JP2849595B2 - Forming method and equipment for large diameter 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 thermal two-stage forming method for a large-diameter rectangular steel pipe and an apparatus therefor. More specifically, the present invention relates to a method of cooling a strip steel sheet or a single-plate steel sheet in parallel with its longitudinal direction. After being bent by inter-plastic working and forming a large-diameter round steel pipe by butt-welding both side edges of the seam, the steel pipe is successively charged into a heating device and uniformly heated to a predetermined temperature. In the step of conveying to a square forming roll device consisting of a plurality of stages and sequentially forming a cross section into a square shape, the square forming roll device is divided into a hot forming step and a cold forming step, and by the end of the hot forming step In addition to completing most of the square steel pipe forming process, it removes and hardens steel work hardening and material deterioration due to cold plastic deformation previously applied to steel, and other factors.
In addition, while preventing the material deterioration of the steel material due to plastic deformation applied during hot, in the cold forming step, the steel pipe cross section is formed to a standard to achieve work hardening of the steel material, and the heating and cooling processes are performed. Deformation such as distortion, torsion, bending, etc. of the steel pipe due to uneven temperature distribution in the inside was corrected.Especially, the deterioration of the toughness of the local material due to the processing distortion of the corner of the steel pipe was improved, and almost all residual stress was generated The present invention relates to a thermal two-stage forming method and apparatus for producing uniform, high-quality, thick-walled, large-diameter rectangular steel pipes that are not required.

[0002]

2. Description of the Related Art A mass production method for a thick-walled, large-diameter rectangular steel pipe, which has been growing in demand as a column of a steel structure, has conventionally been carried out generally by the following method. The hot-rolled coil is hung on a leveler to make a flat steel strip, and the width of both side edges is determined. The strip steel sheet is transported in series through processing steps such as breakdown, cluster, and fin pass stand, during which, the steel sheet is sequentially cold-plastically deformed to form a right-angle cross section into a shape close to a circle, or After cold-plastically deforming a single-sheet steel plate by UO press forming to form a shape close to a circle,

[0003] The seam is welded using a high frequency welding method or an electric arc welding method to form a round steel pipe. After gradually cooling the welding heat of the round steel pipe, the cross section of the steel pipe is deformed into a square shape by cold working such as a sizer, a squaring stand, and a turks head to form a large-diameter square steel pipe. In the above-mentioned known forming method, in any case, a flat or circular curved thick steel plate is formed by cold plastic working using a forming roll or the like for forming a steel pipe corner portion,
In general, a 90 ° bending step is included. In addition, the cold 90 ° bending process for a thick steel plate is performed not only in the forming method by the roll forming described above, but also in a case where the steel plate is bent by a press process to form a square steel pipe directly from a flat steel plate. .

[0004] When a thick steel plate is coldly bent by approximately 90 °, a tensile force is applied to the outer member of the corner portion at the boundary of the neutral surface in the cross section of the steel plate.
Since the inner member is deformed while a compressive force acts, plastic deformation proceeds in spite of applying the required radius to the portion, and distortion hardening occurs at the deformed portion, particularly at the corner member, resulting in mechanical deformation. Conditions are provided for deteriorating the characteristics and causing brittle fracture in the portion. For example, due to the strain hardening of the material based on cold bending, a decrease in toughness, a high residual stress, etc., the steel plate is subjected to welding cracks at the time of low temperature in winter and hot-dip galvanizing. Cracking at the time may occur. In addition, the existence of these cracks,
When a heavy load is applied in a low-temperature use of a thick steel plate based on micro defects in the base material, brittle fracture may occur in the steel plate.

[0005] Generally, steel structures, buildings, and the like using this kind of large-diameter rectangular steel pipe as a column material, once constructed,
It is necessary to not only support the own weight and the weight attached to the structure without distortion for a long time, but also to withstand severe repeated loads caused by external forces such as earthquakes and typhoons. In many cases, construction is performed in a state where replacement or repair is not possible. Particularly, in recent buildings, high-rise buildings occupy the mainstream, and the weight of equipment attached to the building increases, such as installing a cooling and heating device in each room, installing OA equipment and computers, and the like. Due to the tendency, the case of adopting thick-walled large-diameter rectangular steel pipe as a column material tends to increase more and more, so the problem of the above-described deterioration of the material of the cold-formed thick-walled steel pipe is increasingly ignored. You can't do that.

