Apparatus and method for producing a metal powder
The device uses a heated tundish, rotating turntable, and gas nozzles to produce metal particles with controlled shape and size, addressing exposure issues and enhancing retrofittability.
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Patents
- Current Assignee / Owner
- RIMMER KARL
- Filing Date
- 2021-09-08
- Publication Date
- 2026-06-17
AI Technical Summary
Existing metal powder production devices face issues with metal particles being exposed to undesirable reactions and lack the ability to produce particles with highly defined shape and size, and existing devices are not easily retrofittable.
A device with a heated tundish, rotating turntable, primary and secondary gas nozzles, and a classifier, where the secondary gas nozzle guides and cools solidified metal particles away from the turntable, and the turntable geometry and gas flow control the particle shape and size, allowing easy retrofitting of existing devices.
Produces metal particles with defined shape and size, preventing undesirable reactions and enabling easy retrofitting of existing systems.
Smart Images
Figure IMGF0001
Abstract
Description
AREA OF INVENTION
[0001] The present invention relates to a device and a method for
[0002] Production of a metal powder. STATE OF THE ART
[0003] Metal powders can be produced using various methods. In addition to physical processes such as mechanical comminution, evaporation, and condensation, chemical and physicochemical processes are also employed, including chemical reactions, reduction or decomposition of metal compounds, and electrolysis.
[0004] For the particularly precise production of metal powders, devices of this type are used, employing a physical process namely centrifugal atomization. This involves a rapidly rotating turntable, onto which molten metal is thrown by centrifugal force and broken up into small droplets, which then solidify into metal particles.
[0005] CA 2170206 A1 discloses a device and a method for producing a metal powder using two gas nozzles, the method comprising three basic steps, namely Atomizing a molten metal with a gas to create droplets, breaking up the droplets into fine particles using a rapidly rotating disk, and rapidly cooling the fine particles with a coolant.
[0006] GB 2051138 A describes a device for producing a metal powder comprising a primary gas nozzle and a housing in which, among other things, a crucible with associated liquid heating medium, a rotating atomizing medium and a rotating spray plate are arranged.
[0007] A disadvantage of the described state of the art is that the already solidified metal particles are not directed away from the rotating disk or the rotating spray plate and are therefore sometimes exposed to undesirable reactions.
[0008] US 4078873 A relates to the production of metal powders by means of a device comprising a hopper with a nozzle, a nozzle plate arranged around it with several nozzles to create multiple coolant flows, and a rotating disk.
[0009] WO 2008 / 120938 A1 discloses a device and a method for producing silicon-based alloy powder, including the use of a rotary table. In the embodiment shown in Fig. 2, a tundish 201 with a fluidically connected nozzle 202 and a gas flow 203 are shown, which flows through an outlet that at least partially surrounds the nozzle 202. However, in this embodiment, there is no coolant supply pipe 70 and therefore no secondary gas nozzle. In the embodiments shown in Figs. 4-5, neither a nozzle fluidically connected to the tundish nor a primary gas nozzle that at least partially surrounds the nozzle for stabilizing the melt is explicitly disclosed. Furthermore, in all embodiments in which a coolant supply pipe 70 is present, an outlet of the coolant supply pipe 70 is arranged within the rotary table. The distance of the outlet and the nozzles from the rotary table is not adjustable in each case. TASK OF INVENTION
[0010] The object of the invention is to provide an improved device for producing a metal powder. In particular, the metal particles should have a highly defined shape and / or size, the size of which should be easily adjustable. A further object of the invention is that existing devices of this type should be easily retrofitted. PRESENTATION OF THE INVENTION
[0011] This problem is solved by a device according to claim 1.
[0012] Metal powder, which includes metal particles, is considered to be metal powder of a single metal as well as of alloys and mixtures, whereby the metal(s) are selected in particular from the group Al, Zn, Sn, Fe, Mg, Zr, W, Sb, Ni, Cu, Ag, Au.
