Cold tundish, and apparatus and method for producing spheroidal micropowders

Abstract

A cold tundish which has a surface made from a thermally conductive metal, and which is cooled by a cooling fluid, is disposed so as to receive a molten material from a cold crucible; high-speed jets of an inert gas are produced from a nozzle at a narrow portion of an orifice that is open at the exit side of the cold tundish, producing a low-pressure region on the exit side of the orifice that draws the molten material and a plasma through the orifice; the high-speed jets of inert gas impinge on the molten material to achieve atomization thereof, using an apparatus that is compatible with atomization of even reactive and refractory metals.

Description

COLD TUNDISH, AND APPARATUS AND METHOD FORPRODUCING SPHEROIDAL MICROPOWDERSInventors: Sasha Long Rayland O’Neal

[0001] This application claims the benefit of U. S . Provisional Patent Application No. 63 / 602,892, filed Nov 27, 2023, which is herein incorporated by reference in its entirety.FIELD OF THE INVENTION

[0002] The present invention relates to a cold tundish and an apparatus and a method for producing spheroidal powders, and specifically to a cold tundish and an apparatus and method for producing spheroidal powders with high yields of particles of reactive or refractory metals or materials from a variety of feedstock configurations from a broad variety of feedstock configurations, doing so inexpensively and efficiently.BACKGROUND

[0003] Spheroidal powders are used in a broad variety of industries such as in additive manufacturing (3D printing), electronics that require the production of conductive inks and pastes, powder catalysts, powder metallurgy, metal inj ection molding (MIM), biomedical applications that include fabrication of biocompatible implants such as hip and knee prosthetics through sinters of molded powders, thermal spray coatings, powder inj ection molding, hot and cold isostatic pressing, and other powder metallurgy applications. Many applications require highly spherical powders of reactive or refractory metals at ultrasmall particulate sizes (less than 45 pm). For commercial use, the ability to produce high yields of powders with ultrasmall particulate size, from a wide variety of feedstock configurations, doing so inexpensively and efficiently, is extremely important. However, todate there has been no known process able to produce high yields of reactive or refractory powders with ultrasmall particulate size from a wide variety of feedstock configurations, doing so inexpensively and efficiently.

[0004] In conventional methods of powder production, three main approaches have been employed. The first involves the use of a close-coupled gas atomizer, which utilizes a crucible for melting the metal prior to the atomization process, depicted schematically in FIG. 1. This method relies on powerful j ets of an inert gas, such as argon, disposed in a ring around a nozzle 24 that dispenses a molten material . The j ets of the inert gas exert strong shearing forces on the stream of molten material 75, breaking the stream into microdroplets through first stretching the molten material into thin ligaments which, when stretched beyond a critical length, fragment into droplets. Surface tension of the molten material causes the droplets to assume substantially spherical geometries, and the droplets then solidify into microparticles 80 as they fall into a collector. In close-coupled atomization systems, the j ets, in fluid connection to a j et fluid duct 45, are located in or in close proximity to the nozzle that is expelling the molten material, maximizing the shearing forces of the j ets, thereby improving the economic efficiency of the process by enabling the total amount of gas to be reduced when compared to other gas atomizing schemes.

[0005] The second method employs a freefall gas atomizer, as depicted schematically in FIG. 2, where molten material 75, melted in a crucible, is allowed to fall freely from a hole in the crucible, and then i s disintegrated into powder under the influence of high-velocity j ets that are not in proximity to the crucible. As with the close-coupled atomization, these particles al so become substantially spherical, due to the surface tension of the molten material, and solidify into microparticles 80 as they fall into a collector.

[0006] The third method, not illustrated, is that of wire plasma atomization. In this method a wire is fed through a plasma that is producedby one or more pl asma sources, to thereby melt the wire into dropl ets, which are then broken up by powerful j ets of an inert gas.

[0007] In both the close-coupled atomization method and the freefall atomization method, material of any of a variety of forms of stock is melted in a crucible 23 before atomization. The crucible 23 may be of either of a conventional hot crucible design or of a cold crucible design (where the crucible is cooled through a cooling fluid, to maintain a temperature that is cooler than that of the melt, while the material is heated through other means, such as inductive heating (if the material is a metal), heating by a plasma, or the like). This allows for unique advantages in applications where certain metallurgical materials are processed. Col d crucibles are particularly advantageous in dealing with reactive metals or materials that would react with and degrade the ceramic materials from which hot crucibles are formed. Typically, in a cold crucible, a thin layer of the process metal remains frozen on the inner surfaces of the crucible, providing a barrier between the molten material and the crucible, thereby preventing the crucible from being damaged, and preventing contamination of the molten material .

[0008] All three of the approaches described above, while having their merits, present certain limitations in terms of control over particle size, uniformity, efficiency, scalability, and compatibility with various feedstock configurations.

[0009] Close-coupled gas atomizers, such as depicted in FIG. 1 , where the j ets are in close proximity to the outlet of the crucible, have the benefits of not requiring as much gas as i s required with freefall gas atomizers, while providing significantly better performance in terms of producing powders with ultrasmall particle size. Unfortunately, in conventional close-coupled gas atomizers, it has not been possible to prevent the molten material from freezing in the narrow-diameter discharge nozzle 24 unless the discharge nozzle 24 is hot. This is because, in the conventional close-coupled technology, it has not been possible to transfer enough heat through electromagnetic induction into the discharge nozzle 24 material to replacethe heat that i s lost into the wall s of the nozzle 24. Thus attempts to apply the close coupled technology to cold crucible systems such as illustrated in FIG. 1, have been unsuccessful .

[0010] The inability to prevent freezing within the discharge nozzle 24 has led all known close-coupled atomizer equipment manufacturers to use designs wherein the discharge nozzle 24 i s not cooled, but often actually heated to prevent clogging of the discharge nozzle 24 with frozen material. This has required the discharge nozzle to be made out of refractory ceramic in order to endure the high temperatures of the melted metals. Unfortunately, the ceramic refractory materials used in nozzles are quickly deoxidized or denitrided when exposed to reactive metals such as titanium or titanium alloys. Once deoxidized or denitrided, the nozzle material s quickly melt, and thus the nozzles 24 quickly degrade and must be replaced frequently, making close-coupled atomization equipment impractical for use in commercial production of powders of reactive or refractory metals or materials such as titanium and titanium alloys, requiring one of the other approaches to be used when forming powders of reactive or refractory metals or materials.

