WO2014157168A1 - Metal tube-twisting method and device - Google Patents

Abstract

In the metal tube-twisting method of an embodiment, when a metal tube (5) is conveyed by a depression-forming roll set (4a), a standard roll set (4b), and a twisting roll set (4c) in said order, the metal tube (5) is twisted by: pressing the metal tube (5), which has a substantially circular cross-section, toward the tube interior using the depression-forming roll set (5a) to form depressions (53); bringing the standard roll set (4b) into contact with the metal tube (5) from specified directions; and providing the twisting roll set rotated in the tube circumferential direction from the contact surfaces of the standard roll set (4b) according to the desired twisting angle with respect to the pitch from the standard roll set (4b) in the tube axis direction, and pressing the metal tube (5).

Description

Method and apparatus for twisting metal pipe

TECHNICAL FIELD The present invention relates to a method and apparatus for twisting a metal pipe that twists the metal pipe in the outer circumferential direction of the pipe, and relates to a method and apparatus for twisting a metal pipe that are suitable for accurately and stably twisting a metal pipe.

Conventionally, a metal pipe having a polygonal cross section and twisted in the pipe outer peripheral direction around the pipe axis direction has been proposed. Such a twisted metal tube is expected to be applied to various applications such as vertical bars and piles of handrails, decorative members, and shock absorbing members.

In order to actually twist the metal pipe having such a polygonal cross section in the pipe outer peripheral direction, for example, as shown in FIG. 25A, the metal pipe 7 having a quadrangular cross section composed of a plane portion 71 and a corner portion 72 is used. Four rolls 74 are arranged around the center. For example, the roll 74 is disposed at an angle such that the contact surface of the roll 74 and the flat portion 71 can be in surface contact with each other in parallel. Further, the contact position of the flat surface portion 71 with respect to the contact surface of the roll 74 is a portion of the flat surface portion 71 that is extremely close to the corner portion 72.

A plurality of such roll pairs composed of four rolls 74 are provided in the tube axis direction. And about a mutual roll pair, the arrangement | positioning angle is shifted and arrange | positioned toward the pipe | tube outer peripheral direction centering | focusing on the pipe-axis direction. And the rotational force for conveying the metal pipe 7 to a pipe-axis direction is provided about at least one of the four rolls 74 in each roll pair, and this is driven. As a result, an external force in the direction of the arrow in the drawing is applied to the metal tube 7 and a clockwise torque is generated, which causes torsional deformation in the tube outer peripheral direction.

By the way, when paying attention to one flat surface portion 71a, this flat surface portion 71a can be considered as a model of a beam with one end fixed. The external force P actually applied to the flat surface portion 71a from the outside via the roll 74 is in the same direction as the extending direction of the flat surface portion 71a, as shown in FIG. As a result, when the external force applied to the flat portion 71 exceeds the buckling load (= Pcr), the flat portion 71 is buckled. This buckling load Pcr depends on the material strength and material, the length and thickness of the flat portion 71, and also the curvature at the corner portion 72, but until the flat portion 71 exceeds Pcr and starts buckling. A considerable external force P must be applied.

And once buckling generate | occur | produces about this plane part 71, the plane part 71 begins to incline with respect to the load direction of the external force P, As a result, as shown in FIG.25 (c), plane part 71 itself has become. Crushing and deepening buckling. Further, as the buckling progresses and the difference in the inclination angle with respect to the load direction of the external force P of the flat surface portion 71 increases, the bending moment based on the external force P applied to the flat surface portion 71 further increases, and as a result, the buckling progresses rapidly. Will be. By repeating this, the flat surface portion 71 is rapidly bent, irregularly twisted and crushed, and eventually remains in the form of damage. In particular, since the metal tube 7 may be twisted and applied as a decorative member, it is necessary to prevent the flat portion 71 from being crushed irregularly by buckling as much as possible.

As a conventional method for twisting a metal tube, for example, as disclosed in Patent Document 1, rolls are arranged radially, and a starting material is fed into this to perform twisting.

However, in the technique disclosed in Patent Document 1, if the torsion angle is excessively increased, the inclination of the planar portion 71 with respect to the load direction of the external force P increases and buckling occurs. For this reason, it is difficult for the disclosed technique of Patent Document 1 to perform a twisting process with a large torsion angle, and in order to twist without causing buckling, it is at best to set a torsion angle of 25 ° at most. there were.

Further, according to the disclosed technique of Patent Document 2, a round pipe is passed in advance in a metal pipe (square pipe), and twisting is performed in this state. In the twisting process, the inner diameter of the square pipe is reduced. When the square pipe hits the round pipe in the square pipe, no further twisting occurs, and the pitch of the twist can be made uniform. According to this method, it is possible to prevent the above-described buckling of the flat portion 71.

Japanese Patent Laid-Open No. 61-259838 Japanese Patent Laid-Open No. 7-80556

However, in the disclosure techniques of Patent Documents 1 and 2 described above, only the case of processing a metal tube having a substantially polygonal cross section is mentioned. As shown in FIG. 26, in the metal tube having a substantially polygonal cross section, the corner portion 72 is difficult to deform because work hardening due to plastic deformation has already occurred, whereas the plane portion 71 is still plastic. Since no deformation has occurred and work hardening has not occurred, it is easily deformed as shown in FIG.

In other words, the metal tube having a substantially polygonal cross section has a mixture of work-hardened and non-work-hardened parts, so it is going to be deformed by applying external stress to this. However, it is not possible to easily deform such 72 work-cured corner portions. For this reason, there is a problem that the flat portion 71 may be deformed in reverse although it is not intended to be deformed, and a desired twisting process cannot be easily realized.

Further, there is a demand for a technique that can easily twist a cross-section having a special shape such as a shuriken cross-section or a triangular or rhombus cross-section. However, the conventional method of processing a metal tube having a substantially polygonal cross section has a problem that it cannot meet such a demand.

Also, generally, when this torsional stress is applied, torsional deformation forms a starting recess that becomes the starting point of torsional deformation formed in the metal tube, and gradually twists from the recess toward the tube axis. Will progress.

However, in the technique disclosed in Patent Document 2 described above, since the round pipe is merely loosely fitted into the square pipe and twisted, the above-described starting recess is irregularly generated. Then, if the position of the starting recess of the torsional deformation formed first is irregular, the torsional deformation starting from this becomes irregular, and the desired uniform torsional shape is obtained. The problem that it is hard to form arises. Further, particularly in recent years, there is a social request to freely control the twist shape (torsion angle and pitch) according to the user's preference. However, in the disclosed technique of Patent Document 2, the request described above meets the request. I couldn't respond.

