JPS5813245B2 - Manufacturing method of large diameter square steel pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for manufacturing large diameter rectangular steel pipes used for construction and other purposes.

Conventionally, large-diameter square steel pipes used for construction and other purposes have been manufactured by bending two steel plates into a U-shaped cross section, then butting them together and welding them to form a square steel pipe.

In this method, two weld lines are created in one steel pipe, so welding materials and welding work account for a large portion of the steel pipe cost, and a considerable amount of strain relief work is required in conjunction with welding. This has been an obstacle to reducing steel pipe manufacturing costs.

In the case of small diameter steel pipes, a single plate is bent and joined with a single weld line, but usually 350 mm.
In the case of large-diameter steel pipes of 350 mm or more, there are many problems in bending and other aspects, and for this reason, it was considered practically impossible to manufacture large-diameter steel pipes from a single plate.

In addition, the conventional method involves many different processes such as beveling two steel plates, bending them, joining them together, tacking, welding, and removing distortion, so it is difficult to make the process continuous.
For this reason, it takes time and effort to transfer parts between processes, which accounts for a considerable amount of the manufacturing cost.

In view of these points, the present invention was developed as a result of various researches, and by manufacturing square steel pipes from a single steel plate, the amount of welding and associated work can be halved, thereby making it possible to significantly reduce manufacturing costs. This is what I did.

The present invention is a method for manufacturing a large-diameter square steel pipe, in which a single steel plate is transported in the length direction, grooves are formed on both sides, and then the four corners of the square steel pipe are bent using a press to form grooves between the grooves. The gap is formed into a shape similar to a square steel pipe with the minimum dimension from which the mold can be pulled out, and then the shape is formed into a square steel pipe using forming rolls while being transported and tack welded in sequence. After the outer surface is welded by automatic welding, the strain is removed by passing it through a strain relief roll.

Hereinafter, the present invention will be explained with reference to drawings of embodiments.

A flat steel plate 1, which is a single steel plate cut to a predetermined size and supplied to the material supply section, is sent while being positioned by a feed roller 10 and pinch rolls on both sides (not shown), and is sent to a beveling machine 2 to cut both side surfaces. Perform bevel processing.

Then, it is sent into the molding press 3 by the feed roller 10,
Here, the corners of the square steel pipe are bent using a flat pressing die 31 that presses simultaneously over the entire length of the flat steel plate 1.

In this forming process, as shown in FIG. 2, the corner 16 of the flat steel plate 1 is bent at a predetermined angle, then the corner 17 is bent, then the corner 19 is bent, and finally the corner 18 is bent. .

The degree of bending is preferably such that the angle A between the corners 16 and 19 is 92 degrees, and the angle C between the corners 17 and 18 is 115 degrees.

Through this forming process, a cross-sectional shape similar to that of a rectangular steel pipe is obtained as shown by the solid line in FIG.

Here, while being pressed and fed by rollers from above and below, it is pressed down step by step by rollers on both sides, and the corners 17, 1
8 becomes 90 degrees and the grooves 15 are butted together, and then the welding machine 5 temporarily attaches them.

This results in a predetermined square steel pipe molded product 12, and end tabs 13, 13 for submerged arc welding are then attached to both ends of the groove.

Then, it is reversed by reversing devices 6, 6, transferred onto a welding table, and the inner surface is welded by an automatic welding machine 7.

Next, it is further reversed by the reversing devices 6, 6, and the groove portion is welded by the automatic welding machine 8, thereby forming a predetermined square steel pipe 14.

This is sent to the next process by a feed roller 10, and the distortion is removed by passing it through a correction roller 9.

Since the square steel pipe 14 usually bends in the length direction due to welding of the groove, the straightening rollers 9 are arranged in multiple stages in the length direction, and the intermediate rollers are moved up and down. Make sure that the distortion can be corrected.

