JP4177783B2 - Pipe making welding method of pure titanium - Google Patents

Description

The present invention relates to a technique for continuously pipe-forming a butt-welded end face of a hoop using a squeeze roll while rolling a strip-like hoop of pure titanium into a cylindrical shape by roll forming.

  FIG. 1 is a schematic diagram for explaining the influence of a spring back acting on a welded part when welding pipes using a general squeeze device. When a thin metal sheet having a small Young's modulus and a high yield strength, such as titanium, is formed and processed, springback is likely to occur. In the case where a long hoop of such a thin metal plate is rolled into a cylindrical shape by roll forming, the edge surfaces of both ends of the plate are butted with a gap 0 using a squeeze roll, and the butted portion is arc welded to continuously form a pipe. A springback may act before the solidification of the molten part is completed, and as shown in FIG. 2, a fine crack may occur on the surface of the center part in the width direction of the pipe inner surface weld bead. This phenomenon is more likely to occur with a material having a larger springback. In addition, this phenomenon does not appear when the position where the melted part is finally solidified is close to the squeeze point, because the pressing by the squeeze roll is effective, but as the final solidified position of the melted part moves away from the squeeze point. The action of squeeze is weakened and the possibility of cracking is increased. For example, when the pipe making speed is high, the necessary welding heat input is also increased, so that the size of the molten pool is enlarged, and the final solidification position of the molten portion is moved away from the squeeze point. As a result, the above-described fine cracking phenomenon is likely to occur.

Conventionally, to solve this problem, by arranging a plurality of small diameter rolls in the tube forming axis direction using a restraining jig, the spring back of the material is suppressed, and a straight region with a minimum amount of butt gap is secured and welded. Pipe making method (Patent Document 1: Small diameter roll multiple array squeeze device) and pipe making method for reducing spring back of material by welding while heating tubular body (Patent Document 2: warm heating pipe making method) ), And further, a method of reducing spring back during butt welding by alternately forming the left and right regions of the material into a small radius in the roll forming stage before butt welding (Patent Document 3: Asymmetric Bending Forming Pipe) Law) has been proposed.
On the other hand, a method of dealing with this problem by a welding method and welding conditions is conceivable.
One of them is a method of setting the welding torch position upstream of the squeeze point and bringing the final solidification position of the melted part closer to the squeeze point, and a schematic diagram is shown in FIG.
The other is a method using plasma welding, in which a melt is penetrated to the tube inner surface of the butt portion while forming a small melt pool by a plasma arc having a high concentration power, thereby forming a bead on the tube inner surface side. Thereafter, a method of performing at least one decorative welding at the rear (Patent Document 4: Manufacturing method of stainless steel welded steel pipe, Patent Document 5: Manufacturing method of titanium or titanium alloy welded pipe) has been proposed.
JP 09-216094 A Japanese Patent Publication No. 01-054122 Japanese Patent Publication No. 05-05373 JP 47-033855 A JP 2000-158141 A

The inventions described in the above Patent Documents 1 to 3 are all aimed at pressing down the springback of the material to the minimum, and each is an effective solution. It is necessary to incorporate special dedicated jigs, forming roll structures, and heat treatment equipment in the pipe making line, and applying these special equipment to various pipe dimensions is accompanied by engineering difficulties and enormous amounts. Capital investment is necessary and it cannot be said that it is an economical solution. In addition, neither method completely suppresses the action of the springback to zero.
In addition, according to the method shown in FIG. 3, although the occurrence of cracks due to the springback is mitigated, the gap amount at both end faces of the butt portion increases as it goes upstream from the squeeze point. There is a limit to changing the position of the welding torch. For example, in the case of a thin-walled titanium tube with a thickness of 0.5 mm, in order to maintain a sound weld quality without melting, the movable distance of the welding torch position is limited to a range from several mm to at most about 10 mm. Therefore, a great improvement by this method cannot be expected.

In addition, according to the inventions described in Patent Documents 4 and 5, the final solidification position approaches the vicinity of the squeeze point by reducing the molten pool, and cracking is suppressed. Since an arc is used, it is easy to apply when the thickness of the pipe is thick, but when applied to a thin material having a thickness of 0.5 mm or less, for example, there is a high risk of melting during welding. Therefore, it is dangerous to set the above-mentioned welding torch position upstream of the squeeze point for a material having a large springback and a small plate thickness. In addition, since the size of the molten pool increases with an increase in heat input on the high speed pipe making side, the tendency for microcracking to occur is the same as in the case of TIG welding.
By combining the above-mentioned forming and conventional technologies related to welding, it can be expected to have a synergistic effect of preventing microcracking of the pipe inner surface weld bead surface, but the effect of springback has not yet been completely suppressed. In the future, it is expected that the technical limits will be exposed in the future, with the demand for higher strength of materials and higher pipe forming speed. Further, in the future, when it is desired to reduce the thickness of the pipe material, there is a limit to the application of the plasma welding method in which the concentration power of the arc is high, and a solution to this is necessary.

