METHOD AND DEVICE FOR BREAKING UP AN ELECTRICALLY CONDUCTIVE LIQUID

Abstract

The invention relates to a method for splitting an electrically conductive liquid, in particular a melt jet, comprising the steps providing the electrically conductive liquid which moves in a first direction (12) in the form of a liquid jet (10); and generating high-frequency travelling electromagnetic fields surrounding the liquid jet (10) which travel in the first direction (12) and accelerate the liquid jet (10) in the first direction (12), thereby atomizing the liquid jet (10).

Claims

1-15. (canceled)

16. A method for splitting an electrically conductive liquid, comprising: providing the electrically conductive liquid moving in a first direction in the form of a liquid jet; and generating high-frequency travelling electromagnetic fields surrounding the liquid jet that travel in the first direction and accelerate the liquid jet in the first direction thereby atomizing the liquid jet.

17. The method according to claim 16, wherein the travelling electromagnetic fields have an alternating current frequency of at least 0.1 MHz.

18. The method according to claim 16, wherein the high-frequency travelling electromagnetic fields are generated by means of a coil assembly with at least one pole pair.

19. The method according to claim 16, further comprising generating a gas stream surrounding the liquid jet, the gas stream moving substantially in the first direction and further accelerating the liquid jet in the first direction.

20. The method according to claim 16, further comprising generating a further gas stream impacting on the liquid jet by means of an annular nozzle.

21. The method according to claim 16, wherein the liquid jet is generated by melting an electrode by means of an induction coil.

22. The method according to claim 16 further comprising cooling the atomized liquid jet (10) to generate solidified particles.

23. A device for splitting an electrically conductive liquid, comprising: a liquid source for providing a liquid jet of the electrically conductive liquid moving in a first direction, and a coil assembly with at least one pole pair that is arranged downstream of the liquid source and coaxially with the liquid jet; wherein the coil assembly is adapted to generate high-frequency travelling electromagnetic fields surrounding the liquid jet and travelling in the first direction to accelerate the liquid jet in the first direction by means of the high-frequency travelling electromagnetic fields and thereby atomize the liquid jet.

24. The device according to claim 23, wherein the high-frequency travelling electromagnetic fields have an alternating current frequency of at least 0.1 MHz.

25. The device according to claim 23 further comprising an inert gas nozzle adapted to generate a gas stream surrounding the liquid jet and moving substantially in the first direction to additionally accelerate the liquid jet by means of the gas stream in the first direction.

26. The device according to claim 25, wherein the coil assembly is arranged in the inert gas nozzle and/or upstream and/or downstream of the inert gas nozzle viewed along the stream center axis.

27. The device according to claim 23, which further comprises an annular nozzle for generating a further gas stream that is adapted to impact on the liquid jet.

28. The device according to claim 23, wherein the liquid source is an electrode, and the liquid jet is a melt jet.

29. The device according to claim 28, further comprising an induction coil arranged coaxially with the electrode and in the region of one end of the electrode, the induction coil being adapted to melt the electrode so as to generate the melt jet.

30. The device according to claim 23 comprising an atomization tower for cooling and solidifying the atomized liquid jet.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0038] Embodiments of the present invention are explained in more detail below with reference to the enclosed schematic figures. It is depicted:

[0039] FIG. 1 a schematic representation of the mode of operation of the method according to the invention.

[0040] FIG. 2 a schematic representation of the mode of operation of a method of nozzling by means of a Laval nozzle.

[0041] FIG. 3 shows a schematic representation of the mode of operation of the method according to the invention in an EIGA method.

FIGURE DESCRIPTION

[0042] FIG. 1 shows a section of a liquid jet 10 of an electrically conductive liquid in a longitudinal section. In the present example, the liquid jet 10 is substantially a continuous melt jet of a metal melt. Starting from a liquid source (not shown), the liquid jet 10 moves in a first direction 12 along its stream center axis A. In the illustration of FIG. 1 shown, the liquid jet 10 falls from top to bottom due to the gravitational force.

[0043] The liquid jet 10 passes through a device (20) for atomizing the liquid jet 10. In the design example shown, the device 20 comprises a coil assembly 22 with three pole pairs 24A, 24B, 24C. It is understood that in alternative design examples the coil assembly may have more or less than three pole pairs. The coil assembly 22 is downstream of the liquid source not shown in the direction of movement and the windings are arranged parallel to each other and coaxial with the liquid jet 10.

