KR101051667B1 - Tungsten-Inert-Gas Welding Apparatus and Tungsten-Inert-Gas Welding Method - Google Patents

Abstract

The present invention relates to a tungsten-inert-gas welding apparatus and a tungsten-inert-gas welding method, which can form a weld metal part without deteriorating the welding quality, facilitate the welding operation, and also improve the welding efficiency. You can. The tungsten-inert-gas welding apparatus includes an electrode (2) for generating an electric arc (7) between the electrode and the object to be welded (10), a tubular inner nozzle (3) disposed surrounding the electrode (2), and an inner nozzle ( And 3) a tubular outer nozzle 4 disposed surrounding it. The first shielding gas 8 composed of an inert gas can be supplied from the inner nozzle 3, and the second shielding gas 9 containing the oxidizing gas is formed of the inner nozzle 3 and the outer nozzle 4. Can be supplied from.

Tungsten-Inert-Gas Welding, Welding Equipment, Shielding Gas, Inert Gas, Oxide Coating

Description

Tungsten-inert-gas welding apparatus and Tungsten-inert-gas welding method {TIG welding equipment and TIG welding method}

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of the description. The drawings illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

Figure 1 schematically shows the structure of the important part of the welding apparatus according to the first embodiment of the present invention.

FIG. 2A shows the correlation between the surface tension and the temperature in the molten pool, and FIG. 2B is a diagram showing the state of the molten pool.

3a and 3b schematically show the structure of an important part of a welding apparatus according to a second embodiment of the present invention, and FIG. 3a shows the front side of the apparatus, some of which are shown in cross section, The cross section of the device is shown.

4 shows a plane of the welded object obtained using the welding apparatus shown in FIGS. 3A and 3B.

5a and 5b schematically show the structure of an important part of a welding apparatus according to a third embodiment of the present invention, and FIG. 5a shows a front surface of the apparatus, some of which are shown in a cross-sectional state, and FIG. The cross section of the device is shown.                 

6a and 6b schematically show the structure of an important part of a welding apparatus according to a fourth embodiment of the present invention, and FIG. 6a shows a front surface of the apparatus, some of which are shown in a cross-sectional state, and FIG. The cross section of the device is shown.

Fig. 7 shows a plane of the welded object obtained using the welding apparatus shown in Figs. 6A and 6B.

8a and 8b schematically show the structure of the important part of the welding apparatus according to the fifth embodiment of the present invention, and Fig. 8a shows the front side of the apparatus, partly shown in cross section, and Fig. 8b shows The cross section of the device is shown.

Fig. 9 shows the state of the weld metal part as the results of the welding test in cross section.

10 to 13 are graphs showing the results of a welding test.

The present invention relates to a welding apparatus used for welding tungsten-inert-gas (TIG) of steel-based materials and a welding method using the welding apparatus.

Typically, structures using stainless steel-base materials such as steel or stainless steel as the base material are welded by tungsten-inert-gas welding. Tungsten-inert-gas welding is a welding method for welding structures that require high reliability for easy operation and formation of high quality weld metal parts, as disclosed in, for example, Japanese Patent Laid-Open No. 2003-019561. Widely used.

However, since steel-base materials, including recently used stainless steels, often contain less sulfur as an impurity, the weld metal portion is wider and shallower in the tungsten-inert-gas welding process, resulting in insufficient welding effect. Done. In order to form the weld metal part deeply, it is required to increase the number of passes. However, when the number of passes is increased, the welding efficiency is inversely lowered.

Other welding methods include metal-active-gas (MAG) welding, metal-inert-gas (MIG) welding and plasma welding. These welding methods include deep welding metals. It is adopted when welding of parts and high efficiency is required. However, MAG or MIG welding methods involve some problems, including deterioration of welding quality and occurrence of weld defects. In addition, plasma welding has a drawback that the groove accuracy or other acceptable working conditions are too narrow, making it difficult to use the method in construction sites and the like.

A method of using a shielding gas composed of a mixed gas obtained by mixing an inert gas such as argon with hydrogen or helium or the like has been proposed as a method for improving the serious short weld metal part defect in tungsten-inert gas welding. In addition, other tungsten-inert-gas welding methods using active flux have recently been proposed, namely A-TIG welding methods.

