JPH0459130A - Method for forming electric resistance welded steel tube - Google Patents

Abstract

PURPOSE:To reduce the residual stress in longitudinal direction at both edge parts and to manufacture the electric resistance welded steel tube with the good shape by making the draft against the inner side larger than the both edge parts of the blank tube. CONSTITUTION:When the forming to make the curvature large is executed on the break down forming process of the 2nd pass, the draft of the part of length (l) inner side from both edge parts is made large. That is, the above forming is executed by utilizing the upper roll 10A and the lower roll 12A designed so that the clearance delta1 of both upper and lower rolls at the position in contact with both edge parts [(l0-l)divided by 2] of the blank tube is made larger than the clearance delta2 of the position in contact with the inner side part. Here, the circumference directional length (l)of the inner side part is 50-90% of the circumferential length l0 of the blank tube. The difference of the draft between the both edge parts and the inner side part can be not decided at the same rule because it is influenced with every kinds of factors of the material characteristic of the blank tube, the thickness, the width, the forming condition, etc. The difference of the draft of most preferable in the range without generating the shape defect and not influencing for the accuracy of the dimension of tube is adopted.

Description

[Detailed description of the invention] [Industrial application field]

The present invention makes it possible to obtain high-quality products with no welding defects in the welded joints! This invention relates to a method of forming a sewn steel pipe.

[Conventional technology]

For example, the forming technology of ERW steel pipes is disclosed in Japanese Patent Application Laid-Open No. 58-1
Publication No. 96181 discloses that during roller forming, by forming a portion of a certain length from the end of the plate into an elliptical or nearly oval shape without bending it, thin-walled ERW tubes can be formed easily. discloses a method for forming a thin-walled electric resistance welded tube that allows easy welding after forming. Furthermore, Japanese Patent Laid-Open No. 61-165225 discloses a step of bending the vicinity of both edges of the material to be formed in the same direction as the intended tube, and bending the portion other than the vicinity of both edges in the opposite direction to the tube. and by maintaining the trajectory plane of a straight line connecting both ends in each cross section of the material to be formed in a flat or substantially flat shape,
It reduces the difference in the elongation of the locus of each part of the material to be formed in the circumferential direction of the pipe, making it possible to manufacture thin or ultra-thin walled $sewn pipes without causing buckling or shape defects in the material to be formed. A device is disclosed.

[Problem to be achieved by the invention]

However, in the case of the forming method disclosed in JP-A-58-196181, a flat part is formed in the welded part by welding after forming.
In the subsequent sizing process, it is necessary to apply strong pressure to form the tube into a perfect circle. As a result, there are problems in that the sizing roll is more likely to develop flaws and the ductility of the pipe is reduced due to work hardening. Furthermore, if the reduction during sizing is insufficient due to avoidance of strong reduction, the problem of poor roundness of the tube arises. On the other hand, in the case of the apparatus disclosed in JP-A No. 61-165225, the difference in the length of the trajectory of the edge is large, especially in the initial stage of forming (on the entrance side of the forming roll). The film distortion becomes large and it is not possible to sufficiently prevent the edge from extending in the longitudinal direction.
There is a problem in that the edges are bent in the longitudinal direction during edge bending, and compressive stress in the longitudinal direction remains in the edges after forming, resulting in poor shape. The present invention has been made in order to solve the above-mentioned conventional problems, and can prevent shape defects from occurring at both edges of a molded raw pipe. Provided is a method for forming an ERW steel pipe that can prevent welding defects from occurring and produce a well-shaped ERW steel pipe without applying excessive pressure during the sizing process. The task is to do so.

[Means to achieve the task]

The present invention provides an electric resistance welded steel pipe forming method in which an electric resistance welded steel pipe is manufactured through a predetermined process after a breakdown forming process, and in which at least one of the breakdown forming processes is carried out by rolling down the raw pipe between upper and lower rolls. By rolling the bus at a larger rolling reduction ratio for the inner part, which is located inside both edges of the raw pipe and whose circumferential length is 50 to 90% of the circumferential length of the raw pipe, than at both edges of the raw pipe. , the above-mentioned problem has been achieved.

