JPH08155637A - One side butt welding method of fixed tube - Google Patents

Abstract

PURPOSE: To form good penetration bead in unstable region of arc at welding starting part. CONSTITUTION: A ceramic backing strip 4 is abutted on the rear face of groove at welding starting part only, other backing strips use copper backing strips 5a-5o, starting of arc is executed at the ceramic backing strip 4. Because a ceramic has high heat holding to make solidification of molten metal slow as compared with that of copper backing strip, good penetration is obtained, further, because a copper backing strip is used for other parts, cost of backing strip is saved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a back bead at a welding start portion in single-sided butt welding of a fixed pipe.

[0002]

2. Description of the Related Art A good back bead formation is important in the first layer welding in single-sided butt welding of fixed tubes.

Usually, in single-sided butt welding by the arc welding method, a backing material is used to form a good back bead.
Copper backing, ceramics, flux, and the like are used as the backing material, but the copper backing is superior in terms of cost, management, and durability, and is most commonly used.

However, the characteristic of copper alloy having good thermal conductivity and being able to rapidly cool and disperse the arc heat to improve the efficiency of welding has an adverse effect at the start of welding when the base metal is cold, and the arc At the start, the welding arc was unstable, and the welding wire was melted, but there was a problem that the base metal was difficult to melt and the back bead was not formed.

When the welding current value is increased too much in order to secure the welding arc heat at the start of welding, the arc directly hits the copper metal and the melted copper mixes in the weld metal as an impurity, There is a risk of damaging the money.

As a countermeasure, in the one-side butt welding of flat steel plates, a welding arc is started on a start block such as a tab plate attached to the base metal, and when the welding condition becomes stable, the one-side butt welding of the base metal is started. . Then, there is a method of cutting and removing the start block after completion of the one-sided butt welding.

Further, as a method for forming a back bead at a welding start portion in one-sided butt welding of a fixed pipe, Japanese Patent Laid-Open No. 4-228 is known.
Japanese Patent No. 263 discloses a method in which a groove is provided at the bottom of the groove at the welding start position to facilitate melting of the welding start position.

[0008]

In the one-sided butt welding of fixed pipes, since the endless welding bead is used, it is necessary to use a start block as in the case of one-sided welding of flat steel sheets as described above. Occurs and is not a good idea.

Further, as to the method for forming the back bead at the welding start portion in the single-sided butt welding of the fixed pipe disclosed in the above-mentioned Japanese Patent Laid-Open No. 4-228263, after the arc is ignited on the base metal, it is moved in the groove width direction. The method of moving the welding torch and starting the welding complicates the sequence and equipment.

From the above, according to the present invention, in one-sided butt welding of a fixed tube, a good back bead can be formed efficiently including the vicinity of the welding start portion without a complicated work process. It is an object of the present invention to provide a single-sided butt welding method for a fixed tube that can be performed.

[0011]

[Means for Solving the Problems] The above-mentioned problem is that when the backing material is used for the one-sided butt welding by arc welding using the backing material on the back surface of the fixed tube, the backing material in the vicinity of the welding start part is the ceramic backing material. The other backing material is a copper backing metal, and a welding arc is generated at the position of the ceramic backing material, and then the welding is transferred to the position of the copper backing metal to form a back bead. This is solved by a single-sided butt welding method for a fixed tube.

[0012]

[Operation] When welding one side of a fixed pipe, by using a ceramic backing material as the backing material near the welding start part, it is possible to start a welding arc using a high welding current due to the heat resistance of the ceramics. it can. Then, due to the low heat conductivity of the ceramic backing material, the arc heat is accumulated in the vicinity of the welding start portion, whereby the melting of the base material is promoted,
The back bead is formed quickly.

If the welding at the welding start position using the ceramic backing material is performed well, it is possible to directly shift to the normal welding of the steady portion using the copper backing metal.

As described above, according to the present invention, it is possible to efficiently form a good back bead without performing complicated work steps.

[0015]

FIG. 1 is a sectional view showing a contact state of a backing material in an embodiment of a method for single-sided butt welding of a fixed tube according to the present invention.

