The cause and adjustment of uneven steel pipe wall thickness
1. Uneven spiral wall thickness is caused by: the uneven wall thickness caused by the adjustment of the piercing machine's rolling centerline, the inclination of the two rolls, or the reduction of the front head is too small, generally along the full length of the steel pipe. Spiral distribution. During the rolling process, the uneven wall thickness caused by the premature opening of the centering roller, improper adjustment of the centering roller, and the 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 tube 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 capillary exit speed. Do not open the centering roller too early during the rolling process to prevent the ejector rod from shaking and causing uneven wall thickness. The opening degree of the centering roller needs to be adjusted appropriately according to the change of the capillary diameter, and the amount of the capillary beating is considered.
2. Causes of uneven linear wall thickness: improper adjustment of the height of the core rod pre-piercing saddle, the mandrel pre-piercing touches the capillary tube on a certain side, causing the capillary tube to drop too quickly on the contact surface, resulting in uneven wall thickness or even Pull dent defect. The tandem roll gap is too small or too large. Deviation of the centerline of the tube mill. The uneven reduction of single and double frames will cause linear symmetry deviations in the direction of the single-frame (extra-thickness) and the direction of the double frame. The fracture of the mortar and the large gap between the inner and outer rolls will cause the linear asymmetric deviation of the steel pipe. Improper adjustment of continuous rolling, stacking, drawing, and rolling will cause uneven linear wall thickness.
Measures: Adjust the height of the core rod pre-piercing saddle to ensure that the core rod and the capillary are aligned. When changing the pass and rolling specifications, measure the roll gap to keep the actual roll gap consistent with the rolling table. Adjust the rolling centerline with an optical centering device, and correct the centerline of the tube mill during annual overhauls. Change the broken mortar frame in time, measure the inner and outer gap of the continuous roll, and change it in time if there is a problem. During continuous rolling, steel drawing and pile-up should be avoided.
3. Causes of uneven wall thickness at the head and tail: the cutting slope at the front end of the tube blank, excessive bending, and incorrect centering holes of the tube blank can easily cause uneven wall thickness at the head of the tube. During 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 cutting inclination and large reduction. The centering hole should be corrected when changing the hole type or overhauling. A lower piercing speed is used to ensure the stability of rolling and the uniformity of the capillary wall thickness. When the roll speed is adjusted, the matched guide plate is also adjusted accordingly. Pay attention to the use status of the guide plate and increase the inspection of the guide plate bolts, reduce the movement range of the guide plate during steel rolling, and ensure the stability of steel throwing.