JPH06106209A - Piercing rolling for seamless steel tube - Google Patents

Abstract

PURPOSE:To provide a piercing rolling method for a seamless steel tube by which even hard-to-work material can be efficiently piercing rolled at a low cost. CONSTITUTION:In a method by which the seamless steel tube is piercing rolled using a inclined rolling mill which is provided with the main rolls 1, 1 and one plug 4, at the time of piercing a billet 3 with a outside diameter DB into a hollow piece 3A with an outside diameter DH by taking the face angle on the outlet side of a pair of the barrel-shaped main rolls 1, 1 as alpha2 and the effective length of the plug 4 as LP, Z value is defined as follows. Z=[(DH-E)/2 tanalpha2]-(LP-L). Where, E: gorge, L: lead. By setting this Z value so as to fall in the range of 2/tanalpha2 <= Z <= 1.2 DB, even the hard-to-work material material is efficiently piercing rolled at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for piercing and rolling a seamless steel pipe.

[0002]

2. Description of the Related Art The Mannesmann tube making method has been one of the typical methods for producing seamless steel tubes. In this method, a billet, which is a heated rolling material, is pierced by a piercer to form a hollow piece, which is then stretch-rolled by a mandrel mill or a combination of an elongator, a plug mill, and a reeler, and then reduced in size by a reducer or sizer. By doing so, a seamless steel pipe can be efficiently produced.

By the way, in the case of a commonly used piercer, as shown in FIGS. 4 (a), 4 (b) and 4 (c), the main roll 1,
1 has a maximum diameter of the central portion forms a larger barrel type than body length and its diameter, and the surface angle alpha ₁ of the incoming side and outgoing side, alpha
₂ is ₂ to 5 °, respectively. The main rolls 1 and 1 are arranged such that their inclination angles β are 8 to 12 ° parallel to the vertical planes of the pass line PL through which the pellet 3 passes as a hollow piece 3A and opposite to the horizontal plane. It is inclined. Between the main rolls 1 and 1, guide shoes 2 and 2 are installed so as to sandwich the pass line PL from above and below, and hold the hollow piece 3A that bulges during piercing and rolling from above and below. The mandrel 5 supported the rear of the main rolls 1 and 1 at a position separated by a predetermined distance toward the entrance side of the billet 3 from the position where the roll gap was the smallest and the roll gap was minimized. The tip of the piercing plug 4 is positioned and the billet 3 is pierced over its entire length by rotating the main rolls 1, 1 while advancing the billet 3 in the direction of the arrow.

By the way, in the piercer provided with such barrel type main rolls 1, 1, the outer diameter of the roll gradually increases up to the gorge portion as the rolling progresses, and then gradually decreases on the contrary. Therefore, the roll peripheral speed also gradually increases up to the gorge portion, and thereafter gradually decreases. Therefore, shear stress is applied to the rolled material, and the surface thereof is twisted and deformed. For this reason, when drilling a difficult-to-machine material such as stainless steel, a pipe-like flaw in the form of burrs is often produced on the outer surface of the material.

As one of means for solving such a problem, a method for manufacturing a seamless steel pipe as disclosed in, for example, Japanese Patent Laid-Open No. 57-168711 has been proposed. That is, the content is, as shown in FIG. 5, a cone-type main roll 1 in which the roll diameter gradually increases from the inlet side to the outlet side.
A and 1A are used to appropriately set the inclination angle β and the crossing angle γ, thereby reducing the shear stress applied to the rolled material, thereby reducing the twisting deformation of the surface and improving the efficiency of difficult-to-machine materials. It is a very good piercer, because it tends to be rolled well and, in some cases, it can reduce the torsional deformation to zero.

[0006]

However, the cone type roll piercer of the so-called Japanese Patent Laid-Open No. 168711/1982, which is called a cross-type piercer, has drawbacks such as high equipment cost and a large installation space. However, there is a problem that it cannot be easily introduced into an existing rolling line.

The present invention has been made to solve the above-mentioned problems of the prior art. Even if a conventional barrel type roll piercer is used, the twisting deformation of the surface can be made small, so that even difficult-to-process materials can be obtained. An object is to provide a method capable of efficiently piercing and rolling at low cost.

