Note: Descriptions are shown in the official language in which they were submitted.
J.
~p$$0'~~~
saECxFxcATxoN
METHOD 0f AND APPARATUS FOR PRODUCxNG METAL POWDER
TECHNTCAL FIELD
The present invention relates to a mothod of
and an apparatus for producing metal powdexs by supply-
ing a molten metal to a cooling liquid layer in a
swirling movement.
B7~.CKGk~OUND ART
Rapidly solxdi.f~.ed metal powders are in the
foz~m o~ fine crystal grains and can be adapted to
contain alloy elements to supersaturation. so that the
extrudates and sintered materials prepared from rapidly
solidified powdexs are superior to materials prepared
by melting in characteristics and have attracted
attention as materials for making machine parts)
Tt~.e methods of producing rapidly solidified
metal powders include the rotary dxum method as
disclosed in Examined Japanese Patent fubliGatiori HEZ
1-49769. With this method, a rapidly solidified
metal powdex is prepared by rotating a cooling drum
having a bottom and containing a cooling liquid to
centxifugally form a cooling liquid layer ovex the
inner periphery of the drum, and injecting a molten
metal into the cooling liquid layer to divide tk~e
~~8~~~~
metal by the cooling liquid layer. 3.n a swira.ing motion.
On the other hand, U,S. Patents No. 4,7a7,935
and No. 4,869 g 69 disclose methods and systems fox
producing a metal powder by atomizing a molten metal
stream into spherical molten droplets and supplying
the droplets to a swirling downward flow of cooling gas
within a cooling cylinder fox cooling and solidifica-
Lion.
The rotary drum method .is adapted Eor a
so-called batchwise operation and therefore has the
problem o~ being low in productivity. Furthermore,
the speed of rotation of the cooling drum. which is lim-
ited,poses the probelm in that it is difficult to give
an increased flow velocity to the cooling liquid layer
and to obtain a fine powder.'
On the other hand, the production methods of
the U.S. patents are adapted to continuously prepare a
fins powder of 0.1 micrometer in size to a coarse
powder of. about 1000 micrometers. With these produc-
Lion methods, however, the cooling rate is limited to
about lOZ - 107.oC/see and fails to achieve a suffi-
dent rapid Cooling effect Further because the molten
droplets encounter difficulity in undergoing a swirling
motion in the central portion of the swirling cooling
gas flow and are cooled at a reduced ra.ter there arises
CA 02088054 1998-12-09
3
the problem that the quality of the powder produced is liable to involve
variations.
Additionally, the cooling cylinder needs to have a considerably large size to
form therein a
swirling cooling gas flow which is suitable for cooling the molten droplets.
This poses another
problem in that the methods are difficult to practice readily in view of the
installation space and
equipment cost.
An object of the present invention, which has been accomplished in view of the
above problems, is to provide a method of producing metal powders which is
less likely permit
variations in cooling rate, ensures rapid solidification at a great cooling
rate and readily gives
fine particles, and a production apparatus which is suitable for practicing
this method.
DISCLOSURE OF THE INVENTION
Broadly speaking, the present invention overcomes the problems of the prior
art
by providing a method of producing a metal powder, comprising the steps of:
providing a nonrotating fixed cooling tubular body having an upper end and a
lower end through which cooling liquid is discharged;
injecting a cooling liquid generally tangentially into the nonrotating fixed
cooling
tubular body along an inner peripheral surface thereof with a velocity to form
a cooling liquid
layer moving toward a cooling liquid discharge end of the tubular body while
swirling along
the tubular body inner peripheral surface and leaving a liquid free central
space within the
tubular body;
decreasing downward flow velocity of the injected cooling liquid by providing
the cooling tubular body with a narrower width at a lower portion of the
tubular body than at
an upper portion of the tubular body, the narrower width being provided by (a)
providing a ring
CA 02088054 1998-12-09
4
for adjusting the thickness of the cooling liquid layer extending around the
inner peripheral
surface of the cooling tubular body, (b) providing the ring with an inwardly
extending upper
surface extending inwardly from the inner peripheral surface such that the
cooling liquid is
forced to flow over the ring inwardly away from the inner peripheral surface,
and (c) providing
the ring at a location within said cooling tubular body such that the upper
surface of the ring
is in between the upper end and the lower end such that the cooling liquid is
forced to flow
over the ring prior to being discharged from the lower end;
supplying a molten metal to the space inside the cooling liquid layer;
applying
a gas jet to the molten metal to divide the molten metal and supply the
divided molten metal
to the cooling liquid layer; and
discharging the cooling liquid containing a metal powder solidified in the
liquid
layer from the cooling liquid discharge end of the tubular body to outside.