The straightened square steel pipe 14 is sent by the feed roller 10,
After the welded parts are inspected through an inspection device 20 such as ultrasonic flaw detection, they are arranged as finished products 30.

The range of approximation in the shape of the square steel pipe approximation described above varies depending on conditions such as the material of the steel plate to be processed, the plate thickness, and the size of the steel pipe, and the relationship between angle A and angle C also depends on the ease of processing in the subsequent process, etc. Various modifications are possible in consideration of this, but in any case, the gap between the grooves should be the minimum size that allows the mold to be pulled out.

That is, after bending with a press, the mold is pulled out from between the grooves so that it can be easily and quickly transferred to the next process.

In addition, if you use a press to process the specified square steel pipe,
It takes a lot of time to extract the mold, and it is virtually impossible to do the work continuously.

The above process may be performed in one line from feeding the material to taking out the finished product, or the process after internal welding, which takes a relatively long time, may be divided into two lines, and the subsequent processes may be performed in parallel on the two lines. .

Note that when forming the corners in the forming press 3, the bending angle is set to 92° for the corner A and 115° for the corner C, as described above, regardless of the size of the square steel pipe, and the radius of curvature R is, for example, the first Process as shown in the table.

The above bending conditions are the most preferable conditions for making the process continuous and obtaining a product with accurate finished dimensions, but they can be varied depending on the size of the steel plate used, etc.

In order to obtain a steel pipe with accurate finished dimensions and shape, it is preferable to process each angle A and C to an angle as close to 90° as possible in the pressing process, but on the other hand, the ease of extraction from the press mold is also taken into account. From this point of view, the gap between the grooves is wide, and therefore there is a demand for angle A or C to be as large as possible.

In consideration of these requirements, corners A and C are bent so that the gap between the grooves is the minimum size from which the mold can be pulled out.

Further, the forming rolls and strain relief rolls are constructed so that they can be adjusted at least within the range of dimensions shown in Table 1 above, so that they can accommodate square steel pipes of various sizes.

As explained above, the present invention is adapted to continuously manufacture a rectangular steel pipe having only one weld line from a single steel plate, and has many effects as described below.

That is, first of all, the amount of welding is halved compared to the conventional two welding lines, so the welding materials and welding work are halved, and the amount of beveling is also halved.

The reduction in the number of warp welds reduces strain generation, which reduces strain relief work, and the reduction in weld lines also helps prevent overlapping of welds when connecting square steel pipes to other parts by welding. It also has the advantage of being easier.

Furthermore, since each process is carried out continuously from the raw material to the finished product, it is possible to eliminate transfers between processes and other operational irregularities, and therefore, the number of workers can be reduced and mass production can be carried out efficiently.

Because of this rationalization in various aspects, rectangular steel pipes can be manufactured at a very low cost, and are of great industrial value.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a conceptual diagram of an apparatus for carrying out the method of the present invention;
FIG. 2 is a cross-sectional view of the flat steel plate in a bending state, and FIG. 3 is a cross-sectional view of the groove. DESCRIPTION OF SYMBOLS 1... Flat steel plate, 2... Bevel processing device, 3... Forming press, 4... Forming roll, 5... Tacking welding machine,
7, 8... Automatic welding machine, 9... Distortion correction roll, 10
... Feed roller, 11, 12 ... Molded product, 14, 3
0...Square steel pipe.

Claims (1)

[Claims] 1. In the method of manufacturing large-diameter square steel pipes, a single steel plate is transported in the length direction and grooves are formed on both sides, and then the four corners of the square steel pipe are bent using a press to form the gaps between the grooves. is formed into a shape similar to a square steel pipe with minimum dimensions that allow the mold to be pulled out, and then transferred while being formed into a square steel pipe shape with forming rolls and sequentially tack welded. Next, the inner and outer surfaces of the groove are A method for producing a large diameter rectangular steel pipe, characterized in that after welding by automatic welding, strain is removed by passing it through a strain relief roll.