In the welding process, there are many matters needing attention. Once neglected, it may be a big mistake.

1. Ignore the welding voltage

[Phenomenon] During welding, the same arc voltage is selected regardless of the bottoming, filling, and capping, regardless of the size of the groove. In this way, the required penetration depth and fusion width may not be met, and defects such as undercut, pores, and splashes may occur.

[Measures] Generally, according to different situations, the corresponding long arc or short arc should be selected to obtain better welding quality and work efficiency.

For example, short-arc operation should be used in order to obtain better penetration during bottom welding, and the arc voltage can be appropriately increased in order to obtain higher efficiency and fusion width during filling welding or cap welding.

2. Neglect welding speed and welding current

[Phenomenon] When welding, do not pay attention to control the welding speed and welding current, and use the electrode diameter and welding position in coordination.

For example, when rooting welding is performed on fully penetrated corner joints, due to the narrow root size, if the welding speed is too fast, the gas and slag inclusions at the root will not have enough time to discharge, which will easily cause defects such as incomplete penetration, slag inclusions, and pores at the root ; During cover welding, if the welding speed is too fast, it is easy to produce pores; if the welding speed is too slow, the weld reinforcement will be too high and the shape will be irregular; Slow, prone to burn through and so on.

[Measures] Welding speed has a significant impact on welding quality and welding production efficiency. When selecting, select the appropriate welding position according to the welding current, weld position (bottom welding, filling welding, cover welding), weld thickness, and groove size. Speed, under the premise of ensuring penetration, easy discharge of gas and welding slag, no burn-through, and good forming, a higher welding speed is selected to improve productivity and efficiency.

3. Ignore the problem of welding deformation

[Phenomenon] When welding, the deformation is not controlled from the aspects of welding sequence, personnel arrangement, groove form, welding specification selection and operation method, which will lead to large deformation after welding, difficult correction, and increased costs, especially for thick plates and large workpieces. Correction is difficult, and mechanical correction can easily cause cracks or lamellar tears. The cost of flame correction is high and poor operation can easily cause overheating of the workpiece.

For workpieces with high precision requirements, if no effective deformation control measures are taken, the installation size of the workpiece will not meet the requirements for use, and even rework or scrap will be caused.

[Measures] Adopt a reasonable welding sequence and select appropriate welding specifications and operating methods, and also adopt anti-deformation and rigid fixation measures.

4. Ignoring the control of interlayer temperature

[Phenomenon] When welding thick plates with multiple layers, do not pay attention to interlayer temperature control. If the interval between layers is too long, welding without re-preheating will easily cause cold cracks between layers; if the interval is too short, the interlayer temperature will If the temperature is too high (more than 900°C), it will also affect the performance of the weld and the heat-affected zone, which will cause coarse grains, resulting in a decrease in toughness and plasticity, and will leave potential hidden dangers for the joints.

[Measures] When welding thick plates with multiple layers, the control of the temperature between layers should be strengthened. During the continuous welding process, the temperature of the base metal to be welded should be checked so that the temperature between layers can be kept as consistent as possible with the preheating temperature. The maximum temperature is also controlled.

The welding time should not be too long. In case of interruption of welding, appropriate afterheating and heat preservation measures should be taken. When welding again, the reheating temperature should be appropriately higher than the initial preheating temperature.

5. Ignore the control arc length

[Phenomenon] The arc length is not properly adjusted according to the groove type, number of welding layers, welding form, electrode type, etc. during welding. Due to improper use of welding arc length, it is difficult to obtain high-quality welds.

[Measures] In order to ensure the quality of the weld, short-arc operations are generally used during welding, but the appropriate arc length can be selected according to different situations to obtain the best welding quality, such as V-groove butt joints and fillet joints. The first layer should use a shorter arc to ensure penetration without undercutting, and the second layer can be slightly longer to fill the weld. The short arc should be used when the weld gap is small, and the arc can be slightly longer when the gap is large, so that the welding speed can be accelerated. The arc of overhead welding should be the shortest to prevent the molten iron from flowing down; in order to control the temperature of the molten pool during vertical welding and horizontal welding, low current and short arc welding should also be used.

In addition, no matter what kind of welding is used, it is necessary to keep the arc length basically unchanged during the movement, so as to ensure that the fusion width and penetration depth of the entire weld are consistent.

6. Ignore the fillet size of combined welds

[Phenomenon] T-shaped joints, cross joints, corner joints and other butt or corner butt combined welds that require penetration, the size of the weld leg is not enough, or the design of the web and upper wing of a crane beam or similar components that requires fatigue checking If the size of the welding leg of the plate edge connection weld is not enough, the strength and rigidity of the welding will not meet the design requirements.

[Measures] T-shaped joints, cross joints, fillet joints and other butt joints that require penetration must have sufficient fillet requirements in accordance with the design requirements. Generally, the size of the weld fillet should not be less than 0.25t (t is the joint thinner plate thickness). The welding leg size of the welds connecting the web and the upper flange of the crane girder or similar webs with fatigue checking requirements is 0.5t, and should not be greater than 10mm. The allowable deviation of welding size is 0-4 mm.

7. Ignore the cleaning of multi-layer weld slag

[Phenomenon] When welding multiple layers of thick plates, the lower layer is welded directly without removing the welding slag and defects after each layer is welded, which is likely to cause slag inclusions, pores, cracks and other defects in the weld, reducing the connection strength and causing lower layer welding time splash.

[Measures] When welding multiple layers of thick plates, each layer should be welded continuously. After each layer of weld is welded, the welding slag, weld surface defects and spatter should be removed in time, and the defects such as slag inclusions, pores and cracks that affect the welding quality should be completely removed before welding.

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