JP2889886B2 - Forming method for large diameter square steel pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for uniformly heating a cold-formed round steel pipe to a predetermined high temperature and then passing the cross-section through a forming roll stand consisting of a plurality of stages before the heating temperature of the steel pipe decreases. 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 of forming a one-seam thick-walled large-diameter rectangular steel pipe on a commercial base and forming the same is a forming method comprising the following steps (for example, see Japanese Patent Application Laid-Open No. 4-71720). Has been proposed.

FIG. 4 is a block diagram showing the above process. (1) 1 is a hot-rolled coil, and a steel strip constituting the coil is unwound by an uncoiler 2 and is leveled by a leveler. After being corrected into a flat plate, both ends are cut by a trimming knife or cutter 3, and after a width determining process,
It is continuously carried into the breakdown process. (2) The breakdown step is composed of a plurality of round steel tube forming roll devices 4 in which a right-angle cross section of the steel strip is sequentially bent and formed by each roll stand. The round steel pipe 5 is formed.

[0004] (3) The semi-formed steel pipe passes through a fin pass roll and a squeeze roll to correct the difference in the butted surfaces of each other, and resistance welds the butted portion with a high frequency resistance welding machine 6 to form a one-piece steel pipe. Seam ERW round steel pipe 7
Is formed, and after the build-up portion of the welded joint is cut, the traveling cutting machine 8 that moves in synchronization with the transfer speed of the steel pipe,
Cut every unit length. (4) The above-mentioned unit-length round steel pipe (or a single piece) is charged into a heating furnace 9 ′ as a single piece or a plurality of pieces to improve the deterioration of the steel pipe material caused by deformation due to cold plastic working, etc.
After heating uniformly to a temperature that can remove residual stress,
Before the heating temperature is lowered, each product is carried into a square forming roll process including a plurality of forming rolls via a surface scale removing device. The heating furnace 9 ′ may be a direct heating furnace or an indirect heating furnace using a gas, liquid fuel, electric energy, or the like as a heat source, and the steel pipe may be heated batchwise or continuously, and may be unloaded from the furnace. Before heating, it is heated uniformly in the range of 970 ° C to 700 ° C.
It has been tempered.

(5) The heated steel pipe passes through a descaling device, and before the temperature falls to 650 ° C. or less, a square forming roll stand comprising a plurality of forming rolls quickly.
In this step, the round steel pipe in section is sequentially deformed and hot plastically deformed into a square-section steel pipe 11 having substantially the same circumference. The temperature of the rectangular steel pipe shaped through the final roll forming step is approximately 600 ° C. Therefore, the process of forming a round cross section from a round steel pipe is performed at a temperature as high as not to cause residual stress due to plastic deformation of the material. No degradation or increase in residual stress occurs.

Conventionally, the configuration of the angulated roll stand 10 'has a structure in which the number of roll stages is small, the peripheral surface of the forming rolls constituting each forming stage is cylindrical, and a pair of opposing roll rotating shafts are mutually opposed. Since it is held in parallel, the step of sequentially drawing the cross section from the round steel pipe to the square cross-section steel pipe is described with reference to FIG. 2. FIG.
This shows a process of sequentially narrowing the cross-section until the cross-sectional shape is transformed into a square steel pipe 11 as specified. In the case shown, for example, four-step drawing is performed, and the material of the steel plate or strip is SS400, Is 22mm, and the outer diameter of the round steel pipe is 688 φmm.
The process of forming a square steel pipe with m and the corner R radius S set to 77 mm is shown. Therefore, assuming that (drawing amount) is uniformly assigned to the drawing allowance at each processing step of the forming roll, the drawing amount per step is 17.2 mm on one side. That is, the forming amount per one step of the forming roll is relatively large, and the forming action is rough.

