JPS6161914B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The disclosed technology belongs to the technical field of preventing buckling deformation of a welded seam in the production of thin-walled roll-formed pipes.

<Summary of the gist> Therefore, the present invention involves bending a coil-wound plate material by drawing out a coil-wound plate material and asymptotizing both edges by roll forming.
This invention relates to a welded pipe manufacturing method in which the pipes are brought together to form a circular cross section and the joining seam is welded,
In particular, in the bending process of both edges, both edges are heated to relieve the tensile stress, and then the entire tube is heated evenly in the circumferential direction until just before the edges meet and weld. In order to reduce compressive residual stress,
This invention relates to a welded pipe manufacturing method that prevents buckling of seams.

<Prior art> As is well known, pipe materials are widely used in various fields such as transportation pipes and wiring pipe bodies, and there are many types, but they are relatively easy to form from raw materials and are cost-effective. Roll-formed tubes are widely used due to their advantages.

To manufacture the seed seam welded pipe, as schematically shown in FIGS. 1 and 2, a steel plate material 1 made of a coiled material is rolled out,
The edges 2, 2 are brought inward and bent using forming rolls (not shown), gradually curved and brought together, formed into a circular shape at the joint 3, and seam welded 4 to form the tube 5.

Therefore, in the process of bending the edges 2, 2, elongation strain acts on the edges 2, 2 in the length direction (axial direction), and in general, the tensile stress exceeds the elastic limit and plastic strain occurs. do.

<Problems to be solved by the invention> However, after the bending process is completed, both edges 2,
At the time when the edges 2 meet, the elongation strain occurring in the edges 2, 2 decreases, and compressive residual stress comes to act on the edges 2, 2 portion due to the plastic strain generated in the bending process.

Therefore, in the welding process after assembly, this edge part buckles between the rolls, resulting in a so-called wakame-shaped deformation 6, 6, etc., occurring at the edge part.

Although this phenomenon is unlikely to occur in thick-walled tubes, it is more likely to occur in thin-walled tubes, and as a result, manufacturing of thin-walled roll-formed tubes has been difficult.

<Objective of the Invention> The object of the present invention is to solve the problems of manufacturing roll-formed tubes based on the above-mentioned prior art, and to alleviate the tensile plastic strain in the process of bending both edges together. reduces the stress in the entire process by relaxing the compressive stress by heating,
The purpose of this invention is to provide an excellent welded pipe manufacturing method that is useful for piping technology applications in various industries.

<Means and operations for solving the problems> In order to solve the above-mentioned problems, the structure of the present invention, which is based on the above-mentioned object and the gist of the above-mentioned claims, is to unwind a coiled plate material and roll it into a circular shape. In the process of bending and forming the cross section, heating is applied only to both edges to relieve tensile stress and prevent plastic strain from occurring, and as the edges meet, the entire tube is heated in the circumferential direction. Heat is applied to generate compressive thermal stress in the general area, and in balance with this, the compressive residual stress in the edge is reduced by the tensile stress generated in the edge, thereby preventing the occurrence of buckling deformation in the edge. Technical measures have been taken to prevent this and make it possible to manufacture thin-walled welded pipes by arc welding or the like.

<Example> Next, an example of the present invention will be described below with reference to FIG. Note that the same parts as in FIGS. 1 and 2 will be described using the same reference numerals.

The material 1, which is a steel plate, is wound into a coil and fed out, and the physical and mechanical forming itself is exactly the same as the conventional method.Both edges 2, 2 are asymptotic through forming rolls (not shown) to bend them together, and then curved. Then, make it into a circular cross-sectional shape.

Therefore, in the bending process of both edges 2, 2,
For example, a predetermined number of high-frequency heating devices 7, 7, . 8... spread as shown in the figure, thereby relaxing the tensile stress,
Reduces the causes of plastic deformation at the two edges.

Then, at the starting part of the meeting part 3, for example, 2/
A high-frequency heating device 7' is installed in the area of about 3 to heat the area to obtain a temperature distribution 8' that extends to the general area as well. Alleviates the occurrence of compressive stress.

After the edges 2 and 2 have met, welding 4 to the meeting part is performed by arc welding, and a high-frequency heating device 7'' is provided in a ring shape between the rolls around the entire circumference of the tube to heat the area immediately before the seam is welded. , the entire circumference is made to have a uniform temperature distribution of 8'', stress is suppressed over the entire circumferential direction, and welding is performed in a manner that buckling does not occur between the rolls at the seam at the meeting part.

Therefore, when the pipe 5 after welding returns to room temperature, the seam weld is smooth, and the so-called seaweed-like deformation shown in FIG. 2, which is conventional, does not occur even in thin-walled pipes.

It goes without saying that the embodiments of the present invention are not limited to the above-mentioned embodiments; for example, the heating device may be a strip heater, and various other embodiments can be adopted, and the invention can also be applied to thick-walled pipes. It is.

<Effects of the Invention> As described above, according to the present invention, heating is applied to both edges where tensile stress first acts during the process of unwinding a coil plate material and bending both edges together using forming rolls to form a circular cross section. This provides an excellent effect of reducing plastic deformation of both edges.

Furthermore, in the process where both edges come together and tensile stress acts on the general area, and compressive stress acts on the edge, the tensile stress in the general area is reduced by heating the entire circumferential area to create the same uniform temperature distribution. As a result, an excellent effect is achieved in that so-called wakame-like buckling does not occur between the forming rolls at the meeting portion.

In this way, heating is applied to the bending edge to prevent plastic deformation due to tensile stress in the initial stage, while tensile stress is relaxed in the general area during the assemblage period, and just before welding, heating is applied uniformly to the entire circumference. By creating a uniform temperature distribution and eliminating the influence of heating, the temperature is averaged over the entire circumference and lowered to room temperature, so a smooth surface can be maintained over the entire circumference.

The effect of preventing such buckling deformation is particularly effective for thin-walled tubes, and has the effect of satisfying the needs of roll-formed thin-walled tubes.

[Brief explanation of the drawing]

Figure 1 is a plan view of sheet material bending during welded pipe manufacturing.
FIG. 2 is a side view of buckling deformation of a weld line based on the prior art, and FIG. 3 is a schematic side view of one embodiment of the present invention. 1...Plate material, 2...Edge, 3...Meeting (part), 4...Welding, 7, 7', 7''...Heating (device).

Claims (1)

[Claims] 1. In a welded pipe manufacturing method in which coil-wound plate material is paid out and roll-formed to asymptotically bring together both edges of the plate material and welded together, heating is applied to both edges in the bending process of the plate material to relieve tensile stress and reduce tensile stress. A welded pipe manufactured by suppressing the occurrence of plastic strain and applying heat to the entire area in the width direction of the plate material after the two edges meet until immediately before welding to relieve compressive residual stress on the edges. Method.