METHOD AND DEVICE FOR PRODUCING A METAL POWDER

Description

AREA OF INVENTION

[0001] The present invention relates to a method for producing a metal powder, comprising the following steps: Melting at least one metal, in particular from the group consisting of Al, Zn, Sn, Fe, Mg, Zr, W, Sb, Ni, Cu, Ag, Au, in a tundish; pouring a melt from the tundish through at least one nozzle onto a rotating turntable, whereby the melt is atomized into droplets upon impact with the rotating turntable; cooling the atomized droplets, whereby the droplets solidify into metal powder particles; and a suitable apparatus for carrying out the process. STATE OF THE ART

[0002] Various methods and devices for the production of metal powders are known in the prior art.

[0003] Examples of known methods include mechanical processes, such as grinding in a mill; physical processes, such as evaporating the metal and subsequent condensation; chemical processes, such as reduction processes; or electrolytic processes, in which metal is deposited as a powder on a cathode in an electrolytic bath.

[0004] In principle, the atomization of molten metal at high temperatures is already a known method for producing metal powders in the prior art. Centrifugal atomization, in particular, is used in the prior art as a means of producing metal powders with exceptional precision.

[0005] The use of rapidly rotating turntables for the production of metal and alloy powders by atomizing molten metal is already well established. Powder production in this process utilizes centrifugal force. The hot molten metal is poured out and strikes the rotating turntable, which is rotating at a specific speed. As a result of the centrifugal force, the molten metal is flung off the turntable and broken into small droplets – a process known as atomization – which then solidify into metal powder particles.

[0006] CN 105397100 A describes a device and a method for producing fine metal powders using several nozzles and a rotating disc underneath for atomizing the incident liquid metal, wherein the metal jets strike the disc coaxially but laterally offset.

[0007] From CN 104588673 A, a device and a method for producing fine metal powders using several nozzles and a rotating disc underneath for atomizing the impacting liquid metal are also known.

[0008] CN 104550988 A describes a comparable method or apparatus to CN 105397100 A and CN 104588673 A, wherein the pre-atomization of the metal stream at or after the nozzle is effected by an adjustable differential pressure between a container in which the liquid metal is stored and a container in which the rotating metal disk is located. In the three aforementioned publications, the tundish and nozzle are fixed in place.

[0009] From US 4701289 A, a device and a method for producing fine metal powders are known, comprising a rapidly rotating disk and a feed for liquefied metal and coolant arranged coaxially but eccentrically to the axis of rotation of the disk, wherein the rotating disk can be positioned at an angle to the feeds. OBJECT OF THE INVENTION

[0010] The object of the present invention is to provide an improved manufacturing process and a device for producing a metal powder. In particular, the particles of the metal powder should have a size distribution that is as defined as possible or be as uniform in size as possible, and the size should be easily adjustable. PRESENTATION OF THE INVENTION

[0011] The object of the invention is achieved by a method for producing a metal powder, wherein the method for producing the metal powder comprises the following steps: Melting at least one metal, in particular from the group consisting of Al, Zn, Sn, Fe, Mg, Zr, W, Sb, Ni, Cu, Ag, Au, in a tundish; pouring a melt from the tundish through at least one nozzle onto a rotating turntable, whereby the melt is atomized into droplets upon impact with the rotating turntable; cooling the atomized droplets, whereby the droplets solidify into metal powder particles, wherein, according to the invention, a specific area of ​​the rotating turntable in which the melt impacts the rotating turntable is adjusted either by the tundish and / or the at least one nozzle for pouring the melt by movement in a radial direction with respect to the turntable in order to adjust the size and / or shape of the metal powder particles.

[0012] The term "metal powder according to the invention" refers to metal powders of a single metal as well as of alloys and mixtures.

[0013] A tundish according to the invention is any tundish known in the prior art. However, it goes without saying that it must be a heated or heatable tundish in order to prevent the melt from cooling down and to guarantee a temperature of the melt favorable for atomization.