[0013] The tundish is heated to prevent the molten metal from cooling and to guarantee a temperature favorable for atomization. A nozzle is located at the lower end of the tundish (in the direction of flow of the molten metal), through which the molten metal can be poured from the tundish onto the rotating turntable by gravity. Upon impact with the rotating turntable, the molten metal atomizes and subsequently solidifies into metal particles.
[0014] As mentioned previously, the turntable rotates, generating the centrifugal force required to atomize the molten metal. When the turntable rotates at a constant revolutions per unit of time (RPM), the speed at the outer edge is higher than radially within the turntable. This results in droplets of different shapes and sizes being formed, and consequently, metal particles of different shapes and sizes, depending on where the molten metal strikes a particular area of the turntable. Furthermore, the size and shape of the metal particles can also be controlled by the revolutions per unit of time, assuming a constant impact area of the molten metal on the turntable. Lower revolutions per unit of time produce differently shaped and sized metal particles than higher revolutions per unit of time.
[0015] The rotary table of the device according to the invention rotates between 50,000 rpm and 90,000 rpm, in particular between 55,000 rpm and 70,000 rpm, resulting in particularly fine metal particles.
[0016] It is conceivable that the device according to the invention is arranged in at least one chamber. However, it is also possible that the tundish is located in one chamber, namely a furnace chamber, and the rotary plate is arranged in a separate chamber, namely an atomization chamber. Preferably, the chamber(s) are gas-tight to prevent the ingress of air, which could lead to oxidation in the melt or in the metal particles.
[0017] According to the invention, the device comprises a primary gas nozzle and a secondary gas nozzle, from each of which at least one gas stream is discharged. To prevent undesirable reactions of the melt or the metal particles, the gas for the gas streams is air or an inert gas, preferably N2, H2, CO, CO2, He, Ar, Kr, Xe or a mixture thereof.
[0018] The gas stream exiting the primary gas nozzle surrounds the nozzle, at least partially, and serves to stabilize the molten metal exiting the nozzle. Immediately after exiting the nozzle, the molten metal is enveloped, at least partially, by the gas stream, which guides it from the nozzle to the rotary table and protects it from unwanted reactions.
[0019] The gas stream exiting the secondary gas nozzle, viewed radially, encounters the metal particles, which have already solidified at least partially and been flung away from the turntable, and serves two purposes: firstly, to further cool these particles; and secondly, to guide the metal particles away from the turntable into an environment, protecting them from unwanted reactions.
[0020] Furthermore, it is conceivable that the size and / or shape of the metal particles can be easily adjusted by means of the gas flow exiting the secondary gas nozzle. That is, in addition to the rotational speed of the turntable and the impact area of the melt on the turntable, the gas flow from the secondary gas nozzle can also be used to (further) adjust the geometric properties of the metal particles.
[0021] By positioning the secondary gas nozzle between the tundish and the rotary table, existing devices for the production of metal powder can be easily retrofitted without having to significantly change the design of existing devices.
[0022] The geometry of the rotary table also serves to achieve a defined shape and / or size of the metal particles. Therefore, in a first alternative of the invention, a distance parallel to the axis of rotation between the surface of the rotary table and a normal plane perpendicular to the axis of rotation, in which normal plane an outlet of the nozzle is located, is monotonically decreasing in the radial direction.
[0023] That is, the surface of the rotary table of the device according to the invention facing the tundish is at least partially positively curved and / or at least partially linearly rising. Of course, it is also not excluded that the surface of the rotary table runs at least partially parallel to the normal plane, i.e., horizontally in an operating state of the device according to the invention.
[0024] From the foregoing, it follows that the surface of the turntable facing the tundish is at least partially concave. This means the turntable has at least one depression in its inner area. Of course, it is also possible that the turntable has several depressions extending radially outwards from its inner area – the surface of such a turntable would then have a wave-like appearance.
