JPH0116208B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a square steel pipe by electric resistance welding.

Conventionally, square steel pipes are produced by forming and welding a pipe into a normal circular cross section and then reprocessing the pipe into a square cross section by applying pressure from the top, bottom, left and right using rolls with square calibers. In addition, special public relations
As seen in Publication No. 739 and Japanese Patent Application Laid-open No. 55-68121, attempts have been made to produce rectangular electric resistance welded steel pipes in which square pipes are directly formed from plates or coils. but,
Although conventional methods for manufacturing rectangular electric resistance welded steel pipes have devised a method for forming squares, they completely ignore changes in cross-sectional shape caused by the welding process. Therefore, in order to adjust the shape, it is necessary to use a standard machine after welding.
By the way, when a square steel pipe is strongly compressed from its surroundings, buckling tends to occur on the sides. Because of these problems, the method of manufacturing square electric resistance welded steel pipes by direct square tube forming has not been able to become the mainstream technology. However, in recent years, the demand for square steel pipes has increased in the fields of architecture, construction, etc., and there is a desire to develop a highly efficient method for manufacturing square pipes that can easily meet various demands regarding dimensions and shapes.

In view of the actual situation, the present applicant has previously filed the
-032537 (Japanese Unexamined Patent Publication No. 56-128618) "Method for manufacturing square steel pipes" proposed a method for manufacturing square steel pipes with a welded seam on one side by roll forming a steel strip, but the present invention will be described later. This is a further improvement based on the process in the above proposal.

As is well known, electric resistance welded pipes are manufactured by heating and melting the edge portions of pipe materials to be welded using high frequency current, and then welding them under pressure using squeeze rolls.

Fig. 1 is a cross-sectional view of the vicinity of the ERW welded part of the ERW pipe manufactured by this method. This sometimes resulted in the occurrence of a harmful welding defect unique to electric resistance welding called curling.

Further, in electric resistance welding, when the abutting portion is upset, metal near the electric resistance welding portion causes a metal flow, and the direction of the flow rises toward the electric resistance welding portion.

Figure 1 schematically shows this situation.
is the metal flow on one side of the heat affected zone, and θ is called the metal flow rising angle. Needless to say, the metal flow rise angle increases as the upset amount increases. Furthermore, the frequency of occurrence of welding defects is controlled by the metal flow rise angle.

According to experiments conducted by the present inventors, when the edge part is heated with standard heat input, as shown in Figure 2, the penetrator generation rate increases as the metal flow rise angle θ becomes smaller, and when θ is smaller than 30°, the penetrator generation rate increases. Then, cold welding will also occur. Increasing θ can suppress the occurrence of welding defects, but on the other hand, inclusions that are inevitably included in the metal will rise along the metal flow, and if they are exposed on the pipe surface, they will cause cracks called hook craft in the heat affected zone. It may occur. In the same figure, a: cold welding occurs, b: penetrator occurs, c:
This indicates the occurrence of hook craft.

The present inventors have concluded from the experiment shown in FIG. 2 that an appropriate metal flow rise angle is in the range of 30° to 75°.

For circular steel pipes, an appropriate amount of upset (metal flow rise angle) can be easily achieved by adjusting the pressing force of the squeeze roll. Pressure causes some difference in circumferential length and shape, but the size and shape can be easily corrected using a regular roll.

On the other hand, if a square tube material that has been corner-bent by roll forming is pressurized with a squeeze roll during the welding process, depending on the pressure, the length of one side of the weld joint may be the same as the length of the opposite side. There may be cases where this is not the case. At this time, the shape of the pipe after welding becomes a trapezoid, and unlike a circular pipe, it is not easy to correct this with a regular roll.

On the other hand, if you try to make the shape of the pipe after welding similar to the product shape, you will not be able to add an appropriate amount of upset.
This may significantly impair the quality of the weld.

In view of these circumstances, the present invention was made to further improve the previously proposed technology.
The key point is that in the manufacture of square ERW steel pipes, the opening sides of square pipe material that have been corner-bent by roll forming are welded by ERW welding.
The sum of the lengths of the opening sides is the length of the opposite side of the opening side, and the length S (mm) is expressed by the following formula: 0.5t ^0.6 ≦S≦1+ ³ √ ² (t=plate thickness, unit: mm) A method for manufacturing a square electric resistance welded steel pipe, which comprises: bending a corner so that the pipe is longer, and then adding an upset during electric resistance welding so that the length of the side with the weld seam is equal to the length of the opposite side. .

The present invention will be explained in detail below with reference to FIGS. 3 to 8.

Although the roll forming method of the square tube material according to the present invention is not particularly limited, one example thereof will be described below.

The steel strip used may be a strip, a slit coil, or a steel plate, and in order to fully utilize the advantages of the continuous processing of roll forming in this method, a strip or a slit coil is suitable.
Of course, there is no problem in machining a fixed length steel plate.

Coils such as strips of the required width depending on the size of the square steel pipe to be manufactured are passed through an uncoiler, and in the case of fixed-length steel plates, they are fed one by one to pinch rolls using an appropriate feeding device. As usual.