[0044] The individual pole pairs 24A, 24B, 24C can be controlled one after the other in such a way that phase changes φi and hereby high-frequency travelling electromagnetic fields are generated. The sequence of the phase changes (pi is illustrated by the numbering φ1, φ2, φ3 as an example. The high-frequency travelling electromagnetic fields can, for example, have an alternating current frequency between 0.1 and 100 MHz.

[0045] The high-frequency travelling electromagnetic fields also move in the first direction 12 due to the phase change (pi. Due to the arrangement of the windings of the coil order 22 around the liquid jet 10, Lorentz forces 26 generated by the high-frequency travelling electromagnetic fields with strong tangential components mainly impact on external layers of the liquid jet 10 and additionally accelerate them in the first direction 12. Thus, outer layers of the liquid jet 10 are accelerated more strongly than inner layers of the liquid jet 10, resulting in a critical velocity profile with a large velocity gradient in the liquid jet. The velocities prevailing in the course of the liquid jet, which illustrate the velocity profiles within the liquid jet, are represented by the arrows v.sub.m, wherein longer arrows indicate higher velocities and shorter arrows indicate lower velocities (for reasons of clarity, only one arrow is marked with the reference sign v.sub.m). In the longitudinal section, the critical velocity profile at the exit of the liquid jet 10 from the coil assembly 22 is shown as a U-shaped velocity profile 28. The large velocity gradient within the liquid jet 10 increases the pressure within the liquid jet 10. This results in a large pressure difference between the high pressure within the liquid jet 10 and a much lower pressure surrounding the liquid jet. The pressure difference causes the liquid jet 10 to break up into ligaments, i.e. the liquid jet 10 is atomized into microparticles. The microparticles can, for example, have a mean particle size or a mean particle diameter d.sub.50 between 20 μm and 100 μm.

[0046] FIG. 2 shows a section of a melt jet 110 of a metal melt in a longitudinal section. The liquid jet 110 is atomized by means of an inert gas nozzling method or a Laval nozzling. The melt jet 110 passes through an opening of an inert gas nozzle 120 to enter an atomization tower (not shown).

[0047] In contrast to the method shown in FIG. 1, the critical velocity profile in the melt jet 110 in the method shown in FIG. 2 is generated by an inert gas stream 122. The inert gas stream 122 flows through the inert gas nozzle 120 at a high velocity v.sub.g into the atomization tower. Since the melt jet 110 passes centrally through the inert gas nozzle 120, the inert gas flow 122 surrounds the melt jet 110 and acts via shear stresses on the outer layers of the melt jet 110. The outer layers of the melt jet 110 are thus accelerated more strongly in the first direction 12 than the inner layers of the melt jet 110. This generates a critical speed profile 128 within the melt jet 110 and atomizes the melt jet 110 after it leaves the inert gas nozzle 120 or enters the connected atomization tower.

[0048] FIG. 3 shows a schematic representation of the mode of operation of the procedure according to the invention in an EIGA method or a section of a sectional view of the device 20 according to the invention in an EIGA plant 200. The same components and features are provided with the same reference signs as in FIG. 1.

[0049] As can be seen in FIG. 3, the coil assembly 22 in the design example shown is integrated into an inert gas nozzle 30, which is designed in the form of a Laval nozzle. FIG. 3 thus shows an embodiment of the invention comprising a combination of the methods shown in FIGS. 1 and 2. This results in surprising synergy effects, which can lead to a further improved atomization.

[0050] The coil assembly 22 and the inert gas nozzle 30 are arranged coaxially, wherein the coil assembly 22 encloses the inert gas nozzle 30 and the interior of the inert gas nozzle 30, respectively. An inert gas stream 32 flows over the inert gas nozzle 30, which accelerates the liquid jet 10 consisting of several successive drops in a laminar manner (analogous to FIG. 2). This laminar acceleration through the inert gas nozzle 30 or through the intergas flow 32 (analogous to FIG. 2) is superimposed by an electromagnetic acceleration of the electrically conductive liquid jet 10 through the coil assembly 22 (analogous to FIG. 1).

