occurs between the taper roller 3 and the stopper 11 and the shaft shake easily occurs.

According to a fifth aspect of the present invention, as shown in FIG. 5, the taper roller support portion 13 of the retainer 12 for holding the taper roller 3 is formed so as to widen toward the end in the pulling-out direction to prevent axial shake.

According to the sixth aspect of the invention, as shown in FIG. 5, the stopper 11 receives the thrust force applied to the taper roller 3.
The contacting portion of the taper roller 3 is formed as a curved concave portion, and the curved convex portion of the taper roller 3 is fitted into the concave portion so as to widen the contact area between the both, thereby preventing axial deviation during rotation of the taper roller 3. is there. Taper roller 3 and stopper
The same effect can be obtained by reversing the unevenness of 11.

According to the seventh aspect of the present invention, as shown in FIG. 5, the outer peripheral portion 14 of the retainer 12 holding the taper roller 3 on the stopper 11 side is provided with a contact portion 15 between the taper roller 3 and the stopper 11.
The retainer 12 is located further outward in the radial direction to increase the diameter of the retainer 12 to improve the surrounding of the working oil, thereby improving the lubricity and heat dissipation during the drawing process.

[0017]

According to the first aspect of the invention, since the end portion of the taper roller at the tip end is formed into a predetermined shape and is pressed against the outer peripheral surface of the plug insertion position of the metal tube, the pressing area can be reduced and deep groove machining can be performed. Easy to do. Further, since the taper roller is arranged so that the taper surface makes an angle of 10 degrees or less with the outer peripheral surface of the metal tube after the inner surface groove is processed, the pressing trace of the hemispherical end is smoothed by the taper surface and the surface quality is improved. It will be good. Further, since the tapered inner peripheral surface of the rotary die is formed to widen in the drawing direction, the direction of centrifugal force F ₁ applied to the taper roller 3 by the rotation of the rotating die and the direction of thrust force F ₂ applied in the axial direction during drawing are the same direction. Therefore, the taper roller 3 is not shaken during the drawing process, and stable groove processing can be performed.

According to the invention of claim 2, in addition to the effects of (1) to (4), the ratio of the length L of the taper roller to the maximum diameter D of the end portion pressed against the outer peripheral surface of the metal pipe at the tip of the taper surface of the taper roller. Since L / D is limited to 0.5 or more and 3 or less, the shape of the taper roller is well balanced, the balance of the force applied to the taper roller during groove processing is not lost, and the taper roller rotates stably. Further, the following measures (1) to (3) can suppress the axial deviation of the taper roller. That is, the holding angle of the outer peripheral surface of the taper roller and the retainer that holds the taper roller at equal intervals in the circumferential direction is made parallel to or widened toward the drawing direction. The clearance between the taper roller and retainer should be 0.2 mm or less. The angle of the flange surface of the stopper, which receives the thrust force applied to the taper roller from the metal tube during the groove processing, is set to 60 to 85 degrees with respect to the central axis of rotation of the taper roller. By forming the contact surface of the stopper with the roller into a concave or convex end shape of the taper roller, axial deviation of the roller is suppressed, and more stable groove processing can be performed. Furthermore, by positioning the outer peripheral portion of the retainer that holds the taper roller radially outside the contact portion between the taper roller and the stopper,
The diameter of the retainer can be increased, the surroundings of the processing oil are improved, and the lubricity and heat dissipation during drawing are improved.

[0019]

EXAMPLES The present invention will be described in detail below with reference to examples. (Example 1) An inner grooved tube made of copper having an outer diameter of 7 mm was manufactured by the method shown in FIG. As the plug 2, one having 40 spiral grooves provided on the peripheral surface was used. As the taper roller 3, four rollers (FIG. 2A) whose one end for pressing against the metal tube 1 has a radius of 10 mm and whose diameter is reduced to a semicircular cross section (FIG. 2A) are used. The angle α formed between the taper surface 7 of the taper roller 3 and the outer peripheral surface of the metal tube after the inner surface groove processing is selected by selecting the taper angle of the tapered inner peripheral surface of the rotary die 5 and the taper angle of the taper surface 7 of the taper roller 3. It changed variously. The rotation speed of the rotary die 5 is 1.
The drawing speed of the metal tube 1 was set to 0,000 rpm and 20 m / min.

