DEVICE AND METHOD FOR PRODUCING METAL POWDER USING AN INDUCTION COIL AND AN INTERMEDIATE COIL

Abstract

A device for producing metal powder. This includes a melting chamber, a downstream atomization tower, and a nozzle assembly for atomizing a melt jet. The device further includes an induction coil disposed within the melting chamber and operated at a melting frequency f.sub.melt, the induction coil is adapted to locally melt a material rod at least section-wise received therein, to produce the melt jet to be atomized, and a separate intermediate coil disposed within the melting chamber and operated at a base frequency f.sub.base, wherein said intermediate coil is disposed downstream of the induction coil and aligned coaxially with the induction coil. The intermediate coil is configured to superheat the melt jet in a region between the induction coil and the nozzle assembly. The following applies to a frequency ratio F.sub.BS of the base frequency f.sub.base to the melting frequency f.sub.melt, 1?F.sub.BS=f.sub.base/f.sub.melt?500.

Claims

1. A device for producing metal powder, wherein the device comprises: a melting chamber; an atomization tower disposed downstream of the melting chamber; a nozzle assembly for atomizing a melt jet, via which the melting chamber is connected to the atomization tower; an induction coil arranged within the melting chamber and operable at a melting frequency f.sub.melt, which is configured to locally melt a material rod received at least section-wise therein in order to produce the melt jet to be atomized, a separate intermediate coil arranged within the melting chamber and operable at a base frequency f.sub.base and arranged downstream of the induction coil and aligned coaxially with the induction coil, wherein the intermediate coil is configured to superheat the melt jet in a region between the induction coil and the nozzle assembly, wherein the intermediate coil is configured such that a modulation frequency f.sub.mod is modulated onto the base frequency f.sub.base wherein a frequency ratio Fes of the base frequency f.sub.base and the melting frequency f.sub.melt is settable to: $1?F_{\mathrm{BS}}=f_{base}/f_{\mathrm{melt}}?500.$

2. The device according to claim 1, wherein the intermediate coil comprises an interference section formed at an end portion of the intermediate coil facing the induction coil, wherein the intermediate coil has a reduced inner diameter in the interference section.

3. The device according to claim 1, wherein the melting frequency f.sub.melt is settable to between 10 kHz and 500 kHz, preferably between 100 kHz and 400 kHz, more preferably between 200 kHz and 300 kHz, and/or the base frequency f.sub.base is settable to between 100 kHz and 5000 kHz, preferably between 200 kHz and 4500 kHz, further preferably between 500 kHz and 4000 kHz, more preferably between 1000 kHz and 3000 kHz, still more preferably between 1500 kHz and 2500 kHz, and/or the modulation frequency f.sub.mod is settable to between 0.001 kHz and 5 kHz, preferably between 0.005 kHz and 4.5 kHz, further preferably between 0.01 kHz and 4 kHz, more preferably between 0.05 kHz and 3.5 kHz, still more preferably between 0.1 KHz and 3 kHz, still more preferably between 1 kHz and 2.5 kHz.

4. The device according to claim 1, wherein the intermediate coil has a cylindrical shape with preferably predominantly constant diameter.

5. The device according to claim 1, wherein a length of the intermediate coil is greater than four times, preferably greater than five times, more preferably greater than six times the smallest inner diameter of the nozzle assembly.

6. The device according to claim 1, wherein the intermediate coil is adapted to superheat the melt jet in at least 70%, preferably at least 80%, more preferably at least 90%, of a length defined by the smallest distance between the nozzle assembly and the induction coil.

