JP2001179310A - Method for sizing roll of seamless metal pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for sizing roll of rolling a seamless metal pipe without any edge scratch or cracks at the pipe's ends, regardless of a maternal pipe's thickness. SOLUTION: When taking F for dimension of a hole-type flange on a Mandrel Mill's last stand, t for thickness and D for outer diameter of a pipe at the Mandrel Mill's outlet, A1 for dimension of a hole type flange and B1 for dimension of groove bottom at a rolling machine's first stand, A2 for dimension of flange and B2 for dimension of groove bottom of the second stand, it is fixed that K1F<=A1<=K2F, K3F<=B1<=K4F, 5KF<=A24<=K6F, K7F<=B2<=K8F and t/D=0.07 or less. K1-K8 are numerical value of each specified formula and they differs by t/D.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sizing a seamless metal pipe by a sizing machine such as a stretch reducer or a sizer, and more particularly to a method for arranging equipment rows in which mandrel mills are arranged in series on the entrance side thereof. The present invention relates to a method for sizing a seamless metal pipe suitable for sizing by a sizing mill.

[0002]

2. Description of the Related Art Generally, in a manufacturing process of a seamless metal pipe (hereinafter, referred to as a metal pipe), a hollow shell pierced and rolled by a piercer is reduced in diameter and reduced in thickness by a drawing rolling machine such as a mandrel mill. Next, sizing is performed to a predetermined product outer diameter by a sizing machine such as a sizer or a stretch reducer. In addition,
Since the sizer and the stretch reducer have almost the same configuration, the sizer will be described below as an example.

[0003] The arrangement of the mandrel mill and the sizer includes:
The mandrel mill and sizer are arranged in close proximity to each other in series with the pass center matched, a method of performing both stripping and constant diameter rolling of the mandrel bar in the subsequent sizer, and placing the sizer on a line different from the mandrel mill line, There is a method of performing only constant diameter rolling with a sizer.

FIG. 1 is a schematic side view showing the former method.
The mandrel mill 6 and the sizer 7 are arranged close to each other so that the path center PC coincides with each other. The sizer 7 separates the metal tube 3 to be reduced in thickness by the mandrel mill 6 from the mandrel bar 5 while maintaining a predetermined product outer diameter. It is designed to perform constant diameter rolling.

The upstream end (left side in the figure) of the mandrel bar 5 is gripped by a bar moving device (not shown) provided on the entry side of the mandrel mill 6. Then, at the time of rolling, the metal tube 3 is moved toward the sizer at a speed different from the moving speed, and is returned to the entry side of the mandrel mill 6 at the same time as the end of the rolling, and is replaced with another prepared mandrel bar. You.

Each of the mandrel mill 6 and the sizer 7 comprises a plurality of roll stands 1 in which a hole type roll is incorporated. And generally, mandrel mill 6
The roll stand 1 has two paired hole-shaped rolls, and the roll stand 1 of the sizer 7 has three paired hole-shaped rolls.

FIG. 2 is a schematic cross-sectional view showing the shape of the hole of the intermediate stand of the zaizer 7, that is, the view taken along the line II--II of FIG. 1, and FIG. FIG. 1B is a view taken along a roll arrow. As shown in the figure, three hole-type rolls 2 are incorporated around a path center PC in a vertical plane at intervals of 120 °. The roll stands 1 and 1 adjacent to each other are arranged so that the phase in the rolling direction is shifted by 60 °. And, the groove shape is A> B in the former rolling stand.
(Refer to FIG. 4). It is a regular triangular hole type, and in the finishing stand at the subsequent stage, it is a perfect circular hole type of A = B. It is designed to be finished into a perfect circular product pipe by a perfect circular hole type. At this time, the number of used stands is determined by the outer diameter of the product tube to be obtained.

Here, A is the distance from the path center PC to the flange of the roll 2, and B is the distance from the path center PC to the groove bottom of the roll 2, which is the groove bottom.

On the other hand, FIG. 3 is a schematic cross-sectional view showing the hole shape of the final roll stand of the mandrel mill 6 as seen from the direction of arrow C in FIG. 1. As shown in FIG. In order to prevent the mandrel bar 5 and the metal tube 3 from being shrink-fitted, the profile is often an elliptical profile with F> G. This is the same when the mandrel mill line and the sizer are installed on separate lines.

