JPH0520163B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention uses so-called inclined rolls, such as a piercer and an elongator, which are widely adopted in the Mannesmann pipe manufacturing method, which is a typical manufacturing method for seamless metal pipes. This invention relates to a rolling method using a rolling mill. [Prior art] In general, seamless metal pipes manufactured using the Mannesmann pipe manufacturing method are first made by passing a heated round steel piece through a piercer, and then pressing a plug into the center of the piercer to form a hollow shell. If there is, the hollow shell is passed through an elongator to expand its diameter and stretch-roll, then further stretch-rolled in a plug mill, for example, and polished and shaped with a reeler and sizer.
It is manufactured through sizing and finishing processes. By the way, in the above-mentioned piercer and elongator, a so-called inclined rolling mill is used, which is a combination of, for example, a barrel-shaped rolling roll (hereinafter referred to as an inclined roll) whose axis line is inclined with respect to the pass center of the round billet or hollow shell, and a plug. It will be done. For example, in the case of a piercer, as shown in FIG. 5, there is a gorge part 11 with a maximum diameter in the middle in the axial direction, and a truncated cone with a diameter that gradually decreases toward the end on both sides of this gorge part 11. A pair of inclined rolls 1l and 1r each having a shaped entrance surface 12 and an exit surface 13;
It has a warhead shape as a whole, and includes a rolled part 21 that is approximately conical from the distal end side, a reeling part 22 that is approximately truncated conical, and a relief part 23 whose diameter decreases toward the base end. The double inclined rolls 1l and 1r
are placed on both sides of the pass center of the round steel piece B so that the axis line is parallel to the pass center in plan view, and the other inclined roll 1l has its inlet surface 12 facing upward in side view. The plug 1r is arranged to be inclined with respect to the pass center by an inclination angle β so that the tip of the inlet surface 12 faces downward, and the plug 2 is arranged so that its axis line coincides with the pass center. Then, when the heated round steel piece B is transferred in the axial direction as shown by the white arrow, the double inclined roll 1l,
1r, the round steel piece B is rotated around the axis by both inclined rolls 1l, 1r, and the plug 2 is penetrated into the center thereof, and the round steel piece B is inserted between the inclined rolls 1l, 1r. The plug 2 is adapted to be pierced and rolled. In such a piercer, the roll interval, plug advance amount, and guide shoe interval are set to 1, taking into account conditions that allow rolling and conditions that do not cause defects on the pipe.
A rolling control method (Japanese Unexamined Patent Publication No. 115907/1983) has been developed in which a calculation is made each time a book is rolled, and feedback control is performed based on the calculation result during the next rolling. [Problems to be Solved by the Invention] When manufacturing a hollow tube from a billet using a piercer using inclined rolls, if the roll inclination angle is set small, Mannesmann fracture occurs in front of the plug as shown in Figure 5. A hole (cracking) may occur in the center of the material being drilled, and this cracking may cause a flaw on the inner surface of the hollow tube. FIG. 6 shows the relationship between the rice cracking caused by Mannesmann fracture and the roll inclination angle. However, the test material is free-cutting steel (AISI standard 12L14).
The other conditions were a drilling ratio of 2.8, a pipe expansion ratio of 3%, a plug tip draft rate ( _{both diameter reductions of the shortest distance r 1 from} the pass center to the roll circumferential surface at the plug tip with respect to billet radius r 0 (r ₀ − r ₁ ) 7%, perforation diameter 60 mm, roll gorge diameter 350 mm. In addition, the inner surface defects of the hollow tube tend to occur more frequently when the shear strain in the circumferential direction that occurs during piercing and rolling increases. FIG. 7 shows the relationship between circumferential shear strain and roll inclination angle. The circumferential shear strain γ is defined by the following equation. γ=r ₂・θ/t However, r ₂ : Radius of the hollow tube after drilling θ : Torsion angle of the hollow tube after drilling t : Wall thickness of the hollow tube after drilling In addition, Fig. 8 shows the roll The relationship between inclination angle and circumferential shear strain is shown. As is clear from FIG. 8, the larger the roll inclination angle, the smaller the circumferential shear strain. Therefore, in order to suppress the occurrence of inner surface flaws, the roll inclination angle may be increased. The velocity component Vf that advances the perforated material is Vf = VR · sin β However, since VR is the circumferential speed of the roll in the gorge, it is desirable to increase the inclination angle β from the viewpoint of rolling efficiency. By the way, as the inclination angle β increases, the thrust force in the rolling direction that acts on the plug increases.
