JP2735538B2 - Square steel pipe and method for manufacturing square steel pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a square steel pipe used as a pillar of a steel structure or a building, for example, and a method of manufacturing a square steel pipe.

[0002]

2. Description of the Related Art Thick and large-diameter rectangular steel pipes, which have been growing in demand as columns of steel structures, are mass-produced by a cold plastic working method. Such a manufacturing method is adopted.

[0003] A hot-rolled coil is first set on a leveler to form a flat strip steel plate, and both side edges thereof are determined in width to predetermined dimensions and cut. The strip steel sheet is transferred in series through a processing stage such as a breakdown, a cluster, a fin pass stand, etc., during which, the steel sheet is sequentially formed to form a rectangular cross section into a shape close to a circle, followed by high-frequency resistance or induction welding. One-seam round steel pipe is formed through the device and squeeze roll. After gradually reducing the welding heat of the round steel pipe, the round steel pipe is formed into a rectangular cross section through processes such as a sizer, a scoring stand, and a turks head, thereby producing a large-diameter rectangular steel pipe.

[0004] The above-described manufacturing method includes a step of bending a thick steel plate having a flat or circular curved surface by approximately 90 ° by cold plastic working using a forming roll in order to form a square steel pipe. By the way, when a thick steel plate is coldly bent by approximately 90 °, a tensile force is applied to the outer material and a neutral force is applied to the inner material with respect to the neutral surface in the steel plate cross section of the bent portion. Is deformed while a compressive force is applied, so that despite the required radius, plastic deformation proceeds beyond the elastic limit of the material,
The mechanical properties of the material at the deformed portion, particularly at the corners, are degraded, and there is no danger of causing brittle fracture at the portions.

[0005] Generally, once a steel frame structure or a building column material using such a large-diameter rectangular steel pipe as a column is constructed, it is not possible to support its own weight and the weight attached to the structure without distortion for a long period of time. Of course, it is required to safely withstand severe repetitive loads due to external forces such as earthquakes and typhoons, and moreover, these columns are often constructed in such a way that they cannot be replaced or repaired in principle. Especially in modern buildings, each room is equipped with a heating and cooling system,
We cannot ignore the weight that increases due to facilities attached to the building, such as equipment A, computers, etc.,
In addition, there is a tendency that the equipment weight to be considered in advance increases.

Recently, large-diameter rectangular steel pipes of this type formed by cold bending are widely used as columns of building structures, and are also used as columns for middle and high-rise buildings. In view of the above circumstances, deterioration of the material due to the cold plastic working at the time of forming the square steel pipe has been regarded as a problem. Recently, there has been concern among experts about whether this type of large-diameter rectangular steel pipe formed by cold plastic working is suitable as a main structural material for steel structures that occupy most of its applications. is there.

[0007] In order to solve this kind of material problem contained in a cold-formed large-diameter rectangular steel pipe, conventionally, an off-the-shelf prefabricated steel pipe having a unit length, a seamless pipe, etc., have been used.
2. Description of the Related Art A fossil fuel such as oil or gas or electric energy is used as a heat source and heated to form a rectangular cross section through a plurality of rolling mills.

[0008]

However, when the above-mentioned heat molding method is used, the quality of the product is good, but the yield of the product is poor because both ends of the rectangular steel pipe are deformed, When forming from a shape to a rectangular cross section, the flat plate portion is deformed, and there is a problem that the rectangular steel pipe is likely to be twisted and bent, and heating distortion cannot be ignored. In particular, when the residual stress of the steel material (internal stress) was heated steel tube to A ₃ transformation temperature of the steel material to completely eliminate the above problem is remarkable.

[0009] Separately, a method is known in which a molded large-diameter rectangular steel pipe is placed in an annealing furnace, and is heated until the residual stress in the material is substantially removed. In this case, there is a similar problem as described above.

Alternatively, a hot-rolled coil is applied to a leveler and formed into a round steel pipe by cold plastic working through various forming roll stands and a high-frequency welding device, and then the steel pipe is inlined with electric energy (induction), gas or oil or the like. There is also provided a method of heating by fossil fuel, passing through a plurality of stages of hot forming rolls, forming this into a steel pipe having a square cross section, cooling and producing a product. This method is in-line heating, so if it goes smoothly, the yield is good and the productivity is improved, such as less deformation at both ends of the rectangular steel pipe compared to the offline method, but this is a small improvement and it is sufficient However, other problems similar to the above cannot be solved.

