JPS62270204A - Continuous rolling method for steel pipe - Google Patents

Abstract

PURPOSE:To improve the effect of correction for biased thickness by executing thinning rolling at both the end of pipe material at 2 strands just before the last finishing stand and next correcting the bias thickness produced at the circumferential direction at the last stand of non-driving four rolls. CONSTITUTION:In a mandrel mill composing of eight stands, etc., the non-driving four-rolls stand is arrange at No.8 stand as the last finishing roll stand. Then, two sets of caliber type roll pair, No.1, 3 and No.2, 4 are combined as lying the rolling reduction direction at right angle to each other group. Each roll caliber has half angle theta range at about 10-30 deg. and the same curvature radius R1 as the aimed outer radius of the pipe material 13 and forms a curvature radius R2 having 2-3 times of R1 at the both side part and different center. The biased thickness at the time of thinning rolling at the both end of the pipe material 13 by two finishing roll just before the last stand, is effectively squeezed under light rolling by four rolls, and so as the whole, the effect of correction for the biased thickness is remarkably improved.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Industrial Field of Application) The present invention provides an i! ! Concerning a continuous rolling method.

(Prior Art) A mandrel mill is one of the methods for manufacturing seamless steel pipes. As shown in Figure 2, this steel V! The manufacturing apparatus 10 consists of seven to eight stages of two-roll stands 11 facing each other, and a rolled pipe material 13 (hereinafter simply referred to as "pipe material") into which a mandrel lever 12 is inserted passes through each stand 11, and is rolled by a roll 14. After the pipe material has been subjected to the thinning process using the Umandrel mill that performs the thinning process of the pipe +A'13, it is customary that the pipe material is then subjected to a shaping process using a strain relief reducer (not shown).

In addition, in this mandrel mill, in order to prevent uneven wall thickness in the circumferential direction of the pipe, each adjacent stand 11.11 is moved in the rolling direction XX and ``-X'' are sequentially and alternately phased by 90'. However, even with this configuration, it is difficult to measure the internal pressure along the circumferential direction of the tube as shown in FIG. 4 showing the cross-sectional shape of the tube. As shown in FIG. 5, which is a graph of the results, it is impossible to prevent thick portions 15 from forming at locations 45 degrees out of phase with respect to the rolling directions XX and X'-X''.

The reasons for this are as follows.

If you only want to prevent uneven wall thickness in the circumferential direction of the pipe, for example, the method shown in Fig. 6 (
It is sufficient to use a roll 16.16 having a perfect circular hole shape as shown in (n). However, when such a roll is used, the tube material 13 comes into close contact with the mandrel 12. The final finishing rolling stand is a stand that does not apply any rolling reduction to the tube material 13, and is used for shaping the tube material 13 and removing f from the mandrel 12.
f1l+ is in charge of separation, but once the tube material 13 is in close contact with it, it becomes difficult to separate it using this stand.

For this reason, in intermediate stands such as the first finishing stand in the front stage of the Rn finishing rolling stand and the second finishing stand in the preceding stage,
As shown in FIG. 6 (bl), the bottom of the hole in the range of half angle θ has a radius of curvature R9 that is the same center as the pass line and is almost the same as the target outer radius of the tube material 13, and on both sides thereof, R
having a radius of curvature R2 larger than 7 and with different centers;
A so-called double round hole type roll 17.17 is used to create a clearance of 1 between the tube material 13 and the mandrel 12.
8 will occur. Also, when using this roll, the sum of half angle θ1 at the front stand and half angle θ2 at the rear stand of two adjacent stands is 90°.
If this is the case, the close contact portions overlap and it becomes difficult to form the clearance 13, so rolling is performed under the condition of θ1 +θ2<90°. As a result, an insufficiently rolled portion occurs at an intermediate portion between the rolling direction in the front stand and the rolling direction in the rear stand, and this portion remains as the thick wall portion 15 not shown in FIG. 4 described above.

Furthermore, in actual operation, uneven thickness occurs due to mismatch between the center of the mandrel and the center of the hole (the center of the radius of curvature R3).

In addition, if the groove shape is narrowed down from the original design or opened, the two centers mentioned above will not coincide, and uneven thickness will occur even if rolling is performed under the condition of θ1 +02≧90°. will occur.

