JPH0647175B2 - Multi-electrode sub arc welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a tandem-type multi-electrode latent arc (submerged arc) welding adopted when manufacturing a large-diameter welded steel pipe by a so-called UO forming process or the like. Regarding the method.

[Prior Art] Generally, in the production of large-diameter steel pipes, when butt-welding the steel pipe side ends after UO forming, high-speed welding is achieved by tandem latent arc welding using multiple electrodes. In such welding, tab plates are usually used at the start and end of the abutting part for defective penetration, elimination of defects in the crater part, etc., and at the end thereof, energization to a plurality of welding electrodes was stopped simultaneously. After that, the welding machine was stopped.

To explain this in detail, as shown in FIG. 4, when the number of electrodes is 4, welding (I) is continued until the end of the welding is reached at the same time as the welding procedure according to the conventional method. The energization to the first to fourth electrodes 1, 2, 3, 4 arranged in tandem from the downstream (termination) side to the upstream side of the wire was simultaneously stopped (II), and then the welding feed was stopped (III). . This welding feed stop is performed by stopping the feed of the weld when the steel pipe is fixed and the welding machine moves fast, and by stopping the feed of the steel pipe when the welder is fixed and the steel pipe moves.

The welding situation at this time is shown in FIG. 5, in which the crater 5 is generated at the terminal end of the welding line, and the crater length L is as shown in FIG. Although it depends on the wall thickness, it is quite long, 100-300 mm.

Since a part of the crater 5 cannot be used as a product, a target welded product, in this case, a tab plate 7 is additionally provided so as to project from the end of the steel pipe 6, and the crater 5 is mounted on the tab plate 7. The tab plate 7 is cut after the welding is completed so that the product portion is not affected.

[Problems to be Solved by the Invention] However, as in the above-described conventional technique, the welding feed is stopped at the welding end after simultaneously stopping the energization of the welding electrodes, so that the crater length L is as described above. It will be extremely long. Therefore, in order to avoid the influence of the crater on the product part, a long tab plate should be attached. When the tab plate is lengthened, not only the cost for the tab plate is increased, but also the work efficiency is deteriorated due to the increased welding length and the cost is increased due to the increased amount of the welding material used.

On the other hand, the applicant previously proposed in Japanese Utility Model Application Laid-Open No. 56-6569 that the energization and the welding wire are sequentially stopped after a predetermined time from the welding electrode on the front side in the traveling direction.
However, in this embodiment, the energization is sequentially stopped during the process of welding feeding to shorten the distance between the front welding electrode and the rear welding electrode, for example, the tab plate length of 40 mm. In the present invention for shortening the crater length described below, firstly, in the period in which the welding feed is finished and stopped, the current supply is sequentially stopped, and secondly, the current supply stop time is It is fundamentally different in that at least a certain electrode has a longer energization stop time than the previous electrode.

Therefore, the main purpose of the present invention is to provide a latent arc welding method capable of significantly shortening the length of the crater.

[Means for Solving the Problems] The present invention which has solved the problems has the following points.

That is, in a method of performing subarc welding along a welding line using a multi-electrode subarc welding machine in which three or more electrodes are arranged in tandem along the welding line, the welding feed at the welding end portion is terminated. During the stop period, the current to the first electrode counting from the downstream side of the welding line is stopped substantially at the same time as the end of the welding feed, and after this power is stopped, T ₁
After a lapse of time, the energization of the second electrode is stopped, and thereafter, in the same manner, after a lapse of Tn-1 time, the energization of the last n-th electrode is stopped, and each energization stop time interval T ₁ ... Tn -1 satisfies the relations of the following formulas (1) and (2): 0 ≦ T ₁ ≦ …… ≦ Tn-1 ≦ 10 …… (1) T ₁ <Tn-1 …… (2) And multi-electrode latent arc welding method.

[Operation] In the present invention, from the first electrode downstream of the welding line to the final n-th electrode upstream in this order, the welding feed is stopped and the energization of each electrode is not stopped at the same time. If the current supply is stopped sequentially and the current supply stop time intervals between the adjacent electrodes are gradually lengthened in the same order, the crater generated by stopping the power supply to the first electrode is generated by the second electrode. The welding material fills the crater caused by the stop of energization of the second electrode, and the welding material by the third electrode fills the crater. The craters in front of the crater are filled in the same manner until the n-th electrode stops. The length of the remaining crater can be made extremely short as shown in FIG.

Further, since the crater can be shortened, the length of the tab plate can be shortened, the work efficiency can be improved, and the cost of the welding material can be reduced.

On the other hand, even if the Ti is set to zero (however, Tn is not zero) under the condition that the current flow to the downstream electrode is not later than the current flow to the upstream electrode, the effect of the above example is obtained. Although inferior, the crater length L can be made shorter than in the conventional example.

