JPS6297769A - Production of welding pipe - Google Patents

Abstract

PURPOSE:To obtain the smooth bead having no welding defects by performing a seam welding by setting the final solidifying position of a molten pool for the before and behind squeezing roll in the specified range in case of producing the welding pipe of low Young's modulus metal. CONSTITUTION:The butt part of a belt like strip bulgle-formed in the width direction by squeesing roll S1-S4 is seam-welded by the consumable type multielectrode at each position W1-W3 on the welding pier composed of the low Young's mofulus metal of Ti and.Ti alloy, etc. This welding is performed by locating the final solidifying position (a) of a molten pool at the part exceeding 15mm in the pipe making direction from the roll center part of the squeezing roll S2 and not exceeding the intermediate point with the following squeezing roll S3. The smooth bead having to welding defect even in case of the pipe making speed being increased is obtd. accordingly.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a welded pipe made of a low Young's modulus metal such as Ti or a Ti alloy, and in particular, it relates to a method for efficiently welding a welded pipe made of a low Young's modulus metal such as Ti or a Ti alloy. The present invention relates to a method of manufacturing a tube.

[Prior art] Making a welded pipe;
As shown in the figure, a plurality of pairs of forming rolls 2 are provided in the longitudinal direction.
A method is practiced in which a band-shaped strip 1 is supplied between the tubes, and after being curved in the width direction to form a circular tube shape, the abutting portions are seam-welded using, for example, a non-consumable electrode 5 to form a welded tube 6.

By the way, there are no particular problems when manufacturing steel pipes etc. using this welded pipe manufacturing method, but materials such as Ti and Ti alloys, which have a high proof stress relative to their tensile strength and a small Young's modulus, in other words, have a low spring modulus. When attempting to manufacture a welded pipe made of a metal with a large back force, spring back force acts on the molten part during seam welding, often resulting in weld defects such as cracks and undercuts. In particular, when the pipe manufacturing speed increases or the wall thickness of the pipe to be manufactured is large, the welding current is also increased accordingly, making the molten pool large and elongated. The outbreak becomes even more noticeable. For this reason, in the manufacture of Ti or Ti alloy tubes, etc., the welding current is limited in order to avoid the occurrence of welding defects, and the tube manufacturing speed must also be maintained at a low speed.

Under these circumstances, various measures have been proposed to achieve high efficiency production of Tiil welded pipes and the like. For example, in order to increase the force exerted by the forming rolls and reduce the springback force as much as possible, measures such as changing the current squeeze roll to multiple pairs of small-diameter squeeze rolls, or using the small-diameter squeeze rolls and the current squeeze roll in combination, can be taken. It is being Also, in order to improve the bead shape, multi-electrode welding methods have been adopted in which the welding current is supplied in parts rather than all at once to the welding area, but even when these methods are used, welding defects still occur. Without this, it was not possible to achieve high efficiency welding of Ti welded pipes, etc.

[Problems to be Solved by the Invention] The present invention was completed as a result of various studies focusing on these circumstances. An object of the present invention is to provide a method for manufacturing welded pipes that can prevent welding defects even when the welding current is increased due to increased pipe manufacturing speed, increased wall thickness, etc. It is.

[Means for Solving the Problems] The present invention, which has achieved the above object, involves bending a strip of low Young's modulus metal in the width direction into a circular shape using a squeeze roll, and seam welding the butt portions. In a method for manufacturing a pipe body, the final solidification position of the molten pool is 15 m in the pipe manufacturing direction from the center of the squeeze roll.
The gist lies in that welding is performed at a location that exceeds m and does not exceed the midpoint between the squeeze roll and the next squeeze roll.

[Operation] As mentioned above, the cause of welding defects such as cracks and undercuts is the springback force of low Young's modulus metals. However, it is not clear in detail how the springback force acts to cause welding defects. Therefore, the present inventors conducted various studies on the above-mentioned generation mechanism.

