JPS61176414A - Rolling method of pipe stock for seamless steel pipe - Google Patents

Abstract

PURPOSE:To decrease the deviation amount of a rolling plug from a mill center and its speed ratio to a rolling roll, by controlling the rotational speed of plug so as to relate it specifically to that of a rolling roll during the rolling of a pipe stock for a seamless steel pipe by a skew rolling mill. CONSTITUTION:For rolling a pipe stock 3 for seamles steel pipe, a rolling plug 7 is set at a prescribed position between rolling rolls 1, 2 by advancing a thrust block 12. Next, a plug bar 6 is chucked by a chucking fixture 13a of a plug-bar rotating device 13, and the fixture 13a is rotated in the same direction as the rotating direction of stock 3 by a motor 15 through a gear box 14 to rotate the plug 7 together with bar 6. The rotational speed of motor 15 is controlled by a speed controller 16 so that it coincides with an aimed speed, which is decided by an operator 17. Next, the operated value of aimed rotational speed is given to the controller 16, to control the motor 15 through the controller 16 thereby rotating the plug 7 at the aimed rotational speed.

Description

[Detailed description of the invention]

"Industrial Application Field" The present invention relates to a method for rolling a raw pipe for seamless steel pipes. ``Prior Art'' Generally, in a production line for seamless opaque tubes, the rolling process begins by perforating the round billet discharged from the heating furnace using an inclined rolling mill called a piercer. After the round billet is pierced and rolled by a piercer, various rolling mills are used depending on various manufacturing methods. For example, in the case of the Mannesmann plug mill method, rolling mills such as an inclined rolling mill called an elongator, a plug mill, a reeler, a sizer, etc., which are similar to a piercer, are used.
For example, in the case of a mandrel mill method, a rolling mill such as a mandrel mill or a stretch reducer is used. Among these rolling mills, inclined rolling mills such as piercers, elongators, and reelers tend to cause thickness unevenness and flaws in the rolled raw pipe due to their rolling mechanisms, and the steel pipe as a product. 3 It has a significant negative impact on quality. Here, an overview of an inclined rolling mill for producing seamless steel pipes will be explained. As shown in FIGS. 4 to 6, upper and lower rolling rolls 1 and 2
is the entrance surface angle α on the entrance side of the rolling mill. It has a comb-shaped or cone-shaped shape with an exit side angle α2 on the exit side, and the axis of each rolling roll 1, 2 is aligned with the vertical plane of the pass line PL through which the round billet or raw pipe 3 passes. , are inclined at angles of inclination β in opposite directions. As shown in FIG. 6, guide shoes 4 and 5 are disposed on the left and right between the upper and lower rolling rolls 1 and 2, sandwiching the pass line PL. For barrel-shaped rolls, the maximum diameter part of each rolling roll 1, 2 is called the gorge part, and for cone-shaped rolls, the position of the inflection point of the roll diameter is called the gorge part; The tip of the rolling plug 7, which is supported at the rear by the plugper 6, is positioned at a predetermined distance away from the position where the rolls face each other and the roll interval is minimum toward the inlet side of the rolling mill. There is. Both ends of the shafts 1a, 2a of each rolling roll 1, 2 are supported by bearings installed inside the rolling mill main body.
9 to a respective drive motor 10.11, each drive motor to, 11 connects each rolling roll 1 to
, 2 are rotated in the same direction. "Problems to be Solved by the Invention" Next, we will discuss how flaws and uneven thickness occur in the raw pipe when the raw pipe is rolled using an inclined rolling mill.
This will be explained using an example of an elongator with reference to FIGS. 13 to 13. FIG. 7 is an enlarged sectional view taken along the arrow A-A in FIG. FIG. 4 is an enlarged sectional view taken along the line B-B in FIG. 4 during rolling by rolls 1 and 2; In a state as shown in FIG.