In view of such circumstances, deterioration of the material due to cold plastic working of a thick steel plate at the time of forming a steel pipe is regarded as a problem again. Therefore, recently, there has been a demand from a group of consumers to provide a high-quality square steel pipe having a corner portion steel material having sufficient toughness and low residual stress. To solve this kind of material problem inherent in cold-formed thick-walled large-diameter rectangular steel pipes, manufacturers have traditionally used ready-made round steel pipes and seamless pipes to replace fossil fuels such as oil and gas. Or heating using electric energy as a heat source,
It has been proposed that the cross section be processed into a square by hot plastic forming through a plurality of stages of square forming rolls. When the above method is used, the quality of the product is good, but at the time of cross-section molding, both ends of the steel pipe are greatly deformed with respect to the center, so that the yield of the material is poor, or when heating and cooling, uneven heat distortion occurs. However, there is a problem that productivity cannot be reduced because steel pipes are processed one by one. Also,
Since the entire steel pipe is heated at a high temperature, the annealing cost is high.

[0007] Separately, a method is also known in which a molded large-diameter rectangular steel pipe is placed in an annealing furnace, and the steel is heated as a whole until the residual stress of the steel is substantially removed, toughness is improved, and then gradually cooled. . In this case as well, there may be similar problems as described above. Alternatively, the hot-rolled coil is hung on a leveler to form a steel strip, passed through a forming roll stand and electric arc welding, a high-frequency welding device, etc., formed into a round steel pipe by cold plastic working, and then the steel pipe is in-line energy,
After heating using fossil fuels such as gas or oil, and hot forming the cross section of the steel pipe through a multi-stage square forming roll device,
Slow cooling to produce large-diameter rectangular steel pipe (Japanese Patent Application No. 2-1804)
No. 97).

[0008] The above-mentioned method has a problem in that the formed section is defective due to thermal unevenness during heating of the steel pipe, and in particular, deformation of the steel pipe due to uneven temperature distribution during cooling. Temperature control is indispensable, and it is necessary to take a sufficiently long cooling zone and gradually cool the steel pipe. Furthermore, unlike a round steel pipe, even if an attempt is made to uniformly cool the formed steel pipe, in the case of a square steel pipe, during cooling, the hot air flow of the refrigerant gas is disturbed at the corners of the pipe, and it is difficult to cool this uniformly. Then, once the steel pipe is deformed, it is difficult to correct the deformation in the case of a square steel pipe. In addition, when a heating furnace using fossil fuels such as gas and oil is installed in the production line, the forming speed of the steel pipe is high. for because welding speed is required), to heat the steel tube to a ₃ transformation temperature of the steel internal stress of the steel pipe is completely eliminated, a heating furnace length of 200 m~300 m in the middle of the line Space for installation is required, and the production line becomes too long, making it difficult to select location conditions.
Capital expenditures may increase more than expected.

In addition, when a round steel pipe is heated by fossil fuels such as gas and oil, it is difficult to uniformly heat the steel material because a heat source cannot be put inside the steel pipe.
There is a problem in the temperature control, and this is related to forming defects and distortion of the steel pipe cross section, so that a product of uniform quality may not be obtained after all. On the other hand, a heating device using electric energy has the advantage of requiring only a small space for heating and capable of thoroughly controlling the uniform heating of the steel pipe and the heating temperature, but requires an extremely large-capacity device and requires a high power cost. In addition, it may be difficult to obtain the required large capacity power depending on the location conditions. It is known that there are technical problems.