[0011] The freefall atomization approach, on the other hand, has the benefit of not requiring a nozzle at all, as can be seen by comparing FIG. 1 and FIG. 2. While this successfully avoids the problem of solidification of the molten material in the discharge nozzle 24, the j ets for atomizing the molten material 75 must be located substantially away from the molten material stream 77 and from the molten material 75 source that produces the stream. The freefalling stream 77 causes cooling and necking of the stream as it falls, and droplet formation due to Plateau-Rayleigh instability. The relatively large droplets create an inefficient form of metal to enter the gas j et, when compared to a steady stream or pre-film feed. This results in much coarser particles. This problem is exacerbated by the flow of the atomizing gas interacting with the stream at a point that i s further from the gas nozzl e 72, substantially reducing the kinetic energy of the gas imparted to the stream 77 of molten material, also resulting in larger particle size. Forapplications that require ultrafine particles, thi s adversely affects the yiel d of adequately small particles, making freefall atomization unappealing from an economic and throughput perspective. Another disadvantage of this approach is that in freefall atomization the distance between the j ets and the molten material discharge nozzles 24 requires much higher volumes of gases in the j ets than with close-coupled atomization. Given that the gases used in the j ets are costly inert gases, the higher volumes of gas required makes freefall atomization economically unattractive, despite compatibility with reactive and refractory metals.

[0012] The wire plasma atomization approach also has the benefit of not requiring a nozzle 24, and thus there are no concerns about the molten material 75 freezing in the nozzle 24 resulting in clogging. However, there is a serious limitation in that the only form of feedstock that can be used is that of a wire or a thin bar, thus limiting the scope of application of the approach. For example, this approach cannot be used with powders (such as, for example, recycling rej ected powder that is not adequately fine), pellets, chunks, sponge, or chips. Additionally, some metals cannot be formed easily into wires or rods, precluding the use of this approach for those metals.

[0013] Thus there is the need for an apparatus that enables high-yield production of ultrafine microparticles of even reactive and refractory material s such as titanium, niobium, rhenium and other similar metal s or alloys, from a broad variety of feedstock configurations, using a process that is economical and efficient.SUMMARY OF THE INVENTION

[0014] One embodiment of the present invention provides an apparatus for producing spheroidal powders, comprising: a molten material supplying apparatus; a cold tundi sh for receiving molten material from the molten material supplying apparatus, having an orifice at the exit thereof for discharging the received molten material, said orifice passing through the cold tundish, with a relatively wide opening diameter at an entrance portion, with a relatively narrow opening diameter an exit portion; and a j et openingfor produci ng a high velocity flui d fl ow that impinges on, and atomizes, the discharged molten material, wherein: the cold tundish is configured comprising an entrance-side portion that is made from a high thermal conductivity material and a cooling duct configured to carry a cool ant fluid for cooling the thermally conductive entrance-side portion; a second heating device is provided, configured so as to heat molten material that is in or on the cold tundish; and the j et opening i s provided in the cold tundish, opening at a portion on an exit side of the orifice.

[0015] In another embodiment, the molten material supplying apparatus comprises a continuous feed source material delivery device for delivering a source material into a melting device that comprises a first heating device for heating and melting the source material into a molten material .

[0016] In a further embodiment, the first heating device is configured as a plasma source configured to cause a plasma to impinge upon the source material that is in or on the melting device, an inductive heating source configured to cause inductive heating of the source material that is in or on the melting device, or a resistive heating source configured to heat the source material that is in or on the melting device. The j et opening i s configured in a ring shape surrounding a center axis of the orifice.

[0017] In yet another embodiment, the j et opening is configured in a ring shape surrounding a center axis of the orifice.

[0018] In a yet further embodiment, the j et opening is configured from a plurality of j et openings, disposed spaced around the vertical axis of the orifice.

[0019] In still another embodiment, the second heating device is configured as a plasma source for causing a plasma to impinge upon the molten material that i s in or on the cold tundish.

[0020] In a still further embodiment, an inert gas is discharged at a high velocity from the j et opening.

[0021] In an even another embodiment, the inert gas is argon.

[0022] In an even further embodiment, the j et opening i s configured so that a low-pressure region is formed on the exit side of the orifice when a fluid is discharged at a high velocity from the j et opening.

[0023] In a still even another embodiment, the j et opening is configured so that, when a gas is discharged at a high velocity from the j et opening, a plasma, produced by the second heating device, will be drawn into the orifice.

[0024] In a still even further embodiment, the second heating device is configured as a pancake-type inductive heating device configured to heat the molten materi al that i s in or on the col d tundi sh.

[0025] In still yet another embodiment, the cold tundish comprises an annular lip.

[0026] In a still yet further embodiment, the molten material is drawn through the orifice in the form of a sheath.

[0027] An even yet another embodiment comprises an entrance-side housing on the entrance side of the orifice and an exit-side housing on the exit side of the orifice, wherein the entrance-side housing and the exit-side housing are maintained at different static pressures.

[0028] An even yet further embodiment compri ses an entrance-side housing on the entrance side of the orifice and an exit-side housing on the exit side of the orifice, wherein the interior of the entrance-side housing and the interior of the exit-side housing are maintained at different temperatures.

[0029] A still even yet another embodiment comprises a fluid flow temperature controlling device configured to control a temperature of the high velocity fluid flow.

[0030] In a still even yet further embodiment the high velocity fluid flow flows at a supersonic velocity.

[0031] Yet still even another embodiment provides a method for producing spheroidal powders, including : delivering a source material to a melting device; producing heat in the melting device to melt the source material toproduce a molten materi al ; causing the molten material to run into a col d tundish; heating the molten material in the cold tundish; cooling the cold tundi sh from the interior of the structure of the cold tundish through a cooling fluid; discharging a j et of a gas from a j et opening on an exit-side portion of the cold tundish to create a low-pressure region on the exit side of an orifice of the cold tundish so as to draw the molten material through the orifice in the cold tundish; and causing a j et of gas to strike the molten material that has been drawn through the cold tundish; wherein: all of the aforementioned steps are performed concurrently in a continuous process.BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is a vertical sectional diagram depicting schematically a conventional close-coupled gas atomization apparatus for producing spheroidal powders.

