JPH04100632A - Working method for improving quality of material for corner part of large square steel tube - Google Patents

Abstract

PURPOSE:To obtain the square steel tube free from the brittleness and the degradation of the quality of material nearby the corner part by arranging the heating source to heat the neighbourhood of the opposite corner part to the prescribed temperature and moving it along the direction of longitudinal axis as the tempering means after forming the steel tube. CONSTITUTION:The cold formed square steel tube 14 carried in the tempering furnace 7 is passed through the tempering furnace 7 while the neighbourhood of its corner part of steel tube is heated symmetrically during the conveyance in the direction of longitudinal axis by opposing each corner part of the steel tube to the burner flame to heat, maintained at the prescribed heating temperature for the specific time, in the meanwhile, the quality of material of the neibourhood of corner part which is degraded with cold plastic working is gradually refined and improved and then carried out from the tempering furnace 7 and cooled gradually to the corner part heating temperature.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for forming large-diameter square steel pipes, in which a corner portion of a square steel pipe is formed by cold plastic working of a thick steel plate. In order to correct the deterioration of the local material of the steel plate due to bending and the generation of residual stress, the parts corresponding to the corners of the steel pipe are heated to a predetermined temperature for a certain period of time to improve the quality, thereby correcting the deterioration of the steel plate material. This invention relates to a method for improving the material quality of a corner section of a large-diameter square steel pipe where the seam line is located on a side other than the corner section.

[Conventional technology]

The mass production method of one-seam or two-seam large-diameter square steel pipes, which are used as columns in buildings by bending and forming thick-walled steel plates, has conventionally been broadly divided into two types: A steel plate is bent at four corners parallel to the longitudinal axis and overlapping in the width direction, the cross section is formed into a shape similar to a square steel pipe, and the edges on both sides of the steel plate are butt welded. Then, a one-seam steel pipe with a square cross section is formed.

■- A steel plate is bent in two places along the width direction to form a U-shaped cross section, and a pair of steel plates with a rectangular cross section is formed by facing each other, and the edges of both legs are butt welded to form a tool. - Manufacture seam square steel pipes.

■The steel strip is conveyed in the longitudinal direction and passed through a round steel tube forming roll stand to produce a jointed round steel tube, and then the cross section of the round steel tube is shaped into a square shape to create a one-seam size. Form a square diameter steel pipe.

Although there are slight differences in the details of the construction methods, they are widely used.

As mentioned above, conventionally implemented economical manufacturing methods for large-diameter square steel pipes include cold plastic deformation of thick steel plates, that is, rough deformation of steel plates to form corners. Includes 90° cold bending.

By the way, when cold is applied to a flat thick steel plate, the angle is approximately 90°.
When the bending process is performed, even if the required R (outer radius) is given to the bent part of the steel plate, in the cross section of the corner steel material, the tensile force is applied to the material outside the neutral plane. Since there is no compressive force acting on the inside, cold plastic deformation takes place, so even though the processing is performed within the elastic limit of the material, it is inevitable that the material in that area will deteriorate, and the deformed area will be subject to repeated stress. There is no risk of brittle fracture occurring.

Further, even after the external force is removed, residual stress is generated in each of the bent portions due to cold plastic working.

The above phenomenon becomes more noticeable as the thickness of the steel sheet increases and as the radius of radius given to the corner portion during bending decreases.

However, in the past, the specifications of this type of large-diameter rectangular steel pipe were mainly focused on its shape and structural characteristics, namely: (1) the cross-sectional second moment of inertia per weight compared to an H-section steel with the same unit weight; , has a large section modulus and is resistant to external bending and torsion forces.

(2) It has a large secondary radius of cross section and is strong against buckling.

(3) Good balance of cross-sectional characteristics in the X and Y directions.

(4) The cross-sectional area of the column can be made relatively small;
It is possible to increase the usable area ratio for the same building floor area.

