JPH09206934A - Arc welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the amount of deposited metal and to obtain a weld bead having a beautiful appearance shape at a high efficiency by welding the center of a groove with a first electrode to form a first layer and providing a second electrode and a third electrode respectively in both sides interposing the bead welded with the first electrode to generate an arc. SOLUTION: The first electrode 1 is positioned so as to aim at the center part in the width direction of the groove 4, and the arc is generated between the first electrode 1 and a base material 5. The second electrode 2 and the third electrode 3 are arranged to oppose each other and arranged in both sides interposing the groove 4. The arc is generated over between the second electrode 2 and the third electrode 3. By this way, the area of the groove 4 is set to be large, and the range of the plate width of the base material 5 capable of welding in one path is widened.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an arc welding method using multiple electrodes.

[0002]

2. Description of the Related Art Heretofore, as an arc welding method of this type, for example, there is one disclosed in Japanese Patent Publication No. 60-16304. That is, when welding a spiral steel pipe by using three electrodes, the technique is to weld the first electrode and then to fix the two side electrodes sandwiching the welding point to the other second electrode in order to finish the bead shape beautifully. And the third electrode is used for welding. When forming a spiral steel pipe, the weld groove also has a spiral shape.Therefore, even if the spiral steel pipe is installed so that its axial center is horizontal, the weld groove should be at the lowest point and the highest point of the spiral steel pipe. Except for going uphill or downhill. In the related art, down welding is performed. In general, when downward welding is performed, the molten metal near the center of the bead in which the solidification is delayed in the molten pool flows along the slope to form a bead having a hollow shape.
In this conventional technique, the second electrode and the third electrode are arranged as described above, the temperature distribution in the width direction of the molten pool is averaged, and the flow of the molten metal is blocked, so that the formation of the bead in the hollow is prevented. I am trying.

[0003]

However, the above-mentioned conventional welding method has the following problems. That is, the second electrode and the third electrode are simply arranged in parallel, and the two electrodes are used to perform welding at two parallel locations. Moreover, since the polarities of both are the same, if both electrodes are brought too close to each other, an electromagnetic pinch effect works between the arcs generated from each electrode, the two arcs attract each other, and it is as if a single arc is generated. It will be in the state of doing. Therefore, it is meaningless to separate the two poles and arrange them in parallel. That is, in the related art, it is necessary to separate the both poles so that the electromagnetic pinch effect does not act between them. However, as a result, the welding bead formed by the second electrode and the welding bead formed by the third electrode are completely separated depending on welding conditions, and further, both beads are separated from the welding bead formed by the first electrode. In some cases, sound welding could not be performed. Further, in the related art, welding is performed using multiple electrodes in order to improve welding efficiency, but this merely increases the number of electrodes. Therefore, as a general rule, a power source etc. corresponding to the number of electrodes is required, or the amount of power consumption increases according to the number of electrodes, so in order to realize not only welding speed but also overall welding efficiency There was room for improvement.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide an arc welding method capable of obtaining a welding bead having a beautiful appearance and performing efficient welding when performing welding using three electrodes. To do.

[0005]

[Means for Solving the Problems]

(Structure 1) As for the characteristic structure of the arc welding method of the present invention for attaining this object, as described in claim 1, the center of the welding groove is first layer welded with the first electrode, and the first electrode Of the first electrode, an arc is generated between the second electrode and the third electrode, which are respectively installed at two positions on both sides of the welding bead formed by the first electrode, to weld the second layer. (Operation / Effect) That is, the method of the present invention uses three electrodes. The arcs generated are two between the first electrode and the base material and between the second electrode and the third electrode. Is. In the conventional welding method, since the arc is generated between the electrode and the base metal, part of the thermal energy of the arc is consumed to melt the base metal. However, in the method of the present invention, for the second electrode and the third electrode, most of the heat associated with arc generation is used for melting both electrodes. If the conventional welding method consumes half of the thermal energy of the arc when the base material is melted, the method of the present invention can use twice as much thermal energy as the conventional method. That is, in the method of the present invention, two electrodes, the second electrode and the third electrode, are used to generate the trailing arc, but the amount of molten metal by the trailing arc is
It is about twice as much as the conventional method. In other words, the arc welding method according to the present invention obtains the amount of molten metal comparable to the welding using the conventional three electrodes, but its energy consumption is equal to that of the conventional method using two electrodes. It can be said that it is a very efficient arc welding method. On the other hand, since the trailing arc is generated between the second electrode and the third electrode, the effect of digging the base material of the conventional arc cannot be expected. However, since the molten metal is transferred over a wide range between the second electrode and the third electrode, there is an effect that the shape of the molten pool is wide and shallow penetration is formed. That is, the heat input amount per unit area of the base material becomes small. As a result, solidification of the molten pool is accelerated, so that even if the groove is inclined, the flow of molten metal is suppressed and a bead with a beautiful external shape can be obtained.