Therefore, the invention according to claim 1 of the present invention recovers the toughness of the peripheral wall material, reduces the residual stress at each corner of the rectangular steel pipe to an allowable stress or less, and makes the overall material uniform and stable. It is intended to provide a quality square steel pipe.

A second object of the present invention is to provide a method of manufacturing a square steel pipe capable of efficiently manufacturing the square steel pipe according to the first aspect while minimizing a cost increase. is there.

[0013]

Means for Solving the Problems In order to achieve the above-mentioned object, in the present invention, a square steel pipe according to claim 1 is obtained by heating a semi-formed steel pipe having an approximate square steel pipe shape and then forming it into a standard shape. Thus, it is characterized in that the material is formed by preventing material deterioration of the corner portion and reducing residual stress in the corner portion.

Therefore, according to the first aspect of the present invention, the work hardening, residual stress, and work distortion at the corner of the steel pipe caused by bending four places of the peripheral wall of the steel pipe to about 90 ° are substantially (almost completely) not practically affected. It can be removed and there is no risk of residual stress in the square steel pipe. Alternatively, the deterioration of the material of the corner portion is almost negligible. In addition, a high-precision rectangular steel pipe can be obtained by hot forming.

According to a second aspect of the present invention, there is provided a method of manufacturing a square steel pipe, comprising: loading a semi-formed steel pipe having an approximately square steel pipe shape into a heating furnace and heating the whole to a desired temperature; The present invention is characterized in that a steel pipe is formed into a standard shape by a square cross-section forming roll device, thereby obtaining a square steel pipe in which deterioration of material at a corner portion is prevented and residual stress at the corner portion is reduced.

Therefore, according to the second aspect of the present invention, the semi-formed steel pipe is charged into a heating furnace, and while passing through the heating furnace, the temperature at which the residual stress is not generated at the corner portion when forming the rectangular steel pipe. (About 500 ° C or higher), and as soon as the heated semi-formed steel tube is taken out of the heating furnace, before it is heated, it is quickly squeezed on a square cross-section forming roll device, and finally to the standard shape. It can be formed into a square steel pipe. Since the forming by the square section forming roll device at this time is hot plastic working, the size of R formed here and given to the corner of the square steel pipe is manufactured based on the conventional cold bending method. There is no need to be bound by the specifications for square steel pipes.

As described above, since the heated semi-formed steel pipe is used, even if the heating temperature distribution is slightly nonuniform in the peripheral wall material of the steel pipe, the shape of the already semi-formed square cross section is adversely affected. In addition to this, the residual stress of the semi-formed steel pipe which was previously applied and which is accompanied by the cold plastic working is removed, and the subsequent process can be substantially performed smoothly by hot working. At this time, if the semi-formed steel pipe is heated as a whole, the material is entirely heat-treated in the intermediate forming step of the steel sheet, so that the work hardening of the steel material based on the deformation applied before that is reduced. The material can be removed and the material can be made uniform throughout, so that subsequent deformation can be easily and easily performed.

Further, since the steel tube is a heated semi-formed steel pipe, the mechanical energy (power) to be applied for forming a thick-walled square steel pipe is relatively small in the rectangular section forming roll device. Conversely, it is possible to form a square steel pipe with a thicker steel plate with respect to the reference capacity of the square section forming roll device. Therefore, the above-mentioned high-quality square steel pipe can be efficiently formed and produced.

[0019] The method for producing a square tube according to claim 3 of the present invention is heated, in the configuration of claim 2, wherein the above, the semi-molded steel pipe, the whole was charged over A ₃ transformation point in a heating furnace It is characterized by doing.

Therefore, according to the third aspect of the present invention, the A ₃ transformation point (approximately
After heating the semi-formed steel pipe to a temperature of 800 ° C. or higher), it can be applied to a square section forming roll device and finally formed into a square steel pipe having a standard shape.

[0021]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a steel pipe manufacturing method according to an embodiment of the present invention. It is possible to arbitrarily modify the part within the scope of known techniques in the art at the time of the filing of the present application, and based on only the specific structure described in the embodiment of the present invention without special reason. However, it should not be construed that the constituent elements of the present invention are limitedly interpreted. (Embodiment 1) FIG. 1 is a schematic block diagram showing an embodiment of a hot forming apparatus for a large-diameter rectangular steel pipe provided with a composite heating means for carrying out the method of the present invention.

In FIG. 1, a hot rolling coil mounting apparatus 1, a leveler 2, a steel sheet width determining and cutting section 3, a steel sheet breakdown roll step 4,
A multi-stage steel plate section rounding roll device 5, a fin pass roll stage 6, a high-frequency resistance welding device 7, and an inside or outside removing device 8 for welding beads are provided in this order.

