EP0457674B1 - Process and apparatus for preparing powder alloys by rapid solidification - Google Patents

Process and apparatus for preparing powder alloys by rapid solidification Download PDF

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Publication number
EP0457674B1
EP0457674B1 EP19910401246 EP91401246A EP0457674B1 EP 0457674 B1 EP0457674 B1 EP 0457674B1 EP 19910401246 EP19910401246 EP 19910401246 EP 91401246 A EP91401246 A EP 91401246A EP 0457674 B1 EP0457674 B1 EP 0457674B1
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Prior art keywords
nozzle
dish
cup
crucible
opening
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German (de)
French (fr)
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EP0457674A1 (en
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Philippe Arcade
Georges Champier
Gérard Michot
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SOCIETE NOUVELLE DE METALLISATION INDUSTRIES SNMI
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NOUVELLE DE METALLISATION INDUSTRIES SNMI Ste
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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
    • B22F9/10—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 using centrifugal force

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  • the present invention relates to a device and a method for the preparation of powdered alloys, by rapid solidification.
  • the rapid solidification makes it possible to develop alloys whose chemical compositions differ widely from those imposed by the phase diagrams at equilibrium.
  • Heat treatment of the supersaturated solid solution obtained makes it possible, by controlling the precipitation of the second phase, to optimize the mechanical properties of the alloys.
  • the resulting microstructures are very fine, which limits the importance of the chemical segregations inherent in any solidification and avoids the formation of large precipitates capable of reducing the ductility of the material by blocking the plastic deformation.
  • the cooling can be fast enough to prevent crystallization and lead to the formation of a metallic glass.
  • Spraying with a gas jet consists in dividing a jet of molten metal by a jet of subsonic or ultrasonic gas.
  • the cooling rate is of the order of 102 to 104 ° K.s ⁇ 1 with an average particle size of 40 to 70 ⁇ m.
  • the cooling rate is higher by 104 to 105 ° K.s ⁇ 1 and the average particle size is smaller, of the order of 20 ⁇ m.
  • the alloy In the method of spraying by rotating electrode, the alloy is in the form of a cylindrical bar rotating around its axis. It is melted at one of its ends by an arc or a beam of electrons; the molten alloy is projected in the form of droplets under the effect of centrifugal force.
  • the cooling rate is estimated at 102 ° K.s ⁇ 1 with an average particle size of the order of 200 ⁇ m.
  • centrifugal spraying a jet of molten alloy falls in the center of a cup rotating at very high speed. Under the effect of centrifugal force, the liquid expelled towards the periphery is subdivided into fine particles.
  • the cooling rate is estimated at 105 ° K.s ⁇ 1 and the average particle size is around 75 ⁇ m.
  • the molten alloy is supersaturated with pressurized gas. It is then exposed to the vacuum; the gas then escapes from the liquid, producing fine particles.
  • the cooling rate is estimated at 102 ° K.s ⁇ 1; the average particle size varies from 40 to 70 ⁇ m.
  • the surface of the molten metal is subjected to an intense electric field. There appear small protrusions with tearing of liquid in the form of very fine charged droplets which are solidified and collected.
  • the cooling rate is estimated at 106-107 ° K.s ⁇ 1 with an average particle size of the order of a micron.
  • These devices include a pre-crucible into which the molten metal is poured.
  • the molten metal is then poured back into the main crucible from where it can be projected onto a rotating cup via a nozzle.
  • the possible application of an overpressure above the molten metal, allowing the rupture of the oxide layer, facilitates the flow of the metal through the nozzle.
  • the overpressure-nozzle diameter pair best suited to casting.
  • the flow is more or less important. We can therefore only measure an average flow, ratio of the mass ejected to the ejection time.
  • the flow of molten metal can be disturbed either by a hydrodynamic instability which offsets the jet, or by a rebound on the cup. In both cases, the liquid film covering the cup breaks, disturbing the thermal balance and the size distribution of the ejected droplets.
  • the droplets must leave the cup at the temperature T L of the liquidus and reach the walls of the enclosure at a temperature T ⁇ T s , temperature of the solidus, cooling intervening in a period of the order of 10 ms.
  • the temperature difference can be reduced if some supercooling occurs.
  • the temperature T c at which the drop leaves the cup a temperature which in fact fixes the microstructure of the powder, should be kept constant during spraying. This condition is very restrictive because if the initial temperature T co of the cup is imposed, it is not possible to avoid the cooling due to the starting of the turbine nor the subsequent heating at the start of the casting.
  • the present invention relates to a device for the preparation of metal powders by centrifugal spraying making it possible to eliminate the aforementioned drawbacks.
  • the invention also relates to a process for the preparation of metal powders by centrifugal spraying.
  • metal is meant pure metals and metal alloys in the present text.
  • the device for the production of metallic powders by centrifugal spraying comprising a crucible provided with a nozzle at its lower part, a cup associated with means capable of putting said cup in rotation and means for heating said crucible and said cup, the aforementioned elements being placed in a sealed enclosure provided with the openings necessary for the supply of liquid metal, for the passage of various measurement or control means, and for the extraction of the powder obtained, is characterized in that it further comprises means making it possible to adjust the distance between the lower opening of the nozzle and the upper face of the cup, and in that the external diameter ⁇ e of the face bottom of the nozzle is such that ⁇ i +2 mm ⁇ ⁇ e ⁇ ⁇ VS , ⁇ VS being the diameter of the cup and ⁇ i the internal diameter of the nozzle.
  • the means for adjusting the distance between the nozzle and the cup are preferably mechanical means.
  • the nozzle has an internal channel having a length l and an internal diameter ⁇ i .
  • the outside diameter of the underside of the nozzle is designated by ⁇ e . l and ⁇ i are chosen so that the crucible can be emptied by gravity in the absence of a cup and that the clogging phenomena which occur on conventional spraying devices are avoided. Indeed, these blocking phenomena cause a discontinuous supply of the cup and, consequently, a rapid drop in its temperature, inducing additional dispersions in the process.
  • ⁇ i is preferably greater than 2 mm.
  • the process for producing metal powders by centrifugal spraying consisting in supplying molten metal to a rotating cup, the molten metal being contained in a crucible provided at its lower part with a nozzle, the upper face of the cup and the lower opening of the nozzle being opposite and substantially parallel, the opening of the nozzle being centered on the cup, is characterized in that the distance between the lower opening of the nozzle and the face is adjusted upper part of the cup as a function of the surface of the nozzle facing the cup, and the liquid metal is extracted from said crucible by the vacuum created by the cup rotating around a vertical axis.
  • the method of the invention can advantageously be implemented using a device of the present invention, in which the distance H between the upper face of the cup and the lower opening of the nozzle is adjusted so that that in static condition, the molten metal contained in the nozzle does not flow.
  • the liquid film is then subjected to a much more intense shearing than that encountered in conventional centrifugal spraying since here the upper part of the film remains fixed while the lower part takes on the speed of drive of the cup.
  • This shearing specific to the process of the present invention, can have significant metallurgical incidences since the destruction of the solid germs as they are formed can lower the temperature of the bath below the temperature.
  • solidification T S the supercooling thus achieved allows very high solidification rates.
  • the diameter of the particles obtained by centrifugal spraying varies as where D E is the material flow, ⁇ C the diameter of the cup and V the speed of rotation of the cup.
  • Exhibitors obtained experimentally [Cf. Champagne B., Angers R., Modern Developments in Powder Metallurgy, 12, Proc. Conf. Washington (1980), 83; Friedman SJ, Gluckert FA, Marshall WR, Chem. Eng. Prog., 48 , (1952), 181; Kozlov VA, Golubkov VG, Sov. Powder Metall. Met. Ceram, 20 , (1981), 159; Wentzel JM, Powder Metall.
  • the molten metal is brought to the cup without significant loss of heat, the overheating of the bath is minimized, bet, which is appreciable in the case of reactive alloys such as Al-Li alloys for example.
  • the internal diameter ⁇ i of the nozzle is not a critical parameter. Only count the surface of the nozzle opposite the cup, that is to say the surface S where the capillary forces are exerted, and the distance H busecoupelle. It is no longer necessary to create and modulate an overpressure in the crucible during ejection, because the cup always carries the same amount of metal, the device is self-regulating. Consequently, the thermal regime of the assembly remains stable during the experiment, an improvement in the spraying efficiency is observed and a slight narrowing of the particle size distribution spectrum.
  • the internal diameter ⁇ i of the nozzle being no longer critical, it is then possible to substantially increase its dimension in order to avoid the plugging phenomenon which occurs in known devices. Indeed, an unpowered cup, even for a very short time, cools down very quickly, which leads to the beginning of cooling of the metal on its surface: the experiment is then disturbed.
  • FIG. 1 represents a spraying installation according to the invention.
  • Figure 2 shows part of the actual spraying device.
  • FIG. 3 represents the device for driving and adjusting the cup.
  • Figure 4 shows a sectional view of the nozzle and the cup.
  • FIG. 5 represents the variation of the extraction rate D E as a function ⁇ e .
  • the actual spraying device is placed in an enclosure comprising an upper part (1), an intermediate part (2) and a lower part (15).
  • the actual spraying device comprises a graphite crucible (6) provided at its lower part with a nozzle (12) and a cup (3) associated with a turbine.
  • the nozzle (12) has an internal channel of length l and diameter ⁇ i .
  • the outside diameter of the underside of the nozzle opposite the cup is ⁇ e .
  • H is the distance between the underside of the nozzle and the top face of the cup.
  • Two rails (5) fixed inside the part (2) of the enclosure serve to support the crucible (6) by means of two discs, one (26) integral with the rails, the other ( 27) adjustable so that the axis of the crucible-nozzle assembly coincides with that of the cup.
  • the graphite crucible (6) and its insulation (7) are placed inside a high frequency induction coil (8) which provides heating.
  • An alumina tube (20) is placed between the crucible (6) and the insulation (7).
  • the crucible (6) is closed at its upper part by a refractory stainless steel disc (9) surmounted by a control device (10) with a graphite pin (11) which allows the hole to be closed. ejection during the heating period. In fact, it is preferable not to let the metal come to wet the cup as long as the turbine is not in rotation because there would then form an oxide layer which would appreciably decrease the apparent diameter of the nozzle.
  • the device is sealed by graphite seals, an opening allowing either to balance the pressures between the crucible and the enclosure, or to apply an overpressure in the crucible to clean it at the end of the experiment.
  • the crucible ends at its lower part with a nitride nozzle (12) boron; the crucible nozzle seal is ensured by a graphite seal (13).
  • thermocouple (14) which makes it possible to measure the temperature of the molten metal, is placed in an alumina tube closed at one end; this tube passes through the crucible cover, sealing is ensured by a high temperature adhesive.
  • the rotation of the cup (3) is ensured by a gas turbine whose maximum speed of 30,000 rpm is reached for a gas pressure of 0.7 MPa.
  • the turbine is extended by a hollow axis (28) of refractory material mounted on rigid bearings and provided with cooling discs to prevent the heating of certain moving parts.
  • the graphite cup (3) which will receive the flow of molten metal; the bottom of the cup is flat while the shape and height of the edge vary according to the experiment to be carried out.
  • the cup (3) is heated by the induction coil (29) placed around the graphite jacket (4).
  • the cup (3) and the graphite jacket (4) are thermally insulated by kaolin wool (19), the assembly is held in an alumina cylinder (18) surmounted by a graphite crown to avoid wool dispersion during operation.
  • the temperature of the cup is controlled by means of a not shown thermocouple introduced on the side and retracted just before the rotation.
  • the impeller and the axis ball bearings (28) are mounted in a cylindrical sleeve (22) ( Figure 3).
  • the gas supplying the turbine At the lower part of the sheath is introduced the gas supplying the turbine.
  • the cylindrical sheath passes through the spray tank via an airlock (23) provided with isolation solenoid valves. Cylindrical seals placed at the entrance and at the exit of the airlock guarantee the sealing and ensure the displacement in height of the sleeve and consequently the variation of the distance H between the cup and the nozzle.
  • a comparator needle (24) allows to precisely control this distance adjusted by the device (21).
  • the upper part (1) of the enclosure has two lateral openings used for lighting the tank and a large central opening (25) provided for possible supply of liquid metal from the outside.
  • the lower part (15) has two lateral openings for the recovery of the powder (16) and for the connection with a pumping unit, a central opening closed by a disc (17) which supports the turbine-cup assembly ( Figure 3 ).
  • FIGS. 1 to 4 An installation as shown in FIGS. 1 to 4 was used to prepare various powders of alloys or pure metal (examples 1 to 8).
  • the useful internal diameter of the enclosure was 1350 mm, the useful internal height of 800 mm.
  • the internal diameter ⁇ i of the nozzle was 2 mm.
  • the external diameter ⁇ e of the nozzle was 8 mm, and variable for example 8.
  • the gas turbine used can reach a speed of 30,000 rpm for a gas pressure of 0.7 MPa.
  • the spraying then takes place.
  • the powder is collected through the opening (16).
  • Example 6 corresponds to the composition of an amorphizable alloy.
  • the diffraction lines of the crystallized phase very weak for small particle sizes (less than 125 ⁇ m), are reinforced for particles between 125 and 200 ⁇ m.
  • the crystallized fraction is evaluated at less than 1% for 50-100 ⁇ m and 100-125 ⁇ m powders and at less than 5% the crystallized fraction for 125-200 ⁇ m powders.
  • the particle size of the powders obtained essentially depends on the size of the cup and its speed of rotation.

