JPH05309412A - Forming method for large diameter square steel tube - Google Patents

Abstract

PURPOSE:To make the radius of curvature in the radius part at the corner of a large diameter square steel tube small and also to form the large diameter square steel tube without deterioration of material in this part, with good accuracy of flatness of the flat surfaces on four sides of the steel tube and high yield from a round steel tube by hot rolling. CONSTITUTION:Grooves of respective forming rolls constituting a hot forming roll stand are successively changed from a round shape to an outward convex pincushion shape and a square shape as standards, also the groove of the forming roll 19 is closely brought into tight contact with the whole of outer peripheral wall of the steel tube by always making the entire inner circumferential length of the groove approximately coincide with the outer circumferential length of the formed steel tube and, besides reduction per one stage of forming roll is taken as 5 to 7mm, the temp. of the formed steel tube in the vicinity of the final stage of the forming roll 19 is taken as approximately 600 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method in which a cold-formed round steel pipe is uniformly heated to a constant high temperature, and then its cross section is passed through a forming roll stand consisting of a plurality of stages before the heating temperature of the steel pipe is lowered. The present invention relates to a method for forming a large-diameter rectangular steel pipe by hot working.

[0002]

2. Description of the Related Art One of the methods for forming a one-seam thick-walled large-diameter rectangular steel pipe on a commercial base and forming the same is the forming process including the following steps (see, for example, JP-A-4-71720). Is proposed.

FIG. 4 is a block diagram showing the above steps. In the figure, (1) 1 is a hot-rolled coil, and a steel strip constituting the coil is unwound by an uncoiler 2 and then leveled by a leveler. After being flattened, both ends are cut by a trimming knife or a cutter 3 and subjected to a width determining step,
It is continuously carried into the breakdown process. (2) The breakdown step comprises a round steel pipe forming roll device 4 having a plurality of stages, sequentially bends the right-angled cross section of the steel strip by each roll stand, and semi-forms a partially opened round cross section at the final stage. The round steel pipe 5 is formed.

(3) The semi-formed steel pipe is subjected to a fin pass roll and a squeeze roll to correct the misalignment of the abutting surfaces, and the high frequency resistance welding machine 6 resistance-welds the abutting portions to form a Seam ERW Round Steel Pipe 7
And cutting the build-up portion of the welded joint by a traveling cutting machine 8 that moves in synchronization with the transport speed of the steel pipe,
Cut every unit length. (4) The above unit long round steel pipes (or single products) are charged into a heating furnace 9 ′ in a singular or a plurality, and the deterioration of the steel pipe material caused by deformation due to cold plastic working is improved,
After uniformly heating to a temperature that can remove residual stress,
Before the heating temperature is lowered, each of the individual products is conveyed through a surface scale removing device to a square forming roll process including a plurality of forming rolls. The heating furnace 9 ′ may be a direct heating furnace or an indirect heating furnace that uses gas, liquid fuel, electric energy or the like as a heat source, and the steel pipes can be heated batchwise or continuously, and the steel tube can be discharged from the furnace. Before heating, heat evenly in the range of 970 ° -700 ° C.
It has been tempered.

(5) The heated steel pipe passes through a scale removing device and, before the temperature thereof drops to 650 ° C. or lower, a square-shaped roll stand consisting of a plurality of forming rolls is quickly formed.
It is carried into 10 ′, and in this process, the round-section steel pipes are sequentially deformed to be plastically hot-deformed into a rectangular-section steel pipe 11 having substantially the same circumference. The temperature of the rectangular steel pipe shaped through the final roll forming stage is about 600 ° C. Therefore, all the steps of forming a square section from a round steel pipe are processed at a high temperature to the extent that residual stress does not occur due to plastic deformation of the material. No deterioration or increase in residual stress occurs.

The above-described structure of the corner forming type roll stand 10 'has a small number of roll stages in the past, and the peripheral surface of the forming rolls forming each forming stage is cylindrical, and a pair of opposed roll rotating shafts are mutually opposed. Since they are held in parallel, the process of sequentially drawing the cross sections from the round steel pipe to the square cross-section steel pipe is shown in FIG. 2. In FIG. 2, the round steel pipe 7 is roll-formed by the conventional method,
It shows the process of sequentially narrowing down the cross-section until the cross-sectional shape is transformed into a square steel tube 11 according to the standard. In the case shown in the figure, for example, four-stage drawing is used, the material of the steel plate or steel strip is SS400, and the plate thickness. Is 22 mm and the outer diameter of the round steel pipe is 688 φmm.
The process of forming a square steel pipe in which the m and the corner radius R are 77 mm is displayed. Therefore, assuming that the forming allowances (forming amount) in each processing stage of the forming roll are evenly distributed, the drawing amount per one stage is 17.2 mm on one side. That is, the molding amount per one stage of the molding roll is relatively large and the molding action is rough.

