JP2773066B2 - Double pipe bending method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for bending a double pipe comprising an outer pipe and an inner pipe.

[0002]

2. Description of the Related Art In an exhaust pipe for exhausting engine exhaust gas, an inner pipe is inserted into an outer pipe, these pipes are fixed at one end, and a space is formed between the outer pipe and the inner pipe. Heavy pipes are used. This double pipe generally has a bent shape according to the layout of the exhaust system.

[0003] In the case of bending a double pipe as described above, there is a problem that, with the progress of bending, local extension occurs outside the bent portion and buckling occurs inside. Various techniques have been developed as a method of solving this problem and performing good bending.

The technique disclosed in Japanese Patent Publication No. 52-26754 discloses a technique in which a braking force in a direction orthogonal to the axial direction is applied to an outer pipe and an inner pipe in the vicinity of a die to apply a tensile force to these pipes. It is configured so that it can be provided. Further, the technology disclosed in the same publication 55-24971, insert a cylindrical outer core between the inner tube and the outer tube while inserting the inner core into the inner tube,
The double tube is configured to move slightly in the direction of the bent portion in conjunction with the rotation of the bending chuck.

[0005]

Each of the above techniques is a solution for bending a double pipe having a gap between an outer pipe and an inner pipe. However, there is no problem at all, and each has some problems to be solved. That is,
In the former technique, there is a problem of residual stress caused by applying a controlled tensile force to the outer pipe and the inner pipe. In the latter technique, there is a problem that an outer core must be inserted into a space formed by the outer tube and the inner tube.

An object of the present invention is to provide a method of bending a double pipe, which is easy to perform and has a reduced residual stress value.

[0007]

In order to solve the above-mentioned problems, a method of bending a double pipe according to the present invention comprises inserting an inner pipe into an outer pipe and fixing the outer pipe and the inner pipe at a predetermined position. This is a bending method in which a double pipe having a gap between these pipes is bent on the rear side of the fixed portion, and a core is inserted into the inner pipe and the outer pipe is restrained by a bending die. Bending is performed, and the outer pipe and the inner pipe are propelled with different forces in the axial direction from the rear end of the bending direction in synchronization with the progress of the bending on the outer pipe and the inner pipe, and the propulsion applied to the outer pipe. The present invention is characterized in that the force is set to be larger than the propulsion force applied to the inner pipe.

[0008]

According to the above-mentioned method of bending a double pipe, the work is easy and the residual stress can be reduced.

That is, when a core is inserted into the inner tube, and the outer tube is constrained by a die without inserting a core or the like into a gap formed by the inner tube and the outer tube, bending is performed. The bending of the double pipe proceeds with the rotation of. As the bending progresses, a tensile force acts on the wall surfaces of the outer tube and the inner tube outside the bent portion, and a compressive force acts on the wall surfaces of the outer tube and the inner tube inside the bent portion. At this time, if a gap is formed between the outer tube and the inner tube, a local extension occurs on the tube walls of the outer tube and the inner tube due to the tensile force acting on the outside of the bent portion, and the tube wall is crushed. Often occurs.

Therefore, by propelling these tubes with different forces from the tube ends on the rear side of the outer tube and the inner tube in synchronization with the progress of bending by the dies, the outside of the bent portion in each tube is obtained. The tensile force acting on the wall surface can be reduced.
For this reason, it is possible to reduce the residual stress without causing the bent portions of the outer tube and the inner tube to extend.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the above bending method will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a bending method according to the present invention.

In FIG. 1, a double tube A has an outer tube 1 and an inner tube 2 having predetermined specifications, and after the inner tube 2 is inserted into the outer tube 1, Tubes 1 and 2 are fixed to each other at one end (fixed portion 3). Therefore,
A gap 4 is formed between the outer tube 1 and the inner tube 2.

When bending the double pipe A, the core metal 5 is inserted into the inner pipe 2, and the core 4 is held in the gap portion 4 without inserting the core metal or the like. Then, the fixing portion 3 side of the double pipe A is restrained to the die 6 by restraining means (not shown), and the rear end of the outer pipe 1 is brought into contact with the propulsion device 7 and the rear pipe of the inner pipe 2 is connected. The end is brought into contact with the propulsion device 8.

After preparing for the bending operation as described above,
By rotating the die 6 in the direction of arrow a and applying different forces to the outer pipe 1 and the inner pipe 2 by the propulsion tools 7 and 8 in synchronization with the rotation of the die 6 and propelling in the directions of arrows b and c,
The bending on the double tube A is performed.

The driving force applied to the outer pipe 1 and the inner pipe 2 is as follows:
The value differs depending on the diameter, wall thickness, material, curvature of the bent portion, and the like of these tubes 1 and 2. However, since the tensile force acting on the outer wall 1a of the outer tube 1 is larger than the tensile force acting on the outer wall 2a of the inner tube 2, the propulsive force in the direction of arrow b to be applied to the outer tube 1 is 2 is set to a value larger than the propulsive force in the direction of the arrow c to be applied.

As described above, the outer tube 1 and the inner tube 2 are propelled by the propulsion tools 7 and 8 in synchronization with the progress of the bending of the double tube A due to the rotation of the die 6, so that the outer tube 1 and the inner tube 2 are propelled. 2 It is possible to cancel the tensile force acting on the outer walls 1a, 2a.

Accordingly, the outer walls 1a and 2a of the tubes 1 and 2 do not yield due to the tensile force applied by the die 6 and are not locally elongated, and can be bent while maintaining a substantially uniform wall thickness. It is possible. For this reason, the outer walls 1a,
The uniform bending shape can be obtained without the 2a being crushed in the direction of the die 6.

[0018]

As described in detail above, in the method of bending a double pipe according to the present invention, the outer pipe and the inner pipe are propelled with different forces in synchronization with the progress of bending, thereby making it possible to form these pipes. The tensile force acting on the outer wall at the bent portion can be reduced. For this reason, the outer wall does not yield and local elongation does not occur, and the outer tube and the inner tube can be bent while maintaining a substantially uniform thickness, and the outer wall of the bent portion is crushed. Without bending, uniform bending can be performed, and the residual stress of the bent double pipe can be reduced.

Also, since there is no need to insert a core into the space formed by the outer tube and the inner tube, the present invention is characterized in that the bending operation can be easily performed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a bending method according to the present invention.

[Explanation of symbols]

 A Double tube 1 Outer tube 1a, 2a Outer side wall 2 Inner tube 3 Fixing part 4 Void part 5 Core 6 Dice 7, 8 Propulsion tool

Claims (1)

(57) [Claims] 1. An inner tube is inserted into an outer tube, and the outer tube and the inner tube are fixed at a predetermined position. A double tube having a gap between these tubes is provided on the rear side of the fixing portion. A bending method in which a core is inserted into the inside of an inner tube and the outer tube is restrained by a bending die to perform a bending process. The outer pipe and the inner pipe are propelled with different forces in the axial direction from the end on the side, and the propulsive force applied to the outer pipe is set to be larger than the propulsive force applied to the inner pipe. Bending method.