Apparatus and method for producing metal powder using induction coils and intermediate coils

Abstract

The present invention relates to an apparatus (10, 100) for producing metal powder. The apparatus includes a melting chamber (12), a downstream atomization tower (14) and a nozzle assembly (16) for atomizing a melt jet (24). The apparatus further includes a nozzle (16) disposed within the melting chamber (12) and configured to have a melt frequency f melt an induction coil (20) adapted to locally melt a material rod (22) contained at least in sections therein to generate a melt jet (24) to be atomized; and a melting chamber (12) arranged inside the melting chamber (12) and adapted to operate at a fundamental frequency f base The nozzle assembly (16) includes a separate intermediate coil (30, 130) that is disposed downstream of and coaxially aligned with the induction coil (20) and is configured to superheat the melt jet (24) in a region between the induction coil (20) and the nozzle assembly (16). base vs melting frequency f melt The frequency ratio of BS =f base / f melt The relationship ≦500 holds.

Description

[Technical field]

[0001] The present invention relates to an apparatus and method for producing high purity powder by using an induction coil and an intermediate coil. More specifically, the present invention relates to an apparatus and method for melting and atomizing materials to produce powder. In particular, the powder can be high purity metal powder, such as Ni superalloy powder, precious metal powder, or high melting point reactive metal alloy powder. For example, the apparatus and method can be useful for producing titanium, zirconium, niobium and / or tantalum alloy powder. [Background technology]

[0002] Metal powders serve as starting materials for the production of semi-finished products and shaped parts in many fields of application. In particular, they can be further processed for this purpose using sintering or additive manufacturing techniques. Due to the wide range of applications, for example in the aerospace industry, energy technology, chemical industry, electronics industry and biomedical technology, the demand for (metal) powders and the requirements regarding the quality of (metal) powders are constantly increasing.

[0003] Conventional apparatus for producing powder includes a means for producing or providing a melt of material, as well as a means for atomizing or atomizing the melt jet of the melt of material.

[0004] Known processes for producing a material melt are, for example, the Electrode Induction Melting Inert Gas Atomization (EIGA) process, the Vacuum Induction Melting Inert Gas Atomization (VIGA) process and the Plasma Inert Gas Atomization (PIGA) process.

[0005] Apparatuses for producing metal powders by melting a material bar using the EIGA technique and subsequently atomizing the molten material are known from DE 4102101 A1 and EP 3083107 A1. However, the quality of the powders produced by these apparatuses is limited and there is a need for finer and more uniform powders with improved powder quality. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] German Patent Application Publication No. 4102101A1 [Patent Document 2] European Patent Application Publication No. 3083107A1 Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE PRESENT EMBODIMENT It is therefore an object of the present invention to provide an apparatus and method that overcomes the disadvantages of the prior art.

[0008] In particular, it is an object of the present invention to provide an apparatus and a method which allows the production of finer, more uniform and / or quality improved powders, where improving powder quality may mean reducing the formation of satellites in the powder and / or reducing gas inclusions in the powder and / or achieving optimal sphericity. [Means for solving the problem]

[0009] This object is achieved by the subject matter of the independent claims. Further developments and embodiments of the device and method are the subject matter of the dependent claims and the following description.

[0010] One aspect of the invention relates to an apparatus and system for producing powders, in particular metal powders. The apparatus may be for producing high purity powders of titanium, zirconium, niobium and / or tantalum alloys, and / or for producing Ni superalloy powders, precious metal powders or high melting point and reactive metal alloy powders.

[0011] The device includes a melter and an atomization tower downstream of the melter. Downstream here may mean that the atomization tower is located below the melter during operation. A pre-pressure may be applied to the melter. The atomization tower may be subjected to a counter-pressure. The counter-pressure may be lower than the pre-pressure. The counter-pressure may be equal to the pre-pressure. In an embodiment where the counter-pressure is equal to the pre-pressure, the melter may be connected to the atomization tower via a bypass.

[0012] The apparatus includes a nozzle assembly for atomizing the melt jet, through which the melter is connected to an atomization tower.

