JP2852313B2 - Method and apparatus for manufacturing large diameter square steel pipe including hot forming - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for the stepwise production of a large-diameter rectangular steel pipe including hot forming using a rolled steel strip and a steel sheet. In parallel with the direction, it is formed into a round section by cold plastic working, and the both side edge joints are sequentially butt-welded to form a large-diameter round steel pipe, and then charged into a square-shaped roll device consisting of a plurality of stages. In the step of sequentially forming the steel pipe cross section into a square shape, the horn forming roll step is divided into a first forming step and a second forming step, and the rough forming form is formed by cold working in the first forming step following the round steel pipe forming. After applying
It is cut into unit lengths in the longitudinal direction, and the unit length steel pipe is inserted into a heating device provided between the first forming step and the second forming step, and is uniformly heated to a predetermined temperature, whereby the steel pipe is added to the steel sheet material. In addition to removing the residual stress, work hardening, etc. caused by the cold plastic deformation and improving the mechanical properties of the rough-formed steel pipe, the steel pipe is made up of multiple stages including finishing rolls before the heating temperature is reduced. (2) The mechanical properties of the square steel pipe, especially the material deterioration near the corner R, are improved by uniformly cooling the square steel pipe, which is formed by hot plastic working in the forming process and at least the cross section is 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 characterized by the following.

[0002]

2. Description of the Related Art As one of mass production methods by cold plastic working of a large-diameter rectangular steel pipe, which is widely used as a column material of a building structure, the following construction method has been generally carried out. The hot-rolled coil is hung on a leveler to form a flat steel strip, and the edges on both sides are determined. The strip steel plate is passed in series to a processing stage such as a breakdown, a cluster, and a fin pass stand, during which the steel plate is sequentially cold-rolled, and its right-angle cross section is deformed into a shape close to a circle,

[0003] Both side joints of a strip steel plate are welded using high frequency welding, arc welding or the like to form a one-seam round steel pipe. After gradually cooling the welded portion of the round steel pipe, the cross section is sequentially formed into a square shape through processes such as a sizer, a scoring stand, and a turks head to produce a large-diameter square steel pipe. The above-mentioned method includes a step of bending a flat steel plate into an arcuate curved surface, and forming a thick steel plate having an arcuate curved surface by cold plastic working to form a steel pipe corner R portion, approximately 90 °.

By the way, a thick steel strip or a steel sheet is cold
In the case of approximately 90 ° bending, even if the corner is bent by giving a radius, even if a tensile force or a compressive force acts on both sides with respect to the neutral surface in the cross section of the steel plate, the elasticity is increased. Plastic deformation proceeds beyond the limit, and the mechanical properties of the deformed portion, particularly the corner R member material, are degraded, and a condition that causes brittle fracture in the portion becomes latent. For example, due to the work hardening, high residual stress, and reduced toughness that occur in the corner R steel due to cold bending, the local steel based on the welding operation performed at low temperature in winter is applied to the steel at the corner. Cracking and cracking during hot-dip galvanizing may occur.

[0005] Steel structures, buildings and the like using this kind of large-diameter rectangular steel pipe as a column material are generally subjected to earthquakes,
It is required to safely withstand wind pressure, deformation of the foundation ground and other loads, and moreover, these pillars (columns) are often constructed in such a manner that they cannot be replaced or repaired in principle. Especially in recent buildings, high-rise buildings occupy the mainstream, and the weight that increases due to facilities attached to the buildings, such as installing air conditioning and heating equipment in each room, OA equipment, computers, etc., is also increasing. It cannot be neglected, and the equipment weight to be considered in advance tends to increase, so that there is a tendency to frequently use thick-walled large-diameter steel pipes as columns. Is becoming increasingly non-negligible.

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, has been regarded as a problem again.
Therefore, in recent years, there has been a demand from a group of consumers to provide a high-quality large rectangular steel pipe having a small residual stress, sufficient toughness, and having a corner R portion.

[0007] In order to solve this kind of material problem in which a large-diameter thick-walled square steel pipe formed by cold plastic working is included, conventionally, manufacturers have used existing pipes such as oil, gas, etc. After heating by a heating furnace or apparatus using a fossil fuel or electric energy as a heat source, it is proposed to form it into a rectangular 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 becomes defective and the yield of the product is poor because it is cut off. The product value tends to be significantly deviated and unstable. Also heating,
There is a problem that the thermal stress strain generated in the steel pipe during cooling cannot be ignored, and the production is low because the steel pipe is processed one by one.

