Tube Mill Fault Analysis——Analysis of Problems Caused by Sand Hole Tube

There are relatively many failures of the pipe welding machine, and the causes of the failures are also more complicated. Often one result is caused by multiple reasons, or one reason can cause several results. Some failures are tricky to deal with. Today I will give you a brief introduction to the analysis of the problem of sand hole tube produced by tube mill.

Sand-hole pipes are also a kind of quality accident caused by weld leakage, but their gaps are very small, some of them cannot be directly observed by human eyes, and must be found through testing equipment, so we call this kind of pipes sand-hole pipes. The main reasons for sand hole pipes are as follows:

(1) Impurities

In particular, the edge of the hot-rolled steel strip contains more impurities, and excessive oxides are easily formed during welding, and blisters may appear in the weld. In general, this phenomenon rarely occurs, and this phenomenon is even rarer for raw materials that have been slitting.

(2) Bearing damage

When the bearing of the squeeze roller is only slightly damaged, there will be problems with the quality of welds such as sand hole pipes and lap welded pipes. Once the bearing is seriously damaged, the squeeze roller has no extrusion force on the weld of the tube billet, so the weld becomes fully open, accompanied by other quality accidents. At this time, we can also observe the squeeze roller with damaged bearing, and the swing amplitude will increase with the degree of bearing damage.

(3) The current is large

When the current output is too large, the weld is prone to overheating. When overburning occurs, we can see a blue arc at the extrusion point of the extrusion roller, which is unique to arc welding, accompanied by an intermittent "squeak" sound. At the same time, larger and more particle sparks are ejected in bursts, and a large amount of metal becomes liquid and is squeezed out to form sand holes. At this time, the inner welding rod of the pipe becomes an irregular nodular body, and the outer burr sometimes becomes piled up when planing, and cannot be formed into a strip shape or a roll shape. When this happens, speed up immediately, and if it can’t be solved, reduce the number of Impedors, or reduce the output power of the current.

(4) Insufficient extrusion force

Sand hole tubes will also appear when the extrusion force is insufficient. Generally, such sand hole tubes are not easy to see, and sometimes a black line can be seen at the weld. When the burr is planed, it can be seen that the burr has a bifurcation phenomenon, and only when the pipe is cold bent or flattened, the crack appears.

(5) Swing seam

The sand hole pipe caused by the pendulum seam is the most common one, and the pipe seam often does not walk smoothly between the two squeeze rollers during operation. Instead, it swings back and forth from left to right, sometimes as large as nearly ten millimeters. When the pipe seam is turned into the pass and not at the extrusion point of the two rollers, a good extrusion effect cannot be obtained, and it is very likely to cause sand holes in the pipe. The main cause of the swing joint is that the center position of each pass is not correct, and it is generally not easy to find the root of the problem. The adjustment process takes a long time, so it is necessary to re-draw the wire from the sizing to the forming of the closed pass to find the alignment, which can shorten the time for dealing with the accident, and at the same time other problems will be cured. In addition, the bending of the extrusion roller shaft and the guide roller shaft, the sway produced by the bearing wear, and the tube blank can not be effectively controlled after the hole shape is worn out can cause the tube blank to swing. Therefore, the seam is a typical example of a result caused by many reasons, and it is difficult to deal with.

(6) Squeeze roll cracked edge

Under high-temperature operation, the upper edge of the squeeze roll pass is prone to quenching and cracking. When the extrusion roller rotates, insufficient extrusion force will occur at the edge-dropped part. If the amount of edge loss is small, the weld seam can barely bond together. As the amount of edge loss increases, there will be quality problems such as poor bonding, false welding, pinholes, and open seams, accompanied by scratches. When this problem occurs, it is necessary to replace the new hole pattern in time.

(7) Hole type wear

After the hole shape of the extrusion roller is worn, not only the slotted pipe but also the sand hole pipe can be formed, which depends on the wear degree of the hole shape and the condition of the raw material, especially the quality of the hot-rolled steel strip.

(8) Damage to raw materials

Damage to the edge of the tube blank will also cause sand hole 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 accidents is very 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.