Description

La présente invention concerne un dispositif et un procédé pour la préparation d'alliages en poudre, par solidification rapide.The present invention relates to a device and a method for the preparation of powdered alloys, by rapid solidification.

La solidification rapide permet d'élaborer des alliages dont les compositions chimiques s'écartent largement de celles imposées par les diagrammes de phase à l'équilibre. Un traitement thermique de la solution solide sursaturée obtenue permet, en contrôlant la précipitation de la seconde phase, d'optimiser les propriétés mécaniques des alliages. Les microstructures résultantes sont très fines, ce qui limite l'importance des ségrégations chimiques inhérentes à toute solidification et évite la formation de gros précipités susceptibles de diminuer la ductilité du matériau par blocage de la déformation plastique. Pour certaines compositions amorphisables, le refroidissement peut être suffisamment rapide pour empêcher la cristallisation et conduire à la formation d'un verre métallique.The rapid solidification makes it possible to develop alloys whose chemical compositions differ widely from those imposed by the phase diagrams at equilibrium. Heat treatment of the supersaturated solid solution obtained makes it possible, by controlling the precipitation of the second phase, to optimize the mechanical properties of the alloys. The resulting microstructures are very fine, which limits the importance of the chemical segregations inherent in any solidification and avoids the formation of large precipitates capable of reducing the ductility of the material by blocking the plastic deformation. For certain amorphizable compositions, the cooling can be fast enough to prevent crystallization and lead to the formation of a metallic glass.

