JPS63281713A - Production of electric resistance welded tube - Google Patents

Abstract

PURPOSE:To protect edge wave from taking place at the time of forming a tube stock by lowering the height and position of rolls before and behind a standard roll in a group of forming rolls. CONSTITUTION:When a pipe tube stock P is provided in the production process of an electric resistance welded tube, a comparatively high height and position are given to a reference breakdown roll 3BD and comparatively low heights and positions are given to breakdown rolls 2BD, 4BD. In this manner, the amount of downhill of the reference forming roll 3BD is increased and the amounts of downhill of forming rolls 2BD, 4BD before the reference forming roll are decrease. As a result, the pass line is projected upward near the reference forming roll 3BD and a tensile strain takes place at the tube stock edge near the forming rolls 2BD, 4BD before and behind the reference roll. Accordingly, the reducing gradient of edge strain can be relieved and the edge wave can be protected from taking place. Furthermore, the edge waves can be protected from taking place by adjusting the height and position of a group of forming rolls including fin pass rolls 1F-3F.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing an electric resistance welded steel pipe, and is designed to prevent the generation of edge waves during forming of the raw pipe.

``Prior art'' In general, ERW steel pipes with seam lines extending parallel to the pipe axis are produced by cutting rope strips in advance to the developed size of the ERW steel pipe to be manufactured, and forming them in various ways during the initial and middle forming processes. It is sequentially formed into a predetermined shape using rolls, and the joint edges are stably formed using fin bath rolls in the final stage of the forming process. After final forming into a blank pipe of the predetermined shape and dimensions, the joint edges are formed using squeeze rolls. ? Manufactured by S-welding.

In the initial stage of the steel strip in the above-mentioned method of manufacturing electric resistance welded steel pipes,
During the mid-term bending process, the steel strip undergoes a complex three-dimensional forming process, so the strain at each part in the longitudinal direction is not uniform (as the forming process progresses, waves ( In this case, the oven pipe becomes unweldable, resulting in problems such as a reduction in material yield or a reduction in the quality of the welded part.

The frequency of occurrence of the edge waves becomes more pronounced as the ratio of wall thickness t to outer diameter, t/D, becomes smaller.

Conventional technologies to prevent the occurrence of edge waves include:
For example, as shown in FIG. 1, there is a method of producing an electric resistance welded steel pipe using a cage forming method in which the edge portion of the raw pipe is continuously restrained by a large number of cage rolls.

This is the steel strip S, pinch roll PR, Ikl~-4 breakdown roll IBD, 2BD, 3BD, 4BD,
The edge forming roll ER, the outside cage rolls OCR arranged at small intervals, and the inside cage roll ICR are used to sequentially form a cylindrical raw pipe P, and after passing through the final outside cage roll OCR, -1 ~ By applying circumferential reduction in the fin pass rolls IF, 2F, and 3F of Hato 3, the pre-joint edge portion Pe is stably formed, and the finished pipe P is formed into a predetermined shape and size. This is a method of manufacturing an electric resistance welded steel pipe by high-frequency heating the pre-joint edge portion Pe of the finished pipe P and performing ampscent welding with a squeeze roll SQ.

Further, as another technique for preventing the generation of edge waves, there is a downhill forming method having an exponential downhill curve in which the change in the amount of downhill is in-type, as disclosed in JP-A-57-149016, for example. has been proposed, which suppresses the generation of edge waves by making the lengths of the trajectories traced by the edges and the bottom center equal in the process of forming a blank pipe from a steel strip.

"Problems to be Solved by the Invention" By the way, even if the above-mentioned methods for forming a material pipe are used alone or in combination to form a material pipe, the t/D may become small, or the manufacturing size may be unused. Therefore, when the shape of the molded flower is changed, that is, the shape of the roll is changed, edge waves occur, which is not a sufficient prevention technique and has become a problem.