Here, F is the distance from the path center PC to the flange of the roller 4 and G is the distance from the path center PC to the groove bottom of the roller 4 and the groove bottom. The phase in the rolling direction of the adjacent roll stands 1 and 1 of the mandrel mill is 90 °.

For this reason, the mother pipe supplied to the sizer 7 has an elliptical shape. In particular, in the case of a thin material having low rigidity, not only the shape conforms to the hole shape of the final stand of the mandrel mill 6, but also the material is easy to bite into the gap between the hole rolls 4, 4, so that a more prominent ellipse is formed. Shape. That is, in the case of a thin-walled material, an average outer diameter (hereinafter, simply referred to as an outer diameter) in the circumferential direction of the mother pipe at the outlet side of the mandrel mill 6 is increased due to the material overhang in the circumferential direction. On the other hand, in the case of a thick material, since the material overhangs on the flange side of the hole type roll 4 in the final stand of the mandrel mill 6, the outer diameter of the mother pipe on the mandrel mill 6 output side is smaller than that of the thin material.

Therefore, the appropriate groove size of the first stand and the second stand of the sizer 7 is different between the thin material and the thick material, and proper rolling cannot be performed with the same hole. That is,
When the hole size of the first stand and the second stand of the sizer 7 is designed in accordance with the conditions of the thin-walled material, the workability is insufficient for a thick-walled material having a small outer diameter, and the mandrel bar 5 Defective stripping of the metal tube 3 from the air will occur. This stripping defect is likely to occur when the metal tube 3 stretched and rolled by the mandrel mill 6 is a short material. The reason is as follows.

That is, when the metal tube 3 stretched and rolled by the mandrel mill 6 is a long material, the end of the metal tube 3 is extended to the third stand of the sizer 7 having a high working degree or to a mandrel after that. It is sent out by the mill 6 itself, and the pulling force necessary for stripping is obtained by the biting of the second and subsequent stands. On the other hand, in the case of a short material, the tip portion of the metal tube 3 is sent out only to the first stand or the second stand of the sizer 7 having a low working degree, and the pulling force required for stripping cannot be obtained. It is.

Conversely, when the hole dimensions of the first stand and the second stand of the sizer 7 are designed in accordance with the conditions of the mother pipe of the thick material, the thinner material having a larger outer diameter of the sizer 7 has the same size. Since the circumference of the mother pipe is excessively large relative to the circumference of the hole, the material starts to bite out at the flange of the hole-shaped roll 2, and an external flaw (hereinafter, referred to as an edge flaw) is generated. In particular, when the major diameter side of the elliptical shape of the mother pipe coincides with the flange portion of the grooved roll 2, a crack occurs at the pipe end on the rolling front end side. In some cases, the materials in this portion may overlap with each other for a few meters.

As a method for preventing the stripping failure, there is a method disclosed in Japanese Patent Application Laid-Open No. 3-114605. That is, the method is a method in which a bar pulling device including a pipe end stopper jig that can move toward and away from the pass line is installed on the exit side of the final stand of the mandrel mill. According to this method, it is possible to prevent a stripping defect from occurring regardless of the outer diameter or length of the mother pipe. However, this method requires installation of a bar pull-out device and a control device for the bar pull-out device, so that equipment costs are increased and the control thereof is troublesome.

[0016] Further, as a method of performing constant diameter rolling of a thin-walled or thick-walled mother pipe, that is, a mother pipe having a different ellipticity and outer diameter by using the same hole-shaped roll, a method disclosed in Japanese Patent Application Laid-Open No. 7-16616 is known. There is. That is, the method is such that the rotation axis of the hole-type rolls of all stands is freely movable toward and away from the path center, and the ellipticity and diameter of the hole shape having a predetermined shape in the maximum open state are determined by the thickness of the mother pipe. This is a method of adjusting and changing the distance of the rotary shaft from the path center according to the thickness and the outer diameter. According to this method, it is possible to prevent edge flaws and pipe end cracks from occurring regardless of the ellipticity or outer diameter of the mother pipe. However, this method has a drawback that the above-described stripping failure that occurs when the mill is arranged as shown in FIG. 1 cannot be reliably prevented.

[0017]

SUMMARY OF THE INVENTION A first object of the present invention is to reduce the diameter of a mother tube rolled by a mandrel mill with a constant diameter rolling mill having three hole rolls in one stand. It is an object of the present invention to provide a constant diameter rolling method for a seamless metal pipe using a standard rolling mill that does not cause edge flaws or pipe end cracks even when the mother pipe is a thin material or a thick material.