[0014] According to the invention, at least one nozzle for pouring the molten metal is provided at the bottom of the tundish, so that the hot molten metal can be poured onto the rotating turntable. In principle, this is a nozzle with an outlet that is wide enough to prevent clogging by the molten metal. The molten metal is poured from the nozzle by gravity. The outlet opening of the nozzle typically has a diameter of 1 to 5 mm.

[0015] A rotating turntable according to the invention can be any turntable known in the prior art that is suitable for atomizing a molten metal to produce a metal powder. Preferably, the turntable is a disc with a defined diameter and uniform thickness to further influence the shape of the produced metal powder particles. Preferably, the turntable is also heated to prevent solidification and thus adhesion of the molten metal to the turntable, which would otherwise occur due to cooling upon contact with the turntable.

[0016] The metal is melted in the tundish to obtain a hot molten metal, which is then poured through the nozzle onto the rotating turntable. Upon impact with the turntable, the centrifugal force causes the molten metal to be flung away, breaking the jet of molten metal into droplets that subsequently solidify into metal powder particles.

[0017] The production of the metal powder can take place in a separate atomization chamber or in a section of the chamber containing the tundish. This latter chamber is called the furnace chamber. In any case, there is a furnace chamber containing a tundish in which the metal is melted.

[0018] Preferably, the furnace chamber and, optionally, the atomization chamber are heatable to prevent premature cooling of the melt. Furthermore, the atomization chamber and the furnace chamber can be gas-tight to prevent the ingress of unwanted atmospheric oxygen, which could lead to detrimental oxidation in the melt.

[0019] It may also include a device, such as a gas supply, to cool the metal droplets in order to allow them to solidify more quickly into metal powder particles after atomization.

[0020] According to the invention, it is provided that by moving the tundish and / or the at least one nozzle for pouring the melt by moving in a radial direction with respect to the rotary table, a defined size distribution of the droplets or, subsequently, of the metal powder particles can be achieved, since the molten metal always hits a specific area of ​​the rotary table.

[0021] The radial movement of the tundish or at least one nozzle for pouring the molten metal makes it possible to direct hot molten metal onto virtually any area of ​​the rotating turntable. A particular advantage is the controlled selection of the area where the molten metal impacts the turntable, allowing for the targeted production of metal powder particles with a specific size and / or shape.

[0022] The rotary table according to the invention rotates, thereby generating the centrifugal force required to atomize the melt. It is known to those skilled in the art that when the rotary table rotates at a constant number of revolutions per unit of time, approximately rpm, the speed of the rotary table at the outermost edge of the disc is higher than radially within it. This means that, depending on where the melt impacts a given area, differently shaped and / or differently sized melt droplets are formed, and consequently, differently shaped and differently sized metal powder particles are produced.

[0023] This also means, however, that metal droplets with a good size distribution and uniform shape are achieved when the hot melt consistently impacts the turntable in approximately the same specific area. If the melt impacts near the edge of the turntable, the higher velocity and stronger centrifugal force result in smaller melt droplets and thus smaller metal powder particles. Conversely, if the melt impacts the turntable more centrally, the lower velocity and resulting lower centrifugal force produce larger melt droplets and thus larger metal powder particles.

[0024] This means that a specific area is defined in advance where the hot melt should impact the rotating turntable in order to achieve a specific shape and size of droplets and subsequent metal powder particles. This specific area of ​​the turntable is set by moving the tundish and / or by swiveling the nozzle.

[0025] In one embodiment of the invention, the at least one nozzle for pouring the melt is arranged at the bottom of the tundish. This nozzle comprises a section that pivots relative to the tundish about a zero-point position to adjust the specific area of ​​the rotating turntable. This allows for particularly efficient control of the area where the melt impacts the turntable. In principle, any area of ​​the turntable can be targeted by the pivotable nozzle to generate droplets and metal powder particles. The same applies, of course, to a device according to the invention. The zero-point position can, for example, be vertical, where the nozzle section runs parallel to the direction of the poured melt.

