JPH08132244A - Torch and method for plasma arc cutting - Google Patents

Abstract

PURPOSE: To provide a plasma arc cutting torch capable of obtaining the section of excellent quality with small bevel angle. CONSTITUTION: A plasma arc approaching part 803 of inverse conical shape having the conical angle θ smaller than the conical angle α of a gas flow necking part 802 is provided between the gas flow necking part 802 of inverse conical shape which is installed on a hollow tip 8 to concentrically surround a plasma electrode 1 through a gas flow passage and a plasma flow nozzle 801. The conical angle θ of the plasma arc approaching part 803 is set to 20-85 deg. and the ratio L2/L1 of the dimension L2 in the axial direction of the plasma arc approaching part 803 to the dimension L1 in the axial direction of the plasma flow nozzle 801 is set to 0.2-2.5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma arc cutting torch used for cutting a workpiece with a plasma arc, and a plasma arc cutting method using the torch.

[0002]

2. Description of the Related Art Generally, a plasma arc cutting torch has a structure shown in FIG. In FIG. 14, reference numeral 1 is a plasma electrode cooled by a fluid. The electrode 1 is a hollow cylindrical electrode substrate 2 and a recess provided in an end wall that closes the tip of the electrode substrate 2. It is constituted by the insert body 3 mounted inside. The electrode base material 2 is made of copper or a copper alloy, and the insert 3 is made of a high melting point material such as hafnium or zirconium.

Reference numeral 4 denotes a tubular electrode supporting member made of a conductive material and disposed at the center of the torch. The electrode 1 is supported at the tip of the electrode supporting member 4. 5 is an electrode support member 4
An insulating sleeve 6 is provided so as to cover the insulating sleeve 5 from the outside, and a chip supporting member 6 made of a conductive material is provided so as to concentrically surround the insulating sleeve 5 from the outside.
The torch body 7 is constituted by the insulating sleeve 5 and the tip support member 6. An annular gas introduction passage g1 is formed between the insulating sleeve 5 and the chip support member 6, and the gas introduction passage g1 is connected to a gas supply source (not shown).

Reference numeral 8 denotes a hollow tip supported by the tip of the tip support member 6, and this tip has a cylindrical portion 8A that concentrically surrounds the plasma electrode 1 and a tapered first tip toward the tip side of the cylindrical portion. It comprises a convex portion 8B and a similarly tapered tip portion 8C formed on the tip side of the first convex portion 8B.
In the illustrated example, both the first convex portion 8B and the tip portion 8C are formed in an inverted conical shape, and an annular gas passage g2 communicating with the gas introduction passage g1 is formed between the tip 8 and the electrode 1. ing. A plasma flow ejection hole 801 having a uniform inner diameter along the axial direction is formed in the axial center of the tip portion 8C of the tip 8, and the tip end portion 8C has a plasma flow ejection hole inside the first convex portion 8B. An inverse conical surface-shaped gas flow contraction portion 802 is formed continuously at the rear end of the hole 801.

Reference numeral 9 denotes a cup attached to the tip of the tip supporting member 6. The cup 9 has a cylindrical portion 9A that concentrically surrounds the tip portion of the torch body 7 and the cylindrical portion 8A of the tip 8 and the tip 8 of the tip 8. A tapered (in the example shown, an inverted conical shape) second convex portion 9B that concentrically surrounds the first convex portion 8B;
An annular cooling water recirculation passage w4 is formed between the tip 8 and the cup 9 and is composed of an end wall 9C formed on the tip side of the second convex portion 9B. A tapered hole is formed in the center of the cup end wall 9C, and the tip end portion 8C of the tip is fitted into the tapered hole of the cup end wall 9C and a part thereof is led out to the outside.

The axial center portion of the torch body 7 (electrode support member 4
(Inside), a hole 4a for circulating cooling water is provided which communicates with the electrode base material 2, and the electrode base material 2 is passed through the hole 4a.
The cooling water guide pipe 10 is inserted inside the
Cooling water passages w1 and w2 are formed inside and outside, respectively. The cooling water passage w2 is communicated with a cooling water return passage w4 formed between the tip 8 and the cup 9 through a cooling water guide passage w3 provided in the tip support member 6, and the cooling water return passage w4 is connected to the tip. It is connected to a cooling water discharge passage w5 provided in the support member 6.

Reference numeral 11 is a cooling water supply hose connected to a cooling water supply port (not shown) of the torch, and 12 is a cooling water discharge hose connected to the cooling water discharge port of the torch. The supplied cooling water flows into the cooling water passage w1 in the cooling water guide pipe 10 as shown by an arrow A1 in the figure, and then flows into the cooling water passage w2 from the lower end of the guide pipe to cool the plasma electrode 1. After that, it flows into the cooling water guide passage w3 as indicated by arrow A2. The cooling water that has flowed into the cooling water guide passage w3 flows into the cooling water return passage w4 to cool the chip 8 and then into the cooling water discharge passage w5, and further flows into the cooling water discharge hose 12 as indicated by arrow A3. And is discharged from the hose 12 to the outside.

When cutting a workpiece using the above plasma arc cutting torch, electric power is supplied between the plasma electrode 1 and the workpiece, and a plasma arc forming fluid such as air or oxygen is supplied. The (gas) G is supplied to the gas passage g2 between the tip 8 and the electrode 1 through the gas introduction passage g1 in the torch body 7. Then, the plasma arc forming fluid G flowing into the gas flow path g2 is supplied to the gas flow contracting portion 802.
A plasma jet is generated by causing the plasma arc generated by the insert 3 of the plasma electrode 1 to flow into the plasma flow ejection hole 801 while being squeezed by the plasma flow ejection hole 801 to cut a workpiece. I do.

[0009]

In order to obtain a high-quality cut surface with a small bevel angle (the inclination angle of the cut surface) by using the above-described plasma arc cutting torch, the plasma flow ejection hole of the tip 8 is required. It is effective to reduce the diameter of 801 to increase the current density of the plasma arc at the plasma flow ejection holes 801 and to narrow the plasma arc. However, when air or oxygen is used as the plasma arc forming fluid, when the so-called cutting current value used for plasma cutting is increased to increase the current density of the plasma arc, the end portion of the gas flow contracting portion 802 is A part of the rear end portion of the plasma flow ejection hole 801 is broken in a short time, and as shown in FIG. 15, the plasma flow ejection hole 801 and the gas flow contraction portion 80.
A burnout part 81 is formed in the vicinity of the boundary part with 2. When such a burnt-out portion 81 is formed, the plasma arc is disturbed in the burn-out portion 81, so that the bevel angle of the cut surface is inevitably increased.

