JP6029869B2 - Plasma torch - Google Patents

Description

  The present invention relates to a plasma torch capable of reducing electrode wear while maintaining cutting performance.

  A plasma torch that mainly cuts a steel sheet is composed of an electrode having an electrode material embedded in the center, a centering stone that is rotated around the electrode to supply a plasma gas composed of oxygen gas, and a nozzle that forms a plasma chamber between the electrodes. And is configured. This plasma torch is mounted on a cutting device controlled by a control device represented by a numerical control device (NC device), and is configured to cut a preset shape.

  When cutting the material to be cut by the plasma torch, a plasma arc swirled into the plasma chamber is supplied through the centering stone, and a pilot arc formed by discharging between the electrode and the nozzle is cut from the nozzle. It sprays toward the material. Then, after the pilot arc comes into contact with the material to be cut, the material to be cut is burned, melted and eliminated by the plasma arc formed by discharging between the electrode and the material to be cut, and along the preset cutting path. The target shape can be cut.

  The plasma gas supplied to the plasma chamber in a swirled state exerts a negative pressure on the front end face of the electrode, and in particular exerts a strong negative pressure on the electrode material arranged at the center. And the effect | action that the generation | occurrence | production point of the plasma arc in an electrode is stabilized by the effect | action of a negative pressure is exhibited. Moreover, the formed plasma arc is narrowed down by the swirling plasma gas, and its thickness is reduced. This also contributes to the improvement of cutting performance.

  If the plasma gas swirl is strengthened in order to improve the cutting performance, a strong negative pressure acts on the center of the electrode (electrode material) due to the strongly swirled plasma gas, which occurs on the surface of the electrode material when the plasma arc is stopped. The molten material is attracted to the plasma gas and detached from the electrode. As a result, there arises a problem that the electrode wears out.

  In order to prevent the progress of electrode consumption as described above, it is possible to solve the problem by using a thick electrode material. However, when a thick electrode material is used, it is necessary to increase the thickness of the electrode itself, resulting in a problem that the cutting performance deteriorates. When the plasma gas swirl is strengthened in an attempt to solve the problem that the cutting performance deteriorates, there is a problem that the electrode is consumed again.

  In order to solve the problems of electrode consumption and deterioration of cutting performance as described above, the present applicant has developed a plasma torch described in Patent Document 1 and has already obtained a patent right. The plasma torch described in Patent Document 1 supplies a first gas supply path for supplying a first gas from the periphery of the electrode to the periphery of the electrode, and a second gas through a gas supply path provided in the electrode. The second gas supply path is provided independently.

  In the plasma torch, the second gas supply path can be opened near the electrode material regardless of the outer diameter of the electrode, and the apparent electrode tip diameter can be reduced even when a thick electrode material is embedded. It becomes possible to do. For this reason, the life can be increased by using a thick electrode material, and the cutting performance can be prevented from being deteriorated by reducing the apparent diameter of the electrode.

  Also, since the first gas supply path and the second gas supply path are provided independently, different gas supply sources can be connected to these gas supply paths for supply. For this reason, for example, by supplying oxygen gas to the first gas supply path and air to the second gas supply path, it is possible to reduce the oxidation component acting on the electrode material and reduce the consumption of the electrode. .

JP 2002-336967 A (Patent No. 4648568)

  The plasma torch described in Patent Document 1 is practically advantageous because it can reduce electrode wear and ensure cutting performance. However, there is a continuing demand for the development of a plasma torch that can maintain the cutting performance and can reduce the consumption of the electrodes, and there is a problem that such a demand must be constantly met. It is the actual situation.

  An object of the present invention is to provide a plasma torch capable of reducing electrode wear while maintaining cutting performance.

In order to solve the above problems, a plasma torch according to the present invention comprises a plasma gas flow passage between an electrode having an electrode material embedded in the center thereof and an outer peripheral surface of the electrode fitted to the electrode, And a centering stone having a plasma gas swirl hole formed in a portion corresponding to the plasma gas flow passage, and an orifice for injecting a plasma arc at the tip, and is fitted to the centering stone and is attached to the tip of the electrode. A nozzle that forms a plasma gas chamber continuous with the plasma gas flow passage, and the swirl hole formed in the centering stone has a plurality of stages from the upstream side to the downstream side of the plasma gas flow passage. is formed, the orbiting holes formed in each stage are inclined so as to pivot the plasma gas in the same direction, and and in hole axes to open positions tangent Angle is different from the angle between the bore axis and the tangent of the pivot hole formed in the other stages.