[0026] In one embodiment of the invention, the nozzle section is pivoted relative to the tundish within an angular range of 0° to 80°, preferably 0° to 70°, preferably 0° to 60°, preferably 0° to 50°, preferably 0° to 40°, preferably 0° to 30°, preferably 0° to 20°, preferably 0° to 10° around a zero-point position in order to adjust the specific area of ​​the rotating turntable to allow the melt to impact any desired or predetermined area on the turntable. The same applies, of course, to a device according to the invention.

[0027] In a further embodiment of the invention, it is provided that the nozzle for pouring the melt is additionally heated in order to prevent the melt from cooling down in the nozzle, becoming more viscous and consequently clogging the nozzle.

[0028] In a further embodiment of the invention, a gas nozzle is provided from which a gas stream is emitted. This gas stream is directed at an acute angle onto the molten metal exiting the nozzle in order to adjust the specific area in which the molten metal impacts the rotating turntable. This allows for even more precise adjustment of the area in which the molten metal is to impact the turntable. The same applies, of course, to a device according to the invention. The gas stream has, in any case, a component acting in the direction of gravity.

[0029] Any gas nozzle known in the prior art that is suitable for dispensing gas in the form of a gas stream can be considered as a gas nozzle.

[0030] At an acute angle means that the angle is less than 90°.

[0031] The molten metal, whose flow follows gravity, can be influenced by the gas stream, which is directed at the molten metal at an acute angle. This gas stream alters the flow direction of the molten metal, allowing for even more precise control of the area where the molten metal strikes the turntable. This can be achieved by varying both the intensity of the gas stream and the angle at which it strikes the molten metal. By adjusting the angle or intensity of the gas stream, the molten metal is deflected from its gravitational flow as desired.

[0032] To enable precise adjustment, a further embodiment of the invention provides that the gas nozzle is arranged at the bottom of the tundish at a distance from the nozzle for pouring the melt, wherein the gas nozzle comprises a gas nozzle section that is pivoted relative to the tundish about a zero-point position, so that the gas flow strikes the melt at an acute angle. The same applies, of course, to a device according to the invention. The zero-point position can, for example, be the vertical.

[0033] Swiveling means that, in principle, any area of ​​the turntable can be targeted by moving the swiveling nozzle to generate droplets and metal powder particles.

[0034] In an alternative embodiment of the invention, the gas nozzle is movable radially relative to the rotary table, independently of the tundish. The gas nozzle comprises a gas nozzle section that is pivoted about a zero-point position relative to the tundish, so that the gas flow strikes the melt at an acute angle. This allows for larger angular ranges for pivoting the gas nozzle section because the distance between the nozzle for the melt and the gas nozzle is not fixed and can be increased.

[0035] "Movable" in the sense of the present invention means that a suitable device is provided by means of which the gas nozzle can be moved. Preferably, this will be accomplished by means of a rail system.

[0036] To prevent undesired reactions with the melt – depending on the type of melt – one embodiment of the invention provides that the gas for the gas stream is air or an inert gas, preferably N2, H2, CO, CO2, H2O, He, Ar, Kr, Xe, or a mixture thereof. This means that, depending on the desired melt, air – for oxidation-insensitive substances or for desired oxidations – or an inert gas – for oxidation-sensitive substances or for undesired oxidations – can be used.

[0037] The above-mentioned problem is further solved by a device for producing a metal powder according to a method according to the invention, wherein the device comprises a gas-tight chamber, The gas-tight chamber contains a tundish for producing a melt; the gas-tight chamber contains a rotatable turntable for atomizing and solidifying the melt, and at least one nozzle is provided for pouring the melt from the tundish, wherein, according to the invention, an area of ​​the rotatable turntable in which the melt impacts the rotatable turntable can be adjusted by moving the tundish and / or the at least one nozzle for pouring the melt in a radial direction with respect to the turntable in order to adjust the size and / or shape of the metal powder particles, thereby enabling precise adjustment of the area in which the melt impacts the rotatable turntable.

