JPH07166695A - Connection device of cylinder-shaped pipe - Google Patents

Abstract

PURPOSE:To make it possible to connect and disconnect a cylinder-shaped pipe, such as pedestal easily and provide an excellent connected state. CONSTITUTION:A lock pin 5 of a connector housed in a joint pipe 3 is inserted into a lock pin insertion hole 31 and energized projectingly along the outside diameter while a lock pin engagement hole 31 removable from the lock pin 5 is formed on a pedestal 2 on the other side. The lock pin 5 is further provided with a first cam face 51 which is pushed into the end face of the cylindrically shaped pipe and fits the lock pin 5 inwardly or toward the bored diameter when the opposite side-pedestal 2 is outwardly fitted into the joint pipe 3 and a second cam face 51 which is pushed in the end face of the inside circumference of the lock pin insertion hole 31 and forces the lock pin 5 to fit inwardly or the bored diameter when the opposite-side cylindrically shaped pipe 2 is rotated about its own axis with the joint pipe 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circular pipe connecting device which can be suitably applied to, for example, a connecting portion between columns in a temporary scaffold at a construction site.

[0002]

2. Description of the Related Art When connecting stilts to a temporary scaffolding at a construction site, a short pipe joint is inserted into an end of one pedestal and the other stilt is externally fitted to the short pipe joint. Further, a method is known in which both legs are connected by an arm lock. However, this joint method requires a lot of work because it requires a lot of work, as well as the work of inserting / externally fitting the short pipe joint and the pedestal, as well as the work of mounting the arm lock. Is desired.

Conventionally, many pedestal connecting devices which can improve workability have been proposed. For example, Japanese Patent Publication No. 39-536 discloses a small-diameter joint pipe provided at the end of one pedestal. A lock pin that is biased so as to project outward in the inner diameter direction while allowing it to be retracted in the inner diameter direction, and a lock pin engaging hole is formed in the pedestal on the other side in correspondence with the lock pin. A pedestal coupling device is disclosed. This device, when the pedestal on the other side is fitted into the joint pipe,
The lock pin is pushed into the end surface or the inner peripheral surface of the pedestal on the other side to be recessed, and when the lock pin reaches the engagement hole, the lock pin projects in the outer diameter direction and automatically engages with the hole. . In this way, by simply fitting one of the pillars, the pillars can be easily connected to each other, and good connecting workability can be obtained.

[0004]

However, in the above-described conventional pedestal connecting device, it is difficult to disengage the lock pin, which makes disassembling the pedestal difficult. That is, in this device, a lock release pin for sliding the lock pin against the urging force is provided on one of the pedestals, and the lock release pin is slid to operate. Is disengaged from the engagement hole, and one of the columns is pulled out in that state to disassemble the column. This disassembling work has a problem that the disassembling work of the pedestal is complicated because a troublesome lock releasing operation of picking and sliding a small lock releasing pin is required.

The present invention solves the above-mentioned problems of the prior art, and provides a circular pipe connecting device capable of easily connecting and disconnecting circular pipes such as pedestals and obtaining a good connected state. The purpose is to do.

[0006]

In order to achieve the above object, the present invention is a circular pipe connecting device for connecting ends of two circular pipes with their axes aligned with each other. A joint pipe having a diameter smaller than that of the circular pipe is coaxially provided at the end of the circular pipe, and a lock pin insertion hole is formed in the peripheral wall portion of the joint pipe. The lock pin is inserted into the lock pin insertion hole and is urged to project in the outer diameter direction in a state where the lock pin is allowed to be retracted in the inner diameter direction. A lock pin engaging hole for engaging with the lock pin to prevent the lock pipe from coming out of the joint pipe in a state where the circular pipe on the other side is externally fitted to the joint pipe. The other side of the circle In a state in which the lock pin is pushed into the end surface of the pipe to immerse the lock pin in the inner diameter direction and allows the outer fitting operation of the circular pipe on the other side, and the lock pin is engaged with the lock pin engagement hole, When the circular pipe on the other side rotates about the axis relative to the joint pipe, it is pushed into the inner peripheral end surface of the lock pin engagement hole to retract the lock pin in the inner diameter direction and into the engagement hole of the lock pin. And a second cam surface which releases the engagement of the circular tube on the other side and allows the operation of extracting the circular tube on the other side from the joint tube.

