JPH06154850A - Production of square electric resistance welded tube - Google Patents

Abstract

PURPOSE:To produce a square tube without brittle fracture with small electric power. CONSTITUTION:The corner parts of both ends in the breadthwise direction of a band steel coil member 11 are shaped in a circular-arc shape in a rolling shaping process 12. The shaped member is formed in a round tube in a high frequency welding process 14 after formed in a round tube-like body in a round tube forming process 13. Then, the welded round tube is formed in a square tube shape in a square tube forming process 15 and the square tube body is finally formed in the square tube in a hot forming process.

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 electric resistance welded pipes, particularly rectangular electric resistance welded pipes.

[0002]

2. Description of the Related Art Heretofore, cold forming has been used to manufacture a rectangular tube. Firstly, a thick plate is formed into a channel shape by a press to obtain a pair of molded products 1 and 2 as shown in FIG. 5B after the molded products 1 and 2 are butted to form a square shape. As described above, the molded bodies 1 and 2 are joined by the submerged arc welding method to form a rectangular tube.

Second, as shown in FIG. 3c, after a thick plate is semi-formed into a channel shape by pressing, the edges of the seams are high-frequency welded while performing roll forming to produce a rectangular pipe.

Third, as shown in FIG. 6, the strip steel coil material 5
Is continuously formed into a circular tube shape at the round forming portion 6, and the edges of the joints are subjected to high frequency welding at the high frequency welding portion 7, and then, while cold, the square forming portion 8 forms a rectangular pipe. Is taken. The formed rectangular tube is cut into a predetermined length by a cutting device (not shown).

[0005]

As described above, in the case of manufacturing a conventional rectangular tube, the thick plates are strongly bent while cold to form the molded bodies 1 and 2, so that the corner portions are work hardened. Caused deterioration of strength and toughness. In addition, for example, a thick rectangular pipe having a wall thickness of 22 mm or more or an arcuate curvature R of the corner portion is reduced to 3.5 t or less (t is the wall thickness of the pipe) to reduce the working degree of the corner portion. If raised, brittle fracture begins to partially occur, which makes it unsuitable for use in columns of high-rise buildings, which is the main application of rectangular tubes (columns).

Therefore, if the corner portion is processed by hot or warm forming, there is no problem in production, but in order to put hot or warm forming in-line, the furnace length for raising the temperature should be close to 100 m. As a result, the area occupied by the factory site must be increased, and the waste of energy and cost for heating the entire plate to process the corners becomes a problem. In addition, in the case of high frequency electric resistance welded pipe welding, if the hot and warm forming of the corner part is made in-line to maintain the productivity, the normal production scale is reduced to 1
Since it will be at the level of 0,000 tons / month, the required energy for temperature rise requires a heat source equivalent to the level of 100,000 kw (86 million kcal / H), and induction heating is adopted to reduce the space. However, it is difficult to obtain the power supply itself and it is not practical. The reason why the above amount of electric power is necessary is as follows. That is, it is already known that in order to obtain good welding characteristics in high frequency electric resistance welded pipe welding, a good welding result cannot be obtained unless the line (welding) speed is 10 m / min or more. FIG. 7A is a conceptual diagram of a contact-type electric resistance welded pipe welding apparatus that can obtain good welding results.
A tubular body 21 formed by forming a metal plate into a tubular shape is inserted between a pair of pressure rolls 22a and 22b arranged opposite to each other and moved in the arrow direction. In this case, the pressure roll 22a when viewed in the traveling direction of the tubular body 21. A V-shaped gap 23 is formed on the front side of 22b, and the opposite edges 25a, 25
In b, a pair of contacts 28a, 28b connected to a high frequency power source 27 having a frequency of about 100 KHz to 400 KHz.
The high-frequency power is supplied by and the welding current I flows to heat both edges. Further, the pressure roll 22a,
At the V seam welding point 24 where the V-shaped gap 23 is closed by the pressurization by 22b and the both edge portions 25a and 25b are in contact with each other, the temperature of the both edge portions 25a and 25b reaches the vicinity of the melting point and welding is performed while being pressurized. Done. Particularly in the case of high-frequency electric resistance welding of a thick-walled pipe, as shown in FIG. 7B, since the high-frequency current concentrates on the corners 26 of both edges 25a and 25b to be welded by the edge effect, the corners 26 are It becomes difficult to obtain a good weld by overheating. From these things, there is a problem that the amount of electric power becomes the above when calculated in consideration of the speed of 10 m / min or more.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a rectangular electric resistance welded pipe capable of manufacturing a rectangular pipe that does not cause brittle fracture with a small amount of electric power.

[0008]

In order to achieve the above-mentioned object, the present invention removes the corners 26 at both ends in the width direction of a strip steel coil member to form both ends in an arc shape, and then the coil member. Is molded into a round tubular body, the ends of the joints of the round tubular body are made into a round electric resistance welded tube by high frequency welding, and then the circular electric resistance welded tube is sequentially deformed to form a square shape. It is characterized in that it is formed into a tube, the corner portion of the rectangular tube is locally heated by induction heating, and then warm-formed into a predetermined rectangular tube shape. The warm forming is performed within the recrystallization temperature range.