Accordingly, the present invention has been devised in view of the above-described problems, and the object of the present invention is to easily realize a desired twisting process and to realize a twisting process having a special cross-sectional shape. An object of the present invention is to provide a method and apparatus for twisting a metal tube.

In addition, the object of the present invention according to another aspect is to twist a metal tube that enables a uniform torsional shape to be processed accurately and stably, and the torsional shape can be freely controlled according to user's preference. It is to provide a method.

In order to solve the above-mentioned problems, the present inventor easily realizes a desired twisting process by forming a concave part that is plastically deformed by pressing the metal tube toward the inside of the pipe, and then performing a twisting process. Invented a method and apparatus for twisting a metal tube, which can also be twisted with a special cross-sectional shape.

A torsion processing method for a metal tube according to an embodiment of the present invention is a torsion processing method for a metal tube that is torsionally processed around the tube axis direction in the tube outer peripheral direction, and the metal tube having a substantially circular cross section is disposed inside the tube. A concave portion which is plastically deformed by pressing toward it is formed and then twisted.

The twisting device for a metal pipe according to an embodiment of the present invention is a twisting device for a metal tube that twists the tube in the outer peripheral direction around the tube axis direction, and for forming a recess for conveying the metal tube. A roll pair, a reference roll pair, and a twisting roll pair are provided in this order. The recess-forming roll pair forms a recess that is plastically deformed by pressing the metal tube toward the inside of the tube. The reference roll pair is brought into contact with the metal tube from a predetermined direction. The twisting roll pair is provided by rotating from the contact surface of the reference roll pair toward the outer periphery of the pipe according to a desired twist angle with respect to the pitch in the pipe axis direction from the reference roll pair, and the metal pipe Press. The metal tube twisting apparatus according to one embodiment is characterized in that the metal tube is twisted in this manner.

Further, in order to solve the above-described problems, the inventor forms a plurality of concave portions in which the metal tube is plastically deformed on the inner side of the tube, and then inserts the core into the metal tube, so that the tube axis direction It was found that a uniform torsional shape can be machined accurately and stably by twisting in the outer circumferential direction of the tube centering on.

In the method for twisting a metal tube according to one embodiment of the present invention, a plurality of recesses plastically deformed by pressing the metal tube toward the inside of the tube are formed in the pipe circumferential direction, and the inside of the metal tube in which the recesses are formed The core is inserted into the metal pipe, and the metal pipe into which the core is inserted is twisted in the pipe outer peripheral direction around the pipe axis direction.

At this time, when the metal tube having a substantially square cross section composed of a plane portion and a corner portion is conveyed in the order of the recess forming roll pair, the reference roll pair, and the twisting roll pair, the recess forming roll pair performs the above operation. Pressing each flat surface portion in the metal tube toward the inside of the tube to form the concave portion, with respect to the right end or the left end of each flat surface portion, the reference roll pair abuts from a direction substantially perpendicular to the plane, According to a desired twist angle with respect to the pitch in the tube axis direction from the reference roll pair, the metal pipe is rotated by the twisting roll pair provided by rotating from the contact surface of the reference roll pair in the tube outer peripheral direction. The right end or the left end of each of the flat surface portions may be pressed to perform the twist processing.

In the twisting method for a metal tube according to an embodiment of the present invention, a plurality of recesses that are plastically deformed by pressing a metal tube through which a core is inserted in advance toward the inside of the tube are formed in the tube circumferential direction. The metal tube is twisted in the outer circumferential direction around the tube axis direction.

According to one aspect of the present invention having the above-described configuration, it is possible to change the shape of the metal tube little by little, and finally it is possible to obtain a twisted shape in the torque direction for the metal tube. It becomes. In particular, in the present invention, the hardness is different due to the effect of work hardening between the flat plate portion and the corner portion, so that the metal tube is irregularly twisted and crushed, and it does not remain in the form of damage, It becomes possible to process the torsional shape accurately and stably.

Also, according to one aspect of the present invention, even if the torsion angle is large, the torsion processing can be realized more stably, and a highly accurate torsion shape can be obtained. For this reason, it becomes possible to improve the freedom degree about the twist angle which wants to twist. In addition, unlike the prior art, there is no need to insert a round pipe into the metal pipe, so that the working time can be shortened and the manufacturing efficiency can be improved.

Further, according to one aspect of the present invention, a concave portion as a plastic strain is introduced into a metal tube having a substantially circular cross section. The metal tube having a substantially circular cross section originally has uniform work hardening. Therefore, it becomes possible to press and process freely through the roll without the work hardening becoming a barrier. As a result, the twisted shape can be formed into a desired one.

Further, according to one aspect of the present invention having the above-described configuration, it is possible to accurately and stably process a uniform twisted shape. Further, according to one aspect of the present invention having the above-described configuration, the torsional shape can be freely controlled according to the user's preference.

In addition, according to one aspect of the present invention having the above-described configuration, the twist depth and width can be positioned (centered) by twisting by inserting the core, and stable torsion molding without bias is possible. It becomes.

It is a top view of the twist processing apparatus which concerns on one Embodiment of this invention. It is a front view of the twist processing apparatus which concerns on one Embodiment of this invention. In the twist processing apparatus which concerns on one Embodiment of this invention, it is a figure which shows the detailed structure from a side surface. It is a front sectional view of a roll pair for forming a recess in the twisting device according to an embodiment of the present invention. It is an enlarged plan view of the metal tube pressed by the pair of recess forming rolls. It is a front sectional view of the standard roll pair in the twist processing device concerning one embodiment of the present invention. It is a figure for demonstrating the roll pair for a twist process. (A) is a figure which shows the state before the rotation adjustment to the pipe | tube outer periphery direction of the twist pair for twist processing, (b) is a figure which shows the roll pair for twist processing in the state in which the rotation adjustment was made. is there. It is a figure which shows the example which generate | occur | produces the clockwise rotation torque about a metal pipe, and twists. It is a figure which shows the example of the cross-sectional shape of the metal tube actually twisted by the twist processing apparatus which concerns on one Embodiment of this invention. It is a figure which shows the example which starts a twist process from the end of a metal tube, and stops a twist process in the middle. It is a front view of the twist processing apparatus which concerns on one Embodiment of this invention. In the twist processing apparatus which concerns on one Embodiment of this invention, it is a figure which shows the detailed structure from a side surface. It is a front sectional view of a roll pair for forming a recess in the twisting device according to an embodiment of the present invention. It is an enlarged plan view of the metal tube pressed by the pair of recess forming rolls. It is a front sectional view of the standard roll pair in the twist processing device concerning one embodiment of the present invention. It is the figure which carried out the vector display of the external force loaded with a roll with respect to a metal pipe. It is a figure for demonstrating the roll pair for a twist process. (A) is a figure which shows the state before the rotation adjustment to the pipe | tube outer periphery direction of the twist pair for twist processing, (b) is a figure which shows the roll pair for twist processing in the state in which the rotation adjustment was made. is there. It is FIG. 1 for demonstrating the twisting operation | movement by the twisting apparatus which concerns on one Embodiment of this invention. It is sectional drawing for demonstrating the twist processing operation | movement by the twist processing apparatus which concerns on one Embodiment of this invention. It is FIG. 2 for demonstrating the twisting operation | movement by the twisting apparatus which concerns on one Embodiment of this invention. It is FIG. 3 for demonstrating the twisting operation | movement by the twisting apparatus which concerns on one Embodiment of this invention. It is a figure which shows the example which actually twists about the metal pipe of a cross section substantially circular. It is a figure for demonstrating the problem of a prior art. It is a figure for demonstrating the twist process of a cross-section substantially polygonal-shaped metal tube.

