JPH0261854B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for straightening bends in steel pipes online in the manufacturing process of electric resistance welded pipes. (Prior art) Conventionally, steel pipes are straightened by cutting the steel pipes to a specified length and then using a rotary straightening machine installed outside the production line to repeatedly bend the pipes while rotating them in the circumferential direction to straighten the bends. There is. Regarding rotary straightening machine,
For example, it is described in Japanese Patent Laid-Open No. 59-54421. A simple explanation of the mechanism of a rotary straightening machine is that the tsume-shaped rolls are arranged in a crossed manner.
The steel pipe is conveyed while rotating in the circumferential direction. The moment applied to the steel pipe increases as the pipe advances,
After the bending moment reaches its maximum at the time of roll contact, the load becomes unloaded, and the bending is corrected by repeating this process. Due to the contact state between the rolls and the steel pipe, which is a feature of this method, the stress change when a specific cross section moves one pitch (travel distance during one rotation) is spiral-like, and the bending moment is considered for the same cross section. , bending determined from pitch.
The deformation that the steel pipe undergoes is very complicated because it is unbended and the influence of roll reduction is also involved. The disadvantage of rotary straightening machines is that the flattening deformation of the steel pipe is large during straightening, so the ratio of the thickness of the steel pipe to the outside diameter (t/D)
The tendency of dimensional change differs depending on the In other words, as shown in Fig. 1, when t/D is small, the thickness is thin, and at this time, the outer diameter of the steel pipe increases due to shear deformation of the cross section of the steel pipe due to rotation, and therefore the steel pipe's outer diameter increases. Length decreases. Also, when t/D is large, the thickness is large, and in this case, flattening does not occur due to rotation, but bending in the longitudinal direction occurs, and the length of the steel pipe becomes longer. , the length may exceed the standard value and be rejected. In addition, since cross-sectional flattening deformation occurs when steel pipes are straightened, the steel pipe after straightening generates a new circumferential residual stress distribution of external tension and internal compression, so it is required to have crushing strength like oil country tubular goods. quality. Furthermore, this method has poor productivity because the steel pipe rotates on its own axis, so the advancing speed is low and the straightening speed is slow. Moreover, in order to rotate the steel pipe, it is necessary to cut the steel pipe before passing it through a straightening machine, and the deformation of the steel pipe is achieved by passing through all the rolls of the straightening rolls, so that the tip of the steel pipe,
and the length between the rolls at the rear end cannot be straightened. Therefore, it is not possible to remove bends in the tube end up to the length between the stands, and it is impossible to remove bends in the tube end, such as nose bends. (Problems to be Solved by the Invention) As described above, the prior art has the following drawbacks. The dimensional change (particularly the length) of the steel pipe during straightening varies depending on t/D, which impairs the yield. Flattening of the cross section during straightening generates new residual stress and degrades quality. Straightening speed is slow and productivity is poor. It is impossible to straighten the bend in the tube end. The present invention seeks to overcome these drawbacks. That is, an object of the present invention is to provide a method of correcting bending by repeatedly applying bending vertically or horizontally instead of a rotational correcting method. (Means/effects for solving the problem) The purpose of the present invention is to advantageously solve the above-mentioned drawbacks, and the gist of the present invention is to ``in the manufacturing process of electric resistance welded pipes, Before the cutting process, multiple stands are arranged so that the ratio between the distance between stands and the maximum outer diameter that can be made (L/D _nax ) is 2.5 or more, and A method for straightening bends in steel pipes, which comprises installing rolls in the horizontal direction and repeatedly bending the pipes to straighten the bends. In other words, the above-mentioned drawback is a phenomenon that occurs depending on whether the flattening deformation of the cross section or the bending deformation in the longitudinal direction takes priority, and when t/D is small, the cross-sectional causes flattening deformation and deforms as shown by the dotted line in FIG. Point A in the cross section of the steel pipe undergoes repeated bending deformation, so
Since it extends in the circumferential direction, the outer diameter of the steel pipe becomes larger and its length becomes shorter. However, when t/D becomes large, flattening of the cross section is less likely to occur, so bending in the longitudinal direction becomes effective, and the length of the steel pipe increases due to repeated bending in the longitudinal direction. The relationship is shown in FIG. That is,
The horizontal axis shows the set curvature, the vertical axis shows the actual curvature, and it is shown dimensionless by the yield curvature. Figure a shows the case where the distance between the stands is constant, 1 is when t/D is large, and 2 is when t/D is small. Show the time. Moreover, in the case of t/D constant, 3 indicates when l/D is large, and 4 indicates when l/D is small. Therefore, in order to impart bending deformation to the steel pipe, it is necessary to apply a certain bending moment, so it can be seen that by increasing the distance between the stands and reducing the load, flattening deformation of the cross section becomes less likely to occur. Therefore, effective bending deformation occurs and the length of the steel pipe becomes longer, so the length will not be rejected. Furthermore, since the correction is performed in a region where flattening deformation does not occur, no new large residual stress is generated in the circumferential direction, and the above-mentioned drawbacks can be overcome. Fourth
The figure shows the relationship between the distance between stands and the bending deformation efficiency, and it can be seen from the diagram of 5 where t/D is small that bending deformation can be effectively applied when the distance L/D between stands is 2.5 or more. In addition, regarding the disadvantage of , since this straightening device is installed in the tube making line, it can be matched with the tube making speed, which is advantageous in terms of productivity. Similarly, since steel pipes can be continuously straightened before being cut in the pipe making line, the drawbacks of the above can also be solved. Next, regarding the relationship between t/D and L/D, in the case of a thin wall with small t/D, the distance between stands L/
If D is not made large, the steel pipe will be crushed during straightening, which is undesirable.On the other hand, if t/D is large, effective bending straightening will be possible even if the distance between the stands is made small. Furthermore, the L/
Regarding the value of D _nax , since the amount of push of the roll is proportional to the square of the distance between the stands, it is naturally limited in terms of equipment, and therefore, in the present invention, L/D is set at an upper limit of 20. (Example) Examples are shown below. Straightening machine with 7 stages of stands as shown in Figure 5 (L/D=11.7)
A 50.8φ x 2.3t steel pipe was passed through the tube. Table 1 shows the intermesh h _i and set initial curvature K _p /K _e of each stand of the straightening machine.

