JP2000140911A - Method for piercing round billet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for piercing a round billet by which hot only the generation of inside surface flaws is suppressed but productivity is raised than that by conventinal methods. SOLUTION: In a method for piercing the round billet in which the round billet is fed between a pair of rolls, which are inclined to each other, of a piercer and a stock tube for seamless steel tubes is manufactured by piercing the round billet using a shell-shaped plug arranged between these rolls, the inclined angle of the roll is taken as 12-14 deg. and also, when the tip of the plug bites into the round billet, a piercer piercing mill is operated at 0.4-0.6 in the X/Db value which is determined by the equation: X/Db=(1/2 tanβ).(1-E/Db). Where, Db is the outside diameter of the billet before piercing, E is the distance between positions of the max. diameters of the roll, β is the inclined angle of the inlet-side surface of the roll, X is the length where the round billet is not drilled with the roll, L is the length where the billet is drilled with the roll and plug.

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 a round billet, and more particularly, to a technique for piercing a round billet at the beginning of production of a seamless steel pipe to form a raw tube.

[0002]

2. Description of the Related Art For example, to manufacture a seamless steel pipe, as shown in FIG. 5, a round billet 2 (hereinafter referred to as a round billet 2), which is a material to be rolled, is heated to 1200 to 1300 ° C. in a heating furnace 1.
) Is passed through a piercing mill, which is a piercer 3, and a plug 4 having a shell-like appearance is pressed into the center of the piercer 3 to pierce the hole, thereby forming a hollow shell 5. Then, the same plug 4 as described above is inserted into the hole of the raw tube 5, and the elongator 6, the plug mill 7, or the mandrel mill 8 is inserted.
Through a rolling mill to be expanded and stretched, and rolled to a temporary pipe. The stretched pipe is polished and shaped by a rolling mill, which is a reeler 9, and is finally finished to predetermined dimensions using a reducer 10 and a sizing mill 11.

[0003] The piercer 3 comprises a pair of inclined rolls 12.
(Hereinafter referred to as a roll), and the roll 12
However, as shown in FIGS. 2 and 3, each axis is parallel in a plan view, and is inclined at an inclination angle β in a direction opposite to a horizontal plane. Therefore, a solid round billet 2
When the paper is fed between the rolls 12 in the direction of the arrow, the previously inserted and fixed appearance collides with the shell-shaped plug 4 and is perforated by the subsequent cutting action.

At this time, a frictional force is generated between the round billet 2 and the roll 12, and the frictional force increases as the inclination angle β of the roll 12 decreases. It is well-known that when the frictional force increases, the roll 12 is inclined, so that the force for advancing the round billet 2 also increases, and the round billet 2 is easily bitten between the rolls 12 ( Butts are equally easy). As an index for judging the magnitude of the frictional force, a tip draft rate α defined by the following equation is known, and the larger it is, the larger the frictional force becomes.

Α = (D−d) / D where: D: outer diameter of round billet before drilling d: outer diameter of round billet at position drilled at tip of plug

On the other hand, in the piercer 3, when the round billet 2 is bitten by the roll 12 and is pierced by the plug 4,
The round billet 2 is apt to crack at the tip of the plug at the axis of the round billet 2. This crack is called a so-called Mannesmann crack and may remain as an inner surface flaw in the hollow shell after perforation. The generation rate of the flaws increases as the frictional force increases, that is, as the inclination angle β decreases. Therefore, there is a problem that if the biting property of the round billet 2 between the rolls 12 is improved, the quality of the raw tube, and finally, the quality of the seamless steel tube is reduced.

Therefore, Japanese Patent Application Laid-Open No. 62-282713 discloses that "a cylindrical metal material is fed between rolls of an inclined rolling mill, and the metal material is pierced and rolled by a plug arranged between the rolls to form a joint. In the method for manufacturing a pipe, the roll inclination angle and / or the distance between the rolls are changed until the position of the feed direction end of the seamless pipe during piercing and rolling reaches the feed direction end of the plug. Small, and when the position exceeds the end in the feeding direction of the plug, the roll inclination angle and / or the distance between the rolls is increased. " In this way, the frictional force is increased at the time of biting at the beginning of the production, and the frictional force is reduced during the steady state thereafter to suppress the occurrence of the inner surface flaw.

