JPS58103917A - Manufacture of large diameter square steel pipe - Google Patents

Abstract

PURPOSE:To form the bottom flat and to form the corner parts on left and right sides of the bottom accurately to specified curvature by restraining the bottom of a primary formed product from inside and outside by a lower roll and inside rolls. CONSTITUTION:A primary formed product 12 resembling a square steel pipe having corner parts greater than 90 deg. is obtained by pressing a steel plate. The bottom of this primary formed product 12 is supported by a lower roll 71, and pressed from inside by inside rolls 74. Under this condition, the product is deformed continuously by pressing from left and right sides and from above by side rolls 73, 73 and upper rolls 72, 72 so that the parts to be joined of the formed product 12 draw near to each other. In the final stage, the formed product 12 is pressed from four sides by outer rolls 71, 72, 73 to finish the product to specified shape. Under the condition, where the product is formed to specified shape of steel pipe and the parts to be joined are butted, welding is performed successively by a high frequency welding machine.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention (1) relates to a method for manufacturing large diameter rectangular measuring pipes used for construction and other purposes.

Conventionally, small-diameter square steel pipes have been manufactured by bending a single plate, but usually 350 ff1f
In the case of large-diameter rectangular steel pipes larger than 350 mm, there are many problems in bending and other aspects, and it is difficult to manufacture large-diameter rectangular steel pipes from a single sheet.

For this reason, the present inventor previously proposed a method for manufacturing a large-diameter rectangular steel pipe from a single steel plate, but the following problems remained with that method as well. That is, as shown in FIG. 5, the side part of the primary molded product 12', which has been press-formed into a shape approximating a square steel pipe with each corner of 90° or more, is rolled by an outer roll 7.
As a result of the bending moment being applied to the bottom when it is pressed and erected with '5', the bottom bulges outward significantly, and the radius of curvature of the corner b' on the side of the bottom becomes normal as shown by the two-dot chain line. The disadvantage is that the radius of curvature is larger than the radius of curvature.

In view of the above points, the present invention is capable of accurately forming the bottom left and right side corners of a large-diameter square steel pipe made of a single steel plate into a predetermined curvature, and prevents the bottom from bulging outward. The purpose of the present invention is to provide a method for manufacturing a large-diameter square steel pipe that can prevent the above problems.

That is, in this invention, after pressing a single copper plate and forming it into a shape similar to a square steel pipe with each corner of 90 degrees or more,
In a method for producing a large diameter rectangular copper tube, in which a primary molded product having a shape similar to this rectangular steel pipe is pressed from the outside with an outer roll to form a rectangular tube shape, and then the joints of the square steel pipe are welded, the outer roll During molding, the inner surface of the side end of the horizontal portion of the bottom of the primary molded product is pressed by an inner roll having a predetermined gap between the inner surface of the side of the next molded product and the inner surface of the corners on both left and right sides of the bottom. This is a method for manufacturing a large-diameter square steel pipe.

Hereinafter, the present invention will be explained with reference to drawings of embodiments. A steel plate 10 is pulled out from a steel plate material 1 into a material supply section, and the bend is straightened by passing it through a leveler 2. Next, the continuous steel plate 10 is cut into a predetermined length by a shearing machine B, and while being fed in the length direction by a transfer roll 4, both sides are trimmed by a cutting machine 5. The steel plate 11 cut to a predetermined size is sent to a press B by the transfer roll 4, and here the corners of the square steel pipe are bent by a flat press die 61 that presses the entire length of the steel plate 11 at the same time. In this forming process, as shown in FIG. 2, first the corner a is bent to a predetermined angle, then the corner C is bent, and then the corner C is bent, and then the corner d is bent. This bending process is performed at corners a and C.
It is preferable that the angle A of the corner A H is 92°, and the angle B of the corner S and d is 115°. As a result of this press forming, a cross-sectional shape similar to that of a rectangular steel pipe is obtained as shown by the solid line in FIG.

As shown in FIGS. 3 and 4, the forming roll 7 includes an outer roll consisting of a lower roll 71, an upper roll 72, and side rolls 76 on both sides which are driven and rotated, and which are fitted into the molded product 12 and rotated as a result. and an inner roll 74. The rolls 71, 72, 73, 74 are arranged in multiple stages in the length direction of the molded product 12, and except for the inner roll 74 in the final stage, the outer rolls 71,
72.73 are placed.

The upper surface roll 72 consists of a pair of unit rolls formed in a tapered shape corresponding to the upper surface of the joint portion of the primary molded product 12. A support 75 is inserted between each of the unit rolls, and a pair of inner rolls 74 are rotatably engaged with the support 75 via a rotating shaft 76. The support body 75 is held movably up and down by a guide 77, and
A downward force is applied by a feed screw mechanism, a compression spring, a hydraulic cylinder, etc. provided at 7 to press the inner roll 74 against the inner surface of the bottom of the molded product 12.

