JPH1058147A - Torch for plasma arc welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a torch for the plasma arc welding to perform the high- speed plasma welding with large current by providing a third nozzle between a first nozzle and a second nozzle with their axes coincided with each other to increase the critical current for generation of the series arc. SOLUTION: A third nozzle 4 is formed so that its tip part is tapered, and a small gap is demarcated between a connection nozzle member 20b to constitute a first nozzle 2 and a tip side tapered surface of a flange part 20d of a nozzle body 20c which is not brought into close contact with the connection nozzle member. The inert gas such as pure Ar and pure He is fed to the third nozzle 4 using a torch in which the third nozzle 4 is arranged between the first nozzle 2 and the second nozzle 3, the high-speed inert gas flow layer is formed on the surface of the nozzle body 20c to constitute the first nozzle 2 opposite to the material to be welded to surely prevent generation the series arc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a torch for plasma arc welding, and more particularly, to a torch for plasma arc welding excellent in series arc prevention performance.

[0002]

2. Description of the Related Art Normally, plasma arc welding is performed as follows using a torch as shown in FIG.

That is, a pilot arc is blown between a tungsten electrode 1 and a first nozzle 2 made of metal such as copper having a water-cooled structure having a circulation passage 2b for cooling water CW therein. Pure Ar or Ar
A plasma arc is generated by flowing an operating gas DG such as a mixed gas of H ₂ and H ₂ .

Then, the plasma arc is narrowed by a small-diameter orifice 2a formed at the tip of the first nozzle 2 to provide a thermal pinch effect to form a main arc having an increased energy density. The material (all not shown) is reached and welded.

At this time, a shield gas SG such as Ar, He, or N ₂ flows from a second nozzle 3 which is arranged outside the first nozzle 2 with its axis aligned to shield the welded portion from the atmosphere.

As shown in FIG. 4, the first nozzle 2 usually has a base nozzle member 20a and a connecting nozzle member 20b.
And a nozzle body 20c.
If the nozzle body 20c is damaged, it can be replaced.

More specifically, the base nozzle member 20a constituting the first nozzle 2 has a plurality of circulation passages 2b for the cooling water CW penetrating in the axial direction on a concentric circle at the center of the thickness of the cylindrical body. A step portion is formed on the inner surface of the tip portion, and a male screw is formed on the outer surface.

The nozzle body 20c is a tapered cylindrical body, and has a frusto-conical shape with a two-stage taper on the outer periphery of the tip, and a small-diameter orifice 2a at the center. A flange portion 20d is formed.

Further, the connecting nozzle member 20b is a cylindrical body having a tapered taper formed at the distal end thereof in close contact with the tapered surface on the proximal end side of the flange portion 20d of the nozzle body 20c. Has an internal thread.

After the base end of the nozzle body 20c is airtightly inserted into the step on the inner surface of the front end of the base nozzle member 20a, the connecting nozzle member 20b is connected to the base nozzle member 20a.
The first nozzle 2 is configured by being externally screwed and fastened to the first nozzle 2.

Although the illustration of the second nozzle 3 is omitted,
At its base end, it is detachable by the same mechanism as the connecting nozzle member 20b.

A feature of this plasma arc welding method is that a single side penetration welding can be performed by a welding method utilizing the heat concentration of the plasma arc. However, when the welding speed is increased, the undercut is formed on the front and back surfaces of the welded portion. And welding defects such as insufficient amount of molten metal.

Generally, in the plasma arc welding method, the current value is increased or the orifice 2 having a small diameter is used.
High-speed welding is possible by increasing the energy density of the plasma arc by reducing the diameter of a.

However, if the current value is increased or the diameter of the small-diameter orifice 2a is reduced, the arc current is separated from the electrode 1, and the separated arc current passes through the first nozzle 2 (nozzle body 20c) to be welded. And the first nozzle 2
An abnormal discharge phenomenon called a so-called series arc occurs in which an arc different from the main arc is generated between the workpiece and the material to be welded.

If the above-described abnormal discharge phenomenon occurs during welding, the plasma arc, which is the main arc, loses its function as a contraction arc, making it difficult to meander a weld bead or forming a keyhole, thereby performing high-speed welding. You will not be able to do it.

For this reason, various methods for preventing the above abnormal discharge phenomenon have been conventionally developed.
Japanese Unexamined Patent Publication No. 3-5882 discloses an abnormal discharge phenomenon, that is, a series arc, by stabilizing the direction in which the main arc is generated by using a magnetic field and suppressing an increase in the main arc diameter after exiting the first nozzle. There has been proposed a method for preventing the occurrence of the problem.

However, according to the method disclosed in Japanese Patent Application Laid-Open No. 63-5882, when a higher current value and a smaller orifice diameter are used in order to perform higher-speed welding, a series arc is not generated. There was a disadvantage that it could not be reliably prevented.

