JPH09300007A - Method for manufacturing seamless tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent defective bite, the contraction of a tube end, and the occurrence of an uneven thickness, and to improve quality and productivity even when piercing rolling a thick tube with high expansion ratio and low ratio of piercing by specifying the shape of a plug to be used when manufacturing the seamless tubes by Mannesmann tube manufacturing method. SOLUTION: The rolling part of the plug 2 to be used is bisected to preceding stage rolling part and succeeding stage rolling part. And also, when the radius of curvature and length in the axial direction of the tip spherical surface of the preceding stage rolling part are expressed by rp and L1 respectively, a taper angle and length in the axial direction of the succeeding stage rolling part are expressed by θ and L1, and the taper angle and length in the axial direction of a reeling part are expressed by θ1 and L3 respectively, formulas I to IV must be satisfied by these. In addition, this plug can be effectively used at the time of piercing rolling with the expansion ratio 1.15 or over and the ratio of piercing 2 or below. Also, this plug is applicable regardless of a difference between the cone type and the barrel type of a main roll and the type of a guide part, and the same effect can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a seamless pipe, and more specifically, it is widely adopted in a so-called Mannesmann pipe making method which is a typical production method for a seamless metal pipe. The piercing and rolling machine called an inclined piercer has a pipe expansion ratio (material outer diameter after rolling / material outer diameter before rolling) of 1.15 or more and a piercing ratio (material length after rolling / rolling). The former material length) is 2 or less, and relates to a tube expansion piercing and rolling method.

[0002]

2. Description of the Related Art Generally, when a seamless pipe is manufactured by the Mannesmann pipe manufacturing method, a hollow shell is obtained by passing a solid round billet, which is a raw material, through a piercer to punch its center. Next, the obtained hollow shell is expanded or stretch-rolled as it is or through an elongator having the same structure as the piercer, and then stretch-rolled to reduce its outer diameter and wall thickness by passing it through a stretching mill called a plug mill, for example. Then, while smoothing the inner and outer surfaces of the pipe by passing it through a polishing tube rolling machine called a reeler and a constant diameter rolling machine called a sizer, the shape is corrected and sizing is performed, and then the product is refined and then processed. It is normal to do.

Further, the above hollow shell is passed through a multi-stand drawing and rolling machine called a mandrel mill different from the above plug mill to carry out drawing and rolling to reduce its outer diameter and wall thickness, and then called a stretch reducer. There is also a case where the product is passed through a squeezing and rolling machine to be finished to a predetermined size and then subjected to a refining process to obtain a product.

In the above piercer, the inclined rolls (hereinafter referred to as main rolls), which are arranged so as to face each other with the roll axis inclined with respect to the pass line, are barrel type and cone type. There are two types.

The structure of a piercer which is an inclined roll type piercing and rolling machine used in the above-mentioned Mannesmann pipe manufacturing method will be described.

FIG. 7 is a schematic plan view showing the structure of a general piercer, FIG. 8 is a schematic side view of the same, and FIG. 9 is II-II of FIG.
FIG. 10 is a cross-sectional view taken along the arrow, in which reference numerals 10 and 10 are main rolls, 2 is a plug, 3 is a disc roll, B is a billet,
H is a hollow shell and M is a mandrel bar.

The main roll 10 is provided with a gorge portion 11 having a maximum diameter in the vicinity of an intermediate portion in the axial direction of the main roll 10.
1 is provided with an inlet surface 12 and an outlet surface 13 each having a truncated cone shape whose diameter gradually decreases toward the end, and has a barrel shape as a whole.

FIG. 10 is a schematic diagram for explaining the inlet surface angle α1 and the outlet surface angle α2 of the main roll 10. The inlet surface angle α1 is obtained when the inclination angle β of the main roll 10 is 0 (zero). Of the entrance surface 12 in the axial direction and the pass line X
-X, and the exit surface angle α2 is an angle formed by the extension line in the axial direction of the surface of the exit surface 13 and the pass line XX.

The main rolls 10 and 10 have a pass line X.
-X is sandwiched by the billet B which is the material to be rolled, the axis is parallel to the pass line XX in plan view (see FIG. 7), and one main roll 10 has its inlet face in side view. 12 is on the upper side, and the other main roll 10 is arranged opposite to each other with a predetermined inclination angle β (see FIG. 8) so that the inlet surface 12 thereof faces the lower side. It is designed to be rotated in the direction.

