Factors that cause weld quality failures in used roll forming machine include ①lap welding, ②cycle lap welding, ③opening, and ④bathholes. The following is an introduction to the cause of the weld quality failure factor-sand hole.

Trachoma tube is also a quality accident of weld leakage, but its gaps are short and subtle, some of which are not directly observed by the human eye, and can only be found through testing equipment, so we call this type of tube a trachoma tube. The main reasons for blisters caused by used roll forming machine are as follows:

(1) Impurities. In particular, the edges of hot-rolled steel strips contain more impurities, and excessive oxides are likely to be formed during welding, and blisters may appear in the weld. In general, this phenomenon rarely occurs, and it is even rarer for materials that have undergone slitting.

(2) The bearing is damaged. This is also one of the important reasons for the trachoma tube, which we have explained in the previous section of the slit tube.

(3)The current is large. When the current output is too large, the weld is prone to overburning. When over-burning occurs, we can see a blue arc at the squeeze point of the squeeze roller, which is like a unique blue arc during arc welding, accompanied by intermittent "squeaking" sounds, and at the same time bursts of light Larger and more particle sparks are ejected, and a large amount of metal becomes liquid liquefaction and is squeezed out to form blisters. At this time, the inner welding rib of the pipe becomes a random bulge, and the outer burr sometimes becomes piled up during planing, and cannot be striped or rolled. When this happens, speed up the vehicle immediately, and reduce the number of magnet rods or reduce the so-called output power if the problem is still not resolved.

(4) Insufficient squeezing force. When the squeezing force is insufficient, trachoma tubes will also appear. Generally, this kind of trachoma tube is not easy to see. Sometimes a black line can be seen at the weld. Or cracks only appeared during the flattening test.

(5) Swing seam. Blasthole tube caused by oscillating seam is the most common one. Often, the seam does not move smoothly between the two squeezing rollers during operation, but oscillates from left to right, sometimes with a large swing range of about 10mm. When the pipe seam is turned into the hole and not at the squeezing point of the two rollers, a good squeezing effect will not be obtained, which is very likely to cause the production of blisters. The main reason for the swing seam is that the center position of each pass is not correct. Generally, it is not easy to find the source of the problem. It takes a long time to adjust and process. Therefore, it is necessary to re-pull the line from the sizing to the closed pass, which can shorten the accident. Processing time, and some other problems will be cured at the same time. In addition, the bending of the squeeze roller shaft and the guide roller shaft, the sloshing caused by the wear of the bearing, and the large hole shape can cause the pipe blank to wobble. Therefore, the swing seam is a classic example of a result caused by multiple reasons. It's tricky to deal with.

(6) Cracked edges of squeeze roller. Under high temperature operation, the upper edge of the squeeze roll pass is prone to quenching and cracking. When the squeezing roller rotates, insufficient squeezing force occurs at the part where the edge is dropped. If the amount of edge drop is small, the welds can barely bond together. As the amount of edge drop increases, quality problems such as poor adhesion, false welding, pinholes, and open seams will occur, accompanied by scratches. When this problem occurs, a new hole pattern needs to be replaced in time.

(7) Hole type wear. After the pass of the squeeze roll is worn, it can not only cause a slit pipe, but also a blistering pipe. This depends on the degree of wear of the pass and the condition of the raw material, especially the quality of the hot-rolled steel strip.

（8）Material damage.Damage to the edge of the tube blank can also cause blisters. The severity of this kind of trachoma tube is inseparable from the damage condition of 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 make any damage to the edge of the tube blank during production, this quality accident will be overcome.

Due to the above 8 factors, the quality of the welding seam in the used roll forming machine is caused by sand holes. When the welded pipe is made, it is necessary to check whether the used roll forming machine has these problems.