[0009]

FUNCTION The corners of the strip steel coil member are removed by mechanically cutting or rolling the corners. As a result, even when the ends of the joints formed into a round tubular body are subjected to high-frequency welding, the edge effect does not cause overheating at the corners of both ends, and the round shape is excellent even at a speed much lower than 10 m / min. We can make pipes by welding. After that, the round tube is sequentially deformed into a square tube to form a square tube.However, various types can be used for each corner radius by locally heating by induction heating with the corners of the square tube molded to the same radius of curvature. It is possible to perform warm forming by performing induction heating using one type of the same inductor without the need for the above inductor. In addition to the fact that the line speed can be slowed down, it does not require a large amount of power.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 11 is a strip steel coil member, and the coil member 11 is pulled out so that both ends in the width direction of the coil member 11 are first rolled and shaped in a rolling and shaping step 12 so that the corners thereof have an arc shape. The both ends may be mechanically cut so that the corners are arcuate. Coil member 1 having corners formed in an arc shape
1 is formed into a round tube in a round tube forming step 13. Then, in the high frequency welding step 14, the ends of the joints of the round tubular body are welded to each other to form a round electric resistance welded pipe. The welding speed at this time is set to a value including 10 m / min or less for various wall thicknesses.

After being formed into a round tube, in a square tube forming step 15 by straight side expansion forming, the corner forming method is shown in FIGS. Then, the radius R is gradually reduced to form R ₁ > R ₂ > R ₃ and the flat side length F is formed such that F ₁ <F ₂ <F _3. . After forming the rectangular tube as shown in FIG. 2D, the heating coils 16a to 16d of the induction heating step 16 for local heating of the corners as shown in FIGS. After locally heating each corner portion of the tube 17 by induction heating, the corner portion of the rectangular tube 17 is further warmed to a final radius of curvature R ₄ shown in FIG. 2E in a recrystallization temperature range of 450 ° C. to 650 ° C. Molding is performed in the molding step 18. R ₄ is a value when the rectangular tube 17 is used as a product, and this value is, for example, 2.
It is set to 5 to 3.5 t (t: wall thickness). Although only one set of the heating coils 16a to 16d is shown in FIG. 3, the same heating coil is provided at each corner. This eliminates the need to prepare or replace several types of heating coils each time the product shape such as the radius of curvature R ₄ of the rectangular tube 17 changes, and work for coil replacement when changing the size of the tube There is an advantage that no time is lost. In FIG. 4, 19 is an iron core and 20 is a copper pipe.

Next, the operation of the above embodiment will be described. In the rolling and shaping step 12, the corners of both ends of the coil member 11 in the width direction are formed into an arc shape. This is because the corners of the end portions are overheated due to the edge effect if the corner portions of the end portions are present when the end portions are welded together by the high frequency welding process 14 in the latter stage. Since the soundness of the welded portion (such as the inclusion of oxide) is lost, it is necessary to form the corner portion into an arc shape as described above in order to prevent this. The coil member 11 whose corners are formed into an arc shape in the rolling shaping step 12 is formed into a round tubular body in a round tube forming step 13. This round tubular body is welded by electric resistance welding in a high frequency welding process 14 to form a round tube shown in FIG. 2A. Thereafter, as described above, in the rectangular tube forming step 15, the rectangular tube is formed as shown in FIGS. Then, the induction heating step 1 is applied to the corner portion of the rectangular tube.
After heating at 6, the corner R ₄ is further formed in the warm forming step 18 so as to become a product.

[0013]

As described above, according to the present invention,
The following effects can be obtained.

(1) By removing the corners of both ends of the strip steel coil member in the width direction in advance, sound low-speed electric resistance welding of a thick-walled pipe can be performed, and in-line at a low speed of the thick-walled electric resistance welded pipe. Depending on the situation, it will be possible.

(2) The heat source for forming the rectangular tube can be greatly reduced due to the low line speed and local heating only at the corners, and the heat source can be incorporated in a narrow space, making it practical. Is improved.

(3) The induction heating power for forming a rectangular tube is small because of the local heating, and is excellent in controllability and reproducibility.

(4) Since warm forming in the recrystallization temperature range is adopted at the time of forming a rectangular tube, it is possible to prevent the deterioration of the structure and strength of the corner portion due to the forming.

(5) It is possible to efficiently produce a high-quality thick-walled rectangular steel pipe having the strength and soundness of the corner portion at the time of forming the rectangular pipe by the electric resistance welded pipe manufacturing method. This is particularly effective in forming a rectangular tube having a corner with a smaller radius of curvature than the wall thickness of the tube.

[Brief description of drawings]

FIG. 1 is a manufacturing process explanatory view showing an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the embodiment.

FIG. 3 is a perspective view for explaining local heating.

FIG. 4 is an enlarged cross-sectional view of FIG.

5A and 5B show a method of manufacturing a rectangular tube of a conventional example, in which A is a perspective view before welding and B is a perspective view after welding.

FIG. 6 is an explanatory view of a manufacturing process of a rectangular tube of a conventional example.

7A is a conceptual diagram of high frequency electric resistance welded pipe welding (contact type), and B.
[Fig. 3] is an enlarged view of an end portion of a tubular body.

[Explanation of symbols]

 11 ... Strip steel coil member 12 ... Rolling shaping step 13 ... Round tube forming step 14 ... High frequency welding step 15 ... Square tube forming step 16 ... Induction heating step 17 ... Square tube 18 ... Warm forming step

Claims (3)

[Claims] 1. A steel strip coil member is formed into an arc shape by removing the corners of both ends in the width direction, the coil member is formed into a round tubular body, and the round tubular body is rounded by high frequency welding. After making a pipe into an electric resistance welded pipe, then by sequentially deforming the circular electric resistance welded pipe to form a rectangular pipe, the corner portion of the rectangular pipe is locally heated by induction heating, and then warm forming is performed. A method for manufacturing a characteristic rectangular electric resistance welded pipe. 2. The method for manufacturing a rectangular electric resistance welded tube according to claim 1, wherein the warm forming is performed within a recrystallization temperature range. 3. The method for manufacturing a rectangular electric resistance welded pipe according to claim 1, wherein the induction heating of the corner portion of the rectangular pipe is performed with the same radius of curvature of the corner portion.