JPS62286675A - Multi electrode gas shield arc welding method for strip steel - Google Patents

Abstract

PURPOSE:To prevent the defect in welding and to improve the efficiency by using the wire of specific diameter for the preceding DC electrode and the AC power source provided with a refiring means and the wire of the prescribed diameter for the succeeding electrode and regulating the electrode gap in the specific distance. CONSTITUTION:The wire in 1-2mm small diameter is used for the preceding electrode and the wire in >2mm diameter for the succeeding electrode and they are respectively connected to the AC power source 12 provided with a DC power source 11 and pulse generating device 13. A multi electrode shield arc welding is performed with regulating the distance between both electrodes in 25-350mm. Since a DC welding is performed by using a small diameter wire for the preceding electrode 7 a good URANAMIbead 5 is formed and a front bead 17 is formed with preventing a pear shape crack with the enlargement of the bead width because of a large diameter wire and AC power source being used for the succeeding electrode 8. Consequently, the defect in welding can be prevented and the efficiency can be improved.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Industrial Application Field) The present invention provides a gas-shielding system for steel strips in a continuous pipe forming line while connecting the lateral ends of the steel strips. The present invention relates to a welding method for butt joining by arc welding.

(Prior art) In the steel industry, in order to continuously manufacture pipes on production lines for electric resistance welded steel pipes, spiral steel pipes, etc., weld steel strips that will serve as pipe material in lots, and It is necessary to supply

The threading of these steel strips is usually done temporarily while welding, but
The time allowed for this welding depends on the line speed and the capacity of the looper installed on the line, but in order to improve the productivity of pipe making, it is required to be as short as possible.

In addition, high-quality joints that do not cause weld breakage are required, especially in the process of forming thick-walled pipes. Furthermore, the groove shape at the M contact point where these steel strips are to be joined remains in the same shape as the shear cut in order to shorten the process time.

FIG. 5 is a cross-sectional view of a butt weld groove of a steel strip in a steel strip connection processing line.

One end m1-a of the steel strip and the other end 1-b are butted against each other, and a copper butt 2 is pressed against the back surface of the steel strip to form a welding groove 3. The shape of the end of the steel strip is cut by shear cutting because it is necessary to cut the steel strip in a short time, resulting in a narrow bevel with a narrow angle and width as shown in FIG.

As conventional welding methods, flash butt welding, submerged arc welding, carbon dioxide shielded arc welding, etc. have been applied. Flash butt welding allows joining in a short time and is most suitable for welding steel strips.

However, when the thickness of the steel strip becomes 6 cm or more and about 2011111 mm, the power supply capacity for this flash butt welding becomes excessive and it becomes necessary to introduce expensive equipment.

On the other hand, in the case of arc welding such as submerged arc welding,
Thin plates with a thickness of 6 or less can be welded with one electrode, but thicker plates require multi-electrode multi-layer welding to prevent d-junction cracking, and in practice two-electrode ISi welding is required. However, it is limited to cases where thin plates or low-speed welding is permitted, and there are limits to its application to thickening steel strips, shortening welding time, or increasing speed.

Furthermore, among arc welding, submerged arc welding requires a process of removing and recovering flux and slag on the front and back sides of the weld bead, which is disadvantageous for shortening welding time.

On the other hand, gas-shielded arc m-contact normally uses a DC power source, and in order to ensure penetration, a high current density is applied using a small diameter wire.
Although welding is required, the shape is narrow and deep, and hot cracking is likely to occur.

In other words, Fig. 3 shows the bead when the narrow gap 3 shown in Fig. 5 with a plate thickness of 6 mm or more is welded by the conventional single-electrode gas-shielded arc welding method using a DC power source using a small diameter wire. An example of the cross-sectional shape is shown.

In this way, when one layer is in contact with narrow gap welding, the cross-sectional shape of the bead becomes a so-called blank bead, and the 4th layer in the center of the bead
This results in a state in which hot cracking is likely to occur as shown in .