The peripheral surface of each forming roll is cylindrical, and the forming roll is squeezed from the outside of the steel pipe having a circular cross section to the inside of the steel pipe so as to be circumscribed in the same arc. The contact pressure end curve a is discontinuous. That is, the ridge line p is formed. In the round steel pipe cross section, the arc portion that has traveled most on the x and y coordinate axes passing through the central axis, that is, the central arc portion is formed into the flat surface a by the first drawing process. The flat surface a is broadly formed as a → b → c on an arc each time it passes through a plurality of forming roll stages,
The rolls sequentially hit the outside of the arc. Then, as shown in FIG. 2, among the circumferential lengths of the circular cross section 7 which is deformed by the drawing process, the arcuate portion which is not regulated by the forming roll peripheral surface of any of the working stages is a rectangular steel pipe corner after forming. It is known that there exists the R part as the center. That is, the circular arc portion of the cross section of the round steel pipe occupying the position is free for any forming roll, and the forming is only an indirect deformation based on the flat surface forming process of the adjacent circular arc portion.

It is no wonder that the radii of curvature of the respective corners R of the square steel pipe after forming formed as described above are different from each other. That is, the radius of curvature of each corner R is uneven. Further, if the radius of curvature is made too small with respect to the steel plate thickness, the deterioration of the material of the local steel becomes more severe, which is not possible. Further, as described above, since the drawing amount per step is relatively large and there is an arc portion which is not regulated by the forming roll in the circumference of the cross section to be processed, the accuracy of the flat surface formed by the roll is Low. Accurate measurement reveals that irregularities of, for example, about 0.5 to 1.0 mm occur in the flat surface, and in particular, irregularities occur on the flat surface close to the corner R portion.

Since the cross-sectional shape near the front and rear ends of the formed rectangular steel pipe in the longitudinal axis direction is unstable, it is necessary to cut off both ends of the rectangular steel pipe by about 500 to 700 mm in the longitudinal axis direction in order to remove that portion. Therefore, the yield of the material is very poor. (6) As described above, the high-temperature large-diameter rectangular steel pipe 11 whose cross-section is formed through the hot forming roll process has a tubular body temperature of 600 °
While being kept inside or outside 650 ° C., it is carried out to a cooling zone region 12 ′ that is continuous to the roll forming process, and here, for example, cooling air is circulated or is gradually rotated around the longitudinal axis in the lateral direction. Cool it gently by moving it, etc. to prevent the distortion of steel products due to non-uniform cooling, and after the temperature of the steel pipe has dropped to around 500 ° C, perform natural cooling, spraying, or other cooling methods using water. It is also conceivable to enhance the cooling effect and save the substantial space of the cooling zone 12 '.

(7) The hot-formed large-diameter square steel pipe cooled to an extent that can be handled in this way is carried into a straightening machine 13 constituted by a press or roll 14 for each unit length steel pipe, and the strain in the longitudinal direction of the steel pipe is reduced. to correct. In that case, you may include the process of inspecting the quality of a welded joint of a steel pipe, the damage | wound of a base material, and other requirements which influence quality of a product. (8) As described above, the large-diameter rectangular steel pipe having a unit length that has undergone the steel pipe strain correction step 13 has an unstable cross-sectional shape near both end surfaces and cannot be marketed as it is as a product. So 500 ~ 700 each before and after the unit length steel pipe
It is cut in both ends to cut about 15 mm. (9) The unit length, large diameter, thick-walled rectangular steel pipe with the irregular portions at both ends cut is carried out to the product discharge (delivery) table 16.

