JPH06122019A - Manufacture of large diameter square steel pipe including hot forming and device therefor - Google Patents

Abstract

PURPOSE:To hot-roll a large diameter square steel pipe small in the radius of curvature of its corner R parts, free from the deterioration of quality of these part, good in surface precision of the flat surface of four sides of the steel pipe and excellent in the yield from a round steel tube. CONSTITUTION:In a method that following the formation of a round steel tube by cold plastic working, this steel tube is roll-formed into a square to manufacture a large diameter square steel pipe, a stage of roll-forming the round tube into the square pipe is halved and those parts are connected with a heating stage. After the steel pipe rough formed by 1st square forming rolls 6 continuously into an outward projecting spool shape is cut by a unit length, it is inserted into a heating stage 20 to better the deterioration of the quality based on the cold plastic working, then, the heated rough formed steel pipe is inserted into a 2nd square forming roll stage 21 including finishing rolls, the cross section of the rough formed steel pipe 14 is deformed by hot roll-forming in sequence according to a specification into the square shape and the temperature of the formed steel pipe near the final stage of the forming rolls is made not to be below about 700 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stepwise manufacturing method and apparatus for a large-diameter rectangular steel pipe including hot forming using a rolled steel strip and a steel plate, and more specifically, a steel strip or a steel plate After forming into a round cross section by cold plastic working parallel to the direction, and butt-welding both side edge joints sequentially to form a large-diameter round steel pipe, insert it into a multistage corrugating roll device. In the step of sequentially forming a steel pipe cross section into a square shape, the corner forming roll step is divided into a first forming step and a second forming step, and a rough angle forming shape is obtained by cold working in a first forming step that is continuous with round steel pipe forming. After applying
It is added to the steel plate material by cutting it into a unit length in the longitudinal direction, inserting the unit length steel pipe into a heating device installed between the first forming step and the second forming step, and heating it to a predetermined temperature evenly. The residual stress and work hardening caused by cold plastic deformation are removed to improve the mechanical properties of the rough formed steel pipe, and the steel pipe is made up of multiple stages including finish forming rolls before the heating temperature decreases. (2) Improving the mechanical properties of the square steel pipe, especially the deterioration of the material around the corner R part, by charging it into the forming process, forming it by hot plastic working, and at least uniformly cooling the square steel pipe that has been cross-section formed according to the standard The present invention relates to a method and an apparatus for manufacturing a large-diameter rectangular steel pipe including hot forming.

[0002]

2. Description of the Related Art As one of mass production methods by cold plastic working of large-diameter square steel pipes, which are widely used as pillar materials for building structures, the following construction methods have been conventionally practiced. The hot rolled coil is hung on a leveler to form a flat steel strip, and both side edges of the flat steel strip are width-processed. The strip steel plate is passed serially through processing stages such as breakdown, clusters, fin pass stands, etc., during which the steel plates are sequentially cold roll-formed, and their right-angled cross sections are transformed into a shape close to a circle,

The one-seam round steel pipe is formed by welding both side seams of the strip steel by using high frequency welding, arc welding or the like. After gradually cooling the welded part of the round steel pipe, through a process such as a sizer, a squaring stand, and a turks head, the cross-section is sequentially formed into a square shape to manufacture a large-diameter square steel tube. The above-described method includes a step of bending a flat steel plate into an arcuate curved surface, and a thick steel plate having an arcuate curved surface by cold plastic working to form a rounded portion of the steel pipe at an angle of approximately 90 °.

By the way, when a thick steel strip or a steel plate is cold,
In the case of bending by 90 °, even if the corner is bent and bending is performed, the elastic force is exerted while a tensile force or a compressive force acts on both sides of the neutral plane of the steel plate cross section. The plastic deformation progresses beyond the limit, the mechanical properties of the deformed portion, particularly the corner R member material deteriorates, and there is a latent condition that brittle fracture occurs in the relevant portion. For example, in combination with work hardening, high residual stress, and reduction in toughness that occur in the corner R portion steel material due to cold bending, the local material quality based on the welding work performed on the steel sheet in the corner portion at low temperature in winter is performed. Cracks, cracks during hot dip galvanizing, etc. may occur.