[0010]

SUMMARY OF THE INVENTION The method of the present invention has been developed in view of the above-mentioned circumstances, and improves the toughness of steel pipe corner members, reduces the residual stress to below an allowable limit, and reduces the steel material. It is an object of the present invention to provide a method and an apparatus for manufacturing a uniform and stabilized high-quality large-diameter rectangular steel pipe. Another object of the method of the present invention is
Using a known in-line installed steel tube heating furnace,
It is an object of the present invention to develop a new thermal two-stage forming method and apparatus that solves the above-mentioned problems inherent in the method and apparatus for forming a square steel pipe made of a uniform steel material.

[0011]

SUMMARY OF THE INVENTION The present invention has the following components in order to achieve the above object. (1) A round steel pipe formed by forming a strip steel plate or a single-plate steel plate into a cylindrical shape through a forming roll and welding a seam is uniformly heated to a predetermined temperature, and is formed of a plurality of stages before the temperature is lowered. In a method of sequentially forming the steel pipe cross-sectional shape into a square shape by hanging on a square forming roll, the square forming roll process including a plurality of stages is divided into a hot (including warm) forming process and a cold forming process. At the same time, a steel pipe cooling zone is provided between the two steps.
% Of a square steel pipe approximated to a square steel pipe, and then uniformly cooling the whole of the half-formed steel pipe to a temperature around room temperature, and performing the remaining processing amount by a cold forming process to form a square steel pipe. A large diameter square steel pipe forming method characterized by the following.

(2) A round steel pipe forming apparatus for forming a strip steel sheet or a single sheet steel sheet into a cylindrical shape through forming rolls and welding seams, a heating furnace for uniformly heating the entire round steel pipe to a predetermined temperature, A square steel tube forming roll device, the square steel tube forming roll device comprising at least a hot (including warm) forming step and a cold forming step; In the middle of
A device installed between the hot-forming step and the cold-forming step, comprising a device for uniformly cooling the entire steel pipe to a temperature near room temperature, wherein the apparatus including the hot-forming step converts the round steel pipe section into a square steel pipe section. An apparatus including a cold-forming step, while applying approximately 70 to 80% of the total processing amount to form a shape to a semi-formed steel pipe having an approximate cross section of a rectangular steel pipe, performs the remaining processing amount on the semi-formed steel pipe. An apparatus for forming a large-diameter rectangular steel pipe having a rectangular cross section.

[0013]

[Function] The material defects that have been regarded as problems with large-diameter rectangular steel pipes on the market are the reduction in toughness of the corner members of thick steel pipes due to the cold plastic deformation during the steel pipe forming process, and the existence of residual stress. And weakening of structural materials due to deterioration of local member quality. (1) In view of the above-mentioned circumstances, in the present invention, after forming a round steel pipe, the whole round steel pipe is heat-treated before being sent to the horn forming roll process, so that the A ₁ transformation point or the A ₃ transformation is performed. By uniformly heating to near the point, the residual stress, welding distortion, etc. of the steel material caused by the previously applied cold plastic working are removed. Since the round steel pipe is made of a large-diameter thick steel plate and has a large heat capacity, the heating temperature is still maintained at the time when the heated steel pipe is charged into the forming roll process.

By inserting the heated steel pipe into a forming roll process before the temperature of the steel pipe does not decrease, the subsequent steps can be made into plastic working substantially equivalent to hot forming.
Avoid deterioration of local member quality and increase in residual stress due to bending (close to 90 °) of thick steel plate, and reduce the amount of processing at this stage to 70% of the total processing amount for forming round steel pipe cross-sections into square steel pipe cross-sections. Approximately 80%, the right-angled cross-sectional shape is formed into a semi-formed steel pipe with a square approximate cross-section that leaves a small amount of processing (degree) compared to the cross-sectional shape of the final product. After cooling to the temperature of

[0015] The semi-formed steel pipe is carried into a cold forming roll process, and a small amount of remaining processing is formed by cold plastic deformation to obtain a square steel pipe having a standard sectional shape. In addition, while correcting deformation such as distortion, torsion, and bending generated in the steel pipe based on uneven temperature distribution during hot forming and heating and cooling in the previous process, the steel material softened by heat treatment Causes work hardening and improves mechanical properties, especially yield strength.