[First Embodiment]
Hereinafter, as an embodiment of the present invention, a metal tube torsion processing apparatus for twisting a metal tube in the tube outer peripheral direction and a metal tube torsion processing method according to the first embodiment will be described in detail with reference to the drawings. To do.

FIG. 1 is a plan view of a twist processing apparatus 1 according to an embodiment of the present invention, and FIG. 2 is a front view thereof. The twist processing apparatus 1 includes a drive motor 19, a speed reducer 18 connected to the drive motor 19, and a drive shaft 16 connected to the speed reducer 18. The twist processing apparatus 1 includes a molding machine bed 3, a stand frame 10 erected on the molding machine bed 3, and a roll pair 4 including a plurality of rolls 2 provided on the stand frame 10. ing. As shown in FIG. 1, a plurality of stand frames 10 including these roll pairs 4 are provided at intervals toward the tube axis direction of the metal tube 5.

The metal tube 5 processed by the twist processing apparatus 1 is made of, for example, iron or aluminum alloy, but may be made of any material as long as it is made of metal. The metal tube 5 has a substantially circular cross section. The cross-sectional shape of the metal tube 5 may be substantially circular. That is, the cross-sectional shape of the metal tube 5 is not limited to a complete circle, and may be a slightly distorted shape. In the following description, a case where the metal pipe 5 having a completely circular cross-sectional shape is twisted will be described as an example.

The drive motor 19 rotates the drive shaft 16 based on the supplied power. The power based on the drive shaft 16 that is rotationally driven by the drive motor 19 is transmitted to the stand frame 10 side via the speed reducer 18.

The roll 2 provided in the stand frame 10 is incorporated by a roll shaft 21 provided in the stand frame 10, and is provided to be rotatable around the roll shaft 21. A rotational driving force from the drive shaft 16 is transmitted to any one or more of the roll shafts 21. Then, by rotating the roll shaft 21 to which the rotational driving force is transmitted, the roll 2 can rotate. As a result, the metal pipe 5 to be formed can be sent out from the upstream side to the downstream side in the pipe axis direction while performing desired processing as necessary. When actually forming the metal tube 5, the metal tube 5 is inserted into a central region surrounded by the rolls 2.

Further, a reduction adjusting bolt 20 is inserted and screwed from the outer peripheral surface of the stand frame 10. The insertion position of the reduction adjusting bolt 20 corresponds to the position where the roll 2 is disposed. The tip of the reduction adjustment bolt 20 can be brought into contact with the roll 2. By tightening the reduction adjustment bolt 20, it is possible to adjust the position by pushing the roll 2 inward, and it is also possible to adjust the amount of pressing against the metal tube 5.

FIG. 3 is a diagram showing a detailed configuration from the side in the twisting apparatus 1 according to the present embodiment. In the twist processing apparatus 1, a concave forming roll pair 4a, a reference roll pair 4b, and a twist processing roll pair 4c for conveying the metal tube 5 are provided in order from the upstream side to the downstream side in the tube axis direction.

As shown in FIG. 4, the recess forming roll pair 4a presses the metal tube 5 having a substantially circular cross section from the four directions toward the inside of the tube. FIG. 5 shows an enlarged plan view of the metal tube 5. The rolls 2a-1 to 2a-4 in the recess forming roll pair 4a are pressed against the metal tube 5 having a substantially circular cross section.

At this time, the pressing positions of the rolls 2a-1 to 2a-4 against the metal tube 5 may be point-symmetric with respect to the center O of the metal tube 5 as shown in FIG. This is because the torsional external force applied in the subsequent stage is applied more evenly, and a torsional shape with consistency can be obtained. However, it is not particularly essential that the pressing position of each of the rolls 2a-1 to 2a-4 is the above-mentioned place, and any other place may be used.

The shape of the contact surface of each of the rolls 2a-1 to 2a-4 with the metal tube 5 may be provided with a curvature as shown in FIG. 5 (a), but is not limited to this. It may be a shape or may be a tapered shape.

Further, in this embodiment, by pressing the rolls 2a-1 to 2a-4 against the metal tube 5, for example, as shown in FIG. 5B, the metal tube 5 is plastically deformed toward the inside of the tube, A recess 53 is formed. That is, it is not sufficient to press the metal tube 5 within a simple elastic range, and a pressing amount is required to the extent that plastic deformation occurs and the recess 53 is formed. And the location corresponding to the recessed part 53 formed through such plastic deformation has produced work hardening, and has hardened compared with the other location. A convex portion 52 is formed between the concave portion 53 and the concave portion 53.

The depth, size, and diameter of the recess 53 formed by this plastic deformation depend on the shape of each roll 2a-1 to 2a-4 and the relative position of each roll 2a-1 to 2a-4 with respect to the metal tube 5. It is also possible to adjust freely by controlling the position.

FIG. 5 (b) shows an example in which the pressing depth by the rolls 2a-1 to 2a-4 to the metal tube 5 having a substantially circular cross section is made shallower and the diameters of the rolls 2a-1 to 2a-4 are made smaller. .

FIG. 5C is an example in which the pressing depth of the rolls 2a-1 to 2a-4 to the metal tube 5 having a substantially circular cross section is increased and the diameters of the rolls 2a-1 to 2a-4 are increased. . A convex portion 52 is formed between the concave portion 53 and the concave portion 53.

Even if the metal tube is formed into any shape, the metal tube 5 having a substantially circular cross section is processed. The metal tube 5 having a substantially circular cross section has a uniform work hardening as compared with an angular cross section. For this reason, the metal tube 5 can be deformed into an arbitrary shape by applying a stress from the outside toward the metal tube 5 having a substantially circular cross section.

