Note: Descriptions are shown in the official language in which they were submitted.
5~
The present invention relates to the production
of metallic particles or granules. The invention is
primarily directed to a me-thod of production of metallic
granules and extend to the products ob-tained in accordance
with said method as well as to a device which is particu-
larly well suited to -the practical application of said
method.
The invention is of general utility for the
conversion of any metal into granules, this conversion
principle being applicable not only to pure or practically
pure metals but also to metallic compounds or alloys. The
general aim of the invention is to obtain practically
spherical grains having a diameter of the order of 0.1 to
5 mm, for example, thus forming in the aggregate a powder
which has good flow capability, which can readily be
conveyed by pneumatic means, which has relatively high
bulk density and low porosity while also providing the
possibility of obtaining uniform calibration oE grains,
if necessary after a sorting operation which is readily
performed.
To this end, a molten metal bath must necessarily
be employed at the outset. sut the properties of metals,
first in the liquid state, then during transition from the
liquid to the solid state, and finally in the solid state,
represent specific conditions such that the methods of
granulation commonly employed in the treatment of products
~ `'.
7~i6~
of another type such as products in paste form cannot be
applied to these latter in a general manner. Furthermore,
-the methods of production of granules from molten metal
baths which have been in use up to the presenk time do
not yet prove satisfactory from the point of view of
regularity of shapes and dimensions. In regard to methods
related to the atomization process which it has been
sought to apply to products having a base of reactive
metals such as calcium, these methods produce reactive
lo an~ hygroscopic powders which have poox storage stability
and finally offer limited possibilities of use.
In order to overcome these disadvantages, the
invention proposes a method of production of metallic
granules of the type in which metal in the form of
granules is solidified from the molten state. The method
essentially consists in forming a jet of molten metal
which is caused to pass through a vibrating orifice in
order to divide the jet into individual drops and finally
in causing solidification of said drops by cooling so as
20 to form granules. --
The method in accordance with the invention can
be applied to the production of metallic granules from
molten metal baths having any composition. However, it
will be observed -that, in the majority of instances, the
~5 metals being processed are in the molten state at a
temperature within the range of 200 to 1500C and that the
.
-3
vibrating orifice through which the jet of molten metal is
discharged usually opens into an atmosphere which is
cooled by dissipation of heat in the surrounding air, the
temperature of which can therefore be within the range of
; 5 20 to 90C, for example. In practice, the operation is
advantageously performed under conditions such that the
temperature difference between the molten metal at the
point of formation of the jet and the atmosphere into which
the vibrating orifice opens is at least of the order o~
200~ and preferably wi-thin the range of 300 to 1300DC,
and more particularlv within the range of 500 to 100~C.
In accordance with a preferred mode of exacution
of the invention, the drops of the jet are caused to fall
from the vibrating orifice under the action of gravity
through an atmosphere of inert gas which is maintained at a
temperature below the solidification temperature of the
; molten metal. The inert gas atmosphere may be chosen as a
function of the nature of the metal~ of the jet diameter
and of the préssure conditions at the level of the vibrat-
ing orifice so as to ensure that the drops thus formed
' rapidly attain the maximum rate of fall over a height of
fall which is made availabla in the atmosphere and is
sufficient to permit complete solidification of the
granules prior to collection. In practice, the rate of
- 25 fall can be of the order of 2 to 30 meters per second, for
example. Depending on the thermal conditions, solidifica-
. .. ~. , .
~56~3
tion may require a length of time corresponding to a
height of fall of the order of 10 cm to 20 m or preferably
20 cm to 10 m. During solidification or at least at the
beginning of solidification, the metal drops are subjected
to internal stresses which result from the vibrations
imparted at the moment oE division of the jet into drops
at the exit of the vibrating orifice. The invention thus
makes it possible to obtain granular powders in which the
diameters of the granules can be of the order of 0.2 to
3 mm, for example, with dispersions with respect to the
mean dimension which can remain less than ~ 0.5 mm or may
even not exceed approximately + 0.01 mm. ---
In conjunction with the cooling conditions
applied, the powders obtained also have surface qualities
which are usually conducive to the properties sought in
this type of granular product, especially a degree of sur-
face hardness and strength which are conducive to good
; storage stability as well as flowability of the powder. By
way of example, the inert gas can be helium , argon or
'f ~ 20 mixtures of khese gases. In some cases, it may prove
ad~antageous to carry out in addition a dispersion of the
metallic drops during solidification with respect to the
direction of fall of the jet in order to prevent individual
drops from coalescing during solidification.