Separately, a large-diameter rectangular steel pipe 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 is improved. There is also known a method of gradually cooling the water. In this case as well, there may be similar problems as described above. Alternatively, a hot-rolled coil is hung on a leveler, the cross section of the steel sheet is formed into a round shape by cold plastic working through various forming roll stands, and the both side edge joints are sequentially butt-welded by high frequency welding 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, formed into a square-shaped steel pipe and cooled to obtain a product (for example, And Japanese Patent Application No. 2-180 filed earlier by the present applicant.
No. 497).

[0009] (a) The above-described method is not uniform in heat during heating,
In particular, deformation of the steel pipe due to non-uniform temperature distribution during cooling is a problem. To eliminate this problem, it is necessary to provide a sufficiently long cooling zone and gradually cool the steel pipe. In addition, at the time of cooling, unlike the round steel pipe, the air flow is disturbed at the steel pipe corner R,
It becomes difficult to cool the peripheral wall uniformly, and a non-uniform temperature distribution is likely to occur. Once the steel pipe is deformed, it is very difficult to correct it in the case of a square steel pipe.

(B) When a heating furnace utilizing a fossil fuel such as gas or oil is installed in-line, a round steel pipe is formed at a high speed (for obtaining good welding quality by using a high frequency welding method, a certain degree of 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 point 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 location conditions, There is a risk that the investment amount will expand more than expected. In addition, when heating round steel pipes with fossil fuels such as gas and oil, it is difficult to heat the steel pipes uniformly because the heat source cannot be inserted inside the steel pipes, and there is a problem in the temperature control of steel pipe heating. Since this is related to the shape of the cross-section and the occurrence of distortion, a product of uniform quality may not be obtained after all.

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

[0012]

SUMMARY OF THE INVENTION The present invention has been developed in view of the above-mentioned circumstances, and has been made to reduce the residual stress of a rectangular steel pipe material to an allowable stress or less and to improve the toughness of a corner R portion. Another object of the present invention is to provide a method and an apparatus for manufacturing 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 a conventionally known manufacturing apparatus, reduce the capital investment by installing an apparatus for performing off-line heat treatment, and form a square steel pipe of uniform material. Another object of the present invention 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 following components. (1) The steel strip or the steel sheet is formed into a round shape in a cross section perpendicular to the longitudinal axis direction, and the round steel pipe formed by sequentially butting and welding the both-side edge seams is transferred to a square steel pipe forming roll device having a plurality of stages. In the step of sequentially forming the round steel pipe 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 pipe is formed into a rough angle, A step of cutting the coarsely formed steel pipe into a unit length, a heating device for heating the unit length coarsely formed steel pipe, and inserting the heating device for each unit steel pipe into the heating device between the 1 forming step and the second forming step. After being uniformly heated to a predetermined temperature, the high-temperature unit-length roughly formed steel pipe is carried into a second forming step including a plurality of steps including a finish forming roll, subjected to hot plastic working, and is provided with a square having at least a standard cross section. Forming a steel pipe, Next, a cooling device for uniformly cooling the steel pipe having the standard cross section is installed, and after gradually cooling or forcibly cooling the steel pipe, the heat is characterized by correcting distortion such as large bending in the longitudinal axis direction and twisting. A method for manufacturing large-diameter rectangular steel pipes 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 butt-welding both side edges of the steel strip or the steel sheet. , A cutting device for cutting a steel pipe having a roughly formed cross section formed by the first square forming roll device into unit lengths, and A heating device for heating evenly to a temperature, a plurality of stages including a finish forming roll for inserting the high-temperature unit-length coarsely-formed steel pipe unloaded from the heating device and forming the steel pipe cross-section into a square-shaped cross-section as specified by hot plastic working. A large-diameter rectangular steel pipe including hot forming comprising a second square forming roll device, a cooling device for uniformly cooling the standard-section steel pipe, and a device for correcting distortion such as large bending and twisting in the longitudinal axis direction. Manufacturing equipment.

[0015]

[Function] The material defects that have been regarded as problems with large-diameter rectangular steel pipes on the market are the deterioration of the steel pipe materials due to cold plastic working during the steel pipe forming process, especially the reduction of the toughness of the steel sheet at the corner R. , Weakening of the structural material due to brittleness of the material, such as the presence of residual stress, work hardening and the like. (1) In view of the above 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 process), and , Four corners R are formed in the cross section of the round steel pipe under cold plastic working.

