JPH04105709A - Manufacture of resistance welded tube - Google Patents

Abstract

PURPOSE:To make the tips of an inside bead easy and to prevent cracks from generating by forming the end faces of an open pipe into an inverted Y formed groove with a fin pass roll to weld and join the end faces. CONSTITUTION:The end face parts of the open tube are formed by a fin plate 142a of a finish fin pass upper roll 142 of a group 3 of fin pass rolls into the inverted Y formed groove shape, therefore, the molten metal is reduced in case of the weld joining an in case of the upsetting, the molten metal is supported by the end faces opened in the inverted V form on the lower side of the end face parts formed at the inverted Y formed groove, does not sag in the form of a projection, a resistance welded tube having no opening and an easy form at the tip part of the inside bead is obtained and no cracking is generated by bad form of the inside bead.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an electric resistance welded steel pipe that can obtain an electric resistance welded steel pipe with excellent workability and fatigue resistance by improving the inner bead shape of the welded part. This invention relates to a method for manufacturing steel pipes.

[Conventional technology]

FIG. 1O is an explanatory diagram of the configuration of a general manufacturing apparatus for electric resistance welded steel pipes. In the same figure, the raw material band jll+ is uncoiled at a constant speed from the uncoiler 2, and after being shaped into a semicircular shape by the - group of breakdown rolls 3, it is rolled by a group of fin pass rolls 4, which will be described later, as shown in FIG. It is formed into a tubular open pipe 5 having an end face portion (edge portion) 5E or an I-shaped opening shape as shown in FIG. The end face portion 5E of the formed open pipe 5 is heated and melted by a work coil 6 of a high frequency induction welding device, and in this state is upset (pressurized) from the lateral direction using a squeeze roll 7 to join. And the external beat of the weld (
The remaining material is removed by cutting with the cutting tool 8. The inner bead may be removed if necessary, but it is generally difficult to remove the inner bead from small-diameter pipes, so they are used with the inner bead still attached.

Here, regarding the forming of an oven pipe using the above-mentioned group of fin pass rolls 4, Fig. 1) (a) showing the shape of the main part of the conventional first-stage fin pass upper roll and the shape of the main part of the conventional finishing fin pass upper roll are shown. Figure 1) shows (
The following description will be made without reference to bl.

1) As shown in FIG. A fin plate 41a having an approaching inclined surface TC is fixed thereto. Therefore, first, the first stage fin pass upper roll 41 and the first stage fin pass lower roll (not shown) having no fin plate form a tubular open pipe 5a having a V-shaped open end shape. In the - group of fin pass rolls 4, fin pass upper rolls are sequentially arranged from the first stage side toward the finishing side, and the fin plate has a smaller inclination angle and a thinner thickness as it goes toward the finishing side. Furthermore, as shown in FIG. 1(b), the fin plates 42a of the finishing fin pass upper roll 42 have parallel surfaces with no inclination. As a result, as shown in FIG. 12, a tubular open pipe 5 having an end face 5E having an I-shaped opening shape is finally formed.

In this way, the open pipe 5 is formed, and the end faces 5 of the open pipe 5 are welded together to produce an electric resistance welded steel pipe. FIG. 13 is an explanatory cross-sectional view showing an example of a welded part of an electric resistance welded steel pipe by a conventional manufacturing method.

As shown in the figure, the tip of the inner bead has a triangular shape with three protrusions connected in a row, creating a so-called opening. In addition, a white layer whose strength is lower due to decarburization than the surrounding area is formed in the tube wall thickness direction (vertical direction in the figure) at the center of the weld. When an electric resistance welded steel pipe with a wide white layer is used in a product, it is more likely to break than the white layer due to the torsional stress applied thereto. Therefore, when upset is performed using the squeeze roll 7 so that the width of the white layer is narrowed, a phenomenon occurs in which the opening at the tip of the inner bead becomes even larger.