The disc rolls 3 and 3 have a pass line X-
The main roll 10 with the longitudinal direction of the main roll 10 sandwiching X,
It is arranged so as to oppose to 10. The disc rolls 3 and 3 are large-diameter disc-shaped bodies, have a concave hole shape on the outer peripheral surface facing the pass line XX, and are rotationally driven in the arrow direction by a drive motor (not shown). It has become so.

The plug 2, which is an inner surface regulating member, has its base end supported on the tip of the mandrel bar M, and is positioned and held on the path center XX between the main rolls 10 and 10 and the disc rolls 3 and 3. Has been done.

The mandrel bar M is connected at its base end to a thrust block having a forward / backward moving mechanism (not shown), and rotatably supports the plug 2 with the pass line XX as its axis. There is.

Conventionally, the following plugs are used as the plug 2.

FIG. 11 is a schematic vertical sectional view showing a conventional plug. The plug 2 has a warhead shape as a whole, and a rolling portion 2 having a length LL1 which is substantially conical from the tip side.
1. Following this, a reeling portion 22 having a length LL2 and having a substantially truncated cone shape, and a relief portion 23 having a diameter reduced toward the base end portion.
It has.

That is, the rolling portion 21 has a radius of rp at the tip.
And a circular arc surface of radius AR centered on a line whose angle with the perpendicular to the pass line XX at the base end is .theta.3.
Is formed on a tapered surface whose angle with the pass line X--X is .theta.2.

In the figure, Rg is a main roll interval and Ld is a plug lead, both of which are set to predetermined values.

Further, as the main roll 10, there is a cone type as described above, and a piercer adopting this cone type main roll is also generally used.

FIG. 12 is a schematic plan view showing the structure of a general piercer using a cone-type main roll. In the figure, reference numeral 1 is a cone-type main roll.

As shown in FIG. 12, this main roll 1 is
It has a shape in which the diameter gradually decreases toward the entrance side end and gradually increases toward the exit side end with reference to the gorge portion 11 in the middle in the axial direction, and the pass line XX
Are opposed to each other with a predetermined inclination angle β and a predetermined intersection angle γ.

The entrance surface angle α1 and the exit surface angle α2 of the main roll 1 are as shown in FIG. 13 when the inclination angle β is 0 (zero) and they are arranged facing each other with a predetermined crossing angle λ. Extension line in the axial direction and pass line X on the surface of the inlet face 12
The angle formed by −X is the inlet surface angle α1, and the angle formed by the extension line in the axial direction of the surface of the outlet surface 13 and the pass line XX is the outlet surface angle α2.

The other configurations and the state of the piercing and rolling operation of the material to be rolled are the same as those of the piercer shown in FIGS. 7 to 10. Corresponding parts are designated by the same reference numerals, and detailed description will be given. Omit it.

In the piercer described above, the disk rolls 3 and 3 are the members that restrain the swinging of the material to be rolled (the billet B and the hollow shell H pulled out) and the bulging in the radial direction of the pipe wall. However, there is also a piercer in which a plate-shaped guide shoe or a roller shoe is arranged instead of the disc roll 3 so as to be in sliding contact with the material to be rolled, and in the case of this piercer, rolling is performed in the same manner as described above.

Various defects may occur in the seamless pipe manufactured using the piercer as described above, depending on the piercing and rolling conditions. As a method of preventing the occurrence of such defects, the main roll interval Rg, the plug lead Ld, the guide shoe interval, and the like are set based on an appropriate perforation condition expression, whereby the biting property and the trailing edge property of the material to be rolled are set. And the like (Japanese Patent Publication No. 59-44927), a method in which a thick-walled pipe can be easily obtained by closing the main roll interval when the rolled material slips out to prevent clogging of the rolled material (special (Kaisho 64-31504).

[0024]

By the way, in the piercing and rolling with the above piercer, when obtaining hollow shells of the same size, "the outer diameter of the material after rolling (hollow shell) /
The larger the expansion ratio defined by the "material (billet) outer diameter before rolling", the smaller the outer diameter of the billet can be used. As a result, the load characteristics (roll load, roll torque) of the piercer are reduced, which has the advantage of facilitating the manufacture of large diameter pipes. For this reason, piercing and rolling with a high expansion ratio is considered important.

