Method and apparatus for producing fine and spherical particles from a metal bar using plasma torches

Abstract

A method and a system to produce fine and spherical particles by integrating plasma torch technology with an electrode induction melting process. The method comprises integrating a multiple plasma torch system with an electrode induction melting system atomizer; and subjecting liquid atomized droplets to a superheat temperature and energy by plasma plumes generated by plasma torches of the multiple plasma torch system to induce the particles' spheroid ization and refinement. The system comprises an induction melting system atomizer coupled with plasma torches, a feedstock material supply system configured to supply bars to the induction melting system atomizer, and a control system for regulating the plasma torches and feedstock flow of the bars to the induction melting system.

Description

METHOD AND SYSTEM FOR PRODUCING FINE AND SPHERICAL PARTICLES FROM A METAL BAR USING PLASMA TORCHESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to or benefit of United States provisional patent application No. 63 / 669,079, filed July 9, 2024, titled “Method and Apparatus for Producing Fine and Spherical Particles from a Metal Bar Using Plasma Torches”, which is incorporated herein by reference in its entirety.FIELD

[0002] The present disclosure relates to the production of metal powders and more specifically to production of fine and spherical particles using plasma torches.BACKGROUND

[0003] Metal powders are crucial for three-dimensional (3D) printing, enabling intricate metal part production with precision. Engineered for specific properties, metal powders facilitate layer-by-layer fusion in processes like laser sintering. This method allows for complex geometries, enhancing design flexibility and customization. Additionally, metal additive manufacturing reduces material waste and lead time compared to traditional methods. Ongoing research aims to optimize metal powders for broader industrial applications. Hence, the demand for high-quality metallic powders has been increasing lately, especially for 3D applications. The quality term includes particle sphericity with minimum satellites. The sphericity is the most important criterion in terms of powder quality. Satellite formation is another criterion that negatively affects the powder's performance in 3D printing, resulting in PSD and yield shifts. The mentioned criteria become more important in aerospace and medical applications when reactive metals and alloys such as Ti, TI64, Zr, etc., or high melting point materials are used as powder. Such reactive materials are difficult to melt and atomize since they react with crucible materials like graphite or ceramic creating carbides and oxides then introducedin the final powder product or there is no crucible resisting the superheat temperature in addition to their high melting point.

[0004] Various methods for gas atomization and producing metal powders exist. However, all of the known methods have numerous limitations and have challenges, and a new method for producing metal powders is needed.SUMMARY

[0005] A method and a system to produce fine and spherical particles by integrating plasma torch technology with an electrode induction melting process are disclosed herein. Plasma torches supply substantial kinetic energy for atomizing molten metals or alloys, while electrode induction melting delivers the necessary heat for material melting. This integration optimizes particle formation, yielding particles with enhanced properties tailored for various industrial applications. Furthermore, the continuous operation capability of the system ensures uninterrupted particle production, improving efficiency and scalability in the industry.

[0006] According to one aspect of the disclosed technology, there is provided a method for producing fine and spherical particles, the method comprising: integrating a multiple plasma torch system with an electrode induction melting system atomizer; and subjecting liquid atomized droplets to a superheat temperature and energy by plasma plumes generated by plasma torches of the multiple plasma torch system to induce the particles' spheroidization and refinement.

[0007] The method may further comprise atomizing a feedstock material provided in a form of a bar (atomizing a metal bar) while moving the bar downwards in an induction coil by using the electrode induction melting system atomizer to produce the liquid droplets prior to subjecting the liquid droplets to the superheat temperature. Prior to atomizing the feedstock material of each bar of the feedstock material, the bar may be grabbed from a bar stocking by a robot arm automatically and positioned in a bar holder to a melting position, the bar stocking and the induction coil being located in a melting chamber with the same vacuum level. The method may further comprise transferring / moving the bar by the bar holder toward the induction coil at a constantvelocity after the plasma torches of the multiple plasma torch system are ignited. The method may further comprise rotating the bar with a rotation velocity of between 1 and 40 revolutions per minute (RPM) while moving the bar downwards toward the induction coil.

[0008] The method may further comprise: after a length of the bar reaches a predefined bar length, moving a bar remnant of the bar upward and transferring the bar remnant to a consumed bars container by a robot arm, and loading another bar of feed material automatically to the melting position to produce the atomized droplets. The method may further comprise, while subjecting liquid atomized droplets to a superheat temperature, cooling the plasma torches and walls of a reactor by a water-cooling unit. The method may further comprise supplying an atomization gas through a gas supply system, wherein the atomization gas is at least one of argon, nitrogen, helium, and hydrogen.