[0008]

DISCLOSURE OF THE INVENTION The present invention is a method for piercing and rolling a seamless steel pipe using an inclined rolling mill equipped with a pair of barrel type main rolls and one plug. The angle is α ₂ and the effective length of the plug is L _P
When a billet having an outer diameter D _B is bored into a hollow piece having an outer diameter D _H , Z = {( _DH −E) / 2tan α ₂ } − (L _P −L) where E is a gorge distance, L defines the Z value in the lead of the plug is the piercing method of seamless steel pipe and setting the Z value to be in the range of _{2 / tan α 2 ≦ Z ≦} 1.2 D B .

[0009]

[Operation] The principle of the present invention will be described below. Well
First, as shown in FIG. 1, the maximum diameter is D_MAX， Inlet side angle is α
₁， The exit angle is α₂Main roll with gorge distance E of 1,
Effective length L while rotating 1 in the direction of arrow R _PNaru plastic
Lead 4 (advanced amount of plug from gorge portion G) L
And an outer diameter D that advances in the direction of the arrow F_BOutside the billet 3
Diameter D_H, Perforating the hollow piece 3A having a wall thickness t
To do.

At this time, the billet 3 starts to be bitten at the point A of the main roll 1 and, due to the effect of rotary forging, a hole is easily formed in the center thereof, and the tip of the plug 4 is perforated. . Then, by rolling between the main rolls 1 and 1 and the plug 4 up to the reeling end point of point B, and the hollow piece 3A is separated from the main rolls 1 and 1 at the roll-off point of point C, a predetermined outer diameter is obtained. ， Thick hollow piece 3A
Is obtained.

Now, letting Z be the distance between the point B at the reeling end and the point C at the roll-off, this Z can be expressed by the following equation (1). Z = {(D _H −E) / ₂ tan α ₂ } − (L _P −L) (1) The Z value obtained from the formula (1) is the main roll 1 and the plug 4
In the figure, the length of the pipe expanding process after the hollow piece 3A is rolled is shown between the two.

By the way, from the bite to the gorge portion of the roll, the outer diameter of the roll gradually increases with the progress of rolling, so that the peripheral speed of the roll also increases. Therefore, the rolled material is twisted in the rotating direction. On the other hand, from the roll gorge portion to the roll-off, the roll outer diameter is gradually decreased as the rolling progresses, and the roll peripheral speed is also reduced. Therefore, in this portion, the rolled material is twisted back in the direction opposite to the rotating direction.

Therefore, the present inventor has proposed that Z in the above equation (1).
As a result of a detailed investigation and study of the relationship between the value and the piercer perforation characteristics, as shown in Figs. 2 (a) and 2 (b), the twist value of the rolling material surface was reduced by reducing the Z value. I found that I could do it. That is, Fig. 2 (a) is a characteristic diagram showing the relationship between the Z / D _B value and the amount of torsional deformation of the outer surface of the rolled material, and Fig. 2 (b) is the Z / D _B value and the occurrence of external defects. It is a characteristic diagram showing the relationship of the ratio. From these figures, if the Z / D _B value is set to a large value, the tube expansion length becomes longer, and the twisting force exerted by the main roll on the rolled material increases, so The amount of twist deformation on the surface also increases.

In FIGS. 3 (a) and 3 (b), Z / D _B is 0.83 and
It is a sketch of a cross-sectional photograph in the circumferential direction of the hollow piece 3A after piercing perforation when the perforation experiment was set to 1.42. Note that the stainless steel bolt 6 is embedded in the billet 3 in advance in order to clarify the twisting deformation of the cross section.
In FIG. 3 (a) where Z / D _B is 0.83, it can be seen that the material is twisted in the roll rotation direction (arrow R). At this time, the amount of twisting deformation of the outer surface of the hollow piece was −5 ° to the right. On the other hand, Z / D _{B is set} to 1.42 in Fig. 3 (b).
It can be seen that, while the material inner surface side is twisted in the roll rotation direction, the outer surface side is twisted back in the direction opposite to the roll rotation direction. At this time, the degree of twist on the outer surface of the hollow piece was 26 ° to the right.