In accordance with another distinctive feature
of the invention, arrangements may be made to form the
li~ui.d metal jet by withdrawal from a mass of molten metal
maintained in contact with a bath which is not misclble
with said mass and selectively dissolves the derivatives
produced in the event of o~idation. The metal can advant~
ageously be melted, passed in the molten state through the
bath for selective dissolution of the oxidation derivatives
and then separated from the bath by settling so as to co~-
stitute the mass from which the jet is drawn. Steps can
also be taken to ensure that the molten metal is then
conveyed without any further contact with air or an
oxidizing atmosphere up to the point of discharge of the
jet into an inert cooling atmosphere as described earlier,
preferably by means of a section of vertical piping which
terminates in the vibrating orifice. In a particularly
advantageous mode of execution of the method according to
the invention, the mass of molten metal can be forced
through a filter for retaining solid particles, said
; filter being maintained immersed in the bath for dissolu-
tion of solid derivatives, said mass being then separated
from said bath by settling prior to formation of the jet.
In accordance with the invention, it is thus
possible to treat reputedly reactive metals while readily
circumventing all the potential difficulties arising from
the presence of solid oxidation derivatives which would
~5 otherwise be liable to obstruct the holes of the filter or
the jet discharge orifice and thus produce an irregularity
in the formation of drops. The bath employed can advant-
ageously consist of a fused halide ~f at least one metal
of the molten metal mass. Said bath can also consist of a
fused halide of at leas-t one additional metal which has
higher reducing power than the essential metal of the
granules and is incorporated in said mass in a small pro
portion. An additional metal of this type can consist in
particular of calcium, the oxide of this metal being
readily dissolved in a bath of calcium fluoride and/or
chloride. A proportion of calcium of the order of o.5 to
; 10 ~ by weight is usually sufficient in metals such as
aluminium or magnesium, for example. A point to be noted
is that the additional metal can be present in the granules
obtained in accordance with the invention whereas the
recommended conditions of execution are such that molten
salts can be prevented from being present in any proportion
other than that of trace constituents which are detectable
but not objectionable. In particular, the invention makes
it possible to produce granules of reactive metals such as
calcium, magnesium or aluminium which, in spite of the use
of a bath of fused salts, do not have any hygroscopic
character which would be liable to impair storage stability
and flowability of the powders.
The production of metallic granules in
accordance with the method contemplated by the invention
involves the use of a device comprising a furnace for
~L75~
melting metal within a vessel designed to receive a mass
of molten metal, means for forming a je-t of metal with-
drawn from said mass and passed through a vibrating
orifice, means for causing vibration of said orifice and
thus dividing the jet into individual drops, and a
- chamber for subjecting the metal discharged from said
orifice to cooling and solidification over at least the
distance o~ downward travel of the drops during their
solidification. Preferably, the device comprises a siphon
for withdrawing metal from a mass of molten metal separated
from a bath of fused salts by settling within said vessel.
As an advantageous feature~ the device can also comprise a
filter having hol.es smaller in size than the vibrating
orifice or having a maximum size equal to said orifice, and
means for forci.ng the rnolten metal through said filter
which is immersed in the bath of fused salts. Furthermore, -
said vessel and said cooling chamber are preferably gas-
tight and means are advantageously provided for separately
adjusting the pressure of an inert gas within said vessel
and within said cooling chamber.
