JPS63144807A - Reducing method for round pipe - Google Patents

Abstract

PURPOSE:To prevent the generation of the angling phenomenon of the pipe inner face by a reducing and to improve the quality of a finishing pipe by twisting a blank pipe during rolling by the difference in the peripheral directional components in the direction of the force received by the blank pipe material from an asymmetrical roll face. CONSTITUTION:Plural roll stands 10 are continuously arranged and three rolls 11 for reducing a blank pipe 20 are arranged at 120 deg. intervals in the peripheral direction around the rolling pass shaft of each roll stand 10. The roll 11 of adjacent roll stand 10 is arranged by displacing 60 deg. each other by the inner face intersecting at right angles with the rolling pass shaft. The roll 11 varies the angle gamma made around the rolling pass shaft for the min. roll radius part C of the roll face by the max. roll radius part A at one end side of the roll face and the angle gamma+2theta made for around the rolling pass shaft for the min. roll radius part C of the roll face by the max. roll radius part B at the other end side of the roll face.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for reducing and rolling circular pipes such as seamless steel pipes.

[Prior art] Generally, in the manufacturing process of circular pipes, a reducing mill (stretch reducer) is used to finish the outer diameter of the raw pipe to a predetermined value.
is used. A reducing rolling mill usually has a plurality of roll stands arranged in series, and three rolls arranged at 120 degree intervals in the circumferential direction around the rolling pass axis of each roll stand.

The rolls of adjacent roll stands are offset by 60 degrees from each other in a plane perpendicular to the rolling pass axis.

As a result, each portion of the raw pipe finish-rolled by the reducing mill has a deformation history that regularly differs from one another depending on its position in the circumferential direction from the start to the end of rolling. In other words, the part corresponding to the roll knee 2 in the i-stand of the stock pipe is set to the part corresponding to the bottom of the caliber in the (i+1) stand, and the part corresponding to the roll edge in the (i+2) stand, and so on. There is a certain regularity in the contact position. As a result, the raw pipe has a hexagonal inner surface with angularity, which impairs the quality of the finished pipe.

Therefore, in order to prevent the occurrence of the above-mentioned angular phenomenon, a reduction rolling mill as described in Japanese Patent Application Laid-Open No. 58-25805 has been proposed. This reducing rolling mill has a polygonal roll box that is fitted into the housing of each roll stand, and the angular position around the rolling pass line is staggered between the stands. An angular displacement of 30 degrees is applied in a plane perpendicular to the pass line, and plastic deformation is repeated in 12 circumferentially divided areas of the raw tube.

[Problems to be Solved by the Invention] However, the conventional reducing rolling mill described above involves a complicated structure in which the roll box provided on the roll stand is tilted around the rolling pass line.

An object of the present invention is to use a simple structure without complicating the structure of the roll stand, to prevent the occurrence of angularity on the inner surface of the tube due to reduction rolling, and to improve the quality of the finished tube.

[Means for Solving the Problems] The present invention arranges a plurality of roll stands in succession, and in the circumferential direction around the rolling pass axis of each roll stand, n rolls for reducing and rolling the blank pipe are arranged. In a method for reducing circular pipes, the rolls are arranged at intervals of (360/+) degrees, and the rolls of adjacent roll stands are shifted from each other by (180/n) degrees in a plane perpendicular to the rolling pass axis. The angle that the maximum roll radius on one end of the surface makes with respect to the minimum roll radius on the roll surface around the rolling pass axis, and the maximum roll radius on the other end of the roll surface is the minimum roll radius on the roll surface. Using rolls with different angles around the rolling pass axis, the twist angle at which the raw pipe is twisted by the rolls during rolling is determined by the tension between the stands, m! ! ! It was designed to be controlled by

[Function] According to the present invention, the roll caliber of each roll is asymmetrical on the left and right sides of the minimum roll radius portion of the roll surface, and due to the difference in the circumferential direction component of the direction of the force that the raw pipe material receives from this asymmetrical roll surface. , the raw pipe will be twisted during rolling.