A second object is that a mandrel mill and the above-mentioned constant-diameter rolling mill are arranged close to each other in series so that the pass centers are coincident with each other, and the constant-diameter rolling mill is configured to cut a metal pipe from a mandrel bar of the mandrel mill. In a line of equipment that also serves as a separating device, even if the mother pipe supplied to the constant-diameter rolling mill is a thin material or a thick material, no edge flaw or pipe end crack occurs, and the metal tube is separated from the mandrel bar. It is an object of the present invention to provide a method of rolling a seamless metal pipe to a fixed diameter, which does not cause a defect, that is, a stripping defect.

[0019]

The gist of the present invention resides in the following (1) and (2) methods for rolling a seamless metal pipe to a constant diameter.

(1) A constant diameter rolling method for a seamless metal pipe by a constant diameter rolling mill having three hole rolls in one stand, wherein a hole roll is transferred from a pass center of a final stand of a previous mandrel mill. The distance to the flange is F (m
m), the wall thickness of the tube at the outlet side of the mandrel mill is t (mm),
The outer diameter is D (mm), and the distance from the pass center of the first stand of the constant diameter rolling mill to the flange of the roller is A1 (m).
m), the distance from the pass center to the groove bottom of the hole type roll is B
1 (mm), the distance from the pass center of the second stand to the flange of the hole-shaped roll is A2 (mm), and the distance from the path center to the groove bottom of the hole-shaped roll is B2 (mm). A pipe having a ratio t / D of diameter D of 0.07 or less,
The above-mentioned A1, B1, A2, and B2 are respectively represented by the following (1) to
A constant diameter rolling method for a seamless metal pipe that is rolled by setting the value to satisfy equation (4).

K1 × F ≦ A1 ≦ K2 × F (1) K3 × F ≦ B1 ≦ K4 × F (2) K5 × F ≦ A2 ≦ K6 × F (3) K7 × F ≦ B2 ≦ K8 × F (4) However, K1 to K8 have the following values.

K1 = -2.8 (t / D) +1.05 K2 = -1.0 (t / D) +1.12 K3 = -0.2 (t / D) +0.82 K4 = -1. 4 (t / D) +1.03 K5 = −1.4 (t / D) +0.91 K6 = −0.4 (t / D) +1.01 K7 = −0.2 (t / D) +0. 81 K8 = -0.8 (t / D) +0.97 (2) A mandrel mill and a constant diameter rolling mill having three hole-shaped rolls in one stand are arranged close to each other in series with their pass centers matched. A method for sizing a seamless metal pipe by means of an equipment row in which a constant-diameter rolling mill also serves as a device for separating a metal pipe from a mandrel bar of a mandrel mill. Is the distance to F (mm) and the wall thickness of the pipe at the exit side of the mandrel mill is t (mm) The outer diameter is D (mm), the distance from the pass center of the first stand of the constant diameter rolling mill to the flange of the roll is A1 (mm), the distance from the pass center to the groove bottom of the roll is B1 (mm), The distance from the pass center of the second stand to the flange of the hole type roll is A
2 (mm), and when the distance from the pass center to the groove bottom of the grooved roll is B2 (mm), the above A1, B1, A2, B2 is set to a value satisfying the following formulas (1) to (4) or the following formulas (5) to (8).

When t / D ≦ 0.07 K1 × F ≦ A1 ≦ K2 × F (1) K3 × F ≦ B1 ≦ K4 × F (2) K5 × F ≦ A2 ≦ K6 × F (3) K7 × F ≦ B2 ≦ K8 × F (4) However, K1 to K8 have the following values.

K1 = −2.8 (t / D) +1.05 K2 = −1.0 (t / D) +1.12 K3 = −0.2 (t / D) +0.82 K4 = −1. 4 (t / D) +1.03 K5 = −1.4 (t / D) +0.91 K6 = −0.4 (t / D) +1.01 K7 = −0.2 (t / D) +0. 81 K8 = −0.8 (t / D) +0.97 When t / D> 0.07, 0.85F ≦ A1 ≦ 1.05F (5) 0.81F ≦ B1 ≦ 0.93F (6) 0.81F ≦ A2 ≦ 0.98F (7) 0.80F ≦ B2 ≦ 0.91F (8) In the method of the present invention of the above (2), , At least the first
It is preferable to use a fixed-diameter rolling mill in which the stand and the rolls of the second stand are freely movable toward and away from the path center, and the dimensions of the holes in both stands can be changed.