[0013] An induction coil is disposed within the melting chamber. The induction coil may include a plurality of turns. The induction coil is configured to generate a melting frequency f melt The induction coil is adapted to operate at a temperature of 1000° C. and to locally melt at least a material rod accommodated therein in sections to generate a molten jet to be atomized. Local melting here can be understood to mean that the material rod is heated and melted by the induction coil in the area of ​​one end (the end disposed in the induction coil). The material rod can be continuously advanced so that a continuous homogeneous molten jet can be generated. The material rod can be a metal rod. The molten jet can therefore be a metal molten jet. The material rod can comprise titanium, zirconium, niobium and / or tantalum alloys, Ni superalloy powder precious metals or another high melting point reactive metal alloy. The molten jet can be continuous or formed of short successive droplets.

[0014] Melting frequency f meltis adjustable. The diameter of the melt jet and the melting speed and melting rate of the melt jet can be influenced by the specific selection of the melting frequency. The melting rate dm / dt can be between 0.1 kg / min and 10 kg / min, preferably between 0.5 kg / min and 8 kg / min, preferably between 1.5 kg / min and 6 kg / min. The material to be melted may include magnesium and has a melting rate of 1600 kg / m 3 The material to be melted may include aluminum and have a density of 2700 kg / m 3 The material to be melted may comprise tungsten and have a density of 19000 kg / m 3 The melt jet diameter may be between 2 mm and 10 mm, preferably between 3 mm and 9 mm, more preferably between 4.5 mm and 7.5 mm. The melt velocity may be between 0.01 m / s and 9 m / s, preferably between 0.1 m / s and 5 m / s, more preferably between 0.5 m / s and 4 m / s. The specified value ranges for the melt jet diameter and melt velocity as well as the melt rate represent an advantageous combination, i.e. an optimum balance, for providing the smallest possible melt jet diameter while still having a sufficiently high melt velocity.

[0015] Furthermore, a separate intermediate coil is arranged inside the melting chamber. Separate here may mean that the intermediate coil is structurally separate from the induction coil, i.e. does not merely form a section of the induction coil. The intermediate coil may likewise be controllable separately from the induction coil, and the control of the two coils may be coordinated with each other, but may not necessarily be dependent on the control and frequency of the induction coil. The intermediate coil may include multiple turns.

[0016] Each of the intermediate coils and / or the induction coils can be surrounded by a shielding material, for example a ferrite sheath. In this way, a specific field line induction can be achieved. This makes it possible to adapt the frequency ranges of the separate coils while at the same time preventing mutual interference between the coils.

[0017] The intermediate coil is positioned downstream of the induction coil and is coaxially aligned with the induction coil. Thus, the intermediate coil is disposed between the induction coil and the nozzle assembly, where the intermediate coil is spaced apart from the induction coil. The intermediate coil may be spaced apart from the nozzle assembly as well, in particular, the last turn of the intermediate coil may be spaced apart from the inlet opening of the nozzle assembly. Alternatively, the intermediate coil may extend into the nozzle assembly at a lower end. In this case, the last turn of the intermediate coil may be spaced apart from at least the portion of the nozzle assembly having the smallest inner diameter.

[0018] In particular, the induction coil and the intermediate coil are arranged (downstream and in coaxial alignment with each other) in such a way that the melt jet generated by the induction coil passes through the intermediate coil, where downstream can mean that the last turn of the induction coil facing the intermediate coil is axially spaced (along the longitudinal axis of both coils) from the first turn of the intermediate coil facing the induction coil, where the first turn of the intermediate coil is arranged closer to the atomization tower than the last turn of the induction coil, i.e. the first turn of the intermediate coil is spaced from the last turn of the induction coil in the direction of the atomization tower.

[0019] The middle coil has a fundamental frequency of f base The nozzle assembly is configured to operate at a fundamental frequency f baseThe intermediate coil operated at 2000 rpm can heat the melt jet along the longitudinal axis of the intermediate coil and at least in a part of the area between the last turn of the induction coil and the inlet opening of the nozzle assembly facing both coils. In this way, a targeted influence can be exerted on the cooling of the melt jet before it enters the nozzle assembly, which can then be prevented or reduced. By preventing or reducing the cooling of the melt jet in this area, it is possible to avoid (partial) solidification of several areas of the melt jet already before it enters the nozzle assembly. Solidification before atomization has a significant impact on the quality of the powder produced. This can be specifically suppressed by the intermediate coil, which can then improve the quality of the powder.