At this time, while reducing the working ratio as much as possible to avoid deterioration of the steel pipe material, the cross section of the steel pipe is deformed from a round cross section to a thread winding cross section which protrudes outward. In order to determine the arrangement of the corner R portion and the seam portion in the steel pipe cross section, the second problem is to reduce the amount of hot deformation of the steel pipe cross section to a rectangular shape as specified. Since the first forming roll process is a cold plastic working which is continuous to the forming of the round steel pipe as described above, the forming roll attached to the apparatus has a long service life and its maintenance is simple and easy. In addition, the first forming roll step is continuous with the round steel pipe forming step, and the steel pipe material has good angulation formability by plastic deformation due to cold plastic working.

The cutter is intermittently moved in the continuously formed rough-formed steel pipe in synchronization with the transport direction of the rough-formed steel pipe by a running cutting device or the like, and is cut into unit lengths. As a result, it is possible to avoid poor forming of the front and rear end cross sections of the roughly formed steel pipe. Further, by the same step, the first forming roll step before that and the second forming roll step below the heating step are discontinuous, and a coarsely formed steel pipe accommodation space is provided therebetween, and the unit length coarsely formed steel pipe is removed. Hold and buffer any differences in processing efficiency between the two steps.

[0018] temporary, in-line, if an attempt heat the entire steel pipe to A ₃ transformation point of the steel sheet, long heating furnace as described above to heat the steel pipe only heating furnace using fossil fuels to the required temperature Although the equipment of the above may be required, it may be difficult to select the location conditions of the production line.However, by adopting the above-described method, it is possible to reduce the speed of the production line and use a fossil fuel heating furnace. The length of the equipment can be appropriately reduced. In addition, with this molding line, there is ample room for renovating and using existing equipment, and equipment can be economically updated.

[0019] Insert the crude molded steel pipe to the heating device for each unit, and heated to around A ₃ transformation point of the steel material while conveying the steel pipe by feeding a roll in the longitudinal direction (or perpendicular), when cold plastic working processing effects produced on the steel sheet, residual stresses, while the material improvement over such as a decrease in toughness, all heat in the second forming roll step a above the a ₁ transformation point of the steel as much as possible a temperature comprised finish forming roll stage The steel pipe is heated to the extent that hot working is possible. The heating device (furnace) employs a heating furnace using a fossil fuel such as gas or petroleum in consideration of location conditions, equipment costs, economics, a method of obtaining heating energy, operating costs, and the like. However, this does not exclude the use of heating means using electric power, for example, an electric heating method or a high-frequency heating method, if circumstances permit.

Before the heating temperature of the crudely formed steel pipe is lowered, the steel pipe is loaded one by one into a second forming roll device comprising a plurality of stages including a finishing roll stage to perform hot plastic forming. At the same time, the thread-wound cross-section steel pipe is formed into a square steel pipe cross-section having a cross section as specified. (A) In the second forming roll step, since the cross section of the steel pipe is initially (roughly) formed into a square shape in the previous step, the cross section of the inserted steel pipe fits into the mold of the forming roll, and the corner R portion is formed by hot working. Are formed stably with respect to the cross section. (B) In the second forming roll step, the forming amount is reduced in each step for forming the rough forming section into the standard square section, and the forming process is performed so that the entire circumference of the section is narrowed without a gap (for example, the applicant of the present invention). Applied for Japanese Patent Application No. 4-1200
No. 5) and accurately form a cross section as specified. For this reason, there are very few molding defects at the front and rear ends of the formed steel pipe, and the yield is good.

(C) The standard-section steel pipe cooled to about room temperature is then loaded into a straightening roll machine (or straightening press machine), where straightening such as large bending and twisting occurring in the longitudinal axis direction is straightened. Apply some processing for (D) In the second forming roll step, the steel pipe section is roughly formed into a rectangular shape by cold plastic working in advance, so that a small amount of processing is required until a standard rectangular cross section is obtained. (E) Further, because of hot plastic deformation, the radius of curvature of the corner R can be formed smaller than the standard value without increasing residual stress in the material again and without considering the decrease in toughness. .