In the present invention, two lock pins are provided at opposite positions, and two lock pin insertion holes and two lock pin engagement holes are provided corresponding to the lock pins, while the connection is made. The tool has two leg pieces each provided with the lock pin on the distal end side, and is urged in a direction in which the lock pin is extended between the two leg pieces to expand the both leg pieces in the outer diameter direction. An elastic hooking piece for urging the protrusion, the connecting tool being arranged inside the joint pipe in a state in which the front end sides of both leg pieces thereof are directed to the circular pipe side on one side. It can be preferably adopted.

Further, according to the present invention, the connecting device has a positional displacement which is locked to an end surface of the joint pipe to prevent the connecting device from being displaced to one circular pipe side along the axial direction. It is advisable to adopt a configuration in which a preventive piece is provided.

Further, in the present invention, the first cam surface is formed into a curved surface so as to be along the inner edge of the tube at the end surface of the circular tube on the other side, and the second cam surface is It is preferable to adopt a configuration in which a curved surface is formed along the inner edge of the pipe at the inner peripheral end surface of the lock pin engagement hole.

[0010]

In the circular pipe connecting device of the present invention, the lock pin of the connecting member housed in the joint pipe is inserted into the lock pin insertion hole of the joint pipe to be urged to project outward in the radial direction and at the other side. In the state where the circular pipe is fitted onto the joint pipe, the lock pin is engaged with the lock pin engagement hole of the circular pipe on the other side. Therefore, due to the engagement, the circular pipe on the other side is reliably prevented from coming off from the joint pipe, and a good connected state is obtained. In addition, the lock pin is provided with a first cam surface that is pushed into the end surface of the circular pipe to immerse the lock pin in the inner diameter direction when the circular pipe on the other side is externally fitted to the joint pipe. The above-mentioned connected state can be obtained only by externally fitting the circular tube of (1) to the joint tube. Further, when the circular pipe on the other side is rotated around the axis with respect to the joint pipe, the lock pin is pushed into the inner peripheral end surface of the lock pin engagement hole so that the lock pin is retracted in the inner diameter direction and engaged. Since the second cam surface for releasing is provided, the engagement of the lock pin can be released only by rotating one of the circular tubes around the axis.

Further, in the present invention, in the case of adopting the structure in which the displacement preventing piece for engaging with the end face of the joint pipe is provided in the connecting tool, the lock pin is attached to the end face of the circular pipe by the external fitting operation of the circular pipe. When pushed, the connector, in other words, the position shift of the lock pin in the axial direction is prevented, and the lock pin is not locked in the lock pin insertion hole when it is retracted, and is smoothly retracted.

Further, in the present invention, when the circular pipe on the other side is externally fitted to the joint pipe, the pipe inner edge portion of the end face of the circular pipe comes into contact with the first cam surface. At this time, when the first cam surface is formed into a curved surface along the pipe inner edge portion, the contact portion between the pipe inner edge portion and the first cam surface becomes wide, and the lock pin The pushing force acting on the lock pin is not locally concentrated and a stable pushing force is obtained, and the pushing operation of the lock pin is smoothly performed. On the other hand, when the circular tube on the other side is rotated around the axis, the inner edge of the inner peripheral end surface of the lock pin engaging hole comes into contact with the second cam surface. At this time, when the second cam surface is formed as a curved surface along the pipe inner edge portion, the contact portion between the pipe inner edge portion and the second cam surface becomes wider, and the lock is achieved. The pushing force acting on the pin is not locally concentrated, and a stable pushing force is obtained, so that the pushing operation of the lock pin is smoothly performed.

[0013]

EXAMPLE In this example, an example of the circular pipe connecting device of the present invention is applied to a connecting portion between pedestals in a temporary scaffold at a construction site.

As shown in FIG. 1, of the two pillars (1) and (2) connected to each other, the end portion of the one pillar (1) has a smaller diameter dimension and a shorter diameter. The joint pipe (3) of one dimension is fixed by welding in a state where one half of the joint pipe (3) is fitted, and two lock pin insertion holes ( Three
1) (31) is formed.

