Analysis of Quality Problems in Drum Delta (3)

Fourth, the impact of spot welding positioning quality - take over the edge

Occasionally, due to the problem of positioning of spot welds before seam welding in buckets, leakage in some triangles is also caused. Due to inaccurate positioning, the shape of the lap welds that are often formed is shown in Figure 8. In the weld A, B on both sides of the amount of laps serious bad, A side of the lap is too large, B side of the lap volume is too small. When the overlap amount is too large, the welding seam is detached too much to form a double layer without melting, as shown in Fig. 9-1. The resulting curling is not only due to the leakage caused by the thick weld seam ( As shown in Figure 6, there is also leakage due to a gap in the middle of the double layer, as shown in Figure 9-2. When the amount of lap joints is too small, openings often occur. Sometimes the welding seams are disengaged after the burring and are completely separated during the crimping process. Figure 10-1 shows the situation where the weld is disengaged when the flange is folded. Figure 10-2 shows the situation where the weld seam appears. This caused greater leakage.

In order to prevent the seam welding edge from being too wide or too narrow, it is necessary to find a way to locate the spot welder and adopt a “Z” shaped positioning fixture to simultaneously position the two ends of A and B. Only controlling the two points A and B can make the two sides. The same positioning, "Z"-shaped positioning fixture shown in Figure 11. For the fully automatic seam welder, because it has a "Z" shaped guide rail, it does not require spot welding, and the seam welding edge quality can also be strictly controlled.

Fifth, the impact of seam welding quality (a) - burn through

Sometimes the cause of leakage is difficult to analyze, but as long as the triangular area is cut and unfolded, many problems will be discovered. The crimping shown in Figure 12 is such a case. In the figure, holes appearing in the bead seam of the barrel weld were analyzed by unfolding to find that there was a perforation phenomenon in the weld seam. This is the seam welding burn-through.

The causes of local burn-through on the seam welding surface are generally the following four:

(1) The surface of the barrel or the surface of the welding wheel is not clean and there is much dirt;

(2) The electrode pressure is insufficient or the barrel body is not in actual contact with the welding wheel;

(3) The surface of the wheel loses its regular shape;

(4) The welding speed of the seam welding is too fast and the welding wheel is overheated.

In the normal production, if there is excessive burn-through phenomenon, it must be strictly inspected. For the first reason, the surface of the bucket body and the surface of the welding wheel should be cleaned; for the second reason, the electrode pressure should be increased to replace the excessive wear. The welding wheel; for the third reason, the surface of the welding wheel should be repaired; for the fourth reason, the cooling conditions should be improved. In the production, there are generally a few burn-through phenomena, mostly caused by the first reason.

Seam welder current is large, impedance is low, so the secondary voltage is low. In this way, oil, oxides, etc. on the barrel are all poor conductors. Under the action of the electrode pressure, the oxide film and other parts are broken, and the distribution of the current field on the steel plate is changed during the conduction, so that the current lines in individual parts are dense, and the heat is too concentrated, which may easily cause burns at the lap joints or burns along the outer edges of the solder joints. This is the main cause of burns.

Sixth, the quality of seam welding (two) - convex Tsui

In most of the barrel manufacturers in China, the phenomenon of seam welding is very common. This is also one of the major causes of leakage in the delta area. As shown in Figure 13, the shape of the protruding bead at the edge of seam welding is in the process of crimping. The nose will reach the center of the bead first, so that the flanks on both sides cannot be reached and there will be insufficient curling or voids. See Figure 2-2 and Figure 2 for the curling at the center of the nose and on both sides of the nose. 3, the curling situation is basically similar.

There are generally three causes of seam welding convex phenomenon:

(1) The power-on time is too long;

(2) Insufficient electrode pressure;

(3) The current is too large.

For the above-mentioned reasons, the convex nozzle is generally adopted to adjust the welding specifications, change the angle of the weld face cone angle and improve the cooling conditions and other measures to solve. Some use a trimmer to solve.