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EP0308600B1 - Apparatus for the ultrasonic atomization of a fluid - Google Patents

Apparatus for the ultrasonic atomization of a fluid Download PDF

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Publication number
EP0308600B1
EP0308600B1 EP88111182A EP88111182A EP0308600B1 EP 0308600 B1 EP0308600 B1 EP 0308600B1 EP 88111182 A EP88111182 A EP 88111182A EP 88111182 A EP88111182 A EP 88111182A EP 0308600 B1 EP0308600 B1 EP 0308600B1
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EP
European Patent Office
Prior art keywords
transmitters
ultrasonic
transmitter
standing
sound
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP88111182A
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German (de)
French (fr)
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EP0308600A1 (en
Inventor
Ernst-Günter Dr. Lierke
Klaus Lühmann
Sigurf Dr. Jönsson
Michael Dipl.-Ing. Hohmann
Lothar Dipl.-Phys. Bendig
Frieder Dipl.-Ing. Hofmann
Reinhard Dipl.-Ing. Gaa
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Battelle Institut eV
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Battelle Institut eV
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B17/00—Apparatus for spraying or atomising liquids or other fluent materials, not covered by the preceding groups
    • B05B17/04—Apparatus for spraying or atomising liquids or other fluent materials, not covered by the preceding groups operating with special methods
    • B05B17/06—Apparatus for spraying or atomising liquids or other fluent materials, not covered by the preceding groups operating with special methods using ultrasonic or other kinds of vibrations
    • B05B17/0607—Apparatus for spraying or atomising liquids or other fluent materials, not covered by the preceding groups operating with special methods using ultrasonic or other kinds of vibrations generated by electrical means, e.g. piezoelectric transducers
    • B05B17/0623—Apparatus for spraying or atomising liquids or other fluent materials, not covered by the preceding groups operating with special methods using ultrasonic or other kinds of vibrations generated by electrical means, e.g. piezoelectric transducers coupled with a vibrating horn
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/02—Making metallic powder or suspensions thereof using physical processes
    • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
    • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy

Definitions

  • the invention relates to a device for atomizing melts, normal liquids or agglomerated substances, with the aid of ultrasound with a first ultrasound transmitter, to which an ultrasound reflector is mounted at a distance, between which a standing ultrasound wave is formed, into which the medium to be atomized is introduced.
  • German Patent 26 56 330 Such a device, which has proven itself in and of itself, is described in German Patent 26 56 330.
  • the reflector is designed as a passive component there.
  • the distance between the transmitter and the reflector is set there using a suitable mechanism, which only moves the reflector.
  • a gas jet can be blown into the chamber in order to allow the atomized medium to cool down more quickly by spraying it against a cooled metal surface.
  • the object of the invention is to design it in such a way that detuning of the standing sound wave is automatically prevented during operation of the device.
  • the energy of the standing sound wave should be noticeably increased.
  • the invention is characterized in that the reflector is designed as a second ultrasonic transmitter, the electrical and acoustic properties of which are approximately equal to those of the first transmitter.
  • the medium to be atomized should be supplied in the middle between the two transmitters, in a pressure node of the sound wave.
  • the two transmitters are shifted symmetrically, namely by the same distance in the axial direction outwards or inwards.
  • the reflector By designing the reflector as an active ultrasonic transducer, i.e. as a transmitter, the atomized medium is also prevented from settling there because both transducers clean themselves by means of ultrasonic vibrations.
  • the change in distance to adapt to the resonance of the standing sound wave can be carried out by a phase-sensitive or amplitude-sensitive sound pickup, which is preferably attached in the vicinity of the end face of one of the two transmitters, again preferably outside the atomization area.
  • the change in distance can also be checked or regulated automatically or by hand based on the maximum power of the emitted ultrasound, since both transducers have pronounced impedance maxima in the case of standing wave resonance.
  • Both transmitters can be powered by their own or the same frequency generator. If one and the same frequency generator is used, it is ensured without further measures that both transmitters vibrate with the same frequency and amplitude.
  • both transmitters are powered via Own frequency generators can have their frequencies deviated from each other by a small amount, so that the expected beats, which are caused by interference of the waves emitted by both transmitters, occur at a frequency that does not interfere with the atomization.
  • the frequency generator can also be designed as a wobble transmitter, which operates in a narrow frequency band around the natural frequencies of the two transmitters.
  • a housing-fixed, heated tube is provided, which is particularly suitable for the supply of a liquid melt from a corresponding reservoir.
  • the mouth of the tube should be located a few mm in front of the axis connecting the transmitters so that the emerging melt can be atomized under optimal level conditions.
  • the radial distance is, for example, 2 or 3 mm.
  • the diameter of the tube at the outlet should not exceed about 6 to 8 mm.
  • it can be expanded to 20 to 30 mm to accommodate a resistance heating coil in the tube. This ensures that a sufficiently heated melt is released directly into the standing ultrasonic wave.
  • the tube can also be made of BN (boron nitride) to prevent any drops of the melt from sticking.
  • BN boron nitride
  • An important embodiment of the invention is characterized in that the device is installed in a pressure vessel, so that the atomization at feel bar overpressure takes place, for example in the order of magnitude between 3 and 10 bar, possibly also at a higher overpressure. Due to the large surface tension of molten metals, sound levels of over 180 dB are required for atomization. These high sound levels can only be achieved with gas overpressure. An inert gas is usually used as the gas.
  • the atomization of a molten metal at excess gas pressure also has the advantage of achieving high sound levels with relatively small ultrasonic amplitudes of the transducers, so that the transducers have a much longer service life.
  • the gas pressure is increased, the convection cooling of the atomized melt is improved and the solidification time is shortened considerably, so that the metal powder may solidify under amorphous conditions.
  • the dimensions of the pressure vessel are relatively small, so that laboratory systems with dimensions less than 1 m in diameter and 1 to 2 m in height are realizable.
  • an airlock is formed there, which prevents the particles from being transported to these surfaces.
  • the oxygen partial pressure is set to an extremely low value. With deviations This is because spherical powders are produced in the presence of oxygen, while spattering particles are formed at a normal oxygen partial pressure of the air, which may be advantageous during sintering.
  • the device according to the invention is basically suitable for the ultrasonic atomization of all meltable or liquid media. In particular, it is suitable for atomizing metal melts. Further fields of application are listed in the aforementioned German patents 26 56 330 and 28 42 232.
  • the invention is explained in more detail below on the basis of an exemplary embodiment from which further important features result.
  • the figure shows a partially schematic axial section through an atomizing device according to the invention for atomizing a molten metal.
  • a first ultrasonic transmitter 1 and a second ultrasonic transmitter 2 are each mounted on a slide unit 3, which is moved via a stepper motor or DC motor 4. Both transmitters 1, 2 are preferably operated at the same operating frequency, which is, for example, 20 kHz. Both transmitters can be fed by their own frequency generator 5, which works on the principle of the feedback oscillator.
  • Both transmitters 1, 2 are equipped with an airlock 6 as an additional measure to prevent melt from sticking.
  • the movable carriage units 3 adapt the distance between the transmitters 1, 2 to the respective operating conditions, namely symmetrically to a melt beam 7, which transports melt from a melting furnace 16 into the standing ultrasonic field 14 via a heated tube (not shown).
  • a pressure sensor 8 is arranged, which measures the sound pressure of the standing wave 14 and passes it on for maximum electronic tracking.
  • the servomotors 4 receive their actuating impulses from there.
  • the slide units are positioned on the servomotor with the aid of angle encoders 10 or on the slide using linear potentiometers 11.
  • the electronic tracking 9 always searches for the position in which the sound pressure of the sound field 14 has its maximum value.
  • the frequency of the second transmitter 2 can be close to the frequency of the first transmitter 1. In order to prevent beats that are too low in frequency, caused by indifference of the waves emitted by the two transmitters, the two frequencies should differ by at least 0.5%.
  • both ultrasonic transducers 1, 2 with a fre quenzgenerator operated at exactly the same frequency and the same phase position, so that the emitted sound waves are always amplified.
  • the generator can be designed as a wobble transmitter that works in a narrow frequency band around the natural frequencies of the two converters.
  • the two transmitters can be cooled via a direct air connection 12 or via an indirect water connection (cooling coil).
  • the device described is installed in a pressure vessel 13 so that the interior with the standing sound field formed there is pressure-tight to the outside.
  • the internal pressure in the chamber can be increased accordingly and this pressure increase results in a higher energy density of the standing ultrasonic wave 14 with the same amplitude of the ultrasonic transducers. This goes hand in hand with an improvement in the efficiency of atomization while at the same time extending the service life of the transmitters.
  • Air an inert gas or any other gas or gas mixture can be provided in the chamber, and the partial pressure of the oxygen can also be adjusted accordingly.