[Action and effect]

As a result of various studies on break-down forming of raw pipes, the present inventors found that, as shown in Figure 2, an example of stress distribution, the raw pipes were not rolled at any part of their circumference as in the past. Compared to the case of forming or forming while rolling at a uniform reduction rate over the entire circumference, by increasing the reduction rate for the inner side of both edges than for both edges of the raw pipe, the above-mentioned It has been found that the residual stress in the longitudinal direction at both edges can be reduced. Moreover, as shown in the examples described later, by setting the circumferential length of the inner part to 50 to 90% of the circumferential length of the raw pipe,
It is possible to particularly preferably prevent the occurrence of defects in the shape of the edges, etc. caused by the longitudinal compressive stress remaining in both edges, and as a result, the butt shape of both edges when welding becomes good. It has become clear that welding can be performed easily and reliably, and that defects such as poor welding or poor welding shape can be effectively prevented from occurring.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. Figure 1 shows one example! It is a process sectional view showing the outline of the break-down forming process in the forming method of a sewn steel pipe. In this example, after the four-bath break-down molding process shown in FIGS. 1(A) to (D), the electric voltage was
! It is used to form steel pipes. FIG. 1(A) shows the break down molding process of the first bus. In this pass, a raw tube A made of a long steel plate is passed between an upper roll 10 and a lower roll 12 in a direction perpendicular to the plane of the drawing, and the cross section is formed into the shape shown in the figure, and at that time, the rolling reduction ratio for the raw pipe A is the same for the entire circumference of the raw pipe. FIG. 1(B) shows the break-down forming process of the second pass, in which the raw tube A formed in the first stage is
A and the lower roll 12A to form the tube to increase its curvature. At that time, the rolling reduction ratio with respect to the base tube A is as follows:
The rolling reduction ratio is made larger for the inner side portion having a circumferential length of 1 located inside the both edge portions than for the both edge portions. That is,
The upper roll 10A is designed so that the gap δ1 between the upper and lower rolls at the position where both edges of the raw pipe [(fflo-J ri÷2) contact is larger than the gap δ2 at the position where the inner part contacts.
The above molding is performed using the lower roll 12A, where:
The circumferential length 2 of the inner part is 50 to 90% of the raw pipe circumference 1o.
It is. FIG. 1(C) shows break-down forming in the third pass, in which the raw tube A formed in the second bath is passed between the upper roll IOB and the lower roll 12B, and the curvature is further increased. I do. In this path, as well as the second bus above,
Both upper and lower rolls IO where the roll gap δ3 at the position where both edge portions contact is larger than the roll gap δ4 at the position where the inner side portions contact
B and 12B, and also in this third pass (not shown), the circumferential length of the inner part is 50 to 50% of the circumference of the raw pipe.
It is 90%. Figure 1 (D) shows the fourth pass of break-down forming, in which the blank tube A formed in the third pass is rolled down from both sides with a pair of side rolls 14 and 14 to further increase the curvature. Form into approximately U-shape. After the break-down forming of the first to fourth passes described above, the raw pipe is made closer to the tube shape by fin pass molding, and then both ends of the raw pipe are welded together in the next squeeze roll molding to form a pipe. ERW steel pipes are manufactured through the manufacturing process. According to this embodiment, in the second and third passes of the four-pass break-down process, the rolling reduction ratio for the inner part of the raw pipe is made larger than for both edges of the raw pipe, so that the raw material pipe is used in the break-down forming process. Compressive stress generated at both edges of the tube can be reduced, and defects such as poor shape due to residual stress can be effectively prevented from occurring. Note that the pass for increasing the rolling reduction ratio for the inner portion may be only one of the second and third passes. In this example, the difference in rolling reduction between both edges and the inner side is not specifically determined, but is influenced by various factors such as the material properties of the tube, its thickness, width, and molding conditions. In order to be