Thus, in the basic mandrel mill as shown in FIG. 2, uneven thickness in the circumferential direction of the tube is unavoidable.

The tube material rolled in the mandrel mill in this way is
Next, it is finish rolled using a stretch reducer.

It is well known that in trench reducers, the outer diameter is reduced under tension between stands, but no tension is applied to the ends of the tube, resulting in increased wall thickness and yield loss. For this reason, for example, Japanese Patent Publication No. 51-43825 proposes a technique in which both ends of the tube are thinned in a mandrel mill to reduce the thickness of the tube by L1 at the stretch reducer. However, if the roll gap of a particular stand is narrowed in order to roll only the tube end portion thinly, the above-mentioned mismatch between the mandrel center and the hole center becomes large, and the uneven thickness that occurs also becomes large.

Therefore, in recent years, a new mandrel mill with a different roll configuration of the rolling stand has been proposed. This is JP-A-6
As described in Japanese Patent No. 0-87907, a bellows stand in which a pair of drive rolls and a pair of non-drive rolls are combined is assembled into a row of stands. This new type of mandrel mill uses a stretch reducer to finish roll the tube material after passing through the mandrel mill, and both tube ends of the finished material become thickened. The main purpose is to roll the tube material by thinning the end part, but on the other hand, the tube material is rolled by 40 mm.
- The pipe is rolled down from four directions to prevent uneven thickness in the pipe circumferential direction. However, although such a thickness unevenness prevention means is appreciated in terms of using a four-roll stand, it has the following major problems.

(Problems to be Solved by the Invention) In other words, ■Since both side edges are rolled thinly, it is assumed that three 4-roll stands are placed in the intermediate stand that is once subjected to strong rolling, and the hard rolling A stand configuration that can withstand fire is required.

(2) In order to obtain the desired effect, two 4-roll stands whose rolling directions are phased by 45 degrees are required, which further increases the scale of the apparatus.

■In order to thin the tube end using a 4-roll stand, the tube ends up being squeezed out from the roll flange due to the application of strong pressure, making it practically unusable.

An object of the present invention is to provide a continuous rolling method for steel pipes using a mandrel mill that solves these problems and has an easy structure and a high effect of correcting uneven thickness.

(Means for solving the problem) By the way, the conventional basic idea regarding R holly finish rolling in a mandrel mill is as described above.
This is a light rolling process that does not apply any reduction in practice, with the purpose of straightening the pipe material to roundness and loosening the tightness between the pipe material and the mandrel. It was a roll stand. On the other hand, as mentioned in the section on problems with the prior art, ■ uneven thickness occurs specifically at four locations in the circumferential direction of the tube; There is a possibility of recurrence or promotion of uneven thickness.

Here, from the viewpoint of the above-mentioned ■■, the present invention provides the final finishing rolling stand with a thickness correction function by 40-ru,
We propose an extremely rational solution that uses only this final stand to achieve a thickness correction effect comparable to or superior to that of two conventional 4-roll stand quibs.

That is, in the present invention, each rolling stand except the final finishing rolling stand consists of two opposing roll stands in which the rolling direction is sequentially and alternately shifted by 90°, and the final finishing rolling stand has all rolls not driven, and This is a rolling method using a mandrel mill consisting of four roll stands whose phase is 45 degrees with respect to the rolling direction of the immediately preceding rolling stand, and the two stands immediately before the final finishing rolling stand perform thinning rolling on both ends of the pipe material. This continuous rolling method for steel pipes is characterized in that the thickness deviation in the tube circumferential direction caused by this groove-thickening rolling is corrected by a non-driven four-roll stand of the final finishing rolling stand.

Here, both ends of the tube body are approximately 500 to 100 meters from the tube end.
A portion of about 100O+ is shown. In other words, this is the portion corresponding to the length where the tube end becomes thickened in the subsequent process.

In addition, correcting the thickness deviation in the circumferential direction of the tube by the four-roll stand of the final finishing rolling stand means that the thick part of the thickness deviation caused by the two immediately preceding stands is mainly rolled. There is no need to reduce the parts that are not meat, but there is of course no problem if the parts are reduced a little.

(Function) Conventionally, as already mentioned, the thickness deviation in the circumferential direction of the tube material that has passed through the mandrel mill is determined by the rolling direction χ-X and X
17 flesh portions 15 are produced at four locations that are 45 degrees out of phase with '-X'.