[Invention or problem to be solved]

In the conventional ERW steel pipe manufacturing method introduced above, the end face of the open pipe is formed into an IW groove shape using fin pass rolls, so when the end face is welded and joined, the tip of the inner bead of the welded part In the area, the hanging beets form protrusions and extend in the inner circumferential direction, creating an opening. For this reason, when using an ERW steel pipe with an opening in the inner bead when flattening, expanding, bending, etc. is applied to it when used as a product, cracks are likely to occur from the inner bead. There are some problems. In addition, when used in automobile parts and mechanical parts, recently they are often used after being heat-treated by quenching and tempering, or there is a problem that the open part of the inner bead is likely to become a starting point for fatigue fracture. There is also.

This invention was made in order to solve the above-mentioned conventional problems, and by making the inner bead shape of the welding part a gentle shape without an opening, the present invention provides an electric wire with excellent workability and fatigue resistance. The object of the present invention is to provide a method for manufacturing an electric resistance welded steel pipe, which yields a welded steel pipe.

[Means to solve the problem]

In order to achieve the above object, the method for producing an electric resistance welded steel pipe according to the present invention includes a steel strip formed into a semicircular shape by a breakdown roll, and a predetermined groove shape formed at the end surface by a fin pass roll. In a method of continuously manufacturing an ERW steel pipe by forming a tubular open pipe and joining its end face by high frequency welding, the end face of the open pipe is formed into an inverted Y-shaped bevel shape using a fin pass roll. It is characterized by

[For production]

In the method for manufacturing an electric resistance welded steel pipe according to the present invention, the end face of the open pipe is reversely Yff
Since it is formed into an I-bevel shape, when welding it, there is less molten metal compared to the conventional ■-shaped opening shape, and at the time of upset, the molten metal flows into the end face formed into an inverted Y-groove shape. Since it is supported by the inverted V-shaped end face on the lower side of the bead and does not hang down like a protrusion, the tip of the inner bead has a gentle shape with no opening.

〔Example〕

Embodiments of this invention will be described below based on FIGS. 1 to 9.

Fig. 1 is an explanatory diagram of the configuration of an electric resistance welded steel pipe manufacturing apparatus for carrying out the present invention, and Fig. 2 (al and fb) shows the shape of the main part of the roll on the fin pass of the electric resistance welded steel pipe manufacturing apparatus shown in Fig. 1. FIG. 2 (fat) is a diagram showing the shape of the main part of the first stage fin pass upper roll, and FIG. 2 (b) is a diagram showing the shape of the main part of the finishing fin pass upper roll. In addition, the first
In the figure, the same components as in FIG. 10 are indicated by the same reference numerals, and the only different component is the fin pass upper roll of a group of fin pass rolls, so a description of the other components will be omitted.

In FIG. 1, reference numeral 14 denotes a group of fin pass rolls, and in this embodiment, three sets of fin pass rolls each consisting of an upper and a lower pair are arranged.

Among these fin pass rolls 14, as shown in FIG.
a is fixed, and this fin plate 14
Both side surfaces protruding from the arcuate outer circumferential surface of 1a include a first inclined surface TA that approaches each other toward the tip, and a second inclined surface TA that is connected to this first inclined surface TA and also approaches each other toward the tip.
It is formed by the inclined surface TB. The inclination angle θ2 of the second inclined surface TB on the tip side is smaller than the inclination angle θ1 of the first inclined surface TA, and θ2=θ+X.
A value of about (1/20 to 1)5) is appropriate.

In addition, whether the illustration is omitted or the first stage fin pass upper roll 1
41 and the finishing fin pass upper roll 142, there is an inclination angle θ of the first inclined surface TA of the fin plate 141a of the first stage fin pass upper roll 141.
, an intermediate fin pass upper roll to which a fin plate is fixed, which is smaller and whose inclination angle of the second inclined surface is the same as that of the fin play H41a of the first stage fin pass upper roll 141, is disposed. Further, as shown in FIG. 2(b), the fin plate 142a of the finishing fin pass upper roll 142 is thin so as to have parallel surfaces with no inclination. Note that each lower fin pass roll of the fin pass roll 14 is not shown in the drawings, or is a drum-shaped roll having an arcuate outer circumferential surface without a fin plate, as in the prior art.

