JPH0579402B2 - - Google Patents

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 stretching mill (stretch reducer) is used to finish the outer diameter of the raw pipe to a predetermined value. A reducing rolling mill usually has a plurality of roll stands arranged in succession, 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 part 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 edge in the i stand of the raw tube is set to the part corresponding to the caliber bottom in the (i+1) stand, and the part corresponding to the caliber bottom in the (i+2) stand.
There is a certain regularity in the contact position between the raw tube and the roll, as in the case of the stand, it is set at a position corresponding to the roll edge. 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 a roll box provided on a roll stand is tilted around a 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 as set forth in claim 1 is such that a plurality of roll stands are arranged continuously, and in the circumferential direction around the rolling pass axis of each roll stand, there are n
Squeezing rolling of circular tubes in which rolls are arranged at intervals of (360/n) degrees, and the rolls of adjacent roll stands are shifted by (180/n) degrees from each other in a plane orthogonal to the rolling pass axis. In the method, each caliber of the n rolls constituting each roll stand has an elliptical shape with a major axis a and a minor axis b, and the major axis a is set at a position β degrees from the roll edge around the rolling pass axis. The β value of the elliptical caliber is made to differ between adjacent roll stands.

In the present invention according to claim 2, the β value is −40≦
β≦+40.

[Function] According to the present invention as set forth in claim 1, the angular position β degree that the major axis position of the elliptical caliber in each roll stand makes with respect to the roll edge is made different between adjacent roll stands. This results in
The surface pressure distribution that the rolls of each roll stand apply to each part of the blank tube in the circumferential direction is irregularly disturbed between adjacent roll stands. In other words, the simple structure allows you to adjust the shape of the roll caliber without complicating the structure of the roll stand.
By disrupting the regularity of the contact position between the raw pipe and the rolls, it is possible to obtain a finished pipe with good quality and no angularity on the inner surface of the pipe.

According to the present invention as set forth in claim 2, by setting the β value within the range of −40≦β≦+40, the radius of the roll edge portion becomes too small and the edge cuts into the material become strong. This has the advantage of preventing troubles that may cause scratches.

[Example] Fig. 1 is a schematic diagram showing the caliber shape of each of the first to eighth roll stands to which the present invention is applied;
The figure is a schematic diagram showing a reducing rolling mill.

As shown in FIG. 2, the reducing rolling mill has a plurality of roll stands 10 arranged in succession, and three roll stands for reducing and rolling the raw pipe 20 in the circumferential direction around the rolling pass axis of each roll stand 10. 11 rolls
They are arranged at intervals of 120 degrees, and the rolls 11 of adjacent roll stands 10 are arranged offset from each other by 60 degrees in a plane perpendicular to the rolling pass axis.

Therefore, each caliber of the three rolls 11 constituting each roll stand 10 has an elliptical shape with a major axis a and a minor axis b, and the major axis a is positioned at a β degree from the roll edge around the rolling pass axis. The elliptical caliber is configured to have different β values between adjacent roll stands.

In Figure 1, "1" in each caliber -
Each numerical value of "8" indicates that the caliber is one of the first to eighth roll stands, and the position of the major axis a in each caliber is indicated by an "arrow". That is, in the example shown in FIG. 1, β = 0 in the first roll stand and β = 0 in the second roll stand.
=40, and β=-40 in the third roll stand, and the calibers of each roll stand are arranged so as to sequentially rotate around the rolling pass axis at a rotation angle of 20 degrees.

According to the embodiment described above, the angular position β degree of the major axis position of the elliptical caliber in each roll stand 10 with respect to the roll edge is made different between adjacent roll stands. As a result, the surface pressure distribution that the rolls 11 of each roll stand 10 apply to each part of the blank tube in the circumferential direction is irregularly disturbed between adjacent roll stands. That is, the simple structure of adjusting the shape of the roll caliber without complicating the structure of the roll stand 10 disturbs the regularity of the contact position between the raw pipe and the roll,
It is possible to obtain a finished pipe with good quality and no angularity on the inner surface of the pipe.

In the implementation of the present invention, the β value may be set to be different between adjacent roll stands. however,
By setting −40≦β≦+40, there is an advantage that the radius of the roll edge portion becomes too small and the edge cuts into the material become strong, thereby preventing troubles such as occurrence of scratches.

Further, in implementing the present invention, the ellipticity (a/b) of the caliber may be arbitrary. However, 1.015≦a/b
By setting it to 1.050, the occurrence of internal angularity in each caliber itself is reduced, so there is an advantage that the effects of the present invention can be further enhanced.

[Effects of the Invention] As described above, according to the present invention, without complicating the structure of the roll stand, a simple structure prevents the occurrence of angularity on the inner surface of the tube due to reduction rolling, and improves the quality of the finished tube. can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the caliber shape of each of the first to eighth roll stands to which the present invention is applied;
The figure is a schematic diagram showing a reducing rolling mill. 10...Roll stand, 11...Roll, 2
0...Main pipe.

Claims (1)

[Scope of Claims] 1. A plurality of roll stands are arranged continuously, and n rolls (360/n) for reducing and rolling the blank pipe are arranged in the circumferential direction around the rolling pass axis of each roll stand.
In a circular tube reduction rolling method in which the rolls of adjacent roll stands are arranged at 180/n degree intervals and shifted by (180/n) degrees from each other in a plane perpendicular to the rolling pass axis, each roll stand is configured. Each caliber of the n rolls has an elliptical shape with a major axis a and a minor axis b, and the major axis a is set at a position β degrees from the roll edge around the rolling pass axis, and the adjacent roll between the stands,
A method for reducing and rolling a circular tube, characterized in that the elliptical calibers have different β values. 2. The method for reducing and rolling a circular tube according to claim 1, wherein the β value is −40≦β≦+40.