JP2003340506A - Production method for seamless pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently suppress stripping failure and uneven thickness in consideration of misalignment between a core of a mandrel mill and an axial core of a pipe material during rolling. <P>SOLUTION: This mandrel mill rolls a seamless pipe with a value (F/P) of thrusting force of a bar F/pressing force of the bar P to be in the range of 0.25-0.45 at No.1-3 stands thereof. Accordingly, the occurrence of uneven thickness or stripping failure is roughly determined, and rolling is carried out with F/P on at least No.1-3 stands to be in the most adequate range in consideration of misalignment between the core of the mandrel mill and the axial core of the pipe material during rolling. Thus stripping failure and uneven thickness are effectively suppressed. <P>COPYRIGHT: (C)2004,JPO

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 a seamless pipe, and more particularly to a method for producing a seamless pipe which effectively suppresses stripping defects and uneven thickness.

[0002]

2. Description of the Related Art In mandrel mill rolling, the inner surface of the pipe adheres to the mandrel bar during rolling, the mandrel bar and the material are shrink-fitted after rolling, and stripping failure occurs in which the mandrel bar cannot be pulled out from the pipe material. There is a case. This stripping failure is more likely to occur in high alloy steels that have a larger coefficient of thermal expansion and deformation resistance than ordinary steel,
When stripping failure occurs, it is necessary to melt the pipe material and separate it from the mandrel bar.

Suppressing such stripping defects is one of the important issues for mandrel mill rolling, and various proposals have been made in the past. For example, Japanese Patent Application Laid-Open No. 5-185112 proposes that an appropriate gap is formed between the pipe material and the mandrel bar at both pipe end portions. Thus, in order to suppress stripping failure, it is effective to increase the hole-type ellipticity so that the gap between the pipe material and the mandrel bar becomes large.

However, if the ellipticity of the hole type is made too large, the lapping margin of the rolled portion between the adjacent stands becomes small and unrolled portions are generated. As a result, four locations in the circumferential direction and thick portions are formed. Will be formed. Further, if the hole-type ellipticity is too large, it is presumed that the pipe material swings during rolling of the mandrel mill, the core of the mandrel mill and the axial center of the pipe material during rolling shift, and uneven thickness is likely to occur.

Therefore, in the mandrel mill roll hole type, in order to prevent the lapping margin of the rolling section from becoming too small,
Further, the upper limit of ellipticity has been set from the viewpoint of reducing runout of the pipe material during rolling, and the lower limit of ellipticity has been set from the viewpoint of suppressing stripping defects.

Further, as a countermeasure against "a hole defect" in which a pipe material has a hole during rolling, for example, JP-A-5-50115, JP-A-8-57506, JP-A-8-276208, JP-A-2000-351006, and Open 2001-11330
Many proposals such as No. 6 have been proposed, but all of them were dealt with by changing the distribution of the wall thickness reduction amount of each stand and the ellipticity of the hole type.

[0007]

However, the above-mentioned measures against stripping defects and hole defects are all caused by the deviation of the pipe material during rolling and the deviation of the mandrel mill core from the axial center of the pipe material. However, even if the above measures are taken, uneven thickness defects may occur.

The present invention has been made in view of the above-mentioned conventional problems, and takes into consideration the deviation between the core of the mandrel mill and the axial center of the pipe material during rolling, and is effective for stripping defects and uneven thickness defects. It is an object of the present invention to provide a method for producing a seamless pipe that can be effectively suppressed.

[0009]

In order to achieve the above-mentioned object, the method for producing a seamless pipe according to the present invention is at least No. 2 of the mandrel mill for producing the seamless pipe. 1 to N
o. Rolling is performed so that a value (P / F) obtained by dividing the bar rolling force P in the three stands by the bar thrust force F is in the range of 0.25 or more and 0.45 or less. By doing so, it becomes possible to effectively suppress stripping defects and uneven thickness defects.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the case of a mandrel mill that rolls with two rolls, the rolling force is 90 ° with respect to the rolling direction restraining force.
If the constraining force in the shifted thrust direction is weak, the pipe material 1 and the mandrel bar 2 during rolling tend to shift in the thrust direction (see FIG. 1). As a result, it is considered that the core of the mandrel mill and the axial center of the pipe material during rolling are misaligned or wobbled, resulting in uneven thickness. In addition, 3 in FIG. 1 shows a mandrel mill roll.