L'obtention de structures hors équilibre nécessite des taux de refroidissement importants supérieurs à 10³-10⁴°K.s⁻¹. Ceci impose que les interfaces métal liquide - milieu froid soient grandes vis-à-vis du volume de métal impliqué. Deux grandes familles de techniques ont été développées selon que la continuité du fluide métallique est maintenue pendant solidification (méthodes dites "Chill methods") ou que le métal liquide est fragmenté avant solidification (méthodes dites "Spray methods"). En ce qui concerne la première famille, les méthodes les plus usitées sont les méthodes de trempe sur roue : le métal liquide est projeté sur une roue tournante (procédé dit "Melt spinning") ou la roue vient lécher la surface du bain métallique (procédé dit "Melt drag"). Dans les deux cas, un ruban mince est obtenu.Obtaining out of equilibrium structures requires significant cooling rates greater than 10³-10⁴ ° K.s⁻¹. This requires that the interfaces between liquid metal and cold medium be large with respect to the volume of metal involved. Two main families of techniques have been developed depending on whether the continuity of the metallic fluid is maintained during solidification (so-called "Chill methods") or whether the liquid metal is fragmented before solidification (so-called "Spray methods"). As far as the first family is concerned, the most commonly used methods are the quenching methods on a wheel: the liquid metal is sprayed onto a rotating wheel (process known as "Melt spinning") or the wheel comes to lick the surface of the metal bath (process says "Melt drag"). In both cases, a thin ribbon is obtained.

En revanche, si la fabrication de poudres est envisagée, il faut faire appel à des techniques dites "Spray". Différentes méthodes ont été développées pour obtenir des poudres.On the other hand, if the manufacture of powders is envisaged, it is necessary to call upon techniques known as "Spray". Different methods have been developed for obtaining powders.

La pulvérisation par un jet de gaz consiste à diviser un jet de métal fondu par un jet de gaz subsonique ou ultrasonique. Dans le premier cas, la vitesse de refroidissement est de l'ordre de 10² à 10⁴°K.s⁻¹ avec une taille moyenne des particules de 40 à 70 µm. Dans le second cas, la vitesse de refroidissement est plus élevée de 10⁴ à 10⁵°K.s⁻¹ et la taille moyenne des particules est plus faible, de l'ordre de 20 µm.Spraying with a gas jet consists in dividing a jet of molten metal by a jet of subsonic or ultrasonic gas. In the first case, the cooling rate is of the order of 10² to 10⁴ ° K.s⁻¹ with an average particle size of 40 to 70 µm. In the second case, the cooling rate is higher by 10⁴ to 10⁵ ° K.s⁻¹ and the average particle size is smaller, of the order of 20 µm.

Dans la méthode de pulvérisation par électrode tournante, l'alliage se présente sous forme d'un barreau cylindrique tournant autour de son axe. Il est fondu à l'une de ses extrémités par un arc ou un faisceau d'électrons ; l'alliage fondu est projeté sous forme de gouttelettes sous l'effet de la force centrifuge. La vitesse de refroidissement est estimée à 10²°K.s⁻¹ avec une taille moyenne des particules de l'ordre de 200 µm.In the method of spraying by rotating electrode, the alloy is in the form of a cylindrical bar rotating around its axis. It is melted at one of its ends by an arc or a beam of electrons; the molten alloy is projected in the form of droplets under the effect of centrifugal force. The cooling rate is estimated at 10² ° K.s⁻¹ with an average particle size of the order of 200 μm.

Dans la pulvérisation centrifuge, un jet d'alliage fondu tombe au centre d'une coupelle tournant à très grande vitesse. Sous l'effet de la force centrifuge, le liquide chassé vers la périphérie se subdivise en fines particules. La vitesse de refroidissement est estimée à 10⁵°K.s⁻¹ et la taille moyenne des particules est de l'ordre de 75 µm.In centrifugal spraying, a jet of molten alloy falls in the center of a cup rotating at very high speed. Under the effect of centrifugal force, the liquid expelled towards the periphery is subdivided into fine particles. The cooling rate is estimated at 10⁵ ° K.s⁻¹ and the average particle size is around 75 µm.

Dans la méthode de pulvérisation par gaz dissous, l'alliage fondu est sursaturé de gaz sous pression. Il est ensuite exposé au vide; le gaz s'échappe alors du liquide en produisant des particules fines. La vitesse de refroidissement est estimée à 10²°K.s⁻¹ ; la taille moyenne des particules varie de 40 à 70µm.In the dissolved gas spray method, the molten alloy is supersaturated with pressurized gas. It is then exposed to the vacuum; the gas then escapes from the liquid, producing fine particles. The cooling rate is estimated at 10² ° K.s⁻¹; the average particle size varies from 40 to 70 µm.

Dans la méthode de pulvérisation électro-hydrodynamique, la surface du métal fondu est soumise à un champ électrique intense. Il y apparaît de petites protubérances avec arrachement de liquide sous forme de gouttelettes chargées très fines qui sont solidifiées et collectées. La vitesse de refroidissement est estimée à 10⁶-10⁷°K.s⁻¹ avec une taille moyenne des particules de l'ordre du micron.In the electro-hydrodynamic spray method, the surface of the molten metal is subjected to an intense electric field. There appear small protrusions with tearing of liquid in the form of very fine charged droplets which are solidified and collected. The cooling rate is estimated at 10⁶-10⁷ ° K.s⁻¹ with an average particle size of the order of a micron.

Ces différentes méthodes ont été étudiées en comparant cinq caractéristiques de chacune d'elles :

  • limitation due à la composition de l'alliage
  • vitesse de refroidissement
  • possibilité de contrôle du procédé
  • capacités de production
  • caractéristiques du produit obtenu
[J.E.FLINN "Rapid Solidification Technology for Reduced Consumption of Strategic Materials", (1985) NOYES Publication (New Jersey, USA)].These different methods were studied by comparing five characteristics of each of them:
  • limitation due to the composition of the alloy
  • cooling rate
  • possibility of process control
  • production capacities
  • characteristics of the product obtained
[JEFLINN "Rapid Solidification Technology for Reduced Consumption of Strategic Materials", (1985) NOYES Publication (New Jersey, USA)].

La comparaison a fait apparaître que le procédé de pulvérisation centrifuge présentait le maximum d'avantages.The comparison showed that the centrifugal spraying process had the most advantages.

Divers dispositifs ont été mis au point pour élaborer des poudres d'alliage par pulvérisation centrifuge. Comme exemples de tels dispositifs, on peut citer par exemple les dispositifs décrits dans les brevets US 4 025 249, 4 053 264, 4 078 873 et 4 217 082.Various devices have been developed for producing alloy powders by centrifugal spraying. Examples of such devices include, for example, the devices described in US Patents 4,025,249, 4,053,264, 4,078,873 and 4,217,082.

