The Cause of Uneven Thickness of Seamless Steel Pipe

 Seamless steel pipe precision steel pipe finished products will have the problem of uneven thickness, but how is it produced?

The uneven thickness of seamless steel pipe is mostly generated during hot perforation:

According to the anatomical analysis of the steel pipe rolled by the automatic tube rolling machine, we believe that the uneven wall thickness of the perforated tube basically retains the distribution characteristics of the uneven wall thickness of the perforated tube, that is, the steel pipe still has a spiral wall uneven thickness after rolling, and the transverse wall uneven thickness increases significantly.

The causes of uneven wall thickness in automatic tube rolling machines are:

① The existence form and severity of the uneven wall thickness of perforated tube directly affect the existence form and severity of the uneven wall thickness of rolled steel tube.

(2) In the automatic pipe rolling machine, the wall thickness is uneven due to the bending of the top rod, so that the top head position deviates from the center of the pass, and the maximum wall thickness and minimum wall thickness positions on each cross section of the pipe and the pipe head are almost fixed; Therefore, reducing the residual curvature of the ejector rod and reducing the axial force of the ejector rod during the rolling process has a significant effect on reducing the wall thickness heterogeneity.

(3) The greater the amount of wall reduction, the more serious the uneven wall thickness of the pipe, the smaller the amount of wall reduction, the automatic tube rolling machine has the effect of reducing the uneven wall thickness of the perforated tube.

④ The pass adjustment is not correct, and when the roll seam is uneven, the uneven wall thickness of the pipe will be aggravated.

In our seamless steel pipe factory, the measured wall thickness data of Φ400mm automatic rolling pipe unit, perforation, secondary perforation (extension), automatic rolling pipe and leveling four rolling processes were carried out by Fourier transform, and the quantitative analysis of the uneven wall thickness and its formation reasons were obtained, and on this basis, the ways to improve the uneven wall thickness of steel pipe were put forward:

The uneven distribution of spiral wall thickness on the pipe after secondary perforation (extension) has been retained to the finished pipe, so improving the secondary perforation (extension) is the key link to improve the wall thickness accuracy of the finished pipe, the main measure is to improve the tool design, and improve the concentricity of the top rod and the top head in the rotation process and the rolling line.

② Improving the uneven wall thickness of the tube after perforation is an important link, the main measures are to improve the heating uniformity of the tube billet, improve the accuracy of the centering hole, lengthen the length of the top uniform strip and the length of the counter cone, and improve the concentricity of the top rod and the top head in the rotation process and the rolling line.

(3) Although the symmetric wall thickness is serious when rolling the pipe, it has a certain effect on reducing the spiral wall thickness. Therefore, when rolling the pipe, two passes should be rolled, and the waste pipe should be turned 90° between passes.

(4) The leveling process can basically eliminate the symmetrical wall thickness imbalance, but the effect on eliminating the spiral wall thickness imbalance is very small, therefore, the ability of the leveling machine should be improved.

⑤ Fourier transform is an effective means to study the uneven wall thickness during the skew rolling process, and this method can also be used to study the uneven wall thickness of other steel pipe production units.

Any factor that damages the geometry correctness of the deformation zone formed by the roll, head and guide will aggravate the uneven thickness of the pipe wall.

(1) Punch head.

① The shape design of the top, the ideal top rolling cone should be parallel to the roll exit cone, if the design of the top according to the traditional Matvikov formula, the top rolling cone and the roll exit cone are not parallel, the metal deformation in such a gradually expanding gap, is bound to cause insufficient tube wall rolling and lead to uneven tube wall thickness, and, The uneven capillary wall thickness becomes more serious with the increase of feed Angle.

(2) Because the stiffness of the ejector rod is not enough, it is bent during the perforation process, so that the ejector head can not maintain the alignment position, so that the wall thickness of the perforated capillary is uneven;

③ Uneven wear or damage of the top.

(2) Guide plate.

① The guide distance is too large, in the process of perforation is to rely on the limited role of the guide to maintain the center line of the perforation, the guide distance is large, the top change in the upper and lower position, so that the top is unstable, resulting in uneven capillary wall thickness.

The uneven wear of the upper and lower guide plates will also exacerbate the uneven wall thickness.

(3) Roll.

1 Roll center line deflection: In the production process, due to the incorrect installation of the screw on both sides of the perforator, or due to thread and bearing wear, the axial deflection between the two rolls occurs horizontally, and the feed Angle of the two rolls distorts the deformation area, resulting in uneven wall thickness.

② The large feeding Angle causes the top head to be more parallel to the rolling cone of the roll.

③ Improper roll speed will also affect the wall thickness accuracy.

(4) Centering and heating of tube billet.

Centring hole eccentricity and uneven heating will cause uneven wall thickness.

(5) Stiffness, structure and adjustment of the perforator.

The stiffness of the body of the piercing machine is not enough, and the locking mechanism on it is not reliable; The centring device of the ejector rod is not adjusted accurately, the operation is not reliable and the distance from the fuselage is too far; The adjustment of the rolling center line is generally lower than the middle line of the rolling mill, which aims to improve the stability of the rolled parts. If the adjustment is too large, the relative relationship between the tools in the deformation zone will change asymmetrically due to the rolling line moving, and the uneven wall thickness of the capillary will also be affected.

CANGZHOU GALAXY STEEL PIPE CO., LTD

 

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