JPH0438513B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is a method of welding Ti or Ti at high speed by TIG welding.
The present invention relates to a method of manufacturing an alloy tube, and more specifically, to a method of manufacturing a Ti or Ti alloy tube at high speed without causing problems such as interruption of welding due to bulging of molten metal or generation of humping beads. [Prior Art] When manufacturing Ti or Ti alloy (hereinafter referred to as Ti) pipes, for example, as shown in FIG. A breakdown roller 3, a fin pass roller 4, and a squeeze roller 5 rotate horizontally on a base K.
A Ti strip F is curved, its end faces are abutted against each other, and the abutted ends are welded by a welding machine 7. and
The Ti tube is further fed to a sizing roller 6 and finished to a predetermined outer diameter. Note that a single-electrode TIG welding machine is used as a welding machine in the above Ti pipe manufacturing process. By the way, in order to increase the productivity in the above manufacturing method, it is necessary to increase the pipe manufacturing speed, and the welding must be able to penetrate sufficiently into the Ti strip running at high speed, so large welds are required at the welding point. Current must be supplied. However, when such a large current is supplied to the welding point all at once, it is difficult to accurately match the running speed and the current value, and the current value tends to be excessive, resulting in bead undercuts and arc penetration. Defects occur. Since welded titanium tubes are used almost in the welded state, that is, without any post-processing or repair welding of the bead, the requirements for the bead shape and mechanical properties of the bead are particularly strict, and the above defects are fatal. I think it's something like that. In other words, it must be said that the reality is that Ti pipes cannot be welded at high speed using the conventional single electrode TIG welding method. By the way, a method of TIG welding using multiple electrodes is known when manufacturing steel pipes or stainless steel pipes, and various proposals have been made regarding the specific method (Japanese Patent Publication No. 56-28629, Japanese Patent Publication No. 28629).
53-34771, Special Publication No. 52-91139, etc.), and considerably high-speed production was also achieved. In other words, the welding method proposed above uses two or three electrodes, the distance between the electrode tips is 10 to 20 mm, and the electrodes are perpendicular to the material to be welded (steel pipe or stainless steel pipe), or the multiple electrodes are placed at the center point. Welding is performed by directing the molten pool to concentrate, and by integrating the molten pool, heat input efficiency is increased and high-speed production is achieved. [Problems to be Solved by the Invention] The present inventors have been conducting research for some time with the aim of achieving high-speed production of Ti pipes, and therefore, the above-mentioned proposed method for stainless steel pipes, that is, the TIG welding method using multiple electrodes. We focused on this and thought of applying this to the production of Ti tubes. In other words, as mentioned above, with the commonly used single-electrode TIG welding, the welding current is too concentrated in one location, resulting in defects such as undercut beads and arc penetration, but when multiple-electrode TIG welding is adopted, welding This is because it was expected that the welding current per electrode would be small because the current would be supplied in parts, and that the occurrence of defects in the single electrode method would be avoided until higher speed levels were reached. It is true that when the TIG welding method using multiple electrodes was applied to the manufacture of Ti pipes, the above-mentioned defects were resolved, but it became clear that new problems such as molten metal build-up and humping beads would occur. Summer. That is, when a bulge of molten metal occurs behind the leading electrode, the trailing electrode short-circuits with this, making it impossible to continue welding, and even if welding is possible, the bead shape of the product deteriorates. In addition, if the molten metal formed by the leading electrode does not connect in the longitudinal direction and shrinks midway to form a humping bead, the shape of the bead formed by the trailing electrode will collapse and the final product bead shape will be disordered. Summer. [Means for Solving the Problems] The present invention was completed as a result of various studies aimed at solving these problems.
The distance L (mm) between the tips of the final two electrodes is set to satisfy the following formulas () and (), and the inclination angle θ of all the electrodes with respect to the direction of movement of the forming tube is set. are set to be the same or different so as to satisfy the following equation (). 10≦L≦70 …() 0.035VT ^1.5 ≦L≦0.007VT ^1.5 +20 …() Where, V: Pipe manufacturing speed (mm/min) T: Pipe wall thickness (mm) 0゜≦θ≦45゜ … ...() [Function] In order to solve the above-mentioned problems, the present inventors conducted research focusing on welding conditions, particularly the distance between electrode tips, electrode inclination angle, welding current, pipe forming speed, etc. The present invention will be explained below along with the background of the research. The test welding method is roughly the same as the manufacturing method shown in FIG. 3, except that two electrodes are used instead of a single electrode. However, regarding the squeeze roller 5, the conventional single roller was replaced with five rollers having a relatively small diameter. The reason for this is that springback force remains in the Ti strip that has been curved into a tubular shape, and even after welding the butt part, springback force acts on the bead part to separate it. This is because there is a problem in that micro defects occur in the bead. That is, by adopting a structure in which a plurality of small-diameter squeeze rollers press the abutting portions before and after the welding point, the springback force is sufficiently suppressed and the generation of micro defects is prevented. In addition, during test welding, the area near the welding point was shielded with Ar gas to prevent oxygen from entering the bead on the inner and outer surfaces of the tube. Based on the above welding conditions, test welding was first carried out by two-electrode welding with various changes in the distance between the electrodes, etc., and the presence or absence of molten metal build-up was investigated, and the results shown in Tables 1 and 2 were obtained.

