JP2015063101A - Method of producing bent tube and mandrel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a bent tube by using a mandrel capable of achieving good productivity while improving durability of a bent tube to be formed.SOLUTION: A large-diameter mandrel (40) includes a coil spring (41) capable of being inserted into the outer peripheral side of a small-diameter mandrel (30) and a plurality of segments (42) which have an axial-direction width larger than the wire diameter of the coil spring (41) and are formed annularly and arranged continuously along the central axis of the coil spring (41) on the outer peripheral side of the coil spring (41) and are separable from each other. A production method includes a step (S1) of inserting a blank tube (10) on the outer peripheral side of the bendable large-diameter mandrel (40) and a step (S3) of inserting the large-diameter mandrel (40) attached with the blank tube (10) on the outer peripheral side of the small-diameter mandrel (30) having a bent part (33b) to form a bent tube (20).

Description

  The present invention relates to a method for manufacturing a bent pipe and a mandrel used in the manufacturing method.

  Conventionally, a bent tube has been manufactured by inserting an unvulcanized material tube into the outer peripheral side of a mandrel and then vulcanizing it. However, it is not easy for the operator to insert the material tube on the outer peripheral side of the mandrel and to pull out the bent tube from the mandrel.

  Therefore, Patent Document 1 describes that a bent tube is manufactured using a mandrel different from the conventional one. The mandrel includes a mandrel of a coil spring and a rigid mandrel. That is, an unvulcanized material tube is inserted into the outer periphery of the mandrel of the coil spring, and the mandrel of the coil spring is inserted into the outer periphery of the rigid mandrel that is molded corresponding to the final formed tube to obtain a predetermined shape. Sulfur molding is described. Other mandrels are described in Patent Documents 2 and 3.

JP-A-4-182117 Japanese Patent Publication No. 7-80260 JP 2013-71143 A

  However, when the coil spring mandrel and the rigid mandrel are used as in Patent Document 1, the uneven shape of the coil spring is transferred to the inner peripheral surface of the bending pipe to be formed, and the formed bending is performed. The tube is not suitable from the viewpoint of durability. Further, after the bending tube is pulled out from the rigid mandrel, when the coil spring is pulled out from the bending tube, the coil spring is caught on the inner peripheral surface of the bending tube. If the wire diameter of the coil spring is small, the coil spring extends, so it is easy to pull out the coil spring from the bent tube while maintaining the state where the coil spring's non-pulling side end is caught on the bent tube is not.

  On the other hand, by increasing the wire diameter of the coil spring, the amount of extension of the coil spring can be regulated. However, increasing the wire diameter increases the rigidity of the coil spring and makes it difficult to bend and deform, making it difficult to insert the coil spring into the rigid mandrel. Further, it is not easy to pull out the coil spring from the bent pipe.

  The present invention has been made in view of such circumstances, and a method for manufacturing a bent pipe using a mandrel capable of improving the productivity while improving the durability of the bent pipe to be molded, and its It aims at providing the mandrel used for a manufacturing method.

<Manufacturing method of bent pipe>
The method of manufacturing a bent tube according to the present means includes a step of inserting a material tube into the outer peripheral side of a bendable large-diameter mandrel, and And a step of manufacturing a bent tube by inserting the bent tube. The large-diameter mandrel is formed in a ring shape having a coil spring that can be inserted on the outer peripheral side of the small-diameter mandrel and an axial width larger than the wire diameter of the coil spring, and a center of the coil spring on the outer peripheral side of the coil spring. And a plurality of frames arranged continuously along the axis so as to be separable from each other.

  According to this means, the large-diameter mandrel is constituted by the coil spring and the plurality of pieces. Therefore, the member that comes into contact with the inner peripheral surface of the bent pipe to be formed becomes a top, and the coil spring does not contact the inner peripheral surface of the bent pipe. Accordingly, since the coil spring does not directly contact the inner peripheral surface of the bent pipe to be formed, the inner peripheral surface of the bent pipe has a shape corresponding to the axial width of the top regardless of the wire diameter of the coil spring. . Therefore, compared with the case where a coil spring contacts the inner peripheral surface of a bending pipe directly, it contributes to the improvement of durability of a bending pipe.