Ces dispositifs comportent un pré-creuset dans lequel le métal fondu est versé. Le métal fondu est ensuite reversé dans le creuset principal d'où il peut être projeté sur une coupelle en rotation par l'intermédiaire d'une buse. L'application éventuelle d'une surpression au-dessus du métal fondu, en permettant la rupture de la couche d'oxyde, facilite l'écoulement du métal à travers la buse. L'expérience montre que, pour chaque type d'alliage, il faut déterminer le couple surpression-diamètre de buse le mieux adapté à la coulée. Selon la quantité de métal restant dans le creuset, le débit est plus ou moins important. On ne peut donc mesurer qu'un débit moyen, rapport de la masse éjectée au temps d'éjection. L'écoulement du métal fondu peut être perturbé soit par une instabilité hydrodynamique qui décentre le jet, soit par un rebondissement sur la coupelle. Dans les deux cas le film liquide qui couvre la coupelle se rompt, perturbant le bilan thermique et la distribution en taille des gouttelettes éjectées.These devices include a pre-crucible into which the molten metal is poured. The molten metal is then poured back into the main crucible from where it can be projected onto a rotating cup via a nozzle. The possible application of an overpressure above the molten metal, allowing the rupture of the oxide layer, facilitates the flow of the metal through the nozzle. Experience shows that, for each type of alloy, it is necessary to determine the overpressure-nozzle diameter pair best suited to casting. Depending on the amount of metal remaining in the crucible, the flow is more or less important. We can therefore only measure an average flow, ratio of the mass ejected to the ejection time. The flow of molten metal can be disturbed either by a hydrodynamic instability which offsets the jet, or by a rebound on the cup. In both cases, the liquid film covering the cup breaks, disturbing the thermal balance and the size distribution of the ejected droplets.

Si on ne considère que le diagramme d'équilibre, les gouttelettes doivent quitter la coupelle à la température TL du liquidus et atteindre les parois de l'enceinte à une température T < Ts, température du solidus, le refroidissement intervenant en un laps de temps de l'ordre de 10 ms. L'écart de température peut être réduit si une certaine surfusion se produit. La température Tc à laquelle la goutte quitte la coupelle, température qui fixe en fait la microstructure de la poudre, devrait être maintenue constante au cours de la pulvérisation. Cette condition est très contraignante car si on impose la température initiale Tco de la coupelle on ne peut éviter le refroidissement dû à la mise en route de la turbine ni le réchauffement consécutif au début de la coulée. Ces échanges thermiques qui dépendent de la vitesse de rotation, de la température et du débit du métal liquide ainsi que des mécanismes d'interaction liquide-coupelle sont évidemment perturbés par les instabilités du jet.If we only consider the equilibrium diagram, the droplets must leave the cup at the temperature T L of the liquidus and reach the walls of the enclosure at a temperature T <T s , temperature of the solidus, cooling intervening in a period of the order of 10 ms. The temperature difference can be reduced if some supercooling occurs. The temperature T c at which the drop leaves the cup, a temperature which in fact fixes the microstructure of the powder, should be kept constant during spraying. This condition is very restrictive because if the initial temperature T co of the cup is imposed, it is not possible to avoid the cooling due to the starting of the turbine nor the subsequent heating at the start of the casting. These heat exchanges which depend on the speed of rotation, the temperature and the flow rate of the liquid metal as well as the liquid-cup interaction mechanisms are obviously disturbed by the instabilities of the jet.

Le contrôle du procédé est délicat ; les instabilités hydrodynamiques, conjuguées aux exigences thermiques, font que le rendement n'est pas optimal.Process control is tricky; hydrodynamic instabilities, combined with thermal requirements, mean that the efficiency is not optimal.

La présente invention a pour objet un dispositif pour l'élaboration de poudres métalliques par pulvérisation centrifuge permettant de supprimer les inconvénients précités.The present invention relates to a device for the preparation of metal powders by centrifugal spraying making it possible to eliminate the aforementioned drawbacks.

L'invention a également pour objet un procédé d'élaboration de poudres métalliques par pulvérisation centrifuge.The invention also relates to a process for the preparation of metal powders by centrifugal spraying.

Par métal, on entend les métaux purs et les alliages métalliques, dans le présent texte.By metal is meant pure metals and metal alloys in the present text.

Selon l'invention, le dispositif pour l'élaboration de poudres métalliques par pulvérisation centrifuge, comportant un creuset muni d'une buse à sa partie inférieure, une coupelle associée à des moyens capables de mettre ladite coupelle en rotation et des moyens pour chauffer ledit creuset et ladite coupelle, les éléments précités étant placés dans une enceinte étanche munis des ouvertures nécessaires pour l'alimentation en métal liquide, pour le passage de différents moyens de mesure ou de contrôle, et pour l'extraction de la poudre obtenue, est caractérisé en ce qu'il comporte en outre des moyens permettant de régler la distance entre l'ouverture inférieure de la buse et la face supérieure de la coupelle, et en ce que le diamètre externe Φe de la face inférieure de la buse est tel que Φ i +2 mm ≦ Φ e ≦ Φ C , Φ C

Figure imgb0001
étant le diamètre de la coupelle et Φi le diamètre interne de la buse.According to the invention, the device for the production of metallic powders by centrifugal spraying, comprising a crucible provided with a nozzle at its lower part, a cup associated with means capable of putting said cup in rotation and means for heating said crucible and said cup, the aforementioned elements being placed in a sealed enclosure provided with the openings necessary for the supply of liquid metal, for the passage of various measurement or control means, and for the extraction of the powder obtained, is characterized in that it further comprises means making it possible to adjust the distance between the lower opening of the nozzle and the upper face of the cup, and in that the external diameter Φ e of the face bottom of the nozzle is such that Φ i +2 mm ≦ Φ e ≦ Φ VS , Φ VS
Figure imgb0001
 being the diameter of the cup and Φ i the internal diameter of the nozzle.

Les moyens permettant de régler la distance entre la buse et la coupelle sont, de préférence, des moyens mécaniques.The means for adjusting the distance between the nozzle and the cup are preferably mechanical means.

La buse comporte un canal intérieur ayant pour longueur l et pour diamètre intérieur Φi. Le diamètre extérieur de la face inférieure de la buse est désigné par Φe. l et Φi sont choisis de telle sorte que le creuset puisse se vider par gravité en l'absence de coupelle et que les phénomènes de bouchage qui se produisent sur les dispositifs classiques de pulvérisation soient évités. En effet, ces phénomènes de bouchage provoquent une alimentation discontinue de la coupelle et, par conséquent, une chute rapide de sa température, induisant des dispersions supplémentaires dans le procédé. Φi est de préférence supérieur à 2 mm.The nozzle has an internal channel having a length l and an internal diameter Φ i . The outside diameter of the underside of the nozzle is designated by Φ e . l and Φ i are chosen so that the crucible can be emptied by gravity in the absence of a cup and that the clogging phenomena which occur on conventional spraying devices are avoided. Indeed, these blocking phenomena cause a discontinuous supply of the cup and, consequently, a rapid drop in its temperature, inducing additional dispersions in the process. Φ i is preferably greater than 2 mm.

Le procédé d'élaboration de poudres métalliques par pulvérisation centrifuge selon l'invention, consistant à alimenter en métal fondu une coupelle en rotation, le métal fondu étant contenu dans un creuset muni à sa partie inférieure d'une buse, la face supérieure de la coupelle et l'ouverture inférieure de la buse étant en regard et sensiblement parallèles, l'ouverture de la buse étant centrée sur la coupelle, est caractérisé en ce que l'on règle la distance entre l'ouverture inférieure de la buse et la face supérieure de la coupelle en fonction de la surface de la buse en regard avec la coupelle, et le métal liquide est extrait du dit creuset par la dépression créée par la coupelle en rotation autour d'un axe vertical.The process for producing metal powders by centrifugal spraying according to the invention, consisting in supplying molten metal to a rotating cup, the molten metal being contained in a crucible provided at its lower part with a nozzle, the upper face of the cup and the lower opening of the nozzle being opposite and substantially parallel, the opening of the nozzle being centered on the cup, is characterized in that the distance between the lower opening of the nozzle and the face is adjusted upper part of the cup as a function of the surface of the nozzle facing the cup, and the liquid metal is extracted from said crucible by the vacuum created by the cup rotating around a vertical axis.

