JPS6323856B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a thin-walled electric resistance welded pipe (t/D<0.10) in a method of forming a pipe using a roller forming machine.

In general, roller forming of electric resistance welded pipes is divided into breakdown forming, fin pass forming, squeeze roll forming, etc. according to the forming steps. Conventionally, a method has been adopted in which bending is performed near the edge of the plate from the initial stage of breakdown, and the curvature is gradually increased to bring the cross section closer to a circle.

However, in the case of thin-walled tubes, such a forming method has the following drawbacks. That is, in general, in the case of roller forming, as shown in FIG. 1, the vicinity of the edge of the plate extends considerably in the longitudinal direction. Moreover, this elongation strain causes edge buckling. This tendency becomes even more pronounced in the case of edge bends as shown in FIG.

When an edge bend as shown in Fig. 2A is performed, the vicinity of the edge of the plate stretches in the longitudinal direction as shown in B. Therefore, the plate should be balanced by adopting the stress distribution shown in C. In other words, compressive stress occurs near the edge of the plate (indicated by diagonal lines in the figure), and tensile stress occurs at the center of the plate. It is thought that this makes the edge part prone to buckling.

After that, the method is to gradually increase the curvature and make the cross section closer to a circle, but in this case, due to springback, the butt shape of the welded part becomes an I-groove as shown in Figure 3. Instead of forming a V-groove, welding defects are more likely to occur.
Furthermore, if the edge back ring remains at the weld joint, the butt shape may be offset as shown in FIG. 4, resulting in poor welding.

The present invention advantageously solves these drawbacks of conventional forming methods, prevents the occurrence of edge buckling due to edge bending, prevents deterioration of the butt shape due to spring back, etc., and makes it possible to obtain an ideal weld end face shape. It was designed so that

That is, an object of the present invention is to allow thin-walled electric resistance welded tubes to be formed easily and welded after forming, and the gist of the present invention is to:
In roller forming of thin-walled electric resistance welded tubes (t/D<0.10), the length l (2.0t<l<5.0t) from the plate end is formed into an oval (or oval) shape without bending. This is a molding method characterized by:

The thin-walled electric resistance welded tube in the present invention means t/D<
0.10 is a general term and applies to roller molding.
FIG. 5 shows a conventional molding method. In contrast, the molding method of the present invention is shown in FIG.

That is, in FIG. 6, the end portion of the plate is not bent and formed, but is left with zero curvature until the end. It is characterized by the fact that the curvature is zero from beginning to end for a certain distance from the edge of the board. In the figure, 1 shows an example in which the upper roll and the plate edge do not touch, and 2 shows an example in which the lower roll and the plate edge do not touch. However, in the fin pass process, the drawing ratio is made smaller than in the past, and no active bending is attempted, but due to the characteristics of the fin pass, there may be some curvature.

In addition, there are two possible series, I and Ro, before arriving at Finpass. Regarding B, bending within the cross section is similar to UO forming, but since UO forming is approximately two-dimensional bending, it is essentially different from roller forming where the restraint of the front and rear stands influences forming.

As shown in FIG. 6, in order to prevent damage to the edge of the plate at the initial stage of breakdown, the edge of the plate should not come into contact with the roll. However, as for the method of bending near the edges (however, the curvature of the sheet edge is zero), there are two methods: bending with a pair of truncated conical rolls as shown in Figure 7A, and a method of bending with a pair of truncated conical rolls as shown in Figure 7B. Various methods can be considered, such as a method of bending with an inclined roll, but the method is not particularly critical.

Furthermore, edge bending at the early stage of breakdown tends to cause edge buckling as shown in FIG.
As shown in the figure, by stretching not only the edges but also the center, the compressive stress (indicated by diagonal lines in the figure) is distributed not only to the edges but also to the center, reducing the compressive stress at the edges. This has the effect of reducing the size and preventing the occurrence of edge buckling.

As shown in Figure 6B, it is sufficient to form the material into a nearly U-shaped cross section, and the shoulder portion should be bent to the extent that it enters the fin path and is deformed along the hole shape. Even if the bending shown in the figure is applied, the elongation of the edge portion is thought to be slight.

Next, the reason why it is easier to obtain a butted shape with the present invention than with conventional molding methods will be described.

FIG. 10 schematically shows the relationship between bending radius and springback in general. That is, if the bending radius is large as shown in FIG. 10A, the plastic deformation will hardly progress, and the material will almost return to its original state when the load is removed. However, if the bending radius where the plastic deformation permeates in the thickness direction is small, as shown in FIG. Therefore, since the spring back is smaller as the bending radius is smaller, it is thought that the spring back of the present invention is smaller as shown in FIG. 11. Therefore, in the case of the present invention, it is easier to obtain an I groove.

Next, the reason for setting t/D<0.10 is that the present invention has a remarkable effect on thin-walled pipes where phenomena such as edge backling and roofing are likely to occur during forming. This is not preferable because it makes it difficult for buckling to appear.

In the present invention, in which the length from the edge of the plate is formed without bending, the length varies depending on t/D,
For example, when t/D: 0.10, approximately 2t (t is plate thickness) is preferable, and when t/D: 0.01, approximately 5t is preferable. That is, in each of the above, if is made greater than
It is difficult and undesirable to finally round the steel pipe in the sizing process after welding.

Next, examples of the present invention will be described.

FIG. 12 shows an example in which t/D=2.0%, focusing on the elongation strain at the edge portion. With the No. 1 stand, the edges of the board do not stretch, but are rather compressed, so there is no need for edge backling.
As initially expected, an I-bevel close to the ideal was obtained.

[Brief explanation of the drawing]

Figure 1 is a diagram of longitudinal elongation (membrane) strain at the initial stage of breakdown, Figure 2 is an explanatory diagram of the mechanism of edge buckling, Figure 3 is an explanatory diagram of butt failure due to spring back, and Figure 4 is an illustration of the butt failure due to spring back. An explanatory diagram showing an example of a butt failure due to edge backling, Fig. 5 is an explanatory diagram of the conventional forming method, Fig. 6 is an explanatory diagram showing the forming method of the present invention, and Fig. 7 shows an edge bending method. Explanatory diagram, Fig. 8 is a schematic diagram of edge back ring, Fig. 9 is a chart showing longitudinal elongation strain and residual stress distribution in the forming method of the present invention, Fig. 10 is the relationship between bending radius and spring back. FIG. 11 is an explanatory diagram showing the difference in spring back between the conventional method and the molding method of the present invention, and FIG. 12 is a change in elongation strain (film strain) of the edge portion in an example of the present invention. This is a chart showing the following.

Claims (1)

[Claims] 1 Thin-walled electric resistance welded pipe (t/d<0.10. However, t is the plate thickness,
D is the outer diameter).
A method for forming a thin-walled electric resistance welded tube, characterized in that the length portion (2.0t<l<5.0t) is formed into a shape close to an ellipse (or ellipse) without bending.