JPH012709A - Continuous reduction rolling method for steel pipes - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a continuous reduction rolling method for steel pipes using sipes or the like.

<Prior Art> In its manufacturing process, steel pipes are finished to the final product outer diameter using a continuous reducing mill with a sipe or stretch reduction mill.

This continuous reducing mill for mouth tubes will be explained in detail below using sipes as an example. (3rd edition of the Takoyaki Handbook l11(2)
See P, 1037-1039 (Japan Railway LI Association).

) The sipe is a 201 type J with a semicircular hole shape. ! Fn
In a type rolling mill, adjacent stands are arranged alternately at an angle of 90 degrees to each other, and the number of stands is usually 5 to 8.

The groove shape of the roll used for sipes is formed by a circular arc or a combination of circular arcs, but in order to prevent the steel pipe from being scratched at the edge of the groove, it has traditionally been an oval shape where the horizontal width is larger than the vertical width. is doing. An example of this is shown in FIG. 3. Here, the ellipticity α of the hole shape is defined as follows, where Wn is the major axis and Hn is the minor axis.

α=Wn/Hn・・・・・・・・・・・・・・・
(1) This α is given by the following equation as a function of the outer diameter reduction rate R for each stand, and is practically 1.07 or less.

α=1+kR・・・・・・・・・(R here, k
: Coefficient (usually 1.3 to 2.0) Normally, the NO,l stand and the intermediate stand have two curvature radii of 1/2W, for example, as shown in Fig. 3(b), in order to increase the outer diameter reduction rate.
Type B with a radius of curvature of 1/2Wn is used in the final stand, as shown in Figure 3(a), to improve the roundness of the I tube. Ru.

Note that Dn in the figure is the height of the bottom of the hole groove, which is determined by the pipe diameter, and Rn is the flange radius at the end of the hole, which is important for preventing the occurrence of roll edge marks.

As shown in FIG. 4(a), the outer diameter reduction rate per stand is less than 3% at most, and is large at the entrance stand and becomes smaller as it approaches the final stand. Further, the total outer diameter reduction rate in the sipe is less than 10% at most, as shown in FIG. 4(b).

In addition to the above-mentioned 20-1 type sizer, a 40-1 type sizer with an idle roll provided between the upper and lower drive rolls has been commonly used as a reduction rolling mill for, for example, medium-diameter H1-neck pipes. (3rd edition Tetsuguchibin'U III (2)P
, 1070 (Japan Iron Port Association &). ), but its capabilities are almost the same as the 2011 type.

<Problems to be Solved by the Invention> By the way, when performing narrowing rolling of the mouth pipe using such a conventional sipe, compressive stress is generated in the circumferential direction of the J1 pipe. Compressive stress acts as stress that causes the tube wall to buckle in the roll gap, so if the radius of curvature of this tube wall is small, this portion will easily buckle.
It protrudes outward, causing a so-called bulging phenomenon. Therefore, the total outer diameter reduction rate is usually limited to less than 10%. Therefore, when reducing and rolling steel pipes whose finished outer diameters differ by more than 10%, it is necessary to manufacture mother pipes with outer diameters that have a total outer diameter reduction rate of less than 10% with respect to the finished outer diameter. The same level of outer diameter pass schedule is required in the upstream rolling process, and this is a factor that impedes productivity in the rolling process, such as changing the size of the rolling rolls and preparing billets of various diameters.

The present invention has been made to solve the above-mentioned problems, and provides a continuous reduction rolling method for mouth tubes suitable for obtaining products with the same level of finished outer diameter from mother tubes of the same outer diameter. The purpose is to provide.

Means for Solving Problems〉 As a result of intensive research into means for increasing the overall outer diameter reduction rate during reduction rolling of steel pipes, the inventor of the present invention has found that the radius of curvature of the pipe wall at the roll gap portion can be reduced by forming an elliptical shape. They discovered that it is possible to obtain a large amount of material, and have completed the present invention.

That is, the present invention achieves the above object by rolling the steel pipe into an elliptical shape, then strongly reducing the long diameter side of the elliptical shape, and then reducing the diameter into a circular shape. be.

Below, the barrel composition of the present invention will be specifically explained.