  In the plasma torch, the swirl hole formed on the upstream side of the plasma gas flow passage has a large angle formed between the hole axis and the tangent at the opening position of the centering stone, and is downstream of the plasma gas flow passage. It is preferable that the angle formed between the hole axis and the tangent at the opening position of the centering stone is small.

  In any of the above plasma torches, it is preferable that the swirl holes formed in the respective stages have a diameter different from the diameter of the swirl holes formed in the other stages.

  In any of the above plasma torches, the swirl hole formed on the upstream side of the plasma gas flow passage has a large diameter, and the angle formed between the hole axis and the tangent at the opening position of the centering stone. It is preferable that the swirling hole formed on the downstream side of the plasma gas flow passage has a small diameter and that the angle formed between the hole axis and the tangent at the opening position of the centering stone is small.

  In the plasma torch according to the present invention, a plurality of swivel holes are formed in the centering stone from the upstream side to the downstream side of the plasma gas flow passage, and the swivel holes of each step are formed between a hole axis and a tangent line at the opening position. The angle formed is different from the angle formed between the hole axis and the tangent of the swivel hole in the other stage. For this reason, the position where the extended line of the radius of the outer periphery of the electrode intersects the hole axis of the swivel hole is different for each stage, and the strength of swirl can be adjusted.

  Accordingly, the plasma gas can be supplied to the plasma chamber with a weak swirl on the inner side and a strong swirl on the outer side, and a weak negative pressure is applied to the electrode material and the outer periphery of the formed plasma arc is swirled strongly. It can be narrowed down. For this reason, it is possible to hold the cutting performance and suppress the consumption of the electrode.

  In particular, the swirl hole formed on the upstream side of the plasma gas flow path has a large angle between the hole axis and the tangent at the opening position, and the swirl hole formed on the downstream side of the plasma gas flow path is the open position. By reducing the angle formed between the hole axis and the tangent line, the plasma gas supplied to the plasma gas chamber can be swung more strongly on the outer peripheral side than on the central side.

  For this reason, a weak negative pressure due to the weak swirling of the plasma gas acts on the electrode material arranged at the center of the electrode, reducing the amount of the molten electrode material that is released when the plasma arc is stopped, Consumption can be reduced. In addition, the plasma arc injected from the nozzle toward the material to be cut is narrowed down by the strong rotation of the outer peripheral side, and the cutting performance can be maintained.

  In addition, the swirling holes formed in each stage have a diameter different from the diameter of the swirling holes formed in the other stages, and the purpose is to form a plasma arc and to strengthen the swirling. The flow can be configured.

  In particular, the swirl hole formed on the upstream side of the plasma gas flow passage has a large diameter and a large angle between the hole axis and the tangent at the opening position, and is formed on the downstream side of the plasma gas flow passage. If the swivel hole has a small diameter and the angle between the hole axis and the tangent at the opening position is small, the swivel is weak at the center side with a relatively large flow rate, and the swivel hole is at a relatively small flow rate at the outer peripheral side. Plasma gas with strong swirl can be supplied. For this reason, consumption of the electrode material can be reduced and cutting performance can be maintained.

It is a figure explaining the whole structure of a plasma torch. It is an enlarged view explaining the structure of the front-end | tip part of a plasma torch. It is a figure explaining the structure of a centering stone. It is a figure explaining the structure of a turning hole, and is sectional drawing of ac of FIG.

  The plasma torch according to the present invention will be described below. The plasma torch of the present invention is a plasma arc that is ejected from a nozzle by supplying a plasma gas that is swung more strongly on the outer circumference side than the center side to a plasma gas chamber formed between the tip of the electrode and the nozzle. The cutting performance is maintained by narrowing down and the consumption of the electrode material is reduced.

  For this reason, when it is fitted to the electrode, a plurality of swivel holes are formed from the upstream side to the downstream side in the portion corresponding to the flow path in the centering stone that forms the flow path of the plasma gas between the electrode and the electrode. The angle formed between the hole axis and the tangent at the opening position of the swivel hole is different for each stage. The angle between the hole axis and the tangent at the opening position of the swivel hole formed in each stage is not limited, but the conditions such as the dimensions of the plasma gas flow path formed between the electrode and the centering stone It is preferable to set appropriately according to the above.

