JPH02211904A - Rolling method for seamless steel pipe - Google Patents

Abstract

PURPOSE:To decrease the number of rolls and to decrease the frequencies of roll changes by applying a large rolling reduction to the steel pipe in the 1st stand array consisting of 3-roll stands to a prescribed outside diameter size, and then subjecting the pipe to finish rolling in the 2nd stand consisting of 2-roll stands. CONSTITUTION:The 1st stand array I is installed with No.1 to No.22 each of which is disposed with 3 pieces of rolls R11, R12, R13 having nearly semicircu lar calibers at 120 deg. intervals and which are deviated with the roll shafts of the adjacent stands by 60 deg. each. The 2nd stand array II is installed, in series on the outlet side of the 1st stand array I, with two units of the stands No.23 and No.24 each of which is disposed to two pieces of the rolls R1, R2 having nearly the semicircular calibers at 180 deg. interval and facing each other and which are shifted in the roll shafts of the adjacent stands by 90 deg.. The steel pipe is rolled to the prescribed outside diameter size at a large decrease rate of the outside diameter in the 1st stand array I and thereafter, the steel pipe is subjected to finish rolling by finely adjusting the outside diameter thereof to a prescribed size by the 2nd stand array II adjusted in the caliber size by screw down devices 5 to 8.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for rolling seamless steel pipes, and more particularly, to a rolling method for finishing the outer diameter of seamless steel pipes to predetermined dimensions. be.

[Prior Art] In the manufacturing process of seamless steel pipes, the raw pipe that has left the reeler is rolled using a sizer or a stretch reducer in order to finish it to a predetermined outer diameter.

FIG. 2 is a schematic diagram and side view showing an example of a rolling method using a conventional five-stand diameter-sizing machine, and FIG. 3 is a schematic diagram showing an outline of the single stand. In the figure, R and R are rolling rolls having a nearly semicircular caliber C, and the pass line 0-0 of the seamless steel pipe (hereinafter referred to as steel pipe) that is the material to be rolled is
are arranged opposite to each other on both sides to form a single stand (hereinafter referred to as a stand), and a plurality of stands are installed such that their roll axes are shifted by 90 degrees and intersect with the adjacent stands. 1.2.3.4 is a roll chock that supports the rolls R and R2; 5, 6, and 7.8 are roll-down devices that roll down the roll chocks 1, 2, and 3, and 4 to adjust the distance between the rolls R and R2. And between the roll chocks 1.2, 3, and 4, there are separate cylinders 9.10, respectively.
is interposed.

As shown in FIG. 4, the diameter sizing machine configured as described above moves the steel pipe P between the opposing rolls R and R2 along the pass line 0-
0, and is rolled by rolls R and R of each stand to reduce the diameter and finish the outer diameter to a predetermined size. Generally, the outer diameter reduction rate of each stand is 2 to 4%, and this decreases as it approaches the exit side, and the total outer diameter reduction rate is about 6 to 15%.

In this rolling mill, since the rolls R and R2 in the stand are installed facing each other, the roll chocks 1 to 4 can be easily rolled down by the rolling down devices 5 to 8 and the separate cylinder 910. It is possible to roll steel pipes with outer diameter dimensions that are slightly different from the caliber dimensions of. For example, the distance between the bottoms of Caliber C is 100mm.
Even in the case of Since the distance is 99.5+am, the average outer diameter of the steel pipe can be reduced by this amount. In this way, the distance between the bottoms of the caliber C can be finely adjusted to a desired dimension by adjusting the amount of reduction of the roll chocks 1 to 4 using the reduction devices 5 to 8. When the pressure of the roll chocks 1 to 4 is released, the distance between the bottoms of the caliber C returns to its original state.

However, as shown in FIG. 5, this rolling mill has a large radius difference between the bottom (point A) and the outer periphery (point B) of the calibers of rolls R and R2. The difference in circumferential speed is large. On the other hand, the feed speed of the steel pipe P is equal to only one point of the circumferential speed of the roll from point A to point B,
Normally, at point B, roll circumferential speed > steel pipe feed speed, so the surface of the steel pipe is scraped at point B, and B
Dots are likely to seize and scratches are likely to occur on the surface of the steel pipe.

