JPH0340672B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a welded pipe manufacturing method.

(Prior Art) As a conventional example of a welded pipe manufacturing method, for example, Japanese Patent Application Laid-Open No. 184073/1984 can be cited. This manufacturing method will be explained based on FIGS. 6 to 8. In the figures, 1 is a coil plate material, and this coil plate material 1 is formed into a group of forming rolls 2...
2, the welded pipe is formed into a circular cross-section, and the two edges 4, 4 are brought together by the fine pass rolls 3, and then the two edges 4, 4 are welded in the welding step 5. Manufacture.

In this case, in the above molding process, both edges 4, 4
Since the area near the edges 6 undergoes larger tensile plastic deformation than the other parts 6, in the fin pass zone, compressive residual stress exists near both edges 4, 4.
In addition, tensile residual stress is generated in each of the other portions 6, which causes buckling wrinkles in the vicinity of both edges 4, 4, resulting in the problem that sufficient welding cannot be performed. Therefore, in the above conventional example, during the process from forming to welding, especially in the fin pass zone, by heating and expanding the other part 6 other than the vicinity of the edges 4, 4, the area near the edges 4, 4 is heated and expanded. It relieves compressive stress and prevents buckling wrinkles.

(Problems to be Solved by the Invention) By the way, the present inventors conducted various tests in order to put into practical use the welded pipe manufacturing method based on the above basic concept, but as a result, it was found that It has become clear that heating the area can prevent buckling wrinkles in many cases, but does not prevent the occurrence of buckling wrinkles in all cases. Therefore, after studying the above test results, we discovered that the heating width is a factor that has a relatively large influence on the effect of preventing the occurrence of buckling wrinkles, which led us to create the present invention. be.

That is, an object of the present invention is to provide a welded pipe manufacturing method that can more reliably prevent buckling wrinkles caused by compressive residual stress generated near the edges 4, 4 in the welded pipe manufacturing method as described above. It's about doing.

(Means for solving the problem) Therefore, in the welded pipe manufacturing method of the present invention,
A coil plate material is unrolled and curved by roll forming, and both edges of the plate material are gradually brought together and welded. At a position on the side where the material enters from this welding process, heating means is used to heat the parts other than the vicinity of the edges of the plate material. In the method for manufacturing a welded pipe in which heating is performed, the heat application area by the heating means is set to 30 mm of the entire width of the coil plate material on both sides of the coil plate material, centering on the widthwise center of the coil plate material.
% or more and less than 80%.

(Function) In the above, the heating width is 30% of the total width of the coil plate material.
%, thermal deformation of the coil plate material occurs locally, resulting in bending deformation of the entire plate material, and compressive stress due to the bending deformation acts on the edges of the coil plate material, causing buckling wrinkles. This makes it more likely to occur. For this reason, the heating width is set to be wider than the above,
The above phenomenon can be prevented by making the strain generated at the edges such that the tensile strain caused by the overall elongation is larger than the compressive strain caused by bending deformation.
As a result, the occurrence of buckling wrinkles can be effectively prevented. In addition, since the heating width is set to less than 80%, it is possible to prevent the problem of a decrease in the effect of relaxing compressive stress near the edges due to an increase in the heating range, and the occurrence of buckling wrinkles can be further prevented. .

(Example) Next, the welded pipe manufacturing method of the present invention will be specifically explained.

First, as shown in Fig. 1 a and b, when the center part of the coil plate material 1 with the circumference B is heated to a predetermined temperature ΔT within the range of the width b in a rectangular shape, first from the balance of forces, as shown in Fig. 2 As shown, a tensile strain ε1 occurs at the edge 4, and a compressive strain ε2 occurs at the center. That is, the following distortions occur: ε1 = ΔT·α·b/B ε2 = ΔT·α−ε1 (where α is the coefficient of linear expansion).

Next, as shown in Fig. 3, if we consider the bending moment Mb caused by the above-mentioned strains ε1 and ε2, this bending moment Mb is caused by the fact that the coil plate 1 is a cylinder with a radius r and a plate thickness t. Assuming that it is rotatably supported, Mb=2・ΔT・α・E・t・r ²・sin (πb/B). Therefore, the compressive stress σ1 generated at the edge by this bending moment Mb is σ1=Mb/(3.2・^r2・t)=E・(1/1.6)ΔT・α・sin(πb/B), When this is expressed as strain, ε3=(1/1.6)・ΔT・α・sin(πb/B).