  Further, the number of swirl holes formed for each stage is not particularly limited, and there may be one or more. When forming a plurality of swivel holes for each step, it is preferable to form them at equal angular intervals in the same cross section in each step of the centering stone. Thus, by forming the plurality of swirl holes at equiangular intervals, the plasma gas supplied to the flow passage can be swirled substantially uniformly.

  Further, the number of stages of the swirl holes formed in the centering stone from the upstream side to the downstream side of the plasma gas flow passage is not limited. That is, it is sufficient that the swirl hole is formed in at least two stages, and it is preferable that the swirl hole is appropriately set in accordance with conditions such as the length of the flow passage and the flow rate of the plasma gas.

  For example, a step in which a swirling hole is formed in the centering stone that has a large angle with the tangent line at the opening position of the hole axis and is directed toward the center of the plasma gas flow path, and a tangent line at the opening position of the hole axis. And a step in which a swirl hole formed toward the outer peripheral side of the plasma gas flow passage is formed, the plasma gas supplied from the swirl hole toward the center side of the plasma gas flow passage is an electrode. The plasma gas supplied from the swirl hole toward the outer periphery of the plasma gas flow passage can be made to act to strengthen the swirl of the plasma arc. It is.

  For this reason, when the swirl holes are formed in a plurality of stages from the upstream side to the downstream side of the plasma gas flow passage, the angle between the hole axis of the swirl hole and the tangent at the opening position is limited. Not what you want. In particular, swirl considering the conditions such as the speed decay after being supplied to the plasma gas flow path and the plasma gas flow rate necessary to form a plasma arc sufficient to cut the workpiece. It is preferable to appropriately set the number of holes and the angle and diameter formed with the tangent at the opening position of the hole axis of the swivel hole in each stage.

  However, in order to make the negative pressure acting on the electrode material as small as possible and strengthen the swirl of the plasma arc, a swirl hole directed to the center side of the plasma gas flow path is formed in the upstream stage, It is preferable to form a swirl hole in the downstream stage toward the outer peripheral side of the plasma gas flow passage. By forming such a swirl hole, it is possible to cause a strong swirl on the outer peripheral side of the plasma arc.

  As described above, by forming the swirl hole toward the outer peripheral side of the plasma gas flow passage in the downstream stage of the plasma gas flow passage, it is possible to cause a strong swirl on the outer peripheral side of the plasma arc. . Therefore, by increasing the diameter of the swirl hole formed in the upstream stage and decreasing the diameter of the swirl hole formed in the downstream stage, the flow rate of the plasma gas contributing to the formation of the plasma arc is increased. In addition, it is preferable to reduce the flow rate of the plasma gas that causes a strong turning in the plasma arc.

  Hereinafter, the configuration of the plasma torch according to the present embodiment will be described with reference to the drawings. First, the overall structure of the plasma torch A will be schematically described with reference to FIG. In the plasma cutting torch A, an electrode 2 is disposed on the shaft 1a of the torch body 1. The electrode 2 is configured to be fitted to the cylindrical member 3a of the electrode base 3 and attached to the plasma cutting torch A, and to be detached from the plasma cutting torch A by being extracted from the cylindrical member 3a. The electrode 2 and the cylindrical member 3 a are each formed of a conductive material, are in contact with each other and connected to the electrode base 3, and are connected to a power supply device (not shown) through the electrode base 3.

  An insulating cylindrical member 3b is disposed on the outer peripheral portion of the cylindrical member 3a of the electrode table 3, and an insulating centering stone 4 formed in a cylindrical shape is fitted into the cylindrical member 3b. . Furthermore, a conductive nozzle 5 formed in a cup shape on the outer periphery of the centering stone 4 is disposed. An insulating cap 6 is disposed on the outer periphery of the nozzle 5, and the electrode 2, the centering stone 4, and the nozzle 5 are attached to the electrode base 3 by fastening the cap 6 to the torch body 1.

  In particular, the nozzle 5 and the electrode 2 are insulated from each other because the centering stone 4 and the cylindrical member 3b are interposed therebetween. And the nozzle 5 is connected with the power supply device which is not shown in figure through the site | part different from the electrode stand 3 (electrode 2).

  As described above, when the electrode 2, the centering stone 4, and the nozzle 5 are mounted on the electrode base 3 by the cap 6, the plasma gas chamber 10 is formed by the electrode 2, the centering stone 4, and the nozzle 5, A secondary air flow gas passage 11 is formed between the cap 6 and the cap 6.