FIG. 5 is a schematic diagram showing a state in which the end faces of the strip are butted together when the strip is curved and compressed with squeeze rolls SQ to SQ3 (before seam welding). Further, FIG. 6 is a graph showing changes in the seam opening width at the abutting portion. As can be understood from Figure 5.6, the seam opening width W becomes flat at the pinching point of the squeeze roll,
It is maximum at the intermediate position between the pinching points. Here, if we observe the change in the seam opening width in more detail in relation to the springback force of the belt-like strip, we can see that, for example, the pressure point B
The seam opening width becomes smaller toward the pinching point B, especially on the side opposite to the pipe forming direction, from the midpoint between the pinching point B and the pinching point A to the pinching point B, and the springback occurs in this region. Power is in a state of being suppressed. On the other hand, in the pipe forming direction side of the clamping point B, especially in the section up to the next intermediate point, the clamping force by the squeeze rolls is gradually released, and the seam opening width is expanded. In particular, the tangent t13 drawn to the seam opening width change curve
In addition, the degree of expansion of the seam opening width expressed by the slope of L is larger as the seam is closer to the pinching point B and becomes gentler as it is farther away from the pinching point. In other words, a large springback force acts on the abutting portion of the band-like strips in the section close to the clamping point on the pipe forming direction side, and the springback force tends to weaken as the distance from the clamping point increases.

By the way, welding defects such as cracks and undercuts occur when springback force acts on the solidified part when the molten metal is about to solidify when welding current is passed through the electrode, or shortly after solidification, and the yield strength of the solidified part increases. This is thought to occur because it cannot resist this because it is still small.

Therefore, considering the above-mentioned change in springback force, it is possible to prevent the above-mentioned welding defects by adjusting the welding conditions so that the area where the molten metal is about to solidify does not fall into the area where the action of the springback force is large. I came to think that it might be possible.

The present invention was completed as a result of further research based on these findings.

In the present invention, a location that is closely related to the occurrence of welding defects can be selected as the final solidification position of the molten pool. In other words, there is almost no resistance to the springback force at the starting end or intermediate position of the molten pool, so it is not possible to prevent the seam opening width from expanding, but even if the seam opening width becomes slightly larger, the molten metal will flow into the widened area and spread. This does not immediately lead to the occurrence of welding defects. However, since the final solidification position of the molten pool is the position where it is about to solidify, the molten metal has lost its fluidity and the resistance to the springback force is also small. Therefore, in this case, the seam opening width is likely to expand, and defects such as cracks caused by the seam expansion cannot be compensated for with molten metal. For this reason, in order to prevent welding defects from occurring, it is absolutely necessary to prevent cracks from occurring at the final solidification position.

Therefore, in the present invention, in order to prevent the springback force that causes welding defects such as cracks from being applied to the final solidification position, the position of the squeeze roll is set at one point in the pipe forming direction from the roll center of the squeeze roll.
It is configured so that it is located in a region exceeding 5 mm. In other words, as shown in the above analysis, the area where the springback force is large is a certain area from the pinch point, that is, the center of the squeeze roll, in the direction of pipe production. According to this, the range was 0 to 15 mm.
・In other words, if the final solidification position exists in an area where the distance from the roll center of the squeeze roll in the pipe-making direction is less than 0 mm, that is, in the area opposite to the pipe-making direction, there is a force at that position that attempts to expand the seam opening width. It does not work, but rather the squeezing force in the direction of reducing the seam opening width prevails. Therefore, there is no risk of welding defects occurring in this area. However, if the final solidification position is in this region, the weld metal that has lost its fluidity will be pushed into the center by the clamping force, so it is expected that the weld bead will have a convex shape. On the other hand, if the final solidification position exists in an area beyond 15 mm from the center of the squeeze roll roll in the pipe forming direction, the springback force is a positive value, but it is sufficiently small that it will not cause welding defects. Not enough. On the other hand, since the springback force acts strongly in a region 0 to 15 mm from the roll center of the squeeze roll in the pipe forming direction, it is thought that welding defects will occur if the final solidification position exists in this region. Based on the above considerations, in order to manufacture Ti welded pipes while preventing welding defects, welding conditions should be set such that the final solidification position of the molten pool is located at a location more than 15 mm from the roll center of the squeeze roll in the pipe manufacturing direction. need to be set.

