The temperature of the molten pool directly affects the welding quality. The temperature of the molten pool is high, the molten pool is large, and the molten iron has good fluidity, which is easy to fuse. However, when the temperature is too high, the molten iron is easy to flow down, and the back of the single-sided welding and double-sided forming is easy to burn through, forming a weld bead, which is difficult to control, and the plasticity of the joint decreases, 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 the defects such as incomplete penetration, incomplete fusion, and slag inclusion are easy to occur.

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

1. Welding current and electrode diameter

The welding current and electrode diameter shall be selected according to the space position and welding level of the weld. When the welding is started, the welding current and electrode diameter shall be larger, and the vertical and horizontal positions shall be smaller.

For example, the bottom sealing layer of 12mm flat plate butt welding shall be selected φ 3.2mm electrode, welding current: 80-85A, filling, covering layer selection φ 4.0mm welding rod, welding current: 165-175A, reasonable selection of welding current and electrode diameter, easy control of molten pool temperature, is the basis of weld formation.

2. Strip handling method

The temperature of the circular electrode welding pool is higher than that of the crescent electrode welding pool, and the crescent electrode welding temperature is higher than that of the zigzag electrode welding pool. The zigzag electrode welding is used for the bottom sealing layer at 12mm, and the swing amplitude and the pause on both sides of the groove are used to effectively control the temperature of the weld pool, so that the size of the weld hole is basically the same, the probability of no overlap and burn through at the root of the groove is reduced, and the lack of penetration is improved, It is no longer a difficult point to make the single side welding and double side forming of butt welding flat on the plate.

3. Electrode angle

When the included angle between the electrode and the welding direction is 90 degrees, the arc is concentrated, the temperature of the molten pool is high, the included angle is small, the arc is scattered, and the temperature of the molten pool is low, such as the 12mm flat welding backing layer, and the angle of the electrode is 50-70 degrees, which reduces the temperature of the molten pool and avoids the generation of weld beading or raising on the back.

For another example, after replacing the welding rod for the bottom sealing layer of 12mm plate vertical welding, the welding rod angle of 90-95 ° shall be adopted during the joint, so that the temperature of the molten pool can be rapidly increased, the molten hole can be opened smoothly, and the back formation is relatively flat, effectively controlling the concave phenomenon of the joint point.

4. Arc burning time

φ fifty-seven × 3.5 In the practice teaching of horizontal and vertical fixed welding of pipes, the arc breaking method is used for welding. When the back cover is welded, the frequency of arc breaking and the arc burning time directly affect the temperature of the molten pool. Because the pipe wall is thin, the bearing capacity of the arc heat is limited. If the arc breaking frequency is slowed down to reduce the temperature of the molten pool, shrinkage cavity is easy to occur.

Therefore, only the arc burning time can be used to control the temperature of the molten pool. If the temperature of the molten pool is too high and the molten hole is large, the arc burning time can be reduced to reduce the temperature of the molten pool. At this time, the molten hole becomes smaller, and the internal forming height of the pipe is moderate, so as to avoid superelevation of the weld seam inside the pipe or the generation of weld beading.