Method and apparatus for producing high purity spherical metallic powders at high production rates from one or two wires

Abstract

To provide a novel apparatus and method for producing metallic powders at significant rates from one or two wires.SOLUTION: The present application relates to a plasma atomization process and an apparatus for producing metallic powders from at least one wire / rod feedstock. In the process, an electrical arc is applied between the at least one wire / rod feedstock to melt. A plasma torch is employed to generate a supersonic plasma stream at an apex at which the electric arc is transferred to the at least one wire / rod feedstock to atomize the molten wire / rod feedstock into particles. A downstream cooling chamber solidifies the particles into metallic powders. An anti-satellite diffuser is employed to prevent recirculation of the powders in order to avoid satellite formation. In an apparatus where two wires are supplied, one wire acts as an anode and the other as a cathode.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 62 / 681,623, filed June 6, 2018, which is currently pending, and is incorporated herein by reference.

[0002] The present subject matter relates to advanced materials, and more particularly, to the production of metal powders for various applications, such as additive manufacturing for the aerospace and medical industries. [Background technology]

[0003] Plasma spraying typically uses a wire as the feedstock and a plasma source (also called a plasma torch) as the spraying agent to simultaneously melt and break down particles. Using a wire provides the stability required for a narrow plasma jet to be properly aimed at the wire, because the plasma jet must melt the wire and then atomize it in a single step. As is best known, this technology currently produces the finest, most spherical, and densest powders on the market. In other words, the yield of powders produced in the 0-106 micron range is very high, the sphericity is nearly perfect, and gas entrapment is minimized.

[0004] However, this technique has the main drawback of having a relatively low production rate compared to water and gas atomization due to the fact that plasma spraying is a very energetically inefficient process. Reported production rates for plasma spraying are 0.6-13 kg / h for Ti-6Al-4V. However, it is realistic to assume that operating near the upper limit would result in a coarser particle size distribution. For example, U.S. Patent No. 5,707,419, entitled "Method of Production of Metal and Ceramic Powders by Plasma Atomization," issued on January 13, 1998 in the name of Tsantrizos et al., reports a feed rate of 14.7 g / min or 0.882 kg / h for titanium, while U.S. Patent Application Publication No. 2017 / 49-A1, entitled "Process and Apparatus for Producing Powder Particles by Atomization of a Feed Material in the Form of an Elongated Member," issued on November 16, 2017 in the name of Boulos et al. as inventors, reports a feed rate of 1.7 kg / h for stainless steel.

[0005] All three current plasma spraying techniques use either a single centrally fed torch [see Reference 4] or three torches [see References 1, 2 and 3] that target one central wire. For the three torch technique, the heat transferred from the plasma plume to the wire is very low, on the order of 0.4%. The low heat transfer efficiency means that a large amount of plasma gas is required to maintain a certain metal feed rate, which imposes a lower limit on the gas-to-metal ratio, the standard process efficiency metric in spraying. The use of three torches also means that many electrodes wear out over time, which can become a source of contamination and increase operating costs. For the centrally fed torch, an induction-coupled plasma torch is used, for which power supplies are difficult to obtain commercially.

[0006] Wire arc spraying is a mature and reliable technology used in the field of thermal spraying to apply coatings on surfaces. It essentially consists of passing a high current through one or two wires and having an electric arc between the two wires or between a single wire and an electrode. Quality wire arc systems can operate at nearly 100% duty cycle with very high throughput (approximately 20-50 kg / h). Furthermore, the technology is energy efficient since the arc is in direct contact with the wire. However, the purpose of this technology is to produce coatings and not powders. Because this technology uses cold gases to atomize the spray, it produces very irregular and angular shapes, which are undesirable for most applications.

[0007] It is therefore desirable to provide an apparatus and method for producing metal powder from one or two wires at significant production rates while maintaining the quality provided by plasma spraying, i.e., fine, spherical, sufficiently dense powder. Summary of the Invention [Problem to be solved by the invention]

[0008] It is therefore desirable to provide a novel apparatus and method for producing metal powder from one or two wires at a significant rate.

[0009] The embodiments described herein, in one aspect, comprise: A thermal plasma torch, one or two continuously fed wires to be sprayed; an electric arc delivered to one or more wires to be sprayed; and a cooling process adapted to solidify the particles into a spherical powder.

