JP2000094007A - Rolling method of metal tube - Google Patents

Abstract

(57) [Summary] [Problem] The roll phase of each stand can be appropriately set during drawing rolling by a three-roll tandem rolling mill, and the hexagonal inner surface can be reliably prevented, and the occurrence of flaws on the outer surface of the product can also be prevented. Provided is a method for drawing and rolling a metal tube. SOLUTION: The following conditions (1) are set for first to eighth stands.
And rolling (2). (1) Each stand has a different roll phase φ. (2) Roll phase difference Δ between stands
There are two types of φ, the first type is 60 °, the second type is 30 °, 45 °,
It is either 75 ° or 90 °, and the first type and the second type are alternately repeated sequentially from the first stand.

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 and rolling metal pipes, and more particularly to a metal capable of reliably reducing hexagonal tightening of an inner surface caused by reducing rolling by a three-roll tandem rolling mill and preventing occurrence of outer surface flaws. The present invention relates to a method of drawing and rolling a pipe.

[0002]

2. Description of the Related Art Generally, an n-roll type tandem rolling mill is used for drawing rolling for finishing a metal tube having a small diameter to a product outer diameter. This rolling mill is configured by arranging a plurality of stands, in which n caliber rolls are arranged in the circumferential direction, in a tandem arrangement, without applying an inner surface tool while applying tension between stands, the outer diameter of the hollow tube, Finishes the wall thickness to the specified dimensions, and adjusts the number of stands to be used and the tension between stands according to the outer diameter and thickness of the product, and finishes various product dimensions from a raw tube of the same outer diameter with high efficiency. Can be.

In an n-roll tandem rolling mill, a roll phase difference between stands is conventionally set at 180 ° / n in order to uniformly apply drawing in the circumferential direction. For example, in a three-roll tandem rolling mill most frequently used, the roll phase difference is set to 60 ° as shown in FIG. For this reason, especially when t / D (t; wall thickness, D; outer diameter) is large and the diameter reduction ratio is large, the inner surface squared or the inner surface N squared (N = 2n; n = 3)
In the case of (1), there is a problem that the inner surface is called hexagonal tension; FIG.

[0004] As a countermeasure for reducing the inner surface angularity,
It is known to reduce the diameter reduction ratio, increase the tension between stands, and make the shape of the roll caliber a perfect circle. However, reducing the diameter reduction ratio has a problem that the rolling efficiency deteriorates and increases the tension between stands. However, there is a problem that the length of the thickened portion at the front and rear ends of the product becomes longer and the yield is reduced. There is a problem that external flaws are easily generated.

On the other hand, JP-A-61-216806 discloses that the roll phase difference between stands is 180 ° / n and 90 ° / n (n =
A method of drawing and rolling is disclosed as 2, 3). This is because the number of corners on the inner surface is doubled (from 4 to 8 for 2 rolls, from 6 to 12 for 3 rolls), and the inner surface is made closer to a perfect circle shape in the circumferential direction. Is intended to reduce the thickness deviation.

In Japanese Patent Application Laid-Open No. 8-300012, the rolls of a three-roll stand are arranged so as to have an angular displacement (roll phase) of a multiple of 9 ° to 15 ° in a plane perpendicular to the rolling pass line. Method (A), each roll stand is divided into an arbitrary number of pairs in method (A), and the angular displacement within the pair is 60 ° (0 °, 60 °), and the angular displacement between adjacent pairs is 30 °
The method (B) described above and the method (C) in which the combination of the angular displacements is repeated two or more cycles in the method (B) are disclosed. This is because the inner surface is made closer to a perfect circle by forming a 24 squared inner surface by the method (A), and the inner surface is prevented from being distorted due to torsion when the processing amount of the pipe is large by the method (B). ) Is intended to reduce the torsion of the pipe over the entire area of the roll stand having a large amount of rolling.