When cutting a work piece by plasma arc cutting, it is desired to obtain a high-quality cut surface with a bevel angle of 3 degrees or less, and a comparison is made when the work piece is thin. High quality cut surface is obtained even with a relatively small cutting current value. However, when the thickness of the workpiece is large, it is necessary to increase the cutting current value, and it is necessary to increase the cutting current value as the thickness of the workpiece increases.
In the conventional torch for plasma arc cutting, for example, when the cutting current value is set to 120 [A] or more, the burned portion 81 is formed in a short time, so that it is difficult to obtain a high quality cut surface.

An object of the present invention is to provide a plasma arc cutting method capable of obtaining a high quality cut surface having a small bevel angle, and a plasma arc cutting torch used for carrying out the cutting method.

[0012]

A plasma arc cutting torch according to the present invention is a plasma electrode 1 in which a high melting point insert 3 is mounted in a recess provided at the tip of an electrode substrate 2.
And a hollow chip 8 formed so as to concentrically surround the plasma electrode 1 via a gas flow path,
The tip 8 has a tip portion 8 having a plasma flow ejection hole 801.
C and a tapered first convex portion 8B toward the tip,
A gas flow contracting portion 802 having an inverted conical surface is provided inside the first convex portion.
Are formed.

In the present specification, the "tip portion" of each portion
Is the end located on the tip side of the torch from which the plasma jet is ejected.

In this specification, the term "cone" or "conical surface" does not necessarily mean the shape of the entire cone including the bottom surface to the apex, but forms a part of the cone. It is also used as a word to describe a tapered shape. Therefore, the so-called "conical shape" obtained by cutting the head of the cone is also simply referred to as "conical".

Further, the term "inverted cone" or "inverted cone surface" means "a cone whose diameter is gradually reduced toward the tip side of the torch (the apex is the tip side of the torch). (Pointed cone).

In the present invention, the inverse conical surface-shaped plasma having a cone angle θ smaller than the cone angle α of the gas flow contraction portion between the plasma flow ejection hole 801 of the chip 8 and the gas flow contraction portion 802. An arc approach section 803 is provided. The cone angle θ of the plasma arc approaching portion 803 is set to 20 degrees or more and 85 degrees or less. Further, the ratio L2 / L1 of the axial dimension L2 of the plasma arc run-up portion 803 and the axial dimension L1 of the plasma flow ejection hole 801 is set to 0.2 or more and 2.5 or less.

The plasma arc run-up portion 803 may be composed of a single inverted conical surface, or may be composed of a plurality of inverted conical surfaces having different cone angles. When the plasma arc run-up portion is formed by a plurality of reverse conical surfaces, the plurality of reverse conical surfaces are provided so that the cone angle becomes smaller toward the plasma flow ejection hole.

In the present invention, a hollow cup 9 having a second convex portion 9B concentrically surrounding the vicinity of the first convex portion 8B of the chip 8 on the tip side, and a second convex portion of the cup 9 are also provided. Further, a shield cup 15 having a tapered portion 15B concentrically surrounding 9B on the tip side is further provided, and the outer surface of the second convex portion 9B of the cup 9 is formed into an inverted conical surface shape.
Second convex portion 9B and the tapered portion 15 of the shield cup 15
A shield gas passage s3 may be formed between the shield gas passage B and B, and a shield gas outlet sa may be formed at the tip of the shield gas passage so as to concentrically surround the axis of the plasma flow ejection hole.

When the cup 9 and the shield cup 15 are provided as described above, the shield cup has a tapered portion 15
It is preferable that B is formed so as to contact the outer circumference of the second convex portion 9B of the cup. In this case, the second protrusion 9 of the cup
A plurality of grooves 901 extending along the generatrix direction of the conical surface of B are provided radially, and the plurality of grooves form the shield gas flow passage s.
Form 3. Further, in the shield cup 15, the taper angle (cone angle) γ of the taper portion 15B is the same as the cone angle β of the outer surface of the second convex portion of the cup 9, or the taper angle γ is slightly larger than the cone angle β. To form.

In the plasma arc cutting method of the present invention, an inverse conical surface-shaped plasma arc run-up having a smaller cone angle than the gas flow contraction portion is provided between the plasma flow ejection hole of the tip and the gas flow contraction portion. And the cone angle θ of the plasma arc run-up portion is set to 20 degrees or more and 85 degrees or less, and the ratio of the axial dimension L2 of the plasma arc run-up portion to the axial dimension L1 of the plasma flow ejection hole L2 / L1 to 0.
Using the above-described plasma arc cutting torch set to 2 or more and 2.5 or less, electric power is supplied between the plasma electrode of the torch and the workpiece, and air or oxygen is supplied to the gas flow passage in the torch. Plasma arc cutting is performed by supplying as a plasma arc forming fluid.

In the plasma arc cutting method of the present invention, the hollow cup having the second convex portion concentrically surrounding the first convex portion of the chip and the second convex portion of the cup are concentric with each other. An electric power is supplied between the plasma electrode of the torch and the workpiece using a torch for cutting a plasma arc further provided with a shield cup having a tapered portion which surrounds the torch, and air is supplied to a gas flow path in the torch. Alternatively, oxygen is supplied as a plasma arc forming fluid, and oxygen is supplied as a shield gas fluid to the shield gas outflow passage, and the flow rate of the shield gas fluid is 10 liters / min-6.
Plasma arc cutting is performed in the range of 0 liter / minute.

[0022]

As described above, when the reverse arc surface-shaped plasma arc run-up portion having a smaller cone angle than the gas flow contraction portion is formed between the plasma flow ejection hole of the chip and the gas flow contraction portion,
The plasma arc forming fluid that has flowed inside the tip is
First, after the gas flow contraction part that has a large reduction rate of the radius in the axial direction is confined in the radial direction while it is largely throttled in the process of flowing in the axial direction, the plasma arc run-up part, which has a small reduction rate of the radius in the axial direction, makes it easy. It is accelerated while being squeezed, and flows out from the plasma flow ejection hole as a narrow, high-speed gas flow.

Further, in the conventional torch, when the maximum cutting current value is set to 120 [A] or more, when air or oxygen is used as the plasma arc forming fluid, the boundary between the plasma flow ejection hole and the gas flow contraction portion is set. There was a problem that the area near the burnout part was burnt out in a short time.
If the ratio L2 / L1 between the axial dimension L2 of the plasma arc run-up portion and the axial dimension L1 of the plasma flow injection hole is set to 0.2 or more and 2.5 or less while being set to 0 degrees or more and 85 degrees or less, the maximum It was confirmed by an experiment that even if the cutting current value is set to 120 [A] or more, the burned portion does not occur for a long time.

