In the welding process, there are many matters needing attention. Once neglected, it may be a big mistake. These are the points you must pay attention to if auditing the welding process. If you deal with welding quality accidents, you still need to pay attention to these problems!
1. Welding construction does not pay attention to choosing the best 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. Welding does not control the welding current
[Phenomenon] During welding, in order to speed up the progress, the butt welds of medium and thick plates are not beveled. The strength index drops, or even fails to meet the standard requirements, and cracks appear during the bending test, which will make the performance of the welded joints unable to be guaranteed and pose a potential hazard to structural safety.
[Measures] Welding should be controlled according to the welding current in the process evaluation, and 10-15% fluctuation is allowed. The size of the blunt edge of the groove should not exceed 6mm. When docking, when the thickness of the plate exceeds 6mm, a bevel must be opened for welding.
3. Do not pay attention to the welding speed and welding current, and the diameter of the welding rod should be used in harmony
[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, easy 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.
4. Do not pay attention to controlling the arc length when welding
[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 operation is 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 joint, fillet joint first 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.
5. Welding does not pay attention to control 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.
6. Discontinuous welding of multi-layer welding, not paying attention to controlling the temperature between layers
[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.
7. If the multi-layer weld does not remove the welding slag and the surface of the weld has defects, the lower layer is welded
[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.
8. The size of the joint butt joint or corner butt joint combined weld joint that requires penetration is not enough.
[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.
9. Welding plug the electrode head or iron block in the joint gap
[Phenomenon] Because it is difficult to fuse the electrode head or iron block with the welded part during welding, it will cause welding defects such as incomplete fusion and incomplete penetration, and reduce the connection strength. If it is filled with rusty electrode heads and iron blocks, it is difficult to ensure that it is consistent with the material of the base metal; if it is filled with electrode heads and iron blocks with oil, impurities, etc., it will cause defects such as pores, slag inclusions, and cracks in the weld. These situations will greatly reduce the quality of the weld seam of the joint, which cannot meet the quality requirements of the design and specification for the weld seam.
[Measures] <1> When the assembly gap of the workpiece is large, but does not exceed the allowable range of use, and the assembly gap exceeds 2 times the thickness of the thin plate or is greater than 20mm, the surfacing method should be used to fill the recessed part or reduce the assembly gap. It is strictly forbidden to use the method of filling the welding rod head or iron block to repair the welding in the joint gap. <2> When processing and scribing parts, attention should be paid to leaving enough cutting allowance and welding shrinkage allowance after cutting, and controlling the size of the parts. Do not increase the gap to ensure the overall size.
10. When plates of different thickness and width are used for docking, the transition is not smooth
[Phenomenon] When plates of different thicknesses and widths are used for butt jointing, do not pay attention to whether the thickness difference of the plates is within the allowable range of the standard. If it is not within the allowable range and without gentle transition treatment, the weld seam is likely to cause stress concentration and welding defects such as incomplete fusion at the place higher than the thickness of the sheet, which will affect the welding quality.
[Measures] When the relevant regulations are exceeded, the weld should be welded into a slope, and the maximum allowable value of the slope should be 1:2.5; or one or both sides of the thickness should be processed into a slope before welding, and the maximum allowable value of the slope should be 1:2.5 , when the structural slope directly bears the dynamic load and requires fatigue checking, the slope should not be greater than 1:4. When plates of different widths are butt-connected, thermal cutting, machining or grinding wheel grinding should be used according to the factory and site conditions to make a smooth transition, and the maximum allowable slope at the joint is 1:2.5.
11. Pay no attention to the welding sequence for components with cross welds
[Phenomenon] For components with cross welds, if we do not pay attention to rationally arrange the welding sequence by analyzing the welding stress release and the influence of welding stress on component deformation, but weld vertically and horizontally randomly, the result will cause longitudinal and horizontal joints to restrain each other, resulting in large The temperature shrinkage stress will deform the plate, the surface of the plate will be uneven, and it may cause cracks in the weld.
[Measures] For components with cross welds, a reasonable welding sequence should be established. When there are several kinds of vertical and horizontal cross welds to be welded, the transverse seams with large shrinkage deformation should be welded first, and then the longitudinal welds should be welded, so that the transverse welds will not be constrained by the longitudinal welds when welding the transverse welds, so that the shrinkage stress of the transverse seams Released without restraint to reduce weld distortion, maintain weld quality, or weld butt welds first and then fillet welds
12. When surrounding welding is used for the lap joints of section steel rods, continuous welding shall be applied at the corners
[Phenomenon] When the lap joint between the section steel rod and the continuous plate is surrounded by welding, the welds on both sides of the rod are welded first, and the end welds are welded later, and the welding is discontinuous. Although this is beneficial to reducing welding deformation, it is prone to stress concentration and welding defects at the corners of the rods, which affects the quality of welded joints.
[Measures] When the lap joints of section steel rods are welded, the welding should be completed continuously at the corner at one time, and do not weld to the corner and go to the other side for welding.
13. Equal-strength docking is required, and there are no arc-starting plates and lead-out plates at both ends of the crane beam wing plate and web plate
[Phenomenon] When welding butt welds, full-penetration fillet welds, and welds between crane beam flange plates and webs, no arc-starting plates and lead-out plates are added at the arc-starting and leading-out points, so that when welding the starting and ending ends, Since the current and voltage are not stable enough, the temperature at the start and end points is not stable enough, which may easily lead to defects such as incomplete fusion, incomplete penetration, cracks, slag inclusions, and pores in the start and end welds, which will reduce the strength of the weld and fail to meet the design requirements.
[Measures] When welding butt welds, full-penetration fillet welds, and welds between crane girder flange and web, arc strike plates and lead-out plates should be installed at both ends of the weld. After the defective part is drawn out of the workpiece, the defective part is cut off to ensure the quality of the weld.
Post time: Jul-12-2023