JPH07303907A - Production of electric resistance welded steel tube excellent in roundness - Google Patents

Abstract

PURPOSE:To manufacture a steel tube having high roundness over the entire length by dividing sizer rolls of the final stand into four in the circumferential direction of pipe and executing drawing by changing the ratio of the base diameters of upper and lower to right and left rolls in accordance with the ratio of the strength of the electric resistance weld zone to the strength of the base material part. CONSTITUTION:By making the roll into four rolls (upper/lower rolls and side rolls) so that drawing in the peripheral direction of the steel tube is uniform and changing the base diameter ratio (Dtb/Ds) of the upper and lower rolls to the side rolls according to the strength of the electric resistance weld zone and base material, the deformation of tube ends after forming is prevented. When drawing/forming are executed with the rolls having an equal diameter in the case that the strength of the electric resistance weld zone is high, the deformation at the tube end shows an ellipse taking the axis which passes through the electric resistance weld zone as a major axis. At this time, by making the base diameters Dtb of the upper and lower rolls smaller than the base diameters Ds of the side rolls, it is possible to offset this elliptic deformation, so the deformation at the tube end is prevented. In this way, the electric resistance welded steel tube excellent in the roundness of the tubular body and also in the roundness in a part where the steel tube is cut is manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electric resistance welded steel pipe having an excellent roundness, and more particularly to an electric resistance welded steel pipe having an excellent roundness of a tubular body and a roundness of a cut portion of the steel pipe. The present invention relates to a manufacturing method.

[0002]

2. Description of the Related Art A conventional electric resistance welded steel pipe is formed by continuously forming a strip steel into a cylindrical shape by a roll having a hole shape, performing electric resistance welding, and then using a plurality of drawing stands arranged for a fixed shape. We are molding a shape close to a circle. For example, Japanese Patent Laid-Open No. 64-2
As disclosed in Japanese Patent Publication No. 709, the conventional method is to draw with two rolls to form a hole-shaped molding close to a perfect circle, and the front stage of a pair of upper and lower two roll stands. Has a horizontal side roll whose roll axis angle is 90 ° different from that of the stand.
It is common to arrange the reels and perform several stages of draw forming.

In the conventional forming method as described above, the strain history applied to the steel pipe is controlled by setting the position of the side roll before the final draw forming, so that the roundness of the pipe end is made to be close to that of the pipe body. It is necessary to carry out molding.

However, in the case of a thin-walled, high-strength steel pipe, for example, a pipe having a t / D (t: wall thickness, D: outer diameter) of 3% or less, such as a steel pipe for a propeller shaft of an automobile, the roundness of the tubular body is small. However, even if it is good, the cut portion may show an elliptical shape and the roundness may deteriorate, which is difficult to prevent with the above-mentioned two roll stand.

In the conventional two-roll stand in the conventional forming method, the strain history applied to the steel pipe is controlled by setting the position of the side roll before the final draw forming, so that the roundness of the pipe end is a perfect circle close to that of the pipe body. It is necessary to carry out molding so that it can be repeated. However, with this method, it is necessary to change various conditions such as changing the side roll setting and the hole type in the previous stage according to the material strength such as the difference between the seam and the base material and t / D, and stable operation is difficult. .

Further, in Japanese Unexamined Patent Publication No. 5-285508, when the material is homogeneous, a draw ratio of 0.05 to 0.5% is used.
It is said that the pipe end can be prevented from being deformed by performing the fixed shape by dividing the roll.However, if there is a difference in the strength between the seam and the base metal, the pipe end will be deformed due to the influence of the difference in strength and the pipe will be completely deformed. Edge deformation cannot be removed.

[0007]

SUMMARY OF THE INVENTION The present invention provides a method for easily manufacturing a thin electric resistance welded steel pipe having a high roundness at both the pipe end and the pipe body, which has been difficult to achieve by the conventional methods. It is intended.

[0008]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made a detailed analysis of the molding of the sizer to solve the above-mentioned problems, and as a result, increase the roundness of the pipe end of the steel pipe with a steel pipe having a small t / D. The reason why it is not possible is that, in the forming in which the steel pipe after welding is drawn and shaped using two rolls, the bending / bending back deformation in the pipe axial direction and the deformation due to the circumferential compression are different in the pipe circumferential direction. I found a thing.

Moreover, the cause is that the number of roll divisions is 2 rolls.
In addition, in the case where the material strength of the pipes differs in the circumferential direction, the deterioration of the roundness of the pipe end is more remarkable. By locally higher or lower than the part,
It was found that when the plastic deformation is difficult or easy, the pipe end deformation becomes remarkable.

On the other hand, as a result of studying various methods to solve the above problems, the present inventors found that at least the roll of the stand at the final stage was divided into four in the circumferential direction of the pipe in the sizer process. For example, it is possible to improve the roundness of the pipe body and the pipe end, and to change the roll bottom diameter ratio of the upper and lower sides and the left and right sides according to the ratio of the strength of the electric resistance portion and the strength of the base material portion. The present invention has been completed by finding that the roundness of the tube body and the tube end is further improved.

That is, the gist of the present invention is that
In a method of continuously rolling a strip steel to produce an electric resistance welded steel pipe, at least a roll of a stand portion at the final stage is divided into four in the circumferential direction of the pipe in a sizer process for adjusting the size and shape of the electric resistance welded pipe. A method for producing an electric resistance welded steel pipe having an excellent roundness, which is characterized in that the ratio of the bottom diameters of the upper and lower rolls and the left and right rolls is changed according to the strength ratio of the strength and the strength of the base material to perform draw forming.