Furthermore, if the outer diameter reduction rate per stand is increased, the deformation of the steel pipe P in the circumferential direction becomes large, and the roll surface pressure at point B becomes large, making seizure even more likely. For this reason,
The reduction rate of the outer diameter per stand cannot be increased, and the minimum outer diameter when the inlet dimension of the sizing mill is constant cannot be reduced by the reduction rolling mill described below.

FIG. 6 is a schematic diagram and a side view thereof showing an example of a rolling method using a conventional reducing mill. This rolling mill has a stand in which three rolls R, R, R each having an approximately semicircular caliber C are arranged 120' apart from each other.
They are set up at an angle of 0°, and usually consist of 10 to several 2° stands.

As shown in Fig. 7, the reducing rolling mill configured as described above sends the steel pipe P along the pass line between three rolls R11 to R13, reduces the diameter of the steel pipe P in turn by the rolls of each stand, and then externalizes the steel pipe P. It finishes the diameter to a predetermined size, and its function is almost the same as a diameter-sizing machine, but the total outer diameter reduction rate can reach 75%.

Such a reducing mill has rolls R1, ~
Since the R13s are not arranged facing each other like in a diameter-sizing machine, it is extremely difficult to install a roll-down device.

Therefore, even if the target outer diameter differs by, for example, 0.2, it is necessary to replace the roll with a roll of a different caliber size. Therefore, as many rolls as the target size are required, which increases the number of rolls owned and makes it difficult to replace rolls. There are problems such as an increase in production stoppage time.

However, compared to a diameter-sizing machine, even with the same caliber of 100φ, as shown in Figure 8, the difference in radius between point A1 and point B is small, so it is less likely that flaws will occur on the surface of the steel pipe due to seizure at point B1. , Therefore, the outer diameter reduction rate per stand can be selected to be large.

[Problem 8 to be solved by the invention] As mentioned above, either a diameter-sizing mill or a reducing mill is used for rolling to finish the outside diameter of conventional seamless steel pipes. In the case of , the caliber dimensions can be easily adjusted, but the outer diameter reduction rate cannot be increased.
A large number of rolls with different entrance dimensions must be prepared. On the other hand, in the case of a reducing mill, the outer diameter reduction rate can be largely selected, but since the caliber dimensions cannot be adjusted, a large number of rolls must be prepared, and production must be stopped and the rolls replaced each time the steel pipe dimensions differ. The problem is that you have to do it.

As described above, diameter-sizing machines and reducing rolling mills both have their advantages and disadvantages, and problems such as increased equipment costs and impeded productivity improvements have been unavoidable.

The present invention has been developed to solve the above problems, and aims to provide a method for rolling seamless steel pipes that requires fewer rolls and requires less frequent roll replacement.

[Means for Solving the Problems] The method of rolling a seamless steel pipe according to the present invention involves applying a large reduction amount to a material to be rolled in a first row of stands consisting of three roll stands until it reaches a predetermined outer diameter. After rolling, finish rolling is carried out in a second row of stands, which consists of a stand of two rolls and has roll reduction means, and is installed in series on the exit side of the first row of stands.

[Example] FIG. 1(a) is a schematic diagram showing an example of a rolling mill for carrying out the present invention, FIG. 1(b) is a left side view thereof, and FIG. 1(c) is a right side view thereof. In the figure, ■ is the first stand row, and the three rolls R, R, R each having a semicircular caliber are 12
The stands are arranged at 0' intervals, and the roll axes of adjacent stands are shifted by 60' to form 22 stands N.
0.1 to 22 are set. Also, ■ is the second
In the row of stands, two rolls R1 and R2 having semicircular calibers are arranged facing each other with a distance of 180' to form a stand, and the roll axes of the adjacent stands are shifted by 900. Two stands No. 23. No. 24 are installed in series on the exit side of the first stand row (3). In addition,
The stands in the second stand row ■ have rolls R and R, respectively.
It is equipped with two rolling down devices 5 to 8.

