What matters should be paid attention to when submerged arc welding?
1. Too small welding current will lead to poor deformation, edge biting, incomplete welding, slag inclusion and other defects; Excessive welding current will lead to deterioration of physical and chemical properties and crack resistance of welded joints, burning through, rough weld forming, poor slag removal and other defects. One-sided pursuit of efficiency and blindly improve the welding current and the pursuit of performance, while reducing the welding specifications are unfavorable.
2. When welding low-alloy high-strength steel and low-temperature steel, in order to obtain good physical and chemical properties of the weld, it is recommended to conduct multi-layer and multi-pass welding of small and medium-sized specifications. The surface quality of submerged arc welding wire has great influence on physical and chemical properties of welded joint and welding process. Long-term use caused by rust on the surface of the welding wire or due to improper storage caused by the surface of the welding wire with oil, water and other impurities should be thoroughly removed before welding.
3. The diameter of submerged arc welding wire should be consistent with the size of the conductive nozzle. Too large diameter of the conductive nozzle will cause poor conduction, deterioration of weld formation and even arc breaking. When Ar+CO2 or Ar+O2 mixed gas is used for welding, the change of gas ratio has a great impact on the welding process and the mechanical properties of the weld, so a stable gas ratio should be ensured.
4. The inclination direction of the wire and the workpiece will affect the shape and penetration of the weld pass. If the wire is tilted forward or uphill, the penetration is larger. The welding wire tilts back (or downhill welding), its penetration depth is shallow, the width is increased, the gas activity will reduce the sensitivity of oil, rust, moisture and other impurities, so before welding should be strictly removed from the surface of the groove rust, oil, moisture and other impurities, otherwise it is very unfavorable to the welding process performance and weld mechanical properties.
5, although the increase of the length of the welding wire (dry elongation) can improve the rate of welding, but will worsen the welding process and weld performance, such as spatter increase, weld ripple and rough forming, porosity sensitivity, etc. It is recommended that when the welding current is less than 250A, the length of the welding wire should be about 1O ~ 18mm. When the welding current is greater than 250A, the length of the welding wire is between 20 mm and 25mm.
6. Dc reverse welding (DCEP) is adopted, and the welding arc length is generally 4 ~ 6mm. If the arc is too long, it is easy to produce defects such as pores, and if the arc is too short, its infiltration will become worse. Usually, when the filament is welded with small current, the protective gas flow is 10 ~ 15L/min. The flow rate of the protective gas should be 20 ~ 25L/min during the high current welding of coarse wire. For welds requiring high gas protection effect, or outdoor welding, gas flow can be increased to 30L/min.
7. In order to make the arc pit not affect the reliability of the whole weldment, the arc pit can be filled by suspending the welding gun in the original place for a few seconds after extinguishing the arc, intermittent arc burning, arc shifting back and other methods; During the welding process, avoid the influence of wind. When the wind speed is greater than or equal to 1.8m/s or the welding is carried out at a high level, the wind protection measures should be adopted, and the fan should not blow the welding place directly. The workplace should adopt ventilation measures, especially in the relatively closed, poor ventilation occasions, in order to minimize the personal injury to welding personnel.
