The uneven wall thickness of the
thick-walled seamless steel pipe is mainly reflected in the phenomenon of uneven spiral wall, uneven linear wall, and thick and thin walls at the head and tail.
The cause of the uneven thickness of the spiral thick-walled seamless steel pipe is the uneven wall thickness caused by the adjustment of the center line of the piercing machine, the inclination angle of the two rolls, or the reduction amount in front of the plug is too small, generally along the full length of the steel pipe. Helical distribution. The main measure is to adjust the rolling center line of the piercing machine to make the inclination angles of the two rolls equal, and adjust the pipe rolling mill according to the parameters given in the rolling table.
The reason for the uneven thickness of the linear wall is that the height adjustment of the saddle for the pre-piercing of the mandrel is not appropriate. When the mandrel is pre-pierced, it contacts the capillary on a certain side, which causes the temperature of the capillary to drop too fast on the contact surface, resulting in uneven wall thickness or even pulling. concave defects. The roll gap of continuous rolling is too small or too large. Deviation of the centerline of the tube rolling mill. Uneven reduction of single and double racks will result in linear symmetry deviation of ultra-thin (ultra-thick) steel pipes in the direction of single racks and ultra-thickness (ultra-thin) in the direction of double racks. The main measures are to adjust the height of the mandrel pre-piercing saddle and ensure that the mandrel and the capillary are centered. When changing the pass and rolling specifications, the roll gap should be measured to keep the actual roll gap consistent with the rolling table. Adjust the rolling center line with the optical centering device, and the center line of the pipe mill must be corrected during the annual overhaul.
The reason for the uneven wall thickness of the head and tail is that the front end of the tube blank is cut inclination, the bending is too large, and the centering hole of the tube blank is not correct, which is easy to cause the uneven wall thickness of the steel tube head. When piercing, the elongation coefficient is too large, the roll speed is too high, and the rolling is unstable. The unstable steel throwing of the piercer can easily cause uneven wall thickness at the end of the capillary tube. The measure is to check the quality of the tube blank to prevent the front end of the tube blank from being cut inclination and the amount of reduction is large, and the centering hole should be corrected when changing the hole pattern or overhauling. A lower piercing speed is used to ensure rolling stability and uniformity of capillary wall thickness. When the roll speed is adjusted, the matching guide plate is also adjusted accordingly.
Features of thick-walled seamless steel pipe production:
(1) Pipes with various outer diameters can be produced from strips of the same width
(2) The straightness of the pipe is good, the size is more accurate, and the inner and outer spiral welds increase the rigidity of the pipe body, so there is no need for sizing and straightening after welding.
(3) It is easy to realize mechanization, automation and continuous biochemical market
(4) Compared with other equipment of similar scale, it has smaller external dimensions, less land occupation and investment, and faster construction.
(5) Compared with the straight seam welded pipe of the same size, the welding seam per unit length of the pipe is longer, so the productivity is lower
