EP0120506A2 - Metal powder and process for producing the same - Google Patents

Metal powder and process for producing the same Download PDF

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Publication number
EP0120506A2
EP0120506A2 EP84103487A EP84103487A EP0120506A2 EP 0120506 A2 EP0120506 A2 EP 0120506A2 EP 84103487 A EP84103487 A EP 84103487A EP 84103487 A EP84103487 A EP 84103487A EP 0120506 A2 EP0120506 A2 EP 0120506A2
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EP
European Patent Office
Prior art keywords
gas
opening
container
pressure
melt
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Granted
Application number
EP84103487A
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German (de)
French (fr)
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EP0120506A3 (en
EP0120506B1 (en
Inventor
Alfred Prof. Dr.-Ing. Walz
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Dr-Ing Lueder Gerking Te Berlijn Bondsrepubliek
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Walz Alfred Prof Dr-Ing
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Priority to AT84103487T priority Critical patent/ATE34109T1/en
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Publication of EP0120506A3 publication Critical patent/EP0120506A3/en
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    • 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
    • B22F9/082—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 atomising using a fluid
    • 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
    • B22F9/082—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 atomising using a fluid
    • B22F2009/088—Fluid nozzles, e.g. angle, distance

Definitions

  • the present invention relates in particular to finely divided metal powders and a process for their production.
  • Powder metallurgy has led to the development of materials that are no longer accessible to conventional processing methods such as deformation and machining.
  • Sintered alloys in which finely divided metal powders of different metals are mixed and only alloyed during the sintering process have become particularly important.
  • the shaping in the sinter metallurgy takes place through the sintering process.
  • Sintered metallurgy now requires metal powders that are as finely divided as possible in order to be able to achieve surfaces that are as smooth as possible and to provide the largest possible surface for the formation of sintered alloys. Furthermore, it is desirable to use spherical powder particles which are as dense as possible in order to obtain classifier bodies which are as dense as possible.
  • a process has now been found which allows metal powders to be produced, the powder particles of which are dense and non-porous, and which have a very approximate spherical shape and mean diameters of well below 50 ⁇ .
  • the present patent application therefore relates to pore-free metal powders, which are characterized in that the powder particles have simply curved, smooth surfaces and an average diameter of 5 to 35 ⁇ .
  • Preferred metal powders according to the invention have average powder particle diameters between 5 and 20 ⁇ , preferably between 8 and 15 ⁇ .
  • the powder particles preferred according to the invention also have diameter distributions with a standard deviation of at most 2.5, particularly preferably a standard deviation of at most 2.0. The standard deviation is based on the Number frequency of the powder diameter defined in a production batch without looking at coarse powder particles.
  • Particularly preferred metal powders according to the invention consist predominantly of approximately strictly spherical individual powder particles. 90% of the powder particles forming the metal powder should have a deviation of less than 10% from the spherical shape. A deviation of 10% from the spherical shape means that the largest diameter of the powder particle is at most 10% larger than the smallest diameter.
  • the powder particles have simply curved surfaces.
  • a simply curved surface should be understood to mean that each tangent on the surface has only one point of contact with the metal particle.
  • All metals or metal alloys can be used as metals. Iron, cobalt, nickel, chromium, aluminum or their alloys are particularly suitable.
  • the metal powder can have a crystalline structure or be amorphous. In particular, it is also possible, e.g. Obtain iron alloys with additives of crystallization inhibitors such as chromium or boron as the metal powder according to the invention.
  • Metal powders of silver, platinum, iridium or alloys according to the invention are suitable for use as catalysts.
  • the present invention also relates to a process for the production of metal powders, which is characterized in that a molten metal stream and gas are allowed to flow into an opening of a container, the ratio of gas pressure near the inflow opening outside the container and gas pressure inside the container is greater than 5 and the opening of the container is selected so that the ratio of the mass flows of gas and molten metal entering the container is greater than 8.
  • the temperature of the gas flowing through the opening in the container should be in the range between 0.7 and 1.5 times the solidification temperature of the melt in ° K before the inflow.
  • the ratio of the mass flows of gas and melt should preferably be less than 25, particularly preferably less than 15.
  • the molten metal preferably only occurs at a point in the container opening with the gas flowing into the opening. in contact where the gas pressure has dropped to less than 60% of the pressure before opening, i.e. at a point where the gas already has almost the speed of sound.
  • the pressure at the point at which the melt and gas come into contact should be at least a fifth, preferably still at least a third, of the gas pressure before the container opening.
  • the gas should preferably have supersonic speed at the first point of contact with the molten metal.
  • Oxygen should therefore generally be avoided. Highly pure inert gases such as helium or argon are preferably used. Hydrogen can also be used for metals that do not form hydrides. Nitrogen can be used for metals that do not form nitrides. Combustion gases such as carbon monoxide can also be advantageous under certain conditions. It is also possible to achieve special effects by controlling the gas composition. For example, by using a gas with a low oxygen partial pressure, metal powders with a superficial oxide layer can be obtained, which, for example, can advantageously be used as catalysts.
  • the finest metal powder is formed by the process according to the invention via the intermediate stage of the formation of melt threads, the melt threads representing a thermodynamically extremely unstable intermediate state due to the high ratio of surface tension to viscosity. Because of their instability, the melt filaments tend to disintegrate into droplets.
  • the temperature of the gaseous medium must therefore be chosen to be sufficiently high that the melt filaments do not solidify into droplets before decay.
  • the intermediate fiber stage is formed in a very short time. The melt bursts when entering the strong pressure drop and is pulled out into fibers by the high gas velocity. It is therefore essential for the production of very fine powders that the formation of sufficiently thin melt fibers takes place before the disintegration into droplets.
  • the melt exits the crucible at that point, i.e. comes into contact with the gas at which the highest pressure gradient of the gas flow is present and at the same time the gas flow already has a sufficiently high speed but is still of sufficient density to pull out the burst melt flow.
  • the density should preferably still be at least 0.4 bar.
  • the pressure before the opening of the container can be 1 to 30 bar, preferably 1 to 10 bar.
  • a pressure of 1 bar is generally sufficient.
  • the nozzle should be as short as possible in the direction of flow, so that the pressure gradient below the point of the narrowest nozzle cross section is as large as possible.
  • the melt For the formation of powders, the melt must not solidify in the intermediate fiber state.
  • the solidification of fibers can generally be prevented by controlling the gas temperature. Metals with a higher solidification temperature give off their heat mainly through radiation.
  • such metals are preferably heated in the crucible to temperatures of a few 100 K above the solidification temperature.
  • the present invention also relates to a device for producing metal powders, which consists of two gas spaces, the gas spaces being connected by at least one gas passage opening, which furthermore has means for generating a pressure difference between the two gas spaces, which also has a crucible in the gas space with the contains higher pressure, wherein the crucible has at least one melt outlet opening, which is arranged symmetrically to the gas passage opening.
  • the gas passage opening can be designed as a slot-shaped opening, the melting crucible having a plurality of melt outlet openings arranged in the central plane of the slot-shaped gas passage opening.
  • the gas passage openings can, however, also be designed as circularly symmetrical passage openings, a melt outlet opening being provided in the axis of each gas passage opening.
  • the melt outlet openings are preferably designed in the form of melt outlet nipples.
  • the melt outlet nipples preferably open in the plane of the narrowest cross section of the gas passage opening.
  • the length of the gas passage opening in the axial direction should not exceed the diameter of the gas passage opening at the narrowest point.
  • the gas passage opening should preferably widen from the point of the narrowest cross section in the flow direction with an opening angle of more than 90 °, particularly preferably more than 120 °.
  • the melt outlet nipples of the crucible should extend into the gas passage opening to such an extent that the melt outlet openings open in the plane in which the gas passage opening begins to widen.
  • FIG. 1 shows a metal melting crucible 1 which contains the metal melt 2.
  • the melting crucible can consist, for example, of quartz glass, sintered ceramic or graphite.
  • the melt crucible 1 contains at least one melt outlet nipple 3 on its underside.
  • the melt outlet nipple can, for example, have an opening of 0.3 to 1 mm in diameter.
  • the melting pot is also heated.
  • the crucible can be heated by means of a resistance heater 4, which is embedded, for example, in a ceramic mass 5.
  • the person skilled in the art is able to provide other options for heating the melt, for example high-frequency induction heating, direct electrical heating by means of electrodes which are immersed in the melt, etc.
  • one electrode can be the crucible, for example. It is also possible to provide flame heating inside or outside the crucible.
  • the crucible 1 is arranged within a container 6, which is divided into an upper gas space 8 and a lower gas space 9 by a partition 7.
  • the gas spaces 8 and 9 are connected by a passage opening 10.
  • the passage opening 10 is formed by a molded part 11 fitted into the partition 7.
  • the upper gas space 8 has a gas supply line 12 with a valve 13 for adjusting the gas pressure in the upper gas space 8.
  • the lower gas space 9 contains a gas discharge line 14 with a feed pump 15 for adjusting and maintaining the gas pressure in the lower gas space 9.
  • the bottom of the lower Gas space 9 is conical and has a lock 16 for discharging the metal powder formed.
  • a conical intermediate floor 17 can be provided, which serves to collect and separate the metal powder from the gas.
  • Thermal insulation 18 can be provided in particular for the upper gas space.
  • the crucible 1 is filled with the metal to be fiberized. Then the gaseous medium is let in via the valve 13.
  • the lower gas space 9 is evacuated to a pressure of, for example, 10 to 100 torr by means of the pump 15 and at the same time so much gas is supplied via the valve 13 that a pressure of, for example, 1 bar is maintained in the upper gas space remains.
  • the gas supplied can have the temperature of the melt 2, for example.
  • Metal can be fed into the crucible 1, for example by pushing a metal ingot 21 through the upper crucible opening 22, the ingot melting in contact with the melt 2.
  • the molded part 11, which forms the gas passage opening 10, is preferably formed from heat-resistant material, for example ceramic or quartz glass.
  • FIGS 2 to 4 show alternative embodiments for the formation of the gas passage opening 10.
  • the numerals designate the same elements as in Figure 1.
  • a molten metal is produced from solder with a melting point of 300 ° C. Air is used as the gaseous medium. A pressure of 1 bar prevails in the upper gas space 8. A pressure of 0.01 bar is maintained in the lower gas space 9.
  • the nipple 3 of the quartz crucible 1 arranged in the concentric gas passage opening 10 of 3 mm diameter has an open cross section of 0.5 mm diameter and a wall thickness of the nipple of 0.2 mm.
  • the helium gas supplied via line 12 has the temperature of the molten metal of 300 ° C. 19 g of metal powder per second are obtained from a melt outflow opening 3.
  • the powder consists of spheres with diameters between 5 ⁇ and 50 ⁇ .
  • the focus of the diameter distribution is 10 ⁇ . Very few powder particles have diameters above 30 ⁇ . Sporadic deviations from the spherical shape are obtained. These powder particles have an elliptical shape. The individual powder particles have a smooth surface on which individual crystallites can be recognized as differently reflecting areas without the spherical shape being disturbed.

