JPH07135091A - Nozzle for plasma torch - Google Patents

Abstract

PURPOSE:To keep a nozzle hole without splash, prevent double arcs, and provide a stable arc by providing a nozzle in which an outer circumferential part of the front end part is protruded from an inner circumferential part toward the front. CONSTITUTION:A front end angle theta of a nozzle 10 is set to be larger than 180 deg.C, and it is formed in a structure in which an outer circumferential part is protruded from an inner circumferential part, flow of splash 50 by its own weight, an suspended bell-shaped outer flames in forming a main plasma arc are formed to move partly along the recessed nozzle 10, and the splash 50 moves toward the outer circumferential side. There is almost no splash 50 around a nozzle hole 11, therefore, and the arc 30 is stabilized. As time passes, the splash 50 is deposited to glow on an outer circumferential part of a from end surface, but because it grow from the arc 30, double arcs are not generated from the splash 50, thereby effects are not given to the arc 30 from the nozzle hole 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma torch nozzle for restraining a plasma arc, which is installed in a plasma torch used for welding and melting, melting, fusing and cutting of metallic materials.

[0002]

2. Description of the Related Art Conventionally, a plasma torch utilizing the thermal energy of a plasma arc has been used as one means for melting and heating metal materials and the like. The general structure of a plasma torch is shown in FIG.

The plasma torch has a cylindrical nozzle 10
And an electrode 20 concentrically included in the nozzle 10.

The electrode 20 may be a tungsten-based alloy, a force-cooled copper-based alloy, or a high-melting-point metal having a high work function such as hafnium or zirconium fixed at its tip, and is usually a nozzle. It is fixed to the inner part of the nozzle hole 11 in an insulated state with respect to 10, and is electrically connected to the base material 40 via a DC or AC main arc power supply 60.

The nozzle 10 has a nozzle hole 11 at the center of the tip, and in the case of a transfer type plasma, a pilot arc that plays a pilot fire for generating the main plasma arc 30 is generated. Configure one electrode. The plasma gas is ejected from the nozzle hole 11 as a high-temperature main plasma arc 30 whose arc column is the nozzle hole 1
Be bound by 1.

In the case of the non-transfer type plasma torch, in principle, the pilot arc becomes the plasma arc 30 intended for use in melting and heating as it is, and is ejected from the nozzle hole 11. A high frequency power source 70 is a power source for pilot arc ignition.

The nozzle 10 as described above is required to have both conductivity as an electrode and heat resistance to withstand a large amount of heat from the main plasma arc. Usually, the thermal conductivity of a copper or copper alloy system and It is made of a metal material with good electrical conductivity and is forcibly cooled from inside by cooling water. Hereinafter, this structure is represented by the expression of a water-cooled copper structure.

By the way, during use of the transfer type plasma arc torch, an undesired phenomenon of double arc often occurs. This is also called a series arc, and when this phenomenon occurs, the torch, especially the nozzle portion, is seriously damaged, and the torch becomes unusable in a short time. This phenomenon will be described with reference to FIG.

Usually, the main plasma arc 30 generated from the electrode 20 is ejected in a straight line to the base material 40 through the nozzle hole 11 at the center of the nozzle. However, a part of the main plasma arc 30 generated from the electrode 20 is
There is a case where the material jumps to the base material 40 through a portion other than 1. As a result, it has a shape like two arc columns, which is called a double arc.

In the case of the transfer type plasma torch, the nozzle is electrically neutral while the main plasma arc is generated. However, as described above, the nozzle is electrically conductive, so that the plasma arc is caused for some reason. In the normal state, the electrical circuit that was formed between the electrode and the base material
In addition to this, an electric circuit is formed between the electrode, the nozzle, and the base material, and a double arc is generated.