Hereinafter, the present invention will be described in detail with reference to embodiments of the present invention. At the final stage of the sizer molding, as shown in Fig. 1, roll the steel pipe 1 so that the circumferential drawing is uniform.
Individual (upper and lower rolls 5a, 5b and side rolls 5c, 5
d) and the bottom diameter ratio of the upper and lower rolls (5a, 5b) and side rolls (5c, 5d) according to the strength of the electric resistance welded part and the base metal.
By changing (D _tb / D _s ), it becomes possible to prevent deformation of the tube end after molding.

When the strength of the electric resistance welded portion is high as shown in FIG. 2, the pipe end deformation shows an ellipse whose major axis is the axis passing through the electric resistance welded portion when the draw forming is performed by the equal diameter roll. At this time, the bottom diameter D _tb of the upper and lower rolls (5a, 5b) is set to the side roll (5c,
By making it smaller than the bottom diameter D _{s of} 5d), it becomes possible to cancel this elliptical deformation, and therefore it becomes possible to prevent the pipe end deformation.

FIG. 2 shows the effect of changing the diameter of the roll when the strength of the base metal is 500 MPa and the strength of the electric resistance portion is 100 MPa higher than the strength of the base metal, but the roll diameter D of the upper and lower rolls is shown. _{For tb} , the bottom diameter D _s of the side roll is, for example, 0.65 times (D
_tb / D _s = 0.65) With, it can be seen that the deformation is the production of high roundness steel pipe over the entire length without becomes possible.

On the contrary, when the strength of the electric resistance portion is lower than that of the base material portion, D _tb may be made larger than D _s . Further, when the strength of the electric resistance welded portion is higher than that of the base material portion, it is preferable to decrease the D _tb / D _s ratio as the strength increases.

In the sizer roll of the present invention, not only the diameter of the roll for forming the seam portion is changed, but also the upper and lower sides and the left and right sides are made symmetrical as a pair. This is to prevent bending and the like due to deformation.

FIG. 3 shows an example of the construction of a concrete pipe forming apparatus. In the figure, 1 is a steel pipe, 2 is a squeeze roll for welding.
3 is a vertical (side) roll and 4 is a horizontal roll. After arranging a plurality of horizontal and vertical sizer stands, different diameter 4 rolls sizer roll 5
Is set as the final standard process.

[0018]

EXAMPLE As an example of the present invention, the outer diameter D = 75.0
When manufacturing a thin electric resistance welded steel pipe with a wall thickness of t = 1.6 mm (t / D = 2.1%) in (mm), the strength of the base material is 500
In the case of MPa and the strength of the electric resistance welded portion is 600 MPa, the final stage of the sizer is the method of the present invention and the conventional two-roll method.
The roll methods were compared. FIG. 4 shows the roundness measurement results of the pipe end portion when the final stage drawing amount was 0.2%. Figure 4
Is the conventional 2-roll method, isometric 4-roll (D _tb / D _s =
1.0), different diameter 4 rolls according to the present invention (D _tb / D _s =
The pipe end shape of the pipe of 0.65) is shown.

In the method of the present invention, the influence of the high strength of the welded portion is canceled out, and it is clear that the pipe end deformation does not occur with almost the same roundness as the pipe body. On the other hand, in the 2-roll method, the horizontal deformation is remarkable, and in the equal-diameter 4-roll method, an ellipse whose major axis is the axis passing through the electric resistance welded portion is used. Turns out to be significantly inferior.

Further, the present invention may be incorporated into the final stage of an existing sizer or the sizer of the final stage may be changed, and both of them can produce a thin electric resistance welded steel pipe with improved pipe end deformation. Further, the roll may be non-driving or may be a driving system, and either one may be selected according to the cost and the apparatus type up to the preceding stage.

[0021]

The method of the present invention is applicable to thin-wall ERW steel pipes,
It is possible to easily manufacture a steel pipe having a high roundness over the entire length, and it is possible to bring industrially beneficial effects.

[Brief description of drawings]

FIG. 1 is a block diagram of a roll used in the present invention.

FIG. 2 is a diagram showing a relationship between a sizer roll diameter ratio of the present invention and roundness of a pipe end.

FIG. 3 is a configuration diagram of a pipe forming apparatus.

FIG. 4 is a comparison diagram of roundness shapes of steel pipes formed by the conventional 2 rolls and the 4 rolls of the present invention.

[Explanation of symbols]

 1 Steel Pipe 2 SQ Roll for Welding 3 Vertical (Side Roll) 4 Horizontal (Upper and Lower Roll) 5 4 Roll of the Present Invention 5a Upper Roll 5b Lower Roll 5c, 5d Side Roll

Claims (1)

[Claims] 1. A method for producing an electric resistance welded steel pipe by continuously rolling a strip steel, wherein at least a roll of a stand at a final stage is divided into four in a pipe circumferential direction in a sizer process for adjusting a size and a shape. , ERW steel pipe with excellent roundness, characterized in that the ratio of the bottom diameters of the upper and lower rolls and the left and right rolls is changed according to the ratio of the strength of the electric resistance welded portion to the strength of the base metal portion, and draw forming is performed. Manufacturing method.