Next, regarding the forming of an open pipe using the group of fin pass rolls 14 described above, FIG. 2 fa) and FIG.
1 and FIG. 3, which is a diagram showing the groove shape of the end face portion of the open pipe according to the present invention, will be described below.

First, as shown in FIG. 2(a), the steel strip l formed into a semicircular shape by the breakdown rolls 3 is rolled by the first stage fin pass upper roll 141 and the first stage fin pass lower roll (not shown), so that the end face part or the second stage is It is formed into a tubular open pipe 15a having an approximately Y-shaped groove shape with an inclined surface.

Next, the first stage fin path upper roll 14 is formed by the above-mentioned intermediate fin path upper roll and intermediate fin path lower roll.
An open pipe (not shown) is formed in which the opposing end surfaces formed on the first inclined surface TA of the first fin plate 141a are brought close to parallel. In this case, Finplay H41
The inclination angle of the opposing ground (end surface on the root side) formed by the second inclined surface TB of a is maintained as it is.

Then, as shown in FIG. 2(b) and FIG.
A tubular open pipe I5 having an inverted Y-shaped groove shape is formed. In this case, the groove surface length of the root portion shown in Fig. 3 is L = (0,1 to 0.3
) Xt range is appropriate.

Next, an open pipe with a Y-shaped groove shape is formed on the end face in this way, and the end face is welded and joined, and the pipe wall thickness t is 3.0 mm and the outer diameter is 25.4 mm. A steel pipe manufacturing test was conducted under the pipe manufacturing conditions shown in Table 1. For comparison, an open pipe having an end face having a conventional Y-shaped groove shape as shown in FIG. 12 was formed, and a manufacturing test of the electric resistance welded steel pipe was also conducted.

Figure 4 shows the welded part of the manufactured electric resistance welded steel pipe.

Further, Table 2 shows the results of processing tests on the manufactured electric resistance welded steel pipes. This machining test includes a flattening test where the weld is located in the compression direction and the distance between the plates is H = 2t, as shown in Figure 6, and a flattening test where the weld is placed perpendicular to the compression direction as shown in Figure 7. As shown in Figure 8, the flattening test was carried out with the distance between the plates H = 2t, and the distance D, /D = 1.5.
(D is the outside diameter of the tube expansion punch) and a bending test was conducted at 180 degree bending R = 2D (R is the bending radius) as shown in Figure 9. I checked to see if it was there.

(Hereafter, margin) Table 1 (note) t represents the tube wall thickness.

(Hereafter, margin) (note) Table 2 The numbers in the table indicate the number of cracked pieces/the number of pieces tested.

(Hereinafter, blank space) As shown in Fig. 4, in the conventional ERW steel pipe where the end face of the open pipe is shaped like a The width of the white layer in the welded area is wide due to the shortage. In sample No. 2, the width of the white layer is narrower, or there is an opening at the tip of the inner beat.

In addition, the end surface of the open pipe is made into an inverted Y-shaped groove shape, and the length of the groove surface at the root portion is L = (01 to 0.3).
In the electric resistance welded steel pipe according to the comparative example outside the range of xl, sample number 3, which has only a short groove surface length, has a shallow opening at the tip of the inner beat. If the groove surface length L is too long, the white layer will break in the middle of the tube wall thickness direction.

On the other hand, the end face of the open pipe is shaped like an inverted Y-shaped groove, and the length of the groove face at the root is L=(0,1~
0.3) In the electric resistance welded steel pipe according to this invention example in which Xt is in the range, as shown in sample numbers 4 and 5, smooth-shaped inner beads with no openings are obtained.