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  • Special Spraying Apparatus (AREA)
  • Manufacture Of Metal Powder And Suspensions Thereof (AREA)
  • Apparatuses For Generation Of Mechanical Vibrations (AREA)

Description

Die Erfindung betrifft eine Vorrichtung zum Zerstäuben von Schmelzen, normalen Flüssigkeiten oder agglomerier­ten Stoffen, mit Hilfe von Ultraschall mit einem ersten Ultraschallsender, zu dem beabstandet ein Ultraschallre­flektor angebracht ist, zwischen denen eine stehende Ultraschallwelle ausgebildet wird, in die das zu zer­stäubende Medium eingebracht wird.The invention relates to a device for atomizing melts, normal liquids or agglomerated substances, with the aid of ultrasound with a first ultrasound transmitter, to which an ultrasound reflector is mounted at a distance, between which a standing ultrasound wave is formed, into which the medium to be atomized is introduced.

Eine derartige Vorrichtung, die sich an und für sich bewährt hat, ist in der deutschen Patentschrift 26 56 330 beschrieben. Der Reflektor ist dort als passives Bauteil ausgebildet. Der Abstand zwischen Sender und Reflektor wird dort über eine geeignete Mechanik eingestellt, die aber lediglich den Reflektor verschiebt. In dieser Druck­schrift wird auch schon erwähnt, daß eine Erhöhung des statischen Gasdrucks in der die stehende Ultraschallwelle umgebenden Kammer zu einer proportionalen Erhöhung des Schallpegels führt. Weiterhin wird dort erwähnt, daß man einen Gasstrahl in die Kammer einblasen kann, um das zer­stäubte Medium dadurch schneller abkühlen zu lassen, daß es gegen ein gekühlte Metallfläche gespritzt wird.Such a device, which has proven itself in and of itself, is described in German Patent 26 56 330. The reflector is designed as a passive component there. The distance between the transmitter and the reflector is set there using a suitable mechanism, which only moves the reflector. In this document it is also mentioned that an increase in the static gas pressure in the chamber surrounding the standing ultrasonic wave leads to a proportional increase in the sound level. It is also mentioned there that a gas jet can be blown into the chamber in order to allow the atomized medium to cool down more quickly by spraying it against a cooled metal surface.

Einen ähnlichen Stand der Technik beschreibt im übrigen die DE-PS 28 42 232, der auch noch der Gedanke entnommen werden kann, das zu zerstäubende Medium in die Druckkno­ten der stehenden Ultraschallwelle einzubringen.A similar prior art is also described in DE-PS 28 42 232, from which the idea can also be deduced of introducing the medium to be atomized into the pressure nodes of the standing ultrasonic wave.

Bedingt durch die geringen Abstände zwischen Sender und Reflektor beim geschilderten Stand der Technik wird aller dings der Reflektor während des Zerstäubungsvorganges mit flüssiger Schmelze beaufschlagt und setzt sich daher nach einer gewissen Betriebszeit zu. Der Sender dagegen bleibt durch die Vibration des Sendertellers und durch die damit verbundene Erzeugung des Ultraschallwindes frei.Due to the small distances between transmitter and reflector in the described state of the art, everything is However, the reflector is subjected to liquid melt during the atomization process and therefore becomes clogged after a certain operating time. The transmitter, however, remains free due to the vibration of the transmitter plate and the associated generation of the ultrasonic wind.

Weitere Beeinträchtigungen ergeben sich bei dieser be­kannten Vorrichtung durch Veränderungen im Schallfeld, insbesondere bedingt durch Temperaturschwankungen beim Einbringen des Schmelzstrahls in das Schallfeld. Hier­durch ändern sich die Parameter des Schallfeldes, so daß zur Aufrechterhaltung der stehenden Welle der Re­flektor ständig nachgeführt werden muß. Wie erwähnt er­folgt diese Nachführung unsymmetrisch bezüglich der gehäusefesten Zufuhrstelle für die Schmelze bzw. das zu zerstäubende Medium.In this known device, further impairments result from changes in the sound field, in particular due to temperature fluctuations when the melt jet is introduced into the sound field. As a result, the parameters of the sound field change, so that the reflector must be constantly adjusted to maintain the standing wave. As mentioned, this tracking takes place asymmetrically with respect to the supply point for the melt or the medium to be atomized, which is fixed to the housing.