  In addition, as described above, the shape of the inner peripheral surface of the bent pipe depends on the axial width of the top regardless of the wire diameter of the coil spring itself. Therefore, even if the wire diameter of the coil spring is reduced, the uneven shape of the inner peripheral surface of the bent pipe can be reduced by increasing the axial width of the frame. Furthermore, since the wire diameter of the coil spring can be reduced, the ease of bending of the coil spring is improved.

<Embodiment related to manufacturing method of bent pipe>
Preferably, at least some of the plurality of tops have a female screw surface that is fitted into the coil spring by screw fitting, and relative movement with respect to the coil spring is restricted.
Since some of the pieces have the female thread surface, the relative movement with respect to the coil spring is restricted, so that the bent pipe can be reliably formed.

  Preferably, the top having the female thread surface is disposed at a position corresponding to the bent portion of the small-diameter mandrel. Thereby, the bent portion of the bent pipe can be surely formed into a desired shape.

Preferably, another part of the plurality of pieces has a cylindrical inner peripheral surface that does not engage with the coil spring, is allowed to move relative to the coil spring, and has the female screw surface. A top is disposed at a position corresponding to both ends of the bent portion of the small-diameter mandrel, and the top having the cylindrical inner peripheral surface has the female screw surface disposed at both ends of the bent portion. Between the two frames.
Thereby, even if the piece having the female thread surface is a part, the bent portion of the bent pipe can be surely formed into a desired shape.

Preferably, the large-diameter mandrel further includes a string-like member that is locked to one end side and the other end side of the coil spring and regulates the amount of extension of the coil spring.
If the extension amount of the coil spring is not regulated, it is not easy to pull out the coil spring and the plurality of pieces from the bent pipe. Therefore, by restricting the extension amount of the coil spring, it becomes easy to pull out the coil spring and the plurality of pieces.

  Preferably, the string-like member passes a radially inner side of the coil spring in a central axis direction. Thereby, when a piece moves with respect to a coil spring, a string-like member does not regulate. Accordingly, the top can be easily moved with respect to the coil spring while restricting the extension amount of the coil spring. In addition, the piece having the female thread surface can be surely maintained in a state of being caught by the coil spring by passing the string-like member inward in the radial direction of the coil spring.

  Preferably, the plurality of pieces have an outer diameter smaller than an inner diameter of the material tube. That is, there is a gap between the outer peripheral surface of the top and the inner peripheral surface of the material tube. Even if there is a gap with the outer peripheral surface of the frame at the bent portion of the bent tube, it is possible to make the bent portion of the bent tube into a desired shape. And since the said clearance gap exists, it becomes very easy to insert a raw material tube in a large diameter mandrel.

(Mandrel)
In the above, the manufacturing method of the bending pipe using a mandrel was demonstrated. In addition, the present invention can be regarded as a mandrel used for manufacturing a bent pipe.

That is, the mandrel used for manufacturing the bent pipe according to this means is bendable, has a large-diameter mandrel capable of inserting a material tube on the outer peripheral side, and a bent portion, and can insert the large-diameter mandrel on the outer peripheral side. A small diameter mandrel. The large-diameter mandrel is formed in a ring shape having a coil spring that can be inserted on the outer peripheral side of the small-diameter mandrel and an axial width larger than the wire diameter of the coil spring, and a center of the coil spring on the outer peripheral side of the coil spring. And a plurality of frames that are arranged continuously along the axis and that can be separated from each other.
The mandrel according to this means has the same effect as the effect related to the manufacturing method described above.

It is an axial sectional view of the material tube used for the manufacturing method of the bent pipe of this embodiment. It is sectional drawing along the center axis | shaft of a bending pipe. It is the small diameter mandrel which comprises the mandrel of this embodiment. It is an axial direction sectional view of a large diameter mandrel which constitutes a mandrel of this embodiment. It is an axial sectional view of the cap which constitutes the mandrel of this embodiment. It is 3A enlarged view of FIG. 2B. It is 3B enlarged view of FIG. 2B. It is 3C enlarged view of FIG. 2B. It is a flowchart which shows the manufacturing method of a bending pipe. It is an axial sectional view showing the state of S2 of FIG. It is sectional drawing along the central axis which shows the state of S3 of FIG. It is sectional drawing along the central axis which shows the state of S5 of FIG.

