When manufacturing welded pipes for used welded pipe machine, 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 machine 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.

Through-length lap welding

Lap welding refers to the dislocation bonding formed by overlapping the two edges of the tube blank (Figure 19).

In terms of length, lap welding is divided into long and short, and the full-length lap welding is generally more than a few meters, or even longer. There is a slight misalignment of a few tenths of a millimeter in terms of misalignment, and there is a complete misalignment equal to the wall thickness. The reasons for the long lap welding mainly include the following factors:

(1) The squeeze roller moves axially. Due to the unstable positioning of the squeeze roller and the squeeze roller shaft, as well as the open space formed by the incompatibility of other zero parts during assembly, the squeeze roller will move axially and radially swing. The hole pattern of the squeeze roller will not match and cause lap welding.

(2) The bearing is damaged. When the bearing is damaged, it will destroy the normal position of the squeeze roller. Take the two-roller squeezing roll device as an example. Generally, two sets of bearings are installed in the squeezing roll. When one of the sets of bearings is damaged, the squeezing roll loses control, and the welding seam will rise and cause lap welding. During a production run, we can observe the oscillation of the squeeze rollers. When the upper bearing is damaged, the swing of the roller is larger, and when the lower bearing is damaged, the swing of the roller is smaller, which is also related to the degree of bearing damage. After the bearing of the guide roller is damaged, it not only cannot control the welding seam direction of the tube blank well, but also the guide ring may cause pressure loss to the edge of the tube blank due to the damage of the bearing, so that the height of the welding seam changes, which is slightly inappropriate. A lap welding accident will occur.

(3) The extrusion roller shaft is bent. Still taking the two-roller squeeze roller device as an example, there are two reasons for the bending of the squeeze roller shaft: one is the external bending due to insufficient pressure on the top wire for a long time; the other is the internal bending when the top wire pressure is too large. When checking, release the jacking device and place the vertical surface of the steel ruler on the end face of the roller (Figure 20) to check the inclination angle between the end face of the other roller and the steel ruler. When the shaft is bent outside, the scratches are caused by the rollers that bend the shaft; when the shaft is bent inside, the scratches are caused by the rollers that do not bend the shaft.

(4) The extrusion force is large. The lap welded pipe caused by excessive extrusion force generally occurs in the production of thin-walled pipes, and rarely occurs in the production of ordinary thick-walled pipes. This is because in the production of thin-walled tubes, due to the poor rigidity of the tube blank, once the extrusion force is too large, the width of the tube blank can not be accepted after too much margin in the hole pattern, and it will be turned to other Spatial movement to form lap welding. Therefore, when designing the pass, it is necessary to select the appropriate pass radius and roll gap allowance according to different tube wall thicknesses, and at the same time, pay attention to moderately adjust the extrusion amount.

(5) The guide roller is inclined. Normally, the guide roller should be in a horizontal position, in order to better control the welding seam, the guide roller can be tilted. If the angle of inclination is too large, the protruding amount of the guide ring will be large, and with the rotation of the guide roller, the roller ring will press the edge of the tube blank to deform abnormally, especially in the production of thin-walled tubes, it is easier to promote the lap welded tube. produce. The large inclination adjustment of the guide roller is often due to its inability to control the direction of the pipe seam well. Therefore, when the hole type of the guide roller is worn out, it is necessary to replace the new roller in time. When the center is not aligned, check and adjust it immediately, and try to avoid large tilt adjustment.

(6) The bottom diameter of the guide upper roller is different. If the bottom diameters of the two holes of the guiding upper roller are not the same, the problem of lap welded pipes is also prone to occur, especially in the production of thin-walled pipes, this phenomenon is more likely to occur. During shutdown inspection, you can feel whether the welding seam in the welding V-shaped area is smooth by touching it with your fingers. Of course, as long as we strictly control the quality of the rollers, this lap welding phenomenon can be overcome.

The above is one of the reasons for the quality failure of the weld seam when the used welded pipe machine is making pipes, through the long lap welding. The main reasons for the formation of through-length lap welding are (1) the axial movement of the squeeze roller. (2) The bearing is damaged. (3) The extrusion roller shaft is bent. (4) The extrusion force is large. (5) The guide roller is inclined. (6) The bottom diameter of the guide upper roller is different.