JP2015096265A - Method of producing multiple square pipe and multiple square pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems that conventional multiple square pipes with a plurality of square pipes different in outside diameter as nest tend to be inferior in strength characteristics to a bending moment because of inclusion of a clearance between an outer pipe and an inner pipe, and that a method of forming a multiple circular pipe composed of a plurality of circular pipes different in diameter, superposed together, into a square cross section by roll molding provides a multiple square pipe free of a clearance and excellent in strength characteristics but requires high costs.SOLUTION: A finite-length inner square pipe having an external dimension smaller than the inner dimension of a finite-length outer square steel pipe is inserted into the inside of the finite-length outer square steel pipe; a tool having an external dimension larger than the inside of the inner square pipe, e.g. a roll, is inserted into one end and drawn from the other end of the pipe to expand vicinities of the four corner parts of the inner square pipe outward so as to make the outer wall of the inner square steel pipe adhere to the inner wall of the outer square steel pipe in order to fix both steel pipes through friction force throughout the whole length.

Description

The present invention relates to a rectangular tube mainly used for structural members such as columns and beams of buildings and structures, and a method for manufacturing the same.

Conventionally, as described in Non-Patent Document 1 or 2, a square tube used for a structural member of a relatively small building such as a house is formed by forming a steel strip into a circular cross section and then welding both edge portions. The circular cross-section tube obtained in this way is manufactured by a method of re-forming it into a square cross section by roll forming. Alternatively, as shown in Non-Patent Document 3, it is also manufactured by a method of welding both edge portions after forming a base plate directly into a square cross section without passing through a circular cross section by roll forming or the like. According to such a method, since it is possible to use a surface-treated steel strip that has been subjected to a plating treatment for rust prevention in advance on the steel strip that is the material, the plating treatment after being formed into a square tube can be performed. It becomes unnecessary and a square tube excellent in corrosion resistance can be obtained at low cost.

On the other hand, in the above method, due to the limitation of the thickness of the steel strip that can be plated and the limitation of the capacity of the forming equipment to the circular pipe and the square pipe, a large capital investment is required to increase the thickness and improve the strength. There was a problem of becoming.

On the other hand, as a method for improving the strength of a rectangular tube having a limited thickness, there has been proposed a method of increasing the cross-sectional area by making the tube into a multiple structure. In Patent Document 1, an inner tube that is also a hollow rectangular tube having an outer dimension slightly smaller than the inner dimension of an outer tube that is a hollow rectangular tube is inserted, and a rectangular multi-tube with a clearance therebetween is provided. Structural materials have been proposed. Further, Patent Document 2 proposes a reinforced steel pipe in which a long steel material is disposed along the longitudinal direction inside a rectangular pipe and an outer rectangular pipe and an internal long steel material are fixed by welding. A double pipe using a square pipe or a round steel pipe as a long steel material to be inserted into the pipe is also exemplified.

Edited by Japan Society for Technology of Plasticity Plasticity Technology Series 9 Roll Forming Technology, p288, Fig. 8.8 Edited by Japan Society for Technology of Plasticity Plasticity Technology Series 9 Roll Forming Technology, p290, Fig. 8.10 Edited by Japan Society for Technology of Plasticity Plasticity Technology Series 9 Roll Forming Technology, p288, Fig. 8.7

JP-A-5-171688 JP 2000-110303 A

As described in Patent Documents 1 and 2, it is possible to substantially increase the cross-sectional area of the rectangular tube regardless of the upper limit of the thickness of the steel material used by making the rectangular tube into a multiple structure, and to improve the strength as a structural member. Is possible.

However, since the multiple tube shown in Patent Document 1 is overlapped with a clearance between the outer rectangular tube and the inner rectangular tube, the strength in proportion to the cross-sectional area against the axial compression. However, when a bending moment is applied, the bending moment propagates to the inner tube via the outer tube, so the inner tube can only bear a lighter load than the outer tube due to the clearance between the two. Since this is not possible, there is a problem that the bending strength is inferior to that without clearance. Further, since the outer tube and the inner tube are not fixed, there is a concern that the inner tube may come out from the outer tube when the multi-tube is assembled into the structure, and there is a problem in workability. The clearance between the outer tube and the inner tube is inevitable in order to allow the inner rectangular tube to be inserted into the outer rectangular tube when manufacturing the multiple tube.

In addition, the reinforcing steel pipe shown in Patent Document 2 is an outer square pipe and a long steel material inserted inside, which is fixed by welding at its end, and is a long steel material inserted inside from the outer pipe during handling. However, when inserting a long steel material inside the outer square steel pipe, clearance is required between the two, and even if both ends are fixed by welding, Since the inner tube is not fixed, the same problem as in Patent Document 1 occurs when a bending moment is applied. Further, such structural members are generally supplied as long members having a uniform length within a transportable range, and are generally recut into various lengths to form structural members. Even if only both ends are fixed by welding, it is necessary to perform fixing again by welding at the cut portion when cutting to a predetermined length, compared with a general long structural member that does not require such treatment. There is an inconvenience in handling it.