, 20, when it hits the inlet side, rotational force is applied to the raw tube 3 due to the frictional force from the upper and lower rolling rolls 1 and 2.
A slight difference in the coefficient of friction between the surfaces of the upper and lower rolling rolls 1 and 2, a diameter difference between the upper and lower rolling rolls 1 and 2, or rolling roll 1
, a slight difference in the same speed between the upper and lower rolling rolls 1 and 2 due to a difference in rotational speed, a slight asymmetry between the left and right guide shoes 4 and 5, and the shape of the tip of the blank tube 3 on the entrance side of the inclined rolling mill. As a result, slightly different rotational forces from the upper and lower rolling rolls 1 and 2 act on the blank tube 3 on the entry side of the inclined rolling mill. Therefore, the raw pipe 3 is rotated by the different magnitudes of rotational force of the upper and lower rolling rolls 1.2 as described above, and is also deflected to either the left or right side. In the following explanation, since the rotational force from the lower rolling roll 2 is larger than the rotational force from the upper rolling roll 1, the base tube 3 is deviated to the left with respect to the longitudinal centerline in the pass line PL of the rolling mill. An example will be explained in which the location is as follows. At the side where the rolling rolls 1 and 20 are inserted, the perforation or thickness reduction of the raw tube 3 starts, but at this time, the axis of the raw tube 3 has already shifted to the left, so the rolling plug 7 As shown in FIG. 8, the shaft center 7a is also located offset to the left with respect to the longitudinal center line of the pass line PL of the rolling mill, and rolling in this state is difficult due to the reasons described below. It is stable. The inventors carried out experiments using a model inclined rolling mill, and
Through simulation experiments using the theory of plastic deformation of steel, the speed ratio between the rotational speed V of the rolling rolls 1 and 2 and the rotational speed V of the rolling plug 70 (W=v+/vt
), the amount of deviation DH of the rolling plug 7 from the pass line PL, the centripetal force F1 acting on the rolling plug 7 in the direction of the mill core at that time, and the torque T required to externally drive the rolling plug 7. I found it. FIG. 9 and FIG. io are examples of rolling characteristics when rolling a 25-mm-thick raw tube into a 12.5-mm-thick raw tube using the Elongator. Here, the rotation speed V of the rolls 1 and 2 is the circumferential speed of the rolls 1 and 2 at the gorge portion, and the circumferential speeds of the rolls 1 and 2 are set to be equal. The rolling plug 70 rotational speed v2 is defined as the circumferential speed of the rolling plug 7 in the cross section of the rolling roll gorge. The centripetal force r is defined as a horizontal force acting on the biased rolling plug 7 in the direction of the mill core. Looking at FIG. 9 and FIG.
It can be seen that the rolling plug 7 is offset from the mill core and becomes stable. That is, it can be seen that when the rolling characteristics as shown in FIGS. 9, 10 are present, the rolled plug 7 becomes stable at the position of DH=12rrLm. This is because, in FIG. 9, in the case of D , such a rolling state cannot physically exist. On the other hand, in the case of D) I≧12 mm, there is a speed ratio W that satisfies 'I'=O, but as shown in Fig. 10, As is clear from the figure, regardless of the size of DH, the force F toward the mill core is always acting on the rolling plug 7, so even if DH becomes temporarily larger than 12 mm, D will immediately
H is pushed back to the 12 mm position. In this way, the rolled plug 7 continues to be deviated from the mill core to the predetermined position that it always remains in, and once the axial center 7a of the rolled plug 70 is once deviated to the left side of the pass line P'L, the left side is stabilized from then on. For the same reason, when rolling of the raw pipe 3 starts, the axis 7a of the rolling plug 7 is positioned at the pass line P.