The invention also provides an apparatus for producing a metal powder,
comprising:
a nonrotating fixed cooling tubular body, the cooling tubular body having an
upper end and a lower end through which cooling liquid is discharged;
a cooling liquid injection channel means for injecting a cooling liquid
generally
tangentially into the tubular body and creating a cooling liquid layer along
an inner peripheral
surface thereof;
the cooling tubular body having a narrower width at a lower portion of the
tubular body than at a level at which the cooling liquid injection channel
means injects the
cooling liquid;
CA 02088054 1998-12-09
molten metal supply means for supplying a molten metal into a space inside the
cooling liquid layer formed by the cooling liquid injected from the injection
channel;
gas jet injection means for producing a gas jet to divide the molten metal and
supply the divided molten metal to the cooling liquid layer;
cooling liquid supply means for supplying the cooling liquid to the cooling
liquid
injection channel;
wherein the narrower width includes a ring for adjusting the thickness of the
cooling liquid layer extending around the inner peripheral surface of the
cooling tubular body,
the ring having an inwardly extending upper surface extending inwardly from
the inner
peripheral surface such that the cooling liquid is forced to flow over the
ring inwardly away
from said inner peripheral surface; and
the ring being located within the cooling tubular body such that the upper
surface
of the ring is in between the upper end and the lower end such that the
cooling liquid is forced
to flow over the ring prior to being discharged from the lower end.
According to the present invention, the cooling liquid injected from the
injection
channel into the tubular body along the inner peripheral surface thereof moves
toward an
opening at the discharge end of the body while swirling along the inner
peripheral surface,
whereby a cooling liquid layer of approximately uniform inside diameter is
formed on the inner
peripheral surface of the tubular body by virtue of the centrifugal force of
the swirling motion.
This layer is formed by the cooling liquid which is newly supplied at all
times, and therefore
readily maintained at a constant temperature. Since the cooling medium is a
liquid, the medium
is superior to gases in cooling ability. For these reasons, the cooling liquid
layer can be small
CA 02088054 1998-12-09
5A
in the radius of swirling motion and in thickness, with the result that the
cooling tubular body
for forming the layer therein can be compact.
The gas jet injected from the injection means and directed toward the cooling
liquid layer is forced against the molten metal supplied from the molten metal
supply means
into the space inside the cooling liquid
to divide the molten metal. The divided molten m~v-t~
(molten droplets) is sputtered toward the cooling liquid
layer, and a11 the droplets are reliably supplied to
and injected into the liquid layer. The molten droplets
injected into the cooling liquid layer produce a vapor
of the cooling liquid therearound, whereas the vapor
is rapidly l:eleased from around the droplets. The
reason is that since the liquid layer has a flow
velocity which increases toward the center of the swirl-
ing motion, i.e., a gradient distrikaution of flow
velocities. the molten droplets injected into the layer
are in rotating motion. Consequently, the molten
droplets have their outer peripheral surfaces always
held in contact with the cooling liquid, are therefore
cooled at a high rate and make particles which are
free of surface contamination with the vaQox. Further
because the size a~ molten droplets to be foam@d by
dividing is adjustable easily by Controlling the flow
velocity of the gas jet and the flow rate thereof,
the deszred rapidly solidified fine powder can be
prepared with ease. Moreover, the cooling liquid layer
remains unchanged and stabilized in temperature and
surf ace condition, permitting the molten droplets to
cool un.dex a definite condition to give a powder of
stabilized quality,.
7
~~~~~<.D~
Since the cooling liquid layez is continuous-
ly formed, the powder can be produced also continuously
by continuously supplying the mo~.t.er~ metal. and
continuously applying the gas jet to the molten metal
to dzvide the metal and supply the divided metal. to
the liquid layer. The metal powder solidified within
the cooling liquid layer is cantinuously discharged
from the liquid discharge end opening of the tubular
body along with the cooling liquid.