In FIG. 1, 1 and 2 are fixed pipes that are butt-welded on one side, 3 is a welding torch, 4 is a ceramic backing material provided on the back surface of the welding start portion, and 5 is the back surface other than the welding start portion. It is a copper backing metal provided in. Copper back metal 5
Is formed by connecting unit copper backing block 5a to 5o.

The ceramic backing material 4 is a copper backing metal 5
Along with (5a to 5o), an internal clamp mechanism (not shown) is provided on the back surfaces of the fixed tubes 1 and 2 to fix the fixed tubes 1 and 2 to each other.
It is pressure welded to serve as centering.

It is also possible to form the entire backing metal with the copper backing 5 and embed the ceramic backing 4 in the upper part of only the copper backing 5 near the welding start point.

FIG. 2 is a sectional view taken along the line AA of FIG. 1, in which the ends of the fixed tubes 1 and 2 are arranged so as to form a groove 6, and the ceramic backing material 4 is provided on the back surface by the above-mentioned means. Pressed.

The backing range of the ceramic backing material 4 is 15 to 200 mm in the welding length direction with the welding start point as the center.
The range of is desirable.

If it is less than 15 mm, the effect of forming a good back bead at the welding starting point is small. Further, since the ceramic backing material is expensive, if it exceeds 200 mm, the cost is disadvantageous.

The specific welding conditions of the embodiment are shown below. (1) Fixed tube outer diameter: 900 mm (2) Fixed tube plate thickness: 12 mm (3) Groove: Narrow groove The groove bottom is V-shaped, the angle is 75 ° to 120 ° The root face is 0 to 2 mm ( 4) Shielding gas: 100% carbon dioxide (5) Welding current: 400 to 420 A (6) Welding speed: 180 to 200 cm / min, (7) Backing material-Welding start part: Ceramics backing material (dimension) length 100 mm × width 80 mm × thickness 20 mm ・ Except for the welding start part: Copper metal (Unit block size) Length 100 mm × Width 80 mm ×
Welding was started at the position of the ceramic backing material under the condition of a thickness of 20 mm or more, and the welding was moved to the position of the copper backing metal under the welding conditions as it was, and the first layer welding of the single-sided butt welding of the fixed pipe was performed.

As a result, since the ceramic backing material has a lower thermal conductivity than the copper backing metal, arc heat is accumulated in the ceramic backing material and the welding arc is unstable even at the welding start portion. The bead was formed quickly, and the welding operation could be completed efficiently by shifting to the normal welding of the portion of the copper backing metal.

In order to weld the entire circumference of the fixed pipe, it is necessary to connect the welding beads at the welding start portion regardless of whether the welding is performed by the left-right distribution welding or the entire circumference welding in the same direction. By using the method of the present invention that can favorably form the back bead of the welded portion, weld bead splicing at the welding start portion can also be favorably performed.

[0025]

According to the present invention, by using the ceramic backing material as the backing material at the welding start portion, a large heat input due to the high welding current is applied and the arc heat is accumulated in the ceramic backing material. Therefore, a good back bead is formed even at the welding start portion.

By using a copper backing metal as the backing material other than the welding start portion, efficient welding work can be carried out as a whole.

Further, since the expensive ceramic is only the welding start portion and the other portions are inexpensive copper backing materials, a cost-effective backing can be formed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an arrangement state of a backing material in a single-sided butt welding method according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

[Explanation of symbols]

 1 Fixed tube 2 Fixed tube 3 Welding torch 4 Ceramic backing material 5 Copper backing metal 6 Groove

Claims (1)

[Claims] 1. When performing one-side butt welding by an arc welding method using a backing material on the back surface of a fixed tube, the backing material near the welding start portion is used as a ceramic backing material and another backing material is used. One-sided butt welding method for a fixed pipe, characterized in that a copper backing metal is used, a welding arc is generated at the position of the ceramic backing metal, and then welding is transferred to the position of the copper backing metal to form a back bead. .