[0033] FIG. 2 is a vertical sectional diagram depicting schematically a conventional freefall gas atomization apparatus for producing spheroidal powders.

[0034] FIG. 3 is a sectional diagram illustrating an apparatus for producing spheroidal powders, compri sing a cold tundish close-coupled atomizer according to an embodiment.

[0035] FIG. 4 depicts a portion of a cold tundish for a close-coupled atomizer according to an embodiment, showing details of the orifice.

[0036] FIG. 5 depicts a portion of a cold tundish for a close-coupled atomizer according to another embodiment, showing details of the orifice.

[0037] FIG. 6 is a sectional perspective diagram depicting the flow of a molten material along the walls of an orifice, showing in particular formation of a sheath-shaped prefilm flow of the molten materi al, enabling a central flow of ambient gas and plasma therethrough, in an embodiment.

[0038] FIG. 7 i s a sectional perspective di agram depicting an apparatus for producing spheroidal powders, comprising a cold tundish close-coupled atomizer, according to another embodiment.

[0039] FIG. 8 is a flowchart of a method by which to product a spherical powder according to an embodiment.

[0040] Note that identical reference numerals are assigned to identical or analogous elements that appear in separate drawings, and redundant explanations may be omitted.DETAILED DESCRIPTION

[0041] As illustrated in FIG. 3, an apparatus 10 for producing spheroidal powders according to an embodiment comprises: a molten material supplying apparatus 12 comprising a molten material delivery member 15 that is connected to one end of a trough section 20 that is open on the other end so as to enable content thereof to flow into a cold tundish 25, a first plasma source 30 arranged so as to direct a first plasma 50 to impinge upon a metal source material 35 that has been delivered by the delivery member 15 into the trough section 20 and which is configured so as to melt the metal source material 35 within the trough section 20; a second plasma source 40 arranged directed toward the cold tundi sh 25 so as to direct a second plasma 60 to impinge upon molten material 75 that is present in the cold tundish 25, configured so as to provide heat to this molten material 75 and al so so as to provide the second plasma into and through an orifice 70 of the cold tundish 25.

[0042] As depicted in FIG. 4, in embodiments the cold tundi sh 25 is structured with at least an entrance-side portion 55 thereof made from a material that is generally considered to have high thermal conductivity and comprises: a cooling duct 65 for a cooling fluid such as water, glycol, or the like, having an inlet 65a and an outlet connector, not shown, on two openings thereof; the orifice 70, which is formed passing through the cold tundish 25 an hourglass shape that is wide at the entrance side and the exit side and isnarrow in the middle, and through which the molten material 75 and the second plasma 60 (as illustrated in FIG. 3) are drawn; and a j et fluid duct 45 that is in communication with an annular j et nozzle 72 that, in embodiments, is di sposed on the exit side of the narrow neck portion of the orifice 70. Note that high thermal conductivity materials are materials with thermal conductivity of about approximately 54 W / m K or more, including, for example: metal s such as silver, copper, gold, aluminum, brass, iron, steels, and alloys and solid solutions thereof; non-metal materials such as diamond, graphite, silicon carbide, boron nitride, and silicon; and compound materials such as aluminum nitride, and copper alloys. Note also that although the orifice 70 is illustrated as oriented so that the molten material 75 and second plasma 60 pass therethrough in the vertically downward direction, there is no limitation thereto, but instead the orifice may be oriented so that the molten material 75 and second plasma 60 pass therethrough in an arbitrary direction, which in embodiments, may be horizontal, angled, or vertically upward. Note also that although the j et nozzle 72 is described as annular in the present embodiment, there is no limitation thereto, and in other embodiments the j et nozzle 72 may be ported, slotted, or of another arbitrary geometry.

[0043] The cold tundish 25 i s open at least a portion of the entrance side thereof to allow molten material 75 to flow therein, and to enable the molten material 75 therein to be exposed to the second plasma 60. In the cold tundi sh 25, the thermally conductive material for structuring the entrance-side portion 55 may be, for example, copper, tungsten, silver, or the like. Note that throughout this description, “thermally conductive material” refers to a material that has an effectively high thermal conductivity to allow for heat to pass through the material or to allow for thermal equalization, and speci fi cally to m ateri al s that are generally selected by those skilled in the art to provide or enhance thermal conductivity of a component or material .

[0044] Returning to FIG. 3 to provide more detail s about the structure, i n embodiments the delivery member 15 is configured so as to deliver a source material 35 to the trough section 20. The source material may be a selection from any of a variety of metal materials from which powders are commonly formed, such as, for example, titanium, titanium alloys, zirconium, zirconium alloys, cobalt superalloys, nickel superalloys, magnesium, magnesium alloys, niobium, niobium alloys, aluminum, aluminum alloys, molybdenum, molybdenum alloys, tungsten, tungsten alloys, and the like, or a combination thereof, or it may be a non-metal material such as a semimetal, a semiconductor, or even a ceramic, insofar as the material can be melted and caused to flow. The source material may be in any form, such as a bar or rod, a wire, a powder, pellets or chunks, a sponge, chips, or a combination thereof. If a powder, the powder may be a powder of particles that were recovered for rework after an atomization / powder production process, such as particles of sizes that are too large to be used for an intended purpose. The source material 35 delivered through the delivery member may either be of a single moiety, or may include a mixture of powders, for example, of multiple metal moieties in a ratio designed to produce a desired alloy, such as, for example, a mixed powder that is, within the tolerances that are generally used in industry, 90 wt% titanium, 6 wt% aluminum, and 4 wt% vanadium, to produce Ti64.