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  • Manufacture Of Metal Powder And Suspensions Thereof (AREA)
  • Powder Metallurgy (AREA)
  • Physical Or Chemical Processes And Apparatus (AREA)

Abstract

Für die Pulvermetallurgie haben Sinterlegierungen besondere Bedeutung erlangt, bei denen feinteilige Metallpulver unterschiedlicher Metalle gemischt und erst während des Sintervorgangs legiert werden. Die Erfindung betrifft ein Verfahren und eine Vorrichtung zur Herstellung von Metallpulvern sowie dadurch hergestellte Metallpulver. Zur Herstellung von Metallpulvern läßt men einen Metallschmelzestrom und Gas in eine Öffnung eines Behälters einströmen, wobei das Verhältnis von Gasdruck in der Nähe der Einströmöffnung oberhalb des Behälters und Gasdruck innerhalb des Behälters größer als 5 und die Öffnung so gewählt ist, daß das Verhältnis der in den Behälter eintretenden Massenströme von Gas und Metallschmelze größer als 8 ist. Die Herstellungsvorrichtung ist durch zwei durch mindestens eine Gasdurchtrittsöffnung verbundene Gasräume gekennzeichnet, durch Mittel zur Erzeugung einer Druckdifferenz zwischen den beiden Gasräumen, und durch einen in dem Gasraum mit höherem Druck angeordneten Schmelzetiegel mit mindestens einer Schmelzeaustrittsöffnung, wobei die Schmelzeaustrittsöffnung symmetrisch zur Gasdurchlaßöffnung angeordnet ist.Sintered alloys have become particularly important for powder metallurgy, in which finely divided metal powders of different metals are mixed and only alloyed during the sintering process. The invention relates to a method and a device for producing metal powders and metal powders produced thereby. To produce metal powders, a molten metal stream and gas flow into an opening of a container, the ratio of gas pressure near the inflow opening above the container and gas pressure inside the container being greater than 5 and the opening being chosen such that the ratio of the in mass flows of gas and molten metal entering the container is greater than 8. The production device is characterized by two gas spaces connected by at least one gas passage opening, by means for generating a pressure difference between the two gas spaces, and by a melt crucible arranged in the gas space with a higher pressure and having at least one melt outlet opening, the melt outlet opening being arranged symmetrically to the gas passage opening.

