WO2005035154A1

WO2005035154A1 - Method of manufacturing seamless tube by three-roll mandrel mill

Info

Publication number: WO2005035154A1
Application number: PCT/JP2004/014830
Authority: WO
Inventors: Takamitsu Inage; Shigeru Kidani; Hirotsugu Nakaike
Original assignee: Sumitomo Metal Industries, Ltd.
Priority date: 2003-10-07
Filing date: 2004-10-07
Publication date: 2005-04-21
Also published as: CN100368102C; CN1863608A; JP2005111518A; EP1679136A1; JP4103082B2; RU2309015C1; EP1679136A4; DE602004022574D1; EP1679136B1

Abstract

A method of manufacturing a seamless tube, wherein the ratio of the inner peripheral length of a tube material to the outer peripheral length of a mandrel bar is set within the range of 1.07 to 1.17 in the final two stands of stands forming a mandrel mill where wall-thickness increasing processing is applied to the tube material. Thus, the occurrence of the defective extraction of the mandrel bar after rolling and the occurrence of scratches on the inner surface of the tube material by the mandrel bar can be effectively suppressed without excessively increasing a wall thickness difference (nonuniform wall thickness) in the circumferential direction of the tube material after rolling, and an operation by the three-roll mandrel mill can be actually performed. As a result, the method can be widely used as a method for manufacturing the seamless tube by a Mannesmann mandrel mill system.

Description

Specification

Manufacturing method of seamless pipe by 3 roll type mandrel mill

Technical field

The present invention relates to a method for producing a seamless tube using a three-roll mandrel mill.

Background art

[0002]-In the production of seamless pipes using the mandrel mill method, first, a round billet or square billet of a material is heated to 1200-1260 ° C in a rotary hearth heating furnace, and then rolled with a drilling machine using a plug. The hollow shell is manufactured by piercing and rolling with a roll. Then, a mandrel bar is inserted into the inner surface of the hollow shell in a skewered shape, and the outer surface is constrained by a mandrel mill, usually composed of 5-8 stands, and stretched and rolled while being constrained by a grooved roll to obtain a predetermined thickness. Until the thickness is reduced. Then, after extracting the mandrel bar, the reduced thickness pipe material is formed and rolled to a predetermined outer diameter by a reduction mill to obtain a product.

[0003] Here, as a mandrel mill, conventionally, a pair of grooved rolling rolls facing each stand is arranged, and the rolling direction of the rolling rolls is alternately shifted by 90 ° between adjacent stands. In many cases, a roll type mandrel mill is used! In such a two-roll type mandrel mill, due to an excessive peripheral speed difference between the groove bottom of the rolling roll and the flange portion, a seizure flaw generated at a portion corresponding to the flange portion and an excessive amount of tube material are generated. In order to prevent bleeding flaws due to bleeding, the rolls are usually designed so that the curvature at both ends of the die is large.

In this case, the area corresponding to the flange of the roll of the tube roll is not constrained by the roll nor the mandrel bar and only the tension in the longitudinal direction acts. Therefore, the deformation (extension) in the circumferential direction should be controlled. However, there is also a problem that a hole defect or the like is easily generated in a material having low hot deformability such as stainless steel.

To solve the problem of the two-roll type mandrel mill, three stand-shaped rolling rolls with an angle of 120 ° are formed on each stand to reduce the rolling direction of the rolling roll between adjacent stands. The introduction of a three-roll type mandrel mill that is alternately arranged at 60 ° intervals is being considered. [0004] However, in general, in a three-roll type mandrel mill, the contact range (location) between the inner surface of the tube after rolling and the mandrel bar is two-hole type due to the geometric properties of the hole shape of the rolling roll. It will increase compared to the case. As a result, the load required for pulling out the mandrel bar increases, resulting in serious operational and quality problems such as poor pull-out of the mandrel bar after rolling, and easy occurrence of bow I cracks due to the mandrel bar on the inner surface of the tube. Cause problems. Therefore, it is extremely difficult to commercialize a three-roll type mandrel mill.

[0005] Conventionally, the following (1) one to solve the problem in the three-roll type mandrel mill is described.

Methods such as (3) have been proposed.

(1) A method of controlling the cross-sectional shape of the tube by adjusting the stress acting on the tube between stands by adjusting the number of rotations of the rolling rolls of the adjacent stands (for example, `` Basic load characteristics and deformation characteristics ), Pp. 545-548, Proc.

