Causes of eccentricity of seamless steel pipe
The finished products of seamless steel pipe and precision steel pipe will have the problem of uneven eccentric thickness, but how does it happen? Many people don’t understand. Today we will talk about how the eccentricity of seamless steel pipes such as cold drawn steel pipe, cold rolled steel pipe and hot rolled steel pipe is generated, and why the concentricity of seamless steel pipe is not so ideal?
The figure above shows us measuring the thickness of steel pipe.
The figure above shows the finish rolled steel pipe produced by our company. If you look carefully, you can still see a little eccentricity.
The figure above shows that seamless steel pipes produced by other steel pipe plants have obvious eccentricity and out of roundness.
Eccentric steel pipe is most likely to occur in the production process of hot rolled steel pipe, and most of the links are generated during hot piercing:
According to the anatomical analysis of the steel pipe after rolling by the automatic pipe mill, we believe that the form of uneven vertical and horizontal wall thickness of the steel pipe after rolling by the automatic pipe mill basically retains the distribution characteristics of uneven wall thickness of the perforated pipe, that is, the steel pipe still has spiral uneven wall thickness after rolling, and the horizontal uneven wall thickness increases significantly.
The reasons for uneven wall thickness of automatic pipe rolling mill are:
- ① The existing form and severity of uneven wall thickness of perforated capillary pipe directly affect the existing form and severity of uneven wall thickness of steel pipe after rolling.
- ② When rolling a pipe on an automatic pipe mill, due to the bending of the ejector rod, the position of the ejector head deviates from the center of the pass, resulting in uneven wall thickness, and the positions of the maximum wall thickness and the minimum wall thickness on each cross section of the pipe and the pipe head are almost fixed; The uneven degree of wall thickness from pipe tail to pipe head gradually increases. Therefore, reducing the residual bending of ejector rod and reducing the axial force of ejector rod during pipe rolling plays a significant role in reducing the uneven degree of wall thickness.
- ③ The greater the wall reduction, the more serious the uneven wall thickness of the raw pipe. When the wall reduction is small, the automatic pipe mill can reduce the uneven wall thickness of the perforated capillary pipe.
- ④ Incorrect pass adjustment will aggravate the uneven wall thickness of the waste pipe when the roll gap is not parallel.
Our seamless steel pipe factory is right Φ. The measured wall thickness data of raw pipe in four rolling processes of 400mm automatic pipe rolling mill, perforation, secondary perforation (extension), automatic pipe rolling and leveling are Fourier transformed, the quantitative analysis of wall thickness unevenness and its causes are obtained, and on this basis, the ways to improve the wall thickness unevenness of steel pipe are put forward:
- ① After the secondary perforation (extension), the uneven distribution characteristics of spiral wall thickness on the raw pipe are 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 the tool design and improve the concentricity of the ejector rod and head with the rolling line during the rotation process.
- ② It is an important link to improve the uneven wall thickness of the perforated rough pipe. The main measures are to improve the heating uniformity of the pipe blank, improve the accuracy of the centering hole, lengthen the length of the whole belt and the length of the reverse cone of the plug, and improve the concentricity between the ejector rod and the plug and the rolling line during the rotation process.
- ③ Although serious symmetrical wall thickness unevenness will occur during pipe rolling, it plays a certain role in reducing the spiral wall thickness unevenness. Therefore, during pipe rolling, two passes shall be rolled, and the raw pipe shall be turned 90 ° between passes.
- ④ The homogenization process can basically eliminate the symmetrical wall thickness unevenness, but it has little effect on eliminating the spiral wall thickness unevenness. Therefore, the ability of the homogenization machine should be improved.
- ⑤ Fourier transform is an effective method to study the wall thickness unevenness in cross rolling process. This method can also be used to study the wall thickness unevenness of other steel pipe production units.
The figure above shows the site of seamless steel pipe perforation. The eccentricity of many steel pipes is caused at this time, so it is very important to strictly control this perforation link.
Eccentricity of finish rolled steel pipe and cold drawn steel pipe will also occur due to perforation:
Any factor that destroys the geometric correctness of the deformation zone formed by roll, plug and guide plate will aggravate the uneven thickness of capillary wall.
- ① For the shape design of the plug, the ideal plug rolling cone should be parallel to the outlet cone of the roll. If the plug is designed according to the traditional Matveyev formula, the rolling cone of the plug is not parallel to the outlet cone of the roll. If the metal deforms in such a gradually expanding gap, it is bound to cause insufficient rolling of the pipe wall and uneven wall thickness of the capillary pipe, With the increase of feed angle, the uneven wall thickness of capillary becomes more serious;
- ② Due to the insufficient stiffness of the ejector rod, bending occurs in the perforation process, so that the ejector head can not maintain the centering position, resulting in uneven wall thickness of the perforated capillary;
- ③ Uneven wear or damage of the plug.
(2) Guide plate.
- ① If the guide plate distance is too large, it depends on the limiting effect of the guide plate to maintain the perforation center line in the perforation process. If the guide plate distance is large, the top position changes greatly, which makes the top unstable and leads to uneven capillary wall thickness.
- ② The uneven wear of the upper and lower guide plates will also aggravate the uneven degree of wall thickness.
- ① Deflection of roll centerline: in the production process, due to the incorrect installation of the screws pressed on both sides of the piercer, or the horizontal deflection between the two rolls due to the wear of threads and bearings, the feeding angles of the two rolls are inconsistent, resulting in the distortion of the deformation area, resulting in uneven wall thickness.
- ② Under large feed angle, the plug is not 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 blank.
Eccentric centering hole and uneven heating (internal and external surfaces) will cause uneven wall thickness.
(5) Rigidity, structure and adjustment of piercer.
The rigidity of the piercer body is not enough, and the locking mechanism on it is unreliable; The centering device of the ejector rod is not adjusted accurately, the operation is unreliable and far from the fuselage; The adjustment of the rolling center line is generally lower than the center line of the rolling mill, which aims to improve the stability of the rolled piece. If the adjustment is too large, the relative relationship between tools in the deformation area will change asymmetrically after the rolling line moves down, which will also affect the uneven wall thickness of the capillary.
To sum up, there is no way to completely avoid the uneven eccentric thickness of seamless steel pipe, which can only be strictly controlled step by step and minimized. If you have any ideas about our analysis, please leave us a message for discussion.
Source: Network Arrangement – China Seamless Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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