Description

Die vorliegende Erfindung betrifft besonders feinteilige Metallpulver, sowie ein Verfahren zu deren Herstellung. Die Pulvermetallurgie hat zur Entwicklung von Werkstoffen geführt, die nicht mehr üblichen Verarbeitungsmethoden wie Verformung und spanabhebender Verarbeitung zugänglich sind. Besondere Bedeutung haben Sinterlegierungen erlangt, bei denen feinteilige Metallpulver unterschiedlicher Metalle gemischt und erst während des Sintervorganges legiert werden. Die Formgebung bei der Sintermetallurgie erfolgt durch den Sinterprozeß.The present invention relates in particular to finely divided metal powders and a process for their production. Powder metallurgy has led to the development of materials that are no longer accessible to conventional processing methods such as deformation and machining. Sintered alloys in which finely divided metal powders of different metals are mixed and only alloyed during the sintering process have become particularly important. The shaping in the sinter metallurgy takes place through the sintering process.

Die Sintermetallurgie fordert nun möglichst feinteilige Metallpulver, um einerseits möglichst glatte Oberflächen erreichen zu können und andererseits eine möglichst große Oberfläche für die Ausbildung von Sinterlegierungen zur Verfügung zu stellen. Ferner ist es wünschenswert, möglichst dichte, kugelförmige Pulverteilchen einzusetzen, um möglichst dichte Sichterkörper zu erhalten.Sintered metallurgy now requires metal powders that are as finely divided as possible in order to be able to achieve surfaces that are as smooth as possible and to provide the largest possible surface for the formation of sintered alloys. Furthermore, it is desirable to use spherical powder particles which are as dense as possible in order to obtain classifier bodies which are as dense as possible.

Es scheint nun, daß die große Oberflächenspannung der Metallschmelzen den üblichen Verfahren zur Herstellung von Metallpulvern, wie Druckzerstäubung oder Flammenzerstäubung eine natürliche Grenze setzt, die etwa bei 50µm Pulverdurchmesser liegt. Bei Erreichen dieser Grenze ist es kaum noch möglich, Schmelzekugeln weiter zu zerteilen. Die Oberflächenspannung setzt der weiteren Zerteilung einen um so größeren Widerstand entgegen, je enger der Krümmungsradius der Schmelzeoberfläche bereits ist.It now appears that the high surface tension of the metal melts places a natural limit on the customary processes for producing metal powders, such as pressure atomization or flame atomization, which is approximately 50 μm powder diameter. When this limit is reached, it is hardly possible to further break down the melt balls. The surface tension opposes the further division, the greater the resistance, the narrower the radius of curvature of the melt surface is.

Es wurde nun ein Verfahren gefunden, das es erlaubt Metallpulver herzustellen, deren Pulverteilchen dicht und porenfrei sind, sowie eine sehr gut angenäherte Kugelform und mittlere Durchmesser von weit unterhalb von 50 µ aufweisen.A process has now been found which allows metal powders to be produced, the powder particles of which are dense and non-porous, and which have a very approximate spherical shape and mean diameters of well below 50 μ.

Gegenstand der vorliegenden Patentanmeldung sind daher porenfreie Metallpulver, die dadurch gekennzeichnet sind, daß die Pulverteilchen einfach gekrümmmte, glatte Oberflächen und einen mittleren Durchmesser von 5 bis 35 µ aufweisen.The present patent application therefore relates to pore-free metal powders, which are characterized in that the powder particles have simply curved, smooth surfaces and an average diameter of 5 to 35 μ.

Bevorzugte erfindungsgemäße Metallpulver weisen mittlere Pulverteilchendurchmesser zwischen 5 und 20 µ, vorzugsweise zwischen 8 und 15 µ auf. Die erfindungsgemäß bevorzugten Pulverteilchen weisen ferner Durchmesserverteilungen mit einer Standardabweichung von maximal 2,5, besonders bevorzugt einer Standardabweichung von maximal 2,0 auf. Die Standardabweichung wird dabei auf die Anzahlhäufigkeit des Pulverdurchmessers in einer Herstellungscharge ohne Aussichtung grober Pulverteilchen definiert.Preferred metal powders according to the invention have average powder particle diameters between 5 and 20 μ, preferably between 8 and 15 μ. The powder particles preferred according to the invention also have diameter distributions with a standard deviation of at most 2.5, particularly preferably a standard deviation of at most 2.0. The standard deviation is based on the Number frequency of the powder diameter defined in a production batch without looking at coarse powder particles.

Besonders bevorzugte erfindungsgemäße Metallpulver bestehen überwiegend aus annähernd streng kugelförmigen Einzelpulverteilchen. 90 % der das Metallpulver bildenden Pulverteilchen sollen eine Abweichung von weniger als 10 % von der Kugelform aufweisen. Dabei bedeutet ein Abweichen um 10 % von der Kugelform, daß der größte Durchmesser des Pulverteilchens maximal 10 % größer ist als der kleinste Durchmesser.Particularly preferred metal powders according to the invention consist predominantly of approximately strictly spherical individual powder particles. 90% of the powder particles forming the metal powder should have a deviation of less than 10% from the spherical shape. A deviation of 10% from the spherical shape means that the largest diameter of the powder particle is at most 10% larger than the smallest diameter.