However, while the pipe expansion ratio is large, "material after rolling (hollow shell) length / material before rolling (billet)
When performing piercing and rolling with a small piercing ratio defined by `` length '', in addition to frequent biting defects such as jamming and clogging of the bottom of the hollow shell, many misrolls occur. There was a problem that the obtained hollow shell had a large uneven thickness, which deteriorated the production efficiency and the product quality.

Table 1 shows the occurrence of misrolls and uneven thickness of the hollow shell when piercing and rolling was carried out under the conditions shown in Table 2 using the piercer shown in FIG. 12 equipped with the plug having the shape shown in FIG. It is a table which shows the result of having investigated the situation.

As for the results, the uneven thickness of the obtained hollow shells was evaluated by x when the uneven thickness was deteriorated and by ○ when the uneven thickness was not deteriorated. For misroll,
The state in which the plug did not come off from the bottom portion of the hollow shell, that is, the case where so-called clogging of the tail was generated, was marked with X, and the case where the clogging of the bottom was not generated was marked with ◯.

[0028]

[Table 1]

[0029]

[Table 2]

As is clear from the results shown in Table 1, when the pipe expansion ratio is 1.15 or more and the perforation ratio is less than 2, clogging of tails occurs and uneven thickness is deteriorated.

Further, as described above, the piercer is provided with a plate-shaped guide shoe or a disc roll as a guide member for suppressing swinging of the rolled material due to spiral rotation movement and bulging of the outer diameter of the rolled material. It is set up. However, the plate-shaped guide shoe is a fixed type and slides in contact with the material to be spirally rotated, while the disk roll is rotationally moved in the rolling direction of the material to be rolled. The outer surface quality of the obtained hollow shell is superior. For this reason, recent piercers are being widely used that include a disc roll as a guide member.

However, the above-mentioned Japanese Patent Publication No. 59-44927.
The method disclosed in Japanese Laid-Open Patent Publication No. 2003-242242 is directed to a piercer that uses a plate-shaped guide shoe as a guide member, and is 1.0 to 1.0.
As long as piercing and rolling is performed with a pipe expansion ratio of about 5, tail jamming does not occur. However, based on the method disclosed in that publication, without specifying the plug shape, 1.05
When the piercing and rolling is performed at a high pipe expansion ratio of over 2.0 and a low piercing ratio of less than 2.0, there is a drawback that tail jamming occurs and the uneven thickness of the hollow shell deteriorates.

The method disclosed in the above-mentioned Japanese Patent Laid-Open No. 64-31504 is a piercer target using a disk roll as a guide member, and has a high pipe expansion ratio of more than 1.05 and less than 2.0. Even when piercing-rolling with a low piercing ratio, the tail jamming does not occur. However, the method disclosed in this publication reduces the main roll interval when the trailing edge of the material to be rolled leaves the main roll, and therefore is required to change the roll interval of the main roll when the rolling load is applied. The torque is much higher than when there is no load.

For this reason, it is necessary to enlarge the reduction roll axis of the main roll and also to increase the motor capacity for roll reduction, which results in high equipment cost and sufficient equipment strength even if it is applied to existing equipment. Otherwise, it cannot be applied, and it has the drawback of requiring a major remodeling comparable to a new installation.

Furthermore, when piercing and rolling is performed using the conventional plug having the shape shown in FIG. 11, the resulting hollow shell has a significantly reduced rolling bottom portion, as shown in FIG. 14, depending on the piercing ratio. However, there is a problem in that the above-mentioned clogging of the tail becomes remarkable. Further, when this hollow shell is subjected to, for example, a mandrel mill which is a tube rolling machine in the subsequent stage,
There is a problem in that the mandrel bar cannot be inserted into the pipe, which causes a problem of lowering productivity.

Table 3 shows the hollow shell obtained by piercing and rolling under the conditions shown in Table 4, the outer diameter in the axial direction was measured, and the outer diameter d2 of the rolling bottom end was reduced with respect to the outer diameter d1 of the intermediate portion. Diameter ratio KB "KB = (d2-d1) / d1 x10
3 is a table showing the relationship between "0%" and the perforation ratio EL.

