Plasma generator

Abstract

Discharge can occur from the circumferential area at the tip of the electrode rod, and this discharge can cause localized wear of the electrode rod. [Solution] The plasma generator 1 includes a metal nozzle 20 having a gas channel 26 through which process gas flows and an outlet 23 from which process gas is discharged from the gas channel 26, and an electrode rod 11 inserted into the gas channel 26 and to which a voltage is applied between it and the nozzle 20. The gas channel 26 has a constricted space 26A formed therein, in which the cross-section of the channel narrows as it proceeds toward the outlet 23, and a spiral-shaped first groove 25A is formed around the axis L of the electrode rod 11 on the inner wall surface 26a forming the constricted space 26A, so as to form a swirling gas flow F.

Description

Technical Field

[0001] The present invention relates to a plasma generator.

Background Art

[0002] As a technology of this kind, for example, Patent Document 1 discloses a plasma generator (plasma torch) including a nozzle in which a gas flow path is formed and an electrode rod disposed in the gas flow path. When generating plasma, a voltage is applied between the electrode rod and the nozzle, so that a discharge occurs between them, and a part of the process gas is plasmaized (activated). In this plasma generator, a columnar insulating guide having spiral grooves is attached to the electrode rod to generate a swirling flow in the process gas heading toward the tip portion of the electrode rod. Thereby, a thin cooling gas layer is formed on the inner peripheral surface of the nozzle, and the temperature rise of the inner wall of the nozzle is suppressed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the plasma generator disclosed in Patent Document 1, the swirling flow of the process gas reaching the tip portion of the electrode rod is not sufficient, and discharge may occur from a specific location in the circumferential direction of the tip portion of the electrode rod, and the electrode rod may be locally consumed by this discharge.

[0005] The present invention has been made in view of such points, and an object thereof is to provide a plasma generator capable of suppressing local consumption of an electrode rod.

Means for Solving the Problems

[0006] In view of the above problems, the plasma generator according to the present invention comprises a metal nozzle having a gas channel through which a process gas flows and an outlet from which the process gas containing plasma is discharged from the gas channel, and an electrode rod inserted into the gas channel and to which a plasma generation voltage is applied between the electrode rod and the nozzle, wherein the gas channel has a constricted space in which the cross-section of the channel narrows as it proceeds toward the outlet, and a spiral-shaped first groove is formed around the axis of the electrode rod on the inner wall surface forming the constricted space, when viewed from a direction along the axis of the electrode rod, such that a swirling flow of the process gas is formed.

[0007] According to the present invention, a discharge can be generated by applying a voltage between a nozzle and an electrode rod, thereby plasma-generating a portion of the process gas flowing between them. Here, the nozzle has a throttling space in which the flow path cross-section narrows as it approaches the discharge port, and a spiral-shaped first groove is formed on the inner wall surface forming the throttling space. As a result, the process gas that collides with the inner wall surface of the throttling space flows along the first groove, thereby forming a swirling flow of process gas around the throttling space and the electrode rod. This swirling flow prevents discharge from a specific point in the circumferential direction of the tip of the electrode rod, and thus suppresses localized consumption of the electrode rod due to this discharge.

[0008] In a more preferred embodiment, the throttling space has a base portion located upstream of the process gas and a tip portion located downstream of the process gas, along the direction of the axis, and the first groove is formed continuously from the base portion to the tip portion.

[0009] According to this embodiment, since the first groove is formed continuously from the base end to the tip end of the throttling space, a swirling flow of process gas containing plasma can be formed in the throttling space. As a result, the plasma that passes through the throttling space and is emitted from the outlet can be sent far away from the tip of the nozzle.

[0010] In a more preferred embodiment, the plasma generator has a cylindrical body made of an insulating material inserted into the gas flow path along the axis of the electrode rod so as to cover the electrode rod, and the tip portion of the electrode rod protrudes from the end face of the cylindrical body toward the discharge port into the constricted space.

[0011] In this embodiment, in the gas flow path, the tip of the electrode rod protrudes from the end face of the cylindrical body toward the discharge port into a constricted space where a swirling flow is formed, making it easy for discharge to occur at random positions in the circumferential direction of the tip of the electrode rod. In addition, discharge can be suppressed between the portion of the electrode rod covered by the cylindrical body made of insulating material (excluding the tip) and the inner wall surface of the nozzle.

[0012] In a more preferred embodiment, the tip portion of the electrode rod has a hemispherical surface.

