JP3331897B2 - Forming method of 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 for forming a square steel pipe by using a round steel pipe welded by electric resistance welding and forming it into a square steel pipe by a roll forming method.

[0002]

2. Description of the Related Art Square steel pipes have more advantageous cross-sectional characteristics than round steel pipes, and thus have been demanded as architectural structures in the past. With the automation, the demand for the uniformity of the bending radius R at the cross-sectional corners is particularly increasing.

[0003] Square steel pipes are manufactured from a round steel pipe such as an electric resistance welded steel pipe by a roll forming method in a group of a plurality of stages of square forming type stands. FIG. 3 is a schematic front view showing an example of a conventional square forming type stand. The forming stand is composed of an upper roll 1 and a lower roll 2 which are provided symmetrically in the vertical direction and have the same diameter.
And side rolls 3, 3 by continuously passing a round steel pipe between the upper and lower rolls 1, 2 and the side rolls 3, 3 of such a square forming stand as shown in FIG. It is formed into a square steel pipe 4.

[0004] When forming a square steel pipe with the above-described multi-stage square forming stand, as a method of improving the accuracy of bending R at each corner, for example, Japanese Patent Application Laid-Open No. 63-168 is known.
Japanese Patent Publication No. 223 proposes a method of making an element tube shape elliptical (hereinafter, referred to as prior art).

[0005]

However, when an ERW steel pipe is formed into a square steel pipe as a raw pipe, as shown in FIG. 5, due to the effect of the welded portion, both sides of the upper side including the ERW welded portion 5 are formed. The bending R of the two corners a and b is
It is larger than the bending R of the two corners c and d. If there is such a difference in the bending R of the corners a and b and c and d, it becomes difficult to automatically weld the square tubes when used as a material of a building structure, and the appearance becomes poor. Problem arises. Such a problem cannot be solved by the above prior art.

The cause of the difference in the bending radius R at the corner of the rectangular steel pipe is as follows. That is, the electric resistance welded portion existing on the upper surface of the electric resistance welded steel pipe in the longitudinal direction usually has a structure harder than the surrounding base material because it is rapidly heated and quenched. As a result, the upper surface including the welded portion exhibits a peculiar behavior, thereby causing unevenness in the bending R at the four corners of the square steel pipe having the square shape.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problem, and to use a round steel pipe welded by electric resistance welding to form a rectangular steel pipe by a roll forming method, and to uniformly bend R at the corners of the cross section. It is an object of the present invention to provide a method for forming a square steel pipe that can be formed into a square steel pipe having an excellent appearance.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a round steel pipe welded by electric resistance welding is passed through a multi-stage angulated stand composed of four forming rolls of an upper roll, a lower roll and left and right side rolls. In the method for forming a square steel pipe to be formed into a shape, a forming roll in at least one forming stand among the plurality of stages of the square forming stands is formed by an upper roll for forming an upper side where an electric resistance welded portion of the round steel pipe exists. A different diameter roll whose diameter is smaller than the diameter of the lower roll forming the lower side opposite to the upper side is 0.6 to 0.9 times, and a square steel pipe is formed by such a different diameter roll. Thus, it is characterized in that the bending R of each corner portion of the rectangular steel pipe is made uniform.

The above-mentioned forming stand composed of asymmetrical rolls having an asymmetrical roll in which the diameter of the upper roll is smaller than the diameter of the lower roll,
It may be installed on any stand of the multi-stage square-shaped stand or on all stands, but it is effective to install it on the final stand.

[0010] Since the rectangular steel pipe formed into a square shape from the round steel pipe welded by ERW is used for building structures and the like, heat treatment such as annealing for the ERW welded part is not performed.
Not usually done. Further, as shown in FIG. 4, the bead 6 generated on the inner surface of the electric resistance welded portion is not cut but is left as it is. As a result, this was changed to the conventional upper roll 1 shown in FIG.
When the lower roll 2 is formed into a square shape by passing through a forming machine formed of symmetrical square forming rolls having a uniform diameter, the upper surface including the welded portion having a structure harder than the base material is deformed in the longitudinal direction. As a result, the bending R of the upper two corners a and b shown in FIG. 5 is larger than the bending R of the lower two corners c and d shown in FIG.

[0011]

Therefore, in the present invention, as shown in a schematic front view in FIG. 1, an upper roll 1 of at least one of a plurality of angulated stands is provided.
The forming roll composed of the lower roll 2 and the side rolls 3, 3 is formed by lowering the upper roll 1 for forming the upper side where the electric resistance welded portion of the round steel pipe exists, and forming the lower side opposite to the upper side. A small-diameter roll having a small diameter of 0.6 to 0.9 times the diameter of No. 2 is used.