It is desired to provide a closure for the
~.~.quid discharge end opening of the tubular body and
to attach a di9charge pipe to the closure so that the
cooling 7.~.c~ui.d containing the metal powder can be
discharged to outside thz'oufh the pipe with the pipe
filled with the cooling 7.~.quid. When the liquid is
discharged in this way, the space inside the cooling
liquid layer can be filled with the jet-forming gas
easily. The molten droplets can be prevented from
os~~.dat~.on by using a suitable nonoxidizi.ng gas, suckz
as inert gas ox reducing gas, as this gas.
aRZ~~ ~~sc~z~Txc~ o~ zHE D~~.wxrrcs
FIG. 1 is a fragmezatary sectional view of a
metal powder production apparatus embodying th,e
invention;
FIG. 2 is a i:ragmentaxy sectional view of
8
2~~~~'~!~
another embodiment of apparatus;
FIG. 3 is a fragmentary sectional view of a
third embodiment of apparatus;
FIG. 4 is a fragmentary sectional. view of a
fourth embodiment of apparatus;
FzG. 5 is a sectional diagram illustrating a
molten metal continuous feeder;
fIG. 6 is an overall layout of metal powder
continuous production equipment;
FIG. 7 is a fragmentary sectional view of a
metal powder production apparatus used in a preparation
example of the invention;
FIG. 8 is a diagram showing the relation in
position between a thin. stream of molten metal and a
gas bet used in the preparation ea~ample and as seen
from above;
FIG. 9 is a graph showing the particle size
distribution of metal powders prepared in the example
and a comparative preparation erample; and
FIG. 10 is a graph showing the relation
between the cooling rate and the particle size of metal
powder prepared in another preparation example of the
invention.
SEST MODE Of CAR~XZNG OUT THE INVENTION
FzG. 7. shows a metal powder production
r
2~~~~~~
apparatus embodying the present invention. The
apparatus comprises a cooling tubular body 1 having an
inner peripheral surface for forming a cooling liquid
layer 9 thereon, a crucible 15 serving as means for
supplying a molten motal 25 in the form of a thin down-
ward stream to a space 23 inside the cooling liquid
layer 9, a pump 7 serving as means for supplying a
cooling liquid to the tubular body 1, and a jet nozzle
24 serving as gas jet injection means far injecting a
gas bet 26 for dividing the downward stream of molten
metal 25 into molten droplets and supplying the droplets
to the cooling liquid layer 9.
The tubular body 1 is hollow cylindrical, is
installed with its axis positioned vertically and has
an upper~end opening provided with an annular closure
2. The closure 2 is centrally formed With an opening
3 for supplying the molten metal to the interior of the
cooling tubular body 1 therethrough. The cooling body
1 is formed at an upper portion thereof. with a plural-
Z0 ity of cooling liquid injection tubes 4 having a
cooling liquid injection ehannel 5 and arranged at
equal spacings circumferentially of the body. The
channel 5 has an outlet (discharge outlet) which is
so opened as to inject the cooling liquid into the
ZS tubular body 1 along the inner peripheral sur~aee
10
~08~0~~
tangentially thereof. The center line of the opening
portion of the channel 5 extends obliquely downward at
an angle of about 0 to about 20~ with re9pect to a plane
orthogonal to the a:cis of the tubular body, Th2 liqu~.d
infection tubes 4 are connected by piping to a tank 8
by way of a pump 7, which forces up the cooling liquid
within the tank 8 and supplies the liquid to the inner
peripheral surface of the tubular body 1 through the
injection channels S of the injection tubes 4. Thus
the cooling liquid layer 9 is formed on the inner
peripheral surface of the tubular body 1. This layer
flows down while swirling along the inner peripheral
surface. The tank 8 is provided with an unillustrated
a cooling liquid replenishing pipe, A oooler may be
provided suitably within the tank 8 or at an inter-
mediate portion of a channel for recycling the cooling
liquid. Water is generally used as the cooling liquid
since water is excellent in cooling ability and in~
expansive. Alternatively, oil ox like liquid for use
in quenching hot metals may be used. When water is to
be used, it is desired to remove dissolved oxygen
from the water before use. Oxygen removing devices are
readily available commercially.
A ring 10 for adjusting the thickness of the
cooling liquid layer 9 is attached to an inner peri-
11 ~0~80~4
pheral lower portion o~ the cooling tubular body 1
with bolts removably and replaceably. The thickness
adjusting ring 10 limits the downward flow veloc~.ty
of the cooling liquid, whereby, the cooling liquid layer
9 can be readily formed with an approximately uniform
inside diameter at a low fJ.ow rate. The tubular body
1 has a cooling liquid discharge end, i.e., a lower-
end opening, which is provided with a hollow cylindrical
draining net 11. A funnel-shaped powder collecting
container 12 is attached to the lower end of the net 11.
A cooling liquid collecting cover 13 is provided around
and covers the net. 11. 'the collecting cover 13 is
provided in its bottom with a liquid outlet 1~, which
is connected to the tank 8 by piping.