The present invention has been completed based on the following findings. That is, the inventor has studied various methods for solving the above-described problems. As a result, the following was found.

As described above, the shape of the metal tube 3 (mother tube) at the outlet side of the mandrel mill 6 differs between the thin material and the thick material, and the outer diameter (the average outer diameter in the circumferential direction) of both materials is different. different. For this reason, at least the hole size of the first stand of the sizer 7 needs to be changed between a thin material and a thick material, and it is necessary to be large for a thin material and small for a thick material. This is because, in the case of a thin material, the outer diameter of the mother tube is large, so that if the die size of the first stand is small, the circumferential length of the material to be rolled becomes excessively larger than the circumferential length of the die shape. When a crack or a pipe end crack occurs and the pipe end crack is remarkable, a pipe end break occurs. In the case of a thick material, since the outer diameter of the mother tube is small, if the hole size of the first stand is large, the workability is small and the force for gripping the material to be rolled is weak. This is because the pulling force is insufficient and stripping failure occurs.

However, in the case of a thin-walled material, if only the hole diameter of the first stand is increased, the load on the second stand becomes excessively large, so that the hole diameter of the second stand also needs to be increased. At this time, if the groove bottom dimension B is too small even if the flange dimension A is increased, the workability becomes too high, and the material to be rolled starts to bite into the edge, causing edge flaws. Also,
In the case of a thick material, it was found that it is necessary to reduce the die diameter of the second stand because the grip force is insufficient only by reducing the die diameter of the first stand.

Even in the case of a thick material, in a facility row in which the mandrel mill and the sizer are not arranged close to each other in series with the pass line PC coincident, the first stand and the second stand of the sizer 7 are arranged. Does not need to be small.

In the case of a thin material, the flange dimension A
However, if the diameter is excessively increased, the material loss at the time of cutting the hole is increased, and the number of rolling passes is increased. Further, when the wear amount reaches a predetermined value, the grooved roll 2 is refurbished and reused as a holed roll having a larger hole diameter. It becomes difficult. For this reason, the flange dimension A when increasing
Need not be larger than the size at which edge flaws do not occur.

As a result of many manufacturing experiments, the flange size of the final stand of the mandrel mill 6 was changed to F (m
m), the thickness of the mother pipe is t (mm), the outer diameter is D (mm), the flange size of the first stand of the sizer 7 is A1 (mm),
When the groove bottom dimension is B1 (mm), the flange size of the second stand is A2 (mm), and the groove bottom dimension is B2 (mm),
When the ratio t / D between the wall thickness t and the outer diameter D of the mother pipe is 0.07 or less, if the hole type satisfies the above equations (1) to (4), edge flaws and pipe end cracks occur. Not to be.

Further, the ratio t / D between the wall thickness t of the mother pipe and the outer diameter D is t / D.
Exceeds 0.07, if the hole type satisfies the above formulas (5) to (8), the equipment in which the mandrel mill 6 is arranged in close proximity in series with the pass line PC on the entry side of the sizer 7 It was found that stripping defects did not occur in the columns.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the first method of the present invention provides a method in which the ratio t / D between the thickness t and the outer diameter D of a mother pipe stretched and rolled by a mandrel mill is 0.07 or less. If the first
A sizer (constant) that incorporates a grooved roll with the groove dimensions of the stand satisfying the above formulas (1) and (2) and the groove size of the second stand that satisfies the formulas (3) and (4) above This is a method of rolling a seamless metal pipe to a constant diameter using a diameter rolling mill.

The second method is a case where a sizer (constant-diameter rolling mill) is a series of equipment arranged in close proximity in series with a pass line immediately after a mandrel mill. Ratio t between wall thickness t and outer diameter D of the pipe
When / D is 0.07 or less, the hole dimensions of the first stand are the above-described equations (1) and (2), and the hole dimensions of the second stand are the above-described equations (3) and (4). Roll type roll satisfying the formula, ratio t /
When D exceeds 0.07, the groove dimensions of the first stand are the above-mentioned equations (5) and (6), and the groove dimensions of the second stand are the above-mentioned equations (7) and (8). This is a method in which a seamless metal pipe is subjected to constant-diameter rolling using a sizer (constant-diameter rolling mill) in which hole-shaped rolls satisfying the formula are incorporated.

