JP3353880B2 - Manufacturing method of seamless square steel pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a seamless steel pipe having a rectangular cross section, and more particularly to a fixed-size rolling mill (usually a sizer mill) comprising a plurality of stands in which one stand is arranged in series with two rolls. ), And is a technology for producing a seamless rectangular steel pipe by hot rolling.

[0002]

2. Description of the Related Art In recent years, rectangular steel pipes have been frequently used for general structures, building materials, and equipment members. Several manufacturing methods are known for these well-known square steel pipes depending on the size, wall thickness, and the like. For example, a rectangular steel pipe having a complicated cross-sectional shape is manufactured by a hot extrusion molding method, and a normal square steel pipe is manufactured by bending a steel plate and joining a butt portion by welding. This welding method is
As disclosed in JP-A-63-220922, first, a steel plate is formed into a circular shape, and a seam is welded to form a circular raw tube (so-called electric resistance welded tube). It is processed gradually into a square cross section by passing through a steel pipe sizer mill. However, since these methods are usually performed by cold working, there are limitations on the thickness, size, and the like of the square steel pipe to be manufactured, and a step of removing working distortion after working is required.

[0003] Therefore, recently, various attempts have been made with a focus on utilization of a conventional seamless round steel pipe manufacturing facility (see FIG. 4) so that a large-sized, particularly thick-walled rectangular steel pipe can be mass-produced. . For example, JP-A-4-41006 discloses
"After piercing the raw material 12, the raw tube 1 having a circular cross-section is obtained by rolling, and then, after reheating, the tube is reduced to a predetermined cross-section by a sizer mill 2 (a type of fixed rolling mill) composed of a number of stands. Then, hot working is performed by a sizer mill formed of a plurality of rolls 3 and having a rectangular path cross section, which is disposed on at least one or more stands subsequent to the sizer mill 2. A method for manufacturing a steel pipe is disclosed.

By the way, in order to use a rectangular steel pipe for a building structure such as a pillar, Japanese Industrial Standard (JIS G 346) has been adopted.
It is necessary to satisfy 6). One of them is that the dimensions of the corners (S value, defined by the following equation (2)) of the cross section of the steel pipe shown in FIG. 3 are not more than three times the wall thickness t (S ≦ 3.0 t), and Is 0.5% or less of the side length L (P / L ≦
0.005). That is, the corners are as small as possible and the sides are flat. In practice, the dimensions (S values) of the corners are more strict.
5t or less is desired. S = (１ ／) × (L−L _F ) (2) where L: side length (mm) of cross section of square steel pipe L _F : length of flat part of side of cross section of square steel pipe ( mm) t: Wall thickness of square steel pipe (mm) If this demand is to be achieved by cold rolling, which is currently the mainstream in Japan, the radius of curvature R of the corner (which has almost the same meaning as the S value) is large. That is, the roundness increases. In particular, t
The thick steel pipe /L≧0.05, becomes R / t> 3, as a result, also shortened the length L _F of the flat portion of the side shown in FIG. Therefore, it was considered that this problem would be solved by manufacturing by making it easy to work by hot rolling. In fact, the degree of work was increased, and the area reduction rate due to the rolling of the steel pipe section (described later, 1-
When A ₀ / A _i is increased, R becomes smaller, the length of the flat portion of the side becomes longer, and S
The value has also decreased. In addition, as shown in FIG. 3, the area reduction rate is a value at a solid portion of the cross section, and does not include a space portion.

[0005] However, when the area reduction rate is increased in this way, buckling occurs in the steel pipe during rolling, and another problem that the flatness of the side of the cross section of the square steel pipe deteriorates occurs. JP-A-4-41006 describes hot rolling with a sizer mill 2 using three rolls for one stand, but there is no description of the specific conditions to be implemented.
No information on solving such a problem was obtained from the publication.

[0006]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a method for manufacturing a seamless rectangular steel pipe which can obtain a product having a small roundness of a corner and a flat side even if it is thick. It is intended to be.

[0007]

Means for Solving the Problems In order to achieve the above object, the inventor has used a sizer mill of a seamless steel pipe manufacturing facility,
We worked diligently to find out the rolling conditions to reduce the roundness of the corners and flatten the sides of the square steel pipe. As a result, it was found that the object can be achieved by sufficiently filling the corners of the square caliber holes of the rolls used at the time of corner forming with a material, and a method for realizing the object was completed as the present invention.