However, in reality, the free rotation of the coil plate material 1 is restricted by the rolls of each stand, so the actual strain ε4 is 0.5 to 0.7 of the above strain.
decrease by a factor of two. Here, considering the average value 0.6 times,
The strain ε4 caused by bending is ε4=(1/2.7)・ΔT・α・sin(πb/B).

Therefore, the strain ε5 that actually occurs at the edge of the coil plate material 1 is determined. This strain ε5 is determined as the difference between the previously determined strain ε1 due to the average elongation and the compressive strain ε4 due to the bending, as shown below. It will be done.

ε5=ε1−ε4 =ΔT・α・{(b/B) −(1/2.7)・sin(πb/B)} The relationship between the above ε1, ε4 and (b/B) is shown in Figure 4. , as shown in the figure, in the region (b/B)≧0.3, ε1≧
ε4, tensile strain is generated at the edge 4, and local heating acts to prevent the occurrence of buckling wrinkles at the edge 4. On the other hand, in the region (b/B) < 0.3, ε1 <ε4, compressive strain occurs in the edge 4, and therefore local heating acts in a direction that promotes the generation of buckling wrinkles.

From the above, when heating the center part of the coil plate material 1 to prevent the occurrence of buckling wrinkles, the width b of the high temperature region formed in the center part is
It is clear that it is necessary to make the overall width B of the coil plate material 1 30% or more, and this is explained in the fifth section.
This agrees well with the test results shown in the figure. In Fig. 5, buckling deformation occurs even when the heating width ratio exceeds 0.8, but this is because the compressive stress near the edge 4 is alleviated by increasing the heating range. This is because the effect of heating is reduced, and therefore it is preferable that the heating width ratio is less than 0.8.

In the above, we considered the case where the temperature is distributed in a rectangular shape, but even if the temperature distribution is in another shape, this can be converted to an equivalent rectangular distribution. Therefore, there is no particular problem with the above consideration method. The method of the present invention can be applied not only to local heating but also to edge cooling.

(Effects of the Invention) In the welded pipe manufacturing method of the present invention, when heating the central part of the coil plate material to prevent the occurrence of buckling wrinkles, the width of the high temperature region is set to 30% of the total width of the coil plate material. As a result of the above, it is possible to prevent the occurrence of compressive strain at the edges due to bending deformation of the coil plate material, and therefore, even when the coil plate material becomes thin, it is possible to effectively prevent the occurrence of buckling wrinkles. This makes it possible to prevent this and make it possible to manufacture high-quality welded pipes. In addition, since the heating width is set to less than 80%, it is possible to prevent the problem of a decrease in the effect of relaxing compressive stress near the edges due to an increase in the heating range, and the occurrence of buckling wrinkles can be further prevented. .

[Brief explanation of drawings]

1a, b and 2 are explanatory diagrams of the strain occurrence state when no bending deformation occurs in the coil plate material, and FIG. 3 is an explanatory diagram of the strain occurrence state when bending deformation occurs,
Figure 4 is an explanatory diagram showing the relationship between heating width and each strain, Figure 5
The figure is a graph of experimental results showing the relationship between the heating width and the occurrence of buckling wrinkles, and Figures 6 to 8 are explanatory diagrams of the welded pipe manufacturing method. 1...Coil plate material, 4...Edge, 5...Welding process, b...Heating width, B...Full width of coil plate material.

Claims (1)

[Claims] 1. A coil plate material is fed out and curved by roll forming, and both edges of the plate material are gradually brought together and welded. At a position on the side where the material enters from this welding process, parts other than the vicinity of the edges of the plate material are heated. In a method for manufacturing a welded pipe in which heating is performed by means of heating means, the heat application area by the heating means is set to cover the entire width of the coil plate material on both sides of the widthwise center of the coil plate material.
A welded pipe manufacturing method characterized in that the width is 30% or more and less than 80%.