Apparatus, and method for treating powder

Abstract

To provide an apparatus and a method for treating powder capable of stably obtaining a high quality powder by treating a granulated powder as a particle morphology as it is by plasma heating.SOLUTION: An apparatus for treating powder includes: a plurality of discharge electrode parts 20 arrayed in a discharge vessel 10 in a circumference direction so as to be inclined to a downward direction at an angle of 45° or more and less than 90° to a horizontal direction; a powder supply part 30 connected to the discharge vessel 10; and a gas supply part 70 for supplying gas into the discharge vessel 10 by circulating the gas through the discharge electrode parts 20 and the powder supply part 30, where a powder, as a particle morphology as it is, is subjected to heat treatment by generating arc discharge in a region surrounded by the discharge electrode parts 20 by applying multi-phase AC voltage to the discharge electrode parts 20 to generate a plasma region along a vertical direction, and charging the powder from above at a predetermined flow rate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a powder processing apparatus and method for performing surface treatment on powder formed by granulation or the like. [Background technology]

[0002] In recent years, research and development of processing technologies such as coating technology and additive manufacturing technology using powder as a material has progressed, and the powder used as such a material is required to have characteristics and quality corresponding to the processing technology.

[0003] Powders are granulated by a wet technique using spray drying and then heat-treated by sintering, but this type of granulation process has the problem of causing defects in the powder, such as voids, which can lead to quality degradation. Therefore, powder processing is required to improve the quality of the granulated powder. For example, Non-Patent Document 1 proposes that ultra-hard granulated powder (tungsten carbide) used in additive manufacturing is remelted by heat treatment using DC arc plasma to improve quality, such as by imparting high packing properties and high fluidity.

[0004] Furthermore, Patent Document 1 describes a microparticle manufacturing device that uses multiple electrodes to generate plasma in a reaction chamber by applying AC power of different phases, and proposes producing microparticles from material particles by plasma heating treatment. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7266181 [Non-patent literature]

[0006] [Non-Patent Document 1] Hirotomo Itagaki and 3 others, "Introduction of Metal Powder Manufacturing Process for Additive Manufacturing (AM) and DC Arc Plasma Treatment Technology of Irregular Shape Metal Powder Aimed at AM Application", Japan Thermal Spray Society, July 2021, Thermal Spray Vol. 58, No. 3. p. 142-146 Summary of the Invention [Problem to be solved by the invention]

[0007] In the powder processing method using DC arc plasma described in Non-Patent Document 1, the quality such as packing property is improved by remelting the granulated powder, but since the remelting causes the tungsten carbide to change into a brittle phase and reduces the hardness, it is necessary to avoid excessive heating by the plasma heating treatment. For this reason, although the powder processing method described in Non-Patent Document 1 is capable of processing small amounts of powder, there is a problem in terms of mass production.

[0008] Therefore, an object of the present invention is to provide a powder processing apparatus and method that can stably obtain high-quality powder by performing powder processing on granulated powder by plasma heating while the powder remains in particulate form. [Means for solving the problem]

[0009] The powder processing apparatus of the present invention comprises a discharge vessel, a powder supply unit attached to the top of the discharge vessel and supplying powder, a plurality of discharge electrode units attached to the side of the discharge vessel and arranged in a circumferential direction at an angle of 45° or more and less than 90° downward with respect to the horizontal, an AC power supply unit connected to the discharge electrode units and applying a polyphase AC voltage, a gas supply unit that circulates gas through the discharge electrode units and the powder supply units and supplies it into the discharge vessel, and a control unit that controls the AC power supply unit and the gas supply unit to generate an arc discharge in an area surrounded by the discharge electrode units to generate a plasma region along the vertical direction, and to inject the powder into the plasma region from above at a predetermined flow rate so as to heat-treat the powder while it remains in a particulate form.