However, welding methods using a shielding gas containing hydrogen are difficult to apply to materials other than austenitic stainless steel due to some problems, including bubbling and brittleness of the weld metal. In addition, the use of helium is not preferable in view of cost. In addition, the workability of the method using activated flux is poor because it requires coating before the welding process. In addition, since slag is remarkably generated on the weld bead, slag removal is required in the multilayer welding to prevent deterioration of the appearance of the bead. In addition, since the welding method generates a large amount of fume, the working environment is deteriorated.

In addition, in the anode-type (DC electrode positive type) arc welding method including MAG welding, a shielding gas composed of argon gas mixed with an oxidizing component such as carbon dioxide at a concentration of 20% is used to improve the stability of the electric arc. . However, when oxidizing gas is used as the shielding gas in tungsten-inert-gas welding, the electrode is easily degraded and cannot be used for long time welding or repeatedly. If degraded electrodes are used, the weld quality is unstable and welding defects may occur.

The present invention can overcome the problems of the prior art as described above to protect the electrode from deterioration by oxidation to obtain a welded structure of excellent quality, and also can be easily welded by forming a deep weld metal, Provided is a tungsten-inert-gas welding apparatus with excellent welding efficiency and a tungsten-inert-gas welding method.

In view of the above technology, the present invention relates to a tungsten-inert-gas welding apparatus and a tungsten-inert-gas welding method, which not only improves welding efficiency, but also can form deep weld metal parts without degrading welding quality. It is possible to facilitate the welding operation.

As a result of intensive research on this problem, the inventors found that the shape of the weld metal is greatly influenced by the convection in the metal pool, and the main factor affecting the convection is the surface caused by the temperature distribution in the molten pool. It was found to be a tension distribution. The present invention has been conceived based on the above findings. The tungsten-inert-gas welding apparatus of the present invention is an electrode for generating an electric arc between an electrode and a welded object, a tubular inner nozzle disposed surrounding the electrode, and a tubular outer nozzle disposed surrounding the inner nozzle. It includes. The first shielding gas containing the inert gas may be supplied from the inner nozzle, and the second shielding gas containing the oxidizing gas may be supplied from between the inner nozzle and the outer nozzle. According to another embodiment of the present invention, a tungsten-inert gas welding device includes an electrode for generating an electric arc between an electrode and a welded object, a tubular central nozzle disposed surrounding the electrode, and at least two sides of the electrode in the direction of the welding direction. Side nozzles disposed thereon. The central nozzle may supply a first shielding gas including an inert gas, and the side nozzles may supply a second shielding gas containing an oxidizing gas.

In one embodiment of the tungsten-inert-gas welding method according to the invention, an electric arc is generated between the electrode and the object to be welded. The first shielding gas containing the inert gas is directed toward the object surrounding the electrode, and the second shielding gas containing the oxidizing gas is led toward the object along the periphery of the first shielding gas. In another embodiment of the tungsten-inert-gas welding method, an electric arc is generated between the electrode and the object to be welded. The first shielding gas containing the inert gas is directed toward the object surrounding the electrode, and the second shielding gas containing the oxidizing gas is directed toward the object from at least two sides of the electrode when viewed in the welding direction. In both methods, the concentration of the oxidizing gas in the second shielding gas is preferably in the range of 2,000 ppm to 6,000 ppm, more preferably 3,000 ppm to 5,000 ppm. The concentration of the oxidizing gas in the second shielding gas is preferably set in the range of 70 ppm by weight to 220 ppm by weight in the oxygen concentration in the weld metal portion. In the tungsten-inert-gas welding method of the present invention, the thickness of the oxide coating formed on the surface of the weld metal portion is 20 µm or less.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and intended to provide further explanation of the invention as claimed.

A welding apparatus according to an embodiment of the invention is described below with reference to the drawings. Although not shown in the drawings, the welding apparatus requires a welding apparatus, a regulating apparatus, a gas supply, a welding power source, and the like.

<First Embodiment>

1 shows a welding apparatus according to a first embodiment of the present invention. Referring to Fig. 1, a tungsten-inert-gas welding apparatus A includes a tungsten electrode 2, a tungsten electrode 2, for generating an electric arc 7 between an electrode and a base material (weld material) 10. A torch 1 having a multiple tubular structure consisting of a tubular inner nozzle 3 disposed and a tubular outer nozzle 4 disposed around the tubular inner nozzle 3. The base material 10 is, for example, a steel-base material. In short, the torch 1 is a multi-tubular structure having an inner nozzle 3 arranged around the tungsten electrode 2 and an outer nozzle 4 arranged around the inner nozzle 3.

