EP0120506B1 - Metal powder and process for producing the same - Google Patents
Metal powder and process for producing the same Download PDFInfo
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- EP0120506B1 EP0120506B1 EP84103487A EP84103487A EP0120506B1 EP 0120506 B1 EP0120506 B1 EP 0120506B1 EP 84103487 A EP84103487 A EP 84103487A EP 84103487 A EP84103487 A EP 84103487A EP 0120506 B1 EP0120506 B1 EP 0120506B1
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- gas
- container
- opening
- pressure
- molten metal
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- 229910052751 metal Inorganic materials 0.000 title claims abstract description 44
- 239000002184 metal Substances 0.000 title claims abstract description 44
- 239000000843 powder Substances 0.000 title claims abstract description 37
- 238000000034 method Methods 0.000 title claims description 14
- 239000000155 melt Substances 0.000 claims abstract description 29
- 239000002245 particle Substances 0.000 claims abstract description 17
- 238000004519 manufacturing process Methods 0.000 claims description 7
- 229910001111 Fine metal Inorganic materials 0.000 claims description 3
- 238000007711 solidification Methods 0.000 abstract description 6
- 230000008023 solidification Effects 0.000 abstract description 6
- 239000007789 gas Substances 0.000 description 75
- 239000000835 fiber Substances 0.000 description 12
- 210000002445 nipple Anatomy 0.000 description 8
- 238000002844 melting Methods 0.000 description 7
- 230000008018 melting Effects 0.000 description 7
- 238000010438 heat treatment Methods 0.000 description 4
- 150000002739 metals Chemical class 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 239000000919 ceramic Substances 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 239000003380 propellant Substances 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
- 239000001307 helium Substances 0.000 description 2
- 229910052734 helium Inorganic materials 0.000 description 2
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 238000005192 partition Methods 0.000 description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 239000000567 combustion gas Substances 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 239000000284 extract Substances 0.000 description 1
- 239000003779 heat-resistant material Substances 0.000 description 1
- 150000004678 hydrides Chemical class 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 229910000679 solder Inorganic materials 0.000 description 1
Images
Classifications
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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 invention relates to a method and an apparatus for producing fine metal powders.
- a method for producing metal powders in which a molten metal stream and gas are allowed to flow into an opening of a container.
- the melting cone is broken up turbulently by a propellant gas jet at the angle relative to the melting cone axis.
- the resulting relatively coarse powder parts can then only be comminuted by exploding the melt, which has been overheated by 250 ° C., by the vapor pressure of the strongly overheated powder parts. This results in relatively non-uniform particles of various sizes.
- the invention is based on the object of specifying a method and an associated device which make it possible to produce metal powder with powder particles of smaller diameter and a relatively narrow particle size distribution.
- This object is achieved by the features of claim 1, as far as the method is concerned, and the features of claim 5, as far as the device is concerned.
- Advantageous further developments result from the associated subclaims.
- the metal powders produced by the invention have average powder particle diameters between 5 and 35 ⁇ m, preferably between 5 and 201 ⁇ m and preferably between 8 and 15 ⁇ m.
- the powder particles also have diameter distributions with a standard deviation of at most 2.5.
- the metal powders 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: the powder particles also have simply curved surfaces, which is of essential importance for the sintered metallurgy.
- molten metal stream and gas are allowed to flow into an opening of a container, the ratio of gas pressure in the vicinity of the inflow opening outside the container and gas pressure inside the container being predetermined to be greater than 5 and the opening of the container is also selected such that the The ratio of the mass flows of gas and molten metal entering the container is greater than 8.
- the melt stream is first drawn out into fibers under the action of the gas flowing at supersonic speed. These fibers then disintegrate into droplets that form the powder particles after solidification.
- 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 molten metal preferably only comes into contact with the gas flowing into the opening at a point in the container opening at which the gas pressure has dropped to less than 60% of the pressure before the 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.
- All gases that do not react with the molten metal can be used as gases. 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 e.g. 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 filaments tend to disintegrate into droplets.
- the temperature of the gaseous medium must therefore be chosen to be sufficiently high that the melt threads 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. For the production of very fine powders it is therefore essential that sufficiently thin melt fibers are formed into droplets before they break down.
- the melt therefore preferably emerges from the crucible at the point, ie it 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 still a sufficient density for drawing out the burst melt flow .
- the density should preferably still be at least 0.4 bar.
- the pressure before opening 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, the crucible having at least one melt outlet opening which is arranged symmetrically coaxially or concentrically to the gas passage opening.