[0010] The powder processing method of the present invention involves applying a polyphase AC voltage while releasing gas from openings at the tips of a number of discharge electrode sections that are arranged circumferentially within a discharge vessel and inclined downward at an angle of 45° or more and less than 90° with respect to the horizontal, generating an arc discharge in an area surrounded by the discharge electrode sections and generating a plasma region that extends in a vertical direction, circulating powder together with gas from above the plasma region in the vertical direction at a predetermined flow rate, and heat-processing the powder while it remains in particulate form within the plasma region. Effect of the Invention

[0011] The present invention has the above-mentioned configuration, and applies a multiphase AC voltage while discharging gas from the openings at the tips of a plurality of discharge electrodes arranged at an angle of 45° or more and less than 90° downward with respect to the horizontal direction, and generates an arc discharge in an area surrounded by the discharge electrodes to generate a plasma area along the vertical direction, so that the plasma area is formed in a vertically elongated shape that does not expand horizontally but expands vertically, and it is possible to set a heating temperature area that is stable in the vertical direction. In addition, by circulating the powder together with the gas at a predetermined flow rate in the vertical direction from above the plasma area, it is possible to stabilize the residence time of the powder in the plasma area, and it is possible to heat-treat the powder in its particle form without altering it by remelting or the like. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic configuration diagram of a powder processing apparatus. [Diagram 2] FIG. 2 is a schematic cross-sectional view of a discharge electrode portion. [Diagram 3] FIG. 4 is a bottom view of the lid of the discharge vessel as viewed from below. [Figure 4] 2 is a circuit configuration example relating to a power supply circuit of an AC power supply unit. [Diagram 5] FIG. 2 is a schematic cross-sectional view of an ignition electrode portion. [Figure 6] 4 is a schematic cross-sectional view of an observation window portion as viewed from the side. FIG. [Figure 7]FIG. 4 is an explanatory diagram showing a plasma discharge starting process of the discharge electrode portion. [Figure 8] FIG. 1 is an explanatory diagram showing a state in which a plasma region is formed by an arc discharge. [Figure 9] 1 shows a photographed image of the powder surface before treatment and a photographed image of the powder surface after treatment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments of the present invention will be described in detail. Note that the embodiments described below are preferred examples for carrying out the present invention, and therefore various technical limitations are imposed thereon, but the present invention is not limited to these embodiments unless otherwise specified in the following description to limit the invention.

[0014] Fig. 1 is a schematic diagram of a powder processing apparatus. The powder processing apparatus 1 is equipped with a discharge vessel 10 consisting of a highly airtight metallic vacuum chamber, and the discharge vessel 10 has a cylindrical tube portion 10a where powder processing is performed, a lid portion 10b attached to the top of the discharge vessel 10, and a tapered discharge portion 10c is integrally formed at the bottom of the tube portion 10a. The inner wall surface of the discharge portion 10c is inclined so that the diameter decreases toward the central axis of the tube portion 10a in the vertical direction.

[0015] The lid portion 10b is attached airtight to the cylindrical portion 10a, and a plurality of discharge electrode portions 20 are attached and arranged in the circumferential direction so as to penetrate the lid portion 10b. A powder supply portion 30 is connected to the lid portion 10b, and an emission tube 31 of the powder supply portion 30 is attached so as to penetrate the center of the lid portion 10b in the vertical direction. The lower end opening of the emission tube 31 serves as a powder emission port, and is adapted to emit the supplied powder into the discharge vessel 10.

[0016] A powder recovery section 40 is attached to the bottom of the discharge vessel 10, and a recovery pipe 41 of the powder recovery section 40 is connected so as to communicate with the lower end of the discharge section 10c. An ignition electrode section 50 is attached to the side of the discharge vessel 10 so as to penetrate the cylindrical section 10a, and an observation window section 60 for visually observing the inside of the discharge vessel 10 is also attached.

