Patent Application
20250170646
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.
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 injection 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 injection 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 μm). 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, to date 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.
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
The second method employs a freefall gas atomizer, as depicted schematically in
The third method, not illustrated, is that of wire plasma atomization. In this method a wire is fed through a plasma that is produced by one or more plasma sources, to thereby melt the wire into droplets, which are then broken up by powerful jets of an inert gas.
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. Cold 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.
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.
Close-coupled gas atomizers, such as depicted in
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 is 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 materials 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.
The freefall atomization approach, on the other hand, has the benefit of not requiring a nozzle at all, as can be seen by comparing
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 rejected 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.
Thus there is the need for an apparatus that enables high-yield production of ultrafine microparticles of even reactive and refractory materials such as titanium, niobium, rhenium and other similar metals or alloys, from a broad variety of feedstock configurations, using a process that is economical and efficient.
One embodiment of the present invention provides an apparatus for producing spheroidal powders, comprising: a molten material supplying apparatus; a cold tundish 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 jet opening for producing a high velocity fluid flow 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 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 jet opening is provided in the cold tundish, opening at a portion on an exit side of the orifice.
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.
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 jet opening is configured in a ring shape surrounding a center axis of the orifice.
In yet another embodiment, the jet opening is configured in a ring shape surrounding a center axis of the orifice.
In a yet further embodiment, the jet opening is configured from a plurality of jet openings, disposed spaced around the vertical axis of the orifice.
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 is in or on the cold tundish.
In a still further embodiment, an inert gas is discharged at a high velocity from the jet opening.
In an even another embodiment, the inert gas is argon.
In an even further embodiment, the jet opening is 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 jet opening.
In a still even another embodiment, the jet opening is configured so that, when a gas is discharged at a high velocity from the jet opening, a plasma, produced by the second heating device, will be drawn into the orifice.
In a still even further embodiment, 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.
In still yet another embodiment, the cold tundish comprises an annular lip.
In a still yet further embodiment, the molten material is drawn through the orifice in the form of a sheath.
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.
An even yet further 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 interior of the entrance-side housing and the interior of the exit-side housing are maintained at different temperatures.
A still even yet another embodiment comprises a fluid flow temperature controlling device configured to control a temperature of the high velocity fluid flow.
In a still even yet further embodiment the high velocity fluid flow flows at a supersonic velocity.
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 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 jet of a gas from a jet 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 jet 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.
Note that identical reference numerals are assigned to identical or analogous elements that appear in separate drawings, and redundant explanations may be omitted.
As illustrated in
As depicted in
The cold tundish 25 is 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 tundish 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 specifically to materials that are generally selected by those skilled in the art to provide or enhance thermal conductivity of a component or material.
Returning to
In embodiments, the delivery member 15, depicted in
Continuing the description based on
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-side 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 tundish 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.
In embodiments, the trough section 20 is formed as a trough with a substantially U-shaped cross-section that is 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 end of the trough section is positioned so as to be open toward the cold tundish 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 tundish 25 end of the trough section 20 than on the delivery member 15 end of the trough section 20.
As described above and as depicted in
While the embodiments set forth above use an annular jet 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 jet nozzle may instead comprise a discontinuous slit, with multiple discrete openings, or may use multiple discrete jet 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.
As depicted in
As described above, in embodiments the cold tundish 25 also 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 tundish 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.
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 arcjet 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 material 75, there is no limitation thereto, but rather in other embodiments other known heating methods or devices may be used instead of, or in addition 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.
The cold tundish 25 further comprises other structural elements as necessary to support and/or form the entrance-side portion 55, the jet fluid duct 45, the annular jet 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 jet fluid duct 45 and the cooling ducts 65, equipment for supplying gas and cooling fluid to the jet 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.
The operation of embodiments will be explained next. While specific control algorithms and feedback loops that would be obvious to one skilled in the art are omitted from this explanation, it is to be understood that the equipment is 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 discrete 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 discrete melts/pours.
In embodiments, the source material is fed or conveyed continuously through the delivery member 15 to the trough section 20, where it is melted continuously through exposure to the first plasma 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 is caused by other means, such as a pressure differential, to enter into the cold tundish 25.
As described above, substantially conical jet of a fluid, which may be an inert gas such as argon, exiting the annular jet nozzle 72 at the exit of the orifice 70, which is at or after the narrow neck portion of the orifice 70. While
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
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 jet nozzle 72 that is connected to the jet fluid duct 45, and is struck by the high velocity jet of the fluid ejected from the annular jet nozzle 72. The fluid jet 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 subsequently removed from the system for use after grading using a sieve.
In another embodiment of an apparatus for producing spheroidal powder, as illustrated in
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 jet fluid duct and expelled from the jet nozzles. This enables control of the temperature of the jets 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.
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 discrete jet nozzles, provided equally spaced surrounding the axis of the orifice 72, is provided instead of the single annular jet nozzle. These discrete jet 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.
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 jet openings that are configured in ring shapes surrounding the vertical axis of the orifice is used instead of the single annular jet nozzle, where these multiple tiers of annular jets enable even finer control of the atomizing process, which may produce superior results. Different temperatures, pressures, and gasses may be used for respective annular jet openings, enabling even greater control of the atomizing process.
An even further embodiment yet provides a pancake-type induction coil, not illustrated, rather than the second plasma source 40, in proximity to the cold tundish 25, to provide heating to the molten material 75 in the cold tundish 25 and the orifice 70. This enables the entrance of the cold tundish 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.
Note that in the description above the word “cold,” in the context of a “cold tundish,” 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.
While in some embodiments the velocity of the fluid jet from the annular jet 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.
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,” is 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 is compatible with the function of atomizing the molten material through application of shearing forces through a jet 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.
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.
While in the embodiments set forth above the molten material supplying apparatus 12 is of a continuous melt type, comprising 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.
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 tundish 25 and in the orifice 70 and the tundish is able to receive molten material 75 from the molten material supplying apparatus 12.
While in the embodiments set forth above the jet nozzle was described as being an annular nozzle comprising an annular slit, there is no limitation thereto, but rather the annulus may be parted into multiple discontinuous sections, or a plurality of individual non-annular jet nozzles may be provided disposed equally spaced around a circle around the axis of the orifice in the location wherein the annular jet nozzle 72 is illustrated in
A yet further embodiment, as depicted in
In even yet another embodiment, all of the aforementioned steps are performed in parallel in a continuous process.
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. This 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.
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 distinguish one feature or element 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.
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.
| Number | Date | Country | |
|---|---|---|---|
| 63602892 | Nov 2023 | US |