[0010] In another aspect, the embodiments described herein provide an apparatus for producing metal powder from a wire feedstock, the apparatus comprising: a plasma torch; and a wire adapted to be fed to the plasma torch, the plasma torch adapted to atomize molten wire into particles, and an arc adapted to be formed between the wire and an electrode acting as a cathode.

[0011] Further, embodiments described herein may, in another aspect, providing a thermal plasma torch; Continuously supplying one or two wires to be sprayed; an electric arc adapted to be delivered to the one or more wires to produce particles; and providing cooling to solidify the particles into a spherical powder.

[0012] Furthermore, embodiments described herein provide, in another aspect, an apparatus for producing metal powder from a wire feedstock, the apparatus comprising: a plasma torch; and a wire adapted to be fed to the plasma torch, the plasma torch adapted to atomize molten wire into particles, and an arc adapted to be formed between the wire and an electrode acting as a cathode.

[0013] Furthermore, embodiments described herein provide, in another aspect, an apparatus for producing metal powder from wire feedstock, the apparatus comprising: a plasma torch; and at least one wire adapted to be fed into the apparatus, the plasma torch adapted to spray the molten wire into particles, the cooling chamber adapted to solidify the particles into a powder, and the wire adapted to function as a cathode in the plasma torch.

[0014] Additionally, embodiments described herein provide, in another aspect, an apparatus for producing metal powder from wire feedstock, the apparatus comprising: a plasma torch; and at least one pair of wires adapted to be fed into the apparatus, the plasma torch adapted to spray the molten wire into particles, one of the wires adapted to function as an anode and the other wire adapted to function as a cathode.

[0015] Furthermore, embodiments described herein provide, in another aspect, an apparatus for producing metal powder from a wire feedstock, the apparatus comprising: a plasma torch; and a wire adapted to be fed to the plasma torch, the plasma torch adapted to atomize molten wire into particles, and an arc adapted to be formed between the wire and an electrode acting as a cathode.

[0016] Furthermore, embodiments described herein provide, in another aspect, an apparatus for producing metal powder from wire feedstock, the apparatus comprising a plasma torch and at least one wire adapted to be fed to the plasma torch, the plasma torch adapted to atomize the molten wire into particles, the apparatus adapted to be cooled by a gas thereby heating the gas, the gas so heated being adapted to be used as a plasma gas.

[0017] Further, embodiments described herein may, in another aspect, providing a thermal plasma torch; continuously supplying one or two wires to be sprayed, thereby generating atomized metal droplets therefrom; and passing the droplets through an anti-satellite diffuser adapted to prevent recirculation of fine powder and thus satellite formation.

[0018] Further, embodiments described herein may, in another aspect, providing a thermal plasma torch; Providing one or two wires to be sprayed; providing at least two power sources in parallel to control an arc between the two wires or between the single wire and one electrode of the plasma torch, thereby producing particles.

[0019] For a better understanding of the embodiments described herein, and to show more clearly how they may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which at least one exemplary embodiment is shown. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a side cross-sectional view of an apparatus for producing metal powder from a pair of wires using twin-wire arc plasma spraying according to an exemplary embodiment. [Diagram 2] FIG. 1 is a side cross-sectional view of an apparatus for producing metal powder from a pair of wires using twin-wire arc plasma spraying according to an exemplary embodiment. [Diagram 3] FIG. 3 is a schematic elevational view of a system for producing metal powder using the apparatus shown in FIGS. 1 and 2 according to an exemplary embodiment, including that of FIGS. [Figure 4] FIG. 3 is a schematic diagram of an electrical configuration used in accordance with exemplary embodiments including those of FIGS. 1 and 2. [Diagram 5] 13 illustrates an example of an electrical trendline for an embodiment of the present disclosure in operation. [Figure 6] FIG. 3 is a SEM image at 100x magnification of 45-106 μm Ti64 Grade 23 powder produced by means of the embodiment of FIGS. 1 and 2; [Figure 7] FIG. 3 is a SEM image at 100x magnification of 20-120 zirconium powder produced by means of the embodiment of FIGS. 1 and 2; [Figure 8]1 shows a representative laser diffraction powder size distribution graph for raw powder produced by means of at least one embodiment disclosed herein. [Figure 9] 1 is a schematic cross-sectional side view of an apparatus for producing metal powder from a single wire using a plasma torch capable of transmitting an arc with the single wire, according to an exemplary embodiment; [Figure 10] 1 is a schematic cross-sectional side view of an apparatus for producing metal powder from a single wire using a center-fed plasma torch in accordance with an exemplary embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The approach disclosed herein provides a method and apparatus for producing metal powders by combining features of the plasma spraying and wire arc spraying techniques described above, including using some of the concepts of the wire arc spraying technique and adapting it to make it suitable for producing high purity spherical powders. More specifically, the gas jet is replaced by a plasma source and a molten wire is sprayed into a cooling chamber, as in the atomization process.

