JPH0716615A - Method for cold rolling steel tube - Google Patents

Abstract

PURPOSE:To restrain deterioration in the dimensions of outside diameter in drawing rolling at high reduction rate of outside diameter. CONSTITUTION:Cold reducing rolling is executed by combining a drawing stage 2 by three-roll reducer of >=3 stands with a sizing stage 3 by two rolls of >=1 set. The rolls of the stand in the most preceding stage of the drawing stage by the three-roll reducer are made as 0% ellipticity <=5% and 0 < side relief < 2.5%, and drawing rolling is executed at the reduction ratio of outside diameter of 0 < reduction ratio of outside diameter < 2.5%. The rolls of stands from the second stage to two stages before the final are specified as 2% < ellipticity <= 5%, and drawing rolling is executed at the max. reduction rate of outside diameter per one stand of 10%. The rolls of the stand in the stage ahead of the final are specified as 0 < ellipticity <= 3%, and drawing rolling is executed at the max. reduction rate of outside diameter of 5%. By designing the peripheral length of roll of the stand in the final stage equal to the peripheral length of product, specifying side relief as <0 and the rolls as 0 <=ellipticity <= 1.5%, the reduction ratio of outside diameter as >=0.5%, drawing rolling is executed at the max. reduction ratio of outside diameter that is determined when the radius of groove bottom of the stand in the stage ahead of the final is taken as smaller than the radius of flange of roll of the stand in the final stage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cold drawing and rolling a steel pipe with a three-roll drawing machine having three or more stands.

[0002]

2. Description of the Related Art As for the demand trend of steel pipes for machine structures, there is an increasing demand for small diameter thick wall sizes and various outer diameter sizes. On the other hand, since the three-roll reducer can perform reduction rolling at a high outer diameter reduction ratio even in the cold, the thickness t ratio (t
/ D) can be increased and the diameter of the mother tube of the same outer diameter can be reduced to any outer diameter, and it is possible to meet the demands for the small diameter thick wall size and various outer diameter sizes. .

For example, in the case of an electric resistance welded steel pipe, in order to manufacture a small-diameter and thick-walled product at the stage of the mother pipe, not only the edge portion but also the mother material portion is heated when the open pipe is heated, and the welding efficiency is remarkably deteriorated. Therefore, the productivity is deteriorated or the inner cooling water is blown back to make welding difficult. Further, since the inner diameter becomes small, it becomes difficult to cut the inner bead, productivity is significantly deteriorated, and the inner bead remains cut. Further, since the difference between the inner diameter and the outer diameter becomes large, in the step of forming the steel strip into the open pipe, the edge shape of the butt is particularly deteriorated, welding becomes difficult, and the wall thickness shape is deteriorated. Therefore, the manufacturable range of a small-diameter thick-walled ERW steel pipe is generally t / D ≦ 2, where the pipe wall thickness is t and the pipe outer diameter is D.
It is about 0%. As a method to solve the problem in manufacturing small diameter thick products, if the mother tube is squeezed and rolled by a reducer etc., the outer wall thickness is increased by the outer diameter squeezing and the tube diameter becomes smaller. It is known that a small-diameter thick-walled pipe having a high thickness ratio t / D can be manufactured.

As a method of finishing a cold pipe material such as an electric resistance welded steel pipe to have an outer diameter of a product, as shown in FIG. 5 (a), a stand 32 incorporating a pair of hole type rolls 31 is used. )
As shown in the drawings and (c), a drawing rolling machine in which rolls are arranged 90 ° apart from each other between adjacent stands is continuously arranged, and the outer diameter of the mother pipe 33 is drawn successively at each stand 32. Finish to the specified outside diameter with the stand in the last stage. In this two-roll type squeeze rolling mill, the roll hole type is deep and the roll peripheral speeds of the roll groove bottom and the roll flange differ greatly, so when the squeeze rolling is performed at a high outer diameter reduction ratio, the pipe surface and the roll 31 are seized. It has a defect that a flaw is generated on the surface of the pipe. Therefore, the two-roll type reduction rolling mill is not suitable for reduction rolling with a high outer diameter reduction ratio.