The crucible 15 serving as fi.he molten metal
supply means and disposed above the cooling tubuJ.ar body
1 is made of graphite, silicon nitride ox ~.~.ke refrac-
tory and comprises a hollow cylindrical cz~ucible bodx
16 having a bottom 19, and a clousre 17 fare closing an
opening at the upper end of the body 16. The crucible
body 1,6 i.s provided with a heating induction coil 18
thexearound.and has a nozzle orifice 20 extending
veartically through the bottom 19. The nozzle ox~.fice
20 is opposed to the opening 3 of the annular closure
2a 2. The closure 17 of the crucible 15 has a bore 21 for
12
20880e
injecting a pressure medium such as Ar, ~2 or. like
inert gas and molten metal sent foxward into the
crucible therethrough. The molten metal 22 within the
crucible 15 is forced through the nozzle orifice 20
and then through the opening 3 into 'the space 23
inside the cooling liquid laxer 9 by the inert gas or
the like injected into the crucible through the injec -
tion bore 21 undex pressure.
Disposed in the space 23 inside the cooling
ZO liguid layer 9 is a jet nozzle 24 for jetting a
compressed gas, such as aix or inert gas, which is
used in the usual gas atomization pzocess. The nozzle
Z4 is attached to the forward end of a compressed gas
supply pipe 27 inserted thxough the opening 3 of the
annular closure 2 and has an ori~iae which is directed
toward the thin stream of molten metal 25 forced out
from the nozzle orifice 20 and toward the cooling liquid
layer 9.
While the outlets of the cooling liquid
injection channels 5 are formed in the side surface
of an upper portion of the cooling tubulax bady 1 as
illustrated, th.e distance of the outlets from the
thickness adjusting ring 10, if large, results in the
likelihood that the liquid layer 9 will have a reduced
thickness at its midportion when the cooling liquid
13 2~D~80~~
flows down at an increased velocity. It is thexe~oxe
desirable that the outlets o~ the injection channels
be positioned between, the upper face of the adjusting
ring 10 and the midportion between the upper end of
5 the tubular body 1 and the upper face of the ring 10.
Even when the outlets are so pos~.tiot7ed, the cooling
liquid is pentrifugally forced upward above the outlets,
forming the same liquid layer of definite thickness as
below the outlets.
The apparatus described operates in the
following manriex to produce a metal powder. First,
the pump 7 is operated to form a pooling liquid layer
9 on the. inner pex~.phera~. surface of the tubular body 1.
Next, the molten metal 22 within the crucible 15 is
forced out dawnward thx~augh the nozzle oxific~ ~0, with
a gas jetted from the jet nozzle z4 at a high speed
as indicated at 26: The gas jet ~6 from the jet nozzle
24 is applied to the molten metal 25 :~ozced out from
the crucible 15 in the form o~ a thin stream, dividing
the molten metal 25 and sputtering the resulting molten
droplets against the cooling liquid layer ~. The
molten droQlets thus sputtered are xz~jected into the
cooling liquid layer 9 which flows down while swirling
and are rapidly cooled and solidified into metal
particles. In this case, the shage of the particles
~08~Oi~
can be altered from spherx.cal to flat indefinite forms
by suztably determining the distance from the location
where the gas bet 26 collide with the molten metal. 2S
to the cooling liquid layer 9. Fax example, i~ the
S distance to the liquid layer 9 is small, the molten
droplets divided by the gas jet 26 are injected into
the liquid layer ~ before a soldi~ied shell. is formed
over the surface, and are divided by the liquid layer
9 again to form fine particles o~ inde,firlite shape.
l~ conversely, if the distance is sufficiently large, the
sol~.di~ied shell is formed over the surfaces of the
molten droplets, permitting the droplets to remain
substantially spherical when injected into the cooling
l9.quid, layer 9.
15 The metal powder in the cooling l.~.quid layer
then flows down over the thickness adjusting zing 10
while swirling with the cooling liquid and enters the
draining net 11 from the Lower-end opening o~ the
Cooling tubular body 1. The cooling liquid in the net
20 is cezatri~ugally forced radially outward from the net
11, whereby the metal powder has its liqua.d content
reduced by primary drain~.zxg. The me~.aJ. powder thus
drained of the liquid enters the powder collecting
cQnt.ainer 12. The powder is discharged from the coz~-
25 tainer, futhex drained of the liquid by a centrifuge
20880e
or like liquid removing device and dried by a dryer.
The cooling liquid forced our from the net 11 is
returned from the collecting cover 13 to the tank 8
and recylced ~or use.