[0008] That is, the present invention relates to a method for forming a cylindrical tube into a square tube by successively hot rolling a cylindrical raw tube obtained by perforating a billet in a seamless steel pipe manufacturing facility with a plurality of regular rolling mills arranged in series. , between the corner molding stands at least 2 groups of the fixed form rolling machine, the top and bottom flow relationship in said cylindrical blank tube
If the linear speeds of the rolls of the two square forming stands are different from each other
Then multiplied by the compressive force Rutotomoni, roll times to satisfy the following formula
A method for manufacturing a seamless rectangular steel pipe, comprising hot rolling the cylindrical elemental tube into a square tube at a number of turns .

[0009]

[0010]

(Equation 2)

Here, ω: rotation speed of the roll Df: diameter of the flange of the roll Db: bottom diameter of the caliber of the roll i: stand number r: reduction ratio of the side length of the cross section of the rectangular tube at each square forming stand In forming the cylindrical tube into a rectangular tube with the square forming stand, the roll was hot-rolled to the caliber bottom of the roll of the square forming stand so that the flesh of the tube was sufficiently spread. In the cross section of the square steel pipe, the roundness of the corner is reduced, and the flatness of the side also satisfies a desired value.
In the conventional seamless steel pipe equipment, square steel pipes can be mass-produced inexpensively simply by replacing a part of the roll with one having a square caliber.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, FIG. 1 shows three examples of rolls of a fixed rolling mill (sizer mill) 2 used for manufacturing a seamless rectangular steel pipe according to the present invention. In FIG. 1, there are eight stands of sizer mills 2 in series, and rolls 3 from # 1 to # 5 stand have a round cross section for producing a normal cylindrical steel pipe in order to secure the circumferential length of the raw pipe cross section during rolling. Caliber 4 (hole type) is provided. Then, in order to form the cylindrical element tube 1 having the determined peripheral length into a square shape in # 6 to # 8 stands, a roll 3 having a caliber 4 having a square cross section is used for those stands. Thereby, the inner corner is determined corresponding to the outer corner. Also, the # 6 and # 7 stand calipers 4 are designed to prevent dents on the sides during standard format.
The radius of curvature R of the corner is reduced.

According to the present invention, the cylindrical tube 1 is shaped into a rectangular tube by hot rolling using such a sizer mill 2. At this time, as described above, the two tubes having an upstream and downstream relationship are used. A compression force is applied to a raw tube during rolling by changing the number of roll rotations of a square forming stand (preferably adjacent). According to the inventor's research, if this is not done, even if it is hot rolling, the flesh of the raw tube does not sufficiently reach the caliber bottom of the roll, the desired corner is not obtained, and the flatness of the side This is because (P / L) also deteriorates and a product of desired quality cannot be obtained.

Next, specific means for compressing the raw tube will be described with reference to FIG. FIG. 2A shows a sizer mill 2
FIG. 1 shows the arrangement of the roll 3 and the shape of the caliber 4 of the roll 3 is as shown in FIG. In general, when tension is not applied to the tube between the two stands, the position where the speed of the roll and the tube is neutral (neutral line) is the same in the front and rear stands. For example, if the peripheral speed at the caliber bottom position of the roll is equal to the tube speed at the upstream stand, the peripheral speed at the caliber bottom position of the roll is also equal to the tube speed at the downstream stand.

[0015] When the thickness of the mother tube does not change, as base pipe velocity v _i of the two stands, v i _{+ 1} relationship, the reduction rate of the cross-sectional side length of the square base pipe r, v _i / Vi _{+ 1} = 1-r. Therefore, if the speed is matched with the flange portion of the plain tube and the roll, (1-r) · Df i + 1 · ω i + 1 = Df i · ω i is satisfied, the compression force base tube between stands to generate, it is necessary to _{ω i / ω i + 1>} (1-r) · Df i + 1 / Df i.

[0016] Similarly, for if the speed matches in the caliber bottom of the hollow shell and roll, it is necessary to _{ω i / ω i + 1>} (1-r) · Db i + 1 / Db i. Here, Df _i + 1 / Df _i and Db _{i +} 1 /
The magnitude of db _i, side length of blank pipe section and role
Than the ratio or side length reduction ratio of the flange diameter and the like, a result of the invention have studied intensively, in the actual _{rolling, Db i + 1 / Db i} > 0.5 · Df i + 1 / Df i the relationship is established I knew it was there. Therefore, in order to generate a compressive force on the base pipe between stand it should be at least _{ω i / ω i + 1>} 0.5 · (1-r) · Df i + 1 / Df i.