Le procédé de l'invention peut avantageusement être mis en oeuvre à l'aide d'un dispositif de la présente invention, dans lequel la distance H entre la face supérieure de la coupelle et l'ouverture inférieure de la buse est réglée de telle sorte qu'en condition statique, le métal fondu contenu dans la buse ne s'écoule pas.The method of the invention can advantageously be implemented using a device of the present invention, in which the distance H between the upper face of the cup and the lower opening of the nozzle is adjusted so that that in static condition, the molten metal contained in the nozzle does not flow.

Pour des viscosités comprises entre 10⁻³ et 10⁻² Pa.s, caractéristiques des métaux liquides (métaux purs ou alliages eutectiques), cette condition est vérifiée pour une distance H entre la face supérieure de la coupelle et l'ouverture inférieure de la buse comprise entre 0,3 et 0,5 mm.For viscosities between 10⁻³ and 10⁻² Pa.s, characteristics of liquid metals (pure metals or eutectic alloys), this condition is verified for a distance H between the upper face of the cup and the lower opening of the nozzle between 0.3 and 0.5 mm.

La mise en rotation de la coupelle chasse le métal liquide dans le volume défini par la distance H et la surface S = π(Φ e ²-Φ i ²)/4

Figure imgb0002
de la buse en regard avec la coupelle. Le film liquide est alors soumis à un cisaillement beaucoup plus intense que celui rencontré en pulvérisation centrifuge classique puisqu'ici la partie supérieure du film reste fixe alors que la partie inférieure prend la vitesse d'entraînement de la coupelle. L'importance de ce cisaillement, propre au procédé de la présente invention, peut avoir des incidences métallurgiques importantes dans la mesure où la destruction des germes de solide au fur et à mesure de leur formation peut abaisser la température du bain en dessous de la température de solidification TS: la surfusion ainsi atteinte permet des vitesses de solidification très importantes.The rotation of the cup drives the liquid metal into the volume defined by the distance H and the surface S = π (Φ e ²-Φ i ²) / 4
Figure imgb0002
 of the nozzle opposite with the cup. The liquid film is then subjected to a much more intense shearing than that encountered in conventional centrifugal spraying since here the upper part of the film remains fixed while the lower part takes on the speed of drive of the cup. The importance of this shearing, specific to the process of the present invention, can have significant metallurgical incidences since the destruction of the solid germs as they are formed can lower the temperature of the bath below the temperature. solidification T S : the supercooling thus achieved allows very high solidification rates.

Le diamètre des particules obtenues par pulvérisation centrifuge varie comme où DE est le débit de matière, ΦC le diamètre de la coupelle et V la vitesse de rotation de la coupelle. Les exposants obtenus expérimentalement [Cf. Champagne B., Angers R., Modern Developments in Powder Metallurgy, 12, Proc. Conf. Washington (1980), 83 ; Friedman S.J., Gluckert F.A., Marshall W.R., Chem. Eng. Prog., 48, (1952), 181 ; Kozlov V.A., Golubkov V.G., Sov. Powder Metall. Met. Ceram, 20, (1981), 159 ; Wentzel J.M., Powder Metall. Inv., 18 (1986), 16] ont pour valeur 0,12<a²<0,25, 0,3<b²<0,64 et 0,5<c²<1. L'obtention d'une granulométrie fine impose de maîtriser et de limiter le débit. En pulvérisation classique, ceci est réalisé en jouant sur un différentiel de pression entre la surface du bain dans le creuset et la sortie de la buse, ou sur les dimensions intérieures de la buse (Φi ou l). Dans la présente invention, le débit d'extraction est réglé et stabilisé par le diamètre extérieur de la buse Φe, pour une valeur donnée de H.The diameter of the particles obtained by centrifugal spraying varies as where D E is the material flow, Φ C the diameter of the cup and V the speed of rotation of the cup. Exhibitors obtained experimentally [Cf. Champagne B., Angers R., Modern Developments in Powder Metallurgy, 12, Proc. Conf. Washington (1980), 83; Friedman SJ, Gluckert FA, Marshall WR, Chem. Eng. Prog., 48 , (1952), 181; Kozlov VA, Golubkov VG, Sov. Powder Metall. Met. Ceram, 20 , (1981), 159; Wentzel JM, Powder Metall. Inv., 18 (1986), 16] have the value 0.12 <a² <0.25, 0.3 <b² <0.64 and 0.5 <c² <1. Obtaining a fine particle size requires controlling and limiting the flow. In conventional spraying, this is achieved by playing on a pressure differential between the surface of the bath in the crucible and the outlet of the nozzle, or on the internal dimensions of the nozzle (Φ i or l). In the present invention, the extraction rate is adjusted and stabilized by the outside diameter of the nozzle Φ e , for a given value of H.

Le métal fondu est amené sur la coupelle sans perte significative de chaleur, la surchauffe du bain est minimisée, misée, ce qui est appréciable dans le cas d'alliages réactifs tels que les alliages Al-Li par exemple.The molten metal is brought to the cup without significant loss of heat, the overheating of the bath is minimized, bet, which is appreciable in the case of reactive alloys such as Al-Li alloys for example.

Le diamètre interne Φi de la buse n'est pas un paramètre critique. Seuls comptent la surface de la buse en regard de la coupelle, c'est-à-dire la surface S où s'exercent les forces de capillarité, et la distance H busecoupelle. Il n'est plus nécessaire de créer et de moduler une surpression dans le creuset en cours d'éjection, car la coupelle entraîne toujours la même quantité de métal, le dispositif est autorégulant. Par conséquent, le régime thermique de l'ensemble reste stable au cours de l'expérience, on observe une amélioration du rendement de pulvérisation et un léger resserrement du spectre de distribution granulométrique.The internal diameter Φ i of the nozzle is not a critical parameter. Only count the surface of the nozzle opposite the cup, that is to say the surface S where the capillary forces are exerted, and the distance H busecoupelle. It is no longer necessary to create and modulate an overpressure in the crucible during ejection, because the cup always carries the same amount of metal, the device is self-regulating. Consequently, the thermal regime of the assembly remains stable during the experiment, an improvement in the spraying efficiency is observed and a slight narrowing of the particle size distribution spectrum.

Le diamètre interne Φi de la buse n'étant plus critique, on peut alors augmenter sensiblement sa dimension afin d'éviter le phénomène de bouchage qui se produit dans les dispositifs connus. En effet une coupelle non alimentée, même pendant un temps très court, se refroidit très rapidement, ce qui entraîne un début de refroidissement du métal à sa surface : l'expérience est alors perturbée.The internal diameter Φ i of the nozzle being no longer critical, it is then possible to substantially increase its dimension in order to avoid the plugging phenomenon which occurs in known devices. Indeed, an unpowered cup, even for a very short time, cools down very quickly, which leads to the beginning of cooling of the metal on its surface: the experiment is then disturbed.