[0037]

[Table 3]

[0038]

[Table 4]

As is apparent from Table 3, the perforation ratio EL3.
When it is 0, the outer diameter d2 of the rolling bottom end becomes larger than the outer diameter d1 of the middle portion, but when the perforation ratio EL is 2.8 or less, the outer diameter d2 of the rolling bottom end is larger than the outer diameter d1 of the middle portion. The smaller the perforation ratio EL, the smaller the outer diameter d2 of the rolling bottom end.

The present invention has been made in view of the above circumstances, and its problem is a high expansion ratio of 1.15 or more, and 2.
Even when piercing and rolling is performed at a low piercing ratio of less than 0,
It is an object of the present invention to provide a method for manufacturing a seamless pipe which can prevent not only the defective biting but also the tail clogging, especially the clogging of the bottom of the hollow shell where the plug does not come off and the deterioration of the uneven thickness of the hollow shell.

[0041]

Means for Solving the Problems As a result of a number of experiments to achieve the above-mentioned objects, the present inventors have found the following and have completed the present invention.

That is, it was thought that the problems of the above-mentioned respective prior arts were caused by the shape of the plug used, and various studies were made on the shape of the plug.

As a result, the rolled part is formed by a tip spherical surface having a predetermined radius of curvature determined in association with the billet outer diameter as a raw material, and a preceding rolling part formed by a tangential arc surface following the tip spherical surface.
It is divided into two parts, namely, a post-rolling part formed by a taper surface having a predetermined angle in relation to the exit face angle of the main roll, and the reeling part following this rolling part is associated with the exit face angle of the main roll. The total length of the rolling part and the reeling part is set to the specified length in relation to the billet outer diameter, and the length ratio of the pre-rolling part and the post-rolling part is set. It has been found that it is effective to use a plug having a predetermined value of.

The gist of the present invention based on the above findings lies in the following method for producing a seamless steel pipe.

A pair of main rolls provided with an inlet surface and an outlet surface opposed to each other around the pass line, and a pair of disk rolls opposed to each other around the pass line while being out of phase with each other. In the meantime, the diameter of the round billet and the rolling end and the rear end face that become spherical as the tip shape is spherical along the axis of the blank round billet and move toward the rear end while screwing the material round billet in the axial direction In a method for manufacturing a seamless pipe, a hollow shell is obtained by inserting a shell-shaped plug having a smaller escape portion,
As the plug, the rolling section is divided into a pre-rolling section and a post-rolling section, and the radius of curvature and axial length of the tip spherical surface of the pre-rolling section are rp, L1 and the taper angle of the post-rolling section, respectively. The axial lengths are θ1, L2, and
The taper angle of the reeling part and the axial length are θ
2 and L3, these are respectively (1) to
A method for manufacturing a seamless pipe, characterized in that a plug having a shape and size satisfying the expression (6) is used.

0.14 × Bd ≦ rp ≦ 0.23 × Bd (1) 0.4 ≦ L2 / L1 ≦ 3 (2) α2 +0.5 ≦ θ1 ≦ α2 + 6 ° ···· (3) 0.7 ≦ L3 / P ≦ 2 ····· (4) α2 ≦ θ2 ≦ α2 + 1 °… (5) 2 x Bd ≤ L1 + L2 + L3 ≤ 3.5 x Bd ... (6) where, Bd: outer diameter of the material round billet α2: outlet face angle of the main roll P : (Bd + Ds) / 4 × tan β However, Ds: outer diameter β of hollow shell β: inclination angle of main roll In the above invention, the main roll constituting the piercer may be either a cone type or a barrel type, and the guide member may be It can be applied to any of a plate-shaped guide shoe, roller shoe, and disk roll, and the same effect can be obtained.

[0047]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the method of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic plan view showing an example of an embodiment in which the method of the present invention is applied to a piercer whose main roll is a cone type, FIG. 2 is a schematic side view of the same, and FIG. I-
In the cross-sectional view taken along the line I, reference numerals 1 and 1 are main rolls, 2 are plugs, 3 and 3 are disc rolls, B is a billet, H is a hollow shell, and M is a mandrel bar.

The main rolls 1, 1 each have a short cylindrical gorge portion 11, an inlet surface 12 having a substantially truncated cone shape whose diameter is reduced toward both ends of the gorge portion 11, and the end portions are directed. And an outlet surface 13 having a substantially truncated cone shape whose diameter is expanded in accordance with the above, and is formed in a cone shape as a whole.

