1. Field of the Invention
The present invention relates to an submerged arc welding apparatus and method for submerged arc welding capable of performing submerged arc welding in a vertical position.
2. Description of the Related Art
Submerged arc welding is a welding process including previously spreading powder flux over a workpiece (base material), feeding a welding wire into it to strike an arc between the welding wire and the workpiece, and fusion-welding the workpiece and the welding wire by means of the arc heat. This process is referred to as submerged arc welding since the arc is invisible during welding.
This type of submerged arc welding process has the advantages: (1) available large current enables high deposition rate and high efficiency; (2) weld penetration is deep; (3) light-shielding is unnecessary due to the arc covered with flux and substantially no weld fume is made, whereby good working conditions are achieved; (4) beautiful bead appearance is obtained.
There are the following patent documents 1 to 4, for example, as related art documents on the submerged arc welding process.
In the methods disclosed in Patent Document 1 and Patent Document 2, submerged arc welding is performed with flux spread over a workpiece placed in a horizontal position and with a welding torch opposed to the workpiece from thereabove.
In the method disclosed in Patent Document 3, submerged arc welding is performed by disposing an extendable tubular hopper tank under a workpiece placed in a horizontal position, filling the tubular hopper tank with flux, and supplying the flux to a weld zone of the workpiece from below by pushing up the bottom of the tubular hopper tank.
In the method disclosed in Patent Document 4, submerged arc welding is performed with a welding torch opposed in a horizontal position to a workpiece (for example, a side panel of a cylindrical tank) which is placed in a vertical position and has a welding line extending in a horizontal direction.    [Patent Document 1]    Japanese Patent Laid-Open No. H8-281437    [Patent Document 2]    Japanese Patent Laid-Open No. 2002-120068    [Patent Document 3]    Japanese Patent Laid-Open No. H11-347735    [Patent Document 4]    Japanese Patent Laid-Open No. S63-63571
Incidentally, for example, in manufacturing a crude oil tank or an LPG tank, welding in a vertical position is required in the field in some cases. The term “vertical position” in welding means a position that is used for welding a workpiece having a welding line extending in a height direction.
The conventional submerged arc welding methods, however, have not been applicable to the vertical position, since the welding position is limited to the flat position (the methods in Patent Documents 1 and 2), the overhead position (the method in Patent Document 3), and the horizontal position (the method in Patent Document 4) from reasons of necessity to retain flux in a joint (butt joint, groove joint, lap joint, fillet weld joint or the like) of the workpiece.
Therefore, in the case of a need for welding in the vertical position, the welding has been performed using a coated arc welding process or a gas shield arc welding process capable of performing welding in the vertical position. Due to various advantages of the submerged arc welding process including high efficiency, there has been a strong demand for it to be applied to the vertical position.