[0020] For example, immediately after melting through the induction coil and prior to entering the intermediate coil, the molten material may have a temperature above its solidus temperature and at most 70° C. above its liquidus temperature (T sol ≦T≦(T liq +70° C.) after passing through the intermediate coil (i.e., at the lower end of the intermediate coil facing the atomization tower), the molten jet may have a temperature higher than its solidus temperature and up to 100° C. higher than its liquidus temperature due to further heating through the intermediate coil (T sol ≦T≦(T liq +100℃).

[0021] The intermediate coil may serve to compensate for radiation losses (which would result in some cooling of the melt jet) or to further increase the superheat of the melt jet.

[0022] Melting frequency f melt for the fundamental frequency f base Frequency ratio F BS For , the following relationships can be established: 1≦F BS =f base / f melt ≦500; Preferably, 1≦f base / f melt ≦250; More preferably, 1≦f base / f melt ≦100; More preferably, 3≦f base / f melt ≦50; Even more preferably, 8≦f base / f melt <= 25.

[0023] For more details, see F BS may be 5 to 15, preferably 6.5 to 13.5, more preferably 8 to 12, even more preferably 9 to 11, and even more preferably about 10.

[0024] Melting frequency f melt for the fundamental frequency f base The specified frequency ratio F BS represents a very advantageous relationship, since, on the one hand, the cooling can be sufficiently reduced with high reliability and, on the other hand, a smooth transition can be achieved between the melting of the material rod (i.e. the generation of the melt jet) and the heating of the melt jet.

[0025] Melting frequency f melt , fundamental frequency f base and / or frequency ratio F BS can be selected depending on the material to be melted and / or depending on the powder to be produced (and its desired application) and / or depending on the geometry and structure of the coil. In other words, the coil can be controlled as required to operate at a corresponding frequency. Since the design of the arrangement does not have to be modified for this purpose, it is possible to adapt the arrangement according to the invention very flexibly to different applications.

[0026] The area between the induction coil and the nozzle assembly may be the minimum distance between the induction coil and the nozzle assembly, i.e., the distance between the last turn of the induction coil facing the nozzle assembly and the upper inlet opening of the nozzle assembly.

[0027] In a further development, the intermediate coil is mod is the fundamental frequency fbase The fundamental frequency f base Modulated to the modulation frequency f mod It is thus possible to cause or effect a targeted separation or breakup of a continuous melt jet into separate successive droplets having essentially the same size using a modulated modulation frequency f mod represents the perturbation or interference frequency that causes a targeted separation or breakup of the melt jet into individual droplets of the same size. In the case of separation of the melt jet into successive droplets, the subsequent atomization can be optimally prepared, thus achieving a more efficient and better atomization in terms of the achievable powder quality. An additional fundamental frequency f acting on the melt droplets in the area between the induction coil and the nozzle assembly base The modulation frequency f prevents undesired cooling of the melt jet and in particular its solidification, which is even more important in the case of melt jets, especially those formed with a large number of melt droplets, in order to ensure the desired powder quality. mod The targeted collapse of the melt jet using melt This, together with the preceding targeted setting of the melt jet diameter and melting rate of the melt jet using the method described above, makes it possible to set the powder particle size and quality in a targeted and application-relevant manner, which can be varied and easily adapted. Setting droplets of essentially the same size ensures uniform solidification and the production of a very homogeneous powder.

[0028] The intermediate coil may include an interference section or zone formed in the end region of the intermediate coil facing the induction coil. The interference section may therefore also be called an initial interference section or an input interference section, since it is provided in a region of the intermediate coil where the melt jet enters the intermediate coil. The remaining part of the intermediate coil bordering the interference section or interference zone may be described as an overheat section or an overheat zone. The interference section represents a concentrated section and may be designed to locally, briefly and strongly squeeze the melt jet. The intermediate coil may have a smaller inner diameter in the interference section, more specifically a smaller diameter compared to the overheat section or the remaining part of the intermediate coil. The interference section may extend over 5% to 25%, preferably 10% to 20%, more preferably 12.5% ​​to 17.5% of the length of the intermediate coil. The interference section may include certain turns of reduced diameter. In the interference section, a palisade of the cold-wall crucible may be placed inside the turn, which reduces the diameter through which the melt jet passes. The interference section may include a turn separate from and connected in parallel with the remaining turns of the intermediate coil, the separate turn being capable of operating at a higher current than the remaining turns.