(2) By this, the step of forming the round steel pipe section into a square approximate cross section is as follows:
By applying under heating and substantially hot plastic working of the steel material, the residual stress of the steel sheet material including the corner of the steel pipe is reduced, the toughness is improved, welding distortion is eliminated, etc. In order to improve the material quality of the steel sheet, the adverse effects due to mechanical deformation applied to the steel sheet in the cold process in the earlier process are reduced. Through the heating, hot plastic working and (forced) cooling steps, the sum of various strains generated in the semi-formed steel pipe is approximately
Several% of the total processing volume for forming round steel pipe from round steel pipe
(For example, 5%). The semi-formed steel pipe cooled to around normal temperature is charged into the cold forming roll process, and the remaining 20 to 30% of the square forming shape is subjected to cold plastic working to make the steel pipe cross section as specified. Form into shape.

At this time, the distortion or the like caused by the heat treatment or the like occurring in the semi-formed steel pipe can be automatically corrected by the cold working deformation. A small amount of cold working deformation causes a certain degree of work hardening in the steel pipe material, and strengthens the steel material softened by the heat treatment. By the above-described molding, the steel pipe corner can be formed sharply without deterioration of the material of the steel pipe corner, and the residual stress is small, and the usability of the steel pipe is improved, and the appearance is improved. When steel is used, the commercial value is increased, for example, by increasing the section modulus. The hot forming roll process and the cold forming roll process requiring only a small amount of processing can reduce the roll driving power of the forming apparatus.

In the present invention, the same processing and processing as in the case of a continuous round steel pipe can be performed by successively tack-welding and connecting the end face of a pre-made round steel pipe having a standard length in the longitudinal axis direction thereof. After the necessary processing and forming, the front connection joint portion can be cut into a rectangular steel pipe as a unit. In any case, heating the steel pipe removes the residual stress of the steel pipe corner steel based on the machining previously applied to the steel sheet in the cold, improves the toughness of the local material, and then heats the pipe as it is. It is possible to obtain a semi-formed steel pipe which maintains sufficient toughness and has no residual stress, and then cools down to about room temperature once. By performing the additional processing of the amount, the distortion generated in the square steel pipe is corrected, and the mechanical properties, that is, the yield strength is improved, so that a uniform, high-quality large-diameter square steel pipe can be obtained. .

[0019] (3) The present invention method, the apparatus is than the entire steel pipe only combustion heating of fossil fuels to heat up A ₃ transformation point, it becomes necessary to lengthy furnace equipment as described above,
Since it may be difficult to select the location conditions of the production line, it is necessary to pay attention to slightly higher equipment costs and operating costs. In-line high-frequency heating equipment capable of accurate heating and control.

However, it is difficult to employ so-called combined heating means, which uses a heating apparatus which uses fossil fuel, which is easily available in large quantities and is relatively inexpensive, in combination with a high-frequency heating apparatus, as a heating means for steel pipes. Absent. However, even in this case, at least in the cross section perpendicular to the longitudinal axis direction of the steel pipe, the entire steel pipe peripheral wall and the inside and outside of the steel pipe must be able to be heated to a uniform temperature. In the method of the present invention, if a combined heating means of a heating device using electric power and a heating furnace using fossil fuel is provided, the heat treatment cost can be relatively reduced, and thereby the space for the heating facility can be increased. Therefore, advantages such as relatively easy selection of location conditions can be obtained. When it is difficult to install a large-capacity high-frequency heating device as a heating means for the steel pipe, a difference may be provided in the speed between the round steel pipe forming step and the steel pipe peripheral wall heating step.
In other words, a large-capacity high-frequency heating device is required as a heating means for the steel pipe because it satisfies the characteristics of the high-frequency welding device at the time of forming a round steel pipe. Therefore, the speed of the welding device and the speed of the heating means must be separated. For example, the capacity of the high-frequency heating device can be reduced to some extent separately from that of the welding device. As a result, even if the processing efficiency is inevitably reduced slightly, it is possible to greatly reduce the capital investment amount as a whole.

