JPH0686014B2 - Tabless welding method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic welding method without using a tab plate.

[0002]

2. Description of the Related Art As is well known, in spiral pipe making, pipe making is continued while successively adding coils. The coil connection here is generally performed by two-electrode submerged arc welding. With coil splices by welding, the pipemaker must be stopped during welding. For this reason, the coil joining work is a major stoppage factor as well as the setup change work, and the rationalization of the work is an important issue for improving the operation rate of the pipe making machine.

One of the factors that reduce the efficiency of coil splicing work is the attachment and removal of tab plates. That is, in the coil splicing work, before welding, a waste plate called a tab plate is attached on both ends of the steel plate butt line, and welding is started on this tab plate.
finish. As a result, the penetration is secured at the welding start end and the welding end, and the extra weld is secured at the welding end, and the bead shape is made uniform. However, since the tab plate is attached and removed by welding, it takes a long time to attach and remove the tab plate, and the coil joining work occupies 10 to 20% of the work time. Therefore, in part, development of a tabless welding method that does not use a tab plate is underway. As such a welding method, a method of pressing a metal plate instead of attaching a tab plate is disclosed in JP-A-57-81990.

[0004]

However, this tabless welding method merely changes the attachment method of the discard plate from welding to pressing, and the start and end of welding are still performed on the pressing plate. Therefore, the pressing plate is required to have the same function as the tab plate, and it takes time to align the pressing plate. In addition, a large-scale pressing device is required because it is necessary to provide the joint portion with adhesion close to that of welding.

An object of the present invention is to provide a tabless welding method which does not require any waste plates such as tab plates and pressing plates, and ensures the same weldability as when using the waste plates. .

[0006]

In the tabless welding method of the present invention, the arc movement is started after the arc is ignited in the vicinity of one end of the steel plate butt line, and the arc force is applied when the arc reaches the welding end. It is characterized in that the arc is lowered and the arc is moved backward and forward so that the arc reciprocates in the other end of the steel sheet butt line.

FIG. 1 is a schematic view showing an embodiment of the present invention. The welding is a two-electrode submerged arc welding, and the leading electrode 1 and the trailing electrode 2 are moved along the butt line of the steel plate by the welding carriage while maintaining the same positional relationship. FIG. 2 shows changes with time in voltage and current and changes in the vehicle speed at the leading electrode 1 and the trailing electrode 2.

At the start of welding, as shown in FIG. 1 (A), the leading electrode 1 is set at a position slightly in the welding direction from one end of the butt line of the steel plate 3. The distance L1 from one end of the steel plate butt line to the set position of the leading electrode 1 is 15 mm
It is desirable to be within the range, and usually it is 5 to 6 mm. And
An arc is ignited on the leading electrode 1 with the welding carriage stopped.

Immediately after the preceding arc is ignited, the welding carriage remains stopped. The time T1 from the ignition of the preceding arc to the start of the movement of the welding carriage is made longer as the plate thickness t becomes thicker, and is usually 0.1 when the plate thickness t is 6 mm.
Seconds, about 10 mm is about 0.5 seconds, and about 15 mm is about 0.8 to 0.1 seconds. The welding carriage that has started moving is gradually accelerated to reach a predetermined welding speed. The acceleration time T2 of the welding carriage is also lengthened as the plate thickness t becomes thicker, and is usually about 1 second when the plate thickness t is 6 mm, about 0.3 to 0.5 seconds when the plate thickness t is 10 mm, and about 0.1 mm when it is 15 mm. It is about 7 to 2.0 seconds. An arc is ignited on the trailing electrode 2 before and after the welding carriage reaches a predetermined welding speed. As a result, two-electrode submerged arc welding is started as shown in FIG.

When the leading electrode 1 reaches the other end of the steel sheet butt line, the leading arc is stopped. Further, when the trailing electrode 2 reaches the other end of the steel plate butt line, the voltage is slightly increased and the current is increased at the same time as the leading arc is stopped so that the arc force in the trailing electrode 2 is reduced to a predetermined level. Begins to fall. When the trailing electrode 2 reaches the other end of the steel plate butt line, the
As shown in (C), the welding carriage is retracted. The retreat distance L2 of the welding carriage increases as the plate thickness t increases,
Normally, when the plate thickness t is 6 to 9 mm, it is about 35 mm, when the plate thickness t is 10 to 13 mm, it is about 40 mm, and the plate thickness t is 1.
In the case of 7 mm to 19 mm, it is about 50 mm. After the welding carriage is retracted by a predetermined distance, the welding carriage is moved forward again. Then, the trailing arc is stopped when the trailing electrode 2 passes through the other end of the steel sheet butt line. Welding carriage retreat speed V
1 and the speed V2 at the time of re-advancing are made slightly slower than the main welding speed.

[0011]

In the tabless welding method of the present invention, the arc is ignited in the vicinity of one end of the steel plate butt line, and then the movement of the arc is started, whereby a sufficient penetration depth is secured at the welding start end. At the end of welding, since the arc is reciprocated with a low arc force after the welding is completed, sufficient surplus is secured, and the crater is processed to finish the bead shape close to the main welding portion.

[0012]

EXAMPLES Coil splicing in a spiral pipe was carried out according to the above procedure under the conditions shown in Tables 1 and 2. Although no tab plate was used, the weld start and end were finished to the same quality as the main weld.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

As is apparent from the above description, the tabless welding method of the present invention does not require a tab plate or a waste plate such as a pressing plate to replace the tab plate, and the waste plate is used. As in the case of the above, excellent welding quality can be given to the entire length of the welded portion. Therefore, the welding work is simplified and the work time for the coil joining work and the like is shortened.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention.

FIG. 2 is a time chart showing an operation procedure in one embodiment of the present invention.

[Explanation of symbols] 1 Leading electrode 2 Trailing electrode 3 Steel plate

Claims (1)

[Claims] 1. An arc is ignited in the vicinity of one end of a steel plate butt line, and then the movement of the arc is started. When the arc reaches the other end of the steel plate butt line, the arc force is reduced and the arc is welded in that state. A tabless welding method characterized in that the arc is moved backward and forward so as to reciprocate at the terminal end.