The peripheral surface of each forming roll is cylindrical, and the forming roll is drawn inward from the outside of the steel pipe having a circular cross section toward the inside of the steel pipe so as to circumscribe the arc. Is discontinuous. That is, a ridge line p is formed. In the cross section of the round steel pipe, the most arcuate portion on the x and y coordinate axes passing through the central axis, that is, the central arc portion is formed into flat surfaces a and a by the first stage drawing. The flat surface a is formed as a → b → c wide on an arc each time through a plurality of forming roll stages,
The roll is sequentially applied to the outside of the arc. As shown in FIG. 2, among the perimeters of the circular cross section 7 deformed by the drawing, the arc-shaped portions that are not restricted by the forming roll peripheral surface of any of the working steps are the corners of the formed square steel pipe corner. It is known that the compound exists around the position of the R portion. That is, the 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 arc-shaped portion.

It is not surprising that the radius of curvature of each corner R of the formed rectangular steel pipe formed as described above is different from each other. That is, the radius of curvature of each corner R has unevenness. Further, if the radius of curvature is too small with respect to the thickness of the steel sheet, the deterioration of the material of the local steel material becomes more severe, which is not possible. In addition, as described above, since the drawing amount per stage is relatively large, and there is an arc portion which is not regulated by the forming roll in the circumference of the section to be processed, the accuracy of the flat surface formed by the roll is reduced. Low. If measured accurately, it can be seen 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.

Since the cross-sectional shape of the formed rectangular steel pipe near the front and rear ends 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 the section. As a result, the yield of the material becomes very poor. (6) As described above, the high-temperature large-diameter rectangular steel pipe 11 whose cross section has been formed through the hot forming roll process has a pipe body temperature of 600 ° C. to 600 ° C.
With the temperature kept at 650 ° C. inside and outside, it is carried out to the cooling zone area 12 ′ which is continuous with the roll forming process, where it is uniformly distributed, for example, by flowing cooling air or gradually rotating around the longitudinal axis while moving in the horizontal direction. Cool the steel pipe slowly by moving it to prevent distortion of the steel material due to uneven cooling.After the temperature of the steel pipe falls to about 500 ° C, apply natural cooling, spraying, and other cooling methods that use water. It is also conceivable to enhance the cooling effect and to save substantial space in the cooling zone 12 '.

(7) The hot-formed large-diameter rectangular steel pipe thus cooled to such an extent that it can be handled is carried into a straightening machine 13 composed of a press or a roll 14 for each unit length steel pipe to reduce the longitudinal strain in the steel pipe. to correct. At this time, a step of inspecting the quality of the welded joint of the steel pipe, the damage of the base metal, and other requirements that affect the quality of the product may be included. (8) As described earlier, the large-diameter rectangular steel pipe having a unit length that has undergone the steel pipe distortion correcting step 13 has an unstable cross-sectional shape near both end faces, and cannot be distributed as a commercial product as it is. So its before and after each unit steel pipe 500 ~ 700
In order to cut about mm, the both ends cutting process 15 is applied. (9) The unit-length large-diameter thick-walled rectangular steel pipe whose irregular portions at both ends are cut is carried out to the product carry-out (pay-out) table 16.

[0011]

The large-diameter thick-walled rectangular steel pipe manufactured by the above-mentioned hot roll forming method is inherent in the cold roll-formed large-diameter rectangular steel pipe currently distributed on the market and installed on building structures. It is possible to solve various drawbacks, and to satisfy most of the pending issues requested by the construction industry for this kind of large-diameter rectangular steel pipe. As mentioned earlier,

In the cross section of the rectangular steel pipe, the flatness of each flat surface constituting the four sides is slightly poor. In the rectangular steel pipe cross section, the radius of curvature of each corner R portion is not 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 at the front and rear ends becomes unstable, and the portion is cut off, resulting in poor material yield. There are many problems, and there is still room for improvement in the process in terms of improving product uniformity, quality and material yield. Therefore, the method of the present invention is to provide a novel steel pipe forming method capable of solving all of the above-mentioned problems while retaining the advantages based on hot roll forming in the manufacturing process of the rectangular steel pipe. It is the purpose.

[0013]

SUMMARY OF THE INVENTION The present invention has the following components in order to achieve the above-mentioned object. (1) The round steel pipe is heated, a method for hot forming a steel pipe section to rectangular through forming rolls in a plurality of stages, the four forming rows surrounding the steel pipe wall from four directions in each molding stage
Roll caliber formed by Le sequentially from round, KakuNaru
Reduce the depth of the arc surface by the roll and increase the radius.
Through the shape, it is transformed into a square cross section having a corner R, and the roll dies in each forming stage press the entire surface of the peripheral wall of the processed steel pipe without any gap, and the amount of narrowing per one stage of the forming roll is reduced. , Approximately in the range of 5 to 10 mm, and the forming temperature of the square steel pipe in the final forming stage is 700 ° C.
A method for forming large-diameter rectangular steel pipes, characterized by being held back and forth.