[0013] According to this embodiment, since the tip of the electrode rod has a hemispherical surface, the surface of the tip of the electrode rod becomes rounded, which makes it possible to suppress discharge from a specific position on the tip of the electrode rod.

[0014] In a more preferred embodiment, a cylindrical communication space is formed between the throttling space and the discharge port, along the axis of the electrode rod, connecting the throttling space and the discharge port, and a spiral second groove is formed on the inner wall surface forming the communication space, continuous with the first groove, so as to form a swirling flow in the same direction as the swirling flow of the process gas formed by the first groove.

[0015] In this embodiment, a spiral second groove is formed on the inner wall surface forming the cylindrical communication space, continuous with the first groove, so as to form a swirling flow. Therefore, the process gas containing plasma is discharged from the outlet with a swirling flow formed in the same direction as the swirling gas flow formed by the first groove. As a result, the plasma discharged from the outlet can be sent far away from the tip of the nozzle. [Effects of the Invention]

[0016] According to the present invention, localized consumption of the electrode rod can be suppressed. [Brief explanation of the drawing]

[0017] [Figure 1] This is an exploded perspective view of a plasma generator according to an embodiment of the present invention, with the cover removed. [Figure 2] (a) is a perspective view of the nozzle tip shown in Figure 1, viewed from below; (b) is a perspective view of the nozzle tip, viewed from above; (c) is a top view of the nozzle tip; and (d) is a cross-sectional view of the nozzle tip. [Figure 3] Figure 1 is a cross-sectional view of the main part of the plasma generator. [Modes for carrying out the invention]

[0018] A plasma generator 1 according to an embodiment of the present invention will be described below with reference to Figures 1 to 3. The plasma generator 1 generates plasma from a portion of the supplied process gas by applying a plasma generation voltage V between a nozzle 20 supplied with process gas and an electrode rod 11 inserted into the nozzle 20, thereby causing a discharge between the electrode rod 11 and the nozzle 20. The generated plasma is then discharged from an outlet 23.

[0019] Examples of the discharge between the electrode rod 11 and the nozzle 20 include arc discharge, streamer discharge, glow discharge, etc. As long as plasma can be generated, the form of the discharge is not particularly limited. The type of discharge can be set according to the type of process gas and the conditions of the applied voltage (such as the magnitude of the voltage and the shape of the voltage waveform). In this specification, since a part of the process gas becomes plasma, the process gas containing plasma may sometimes be referred to as plasma hereinafter.

[0020] In such a plasma generator 1, a part of the process gas (for example, O2, etc.) flowing from the upstream is ionized to generate plasma. The process gas containing the generated plasma is sprayed, and a predetermined treatment is performed with the sprayed plasma. For example, the surface of a metal member or the like is modified using plasma. Of course, it can also be used for other applications.

[0021] As shown in FIG. 3, the electrode rod 11 is, for example, a rod-shaped metal member mainly made of copper. The electrode rod 11 is inserted into the gas flow path 26 of the nozzle 20 described later in a non-contact state with the nozzle 20, and a voltage V is applied between the electrode rod 11 and the nozzle 20. The tip portion 11a of the electrode rod 11 may have a conical or frustum shape, but in this embodiment, it has a hemispherical surface. Thereby, the surface of the tip portion 11a of the electrode rod 11 becomes a rounded surface, so that discharge from a specific position of the tip portion 11a of the electrode rod 11 can be suppressed.

[0022] The base end of the electrode rod 11 is attached to an electrode holder (not shown) made of metal such as copper, and the electric wire 71 shown in FIG. 1 is attached to the electrode holder. Thereby, the voltage V (specifically, a voltage with a pulse waveform) from a power source (not shown) connected to the electric wire 71 can be supplied to the electrode rod 11.

[0023] Furthermore, a columnar rectifying member 12 having a plurality of spiral grooves 12a formed on its outer peripheral surface is attached to the electrode rod 11. The rectifying member 12 is a member that rectifies the process gas so that the process gas that travels linearly along the gas flow path 26 forms a swirling flow, and is inserted into the internal space 31a of a cylindrical body 31 described later. Due to the grooves 12a formed on the outer peripheral surface of the rectifying member 12, the process gas that passes through the grooves 12a forms a swirling flow F downstream of the rectifying member 12. The grooves 12a are formed so that the direction of the swirling flow F of the gas that has passed through the rectifying member 12 is the same as the direction of the swirling flow F of the first concave groove 25A described later. Thereby, the formation of the swirling flow F of the gas by the first concave groove 25A can be enhanced.

