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Welding operation

1 Grounding welding

1.1 Arc welding bottoming operation

Firstly ignite the arc at the welding end of the specimen at the beginning of the welding end, keeping the angle of the welding rod 90°-100° along the welding direction. After a slight pause to form a molten pool, quickly lower the arc to make a small sawtooth swing forward. When swinging to the root of the groove, the electrode will be topped up, at least 3/4 of the arc will burn on the back of the groove, when you hear “噗” The sound indicates that the arc has penetrated the back of the test piece and observed that the melt hole has been formed. The size of the melt hole is about 1.5 times the diameter of the electrode. Because the temperature of the test piece is low at this time, the partial blow is easy to occur, causing one side of the melt hole to open. If the other side is unmelted, the electrode should be quickly pulled toward the unmelted side or the angle of the electrode changed to continue melting. After the hole is normal, the electrode is quickly moved obliquely forward to achieve the purpose of arc extinguishing. The temperature of the molten pool gradually decreases. When the color of the molten pool changes slightly to dark red, the electrode is placed on the 1/2 part of the original molten pool, the upper arc is turned on, the molten hole is opened, the above action is repeated, and the rhythm is extinguished forward. Arc welding. 

During operation, it is necessary to pay attention to controlling the size of the melt hole and the shape of the molten pool as much as possible. If the dissolved pores are too large or the molten iron has a tendency to squat, the molten pool temperature is too high. If the treatment is not timely, the front weld will be welded. The tumor and the back weld are severely sunken, which makes the welding impossible. At this time, the arc should be extinguished quickly. After the arc extinguishing, the temperature should be slightly lowered (before the color of the molten pool becomes dark red), and the arc should be welded immediately. The arcing part should be in the molten pool. On both sides, the two-click wear operation is performed, and once the edge of the original melt hole is fused, the arc is immediately extinguished. After the temperature of the molten pool and the size of the molten hole are normal, the welding is performed by a one-click method; for example, the gap is changed during the welding process. Small, the melting hole becomes smaller, the cooling rate of the molten pool is increased, the arc burning time should be prolonged, the welding rod is pushed to the root, the arc is basically kept burning on the back side of the groove, and the angle of the welding rod is appropriately changed to avoid the phenomenon of unilateral unmelting. After the size of the hole to be melted is appropriate, adjust the angle of the electrode and the burning time of the arc; before replacing the electrode, the top of the electrode is made to make the hole slightly larger than the hole in the normal welding, and the arc is slowly brought to the rear of the groove. About 10mm arc-quenching, so as to form a gentle slope, and is conducive to prevent the shrink fitting hole. 

The joint has a cold connection method and a hot connection method. When the heat connection method is used, the welding rod speed is fast, and the arc welding is ensured immediately before the molten pool is completely cooled, and the top time of the welding rod is mastered to obtain a good joint. In the cold connection method, the angle-increasing machine or the flat shovel can be used to grind the arc-receiving portion into a slope shape. When the arc is led in front of the slope, the arc is quickly pressed down to the root of the groove, and the sound is broken after hearing the puncture sound. , normal welding is restored; when there is a weld bead or a sticky electrode in the welding process, try to use a flat shovel to remove the cleanliness to prevent the impact of the back forming and flaw detection quality. At the same time, special attention should be paid to the prevention of burns caused by slag, splashing and smoldering molten iron during the welding process. The key of this welding method is to pay attention to controlling the temperature of the molten pool and the size of the dissolved pores. The position of the arc starting point should be accurate, pay close attention to the arc topping operation of the joint part, and the arc starting and extinguishing action should be timely, so that the judgment is accurate and the operation is stable;

1.2 continuous arc welding bottoming operation

At the front end of the positioning weld of the test piece, the arc is placed at an angle of 90-100 degrees along the welding direction, the arc is slightly paused, and the preheating is about 1-2 s. The weld to be positioned forms a molten pool, and the arc is quickly pressed to make a small sawtooth swing. At this time, pay attention to the speed of the moving bar and the dwell time on both sides. The welding layer should be thin and welded to the joint. The welding speed is slightly slowed down, and the welding rod is topped and slightly oscillated. At this time, the end of the welding rod reaches the bottom edge of the groove, almost The entire arc burns in the plate. When the arc passes through the back of the test piece and forms a molten hole, it is made into a transverse zigzag arc. The advancement step is appropriate. If the step is too large, it will cause unmelting. 