Steel structures, buildings, etc., using this kind of large-diameter rectangular steel pipe as a pillar material are generally
It is required to safely withstand wind pressure, deformation of the foundation ground, and other loads, and in many cases, these pillars (columns) are generally constructed so that they cannot be replaced or repaired. In particular, high-rise buildings occupy the mainstream of recent buildings, and the weight that increases due to the equipment attached to the building, such as installing air-conditioning and heating equipment in each room, equipping OA equipment and computers, etc. It cannot be ignored, and since the equipment weight that should be considered in advance tends to increase, there is a tendency to frequently use thick and large diameter steel pipes as columns, so deterioration of the steel pipe material due to the cold plastic working The problem of is becoming more and more difficult to ignore.

In view of such circumstances, deterioration of the material of the rectangular steel pipe due to cold plastic working at the time of forming the rectangular steel pipe, particularly deterioration of the material of the corner R portion, is once again regarded as a problem.
Therefore, in recent years, there is a demand from a consumer group to provide a high-quality large-sized rectangular steel pipe having a small residual stress, sufficient toughness, and a corner R portion.

[0007] In order to solve this kind of material problem that a large-diameter thick-walled rectangular steel pipe by cold plastic working is included, the manufacturer has conventionally used ready-made round steel pipes, seamless pipes, etc. for oil, gas, etc. It has been proposed to heat a fossil fuel or an electric energy in a heating furnace or apparatus using a heat source as a heat source, and then form it into a square cross section by hot plastic working through a plurality of rolling mills. When the above method is used, the quality of the product is good, but the cross section at both ends of the steel pipe has a poor shape, and the product yield is poor because it is cut off. The value of the product tends to deviate and become unstable, resulting in a decrease in product value. Also, heating,
There are problems that the thermal stress strain that occurs in the steel pipe during cooling cannot be ignored and that the production is low because the steel pipe is machined to one pipe.

Separately, a large-diameter rectangular steel pipe which has been formed by cold working is inserted into an annealing furnace, and the residual stress in the steel material is substantially removed, and the whole is heated until the toughness of the corner member material is improved. A method of gradually cooling is also known. Also in this case, there may be the same problems as described above. Alternatively, the hot-rolled coil is hung on a leveler, the steel plate cross-section is formed into a round shape by cold plastic working through various forming roll stands, and the side edge joints are sequentially butt-welded by a high-frequency welding method or the like to form a round steel pipe. After that, the steel pipe is heated in-line with fossil fuel such as electric energy, gas or oil, passed through a multi-stage hot forming roll device, shaped into a steel pipe having a rectangular cross section, and cooled to obtain a product (for example, , Japanese Patent Application No. 2-180 filed by the applicant earlier
No. 497) is considered.

(A) In the above-mentioned construction method, thermal non-uniformity during heating,
In particular, deformation of the steel pipe due to uneven temperature distribution during cooling is a problem, and in order to eliminate this, it is necessary to make the cooling zone sufficiently long and gradually cool the steel pipe. Also, unlike the round steel pipe, the air flow is disturbed at the steel pipe corner R part during cooling,
It becomes difficult to uniformly cool the peripheral wall, and a non-uniform temperature distribution is likely to occur. And, once a steel pipe is deformed, it is very difficult to correct it in the case of a rectangular steel pipe.