(Structure 2) According to the arc welding method of the present invention, as described in claim 2, when the welding groove is inclined in the longitudinal direction thereof, particularly when the welding is performed ascending welding. You can get a beautiful and healthy weld bead. (Operation / Effect) In the case of up welding, the molten metal is effectively discharged backward from the arc generation point, and a large penetration depth at the groove bottom can be secured. However, solidification of the molten metal is delayed in the center of the molten pool, so that the unsolidified metal flows backward along the slope. This flowing molten metal is concentrated in the unsolidified portion behind the bead, that is, in the center of the bead, so that only the center of the bead rises extremely, and beads on both sides of which tend to have insufficient build-up amount are formed. Will be done. However, in the arc welding method of the present invention, an arc is generated between the second electrode and the third electrode, and the molten metal mainly moves below the tips of these electrodes. Therefore, by appropriately setting the arc length and controlling the transfer position of the molten metal, it is possible to replenish the molten metal to both sides of the preceding bead where the build-up amount is small. Further, although the arc is mainly generated between the second electrode and the third electrode, the preceding bead is also heated by the arc to some extent, or a part of the arc is between the base metal. It is thought to have occurred. That is, the effect of correcting the convex shape by melting the convex portion of the preceding bead to some extent can be expected. Furthermore, as described above, since the heat input amount per unit area is small, the flow tendency itself of the molten pool can be suppressed. As described above, according to the arc welding method of the present invention, a beautiful weld bead appearance can be obtained even in the case of up welding.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. The arc welding method of the present invention, for example,
It can be applied to a submerged arc welding method as shown in FIG.

First, the first electrode 1 is arranged as a leading electrode. The first electrode 1 is not different from the usual submerged arc welding method. The first electrode 1 is positioned so as to aim at the widthwise central portion of the welding groove 4. The first electrode 1 needs to reliably melt the bottom of the welding groove 4 in order to prevent defects such as defective fusion. Therefore, welding is performed using a larger current than that of the trailing electrode. As a welding power source for the first electrode 1, a normal DC welding power source or an AC welding power source is used. In the first electrode 1, an arc is generated between the first electrode 1 and the base material 5.

The arc welding method of the present invention is characterized by the trailing electrode. That is, the second electrode 2 serves as a trailing electrode.
And the third electrode 3 are used, but as in a normal submerged arc welding method, these electrodes 2 and 3 are arranged in tandem along the longitudinal direction of the welding groove 4, and the direction of each electrode 2 and 3 is changed. The second electrode 2 is not directed to the base material 5 side.
And the third electrode 3 are arranged to face each other. That is, as shown in FIG. 1, the second electrode 2 and the third electrode 2
The electrodes 3 are arranged substantially equidistant from the first electrode 1 behind the welding, and are arranged on both sides of the welding groove 4 therebetween. The electrode direction of the second electrode 2 and the electrode direction of the third electrode 3 face each other, and extension lines of both electrode directions intersect in the upper space of the central portion of the welding groove 4. In this case, an arc is generated between the second electrode 2 and the third electrode 3, and the electrodes 2 and 3 are maintained in a state of being fed toward each other. The arc length in this case is mainly determined by the voltage between the electrodes 2 and 3. An AC welding power source is used as a power source for the second electrode 2 and the third electrode 3. As a result, the polarities of both electrodes 2 and 3 are switched at regular intervals, so that the melting conditions of both electrodes 2 and 3 can be made equal. As described above, as a result of the arc being generated between the second electrode 2 and the third electrode 3, the amount of the molten metal transferred to the base metal 5 side, that is, the welding, as compared with the usual arc welding method. The amount of metal increases. In the case of a normal welding method, an arc is generated between the electrode and the base material, so that part of the thermal energy of the arc is consumed in melting the base material. This merely melts the base material and does not add new molten metal. That is, only the remaining heat energy is consumed to melt the wire as the electrode. However, in the case of the present invention, since an arc is generated between the second electrode 2 and the third electrode 3, most of its thermal energy is used for melting both electrodes 2, 3. Therefore, the area of the welding groove 4 can be set large even if the current / voltage conditions are similar to those of the conventional arc welding. As a result,
The plate thickness range of the base material 5 that can be welded in one pass is expanded. Further, when the groove areas are the same, the welding speed can be improved by the amount of the deposited metal.