If the step is too small, the welding will accumulate until the weld is accumulated. A weld bead appears. At this time, nearly 3/4 arc is burned on the back side of the weld. The speed of the moving rod is small, the speed is fast, the arc is short, and there must be enough residence time on both sides to ensure good fusion and support the high temperature molten pool in the center of the weld bead. metal. At the same time, it is necessary to pay attention to the feeding depth of the welding rod, control the size of the melting hole, the volume and temperature of the molten pool, the welding layer should be thin, and the droplets should be transported to the root and the back of the groove as much as possible by the arc blowing force. After the end of a welding rod, the arc is stopped 10 mm backward on the side of the groove, and the arc is stopped by an angle grinder or a curved tweezers to form a gentle slope to facilitate the joint. The operation principle of the joint is basically the same as that of the welding. In order to ensure sufficient preheating and anti-sticking, the arc can be drawn along the center of the weld bead at a distance of 20 mm from the joint, so that it forms a strip with the parent metal. The welded small independent weld bead is welded to the joint crater for lateral swinging. However, after the completion of the entire bottom weld bead, the small weld bead of the first weld of 10 mm must be removed. After the end of the weld bead is finished, clear Root, ready for welding of the fill layer.

2 Filling layer welding

The slag should be carefully cleaned before filling, and the slag and splash treatment should be thorough and clean. If the joint is too high, it must be removed with an angle grinder or flat shovel.

The angle of the electrode is referred to the angle of the electrode when the bottom is welded (the same angle is used for the welding of the cover layer). The first layer of filling current can be appropriately increased, which is advantageous for eliminating slag which is difficult to remove at the weld toe. The moving bar adopts a rectangular tooth shape or an anti-cavity shape moving bar method to control the welding rod angle, short arc welding, and sufficient residence time on both sides of the welded joint to ensure good integration on both sides and smooth bead. The second layer of filled welds should control the shape of the molten pool to ensure that the weld is flat and its height is about 1 mm from the surface of the test piece. The residence time of the arc on both sides is extended as much as possible to make the center of the filled bead slightly concave. The welding of the layers plays a vital role. During the filling process, care should be taken to avoid melting the edge of the groove to ensure that the width of the weld is uniform and straight. When connecting, the arc is led at 10-15mm in front of the arc pit, the short arc is dragged to the arc pit, and the arc is transported along the arc of the arc pit. After the molten pool is formed, the two sides are fully fused and then welded normally.

3 welding of the cover layer:

The slag and splash of the packed layer should be thoroughly removed before the cover is welded. When welding, lower the arc, control the angle of the electrode, and keep the handle steady. Pay attention to the shape and temperature of the molten pool, control the residence time of the arc on both sides of the groove, and prevent defects such as welding deviation, undercut, and unfusion. When connecting the joint, the speed of replacing the welding rod should be fast, and the joint should be in place to avoid the occurrence of super high and Out of touch.

Conclusion

In the case of single-sided welding double-sided forming of the upright plate by hand arc welding with alkaline electrode, in order to obtain an excellent welded joint, it should be done as follows: 1. Select the welding process parameters correctly; 2. Observe and control the size of the weld hole. , the temperature of the molten pool and the shape of the molten pool; Third, adjust the angle of the welding rod and the length of the arc in a timely manner; Fourth, master the pace of the good moving strip, the amplitude of the swing and the dwell time on both sides of the groove; five, the eye is handy, not panic. With a certain theoretical foundation, coupled with our diligent thinking, the most important thing is that through continuous practice, we believe that each of our welding operators can get excellent welds from the appearance size to the internal quality, in order to improve the operation skills. To ensure the welding quality of various projects laid a good foundation.