Ausgehend von einer Vorrichtung mit den eingangs genannten Merkmalen liegt daher der Erfindung die Aufgabe zugrunde, diese so auszugestalten, daß eine Verstimmung der stehen­den Schallwelle im Betrieb der Vorrichtung selbsttätig verhindert wird. Außerdem soll die Energie der stehenden Schallwelle fühlbar erhöht werden können.Starting from a device with the features mentioned at the outset, the object of the invention is to design it in such a way that detuning of the standing sound wave is automatically prevented during operation of the device. In addition, the energy of the standing sound wave should be noticeably increased.

Zur Lösung dieser Aufgabe ist die Erfindung dadurch ge­kennzeichnet, daß der Reflektor als ein zweiter Ultra­schallsender ausgebildet ist, dessen elektrische und akustische Eigenschaften etwa gleich denjenigen des ersten Senders sind.To achieve this object, the invention is characterized in that the reflector is designed as a second ultrasonic transmitter, the electrical and acoustic properties of which are approximately equal to those of the first transmitter.

Durch den hiermit vorgesehenen Einsatz zweier gleich starker, aktiver Ultraschallwandler oder Ultraschall­sender, die gleichzeitig als Sender und Reflektor wir­ ken, ergibt sich neben einer Erhöhung des Schallpegels eine thermische und akustische Symmetrie im Bereich der stehenden Schallwelle, die eine automatische Abstimmung der Schallwelle bei einer Änderung der Temperatur oder anderer Betriebsparameter ermöglicht.Through the intended use of two equally strong, active ultrasonic transducers or ultrasonic transmitters, which act as transmitters and reflectors at the same time ken, in addition to an increase in the sound level, there is a thermal and acoustic symmetry in the area of the standing sound wave, which enables the sound wave to be automatically adjusted when the temperature or other operating parameters change.

Die Zufuhr für das zu zerstäubende Medium soll in der Mitte zwischen den beiden Sendern erfolgen, und zwar in einem Druckknoten der Schallwelle. Die beiden Sender werden dann dazu symmetrisch verschoben, und zwar um einander gleiche Wegstrecken in axialer Richtung nach außen oder innen gefahren.The medium to be atomized should be supplied in the middle between the two transmitters, in a pressure node of the sound wave. For this purpose, the two transmitters are shifted symmetrically, namely by the same distance in the axial direction outwards or inwards.

Durch die Ausbildung des Reflektors als aktiver Ultra­schallwandler, d.h. als Sender, wird auch dort ein An­setzen des zerstäubten Mediums verhindert, weil beide Wandler sich durch Ultraschallschwingungen selbst reinigen.By designing the reflector as an active ultrasonic transducer, i.e. as a transmitter, the atomized medium is also prevented from settling there because both transducers clean themselves by means of ultrasonic vibrations.

Die Abstandsänderung zur Anpassung an die Resonanz der stehenden Schallwelle kann durch einen phasensensitiven oder amplitudensensitiven Schallaufnehmer erfolgen, der vorzugsweise in der Nähe der Stirnfläche eines der beiden Sender angebracht wird, abermals vorzugsweise außerhalb des Zerstäubungsbereiches. Die Abstandsänderung kann aber auch anhand des Leistungsmaximums des abgestrahlten Ultraschalls automatisch oder von hand kontrolliert bzw. geregelt werden, da beide Wandler bei Stehwellenresonanz ausgeprägte Impedanzmaxima besitzen.The change in distance to adapt to the resonance of the standing sound wave can be carried out by a phase-sensitive or amplitude-sensitive sound pickup, which is preferably attached in the vicinity of the end face of one of the two transmitters, again preferably outside the atomization area. However, the change in distance can also be checked or regulated automatically or by hand based on the maximum power of the emitted ultrasound, since both transducers have pronounced impedance maxima in the case of standing wave resonance.