(2) This is an example of a two-roll type mandrel mill, but by setting the hole circumference of the first stand and the third stand of the mandrel mill to be at least a predetermined multiple of the finish circumference of the mill outlet tube, A method of producing an appropriate clearance between the inner surface of the tube material on the mill exit side and the mandrel bar (for example, see Japanese Patent Application Laid-Open No. 5-185112).

(3) A method in which a sizing stand is installed at the final stand constituting the mandrel mill, and a clearance is created between the mandrel bar and the pipe without reducing the wall thickness of the pipe (for example, JP-A-7-214110) reference).

[0006] In the conventional method disclosed in the above (1), while controlling the shape, the shape of the central portion of the tube material that is simultaneously intruded into a plurality of stands can be controlled, but the compression force between the stands does not sufficiently act. The shape of the tube end cannot be controlled. For this reason, it is known that the both ends of the pipes are in close contact with the mandrel bar on the entire circumference, which is a so-called underfill tendency, and the mandrel bar after drawing is poorly pulled out, and the inner surface of the pipe is pulled by the mandrel bar. It is difficult to solve the problem that scratches are likely to occur.

[0007] Further, the deformation phenomenon of the pipe material in the rolling rolls in the three-roll type mandrel mill is greatly different from that of the two-roll type mandrel mill, and is disclosed in JP-A-5-185112. As in the conventional method of (2), the hole-shaped perimeter of the first stand and the third stand is set. It is not sufficient to solve such problems that the pulling of the mandrel bar after the rolling is insufficient and that the mandrel bar on the inner surface of the tube material easily causes a bow I crack.

In other words, in a three-roll type mandrel mill, the overhang is secured due to the large deformation in the longitudinal direction of the tube material due to the characteristics of the hole shape, and the clearance after rolling cannot be sufficiently secured depending on the method of rolling the post stand. . For this reason, the problem that the mandrel bar is not pulled out, or even if it is pulled out, occurs when the load is significantly increased as compared with the two-roll type mandrel mill.

[0008] Further, in the conventional method (3) as disclosed in Japanese Patent Application Laid-Open No. 7-214110, the clearance between the mandrel bar and the pipe material already disappears before caulking with the sizing stand. In such cases, there is a problem that sufficient effects cannot be obtained.

Disclosure of the invention

[0009] As described above, since the deformation phenomenon of the pipe material in the rolling roll in the three-roll mandrel mill is significantly different from that of the two-roll mandrel mill, the knowledge of the two-roll mandrel mill is used as it is. It is not possible. For this reason, the conventionally proposed method can effectively solve the problems of the three-roll type mandrel mill, such as poor pull-out of the mandrel bar after rolling and the occurrence of scratches due to the mandrel bar on the inner surface of the tube. It is difficult to put a 3-roll mandrel mill into practical use!

[0010] The present invention has been made to solve such a problem of the prior art, and it is intended that a bow I of a mandrel bar after rolling is poorly removed and a bow I flaw caused by a mandrel bar on the inner surface of a tube material. It is an object of the present invention to provide a seamless pipe manufacturing method using a three-roll type mandrel mill that can effectively suppress the generation and operate in practice.

[0011] The present invention to solve the above-mentioned problem is directed to a method of manufacturing a seamless pipe using a three-roll type mandrel mill, wherein, among the stands constituting the mandrel mill, a pipe material has a thick wall. In the last two stands, the ratio of the inner circumference of the pipe to the outer circumference of the mandrel bar is set in the range of 1.07-1.17. Is provided.

[0012] Preferably, the ratio of the inner peripheral length of the pipe to the outer peripheral length of the mandrel bar is set in a range of 1.10-1.17. [0013] Preferably, the ratio of the outer diameter of the tube material on the exit side of the mandrel mill to the groove bottom diameter of the rolling roll in the last two stands is set to 0.25 or less.

[0014] More preferably, the ratio of the outer diameter of the tube material on the mandrel mill exit side to the groove bottom diameter of the rolling roll in the last two stands is set to 0.20 or less.

[0015] Preferably, the ratio of the bar clearance on the entry side of the mandrel mill to the inner diameter of the pipe material on the entry side of the mandrel mill is set to 0.04 to 0.12.