[0007]

However, according to the above prior art, which merely regulates only the roll phase difference or only the roll phase, it is not enough to reduce the hexagonal inner surface. It was found through intensive studies and experiments. For example, there are a very large number of combinations having a roll phase that is a multiple of 15 ° (15 ° pitch combination), and among them, those having an effect of preventing inner surface hexagonal tension are limited,
The effect is also influenced by the arrangement order of the stand to which the combination is applied in the entire arrangement. Further, in the 15 ° pitch combination, the biting at the roll edge portion (FIG. 6A) Becomes larger and the edge mark 3
Some flaws may cause flaws such as (FIG. 6 (b)) and collapse flaw 4 (FIG. 6 (c)).

That is, in the range of the prior art, there is a portion that not only lacks certainty in the effect of preventing hexagonal tightening of the inner surface but also promotes generation of flaws on the outer surface. In view of the above-mentioned drawbacks of the prior art, the present invention can appropriately set the roll phase of each stand during drawing rolling by a three-roll tandem rolling mill, and can reliably prevent hexagonal tightening of the inner surface.
It is an object of the present invention to provide a method of drawing and rolling a metal tube that can also prevent the occurrence of a product outer surface flaw.

[0009]

The present invention (1) relates to a method for drawing and rolling a metal tube using a drawing rolling mill in which eight or more three-roll stands are arranged. A method for rolling and reducing a metal tube, characterized in that rolling is performed by imposing (1) and (2). Note (1) The roll phases of each stand are different from each other. (2) There are two types of roll phase differences between stands.
60 ° and the second type are any of 30 °, 45 °, 75 °, and 90 °, and the first type and the second type are alternately repeated sequentially from the first stand.

In the present invention (2), when the stand number at which the total diameter reduction ratio from the first stand reaches a predetermined value or more is K and K> 8, the above conditions (1) and (2) are satisfied. Further ninth-
The method according to the present invention (1), wherein the method is applied to each of a group of stands that can be sequentially grouped every eight stands in the K-th stand and a group of stands that cannot be grouped. The predetermined value of the total diameter reduction rate is preferably 30%, more preferably 50%.

Formula 1 defines the total diameter reduction ratio.

[0012]

(Equation 1)

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the reasons for limiting the present invention (1) will be described. The present inventors performed a metal tube rolling experiment using an 8-stand 3-roll experimental rolling mill with variously changing the roll phase of each stand with a minimum unit of 15 °. We searched for the combination condition of the roll phase to obtain a 24 squared inner surface with even corners. In addition,
The roll phase of a three roll stand is defined as follows. That is, the rolling pass line is used as a central axis, and a semi-vertical plane having this central axis as a lower end is used as a reference plane. In a polar coordinate system in which the plane that rotates (excluding 120 °) is the radial plane and the angle between the rotating plane and the reference plane at each position is the phase of the radial plane, the center cross section of any roll for each stand The phase of the matching radial surface is defined as the roll phase of the stand.

As a result, the roll phases of the stands are set to different values, and the roll phase difference between the stands is
60 ° between the first stands, A between the next stands
Group (15 °, 30 °, 45 °, 75 °, 90 °, 105 °), and this pattern (60 °
→ One of the groups A) was repeated, so that it was found that the inner surface 24 squares could be obtained with certain reproducibility on the exit side of the eighth stand. If there is a stand having the same roll phase among the eight stands, it is not possible to obtain a 24 square inner surface. The same applies even if 60 ° is added to the group A.

However, when 15 ° in the group A is applied between any stands, the outer surface flaws shown in FIG. 6 always occur. The same applies to 105 °. This is considered to be because the material portion located on the roll flange side in the front stand between the stands is located on substantially the same side in the rear stand as well, and the biting of the material is promoted in that portion.

That is, in order to surely form the inner surface 24 squares without generating external surface flaws using a continuous 8 stand 3 roll type rolling mill, the following conditions (1) and
It is necessary to impose (2). Note (1) The roll phases of each stand are different from each other. (2) There are two types of roll phase differences between stands.
60 ° and the second type are any of 30 °, 45 °, 75 °, and 90 °, and the first type and the second type are alternately repeated sequentially from the first stand.