If the metal tube 5 having an angular cross section has the same pressing depth and roll shape by the rolls 2a-1 to 2a-4 as shown in FIG. 5C, the metal tube 5 having an angular cross section is shown in FIG. Since the corner portion 72 has already been work-hardened as shown in FIG. 3, the corner portion 72 remains as it is without being crushed by deformation. That is, the work hardening of the corner 72 prevents the deformation into a desired shape.

In contrast, according to the present embodiment, the metal tube 5 having a substantially circular cross section is pressed by the roll 2a, so that it can be formed into a desired shape.

In particular, in the form shown in FIG. 5C, when the thickness of the metal tube is t, the thickness can be reduced to 2t. As a result, when the torsional stress in the subsequent stage is applied to the metal tube, the metal tube can be easily torsionally deformed.

The metal tube 5 in which the recess 53 is formed in this way is conveyed from the upstream side to the downstream side in the tube axis direction and reaches the reference roll pair 4b.

FIG. 6 is a configuration diagram of the reference roll pair 4b. In FIG. 6 which shows this reference | standard roll pair 4b, about the same component and member as FIG. 2 mentioned above, the description below is abbreviate | omitted by attaching | subjecting the same code | symbol.

The reference roll pair 4 b includes a drive motor 19, a speed reducer 18 connected to the drive motor 19, and a drive shaft 16 connected to the speed reducer 18. Further, a roll shaft 21 to which power from the drive shaft 16 is transmitted, and the rolls 2b-1 to 2b-4 in the reference roll pair 4b connected to the roll shaft 21 are provided in the stand frame 10. . The stand frame 10 is further provided with a reduction adjusting bolt 20 that can push the roll 2 inward.

The rotational driving force from the drive motor 19 is transmitted to the rolls 2b-1, 2b-3 in the reference roll pair 4b, and the rolls 2b-1, 2b-3 can rotate to transport the metal tube 5. Become. Incidentally, the rotational driving force from the drive motor 19 is sufficient for conveying the metal tube 5 as long as it is provided at least in the recess forming roll pair 4a in FIG. 3 described above. May not be particularly arranged.

As shown in FIG. 6, with respect to the periphery of the recess 53 of the metal tube 5, for example, the periphery of the protrusion 52 formed between the recess 53 and the recess 53, each roll 2b-1 to 2b- 4 is brought into contact. The contact direction is not particularly determined, but once determined, the contact direction is fixed without being changed, and therefore, the contact direction comes from a predetermined direction. The contact position may be the recess 53 or may be near the recess 53.

It should be noted that the external force applied by the reference roll pair 4b is a small external force that can be accommodated in the elastic deformation region. That is, the reference roll pair 4b only needs to have a pressing force enough to support the metal tube 5.

Thus, the metal pipe 5 supported by the rolls 2b-1 to 2b-4 is conveyed from the upstream side to the downstream side in the pipe axis direction, and reaches the twisting roll pair 4c.

As shown in the side view of FIG. 3 and FIG. 7, the rolls 2c-1 to 2c-4 constituting the twisting roll pair 4c are provided so as to be rotated and adjusted in the pipe outer peripheral direction in accordance with a desired twist angle θ. It has been. The turntable 9 and a fixing plate 11 for fixing the turntable 9 are provided on a pedestal 17. The turntable 9 has a gear 9a formed on a part of the outer periphery thereof, and a rotation control unit 13 configured to be able to rotate the gear 9a in the outer peripheral direction. Further, the fixed plate 11 is provided with a lock mechanism 12 for fixing the rotational position of the rotating disk 9. The rolls 2c-1 to 2c-4 are brought into contact with the periphery of the concave portion 53 of the metal tube 5, for example, the convex portion 52 formed between the concave portion 53 and the concave portion 53 in the twisting direction.

The fixing plate 11 is erected on the pedestal 17 and is provided with a hole 14 through which the metal pipe 5 is inserted. A locking mechanism 12 is attached to the fixed plate 11.

As shown in FIG. 3, the lock mechanism 12 may be configured in any shape capable of gripping the turntable 9. The gripping of the turntable 9 by the lock mechanism 12 may be realized through tightening of the screws 15.

The rotation control unit 13 is provided with a concavo-convex portion 13 a that can be fitted to a gear 9 a formed on the outer periphery of the rotating disc 9. By rotating the rotation control unit 13, it is possible to control the turntable 9 to be rotatable in the outer peripheral direction via a gear 9 a fitted to the rotation control unit 13.

FIG. 8A shows a state before the rotation adjustment of the twisting roll pair 4c in the pipe outer peripheral direction. Incidentally, the configuration of the gear 9a is omitted in FIG. The twist angle θ is set with reference to the reference line A in the rolls 2c-1 to 2c-4 before the rotation adjustment. The twist angle θ is adjusted based on a desired twist angle with respect to the distance (pitch length) between the reference roll pair 4b and the twist processing roll pair 4c. Then, the rotation is adjusted by rotating the turntable 9 constituting the twisting roll pair 4c in the pipe outer peripheral direction over the twist angle θ. FIG. 8B shows the twisting roll pair 4c in a state where the rotation is adjusted. FIG. 8B shows a state in which the turntable 9 is rotated from the reference line A in the tube outer peripheral direction (twisting direction) just by the twist angle θ.

By passing the metal tube 5 through the twisting roll pair 4c adjusted for rotation in this way, external force is applied to the metal tube 5 from the rolls 2c-1 to 2c-4. As a result, an external force having a vector direction as shown in FIGS. 9A and 9B is applied, and a counterclockwise torque is generated in the metal tube 5. At this time, the recess 53 has undergone plastic deformation and is work-hardened. For this reason, when the external force which consists of such a vector direction is loaded, the metal pipe 5 will deform | transform as shown by the dashed-two dotted line in a figure.

That is, according to the present embodiment, the concave portion 53 as a plastic strain is introduced into the metal tube 5 having a substantially circular cross section. The metal tube 5 having a substantially circular cross section originally has a uniform work hardening. Since it has arisen, it becomes possible to press-process freely through the roll 2a, without the work hardening becoming a barrier. As a result, since the metal tube 5 processed into a desired shape is conveyed to the roll 2c, the twisted shape can be obtained by pressing the metal tube 5. It becomes possible to mold into.

FIG. 10 shows an example of a cross-sectional shape of the metal tube 5 actually twisted by the twisting apparatus 1 according to the present embodiment. FIG. 10A shows a metal tube 5 processed into a diamond shape in cross section. FIG. 10B shows the metal tube 5 processed into a triangular cross section. FIG. 10C shows a metal tube 5 whose cross section is processed into a so-called shuriken shape. However, the cross-sectional shape of the metal tube 5 is not limited to these, and twisting with various cross-sectional shapes can be performed.

