JPS6150688B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pipe forming method in the production of steel pipes using the UOE method, and in particular, by reducing the O press load necessary to obtain a perfect circular shape,
The present invention relates to a tube forming method that makes it possible to form a thicker-walled, high-strength, large-diameter tube within a press load.

The tube forming method in steel tube manufacturing using the UOE method basically involves the following steps. That is, as shown in the explanatory diagram of FIG. 1, first, both edge portions 1', 1' of the material steel plate 1 are bent upward using a C press (C-bending process), and then the C-bending process is performed using a U press-thro. The center part of the finished formed material is wrapped around the U punch 2 to form a U shape (U bending process), and then this C-U bent formed material is
In the pressing (c) process, it is formed into a tubular shape using an O-die (O-bending process).

In the C-pressing process, C-bending is normally performed over the entire length of the steel sheet 1 by performing C-pressing several times sequentially from one longitudinal end to the other end. In the case of thick-walled tube forming, O
It is not possible to obtain a sufficiently perfect circular shape by pressing, so this step has a particularly important meaning in forming thick-walled tubes.

In the U-press, the C-bending material is formed into a U-shape, but unlike the case of the C-press, this molding is performed to form the U-shape over the entire length at once. Specific methods include one that performs U-bending using a pair of left and right pressing rolls equipped with a drive device independent of the U-punch 2 (as shown in Figure 1B), and one that performs U-bending using a pair of pressing rolls similar to the above that are linked to the U-punch. There are various types, such as those that use a U-bend, and those that use a rotating tool called a rocker on the left and right that is activated by the movement of a U-punch, but all of them have a shape that can be wrapped around it using a U-punch 2. They agree that it should be molded with The U press has the meaning of preliminary forming from the perspective of the O-bending process with the O-dies 3, 3 in the next process, and it goes without saying that the forming process is performed by using the O-dies 3, 3 of the C-U bending material. 3 must be able to be inserted without any problem.

As in the case of the U press, the O press is used to form the C-U bent material into an O shape over its entire length in one press operation.

In other words, the pipe forming method (hereinafter referred to as the C-U-O press forming method) in manufacturing steel pipes by the UOE method is such that the shape change of the material steel plate 1 during the forming process is C-shaped as shown in Fig. 1. It is characterized by being divided into three stages: , U-shape, and O-shape.

This C-U-O press forming method is currently the most popular method for forming straight seam welded steel pipes, as it is relatively highly efficient and favorable in terms of quality. Applicable to tube forming with wall thickness of 64~40mm and length of 10~18m.

Now, in the above-mentioned C-U-O press forming method, in general, during the forming process of the O press, as shown in Figure 2 A or B, a part of the formed tube is formed in a straight part (hereinafter referred to as an incompletely formed part). ) 4, but in order to completely blend it into the inner surface of the die and make it a perfect circle, approximately P = 2ltσe However, P: Press load l: Pipe length t: Wall thickness σe: Material It was necessary to perform strong circumferential drawing by applying a large press load calculated from yield strength.

For this reason, when attempting to form thick-walled, high-strength, large-diameter pipes such as those used in recent line pipes, the O-press load required for circumferential drawing (hereinafter referred to as "required O-press load") becomes extremely large, resulting in equipment problems. Because the above limit was exceeded, O-forming could not be performed sufficiently and a tube with a good shape could not be obtained.

The purpose of the present invention is to provide a C-U-O press forming method that allows the O-press to form even thick-walled, high-strength, large-diameter pipes into a perfect circular shape within the limit load value. - By improving the shape of the U-bending material, we have reduced the tendency for incompletely formed parts to remain during O-pressing.
The purpose is to reduce the above-mentioned necessary O press load and eliminate it as much as possible.