(B) When a heating furnace that uses fossil fuels such as gas and oil is installed in-line, the forming speed of the round steel pipe is fast (in order to obtain good welding quality using the high frequency welding method, to some extent the welding speed is from is required) for the, steel internal stress of square steel is completely eliminated a ₃
In order to heat the steel pipe to the transformation temperature, a space for installing a heating furnace with a length of 100 m to 150 m is required, and the production line becomes too long, making it difficult to select site conditions. The amount of investment may rise more than expected. In addition, when heating a round steel pipe with fossil fuel such as gas or oil, the heat source cannot be put inside the steel pipe, so it is difficult to heat the steel pipe uniformly, and there is a problem in terms of temperature control of the steel pipe heating. However, since this is related to the molding shape of the cross section and the occurrence of distortion, a product of uniform quality may not be obtained in the end.

(C) Further, the forming roll used for the hot plastic working is liable to have slip flaws on the peripheral surface of the roll and has a short service life. Therefore, the maintenance is more troublesome as the number of stages of the hot forming roll is increased. (D) On the other hand, the heating device using electric energy has a small space for heating the steel pipe, and has an advantage that the uniform heating of the steel pipe material and the control of the heating temperature can be easily performed, but the power cost is high and the location is high. Depending on the conditions, it may be difficult to obtain the required large amount of power. It is known that there are technical problems.

[0012]

SUMMARY OF THE INVENTION The present invention was developed in view of the above-mentioned circumstances, and the residual stress of the material of the rectangular steel pipe is made to be less than the allowable stress and the toughness of the corner R portion is improved. An object of the present invention is to provide a method and an apparatus for producing a high-quality large-diameter rectangular steel pipe made of a uniform and stable material while avoiding deterioration of the material of the entire steel pipe. Further, another object of the present invention is to improve the conventionally known manufacturing apparatus, to reduce the capital investment by installing an apparatus for performing the heat treatment off-line, and to form a square steel pipe of a uniform material. The purpose is to develop a new means capable of solving the above-mentioned problems inherent in the conventional manufacturing method as much as possible.

[0013]

In order to achieve the above-mentioned object, the method of the present invention has the respective constituent features as described below. (1) A round steel pipe formed by forming a steel strip or a steel plate into a round shape at a right-angled cross section in the longitudinal axis direction and sequentially butt-welding both side edge seams thereof is conveyed to a square steel pipe forming roll device having a plurality of stages, In the step of sequentially forming a round steel pipe cross section into a square cross section, the square steel pipe forming roll step is divided into a first forming step and a second forming step, and in the first forming step, the round steel tube is formed into a coarse angle forming shape, and Between the first forming step and the second forming step, a step of cutting the roughly formed steel pipe into unit lengths, a heating device for heating the unit length roughly formed steel pipes are arranged, and each unit steel pipe is inserted into the heating device. After being uniformly heated to a predetermined temperature, the high-temperature unit-length rough-formed steel pipe is carried into a second forming step consisting of a plurality of stages including finish forming rolls, subjected to hot plastic working, and a square shape having at least a standard cross section. Forming a steel pipe, Next, a cooling device for uniformly cooling the standard cross-section steel pipe is installed, and after gradually cooling or forcibly cooling the steel pipe, a large bending in the longitudinal axis direction, a heat characterized by correcting distortion such as twisting Large diameter square steel pipe manufacturing method including hot forming.

(2) A round steel pipe forming apparatus for forming a steel strip or a steel sheet into a round shape with a cross section perpendicular to the longitudinal axis direction, and sequentially welding both side edge joints by butt welding, and a round steel pipe cross section connected to the apparatus. Corner forming type roll device for roughly forming by cold working, a cutting device for cutting a steel pipe having a rough forming cross section formed by the first corner forming type roll device for each unit length, and the unit length rough formed steel pipe is predetermined. A heating device that uniformly heats to temperature, a plurality of stages including a finish forming roll that inserts the high temperature unit length rough formed steel pipe carried out from the heating device and forms the steel pipe cross section into a standard rectangular cross section by hot plastic working Made of a large-diameter square steel pipe including hot forming, which comprises a second square forming roll device, a cooling device for uniformly cooling the standard section steel pipe, a device for correcting distortion such as large bending in the longitudinal axis direction and twist Manufacturing equipment.

