JPS58110604A - Method and device for manufacturing spherical metal powder - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides for splashing a liquid metal stream by means of a resonator vibrating at an ultrasonic frequency with a scattering surface inclined with respect to the horizontal and subsequently being shaken out of the resonator with a horizontal impact component. The present invention relates to a method for producing spherical metal powders by cooling melt particles as they fly through a directed gas stream.

It is known to scatter a liquid metal stream in the form of a free-falling metal flux from the upper end of a cylindrical container by compressed gas. The metal particles are accelerated by the compressed gas in the direction of the vertical container axis, so that a correspondingly long fall path occurs until the metal particles are sufficiently cooled, which path adversely affects the overall height of the container. In this case, it should be noted that sufficient cooling of the metal particles must take place in order to reliably prevent sintering into agglomerates in any case.

Furthermore, the falling path of the metal particles produced in this manner is such that a cooling gas flow that fills the entire cross section of the container is allowed to flow through the container in the reaction direction and without changing the orientation of the particles. It is known that it can be shortened by

These known methods are also referred to as metal vaporization. These methods are associated with the disadvantage that the particle size spectrum is disadvantageously broad.

Therefore, a method was described in which a metal stream was dispersed in a gas column vibrating at a constant wavelength (West German Patent Application No. 2).
6.56330 λ or a metal stream in the form of a thin layer,
The metal layer is spread on an ultrasonic resonator with a scattering surface inclined with respect to the horizontal, and the metal layer is broken down into fine droplets on the surface. The metal particles are then caused to take a ballistic flight trajectory after leaving the resonator surface, allowing them to cool sufficiently over a suitably long journey (UK Patent No. 2,073,616).
.

- On the surface, ultrasonic atomization of metals yields the desired narrow particle size spectrum, whereas on the multiplane, in this case, the high-velocity gas flow had to be abandoned, since the particle size spectrum is undesirable with high-velocity gas flows. This is because they were afraid that it would lead to The known ultrasonic scattering methods were therefore generally carried out in a stationary gas atmosphere, or in the worst case in a vibrating gas atmosphere (DE 2 656 330). However, this method requires a correspondingly long flight trajectory after the end of the dispersal process;
Consequently, large chambers or containers are required. These vessels have a particularly large horizontal extension, since the resonator surface used for the splash reservoir is oriented at an acute angle to the horizontal, so that the flight trajectory has a significant horizontal component. (UK Patent No. 20736)
16 Specification, Figure 8). The resulting low curing rate results in low throughput or low productivity. Furthermore,
Due to the low cooling rate a coarse crystalline structure is observed within the individual particles, ie a relatively coarse microstructure which is undesirable for many applications.

A method of the type mentioned at the outset is known from DE 15 58 356 A1. in this case,
In particular, the direction of flow of the gas used to oxidize the metal powder is oriented in the opposite direction to the direction of movement of the powder. Furthermore, the supply of gas takes place approximately from the end of the flight trajectory or just before the powder enters the collecting hole ξ-. The quenching effect of such measures is low and also it is not possible to reduce the container dimensions to the desired extent.

From GB 1,084,908 a method for producing metal powder is known, which consists in blowing melt particles against a fixed surface by means of a directed gas stream, but which does not produce spherical particles. particles cannot be obtained. The ultrasonically vibrating scattering surface is horizontally oriented, so the individual particles do not get a horizontal impact component. In principle, the melt particles are accelerated in the height direction and fall again onto the scattering surface.

To ensure that a large amount of melt is collected on the splash surface,
Only horizontal displacements of the melt particles are possible.

exclusively by secondary impact between individual vibrating melt particles,
A gradual forcing towards the edge of the scattering surface takes place, so that further melt particles then reach into the region of the oriented gas stream. However, this format does not provide narrow particle spectra.

When producing spherical metal powders, it should be noted that an important field of application for the metal powders produced in this way is the production of complex and highly loaded components, such as aircraft parts. In this case, the required alloy does not form a sufficiently fine grain structure during the casting process. Measures are therefore taken to press and sinter such molded parts from metal powder in order to obtain as fine a microstructure as possible. This requirement is of course contradictory to the coarse microstructure of the metal powder obtained.

The object of the invention is therefore to provide a method of the type mentioned at the outset which can be carried out with high productivity in compact equipment and which nevertheless results in fine microstructures up to amorphous structures. The purpose was to provide a method.

According to the invention, in the method described at the outset, the metal particles are bombarded with a cooling gas flow oriented approximately perpendicular to the direction of flight at the beginning of their ballistic flight and diverted to another ballistic flight trajectory. This is solved by

This measure is to be understood in direct relation to the feature that the resonator has a scattering surface inclined with respect to the horizontal, so that the melt particles obtain a horizontal impact component.