In the present invention, which uses a rolling mill configured as described above, when the first stand row Ij,:m pipe is fed in from the direction of the arrow, the first stand row I has a large outer diameter reduction rate that almost cuts the steel pipe. The steel pipe is rolled until it reaches a predetermined outer diameter, and then sent to the second stand row H where the caliber dimensions are adjusted by rolling devices 5 to 8, where the outer diameter of the steel pipe is finely adjusted to the predetermined dimension and finish rolling is performed. Let's do it.

In the above rolling mill example, the first row of stands has 22 stands for 3 rolls, and the second row of stands has 22 stands for 3 rolls.
Although the case where two roll stands are each installed is shown, the number of stands constituting each stand row can be increased or decreased as appropriate depending on the type, outer diameter, etc. of the steel pipe to be rolled.

Next, Table 1 shows the comparison results between the prior art and the present invention when rolling a raw tube with an entry side outer diameter of 200φ into a steel pipe with an outer diameter of 127.0φ. Note that the target outer diameter is 12B, 8φ.

There are three types: 127.0φ and 127.3φ.

As is clear from the above comparative example, the present invention requires the least number of retained rolls compared to the prior art.

Next, the outer diameter is 45.0φ, 55.0φ, 73.0φ
Table 2 shows the comparison results between the conventional technology and the present invention when rolling steel pipes of 114.3φ and 139.8φ, respectively.

As is clear from Table 2, according to the present invention, the number of stands and the number of required rolls are significantly reduced compared to the prior art.

In addition, as in the case of Table 1, the target outer diameter for each steel pipe outer diameter is -0.2 mm, O1 + 0.2 mm, 3.
If there are different types, the case using a diameter-sizing machine and the case using the rolling method of the present invention do not require any more stands because the caliber dimensions can be adjusted by rolling down the rolls, but the case using a reducing mill requires two stands for each steel pipe outer diameter, so in the end, 3B + 2 x 5 x 3-66
A stand is required, and the number of rolls is 3x66-198.

Further, as is clear from Table 2, when using a diameter-sizing machine, not only a large number of stands are required, but also four types of rolls are required for the entrance stand, and these rolls must be replaced in the previous process.

[Effects of the Invention] As is clear from the above description, the present invention provides rolling material with
A first row of stands consisting of a three-roll stand applies a large reduction amount to roll the product to around a predetermined outer diameter dimension, and then a second row of stands consisting of a two-roll stand having roll reduction means performs finish rolling. Therefore, it is possible to realize a rolling method that requires fewer rolls and less frequent roll replacement due to work stoppages. Therefore, the implementation has great effects, such as not only reducing equipment costs but also improving productivity.

[Brief explanation of the drawing]

FIG. 1(a) is a schematic diagram showing an embodiment of a rolling mill for carrying out the present invention, FIG. 1(b) is a left side view thereof, (c) is a right side view, and FIG. 2(a) is a conventional Schematic diagram of the diameter measuring machine, (b) is its side view, Figure 3 is a schematic diagram showing the outline of the stand, Figure 4
The figure is a perspective view showing the method of rolling steel pipes using a diameter-sizing machine, Figure 5 is an explanatory diagram of the circumferential speed of the roll caliber, Figure 6 (a) is a schematic diagram of a conventional reducing mill, and (b) is its side view. 7(a) is a perspective view showing a method of rolling a steel pipe using a reducing mill, FIG. 7(b) is a side view thereof, and FIG. 8 is an explanatory diagram of the circumferential speed of the roll caliber. R, R, R, R roll, C: Caliba 1 2 11 12' 1-4: Roll chock, 5-8: Lowering device, I: First stand row, (2): Second stand row.

Claims (1)

[Claims] Rolling the material to be rolled to around a predetermined outer diameter dimension by applying a large reduction amount with a first stand row consisting of three roll stands,
A method for rolling a seamless steel pipe, characterized in that finish rolling is then carried out in a second row of stands comprising a stand of two rolls having roll-down means and installed in series on the exit side of the first row of stands.