Here, the groove size of the first stand of the sizer (constant diameter rolling mill) is determined by the above equation (1), equation (2) or equation (5).
The reason why the equation (6) and the groove size of the second stand are set to values satisfying the above equations (3) and (4) or the equations (7) and (8) will be described.

The ratio t / D of the thickness t of the mother pipe to the outer diameter D is equal to 0.
07 or less (thin material), A1 is less than K1 × F, A2
If less than K5 × F, the dimensions of the flange are too small, causing edge flaws and pipe end cracks. On the other hand, A1 is K2 × F
If A2 exceeds K6 × F, the effect of preventing edge flaws and pipe end cracks saturates, leading to a loss of material and an increase in the number of rolling passes at the time of hole cutting, and it becomes difficult to re-use and re-cut. is there. When B1 is less than K3 × F and B2 is less than K7 × F, the groove bottom dimension is too small, and an edge flaw is generated. on the other hand,
If B1 is larger than K4 × F and B2 is larger than K8 × F, the groove bottom dimension is too large, and stripping failure occurs in the case of an equipment row in which a mandrel mill and a sizer are arranged close to each other.

When the ratio t / D is more than 0.07 (thick material), when A1 is less than 0.85 × F and A2 is less than 0.81 × F, the flange size is too small, and the edge flaw is reduced. appear. On the other hand, A1 exceeds 1.05 × F and A2 is 0.98 × F
If it is excessive, the effect of preventing edge flaws is saturated, which leads to a loss of material and an increase in the number of rolling passes at the time of hole cutting, and furthermore, it is only difficult to recycle and reuse. Also, B1 is less than 0.81 × F,
When B2 is less than 0.80 × F, the groove bottom dimension is too small, and an edge flaw occurs. On the other hand, B1 exceeds 0.93 × F and B2
Is more than 0.91 × F, the groove bottom dimension is too large, and stripping failure occurs in the case of an equipment row in which a mandrel mill and a sizer are arranged close to each other. This is clear from the results of the examples described later.

It is to be noted that when the ratio t / D is equal to or less than 0.07 and when the ratio t / D exceeds 0.07, the above-mentioned groove dimensions A1, B1 and A
2 and B2, for example, when the hole type roll 2 designed for the ratio t / D of 0.07 or less is incorporated in the first stand and the second stand so as to be able to freely move toward and away from the path center, the ratio t / D is used.
Die size A1, B1 and A2, B for D greater than 0.07
2 can be secured, and the same roll-to-roll can be manufactured with the ratio t / D
Can be used for 0.07 or less and 0.07 or more.

Therefore, as a sizer (constant-diameter rolling mill), at least the first and second stand-shaped rolls are incorporated so as to be able to move toward and away from the path center, and the hole dimensions of both stands are changed. It is preferable to use a possible constant diameter rolling mill. In this case, the same hole type roll can be used for a thin-walled material and a thick-walled material pipe, and the rolling efficiency is improved by the amount that the stand exchange is unnecessary.

It should be noted that the above-mentioned "movable contact / separation" means that the separation distance from the groove bottom of the grooved roll to the pass center can be set and maintained at an arbitrary distance.

[0040]

[Embodiment] An equipment row in which three-roll type sizers are arranged in close proximity in series on the output side of a mandrel mill, and the nominal outer diameter D is 3
Three kinds of mother pipes having a diameter of 00 mm and a nominal thickness t of 9, 21, and 45 mm were respectively formed with an outer diameter of 210 mm and a thickness of 10, 22, 4, and 4.
Constant diameter rolling was performed to finish three types of product tubes of 5 mm.

At this time, the hole dimensions of the final stand of the mandrel mill were such that the groove bottom dimension G was 150 mm and the flange dimension F was
Was set to 160.5 mm. Also, the hole dimensions of the first stand and the second stand of the sizer (A1, B1 and A2, B
2), as shown in Tables 1, 2 and 3, the ratio t / D
Each time, the size of each of the seven combinations was determined, and the hole-shaped rolls were replaced each time according to the combination.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

Then, while checking for the occurrence of stripping defects during rolling, the product pipe after fixed diameter rolling is visually inspected for the occurrence of edge flaws and pipe end cracks, and evaluated according to the following criteria. The results are shown in Tables 1 to 3.

The evaluation of the pipe end crack was evaluated as “「 ”when no crack occurred,“ ○ ”when the crack occurred only within the crop margin, and“ × ”when the crack exceeded the crop margin.