Le fait d'amener le métal fondu rigoureusement au centre de la coupelle contribue à une meilleure répartition des gouttelettes à la périphérie de la coupelle. On élimine par la même occasion les phénomènes d'instabilité et de rebondissement du jet.Bringing the molten metal rigorously to the center of the cup contributes to a better distribution of the droplets at the periphery of the cup. At the same time, the phenomena of instability and rebound of the jet are eliminated.

L'invention sera décrite plus en détail par référence aux figures 1, 2, 3, 4 et 5.The invention will be described in more detail with reference to Figures 1, 2, 3, 4 and 5.

La figure 1 représente une installation de pulvérisation selon l'invention.FIG. 1 represents a spraying installation according to the invention.

La figure 2 représente une partie du dispositif de pulvérisation proprement dit.Figure 2 shows part of the actual spraying device.

La figure 3 représente le dispositif d'entraînement et de réglage de la coupelle.FIG. 3 represents the device for driving and adjusting the cup.

La figure 4 représente une vue en coupe de la buse et de la coupelle.Figure 4 shows a sectional view of the nozzle and the cup.

La figure 5 représente la variation du débit d'extraction DE en fonction Φe.FIG. 5 represents the variation of the extraction rate D E as a function Φ e .

Dans l'installation représentée sur les figures 1 et 2, le dispositif de pulvérisation proprement dit est placé dans une enceinte comportant une partie supérieure (1), une partie intermédiaire (2) et une partie inférieure (15).In the installation shown in Figures 1 and 2, the actual spraying device is placed in an enclosure comprising an upper part (1), an intermediate part (2) and a lower part (15).

Le dispositif de pulvérisation proprement dit comporte un creuset (6) en graphite muni à sa partie inférieure d'une buse (12) et une coupelle (3) associée à une turbine.The actual spraying device comprises a graphite crucible (6) provided at its lower part with a nozzle (12) and a cup (3) associated with a turbine.

La buse (12) comporte un canal interne de longueur l et de diamètre Φi. Le diamètre extérieur de la face inférieure de la buse en regard de la coupelle est Φe. H est la distance entre la face inférieure de la buse et la face supérieure de la coupelle.The nozzle (12) has an internal channel of length l and diameter Φ i . The outside diameter of the underside of the nozzle opposite the cup is Φ e . H is the distance between the underside of the nozzle and the top face of the cup.

Deux rails (5) fixés à l'intérieur de la partie (2) de l'enceinte servent de support au creuset (6) par l'intermédiaire de deux disques, l'un (26) solidaire des rails, l'autre (27) ajustable de façon à ce que l'axe de l'ensemble creuset-buse coïncide avec celui de la coupelle.Two rails (5) fixed inside the part (2) of the enclosure serve to support the crucible (6) by means of two discs, one (26) integral with the rails, the other ( 27) adjustable so that the axis of the crucible-nozzle assembly coincides with that of the cup.

Le creuset en graphite (6) et son isolation (7) sont placés à l'intérieur d'une bobine d'induction haute fréquence (8) qui assure le chauffage. Un tube d'alumine (20) est placé entre le creuset (6) et l'isolation (7). Le creuset (6) est fermé à sa partie supérieure par un disque d'acier inoxydable réfractaire (9) surmonté d'un dispositif de commande (10) d'un axe de graphite (11) qui permet d'obturer le trou d'éjection pendant la période de chauffage. En effet, il est préférable de ne pas laisser le métal venir mouiller la coupelle tant que la turbine n'est pas en rotation car il se formerait alors une couche d'oxyde qui diminuerait sensiblement le diamètre apparent de la buse. L'étanchéité du dispositif est assurée par des joints en graphite, une ouverture permettant soit d'équilibrer les pressions entre le creuset et l'enceinte, soit d'appliquer une surpression dans le creuset pour le nettoyer en fin d'expérience. Le creuset se termine à sa partie inférieure par une buse (12) en nitrure de bore ; l'étanchéité buse-creuset est assurée par un joint en graphite (13).The graphite crucible (6) and its insulation (7) are placed inside a high frequency induction coil (8) which provides heating. An alumina tube (20) is placed between the crucible (6) and the insulation (7). The crucible (6) is closed at its upper part by a refractory stainless steel disc (9) surmounted by a control device (10) with a graphite pin (11) which allows the hole to be closed. ejection during the heating period. In fact, it is preferable not to let the metal come to wet the cup as long as the turbine is not in rotation because there would then form an oxide layer which would appreciably decrease the apparent diameter of the nozzle. The device is sealed by graphite seals, an opening allowing either to balance the pressures between the crucible and the enclosure, or to apply an overpressure in the crucible to clean it at the end of the experiment. The crucible ends at its lower part with a nitride nozzle (12) boron; the crucible nozzle seal is ensured by a graphite seal (13).

Un thermocouple (14) qui permet de mesurer la température du métal fondu, est placé dans un tube d'alumine fermé à une extrémité ; ce tube traverse le couvercle du creuset, l'étanchéité est assurée par une colle haute température.A thermocouple (14) which makes it possible to measure the temperature of the molten metal, is placed in an alumina tube closed at one end; this tube passes through the crucible cover, sealing is ensured by a high temperature adhesive.

La rotation de la coupelle (3) est assurée par une turbine à gaz dont la vitesse maximum de 30 000 tr/mn est atteinte pour une pression de gaz de 0,7 MPa. La turbine est prolongée par un axe creux (28) en matériau réfractaire monté sur des paliers rigides et muni de disques de refroidissement pour éviter l'échauffement de certaines pièces en mouvement.The rotation of the cup (3) is ensured by a gas turbine whose maximum speed of 30,000 rpm is reached for a gas pressure of 0.7 MPa. The turbine is extended by a hollow axis (28) of refractory material mounted on rigid bearings and provided with cooling discs to prevent the heating of certain moving parts.

A l'extrémité de l'axe (28) est fixée la coupelle en graphite (3) qui recevra le flux de métal fondu ; le fond de la coupelle est plat tandis que la forme et la hauteur du bord varient en fonction de l'expérience à réaliser.At the end of the axis (28) is fixed the graphite cup (3) which will receive the flow of molten metal; the bottom of the cup is flat while the shape and height of the edge vary according to the experiment to be carried out.

Le chauffage de la coupelle (3) est assuré par la bobine d'induction (29) placée autour de la chemise de graphite (4). La coupelle (3) et la chemise de graphite (4) sont isolées thermiquement par de la laine de kaolin (19), l'ensemble est maintenu dans un cylindre d'alumine (18) surmonté d'une couronne en graphite pour éviter la dispersion de la laine en cours de fonctionnement. Pendant la période de chauffage, la température de la coupelle est contrôlée au moyen d'un thermocouple non représenté introduit sur le côté et escamoté juste avant la mise en rotation.The cup (3) is heated by the induction coil (29) placed around the graphite jacket (4). The cup (3) and the graphite jacket (4) are thermally insulated by kaolin wool (19), the assembly is held in an alumina cylinder (18) surmounted by a graphite crown to avoid wool dispersion during operation. During the heating period, the temperature of the cup is controlled by means of a not shown thermocouple introduced on the side and retracted just before the rotation.