Particularly, according to the present embodiment, even if the torsion angle is large, it is possible to realize a more stable torsion process and to obtain a highly accurate torsion shape. For this reason, it becomes possible to improve the freedom degree about the twist angle which wants to twist.

The twisting roll pair 4c may be provided not only in one stage but also in a plurality of stages from upstream to downstream in the tube axis direction. In such a case, adjustment is made so that the torsion angle θ from the reference line A increases as it goes downstream so that it can be finished with the same torsion angle shape.

Incidentally, the distance between the reference roll pair 4b and the twisting roll pair 4c may be as small as possible. This is because, as these intervals are smaller, the elastic deformation can be made smaller, and the twisting process can be effectively realized by increasing the amount of plastic deformation.

The embodiment described above is not limited to the case where the recesses 53 are formed at four locations from four directions, but can be embodied in any configuration as long as the recesses 53 are provided at two or more locations in two or more directions. It may be done. In such a case, the number, position, and direction of each roll pair 4a to 4c are adjusted according to the direction and the location of the recess.

In the above-described embodiment, the case of twisting in the counterclockwise direction is described as an example. However, the present invention is not limited to this, and the case of twisting in the clockwise direction can be realized based on the same method. .

Further, the present embodiment is not limited to the case where all of the one metal tube 5 as described above is twisted from one end to the other end. For example, as shown in FIG. 11, the twisting process may be started from one end (end part 5a) of the metal tube 5, and the twisting process may be stopped halfway. As a result, the other end 5b of the metal tube 5 is left in the original circular cross section without any twisting process. Thereby, it becomes possible to join between other metal pipes 5 'having a circular cross section through the other end 5b of the metal pipe 5. In particular, when the metal tubes 5 are joined together, it is desirable that the cross-sectional shapes of the metal tubes 5 coincide with each other. Therefore, by setting the other end 5b of the metal tube 5 to a circular shape as it is, the advantage can be obtained. It becomes possible to demonstrate.

Note that it is not essential to use the twisting apparatus 1 described above in order to realize the twisting method according to the present embodiment. That is, it is not essential to convey the metal pipe 5 from the upstream side to the downstream side by the concave portion forming roll pair 4a, the reference roll pair 4b, and the twisting roll pair 4c. Any method can be used in the same way as long as the metal tube 5 is pressed toward the inside of the tube to form a concave portion that is plastically deformed and then twisted.

In the present embodiment, the recess forming roll pair 4a, the reference roll pair 4b, and the twisting roll pair 4c are each configured in one stage, but the present invention is not limited to this, and each of the plurality of stages is not limited thereto. It may be configured and gradually processed.

Further, in the twisting apparatus 1, the concave forming roll pair 4a may be omitted, and only the reference roll pair 4b and the twisting roll pair 4c may be configured. Even in such a case, since it is assumed that the recess 53 is always formed before being inserted into the reference roll pair 4b, the recess 53 is formed by pressing the metal tube 5 inward by some means in advance. Of course, it is necessary to keep it.

Furthermore, in the twisting apparatus 1, the reference roll pair 4b may be omitted, and only the recess forming roll pair 4a and the twisting roll pair 4c may be configured. This is because, even if the reference roll pair 4b does not exist, the reference position alignment by the reference roll pair 4b can be realized through the recess forming roll pair 4a. Of course, the above-described effects can be obtained even in such a case.

[Second Embodiment]
A method for twisting a metal pipe according to the second embodiment of the present invention will be described with reference to FIGS. The method for twisting a metal tube according to the present embodiment is different from the method for twisting a metal tube according to the first embodiment in that a core is mainly inserted into the metal tube. The twisting apparatus 1 used in the method for twisting a metal pipe according to the present embodiment is the same as the twisting apparatus 1 used in the method for twisting a metal pipe according to the first embodiment. As shown in FIG. 12A, in the metal tube twisting method according to the present embodiment, a core 41 is inserted into the metal tube 5.

The metal tube 5 processed by the twisting apparatus 1 is made of, for example, iron or aluminum alloy, but may be made of any material as long as it is made of metal. Moreover, the metal tube 5 may be comprised by the cross-sectional polygonal shape, for example, is comprised by the cross-sectional regular polygon. In the following example: A description will be given by taking the metal tube 5 having a regular square cross section as an example.

The metal tube 5 having a quadrangular cross section includes a form in which corners 54 are rounded as shown in FIG. 12B, for example. In such a case, the flat portion 51 formed between the corner portions 54 is not limited to a complete flat surface, and includes one having a certain degree of curvature. In other words, the metal tube 5 is not limited to a polygon having a cross section in a complete geometric sense, but is a substantially regular polygon in which the corner portion 54 and the plane portion 51 have a certain degree of curvature. May be.

Further, the metal tube 5 is not limited to a square shape in cross section, and may have a circular cross section or an irregular cross sectional shape.

The core 41 is composed of, for example, a metal pipe. The core 41 preferably has a substantially circular outer periphery in cross section, but is not limited thereto, and may have any cross sectional shape. The core 41 may have any diameter as long as it can be inserted into the inside of the metal tube 5, and has an outer diameter that is loosely fitted to the inner diameter of the metal tube 5. May be.

FIG. 13 is a diagram showing a detailed configuration from the side in the twisting apparatus 1 according to the present embodiment. In the twist processing apparatus 1, a concave forming roll pair 4a, a reference roll pair 4b, and a twist processing roll pair 4c for conveying the metal tube 5 are provided in order from the upstream side to the downstream side in the tube axis direction. Further, the above-described core 41 is inserted into the metal tube 5.

As shown in FIG. 14, the recess-forming roll pair 4a presses the metal tube 5 having a square cross section from the four directions toward the inside of the tube. FIG. 15 shows an enlarged plan view of the metal tube 5. The rolls 2a-1 to 2a-4 in the recess forming roll pair 4a are pressed against the flat portions 51 in the metal tube 5 having a square cross section composed of the flat portions 51 and the corner portions 54. Each of the rolls 2a-1 to 2a-4 is provided according to the number of surfaces of the flat portion 51. In the metal tube 5 having a quadrangular cross section, the pressing directions are four directions with respect to each surface.

At this time, the pressing position of each of the rolls 2a-1 to 2a-4 with respect to the flat surface portion 51 may be exactly the center of the cross section of the flat surface portion 51 as shown in FIG. This is because the torsional external force applied in the subsequent stage is applied more evenly, and a torsional shape with consistency can be obtained. However, it is not particularly essential that the pressing position of each of the rolls 2a-1 to 2a-4 is set at the center of the cross section of the plane portion 51, and any other location may be used.