[0038] A gas-tight chamber as defined by the invention can be any furnace chamber known in the prior art that is suitable for producing a melt. Gas-tight means that unwanted atmospheric oxygen cannot enter the furnace chamber, thus preventing unwanted oxidation.

[0039] Of course, it is not out of the question that the device contains a further mechanism which enables the cooling of the metal droplets, thereby achieving a faster and more targeted solidification of the metal droplets into metal powder particles.

[0040] In one embodiment of the invention, a device is provided in which the tundish can be moved in a radial direction with respect to the rotary table in order to enable a particularly good method of the tundish in the radial direction.

[0041] A rail system, e.g. with a traveling crane, is particularly suitable as a device according to the invention. However, it goes without saying that other suitable devices are not excluded.

[0042] In order to ensure the swivelling of the nozzle, one embodiment of the invention provides that the nozzle section is movably connected to the rest of the nozzle via a joint, preferably a ball joint.

[0043] It goes without saying that this ball joint is also made of a material suitable for use in connection with hot melts.

[0044] In order to prevent the hot melt from escaping from the ball joint, one embodiment of the invention provides that the joint is surrounded by at least one sleeve, preferably two sleeves, to seal the joint, preferably the ball joint.

[0045] In order to make the at least one cuff stable for use with hot melts in the long term, it is provided in one embodiment that the at least one cuff is made of a sintered metal, preferably a carbide, particularly preferably tungsten carbide.

[0046] In order to prevent the melt from cooling and solidifying and thus from clogging the device, one embodiment of the invention provides that the nozzle for pouring the melt, comprising the nozzle, optionally the joint, preferably the ball joint, and optionally the at least one cuff, is additionally heatable.

[0047] Heating, of course, means that the nozzle for pouring the melt, the joint (preferably a ball joint), and the at least one sleeve (if applicable) are heated not only by the hot melt itself, but also by external heating sources. Any heating source known in the prior art that is suitable for heating these device components is eligible.

[0048] The distance between the tundish and the turntable is preferably between 2 and 500 mm. BRIEF DESCRIPTION OF THE FIGURES

[0049] The invention will now be explained in more detail using an exemplary embodiment. The drawings are exemplary and are intended to illustrate the inventive concept, but in no way to restrict or even exhaustively represent it.

[0050] This shows: Fig. 1 is a schematic representation of a device according to the prior art, Fig. 2 is a schematic representation of a device according to the invention. WAYS TO IMPLEMENT THE INVENTION

[0051] In Fig. 1 A tundish 1, also called a melting furnace, for producing a melt 9 is shown, which is part of a gas-tight chamber 11. The gas-tight chamber 11 contains a rotary table 4 with drive and thus forms the atomization chamber. A nozzle 2 is provided in the bottom of the tundish 1, the outlet of which has, for example, a diameter of 2 mm. A device 12 for adjusting the atmosphere in the gas-tight chamber 11 comprises at least a gas container 13 for inert gas, as well as corresponding control devices and lines. An oxygen measuring device 14 and a vacuum sensor 15 provide the necessary measurement data for the device 12 for adjusting the atmosphere.

[0052] In the highly schematic Fig. 2 mainly those components of a device according to the invention are shown which differ from a device in Fig. 1 The device according to the invention also has a rotary table 4, which is arranged below a tundish 1 and from which molten metal 9 can be poured onto the rotary table through a nozzle 2 in the base of the tundish. The gas-tight chamber 11, which is all in Fig. 2 The plant components shown, as well as the device 12 for adjusting the atmosphere in the gas-tight chamber 11, are in Fig. 2 not shown.