[0045] In embodiments, the delivery member 15, depicted in FIG. 3, may be formed with a conveyor system built therein, may be gravity fed, fed through a pressure differential, or fed through other means. The delivery member 15may or may not be provided with a heating element to preheat the source material 35 prior to arrival at the first plasma 5. The delivery member 15may or may not be provided with a system for cooling the delivery member 15 itself. The delivery of the source material 35 by the delivery member 15 to the trough section 20 may be controlled so that the rate at which the source material 35 i s delivered by the delivery member 15 will be equal to the rate at which the source material 35 is melted by the first plasma 5 into moltenmaterial 75. Because methods and devi ces for such control are well known in the industry, no further explanation thereof will be provided here.

[0046] Continuing the description based on FIG. 3 , in embodiments a first plasma source 30, as a first heater, may be configured so as to produce the first plasma 50. In embodiments, the first plasma source 30 is oriented so that the first plasma 50 produced thereby impinges upon the source material 35 that is in the trough section 20, causing the impinged portion of the source material 35 to incrementally melt so as to be transformed into the molten material 75. Note that it is not necessary for the entirety of the source material 35 to be present within the trough section 20 at any given time, but rather in a case wherein, for example, the source material 35 i s an elongate bar, not shown, it is sufficient for only one end of the bar to be within the trough section 20. The heating conditions with which the first plasma source 30 is controlled so as to cause the source material 35 to be melted by the first plasma 50, such as applied power, gas flow, and the like, may be set in accordance with the moiety of the source material 35, the geometry of the source material 35, the rate with which the source material 35 is fed and the molten material 75 is subsequently processed, and the like. Such conditions can be set easily by one skilled in the art without unreasonable or undue experimentation, so will not be described in greater detail here. The first plasma source 30 may be configured so as to produce a DC plasma arc, an AC plasma arc, an RF induction plasma, a microwave plasma, an inductive coupled plasma, a torch plasma, a hollow cathode plasma, an arcj et plasma, or the like, as the first plasma 50, where the selection of the first plasma source 30 whereby the first plasma 50 is produced can be made easily by a person skilled in the art through use of an existing technology, so no further description thereof will be given here. Note that while in this embodiment a first plasma source 30 and a first plasma 5 are presented as an example of a heat producing element for melting the source material 35 into the molten material 75, there i s no limitation thereto, but rather in other embodiments other known heating methods or devices may be used instead of, or inaddition to, the first plasma source 30 and the first plasma 50. Examples of such other known heating methods and devices include induction heating, resistance heating, microwave heating, radiant heating, and the like. A gas flow source, not shown, may also be provided in the vicinity of the trough section 20, or incorporated into the first plasma source 30, so as to blow an inert gas over the melting surface of the source material 35 so as to exclude atmosphere from the melting surface of the source material 35. Conversely, the molten material supplying apparatus 12 may be placed in a closed chamber, and a vacuum may be drawn to exclude atmosphere from the melting surface of the source material 35.

[0047] In embodiments, the trough section 20 forms a horizontal cold crucible for continuously producing the molten material 75. As a cold crucible, the interior surfaces thereof are made from a thermally conductive material that is known to be appropriate for use as the surface of a cold crucible. This material may be copper, tungsten, silver, or the like, but is not limited thereto. The selection of the material may be made easily by a person skilled in the art of cold crucible design. The trough section 20 may be provided with one or more cooling ducts, not shown, or may be cooled through thermal conduction to, for example, the entrance-si de portion 55 of the cold tundish 25, described below, or cooled through some other means such as convection or gas flow. The trough section 20 may be formed continuously with the delivery member 15 and / or the entrance-side portion 55 of the cold tundi sh 25, or it may be formed as a discrete unit. If formed continuously with the entrance-side portion 55 of the cold tundish 25, cooling ducts may be provided in the trough section 20 so as to be in fluid communication with a cooling duct 65 of the cold tundish 25, described below.

[0048] In embodiments, the trough section 20 is formed as a trough with a substantially U-shaped cross-secti on that i s open toward the top and open on both ends. In embodiments, one end of the trough section 20 mates with an open end of the delivery member 15, as described above, and the other endof the trough section i s positioned so as to be open toward the cold tundi sh 25 so as to allow the molten material 75 to flow from the trough section 20 into an upward-facing opening of the cold tundish 25. The open top of the trough section 20 enables the first plasma 50 to enter into the trough section 20 to impinge upon the source material 35. The open ends of the trough section 20 enable the source material 35 to enter into the trough section 20 from the delivery member 15, and the molten material 75 to exit the trough section 20 to the cold tundish 25. This enables the molten material 75, produced through melting of the source material 35 in the trough section 20 by the first plasma 50, described above, to flow into the cold tundish 25. The trough section 20 may have sidewalls that are shorter in height on the cold tundi sh 25 end of the trough section 20 than on the delivery member 15 end of the trough section 20.

[0049] As described above and as depicted in FIG. 4, in embodiments the cold tundish 25 comprises: an entrance-side portion 55 that is made from a thermally conductive material such as is used in cold crucibles, which may be copper, tungsten, silver, or the like, but is not limited thereto; an orifice 70 that serves as a passage in the vertical direction through the cold tundish 25; a j et fluid duct 45 connected between an inlet, not shown, on the outside of the cold tundish 25, and the annular j et nozzle 72 that is disposed within the orifice 70, on the exit side of the narrow neck portion thereof. In embodiments, the annular j et nozzle 72 i s configured so as to create, through Bernoulli ’ s principle, a region with reduced pressure, on the exit side of the neck portion of the orifice 70 of the cold tundi sh 25, when a gas or other fluid is expelled with high velocity from the annular j et nozzle 72. Here “high velocity” is defined as a velocity that is adequate to cause atomization of the molten material 75 when the fluid flow strikes the molten material 75. Although the fluid j et from the annular j et nozzle 72 di sperses after exiting the annular j et nozzle 72, making the direction of the flow of the fluid j et difficult to characterize, in embodiments the annul ar j et nozzl e 72 i s configured so that, at the instant that the fluid exits the annular j et nozzle72, the fluid mass can be characterized as flowing, on average, inwardly radially toward the axis of the orifice 70, with an angle between 5 ° and 50° relative to the axis of the orifice 70. It has been found empirically by the inventors that the performance suffers if the angle of the annular j et nozzle 72 is outside of this range; if this angle were less than 40°, the low-pressure region under the orifice 70 would not be of sufficiently low pressure to draw the material through the orifice 70, but if greater than 85°, the j et flows would not impart adequate shearing forces or kinetic energy to the molten material 75 to produce an efficient atomizing effect.