Wesentlich für die besondere Eignung der erfindungsgemäßen Metallpulver für die Sintermetallurgie ist, daß die Pulverteilchen einfach gekrümmte Oberflächen aufweisen. Dabei soll unter einer einfach gekrümmten Oberfläche verstanden werden daß jede Tangente an der Oberfläche nur einen Berührungspunkt mit dem Metallteilchen aufweist.It is essential for the particular suitability of the metal powders according to the invention for sintered metallurgy that the powder particles have simply curved surfaces. A simply curved surface should be understood to mean that each tangent on the surface has only one point of contact with the metal particle.

Als Metalle können alle Metalle bzw. Metall-Legierungen eingesetzt werden. Insbesondere kommen Eisen, Kobalt, Nickel, Chrom, Aluminium oder deren Legierungen in Frage. Die Metallpulver-können kristalline Struktur aufweisen oder amorph sein. Insbesondere ist es auch möglich, z.B. Eisenlegierungen mit Zusätzen von Kristallisationsinhibitoren wie Chrom oder Bor als erfindungsgemäße Metallpulver zu erhalten. Erfindungsgemäße Metallpulver aus Silber, Platin, Iridium oder Legierungen hiermit eignen sich für den Einsatz als Katalysatoren.All metals or metal alloys can be used as metals. Iron, cobalt, nickel, chromium, aluminum or their alloys are particularly suitable. The metal powder can have a crystalline structure or be amorphous. In particular, it is also possible, e.g. Obtain iron alloys with additives of crystallization inhibitors such as chromium or boron as the metal powder according to the invention. Metal powders of silver, platinum, iridium or alloys according to the invention are suitable for use as catalysts.

Gegenstand der vorliegenden Erfindung ist ferner ein Verfahren zur Herstellung von Metallpulvern, das dadurch gekennzeichnet ist, daß man ein Metallschmelzestrom und Gas in eine öffnung eines Behälters einströmen läßt, wobei das Verhältnis von Gasdruck in der Nähe der Einströmöffnung außerhalb des Behälters und Gasdruck innerhalb des Behälters größer als 5 vorgegeben wird und ferner die öffnung des Behälters so gewählt ist, daß das Verhältnis der in den Behälter eintretenden Massenströme von Gas und Metallschmelze größer als 8 ist. Die Temperatur des in dem Behälter durch die öffnung einströmenden Gases soll vor dem Einströmen im Bereich zwischen dem 0,7 und 1,5-fachen der Erstarrungstemperatur der Schmelze in °K betragen. Das Verhältnis der Massenströme von Gas und Schmelze soll vorzugsweise kleiner als 25, besonders bevorzugt kleiner als 15 sein.The present invention also relates to a process for the production of metal powders, which is characterized in that a molten metal stream and gas are allowed to flow into an opening of a container, the ratio of gas pressure near the inflow opening outside the container and gas pressure inside the container is greater than 5 and the opening of the container is selected so that the ratio of the mass flows of gas and molten metal entering the container is greater than 8. The temperature of the gas flowing through the opening in the container should be in the range between 0.7 and 1.5 times the solidification temperature of the melt in ° K before the inflow. The ratio of the mass flows of gas and melt should preferably be less than 25, particularly preferably less than 15.

Die Metallschmelze tritt vorzugsweise erst an einer Stelle in der Behälteröffnung mit dem in die Öffnung einströmenden Gas. in Berührung, an der der Gasdruck auf weniger als 60 % des Drucks. vor der öffnung abgefallen ist, d.h. an einer Stelle, an der das Gas bereits fast Schallgeschwindigkeit aufweist. Der Druck an der Stelle, an der Schmelze und Gas in Berührung treten, soll jedoch mindestens noch ein fünftel, vorzugsweise noch ein mindestens drittel des Gasdrucks vor der Behälteröffnung sein. Vorzugsweise soll das Gas an der ersten Berührungsstelle mit der Metallschmelze Überschallgeschwindigkeit aufweisen.The molten metal preferably only occurs at a point in the container opening with the gas flowing into the opening. in contact where the gas pressure has dropped to less than 60% of the pressure before opening, i.e. at a point where the gas already has almost the speed of sound. However, the pressure at the point at which the melt and gas come into contact should be at least a fifth, preferably still at least a third, of the gas pressure before the container opening. The gas should preferably have supersonic speed at the first point of contact with the molten metal.

Als Gase können alle Gase eingesetzt werden, die nicht mit der Metallschmelze reagieren. Sauerstoff ist daher im allgemeinen zu vermeiden. Vorzugsweise werden hochreine Inertgase wie Helium oder Argon eingesetzt. Bei Metallen, die keine Hydride bilden, kann auch Wasserstoff eingesetzt werden. Bei Metallen, die keine Nitride bilden, kann Stickstoff eingesetzt werden. Auch Verbrennungsabgase wie Kohlenmonoxid können unter gewissen Bedingungen vorteilhaft sein. Ferner ist es möglich, über die Steuerung der Gaszusammensetzung besondere Effekte zu erzielen. Zum Beispiel durch Einsatz eines Gases mit geringem Sauerstoffpartialdruck können Metallpulver mit einer oberflächlichen Oxidschicht erhalten werden, die z.B. vorteilhaft als Katalysatoren eingesetzt werden können.All gases that are not can be used as gases react with the molten metal. Oxygen should therefore generally be avoided. Highly pure inert gases such as helium or argon are preferably used. Hydrogen can also be used for metals that do not form hydrides. Nitrogen can be used for metals that do not form nitrides. Combustion gases such as carbon monoxide can also be advantageous under certain conditions. It is also possible to achieve special effects by controlling the gas composition. For example, by using a gas with a low oxygen partial pressure, metal powders with a superficial oxide layer can be obtained, which, for example, can advantageously be used as catalysts.