The double arc is usually caused by improper use conditions of the torch (current, voltage, type of plasma gas, composition and flow rate, arc interval, etc.). This often occurs when the design shapes (especially the diameter of the nozzle hole and the length of the nozzle hole) do not match well. The relationship between the current and the nozzle diameter, which affects the arc stability under specific conditions, is shown in Fig. 3 (Welding and Joining Handbook, Welding Society, September 30, 1990, published by Maruzen). The arc stability region is relatively wide and it is not difficult to choose.

However, a double arc may occur even if the usage conditions of the torch and the design inside the nozzle are appropriate. For example, this is a case of melting and heating a metal that often causes splash. Examples of metallic materials that frequently generate splashes include sponge-like titanium and zirconium.

That is, the most general method for producing titanium, zirconium, etc. is to reduce a chloride such as titanium, zirconium, etc. with metallic magnesium, metallic sodium, etc. to obtain a crude sponge mass, which is vacuum separated or Purification treatment such as the leaching method is performed to obtain a purified sponge. When this is melted and heated by using a plasma torch, MgCl ₂ , Mg, NaCl, etc. evaporate and foam, causing a splash phenomenon.

If a plasma torch is used for a long time due to this splash phenomenon, a large amount of splash adheres to and accumulates at the tip of the nozzle. As a result, a new electric circuit is formed through the system path of electrode-nozzle-deposited splash-base material, and a double arc is generated. Until the splash attaches to the tip of the torch, even if a plasma arc normally occurs, once a large amount of splash attaches to the torch, a double arc occurs and the arc is scattered.

Due to this double arc, a sound bead cannot be obtained in the case of welding or the like. Not only this, but due to the occurrence of the double arc, the torch may be seriously damaged in a short time (for example, the nozzle is melted) and become unusable. For this reason, it is necessary to stop the work and replace the damaged parts, which inevitably reduces the work efficiency.

As a measure for preventing this double arc, a technique of attaching an insulating ring made of ceramics or the like to the tip of the nozzle has been proposed (Actually, Sho 60-60).
No. 88). In addition, research on using a new material for the nozzle is also underway (Japanese Patent Laid-Open No. 48-30647).
JP-A-3-25900).

[0017]

However, since the nozzle constitutes one of the electrodes regardless of the torch type of the transfer type or the non-transfer type as described above, it must be conductive, so that the whole nozzle is made of ceramics. It cannot be made of non-conductive material (insulating material). For this reason, the nozzle has a configuration in which water-cooled copper and an insulating ring are combined, and a seal such as an O-ring is required between them, which makes the torch extremely complicated and maintenance is complicated.

Ceramics are both an insulator and a heat insulating material. For this reason, even if the cooling water circulates on this outer surface, the heat conduction is poor, so it is not possible to prevent the surface temperature from rising due to the intense heat from the plasma arc, and the high output of the torch. However, there were many problems when used for a long time. For these reasons, even if a ceramic nozzle is manufactured, the problem of unstable arc due to splash adhesion is fundamentally unsolved, and the torch is expensive due to its complicated structure, and maintenance is complicated. The problem remains that running costs cannot be reduced.

Similarly, the introduction of new materials is expensive, and there are problems in terms of reliability and the like.

The object of the present invention is to reduce the generation of double arc due to the adhesion of splash even when low-priced and proven water-cooled copper is adopted, and to make the arc stable for a long time with a simple structure and economical efficiency. It is to provide a nozzle for a plasma torch that is excellent and has a long life.

[0021]

By the way, as shown in FIGS. 4A and 4B, the tip surface of a conventional plasma torch nozzle is a flat surface having a tip angle of 180 ° perpendicular to the central axis, or The tip shape is a tip angle of less than 180 ° that gradually protrudes toward the tip side from the outer peripheral portion toward the inner peripheral portion, and in most cases, the pointed shape shown in FIG. 4 (A) is adopted.

In the nozzle 10 as described above, the splash 50 attached to the tip surface is melted by the intense heat of the main plasma arc 30 and concentrated on the inner peripheral side. In such a state, the main plasma arc is more likely to be disturbed, and double arcs frequently occur. Therefore, the life of the nozzle is significantly shortened. In the case of the flat surface shown in FIG. 4 (B), this tendency is somewhat alleviated, but the double arc is still generated due to the concentration of the splash 50.