Further distinctive features of the invention
will become apparent from the following description and in
particular from the more detailed description of a device
for the production of metallic granules, reference being
made to the accompanying drawings in which :
- Fig. 1 is a diagrammatic sectional view of the
~7~6~
, :
different elements of the device in accordance with the
invention in a fixst embodiment of said device ;
- Fig. 2 is a vertical sectional view of a
second embodiment of said device ;
- Fiq. 3 is a more detailed view of the upper
portion of the device of Fig. 2.
As described hereinafter, the device in
accordance with the invention comprises a heating cell
provided with a gas-tight enclosure forming a vessel and
heating means, a unit for the introduction of raw materials
into the cell, a cooling chamber adapted to communicate
with the cell via a duct having a siphon and a zone
pierced with at least one vibrating orifice, first pneu-
; matic means for establishing and controlling the pressure
; 15 of the atmosphere within the enclosure, a vibrator
connected to the zone which includes the vibrating orifice
and adapted to produce continuous vibration of said ori- ~
fice, second pneumatic means for establishing and control-
ling the pressure of the atmosphere contained within the
cooling chamber, and a device for discharging solid
material from sald chamber.
; Thus the device shown in Fig. l comprises a
closable unit l for the introduction of material in order
to convey the metal into a heating cell 2 from which the
molten metal is injected into a cooling chamber or tower
3 via a duct 4. A closable discharge unit 5 serves to
~7~6~L8
remove the solid metal granules formed within the cooling
tower 3.
The heating cell 2 comprises a gas-tight en-
closure 6 forming a vessel for containing the molten metal.
Said enclosure 6 is heated by a furnace 7 which surrounds
its side walls and serves to maintain within the enclosure
a temperature which is higher than the melting point of
the metal. The molten metal 8 occupies the lower portion
of the enclosure 6 and a gaseous atmosphere 9 is present
-~ 10 above said molten metal. The pressure of said atmosphere
is controlled by a first pneumatic means lO to which said
atmosphere 9 is connected by means of a duct 23. Said
pressure can be either increased or reduced so as to cause
injection of the molten metal 8 through the duct 4 at a
higher or lower rate.
Said duct is constituted by a U-shaped tube 11,
one extremity 12 of which is immersed in the molten metal 8
and the other extremity 13 of which extends vertically
within the upper portion of the cooling tower 3. The
upper portion of the tube in the vicinity of the extremity
12 is bent so as to form a siphon, the elbowed portion of
which projects above the leve] of molten metal. The
extremity 12, the opening of which is directed towards the
bottom end-wall 14 of the enclosure 6, is fitted with a
filter 15 for retaining the impurities contained in the
molten metal. That zone of the enclosure 6 which is
~10--
,
~7S6~L~
located in the vicinity of the bottom end-wall 14 is a
settling zone in which impurities having a higher denslty
than the rest of the liquid are permitted to accumulate.
It will be possible to place -the filter directly above
said molten-metal set-tling zone in order to prevent solid
inclusions in suspension from causing rapid clogging of
the filter. The heating cell 2 is also provided with
mechanical stirring means represented diagrammatically by
the impeller 18 for producing a stirring and homogenizing
action on the liquid. The extremity 13 of the tube 11
terminates in at least one orifice for the iniection of
molten metal into the cooling tower 3. The threadlike flow
of molten metal thus obtained forms a vertical downflow jet
to which vibrations are applied in order to produce uniform
drops of liquid. In accordance with one embodiment, the
extremity 13 of the tube is subjected to vibrations by
means of a vibrator 16 and a connecting device represented
diagrammatically by the rod 17. 'rhe drops of molten metal
formed at the extremity 13 of the duct 4 are dispersed
within the cooling tower by dispersion means 19 consisting,
for example, of an annular electrode whi~h surrounds the
jet and i5 electrically charged with respect to the
extremity 13 of the tube 11, thus conferring on the drops
electric charges which are all of the same sign. The
liquid drops are dispersed and moved away from the
vertical direction of the jet, then solidify before
11 -
~75~
dropping to the bottom end-wall 20 of the cooling tower 3.