Therefore, according to the plasma arc cutting torch of the present invention, it is possible to squeeze the plasma arc forming fluid in the axial direction at a high speed by narrowing it down and to set the maximum cutting current value higher than the conventional value. Therefore, it is possible to generate a plasma arc that has a higher current density than before and is narrowed down, and it is possible to obtain a high-quality cut surface with a small bevel angle.

[0025]

1 and 2 show an embodiment of the present invention. FIG. 1 is a longitudinal sectional view showing a main part of a torch of the embodiment.
FIG. 2 is an enlarged vertical sectional view of the vicinity of the tip portion of the torch of FIG. The basic structure of the plasma arc cutting torch of this embodiment is similar to that of the conventional one shown in FIGS. 14 and 15, and is equivalent to each part of the torch shown in FIGS. 14 and 15 in FIGS. 1 and 2. The same reference numerals are respectively attached to the portions.

In FIGS. 1 and 2, reference numeral 1 denotes a plasma which is composed of an electrode base material 2 made of copper or copper alloy and formed in a hollow cylindrical shape, and an insert body 3 made of a high melting point material such as hafnium or zirconium. At the electrode, the insert 3 is mounted in a recess provided in an end wall that closes the tip of the electrode substrate 2. The plasma electrode 1 is screwed to and supported by the tip of a tubular electrode supporting member 4 made of a conductive material and arranged in the center of the torch. An insulating sleeve 5 is provided so as to cover the electrode supporting member 4 from the outside, and a tubular tip supporting member 6 made of a conductive material is provided so as to concentrically surround the insulating sleeve 5 from the outside. A torch body 7 is composed of the electrode supporting member 4, the insulating sleeve 5 and the tip supporting member 6, and an annular gas introducing passage g1 connected between a gas supply source (not shown) is provided between the insulating sleeve 5 and the tip supporting member 6. Are formed.

A hollow chip 8 is attached to the tip of the chip support member 6 by screwing. This chip 8
Is a cylindrical portion 8A that concentrically surrounds the plasma electrode 1, and
Tapered first convex portion 8B formed on the tip side of the cylindrical portion
And a tip portion 8C formed on the tip side of the first convex portion 8B.
It consists of In the illustrated example, the first convex portion 8B and the tip portion 8C are both formed in an inverted conical shape, and an annular gas flow channel g communicating with the gas flow channel g1 is provided between the tip 8 and the electrode 1.
2 is formed. A plasma flow ejection hole 801 having a uniform inner diameter d along the axial direction is bored in the axial center portion of the tip portion 8C of the tip 8, and inside the first convex portion 8B,
With a space between it and the plasma flow ejection hole 801,
An inverse conical surface-shaped gas flow contraction portion 802 is formed whose diameter gradually decreases toward the plasma flow ejection hole 801 side.

In the present invention, the plasma flow ejection hole 80
1 and the gas flow contracting section 802, the gas flow contracting section 802
An inverse conical surface-shaped plasma arc runner 803 having a cone angle θ (see FIG. 2) smaller than the cone angle α of
The plasma arc forming fluid G that has flowed into the gas flow path g2 from a gas supply source (not shown) through the gas introduction passage g1 flows through the gas flow contraction portion 802 and then flows into the plasma flow ejection hole 801 through the plasma arc run-up portion 803. It looks like this. Here, as shown in FIG.
The dimension of the axial direction of 1 is L1, and the plasma arc run-up part 8
Let L2 be the axial dimension of 03.

A cup 9 is attached to the tip of the tip support member 6. The cup 9 has a cylindrical portion 9A that concentrically surrounds the tip portion of the torch body 7 and the cylindrical portion 8A of the tip 8 and a tapered portion that concentrically surrounds the first convex portion 8B of the tip 8 (in the example shown in the figure, The second projection 9B (conical shape) and the end wall 9C formed on the tip side of the second projection 9B. A tapered hole into which the tip portion 8C of the chip is fitted is bored in the center of the end wall 9C of the cup, and a part of the tip portion 8C of the chip is led out through the tapered hole. A cooling water return passage w4 is formed between the cup 9 and the tip 8.

Inside the electrode support member 4, there is provided a hole 4a for circulating cooling water which communicates with the inside of the electrode base material 2, and the cooling water guide pipe 10 is inserted into the inside of the electrode base material 2 through the hole. The cooling water passages w1 and w2 are formed inside and outside the guide tube 10, respectively. The cooling water passage w2 is communicated with a cooling water return passage w4 formed between the tip 8 and the cup 9 through a cooling water guide passage w3 provided in the tip support member 6, and the cooling water return passage w4 is connected to the tip. A drain hose 12 is communicated with a cooling water discharge passage w5 provided in the support member 6.

Although not shown, the torch is provided with a cooling water supply port to which a cooling water supply hose 11 is connected and a cooling water discharge port to which a cooling water discharge hose 12 is connected. → Cooling water passage w1 in the cooling water guide pipe 10
→ Cooling water passage w2 outside the guide tube 10 → Cooling water guiding passage w3 → Cooling water return passage w4 → Cooling water discharge passage w5 → Cooling water flows through the passage of the cooling water discharge hose 12 and the plasma electrode 1 and the tip 8 And are cooled.

In the torch structure of this embodiment, the plasma arc run-up portion 803 having a smaller cone angle than the gas flow contraction portion is formed between the gas flow contraction portion 802 of the tip 8 and the plasma flow ejection hole 801. Except for the points, the structure is the same as that of the conventional torch shown in FIG.

The inventor of the present invention conducted various experiments in order to determine the influence of the cone angle of the plasma arc run-up portion of the torch according to the present invention and its axial dimension on the Beher angle of the cut surface. As a result, the plasma arc approach portion 803
Is set to 20 degrees or more and 85 degrees or less, and the ratio L2 / L1 between the axial dimension L2 of the plasma arc advancing portion 803 and the axial dimension L1 of the plasma flow ejection hole 801 is set to 0.
It has been clarified that a high-quality cut surface with a small bevel angle can be obtained by setting it to 2 or more and 2.5 or less.

When the work is cut using the above-mentioned torch, electric power is supplied between the plasma electrode 1 and the work, and the plasma arc forming fluid G such as air or oxygen is torched. It is supplied to the gas flow path g2 between the chip 8 and the electrode 1 through the gas introduction passage g1 in the body 7.
Then, the plasma arc forming fluid G flowing into the gas flow path g2 is accelerated while being squeezed by the gas flow contracting portion 802 and the plasma arc advancing portion 803 to accelerate the plasma flow ejection hole 80.
1, and a plasma arc generated from the insert body 3 of the plasma electrode 1 is ejected from the plasma flow ejection hole 801 to generate a plasma jet to cut the workpiece.