Es wird angenommen, daß die Bildung feinster Metallpulver nach dem erfindungsgemäßen Verfahren über die Zwischenstufe der Ausbildung von Schmelzefäden erfolgt, wobei die Schmelzefäden aufgrund des hohen Verhältnisses von Oberflächenspannung zu Viskosität einen thermodynamisch extrem instabilen Zwischenzustand darstellen. Aufgrund ihrer Instabilität neigen die Schmelzefäden zum Zerfall in Tröpfchen. Die Temperatur des gasförmigen Mediums muß daher hinreichend hoch gewählt werden, daß die Schmelzefäden nicht vor dem Zerfall in Tröpfchen erstarren. Die Ausbildung der Faserzwischenstufe erfolgt innerhalb sehr kurzer Zeit. Die Schmelze zerplatzt beim Eintritt in das starke Druckgefälle und wird durch die: hohe Gasgeschwindigkeit zu Fasern ausgezogen. Für die Herstellung sehr feiner Pulver ist es daher wesentlich, daß die Ausbildung hinreichend dünner Schmelzefasern vor dem Zerfall in Tröpfchen erfolgt.It is assumed that the finest metal powder is formed by the process according to the invention via the intermediate stage of the formation of melt threads, the melt threads representing a thermodynamically extremely unstable intermediate state due to the high ratio of surface tension to viscosity. Because of their instability, the melt filaments tend to disintegrate into droplets. The temperature of the gaseous medium must therefore be chosen to be sufficiently high that the melt filaments do not solidify into droplets before decay. The intermediate fiber stage is formed in a very short time. The melt bursts when entering the strong pressure drop and is pulled out into fibers by the high gas velocity. It is therefore essential for the production of very fine powders that the formation of sufficiently thin melt fibers takes place before the disintegration into droplets.

Vorzugsweise tritt daher die Schmelze an der Stelle aus dem Tiegel aus, d.h. tritt mit dem Gas in Berührung, an der der höchste Druckgradient der Gasströmung vorliegt und gleichzeitig die Gasströmung bereits eine hinreichend hohe Geschwindigkeit, aber noch eine ausreichende Dichte zum Ausziehen des zerplatzten Schmelzestroms aufweist. Die Dichte soll vorzugsweise noch mindestens 0,4 bar betragen.Preferably, therefore, the melt exits the crucible at that point, i.e. comes into contact with the gas at which the highest pressure gradient of the gas flow is present and at the same time the gas flow already has a sufficiently high speed but is still of sufficient density to pull out the burst melt flow. The density should preferably still be at least 0.4 bar.

Der Druck vor der öffnung des Behälters kann 1 bis 30 bar, vorzugsweise 1 bis 10 bar betragen. Im allgemeinen ist ein Druck von 1 bar ausreichend. Durch Anwendung von höherem Druck ist es möglich, sowohl den Druckgradienten Δp/Δ1, der das Zerplatzen des Schmelzestromes bewirkt, als auch die Dichte der das Ausziehen der zerplatzten Schmelze bewirkenden Überschallströmung zu erhöhen.The pressure before the opening of the container can be 1 to 30 bar, preferably 1 to 10 bar. A pressure of 1 bar is generally sufficient. By using higher pressure, it is possible to increase both the pressure gradient Δp / Δ1, which causes the melt flow to burst, and the density of the supersonic flow causing the burst of the melt to pull out.

Würde man demnach die Einströmöffnung für das Gas in Analogie zum Düsenblasverfahren zur Herstellung von Fasern als Düse betrachten, so soll die Düse in Strömungsrichtung möglichst kurz ausgebildet sein, so daß der Druckgradient unterhalb der Stelle des engsten Düsenquerschnitts möglichst groß ist.If one were to consider the inflow opening for the gas in analogy to the nozzle blowing process for producing fibers as a nozzle, the nozzle should be as short as possible in the direction of flow, so that the pressure gradient below the point of the narrowest nozzle cross section is as large as possible.

Für Ausbildung von Pulvern darf die Schmelze nicht im Faserzwischenzustand erstarren. Für Metallschmelzen mit Schmelzetemperaturen bis 600°C läßt sich die Erstarrung von Fasern durch die Steuerung der Gastemperatur im allgemeinen verhindern. Metalle mit höherer Erstarrungstemperatur geben ihre Wärme überwiegend durch Strahlung ab.For the formation of powders, the melt must not solidify in the intermediate fiber state. For metal melts with melt temperatures up to 600 ° C, the solidification of fibers can generally be prevented by controlling the gas temperature. Metals with a higher solidification temperature give off their heat mainly through radiation.

Zur Ausbildung von möglichst angenähert kugelförmigen Pulverteilchen werden solche Metalle im Schmelztiegel vorzugsweise auf Temperaturen von einigen 100 K über die Erstarrungstemperatur aufgeheizt.To form approximately spherical powder particles, such metals are preferably heated in the crucible to temperatures of a few 100 K above the solidification temperature.

Gegenstand der vorliegenden Erfindung ist auch eine Vorrichtung zur Herstellung von Metallpulvern, die aus zwei Gasräumen besteht, wobei die Gasräume durch mindestens eine Gasdurchtrittsöffnung verbunden sind, die ferner Mittel zur Erzeugung einer Druckdifferenz zwischen den beiden Gasräumen aufweist, die ferner ein Schmelzetiegel im Gasraum mit dem höheren Druck enthält, wobei der Schmelzetiegel mindestens eine Schmelzeaustrittsöffnung, die symmetrisch zur Gasdurchlaßöffnung angeordnet ist, aufweist. Die Gasdurchtrittsöffnung kann als schlitzförmige öffnung ausgebildet sein, wobei der Schmelzetiegel eine Vielzahl von in der Mittelebene der schlitzförmigen Gasdurchtrittsöffnung angeordnete Schmelzeaustrittsöffnungen aufweist. Die Gasdurchlaß- öffnungen können aber auch als kreissymmetrische Durchlaßöffnungen ausgebildet sein, wobei in der Achse jeder Gasdurchlaßöffnung eine Schmelzeaustrittsöffnung vorgesehen ist. Die Schmelzeaustrittsöffnungen sind vorzugsweise in Form von Schmelzeaustrittsnippeln ausgebildet. Die Schmelzeaustrittsnippel münden vorzugsweise in der Ebene des engsten Querschnitts der Gasdurchlaßöffnung.The present invention also relates to a device for producing metal powders, which consists of two gas spaces, the gas spaces being connected by at least one gas passage opening, which furthermore has means for generating a pressure difference between the two gas spaces, which also has a crucible in the gas space with the contains higher pressure, wherein the crucible has at least one melt outlet opening, which is arranged symmetrically to the gas passage opening. The gas passage opening can be designed as a slot-shaped opening, the melting crucible having a plurality of melt outlet openings arranged in the central plane of the slot-shaped gas passage opening. The gas passage openings can, however, also be designed as circularly symmetrical passage openings, a melt outlet opening being provided in the axis of each gas passage opening. The melt outlet openings are preferably designed in the form of melt outlet nipples. The melt outlet nipples preferably open in the plane of the narrowest cross section of the gas passage opening.