  The plasma gas chamber 10 is formed in a ring shape between the centering stone 4 and the electrode 2 through the centering stone 4 and the plasma gas supply path 12 formed between the cylindrical member 3a and the cylindrical member 3b. The plasma gas flow passage 13 is connected. Further, the plasma gas supply path 12 is connected to a plasma gas supply member (not shown) through a pipe 14 provided on the electrode table 3. The secondary airflow gas passage 11 is connected to a secondary airflow gas supply member (not shown) through a pipe 15.

  Reference numerals 16a and 16b denote cooling water passages for cooling the electrode 2, and the cooling water supplied from the pipe 16c cools the back surface of the electrode 2 through the passage 16a and then passes through the passage 16b to the torch body 1. It passes through the inside and is discharged from the pipe 16d to the outside.

  As shown in FIG. 2, the electrode 2 has an electrode material 2 b made of, for example, hafnium embedded in the center of the tip surface 2 a, and a cylindrical portion 2 c is formed on the outer periphery, and the cylindrical portion 2 c and the tip surface 2 a A tapered portion 2d is formed therebetween. The front end surface 2 a constitutes a plasma gas chamber 10 together with the nozzle 5, and the cylindrical portion 2 c and the tapered portion 2 d constitute a plasma gas flow passage 13 together with the centering stone 4.

  As shown in FIGS. 3 and 4A to 4C, the centering stone 4 is formed in a cylindrical shape, and is located on the upstream side (the right side in FIG. 3) at a portion corresponding to the plasma gas flow passage 13. ) To the downstream side (left side in FIG. 3), swirl holes 4a, 4b, 4c are formed in three stages. Further, a flange 4d is formed at the tip, which is the downstream end, and the plasma gas supply path 12 is defined by the flange 4d contacting the inner surface of the nozzle 5 as shown in FIG. Yes.

  In this embodiment, three swirl holes 4a, 4b, 4c are formed at equal angular intervals for each step (120 degree intervals for each step), and the swivel holes of each step are shifted from each other. Is formed. Therefore, when the centering stone 4 is seen through in the axial direction, a total of nine turning holes are formed in the centering stone 4 at positions shifted from each other. And although the three turning holes formed in the same step | paragraph have the mutually same specification, they have a different specification for every step. In addition, there is no limitation on how much the swivel holes of each stage are shifted with respect to the swivel holes of other stages.

  The swirl hole 4a formed at the most upstream side of the plasma gas flow passage 13 has an angle α formed between the hole axis and the tangent at the opening position larger than the angles β and θ of the other swirl holes 4b and 4c. The diameter is formed larger than the diameters of the other swivel holes 4b and 4c. The value of the angle α is not particularly limited, and the inner periphery of the plasma gas flow passage 13 in which the hole axis of the swivel hole 4 a is formed in a ring shape by the cylindrical portion 2 c of the electrode 2 and the inner peripheral surface of the centering stone 4. It has such a value that it can be very close to the cylindrical part 2c constituting the. In this embodiment, the diameter of the swivel hole 4a is set to about 1 mm which is the largest compared with the diameters of the other swirl holes 4b and 4c.

  For this reason, the plasma gas supplied to the plasma gas flow passage 13 from the swivel hole 4a swirls along the surface of the cylindrical portion 2c in the electrode 2 toward the electrode material 2b embedded in the center of the electrode 2. It is possible to apply a negative pressure to the electrode material 2b. Further, since the swirl hole 4a is formed on the most upstream side of the plasma gas flow passage 13, the negative pressure acting on the electrode material 2b is attenuated in the process of flowing into the plasma gas chamber 10 through the plasma gas flow passage 13. Will decline.

  The swirl hole 4c formed on the most downstream side of the plasma gas flow passage 13 has an angle θ formed between the hole axis and the tangent at the opening position smaller than the angles α and β of the other swirl holes 4a and 4b. The diameter is formed smaller than the diameters of the other swivel holes 4a and 4b. The value of the angle θ is not particularly limited, and the hole axis of the swivel hole 4c can be very close to the inner peripheral surface of the centering stone 4 constituting the outer periphery of the plasma gas flow passage 13 formed in a ring shape. Has a value. In the present embodiment, the diameter of the turning hole 4c is set to about 0.4 mm, which is the smallest compared with the diameters of the other turning holes 4a and 4b.