Said tower contains a gaseous atmosphere which permits
rapid cooling of the metal and is inert with respect to
this latter. Dif~erent means such as gas-circulating
means, for example, can be provided within the tower in
order to ensure accelerated cooling of the metal. The
rate of cooling of the drops may govern the nature of the
phase of the solidified material and thus the,quality of
,~ the product obtained. The use of a gas-tight cooling
tower makes it possible to prevent any communication
between its internal atmosphere and the surrounding air,
The pressure of the gaseous atmosphere of the tower can
be controlled by a second pneumatic means 25 to which the
, tower is connected by means of a pipe 24.
, 15 In accordance with one embodiment~ the metal ` --
,' introduction unit 1 comprises a communication lock-chamber
,' 21 and the discharge unit 5 comprises a lock-chamber 22 so
~ as to permit continuous operation of the installation. The
,',, unit 1 for the supply of raw material serves to introduce
,~ ~ 20 into the heating cell either molten metal or metal in the
' solid state ; in the latter event, melting takes place
within the heating cell and the metal is injected into the
cooling tower only when it is completely melted and in a --
homogeneous state. It is possible to treat metals which
react with oxygen since t.he hermetically sealed assembly
comprising the heating cell 6, the pressure control means
-12-
~L7~6~
10 and 25, the communication duct 4 and the cooling tower
3 can be subjected to a controlled akmosphere of a gas
which does not react with the metal.
The practical application of the invention by
means of the device shown in Fig. 1 consists in intro-
ducing the metal into the heating enclosure 6 either in
the solid form or in the liquid form via the lock-chamber
21, ln maintaining the temperature of the metal slightly
above its melting point by means of the heating means 7
and in homogenizing the molten mass either by agitation or
by bubbling produced by the stirring means lB. When the
molten mass is homogeneous, it is injected into the
;~ cooling tower 3 via the tube 11 and the vibrating orificeO
Priming of the siphon is carried out, for example, by
means of an overpressure of the order of 50 to S00 g/cm2
within the enclosure 6, this overpressure being produced
by the pneumatic device 10. Dur:ing their downward fall,
the drops thus formed are dispersed if -the annular electrode
of the dispersion means 19 is energized and are then cooled
by the atmosphere of the tower until they form solid
spherical granules. The rate of injection of the molten
metal through the vibrating orifices is regulated by means~
of the gas-pressllre difference between the atmosphere 9
which is present above said molten metal within the heatlng
enclosure and the atmosphere of the tower 3. This con-
trolled and r~gulated injection rate makes it possible to
-13-
take into account the nature of the metal, the vibration
frequency of the vibrating orifices and a number of
different physical parameters of the molten metal such as
its temperature. The pneumatic means 10 and 25 thus ser~e
to establish, regulate and stop the flow of injected liquld
metal~ At the end of the operation, said pneumatic means
also permit reversal of the pressure difference between the
two enclosures 6 and 3, thus making it possible to clean
the filter without any need to open the enclosure a~d to
put this latter in contact with oxygen.
Homogenization of the molten mass can be carried
out in diffexent ways. If the inclusions are of suffi-
ciently small size, it is possible to form a homogeneous
suspension of these particles by making use of the
stirring means 18 in order to pro~uce effective agitation.
On the contrary, if the inclusions are of large size and
are liable to cause e~cessively rapid clogging of the
filter and/or of the injection orifices, a settling or
sedimentation operation is performed in the bottom portion
of the enclosure 6. In order to make it possible in
particular to facilitate cleaning of the enclosure after
~; sedimentation, provision can be made for a substantially
and/or partially conical bottom end-wall 14, the apex of
the cone being directed downwards in order to produce an
accumulation of sedimentation products within a removable
container (not shown in the figure) which is placed at the
-14-
~7b~
lower end of the cone. The container can be withdrawn
for removal of said sedimentation products. Transfer of
the container can be facilitated by means of a relatively
displaced, asymmetrical arrangement of the conical end-
wall 14 and/or of the communication duct 4 with respectto the enclosure 6 so as to permit vertical withdrawal of
the container without coming up against the siphon or the
filter 15.