- the gas passage opening is designed in such a way that during operation of the device the gas at a certain speed first extracts the melt flow into fibers and then the fibers disintegrate into droplets.
- 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 also be designed as circularly symmetrical passage openings, with 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 crucible can e.g. consist of quartz glass, sintered ceramic or graphite.
- the crucible 1 contains at least one melt outlet nipple 3 on its underside.
- the melt outlet nipple can e.g. 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, e.g. is embedded in a ceramic mass 5, take place.
- the person skilled in the art is able to provide other options for heating the melt, e.g. high-frequency induction heating, direct electrical heating by means of electrodes which are immersed in the melt, etc.
- a graphite crucible e.g.
- the crucible 1 is arranged inside 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 added to the shredded metal filled. Then the gaseous medium is let in via the valve 13.
- the lower gas space 9 is evacuated to a pressure of, for example, 1.3x10 3 to 1.3x10 4 Pa (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.
- 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.
- FIG. 2 to 4 show alternative embodiments for the formation of the gas passage opening 10.
- the numerals designate the same elements as in 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 ⁇ m and 50 ⁇ m.
- the focus of the diameter distribution is 10 ⁇ m. Very few powder particles have diameters above 30 1 1m. 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
Description
Die Erfindung betrifft ein Verfahren sowie eine Vorrichtung zur Herstellung von feinen Metallpulvern.The invention relates to a method and an apparatus for producing fine metal powders.
Aus GB-A 952457 ist ein Verfahren zur Herstellung von Metallpulvern bekannt, bei welchem man einen Metallschmelzstrom und Gas in eine Öffnung eines Behälters einströmen lässt. Nach den Fig. 1 und 2 dieser Druckschrift wird der Schmelzkegel durch einen Treibgasstrahl bei dem Winkel gegenüber der Schmelzkegelachse turbulent zerschlagen. Die entstandenen relativ groben Pulverteile können dann nur noch durch Explodieren der um 250°C überhitzten Schmelze zerkleinert werden und zwar durch den Dampfdruck der stark überhitzten Puverteile. Daraus resultieren relativ ungleichförmige Teilchen unterschiedlichster Grösse.From GB-A 952457 a method for producing metal powders is known, in which a molten metal stream and gas are allowed to flow into an opening of a container. According to FIGS. 1 and 2 of this document, the melting cone is broken up turbulently by a propellant gas jet at the angle relative to the melting cone axis. The resulting relatively coarse powder parts can then only be comminuted by exploding the melt, which has been overheated by 250 ° C., by the vapor pressure of the strongly overheated powder parts. This results in relatively non-uniform particles of various sizes.
Ferner ist aus der GB-PS 1 123825 ein Pulverherstellungsverfahren bekannt, bei welchem das Treibgas etwa senkrecht zum Schmelzestrahl geführt wird. Ausdrücklich wird von einem Auftreffen des Treibgases mit stumpfem Winkel auf den Schmelzestrahl gesprochen. Ungleichmässige Teilchen sind somit die unvermeidliche Folge.Furthermore, from GB-PS 1 123825 a powder manufacturing process is known in which the propellant gas is guided approximately perpendicular to the melt jet. We expressly speak of an impingement of the propellant gas at an obtuse angle on the melt jet. Uneven particles are the inevitable consequence.
Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren sowie eine zugehörige Vorrichtung anzugeben, die es ermöglichen, Metallpulver mit Pulverteilchen kleineren Durchmessers und einer relativ engen Teilchengrössenverteilung herzustellen. Diese Aufgabe wird durch die Merkmale des Anspruches 1, was das Verfahren anbelangt, sowie die Merkmale des Anspruches 5, was die Vorrichtung anbelangt, gelöst. Vorteilhafte Weiterbildungen ergeben sich aus den jeweils zugehörigen Unteransprüchen.The invention is based on the object of specifying a method and an associated device which make it possible to produce metal powder with powder particles of smaller diameter and a relatively narrow particle size distribution. This object is achieved by the features of claim 1, as far as the method is concerned, and the features of
Die durch die Erfindung hergestellten Metallpulver weisen mittlere Pulverteilchendurchmesser zwischen 5 und 35 µm, bevorzugt zwischen 5 und 201im und vorzugsweise zwischen 8 und 15 um auf. Die Pulverteilchen weisen ferner Durchmesserverteilungen mit einer Standardabweichung von maximal 2,5 auf. Die 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: Die Pulverteilchen weisen weiter einfach gekrümmte Oberflächen auf, was für die Sintermetallurgie von wesentlicher Bedeutung ist.The metal powders produced by the invention have average powder particle diameters between 5 and 35 μm, preferably between 5 and 201 μm and preferably between 8 and 15 μm. The powder particles also have diameter distributions with a standard deviation of at most 2.5. The metal powders 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: the powder particles also have simply curved surfaces, which is of essential importance for the sintered metallurgy.