[0011]

The large-diameter thick-walled square steel pipe manufactured by the above-mentioned hot roll forming method is inherent in the cold-roll-formed large-diameter square steel pipe which is currently on the market and installed in building structures. It is possible to solve all of the drawbacks described above and to satisfy most of the pending demands from the construction industry for this type of large-diameter square steel pipe. In addition, like the one mentioned above,

In the cross section of the rectangular steel pipe, the flatness of each flat surface forming the four sides is slightly poor. In a rectangular steel pipe cross section, the radius of curvature of each corner R portion is non-uniform, and it is difficult to reduce the radius of curvature with respect to the thickness of the steel plate. When the cross section of the unit length steel pipe is roll-formed into a square shape, the cross-sectional shape of the front and rear ends becomes unstable, and that portion is cut off, resulting in poor material yield. However, there is still room for improvement in terms of process in terms of improving product uniformity, improving quality, and improving material yield. Therefore, the method of the present invention provides a novel method for forming a steel pipe, which can eliminate all of the above problems while maintaining the advantages of hot roll forming in the manufacturing process of a rectangular steel pipe. It is intended.

[0013]

In order to achieve the above-mentioned object, the present invention has the following respective constitutional requirements (1) A round steel pipe is heated, and a steel pipe cross section is passed through a plurality of stages of forming rolls. A method of hot forming into a polygonal shape, wherein the roll hole die of each forming stage described above is sequentially transformed from a round shape to an outwardly convex bobbin shape, and is transformed into a square cross section having a corner R, and
The roll die in each forming stage presses the entire surface of the peripheral wall of the worked steel pipe with no gap, and at the same time,
The narrowing amount (one side) per step is in the range of 5 to 10 mm, and the square steel pipe forming temperature in the final forming step is 650 °.
A method for forming a large-diameter rectangular steel pipe, which is characterized by holding at about 700 ° C.

[0014]

FIG. 3 is a conceptual drawing of a hot forming method for carrying out the method of the present invention. In the figure, 17 is a product receiving floor, which is thick-wall cold-formed by a known method by the receiving floor. A round steel pipe obtained by cutting the round steel pipe into unit lengths is received and stored, and this is sequentially charged into the continuous heating furnace 9. 9 is a continuous heating furnace of unit length round steel pipe, using gas, liquid fuel or electric energy as a heat source, by direct or indirect heating,
The round steel pipes were loaded into the furnace and transported at approximately 900 °
Removal of residual stress generated by cold plastic working that was previously applied to the steel strip or steel sheet by heating to ~ 1050 ° C,
Improve material deterioration.

Reference numeral 18 denotes a descaling device for removing an oxide film and the like formed on the surface of the steel pipe based on the heating by the continuous heating furnace 9 to clean the surface of the heated round steel pipe and carrying it into the roll forming process. 10 is a hot roll forming stand, the stand is compared to the known rectangular steel pipe forming roll method,

Since the amount of reduction (deformation) per step is extremely small, for example, about 5 to 7 mm on one side, the number of forming steps inevitably increases in the process of forming the round steel pipe into a rectangular cross section. ing. It will be appreciated that under these conditions, a larger diameter steel pipe forming process will require more forming stages accordingly. Therefore, the unstable area of the rectangular cross section near both ends of the unit long rectangular steel pipe in the longitudinal axis becomes extremely small.For example, the unstable cross section is cut off by cutting off the front and rear ends by 20 to 50 mm in the longitudinal direction. Therefore, the yield of the material is greatly improved as compared with the conventional method. That is, the production cost can be reduced.

The hole forming die of the known square forming type roll does not restrain the entire surface of the steel pipe peripheral wall when forming the round steel pipe cross section (see FIG. 2), but the forming die of the forming roll of the present invention has a round steel pipe cross section. During the forming process, the round (deformed) steel pipe peripheral wall is entirely and completely restrained from the first stage to the final stage forming roll hole die. That is, the inner peripheral length of the roll hole die in the forming roll of any processing stage,
It is almost the same as the outer peripheral length of the formed steel pipe. More specifically, the cross section of the round steel pipe is sequentially formed by hot working as it passes through the square-shaped stand 10, through the outward convex winding shape, and is formed into a standard square cross section having a corner R portion. It

Therefore, at this time, since the radius of curvature of the corner R portion of the square steel pipe can also be restricted by the hole die of the forming roll, it is possible to regulate the radius of curvature of each corner R portion to be equal. it can. Therefore, the radius of curvature of the corner R portion of the formed rectangular steel pipe is extremely smaller than that of the conventional product with respect to the steel plate thickness t, without lowering the toughness of the steel plate material in the vicinity of the relevant portion or causing deterioration of the material properties. can do. That is, the section modulus of the square steel pipe can be increased by providing the sharp corner R portion, and the steel pipe cross section is formed by the work of restricting and narrowing down the entire peripheral wall without any gaps. It provides a rectangular steel pipe with improved flatness of the flat parts, which enhances the product value in terms of appearance, and is convenient for decoration of the outer wall of the steel pipe.