(Embodiment 2) A taper portion and an inner surface groove are processed by using a taper roller which is pressed against a metal tube and has one end portion having a radius of 5 mm to be reduced in diameter and a flat tip portion (FIG. 2B). An inner grooved tube was manufactured by the same method as in Example 1 except that the angle α formed with the outer peripheral surface of the metal tube later was 10 degrees.

(Embodiment 3) The end portion is tapered (straight) so that the angle formed by the end portion of the taper roller pressed against the metal pipe and the outer peripheral surface of the metal pipe is an angle β. Reduced diameter with a flat tip (Fig. 2
An inner grooved pipe was manufactured by the same method as in Example 1 except that the angle α between the tapered portion and the outer peripheral surface of the metal tube after the inner groove was formed was set to 10 degrees. The joint (boundary) between the end of the taper roller pressed against the metal pipe and the taper portion was chamfered with a radius of 1 mm so as not to damage the metal pipe.

FIG. 7 shows a situation in which the metal tube 1 is pressed using the taper roller 3 shown in FIG. 2D. The end 4 of the taper roller 3 at the tip of the taper surface 7 is flat,
The metal pipe 1 is pressed by this flat portion, and the pressing portion is brought into contact with the taper surface 7 to level it. The angle formed by the end portion 4 of the taper roller 3 at the tip of the tapered surface 7 and the outer peripheral surface 10 of the metal tube 1 is β.

(Comparative Example 1) Except that the angle α formed by the taper portion of the taper roller and the metal tube after the inner surface groove processing is 15 degrees,
An inner grooved tube was manufactured by the same method as in Example 1.

(Comparative Example 2) By the conventional method shown in FIG.
An inner grooved tube was manufactured by the same method as in Example 1 except that the ball was pressed against the outer peripheral surface of the metal tube at the plug insertion position.

(Comparative Example 3) By the conventional method shown in FIG.
An inner grooved tube was manufactured by the same method as in Example 1 except that the tapered surface of the tapered roller was pressed against the outer peripheral surface of the metal tube at the plug insertion position.

Regarding the obtained inner grooved tube, the surface quality,
The depth of the inner surface groove and the state of shaft deviation during manufacturing were examined. The results are shown in Table 1.

[0027]

[Table 1]

As is clear from Table 1, all the products of the present invention (Nos. 1 to 5) have deep grooves machined, good surface quality, and stable production without axial deviation during processing. Made On the other hand, in Comparative Example No. 6, since the angle α formed by the tapered surface and the outer peripheral surface of the metal tube after the inner groove was formed was as large as 15 degrees, a pressing mark remained on the surface of the metal tube. In No. 7, the groove was deeply machined because a small-diameter ball was used, but the pressing trace was clearly left on the surface of the metal tube. In No.8, the ball diameter was large, so the pressing force per cross-sectional area was insufficient and the inner groove could not be deeply machined. In No. 9, the groove processed by pressing with the taper surface of the taper roller is shallow, and the drawing speed was high, so there was a slip between the taper surface and the outer peripheral surface of the metal tube and there was a pressing mark on the metal tube surface. The remaining.

Example 4 An inner grooved pipe made of copper having an outer diameter of 7 mmφ was manufactured by the method shown in FIGS. 3 and 4. The angle α formed between the tapered surface of the taper roller and the outer peripheral surface of the metal tube after the inner groove is machined, the length L of the taper roller, and the maximum diameter D of the end pressed against the outer peripheral surface of the metal tube at the tip of the tapered surface of the taper roller. Ratio L / D, the clearance C between the taper roller and the retainer, and the angle γ between the surface of the stopper in contact with the taper roller that receives the thrust force applied to the taper roller and the central axis of rotation of the taper roller are variously changed. The other shapes of the plug and the taper roller, the number of rotations of the rotary die, the drawing speed of the metal tube, and the like were all the same as in Example 1. With respect to the obtained inner grooved tube, the surface quality, the depth of the inner groove, and the state of axial deviation during manufacture were examined. The results are shown in Table 2.