[0016] More preferably, the ratio of the bar clearance on the mandrel mill entry side to the tube inner diameter on the mandrel mill entry side is set to 0.06-0.12.

[0017] Preferably, a sizing stand is installed at a stage subsequent to the last two stands, and the working ratio at the groove bottom of the rolling roll in the sizing stand is 5% or more.

According to the present invention, the ratio of the inner peripheral length of the pipe to the outer peripheral length of the mandrel bar is set to 1.0 in the last two stands that apply thick calorie to the pipe among the stands constituting the mandrel mill. By setting the value in the range of 7- 1.17, the difference in wall thickness (uneven thickness) in the circumferential direction of the tube after rolling is not excessively large, and the mandrel bar is not pulled out properly after rolling, and the mandrel bar on the inner surface of the tube is not damaged. This makes it possible to effectively suppress the occurrence of bow I scratches due to the first method, and provides a method of manufacturing a seamless pipe using a three-roll mandrel mill that can be actually operated.

Brief Description of Drawings

[0019] Fig. 1 is a diagram showing the effect of the ratio of the inner peripheral length of the pipe to the outer peripheral length of the mandrel bar in the last two stands of the mandrel mill, and (a) shows the effect on the pull-out property of the mandrel bar. (B) shows the effect on the inner surface quality of the tube, and (c) shows the effect on the uneven wall thickness of the tube (difference in circumferential thickness of the tube after rolling).

FIGS. 2A and 2B are diagrams for explaining the inner circumferential length of a pipe material set in the seamless pipe manufacturing method according to the present invention. FIG. 2A is a layout diagram of each rolling roll, and FIG. 2B is a broken line in FIG. An enlarged view of the part surrounded by is shown.

FIG. 3 is a diagram for explaining the effect of the groove bottom diameter of the rolling roll set on the pipe material in the seamless pipe manufacturing method according to the present invention.

Fig. 4 shows the effect of the ratio between the outer diameter of the tube at the exit side of the mandrel mill and the groove bottom diameter of the rolling rolls in the last two stands. (A) shows the effect on the pullability of the mandrel bar. (B) shows the effect on the inner surface quality of the tube, and (C) shows the effect on the wall thickness deviation of the tube.

Fig. 5 shows the effect of the ratio of the bar clearance on the mandrel mill entry side to the inner diameter of the tube material on the mandrel mill entry side, where (a) shows the effect on the pull-out property of the mandrel bar and (b) shows the effect on the tube material. (C) shows the effect on the inner surface quality of the pipe, and (c) the effect on the uneven wall thickness of the pipe.

Fig. 6 shows the effect of the degree of work at the bottom of the groove of the rolling roll in the sizing stand, (a) the effect on the pull-out property of the mandrel bar, and (b) the effect on the inner surface quality of the pipe. (C) shows the effect on uneven wall thickness of the pipe.

FIG. 7 is a view for explaining the degree of processing at the bottom of the groove of the rolling roll in the sizing stand set in the method for manufacturing a seamless pipe according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings as appropriate.

In a seamless pipe manufacturing method using a mandrel mill, in order to suppress poor pulling out of the mandrel bar after rolling and to prevent the occurrence of drawing flaws due to the mandrel bar on the inner surface of the pipe material, the pipe material after rolling and the mandrel bar must be joined together. Although it is necessary to generate an effective clearance between them, the present inventors have found that, particularly in the case of a three-roll type mandrel mill, when the final wall thickness processing is performed, the pipe material does not cover the outer peripheral length of the mandrel bar. It was found that the length of the inner circumference greatly depends on how much the inner circumference is set! /.

In other words, whether or not the force at which the effective clearance is generated is determined by the final two stands where the wall material is subjected to the wall thickness processing, that is, the inner shape of the rolling roll in the final stand and the immediately preceding stand, etc. It was clarified that the ratio of the circumference to the circumference of the mandrel bar had a significant effect.

