Important structures such as boilers and pressure vessels require joints to be welded safely, but due to structural size and shape constraints, double-sided welding is sometimes not possible. The special operation method of single-sided groove can only be single-sided welding and double-sided forming technology, which is a difficult operation skill in manual arc welding.
When welding vertical welding, due to the high temperature of the molten pool, under the action of gravity, the molten droplets formed by the melting of the electrode and the molten iron in the molten pool are easy to drip down to form welding bumps and undercuts on both sides of the weld. When the temperature is too low, slag inclusions are likely to occur, and defects such as incomplete penetration and welding spots are easily formed on the reverse side, making it difficult to form welds. The temperature of the molten pool is not easy to determine directly, but it is related to the shape and size of the molten pool. Therefore, as long as the shape and size of the molten pool are carefully observed and controlled during welding, the temperature of the molten pool can be controlled and the purpose of ensuring welding quality can be achieved.
According to the experience of the master for more than ten years, this rule can be summarized in the following words:
1. The angle of the welding rod is very important, and the welding specification is indispensable
During vertical welding, due to the droplet formed by the melting of the electrode and the molten iron in the molten pool, it is easy to drip down to form a welding bump, and the undercuts are formed on both sides of the weld, which deteriorates the weld shape. Master the correct welding specifications and adjust the angle of the electrode and the speed of the electrode according to the changes in the welding situation. The angle between the welding rod and the surface of the weldment is 90° in the left and right direction, and the welding seam
The angle of welding is 70°~80° at the start of welding, 45°~60° in the middle, and 20°~30° at the end. The assembly gap is 3-4㎜, and the smaller electrode diameter Φ3.2㎜ and smaller welding current should be selected. The bottom welding is 110-115A, the intermediate transition layer is 115-120A, and the cover layer is 105-110A. . The current is generally smaller than that of flat welding
12% to 15%, in order to reduce the volume of the molten pool, so that it is less affected by gravity, which is conducive to the excessive droplet. Short-arc welding is used to shorten the distance from the droplet to the molten pool to form an excessive short circuit.
2. Observe the melting pool, listen to the arc sound, and keep the shape of the melting hole in mind
Backing welding at the root of the weld is a key to ensure welding quality. The arc extinguishing method is used for welding. The arc extinguishing rhythm of vertical welding is slightly slower than that of flat welding, 30 to 40 times per minute. The arc burns slightly longer when welding at each point, so the welding meat of vertical welding is thicker than that of flat welding. When welding, start welding from the lower end. The angle of the bottom electrode is about 70°~80°. Two-click penetration welding is adopted. The arc is ignited on the side of the groove and preheated and melted along the spot welding point to the root. When the arc penetrates There is a “flutter” sound from the bevel, and when you see the melting hole and the formation of the molten pool seat, immediately lift the electrode to extinguish the arc. Then re-ignite the other side of the groove, and the second molten pool should press 1/2 to 2/3 of the first molten pool that started to solidify, so that the entire weld can be obtained by using left and right arc extinguishing breakdowns. The flexibility of the wrist should be used to extinguish the arc, and the arc should be extinguished cleanly every time, so that the molten pool has a chance to solidify instantaneously.
When the arc is extinguished, the fusion hole formed by the punctured blunt edge can be clearly seen. The fusion hole of the vertical welding is about 0.8mm, and the size of the fusion hole is closely related to the formation of the back side. The back of the fusion hole is often not penetrated, and the size of the fusion hole must be kept uniform during operation, so as to ensure uniform penetration at the root of the groove, a full back weld bead, and uniform width and height. When priming and changing the welding rod joint, the coating of the joint part must be cleaned every time, and the arc is ignited again in the groove, and the angle of the welding rod is continuously welded at about 10mm along the formed weld seam, and it extends into the weld seam when it reaches 90 degrees. Swing the center left and right slightly, and press the arc down at the same time, when you hear the arc sound, a melting hole is formed, and the arc is extinguished immediately, so that the arc of the electrode extends into the root of the weld, and the melting hole is formed and the arc is extinguished immediately. Then it is the same as the bottoming welding method of the first electrode, alternately cycle arc extinguishing breakdown from left to right, concentrate on every movement, pay attention to the outline of the melting hole and the melted gap on both sides, and the melted gap at the root of the groove, only It can be seen when the arc moves to the other side. It is found that the blunt edge is not fused well and the arc is slightly lowered to achieve good fusion. The arc extinguishing time is controlled until one third of the molten pool is not solidified. Restart the arc.