[0015]

[Function] A material defect that has been regarded as a problem with large-diameter rectangular steel pipes on the market is deterioration of the steel pipe material due to cold plastic working during the steel pipe forming process, particularly deterioration of steel plate toughness at the corner R part. The weakening of the structural material due to brittleness of the material due to the presence of residual stress, work hardening, and the like. (1) In view of the above-mentioned circumstances, in the present invention, after forming a round steel pipe by cold plastic working, the steel pipe is subsequently carried into a square rough forming roll device (first forming roll step), and the same device is used. In, the four corners R are formed in the cross section of the round steel pipe under cold plastic working.

At this time, the working rate is made as small as possible to avoid the deterioration of the material of the steel pipe, and the steel pipe cross section is deformed from the round cross section to the thread winding type cross section which is convex outward. The arrangement of the corner R part and the seam part in the cross section of the steel pipe is determined, and secondly, the working amount of hot deformation of the steel pipe cross section to a standard rectangular shape is reduced as much as possible. Since the first forming roll process is cold plastic working that is continuous with forming of the round steel pipe as described above, the forming roll mounted on the apparatus has a long service life, and its maintenance is simple and easy. Further, the first forming roll process is continuous with the round steel pipe forming process, and because of the cold plastic working, the corner forming formability of the steel pipe material due to plastic deformation is good.

The cutter for the continuously formed rough formed steel pipe is intermittently moved in synchronization with the conveying direction of the rough formed steel pipe by a running cutting device or the like, and the cutter is cut into unit lengths. This makes it possible to avoid defective molding of the front and rear end cross sections of the rough-formed steel pipe. Further, by the same process, the first forming roll process before that and the second forming roll process after the heating process are made discontinuous, and a coarse formed steel pipe accommodation space is provided between them to form the unit length coarse formed steel pipe. Hold and buffer the difference in processing efficiency between both steps.

If it is attempted to heat the entire steel pipe in-line to the A ₃ transformation point of the steel sheet in-line, a heating furnace using fossil fuel alone would be too long to heat the steel pipe to the required temperature. However, it may be difficult to select the location conditions for the production line, but by adopting the above method, the production line speed will be slowed down even if a fossil fuel heating furnace is used. The equipment length can be shortened as appropriate. Also, with this molding line, there is a lot of room for refurbishing and using existing equipment, and the equipment can be economically renewed.

The roughly formed steel pipes are inserted into a heating device in units, and while the steel pipes are conveyed by a feed roll in the longitudinal direction (or the right angle direction), they are heated to near the A ₃ transformation point of the steel material, and during cold plastic working. The material is improved against the processing effect, residual stress, deterioration of toughness, etc. that occurred on the steel sheet, and the second forming roll process including the finish forming roll stage is heated at a temperature not lower than the A ₁ transformation point of the steel as much as possible. The steel pipe is heated to such an extent that hot working can be performed. As the above-mentioned heating device (furnace), a heating furnace using fossil fuel such as gas or petroleum is adopted in consideration of site conditions, equipment cost, economical efficiency, method of obtaining heating energy, operating cost and the like. However, if circumstances permit, the adoption of a heating means by electric power, for example, an electric heating method, a high frequency heating method, or the like is not excluded.

While the heating temperature of the rough formed steel pipe is not lowered, the steel pipe is charged into a second forming roll device having a plurality of stages including finishing roll stages for hot plastic working. In addition, a thread-wound cross-section steel pipe is formed into a square steel pipe cross-sectional shape having a standard cross-section. (A) In the second forming roll step, since the steel pipe cross section is initially (roughly) formed into a quadrangular shape in the previous step, the inserted steel pipe cross section conforms to the mold of the forming roll, and the corner R portion by hot working is formed. The deformed position and the relative position of the seam portion are stably formed with respect to the cross section. (B) In the second forming roll step, the processing amount for each step for forming the rough forming cross section into the standard rectangular cross section is reduced, and the forming operation is performed so as to squeeze the entire cross section without a gap (for example, the present applicant). Japanese Patent Application No. 4-14200 filed earlier
(See No. 5) and accurately mold the cross section according to the standard. For this reason, there are very few defective moldings at the front and rear ends of the molded steel pipe, and the yield is good.