(1. Description of material tube 10 and bent tube 20)
As shown in FIG. 1A, the material tube 10 is formed into a cylindrical shape made of unvulcanized rubber, for example, by extrusion molding. The cross-sectional shape in the radial direction of the material tube 10 is formed in the same shape over the entire length in the axial direction. The bent tube 20 shown in FIG. 1B is formed by bending the material tube 10. As shown in FIG. 1B, the bent pipe 20 has straight pipe parts 21 and 23 at both ends, and has a bent part 22 at the center of the straight pipe parts 21 and 23. In the present embodiment, the bent tube 20 has one bent portion 22, but may have two or more bent portions.

(2. Explanation of mandrels)
In order to manufacture the bent pipe 20, a mandrel is used. The mandrel includes a small-diameter mandrel 30 shown in FIG. 2A, a large-diameter mandrel 40 shown in FIG. 2B, and a cap 60 shown in FIG. 2C.

(2-1. Description of the small-diameter mandrel 30)
As shown in FIG. 2A, the small-diameter mandrel 30 is a shaft member that is previously formed into a desired bent shape. The small-diameter mandrel 30 is formed by plating a steel material. That is, the small-diameter mandrel 30 is formed so as to maintain a pre-shaped bending shape. The small diameter mandrel 30 includes a base portion 31, a tube end mounting portion 32, and a bend forming shaft portion 33.

  For example, the base 31 is fixed to a wall surface of a fixed facility. The tube end mounting portion 32 is a portion that is fitted into one end of the bent tube 20 and has an outer diameter that is the same as the inner diameter of one end of the bent tube 20. The bend forming shaft part 33 includes a first straight pipe part 33a, a bent part 33b, and a second straight pipe part 33c. The bend forming shaft portion 33 is formed in advance so as to correspond to the shape of the bent tube 20. The outer diameter of the bend forming shaft portion 33 is smaller than the outer diameter of the tube end mounting portion 32 and smaller than the inner diameters of the material tube 10 and the bent tube 20.

(2-2. Description of Large Diameter Mandrel 40)
The large-diameter mandrel 40 is formed in a bendable cylindrical shape, can be inserted into the outer peripheral side of the bending-molded shaft portion 33 of the small-diameter mandrel 30, and can be inserted into the material tube 10. As shown in FIGS. 2B and 3A to 3C, the large-diameter mandrel 40 includes a coil spring 41, a plurality of pieces 42, an end member 43, a string-like member 44, and a locking ring 45.

  The coil spring 41 is formed of, for example, a steel material such as stainless steel, and is formed in a shape that can be inserted into the outer peripheral side of the bending shaft portion 33 of the small-diameter mandrel 30. The coil spring 41 is formed in the same diameter over the entire axial length, and can naturally be bent. The inner diameter of the coil spring 41 is formed to be approximately the same as or slightly larger than the outer diameter of the bending shaft portion 33 of the small-diameter mandrel 30. That is, when the coil spring 41 is inserted into the outer peripheral side of the bending shaft portion 33 of the small-diameter mandrel 30, the coil spring 41 slides on the outer peripheral surface of the bending shaft portion 33. Here, since both the bend forming shaft portion 33 and the coil spring 41 of the small-diameter mandrel 30 are made of metal, the slidability is good.

  The plurality of pieces 42 are formed of a steel material such as stainless steel, for example. The plurality of pieces 42 are formed in an annular shape having an axial width larger than the wire diameter of the coil spring 41, and are continuously arranged along the central axis of the coil spring 41 on the outer peripheral side of the coil spring 41. Further, the plurality of frames 42 are provided so as to be separated from each other. The large-diameter mandrel 40 in the present embodiment includes 24 pieces 42.

  The plurality of frames 42 includes a plurality of types of frames 51, 52, 53, and 54. The outer diameters of the plurality of pieces 42 are smaller than the inner diameter of the material tube 10 and smaller than the outer diameter of the tube end mounting portion 32 of the small-diameter mandrel 30. The plurality of pieces 42 includes an end piece 51, a string locking piece 52, a plurality of cylindrical pieces 53, 53,..., And a plurality of female screw pieces 54, 54.