When extinguishing the arc, it should be noted that when each electrode is only 80-100mm long, the electrode will melt faster due to overheating. At this time, the arc extinguishing time should be increased to make the molten pool solidify instantaneously, so as to prevent the high-temperature molten pool from falling and forming welding lumps. . When there are only 30-40mm left of the electrode, prepare to do arc extinguishing action. Continuously drop two or three times on one side of the molten pool to make the molten pool cool down slowly, which can prevent shrinkage cavity and arc crater cracks on the front and back of the weld bead. defect.
3. The temperature of the molten pool is well controlled, and the quality of the weld can be improved
It is required that the solder waves in the middle layer be smooth. For the middle two layers, the diameter of the electrode is φ3.2㎜, the welding current is 115-120A, the angle of the electrode is about 70°-80°, and the zigzag method is used to make use of the angle of the electrode, the length of the arc, the welding speed and the stay on both sides of the groove. time to control the molten pool temperature. Make both sides well fused and keep the shape of oblate molten pool.
When welding the third layer, do not damage the edge of the groove, and leave a depth of about 1mm to make the entire filling bead smooth. The edge of the groove above the depth is used as the reference line to lay the foundation for the cover surface. Generally, the left and right swings are used to stop a little longer on both sides of the groove to melt the edge of the groove by 1-2mm, and to ensure the temperature of the molten pool and both sides of the groove. Balance, mainly observe the shape of the molten pool, control the molten pool into a crescent shape, stay less on the side with more molten pool, and stay more on the side with less, and calculate the height and width of the weld while welding. Because the welding meat of vertical welding is thicker than that of flat welding, pay attention to observe the shape of the molten pool and the thickness of the welding meat. If the lower edge of the molten pool protrudes from the gentle side, it means that the temperature of the molten pool is too high. At this time, the arc burning time should be shortened and the Arc extinguishing time to reduce the molten pool temperature. Craters must be filled before electrode replacement to prevent crater cracks.
4. The way of transportation is correct, so that the welding seam can be formed well
When welding the cover surface, the zigzag or crescent-shaped strip transport method can be used during welding. The strip transport should be stable, the speed should be slightly faster in the middle of the weld bead, and a short stop should be made at the edges on both sides of the groove. The process specification is that the diameter of the electrode is φ3.2㎜, the welding current is 105-110A, the angle of the electrode should be kept at about 80°, the electrode swings left and right to melt the edge of the groove by 1-2㎜, and vibrate slightly up and down when the sides pause. But when the electrode goes from one side to the other, the arc in the middle is slightly lifted to observe the shape of the entire molten pool. If the molten pool is flat and oval, it means that the temperature of the molten pool is more suitable, normal welding is performed, and the weld surface is well formed. If it is found that the belly of the molten pool becomes round, it means that the temperature of the molten pool is slightly higher, and the method of transporting the rod should be adjusted immediately, that is, the residence time of the electrode on both sides of the groove should be increased, the transition speed in the middle should be accelerated, and the length of the arc should be shortened as much as possible. If the molten pool cannot be restored to a flat elliptical state, and the bulge increases, it means that the temperature of the molten pool is too high, and the arc should be extinguished immediately, and the molten pool should be allowed to cool down, and then continue welding after the temperature of the molten pool drops.
When covering the surface, it is necessary to ensure that the edge of the weld is good. If it is found that the undercut electrode moves a little, or stays a little longer to make up for the defect, the surface can be smooth only if the surface is excessive. When the cover joint is welded, the temperature of the weldment is low, which is prone to defects such as poor fusion, slag inclusion, joint disjoint, and excessive height. Therefore, the quality of the cover directly affects the surface shape of the weld. Therefore, the preheating method is used for welding at the joint, and the arc is ignited from top to bottom by scratching at about 15mm above the starting welding end, and the arc is elongated by 3 to 6mm, and the starting point of the welding seam is pre-welded. hot. Then depress the arc and place it at 2/3 of the original arc crater for 2 to 3 times to achieve good fusion and then switch to normal welding.
Although the positions of the welds are different, they also have a common rule. Practice has proved that selecting the appropriate welding process parameters, maintaining the correct electrode angle and mastering the three actions of the good luck rod, strictly controlling the temperature of the molten pool, welding When welding vertically, you can get excellent weld quality and beautiful weld shape.
Post time: Mar-29-2023