The process in which the molded material becomes circular during O-pressing (hereinafter referred to as
Even if the material plate thickness t and target pipe diameter D are constant, the forming process (forming process) changes depending on the shape of the C-U bending material carried into the O press. Among them, the C-bending length S and the U-bending width B are representative of the C-U bending shape.
(See Figure 3) has a large influence. However, the forming process of the O press cannot be completely understood with just these two conditions. That is, the U punch 2 used in the U press can generally be broadly classified into a single radius type and a double radius type, and the above-mentioned forming process changes depending on the type. The single radius type has a circumferential surface 2' consisting of one type of circular arc, and when this is used, incomplete forming occurs at around ±45° of the center angle based on the seam position as shown in Figure 2 A during O press. Some parts tend to remain. On the other hand, the double-radius type has a peripheral surface 2' that combines two or more types of circular arcs, and differs from the single-radius type in that the radius of curvature R ₁ of the shoulder of the peripheral surface is made smaller. As shown in FIG. 2B, the incompletely molded portion tends to have a polygonal shape over the entire circumference. The difference between the types of U punches is the difference in the radius of curvature R of the U-bending shoulder of the C-U bending material, so it can be said that this R also greatly changes the forming.

The inventors have determined that these three conditions, namely C bending length S, U bending width B, and radius of curvature R of the bending shoulder,
As a result of experiments and studies, we have succeeded in eliminating as much as possible the tendency for incompletely formed parts to remain during C-pressing and minimizing the required O-pressing load by appropriately selecting these. . Moreover, the appropriate ranges of these three conditions are constant regardless of the material plate thickness and material, and even if the target pipe diameter D changes, S/L, B/
It was found that D and R/D were approximately constant.

That is, the present invention provides the following conditions for providing a proper shape: (a) 0.06<S/L<0.10 (b) 0.75<B/D<1.0 (c) 1/5B/D+0.15<R/D<1/ 2B/D-0.
It is characterized by performing C press and U press so as to satisfy 05, and then O press.
In FIG. 4, the horizontal axis represents B/D and the vertical axis represents R/D, and the range of the U molding shape of the present invention (above B and C) is shown with diagonal lines. Referring to the figure, the range of U-bending shapes that can be obtained with a conventionally commonly used U punch is explained.The range of U-bending shapes that can be obtained with a conventionally commonly used U punch is as follows: In the single-radius type, the shape lies on straight line A, and in the double-radius type, it falls on the broken line B. As described above, the shape of the C-U bending material of the present invention differs from that of the conventional one in the radius of curvature R of the U-bending shoulder. Therefore, this shape can be formed using a double-radius type U-punch in which the shoulder radius R ₁ is formed larger than the conventional one.

By implementing the present invention, it is possible to always minimize the required O press load during C-U-O press forming, and even with thick-walled, high-strength, large-diameter pipes, a good circular shape can be achieved within the press load value limited by equipment. It becomes possible to mold it into.

Next, the reason why the shape of the C-U bending material is limited as described above in the present invention will be described.

If S/L is less than 0.06, the length along the inner surface of the die during O-pressing of the C-bending portion becomes short and good formability cannot be obtained, so it is necessary to set it to 0.06 or more, but it is also necessary if it exceeds 0.10. The O-press load does not decrease much, and on the contrary, it causes operational problems such as side shoes slipping through during U-pressing and reverse bending of the molded material. So 0.06<
S/L<0.10.

Regarding B/D, setting it to 0.75 or more improves the formability during O-pressing, but due to the structure of O-pressing, it is unlikely that it will exceed 1.0, that is, the U bending width B will become larger than the target pipe diameter D. Since there is no such thing, I set it to 0.75<B/D<0.10.

In addition, R/D is determined in relation to the above B/D, but if the value is less than 1/5B/D+0.15, the tendency shown in Figure 2 B will appear in the O press forming process, and 1/2B When /D-0.05 is exceeded, the tendency shown in Figure 1A occurs and the required O press load increases in both cases.
Therefore, 1/5B/D+0.15<R/D<1/2B/D-0.
05 range.

Next, examples of the present invention will be described.