Beide Sender können über eigene oder über denselben Fre­quenzgenerator gespeist werden. Bei Verwendung ein und desselben Frequenzgenerators wird ohne weitere Maßnahmen sichergestellt, daß beide Sender mit derselben Frequenz und Amplitude schwingen. Bei Speisung beider Sender über eigene Frequenzgeneratoren kann man deren Frequenzen um ein geringes Maß voneinander abweichen lassen, so daß die zu erwartenden Schwebungen, die durch Interferenz der von beiden Sendern abgestrahlten Wellen entstehen mit einer Frequenz erfolgen, die die Zerstäubung nicht stört. Zu demselben Zweck kann auch der Frequenzgenerator als Wobbelsender ausgebildet sein, der in einem schmalen Fre­quenzband um die Eigenfrequenzen der beiden Sender arbeitet.Both transmitters can be powered by their own or the same frequency generator. If one and the same frequency generator is used, it is ensured without further measures that both transmitters vibrate with the same frequency and amplitude. When both transmitters are powered via Own frequency generators can have their frequencies deviated from each other by a small amount, so that the expected beats, which are caused by interference of the waves emitted by both transmitters, occur at a frequency that does not interfere with the atomization. For the same purpose, the frequency generator can also be designed as a wobble transmitter, which operates in a narrow frequency band around the natural frequencies of the two transmitters.

Für die Zufuhr des zu zerstäubenden Mediums zu der stehenden Schallwelle wird ein gehäusefestes, beheiztes Röhrchen vorgesehen, das insbesondere für die Zufuhr einer flüssigen Schmelze aus einem entsprechenden Re­servoir geeignet ist. Die Mündung des Röhrchens sollte wenige mm vor der die Sender verbindenden Achse ange­ordnet sein, damit die austretende Schmelze unter op­timalen Pegelbedingungen zerstäubt werden kann. Der radiale Abstand liegt beispielsweise bei 2 oder 3 mm. Der Durchmesser des Röhrchens sollte am Auslauf etwa 6 bis 8 mm nicht überschreiten. In einem Abstand von ca. 20 mm von der Zerstäuberachse kann er aber auf 20 bis 30 mm erweitert werden, um eine Widerstands-Heizwicklung im Röhrchen unterbringen zu können. Dadurch wird sicher­gestellt, daß eine ausreichend erhitzte Schmelze direkt in die stehende Ultraschallwelle abgegeben wird.For the supply of the medium to be atomized to the standing sound wave, a housing-fixed, heated tube is provided, which is particularly suitable for the supply of a liquid melt from a corresponding reservoir. The mouth of the tube should be located a few mm in front of the axis connecting the transmitters so that the emerging melt can be atomized under optimal level conditions. The radial distance is, for example, 2 or 3 mm. The diameter of the tube at the outlet should not exceed about 6 to 8 mm. At a distance of approx. 20 mm from the atomizer axis, it can be expanded to 20 to 30 mm to accommodate a resistance heating coil in the tube. This ensures that a sufficiently heated melt is released directly into the standing ultrasonic wave.

Das Röhrchen kann auch aus BN (Bornitrid) gefertigt werden, um ggf. ein Anhaften von Tropfen der Schmelze zu verhindern.The tube can also be made of BN (boron nitride) to prevent any drops of the melt from sticking.

Eine wichtige Ausgestaltung der Erfindung ist dadurch gekennzeichnet, daß die Vorrichtung in einem Druckbe­hälter eingebaut ist, so daß die Zerstäubung bei fühl­ barem Überdruck stattfindet, beispielsweise in der Größenordnung zwischen 3 und 10 bar, ggfs. auch bei einem höheren überdruck. Wegen der großen Oberflächenspannung von Metallschmelzen sind zum Zerstäuben Schallpegel von über 180 dB erforderlich. Diese hohen Schallpegel können nur bei Gasüberdruck erreicht werden. Als Gas nimmt man üblicherweise ein Inertgas.An important embodiment of the invention is characterized in that the device is installed in a pressure vessel, so that the atomization at feel bar overpressure takes place, for example in the order of magnitude between 3 and 10 bar, possibly also at a higher overpressure. Due to the large surface tension of molten metals, sound levels of over 180 dB are required for atomization. These high sound levels can only be achieved with gas overpressure. An inert gas is usually used as the gas.

Die Zerstäubung einer Metallschmelze bei Gasüberdruck hat auch den Vorteil, hohe Schallpegel bei relativ kleinen Ultraschallamplituden der Wandler zu erreichen, so daß man zu sehr viel größeren Standzeiten der Wandler kommt.The atomization of a molten metal at excess gas pressure also has the advantage of achieving high sound levels with relatively small ultrasonic amplitudes of the transducers, so that the transducers have a much longer service life.