However, according to the mandrel mill used in the present invention, the 17 wall portions 15 at four locations in the circumferential direction of the tube, which are formed before entering the final finishing rolling stand, 'When passing, 4
1: It is crushed under concentrated load from the I-ru, and uneven wall thickness in the pipe circumferential direction is corrected under light pressure similar to conventional methods.Furthermore, since there is no passage through the stand after that, uneven wall thickness can be prevented from reoccurring or being exacerbated. do not have.

Also, unlike the method disclosed in JP-A No. 60-87907, only the thick parts formed in four directions are rolled, and the other parts are not subjected to wall thickness reduction. is possible. Therefore, the stand can be made extremely compact since it is not necessary to withstand many loads. Further, since the rolling is performed under light rolling pressure, rolling can be performed even if all four rolls are idle rolls, so that the structure can be made fiMip-.

At the same time, the outer shape of the tube material is shaped by the opposed 40-rustand, and the close contact between the tube material and the mandrel is also eliminated, and the function as a g&+ finish rolling stand is fully exhibited.

FIG. 1 shows an example of a four-roll stand incorporated as a final rolling stand of the mandrel mill of the present invention.
It is a front view showing the roll configuration.

FIG. 8 is a perspective view of a mandrel mill incorporating this four-wheel stand as a final rolling stand. 4-roll stand 19 that constitutes the final finishing rolling stand
is installed so that the rolling direction is the sum of about 45 degrees with respect to the rolling direction of the immediately preceding two-roll stand.

According to FIG. 1, a pair of non-driven two-string grooved rolls 1.3 and 2.4 are assembled with their rolling directions perpendicular to each other. As shown in Fig. 2 and Fig. 3 ta+ (b), the rolling direction in the immediately preceding stand has a phase of 45" with respect to the horizontal line and the vertical line, so the horizontal direction and The vertical direction is the rolling direction in the four-roll stand.

Each a-rule [2, 3, and 4] has a radius of curvature R9 at the bottom of the hole in the range of half angle θ, that is, at the center surface of the hole, which is co-centered with the pass line and approximately equal to the target outer radius of the tube material 13. However, it has a so-called double radius shape, which is thicker than L on both sides of the surface (and has a different radius of curvature R2 at the center). Originally, this double radius hole type roll was used for an intermediate stand where strong pressure is required. In the present invention, the four-roll stand is used for the final finishing rolling stand, which has a perfect circular hole type. It is preferable to use a double radius hole type roll, which is commonly used for intermediate stands, because it has the function of crushing thick parts in addition to creating clearance.

The half angle θ indicating the area of radius R1 is preferably 10 to 30 degrees. The reason for this is that if the angle is smaller than 10°, the range for correcting uneven thickness will be too narrow, reducing its practical value.
This is because if it is larger than 0, the clearance between the tube material and the mandrel bar becomes too small, making it difficult to pull out and separate the tube material.

On the other hand, radius 1? Since the size of t does not have any influence on the thickness correction effect, it is mainly determined from the viewpoint of securing the cross-sectional shape of the finished pipe and the clearance between the pipe material and the mandrel bar. like 11
It is preferable to set it to about 2 to 3 times.

It goes without saying that the rolls used in the final rolling stand of the present invention are not limited to the above-mentioned double round hole type rolls, but also triple round hole type rolls as shown in FIG. 7. That is, the entire hole surface is composed of a region with a radius R1 of half angle θ, a region with a radius R8 on both sides of the hole surface, and a region with a radius in the middle. In addition, in the figure, the reference number is 6th.
Identical to the figure.

The roll pairs 1.3 and 2.4 may be phased back and forth in the pass line direction to avoid roll interference, drive mechanism interference, and the like.

The present invention will be described in more detail below with reference to specific examples.

As shown in the perspective view in Figure 8, the 98% finish rolling stand of the FF18 stand in the existing mandrel mill consisting of 8 stands was changed to a 4-roll stand with no drive. The 6.7.8 stands, including this stand, have been changed to a hydraulic reduction control system that allows the opening and closing of the roll gap at high speed using a hydraulic cylinder.Using this mandrel mill, the ends of the pipe materials are tapered 1000 mm from the end face position. The effects of the present invention were confirmed by conducting experiments in which only 6.7 stands were used for thinning rolling, and in which 8 stands were used as stands for correcting uneven thickness.

