Wall thickness accuracy and straightening method of straight seam steel pipe

Controlling the wall thickness of straight seam steel pipe is a difficult point in steel pipe production. At present, the methods of wall thickness accuracy of straight seam steel pipe manufacturers in production generally include:

1. Heating of pipe blank: heating should be uniform, and rapid temperature rise and fall should be avoided. Each temperature rise and fall should be stable and slow, and the maximum temperature rise and fall should not exceed 30℃.

2. Rolling mill mandrel: thick-walled pipes and solid billets with uniform wall thickness greatly reduce the probability of bending and deformation of the mandrel, which can effectively improve the wall thickness accuracy of the steel pipe.

3. Mandrel accuracy: the external processing accuracy of the mandrel is controlled at ±0.1mm, and the straightness deviation of the mandrel does not exceed 5mm. During welding, a finely processed pin is inserted between the two mandrels for positioning to avoid excessive total straightness deviation caused by welding.

4. Process: Determine whether the centering roller is installed in place, adjust the center of the relevant core roller, the opening angle, and the opening size of each action, and the center of the core roller should be on the rolling line.

5. Centering roller: Process, avoid the occurrence of center thinning and wall thickness increase beyond the control limit, and improve the wall thickness accuracy.

6. Perforating mandrel: The perforating mandrel generally selects thick-walled tubes with an outer diameter of Φ108mm-Φ114mm, a wall thickness requirement of ≥25mm, and uniform wall thickness.

7. Rolling center line: Ensure that the rolling center line of the piercing machine is consistent with the center line of the piercing trolley, avoid "upward rolling" or "downward rolling", and keep the tube billet under uniform force during piercing.

8. Rolling tools: Wearing head, guide plate, roller, and other rolling tools should be replaced in time.

9. Rolling tool installation: The center of the roller pitch and guide pitch must be on the rolling line. The middle line of the pipe lead and roller pitch is on the middle line of the perforation rolling, that is, the upper and lower roller pitches are equal, and the left and right lead pitches are equal.

Methods for straightening straight seam steel pipes:

First, the straight seam steel pipe bends in the same direction as the weld

Reason: The weld normalizing treatment is not sufficient, and there is thermal stress on the side of the steel pipe close to the weld, so it bends in one direction after cooling.

Solution: 1. Adjust the middle roller and increase the deflection curve appropriately; 2. Straighten twice; 3. When it is impossible to straighten directly, temper the steel pipe as a whole.

Second, the straight seam steel pipe is irregularly bent

Reason: 1. The pressure between the three rollers is inconsistent; 2. The straightening roller is worn out.

Solution: Check and adjust whether the upper straightening roller is loose, and use a sample rod to straighten the length of the contact line between the three passes.

Third, the length of the straight seam steel pipe is shortened significantly.

Reason: The roller pressure angles between the three straightening rollers are too different; the straightening pressure is large.

Solution: Adjust the roller pressure angle to make it as consistent as possible; adjust the straightening pressure appropriately.

Fourth, one end of the straight seam steel pipe is bent

Reason: The spacing between the rollers is too large.

Solution: Select a straightening machine with a smaller spacing that is suitable for the corresponding pipe diameter.

Fifth, the head of the straight seam steel pipe is not round

Reason: The contact phase distribution between the three straightening rollers is improper or overlapped, and the roller pressure is too large.

Solution: Properly adjust the angle between the rollers and adjust the pressure of the rollers on the steel pipe.

With the advancement of science and technology, many new technologies have been applied to steel pipe straightening machines. For example, a seven-roller straightening machine improved and applied by a company is a 3-1-3 steel pipe straightening machine. It uses a different structural form from the usual six-roller straightening machine and solves the problem of adjusting the straightening roller group in the circumferential direction. The feature is that the active roller uses an adjustable inclined iron to adjust its upper and lower heights so that the three straightening rollers can be radially adjusted in the 120° direction of the circumference, while the straightening center line remains unchanged. The advantage is that the structure is simple and easy to adjust, and the straightened pipe is evenly stressed on the circumference. Therefore, the straightening accuracy is high, the quality is good, and the applicable specifications range is wide.