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Qingdao KXD Steel Structure Co.,Ltd

We are professionally engaged in steel structure design, manufacture and installation.

Address: Ruiping Center, Hongqi Road, Pingdu, Qingdao, China.

City: Qingdao

State: Shandong

Postal Code: 266700

Country: China

Manager: Andy

E-mail: kxdandy@chinasteelstructure.cn

Tel: 86-532-88336188

Fax: 86-532-85397878

Steel Structure 13 Easy Problems In Welding

- Sep 18, 2017 -

Steel structure refers to the structure mainly composed of steel material, is one of the main building structure type. The structure is mainly composed of steel and steel plate, steel column, steel truss and other components, the components or components are usually used between the weld, bolt or rivet connection. Because of its relatively light weight, and the construction is simple, widely used in large factories, venues, high-level areas.

1. Welding construction does not pay attention to choose the best voltage

【phenomenon】

When welding, whether it is primer, fill, cover, regardless of the size of the groove, select the same arc voltage. This may not meet the requirements of the depth of penetration, melting width, there are undercut, stomata, splash and other defects.

【Measures】

Generally for different situations should choose the corresponding long arc or short arc can get better welding quality and efficiency. For example, when the bottom of the welding in order to get a better penetration should be used short arc operation, filling or cover welding in order to get a higher efficiency and width can be appropriate to increase the arc voltage.

2. Welding does not control the welding current

【phenomenon】

Welding, in order to grab the progress, for the plate butt weld not take the groove. Strength indicators decline, or even fail to meet the standard requirements, bending test cracks, this will make the weld joint performance can not be guaranteed, the structure of the security poses a potential hazard.

【Measures】

Welding according to the process of assessment of the welding current control, allowing 10 to 15% of the float. The size of the blunt edge of the groove should not exceed 6mm. When docking, when the thickness of more than 6mm, to open the groove for welding.

3. Do not pay attention to the welding speed and welding current, electrode diameter coordinated use

【phenomenon】

Welding does not pay attention to control the welding speed and welding current, electrode diameter, welding position coordinated use. Such as the full penetration of the corner seam for welding, due to the root size is narrow, such as welding speed too fast, the root gas, slag does not have enough time to discharge, easy to make the root does not melt, slag, porosity and other defects ; Welding, if the welding speed is too fast, but also easy to produce pores; welding speed is too slow, the weld will be too high, the shape is not neat; welding sheet or blunt edge size of the weld, the welding speed too Slow, easy to burn and so on.

【Measures】

Welding speed on the welding quality and welding production efficiency has a significant impact, when selected with the welding current, weld location (bottom welding, filling welding, cover welding), weld thickness, groove size to select the appropriate welding speed, To ensure that the penetration, gas, welding slag easy to discharge, do not burn, forming a good premise under the choice of a larger welding speed to improve productivity efficiency.

4. Do not pay attention to the control arc length

【phenomenon】

Welding is not based on the groove form, the number of welding layers, welding forms, electrode models and other appropriate adjustment arc length. 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, welding generally use short arc operation, but according to different circumstances to choose the appropriate arc length to obtain the best welding quality, such as V-shaped groove docking, cornering the first layer should be used Short arcs to ensure penetration, and no biting phenomenon, the second layer can be slightly longer to fill the weld. Weld gap is appropriate to use short arc, the gap can be slightly longer when the arc, welding speed. Arc welding arc should be the shortest to prevent the molten iron downstream; vertical welding, horizontal welding in order to control the bath temperature, but also with a small current, short arc welding. In addition, regardless of what welding, in the course of the movement should pay attention to always keep the arc length is basically unchanged, in order to ensure that the entire weld width and penetration of the same.

5. Welding does not pay attention to control welding deformation

【phenomenon】

Do not pay attention to welding from the welding sequence, personnel layout, groove form, welding specifications selection and operation methods such as control deformation, resulting in deformation after welding, correction difficulties, increase costs, especially thick and large parts, correction difficult , With mechanical correction can cause cracks or layered tear. With the high cost of flame correction and operation is not easy to cause the workpiece overheating. High precision requirements of the workpiece, do not take effective control deformation measures, will lead to the installation of the workpiece size does not meet the requirements, and even cause rework or scrapped.

【Measures】

The use of a reasonable welding order and select the appropriate welding specifications and methods of operation, but also the use of anti-deformation and rigid fixed measures.

6. Multi-layer welding is not continuous welding, do not pay attention to control the inter-layer temperature

【phenomenon】

Thick plate multi-layer welding, do not pay attention to the inter-layer temperature control, such as the interval between the interval is too long, do not re-warm up on the welding is easy to produce cold cracks in the layer; such as over time is too short, More than 900 ℃), the impact of the weld and heat affected area will also have an impact, will cause coarse grain, resulting in toughness and plasticity decline, will leave potential defects on the joint.

【Measures】

Thick plate multi-layer welding, should strengthen the control of the interlayer temperature, continuous welding process should be tested in the welding of the base metal temperature, so that the temperature between the layers as much as possible with the preheating temperature consistent with the highest temperature between the layers To be controlled. Welding time should not be too long, in case of welding interruption should take appropriate post-heat, insulation measures, re-welding, reheating temperature should be higher than the initial preheating temperature.

