JP2939693B2 - Nozzle for plasma torch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nozzle for a plasma torch, which is provided in a plasma torch used for melting and heating such as welding, melting, fusing and cutting of a metal material and restraining a plasma arc.

[0002]

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

[0003] The plasma torch has a cylindrical nozzle 10
And an electrode 20 concentrically included in the nozzle 10.

The electrode 20 includes a tungsten-based alloy, a forcedly cooled copper-based alloy, and a high-melting-point metal such as hafnium or zirconium having a small work function at its tip. It is fixed to the back 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.

[0005] The nozzle 10 has a nozzle hole 11 at the center position of the tip portion. In the case of the transfer type plasma, the nozzle 10 is used to generate a pilot arc which plays a pilot role for generating the main plasma arc 30. Configure one electrode. The plasma gas is ejected from the nozzle hole 11 as a high-temperature main plasma arc 30, and the arc column forms the nozzle hole 1.
1 bound.

In the case of the non-transfer type plasma torch, in principle, the pilot arc is directly used as the plasma arc 30 to be used for the melting and heating processing, and is ejected from the nozzle hole 11. Reference numeral 70 denotes a high frequency power supply, which is a power supply for pilot arc ignition.

[0007] Such a nozzle 10 is required to have both the conductivity as an electrode and the heat resistance to withstand strong heat from the main plasma arc. It is made of a metal material with good electrical conductivity and is forcibly cooled from inside with cooling water. Hereinafter, this structure is represented by a water-cooled copper structure.

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

Normally, the main plasma arc 30 generated from the electrode 20 is ejected linearly to the base material 40 through the nozzle hole 11 at the center of the nozzle. However, part of the main plasma arc 30 generated from the electrode 20
In some cases, the ball may fly to the base material 40 via a portion other than 1. As a result, the shape becomes such that two arc columns are formed, which is called a double arc.

In the case of the transfer type plasma torch, while the main plasma arc is generated, the nozzle is electrically neutral. However, since the nozzle is electrically conductive as described above, the plasma arc is generated for some reason. Is disturbed, under normal conditions, an electric circuit was formed between the electrode and the base material,
In addition, 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 inappropriate use conditions (current, voltage, type of plasma gas, composition and flow rate, arc interval, etc.) of the torch. This often occurs when the design shape (especially the diameter of the nozzle hole and the length of the nozzle hole) does not match well. Indeed Japanese basis of FIG. 3 (plasma cutting the relationship between the current and the nozzle diameter on the stability of the arc in a specific condition
Ed. Welding Society , December 1, 1983 , published by Sanho Publishing Co., Ltd. ). The arc stability region is relatively wide and it is not difficult to select it.

However, a double arc may occur even if the conditions of use of the torch and the design inside the nozzle are appropriate. For example, there is a case where a metal that generates a large amount of splash is melt-heated. Examples of the metal material that frequently generates splash include sponge-like titanium and zirconium.

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

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

Due to the double arc, a sound bead cannot be obtained in the case of welding or the like. In addition, the occurrence of the double arc may cause the torch to be seriously damaged (for example, the nozzle is melted) within a short period of time and become unusable. For this reason, the work must be stopped and the damaged part must be replaced, and the work efficiency has to be reduced.

As a countermeasure for preventing the double arc, a technique of attaching an insulating ring made of ceramics or the like to the tip of the nozzle has been proposed (Japanese Utility Model Application Laid-Open No. 60-15 / 1985).
No. 88). In addition, research using a new material for the material of the nozzle is also proceeding (Japanese Patent Application Laid-Open No. 48-30647,
JP-A-3-25900).

[0017]

However, since the nozzle constitutes one of the electrodes irrespective of the type of the torch, i.e., the transfer type or the non-transition type, as described above, the nozzle must be electrically conductive. It cannot be made of non-conductive material (insulating material) such as. 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 also required between the nozzles, so that the torch becomes very complicated and maintenance becomes complicated.

Ceramics are both insulators and heat insulators. 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 strong heat from the plasma arc, and the large output of the torch However, there were many problems with the use of the ink for long periods of time. For these reasons, even if a ceramic nozzle is manufactured, the problem of unstable arc due to splash adhesion is still unsolved, and the torch is expensive due to its complicated structure, and maintenance is complicated. The problem that running costs cannot be reduced remains.