Thereby, the individual volume elements of the melt have approximately the same residence time on the scattering surface, while GB 10849
The residence time of the vibrating particles in the method described in '08 is quite large and depends on the decomposition. In the state of the art, individual melt particles are immediately pushed over the edge of a horizontal scattering surface, and other melt particles receive a large number of vertical impacts by frequently impacting on the scattering surface. This phenomenon can occur.

Ballistic flight therefore corresponds, ignoring the cooling gas flow, to the flight of a cannonball when the cannon is tilted, for example, at 45 degrees to the horizontal.

To explain the deflection effect regarding the cooling gas flow, the impact acting perpendicularly to the direction of flight is caused by the impact on the metal particles.
1.Moreover, Western Patent Application Publication No. 1558356
A method different from that described in that patent uses a high-velocity gas flow that is applied sufficiently early in suborbital flight. In contrast to known gas flows, therefore, a very effective and significantly early cooling is achieved and, moreover, the vertical component of the flight motion is increased on the basis of the horizontal component. The metal particles are thereby forced into a new, but still ballistic flight trajectory, ie the particles do not impact the hard surface before they have completely hardened. Therefore,
No rupture occurs.

According to the technical measures of the invention, a container is produced which, despite the relatively long flight path until hardening, is extremely consecrated and which can be charged with high metal loadings. be able to. Furthermore, the high spray speed results in a significantly faster cooling of the metal particles, thus resulting in a finer microstructure up to an amorphous structure. Surprisingly, it has been found that a narrow particle size spectrum is obtained in this case despite the use of a cooling gas stream. This is due to the fact that the cooling gas acts only after the metal particles have left the scattering surface and acquired their final particle size.

Cooling gases in this case include all gases which do not cause undesirable reactions with the metal powder to be produced. Cooling gas can be supplied at room temperature. If a cooling gas is supplied with a suitably high pressure, e.g. 2 to 20 g, significant adiabatic cooling will occur as the cooling gas is relieved to a pressure of e.g. Effectively affects the effect. The higher the temperature, the higher the density of the gas.

In this case, according to a particularly advantageous embodiment of the invention, the cooling gas stream is generated by means of a nozzle, the nozzle axis being the same as the gas stream after the melt particles have been deflected by the gas stream. It is oriented so that it continues to move in the direction and does not reach a hard surface before it hardens. By spraying the metal particles with the nozzle, a high impact of the gas molecules is exerted on the metal particles, which in turn causes strong cooling. In this case, the melt particles are forced to move further in the same direction together with the gas particles, the heat exchange being completed by the inevitable difference in the speed of movement.

According to another advantageous embodiment of the invention, the metal particles are impinged on their continued flight path with at least one further cooling gas stream oriented approximately perpendicular to the preceding flight trajectory section. . In this case, the corresponding nozzle can be oriented with respect to the flight path section of the metal particles in such a way that the metal particles are forced into an opposite direction of movement.

This allows the metal particles to pass through the cooling gas stream in different directions in a substantially zigzag manner, thereby significantly enhancing the heat exchange.

The invention also relates to a device for carrying out the method according to the invention, consisting of an ultrasonic resonator and a melt supply device assigned to the resonator. The device according to the invention has a cooling gas nozzle which is arranged above the lower edge of the resonator and whose axis is directed downward substantially parallel to the scattering plane of the resonator. Characterized by being oriented.

Considering the fact that the metal particles are ejected almost perpendicularly to the resonator ejection plane, the gas stream starting from the cooling gas nozzle captures the metal particles perpendicular to their preceding flight trajectory, thus achieving the desired high intensity. cooling is performed. It is understood that in this case the distance from the nozzle axis to the surface of the resonator is chosen such that the metal particles are not captured by the gas flow unless they move approximately at right angles to the surface of the resonator. It should be.

Otherwise, the optimum orientation of the nozzle axis relative to the resonator surface can be determined by experiment. If the cooling gas flow is too far away from the resonator surface, the cooling effect is clearly reduced. On the other hand, if the nozzle axis is moved too close to the resonator surface, this will not interfere with the movement of the melt particles in the desired effect and will result in the particles being blown into each other or towards the resonator drive. obtain. The optimum position of the nozzle axis can be ascertained as described above. This position is achieved when the nozzle axis is oriented approximately parallel to the surface of the resonator.

The invention will now be described in detail with reference to the illustrated embodiments.

