The uneven wall thickness of seamless carbon steel pipes is mainly manifested in the phenomenon of uneven spiral wall thickness, uneven straight wall thickness, and thinning wall thickness at the head and tail. The influence of continuous rolling process adjustment on CS seamless steel pipes is an important factor leading to uneven wall thickness of finished pipes. Specifically
Uneven spiral wall thickness of seamless steel pipes
As a result of:
- Seamless steel pipes have uneven wall thickness due to adjustment reasons such as inaccurate rolling center line of the piercing machine, inclination angle of the two rollers, or small reduction before the plug, and are generally distributed in a spiral shape along the entire length of the steel pipe.
During the rolling process, the center roller is opened too early, adjusted improperly, and the top rod vibrates, resulting in uneven wall thickness, generally distributed in a spiral shape along the entire length of the steel pipe.
Adjust the rolling centerline of the piercing machine so that the inclination angles of the two rollers are equal, and adjust the rolling mill according to the parameters given in the rolling table.
For the second case, adjust the opening time of the centering roller according to the outlet speed of the capillary tube. Do not open the centering roller too early during the rolling process to prevent the top rod from shaking and causing uneven wall thickness of the seamless steel pipe. It is necessary to adjust the opening of the centering roller appropriately based on the change in capillary diameter, and consider the pulsation of the capillary.
- Uneven linear wall thickness of seamless steel pipes
The height adjustment of the pre perforated saddle of the core rod is not appropriate. When the core rod is pre perforated, it contacts the capillary tube on one side, causing the temperature of the capillary tube on the contact surface to drop too quickly, resulting in uneven wall thickness of the seamless steel pipe and even the appearance of concave defects.
The gap between continuous rolling rolls is too small or too large.
Deviation of the centerline of the rolling mill.
Uneven compression of single and double racks can cause linear symmetry deviation of steel pipes, which is ultra-thin (ultra-thick) in the direction of single racks and ultra-thick (ultra-thin) in the direction of double racks.
The safety support is broken, and the difference between the inner and outer roller gaps is significant, which can cause asymmetric deviation in the straight line of the steel pipe.
Improper adjustment of continuous rolling, steel stacking, and rolling can cause uneven wall thickness in straight lines.
Adjust the height of the pre perforated saddle of the spindle to ensure alignment between the spindle and the capillary.
When changing the pass and rolling specifications, the roll gap should be measured to ensure that the actual roll gap is consistent with the rolling table.
Adjust the rolling centerline with an optical alignment device, and the rolling mill centerline must be calibrated during annual major repairs.
Timely replace the frame with broken safety mortar, measure the inner and outer roll gaps of the continuous rolls, and replace them promptly if there are any problems.
During continuous rolling, pulling and stacking of steel should be avoided.