JP5525434B2 - Steel pipe bending method - Google Patents

Description

  The present invention relates to a method of bending a steel pipe used for structural applications such as transportation equipment such as automobiles, machine parts, and construction.

In general, as a method of bending a steel pipe, after holding the steel pipe between the bending die and the clamp with the metal core installed in the steel pipe, the bending die is moved while moving the clamp along the circumferential direction of the bending die. A rotary drawing bending method is often used in which a steel pipe is bent by rotating it.
However, when a thin steel pipe is bent by this bending method, the rigidity is lower than that of a thick steel pipe, causing problems such as wrinkling inside the machined part and flattening of the steel pipe (deforms into an elliptical shape). is there.

On the other hand, conventionally, various methods of bending a steel pipe by press-fitting a fluid into the steel pipe have been proposed in order to suppress the generation of wrinkles and flattening in the rotary pull bending process.
For example, in Patent Document 1, a sealing plug having a water pressure adjusting valve and an air vent function is attached to both ends of a steel pipe to be bent, and an incompressible fluid is directly press-fitted into the steel pipe to be bent by three rolls. Proposes a way to do.

Citation 2 proposes that a steel pipe is sandwiched between a bending die and a clamping die, a stopper is attached to both ends of the steel pipe, a liquid is injected into the steel pipe, and bending is performed in a pressurized state. ing.
Furthermore, in Patent Document 3, a jig in which blocking members are attached to both ends of a flexible connecting member is prepared, the steel pipe is sandwiched between a bending die and a clamping die, and the above-described jig is inserted into the steel pipe. It has been proposed to inject liquid between the blocking members and perform bending in a pressurized state.

JP-A-9-38726 JP 2002-254112 A Japanese Patent No. 3773307

By the way, in the methods proposed in Patent Documents 1 and 2, since the bending of the steel pipe is performed in a state where the fluid is directly pressed into the steel pipe, the generation of wrinkles and flattening can be suppressed, but the entire steel pipe is filled with the fluid. Since it is necessary and it takes time to install and handle the sealing plug, the processing time becomes long and the productivity is not always good.
In the method proposed in Patent Document 3, bending is performed in a state where a fluid is press-fitted into the entire bent portion of the steel pipe. And since the sealing plug is inserted in the both ends of the bending start of a steel pipe, and the bending end, the operation | work which extracts a sealing plug after a process is difficult. In addition, when performing the multistage bending process, it is necessary to pull out the sealing plug, so that the work is difficult even in the multistage bending process. That is, there is a big problem in terms of productivity.

  The present invention has been devised to solve such problems, and when bending a thin-walled steel pipe using the rotary drawing bending method, the bent portion does not wrinkle or flatten, and it is efficient. It aims at providing the method which can perform a bending process.

In order to achieve the object, the steel pipe bending method of the present invention is a rotary pulling bending method in which an incompressible fluid is press-fitted into a steel pipe and the steel pipe is bent in a state in which the fluid pressure is applied. Bending is performed with the fluid pressure applied only to the bending start point and a steel pipe bending part with a bending angle in the range of 5 ° <θ ≦ 45 ° with respect to the bending starting point when It is characterized by.
Using a sealing device having a first sealing member and a second sealing member connected to the first sealing member via a connecting member, the first sealing member is a steel pipe to be processed. It is preferable that the steel pipe be bent so that the second sealing member is positioned in a range of a bending angle of 5 ° <θ ≦ 45 ° with respect to the bending starting point .

In the bending method of a steel pipe provided by the present invention, the water pressure is only between two sealing plugs by connecting the fixed sealing plug and the non-fixing sealing plug with a metal chain or the like. Can be added. As a result, bending is performed in a state where water pressure is applied only to the bending portion of the steel pipe bent within the range of bending angle 5 ° <θ ≤ 45 ° from the bending starting point (bending angle 0 °), where deformation of the work material proceeds during bending. It can be performed.
Since the unsealed sealing plug is installed in the bent portion of the steel pipe having a bending angle of 5 ° <θ ≦ 45 °, it is easy to remove the sealing plug after bending. Therefore, multistage bending can be easily performed. In addition, since water is added only to the bending part of the steel pipe with a bending angle of 5 ° <θ ≤ 45 ° from the bending starting point (bending angle 0 °), the time for filling the steel pipe with water can be shortened, and productivity is reduced. The steel pipe can be bent well.

