Reason for the eccentricity (uneven thickness) of the hot-rolled seamless steel pipe
Eccentric steel pipes are the easiest to produce during the production of hot-rolled steel pipes, and most of the links are produced during hot piercing:
According to the anatomical analysis of the steel pipe after the automatic rolling mill, we believe that after the pierced capillary is rolled by the automatic rolling mill, the uneven wall thickness of the steel pipe in the vertical and horizontal directions basically retains the distribution characteristics of the uneven wall thickness of the perforated capillary. That is, the steel pipe still has spiral wall thickness unevenness after rolling, and the lateral wall thickness unevenness increases significantly.
The reasons for the uneven wall thickness of the automatic rolling mill are:
① The existence form and severity of uneven wall thickness of perforated capillary tube directly affects the existence form and severity of uneven wall thickness of 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 head is deviated from the center of the pass, resulting in uneven wall thickness. The positions of the maximum wall thickness and minimum wall thickness on each cross section of the pipe and the pipe head are almost fixed No change; while the unevenness of the wall thickness from the end of the tube to the tube head gradually increases. Therefore, reducing the residual curvature of the ejector rod and reducing the axial force of the ejector rod during tube rolling has a significant effect on reducing the unevenness of the wall thickness. effect.
③The greater the amount of wall reduction, the more serious the uneven wall thickness of the waste pipe. When the amount of wall reduction is small, the automatic rolling mill has the effect of reducing the uneven wall thickness of the perforated capillary. ④ 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. To
Our seamless steel pipe factory performed Fourier transform on the measured wall thickness data of the Φ400mm automatic tube rolling mill, piercing, secondary piercing (extension), automatic tube rolling and leveling, and obtained the uneven wall thickness. Based on the quantitative analysis and the reasons for its formation, a way to improve the uneven wall thickness of steel pipes is proposed:
① After the secondary perforation (extension), the uneven distribution of the spiral wall thickness on the waste pipe remains until the finished pipe. Therefore, improving the secondary perforation (extension) is the key link to improve the accuracy of the finished pipe wall thickness. The tool design improves the concentricity of the ejector pin and the ejector head with the rolling line during the rotation process.
②Improving the uneven wall thickness of the capillary tube after perforation is an important link. 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 entire belt and the length of the reverse cone, and increase the distance between the ejector rod and the ejector head. Concentricity with the rolling line during rotation.
③ Although serious symmetrical wall thickness unevenness occurs during tube rolling, it does not have a certain effect on reducing the spiral wall thickness. Therefore, two passes should be rolled when rolling the tube, and the waste tube should be turned 90° between passes.
④ The leveling process can basically eliminate symmetrical wall thickness unevenness, but has little effect on eliminating spiral wall thickness unevenness. Therefore, the ability of the leveling machine should be improved.
⑤ Fourier transform is an effective method to study the uneven wall thickness in the cross-rolling process. This method can also be used to study the uneven wall thickness of other steel pipe production units.
The picture above shows the perforation site of seamless steel pipes. Many steel pipes have eccentricity at this time, so it is very important to strictly control this perforation link.