JPS628266B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for seam welding steel pipes.

Generally speaking, seam welding of steel pipes is carried out by first placing a welding head 2 supported by a boom 3 opposite the seam of a steel pipe 1 to be welded, and then attaching a core wire 4 to the welding head 2, as shown in FIG. A DC current is supplied from a power source 7 between the welding head 2 and the steel pipe 1 through captire cords 5 and 6, and the inner surface of the seam is welded.
Next, external welding is performed in the same manner.

However, traditional steel pipe seam welding, such as lever
Especially when welding the inner surface, the direct current flowing through the captire cord 5 introduced into the steel pipe 1 causes
A circumferential magnetic field is generated around the captire cord 5 according to the right-handed screw rule, and the steel pipe 1 with high magnetic permeability forms a magnetic circuit, and the seam is saturated magnetized, causing a large leakage magnetic field. will occur. According to the inventor's measurements, a welding current of 800A caused the seam to
It is magnetized to about 200 to 300 Gauss, which causes defects in the bead shape due to magnetic blowing phenomenon, which tends to cause welding defects.Also, when welding the outer surface, the seam part The residual magnetism caused the arc to deflect, causing similar problems.

In view of the above-mentioned drawbacks of the conventional welding head, the present invention covers a core conductor through which direct current is passed through the welding head with a peripheral conductor through an insulator, and the peripheral conductor is coated with an insulator that is opposite to the current flowing through the core conductor. By passing a current in the same direction, the circumferential conductor prevents magnetic leakage and also suppresses the generation of a circumferential magnetic field.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS. 2 and 3.

FIG. 2 shows a steel pipe seam welding apparatus to which the present invention is applied, in which, similarly to the conventional example, a welding head 12 is disposed opposite to the seam of a steel pipe to be welded 11 via a boom (not shown). In addition, in a structure in which a direct current is supplied from an energizing roller 14 to a welding core wire 13 fed to this welding head 12, an arc 15 is generated between the welding core wire 13 and the steel pipe 11, and welding 16 is performed. Now, as a power transmission line connecting the welding head 12 and the power supply 17, as shown in the cross section of FIG.
Using a captire-shaped power transmission line 18 coated with c, the core conductor 18a of this power transmission line 18 is connected to the current-carrying roller 14 and the power source 17 through a connecting wire 19.
The + side of the welding head 12 can be connected to the + side of the welding head 12, and the peripheral conductor 18c
The welding head side end of the welding head is connected to the steel pipe 11 with a connecting wire 20 and a ground roller 21, and the power source side end is connected to one side of the power source 17 with a connecting wire 22. A current flows in the opposite direction to the current flowing through the conductor 18a.

Here, the core conductor 18a may be, for example, a copper wire, and the peripheral conductor 18c is preferably made of copper, iron, silicon steel, etc., which are effective in preventing magnetic leakage and have low conductive resistance. The above configuration is applied to a so-called reverse polarity connection in which the core conductor 18a is connected to the power supply + side and the peripheral surface conductor 18c is connected to the power supply - side, but it is of course also applicable to a positive polarity connection. .

Therefore, in the present invention having the above-mentioned configuration, the peripheral conductor 18c is placed around the core conductor 18a through which the DC current is passed through the welding head 12 via the insulator 18b.
Since it is coated with
The leakage is prevented by the shielding effect caused by the magnetic flux leakage, and since the current flowing in the direction opposite to the current flowing through the core conductor 18a is caused to flow through the peripheral conductor 18c, the leakage is prevented by the leakage magnetic flux. The circumferential magnetic field is canceled by the magnetic flux in the opposite direction formed by the current flowing through the circumferential conductor 18c, completely preventing magnetic leakage to the outside of the power transmission line 18 , and eventually The steel pipe is not magnetized, and the magnetic blow phenomenon at the seam weld can be prevented. Further, the current flowing through the circumferential conductor 18c does not have to be the entire ground current, and this can be appropriately determined based on the material of the circumferential conductor, the number of laminated layers, current capacity, etc.

As detailed above, according to the present invention, in order to prevent the magnetic flux generated in the power transmission line due to the application of welding current to the welding head, the power transmission line is insulated between the core conductor and the area around the core conductor. The magnetic flux is canceled by constructing a peripheral conductor coated with an object, and by passing a current in the opposite direction to the current flowing through the core conductor through the peripheral conductor.
It is possible to perform effective seam welding without the risk of insufficient penetration, poor bead shape, or welding defects due to magnetization and magnetic blowing at the seam weld.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an overview of the configuration of conventional steel pipe seam welding, and FIG. 2 is a sectional view showing an overview of the configuration of steel pipe seam welding to which an embodiment of the present invention is applied.
FIG. 3 is a cross-sectional view of the same power transmission line. 11...Steel pipe to be welded, 12...Welding head, 1
7... Power supply, 18 ... Power transmission line, 18a... Concentric conductor, 18b... Same insulator, 18c... Same peripheral part conductor.

Claims (1)

[Claims] 1. A welding method in which seam welding of steel pipes is performed by passing a direct current to a welding head, comprising: a core conductor for passing a direct current to the welding head;
Using a captire-shaped power transmission line consisting of a peripheral conductor surrounding a core conductor through an insulator, welding is performed by passing a current in the opposite direction to the current flowing through the core conductor through the peripheral conductor. Features a seam welding method for steel pipes.