JP3578052B2 - Piercing and rolling method of seamless steel pipe - Google Patents

Description

上記シミュレーション結果から、ディスクロール周速Ｖｄが同一、すなわち、ホローシェルとディスクロールの接触時間が同一である場合には、Ｖｒを増加させると、ホローシェルとディスクとの摩擦発熱による昇温によって、ディスクロールの表面最高温度が上昇することが分かる。
【００３５】
一方、穿孔用ロールの軸方向速度成分Ｖｒが同一である場合には、Ｖｄが所定の範囲にある限りにおいて、Ｖｄを増加させるとホローシェルとディスクロールとの接触時間が短くなることによって、ディスクロールの表面温度は低減する。しかし、Ｖｄが所定の範囲を超えるようになると、Ｖｄを増加させるとホローシェルとディスクとの摩擦発熱によって、ディスクロールの表面最高温度は低減しないことが判明した。次に、ＶｄとＶｒとの関係を明らかにした。
【００３６】
図６は、シミュレーション結果に基づいてα（＝Ｖｄ／Ｖｒ）とディスクロール表面最高温度（℃）との関係を示す図である。いずれのＶｒであっても、αが減少するのにともなって、ディスクロール表面最高温度（℃）が上昇している。
【００３７】
焼き付きによって使用不能となったディスクロールの表面組織を観察した結果から、焼き付きを発生する場合には、ロール溝底表面の最高温度が９００℃以上に達していることを確認している。したがって、焼き付き防止対策としては、ディスクロールの表面最高温度を９００℃未満にすることが有効である。そこで、図６に示す結果から、α≧１．５の関係を確保する必要があることが分かる。
【００３８】
次に、Ｖｒに関しては、前述の通り、穿孔用ロールの回転数は操業能率に大きく影響することから、通常、下記（４）式を満足するように管理する必要がある。
【００３９】
６００ ≦ Ｖ ｒ ≦ １３００ ・・・ （４）
実機の穿孔圧延機を用いて、圧延後のホローシェル寸法で外径２４４．５ｍｍ×肉厚１０〜１４ｍｍ、規格Ｎ８０グレード材を穿孔用ロールの軸方向成分速度Ｖｒを８００〜１２００ｍｍ／ｓｅｃの範囲で変動させ、同時にディスクロールの周速Ｖｄも変動させて、αを変化させて圧延を行った。実機での品質状況を確認するため、圧延し冷却した後の素管表面の焼き付き疵発生率とディスクロール表面の塑性流動の有無を確認した。
【００４０】
焼き付き疵発生率は、同一条件（Ｖｒおよびα）で５００本圧延を行い、本数比率で発生率（％）を測定した。また、塑性流動の有無は、各条件の圧延終了毎にディスクロールの溝底面を肉眼で観察して調査した。その結果を表２に示し、図７には、αと被圧延材の表面焼き付き疵発生率（％）との関係を示す。
【００４１】
【表２】

上記の結果から、αを増加させることによって、素管表面の焼き付き疵発生率を減少できると同時に、ディスクロール表面の塑性流動を少なくすることができる。さらに望ましくは、αを２．３以上にすることによって、その効果をより向上させることができる。
【００４２】
しかしながら、αを８．０まで増加すると、穿孔失敗、具体的には穿孔終了直前での穿孔停止のトラブルが発生することが明らかになった。したがって、αは下記（５）式の関係を満足する必要がある。
【００４３】
１．５ ≦ α ＜ ８．０ ・・・ （５）
【００４４】
【発明の効果】
本発明に係る穿孔圧延方法によれば、穿孔用ロールおよびディスクロールの回転数をコントロールすることによって、ディスクロールとホローシェルとの接触部に生じる焼き付きをなくし、外面欠陥の低減による製品歩留まりを向上させるとともに、ディスクロールの整備に要する停機時間を削減して、効率的に継目無鋼管を製造することができる。特に近年のように、鋼管製造の効率化の観点から、マンネスマン製管設備の連続化が実施されるようになると、高効率化の達成に合わせ、製造ラインの全体効率の向上を実現することができる。
【図面の簡単な説明】
【図１】穿孔用ロールとしてバレル型ロールを用いて被圧延材を穿孔圧延する状況を説明する図であり、（ａ）は模式的平面図を示し、（ｂ）は同側面図を、（ｃ）は（ｂ）におけるＩ−Ｉ矢視の縦断面図を示している。
【図２】ディスクロールの外面形状を示す図である。
【図３】穿孔用ロールとしてコーン型ロールを用いて被圧延材を穿孔圧延する状況を説明する図であり、（ａ）は模式的平面図を示し、（ｂ）は同側面図を示している。
【図４】ディスクロールとホローシェルの接触部での温度解析の結果に基づく圧延時間とディスクロール表面温度との関係を示す図である。
【図５】ディスクロール周速Ｖｄ（ｍｍ／ｓｅｃ）とディスクロール（溝底）表面最高温度（℃）との関係を示す図である。
【図６】シミュレーション結果に基づいてα（＝Ｖｄ／Ｖｒ）とディスクロール表面最高温度（℃）との関係を示す図である。
【図７】αと被圧延材の表面焼き付き疵発生率（％）との関係を示す図である。
【符号の説明】
１：穿孔用ロール、 ２：穿孔用プラグ
３：ディスクロール、 ３ｄ：溝底
１１：ゴージ部、 １２：入側面
１３：出側面
Ｂ：中実丸ビレット、 Ｈ：ホローシェル[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a seamless steel pipe using a piercing mill having a disc roll, and more specifically, to prevent seizure occurring on the disc roll, to maintain the disc roll, and reduce the downtime required for replacement, The present invention relates to a method for piercing and rolling a seamless steel pipe, which can improve product yield by reducing external surface defects occurring in a material to be rolled.