Therefore, the present inventors have developed a ratio of the inner peripheral length of the tube material to the outer peripheral length of the mandrel bar (hereinafter, referred to as “mandrel mill”) in each of the last two stands of the mandrel mill, in which the tube material is thickened. Rolling tests were performed on 10 tubes each made of carbon steel and 9% Cr steel while changing the perimeter ratio as appropriate), and the effect of the perimeter ratio on the pullability of the mandrel bar after rolling was investigated. . Fig. 1 shows the effect of the ratio of the inner circumference of the pipe to the outer circumference of the mandrel bar at the last two stands of the mandrel mill. Fig. 1 (a) shows the effect on the pull-out property of the mandrel bar. ) Shows the effect on the inner surface quality of the tube, and (c) shows the effect on the uneven wall thickness of the tube (the difference in wall thickness in the circumferential direction of the tube after rolling).

The vertical axis in Fig. 1 (a) indicates that "2" is good for both carbon steel and 9% Cr steel ("good" means that all 10 can be extracted), and "1" is good for "1". It shows that only carbon steel is good, and "0" indicates that both carbon steel and 9% Cr steel are bad.

In addition, the vertical axis in Fig. 1 (b) indicates that "3" indicates that there is no internal disease (scratch due to mandrel bar) on the tubing, and "2" indicates that the incidence rate is 10% or less. "1" indicates that the incidence is less than or equal to 20%, and "0" indicates that the incidence is greater than 20%.

Further, the vertical axis of FIG. 1 (c) indicates that “2” indicates that the uneven thickness ratio of the pipe is less than 15%, and “1” indicates that the unevenness is 15% or more.

[0022] As shown in Figs. 1 (a) and (b), by setting the circumference ratio to 1.07 or more, the clearance between the pipe and the mandrel bar can be ensured, and the pull-out property of the bar and the inner surface of the pipe can be secured. In terms of quality, it was a compelling factor that relatively good results were obtained. However, as shown in Fig. 1 (c), when the perimeter ratio is larger than 1.17, good results can be obtained for the pull-out property of the bar and the inner surface quality of the pipe (Figs. 1 (a) and (b)). However, it was a component that caused a quality problem that the wall thickness of the pipe became too large.

Therefore, by setting the circumference ratio in the range of 1.07-1.17, pulling out the mandrel bar after rolling without excessively increasing the circumferential thickness difference (uneven thickness) of the pipe after rolling. It has been found that defects and the occurrence of scratches caused by a mandrel bar on the inner surface of the tube can be effectively suppressed. As shown in FIG. 1 (a), in order to further suppress the pull-out failure of the mandrel bar, it is preferable to set the circumference ratio in the range of 1.10 to 1.17.

FIG. 2 is a view for explaining the inner circumferential length of a pipe material set in the method for manufacturing a seamless pipe according to the present invention. FIG. 2 (a) shows an arrangement diagram of each rolling roll, and FIG. () Shows an enlarged view of a portion surrounded by a broken line in (a). As shown in FIG. 2 (b), the inner circumferential length of the tube material is 6 in the circumferential direction with respect to the center of the hole shape C, based on the hole shape profile from the groove bottom B to one end E of each roll roll. Determine the outer surface shape (curve BE ') of the divided tube material, and It is a value obtained by integrating the length of the inner surface shape (curve BIE1) of the 6 divided pipes calculated by correcting for the bottom wall thickness t for six pieces.

Here, in order to determine the outer shape of the pipe (curve BE ') based on the profile of the pipe (curve BE), for example, the arc forming the profile of the pipe near the end E should be angled by 60 ° with the straight line BC. To the straight line CC ', and the intersection of the extended arc and the straight line CC' can be set as a point E,.

Correcting the outer surface shape (curve BE ') with the groove bottom thickness t means moving each point constituting the curve BE' inward in the normal direction of each point by the thickness t. I do. The groove bottom thickness t is a value determined by the rolling schedule, and the mandrel bar outer circumference is a value that also calculates the outer diameter force of the mandrel bar determined by the rolling schedule.

[0024] As described above, by setting the circumference ratio in a predetermined range, it is usually possible to effectively prevent poor pull-out of the mandrel bar, etc., but depending on the material of the tube material, rolling conditions, and the like. Since the pipe material does not fill the hole and adheres tightly to the mandrel bar, the pull-out property may be reduced, or a draw-off flaw may be generated by the mandrel bar. The inventors of the present invention have made various studies to prevent the pull-out property from being lowered by extending the tube material as much as possible along the groove shape of the rolling roll, and as a result, the groove bottom diameter of the rolling roll, that is, By setting the length of the line segment BB 'connecting the groove bottom B and the opposite groove bottom B' shown in FIG. We paid attention to the fact that the contact length between the bottom and the pipe was long.

