There is no difference in process between full argon arc welding and argon arc welding. Full argon arc welding is suitable for thin-walled small pipe diameter pipes (generally DN50 and below, wall thickness 4mm) and below, in order to ensure good appearance of the weld root quality.
When the pipe diameter is large and the wall thickness is thicker, argon arc welding should be used for the bottoming and manual welding of the cover. The purpose of manual welding is to ensure the appearance quality of the pipe. Manual welding can ensure the appearance quality and the work efficiency is higher than that of argon arc welding. Lower than argon arc welding.
1. The advantages of argon arc welding
1.1 Good quality
As long as the appropriate welding wire, welding process parameters and good gas protection are selected, the root can get good penetration, and the penetration is uniform, and the surface is smooth and tidy. There are no defects such as weld bumps, incomplete penetration, dents, pores and slag inclusions that are easily produced during arc welding with general electrodes.
1.2 High efficiency
In the first layer welding of the pipeline, manual argon arc welding is continuous arc welding. The electrode arc welding is a broken arc welding, so manual argon arc welding can increase the efficiency by 2 to 4 times. Since argon arc welding will not produce welding slag, there is no need to clean up the slag and repair the weld bead, and the speed will increase faster. When arc welding the cover surface of the second layer, the smooth and neat argon arc welding bottom layer is very conducive to the arc welding cover surface and can ensure good fusion between the layers, especially in the welding of small diameter pipes, the efficiency is more significant.
1.3 Easy to master
The welding of the root weld of manual arc welding must be performed by welders with rich experience and high technical level. Manual argon arc welding is used for bottoming. Generally, workers engaged in welding can basically master it after a short period of practice.
1.4 Small deformation
The heat-affected zone during argon arc welding is much smaller, so the deformation of the welded joint is small, and the residual stress is also small.
2. Tack welding:
2.1 Spot welding fixation adopts three-point circumferential symmetrical spot welding fixation method, the solder joints should be small, start welding from one end and then transition to the other end, to ensure that the solder joints have no defects in penetration.
2.2 Key points of tack welding operation: tack welding is a part of the weld, and it must be welded firmly and no defects are allowed. The tack weld should not be too high to avoid difficulty in welding to the tack weld joint. If this happens, it is best to grind the tack weld low and grind the two ends into a slope to make the joint easier when welding. If cracks, pores and other defects are found on the tack welds, they should be polished off and re-welded, and remelting is never allowed.
2.3 Split semi-reverse welding, in order to reduce the possibility of porosity, there is no spot welding fixed point at the six points of welding. The relative position between the workpiece and the welding wire is shown in Figure 1.
3. Key points of welding operation process:
The bottom welding should be done in one go as far as possible. The bottom layer should have a certain thickness. If the tube is δ>10mm, the thickness should be ≥4mm. Figure 1
3.1 Start the arc at point A at 5-8 points before 6 o’clock in the overhead welding position. The welding wire and the blunt edge of the groove should be kept at a distance of 1-1.5mm. During flat welding, the welding wire should be parallel to the blunt edge of the inner wall. Keep this distance so that there will be no depression on the back of the weld, and the remaining height is about 0.5-1mm. When welding,
A molten pool is formed at the opposite port (no breakdown). Insert the welding wire into the molten pool. With the help of arc blowing force, the molten droplets are squeezed into the gap and penetrated. The blunt edges on both sides (melted) are bridged. Welding is gradually applied on the basis of “bridge”. The arc starting position is about 10mm in front of the welding direction, and it is never allowed to ignite the arc on the pipe wall. After the arc is ignited, the arc is always kept in the center of the gap.
3.2 During the welding process, because the tube is fixed horizontally, the welder’s body will move with the change of the welding position. In order to maintain stability, when performing upside welding, you can extend your fingers to support the tube at the same time;
3.3 Adopt the “two-point method” welding, control the arc length 2～3mm, heat both sides of the root of the groove at the same time, twist and feed the wire, so that the end of the welding wire is always in the argon gas protection range, and the welding wire is fed while melting. Insert the molten pool directly. In front of the molten pool, the end of the welding wire should be round, and the wire feeding action should be clean and neat, and the two sides of the groove should be controlled to penetrate evenly to ensure that the inner wall of the tube is uniformly formed.