As in the present embodiment, between the plasma flow ejection hole 801 of the tip 8 and the gas flow contraction portion 802, a reverse arc surface-shaped plasma arc run-up having a smaller cone angle than the gas flow contraction portion. When the portion 803 is formed, the plasma arc forming fluid G flowing into the inside of the tip is first constrained by the gas flow contraction portion 802 having a large reduction rate of the radius with respect to the axial direction of the torch, and is radially moved in the process of flowing in the axial direction. After being greatly narrowed down to a high speed, the plasma arc accelerating portion 803 has a small reduction rate of the radius with respect to the axial direction and is accelerated while being reasonably narrowed down to a high-speed gas flow that is narrowed down narrowly from the plasma flow ejection hole 801 and flows in the axial direction. It will be leaked.

Further, in the present invention, the conical angle θ of the plasma arc runaway portion 803 is set to 20 degrees or more and 85 degrees or less, and the axial dimension L2 of the plasma arc runaway portion 803 and the axial dimension of the plasma flow ejection hole are set. By setting the ratio L2 / L1 with L1 to 0.2 or more and 2.5 or less, the maximum cutting current value can be set to 120 [A] or more and it can be used for a long time. A high-quality cut surface having a bevel angle of 3 degrees or less can be obtained by generating a plasma arc that has a high current density and is narrowed down.

FIG. 6 is a diagram showing the relationship between the cone angle θ [degree] of the plasma arc run-up portion 803 and the actual measurement value of the maximum cutting current value [A] that is allowable for each cone angle θ. is there.
In this experimental example, the cone angle α of the gas flow contracting portion 802 is set to 10
The dimension L2 in the axial direction of the plasma arc run-up portion 803 and the dimension L1 in the axial direction of the plasma flow ejection hole were made equal to each other, and L2 / L1 = 1 (constant). Air was used as the fluid for plasma arc formation. In this example, the case of θ = 0 ° and the case of θ = 100 ° show the case (the same as the conventional example) in which the plasma arc accelerating portion 803 is not provided.

As shown in FIG. 6, as the cone angle θ of the plasma arc run-up portion 803 is increased from 0, the maximum allowable cutting current value rises and reaches a peak near θ = 60 degrees. . When the cone angle θ is further increased beyond 60 degrees, the maximum allowable cutting current value gradually decreases. In the example of FIG. 6, the maximum allowable cutting current value is 105 [A] when θ = 0 ° and θ = 100 ° (when the plasma arc approaching portion 803 is not provided), and θ = 20 ° and θ = 85
The maximum allowable cutting current value in the case of ° was 120 [A]. Therefore, from this experiment, the plasma arc approach portion 80
By setting the cone angle θ of 3 in the range of 20 ° ≦ θ ≦ 85 °, the maximum allowable cutting current value can be set to 120 A or more, and the cone angle θ of the plasma arc run-up portion 803 is set in the same range. The conventional torch (θ = 0 °
The maximum allowable cutting current value is at least 14% compared to
It became clear that it could be raised.

In particular, the cone angle θ of the plasma arc run-up portion
Is set in the range of 40 ° ≦ θ ≦ 70 °, the maximum allowable current value can be set to 150 A or more, and the maximum allowable cutting current value can be increased by about 43% or more of the conventional value.

FIG. 7 shows the relationship between the cone angle θ of the plasma arc run-up portion 803 and the bevel angle of the cut surface of the workpiece when air is used as the plasma arc forming fluid and the cutting current value is 120 [A]. From the figure, the bevel angle becomes approximately 3 ° when θ = 20 ° and θ = 85 °, and the cone angle θ of the plasma arc run-up portion is 20 ° ≦ 20 ° ≦ It can be seen that the bevel angle of the cut surface becomes 3 ° or less by setting the range of θ ≦ 85 °.
Further, it is understood that when the cone angle θ is set in the range of 40 ° ≦ θ ≦ 70 °, the bevel angle of the cut surface becomes approximately 2 ° or less.

FIG. 8 shows the axial dimension L2 of the plasma arc run-up portion 803 and the axial dimension L1 of the plasma flow ejection hole.
The ratio of L2 / L1 to the bevel angle of the cut surface is measured, and in this example, the gas flow contracting section 80
The cone angle α of 2 was 100 ° (constant), and the cone angle θ of the plasma arc run-up portion 803 was 50 ° (constant). FIG.
From L2 / L1 = 0.2 and L2 / L1 = 2.
In the case of 5, the bevel angle of the cut surface becomes almost 3 °, and L2 /
It can be seen that by setting L1 in the range of 0.2≤L2 / L1≤2.5, it is possible to obtain a high quality cut surface with a bevel angle of 3 ° or less. Especially L2 / L1 is 0.5
By setting the range of ≤L2 / L1 ≤2.0, a very high quality cut surface with a bevel angle of the cut surface of approximately 2 ° or less can be obtained.

The results of the above-mentioned experiments are summarized as shown in Table 1 below. “Good” in the cutting results in the table means that the range of variation in the bevel angle of the cut surface was 3 ° or less. Meaning, “excellent” means that the range of variation of the bevel angle is smaller than that in the case of “good”. Also "best"
Means that a very high quality cut surface with a bevel angle variation range of 2 ° or less was obtained.

[0043]

[Table 1] In the example shown in FIGS. 1 and 2, the plasma arc run-up portion 8
03 is formed by a single reverse conical surface, but the conical angles are different from each other, and the plasma arc run-up portion is formed by a plurality of reverse conical surfaces formed so that the conical angle becomes smaller toward the plasma flow ejection hole 801. May be configured. For example, as shown in FIG. 3, a reverse conical surface 803a having a rear end continuous with the tip of the gas flow contracting portion 802, and a rear end contiguous with the tip of the reverse conical surface 803a having a plasma flow ejection hole 801 at the front end. The plasma arc run-apart 803 may be formed by the inverted conical surface 803b that is continuous. In this case, the conical angle α of the gas flow contracting portion 802 and the reverse conical surface 803
The relationship of α>θ1> θ2 is established between the cone angle θ1 of a and the cone angle θ2 of the inverted conical surface 803b, and θ
Both 1 and θ2 are set in the range of 20 ° to 85 °.