FIG. 3 is a diagram for explaining the effect of the groove bottom diameter of the rolling roll on the pipe material at this time. As shown in FIG. 3, by setting the groove bottom diameter of the roll to be larger than the outer diameter of the tube at the mandrel mill exit side, the contact length between the groove bottom of the roll and the tube becomes longer. As a result, the deformation resistance in the rolling direction is increased, and as a result, the deformation of the rolling roll toward the flange portion side is promoted, and the overhang along the hole shape of the rolling roll is promoted.

[0025] The present inventors have determined the ratio of the outer diameter of the tube material on the exit side of the mandrel mill to the groove bottom diameter of the rolling roll in the last two stands (hereinafter referred to as "finish diameter Z roll groove bottom diameter" as appropriate). Rolling test was performed on 10 tubes each made of carbon steel and 9% Cr steel while changing Figure 4 shows the effect of the ratio between the outer diameter of the tube at the exit side of the mandrel mill and the groove bottom diameter of the rolling rolls at the last two stands. (A) shows the effect on the pull-out property of the mandrel bar, (b) shows the effect on the inner surface quality of the tube, and (c) shows the effect on the uneven wall thickness of the tube.

The meaning of the numerical values shown on the vertical axis in FIGS. 4 (a)-(c) is the same as that in the case of FIG. 1, and the description is omitted. In this rolling test, the perimeter ratio described above was included in the above-mentioned range of 1.07, and the it between the bar clearance on the mandrel mill entry side and the pipe inner diameter on the mandrel mill entry side described later was 0.04. did.

As shown in FIGS. 4 (a) and 4 (b), by setting the finishing diameter Z roll groove bottom diameter to 0.25 or less (more preferably 0.20 or less), the pull-out property of the bar and the pipe material It was found that relatively good results were obtained for the inner surface quality. However, if the finished diameter Z roll groove bottom diameter is less than 0.1, good results can be obtained for the bar pull-out property and the inner surface quality of the tube material, but they are too large to be practical. Therefore, the finished diameter Z-roll groove bottom diameter is preferably 0.1-0.25, more preferably 0.1-0.2. The outside diameter of the pipe at the outlet side of the mandrel mill is a value determined by a rolling schedule.

[0027] The present inventors also adjusted the ratio of the bar clearance at the entry side of the mandrel mill to the inner diameter of the tube material at the entry side of the mandrel mill, so that the tube material could follow the hole shape of the rolling roll. It was thought that it was possible to prevent the pull-out property from being lowered by overhanging. Therefore, while changing the ratio of the bar clearance at the entry side of the mandrel mill to the inner diameter of the pipe material at the entry side of the mandrel mill (hereinafter referred to as “entrance bar clearance Z finish diameter” as appropriate), the pipe material that also has carbon steel and 9% Cr steel strength A rolling test was performed on each of the ten bars, and the effect of the entry side bar clearance Z finish diameter on the pull-out property of the mandrel bar after rolling was investigated.

Fig. 5 shows the effect of the ratio of the bar clearance on the mandrel mill entry side to the inner diameter of the tube material on the mandrel mill entry side. (C) shows the effect on the wall thickness deviation of the pipe material. ing.

The meanings of the numerical values shown on the vertical axis in FIGS. 5A and 5C are the same as those in FIG. In the present rolling test, the above-described circumference ratio was set to 1.07 included in an appropriate range, and the above-described finish diameter / roll groove bottom diameter was set to 0.25 included in an appropriate range.

[0028] As shown in Figs. 5 (a) and 5 (b), by setting the entry side bar clearance Z finish diameter to be 0.04 or more (more preferably, 0.06 or more), the bar can be pulled out easily. It was a component that relatively good results were obtained for both the inner surface quality of the tubing. However, if the entry side bar clearance Z finish diameter is larger than 0.12, the outer peripheral length of the tube material will be excessively large and rolling may not be possible due to excessive protrusion, so it is not practical. Absent.

Therefore, the entry side bar clearance Z finish diameter is preferably set to 0.04 to 0.12, more preferably to 0.06 to 0.12. The bar clearance is defined by (the inner diameter of the tube material on the entry side of the mandrel mill and the outer diameter of the mandrel bar) and is a value determined by a rolling schedule.

