JPS6339347B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to in-groove welding of thick plates by plasma arc, and is suitable for mainly butt welding of thick plate members having a plate thickness of 25 mm or more.

Due to the keyhole effect, which is the most important feature of plasma arc, it is possible to weld plates with a uniform back wave by die butt single layer welding on plates as thick as about 10 mm.

On the other hand, for plate members with a thickness of 10 mm or more, V with a root face of about 5 to 8 mm at the weld joint
Welding is performed by providing a groove in the shape of a letter or U.
In this case, as shown in Figure 1 a, the groove is facing upward and the root face is keyhole welded from above the groove, and conversely, as shown in Figure 1 b, the groove is facing downward and the root face is keyhole welded. There is a way to do it. The plasma torch normally used for these welds is
As shown in the figure, the plasma gas flows into the nozzle hole 4 through the electrode 1 and the nozzle 2, the insulating ring 3 that insulates the two, and the inner circumferential surface of the electrode 1, and the nozzle 2 is further shielded by a shield cap 5 around the outer periphery of the nozzle 2. Constructed to allow gas to flow. Plasma torches are water-cooled to prevent melting due to arc heat, and in this case, in order to increase the capacity of the current used, it is necessary to increase the cooling of the nozzle as well as the electrode. , the torch tip is directly water-cooled. Therefore, the first
When welding with the groove facing upward as shown in Figure a, the tip of the torch must be brought close to the surface of the material to be welded to generate a plasma arc within the groove. In this case, the deeper the groove depth, the more difficult it is for the arc to migrate, and even if an arc is generated, the arc length is long, making the arc unstable and welding difficult. Therefore, the groove depth that can be welded using this method is 10
~15mm is the limit. Furthermore, when welding a deep groove, the torch must be inserted into the groove. For example, patent application No. 50-143951
There is a method of elongating the tip diameter of the nozzle and inserting the torch into the groove, as shown in No. 1 and Figure 3. However, in this case, since cooling water is not circulated through the tip of the nozzle, it is easily overheated by arc heat, making it difficult to flow the current necessary for welding. Furthermore, the shielding gas passage remains provided on the plate surface, and with this method, it is difficult for the shielding gas to be guided to the inner bottom of the groove, so the shielding effect is reduced and good welding results cannot be obtained. In order to create a torch that can be inserted into a groove, the shape of the tip of the torch must be made thin while maintaining the current value necessary for welding, and the cooling structure and gas passage must be determined. This has become a major issue.

On the other hand, when welding is performed with the groove facing downward as shown in FIG. 1b, the root face portion 4 can be keyhole welded with a conventional plasma torch regardless of the depth of the groove. However, the drawback in this case is that after keyhole welding of the first layer, the material to be welded must be turned over in order to weld the groove. The larger the material to be welded and the thicker the plate, the more difficult the reversing operation becomes.

As a welding torch other than a plasma torch that can be inserted into a groove, there is, for example, Utility Model Publication No. 52-50203 (Narrow Gap Teig Welding Torch). The flat torch body is water-cooled, but the cooling water holes are provided in a U-shape on both outsides of the torch body, and the structure is such that the cooling water does not flow around the tungsten electrode insertion part in the center. It's summery. Since the tungsten electrode itself is chucked by a collector installed at the tip of the torch, cooling is insufficient and a large arc current cannot flow through it. Unlike plasma arc, which has a high current density where the arc is constricted by a nozzle, TIG arc does not use a nozzle, so the current density is low, the welding penetration is shallow, and the welding speed is slow.

In addition, as an example of narrow gap MIG welding, the structure of a MIG welding torch is disclosed in Japanese Patent Publication No. 50-27038.

The structure of the cooling water passage and shield gas passage is as described above.
This is almost the same as a TIG welding torch, except that a welding wire is fed into the center of the torch body instead of a tungsten electrode.

In the case of a MIG welding torch, in addition to the supply of welding wire, the structure only needs to be considered for the cooling of the torch body and the outflow of shield gas.
As shown in the figure, in the case of a plasma torch,
The structure is complicated, and the tungsten electrode and nozzle must be electrically isolated and cooled, and a plasma gas passage must be installed.