[0009] The power of each plasma torch Is between 100 kilowatts (kW) and 200 kW. The method may further comprise producing between 150 and 300 pounds per square inch (psi) gas pressure and a temperature range of between 3000 and 4000 degrees Celsius (°C) at a plasma torch exit of each plasma torch when the bar is made of a high melting point alloy. The method may further comprise producing between 150 and 200 psi gas pressure and a temperature range of between 2000°C and 3000 °C at a plasma torch exit of each plasma torch for the bar made of a low melting point alloy. In at least one embodiment, the multiple plasma torch system may comprises at least three plasma torches. The plasma torches may be positioned around the electrode induction melting system atomizer. The method may further comprise collecting the powder into a hopper.

[0010] According to another aspect of the disclosed technology, there is provided a system for producing fine and spherical particles, the system comprising: an induction melting system atomizer coupled with plasma torches, both located in a melting chamber, a feedstock material supply system (bar-loading system) located in the melting chamber and having the same vacuum as the induction melting system, the feedstock material supply system being configured to supply bars to the induction melting system atomizer, and a control system for regulating the plasma torches and feedstock flow of the bars to the induction melting system.

[0011] In at least one embodiment, the system further comprises a bar holder configured to hold the bar, the bar holder being attached to a holder arm configured to move the bar holder downwards with the bar to move the bar into an induction coil at a constant velocity. In at least one embodiment, the bar holder is configured to rotate the bar with a rotation velocity of between 1 and 40 revolutions per minute (RPM) while moving the bar downwards. Each one of the plasma torches may be covered by a magnetic shield. The magnetic shields may have a thickness of between 0.05 and 2 millimeters (mm) cover the whole body of the plasma torches. The high-enthalpy plasma torches may be positioned at between 30 degrees and 45 degrees with respect to an axis of the bar. The high-enthalpy plasma torches may be positioned at 30 degrees with respect to an axis of the bar.

[0012] According to a further aspect of the disclosed technology, there is provided a method for producing fine and spherical particles, the method comprising: melting a bar made of metal by an induction coil surrounding a lowest section of the bar to obtain molten droplets, the bar moving downward; atomizing molten droplets by plasma plumes; and disintegrating the liquid drops produced in powders. The method may further comprise sending the powders to an air classifier system or a cyclone system. The method may further comprise collecting the powders in a hopper connected to the end of the atomization reactor. The method may further comprise, prior to melting the bar, grabbing the bar from a bar stocking with a robot arm automatically and positioning the bar in a bar holder to a melting position, the bar stocking and the induction coil being located in a melting chamber with the same vacuum level. The method may further comprise moving the bar by a bar holder toward the induction coil at a constant velocity after the plasma torches of the multiple plasma torch system are ignited. The method may further comprise rotating the bar with a rotation velocity of between 1 and 40 revolutions per minute (RPM) while moving the bar downwards toward the induction coil.

[0013] The method may further comprise: after a length of the bar reaches a predefined bar length, moving a bar remnant of the bar upward and transferring the bar remnant to a consumed bars container by a robot arm, and loading another bar of feed material automatically to the melting position to produce the atomized droplets. The method may further comprise, while subjecting liquid atomized droplets to a superheattemperature, cooling the plasma torches and walls of a reactor by a water-cooling unit. The method may further comprise supplying an atomization gas through a gas supply system, wherein the atomization gas is at least one of argon, nitrogen, helium, and hydrogen. The power of each plasma torch may be between 100 kilowatts (kW) and 200 kW. The method may further comprise producing between 150 and 300 psi gas pressure and a temperature range of between 3000 and 4000 °C at a plasma torch exit of each plasma torch when the bar is made of a high melting point alloy. The method may further comprise producing between 150 and 200 psi gas pressure and a temperature range of between 2000°C and 3000 °C at a plasma torch exit of each plasma torch for the bar made of a low melting point alloy.

[0014] The method and the system to produce fine and spherical particles by integrating plasma torch technology with an electrode induction melting process are described herein. In at least one embodiment, the method comprises integrating a multiple plasma torch system with an electrode induction melting system atomizer; and subjecting liquid atomized droplets to a superheat temperature and energy by plasma plumes generated by plasma torches of the multiple plasma torch system to induce the particles' spheroidization and refinement. In at least one embodiment, the system comprises an induction melting system atomizer coupled with plasma torches, a feedstock material supply system configured to supply bars to the induction melting system atomizer, and a control system for regulating the plasma torches and feedstock flow of the bars to the induction melting system.