The shape of the abutting surface of each of the rolls 2a-1 to 2a-4 with respect to the flat surface portion 51 may be provided with a curvature as shown in FIG. 14, but is not limited to this and is a flat shape. It may also be a tapered shape.

Further, in the present embodiment, by pressing the rolls 2a-1 to 2a-4 against the flat portion 51, for example, as shown in FIG. 15B, the flat portion 51 is plastically deformed toward the inside of the tube, A recess 53 is formed. That is, it is not sufficient to press the flat portion 51 to such an extent that the flat portion 51 can be accommodated in a simple elastic region, and a pressing amount is required to the extent that plastic deformation occurs and the concave portion 53 is formed. And the location corresponding to the recessed part 53 formed through such plastic deformation has produced work hardening, and has hardened compared with the other location.

In addition, in the stage where this recessed part 53 was formed, the core 41 and the recessed part 53 may be mutually spaced apart as shown in FIG.15 (b), and may mutually contact. In the following example, a case where the core 41 and the recess 53 are separated will be described as an example.

As shown in FIG. 15B, the metal tube 5 having the recess 53 formed in the flat portion 51 is conveyed from the upstream side to the downstream side in the tube axis direction and reaches the reference roll pair 4b. To do.

FIG. 16 is a configuration diagram of the reference roll pair 4b. Since the configuration of the reference roll pair 4b is the same as the configuration of the reference roll pair 4b described in the first embodiment, detailed description thereof is omitted.

As shown in FIG. 16, each roll 2b-1 to 2b- in the reference roll pair 4b from the direction substantially perpendicular to the plane of the left end when viewed to the center of the metal tube in each plane 51 of the metal tube 5 is shown. 4 is brought into contact. This abutting position may be extremely close to the corner portion 54 at the left end of the plane portion 51. Further, the contact position of each roll 2b-1 to 2b-4 to the metal tube 5 may be the right end when viewed from the center of the metal tube of each flat portion 51. Even in such a case, the contact position needs to be the right end of all the plane portions 51, not the right end of one plane portion 51. Each of the rolls 2b-1 to 2b-4 is provided according to the number of surfaces of the flat portion 51.

FIG. 17 is a vector display of the external force applied to the metal tube 5 by the rolls 2b-1 to 2b-4. As long as the vector direction of the external force applied to the metal tube 5 by the rolls 2b-1 to 2b-4 can support each flat surface portion 51, the flat surface portion before formation of the concave portion 53 indicated by the dotted line is shown. 51 may be inclined.

It should be noted that the external force applied by the reference roll pair 4b is a small external force that can be accommodated in the elastic deformation region. That is, the reference roll pair 4b may simply have a pressing force that can support the flat portions 51 of the metal tube 5.

The metal pipe 5 in which the flat portion 51 is supported by the rolls 2b-1 to 2b-4 in this way is conveyed from the upstream side to the downstream side in the pipe axis direction, and reaches the twisting roll pair 4c. It will be. As shown in FIGS. 13 and 18, the configuration of the twisting roll pair 4c is the same as the configuration of the twisting roll pair 4c described in the first embodiment, and a detailed description thereof will be omitted.

FIG. 19 (a) shows a state before the rotation adjustment of the twisting roll pair 4c in the pipe outer peripheral direction. Incidentally, the configuration of the gear 9a is omitted in FIG. The twist angle θ is set with reference to the reference line A in the rolls 2c-1 to 2c-4 before the rotation adjustment. The twist angle θ is adjusted based on a desired twist angle with respect to the distance (pitch length) between the reference roll pair 4b and the twist processing roll pair 4c. Then, the rotation is adjusted by rotating the turntable 9 constituting the twisting roll pair 4c in the pipe outer peripheral direction over the twist angle θ. FIG. 9B shows the twisting roll pair 4c in a state where the rotation is adjusted. FIG. 9B shows a state in which the turntable 9 is rotated from the reference line A by the torsion angle θ in the tube outer peripheral direction.

The twisting roll pair 4c may be provided not only in one stage but also in a plurality of stages from upstream to downstream in the tube axis direction. In such a case, adjustment is made so that the torsion angle θ from the reference line A increases as it goes downstream so that it can be finished with the same torsion angle shape.

Incidentally, the distance between the reference roll pair 4b and the twisting roll pair 4c may be as small as possible. This is because, as these intervals are smaller, the elastic deformation can be made smaller, and the twisting process can be effectively realized by increasing the amount of plastic deformation.

The actual processing method by the twist processing apparatus 1 having the above-described configuration will be described.

As shown in FIG. 20, first, at a time t1 before twisting, a core 53 is inserted after a recess 53 as plastic strain is formed in the end 5a of the metal tube 5 in advance. As a result, as shown in FIG. 21, when the cross sections P, Q, and R are sequentially viewed from the end portion 5a of the metal pipe 5 toward the tube axis direction C, any cross section P, Q, R is obtained at time t1. In this case, the recess 53 and the core 41 are slightly separated from each other. In the following description, for the sake of simplicity, it is assumed that the recesses 53 as pre-strains are formed for all of the cross sections P, Q, and R. However, the recesses become closer to the cross section R located further downstream. It is possible that 53 is not formed.

Next, the metal tube 5 is transported from the upstream side to the downstream side through the twisting device 1 in the tube axis direction C. As a result, torsional stress is applied to the metal tube 5 toward the torque direction T shown in FIG. 20 by the twisting roll pair 4c. The time at this stage is t2.

FIG. 22 shows a torsional deformation state of the metal tube 5 at time t2. As shown in FIG. 21, as a result of the torsional deformation from the end 5a side of the metal tube 5 toward the torque direction T, the recess 53 in the cross section P tends to be further deformed inward at time t2. However, in the process of deforming inward, since the core 41 is disposed in the pipe, the force that the concave portion 53 tries to deform further inward is suppressed. That is, when torsional stress is applied, the concave portion 53 in the cross section P is deformed inward and comes into contact with the core 41. However, this metal core 41 can resist the force to be deformed to the inside of the recess 53, and the deformation to the inside of the recess 53 itself is suppressed. In the cross section P, the depth of all the recesses 53 is made uniform by the core 41.

As a result of conveying the metal tube 5 further in the tube axis direction C from the time t2 and applying a torsional stress in the torque direction T by the twisting roll pair 4c, Due to the presence of the child 41, the inward deformation of the recess 53 is restrained. However, the stress based on the torsional stress described above propagates in the tube axis direction C where the inward deformation is not constrained. Specifically, the stress based on the torsional stress described above propagates in the direction of the arrow starting from the recess 53 shown in FIG.