A multi-stage square section forming roll device 9 is provided below the inside or outside removing device 8 of the welding bead. Step 9B. Then, between the preforming step 9A and the inferior finish forming step 9B, a heating furnace 10 for entirely heating the square steel pipe using fossil fuel as a heat source and a high-frequency heating furnace 11 for partially heating the square steel pipe are arranged in this order. Is provided.

Further, in the finish molding step 9B,
A formed steel pipe cooling and cooling section 12, a steel pipe length measuring mechanism 13, a straight forming section 14, a traveling cutter 15, a straightening device 16, and a steel pipe sizing machine 17 are provided in this order. However, there are many means not shown, such as a coil rewinding mechanism, a pinch roller, an emergency cutting machine, and an inspection device.

In the above forming line, the hot-rolled coil mounting device 1
, And the cold forming in the steel pipe preforming step 9A is almost the same as the conventionally known one-seam ERW round steel pipe manufacturing apparatus. As the steel sheet material used for this, a thick-walled hot-rolled coil (for example, SS400, SM
490 A), the coil width ultimately limits the maximum diameter of the final product (large-diameter rectangular steel pipe) (in the case of a one-seam pipe).

In the preforming step of the round steel pipe, the thick steel plate (t = 16 to 25 mm) is deformed by cold plastic working.
In order to eliminate residual stress and to reduce welding distortion of the steel material caused by high frequency welding after forming as much as possible, a space for gradually cooling the steel pipe over a long section was required.

In the method of the present invention, the space required for the above-described slow cooling step of the steel pipe is diverted or the space is expanded, and a relatively long heating is performed in the transport direction using fossil fuel as a heat source. A furnace 10 and a high-frequency induction heating furnace 11 are installed. Therefore, compared to the conventional apparatus, the equipment can be installed without extremely increasing the total length of the production line.

The semi-formed steel pipe formed in the preforming step 9A is entirely heated to a predetermined temperature in the heating furnaces 10 and 11, and the heated semi-formed steel pipe enters the finish forming step 9B before being cooled. Conveyed and rolled by
Since the cross section is formed sequentially or gradually, the steel material is hot-worked, so that no residual stress is generated by plastic working of the corner part.Bends can be corrected, and sharper corner parts can be formed. obtain. The above-mentioned effect is the same when the high-frequency induction heating furnace 11 is installed in the first stage to perform the entire heating, and the heating furnace 10 using fossil fuel is installed in the second stage to perform the partial heating.

FIG. 2 or FIG. 3 is a schematic front view of a one-roller stand of the forming roll stage in the preforming step 9A, for example, of the multi-stage rectangular section forming roll device 9. In the figure,
Reference numeral 18 denotes a cross section of a semi-formed steel pipe having an approximate square steel pipe shape slightly deformed into a square shape.

In FIG. 2, the round steel pipe is fixed to two axes parallel to each other at right angles to the longitudinal axis of the steel pipe. Is pressed from four directions, for example, up and down and left and right directions, so as to gradually approach a square cross section, and is formed so as to approach a square cross section every time the number of steps passes. After passing through the roll stand step of the preforming step 9A, the size of the corner portion R of the thus formed semi-formed steel pipe 18 shrinks to about R = (4-5) × t, 18
Cross section approaches a cross section that approximates a square. Here, t is the thickness of the steel material.

FIG. 3 is a schematic front view of another forming roll apparatus, in which the peripheral surface is fixed to two axes perpendicular to the longitudinal axis of the steel pipe and parallel to each other, and the peripheral surface is formed in a deep conical shape. (Inverted abacus ball shape) Two forming rolls 20a, 20b
By pressing the peripheral surface of the round steel pipe from four directions, forming,
A roll can be formed so that the cross section gradually approaches a square.

The roll stage in the preforming step 9A usually comprises three or more forming steps. The specific example of the roll stage in the finish forming step 9B is almost the same as that described above. However, only the shape of the roll peripheral surface changes sequentially so as to approach a square cross section. However, since the heated half-formed steel pipe 18 is handled in the roll stage of the finish forming step 9A, the apparatus needs to be provided with a necessary and sufficient cooling means.

FIG. 4 is a schematic view of a section perpendicular to the longitudinal axis of the heating furnace 10 using fossil fuel.
Guide rollers on both sides of the semi-formed steel pipe 18 installed in 10, the lower guide and transport roller 22, at least the lower guide and transport roller 22 has a contiguous peripheral surface, widening the contact area with the semi-formed steel pipe 18 It is desirable to take. The inner wall of the heating furnace 10 is generally constructed by stacking refractory bricks, and the ceiling is formed in an arch shape. The heating temperature of the semi-formed steel pipe 18 is, for example, 50
The temperature may be about 0 to 600 ° C. The illustration of the smoke exhaust and exhaust gas devices is omitted.

