The problem of uneven wall thickness of large-diameter seamless steel pipes is relatively common in the production of seamless steel pipes, and it is also a headache for customers. The unevenness of the thick-walled seamless steel pipe is mainly reflected in the uneven spiral wall, the uneven linear wall thickness, and the thickness of the head and tail is slightly thicker and thinner.
The reason for the unevenness of the large-diameter seamless steel pipe is the inclination of the center line of the cold rolling of the cutting machine, the different inclination angles of the two hot-rolled strips, or the unevenness of the wall thickness caused by the adjustment reasons such as the small amount of reduction in the front of the top. The entire length of the tube is spiraled throughout. An important preventive measure is to adjust the cold rolling center line of the cutting machine so that the inclination angles of the two hot-rolled strips are the same, and adjust the cold drawing machine according to the basic parameters obtained from the cold rolling table.
The reason for the uneven thickness of the linear wall is that the height of the mandrel pre-piercing saddle is not adjusted properly, and the mandrel touches the capillary on a certain side during pre-piercing, which causes the temperature drop of the surface layer of the capillary to drop too fast, resulting in uneven wall thickness or even concave defects. . The hot strip gap of the rolling mill is too small or too large. The centerline deviation of the cold drawing machine. Uneven reduction of single and double racks will result in linear symmetry deviation of ultra-thin (ultra-thick) in the direction of single rack and ultra-thin (ultra-thin) in the direction of double racks. An important preventive measure is to control the height of the mandrel pre-piercing saddle to ensure that the mandrel and the capillary are centered. When changing the plate hole and cold-rolled model specifications, it is necessary to accurately measure the hot-rolled strip gap, so that the actual hot-rolled strip gap is consistent with the cold-rolled table.
The reason for the uneven wall thickness of the head and tail is that the cutting slope of the front end of the large-diameter seamless steel pipe, the bending is too large, and the inclination of the relief hole is easy to cause uneven wall thickness of the head of the seamless pipe. When the hole is broken, the widening index value is very large, the transmission ratio of the hot-rolled strip is too high, and the cold-rolling is unstable. The unstable steel throwing of the cutting machine can easily cause uneven wall thickness at the end of the capillary tube. The preventive measures are to check the quality of the large-diameter seamless steel pipe, prevent the front end of the large-diameter seamless steel pipe from cutting the slope, and the reduction amount is large. A lower hole breaking speed is used to ensure the stability of cold rolling and the accuracy of very thick walls. When the transmission ratio of the hot-rolled strip is adjusted, the matching guide plate is also adjusted relatively.