[0024] As shown in FIG. 3, the plasma generator 1 includes at least a metal nozzle 20 and an electrode rod 11. The nozzle 20 is formed with a gas flow path 26 through which a process gas flows and a discharge port 23 from which the process gas containing plasma is discharged. The nozzle 20 is connected to the ground and includes a cylindrical nozzle body 21 and a nozzle tip 22 screwed to the tip portion of the nozzle body 21. Further, although the structure on the upstream side of the gas flow path 26 is not shown, it communicates with the gas supply pipe 72.

[0025] In the present embodiment, the nozzle body 21 is a cylindrical body having a large-diameter portion 21a and a small-diameter portion 21b. A nozzle tip 22 is attached to the tip side of the small-diameter portion 21b so that the gas flow path 26 is formed along the axis L of the inserted electrode rod 11. In the present embodiment, the nozzle 20 is composed of the nozzle body 21 and the nozzle tip 22, but the nozzle body 21 and the nozzle tip 22 may be integrally formed as long as the electrode rod 11 and a cylindrical body 31 described later can be inserted.

[0026] In this embodiment, a cylindrical body 31 made of an insulating material such as ceramics (e.g., alumina) is inserted into the gas flow path 26 along the axis L of the electrode rod 11 and covering the electrode rod 11. The internal space 31a of the cylindrical body 31 becomes part of the gas flow path 26 of the nozzle 20.

[0027] In this embodiment, an electrode rod 11 is inserted into the cylindrical body 31, and the tip portion 11a of the electrode rod 11 protrudes from the end face 31b of the cylindrical body 31 toward the discharge port 23 into the constricted space 26A. This makes it easy for discharge to occur at random positions in the circumferential direction of the tip portion 11a of the electrode rod 11. In addition, the cylindrical body 31 made of insulating material can suppress discharge between the portion of the electrode rod covered (excluding the tip portion) and the inner wall surface of the nozzle body 21 of the nozzle 20.

[0028] As shown in Figures 2(a) and 2(b), the nozzle tip 22 has a screw groove (not shown) formed on its outer surface 22b and a seal groove 22c. As shown in Figure 3, an O-ring 83 is placed in the seal groove 22c, and the nozzle tip 22 is screwed to the nozzle body 21 by screwing the screw groove of the nozzle tip 22 into the nozzle body 21. The nozzle tip 22 has an opening 27 into which the tip of a cylindrical body 31 made of insulating material is inserted. The cylindrical body 31 is inserted from the opening 27 along the inner circumferential surface 22d continuous with the opening 27 until the end face 31b of the cylindrical body 31 abuts against the ring-shaped bottom surface 22e of the nozzle tip 22 (see Figure 2(d)). An outlet 23 is formed at a position corresponding to the tip 22a of the nozzle tip 22 (the tip 20a of the nozzle 20) from which process gas containing plasma is released.

[0029] As shown in Figures 2(c) and 2(d), a throttling space 26A is formed in the gas flow path 26 of the nozzle tip 22, where the flow path cross-section narrows as it proceeds toward the discharge port 23. The throttling space 26A is a space with the shape of a frustocone. The throttling space 26A has a base end portion 26f located upstream of the process gas along the axis L of the electrode rod 11, and a tip portion 26c located downstream of the process gas. Between the tip portion 26c of the throttling space 26A and the discharge port 23, a cylindrical communication space 26B is formed along the axis L of the electrode rod 11, connecting the throttling space 26A and the discharge port 23. The communication space 26B is a cylindrical space formed by the inner wall surface 26b.

[0030] In this embodiment, as shown in Figures 2(c) and 2(d), a spiral-shaped first groove 25A is formed around the axis L of the electrode rod 11 on the inner wall surface 26a forming the throttling space 26A, when viewed from a direction along the axis L of the electrode rod 11, so that a swirling flow F of the process gas is formed. In this embodiment, the first groove 25A is formed continuously from the base end 26f of the throttling space 26A to the tip end 26c of the throttling space 26A. In this embodiment, one (single) first groove 25A is formed, but multiple (for example, two or more) first grooves 25A overlapping each other may be formed. However, in this embodiment, by providing one (single) first groove 25A, a groove with a wider groove width can be formed, making it easier to form a swirling flow F of the process gas.