The main rolls 1 and 1 are opposed to each other with a crossing angle γ (see FIG. 1) provided on both sides of the path center XX line, while an inclination angle β (see FIG. 2) with respect to the path center XX line. (Refer to FIG. 3), they are tilted in opposite directions, and are rotationally driven in the arrow direction by a drive source (not shown).

The inlet face angle α1 and the outlet face angle α2 of the main rolls 1 and 1 are the same as in the case of FIG. 13 described above, and the inlet face angle 1 under the condition that the inclination angle β is 0 (zero), respectively.
2 and the angle between the surface or its tangent and the pass line X-X, and the surface of the outlet surface 13 or its tangent and the path line X-X.
It is the angle formed by -X.

The above-mentioned main rolls 1 and 1 have mutual roll intervals Rg in the gorge portion 11 (see FIG. 4 described later).
Is set to a predetermined value.

The disk rolls 3 and 3 are disc bodies having concave sliding surfaces 3d formed on the outer peripheral surfaces thereof, and the sliding surfaces between the main rolls 1 and 1 on both sides of the path center XX line. Three
d is arranged so as to face the moving range of the material to be rolled, and is driven to rotate in the arrow direction by a drive source (not shown).

The plug 2 is positioned and held on the path center X-X between the main rolls 10 and 10 and the disc rolls 3 and 3 with the base end of the plug 2 supported by the tip of the mandrel bar M.

The mandrel bar M is connected at its base end to a thrust block having a forward / backward moving mechanism (not shown), and rotatably supports the plug 2 with the pass line XX as its axis. There is.

When the billet B is piercing-rolled by using the piercer configured as described above, the solid round bar-shaped billet B heated to a predetermined temperature in the heating furnace is shown by an outlined arrow in the figure. So that the two main rolls 1
It is bitten between 0, 10 inlet faces 12, 12. After that, the billet B is spirally moved by the rotation of the main rolls 10 and 10 along the path center XX line by the disc rolls 3 and 3, and the plug 2 is inserted into the axial center portion thereof. Then, the billet B is subjected to intermittent rolling once per half rotation between the plug 2 and the main rolls 1 and 1, and is pierced and rolled to form a hollow shell H.

At this time, the rolled material portion which is not subjected to the reduction by the plug 2 and the main rolls 1 and 1 bulges outward in the radial direction by its own rotational force, but the disc roll 3 is driven to rotate following it. The amount of bulging is restricted by 3. As a result, the hollow shell H formed by the main rolls 1 and 1 and the plug 2 while exhibiting an elliptical shape is gradually corrected into a circular shape as it reaches the downstream side in the moving direction, and is formed into a substantially perfect circular shell H.

In the method of the present invention for performing such piercing and rolling, it is necessary to use the plug 2 having the shape described below.

FIG. 4 is a schematic vertical sectional view showing a plug used in the present invention. The plug 2 has the same structure as the conventional plug.
It is in the shape of a cannonball as a whole, and its rolling part has a length L where the length ratio (L2 / L1) of the two satisfies the following formula (2)
It is divided into two parts, a first-stage rolling part 21a having a length of 1 and a second-stage rolling part 21b having a length L2.

The former rolling section 21a has the following (1)
Of a tip spherical surface having a radius of curvature rp satisfying the expression and a tangential arc surface having a radius of curvature AR centered on a line whose angle at the base end of the tip spherical surface with respect to the pass line XX is θ3 It is shaped like a cone. Further, the post-rolling section 21b has an angle θ that satisfies the following expression (3).
It is shaped like a truncated cone with a tapered surface.

The above-mentioned two-divided rolling section (21a + 21)
The reeling part 22 is provided on the downstream side of b),
The reeling portion 22 has an angle θ2 that satisfies the following equation (5).
And has a truncated cone shape having a length L3 satisfying the following expression (4).

Further, on the downstream side of the reeling portion 22, there is formed a relief portion 23 having a length L4 which is reduced in diameter toward the base end, and its effective length L1 + L2 + L3.
(= L) is formed so as to satisfy the following expression (6).