[0053] According to Fig. 2 The nozzle 2 is not rigid, but comprises a nozzle section 3 that is pivotable relative to the rest of the nozzle 2 or the tundish 1, such that it is vertically aligned at a pivot angle of 0° (zero point position), i.e., parallel to the flow direction of the melt 9, and then pivoted against the vertical by a maximum of approximately 80° (see arrows), so that the melt 9 exiting the nozzle section 3 strikes the rotary table 4 radially further outwards. The joint 7 connecting the nozzle section 3 to the rest of the nozzle 2 is a ball joint. It is surrounded by at least one sleeve 8 to prevent the melt 9 from escaping.

[0054] Unlike in Fig. 1 is in Fig. 2The tundish 1 is arranged to be movable perpendicular to the axis of rotation of the turntable 4, as indicated by the arrows, so that the position of the nozzle 2 relative to the turntable 4 can be adjusted additionally or alternatively. The tundish 1 can be suspended, for example, from a trolley that is movable on a rail system, particularly a straight one.

[0055] To allow for even more precise adjustment of the radial position at which the melt impacts the turntable 4, an additional gas nozzle 5 is provided. This nozzle is movable independently of the tundish 1, perpendicular to the axis of rotation of the turntable 4 (see arrows). The gas nozzle 5 has a gas nozzle section 6 that can be pivoted relative to the rest of the gas nozzle 5 by means of a joint 7 (see arrows). At a pivot angle of 0° (zero point position), the gas nozzle section 6 is vertically oriented, i.e., parallel to the flow direction of the melt 9. It can then be pivoted by a maximum of approximately 80° relative to the vertical, so that the gas stream then impacts the vertically flowing melt 9 with a lateral component, i.e., a radial component with respect to the turntable 4. This changes the area in which the melt 9 impacts the turntable 4 accordingly.The resulting metal powder particles 10 then have a correspondingly different size and / or shape than if no gas stream were to hit the melt 9. REFERENCE MARK LIST

[0056] 1 Tundish 2 Nozzle 3 Nozzle section 4 Rotary plate 5 Gas nozzle 6 Gas nozzle section 7 Joint 8 Sleeve 9 Melt 10 Metal powder particles 11 Gas-tight chamber 12 Device for adjusting the atmosphere in the gas-tight chamber 11 13 Gas container 14 Oxygen meter 15 Vacuum sensor

Claims

1. Method for producing a metal powder, which comprises the following steps of: - melting at least one metal, in particular from the group Al, Zn, Sn, Fe, Mg, Zr, W, Sb, Ni, Cu, Ag, Au, in a tundish (1); - pouring a melt (9) from the tundish (1) via at least one nozzle (2) onto a rotating turntable, causing the melt to be atomized into droplets by striking the rotating turntable; - cooling the atomized droplets, causing the droplets to solidify into metal powder particles (10), characterized in that a specific region of the rotating turntable (4), in which the melt strikes the rotating turntable, is adjusted either by the tundish (1) and / or the at least one nozzle (2) for pouring out the melt (9) by movement in a radial direction with respect to the turntable (4) in order to adjust the size and / or the shape of the metal powder particles (10).

2. Method for producing a metal powder according to claim 1, characterized in that the at least one nozzle (2) for pouring out the melt (9) is arranged at the bottom of the tundish (1), wherein the at least one nozzle for pouring out the melt comprises a nozzle section (3) which is pivoted relative to the tundish (1) about a zero point position in order to adjust the specific region of the rotating turntable (4).

3. Method for producing a metal powder according to claim 2, characterized in that the nozzle section (3) is pivoted relative to the tundish (1) in an angular range between 0° and 80°, preferably 0° and 70°, preferably 0° and 60°, preferably 0° and 50°, preferably 0° and 40°, preferably 0° and 30°, preferably 0° and 20°, preferably 0° and 10° about a zero point position in order to adjust the specific region of the rotating turntable (4).