Moreover, from Table 2, it can be seen that the electric resistance welded steel pipe obtained by the present invention has excellent workability.

FIG. 5 is a diagram showing the results of a torsional fatigue test on an electric resistance welded steel pipe. This fatigue test was conducted with a pipe wall thickness of 2.6 mm and an outer diameter of 22 mm.
．． This was carried out on a 2mm ERW steel pipe. In the same figure, the pipe-making conditions for the sample are the same as those for sample number 2 in Table 1, and the pipe-making conditions for sample B are as shown in Table 1. The tube-making conditions for Sample C are the same as those for Sample No. 5 in Table 1.

As shown in FIG. 5, electric resistance welded steel pipes manufactured using the conventional method tend to break at the inner surface beat, and their fatigue life is short. On the other hand, it can be seen that according to the method according to the present invention, an IER steel pipe that does not break from the inner bead and has a longer fatigue life than the method using the conventional method can be obtained.

〔Effect of the invention〕

As explained above, in the method for manufacturing an ERW steel pipe according to the present invention, the end face of the oven pipe is formed into an inverted Yffi bevel shape using fin pass rolls, and the end face is welded and joined. It is possible to obtain an electric resistance welded steel pipe having a rounded tip end. As a result, even if the electric resistance welded steel pipe obtained according to the present invention is subjected to flattening, pipe expansion, bending, etc., cracking will only occur due to poor shape of the inner bead. Further, even when used as automobile parts, mechanical parts, etc. after processing, the fatigue life can be extended compared to conventional ones without the occurrence of breakage due to defective shape of the inner bead.

That is, according to the present invention, it is possible to provide an electric resistance welded steel pipe with excellent workability and fatigue resistance.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the configuration of an electric resistance welded steel pipe manufacturing apparatus for carrying out the present invention, and FIGS. FIG. 2 (al is a diagram showing the shape of the main part of the upper roll on the initial fin pass, FIG. 2 (bl is a diagram showing the shape of the main part of the upper roll on the finishing fin pass, and FIG. 3 is a diagram showing the shape of the main part A diagram showing the groove shape of the end face of the oven pipe according to the present invention, FIG. 4 is a diagram showing a welded part of an ERW steel pipe in a manufacturing test, and FIG. 5 is a diagram showing the results of a torsional fatigue test of an ERW steel pipe. , 6th
Figures 8 and 7 are diagrams for explaining the flattening test.
Figure 9 is a diagram for explaining the tube expansion test, Figure 9 is a diagram for explaining the bending test, Figure 10 is a diagram explaining the configuration of a general manufacturing equipment for ERW steel pipes, and Figure 1 (al. 1) is a diagram showing the shape of the main part of the conventional first-stage fin pass upper roll, FIG. 1) (b) is a diagram showing the shape of the main part of the conventional finishing fin pass upper roll, and FIG. FIG. 13 is a cross-sectional explanatory view showing an example of a welded portion of two ERW steel pipes by a conventional method. ■...Strip steel, 2-Uncoiler, 3-Breakdown roll group, 4.14-Fin pass roll group, 5, 5a
, 15. 15a-Oven pipe, 6...-Work coil of high frequency induction welding device, 7--Squeeze roll, 8-1. Cutting tool, 41, 141--First stage fin pass upper roll, 41a, 141a Fin plate of first stage fin pass upper roll, 42, 142-1 Finishing fin pass upper roll, 42a, 142a--Fin plate of finishing fin pass upper roll, TA No. 1 inclined surface, TB...-2nd inclined surface.

Claims (1)

[Claims] (1) A steel strip formed into a semicircular shape by a breakdown roll is formed into a tubular open pipe whose end face has a predetermined bevel shape by a fin pass roll, and the end face is joined by high frequency welding. A method for continuously manufacturing an electric resistance welded steel pipe, characterized in that the end face portion of the open pipe is formed into an inverted Y-shaped bevel shape using a fin pass roll.