Die Länge der Gasdurchtrittsöffnung in Achsenrichtung soll den Durchmesser der Gasdurchlaßöffnung an der engsten Stelle nicht übersteigen. Vorzugsweise soll sich die Gasdurchtrittsöffnung von der Stelle des engsten Querschnitts in Strömungsrichtung mit einem öffnungswinkel von mehr als 90°, besonders bevorzugt mehr als 120°, erweitern.The length of the gas passage opening in the axial direction should not exceed the diameter of the gas passage opening at the narrowest point. The gas passage opening should preferably widen from the point of the narrowest cross section in the flow direction with an opening angle of more than 90 °, particularly preferably more than 120 °.

Vorzugsweise sollen ferner die Schmelzeaustrittsnippel des Schmelzetiegels in die Gasdurchlaßöffnung soweit hineinreichen, daß die Schmelzeaustrittsöffnungen in der Ebene münden, in der die Gasdurchtrittsöffnung sich zu erweitern beginnt.Preferably, the melt outlet nipples of the crucible should extend into the gas passage opening to such an extent that the melt outlet openings open in the plane in which the gas passage opening begins to widen.

Das erfindungsgemäße Verfahren und die erfindungsgemäße Vorrichtung werden anhand der anliegenden Figuren näher erläutert:

  • Fig. 1 zeigt beispielhaft eine Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens.
  • Fig. 2 bis 4 zeigen erfindungsgemäße Gestaltungsmöglichkeiten für die Gasdurchtrittsöffnung.
The method and the device according to the invention are explained in more detail with reference to the attached figures:
  • 1 shows an example of a device for carrying out the method according to the invention.
  • 2 to 4 show design options according to the invention for the gas passage opening.

Figur 1 zeigt einen Metallschmelzetiegel 1, der die Metallschmelze 2 enthält. Der Schmelzetiegel kann z.B. aus Quarzglas, Sinterkeramik oder Graphit bestehen. Der Schmelzetiegel 1 enthält an seiner Unterseite mindestens einen Schmelzeaustrittsnippel 3. Der Schmelzeaustrittsnippel kann z.B. eine öffnung von 0,3 bis 1 mm Durchmesser aufweisen. Der Schmelzetiegel ist ferner beheizt. Die Beheizung des Schmelzetiegels kann mittels einer Widerstandsheizung 4, die z.B. in eine keramische Masse 5 eingebettet ist, erfolgen. Der Fachmann ist in der Lage, auch andere Möglichkeiten der Beheizung der Schmelze vorzusehen, z.B. eine Hochfrequenzinduktionsheizung, eine direkte elektrische Heizung mittels Elektroden, die in die Schmelze eintauchen, usw. Bei Verwendung eines Graphittiegels kann z.B. die eine Elektrode der Tiegel sein. Ferner ist es möglich, eine Beheizung durch Flammen innerhalb oder außerhalb des Schmelzetiegels vorzusehen. Der Schmelzetiegel 1 ist innerhalb eines Behälters 6 angeordnet, der durch eine Trennwand 7 in einen oberen Gasraum 8 und einen unteren Gasraum 9 unterteilt ist. Die Gasräume 8 und 9 sind durch eine Durchtrittsöffnung 10 verbunden. Die Durchtrittsöffnung 10 ist durch ein in die Trennwand 7 eingepaßtes Formteil 11 ausgebildet. Der obere Gasraum 8 weist eine Gaszufuhrleitung 12 mit einem Ventil 13 zur Einstellung des Gasdrucks im oberen Gasraum 8 auf. Der untere Gasraum 9 enthält eine Gasabfuhrleitung 14 mit einer Förderpumpe 15 zur Einstellung und Aufrechterhaltung des Gasdrucks im unteren Gasraum 9. Der Boden des unteren Gasraums 9 ist konisch ausgebildet und weist eine Schleuse 16 zur Ausschleusung des gebildeten Metallpulvers auf. Ferner kann ein konischer Zwischenboden 17 vorgesehen sein, der der Sammlung und Abtrennung des Metallpulvers vom Gas dient. Dabei kann eine thermische Isolierung 18 insbesondere für den oberen Gasraum vorgesehen sein.FIG. 1 shows a metal melting crucible 1 which contains the metal melt 2. The melting crucible can consist, for example, of quartz glass, sintered ceramic or graphite. The melt crucible 1 contains at least one melt outlet nipple 3 on its underside. The melt outlet nipple can, for example, have an opening of 0.3 to 1 mm in diameter. The melting pot is also heated. The crucible can be heated by means of a resistance heater 4, which is embedded, for example, in a ceramic mass 5. The person skilled in the art is able to provide other options for heating the melt, for example high-frequency induction heating, direct electrical heating by means of electrodes which are immersed in the melt, etc. When using a graphite crucible, one electrode can be the crucible, for example. It is also possible to provide flame heating inside or outside the crucible. The crucible 1 is arranged within a container 6, which is divided into an upper gas space 8 and a lower gas space 9 by a partition 7. The gas spaces 8 and 9 are connected by a passage opening 10. The passage opening 10 is formed by a molded part 11 fitted into the partition 7. The upper gas space 8 has a gas supply line 12 with a valve 13 for adjusting the gas pressure in the upper gas space 8. The lower gas space 9 contains a gas discharge line 14 with a feed pump 15 for adjusting and maintaining the gas pressure in the lower gas space 9. The bottom of the lower Gas space 9 is conical and has a lock 16 for discharging the metal powder formed. Furthermore, a conical intermediate floor 17 can be provided, which serves to collect and separate the metal powder from the gas. Thermal insulation 18 can be provided in particular for the upper gas space.

