JP3003553B2 - Perforation rolling method for seamless metal pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of piercing and rolling a seamless metal pipe, and more particularly to a method of piercing and rolling at a high expansion ratio of 1.15 or more.

[0002]

2. Description of the Related Art In general, when a seamless metal pipe is manufactured by the Mannesmann pipe manufacturing method, for example, in a Mannesmann-plug mill system, a product is generally manufactured through the following four steps. That is, a piercing and rolling step of passing a solid round billet (a billet) through a piercer (inclined rolling mill) to pierce a central portion thereof to obtain a hollow shell, and directly or as necessary using the hollow shell as an elongator. (A tilt rolling mill with the same structure as the piercer), and then through a plug mill to elongate rolling process to reduce the wall thickness, and to reduce and reduce the diameter of the reduced tube with a reeler and a sizer. While the pipe after the diameter step and the fixed diameter of the polishing pipe is straightened through a straightening machine, the ends of both pipes are cut and removed, and further, a refining step of inspecting the inner and outer surface for flaws, etc., to produce a product. .

[0003] In the Mannesmann-mandrel mill method, a hollow shell obtained through the same piercing and rolling step as described above is passed through a mandrel mill, subjected to elongation rolling to reduce the wall thickness, and then passed through a reducer to have an outer diameter. Is subjected to reduction rolling to reduce the diameter, and then subjected to the same refining process as described above to obtain a product.

As the piercer, generally, a pair of barrel-type or cone-type main rolls serving as rolling rolls, a plug serving as an inner surface regulating tool, and a pair of plate-shaped guide shoes or disc rolls serving as a material to be rolled are provided. And a combination thereof.

FIGS. 5 to 7 are schematic views showing a general piercer using a barrel-type main roll as a rolling roll and a disc roll as a rolling member guide member. FIG. 5 is a plan view, and FIG. FIG. 7 is a sectional view taken along the line II-II of FIG.

In the figure, reference numerals 10 and 10 denote main rolls and reference numeral 2
Denotes a plug as an inner surface regulating tool, and reference numerals 3 and 3 denote disc rolls as guide members for a material to be rolled.

The main rolls 10, 10 are provided with a gorge portion 11 having a maximum diameter at an intermediate portion in the axial length direction.
1 has a barrel-shaped shape having a conical entrance surface 12 and an exit surface 13 whose diameter is gradually reduced toward the terminal on both sides, respectively, and the left and right sides of a path center XX of a billet B to be rolled. Alternatively, they are arranged vertically facing each other.

The plug 2 has a warhead shape as a whole,
Its proximal end is supported by the distal end of the mandrel bar M. The plug 2 is positioned and held on the pass center XX in the middle of the main rolls 10, 10.
It is rotatable around -X as a rotation axis. The base end of the mandrel bar M is connected to a thrust block device (not shown) capable of moving forward and backward.

As shown in FIG. 7, the disc rolls 3, 3 are discs having a concave outer peripheral surface facing the plug 2, and a pair of upper and lower or left and right is driven by a drive motor (not shown). The main rolls 10 and 10 are alternately arranged around the pass center XX.

In such a piercer, billet B
Is transported in the axial direction as indicated by the white arrow, and is caught between the entrance surfaces 12 and 12 of both main rolls 10 and 10,
The hollow shell H is drawn out in sliding contact with the outer periphery, and piercing rolling is performed while suppressing the hollow shell H from bulging outward in the radial direction by the disc rolls 3 and 3.

A technique for performing high-efficiency and high-quality piercing rolling using such a piercer is disclosed in Japanese Patent Publication No. 59-4492.
There is a method disclosed in Japanese Patent Application Laid-Open No. 7-No.

The method disclosed in the above publication takes into consideration the biting property and the trailing edge of the material to be rolled, and based on a plurality of theoretically determined conditional expressions, the perforation such as the main roll interval and the guide shoe interval. This is a method of performing piercing and rolling while setting the setup to an appropriate value. In this method, the expansion ratio (the ratio of the outer diameter of the hollow shell after piercing / rolling to the outer diameter of the billet before piercing) is 1.
This is a method of performing parallel piercing and rolling of 0 to 1.05. In this limit, stable piercing and rolling without misrolling is enabled.