[0018]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object the problem of generating a high-energy-density plasma arc due to a higher current value and a smaller orifice diameter. Another object of the present invention is to provide a plasma arc welding torch capable of reliably preventing the generation of a series arc.

[0019]

The gist of the present invention resides in the following torch for plasma arc welding.

A tungsten electrode is arranged at the center, a first nozzle for restraining plasma arc having a working gas ejection hole at the tip, and an outer periphery of the first nozzle coaxially with the first nozzle. What is claimed is: 1. A torch for plasma arc welding comprising a second nozzle for supplying a shielding gas, wherein the torch is provided between the first nozzle and the second nozzle so that their axes are aligned, and faces the material to be welded of the first nozzle. A torch for plasma arc welding, comprising a third nozzle for forming a high-speed gas flow layer of an inert gas on a surface to be heated.

The present inventors conducted various experiments to determine the cause of the series arc. As a result, they have found the following, and have accomplished the present invention.

That is, a high-speed gas flow layer of inert gas is formed on the tip surface of the first nozzle having a small-diameter orifice from the outer periphery of the nozzle toward the nozzle axis, and a discharge space near the tip surface of the first nozzle is formed. If the impurity gas such as metal vapor or oxygen generated from the welded portion of the material to be welded and the shielding gas supplied from the second nozzle are not retained, it is possible to surely prevent the generation of a series arc. I learned.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a torch for plasma arc welding according to the present invention will be described in detail with reference to FIGS.

FIG. 1 is a schematic longitudinal sectional view showing an example of a torch for plasma arc welding according to the present invention, and FIG. 2 is an enlarged longitudinal sectional view of an essential part thereof. Is shown.

As shown in FIG. 1, the torch according to the present invention has an axial center between a first nozzle 2 for restraining a plasma arc and a second nozzle 3 for supplying a shielding gas. Is provided with a cylindrical third nozzle 4 arranged with its axis aligned.

The tip of the third nozzle 4 is formed in a tapered shape, and the nozzle body 2 does not come into close contact with the connecting nozzle member 20b constituting the first nozzle 2.
A minute gap g (see FIG. 2) is defined between the flange portion 20d and the front tapered surface of the flange portion 20d.

As described above, the first nozzle 2 and the second nozzle 3
An inert gas such as pure Ar or pure He is supplied to the third nozzle 4 using a torch in which the third nozzle 4 is disposed between the first nozzle 2 and a to-be-welded material (not shown) of the nozzle body 20c constituting the first nozzle 2. When a high-speed airflow layer of an inert gas is formed on the surface opposite to the above, generation of a series arc can be prevented more reliably.

The reason is presumed to be as follows. That is, at the time of plasma arc welding, an impurity gas such as metal vapor or oxygen generated from a molten metal portion of the material to be welded and a low-concentration shield gas supplied from the second nozzle 3 are mixed into the discharge space. Among them, the low-concentration shield gas is easily ionized under high-temperature conditions.

Therefore, in the conventional torch, the first nozzle 2
The ionized metal vapor, low-concentration shield gas, and impure gas such as O ₂ always stay on the surface of the nozzle body 20c facing the material to be welded, which causes the series arc to be easily generated.

On the other hand, in the nozzle of the present invention, a large amount of inert gas is supplied from the third nozzle 4 so that a high-speed airflow layer is formed on the surface of the nozzle body 20c constituting the first nozzle 2 facing the material to be welded. Is formed. For this reason, the nozzle body 2
On the surface facing the material to be welded, 0c, the metal vapor and the low-concentration shielding gas do not stay, and an insulating layer in which there is no ionized discharge space is always formed. As a result, a series arc is generated. It is estimated that it will not.

The shape of the tip of the third nozzle 4 may be any shape as long as a high-speed airflow layer can be formed on the surface of the nozzle body 20c constituting the first nozzle 2 facing the material to be welded. Well, not particularly limited. However, in order to maximize the effect, it is preferable to adopt the following shape and dimensions.

That is, the taper angle θ at the tip is
It is preferable that the outer surface taper angle on the distal end side of the flange portion 20d formed at the distal end portion of the nozzle main body 20c of the first nozzle 2 is the same, and the minute gap g between them is about 0.5 mm.

The inner diameter d of the tip is, for example, the first
When the diameter a of the orifice 2a of the nozzle 2 is 2 to 4 mm and the outer diameter b of the tip is about 5 mm, the maximum diameter c of the tip side tapered portion of the flange portion 20d of the nozzle body 20c is 4
It is preferable to make the diameter smaller by about 6 mm.

On the other hand, as the gas to be supplied to the third nozzle 4, any of pure He, pure Ar and a mixed gas of Ar and He may be supplied, but in order to form a more reliable insulating layer. It is more preferable to supply pure He that is less likely to be ionized at a higher temperature than pure Ar. Further, the gas flow rate injected from the minute gap g is 15 to 25 N
(Normal) It is preferable to be about liter / min.