FIG. 2 shows another metal powder production
apparatus embodying the invention. Throughout FzGS. 1
and 2, like parts are designated by like reference
numerals.
This embodiment hag a cooling tubular body 1
which is installed with its axis inclined, and a cooling
liquid injection channel 5 formed directly in the
tubular body 1 which has a large wall thickness. The
channel 5 has an inlet formed in the outer peripheral
surface of the tubular body 1 and connected to a pump
7 by, piping. The bodx 1 has a lower-end opening
which is provided with a funnel-shaped closuxe 31 fox
closing the opening. The closure has a discharge pipe
33 attached to its bottom. The interior of the pipe
serves as a discharge channel 32 for a cooling liquid.
~ thickness adjusting ring 10 having a tapered upper
faoe is attached with bolts to the inner pe~~z.phery of
a lower portion of the tubular body 1, The discharge
pipe 33 so extends that an outer-end opening (outlet)
thereof is positioned above a tank 8, anti is provided
with a flow regulating valve 3~ at an a.z~texmedxate
20~8fl~~
1G
portion thereof. The tank 8 has an upper opening
cohich is removably provided with a net basket 35.
With the present embodiment) the cooling
liquid can be discharged with the discharge channel
32 filled with the lic~ui.d by suitably adjusting the
opened position of 'the flaw regulating valve? 34. This
makes it possible to prevent gas from flowing out
through the discharge pipe,33 and to fill the space 23
inside the cooling liquid layer' 9 with the gas of gas
jet 76 from a jet nozzle 24. Accordingly, 'the oxidation
of divided molten droplets Can be prevented effectively
by using an inert gas or like nonoxidizing gas.
FIG. 3 shows a third embodiment o~ metal
powder production apparatus, wherein a cooling tubu~.ar
body 1 is formed in its inner peripheral surface With
outlets of cooling liquid injection Channels 5 as
arranged in a plurality of (two) stages. The number of
stages of injection channels 5 and the spacing there-
between with respect to the axial dizectian of the
tubular body differ in accordance with the inside
d~.a~tteter of the tubular body, rate of discharge of
the coali.ng liquid, pressure of injection, position
of lower thicl~ness adjusting ring 10, et.c. A suitable
number o~ stages may be provided as approximately
equidistantlx spaced apart so as to obtain a cooling
l~ ~L~38'~~~~
liquid layer of substantially unifarm in side diameter.
The present embodiment has a plurality of stages of
cooling l.i.quid injection channels S above the thickness
adjusting ring 10. This arrangement serves to prevent
the liquid layer 9 above the r~.ng 10 from decreasing in
thickness owing to an increase in the downward flow
velocity of the cooling liquid. The liquid layer 9
can therefore be foamed easily with a substantially
uniform inside diameter and a constant swirling
velocity over 3n elongated region on the inner peri-
Qheral Surface of the tubular body l, hence an elongated
cooling zone. As seen in the drawing, the thickness
adjust~.n.g zing may be provided between the stages of
injection Channels 5 adjacent to each other ayially
of the tubular body as indicated at 10A, whereby the
thickness and flow velocity of the layer 9 can be mare
stabilized. I3owever, the codling liquid injection
chan.z~e1 5 provided in a single stage in combination.
wit~Z a plurality of thickness adjusting rings is also
effective for preventing the decrease in the thickness
of the layer 9.
With, the third embodiment of FZG. 3, a buffer
flange 28 is xemovably attached to the znner periphery
of the net 11 as by bolts. The flange Z6 reduces the
do~az~ward flow velocity of the Coo~.ing liquid ~ta ensure
18
2088~~~
drainage for a longer period of time far effective
centrifugal removal o~ the liquid.
FIG. 4 shows a fourth embodiment o~ metal
powder production apparatus, which has a cooling tubular
body 1 installed with irs axis inclined, and two jet
nozzles 24, 24 attached to compressed gas supply pipes
27, 27 for producing gas jets Z6 intersecting each
other in a v-form in a space 23 inside a cooling liquid
layer 9 on the inner peripheral surface o~ the body.