However, according to this technique, the wall thickness of the tube after rolling changes before and after the roll opening or the inclination angle is changed.
There is a possibility that the dimensional accuracy in the longitudinal direction of the tube may be poor, and there is a problem in practical use.

To solve this problem, Japanese Patent Laid-Open Publication No.
No. 222 (Japanese Patent No. 2697144) discloses that “a rolled material is spirally moved in the axial direction by using an inclined roll, and a plug is penetrated along the axial direction, and the material to be rolled is pierced and rolled. In the process, the tip draft rate of the plug in the middle part of the material to be rolled is set to be smaller than the tip draft rate at the time of rolling at the top (tip) part and the bottom (tail) part of the material to be rolled. The piercing-rolling technique in which the opening degree and the plug advance amount are simultaneously changed without changing the thickness of the material to be rolled is proposed.

However, in this technique, the change in the thickness in the longitudinal direction can be reduced and the inner surface flaw can be suppressed to some extent, but there is another problem that the productivity is low.

[0011]

SUMMARY OF THE INVENTION In view of such circumstances, an object of the present invention is to provide a method of perforating a round billet which can not only suppress the occurrence of internal surface flaws but also increase the productivity as compared with the conventional method. I have.

[0012]

Means for Solving the Problems In order to achieve the above object, the inventor reviewed the piercing and rolling conditions in the piercer, made intensive studies on high-speed rolling, and embodied the results in the present invention.

That is, according to the present invention, a round billet is fed between a pair of inclined rolls of a piercer piercing mill, and the round billet is pierced by using a bullet-shaped plug arranged between the rolls. In a method for drilling a round billet for producing a seamless pipe for producing a seamless steel pipe, the roll has an inclination angle of 1
While the 2 to 14 °, Once crowded viewed bite the tip of the plug is a round billet, the value of X / D _b determined by the following equation 0.
A method of piercing a round billet, wherein a piercer piercing mill is operated under rolling conditions of 4 to 0.6. _{X / D b = (1 /} 2tanβ) · (1-E / D b) - (L / D b) ·· (1) where, D _b: outer diameter before piercing billets E: maximum diameter position of the roll Distance between the rolls (referred to as gorge) β: Inclination angle of the roll entry side X: Length of the round billet seen from the roll L: Length between roll and plug (referred to as lead)

According to the present invention, the piercer piercing and rolling mill is operated in a state where the roll inclination angle is larger than in the past, so that not only the inner surface flaws can be suppressed, but also the productivity of the raw tube can be increased.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the inventor repeated experimental studies in order to improve low productivity which is one of the problems of the prior art. As a result, even if the angle of inclination of the roll 12 is conventionally considered to be too bad for the round bite 2 to bite into the roll 12 and is increased to a range that has not been experienced,
We found that the operation was possible, and decided to utilize this knowledge effectively. That is, in the present invention, the first requirement is that the inclination angle of the roll 12 be 12 to 14 °. The reason for such limitation is that if the angle exceeds 14 °, the biting and trailing-out will be too poor, and if the angle is less than 12 °, the productivity will not be improved as compared with the related art.

Next, a description will be given of a second requirement of the present invention with respect to suppression of occurrence of inner surface flaws. As described above, after the round billet 2 bites into the roll 12 and passes through the “lean region” 13 shown in FIG.
It has been conventionally known to reduce the interval between them, or to increase the inclination angle, and to change the amount of lead (lead).

