The control of the wall thickness of seamless steel pipe is a difficult point in the production of steel pipes. The measures to improve the accuracy of the wall thickness in the production mainly include the following aspects:
1. Tube billet heating
Heating must be uniform, and rapid temperature rise and fall are prohibited. The temperature rise and fall should be kept steady and slow each time, and the maximum temperature rise and fall should not exceed 30°C.
2. Centering roller
Determine whether the centering roller is installed in place, adjust the center, opening angle and the opening size of the relevant core-holding roller to be consistent, and the center of the core-holding roller should be on the rolling line.
3. Rolling center line
Ensure that the rolling centerline of the piercing machine is consistent with the centerline of the piercing trolley, avoiding “up rolling” or “down rolling”, so that the tube billet maintains uniform force during piercing.
4. Rolling tools
The worn plugs, guide plates, rolls and other rolling tools should be replaced in time.
5. Installation of rolling tools
The center of roll pitch and lead must be on the rolling line. Ensure that the centerline of the guide and roll pitch is on the piercing and rolling centerline, that is, the upper and lower roll pitches are equal, and the left and right guide pitches are equal.
6. Perforated ejector
The perforated ejector rod generally chooses a thick-walled pipe with an outer diameter of Φ108mm-Φ114mm, a wall thickness of ≥25mm, and a uniform wall thickness.
7. Rolling mill mandrel
The mandrel should be processed by a thick-walled tube with a thicker wall. For the mandrel with a smaller specification, a solid blank can be used instead. Thick-walled pipes and solid blanks with uniform wall thickness can greatly reduce the probability of bending deformation of the mandrel, and can effectively improve the wall thickness accuracy of the steel pipe.
8. The accuracy of the mandrel
The length of the mandrel is relatively large. Generally, the outer diameter of the mandrel is turned first and then the weld is broken, or the long material is directly turned into shape. The outer machining accuracy of the core rod is controlled within ±0.1mm, and the deviation of the straightness of the core rod does not exceed 5mm. When welding, a precision-machined pin is inserted between the two core rods for positioning to prevent the overall straightness deviation caused by welding from being too large.
9. Improve the craftsmanship
Improve the process to prevent the occurrence of intermediate thinning and increase of wall thickness beyond the control range, and improve the accuracy of wall thickness.