[0013]

As described above, there is no problem as long as the parallel piercing and rolling is performed by the method disclosed in the above publication. However, in order to obtain a large-diameter hollow shell from a small-diameter billet by this method, when piercing and rolling at a high expansion ratio such that the expansion ratio is 1.15 or more, as shown in FIG. It has been clarified that the inner surface of the base tube H has a drawback that a plurality of spirally continuous scratches K occur frequently.

This is because, as shown in FIG. 9, in the piercing and rolling at a high expansion ratio such that the expansion ratio is 1.15 or more, as compared with the parallel piercing and rolling with the expansion ratio of 1.05 or less, the hollow shell H
Since the outer diameter of the main roll 10 becomes large, the separation point A of the hollow shell H from the main roll 10 is located in the latter half of the exit surface 13 of the main roll 10 on the exit side. As a result, when the main roll diameter D at the point B of the main roll 10 corresponding to the position of the maximum diameter dp of the plug 2 is a barrel-type roll (see FIG. 9A).
Will be smaller.

Therefore, the main roll 10 determined by the following equation
The rotational speed Vr at the point B is reduced by the reduction of the main roll diameter D, and accordingly, the hollow shell being rolled as the material to be rolled at the point B in contact with the main roll 10 The rotational speed Vr of H becomes smaller than that during parallel piercing and rolling.

Vr = π · D · N / 60 · sin β where N: number of rotations of main roll 10 (rpm) β: inclination angle of main roll 10 (deg.) In the case of the cone type (see FIG. 9B), the main roll diameter D at the point B is larger than that of the barrel type, and the main roll 10 is in contact therewith. The rotational speed Vr of the hollow shell H, which is the material to be rolled, during rolling at the point B is larger than that during parallel piercing rolling.

In any of the above cases, the rotational speed Vr of the hollow shell H being rolled as the material to be rolled at the position of the maximum diameter dp of the plug 2 changes greatly as compared with that during parallel drilling. On the other hand, since the plug 2 rotates at a constant rotation speed, the relative speed difference in the rotation direction between the plug 2 and the hollow shell H during rolling increases.

As a result, the frictional force between the outer surface of the plug 2 and the inner surface of the hollow shell H being rolled increases, and the inner surface of the hollow shell H is formed by the plug 2 near the maximum diameter dp of the plug 2. The spiral scratch K is generated.

In actual piercing and rolling, the deflection of the mandrel bar M, the difference in the coefficient of friction of the surface of the main roll 10,
Due to the eccentricity of the plug 2, the material to be rolled advances while eccentrically moving. For this reason, the contact between the vicinity of the maximum diameter dp portion of the plug 2 and the inner surface of the hollow shell H being rolled increases more and more, and scratches K occur more frequently.

If the scratch K is stretched and rolled by a plug mill or mandrel mill in the next step, it remains as a rash on the inner surface of the pipe, and not only requires a great number of man-hours to remove, but also deteriorates the product quality. There was a problem.

The object of the present invention has been made in view of the above circumstances, and even in the case of piercing and rolling at a high expansion ratio of 1.15 or more, friction between the plug and the inner surface of the tube causes the inner surface of the hollow shell to be pierced. resulting suppressing the occurrence of rubbing scratches of the plug due to provide a piercing method of seamless metal tubes can be manufactured inner surface quality good hollow Motokan.

[0022]

Means for Solving the Problems The present inventors have made 1.15.
In order to find rolling conditions that do not cause the above-mentioned scratches even when piercing and rolling are performed at the above-mentioned high pipe expansion ratio, various experimental studies were conducted, and the following was found.