[0017] Gas supply unit 70 connects gas supply pipes to discharge electrode unit 20 and powder supply unit 30 to circulate an inert gas such as argon gas and supply it into discharge vessel 10. Gas supply unit 70 also supplies gas directly into discharge vessel 10 via the gas supply pipe, connects to recovery pipe 41 via the gas supply pipe to supply gas to powder recovery unit 40, and also supplies gas to observation window 60 via the gas supply pipe. A supply valve (not shown) is attached to each gas supply pipe to adjust the flow rate of the gas supplied.

[0018] Powder recovery section 40 is equipped with recovery container 42 connected to recovery pipe 41, and exhaust pump 80 is connected to recovery container 42 as a gas exhaust section via exhaust pipe 82 attached so as to communicate with the upper part, and exhaust filter 81 is attached to the pipeline between exhaust pump 80 and exhaust pipe 82. Gas is circulated from inside discharge vessel 10 to powder recovery section 40 by exhaust pump 80, so that the heat-treated powder can be efficiently recovered in recovery container 42.

[0019] Although omitted in FIG. 1, a coolant supply section is provided for supplying a coolant such as cooling water to parts that require cooling, such as the cylindrical section 10a, the discharge electrode section 20, and the observation window section 60, and as will be described later, conduits and piping for circulating the coolant are attached.

[0020] 2 is a schematic cross-sectional view of the discharge electrode unit. In the discharge electrode unit 20, conduits serving as an outer refrigerant flow path 22a, a gas flow path 22b and an inner refrigerant flow path 22c are formed concentrically inside an outer cylinder 22, and a conductive path 22c for power supply made of a conductor is disposed between the conduits, and an electrode body 21 is connected and fixed to the tip of the conductive path 22c.

[0021] A connector 23 is fixed to the rear end of the outer cylinder 22, and inside the connector 23, there are formed pipelines that respectively communicate with the outer refrigerant flow path 22a, the gas flow path 22b, and the inner refrigerant flow path 22c. Each pipeline is connected to a pipe (not shown) so that the gas G and the refrigerant W can flow through it. In addition, a power supply wiring L is connected to the connector 23, and is connected to the conductive path 22d by a conductor arranged between the pipelines so as to supply power to the electrode body 21.

[0022] The gas G that has flowed into the connector 23 flows through the gas flow passage 22b formed concentrically inside the outer cylinder 22, and is discharged along the axial direction of the electrode body 21 from a gas discharge port that opens annularly around the electrode body 22. The coolant W1 that has flowed into the connector 23 flows through the outer coolant flow passage 22a formed on the periphery, and the coolant W2 flows through the inner coolant flow passage 22c formed in the center to cool the center side and the periphery side of the electrode body 21, and then turns around and flows out of the connector 23 at the rear end.

[0023] A cylindrical sleeve 11 is attached to the cover portion 10b of the discharge vessel 10 by inserting it into a through mounting hole, and the outer cylinder 22 is inserted into the sleeve 11 so that its tip protrudes into the discharge vessel 10 and can move back and forth. One end of a vacuum bellows 24 is fixed to a flange portion exposed to the outside of the sleeve 11, and a support frame 25 is fixed to the other end of the vacuum bellows 24. The outer cylinder 22 passes through the vacuum bellows 24 and is fixed to the support frame 25 at its middle portion, so that the vacuum bellows 24 expands and contracts as the outer cylinder 22 moves back and forth. Therefore, the outer cylinder 22 can perform stable forward and backward movement while maintaining the reduced pressure inside the discharge vessel 10.

[0024] A moving mechanism 26 is attached to the support frame 25, and by driving the moving mechanism 26, the outer cylinder 22 moves forward and backward along the axial direction of the electrode body 21 via the support frame 25. The moving mechanism 26 has a linear guide 26c provided on a base 27 fixed to the cover portion 10b, and the support frame 25 is fixed to a support base 26b movably attached to the linear guide 26c. The support base 26b is moved on the linear guide 26c by a drive motor 26a. Therefore, by controlling the driving of the moving mechanism 26, the electrode body 21 arranged at the tip of the outer cylinder 22 can be moved forward and backward toward the central axis of the cylinder portion 10a of the discharge vessel 10, and positioned.