0.14 × Bd ≦ rp ≦ 0.23 × Bd (1) 0.4 ≦ L2 / L1 ≦ 3 (2) α2 +0.5 ≦ θ1 ≦ α2 + 6 ° ···· (3) 0.7 ≦ L3 / P ≦ 2 ····· (4) α2 ≦ θ2 ≦ α2 + 1 °… (5) 2 x Bd ≤ L1 + L2 + L3 ≤ 3.5 x Bd ... (6) where, Bd: outer diameter of the material round billet α2: outlet face angle of the main roll P : (Bd + Ds) / 4 × tan β where Ds: outer diameter of hollow shell β: inclination angle of main roll As described above, the plug 2 used in the present invention divides the rolled part into two parts, and the shape and size of each part. Is required to be a value that satisfies each of the above formulas, and the reason is as follows.

That is, if the radius of curvature rp of the spherical surface at the tip of the front-stage rolling portion 21a is set to a value less than the lower limit value of the above formula (1), the plug tip is likely to be melted by heat during piercing and rolling. If the value exceeds the upper limit, the billet B will not be caught between the main rolls 1 and 1, and a biting failure will occur. Therefore, the radius of curvature rp of the tip spherical surface can be calculated from the above (1)
Must be a value that satisfies the expression.

When the rolling section is divided into the front rolling section 21a and the rear rolling section 21b, the degree of wall thickness machining in the rear rolling section 21b can be increased, and the inner peripheral length of the material to be rolled during piercing rolling can be increased. Can be larger. As a result, it becomes possible to easily pierce and roll a thick-walled pipe having a pipe expansion ratio of 1.15 or more and a piercing ratio of less than 2.0.

However, unless the length ratio (L2 / L1) and the taper angle θ1 of the post-rolling portion 21b satisfy the above expressions (2) and (3), the pipe expansion ratio is 1.15 or more and the perforation ratio 2 When the piercing / rolling is performed at less than 0.0, particularly when the piercing / rolling ratio is made smaller, the wall thickness workability is reduced and the bulging of the inner and outer diameters of the rolled material is reduced. In addition, the diameter reduction amount at the end of the rolling bottom becomes particularly large, and the rolling becomes unstable, and the uneven thickness of the hollow shell H and the tail clogging occur. Furthermore, when this hollow shell H is applied to a mandrel mill which is a rolling mill in the subsequent stage, a trouble occurs in which the mandrel bar cannot be inserted into the pipe. Therefore, the length ratio (L2 / L1) and the taper angle .theta.1 must be values satisfying the expressions (2) and (3), respectively.

Further, if the length L3 of the reeling portion 22 and the taper angle θ2 do not satisfy the above equations (4) and (5), the uneven thickness generated in the two-stage pre-rolling portion 21a and the post-rolling portion 21b is generated. Not only can not be corrected sufficiently, but also clogging of the tail occurs. Therefore, its length L3 and taper angle θ2
Must be values satisfying the above equations (4) and (5), respectively.

Furthermore, the effective length L (= L1 + L2
If + L3) is less than the lower limit of the above formula (6), the spiral undulation generated on the inner and outer surfaces of the hollow shell H cannot be corrected to obtain a smooth surface in both the circumferential direction and the axial direction. On the contrary, when the effective length L exceeds the upper limit value of the above formula (6), clogging of the tail occurs. Therefore, its effective length L
(= L1 + L2 + L3) must be a value that satisfies the above equation (6).

The above is clear from the results of Examples described later.

By the way, the radius of curvature AR of the tangential arc surface continuing to the spherical surface of the tip of the preceding rolling section 21a and the angle .theta.3 for determining the straight line on which the center is located are the outer diameter of the base end of the reeling section 22 and the plug. Since it is determined by setting the diameter dp to a predetermined value, it need not be specified.

The plug shown in FIG. 4 is a case where the front-stage rolling portion 21a is composed of a tip spherical surface and a tangential arc surface with respect to the tip spherical surface so that the wall thickness processing can be performed smoothly.

However, the arcuate surface forming the front-stage rolling section 21a does not necessarily have to be a tangential arcuate surface with respect to the tip spherical surface, and an arcuate surface having an arbitrary curvature centered on a straight line where θ ₃ is θ ₁ or more. It doesn't matter.

The effective length L is preferably as short as possible from the viewpoint of reducing the manufacturing cost of the plug.

Further, Rg in FIG. 4 is the roll interval, Ld
Indicates plug leads, each of which is set to a predetermined value. The line 14 in FIG. 4 is the pass line XX.
The shortest distance between the inlet line 12 and the outlet face 13 of the main roll 1 and the pass line XX, which are arranged at an inclination angle β in a plane orthogonal to, is geometrically calculated for each position in the axial direction. The calculated values are plotted on the vertical sectional view of the plug.