On the other hand, when the restraining force in the thrust direction is too strong with respect to the restraining force in the rolling direction, the pipe material 1 is likely to adhere to the mandrel bar 2 and stripping failure is likely to occur.

Therefore, the inventors of the present invention have determined that the number of mandrel mills whose number of occurrences of uneven thickness and stripping defects is generally determined by numerical calculation using the approximate three-dimensional finite element method. 1-No. As a result of calculating the P / F of the three stands, for example, an analysis result as shown in FIG. 2 was obtained, it is considered that uneven thickness and stripping failure can be predicted depending on the size of the F / P. A rolling experiment was conducted to find a range of F / P that can effectively suppress uneven thickness and stripping defects. In addition, FIG. The result in two stands is shown.

Numerical calculation using the approximate three-dimensional finite element method is performed by replacing each stage of rolling by tube rolling with compression in a generalized plane strain state by a die, and analyzing by generalized plane. By applying the strain analysis, considering that the shear strain in the rolling direction becomes relatively large, the analysis was performed by the method that handles the shear strain rate in the rolling direction.

As the conditions used for the numerical calculation using the approximate three-dimensional finite element method, the outer diameter of the pipe material at the inlet of the mandrel mill is 130 to 500 mm, and the wall thickness is 13 to 6.
0 mm, the outer diameter of the pipe material at the mandrel mill outlet is 10
0-450 mm, wall thickness 3-50 mm, mandrel bar outer diameter 65-435 mm. Under these calculation conditions, mandrel mill inlet dimensions, outlet dimensions, mandrel mill roll hole ellipticity ψ (= A / B: Refer to Fig. 3), the thickness reduction amount of each stand is changed, and about 100 kinds of numerical calculations are performed to calculate each F / P, and based on the result, the F / P is calculated.
The optimal range and the approximate expression of were derived.

According to the experiments and calculation results of the present inventors,
As shown in FIG. 5, F / P is 0.45 when 0.25 or more.
It has been found that both uneven thickness and stripping defects can be effectively suppressed when the following range is satisfied, and more preferably 0.3 to 0.4 is satisfied.

Further, as shown in FIG. 4, the F / P is a wall thickness reduction amount dt / t (No. 1 stand: (wall thickness-N
o. 1 stand groove bottom wall thickness) / wall thickness, No. Other than 1 stand: (front stand groove bottom wall thickness-corresponding stand groove bottom wall thickness) / previous stand groove bottom wall thickness) and ellipticity ψ can be expressed as a function of these wall thickness reduction amounts dt / t and ellipticity. ψ
It has also been found that it can be approximated linearly by using

[0017]

## EQU1 ## F / P = f (dt / t, ψ) = A + B × (dt / t) + C × (ψ−1) However, A: 0.3 to 0.5 B: 0.1 to 0.2 C: -0.1 to -1.0

The method for producing a seamless pipe according to the present invention is based on the above-mentioned findings of the present inventors, and is at least No. 2 of the mandrel mill for producing a seamless pipe. 1-No. P / F in 3 stands is 0.2
Rolling is performed so as to fall within a range of 5 or more and 0.45 or less, and the P / F is obtained as a function of the wall thickness reduction amount dt / t and the ellipticity ψ.

In the method for producing a seamless pipe according to the present invention, at least No. 1 in the mandrel mill, which determines whether or not uneven thickness or stripping defects occur, is determined. 1 to N
o. The three-stand P / F is rolled in the optimum range in consideration of the misalignment between the core of the mandrel mill and the axial center of the pipe material during rolling, so that stripping defects and uneven thickness defects are effective. Can be suppressed to.

In the method for producing a seamless pipe according to the present invention, at least No. 1 in the mandrel mill is used. 1 to N
o. The reason that the P / F of the three stands is set in the range of 0.25 or more and 0.45 or less is based on the experiments and calculation results of the present inventors. That is, P / F is the wall thickness reduction amount dt /
As shown in FIG. 5, which is an example obtained as a function of t and ellipticity ψ, when P / F is 0.45 or less, there is a case where the stripping force is high. Is not reached (see Fig. 5 (a)), and P / F
This is because when the value is 0.25 or more, uneven thickness of 15% or more did not occur (see FIG. 5 (b)).

