JP2520547B2 - Electric resistance welding equipment for spiral steel pipe - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of a spiral steel pipe in which a strip-shaped steel plate (coil) is spirally wound, welded by high frequency or low frequency electric resistance welding, and then finish welded by submerged arc welding. The present invention relates to a device for favorably performing electric resistance welding.

[0002]

2. Description of the Related Art Conventionally, most spiral steel pipes have been manufactured by submerged arc welding. In recent years, however, in order to improve welding efficiency, the coil edge portion is first pressure-welded by electric resistance welding at the same time as forming, and then The welding method of finishing by submerged arc welding has come to be used.

As for this welding method, there is an invention described in Japanese Patent Application Laid-Open No. 52-72353 as an initial method. The high-frequency electric resistance welding described in the relevant publication employs a method in which the groove projections of the coil edge are overlapped with each other from above and below. Further, as a method for producing a spiral steel pipe simply by electric resistance welding, Japanese Patent Publication No. 43-113.
There is one disclosed in Japanese Patent Publication No. 77.

[0004]

All of the above-mentioned prior arts form the basic technique of the electric resistance welding method for spiral steel pipes, but depending on the conditions, it may not be possible to satisfy the recent demand for high quality welded parts. In particular, some of the welding defects may occur due to flashing during welding (also called sputtering, which is a phenomenon in which current is short-circuited near the welding start point and molten steel is blown away), which is due to the nature of electric resistance welding itself. There was a drawback.

FIG. 2 is a diagram showing a conventional electric resistance welding method in manufacturing a spiral steel pipe. In FIG. 2, 1 is a spiral steel pipe, 2 is an outer surface pressing roll, 3 is a forming roll, 4 is a pressure roll, 5 is a contact tip for electric resistance welding, and θ is an APEX angle in electric resistance.

In the conventional welding of spiral steel pipes,
Submerged arc welding is the mainstream, and since the apex angle θ in FIG. 2 is mainly formed in the forming of the steel pipe, rolling and submerged arc welding were usually performed even at a narrow angle.

However, when the spiral steel pipe 1 is welded from the steel strip coil 8 as shown in FIG. 3 after the electric resistance welding is used together, the steel strip coil 8 and the spiral steel pipe 1 contact with each other at the contact point of the welding electrode. The angle (apex angle; θ) formed between the position (contact tip position) and the welding contact point 6 necessarily inevitably changes depending on the outer diameter size of the spiral steel pipe 1. Therefore, depending on the manufacturing conditions of the spiral steel pipe 1, The apex angle θ becomes smaller and the welding contact point 6
Flushing 7 occurs in the vicinity of, causing problems such as poor welding, scattering of molten steel, and melting of molten steel.

The present invention provides an apparatus for eliminating the flushing phenomenon at the time of electric resistance welding in the conventional spiral steel pipe manufacturing and realizing a method in which flushing does not occur.

[0009]

According to the present invention, the distance between one coil edge of the steel strip coil 8 to be welded shown in FIG.
If the distance from the welding point 6 to the welding point 6 is L and the angle between the welding point 6 and the coil edges is θ (apex angle), θ = tan ^-1 C / L is wider than before. It is an electric resistance welding device for a spiral steel pipe, which is characterized by adjusting an angle θ formed by a coil edge.

First, in welding, when the welding current is I, the frequency is f, and the output of the oscillator is EpIp, there is a relation of I = k · EpIp / f, and the welding current I is directly proportional to the output EpIp and It is known to be inversely proportional to f.

4 and 5 show an outer diameter of 1600φ and a plate thickness of 12
mm, welding speed 6 m / min, L = 200 mm is a graph showing the relationship between the flushing generation level and the apex angle θ and the output EpIp when electric resistance welding is performed. As shown in FIG. 5, it can be seen that the amount of flushing decreases as the apex angle θ increases, as shown in FIG. (In the figure, the flushing generation level indicates a level at which flushing does not occur at all.) That is, if the frequency f is constant from the above relational expression, the current I
Indicates that the larger the value is and the smaller the apex angle θ is, the more the flushing is likely to occur.