(C) The standard cross-section steel pipe cooled to about room temperature is then loaded into a straightening roll machine (or straightening press machine), where straightening, twisting, and other distortions caused in the longitudinal axis are corrected. Apply some processing for. (D) In the second forming roll step, since the steel pipe cross section is roughly formed into a rectangular shape by cold plastic working in advance, a small amount of work is required to obtain a standard rectangular cross section. (E) Further, since it is hot plastic deformation, it is possible to form the radius of curvature of the corner R portion smaller than the standard value without increasing the residual stress again in the material and considering the deterioration of toughness. .

In short, the total working amount at the stage of forming a round steel pipe from a rolled steel strip into a square steel pipe by cold forming is substantially heat treated or under the hot plastic working. As a result, the mechanical properties of the steel material are not deteriorated by the deformation of the steel sheet. (A) Moreover, in the same forming process, since the hot plastic working amount is smaller than that in which all the steps of the square forming roll device are applied to the hot plastic working, extra labor is required for the maintenance of the forming roll. No need to spend. (B) The second forming roll device in which the roll peripheral surface is relatively easily damaged can be installed as a set so that it can be collectively replaced and installed, thereby improving the efficiency of maintenance. (C) The driving power of the second forming roll device for performing the hot plastic working may have a relatively small capacity.

After the hot plastic working, the standard cross-section steel pipe is separated from the forming roll device before the heating temperature is lowered, and is immediately carried into the cooling device, where it is cooled to near normal temperature as much as possible. . The cooling device is generally by natural cooling, but for example, cooling air is blown from around the conveying steel pipe, or a mechanism for injecting mist is provided,
Further, the rectangular steel pipes of 200 ° C. or lower can be equipped with a forced cooling means for the rectangular steel pipes such as injecting cooling water as needed. The total strain generated in the steel pipe after cooling due to the thermal stress due to the above-mentioned hot working, heat treatment, etc. does not exceed a negligible degree. In addition, the cooling speed is controlled and adjusted to allow such a degree of distortion to reduce the space of the device.

A well-cooled standard cross-section steel pipe is cut off at the front and rear end cross-section defects to form a product having a shape according to the standard length. However, it goes without saying that the product is shipped to the market after the inspection of the welded portion of the steel pipe is inspected through the process such as the strain straightening machine. by this,
The corner R part can be formed sharply without causing deterioration of the steel pipe material and without deteriorating the toughness of the steel material, creating a product that is easy to use and has a good appearance. Get a big steel pipe.

According to the method and apparatus of the present invention, after the first forming roll step of continuously forming a round steel pipe formed from a rolled steel strip into a rough square section by cold plastic working, the rough formed steel pipe is cut into unit lengths. Then, by heating the steel pipe as a whole to near the A ₃ transformation point of the steel material and subjecting it to heat treatment, the residual stress of the steel pipe caused by plastic working and butt welding in the previous process is removed, and the steel material at the corner R part is removed. While improving the toughness of the steel pipe, in the second forming roll step, the steel pipe is formed into a standard cross-sectional shape at a high temperature by substantially not lowering the A ₁ transformation point of the steel sheet by hot plastic working. A uniform and high-quality forming method for large-diameter rectangular steel pipes that reduces the toughness of the steel pipe material caused by bending the four corners of the four corners of the steel pipe at approximately 90 °, work hardening of the steel plate, and material deterioration such as residual stress. To provide Together, they have developed an excellent device economically.