  Therefore, the plasma gas supplied from the swirl hole 4c to the plasma gas flow passage 13 flows toward the nozzle 5 while swirling along the inner peripheral surface of the centering stone 4, and in the process of this flow, the plasma gas chamber 10 It acts to strengthen the swirl around the outer periphery of the plasma gas or plasma arc. In particular, since the swirl hole 4c is formed on the most downstream side of the plasma gas flow passage 13, the flow velocity is less attenuated, and the swirl of the plasma gas or plasma arc flowing to the orifice 5a of the nozzle 5 can be enhanced. .

  In the swirl hole 4b formed in the middle of the swirl holes 4a and 4c in the plasma gas flow passage 13, the angle β formed between the hole axis and the tangent at the opening position is the angle α of the other swirl holes 4a and 4c, It is formed with an angle approximately in the middle of θ, and the diameter is also formed with an intermediate diameter between the diameters of the other swivel holes 4a and 4c. The value of the angle β is not particularly limited, and has a value such that the hole axis of the swivel hole 4b points to a substantially central portion of the plasma gas flow passage 13 formed in a ring shape. In this embodiment, the diameter of the swivel hole 4b is set to about 0.5 mm, which is the middle of the diameters of the other swivel holes 4a and 4c.

  For this reason, the plasma gas supplied from the swirl hole 4b to the plasma gas flow passage 13 flows while swirling the intermediate portion of the plasma gas flow passage 13 whose section is ring-shaped, and is supplied from the swirl hole 4a in the course of this flow. It acts to prevent the flow velocity of the plasma gas from decaying.

  The nozzle 5 has an orifice 5a at the center, and a function of forming a plasma gas chamber 10 with the tip surface 2a of the electrode 2 and discharging the electrode 2 to form a pilot arc to be ejected from the orifice 5a. Have

  In the plasma cutting torch A configured as described above, it is possible to supply the plasma gas to the plasma gas supply path 12 by operating the plasma gas supply member. The plasma gas supplied to the plasma gas supply path 12 circulates in a state of being swirled with respect to the plasma gas flow path 13 from the swirl holes 4 a to 4 c formed in the centering stone 4, and the plasma gas flows from the plasma gas flow path 13 to the plasma. The gas chamber 10 is supplied.

  When the plasma gas is supplied to the plasma gas chamber 10, a pilot arc is formed by discharging between the nozzle 5 and the electrode 2, and the pilot arc is injected from the orifice 5 a toward the material to be cut. When the material to be cut comes into contact, the discharge between the nozzle 5 and the electrode 2 is stopped. At the same time as the discharge between the nozzle 5 and the electrode 2 is stopped, the discharge between the material to be cut and the electrode 2 forms a plasma arc capable of cutting the material to be cut. And the target cutting | disconnection can be performed by moving the plasma torch A which formed the plasma arc along the cutting line set to the to-be-cut material.

  As described above, the plasma gas supplied from the swirl hole 4 a to the plasma gas flow passage 13 flows into the plasma gas chamber 10 while swirling along the cylindrical portion 2 c of the electrode 2. In this process, the flow velocity is attenuated, and the negative pressure acting on the electrode material 2b embedded in the electrode 2 is weak although the flow rate is large.

  The plasma gas supplied from the swirl hole 4b to the plasma gas flow passage 13 flows through a substantially intermediate portion in the cross section of the plasma gas flow passage 13, and is supplied from the swirl hole 4a and swirls in the course of this flow. It acts to contribute to the swirl of the plasma gas flowing along the cylindrical portion 2c of the electrode 2 on the outer peripheral side.

  Further, the plasma gas supplied from the swirl hole 4c to the plasma gas flow passage 13 flows along the inner peripheral surface of the centering stone 4 on the outer peripheral side in the cross section of the plasma gas flow passage 13, and in the process of this flow It acts to reinforce the swirl on the outer peripheral side (the inner peripheral surface side of the nozzle 5) of the plasma gas that flows from the swirl holes 4a and 4b and flows toward the plasma gas chamber 10 while swirling.

  For this reason, the flow of the plasma gas in the plasma gas chamber 10 acts on the electrode material 2b provided at the center of the tip surface 2a of the electrode 2 with a large amount and a weak swirling flow, and along the inner peripheral surface of the nozzle 5. A strong swirl flow is formed. That is, even when a weak negative pressure acts on the electrode material 2a to stop the plasma arc, it is possible to reduce the suction to the molten electrode material. Moreover, the outer peripheral part of the plasma gas which forms a plasma arc becomes a strong swirl flow, and it becomes possible to maintain the cutting performance by narrowing the formed plasma arc.