The device shown in Figs.2 and 3 is largely
; lO composed of the same essential elements as the device of
the preceding embodiment but is so designed as to p~rmit
easier production of readily oxidizable reactive-metal
granules. By means of this device, the metal which has
already melted can in fact be purified immediately prior
to formation of the jet and of the liquid drops by reacting
with a fused-salt bath which is capable of dissolving the
oxidation products and re-taining them in said bath, thus
preventing entrainment of solid inclusions in the liquid-
metal jet and untimely solidi~ications at the time of
formation of drops.
ccordingly, there is again shown in Fig. 2 a
furnace 31 surrounding a gas-tight cell 32 mounted above
a tower 33 which closes a gas-tight chamber, said chamber
being separated from the cell 32. A communication between
said chamber and said cell takes place only by means o~ a
siphon 34 (as shown in Fig. 3).
-15-
~5~
The furnace 31 serves to heat the cell 32 so as
to melt the materîals which are introduced therein and to
maintain these latter in the molten state, namely both the
metal which is intended -to constitute the granules pro-
duced and the metal halides which constitute the puriflca-
tion bath. The cell 32 is equipped so as to define within
the interior of the furnace two separate compartments ~Ihich
communicate with each other through a filter 35. The con-
struction shown in detail in Fig. 3 corresponds to the case
in which the bath employed consists of purification salts
having a higher density than the molten metal. A tubular
shaft 36 placed vertically within the enclosure 32 extends
in leak-tight manner through the cover 37 and opens to the
exterior via a lock-chamber 38 for the loading of solid
products. The filter 35 is placed across the lower end of
the shaft 36 above the bottom end-wall 39 of the cell 32.
A first compartment 41 is thus constituted by the internal
space of the shaft 36. During operation, the metal is
introduced in the form of solid lumps through the lock-
chamber 38 and then subjected to the melting process. Themetal is protected against oxidation by means of an inert
gas which is admitted into said compartment at 42. The
other compartment 43 is constituted by the intermediate
space between the shaEt 36 and the vessel which limits the
cell 32. The design function of said compartment 43 is
to permit separation by settling between the molten metal
;6~
; and the purification bath after the me-tal has passed
through said bath. By means of said compartment 43, a
mass of molten metal 44 from which a withdrawal will sub
sequently be made in order to form the liquid metal jet
can thus be formed within the cell 32. In the case of the
figure, the mass of liquid metal 44 settles above the
fused-salt bath 45 and an inert gas atmosphere int~oduced
into the cell 32 at 46 is present above said mass 44. The
purification salt is present in sufficient quantity to
ensure that the filter 35 always remains immersed in the
bath 45. By modifying the inert-gas pressures at 42 and
46, liquids may be forced through the filter 35 either in
order to cause transfer of the molten metal from the
melting compartment 41 to the settling compartment 43 or
to circulate the fused salt through the holes of the
; filter for cleaning purposes.
The constructional design of the means for
withdrawing liquid metal, for forming the jet and for
dividing said jet into drops is also apparent from the
details illustrated in Fig. 3. The duct forming a siphon
34 comprises two coa~ial vertical tubes which slide one
inside the other. The inner tube 40 passes through the
bottom end-wall 39 of the cell 32. The upper end of the
inner tube opens at 47 into the inert gas atmosphere
which is present above the mass of molten metal 44 ; the
lower end of said inner -tube extends vertically downwards
~7~6~L~
.. ...
within the top portion of the tower 33 and terminates in
the vibra-ting orifice 48. There is shown at 49 a
vibrator which produces action on the extremity of the
tube 46 and thus causes division of the jet into liquid
drops as soon as this latter passes out of the orifice 48.
The outer tube 51 of the siphon is closed at its upper
end and can be displaced from the exterior of the cell by
means of a rod 52 ; when moved downwards -to the full
extent, its lower end opens at the level of the molten
10 mass 44. The operation o-E said outer tube thus makes it -
possible to prime the siphon and to initiate the flow of
: liquid metal through the inner tube 46.