Therefore, according to the method and apparatus of the present invention,
It is possible to improve the defect of material deterioration of the steel pipe corner R portion due to the plastic deformation of the corner portion of the large-diameter square steel pipe, which has been regarded as a problem in recent years, within a range where practically no problem occurs. Moreover, compared with the one equipped with an annealing furnace using a fossil fuel as a heat source, the method of the present invention has a high productivity, and the steel pipe steel material is substantially heat-treated off-line as in the conventional method. Has little impact on cost. In addition, the equipment space is smaller compared to the heating furnace in the conventional method installed inline, there is also room to improve the existing equipment, and is excellent in the control of the heating temperature of steel materials and uniform heating, Furthermore, since the forming process can be performed with high precision, the method and apparatus of the present invention can eventually produce a high-quality and uniform large-diameter square steel pipe.

[0027]

EXAMPLE An example of the method of the present invention and a large-diameter square steel pipe production line for carrying out the method will be described below with reference to the drawings. The structure can be partially modified by those skilled in the art within the range of known technology in the art at the time of the application of the present application, and therefore, based on only the specific structure described in this embodiment without giving any particular reason. Therefore, a limited interpretation of the gist of the method and apparatus of the present invention is not allowed.

FIG. 1 is a schematic block diagram showing an embodiment line of the method of the present invention and a large-diameter square steel pipe forming apparatus for carrying out the same method, and FIG. 2 is a thick steel corresponding to each step of the apparatus. It shows the state of molding and processing of the strip. In the figure, 1 is an uncoiler linearly along the material conveying direction,
The coiled thick steel strip 11 is unwound and subjected to leveling to continuously correct the winding distortion and form the flat strip steel plate 12. Reference numeral 2 denotes a steel plate width determining device, which cuts both sides of the flat strip steel plate 12 with a trimming cutter to form a predetermined width.

Reference numeral 3 denotes a round steel pipe forming roll device, which comprises a preform, a breakdown roll, a cluster, a fin pass roll, a high frequency welding device 4, a squeeze roll, and the like, and the strip steel plate 12 passes through the device. The ERW steel pipe 13 having a round cross section is formed by cold plastic working. The round steel pipe 13 had a diameter of 637 mm and a plate thickness of 16 mm. 5 is an outer bead cutting machine, a pull-out roll, etc., and is a cooling zone for cooling the heating of the steel pipe by welding to return the steel pipe to a uniform constant temperature, and 6 is a first angle forming roll device, usually one stage A round steel pipe is continuously charged therein, and the steel pipe cross-section is sequentially deformed from the round cross-section to the roughly formed rectangular approximate cross-section by cold plastic working.

As a result, the cross section of the roughly formed steel pipe 14 formed through the first corner forming roll process has a substantially wound bobbin shape with the corner R portion formed, and the above corners on the circumference of the cross section. The relative positions of the R portion and the butt welded joint (seam line) of steel materials are fixed. In short, the cold plastic working bears a part of the corner forming work and completes the basic forming of the steel pipe cross-sectional shape of the final square product. Reference numeral 7 denotes a running cutting device, which cuts the continuously formed rough-formed steel pipe 14 at predetermined unit lengths. 8
Is a deposit space, where a considerable area is allocated, the cut unit length steel pipes 14 are received and accumulated, and are transported, and each unit length steel pipe is transported to the heating device of the next process. .

Reference numeral 20 denotes a heating device (furnace), which in this embodiment is a heating furnace which uses a fossil fuel composed of gas or liquid fuel as a heat source, and in which unit-length rough-formed steel pipes 15 are sequentially inserted and rotated. While passing through the same device, the steel pipe is heated to a substantially uniform temperature on the inner and outer surfaces of the steel within the longitudinal axis direction and the right-angled cross section, and the heating temperature at the final stage of the heating device is Depending on the temperature, the material of the square steel pipe, the outer diameter and the plate thickness, etc., the residual stress during forming does not remain and the toughness of the steel near the corner R can be improved.
It is heated to about 1050 ℃.