On the other hand, as shown in FIG. 6, a three-roll type reducer generally used for a seamless steel pipe has a stand in which three hole type rolls 41 are assembled at 120 ° intervals in a vertical plane. As shown in FIGS. (A) and (b), the rolls are continuously arranged by changing the roll arrangement between adjacent stands by 60 °. According to this 3-roll type reducer, since the roll hole type is shallower than that of the 2-roll type, the difference in roll peripheral speed between the roll groove bottom portion and the roll flange portion is small, and flaws caused by seizure of the pipe surface and roll are generated. Since it is significantly reduced, it is advantageous for drawing rolling with a high outer diameter reduction ratio.

In the conventional cold-drawing with a three-roll reducer, the outer diameter reduction rate per stand is about 10% at the maximum, and as shown in FIG. From this, a bite 44 on the surface of the steel pipe 43 occurs. Therefore, the roll hole type is made elliptical so that the radius of the groove bottom of the roll of the front stand is smaller than the radius of the flange portion of the roll of the rear stand. The roll ellipticity increases as the outer diameter reduction rate per stand increases. Therefore, it is necessary to use a roll having a considerably large ellipticity in order to perform reduction rolling with a high outside diameter reduction rate of about 10% per one stand. In the reduction rolling of the mother pipe cold-rolled by the three-roll reducer, if the reduction rolling is performed at a high outer diameter reduction ratio, the three-roll reducer will not work because of the springback and insufficient stand rigidity caused by the cold mother pipe. Although the finished outer diameter after the squeeze rolling has the same roll hole shape, there occurs a phenomenon that a difference occurs depending on the wall thickness, strength, etc. of the mother tube.

In order to solve the unevenness of the finish outer diameter dimension in the reduction rolling of the three-roll type reducer, the amount of reduction rolling of the roll may be changed, but in the conventional three-roll type reducer, the roll and the roll shaft are not changed. The relative positional relationship is fixed, and the amount of reduction rolling of the roll cannot be changed. As a method for solving the unevenness of the finished outer diameter in the above-mentioned drawing rolling, 3
The housing of the roll type roll and the housing of the two roll type roll can be exchanged, and the two roll type roll is incorporated into at least the final stand or the last stand and the stand in front of the final stand. A squeeze rolling mill in which a 3-roll type hole roll is incorporated in a stand (Japanese Patent Laid-Open No. 58-116907), and a material to be rolled is given a large amount of reduction in a first row of stands consisting of three-roll stands to give a predetermined amount. A method of rolling to a size close to the outer diameter size, and then finish rolling with a second stand row which is composed of two roll stands having roll reduction means and which is installed in series on the outlet side of the first stand row (JP-A-2- 211904),
The bearing part shaft center that supports the two roll shafts of the three-roll reducer and the bearing part shaft center that supports the two rolls are eccentric, and the bearing parts of the two rolls are rotated to rotate the roll parts. A squeezing and rolling mill in which the relative spacing can be adjusted and a shaft slide mechanism is further provided at the ends of the two rolls so that the two rolls can be adjusted in the axial direction of the roll (Japanese Patent Laid-Open No. 3-2).
No. 94008) has been proposed.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The method disclosed in Japanese Patent No. 6907 and Japanese Patent Application Laid-Open No. 221904/1990 provides a large amount of reduction in a first stand row consisting of three roll stands and rolls them to a predetermined outer diameter,
Then, since the finish rolling is performed by the second stand row of two rolls with adjustable roll gap, it is possible to improve the accuracy of the outer diameter dimension. However, when the outer diameter reduction rate per stand is reduced, The problem remains that the outer diameter of the finished product becomes extremely poor. In addition, JP-A-3-29
The squeezing and rolling mill disclosed in Japanese Patent No. 4008 cannot be adjusted online on the production line, and is adjusted offline or replaced with a roll having a changed roll hole shape.
Therefore, if this method is selected, the mill must be stopped every time the material and strength of the mother pipe changes, even though pipes with the same outer diameter are being manufactured. This is not practical because it causes yield deterioration.