In addition, in the case of narrow gap MIG welding, there is no key home effect as in plasma welding, so it is difficult to weld the first layer with an underwave bead, and arc breakage and spatter occur. This requires reversing the workpiece, gouging, and welding, and has the drawback that welding defects are likely to occur.

The present invention was made in view of the above, and it is an object of the present invention to create a thin plasma torch that can insert the torch into the groove while securing the current necessary for welding, and to invert the material to be welded with the groove. The purpose of the present invention is to provide an in-groove welding method for thick plates using a plasma arc, which allows efficient welding in the same orientation without any problems.

In a method of butt plasma arc welding thick plate members with a thickness of 25 mm or more, the plasma torch used in the present invention has a flat nozzle with a nozzle hole at its tip, and a shield cap is installed around the nozzle. , and an electrode is built into the space at the tip of the nozzle facing the nozzle hole. Further, an electrode holder for fixing the electrode is built into the nozzle so as to be located coaxially with the electrode, and two plasma gases, which are independent of each other, are placed inside the nozzle on both sides of the electrode and the electrode holder. The plasma gas passage has a structure in which passages are formed, and each plasma gas passage communicates with the nozzle hole through the space. Further, a cooling water passage is similarly formed in the nozzle around the electrode and the electrode holder and outside each of the plasma gas passages, and the cooling water passages on both sides are communicated through a communication passage provided around the nozzle hole. ing. Further, a shielding gas passage is formed between the nozzle and the shielding cap. The present invention uses a plasma torch characterized by the above configuration, and the butt joint portion is provided with a groove and a root face having a width sufficient to insert the plasma torch, and the plasma arc is transferred within this groove. This is to form an initial layer bead. After keyhole welding the root face using a plasma torch inserted into the groove, weld the second and subsequent layers while feeding the wire using the same plasma torch as the first layer.

The present invention will be explained below with reference to Examples. FIG. 4 shows a thin plasma torch 6 with a flattened torch tip inserted into a groove 7 to weld the root face portion. The groove may be either a U-groove or a V-groove, as long as it has a width sufficient to allow the plasma torch 6 to be inserted.

Next, the structure of the thin plasma torch will be explained. FIG. 5 is an assembly diagram of a thin plasma torch developed for carrying out the present invention, in which the torch tip is flattened so that the torch tip can be inserted into the groove.

Specifically, Figure A is a longitudinal sectional view, and Figure B is a longitudinal sectional view taken along line A-A' in Figure A. In the figure, an electrode (tungsten) 8 is fixed to a water-cooled electrode holder 9, and a plasma arc is generated from the tip of this electrode. inner tube 1
0 is inserted into the electrode holder 9 to form a cooling water passage 11. The flat nozzle 12 has a flat cross section, is fixed to the torch body 13 by a fastening ring 14, and has a structure in which its tip can be freely attached and detached. The insulating sleeve 15 is
It is located between the electrode holder 9 and the flat nozzle 12 to insulate them. The shield cap 16 is fixed to the torch body 13 with a screw 17, and a shield gas passage 18 is formed between the flat nozzle 12 and the shield cap 16. Plasma gas passages 19 are provided on both sides (left and right or top and bottom) of electrode 8, communicate with nozzle holes 20, and emit plasma gas 27. Similarly, the cooling water passages 21 are provided on both sides of the plasma gas passage 19 further outward from the electrode 8, and communicate with communication passages 22 provided near the nozzle holes 20. Plasma gas passage 23 communicates with passage 19 . O-rings 24, 25, and 26 each have a sealing function.

By using a thin plasma torch like the one mentioned above, it is possible to insert the plasma torch into the groove of a thick plate.Moreover, the tip of the torch, which is easily heated by arc heat, is water-cooled, so it can handle high current. Can withstand loads. Further, since the shielding gas is also supplied to the tip of the torch, the welded portion can be shielded regardless of the groove depth.