Schematic diagram of conventional hydraulic bending process Schematic of the hydraulic bending method of the present invention in which hydraulic pressure is applied to the steel pipe bending part Schematic of processing procedure using the hydraulic bending method of the present invention Hydraulic bending method according to the present invention when hydraulic pressure is applied to a bent portion of a steel pipe with a bending angle θ> 45 ° Diagram explaining the installation position of the second sealing plug that is not fixed (bending angle θ (°))

When bending a steel pipe, in order to prevent wrinkling and flattening of the steel pipe to be processed, for example, as shown in FIG. Yes.
As shown in FIG. 1, when sealing plugs are fitted on both ends of the steel pipe to be processed, it is necessary to press-fit a fluid into a wide area in the steel pipe, and the sealing plug is removed every time processing is performed. Productivity decreases due to the work of draining water. Furthermore, the method of sealing with a bending die and a clamp makes it impossible to perform multistage bending due to the structure.

Therefore, the present inventors have shortened the time for fluid injection into the steel pipe to be processed by making the arrangement position of the sealing plug narrow before and after the part where the deformation of the steel pipe to be processed progresses, We have been intensively studying methods to increase efficiency.
In the process, the fixed first sealing plug and the fixed second sealing plug connected to the fixed first sealing plug through a connecting member such as a metal chain. It has been found that if it is possible to apply a fluid pressure only between two sealing plugs, it is possible to apply a fluid pressure only to a narrow region before and after the portion where the deformation of the steel pipe to be processed proceeds.
Details will be described below.

First, the outline of the method of the present invention will be described with reference to FIG.
The rotary pull bending method of the present invention uses an apparatus composed of a bending die 1, a clamp 2, a side booster 3, a back booster 4, and a wiper 5. The back booster 4 includes a first sealing plug 8 attached to the tip of a support 7 extending into the steel pipe 6 to be processed, and a position and orientation of the first sealing plug 8 via a metal chain 9. A second sealing plug 10 variably attached is provided continuously. A through hole 11 for passing a fluid is formed in the inside of the support 7 extending into the workpiece steel pipe 6 and the first sealing plug 8 at the tip thereof, and the through hole is formed in the other end of the support 7. A hydraulic pump 12 for press-fitting fluid through 11 is attached.
Note that an O-ring 13 is attached to the outer periphery of the first sealing plug 8 and the second sealing plug 10 in order to ensure liquid-tightness with the workpiece steel pipe 6.
And the fluid pressure is applied only to the area | region before and behind the site | part where a deformation | transformation of a to-be-processed steel pipe advances.

By the way, when bending a steel pipe using a rotary drawing bending apparatus as shown in FIG. 1 or FIG. 2, the region where the deformation degree of the steel pipe itself is large is in the vicinity of the tip of the wiper. And when a deformation | transformation of the steel pipe itself to be processed progresses, wrinkles are generated or flattened if there is no constraint.
Therefore, the present inventors have speculated that wrinkles and flattening can be suppressed by applying a high fluid pressure only to the region where the deformation degree of the steel pipe itself to be processed is large, that is, near the wiper tip. .

Next, a specific example method of the present invention will be described.
As shown in FIG. 3A, two sealing plugs are used: a first sealing plug 8 fitted with an O-ring and a second sealing plug 10 that is not fixed. Even if fluid pressure is applied between the two sealing plugs, they are connected by a metal chain 9 that does not break in the axial direction. An O-ring is attached to the wiper tip corresponding portion on the outer periphery of the first sealing plug.
In this state, bending is performed with fluid pressure applied between the two sealing plugs.

Since the fluid pressure is applied to the portion where the deformation proceeds, molding that suppresses wrinkles and flattening is possible.
Although details will be described later, the portion where the fluid pressure is loaded into the steel pipe is sufficient only for the bending part of the steel pipe with a bending angle of 5 ° <θ ≤ 45 ° from the bending start point (bending angle 0 °). The filling time is shortened, and the machining time is shortened accordingly. Further, as shown in FIG. 3 (b), the second sealing plug 10 which is not fixed after bending is installed in a steel pipe bending portion with a bending angle of 5 ° <θ ≦ 45 °. It is easy to pull out. As a result, bending can be performed with high productivity.

Many steel pipes are bent in multiple stages depending on the application, and if the method of the present invention is applied, multi-stage bending can be easily performed.
3 (a) and 3 (b), after performing the first stage bending process, if the bending position is changed again as shown in FIG. The second stage of bending can be easily performed without draining during removal. By performing this operation continuously, multistage bending can be performed.