[0015] The embodiments described herein provide in one aspect a method for producing fine and spherical particles, comprising: integrating a multiple plasma torch system with an electrode induction melting system atomizer; and subjecting atomized droplets to a superheat temperature by plasma plumes created by multiple plasma torches to induce the particles' spheroidization and refinement. Also, the embodiments described herein provide in another aspect a method wherein the multiple plasma torch system comprises at least three plasma torches. Furthermore, the embodiments described herein provide in another aspect a method for producing fine and spherical particles continuously and without interruption: whereby a new bar of feed material is loaded automatically to a melting position and a previous bar that has been consumed bya previous atomization run is transferred to a consumed bar bin. Furthermore, the embodiments described herein provide in another aspect a method wherein an electromagnetic shield is used to avoid the effect of the induction coil electromagnetic field on the plasma torches' internal arc and plumes. Furthermore, the embodiments described herein provide in another aspect a method wherein the plasma torches are positioned around the electrode induction melting system atomizer to ensure substantially uniform heating and spheroidization of atomized droplets.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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, which show at least one exemplary embodiment, and in which:

[0017] Figure 1 is a schematic view of a melting and atomization subsystem, in accordance with at least one embodiment of the present disclosure;

[0018] Figure 2 illustrates a process diagram of a method for producing fine and spherical particles, in accordance with at least one embodiment of the present disclosure;

[0019] Figure 3 is a schematic cross-sectional view of a system for producing fine and spherical particles, illustrating a melting chamber with bar stocking, loading robot, bar holder, moving system and the melting and atomization subsystem of Fig. 1 , in accordance with at least one embodiment of the present disclosure; and

[0020] Figure 4 is a flowchart illustrating a method for producing fine and spherical particles, in accordance with at least one embodiment of the present disclosure.

[0021] It will be noted that throughout the appended drawings, like features are identified by like reference numerals.DESCRIPTION OF VARIOUS EMBODIMENTS

[0022] The present disclosure introduces a new approach for powder production by coupling plasma torches technology with an electrode induction melting process. Themethod involves atomizing a feedstock material in the form of bars using an induction system to produce liquid droplets and subjecting the droplets to intense superheat and energy from plasma torches. This dual-stage process induces rapid spheroidization and refinement, producing fine and spherical particles.

[0023] Gas Atomization is the most widespread technology for the mass production of metal powders for additive manufacturing. Gas atomization involves the disintegration of molten metal into fine droplets using high-velocity jets of gas. This method ensures precise (to some extent) control over particle size distribution and morphology, essential for tailored material properties. Gas atomization has become integral in metallurgy, facilitating the production of powders used in additive manufacturing, thermal spray coatings, and powder metallurgy processes. It offers advantages over traditional methods like water atomization, including finer particle size and sphericity control as well as reduced oxidation of the metal.

[0024] The commonly employed methods for gas atomization include the following.

[0025] VIGA (Vacuum Induction Gas Atomization) technology stands out as a routine method for manufacturing metal / alloy powders, yielding fine and spherical particles. However, its efficacy can be hindered in certain scenarios. Limitations arise, notably in processing reactive metals like titanium, which tend to interact with crucibles, and in identifying appropriate resistance crucibles for melting high-melting-point metals such as chromium. In the conventional crucible argon atomization method (VIGA) when the liquid metal contact with the crucible, it can lead to refractory erosion, potentially introducing ceramic inclusions into the metal powder, especially in the preparation of reactive metals and alloys (such as titanium and zirconium alloys), the liquid metal will react with the refractory, not only will increase contamination, refractory elements will be introduced into the liquid metal, so that the powder composition changes.

[0026] In 1990, ALD Germany developed the EIGA (Electrode Induction Gas Atomization) technology featuring a crucible-less method of metal melting. Titanium raw material is processed into bars directly, which are heated to melt in a high-frequency induction coil. The molten titanium is atomized into spherical titanium powder by an inert gas such as argon. This method has the advantages of non-contamination of the rawmaterials, fast heating rate, high sphericity, and high purity. However, the long fall distance from the heated bar tip into the atomizing jets results in the loss of superheating. Therefore, the superheat of the solution into the atomization zone is very low, and the particle size of the powder is 100-200 micrometers (pm) and the yield of the fine powder is low (see, for example, U.S. patent No. US 5,284,329).