The object of the present invention is to suppress deterioration of the outer diameter dimension in the reduction rolling at a high outer diameter reduction rate in the cold drawing process of a steel pipe using a three-roll reducer, and to reduce the wall thickness ratio t / D to the outer diameter. (EN) Provided is a cold rolling method capable of manufacturing a small-diameter thick-walled steel pipe having high temperature.

[0010]

[Means for Solving the Problems] The present inventors have conducted various test studies in order to achieve the above object. As a result, in the outer diameter drawing process of the steel pipe, the drawing process using the three-roll reducer with two or more stands and the constant-diameter process using two rolls are combined to obtain the three-roll ellipticity and the outer diameter reduction rate of the final stand of the three-roll reducer. By setting the roll ellipticity, outer diameter reduction ratio and roll circumference of the final stand to be within the predetermined ranges, it is possible to obtain a highly accurate finished outer diameter dimension even when drawing and rolling at a high outer diameter reduction ratio. It has been clarified that a small-diameter thick-walled steel pipe having a high wall-thickness ratio t / D with respect to the outer diameter can be manufactured, and a patent application has already been filed as Japanese Patent Application No. 4-328397.

The invention of Japanese Patent Application No. 4-328397 mentioned above is
Cold drawing rolling combines a drawing process with a 3-roll reducer with 2 or more stands and a constant diameter process with 1 set or more of 2 rolls, and the roll of the final stand of the 3 roll reducer is 0 <ellipticity ≤ 3%, maximum. The outer circumference reduction rate is 5%, the final circumference of the roll is designed to be the same as the product circumference, and 0 <side relief, 0 ≤ ellipticity ≤ 1.5%, and outer diameter reduction rate is 0. The maximum outer diameter reduction ratio determined when the roll groove bottom radius of the final front stage ≦ the roll flange radius of the final stage stand is 0.5% or more. It is possible to suppress the deterioration of the outer diameter dimension and manufacture a small-diameter thick-walled steel pipe having a high wall thickness ratio t / D to the outer diameter. However, since a steel pipe having a shape close to a perfect circle is inserted into the frontmost stand of the 3-roll reducer and the outer diameter varies, a bite flaw is likely to occur unless there is some side relief. Also, if the ellipticity of the roll to the final two-stage stand exceeds 5%, the flange of the roll becomes sharp, and the shape of the groove bottom does not become smooth even when rolled by the next stand, and the normal product shape is obtained. It turned out that I could not get it.

As a result of further tests and studies, the present inventors have found that in the invention of Japanese Patent Application No. 4-328397 mentioned above, 3
3 roll hole side relief of frontmost stand of roll reducer, ellipticity, outer diameter reduction rate are within the specified range,
By setting the three-roll ellipticity and the maximum outer diameter reduction rate of each stand up to the final two-stage stand within a predetermined range, the occurrence of biting flaws can be suppressed, and even if it is drawn and rolled at a high outer diameter reduction rate. It was found that a highly accurate finished outer diameter dimension can be obtained and a small-diameter thick-walled steel pipe having a high wall-thickness ratio t / D to the outer diameter can be manufactured, and the present invention has been achieved.