【table】

[Table] Next, test welding was performed under the same conditions as above except that three electrodes were placed in the welding area, and the distance L ₂₃ between the second electrode tip and the third electrode tip was variously changed. When the presence or absence of molten metal buildup was investigated, the results shown in Tables 3 and 4 were obtained.

【table】

【table】

[Table] When we observed the above test welding process, we found that the molten metal build-up phenomenon occurs between the leading electrode and the trailing electrode when two electrodes are used, and between the leading electrode and the trailing electrode when three electrodes are used. It was confirmed that this phenomenon occurred between the electrode and the third electrode. In addition, the phenomenon of molten metal rising is explained in the above 2.
It was found that when the molten metal between the electrodes was connected in a molten state, the molten metal on the rear side flowed backwards. From the results in Tables 1 to 4, it was found that such molten metal swelling phenomenon occurs more easily as the pipe forming speed is faster, the wall thickness of the Ti pipe is larger, and the distance between the electrode tips is shorter. . Therefore, the results in Tables 1 to 4 are used as the distance between the electrode tips,
The results shown in Figure 1 were obtained by organizing the results as a function of Ti pipe wall thickness and pipe forming speed. That is, as shown in Fig. 1, the phenomenon of molten metal rising is L<
It occurs in the area of 0.0035VT ^1.5 (area A),
Therefore, in order to prevent molten metal from rising, L≧
It turns out that it is necessary to set it to 0.0035VT ^1.5 . However, when L>70 (region B), not only the heat input efficiency deteriorates but also problems arise in shielding performance. Furthermore, when L>0.007VT ^1.5 +20 (region C), the heat input efficiency deteriorates and the advantage of using multiple electrodes disappears. Furthermore, when L<10 (D region), arc interference becomes severe and welding becomes unstable. Therefore, in order to prevent the molten metal from rising and to obtain satisfactory weldability, the distance between the final two electrode tips should be set as follows (),
We came to the conclusion that it is necessary to set it so that the formula () is satisfied. 10≦L≦70 …() 0.0035VT ^1.5 ≦L≦0.007VT ^1.5 +20 …() As mentioned above, in the conventional multi-electrode welding method for stainless steel pipes, a single molten pool is formed overall. With the aim of increasing heat input efficiency, the distance between the electrode tips has been set relatively short. However, when welding titanium pipes, a unique phenomenon of molten metal buildup occurs, so it is better to avoid integrating the molten pool.
It became clear that it was necessary to adopt setting conditions that were completely different from those used in the past. Next, regarding the humping bead, the shape of the bead formed by the first electrode is important, and if the bead width narrows or breaks, it will be formed by the second and subsequent electrodes. The bead shape also deteriorates. Therefore, as shown in Figure 2, the distance between the electrode tips was set to 20 mm or 30 mm under test welding conditions with a two-electrode arrangement.
Welding was carried out with the angle of inclination θ ₁ of the first electrode fixed at mm and variously changed, and the occurrence of humping beads was investigated, and the results shown in Table 5 were obtained. Other test conditions are T = 0.7mm, Ti tube diameter = 25.4mm, I ₁ =
300A or 200A, V=10m/min, respectively, were constant.