The jet of liquid metal divided into drops falls
into the tower 33, said tower being filled with an inert
gas which is admitted at 51 and withdrawn at 52 (as shown
in Fig. 2). The internal atmosphere within the tower is
cooled by heat dissipation in the surrounding air through
the tower walls. The height of the tower is sufficient to
ensure that the drops of liquid metal solidify completely
while falling. The solid granules thus obtained are
collected at the bottom of the tower 33 and extracted
through a lock-chamber 53. The filter 35 which is
intended to prevent the passage of any solid inclusion
which would otherwise be liable to clog the vibrating
orifice 48 is provided with holes which are smaller in
size than the orifice or equal at a maximum to the size of
-18-
~7~6~
said orifice. By way of example, the diameter of said
holes can be smaller than 200 microns in the case of
vibrating orifices having diameters which can vary
between 200 microns and 3 mm.
With respect to the foregoing description, the
device in accordance with the invention can be designed
differently in other forms oE embodiment. At the level
of the melting furnace, for example, the shape of the
- shaft 36 and of the siphon 34 can be modified so as to
adapt the cell 32 to receive a fused-salt bath having a
density which is lower than that of the molten metal.
Withdrawal of liquid metal accordingly takes place within
the mass which settles beneath the fused-salt bath.
Furthermore, the granule production yield can be increased
in an industrial manufacture by replacing the single
orifice 48 by a vibrating plate provided with holes whlch
form separate jets. A series of jets can thus be formed
in the same cooling atmosphere and at the end of the same
withdrawal device~ It is also possible to increase the
number of devices for withdrawal by siphoning from the
same mass of liquid metal and these different withdrawal
devices may result in jets formed either in the same
cooling tower or in different towers.
Examples of practical application of the
in~ention in the production of different metallic granules
will now be described. In the case of reactive metalsr
--19--
~7~
granulation is performed by employing a device of the
type shown in Figs. 2 and 3 with purification by a fused-
salt bath. There is added in some cases a device for dis
persion of metal drops such as the device described with
S reference to Fig. l.
Depending on requirements, the purification bath
employed consists either of a halide of the metal to be
granulated, namely a fluoride or a chloride as a general
rule, or a mixture of these salts, or a halide of a metal
which has higher reducing power and the oxide o~ which is
formed preferentially with respect to the oxide of the
metal to be granulated. ~onsideration is given in
particular to the requirement which consists in dissolving
the oxides of calcium or lanthanum in their halides. To
this end/ calcium can be added to a metal such as aluminium
or magnesium, for example, by employing a proportion of
calcium which is sufficient to permit reduction of sub-
stantially the entire quantity of oxide which may be
present in the metal to be granulated and to retain the
oxides by reaction of the lime with a bath of calcium
fluoride ana/or chloride through which the molten metal
mixture is passed.
For example, in the production of tin granules
intended for use as soldering material, there is no
important oxidation problem to be solved. However, the
mass of molten metal within the melting cell has been
-20-
S ~
protected by a blanket bath formed by the eutectic
compound LiCl-KCl and heated together with this latter
at 350C. The cooling tower contained argon which had been
introduced under normal conditions of temperature and
pressure and the jet discharged from the vibrating orifice
passed through an annular electrode brought to 5000 V. The
granules thus obtained had a particle size spectrum of
1 mm + 0.01 mm.
Under s:imilar conditions, a powder which was
intended to be employed in aluminothermy was produced from
molten aluminium heated to 850C by employing in addition a
bath of fused cryolite (Na3AlF6) in order to dissolve the
alumina. The molten aluminium has a higher density than
said bath and is thereEore drawn-off at the bottom of the
cell. The cooling gas was helium.
In the case of magnesium, the fused-salt bath
employed by way of example consists of a mixture of
magnesium chloride and fluoride.
Calcium is widely employed for such purposes as
refining cast-iron and s-teel, for example.
