Causes of eccentricity of seamless steel pipes

Causes of eccentricity (uneven thickness) of seamless steel pipes :

The finished product of seamless steel pipe precision steel pipe will have the problem of uneven thickness of eccentricity, but how does it happen? Many people don't understand. Today, let's talk about how the eccentricity of seamless steel pipes such as cold-drawn steel pipes, cold-rolled steel pipes, and hot-rolled steel pipes is generated. Why is the concentricity of seamless steel pipes not so ideal?

Eccentric steel pipes are most likely to occur in the production process of hot-rolled steel pipes, and most of the generated links are generated during hot piercing:
 

According to the anatomical analysis of the steel pipe rolled by the automatic pipe rolling mill, we believe that after the perforated capillary tube is rolled by the automatic pipe rolling mill, the form of uneven wall thickness in the longitudinal and lateral directions of the steel pipe basically retains the distribution characteristics of the uneven wall thickness of the perforated capillary tube. That is, after rolling, the steel pipe still has helical wall thickness unevenness, and the lateral wall thickness unevenness increases significantly.

The reasons for the uneven wall thickness of automatic pipe rolling mills are:

①The existence form and severity of the uneven wall thickness of the perforated capillary directly affect the existence form and severity of the uneven wall thickness of the steel pipe after rolling.

②When the pipe is rolled on the automatic pipe rolling mill, due to the bending of the ejector rod, the position of the plug head deviates from the center of the pass, resulting in uneven wall thickness. The unevenness of the wall thickness from the end of the tube to the head of the tube increases gradually. Therefore, reducing the residual curvature of the ejector pin and reducing the axial force of the ejector pin during tube rolling have a significant effect on reducing the unevenness of the wall thickness. .

③The greater the wall reduction, the more serious the uneven wall thickness of the barren pipe. When the wall reduction is small, the automatic pipe rolling machine has the effect of reducing the uneven wall thickness of the perforated capillary. 
④ If the hole type is not adjusted correctly, when the roll gap is not parallel, the uneven wall thickness of the waste pipe will be aggravated.

We carried out Fourier transform on the measured wall thickness data of the 400mm automatic tube rolling unit, piercing, secondary piercing (extension), automatic tube rolling and uniform rolling, and obtained the quantitative analysis and analysis of uneven wall thickness. The reasons for its formation, and based on this, put forward ways to improve the uneven wall thickness of steel pipes:

①After the secondary perforation (extension), the uneven distribution of the spiral wall thickness on the waste pipe is retained until the finished pipe. Therefore, 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 Tool design to improve the concentricity of the mandrel and head to the pass line during rotation.

②It is an important link to improve the uneven wall thickness of the capillary after perforation. The main measures are to improve the heating uniformity of the tube blank, improve the accuracy of the centering hole, lengthen the length of the uniform belt of the plug and the length of the reverse cone, and improve the distance between the ejector rod and the plug. Concentricity to the pass line during rotation.

③Although serious symmetrical uneven wall thickness will occur during tube rolling, it has a certain effect on reducing the spiral wall thickness unevenness. Therefore, when rolling the tube, two passes should be rolled, and the waste tube should be turned 90°between passes.
④ The leveling process can basically eliminate the uneven wall thickness of symmetry, but it has little effect on eliminating the uneven thickness of the spiral shape. Therefore, the ability of the leveling machine should be improved.

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