Since the frequency and current during welding have a great influence on the welding itself, it cannot be changed significantly.
Generally, for a spiral steel pipe having a large outer diameter, it is necessary to forcibly increase the apex angle θ in order to solve the problem that the apex angle θ becomes small. However, this also cannot be easily changed because the rigidity of the steel strip coil itself is usually high. Therefore, the inventors of the present invention can increase the apex angle by using the device shown below.
Wide apex angle θ for most tube sizes,
Enabled to hold enlarged.

FIG. 1 is a diagram showing the apparatus of the present invention. FIG.
In (a), 9 is a coil side pressing roll, which is a roll newly provided in the conventional spiral steel pipe manufacturing apparatus. The apex angle enlarging operation according to the present invention is performed by the coil pressing roll 9 shown in FIG. This is a method in which the coil edge on the side of the steel strip coil is locally pushed down just before welding, and is performed by the coil pressing roll 9 in FIGS. 1 (a) and 1 (b). And their effects are shown below.

In FIG. 6, the coil pressing roll 9 is
It is connected to the bracket 11 via the roll bearing 14. The bracket 11 is housed in a tubular outer cylinder 13 in a state where it can move freely in the vertical direction. In order to adjust the vertical movement of the bracket 11, a hydraulic jack 12 is housed in the bottom of the bracket 11, and the pushing force and stroke of the hydraulic jack 12 are transmitted to the bracket 11 to cause the bracket 11 to move. 11
It is possible to vertically move the coil pressing roll 9 connected to and to control the adjustment amount. Since the outer cylinder 13 is fixed to the forming stand 10, a force for pushing down the edge of the steel strip coil 8 is applied to the vertical movement device of these coil pressing rolls 9.

FIG. 7 shows an actual outer diameter 16 using this device.
00φ, plate thickness 12mm, welding speed 6m / min, L = 200mm
2 shows the relationship between the vertical movement amount of the coil pressing roll 9 and the apex angle in the case of electric resistance welding in FIG.
The apex angle is improved, which shows that a wider angle than before can be reliably ensured. That is, at least, by using the coil pressing roll 9 in addition to the conventional method, a wide apex angle can be secured in most tube sizes.

[0016]

As described above, according to the present invention,
Eliminates the occurrence of flashing during electrical resistance welding, which was caused by the conventional narrowing of the apex angle while depending on the forming of spiral steel pipes, resulting in a significant reduction in welding defects, improving welding efficiency and welding. It can contribute to the improvement of quality.

[Brief description of drawings]

FIG. 1 is a diagram showing a method for expanding the apex angle in the present invention.

FIG. 2 is a diagram showing a conventional method for manufacturing a spiral steel pipe.

FIG. 3 is a diagram showing a phenomenon of occurrence of flushing during welding in the conventional method.

FIG. 4 is a diagram showing a relationship between a welding output, a flashing occurrence state, and an apex angle.

FIG. 5 is a diagram showing a relationship between an apex angle and a flashing occurrence state.

FIG. 6 is a diagram showing a device configuration for forcibly pushing down the edge on the steel strip coil side.

FIG. 7 is a diagram showing an effect of expanding an apex angle by a coil pressing roll.

[Explanation of symbols]

 1 Spiral Steel Pipe 2 Outer Press Roll 3 Forming Roll 4 Pressure Roll 5 Contact Tip for Electric Resistance Welding 6 Welding Point 7 Flushing 8 Steel Strip Coil 9 Coil Side Holding Roll 10 Forming Stand 11 Bracket 12 Hydraulic Jack 13 Outer Cylinder 14 Roll Bearing

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasunori Mori No.1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Co., Ltd. Kimitsu Works (72) Inventor Takeshi Kitasato 46-59 Nakahara, Tobata-ku, Kitakyushu, Fukuoka Nittetsu Plant Design Co., Ltd.

Claims (1)

(57) [Claims] 1. A spiral steel pipe manufacturing apparatus in which a steel strip is spirally wound and electric resistance welding is performed by pressing a coil edge on the steel strip side and a coil edge on the steel pipe side, and a coil on the steel strip side is provided immediately before welding. An electric resistance welding device for a spiral steel pipe, characterized by having a coil side pressing roll for pushing down the edge to widen an angle θ represented by the following formula. θ = tan ^-1 C / L where C is the distance between the steel strip side coil edge and the steel pipe side coil edge at the welding electrode contact point position L is the distance from the steel strip side welding electrode contact point position to the welding point