According to the arc welding method of the present invention, the bead shape can be finished beautifully even when the welding groove 4 is inclined in the longitudinal direction. In the conventional arc welding method, for example, when welding the inclined welding groove 4 in the upward direction, that is, when performing so-called upward welding, as shown in FIGS. The central part may be extremely convex. This is due to the solidification rate of the molten pool 6 extending from directly below the arc to the rear of the weld. That is, both side portions of the molten pool 6 are formed on the base material 5
The heat is taken away and it is cooled quickly, so the solidification is fast. Therefore, even if the welding groove 4 is inclined, the molten metal solidifies before flowing out. However, solidification is delayed in the central portion of the molten pool 6, and the molten metal flows backward along the slope. The flowing molten metal concentrates on the unsolidified portion behind the weld bead B, that is, at the center of the bead, and as a result, a convex weld bead B is formed in which only the center of the bead is extremely raised. This molten metal flowing backward is originally a metal to be filled on both sides of the weld bead B. Therefore, the welding groove 4 cannot be filled on both sides of the welding bead B, and so-called undercutting occurs. On the other hand, in the case of down welding, as shown in FIGS. 3A and 3B, conversely, the central portion of the welding bead B is likely to have a concave shape. In this case, the molten metal is likely to accumulate immediately below the arc. The electrode melts, and the molten metal becomes the base material 5
Immediately after shifting to the side, the momentum of the arc pushes it backward in the welding direction. However, the inclination of the welding groove 4 causes the molten metal to return to the direction of the arc again. As a result,
The molten metal stays at a position where both effects are balanced, and is mainly concentrated near the arc and on both outer sides of the welding groove 4. Therefore, the weld bead B formed by the down welding is likely to have a shape of a hollow having both sides raised.

The arc welding method of the present invention is particularly effective in suppressing the formation of convex beads associated with upward welding.
That is, in the present welding method, since an arc is generated between the second electrode 2 and the third electrode 3, as shown in FIG. 4, particularly below the tip of the second electrode 2, and
The amount of molten metal that moves below the tip of the third electrode 3 increases. Therefore, the welding voltage is appropriately set, and the leading ends of both electrodes 2 and 3 are connected to the leading bead B1 formed by the first electrode 1.
This is because the molten metal can be replenished to both side portions of the preceding bead B1 where the build-up amount is small by locating the molten metal on both sides. The molten metal transferred to the side of the base material 5 remelts the preceding bead B1 by its retained heat and fuses with it. On the other hand, although the arc is mainly generated between the second electrode 2 and the third electrode 3, the preceding bead B1 is slightly heated by the arc, or a part of the arc is generated. It is considered that this occurs between the base material 5 and the base material 5. That is, since the convex portion of the preceding bead B1 is melted to some extent, the convex shape is relaxed, and new molten metal is filled, the appearance of the succeeding bead B2 finally formed is as if one electrode It becomes beautiful as if it was welded using. Furthermore, according to the arc welding method of the present invention, the flow tendency itself of the molten pool 6 can be suppressed. That is, the molten metal by the second electrode 2 and the third electrode 3 mainly moves to the lower side of each electrode, but moves to a wide range between the two electrodes 2 and 3 by the momentum of the arc. It can be said that this is a remarkably wide range as compared with the case where the transfer of the molten metal in the usual welding method is performed almost directly under the arc. In other words, the heat input amount per unit area of the base material 5 is smaller than that in the normal welding method. Therefore, even if the solidification speed of the molten metal is increased and the weld groove 4 is inclined, the molten metal is solidified before flowing out, so that generation of convex beads can be prevented and a beautiful weld bead appearance can be obtained. it can.