A steel plate with a thickness of 8.7 mm was used as a material, and the shape of the C-U bending material was S/L=0.08, B/D=
0.85, R/D = 0.34, C press and U press, then O press with a press load of 122T, which is 85% of the theoretical value (=2ltσe),
The seam portion was welded to obtain a pipe with a target pipe diameter D = 187 mm.

For comparison, we used the conventional single-radius type and double-radius type for U press, and changed only R/D to 0.42 and 0.25, respectively, to obtain tubes B and C.

The conditions for the three U-shaped shapes mentioned above are shown in FIG. 4 as A, B, and C, respectively.

The results of investigating the molding conditions of pipes A, B, and C are summarized in the fifth section.
Shown in Figures A, B, and C. The horizontal axis of the figure shows the position in the pipe circumferential direction, expressed as the central angle θ taken clockwise with the seam position as a reference, as shown in Figure 6, and the vertical axis shows the curvature at that position relative to the normal curvature. The ratio is X.

In Figure 5, when the single-radius type is used, the variation in curvature around 45° is extremely large in case A, and when the conventional double-radius type is used, there is also large variation overall. In contrast, B according to the present invention is clearly improved, and this degree of variation is within a range that can be used as a product.

As explained above, the C-U-O press forming method of the present invention can reduce the required O press load to about 85% of the conventional one. Even for thick-walled, high-strength, large-diameter pipes that were previously thought to be impossible to form, it is now possible to obtain a good O-shape within the load limit.
The quality of this kind of large diameter pipe is greatly improved. Moreover, since the method of the present invention performs U-pressing using a double-radius type punch, the spring back of the U-bending material is reduced, so it can be prepared for pipe manufacturing with different pipe sizes, material plate thicknesses, and materials. This method has the advantage of requiring fewer types of U-punch (number of tools), and together with the above-mentioned effect of reducing the press capacity, it achieves a significant reduction in equipment costs for manufacturing large diameter pipes. .

[Brief explanation of the drawing]

FIG. 1 is a process diagram of the C-U-O press molding method, in which A shows the C-pressing process, B shows the U-pressing process, and C shows the O-pressing process. FIG. 2 is an explanatory view showing the forming process of the material in the O-press process, where A shows the case where a single radius type is used as the U punch of the U press, and B shows the case where a double radius type is used as the U punch of the U press. Fig. 3 is a front view for explaining the C-U molding shape in the present invention, and Fig. 4 shows the ranges of R/D and B/D in the molding method of the present invention, and the horizontal axis is B/D, The vertical axis is R/D. Figure 5 shows the curvature measured at various circumferential parts of a steel pipe using the C-U-O press forming method, where A is the one according to the present invention and B is the case where a single radius type is used as the U punch. , C respectively show the case of a conventional double radius type, the horizontal axis represents the circumferential position in terms of the central angle θ, and the vertical axis represents the ratio X of the curvature at that position to the normal curvature. FIG. 6 is an explanatory diagram of the horizontal axis θ in FIG. In the figure, 1: raw steel plate, 2: U punch, 3: O die, 4: incompletely formed part.

Claims (1)

[Claims] 1. A method of forming a raw material flat steel plate into a tubular shape in pipe manufacturing by the UOE method, in which both edge portions of the raw material flat steel plate are formed using a C press so that the bending length (S) is as follows (a) The C-bending material is then subjected to C-bending so that it satisfies the following formulas, and then this C-bending material is U-pressed using a U press so that the U-bending width B and the outer radius R of the bending shoulder satisfy the following formulas (B) and (C). After bending, this C-U
A forming method for pipe manufacturing using the UOE method, which is characterized by O-bending a bent material into a tubular shape using an O-press. 0.06＜S/L＜0.10……(A) 0.75＜B/D＜1.0……(B) 1/5B/D+0.15＜R/D＜1/2B/D−0.05…
(c) However, L: Outer circumference length of finished pipe D: Outer diameter of finished pipe