The tip (lower end) of the tungsten electrode 2 is formed to protrude more in the tip direction (downward direction) than that of the inner nozzle 3. The inner nozzles 3 are arranged in a substantially concentric manner at a certain distance from the tungsten electrode 2. The internal nozzle 3 can supply a first shielding gas 8 composed of a high purity inert gas. The first shielding gas 8 may be, for example, argon (Ar) or helium (He).

The outer nozzle 4 is arranged in a substantially concentric manner at a distance from the inner nozzle 3, and the second shielding gas 9 containing oxidizing gas is disposed between the outer nozzle 4 and the inner nozzle 3. It can be supplied through the interval of. The second shielding gas 9 may be a mixed gas obtained by adding an oxidizing gas into the inert gas. The oxidizing gas can be, for example, oxygen (O ₂ ) or carbon dioxide (CO ₂ ) and the inert gas can be argon or helium.

The welding method of the base material 10 using the said welding apparatus A is described as follows. As shown in Fig. 1, the tungsten electrode 2 serves as a cathode, the base material 10 serves as an anode, and a voltage is applied between the torch 1 and the base material 10 to induce discharge, and the electric arc (7) is generated. To weld the base material 10, the torch 1 moves to the left side of the drawing to melt the base material 10 by heat from the electric arc 7 to form the melt pool 5. In addition, the weld bead is indicated by reference numeral "6" in the drawing.

During the welding operation, the first shielding gas 8 is supplied from the inner nozzle 3. The first shielding gas 8 is directed towards the tip of the inner nozzle 3, surrounding the tungsten electrode 2, and sprayed from the tip onto the base 10. The first shielding gas 8 is sprayed on the central part of the molten pool 5.

At the same time, the second shielding gas 9 containing the oxidizing gas is supplied through the gap between the inner nozzle 3 and the outer nozzle 4. The second shielding gas 9 is directed towards the tip of the outer nozzle 4 and sprayed on the base 10 from the tip. At that time, the second shielding gas 9 is guided along the periphery of the first shielding gas 8 while surrounding the first shielding gas 8, and on the periphery (part located at the periphery of the center) of the molten pool 5. Is sprayed on. The concentration of the oxidizing gas such as O _{2 in} the second shielding gas 9 is preferably 2,000 ppm to 6,000 ppm, more preferably 3,000 ppm to 5,000 ppm. The use of the second shielding gas 9 containing the oxidizing gas dissolves oxygen in the weld metal portion 5a, and the concentration of the oxidizing gas in the second shielding gas is preferably 70% by weight of the oxygen in the weld metal portion. It is set to be ppm to 220 ppm by weight. This operation yields a welded structure with molten metal portion 5a. Further, an oxide coating is formed on the surface of the weld metal portion, and the thickness of the oxide coating is preferably 20 μm or less.

On the other hand, the surface tension of the molten metal changes due to temperature or the concentration of dissolved residual impurities such as sulfur or oxygen. 2A shows an example of the correlation between the surface tension and the temperature of the molten metal, where sulfur or oxygen is dissolved in the molten metal at a certain concentration. According to Fig. 2A, the surface tension increases with increasing temperature. In this case, the temperature in the peripheral portion R2 of the melt pool 5 is lower than in the central portion R1, so that as shown in FIG. Smaller than Also, even if the temperature is constant, the surface tension decreases with increasing oxygen concentration dissolved in the molten iron.

The following effects are obtained because the welding apparatus A has a torch 1 having a tubular inner nozzle 3 surrounding the tungsten electrode 2 and a tubular outer nozzle 4 around the tubular inner nozzle 3. .

(1) Since the first shielding gas 8 is guided while surrounding the tungsten electrode 2, the tungsten electrode 2 is protected by the first shielding gas 8, and can be prevented from being degraded by oxidation. have. Thus, the welded structure can obtain excellent welding quality.