[0025] FIG. 3 is a bottom view of the lid body 10b as viewed from below. In this example, six discharge electrode sections 20a to 20f are attached to the lid body 10b penetrating therethrough, and are arranged at equal intervals, shifted by an angle of 60° in the circumferential direction of the discharge vessel 10. Each discharge electrode section is attached at an inclination downward so that the axial direction of the rod-shaped electrode body 21 attached to the tip forms an angle of 45° or more and less than 90° with respect to the horizontal direction. When attaching the discharge electrode section 20 to the discharge vessel 10 at such an inclination angle, it is difficult to attach it to the side wall of the cylindrical section 10a because of the steep angle, and the degree of freedom in design can be increased by attaching the discharge electrode section 20 to the lid body 10b. In addition, by configuring the lid body 10b to be detachably attached separately from the cylindrical section 10a, the discharge electrode section 20 can be removed together with the lid body 10b, and the inside of the discharge vessel 10 can be easily cleaned.

[0026] Each discharge electrode unit is connected to an AC power supply unit 90 via wiring connected to its rear end. Fig. 4 shows an example of the circuit configuration of a power supply circuit of the AC power supply unit 90. In this example, a three-phase to six-phase conversion transformer is used, which includes a transformer whose primary coil side is star-connected and whose secondary coil side has a center tap, and an output of an AC waveform having a phase difference of 60° is applied to each discharge electrode unit in sequence, so that an arc discharge is continuously generated between the electrode bodies.

[0027] 5 is a schematic cross-sectional view of the ignition electrode part. The ignition electrode part 50 is attached so as to penetrate the side wall surface of the cylindrical part 10a of the discharge vessel 10. A sleeve 52b is attached to a hole of a mounting base 52a fixed to the outer wall surface of the cylindrical part 10a, and a cylindrical holder 53 is inserted into the sleeve 52b so as to be movable forward and backward, with the tip part protruding into the inside of the discharge vessel 10.

[0028] A conductive path 53a for power supply and a flow path 53b for the coolant are formed concentrically inside the holder 53, and a rod-shaped ignition electrode 51 is connected and fixed to the tip of the conductive path 53a. The holder 53 is set so that its axial direction coincides with the axial direction of the ignition electrode 51 and intersects with the central axis of the discharge vessel 10 in an orthogonal direction. The axial direction of the ignition electrode 51 may be any direction that intersects with the central axis, and may, for example, be set to intersect with the central axis at an angle of 0° or more and less than 45° with respect to the horizontal direction.

[0029] A power supply connection part 54 is attached to the middle part of the holder 53 and is electrically connected to the conductive path 53a, and is connected to wiring supplied to the discharge electrode part 20 via the connection part 54. Then, as shown in Fig. 1, a switch circuit 57 is attached between the connection part 54 and the wiring, so that when ignition is performed, the switch circuit 57 is made conductive to apply an output similar to that of the discharge electrode part 20.

[0030] A connecting pipe 56 for the refrigerant is attached to the rear end of the holder 53, and has an inlet portion 56a through which the refrigerant W flows and an outlet portion 56b through which the refrigerant W flows out. The inlet portion 56a and the outlet portion 56b communicate with a flow path 53b to circulate inside the holder 53 for cooling.

[0031] A moving mechanism 55 is attached to the mounting base 52a so as to protrude outward and move along the axial direction of the holder 53. A guide rail 55c is fixed to a base 55b attached to the mounting base 52a, and a support base 55a fixed to the connection part 54 is movably attached to the guide rail 55c. A ball screw 55d rotatably supported on the base 55b at both ends of the support base 55a is screwed into the base 55b, and an operating mechanism 55e for rotating the ball screw 55d is attached to the rear end of the ball screw 55d. The operating mechanism 55e can be configured to be operated electrically or manually.