(5) Since the cross section is box-shaped, the material can be used exposed without damaging its aesthetic appearance.

(6) Fireproof coating, painting, and other decorations and construction around the column are easy and economical.

Demand is growing due to the recognition of the merits of these construction features, but considering the processing conditions mentioned above, it is important to objectively and technically analyze the material weaknesses or uncertainties inherent in square steel pipes. There is a tendency for the large diameter rectangular steel pipes to be distributed on the market without sufficient consideration.

On the other hand, steel structures, buildings, etc. that use this kind of large-diameter rectangular steel pipe as a column generally cannot support the weight of itself and the attached structure for a long period of time once the column is constructed. Of course, these columns are also required to safely withstand severe repeated loads due to external forces such as earthquakes and typhoons, and in many cases these columns are in such a construction state that, in principle, they cannot be replaced or repaired.

In recent years, large-diameter square steel pipes formed by cold bending have been frequently used as columns in buildings, and as they are being used as columns in medium- and high-rise buildings, Consumers are becoming increasingly concerned or concerned about the problem that deterioration of the material due to bending may promote brittle changes at the relevant locations.

Recently, users and third parties have pointed out this kind of material problem with large-diameter rectangular steel pipes, and manufacturers need to take immediate countermeasures.

[Problem to be solved by the invention]

In response to the requests from users, the method of the present invention improves the conventional corner forming method based on cold plastic deformation of large-diameter square steel pipes, and avoids cost increases as much as possible. The object of the present invention is to provide a method for improving the material quality of a corner portion of a square steel pipe, which repairs the deterioration of the material of a steel plate corresponding to the corner portion of a square steel pipe due to bending of a thick steel plate.

[Means to solve the problem]

In order to achieve the above object, the construction method of the present invention has the following constituent elements.

(1) Cold bend a steel strip or a single steel plate along its longitudinal axis, form the cross section of the steel plate into a shape approximating a square steel pipe, and butt-weld the edges of the steel plate to each other to form a cross-section of the steel plate. For a large-diameter rectangular steel pipe formed by shaping it into a rectangular shape, a heat source that heats the vicinity of each corner to a predetermined temperature is placed opposite each corner of the steel pipe, and the heat source is heated to a predetermined temperature. A method for improving the material quality of a corner portion of a large-diameter square steel pipe, which comprises a step of moving the square steel pipes in cooperation with each other along the longitudinal axis direction.

[For production]

Large-diameter square steel pipes formed using conventional manufacturing methods that include cold plastic working are processed in the longitudinal direction after the main welding of the seam line of the steel pipe has been completed or after the welded joint has passed a flaw detection device. In a plane perpendicular to the axial direction, the steel pipe is charged into a tempering furnace equipped with heating means installed opposite to and close to each corner around the cross section of the steel pipe, and During this period, the vicinity of each corner of the square steel pipe formed by cold bending is continuously heated to about 67° to 760° C. by the heating means.

Gas or liquid fuel burners are used for the heating means provided opposite each corner of the steel pipe.
Gas flow within the combustion chamber of a refining furnace is typically of the corner-firing type.

At this time, the position of the burner in the combustion chamber may be provided axially symmetrically with respect to the steel pipe. That is, thermal expansion due to heating of the corner portion of the steel pipe is designed to occur symmetrically with respect to the central axis of the cross section of the steel pipe.

Moreover, a plurality of burners facing each other and arranged at the corner of the steel pipe can be arranged in parallel in the longitudinal axis direction of the steel pipe.

In this way, while the formed large-diameter rectangular steel pipe passes through the forging furnace, it continuously moves around each corner for a certain period of time.
By heating to a temperature of about 70° to 760°C and then allowing it to cool naturally, the material near the corners of the steel pipe, where the material has deteriorated due to the bending process due to cold plastic deformation of the thick steel plate, is tempered. This aims to restore the original state and eliminate the residual stress caused by the processing.