[0029] The intermediate coil may be surrounded in sections by a non-conductive ferrite material to further increase the inductance of the intermediate coil.

[0030] Due to the relatively small inner diameter or inner cross section of the interference section, the intermediate coil, in particular the modulated modulation frequency f mod It is possible to achieve a concentration of the influence of the melt jet by the interference section, so that the melt jet can break up in this interference section and thus already at the beginning of its entry into the intermediate coil into separate continuous droplets, which are then superheated when passing through the superheating section.

[0031] Melting frequency f melt The melting frequency f may be 10 kHz to 500 kHz, preferably 100 kHz to 400 kHz, and more preferably 200 kHz to 300 kHz. meltmay be at least 10 kHz, preferably at least 50 kHz, more preferably at least 100 kHz, more preferably at least 200 kHz, and even more preferably at least 250 kHz. melt The melting frequency f within the specified range may be 500 kHz or less, preferably 450 kHz or less, more preferably 350 kHz or less, more preferably 300 kHz or less, and even more preferably 250 kHz or less. melt makes it possible to set melt jet diameters between 2 mm and 10 mm for the materials concerned in this specification.

[0032] fundamental frequency f base The fundamental frequency f may be 100 kHz to 5000 kHz, preferably 200 kHz to 4500 kHz, more preferably 500 kHz to 4000 kHz, more preferably 1000 kHz to 3000 kHz, and even more preferably 1500 kHz to 2500 kHz. base may be at least 100 kHz, preferably at least 200 kHz, more preferably at least 500 kHz, more preferably at least 1000 kHz, and even more preferably at least 1500 kHz. base The fundamental frequency f within the specified range may be 5000 kHz or less, preferably 4500 kHz or less, more preferably 4000 kHz or less, more preferably 3000 kHz or less, and even more preferably 2500 kHz or less. base can prevent or reduce undesired cooling of the melt jet for the materials concerned here, in particular of the melt jet with a melt jet diameter preferably set between 2 mm and 10 mm.

[0033] Modulation frequency f mod The modulation frequency f may be 0.001 kHz to 5 kHz, preferably 0.005 kHz to 4.5 kHz, more preferably 0.01 kHz to 4 kHz, more preferably 0.05 kHz to 3.5 kHz, even more preferably 0.1 kHz to 3 kHz, and even more preferably 1 kHz to 2.5 kHz. modmay be at least 0.001 kHz, preferably at least 0.005 kHz, more preferably at least 0.01 kHz, more preferably at least 0.05 kHz, even more preferably at least 0.1 kHz, and even more preferably at least 1 kHz. mod The modulation frequency f within the specified range may be 5 kHz or less, preferably 4.5 kHz or less, more preferably 4 kHz or less, more preferably 3.5 kHz or less, even more preferably 3 kHz or less, and even more preferably 2.5 kHz or less. mod This makes it possible to achieve targeted breakup of the melt jet into continuous droplets with the desired diameter for the materials concerned herein, in particular with a melt jet diameter preferably set between 2 mm and 10 mm.

[0034] Modulation frequency f mod can be selected in particular depending on the melt jet diameter and the melting rate in the interaction region, where the following relationship holds:

number

number

[0035] The intermediate coil may have a cylindrical shape. The intermediate coil may have a cylindrical shape with at least section-wise and / or predominantly constant diameter. Predominantly constant diameter may mean here that at least 70% of the intermediate coil, preferably at least 80% of the intermediate coil, more preferably at least 85% of the intermediate coil, have a constant diameter when viewed along the longitudinal axis of the intermediate coil. This allows the melt jet to receive the same energy input at each location within the area of ​​the intermediate coil and thus to be heated substantially equally at each location throughout its passage (drop) within the intermediate coil.