Zur Durchführung des erfindungsgemäßen Verfahrens wird der Schmelzetiegel 1 mit dem zu zerfasernden Metall gefüllt. Danach wird über das Ventil 13 das gasförmige Medium eingelassen. Wenn das Metall im Tiegel zu schmelzen beginnt, wird mittels der Pumpe 15 der untere Gasraum 9 auf einen Druck von z.B. 10 bis 100 Torr evakuiert und gleichzeitig über das Ventil 13 soviel Gas nachgeliefert, daß im oberen Gasraum ein Druck.von z.B. 1 bar aufrechterhalten bleibt. Das zugeführte Gas kann z.B. die Temperatur der Schmelze 2 aufweisen. Wenn das Metall im Tiegel 1 geschmolzen ist, tritt am Nippel 3 ein Schmelzestrom aus, der unter der Wirkung des sich in der Gasdurchtrittsöffnung ausbildenden Druckgradienten aufgeteilt und unter der Wirkung des mit Überschallgeschwindigkeit strömenden Gases zunächst in Fasern 19 ausgezogen wird, wobei die Fasern 19 dann in Tröpfchen 20 zerfallen. Die Abkühlung erfolgt aufgrund der adiabatischen Abkühlung des gasförmigen Mediums beim Hindurchtreten durch die öffnung 10. Wenn als gasförmiges Medium ein Inertgas eingesetzt wird, kann dieses über die Pumpe 15 und eine nicht gezeichnete Verbindungsleitung über die Gaszufuhrleitung 12 in den oberen Gasraum 8 zurückgeführt werden. Das sich bildende Metallpulver wird durch die Schleuse 16 unter Aufrechterhaltung des Gasdrucks im Gasraum 9 periodisch ausgeschleust. Die Zuführung von Metall in den Tiegel 1 kann z.B. durch Nachschieben eines Metallbarrens 21 durch die obere Tiegelöffnung 22 erfolgen, wobei der Barren in Kontakt mit der Schmelze 2 abschmilzt. Das Formteil 11, daß die Gasdurchtrittsöffnung 10 bildet, wird vorzugsweise aus wärmebeständigem Material, z.B. Keramik oder Quarzglas ausgebildet.To carry out the method according to the invention, the crucible 1 is filled with the metal to be fiberized. Then the gaseous medium is let in via the valve 13. When the metal in the crucible begins to melt, the lower gas space 9 is evacuated to a pressure of, for example, 10 to 100 torr by means of the pump 15 and at the same time so much gas is supplied via the valve 13 that a pressure of, for example, 1 bar is maintained in the upper gas space remains. The gas supplied can have the temperature of the melt 2, for example. When the metal in the crucible 1 has melted, a melt flow emerges at the nipple 3, which is divided under the effect of the pressure gradient which forms in the gas passage opening and is first drawn out into fibers 19 under the effect of the gas flowing at supersonic speed, the fibers 19 then disintegrate into droplets 20. The cooling takes place due to the adiabatic cooling of the gaseous medium as it passes through the opening 10. If an inert gas is used as the gaseous medium, this can be fed via the pump 15 and a connecting line (not shown) via the gas Guide line 12 are returned to the upper gas space 8. The metal powder that forms is periodically discharged through the lock 16 while maintaining the gas pressure in the gas space 9. Metal can be fed into the crucible 1, for example by pushing a metal ingot 21 through the upper crucible opening 22, the ingot melting in contact with the melt 2. The molded part 11, which forms the gas passage opening 10, is preferably formed from heat-resistant material, for example ceramic or quartz glass.

Figuren 2 bis 4 zeigen alternative Ausführungsformen für die Ausbildung der Gasdurchlaßöffnung 10. Dabei bezeichnen die Ziffern jeweils gleiche Elemente wie in Figur 1.Figures 2 to 4 show alternative embodiments for the formation of the gas passage opening 10. The numerals designate the same elements as in Figure 1.

Beispielexample

In einer Vorrichtung gemäß Figur 1 wird eine Metallschmelze aus Lötzinn mit einem Schmelzpunkt von 300°C erzeugt. Als gasförmiges Medium wird Luft eingesetzt. Im oberen Gasraum 8 herrscht ein Druck von 1 bar. Im unteren Gasraum 9 wird ein Druck von 0,01 bar aufrechterhalten. Der in der konzentrischen Gasdurchlaßöffnung 10 von 3 mm Durchmesser angeordnete Nippel 3 des Quarztiegels 1 weist einen offenen Querschnitt von 0,5 mm Durchmesser und eine Wandstärke des Nippels von 0,2 mm auf. Das über die Leitung 12 zugeführte Heliumgas hat die Temperatur der Metallschmelze von 300°C. Es werden 19 g Metallpulver pro Sekunde aus einer Schmelzeausflußöffnung 3 erhalten. Das Pulver besteht aus Kugeln mit Durchmessern zwischen 5 µ und 50 µ. Der Schwerpunkt der Durchmesserverteilung liegt bei 10 µ. Nur sehr wenige Pulverteilchen weisen Durchmesser von oberhalb 30 µ auf. Vereinzelt werden Abweichungen von der Kugelform erhalten. Diese Pulverteilchen weisen ellipsenförmige Gestalt auf. Die einzelnen Pulverteilchen haben eine glatte Oberfläche, auf der als unterschiedlich reflektierende Bereiche einzelne Kristallite erkennbar sind, ohne daß die Kugelform gestört ist.In a device according to FIG. 1, a molten metal is produced from solder with a melting point of 300 ° C. Air is used as the gaseous medium. A pressure of 1 bar prevails in the upper gas space 8. A pressure of 0.01 bar is maintained in the lower gas space 9. The nipple 3 of the quartz crucible 1 arranged in the concentric gas passage opening 10 of 3 mm diameter has an open cross section of 0.5 mm diameter and a wall thickness of the nipple of 0.2 mm. The helium gas supplied via line 12 has the temperature of the molten metal of 300 ° C. 19 g of metal powder per second are obtained from a melt outflow opening 3. The powder consists of spheres with diameters between 5 µ and 50 µ. The focus of the diameter distribution is 10 µ. Very few powder particles have diameters above 30 µ. Sporadic deviations from the spherical shape are obtained. These powder particles have an elliptical shape. The individual powder particles have a smooth surface on which individual crystallites can be recognized as differently reflecting areas without the spherical shape being disturbed.