In short, the total amount of processing at the stage of forming a rolled steel strip into a round steel pipe by cold forming and then forming the round steel pipe into a square steel pipe is substantially heat-treated or subjected to hot plastic working. Therefore, there is no deterioration of the mechanical properties of the steel material due to the deformation of the steel sheet. (A) In addition, in the same forming step, the amount of hot plastic working is smaller than that in which all steps of the square forming roll device are applied to hot plastic working, so that extra labor is required for forming roll maintenance. No need to spend. (B) The efficiency of maintenance / maintenance can be enhanced by providing the second forming roll device in which the roll peripheral surface is relatively easily damaged so as to be able to be replaced and mounted collectively as a set. (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-section steel pipe is separated from the forming roll device and immediately carried into the cooling device before the heating temperature is lowered, where it is cooled as much as possible to around room temperature as uniformly as possible. . The cooling device is generally naturally cooled, for example, by blowing cooling air from around the transport steel pipe, or by installing a mechanism to spray mist,
The rectangular steel pipe having a temperature of 200 ° C. or less may be provided with a forced cooling means for the rectangular steel pipe, such as spraying cooling water as necessary. The sum of the strains generated in the steel pipe after cooling by the thermal stress based on the above-mentioned hot working, heat treatment and the like does not exceed a negligible level. In addition, the cooling speed is controlled and adjusted to allow such distortion, thereby saving the space of the apparatus.

A sufficiently cooled section of the steel pipe having a cross section at the front and rear ends is cut off to form a product having a shape conforming to the standard length. However, it is natural that the product is shipped to the market after the inspection of the welded portion of the steel pipe by a flaw detector through a process such as a straightening machine. by this,
The corner R part can be formed sharply without deteriorating the steel pipe material and without deteriorating the toughness of the steel material, and it is easy to use and creates a good-looking product. Obtain a large steel pipe.

The method and apparatus according to the present invention are characterized in that after the first forming roll step of continuously forming a round steel pipe formed from a rolled steel strip into a rough rectangular section by cold plastic working, the rough formed steel pipe is cut into unit lengths. to, by performing a heating and heat treated to near a ₃ transformation point of overall steel of the same steel, to remove residual stress of the resulting steel pipe due plastic working and butt welding of the previous step, the corner R part steel On the other hand, in the second forming roll step, the steel pipe is formed into a standard cross-sectional shape at a high temperature that does not fall below the A ₁ transformation point of the steel sheet as much as possible by substantially hot plastic working, A uniform, high-quality, large-diameter rectangular steel pipe forming method that improves the toughness of the steel pipe material caused by bending the four corners R of the steel pipe to approximately 90 °, work hardening of the steel pipe, and material deterioration such as residual stress. When you provide Both have developed equipment that is economically excellent.

Therefore, according to the method and apparatus of the present invention,
It is possible to improve the defect of material deterioration at the corner R of the steel pipe due to plastic deformation at the corner of the large-diameter rectangular steel pipe, which has been regarded as a problem in recent years, within a range that does not hinder practical use. In addition, the method according to the present invention has a higher productivity and is substantially heat-treated for steel pipe steel, compared with the case where an annealing furnace using a fossil fuel as a heat source is installed in an off-line as in the conventional method. Has little effect on cost. In addition, the equipment space is smaller than the heating furnace in the conventional method installed in-line, and there is room for improvement of existing equipment, and it is excellent in terms of controlling the heating temperature of steel materials and uniform heating, Further, since the forming process can be performed with high accuracy, the method and apparatus of the present invention can eventually produce a high-quality and uniform large-diameter rectangular steel pipe.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention and a production line of a large-diameter rectangular steel pipe for carrying out the same will be described below with reference to the drawings. The structure can be arbitrarily modified by those skilled in the art without departing from the scope of the technology known in the art at the time of the filing of the present application. Therefore, it is not permissible to interpret the gist of the method and apparatus of the present invention in a limited manner.

FIG. 1 is a schematic block diagram showing an embodiment of the method of the present invention and an apparatus for forming a large-diameter rectangular steel pipe for implementing the method of the present invention. FIG. 2 is a thick steel sheet corresponding to each step of the apparatus. This shows the state of forming and processing the belt. In the figure, 1 is an uncoiler linearly along the material conveyance direction,
The coil-shaped thick steel strip 11 is unwound, applied to leveling, and continuously corrected for winding distortion to form the flat strip steel sheet 12. Reference numeral 2 denotes a steel sheet width determining device which cuts both sides of the flat strip steel sheet 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. Then, it is formed into an electric resistance welded steel pipe 13 having a round cross section by cold plastic working. The round steel pipe 13 had a diameter of 637 mm and a plate thickness of 16 mm. 5 is a cooling zone for cooling the heating of the steel pipe by welding and returning the steel pipe to a uniform constant temperature, which is provided with an external bead cutting machine, a pull-out roll, and the like. A round steel pipe is continuously charged therein, and the cross section of the steel pipe is sequentially deformed from a round cross section to a roughly approximated square cross section by cold plastic working.