[0036] The length of the intermediate coil along its longitudinal axis may be more than four times, preferably more than five times, and more preferably more than six times the minimum diameter of the nozzle assembly In this way, highly effective superheating of the melt jet in the region between the induction coil and the nozzle assembly can be achieved.

[0037] The intermediate coil may be configured to superheat the melt jet within at least 50%, preferably at least 60%, more preferably at least 70%, more preferably at least 75%, and even more preferably at least 80% of a distance defined by the minimum distance between the nozzle assembly and the induction coil (as viewed along the longitudinal axis of the intermediate coil or the apparatus). By covering such a minimum portion of this distance, undesired cooling of the melt jet can be effectively and sufficiently reduced.

[0038] The induction coil may have a shape that is conical in at least a section in a direction towards the nozzle assembly, thus achieving effective melting of the material rod.

[0039] The nozzle assembly may include or be in the form of a Laval nozzle.

[0040] The nozzle assembly may include or be formed in the shape of an annular nozzle.

[0041] The Laval nozzle may be configured and arranged in such a way that the melt jet passes through the Laval nozzle from the melter into the atomization tower and the additional gas flows from the melter into the atomization tower through the Laval nozzle, where the additional gas accelerates the melt jet as it flows through the Laval nozzle. The annular nozzle may be arranged downstream of the Laval nozzle and / or in a region of the Laval nozzle such that the additional atomizing gas flows from the atomizing gas source to the atomization tower through the annular nozzle, whereby a locally reduced back pressure may be generated in a region of the outlet opening of the Laval nozzle adjacent to the atomization tower, such that the pressure ratio D between the pre-pressure P0 of the melter and the locally reduced back pressure P2 may include: D=P0 / P2≧2 A relationship like this is now established.

[0042] With such a dual nozzle assembly and a defined pressure ratio, critical flow through the nozzle can be achieved, resulting in improved atomization of the melt jet.

[0043] Another aspect of the invention relates to a method for producing a metal powder.

[0044] The method includes: - generating a melt jet to be atomized by locally melting the material rod inside the melting chamber by means of an induction coil which surrounds the material rod at least in sections, the induction coil being operated at a melting frequency f melt and operating the device according to claim 1 ; - superheating the melt jet in a region between the induction coil and the nozzle assembly using a separate intermediate coil disposed downstream of and coaxially aligned with the induction coil, the intermediate coil having a fundamental frequency f base and operates at a fundamental frequency of f base vs melting frequency f melt Frequency ratio F BS About: 1≦F BS =f base / f melt <=500 The relationship is established as follows: - atomizing the superheated melt jet with a nozzle assembly, the melter being connected to the atomization tower via the nozzle assembly; Includes.

[0045] Another aspect of the invention relates to an apparatus for producing metal powder, the apparatus comprising: With melting chamber; an atomization tower disposed downstream of the melter; a nozzle assembly connecting the melter to the atomization tower for atomizing the melt jet; The melting frequency f melt an induction coil operated at 300 rpm and configured to melt a material rod contained at least in sections therein for producing a molten liquid jet to be atomized; A fundamental frequency f base a separate intermediate coil operated at a temperature above 1000° C., the separate intermediate coil being disposed downstream from and coaxially aligned with the induction coil and configured to superheat the melt jet in a region between the induction coil and the nozzle assembly; Including, Here, the middle coil is modulated at frequency f mod is the fundamental frequency f base It is constructed in such a way that it is modulated into

[0046] Although certain features, advantages, functions, modes of operation, embodiments and further developments have been described above in relation to only one aspect of the device, these can be applied mutatis mutandis to the method and other aspects and vice versa.

[0047] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings, in which: FIG. [Brief description of the drawings]

[0048] [Figure 1] FIG. 1 is a schematic diagram of an apparatus according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of an apparatus according to a further embodiment of the invention. [Diagram 3] FIG. 3 is a diagram showing the base frequency fbase and the modulation frequency fmod at which the intermediate coil is operated. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] 1 illustrates an apparatus or system 10 for producing high purity metal powders. The apparatus 10 includes a melter 12 and an atomization tower 14 downstream from the melter 12. In the illustrated embodiment, the melter 12 is disposed above the atomization tower 14 during operation. The melter 12 is coupled to the atomization tower 14 via a nozzle assembly 16. That is, an upper end of the nozzle assembly 16 is disposed adjacent to the melter 12 or extends into the melter 12. A lower end of the nozzle assembly 16 is disposed adjacent to the melter 12 or extends into the atomization tower 14.