[0050] While the embodiments set forth above use an annular j et nozzle 72 formed through a continuous slit on the inner surface of an exit-side portion of the cold tundish, on the exit side of the neck portion of the orifice 70, in other embodiments the j et nozzle may instead compri se a di scontinuous slit, with multiple discrete openings, or may use multiple discrete j et apertures arranged around the axis of the orifice 70, directed toward said axis, with an angle between 50° and 5° relative to the axis of the orifice 70.FIG. 5 depicts the geometry of the annular j et nozzle 72 according to embodiments. High-performance atomization depends on the narrow neck portion of the orifice 70 having an "overbite" 71, as depicted, with respect to the annular j et nozzle 72. As depicted in FIG. 5, this overbite is formed with the side thereof that faces the flow of j et fluid within the annular j et nozzle being smooth, to prevent imparting turbulence to the flow of the j et fluid, and with a sharp angle on the downward distal end thereof to provide a location for the molten material 75 to detach and form into ligaments. This overbite 71 ensures that the j et of atomizing fluid will interact, with the molten material that passes through the orifice, in such a way as to draw the material through the orifice 70, with the material running along the inner wall of a region 75a of the orifice 70 where the molten material 75 is stretched and thi ns, and to apply shearing forces to properly stretch the material into ligaments to ensure fine atomization. In embodiments, the j et nozzle 72 is of a shape that allows the gas flow without the creation ofexcessive turbulence, so has no sharp corners prior to the location where the gas exits the j et nozzle 72.

[0051] As depicted in FIG. 6, which depicts another embodiment, the diameter of the neck portion of the orifice is between 1 mm and 50 mm, where the greatest efficiency is achieved if the diameter is slightly longer than the natural droplet size of the material being processed. The actual diameter can be set by a person skilled in the art based on the material to be processed. As depicted in FIG. 6, in embodiments there is an annular lip 27 within the cold tundish 25, a region where the slope of the surface of the cold tundish 25 is reduced, defining the entrance of the orifice 70. Molten material 75 entering the cold tundish 25 may run along the inner surface of the cold tundish 25 until reaching this lip 27, and upon reaching this lip 27 travels around the lip 27 to encompass, at least partially, the orifice 70, to run along the surface of the orifice 70 in the shape of a sheath or a partial sheath, as depicted in FIG.6. As the molten material 75 i s drawn through the orifice, due to a low-pressure region 73, on the exit side of the orifice, which is generated by the Bernoulli effect by the fluid j et that is expelled from the annular j et nozzle 72, this sheath becomes thinner. For optimal performance, the distance d, in the axial direction of the orifice 70, between the lip 27 and the overbite, as depicted in FIG. 7, should be as short as possible. At this time, high heat energy is applied, as described below, in the entire area where the molten material 75 i s present in the cold tundish 25 and in the orifice 70. While in this embodiment this energy is applied through a second plasma 60 that is applied from a second plasma source 40, described below, there is no limitation thereto, but rather in other embodiments the area may be heated by an arc, induction, or the like. After this sheath of molten material 75 is drawn, by the pressure differential and / or by gravity, to a location immediately past the overbite portion of the exit side of the orifice, it i s then sheared, drawn into ligaments, and fractured by the high velocity fluid that exits the annular j et nozzle 72.

[0052] As described above, in embodiments the cold tundi sh 25 al so includes a cooling duct 65, configured so as to carry a coolant fluid so as to remove heat from the cold tundish 25, enabling heat from the molten material 75 to be conducted through the thermally conductive entrance-side portion 55 of the cold tundi sh 25 to the coolant fluid within the cooling ducts 65, and thence carried by the cooling ducts 65 outside of the system, thereby reducing the temperature of the surface of the entrance-side portion 55. The selection of the coolant fluid and the configuration of the cooling ducts 65 may be designed as appropriate by one skilled in the art through standard techniques that are often applied to cooling of cold crucibles, so need not be described in detail here. The mechanisms and techniques for controlling the flow of the coolant fluid, dissipating heat, and the like, should be determined by a person skilled in the art based on the total thermal load that is to be dissipated, which is a function of the desired process throughput, the physical characteristics of the source material (melting point, specific heat, and so forth), and other factors, and can be determined by one skilled in the art analytically or through routine experimentation, without unreasonable or undue experimentation, so are not described in detail here.

[0053] In embodiments, the second plasma source 40 is disposed, directed downward, above the cold tundish 25, so as to produce a second plasma 60 for heating the molten material 75 within the cold tundish 25. As with the first plasma source 30, the second plasma source 40 may be configured so as to produce a DC plasma arc, an AC plasma arc, an RF induction plasma, a microwave plasma, an inductive coupled plasma, a torch plasma, a hollow cathode plasma, an arcj et plasma, or the like, as the second plasma 60, where the selection of the second plasma source 40 and of the second plasma 60 can be made easily by a person skilled in the art using an existing technology, so no further description thereof will be given here. Moreover, while in this embodiment a second plasma source 40 and a second plasma 60 are presented as an example of a heat producing element for heating the molten materi al 75, there is no limitation thereto, but rather in other embodiments otherknown heating methods or devi ces may be used instead of, or in additi on to, the second plasma source 40 and second plasma 60. Examples of such other known heating methods and devices include induction heating, resistance heating, microwave heating, radiant heating, and the like.

[0054] The cold tundi sh 25 further comprises other structural elements as necessary to support and / or form the entrance-side portion 55, the j et fluid duct 45, the annular j et nozzle 72, and the cooling duct 65. As these structural elements are merely mechanical elements that can be designed easily by those skilled in the art, further explanations thereof are omitted. Other peripheral elements of the system, such as external connections for the j et fluid duct 45 and the cooling ducts 65, equipment for supplying gas and cooling fluid to the j et fluid duct 45 and the cooling ducts 65, power supplies and gas supplies for the first and second plasma sources 30 and 40, monitoring and control equipment, and other elements that are known and / or obvious to those of ordinary skill in the art are omitted from the drawings and from the description of this embodiment.