(2) Since the second shielding gas 9 is supplied from the gap between the inner nozzle 3 and the outer nozzle 4, the first shielding gas 8 can be supplied to the central portion R1 of the molten pool 5. At the same time, the second shielding gas 9 containing the oxidizing gas can be supplied to the peripheral portion R2 of the melting pool 5. Thereby, the molten pool 5 can be supplied with oxygen at the required concentration, and the oxygen concentration in the peripheral portion R2 is higher than in the central portion R1. Thus, the surface tension at the periphery R2 with lower temperature and higher oxygen concentration in the melt pool 5 is smaller, and the surface tension at central portion R1 with higher temperature and lower oxygen concentration is greater. As a result, internal convection is induced in the molten pool 5 so that the molten pool 5 can be deeply formed. Thus, the weld metal portion 5a can be deeply formed in the base material 10.

(3) Compared with the conventional method using the active flux, slag is hardly generated and thus no slag removal operation is required. At the same time, little fume is generated during the welding process. Thus, the welding operation can be easily performed.

(4) Since the weld metal portion can be formed deep, insufficient welding-welding or a decrease in welding efficiency can be prevented.

Second Embodiment

3a and 3b show a welding apparatus according to a second embodiment of the invention. In addition, in the drawings and the following description, parts similar to those of the welding apparatus A of FIG. 1 are denoted by the same reference numerals, and these are not described again and again. In addition, "welding direction" is defined as the movement direction of the torch below, "front surface" is a surface along a welding direction, and "back surface" is a surface opposite to a welding direction.

Welding device B comprises a tungsten electrode 2, a central nozzle 13 enclosed around the tungsten electrode 2, and side nozzles 14 arranged between the tungsten electrode 2 and the central nozzle 13. The torch 11 is provided. That is, the torch 11 has a structure including a central nozzle 13 disposed around the tungsten electrode 2 and side nozzles 14 disposed between the tungsten electrode 2 and the central nozzle 13.

The central nozzle 13 is arranged in a substantially concentric manner at a constant distance from the tungsten electrode 2, and can supply the first shielding gas 8.                     

Referring to Fig. 3B, side nozzles 14 are disposed on each of two sides of the tungsten electrode 2 along the welding direction. The side nozzles 14 can supply the second shielding gas 9, and are preferably formed to protrude more than the tip of the central nozzle 13 in the tip direction. Further, the side nozzles 14 can be arranged at least at their tips on the sides of the tungsten electrode 2 without directly spraying the second shielding gas 9 on the weld bead.

As shown in Figs. 3A, 3B and 4, when the welding apparatus B is used to weld the base material 10, the torch 11 moves to the electric arc 7 in order to weld the base material 10. ) Melts the base material 10 and forms a molten pool 15. Weld beads are designated by reference numeral "16" in the figures. During the welding operation, the first shielding gas 8 is supplied from the central nozzle 13. The first shielding gas 8 is directed towards the tip of the central nozzle 13 while enclosing the tungsten electrode 2 and sprayed onto the base material 10 from the tip. At the same time the second shielding gas 9 is supplied from the side nozzles 14. The second shielding gas 9 is directed towards the tip of the side nozzles 14 and sprayed onto the base 10 from the tip. Since the second shielding gas 9 is guided along the periphery of the first shielding gas 8 and sprayed on the side portions of the periphery of the molten pool 15, the second shielding even if the torch 11 is moved at a high speed. The gas 9 is not supplied to the center part. Thereby, the welding structure which has the welding metal part 15a is obtained.

Since the welding device B has a torch 11 comprising a tubular center nozzle 13 arranged around the tungsten electrode 2 and side nozzles 14 between the tungsten electrode 2 and the center nozzle 13. As in the case of using the welding apparatus A shown in Fig. 1, the tungsten electrode 2 can be protected from deterioration by oxidation. Thus, the welded structure can be obtained with good quality. In addition, since the second shielding gas 9 containing the oxidizing gas can be supplied to the periphery of the molten pool 15, the internal convection in the molten pool 15 is improved so that the molten pool 15 can be deeply formed. have. Therefore, the weld metal part 15a can be formed deep among the base materials 10. In addition, the use of welding device B facilitates the welding operation and improves the welding efficiency.