Large-diameter square steel pipes that have undergone material refining near the corners of the steel pipe,
It is then transported to undergo finishing processes such as cutting it into a standard length in the longitudinal direction, passing it through a flaw detector for welded joints, etc., and passing it through a longitudinal strain straightening machine.

As described above, the method of the present invention achieves its purpose at a relatively low cost as a means of refining the brittleness or residual stress of the steel plate constituting the large-diameter square steel pipe after forming the same. This makes it possible to efficiently provide a high-quality square steel pipe that eliminates the brittleness and deterioration of the material near the corners, which had been a concern in the past.

〔Example〕

Below, an embodiment of the construction method of the present invention and an apparatus for improving the material quality of the corner portion of a large-diameter square steel pipe that implements the construction method will be described with reference to the drawings. Since partial modification is possible within the technical level of isn't it.

Figure 1 shows the processing line of the equipment for improving the material quality of corner parts of large-diameter square steel pipes, which implements the construction method of the present invention.
Fig. 1(b) shows the equipment constituting the processing line.
) indicates the forming or processing state of the steel plate corresponding to each process on the same device.

In the square steel pipe forming line in this embodiment, a coiled thick-walled steel plate 1 is passed through an unwinding mechanism 2, passed through a leveler and a width determining device 3, and then passed through a round steel pipe forming roll stage 4. After forming the round steel pipe 13, the steel pipe 13 is passed through the square steel pipe forming roll stage 6 to shape its cross section into a square shape of standard size to produce the large diameter square steel pipe 14, but this process is , - A sheet steel plate is put on a bending press to bend the steel plate at four points in the width direction, and the cross section is formed into a shape approximating a square steel pipe, and then put on a shaping roll to bend the steel plate in the longitudinal direction edge part. It may be replaced with a device (not shown) that butt-welds and forms square steel pipes.

In addition, it is also possible to use a manufacturing apparatus for large-diameter square steel pipes based on known cold plastic working.

The thus shaped large-diameter square steel pipe 14 is carried along its longitudinal axis into a tunnel-type tempering furnace 7 whose inner wall surface is lined with refractory bricks. Further, a burner for heating the vicinity of each corner of the steel pipe is installed in the furnace symmetrically with respect to the central axis of the cross section of the steel pipe, and a burner for injecting the flame into the furnace. It has multiple windows.

The cold-formed rectangular steel pipe carried into the refining furnace 7 is transported in the longitudinal axis direction against the burner flame that heats the vicinity of each corner of the steel pipe. Either it is heated to reach 700° to 800°C near the rotating part, or it is gradually exposed to a burner flame multiple times and heated to 700° to 800°C, and then passed through a tunnel-type tempering furnace to achieve the required heating. The temperature is maintained for a specific period of time, during which time the material near the corner of the steel pipe that has deteriorated due to cold plastic working is gradually refined and improved, and then the steel pipe corner is heated to a temperature after being carried out of the refining furnace. gradually cool down.

The burner fuel may be coal gas, LNG, LPG, or other liquid fuel such as light oil, kerosene, or heavy oil.

The combustion gas is sucked into an exhaust device provided near the material exit of the refining furnace, and is prevented from accidentally leaking outside through the material entrance/exit of the furnace, the burner flame injection window, etc.

However, curtain-like members made of heat-resistant material are installed at the entrance and exit of the steel pipes of the refining furnace to prevent unnecessary release of thermal energy to the outside from the openings and to prevent cooling air from blowing in from the outside. This increases thermal efficiency.

Of course, the compressed air used in the burner is also preheated by thermal energy leaking from the combustion gas exhaust device or the refining furnace wall. This cools the combustion gases passing through the gas exhaust system and extends the service life of the system.

In this way, the large diameter rectangular steel pipe carried out from the refining furnace 7 is fed into the cutting machine 8 and cut into a standard length in the longitudinal axis direction by a cutter that slides in synchronization with the movement of the steel pipe 14, thereby cutting the large diameter of the unit length. A square steel pipe 15 is formed.

