Welding knowledge: how to improve the technical level of welding operation

【Summary Description】 Important structures such as boilers and pressure vessels require safe welding joints, but due to the limitation of structural size and shape, double-sided welding is sometimes impossible. A special method of operation that can only be slotted on one side. Single-sided welding and double-sided forming technology. In manual arc welding is a more difficult operation skills. During vertical welding, due to the high temperature of the molten pool, under the action of gravity, the molten metal droplets formed by the melting of the electrode and the molten iron in the molten pool are easy to drip downward, forming welding bumps and undercuts on both sides of the weld. When the temperature is too low, slag inclusion is easy to occur, defects such as incomplete penetration and solder joints are easy to form on the back, and it is difficult to form a weld. 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 to ensure the quality of welding. 1. The angle of welding rod is very important, and welding specification is essential. During vertical welding, the molten droplets formed by melting the electrode and molten iron in the molten pool can easily drop down to form welding bumps, forming undercuts on both sides of the weld, deteriorating the shape of the weld. Master the correct welding specification and adjust the angle of the welding rod and the speed of the welding rod according to the change of the welding situation. The angle between the welding rod and the surface of the welding piece is 90 ° in the left and right direction, which is consistent with the welding seam. The welding angle is 70 ° to 80 ° at the beginning of welding, 45 ° to 60 ° in the middle, and 20 ° to 30 ° at the end of welding. The assembly gap is 3-4mm, and the smaller electrode diameter Φ3.2mm and the smaller welding current should be selected. The bottom weld is 110-115A, the intermediate transition layer is 115-120A, and the cover layer is 105-110A. Current is generally smaller than flat welding. 12% ~ 15%, in order to reduce the volume of the molten pool, so that it is less affected by gravity, which is conducive to the excess of droplets. Short arc welding is to shorten the distance from the droplet to the molten pool, thereby forming an excessive short circuit. 2. Observe the molten pool, listen to the sound of the arc, and keep in mind the shape of the molten hole. Bottom welding at the root of the weld is the key to ensure welding quality. Arc extinguishing method is adopted for welding. The arc extinguishing rhythm of vertical welding is slightly slower than that of flat welding, 30~40 times per minute. The arc burning time is slightly longer when welding 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 ° to 80 °. Two-point penetration welding is adopted. The arc is ignited on the side of the groove and preheated along the spot weld to melt to the root. When the arc penetrates, there is a "chatter" sound from the inclined plane. When the molten hole and the molten pool seat are formed, the electrode is immediately lifted to extinguish the arc. Then ignite the other side of the groove, and the second molten pool should be 1/2 to 2/3 of that when the first molten pool starts to solidify, so that the whole weld can be broken down by extinguishing the left and right arcs. To use the flexibility of the wrist to extinguish the arc, each time to cleanly extinguish the arc, so that the molten pool has the opportunity to solidify instantly. When the arc is extinguished, the fused hole formed by the pierced blunt edge can be clearly seen. The fusion hole of vertical welding is about 0.8mm, and the size of the fusion hole is closely related to the formation of the back surface. The back of the fusion hole is often not penetrated. During the operation, the size of the fusion hole must be consistent, so as to ensure uniform penetration at the root of the groove, forming a full back weld, and uniform width and height. When bottoming and replacing the welding rod joint, clean up the coating at the joint every time, ignite the arc again in the groove, continuously weld the welding rod angle along the welding seam formed by about 10mm, extend into the center of the welding seam at 90 degrees, swing around slightly, press the arc downward at the same time, hear the arc sound, form a melting hole, and immediately extinguish the arc, so that the welding rod arc extends into the root of the welding seam, formation of dissolved pores immediately extinguish the arc. Then it is the same as the bottom welding method of the first electrode, alternating cycles of arc extinguishing and breakdown from left to right, pay attention to each action, pay attention to the contours of the molten holes and molten seams on both sides, and the molten seams at the root of the groove, only when the arc It can be seen when moving to the other side. It was found that the blunt edge did not fuse well, and the arc was slightly reduced to achieve good fusion. The arc extinguishing time is controlled until the 1/3 of the molten pool does not solidify. 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 instantly to prevent the high temperature molten pool from falling off and forming weld tumor. When the electrode is only 30-40mm, ready to do arc extinguishing action. Falling two or three times on one side of the molten pool to slowly cool the molten pool can prevent shrinkage cavities and crater cracks on the front and back of the weld. Defects 3. The temperature of the molten pool is well controlled and the quality of the weld is improved. The welding wave of the intermediate layer is required to be smooth. The diameter of the middle two layers of welding rod is φ3.2 ㎜, the welding current is 115-120A, and the angle of the welding rod is about 70-80. The zigzag method is adopted to control the temperature of the molten pool by using the angle, arc length, welding speed and the retention time on both sides of the groove of the welding rod. Make good fusion on both sides and keep the shape of oblate molten pool. When welding the third layer, do not damage the edge of the groove, leave a depth of about 1mm, so that the entire filling bead is smooth. The edge of the groove above the depth is used as a reference line to lay the foundation for the coverage. Generally, the left and right swing method is adopted, and the stay time on both sides of the groove is slightly longer, so that the edge of the groove is melted by 1-2mm, and the temperature on both sides of the molten pool and the groove is guaranteed. Balance is mainly to observe the shape of the molten pool, control the molten pool into a crescent shape, leave less on the side with more molten pool and more on the side with less molten pool, and calculate the height and width of the weld while welding. Since the welding meat of vertical welding is thicker than that of flat welding, the shape of the molten pool and the thickness of the welding meat should be observed. 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 time and arc extinguishing time should be shortened to reduce the temperature of the molten pool. The crater must be filled before the electrode is replaced to prevent the crater from cracking.

Previous Page

Laser technology for copper welding with flexibility and automation

Next Page

"Shake" welding operation method and characteristics