The plasma torch nozzle of the present invention was developed by paying attention to the fact that the concentration of splash is alleviated when the nozzle tip surface is a flat surface rather than a pointed shape. As shown in C), contrary to the conventional case, the outer peripheral portion of the tip end surface is made to project from the inner peripheral portion to the tip end side, and typically the tip end surface is gradually tapered toward the outer end portion from the inner peripheral portion. It is a concave taper surface with a tip angle of more than 180 ° protruding to the inside.

FIG. 5 illustrates the shape of the tip surface of the plasma torch nozzle of the present invention. As shown in the figure,
A flat surface or the like may be mixed on the tip surface within a range in which no major functional disorder occurs. Further, the tapered surface may be curved.

By adopting such a tip surface shape, the splash 50 adhering to the tip surface of the nozzle 10 diffuses to the outer peripheral side, and the splash 50 is removed from the periphery of the nozzle hole 11, so that the nozzle 10 is Even in the case of a general-purpose structure such as water-cooled copper, that is, an integrated structure of a metal that is excellent in thermal conductivity and electric conductivity and is forcibly cooled from the inside, generation of a double arc due to adhesion of the splash 50 is suppressed.

[0026]

In other words, when a metallic material or the like that frequently generates splash is melted and heated for a long time, the splash adheres to the torch tip (nozzle tip surface) with the passage of time. The splash attached to the tip surface of the nozzle is remelted by the heat from the main plasma arc and becomes partly liquid.

However, when the outer peripheral portion of the nozzle tip surface is located closer to the tip side than the inner peripheral portion, the flow of splash due to its own weight and the bell-shaped external flame formed when a stable main plasma arc is formed are concave. The liquid splash moves to the outer peripheral side due to the synergistic effect with the shape of a part of the nozzle tip surface. Therefore, there is almost no splash around the nozzle hole for a long time, and the arc is extremely stable.

Splash gradually builds up and grows on the outer peripheral portion of the tip surface with the passage of time, but since it grows at a position sufficiently away from the position of the main plasma arc, a double arc is generated from this grown splash. In addition, it does not affect the main plasma arc ejected from the nozzle hole.

The splash accumulated on the outer periphery of the tip surface is
When it grows, it greatly hangs outside the bell-shaped external flame, but due to the radiant heat from the plasma arc and the molten pool, part of the tip falls off, and the growth of the splash is interrupted here. Even when this heap splash falls off,
As described above, since it occurs at a position sufficiently distant from the main plasma arc, there is no concern about double arc generation.

As described above, the splash formed on the outer peripheral portion of the tip surface is a phenomenon in which deposition-growth-dropping is repeated, but it is a phenomenon far away from the nozzle hole, and there is always almost no splash around the nozzle hole. Since the main plasma arc continues to fly, the arc is extremely stable over a long period of time.

Further, it is not necessary to use an insulating material such as ceramics for the nozzle, and an integrated structure of water-cooled copper, that is, metal which is forcibly cooled from the inside can be adopted. Therefore, even if it receives a large amount of heat from the main plasma arc, the thermal conductivity is good,
With sufficient cooling, the torch output can be increased and it can be used for a long time. Furthermore, the structure is simple because it is integrated,
The nozzle does not become expensive, including the material cost, and maintenance is easy.

The positional relationship between the inner peripheral portion and the outer peripheral portion of the nozzle tip surface is represented by the tip angle when the tip surface is a concave taper surface, preferably 250 ° or less, particularly 190 ° or more and 200 ° or less.

When the tip angle approaches 180 °, the effect of diffusing the splash attached to the tip surface cannot be sufficiently obtained. On the other hand, if it greatly deviates from 180 °, the bell-shaped outer flame of the main plasma arc will come too close to the concave tip surface of the nozzle, and the nozzle is likely to be damaged by strong heat and the main plasma arc. Since the distance from the nozzle tip to the base metal becomes shorter than the arc length of No. 2, the frequency of occurrence of double arc increases due to the adhesion of splash.