The section Q is in a state where the deformation is not constrained by the core 41 since it has not yet been deformed inward at the time of the initial t1. For this reason, when such stress in the direction of the arrow is applied, the flat portion 51 in the cross section Q is easily deformed inward. As a result of applying stress in the direction of the arrow at the stage of time t2, the plane portion in the cross section Q is deformed inward as shown in FIG. 21, and a new recess 53 is formed. Become. That is, as a result of suppressing the inward deformation due to the presence of the core 41 as in the cross section P, energy based on the torsional stress is spent on plastic deformation of the cross section P shifted in the tube axis direction C side.

FIG. 23 shows a torsional deformation state of the metal tube 5 at time t3. As shown in FIG. 21, as a result of torsional deformation from the end 5a side of the metal tube 5 toward the torque direction T, not only the cross section P but also the concave portion 53 of the cross section Q is further deformed inward. In the process of deforming inward, the recess 53 in the cross section Q is deformed inward and comes into contact with the core 41. In such a case as well, it becomes possible for the core 41 to counteract the force to be deformed inwardly with respect to the concave portion 53 of the cross section Q. It becomes. In the cross section Q, the depth of all the recesses 53 is made uniform by the core 41.

Incidentally, the cross-section R is not deformed inward by the core 41 since it has not yet deformed inward at the time t2. For this reason, when a torsional stress is applied, the flat portion 51 in the cross section R is in a state where it is easily deformed inward. Then, at the stage of time t3, as a result of applying a stress in the direction of the arrow in the drawing, the plane portion in the cross section R is deformed inward as shown in FIG. 21, and a new recess 53 is formed. It will be. That is, as a result of suppressing the inward deformation due to the presence of the core 41 like the cross section Q, the energy based on the torsional stress is spent on the plastic deformation of the cross section Q shifted in the tube axis direction C side. As a result, it becomes possible to advance the inward deformation along the direction corresponding to the torsion angle.

繰 り 返 し By repeating such an action, the torsional deformation is gradually applied toward the tube axis direction C. Then, this torsional deformation starts from the recess 53 provided in the end portion 5a in the tube axis direction C in advance and gradually moves the metal tube 5 inward along the direction corresponding to the torsion angle by the torsion processing. Deform. Then, by gradually developing the recess 53 in the tube axis direction C, it is possible to form a single twisted line in which the recess 53 is connected in the direction of the arrow in the figure. If a plurality of the recesses 53 are provided, a plurality of torsion lines starting from these will be formed, and a torsion pattern will be applied to the entire metal tube 5.

Incidentally, if it is desired to control this twist pattern, it can be realized by adjusting the twist angle θ in the rotary disk 9 constituting the processing roll pair 4c. As a result, the torque in the torque direction T is determined, the torsion angle by twisting is also determined, and the flat portion 51 of the metal tube 5 can be gradually crushed in the direction of the arrow in the drawing to form a recess 53. It becomes. That is, the direction of the torsion line can be freely controlled.

In addition to this, the twist pattern may be controlled by controlling the position of the recess 53 formed on the metal pipe 5 from the beginning by the recess forming roll pair 4a. Since the twist line is extended from the concave portion 53 which is the starting point, a desired twist pattern can be realized by extending the twist line from the concave portion 53 whose position is controlled.

Further, according to the present embodiment, since the core 41 is inserted into the metal tube 5 to be processed, the depth of the concave portion 53 can be uniformly controlled by the core 41. As a result, the metal tube 5 can be provided with a twist pattern that is generally uniform. In addition, since the torsional stress at the time of twisting can be applied to the whole in a well-balanced manner, workability can also be improved.

The shape of the recess 53 formed by the recess forming roll pair 4a is based on the shape of the contact surface of the rolls 2a-1 to 2a-4 with the flat surface 51, but is actually formed. The torsional shape is controlled by the shape of the recess 53. Therefore, conversely, by optimizing the shape of the concave portion 53 in accordance with the target torsional shape, the final torsional shape itself can be controlled. Similarly, the depth and width of the recess 53 can be optimized according to the target twist shape.

In the second embodiment described above, the case where the metal tube 5 is a pipe having a substantially square cross section has been described as an example. However, the present invention is not limited to this, and the cross section is substantially a regular polygon other than a square. The cross section may be substantially circular.

FIG. 24A shows an example of actually twisting the metal tube 5 having a substantially circular cross section. The rolls 2a-1 to 2a-4 in the recess forming roll pair 4a are pressed against the metal tube 5 having a substantially circular cross section. As a result, the core 41 is inserted into the metal tube 5 into which the concave portion 53 as pre-strain is introduced. The subsequent process is the same as that of the above-described metal pipe 5 having a substantially square cross section. As a result, the metal tube 5 having a substantially circular cross section can be similarly twisted.

Further, the metal tube 5 is not limited to the case where the concave portion 53 is formed as a pre-strain in the end portion 5a, and may be provided at any location. Even when the concave portion 53 as the pre-strain is formed at the center in the tube axis direction C, the torsion line extends from the pre-strain concave portion 53 as a starting point.

In the second embodiment described above, the case of twisting in the counterclockwise direction has been described as an example. However, the present invention is not limited to this, and the case of twisting in the clockwise direction can be realized based on the same method. is there. In such a case, the right end of the plane portion 51 is pressed by the reference roll pair 4b, and the left end of the plane portion 51 is pressed by the processing roll pair 4c.

In the present embodiment, it is not essential to use the twisting device 1 described above. First, a plurality of concave portions 53 plastically deformed by pressing the metal tube 5 toward the inside of the tube by a known means is formed in the tube circumferential direction, and then the core 41 is inserted into the metal tube 5. Next, if the metal tube 5 through which the core 41 is inserted is simply twisted in the tube outer peripheral direction with the tube axis direction C as the center, the same effects as described above are produced. That is, this embodiment is not limited to the case of processing while conveying the metal tube 5 from the upstream side to the downstream side, and after fixing one end side of the metal tube 5, the other end side of the metal tube 5 It is possible to embody even a simple twist.

In any embodiment, the core 41 may be inserted into the metal tube 5 first, and then a plurality of recesses 53 may be formed in the tube circumferential direction. Even if it does in this way, of course, there exists an effect similar to the case where the core 41 is inserted in the metal pipe 5 after forming the recessed part 53 initially.

