The best voltage is not selected for welding construction
Phenomenon: During welding, the same arc voltage must be selected regardless of the groove size, filling and capping.
In this way, the required depth and width of penetration may not be achieved and defects such as undercuts, air holes and splashes may occur.
Measurements: Generally, the corresponding long or short arc should be selected according to different situations, so as to achieve better welding quality and work efficiency.
For example, to achieve better penetration, short arc operation should be adopted in backing welding.
In order to obtain greater efficiency and fusion width, the arc voltage can be increased appropriately in fill welding or cover welding.
Welding does not control the welding wall
Phenomenon: During welding, to speed up the progress, no groove is adopted for butt welding of medium and thick plates.
The resistance index decreases, even does not meet the standard requirements, and cracks appear in the dome test, which will not guarantee the performance of the welded joint and will represent a potential risk to the safety of the structure.
Measures: During welding, the welding current should be controlled according to the welding current in the process qualification, and 10 ~ 15% fluctuation is allowed. The size of the blunt edge of the slope return should not exceed 6 mm.
When the plate thickness exceeds 6 mm during butt jointing, the slope opening should be opened for welding.
Do not pay attention to the coordinated use of welding speed, current and electrode diameter
Phenomenon: When welding, do not pay attention to controlling the welding speed and current, and coordinate the use of electrode diameter and welding position.
For example, when backing welding is performed for full penetration corner seam, due to the very fast welding speed in the root size chamber, the root gas and slag inclusion do not have enough time to be discharged, which is easy to produce welding defects such as incomplete penetration, slag inclusion, air hole and so on;
During overlay welding, if the welding speed changes too quickly, it will also be easy to produce pores;
If the welding speed is too slow, the weld reinforcement will be too high and the shape will be irregular;
When welding the solder with small size of calcium plate or edge, the welding speed is very slow and it is easy to burn
Measurements : Welding speed has a significant impact on welding quality and welding production efficiency.
When selecting, it must cooperate with the welding current and welding thread position for backing welding.
The appropriate welding speed must be selected for the thickness and size of the weld groove.
On the premise of ensuring penetration, easy discharge of welding gas and slag, no burning and good formation, a higher welding speed should be selected to improve productivity and efficiency.
Arc length is not controlled during welding
Phenomenon: During welding, the arc length is not adjusted properly according to the groove shape, number of welding layers, welding shape, electrode model, etc.
Due to improper use of welding arc length, it is difficult to obtain high-quality welding
Measures: To ensure welding quality, short arc operation is generally used during welding, but the appropriate arc length can be selected according to different conditions to obtain the best welding quality.
For example, a short arc should be used for the first layer of V-groove butt joint and fillet joint to ensure penetration and no undercutting.
The second layer can be a little longer to fill in the weldment.
The short arc should be used when the welding gap is small. When the gap is large, the arc can be a little longer and the welding speed can be accelerated.
The overhead welding arc should be as short as possible to prevent the molten iron from flowing downward;
In order to control the temperature of the molten pool during vertical and horizontal welding, small current and short arc welding should also be used.
Furthermore, regardless of the flexible welding adopted, the length must be kept basically unchanged during the welding process, so as to ensure the consistency of the weld width and the penetration of the entire weld.
No inspection should be done for welding to control the shape of the weld
Phenomenon: during welding, the deformation is not controlled by the aspects of welding sequence, personnel arrangement, groove shape, selection of welding specifications and operation method, resulting in large deformation after welding, difficult correction and increased cost .
Especially for thick plates and large parts, it is difficult to correct, and mechanical correction is easy to cause layer cracks or tears.
Flame correction has high cost and malfunction, which can easily cause parts to overheat.
If effective deformation control measures are not taken for workpieces with high precision, the installation size of workpieces will not meet the usage requirements and even rework or scrap will be caused.
Measures: use a reasonable welding sequence, select appropriate welding specifications and operation methods, and take anti-deformation and rigid fixation measures