The cross section of the roughly formed steel pipe 14 formed through the first square forming roll process has a substantially thread-shaped outwardly convex shape with a corner R formed therein. The relative positions of the R part and the butt weld joint (seam line) of the steel material are determined. In short, by the cold plastic working, a part of the square forming process is borne, and the basic forming of the sectional shape of the steel pipe of the final square product is completed. 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, which allocates a considerable area here, receives and accumulates the cut unit length steel pipes 14, and conveys them, respectively, and conveys each unit length steel pipe to the heating device in the next process. .

Numeral 20 denotes a heating device (furnace), which in this embodiment is constituted by a heating furnace using a fossil fuel made of gas or liquid fuel as a heat source. Before passing through the same device, the steel pipe is heated to a substantially uniform temperature on the inner and outer surfaces of the steel material in the longitudinal axis direction and in the cross section perpendicular to the longitudinal direction of the steel pipe. Although it depends on the temperature at which there is no residual stress during molding and the toughness of the steel near the corner R can be improved, the material of the square steel pipe, the outer diameter and the plate thickness, it is approximately 900 ° C.
Heated to about 1050 ° C.

Depending on the thickness of the steel pipe and the capacity of the heating device (furnace) with respect to the conveying speed, heating at a higher temperature is more effective for work hardening of the steel material during cold plastic working, removal of residual stress, and improvement of toughness. However, the degree of skin roughness (mil scale) with respect to the steel material surface can be maintained better by heating at a lower temperature. Also, heat treatment costs can be reduced.

Reference numeral 21 denotes a second square forming roll device, which includes a finish forming roll step and is hot plastic working, and the constituent steps thereof are substantially composed of three to six steps. (Degree) accounts for approximately 70 to 95% of the total processing amount of the square, passes through the pinch roll and the second square forming roll process, and has a square cross section as specified.

The rough forming unit long 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. Is performed, and the material is not deteriorated based on the corner forming shape. Since the heat energy from the heated steel pipe 15 is constantly transmitted and radiated to the forming roll used in this step, a cooling means for the roll and the like must be provided. In addition, since the roll member in the process is liable to cause roll flaws and the like and the service life thereof is relatively short, a structure in which the roll exchange operation, the adjustment operation, and the like can be easily managed, for example, a second forming roll device uses a crane Equipment that can be replaced at one time.

Reference numeral 22 denotes a cooling device for the standard-shaped section steel pipe 15,
In the cooling zone, it is required that the steel pipe 15 carried in is cooled substantially and uniformly in the same cross section and substantially uniformly in the longitudinal axis direction. In the same cooling zone, even if the non-uniform temperature distribution deviates from the heat control of the hot forming and cooling device, bending of the steel pipe in the axial direction, distortion of the cross-sectional shape, dent in the sheet thickness direction, distortion, etc. will occur. The size may be considered insignificant. The cooling speed of the unit length steel pipe 15 in the cooling device 22 is substantially
On the premise that the above-described deformation of the steel material is allowed, the temperature of the steel pipe is eventually cooled to approximately the room temperature. At this stage, the steel pipe material maintains the toughness close to that of the base material as a whole, and keeps 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 is uniformly and sharply formed without deteriorating the corner material. (2 to 2.5) × t. Where R = outer radius of curvature, t = thickness of steel pipe material

Reference numeral 23 denotes a machine for correcting a distortion such as a large bend or torsion of the standard rectangular steel pipe 16 in the longitudinal axis direction, a welded joint, and a flaw detector for ultrasonic inspection of other parts. Numeral 24 denotes a both-end cutting machine, which cuts the defective cross-section portions at both ends of the unit-length standard cross-section steel pipe 15 caused by the second forming roll processing to obtain a standard rectangular steel pipe (product) 16. Reference numeral 25 denotes a product carry-out table, which accommodates and stores the standard-length steel pipe 16.