If it deviates to the right side of L, for the raw pipe 3,
Thereafter, rolling will be continued with the right side as the stable position. As described above, when considering the force applied to the left and right guide shoes 4 and 5 when the rolled plug 7 is biased toward either the left or right guide shoe with respect to the pass line PL, the force relationship is asymmetrical. That is, the axis 7a of the rolled plug 7 is on the pass line PI+
On the other hand, if it deviates in the direction of the left guide shoe 4,
The force applied to the left guide shoe 4 by the raw pipe 3 is greater than the force applied to the right guide shoe 5 by the raw pipe 3, and on the contrary, the axis 7a of the rolled plug 7 is aligned with the pass line PL. When the force is applied to the right guide shoe 5 by the raw tube 3, the force applied to the right guide shoe 5 by the raw tube 3 is applied to the left guide shoe 4 by the raw tube 3.
is greater than the force applied to it. Further, the contact situation between each guide shoe 4, 5 and the raw pipe 3 is also different on the left and right sides. FIG. 11 is a sketch showing the wear status of the left guide shoe 4 and the right guide shoe 5 when the rolled plug 7 is biased to the left. As is clear from FIG. 11, the left guide shoe 4 The contact surface of the raw pipe 3 on the guide shoe 5 on the right side is wider than the contact surface of the raw pipe 3 on the guide shoe 5 on the right side, and the way the raw pipe 3 contacts each guide shoe 4, 5 is asymmetrical. It turns out that it is. No.

[Figure 2] is a sketch showing the wear status of the left guide shoe 4 and the right guide shoe 5 when the rolling plug 7 is biased to the right. The contact surface of the raw pipe 3 with the guide shoe 5 on the left side is wider than the contact surface of the raw pipe 3 with the guide shoe 4 on the left side, and the way the raw pipe 3 contacts each guide shoe 4, 5 is different. , it can be seen that the left and right sides are asymmetrical. In addition, in FIG. 11 and FIG. 2, the shaded areas are the areas where the guide shoes 4 and 5 are worn out by the raw tube 3. In this way, the pass line PL of the shaft center 7a of the rolled plug 7
Each guide shoe 4 of the raw pipe 3
, 5 and the contact conditions are also different. This has a serious effect on the raw pipe 3 and each guide shoe 4.5 as described below. That is, when the raw pipe 3 is bitten by the upper and lower rolling rolls 1.2, after the axis 7a of the rolling plug 7 is deflected in a constant direction, either left or right, over the continuous rolling of a plurality of raw pipes 3, If the rollers are suddenly biased and rolled in the opposite direction due to external conditions, the shape of the contact surfaces that were previously attached to the guide shoes 4 and 5 due to friction will be different from the shape of the contact surface. Since the raw pipe 3 comes into contact with the guide shoes 4 and 5, rolling flaws called shoe marks occur in a spiral shape on the outer surface of the raw pipe 3. Furthermore, if the axis 7a of the rolling plug 7 deviates in a constant direction on either the left or right side during the rolling of a plurality of continuous blank pipes 3, in conventional rolling, greater pressure is applied to the guide shoe on either the left or right side. As a result, the wear becomes unbalanced between the left and right sides, resulting in a problem that the lifespan of the guide shoes 4 and 5 is significantly shortened. In extreme cases, serious trouble may occur, such as the guide shoe with higher pressure cracking during rolling. Furthermore, in conventional rolling, the respective forces that the left and right guide shoes 4.5 receive from the raw tube 3 are different as described above. The part of the raw pipe 3 (hereinafter referred to as the upper part) that is rolled by the rolling plug 7 and the lower rolling roll 2
The stresses acting from the guide shoes 4 and 5 on the portion of the raw pipe 3 (hereinafter referred to as the lower portion) that is rolled by the rolling plug 7 and the rolling plug 7 are different from each other. Therefore, if the thickness of the upper part of the raw pipe 3 before rolling and the lower part of the raw pipe 3 after rolling are equal, the plastic yield of the raw pipe 3 acting on the raw pipe 3 from each rolling roll 1゜2 and the rolling plug 7 The required rolling pressure will differ between the upper and lower portions of the raw tube 3. However, since the rolled plug 7 is almost freely movable in the vertical and horizontal directions when viewed from the cross section of the rolling mill, the rolling pressure acting on the rolled plug 7 from the upper part of the raw pipe 3 and the lower part of the raw pipe 3 The rolling pressures acting on the rolling plug 7 from the parts must be equally balanced. As a result, the rolling plug 7 moves to a position where the vertical forces are exactly balanced, so that the thicknesses of the upper and lower parts of the raw pipe 3 after rolling are no longer equal. As mentioned above, the rolling plug 7 is connected to the pass line p of the mill.