"Means for Solving the Problems" In order to solve the above-mentioned conventional problems, the present inventors conducted various experimental studies and found that in the process of forming a raw pipe from a steel strip, The length is longer than the trajectory length followed by the bottom center, so the edge is elongated in the early and middle stages of forming, and then from the middle to the end, the edge undergoes compression molding, but the longitudinal film strain of this edge decreases. It was found that at a position where the amount of compression (amount of compression) is large, that is, at a position where the gradient of decrease in longitudinal film strain is large, a sharp compressive stress acts on the edge, which causes the edge to buckle, resulting in the generation of edge waves.

Therefore, in order to prevent edge waves from occurring, it is sufficient to reduce the amount of decrease (that is, to make the decreasing slope gentler) at the position where the longitudinal film strain of the edge rapidly decreases.

The present invention has been made based on the findings of the above experimental research results, and its gist is that a steel strip is passed through forming roll stands arranged in tandem in the longitudinal direction of the steel strip. In the manufacturing method of the electric resistance welded steel pipe in which the material is bent in the width direction, then formed into a substantially circular cross-section material pipe by fin pass rolls, and the edge portion of this material pipe before the seam is welded, the required standards in the forming roll group are provided. The present invention provides a method for manufacturing an electric resistance welded steel pipe, characterized in that forming is carried out by lowering the height position of forming rolls before and after the forming rolls compared to the height position of the forming rolls that should be formed.

"Function" As mentioned above, when forming an ERW steel pipe, the height position of the forming rolls before and after it is lowered compared to the height position of the forming roll that should be the required standard in the forming roll group. (By forming with Tensile strain occurs at the edge of the raw tube, and therefore, the strain reduction gradient at the position where the longitudinal membrane strain of the edge rapidly decreases can be made warmer, so the generation of edge waves can be prevented.

"Example" Next, an example of the method for manufacturing an electric resistance welded steel pipe according to the present invention will be described based on FIGS. 1 to 4.

As shown in Fig. 1, the steel strip S is rolled on a pinch roll PR5
~lk4 breakdown roll IBD.

2BD, 3BD, 4BD, Edge forming roll E
R, outside cage roll OCR, inside cage roll [Sequentially formed into a cylindrical elementary vP by CR, and after passing through the final outside cage roll OCR, to the fin pass rolls IF, 2F, and 3F of Kan 1 to Nh3. By applying reduction in the circumferential direction, while aiming at stable forming of both joint edges Pe, finish forming the raw pipe P with a predetermined shape and dimensions, and forming the joint both edges of the finished raw pipe P. Part Pe is subjected to high frequency heating and upset welded using a squeeze roll SQ to produce an electric resistance welded steel pipe.

Figure 2 (A), (B), (C), (D), (E)
, CF), (G), and (H) are AA sectional views, BB sectional views, and C in FIG. -C sectional view, D
-, E-E cross-section, F-F cross-section, G-C cross-section, and H-H cross-section, but conventionally, the pass line of such a forming process is the 3rd rgJ curve. The change in the downhill coefficient (downhill 31/tube outer diameter) as shown in FIG. 2 shows a gradually decreasing so-called exponential downhill curve.

In Fig. 3, the horizontal axis shows the position of each forming roll, and the vertical axis shows the downhill coefficient.
When forming a raw pipe P with a substantially U-shaped cross section as shown in the figure, the longitudinal film strain of the steel strip edge during this forming is the fourth
It occurs as shown in the curve in the figure, and near the -3 breakdown roll 3BD, it shows a sudden change like ΔC and a large strain reduction amount, that is, a large change in the strain reduction slope, indicating a -3 break down roll 3BD. Generates an edge wave near the Down Roll 3BD.

In the manufacturing process of electric resistance welded steel pipes as shown in FIG. 1, the present invention is designed to increase the downhill amount of the F&L3 breakdown roll 3BD as shown in the 8th curve of 3rd ryJ when forming the raw pipe P. The height of the t3 breakdown roll 3BD is made relatively high, and the 2nd breakdown roll 2BD and the 14th breakdown roll 4B are
In order to reduce the downhill amount of D, the height positions of Arashi 2 Breakdown Roll 2BD and Ichi 4 Breakdown Roll 4BD are set relatively low (so that they protrude upward near the pass line h3 Breakdown Roll 3BD). ,
Breakdown roll 2BD, 3BD.