[0031] Furthermore, a spiral second groove 25B is formed on the inner wall surface 26b that forms the communication space 26B. This second groove is continuous with the first groove 25A and is formed in the same direction as the swirling flow F of the process gas formed by the first groove 25A. In this embodiment, the first groove 25A and the second groove 25B have the same groove width, thereby forming a single continuous groove on the inner wall surfaces 26a and 26b.

[0032] In this embodiment, in the groove cross-sections of the first groove 25A and the second groove 25B, the valley bottoms are rounded, and the adjacent peaks of the first grooves 25A are also rounded. This reduces discharge at specific positions on the adjacent peaks of the first grooves 25A, and makes it easier for discharge to occur at random positions on the tip portion 11a of the electrode rod 11.

[0033] According to this embodiment, a discharge is generated by applying a voltage between the nozzle 20 and the electrode rod 11, and a portion of the process gas flowing between them can be turned into plasma. Here, the nozzle 20 has a throttling space 26A in which the flow path cross-section narrows as it proceeds towards the discharge port 23, and a spiral-shaped first groove 25A is formed on the inner wall surface 26a that forms the throttling space 26A.

[0034] As a result, the process gas that collides with the inner wall surface 26a of the throttling space 26A flows along the first groove 25A, thereby forming a swirling flow F of the process gas around the throttling space 26A and the tip portion 11a of the electrode rod 11. This swirling flow F prevents discharge from specific points in the circumferential direction of the tip portion 11a of the electrode rod 11, thereby suppressing localized consumption of the electrode rod 11 due to this discharge. Furthermore, due to this discharge, a portion of the process gas becomes plasma, and the process gas containing the plasma can be discharged from the outlet 23.

[0035] In particular, since the first groove 25A is formed continuously from the base end 26f to the tip end 26c of the throttling space 26A, a swirling flow F of the process gas (process gas including plasma) is formed in the throttling space 26A. As a result, the plasma that passes through the throttling space 26A and is emitted from the outlet 23 can be sent further away from the tip 20a of the nozzle 20.

[0036] Furthermore, since the second groove 25B is formed in a continuous manner with the first groove 25A, and a swirling flow F is formed, the process gas containing plasma is discharged from the outlet 23 with a swirling flow formed in the same direction as the swirling flow F of the process gas formed by the first groove 25A. As a result, the plasma discharged from the outlet 23 can be sent further away from the tip 20a of the nozzle 20.

[0037] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various design modifications can be made without departing from the spirit of the invention as described in the claims. [Explanation of Symbols]

[0038] 1: Plasma generator, 11: Electrode rod, 11a: Tip part, 20: Nozzle, 23: Discharge port, 25A: First groove, 25B: Second groove, 26: Gas flow path, 26A: Throttle space, 26B: Communication space, 31: Cylindrical body, F: Swirling flow, L: Axial center

Claims

1. A metal nozzle having a gas channel through which a process gas flows, and an outlet from which the process gas containing plasma is discharged from the gas channel, A plasma generator comprising an electrode rod inserted into the gas flow path and to which a voltage for plasma generation is applied between the nozzle, The gas flow path has a constricted space formed in which the cross-sectional area of ​​the flow path narrows as it proceeds toward the outlet side. A plasma generator characterized in that, when viewed from a direction along the axis of the electrode rod, a spiral-shaped first groove is formed around the axis of the electrode rod on the inner wall surface forming the throttling space, such that a swirling flow of the process gas is formed.

2. The throttling space has a base portion located upstream of the process gas and a tip portion located downstream of the process gas, along the direction of the axis. The plasma generator according to claim 1, characterized in that the first groove is formed continuously from the base end to the tip end.

3. In the plasma generator, a cylindrical body made of an insulating material is inserted into the gas flow path along the axis of the electrode rod and so as to cover the electrode rod. The electrode rod is inserted into the cylindrical body. The plasma generator according to claim 1, characterized in that the tip portion of the electrode rod protrudes from the end face of the cylindrical body toward the discharge port into the constricted space.

4. The plasma generator according to claim 1, characterized in that the tip portion of the electrode rod has a hemispherical surface.

5. Between the throttling space and the discharge port, a cylindrical communication space is formed along the axis of the electrode rod, connecting the throttling space and the discharge port. The plasma generator according to claim 1, characterized in that a spiral second groove is formed on the inner wall surface forming the communication space, continuous with the first groove, and in the same direction as the direction in which the swirling flow of the process gas is formed by the first groove, so as to form a swirling flow.

Images