[0002]
[Prior art]
As a method for producing a seamless steel pipe by hot, a so-called Mannesmann pipe method is widely used. In this pipe making method, a solid round billet heated to a high temperature is used as a material to be rolled, and this round billet is fed to a piercing mill (a so-called piercer), and a hollow shell is formed by making a hole in the axial center thereof. (Hollow shell). Then, the obtained hollow shell as it is, or through an elongator having the same configuration as the piercing mill as necessary, after diameter expansion and thinning, and then fed to a subsequent elongation rolling mill such as a plug mill and a mandrel mill. And stretch-roll. Thereafter, the pipe is passed through a stretch reducer, a reeler, a sizer, or the like, and is subjected to polishing, shape correction, and sizing, thereby producing a seamless steel pipe.
The piercing and rolling machine includes a pair of piercing rolls arranged in the left-right direction or up and down direction with respect to the pass line of the material to be rolled, and a pair of disc rolls arranged in a direction perpendicular to the arrangement direction of the piercing rolls. The rolling material is supported and rotated by the roll and the disc roll, and piercing rolling is performed by a plug which is an inner surface regulating tool disposed on the pass line. Rolls for punching used in the rolling mill are classified into two types, a barrel type and a cone type.
[0003]
FIG. 1 is a diagram illustrating a situation in which a material to be rolled is pierced and rolled using a barrel-type roll as a piercing roll. 2A shows a schematic plan view, FIG. 2B shows a side view, and FIG. 2C shows a vertical cross-sectional view taken along the line II in FIG. 2B. In the figure, the arrangement and operation of the perforating roll 1, the perforating plug 2 and the disc roll 3 are shown.
[0004]
When the perforating roll 1 is a barrel-type roll, a gorge portion 11 that changes the diameter by a tentative amount is provided at an intermediate portion in the axial direction, and the roll surface is divided into an input side surface 12 and an output side surface 13. The pair of rolls 1 and 1 are arranged to face each other in the left-right direction or the up-down direction of the pass line XX of the solid round billet B as the material to be rolled, and a predetermined roll opening Rg is set. Further, as shown in FIG. 1B, the rotation axis of the perforating roll 1 is inclined by an inclination angle β with respect to the pass line XX.
[0005]
The drilling plug 2 is formed in a warhead shape as a whole, and its base end is supported by the tip of the mandrel M. As shown in FIG. 1 (a), the plug 2 is supported on the pass line XX between the perforating rolls 1 and 1 such that its axis is aligned, and a predetermined lead Ld, that is, a gorge It is positioned so that the distance from the part 11 to the tip of the plug can be ensured. The plug 2 supported in this manner is rotatable around the pass line XX as a rotation axis.
[0006]
As shown in FIG. 1 (c), the disc rolls 3, 3 are arranged in the vertical direction or the horizontal direction of the path center XX so as to face the plug 2 during piercing and rolling. It is designed to be driven to rotate.
[0007]
FIG. 2 is a diagram showing the outer shape of the disk roll shown in FIG. The disc roll 3 is formed in a disc shape, and a contact portion with the material to be rolled forms a groove bottom 3d, and a hole type having a minimum diameter dD along the outer peripheral surface of the billet B or the hollow shell H after perforation. Is formed.