[0022] One important consideration is the quality of the powder. The wire arc was not developed for high quality powder production and must therefore be adapted and adjusted to the powder quality. The present disclosure includes a control strategy to improve the stability of the melting process, which is described in more detail below.

[0023] A plasma source (such as one or more plasma torches or an electric arc) delivers a plasma stream that can be accelerated to supersonic speeds before or after impinging on the molten stream with high momentum.

[0024] In this embodiment, the supersonic plasma jet source is produced via an arc plasma torch, since it is widely available. However, many other methods can be used to achieve the same supersonic plasma jet. For example, any thermal plasma source, such as an inductively coupled plasma source and a microwave plasma source, can be used as well.

[0025] Example 1: Twin Wire Arc Plasma Spraying (Main Embodiment) The details of this embodiment will be described below.

[0026] The advantages of using this embodiment over the known technology (Reference 2) are shown in Table 1, which shows clear advantages in favor of using the subject matter of the present invention as opposed to the technology of Reference 2.

[0027] [Table 1]

[0028] The recommended operating conditions of the main embodiment are disclosed in Table 2 for two materials: Ti64 Grade 23 and Zirconium.

[0029] [Table 2]

[0030] The performance of two products produced via the main embodiment is disclosed in Table 3, the two products are TA-015-EK-01 and ZH-006-FQ-01, which correspond to Ti64 20-63μm and Zr 20-120μm, respectively.

[0031] [Table 3]

[0032] Figure 1 details the specific components that make up Apparatus A. These include a high flow plasma torch 501 and an integrated anode supersonic nozzle 505 that emits a spray jet onto a pair of wires 502 fed toward an apex 508 where an electric arc is transferred from one wire to the other. This current provides the energy necessary for the continuous melting of a continuously fed electrically conductive feedstock. The current is delivered to the wires 502 by a contact tip 509 made of a high electrical conductivity alloy, e.g., copper zirconium, that has good wear resistance at high temperatures.

[0033] The ceramic tip 510 provides electrical insulation for the water-cooled contactor 514 from the body of the reactor through the torch's supersonic nozzle 505 and through the gas sheath nozzle 513. The high heat emitted by the plasma torch 501 and the transferred arc require the contactor to be water-cooled, while the contact tip itself is a replaceable consumable. Thus, water enters the rear of the contactor manifold 515 at 503 and is directed towards the tip where it returns upwards again and exits through outlet 504. Power is supplied to the transferred arc system via the manifold through lug mount 511.

[0034] FIG. 2 shows a vertical cross-sectional view of apparatus A, where a high flow plasma torch emits an atomizing jet through a supersonic nozzle 605 at the wire apex 608. Here, sheath gas is injected into the reactor at 602, filling the cavity surrounding the nozzle of the torch and the water-cooled contactor 607. This sheath gas is emitted into the reactor surrounding the electric arc between the wires through a sheath gas nozzle 606. This sheath gas serves multiple purposes, such as preventing backflow of powder and hot gases, as well as helping to maintain the arc within the supersonic plume. The mixed gas stream and molten atomized metal droplets are then projected at high velocity into the settling chamber of the reactor through an anti-satellite diffuser 610. The recirculation zone around the high velocity jet, where fine powder can accumulate in suspension, is the primary cause of satellites in plasma atomized powder, as new droplets are projected through the cloud of fines, thus welding the fines to the surface. The diffuser 610 eliminates most of this generation, thus greatly reducing satellite formation. The torch receiver 611 is water cooled as is the reactor jacket, with water entering through an inlet 603 at the bottom and an outlet 604 at the top.