  As shown in FIG. 3A, the end piece 51 has an internal thread surface on the inner peripheral surface, and is fitted into one end of the coil spring 41 by screw fitting. For example, the end piece 51 is screw-fitted with 2 to 4 turns of the coil spring 41. That is, the end piece 51 is restricted from moving relative to one end of the coil spring 41.

  As shown in FIG. 3A, the string locking piece 52 is disposed next to the end piece 51, and has a through hole 52a into which both ends of the string-like member 44 are inserted. The string locking piece 52 locks the string-like member 44 by inserting both ends of the string-like member 44 into the through holes 52a. The inner peripheral surface of the string locking piece 52 is formed in a cylindrical shape and is slightly larger than the outer diameter of the coil spring 41.

  As shown in FIG. 3B, the female screw pieces 54, 54 have a female screw surface on the inner peripheral surface. As with the end piece 51, the internal thread pieces 54 and 54 are restricted from moving relative to the coil spring 41 by being fitted into the coil spring 41 by screw fitting. The female screw pieces 54, 54 are arranged at positions corresponding to the bent portions 33 b of the bending shaft portion 33 of the small-diameter mandrel 30. More specifically, the internal thread pieces 54 and 54 are disposed at positions corresponding to both end sides of the bent portion 33b.

  As shown in FIGS. 3A, 3B, and 3C, the plurality of cylindrical pieces 53, 53,... Are formed in a cylindrical shape on both the outer peripheral surface and the inner peripheral surface. The cylindrical pieces 53, 53,... Have a cylindrical inner peripheral surface that does not engage with the coil spring 41, and are allowed to move relative to the coil spring 41. The cylindrical pieces 53, 53,... Are arranged between the string locking piece 52 and one female screw piece 54 and between the two female screw pieces 54, 54, and the other female screw piece 54. To the other end side.

  The end member 43 is disposed on the other end side of the plurality of pieces 42 and includes a cylindrical inner peripheral portion 43a and a cylindrical outer peripheral portion 43b. The outer peripheral surface of the inner peripheral portion 43 a of the end member 43 is formed in the same shape as the tube end mounting portion 32 of the small diameter mandrel 30. That is, the outer peripheral surface of the inner peripheral portion 43 a of the end member 43 is a portion that fits into one end of the material tube 10 and the bent tube 20, and has an outer diameter comparable to the inner diameter of one end of the material tube 10 and the bent tube 20. Have. A female screw surface is formed on the inner peripheral surface of the inner peripheral portion 43 a of the end member 43 in the same manner as the female screw piece 54. The end member 43 is fitted into the other end of the coil spring 41 by screw fitting.

  Further, the outer peripheral portion 43b of the end member 43 is formed in a cylindrical shape through a radial gap 43c so as to face the outer peripheral portion 43a radially outward. The radial gap 43 c between the inner peripheral portion 43 a and the outer peripheral portion 43 b corresponds to the thickness of the material tube 10. That is, the inner diameter of the outer peripheral portion 43 b is approximately the same as the outer diameter of the material tube 10.

  The string-like member 44 has flexibility and high tensile strength. The string-like member 44 is formed by, for example, a metal wire. The string-like member 44 is locked to one end side and the other end side of the coil spring 41, and regulates the extension amount of the coil spring 41. That is, the length of the string-like member 44 is a length that restricts the coil spring 41 from being greatly expanded while allowing the coil spring 41 to extend to some extent. Specifically, the string-like member 44 positioned on one end side of the coil spring 41 is locked by the string-locking piece 52, and the string-shaped member 44 positioned on the other end side of the coil spring 41 is the axis of the end member 43. It is hooked on a locking ring 45 located on the outer side in the direction.

