Due to the large current and deep penetration, the submerged arc welding has the requirements of the groove form and size: the thickness is less than 12mm, the plate does not need to open the groove, the thickness between 12 and 20mm can be single-sided welding, and the reverse surface is used for welding.
The bevel is required at 20mm, but the blunt edge is required to be 5~6mm. The welding current is selected based on the diameter of the wire, the thickness of the weldment, and the type of flux. Due to the large welding current of submerged arc welding, the first layer of welding is prone to burn through, and the following welding processes are often used: electrode arc welding bottom sealing, permanent pad submerged arc welding, bottom butt joint submerged arc welding, solder pad Submerged arc welding.
LSAW steel pipe is a method in which an arc is burned under the flux layer for welding. The welding arc is burned between the welding wire and the weldment. The arc heat melts the base metal and the base metal near the arc and the flux. The welding wire is continuously fed and advances along a certain trajectory.
After the arc is removed, the molten pool metal solidifies. In the weld, the molten flux solidifies into a slag shell covering the surface of the weld, and the slag protects the weld pool and the weld metal from the outside air and prevents the arc and the weld pool from being invaded by the outside air. In addition, the slag participates in the metallurgical reaction of the molten pool, and the alloying elements such as Cr and Mn in the welding wire may be burnt, and the Si, S, P, etc. of the flux enter the weld metal.
Submerged arc welding, such as arc ignition, wire feeding, wire transfer and arc extinguishing, is usually done by machinery, so it is called submerged arc automatic welding. Submerged arc welding has the following advantages:
1. High degree of mechanization, low requirements on the skill level of the welder;
2. Large welding current, can reduce the bevel of the weldment, high welding efficiency;
3 Flux can separate the contact between the molten metal and the air, the protection effect Good, high weld quality;
4. Covered with arc radiation, good working conditions. The disadvantage is that it can only be welded in the flat welding position, which requires high requirements for welding equipment and tooling equipment.
There are two types of welding equipment for submerged arc welding. One is a constant-speed wire submerged arc welding machine. The wire feeding speed is constant at a set speed, and the arc is relatively stable due to the self-regulation of the arc.
The other is a variable speed wire submerged arc welding machine, which uses the arc voltage as a feedback signal to change the wire feed speed through the control system to maintain the relative stability of the arc. In addition, in order to ensure that the welding process is in the most suitable position and the welding process is stable and reliable, submerged arc welding also requires more complicated auxiliary equipment to cooperate with the welding machine.
Common auxiliary equipments include: welding parts displacement equipment, welding operation machine (ie welding machine head displacement equipment), welding fixtures and weld forming equipment.