After inserting a circular tube into the outer tube and the inner tube with a slight clearance, it is formed into a rectangular tube by the method shown in Non-Patent Document 1 or Non-Patent Document 2, so that the inner and outer steel tubes are in close contact with each other. A tube can be obtained, but since it is necessary to make and overlap the circular tubes separately, it is necessary to roll-form a finite-length circular tube to form a square tube. In addition, since a defective shape portion is generated at the rear end, it takes time and effort to remove these, and there is a problem in that the yield is reduced and the cost is increased.

SUMMARY OF THE INVENTION An object of the present invention is to solve such problems and to provide, at low cost, a multi-square tube having excellent bending strength characteristics without a clearance between an outer square tube and an inner square tube.

In order to achieve the above-mentioned object, a state in which a finite-length inner rectangular tube having a slightly smaller external dimension than the inner dimension of the outer rectangular steel tube has a clearance enough to be easily inserted into the finite-length outer rectangular steel tube. After inserting the tool, insert a tool, such as a roll, with an outer dimension larger than the inner dimension of the inner tube from one end of the tube and pull it out from the other end to push the vicinity of the four corners of the inner tube from the inner side. By welding the outer wall of the inner square steel pipe to the inner wall of the outer square steel pipe, the two steel pipes are fixed with frictional force over almost the entire length, and welding is performed as a means for restraining the outer pipe and the inner pipe at any part of a finite length. And a multi-angle tube characterized in that the outer square tube and the inner square tube obtained by the method are fixed by friction. It is a tube.

Explanatory drawing which shows the cross-sectional shape of the multiple | angular square tube in the 1st process of this invention by which the inner side square tube was inserted in the inside of the outer side square tube with clearance. A state in which a mandrel composed of four rolls having an outer dimension larger than the inner dimension of the inner rectangular tube is inserted into the inner rectangular tube, and the outer rectangular tube is pushed and spread through the inner rectangular tube. FIG. An explanatory view showing a state in which the inner square tube is expanded by the mandrel, the clearance between the outer square tube and the inner square tube disappears, and the outer square tube and the inner square tube are in close contact with each other. The side view which shows the process of drawing out a mandrel and pushing and expanding an inner side square pipe, and the front view which shows the integration state to the mandrel of the roll for pipe expansion. The side view which shows the process of combining the mandrel from which an external dimension differs in series, and performing the two-stage expansion process by one drawing, and the front view which shows the integration state to the mandrel of the pipe for roll expansion.

The manufacturing method of the double square tube by this invention is demonstrated. In the production of the double rectangular tube according to the present invention, a rectangular tube is used as the single tube element tube. The outer rectangular tube should be approximately equal to the external dimension of the target double rectangular tube. Since the outer tube may be slightly expanded from the inside through the inner tube, the size may be slightly smaller than the target product size in anticipation of an increase in size due to the expansion. Since there is a possibility that the side swells and becomes convex due to the expansion from the inside, the base tube to be used may be one in which the side is adjusted to a slightly concave shape. When a rectangular tube that is high-frequency welded is used as a material, the rectangular tube that serves as the outer tube may have a back bead that protrudes to the inner surface side of the welded portion. If there is a large back bead, there is a concern that it may hinder the insertion of the inner pipe. Therefore, the back bead may be cut or crushed at the time of or after pipe making, or the shape of the butt edge before welding and / or It is preferable to suppress the height as much as possible by devising the welding conditions. For the inner tube inserted into the outer tube, the vertical and horizontal outer dimensions are smaller than the inner dimension of the outer tube, and the clearance can be substantially eliminated by spreading from the inner surface of the inner tube. The one having an outer dimension not smaller than the size that can secure the clearance is used. By inserting the inner tube into the outer tube described above, a double rectangular tube having a clearance between the outer tube and the inner tube shown in FIG. 1 is obtained.

A mandrel consisting of four spreading rolls 4 assembled to an outer dimension larger than the dimension obtained by adding the clearances of the upper and lower sides and the left and right sides to the inner dimension of the double square pipe obtained as described above is provided on one side of the double square pipe. The roll 4 is arranged outside the tube end in a state in which the positions of the corner portions of the roll 4 and the square tube correspond to each other. A rod that penetrates the inside of the tube from the other tube end of the double-rectangular tube and is coupled to the mandrel is disposed at the tube end of the rectangular tube on the rod side to restrict movement in the axial direction of the tube. (Not shown). The receptacle (not shown) is provided with a hole or notch that does not interfere with the rod 6. In this state, the mandrel rod 6 is pulled out in a direction parallel to the tube axis, so that the mandrel is drawn into the square tube and moves inside the tube while expanding the corner of the inner tube, and finally the square tube. The other end of the tube is pulled out and the entire length of the rectangular tube is expanded. As a result, the corner portion is pressed against the inner surface of the outer tube, and a double rectangular tube is obtained in which the inner tube and the outer tube are fixed by friction over the entire length of the inner tube.

