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Causes and measures of uneven wall thickness of seamless steel pipes

The uneven wall thickness of seamless steel pipes is mainly reflected in the uneven spiral wall thickness, the linear uneven wall thickness, and the thicker and thinner wall thickness at the head and tail. The influence of seamless pipe continuous rolling process adjustment is an important factor leading to uneven wall thickness of the finished pipe.

Specifically divided into the following situations

The causes of uneven spiral wall thickness of seamless steel pipe are:

1) The uneven wall thickness of seamless steel pipes caused by adjustments such as the improper rolling center line of the piercer, the unequal inclination angle of the two rolls, or the too small front pressing amount of the head, is generally spirally distributed along the entire length of the steel pipe.
2) During the rolling process, the centering roller is opened too early, the centering roller is adjusted improperly, and the wall thickness is uneven due to the jitter of the ejector rod, which is generally distributed in a spiral shape along the entire length of the steel pipe.

Measures:

1) Adjust the rolling center line of the piercing machine to make the inclination angles of the two rolls equal, and adjust the tube rolling machine according to the parameters given in the rolling table.
2) For the second case, adjust the opening time of the centering roller according to the capillary outlet speed. Do not open the centering roller too early during the rolling process to prevent the ejector rod from shaking and cause uneven wall thickness of the seamless steel pipe. The opening degree of the centering roller needs to be adjusted appropriately according to the change of capillary diameter, and the amount of capillary beating is considered.

The causes of uneven straight wall thickness of seamless steel pipe are:

1) The height of the mandrel pre-wearing saddle is not adjusted properly. When the mandrel pre-wears, it touches the capillary tube on a certain surface, causing the capillary tube to drop too quickly on the contact surface, resulting in uneven wall thickness of the seamless steel pipe or even dent defects.
2) The gap between the continuous rolls is too small or too large.
3) Deviation of the center line of the tube mill.
4) The uneven reduction of single and double frames will cause linear symmetry deviations of ultra-thin (extra-thick) steel pipe in the direction of single frame and ultra-thick (ultra-thin) in the direction of double frames.
5) The safety mortar breaks and the gap between the inner and outer rolls is large, which will cause the linear asymmetric deviation of the steel pipe.
6) Improper adjustment of continuous rolling, stacking, drawing and rolling will cause uneven linear wall thickness.

Measures:

1) Adjust the height of the core rod pre-piercing saddle to ensure that the core rod and the capillary are aligned.
2) When changing the pass and rolling specifications, measure the roll gap to keep the actual roll gap consistent with the rolling table.
3) The optical centering device is used to adjust the rolling center line, and the center line of the tube mill must be corrected during the annual overhaul.
4) Replace the broken frame of the safety mortar in time, measure the inner and outer gap of the continuous roll, and replace it in time if there is a problem.
5) During continuous rolling, avoid drawing and pile steel.

Causes of uneven wall thickness at the head and tail of seamless steel pipe:

1) The cutting angle of the front end of the tube blank, the excessive bending, and the incorrect centering hole of the tube blank can easily cause uneven wall thickness of the steel tube head.
2) The elongation coefficient is too large during piercing, the roll speed is too high, and the rolling is unstable.
3) The unstable steel throwing of the piercer may cause uneven wall thickness of the capillary tail.

Measures:

1) Check the quality of the tube blank to prevent the front end of the tube blank from cutting slope and large reduction. The centering hole should be corrected when changing the hole pattern or overhauling.
2) Use a lower piercing speed to ensure the stability of rolling and the uniformity of the capillary wall thickness. When the roll speed is adjusted, the matching guide plate is also adjusted accordingly.
3) 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.
 

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