FIG. 1 shows a resonator 1 in the form of a thin-walled hollow cone and in a state of vibration, the maximum amplitude being in the region of the lower edge of the resonator 1. In FIG. To excite the resonator, a coupled vibrator 2 excited by two piezoelectric elements 3 is activated. Transmission of vibrations takes place via a cylindrical body piece, on which the resonator 1 is mounted by means of a neck portion 5 and a screw connection (not shown).

Oscillable systems with resonators of this kind are described in German patent application no.
073616, and therefore will not be described in detail here. The vibratory system is connected by means of a base plate 6 and screws 7 to a fixed part of a gas-tight chamber (not shown), in which a sufficient negative pressure and/or protective gas atmosphere can be maintained.

A melt supply device 8 is arranged above the resonator 1 and concentrically to the resonator. The melt guided to the conical tip of the resonator 1 spreads out toward the lower edge of the resonator while decreasing its film thickness.

The so-called high-velocity nodes are located in the tip region of the hollow cone and in the transition region of the coupling oscillator 2 and the cylindrical arm. Therefore, no melt splashing occurs at the tip of the cone. The scattering intensity increases even further towards the lower edge of the resonator, and the melt droplet is essentially shaken off in the form of fine powder droplets or mist from the face of the resonator located below the melt in each case.

The flight trajectory of the thrown particles is indicated by a dotted line. If no special influences are encountered during the flight, the metal particles are collected, for example, following the ballistic flight trajectory 9 and with a significant outward spread at the bottom of the chamber configured as a collection vessel for the metal powder reservoir. At this time, as is clear from FIG. 1, the metal powder forms an almost rotationally symmetrical umbrella shape having a recess in the area of the resonator 1.

A cooling gas nozzle 1 is installed concentrically to the melt supply device 8 and above the lower edge 11 of the resonator 1 in order to influence the flight trajectory and for effective cooling or quenching of the metal particles.
0 is placed. The cooling gas nozzle 10 forms in this embodiment a ring-slit nozzle in which the nozzle slit 12 slopes downwardly and outwardly.

This nozzle slit 12 has a nozzle axis 13 relative to the radial cross section of the cooling gas nozzle 10 . In this case, the nozzle axes of all possible radial sections lie in a conical plane with substantially the same opening angle as the conical scattering surface 14 of the resonator 1. However, the two conical surfaces are axially offset to an extent that has been confirmed experimentally, ie all nozzle axes 13 lie well above the spray surface 14.

This arrangement achieves that all nozzle axes run parallel to the respective associated generatrix of the spray surface.

The cooling gas nozzle 10 is connected to a gas supply conduit 15 via which a suitable cooling gas, for example helium, is supplied. From the nozzle slit 12, a rapidly flowing, rotationally symmetrical gas curtain emerges with corresponding dimensions and pressure steps, the path of which, at least initially, coincides with the conical surface in which all nozzle axes 13 lie.

In this way, the metal particles are diverted to a flight trajectory that is significantly below the flight trajectory 9. Due to the chosen arrangement, the gas curtain is oriented in the immediate vicinity of the expression of the resonator 1 at an angle of approximately 90° to the initial flight trajectory of the metal particles. However, the gas curtain deflects the metal particles approximately in the direction of the nozzle axis, thus causing them to move further in approximately the same direction as the gas flow.

Furthermore, below the cooling slit 1o, another cooling gas nozzle 10a can be arranged, which nozzle has substantially the same construction principle, except that its nozzle slit 12a is oriented upwardly inclined. Therefore, the gas curtain ejected in the direction of the arrow shown is the cooling gas nozzle 1.
Under the action of 0, the metal particles collide again almost perpendicularly to the flight trajectory of the metal particles. According to this means, it is possible to force the flight trajectory of the metal particles to follow a zigzag path, effectively quenching the metal particles along this path, and thus forming a desired microstructure inside each particle. Furthermore, the length of the overall flight trajectory is effectively shortened thereby, and thus the diameter of the chamber or collection vessel is reduced.

In this case as well, the nozzle slit 12,1 lies in a conical surface with a generatrix extending perpendicularly to the generatrix of the conical surface on which the nozzle axis 13 of the cooling gas nozzle IQ lies.

The direction and opening angle of the gas curtain can be varied within certain limits,5 and the optimum orientation can then be determined by experiment. In this case, care should be taken that as far as possible the metal particles are not directed towards another cooling gas and/or the vibration system of the resonator 1.

In FIG. 2, which is a modification of the embodiment of FIG. 1, the resonator 1a has the shape of a roof instead of a hollow cone.