Each of the jet nozzles 24, 24 has an orifice which
is in the form of a slit, and the gas jet 26 is in the
foam oz a film having a given width. The intersecting
gas jets are v-shaped in section as illustrated in the
drawing. A molten metal 25 flows out from a nozzle
orifice 20 of a crucible 15 downward to the region
where the V-shaped gas jets intersectoand is thereby
divided. The V-shaped gas jets effectively divide
the molten metal, forcing the divided molten droplets
~rom the region of inter3ection into the._.innex periphery
of the cooling liquid layer 9 over a specified area
fox the injection of the droplets even if the molten
metal 25 flows down as somewhat deflected. Incidental-
ly, a jet nozzle may be used which has a nozzle orifice
in the form of an inverted conical slit for forming
a gas jet defining an inverted conical face, such that
1~ ~0880~~
the molten metal. is supplied to the vertex of the
jet. Alternative).y, a plurality of jet nozzles each
adapted to produce a lirieaz~ gas jet may, be arranged in
an inverted conical form to provide an inverted conical
assembly o~ linear gas jets for the molten metal to be
supplied to the vertex of the assembly.
With the third and Fourth embodiments, the
cooling tubular body 1 is Q.r4vided at its lower-end
opening with a draining net 11, through which the gas
forming the jet or jets 26 flows out. However, the
lower-end opening znay be provided with the closure 31
shown in k'TG. 2 and having the discharge pipe 33. The
space 23 inside the cooling lic~u~.d layer 9 cart then be
readily filled with the jet-forming gas bx contr'olling
1S the flow regulating valve 34 mounted on an intermediate
portion of the discharge pipe 33.
With the Foregoing embodiments, the cooling
tubulat body 1 is in the form of a hollow cylindez, Y~ut
is not limited to this shape. The body may, be so shaped
as to have a rotationally symmetrio inner peripheral
surface the diameter of which gradually decreases
toward the direction of movement of the cooling lic~u~.d.
~'or example, the body may be in the form of a funnel.
In the case where the body is trumpet~shaped with a
paxaboloid of revolution, a cooling liquid layer of
r
' 20
~Q~~~~4
uniform inside diameter can be formed even i~ no
thickness adjusting ring is used. Further with the
illustrated embodiments, the coolzng tubular body is
installed with its aril positioned vertically or
obliquely, whereas this position is not limitative.
The axis of the tubular body may be in any position
insofar as doling water can be injected into the body
at a sufficient rate so as to form a coo ing liquid
layer 9 on the tubular body inner peripheral surface.
Further in the case of the illustrgted
embodiments, the thickness adjusting ring 10 has a
horizontal or tapered upper face, which nevertheless
is not limitative, For example, the ring may have a
streamlined curved face extending from the outer
peripheral edge of its upper end toward the inner
peripheral edge of its lower end with a gradually
decreasing diameter. Although the moltem metal 22 in
the crucible 15 is forced out through the nozzle ori~iGe
under the pressure exerted by a pressure medium,
20 the metal 22 may be forced out (caused to flow out)
from the nozzle orifice 20 under gravity acting on
itself without using the pressure medium.
The powders to be produced according td the
invention axe not limited to those of metals having a
low melting point, such as aluminum and alloxs thereof,
zl 20~8~~~~
but include those o,f metals having a high melting
point, such as titanium, nickel, iron and alloys there-
of, Thus the metals to be treated are not limited
specifically.
FIGS. 5 and 6 show the overall construction
of an examp~.e of metal powder continuous production
equipznewt which includes the metal powder production
apparatus already described with reference to FZG. ~.
as the first embodiment and which is adapted to
ZO carry out d sequence of operations from th.e supply of
molten metal. through the production of metal powder,
removal. of the liquid anal drying . With. this equipment,
the molten metal. supplied From a molten mcta7. cont~.nuous
feeder 41 is treated bx the metal powder psoduct:ion
1S apparatus 42 already described, 3 continuous liquid
removing device 43 and a continuous drxex' 44 and made
into a metal. powder product. one of the other embodi-
m@nts is of course usable as the metal powder produc-
tiara apparatus.
20 The cnoltea metal continuous feeder ~l
comprises a container 46 made of a heatTinsulating
refractory material. The conts,iner 46 has a molten
rttetaZ inlet 48 closable witkz a closure 47, a pipe 49
for supplying an inert gas gar like pressure medium, a
25 discharge pipe SO for molten metal 53 within tlxe
zz ~~c~c~QS~
container, and a bottom cavity 52 provided with an
induction heating coil 51. The molten metal 53 in the
contaJ.nex 46 has its temperature controlled by the
coil 51 and is fed to the crucible 15 of the apparatus
42 t.hxough the discharge pipo 50 under the pxes5uxe of
the inert gas, such as argon gas, injected through the
supply pipe 4.9. The di.schargo pipe 50 is heat-
insulated by suitable means such as a heat-insulating
layer or induction heater.
