JPH07284842A - Manufacture of welded tube - Google Patents

Abstract

PURPOSE:To reduce deviation in thickness of a welded tube by grinding welding bead and performing drawing so that the average thickness of the bead part against that of other parts is in a specific ratio. CONSTITUTION:A slit-shaped metallic plate 1 is formed into a cylinder, and the abutting part of the formed metallic plate 1 is welded. The bead 2 of the welded zone is ground so as to make the average thickness of the bead 2 part 1 to 1.1 times as thick as that of the parts other than the bead part. Then, upon performing drawing, increased thickness 3 is generated. The increased thickness 3 is influenced by the thickness before rolling and tension. As the tension at the time of drawing is small, the increased thickness becomes large; and as the thickness before drawing is large, it is more susceptible to the influence of the tension. The ratio of the increased thickness of the bead part over other parts is different depending on materials. Grinding is controlled on the inside face of the bead part; and the thickness deviation between the bead part and other parts is approximated to 0 after drawing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing wall thickness deviation between a bead portion and another portion caused by cold-draw rolling of a welded pipe.

[0002]

2. Description of the Related Art Conventionally, a seamless circular pipe having an outer diameter of 3 to 4 is used.
For products that are less than inch, a hollow billet is made using a solid billet, for example, by the Mannesmann Piasa method, and then rolled by a plug mill, mandrel mill, or semi-floating mandrel mill, and then reheated. Then, it was contracted and rolled by a reduction rolling machine (stretch reducer) to obtain circular pipe products with various outer diameters and wall thicknesses.

As this drawing rolling equipment, several to 20 or more rolling mills having two to four rolling rolls are continuously arranged in series, and the angle formed by each roll in each rolling mill is It is evenly arranged around the pipe axis so that it is 180 ° when it is two, 120 ° when it is three, and 90 ° when it is four, and it is formed by the rolls of each rolling mill. The die was configured to form a coaxial path. The rolls in the rolling mills that make up the rolling mill train are
90 rolls for a two-roll mill for adjacent mills
In the case of a three-roll rolling mill, 60 °, and in the case of a four-roll rolling mill, 45 °, that is, the angles are shifted in the plane perpendicular to the rolling direction by half the angle formed by the rolls. Further, the diameter of the circular path formed by each hole type of a plurality of rolls in each rolling mill from the first rolling mill to the final rolling mill is gradually reduced as the number of rolling stages is increased, and the diameter is reduced to a circular pipe having a predetermined pipe diameter. At this time, in order to obtain a product with a predetermined wall thickness, the roll speed is set so that tension is applied to each pipe between the rolling mills, and the wall thickness of the pipe is controlled by tension rolling. is doing.

The drawing and rolling equipment described heretofore has been generally used for reheated tubes as part of a seamless steel tube manufacturing process, but the same drawing and rolling equipment was used for cold drawing and rolling. By doing so, a circular tube with a smooth surface and high processing accuracy can be obtained. For example, in the conventional electric resistance welded pipe, a metal plate cut in a slit shape is cold formed into a cylindrical shape by, for example, a breakdown mill or a fin pass mill, and a seam is welded, and then formed into a perfect circular shape by a two-roll sizer. It was manufactured by doing, but for the pipe after welding, 2
By using the above-mentioned drawing and rolling equipment instead of the roll sizer, it is possible to manufacture circular pipes with various outside diameters and wall thicknesses by cold drawing and rolling, and the surface is smooth and processing accuracy is high. A high circular tube can be obtained.

In such cold drawing rolling,
Since the rolling reaction force becomes large as compared with the hot-drawing rolling, JP-A-3-294008 discloses a structure of a high-rigidity cold-drawing machine. In addition, since the frictional force acting between the roll surface arranged in the rolling mill and the surface of the pipe to be rolled is smaller in the cold state than in the hot-rolled rolling, stable rolling without slippage is performed. The reduction setting for this is disclosed in Japanese Patent Laid-Open No. 4-4905.

[0006]

In cold reduction rolling, since the pipe surface has a low friction coefficient, it is not possible to apply a large tension during rolling. Generally increased compared to. In a welded pipe, there is a difference in the metal structure between the bead and other parts due to the heat effect of welding.Therefore, when performing cold reduction rolling of a welded pipe, there is a difference in the amount of thickness increase due to rolling between the two. There is a problem that it will occur. FIG. 7 shows the wall thickness distribution in the vicinity of the bead portion when the welded pipe was actually subjected to 10% reduction rolling. It can be seen that there is a large thickness deviation after rolling because the increase in thickness at the bead portion is extremely small compared to other portions. That is, the difference in the amount of increase in the thickness of the bead portion and the other portion remains as the thickness deviation of the product as it is, which is a problem when aiming for highly accurate pipe making. Therefore, an object of the present invention is to provide a means for eliminating the wall thickness deviation of a pipe when manufacturing a welded pipe by cold drawing rolling.

[0007]

DISCLOSURE OF THE INVENTION According to the present invention, a slit-shaped metal plate is formed into a cylindrical shape, a butt portion of the formed metal plate is welded, the excessive bead produced is cut, and further drawn and rolled. In the method for producing a welded pipe, the bead is cut so that the ratio of the average thickness of the bead portion to the average thickness of the portion other than the bead portion is in the range of 1.0 to 1.1. It is a method for manufacturing a welded pipe.