A grooved roll used for forming a steel pipe into an elliptical shape will be explained based on FIG. 1.

FIG. 1 is a front view schematically showing a hole diameter roll;
(a) is for the sipe 1st stand, (b) is for the 2nd stand. Out of 0 times, 1 is the mouth tube, 2 is the hole-shaped roll of the first stand, and 3 is the hole-shaped roll of the second stand. .

As shown in FIG. 1(a), the groove shape of the groove roll 2 of the first stand is (; 1 circular shape, the groove width A-B is the major axis, the groove bottom distance gE, (-D corresponds to the minor axis. In this case, the ellipticity α obtained from the major axis W1 and the minor axis H7
+ (= W + / H+) is 1.01 to 3.0
It is desirable to set it to 0, because the lower limit is
As has been known in the past, this value is necessary to prevent roll edge flaws, and the upper limit is the value required to prevent collapse (buckling) of the pipe wall when applying strong pressure from the long diameter side of the elliptical shape in the next stand. It is determined based on the practical range in which the phenomenon does not occur.

Next, the shape of the groove roll 3 of the second stand is also an ellipse as shown in FIG. 1(b), but the groove width is A-
B corresponds to the short axis, and the hole-shaped groove bottom interval C-D corresponds to the long axis.

The ellipticity J (
=W, /)Iz) is preferably 0.350 to 1.50.The lower limit is the maximum ellipticity (α, = 3.OO) in the front stand. The upper limit is determined based on the conditions to avoid roll edge flaws in the stand, and the upper limit is determined based on the conditions for not producing roll edge flaws.

Determined based on the condition that the pipe wall that comes into contact with the part does not buckle.

Note that the above explanation was made using the 20-1 formula, but 4
A similar configuration can be made using the 01 formula.

Effect> After flattening and rolling the mouth pipe 1 using the elliptical groove roll 2 of the first stand and once making it inert, the elliptical groove roll 2 of the second stand is rolled from the long diameter side of the elliptical shape. When strong pressure is applied by the rolls 3, the outer circumference of the steel pipe 1 is reduced by 10% at once.
It is possible to narrow it down. In addition, when applying strong pressure with the second stand, the steel pipe l in contact with the grooved end 3a of the grooved roll 3
Since the bulging phenomenon seen in the conventional example does not occur on the tube wall portion of the pipe, surface flaws such as roll edge marks do not occur.

<Example> Two seamless pipes with an outer diameter of 88.9 mm and a wall thickness of 3.0 mm
Using the 01 type 5 stand sizer, outer diameter: 76.0
The present invention was applied to finish a product with a thickness of 3.2 mm x 3.2 m. The pass schedule for each stand is shown in Figure 2S. The hole shape and dimensions of these rolls and the rolling results are also shown in Table 1.

Table 1 As is clear from Table 1, the tube outer circumference length was reduced by approximately 13% in the second stand, and the total outer diameter reduction rate was approximately 15%.
%, it can be seen that this is remarkable compared to the maximum of 3% per stand in the conventional example.

<Effects of the Invention> As explained above, according to the present invention, since the elliptical shape is formed and the pressure is applied strongly from the long diameter side, the overall outer diameter reduction rate can be increased. It is possible to squeeze and roll products with different outer diameters from the main tube of
Contributes to improving productivity and reducing costs in upstream rolling processes.

[Brief explanation of drawings]

FIG. 1 is a partial front view schematically showing a grooved roll used in the present invention, FIG. 2 is a partial front view schematically showing an example of the Sipe bus schedule according to the present invention, and FIG. 4 is a partial front view schematically showing a conventional grooved roll;
The figure is a characteristic diagram illustrating the outer diameter reduction rate of a conventional example. 1... Steel pipe, 2, 3... Groove roll Patent applicant Kawa 11 Steel Co., Ltd. Figure 1 (a) (b) Figure 3 (a) (b) W, Figure 4 (a) Star/ number (b) outside Cin)

Claims (1)

[Claims] A continuous reduction rolling method for steel pipes, which comprises rolling the steel pipe into an elliptical shape, then strongly reducing the long diameter side of the elliptical shape, and then reducing the diameter into a circular shape.