JPH07314047A - Production of square steel tube - Google Patents

Abstract

PURPOSE:To inexpensively reduce the deformation of a cut-edge of a square steel tube by applying bending to the correspondent circumference part of a round steel tube to be formed into respective sides of a steel tube from the inner surface side of tube so as to cause the compression strain on the outer surface side of the tube in the longitudinal direction of the tube in a stage of the round steel tube before the square steel tube forming process. CONSTITUTION:Two contact tips 12 are brought into contact with both edge parts of an open tube 1A formed in a round and the high frequency current is allowed to flow, the heated edges are pressure welded with a squeeze roll 13 and a round electro-resistance-welded tube is obtained. Weld bead is removed with a cutting tool 14. In a stage of the round steel tube 1B before the square forming process, to four correspondent circumference parts of the round steel tube 1B to be formed into four sides of a square steel tube 2, bending is executed from the inner surface side of the tube by four inner expanding rolls 21A to 21D. The square inner expanding rolls 21A to 21D execute bending so as to cause tensile strain on the outer surface side of the tube and compression strain on the inner surface side of the tube in the longitudinal direction of the round steel tube 1B. The inner expanding rolls 21A to 21D are attached pivotally in freely rotatable at the top end of a holder bar 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a square steel pipe by a roll forming method.

[0002]

2. Description of the Related Art A roll forming method, which is one of the methods for manufacturing square steel pipes, forms a steel strip as a raw material into an open pipe shape by passing it through a plurality of round-shaped rolls, and A round steel pipe is formed by electric resistance welding, and the round steel pipe is passed through a plurality of stages of corner forming rolls (reshaping stands R1 to R4 in FIG. 4) to form a square steel pipe.

However, when the square steel pipe manufactured by the roll forming method is cut, as shown in FIG. 1, a phenomenon of opening deformation occurs in which the side portion of the cut edge bulges outward along the forming direction.

Such a cut deformation deteriorates the dimensional accuracy of the square steel pipe, and when the square steel pipe is used as a building member, the dimensional accuracy of the square steel pipe is originally used in the processing and assembling steps thereof. It becomes impossible to carry out automatic welding, and manual welding is inevitable, resulting in a decrease in production efficiency. Also,
When connecting two square steel pipes and providing a backing metal on the inner surface of the abutting portion of both square steel pipes, the above-mentioned cut deformation causes a gap between the inner surface of the pipe and the backing metal, thus improving the connection strength. Lower. In addition, since the side of the square steel pipe bulges outward due to the above-mentioned cut deformation, a high residual tensile stress is generated on the inner surface of the pipe corner, cracks due to welding processing performed at low temperatures in winter, during hot dip galvanizing There is a case where cracks occur, and it is difficult to secure the performance as a building member.

Therefore, as a conventional method for reducing residual stress, which is considered to be the cause of cut end deformation of a square steel tube, for example, Japanese Patent Laid-Open No.
As described in JP-A-5-23738, a part or all of the corner forming process is hot-formed, or as described in JP-A-5146821, the entire surface of the tube after corner forming is heated, and SR ( There is something that causes stress relief.

[0006]

However, in the prior art, the pipe is hot-formed or heat-treated in order to reduce the residual stress that is considered to be the cause of the cut deformation of the square steel pipe, and fuel such as heavy oil or gas is used. Or even if it uses electricity,
Heating energy is required, resulting in high cost. Also, SR
On the other hand, when an off-line heating furnace is used, the productivity is lowered and the cost is further increased.

It is an object of the present invention to reduce cut deformation of a square steel pipe at low cost in a method for manufacturing a square steel pipe by a roll forming system.

[0008]

The present invention according to claim 1 is a method of manufacturing a square steel pipe in which a round steel pipe is squarely formed by rolls to produce a square steel pipe. , In the circumference equivalent part of the round steel pipe which is the side part of the square steel pipe,
Bending is performed from the inner surface of the pipe so that the outer surface of the pipe has tensile strain and the inner surface of the pipe has compressive strain in the longitudinal direction of the pipe.

According to a second aspect of the present invention, in addition to the first aspect of the present invention, the bending is performed after the round steel pipe is electric resistance welded.