  Therefore, the present invention proposes a method for solving the problem of occurrence of fine cracks on the pipe inner surface weld bead surface by completely pressing down the influence of the spring back and welding, and as an application range thereof, The steel type, thickness, and pipe diameter are not particularly limited. The present invention basically uses the conventional welded tube line as it is, and the countermeasure on the equipment is mainly based on a very small-scale modification related to the expansion of the welding torch.

The present invention proposes the following means for solving the problem mainly by utilizing a welding technique using a conventional squeeze device. That is, the gist of the present invention is as follows.
The band hoop (1) pure titanium, while rounding into a cylindrical shape by roll forming, for pipe-making to continuously welded butt both end faces of the hoop by using a squeeze roll, the pipe forming method of welding pure titanium, is first In the vicinity of the squeeze point, using the first welding torch, continuous tack welding was performed under the heat input condition in which the back bead was not formed, and subsequently downstream of the position where the solidification of the tack welded portion was completed, A pipe making and welding method for pure titanium , wherein the main welding is performed under a heat input condition in which a back bead is formed from above the tack welded portion using a second welding torch.
(2) After the main welding, cosmetic welding is performed on the main welding bead using the third welding torch or further using the fourth welding torch (1) ) For pipe making and welding of pure titanium .

The present invention provides a production method that prevents the occurrence of fine cracks on the inner surface of the pipe inner weld bead and enables high-speed welded pipe production in the case of continuous welding pipe production of pure titanium. Can bring about.

Hereinafter, the present invention will be described in detail. FIG. 4 shows a pipe making welding method according to an embodiment of the present invention.
In a method using at least one pair of squeeze devices and two or more welding torches, first, the first welding torch 1 is used in the vicinity of the squeeze point of the squeeze 6 so that the back bead is not formed. Continuous tack welding to integrate the butt seam. Subsequently, using the second welding torch 2, beadon plate welding is performed from above the welded portion 11 temporarily attached by the first welding torch 1 to form a back bead. At this time, the welding start position by the second welding torch 2 is set to the downstream side after the region where the metal melted by the first welding torch is at least completely solidified.

TIG welding is considered optimal for the tack welding method performed with the first welding torch 1. The first reason is that the surface bead shape 11 of the tack welded portion is desirably smooth in order to stably perform the main welding performed by the second welding torch 2, and for that purpose, TIG welding is performed. Is optimal. The second reason is that it is not necessary to form a back bead, so that deep penetration like plasma welding or laser welding is not necessary.
As a main welding method to be performed by the second welding torch 2, plasma welding, laser welding, etc. can be considered as options in addition to TIG welding. As a method of selection, for example, in the case of a thick pipe having a tube thickness of 1.0 mm or more, and a high penetration is required for high-speed pipe making, a welding method with high arc concentration is effective. Yes, plasma welding or laser welding can be considered. On the other hand, for example, in the case of a thin-walled tube with a tube thickness of 0.5 mm or less, if the arc concentrating power is high, the melting phenomenon tends to occur, so that plasma welding and laser welding are dangerous. The choice is safe.

According to the present invention, the tube body that has been integrated by tack welding by the first welding torch 1 is no longer subjected to spring back using the squeeze roll when the back welding is performed by the second welding torch 2. There is no need to control the pressing and butting gaps to zero. In addition, the molten pool formed by the second welding torch 2 is subjected to strong restraint by the main welded portion 13 that has been solidified in the same manner as the tack welded portion 11 that has been solidified. However, when the size of the molten pool is enlarged during high speed pipe forming, the squeeze 7 may be used as a backup. The position of the second welding torch 2 when using the squeeze 7 does not need to consider the gap of the butt portion as in the prior art, so the final solidification position is determined by taking advantage of the ability to freely select the position in the tube axis direction. What is necessary is just to set so that it may correspond to a squeeze point. By applying the above technique, the problem of bead surface microcracking is solved.
When undercut occurs in the surface shape of the main welding bead 13 carried out with the second welding torch 2 under high-speed welding conditions, the surface is used under the condition of small heat input using TIG welding as the third welding torch 3. The undercut can be repaired by performing decorative overlay welding that remelts only the part and smoothes the bead shape. If the third TIG welding alone is not enough to melt the entire width of the second main welding bead, the fourth TIG welding torch 4 is introduced to smooth the remaining part. Just do it.