[0035] FIG. 3 shows a schematic of a system S adapted to produce metal powder and embodying any one of the apparatuses A, A' and A'' of FIGS. 1-2, 9 and 10, respectively. More specifically, the system S includes a dual-wire or single-wire plasma-based atomization apparatus A, A' or A''. The system S is shown specifically in its twin-wire arc configuration A with a centrally located high-flow plasma torch 301 and two servo-driven wire feeders 302. The atomization zone 303 contains the transferred arc between one or two wires, sheath gas and plasma torch flow and is directed into the reactor by an anti-satellite diffuser 304. The reactor comprises a settling chamber 305 where spheroidization and solidification occur, and a water-cooled jacket 306 to maintain a constant cooling rate in the chamber 305 for the powder. The powder is then conveyed via a pneumatic conveyor 307 to a cyclone separator 308 where the bulk powder settles into a collection canister 309. A valve 310 is used to isolate the canister 309 for collection during continuous operation. The argon is then exhausted from the system through a filtration unit 311 for powders that are too fine to settle in the cyclone separator 308.

[0036] In this embodiment, wire 502 (FIG. 1), wire 110 (FIG. 10) and wire 405 (FIG. 9) can be made of a variety of conductive materials, such as titanium, zirconium, copper, tin, aluminum, tungsten, carbon steel, stainless steel, and the like, and alloys thereof.

[0037] To ensure the stability of a wire arc system for atomization, the system needs to control two of three parameters: voltage, current and feed rate. These three parameters need to reach a steady state in equilibrium to be considered in continuous operation. At steady state, the distance between the wires, the length of the arc and the power will be constant. To reach this steady state, several configurations can be used, such as:

[0038] Fixed wire speed, one power supply in voltage control mode, one power supply in current control mode (primary embodiment);

[0039] Fixed wire speed, one or more voltage controlled power supplies. This configuration is functional, but the current is highly unstable, adversely affecting particle size distribution and product consistency. Furthermore, there are high demands on both power supplies; current controlled power supplies, variable wire speed.

[0040] This configuration has not yet been tested, but in theory it could work.

[0041] A fixed wire speed, current / voltage controlled hybrid power supply has been found to be most suitable for this application. Figure 4 conceptually illustrates how the main embodiment was operated to obtain the results shown in this disclosure.

[0042] Using a servo motor it is possible to have a very accurate and constant feed rate.

[0043] Using two power supplies in parallel, one in voltage control mode and the other in current control mode, is the key to achieving a stable configuration. Since the two supplies are in parallel, the voltage controlled supply forces both supplies to fix the same voltage. This removes another variable. To add another layer of stability, the other supply is set in current control mode with a relatively high current setting (about 2 / 3 of the total current needed), which helps create a current baseline.

[0044] The only variable in the process is the fraction of the total current that must be varied to keep the other parameters constant (degrees of freedom). Therefore, the voltage controlled power supply provides an additional current that is variable to make up for what is lost to the current already provided by the current controlled power supply to melt the proper amount of metal, and therefore the system remains in steady state.

[0045] For example, assume that 20 kW is required to melt a certain metal at a certain feed rate, and assume that this feed rate remains constant, if the voltage is fixed at 30 V by the voltage controlled power supply, a total of 667 A must be supplied by the power supply. If the current controlled power supply is set to 400 A, the voltage controlled power supply will fluctuate around 267 A with almost no ripple. This residual variation is necessary to keep the system in a steady state by compensating for all other sources of variability in the process such as wire diameter changes, argon flow rate variations, arc length variability, arc restrike patterns, mechanical vibrations of the wire, wire feed speed micro-variations, etc.

[0046] Figure 5 shows the electrical trendlines recorded for the main embodiment during operation using the electrical control strategy proposed herein. In summary, it shows that all variables are very stable, except for the current of the voltage controlled power supply, for the reasons discussed above.

[0047] Such stable operation makes it possible to produce highly spherical powders, as shown in Figure 5, and Figures 6 and 7, for Ti64 and zirconium, respectively.

[0048] FIG. 8 shows a typical particle size distribution curve of a powder produced using the main embodiment with the electrical control strategy described herein.

[0049] Although the current control presented herein is specifically mentioned and tested for the main embodiment, the same control strategies will apply to the other embodiments presented.