-Fi is within a range that does not cause shape defects and has little effect on the dimensional accuracy of the tube, which cannot be determined in a specific manner. An appropriate rolling reduction rate difference will be adopted. Here, the above-mentioned rolling reduction rate difference when the pipe size is 42.7φ x 1.2t will be specifically explained. However, for convenience, this will be explained as a difference in the amount of reduction. When the reduction amount of the entire circumference of the above-mentioned raw pipe is the same and the reduction rate difference is O (corresponding to δ1 = δ2 in Fig. 1 CB), usually 0.2 to 0.3% is applied to both edges. Compressive strain occurs. Now, assuming that the compressive strain is reduced by 0.2%, the difference in rolling reduction between the inner part and both edges is calculated as 0.002 to 0.00:3+n using the calculation formula (1) below. be able to. However, for the actual rolling reduction amount difference, not all of the above calculated values are necessarily adopted, and it is also possible to take other conditions into consideration and adopt an appropriate value within the calculated values. Amount of decrease in compressive strain at the edge ki (difference in longitudinal film strain caused by the difference in rolling reduction between the inner part and both edges) xk = (inner film strain - film strain at both edges) where, k: constant determined by rolling conditions (usually 1 to 1.
5) An appropriate reduction amount difference can be determined by the above equation (1). Next, the pipe size is 42.7φX1. Ot's 5US41
When manufacturing an am tube made of OL, the first
Table 1 shows the results obtained by mainly changing the length a in the circumferential direction of the inner part in the pass shown in FIG. 1B. In addition, in Table 1, the length of the inner part is expressed as the circumference of the raw pipe J.
It is expressed as a ratio to io. In addition, the above °C, flo, and the gaps δ1 and δ2 between the upper and lower rolls in the table are shown in Fig. 1 (B) above.
The same is true for . In addition, in other passes of forming using the upper and lower rolls, the rolling reduction rate over the entire circumference of the raw tube was kept the same. Table 1 In Table 1 above, when comparing conditions 1 to 4 where δ1-δ2 is 0.00511, in the case of condition 1 where the bulge ratio is 40%, a defective shape due to belly elongation occurs, and the bulge is The ratio is 1
In the case of condition 4, which is 00%, a defective edge shape occurs. On the other hand, in the case of conditions 2 and 3, where the ratio of bulges is 60% and 80%, no shape defects occur during forming, so the butt shape of the ends during welding is also stable. In addition, the dimensional accuracy of the product was also good because there was no difference in product wall thickness. Condition 5 is a case where the ratio of 1 is 100% and the difference in rolling reduction is very large, 0.02 m1, and no shape defects occurred, but a difference in product wall thickness of 0.02 rxn appeared. . From the above results, the ratio of the inner length is 50 to 90%.
It turns out that it is effective. At that time, δ1−δ
2[ni] is preferably on the order of 10<-2> or less. Note that the ratio of 50 to 90% of the length 1 of the inner part is effective not only for the steel pipe made of 5US410L of 42.7φxlOt, but for example, for steel pipes of 31.8 to 54.
It was also effective in a wide range of 0.8 to 1.5 t at 0φ. In addition, there are various types of sea bream, not only 5US41OL.
It was effective against one species. Although the present invention has been specifically explained above, the present invention is not limited to what was shown in the above embodiments. For example, forming with a larger rolling reduction ratio for the inner portion than for both edges may be performed in the first pass. Further, the method of increasing the rolling reduction ratio for the inner part than for the edge part is not limited to the method of using upper and lower rolls with different gaps as shown in the above embodiment. It is also possible to use a shape that does not make contact with each other.

[Brief explanation of the drawing]

FIG. 1 is a process sectional view showing an outline of break-down molding in an embodiment of the present invention, and FIG. 2 is a graph showing the relationship between break-down molding and longitudinal residual stress at the edge. . A...Main pipe, 10, IOA, IOB...Top roll, 12.12A,
12B...Bottom roll, 14...Side roll. Figure 1

Claims (1)

[Claims] (1) In the forming method for ERW steel pipes in which ERW steel pipes are manufactured through a predetermined process after the break-down forming process, at least one pass of the break-down forming process in which the raw pipe is rolled down between upper and lower rolls. The inner part, which is located inside both edges of the raw pipe and whose circumferential length is 50 to 90% of the circumferential length of the raw pipe, is rolled at a larger rolling reduction ratio than that of both edges of the raw pipe. A method for forming ERW steel pipes.