[0027] The PREP (Plasma Rotating Electrode Process) was first developed by the U.S. Nuclear Metals Company. This process takes a bar of the required alloy as a consumable rotating electrode, and then the end of the bar is heated by plasma to melt it. The liquid metal is ejected by the centrifugal force of the electrode rotating at a high speed and pulverized into fine droplets. The PREP powder has very high purity, low oxygen content and a complete spherical shape. However, even at high-speed electrode rotation speed, the generated centrifuge force is not generally enough to produce a high yield of fine particles for AM applications. As an example, in the case of Ti64, D10, D50 and D90 are 92.7, 156 and 258 pm, respectively at a rotation speed of 14000 revolutions per minute (RPM) for a bar of 75 millimeters (mm) (J. Tang, Y. Nie, Q. Lei, Y. Li, Characteristics and atomization behavior of Ti-6AI-4V powder produced by plasma rotating electrode process, Advanced Powder Technology, 30, 2019, pp. 2330-2337), while the sought for particles for AM applications are typically in the 15-65 pm range. As another example, for a bar of Ti64 of 25 mm outer diameter (OD) and a rotation speed of 11700 RPM, the particle size range is between 100-600 pm (Y. Cui, Y. Zhao, H. Numata, H. Bian, K. Wako, K. Yamanaka, K. Aoyagi, C. Zhang, A. Chiba, Effects of plasma rotating electrode process parameters on the particle size distribution and microstructure of Ti- 6AI-4 V alloy powder, Powder Technology 376, 2020, pp. 363-372). To increase the atomization rate by using higher bar diameters, higher fine particle yield and less satellite formation in the case bigger particles, a higher rotation speed is required (L.V.M. Antony, R.G. Reddy, Processes for production of high-purity metal powders, JOM, The Journal of The Minerals, Metals & Materials Society, 55, 2003 pp. 14-18), thereby demanding more electric power in production scale systems.

[0028] The PAS (Plasma Atomization System) (see, for example, U.S. patent No. US 5,707,419) has been used commercially for producing spherical titanium powder. The heat source for this technology consists of three plasma torches. The raw material wireis heated and melted into droplets and then atomized by plasma plumes and finally solidified into a metal powder. Compared to a typical cold gas atomization with a close- coupled nozzle, this method uses hot low-flow-rate plasma plumes for atomization which has a higher velocity inducing more energy for liquid break-up and disintegrating to more fine particles. In addition, the plasma plumes create a second superheat to the liquid stream, resulting in longer solidification time and higher spheroidization rate, avoiding rapid freezing and irregular particle formation. The PAS powder is relatively fine. The average size of the powder is 40 pm and the particle size distribution is narrow. However, the production efficiency is low due to the low atomization rate and high-power consumption. Another important limitation is that the feedstock must be exclusively in the form of wire (see, for example, patent publication no. WO 2016 / 191854).

[0029] PCT Publication No. WO 2016 / 191854 describes a similar atomization process in which the metal in the form of a wire passes through a wire guide in graphite or ceramic and is preheated by an induction coil to a temperature below its melting point. Once the preheated wire enters the apex of three plasma torch plumes, it melts, and the liquid layers detach from the wire and are atomized. In this process, the wire feed rate could be higher, resulting in a higher atomization rate since the wire is at a higher temperature and a smaller fraction of the plumes heat is consumed to melt the wire. However, the cost of feedstock wire and keeping the wire aligned in the apex are the limiting factors in this powder production method.

[0030] U.S. Patent Application Publication No. US 2020 / 0180034 discloses a metal powder plasma atomization process and apparatus comprising at least one plasma torch, a confinement chamber, a nozzle positioned downstream of the confinement chamber and a diffuser positioned downstream of the nozzle. The nozzle accelerates liquid metal particles produced by at least one plasma torch and also plasma gas to supersonic velocity such that the liquid metal particles are sheared into finer powders. The diffuser provides a Shockwave to the plasma gas to increase temperature of the plasma to avoid stalactite formation at an exit of the nozzle. Nonetheless, this technology exhibits the risk of powder contamination by graphite, wire misalignment in the apex and blockage of the diffuser.

[0031] U.S. Patent No. US 11 ,839,918 describes a plasma atomization process in which an electric arc is generated between two wire feedstocks to melt the same. The wires serve as an anode-cathode system and are fed continuously into the atomization chamber. A plasma torch is employed to generate a supersonic plasma plume to atomize the molten feedstock into particles at the apex at which the electric arc produces liquid metal. Although the atomization rate is comparatively high compared to other atomization techniques and high fine particle yield because the speed of the two wires must be controlled precisely, the process is prone to instabilities. Wire alignment, arc stability and alloying elements vaporization can also be considered as drawbacks of the method.

[0032] U.S. Patent No. US 11 ,772,159 describes an apparatus to produce metallic powders from a molten feedstock. Akin to VIGA or traditional gas atomizers, the feedstock is melted in a crucible by an induction heating system at the desired liquid metal temperature, and the melted feedstock is transferred through a liquid guide to the atomization zone. A closed-coupled nozzle is used to atomize a liquid metal stream. Instead of a cold gas source, plasma torches are connected to the nozzle from which generated plasma plumes pass through the nozzle to produce supersonic hot gas for atomization. The major challenges in this atomization technique are to avoid nozzle melting by plasma plumes and liquid guide clogging by liquid metal freezing. In addition, using a crucible to melt a metal or alloy increases the risk of contamination, particularly for highly reactive materials such as Ti and Zr alloys.