[0008]

In order to solve the above problems, the present invention, as shown in FIG. 1, when cutting the bead portion 2 on the inner surface of the pipe after welding, the average wall thickness of the bead portion and the average wall thickness of the portion other than the bead portion are The cutting amount is controlled so that the difference in the thicknesses compensates for the difference in the amount of increase in the thickness of the bead portion and the other portion caused by the reduction rolling.

As shown in FIG. 6, for example, the average thickness increase at a portion other than the bead portion due to cold reduction rolling on a welded pipe is influenced by the wall thickness before rolling and the tension, and the tension at the time of reduction rolling decreases. The smaller the thickness, the larger the thickness increase, and the larger the thickness before the squeeze rolling, the more easily it is affected by the tension. In addition, the ratio of the amount of increase in the thickness of the bead portion to that of the other portion varies depending on the material, and for example
As shown in, various values are taken in the range from 0 to 1 near. Assuming that the average amount of increase in the thickness of the portion other than the bead portion is A and the ratio of the amount of increase in the thickness of the bead portion and the other portion is B, the amount of thickness increase by drawing rolling is A × B in the bead portion, The area becomes A, and a wall thickness deviation of A−A × B occurs between the bead portion and the portion other than the bead portion. Therefore, in the present invention, the thickness of the bead portion before reduction rolling is A-
The cutting amount on the inner surface of the bead portion was controlled so that the bead portion was thickened by A × B, and the wall thickness deviation between the bead portion and other portions was made close to 0 after the reduction rolling.

The values of A and B can be experimentally obtained according to various drawing rolling conditions and materials. However, when the present invention is carried out when the material and the rolling conditions are such that the thickness deviation between the bead portion and the other portion becomes extremely large, as shown in FIG. 2, the boundary portion between the bead portion 2 and the other portion is A fold-like flaw 4 is generated at the end. FIG. 3 collectively shows examples of carrying out the present invention under various conditions. By making the bead portion thickness before drawing rolling thicker than other portions, the thickness deviation after drawing rolling, that is, the difference between the bead portion thickness and the thickness of the portion other than the bead portion is suppressed, Thickness deviation is 10% of initial thickness
When the above occurs, a fold-like flaw has occurred. Therefore, even when the wall thickness deviation is 10% or more, the difference in the average wall thickness between the bead portion and the other portion due to the bead cutting amount control is 1.1 at the maximum, that is, up to the state where the bead portion average wall thickness is 10% thicker. It is necessary to
Up to 10% of the initial wall thickness. That is, the above A
-When AxB is within 10% of the initial wall thickness, the bead part inner surface cutting amount is controlled so that the average wall thickness of the bead part is thicker by A-AxB than other parts, and When A-AxB is 10% or more of the initial wall thickness, the bead portion inner surface cutting amount is controlled so that the average thickness of the bead portion becomes 10% thicker than other portions, so that the bending It is possible to effectively reduce the wall thickness deviation without the occurrence of indented flaws.

[0011]

[Example] A welded pipe having a diameter of 34 mm and a wall thickness of 3.5 mm, in which the wall thickness of the bead portion was controlled to be 0.128 times thicker than that of other portions, and the cutting was controlled, Drawing rolling was performed with a tension of 140 kg and a reduction amount of 10%. FIG. 4 shows the results of measuring the wall thickness in the circumferential direction before and after drawing and rolling. The difference in wall thickness increase between the bead portion and the other portion was about 0.1 mm, and a tube with a small wall thickness deviation was obtained after squeeze rolling.

[0012]

According to the present invention, it is possible to reduce the wall thickness deviation caused by the cold drawing rolling of the welded pipe.

[Brief description of drawings]

FIG. 1 is a conceptual diagram illustrating that the thickness deviation after reduction rolling is reduced by controlling the cutting amount of a bead portion according to the present invention.

FIG. 2 is a diagram showing a state of occurrence of a broken flaw.

FIG. 3 is a diagram showing a range of a difference in wall thickness between a bead portion and another portion where breakage flaws occur.

FIG. 4 is a diagram showing a wall thickness in an example.

FIG. 5 is a diagram showing that the increase in the thickness of the bead portion by drawing rolling is influenced by the material.

FIG. 6 is a diagram showing the relationship between wall thickness, tension, material before squeeze rolling and the increase in wall thickness generated by squeeze rolling.

FIG. 7 is a diagram showing an example of a situation in which a difference in wall thickness occurs in a bead portion when a welded pipe is subjected to reduction rolling.

[Explanation of symbols]

 1 Metal plate 2 Bead part 3 Thickening 4 Defect

Claims (1)

[Claims] 1. A slit-shaped metal plate is formed into a cylindrical shape,
After welding the butt portion of the formed metal plate, the excess bead produced is cut, and in the welded pipe manufacturing method of further drawing rolling, the bead is an average of parts other than the bead part of the bead part average wall thickness. Ratio to wall thickness is 1.0 ~
1. A method for manufacturing a welded pipe, which comprises cutting so as to be within a range of 1.1.