The pedestal (2) on the other side is formed to have the same diameter as the pedestal (1) on the one side, and the other half of the joint pipe (3) can be fitted into the end portion. Is configured. Further, on the end peripheral wall portion of the pedestal (2), two locks that respectively fit the two lock pin insertion holes (31) (31) in a state where the end portion is fitted onto the joint pipe (3). Pin engagement holes (21) (21) are formed.

As shown in FIGS. 1 to 3, the connecting tool (4) for connecting the two columns (1) and (2) is made of metal U.
It is formed so as to be bent into a letter shape (inverted U shape), and is stretched between both leg pieces (41) (41) and the both leg pieces (41) (41) to be elastic. And an elastic hooking piece (42) having.

Hanging piece (42) of both leg pieces (41) (41)
The end portions on the side are partially cut and raised, and the displacement preventing pieces (43) (4
3) is formed. Also, both leg pieces (41) (41)
On the outer surface of the front end side of the
3) at a position equal to the distance from the joint pipe (3) to the lock pin engagement holes (31) (31), and the tip portions (41a) of both leg pieces (41) (41).
Lock pins (5) and (5) are fixed so as to respectively project outwardly on the side of the hanging piece (42) rather than (41a).

These lock pins (5) and (5) are connected to the joint pipe (3), as will be described later, in a state in which one side region in the axial direction, that is, FIG.
(A) to (c) of the figure, the upper region is cut obliquely toward the paper surface of the first cam surface (51) (5).
1) is formed respectively, and one side region in the direction around the axis in the state of being attached to the joint pipe (3),
In other words, the left side regions are respectively cut obliquely toward the paper surface of FIGS. 3B and 3C, and the second cam surface 52 is formed.
(52) are formed respectively. As will be described in detail later, the first cam surface (51) is not a flat surface, but is configured by a curved surface along the pipe inner edge portion at the end surface of the pedestal (2) on the other side, and Second cam surface (5
Also 2) is not a flat surface, but is formed into a curved surface along the pipe inner edge portion at the inner peripheral end surface of the lock pin engagement hole (21) of the pedestal (2) on the other side.

The connector (4) is housed in the joint pipe (3) with the elastic hooking piece (42) bent inward. At this time, the misalignment prevention pieces (43) (4
3) is locked to the end surface (3a) of the joint pipe (3), and the lock pins (5) and (5) are inserted into the lock pin insertion holes (31) and (31) to form the outer periphery of the joint pipe (3). It is arranged so as to project outward from the surface. In this state, when the lock pins (5) (5) are pushed inward, the elastic hooking piece (42) bends and both leg knitting (41) (4).
When the lock pin (5) (5) is retracted into the lock pin insertion hole (31) (31) by closing 1), the elastic hooking piece (5) is released when the lock pin (5) (5) is released. 42) The elastic restoring force of the lock pin (5) (5)
Is configured to be held in a state of protruding outward from the position of the outer peripheral surface of the joint pipe (3).

In order to connect the pedestals (1) and (2) having such a structure, the lock pins (5) and (5) and the lock pin engagement holes (21) (of the pedestal (2) on the other side are formed. 21), the end of the pedestal (2) on the other side may be externally fitted to the joint pipe (3) as shown in FIG. 4 (a). As a result, as shown in FIG. 4B, the end surface (2a) of the pedestal (2) on the other side comes into contact with the first cam surface (51) of the lock pin (5) and the lock pin (5). Moving inward on the cam surface while pushing inwardly, and as shown in FIG. 4 (c), the pedestal (2) on the other side moves the lock pin (5) inward on the inner peripheral surface. It is externally fitted while being pushed in. Continuing with FIG. 4 (d) and FIG.
As shown in (a), when the pedestal (2) on the other side is externally fitted until it hits the end face of the pedestal (1) on the one side, the lock pin (5) is engaged with the lock pin engagement hole (21). ) Is reached, and due to the restoring force of the elastic hooking piece (42), it projects outward and is inserted into the lock pin engagement hole (21). By this insertion, the lock pin (5) engages with the inner peripheral end surface of the lock pin engagement hole (21), and the stud (2) on the other side is prevented from coming off from the joint pipe (3) in the axial direction. As a result, both pedestals (1) and (2) are connected.