[0032] By operating the operating mechanism 55e and rotating the ball screw 55d, the support base 55a moves, and the holder 53 moves forward and backward in the axial direction together with the support base 55d. As a result, the ignition electrode 51 attached to the tip of the holder 53 moves forward and backward toward the central axis inside the discharge vessel 10.

[0033] 6 is a schematic cross-sectional view of the observation window seen from the side. The observation window 60 is equipped with a cylindrical support cylinder 61 that is attached to the side wall of the cylinder portion 10a of the discharge vessel 10 by penetrating through it. The axial direction of the support cylinder 61 is set in a direction perpendicular to the central axis of the discharge vessel 10, and the opening is positioned so as to face the plasma region.

[0034] A supply port 61a is formed in the portion of the support cylinder 61 that protrudes outward and is connected to a gas supply unit 70 via a gas supply pipe, into which gas G flows. The gas G that flows into the supply port 61a flows through the inner surface of the support cylinder 61 and is released into the discharge vessel 10, so that the powder being processed in the discharge vessel 10 is not scattered toward the observation window 60.

[0035] An annular holder 63 that holds a pair of transparent plates 62 is attached to the outer opening of the support cylinder 61. The transparent plates 62 are fixed in close contact with both sides of the holder 63 in a watertight manner, and a coolant W is introduced from an inlet 63a formed in the holder 63 to fill the inside. Therefore, the transparent plates 62 are constantly cooled by the coolant W, and the state of the plasma region inside the discharge vessel 10 can be directly observed from the outside through the transparent plates.

[0036] A support flange 64 is fixed to the side of the holder 63 opposite the support cylinder 61, and a visual protective plate 66 is attached to the support flange 64 via a rod-shaped spacing member 65, disposed opposite the transparent plate 62. This makes it possible to visually check the state of the plasma region inside the discharge vessel 10 through the protective plate 66.

[0037] The powder processing apparatus 1 is equipped with a control unit that controls the AC power supply unit 90 and the gas supply unit 70 so as to heat-treat the powder while it remains in its particulate form, and the control unit controls the output applied to each discharge electrode unit 20a-20f so as to generate an arc discharge in the area surrounded by the discharge electrode units 20a-20f to generate a plasma region along the vertical direction, and controls the flow rate so as to introduce powder at a predetermined flow rate from above into the generated plasma region.

[0038] When powder processing is performed using the powder processing device 1 described above, first, the exhaust pump 80 is operated to reduce the pressure inside the discharge vessel 10, and an inert gas such as argon gas is introduced into the discharge vessel 10 from the gas supply unit 70. Gas is also released from the discharge electrode unit 20 and the powder supply unit 30 to adjust the flow rate, and the inside of the discharge vessel 10 is also adjusted to a predetermined reduced pressure state. A coolant is supplied from the coolant supply unit and circulated to each part that requires cooling, setting it to a cooling state.

[0039] Next, application of a predetermined AC output to the discharge electrode portions 20a to 20f is started. Fig. 7 is an explanatory diagram showing the plasma discharge starting process of the discharge electrode portions. In this example, the ignition electrode portion 50 is arranged to face the discharge electrode portion 20d, while the discharge electrode portions 20a and 20d are arranged to face each other.

[0040] Then, the discharge electrode section 20d is advanced toward the central axis within the discharge vessel 10, and the ignition electrode section 50 is similarly advanced toward the central axis, so that the electrode body 21d of the discharge electrode section 20d and the ignition electrode body 51 are set in a state in which they are closely arranged on the central axis. The advancement of the ignition electrode section 50 can be performed while visually checking the position of the ignition electrode body 51 through the observation window.