FIG. 5 is a conceptual diagram of a cross section perpendicular to the axis of the high-frequency induction heating furnace 11. In the figure, reference numeral 23 denotes a high-frequency induction coil installed along the peripheral surface of the semi-formed steel pipe 18. When the heating furnace 10 for performing overall heating of the semi-formed steel pipe 18 is arranged at the front stage and the high-frequency induction heating furnace 11 is arranged at the latter stage, the high-frequency induction coil 23 is positioned close to the peripheral surface of the heated semi-formed steel pipe 18. Since they are provided to face each other, they are always heated by the semi-formed steel pipe 18. In this case, the high-frequency induction coil 23 is constituted by a steel pipe, and cooling water is circulated therein.

However, the entire heating means of the semi-formed steel pipe 18 is as follows:
Only the heating furnace 10 using fossil fuel may be used, only the high-frequency induction heating furnace 11 may be used, or a composite heating means may be used.

FIGS. 6 and 7 are schematic views of a section perpendicular to the axial direction showing an example of partial heating near all corners on the peripheral wall of the semi-formed steel pipe 18. As shown in FIGS. In the figure, 24a, 24
b is a high-frequency induction coil that uses electric energy, and is close to the peripheral surface of the scheduled corner of the semi-formed steel pipe 18;
The semi-formed steel pipe 18 that is heated because it is
Therefore, it is necessary to provide a high-frequency induction coil cooling means. The heating temperature of the steel in this case, for example, be a 800 ~900 ℃ (A ₃ transformation point or higher). In this case, the high-frequency induction coils 24a, 24
b are installed in a section perpendicular to the longitudinal central axis of the semi-formed steel tube 18 symmetrically with respect to said axis and out of phase with each other by 90 °. The pair of the high-frequency induction coils 24a and the pair of the high-frequency induction coils 24b can be disposed slightly shifted from each other in the longitudinal direction of the steel pipe.

In the figure, the hatched portions on the cross-sectional peripheral wall material of the semi-formed steel pipe 18 indicate portions where the temperature has increased particularly by partial heating. In the case of FIG. 7, the inside of the steel pipe material is shown. The frequency applied to the high-frequency induction coil 24a is adjusted so that more heating can be performed, so that each corner can be deformed more freely and without difficulty at the time of forming the square steel pipe. This is to obtain a sharp rectangular shaped square steel pipe.

The heat source for the partial heating of the peripheral wall of the semi-formed steel pipe 18 may be, of course, only a burner using fossil fuel. In addition, the heating method of only FIG. 6 or FIG. 7 can be used. At this time, the modes of the overall heating of the steel material and the partial heating may be various combinations, but are not exemplified.

However, when the heating temperature of the peripheral wall of the steel pipe is non-uniform and an extreme error occurs during the heating, in the finish forming step 9B, the steel pipe is loaded into a finish forming roll device substantially equivalent to that shown in FIGS. However, it is known that a good rectangular cross-sectional shape cannot be obtained. The semi-formed steel pipe 18 subjected to the whole heating and the partial heating is conveyed into the finish forming step 9B shown in FIG. 1 while maintaining the heated state, for example, the temperature of 500 ° C. to 600 ° C. In FIG. 2 or FIG. 3, a high-quality large-diameter rectangular steel pipe as shown in FIG.
25 are formed.

FIG. 8 shows a cross section of a large-diameter rectangular steel pipe 25 formed through the roll device in the finish forming step 9B. The features of the rectangular steel pipe 25 manufactured by hot forming are apparent. That is, R at each corner is extremely small. In the cross section of the steel pipe, the hatched portion is the square steel pipe 25.
The other corners are plastically deformed by hot working, and have very little residual stress as a whole, and no deterioration of the material is observed.

According to the above-described manufacturing method, (a) an existing rectangular steel pipe is heated and heat-treated to near the A ₃ or A ₁ transformation point of the steel material, and an effect on a substantially uniform rectangular steel pipe material is expected. Production efficiency is good, and heat treatment equipment can be downsized.
Fuel and / or power consumption can be reduced.

(B) After the steel pipe is half-formed into a square cross section, the whole is heated. Therefore, even if the distribution of the heating temperature is slightly inaccurate, the work hardening of the steel material up to that point is removed and the steel material is softened. It can be easily deformed and finish-formed a rectangular steel pipe 25 with uniform and high precision dimensions.