The dimensions of the hole type and rolled pipe material used in the experiment are shown in Tables 1 and 2.

FIGS. 9 and 10 show the measurement results of the wall thickness after mandrel rolling of the tube material which was subjected to end wall thinning rolling. 9th
In the figure and FIG. 10, the solid line shows the case where only the 6.7 stand is used. Moreover, the broken line shows the case where the 6.7 stand is used for thinning rolling and the 8 stand is used as a stand for correcting uneven thickness. The average direction Iγ is the average value of the wall thicknesses at 36 points in the circumferential direction in each section of the pipe in the papier mache direction. In addition, when the groove bottom of the two-roll stand is 0°, the thickness deviation is approximately 45°, 135°, and 22° in the circumferential direction.
5'', the above-mentioned average thickness is subtracted from the average of the maximum thickness values occurring near 315°.

From the results shown in the figure, in rolling to reduce the thickness of the ends of a tube using a two-roll stand, which is a typical example of the conventional technique, uneven thickness occurs due to the thinning of both ends of the tube, and after the stretch reducer. Even if it were possible to make the wall thickness uniform, there would be parts that could not be used as finished products due to the considerable thickness deviation. On the other hand, as is clear from the results shown in FIGS. 9 and 10, according to the present invention, the occurrence of uneven thickness can be effectively suppressed by thinning the end portion of the pipe material, and the stretching in the subsequent process This has a great effect on reducing cropping after the reducer.

Table 1 Table 2 (lIIIl+) (Effects of the invention) As is clear from the above explanation, the mandrel mill used in the present invention has a 4-roll stand only on the final stand for the purpose of correcting uneven thickness. Not only can the cost increase associated with this process be minimized, but also the thick part is effectively crushed by the concentrated load due to the light reduction with 40-ru, and there is no bath afterwards, which prevents the recurrence of uneven thickness.
There is no concern that the remaining uneven thickness will be promoted (but when viewed as a whole, the effect of correcting uneven thickness is large.

Moreover, since the end portion of the tube is thinned in two stands immediately before the final finish rolling, thickening of the end portion in the next step is effectively prevented.

Furthermore, since the 4-roll stand only needs to be used for light pressure, a strong structure is not required, and this, along with the fact that only one 4-roll stand is required, and other stands can be used for recreational purposes, This is extremely advantageous in terms of equipment costs.

Furthermore, since the final finish rolling is performed on a four-roll stand, material shaping and material peeling, which are the original objectives of the final finish rolling, can be performed more effectively.

[Brief explanation of the drawing]

Fig. 1 is a front view showing the roll configuration of an example of a four-roll stand used in the mandrel mill of the present invention; Fig. 2 is a perspective view showing the overall structure of a conventional basic mandrel mill; Fig. 3 Figure Fal (bl is a front view showing the roll configuration; Figure 4 is a cross-sectional view showing uneven thickness of a pipe material rolled in a conventional mill; Figure 5 is a distribution diagram of wall thickness deviation; Figure 6 ta+ (bl is a front view showing the hole shape of the rolls used in conventional mills; FIG. 7 is a front view showing the triple round hole type roll configuration; FIG. 8 is the final view of the four-roll stand according to the present invention. A perspective view of the mandrel mill incorporated into the finishing stand; and FIGS. 9 and 10 are graphs showing the measurement results of wall thickness after rolling with the mandrel mill. 1.2.3.4.14.16 .17 one hole type one call 11
: Stand 12: Mandrel bar 13: Pipe material 15: Thick wall part 18: Clearance

Claims (1)

[Claims] Each rolling stand except the final finishing rolling stand consists of two opposing roll stands whose rolling directions are sequentially and alternately phased by 90 degrees, and the final finishing rolling stand is all rolls not driven,
This is a rolling method using a mandrel mill consisting of four roll stands whose rolling direction is 45 degrees out of phase with the rolling direction of the immediately preceding rolling stand. A method for continuous rolling of steel pipes, characterized in that a non-driving 4-roll stand of the final finishing rolling stand corrects uneven wall thickness in the pipe circumferential direction caused by the groove-thickening rolling.