[0041] By turning on the switch circuit 57 of the ignition electrode unit 50 and applying the same AC output as that of the discharge electrode unit 20, an arc discharge occurs between the electrode body 21d and the ignition electrode body 51. Then, while the arc discharge is occurring, the discharge electrode units are advanced to adjust the distance between them, thereby inducing an arc discharge between the electrode bodies of the discharge electrode units. After confirming through the observation window 60 that the arc discharge continues to occur between the discharge electrode units, the ignition electrode unit 50 is retracted to the standby position, and the switch circuit 57 is turned off.

[0042] In this case, it is possible to generate an arc discharge by arranging the electrode bodies of the discharge electrode units 20a and 20d close to each other without using the ignition electrode unit 50, but since the discharge electrode units are arranged at an angle of 45° or more with respect to the horizontal direction, the forward distance required to arrange the discharge electrode units close to each other becomes long, which is not practical. By using an ignition electrode unit that can be easily arranged close to the discharge electrode unit arranged at an angle, ignition processing can be performed quickly and reliably.

[0043] A plasma region is formed by the continuous generation of arc discharge between the electrode bodies of each discharge electrode section. Fig. 8 is an explanatory diagram showing a state in which a plasma region is formed by arc discharge. Gas is emitted from around the electrode bodies of the discharge electrode section in a direction inclined downward along the axial direction of the electrode bodies, and gas is emitted downward along the central axis of the discharge vessel from the emission tube 31 of the gas supply section, so that a plasma region D generated between the discharge electrode sections is formed to extend and expand in the vertical direction along the central axis.

[0044] The heating temperature of the plasma region D can be controlled by adjusting the current value applied to the discharge electrode, and it is possible to set a stable heating temperature region in the vertical direction. Therefore, the powder P introduced from the discharge tube 31 into the plasma region D falls on the gas flow along the heating temperature region formed in the vertical direction, and the time during which the powder P passes through the heating temperature region can be set by adjusting the flow rate of the gas for introducing the powder P. Therefore, by controlling the current value applied to the discharge electrode and the flow rate of the gas, it is possible to heat-treat the powder P while it is in a particulate form.

[0045] The heat-treated powder P' falls inside the discharge part 10c on the downward flow of the gas, and is introduced into the recovery pipe 41 connected to the bottom of the discharge part 10c. Since the inner wall surface of the discharge part 10c is tapered toward the bottom, the powder P' scattered by the heat treatment also falls toward the bottom and can be efficiently recovered.

[0046] Within the recovery pipe 41, a gas flow toward the recovery container 42 is formed by the exhaust pump 80 evacuating the inside of the recovery container 42 and supplying gas, and the powder P' introduced into the recovery pipe 41 is recovered into the recovery container 42 without stagnation.

[0047] In this way, the powder P supplied from the powder supply section 30 into the discharge vessel 10 passes through the plasma region that expands in the vertical direction, allowing the powder P to continue to be stably heated while still in particulate form, making it possible to efficiently recover the heat-treated powder P' and improve the recovery rate.

[0048] When the heat treatment is to be stopped, the supply of powder is stopped and the output to each discharge electrode is stopped. Then, the exhaust pump 80 is stopped to return the inside of the discharge vessel 10 to atmospheric pressure, and the supply from the coolant supply unit is stopped, after which the recovery vessel is removed and the heat-treated powder P' is taken out. Then, the lid 10b of the discharge vessel 10 is removed and the inside is cleaned, etc.

[0049] Powder processing was carried out using a multiphase AC arc plasma device with the configuration shown in Figure 1. The discharge electrode was attached to the lid of the discharge vessel, tilted downward at an angle of 60° to the horizontal. Commercially available granulated ultra-hard powder (WC-12%Co; manufactured by Nippon Steel Hardfacing Co., Ltd.) was used as the powder.