The roll phase difference between the stands is the absolute value of the difference between the roll phases of the stands that are adjacent to each other. Next, the n-th to (n + 8) -th stands (where n = 1 to n + 8) were used using a 12-stand three-roll type rolling mill.
4) The roll phase satisfying the above conditions (1) and (2) was given, and a metal pipe rolling experiment was conducted with the other roll phase difference being 60 ° as in the past. When n = 2 to 4, the inner surface was hexagonal.

[0018] Therefore, the inner surface of the metal tube is rolled by a three-roll type rolling mill with eight or more stands without causing any flaws on the outer surface.
In order to form a 24-square tension, the first to eighth stands need to have a roll phase that satisfies the above conditions (1) and (2). FIG. 1 is a schematic diagram showing an example of the roll arrangement of the first to eighth stands according to the present invention (1). In the figure, φ is the roll phase, and Δφ is the roll phase difference.

According to the present invention (1), when the number of stands is a multiple of 8, if the above conditions are repeatedly imposed for every eight stands,
It will be readily appreciated that a tube rolled product free of hexagonal inner surfaces and flaws on the outer surface can be obtained. However, the present invention (1) does not have a method of applying to a three-roll type rolling mill in which the number of stands is not a multiple of 8, and the present invention (2) defines this.

According to the experiments and calculations of the present inventors, in normal rolling with a roll phase difference of 60 °, the hexagonal inner surface is formed in the initial stage of rolling, and the total diameter reduction ratio exceeds a certain value. From the inner surface shape does not change. That is, it is necessary to suppress the formation of the hexagonal inner surface by the stand until the total diameter reduction ratio reaches this “certain value” or more. Therefore,
In the present invention (2), this "certain value" is a predetermined value, and K is a stand number at which the total diameter reduction ratio reaches the predetermined value or more. The above-mentioned condition is imposed on the eighth stand. On the other hand, when K> 8, each of the ninth to K-th stands is further divided into stand groups that can be grouped every eight stands and stand groups that cannot be grouped. The above conditions were imposed. For example, if K = 11 in a reduction rolling mill with a total of 20 stands, first to eighth stands,
The above conditions are imposed on the ninth to eleventh stands. For the twelfth to twentieth stands, Δφ = 60 ° or Δφ =
There is no problem as 30 °.

The reason for this is that, by imposing the above-mentioned conditions for each of the standable groups of stands among the first to K-th stands, an inner surface shape close to a perfect circle can be obtained on the exit side for every eight stands. In the case where the last stand (surplus stand) which cannot be tied up, that is, the last remaining stand (remaining stand) which takes eight stands in sequence from the first to Kth stands does not satisfy the above condition, the inner surface is hexagonally tightened with this surplus stand. Is formed, and may be maintained from the (K + 1) th stand to the last stand.

The predetermined value of the total diameter reduction ratio is determined by
If it is less than 30%, a remarkable effect cannot be obtained on the suppression of hexagonal tension on the inner surface, so it is necessary to set it to 30%, but more preferably 50%.

[0023]

(Embodiment 1) The roll ellipticity (defined in FIG. 2) of each stand is 2%, the roll phase φ, the roll phase difference Δφ,
Using a three-roll tandem rolling mill with 8 stands, the total diameter reduction ratio R of which is set as shown in Table 1, was measured according to JIS-STKM13.
A pipe equivalent to A (outer diameter 88 mm, average wall thickness 3.5 mm) is supplied to the first stand at the inlet material temperature of 725 ° C and the final stand outlet material speed.
The table shows the degree of squareness, the rate of uneven wall thickness (defined in FIG. 3), and the occurrence of external flaws of a product pipe (outer diameter 52 mm, average thickness 3.3 mm) drawn and reduced at 150 m / min.

In the embodiments (Nos. 1 to 4) in which the roll phase setting of the first to eighth stands satisfies both the conditions (1) and (2), the degree of angularity and the thickness deviation are small, and there are no external surface flaws. And good results were obtained. However, in Comparative Examples (Nos. 5 to 8) in which one or both of the conditions (1) and (2) are not satisfied,
The uneven thickness ratio was large, and outer surface flaws were generated except for No. 7.