[0050] The nozzle assembly 16 may be integrated as a component within the melter 12. The nozzle assembly 16 may be integrated as a component within the melter 12 and within the atomization tower 14. The nozzle assembly 16 may be integrated as a component within the atomization tower 14. The nozzle assembly 16 may be provided as a separate component between the melter 12 and the atomization tower 14. In the embodiment shown in FIG. 1, the nozzle assembly 16 is provided as a separate component between the melter 12 and the atomization tower 14.

[0051] Provided within melter 12 is an Electrode Induction Melting Inert Gas Atomization (EIGA) assembly 18 that includes an induction coil 20 having a number of turns. Induction coil 20 is disposed above nozzle assembly 16 and is coaxial with nozzle assembly 16. Induction coil 20 has a tapered shape toward nozzle assembly 16.

[0052] Furthermore, a material rod 22, in this case made of a metal or metal alloy, preferably a Ti64 alloy, is disposed inside the melter 12. The end of the material rod 22 facing the nozzle assembly 16 is at least partially housed or extends within the induction coil 20.

[0053] The induction coil 20 has a melting frequency f melt 2, where the induction coil is operated at a melting frequency f of 250 kHz and is configured to locally melt the end of the rod of material 22 contained therein. melt The material rod 22 is operated at 1000 rpm. In this way, a melt jet 24 to be atomized is generated, which has a melt jet diameter d0 of 5 mm in this example. In the illustrated embodiment, the melt jet 24 is initially a substantially continuous coherent melt jet 24. As indicated by the arrows 26, 28, the material rod 22 is mounted in a movable manner. The material rod 22 can thus be rotated about its longitudinal axis A (arrow 28), which allows a uniform melting of the material rod 22 to be achieved. Furthermore, the material rod 22 is displaceable in the direction of the nozzle assembly 16 (arrow 26) so that the material rod 22 can be continuously replenished and the material to be melted (and subsequently atomized or sprayed) can be continuously replenished during the atomization or atomization process. To move the material rod 22, the material rod is connected at its opposite end to a corresponding actuator (not shown). The material rod 22 is arranged coaxially with the induction coil 20 and with the nozzle assembly 16. Axis A represents the longitudinal or central axis of the EIGA assembly 18 , the induction coil 20 , the material rod 22 and the nozzle assembly 16 .

[0054] The apparatus 10 is disposed within a melting chamber 12 and has a fundamental frequency f base In the illustrated embodiment, the fundamental frequency is 2000 kHz. Thus, the melting frequency f melt for the fundamental frequency f base Frequency ratio F BSis 8.

[0055] As can be seen in FIG. 1 (as well as FIG. 2 ), the intermediate coil 30 is formed as a separate intermediate coil 30 that is in addition to and structurally separate from the induction coil 20. The intermediate coil 30 is disposed downstream of and coaxially aligned with the induction coil 20. Thus, the melt jet 24 passes through or falls through the intermediate coil 30 along the longitudinal axis A from the induction coil 20 into the nozzle assembly 16. The fundamental frequency f of the intermediate coil 30 is base is selected such that the intermediate coil 30 superheats the melt jet 24 in the region between the induction coil 20 and the nozzle assembly 16, thus preventing or at least reducing cooling of the melt jet 24 prior to entering the nozzle assembly 16. In the illustrated embodiment, the intermediate coil 30 superheats the melt jet 24 over a distance that is approximately 50% of the shortest distance between the induction coil 20, more specifically the lower end of the induction coil 20, and the nozzle assembly 16, more specifically the upper inlet opening of the nozzle assembly 16.

[0056] The intermediate coil 30 of the apparatus 10 shown in Figure 1 includes an interference section or zone 32 and an adjacent overheat section or zone 34. The interference section 32 is formed in an upper end region of the intermediate coil 30 facing the induction coil 20, i.e., in the region where the melt jet 24 enters the intermediate coil 30. In the region of the interference section 32, the intermediate coil 30 has an inner diameter that is smaller than the inner diameter of the overheat section 34. Here, the interference section 32 extends over about 15% of the total length of the intermediate coil 30.