In other words, the force that impedes the advancement of the perforated material increases, so it is necessary to provide the perforated material with a sufficient driving force from the rolls to rotate and advance the perforated material. However, during unsteady rolling, when biting and bottoming out, the contact area between the roll and the material decreases, so there is insufficient thrust to advance the material, resulting in poor biting to the top of the material and bottoming out to the bottom of the material. (Uncoupling) defects may occur, leading to rolling stoppage. The limit angle of inclination at which such defects occur is determined by the material, temperature, perforation ratio, amount of plug advanced, roll surface condition, etc., and can be determined by empirical rules, so it is possible to determine it based on operational experience or experiments in advance. Therefore, we have decided to establish the following. Furthermore, if the inclination angle β is increased under the condition where the thrust is insufficient as described above, the amount of reduction of the perforated material per half rotation will increase, the slip between the roll and the material will increase, and the perforated rolling will stop. . Furthermore, as shown in Fig. 9, there is a phenomenon in which the current of the drive motor of the tilted roll increases just before the roll is released, but if the tilt angle is large, the current at this time becomes excessive, and the drive motor with a small margin increases. The protection circuit may be activated. [Means for solving the problems] The present invention has been made in view of the above circumstances, and its purpose is to avoid rolling stoppage,
Another object of the present invention is to provide a method for rolling a seamless pipe with inclined rolls, which improves rolling efficiency, suppresses the occurrence of internal defects, and improves the quality of the pipe. The present invention provides a process in which the material to be rolled is subjected to piercing rolling, diameter expansion, and elongation rolling by using inclined rolls to move the material to be rolled in the axial direction while penetrating the plug along the axial direction. The method is characterized in that when rolling a predetermined length at the top and bottom of the material to be rolled, the inclination angle of the inclined rolls is made smaller than the angle of inclination during rolling of the intermediate portion of the material to be rolled. The roll inclination angle at the time of rolling a predetermined length at the top and bottom is determined and set based only on the biting property and the tailing property, or by preferentially considering these properties. At that time, consider the material, temperature, drilling ratio, amount of plug advancement, etc. [Example] The present invention will be described below based on drawings showing examples thereof. FIG. 1 is a schematic block diagram of a rolling mill used in carrying out the method of the present invention. In the figure, 1l and 1r are inclined rolls whose axes are inclined in different directions with respect to the pass line, and the inclination angle β of each inclined roll is changed by the automatic positioning device 8. Load cells 5, 5 for detecting the load applied to the inclined roll 1r are provided on the entry side and the exit side of one inclined roll 1r, respectively, and the outputs of both load cells 5, 5 are given to the arithmetic and control device 6. There is. Further, a material position detecting device 9 using an HMD is arranged at a predetermined position on the entrance side of the inclined rolls 1 l and 1 r, and the output of the material position detecting device 9 is given to the arithmetic and control device 6 . The arithmetic and control device 6 includes an output from a timer setting device 10 for setting a time _t4 for changing the inclination angle of the inclined rolls 1l and 1r during rolling of the bottom portion of the material to be rolled, which will be described later. roll 1
The output of the inclination angle control length setter 11 is given to set the lengths l ₁ , l ₂ , l ₃ for which the inclination angles of l and 1r should be changed, and the output of the arithmetic and control unit 6 is provided to the automatic positioning device 8. The arithmetic control device 6 changes the inclination angle of the inclined roll according to the rolling position of the material to be rolled, and performs this control based on the dimensional diagram of the material to be rolled in FIG. 2 and the time chart in FIG. 3. explain. First, when the material to be rolled is not bitten by the inclined roll, the arithmetic and control device 6 drives the automatic positioning device 8 to set the inclination angle to β ₀ , and after the material to be rolled is bitten by the inclined roll, it drives the automatic positioning device 8 from the top. While the part up to length l ₁ is being rolled, the automatic positioning device 8 is driven to increase the inclination angle of the inclined roll from β ₀ to β ₁ , and after that, the part with length l ₂ is being rolled. In the meantime, the automatic positioning device 8 is driven to set the inclination angle of the inclination roll to β ₂ which is even larger than β ₁ . Then, while the intermediate portion of the material to be rolled having a length l ₃ is being rolled, the automatic positioning device 8 is driven to set the inclination angle of the inclined roll to β ₃ which is even larger than β ₂ . During this time, the material position detection device 9 detects the bottom of the material to be rolled, and when the bottom part of the material to be rolled begins to be rolled,
The automatic positioning device 8 sets the inclination angle of the inclined rolls 1l and _1r to β4, which is slightly smaller than the inclination angle _β1 during rolling of the top portion, over time _t4 . In other words, the arithmetic and control unit 6 sets the inclination angle of each inclined roll 1l, 1r to β ₀ until the rolled material is bitten by the inclined rolls 1l, 1r, and after the load cell 5 detects the biting of the rolled material, the The inclination angle of the inclined roll is increased from β 0 to β ₁ while the part from the top of the rolled material to the length l 1 is being rolled, and the inclination angle of the roll is increased from β ₀ to β ₁ while the length l ₂ part of the joint part is being rolled. angle β ₁ to β ₂
is made larger, and the inclined roll 1 is rolled while the middle part of the material to be rolled, which has a length l ₃ of the connecting part, is rolled.
