1. The best voltage is not selected for welding construction
Phenomenon: during welding, the same arc voltage shall be selected regardless of the size of the groove, filling and capping.
In this way, the required penetration depth and width may not be reached, and defects such as undercut, air hole and splash may occur
Measures: generally, corresponding long arc or short arc shall be selected according to different situations, so as to obtain better welding quality and work efficiency.
For example, in order to obtain better penetration, short arc operation should be adopted in backing welding.
In order to obtain higher efficiency and fusion width, arc voltage can be appropriately increased in filler welding or cover welding.
2. Welding does not control the welding wall
Phenomenon: during welding, in order to speed up the progress, no groove is adopted for the butt weld of medium and thick plate.
The strength index decreases, even fails to meet the standard requirements, and cracks appear in the dome test, which will not guarantee the performance of the weld joint and pose a potential hazard to the safety of the structure
Measures: during welding, the welding current shall be controlled according to the welding current in the process qualification, and 10 ~ 15% floating is allowed. The blunt edge size of slope return shall not exceed 6mm.
When the plate thickness exceeds 6mm during butt joint, the slope opening shall be opened for welding.
3. Do not pay attention to the coordinated use of welding speed, current and electrode diameter
Phenomenon: when welding, do not pay attention to control the welding speed and welding current, and coordinate the use of electrode diameter and welding position.
For example, when backing welding is carried out for the full penetration corner seam, due to the too 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 cover welding, if the welding speed changes too fast, it is also 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 weld with small size of plate or calcium edge, the welding speed is too slow and it is easy to burn through
Measures: the welding speed has a significant impact on the welding quality and welding production efficiency.
When selecting, it shall cooperate with the welding current and welding thread position for backing welding.
Proper welding speed shall be selected for the thickness and groove size of the weld.
On the premise of ensuring penetration, easy discharge of gas and welding slag, no burn through and good forming, a larger welding speed shall be selected to improve productivity and efficiency.
4. The arc length is not controlled during welding
Phenomenon: during welding, the arc length is not properly adjusted according to the groove form, number of welding layers, welding form, electrode model, etc.
Due to improper use of welding arc length, it is difficult to obtain high-quality welding
Measures: in order to ensure the weld quality, short arc operation is generally used during welding, but appropriate arc length can be selected according to different conditions to obtain the best welding quality.
For example, short arc shall be used for the first layer of the V-groove butt joint and fillet joint to ensure penetration and no undercut.
The second layer can be slightly longer to fill the welding.
Short arc should be used when the welding gap is small. When the gap is large, the arc can be slightly longer and the welding speed can be accelerated.
Overhead welding arc shall be the shortest to prevent molten iron from flowing down;
In order to control the temperature of the molten pool during vertical welding and horizontal welding, small current and short arc welding shall also be used.
In addition, no matter what flexible welding is adopted, the length shall be kept basically unchanged during the welding process, so as to ensure the consistency of the weld width and penetration of the whole weld.
5. No inspection shall be made for welding to control the welding shape
Phenomenon: during welding, the deformation is not controlled from the aspects of welding sequence, personnel arrangement, groove form, welding specification selection and operation method, resulting in large deformation after welding, difficult correction and increased cost.
Especially for thick plates and large workpieces, it is difficult to correct, and mechanical correction is easy to cause cracks or layered tears.
The flame correction has high cost and poor operation, which is easy to cause overheating of workpieces.
If effective deformation control measures are not taken for workpieces with high precision, the installation size of workpieces will not meet the use requirements and even rework or scrap will be caused.
Measures: use reasonable welding sequence, select appropriate welding specifications and operation methods, and take anti-deformation and rigid fixing measures