[0014]

FIG. 3 is a conceptual diagram of a hot forming method for implementing the method of the present invention. In the figure, reference numeral 17 denotes a product receiving floor, which is a thick wall formed by cold plastic forming on the receiving floor by a known method. The round steel pipe obtained by cutting the round steel pipe for each unit length is received and stored, and is sequentially charged into the continuous heating furnace 9. Reference numeral 9 denotes a continuous heating furnace of a unit-length round steel pipe, using a gas, liquid fuel or electric energy as a heat source, by direct or indirect heating.
The round steel pipe while being charged and transported in the furnace is almost 900 °
Heating to ~ 1050 ° C to remove residual stresses that have been generated based on the cold plastic working that the steel strip or steel sheet had previously received,
Improve material deterioration.

A de-scaling device 18 for removing an oxide film or the like formed on the surface of the steel pipe based on heating by the continuous heating furnace 9, cleaning the surface of the heated round steel pipe, and carrying it into a roll forming process; 10 is a hot roll forming stand, which is compared with the known square steel tube forming roll method described above.

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 cross section of the round steel pipe into a square shape. ing. It will be understood that under this condition, the forming process of a larger diameter steel pipe requires more forming steps accordingly. For this reason, the unstable region of the rectangular cross section near both ends in the longitudinal axis direction of the unit rectangular steel pipe becomes extremely small.For example, the unstable cross section is cut off only by cutting off its front and rear ends by about 20 to 50 mm in the longitudinal axis direction. Therefore, the yield of materials is greatly improved as compared with the conventional method. That is, production costs can be reduced.

The hole shape of the known square forming roll did not restrain the entire surface of the peripheral wall of the steel pipe in forming the cross section of the round steel pipe (see FIG. 2). During the forming process, the peripheral wall of the round (deformed) steel pipe is entirely and completely restrained from the first stage to the final stage forming roll die. In other words, the inner peripheral length of the roll die in the forming roll of any processing stage,
It is almost the same as the outer peripheral length of the formed steel pipe. Section of specifically described the round steel pipe sequentially by hot molding as it passes through the rectangular shaped stand 10, each forming row
To reduce the depth of the circular arc surface and increase the radius
Through a dense shape into the hole type (through a
) , And is formed into a square cross section of a standard having a corner R portion.

Therefore, at this time, the radius of curvature of the corner R portion of the rectangular steel pipe can also be restrained by the groove of the forming roll, so that the radius of curvature of each corner R portion is regulated to be equal. it can. Therefore, the curvature radius of the corner R portion of the formed rectangular steel pipe is extremely small with respect to the steel plate thickness t, as compared with the conventional product, without lowering the toughness of the steel plate material in the vicinity of the portion and deteriorating the material properties. can do. That is, by providing the sharp corner R portion, the section modulus of the square steel pipe can be increased, and the four sides of the square cross section formed because the forming of the steel pipe cross section is performed by constraining the entire peripheral wall with no gaps and drawing down. Provided is a rectangular steel pipe which has improved flatness of a flat portion to be formed, enhances its commercial value in appearance, and has a convenient and easy-to-use steel pipe outer wall decoration.

Since the temperature of the heated steel pipe when the formed rectangular steel pipe is carried out of the forming stand 10 is approximately 700 ° C. or outside, all the roll forming of the cross section of the steel pipe before that is performed under the so-called hot working conditions. Therefore, there is no adverse effect on the steel pipe and the steel sheet, such as generation of new internal stress based on the cross-sectional deformation, increase of residual stress, and deterioration of the material.