Further, in order to make the corner portion and the flat portion of the formed rectangular steel pipe have the same mechanical properties, the rounded corner of the round steel pipe is heated in a selected step in the heating step so that the bending plastic working amount is increased. It is also possible to increase the heating temperature of the corner portion where the temperature is large, to save energy in the overall heating and to improve the productivity. To cool the semi-formed steel pipe, use natural cooling and forced cooling together, or spray and discharge water evenly from the direction perpendicular to the transport steel pipe peripheral wall to cool the steel pipe peripheral wall as uniformly as possible. , Preventing the occurrence of distortion and shortening the steel pipe cooling zone. Here, the temperature of the steel pipe in the cooling device does not necessarily need to be correctly lowered to room temperature. In addition, by allowing a slight heat treatment distortion to occur in the cooling steel pipe, the cooling speed can be increased accordingly, and the space in the cooling zone can be reduced. In the same device, the steel pipe cooled to around room temperature does not generate distortion, bending, twisting, etc., even when cooled by cooling water.

(4) In short, according to the method of the present invention, work hardening, residual stress and material deterioration of the corner material of the steel pipe caused by bending the steel plate at the four locations on the steel pipe peripheral wall by approximately 90 ° are practically supported. It is removed and improved to an insignificant degree, and the semi-formed steel pipe material is, on the whole, uniformly uniform and stabilized.
Or, the deterioration of the corner member quality is almost negligible.
Therefore, according to the method and apparatus of the present invention, defects such as deterioration of the material of a steel pipe corner portion due to plastic deformation at the corner portion of a large-diameter rectangular steel pipe which has been regarded as a problem these days, and existence of large residual stress are completely removed. be able to.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method of the present invention and a production line of a large-diameter rectangular steel pipe for carrying out the method will be described below with reference to the drawings. Since the structure can be arbitrarily partially modified within the range of known technology in the art at the time of the filing of the present application, the present invention can be implemented based on only the specific structure described in the present embodiment without any special reason. It is not permissible to restrictively interpret the constituent elements of the invention method.

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 plate corresponding to each step of the apparatus. 1 shows the molding state of the molding. In the drawing, 1 linearly rewinds the coiled thick steel plate 11 with an uncoiler, applies it to leveling and continuously corrects the winding distortion, and straightens the flat steel plate 12 along the material conveying direction. Molding.
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 and forms the sheet into a required width.

Numeral 3 is a round steel tube 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 is formed into an ERW steel pipe 14 having a round cross section. Before passing through the high-frequency induction heating device, the ERW steel pipe 14 is shaped and placed so that its cross section becomes a perfect circle. The round steel pipe 14 had a diameter of 565 mm and a plate thickness of 22 mm. Reference numeral 5 denotes a heating device, which is a high-frequency induction heating device in the present embodiment, and sequentially heats steel materials in a section of a steel pipe passing through the device so as to have a substantially uniform temperature distribution. The heating temperature in the final stage can be in the range of 450 ° C. to 1050 ° C. depending on the material of the steel material.

When the above-mentioned device is a high-frequency induction heating device, if the distance between the heating coil and the surface of the steel pipe is not the same in all circumferential directions of the steel pipe, the entire circumference of the steel pipe can be heated to a uniform temperature. Because of the difficulty, the round section of the steel pipe must be shaped and placed in a perfect circle before loading the steel pipe into the heating device. Depending on the length of heating time for steel materials, higher temperature heating is more effective at removing the residual stress and improving the toughness at the Kawaguchi port of the steel material due to cold plastic deformation, but the following hot cross-section The formation of the shape is easier when the temperature is slightly lower, and the degree of skin roughness on the surface of the steel material can be better maintained by heating at a lower temperature. Also, heat treatment costs can be reduced.