[0030]

[Table 2]

As is clear from Table 2, all the products of the present invention (Nos. 10 to 19) have deep grooves machined, have a good surface quality, and are stable in production without axial deviation during processing. Made In No. 17, the clearance C between the taper roller and the retainer was slightly large, and in Nos. 18 and 19, the angle γ between the surface of the stopper in contact with the taper roller and the rotation center axis of the taper roller was slightly outside the optimum value. As a result, in each case, a slight axial deviation occurred, and very shallow pressure marks were observed in places on the surface. On the other hand, the comparative example product No. 20
Since the angle α formed between the tapered surface and the outer peripheral surface of the metal tube after the inner groove was formed was as large as 15 degrees, a pressing mark remained on the surface of the metal tube. In Nos. 21 and 22, the shaft was shaken and a defect was generated on the surface of the metal tube.

Example 5 An inner grooved tube was manufactured by the method shown in FIG. The angle α formed between the tapered surface of the taper roller and the outer peripheral surface of the metal tube after the inner groove is formed is 10 degrees, the maximum length of the taper roller L and the maximum end portion pressed against the outer peripheral surface of the metal tube at the tip of the tapered surface of the taper roller. Ratio L / D with diameter D
1.0, the clearance C between the taper roller and the retainer
0.2, the angle γ between the surface of the stopper that contacts the taper roller and the center axis of rotation of the taper roller that receives the thrust force applied to the taper roller is 75 degrees. The shapes of the plug and the taper roller, the rotation speed of the rotary die, the drawing speed of the metal tube, and the like were all the same as in Example 1. Since the stopper that receives the thrust force applied to the taper roller and the taper roller are brought into surface contact with each other in an uneven shape, and the outer peripheral portion of the retainer that holds the taper roller is located radially outside the contact portion between the taper roller and the stopper, Shaft shake was reliably prevented and the surroundings of processing oil were improved. As a result, a deep groove (0.35 mm) inner surface grooved tube excellent in surface quality could be manufactured at a high speed (1.3 times the speed in the case of Example 4).

(Embodiment 6) FIG. 6 is a vertical cross-sectional view showing another embodiment in which the outer peripheral portion of the retainer 12 holding the taper roller 3 is positioned radially outside the contact portion between the taper roller 3 and the stopper 11. It is a side view. The entire outer peripheral portion of the retainer 12 is located radially outside the contact portion between the taper roller 3 and the stopper 11. Also in this case, the circumference of the working oil was good, and the inner grooved tube having excellent surface quality could be manufactured at high speed.

The case where a copper pipe is used as the metal pipe has been described above, but the present invention can be applied to any metal pipe such as a copper alloy pipe, aluminum or an aluminum alloy pipe to obtain the same effect.

[0035]

As described above, according to the method of the present invention, it is possible to manufacture a deep grooved inner surface grooved pipe at high speed and with high quality, and it is possible to achieve a remarkable industrial effect.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a first embodiment of the method of the present invention.

FIG. 2 is a vertical cross-sectional view showing an aspect of a taper roller used in the method of the present invention.

FIG. 3 is an explanatory diagram showing a second embodiment of the method of the present invention.

FIG. 4 is an explanatory cross-sectional view of a state in which a taper roller is arranged inside a retainer.

FIG. 5 is an explanatory view showing a third embodiment of the method of the present invention.

FIG. 6 is an explanatory diagram showing a fourth embodiment of the method of the present invention.

FIG. 7 is a vertical cross-sectional view showing a situation in which a metal tube is pressed using a taper roller in the method of the present invention.

FIG. 8 is a vertical cross-sectional view showing a situation in which a taper roller causes shaft shake.

FIG. 9 is a view showing manufacturing of a tube with an inner groove using a taper roller,
It is an explanatory view of the situation where a press mark remains on the surface of a metal tube.

FIG. 10 is a method for manufacturing an inner grooved tube using a conventional ball.