The metal powder produced by the apparatus 42
is fed to the continuous liquid removing device 43 by,
way of the powder collecting container 12 along with
the cooling liquid xe~naining after the primary draining
by the draining net. 11, and is centrifugally acted on
and thereby separated from the liquid. The continuous
liquid removing device 43 aompx~.ses a rotary drum 55
~lax'7.ng upward and having, an intermediafi.e pex'ipheral
wall which is formed by a scxeez~ plate with a multipli-
city of small holes. The drum 55 has a mult.~.pl~.pi.ty
of projecting ribs 56 on its inner periphery for upwardly
delivering the powder separated from the liquid. The
rotary drum 55 is surrounded by a cooling liquid
co~.l~cting cover 57, ~xom the bottom of which the
cooling liquid separated o~f is collected ~.n. the tams 8.
Provided over the drum 55 is a metal powder collecting
z3
cover 5$ having a discharge chute S9.
~~88~~~
The wet metal powder delivered ~rom the
discharge chute 59 of the device 43 is subsequently fed
to the continuous dryer 44. The dryer 44 comprises a.
drying container 62 having a porous membrane 61 with a
multiplicity of p4res, feed means G3 having a rotary
feeder for supplying the wet material to an upper
portion of the container 62) a hot air producing device
64 for supplying hot air from the bottom o~ the
container 62, and a cyclone 65 for collecting fine
particles from the air discharged from the top of the
container 62. A discharge pipe 66 is attached to the
side wall of the container 62 at its upper to lower
portions.
A fluidiaed layer 67 is formed inside the
drying container 67. Tk~e wet metal powder is vigorous-
1.y mixed with the hot air within the layer 67 ~or heat
exchange, rapidly dried and discharged usually in the
~oxm. of an overflow from the container through the
discharge pipe 66.
The molten metal continuous feeder. continu-
ous liquid removing dcwice and cont~.nuous dryer for use
in practicing the present inveri.tion are not limited
to those described above, l~ut. suitable devices
z5 commercially available are usable.
24
2~~$~~~.~
Metal powder preparation examples will be
described below in detail.
Preparation Example 1
The production apparatus shown in ~'IG. 7 was
used ~o~: preparing an aluminum alloy powder. 2'he
cooling tubular bodx 1 shown was l00 mm in inside
diameter D. The cooling liquid injection channel 5
had outlets positioned at the midpoint between the
upper and of the body ~, and the upper end of the thick-
ness adjusting ring 10. Cooling water was injected
into the body at a flow rate o~ 0.3 m3/min frvm the
channel outlets which were 11.5 mm in diameter'.
Consequently formed above the xi.~xg 10 was a cooling
liquid layer 9 which was 55 mm tin inside diameter d,
50 mm in length h and 43 m/sec in ~low velocitx at the
surface o~ tk~e water layer.
1~ molten aluminum alloy (composition: l~l-
7.2 Si~1 Mg-1 Cu, in wt. ~) was prepared in the crucible
15 at 1O00~ C. The molten metal ~2 in the crucible 15
was pressurized by, supplxing argon gas thereto at
1.4 kgf/cm2, and a thin stream of molten metal 25. 2
mm in diameter, was injected from the nozzle orifice
20 0~ trie crucible 15 into a space Z3 inside the liguid
layer 9. The stream of molten metal, 25 made an
2S injection angle 91 of 30 deg with a horizontal plane.
208~~~~~
An air jet 26 was ~orced out at S kgf/cmZ
from the jGt nozzle 24 with a nozzle orifice diameter
of 6 mm against the molten metal 25 in the space 2~,
at an angle 6~ of 4S deg between the jet 2G and a
horizontal plane. When seen ~zom above as shown in
FzG. 8, the angle 9~ made by the jet 26 w~.tk~ the thin
stream of molten metal 25 was 45 deg as measured from
the molten metal 25 in the swixling direction A of
the cooling liquid layer.
The aluminum alloy powder consequently
obtained had a paxt.icle sine distribution (relation
between the particle size of particular particles
in the powder arid tk~e oontent in wt. ~ of t~.e particles
of the size based on the whole amount of the powder)
iz~d~.eated at A in FIG. 9. The powder was 291.8 micro-
meters in mean particle size and 0,90 g/cm3 in bulk
density. The particles were found to be ~lat and
indefinite in shape. This appears to indicate that
the molten droplets divided by, the air jet were
divided again by the cooling liquid laxer.