DESCRIPTION OF SYMBOLS 1 ... Processing apparatus, 2 ... Roll, 3 ... Forming machine bed, 4 ... Roll pair, 5 ... Metal pipe, 9 ... Rotating disk, 10 ... Stand frame, 11 ... Fixed plate, 14 ... Hole part, 16 ... Drive shaft, DESCRIPTION OF SYMBOLS 17 ... Base, 18 ... Reduction gear, 19 ... Drive motor, 20 ... Rolling-down adjustment bolt, 21 ... Roll shaft, 41 ... Core, 51 ... Planar part, 52 ... Convex part, 53 ... Concave part, 54 ... Corner part.

Claims (15)

A twisting method for a metal pipe that is twisted in the pipe outer circumferential direction around the pipe axis direction,
Forming a concave part plastically deformed by pressing the metal tube toward the inside of the tube;
A method of twisting a metal tube, wherein the twisting process is performed thereafter. The method of twisting a metal tube according to claim 1, wherein the metal tube has a substantially circular cross section. The said twisting process WHEREIN: The convex part periphery formed between the said plastically deformed recessed parts in the said metal pipe is pressed in a twist direction. The twisting method of the metal pipe of Claim 1 or 2 characterized by the above-mentioned. When transporting the metal tube in the order of the recess-forming roll pair, the reference roll pair, and the twisting roll pair,
The concave portion is formed by pressing the metal tube toward the inside of the tube with the pair of concave portion forming rolls,
The reference roll pair is brought into contact with the periphery of the convex portion formed between the concave portions of the metal tube in which the concave portion is formed, from a predetermined direction,
According to a desired twist angle with respect to the pitch in the tube axis direction from the reference roll pair, the metal pipe is rotated by the twisting roll pair provided by rotating from the contact surface of the reference roll pair in the tube outer peripheral direction. The method of twisting a metal tube according to any one of claims 1 to 3, wherein the twisting process is performed by pressing. In the twisting process, the metal pipe is transported in the order of a reference roll pair and a twisting roll pair,
The reference roll pair is brought into contact with the metal tube in which the concave portion is formed from a predetermined direction,
According to a desired twist angle with respect to the pitch in the tube axis direction from the reference roll pair, the metal pipe is rotated by the twisting roll pair provided by rotating from the contact surface of the reference roll pair in the tube outer peripheral direction. The method of twisting a metal tube according to any one of claims 1 to 3, wherein the twisting process is performed by pressing. When transporting the metal tube in the order of the recess-forming roll pair and the twisting roll pair,
The concave portion is formed by pressing the metal tube toward the inside of the tube with the pair of concave portion forming rolls,
The twisting process is performed by pressing the metal tube by the twisting roll pair provided by rotating in the outer circumferential direction of the pipe in accordance with a desired twisting angle. A method for twisting a metal tube according to one item. A twisting device for a metal pipe that twists in a pipe outer peripheral direction around a pipe axis direction,
A pair of concave forming rolls for conveying the metal tube, a reference roll pair, and a twisting roll pair are provided in this order,
The recess-forming roll pair forms a recess that is plastically deformed by pressing the metal tube toward the inside of the tube,
The reference roll pair is brought into contact with the metal tube from a predetermined direction,
The twisting roll pair is provided by rotating from the contact surface of the reference roll pair toward the outer periphery of the pipe according to a desired twist angle with respect to the pitch in the pipe axis direction from the reference roll pair, and the metal pipe A twisting device for a metal tube, wherein the metal tube is twisted by pressing the metal tube. Forming a plurality of recesses plastically deformed by pressing the metal tube toward the inside of the tube,
Insert the core through the metal tube in which the recess is formed,
The metal tube twisting method according to claim 1, wherein the metal tube through which the core is inserted is twisted in the tube outer peripheral direction centering on the tube axis direction. Forming a plurality of recesses plastically deformed by pressing a metal tube inserted through the core in advance toward the inside of the tube;
The method of twisting a metal tube according to claim 1, wherein the metal tube is twisted in the tube outer peripheral direction with the tube axis direction as a center. The method for twisting a metal pipe according to claim 8 or 9, wherein the metal pipe is plastically deformed by pressing any one end in the pipe axis direction. When transporting the metal tube having a substantially square cross section composed of a flat surface portion and a corner portion in the order of a recess forming roll pair, a reference roll pair, and a twisting roll pair,
Pressing each flat portion of the metal tube toward the inside of the tube with the pair of recess-forming rolls to form the recess,
With respect to the right end or the left end of each plane part, the reference roll pair is brought into contact from a direction substantially perpendicular to the plane,
According to a desired twist angle with respect to the pitch in the tube axis direction from the reference roll pair, the metal pipe is rotated by the twisting roll pair provided by rotating from the contact surface of the reference roll pair in the tube outer peripheral direction. The method of twisting a metal tube according to any one of claims 8 to 10, wherein the twisting is performed by pressing a right end or a left end of each of the planar portions in the above. In the twisting process, the metal tube having a substantially square cross section composed of a plane part and a corner part is conveyed in the order of a reference roll pair and a twisting roll pair,
With respect to the right end or the left end of each plane portion in the metal tube, the reference roll pair is brought into contact from a direction substantially perpendicular to the plane,
According to a desired twist angle with respect to the pitch in the tube axis direction from the reference roll pair, the metal pipe is rotated by the twisting roll pair provided by rotating from the contact surface of the reference roll pair in the tube outer peripheral direction. The method of twisting a metal tube according to any one of claims 8 to 10, wherein the twisting is performed by pressing a right end or a left end of each of the planar portions in the above. When transporting the metal tube having a substantially square cross section composed of a flat surface portion and a corner portion in the order of a recess forming roll pair and a twisting roll pair,
Pressing each flat portion of the metal tube toward the inside of the tube with the pair of recess-forming rolls to form the recess,
The twisting process is performed by pressing the right end or the left end of each flat portion of the metal pipe with the twisting roll pair provided by rotating in the pipe outer peripheral direction according to a desired twist angle. The method for twisting a metal tube according to any one of claims 8 to 10. The method of twisting a metal tube according to any one of claims 8 to 13, wherein the metal tube having any one of a substantially square shape in cross section, a substantially triangular shape in cross section, and a substantially rhombus shape in cross section is twisted. In the twisting process, first, the concave portion formed in the metal tube is deformed inward,
Next, when the concave portion is brought into contact with the core, further inward deformation of the concave portion is suppressed, and starting from the concave portion, the direction along the direction corresponding to the torsion angle by the twist processing is described above. Deform the metal tube inward,
Further, the inner side along the direction corresponding to the torsion angle is suppressed while the new concave portion formed by further inward deformation is brought into contact with the core to suppress the inner side deformation of the new concave portion. The method of twisting a metal tube according to any one of claims 8 to 14, wherein the step of repeatedly deforming the metal tube is repeatedly performed.

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