In the present invention, one or more side nozzles may be further disposed on the front and / or back side of the electrode. 5A and 5B showing a welding apparatus according to a third embodiment of the present invention, welding apparatus B 'is further characterized in that two side nozzles 14a and 14b are additionally included. It is different from the welding apparatus B shown in FIG. 3B. Two side nozzles 14a and 14b can be disposed between the tungsten electrode 2 and the central nozzle 13 on the front and the rear of the tungsten electrode 2 respectively to supply the second shielding gas 9. have.

6a and 6b show a welding apparatus according to a fourth embodiment of the invention. Welding device C is different from welding device B shown in FIGS. 3A and 3B in that the side nozzles 24 are disposed outside the center nozzle 23. That is, the welding apparatus includes a torch including a tungsten electrode 2, a tubular center nozzle 23 disposed surrounding the tungsten electrode 2, and side nozzles 24 disposed outside the tubular center nozzle 23. 21 is provided.

Each of the two sides of the tungsten electrode 2 is arranged with the side nozzles 24 when viewed in the welding direction, preferably formed such that the tips of the side nozzles 24 protrude more than the tips of the central nozzles 23. Is arranged to be. The side nozzles 24 can also be otherwise arranged at least at their tips on the sides of the tungsten electrode 2 without directly spraying the second shielding gas 9 on the weld bead. In addition, the welding direction can be changed in the arrangement of the welded portions, but the side nozzles 24 are on both sides of the tungsten electrode 2 when viewed in the welding direction even when the welding direction is changed to, for example, 90 ° C. Stays constant.

As shown in Fig. 7, when the welding apparatus C is used to weld the base material 10, the electric arc 7 melts the base material 10 to form a molten pool 25, so that the base material 10 is formed. Can be welded. The weld bead is indicated by reference numeral "26" in FIG. During the welding operation, the first shielding gas 8 is supplied from the central nozzle 23. The first shielding gas 8 is directed toward the tip of the central nozzle 23, surrounding the tungsten electrode 2, and sprayed from the tip onto the base 10. At the same time the second shielding gas 9 is supplied from the side nozzles 24. The second shielding gas 9 is directed towards the tip of the side nozzles 24 and sprayed onto the base 10 from the tip. More specifically, the second shielding gas 9 is sprayed on two side portions of the periphery of the melt pool 25. Thereby, the welding structure which has the welding metal part 25a is obtained.

Since the welding device C has a torch 21 including a tubular center nozzle 23 disposed surrounding the tungsten electrode 2 and side nozzles 24 disposed outside the tubular center nozzle 23, The tungsten electrode 2 can be prevented from being degraded by oxidation as in the case of using the welding apparatus A shown in FIG. Thus, the welded structure can be obtained with good quality. Further, since the second shielding gas 9 containing the oxidizing gas is supplied to the periphery of the molten pool 25, the internal convection in the molten pool 25 is improved, and the molten pool 25 can be deeply formed. Therefore, the weld metal part 25a can be formed deep among the base materials 10. In addition, the use of welding apparatus C facilitates the welding operation and improves the welding efficiency. In addition, the side nozzles 24 are arranged outside the central nozzle 23 so that the second shielding gas 9 can be reliably supplied along the periphery of the first shielding gas 8.

In the present invention, one or more side nozzles may be further disposed on the front and / or back side of the electrode. 8A and 8B showing a welding apparatus according to a fifth embodiment of the present invention, welding apparatus C 'is further characterized in that two side nozzles 24a and 24b are additionally included. It is different from the welding apparatus C shown in FIG. 6B. Two side nozzles 24a and 24b are disposed on the front and the rear of the tungsten electrode 2 and can supply the second shielding gas 9 between the tungsten electrode 2 and the central nozzle 23, respectively. have.

Also, in the welding device B, B ', C, or C', the side nozzles 14 or 24 need not be precisely placed on both sides of the tungsten electrode 2, and their positions are before or after. Can escape.