Although it depends on the thickness of the steel pipe and the capacity of the heating device (furnace) with respect to the conveying speed, higher temperature heating removes work hardening and residual stress and improves toughness of the steel material during cold plastic working. As for the degree of skin roughness (mill scale) on the surface of the steel material, it is natural that the lower temperature heating can maintain better. Also, the heat treatment cost can be reduced.

Reference numeral 21 is a second angle forming type roll device, which includes a finish forming roll process, is a hot plastic working, and the constituent stages thereof are substantially composed of three to six stages, and the steel pipe cross section of the forming process is the same. The processing amount (degree) for occupies approximately 70 to 95% of the total processing amount of the prism, passes through the pinch roll and second corner forming roll process, and becomes a standard square cross section.

Since the rough forming unit length steel pipe 15 is heated before being subjected to the second forming roll process and is carried into the second forming roll device 21 at a high temperature, there is substantially a hot plastic deformation there. Therefore, the deterioration of the material based on the corner formation does not occur. Since the heat energy from the heated steel pipe 15 is constantly conducted and radiated to the forming roll used in this step, a cooling means for the roll and others must be installed. In addition, since the roll member in the process is prone to roll flaws and the service life is relatively short, a structure in which roll replacement work, adjustment work, and the like are easy to manage, for example, a second forming roll device uses a crane. And make equipment that can be replaced at once.

Reference numeral 22 is a cooling device for the standard shaped cross-section steel pipe 15,
In this cooling zone, the steel pipe 15 carried in is required to be symmetrically and substantially symmetrically cooled within the same cross section, and substantially uniformly in the longitudinal axis direction. In the same cooling zone, due to uneven temperature distribution outside the hot forming and heat control of the cooling device, axial bending of the steel pipe, distortion of the cross-sectional shape, dents in the plate thickness direction, distortion, etc. You can see that the size is insignificant. Further, the cooling speed of the unit length steel pipe 15 in the cooling device 22 is approximately
On the assumption that the above-mentioned deformation of the steel material is allowed, the steel pipe temperature is finally cooled to about room temperature. At this stage, the steel pipe material as a whole maintains the toughness close to that of the base material and maintains a state in which there is almost no residual stress.

By this second forming roll processing, the cross-sectional shape of the steel pipe is formed into a standard cross-sectional shape, and the portion concerned is uniformly and sharply, without causing deterioration of the corner material, for example, R = Mold to (2-2.5) × t. Where R = outer radius of curvature, t = thickness of steel pipe material

The reference numeral 23 designates a straightening machine for distortion such as large bending and twisting of the standard long rectangular steel pipe 16 in the longitudinal axis direction, a welded joint, and a flaw detector using ultrasonic waves for other portions. Reference numeral 24 denotes a double-sided cutting machine, which cuts defective cross-section portions at both ends of the unit-length standard-section steel pipe 15 caused by the second forming roll processing to obtain standard-length rectangular steel pipes (products) 16. Reference numeral 25 denotes a product unloading table, which stores and stores the standard length steel pipe 16.

In FIG. 2, 11 is a hot rolled steel strip, 12 is a thick strip steel plate forming a plane, 13 is a round steel pipe, and 14 is rough forming cold-worked by a first angle forming roll. The steel pipe, 15 is a standard cross-section steel pipe hot-plastic formed by the second forming roll device, and its size is, for example, 500 mm square. 16
Indicates a standard length product of the same type. The plate thickness of the steel plate that can be processed by the method and apparatus of this example is 9
~ 28 mm, square steel pipe outer diameter is planned to be approximately 200 mm to 600 mm. As described above, in the present embodiment,
The details of the other actions and effects are as described in detail in the section (Action) described above, and therefore will be omitted.