In addition, the end e of this inner roll 74 contacts the inner surface of the side end of the horizontal portion E at the bottom of the molded product 12, and the inner surface of the side portion of the molded product 12 and the inner surface of the corner portions on the right and left sides of the bottom and the forming roll 74, a predetermined gap is formed therebetween. That is, the forming roll 74 is formed to have a width that does not contact the inner surface of the side portion of the molded product 12, and is chamfered at a certain point so as not to contact the inner surface of the corner portion on the side of the bottom portion.

On the other hand, the lower roll 71 has a crown T formed by bulging the center part, and the side rolls 73 are inclined corresponding to the sides of the molded product 12, and this angle of inclination is determined by the side part of the molded product 12. It changes step by step as if it were pressed to stand up.

If such a forming roll 7 is used, the bottom part of the molded product 12 is received by the lower roll 71 and pressed from the inside by the inner roll 74, while the side roll 73 and the upper roll 72
Then, the molded product 12 is continuously deformed by pressing from both left and right sides and from above so that the joints of the molded product 12 approach each other, and in the final stage, the molded product 12 is pressed from all sides by outer rolls 71, 72, and 73 to achieve a predetermined measurement. Can be finished into a tube shape.

When this next molded product 12 is formed into a predetermined steel pipe shape using forming rolls, if it is pressed only by the outer rolls from beginning to end, the bending moment due to the pressing force from the sides will be concentrated only at the corners. However, since it also acts on the bottom part, it has the drawbacks mentioned above (see Fig. 5). By bundling them together, the bottom can be formed flat, and the left and right corners of the bottom can be accurately formed to a predetermined curvature. That is, the inner surface of the side end of the horizontal portion E of the bottom is pressed by the end e of the inner roll 74, the corner is bent using this as a fulcrum, and the bending moment by the side roll 73 acts on the bottom. This prevents the bottom from bulging outward, and the radius of curvature of the corners also does not increase. In this way, the flatness of the bottom part and the uniformity of the radius of curvature of the corner parts can be reliably obtained very easily, so that high-quality square steel pipes can be manufactured at low cost. Furthermore, since the side portion f of the inner roll 74 is configured so as not to come into contact with the inner surface of the molded product 12, unnecessary frictional force is not generated, and the molded product 12 can be smoothly transferred and molded. .

In addition, as shown in the figure, a crown T- is provided on the lower roll 71, and the inner roll 74 is pressed down so that the bottom part is attached to the lower roll 71.
By curving in the opposite direction along the curve, springback can create a flatter bottom. This crown T
The size may be set according to the thickness of the steel pipe, and for thin steel pipes, the crown T may not be provided and a straight lower roll may be used.

In this way, the pipes are formed into a predetermined steel pipe shape, and welding is sequentially performed by a high-frequency welding machine 8 with the joined portions butted together. In this welding, the entire plate thickness is welded, so
Welding from the inside is not necessary, so welding is completed in one step. In addition, unlike conventional submerged arc welding, the amount of heat applied is small because no deposited metal is used, reducing distortion in the product, and there is no need for processes such as beveling and tack welding. And the device can be extremely simplified.

Note that this welding may be performed by high-frequency induction welding or high-frequency resistance welding, and may also be conventional submerged arc welding.

After welding has been completed, the secondary molded product 16 is smoothed by scraping the excess thickness of the welded part on the outer surface as necessary, and then sent to the strain correction device 9, where the strain is removed by a press or a roll. The rectangular steel pipes 14 that have undergone strain correction are passed through an inspection device 20 such as an ultrasonic flaw detector to inspect the welded parts, and are then arranged as finished products 15.

As explained above, this invention is a method for manufacturing a large-diameter square steel pipe having only one weld line from a single sake plate, which improves the flatness of the bottom and the uniformity of the radius of curvature of the left and right corners of the bottom. This method has the advantage of being able to accurately obtain square steel pipes and producing high quality square steel pipes at low cost.

[Brief explanation of the drawing]

Fig. 1 is a process diagram showing an embodiment of the present invention, Fig. 2 is a cross-sectional view of a single steel plate in a state of bending, Fig. 3 is a longitudinal cross-sectional side view showing a state of forming by forming rolls, and Fig. 4 is a I in Figure 6
A sectional view taken along the line V-IV, and FIG. 5 is a cross-sectional view showing the shape of a steel pipe made by a conventional method. 6... Forming press, 7... Forming roll, 8... Welding machine, 10... Single steel plate, 12... - Next molded product, 7
1°72, 74...Outer roll, 74...Inner roll, E-Horizontal portion, f...Side part of the inner roll. Patent Applicant Nakajima Co., Ltd. Agent Patent Attorney Kotani Hatai-8'

Claims (1)

[Claims] 1. After pressing a single sheet steel plate and forming it into a shape that approximates a square steel pipe with 900 or more corners, this primary molded product with a shape that approximates a square 8M pipe is pressed from the outside with external rolls to form a square steel pipe. In the manufacturing method of large-diameter square steel pipes in which the joints of the square pipes are welded after forming, the inner surface of the side end of the horizontal part of the bottom of the primary formed product is 1. A method for producing a large-diameter square steel pipe, characterized in that the product is pressed by inner rolls having a predetermined gap between the inner surface of the side and the inner surface of the corners on both left and right sides of the bottom.