1. Field of the Invention
The present invention relates to an improvement of an arc welding process for welding a circumferential surface of a fixed pipe etc. by shielding a work part with an inert gas etc.
2. Description of the Prior Art
Heretofore, the apparatus shown in FIG. 1 has been known as an apparatus for arc welding for such purpose. FIG. 1 shows a welding apparatus for automatically welding an outer surface of a fixed pipe wherein (1) designates a welding head; and the welding head (1) automatically weld a joint of the fixed pipe (2) under rotating along a guide rail (3) around the fixed pipe (2); (4) designates a power source for welding which feeds work energy to the welding head (1); (5) designates a controller for controlling the work energy and the speed for feeding a filler wire for the automatic welding; (6) designates an operation box for commands for start and stop of the welding and sets of conditions for the welding by a manual operation; (7) designates a power cable for connecting the power source (4) for the welding and the welding head (1); (8) and (9) respectively designate control cables for connecting between the controller (5) and the welding head (1) and between the controller (5) and the operation box (6).
FIG. 2 shows the welding head (1) in detail wherein (10) designates a welding torch which has an electrode (11) for generating arc between the fixed pipe (2) and a structure for mechanically oscillating the electrode (11) to the direction perpendicular to the welding line; (12) designates a shield gas nozzle which covers the welded part and flows a shield gas such as an inert gas for protecting from air; (13) designates a fine adjuster for finely adjusting the welding torch (10) to the work part of the fixed pipe (2) in vertical and transversal directions; (14) designates a wire feeder to feed a filler wire (16) wound on a wire reel (15) to the work part; (17) designate a truck which runs on the guide rail (3) to turn around the fixed pipe (2) and the welding torch (10) and the wire feeder (14) etc. are mounted on the truck (17).
In the circumferential welding of the fixed pipe by the automatic welding apparatus, butt (2A) of all end surface of the fixed pipe (2) in a form of V-shape or U-shape groove shown in FIG. 3(a), 3(b) is welded from the outer surface of the fixed pipe (2). In the welding process, especially the welding for a first layer welding, it is necessary to form a convex penetration bead (2B) in the inner side of the fixed pipe (2) (referring to FIG. 4(a), 4(b)). In the circumferential welding of the fixed pipe, the welding elements for all postures as shown by a clock display in FIG. 5; as substantially downward directional posture between 10 to 2 o'clock; substantially horizontal downward gain posture between 2 to 4 o'clock; substantially upward directional posture between 4 to 8 o'clock and substantially horizontal upward gain posture between 8 to 10 o'clock.
In the upward directional posture, the gravity is applied to the molten metal, the required convex penetration bead (2B) can be formed under only a remarkably limited condition for the welding. In the case varying the welding condition in timing such as the welding of the joint of the fixed pipe, the required limited condition can not be maintained in high accuracy and the penetration bead (3B) often is downwardly concaved. (Referring to FIG. 6(a), 6(b)).