  The inventors of the present invention conducted comparative experiments on changes in electrode wear using the plasma torches (two) that have been conventionally used and the plasma torches A (five) according to the present invention. In this experiment, both the conventional plasma torch and the plasma torch of the present invention have the same current value, plasma gas flow rate, and pressure conditions, and after a plasma arc is formed for 60 seconds, it is stopped for 30 seconds to be one cycle. Every time the number of cycles reached 30, the electrode 2 was taken out and the consumption depth of the electrode material 2b was measured.

  The result of the comparative experiment will be described. When the number of cycles was 90, the average consumption depth of the electrode material 2b of the conventional plasma torch (hereinafter referred to as “consumption depth of the conventional torch”) was 0.26 mm. In contrast, the average value of the depth of consumption of the electrode material 2b of the plasma torch of the present invention (hereinafter referred to as “the depth of consumption of the present torch”) was 0.20 mm. When the number of cycles was 180, the consumption depth of the conventional torch was 0.65 mm. In contrast, the consumption depth of the torch of the present invention was 0.51 mm.

  When the number of cycles was 270, the consumption depth of the conventional torch was 1.02 mm. In contrast, the consumption depth of the torch of the present invention was 0.81 mm. When the number of cycles was 360, the consumption depth of the conventional torch was 1.31 mm. In contrast, the consumption depth of the torch of the present invention was 1.04 mm. Furthermore, when the number of cycles was 450, the consumption depth of the conventional torch was 1.55 mm. In contrast, the consumption depth of the torch of the present invention was 1.23 mm.

  From the above experiment, it can be said that the consumption of the plasma torch of the present invention is reduced as compared with the consumption of the electrode material in the conventional plasma torch. That is, in this experiment, the consumption depth of the conventional torch when the number of cycles is 270 is substantially equivalent to the consumption depth when the number of cycles of the plasma torch of the present invention is 360. It is clear that is sufficiently reduced.

  The present invention is advantageous when used in a plasma torch in which a plasma arc is formed by a swirling flow of plasma gas.

A Plasma cutting torch 1 Torch body 1a Axis 2 Electrode 2a Tip surface 2b Electrode material 2c Cylindrical part 2d Taper part 3 Electrode base 3a, 3b Cylindrical member 4 Centering stone 4a-4c Swivel hole 4d Flange 5 Nozzle 5a Orifice 6 Cap 10 Plasma gas Chamber 11 Secondary gas flow passage 12 Plasma gas supply passage 13 Plasma gas flow passage 14, 15, 16c, 16d
Piping 16a, 16b passage

Claims (4)

An electrode with an electrode material embedded in the center;
A centering stone that is fitted to the electrode and forms a plasma gas flow path between the electrode and an outer peripheral surface of the electrode, and a plasma gas swirl hole is formed in a portion corresponding to the plasma gas flow path;
An orifice for injecting a plasma arc at the tip, and a nozzle that is fitted to the centering stone and forms a plasma gas chamber continuous with the plasma gas flow passage between the tip of the electrode,
The swirl holes formed in the centering stone are formed in a plurality of stages from the upstream side to the downstream side of the plasma gas flow passage, and the swirl holes formed in each stage are inclined so as to swirl the plasma gas in the same direction. The plasma torch is characterized in that the angle formed between the hole axis and the tangent at the opening position is different from the angle formed between the hole axis and the tangent of the swivel hole formed at the other stage. The swirling hole formed on the upstream side of the plasma gas flow passage has a large angle formed by the hole axis and the tangent at the opening position of the centering stone,
The swirling hole formed on the downstream side of the plasma gas flow passage has a small angle between the hole axis and the tangent at the opening position of the centering stone.
The plasma torch according to claim 1, wherein:   3. The plasma torch according to claim 1, wherein the swirl holes formed in each of the stages have a diameter different from the diameter of the swirl holes formed in the other stages. The swirl hole formed on the upstream side of the plasma gas flow passage has a large diameter and a large angle between the hole axis and the tangent at the opening position of the centering stone,
The swirl hole formed on the downstream side of the plasma gas flow passage has a small diameter, and the angle formed between the hole axis and the tangent at the opening position of the centering stone is small.
The plasma torch according to any one of claims 1 to 3, wherein

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