When the arc welding method of the present invention is applied to the submerged arc welding method, as shown in FIG. 1, it is needless to say that the welding is performed while spreading the flux 7 in front of the first electrode 1. Absent. When the arc welding method of the present invention is applied to, for example, a gas shield welding method, although not shown, it is necessary to shield the circumference of each electrode with carbon dioxide gas or argon gas.

(Embodiment) FIG. 5 shows a schematic diagram when the arc welding method of the present invention is applied to the production of a spiral steel pipe, and FIG. 6 shows the welding groove and the arrangement conditions of each electrode. The spiral steel pipe 8 to be manufactured is JIS A 552.
SKK400 or SKK4 specified in 5
90, the pipe diameter D is 600 mmφ, and the plate thickness t is 9 mm
It is assumed that The position of the joint point 10 when the steel sheet 9 is wound in a spiral shape is about 24 ° at the central angle θ1 of the spiral steel pipe 8 from the lowest point 11 to the side of good welding. The shape of the weld groove 4 is a V groove having a groove angle θ2 of 10 ° and a root gap RG of 0 mm. The welding method is the submerged arc welding method. The first electrode 1, the second electrode 2, and the third electrode 3 are all 4.8.
Use mm solid wire. The first electrode 1 is
It is installed at a position where it will be an up weld and within about 10 ° from the lowest point 11 to the central angle θ3 of the spiral steel pipe 8. This angle range is the pipe diameter D of the spiral steel pipe 8.
-Although it varies depending on the plate thickness t, it is desirable to install each electrode so that the molten pool 6 is located near the lowest point 11 of the spiral steel pipe 8. The distance h1 between the tip of the first electrode tip C1 of the first electrode 1 and the base material 5 is about 30 m.
m. The second electrode 2 and the third electrode 3 are separated from the first electrode 1 by about 30 mm behind welding. If this distance is too short, the first electrode 1 and the second electrode
Between the electrode 2 or the first electrode 1 and the third electrode
An arc is generated between the electrodes 3. In this case, a predetermined penetration depth cannot be obtained in the first electrode 1, and a penetration failure may occur. On the contrary, if the second electrode 2 and the third electrode 3 are separated from the first electrode 1 too much,
Since the molten slag by the first electrode 1 is solidified, the slag cannot be re-melted by the second electrode 2 and the third electrode 3, and slag entrainment may occur. The distance h2 between the tip of the second electrode tip C2 of the second electrode 2 and the base material 5 and the distance h3 between the tip of the third electrode tip C3 of the third electrode 3 and the base material 5 are both about 30 mm. Is. The welding current is 1700 A for the first electrode 1, 700 A for the second electrode 2 and the third electrode 3, and the welding voltage is the first electrode.
Electrode 1 is 28 V, the second electrode 2 and the third electrode 3
Are both 40V. The welding speed is about 4 m / min.

As a result of manufacturing the spiral steel pipe 8 using the welding conditions described above, solidification of the molten pool 6 is faster than in the conventional submerged arc welding method, and the amount of deposited metal is increased. Due to the effect, a weld bead with a beautiful appearance could be obtained with high efficiency.

In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the configuration shown in the attached drawings.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an arc welding method according to the present invention.

FIG. 2 is a schematic view showing a convex bead formed in up welding.

FIG. 3 is a schematic view showing a concave bead formed in down welding.

FIG. 4 is a schematic diagram showing a procedure for forming a trailing bead.

FIG. 5 is a schematic diagram when the arc welding method of the present invention is applied to manufacturing a spiral steel pipe.

FIG. 6 is a schematic diagram showing welding groove of spiral steel pipe and arrangement conditions of each electrode.

[Explanation of symbols]

 1 1st electrode 2 2nd electrode 3 3rd electrode 4 Welding groove B Welding bead

Claims (2)

[Claims] 1. The first electrode (1) is located at the center of the welding groove (4).
Weld the first layer with, and behind this first electrode (1),
An arc is generated between the second electrode (2) and the third electrode (3) which are respectively installed at two positions on both sides of the welding bead (B) sandwiched by the first electrode (1) to perform the second layer welding. Arc welding method. 2. The welding groove (4) is inclined in the longitudinal direction thereof and is welded up.
5. The arc welding method according to 1.