If it deviates from p to either the left or right direction, the stress that the raw tube 3 receives from the guide shoes 4 and 5 will be different on the left and right, which will cause uneven thickness in the raw tube 3 during rolling. . In addition, rash scratches different from the shoe marks described above occur on the inner and outer circumferential surfaces of the raw tube 3 for the following reasons. When the raw tube 3 being rolled is rolled by an inclined rolling mill, it is simultaneously subjected to shearing deformation in three directions: shearing deformation in the longitudinal direction of the tube, torsional deformation of the tube surface, and shearing deformation in the circumferential direction. As shown in FIG. 13A, the shear deformation in the pipe circumferential direction is caused by the shear deformation when the billet or the raw pipe 3 is inclinedly rolled, assuming that the billet or the raw pipe 3 has a diametrically thick element. This produces a metal flow as shown in Figure 13B. Such shearing deformation in the pipe circumferential direction generates cracks originating from inclusions contained in the raw pipe 3, which become scratches on the inner and outer circumferential surfaces of the raw pipe 3 after rolling. Therefore, in order to prevent the occurrence of scratches on the raw pipe 3,
It is important to reduce shear deformation in the tube circumferential direction. ``Means for Solving the Problems'' The present invention is intended to solve the above-mentioned problems of the conventional rolling method for seamless steel pipes using an inclined rolling mill. That is, the present invention firstly provides rolling plugs 7 in a predetermined relationship with the rotational speeds of rolling rolls 1 and 2 during rolling of raw pipe 3 in rolling a raw pipe for seamless steel pipes using an inclined rolling mill. Second, during rolling of the raw pipe for seamless steel pipes using an inclined rolling mill, during rolling of the raw pipe 3,
The gist is to control the rotation of the rolled plug 7 so that its rotational torque becomes a predetermined value. "Example" The first method of the present invention will be described below with reference to FIGS. 1 and 2. The control circuit shown in FIG. 1 is an example of an elongator in a seamless steel pipe production line, and the thrust load applied to the rolling plug 7 during rolling of the raw pipe 3 is applied to the thrust block through the plugper 6. [Supported by 2. The rolling plug 7 and the plugper 6 are connected at their mutual contact surfaces so as not to slip during rolling, and the rotational angular velocity of the rolling plug 7 is made to match the rotational angular velocity of the plugper 6. Furthermore, when the rolling of the raw pipe 3 is completed, the thrust block 12
moves backward in the right direction in FIG. 1, pulls out the plugper 6 together with the rolling plug 7 from inside the raw pipe 3 after rolling, and kicks out the raw pipe 3 in the lateral direction. Next, in preparation for the next rolling, the thrust block [2
is moved forward again to set the rolling plug 7 at a predetermined position between the rolling rolls 1 and 2. Once the tip of the rolling plug 7 is set at a predetermined position between the rolling rolls 1 and 2, the plugper 6 is chucked by the chucking fitting 13a of the plug bar rotating device 13 shown in FIG. The king fitting 13a is rotated by an electric motor 15 via a gear box 14 in the same direction as the rotational direction of the raw tube 3, thereby rotating the rolled plug 7 together with the plugper 6. The rotational speed of the electric motor 150 is controlled by a speed controller 16 to match a target speed, and the target speed is determined by a calculator 17. A rotational speed detection signal from a speed detector 18 for detecting the rotational speed of the rolling roll 10 is input to the arithmetic unit 17 . Then, the calculator 17 corrects the roll diameter of the rotational speed of the roll 10 obtained by the speed detector 18, calculates the gorge local speed of the roll 1, and also calculates the speed ratio set