Bei dem Verfahren lässt man Metallschmelzestrom und Gas in eine Öffnung eines Behälters einströmen, 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 dem Behälter eintretenden Massenströme von Gas und Metallschmelze grösser als 8 ist. Der Schmelzestrom wird unter der Wirkung des mit Überschallgeschwindigkeit strömenden Gases zunächst in Fasern ausgezogen. Diese Fasern zerfallen dann in Tröpfchen, die nach Erstarrung die Pulverteilchen bilden. Die Temperatur des in dem Behälter durch die Öffnung einströmenden Gases soll vor dem Einströmen im Bereich zwischen dem 0,7 und 1,5fachen der Erstarrungstemperatur der Schmelze in °K betragen.In the process, molten metal stream and gas are allowed to flow into an opening of a container, the ratio of gas pressure in the vicinity of the inflow opening outside the container and gas pressure inside the container being predetermined to be greater than 5 and the opening of the container is also selected such that the The ratio of the mass flows of gas and molten metal entering the container is greater than 8. The melt stream is first drawn out into fibers under the action of the gas flowing at supersonic speed. These fibers then disintegrate into droplets that form the powder particles after solidification. 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.
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.The molten metal preferably only comes into contact with the gas flowing into the opening at a point in the container opening at which the gas pressure has dropped to less than 60% of the pressure before the 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.
Vorzugsweise soll das Gas an der ersten Berührungsstelle mit der Metallschmelze Überschallgeschwindigkeit aufweisen.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 do not react with the molten metal can be used as gases. 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 e.g. 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 Schmelzfäden 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 filaments tend to disintegrate into droplets. The temperature of the gaseous medium must therefore be chosen to be sufficiently high that the melt threads 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. For the production of very fine powders it is therefore essential that sufficiently thin melt fibers are formed into droplets before they break down.
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.The melt therefore preferably emerges from the crucible at the point, ie it 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 still a sufficient density for drawing 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 Ap/A1, der das Zerplatzen des Schmelzestromes bewirkt, als auch die Dichte der das Ausziehen der zerplatzten Schmelze bewirkenden Überschallströmung zu erhöhen.The pressure before opening 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 Ap / A1, which causes the melt flow to burst, and the density of the supersonic flow, which causes the burst 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 as a nozzle in analogy to the nozzle blowing process for the production of fibers, 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 koaxial bzw. konzentrisch zur Gasdurchlassöffnung angeordnet ist, aufweist. Die Gasdurchlassöffnung ist so ausgestaltet, dass während des Betriebes der Vorrichtung das Gas bei einer bestimmten Geschwindigkeit den Schmelzestrom zunächst in Fasern auszieht und dann die Fasern in Tröpfchen zerfallen. Die Gasdurchtrittsöffnung kann als schlitzförmige Öffnung ausgebildet sein, wobei der Schmelzetiegel eine Vielzahl von in der Mittelebene der schlitzförmigen Gasdurchtrittsöffnung angeordnete Schmelzeaustrittsöffnungen aufweist. Die Gasdurchlassöffnungen 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, the crucible having at least one melt outlet opening which is arranged symmetrically coaxially or concentrically to the gas passage opening. The gas passage opening is designed in such a way that during operation of the device the gas at a certain speed first extracts the melt flow into fibers and then the fibers disintegrate into droplets. 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. However, the gas passage openings can also be designed as circularly symmetrical passage openings, with 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 Gasdruchtrittsöffnung 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. zeigt beispielhaft eine Vorrichtung zur Durchführung des erfindungsgemässen Verfahrens.
- Fig. bis 4 zeigen erfindungsgemässe Gestaltungsmöglichkeiten für die Gasdurchtrittsöffnung.
- FIG. 1 shows an example of a device for carrying out the method according to the invention.
- 4 to 4 show design options according to the invention for the gas passage opening.