By the way, as shown in FIG. 6 (a), when the pedestal (2) on the other side is externally fitted to the joint pipe (3), a lock pin is included in the end surface (2a) of the pedestal (2). (5)
It is the tube inner edge (X) that actually abuts the first cam surface (51) of the tube inner edge (X) according to the insertion of the joint tube (3). Line (X1) ~
As shown in (X5), the lock pin (5) moves on the first cam surface (51). In this case, in this embodiment, as described above, the first cam surface (5
Since 1) is formed as a curved surface along the pipe inner edge (X), when the pipe inner edge (X) moves while pushing the cam surface (51), the contact portions of the two are Since the pushing force of the lock pin (5) by the pipe inner edge portion (X) is not locally concentrated, a stable pushing force is obtained, and the lock pin (5) is smoothly moved in and out. Therefore, when the pedestal (2) on the other side is externally fitted to the joint pipe (3), the external fitting operation can be satisfactorily performed without causing a catch or the like.

Further, in this embodiment, the displacement preventing piece (43) of the connector (4) is attached to the end surface (3) of the joint pipe (3).
Since it is locked to a), the external fitting operation of the pedestal (2) on the other side can be performed more favorably, as described below. That is, in a state where the coupling tool (4) is simply housed in the joint pipe (3) without forming a displacement prevention piece or the like, for example, as shown by an imaginary line in FIG. 6 (b), When the pedestal (2) on the other side is externally fitted to the joint pipe (3), the lock pin (5) is pushed by the end surface (2a) of the pedestal (2) and the coupling tool (4) along with the axial direction. May be displaced to the side of the pedestal (1) on the one side. When the displacement occurs, as shown by the imaginary line in FIG.
Even if the lock pin (5) tries to be retracted inward, the lock pin (5) is locked in the lock pin insertion hole (31) and the retraction operation is hindered. The pedestal (2) on the side cannot be fitted on the outside. On the other hand, in this embodiment, since the displacement prevention piece (43) of the connector (4) is locked to the end surface (3a) of the joint pipe (3), the lock pin (5) is on the other side. Pedestal (2)
Thus, even if the connector (4), that is, the lock pin (5) is pushed in in the axial direction, the positional displacement in the axial direction is prevented. Therefore, the lock pin (5) is not locked in the lock pin insertion hole (31) when the lock pin is retracted,
Since the lock pin (5) can be smoothly moved in and out, the pedestal (2) can be fitted well.

Further, in this embodiment, the lock pin (5) is attached to the tip portions (41a) (41a) of the leg pieces (41) (41).
Since it is attached to the side of the hanging piece (42) rather than the locking pin (5), the protrusion (41
Since a) (41a) exists, the pedestal connection state is not unintentionally released. That is, as shown in FIG. 8, when a force that pulls out the pedestal (2) on the other side is generated in the pedestal connected state, as shown by the imaginary line in FIG. , And is pushed by the inner peripheral end surface (21a) of the lock pin engagement hole (21) of the pedestal (2) and tries to sink inward. At this time, the tip ends (41a) (41a) of the leg pieces (41) (41) are locked to the lock pin insertion hole peripheral portion on the inner peripheral surface of the joint pipe (3), so that the lock pin (5) is It is prevented that the lock pin (5) and the engagement hole (21) are engaged with each other. Therefore, the connected state will not be unintentionally released.

On the other hand, in order to release the connection from the pedestal connection state shown in FIG. 5A, first, as shown in FIG. 5B, the other pedestal (2) is moved to the one pedestal (1). ) Or the joint tube (3) is rotated in one direction around the axis, clockwise in the drawing. As a result, the inner peripheral end surface of the lock pin engagement hole (21) comes into contact with the second cam surface (52) of the lock pin (5) and moves on the cam surface while pushing the lock pin (5) inward. I will do it. As a result, FIG.
As shown in (c), the lock pin (5) is retracted into the lock pin insertion hole (31) and the engagement with the lock pin engagement hole (21) is released.

After releasing the engagement of the lock pin (5) in this way, the joint pipe (3) is pulled out from the pedestal (2) on the other side to release the connection between the pedestals. The pillars (1) and (2) can be disassembled.