That is, according to the present invention, in a method for cold drawing and rolling a steel pipe to manufacture a steel pipe having a highly accurate outer diameter dimension, the cold drawing and rolling process is performed by a three-roll reducer having three or more stands, and one set. By combining the above-mentioned constant diameter process with 2 rolls, 0% <ellipticity ≦ 5%, 0
% <Side relief <2.5%, outer diameter reduction rate 0%
<Outer diameter reduction ratio <2.5%, squeeze rolling is performed, and rolls of the stand from the second stage to the last two stages before are 2% <Ellipticity ≤ 5
%, The maximum outer diameter reduction rate per stand was 10%, and the final roll of the front stand was rolled with 0 <ellipticity ≦ 3.
%, The maximum outer diameter reduction rate is 5%, and the roll circumference of the final stand is designed to be equal to the product circumference, and 0 <side relief, roll 0 ≤ ellipticity ≤ 1.5%, outer diameter reduction When the ratio is 0.5% or more, the roll groove bottom radius of the final front stand is ≤
A cold rolling method for a steel pipe, which is characterized in that reduction rolling is performed at a maximum outer diameter reduction ratio determined when the roll flange radius of the final stage stand is used.

[0014]

In the present invention, the cold drawing rolling is combined with the drawing process using the three-roll type reducer having three or more stands and the two-roll type constant diameter process. Variations in the finishing outer diameter caused by insufficient rigidity of the springback and the stand can be adjusted by a two-roll type constant diameter machine that can adjust the subsequent roll gap online, so that a highly accurate finishing outer diameter dimension can be obtained. In addition, the roll of the stand in the front stage of the drawing process by the 3-roll reducer is set to 0% <ellipticity ≤
5%, 0% <side relief <2.5%, outer diameter reduction ratio is 0% <outer diameter reduction ratio <2.5%, and squeeze rolling is performed, and the roll hole type of the stand up to the last two stages is 2 % <Ellipticity ≤ 5
%, The rolling is performed at the maximum outer diameter reduction rate of 10% per stand, so that even if a steel pipe having a variation in the outer diameter of the pipe and a nearly perfect circle is inserted, the occurrence of biting flaws is prevented. Furthermore, since the roll ellipticity of the final front stage stand is 3% or less and the maximum outer diameter reduction ratio is 5%, the deterioration of the roundness due to the reduction rolling in the front stand at the high outer diameter reduction ratio is adjusted. . Furthermore, the roll circumference of the last stage stand is designed to be equal to the product circumference, and 0 <side relief, the roll ellipticity is 0 to 1.5%, and the outer diameter reduction rate is 0.5% or more. The roll groove bottom radius of the stand ≤ the roll flange radius of the final stage The roll rolling is performed at the maximum reduction ratio of the outer diameter that is determined, so that biting is prevented and the perfect circular caliber three-roll type two-stage rolling is performed. It is possible to obtain a finished outer diameter dimensional accuracy equivalent to that in the case.

In the present invention, the roll of the front stand in the drawing process by the three-roll reducer is set to 0% <ellipticity ≦ 5%, 0% <side relief <2.5%, and the outer diameter reduction ratio is 0%. <Outer diameter reduction ratio <2.5% is because the steel pipe of a shape close to a perfect circle is inserted in the frontmost stand and there is variation in the outer diameter of the pipe, so there must be some side relief. This is because biting flaws occur. Further, when the roll ellipticity exceeds 5%, the flange portion of the roll becomes sharp, and the shape of the groove bottom portion does not become smooth even if it is rolled by the hole type of the next stand, and a normal product shape cannot be obtained. The maximum outer diameter reduction rate when the shape of the groove bottom became smooth was 2.5%. Further, the reason why the roll hole type of the second to the last two-stage stand is 2% <ellipticity ≦ 5% and the maximum outer diameter reduction rate per stand is 10% is that the roll ellipticity exceeds 5%. When the roll ellipticity is 2% or less, the flange of the roll becomes sharp and the shape of the groove bottom does not become smooth even if it is rolled with the hole type of the next stand, and the normal product shape cannot be obtained. This is because drawing rolling cannot be performed at a high outer diameter reduction rate of 10%.