[0033] Using hot gas instead of cold gas for gas atomization provides several advantages. Firstly, it enhances atomization efficiency by promoting better breakdown of the molten material into finer droplets, resulting in finer powder particles. This process also reduces the likelihood of premature solidification, ensuring the production of finer particles. Additionally, hot gas atomization leads to powder with improved flow characteristics, controlled particle size distribution, and higher production rates than cold gas methods. Furthermore, this process may result in powder with superior properties, such as enhanced density and reduced porosity, making it useful for various industrial applications. Nevertheless, in common atomization methods that utilize hot gas, the overall cost of providing high quantity of hot gas in the gas atomization can be excessively high.

[0034] A novel method for producing particles from a metal bar using a plasma torch is provided herein. A system for producing particles as described herein comprises an induction melting system coupled with multiple plasma torches 305 (see Figs. 1 , 3), a feedstock material supply system 320 (also referred to herein as “the bar-loading subsystem 320”, see Fig. 3) which delivers the feedstock material provided in the form of bars 309, and a control system 220 (Fig. 2) for operating and regulating the plasma torches 305 and feedstock flow. Additionally, the system for producing particles as described herein features a continuous operation mechanism to ensure uninterrupted particle production.

[0035] The bar-loading subsystem 320 has a capacity of 24-36 bars. After each atomization run, the bar-loading subsystem 320 which comprises, for example, a robot arm 308, removes the bar remnant from the bar holder 310 and transfers the bar remnant to a consumed bar bin 318 (also referred to herein as the “consumed bars container 318”). Thereupon, the robot arm 308 holds and guides the new bar to the melting chamber 301 and positions it at the desired position in the induction coil. The advantage of the automatic bar-loading system is the reduction of operator intervention and time to load a new bar 309 into the melting chamber 301 after each atomization run. It provides a reliable and consistent operation and operates under the same vacuum level as the rest of the atomization system.

[0036] The system and the method as described herein offer significant advantages over existing systems and methods, including improved particle uniformity, size control, and scalability, making it a valuable tool for various industrial applications. Since the present process uses significantly less gas than in conventional atomization, the gas turbulence in the atomization chamber is reduced reducing the production of undesirable satellites. Therefore, the system and method as described herein address the challenge of high gas utilization and associated costs by employing at least three low- flow rate plasma torches producing a high-temperature source of gas instead of relying solely on a high-flow rate of gas warmed by a heater. This approach not only mitigates excessive gas consumption, but also enhances the efficiency of the atomization process, thereby offering a more sustainable and cost-effective solution.

[0037] Fig. 1 illustrates a schematic view of a melting and atomization subsystem 100 (also referred to herein as “a melting and atomization arrangement”), in accordance with at least one embodiment of the present disclosure. The melting and atomization process as described herein may be also referred to as “electrode induction plasma atomization” (EIPA) process or method or a method for producing fine and spherical particles. Fig. 2 illustrates a process diagram for implementing an EIPA method by an EIPA system 300 (also referred to herein as a “system 300 for producing fine and spherical particles”) illustrated in Fig. 3, in accordance with at least one embodiment of the present disclosure. Fig. 4 illustrates a flowchart of the EIPA method 400 (also referred to herein as a “method 400 for producing fine and spherical particles”), in accordance with at least one embodiment of the present disclosure. In the description below, reference will be made to Figs. 1-4.

[0038] In Fig. 1 , which schematically illustrates the subsystem 100 (located partially in a melting chamber 301 and partially in a reactor 207 of Figs. 2, 3, also referred to herein as an “atomization chamber 207"), a downward-moving metal bar 309 is melted by induction coil(s) 304 surrounding the lowest section of the bar 309. Subsequently, molten droplets 314 are atomized by plasma plumes 315 produced by high-enthalpy plasma torches 305 positioned at between 30° and 45° with respect to an axis of the bar 309 (also referred to herein as a “bar axis 110”), preferably at 30° to the bar axis 110, disintegrating the produced liquid drops into powders 316 which are sent to an air classifier system or a cyclone system 211 and collected in a hopper 205 (Fig. 2) connected to the end of the atomization reactor 207.

