Porosity during welding is a common problem encountered during the semi-automatic welding of self-shielded flux-cored wires, which has always troubled welders. To this end, we analyzed the causes of pores during semi-automatic welding of self-shielded flux-cored wires and proposed corresponding control measures.
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Causes of welding pores
(1) Influence of cooling speed during welding
Due to the gravity of the liquid metal itself, the welding speed is faster and the weld penetration is shallower in the vertical welding section, which accelerates the cooling speed of the liquid metal in the weld and reduces the chance of gas escape, resulting in more pores in the weld.
(2) Influence of spatter during welding
The self-shielded flux-cored welding wire currently used produces large metal oxidation spatter during welding. When the amount of oxidized metal spatter adhered to the front end of the conductive nozzle reaches a certain amount, it enters the molten pool along with the moving welding wire. This phenomenon becomes more serious as the amount of filler metal in the weld increases, resulting in pores in the weld.
(3) Influence of weld joints
Due to spatial limitations, welders stop arcing during welding. Therefore, the weld joints of the hot weld layer, filler layer and cover layer are easily overlapped, increasing the chance of dense pores in the weld.
(4) Influence of natural environment
When working in an environment with high humidity, the remaining welding wire is placed in an open air environment at the end of work without proper storage, causing the welding wire to become damp. In addition, when the wind speed in the construction environment is greater than 8m/s, if no corresponding wind protection measures are taken, it is also an important factor that causes pores in the weld.
(5) Influence of welding process parameters
The adjustment range of welding process parameters for self-shielded flux-cored semi-automatic welding is relatively narrow. Generally, the arc voltage is 18~22V and the wire feeding speed is 2000~2300mm/min. Therefore, these two parameters must be adjusted properly. Otherwise, excessive voltage will easily cause poor slag protection on the weld surface and easily generate pores.
Control measures
(1) When welding, pay attention to the angle of the welding gun. Before welding the cover layer, if the filling layer of the vertical welding section is too low or too high, it should be trimmed to achieve a height of the filling layer weld that is about 0.5~1.0mm lower than the parent material before the next welding process can be carried out.
(2) During welding, control the extension length of the welding wire as much as possible. When using Jieente self-shielded flux-cored welding wire as surfacing material, the wire extension length is 15~20mm. If it is too short, the oxidized metal splashes will accumulate too quickly at the front end of the conductive nozzle; if it is too long, the arc voltage will be reduced, affecting the welding quality. In addition, it is necessary to check and clean the conductive nozzle before welding.
(3) The weld joints between each weld layer should be arranged reasonably. Before welding, the welder should first squat to determine the position of the overhead welding, then stand up and weld without moving his feet.
(4) When welding under 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 should be covered with a rainproof protective cover because it is more troublesome to disassemble.
(5) Before welding, the arc voltage and wire feeding speed should be carefully adjusted. 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 a steel plate to determine reasonable process parameters.
Post time: Jan-06-2025