[0051] Both accelerations together impact on the liquid jet 10 in such a way that it is accelerated in the first direction 12. These superimposed accelerations cause the formation of a critical U-shaped velocity profile in the liquid jet 10, corresponding to the velocity profiles of FIGS. 1 and 2. The large velocity gradient within the liquid jet 10 thus generated increases the pressure within the liquid jet 10, resulting in a large pressure difference between the high pressure within the liquid jet 10 and a much lower pressure surrounding the liquid jet. The pressure difference causes the liquid jet 10 to break up into ligaments, i.e. the liquid jet 10 is atomized into microparticles.

[0052] As also shown in FIG. 3, the liquid jet 10 is generated by the so-called EIGA method. For this purpose, an EIGA coil 40 or an induction coil 40 is mounted in front of the coil assembly 22 and inert gas nozzle 30. The induction coil 40 is arranged coaxially to the coil assembly 22 and the inert gas nozzle 30. The induction coil 40 is tapered when viewed in the first direction 12, i.e. it has a decreasing diameter when viewed in the first direction 12.

[0053] An electrode 42 is provided coaxially with the induction coil 40 and at least partially in front of it, which is melted off by means of the induction coil 40 in order to generate the liquid jet 10. The electrode shown may, for example, consist of titanium, a titanium alloy, an alloy based on zirconium, niobium, nickel or tantalum, a precious metal or a precious metal alloy, a copper or aluminum alloy, a special metal or special metal alloy. The electrode 42 is suspended at an upper end (not shown) and is axially displaceable in the first direction, i.e. in the direction of the arrangement of coil arrangement 22 and inert gas nozzle 30. This allows the electrode 42 to be continuously tracked during melting of the electrode 42.

[0054] Downstream of the coil assembly 22 and inert gas nozzle 30 is an annular nozzle 50, through which a further inert gas flow 52 can be introduced into the overall assembly. The further inert gas flow 52 in the design shown hits the liquid jet 10 emerging from the coil assembly 22 and inert gas nozzle 30 impulse-like or impact-like. The emerging liquid jet 10 may already be at least partially atomized when the further inert gas flow 52 from the annular nozzle 50 impacts on it. By the impact of the further inert gas stream 52 on the liquid jet 10 or the at least partially atomized liquid jet 10, it will be further nozzled.

[0055] As shown in FIG. 3, the coil assembly 22, the inert gas nozzle (Laval nozzle) 30 and the annular nozzle 50 can be designed as a common device 20. The device 20 can, for example, be in one piece.

[0056] The overall arrangement shown in FIG. 3 can be followed by an atomization tower for cooling and solidifying the atomized liquid jet, which is only indicated here and is not shown in full. The atomization tower may comprise a collecting tank for collecting the solidified powder.

[0057] It is understood that instead of the EIGA method for generating the liquid jet, alternative crucible-free methods or methods with crucibles may be provided, for example a VIGA method, a PIGA method, a CCIM method or any other method. Accordingly, in the system shown in FIG. 3, instead of the induction coil, one or more devices required for the above-mentioned methods may be provided upstream of the coil assembly.

[0058] It is understood that the method according to the invention and device according to the invention may also comprise a combination of a device with coil assembly and an annular nozzle, without inert gas nozzle, in an embodiment.

[0059] By means of the method according to the invention or the device according to the invention, operating costs can in particular be reduced compared to conventional inert gas nozzling methods by saving inert gas consumption.

LIST OF REFERENCE SIGNS

[0060] 10 liquid jet [0061] A stream center axis [0062] 12 first direction [0063] 20 device for atomizing the liquid jet [0064] 22 coil arrangement [0065] 24A, 24B, 24C pole pairs/windings [0066] 26 Lorentz forces [0067] 28 U-shaped speed profile [0068] v.sub.m velocity within the liquid jet [0069] φ.sub.i, φ.sub.1, φ.sub.2, φ.sub.3 phase change [0070] 30 inert gas nozzle (Laval nozzle) [0071] 32 inert gas flow [0072] 40 induction coil [0073] 42 electrode [0074] 50 annular nozzle [0075] 52 further inert gas flow [0076] 110 melt jet (SOTA) [0077] 120 Inert gas nozzle (SOTA) [0078] 122 Inert gas flow (SOTA) [0079] 128 velocity profile (SOTA) [0080] 200 EIGA system