The inclination angles of l and 1r are set from β ₂ 2 to β ₃ , but the inclination angles are reduced from β ₃ to β ₄ over a predetermined time t ₄ during rolling of the bottom portion. Next, the calculation contents of the arithmetic and control device 6 will be explained. Based on the lengths l ₁ , l ₂ , l ₃ set by the inclination angle control length setting device 11, each length l of the material to be rolled is The times t _{1 ,} t ₂ , and t ₃ required to roll ₁ , l ₁ +l 2 , l ₁ +l ₂ +l ₃ are calculated using the following equations (1), (2), and (3). t ₁ = 120×l ₁ ×K ₁ /π×D×N (sinβ ₀ +sinβ ₁ )……(
1) t ₂ = 120×l ₂ ×K ₂ /π×D×N×(sinβ ₁ +sinβ ₂ )+t
₁ ...(2) _t3 =120× _l3 × _K3 /π×D×N×( _sinβ2 + _sinβ3 )
+t ₁ +t ₂ ...(3) However, D: Diameter of the gorge part of the inclined roll N: Number of rotations of the roll K ₁ , K ₂ , K ₃ : Correction coefficient On the other hand, the time t ₄ set by the timer setting device 10
Since is set as a standard time, the arithmetic and control device 6 takes into account changes in the piercing rolling speed due to changes in roll diameter and roll rotation speed and makes corrections using equation (4) below. _{t 4} ′=t _{4 × D 0} /D _′ Diameter N ₀ : Standard rotational speed (roll rotational speed when standard time t ₄ is set) N′ : Actual roll rotational speed K ₄ : Correction coefficient Note that t ₁ to _{t 3} are also based on the above D and the actual gorge diameter. Similar corrections will be made from time to time based on the above. The arithmetic and control unit 6 changes the inclination angle of the inclination roll based on the times t ₁ to _{t 4} calculated and corrected in this manner. Incidentally, the inclined rolls 1l, 1 by the arithmetic and control device 6
Although the control times t ₁ , t ₂ , and t ₃ of the inclination angle of r are determined based on the rolling length of the material to be rolled, each time may be directly set and corrected using equation (4). Moreover, the time chart shown in FIG. 3 is only an example, and it goes without saying that other different patterns may be used. Further, the method of the present invention can be applied even when the number of rolls is three, and the roll shape may be either a cone shape or a barrel shape.Furthermore, in the case of a two roll type, the guide shoe may be either a plate or a disk. In the above-described embodiment, the first piercer is described in detail in which the occurrence of cracking due to Mannesmann fracture and circumferential shear strain are problems, but the present invention can also be applied to the second piercer in which only the occurrence of circumferential shear strain is a problem. Applicable. [Effect] The method of the present invention was carried out under the following conditions. Billet: Round continuous cast slab, diameter 282mm
Steel type: 0.5% C steel Billet dimensions: Diameter 70mm x Length 300mm Perforation ratio: 2.5 Heating temperature: 1230℃ Plug tip draft ratio: 5% Change of roll inclination angle Pattern: Inclined when rolling at the top part The inclination angle of the roll was 12 degrees, 17 degrees when rolling the middle part, and 12 degrees when rolling the bottom part.The number of inner peripheral surface defects per perforated material when perforated and rolled under these conditions was calculated. The number of internal surface flaws per perforated material was compared in the case of the conventional method in which the inclination angle of the inclined roll was fixed at 12 degrees and perforation rolling was performed under the same conditions, and the results are shown in Table 1.

[Table] According to the method of the present invention, the number of internal surface flaws generated is significantly reduced compared to the conventional method, showing an excellent effect in suppressing the occurrence of internal surface flaws. In addition, by reducing the roll inclination angle at the top and bottom, it is possible to avoid rolling stoppage due to poor biting, bottom-out failure, or activation of the drive motor protection circuit, and by increasing the roll inclination angle at the middle part, The present invention has excellent effects such as high rolling efficiency.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the equipment used to carry out the method of the present invention, Figure 2 is a dimensional diagram of the billet, Figure 3 is a control time chart, and Figure 4 is the current value of the roll drive motor in the method of the present invention. Graph showing 5th
The figure is a schematic diagram showing the rolling state in an inclined rolling mill.
Figure 6 is a graph showing the relationship between the occurrence of cracks due to Mannesmann fracture and the inclination angle, Figure 7 is a graph showing the relationship between the circumferential shear strain and the rate of occurrence of internal defects, and Figure 8 is the graph showing the relationship between the roll inclination angle and the circle A graph showing the relationship with the circumferential shear strain, and FIG. 9 is a graph showing the current value of the roll drive motor according to the conventional method. 1l, 1r... Inclined roll, 2... Plug, 5
...Load cell, 9...Material position detection device.

Claims (1)

[Claims] 1. In the process of piercing, expanding, or elongating the material to be rolled by using inclined rolls to move the material to be rolled in the axial direction, a plug is inserted along the axial direction of the material to be rolled. A method for rolling a seamless pipe, characterized in that when rolling a predetermined length at the top and bottom of a material, the angle of inclination of the inclined rolls is made smaller than the angle of inclination during rolling of the middle part of the material to be rolled.