Lap welding refers to the dislocation bonding formed after the two sides of the tube blank are stacked together. In terms of length, lap welding can be divided into long and short, and the general length of lap welding is generally more than several meters, or even longer. In terms of misalignment, there is a slight misalignment of a few tenths of a millimeter, and there is a complete misalignment equal to the wall thickness.
The main reasons for the long lap welding are as follows:
1 Axial movement of extrusion roller.
Due to the unstable positioning of the squeeze roller and the squeeze roller shaft, as well as the gap formed by the loose fit of other parts during assembly, the squeeze roller will have axial movement and radial swing. The pass pattern of the squeeze roller will not match and cause lap welding.
2 bearing damage.
After the bearing is damaged, it will destroy the normal position of the squeeze roller. Take the two-roller extrusion roller device as an example. Generally, there are two sets of upper and lower bearings installed in the extrusion roller. When one of them is damaged, the extrusion roller will lose control, and the weld seam will be higher and cause lap welding. During a production run, we can observe the wobble of the squeeze roller. When the upper end bearing is damaged, the swing range of the roller is larger, and when the lower end bearing is damaged, the swing range of the roller is smaller, and it also has a certain relationship with the damage degree of the bearing.
After the bearing of the guide roller is damaged, not only can it not control the weld seam direction of the tube blank well, but the guide ring may also cause pressure loss to the edge of the tube blank due to the damage of the bearing, so that the height of the weld seam changes, and it is slightly inappropriate. Welding accidents may occur.
3 Extrusion roller shaft bending.
Still taking the two-roller extrusion roller device as an example, there are two reasons for the bending of the extrusion roller shaft: one is external bending due to insufficient pressure on the top wire for a long time; the other is internal bending when the pressure on the top wire is too large. When checking, release the jacking device, and place the vertical surface of the steel ruler on the end surface of the roller to check the inclination angle between the end surface of the other roller and the steel ruler. When the shaft is bent outside, the scratches are caused by the bent rollers; when the shaft is bent inside, the scratches are caused by the non-bent rollers.
4 Extrusion force is large.
Lap welded pipes caused by excessive extrusion force generally occur in the production of thin-walled pipes, and rarely occur 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 tube blank width cannot be accepted after too much margin in the pass, and it will be transferred to other Spatial movement to form a lap weld. Therefore, when designing the pass, it is necessary to select an appropriate pass radius and roll gap allowance according to different pipe wall thicknesses, and at the same time pay attention to moderately adjust the extrusion amount.
5 guide roller tilt.
Under normal circumstances, the guide roller should be in a horizontal position, in order to better control the welding seam, the guide roller can be tilted and adjusted. If the inclination angle is too large, the protruding amount of the guide ring will be large. With the rotation of the guide roller, the roller ring will press the edge of the tube blank and deform abnormally. Especially in the production of thin-walled tubes, it is easier to promote the lap welded tube. produce. Often the large inclination adjustment of the guide roller is because it cannot control the direction of the pipe seam well. Therefore, when the hole shape of the guide roller is large, it is necessary to replace the new roller in time, and check and adjust the center immediately if the center is not correct and try to avoid large inclination adjustments.
6 The bottom diameter of the upper guide roller is different.
If the bottom diameters of the two passes of the guide upper roller are not the same size, the problem of overlapping welded pipes is also prone to occur, especially in the production of thin-walled pipes, this phenomenon is more likely to occur. When shutting down for inspection, you can feel whether the weld seam in the welding V-shaped area is smooth by touching your fingers. Of course, as long as we strictly control the quality of the rollers, this lap welding phenomenon can be overcome.
Tengdi Machinery. specializes in the design and manufacture of various types of high-frequency welded pipe units, stainless steel precision welded pipe units, high-precision steel-plastic, stainless steel composite welded pipe units; design and manufacture of various specifications and models of welded pipe molds – rolls, special-shaped rolls, so that the products have been serialized and enjoy a high reputation among domestic and foreign merchants.
Post time: Feb-25-2023