The molten pool refers to the part of the base metal that is melted into a pool-like shape due to the heat of the welding arc. The part of the liquid metal with a certain geometric shape formed on the weldment during welding is called the molten pool.
The temperature of the liquid metal in the molten pool is much higher than that of the general pouring molten steel. The average temperature of the transition droplet is about 2300 °C, the average temperature of the molten pool is about 1700 °C, and the maximum can reach more than 2900 degrees. Liquid metal is overheated.
In the welding teaching, the students often have defects such as welding flash, burn-through, incomplete penetration, concave, slag inclusion, and poor forming during the welding practice operation. The reasons for these defects are analyzed. , is not good at observing changes in the temperature of the molten pool, and does not effectively control the temperature of the molten pool to produce the above-mentioned defects.
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 and is easy to fuse. Welding and forming are also difficult to control, and the plasticity of the joint decreases, and the bending is easy to crack.
When the molten pool temperature is low, the molten pool is small, the molten iron is dark, and the fluidity is poor, and defects such as incomplete penetration, incomplete fusion, and slag inclusion are easy to occur.
During fusion welding, the current flowing back through the weldment is called welding current. The electrode diameter refers to the section size of the filler metal rod.
In simple terms, the proper melting of the electrode is determined by the current passing through it.
If the current is too small, it is difficult to start the arc, the electrode is easy to stick to the weldment, the fish scale pattern is thick, and the two sides are not well fused; if the current is too large, the spatter and smoke during welding are large, the electrode is red, the surface of the molten pool is very bright, and it is easy to burn wear, undercut;
The current is suitable, it is easy to ignite and the arc is stable, the spatter is small, and a uniform crackling sound can be heard. The two sides of the welding seam smoothly transition to the base metal, the surface fish scale pattern is very fine, and the welding slag is easy to knock off. In terms of its application, there is a complex relationship
In vertical, horizontal and vertical positions, the current is correspondingly smaller than that in flat welding, and the current should usually be about 10% smaller than that in flat welding. Similarly, in vertical, horizontal and vertical positions, the diameter of the electrode is usually smaller than that in flat welding.
Shipping method:
After the electrode is fed in the direction of the molten pool along the axis to melt the electrode, the length of the arc can continue to be kept unchanged, so the speed at which the electrode is fed in the direction of the molten pool is equal to the speed at which the electrode melts.
If the feeding speed of the electrode is less than the melting speed of the electrode, the length of the arc will gradually increase, resulting in arc breakage; if the feeding speed of the electrode is too fast, the arc length will be shortened rapidly, and the end of the electrode will be in contact with the weldment and a short circuit will occur. will extinguish the arc.
Crescent-shaped transportation method: The end of the electrode swings left and right in a crescent shape along the welding direction, the middle action should be fast, and the two sides should stay for a while. This method can effectively control the temperature of the molten pool, the molten pool is shallow, and the front and back sides should be prevented from undercutting. Crescent-shaped transport is one of the main transport methods for single-sided welding and double-sided forming arc welding.
The method of zigzag transportation: the end of the electrode swings forward in a zigzag manner, and stops for a while on both sides to prevent undercut. This method is easy to operate and widely used. It is suitable for welding all layers of butt welds in horizontal, vertical and overhead welding positions.
The temperature of the molten pool in the circle-shaped strip is higher than that of the crescent strip, and the temperature of the crescent strip is higher than that of the zigzag strip.
The zigzag strip is adopted, and the swing amplitude and the pause on both sides of the groove effectively control the temperature of the molten pool, so that the size of the molten hole is basically the same, and the probability of no welding flash and burn-through at the root of the groove is reduced. , the incomplete penetration has been improved, so that the single-sided welding and double-sided forming of butt flat welding is no longer difficult.
Welding rod angle:
When the angle between the electrode 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 scattered, and the temperature of the molten pool is low.
Arc burning time:
The arc burning time is 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 is moderate to avoid the pipe The internal weld seam is super high or has a weld flash.
In welding practice, learning to observe the change of the temperature of the molten pool and mastering the method of effectively controlling the temperature of the welding pool is the foundation of learning welding technology. Only by laying this solid foundation can you make breakthroughs and become an excellent welding technician.
