24 Feb 2022
Welding technology is an important metal processing technology. Although welding technology has developed rapidly and the degree of automation has become higher and higher, manual welding still occupies an irreplaceable position, especially in welding small-diameter containers and pipes using welding machine. However, in the process of horizontal welding of pipes, due to equipment, material, process and operation, etc., the formed weld does not meet the quality requirements, which will have a serious impact on the working quality and service life of the structure. For this problem, we need to find a solution from the source, so as to avoid more factors that affect the welding results. Next, we will explain the pre-welding preparation, operation points and precautions for fixed welding of the horizontal position of the pipe in practice.
First of all, let's talk about the pre-welding preparation for the practical explanation of the horizontal position of the pipe. First, the size and requirements of the test piece: the material of the test piece is 20 steel pipe, the size of the test piece is ф60.3mmx100mmx5.4mm, and the bevel angle is 60°±5° (see Figure 1). Before welding, it is necessary to clean the groove and oil stains and rust within 20mm on both sides until the metallic luster is exposed, and the welding wire is not allowed to be stained. Second, welding requirements: single-sided welding and double-sided forming. Third, welding materials: the welding wire is JG-50, ф2.4mm, the electrode is cerium tungsten electrode with ф2.0mm, and the purity of argon is 99.99%. Fourth, welding polarity: DC positive connection. Fifth, inspection before welding: Before welding, carefully check whether the wiring of the welding machine is correct, firm and reliable, and adjust the welding parameters as required. If a fault is found, it should be solved immediately. Sixth, tack welding: using two-point positioning, tack welding is welded at the positions of the pipe cross-section equivalent to 10 o'clock and 2 o'clock on the clock (see Figure 2-1). The length of the solder joint should be determined according to the size of the pipe diameter. Generally speaking, if the pipe diameter is small and the pipe wall is thin, the length of the solder joint should be shorter, otherwise it should be longer, usually 5~10mm. Pre-grind the joint end of the solder joint into a slope to ensure that the root of the joint is penetrated. See Figure 2-2 for the welding parameters of the pipe butt joint at the horizontal fixed position.
Then talk about the operation points and precautions of the practical explanation of the horizontal position of the tube. As shown in Figure 3, the welding is carried out in two half circles on the left and right. The arc starts at 4~5mm before the centerline of the overhead welding and ends at 4~5mm behind the centerline of the flat welding. If solder the right half circle first. The arc starts from the position of point A ("7 point" in Figure 2-1, that is, 5~10mm before the central axis of the overhead welding), and ends at the position of point B (that is, 5~10 mm after the flat welding of the central axis. If the left half circle is welded first , start the arc from point A ("5 points" in Figure 2-1, that is, 5~10mm before the central axis overhead welding), and end at point B' (that is, 5~10mm after the central axis is flat welding). Whether welding the right half circle or the left half circle, the flat welding position of the second half circle should overlap the welding seam of the first half circle by 5~10mm when the arc is closed. The purpose is to ensure that the joint is fully fused and the weld on the opposite side is full.
Then, we will talk about the operation points and precautions of backing welding, filling welding and cover welding in detail. First, bottom welding. During bottom welding, the nozzle is close to the surface of the groove of the weldment to start the arc, and the wire filling starts after the root of the groove is melted. The backing welding can be used by the inner wire filling method, the outer wire filling method and the combination of the two methods. The combination of the two methods is to use the inner filler wire at the position of overhead welding and upward climbing (between "4 points" and "8 points" in Figure 2-1), and use vertical welding to the flat welding position ("4 points in Figure 2-1"). "~"12 o'clock" and "8 o'clock" ~ "12 o'clock") use external filling wire. Since the weld metal is easy to fall, the welder must send the end of the welding wire to 1.5~2mm of the inner wall of the pipe, and form a bottom weld after melting. With the extension of the weld bead, the position of the weld gradually changes from the overhead welding position to the vertical welding position, and finally to the position of the flat welding seam, and the welding wire is also fed from the inside.The wire gradually becomes an external feeding wire. The angle of the nozzle also varies with the welding position (see Figure 4). In order to fully fuse both sides of the groove during welding, the nozzle swings left and right and moves forward at a constant speed. It is necessary to coordinate the wire feeding in order to ensure the formation of single-sided welding and double-sided welding, and the welding seam is smooth and beautiful. At the end of the joint, the welding wire must be melted all the way around before the welding wire can be continued. The second, filler welding. Filling welding is basically the same as backing welding, the difference is that the welding current and nozzle swing amplitude are increased during filling welding. Third, cover welding. For cover welding, single pass welding or multi pass welding shall be adopted according to the size of the groove of the pipe fittings. 1~1.5mm on both sides of the fusion groove of the molten pool. The nozzle swings laterally, and the welding wire should be moved at the center of the weld bead or slightly left and right.
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Keywords: welding machine
Originally published 24 Feb 2022, updated 24 Feb 2022.