[0010]

The present inventors investigated the cause of the cut deformation of the square steel pipe and obtained the following findings. The cause of the deformation of the cut end of the square steel pipe is as shown in FIG. That is, the bending strain in the longitudinal direction of the pipe (tensile on the inner surface of the plate thickness and compressed on the outer surface) caused by winding of the material to be rolled around the roll causes the material thickness to return to the linear shape after the completion of roll forming. Bending residual stress is compressive on the inner surface and tensile on the outer surface. After that, when the residual stress is released by cutting the pipe, the cut end has the same shape as the winding on the roll, that is, the side portion is bent downward in the longitudinal direction. Therefore, the cut edge deformation tends to increase as the product side length D increases, the product plate thickness t decreases, and the yield strength of the product increases.

Therefore, in the present invention, the deformation opposite to the bending strain in the lengthwise direction of the pipe during the roll forming described above is performed at the stage of the round steel pipe before the corner forming step, and the circle of the round steel pipe which becomes the side portion of the square steel pipe. It is added to the circumference equivalent part. As a result, the residual bending stress in the longitudinal direction of the square steel pipe after the corner forming step becomes extremely small, and as a result, the deformation of the cut end of the pipe end is suppressed.

[0012]

EXAMPLE FIG. 1 is a schematic view showing the deformation of the cut end of a square steel pipe, FIG.
Is a schematic diagram showing the cause of the cut deformation of a square steel pipe, FIG. 3 is a schematic diagram showing a round steel pipe forming process in one embodiment of the present invention, FIG. 4 is a schematic diagram showing a square steel pipe forming process in one embodiment of the present invention, 5 is an enlarged view of a main part of FIG. 3, FIG. 6 is a schematic diagram showing a modified example of the arrangement of the lining rolls, FIG. 7 is a schematic diagram showing the effects of the present invention, and FIG. 8 is a cut deformation amount after cutting a square steel pipe. FIG.

FIG. 3 shows a round steel pipe forming process, in which an open pipe 1A formed into a round shape by a round forming roll group is passed through a fin pass roll 11 which is the final roll of the round forming roll group. After that, open pipe 1
Two contact tips 12 are brought into contact with both edge portions of A and a high-frequency current is flown, and the heated edge is pressure welded by a squeeze roll 13 (electric resistance welding).
Then, a round electric resistance welded steel pipe (round steel pipe 1B) is obtained. Then, the weld beads of the round steel pipe 1B are cut and removed by the outer bead cutting tool 14. Also, the inner bead may be cut and removed by the inner bead cutting bead depending on the specifications. A holder bar 15 for supporting the inner bead cutting tool extends from the open pipe 1A inside the round steel pipe 1B.

Then, the round steel pipe 1B is continuously passed through the angle forming roll group shown in FIG. In FIG. 4, 16 is a sizing roll for the round steel pipe 1B, and 17A to 17D are reshaping rolls for forming the square steel pipe 2 into a square shape.

However, in this embodiment, at the stage of the round steel pipe 1B before the corner forming step (the stage after electric resistance welding), the four circumference equivalent parts of the round steel pipe 1B which are the four sides of the square steel pipe 2. On the other hand, the bending process is performed from the inner surface side of the pipe by the four lining rolls 21A to 21D. Each of the lining rolls 21A to 21D is bent so that the pipe outer surface side has a tensile strain and the pipe inner surface side has a compression strain in the longitudinal direction of the round steel pipe 1B.

The lining rolls 21A to 21D are rotatably attached to the tip of the holder bar 15 described above. At this time, the lining rolls 21A to 21D may be arranged in the same plane in the pipe longitudinal direction (FIG. 5), and the arrangement surface of the upper and lower lining rolls 21A and 21C and the left and right lining rolls 21B,
21D may be arranged so as to be offset from each other in the pipe longitudinal direction (FIG. 6), or may be arranged one by one at different positions in the pipe longitudinal direction.

Further, the roll diameter D of the lining rolls 21A to 21D for bending the round steel pipe 1B, and the overhang amount are the outer diameter of the round steel pipe 1B, the plate thickness, the strength, the cut deformation amount of the square steel pipe 2, and the like. It can be set and adjusted according to.

The above-mentioned inner rolls 21A to 21D are
It can be replaced with a shoe. At this time, the shoe does not rotate, and the lubricant is supplied to the contact portion with the inner surface of the pipe.