As described above, the abrasion is caused by the fact that the relative speed difference in the rotational direction between the plug and the hollow shell being rolled is large, and the outer surface of the plug near the maximum diameter portion of the plug and the hollow shell being rolled. It occurs due to friction with the inner surface of the pipe. Therefore, the present inventors focused on the contact between the outer surface of the plug and the inner surface of the hollow shell during rolling in the vicinity of the maximum diameter portion of the plug, and determined the frictional region between the plug 3 and the plug 3 at the position of the maximum diameter dp of the plug 2. The following experiment was conducted on the assumption that reducing the contact length L (see FIG. 10) with the hollow shell would reduce the frictional force and eliminate the occurrence of scratches .

That is, two types of conventional inclined rolling mills having a disk roll 3 as a material to be rolled and a main roll 10 having a cone type and a barrel type (FIGS. 5 to 7).
A large number of piercing rolling experiments were performed using plugs 2 having variously changed outer diameters dp (see FIG. 9) of the maximum diameter portion in order to reduce the contact length L.

As a result, the outer diameter dp of the maximum diameter portion of the plug 2
And the inner diameter ds of the hollow shell H to be obtained (see FIG. 9), that is, the clearance Δd obtained by the following equation, in other words, the inner circumference of the hollow shell H and the outer circumference of the maximum diameter dp portion of the plug 2. There is a strong correlation between the circumferential length difference between the plug and the occurrence of scratches, and the clearance Δd is 4 to 12%, in other words, the inner circumferential length of the hollow shell is 4 to 4 times larger than the maximum outer circumferential length of the plug.
It was found that when the size was increased by 12%, no abrasion occurred.

Δd = ((ds−dp) / dp) × 100 (%) where the outer diameter dp of the maximum diameter portion of the plug 2 is an average outer diameter at the position of the plug maximum diameter portion. (Value obtained by dividing the outer peripheral length of the plug maximum diameter portion by π). Also, the inner diameter ds of the hollow shell H
Is an average inner diameter (a value obtained by dividing the inner peripheral length of a hollow shell to be obtained by π) because the inner diameter is not necessarily a perfect circle. Hereinafter, the outer diameter dp and the inner diameter ds are simply referred to as the average outer diameter and the average inner diameter, respectively.

FIG. 1 shows the results of the above experiment.
In the figure, the mark ● indicates the occurrence of scratches, the mark ▲ indicates that the thickness deviation has worsened, and the mark △ indicates the ellipticity ( the outer diameter of the rolled material in the disk roll direction / Primary roll
When the direction of the outer diameter) is large, a state where the pressure <br/> Nobezai bottom portion during piercing ends can not be detached from the main roll, uneven thickness worse Misuroru of so-called Shirinuke failure has occurred, ○ The marks indicate the case where there was no problem.

As is apparent from FIG. 1, the above-described clearance is required to perform piercing and rolling at a high expansion ratio of 1.15 or more without causing misroll such as abrasion and poor bottom loss, and deterioration of uneven thickness. It can be seen that Δd needs to be in the range of 4 to 12%, in other words, in the range where the inner peripheral length of the hollow shell is 4 to 12% larger than the outer peripheral length of the maximum diameter portion of the plug.

On the other hand, when the expansion ratio is up to 1.10,
Even when the above clearance Δd is 4% or less, no scratch is generated, and the conventional parallel piercing and rolling technique is applied at a pipe expansion ratio of 1.15.
It is clear that the present invention cannot be applied to the piercing and rolling at the high pipe expansion ratio described above, and the difference between the present invention in which the clearance Δd is limited to the range of 4 to 12% and the prior art is apparent.

The experimental conditions are as shown in Table 1.

[0031]

[Table 1]

The present invention has been made based on the above findings, and the gist of the invention lies in the following method of piercing and rolling a seamless metal pipe.

A plug is arranged along a pass line between a pair of main rolls and a pair of disc rolls which are arranged opposite to each other around the pass line while being inclined in the opposite direction, and the material to be rolled is moved while being screwed. In a method of piercing and rolling a seamless metal pipe to obtain a hollow shell at a high expansion ratio of 1.15 or more, the inner peripheral length of the hollow shell is set to be 4 to 12 larger than the maximum outer peripheral length of the plug.
A piercing and rolling method for a seamless metal pipe, characterized in that the piercing and rolling is performed by increasing the piercing and rolling ratio.