Claims (12)

1. Porenfreie Metallpulver gekennzeichnet durch Pulverteilchen mit einer einfach gekrümmten, glatten Oberfläche und einem mittleren Durchmesser von 5 bis 35 µ.1. Pore-free metal powder characterized by powder particles with a simply curved, smooth surface and an average diameter of 5 to 35 µ. 2. Metallpulver nach Anspruch 1, gekennzeichnet durch eine Pulverteilchendurchmesserverteilung mit einer Standardabweichung von maximal 2,5.2. Metal powder according to claim 1, characterized by a powder particle diameter distribution with a standard deviation of at most 2.5. 3. Metallpulver nach Anspruch 1 oder Anspruch 2, gekennzeichnet dadurch, daß mindestens 90 % der Pulverteilchen eine Abweichung von weniger als 10 % von der Kugelform aufweisen.3. Metal powder according to claim 1 or claim 2, characterized in that at least 90% of the powder particles have a deviation of less than 10% from the spherical shape. 4. Metallpulver nach einem der Ansprüche 1 bis 3, gekennzeichnet durch einen mittleren Pulverteilchendurchmesser von 5 bis 20 µ, vorzugsweise 8 bis 15 µ.4. Metal powder according to one of claims 1 to 3, characterized by an average powder particle diameter of 5 to 20 µ, preferably 8 to 15 µ. 5. Verfahren zur Herstellung von Metallpulvern, dadurch gekennzeichnet, daß man .einen Metallschmelzestrom und Gas in eine öffnung eines Behälters einströmen läßt, wobei das Verhältnis von Gasdruck in der Nähe der Einströmöffnung oberhalb des Behälters und Gasdruck innerhalb des Behälters größer als 5 vorgegeben wird und die öffnung so gewählt ist, daß das Verhältnis der in den Behälter eintretenden Massenströme von Gas und Metallschmelze größer als 8 ist.5. A process for the production of metal powders, characterized in that. A molten metal stream and gas can flow into an opening of a container, the ratio of gas pressure in the vicinity of the inflow opening above the container and gas pressure inside the container being predetermined to be greater than 5 and the opening is chosen so that the ratio of the mass flows of gas and gas entering the container Molten metal is greater than 8. 6. Verfahren nach Anspruch 5, dadurch gekennzeichnet, daß das in dem Behälter einströmende Gas vor dem Einströmen eine-Temperatur im Bereich zwischen dem 0,7 und 1,5-fachen der Erstarrungstemperatur der Schmelze in °K aufweist.6. The method according to claim 5, characterized in that the gas flowing into the container has a temperature in the range between 0.7 and 1.5 times the solidification temperature of the melt in ° K before the inflow. 7. Verfahren nach Anspruch 5 oder 6, dadurch gekennzeichnet, daß die Metallschmelze an einer Stelle in der Behälteröffnung mit dem Gas in Berührung gebracht wird, an der der Gasdruck auf weniger als 60 % des Drucks vor der öffnung abgefallen ist.7. The method according to claim 5 or 6, characterized in that the molten metal is brought into contact with the gas at a point in the container opening at which the gas pressure has dropped to less than 60% of the pressure before the opening. 8. Verfahren nach einem der Ansprüche 5 bis 7, dadurch gekennzeichnet, daß die Metallschmelze an einer Stelle in der Behälteröffnung mit dem Gas in Berührung gebracht wird, an der der Gasdruck noch mindestens ein Fünftel, vorzugsweise mindestens ein Drittel des Drucks vor der Behälteröffnung beträgt.8. The method according to any one of claims 5 to 7, characterized in that the molten metal is brought into contact with the gas at a point in the container opening at which the gas pressure is still at least one fifth, preferably at least one third of the pressure before the container opening . 9. Vorrichtung zur Herstellung von Metallpulvern, gekennzeichnet durch zwei durch mindestens eine Gasdurchtrittsöffnung verbundene Gasräume, Mitteln zur Erzeugung einer Druckdifferenz zwischen den beiden Gasräumen, einem in dem Gasraum mit höherem Druck angeordneten Schmelzetiegel mit mindestens einer Schmelzeaustrittsöffnung, wobei die Schmelzeaustrittsöffnung symmetrisch zur Gasdurchlaßöffnung angeordnet ist.9. Device for the production of metal powders, characterized by two gas spaces connected by at least one gas passage opening, means for generating a pressure difference between the two gas spaces, a melt crucible arranged in the gas space with a higher pressure and at least one melt outlet opening, wherein the melt outlet opening is arranged symmetrically to the gas passage opening. 10. Vorrichtung nach Anspruch 9, dadurch gekennzeichnet, daß sich die Gasdurchtrittsöffnung von der Stelle des entsten Querschnitts an in Strömungsrichtung mit einem Winkel von mindestens 90°, vorzugsweise 120° erweitert.10. The device according to claim 9, characterized in that the gas passage opening widens from the point of the first cross section in the flow direction at an angle of at least 90 °, preferably 120 °. 11. Vorrichtung nach Anspruch 10 oder 11, dadurch gekennzeichnet, daß die Schmelzeaustrittsöffnung etwa in der Ebene der engsten Stelle der Gasdurchlaßöffnung mündet.11. The device according to claim 10 or 11, characterized in that the melt outlet opening opens approximately in the plane of the narrowest point of the gas passage opening. 12. Verwendung der Metallpulver nach einem der Ansprüche 1 bis 4 zur Herstellung von hochtemperaturbeständigen Sinterlegierungen und Sinterformkörpern.12. Use of the metal powder according to one of claims 1 to 4 for the production of high-temperature-resistant sintered alloys and sintered moldings.
EP84103487A 1983-03-29 1984-03-29 Metal powder and process for producing the same Expired EP0120506B1 (en)

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Also Published As

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EP0120506A3 (en) 1984-11-21
JPS59229402A (en) 1984-12-22
JPH0253482B2 (en) 1990-11-16
DE3311343A1 (en) 1984-10-04
CA1224947A (en) 1987-08-04
ATE34109T1 (en) 1988-05-15
US4534917A (en) 1985-08-13
EP0120506B1 (en) 1988-05-11
DE3311343C2 (en) 1987-04-23

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