As described above, when the plasma arc run-up portion is formed by a plurality of inverted conical surfaces arranged so that the cone angle becomes gradually smaller toward the plasma flow ejection hole side, the plasma arc run-up portion flows into the plasma arc run-up portion. Since the generated gas is gradually narrowed and accelerated, the gas flow in the gas flow path from the gas flow constriction part to the plasma flow ejection part to the plasma flow ejection hole is made smooth and the speed is increased. be able to. Therefore, the plasma jet ejected from the plasma flow ejection hole 801 becomes extremely strong with a narrow ejection force and strong ejection force in the axial direction, and a high-quality cut surface with a small bevel angle can be obtained.

In the present invention, it is necessary that the plasma arc run-up portion is not provided with a portion for directing gas inward in the radial direction in the middle of the run-up portion,
When the plasma arc approaching portion is composed of a plurality of reverse conical surfaces, the cone angle of the reverse conical surface located on the downstream side of the runway should not be larger than the cone angle of the reverse conical surface located on the upstream side. It is an essential requirement. For example, in FIG.
As shown in FIG. 5, it is necessary to avoid providing the reverse conical surface 803b ′ having a cone angle θ2 ′ larger than the cone angle θ1 of the upstream reverse conical surface 803a on the downstream side of the plasma arc run-up portion 803. That is, as shown in FIG. 4, when the plasma arc run-up portion is configured, the inverted conical surface 803b 'is formed.
As a result, the gas is directed inward in the radial direction, and this causes a gas flow in a direction intersecting with the gas flow flowing in the axial direction, so that the gas flow is disturbed and the binding force of the plasma arc is reduced. Therefore, it becomes impossible to obtain a plasma jet that is narrowed down, and good results cannot be obtained.

Also, as shown in FIG. 5, when a curved portion 803c that is curved inward in the radial direction is formed on the downstream side of the plasma arc run-up portion 803, the curved portion is also directed inward in the radial direction. Since the gas flow is generated, the gas flow is disturbed and the good result is not obtained.

In the above embodiment, air or oxygen was used as the plasma arc forming fluid G, but the use of air or oxygen is the most severe operating condition of the torch, and air or oxygen is used as the plasma arc forming fluid. When oxygen is used, the torch is most likely to be damaged. Therefore, if the torch is not damaged when air or oxygen is used as the plasma arc forming fluid, no problem occurs when another fluid such as an inert gas is used as the plasma arc forming fluid. . Therefore, the present invention is not limited to the use of air or oxygen as the plasma arc forming fluid.

FIG. 9 shows another embodiment of the present invention. In this embodiment, the outer tube 13 is attached so as to concentrically surround the chip support member 6, and the electrode support member 4,
The insulating sleeve 5, the tip support member 6 and the outer tube 13 constitute a torch body 7. An annular shield gas flow path s1 is formed between the outer tube 13 and the chip support member 6, and the shield gas flow path s1 is connected to a shield gas supply means (not shown) such as a gas cylinder or a pump.

At the tip of the outer tube 13 of the torch body 6, a cylindrical portion 15A that concentrically surrounds the tip portion of the torch body 7 and the cylindrical portion 9A of the cup 9 and a second convex portion of the cup 9 are concentrically provided. A shield cup 15 including a taper portion 15B surrounding it is attached. A shield gas flow passage s2 communicating with the shield gas flow passage s1 is formed between the cylindrical portion 15A of the shield cup and the tip portion of the torch body 7 and the cylindrical portion 9A of the cup.
The shield gas flow passage s3 communicating with the shield gas flow passage s2 is provided between the tapered portion 15B and the second convex portion 9B of the cup.
Are formed. Tapered part of shield cup 15B
Is provided so that its tip ends at a position before the end wall 9C of the cup 9, and the inner circumference of the tip of the tapered portion 15B and the outer circumference of the second convex portion 9B of the cup. A shield gas ejection port sa concentrically surrounding the central axis of the plasma flow ejection hole sa is formed therebetween. The shield gas ejection port sa is arranged concentrically with the plasma flow ejection port 801, and the shield gas supplied through the shield gas flow passages s1, s2, s3 is supplied from the shield gas ejection port sa.
It is designed to eject toward the plasma jet.

Although the method of attaching the shield cup is arbitrary, in the illustrated example, a screw 13a is provided on the outer periphery of the tip portion of the outer tube 13 of the torch body 7, and the screw 13a is provided inside the cylindrical portion 15A of the shield cup 15. Screw 1 on the circumference
5A1 is screwed and shield cup 15 is torch body 7.
Attached to. The other points are similar to those of the torch shown in FIG.
03 is composed of a single inverted conical surface having a cone angle θ smaller than the cone angle α of the gas flow contracting portion 802.

When cutting is performed using the torch shown in FIG. 9, power is supplied between the plasma electrode 1 and a workpiece (not shown), and the plasma arc is supplied to the gas flow passage g2 through the gas introduction passage g1. The forming fluid G is supplied and the shield gas S is supplied to the shield gas passages s1 and s2. As a result, a plasma jet is generated from the plasma flow ejection hole 801, and the shield gas is ejected from the shield gas ejection port sa to cut the workpiece.

FIG. 10 shows the results of an experiment in which the bevel angle of the cut surface is measured by changing the flow rate of the shield gas when the workpiece is cut using the torch shown in FIG. Is. In this experiment, the cone angle α of the gas flow contracting portion 802 was 100 °, the cone angle θ of the plasma arc runner portion 803 was 50 °, and oxygen was used as the shield gas S. Further, the cutting current value was set to 120 [A], and the experiment was performed using air as the plasma arc forming fluid G and using nitrogen. In FIG. 10, the solid line curve shows the case where air is used as the plasma arc forming fluid, and the broken line curve shows the case where nitrogen is used as the plasma arc forming fluid.

From FIG. 10, when the shield gas flow rate is set in the range of 10 liters / minute to 60 liters / minute,
It was revealed that the bevel angle of the cut surface can be reduced by 0.5 ° or more as compared with the case where no shielding gas is flown, and the effect of improving the quality of the cut surface is high.

In the torch shown in FIG. 9, when the shield cup 15 is attached, when the central axis of the shield cup 15 is inclined with respect to the central axis of the cup 9 (the central axis of the torch) as shown in FIG. The cross-sectional areas of the gas flow paths s2 and s3 become non-uniform, and the shield gas ejection port s
Since the opening area of a becomes non-uniform and the shield gas ejection port sa is inclined, the flow of the shield gas ejected from the shield gas ejection port sa is biased and the shielding effect is reduced.