Here, the portion where the fluid pressure is loaded in the steel pipe is only the bent portion of the steel pipe with a bending angle of 5 ° <θ ≦ 45 °. The reason for setting the upper limit will be described.
FIG. 4 shows a hydraulic bending method in which a fluid pressure is applied to a steel pipe bending portion having a bending angle θ> 45 °. As shown in FIG. 4 (a), bending can be performed even if a second sealing plug that is not fixed to a steel pipe bending portion having a bending angle θ> 45 ° is installed. However, when the second sealing plug is extracted from the steel pipe bending portion as shown in FIG. 4B, the edge of the sealing plug is in strong contact with the steel pipe bending portion and the steel pipe bending portion is broken (A portion in the figure). Sometimes. When the steel pipe is thick, there is no breakage of the steel pipe due to contact with the sealing plug edge, but the second sealing plug cannot be removed, and in some cases, the metal chain may be broken (part B in the figure). .

As described above, if the second sealing plug installation position that is not fixed is deep, it is difficult to pull out and bending molding may not be possible. Therefore, the installation position needs to be set at a bending angle θ ≦ 45 °.
In addition, the steel pipe bending part installation position of the lower limit bending angle 5 ° <θ is based on the results of Examples described later.

A bending test was performed using an austenitic stainless steel pipe.
Table 1 shows the dimensions and mechanical properties of the austenitic stainless steel pipe. Table 2 shows the processing conditions.
The bending radius (pipe center) was 80 mm, the set bending angle was 90 °, and the hydraulic pressure used in the hydraulic bending method was 6 MPa.

The first sealing plug is installed near 0 ° which is the bending start point of the steel pipe to be processed, and the second sealing plug which is not fixed is installed near the bending angle of 5 ° to 75 °. The sex was investigated.
As the test material, an austenitic stainless steel pipe having a thickness of 0.6 mm, which is likely to be wrinkled or broken, was used. An incompressible fluid was press-fitted with two sealing plugs connected by a metal chain inserted into the steel pipe, and bending was performed with the fluid pressure at 6 MPa.

As shown in FIG. 5, the first sealing plug fixed was installed in the vicinity of 0 ° which is the bending starting point. Table 3 shows the implementation results.
As a comparative example, wrinkles were produced in the rotational pull bending method using a core metal which is a normal process. In Examples 2 to 5, wrinkle-free processing is possible, but the second sealing plug that is not fixed as in Example 1 is installed in a bent part with a bending angle θ of 5 ° and water pressure is applied. Wrinkles occurred under the conditions. It is thought that wrinkles occurred inside the bend where water pressure was not applied because the area where water pressure was applied to the steel pipe bend was small.

As shown in Example 2, bending molding was possible under the condition that a second sealing plug that was not fixed was installed in a bending portion having a bending angle θ of 7 ° and water pressure was applied.
In addition, the second sealing plug that was not fixed as in Examples 3 to 5 was installed in a bending portion having a bending angle θ of 15 ° to 45 °, and bending molding was possible even under a condition where water pressure was applied. From this result, it was found that bending can be performed up to a bending angle θ of 45 ° even in a region where the rate of change in the plate thickness is substantially constant on both the outer side and the inner side.

As shown in Examples 6 and 7, the second sealing plug, which is not fixed, was installed in a bending portion where the bending angle θ was 50 ° and 75 °, and bending was possible under the condition that water pressure was applied. When a sealing plug that was not fixed after bending was pulled out, bending was not possible because a fracture occurred in the bent portion of the steel pipe. This is because when the second sealing plug that is not fixed after processing is pulled out, the edge portion of the sealing plug comes into contact with the bent portion of the steel pipe and breakage occurs.
From these results, bending molding became possible by installing a sealing plug that was not fixed to the steel pipe bending portion where 5 ° <bending angle θ ≦ 45 °.

Claims (2)

A rotary pulling bending method in which an incompressible fluid is press-fitted into a steel pipe and the steel pipe is bent with fluid pressure applied, and the bending start point and the bending start point when the bending start point of the steel pipe to be processed is 0 °. A bending method for a steel pipe, characterized in that the bending is performed in a state where the fluid pressure is applied only to a bending portion of the steel pipe in a bending angle range of 5 ° <θ ≦ 45 ° . Using a sealing device having a first sealing member and a second sealing member connected to the first sealing member via a connecting member, the first sealing member is a steel pipe to be processed. The steel pipe is bent so that the second sealing member is positioned in a range of a bending angle of 5 ° <θ ≦ 45 ° with respect to the bending starting point. A method of bending steel pipes.

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