Apparatus for pulverizing at least a jet of a pulverizing fluid, preferably a molten metal

The invention relates to an apparatus for pulverizing at least a jet of a quid or solid material in a standing ultrasonic field which is generated between at least a pair of ultrasonic devices. To increase the pulverizing capacity a plurality of pulverizing fluid jets and in addition supplementary fluid jets, for example a gas is introduced through separate nozzles at each nodal pressure area of the standing ultrasonic wave. In addition the pulverizing capacity is further increased by providing special horn shapes of the ultrasonic devices.

BACKGROUND OF THE INVENTION 
The present invention refers to an apparatus for pulverizing at least a jet 
of a liquid or solid material, preferably molten metal. 
According to a prior art device (European Al 0308933) a pair of ultrasonic 
generators are located opposite each other in a throttle section of a 
nozzle through which an inert or reaction gas enters the ultrasonic field 
created between the ultrasonic generators. The gas stream facilitates the 
pulverizing process and allows a well defined transfer of particles out 
from the pulverizing area. 
According to another known device (German C2 28 42 232) for pulverizing 
coal particles used in a heating application the combustion air may be 
radially blown through slot or ring nozzles in the pressure loops or nodal 
areas of a standing wave of an ultrasonic field which is generated between 
an ultrasonic device and a reflector. 
It is an object of the present invention to improve an ultrasonic device of 
the type referred to above in order to substantially increase the 
pulverizing capacity. A further object is to improve the control of the 
pulverizing process. 
SUMMARY OF THE INVENTION 
According to the present invention, an apparatus for pulverizing at least a 
jet of a pulverizing fluid, preferably molten metal, has at least a pair 
of ultrasonic devices which are provided opposite to each other on a 
common axis at a predetermined distance, to generate a standing ultrasonic 
field therebetween including pressure nodal areas in which said 
pulverizing fluid is pulverized by ultrasonic energy and in the presence 
of a supplementary fluid, wherein a jet of pulverizing fluid and at least 
a jet of supplementary fluid are introduced in said pressure nodal areas 
through separate nozzles each. 
According to the present invention the supplementary fluid which is gaseous 
in most applications is introduced through nozzles aiming at the nodal 
pressure areas of the standing ultrasonic wave in addition to the fluid 
jet of the medium to be pulverized which is liquid in most applications. 
The capacity of supplementary fluid through the nozzles is individually 
adjustable with respect to the pulverizing fluid. Preferrably a plurality 
of pulverizing and supplementary fluid jets are introduced. The volume of 
pulverizing fluid should be limited by a maximum level as the jet may 
otherwise break through the pulverizing area resulting in a reduced 
pulverizing capacity. 
However, by introducing a plurality of supplementary fluid jets in addition 
to the pulverizing fluid jet at the pulverizing areas in the pressure 
nodals both the pulverizing and fluid mass capacity is substantially 
increased. This is due to a local rise of the gas density (impact 
pressure) within the pulverizing area of the nodal points and due to the 
increase of turbulances in the pulverizing areas caused by the well 
defined introduction of supplementary fluid mass volume. By aiming and 
locally limiting both the beams of pulverizing and supplementary fluids a 
two-phase-pulverization is obtained. Within the pulverizing area the 
supporting supplementary gas causes a pulse transfer in addition to the 
ultrasonic energy resulting in a substantial power increase of the 
process. It was further observed that the size of the droplets is shifted 
towards smaller droplets. Still further the control of the process by 
modifying the supplementary gas stream is improved. There is an increased 
cooling effect and a higher cooling velocity within the pulveriziation 
area and the transport of particles therefrom is improved. 
It should be understood that the pulveriziation fluids include liquids, in 
particular molten materials and solid materials such as minerals, powders 
or foams. The supplementary fluids include gases, vapours, mist, liquid, 
powder and the like.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows an apparatus which was earlier disclosed in European A-0308 
933 in which an ultrasonic standing wave 3 comprising pressure nodals and 
pressure loops is generated between a pair of horns 1 and 2 being part of 
ultrasonic devices not shown in FIG. 1. The outlets of crucibles 4 are 
directed towards the nodal points to release one or more molten material 
jets which are pulverized in the ultrasonic field in the presence of a gas 
entering the pulverizing area between the horn surfaces 5 and 6. 
The horn 2 is part of an ultrasonic device which is shown in FIG. 2 and 
which has a booster 11 and a converter 12. A casing 15 is pressure tight 
connected at a nodal point 14 of the booster 11. The casing 15 encloses 
the converter 12 and the booster 11. The casing 15 is connected by means 
of a sleeve 17 having seals 16 to an outer housing 18 which defines a 
cartridge mounted in a wall 19 separating the outer atmosphere 20 from the 
pressure chamber 21 in which the pulverizing process takes place. An 
electrical cable 22 is connected to the converter 12 by means of the 
housing 18. The casing 15 is axially adjustable by means of an adjusting 
device 23. 
FIG. 3 shows a front view of the surface 5 of the horn 1. Adjacent the 
pulverizing fluid nozzles 25 there are individual supplementary fluid 
nozzles 26 which are connected to pressure fluid sources not shown. Both 
the nozzles 25 and 26 are radially directed and peripherally spaced. 
Through the nozzles 25 and 26 the fluid jets are aimed at the longitudinal 
axis 7 of the ultrasonic device. Preferably the jets enter the nodal 
pressure areas of the ultrasonic field as shown in FIG. 5. According to 
FIG. 3 the nozzles alternate so that a supplementary fluid jet originates 
from nozzle 26 adjacent a pulverizing fluid jet each originating from a 
nozzle 25. The special combination of nozzles which may continue around 
the periphery of the horn results in a highly increased fluid capacity and 
pulverizing output. 
FIG. 4 shows annular nozzles 28 from which central opening 29 the 
pulverizing fluid jet and from an annular opening 30 the supplementary 
fluid jet originates which annular opening encloses the central opening. 
All the nozzles are aimed at a nodal pressure point each in the standing 
wave. 
FIG. 5 shows a number of separate or annular nozzles 25, 26, 28 according 
to FIG. 3 or 4 to introduce pulverizing and supplementary fluid jets each 
aimed at an individual nodal pressure area of the standing wave. A 
plurality of nozzles 25, 26 and 28 is provided for each nodal pressure 
area. 
FIG. 6 shows a flat nozzle 35 including conduits 36 for the pulverizing 
fluid and conduits 37 for supplementary gas. The supplementary gas jet is 
supplied at both sides of the centrally originating pulverizing gas jet 
and is aimed at the pulverizing area of the ultrasonic wave. 
FIG. 7 shows the front surface 5 of a rectangular horn 1 which is 
preferrably used with a flat nozzle 35. This type of large area horn 
increases the pulverizing capacity. The same is true for the embodiment 
shown in FIG. 8. This embodiment comprising a large rectangular horn 1 and 
a number of nozzles 25, 26 or, respectively annular nozzles 28 arranged 
side by side in rows which nozzles again are provided in the planes of the 
nodal pressure areas. 
All embodiments may be accomodated in a pressure container in which the gas 
jets are subjected to a compression such that the energy transfer is 
increased in the compressed medium. 
FIG. 9 shows a further embodiment to improve the pulverizing capacity. The 
surfaces 5 and 6 of the horn are shaped concave so that the energy focuses 
in the node of the ultrasonic standing wave to increase the sonic 
alternating pressure. Furthermore the horn surfaces may be coated to 
lessen the wettability. For example a coating of boron nitrite, titanium 
nitrite may be evaporated or the surfaces may be coated by chromium or an 
anodizing process.