Causes and Adjustment of Uneven Wall Thickness of Steel Pipe

1. The causes of the uneven wall thickness of the spiral shape are: the uneven wall thickness caused by the adjustment reasons such as the uneven rolling centerline of the piercer, the inclination angle of the two rolls, or the reduction amount in front of the plug is too small, generally along the whole length of the steel pipe. Spiral distribution. During the rolling process, the uneven wall thickness caused by the premature opening of the centering roll, improper adjustment of the centering roll, and jitter of the ejector rod are generally distributed in a spiral shape along the entire length of the steel pipe.

Measures: Adjust the rolling centerline of the piercing machine to make the inclination angles of the two rolls equal, and adjust the rolling mill according to the parameters given in the rolling table. Because of this situation, adjust the opening time of the centering roller according to the speed of the capillary outlet, and do not open the centering roller too early during the rolling process to prevent the ejector from shaking and causing uneven wall thickness. The opening of the centering roller needs to be adjusted appropriately according to the change in the diameter of the capillary, and the amount of the capillary runout should be considered.

2. Causes of uneven linear wall thickness: the height of the mandrel pre-piercing saddle is not properly adjusted, and the mandrel is pre-pierced when it touches the capillary on a certain side, which causes the capillary temperature 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. The centerline deviation of the tube mill. Uneven reduction of single and double racks will cause linear symmetrical deviations in the direction of the single rack (super thick) and the direction of the double rack (super thick). The mortar is broken, and the difference between the inner and outer roll gaps is large, which will cause the straight line asymmetric deviation of the steel pipe. Improper adjustment of continuous rolling will cause uneven wall thickness in straight lines.

Measures: Adjust the height of the mandrel pre-piercing saddle, and ensure that the mandrel and the capillary are centered. The roll gap should be measured when changing the pass type and rolling specifications so that the actual roll gap is consistent with the rolling table. Adjust the rolling centerline with the optical centering device, and correct the centerline of the tube mill during the annual overhaul. Replace the broken frame in time, measure the inner and outer roll gaps of continuous rolls, and replace them in time if there is a problem. During continuous rolling, steel drawing and stacking should be avoided.

3. Causes of the uneven wall thickness of the head and tail: 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.

Measures: Check 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 for hole type change or maintenance. 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. Pay attention to the use state of the guide plate and increase the inspection of the guide plate bolts, reduce the movement of the guide plate during rolling, and ensure the stability of the steel casting.