4. Method for producing a metal powder according to one of claims 1 to 3, characterized in that a gas nozzle (5) is also provided, from which a gas stream is emitted, wherein the gas stream is directed at an acute angle onto the melt (9) emerging from the nozzle (2) in order to adjust the specific region in which the melt strikes the rotating turntable (4).

5. Method for producing a metal powder according to claim 4, characterized in that the gas nozzle (5) is arranged at the bottom of the tundish (1) at a distance from the nozzle (2) for pouring out the melt, wherein the gas nozzle (5) comprises a gas nozzle section (6) which is pivoted relative to the tundish (1) about a zero point position so that the gas stream strikes the melt (9) at an acute angle.

6. Method for producing a metal powder according to claim 4, characterized in that the gas nozzle (5) can be moved independently of the tundish (1) in a radial direction with respect to the turntable (4), wherein the gas nozzle (5) comprises a gas nozzle section (6) which is pivoted relative to the tundish (1) about a zero point position, so that the gas stream strikes the melt (9) at an acute angle.

7. Device for producing a metal powder by a method according to one of claims 1 to 6, wherein the device comprises a gas-tight chamber, - the gas-tight chamber contains a tundish (1) for producing a melt (9); - the gas-tight chamber contains a rotatable turntable (4) for atomizing and solidifying the melt (9), - and at least one nozzle (2) is provided for pouring out the melt from the tundish (1), characterized in that a region of the rotatable turntable (4), in which the melt (9) strikes the rotatable turntable (4), can be adjusted by movement of the tundish (1) and / or of the at least one nozzle (2) for pouring out the melt (9) in a radial direction with respect to the turntable (4) in order to adjust the size and / or the shape of the metal powder particles (10).

8. Device for producing a metal powder according to claim 7, characterized in that the at least one nozzle (2) for pouring out the melt (9) is arranged at the bottom of the tundish (1), wherein the at least one nozzle (2) for pouring out the melt (9) comprises a nozzle section (3) which is pivotable relative to the tundish (1) about a zero point position in order to adjust the defined region of the rotating turntable (4).

9. Device for producing a metal powder according to claim 8, characterized in that the nozzle section (3) can be pivoted relative to the tundish (1) within an angular range between 0° and 80°, preferably 0° and 70°, preferably 0° and 60°, preferably 0° and 50°, preferably 0° and 40°, preferably 0° and 30°, preferably 0° and 20°, preferably 0° and 10° about a zero point position in order to adjust the defined region of the rotating turntable (4).

10. Device for producing a metal powder according to one of claims 7 to 9, characterized in that a gas nozzle (5) is also provided, from which a gas stream can be emitted, wherein the gas stream can be directed at an acute angle onto the melt (9) emerging from the nozzle (2) in order to adjust the region in which the melt strikes the rotating turntable (4).

11. Device for producing a metal powder according to claim 10, characterized in that the gas nozzle (5) is arranged at the bottom of the tundish (1) at a distance from the nozzle (2) for pouring out the melt (9), wherein the gas nozzle (5) comprises a gas nozzle section (6), and wherein the gas nozzle section (6) is pivotable relative to the tundish (1) about a zero point position, so that the gas stream strikes the melt (9) at an acute angle.

12. Device for producing a metal powder according to claim 10, characterized in that the gas nozzle (5) can be moved independently of the tundish (1) in a radial direction with respect to the turntable (4).

13. Device for producing a metal powder according to one of claims 7 to 12, characterized in that a device, e.g. an overhead crane, is provided, on which the tundish (1) can be moved in the radial direction with respect to the turntable (4).

14. Device for producing a metal powder according to one of claims 8 to 13, characterized in that the nozzle section (3) is movably connected to the rest of the nozzle (6) via a joint (7), preferably a ball-and-socket joint.

15. Device for producing a metal powder according to claim 14, characterized in that the joint (7) is surrounded by at least one collar (8), preferably two collars (8), in order to seal the joint (7), preferably the ball-and-socket joint.