JPH07328716A - Manufacture of square steel pipe - Google Patents

Abstract

PURPOSE:To reduce the deformation of the cut section of a square steel pipe at low cost by specifying the whole drawing quantity of square forming, and specifying the total drawing quantity of the stands of half of the numbers or below or the drawing quantity of a single stand. CONSTITUTION:A square steel pipe 2 is attained by passing a round steel pipe 1B through a sizing roll 16, further, by passing it through reshaving rolls 17A to 17D and by forming it to a square. In a square forming process by this square forming roll group R1 to R4, the whole drawing quantity of the outer peripheral length of square forming expressed by Napierian logarithm is set to 1.5% or over. Also, out of total square forming stands, the total drawing quantity of continuous stands of half of the numbers or below is set to 70% of the whole drawing quantity or over, or the drawing quantity of a single stand is set to 50% of the whole drawing quantity or over to perform square forming. Consequently, the deformation of the cut section of a square steel pipe can be reduced without performing hot forming or a heat treatment.

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 a square steel pipe manufactured by the roll forming method is cut, as shown in FIG. 1, an opening in which the side of the cut portion bulges outward is formed along the forming direction, particularly on the downstream side of the cutting position. Deformation phenomenon occurs.

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]

SUMMARY OF THE INVENTION The present invention is a method of manufacturing a square steel pipe in which a round steel pipe is formed by rolls of each stand by using a plurality of stages of square-formed stands. The total drawing amount of the long length is 1.5% or more, and the total drawing amount of less than half of the full-angle forming stands is 70% or more of the total drawing amount, or the drawing amount of a single stand is all. It is a corner forming type with 50% or more of the drawing amount.

[0009]

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, the present inventors have conducted a research study on the effect of the outer peripheral length drawing amount at each stand of the corner forming type in order to reduce the cut deformation, and as a result, when the total drawing amount of the corner forming type outer peripheral length is 1.5% or more. It was found that it is effective to reduce the cut deformation by increasing the drawing amount of half or less of a plurality of continuous stands or a single stand among the full-angle forming stands, and has completed the present invention.

That is, the corner forming type is usually formed by drawing and bending the material to be formed at each stand of a plurality of stages of the corner forming type. The reason why the drawing is added is to promote the plastic deformation of the corner portion and reduce the corner R. When drawing is applied, a large circumferential film stress (a stress that is evenly applied to the entire plate thickness) is applied to the corners, which overlaps the stress due to bending and promotes plastic deformation. It gets smaller. Therefore, first, in order to obtain the desired corner shape, the total drawing amount in the corner forming shape is set to 1.5.
It must be at least%. Then, in the case of an approximately uniform normal drawing amount for each stand, the circumferential film stress applied to the side portion is smaller than that at the corner portion, which promotes plastic deformation of the side portion and is the main cause of cut deformation in the longitudinal direction. The distribution of bending residual stress cannot be reduced. Here, if the amount of reduction per stand is increased, the circumferential film stress applied to the side portions as well as the corner portions increases accordingly. As a result, a larger film stress than usual is applied in the direction orthogonal to the distribution of longitudinal bending residual stress, which is the main cause of cut deformation, and as a result, the yielding of the material in the plate thickness direction is promoted under biaxial stress. ,
The longitudinal bending residual stress in the plate thickness, which is the main cause of cut deformation, becomes small.

FIG. 5 shows the definition of the aperture amount when the corner forming is performed with four stands. Ratio of total aperture (r1 +2) of two consecutive stands to total aperture (rt) in FIG.
The relationship between the total drawing amount (rt) of the angle forming type when (r1 +2) / rt is changed, the ratio of the cut deformation of the product pipe (dc) to the product side length H (dc / H) is shown. When rt is 1.5% or more and (r1 + 2) / rt is 70% or more, the amount of cut deformation is significantly reduced, which shows the effect of reducing cut deformation. 7 and 8 show the ratio of the total aperture of the two stands to the total aperture (r1) when the total aperture (rt) is 1.5%.
2 shows the relationship between +2) / rt and dc / H, and the relationship between the ratio r1 / rt and the ratio dc / H of the single-stand draw amount to the total draw amount. Also in this case, (r1 +2) / rt is 70% or more or r1 /
When rt is 50% or more, the amount of cut deformation significantly decreases, which shows the effect of reducing cut deformation.