(C) Due to the hot forming, the R at the corners of the square steel pipe 25 can be formed extremely small, the section modulus of the square steel pipe 25 can be increased, and the residual stress due to working is small, and the vicinity of the corner is small. The material is hardly deteriorated.

(D) Because of hot forming, the driving energy of the forming roll device is significantly smaller than that of cold working. (E) Since the forming process is easy and the deformation of the steel plate is not excessive, it is possible to prevent the steel pipe from being twisted due to the square steel tube forming process or to correct the bending. (Embodiment 2) The line shown in FIG. 1 is basically provided with a heating means for using both the entire heating and the partial heating of the steel pipe. , for example, to the vicinity of a ₃ transformation point of the steel material or a ₃ transformation point or more heating, being able to corresponding parts to achieve it is a matter of course. When this method is carried out, a high frequency induction heating furnace 11 for performing partial heating from the forming line shown in FIG.
Only need to be removed.

[0045]

According to the first aspect of the present invention, it is possible to prevent deterioration of the quality of each corner member of a steel pipe, which has been regarded as a problem in a conventionally known large-diameter rectangular steel pipe manufactured by cold plastic working. In addition to keeping the residual stress below the allowable level, it is possible to obtain a stable rectangular steel pipe with a uniform cross section, and to form sharp corners as much as possible without deterioration Steel pipe can be provided.

According to the second aspect of the present invention,
Since it is a heated semi-formed steel pipe, in a square section forming roll device, relatively little mechanical energy (power) is input for forming a thick-walled rectangular steel pipe. In addition, it is possible to form a square steel pipe with a thicker steel plate with respect to the reference capacity of the square section forming roll device. Therefore, the high-quality square steel pipe described above
In addition to being able to form and produce efficiently, the capacity of the equipment can be made relatively small, and equipment costs can be reduced. That is, the high-quality rectangular steel pipe according to the first aspect can be efficiently shaped and produced while minimizing cost increase.

According to the third aspect of the present invention, the semi-formed steel pipe is heated to the A ₃ transformation point (about 800 ° C. or higher) of the steel material at which the residual stress of the steel pipe material is completely eliminated.
The entire cross section of the standard shape can be finally formed into a square steel pipe having a uniform cross section by being applied to a square section forming roll device.

[Brief description of the drawings]

FIG. 1 shows an example of an embodiment of the present invention and is a block diagram of a method for manufacturing a rectangular steel pipe.

FIG. 2 is a front view of a corner forming roller portion in the method of manufacturing the same square steel pipe.

FIG. 3 is a front view of another type of a horn forming roller portion in the method of manufacturing the same square steel pipe.

FIG. 4 is a cross-sectional view of a whole heating furnace using a fossil fuel as a heat source used in a heat treatment facility in the method of manufacturing the rectangular steel pipe.

FIG. 5 is a front view of an entire heating furnace provided with a high-frequency induction coil in the method of manufacturing a square steel pipe.

FIG. 6 is a front view of a partial heating furnace equipped with a high-frequency induction coil in the method of manufacturing a square steel pipe.

FIG. 7 is a front view of another type of a partial heating furnace provided with a high-frequency induction coil in the method of manufacturing a square steel pipe.

FIG. 8 is a sectional view of a large-diameter rectangular steel pipe manufactured by the method of the present invention.

[Explanation of symbols]

 9 Multi-stage square section forming roll device 9A Preforming step 9B Finish forming step (square section forming roll apparatus) 10 Heating furnace using fossil fuel as heat source 11 High frequency induction heating furnace 18 Semi-formed steel pipe 23 High frequency induction coil 24a High frequency induction coil 24b High frequency Induction coil 25 Large diameter square steel pipe

Claims (3)

(57) [Claims] 1. A semi-formed steel pipe having an approximately square steel pipe shape, which is formed into a standard shape after heating, thereby preventing deterioration of material at a corner portion and reducing residual stress at the corner portion. Square steel pipe. 2. A semi-formed steel pipe having an approximately square steel pipe shape is charged into a heating furnace and the whole is heated to a desired temperature, and the heated semi-formed steel pipe is formed into a standard shape by a square section forming roll device. Thus, a method of manufacturing a square steel pipe is provided, in which deterioration of the material of the corner part is prevented and a square steel pipe with reduced residual stress in the corner part is obtained. 3. The method for producing a rectangular steel pipe according to claim 2, wherein the semi-formed steel pipe is charged into a heating furnace and the whole is heated to an A ₃ transformation point or higher.