[0025]

[Table 1]

(Embodiment 2) The roll ellipticity of each stand is 4%, the roll phase φ, the roll phase difference Δφ, and the total diameter reduction rate R.
Using a 24-stand three-roll tandem rolling mill set as shown in Table 2, a raw tube (outer diameter: 172 mm, average wall thickness: 15 mm) corresponding to JIS-STKM15A was placed at the first stand entrance material temperature 920 ° C. Table 3 shows the degree of squareness, uneven wall thickness, and occurrence of external flaws of a product pipe (outer diameter 43 mm, average thickness 15 mm) drawn and rolled at a final stand exit side material speed of 350 m / min.

In Comparative Example No. 13, the condition (2) was applied between all stands.
(Δφ = 15 °), the inner surface shape was poor, and the outer surface flaw was generated. In Comparative Example No. 14, R reaches 50% or more.
The condition (1) of the present invention (2) is satisfied up to 16 stands, but the condition (2) is not satisfied (including Δφ = 15 °).
The inner surface shape is not so improved and the outer surface is not flawed.

Comparative Example No. 15 was performed under the conditions of the first to eighth stands.
(1) is off (φ of the first and third stands are both 0 °, φ of both the second and fourth stands is both 60 °), and conditions
(2) also deviates (Δφ = 60 ° between the second and third stands)
Therefore, the inner surface shape is poor. For these comparative examples, Example N
In o.9 and No.12, up to the eleventh stand where R reached 30% or more was adapted to the present invention (2), so that the inner surface shape was good and no outer surface flaw was generated.

In Examples No. 10 and No. 11, R was 50
%, The inner surface shape was better than that of Nos. 9 and 12. In No.11, the present invention (2) covers up to the final stand.
, The inner shape is the best.

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

As described above, according to the present invention, the roll phase of each stand can be appropriately set at the time of reducing rolling by a three-roll tandem rolling mill, and the hexagonal inner surface, which causes uneven thickness, can be effectively reduced. At the same time, an excellent effect of preventing the occurrence of flaws on the outer surface of the product can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a roll arrangement of first to eighth stands according to the present invention (1).

FIG. 2 is an explanatory diagram of a definition of a roll ellipticity.

FIG. 3 is an explanatory diagram of definitions of a degree of squareness and an uneven thickness ratio.

FIG. 4 is a schematic view showing a conventional roll arrangement.

FIG. 5 is a sectional view showing a hexagonal inner surface.

FIG. 6 (a) is a biting portion at a roll edge portion, and (b)
Is a schematic diagram showing an edge mark, and FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Roll 2 Metal pipe (steel pipe) 3 Edge mark 4 Fall-down flaw 5 Protruding part

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Akira Ito 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Inside the Chita Works, Kawasaki Steel Works (72) Inventor Motoaki Itani 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Yuji Hashimoto 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Masanori Nishimori 1-1-1, Kawasaki-cho, Handa-city, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Nochika Okabe 1-1-1, Kawasakicho, Handa City, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Nobuki Tanaka 1-1-1, Kawasakicho, Handa City, Aichi Prefecture Address Kawasaki Steel Corporation Chita Works

Claims (4)

[Claims] 1. A method for drawing and rolling a metal tube using a drawing rolling mill in which eight or more three-roll stands are arranged, wherein the first to eighth stands have the following conditions (1) and (2).
And rolling the metal tube. Note (1) The roll phases of each stand are different from each other. (2) There are two types of roll phase differences between stands.
60 ° and the second type are any of 30 °, 45 °, 75 °, and 90 °, and the first type and the second type are alternately repeated sequentially from the first stand. 2. When the stand number at which the total diameter reduction rate from the first stand reaches a predetermined value or more is K and K> 8, the conditions (1) and (2) are further satisfied, and 2. The method according to claim 1, wherein each of the groups of stands in the K stand that can be grouped every eight stands and the group of stands that cannot be grouped are set. 3. The method according to claim 2, wherein the predetermined value of the total diameter reduction ratio is 30%. 4. The method according to claim 2, wherein the predetermined value of the total diameter reduction ratio is 50%. .