Further, since the tube 1 is normally rolled without tension, normal rolling cannot be performed if complete slippage occurs at each stand. Therefore, it is necessary to prevent the occurrence of complete slip. The condition is that the pipe portion that was at the bottom of the caliber 4 of the roll 3 in the upstream stand comes to the flange end of the roll 3 in the downstream stand, so that ω _i · Db _i ≦ ω _{i + 1} · Df _{i +} It becomes ₁ . To _{summarize, ω i ≦ ω i + 1} · (Df i + 1 / Db i) is satisfied.

Therefore, in order to apply a compressive force to the raw tube 1 and to perform smooth rolling, it is preferable that the above-mentioned relationship (1) is satisfied. Further, in the present invention, it is preferable that one stand of the square forming stand be two rolls, and three or more stands be formed for a desired square forming. This is because the use of two rolls is most suitable to improve the symmetry of the cross-sectional shape of the rectangular cylinder, and at least three stands are required to obtain the rolling force for forming the rectangular cylinder. Further, in the present invention, it is preferable that the temperature of the raw tube 1 at the square forming stand be set to 600 to 1100 ° C. for rolling. If the temperature is lower than 600 ° C., the processing of the raw tube 1 becomes difficult, and the S value ≦ 1.5t cannot be achieved with a thick-walled product. On the other hand, if the temperature exceeds 1100 ° C., the generation of scale increases, the surface properties of the product square steel pipe deteriorate, and flaws also occur.

[0019]

EXAMPLE A seamless square steel pipe 11 was manufactured by applying the manufacturing method according to the present invention to a cylindrical raw pipe 1 having various outer diameters perforated by a piercer mill 3 in FIG. In addition, the steel type of the raw tube 1 is STK490 of JIS G 3466, and the reheating temperature after piercing-thinning and elongation rolling is all within 850 to 1050 ° C. Sizer used
The mill 2 had eight stands with two rolls, and the roll 3 of each stand used had a caliber 4 as shown in FIG. In other words, the rolls having the round calipers 4 are used for the stands # 1 to # 5, and the rolls having the horns 4 are used for the stands # 6 to # 8. Table 1 shows the sizes and rotation speeds (angular velocities) of the rolls 3 of the stands # 6 to # 7 used in the embodiment of the present invention and the conventional example.

[0020]

[Table 1]

Table 1 shows the s / t value of each square steel pipe manufactured under the above conditions. According to Table 1, the s / t value of the square steel pipe manufactured according to the present invention is a desired value (1.5), but those not following the method of the present invention are results that cannot satisfy the desired value.

[0022]

As described above, according to the present invention, a seamless rectangular steel pipe having a small rounded corner and a flat side can be efficiently and inexpensively manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a caliber shape of a roll arranged in a sizer mill for forming a seamless rectangular steel pipe according to the present invention.

FIG. 2 is a perspective view of a sizer mill in which the rollers of FIG. 1 are arranged, (a) is an entire arrangement, (b) and (c) are #
It is a figure explaining the shape of the roller used for 6 stands and # 7 stands.

FIG. 3 is a cross-sectional view illustrating the size of each part of a rectangular steel pipe.

FIG. 4 is a flowchart showing a facility for manufacturing a seamless steel pipe.

[Explanation of symbols]

 DESCRIPTION OF REFERENCE NUMERALS 1 raw tube (cylindrical raw tube) 2 fixed rolling mill (sizer mill) 3 roll 4 caliber 5 heating furnace 6 piercer mill 7 elongator 8 plug mill 9 reeler 10 reheating furnace 11 seamless square steel pipe (square tube) 12 materials (billets)

Continued on the front page (72) Inventor Masaharu Kita 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Kenichi Yamamoto 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corp. Chita Inside the factory (72) Inventor Takaaki Toyooka 1-1-1 Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation Chita Works (56) References JP-A-7-328715 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) B21B 17/14 B21C 37/15

Claims (1)

(57) [Claims] 1. The method according to claim 1, further comprising the steps of: forming a cylindrical tube obtained by piercing a billet in a seamless steel pipe manufacturing facility, followed by hot rolling with a plurality of regular rolling mills arranged in series to form a rectangular tube; between the corner forming stand at least 2 groups of the machine, the two corners forming in the upstream and downstream relationship in said cylindrical blank tube
Multiplying <br/> a compressive force at different roll linear speed of the stand together Rutotomoni, a roll rotational speed which satisfies the following formula, characterized by hot rolling a cylindrical shape mother tube square tube Manufacturing method of seamless square steel pipe. (Equation 1) Here, ω: roll rotation speed Df: roll flange diameter Db: roll caliber bottom diameter i: stand number r: reduction ratio of the side length of the cross section of the rectangular tube at each square forming stand