By the way, in order to eliminate, for example, the hexagonal shape (the thick and thin parts are spaced apart by 30 degrees) that occurs on the inner surface of the tube, it is sufficient to twist the raw tube by 30 degrees or more during rolling. Methods for controlling the torsion angle of the raw tube include: ■ A method of changing the angle difference that the left and right maximum roll radius parts of the roll caliber make around the rolling pass axis with respect to the minimum roll radius part, that is, the degree of asymmetry; Possible methods include changing the tension between the stands in order to change the contact pressure between the tube and the roll. Since the method (2) above is uneconomical because the number of rolls increases, the present invention has decided to adopt the method (2) above.

That is, according to the present invention, the raw tube being rolled is twisted at an angle that does not cause internal angularity to disrupt the regularity of the contact position between the raw tube and the rolls, thereby obtaining a finished tube without internal angularity. be able to.

"Example" Fig. 1 is a front view showing a roll used in carrying out the present invention, Fig. 2 is a schematic diagram showing a reducing rolling mill, Fig. 3 is a diagram showing the relationship between twist angle and stretch coefficient, and Fig. 3 is a diagram showing the relationship between twist angle and stretch coefficient. FIG. 4 is a schematic diagram showing the state of reduction rolling.

As shown in FIG. 2, the reducing rolling mill has a plurality of roll stands 1O arranged in succession, and 3 rollers for reducing and rolling the raw pipe 20 in the circumferential direction around the rolling pass axis of each roll stand 10. The rolls 11 are spaced apart by 120 degrees, and the rolls 11 of adjacent roll stands 10 are spaced apart from each other by 80 degrees in a plane perpendicular to the rolling pass axis.

As shown in FIG. 1, the roll 11 has an angle γ that the maximum roll radius portion A on one end side of the roll surface makes with respect to the minimum roll radius portion C of the roll surface, and the roll The angle γ+20 that the maximum roll radius portion B on the other end side of the surface makes with respect to the rolling pass axis is different from the minimum roll radius portion C of the roll surface.

In other words, the roll caliber of the roll 11 has a shape that is a normal symmetrical roll caliber rotated by an angle θ (asymmetric angle), and the shapes of the left and right sides of the minimum roll radius part of the roll surface are asymmetrical, and this asymmetrical shape Due to the difference in the circumferential component of the force that the raw tube material receives from the roll surface, the raw tube becomes twisted during rolling.

By the way, in order to eliminate the hexagonal shape (thick wall part and thin wall part are 30 degrees apart) that occurs on the inner surface of the tube in a reducing rolling mill where each roll stand is 30 mm long, it is necessary to All you need to do is to twist it by 30 degrees or more. Here, the method to control the twist angle of the raw tube is: ■ The difference in angle around the rolling pass axis between the maximum roll radius part of the left and right sides of the roll caliber and the minimum roll radius part of the roll caliber. In other words, there are two methods: (1) changing the degree of asymmetry; and (2) changing the tension between the stands to change the contact pressure between the raw pipe and the roll.

Since the method (2) above is uneconomical because it requires a large number of rolls, the present invention adopts the method (2) above, in which the raw pipe is twisted and rotated by 30 degrees or more during rolling. In other words, for example, when the number of stands that make up a reducing rolling mill is small and you want to increase the twist angle per stand, the contact surface pressure should be increased in order to increase the twisting rotational force that the rolls give to the raw tube. , set the tension between the stands to be smaller.

In the following, a specific procedure for adjusting the tension between stands when the torsion angle of the raw pipe per stand is determined in carrying out the present invention will be described.