[0034]

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

FIG. 2 is a schematic plan view showing an example in which the inclined rolling mill according to the present invention is applied to a piercer, FIG. 3 is a schematic side view, and FIG. 4 is a partially broken front view taken along line II of FIG. It is.

As shown in the figure, the piercer is constituted by a pair of main rolls 1, 1, a plug 2, and disk rolls 3, 3. Each of the main rolls 1 and 1 has a gorge portion 11 having a short cylindrical shape, and an entrance surface 12 and an outgoing end portion each having a substantially frustoconical shape whose diameter is reduced toward the entrance end of the gorge portion 11. The outlet surface 13 also has a substantially frustoconical shape, and the diameter of the outlet surface 13 is increased as it goes.
The main rolls 1 and 1 are disposed opposite to each other on both sides of the path center XX, and are inclined at an inclination angle β with respect to the path center XX as shown in FIG. 3, and as shown in FIG. It is inclined with respect to the X-rays by a predetermined intersection angle γ, and is rotated in the same direction by a drive device (not shown) around the axis thereof.

The plug 2 has a shell shape as a whole, and its base end is supported by the front end of a mandrel bar M. The base end of the mandrel bar M is connected to a thrust block device (not shown) capable of moving forward and backward. ing.

A pair of disc rolls 3, 3 each have an R-shaped (concave) sliding surface 3 separated by a pass center XX line.
d is arranged to face the moving area of the material to be rolled, and is rotated in the traveling direction of the material to be rolled by a driving device (not shown).

In such a tilt rolling mill, a solid round billet B heated to a predetermined temperature in a heating furnace is connected to a roll shown in FIG.
, The entrance surface 1 of the main rolls 1 and 1 as shown by white arrows
From the second side, it is transported to the path center XX with its axis aligned, and from the leading end thereof, the entrance surfaces 12, 1 of the inclined rolls 1, 1
Bite between two. After this biting, the solid round billet B is moved along the path center XX by the disc rolls 3 and 3 and penetrated into its axial center position while being screwed by the rotation of the two main rolls 1 and 1. The piercing rolling is performed between the plug 2 and the main rolls 1 and 1 under intermittent pressure once per half turn. When not subjected to the reduction by the main roll 1 and the plug 2, the hollow shell H being pierced and rolled, which is the material to be rolled, swells radially outward due to the rotation, but as shown in FIG. Roll 3, 3
Is slid in contact with the outer periphery of the swollen portion and suppresses the outward swelling, so that it is rolled while exhibiting an elliptical shape, and gradually becomes circular toward the downstream side in the moving direction (right side in the figure). It is formed into a hollow shell H. The roll opening Rg of the main rolls 1 and 1, the guide opening Dg of the disc rolls 3 and 3, and the advanced amount Lp of the plug 2 are determined by the hollow shell H.
Are set so that the outer diameter and wall thickness, in other words, the inner diameter ds (see FIG. 9), have desired dimensions.

In the piercing and rolling, according to the present invention, the outer diameter dp of the maximum diameter portion of the plug 2 and the inner diameter d of the hollow shell to be obtained.
s (both refer to FIG. 9), the piercing and rolling is performed using the plug 2 having the maximum diameter outer diameter dp in which the clearance Δd based on the above-described equation is a value within the range of 4 to 12%. Do. As described above, when the piercing rolling is performed using the plug 2 having the maximum diameter portion outer diameter dp in which the clearance Δd with the inner diameter ds of the hollow shell H to be obtained is in the range of 4 to 12%, The contact length L (see FIG. 10) between the plug 2 and the inner surface of the material to be rolled near the maximum diameter portion is reduced. As a result, the contact area between the plug 2 and the material to be rolled is reduced, the frictional force between them is reduced, and the generation of the scratch K (see FIG. 8) can be suppressed or prevented. Also,
It is possible to prevent the occurrence of misrolling such as poor bottom loss and deterioration of uneven thickness, and to stably perform piercing and rolling.