[0025] If the distance between the surface of the turntable and the normal plane decreases monotonically radially outwards, the molten metal exiting the nozzle typically strikes the surface of the turntable in a depression. The molten metal, which has solidified at least partially into metal particles, is at least partially flung radially outwards from the surface of the turntable towards the secondary gas nozzle, particularly towards the outlet of the secondary gas nozzle. Those metal particles that are either flung back towards the turntable from a surface of the secondary gas nozzle facing the turntable, or that are not flung away from the turntable at all and remain on its surface, are carried radially outwards by the rotation of the turntable and, due to the monotonous slope of the turntable's surface, are carried towards the outlet of the secondary gas nozzle.The geometry of the rotary table serves to guide the metal particles, at least in sections, to the outlet of the secondary gas nozzle.
[0026] It is conceivable that the shaping of the metal particles essentially takes place on the surface of the turntable facing the tundish, and that the gas flow exiting the secondary gas nozzle only slightly influences the size and / or shape of the metal particles, if at all.
[0027] In a second alternative of the invention, it is provided that a distance parallel to the axis of rotation between the surface of the rotary table and a normal plane perpendicular to the axis of rotation, in which normal plane an outlet of the nozzle is located, is monotonically increasing in the radial direction.
[0028] That is, the surface of the rotary table of the device according to the invention facing the tundish is at least partially negatively curved and / or at least partially linearly decreasing. Of course, it is also not excluded in this case that the surface of the rotary table runs at least partially parallel to the normal plane, i.e., horizontally in an operating state of the device according to the invention.
[0029] From what has been said above, it follows that the surface of the turntable facing the tundish is at least partially convex. This means that the turntable has at least one raised area in its inner region. Of course, it is also possible that the turntable has several raised areas extending radially outwards from its inner region – the surface of such a turntable would then have a wave-like appearance.
[0030] Since the melt exiting the nozzle strikes the surface of the turntable at a raised area, it is conceivable that the surface of the turntable facing the tundish only slightly influences the size and / or shape of the metal particles, and that the shaping of the metal particles is essentially achieved by means of the gas flow exiting the secondary gas nozzle.
[0031] In one embodiment of the invention, the rotary table has an inner region and an outer region, wherein the tundish-facing surface of the inner region extends along the radial direction, and the tundish-facing surface of the outer region is arranged at an angle of 5° to 60°, preferably 15° to 45°, and particularly preferably 25° to 35°, to the tundish-facing surface of the inner region. That is, the tundish-facing surface of the outer region can be inclined towards the tundish or inclined away from the tundish.
[0032] Depending on whether the outer surface facing the tundish is inclined towards or away from the tundish, the tundish-facing surface of the turntable is sectionally concave or convex. That is, the turntable has at least one depression or at least one raised area.
[0033] Furthermore, according to the invention, the distance between the normal plane and the surface of the rotary table and / or a distance between a further normal plane perpendicular to the axis of rotation, in which a secondary gas nozzle outlet is located, and the surface of the rotary table can be adjusted to control the size and / or shape of the metal particles. This means that, on the one hand, it is conceivable that the two distances can be varied independently of each other using the device according to the invention. On the other hand, it is also conceivable that the two distances can be adjusted together, i.e., dependently on each other.
[0034] Depending on the type of melt, especially its composition, as well as the desired size and shape of the metal particles, the two distances can be adjusted to always achieve the optimal end product.
[0035] In the operating state of the device, the outlet of the nozzle for pouring the melt is usually located lower than the outlet of the secondary gas nozzle.
[0036] In a further embodiment of the invention, the discharge direction of the secondary gas nozzle is parallel to the axis of rotation. This ensures, on the one hand, that the metal particles coming from the rotary table are not thrown back onto it and, on the other hand, that the metal particles are cooled further. Furthermore, this design allows for the simplest adjustment of the size and / or shape of the metal particles.
[0037] The best results are achieved when the gas flow exiting the at least one outlet of the secondary gas nozzle acts as uniformly as possible on the metal particles flung away from the rotating plate. Therefore, in a further embodiment of the invention, the outlet of the secondary gas nozzle is provided to be at least partially annular and to surround the rotating plate at least partially. The at least partially annular design of the outlet of the secondary gas nozzle ensures a particularly uniform and constant gas flow. Furthermore, the blowing force and airflow can be regulated or adjusted particularly easily with the annular outlet. Preferably, the secondary gas nozzle has at least one continuously annular outlet.