However, the inventor made various investigations to further suppress the occurrence of inner surface flaws, and arranged past operation data, and found that there was a very good operation management index. It is an index obtained by combining the specifications required for the operation of the piercer 3 as shown in the following equation. _{X / D b = (1 /} 2tanβ) · (1-E / D b) - (L / D b) ·· (1) where, D _b: outer diameter before piercing billets E: maximum diameter position of the roll Distance between the rolls (referred to as gorge) β: Inclination angle of the roll entry side X: Length of the round billet seen from the roll L: Length between roll and plug (referred to as lead)

FIG. 1 shows the results of trials conducted by the inventor based on this discovery with various indices changed. That is, as soon as the round billet 2 has passed through the "fir tree region" 13, the operation of changing the specifications in the above equation (1) is performed so that this index becomes various values, and the piercer 3 is operated. From FIG. 1, it was clarified that when the index was operated in the range of 0.4 to 0.6, the generation of inner surface flaws hardly occurred.

Therefore, in the present invention, this index is set to 0.4 to
The second requirement was that the piercer 3 be operated under operating conditions in the range of 0.6. This operation is performed, for example, as shown in FIG.
It can be performed with the system configuration as shown in

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the above-described trial when the inclination angle of the roll 12 is 13 ° will be described below.

Until the round billet 2 having an outer diameter (D _b ) of 207.0 mm passed through the “leather region” 13 by the roll 12, the operation was performed at L = 120 mm and X = 183.5 mm. In this case, the exponent X / D _b is 0.66. Then, as soon as the round billet 2 enters the “leather region” 13, X / D _b becomes 0.54,
The vehicle was operated for a predetermined time while gradually changing L and X.

Note that this time (T ₁ ) is determined in advance by T ₁ = L
Previously obtained in the ₁ / V _1.

Here, L ₁ is a length effective for rolling a plug, and V ₁ is a piercing speed (roll peripheral speed × sinFA ×
Perforation efficiency).

When the method of perforating the round billet 2 by the piercer 3 according to the present invention as described above was carried out many times, productivity was improved by 19%, inner surface flaws were reduced by 20%, and plug life was improved. Has been extended by 20%.

[0025]

As described above, according to the present invention, the piercer piercing and rolling mill is operated in a state where the roll inclination angle is larger than the conventional one, and the inner surface flaw is generated while the productivity of the raw tube is higher than the conventional one. It can now be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the operation index and the incidence of inner surface flaws according to the present invention.

FIG. 2 is a longitudinal sectional view illustrating a method of piercing a round billet by a piercer.

FIG. 3 is a diagram illustrating the inclination of a roll.

FIG. 4 is a view showing a facility modification for carrying out a method of perforating a round billet according to the present invention.

FIG. 5 is a diagram showing an arrangement of a general rolling mill for producing a seamless steel pipe.

[Explanation of symbols]

 Reference Signs List 1 heating furnace (reheating furnace) 2 round billet (round billet) 3 piercer 4 plug 5 raw pipe 6 elongator 7 plug mill 8 mandrel mill 9 reeler 10 reducer 11 sizing mill 12 inclined roll (roll) 13 Area 14 Reduction gear 15 Mill process control 16 Mill main control panel 17 Roll reduction control panel 18 Reduction motor control panel 19 Reduction motor 20 Reduction position detector

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomomitsu Kimura 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Inside the Chita Works, Kawasaki Steel Works (72) Inventor Hiroshi Oka 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Prefecture ( No address) Inside the Kawasaki Steel Works, Mizushima Works

Claims (1)

[Claims] 1. A round steel billet is fed between a pair of inclined rolls of a piercer piercing mill, and the round billet is pierced by using a bullet-shaped plug arranged between the rolls to produce a seamless steel pipe. In the method of punching a round billet for producing a raw tube, the roll is inclined at an angle of 12 to 14 °, and when the tip of the plug bites into the round billet,
Drilling method of the round billet value of determined X / D _b in the following equation is characterized by driving the piercer piercing mill with rolling conditions to be 0.4 to 0.6. _{X / D b = (1 /} 2tanβ) · (1-E / D b) - (L / D b) ·· (1) where, D _b: outer diameter before piercing billets E: maximum diameter position of the roll The distance between the rolls (called gorge) β: The angle of inclination of the roll entrance side X: The length of the round billet seen by the roll L: The length of the roll and plug (called the lead)