If the power capacity to be supplied to the high-frequency induction heating device cannot be obtained by the required amount, a composite heating means using fossil fuel may be employed. , Post heating, square tube forming process and
By providing a difference between the speed of the cooling step and the subsequent steps, the capacity of the high-frequency induction heating device can be reduced to a level that can be installed, by releasing the subsequent steps from the constraint of the ERW tube forming speed. Reference numeral 6 denotes a hot-angle forming roll, the constituent stages of which are, for example, from a round steel tube to a final forming stage from a round steel tube to a square steel tube, that is, when the entire forming process is composed of five stages, three of them are provided. (If the entire forming process is composed of ten steps, it is composed of six steps.) The amount of processing (degree) on the steel pipe in the same roll process is passed through the hot forming roll. The cross-sectional shape of the semi-formed steel pipe 16 is approximately 20 to 30 compared to the cross-section of the final product 20.
% Processing amount is left. That is, about 70 to 80% of the processing amount of forming from the round steel pipe cross section to the square steel pipe cross section is performed by the hot plastic working.

The round steel pipe 14 carried into the hot forming step has been heated and refined in the previous step, and is put on a forming roll at a high temperature. There is no deterioration of the material due to molding. In this roll forming process, hot plastic working is performed on the steel pipe, so that the driving power is smaller than the amount of working. Since the heat energy from the heated steel pipe is constantly transmitted to the forming roll in this step, cooling means for the roll and the like must be provided. In addition, the roll member used in the process is likely to have roll flaws and the like, and has a relatively short service life.

Numeral 7 is a cooling device for the steel pipe, and it is required to cool the semi-formed steel pipe processed in this zone substantially and evenly in the same cross section in the longitudinal direction in order. . In the same zone, due to the non-uniform temperature distribution deviating from the thermal control of hot forming and cooling equipment,
Even if the steel pipe is bent in the axial direction, distorted in cross-sectional shape, dented or distorted in the plate thickness direction, the size thereof may be regarded as about 5% or less of the entire processing amount. In addition, the cooling speed of the steel pipe in the cooling zone is based on the premise that the above-described deformation of the steel material is tolerated. After all, the temperature of the steel pipe is cooled substantially to near room temperature. At this stage,
As a whole, the steel pipe material maintains a toughness close to that of the base material and maintains a state where there is almost no residual stress.

Reference numeral 8 denotes a cold forming roll for steel pipe, which is composed of two stages (or three stages is also possible). Here, as described above, the processing amount for the cross section of the steel tube is approximately 20 to approximately.
It is about 30%. Of course, in this case, even if the processing amount exceeds or does not exceed 10%, this is not excluded. In short, it is necessary that the cold forming does not remarkably degrade the steel material, particularly the quality of the corner member again. By this cold working, the cross-sectional shape of the steel pipe is formed into a standard shape, and the portion is sharpened, for example, approximately to R <(2) without deteriorating the corner material.
~ 2.5) × t. However, R = outside radius of curvature, t = plate thickness of the steel pipe material, and corrects twisting, cross-sectional deformation and bending of the rectangular steel pipe caused by cooling. Although the amount of processing in the same step exceeds the amount of strain generation, the cold forming does not cause the deterioration of the steel pipe material again, and the amount of processing until such time is not required. Further, the mechanical strength, particularly the yield point strength, of the steel material softened by the heat treatment is increased.

Numeral 9 denotes a cutting machine, which is provided with a cutting mechanism during running, and moves the formed steel pipe to a specified length in the longitudinal axis direction while moving the milling in accordance with the conveying speed of the thick-walled large-diameter rectangular steel pipe to be continuously formed. Each product is cut to make a unit product 20.
Reference numeral 10 denotes a product carry-out table, which accommodates and stores the standard length steel pipe. If necessary, the product will be shipped to the market after conducting a flaw detection inspection and distortion correction inspection of welded joints and other parts of the square steel pipe.

In FIG. 2, 11 is a hot-rolled coil, 12 is a thick steel strip constituting a flat surface, 14 is a cross section of a round steel pipe, 16 is a square cross section steel pipe formed by hot plastic working, 18 is
The cross section of the final square steel pipe formed by cold working, and its size is, for example, 450 mm square. 20 indicates a product of the same type. As described above, the details of the other operations and effects in the present embodiment are as described in detail in the section of (operation) described above, and thus description thereof will be omitted.