[0055] The operation of embodiments will be explained next. While specifi c control algorithms and feedback loops that would be obvi ous to one skilled in the art are omitted from this explanation, it is to be understood that the equipment i s to be monitored and controlled using known methods. The explanation below will follow the same basic sequence that is followed by material that passes through this system. It should be appreciated that, in embodiments, this is a continuous processing system that processes the source material through a continuous crucible and continuous atomizing process, as opposed to a batch system that is based on a batch crucible that produces di screte melts discontinuously. Nevertheless, there is nothing about this system that requires the crucible to be a continuous flow crucible, but rather the molten material may be provided from a discrete batch crucible in di screte melts / pours.

[0056] In embodiments, the source material is fed or conveyed continuously through the delivery member 15 to the trough section 20, whereit i s melted continuously through exposure to the first pl asma 5, to be converted into the molten material 75. In embodiments, the molten material 75, as a fluid, runs into the cold tundish 25 due to the force of gravity, while in other embodiments the molten material 75 i s caused by other means, such as a pressure differential, to enter into the cold tundish 25.

[0057] As described above, substantially conical j et of a fluid, which may be an inert gas such as argon, exiting the annular j et nozzle 72 at the exit of the orifice 70, which is at or after the narrow neck portion of the orifice 70. While FIG. 4 illustrates a cold tundi sh 25 that has an orifice 70 of an hourglass shape that is wider at the entrance side and the exit side than a narrow neck portion located therebetween, with the annular j et nozzle 72 disposed on the exit side of the widening section that is on the exit side of the narrow neck portion, in another embodiment the orifice 70 may instead be of a funnel shape that is wide at the entrance side and narrow toward the exit side, with the annual j et nozzle 72 disposed at the narrowest portion, as depicted in FIG. 5. Along with other effects, explained below, the high- velocity gas flows of the inert gas create a low-pressure region immediately beyond the orifice 70. The pressure differential across the orifice 70 has the effect of forcibly drawing the molten material 75 through the orifice 70. The second plasma 60, and ambient gas from the entrance side of the orifice 70, may also be drawn through the orifice 70 due to the vacuum effect produced by the low-pressure region 73 that i s the result of the Bernoulli effect that is caused by the high velocity gas flow.

[0058] One result is that this molten material 75 does not pool within the cold tundish 25, but rather runs along the inner wall of the orifice 70 while also spreading around some or all periphery of the orifice 70, creating the configuration depicted in FIG. 6 wherein, in the entrance side of the orifice 70, the orifice surface is covered with a full or partial sheath of the molten material 75 (termed “pre-filming”), with the ambi ent gas and plasma, from the second plasma source 40, drawn through the center thereof. The molten material 75 is al so accelerated through the orifice 70 by the effect of theshearing force of the plasma and ambient gas that i s being drawn through the center of the orifice 70, causing thinning of the flow of the molten material 75. As is well known in the art of cold crucibles, at this time, the entranceside portion 55 of the cold tundish 25 has poor wettability with respect to the molten material 75. This poor wettability reduces the intimacy of contact between the molten material 75 and the entrance-side portion 55 of the cold tundi sh 25, reducing the thermal transfer from the molten material 75 into the entrance-side portion 55. As a result of this poor thermal transfer between the molten material 75 and the entrance-side portion 55 of the cold tundi sh 25 (the surface of the orifice 70), combined with the heating effect of the plasma that is being drawn through the narrow portion of the orifice 70, the molten material 75 tends to not solidify within the orifice 70, thereby preventing clogging of the orifice 70. While there may be some minor freezing of the surface-most layer of the molten material 75, the combination of the constant heating of the molten material, the physical forces by the flow of heated molten material 75, and the poor adhesion of this frozen material 75 to the surface of the orifice 70 through the same effect that is well known in the field of cold crucibles, this minor freezing of the surface- most layer of the molten material 75 flakes off quickly, without clogging the orifice.

[0059] When the molten material 75 passes the neck of the orifice 70 and passes over the overbite portion, not numbered, it passes beyond the annular j et nozzle 72 that is connected to the j et fluid duct 45, and is struck by the high velocity j et of the fluid ej ected from the annular j et nozzle 72. The fluid j et exerts shearing forces on the molten material stream, causing it to elongate into thin ligaments. These ligaments are initially continuous sections of the molten material, but then surface tension and aerodynamic forces cause the ligaments to narrow at certain points, creating thinner sections known as necks. When the ligaments extend to reach a critical length or instability point, the necks formed during necking become unstable, and the ligaments break at these points, transforming into individual droplets.These droplets form themselves into spheroidal shapes, due to the effects of surface tension, and quickly cool as they fall through the ambient atmosphere, producing spherical microparticles. These spherical microparticles fall into a collector, not shown, and are sub sequently removed from the system for use after grading using a sieve.

[0060] In another embodiment of an apparatus for producing spheroidal powder, as illustrated in FIG. 7, the system that is depicted in FIG. 3, with the exclusi on of the exit side of the cold tundish 25 and thereafter, is enclosed within an entrance-side housing 85, depicted in FIG. 7, so as to exclude the incursion of external atmosphere, and a predetermined gas is delivered through a gas delivery inlet, not shown, so as to provide a positive gas pressure in the chamber formed on the entrance side of the orifice 70 with respect to a lower ambient pressure on the exit side of the orifice 70. The region on the exit side of the cold tundish 25 is also enclosed within an exit-side housing 90 so as to exclude the incursion of external atmosphere, and the pressure within the interior of this sealed container i s reduced to less than atmospheric pressure, through a vacuum system, not shown, connected thereto. In embodiments the exit-side housing 90 is partially back-filled with an arbitrary gas, not shown, prior to operation. The relative pressures between the entrance-side and exit-side housings 85 and 90, which are in communication through the orifice 70, are controlled using known pressure controlling techniques and equipment to set a specific predetermined pressure differential between the entrance-side and exit-side housings 85 and 90, to control the flow of gas and plasma through the orifice 70. The temperatures within the entrance-side and exit-side housings 85 and 90 are controlled independently through respective temperature controlling devices, not shown, attached thereto. This embodiment provides the same benefits as the embodiments described above, with the additional benefit that it is possible to control with greater precision the particle sizes in the powders through controlling more finely the temperatures in the respectivechambers and the orifice 70. Thi s has the effect of further increasing yi elds and further decreasing costs.

