When manufacturing welded pipes for used welded pipe units, judging that the quality of the welded pipes meets the standard depends on the quality of the welds. Therefore, the quality of the weld is very important, so sometimes it is necessary to rule out the quality of the weld. We perform analyses to understand weld quality failures.

These weld quality failures will occur when the used welded pipe units is making pipes: ① through-length lap welding. ② Periodic lap welding. ③ Open the seam. ④ Trachoma. ⑤ Peach-shaped tube. ⑥ Weld seam gnawed. ⑦Outer burr planing. ⑧ Heating. ⑨ The current is small. ⑩ Melting of induction coils and electrodes. ⑪ Fire. ⑫ "No high pressure" phenomenon. We can summarize 12 causes of weld quality failures.

Trachoma

The trachoma tube is also a quality accident of weld leakage, but its gaps are short and tiny, some of which are not directly observed by the human eye and must be found through testing equipment, so we call this type of tube a trachoma tube. The main reasons for the trachoma tube are as follows:

(1) Impurities. In particular, the edge of the hot-rolled steel strip contains a lot of impurities, and it is easy to form excessive oxides during welding, and the weld may have blisters. In general, this phenomenon rarely occurs,

This phenomenon is even rarer for raw materials that have undergone slitting.

(2) The bearing is damaged. This is also one of the important reasons for the trachoma tube. We have already explained it in the previous section on the slotted tube, and will not be introduced in detail here.

(3) The current is large. When the current output is too large, the welding seam is prone to over-burning. In the event of over-burning, we can see a blue arc like arc welding at the extrusion point of the extrusion roller, accompanied by intermittent "squeak" sound, and bursts Larger and more particle sparks are ejected, and a large amount of metal becomes liquid and extruded to form blisters. At this time, the inner welding rib of the pipe becomes an irregular tumor-like body, and the outer burr sometimes becomes a pile-like shape when it is planed, and cannot be formed into strips or rolled. When this happens, it is necessary to speed up the vehicle immediately, and if it cannot be solved, reduce the number of magnetic rods, or reduce the output power of the current.

(4) Insufficient extrusion force. When the extrusion force is insufficient, a trachoma tube will also appear. Generally, this kind of trachoma tube is not easy to see. Sometimes a black line can be seen at the weld. When the burr is planed, it can be seen that the burr has a split phenomenon, and only the tube is cold-bending. Or cracks appear during the flattening test.

(5) Swing seam. The most common type of trachoma tube is caused by the swinging seam. Often, the tube seam does not run smoothly in the middle of the two squeeze rollers during operation, but swings back and forth suddenly from left to right, sometimes the swing amplitude is as large as 10 mm about. When the pipe seam is turned into the hole pattern and not at the extrusion point of the two rollers, a good extrusion effect cannot be obtained, which is very likely to cause the generation of trachoma. The main reason for the swing seam is that the center position of each hole is not correct. Generally, it is not easy to find the root cause of the problem, and the adjustment processing time is long. Therefore, it is necessary to re-draw the line from the sizing to the forming closed hole, which can shorten the accident. Time to deal with, and some other problems will also be cured. In addition, the bending of the extrusion roller, the guide roller, the amount of sloshing generated by the bearing wear, and the inability to effectively control the tube blank after the hole shape is ground can cause the tube blank to swing. Therefore, the swing seam is a typical example of a result caused by multiple reasons, and it is more difficult to deal with.

(6) Squeeze roller cracked edge. Under high temperature operation, the upper edge of the extrusion roll pass is prone to quenching and cracking. When the squeezing roller rotates, insufficient squeezing force occurs in the part where the edge is dropped. When the amount of edge drop is small, the welds can barely stick together. As the amount of edge drop increases, there will be quality problems such as poor adhesion, false welding, pinholes, and slits, and accompanied by scratches. When this problem occurs, it is necessary to replace the new hole type in time.

(7) The hole type is worn. After the pass of the extrusion roller is worn, it can not only cause slit pipes, but also cause trachoma, which depends on the wear degree of the pass and the condition of the raw materials, especially the quality of the hot-rolled steel strip.

(8) Raw material damage. Damage to the edge of the tube blank can also cause the generation of trachoma tubes. The severity of this trachoma tube is inseparable from the damage to the edge of the tube blank. Under normal circumstances, the probability of such an accident is extremely small. As long as we strictly check the supply of raw materials during production, and do not do any damage to the edge of the tube blank during production, then this quality accident will be overcome.

The above is one of the reasons for the quality failure of the weld seam when the used welded pipe units is making pipes, trachoma. The main reasons for the formation of blisters are (1) impurities. (2) The bearing is damaged. (3) The current is large. (4) Insufficient extrusion force. (5) Swing seam. (6) Squeeze roller cracks. (7) The hole type is worn. (8) Raw material damage.

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