In the welding practice teaching, students often have defects such as welding, burning, incomplete penetration, concave, slag inclusion, poor forming, etc. during the welding arc welding practice. The reasons for these defects are mainly analyzed. During the operation, it is not good to observe the change of the temperature of the molten pool, and the above defects are not effectively controlled by the temperature of the molten pool.

The temperature of the molten pool directly affects the quality of welding, the temperature of the molten pool is high, the molten pool is large, the fluidity of molten iron is good, and it is easy to fuse. However, when it is too high, the molten iron is easy to smash, and the back surface of the double-sided forming is easy to burn through. The weld is not difficult to control, and the joint plasticity is reduced, and the bending is easy to crack. When the temperature of the molten pool is low, the molten pool is small, the molten iron is dark, the fluidity is poor, and defects such as incomplete penetration, unfusion, and slag inclusion are easily generated.

The temperature of the molten pool is closely related to the welding current, the diameter of the welding rod, the angle of the welding rod, the burning time of the arc, etc. The following measures are taken to control the temperature of the molten pool for relevant factors.

1. Welding current and electrode diameter: The welding current and the diameter of the welding rod are selected according to the spatial position of the weld and the welding level. When welding, the welding current and the diameter of the welding rod are larger, and the vertical and horizontal positions are smaller. For example, 12mm flat butt welding flat layer is made of φ3.2mm electrode, welding current: 80-85A, filling, cover layer is φ4.0mm electrode, welding current: 165-175A, reasonable selection of welding current and electrode diameter, Easy control of bath temperature is the basis for weld formation.

2. The method of transporting the strip, the temperature of the molten pool of the circle shaped strip is higher than the temperature of the crescent-shaped moving strip, and the temperature of the crescent-shaped moving strip is higher than the temperature of the molten pool of the zigzag moving strip, and the bottom of the 12 mm flat welding seal adopts a zigzag moving strip. And with the amplitude of the swing and the pause on both sides of the groove, the temperature of the molten pool is effectively controlled, the size of the molten holes is basically the same, the probability of no weld formation and burn through at the root of the groove is decreased, and there is no penetration. The improvement has made it difficult to make double-sided forming of single-sided welding of butt-welded flat welding.

3. the angle of the welding rod, the angle between the welding rod and the welding direction is 90 degrees, the arc is concentrated, the temperature of the molten pool is high, the angle is small, the arc is dispersed, the temperature of the molten pool is low, such as the bottom layer of 12mm flat welding, the angle of the welding rod: 50- 70 degrees, so that the temperature of the molten pool has decreased, avoiding the formation of a weld on the back or lifting up. For example, after adjusting the welding electrode at the bottom of the 12mm plate welding seal, the angle of the electrode is 90-95 degrees, the temperature of the molten pool is rapidly increased, the melt hole can be opened smoothly, and the back surface is formed flat, effectively controlling the joint point. Concave phenomenon.

4. arc burning time, φ57 × 3.5 pipe horizontal fixed and vertical fixed welding practice teaching, using arc breaking method welding, sealing the bottom layer welding, the frequency of arc breaking and arc burning time directly affect the molten pool temperature, due to The wall of the pipe is thin, and the heat resistance of the arc is limited. If the arc breaking frequency is slowed down to reduce the temperature of the molten pool, shrinkage holes are easily generated. Therefore, the arc burning time can only be used to control the temperature of the molten pool. If the temperature of the molten pool is too high, When the melting hole is large, the arc burning time can be reduced, and the temperature of the molten pool is lowered. At this time, the melting hole becomes small, and the internal forming height of the pipe is moderate, so that the weld seam inside the pipe is prevented from being too high or a weld bead is generated.

In summary, in the welding practice teaching, let students learn to observe the change of molten pool temperature, master the method of effectively controlling the temperature of the welding pool, is to learn the basis of welding technology, lay a solid foundation, in order to make a breakthrough, in order to become a An excellent welding technician.