[0038] In a further embodiment of the invention, it is provided that one discharge direction of the primary gas nozzle points towards the melt exiting the nozzle. This allows the melt, whose flow direction – as already mentioned – follows gravity, to be selectively influenced between exiting the nozzle and impacting the rotary table.
[0039] The gas flow can be used to influence / deflect the direction of the molten metal flow so that it strikes a specific area of the turntable. This can be achieved by varying both the strength of the gas flow and the angle at which it impacts the molten metal. The size and / or shape of the metal particles can also be influenced or adjusted. If the molten metal strikes an area near the edge of the turntable, the higher velocity and stronger centrifugal force result in smaller droplets and thus smaller metal particles. Conversely, if the molten metal strikes the turntable more centrally, the lower velocity and resulting lower centrifugal force produce larger droplets and thus larger metal particles.
[0040] In a further embodiment of the invention, it is provided that the diameter of the nozzle, in particular the outlet, is adjustable for metering the melt.
[0041] Typically, the nozzle, and especially its outlet, has a diameter of 1 mm to 5 mm. This diameter must be large enough to prevent the outlet from becoming clogged with molten metal, while also being suitable for the desired shape and / or size of the metal particles. The more molten metal passes through the nozzle, particularly the outlet, per unit of time, the larger the metal particles ejected from the turntable.
[0042] To classify the metal particles ejected from the rotary table into the surrounding area, a further embodiment of the invention provides that the device includes a classifier, the classifier being arranged downstream of the rotary table in the direction of melt flow. The classifier can be located within the at least one chamber in which, among other things, the tundish and rotary table may be arranged, or it can be spatially separated from the at least one chamber.
[0043] The classifier, as described in the invention, is a device for classifying metal particles according to a defined criterion such as particle size. Classification typically utilizes the different inertial forces and flow resistances of the various-sized metal particles in a medium, such as an airflow.
[0044] To solve the problem described at the beginning, a method for producing a metal powder according to claim 8 is also provided. BRIEF DESCRIPTION OF THE FIGURES
[0045] The invention will now be explained in more detail using an exemplary embodiment. The drawing is exemplary and is intended to illustrate the inventive concept, but in no way to restrict or even exhaustively represent it.
[0046] This shows: Fig. 1 a schematic sectional view of an embodiment of a device according to the invention for the production of a metal powder. WAYS TO IMPLEMENT THE INVENTION
[0047] Fig. 1 shows a schematic sectional view of an embodiment of a device 1 according to the invention for producing a metal powder, which device 1 has a tundish 2, a rotary table 5, a nozzle 7, a primary gas nozzle 8 and a secondary gas nozzle 9, wherein the device 1 according to the invention is arranged in a gas-tight chamber (not shown).
[0048] The tundish 2 serves to produce a melt 3, wherein a nozzle 7, fluidically connected to the tundish 2, is arranged at a lower end of the tundish 2 as seen in a flow direction 6 of the melt 3, which is suitable for pouring the melt 3 from the tundish 2 onto the rotary table 5.
[0049] Viewed in the flow direction 6 of the melt 3, the rotary table 5 is thus arranged after the tundish 2 and after the nozzle 7. Furthermore, the rotary table 5 rotates at 60,000 rpm about a rotational axis 4 in order to atomize the melt 3 impacting a surface 5a of the rotary table 5 and to eject it in the form of droplets, which subsequently solidify into metal particles 11.
[0050] The nozzle 7 has an outlet 7a, the diameter of which is adjustable, wherein in this embodiment the diameter is adjustable in a range from 1 mm to 5 mm.
[0051] In this embodiment, the nozzle 7 is completely surrounded by a primary gas nozzle 8, which in this case has an annular cross-section. Furthermore, the device 1 according to the invention has a secondary gas nozzle 9, which is arranged between the tundish 2 and the rotary table 5, wherein an annular outlet 9a of the secondary gas nozzle 9 is located further outwards than the rotary table 5 in a radial direction 10 with respect to the axis of rotation 4.