Even when the shield cup 15 and the cup 9 are mounted so that the center axis of the shield cup 15 and the center axis of the cup 9 coincide with each other, the cone angle of the outer surface of the second convex portion 9B of the cup 9 and the taper portion 15B of the shield cup 15 are the same. Since the taper angle of 1 has a variation in processing accuracy, the cross-sectional area of the shield gas passage s3 varies, and as a result, the flow velocity of the shield gas ejected from the shield gas ejection port sa may vary.

FIGS. 12 and 13 show an embodiment in which these problems are solved. FIG. 12 shows the structure of the main part, and FIG. 13 shows the cup used in the same embodiment.
In this embodiment, as shown in FIG.
A plurality of grooves 901 extending radially along the generatrix direction of the outer conical surface of the second convex portion are provided on the outer periphery of the convex portion 9B. The shield cup 15 is formed such that its tapered portion 15B abuts on the outer periphery of the second convex portion 9B of the cup 9, and the shield gas flow path s3 is formed by the groove 901 on the outer surface of the second convex portion of the cup 9. ing. Further, the shield cup 15 is formed such that the taper angle γ of the taper portion 15B is the same as the cone angle β of the outer surface of the second convex portion 9B of the cup 9 or the taper angle γ is slightly larger than the cone angle β. Has been done.

With the structure shown in FIG. 12, the shield cup 15 is provided on the outer periphery of the second convex portion 9B of the cup 9 coaxially attached to the torch body 7 with the outer periphery of the tip portion 8C of the tip 8 as a reference. Since the tapered portion 15B is brought into contact with and positioned, the central axis of the shield cup 15 can be always aligned with the central axes of the tip 8 and the cup 9, and the shield gas ejection port sa can be made the plasma flow ejection hole 801.
Can be arranged concentrically with respect to. Therefore,
It is possible to prevent the flow of the shielding gas from being biased and reducing the shielding effect.

Further, as in the embodiment shown in FIG. 12, the taper angle γ of the taper portion 15B of the shield cup 15 is the same as the cone angle β of the outer surface of the second convex portion 9B of the cup 9 or the taper angle γ. Is formed to be slightly larger than the cone angle β, the cup 9 and the shield cup 15 are brought into contact with each other in the vicinity of the shield gas ejection port sa, and the shield gas can be ejected in a desired state.

In the above-described embodiment, the first convex portion 8B of the chip 8 is formed in an inverted conical shape so that both the inner peripheral surface and the outer peripheral surface thereof have an inverted conical surface shape. It is sufficient that the convex portion 8B has a tapered shape toward the tip of the tip and at least the inner peripheral surface thereof is formed into an inverted conical surface shape, and the outer peripheral surface thereof is not necessarily formed into an inverted conical surface shape. You don't have to. For example, the outer peripheral surface of the first convex portion 8B of the chip may have a shape in which the outer diameter gradually decreases toward the tip (stepped shape).

In the above embodiment, the second convex portion 9B of the cup 9 has an inverted conical shape so that both the inner peripheral surface and the outer peripheral surface thereof have an inverse conical surface shape. The inner peripheral surface of the convex portion 9B does not necessarily have to be an inverted conical surface,
The shape may be such that the inner diameter gradually decreases toward the tip (stepped shape).

The preferred embodiments of the present invention have been described above. The main aspects of the invention disclosed in this specification are as follows.

(1) A plasma electrode 1 in which an insert 3 made of a high melting point material is mounted in a recess provided in an end wall that closes the tip of a hollow tubular electrode substrate 2, and the plasma electrode is annular. And a hollow tip 8 formed so as to concentrically surround the gas flow path g2, the tip 8C having a cylindrical portion 8A concentrically surrounding the plasma electrode and a plasma flow ejection hole 801. And a tapered first convex portion 8B between the cylindrical portion 8A and the distal end portion 8C, which is directed toward the distal end portion 8C, and has a reverse conical gas flow contraction flow inside the first convex portion 8B. In the plasma arc cutting torch in which the portion 802 is formed, a cone angle θ smaller than the cone angle α of the gas flow contraction portion is formed between the plasma flow ejection hole 801 of the tip 8 and the gas flow contraction portion 802. Inverse conical plasma arc run-up part with a groove 803 is provided, the cone angle θ of the plasma arc run-up portion 803 is set to 20 degrees or more and 85 degrees or less, and the axial dimension L2 of the plasma arc run-up portion 803 and the axial dimension L of the plasma flow ejection hole 801 are provided.
A plasma arc cutting torch in which the ratio L2 / L1 with 1 is set to 0.2 or more and 2.5 or less.

(2) A plasma electrode 1 in which an insert 3 made of a high melting point material is mounted in a recess provided in an end wall that closes the tip of a hollow tubular electrode substrate 2, and the plasma electrode is formed into an annular shape. A hollow chip 8 formed so as to concentrically surround the gas flow path g2 and a cup 9 formed so as to concentrically surround the chip 8, the chip being concentric with the plasma electrode. 8A surrounding a cylindrical portion, a tip portion 8C having a plasma flow ejection hole 801, and the cylindrical portion 8A.
And a tip portion 8C and a tapered first convex portion 8B directed toward the tip portion 8C, and a gas flow constricting portion 802 having an inverted conical surface shape is formed inside the first convex portion 8B. The cup 9 has a cylindrical portion 9A that concentrically surrounds the cylindrical portion 8A of the tip 8, a second convex portion 9B that concentrically surrounds the first convex portion 8B of the chip 8, and the second convex portion. A plasma arc cutting torch having an end wall 9C for closing the tip of the portion 9B, and a part of the tip 8C of the tip being led out to the outside through a hole provided in the end wall, The cup 9
Is further provided with a tapered portion 15B of the shield cup 15 having a cylindrical portion 15A concentrically surrounding the cylindrical portion 9A and a tapered portion 15B concentrically surrounding the second convex portion 9B of the cup. Second convex portion 9B of the cup
And a shield gas flow passage s3 is formed between them and an annular shield gas jet sa that concentrically surrounds the central axis of the plasma flow jet hole at the tip of the shield gas flow passage,
Between the plasma flow jetting hole 801 and the gas flow contracting portion 802 of the tip 8, the reverse arc surface-shaped plasma arc run-up portion 8 having a cone angle θ smaller than the cone angle α of the gas flow contracting portion.
03 is provided, the cone angle θ of the plasma arc run-up portion 803 is set to 20 degrees or more and 85 degrees or less, and the axial dimension L2 of the plasma arc run-up portion 803 and the axial dimension L1 of the plasma flow ejection hole 801 are set. A torch for plasma arc cutting, wherein the ratio L2 / L1 is set to 0.2 or more and 2.5 or less.