The invention makes it possible to utilize
calcium in the form of a uniform powder of spherical
granules which can readily be conveyed and added in pre-
determined proportions without incorporating undesirable
Z5 constituents.
Starting from calcium which has been melted at
-21-
56~
880C, purified through a filter having a hole diameter
of 0.2 mm, immersed in a bath of the eutectic mixture
consisting of calcium chloride/fluoride (containing
13.76 % by weight of calcium fluoride) and, after settling
of the metal abo~e said bath and Eorming the jet through a
nozzle having a diameter of 0.4 mm and vibrated at 1500 C/5,
then causing the drops to fall without dispersion into
helium employed as a coolant gas, the powder finally
obtained consisted of spherical grains having a smooth
surface and a diameter within -the range of 0.6 to 1.6 mm.
The powder is reactive to air, oxygen and water only to a
very slight extent.
The addition of magnesium to -the calcium makes
; it possible to reduce the melting point of the alloy.
; 15 From 11.5 % by weight of magnesium in the alloy to the
eutectic compound containing 28 % by weight of magnesium,
the temperature to be imposed on the molten alloy is in
fact determined by the melting point of the salts : ~5C
in the case of the eutectic compound CaC12-CaF2. The
melting cell is therefore brought to a temperature of
700C, for example. ~
In another example, the same bath of salts is
employed in the field of granulation of aluminium.
Calcium is then added to -the solid aluminium which has
been introduced, the quantity of calcium being at least
stoichiometric for the reduction of the oxygen which it
-22-
~.~7~
may contain, namely and by way of example 0.5 % by weight
of calcium in the case of commerclal aluminium.
Under the same conditions but in the case of
granula-tion of magnesium, a larger proportion of calcium
was added, with the result that the greater pa~t of the
calcium was present in the magnesium produced in the form
of granules, for example in a proportion of 8 % by weight.
In the case of an initial oxygen content of the order of
o.l %, only a proportion of the order of 0.25 % of the
metallic mixture is consumed in the salt bath, the
necessary quantity of salts heing approximately 50 g of
bath per kilogramme of magnesium to be treated.
In all these eYamples, the frequency of vibra-
tions imparted to the jet discharge orifice was 1500 c/s,
but this frequency can be increased to 6000 c/s. Alter-
: natively, any frequency within the range of 1000 to
16000 c/s may be employed. Furthermore, the height of
fall within the coolant gas is chosen so as to be
sufficient to ensure that complete solidification of the
drops always takes place during the fall immediately upondischarge from the vibrating orifice in order to benefit
by the effect produced on the drops by the vibration. The
data given below have been used as a basis for evaluating
the coolant gas temperature a-t 50C and the metal tempera-
- 25 ture at the vibrating orifice at 70C above the melting
point :
-23-
Height of
Maxium v~locitysolidification
Calcium in helium
Diameter 0.5 mm4.5 m/s 15 cm
Diameter 1 mm9.8 m/s 85 cm
Diameter 2 mm21.0 m/s 4 m
Calcium in argon
Diameter 0.5 mm2 m/s 0.4 m
Diameter 1 mm4.7 m/s 2 m
Diameter 1.6 mm8 m/s 5.6 m
Magnesium in helium
Diameter 0.5 mm4.8 m/s 0.4 m
Diameter 1 mm10.7 m/s 2.2 m
; Diameter 2 mm23 m/s 11 m
Ca 88.5 % + Mg 11.5 % in helium
Diameter 0.5 mm4.5 m/s 0.25m
; Diameter 1 mm10 m/s 1.4 m
Diameter 2 mm22 m/s 7 m
Diameter 2.5 mm28 m/s 1105 m
Aluminium in helium
Diameter 0.5 mm6.6 m/s 0.9 m
Diameter 1 mm15 m/s 4.3 m
As will readily be understood, the invention is
not limited either to the description or to the examples
given in the foregoing or to the accompanying drawings and
any variant within the capacity oE those versed in the art
accordingly forms part of the present invention.
-24-
