JPH0474117B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Application of the Invention) The present invention relates to a method for starting electroslag welding. (Prior art and its problems) When starting electroslag welding,
The energized wire is sent to the welding start point to generate an arc between it and the base metal, and after the arc is generated, flux is introduced. The flux is melted by arc heat to form a slag bath, and thereafter the base metal and wire are melted by resistance heat generation in the slag bath, and electroslag welding is performed. However, according to the above method, the wire and base metal are melted by arc heat and a weld metal is formed until the flux is melted and an appropriate amount of slag bath is formed. However, electroslag welding wires and fluxes typically do not contain gas-generating components to shield the molten metal from the atmosphere, as do flux-cored wires or coated arc welding rods used in other welding processes.
Therefore, until a slag bath is formed, it is inevitable that the weld metal will be adversely affected by the atmosphere and will contain blowholes. Conventionally, in order to avoid leaving the weld metal containing the blowhole inside the structure to be welded, welding was started by generating an arc in a tab made of the same material as the base material provided at the end of the base metal, and then the welding was completed. Either remove the rear tab, or weld by generating an arc in a tab made of a material such as copper that is removably provided at the end of the base metal, as proposed in Japanese Patent Publication No. 50-20022. After welding has started, the copper tab is removed and only the welded metal is cut off. However, this measure requires time and effort to attach and remove the tabs, resulting in a decrease in efficiency. Furthermore, if the member to be welded intersects with another member, it is difficult to provide a tab. (Object of the Invention) The present invention has been made in view of the above-mentioned problems, and provides a welding start method that can obtain a sound weld metal free of internal defects during electroslag welding, particularly at the welding start part. It is something to do. (Structure of the Invention) Prior to the start of electroslag welding, the present invention supplies shielding gas to the inner bottom of the welding groove from the tip of a shielding gas supply tube provided separately close to the wire guide nozzle to open the welding groove. After creating a shielding gas atmosphere at the inner bottom of the groove, a wire is fed into the groove from a wire guide nozzle to generate an arc, and then a slag bath is formed at a predetermined depth by flux injection, and electroslag welding begins. The shielding gas is supplied until then. Hereinafter, the present invention will be explained in detail with reference to the drawings. 1 and 2 are explanatory diagrams of a conventional starting method in electroslag welding, and FIGS. 3 and 4 are explanatory diagrams of a starting method of electroslag welding according to the present invention. In the figure, 1 and 2 are base materials,
3 is the material, 4 is a component that adjoins and intersects with the base materials 1 and 2, and 5 is a wire guide nozzle.
The nozzle is installed in a groove surrounded on all sides by the base materials 1 and 2, the base material 3, and another base material (not shown) that is placed opposite the base materials 1 and 2. It is inserted from above. A welding wire 6 passes through the wire guide nozzle 5 and is supplied to the welding part. 7 shows the flux that is injected and dispersed into the welding area after welding starts. The above components are common to the conventional method and the method of the present invention, but in addition to these, the method of the present invention uses a welding shield gas 8 such as carbon dioxide gas or a mixed gas of carbon dioxide gas and argon as shown in FIG. , a tube 9 for supplying to the welding part is a component. Also, 10 is weld metal, 11 is molten metal, 12
is a slag bath. The electroslag welding procedure according to the conventional method will be explained with reference to FIGS. 1 and 2. First, the wire 6 is fed to the welding part to generate an arc, and then the flux 7 is introduced, and the arc heat melts the flux 7 into the slag bath 12.
form. By the time the slag bath 12 reaches an appropriate depth (usually 15 to 40 mm, depending on the welding conditions), the wire 6 and the groove walls of the base metals 1 and 2 are melted by the arc heat, and the weld metal 10 and the molten It becomes metal 11. After the slag bath 10 reaches an appropriate depth, the flux 7, wire 6, base material 1,
The groove walls of 2 are melted. Therefore, after the arc is generated, until the slag bath 10 reaches an appropriate depth, that is, until electroslag welding is started, incomplete arc welding is performed in which the molten metal is not shielded from the atmosphere, and welding is difficult. The molten metal 10 after progressing becomes defective weld metal containing blowholes 13. On the other hand, in the method of the present invention, as shown in FIG. 3, prior to welding, a shielding gas 8 is first supplied into the groove through a separately provided shielding gas supply tube 9 in the vicinity of the wire guide nozzle 5. After the inner bottom of the groove is surrounded by shielding gas, the wire 6 is fed from the wire guide nozzle 5 to generate an arc and start welding. After the arc occurs,
As in the conventional method, flux 7 is introduced from above the groove to form a slag bath 12 to perform welding, but carbon dioxide gas 8 is continued until the depth of the slag bath 12 reaches the appropriate depth described above. supply When the slag bath 12 reaches a predetermined depth and there is no longer any fear that the molten metal will come into contact with the atmosphere, the supply of shielding gas from the tube 9 is stopped, and the tube 9 is pulled up as shown in FIG. Continue electroslag welding in this condition. By doing so, the molten metal 11 is shielded from the atmosphere from arc generation to electroslag welding, making it possible to obtain weld metal 10 that does not contain blowholes, that is, has no defects. (Example) Next, examples will be given to demonstrate the effects of the present invention. In the arrangement shown in Figure 3, the test base materials (mild steel, plate thickness 14 mm) were butted together with a groove interval of 20 mm, and the copper material 3
Both sides of the groove were covered and vertical advancement welding was performed. The wire guide nozzle 5 used a pipe made of copper (outer diameter 10 mm, inner diameter 2 mm), and carbon dioxide gas was used as the shielding gas. Further, the tube 9 for supplying carbon dioxide gas was made of Teflon (outer diameter 10 mm, wall thickness 0.5 mm). Other welding conditions are shown in Table 1 together with the welding results.

[Table] As shown in Table 1, the method of the present invention, in which carbon dioxide gas is supplied to the weld zone from before welding until the formation of the slag bath, produces a good weld with no defects in the weld metal at the starting point, as seen in the conventional method. was held. In addition, in the examples, only the case where carbon dioxide gas is used as the shielding gas is shown, but a mixed gas of carbon dioxide gas and argon (carbon dioxide concentration 5 to 30%), which is normally used in gas shielded arc welding, is used as the shielding gas. Even if it is used as an example, the same effect as in the example can be obtained. (Effect of the invention) As described above, according to the method of the present invention, after starting welding,
During the transition period before transitioning to electroslag welding, a stable welding condition can be maintained using shielding gas, which prevents defects near the welding start position, which were unavoidable with conventional methods, and produces sound weld metal. This eliminates the need for tab preparation before welding and rework after welding, which were conventionally required, and enables the high-speed performance of electroslag welding to be fully demonstrated.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams of the conventional method, and FIGS. 3 and 4 are explanatory diagrams of the method of the present invention. 1, 2: base metal, 3: current material, 4: member adjacent to and intersecting the base metal, 5: wire guide nozzle, 6: wire, 7: flux, 8: shielding gas, 9: tube, 10: weld metal, 11: Molten metal, 1
2: Slag bath, 13: Blowhole.

Claims (1)

[Claims] 1 Prior to the start of electroslag welding, shielding gas is supplied to the inner bottom of the welding groove from the tip of a shielding gas supply tube that is separately installed close to the wire guide nozzle to create a shielding gas atmosphere in the inner bottom of the welding groove. After feeding the wire from the wire guide nozzle into the groove to generate an arc,
A method for starting electroslag welding, characterized in that the shielding gas is supplied until a slag bath is formed at a predetermined depth by flux injection and electroslag welding begins.