  The string-like member 44 passes through the inside in the radial direction of the coil spring 41 while it extends from one end side to the other end side of the coil spring 41. When the cylindrical piece 53 moves relative to the coil spring 41, the string-like member 44 is not restricted. Accordingly, the cylindrical piece 53 can easily move with respect to the coil spring 41 while restricting the amount of extension of the coil spring 41. Further, since the string-like member 44 passes inward in the radial direction of the coil spring 41, the internally threaded piece 54 can be reliably maintained in a state of being caught by the coil spring 41.

  In the present embodiment, one string-like member 44 is used. Therefore, both end sides of the string-like member 44 are formed so as not to come out from the respective through-holes 52a in a state of being inserted into the respective through-holes 52a of the string-locking pieces 52. The central part of the string-like member 44 is hooked on the locking ring 45.

  Here, the locking ring 45 is formed in an annular shape, and the outer diameter of the locking ring 45 is larger than the inner diameter of the inner peripheral portion 43 a of the end member 43. Therefore, the locking ring 45 cannot pass through the through hole of the inner peripheral portion 43 a of the end member 43.

(2-3. Description of cap 60)
As shown in FIG. 2C, the cap 60 is formed of a resin, for example, and is formed in a cylindrical shape having a flange portion 61 projecting radially inward on one end side. The inner diameter of the flange 61 is smaller than the outer diameter of the material tube 10 and slightly larger than the outer diameter of the tube end mounting portion 32 of the small diameter mandrel 30. The cap 60 is attached to one end of the material tube 10.

(3. Manufacturing method of bent pipe 20)
Next, a procedure for manufacturing the bent pipe 20 from the material tube 10 using the mandrel will be described. As shown in S1 of FIG. 4 and FIG. 5, the operator inserts the material tube 10 into the outer peripheral side of the large-diameter mandrel 40 (S1: large-diameter mandrel insertion step). At this time, since the outer diameter of the large-diameter mandrel 40 is slightly smaller than the inner diameter of the material tube 10, the material tube 10 can be easily inserted. Then, the other end side of the material tube 10 is fitted into the radial gap 43 c between the inner peripheral portion 43 a and the outer peripheral portion 43 b of the end member 43 constituting the large-diameter mandrel 40. In this state, since the material tube 10 is a straight tube, the large-diameter mandrel 40 is a straight tube.

  Subsequently, as shown in S2 of FIG. 4 and FIG. 5, the cap 60 is mounted on the distal end side of the large-diameter mandrel 40 (S2: cap mounting step). In this state, one end of the material tube 10 is restricted by the cap 60 and the other end of the material tube 10 is restricted by the end member 43 of the large-diameter mandrel 40.

  Subsequently, as shown in S3 of FIG. 4 and FIG. 6, the large-diameter mandrel 40 fitted with the material tube 10 and the cap 60 is inserted into the outer peripheral side of the small-diameter mandrel 30 (S3: small-diameter mandrel insertion step). At this time, the coil spring 41 of the large-diameter mandrel 40 slides on the outer peripheral surface of the bending shaft portion 33 of the small-diameter mandrel 30. Here, the bend forming shaft portion 33 and the coil spring 41 of the small-diameter mandrel 30 are made of metal. Therefore, the slidability is good. That is, the operator can easily insert the large-diameter mandrel 40 into the bending shaft portion 33 of the small-diameter mandrel 30.

  Here, the bend forming shaft portion 33 of the small-diameter mandrel 30 has a bent portion 33b. Therefore, the large-diameter mandrel 40 has a shape corresponding to the shape of the bend forming shaft portion 33 of the small-diameter mandrel 30. As a result, the material tube 10 is bent so as to correspond to the outer peripheral surface shape of the large-diameter mandrel 40, and becomes the shape of the bent tube 20. At this time, the details of the large-diameter mandrel 40 are as follows. The coil spring 41 has a bent shape, and the plurality of pieces 42 change the posture according to the deformation of the coil spring 41.

  In this state, as shown in FIG. 6, the internal thread pieces 54 and 54 are arranged at positions corresponding to the bent portions 33 b of the small-diameter mandrel 30. More specifically, the internal thread pieces 54 and 54 are disposed on both ends of the bent portion 33b. Accordingly, the internal thread pieces 54, 54 are restricted from moving relative to the bent portion 33b. As a result, the plurality of cylindrical pieces 53 positioned between the female screw pieces 54 and 54 are positioned without increasing the axial clearance. That is, the bent portion 22 of the bent pipe 20 can be formed into a desired shape by the female screw pieces 54 and 54 and the plurality of cylindrical pieces 53 positioned therebetween.