[0008]
FIG. 3 is a diagram illustrating a situation in which a material to be rolled is pierced and rolled using a cone-shaped roll as the piercing roll 1. FIG. 3A shows a schematic plan view, and FIG. 3B shows a side view of the same. However, the vertical sectional view is omitted because it has the same configuration as that of the barrel-type roll shown in FIG.
[0009]
Even a cone-type roll is provided with a gorge portion 11 that changes the temporary increase in the diameter in the axial direction, and divides the roll surface into an input side surface 12 and an output side surface 13. The pair of rolls 1 and 1 are arranged so as to face the pass line XX and provide a predetermined roll opening. Further, the rotation axis of the cone-shaped roll is provided with an intersection angle γ shown in FIG. 3A with respect to the pass line XX, and at the same time an inclined angle β shown in FIG. 3B.
[0010]
Even when a cone-type roll is used, the positioning of the perforating plug 2 and the arrangement of the disc roll 3 are the same as those in the case of using a barrel-type roll.
[0011]
In the piercing and rolling mill configured as described above, the solid round billet B fed in the direction of the white arrow on the pass line XX is bitten between the input side surfaces 12 and 12 of the piercing roll 1. After that, it moves on the pass line while turning, and a hole is made in its axial center by the perforation plug 2 to form a hollow shell (hollow shell) H.
[0012]
At this time, as shown in FIG. 1 (c), as the solid round billet B is pierced, the hollow shell H expands in an outer peripheral length and expands radially outward. For this reason, the disc roll 3 rotates on the pass line XX so that the contact surface with the hollow shell is in the same direction as the traveling direction of the hollow shell. This makes it possible to suppress the swinging of the billet and to suppress the hollow shell from bulging outward in the radial direction, so that piercing and rolling can be performed smoothly.
[0013]
The number of rotations of the perforating roll is determined from the viewpoint of operation efficiency. The operating efficiency can be improved as the hollow shell piercing speed increases, and usually, the hollow shell piercing speed is set in consideration of the slip ratio that is included in the axial component speed of the piercing roll. Then, the axial component velocity Vr (mm / sec) of the perforating roll is grasped as the axial component velocity at the gorge part, the gorge part diameter of the perforating roll is rD (mm), and the number of rotations of the perforating roll is determined. rN (rpm), and the inclination angle of the perforating roll is β (°), which is obtained by the following equation (1).
[0014]
Vr = rD · π · sinβ · rN / 60 (1)
The rotation speed of the perforating roll is set so that the axial component velocity Vr of the perforating roll is generally 600 to 1300 mm / sec, although it depends on the production equipment for the seamless steel pipe.
[0015]
The disc roll is rotated in the same direction as the hollow shell travels, but its peripheral speed needs to be set so as not to hinder the progress of the hollow shell. The peripheral speed Vd (mm / sec) of the disc roll is grasped as the peripheral speed at the bottom of the groove of the roll hole type, the minimum diameter of the bottom of the disc roll groove is dD (mm), and the rotation speed of the disc roll is dN (rpm). Is calculated by the following equation (2). Then, the calculated ratio between Vr and Vd is expressed by the following equation (3).
[0016]
Vd = dD · π · dN / 60 (2)
α = Vd / Vr (3)
Based on the conventional experience, the peripheral speed of the disc roll is generally set in the range of α <1.3 so as not to hinder the advance of the hollow shell. However, since the hollow shell is formed while rotating at a high speed, the friction causes seizure and wear on the contact surface between the disk roll and the hollow shell. As described above, in order to prevent seizure occurring on the disk roll surface, efforts were made to improve the disk roll by cooling the disk roll, applying a lubricant to the disk roll surface or the hollow shell surface, and optimizing the material of the disk roll. It has not yet been eliminated.
[0017]
[Problems to be solved by the invention]
As described above, conventional countermeasures such as peripheral speed control of the perforating roll and the disc roll, cooling of the disc roll, and application of a lubricant have not yet completely prevented seizure occurring on the disc roll. When the disc roll is seized, a defect is immediately generated on the outer surface of the hollow shell, which lowers the product yield. In addition, it is necessary to perform an operation of removing burned-in substances adhered to the surface of the disk roll and an operation of replacing the disk roll, and the downtime of the piercing mill increases.
[0018]
Such an increase in the stoppage time not only lowers the operation rate of the piercing mill, but also in particular, as in recent years, continuous production of Mannesmann pipe facilities has been carried out for the purpose of high-efficiency production of seamless steel pipes. As a result, the overall efficiency of the production line is degraded.