Next, an example of welding results obtained when a welding test was conducted using the above-mentioned thin plasma torch will be shown. Figure 6 a and b show a root face of 7 mm and a groove width of 20 mm.
This is a cross-sectional structure of plasma keyhole welded stainless steel sheets with a groove thickness of 50 mm and 150 mm. As shown in the figure, the plasma torch is inserted into the groove and welded, and the welding speed at this time is
At 200mm/min, the plasma current is 280A. Unlike welding of flat plates, when welding within a groove, the shielding gas has less diffusion due to both walls of the groove and the shielding effect is good, so a good welded area as shown in the cross-sectional structure diagram is obtained regardless of the groove depth. was found to be obtained.

Further, as shown in Fig. 7, after keyhole welding the root face part 31 with the plasma torch 30 inserted into the groove, the wire 33 is fed to the second layer 32 and subsequent layers using the same plasma torch 30 as the first layer. This is an example in which welding is performed while Plasma current is 300A
In this case, the appropriate amount of wire that can be fed into the arc is 3 to 4 m/min when the wire is 1.2φ, and when this wire is energized and fed, the amount of welding is about 1.5 to 4 m/min compared to the case of cold wire. Increased by 2 times.

As explained below, according to the present invention, by using a thin plasma torch with a flattened torch tip, it is possible to perform groove welding of thick plates, which was previously impossible to weld with a conventional torch with a large diameter. , greatly improving welding efficiency. Not only the first layer welding but also the second and subsequent layers can be welded continuously using the same plasma torch, which simplifies the welding process. In contrast, with this method, there is no need to make the groove particularly wide; in fact, the groove can be narrowed, so the amount of wire required to fill the groove is small, making it economical. . Note that although we have described welding within the groove of thick plate members here, it goes without saying that this technique can be directly applied to fillet welding.

[Brief explanation of drawings]

Figures 1a and b are illustrations of conventional groove welding of thick plate members using plasma arc, Figure 2 is a vertical cross-sectional view of a conventional plasma torch, and Figure 3 is a diagram of another conventional plasma torch. Figure 4 is a basic explanatory diagram of the welding method of the present invention.
Figure a is a longitudinal cross-sectional view of a plasma torch for carrying out the welding method of the present invention, and figure b is a line taken along line A in figure a.
A vertical cross-sectional view taken along the line A', Figures 6a and b are cross-sectional microstructure diagrams of the metal according to the present invention, Figure 7a is a concrete explanatory diagram of narrow gap welding, and Figure b is Figure a. A-
FIG. 3 is a cross-sectional view taken along line A'. 8... Electrode, 9... Electrode holder, 10... Inner tube, 12... Flat nozzle, 13... Torch body, 14... Fastening ring, 15... Insulating ring, 16... Shield cap, 18, 32,
33... Shield gas passage, 19, 23... Plasma gas passage, 20... Nozzle hole, 21... Cooling water passage, 22... Communication passage, 30... Plasma torch.

Claims (1)

[Scope of Claims] 1. In a method of plasma arc welding using a plasma torch by butting thick plate members together, the plasma torch has a flat nozzle with a nozzle hole at its tip, and a shield cap surrounds the nozzle. an electrode is built into the space at the tip of the nozzle facing the nozzle hole; an electrode holder for fixing the electrode is built into the nozzle so as to be coaxial with the electrode; two mutually independent plasma gas passages are formed on both sides of the electrode and electrode holder;
Each of the plasma gas passages communicates with the nozzle hole through the space, and a cooling water passage is also formed in the nozzle around the electrode and electrode holder and outside of each of the plasma gas passages. A cooling water passage is communicated with a communication passage provided around the nozzle hole, a shielding gas passage is formed between the nozzle and the shielding cap, and the nozzle tip is connected to the bevel and route with the shielding cap. Opening of a thick plate by plasma arc, characterized in that the plasma arc is inserted into the groove of a butt joint portion having a face, and the plasma arc is transferred within the groove to form an initial layer bead. Tip welding method. 2. In the welding method described in claim 1, after keyhole welding the root face portion with a plasma torch tip nozzle inserted into the groove,
Furthermore, a plasma arc in-groove welding method for thick plates, characterized in that the second and subsequent layers are welded with the same plasma torch as the first layer, while feeding the wire.