JPH08252636A - Bending of steel tube - Google Patents

Abstract

PURPOSE: To prevent buckling generated at the joining part between bent part and straight part in bending a steel tube with a roll bender. CONSTITUTION: In bending with a three roll bender, the joining part between bent part and straight part is turned to geometrically incontinuous, buckling is likely generated. While inserting/filling a core material having a length of <=3.5 time of outer diameter D from tube end and executing bending, buckling is prevented. Further, the filling rate is 60-90%, the end of core material is inclined so as not to mark its trace, the diameter of core material is made larger in center part and smaller at peripheral part, workability and prevention of buckling are made compatible.

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 steel pipe.

[0002]

2. Description of the Related Art There is a roll bender as a method for bending a steel pipe, which is used for bending a large diameter pipe or the like.
Figure 4 shows the processing method using a roll bender. When bending by this method, flattening of the steel pipe (Fig. 5) occurs along with the bending, bending is performed while hot, and the heating part outlet side is rapidly cooled to localize the deformation (Fig. 6). Method to suppress flatness by Ichise et al .: "Dieless bending of pipes", Showa 59
Of Plastic Processing Spring Lectures, 291, Tamai et al .:
"Accuracy test of small radius bending pipe by high frequency induction heating bending work" Ishikawajima Harima Technical Report, 17-2 (1977), 162)
Is taken. For aluminum profiles, etc., a method of preventing distortion and wrinkling of the cross section by filling the core material and bending it (Hasegawa et al .: "Wrinkle suppression effect in press bending of oddly shaped cross-section materials", 45th Plasticity Processing Conference Lecture Conference Proceedings, 497) is adopted. (FIG. 7).

As a shape defect different from these flat deformations, buckling may occur in the vicinity of a connecting portion (R stop portion) between a bent portion formed by bending and a straight portion not formed by bending. Fig. 8 shows the buckling of the connecting portion caused by the roll bender processing. Conventionally, effective measures have not been taken against the buckling of the connecting portion.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent buckling which occurs at a connecting portion between a bent portion and a straight portion in the above bending process of a steel pipe.

In bending by a roll bender,
Various studies have been carried out because the bent portion becomes the main body of the bent product, but the joint portion between the bent portion and the straight portion has not been studied so far. Since the shape of the connecting portion changes from the bent portion to the straight portion, the buckling occurs due to the discontinuity of the geometric shape. When such a connecting portion is used in a product, if such buckling occurs, the dimensional accuracy cannot be satisfied, which is a problem.

It is conceivable to insert the core material over the entire length of the bending main body portion for such a defective shape of the connecting portion between the bending portion and the straight portion. In this case, since the steel pipe is bent and flattened, the core material is removed after the bending work, that is,
There is a problem that it is difficult to remove the core material.

The present invention provides a method for bending a steel pipe aiming to improve the shape of the connecting portion between the bent portion and the straight portion by using a core material and to facilitate the extraction of the core material. To aim.

[0008]

The present invention has been made to solve the above problems, and the gist thereof is as follows. (1) When a bending process is performed by a roll bender, the sleeve part of the bending process is filled with a core material, that is, the length from the R stop to the bending side is 3.5 times or less of the pipe diameter D (3.5D). Bending method that inserts the core material up to and improves the shape of the R-stop portion. (2) A bending method, wherein the filling rate of the core material is 60% or more and 90% or less. (3) A bending method characterized by filling the core material so that the filling rate of the core material decreases toward the inside of the pipe. (4) A bending method characterized in that, when the core material is filled, a thick core material is arranged in a portion close to the center of the steel pipe.

[0009]

By filling the core material only from the sleeve portion to the vicinity of the R-stop portion, it is possible to prevent buckling of the connecting portion between the bent portion and the straight portion without significantly impairing workability in bending. Insert the core material from the bending sleeve into the filling range of the core material, and insert the core material from the insertion length L to the stop R to a length 3.5 times the pipe diameter D or less (3.5D) or less. However, this is a bending method for improving the shape of the R stop portion (FIG. 1). If this insertion length is long, it becomes difficult to remove the core material, so 3.5 D or less is appropriate. If the insertion length is 3D or less, the extraction becomes easier.