[0019]
The present invention solves the problem of seizure that occurs in a conventional piercing mill, eliminates seizure that occurs at the contact portion between the disk roll and the hollow shell, improves the product yield by reducing external surface defects, and improves the disc roll. An object of the present invention is to provide a method of piercing and rolling a seamless steel pipe that can reduce the downtime required for maintenance and improve the overall efficiency of a production line.
[0020]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors have repeatedly observed the burn-in portion on the surface of the disk roll and performed temperature analysis at the contact portion between the disk roll and the hollow shell, and obtained the following findings (a) to (c). I got it.
(A) Observation from the observation result of the seized part on the surface of the disk roll At the seized part of the disk roll, plastic flow occurs first, and as a result, an uneven portion is generated on the roll surface, and the portion is formed with a hollow shell in a high temperature state. It will burn. The occurrence of this plastic flow is caused by the fact that the surface of the disk roll becomes extremely hot at the time of contact with the hollow shell, and the surface strength decreases accordingly.
(B) Findings from Temperature Analysis at the Contact between the Disk Roll and the Hollow Shell FIG. 4 is a diagram showing the relationship between the rolling time and the disk roll surface temperature based on the result of the temperature analysis at the contact between the disk roll and the hollow shell. is there. Since it was difficult to measure the disk roll surface temperature in contact with the hollow shell, a simulator was developed and the surface temperature was analyzed from the simulation results. The conditions are a billet heating temperature of 1230 ° C. and a hollow shell speed of 1 m / sec.
[0021]
From the results shown in FIG. 4, it was found that the surface temperature of the disk roll reached a high temperature exceeding 800 ° C. by one contact with the hollow shell. However, it can be seen that the surface of the disk roll, which has become high in temperature due to the contact, rapidly drops when leaving the hollow shell, and immediately before the next contact with the hollow shell, the temperature drops below 100 ° C. to the temperature before the previous contact.
[0022]
In other words, the temperature rise of the disk roll surface which causes plastic flow is not caused gradually by repeated contact with the hollow shell, but is caused by one contact with the hollow shell. Therefore, it is apparent that the method of simply cooling the surface of the disk roll with water at the time of non-contact cannot basically prevent burning of the disk roll. Note that FIG. 4 shows that the disc roll makes three rotations by perforating one billet, and the specific position of the disc roll contacts the hollow shell three times.
(C) Knowledge on the cause of the increase in the surface temperature of the disk roll Based on the findings of the above (a) and (b), the inventors further examined the cause of the increase in the surface temperature of the disk roll. He clarified that the following two factors are involved. That is,
I. Temperature rise due to heat transfer when the hollow shell contacts the disc roll; Temperature rise due to heat generated by sliding friction between the hollow shell and the disc roll.
[0023]
Moreover, the above factors (a) and (b) are caused by controlling the axial component speed Vr (mm / sec) of the perforating roll and the peripheral speed Vd (mm / sec) of the disc roll in a fixed relationship. The effect can be mitigated.
[0024]
The present invention has been completed based on the above findings, and has a gist of the following method of piercing and rolling a seamless steel pipe.
[0025]
That is, a method of piercing and rolling a seamless steel pipe using a rolling mill including a pair of piercing rolls disposed opposite to each other around the pass line and a pair of disc rolls disposed at right angles to the arrangement direction of the piercing rolls. Wherein the axial component velocity Vr (mm / sec) of the perforating roll, the peripheral velocity Vd (mm / sec) of the disc roll, and the ratio α thereof are defined by the following equations (1) to (3). In this case, Vr and α defined here satisfy the relations of the following equations (4) and (5).
[0026]
Vr = rD · π · sinβ · rN / 60 (1)
Vd = dD · π · dN / 60 (2)
α = Vd / Vr (3)
600 ≦ Vr ≦ 1300 (4)
1.5 ≦ α <8.0 (5)
Further, in the above-described method of piercing and rolling a seamless steel pipe, it is desirable to replace the above-mentioned equation (5) with the following equation (6).
[0027]
2.3 ≦ α <8.0 (6)
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
As described above, in the disk roll provided in the piercing rolling mill targeted by the present invention, the temperature rise of the roll surface is caused by the temperature rise due to the heat transfer at the time of contact with the hollow shell, and the temperature rise due to the sliding friction heat with the hollow shell. Is a factor.