As an example, the above is an example in which the total drawing amount of continuous stands including the first stage of less than half of the full-angle forming stands is 70% or more of the total drawing amount, or the first stand. The effect of adding a strong squeeze was explained in the case of forming a horn with a squeezing amount of 50% or more of the total squeezing amount). 70% of the total aperture of continuous stands excluding the stand
Or, the square forming is performed with the drawing amount of the single stand excluding the first stand and the final stand being 50% or more of the total drawing amount), the latter stage (less than half of the full-angle forming stands, Reduce the cut deformation even if the total drawing amount of continuous stands including the final stand is 70% or more of the total drawing amount, or if the drawing amount of the final stand is 50% or more of the total drawing amount and the corner forming is performed. The effect is similar.

Here, the reason why the stand to which the strong drawing is applied is limited to a single stand or a continuous stand of less than half of the full-angle forming type stands is that the effect of reducing the cut deformation can be obtained even if the strong drawing is applied to more stands. Not much improved,
Rather, the adverse effects such as an increase in wall thickness of the corner portion, a defective shape such as an excessively small corner R, and deterioration of the material due to work hardening of the corner portion are large.

When a strong squeeze is applied to the material in the square-shaped form, the power consumption of the motor for driving the roll increases as compared with the case of the normal squeeze, but the increase cost is only about 20% increase at the maximum, It is possible to manufacture a square steel pipe with much lower cost and less deformation of the cut end as compared with the conventional technique involving heat treatment.

[0016]

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, FIG. 5 is a schematic diagram showing the definition of the drawing amount in the corner forming stand, FIG. 6 is a diagram showing the influence of the total drawing amount on the cut deformation reduction effect, and FIG. 7 is the total drawing amount of the plurality of stands showing the cut deformation reduction effect. FIG. 8 is a diagram showing the effect of the drawing amount of the single stand on the cut deformation reduction effect.

FIG. 3 shows a round steel pipe forming process in which an open pipe 1A which is formed into an open pipe 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 bead of the round steel pipe 1B is cut and removed by the outer bead cutting bite 14 and the inner bead cutting bite (not shown).

Then, the round steel pipe 1B is continuously passed through the corner 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, in the corner forming process using the group of rolls (R1 to R4), the total drawing amount of the outer peripheral length of the corner forming represented by natural logarithm as defined in FIG. 1 is 1.5%. That's it. In addition, of the full-angle forming stands r1 to r4, (a) the total aperture of less than half of the continuous stands must be 70% or more of the total aperture, or (b) the aperture of a single stand must be full aperture. A horn forming shape was defined as 50% or more of the amount.

The present inventor changes the drawing amount of each stand (R1 to R4) in manufacturing square steel pipes of various sizes, and the total drawing amount and a total of half or less of the full-angle forming type stands are continuous. A strong drawing ratio of the drawing amount or the drawing amount of a single stand to the total drawing amount was obtained. Then, the relationship between the total drawing amount and the strong drawing ratio and the cut deformation amount dc was investigated, and Table 1 was obtained.

From Table 1, it is recognized that the method of the present invention can manufacture a square steel pipe having a small cut deformation.

[0022]

[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.

[0024]

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.

FIG. 5 is a schematic diagram showing the definition of the aperture amount in a square-shaped stand.

FIG. 6 is a diagram showing the influence of the total aperture amount on the cut deformation reduction effect.

FIG. 7 is a diagram showing the effect of the total drawing amount of a plurality of stands on the cut deformation reduction effect.

FIG. 8 is a diagram showing the influence of the drawing amount of a single stand on the cut deformation reduction effect.

[Explanation of symbols]

 R1 to R4 Square forming stand 1B Round steel pipe 2 Square steel pipe

Claims (1)

[Claims] 1. A method for manufacturing a square steel pipe in which a round steel pipe is formed into a square shape by a roll of each stand by using a plurality of stages of the angular formation type, in which a total drawing amount of the outer peripheral length of the angular formation type represented by natural logarithm is expressed.
Out of the full-angle forming stands that are 1.5% or more, the total drawing amount of less than half of the continuous stands is 70% of the total drawing amount.
Or more, or set the single stand's aperture to
A method for manufacturing a square steel pipe, characterized by forming a corner as 50% or more.