Each member constituting the first nozzle 2 is usually
Although it is made of Cu having high thermal conductivity, the nozzle body 20c may be made of a noble metal such as Ag or Au, and the connecting nozzle member 20b is hardly affected by external influence (O ₂ , metal vapor). Therefore, it may be made of stainless steel.

The second nozzle 3 is usually made of ceramics. Further, the third nozzle 4 is connected to the first nozzle 2
It is preferable to be made of Cu having high thermal conductivity as in
When the diameter d is increased, it is preferable to use a non-conductive ceramic from the viewpoint of erosion.

Although the first nozzle 2 in the illustrated example comprises three members, these three members may be formed as an integral member.

[0038]

EXAMPLE A SUS304 stainless steel pipe having an outer diameter of 34 mm and a thickness of 3 mm was welded at a welding speed of 2.0 m / min using a transfer type plasma welding machine having a maximum current of 500 A, as shown in FIG. Conventional torch with configuration and Fig. 1
In the case where the torch of the present invention having the structure shown in Fig. 1 was used, the generation limit current value of the series arc was examined.

In the conventional torch and the torch of the present invention, the outer diameter b of the tip is 5 mm, the maximum diameter c of the tapered portion on the tip side is 20 mm, the taper angle is 35 °, and the diameter a of the orifice 2a is various. Change (1.6mm, 2.0m
m, 2.4 mm, 3.2 mm), and a nozzle body having four types of first nozzles 2 including a tungsten electrode 1 having an outer diameter of 4.8 mm. The third nozzle 4 constituting the torch of the present invention has a taper angle θ of 35 ° at the tip and an inner diameter d of 14 m.
m, and the minute gap g was set to 0.5 mm.

In both of the conventional torch and the torch of the present invention, Ar and H ₂ are used as the working gas DG at a ratio of 9: 1 by volume, regardless of the size of the diameter a of the orifice 2a. 0.33N gas mixed with
(Normal) liter / min · mm ^{2 It} was supplied at a constant flow rate.

On the other hand, in the case of the conventional torch, two kinds of shielding gas SG of Ar and He
It was supplied at a constant flow rate of N (normal) liter / min. On the other hand, in the torch of the present invention, the shielding gas SG of only Ar1 type was supplied from the second nozzle 3 by 15 N.
While supplying at a constant flow rate of (normal) liter / min, two gases, Ar and He, were supplied from the third nozzle 4 at a constant flow rate of 15 N (normal) liter / min. Note that the standoff was constant at 2 mm in each case.

Table 1 shows the results when the conventional torch was used.
Table 2 shows the results when the torch of the present invention was used, and FIG. 3 summarizes the results.

[0043]

[Table 1]

[0044]

[Table 2]

As is clear from the results shown in Tables 1 and 2 and FIG. 3, when the torch of the present invention is used, the generation limit current of the series arc is greatly increased. Especially,
When the diameter a of the orifice 2a of the first nozzle 2 is large,
The effect is remarkable.

In the conventional torch, there is almost no difference in the generation limit current value of the series arc depending on the type of the shield gas SG supplied from the second nozzle 3, whereas in the torch of the present invention, the third nozzle 4 The generation limit current value of the series arc greatly differs depending on the kind of gas supplied. This is because, when metal vapor remains on the surface of the first nozzle 2 facing the material to be welded, whether or not a series arc is generated is limited by the ionization of the metal vapor. It is presumed that the rate is limited by the ionization degree inherent to the gas.

[0047]

According to the torch of the present invention, the generation limit current of the series arc can be greatly increased, and high-speed plasma welding with a large current can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing an example of a torch for plasma arc welding according to the present invention.

FIG. 2 is an enlarged vertical sectional view showing a main part of the torch for plasma arc welding of the present invention.

FIG. 3 is a view showing a result of an example.

FIG. 4 is a schematic longitudinal sectional view showing an example of a conventional torch for plasma arc welding.

[Explanation of symbols]

 1: electrode, 2: first nozzle, 2a: orifice, 2b: cooling water circulation passage, 20a: base end nozzle member, 20b: connecting nozzle member, 20c: nozzle body, 20d: flange portion, 3: second nozzle 4: Third nozzle.

Claims (1)

[Claims] A first electrode for restraining a plasma arc having a tungsten electrode disposed at a central portion thereof and a jetting hole of an operating gas at a tip portion, and disposed on an outer periphery of the first nozzle coaxially with the first nozzle. A torch for plasma arc welding comprising a second nozzle for supplying a shielding gas, wherein the torch is provided between the first nozzle and the second nozzle so that their axes are aligned, and the material to be welded of the first nozzle is provided. A third nozzle for forming a high-speed gas flow layer of an inert gas on a surface opposed to the torch.