When welding thick plates, it is generally known to use multiple electrodes, but in this case, for example, even if two electrodes are used with small diameter wires, hot cracking of the bead in the second box will occur for the same reason as above. cannot be completely prevented.

In addition, in multi-electrode welding of gas-shielded arc welding using a DC power source, all poles are of the same polarity, and magnetic blowing of the arc due to excessive ground current is likely to occur, resulting in welding defects such as poor penetration due to arc instability. There is a problem that this occurs.

In other words, Fig. 4 is another example of welding by the conventional method, and shows a case where two layers are welded by a two-electrode gas/rued arc hard contact method using a DC power source using a small diameter wire.
In this case, the initial 765 hot crack caused by the leading electrode is re-bath-dissolved and disappears by the trailing electrode, but the weld bead width by the trailing electrode does not widen with the small diameter wire and becomes narrow (deep bath shape), resulting in high temperature Because cracks 6 occur, it is difficult to weld thick plates at high speed.

Furthermore, the two-electrode arc of this DC welding is affected by mutual magnetic interference between the arcs, and by the strong magnetism caused by excessive earth current, since the wire is normally of opposite polarity and has the same polarity as the positive pole. It tends to become unstable, causing welding defects such as poor fusion and one-sided centering, which impedes good welding.

As a method for reducing such drawbacks of the conventional gas-shielded arc, the present inventors have already disclosed an AC gas-shielded arc welding method in Japanese Patent Publication No. 7545/1983. However, there is room for improvement in this method when it is used in multi-electrode gas-shielded arc welding of steel strips as the object of the present invention.

(Problems to be Solved by the Invention) The present invention provides a method for high-efficiency, high-speed welding of a narrow-angle groove in a steel strip that has been cut using a multi-electrode gas-shielded arc welding method. In addition, the present invention provides a high welding method that ensures sufficient bath penetration to the back surface of the groove and does not cause hot cracks in the high-temperature part (polarized cracks due to poor bead shape) or weld defects due to arc interference.

(Means for solving the problems) The present invention is intended to solve the above problems,
The gist is that in gas-shielded arc welding, which butt-welds a steel strip with a thickness of 6II11N or more with a groove shape that has been shear cut, a DC power source is used as the leading electrode,
A consumable wire with a diameter of 1 to 2 mm is used, and an AC power source, a restriking means (pulse generator), and a consumable electrode wire with a diameter of 2 mm or more are used for the trailing electrode. The distance between the poles is between 25 and 350.

Next, the arc welding method of the present invention will be explained in detail with reference to FIGS. 1 and 6 below.

In FIG. 1, numerals 11 and 12 are a direct OFF power supply, an m-contact power supply, and an AC power supply used in the present invention, respectively, and 13 is a pulse generator for maintaining an AC arc. This pulse generator is necessary for performing gas seven-fold arc welding using alternating current.

In the same figure, 7.8 indicates the consumable electrode wire used in the present invention, and the leading electrode 7 is a small diameter wire of 1 to 2 diameters, and the trailing electrode 8 is a large diameter wire of 2 diameters or more. Using diameter wires, welding is performed by arranging them in the welding direction 14.

The reason why a small diameter wire is used for the leading electrode is that in combination with a DC power supply, deep saponification can be obtained, and the back surface of the groove can be sufficiently melted by Km.
This is to form a good Uranami peak. The reason why a large-diameter wire is used for the trailing f4 is to widen the bead width in combination with an AC power supply, thereby preventing mold cracking and obtaining a good surface bead 17, as shown in FIG. .

The distance between the leading electrode 7 and the trailing electrode 8 is limited to 25 to 350 degrees, so that there is no arc interference (it can be freely selected) due to the combination of DC arc and AC arc.