In this case, the melt supply device 8a has a rectangular cross section, so that the metal melt can be supplied over a long section of the resonator 1a. In this case as well, there is one high-speed node in the region of the ridge of the resonator 1a, while the linear lower edge 11a vibrates with maximum amplitude. In this case too, the melt 16 spreads out in the form of a thin film on the resonator la, the thickness of which decreases towards the lower edge 11a, until finally the liquid metal is in the form of small particles 17. It is blown away in the direction of the arrow shown. In this case, the flight trajectory initially runs parallel, but otherwise follows the known ballistic course of a flight trajectory of this kind.
Two linear cooling gas nozzles 18 and 19 are arranged mirror-symmetrically with respect to
are oriented so as to extend parallel to the respective roof surfaces of the resonators 1a. In this case, all nozzle axes of the cooling gas nozzles lie in the plane of symmetry of the respective nozzles. All arrangements are completely mirror symmetrical and similar to the embodiment shown in FIG.

It should be understood that the device of FIG. 2 is fully valid according to the inventive concept even if only half of the device is present on one side of a hypothetical vertical plane of symmetry. In this case, it is sufficient to ensure that the melt supply device 8a is shifted laterally so that the melt flow completely reaches the resonator la. This also shows that the resonator can be varied within a wide range, provided that the condition is met that the melt applied in the form of a thin film on it is splashed at the latest in the area of the lower edge of the resonator. That is clear.

The embodiments that have been described thus far relate to vibratable systems in which the resonator performs natural oscillations. However, the principles of the present invention up to part 1 can be applied to a resonator fixedly coupled to an ultrasonic generator. Such a case may occur, for example, when a liquid metal jet impinges on the end face of a tilted solid cylinder connected to an ultrasonic generator and the metal particles accelerate in space in the direction normal to the impact surface. arise. As soon as the droplet stream thus formed is blown in a completely similar manner through a correspondingly oriented cooling gas nozzle, it brings about the above-mentioned result.

Another field of application is the production of alloyed aluminum powders. For example, in the case of some aluminum alloys, dissociation occurs during hardening when a certain alloy proportion is exceeded. However, with the fast cooling of the present invention, a significantly higher alloy proportion is maintained in the alloyed state within the powder particles.

[Brief explanation of the drawing]

FIG. 19 is a vertical sectional view of one embodiment of the device of Akimei Hon, and FIG. 2 is a schematic sectional view corresponding to FIG. 1 of another embodiment. 1, l a-resonator, 10,10a, 18.19
...Cooling gas nozzle, 11, 11a... Lower edge of resonator, 13, 22, 23... Nozzle axis, 14...
Scattering surface↓↓ FIG, 1 FIG, 2

Claims (1)

[Scope of Claims] 1. Molten particles splashed in a liquid metal stream by a resonator vibrating at an ultrasonic frequency and having a scattering surface inclined with respect to the horizontal, and subsequently shaken out of the resonator by a horizontal impact component A method for producing spherical metal powder by cooling the particles as they fly in a directed gas stream, wherein the metal particles are oriented substantially perpendicular to the direction of flight at the beginning of their trajectory. A method for producing spherical metal powder, characterized in that it is impinged with a directed cooling gas stream and diverted into another ballistic flight trajectory. 2. A cooling gas flow is generated by a nozzle, and at that time, the direction of the nozzle axis relative to the melt particles is changed such that the melt particles move further in approximately the same direction as the gas flow after being turned by the gas flow, and yet before hardening. A method according to claim 1, characterized in that it does not impinge on hard surfaces. 3. During the course of their flight, the metal particles are bombarded with at least one further cooling gas stream oriented substantially perpendicular to the preceding flight trajectory segment. the method of. tun A liquid metal stream is splashed by a resonator vibrating at an ultrasonic frequency with a scattering surface inclined with respect to the horizontal, and the melt particles are subsequently blown away from the resonator by a horizontal impact component, and the particles are directed. An ultrasonic resonator for producing spherical metal powder by cooling it while flying through a gas flow, the ultrasonic resonator having a scattering surface inclined with respect to the horizontal and a melt supply device attached to the scattering surface. cooling gas nozzle (10, loa, 1
8°19), and the nozzle has a resonator (1, 1a
) is arranged above the lower edge (11, 1la) and the axis (13°22.23) of the nozzle is directed downward approximately parallel to the scattering surface (14) of the resonator. An apparatus for producing spherical metal powder, characterized in that: 5. The resonator (1) has a conical scattering surface (14) and the cooling gas nozzle (10) is configured as an annular slit nozzle arranged concentrically with respect to the resonator. The device according to scope item 4. 6. The resonator (1a) has at least one flat scattering surface inclined with respect to the horizontal and the cooling gas nozzle (18
, 19) is configured as an elongated slit-like nozzle extending horizontally and parallel to the scattering surface.