The case where the main roll 1 uses a cone-type inclined rolling mill has been described above, but it goes without saying that the same result can be obtained when the main roll is a barrel-type inclined rolling mill. Absent. However, when the main roll is subjected to high expansion ratio piercing and rolling at a pipe expansion ratio of 1.15 or more with a barrel-type inclined rolling mill, compared to the case where the main roll 1 is pierced and rolled with a cone-type inclined rolling mill, Additional shear deformation such as circumferential shear deformation and surface torsional shear deformation increases, and depending on the material of the material to be rolled, flaws due to shear deformation may occur frequently on the inner and outer surfaces. Therefore, it is preferable to use an inclined rolling mill in which the main roll is a cone type without such a fear.

[0042]

Next, the results of the application of the method of the present invention to actual piercing and rolling will be described.

The operating conditions are shown in Table 2, and the results are shown in Table 3.

[0044]

[Table 2]

[0045]

[Table 3]

In Table 3, the mark x indicating the presence or absence of inner surface flaw indicates the case where abrasion caused by a plug which causes rash is generated on the inner surface of the pipe, and the mark x indicating presence / absence of mis-roll indicates a case where a defect in the bottom has occurred. And ○ indicate the case where piercing and rolling could be performed without any problem.

As is evident from Table 3, in the present invention, the rubbing was performed.
No flaws or misrolls occurred. On the other hand, in the comparative example, either a scratch or a misroll occurred.

[0048]

According to the method of the present invention, even in piercing rolling at a high expansion ratio of 1.15 or more, there is no rolling trouble such as abrasion and misroll caused by the frictional force between the plug and the inner surface of the hollow shell. Thus, piercing and rolling can be performed stably. As a result, in addition to reducing the man-hours for product maintenance,
The present invention exerts excellent effects, such as being able to efficiently produce products having excellent inner surface quality and reducing the cost of pipe production.

[Brief description of the drawings]

FIG. 1 is a view showing the effects of a clearance Δd between an outer diameter of a maximum diameter portion of a plug and an inner diameter of a hollow shell and a pipe expansion ratio on a piercing-rolling result.

FIG. 2 is a schematic plan view showing an example of a tilt rolling mill used in the piercing rolling method of the present invention.

FIG. 3 is a schematic side view showing an example of a tilt rolling mill used in the piercing rolling method of the present invention.

FIG. 4 is a sectional view taken along line II of FIG. 2;

FIG. 5 is a schematic plan view showing an example of a conventional inclined rolling mill.

FIG. 6 is a schematic side view showing an example of a conventional inclined rolling mill.

FIG. 7 is a sectional view taken along line II-II of FIG. 5;

FIG. 8 is a schematic diagram showing scratches generated on the inner surface of the hollow shell.

FIG. 9 is a diagram showing a relative relationship between a main roll, a plug and a hollow shell during piercing rolling at a high expansion ratio, and FIG.
FIG. 4B shows a case where the main roll is a barrel type, and FIG. 4B shows a case where the main roll is a cone type.

FIG. 10 is a view for explaining a mechanism of generating scratches .

[Explanation of symbols]

1: Main roll, 10: Main roll, 11: Gorge part, 12: Inlet face, 13: Outlet face, 2: Plug, 3: Disc roll, 3d: Sliding face, B: Billet, H: Hollow shell, M: mandrel bar, K: abrasion , β: inclination angle, γ: crossing angle, Rg: roll opening of main roll, Dg: guide opening of disc roll, Lp: advanced amount of plug.

──────────────────────────────────────────────────の Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B21B 19/04

Claims (1)

(57) [Claims] 1. A plug is arranged along a pass line between a pair of main rolls and a pair of disk rolls arranged opposite to each other while being inclined in opposite directions around a pass line, and a material to be rolled is spirally moved. In the piercing and rolling method of a seamless metal tube for obtaining a hollow shell at a high expansion ratio of 1.15 or more, the inner peripheral length of the hollow shell is set to be 4 to 12 larger than the maximum outer length of the plug.
A piercing and rolling method for a seamless metal pipe, characterized in that the piercing and rolling is performed by increasing the piercing and rolling ratio.