Fig. 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 seinerunterseite 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
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. 1,3x103 bis 1,3x104 Pa (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 added to the shredded metal filled. Then the gaseous medium is let in via the
Fig. 2 bis 4 zeigen alternative Ausführungsformen für die Ausbildung der Gasdurchlassöffnung 10. Dabei bezeichnen die Ziffern jeweils gleiche Elemente wie in Fig. 1.2 to 4 show alternative embodiments for the formation of the
In einer Vorrichtung gemäss Fig. 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 jim und 50 µm. Der Schwerpunkt der Durchmesserverteilung liegt bei 10 um. Nur sehr wenige Pulverteilchen weisen Durchmesser von oberhalb 30 11m 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
Claims (7)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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AT84103487T ATE34109T1 (en) | 1983-03-29 | 1984-03-29 | METAL POWDER AND METHOD OF PRODUCTION. |
Applications Claiming Priority (2)
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DE3311343A DE3311343C2 (en) | 1983-03-29 | 1983-03-29 | Process for producing fine metal powders and apparatus for carrying out the process |
DE3311343 | 1983-03-29 |
Publications (3)
Publication Number | Publication Date |
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EP0120506A2 EP0120506A2 (en) | 1984-10-03 |
EP0120506A3 EP0120506A3 (en) | 1984-11-21 |
EP0120506B1 true EP0120506B1 (en) | 1988-05-11 |
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EP84103487A Expired EP0120506B1 (en) | 1983-03-29 | 1984-03-29 | Metal powder and process for producing the same |
Country Status (6)
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US (1) | US4534917A (en) |
EP (1) | EP0120506B1 (en) |
JP (1) | JPS59229402A (en) |
AT (1) | ATE34109T1 (en) |
CA (1) | CA1224947A (en) |
DE (1) | DE3311343C2 (en) |
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FR2605538B1 (en) * | 1986-10-27 | 1989-12-22 | Serole Bernard | AERODYNAMICALLY STABILIZED LIQUID FLOW GAS ATOMIZATION NOZZLE |
JPS63262405A (en) * | 1987-04-20 | 1988-10-28 | Fukuda Metal Foil & Powder Co Ltd | Production of metal powder |
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DE3913649A1 (en) * | 1989-04-26 | 1991-01-17 | Krupp Pulvermetall Gmbh | Atomising fine grain powder - by using inert gas which is preheated prior to blowing onto free falling melt stream |
US5238482A (en) * | 1991-05-22 | 1993-08-24 | Crucible Materials Corporation | Prealloyed high-vanadium, cold work tool steel particles and methods for producing the same |
JPH05117724A (en) * | 1992-04-16 | 1993-05-14 | Fukuda Metal Foil & Powder Co Ltd | Production of metal powder |
DE19607114A1 (en) * | 1995-01-28 | 1996-12-05 | Lueder Dr Ing Gerking | Filament melt spinning |
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PT1239983E (en) * | 1999-10-15 | 2004-02-27 | Applikations U Tec F Ene Umw U | PROCESS FOR THE PRODUCTION OF A PO |
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AT409136B (en) * | 2000-05-19 | 2002-05-27 | Tribovent Verfahrensentwicklg | DEVICE FOR SPRAYING AND CRUSHING LIQUID MELT |
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GB1604019A (en) * | 1978-05-31 | 1981-12-02 | Wiggin & Co Ltd Henry | Atomisation into a chamber held at reduced pressure |
US4469313A (en) * | 1981-06-19 | 1984-09-04 | Sumitomo Metal Industries | Apparatus for production of metal powder |
US4402885A (en) * | 1982-04-30 | 1983-09-06 | Owens-Corning Fiberglas Corporation | Process for producing atomized powdered metal or alloy |
-
1983
- 1983-03-29 DE DE3311343A patent/DE3311343C2/en not_active Expired
-
1984
- 1984-03-27 JP JP59057514A patent/JPS59229402A/en active Granted
- 1984-03-28 CA CA000450788A patent/CA1224947A/en not_active Expired
- 1984-03-29 AT AT84103487T patent/ATE34109T1/en not_active IP Right Cessation
- 1984-03-29 US US06/594,829 patent/US4534917A/en not_active Expired - Lifetime
- 1984-03-29 EP EP84103487A patent/EP0120506B1/en not_active Expired
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DE3311343C2 (en) | 1987-04-23 |
ATE34109T1 (en) | 1988-05-15 |
EP0120506A3 (en) | 1984-11-21 |
JPS59229402A (en) | 1984-12-22 |
CA1224947A (en) | 1987-08-04 |
EP0120506A2 (en) | 1984-10-03 |
JPH0253482B2 (en) | 1990-11-16 |
US4534917A (en) | 1985-08-13 |
DE3311343A1 (en) | 1984-10-04 |
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