Similarly, introduction of a new material is expensive, and there remains a problem in reliability and the like.

An object of the present invention is to reduce the occurrence of double arc due to splash adhesion even when water-cooled copper, which is inexpensive and proven in practice, is employed, and to provide a simple and economical structure that can stabilize the arc for a long time. An object of the present invention is to provide an excellent and long-life nozzle for a plasma torch.

[0021]

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. The tip has a tip angle of less than 180 ° that gradually projects toward the tip from the outer periphery toward the inner periphery, and in most cases, the tip shape shown in FIG.

In such a nozzle 10, the splash 50 attached to the tip surface is melted by the intense heat of the main plasma arc 30 and concentrates on the inner peripheral side. In such a state, the main plasma arc is more likely to be disturbed, and a double arc frequently occurs. This significantly reduces the life of the nozzle. In the case of the flat surface shown in FIG. 4B, this tendency is slightly alleviated, but the occurrence of double arc due to the concentration of the splash 50 is still large.

The nozzle for a plasma torch of the present invention has been developed with a focus on the fact that the flat surface of the nozzle tip is less sharp than the pointed shape, and the concentration of splash is reduced. as shown in C), the contrary to the conventional
Have a tip surface, gradually protruding tip angle of 180 ° than the concave tapered surface toward the distal end toward the inner periphery to the outer periphery
And the entire outer part protrudes toward the tip from the inner part.
It is a shape .

FIG. 5 illustrates the shape of the tip surface of the nozzle for a plasma torch of the present invention. As shown in the figure,
A flat surface or the like may be present on the distal end surface within a range that does not cause a major functional failure. Further, the tapered surface may be curved. The height of this tapered surface changes continuously.
Not only smooth slopes, but also floors where the height varies in multiple steps
It also includes a step-like slope. Because the height is multi-step
Due to the stepwise slope that changes gradually,
Splash attached to the end face can be diffused to the outer peripheral side.
Because it can be done.

By adopting such a shape of the front end surface, the splash 50 attached to the front end surface of the nozzle 10 is diffused to the outer peripheral side, and the splash 50 is eliminated 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 which is excellent in heat conductivity and electric conductivity and is forcibly cooled from the inside, generation of a double arc due to the adhesion of the splash 50 can be suppressed.

[0026]

When a metal material or the like which generates a lot of splash is melted and heated for a long time, the splash adheres to the tip of the torch (nozzle tip) with the passage of time. The splash adhering to the nozzle tip surface is re-melted by heat from the main plasma arc, and partially becomes liquid.

However, the nozzle tip surface moves from the inner peripheral portion to the outer peripheral portion.
Concave tapered surface that gradually protrudes toward the tip as it goes
With the outer periphery projecting to the distal end side from the inner periphery as a whole
Shape, the synergistic effect of the flow of the splash due to its own weight and that the bell-shaped outer flame created when a stable main plasma arc is formed partially follows the concave nozzle tip surface As a result, the liquid splash moves to the outer peripheral side. Therefore, there is almost no splash for a long time around the nozzle hole, and the arc is extremely stabilized.

Splash gradually accumulates and grows on the outer peripheral portion of the tip surface with the passage of time. However, since it grows at a position sufficiently distant from the position of the main plasma arc, a double arc is generated from the grown splash. There is no effect on the main plasma arc ejected from the nozzle hole.

The splash deposited on the outer peripheral portion of the tip surface is as follows:
As it grows, it droops greatly outside the bell-shaped exoflame, but its tip falls off due to the plasma arc or radiant heat from the molten pool, and the growth of the splash is interrupted here. When this sediment splash falls off,
As described above, since it occurs at a position sufficiently distant from the main plasma arc, there is no fear of double arc generation.

As described above, the splash formed on the outer peripheral portion of the tip surface repeats deposition-growth-fall, but is a phenomenon at a position sufficiently distant from the nozzle hole, and there is almost no splash around the nozzle hole. As the main plasma arc continues to fly, the arc is extremely stable for a long time.