[0039]

EFFECTS OF THE INVENTION Since the method and apparatus of the present invention are as described above, (1) Machining of thick-walled steel pipe material which has been regarded as a problem in the conventional large-diameter square steel pipe formed by cold plastic working. Hardening and deterioration of the toughness of the corner R portion can be improved, residual stress generated in the steel material can be removed to be less than the allowable amount, and a high-quality large-diameter square steel pipe can be formed as a whole. (2) The corner R part is formed as sharply as possible without deterioration of the material, and each square steel pipe is made uniform to improve the usability and the appearance of the product. By using the same steel material, we will provide a tougher steel pipe with high commercial value and high quality.

(3) Since the round steel pipe is initially (preliminarily) formed by cold working to determine the positions of the corner R portion and the seam line on the cross section of the square steel pipe, even if the square cross section is hot formed. Regardless, the position of the seam line on the product can always be kept constant (near the center of the flat surface on one side). (4) Upon forming a rectangular roll, the length of the defective cross section at both ends of the steel pipe is significantly reduced, and the yield is improved. (5) In addition, each effect described in the above section (action) is exhibited. And so on, it is possible to obtain special actions and effects that cannot be expected from the conventionally known construction methods and devices.

[Brief description of drawings]

FIG. 1 is a block diagram of an example line of a large-diameter rectangular steel pipe forming apparatus for carrying out the method of the present invention.

FIG. 2 is a sectional shape view of a steel pipe and a steel material corresponding to each step in the apparatus.

[Explanation of symbols]

 1 Uncoiler 2 Steel strip width determining device 3 Round steel pipe forming roll (cold) 4 High frequency welding device 5 Cooling zone 6 1st angle forming roll device (cold) 7 Running cutting device 8 Deposit space 11 Hot rolled steel strip 12 Thick steel plate 13 ERW round steel pipe 14 Rough forming square steel pipe 15 Unit long rectangular steel pipe 16 Product 20 Heating device 21 Second angle forming roll device (hot) 22 Cooling device 23 Strain corrector, flaw detector 24 Both ends cutting machine 25 Product unloading table.

Claims (2)

[Claims] 1. A round steel pipe formed by forming a steel strip or steel plate into a round shape in a cross section perpendicular to the longitudinal axis direction and sequentially butt-welding both side edge joints of the round steel pipe to a multi-stage square steel pipe forming roll device. Then, in the step of sequentially forming the round steel pipe cross sections into the rectangular cross section, the square steel pipe forming roll step is divided into a first forming step and a second forming step, and in the first forming step, the round steel tube is formed into a rough angle. , A step of cutting the roughly formed steel pipe into unit lengths, a heating device for heating the unit length roughly formed steel pipes is arranged between the first forming process and the second forming process, and each unit steel pipe is inserted into the heating device. Then, after uniformly heating to a predetermined temperature, the high temperature unit length rough formed steel pipe is carried into a second forming step consisting of a plurality of stages including finish forming rolls and subjected to hot plastic working to provide at least a standard cross section. Made square steel pipe Characterized by installing a cooling device for uniformly cooling the standard cross-section steel pipe, gradually cooling the steel pipe or forcibly cooling the steel pipe, and then correcting distortion such as large bending in the longitudinal axis direction and twisting. Large diameter rectangular steel pipe manufacturing method including hot forming. 2. A round steel pipe forming device for forming a steel strip or a steel plate into a round shape with a cross section perpendicular to the longitudinal axis direction, and sequentially butt-welding both side edge seams thereof to form a round steel pipe cross section connected to the device. A first horn forming roll device for rough forming by cold working, a cutting device for cutting a steel pipe having a rough forming cross section formed by the first horn forming roll device for each unit length, and the unit length rough formed steel pipe at a predetermined temperature A heating device for uniformly heating to, inserting the high temperature unit length rough forming steel pipe carried out from the heating device, from a plurality of stages including a finish forming roll for forming the steel pipe cross section into a standard rectangular cross section by hot plastic working Large-diameter square steel pipe manufacturing apparatus including hot forming, which comprises a second square forming roll device, a cooling device for uniformly cooling the standard cross-section steel pipe, a device for correcting distortion such as large bending in the longitudinal axis direction and twist .