[0057] Additional modulation frequency f of 0.006 kHz mod is the fundamental frequency f base That is, this modulation frequency f mod is the fundamental frequency f base This modulation frequency f mod, the melt jet 24 is disturbed and thus broken up into individual droplets T in a targeted manner. These droplets T follow each other in succession, thus forming together the melt jet 24. As a result, in the illustrated embodiment, the melt jet 24 enters the nozzle assembly 16 already in the form of individual droplets T, which are then atomized by the nozzle assembly 16. The melting frequency f of the induction coil 20 melt Selectively set the melt jet diameter d0 using f melt or the modulation frequency f depending on the melt jet diameter d0 and the melting rate mod By selectively setting the fundamental frequency f, the device 10 can affect and set the droplet size in a targeted manner, and thus affect the powder properties in a targeted manner. base and modulation frequency f mod is shown diagrammatically in FIG.

[0058] After atomization of the molten jet 24 (ie, droplets T), the atomized droplets cool in the atomization tower 14 where they solidify to form a powder.

[0059] 2 shows an apparatus or system 100 for producing high purity metal powders according to a further embodiment. The apparatus 100 is essentially similar to the apparatus 10 of FIG.

[0060] In contrast to the apparatus 10 of FIG. 1, the intermediate coil 130 of the apparatus 100 of FIG. 2 does not include distinct sections or zones, but is formed continuously throughout its length as a superheat zone 134. Nevertheless, even in this embodiment, the fundamental frequency f at which the intermediate coil 130 is operated to superheat the melt jet (not shown in FIG. 2) is the fundamental frequency f base Above, the modulation frequency f mod can be arbitrarily modulated. The same or other frequencies as in the embodiment of FIG. 1 may be provided.

[0061] A further difference between the device 100 of Fig. 2 and the device 10 of Fig. 1 is that the intermediate coil 130 of the device 100 extends section-wise into the nozzle assembly 1. In particular, at least one last turn of the intermediate coil 130 facing the atomization tower 14 is now disposed inside the nozzle assembly 130.

[0062] 2, the intermediate coil 130 covers approximately 80% of the shortest distance between the last turn of the induction coil 130 facing the nozzle assembly 16 and the upper inlet opening of the nozzle assembly 16, superheating the melt jet in this region. Moreover, in this embodiment, the intermediate coil 130 extends over approximately 77% of the range of the shortest distance between the last turn of the induction coil 20 facing the nozzle assembly 16 and the portion of the nozzle assembly 16 having the smallest inner diameter. Thus, the intermediate coil 130 still superheats the melt jet even in the inlet section of the nozzle assembly 16.

[0063] 3 shows a schematic diagram of one embodiment illustrating the frequency at which the intermediate coils 30, 130 are operated. The diagram thus shows the fundamental frequency f base and the modulated modulation frequency f mod The following is an example.

Claims

1. In an apparatus (10, 100) for producing a metal powder: A melter (12); an atomization tower (14) disposed downstream of the melter (12); a nozzle assembly (16) connecting the melter (12) to an atomization tower (14) for atomizing the melt jet (24); A melting frequency f ｍｅｌｔ an induction coil (20) operable at least partially in a direction parallel to the axis of the nozzle, the induction coil (20) being configured to locally melt a rod of material (22) contained therein in at least a portion thereof in order to generate a melt jet (24) to be atomized; A fundamental frequency f ｂａｓｅ a separate intermediate coil (30, 130) operable at and disposed downstream of and coaxially aligned with the induction coil (20), the separate intermediate coil (30, 130) configured to superheat the melt jet (24) in a region between the induction coil (20) and the nozzle assembly (16); Including, The intermediate coil (30, 130) is configured such that a modulation frequency f is modulated onto a fundamental frequency f; The fundamental frequency f ｂａｓｅ and the melting frequency f ｍｅｌｔ Frequency ratio F ＢＳ About 1≦F ＢＳ =f ｂａｓｅ / f ｍｅｌｔ ≦500 The apparatus (10, 100) is configurable to:

2. 2. The apparatus (10, 100) of claim 1, wherein the intermediate coil (30, 130) includes an interference section (32) formed at an end portion of the intermediate coil (30, 130) facing the induction coil (20), and the intermediate coil (30, 130) has a small inner diameter within the interference section (32).