The roll of the final front stand is 0 <ellipticity ≦
The reason why the maximum outer diameter reduction rate is 3% is 5% because the roundness is extremely deteriorated when the roll ellipticity exceeds 3%, and the maximum outer diameter reduction rate at that time was 5%. Furthermore, the roll circumference of the last stand is designed to be equal to the product circumference, and 0 <side relief, 0 ≦ ellipse ratio ≦ 1.5% of roll, and outer diameter reduction ratio of 0.5% or more. The maximum outer diameter reduction ratio determined when the roll groove bottom radius of ≦ roll flange radius of the final stage stand is that biting occurs when the side relief is 0, and the ellipticity of the roll is This is because if it exceeds 1.5%, it is not possible to obtain the accuracy of the finished outer diameter equivalent to that obtained by rolling two rounds of three perfect circles. If the outer diameter reduction ratio is less than 0.5%, a deviation occurs in the finished outer diameter dimension, and it is determined when 0.5% or more and the roll groove bottom radius of the final front stage stand is equal to or less than the roll flange radius of the final stage stand. This is because a highly accurate finished outer diameter dimension can be obtained with the maximum outer diameter reduction ratio.

In the present invention, the constant diameter step with two rolls is installed after the drawing step with the three roll reducer because it is difficult to adjust the gap in the three roll reducer, and thus the final outer diameter adjustment is impossible. If the base material strength and the wall thickness are different, the final finishing outer diameter is different even if the roll gap is the same. In cold three-roll rolling, the outer diameter of the pipe after three-roll rolling becomes larger than that of the three-roll hole type due to the spring back of the pipe, and this ratio is proportional to the wall thickness and strength of the mother pipe. For this reason, a two-roll constant diameter stand is installed for final outer diameter adjustment. The two-roll constant diameter stand consists of a combination of one vertical roll stand and one horizontal roll stand.

[0018]

【Example】

Embodiment 1 Hereinafter, details of the present invention will be described with reference to FIGS. 1 to 3 showing an embodiment. FIG. 1 shows a schematic layout of a squeeze rolling mill for carrying out the method of the present invention. FIG. 1 (a) is a schematic layout of a squeeze rolling mill, and FIG. 1 (b) is a two-roll vertical roll stand and a two-roll horizontal. 1 is a schematic layout diagram of a reduction rolling mill having a constant diameter roll roll stand, FIG. 2 is an explanatory diagram of ellipticity of a three-roll reducer, and FIG. 3 is a schematic explanatory diagram of a side riff calculation method. Is a cold steel pipe, 2 is a stand group of a 3-roll type reducer consisting of 3 or more stands, 3 is a 2-roll type constant diameter machine provided in the latter stage of the stand group 2 of the 3-roll type reducer, and is a 2-roll type constant diameter machine 3 Consists of a two-roll vertical roll stand 4 and a two-roll horizontal roll stand 5.

Although not shown, the stand group 2 of the three-roll type reducer consisting of three or more stands has rolls of the frontmost stand, 0% <ellipticity ≦ 5%, 0% <side relief <2.5%. The outer diameter reduction rate is 0% <outer diameter reduction rate <2.5%, and the rolls of the stand from the second stage to the final two stages before the final stage are 2% <ovality <5%, 1 stand. Squeeze rolling with a maximum outer diameter reduction rate of 10% per roll, and the roll of the final front stage stand is squeezed with 0 <ellipticity ≤ 3% and maximum outer diameter reduction rate of 5% to determine the roll circumference of the final stage stand. Designed to be equal to the length, 0 <side relief, 0 roll
≤ Ellipticity ≤ 1.5%, Outer diameter reduction rate is 0.5% or more, and the maximum outer diameter reduction rate determined when the roll groove bottom radius of the final front stand is the roll roll radius of the final stand It is configured to be rolled. Further, the constant diameter machine 3 including the 2-roll type vertical roll stand 4 and the 2-roll type horizontal roll stand 5 adjusts the outer diameter of the pipe subjected to the reduction rolling with a high outer diameter reduction ratio, and at the same time, the three-roll reducer. The roundness of the last stand is maintained.