Some embodiments of the invention are described as follows. In the examples, SUS304-type stainless steels with low concentrations of sulfur were used as the base material 10. The constituents of the stainless steels are listed in Table 1.                     

ingredient C Si Mn Ni Cr P S O Fe amount
(weight%) 0.06 0.44 0.96 8.19 18.22 0.027 0.001 0.0038 ---

In this embodiment, the welding apparatus A shown in Fig. 1 is used, and the first shielding gas 8 is argon, and the second shielding gas 9 adds oxygen (O ₂ ) as an oxidizing gas to argon as an inert gas. Mixed gas obtained by Some welding tests of the base material 10 were carried out under the above conditions, and then the cross sections of the weld metal portion 5a were observed. In welding tests, the oxygen concentration in the second shielding gas 9 is in the range of 1,000 ppm to 9,000 ppm by volume, and the flow rate of the second shielding gas 9 is 10 L / min or 20 L / min. The cross section of the welded metal part 5a obtained in each test is shown in Fig. 9, and test results obtained using pure argon instead of the second shielding gas 9 are included for comparison. Other welding conditions are listed in Table 2.

Item Condition Electrode type DCEN, W-2% ThO ₂
(Tungsten Electrode Containing 2% Thorium) Electrode diameter 1.6mm Tip angle of electrode 60 ° Shielding gas Ar gas, O ₂ / Ar mixed gas Gas flow rate 10L / min or 20L / min Arc length 3mm Bead length 50 mm Welding time 3 sec Welding current 160A Welding speed 2 mm / sec

As shown in FIG. 9, compared to the test using pure argon (O ₂ concentration = 0 ppm by volume) instead of the second shielding gas 9, the weld metal portion 5a is a second shielding gas containing oxygen ( Can be formed deeper in tests using 9). In addition, when the oxygen concentration in the second shielding gas 9 is in the range of 2,000 ppm to 6,000 ppm, particularly 3,000 ppm to 5,000 ppm, the weld metal portion 5a is formed particularly deeply.

10A and 10B show a correlation between the oxygen concentration in the second shielding gas 9 and the dimensions of the weld metal portion 5a, where FIGS. 10A and 10B show that the flow rate of the second shielding gas 9 is 10 /. Results at 20 L · min ⁻¹ are shown.

As shown in Figs. 10A and 10B, the oxygen concentration in the second shielding gas 9 is 2,000 vol ppm to 6,000 vol ppm, preferably 3,000 vol ppm to 6,000 vol ppm, and more preferably 3,000 vol ppm to 5,000 vol. In the range of ppm, the width of the weld bead 6 is small, and the weld metal portion 5a is formed particularly deeply. The comparison is also made when the concentration of oxygen is less than 1,000 volume ppm or more than 7,000 volume ppm.

11A and 11B show a correlation between the oxygen concentration in the second muddy gas 9 and the aspect ratio and oxygen content (weight ppm) of the weld metal portion 5a, where FIGS. 11A and 11B show the second shielding gas. The results when the flow rate of (9) is 10/20 L · min ⁻¹ are shown. The aspect ratio of the weld metal portion 5a is defined as the ratio of the depth D to the width W of the weld metal portion 5a. As shown in Figs. 11A and 11B, the weld metal portion 5a in the case of using the second shielding gas 9 containing oxygen, as compared with the case of using pure argon instead of the second shielding gas 9; The aspect ratio of is higher. It is also noted that the aspect ratio of the weld metal portion 5a is relatively high when the oxygen concentration in the second shielding gas 9 is in the range of 2,000 vol ppm to 6,000 vol ppm, particularly 3,000 vol ppm to 5,000 vol ppm.

In addition, the oxygen concentration in the weld metal portion 5a also increases with the increase in the oxygen concentration in the second shielding gas 9. When the oxygen concentration in the second shielding gas 9 reaches about 5,000 volume ppm, the oxygen concentration in the weld metal portion 5a is about 200 ppm by weight, and the oxygen concentration in the second shielding gas 9 is about 6,000. When the volume is exceeded, the oxygen concentration of the weld metal portion 5a is approximately constant (220 ppm by weight). The aspect ratio of the weld metal portion 5a is relatively high when the oxygen concentration in the weld metal portion 5a is 70 to 220 ppm by weight, especially 70 to 200 ppm by weight, and when the oxygen concentration is outside the above range, the weld metal portion becomes shallow. This is because the thickness of the oxide coating formed on the weld bead surface is excessively large.