3. The melting frequency f ｍｅｌｔ is configurable between 10 kHz and 500 kHz, preferably between 100 kHz and 400 kHz, more preferably between 200 kHz and 300 kHz; and / or The fundamental frequency f ｂａｓｅ can be set between 100 kHz and 5000 kHz, preferably between 200 kHz and 4500 kHz, more preferably between 500 kHz and 4000 kHz, more preferably between 1000 kHz and 3000 kHz, and even more preferably between 1500 kHz and 2500 kHz; and / or The modulation frequency f ｍｏｄ can be set between 0.001 kHz and 5 kHz, preferably between 0.005 kHz and 4.5 kHz, more preferably between 0.01 kHz and 4 kHz, more preferably between 0.05 kHz and 3.5 kHz, even more preferably between 0.1 kHz and 3 kHz, and even more preferably between 1 kHz and 2.5 kHz.

3. Apparatus (10, 100) according to claim 1 or 2.

4. 2. The apparatus (10, 100) of claim 1, wherein the intermediate coil (30, 130) preferably has a mainly cylindrical shape with a constant diameter.

5. The apparatus (10, 100) of claim 1, wherein the length of the intermediate coil (30, 130) is greater than four times, preferably greater than five times, and more preferably greater than six times the minimum inner diameter of the nozzle assembly (16).

6. 2. The apparatus (10, 100) of claim 1, wherein the intermediate coil (30, 130) is adapted to superheat the melt jet (24) within at least 70%, preferably at least 80%, and more preferably at least 90% of a length defined by a minimum distance between the nozzle assembly (16) and the induction coil (20).

7. The apparatus (10, 100) of claim 1, wherein the nozzle assembly (16) comprises a Laval nozzle.

8. The apparatus (10, 100) of claim 1 , wherein the nozzle assembly (16) comprises an annular nozzle.

9. The nozzle assembly (16) includes a Laval nozzle and an annular nozzle, the Laval nozzle is configured and arranged such that the melt jet (24) passes through the Laval nozzle from the melter (12) into the atomization tower (14) and an additive gas flows from the melter (12) into the atomization tower (14) through the Laval nozzle, the additive gas accelerating the melt jet (24) as it passes through the Laval nozzle; The annular nozzle is arranged downstream of and / or in a region of the Laval nozzle in such a way that additional atomizing gas can flow through the annular nozzle from an atomizing gas source to the atomizing tower (14), as a result of which a locally reduced counter pressure can be generated in a region of the outlet opening of the Laval nozzle adjacent to the atomizing tower (14), thus increasing the pre-pressure P ０ and the locally reduced back pressure P ２ The pressure ratio D between D=P ０ / P ２ ≧2 This creates a relationship between 2. The apparatus (10, 100) of claim 1.

10. 1. A method for producing a metal powder comprising: - generating a melt jet (24) to be atomized by locally melting the material rod (22) inside the melting chamber (12) by means of an induction coil (20) which surrounds said material rod (22) at least in sections, said induction coil (20) being operated at a melting frequency f ｍｅｌｔ and - superheating the molten jet (24) in a region between the induction coil (20) and a nozzle assembly (16) using a separate intermediate coil (30, 130) disposed downstream of and coaxially aligned with the induction coil (20), the intermediate coil (30, 130) oscillating at a fundamental frequency f ｂａｓｅ The modulation frequency fmod is modulated onto the fundamental frequency fbase, and the fundamental frequency f ｂａｓｅ vs. melting frequency f ｍｅｌｔ Frequency ratio F ＢＳ for: 1≦F ＢＳ =f ｂａｓｅ / f ｍｅｌｔ ≦500 The relationship is established between steps and - atomizing the superheated melt jet (24) with the nozzle assembly (16), the melter (12) being connected to an atomization tower (14) via the nozzle assembly (16); The method includes:

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