The above description is for the case where the main roll is a cone type piercer, but the same applies to the case where the main roll is a piercer having the barrel type main roll shown in FIG. is there. However, when the main roll uses a barrel type piercer, the material of the material to be rolled is inferior in hot workability, for example, stainless steel, etc., defects such as scratches occur on the inner surface of the obtained hollow shell. It may be easy and may cause problems such as deterioration of product quality. On the other hand, when a piercer equipped with a cone-shaped main roll is used, the above problem does not occur.
Therefore, as the piercer, it is preferable to use one having a cone type main roll. If seizure due to the guide member poses a problem, it is preferable to use a piercer whose guide member is a disk roll or a roller shoe.

[0076]

【Example】

(Example 1) Using a plug having the shape shown in FIG. 4, piercing and rolling was carried out under various conditions shown in Table 5, occurrence of clogging of the tail and uneven thickness, presence or absence of diameter reduction at the rolling bottom end, and the diameter reduction rate thereof. KB
Was examined. Evaluation is based on clogging of the bottom, specifically, plug clogging in which the plug cannot be pulled out from the rolling bottom part of the hollow shell, deterioration of the uneven thickness ratio of "5.0%" or more, or the rolling bottom end of the hollow shell. When the outer diameter of the above-mentioned is significantly reduced by "-5.0%" or more at the diameter reduction rate KB, one or more problems occur x, and when none of the above problems occur, it is ○. Evaluated as.

The results are shown in FIG. Further, the above-mentioned uneven thickness ratio is a value obtained by the following formula (hereinafter the same).

Uneven thickness ratio (%) = {((maximum wall thickness-minimum wall thickness) / maximum wall thickness) × 100}

[0079]

[Table 5]

(Embodiment 2) Using a plug having the shape shown in FIG. 4, piercing and rolling were carried out under various conditions shown in Table 6, occurrence of clogging of the tail and uneven thickness, and presence / absence of diameter reduction at the bottom end of the rolling. The diameter reduction rate KB was examined. The evaluation was performed by the same method as in Example 1. The results are shown in Fig. 6.

[0081]

[Table 6]

As is clear from the results shown in FIGS. 5 and 6, when the plug having the shape and size defined in the present invention is used, the pipe expansion ratio is as high as 1.4, but is 2.0. No problems occurred even when piercing-rolling was performed at the piercing ratio.

On the other hand, when the shape and size of the plug is out of the range defined by the present invention, clogging of the tail occurs, the uneven thickness ratio deteriorates, or the outer diameter of the rolling bottom portion is decreased. One of the problems was that the diameter decreased significantly.

(Embodiment 3) Using the plug of the present invention having the shape shown in FIG. 4 and the conventional plug having the shape shown in FIG. 11, piercing and rolling were carried out under various conditions shown in Table 7 to cause clogging of the tail and uneven thickness. The situation, the presence or absence of a diameter reduction at the end of the rolling bottom, and the diameter reduction rate KB were examined. The evaluation was performed by the same method as in Example 1. Table 8 shows the results.

The dimensions of the used plug are shown in Table 7. In addition, "-" in the column of the diameter reduction ratio KB in Table 8 indicates that the dimension measurement could not be performed due to clogging of the tail.

[0086]

[Table 7]

[0087]

[Table 8]

As is clear from the results shown in Table 8, when the plug having the shape and size defined in the present invention was used, the high expansion ratio was 1.3 to 1.4 and 1.4 to 1.4. 1.5
Despite the low piercing ratio of piercing and rolling, no problems occurred.

On the other hand, in the case of using the plug having the conventional shape, the outer diameter of the rolling bottom end was greatly reduced when the tail clogging and the uneven thickness were not generated. Other than that, clogging of the tail occurred or both clogging of the tail and deterioration of uneven thickness occurred.

(Experimental Example 4) Using the plug of the present invention having the shape shown in FIG. 4 and the conventional plug having the shape shown in FIG. 11, piercing and rolling were carried out under various conditions shown in Table 9 to cause clogging of tails and uneven thickness. The situation, the presence or absence of a diameter reduction at the end of the rolling bottom, and the diameter reduction rate KB were examined. The evaluation was performed by the same method as in Example 1. The results are shown in Table 10.

