CO2 gas shielded welding of pipes is difficult to butt, and operation practice can only be carried out after mastering the essentials of flat butt welding. Only two welding methods often used for butt welding of pipes are introduced here, namely horizontal rotating butt welding and horizontal fixed butt welding.
For butt joints for welding small diameter pipes, in addition to mastering the operation technology of single-side welding and double-side forming, it is also necessary to continuously rotate the wrist according to the radius of curvature of the pipe to change the angle and centering position of the welding torch at any time. Due to the thin pipe wall, use φ1. 2 mm wire is prone to burn through when welding. Compared with the welding of plate materials, the welding of pipe welding must first establish a more careful and meticulous ideology of operation and observation, that is, when welding, the arc connection should be more accurate, the rhythm should be slightly faster, the welding time should be short, and the start should be gentle. When the horizontally rotating pipe is welded, two methods can be used for welding: one is that the steel pipe is placed on the roller frame, the roller rotates to drive the steel pipe to rotate through friction, and the speed of the steel pipe rotation is the welding speed; the other is that the operator wears a helmet. Mask, turn the steel pipe with one hand, and hold the welding tongs with the other hand for welding. The speed of turning the steel pipe by hand is the speed of welding. position) for welding, this method is simple to operate. For the annular welds of unfixed pipes with small lengths (such as pipe flanges, etc.), the horizontal rotation method can be used for welding. This method is also suitable for single-sided welding and double-sided forming of small diameter pipe girth.
When positioning, place the steel pipe on the assembly positioning tire of the L 50x50x5 equilateral angle steel (Figure weldment placement)
The tack weld shall not have any defects, the length of the tack weld shall not be greater than 10mm, and shall be evenly distributed in 2 places according to the circumferential direction.
A well-positioned weldment should reserve a gap, and ensure that the two weldments are concentric. In addition to direct welding in the groove of the pipe, the tack welding can also be assembled and fixed outside the groove with a connecting plate. The assembly positioning of the weldment can take any one of the following three forms, as shown in Figure Several ways of positioning welds.
Figure Several ways of positioning welds-a shows tack welding directly in the groove of the pipe. The tack weld is a part of the formal weld, so the tack weld should ensure penetration and no welding defects. After the weldment is positioned, grind both ends of the tack weld into a gentle slope. When the welding is completed to the tack weld, it is only necessary to feed the electrode slightly into the groove, pass through the tack weld at a faster speed, transition to the previous groove, and continue to weld forward.
Figure Several ways of positioning welds-b is an informal tack weld. The edge of the groove root of the weldment should not be damaged during welding. When the formal weld is welded here, the informal tack weld should be polished off and continue to be welded forward.
Figure Several ways of positioning welds-c shows the tack welding using the connecting plate. This method does not damage the groove of the weldment. When it is officially welded to the positioning plate, the positioning plate is knocked off, and the welding is continued.
4.Pipe welding tack welds are generally used in two places, and the two welds are 180° apart. The starting point of the formal welding should be 180° away from the two tack welds. It is worth noting that no matter what kind of tack welding is used, tack welding is absolutely not allowed at the position of the overhead welding (at 6 points).
The welding parameters of butt-turn welding of small-diameter pipes for CO2 gas shielded welding are very important, and the data in Table Welding parameters for butt-turn welding of small diameter pipes can be selected as a reference during operation.
C02 gas shielded welding diameter pipe butt rotary welding adopts left welding method with single layer and single bead.FIG Torch Angle and Arc Centering Position for Butt Rotary Welding of Small Diameter Pipe
Adjust the height of the weldment rack to ensure that the operator can easily move the welding torch and turn the weldment while sitting or standing, place the small diameter pipe on the weldment rack, and place a tack weld at 1 o’clock on the clock.
After debugging the welding parameters, the welding can be carried out according to the following steps: start the arc on the positioning weld at the 1 o’clock position of the clock, and weld from right to left to the arc extinguishing at the 11 o’clock position of the clock, immediately use the left hand to push the pipe clockwise Turn the direction – an angle, turn the arc extinguishing point to the 1 o’clock position of the clock and then weld, and so on continuously until the welding is completed. When welding pipes, pay special attention to the following two points:
①Weld the gun with the right hand as much as possible, and turn the tube with the left hand to keep the molten pool in the flat welding position.