Referring again to FIG. 3, in the figure, reference numeral 12 denotes a square for receiving a high-temperature (for example, 700 ° C.) unit-length hot-formed large-diameter square steel pipe carried out of the forming stand 10 and uniformly cooling it. A cooling floor (zone) for steel pipes. In this zone, for example, cooling while rotating around the longitudinal axis or cooling air flow so as not to cause distortion due to uneven thermal stress in the longitudinal direction of the long steel pipe. Must be set along the longitudinal direction of the steel pipe, or conditions must be set for uniform radiation, conduction and heat dissipation by convection throughout the steel pipe including the longitudinal direction. Thus, the unit-length large-diameter rectangular steel pipe is cooled on the cooling bed 12 while being gradually cooled, while being transported in a direction perpendicular to the longitudinal axis, and when the temperature falls below approximately 500 ° C, forced cooling by spraying is performed. By doing so, the space of the cooling floor used in the steel pipe cooling process is reduced as much as possible. However, if there is space, natural slow cooling may be used.

Reference numeral 13 denotes a press for correcting the distortion in the longitudinal axis direction of the unit rectangular steel pipe cooled to near room temperature, but it may be a correction using a roll. Conventionally known devices can be used for these correction processes. In other words, the cross-sectional shape of the large-diameter rectangular steel pipe is not symmetrical with respect to its central axis, but because there is a welded joint on only one side, heat treatment and cooling are applied uniformly to the heat treatment of the steel pipe. However, it is naturally expected that non-uniform distortion occurs in the longitudinal axis direction. Straightening press 13
This is to correct the uneven distortion.

Reference numeral 15 denotes a double-end cutting machine, which may be a conventionally used milling saw. The cross-sectional shape of the unit-length large-diameter rectangular steel pipe formed by the method of the present invention is as described above. There is no unstable part near the both end surfaces according to the standard, or even if there is, in the longitudinal axis direction, if it moves at most about 50 mm, it returns to the standard shape, so the unit by the cutting machine 15 The cut-off length at 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, production with a good yield becomes possible. Reference numeral 16 denotes a delivery floor for products (large-diameter rectangular steel pipes) or a carry-out table.

[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.
Since the device of the present embodiment can be variously modified within the technical level in the art known at the time of the filing of the present application, the present invention is based on only the specific structure of the present embodiment without special reasons. The gist should not be construed as limiting. The feature of the method of the present invention lies in a step of obtaining a large-diameter rectangular steel pipe having a rectangular cross section according to a standard by hot roll forming a round steel pipe cross section. Therefore, an embodiment method relating to this portion will be described in detail.

[0024] FIG. 1 (A) is a graph showing changes in roll caliber of the forming roll stage in the hot forming roll stand 10 comprising a plurality stages of an embodiment (form) of the present invention. The outer diameter of the round steel pipe 7 carried into the forming roll stand 10 is 508 mm, the axial length is 12 m, the plate thickness is 22 mm,
The material is SN400B .
It is uniformly heated to about 050 ° C.

Referring also to FIG. 3, the above-mentioned forming roll stand
The cross-sectional shape of the large-diameter rectangular steel pipe 11 finally formed by the step 10 is D = 400 mm, plate thickness = 22 mm, and corner radius R = 16 mm. Equal to the roll hole type. In other words, the radius of curvature of the corner R forming part of the die of the last forming roll is 16
mm. The forming roll stand 10 has an eight-stage structure in the present embodiment, and each forming roll 19 is supported by a flat portion of a square steel pipe, that is, a rotating shaft parallel to each side in a cross section of the steel pipe, from four directions. It is configured to surround the steel pipe surrounding wall,

The die (drawing shape) formed on the peripheral surface of the forming roll is provided continuously along the four peripheral surfaces of the roll, and the entire roll die is shown in FIG. Show
Each forming roll shown in FIG.
Shape of shallow arc surface and large radius according to 19
(Outwardly convex thread-wound shape)
Have deformed rectangular cross-section having a Na R, the length of the entire inner peripheral surface (dimension), the length of the shaped steel pipe circumferential surface (dimension) is always are designed substantially equal. The outer peripheral wall of the steel pipe in each forming step is restrained (contact pressure) by a forming roll die without any gap. As shown in FIG. 1 (B) , the forming roll dies in each forming stage are sequentially arranged as the process stages progress .
Each forming roll 19 shown in circle → FIG 1 (C) shown in
Largely form → Fig shallow and radially the depth of the arcuate surface by
Although it is deformed into the square shape shown in FIG .