Therefore, when the Z value is increased, that is, the tube expansion length is increased, the degree of decrease in the peripheral length of the barrel-type roll, that is, the degree of decrease in the roll peripheral speed is increased, so that the outer surface of the material is rotated by the roll. It is presumed that the degree to which it is twisted back, contrary to the direction, will also increase. Further, the greater the degree of untwisting of the outer surface, the greater the amount of shear deformation of the material, and therefore it is considered that the flaws are more likely to occur on the outer surface of the material after perforation. Therefore, it is understood that the occurrence rate of external surface defects can be reduced by reducing the Z value as much as possible.

Here, when the present inventor investigated the upper limit value and the lower limit value of Z of stainless steel which is a difficult-to-machine material, first, regarding the upper limit value, Z / D _B ≦ 1.2 (2 It has been found that the amount of twisted deformation of the surface of the rolled material can be reduced by the above-mentioned method, and as a result, the outer surface flaw generated during perforation can be significantly reduced (see FIG. 2 (b) above).

However, if the Z value is too small,
Due to insufficient pipe expansion, misrolling is likely to occur. Therefore, as for the lower limit of the Z value, according to the investigation by the present inventor, it was found that if Ztan α ₂ ≧ 2 (3), then misroll due to insufficient pipe expansion does not occur. Therefore, the desirable range of the Z value is expressed by the following equation (4).

2 / tan α ₂ ≦ Z ≦ 1.2 D _B (4)

[0019]

[Example] When drilling an austenitic stainless steel billet having an outer diameter D _B of 110 mmφ, the maximum diameter D _MAX was 11
At 00 mm, both entrance side angle α ₁ and exit side angle α ₂ are 3 °
Piercer with barrel type roll and effective length L _P is 23
A 0 mm plug was used. At this time, the gorge E and the lead L, the target outer diameter D _H , and the tube expansion length Z were set as shown in Table 1 for punching. The results are shown in Table 2.

[0020]

[Table 1]

[0021]

[Table 2]

In Table 2, in the column of presence / absence of external surface flaws, ○ indicates that no flaw was generated, x indicates that a flaw was generated, and ○ in the column of whether or not misroll occurred, no misroll occurred. In the column of the comprehensive judgment, the symbol "x" indicates that a misroll has occurred, and the symbol "x" indicates good and the symbol "x" indicates defective. As is clear from these tables, the Z / D _B value is 1.
In each of the five invention examples of Experiment Nos. 3, 4, 5, 6, and 7 which were 2 or less, the amount of twist deformation on the surface of the rolled material can be set to 10 ° or less, and the outer surface has a fog-like shape. It can be seen that the holes were drilled without causing tube defects.

[0023]

As described above, according to the present invention,
When drilling using a piercer with a barrel-shaped roll,
Since the Z value is set to fall within a predetermined range and rolling is performed, even a difficult-to-machine material such as stainless steel can be rolled with less twisting deformation and less outer surface flaws. It is a great contribution to the improvement of product quality and yield.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating the principle of the present invention.

FIG. 2 (a) is a characteristic diagram showing the relationship between the Z / D _B value and the amount of torsional deformation of the outer surface of the rolled material, and (b) shows the relationship between the Z / D _B value and the occurrence rate of external surface defects. It is a characteristic diagram.

FIG. 3 (a) shows Z / D _B of 0.83, and (b) shows Z / D _B of 1.
It is the figure which sketched the cross-sectional photograph of the hollow piece when it set to 42 and performed a perforation experiment.

4 (a) is a plan view, FIG. 4 (b) is a side view, and FIG. 4 (c) is a front view showing a conventional barrel type roll piercer.

FIG. 5 is a plan view showing another conventional example.

[Explanation of symbols]

 1 Main roll 3 Billet 3A Hollow piece 4 Plug 6 Stainless bolt

Claims (1)

[Claims] 1. A method of piercing-rolling a seamless steel pipe using an inclined rolling mill equipped with a pair of barrel-type main rolls and one plug, wherein the main roll has a flank angle of α ₂ and the plugs. When the billet having the outer diameter D _B is bored into the hollow piece having the outer diameter D _H , the effective length of is set to L _P , and Z = {(D _H −E) / 2tan α ₂ } − (L _P −L) where in, E is gorge spacing, L is defines the Z value in the lead of the plug, Mu seam and sets the Z value to be in the range of _{2 / tan α 2 ≦ Z ≦} 1.2 D B Method for piercing and rolling steel pipes.