Table 1 shows the welding conditions for the conventional method and the method of the present invention, in which the welded pipes were formed. Using pure titanium, TIG welding pipe making of a pipe having an outer diameter of 25.4 mm and a plate thickness of 0.5 mm at three levels of 5 m / min, 6 m / min, and 7 m / min was performed. Table 2 shows the results of comparing the presence or absence of microcracking on the surface of the pipe inner surface weld bead and the surface bead shape. When using the two TIG welding torches of the present invention example, the TIG welding torch is used as the first welding torch 1 in FIG. 4, arranged at the squeeze point of the squeeze 6, the welding current 100 to 120 A is input, Continuous tack welding was performed without forming a bead. The second welding torch 2 is also a TIG welding torch, and is placed at a position 100 mm behind the first TIG welding torch 1. Welding was performed to form a bead. When four TIG welding torches according to the present invention are used, the conditions up to the second are the same. The third TIG welding torch 3 was placed 100 mm behind the second, and the fourth TIG welding torch 4 was placed 100 mm behind the third. The third and fourth TIG welding currents are suppressed to 110 to 130 A below the second welding current value, and the front bead portion 13 formed by the second TIG welding is remelted and smoothed to restore the undercut shape. Performed decorative welding. The third and fourth TIG torch positions in the pipe circumferential direction were arranged so as to be slightly overlapped with each other in the center of the bead to cover the entire width region of the second TIG weld bead 13.
The comparative example is a conventional method shown in FIG. 1, and the squeeze device has the same specifications as the example of the present invention. Only one TIG welding torch was used as the welding torch, and the welding torch was placed at the squeeze point of the squeeze 6, and the welding current 140 to 170A was applied to form the back bead.
In the comparative example, fine cracks occurred on the pipe inner surface weld bead surface at a pipe making speed of 6 m / min, and a surface bead shape defect due to undercut occurred at a pipe making speed of 7 m / min. In the example of the present invention, there is no occurrence of fine cracks on the pipe inner surface weld bead surface even at a pipe making speed of 7 m / min. As for the surface bead shape, in the case of two TIG welding torches, a shape defect due to undercut occurs at a pipe forming speed of 7 m / min as in the comparative example, but when four TIG welding torches are used, the bead shape is As a result, a smooth surface bead shape was obtained even at a pipe forming speed of 7 m / min.

It is the schematic explaining the influence of the spring back which acts on a welding part, when welding pipe-forming using a general squeeze apparatus, and is a figure explaining a comparative example. (A) is a side view, (b) is a plan view. It is a welding section sectional view of a welded pipe for explaining fine cracking of a pipe inner surface weld bead surface. It is the schematic explaining the fine crack relaxation effect of the pipe inner surface bead surface by the change of a welding torch position, (a) is a side view, (b) is a top view. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic explaining the principle of this invention, and an Example, (a) is a side view, (b) is a top view. (C) is the schematic explaining the cross-sectional shape of the welding part in each position of the A'-A cross section, B'-B cross section, and C'-C cross section of (b).

Explanation of symbols

1, 2, 3, 4 1st to 4th welding torches 5, 6, 7 Squeeze device 8 Welded pipe material 9 Situation where butt portion before welding is opened by springback 10 Temporary welding with first welding torch Molten pool 11 weld bead portion obtained by tack welding with the first welding torch 12 molten pool when the main welding is performed with the second welding torch 13 welding obtained by the main welding with the second welding torch Bead part 14 Melt pool when cosmetic welding is performed with the third welding torch 15 Weld bead part 16 obtained by cosmetic welding with the third welding torch 16 Melting pool when cosmetic welding is performed with the fourth welding torch 17 A weld bead portion obtained by cosmetic welding with a fourth welding torch 18 Molten pool when forming a pipe inner surface weld bead with one TIG torch 19 18 18 Molten pool The size of the spring back that works at the final solidifying position 20 When forming a pipe inner surface weld bead with one TIG torch, the molten pool 21 20 expanded when the welding heat input is increased for high speed pipe forming. The size of the spring back that works at the position where the molten pool finally solidifies. 22 The surface microcrack of the pipe inner surface weld bead. 23 The gap at the end face of the butt part. 24. Pool 25 when moving to the front 25 25 The size of the spring back that acts at the position where the 24 24 melt pool finally solidifies

Claims (2)

A strip hoop pure titanium, while rounding into a cylindrical shape by roll forming, welding continuously for pipe-making by abutting the end surfaces of the hoop by using a squeeze roll, the pipe forming method of welding pure titanium, firstly, a squeeze point A continuous tack welding is performed using the first welding torch under the heat input condition in which no back bead is formed, and the second welding is performed downstream of the position where the solidification of the tack welded portion is completed. A pipe manufacturing and welding method for pure titanium , wherein main welding is performed under heat input conditions in which a back bead is formed from above a tack welded portion using a welding torch. 2. The pure welding according to claim 1, wherein cosmetic welding is performed from above the main welding bead using the third welding torch or further using the fourth welding torch subsequently to the main welding. Titanium pipe making method.

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