[0061] A further embodiment of an apparatus for producing spheroidal powder provides an apparatus for producing spheroidal powder as set forth in any of the foregoing embodiments, wherein a temperature controlling device, not shown, is attached to the source, not shown, of the gas that is forced into the j et fluid duct and expelled from the j et nozzles. This enables control of the temperature of the j ets that impinge upon the molten material, enabling finer control of the atomizing process, enabling finer control of the particle sizes in the powder. This has the effect of increasing yields and decreasing costs even further.

[0062] Even another embodiment of an apparatus for producing spheroidal powder provides an apparatus for producing spheroidal powder as set forth in any of the foregoing embodiments, wherein a plurality of di screte j et nozzles, provided equally spaced surrounding the axis of the orifice 72, is provided instead of the single annular j et nozzle. These discrete j et nozzles may be provided directed at a slight angle away from the axis of the orifice 70. This enables a reduction in turbulence through the creation of a fluid vortex, thereby enabling a greater range of control of the atomization, and thus a finer and more uniform product.

[0063] An even further embodiment of an apparatus for producing spheroidal powder provides an apparatus for producing spheroidal powder as set forth in any of the foregoing embodiments, wherein a plurality of annular j et openings that are configured in ring shapes surrounding the vertical axis of the orifice is used instead of the single annular j et nozzle, where these multiple tiers of annular j ets enable even finer control of the atomizing process, which may produce superior results. Different temperatures, pressures, and gasses may be used for respective annular j et openings, enabling even greater control of the atomizing process.

[0064] An even further embodiment yet provides a pancake-type induction coil, not illustrated, rather than the second plasma source 40, in proximityto the col d tundi sh 25, to provide heating to the molten materi al 75 in the cold tundish 25 and the orifice 70. This enables the entrance of the cold tundi sh 25 to be fully closed and sealed, with only an inlet, not shown, for the molten material 75, from the molten material supplying apparatus 12. This enables tighter control of the atmosphere within the cold tundish 25.

[0065] Note that in the description above the word “cold,” in the context of a “cold tundi sh,” or the like, does not imply any specific temperature range, but rather implies that the tundish, or the like, is of a structure wherein there is forced cooling to ensure that the surface thereof that comes into contact with the molten material will be at a temperature that is less than that of the molten material , and, more specifically, less than the melting point of the material from which the surface of the tundish, or the like, is formed.

[0066] While in some embodiments the velocity of the fluid j et from the annular j et nozzle 72 may be a subsonic velocity, on other embodiments it may be a supersonic velocity. With the cold tundish and apparatus for producing spheroidal powders according to the embodiments set forth above, as with any apparatus commercially available for producing spherical powders, there are various parameters that must be set depending on the nature of the material being processed, the desired throughput, the required product specifications, and so forth. These may be set as appropriate by those skilled in the art.

[0067] Note that while, throughout this disclosure, references are made to "gas" and "gas atomization," this is merely for convenience in matching the terminology that is commonly used in the art, and it should be understood that the fluid used in atomization, although referred to as a "gas," i s not necessarily limited to being a gas, but rather refers to any fluid, and thus may be a liquid, such as water, instead. Note that the fluid may be an inert gas such as helium, neon, argon, krypton, xenon, radon, or the like, or a semi-inert gas such as diatomic nitrogen, air, water, or any other fluid that i s compatible with the function of atomizing the molten material throughapplication of shearing forces through a j et of the fluid infringing on the molten material . Furthermore, the fluid may be a functional gas or liquid, selected to physically or chemically interact with the microdroplets that are produced during the atomizing process. These may be selected as appropriate by a person skilled in the art depending on the properties of the material being processed, the properties of the desired product, and other parameters and constraints in the system as a whole.

[0068] While in the embodiments above references have been made to atomizing metal materials, there is no limitation to the material being metal, but rather the cold tundish and apparatus and method for producing spheroidal powders can be applied to atomization of nonmetals as well, such as semimetals, semiconductors, and nonmetals (such as certain ceramics), insofar as the material can melt and flow.

[0069] While in the embodiments set forth above the molten material supplying apparatus 12 i s of a continuous melt type, compri sing a delivery member, a trough section, and a plasma source, there is no particular limitation thereto, but rather any apparatus configured so as to provide molten material into the cold tundish 25 may be used. The molten material supplying apparatus 12 need not be of a continuous melt type, but may be of a batch melt type, and the transfer of molten material into the tundish may be through pouring, gravity feeding, pumping, or the like.

[0070] While in the embodiments set forth above the tundish 25 is illustrated as being open at the entrance, there is no limitation thereto; rather the tundish 25 may be partially or fully closed at the entrance, insofar as the second heater 40 is able to heat the molten material 75 that is in the cold tundi sh 25 and in the orifice 70 and the tundish is able to receive molten material 75 from the molten material supplying apparatus 12.

[0071] While in the embodiments set forth above the j et nozzle was described as being an annular nozzle comprising an annular slit, there i s no limitation thereto, but rather the annulus may be parted into multiple discontinuous sections, or a plurality of individual non-annular j et nozzlesmay be provided di sposed equally spaced around a circle around the axi s of the orifice in the location wherein the annular j et nozzle 72 is illustrated in FIG. 4 or FIG. 5, for example.

[0072] A yet further embodiment, as depicted in FIG. 8 i s a method for producing spheroidal powders, including: delivering 100 a source material 35 to a melting device; producing heat 110 in the melting device to melt the source material 35 to produce a molten material 75; allowing 120 the molten material 75 to run, under a gravitational force, into a cold tundish 25; applying heat 130 to the molten material 75 in the cold tundish 25; cooling 140 the cold tundish from an interior of the cold tundish 25 through a cooling fluid; discharging 150 a j et of a gas from a j et opening on an exit-side portion of the cold tundish 25 to create a low-pressure region on the exit side of an orifice 70 of the cold tundish 25 so as to draw the molten material 75 through the orifice 70 in the cold tundish 25 ; and causing 160 a j et of gas to strike molten material 75 that has been drawn through the cold tundish.