Fox comparison, an aluminum alloy powder
was prepared undex the same conditions as above except
that no air jet was applied to the molten metal. The
result achieved is shown also in FzG. 9 as indicated
at a. T'he powdex was 4Z0 micsometexs a.n mean particle
z6 ~~880~~
size and 0.70 g/cm3 ire bulk density. '~h.is reveals
that the application o~ the six jet according to the
invention readily produces Finer particles.
Preparation example 2
An aluminum alloy powder having the same
compositian as in Pregaratian Example 1 was prepared
using the apparatus shown in FzG, 2. The cooling
tubular body 1 ws.s 200 mm in inside diameter, and the
axis of the body ~.~as inc:lined at an angle of 25 deg
with respect to a vert~.cal. The cooling liquid injec
tion channel 5 had outlets which were 11.5 mm in
diameter and through which cooling water was injected,
into the body at a flow rate of 0.3 m3/min. As a
result, a cooling liquid layer 9, Z50 mm in inside
diameter. 300 mm in length and 20 m/sec in average flow
e2loc~.ty, was formed between the annular closure 2 and
the Ch zckness adjusting z~~.ng 10. The flow regulating
valve 3~ was adjusted to fill the discharge channel 32
wz'th the cooling' liquids
A molten aluminum allay was p~e,pared at
1000o C in the crucible 15) and the molten metal 22
within the crucible was forced out in the foxzn of a .
thin stream of molten metal 25, 2 min in dzatrzeter, from
the nozzle orifice 20 of the crucible 15 vextica.lly
downward into a space 23 inside the lic~~.d layer 9
, z7 ~~1~~~~~~
by supplying argon gas to the crucible 15 at 1.0 kgf/cm2.
An argon gas jet 26 was applied at 10 kgf/cm2
from the jet nozzle 24 with a nozzle orifice diameter
of 6 mm to the molten metal 25 in the space 23, whexeby
S the molten metal 25 w'as made into particles. 7.'he
angle made by the argon gas jet 26 with the molten
metal 29 was 30 deg,
The powder obtained was Z00 micrometers in
mean particle size and 1.3 g/cm3 in bulk density.
FzG. 10 shows the reJ.a~.ion between the particle size
and the cooling rate. The coolzng rate was determined
from the metal structure of particles o.f the powder.
T.he draw~.ng shows that in the case of the metal powder
prepared according to the invention, the cooling rate
is J.04 to 105 oC/sec even when relatively laz'ge
partlGlea, 100 to l000 micrometers in size, are formed.
This ir~d~.cates that the invention affords a micro;~i,ne
structure. The drawing appears to indicate that the
cooling rate for giving particles of 0.1 micrometer i.n
size is at least l08 oC/sec.
Next, the powder was checked for gas contents,
which were found to be 12 ppm of HZ and 50Q ppm o~ 02.
k'ox comparison, an aluminum alloy powder was prepared
under the same conditions as above except that the
flow regulat~.ng valve 34 was fuller opened so as not to
2~ 2~88~J~~
close the discharge pipe 3a with the cooling water.
The resulting powder was found to Contain 20 ppm of H2
arid 820 ppm of Oz. Th~.s indicates that the product
of the irivet~tion is much lower in gas contents than
the comparative example.
Preparation Fxacn~le 3
~1n iron alloy powder was prepared undex the
same conditions as in Preparation Example 2. The iron
alloy had the composition of Fe-1.3 C-4 Cr-3.S Mo-10 W-
3.5 V-10 Co as expressed in wt. &, and was melted at
1G00~ C.
The powder obta~.ned was 250 micrometezs ~.n
mean particle si.~e. When checked for gas Contents, the
powder was Eound to contain 9 ppm o~ H2, 580 ppm of 02
and 720 ppm of N2. When an ,iron alloy powdar of the
same composition as above was prepared undez' the same
conditions as above except that the average Flow
velocity of the cooling liquid layer was S m/sec, the
powdez was found to contain L5 ppm of Hz, l200 p.pm of
OZ and 740 ppm of NZ. Th~.s ,reveals that as the flow
velocitx of the cooling liquid layer is increased, the
moJ.ten dzoplets can be mare rap~.dly separated ~r
released from the vapor of the cooling l;i.quid produced
the7Ceaxound So as to be ErBe from Contaminants more
effectively.
~~ 20880e
xNnvsTRxa.~ Anpz.zcaszz,zTx
The present invention is useful fox the
production o.~ metal gowdexs fox use as powdery ma.teri,als
fox powder metallurgy, hat isostatic pressing, hot
forging, hot ertrusion, etc., as compounding powders
for synthetic resins, xubbers, metals, etc. and as
magnetic powders for electromagnetic clutches or brakes.