[Table] Figure 6 shows the relationship between the initial curvature and the curvature after correction, and secondly, the quantitative values are shown.

[Table] However, upward bending refers to bending in the seam direction, and bending amount refers to the amount of bending per 12m length. Table 2
The bending direction is expressed as an angle clockwise from the seam. As is clear from the results, the amount of bending after correction was within the standard value (8 mm/12 m), indicating that the correction was effective. In addition, the length change clearly shows a uniform tendency in the increasing direction, and the roundness ((longitudinal diameter - lateral diameter)/average diameter) is almost the same before and after correction, so the cross-sectional Almost no flattening deformation occurs, and it is considered that no new residual stress is imparted in the circumferential direction. Therefore, the above drawbacks can be solved. In the embodiment, a roller straightening machine with a staggered arrangement is shown, but a stand with two upper and lower rolls or a stand with four rolls can have the same function. (Effects of the Invention) By straightening the bends of steel pipes on-line as in the present invention, it is an extremely advantageous method because the yield is high and productivity can be improved without deterioration of quality.

[Brief explanation of the drawing]

Figure 1 is a diagram showing that the change in length before and after straightening differs depending on plate thickness/outer diameter (t/D), Figure 2 is a diagram showing cross-sectional deformation during straightening of a steel pipe, and Figure 3 is a diagram showing how the length changes before and after straightening. Figures a and b show the relationship between the set curvature and the actual curvature during straightening, the horizontal and vertical axes are diagrams rendered dimensionless by the yield curvature, and Figure 4 shows the straightening efficiency η (actual curvature/set curvature) and the stand 5 is a diagram showing the straightening machine used in the example, and FIGS. 6a and 6b are diagrams showing the amount of bending of the steel pipe before and after straightening. Δl/l...change in length of steel pipe, t/D...plate thickness/outer diameter, A, A'...any position on the cross section of the steel pipe,
L/D...Distance between stands/outer diameter, K _p /K _e ...
Actual curvature/yield curvature, K _p /K _e ...Setting curvature/yield curvature, 1...When t/D is large, 2...When t/D is small, 3...When L/D is large, 4 ...When I was in L/D elementary school,
η... Straightening efficiency (K _p /K _p ), L/D... Distance between stands/outer diameter, 5... t/When D is large, 6... t/
For D small, 1 to 7...Stand number, h ₂ , h ₄ , h ₆
...intermediate amount.

Claims (1)

[Claims] 1. In the manufacturing process of ERW pipes, before the steel pipe cutting process, multiple stands are arranged so that the ratio between the distance between stands and the maximum outside diameter that can be made (L/D _nax ) is 2.5 or more, A method for straightening a bend in a steel pipe, which comprises installing rolls vertically and/or horizontally at right angles to the pipe-making direction, and repeatedly bending the pipe to straighten the bend.