The ten most overlooked problems in welding, the details make the difference
2022-11-22
1 . Welding construction does not pay attention to choose the best voltage
[phenomenon]welding whether bottoming, filling, cover, regardless of the size of the bevel, are selected the same arc voltage. This may not achieve the required melt depth, melt width, edge biting, porosity, spatter and other defects.
[Measures] Generally for different situations should be selected for the corresponding long arc or short arc can get better welding quality and work efficiency.
For example, bottoming welding in order to get a better melt depth should be used to operate a short arc, filler welding or cover welding in order to get a higher efficiency and melt width can be properly increased arc voltage.
2 . Welding without control of welding current
[Phenomenon]Welding, in order to seize the progress, for the thick plate butt welding seam to take no open bevel. Strength indicators decline, and even fail to meet the standard requirements, bending test cracks, which will make the performance of the welded joint can not be guaranteed, posing a potential hazard to structural safety.
Measures] Welding should be controlled according to the welding current in the process assessment, allowing 10-15% floating, the blunt edge size of the bevel should not exceed 6mm. butt joint, the plate thickness exceeds 6mm, to open the bevel for welding.
3 . Do not pay attention to the welding speed and welding current, welding rod diameter coordinated use
Phenomenon]Welding does not pay attention to the control of welding speed and welding current, welding rod diameter, welding position to coordinate the use.
Such as full penetration of the corner seam bottoming welding, due to the narrow size of the root, such as welding speed is too fast, the root gas, slag does not have enough time to discharge, easy to make the root of the impermeable, slag, porosity and other defects; cover welding, such as welding speed is too fast, also easy to produce porosity; welding speed is too slow, the residual height of the weld will be too high, the shape is not neat; welding thin plate or blunt edge size of the weld, welding speed is too slow The welding speed is too slow when welding thin plate or small size of blunt edge, the welding speed is too slow, easy to burn through and so on.
Measures] welding speed has a significant impact on the quality of welding and welding productivity, the choice of welding current, welding position (bottoming, filler welding, cover welding), the thickness of the weld, bevel size to select the appropriate welding speed, in order to ensure penetration, gas, slag easy to discharge, not burn through, the premise of the formation of a good choice of larger welding speed to improve productivity efficiency.
4 . Welding without attention to control the arc length
[Phenomenon] Not according to the bevel form, the number of layers of welding, welding form, welding rod type and so on appropriate adjustment arc length. Due to the improper use of welding arc length, it is more difficult to get a high-quality weld.
[Measures]In order to ensure the quality of the weld, welding generally use a short arc operation, but you can choose the right arc length according to different situations to obtain the best welding quality, such as V-shaped bevel butt joint, angle joint of the first layer should use a shorter arc to ensure that the weld through, and does not occur biting phenomenon, the second layer can be slightly longer to fill the weld. The arc should be short when the gap is small, and slightly longer when the gap is large, to speed up the welding speed. The arc of back welding should be the shortest in order to prevent the downward flow of iron; vertical welding, horizontal welding in order to control the temperature of the molten pool, but also to use a small current, short arc welding.
In addition, no matter what kind of welding is taken, attention should always be paid to keeping the arc length basically the same during the movement, so as to ensure that the entire weld is of the same melt width and depth.
5 . Welding does not pay attention to control welding deformation
Phenomenon]Welding does not pay attention to control the deformation from the welding sequence, personnel arrangement, bevel form, welding specification selection and operation methods, resulting in large deformation after welding, correction difficulties, increased costs, especially thick plates and large workpieces, correction difficulties, mechanical correction is easy to cause cracks or lamellar tearing. With flame correction high cost and poor operation is easy to cause workpiece overheating.
High precision requirements for the workpiece, do not take effective measures to control deformation, will lead to the workpiece installation size can not meet the requirements of use, or even cause rework or scrap.
Measures] Use a reasonable welding sequence and choose the appropriate welding specifications and operating methods, but also the use of anti-deformation and rigid fixing measures.