The evaluation of edge flaws was as follows: "◎" when there was no occurrence, "O" when it occurred in a part of the longitudinal direction but no care was required, The case where care for the scratches was required was marked as “×”.

The stripping was evaluated as “◎” when stripping was possible with the sizer, and “×” when stripping was not possible.

The overall evaluation was “pass” when all of the pipe end cracks, edge flaws and stripping were “「 ”or“ ○ ”, and“ fail ”otherwise.

As can be seen from the results shown in Tables 1 to 3,
When sizing is performed according to the method of the present invention (Trial No. 1,
In 8 and 15), all evaluations of pipe end cracks, edge flaws, and stripping were “◎” or “○”, and the overall evaluation passed.

On the other hand, when constant diameter rolling was performed using a grooved roll that did not satisfy the conditions specified in the present invention (Trial No. 2 to No. 2).
7, 9, 14 and 16 to 21), any one or more of pipe end cracks, edge flaws and stripping was evaluated as "x", and the overall evaluation was all failed.

More specifically, when the t / D is 0.03 and the base pipe is made of an extremely thin material, the sample No. 2 shows that the flange size A2 of the second stand is too small and the end of the pipe exceeds the crop margin. Edge flaws requiring maintenance occurred. In Test No. 3, since the groove bottom dimension B2 of the second stand was too small, the workability was too high, the material began to bite into the edge, and an edge flaw requiring maintenance was generated. In Test No. 4, since the groove bottom dimension B2 of the second stand was too large, the workability was insufficient and stripping failure occurred. In Test No. 5, since the flange dimension A1 of the first stand was too small, a pipe end crack exceeding the crop margin and an edge flaw requiring maintenance were generated. In Test No. 6, since the groove bottom dimension B1 of the first stand was too large, the workability was insufficient and stripping failure occurred. In Test No. 7, since the groove bottom dimension B1 of the first stand was too small, the workability was too high, the material began to bite into the edge, and an edge flaw requiring maintenance was generated.

In the case of a thin-walled material, but with a t / D of 0.07 and a medium-walled mother tube, in Test No. 9, an edge flaw requiring maintenance was generated because the flange size A2 of the second stand was too small. However, the pipe end crack did not occur because it was a medium thickness material. In Test No. 10, since the groove bottom dimension B2 of the second stand was too small, the workability was too high, the material began to bite into the edge, and an edge flaw requiring maintenance was generated. In Test No. 11, the groove bottom dimension B2 of the second stand was too large, and the workability was insufficient, resulting in stripping failure. Test number 12 is the first
Edge flaws requiring maintenance were generated because the flange dimension A1 of the stand was too small, but no pipe end cracks were generated because it was a medium thickness material. In Test No. 13, since the groove bottom dimension B1 of the first stand was too large, the workability was insufficient, resulting in defective stripping. In Test No. 14, since the groove bottom dimension B1 of the first stand was too small, the workability was too high, the material began to bite into the edge, and an edge flaw requiring maintenance was generated.

When the t / D is 0.15 and the mother pipe is made of a thick material,
In Test No. 16, although the flange dimension A2 of the second stand was too small, an edge flaw requiring maintenance was generated, but no pipe end crack was generated because it was a thick material. In Test No. 17, since the groove bottom dimension B2 of the second stand was too small, the workability was too high, the material began to bite into the edge, and an edge flaw requiring maintenance was generated. In Test No. 18, the groove bottom dimension B2 of the second stand was too large, and the workability was insufficient, resulting in defective stripping. In test number 19, an edge flaw occurred because the flange dimension A1 of the first stand was too small.
Pipe end cracks did not occur because of the thick material. Trial number 2
In the case of No. 0, the groove depth B1 of the first stand was too large, resulting in insufficient stripping and poor stripping. In Test No. 21, since the groove bottom dimension B1 of the first stand was too small, the workability was too high, and the material began to bite into the edge, and an edge flaw requiring maintenance was generated.

[0055]

According to the method of the present invention, it is possible to surely obtain a product pipe free from edge flaws requiring maintenance and a pipe end crack exceeding a crop margin, thereby improving productivity and yield. Further, even when the constant diameter rolling mill also serves as a mandrel bar pulling-out device of a mandrel mill, productivity is improved because stripping defects do not occur.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing the entire configuration of an equipment row in which a sizer also serves as a mandrel bar pulling-out device of a mandrel mill.