[0050] The powder treatment was carried out by setting the inside of the discharge vessel to a reduced pressure state (60 kPa to 90 kPa), setting the flow rate of the gas supplying the powder to 30 liters / min, and setting the current value applied to the discharge electrode to 100 A, 130 A, and 150 A. In the powder treatment, the particles constituting the powder were heated while still in particulate form, and it was not confirmed that the particles melted and deformed due to the heat treatment, or adhered to each other and merged.

[0051] FIG. 9 shows a photograph of the powder surface before treatment (FIG. 9(a)) and a photograph of the powder surface after treatment with a current value of 100A to 150A (FIG. 9(b)). It was confirmed that a large number of tiny voids were formed on the powder surface before treatment during the granulation process, but the voids disappeared in the powder after treatment, resulting in a dense surface. It was also confirmed that the WC portion contained in the powder was hardly melted by heating, and the formation of W2C, a brittle phase, was suppressed. When the bulk density of the powder after heat treatment was measured, the apparent density (g / cc) was improved by 1.4 to 1.6 times compared to before treatment, confirming that the quality of the powder was improved. [Explanation of symbols]

[0052] 1 powder processing device, 10 discharge vessel, 10a cylindrical portion, 10b lid portion, 10c discharge portion, 20a to 20f discharge electrode portion, 21a to 21f electrode body, 30 powder supply portion, 31 discharge tube, 40 powder recovery portion, 41 recovery tube, 42 recovery vessel, 50 ignition electrode portion, 52 ignition electrode body, 60 observation window portion, 70 gas supply portion, 80 exhaust pump, 81 exhaust filter, 90 AC power supply portion

Claims

1. a control unit that controls the AC power supply unit and the gas supply unit so as to generate an arc discharge in an area surrounded by the discharge electrode units to generate a plasma area along a vertical direction, and to input the powder into the plasma area from above at a predetermined flow rate so as to heat-treat the powder while it remains in a particulate form.

2. 2. The powder processing device according to claim 1, wherein the discharge electrode portion includes an electrode body attached to a tip portion and a gas discharge port that opens around the electrode body and discharges gas, and the powder supply portion includes a powder discharge port that opens downward toward a region surrounded by the discharge electrode portion and discharges powder together with the gas.

3. 3. The powder processing apparatus according to claim 1, further comprising an ignition electrode portion disposed opposite the specific discharge electrode portion and attached to the discharge vessel so as to be movable toward and away from the tip of the specific discharge electrode portion.

4. 3. The powder processing apparatus according to claim 1, further comprising: a powder recovery section attached to a lower portion of the discharge vessel for recovering the heat-treated powder; and a gas exhaust section for circulating gas from within the discharge vessel to the powder recovery section and exhausting the gas.

5. The powder processing apparatus according to claim 4 , wherein the discharge vessel has an inner wall surface tapered toward the powder recovery section.

6. 3. The powder processing apparatus according to claim 1, wherein an observation window portion is provided on a side of the discharge vessel and arranged to face the plasma region, and a supply port portion is formed in the observation window portion to allow the gas supplied from the gas supply portion to flow along an inner surface of the observation window portion.

7. A powder processing method in which a gas is released from openings at the tips of a plurality of discharge electrode sections arranged in a circumferential direction within a discharge vessel and inclined downward at an angle of 45° or more and less than 90° with respect to the horizontal, while a polyphase AC voltage is applied to generate an arc discharge in a region surrounded by the discharge electrode sections, thereby generating a plasma region along a vertical direction, powder is circumferentially generated in the plasma region together with the gas at a predetermined flow rate, and the powder is heat-processed within the plasma region while remaining in particulate form.

8. 8. The powder processing method according to claim 7, further comprising the steps of: applying a polyphase AC voltage to generate an arc discharge while an ignition electrode portion is brought close to a tip end of a specific discharge electrode portion; and inducing an arc discharge between the ignition electrode portion and another discharge electrode portion while moving the ignition electrode portion away from the specific discharge electrode portion, thereby generating the plasma region.

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