The amount of drawing (rolling down) per one 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 roll is equalized. Therefore, when the amount of forming into a square cross section is large, when forming a steel pipe having a larger diameter, a larger number of stages of forming roll stands should be required. In this embodiment, a roll stand having 12 steps is planned. This makes it possible to form a large-diameter square steel pipe of 680 mm square from a round steel pipe with a maximum diameter of 850 mm by the method of the present invention. The temperature of the square steel pipe unloaded from the rolls of the final forming stage is maintained at approximately 700 ° C.

[0028]

As described above, according to the method of the present invention, the amount of drawing per one stage is small due to hot forming.
In addition, since the roll hole mold is made to contact the entire circumference of the steel pipe without any gap, compared to the conventional method,

(1) It is possible to extremely reduce the length of defective section in the vicinity of the front and rear ends of a formed rectangular steel pipe having a unit length.
The yield rate of the material is improved. In short, it is possible to reduce the manufacturing cost of the product. (2) Each corner R of the four corners of the square steel pipe becomes uniform and can be compared with the steel pipe plate thickness without deterioration of the local member quality.
The radius of curvature can be made extremely small. As a result, the section modulus can be increased, for example, the bending force in the direction perpendicular to the longitudinal axis of the rectangular steel pipe and the resistance to torsional torque around the longitudinal axis can be increased. Not only that, it is convenient in terms of construction and aesthetics. That is, a high-quality and good-quality large-diameter rectangular steel pipe can be obtained.

(3) The flat portions forming the four peripheries of the large-diameter rectangular steel pipe have few irregularities, and the flatness is significantly improved. Therefore, the product value of the product is enhanced in appearance. And so on,
Special functions and effects that cannot be expected from the conventional square steel pipe forming method can be achieved.

[Brief description of the drawings]

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

FIG. 2 shows a change in a die for each forming roll of a hot forming roll stand in a conventional method.

FIG. 3 is a schematic diagram of a line for implementing the method of the present invention.

FIG. 4 is a diagram showing steps of a production line for implementing a hot roll forming method for a large-diameter rectangular steel pipe proposed before the application of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hot-rolled coil 2 Uncoiler 3 Width determining device 4 Round steel tube forming roll stand 5 Semi-formed round steel tube 6 Welding machine 7 Round steel tube 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 Both ends cutting machine 16 Product delivery table (delivery floor) 17 Round steel pipe receiving floor 18 De-scaling 19 Forming roll.

──────────────────────────────────────────────────続 き Continuing from the front page (73) Patent holder 598134835 Shin Nakajima 4-26-27 Kichijoji Honmachi, Musashino City, Tokyo (72) Inventor Isao Nakajima 1-1-11-5 Higashi Toyonakacho, Toyonaka City, Osaka (72) Invention Taku Nakajima 3-70 Midorigaoka, Itami City, Hyogo Prefecture (72) Inventor Norio Nakajima 12-26, Ogawamachi, Fukuroi City, Shizuoka Prefecture (72) Inventor Shin Nakajima 4-26-27, Kichijoji Honmachi, Musashino City, Tokyo (56) References JP-A-3-97810 (JP, A) JP-A-3-151117 (JP, A) JP-A-4-224022 (JP, A) JP-A-4-224023 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) B21C 37/15

Claims (1)

(57) [Claims] 1. A method for heating a round steel pipe and hot-forming the cross section of the steel pipe into a square through a plurality of forming rolls, wherein four rounds surrounding the steel pipe peripheral wall from four directions in each of the forming stages .
Roll caliber formed by forming rolls sequentially from round, a shallow and radially to the depth of the arcuate surface by the forming roll
Through the enlarged shape, it is deformed into a rectangular cross section having a corner R, and the roll hole dies in each forming step press the entire surface of the peripheral wall of the processed steel pipe without any gaps, and the amount of reduction of the forming roll per step is reduced. About 5 to 10 m
m, and the forming temperature of the square steel pipe in the final forming step is maintained at about 700 ° C. A method for forming a large-diameter square steel pipe.