[0029] Further, the present inventors set up a sizing stand after the last two stands for performing wall thickness processing on the pipe material, and perform processing beyond a specified amount on the groove bottom of the rolling roll in the sizing stand. Thus, unlike the case where a sizing stand was simply installed, the tube material was deformed in the flange direction, and an effective clearance was generated, so that it was considered that the pull-out property could be further improved.

Therefore, a rolling test was performed on 10 pipes each made of carbon steel and 9% Cr steel with various degrees of workability at the bottom of the groove of the rolling roll in the sizing stand, and the pulling properties of the mandrel bar after rolling were examined. The effect on the was investigated.

The meanings of the numerical values shown on the vertical axis in FIGS. 6A and 6C are the same as those in FIG. In this rolling test, the above-mentioned perimeter ratio was set to 1.07, which is included in an appropriate range, and the finish diameter Z, described above, was set to 0.25, which was included in an appropriate range. The entry side bar clearance / finished diameter was set to 0.04 which is included in the appropriate range. [0030] As shown in Figs. 6 (a) and (b), by setting the working ratio to 5% or more, it is possible to obtain relatively good results in both the pull-out property of the bar and the inner surface quality of the pipe material. FIG. 7 is a schematic view of a method for manufacturing a seamless pipe according to the present invention.

FIG. 4 is a diagram for explaining the degree of processing at the groove bottom of the rolling roll in FIG. As shown in Fig. 7, the above-mentioned strength is determined by the long diameter (line CE of Fig. 2 (b)) at the final stand (the N-1st stand) where the wall thickness is applied to the pipe. Is equivalent to A, and the minor axis at the sizing stand (Nth stand)

N-1

When B (corresponding to the line segment BC in FIG. 2 (b)) is B, it is calculated by the following equation (1).

N

Degree of processing = (A / B) X 100 (%)

N-1 N-1

Example

Hereinafter, the characteristics of the present invention will be further clarified by showing examples. Table 1 shows the conditions and the evaluation results of the examples of the seamless pipe manufacturing method according to the present invention.

[table 1]

According to the conditions shown in Table 1 (Examples 1-116 and Comparative Examples 1-2), a rolling test was performed on each of 10 tubes each made of carbon steel and 9% Cr steel. Here, the rolling test is Examples 11 and 11 and Comparative Examples 1 and 2 were carried out using a mandrel mill with a total of 5 stand strengths (the 4th and 5th stands correspond to the last 2 stands for thickening the pipe). For Examples 12-16, each was performed using a mandrel mill in which a sizing stand (sixth stand) was installed after the last two stands.

The abbreviation `` outside tZD '' shown in Table 1 indicates the wall thickness Z outer diameter of the tube at the mandrel mill outlet side, and the `` final wall thickness 2Std circumference ratio '' indicates the wall thickness of the tube. The ratio of the inner circumference of the tube to the outer circumference of the mandrel bar at the last two stands (the fourth and fifth stands) is defined as the “sizing Std groove bottom reduction” at the bottom of the rolling roll groove at the sizing stand (the sixth stand). Means the degree of processing.

[0033] The results of the above rolling test were evaluated from the viewpoints of (1) the pullability of the mandrel bar, (2) the inner surface quality of the pipe, and (3) the wall thickness deviation of the pipe. The numerical values of the bar pullability, inner quality of the pipe material, and uneven thickness evaluation shown in Table 1 for the evaluation results of these items have the same meanings as the numerical values shown on the vertical axis of FIG. Omitted.

[0034] As shown in Table 1, the pullability and the inner surface quality of the tube material for Examples 1 to 16 were all "3", "2", or "1". It was found that poor pulling out of the mandrel bar and generation of scratches due to the mandrel bar on the inner surface of the pipe material could be effectively suppressed.

Furthermore, the wall thickness deviation of the pipe material was all "1", and it was confirmed that the problem of wall thickness deviation did not occur. In particular, when the ratio of the inner peripheral length of the pipe to the outer peripheral length of the mandrel bar is set to 1.10-1.17 (Examples 2, 3, 6, 7, 10, 11, 15, 16), the pull-out property is low. All were "2", indicating a remarkable effect.

