Welding produces porosity, which is a problem often encountered in the semi-automatic welding process of self-shielded flux-cored wire, which has always plagued welders. Next, we will analyze the reasons for the generation of pores in semi-automatic welding of self-shielded flux-cored welding wires.
Causes of Welding Porosity
1) Influence of cooling rate during welding
In the vertical welding section, due to the gravity of the liquid metal itself, the welding speed is faster and the penetration depth of the weld bead is shallower, which accelerates the cooling rate of the liquid metal in the weld and reduces the chance of gas escape, resulting in more pores in the weld bead.
2) Influence of spatter during welding
The self-shielded flux-cored wire currently used has large metal oxidation spatter during welding. When a certain amount of oxidized metal splashes adhered to the front end of the contact tip, it enters the molten pool together with the moving wire. This phenomenon is more serious with the increase of the amount of filler metal in the weld bead, resulting in the generation of pores in the weld bead.
3) Influence of weld joints
When the welder is welding, due to the limitation of the space position, the arc is stopped during welding. Therefore, the weld joints of the thermal welding layer, the filling layer and the capping layer are easily superimposed, which increases the chance of generating dense pores in the weld bead.
4) Influence of the natural environment
Construction is carried out in an environment with high humidity, and the remaining welding wire is placed in the open air environment at the end of the work, and the welding wire is not properly kept, causing the welding wire to be damp. In addition, when the wind speed of the construction environment is greater than 8m/s, if no corresponding windproof measures are taken, it is also an important factor that leads to the generation of pores in the weld bead.
5) Influence of welding process parameters
The self-shielded flux-cored semi-automatic welding process parameter adjustment range is narrow. Generally, the arc voltage is 18~22V, and the wire feeding speed is 2000~2300mm/min. Therefore, these two parameters must be adjusted well. Otherwise, if the voltage is too high, the slag protection effect on the surface of the weld bead is not good, and it is easy to generate pores.
1) When welding, pay attention to the angle of the welding torch.
Before the capping layer is welded, when the filler layer of the vertical welding section is too low or too high, it should be trimmed, and the welding of the next process can be carried out after the height of the filler layer is about 0.5~1.0mm lower than that of the base metal. .
2) Control the extension length of the welding wire as much as possible during the welding process.
When using Giant’s self-shielded flux-cored welding wire as the surfacing material, the extension length of the welding wire is 15~20mm. If it is too short, the oxidized metal splashes at the front end of the contact tip will accumulate too quickly; if it is too long, the arc voltage will decrease and the welding quality will be affected. In addition, pay attention to inspection and cleaning of the contact tip before welding.
3) The weld joints between the bead layers should be arranged reasonably.
Before welding, the welder first squatted down to determine the position of the overhead welding, and then stood up and did not move his feet to weld.
4) When welding is carried out under the condition of high wind speed, windproof measures should be taken.
The remaining welding wire should be properly kept at the end of each day to prevent moisture. The wire feeder is troublesome to disassemble, so it should be covered with a rain protection cover.
5) Carefully adjust the arc voltage and wire feeding speed before welding.
After long-term use of welding equipment in field construction, the ammeter and voltmeter are not very accurate and can only be used as a reference. It is best to test welding on the steel plate to determine reasonable process parameters.