Here, Q is the heat input to the disc roll, Qc is the heat transfer at the time of contact with the hollow shell, QfL is the frictional heat generated by the relative speed difference between the axial traveling speed of the hollow shell and the peripheral speed of the disc roll, and QfL is the If the heat input to the disc roll is formulated by setting the frictional heat generated by the rotational peripheral speed to Qfr, the following equations (7) to (10) are obtained.
[0029]
Q = Qc + QfL + Qfr (7)
Qc = C · ΔT · t (8)
Here, C: heat transfer coefficient, ΔT: temperature difference between disk roll and hollow shell t: contact time QfL = μ · p · Vrel · t (9)
Where μ: coefficient of friction, p: surface pressure, t: contact time Vrel: relative speed difference Qfr = μ · p · Vrer · t (10)
Here, μ: friction coefficient, p: surface pressure, t: contact time Vrer: difference in speed between the circumferential direction of the hollow shell and the disk roll in the same direction. Vrr is assumed to be equal to the circumferential speed of the enamel shell in the rotational direction, ignoring the disc roll speed component.
[0030]
In the above relationship, if the peripheral speed of the disc roll is increased while the rotation speed of the perforating roll is kept constant, that is, the traveling speed of the hollow shell is kept constant, QfL increases from the above equation (9), but the disc roll and the hollow shell The heat transfer Qc is reduced because the contact time with the heat is reduced.
[0031]
On the other hand, when the peripheral speed of the disc roll is kept constant and the number of rotations of the perforating roll is increased, the traveling speed and the rotating peripheral speed of the hollow shell increase. Therefore, from the above equation (10), Qfr increases. Since the required time is shortened, the heat transfer Qc is reduced. At this time, QfL may increase or decrease depending on the relative speed difference at the time of the setting. As described above, the amount of heat input to the disc roll changes depending on the setting of the peripheral speed of the disc roll and the traveling speed of the hollow shell, that is, the axial component speed of the perforating roll.
[0032]
The effects of the above-mentioned heat transfer due to heat transfer and the rise in temperature due to sliding friction heat are quantitatively evaluated, and the axial component velocity Vr (mm / sec) of the perforating roll and the disc roll can be controlled to control the surface temperature of the disc roll. To clarify the peripheral speed Vd (mm / sec), a temperature simulation analysis was applied.
[0033]
In the simulation analysis, three levels of the axial speed component Vr of the perforating roll were selected from the setting range during normal operation, and three levels of the disk roll peripheral speed Vd were selected for each Vr, and the simulation analysis was performed under a total of nine conditions. The simulation conditions and results at this time are shown in Table 1, and FIG. 5 shows the relationship between the disk roll peripheral speed Vd (mm / sec) and the disk roll (groove bottom) surface maximum temperature (° C.).
[0034]
[Table 1]

From the above simulation results, when the disk roll peripheral speed Vd is the same, that is, when the contact time between the hollow shell and the disk roll is the same, when Vr is increased, the temperature of the disk shell increases due to frictional heat generated between the hollow shell and the disk. It can be seen that the maximum temperature of the surface increases.
[0035]
On the other hand, when the axial velocity component Vr of the perforating roll is the same, as long as Vd is within a predetermined range, increasing Vd shortens the contact time between the hollow shell and the disc roll. Surface temperature is reduced. However, it has been found that when Vd exceeds a predetermined range, increasing Vd does not reduce the maximum surface temperature of the disk roll due to frictional heat generated between the hollow shell and the disk. Next, the relationship between Vd and Vr was clarified.
[0036]
FIG. 6 is a diagram showing the relationship between α (= Vd / Vr) and the disk roll surface maximum temperature (° C.) based on the simulation results. Regardless of the Vr, the disk roll surface maximum temperature (° C.) increases as α decreases.
[0037]
From the result of observing the surface structure of the disc roll which became unusable due to seizure, it was confirmed that the maximum temperature of the roll groove bottom surface reached 900 ° C. or more when seizure occurred. Therefore, as a measure to prevent image sticking, it is effective to make the maximum surface temperature of the disk roll less than 900 ° C. Therefore, it is understood from the results shown in FIG. 6 that it is necessary to secure the relationship of α ≧ 1.5.
[0038]
Next, as for Vr, as described above, since the rotation speed of the perforating roll greatly affects the operation efficiency, it is usually necessary to manage Vr so as to satisfy the following expression (4).