Since the temperature of the heated steel pipe when the formed rectangular steel pipe is carried out from the forming stand 10 is approximately 700 ° C. or less, all the roll forming of the steel pipe cross section before that requires the so-called hot working condition. Therefore, the internal stress is not newly generated based on the cross-sectional deformation, the residual stress is not increased, and the deterioration of the material is not adversely affected.

Referring again to FIG. 3, reference numeral 12 in the figure is a rectangular shape for accepting a high-temperature (for example, 700 ° C.) unit-length hot-forming large-diameter rectangular steel pipe carried out from the forming stand 10 and uniformly cooling it. A cooling bed (zone) for steel pipes. In this zone, to prevent distortion due to non-uniform thermal stress in the longitudinal direction of the long steel pipe, for example, cooling while rotating around the longitudinal axis, or cold air flow Must be passed along the longitudinal axis of the steel pipe, or conditions must be set such that heat is uniformly dissipated by radiation, conduction, and convection throughout the steel pipe including the longitudinal axis. Thus, the unit-length large-diameter rectangular steel pipe is gradually cooled while cooling on the cooling bed 12 while being transported in the direction perpendicular to its longitudinal axis, and is forcedly cooled by spraying when the temperature drops below approximately 500 ° C. By doing so, the space of the cooling bed used in the steel pipe cooling process can be reduced as much as possible. However, if there is a space, it may be a natural slow cooling.

Numeral 13 is a press machine for correcting the distortion in the longitudinal axis direction of the unit long-angled steel pipe cooled to near room temperature, but this may be a straightening process using rolls. Conventionally known devices can be used for these straightening processes. In other words, the cross-sectional shape of a large-diameter rectangular steel pipe does not have a symmetrical structure with respect to its central axis, and because there is a welded joint on only one side, it is assumed that the steel pipe is uniformly heated and cooled during heat treatment. As a matter of course, it is expected that non-uniform strain will occur in the longitudinal axis direction. Orthodontic press 13
The uneven distortion is corrected.

Reference numeral 15 is a double-end cutting machine, which may be a conventionally used milling saw, and the cross-sectional shape of the unit length large diameter square steel pipe formed by the method of the present invention is as described above. , There is no unstable part that is close to both end faces according to the standard, or even if there is, it will return to the standard shape by moving about 50 mm at most in the longitudinal axis direction, so the unit by the cutting machine 15 The cut-off length of both ends of the long steel pipe is extremely small as compared with the conventional method. That is, according to the method of the present invention, it is possible to perform production with a good yield. Reference numeral 16 denotes a delivery floor or a delivery table for the product (large-diameter square steel pipe), and the equipment is the same as the conventional equipment.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction method of the present invention and a typical apparatus for carrying out the construction method will be described below with reference to the drawings.
The device of the present embodiment can be modified in various ways within the technical level known in the art at the time of the application of the present application, and therefore, based on only the specific structure of the present embodiment without showing any special reason, The abstract should not be interpreted in a limited way. The feature of the method of the present invention lies in the step of hot-rolling a round steel pipe cross section to obtain a large-diameter rectangular steel pipe having a standard rectangular cross section.

FIG. 1 is a view showing a change (shape) of the roll hole type of each forming roll stage in a hot forming roll stand 10 having a plurality of stages according to an embodiment of the present invention. The outer diameter of the round steel pipe 7 carried into the forming roll stand 10 is 508 φmm,
The axial length is 12 m, the plate thickness is 22 mm, the material is SS400, and it is preheated uniformly to about 900 ° to 1050 ° C.

