The Eight Most Easily Overlooked Problems In Welding
1. Welding construction does not pay attention to choose the best voltage
【Phenomenon】During welding, the same arc voltage is selected regardless of the size of the groove, whether it is priming, filling, covering, or the size of the groove. In this way, the required penetration depth and width may not be achieved, and defects such as undercuts, pores, and splashes may appear.
【Measures】Generally, according to different situations, the corresponding long arc or short arc should be selected respectively 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 penetration width during filler welding or cover welding.
2. Do not pay attention to the welding speed and welding current, the electrode diameter is used in harmony
【Phenomenon】Welding without attention to control the welding speed and welding current, welding rod diameter, welding position coordination up to 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 small weld, welding speed is too slow, easy to burn through and other situations.
【Measures】Welding speed has a significant impact on the quality of welding and welding productivity, the choice of welding current, welding seam 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, do not burn through, the premise of good shape selection of a larger welding speed to improve productivity efficiency.
3. Welding without control of welding current
【Phenomenon】Welding, in order to seize the progress, for the medium-thick plate butt weld to take no open bevel. Strength index decreases, and even fails to meet the standard requirements, cracks appear in the bending test, 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 by the welding current in the process evaluation, allowing 10-15% floating, the blunt edge size of the bevel should not exceed 6mm. butt joint, the plate thickness of more than 6mm, to open the bevel for welding.
4、Welding does not pay attention to the control of welding deformation
【Phenomenon】Welding does not pay attention to the welding sequence, personnel arrangement, bevel form, welding specification selection and operation methods to control deformation, resulting in large deformation after welding, correction difficulties, increased costs, especially thick plate and large workpiece, correction is difficult, mechanical correction is easy to cause cracks or lamellar tearing. Flame correction with high cost and poor operation is easy to cause the workpiece overheating. High precision requirements of the workpiece, do not take effective measures to control deformation, will lead to the workpiece installation size does not meet the requirements of use, or even cause rework or scrap.
【Measures】Use a reasonable welding sequence and select appropriate welding specifications and operation methods, and also adopt anti-deformation and rigid fixing measures.
5. Multi-layer welding is discontinuous and does not pay attention to controlling the temperature between layers
【Phenomenon】 Thick plate multi-layer welding, do not pay attention to the interlayer temperature control, such as the interlayer interval is too long, without reheating on the application of welding easy to produce cold cracks in the interlayer. Such as the interval is too short, the interlayer temperature is too high (more than 900 ℃), the performance of the weld and heat-affected zone will also have an impact on the grain coarseness, resulting in toughness and plasticity decline, will leave potential hidden problems on the joint.
【Measures】Thick plate multi-layer welding, should strengthen the control of the interlayer temperature, in the process of continuous welding should check the temperature of the base material welded, 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. The welding time should not be too long, such as 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.
6. Do not pay attention to control the arc length when welding
【Phenomenon】The arc length is not properly adjusted according to the bevel form, the number of welding layers, the welding form, and the type of welding rod when welding. Due to improper use of the 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 can be selected according to the different circumstances of the appropriate arc length to obtain optimal welding quality, such as V-shaped bevel butt, 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. Weld gap hours should be used when the short arc, the gap can be slightly longer arc, welding speed up. Back welding arc should be the shortest to prevent the 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 welding is taken, attention should always be paid to keep the arc length basically unchanged during the movement, so as to ensure that the entire weld is consistent with the melt width and melt depth.
7. Requirement of fusion through the joint butt or angle Butt joint combination weld angle size is not enough
【Phenomenon】T-joints, cross joints, angle joints and other requirements fusion through the butt or angle butt combination weld, the foot size is not enough, or the design of the 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 weld are not designed to meet the requirements.
【Measures】T-joints, cross-joints, corner joints and other requirements fusion penetration of butt combination welds, 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 design of the fatigue test requirements of the crane beam or similar web and upper flange connection weld foot size 0.5t, and should not be greater than 10mm. welding size of the allowable deviation of 0 ~ 4 mm.
8. Multi-layer weld does not remove the slag and weld surface, there are defects in the next layer of welding
【Phenomenon】Thick plate multi-layer welding, 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 the next layer of welding spatter.
【Measures】When welding thick plate multi-layer, each layer should be continuous welding. 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.