In FIG. 2, reference numeral 11 denotes a hot-rolled steel strip, 12 denotes a thick steel strip constituting a plane, 13 denotes a round steel pipe, and 14 denotes a rough forming cold-worked by a first square forming roll. The steel pipe 15 is a standard-section steel pipe hot-plastically 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 thickness of the steel sheet that can be processed by the method and apparatus of the present embodiment is 9
The outer diameter of the square steel pipe is about 200 mm to 600 mm, which is about 28 mm. As described above, in the present embodiment,
The details of the other functions and effects are the same as those described in the section of (function) described above, and thus will not be described.

[0039]

The method and apparatus of the present invention are as described above. (1) Processing of a thick steel pipe material which is regarded as a problem in a conventional large-diameter rectangular steel pipe formed by cold plastic working. Hardening and deterioration of toughness of the corner R portion can be improved, and residual stress generated in the steel material can be reduced to an allowable value or less, and a high-quality large-diameter rectangular steel pipe can be formed as a whole. (2) The corner R portion is formed as sharply as possible without deteriorating the material, and a square steel tube is formed, each of which is uniform, to improve the usability and improve the appearance of the product. Using the same steel material, we will provide more durable, high commercial value, and high quality steel pipes.

(3) Since the round steel pipe is initially (preliminarily) formed by cold working to determine the positions of the corner R and the seam line on the cross section of the square steel pipe, the round cross section is hot formed. Regardless, the position of the seam line on the product can always be kept constant (near the center of a flat surface on one side). (4) In forming the square roll, the length of the defective section at both ends of the steel pipe is extremely small, and the yield is improved. (5) In addition, each of the effects described in the above section (action) is exhibited. For example, special functions and effects that cannot be expected from conventionally known methods and apparatuses are exhibited.

[Brief description of the drawings]

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

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 uncoiler 2 steel strip width determining device 3 round steel tube forming roll (cold) 4 high frequency welding device 5 cooling zone 6 first square forming roll device (cold) 7 running cutting device 8 deposit space 11 hot rolled steel strip 12 Thick strip steel plate 13 ERW round steel pipe 14 Rough-formed rectangular steel pipe 15 Unit rectangular steel pipe 16 Product 20 Heating device 21 Second square forming roll device (hot) 22 Cooling device 23 Strain straightening machine, flaw detector 24 Both ends cutting machine 25 Product delivery table.

──────────────────────────────────────────────────続 き Continued on the front page (73) Patent holder 598134835 Shin Nakajima 4-26-27 Kichijoji Honmachi, Musashino City, Tokyo (72) Inventor Taku Nakajima 3-70 Midorigaoka, Itami City, Hyogo Prefecture (56) References JP JP-A-61-115614 (JP, A) JP-A-1-266913 (JP, A) JP-A-3-97810 (JP, A) JP-A-3-151117 (JP, A) (58) Fields investigated (Int .Cl. ⁶ , DB name) B21C 37/15

Claims (2)

(57) [Claims] 1. A round steel pipe formed by forming a steel strip or a steel sheet into a round shape with a cross section perpendicular to the longitudinal axis direction, and butt-welding both side edge joints thereof sequentially to a square steel pipe forming roll device comprising a plurality of stages. Then, in the step of sequentially forming the 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 pipe is formed into a coarse angle. A step of cutting the coarsely formed steel pipe into a unit length, a heating device for heating the unit length coarsely formed steel pipe disposed between the first forming step and the second forming step, and inserting the united steel pipe into the heating apparatus. After uniformly heating to a predetermined temperature, the high-temperature unit-length coarsely formed steel pipe is carried into a second forming step including a plurality of steps including a finish forming roll and subjected to hot plastic working, and has at least a cross section as specified. Formed square steel pipe Forming and then installing a cooling device for uniformly cooling the steel pipe with the specified cross section, gradually cooling or forcibly cooling the steel pipe, and then correcting a distortion such as a large bending in the longitudinal axis direction and a twist. Large diameter square steel pipe production 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 butt-welding both side edge joints thereof sequentially. A first square forming 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 square forming roll device for each unit length, and a predetermined temperature for the unit length roughly formed steel tube. A plurality of stages including a heating device for evenly heating the steel tube inserted from the heating device, a finish forming roll for forming the steel tube cross-section into a rectangular cross-section according to a standard by inserting the high-temperature unit-length roughly-formed steel pipe, and performing hot plastic working. A large-diameter rectangular steel pipe manufacturing apparatus including hot forming comprising a second square forming roll device, a cooling device for uniformly cooling the steel pipe having the specified cross section, and a device for correcting distortion such as large bending and twisting in the longitudinal axis direction. .