Bei einem erhöhten Gasdruck ist die Konvektionskühlung der zerstäubten Schmelze verbessert und damit wird die Erstarrungszeit erheblich verkürzt, so daß man unter Umständen zu einer amorphen Erstarrung der Metallpulver kommt.If the gas pressure is increased, the convection cooling of the atomized melt is improved and the solidification time is shortened considerably, so that the metal powder may solidify under amorphous conditions.

Wegen der bei extrem schneller Erstarrung und relativ geringen Fluggeschwindigkeit der Tröpfchen (um 1 m/s) zu erwartenden kurzen Flugstrecke in der schmelzflüssigen Phase sind die Abmessungen des Druckbehälters relativ klein, so daß Laboranlagen mit Abmessungen unter 1 m Durchmesser und 1 bis 2 m Höhe realisierbar sind.Because of the short flight distance in the molten phase to be expected with extremely rapid solidification and relatively low flight speed of the droplets (around 1 m / s), the dimensions of the pressure vessel are relatively small, so that laboratory systems with dimensions less than 1 m in diameter and 1 to 2 m in height are realizable.

Um ein Anhaften der zerstäubten Teilchen an den Sendern bzw. an der Wand des Druckbehälters zu verhindern, wird es weiterhin bevorzugt, wenn dort eine Luftschleuse aus­gebildet wird, die den Transport der Teilchen zu diesen Flächen verhindert.In order to prevent the atomized particles from adhering to the transmitters or to the wall of the pressure vessel, it is further preferred if an airlock is formed there, which prevents the particles from being transported to these surfaces.

Weiterhin wird es bevorzugt, den Sauerstoff-Partialdruck auf einen extrem niedrigen Wert einzustellen. Bei Abwe­ senheit von Sauerstoff entstehen nämlich kugelige Pulver, während bei einem normalen Sauerstoff-Partialdruck der Luft spratzige Teilchen entstehen, die ggf. beim Sintern vorteilhaft sind.It is further preferred to set the oxygen partial pressure to an extremely low value. With deviations This is because spherical powders are produced in the presence of oxygen, while spattering particles are formed at a normal oxygen partial pressure of the air, which may be advantageous during sintering.

Die Erhöhung des Schallpegels infolge einer Erhöhung der Schallamplitude und/oder des Gasdrucks führt insgesamt zu feineren Pulvern, ohne daß, wie dies sonst bei der Ultra­schallzerstäubung der Fall ist, die Frequenz geändert werden muß.The increase in the sound level as a result of an increase in the sound amplitude and / or the gas pressure leads overall to finer powders without the frequency having to be changed, as is otherwise the case with ultrasonic atomization.

Die erfindungsgemäße Vorrichtung eignet sich grundsätzlich für die Ultraschall-Zerstäubung aller schmelzbaren oder flüssigen Medien. Insbesondere ist sie zur Zerstäubung von Metallschmelzen geeignet. Weitere Anwendungsgebiete sind in den eingangs erwähnten deutschen Patentschriften 26 56 330 und 28 42 232 aufgeführt.The device according to the invention is basically suitable for the ultrasonic atomization of all meltable or liquid media. In particular, it is suitable for atomizing metal melts. Further fields of application are listed in the aforementioned German patents 26 56 330 and 28 42 232.

Die Erfindung wird im folgenden anhand eines Ausführungs­beispiels näher erläutert, aus dem sich weitere wichtige Merkmale ergeben. Die Figur zeigt einen teilweise sche­matischen Axialschnitt durch eine erfindungsgemäße Zer­stäubungsvorrichtung zum Zerstäuben einer Metallschmelze.The invention is explained in more detail below on the basis of an exemplary embodiment from which further important features result. The figure shows a partially schematic axial section through an atomizing device according to the invention for atomizing a molten metal.