[0035] Further, when Example 4 and Example 5 are compared or Example 6 and Example 7 are compared, even if the circumference ratio is the same, the outer diameter of the pipe material on the mandrel mill exit side and the final By making the ratio of the rolling roll to the groove bottom diameter of the two stands 0.2, the pulling power and the Z or inner surface quality of the tube material were improved.

[0036] Further, when Example 8 and Example 9 are compared, or Example 10 and Example 11 are compared, the rolling ratio in the circumference ratio, the outer diameter of the tube material on the mandrel mill exit side, and the final two stands is obtained. Even if the ratio to the groove bottom diameter is the same, the bar clearance on the mandrel mill entry side and the mandrel mill By setting the ratio to the inner diameter of the pipe on the inlet side to be 0.06, the pulling power and the quality of the inner surface of the pipe or Z were improved.

Further, comparing Examples 12, 14 and 15 with Examples 13 and 16, the ratio of the circumference, the outer diameter of the tube material on the exit side of the mandrel mill, and the groove bottom diameter of the rolling roll in the last two stands are described. Even if the ratio and the ratio between the bar clearance on the inlet side of the mandrel mill and the inner diameter of the pipe material on the inlet side of the mandrel mill are the same, the degree of processing at the bottom of the groove of the rolling roll in the sizing stand should be 5% or more. It has been found that the drawability and Z or the inner quality of the pipe material are improved.

[0038] On the other hand, in Comparative Example 1, the circumference ratio was less than 1.07 (1.05), and it was a component that both the pull-out property of the mandrel bar and the inner quality of the pipe material were poor. . On the other hand, in Comparative Example 2, good results were obtained for both the pull-out property of the force mandrel bar having a circumference ratio larger than 1.17 (1.19) and the inner surface quality of the pipe. However, the wall thickness deviation rate is 15% or more ("0"), and cannot be adopted as a method for manufacturing a seamless pipe that can be a product. Industrial potential

According to the seamless pipe manufacturing method of the present invention, in each of the last two stands of the mandrel mill, in which the pipe is thickened, the inner circumference of the pipe and the outer circumference of the mandrel bar are used. By setting the ratio to 1.07-1.17, the difference in wall thickness in the circumferential direction (uneven thickness) of the post-rolled tube material does not become too large. It is possible to effectively suppress the occurrence of bow I scratches due to the mandrel bar on the inner surface of the pipe, and it is possible to actually operate with a three-roll mandrel mill. This allows

-Widely applied as a seamless pipe manufacturing method using the mandrel mill method

Claims

The scope of the claims

[1] A method for producing a seamless tube using a three-roll mandrel mill,

Of the stands constituting the mandrel mill, the ratio of the inner peripheral length of the pipe to the outer peripheral length of the mandrel bar in the last two stands for applying the wall thickness to the pipe in the range of 1.07-1.17. A method of manufacturing a seamless tube using a three-roll mandrel mill, which is characterized by setting.

[2] The three-roll type mandrel mill according to claim 1, wherein a ratio of an inner peripheral length of the pipe to an outer peripheral length of the mandrel bar is set in a range of 1.10-1.17. Production method.

[3] The 3-row according to claim 1 or 2, wherein the ratio of the outer diameter of the tube material on the mandrel mill exit side to the groove bottom diameter of the rolling roll in the last two stands is set to 0.25 or less. Manufacturing method of seamless pipes using a mandrel mill.

4. The three-roll mill according to claim 3, wherein a ratio of an outer diameter of the tube at the outlet side of the mandrel mill to a groove bottom diameter of a rolling roll in the last two stands is set to 0.20 or less. A method for producing seamless pipes using a drel mill.

5. The method according to claim 1, wherein a ratio of a bar clearance at the inlet side of the mandrel mill to an inner diameter of a pipe at the inlet side of the mandrel mill is set to 0.04 to 0.12. A method of manufacturing a seamless tube using a three-roll mandrel mill.

6. The three-roll type mandrel mill according to claim 5, wherein a ratio of a bar clearance at the entrance side of the mandrel mill to an inner diameter of a pipe material at the entrance side of the mandrel mill is set at 0.06-0.12. Method for producing seamless pipes.

7. The sizing stand according to claim 1, wherein a sizing stand is provided at a stage subsequent to the last two stands, and a working degree at a groove bottom of a rolling roll in the sizing stand is 5% or more. A method for producing a seamless tube using a three-roll mandrel mill as described in Crab.