[0039] To neutralize the effect of the induction coil electromagnetic field interference with the plasma torch functioning, the plasma torches 305 are shielded by magnetic resistance shields 313 (also referred to herein as “magnetic shield(s) 313” or “electromagnetic shield(s) 313”), such as annealed Ni?7Fei4Cu5Mo4 from Millipore Sigma. The magnetic shields 313, which have a thickness of 0.05-2 mm depending on the induction coil electromagnetic field level, cover the whole body of the plasma torches 305. In at least one embodiment, each one of the plasma torches 305 is covered with the magnetic shield 313. The magnetic shields 313 are used to avoid the effect of the induction coil electromagnetic field on the plasma torches' internal arc and plumes.

[0040] Before commencing the atomization process, the melting and atomization subsystem 100 (Fig. 1 ) is in a vacuum condition (0.05 mbar) facilitated by a vacuum system 206 to eliminate (any) moisture and oxygen present in the reactor 207 (Fig. 2). A metal / alloy rod 309, having the outer diameter (OD) of between 50 to 70 millimeters (mm), preferably 50 mm, and with a length of 1000-1200 mm, is heated in a melting chamber 301 by an induction coil, drawing energy from an induction power supply 202 generating 120-150-kilowatt (kW) power and a 100-400 kilohertz (kHz) frequency.

[0041] Subsequently, the molten metal / alloy is atomized by three plasma torches 305, each powered by its dedicated power supply 201 (Fig. 2). The power of each plasma torch 305 is in the range of 100-200 kW producing 150-300 pounds per square inch (psi) gas pressure and a temperature range of 3000-4000 degrees Celsius (°C) at the torch exit for high melting point alloys and 150-200 psi gas pressure and a temperature range of 2000-3000 °C at the torch exit for low melting point alloys. The plasma forming is preferably an inert gas such as argon, or a non-oxidizing gas such as nitrogen, to prevent oxidation of the metal being atomized. For example, in the case of argon, the gas flow rate at the exit of the plasma torches 305 ranges from 850 to 1000 standard liters per minute (slpm), preferably 900 slpm and 750-950 slpm, preferably 800 slpm for high and low melting point metal and alloys, respectively.

[0042] To maintain operational efficiency, the plasma torches 305, preferably the three plasma torches 305, and walls of the reactor 207 are cooled by a water-cooling unit 204 (schematically illustrated in Fig. 2), having two skids. Depending on the feedstock material, the atomization gas, which may be argon, nitrogen, helium, hydrogen, or a mixture thereof, is supplied through a gas supply system 203.

[0043] The resulting powder 316 is collected into a hopper 205, and then the remaining particles are further collected through either an air classifier system or a cyclone system 211. To ensure continuous operation, a feedstock automatic loader 212 is employed in which a robotic system transfers new bars to be atomized, such as bars 309, to the melting chamber 301 once the previous one (bar) is atomized.

[0044] The resulting clean plasma forming gas exiting the cyclone system 21 1 may be further cleaned of residual particulates by, for example, a higher efficiency particulateair (HEPA) filter and even further an ultra-low particulate air (ULPA) filter to allow for recompressing the plasma gas (argon). Depending on its temperature, the plasma forming gas may need to be cooled down to make it suitable to be fed to a high-pressure compressor. The cooling is performed indirectly, using, for example, a cooling coil or cooling fingers in a gas-tight enclosure.

[0045] In at least one embodiment, the EIPA system 300 has a control system 220 schematically illustrated in Fig. 2, in accordance with at least one embodiment of the present disclosure. The control system 220 helps to execute steps of the EIPA method as described herein. The control system 220 comprises a processor configured to execute instructions to provide uninterrupted particle production by operating feedstock material supply system 320 (feedstock automatic loader 212), movement of the bar 309, and operating and regulating the plasma torches 305. The control system 220 coordinates and controls the operation of these and other systems, such as, for example, the induction power supply 202, the gas supply system 203, the water-cooling unit 204, the vacuum system 206, the cyclone system 211. The control system 220 has a memory for storage of such instructions, the execution of such instructions by the processor allowing to execute the steps of the EIPA method. The control system 220 is configured to receive from various systems and units of the EIPA system (as illustrated, for example, in Fig. 2) data that helps adjust the execution of the steps of the EIPA method. For example, the control system 220 may be configured to detect (receive data, for example, from a sensor) when the length of the bar 309 reaches a predefined bar length to determine that the bar holder 310 has to move the bar 309 upward and that the bar remnant 317 has to be removed and a new bar 309 to be loaded to the bar holder 310. The control system 220 may be configured to receive data from other sensor(s) and adjust the operation of various units and systems of the EIPA system 300.

