JPH08243646A - Manufacture of square steel tube - Google Patents

Abstract

PURPOSE: To suppress the yield ratio of a side part to be small, and to manufacture a square steel tube at a low cost in manufacturing the square steel tube by the rolling method by specifying the drawing quantity of the outer circumferential length of a first stand for forming the angle of the square steel tube, and a second and subsequent steel tubes. CONSTITUTION: The drawing quantity r1 of the outer circumferential length of a first stand for forming the angle is in the range of the drawing quantity to be specified by the formula I, while the drawing quantity of the outer circumferential length of a second and subsequent stands is below 1.2 times that of the first stand to form the angle. In the formula I, (t) is the thickness and H is the side length of the square tube. In addition, the drawing quantity of the outer circumferential length is defined in the formula II. In the formula II, r1 is the drawing quantity % of the outer circumferential length of the i-th stand, Li-1 is the outer circumferential length on the i-th stand outlet side, and li is the outer circumferential length on the i-th stand outlet side. In manufacturing the square steel tube by the rolling method, the square steel tube of low yield ratio is manufactured by suppressing the work hardening of the material without modifying the structure, and the heating process can be dispensed with.

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 having a low yield ratio by a roll forming method.

[0002]

2. Description of the Related Art In recent years, in the field of construction, from the viewpoint of ensuring the seismic safety of structures, there is an increasing demand for materials having excellent seismic energy absorption capacity, that is, materials having a low yield ratio.

As a method for manufacturing a square steel pipe having a low yield ratio,
For example, as disclosed in Japanese Patent Application Laid-Open No. 3-87317, a tube after corner forming is heated to an Ac3 point or higher, then cooled in the order of air cooling and water cooling, and tempered if necessary, or, for example, As disclosed in Kaihei 3-97810, a round steel pipe is
There is a method in which square molding is performed while heating to three or more points, then cooling is performed in the order of air cooling and water cooling, and tempering is performed if necessary. The purpose of these is to remove the influence of work hardening at the time of forming by heat treatment, and further to convert the structure into two phases to manufacture a square steel pipe having a low yield ratio.

In these methods, basically, a square steel pipe having a low yield ratio can be manufactured by modifying the structure, but a process of heating the square steel pipe or the round steel pipe is required, and fuel such as heavy oil or gas or electric power is required. However, there is a drawback in that enormous cost is added because of the energy required for heating and the product becomes expensive even if it is used.

In order to solve the drawbacks of the high cost manufacturing method, the following situation has been considered when considering a manufacturing method of a square steel pipe having a low yield ratio while being cold-formed. That is, in the roll forming method, which is one of the methods for manufacturing square steel pipes, a steel strip as a raw material is passed through a series of forming rolls, and electric resistance welding is performed to make a round steel pipe. It is formed into a square cross section using a forming roll. In roll forming, the forming process is performed while applying a drawing corresponding to the compressive strain in the circumferential direction, and after the side part is once formed into a round shape,
Since bending back is performed, a considerable plastic strain is applied to the sides from the material stage. on the other hand,
In order to obtain a low yield ratio, it is a common practice to minimize the processing strain during forming to suppress the increase in yield ratio. However, if the drawing during corner forming is simply reduced, corner R
This will adversely affect the product shape such as the flatness of edges and edges. Under these circumstances, while maintaining the product shape,
The manufacturing technology for square steel pipes that suppresses the increase in yield ratio has not been established.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a low cost manufacturing method in which a yield ratio of a side portion is suppressed to be low when manufacturing a square steel pipe by a roll forming method.

[0007]

According to the present invention, in a method for manufacturing a square steel pipe in which a square steel pipe is roll-formed from a round steel pipe by using a plurality of stages of stands, the outer peripheral length drawing amount of the first stand for square forming is ( The angle forming is performed within the range of the drawing amount specified by the formula (1), and the outer peripheral drawing amount of each stand after the second stand is 1.2 times or less than the outer peripheral drawing amount of the first stand.