Ein erster Ultraschallsender 1 und ein zweiter Ultra­schallsender 2 sind je auf einer Schlitteneinheit 3 mon­tiert, die über einen Schrittmotor oder Gleichstrommotor 4 bewegt wird. Beide Sender 1, 2 werden vorzugsweise mit derselben Betriebsfrequenz betrieben, die beispielsweise bei 20 kHz liegt. Beide Sender können durch einen ei­genen Frequenzgenerator 5 gespeist werden, der nach dem Prinzip des rückgekoppelten Oszillators arbeitet.A first ultrasonic transmitter 1 and a second ultrasonic transmitter 2 are each mounted on a slide unit 3, which is moved via a stepper motor or DC motor 4. Both transmitters 1, 2 are preferably operated at the same operating frequency, which is, for example, 20 kHz. Both transmitters can be fed by their own frequency generator 5, which works on the principle of the feedback oscillator.

Beide Sender 1,2 sind mit einer Luftschleuse 6 als zu­sätzliche Maßnahme zur Verhinderung des Anhaftens von Schmelze ausgerüstet.Both transmitters 1, 2 are equipped with an airlock 6 as an additional measure to prevent melt from sticking.

Durch die beweglichen Schlitteneinheiten 3 wird der Ab­stand zwischen den Sendern 1,2 den jeweiligen Betriebs­bedingungen angepaßt, und zwar symmetrisch zu einem Schmelzenstrahl 7, der über ein - nicht gezeigtes - be­heiztes Röhrchen Schmelze aus einem Schmelzofen 16 in das stehende Ultraschallfeld 14 transportiert.The movable carriage units 3 adapt the distance between the transmitters 1, 2 to the respective operating conditions, namely symmetrically to a melt beam 7, which transports melt from a melting furnace 16 into the standing ultrasonic field 14 via a heated tube (not shown).

In der Nähe eines der beiden Sender 1,2 ist ein Druck­sensor 8 angeordnet, der den Schalldruck der stehenden Welle 14 mißt und anhand eines Maximums zur elektroni­schen Nachführung weitergibt. Von dort erhalten die Stellmotoren 4 ihre Stellimpulse.In the vicinity of one of the two transmitters 1, 2, a pressure sensor 8 is arranged, which measures the sound pressure of the standing wave 14 and passes it on for maximum electronic tracking. The servomotors 4 receive their actuating impulses from there.

Die Schlitteneinheiten werden mit Hilfe von Winkelko­dierern 10 am Stellmotor oder von Linearpotentiometern 11 am Schlitten positioniert.The slide units are positioned on the servomotor with the aid of angle encoders 10 or on the slide using linear potentiometers 11.

Die elektronische Nachführung 9 sucht immer diejenige Position, in der der Schalldruck des Schallfeldes 14 seinen maximalen Wert hat.The electronic tracking 9 always searches for the position in which the sound pressure of the sound field 14 has its maximum value.

Die Frequenz des zweiten Senders 2 kann nahe bei der Frequenz des ersten Senders 1 liegen. Zur Verhinderung von zu niederfrequenten Schwebungen, die durch Indif­ferenz der von den beiden Sendern abgestrahlten Wellen entsteht, sollen sich beide Frequenzen um wenigstens 0,5% unterscheiden.The frequency of the second transmitter 2 can be close to the frequency of the first transmitter 1. In order to prevent beats that are too low in frequency, caused by indifference of the waves emitted by the two transmitters, the two frequencies should differ by at least 0.5%.

Bei einer abgeänderten Ausführungsform der Erfindung werden beide Ultraschallwandler 1,2 mit einem Fre­ quenzgenerator bei exakt der gleichen Frequenz und gleicher Phasenlage betrieben, so daß die abgestrahl­ten Schallwellen sich immer verstärken.In a modified embodiment of the invention, both ultrasonic transducers 1, 2 with a fre quenzgenerator operated at exactly the same frequency and the same phase position, so that the emitted sound waves are always amplified.

Der Generator kann als Wobbelsender ausgebildet sein, der in einem schmalen Frequenzband um die Eigenfrequenzen der beiden Wandler arbeitet.The generator can be designed as a wobble transmitter that works in a narrow frequency band around the natural frequencies of the two converters.

Die beiden Sender können über einen direkten Luftanschluß 12 oder über einen indirekten Wasseranschluß (Kühlschlange) gekühlt werden.The two transmitters can be cooled via a direct air connection 12 or via an indirect water connection (cooling coil).