  Subsequently, the bent tube 20 is formed by vulcanization (S4: vulcanization step). Subsequently, as shown in S5 of FIG. 4 and FIG. 7, the large-diameter mandrel 40 with the bent tube 20 and the cap 60 attached is removed from the small-diameter mandrel 30 (S5: small-diameter mandrel removal step). At this time, similarly to the insertion, the coil spring 41 slides on the small-diameter mandrel 30 so that the large-diameter mandrel 40 can be easily removed. Subsequently, the cap 60 is removed from the large-diameter mandrel 40 (S6: cap removal step).

  Subsequently, the large-diameter mandrel 40 is removed from the bent tube 20 (S7: large-diameter mandrel removal step). Here, the large-diameter mandrel 40 is composed of a coil spring 41 and a plurality of pieces 42, so that it can be bent. Furthermore, since the large-diameter mandrel 40 is formed by connecting a plurality of pieces 42, the plurality of pieces 42 can be separated from each other. Therefore, the large-diameter mandrel 40 can be easily removed from the bent tube 20.

  However, when the large-diameter mandrel 40 is pulled out from the bent tube 20, the large-diameter mandrel 40 acts so as to extend. At this time, if the extension amount of the coil spring 41 is not restricted, it is not easy to pull out the coil spring 41 and the plurality of pieces 42 from the bent tube 20. However, the extension amount of the coil spring 41 is regulated by the string-like member 44. Therefore, the large-diameter mandrel 40 can be reliably removed from the bent tube 20 by restricting the amount of expansion while the coil spring 41 is extended.

  Further, the outer diameters of the plurality of pieces 42 are formed smaller than the inner diameter of the material tube 10. That is, a slight gap exists between the outer peripheral surface of the plurality of pieces 42 and the inner peripheral surface of the bent pipe 20. Here, even if there is a gap between the outer peripheral surfaces of the plurality of pieces 42 in the bent portion 22 of the bent tube 20, the shape of the bent portion 22 of the bent tube 20 can be changed to a desired shape.

  According to the manufacturing method, since the large-diameter mandrel 40 is configured by the coil spring 41 and the plurality of pieces 42, the member that contacts the inner peripheral surface of the bending pipe 20 to be formed becomes the plurality of pieces 42, The coil spring 41 does not contact the inner peripheral surface of the bent tube 20. Accordingly, since the coil spring 41 does not directly contact the inner peripheral surface of the bent tube 20 to be formed, the inner peripheral surface of the bent tube 20 is in the axial direction of the plurality of pieces 42 regardless of the wire diameter of the coil spring 41. The shape depends on the width. Therefore, compared with the case where the coil spring 41 directly contacts the inner peripheral surface of the bent tube 20, it contributes to the improvement of the durability of the bent tube 20.

  Further, as described above, the shape of the inner peripheral surface of the bent tube 20 depends on the axial width of the plurality of pieces 42 regardless of the wire diameter of the coil spring 41 itself. Therefore, even if the wire diameter of the coil spring 41 is reduced, the uneven shape of the inner peripheral surface of the bent tube 20 can be reduced by increasing the axial width of the plurality of pieces 42. Furthermore, since the wire diameter of the coil spring 41 can be reduced, the ease of bending of the coil spring 41 is improved.

<Others>
In the above embodiment, one string-like member 44 is used to lock both ends to the string-locking piece 52 and hook onto the locking ring 45 on the outer side in the axial direction of the end member 43. In addition, one end of the string-like member 44 may be locked to the string locking piece 52 and the other end may be locked to the end member 43. In this case, two or more string-like members 44 can be used.