FIG. 11 is an explanatory diagram of a situation where a pressure mark remains on the surface of a metal tube in the production of an inner grooved tube using balls.

FIG. 12 is a vertical cross-sectional view of a method for manufacturing an inner grooved tube that is pressed by the taper surface of a conventional taper roller.

[Explanation of symbols]

1 Metal Tube 2 Plug 3 Tapered Roller 4 End of Tapered Roller Tip than Tapered Surface 5 Rotating Die 6 Tapered Inner Surface of Rotating Die 7 Tapered Surface of Tapered Roller 8 Ball 9,19 Pressed Trace 10 Metal Tube after Inner Groove Machining Outer peripheral surface 11 Stopper 12 Retainer 13 Tapered roller support part of retainer 14 Outer peripheral part of retainer stopper side 15 Contact part between taper roller and stopper C Clearance between taper roller and retainer F ₁ Direction of centrifugal force applied to taper roller during machining F ₂ Groove processing Direction of thrust force sometimes applied to taper roller

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshiaki Hashizume 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (7)

[Claims] 1. A plug having a large number of grooves provided on its peripheral surface is rotatably inserted into a metal tube, and the plug is arranged along the tapered inner peripheral surface of a rotary die on the outer peripheral surface of the plug insertion position of the metal tube. A method for manufacturing an inner grooved pipe in which a plurality of taper rollers that rotate and revolve by the rotational force of the rotary die are pressed and the metal pipe is pulled out in a predetermined direction to reduce the diameter and a groove is formed on the inner surface of the metal pipe. In the above, the tapered inner peripheral surface of the rotary die is formed so as to widen in the drawing direction, and the end portion of the tip end of the taper roller is formed into a predetermined shape so as to be pressed against the outer peripheral surface of the plug insertion position of the metal tube. A method for manufacturing an inner grooved pipe, wherein the tapered roller is arranged such that the tapered surface forms an angle of 10 degrees or less with the outer peripheral surface of the metal tube after the inner groove is processed. 2. A plug provided with a large number of grooves on its peripheral surface is rotatably inserted into a metal tube, and is arranged along the tapered inner peripheral surface of a rotary die on the outer peripheral surface at the plug insertion position of the metal tube. A method for manufacturing an inner grooved pipe in which a plurality of taper rollers that rotate and revolve by the rotational force of the rotary die are pressed and the metal pipe is pulled out in a predetermined direction to reduce the diameter and a groove is formed on the inner surface of the metal pipe. In the above, the tapered inner peripheral surface of the rotary die is formed to widen in the drawing direction, the taper rollers are held in the retainer at equal intervals, and the stopper for receiving the thrust force applied to the taper roller is arranged in the rotary die. The end portion of the tip of the metal pipe is formed into a predetermined shape and is pressed against the outer peripheral surface of the metal pipe at the plug insertion position, and the taper roller is formed into a metal pipe whose inner surface is grooved. Arranged at an angle of 10 degrees or less with the outer peripheral surface, and the ratio L / of the length L of the taper roller and the maximum diameter D of the end pressed against the outer peripheral surface of the metal pipe at the tip of the taper surface of the taper roller. A method for manufacturing an inner grooved tube, wherein D is 0.5 or more and 3 or less. 3. The method of manufacturing an inner grooved tube according to claim 2, wherein the taper roller is held in the retainer such that the clearance between the taper roller and the retainer is 0.2 mm or less. 4. The angle between the surface of the stopper, which is in contact with the taper roller, which receives the thrust force applied to the taper roller, and the central axis of rotation of the taper roller is 60 to 85 degrees. Inner grooved tube manufacturing method. 5. The method for manufacturing an inner grooved tube according to claim 2, wherein the taper roller support portion of the retainer holding the taper roller is formed so as to widen in the drawing direction. 6. The method for manufacturing an inner grooved tube according to claim 2, wherein the stopper that receives the thrust force applied to the taper roller and the taper roller are in surface contact with each other in an uneven shape. 7. The method of manufacturing an inner grooved pipe according to claim 2, wherein the outer peripheral portion of the retainer holding the taper roller is located radially outside the contact portion of the taper roller and the stopper. .