The steel strip 5 is fed by one or two passes of the pinch rolls 6 while being prevented from meandering. For this reason, it is advisable to use a roll with a brim as the pinch roll, or to combine it with a vertical roll (Fig. 3). The steel strip 5 is first fed from the pinch rolls 6 to the upper corner bending rolls 7.

In this specification, the upper side corner refers to the corner where the upper side intersects the right and left sides in the cross section of the rectangular tube, and the lower side corner refers to the corner where the lower side intersects the left and right sides.

The upper side corner bending roll 7 consists of upper and lower horizontal rolls, and has a profile that bends the steel strip at positions 8, 8 that should become the left and right upper corners when it is made into a square tube to form open sides on the left and right (4th corner bending roll 7). figure).

The steel strip is bent at positions 8 and 8, leaving open side lengths l ₁ and l ₂ so that the length of the upper side of the rectangular tube becomes the same when the joint is welded. The bending positions 8, 8 are preferably symmetrical with respect to the roll center cc.

In the upper side corner bending process, the bending angle a of the corner portion is determined by passing through the upper side bending roll for 3 to 5 passes.
Bend it to approximately 70°±10° to form material 9.

Next, the material 9 is sent to a lower corner bending roll 10 consisting of upper and lower rolls. Lower side bending roll 10
Now, bend the material 9 at the positions of the lower corners 11, 11 so that the intermediate portions of the left and right upper corners 8, 8 become the left and right sides and the lower side of the rectangular tube (FIG. 5). This lower side corresponds to the opposite side to the opening side.
The upper roll 10a has open ends 12,1 on both sides of the material 9.
The lower roll 10b passes through the center part of the cross section of the material
Since the corners 11 and 11 must be bent between the opening ends 12 and 11, the limit is to bend the corners 11 and 11 until the gap between the opening ends 12 and 12 is the same as the length of the lower side 11 and 11. In order to narrow the gap of -12, a forming roll that is a combination of a suspended upper roll, left and right vertical rolls, and a lower roll may be used.

In this case as well, 3
The material 9 is roughly formed into a pentagonal shape with open vertices by bending the corner bending angle b to approximately 70°±10° in 5 passes.

The material 9 whose upper and lower corners are bent to an intermediate angle is then passed through a fine pass roll 1.
3 (Figure 6).

The fin pass roll 13 consists of an upper roll consisting of a fin roll 13a and a flange roll 13b, a vertical conical profile left and right roll 13c, and a cylindrical lower roll 13d. Insert between the flange roll 13b, left and right rolls 13
c. The material 9 in the caliber consisting of the lower roll 13d is pushed from all four sides and the open ends 12, 12 are pressed against both sides of the fin roll 13a, and the thickness of the fin roll is made thinner with each pass to make the shape of the material 9 square. , and bend it in 1 to 3 passes until the bending angles a and b of each upper and lower corner are approximately 85° ± 5°.

In this way, the corner bending is performed in the process up to the fine pass roll 13, and the raw material 9, which is formed into an open section with a roughly square cross section, is sent to the next welding roll 14 (FIG. 7).

Although the hole shape of the welding roll 14 is not particularly limited,
Preferably, as shown in FIG. 7, the upper rolls 14a, 14b, left and right rolls 14c, 14d, and lower roll 14e have a radius of curvature that is 3 to 6 times the side length of the square material 9, so as to give each side of the square material curvature. It is effective to use a concave roll with a concave roll to prevent edge misalignment (lap) at the welding surface.

In this way, the open ends of the upper sides are brought together and electrically welded, resulting in a rectangular steel pipe 16 with the welded seam 15 on the upper side (FIG. 7).

This steel pipe 16 is then passed through a straightening Turks head roll 17 with a rectangular caliber to adjust its cross-sectional and longitudinal shape (Fig. 8), and then cut to the required length by a suitable conventional cutting machine. It becomes a product.

Next, the present inventors investigated the opening side lengths l ₁ and l ₂ (however, l ₁ = l ₂ ) and accordingly flange roll 13b
Welding experiments were conducted with various flange widths, and welding stability, weld quality, and weld shape were investigated.

The output of the welding machine used was 140 KW for steel strips with a thickness of less than 5 mm, and 560 KW for steel strips with a thickness of 5 mm or more, and the welding speed was 10 m/min to 40 m/min depending on the plate thickness. Changed within the range of min.

The results obtained from this experiment are listed below.

(1) The sum of the lengths of the opening sides of the square tube material 9 after passing through the final fin pass roll must be longer than the length of the lower side by the required upset amount.

(2) As mentioned above, even if the sum of the lengths of the opening sides is longer than the length of the bottom side, the difference in length (side length difference) is mostly due to melting at the opening end and deformation of the heat affected zone (metallic flow). On the other hand, in the case of normal welding, the upper base metal part and the lower part of the square tube, excluding the welded part and heat affected zone, will shrink almost evenly from top to bottom due to the pressure applied from the sides during welding. Therefore, even if the length of each side of a square tube becomes longer, if the plate thickness remains the same, the difference in side length will remain the same to meet the required amount of upset, and only when the plate thickness changes It's going to change.