By the way, as shown in FIG. 9, when the pedestal (2) on the other side is rotated about its axis, the lock pin (5) in the inner peripheral end surface (21a) of the lock pin engagement hole (21) is rotated. It is the pipe inner edge (Y) that abuts the second cam surface (52) of (1), and as the pedestal (2) rotates, the pipe inner edge (Y) changes to the imaginary line (Y) of FIG. As indicated by (Y1) to (Y4), it will move on the second cam surface (52). In this case, as described above, the second cam surface (5
Since 2) is formed as a curved surface along the pipe inner edge (Y), the contact portion between the pipe inner edge (Y) and the cam surface (52) becomes wide, and the lock pin (5) is formed. Since a stable pushing force can be obtained, the lock pin (5) can be smoothly moved in and out, and the pedestal (2) on the other side can be rotated, that is, the pedestal (2) can be disassembled. it can.

As described above, according to the pedestal connecting device of this embodiment, the joint pipe (3) is connected to the pedestal (2) on the other side.
The pedestals (1) and (2) can be easily connected to each other by simply inserting the pedestal into the pod, and the pedestal can be easily disassembled by rotating and pulling out one of the pedestals.

Further, the pedestal connecting device of the present embodiment is designed to realize the device structure by accommodating the connecting member (4) in the joint pipe (3). If the tool (4) is damaged, it can be used again without any trouble by replacing only the connector (4) without discarding the pedestal (1) (2) or the joint pipe (3). Therefore, it is possible to effectively use the parts. further,
In this embodiment, it is not necessary to separately provide a member for unlocking, for example, a lock releasing pin, and the number of parts can be reduced accordingly.

[0029]

As described above, according to the circular pipe connecting device of the present invention, the lock pin of the connecting member housed in the joint pipe is inserted into the lock pin insertion hole of the joint pipe and protrudes in the outer diameter direction. When the circular pipe on the other side is externally fitted to the joint pipe while being biased, the lock pin is engaged with the lock pin engaging hole of the circular pipe on the other side. Thus, the circular pipe on the other side is reliably prevented from coming off the joint pipe, and a good connected state can be obtained. In addition, the lock pin is provided with a first cam surface that is pushed into the end surface of the circular pipe to immerse the lock pin in the inner diameter direction when the circular pipe on the other side is externally fitted to the joint pipe. If the circular pipe of No. 1 is externally fitted to the joint pipe, the lock pin automatically engages with the lock pin engaging hole to prevent the lock pipe from being pulled out. Can be achieved. Further, when the circular pipe on the other side is rotated relative to the joint pipe about the axis, the lock pin is pushed into the inner peripheral end surface of the lock pin engaging hole to immerse the lock pin in the inner diameter direction. Since the second cam surface for releasing the engagement is provided, the engagement of the lock pin is released only by rotating one of the circular tubes around the axis, and the other circular tube is pulled out from the joint tube. be able to. Therefore, the effect that the connection of the circular tubes can be released by a simple operation of rotating and pulling out one circular tube is obtained.

Further, in the present invention, in the case where the connecting tool is provided with the displacement preventing piece for engaging with the end face of the joint pipe, the lock pin is attached to the end face of the circular pipe by the external fitting operation of the circular pipe. When is pressed, the displacement of the connecting tool, in other words, the lock pin in the axial direction is prevented, and the lock pin is prevented from being locked in the lock pin insertion hole. For this reason, there is an advantage that the lock pin can be smoothly moved in and out, and the external fitting operation of the circular tube can be favorably performed.

Further, in the present invention, the first cam surface is
When a curved surface is formed along the pipe inner edge of the end surface of the other circular pipe, the contact portion between the pipe inner edge and the first cam surface becomes wider, and the push pin that acts on the lock pin is pushed. The force is not concentrated locally and a stable pushing force is obtained, so that the outer fitting operation of the circular pipe can be performed more favorably, and further, the second cam surface is connected to the inner circumference of the lock pin engaging hole. When forming a curved surface along the pipe inner edge of the end face, the contact portion between the pipe inner edge and the second cam surface becomes wider, and the pushing force acting on the lock pin is locally concentrated. There is an advantage that a stable pushing force can be obtained without doing so, and the extracting operation of the circular tube can be performed more favorably.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a connecting device for a circular tube such as a temporary scaffolding pedestal according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a connecting tool applied to the connecting device of the embodiment.