7. The device according to claim 1, wherein the nozzle assembly comprises a Laval nozzle.

8. The device according to claim 1, wherein the nozzle assembly comprises an annular nozzle.

9. The device according to claim 7, wherein the Laval nozzle is configured and arranged in such a way that the melt jet passes through the Laval nozzle from the melting chamber into the atomization tower and an additive gas flows through the Laval nozzle from the melting chamber into the atomization tower, wherein the additive gas accelerates the melt jet as it passes through the Laval nozzle, and wherein the annular nozzle is arranged downstream of the Laval nozzle and/or in the region of the Laval nozzle in such a way that an additional atomizing gas flows through the annular nozzle from an atomizing gas source into the atomization tower, as a result of which a locally reduced counterpressure can be generated in a region of an outlet opening of the Laval nozzle adjacent to the atomization tower, so that the following applies to a pressure ratio D between a pre-pressure P.sub.0 of the melting chamber and the locally reduced counterpressure P.sub.2: $D=P_0/P_2?2.$

10. A method for producing metal powder, comprising the steps of: generating a melt jet to be atomized by locally melting a material rod by an induction coil which surrounds the material rod at least section-wise within the melting chamber, wherein the induction coil is operated at a melting frequency f.sub.melt; superheating the melt jet in a region between the induction coil and a nozzle assembly by means of a separate intermediate coil arranged downstream of the induction coil and aligned coaxially with the induction coil, wherein the intermediate coil is operated at a base frequency f.sub.base, and wherein a modulation frequency f.sub.mod is modulated onto the base frequency f.sub.base, and wherein the following applies to a frequency ratio F.sub.BS of the base frequency f.sub.base to the melting frequency f.sub.melt: 1?F.sub.BS=f.sub.base/f.sub.melt?500; and atomizing the superheated melt jet by the nozzle assembly, wherein the melting chamber is connected to an atomization tower via the nozzle assembly.

11. The device according to claim 2, wherein the melting frequency f.sub.melt is settable to between 10 kHz and 500 kHz, preferably between 100 kHz and 400 kHz, more preferably between 200 kHz and 300 kHz, and/or the base frequency f.sub.base is settable to between 100 kHz and 5000 kHz, preferably between 200 kHz and 4500 kHz, further preferably between 500 kHz and 4000 kHz, more preferably between 1000 kHz and 3000 kHz, still more preferably between 1500 kHz and 2500 kHz, and/or the modulation frequency f.sub.mod is settable to between 0.001 kHz and 5 kHz, preferably between 0.005 kHz and 4.5 kHz, further preferably between 0.01 kHz and 4 kHz, more preferably between 0.05 kHz and 3.5 kHz, still more preferably between 0.1 KHz and 3 kHz, still more preferably between 1 kHz and 2.5 kHz.

12. The device according to claim 11, wherein the intermediate coil has a cylindrical shape with preferably predominantly constant diameter.

13. The device according to claim 12, wherein a length of the intermediate coil is greater than four times, preferably greater than five times, more preferably greater than six times the smallest inner diameter of the nozzle assembly.

14. The device according to claim 13, wherein the intermediate coil is adapted to superheat the melt jet in at least 70%, preferably at least 80%, more preferably at least 90%, of a length defined by the smallest distance between the nozzle assembly and the induction coil.

15. The device according to claim 14, wherein the nozzle assembly comprises a Laval nozzle.

16. The device according to claim 14, wherein the nozzle assembly comprises an annular nozzle.

17. The device according to claim 15, wherein the nozzle assembly comprises an annular nozzle.

18. The device according to claim 16, wherein the Laval nozzle is configured and arranged in such a way that the melt jet passes through the Laval nozzle from the melting chamber into the atomization tower and an additive gas flows through the Laval nozzle from the melting chamber into the atomization tower, wherein the additive gas accelerates the melt jet as it passes through the Laval nozzle, and wherein the annular nozzle is arranged downstream of the Laval nozzle and/or in the region of the Laval nozzle in such a way that an additional atomizing gas flows through the annular nozzle from an atomizing gas source into the atomization tower, as a result of which a locally reduced counterpressure can be generated in a region of an outlet opening of the Laval nozzle adjacent to the atomization tower, so that the following applies to a pressure ratio D between a pre-pressure P.sub.0 of the melting chamber and the locally reduced counterpressure P.sub.2: $D=P_0/P_2?2.$

Description

BRIEF DESCRIPTION OF THE FIGURES

[0060] Hereinafter, exemplary embodiments of the present invention are explained in more detail with reference to the accompanying schematic figures. In the figures:

[0061] FIG. 1 is a schematic representation of a device according to one embodiment of the invention;

[0062] FIG. 2 is a schematic representation of a device according to a further embodiment of the invention.

