Technical Articles
Reasons for the Uneven Thickness of the Seamless Steel Pipe (Part Two)
Posted: 12/08/2020 09:43:59 Hits: 17
The picture above shows the perforation site of seamless steel pipes. Many steel pipes with uneven thickness occur at this time, so it is very important to strictly control the perforation link.
Fine rolled steel pipes and cold drawn steel pipes may also have uneven thickness problems due to perforation. Any factor that destroys the correctness of the geometric shape of the deformation zone formed by the roller, the piercing head and the guide plate will aggravate the uneven wall thickness of the steel pipe.
(1) Piercing heads
①The shape of the head is designed. The ideal piercing head rolling cone should be parallel to the roller outlet cone. If the piercing head is designed according to the traditional Matveyev formula, the piercing head rolling cone and the roller outlet cone are not parallel. The metal being deformed in such a gradually enlarged gap will inevitably cause insufficient rolling on tube walls and lead to uneven wall thickness of the steel pipe. The uneven thickness of the steel pipe will be more serious with the increase of the feed angle.
②Because of the insufficient rigidity of the rod, bending occurs in the perforation process. The rod can not maintain the centering position, and the wall thickness of the penetrating steel pipe is uneven.
③The piercing head is unevenly worn or damaged.
(2) Guide plates
①The guide plate distance is too great. During the perforation process, the guide plate is used to maintain the center line of the perforation. The guide plate distance is great, and the top and bottom positions of the piercing head vary greatly, which make the piercing head unstable and cause uneven wall thickness for the steel pipe.
②The uneven wear of the upper and lower guide plates will also increase the unevenness of the wall thickness.
(3) Rollers
① Roller centerline is deviated. In the production process, the screws on both sides of the piercing mill are not installed correctly, or the threads and bearings are worn, which make two rollers axially deviated, and the feed angles of the two rollers not consistent. Distortion occurs in the deformation zone and causes uneven wall thickness.
②At the large feed angle, the piercing head and the rolling cone of the roller are more not parallel.
③Improper rolling speed will also affect accuracy of wall thickness.
(4) Centering and heating of the pierced steel pipe
Improper centering holes and uneven heating will cause uneven wall thickness.
(5) The rigidity, structure and adjustment of the punching machine
The body rigidity of the piercing mill is insufficient, and the locking mechanism on it is unreliable; the centering device of the rod is not adjusted accurately; the operation is unreliable and the distance from the body is far; the adjustment of the rolling center line is generally lower than the center line. Its purpose is to improve the stability of the rolled piece. If the adjustment is too great, the relative relationship between the tools in the deformation zone will change asymmetrically after the rolling line moves down, which will also affect the uneven wall thickness of the pierced pipe.
In summary, the uneven thickness of seamless steel pipes cannot be completely avoided, and can only be minimized by strict control step by step.
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