The double rectangular tube obtained in this way shows strength corresponding to the cross-sectional area of the outer tube and the inner tube against axial load, and the outer tube and inner tube are integrated against bending load. It shows excellent bending strength because it receives bending moment. When a bending load is applied to the superposed rectangular tubes in this way, there is no deviation at the interface between the outer tube and the inner tube even with relatively weak fixing means due to friction. It can exhibit strength characteristics almost equivalent to a single pipe corresponding to the total thickness. The multi-angled tube according to the present invention may be a double tube composed of an outer tube and an inner tube or a triple or more multi-tube having an inner tube inserted therein. Further, the outer tube and the inner tube do not necessarily have the same material, surface treatment, and thickness. For example, the outer tube and the inner tube may be combined with different strengths, surface treatments, steel types such as ordinary steel and stainless steel, and wall thicknesses. In addition, by using tubes having different lengths of the outer tube and the inner tube, a partially reinforced square tube in which only a part of the length direction is partially multiplexed can be obtained.

The object of the present invention can be applied to a rectangular tube as well as a square tube. However, in the case of a square tube, the spreader roll 6 has a trapezoidal profile as shown in FIG. Since the rolls 6 can be arranged so as to be in contact with each other and supported, the load acting on the bearing of the spreading roll 6 can be reduced by canceling the plate force due to the tube expansion molding, and the displacement of the spreading roll 6 due to the load can be reduced. Therefore, there is an advantage that machining accuracy is improved. Since a large gap is formed in the corner R portion as shown in FIG. 1 when the square tubes are overlapped, the profile shape of the spreading roll 6 is also the corner R portion from the viewpoint of effectively expanding the tube by the spreading roll 6. It is preferable to form a trapezoidal profile in which the angle formed by both hypotenuses is 90 ° and the tip is flat so that the corner R portion is avoided and the flat portions on both sides of the corner are pressed rather than pressing.

Square steel pipe corresponding to the general structural square steel pipe STKR400 defined in JIS G 3466, which is manufactured from hot-dip zinc-6 mass% aluminum-3 mass% magnesium alloy-plated steel sheet and has an outer dimension of 100 mm × 100 mm, a thickness of 4.5 mm, and a length of 6 m. And a square steel pipe corresponding to STKR400 having an outer dimension of 90 mm × 90 mm, a thickness of 4.5 mm, and a length of 6 m manufactured from a hot-dip zinc-6 mass% aluminum-3 mass% magnesium alloy plated steel sheet, and an inner pipe. The tube was inserted into the outer tube so that the entire length of the tube could be accommodated. At this time, the clearance between the inner surface of the outer tube and the outer surface of the inner tube was about 0.5 mm in average value at the two positions on the upper and lower sides and the left and right sides. In the double square steel pipes stacked in this way, a roll group in which four rolls are radially assembled so as to form an angle of 90 ° with each other so as to be inscribed in a square having a side dimension of 82.2 mm. The mandrel to be formed was inserted from one end of the square steel pipe and pulled out from the other end, and the corner portion of the inner pipe was spread from the inside over the entire length of the pipe. In the middle of the spreading process, it was observed that the outer tube was slightly distorted from the outside of the outer tube where the mandrel was present, but after passing through the mandrel, the cross-sectional shape was within tolerance due to the springback. The double square steel pipe which the outer wall of the inner square steel pipe contacted the inner wall of the outer square steel pipe and was fixed by friction by the above process was obtained. The obtained double square steel pipe showed almost the same bending strength as a square steel pipe corresponding to STKR400 having an outer dimension of 100 mm × 100 mm and a wall thickness of 9 mm.

According to the method for manufacturing a multi-angle tube according to the present invention, a double-angle tube excellent in bending strength characteristics in which the outer wall of the inner square tube is in contact with the inner wall of the outer square tube and both sides are fixed by friction is inexpensively manufactured. It becomes possible to do. Further, the double rectangular tube obtained by the present invention can be used with processing such as cutting and welding in the same manner as the single-layered rectangular tube.

DESCRIPTION OF SYMBOLS 1 Outer square pipe 2 Inner square pipe 3 Clearance 4 Pushing roll 4a Pushing roll 4b with a small outer diameter size Pushing roll 5 with a large outer diameter size 5 Spreading roll support / holding member 6 Pushing roll pulling rod

Claims (2)

After inserting a finite-length inner square tube having an outer dimension smaller than the inner dimension of the outer square steel pipe into the finite-length outer square steel pipe with a clearance that allows easy insertion, the inside of the inner pipe Insert a tool such as a roll assembled in a larger external dimension from one end of the pipe and pull it out from the other end to expand the vicinity of the four corners of the inner pipe from the inside to the inner wall of the outer square steel pipe and the outer wall of the inner square steel pipe A method of manufacturing a multi-square tube, characterized in that both steel pipes are fixed with frictional force over substantially the entire length thereof by bringing them into close contact with each other. An outer rectangular tube and an inner rectangular tube obtained by the manufacturing method according to claim 1 are fixed by friction.

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