(3) The plasma electrode 1 in which the insert 3 made of a high melting point material is mounted in the recess provided in the end wall that closes the tip of the hollow tubular electrode substrate 2, and the plasma electrode A hollow chip 8 formed so as to concentrically surround the gas flow path g2 and a cup 9 formed so as to concentrically surround the chip 8, the chip being concentric with the plasma electrode. 8A surrounding a cylindrical portion, a tip portion 8C having a plasma flow ejection hole 801, and the cylindrical portion 8A.
And a tip portion 8C and a tapered first convex portion 8B directed toward the tip portion 8C, and a gas flow constricting portion 802 having an inverted conical surface shape is formed inside the first convex portion 8B. The cup 9 has a cylindrical portion 9A that concentrically surrounds the cylindrical portion 8A of the tip 8, a second convex portion 9B that concentrically surrounds the first convex portion 8B of the chip 8, and the second convex portion. A plasma arc cutting torch having an end wall 9C for closing the tip of the portion 9B, and a part of the tip 8C of the tip being led out to the outside through a hole provided in the end wall, The cup 9
The outer surface of the second convex portion 9B is formed in an inverted conical surface shape and concentrically surrounds the cylindrical portion 9A of the cup 9.
And a tapered portion 15B that abuts the outer periphery of the second convex portion 9B of the cup and concentrically surrounds the second convex portion 9B of the cup.
Is further provided with a shield cup 15 having a plasma flow injection hole 801 and a gas flow contraction portion 802 of the chip 8.
And a reverse arc surface-shaped plasma arc runner 803 having a cone angle θ smaller than the cone angle α of the gas flow contraction part, and the cone angle θ of the plasma arc runner 803.
Is set to 20 degrees or more and 85 degrees or less, and the ratio L2 / L1 of the axial dimension L2 of the plasma arc run-up portion 803 and the axial dimension L1 of the plasma flow ejection hole 801 is set to 0.2 or more and 2.5 or less. The second convex portion 9 of the cup 9
A plurality of grooves 901 extending along the generatrix direction of the conical surface of the second convex portion are radially provided on the outer periphery of B, and the plurality of grooves form a shield gas flow path s3. Is characterized in that the taper angle γ of the tapered portion 15B is the same as the cone angle β of the outer surface of the second convex portion of the cup 9 or the taper angle γ is slightly larger than the cone angle β. Torch for plasma arc cutting.

(4) From the torch body 7, the hollow tubular electrode base material 2 and the high melting point insert body 3 mounted in the recess provided in the end wall closing the front end portion of the electrode base material. The plasma electrode 1 supported in the center of the torch body, and the tip 8 supported by the torch body 7 so as to concentrically surround the plasma electrode via an annular gas passage g2. And a cup 9 supported by the torch body 7 so as to concentrically surround the tip via a cooling water return passage w4, and the tip 8 has a cylindrical portion 8A surrounding the plasma electrode 1.
And a tip portion 8C having a plasma flow ejection hole 801 and a tapered first convex portion 8B between the cylindrical portion and the tip portion and directed toward the tip portion, and an inverted cone is formed inside the first convex portion. A planar gas flow contracting portion 802 is formed, and the cup 9 concentrically surrounds the cylindrical portion 8A of the tip and the tapered second second portion concentrically surrounds the first convex portion 8B of the tip.
Part of the tip part 8C of the tip 8 through a hole provided in the end wall of the cup and having an end wall 9C for closing the tip of the second projection 9B. Is discharged to the outside, and the torch body 7 has a cooling water circulating hole 10a communicating with the inside of the electrode base material 2 of the plasma electrode 1 and the cooling water in the cooling water circulating hole. A cooling water guide passage w3 for guiding the cooling water, a cooling water discharge passage w5 for discharging the cooling water recirculated in the cooling water recirculation passage to the outside, and a plasma arc forming fluid in the annular gas passage g2. In a plasma arc cutting torch having a gas introduction passage g1 to be introduced therein, a cone angle of the gas flow contraction portion is provided between the plasma flow ejection hole 801 and the gas flow contraction portion 802 of the tip 8. Cone angle θ less than α
And a conical angle θ of the plasma arc runner 803 is set to 20 degrees or more and 85 degrees or less, and the axial dimension L2 of the plasma arc runner 803 and the plasma arc runner 803 are set. Flow spout hole 8
A plasma arc cutting torch in which the ratio L2 / L1 with respect to the axial dimension L1 of 01 is set to 0.2 or more and 2.5 or less.

(5) The outer surface of the second convex portion of the cup is formed in an inverted conical shape, and the cylindrical portion 15A surrounding the cylindrical portion of the cup 9 and the second convex portion 9B of the cup 9 are concentric with each other. Shield cup 15 having tapered portion 15B surrounding
Is further provided, and a shield gas flow passage s3 is formed between the second convex portion 9B of the cup 9 and the tapered portion 15B of the shield cup 15, and a shield gas jet port sa is formed at the tip of the shield gas flow passage. The torch for plasma arc cutting according to the above item 4, which is formed.

(6) The shield cup 15 is formed such that its tapered portion abuts on the outer circumference of the second convex portion 9B of the cup 9, and the taper portion is formed on the outer circumference of the second convex portion 9B of the cup 9. A plurality of grooves 901 radially extending along the generatrix direction of the conical surface of the second convex portion are provided, the shield gas flow passage s3 is formed by the plurality of grooves, and the shield cup 15 has a tapered portion. The taper angle γ of 15B is the same as the cone angle β of the conical surface of the second convex portion 2B of the cup 9, or the taper angle γ is formed to be slightly larger than the cone angle β. The torch for plasma arc cutting according to the above item 5.

(7) By using the plasma arc cutting torch described in the above item 1 or 4, electric power is supplied between the plasma electrode of the torch and the workpiece, and a gas flow path in the torch is provided. A plasma arc cutting method characterized by performing plasma arc cutting by supplying air or oxygen as a plasma arc forming fluid.

(8) Electric power is supplied between the plasma electrode of the torch and the workpiece by using the torch for plasma arc cutting described in the above item 2, 3, 5, or 6, and inside the torch. Of air or oxygen as a fluid for plasma arc formation is supplied to the gas flow passage of the above, and oxygen is supplied to the shield gas flow passage as a shield gas fluid, and the flow rate of the shield gas fluid is 10 liters / minute to 60 liters / minute. The plasma arc cutting method is characterized in that the plasma arc cutting is performed by setting the range within the range.