[0052] A gas stream exits both the primary gas nozzle 8 and the secondary gas nozzle 9, with Ar exiting in this embodiment to prevent undesirable reactions of the melt 3 or the metal particles 11.
[0053] The gas stream exiting the primary gas nozzle 8 serves to stabilize the melt 3, with a discharge direction 8a pointing towards the melt 3 exiting the nozzle 7, in particular from the outlet 7a. The gas stream completely envelops the melt 3, thereby guiding the melt 3 from the nozzle 7 towards the rotary table 5.
[0054] The gas flow exiting the outlet 9a of the secondary gas nozzle 9, viewed in a radial direction 10, again encounters the metal particles 11 flung away from the rotary table 5, with one discharge direction 9b being parallel to the axis of rotation 4. The gas flow of the secondary gas nozzle 9 serves, on the one hand, to (further) cool the metal particles 11 and, on the other hand, to guide the metal particles 11 away from the rotary table 5 into an environment.
[0055] In this embodiment, the surface 5a of the rotary table 5 has a concave shape. The rotary table 5 has an inner region 5b and an outer region 5c, wherein the surface of the inner region 5b facing the tundish 2 extends along the radial direction 10 and the surface 5a of the outer region 5c facing the tundish 2 is arranged at an angle α of 25° to the surface 5a of the inner region 5b facing the tundish 2, whereby the majority of the metal particles 11 are conveyed to the outlet 9a of the secondary gas nozzle 9.
[0056] To adjust the size and shape of the metal particles, both a distance 13 between a normal plane 12, in which the outlet 7a of the nozzle 7 is located, and the surface 5a of the rotary table 5, and a distance 15 between another normal plane 14 and the surface 5a of the rotary table 5 can be adjusted, wherein the normal plane 12 and the other normal plane 14 are each normal to the axis of rotation 4.
[0057] Furthermore, the device 1 according to the invention has a classifier (not shown) for classifying the metal particles 11, wherein the classifier is arranged spatially separate from the chamber. REFERENCE MARK LIST
[0058] 1 Device for producing a metal powder 2 Tundish 3 Melt 4 Axis of rotation 5 Rotary table 5a Surface 5b Inner area 5c Outer area 6 Flow direction 7 Nozzle 7a Outlet 7b Diameter 8 Primary gas nozzle 8a Blowout direction 9 Secondary gas nozzle 9a Outlet 9b Blowout direction 10 Radial direction 11 Metal particles 12 Normal plane 13 Distance between surface 5a and normal plane 12 14 Further normal plane 15 Distance between surface 5a and further normal plane 14 α angle
Claims
1. A device (1) for producing a metal powder, comprising: - a tundish (2) for producing a melt (3); - a rotary table (5) having an axis of rotation (4), the rotary table (5) being arranged downstream from the tundish (2) as viewed in a flow direction (6) of the melt (3), and the rotary table (5) being rotatable so as to atomize the melt (3) on a surface (5a) of the rotary table (5); - a nozzle (7) that is fluidically connected to the tundish (2) for pouring the melt (3) onto the rotary table (5); - a primary gas nozzle (8) surrounding the nozzle (7) at least in sections for stabilizing the melt (3); and - a secondary gas nozzle (9) arranged between the tundish (2) and the rotary table (5), characterized in that at least one outlet (9a) of the secondary gas nozzle (9) at least in sections is arranged in a radial direction (10), based on the axis of rotation (4), further to the outside than the rotary table (5) so as to act on the atomized melt (3), which has solidified to form metal particles (11) and is leaving the rotary table (5), - a distance (13) between a normal plane (12) that is perpendicular to the axis of rotation (4), with an outlet (7a) of the nozzle (7) being located in the normal plane (12), and the surface (5a) of the rotary table (5), and / or a distance (15) between a further normal plane (14) that is perpendicular to the axis of rotation (4), with an outlet (9a) of the secondary gas nozzle (9) being located in the further normal plane (14), and the surface (5a) of the rotary table (5) being adjustable for setting the size and / or shape of the metal particles (11); - the rotary table being designed to rotate at between 50,000 rpm and 90,000 rpm; and - the distance (13), which is parallel to the axis of rotation (4), between the surface (5a) of the rotary table (5) and the normal plane (12) that is perpendicular to the axis of rotation (4), with the outlet (7a) of the nozzle (7) being located in the normal plane (12), decreasing monotonically in the radial direction (10), or the distance (13), which is parallel to the axis of rotation (4), between the surface (5a) of the rotary table (5) and the normal plane (12) that is perpendicular to the axis of rotation (4), with the outlet (7a) of the nozzle (7) being located in the normal plane (12), increasing monotonically in the radial direction (10).