3.4 When the front semicircle is welded to the flat welding position, fill the arc pit and close the arc at point B to facilitate the rear semicircle joint. The back semicircle is polished to bevel the joints to reveal the metallic luster before welding, and the welding starts from the overhead welding position to the flat welding position.
3.5 When closing the arc. Send two drops of filler metal to the molten pool before the arc is extinguished. Move the molten pool to the side of the groove to close the arc. After the arc is extinguished, cover the nozzle over the molten pool, and then remove it after it is completely cooled and darkened.
3.6 Each semicircle welding is completed once, without stopping in the middle. If the welding is started again in the middle, polish the end and make the weld overlap by 5-7 mm.
3.7 If the arc atmosphere is found to be blue during welding, or the molten pool is foaming, immediately stop grinding, remove the defects and continue welding until completion.
3.8 When welding, the angle of the welding torch must be mastered, the wire feeding is in place, and the wire feeding is uniform, so as to ensure the beautiful appearance of the weld. Oxidation.
4. Note for filling wire:
4.1 The wire must be filled after both sides of the groove are melted to avoid poor fusion. When filling the wire, the angle between the welding wire and the surface of the workpiece should be about 15°. Fill the wire evenly, the speed is appropriate, the margin of the weld is too fast, and the weld will be concave and undercut if it is too slow. The end of the wire should always be in the argon protection zone. When the counter gap is greater than the diameter of the welding wire, the welding wire should follow the arc to swing laterally, and the argon protective layer must not be disturbed to prevent air intrusion.
4.2 If the tungsten electrode is accidentally touched with the welding wire during the operation, an instant short circuit will occur, which will produce a large amount of splash and smoke, which will cause welding seam pollution and tungsten inclusion. At this time, immediately stop welding and use a grinding wheel to grind away the contaminated Until the metallic luster is polished out. The contaminated tungsten electrode should be re-ignited elsewhere to melt the contaminated end or re-sharpened before welding.
4.3 When withdrawing the welding wire, do not allow the end of the welding wire to withdraw from the protected area to prevent the end of the welding wire from being oxidized, which may cause oxide slag inclusion or molten holes when it enters the molten pool next time.
5. Arc closing and joints:
5.1 Improper arc closing will affect the quality of the weld, make the arc crater too deep or cause crater cracks, and even cause rework. When closing the arc, the welding handle should be pulled out slightly from the inner groove until the arc is extinguished, and attention should be paid to controlling the speed, not too fast to avoid shrinkage.
All welds at the joints should be ground into bevels with or without defects, and then start the arc at 10 mm in the opposite direction of the welding direction, and move the welding handle backwards until the length of the original welds is 3~5 mm. It melts, and then starts to feed the wire until the weld is complete.
When the arc is finally closed, generally use a slightly drawn arc, overlap the welding seam by 10mm-20mm, and add no or less welding wire in the overlapping part, and the speed should be fast. After stopping the arc, the argon gas switch should be closed with a delay of about 10s to prevent the metal from continuing to oxidize at high temperatures.
5.2 In the case of joints, the welding wire can be filled to complete the joint after the molten pool is formed in the middle or later of the welding pit. The “head-to-head” connection is when welding horizontal or oblique fixed pipes. When starting, only use the arc to melt the original weld end of the joint to form a molten pool, and then the wire can be fed to complete the joint.
5.2.1 Quality control of joints:
The joint treatment must have a slope and no dead corners. The re-ignition position is behind the original arc pit so that the welding seam overlaps by 5mm-10mm. Generally, no wire is filled in the overlap. The shape is closely attached to the groove gap, and the welding arc melts the blunt edge of the groove while also melting the welding wire.
6. Finishing method
At the end of the welding process, fill the pit, pull the arc to the opposite side, and extinguish the arc. At the end, melt the end of the weld bead on the side of the beginning of the welding, and connect the molten metal to the newly melted pool. , And then fill up the newly appeared molten pool and connect them together. If possible, the current attenuation method can be used. When the welding is terminated, the wire filling is stopped to gradually reduce the welding current, so that the volume of the molten pool is continuously reduced, and finally the power is cut off and the walking is stopped.
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