FIG. 3 is a view showing a connector applied to the embodiment,
The figure (a) is a front view, the figure (b) is a right side view, the figure (c) is a left side view, the figure (d) is a top view, and the figure (e) is a bottom view.

4A and 4B are side sectional views showing a coupling device of an embodiment, wherein FIGS. 4A to 4C are views showing a state where the joint pipe is being inserted, and FIG. 4D is a sectional view of the joint pipe. It is a figure showing the state where insertion was completed.

FIG. 5 is a plan sectional view showing the coupling device of the embodiment, in which FIG. 5 (a) shows a state immediately after the start of rotation of the pedestal on the other side, and FIG. 5 (b) shows a state in the middle of rotation. Figure, (c)
FIG. 6 is a diagram showing a state in which rotation has been completed.

FIG. 6 is a cross-sectional view showing a contact state between a lock pin and a pedestal in the coupling device of the embodiment.

FIG. 7 is a perspective view showing a contact state between the lock pin and the end face of the pedestal on the other side in the coupling device of the embodiment.

FIG. 8 is a cross-sectional view showing an engagement state between the lock pin and the engagement hole of the other-side pedestal in the coupling device of the embodiment.

FIG. 9 is a cross-sectional view showing a contact state between the lock pin and the inner peripheral end surface of the engagement hole of the other-side pedestal in the coupling device of the embodiment.

FIG. 10 is a perspective view showing a contact state between the lock pin and the inner peripheral end surface of the engagement hole of the other side pedestal in the coupling device of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... One side pedestal 2 ... The other side pedestal 2a ... The pedestal end surface 3 ... Joint pipe 3a ... Joint pipe end surface 4 ... Coupling tool 5 ... Lock pin 21 ... Lock pin engagement hole 21a ... Inner peripheral end surface 31 ... Lock pin insertion hole 41 ... Leg piece 42 ... Elastic spanning piece 43 ... Displacement prevention piece 51 ... First cam surface 52 ... Second cam surface X, Y ... Pipe inner edge

Claims (4)

[Claims] 1. A connecting device for circular pipes for connecting the ends of two circular pipes with their axes aligned with each other, wherein a diameter of the circular pipe on one side is smaller than that of the circular pipe. The joint pipe is provided coaxially, and a lock pin insertion hole is formed in the peripheral wall portion of the joint pipe, and the lock pin of the connector housed in the joint pipe is
It is inserted into the lock pin insertion hole and is urged to project in the outer diameter direction while allowing it to be recessed in the inner diameter direction. In the state where the lock pin is engaged with the lock pin to prevent the lock pipe from coming out of the joint pipe, the lock pin has a circular pipe on the other side fitted to the joint pipe. The lock pin engages the lock pin engagement hole with the first cam surface that is pushed into the end face of the circular pipe on the other side to immerse the lock pin in the inner diameter direction and allows the external fitting operation of the circular pipe on the other side. In this state, when the circular pipe on the other side rotates about the axis relative to the joint pipe, the circular pin is pushed into the inner peripheral end surface of the lock pin engagement hole and the lock pin is retracted in the inner diameter direction. Release the engagement to the engagement hole, Coupling device of the circular tube, characterized the second cam surface to allow the sampling operation from the joint pipe of the circular tube side, that is provided. 2. The lock pins are provided at two positions facing each other, and two lock pin insertion holes and two lock pin engagement holes are provided corresponding to the lock pins, respectively, while the connecting device is provided with: Two leg pieces each provided with the lock pin on the tip end side, and a biasing force applied to the outside of the lock pin by urging the leg pieces in a direction in which the lock pin is spread over the leg pieces. The elastic hooking piece for performing the above, and the connector is arranged inside the joint pipe in a state in which the tip end sides of both leg pieces thereof face the circular pipe side on one side. Circular pipe interlocking device. 3. The displacement tool is provided on the coupling tool to prevent the coupling tool from being displaced to one circular tube side along the axial direction by being locked to the end surface of the joint tube. The connecting device for a circular tube according to claim 1 or 2, wherein 4. The first cam surface is formed as a curved surface along the tube inner edge portion of the end surface of the circular tube on the other side, and the second cam surface has a lock pin engagement hole. The circular pipe connecting device according to any one of claims 1 to 3, wherein the circular pipe is formed into a curved surface along the inner edge of the inner peripheral end face of the pipe.