[0046] Fig. 3 shows a cross-sectional view of a melting chamber 301 , including bars stocking 302, a loading-unloading robot 303, an electrode induction coil 304 and plasma torches 305. The melting chamber 301 is installed on a mezzanine 306 and connected to an atomization chamber 307. A robot arm 308 of the loading-unloading robot 303 transfers a bar 309 to a mechanical bar holder 310 coupled to a holder arm 311 . Theholder arm 311 can move in a Y-axis direction using a hydraulic actuator and a control box 312 of the control system.

[0047] Once the plasma torches 305 covered by the magnetic shields 313 are ignited, the bar holder 310 transfers the bar 309 using the control box 312 toward the induction coil 304 at a constant velocity depending on the bar material. The bar 309 takes a so-called “melting position” where the lower portion of the bar 309 melts. In at least one embodiment, the bar holder 310 may also rotate the bar 309 with a rotation velocity of 1- 40 revolutions per minute (RPM) while moving the bar 309 downwards. The induction coil 304 starts to heat the bar 309 and once, at the lowest induction coil 304 turn, the bar end temperature (temperature at the end of the bar 309, in other words, temperature of the lower section / portion of the bar 309 which is heated by the induction coil 304) attains its melting point, liquid droplets 314 are detached from the bar 309 and arrive at the atomization zone where plasma plumes 315 impact the liquid droplets 314 producing atomized particles 316. When the lower section / portion of the bar 309 bar 309 melts, the bar 309 is in a so-called “melting position”.

[0048] At a predefined bar length, for example, 50 mm, the bar holder 310 moves the bar 309 (in other words, what is left of the bar 309, also referred to herein as a “bar remnant 317”) upward where the robot arm 308 transfers the bar remnant 317 to a consumed bars container 318 and the bar loading process restarts. The remaining parts / portions of the bars 309 (bar remnants 317) may be sintered together in a sintering furnace by a separate process to make new bars. Alternatively, the bars (the bar remnants 317) may be recycled by an external metal recycling system to be reprocessed into bars or other products.

[0049] Fig. 4 illustrates a flowchart of the method 400 for producing fine and spherical particles. At step 401 , a multiple plasma torch system is integrated with an electrode induction melting system atomizer. At step 405, the metal bar 309 is atomized while the bar 309 is moved downwards in the induction coil 304 (and toward the induction coil) to produce the liquid droplets 314 prior to subjecting the liquid droplets 314 to the superheat temperature. At step 410, the liquid atomized droplets 314 are subjected to a superheat temperature and energy by plasma plumes 315. At step 415, the powder iscollected into the hopper 205. At step 420, after a length of the bar 309 reaches a predefined bar length, moving the bar remnant of the bar 309 upward and transferring the bar remnant to the consumed bars container 318 by the robot arm 308. At step 425, another bar 309 is loaded of feed material automatically to the melting position (Fig. 1 ) to produce the atomized droplets.

[0050] While the above description provides examples of the embodiments, it will be appreciated that some 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. Accordingly, what has been described above has been intended to be illustrative of the embodiments and non-limiting, and it will be understood by persons skilled in the art that other variants and modifications may be made without departing from the scope of the embodiments as defined in the claims appended hereto.

Claims

CLAIMS1. A method for producing spherical particles, the method comprising: integrating a multiple plasma torch system with an electrode induction melting system atomizer; and subjecting liquid atomized droplets to a superheat temperature and energy by plasma plumes generated by plasma torches of the multiple plasma torch system.

2. The method of claim 1 , further comprising: atomizing a feedstock material provided in a form of a bar while moving the bar downwardly in an induction coil by using the electrode induction melting system atomizer to produce the liquid droplets prior to subjecting the liquid droplets to the superheat temperature.

3. The method of claim 2, further comprising, prior to the atomizing the feedstock material, grabbing a first bar from a bar stocking by a robot arm and positioning the first bar in a bar holder to a melting position, the bar stocking and the induction coil being located in a melting chamber with a common vacuum level.

4. The method of claim 3, further comprising moving the first bar in the bar holder toward the induction coil at a constant velocity after the plasma torches of the multiple plasma torch system are ignited.

5. The method of claim 4, further comprising rotating the first bar with a rotation velocity of between 1 and 40 revolutions per minute (RPM) while moving the first bar downwardly toward the induction coil.

6. The method of any one of claims 2 to 5, further comprising: after a length of the first bar reaches a predefined bar length, moving a bar remnant of the first bar upwardly and transferring the bar remnant to a consumed bars container using a robot arm, and loading a second bar of the feedstock material automatically to a melting position to produce the liquid atomized droplets.

7. The method of any one of claims 1 to 6, further comprising, while subjecting liquid atomized droplets to the superheat temperature, cooling the plasma torches and walls of a reactor by a water-cooling unit having two skids.

