Controlling the wall thickness of straight seam steel pipes is a difficulty in steel pipe production. At present, the methods for wall thickness accuracy in production by straight seam steel pipe manufacturers generally include:
1. Heating of tube blanks: Heating should be even and avoid rapid temperature rise and fall. Each temperature rise and fall should be kept steady and slow, and the maximum temperature rise and fall should not exceed 30°C.
2. Rolling mill mandrel: thick-walled tubes with uniform wall thickness and solid blanks greatly reduce the probability of bending and deformation of the mandrel, which can effectively improve the wall thickness accuracy of steel pipes.
3. Precision of the mandrel: The external processing accuracy of the mandrel is controlled at ±0.1mm, and the straightness direction of the mandrel does not exceed 5mm. During welding, a precision-machined pin is inserted between the two sections of a mandrel for positioning to prevent the total straightness deviation caused by welding from being too large.
4. Process: Determine whether the centering roller is installed in place, adjust the center of the core-holding roller, the opening angle, and the opening size of each movement to be consistent. The center of the core-holding roller should be on the rolling line.
5. Centering roller: technology to prevent center thinning and wall thickness increase beyond the control range, and improve wall thickness accuracy.
6. Perforated ejector: For perforated ejectors, thick-walled pipes with an outer diameter of Φ108mm-Φ114mm, a wall thickness of ≥25mm, and an average wall thickness are generally selected.
7. Rolling center line: Ensure that the rolling center line of the piercing machine is consistent with the center line of the piercing car to avoid “upper rolling” or “lower rolling” so that the tube blank maintains uniform stress during piercing.
8. Rolling tools: Worn rolling tools such as heads, guide plates, rollers, etc. must be replaced in time.
9. Rolling tool installation: The center of the roller pitch and guide pitch must be on the rolling line. The center line that guarantees the guide distance and roller distance is on the piercing and rolling center line, that is, the upper and lower roller distances are equal, and the left and right guide distances are equal.
Straight seam steel pipe straightening method:
First, the straight seam steel pipe is bent in the same direction as the weld seam
Reason: The normalizing treatment of the weld seam was insufficient, and there was thermal stress on the side of the pipe close to the weld seam, so it bent in one direction after cooling.
Solution: 1. Adjust the intermediate roller to appropriately increase the deflection curve; 2. Straighten twice; 3. When direct straightening is not possible, temper the entire pipe.
Second, the straight seam steel pipe bends irregularly
Reasons: 1. The pressure between the three rollers is inconsistent; 2. The straightening roller is greatly worn.
Solution: Check 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 straight seam steel pipes is greatly shortened.
Reason: The rolling angle between the three straightening rollers is too different; the straightening pressure is large.
Solution: Adjust the roller pressure angle to be as consistent as possible; adjust the straightening pressure appropriately.
Fourth, one end of the straight seam steel pipe is bent
Reason: The distance between rollers is too large.
Solution: Choose a straightening machine with smaller spacing 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 overlapping, and the roller pressure is too large.
Solution: Properly adjust the angle between the rollers and adjust the pressure of the rollers on the pipe.
With the advancement and development of science and technology, many new technologies have been applied to steel pipe straightening machines. For example, a company has improved and applied a seven-roller straightening machine, the model is a 3-1-3 steel pipe straightening machine. It uses a different structural form from the usual six-roller straightening machine to solve the problem of adjusting the straightening roller group in the circumferential direction. The characteristic is that the driving roller uses an adjustment inclined iron to adjust its upper and lower height so that the three straightening rollers can be adjusted radially 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 pipe being straightened is evenly stressed on the circumference. Therefore, the straightening accuracy is high, good, and applicable to a wide range of specifications.
Post time: Jan-12-2024