FIG. 2 is a schematic diagram showing a hole shape of a three-roll type sizer;
FIG. 2A is a view taken along the line II in FIG. 1, and FIG. 2B is a view taken along the line II in FIG.

FIG. 3 is a schematic diagram showing a hole shape of a final stand of the mandrel mill, and is a view taken along the arrow line in FIG. 1;

FIG. 4 is a schematic diagram for explaining a groove size of a grooved roll of a three-roll type sizer.

[Explanation of symbols]

 PC: pass center, 1: roll stand, 2: hole size roll of sizer, 3: metal tube, 4: hole type roll of mandrel mill, 5: mandrel bar, 6: mandrel mill, 7: sizer.

Claims (3)

[Claims] 1. A method for constant diameter rolling of a seamless metal pipe by a constant diameter rolling mill having three hole rolls in one stand, wherein a flange of the hole roll is moved from a path center of a final stand of a former mandrel mill. Is F (mm), the wall thickness of the tube at the exit side of the mandrel mill is t (mm), and the outer diameter is D.
(Mm), the distance from the pass center of the first stand of the constant diameter rolling mill to the flange of the grooved roll is A1 (mm), and the distance from the path center to the groove bottom of the grooved roll is B1 (m).
m), when the distance from the pass center of the second stand to the flange of the hole-shaped roll is A2 (mm) and the distance from the path center to the groove bottom of the hole-shaped roll is B2 (mm), the wall thickness t and the outer diameter D A tube having a ratio t / D of 0.07 or less is
1, a method of rolling a seamless metal pipe with a constant diameter, wherein B1, A2, and B2 are set to values satisfying the following equations (1) to (4), respectively. K1 × F ≦ A1 ≦ K2 × F (1) K3 × F ≦ B1 ≦ K4 × F (2) K5 × F ≦ A2 ≦ K6 × F (3) K7 × F ≦ B2 ≦ K8 × F (4) However, K1 to K8 have the following values. K1 = −2.8 (t / D) +1.05 K2 = −1.0 (t / D) +1.12 K3 = −0.2 (t / D) +0.82 K4 = −1.4 (t /D)+1.03 K5 = -1.4 (t / D) +0.91 K6 = -0.4 (t / D) +1.01 K7 = -0.2 (t / D) +0.81 K8 = −0.8 (t / D) +0.97 2. A mandrel mill and a constant-diameter rolling mill having three hole-shaped rolls in one stand are arranged in series close to each other with the pass centers coincident with each other, and the constant-diameter rolling mill is moved from a mandrel bar of the mandrel mill. In this method, the distance from the pass center of the final stand of the mandrel mill to the flange of the hole roll is F (mm), and the mandrel mill exit side The wall thickness of the tube at t is (mm) and the outer diameter is D (m
m), the distance from the path center of the first stand of the constant diameter rolling mill to the flange of the grooved roll is A1 (mm), the distance from the path center to the groove bottom of the grooved roll is B1 (mm), the path center of the second stand The distance from the pipe to the flange of the roll is A2 (mm), and the distance from the path center to the groove bottom of the roll is B2 (mm). A1, B1, A2, B
2 is the following formula (1) to (4) or the following (5) to (8)
A method for rolling a seamless metal tube to a value that satisfies the formula. When t / D ≦ 0.07 K1 × F ≦ A1 ≦ K2 × F (1) K3 × F ≦ B1 ≦ K4 × F (2) K5 × F ≦ A2 ≦ K6 × F (3) K7 × F ≦ B2 ≦ K8 × F (4) However, K1 to K8 have the following values. K1 = −2.8 (t / D) +1.05 K2 = −1.0 (t / D) +1.12 K3 = −0.2 (t / D) +0.82 K4 = −1.4 (t /D)+1.03 K5 = -1.4 (t / D) +0.91 K6 = -0.4 (t / D) +1.01 K7 = -0.2 (t / D) +0.81 K8 = −0.8 (t / D) +0.97 When t / D> 0.07, 0.85F ≦ A1 ≦ 1.05F (5) 0.81F ≦ B1 ≦ 0.93F・ (6) 0.81F ≦ A2 ≦ 0.98F (7) 0.80F ≦ B2 ≦ 0.91F (8) 3. A constant diameter rolling mill in which at least rolls of a first stand and a second stand are incorporated so as to be able to move toward and away from a path center, and the roll diameter of both stands can be changed. The method for constant diameter rolling of a seamless metal pipe according to claim 2, wherein a rolling mill is used.