Further, it is not necessary to use an insulating material such as a ceramic for the nozzle, and an integral structure of water-cooled copper, that is, a metal which is forcibly cooled from the inside can be adopted. For this reason, even if it receives strong heat from the main plasma arc, its thermal conductivity is good,
Sufficient cooling is performed, and it is possible to increase the output of the torch and use it for a long time. Furthermore, the structure is simple because of integration,
The nozzle is not expensive, including the material cost, and maintenance is easy.

The concave taper surface formed on the nozzle tip surface
The tip angle is desirably 250 ° or less, and is 190 ° or more and 200
゜ The following are particularly desirable.

When the tip angle approaches 180 °, the effect of spreading the splash attached to the tip face cannot be sufficiently obtained. On the other hand, if the angle is far from 180 °, the bell-shaped outer flame of the main plasma arc becomes too close to the concave tip surface of the nozzle, and the nozzle is easily damaged by receiving strong heat. Since the distance from the nozzle tip to the base metal becomes shorter with respect to the arc length, the frequency of occurrence of the double arc increases due to the attachment of splash and the like.

As another condition, the outer diameter of the nozzle is relatively important. That is, even when the outer diameter of the nozzle is too small, even if the tip angle is more than 180 °, even if the outer diameter of the nozzle is too small, the deposition-growth of the splash only within the small range of the outer diameter of the nozzle
Since the falling off is not repeated and the phenomenon occurs in the vicinity of the main plasma arc, it is easy to generate a double arc. On the other hand, if the outer diameter of the nozzle is too large, not only will most of the generated splash be received by this nozzle, but also the nozzle will become large and the manufacturing cost will increase, which is not preferable. The optimum nozzle outer diameter is approximately equal to the diameter of 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 in comparison with comparative examples.

In welding titanium sponge (compression molded product) using a plasma torch, a copper integrated nozzle that is forcibly cooled from the inside is used, and the tip angle of the tip face of the nozzle is changed variously, and the tip angle is changed to the nozzle angle. The effect on life was investigated. Here, the life of the nozzle is the working time up to the point when the nozzle is significantly melted and the cooling water inside leaks out, or the arc becomes unstable due to the nozzle melt and a normal weld bead cannot be obtained. is there.

All conditions were the same except for the tip angle of the tip face of the nozzle. Table 1 shows the common conditions and Table 2 shows the survey results.

[0038]

[Table 1]

[0039]

[Table 2]

The present invention, in which the tip surface has a concave tapered surface having a tip angle θ exceeding 180 °, has a significantly longer life than the conventional example. For example, when the tip angle θ is 195 °, The life was approximately six times as long as θ was 90 °, and approximately twice as long as the tip angle θ was 180 °.

[0041]

As described above, in the nozzle for a plasma torch of the present invention, the front end surface is directed from the inner peripheral portion to the outer peripheral portion.
As it has a concave tapered surface that gradually protrudes toward the distal end,
As a whole, the outer periphery protrudes toward the tip from the inner periphery
Because of this, the splash attached to the tip surface is diffused to the outer peripheral side, and the area around the nozzle hole is always kept free of splash, preventing the occurrence of double arc due to splash attachment, and extremely stable arc for a long time Can be generated. For this reason, consumption and melting damage of the nozzle are remarkably reduced, and the life of the nozzle is greatly extended. In addition, 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, so that the output of the torch can be increased and long-term use is possible. Further, the structure of the nozzle is simple, the cost of the torch is suppressed, and complicated maintenance is avoided. For these reasons, a significant reduction in total running cost is achieved.

[Brief description of the 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 the influence of a nozzle hole diameter and an 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 a conventional nozzle.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Nozzle 11 Nozzle hole 20 Electrode 30 Main plasma arc 40 Base material 50 Splash

Claims (2)

(57) [Claims] 1. A plasma gas in a plasma torch.
Provided with a gap on the outer peripheral side of the electrode to eject
A cylindrical nozzle having a nozzle tip surface having a nozzle hole opening at the center portion has a concave tapered surface that gradually projects toward the tip end from the inner peripheral portion toward the outer peripheral portion, and the outer peripheral portion as a whole has an inner peripheral portion. A nozzle for a plasma torch, characterized in that it has a shape protruding from a peripheral portion to a tip side. 2. The nozzle for a plasma torch according to claim 1, wherein the nozzle is excellent in heat conductivity and electric conductivity and has an integral structure of a metal which is forcibly cooled from the inside.