[0021]

EXAMPLES The results of experiments carried out to confirm the effects of the method for producing a seamless pipe according to the present invention will be described below.
The present inventors carried out rolling experiments based on the above calculation results,
It was confirmed whether the above F / P range was appropriate.

The equipment used for the experiment was a five-stand mandrel mill. The outer diameter of the pipe material at the mandrel mill inlet was 335 mm, the wall thickness was 28 mm, the outer diameter of the pipe material at the mandrel mill outlet was 276 mm, the wall thickness was 13 mm, and the mandrel was used. The outer diameter of the bar used is 250 mm. 1
~ No. Experiments were performed by changing the wall thickness reduction rate and the hole type ellipticity of each stand of No. 3, and judged the uneven thickness rate and the stripping property.

The results are shown in Table 1 below. In Table 1, among the uneven thickness ratios, ⊚ indicates that the uneven thickness ratio is 10% or less, ○ indicates that the uneven thickness ratio is 10 to 15%, and × indicates that the uneven thickness ratio is 15% or more. Show. Further, among the stripping properties in Table 1, the symbol ⊚ indicates good one, the symbol ◯ indicates that stripping failure does not occur, but the current value is high, and the symbol x indicates that one or more stripping failures occur.

[0024]

[Table 1]

As is clear from Table 1 above, the mandrel mill No. 1-No. P / F in 3 stands
When rolled in the range of 0.25 or more and 0.45 or less (N
o. 1, 4, 5, 8, 9, 14 to 16), none of them had an uneven thickness ratio of 15% or more and one or more stripping defects occurred.

In particular, the mandrel mill No. 1-No. Three
When the P / F in the stand is rolled in the range of 0.3 or more and 0.4 or less (No. 1), the uneven thickness ratio is 10%.
Below, the stripping property was also good.

On the other hand, the mandrel mill No. 1-No.
At least one P / F in the three stands
When rolled in a range of less than 0.25 or more than 0.45 (No. 2, 3, 6, 7, 10 to 13, 17), the uneven thickness ratio is 15% or more, or , One or more stripping defects occurred.

[0028]

As described above, in the method for manufacturing a seamless pipe according to the present invention, at least No. 2 in the mandrel mill, which determines whether or not uneven thickness or stripping defects occur, is generally determined. 1-No. The 3-stand P / F is rolled in the optimum range in consideration of the deviation between the core of the mandrel mill and the axis of the pipe during rolling, so that stripping defects and uneven thickness defects are effectively suppressed. become able to. By the way, when the present invention is applied to all the stands of the mandrel mill, the defective thickness is 0.4% to 0.
It is halved to 2%, and stripping failure is 0.02%
To 0.005% or less.

[Brief description of drawings]

FIG. 1 is a diagram showing an image of uneven thickness generation in a mandrel mill stand.

Fig. 2 Definitions of bar rolling force and bar thrust force, and No. 1 of mandrel mill. It is the figure which showed the analysis result of 2 stands.

FIG. 3 is a diagram illustrating the definition of hole ellipticity.

FIG. 4 is a diagram showing a correlation between a hole ellipticity, a wall thickness reduction rate, and F / P.

FIG. 5 (a) is a No. 1 in a mandrel mill in order to evaluate the stripping property. 1-No. Of the three stands, F / P = 0.474 + 0.16 (dt / t)
Dt of the stand where -0.63 (ψ-1) is the largest
/ T and ψ-1 are plotted in the figure, (b) is a No. in the mandrel mill in order to see the evaluation of uneven thickness. 1 to
No. F / P = 0.474 + 0.1 out of 3 stands
It is the figure which plotted dt / t and the example of (psi) -1 of the stand with which 6 (dt / t) -0.63 ((psi) -1) becomes the smallest.