[0050] Example 2: Single-wire arc plasma spraying In a second embodiment shown in FIG. 9, an apparatus A' for producing metal powder from a conductive wire feedstock is also disclosed, in which a wire 405 is fed centrally along the arrow 409 in front of a transferred plasma torch 401 with a supersonic nozzle 411, and an arc 403 is formed between the wire 405 and one electrode 402. By inserting the conductive wire 405 through a wire guide 407 in front of the plasma torch 401, the wire 405 itself can be melted very efficiently through the transferred arc. The remaining energy is then used to warm an inert gas (e.g. argon) fed through a preheated gas channel 404 to a plasma state, and the gas is then accelerated through the supersonic nozzle 411. This acceleration of the carrier gas further atomizes the metal droplets by shredding them. The particles then solidify into small spherical particles in a cooling chamber (as illustrated in FIG. 3), for example filled with an inert gas (e.g. argon). Reference number 408 denotes a plasma plume.

[0051] Example 3: Centrally fed single wire arc plasma spraying In a third embodiment shown in FIG. 10, an apparatus A″ for producing metal powder from a conductive wire feedstock is also disclosed, in which a wire 110 is fed centrally along the arrow 111 into a plasma torch 112, and an arc 128 is formed between the wire 110, which acts as a cathode, and one electrode (see anode 114). By inserting the conductive wire 110 through the wire guide 116 of the plasma torch 112, the wire 110 itself can be melted very efficiently through the transmitted arc. This method is selected as having a scalable capacity, in the sense that the wire can be most easily replaced with rods or billets up to 2.5 inches in diameter. The wire guide 116 can double as the ignition cathode. The remaining energy is then used to warm an inert gas (e.g., argon) fed through a preheated gas channel 118 to a plasma state, and the gas is then accelerated through a supersonic nozzle 120. This acceleration of the carrier gas further atomizes the metal droplets by chopping them. The particles then solidify into small spherical particles, for example in a cooling chamber (as illustrated in FIG. 3) filled with an inert gas (eg, argon). Reference numeral 122 denotes the plasma plume.

[0052] Embodiments described herein provide, in one aspect, an apparatus for producing metal powder from wire feedstock, the apparatus comprising a plasma torch and one or two wires adapted to be fed into the apparatus, the plasma torch adapted to spray the molten wire into particles, the cooling chamber adapted to solidify the particles into a powder, and the wire adapted to function as a cathode in the plasma torch.

[0053] In another aspect, the embodiments described herein provide an apparatus for producing metal powder from wire feedstock, the apparatus comprising a plasma torch and a pair of wires adapted to be fed into the apparatus, the plasma torch adapted to spray the molten wire into particles, one of the wires adapted to function as an anode and the other wire adapted to function as a cathode.

[0054] Additionally, embodiments include electronic control strategies that enable smooth and stable operation of the embodiments.

[0055] Furthermore, embodiments described herein provide, in another aspect, an apparatus for producing metal powder from a wire feedstock, the apparatus comprising a plasma torch and a wire adapted to be fed into the apparatus, the plasma torch adapted to atomize the molten wire into particles, and an arc adapted to be formed between the wire acting as a cathode and an electrode of the torch.

[0056] Finally, embodiments described herein provide, in another aspect, an apparatus for producing metal powder from a wire feedstock, the apparatus comprising a plasma torch and at least one wire adapted to be fed centrally into the interior of the plasma torch, the plasma torch adapted to atomize the molten wire into particles, and an arc adapted to be formed between the wire acting as a cathode and an electrode within the torch.

[0057] While the above description provides examples of embodiments, it will be understood that certain features and / or functions of the described embodiments are susceptible to modification without departing from the spirit and principles of operation of the described embodiments. Thus, what has been described above is intended to be illustrative and non-limiting of embodiments, and it will be appreciated by those skilled in the art that other variations and modifications may be made without departing from the scope of the embodiments as defined in the claims appended hereto.

[0058] [References] TIFF2025010572000005.tif69170

Claims

1. 1. A plasma spray process comprising: - a thermal plasma torch; one or two continuously fed wires to be sprayed; an electric arc transmitted to one or more wires to be sprayed; a cooling process adapted to consolidate the particles into a spherical powder; The plasma spray process includes:

2. The process of claim 1 , wherein the plasma torch comprises a supersonic nozzle.

3. 2. The process of claim 1, wherein an electric arc is delivered to the wire at an apex within the supersonic flow of the plasma torch.