FIG. 2 is a view showing a process of forming a square steel pipe by changing the cross-sectional shape of the pipe. As shown in FIG.
No. 1 to No. 1 pipes made of ERW steel pipes with round cross sections
No. 4 forming stand, which is the final stand, is formed by continuously passing between the upper and lower rolls 1 and 2 and the side rolls 3 and 3 of the four-stage forming stand of No. 4 according to the present invention. The diameter of the upper roll 1 is 0.6 to 0.9 times the diameter of the lower roll 2 shown in FIG. Following such four-stage forming stands of No. 1 to No. 4, a non-driving stand (not shown) for correcting flatness of each side is arranged. The number of the molding stands is usually three to six, but is not limited thereto.

As described above, since the diameter of the upper roll 1 of the final forming stand is smaller than the diameter of the lower roll 2, the formation of the upper surface of the pipe is promoted, and the upper two corners of the rectangular steel pipe 4 shown in FIG. The bending R of a and b becomes smaller, and the lower 2
The bending R of the corners c and d is approximated, and the bending R of each corner a, b, c and d can be made uniform.

If the diameter of the upper roll 1 exceeds 0.9 times the diameter of the lower roll, it is not possible to make the above-mentioned corner radius R uniform. On the other hand, if the diameter of the upper roll is less than 0.6 times the diameter of the lower roll, which is too small, there is a problem in equipment and the molding operation becomes difficult. Therefore, the diameter of the upper roll is in the range of 0.6 to 0.9 times the diameter of the lower roll, preferably 0.8 to 0.9.
It should be in the range of 0.85 times.

The effect of equalizing the corners R by the vertically asymmetric rolls having different diameters is more effective as it is closer to the final stand. In particular, the roll caliber is flat, and the bending R of the corners determines the shape. Excellent effects can be obtained when implemented on the final stand.

[0016]

Next, the present invention will be described with reference to examples and comparative examples. The apparatus shown in FIGS. 1 and 2 has an outer diameter of 238.3 to 246.5 mm, a pipe thickness of 6.0 mm,
No. 1 to No. 3 forming stands of 9.0 mm and 12.0 mm ERW steel pipes with both upper and lower roll diameters of 650 mm and, as shown in Table 1, upper roll diameter and lower roll diameter No. 4 molding stand of different diameters within the scope of the present invention has a side length of 200 × 200 mm, a tube thickness of 6.0 mm,
Various square steel pipe Nos. 1 to 7 of 9.0 mm and 12.0 mm were prepared.

For comparison, as shown in Table 1, No. 4
The upper roll diameter and the lower roll diameter of the forming stand are outside the range of the present invention, and the outer diameters are 238.3 to 246.
ERW steel pipes of 5 mm, 6.0 mm, 9.0 mm and 12.0 mm in thickness are used as raw tubes, the side length is 200 × 200 mm, and the thickness is 6.0.
mm, 9.0 mm, 12.0 mm square steel pipe Nos. 1-4 were prepared.

[0018]

[Table 1]

The square steel pipe No.
The values obtained by dividing the bending R of each of the corners a, b, c, and d shown in FIG. 5 by the pipe thickness of the square steel pipes Nos. 1 to 4 of the comparative examples and the maximum and minimum values thereof. Table 1 also shows the difference.

As is clear from Table 1, the corners a, b, c, and d of the rectangular steel pipes Nos. 1 to 7 of the present invention had almost uniform bending R. On the other hand, in the rectangular steel pipes Nos. 1 to 4 of the comparative example, the bending R of the corner portions a and b on both sides of the side including the welded portion is different from the other two corner portions c and c.
It was larger than the bending R of d and was non-uniform.

[0021]

As described above, according to the present invention,
When using ERW welded round steel pipes and forming them into square steel pipes by the roll forming method, the bending R at the corners of the cross section can be made uniform without the need for heat treatment or the like for the welded parts. An industrially useful effect that can be formed into a rectangular steel pipe having an excellent shape is provided.

[Brief description of the drawings]

FIG. 1 is a front view of a rectangular steel tube forming stand used in the method of the present invention.

FIG. 2 is a view showing a forming process of a square steel pipe.

FIG. 3 is a front view of a conventional rectangular steel tube forming stand.

FIG. 4 is a partial perspective view of a formed square steel pipe.

FIG. 5 is a cross-sectional view of a formed rectangular steel pipe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper roll 2 Lower roll 3 Side roll 4 Square steel pipe 4'base pipe 5 ERW welded part 6 Bead

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B21D 5/12 B21C 37/15

Claims (1)

(57) [Claims] 1. An ERW welded round steel pipe is rolled into an upper roll,
A method of forming a square steel pipe which is formed into a square shape by passing through a plurality of stages of a square forming stand comprising four forming rolls of a lower roll and left and right side rolls, wherein at least one forming stand of the plurality of stages of a square forming stand The forming roll in the diameter of the upper roll for forming the upper side where the ERW weld of the round steel pipe exists,
By forming a different-diameter roll having a small diameter of 0.6 to 0.9 times the diameter of the lower roll forming the lower side opposite to the upper side, and forming a square steel pipe by such a different-diameter roll, A method for forming a rectangular steel pipe, wherein the bending R of each corner portion of the steel pipe is made uniform.