Since the vicinity of each corner of the steel pipe 15 still maintains a high temperature, the cut steel pipes are arranged on the cooling zone 9 and cooled by air or water, and the steel pipes 15 that have been cooled to room temperature are transferred to the product unloading table. It will be carried out on 10th.

Although not shown, a weld joint inspection device is attached to the cooling zone 9 to prevent unexpected defective products from being mixed into the products.

If the steel pipe forming speed of the square steel tube forming roll stage 6 does not match the steel material refining capacity of the refining furnace 7, the steel pipe forming speed of the square steel pipe forming roll stage 6 is immediately after the square pipe forming roll stage 6 in FIG. 1(a).

If the cutting machine 8 is installed to first form square steel pipes of standard length and then sequentially charge them into the refining furnace 7, which has a plurality of them installed in parallel, it is possible to match the machining efficiency of both. becomes possible.

In addition, in consideration of cases where square steel pipes are formed using a bending press and distortion occurs in the longitudinal axis direction of the formed steel pipes due to butt welding of the longitudinally etched portions of the steel material, a strain straightening machine (not shown) was installed. , may be installed in a part of the line.

As described above, according to the construction method according to the embodiment of the present invention, a square steel pipe is formed by a conventional method for manufacturing a large diameter square steel pipe, in which a thick steel plate is bent by cold plastic working to form a corner part. The degree of brittleness, deterioration, or residual stress of the corner member material is completely different from that of the standard.

Further, residual stress near the corners of the steel pipe is extremely small, and in addition to providing a product with improved quality, various effects described in the above [Operations] section can be achieved.

〔Effect of the invention〕

As described above, the method of the present invention (1) does not cause brittle deterioration of the material due to cold plastic deformation of the corner portion of the steel pipe, which was a matter of course in conventional products in thick-walled large-diameter rectangular mesh pipes; , it is possible to provide high-quality products with almost no residual stress caused by corner molding.

(2) Although the forming process includes a heat refining process for the steel pipe material, the forming efficiency of the steel pipe does not decrease.

(3) Cheap fuel can be used as much as possible in the steel refining furnace, and materials can be refined by heating relatively inexpensively.

(4) Although it is inevitable that the cost will increase due to the amount of heating required, since the constituent steel plates of large-diameter square steel pipes are tempered to the minimum extent necessary, high-quality tempered steel pipes can be obtained. We are able to maintain low prices for our products.

The method for improving the material quality of corner portions of square steel pipes of the present invention achieves special functions and effects that cannot be expected from conventional methods of forming thick-walled, large-diameter square steel pipes.

[Brief explanation of drawings]

FIG. 1 shows the method for improving the material quality of the corner portion of a steel pipe according to the present invention, an outline of the equipment for implementing the method, and the shape of a steel plate formed based on the method. 1...Hot rolled coil, 2...Uncoiler-3
...Trimming cutter, 4..Round steel pipe forming roll stand, 5..Welding machine, 6..Square steel pipe forming roll stand, 7..Refining furnace, 8..Cutting machine, 9..・
Cooling zone, 10...Product unloading table, 11
・・Strip steel plate, 12・・Round steel pipe formation, 13・・
・Round steel pipe, 14...Square steel pipe, 15...
product.

Claims (1)

[Claims] (1) Cold bend a steel strip or a single steel plate along its longitudinal axis, form the cross section of the steel plate into a shape approximating a square steel pipe, and butt-weld the edges of the steel plate to each other to form a cross-section of the steel plate. For a large-diameter rectangular steel pipe formed by shaping it into a rectangular shape, a heat source that heats the vicinity of each corner to a predetermined temperature is placed opposite each corner of the steel pipe, and the heat source is heated to a predetermined temperature. A method for improving the material quality of a corner portion of a large-diameter square steel pipe, which comprises a step of moving the square steel pipes in cooperation with each other along the longitudinal axis direction.