Die beschriebene Vorrichtung ist in einem Druckbehälter 13 eingebaut, so daß der Innenraum mit dem dort ausge­bildeten stehenden Schallfeld druckdicht nach außen ist. Dadurch kann der Innendruck in der Kammer entsprechend erhöht werden und durch diese Druckerhöhung erhält man eine höhere Energiedichte der stehenden Ultraschallwelle 14 bei gleicher Amplitude der Ultraschallwandler. Damit geht eine Verbesserung des Wirkungsgrades der Zerstäu­bung bei gleichzeitiger Verlängerung der Lebensdauer der Sender einher.The device described is installed in a pressure vessel 13 so that the interior with the standing sound field formed there is pressure-tight to the outside. As a result, the internal pressure in the chamber can be increased accordingly and this pressure increase results in a higher energy density of the standing ultrasonic wave 14 with the same amplitude of the ultrasonic transducers. This goes hand in hand with an improvement in the efficiency of atomization while at the same time extending the service life of the transmitters.

In der Kammer kann Luft, ein Inertgas oder auch ein beliebiges anderes Gas oder Gasgemisch vorgesehen sein, wobei man auch den Partialdruck des Sauerstoffs ent­sprechend einstellen kann.Air, an inert gas or any other gas or gas mixture can be provided in the chamber, and the partial pressure of the oxygen can also be adjusted accordingly.

Claims (15)

1. Device for atomising melts, normal liquids or agglomerated substances by means of ultrasonics using a first ultrasonic transmitter which is spaced from an ultrasonic reflector, between said transmitter and reflector a standing ultrasonic wave being formed, into which the medium to be atomised is introduced, comprising: executing the reflector as a second ultrasonic transmitter (2), whose electric and acoustic properties are approximately identical with those of the first transmitter (1).
2. Device as claimed in Claim 1, wherein a device (3, 4) is provided, which displaces the two transmitters (1, 2) symmetrically in axial direction.
3. Device as claimed in Claim 2, wherein the medium to be atomised is supplied to the pressure node of the sound wave (14) at a fixed position in the centre between the two transmitters (1, 2).
4. Device as claimed in any of Claims 1 to 3, wherein a sound sensor (8) is provided in the sound field (14).
5. Device as claimed in any of Claims 1 to 3, wherein a measuring instrument is provided which measures the power consumption of at least one of the transmitters (1, 2).
6. Device as claimed in Claim 4 or Claim 5, wherein the spacing of the transmitters (1, 2) is controlled by the output signals of the sound sensor (8) or of the measuring instrument.
7. Device as claimed in any of Claims 1 to 6, wherein the two transmitters (1, 2) are supplied via separate frequency generators (5).
8. Device as claimed in any of Claims 1 to 6, wherein the two transmitters (1, 2) are supplied via the same frequency generator (5).
9. Device as claimed in any of Claims 1 to 8, wherein the basic frequencies of the two transmitters (1, 2) differ only insignificantly from each other.
10. Device as claimed in any of Claims 1 to 8, wherein the basic frequencies of the two transmitters (1, 2) are identical.
11. Device as claimed in any of Claims 6 to 10, wherein the frequency generator (5) is executed as sweep frequency generator.
12. Device as claimed in any of Claims 1 to 11, wherein a heated fixed tube is provided for feeding the medium to the standing sound wave (14), the orifice of said tube being located some mm above the axis connecting the transmitters.
13. Device as claimed in any of Claims 1 to 12, wherein said device is mounted inside a pressure vessel (13).
14. Device as claimed in any of Claims 1 to 13, wherein a nozzle arrangement (6) for generating a circular downward air flow curtain is provided above the transmitters (1, 2) and/or in front of the inner wall of the pressure vessel (13).
15. Device as claimed in any of Claims 1 to 14, wherein a device for adjusting the oxygen partial pressure is provided in the vessel (13) which encloses the standing sound wave (14).
EP88111182A 1987-09-25 1988-07-13 Apparatus for the ultrasonic atomization of a fluid Expired - Lifetime EP0308600B1 (en)

Applications Claiming Priority (2)

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DE19873732325 DE3732325A1 (en) 1987-09-25 1987-09-25 DEVICE FOR SPRAYING A LIQUID MEDIUM WITH THE AID OF ULTRASOUND
DE3732325 1987-09-25

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EP0308600B1 true EP0308600B1 (en) 1991-03-06

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DE3732325A1 (en) 1989-04-13
US4981425A (en) 1991-01-01
EP0308600A1 (en) 1989-03-29

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