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The welding process has been continuously improved with the development of today's science and technology. The emergence and development of self-shielded flux-cored wire semi-automatic welding in pipeline welding is a technical revolution in traditional manual arc welding. With the construction of major projects at home and abroad such as Sudan Engineering, Suininglan Project, Lanchengyu Project, West-East Gas Pipeline, etc., semi-automatic welding is fast, easy to operate, high in pass rate, beautiful in appearance, strong in adaptability to the environment, etc. The advantages gradually replaced the traditional manual arc welding, which became the mainstream of the long-distance pipeline construction welding process.
Semi-automatic welding is an advanced welding process, but for some inexperienced welders, various welding defects are often caused by poor control of the bath temperature. The following describes a welding method that can effectively control the temperature of the molten pool - arc welding.
First, semi-automatic welding often occurs in welding defects
1. Pipe joint welding seam flat welding, overhead welding two positions are often in the heat welding due to the molten pool temperature is too high, the weld bead penetration increases, and due to gravity, iron underwater drops, causing the weld bead burned or The undercut position forms a root weld recess.
2. After the root bead has been polished and cleaned, there is a case where the thickness is uneven. Since the semi-automatic weld pool has a high temperature and a large penetration depth, if the conventional method is used for welding at a thinner position of the root bead, it is highly probable that the root weld metal is completely melted to cause burn-through.
3. In the position of the surface welding of the cover welding, when the temperature of the molten pool is too high, the molten iron will fall down due to its own weight during welding, and it is difficult to control the shape and size of the molten pool, thereby causing defects such as super high, too narrow, biting meat and the like.
Second, the basic principle of arc welding and welding methods
1. Basic principle: Although the above-mentioned welding defects are different, the causes of various defects have one thing in common: the molten pool temperature is too high. Therefore, the basic principle of arc welding is to use the arc breaking method to temporarily cool the molten pool when the temperature of the molten pool is too high, and then continue welding, so as to control the temperature of the molten pool within a suitable range.
2. Welding method: arcing according to the angle of normal operation, forming the molten pool and transporting the strip according to the conventional moving method, and then immediately breaking the arc (one step and one breaking method) or forming several welding waves forward and breaking the arc (a few steps and one break) Method), after the arc is broken, the molten pool is slightly cooled to quickly start the arc, forming the next molten pool, then breaking the arc, starting the arc... and so on. (When welding, the specific use of "one step, one break" or "several steps and one break" should be reasonably selected according to the temperature of the molten pool)
Third, the application and operation essentials of arc welding
1. When the pipe girth weld is heat-welded at the flat welding, the up-welding position and the thinner root-grinding, it is found that the molten pool temperature is too high (the molten pool is increased), and the arc welding can be used for the welding transition until it leaves the dangerous area. This can effectively avoid the occurrence of burn through and concave.
2. When the welding is carried out at the surface of the overlay welding, after the arc is formed into the molten pool, the molten iron is rapidly swayed to form a sheet, so that the metal and the mother material on both sides of the groove are well fused, and then the arc is broken, the arc is broken, and the arc is broken. ... until the finish welding of the overhead welding position is completed. The use of arc welding can make the appearance of the cover welding position smooth, wide and narrow, and avoid the phenomenon of biting.
3. The essentials of arc welding: the interval between arc breaking and arcing is extremely short (not more than 1 second), so the action must be rapid, if the cooling time of the molten pool is too long (the molten pool is dark red), then the arc, the weld bead It is highly probable that slag will be produced. In addition, the distance between the two welding waves is not too large, so that the adjacent two welding waves are stacked to form a dense scale shape, otherwise the welding wave will be disjointed, and the appearance is not beautiful enough.
Fourth, the improvement of the arc welding method
Although arc welding is easy to learn and can avoid the occurrence of many defects, because it is intermittent welding, the welding speed is relatively slow. In order to improve the welding speed, it is necessary to improve the arc welding according to the basic principle of arc welding (the molten pool with too short cooling temperature and the effective control of the bath temperature) on the basis of the arc welding technology: when the bath temperature When it is too high, the welding rod is quickly and vertically oriented in the unwelded direction (in the groove, do not put the slope to damage the base metal) (continuous arc), and then quickly swing back to continue normal welding, thus reaching the cooling pool The purpose is to make the welding continuous, which not only ensures the welding quality, but also improves the welding speed.
In the semi-automatic welding of long-distance pipelines, if the above-mentioned welding method can be mastered and used reasonably, the purpose of controlling the temperature of the molten pool and ensuring the welding quality can be achieved.
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