[0073] In even yet another embodiment, all of the aforementioned steps are performed in parallel in a continuous process.

[0074] The foregoing descriptions of the embodiments of the invention have been presented for the purposes of illustration and description. All elements of the various embodiments set forth above may be recombined into yet further embodiments, with all possible combinations falling within the scope of the present invention. Each and every page of this submission, and all contents thereon, however characterized, identified, or numbered, is considered a substantive part of this application for all purposes, irrespective of form or placement within the application. Thi s specification is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of this disclosure.

[0075] Although terms such as “first” and “second” are used herein to describe various features or elements, the features or elements are not be limited by these terms unless the context explicitly indicates otherwise.These terms are used merely to di stingui sh one feature or el ement from another. Therefore, a first feature or element described herein could be referred to as a second feature or element, and vice versa, without departing from the teachings of the present invention. Additionally, the presence of a feature or element termed “second” does not necessarily imply the existence of a “first” feature or element in that embodiment or claim. Unless an ordinal relationship is explicitly stated, terms such as “first” and “ second” are to be interpreted as mere arbitrary nominal identifiers with no implications regarding sequence or quantity.

Claims

CLAIMSAmong my claims are:

1. An apparatus for producing spheroidal powders, comprising: a molten material supplying apparatus; a cold tundish configured to receive a molten material from the molten material supplying apparatus, having an orifice at the exit thereof configured to discharge the received molten material, said orifice passing through the cold tundish, with a relatively wide opening diameter at an entrance portion, with a relatively narrow opening diameter in a portion thereafter; and a j et opening configured to produce a high velocity fluid flow that impinges on, and atomizes, the discharged molten material, wherein : the cold tundish is configured compri sing an entrance-side portion that is made from a high thermal conductivity material and a cooling duct configured to carry a coolant fluid for cooling the thermally conductive entrance-side portion; a second heating device is provided, configured so as to heat molten material that is in or on the cold tundish; and the j et opening is provided in the cold tundish, opening at an exit-side portion of the orifice.

2. The apparatus for producing spheroidal powders of claim 1 wherein : the molten material supplying apparatus comprises a continuous feed source material delivery device configured to deliver a source material into a melting device that comprises a first heating device that is configured to heat and melt the source material into a molten material .

3. The apparatus for producing spheroidal powders of claim 2 wherein:the first heating devi ce i s configured as a plasma source configured to cause a plasma to impinge upon the source material that is in or on the melting device, an inductive heating source configured to cause inductive heating of the source material that is in or on the melting device, or a resistive heating source configured to heat the source material that is in or on the melting device.

4. An apparatus for producing spheroidal powders of any of claims 1 through 3 wherein: the j et opening is configured in a ring shape surrounding a center axis of the orifi ce.

5. An apparatus for producing spheroidal powders of any of claims 1 through 4 wherein: the j et opening is configured from a plurality of j et openings, disposed equally spaced around the vertical axis of the orifice.

6. An apparatus for producing spheroidal powders of any of claims 1 through 5 wherein: the second heating device is configured as a plasma source for causing a plasma to impinge upon the molten material that is in or on the cold tundish.

7. An apparatus for producing spheroidal powders of any of claims 1 through 6 wherein: an inert gas is discharged at a high velocity from the j et opening.

8. An apparatus for producing spheroidal powders of claim 7 wherein: the inert gas is argon.

9. An apparatus for producing spheroidal powders of any of claims 1 through 8 wherein: the j et opening is configured such that a low-pressure region is formed on the exit side of the orifice when a fluid is discharged at a high velocity from the j et opening.

10. An apparatus for producing spheroi dal powders of any of claim s 1 through 9 wherein: the j et opening is configured so that, when a fluid is di scharged at a high velocity from the j et opening, a plasma, produced by the second heating device, will be drawn into the orifice.

11. An apparatus for producing spheroidal powders of any of claims 1 through 10 wherein: the second heating device is configured as a pancake-type inductive heating device configured to heat the molten material that is in or on the cold tundish.

12. An apparatus for producing spheroidal powders of any of claims 1 through 1 1 wherein: the cold tundi sh compri ses an annular lip .

13. An apparatus for producing spheroidal powders of any of claims 1 through 12 configured such that: the molten material is drawn through the orifi ce in the form of a sheath.

14. An apparatus for producing spheroi dal powders of any of claim s 1 through 13 , further comprising: an entrance-side housing on the entrance side of the orifice and an exit-side housing on the exit side of the orifice.

15. The apparatus for producing spheroidal powders of claim 14, wherein: the entrance-side housing and the exit-side housing are maintained at different static pressures.

16. An apparatus for producing spheroidal powders of claim 14 or 15, wherein: the interior of the entrance-side housing and the interior of the exitside housing are maintained at different temperatures.

17. An apparatus for producing spheroi dal powders of any of claim s 1 through 16, further comprising: a fluid flow temperature controlling device configured to control a temperature of the high velocity fluid flow.

18. An apparatus for producing spheroidal powders of any of claims1 through 17, wherein: the high velocity fluid flow flows at a supersonic velocity.

19. An apparatus for producing spheroidal powders of any of claims1 through 18, wherein: the orifice passes substantially vertically through the cold tundi sh.

20. A method for producing spheroidal powders, including: delivering a source material to a melting device; producing heat in the melting device to melt the source material to produce a molten material; causing the molten material to run into a cold tundish; heating the molten material in the cold tundish; cooling the cold tundish from the interior of the structure of the cold tundish through a cooling fluid; discharging a j et of a gas from a j et opening on an exit-side portion of the cold tundish to create a low-pressure region on the exit side of an orifice of the cold tundish so as to draw the molten material through the orifice in the cold tundish; and causing a j et of gas to strike the molten material that has been drawn through the cold tundish; wherein: all of the aforementioned steps are performed concurrently in a continuous process.

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