35011111 or less, by using a large diameter wire for the trailing electrode, it not only improves the shape of the peak surface, but also makes it possible to use leakage current, and increases the total heat input of the leading and trailing electrodes. In order to prevent the hardening and cracking of the welding part (-welt metal and d heat-affected capital), the distance between the leading electrode and the trailing electrode is made as small as possible, and the distance between the leading electrode and the trailing electrode is made as small as possible. This is to shorten the time (from arc start to trailing electrode arc stop).

The reason why the interelectrode distance is set to 25 mm or more is to separate the bath melting boule into the preceding electrode and the subsequent electrode, thereby reducing the bead height and preventing the above-mentioned hot cracking.

In addition, the shielding gas composition of the AC gas shielded arc is:
In the invention described in Japanese Patent Publication No. 59-7545, A
CO in r + Cot or Ar + Oz gas is 1
Although it is limited to 5% or less or 0.25% or less, subsequent research by the present inventors has shown that by increasing the capacity f of the pulse generator, the C in Ar + CO2 (or 02) gas
It has been found that even if O2 (or 02) is 15% (or 5%) or more, restriking is possible and stabilization of restriking of an AC arc can be achieved, so the shielding gas composition of the present invention is as follows:
There are no particular restrictions.

Also, the explanation so far is based on the preceding electrode D, which is the basis of non-invention.
This is a combination of 10 CI poles, 10 trailing electrodes, and 2 AC poles, or 1 leading DC pole and 1 trailing AC pole, or 2 leading DC poles and 1 trailing AC pole, or 2 leading DC poles and 1 trailing AC pole to perform butt sieve welding of steel strips with even higher efficiency. A multi-electrode gas-shielded arc welding method using a combination of more than one set is also easily possible according to the present invention.

(Example) Examples of the present invention will be compared with conventional examples. In the case of a plate thickness of 9 mm shown in Table 1, the welding time of Example 1 of the present invention is halved compared to Conventional Example 1. With.

Good welds with no defects can be obtained.

In the case of plate thickness 19rftJR, in Conventional Example 2, high temperature cracking occurred due to defective shape of the bead cross section, and DC211t4! ! Although poor fusion defects due to arc interference are inevitable, in the embodiments of the present invention, good welds without defects can be obtained even with similar high-efficiency welding.

(Effects of the Invention) As described above, according to the welding method of the present invention, the welding of the butt groove of the steel strip as it is shear-cut is defect-free and has a special ridge with high efficiency.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an apparatus for carrying out the welding method of the present invention, FIGS. 2(a) and (bl are explanatory diagrams of an embodiment, and FIG. Fig. 5 shows a cross-sectional view of the bead when the groove is welded by the conventional method, Fig. 5 shows a cross-sectional view of the welding groove used in the present invention, and Fig. 6 shows a cross-sectional view of the bead of @kai welded by the present invention. -a: One end of the steel strip 1-b: The other end of the steel strip 2: Copper dowel 3: Welding groove 4-bead center 5: Initial layer by leading electrode 6: Hot cracking 7: Leading Electrode 8: Trailing electrode 9: Leading electrode torch
Polarizing torch 11: DC welding power source 12: AC welding power source
13: Pulse generator 14: Welding direction 15-
Leading arc 16: Trailing arc 147: Table bead agent Patent attorney Tatsuo Chanoki Figure 1 ((:L) (b) 1α, Kusu 3 Figure 4 Figure 5 Inhibited 6 areas

Claims (1)

[Claims] In consumable electrode type gas-shielded arc welding where steel strip is butt welded with the groove shape as it was sheared, a DC power supply is used as the leading electrode and a consumable electrode wire with a diameter of 1 to 2 mmφ is used, and the trailing electrode is re-ignited. A multi-electrode gas-shielded arc welding method for steel strip, characterized in that the distance between the leading electrode and the trailing electrode is 25 to 350 mm, using an AC power source equipped with an AC power source and a consumable electrode wire having a diameter of 2 mm or more.