[0033]

The method and apparatus according to 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. The hardening and the deterioration of the quality of each corner member, particularly the toughness, can be improved, and the residual stress generated in the local steel material can be reduced to an allowable level or less, and a large-diameter rectangular steel pipe of high quality can be formed as a whole. (2) By applying a small amount of cold forming at the final stage, a square steel pipe with sharp corners is formed as much as possible without deteriorating the material, making it easier to use. While improving the appearance of the same, using the same steel material,
Provide more durable, high commercial value and high quality steel pipes.

(3) The distortion generated in the semi-formed steel pipe is corrected and the steel material is work-hardened by a final cold working amount of about 20 to 30% to increase the mechanical strength. (4) In addition, the respective effects described in the above section (action) are exhibited. For example, a special function and effect that cannot be expected from conventionally known methods and apparatuses can be obtained.

[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]

 DESCRIPTION OF SYMBOLS 1 Uncoiler 2 Steel plate width determining device 3 Round steel tube forming roll 4 High frequency welding device 5 Heating device 6 Hot angle forming roll 7 Cooling device 8 Square cold forming roll 9 Cutting machine 10 Product delivery table 11 Hot rolled coil 12 Strip steel plate 14 Round steel pipe 16 Semi-formed square approximate steel pipe 18 Square formed steel pipe 20 products.

Continued on the front page (73) Patent holder 598134835 Shin Nakajima 4-26-27 Kichijoji Honmachi, Musashino City, Tokyo (72) Inventor Isao Nakajima 1-1-5 Higashi Toyonakacho, Toyonaka City, Osaka Prefecture (72) Inventor Taku Nakajima 3-70 Midorigaoka, Itami-shi, Hyogo (72) Inventor Norio Nakajima 12-26, Ogawa-cho, Fukuroi-shi, Shizuoka (72) Inventor Shin Nakajima 4-26-27, Kichijoji-Honmachi, Musashino-shi, Tokyo (56) References JP Akira 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 strip steel plate or a single-plate steel plate into a cylindrical shape through a forming roll and welding a seam to the steel tube is uniformly heated to a predetermined temperature. In the method of sequentially forming the cross-sectional shape of the steel pipe into a square shape by applying the same on a square forming roll formed of a plurality of steps, the step of forming the square forming roll comprising a plurality of stages is performed by hot (including warm).
Along with the two steps into a forming step and a cold forming step, a steel pipe cooling zone is provided between the two steps, and in the hot forming step, the total processing amount for forming the round steel pipe cross section into a square steel pipe cross sectional shape,
Form a semi-formed steel pipe similar to a square steel pipe with 70-80% applied,
Next, the entire semi-formed steel pipe is uniformly cooled to a temperature around room temperature, and the remaining processing amount is applied by a cold forming step.
A method for forming a large-diameter rectangular steel pipe, which comprises forming a rectangular steel pipe. 2. A round steel pipe forming apparatus for forming a strip steel sheet or a single sheet steel sheet into a cylindrical shape through a forming roll and welding a seam, a heating furnace for uniformly heating the entire round steel pipe to a predetermined temperature, and the steel pipe. A forming roll process comprising a plurality of stages for sequentially forming a cross section into a square is at least a square steel tube forming roll apparatus comprising a hot (including warm) forming step and a cold forming step; In the middle, it consists of a device installed between the hot forming process and the cold forming process, which uniformly cools the entire steel pipe to a temperature near normal temperature,
The apparatus including the hot forming step is capable of forming a semi-formed steel pipe having an approximate cross section of a square steel pipe by applying approximately 70 to 80% of the entire processing amount for forming a round steel pipe cross section into a square steel pipe cross section, and cold forming. An apparatus including a step is a device for forming a large-diameter rectangular steel pipe, wherein the semi-formed steel pipe is subjected to the remaining processing amount to form a square cross section.