6 . Multi-layer welding is not continuous welding, do not pay attention to control the interlayer temperature
[Phenomenon] thick plate multi-layer welding, do not pay attention to the interlayer temperature control, such as the interlayer interval is too long, not reheat the welding is easy to produce cold cracks in the interlayer; such as too short interval, the interlayer temperature is too high (more than 900 ℃), the performance of the weld and heat-affected zone will also have an impact, will cause coarse grain, resulting in toughness and plasticity decline, will leave potential hidden problems on the joint.
[Measures] When welding thick plate multi-layer, should strengthen the control of the interlayer temperature, in the process of continuous welding should check the temperature of the base material of welding, so that the interlayer temperature as far as possible to maintain the same temperature with the preheating temperature, the highest temperature between the layers should also be controlled.
Welding time should not be too long, such as in the case of welding interruption should take appropriate post-heating, insulation measures, re-application of welding, re-heating temperature should be appropriately higher than the initial preheating temperature.
7 . Multi-layer welding seam does not remove welding slag and weld surface defects on the next layer of welding
[Phenomenon] When multi-layer welding of thick plates, each layer of welding is completed without removing the slag and defects directly to the next layer of welding, easy to cause the weld slag, porosity, cracks and other defects, reducing the strength of the connection, while causing spatter in the next layer of welding.
[Measures]When welding multiple layers of thick plates, each layer should be welded continuously. After each layer of welding seam welding should be timely removal of welding slag, weld surface defects and spatter, found to have an impact on the quality of welding slag, porosity, cracks and other defects should be thoroughly removed before welding.
8 . Requirement of fusion through the joint butt or angle butt combination weld welding angle size is not enough
[Phenomenon] T-joint, cross-joint, corner joint and other requirements fusion through the butt or corner butt combination weld, the weld foot size is not enough, or the design of fatigue test requirements of the crane beam or similar members of the web and the upper flange edge connection weld foot size is not enough, will make the strength and stiffness of the welding are not designed to meet the requirements.
[Measures]T-shaped joints, cross joints, corner joints and other requirements of fusion through the butt combination weld, should be in accordance with the design requirements, must have sufficient welding foot requirements, general welding foot size should not be less than 0.25t (t for the connection of the thinner plate thickness). The allowable deviation of the weld size is 0 to 4 mm.
9 . Welding in the joint gap plug welding rod head or iron block
[phenomenon] Because of the difficulty of welding the welding rod head or iron and the welded parts fused together, it will cause welding defects such as not fused, not fused through, reducing the strength of the connection. If the rusty welding rod head, iron filler, it is difficult to ensure that the material with the parent material; such as with oil, impurities, etc., the welding rod head, iron filler, will make the weld produces pores, slag, cracks and other defects. These conditions will make the joint weld quality is greatly reduced, not up to the design and specification of the quality requirements of the weld.
[Measures
(1) When the workpiece assembly gap is large, but does not exceed the range allowed for use, the assembly gap exceeds 2 times the thickness of the thin plate or greater than 20mm, the application of overlay welding method to fill the depressed parts or reduce the assembly gap. It is strictly forbidden to use the method of filling the welding rod head or iron block to fill the gap in the joint.
(2) Parts processing scribing, should pay attention to leave enough cutting margin and welding shrinkage margin after cutting, control the size of the parts, do not increase the gap to ensure the shape size.
10 . No attention is paid to the welding sequence of the components with cross welds
[Phenomenon] for cross-welded components, do not pay attention to the analysis of welding stress release and welding stress on the impact of component deformation and reasonable arrangements for welding order, but the vertical and horizontal arbitrary welding, the result will cause the vertical and horizontal seams constrain each other, resulting in greater temperature contraction stress, plate deformation, plate surface unevenness, and may cause cracks in the weld.
[Measures] For members with cross welds, a reasonable welding sequence should be developed. When there are several longitudinal and transverse cross welds welding, should first weld shrinkage deformation of the horizontal seam, and then weld the longitudinal seam, so that when welding the transverse weld will not be constrained by the longitudinal seam, so that the contraction stress of the transverse seam in the absence of constraint is released, can reduce the welding deformation, to ensure the quality of the weld, or first welding butt weld after welding corner weld.
Source: Chemical Equipment Man
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