FIG. 12 is a graph showing a correlation between the oxygen concentration in the second shielding gas 9 and the thickness of the oxide coating formed on the surface of the weld metal portion 5a. 13 shows the correlation between the concentration of CO ₂ in the second shielding gas 9 and the thickness of the oxide coating formed on the surface of the weld metal portion 5a when CO ₂ is used as the oxidizing gas in the second shielding gas 9. Graph showing the relationship. As shown in the two graphs, when the concentration of the oxidizing gas exceeds 6,000 ppm by volume, the thickness of the oxide coating becomes thick, and the thick oxide coating delays the convection in the molten pool 5 to deepen the weld metal part 5a. It cannot be formed. On the other hand, the corrosion resistance and the appearance of the welded structure are also deteriorated. Therefore, the concentration of the oxidizing gas is preferably 6,000 vol ppm or less, and more preferably 5,000 vol ppm or less.

Therefore, when the composition of the second shielding gas 9 is set so that the oxygen concentration of the weld metal portion 5a is 70 to 220 ppm by weight, the weld metal portion 5a can be formed in an excellent shape. In the case of using the second shielding gas obtained by adding oxygen to argon, the welding current is 160 A, the welding speed is 2 mm / sec, and the oxygen concentration in the second shielding gas 9 is 2,000 volppm to 6,000 vol. When in ppm, both the shape of the weld metal portion 5a and the welding efficiency can be improved.

In addition, in the case of other welding conditions, it is preferable that the working conditions are set so that the oxygen concentration in the weld metal portion 5a becomes 70 volppm to 220 ppm by weight even when, for example, CO ₂ or the like is used as the oxidizing gas.

The tungsten-inert-gas welding apparatus of the present invention provides at least the following advantages. First of all, since the first shielding gas composed of the inert gas is guided while surrounding the electrode, the electrode can be protected from deterioration by oxidation. Thus, the welded structure can be obtained with good quality.

Further, the first shielding gas composed of the inert gas can be supplied to the center of the molten pool, and the second shielding gas containing the oxidizing gas can be supplied to the periphery of the molten pool. This allows the molten pool to be supplied with oxygen at the required concentration and the oxygen concentration in the periphery of the molten pool can be higher than the central oxygen concentration. Thus, the surface tension in the periphery with lower temperature and higher oxygen concentration in the melt pool is smaller, and the surface tension in the center with higher temperature and lower oxygen concentration is greater. As a result, internal convection is induced in the molten pool, and the molten pool can also be formed deep. Thus, the weld metal portion can be formed deep in the welded object.

In addition, as compared with conventional welding methods using active flux, slag is hardly generated in the present invention, and thus no slag removal operation is required. In addition, smoke is rarely generated during operation. Therefore, the welding operation can be easily performed.

In addition, since the weld metal portion can be formed deep, the occurrence of insufficient weld-intrusion or a decrease in the welding efficiency can be prevented.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the following claims and their equivalents.

Claims (16)

delete delete Generating an electric arc between the electrode and the object to weld the object, wherein a first shielding gas comprising an inert gas is directed towards the welding object surrounding the electrode and contains an oxidizing gas Gas is directed along the periphery of the first shielding gas towards the welding object, The concentration of the oxidizing gas in the second shielding gas is set so that the oxygen concentration in the weld metal part of the welding target is in the range of 70 ppm by weight to 220 ppm by weight. Generating an electric arc between the electrode and the object to weld the object, wherein a first shielding gas comprising an inert gas is directed towards the welding object surrounding the electrode and contains an oxidizing gas Gas is directed from at least two sides of the electrode towards the welding object when viewed in the welding direction, The concentration of the oxidizing gas in the second shielding gas is set so that the oxygen concentration in the weld metal portion of the welded object is in the range of 70 ppm by weight to 220 ppm by weight. The tungsten-inert-gas welding method according to claim 3, wherein the concentration of the oxidizing gas in the second shielding gas is in the range of 2,000 to 6,000 ppm by volume. The tungsten-inert gas welding method according to claim 4, wherein the concentration of the oxidizing gas in the second shielding gas is in the range of 2,000 to 6,000 ppm by volume. The tungsten-inert-gas welding method according to claim 3, wherein the concentration of the oxidizing gas in the second shielding gas is in the range of 3,000 vol ppm to 5,000 vol ppm. The tungsten-inert-gas welding method according to claim 4, wherein the concentration of the oxidizing gas in the second shielding gas is in the range of 3,000 vol ppm to 5,000 vol ppm. delete delete delete delete delete delete delete delete

Images