How to control the temperature of the molten pool in order to weld beautiful welds?
1. Common states of molten pool
The temperature of medium liquid metal is much higher than that of general molten steel pouring. The average temperature of transition droplets is about 2300 ℃, and the average temperature of the molten pool is about 1700 ℃, with a maximum of over 2900 degrees. Therefore, the liquid metal in the molten pool is in an overheated state.
During welding operations, defects such as weld overlap, burning through, incomplete penetration, concave, slag inclusion, and poor forming often occur. The main reason for these defects is that during the welding operation, one is not good at observing the temperature changes of the molten pool and not effectively controlling the temperature of the molten pool, resulting in the above-mentioned defects.
2. Bath temperature
It directly affects the welding quality. The temperature of the molten pool is high, the molten pool is large, the fluidity of the molten iron is good, and it is easy to fuse. However, when it is too high, the molten iron is easy to flow down, and the back side formed by single-sided welding and double-sided forming is easy to burn through, forming weld nodules, and forming is difficult to control. Moreover, the plasticity of the joint decreases, and bending is easy to crack.
When the temperature of the molten pool is low, the molten pool is smaller, the molten iron is darker, and the fluidity is poor, which is prone to defects such as incomplete penetration, incomplete fusion, and slag inclusion.
During fusion welding, the current flowing back through the weldment is called welding current. The diameter of the welding rod refers to the cross-sectional size of the filler metal rod.
3. Current determination
The current is too small, making it difficult to start the arc. The welding rod is prone to sticking to the weldment, with thick fish scales and poor fusion on both sides; If the current is too high, there will be splashing and smoke during welding, the welding rod will turn red, and the surface of the molten pool will be very bright, making it easy to burn through and undercut;
The current is suitable, easy to ignite, and the arc is stable. The splash is very small, and a uniform cracking sound can be heard. The transition to the base metal is smooth on both sides of the weld seam, and the surface fish scale lines are very fine. The welding slag is easy to knock off. In terms of its application, there are complex relationships.
In vertical, horizontal, and vertical positions, the current is correspondingly lower than that in flat welding, and the current should usually be about 10% lower than that in flat welding. Similarly, in the vertical, horizontal, and vertical positions, the diameter of the welding rod is usually smaller than that in flat welding.