The dimensions of the plug used are as shown in Table 9.

[0092]

[Table 9]

[0093]

[Table 10]

As is clear from the results shown in Table 10, when the plug having the shape and size defined in the present invention was used, the high expansion ratio was 1.3 to 1.4 and 1.4 to 1.4. 1.
Despite the piercing and rolling with a high expansion ratio and a low piercing ratio of 5, no problems occurred. On the other hand, when using the plug having the conventional shape, both clogging of the tail and deterioration of the uneven thickness occurred. Regarding the outer diameter reduction ratio KB at the end of the rolling bottom, the dimension could not be measured due to clogging of the tail, as in the above case.

[0095]

EFFECTS OF THE INVENTION According to the method of the present invention, even in the case of performing the thick piercing rolling with a high pipe expansion ratio of 1.15 or more and a low piercing ratio of less than 2.0, it is of course possible to prevent the bite from occurring. Since clogging of the tail and deterioration of the uneven thickness of the hollow shell do not occur, the production efficiency can be improved, and the manufacturable size range can be significantly expanded, and the pipe manufacturing cost can be significantly reduced. Further, the present invention has excellent effects such as being applicable to an existing rolling mill as it is.

[Brief description of drawings]

FIG. 1 is a schematic plan view for explaining a method of the present invention.

FIG. 2 is a schematic side view for explaining the method of the present invention.

3 is a cross-sectional view taken along the line I-I of FIG.

FIG. 4 is a schematic vertical sectional view for explaining a plug used in the present invention.

FIG. 5 is a diagram showing a result of an example of the present invention.

FIG. 6 is a diagram showing the results of another example of the present invention.

FIG. 7 is a schematic plan view for explaining a conventional piercing and rolling method using a piercer.

FIG. 8 is a schematic side view for explaining a conventional piercing and rolling method using a piercer.

9 is a sectional view taken along the line II-II of FIG.

FIG. 10 is a diagram for explaining an inlet face angle and an outlet face angle of a barrel type main roll.

FIG. 11 is a diagram for explaining a plug used in conventional piercing and rolling.

FIG. 12 is a schematic plan view showing a piercer provided with a conventional cone type main roll.

FIG. 13 is a diagram for explaining an inlet face angle and an outlet face angle of the cone type main roll.

FIG. 14 is a schematic vertical cross-sectional view for explaining the diameter reduction phenomenon that occurs at the rolling bottom end portion of the hollow shell.

[Explanation of Codes] 1: Main roll, 11: Gorge portion, 12: Entrance surface, 13: Exit surface, 2: Plug, 3: Disc roll (guide member), B: Billet, H: Hollow shell, M: Mandrel bar .

Claims (1)

[Claims] 1. A pair of main rolls provided with an inlet surface and an outlet surface opposed to each other around a pass line, and a pair of disk rolls opposed to each other around the pass line while being out of phase with each other. In the rolling part, the reeling part and the rear end face, the material round billet is screwed in the axial direction and the tip shape is spherical along the axis and the diameter increases toward the rear end. In a method for manufacturing a seamless pipe, a hollow shell is obtained by inserting a shell-shaped plug having an escape portion having a small diameter,
As the plug, the rolling section is divided into a pre-rolling section and a post-rolling section, and the radius of curvature and the axial length of the tip spherical surface of the pre-rolling section are rp, L1 and the taper angle of the post-rolling section, respectively. The axial lengths are θ1, L2, and
The taper angle of the reeling part and the axial length are θ
2 and L3, these are respectively (1) to
A method for manufacturing a seamless pipe, characterized in that a plug having a shape and size satisfying the expression (6) is used. 0.14 × Bd ≦ rp ≦ 0.23 × Bd (1) 0.4 ≦ L2 / L1 ≦ 3 (2) α2 + 0.5 ≦ θ1 ≦ α2 + 6 ° ··· (3) 0.7 ≦ L3 / P ≦ 2 ···· (4) α2 ≦ θ2 ≦ α2 + 1 ° ··· (5) 2 × Bd ≦ L1 + L2 + L3 ≦ 3.5 × Bd ··· (6) where, Bd: outer diameter of the material round billet α2: outlet face angle of the main roll P: (Bd + Ds ) / 4 × tan β However, Ds: outer diameter of hollow shell β: inclination angle of main roll