The operation of this embodiment will be described below.
Each of the forming rolls (the sizing roll 16 and the reshaping roll 17A) forming the corner forming process is formed on the square steel pipe 2.
To 17D), bending strain in the pipe longitudinal direction (tensile on the inner surface of the plate thickness, compression on the outer surface) is applied by winding around the molding roll, and when the material returns to a linear shape after the roll molding, Bending residual stress of compression remains on the inner surface and tension remains on the outer surface.
However, in this embodiment, the lining rolls 21A to 21D are
Is bent from the inner surface side of the round steel pipe 1B after electric resistance welding, and a tensile strain is applied to the outer surface side of the round steel pipe 1B, which is a side portion of the square steel pipe 2, in the longitudinal direction of the pipe. Apply compressive strain to the surface side.

That is, the deformation opposite to the bending strain (tensile on the inner surface and compression on the outer surface) in the longitudinal direction of the pipe during roll forming in the corner forming process is performed at the stage of the round steel pipe 1B before the corner forming process to form the square steel pipe 2. By providing the portions corresponding to the circumference of the round steel pipe 1B which are the side portions, the bending residual stress in the pipe longitudinal direction remaining in the square steel pipe 2 after the corner forming process is made extremely small. Therefore, even if the square steel pipe 2 is cut and the residual stress thereof is released, the occurrence of cut deformation at the pipe end is minimized.

The concrete results of this embodiment will be described below. After performing the above-mentioned bending work on the round steel pipe after the electric resistance welding by using the lining rolls 21A to 21D of the above-described example, in the electric resistance welded pipe manufacturing facility in which the round-formed roll group and the square-formed roll group are continuously arranged. , 550mm square, 16mm plate thickness, STKC
490 square steel pipes were manufactured. This square steel pipe was cut and the amount of deformation of the cut was investigated, and FIG. 7 and Table 1 were obtained. The cut deformation amount is represented by the difference in flatness of each side before and after cutting. The flatness of the side before cutting Δd ₁ = d −d ₁ and the flatness of the side after cutting Δd ₂ = d −
When the d _2, cut the amount of deformation is represented by Δd ₂ -Δd ₁ (FIG. 8).

According to FIG. 7 and Table 1, it is recognized that the amount of cut deformation can be significantly reduced by carrying out the method of the present invention as compared with the conventional method.

[0023]

[Table 1]

The embodiment of the present invention has been described in detail above with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and changes in design within the scope not departing from the gist of the present invention can be made. Even if it exists, it is included in the present invention. For example, the present invention is not limited to a square steel pipe, but can be applied to any square steel pipe such as a triangle or a pentagon.

[0025]

As described above, according to the present invention, in the method for manufacturing a square steel pipe by the roll forming method, the cut deformation of the square steel pipe can be reduced at low cost.

[Brief description of drawings]

FIG. 1 is a schematic view showing a cut end deformation of a square steel pipe.

FIG. 2 is a schematic diagram showing a cause of deformation of a cut end of a square steel pipe.

FIG. 3 is a schematic view showing a round steel pipe forming process in one embodiment of the present invention.

FIG. 4 is a schematic diagram showing a process of forming a square steel pipe in one embodiment of the present invention.

5 is an enlarged view of a main part of FIG.

FIG. 6 is a schematic view showing a modified example of the arrangement of the lining rolls.

FIG. 7 is a schematic diagram showing the effect of the present invention.

FIG. 8 is an explanatory diagram of a cut deformation amount after cutting a square steel pipe.

[Explanation of symbols]

 1B Round steel pipe 2 Square steel pipe 11 Fin pass roll (roll) 13 Squeeze roll 21A-21D Lined roll

Claims (2)

[Claims] 1. A method for manufacturing a square steel pipe in which a round steel pipe is formed into a square shape by rolls to produce a square steel tube, wherein at the stage of the round steel pipe before the corner forming step, the circumference of the round steel pipe becomes a side portion of the square steel pipe. A method for manufacturing a square steel pipe, wherein the portion is bent from the pipe inner surface side so that the pipe outer surface side has tensile strain and the pipe inner surface side has compressive strain in the pipe longitudinal direction. 2. The method for manufacturing a square steel pipe according to claim 1, wherein the bending is performed after the round steel pipe is electric resistance welded.