[Explanation of symbols]

1 pipe material 2 Mandrel bar 3 Mandrel mill roll

[Procedure amendment]

[Submission date] November 5, 2002 (2002.11.
5)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

[0009]

In order to achieve the above-mentioned object, the method for producing a seamless pipe according to the present invention is at least No. 2 of the mandrel mill for producing the seamless pipe. 1 to N
o. Bar thrust force F in 3 stands
The rolling is performed so that the value ( F / P ) divided by P falls within the range of 0.25 or more and 0.45 or less. By doing so, it becomes possible to effectively suppress stripping defects and uneven thickness defects.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

Therefore, the inventors of the present invention have determined that the number of mandrel mills whose number of occurrences of uneven thickness and stripping defects is generally determined by numerical calculation using the approximate three-dimensional finite element method. 1-No. As a result of calculating the F / P of the three stands, for example, an analysis result as shown in FIG. 2 was obtained, it is considered that unevenness of thickness and stripping failure can be predicted by the magnitude of this F / P, A rolling experiment was conducted to find a range of F / P that can effectively suppress uneven thickness and stripping defects. In addition, FIG. The result in two stands is shown.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

The method for producing a seamless pipe according to the present invention is based on the above-mentioned findings of the present inventors, and is at least No. 2 of the mandrel mill for producing a seamless pipe. 1-No. F / P in 3 stands is 0.2
The rolling is performed so as to be in a range of 5 or more and 0.45 or less, and the F / P is obtained as a function of the wall thickness reduction amount dt / t and the ellipticity ψ.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction content]

In the method for producing a seamless pipe according to the present invention, at least No. 1 in the mandrel mill, which determines whether or not uneven thickness or stripping defects occur, is determined. 1 to N
o. The F / P of 3 stands is rolled in the optimum range in consideration of the deviation between the core of the mandrel mill and the axial center of the pipe material during rolling, so that stripping defects and uneven thickness defects are effective. Can be suppressed to.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

In the method for producing a seamless pipe according to the present invention, at least No. 1 in the mandrel mill is used. 1 to N
o. The reason that the F / P of the three stands is in the range of 0.25 or more and 0.45 or less is based on the experiments and calculation results of the present inventors. That is, F / P is the wall thickness reduction amount dt /
As shown in FIG. 5, which is an example obtained as a function of t and ellipticity ψ, when F / P is 0.45 or less, there is a case where the stripping force is high. Is not reached (see FIG. 5 (a)), and F / P
This is because when the value is 0.25 or more, uneven thickness of 15% or more did not occur (see FIG. 5 (b)).

[Procedure Amendment 7]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction content]

As is clear from Table 1 above, the mandrel mill No. 1-No. F / P in 3 stands
When rolled in the range of 0.25 or more and 0.45 or less (N
o. 1, 4, 5, 8, 9, 14 to 16), none of them had an uneven thickness ratio of 15% or more and one or more stripping defects occurred.

[Procedure Amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

In particular, the mandrel mill No. 1-No. Three
When F / P in the stand is rolled in the range of 0.3 or more and 0.4 or less (No. 1), the uneven thickness ratio is 10%.
Below, the stripping property was also good.

[Procedure Amendment 9]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

On the other hand, the mandrel mill No. 1-No.
At least one of F / P in the three stands is
When rolled in a range of less than 0.25 or more than 0.45 (No. 2, 3, 6, 7, 10 to 13, 17), the uneven thickness ratio is 15% or more, or , One or more stripping defects occurred.

[Procedure Amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction content]

[0028]

As described above, in the method for manufacturing a seamless pipe according to the present invention, at least No. 2 in the mandrel mill, which determines whether or not uneven thickness or stripping defects occur, is generally determined. 1-No. The F / P of 3 stands is rolled in the optimum range in consideration of the deviation between the core of the mandrel mill and the axial center of the pipe material during rolling, so that stripping defects and uneven thickness defects are effectively suppressed. become able to. By the way, when the present invention is applied to all the stands of the mandrel mill, the defective thickness is 0.4% to 0.
It is halved to 2%, and stripping failure is 0.02%
To 0.005% or less.

Claims (2)

[Claims] 1. A mandrel mill for producing a seamless pipe,
At least No. 1-No. The value (P / F) obtained by dividing the bar pressing force P in the three stands by the bar thrust force F is
A method for producing a seamless pipe, which comprises rolling in a range of 0.25 or more and 0.45 or less. 2. The method for producing a seamless pipe according to claim 1, wherein the P / F is obtained as a function of the wall thickness reduction amount dt / t and the ellipticity ψ. However, No. Wall thickness reduction amount of 1 stand dt / t = (wall thickness of base tube-No. 1 stand groove bottom wall thickness) / wall thickness No. 1 Wall thickness reductions other than one stand dt / t = (pre-stage stand groove bottom wall thickness-the relevant stand groove bottom wall thickness) / pre-stage stand groove bottom wall thickness)