In addition, in the above configuration, the squeeze rolls are specified as one pair in the case of large force under the actual welding conditions, but the situation of change in the seam opening width before and after the squeeze roll pinching point does not change depending on the specified squeeze rolls. In short, no matter which squeeze roll is specified, if the final solidification position of the molten pool is located at a location more than 15 mm from the roll center of the squeeze roll in the pipe forming direction, welding defects can be prevented. It can be prevented. As is clear from the above description, it goes without saying that even if the length exceeds 15 mm, there should be no position where a convex bead will be formed by the squeezing force of the next squeeze roll.

[Example Fig. 1 shows that the vicinity of the seam weld is held between four pairs of small-diameter squeeze rolls S1 to S4, and three non-consumable electrodes are placed between W1 to W, respectively.
FIG. 3 is a main part explanatory diagram showing an embodiment arranged at position No. 3; W
The bead cross-sectional shapes at positions 1 to W3 are as shown in Figures 2 to 4, respectively, and preliminary welding is performed at Wl,
As a result, almost no molten pool is generated, or even if it is generated, it immediately solidifies, and the molten pool generated by welding at W2 and W3 is solidified between the squeeze rolls S2 and 33. That is, the final solidification position a of the welding molten pool is 25+ in the pipe forming direction from the roll center of the squeeze roll S2.
Since it was located at a distance of ++ m and more than 15 mm from the center of the roll, no cracks were observed, and no convex beats were observed. In addition, in the above example, there are 3 non-consumable electrodes.
Although two cases were shown, a good weld bead (fourth
) shown in the figure, the final solidification position is also W
This is the solidification position of the molten pool according to 2 or wi, and the position may be located at a position more than 15 mm from the center of the squeeze roll (Sz or S2) in the pipe forming direction.

Next, Table 1 shows the welding results when Ti pipes were manufactured using the method of the present invention. In addition, the relationship between the pipe forming speed and the length of the crater part (molten pool) in the welding examples shown in Table 1 is shown in Table 7.
As shown in the figure.

As shown in Table 1, in all cases of N011-3, when L was Om[11 or less, no cracking was observed, but the bead shape became convex and satisfactory results were obtained. I couldn't get it. One side exceeds Omm +15m
In the case of n+ or less, a smooth bead shape was obtained, but cracks occurred, and a satisfactory result was still not obtained. On the other hand, when the distance exceeded +15 mm, no cracking occurred and a smooth bead shape was obtained. Since there is a relationship between the pipe forming speed and the crater length as shown in Figure 7, the aim of the final non-consumable electrode is determined by taking the above relationship into account when adjusting the final solidification position of the molten pool as shown in Table 1. All you have to do is set the location.

[Effects of the Invention] The present invention is configured as described above, and when welding low Young's modulus metal pipes, the arrangement of non-consumable electrodes is adjusted while taking into account the wall thickness of the pipe to be made and the pipe-making speed. By doing so, the final solidification position of the molten pool is set at a location that is more than +15 mm from the roll center of the squeeze roll in the pipe forming direction and does not exceed the midpoint with the next squeeze roll. As a result, a smooth bead without welding defects such as cracks and undercuts can be obtained. In particular, even if the tube manufacturing speed increases, the above effects can be obtained, and productivity can be improved.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an example of application of the method of the present invention, Figs. 2 to 4 are explanatory diagrams showing the cross-sectional shape of the weld bead at welding positions W1 to W3 in Fig. 1, and Fig. 5 is an explanatory diagram showing the seam opening between squeeze rolls. A schematic diagram showing changes in width, Figure 6 is a graph showing the amount of displacement of seam opening width viewed in the length direction, Figure 7 is a graph showing the relationship between pipe production speed and crater length, and Figure 8 is a welded pipe. It is a side explanatory view which shows an example of the manufacturing method.

Claims (1)

[Claims] In a method of manufacturing a tube body by curving a strip of low Young's modulus metal in the width direction using a squeeze roll to form a circular shape and seam welding the butt portions, the final solidification position of the molten pool is at the center of the squeeze roll. A method for manufacturing a welded pipe, characterized in that welding is performed at a position extending more than 15 mm in the pipe-making direction and not exceeding the midpoint between the next squeeze roll and the next squeeze roll.