②Because the welding wire is thicker and the deposition efficiency is higher, single-layer single-pass welding is used to ensure that the back of the weldment is formed and the front is beautiful, which is difficult to master. In order to prevent burn-through, the “intermittent” welding method can be used, like the arc ending, the welding is carried out by the method of continuous arc ignition and arc breaking.
Horizontal fixed pipe welding is a welding method in which the nozzle is oriented to the left and right, and the welding seam rotates in a vertical and circular shape. During the welding process, the axis of the pipe is fixed in a horizontal position and is not allowed to rotate. It is necessary to master the operation skills of single-sided welding and double-sided forming in three positions of flat welding, vertical welding and overhead welding at the same time, in order to weld qualified welds.
The characteristics of horizontal fixed pipe welding are:
For the same welding current (which can be adjusted when necessary), a complete seam welding process must go through various welding positions such as overhead welding, vertical welding, climbing, and flat welding. The change in angle and the change in the operator’s body position are large. Horizontal fixed pipe welding, also called all-position welding, is one of the most difficult welding positions in welding.
Due to the poor control of the shape of the welding pool during pipe welding, during the welding process, the degree of penetration of the first layer of the root of the bottom layer is often uneven, and the surface of the weld bead is uneven. Figure Defect distribution of v-groove in horizontal fixed pipe welding shows the common root defects of the weld in the V-groove of horizontal fixed pipe welding. Among them, positions 1 and 6 are prone to various defects; position 2 is prone to collapse waist and pores; positions 3 and 4 are prone to separation of molten iron and slag, and the penetration is good; uneven.
If the welded pipe is to withstand high temperature and high pressure, the technology of single-sided welding and double-sided forming must be adopted during welding. This technology is more demanding on the operator.
The pre-weld preparation for horizontal fixed all-position welding of small-diameter pipe is basically the same as the preparation for horizontal rotating butt welding of small-diameter pipe, so it will not be described in detail here.
The welding parameters of the horizontal fixed all-position welding of CO2 gas shielded small-diameter pipes are very important, and the data in Table Welding Parameters for Horizontal Fixed All-Position Welding of Small Diameter Pipes can be selected as a reference during operation.
When welding the small diameter pipe, divide the pipe into left and right half circles according to the clock position. Using single-layer single-pass welding, during the welding process, the change of the welding torch angle and the arc centering position for all-position welding of the small diameter pipe is shown in Figure Torch Angle and Arc Centering Position for Butt Rotary Welding of Small Diameter Pipe.
Adjust the height of the fixture to ensure that the operator can weld from the 7 o’clock position of the clock to the 3 o’clock position when kneeling on one leg. Then fix the small-diameter tube to ensure that the axis of the small-diameter tube is in the horizontal plane, and the 0 o’clock position of the clock is at the top. The relative position of the small diameter tube cannot be changed during the welding process.
After debugging the welding parameters, you can refer to the following steps for welding:
①Start the arc on the tack weld at the 7 o’clock position of the clock, keep the angle of the welding torch clockwise and weld until the arc is broken at the 3 o’clock position. It is not necessary to fill the arc crater. molten pool until it solidifies.
②Grind the second tack weld at the arc crater into a bevel.
③ Ignite the arc at the highest point of the inclined plane at the 3 o’clock position of the clock, and weld it clockwise to the 11 o’clock position to break the arc.
④ Grind the head of the welding seam at the 7 o’clock position of the clock into a bevel, ignite the arc from the highest point and connect the head quickly, and weld counterclockwise to the 9 o’clock position of the clock to break the arc.
⑤ Grind the welding seam ends at 9 o’clock and 11 o’clock of the clock into a bevel, then start the arc from the 9 o’clock position of the clock, and finish welding the closed section welding seam in the counterclockwise direction, and stop the arc at the 0 o’clock position. , and fill the crater.
Note: The purpose of dividing the two sections of the front and back welds into several sections of welding is to enable the operator to master the joint technology during the practice process. Once the joint is learned, the two sections of the weld should be completed at one time.
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