8. The method of any one of claims 1 to 7, further comprising supplying an atomization gas through a gas supply system, wherein the atomization gas is selected from the group consisting of argon, nitrogen, helium, hydrogen and a combination thereof.

9. The method of any one of claims 1 to 8, wherein a power of each plasma torch is between 100 kilowatts (kW) and 200 kW.

10. The method of any one of claims 2 to 9, further comprising producing between 150 and 300 pounds per square inch (psi) gas pressure and a temperature range of between 3000°C and 4000°C at a plasma torch exit of each plasma torch when the feedstock material is made of a high melting point alloy.11 . The method of any one of claims 2 to 9, further comprising producing between 150 psi and 200 psi gas pressure and a temperature range of between 2000°C and 3000 °C at a plasma torch exit of each plasma torch when the feedstock material is made of a low melting point alloy.

12. The method of any one of claims 1 to 11 , wherein the multiple plasma torch system comprises at least three plasma torches.

13. The method of any one of claims 1 to 12, wherein the plasma torches are positioned around the electrode induction melting system atomizer.

14. The method of any one of claims 1 to 13, further comprising collecting powder into a hopper.

15. A system for producing spherical particles, the system comprising:an induction melting system coupled with plasma torches, both located in a melting chamber; a feedstock material supply system located in the melting chamber and having the same vacuum as the induction melting system, the feedstock material supply system being configured to supply bars to the induction melting system atomizer; and a control system for regulating the plasma torches and a flow of the bars to the induction melting system.

16. The system of claim 15, further comprising a bar holder configured to hold the bars, the bar holder being attached to a holder arm operative to move the bar holder downwardly with a first bar of the bars so as to move the bar into an induction coil at a constant velocity.

17. The system of claim 16, wherein the bar holder is configured to rotate the bar with a rotation velocity of between 1 and 40 revolutions per minute (RPM) while moving the bar downwardly.

18. The system of any one of claims 15 to 17, wherein each one of the plasma torches is covered by a magnetic shield.

19. The system of claim 18, wherein the magnetic shield has a thickness of between 0.05 mm and 2 mm, the magnetic shield covering a whole body of each one of the plasma torches.

20. The system of any one of claims 15 to 19, wherein the high-enthalpy plasma torches are positioned at between 30 degrees and 45 degrees with respect to an axis of the first bar.

21. A method for producing spherical particles, the method comprising: melting a bar made of a metal by an induction coil surrounding a lowest section of the bar to obtain molten droplets, the bar moving downwardly;atomizing molten droplets by plasma plumes of plasma torches and disintegrating liquid drops produced into powders.

22. The method of claim 21 , further comprising sending the powders to an air classifier system or a cyclone system and collecting the powders in a hopper connected to an end of an atomization reactor.

23. The method of claim 21 or 22, further comprising, prior to melting the bar, grabbing the bar from a bar stocking with a robot arm automatically and positioning the bar in a bar holder to a melting position, the bar stocking and the induction coil being located in a melting chamber with a same vacuum level.

24. The method of claim 23, further comprising moving the bar by a bar holder toward the induction coil at a constant velocity after the plasma torches of a multiple plasma torch system are ignited.

25. The method of claim 24, further comprising rotating the bar with a rotation velocity of between 1 and 40 revolutions per minute (RPM) while moving the bar downwards toward the induction coil.

26. The method of any one of claims 21 to 25, further comprising: after a length of the bar reaches a predefined bar length, moving a bar remnant of the bar upward and transferring the bar remnant to a consumed bars container by a robot arm, and loading another bar of feed material automatically to a melting position to produce the atomized droplets.

27. The method of any one of claims 21 to 25, further comprising, while subjecting liquid atomized droplets to a superheat temperature, cooling the plasma torches and walls of a reactor by a water-cooling unit, having two skids.

28. The method of any one of claims 21 to 26, further comprising supplying an atomization gas through a gas supply system, wherein the atomization gas is selected from the group consisting of argon, nitrogen, helium, hydrogen and a combination thereof.

29. The method of any one of claims 21 to 28, wherein a power of each plasma torch is between 100 kilowatts (kW) and 200 kW.

30. The method of any one of claims 21 to 29, further comprising producing between 150 psi and 300 psi gas pressure and a temperature range of between 3000°C and 4000 °C at a plasma torch exit of each plasma torch when the bar is made of a high melting point alloy.31 . The method of any one of claims 21 to 29, further comprising producing between 150 psi and 200 psi gas pressure and a temperature range of between 2000°C and 3000 °C at a plasma torch exit of each plasma torch for the bar made of a low melting point alloy.

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