Outer perimeter drawing of the first stand: r ₁ (%)

(Equation 3) Definition of peripheral length reduction:

[Equation 4]

[0009]

As a result of the research conducted by the present inventors, the first stand in corner forming is the most round shape as compared with the other stands regardless of the caliber design, so that the diaphragm is formed in the side part. It was found that the ratio of addition was larger than that of the other stands, so that the drawing of the first stand had the greatest effect on the increase in the yield ratio at the side of the square steel pipe. Here, the drawing of the first stand and the increase of the yield ratio from the strip material of the square steel pipe have a relationship as shown in FIG. That is, the yield ratio rises slowly below a certain limit, but the yield ratio rises sharply above this limit. Further, the drawing of the first stand where the rate of increase in the yield ratio changes is determined by the ratio of the plate thickness of the square steel pipe and the side length (the plate thickness and side length of the product pipe on the exit side of the final stand), as shown in FIG. It becomes a relationship. By the way, basically, the smaller the drawing, the smaller the increase in the yield ratio, and a product with a low yield ratio can be obtained. However, if the drawing is in a range where the increase in the yield ratio is moderate, the increase in the yield ratio is small. The diaphragm of the stand is limited to the range expressed by equation (1).

As described above, in order to reduce the yield ratio of the side portion of the square steel pipe, it is sufficient to reduce the drawing of the first stand. On the other hand, in order to make the corner R into a predetermined shape, there is a condition that the diaphragm after the second stand must be taken to some extent. In the case of an unbalanced pass schedule in which the diaphragm of the first stand is extremely lowered and the diaphragms of the second stand and thereafter are secured at a certain value or more in order to satisfy the requirements of both, a defective shape or a poor stripability may be caused. Therefore, as a result of the research conducted by the present inventors, as shown in FIG. 3, if the aperture of each of the second and subsequent stands is 1.2 times or less than the aperture of the first stand, no shape defect or defective stripability occurs. It became clear. For this reason, the perimeter of each stand after the second stand should be set to the first stop.
The outer circumference of the stand is limited to 1.2 times or less.

[0011]

EXAMPLE FIG. 4 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 used as a fin-pass roll 11 which is the final roll of the round forming roll group. After passing through, open pipe 1A
The two contact tips 12 are brought into contact with both edge portions of, and a high-frequency current is flown, whereby the heated edges are pressure welded (electric resistance welding) by the squeeze roll 13.
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. The inner bead may be cut and removed by the inner bead cutting tool 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. 5, 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, with respect to the side length H and the plate thickness t of the square steel pipe 2, (a) the outer peripheral length reduction amount r ₁ of the first stand (reshaping roll 17A) is expressed by the above formula (1). (B) The outer peripheral length reduction amounts r _{2 to} r ₄ of the respective stands (reshaping rolls 17 </ b> B to 17 </ b> D) subsequent to the second stand of the outer peripheral length reduction amount r ₁ of the first stand.
The above-mentioned horn formation was performed with a magnification of 1.2 or less. The yield ratio of the side of the square steel pipe 2 manufactured by this was investigated, and Table 1
I got

[Table 1]

As is clear from the results shown in Table 1, when manufacturing square steel pipes having the same dimensions, the yield ratio of the side portion of the square steel pipe was reduced by 10% or more in the present invention example as compared with the comparative example, and the yield ratio of the low yield ratio was low. Square steel pipe can be manufactured.

Further, in the example of the present invention, a square steel pipe having a low yield ratio is
Since it is possible to manufacture by suppressing the work hardening of the material without modifying the structure, a heating process is not necessary and the cost is reduced.

[0016]

As described above, according to the present invention, it is possible to obtain a low cost manufacturing method in which the yield ratio of the side portion is suppressed to be low when manufacturing a square steel pipe by the roll forming method.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a first stand drawing amount and an increase in a yield ratio from a strip material of a square steel pipe.

FIG. 2 is a diagram showing a relationship between a thickness side length ratio and a yield ratio change point of a yield ratio.

FIG. 3 is a diagram showing a relationship between a drawing amount of a corner forming stand and quality of a product shape.

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

FIG. 5 is a schematic view showing a process of forming a square steel pipe in one embodiment of the present invention.

[Explanation of symbols]

 Diagonal Steel Pipe 17A-17D Reshaping Roll

Claims (1)

[Claims] 1. A method for manufacturing a square steel pipe in which a square steel pipe is roll-formed from a round steel pipe using a plurality of stands, in which the outer peripheral drawing amount of the first stand for square forming is defined by the formula (1). A method for manufacturing a low yield ratio angle steel pipe, characterized in that the angle forming is performed within a range of the amount of the second stand and the outer peripheral length drawing amount of each stand after the second stand is 1.2 times or less the outer peripheral length drawing amount of the first stand. Outer perimeter of first stand: r ₁ (%) [Equation 1] Definition of perimeter length reduction: [Equation 2]