FIG. 3 is a diagram showing the relationship between the twist angle of the raw pipe per 1 stand and the stretch coefficient X when the asymmetric angle of the roll is θ (see FIG. 1). X is (longitudinal stress σ of the raw pipe/resistance due to deformation of the raw pipe K). That is, when using rolls with an asymmetric angle θ of 10 degrees, the total number of stands in the reducing mill is 20, and the number of rolls in each stand is 3, the twist angle of the raw pipe per stand is 1.5 degrees (30 degrees 120
), and the stretch coefficient corresponding to this twist angle in FIG. 3 is 0.4.

Next, in each stand, a predetermined stretch coefficient Xi
The set rotational speed Ni of the roll drive motor of each roll stand to obtain the following results. In other words, the stretch coefficient of the i-th stand is xi, and the wall thickness of the inlet pipe is t i-
1. If the outer diameter of the inlet tube is Di-1, the wall thickness of the outlet tube is ti, and the outer diameter of the outlet tube is Di, then ti = f (Xi, ti-1, 0i, Di
-1) ...(l) There is a relationship. That is, when a pattern of a certain diameter reduction rate is given and the wall thickness of the inlet pipe is given, the wall thickness of the outlet side is calculated by the above equation (1) using the stretch coefficient. Due to this wall thickness on the exit side, the cross-sectional area S on the exit side of the raw pipe is
i is given by the following equation (2).

Si=π・ti(Di-ti)...(2
) Furthermore, the set rotational speed Ni of the roll drive motor of the i-th stand is given by the following equation (3) based on the constant mass flow law.

Ni=C/Si ・Gi*Dpi ・・
- (3) where C is a constant, Gi is the reduction ratio between the motor and the roll, and Dpi is the roll diameter at the driving point where the speeds of the raw pipe material and the roll match.

That is, in implementing the present invention.

■Determine in advance the relationship between the roll asymmetric angle θ, the stretch coefficient, and the torsion angle as shown in Figure 3; After setting the torsion angle of the raw pipe, and determining the stretch coefficient Xi to be controlled at each stand using ■ and ■ above, set the rotational speed of the roll drive motor for each stand according to formulas (1) 2 to (3) above. N
i is determined and the operation of each roll drive motor is controlled.

Note that the present invention is applicable not only to those in which each roll stand is 30 lbs, but also to those in which each roll stand is 20 lbs or 40 lbs or more.

[Effects of the Invention] As described above, according to the present invention, the raw pipe being rolled can be twisted at an angle that does not cause internal angularity, without complicating the structure of the roll stand, and with a simple structure. This disturbs the regularity of the contact position between the tube and the rolls, making it possible to obtain a finished tube with good quality and no internal angularity.

[Brief explanation of the drawing]

Fig. 1 is a front view showing a roll used in carrying out the present invention, Fig. 2 is a schematic diagram showing a reducing rolling mill, Fig. 3 is a diagram showing the relationship between twist angle and stretch coefficient, and Fig. 4 is a drawing showing the relationship between the twist angle and the stretch coefficient. It is a schematic diagram showing a rolling state. 10...roll stand, 11...roll, 20...
Raw pipe, A, B...Maximum roll radius. C...Minimum roll radius portion, θ...Asymmetrical angle. Agent Patent Attorney Osamu Shiokawa 1 Figure 2 Figure n Figure 3

Claims (1)

[Claims] (1) A plurality of roll stands are arranged continuously, and n rolls for pipe reduction rolling are arranged at intervals of (360/n) degrees in the circumferential direction around the rolling pass axis of each roll stand. In the reduction rolling method for circular pipes in which the rolls of adjacent roll stands are arranged to be shifted (180/n) degrees from each other in a plane perpendicular to the rolling pass axis, the maximum roll radius on one end of the roll surface corresponds to The angle made around the rolling pass axis with respect to the minimum roll radius part of the roll surface, and the angle made around the rolling pass axis by the maximum roll radius part on the other end side of the roll face with respect to the minimum roll radius part of the roll surface. 1. A method for reducing and rolling a circular tube, characterized in that the twist angle at which the raw tube is twisted during rolling by the rolls is controlled by adjusting the tension between the stands, using rolls having different diameters.