[0070]

As described above, according to the present invention, an inverted conical surface having a smaller cone angle than the gas flow contraction portion is provided between the plasma flow ejection hole of the chip and the gas flow contraction portion. After forming the plasma arc run-up portion, the plasma arc forming fluid that has flowed into the inside of the tip is radially restricted by the gas flow contraction portion with a large reduction rate of the radius with respect to the axial direction, and then squeezed,
Since the acceleration is performed by the plasma arc run-up portion whose radius reduction rate with respect to the axial direction is small, a high-speed gas stream that is narrowed and narrowed can be discharged from the plasma stream ejection hole.

Further, according to the present invention, the plasma arc run-up portion is provided, and the cone angle θ of the plasma arc run-up portion is 20.
The ratio L2 / L1 between the axial dimension L2 of the plasma arc run-up portion and the axial dimension L1 of the plasma jet hole is set to 0.2 or more and 2.5 or less, The maximum cutting current value can now be set higher than before.

Therefore, according to the present invention, the plasma arc forming fluid can be thinly squeezed out at a high speed, and the maximum cutting current value can be set higher than the conventional value, so that the current can be increased more than the conventional value. It is possible to generate a plasma arc that has a high density and is narrowed down, and to obtain a high-quality cut surface with a small bevel angle.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a main part of an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view showing a further enlarged main part of the embodiment of FIG.

FIG. 3 is an enlarged sectional view showing a main part of another embodiment of the present invention.

FIG. 4 is an enlarged cross-sectional view showing the shape of a plasma arc run-up portion that cannot be used in the present invention.

FIG. 5 is an enlarged cross-sectional view showing another shape of the plasma arc run-up portion that cannot be adopted in the present invention.

FIG. 6 is a diagram showing a result of measuring an allowable maximum cutting current value when a cone angle of a plasma arc running portion is changed in the torch according to the present invention.

FIG. 7 is a diagram showing a result of measuring a change in bevel angle of a cut surface when a cone angle of a plasma arc running portion is changed in the torch according to the present invention.

FIG. 8 shows changes in the bevel angle of the cut surface when the ratio L2 / L1 between the axial dimension L2 of the plasma arc run-up portion and the axial dimension L1 of the plasma flow ejection hole in the torch according to the present invention is changed. It is a diagram.

FIG. 9 is a vertical cross-sectional view showing the structure of a main part of still another embodiment of the present invention.

10 is a diagram showing the results of measuring changes in the bevel angle of the cut surface when the shield gas flow rate is changed in the torch of the embodiment of FIG.

FIG. 11 is a vertical cross-sectional view showing a state in which the shield cup is tilted and attached in the torch of the embodiment of FIG.

FIG. 12 is a vertical sectional view showing a main part of still another embodiment of the present invention.

13 is a perspective view showing a cup used in the embodiment of FIG. 12. FIG.

FIG. 14 is a vertical sectional view showing a main part of a conventional torch.

FIG. 15 is an enlarged cross-sectional view showing a further enlarged main part of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma electrode 2 Electrode base material 3 Insert body 4 Electrode support member 5 Insulating sleeve 6 Chip support member 7 Torch body 8 Chip 8A Cylindrical part 8B First convex part 8C Tip part 801 Plasma flow ejection hole 802 Gas flow contraction part 803 Plasma arc run-up part 9 Cup 9A Cylindrical part 9B Second convex part 9C Tip part 15 Shield cup 15A Cylindrical part 15B Tapered part g1 Gas introduction passage g2 Gas flow passage s1 to s3 Shield gas flow passage w1, w2 Cooling water passage w3 Cooling Water guide passage w4 Cooling water return passage w5 Cooling water discharge passage G Plasma arc forming fluid S Shield gas W Cooling water

Claims (5)

[Claims] 1. A plasma electrode (1) in which a high melting point insert (3) is mounted in a recess provided at the tip of an electrode substrate (2), and the plasma electrode is concentric with a gas flow path. A tip (8C) having a plasma flow ejection hole (801) and a tapered first convex portion (8B) directed toward the tip. ) And a reverse conical gas flow contracting flow portion (802) is formed inside the first convex portion, the plasma flow injection hole of the tip (8) is provided. Between (801) and the gas flow contracting section (802), the cone angle α of the gas flow contracting section is
An inverted conical surface-shaped plasma arc runner (803) having a smaller cone angle θ is provided, and the plasma arc runner (803) has a cone angle θ of 20.
Is set to be not less than 85 degrees and not more than 85 degrees, and the dimension L in the axial direction of the plasma arc run-up portion (803)
A plasma arc cutting torch in which the ratio L2 / L1 between 2 and the axial dimension L1 of the plasma flow ejection hole (801) is set to 0.2 or more and 2.5 or less. 2. The first protrusion (8B) of the chip (8)
A hollow cup (9) having a second convex portion (9B) concentrically surrounding the vicinity on the tip side, and a tapered portion (15B) concentrically surrounding the second convex portion (9B) of the cup at the tip. And a shield cup (15) provided on the side, and the outer surface of the second convex portion (9B) of the cup (9) is formed into an inverted conical surface, and the second convex portion (9B) and A shield gas flow passage (s3) is formed between the shield cup (15) and the taper portion (15B), and the shield gas flow outlet (801) concentrically surrounds the plasma flow ejection hole (801) at the tip of the shield gas flow passage. The plasma arc cutting torch according to claim 1, wherein (sa) is formed. 3. The shield cup (15) is formed so that its tapered portion abuts on the outer periphery of the second convex portion (9B) of the cup (9), and the second convex portion of the cup (9) is formed. A plurality of grooves (901) extending along the generatrix direction of the conical surface of the second convex portion are radially provided on the outer periphery of the portion (9B), and the shield gas flow path (s3) is formed by the plurality of grooves. And the shield cup (15) has a tapered portion (15).
The taper angle γ of B) is the second convex portion (9B) of the cup (9).
3. The torch for plasma arc cutting according to claim 2, wherein the torch is the same as the cone angle β of the outer surface or is formed such that the taper angle γ is slightly larger than the cone angle β. 4. The plasma arc cutting torch according to claim 1 is used to supply electric power between a plasma electrode of the torch and a workpiece, and air or oxygen is supplied to a gas passage in the torch. Is supplied as a fluid for plasma arc formation to perform plasma arc cutting. 5. A plasma arc cutting torch according to claim 2 or 3 is used to supply electric power between a plasma electrode of the torch and a workpiece, and to a gas passage in the torch. Air or oxygen is supplied as a plasma arc forming fluid, and oxygen is supplied to the shield gas channel as a shield gas fluid, and the flow rate of the shield gas fluid is set in the range of 10 liters / minute to 60 liters / minute. A plasma arc cutting method, which comprises performing plasma arc cutting by means of a method.