The ellipticity D of the roll in this invention is
Is the radius R of the flange of the roll 11 as shown in FIG.
n, groove bottom radius rn, average radius l = (Rn + rn) /
2, n = 0, 1, 2, ..., D ^{n + 1} = {Rn ^{n + 1} −
rn ^{n + 1} / (ln ^{+ 1} )} × 100 (%). Also, it reduced outer diameter ratio Red ^{is, Red n + 1 = (l} n
^{-L n + 1) / l n} × 100 (%) by those determined. Further, as shown in FIG. 3, the side relief S in the present invention is S ^{n + 1} = (Rn when the radius of the front roll groove bottom is rn−1 and the radius of the rear roll flange portion is Rn.
-R ^n-1 ) / r ^n-1 × 100 (%). From the above results, the roll hole type of the frontmost stand of the three roll reducer is, as shown in FIG. 4, 0% <outer diameter reduction rate <2.5%, 0% <side relief <2.5%, 0.
It must be in the range of% <ellipticity <5%.

With the above configuration, the rolls of the first stage stand in the drawing process using the three roll reducer are 0% <ellipticity ≦ 5%, 0% <side relief <2.
5%, the outer diameter reduction ratio is 0% <outer diameter reduction ratio <2.5%, and the rolling from the second stage to the final two-stage stand is 2% <ovality <5%, one stand Squeeze rolling with a maximum outer diameter reduction rate of 10%, and the roll of the final front stand with 0 <ellipticity ≤ 3%, maximum outer diameter reduction rate of 5%. There is no deterioration of the shape caused by the flange and the flange, and the deterioration of the roundness due to the reduction rolling at a high outer diameter reduction ratio in the stand up to the last two stages before the final stage is adjusted by the rolling in the final front stage. .

Further, the roll circumference of the final stage stand is designed to be equal to the product circumference, and 0 <side relief, 0 ≦ ellipse ratio ≦ 1.5% for rolls, and an outer diameter reduction ratio of 0.5% or more,
The rolling radius of the final front stand is less than the roll groove radius of the final stand. The rolling is performed at the maximum outer diameter reduction ratio that is determined, so that biting is prevented, and the round caliber is a three-roll two-stage drawing. It is possible to obtain the finished outer diameter dimensional accuracy equivalent to that when rolled. Moreover, the method of the present invention combines cold drawing rolling with a drawing process using a three-roll reducer with three or more stands and a two-roll constant diameter process with one or more stands. Variations in finishing outer diameter caused by insufficient strength of springback and stand due to difference in strength can be adjusted with a two-roll type constant diameter machine that allows online adjustment of the subsequent roll gap, so highly accurate finishing outer diameter can be obtained. it can.

Example 2 A three-roll reducer consisting of six stands arranged with a phase difference of 60 ° for each stand was used, and the roll of the first stage stand had an ellipticity of 4.5% and a side relief of 0.75.
%, And squeeze-rolled at an outer diameter reduction ratio of 1.5%. Up to the second to fourth stands, the roll ellipticity was 4.5% and the squeeze rolling was performed at a maximum outer diameter reduction ratio of 5% per stand. Steel pipe
The 3rd roll of the 5th stand has an ellipticity of 3% and the maximum outer diameter reduction ratio is 5%. The final roll of the 6th stand has an ellipticity of 1.25% and the outer diameter reduction ratio of 1%. With respect to the cold-rolled cold rolled steel pipe of the present invention method, the presence or absence of surface bleeding flaws was visually inspected. For comparison, using the same 3-roll type reducer, up to the 4th stand, 5 stages of cold-rolled steel pipes rolled with a roll ellipticity of 3% or more and an outer diameter reduction rate of maximum 10% per stand are used. The ellipticity of the three rolls of the third stand is changed to 3 to 5% and drawn and rolled at an outer diameter reduction ratio of up to 5%. The ellipticity of the three rolls of the final sixth stand is 0%, 1.25%, With respect to the cold steel pipe of the conventional method which was changed to 2.75% and was drawn and rolled at an outer diameter reduction ratio of 1%, the presence or absence of surface entanglement flaws was visually inspected. As a result, in the case of the method of the present invention, there was no occurrence of bite-out flaws, but in the conventional method, some bite-out flaws were recognized.