[0039]
600 ≦ Vr ≦ 1300 (4)
Using an actual piercing and rolling machine, the hollow shell dimensions after rolling are an outer diameter of 244.5 mm x a wall thickness of 10 to 14 mm, and a standard N80 grade material with an axial component velocity Vr of a piercing roll of 800 to 1200 mm / sec. The rolling was performed while changing the α, while also changing the peripheral speed Vd of the disk roll. In order to confirm the quality status in the actual machine, the occurrence rate of seizure flaws on the surface of the raw tube after rolling and cooling and the presence or absence of plastic flow on the disk roll surface were confirmed.
[0040]
The burn-in flaw occurrence rate was determined by performing 500 rolls under the same conditions (Vr and α) and measuring the occurrence rate (%) in the number ratio. The presence or absence of plastic flow was checked by visually observing the bottom of the groove of the disk roll each time rolling was completed under each condition. The results are shown in Table 2, and FIG. 7 shows the relationship between α and the rate of occurrence of surface burn-in flaws (%) of the material to be rolled.
[0041]
[Table 2]

From the above results, by increasing α, it is possible to reduce the occurrence rate of seizure flaws on the surface of the raw tube, and at the same time, to reduce the plastic flow on the disk roll surface. More preferably, the effect can be further improved by setting α to 2.3 or more.
[0042]
However, when α was increased to 8.0, it was clarified that drilling failed, specifically, a problem of stopping drilling immediately before the end of drilling. Therefore, α needs to satisfy the relationship of the following equation (5).
[0043]
1.5 ≦ α <8.0 (5)
[0044]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the piercing-rolling method which concerns on this invention, the seizure which arises in the contact part of a disc roll and a hollow shell is eliminated by controlling the rotation speed of a piercing roll and a disc roll, and the product yield by reduction of an outer surface defect is improved. At the same time, the downtime required for the maintenance of the disk roll can be reduced, and the seamless steel pipe can be manufactured efficiently. In particular, as in recent years, from the viewpoint of increasing the efficiency of steel pipe production, when the continuous use of Mannesmann pipe-making equipment is being implemented, it is possible to improve the overall efficiency of the production line in accordance with the achievement of higher efficiency. it can.
[Brief description of the drawings]
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view for explaining a situation in which a material to be rolled is pierced and rolled using a barrel-type roll as a piercing roll, (a) showing a schematic plan view, (b) showing the side view, (c) is a longitudinal sectional view taken along the line II in (b).
FIG. 2 is a diagram showing the outer shape of a disk roll.
3A and 3B are diagrams illustrating a situation in which a material to be rolled is pierced and rolled using a cone type roll as a piercing roll, wherein FIG. 3A is a schematic plan view, and FIG. I have.
FIG. 4 is a diagram showing a relationship between a rolling time and a disk roll surface temperature based on a result of a temperature analysis at a contact portion between a disk roll and a hollow shell.
FIG. 5 is a diagram showing a relationship between a disk roll peripheral speed Vd (mm / sec) and a disk roll (groove bottom) surface maximum temperature (° C.).
FIG. 6 is a diagram showing a relationship between α (= Vd / Vr) and a disk roll surface maximum temperature (° C.) based on a simulation result.
FIG. 7 is a diagram showing the relationship between α and the rate of occurrence of surface burn-in flaws (%) of a material to be rolled.
[Explanation of symbols]
1: Roll for perforation, 2: Plug for perforation 3: Disc roll, 3d: Groove bottom 11: Gorge part, 12: Entering side 13: Outer side B: Solid round billet, H: Hollow shell

Claims (2)

A method for piercing and rolling a seamless steel pipe by using a rolling mill including a pair of piercing rolls arranged opposite to each other around a pass line and a pair of disc rolls arranged at right angles to the arrangement direction of the piercing rolls. When the axial component velocity Vr (mm / sec) of the perforating roll, the peripheral velocity Vd (mm / sec) of the disc roll, and their ratio α are defined by the following equations (1) to (3), Wherein Vr and α defined herein satisfy the relations of the following equations (4) and (5).
Vr = rD · π · sinβ · rN / 60 (1)
Vd = dD · π · dN / 60 (2)
α = Vd / Vr (3)
600 ≦ Vr ≦ 1300 (4)
1.5 ≦ α <8.0 (5)
However, rD: gorge diameter of the perforation roll (mm)
rN: number of rotations of the perforating roll (rpm)
β: Tilt angle of perforating roll (°)
dD: minimum diameter of the groove bottom of the disc roll (mm)
dN: Rotation speed of disk roll (rpm) 2. The method according to claim 1, wherein the equation (5) is replaced with the following equation (6).
2.3 ≦ α <8.0 (6)

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