Referring also to FIG. 3, the molding roll stand described above.
The cross-sectional shape of the large-diameter rectangular steel pipe 11 finally formed by 10 is D = 400 mm, plate thickness = 22 mm, and corner radius R = 16 mm, which is the final stage forming forming the roll stand 10. It is equal to the hole type of the roll. That is, the radius of curvature of the rounded corner R forming portion of the forming roll at the final stage is 16
mm. In the present embodiment, the forming roll stand 10 has an eight-stage structure, and each forming roll 19 is supported by a flat portion of a rectangular steel pipe, that is, a rotary shaft parallel to each side in the steel pipe cross section, from four directions. It is configured to surround the steel pipe peripheral wall,

The hole die (drawing shape) formed on the peripheral surface of the forming roll is continuously provided along the peripheral surfaces of the four rolls, and the whole of the roll hole die is close to a circle. A convex bobbin shape is formed, and the length of the entire inner peripheral surface and the length of the formed steel pipe peripheral surface are always designed to be substantially equal. The outer peripheral wall of the steel pipe in each forming stage is constrained (contact pressure) by a forming roll hole die without a gap. The forming roll die in each forming stage is sequentially deformed from a circle to an outwardly convex bobbin shape to a polygonal shape as the process steps progress, but in any case, the conditions described in the preceding paragraph and the description are satisfied.

The amount of reduction (rolling down) per one stage of the forming roll is (508 −400) / 8 mm, that is, 6.7 mm on one side, assuming that the distribution of the drawing allowance of each forming stage is made uniform. Therefore, if a large amount is formed into a rectangular cross section, a larger number of forming roll stands should be required when forming a steel pipe having a larger diameter. In this embodiment, the roll stand equipment consisting of 12 stages is planned. As a result, it is possible to form a 680 mm square large-diameter rectangular steel pipe from a maximum of 850 φ mm round steel pipe by the method of the present invention. The temperature of the square steel pipe discharged from the roll of the final forming stage is maintained at about 700 ℃.

[0028]

As described above, according to the method of the present invention, it is hot forming and the drawing amount per stage is small,
Moreover, since the roll hole die is brought into contact with the entire peripheral surface of the steel pipe without a gap, compared with the conventional method,

(1) It is possible to extremely shorten the defective length of the molding cross section near the front and rear ends of the unit rectangular steel pipe.
The material yield rate is improved. In short, it is possible to reduce the manufacturing cost of the product. (2) The corners R of the four corners of the square steel pipe are uniform, and compared with the steel pipe sheet thickness without deterioration of local material quality,
The radius of curvature can be made extremely small. As a result, the cross-section coefficient can be increased, for example, the bending force in the direction perpendicular to the longitudinal axis of the rectangular steel pipe and the resistance against the twisting torque around the longitudinal axis can be increased. Not only is it easy to use in terms of construction and aesthetics. That is, a high-quality and high-quality large-diameter square steel pipe can be obtained.

(3) The flatness forming the four peripheral portions of the large-diameter rectangular steel pipe has few irregularities, and the flatness thereof is remarkably improved. Therefore, it enhances the product value of the product in terms of appearance. And so on,
It is possible to achieve special actions and effects that cannot be expected from the conventional rectangular steel pipe forming method.

[Brief description of drawings]

FIG. 1 shows a change in a hole shape for each forming roll in a hot forming roll stand of the present invention.

FIG. 2 shows changes in the hole shape of each forming roll of the hot forming roll stand in the conventional method.

FIG. 3 is a schematic layout conceptual diagram of a line for carrying out the method of the present invention.

FIG. 4 is a diagram showing a process of a production line for carrying out a hot roll forming method for a large-diameter rectangular steel pipe, which has been proposed before the application of the present invention.

[Explanation of symbols]

 1 Hot-rolled coil 2 Uncoiler 3 Width determining device 4 Round steel pipe forming roll stand 5 Semi-formed round steel pipe 6 Welding machine 7 Round steel pipe 8 (Running) cutting machine 9 Continuous heating furnace 10 Hot forming roll stand 11 Hot forming square Steel pipe 12 Cooling floor (zone) 13 Straightening device 14 Straightening roll 15 Double-sided cutting machine 16 Product unloading table (discharging floor) 17 Round steel pipe receiving floor 18 De-scaling 19 Forming roll.

Claims (1)

[Claims] 1. A method for heating a round steel pipe and hot forming the steel pipe cross-section into a square shape through a plurality of stages of forming rolls, wherein the roll hole die of each forming stage is sequentially rounded from the round shape. Deforms into a square cross section with a corner R through the pincushion shape,
Moreover, the roll hole die in each forming stage presses the entire surface of the peripheral wall of the worked steel pipe with no gap, and the narrowing amount per stage of the forming roll is in the range of about 5 to 10 mm. A method for forming a large-diameter rectangular steel pipe, characterized in that the steel pipe forming temperature is maintained at around 700 ° C.