in the calculator 17 in advance. A target rotational speed of the rolling plug 7 is calculated, the target rotational speed calculation value is given as an input signal to the speed controller 16, the electric motor 15 is controlled via the speed controller 16, and the rolling plug 7 is set to the target rotational speed. Rotate it. Next, a second method of the present invention will be explained based on FIG. As shown in FIG. 3, the rotational torque of the electric motor 150 is detected by a torque detector 19, and the detected rotational torque value is supplied to a calculator 17 as an input signal. A target torque value is set in advance in the arithmetic unit 17, and this target torque set value is compared with the detected rotational torque value, and the rotational speed of the electric motor 15 is corrected so that it matches the target torque set value. The rotational speed correction calculation value is given to the speed controller 16 as an input signal, and the electric motor 15 is controlled via the speed controller 16 to set the rotational torque of the rolling plug 7 to a target value. "Effects of the Invention" As described above, the present invention provides for forcibly rotating the rolling plug with a rotational driving force of a predetermined magnitude during rolling of the raw pipe for seamless steel pipes using an inclined rolling mill. Therefore, the amount of deviation of the core of the rolling plug and the speed ratio with the rolling roll can be made as small as possible. Therefore, the wear condition of the left and right guide shoes can be made equal, and uneven thickness of the raw pipe can be reduced. In addition, it is possible to reduce the occurrence of scratches on the inner and outer circumferential surfaces of the raw pipe, thereby contributing to improving the product quality of seamless steel pipes.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the first method of the present invention, FIG. 2 is an enlarged view taken along the arrow A-A in FIG. 1, and FIG. 3 shows an embodiment of the second method of the present invention. Fig. 4 is a schematic plan view of the inclined rolling mill, Fig. 5 is a schematic side view of the same as above, Fig. 6 is a schematic front view of the same as above, and Fig. 7 is an entrance side of the rolling roll with upper and lower blank tubes. Fig. 4 is an enlarged cross-sectional view taken along the arrow A-A at the moment when the blank pipe is bitten, and Fig. 8 shows the
Figure 9 is a rolling characteristic diagram showing the relationship between speed ratio and torque, Figure 10 is a rolling characteristic diagram showing the relationship between deviation amount and centripetal force, and Figure 1j is a rolled plug. A sketch showing the wear status of the left and right guide shoes when the rolling plug is biased to the left; [Figure 2 is a sketch showing the wear status of the left and right guide shoes when the rolling plug is biased to the right;
Figures A and B are explanatory diagrams showing changes in shear deformation in the tube circumferential direction. 1.2...Rolling roll 3...Main pipe 4,5.
...Guide shoe 6...Plug par 7...
Rolled plastic. 13... Plug bar rotating device 14... Gear box 15... Electric motor 16... Speed controller 17... Arithmetic unit 18... Speed detector 1
9...Torque detector applicant Kawasaki Steel Corporation Figure 1 Figure 2 iJ3 Figure 4 Figure 1I Tortoise 6 Figure 7 Figure 8 Figure 9 Liao) I-r Otsu V Figure 10 4 4? 1 -f DH (mm) Soon II Figure 12 Figure 13 (A) Figure (B)

Claims (2)

[Claims] (1) In the rolling of a seamless steel tube base pipe by an inclined rolling mill, the rotation of a rolling plug is controlled to have a predetermined relationship with the rotational speed of a rolling roll during rolling of the base pipe. A method of rolling raw pipes for steel pipes. (2) A seamless steel pipe element characterized in that, in rolling a seamless steel pipe base pipe by an inclined rolling mill, the rotation of a rolling plug is controlled so that its rotational torque becomes a predetermined value while the base pipe is being rolled. Tube rolling method.