La turbine et les roulements à billes de l'axe (28) sont montés dans un fourreau cylindrique (22) (figure 3). A la partie inférieure du fourreau est introduit le gaz d'alimentation de la turbine. Pour assurer l'étanchéité de l'ensemble et l'évacuation du gaz d'alimentation de la turbine, le fourreau cylindrique traverse la cuve de pulvérisation par l'intermédiaire d'un sas (23) muni d'électrovannes d'isolement. Des joints cylindriques placés à l'entrée et à la sortie du sas garantissent l'étanchéité et assurent le déplacement en hauteur du fourreau et par conséquent la variation de la distance H entre la coupelle et la buse. Un comparateur à aiguille (24) permet de contrôler avec précision cette distance ajustée par le dispositif (21).The impeller and the axis ball bearings (28) are mounted in a cylindrical sleeve (22) (Figure 3). At the lower part of the sheath is introduced the gas supplying the turbine. To seal the assembly and evacuate the gas supplying the turbine, the cylindrical sheath passes through the spray tank via an airlock (23) provided with isolation solenoid valves. Cylindrical seals placed at the entrance and at the exit of the airlock guarantee the sealing and ensure the displacement in height of the sleeve and consequently the variation of the distance H between the cup and the nozzle. A comparator needle (24) allows to precisely control this distance adjusted by the device (21).

La partie supérieure (1) de l'enceinte comporte deux ouvertures latérales utilisées pour l'éclairage de la cuve et une grande ouverture centrale (25) prévue pour une éventuelle alimentation en métal liquide par l'extérieur.The upper part (1) of the enclosure has two lateral openings used for lighting the tank and a large central opening (25) provided for possible supply of liquid metal from the outside.

La partie intermédiaire (2) de l'enceinte est équipée par de nombreux passages étanches au vide utilisés pour :

  • le chauffage du creuset par haute fréquence
  • les mesures de température de l'alliage fondu, de la coupelle (3) (pendant la période de montée en température)
  • le remplissage de la cuve
  • les mesures de pression
  • le contrôle de l'atmosphère.
The intermediate part (2) of the enclosure is equipped with numerous vacuum-tight passages used for:
  • high frequency heating of the crucible
  • temperature measurements of the molten alloy, of the cup (3) (during the temperature rise period)
  • filling the tank
  • pressure measurements
  • control of the atmosphere.

La partie inférieure (15) comporte deux ouvertures latèrales pour la récupération de la poudre (16) et pour la liaison avec un groupe de pompage, une ouverture centrale fermée par un disque (17) qui supporte l'ensemble turbine-coupelle (figure 3).The lower part (15) has two lateral openings for the recovery of the powder (16) and for the connection with a pumping unit, a central opening closed by a disc (17) which supports the turbine-cup assembly (Figure 3 ).

Une installation telle que représentée sur les figures 1 à 4 a été mise en oeuvre pour préparer diverses poudres d'alliages ou de métal pur (exemples 1 à 8).An installation as shown in FIGS. 1 to 4 was used to prepare various powders of alloys or pure metal (examples 1 to 8).

Pour l'installation utilisée : le diamètre intérieur utile de l'enceinte était de 1350 mm, la hauteur intérieure utile de 800 mm.For the installation used: the useful internal diameter of the enclosure was 1350 mm, the useful internal height of 800 mm.

Le diamètre interne Φi de la buse était de 2 mm.The internal diameter Φ i of the nozzle was 2 mm.

Le diamètre externe Φe de la buse était de 8 mm, et variable pour l'exemple 8.The external diameter Φ e of the nozzle was 8 mm, and variable for example 8.

La turbine à gaz utilisée peut atteindre une vitesse de 30 000 tr/mn pour une pression de gaz de 0,7 MPa.The gas turbine used can reach a speed of 30,000 rpm for a gas pressure of 0.7 MPa.

Le procédé d'élaboration de poudres comporte les étapes suivantes :

  • centrage du creuset par rapport à la coupelle;
  • mise en place de la charge d'alliage dans le creuset;
  • mise en place du thermocouple donnant la température de la coupelle;
  • fermeture de l'enceinte;
  • mise en route de la pompe primaire jusqu'à obtention d'une pression de 0,2 à 0,5 hPa dans l'enceinte;
  • remplissage de l'enceinte par un gaz inerte (hélium) jusqu'à la pression atmosphérique;
  • mesure de la teneur en oxygène de l'atmosphère de l'enceinte. Cette teneur doit être inférieure à 1% pour que l'expérience se déroule sans risque d'explosion.
  • montée en température du creuset, de la coupelle;
  • escamotage du thermocouple de la coupelle;
  • réglage de la distance buse-coupelle. Durant la période de montée en température, une distance minimale est imposée afin de permettre la libre dilatation des différentes parties. Une fois l'équilibre thermique atteint, la coupelle est amenée au contact de la buse puis descendue d'une hauteur H, repérée au comparateur;
  • mise en rotation de la coupelle;
  • escamotage de la tige de graphite qui sert à obturer le trou d'éjection du métal pendant la période de chauffage.
The powder production process comprises the following stages:
  • centering of the crucible relative to the cup;
  • placing the alloy charge in the crucible;
  • installation of the thermocouple giving the temperature of the cup;
  • enclosure closure;
  • starting the primary pump until a pressure of 0.2 to 0.5 hPa is reached in the enclosure;
  • filling the enclosure with an inert gas (helium) up to atmospheric pressure;
  • measurement of the oxygen content of the enclosure atmosphere. This content must be less than 1% for the experiment to proceed without risk of explosion.
  • temperature rise of the crucible, the cup;
  • retraction of the cup thermocouple;
  • nozzle-cup distance adjustment. During the temperature rise period, a minimum distance is imposed to allow free expansion of the different parts. Once the thermal equilibrium has been reached, the cup is brought into contact with the nozzle and then lowered by a height H, identified with the comparator;
  • rotation of the cup;
  • retraction of the graphite rod which is used to close the metal ejection hole during the heating period.

La pulvérisation a alors lieu.The spraying then takes place.

La poudre est récupérée par l'ouverture (16).The powder is collected through the opening (16).

EXEMPLES 1 à 6 EXAMPLES 1 to 6

Les conditions particulières de préparation et la caractérisation de différentes poudres d'alliage sont rassemblées dans le tableau I ci-dessous dans lequel :

  • ΦC représente le diamètre de la coupelle en mm ;
  • Ci et M représentent respectivement la composition atomique et la masse en g de la charge de départ ;
  • H représente la distance buse-coupelle en mm ;
  • DE représente le débit d'alliage fondu en g/s ;
  • V représente la vitesse de rotation de la coupelle en tours/mn ;
  • R₂₀₀ représente le rendement (en %) de la poudre obtenue ayant un diamètre inférieur à 200 µm par rapport à la charge initiale ;
  • R₅₀₋₁₀₀ représente le pourcentage en masse de poudre ayant un diamètre compris entre 50 et 100 µm, par rapport à la masse totale de poudre obtenue.
Figure imgb0003
 The specific conditions of preparation and the characterization of different alloy powders are collated in Table I below in which:
  • Φ C represents the diameter of the cup in mm;
  • C i and M respectively represent the atomic composition and the mass in g of the starting charge;
  • H represents the nozzle-cup distance in mm;
  • D E represents the flow of molten alloy in g / s;
  • V represents the speed of rotation of the cup in revolutions / min;
  • R₂₀₀ represents the yield (in%) of the powder obtained having a diameter of less than 200 μm relative to the initial charge;
  • R₅₀₋₁₀₀ represents the percentage by mass of powder having a diameter between 50 and 100 μm, relative to the total mass of powder obtained.
Figure imgb0003

L'exemple 6 correspond à la composition d'un alliage amorphisable. Des diffractogrammes de rayons X ont été effectués avec le rayonnement Kα1=0,17889 nm du cobalt. Sur ces diffractogrammes, les raies de diffraction de la phase cristallisée, très peu intenses pour les faibles granulométries (inférieures à 125 µm), se renforcent pour les particules comprises entre 125 et 200 µm. On évalue à moins de 1% la fraction cristallisée pour les poudres 50-100 µm et 100-125 µm et à moins de 5% la fraction cristallisée pour les poudres 125-200 µm.Example 6 corresponds to the composition of an amorphizable alloy. X-ray diffractograms were performed with the K α1 = 0.17889 nm radiation of cobalt. On these diffractograms, the diffraction lines of the crystallized phase, very weak for small particle sizes (less than 125 µm), are reinforced for particles between 125 and 200 µm. The crystallized fraction is evaluated at less than 1% for 50-100 μm and 100-125 μm powders and at less than 5% the crystallized fraction for 125-200 μm powders.

