JPS6072615A - Method for roll-forming electric welded pipe - Google Patents

Abstract

PURPOSE:To prevent edge buckling by bending the central part of a plate into the reverse curvature to that of a product and bending both end parts to the same side as that of the product, before reverse-bending the reversely bent part and forming, at the same time, a joining part of the reversely bent part and both-ends bent parts. CONSTITUTION:At the initial forming stage of an electric welded pipe manufacturing process where a band-shaped plate is continuously roll-formed to weld the formed end-faces to each other; the central part of plate is bent so as to provide a reverse curvature to that of a final product, and both end parts are bent to the same side as that of the product, before reverse-bending the reversely bent part of sheet central part, and at the same time, a joining part of the central reversely-bent part and both ends bent-parts, is formed. In this way, the strain in the lingitudinal direction of edge part is reduced, and the edge buckling of plate is prevented within a small range of a wall-thickness/outer diam.

Description

[Detailed description of the invention] (industrial) 1” field) The present invention relates to a roll forming method for an electric resistance welded pipe.

In particular, this is to prevent edge buckling when a strip-shaped steel plate is continuously roll-formed to produce a tubular product.

(Prior art) The roll forming method for steel pipes in the manufacture of ERW pipes is
- There are bending, zergular bending, edge bending, etc., and combination methods of these have been put into practical use.

In either method, when the wall thickness-to-outer diameter ratio (t/D) decreases, the rigidity decreases, resulting in edge buckling. Therefore, it becomes impossible to form it into a steel pipe. □In the case of slight buckling, even when the steel pipe can be formed, the 5-bath welding joint 71'I will not be stable and the weld quality will be poor.

From this point of view, the range in which electric resistance welded pipes can be manufactured is generally limited to a t/D of about 2%.

As shown in FIG. 1, the inventor has developed a forming roll 1, a,
In this case, the plate 2 is formed by the conventional forming method to gradually make it circular in step 1b.
e has a larger elongation in the longitudinal direction than the center portion 1c, and the difference in elongation is also large. As a result, as shown in FIG. 5(A), it was found that the compressive residual stress in the longitudinal direction of the edge portion was large, causing edge buckling.

As shown in Fig. 3, according to Japanese Patent Application Laid-Open No. 56-136230, there is a method of reversely bending the central part of the plate and simultaneously bending both ends of the plate in the initial stage of forming. After flattening the plate, the plate is further bent in a forming process. Therefore, the following problems arise.

1) After bending the middle part of the board and bending the edge of the print, we paid attention to the edge of the board to flatten it, and as shown in Figure 6 (A), the amount of horizontal movement was large and the edge was stretched. growing. Therefore, it is disadvantageous for edge buckling.

2) Since the plate is flat, the bending rigidity in the longitudinal direction is lower than when the plate has a curvature as a whole, which is disadvantageous to edge buckling.

, 3) Because there are flat parts, rolls are likely to cause scratches unless formed in the primary process. However, the formability of the cross section is poor.

(Structure and operation of the invention) The present inventor has discovered that at the initial stage of molding, as shown in FIG.
The center part of the plate is bent to give a curvature opposite to that of the final product, and both ends are bent to the same side as the final product.In the next step, the center part is bent back.1--Discover the forming method. When molded by this method, as shown in FIG. 4(B), the difference in elongation in the longitudinal direction between the edge portion 1c and the center portion tC is small, and the average elongation in the width direction of the plate is also small. At this point, the compressive residual stress in the longitudinal direction is dispersed and reduced as shown in FIG. 5 (13). Therefore, edge buckling can be prevented.

The present invention bends the central part of the board so that it has a curvature 15 opposite to that of the final product.After bending both ends to the same degree as the final product (llll), the central part of the board is bent back, and at the same time, the central part Form the connecting part between the reversed part and the bent parts at both ends, and perform the flattening process.'1. Therefore, Figure 6 (B
) As shown in T, the amount of movement of the edge is small, the rigidity of the bottom and longitudinal surfaces is high, and the formability of the cross section is also good, making it extremely advantageous.

Furthermore, the present inventor found that in the above molding method, when the height of the center part is not maintained at a constant height, but is combined with a method (downhill) in which the height of the center part is lowered as shown in FIG. It has been found that the elongation in the longitudinal direction of the part is further reduced, and the effect of preventing edge buckling is enhanced. The reason is that by going downhill, the amount of movement of the etch is reduced,
This is because the difference in elongation between the edge portion and the center portion is alleviated.

Next, one embodiment of the present invention will be described.

Taking as an example a plate with a thickness of 0.8 mm and an outer diameter of 76.3 mm (t/D ratio of 1%), examples of molding using the single molding method (Fig. 2) and the conventional method (Fig. 1) are shown. In the conventional method shown in FIG. 8, the strain in the longitudinal direction of the edge portion is large and accumulates as the molding progresses, and the difference from the strain in the longitudinal direction of the center portion is large. On the other hand, in the present forming method shown in FIG. 9, the longitudinal strain at the edge portion is small, and 17C does not accumulate. Therefore, it is clear that the present invention has a significant effect on edge buckling, and is extremely advantageous.

In addition, the elongation strain in the longitudinal direction is shown in Fig. 10 and the strain in the circumferential direction is shown in Fig. 11 when downhill is used together.
It can be seen that the longitudinal elongation strain is suppressed as the downhill amount increases ζ, and is effective in preventing edge buckling.

(Effects of the Invention) According to the present invention, edge buckling can be prevented within a small range of wall thickness-to-outer diameter ratio (t/D). Also.

This makes it possible to stabilize welding butt and ensure welding quality.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the molding process of the conventional method, Figure 2 is an explanatory diagram showing the molding process of the present invention, Figure 3 is an explanatory diagram showing the molding process of the cited example, and Figure 4 (A ), (L is an explanatory diagram showing the elongation of edges and centers by the conventional method and the present invention method, Figure 5 (A), (L is an explanatory diagram showing the residual stress due to molding by the conventional method and the present invention method. ;J@Figure 6 (A), CB)
Figure 7 is an explanatory diagram showing the movement of the molding machine between the conventional method and the method of the present invention. Figure 7 is an explanatory diagram of downhill molding. Figure 8 is an explanatory diagram showing longitudinal elongation strain by the conventional method. The figure is an explanatory diagram showing the longitudinal elongation strain by the method of the present invention, Fig. 10 is an explanatory diagram showing the longitudinal elongation strain during downhill molding, and Fig.
The figure is an explanatory diagram showing circumferential strain during downhill molding. Patent Applicant Representative Patent Attorney Tomoyuki Yafuki (and 1 other person) No. 2@, Figure 3 (A) (B) Lennoc IpinoC Figure 5 (A), CB) el 6 Figure tA) (B) No. 7, No. 8, No. 9, No. 10, 〆/de

Claims (2)

[Claims] (1) In the manufacturing process of electric resistance welded pipes, in which a strip plate is continuously roll-formed and the formed end faces are welded, the central part of the plate is given a curvature opposite to that of the final product during the multiple roll-forming processes. a step of bending the opposite ends of the central part to the same side as the final product; and a step of bending back the reverse side of the central part and forming a connecting part between the reverse bent part of the central part and the bent parts of both ends. A roll-forming method for an ERW pipe, comprising: (2) A roll forming method for an electric resistance welded pipe as described in Item 1 of the Patent Claim, characterized in that in the forming step of the above forming method, the vertical line through which the material passes is gradually lowered.