(3) However, as the plate thickness increases, the welding speed must be slowed down by the output of the welding machine, which increases the width of the heat-affected zone. Therefore, if the amount of upset is the same, the metal flow will not rise as the plate thickness increases. The amount of upset to obtain the same metal flow rise angle gradually increases as the plate thickness t increases. Its thickness dependence is experimentally expressed as approximately t ^0.6 to t ^2/3 .

(4) The required minimum forge amount is experimentally expressed as 0.5t ^0.6 . If the amount of upset is less than this amount, the welding becomes unstable, and the metal flow rise angle θ becomes smaller than 30°, causing many harmful defects in the weld.

(5) The maximum amount of upset required is experimentally determined as 1 + ³ √ ²
It is expressed as If the amount of upset exceeds this amount, a defective shape (lap) of the welded part will occur, or the metal flow rising angle θ will become larger than 75°, making hook craft more likely to occur.

Based on the above experimental results, the present inventors determined that the sum of the lengths of the opening sides of the square tube material, relative to the length of the opposite side of the opening side, is expressed by the following formula: S 0.5t ^0.6 ≦S≦1+ ³ It was concluded that the corner bend must be made so that the length is increased by √ ² (1). Also, if corner bending is performed in this way, under normal welding heat input,
If the length of the upper and lower surfaces are equalized after welding, the metal flow angle will be between 30° and 75°, making it possible to manufacture rectangular ERW steel pipes with excellent shape and weld quality. It is possible.

FIG. 9 shows this relationship. As is clear from the figure, it goes without saying that the most stable properties of the weld are obtained approximately midway between the upper and lower limits of equation (1).

The symbols in the figure are a: normal welding, b: lapping occurred,
c: Frequent welding defects, d: Occurrence of hook cracks,
e: Indicates welding instability.

Industrially, it is required to manufacture square steel pipes with the same external shape and various thicknesses using the same set of rolls, that is, without changing the rolls. If the flange width of the flange roll 13b is determined so that the median value of the upper and lower limits of equation (1) can be obtained, the condition of equation (1) is usually satisfied for the entire wall thickness, and a good weld can be obtained. Obtainable.

Although the above explanation has been made based on drawings showing a method for manufacturing a rectangular tube with a substantially square cross section, the present invention is not limited thereto, and can also be applied to the manufacture of a rectangular tube with a rectangular cross section. It goes without saying that there is. In addition, in the examples, 140kw and 560kw welding machines were used, but the output capacity of the welding machines is not limited to these, and the corner bending method and upset method of the present invention can be used in an industrial range regardless of the welding function. be able to.

As explained above, the method of the present invention does not involve any pressing work, and is extremely efficient as it manufactures pipes only by roll forming. Since the amount of bending is extremely small, there is less change in the mechanical properties of the material, and a welded part with stable quality and shape can be obtained, which improves productivity and quality at the same time, making it extremely industrially superior. It has technical value.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing a cross section near the electric resistance welding part, Figure 2 is a diagram showing the relationship between metal flow rise angle and welding defect incidence rate, and Figures 3 to 8 are diagrams showing the method of the present invention. FIG. 3 is a cross-sectional view of a main part for explaining the manufacturing process of a square steel pipe according to the method of the present invention using rolls suitable for the purpose of the present invention. FIG. 3 is a pinch roll, FIG. 4 is a top corner bending roll, and FIG. Corner bending roll, Figure 6 is Finpass roll, Figure 7
The figure shows the welding roll, the figure 8 shows the relationship between the straightening turquoise head roll, the steel strip, the material, and the steel pipe, and the figure 9 shows the opening side length of the square tube material after passing through the final fine pass roll. It is a figure showing the relationship between the amount S obtained by subtracting the length of the lower side from the sum of the lengths, the wall thickness t of the square tube material, and the properties of the welded part. 1... Electric resistance stitching abutment part, 2, 2'... Heat affected zone, 3,
3'...Base metal part, 4...Metal flow, θ...Metal flow rising angle, 5...Strip steel plate, 6...Pinch roll, 7...Top corner bending roll, 8
...Top corner bending position, 9...Square pipe material,
10... Bottom corner bending roll, 11... Bottom corner bending position, 12... Open end, 13... Fin pass roll, 14... Welding roll, 15...
...Welded seam, 16... Steel pipe, 17... Turks head roll for straightening.

Claims (1)

[Scope of Claims] 1. In manufacturing a square electric resistance welded steel pipe by welding the opening sides of a square pipe material with corners bent by roll forming by electric resistance welding, the sum of the lengths of the opening sides is defined as the sum of the lengths of the opening sides. Bend the corner so that it is longer by the length S (mm) expressed by the following formula with respect to the length of the opposite side: 0.5t ^0.6 ≦S≦1+ ³ √ ² (t: plate thickness, unit: mm), and then continue with the electric sewing A method for producing a rectangular electric resistance welded steel pipe, which comprises adding an upset during welding so that the length of the side with the weld seam is equal to the length of the opposite side.