As another condition, the outer diameter of the nozzle is relatively important. That is, if the nozzle outer diameter is too small, even if it is a concave taper surface having a tip angle of more than 180 °, splash accumulation-growth-only within a range where the nozzle outer diameter is small.
Since the falling off is not repeated and a phenomenon occurs in the vicinity of the main plasma arc, the double arc is easily generated. On the other hand, when the outer diameter of the nozzle is too large, most of the generated splash is not only received by this nozzle, but also the nozzle becomes large and the manufacturing cost becomes high, which is not preferable. The optimum nozzle outer diameter is approximately the same as the bell-shaped outer flame of the plasma arc.

[0035]

EXAMPLES Examples of the present invention will be described below, and the effects of the present invention will be clarified by comparison with Comparative Examples.

When welding titanium sponge (compression molded product) with a plasma torch, a nozzle having an integral structure made of copper, which is forcibly cooled from the inside, is used, and the tip angle of the nozzle tip surface is variously changed. The effect on lifespan was investigated. Here, the life of the nozzle is the operating time up to the point when a normal welding bead cannot be obtained because the arc has become unstable because the nozzle has melted significantly and the cooling water inside has leaked out or the nozzle has melted. is there.

All conditions were the same except for the tip angle of the nozzle tip surface. The common conditions are shown in Table 1 and the survey results are shown in Table 2.

[0038]

[Table 1]

[0039]

[Table 2]

The example of the present invention, in which the tip surface is a concave taper surface with the tip angle θ exceeding 180 °, has a significantly longer life than the conventional example. For example, when the tip angle θ is 195 °, the tip angle θ is 195 °. The life was about 6 times that when θ was 90 ° and about twice that when the tip angle θ was 180 °.

[0041]

As described above, in the plasma torch nozzle of the present invention, the outer peripheral portion of the tip surface is projected from the inner peripheral portion toward the tip side so that the splash adhered to the tip surface is diffused toward the outer peripheral side. Since the area around the nozzle hole is always maintained in a splash-free state, it is possible to prevent the occurrence of double arc due to the adhesion of splash, and to generate an extremely stable arc for a long time. Therefore, the consumption and melting loss of the nozzle are significantly reduced, and the life of the nozzle is significantly extended. Further, since it is not necessary to use a material such as ceramics for the nozzle and a general-purpose structure such as water-cooled copper can be adopted, the nozzle is sufficiently cooled, the torch output can be increased, and the torch can be used for a long time. Moreover, the structure of the nozzle is simple, the torch price is kept low, and complicated maintenance is avoided. For these reasons, the total running cost is significantly reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a general configuration of a plasma torch.

FIG. 2 is an explanatory diagram of a double arc.

FIG. 3 is a graph showing effects of nozzle hole diameter and arc current on arc characteristics.

FIG. 4 is a cross-sectional view showing a typical configuration of the nozzle of the present invention and its function in comparison with the case of a conventional nozzle.

FIG. 5 is a cross-sectional view illustrating the tip surface shape of the nozzle of the present invention.

[Explanation of symbols]

 10 Nozzle 11 Nozzle Hole 20 Electrode 30 Main Plasma Arc 40 Base Material 50 Splash

Claims (3)

[Claims] 1. A nozzle for a plasma torch, characterized in that an outer peripheral portion of a nozzle tip surface having a nozzle hole opened at a central portion thereof protrudes toward the tip side from an inner peripheral portion. 2. The nozzle for a plasma torch according to claim 1, wherein the nozzle tip surface is a concave taper surface that gradually protrudes toward the tip side from the inner peripheral portion toward the outer peripheral portion. 3. The nozzle for a plasma torch according to claim 1, wherein the nozzle has a metal integrated structure that is excellent in thermal conductivity and electrical conductivity and is forcibly cooled from the inside.