【table】

[Table] As shown in Table 5, when θ ₁ is -15° or less, that is, when the electrode is tilted in the opposite direction to the direction of movement of the forming tube, humping beads are likely to occur.
As a result, welding using the second and subsequent electrodes became unstable and the final bead shape deteriorated. A similar tendency was observed in the occurrence of humping beads when three electrodes were used, and it was found that in order to avoid this problem, it was necessary to set θ ₁ to 0° or more. Although the electrode inclination angle θ ₂ or θ ₃ after the second pole did not affect the generation of humping bead, it is necessary to satisfy θ ₁ ≦ θ ₂ ≦ θ ₃ due to the structure of the electrode arrangement, and therefore the angle of inclination of all electrodes is The angle of inclination must be 0° or more. However, if the electrode tilt angle exceeds 45°, there will be problems with arc stability and workability in practice, so we learned that the electrode tilt angle must be set to satisfy the following formula (). . 0゜≦θ≦45゜ ... () From the viewpoint of penetration and shielding properties during high-speed welding, 15゜≦θ≦30゜ is the optimal range. Further, in order to stabilize the flow of gas near the tip of the electrode and improve shielding properties, it is desirable to arrange all the electrodes or at least two electrodes in parallel. The basic configuration of the present invention is as described above. However, in multi-electrode TIG welding, the distribution of welding current in each electrode tends to affect the product bead and the stability of the arc during welding. Therefore, welding tests were conducted with various changes in welding current distribution in three-electrode welding, and the following results were obtained. When the pipe wall thickness is thin (or when the pipe manufacturing speed is slow), the total amount of welding current (It) can be relatively small. In particular, when (It)≦600A, it is desirable to make the welding current distribution of the electrode almost uniform, specifically, I ₁ : I ₂ : I ₃ = 1: (0.9 to 1.1): (0.9 to 1.1) It is recommended that Note that if the welding current of any one electrode is made too low, the arc becomes unstable and tends to be biased toward other electrodes or the squeeze roll. Moreover, this tendency is particularly remarkable when any one of the welding currents is less than 100A. On the other hand, if the pipe wall thickness is large (or if the pipe manufacturing speed is fast), the total amount of welding current (It) must be increased, and if It>600A, the distribution of the three electrodes should be made uniform. It is preferable to lower the current of the final third electrode because a higher quality bead can be obtained.
In particular, in high-current welding where the current value of the third electrode exceeds 250 A, the amount of molten metal increases, so the macrostructure after solidification tends to become larger and the rebead surface tends to become rougher. A way to improve this is to increase the final electrode's welding current by up to 30% compared to the preceding electrode's welding current.
It is advantageous to reduce the amount. Therefore, the welding current distribution ratio is I ₁ :I ₂ :I ₃ =1:(0.9~
1.1): (0.7 to 1.1) is recommended. In addition, in carrying out the present invention, a small diameter multi-stage squeeze roller was used in order to prevent the occurrence of micro-defects in the weld bead. If you use a method to eliminate the spring bag of the material by appropriately determining the roll flower (the hole shape of each forming roller) at the stage, or a method to suppress the spring bag by heating the material to about 200 to 400 degrees Celsius, it is possible to Manufacturing is possible even if a squeeze method such as this is adopted. [Effects of the Invention] The present invention is configured as described above, and can perform TIG welding of Ti pipes at high speed without generating molten metal buildup or humping beads.
Good quality Ti tubes can be obtained with high productivity.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between L and VT ^1.5 , Figure 2 is a graph showing the relationship between L and VT 1.5.
The figure is a schematic diagram showing a test welding method, and FIG. 3 is a schematic diagram showing a Ti pipe manufacturing method. F... Band plate, 2... Drive roller, 5... Squeeze roller, 7... Welding machine.

Claims (1)

[Claims] 1. A method of manufacturing a pipe by bending a Ti or Ti alloy strip plate and TIG welding the abutting portions of the end faces, comprising two or more non-consumable electrodes for TIG welding in the direction of welding progress. Set the distance L (mm) between the tips of the final two electrodes to satisfy the following formulas () and (), and set the inclination angle θ of all electrodes to the direction of movement of the forming tube, respectively. A method for manufacturing a Ti or Ti alloy tube, characterized by setting the same or different conditions to satisfy the following formula (). 10≦L≦70 …() 0.0035VT ^1.5 ≦L≦0.007VT ^1.5 +20 …() Where, V: Pipe manufacturing speed (mm/min) T: Pipe wall thickness (mm) 0゜≦θ≦45゜ … …()