[0063] FIG. 3 is a diagram showing the base frequency f.sub.base and the modulation frequency f.sub.mod at which the intermediate coil is operated.

DETAILED DESCRIPTION OF THE INVENTION

[0064] FIG. 1 shows a device or system 10 for producing high purity metal powder. The device 10 comprises a melting chamber 12 and an atomization tower 14 downstream of the melting chamber 12. In the embodiment shown, the melting chamber 12 is arranged above the atomization tower 14 during operation. The melting chamber 12 is connected to the atomization tower 14 via a nozzle assembly 16. That is, an upper end of the nozzle assembly 16 is disposed adjacent to or extends into the melting chamber 12. A lower end of the nozzle assembly 16 is disposed adjacent to or extends into the atomization tower 14.

[0065] The nozzle assembly 16 may be integrated as a component into the melting chamber 12. The nozzle assembly 16 may be integrated as a component into the melting chamber 12 and into the atomization tower 14. The nozzle assembly 16 may be integrated as a component into the atomization tower 14. The nozzle assembly 16 may be provided as a separate component between the melting chamber 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 melting chamber 12 and the atomization tower 14.

[0066] Within the melting chamber 12 an EIGA (Electrode Induction Melting Inert Gas Atomization) assembly 18 comprising an induction coil 20 having a plurality of turns is provided. The induction coil 20 is disposed above and coaxial with the nozzle assembly 16. The induction coil 20 has a shape tapering towards the nozzle assembly 16.

[0067] Furthermore, a material rod 22 is arranged within the melting chamber 12, in this case a material rod 22 made of a metal or a metal alloy, preferably Ti64 alloy. An end of the material rod 22 facing the nozzle assembly 16 is at least partially received in the induction coil 20 or extends into the induction coil 20.

[0068] The induction coil 20 is operated at a melting frequency f.sub.melt and is configured to locally melt the end of the material rod 22 received therein. Here, the induction coil is operated at a melting frequency f.sub.melt of 250 kHz. In this way a melt jet 24 to be atomized with a melt jet diameter do of 5 mm in the present example is generated. In the embodiment shown, the melt jet 24 is initially a substantially continuously coherent melt jet 24. As indicated by the arrows 26, 28, the material rod 22 is movably mounted. Thus, the material rod 22 is rotatable about its longitudinal axis A (arrow 28), whereby a uniform melting of the material rod 22 can be achieved. In addition, 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 fed so that material to be melted (and subsequently atomized or nebulized) can be continuously fed during the atomization or nebulization process. To move the material rod 22, it 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 coaxially with the nozzle assembly 16. The 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.

[0069] The device 10 includes an intermediate coil 30 disposed in the melting chamber 12 and operated at a base frequency f.sub.base. In the embodiment shown, the base frequency is 2000 kHz. Thus, here the frequency ratio F.sub.BS of the base frequency f.sub.base to the melting frequency f.sub.melt is 8.

[0070] As can be seen in FIG. 1 (and also FIG. 2), the intermediate coil 30 is formed in addition to the induction coil 20 as a separate intermediate coil 30 structurally separate therefrom. The intermediate coil 30 is disposed downstream of the induction coil 20 and is aligned coaxially with the induction coil 20. Thus, the melt jet 24 passes or falls through the intermediate coil 30 along the longitudinal axis A from the induction coil 20 into the nozzle assembly 16. The base frequency f.sub.base of the intermediate coil 30 is selected such that the intermediate coil 30 superheats the melt jet 24 in a region between the induction coil 20 and the nozzle assembly 16, thereby preventing or at least reducing a cooling of the melt jet 24 prior to entry into the nozzle assembly 16. In the embodiment shown, the intermediate coil 30 superheats the melt jet 24 over a distance of about 50% of the shortest distance between the induction coil 20, more specifically a lower end of the induction coil 20, and the nozzle assembly 16, more specifically an upper inlet opening of the nozzle assembly 16.