  In FIG. 6, one end of the bent tube 20 is mounted between the cap 60 and the tube end mounting portion 32 of the small diameter mandrel 30, and the other end of the bent tube 20 is the end member 43 of the large diameter mandrel 40. It is attached to. In addition, the cap 60, the tube end mounting portion 32, and the end member 43 may be reversed. In this case, the small-diameter mandrel 30 does not have the tube end mounting portion 32, and is formed by the base portion 31 and the bending shaft portion 33. The large-diameter mandrel 40 has a member corresponding to the end member 43 on the insertion side (front end side) of the small-diameter mandrel 30, and a member corresponding to the cap 60 can be attached to the other end.

  Moreover, in the said embodiment, although the manufacturing method of the rubber bending pipe | tube 20 was demonstrated, it can apply similarly to the manufacturing method of the resinous bending pipe | tube 20. FIG. Moreover, in the said embodiment, although the small diameter mandrel 30 and the large diameter mandrel 40 were made from metal, it is not restricted to this. The small-diameter mandrel 30 and the large-diameter mandrel 40 can be made resinous, and a part of the structure can be made of metal and the other part of the structure can be made resinous. An optimum material is selected in consideration of durability, cost, rigidity, and the like.

10: material tube, 20: bent tube, 21, 23: straight tube portion, 22: bent portion, 30: small-diameter mandrel, 31: base portion, 32: tube end mounting portion, 33: bending shaft portion, 33a: first Straight pipe portion, 33b: bent portion, 33c: second straight pipe portion, 40: large-diameter mandrel, 41: coil spring, 42: top, 43: end member, 43a: inner peripheral portion, 43b: outer peripheral portion, 43c: Clearance in radial direction 44: String-like member 45: Locking ring 51: End piece 52: String-locking piece 52a: Through hole 53: Cylindrical piece 54: Female screw piece 60: Cap 61 Part

Claims (8)

Inserting a material tube into the outer periphery of a bendable large-diameter mandrel;
A step of manufacturing a bent tube by inserting the large-diameter mandrel with the material tube attached to the outer peripheral side of the small-diameter mandrel having a bent portion;
A method of manufacturing a bent pipe comprising:
The large-diameter mandrel is
A coil spring which can be inserted into the outer peripheral side of the small-diameter mandrel;
A plurality of frames formed in an annular shape having an axial width larger than the wire diameter of the coil spring, continuously disposed along the central axis of the coil spring on the outer peripheral side of the coil spring, and provided to be separated from each other. When,
A method for manufacturing a bent pipe. At least some of the plurality of pieces have a female screw surface that is fitted into the coil spring by screw fitting, and relative movement with respect to the coil spring is restricted.
The manufacturing method of the bent pipe of Claim 1. The top having the female thread surface is disposed at a position corresponding to the bent portion of the small-diameter mandrel.
The manufacturing method of the bent pipe of Claim 2. The other part of the plurality of pieces has a cylindrical inner peripheral surface that does not engage with the coil spring, and is allowed to move relative to the coil spring.
The top having the female thread surface is disposed at a position corresponding to both end sides of the bent portion of the small-diameter mandrel,
The top having the cylindrical inner peripheral surface is disposed between the two tops having the female screw surfaces disposed on both ends of the bent portion.
The manufacturing method of the bent pipe of Claim 3. The large-diameter mandrel is further provided with a string-like member that is locked to one end side and the other end side of the coil spring and restricts the amount of extension of the coil spring.
The manufacturing method of the bent pipe as described in any one of Claims 1-4. The string-like member passes the radially inner side of the coil spring in the central axis direction.
The manufacturing method of the bent pipe of Claim 5. The outer diameter of the plurality of pieces is formed smaller than the inner diameter of the material tube,
The manufacturing method of the bent pipe as described in any one of Claims 1-6. A mandrel used for manufacturing a bent pipe,
The mandrel is
A large-diameter mandrel that can be bent and a material tube can be inserted on the outer peripheral side;
A small-diameter mandrel having a bent portion and capable of inserting the large-diameter mandrel on the outer peripheral side;
With
The large-diameter mandrel is
A coil spring which can be inserted into the outer peripheral side of the small-diameter mandrel;
A plurality of frames formed in an annular shape having an axial width larger than the wire diameter of the coil spring, continuously disposed along the central axis of the coil spring on the outer peripheral side of the coil spring, and provided to be separated from each other. When,
A mandrel used for manufacturing a bent pipe.

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