4. A process according to any one of claims 1 to 3, wherein the atomised metal droplets pass through an anti-satellite diffuser adapted to prevent recirculation of fine powder and thus satellite formation.

5. 10. The process of claim 1, wherein two or more power sources are used in parallel to control the arc between the two wires or between the single wire and one electrode of the torch.

6. The process of any one of claims 1 to 5, wherein at least one power supply for the wire arc is voltage controlled.

7. The process of any one of claims 1 to 6, wherein at least one power supply for the wire arc is current controlled.

8. The process of any one of claims 1 to 7, wherein the parallel power supplies are used simultaneously in a combination of voltage control mode and current control mode.

9. 1. An apparatus for producing metal powder from a wire feedstock, comprising: a plasma torch; and a wire adapted to be fed to the plasma torch, the plasma torch adapted to atomize the molten wire into particles, and an arc adapted to be formed between the wire and an electrode acting as a cathode.

10. The apparatus of claim 9 , wherein the wire is fed into the center of the plasma torch.

11. 11. Apparatus according to claim 9 or 10, wherein a supersonic nozzle is provided, and the electric arc is generated within the supersonic nozzle.

12. The apparatus of any one of claims 9 to 11, wherein the wire feedstock is replaced by a rod or billet having a diameter of 0.25 to 2.5 inches.

13. An apparatus according to any one of claims 9 to 12, wherein a cooling chamber is provided downstream of the plasma torch for consolidating the particles into a spherical powder.

14. 1. A plasma spray process comprising: providing a thermal plasma torch; - continuously supplying one or two wires to be sprayed; an electric arc adapted to be transmitted to said one or more wires to produce particles; - providing cooling to solidify the particles into a spherical powder.

15. The process of claim 14 , wherein the plasma torch comprises a supersonic nozzle.

16. 15. The process of claim 14, wherein an electric arc is adapted to be delivered to the wire at an apex within the supersonic flow of the plasma torch.

17. A process according to any one of claims 14 to 16, wherein the atomised metal droplets pass through an anti-satellite diffuser adapted to prevent recirculation of fine powder and thus satellite formation.

18. 15. The process of claim 14, wherein at least two power sources are used in parallel to control the arc between the two wires or between the single wire and one electrode of the plasma torch.

19. The process of any one of claims 14 to 18, wherein at least one power supply for the wire arc is voltage controlled.

20. The process of any one of claims 14 to 19, wherein at least one power supply for the wire arc is current controlled.

21. The process of any one of claims 14 to 20, wherein the parallel power supplies are used simultaneously in a combination of voltage control mode and current control mode.

22. 1. An apparatus for producing metal powder from a wire feedstock, comprising: a plasma torch; and a wire adapted to be fed into the plasma torch, the plasma torch adapted to atomize the molten wire into particles, and an arc adapted to be formed between the wire and an electrode acting as a cathode.

23. 23. The apparatus of claim 22, wherein the wire is fed into the center of the plasma torch.

24. 24. Apparatus according to claim 22 or 23, wherein a supersonic nozzle is provided, and wherein the electric arc is generated within the supersonic nozzle.

25. The apparatus of any one of claims 22 to 24, wherein the wire feedstock is in the form of a rod or billet having a diameter of 0.25 to 2.5 inches.

26. An apparatus according to any one of claims 22 to 25, wherein a cooling chamber is provided downstream of the plasma torch for consolidating the particles into a spherical powder.

27. 1. An apparatus for producing metal powder from a wire feedstock, comprising: a plasma torch; and at least one wire adapted to be fed into the apparatus, the plasma torch adapted to spray molten wire into particles; a cooling chamber adapted to solidify the particles into a powder; and the wire adapted to function as a cathode in the plasma torch.

28. 28. The apparatus of claim 27, wherein the plasma stream delivered by the plasma torch is adapted to be supersonically accelerated into a supersonic jet.

29. 29. Apparatus according to claim 27 or 28, wherein a supersonic nozzle is provided, the wire being adapted to be fed into the supersonic nozzle either before or after the throat of the supersonic nozzle.