EXEMPLE 7EXAMPLE 7

On a préparé des granules de Mg pur à l'aide du dispositif selon l'invention identique à celui utilisé dans les exemples 1 à 6, dans les conditions suivantes : Ci = 100% (Mg pur) M = 304 g ΦC = 12,5 mm H = 0,4 mm DE = 2,5 g/s V = 23 000 t/mn Granules of pure Mg were prepared using the device according to the invention identical to that used in Examples 1 to 6, under the following conditions: C i = 100% (pure Mg) M = 304 g Φ C = 12.5 mm H = 0.4 mm D E = 2.5 g / s V = 23,000 rpm

85% des granules obtenus ont un diamètre compris entre 0,4 et 0,8 mm.85% of the granules obtained have a diameter of between 0.4 and 0.8 mm.

Il apparaît ainsi que le procédé et le dispositif selon l'invention permettent d'obtenir aussi bien des poudres fines (<100 µm) que des billes de quelques dixièmes de millimètres.It thus appears that the method and the device according to the invention make it possible to obtain both fine powders (<100 μm) and beads of a few tenths of a millimeter.

La granulométrie des poudres obtenues dépend essentiellement de la taille de la coupelle et de sa vitesse de rotation.The particle size of the powders obtained essentially depends on the size of the cup and its speed of rotation.

EXEMPLE 8EXAMPLE 8

On a préparé une poudre d'alliage d'aluminium à partir de l'alliage classique 2017A à l'aide du dispositif selon l'invention identique à celui utilisé dans les exemples 1 à 6, dans les conditions suivantes : M = 440 ± 4 g Φi = 2 mm ΦC = 43 mm H = 0,4 mm V = 30 000 t/mn An aluminum alloy powder was prepared from the classic 2017A alloy using the device according to the invention identical to that used in Examples 1 to 6, under the following conditions: M = 440 ± 4 g Φ i = 2 mm Φ C = 43 mm H = 0.4 mm V = 30,000 rpm

Différents essais ont été effectués en changeant la buse de manière à étudier l'influence du diamètre extérieur Φe de la buse sur le débit d'extraction DE du métal liquide, toutes choses étant égales par ailleurs.Various tests have been carried out by changing the nozzle so as to study the influence of the outside diameter Φ e of the nozzle on the extraction rate D E of the liquid metal, all other things being equal.

La figure 5 représente l'évolution du débit d'extraction DE en g/s en fonction du diamètre extérieur Φe, en mm. Il apparaît clairement que, toutes choses étant égales par ailleurs, l'augmentation du diamètre externe de la buse Φe, qui permet l'augmentation de la surface S = π(Φ e ²-Φ i ²)/4

Figure imgb0004
de la buse en regard avec la coupelle, améliore le débit d'extraction DE de métal liquide.FIG. 5 represents the evolution of the extraction flow rate D E in g / s as a function of the external diameter Φ e , in mm. It is clear that, all other things being equal, the increase in the external diameter of the nozzle Φ e , which allows the increase of the surface S = π (Φ e ²-Φ i ²) / 4
Figure imgb0004
 of the nozzle opposite the cup, improves the extraction rate D E of liquid metal.

Claims (6)

  1. A device for producing metal powder by centrifugal spraying, comprising a crucible with a nozzle at the bottom, a dish associated with means capable of driving the dish in rotation, and means for heating the crucible and the dish, the aforementioned components being placed in a sealing-tight chamber formed with openings for supplying liquid metal, for inserting various measuring or monitoring means, and for extracting the resulting powder,
    the device being characterised in that it also comprises means for adjusting the distance between the opening at the bottom of the nozzle and the upper surface of the dish, and in that the outer diameter Φe of the bottom surface of the nozzle is such that Φ i +2 mm ≦ Φ e ≦ Φ c
    Figure imgb0006
     , Φc being the diameter of the dish and Φi being the inner diameter of the nozzle.
  2. A device according to claim 1, characterised in that the means for adjusting the distance between the opening at the bottom of the nozzle and the upper surface of the dish are mechanical means.
  3. A device according to claim 1 or 2, characterised in that the inner diameter Φi of the nozzle is greater than or equal to 2 mm.
  4. A method of producing metal powder by centrifugal spraying, comprising supplying molten metal to a rotating dish, the molten metal being contained in a crucible formed at the bottom with a nozzle, the upper surface of the dish and the opening at the bottom of the nozzle being substantially parallel and facing one another, the nozzle opening being centred on the dish,
    characterised in that the distance between the opening at the bottom of the nozzle and the upper surface of the dish is adjusted in dependence on the surface area of the nozzle opposite the dish, and the liquid metal is extracted from the crucible by the negative pressure produced by the dish when rotating around a vertical axis.
  5. A method according to claim 4, characterised in that it is worked by means of a device according to any of claims 1 to 3, wherein the distance between the upper surface of the dish and the opening at the bottom of the nozzle is adjusted so that under static conditions, the molten metal in the nozzle does not flow out.
  6. A method according to claim 4 or 5, characterised in that the rate of extraction is adjusted via the outer diameter of the bottom surface of the nozzle opposite the dish.
EP19910401246 1990-05-16 1991-05-15 Process and apparatus for preparing powder alloys by rapid solidification Expired - Lifetime EP0457674B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9006104A FR2662102B1 (en) 1990-05-16 1990-05-16 DEVICE FOR THE PREPARATION OF POWDER ALLOYS BY RAPID SOLIDIFICATION.
FR9006104 1990-05-16

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EP0457674A1 EP0457674A1 (en) 1991-11-21
EP0457674B1 true EP0457674B1 (en) 1995-10-18

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CN110961640B (en) * 2019-12-27 2023-12-01 深圳微纳增材技术有限公司 Device and method for preparing metal powder for 3D printing
CN113399674B (en) * 2021-06-18 2023-02-03 唐山市嘉恒实业有限公司 Metal granulating device with more uniform particles and preparation method

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JPS5940054B2 (en) * 1978-08-29 1984-09-27 株式会社佐藤技術研究所 Method for producing spherical particles of a specific size from a melt
DE3326831A1 (en) * 1983-07-26 1985-03-07 Bayer Ag, 5090 Leverkusen Process and apparatus for the division of melts
US4648820A (en) * 1985-11-14 1987-03-10 Dresser Industries, Inc. Apparatus for producing rapidly quenched metal particles

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FR2662102A1 (en) 1991-11-22
FR2662102B1 (en) 1992-07-31
EP0457674A1 (en) 1991-11-21
DE69113861D1 (en) 1995-11-23

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