7. Multi-layer weld does not remove the welding slag and weld surface defects on the lower welding

【phenomenon】

Thick plate multi-layer welding, each layer of welding is not clear after the completion of welding slag and defects directly on the next layer of welding, easy to cause cracks in the weld slag, pores, cracks and other defects, reduce the connection strength, and will cause the lower welding splash The

【Measures】

Thick plate multi-layer welding, each layer should be continuous welding. After each layer of welding welding should be promptly removed after the welding slag, weld surface defects and spatter, found that the impact of welding quality slag, pores, cracks and other defects should be completely removed and then welding.

8. Require the penetration of the joint butt or the butt joint weld weld angle size is not enough

【phenomenon】

T-shaped joints, cross fittings, corner joints, etc., are required to be welded to the butt joint or toothed joint welds with insufficient foot size or a web of crane beams or similar components designed for fatigue inspection Weld the foot size is not enough, will make the welding strength and stiffness are not up to the design requirements.

【Measures】

T-joints, cross fittings, corner joints and other requirements of the penetration of the butt joint welding joints, should be in accordance with the design requirements, there must be sufficient foot requirements, the general foot size should not be less than 0.25t (t for the connection of thinner Thickness). Designed to have a fatigue check the requirements of the crane beam or similar webs and the upper flange connection weld the foot size 0.5t, and should not be greater than 10mm. The allowable deviation of the welding size is 0 ~ 4mm.

9. Welding in the joint gap in the plug head or iron

【phenomenon】

As the welding is difficult to weld the head or iron and welded parts welded together, will result in non-fusion, not penetration and other welding defects, reduce the connection strength. Such as with rusty welding head, iron filled, it is difficult to ensure consistent with the material of the base material; such as with oil, impurities and other welding head, iron filled, will make the weld hole, slag, cracks and other defects. These conditions will greatly reduce the quality of the joint weld, fail to design and specification of the quality requirements of the weld.

【Measures】

(1) When the workpiece assembly gap is large, but does not exceed the required allowable range, the assembly gap exceeds the thickness of the sheet 2 times or more than 20mm, the application of surfacing method to fill the depression or reduce the assembly gap. It is strictly forbidden to use the method of filling the welding head or iron welding in the joint gap.

(2) parts processing crossed, should pay attention to cut the remaining cutting and cutting after the welding shrinkage, control the size of parts, do not increase the gap to ensure that the size.

10. When using different thickness and width of the plate docking, not smooth transition

【phenomenon】

When using different thickness and width of the plate docking, do not pay attention to whether the thickness of the plate within the standard allowable range. If it is not within the allowable range and does not do the gentle transition processing, the weld in the thickness of the sheet can easily lead to stress concentration and produce non-fusion welding defects, affecting the quality of welding.

【Measures】

When the relevant provisions should be exceeded when the weld should be welded into a slope, the slope of the maximum allowable value should be 1: 2.5; or thickness of one or both sides before welding into a slope, and the slope of the maximum allowable value of 1: 2.5, when the direct The slope of the structure that is subjected to dynamic loads and requires fatigue checking shall not be greater than 1: 4. Different width of the plate docking, should be based on the factory and site conditions using thermal cutting, machining or grinding wheel grinding method to make it a smooth transition, and its maximum allowable slope of the connection point of 1: 2.5.

11. Do not pay attention to the welding sequence for components with crossed welds

【phenomenon】

For the components with cross welds, do not pay attention to the welding stress release and welding stress on the deformation of the components and reasonable arrangements for the welding sequence, but the vertical and horizontal random welding, the result will cause vertical and horizontal joints are mutually constrained, resulting in a larger temperature contraction Stress, deformation of the board, the board is uneven, and there may be cracks in the weld.

【Measures】

For fittings with crossed welds, a reasonable welding sequence should be established. When there are several vertical and horizontal cross welding welding, should first shrink the larger deformation of the transverse joints, and then welding the longitudinal weld, so that when welding horizontal welds will not be subject to longitudinal weld constraints, so that the shrinkage of the transverse stress In the case of no restraint to be released, can reduce the welding deformation, to ensure the quality of the weld, or welding the first butt weld after the weld angle weld.

12. Type steel bar lap joint with welding, the continuous welding at the corner

【phenomenon】

Type steel bar and continuous plate lap joint with the use of welding, the first welding on both sides of the weld, after welding the end of the weld, not continuous welding. Although this is beneficial to reduce the welding deformation, but in the corner of the rod is easy to produce stress concentration and welding defects, affecting the quality of welded joints.

【Measures】

Type steel bar lap joint with welding, the corner should be a continuous welding to complete, do not weld to the corner and went to the other side to welding.

13. Requires strong butt, crane beam wings and webs at both ends without the arc plate and lead plate

【phenomenon】

In the welding butt welds, full penetration fillet welds, crane beam flange plate and web of the weld, the arc and lead out without the arc plate and lead plate, so that the welding from the end, because the current voltage Not stable enough, the starting and ending point of the temperature is not stable enough to easily lead to the beginning of the weld has not fused, not penetration, cracks, slag, porosity and other defects, reduce the weld strength, fail to meet the design requirements.

【Measures】

When welding butt welds, full penetration fillet welds and weld girder wings and webs, the arcs and lead-out plates shall be provided at both ends of the weld so that the ends are liable to be defective Lead to the workpiece outside, and then cut off the defect part to ensure the quality of the weld.


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