Further, with respect to the cross-sectional area π / 4 · Di ² determined by the filling rate of the core material by the pipe inner diameter Di, the filling rate of the core material = (sum of cross-sectional area of core material) / (pipe cross-sectional area π / 4 ・ D
i ² ) is 60% or more and 90% or less, which is a bending method. If the filling rate is not 60% or more, there is no force to restrain the buckling deformation of the steel pipe, and if it is 90% or more, it becomes difficult to fill and remove the core material.

As a constraint from another viewpoint of filling the core material, when the ends of the core material are aligned, that is, when the ends of the core material are aligned linearly as shown in FIG. 2, buckling occurs at the ends of the core material. Will occur.
Therefore, in the present invention, the end of the core material is tapered as shown in FIG. 1 to prevent buckling of the end of the core material.

Further, when the core material is filled, if the diameter of the core material is made smaller and the filling rate is increased, the effect of preventing buckling is improved, but the core material becomes thinner, which causes the following problems. That is, there is a problem that the core material is gripped by the bending process and the core material is broken when the core material is removed, which makes it difficult to remove the core material. On the other hand, the diameter of the core material that is in direct contact with the steel pipe remains thin, and the diameter of the core material that fills the central part of the steel pipe is increased,
First, the inventors invented a method (FIG. 3) for extracting the core material in the central portion. In this method, since the diameter of the core material in the center part to be extracted first is large, the core material does not break, and if the core material in the center part is removed, a void is created, so the core material around the core material can be easily removed. You can

[0013]

EXAMPLES Examples of the present invention will be described below. Table 1
The dimensions of the steel pipe used for the above, the bending radius (R), and the dimensions of the resin rod used for the core material are shown.

Under the conditions shown in Table 2, the core material was filled as shown in FIG. 1, and no shape defect was recognized at the core material insertion end. However, when the core material was filled as shown in FIG. As a result, irregularities with a steepness of about 1% were generated at the core material insertion end.

As shown in Table 2, when the filling rate of the core material is as low as 50%, the buckling is not sufficiently eliminated, but the filling rate is 65%.
When it was raised to%, the buckling became slight. Further, buckling was reduced when the core material was increased to 5φ to increase the filling rate, but the core material was ruptured during the core material removal after bending, and it was difficult to remove the core material. On the other hand, when the thickness of the core material was changed between the central part and the peripheral part, buckling could be suppressed without troubles of extracting the core material.

[0016]

[Table 1]

[Table 2]

[0017]

As is apparent from the above embodiment, the present invention can prevent buckling of the connecting portion between the straight portion and the bent portion and the defective shape. Further, even if the core material is used, the core material can be removed without trouble such as breakage of the core material, and the efficiency of the entire bending process can be improved. The present invention is also effective for bending a large-sized frame.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a filling method and filling range of a core material according to the present invention.

FIG. 2 is an explanatory view showing a normally considered method of filling a core material.

FIG. 3 is an explanatory view showing a filling method of a core material in which the thickness of the core material is changed in the present invention.

FIG. 4 is an explanatory view of bending processing by a roll bender.

FIG. 5 is an explanatory view showing a flattened state associated with bending.

FIG. 6 is a schematic view of hot bending.

FIG. 7 shows an example of bending of a shape member using a core, (a) is an example of various cores, and (b) is an explanatory view showing a bending state using the core.

FIG. 8 is an explanatory diagram of buckling at a connecting portion between a straight portion and a bent portion.

Claims (4)

[Claims] 1. In a method for bending a steel pipe using a roll bender, a core material is inserted from a boundary between a bent portion and a non-bent portion to a bent portion side to a length of 3.5 times or less of a pipe diameter D. A method for bending a steel pipe characterized by: 2. The method for bending a steel pipe according to claim 1, wherein the filling rate of the core material is 60% or more and 90% or less. 3. The method for bending a steel pipe according to claim 1, wherein the filling of the core material is performed so that the filling rate of the core material decreases from the pipe end toward the inside of the pipe. . 4. The method for bending a steel pipe according to claim 1, wherein a thick core material is arranged in a portion close to the center of the steel pipe when the core material is filled.