[0024]

As described above, according to the method of the present invention, it is possible to perform reduction rolling at a high reduction ratio of outer diameter in cold outer diameter reduction rolling of a steel pipe, and to reduce the wall thickness ratio t / D to the outer diameter. It is possible to manufacture high-diameter, thick-walled steel pipes with high-precision product outer diameter dimensions.

[Brief description of drawings]

FIG. 1 is a schematic layout diagram of a squeeze rolling mill for carrying out the method of the present invention, FIG. 1 (a) is a schematic layout diagram of a squeeze rolling mill, and FIG. 1 (b) is a two-roll vertical roll stand and a two-roll horizontal roll stand. FIG. 3 is a schematic layout view of a reduction rolling machine including a constant diameter machine including

FIG. 2 is an explanatory diagram of an ellipticity of a 3-roll reducer.

FIG. 3 is a schematic explanatory diagram of a method for calculating a side relief of a three-roll reducer.

FIG. 4 is a graph showing the relationship between the roll ellipticity, the side relief, and the outer diameter reduction ratio of the frontmost stand of the three-roll reducer.

FIG. 5 is an explanatory view of a conventional 2-roll type reducer,
(A) is a schematic side view, (b) is a front view of the first-stage stand, and (c) is a front view of the first-stage stand.

6A and 6B are explanatory views of roll arrangement of a three-roll reducer, in which FIG. 6A is a front view of a front stand and FIG. 6B is a front view of a next stand.

FIG. 7 is an explanatory diagram of biting out of a three-roll reducer.

[Explanation of symbols]

 1 Cold Steel Pipe 2 3 Roll Type Reducer Stand Group 3 Constant Diameter Machine 4 2 Roll Type Vertical Roll Stand 5 2 Roll Type Horizontal Roll Stand 11 Roll 31 Hole Roll 32 Stand 33 Mother Tube 41 Hole Roll 42 Gap 43 Steel Tube 44 Biting out

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location B21B 37/16 37/78 (72) Inventor Hiromi Iwanaga 1850 Minato, Wakayama, Wakayama Sumitomo Metal Industries Wakayama Steel Works Co., Ltd.

Claims (1)

[Claims] 1. A method for producing a steel pipe having a highly accurate outer diameter by cold-drawing a steel pipe, wherein cold-drawing is performed by a three-roll reducer having three or more stands, and a set of two or more sets. Combining constant diameter process with rolls,
The roll of the frontmost stand in the drawing process using the 3-roll reducer is 0% <ellipticity ratio ≦ 5%, 0% <side relief <2.5%, and the outer diameter reduction ratio is 0% <outer diameter reduction ratio <2.
The rolls of the stand from the second stage to the final two stages before the final stage are subjected to a squeeze rolling at a rate of 5%, and are squeezed at a maximum outer diameter reduction rate of 10% at a maximum outer diameter reduction rate per stand of 2% <ellipticity ≤ 5%, and the final front stage stand. Roll of 0, ellipticity ≤ 3%, maximum outer diameter reduction ratio 5%
Squeeze rolling with, the roll circumference of the final stage stand is designed to be equal to the product circumference, and 0 <side relief, roll 0 ≦ ellipse ratio ≦ 1.5%, outer diameter reduction ratio 0.5% or more, A method for cold rolling a steel pipe, comprising performing reduction rolling at a maximum outer diameter reduction ratio determined when the radius of the roll groove of the final stand is less than the radius of the roll flange of the final stand.