[0071] The intermediate coil 30 of the device 10 shown in FIG. 1 includes an interference section 32, or an interference zone 32, and a superheating section 34 or superheating zone 34 adjacent thereto. The interference section 32 is formed at an upper end region of the intermediate coil 30 facing the induction coil 20, that is, in a region where the melt jet 24 enters the intermediate coil 30. The intermediate coil 30 has an inner diameter in the region of the interference section 32, which is reduced compared to an inner diameter of the superheating section 34. Here, the interference section 32 extends over about 15% of the total length of the intermediate coil 30.

[0072] An additional modulation frequency f.sub.mod of 0.006 KHz is modulated onto the base frequency f.sub.base at which the intermediate coil 30 is operated, i.e. the base frequency f.sub.base is superimposed with this modulation frequency f.sub.mod. The effect of this modulation frequency f.sub.mod is that the melt jet 24 is disturbed and thus broken up into individual droplets T in a targeted manner. These droplets T follow one another continuously and thus together form the melt jet 24. Consequently, in the embodiment shown, the melt jet 24 already enters the nozzle assembly 16 in the form of individual droplets T, which are subsequently atomized by the nozzle assembly 16. By selectively setting the melt jet diameter do by means of the melting frequency f.sub.melt of the induction coil 20 and the selective setting of the modulation frequency f.sub.mod in accordance with f.sub.melt or the melt jet diameter do and the melting speed, the device 10 can targetedly influence and set the droplet size. In this manner, the powder properties can be targetedly influenced. The base frequency f.sub.base and the modulation frequency f.sub.mod are shown schematically in FIG. 3.

[0073] After atomization of the melt jet 24 (i.e. the droplets T), the atomized droplets cool in the atomization tower 14 and solidify there to form powder.

[0074] FIG. 2 shows a device or system 100 for producing high-purity metal powder according to a further embodiment. The device 100 is essentially similar to the device 10 of FIG. 1.

[0075] In contrast to the device 10 of FIG. 1, the intermediate coil 130 of the device 100 of FIG. 2 does not comprise different sections or zones, but is formed continuously over its entire length as a superheating zone 134. Nevertheless, in this embodiment, too, a modulation frequency f.sub.mod may optionally be modulated onto a base frequency f.sub.base at which the intermediate coil 130 is operated for superheating the melt jet (not shown in FIG. 2). The same or other frequencies may be provided as in the embodiment of FIG. 1.

[0076] 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 arranged here within the nozzle assembly 130.

[0077] In the embodiment of FIG. 2, the intermediate coil 130 covers about 80% of a smallest distance between a last turn of the induction coil 130 facing the nozzle assembly 16 and an upper inlet opening of the nozzle assembly 16 and superheats the melt jet in this region. Moreover, in this embodiment, the intermediate coil 130 extends over about 77% of the range of the smallest distance between the last turn of the induction coil 20 facing the nozzle assembly 1 and a portion having the smallest inner diameter of the nozzle assembly 16. Thus, the intermediate coil 130 still superheats the melt jet even in an inlet section of the nozzle assembly 16.

[0078] FIG. 3 shows a schematic diagram of one embodiment illustrating the frequencies at which the intermediate coil 30, 130 is operated. Thus, the diagram illustrates the base frequency f.sub.base and the modulated modulation frequency f.sub.mod over the time axis.

LIST OF REFERENCE SYMBOLS

[0079] 10 device [0080] 12 melting chamber [0081] 14 atomization tower [0082] 16 nozzle assembly [0083] 18 EIGA assembly [0084] 20 induction coil [0085] 22 material rod [0086] 24 melt jet [0087] 26 direction of motion [0088] 28 direction of motion [0089] 30 intermediate coil [0090] 32 interference section [0091] 34 superheating section [0092] do melt jet diameter [0093] A longitudinal axis [0094] T droplet