Adjust the relative height position of 4BD.

Note that the height position of only the l1h3 breakdown roll 3BD may be made relatively high so that the pass line protrudes upward in the vicinity of the circle 3 breakdown roll 3BD.

By adjusting the relative height position of the breakdown rolls as described above, the raw pipe undergoes bending deformation in the longitudinal direction like a kind of continuous beam, and tensile strain is generated at the raw pipe edge Pe near the -3 breakdown roll 3BD. , the longitudinal film strain distribution of the raw tube edge Pe can have a gentle strain reduction gradient, as shown by curve 8 in FIG. 4, and can therefore prevent the generation of edge waves.

By the way, the outer diameter is 24 inches, the wall thickness is 4.78 m, and the grade is A.
P 15 LXX6017>Place the base tube of the ERW IT tube into the third
The amount of downhill at each breakdown roll position (downhill coefficient D) -
Examples are shown in Table 1 below.

Table 1 In the conventional method shown in Table 1 above, the edge of the steel strip is
Buckling occurred in the forming area of -2 breakdown roll 2BD to -14 breakdown roll 4BD, and generation of edge waves was observed, making it impossible to weld in the squeeze roll SQ in the subsequent process.

In the method of the present invention shown in Table 1 above, the distribution of the edge longitudinal film strain becomes clearer as shown by line B111 in FIG. 4, and the maximum strain value also decreases from 0.56% to 0.4%. No edge waves were observed.

In this example, the generation of edge waves is prevented by adjusting the height of the breakdown roll group, but edge waves can also be prevented by adjusting the height of the forming roll group including the fin pass rolls. Occurrence can be prevented.

"Effects of the Invention" As described above, according to the method of the present invention, it is possible to prevent the occurrence of edge waves of the raw pipe in the raw pipe forming process of ERW steel pipes, so that it is possible to prevent forming defects of the raw pipe and There is no occurrence of welding defects at seam edges, which contributes to improved yield and product quality.

Furthermore, stable molding of raw tubes with a small ratio of wall thickness to outer diameter and stable molding of various molded flowers can be achieved, and it is possible to improve roll shape and reduce roll modification costs and manufacturing costs.

[Brief explanation of the drawing]

Fig. 1 is a schematic plan view showing the process of forming an ERW steel pipe by the cage forming method which is applicable to the method of the present invention;
Figures (A), (B), (C), (D), (E), C
F), (G), and (11) are respectively A- in Figure 1.
A, B-B, C-C, D-D, E-E, F-FSG~G
,, sectional view taken along line H-H. FIG. 3 is a graph showing the downhill curves of the conventional method and the method of the present invention, and FIG. 4 is a graph showing the edge longitudinal film strain curve of the conventional method and the method of the present invention. PR...Vintirol, IBD, 2B [l, 3BD,
4BD -...-1 to Na4 breakdown roll,
ER...edge forming roll, OCR...outside cage roll, ICR...inside cage roll, IF, 2F, 3F...Ikl~positive 3 fin bath roll, SQ...squeeze roll, S ...Steel strip, P...Made pipe, Pe...Joint edge part Fig. 2 (A)
(B) Figure 2

Claims (2)

[Claims] (1) The steel strip is passed through forming roll stands arranged in tandem in the longitudinal direction, the steel strip is bent in the width direction, and then formed into an approximately circular cross-section blank tube by fin pass rolls. In the manufacturing method of an electric resistance welded steel pipe in which both edges of the seam are welded, the height positions of the forming rolls before and after the forming rolls are lowered compared to the height position of the forming rolls that should be used as the required standard in the group of forming rolls. 1. A method for producing an ERW steel pipe, characterized by forming the same. (2) The standard forming roll is used as an intermediate breakdown roll, and the height positions of the breakdown rolls before and after it are lowered compared to the height position of the intermediate breakdown roll. A method for manufacturing an electric resistance welded steel pipe according to claim 1.