30. 1. An apparatus for producing metal powder from wire feedstock, comprising: a plasma torch; and at least one pair of wires adapted to be fed into the apparatus, the plasma torch adapted to spray molten wire into particles, one of the wires adapted to function as an anode and the other wire adapted to function as a cathode.

31. 31. The apparatus of claim 30, wherein a cooling chamber is provided downstream of the plasma torch for consolidating the particles into a powder.

32. 32. The apparatus of claim 30 or 31, wherein the plasma stream delivered by the plasma torch is adapted to be supersonically accelerated into a supersonic jet.

33. 33. The apparatus of claim 32, wherein a supersonic nozzle is provided, the wire being adapted to be fed into the supersonic nozzle either before or after a throat of the supersonic nozzle.

34. 34. Apparatus according to any one of claims 30 to 33, wherein a power source is provided and adapted to force an electric current through the wires such that an electric arc is generated between the two wires.

35. 34. The apparatus of claim 33, wherein a power source is provided and adapted to force an electric current through the wires such that an electric arc is generated between the two wires and within the supersonic nozzle.

36. 1. An apparatus for producing metal powder from a wire feedstock, comprising: a plasma torch; and a wire adapted to be fed into the plasma torch, the plasma torch adapted to atomize the molten wire into particles, and an arc adapted to be formed between the wire and an electrode acting as a cathode.

37. 37. The apparatus of claim 36, wherein the wire is fed into the center of the plasma torch.

38. 38. Apparatus according to claim 36 or 37, wherein a wire guide is provided for the wire, whereby by inserting the wire through the wire guide, the wire can be efficiently melted via a transmitted arc.

39. 40. The apparatus of claim 38, wherein the wire guide is adapted to double as an ignition cathode.

40. Apparatus according to any one of claims 36 to 39, wherein a supersonic nozzle is provided, and wherein the electric arc is generated within the supersonic nozzle.

41. An apparatus according to any one of claims 36 to 40, wherein a cooling chamber is provided downstream of the plasma torch for consolidating the particles into a powder.

42. 1. An apparatus for producing metal powder from a wire feedstock, comprising: a plasma torch; and at least one wire adapted to be fed to said plasma torch, said plasma torch adapted to atomize molten wire into particles, said apparatus adapted to be cooled by a gas thereby heating said gas, said gas so heated being adapted to be used as plasma gas.

43. 43. The apparatus of claim 42, wherein the gas comprises an inert gas, such as argon.

44. 44. Apparatus according to claim 42 or 43, wherein a gas channel is provided for supplying the gas to the plasma torch.

45. Apparatus according to any one of claims 42 to 44, wherein a supersonic nozzle is provided, the gas being accelerated through the supersonic nozzle and adapted to shred the particles.

46. An apparatus according to any one of claims 42 to 45, wherein a cooling chamber is provided downstream of the plasma torch for consolidating the particles into a powder.

47. 44. Apparatus according to claim 42 or 43, wherein a gas channel is provided, the gas being adapted to be heated prior to contacting an electric arc provided at the tip of the wire.

48. 47. The apparatus of any one of claims 27, 31, 41 and 46, wherein the cooling chamber contains an inert gas, such as argon.

49. 1. A plasma spray process comprising: providing a thermal plasma torch; - continuously supplying one or two wires to be sprayed, thereby generating atomized metal droplets therefrom; - passing said droplets through an anti-satellite diffuser adapted to prevent recirculation of fine powder and thus satellite formation; The plasma spray process includes:

50. 1. A plasma spray process comprising: providing a thermal plasma torch; Providing one or two wires to be sprayed; providing at least two power sources in parallel to control an arc between the two wires or between the single wire and one electrode of the plasma torch, thereby producing particles; The plasma spray process includes:

51. 51. The process of claim 50, wherein at least two power sources are used in parallel to control the arc between the two wires or between the single wire and one electrode of the plasma torch.

52. 52. The process of claim 50 or 51, wherein at least one power supply for the wire arc is voltage controlled.

53. The process of any one of claims 50 to 52, wherein at least one power supply for the wire arc is current controlled.

54. A process according to any one of claims 50 to 53, wherein the parallel power supplies are used simultaneously in a combination of voltage control mode and current control mode.

Images