[Specific Configuration of the Invention] The present invention will be described in more detail below with reference to the drawings.

In the method of the present invention, as shown in FIG. 1 and FIG. 2, a multi-electrode latent arc welding machine in which three electrodes or more, for example, four electrodes are arranged in tandem along the welding line is used to perform the latent welding along the welding line. When performing arc welding, the current supply to the first electrode 1 (see FIG. 5) counting from the downstream side of the welding line is stopped at substantially the same time as the end of the welding feed at the weld end, and after this power supply is stopped, After the lapse of T ₁ time, the energization to the second electrode 2 is stopped, and then the energization to the third electrode 3 is stopped after the lapse of T ₂ time from the time when the energization is stopped, and so on. When the energization of the last n-th electrode is stopped after a lapse of time, these energization time intervals T ₁ ... Tn-1 are set so as to satisfy the following relationships (1) and (2).

0 ≦ T ₁ ≦ ... Ti ≦ ... ≦ Tn-1 ≦ 10 (1) T ₁ <Tn-1 (2) According to this relationship, Tn-1 is not zero. However, Ti can be zero. For example, under four electrodes, the energization to the first to third electrodes is stopped at the same time, and then the energization to the fourth electrode is stopped later. Of course, it is more preferable that the Ti is not zero, that is, the current supply is stopped sequentially at time intervals from the first electrode to the final electrode.

If Tn-1 exceeds 10 seconds, welding or insufficient arc results in an open arc, resulting in bead failure.

In the present invention, the target steel pipe has a wall thickness of 5 to 50 mm, particularly 10 to 40
The effect of the present invention becomes remarkable when welding with a thickness of mm. The distance between the electrodes (see FIG. 6) is preferably 10 to 30 mm. A heat input amount of 20,000 J / cm to 100,000 / cm can be usually used.

A preferred specific example of the distribution of Ti is shown in Table 1 in relation to the wall thickness (mm) and the welding feed rate (vmm / min).

Next, the magnitude relationship between T ₁ , T ₂ , and T ₃ will be described. Table 2 shows the numerical values of T ₁ , T ₂ and T ₃ , the crater length, etc. and their evaluation when the wall thickness is 20 mm, the welding feed rate is 2000 mm / min, and the heat input is 40 kJ / cm. The meanings of the evaluation symbols are as follows.

◯: Crater length is relatively short △: Crater length is not too short X: Open arc and no bead (Open arc means excessive heat input, making welding impossible) The conditions adopted for creating the data in this table are shown in Table 3. The definition of the electrode intervals (E, l ₁ , l ₂ , l ₃ ) shown in Table ₃ is shown in FIG.

As is clear from Table 2 above, it is understood that only those satisfying the relationships (1) and (2) above are effective for shortening the crater. As long as this size relationship is satisfied, the optimum numerical values of T ₁ , T ₂ , and T ₃ may be selected according to various welding conditions.

Next, the effect of the method of the present invention is shown in FIG. 3 in contrast to the conventional method. However, the heat input conditions were 20 to 100 kJ / cm.

It is clear from FIG. 3 that according to the method of the present invention, even if the wall thickness changes, the crater length is extremely short and small as compared with the conventional method.

[Effects of the Invention] As described above, according to the present invention, the crater length can be shortened, the cost for the tab plate and the welding material can be reduced, and the work efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of the method of the present invention, FIG. 2 is a flow chart exemplifying diagram thereof, FIG. 3 is a comparative graph of the present invention method of crater length and a conventional method, and FIG. 4 is a schematic explanatory view of the conventional method. , Fifth
The figure shows the front and plan views of the welded state at the end, 6th
The figure is an illustration of the spacing between electrodes.

Continued Front Page (72) Inventor Yoshio Kato, 3rd, Hikari, Kashima, Kashima-cho, Kashima-gun, Ibaraki Sumitomo Metal Industries, Ltd. Kashima Works (56) References

Claims (1)

[Claims] 1. A method of performing latent arc welding along a welding line using a multi-electrode latent arc welding machine in which three or more electrodes are arranged in tandem along the welding line, wherein welding feed at a welding end portion is performed. within a period ends to have stopped, the power supply to the first electrode to stop counting from the downstream side of the welding feed ends substantially simultaneously weld line, the energization is stopped after T ₁
After a lapse of time, the energization of the second electrode is stopped, and thereafter, in the same manner, after a lapse of Tn-1 time, the energization of the last n-th electrode is stopped, and each energization stop time interval T ₁ ... Tn -1 satisfies the relations of the following formulas (1) and (2): 0 ≦ T ₁ ≦ …… ≦ Tn-1 ≦ 10 …… (1) T ₁ <Tn-1 …… (2) And multi-electrode latent arc welding method.