2. The device (1) according to claim 1, characterized in that the rotary table (5) comprises an inner region (5b) and an outer region (5c), the surface (5a) of the inner region (5b) facing the tundish (2) extending along the radial direction (10), and the surface (5a) of the outer region (5c) facing the tundish (2) being arranged at an angle (α) of 5° to 60°, preferably 15° to 45°, particularly preferably 25° to 35°, with respect to the surface (5a) of the inner region (5b) facing the tundish (2).
3. The device (1) according to any one of claims 1 to 2, characterized in that a blow-out direction (9b) of the secondary gas nozzle (9) is parallel to the axis of rotation (4).
4. The device (1) according to any one of claims 1 to 3, characterized in that the outlet (9a) of the secondary gas nozzle has an annular design at least in sections and surrounds the rotary table (5) circumferentially at least in sections.
5. The device (1) according to any one of claims 1 to 4, characterized in that a blow-out direction (8a) of the primary gas nozzle (8) points toward the melt (3) emerging from the nozzle (7).
6. The device (1) according to any one of claims 1 to 5, characterized in that a diameter (7b) of the nozzle (7), in particular of the outlet (7a), is adjustable for metering the melt (3).
7. The device (1) according to any one of claims 1 to 6, characterized in that the device (1) comprises a classifier for classifying the metal particles (11), the classifier being arranged downstream from the rotary table (5) as viewed in the flow direction (6) of the melt (3).
8. A method for producing a metal powder comprising the following steps: - melting at least one metal in a tundish (2); - pouring a melt (3) from the tundish (2) by way of a nozzle (7) onto a rotary table (5) rotating about an axis of rotation (4) at a speed between 50,000 rpm and 90,000 rpm; - stabilizing the melt (3) by way of a gas stream directed at the melt (3) from a primary gas nozzle surrounding the nozzle (7) at least in sections; - atomizing the melt (3) by impingement onto the rotating rotary table (5); - solidifying the atomized melt (3) to form metal particles (11); - having a further gas stream act on the metal particles (11) leaving the rotary table (5), the further gas stream emerging from a secondary gas nozzle (9) arranged between the tundish (2) and the rotary table (5), and at least one outlet (9a) of the secondary gas nozzle (9) at least in sections being arranged in a radial direction (10), based on the axis of rotation (4), further to the outside than the rotary table (5) so as to act on the atomized melt (3), which has solidified to form metal particles (11) and is leaving the rotary table (5); - a distance (13) between a normal plane (12) that is perpendicular to the axis of rotation (4), with an outlet (7a) of the nozzle (7) being located in the normal plane (12), and a surface (5a) of the rotary table (5), and / or a distance (15) between a further normal plane (14) that is perpendicular to the axis of rotation (4), with an outlet (9a) of the secondary gas nozzle (9) being located in the further normal plane (14), and the surface (5a) of the rotary table (5) being adjusted for setting the size and / or shape of the metal particles (11); and - the distance (13), which is parallel to the axis of rotation (4), between the surface (5a) of the rotary table (5) and the normal plane (12) that is perpendicular to the axis of rotation (4), with the outlet (7a) of the nozzle (7) being located in the normal plane (12), decreasing monotonically in the radial direction, or the distance (13), which is parallel to the axis of rotation (4), between the surface (5a) of the rotary table (5) and the normal plane (12) that is perpendicular to the axis of rotation (4), with the outlet (7a) of the nozzle (7) being located in the normal plane (12), increasing monotonically in the radial direction (10).