Note: Descriptions are shown in the official language in which they were submitted.
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~_-218 SPHEROIDIZATIO~I METHOD AND APPARATUS
DMR: fdc
. . . This invention relates to a method of manuracturing
small spheres and particularly to a method for making metal
spheres of uniform size and shape with a relatively high yield
~actor.
- Rounded metal particles find general commercial utility
in various processes, devices and apparatus. One particular
use for such particles is as a carrier or toner in an
- electrostatographic reproduction device. Spheroidiæation
.techniques for producing rounded metal particles are generally
10 known in the industry. One early technique, known as the
metal spraying method, involves the atomizing of metallic
wires in the presence of a flame by means of a jet of compressed
- . air~ Particle uniformity, production rate and yi~eld from such
a technique left much to be desired. A reflnement of the
.~15 fore~oing techniqua, known as the arc-spraying method, involves
.- . . the simultaneous fusing and atomizing of two conductive,
current carrying wires producing an arc on contact with each
other~ This technique employs a feed mechanism for providing
- .. an infinitely variable continuous feed of both wires às required
as well as a contact means for transmltting current to the
... .wires. Also, suitable a-omizing means is positioned adjacent
the wires for blowing the fused metal particles away from the
contact or.fusing area. The atomizing means conventionally
- takes the orm of a jet of compressed air which serves to remove
.25 the fused metal particles. The removed metal particles are
directed toward a collec~ion device which includes some ~orm
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of collection medium which may also serve a cooling function.
The arc spraylng technique, while improving the yie~d factor
xelative to the flame spraying method, still leaves much to
be desired in terms of yields, particle roundness, and particle
density. An improved version of f:Lame fusion is shown in U.S.
patent ~,269,528 to GallupO Here, a flame fusion method of
manufacturing small metal spheres is disclosed wherein the
flame fused molten metal is caused to fall through space onto a
resilient material, breaking the metal into smaller metallic
particles which are then solidified and cooled. The randomness
of this operation, however, results in a yield factor as well
as roundness and density factors which also leave room for
improvement.
One important factor which has been found to
- 15 affect the effectiveness of a spheroidization process is
; ~ oxidation. By insuring against oxidation of the molten metal,
the ultimate particle will have improved characteristics in
terms of uniformity, roundness and density, thereby
improving the yield factor. In most prior art devices, however,
oxidation is in~erent in the operation of the droplet
- ormation and cooling process. In the aforementioned .
Gallup patent, a non-oxidizing chamber eonveys the particles
- ~rom the flame area to the resilient contact surface. However,
while ~eduction of oxidation during cooling is advantageous
in modifying the extent of oxidation, the particle does
encounter oxygen during its flame formative process. In
addition, the particles in striking the contact surface
suffer in reduction of roundness and-uniformity.
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It is, therefore, an object of an aspect of the
present invention to provide a novel and unique method and
apparatus for manufacturing particles or spheres of acceptable
roundness and density with a yield heretofore higher than that
achieved by prior art processes.
It is an object of an aspect of the present
invention to utilize an arc fusion technique for the manu-
facture of metallic particles which will provide processing
rates higher than heretofore attainable.
It is an object of an aspect of the present invention
to provide a method and apparatus for manufacturing metallic
particles with high yields which substantially reduces or
controls the degree of oxidation.
It is an object of an aspect of the present invention
to utilize an arc spraying technique to form metallic particles
in a continuous or discontinuous process with substantially
reduced oxidation and with yields higher than heretofore
attainable.
It has been discovered that a major cause of
oxidation during particle formation is the presence of oxygen
in the jet of compressed air conventionally employed to
atomize the globules formed at the fusion area. In accordance
with one aspect thereof, the present invention employs method
and apparatus for melting a source of material to form a
successive plurality of molten globules, and directing a flow
of an inert or non-oxidizing compressed gas against the area
of contact, causing the globules to be atomized and propelled
away from the molten area as droplets into a non-oxidizing
cooling chamber, wherein the droplets cool and solidify into
particles.
In preferred form, the inventive concept utilizes
arc-spraying metalizers wherein two metal wires maintained
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at a difference of potential are fed into an arc gun which
positions the wires for contact at a point, such contact
generating intense electrical heat sufficient for fusion to
be produced as a result of the current flow through the
wires at the area of resistance forming t:he point contact,
causing a globule of molten wire to be formed. A jet of non-
oxidizing gas is directed towards the contact junction of the
wires and causes globules released by the fusing contact to
be directed as droplets to a controlled atmosphere chamber
wherein the molten metal droplet takes on a spherical shape,
cools and solidifies. The chamber wherein the heating process
occurs is substantially sealed and filled with inert gas. In
addition, the inner walls of the chamber are provided with a
specific liquid wash curtain preventing metal particles
from sticking to the chamber walls.
In accordance with one aspect of this invention
there is provided a method of manufacturing particles comprising
the steps of meltins a source material in the substantial
absence of o~ygen to form molten globules at a point, said
source material being provided by feeding first and second metal
wires from first and second sources to said point, providing
; sufficient electrical current flow along said wires through
said point to create fusion and cause globules of molten wire
to be formed, said globules being formed from both of said
wires, directing a flow of an inert non-oxidizing compressed
gas toward said point against said globules to atomize globules
into droplets and propel said droplets away from said point
into a chamber where said droplets cool and solidify into
particles.
In accordance with another aspect of this invention
there is provided an apparatus for manufacturing metal
particles comprising a walled chamber, means for feeding at
least a first and second wire to a common point within said
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chamber, a power source coupled to said first and second wires
for providing a current flow through sa:id wires and said
common point, said current flow sufficient to generate heat
at said common point causing said metal to globulize at said
point and form a globule of molten meta:L thereon, a substan-
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tially non-oxidizing gas, means for directing a flow of said
substantially n~n-oxidizing gas from a source of said gas
toward said common point at a rate sufficient to dislodge
and atomize said globule into droplets and envelope said
droplets into a substantially non-oxidiz:ing environment,
said flow propelling said droplets into said chamber, said
atomized globule droplets corresponding to said particles.
In accordance with another aspect of this invention
there is provided an apparatus for manufacturing metal
particles comprising a walled spheroidization chamber and a
walled collection chamber, said spheroidization chamber and
said collection chamber each sealed in an air tight manner, a
plurality of wire sources, means for feeding wire from each
source into said spheroidization chamber, a plurality of wire
guides mounted to said spheroidization chamber, each of
said wire guides positioned with respect to each other for
permitting passage of a wire thexein to a common point
formed by the intersection of said plurality of wires within
said spheroidization chamber, a power supply coupled to said
wire guides for providing a current flow along said plurality
of wires through said common point, said current flow through
said common point sufficient to generate heat causing said
wires to gl.obulize, forming a globule of molten metal at said
-point, a source of inert non-oxidizing compressed gas, means
for directing a flow of said inert gas from said source of
gas into said spheroidization chamber toward said common
point, said flow of gas sufficient to dislodye said globule
and direct the resultant droplet corresponding to one of said
particles along a path toward said collection chamber; said
droplet cooling and solidifying along said path, wash means,
a recycle conduit coupling said wash means to said spheroid-
ization chamber, said wash means forcing a wash liquid through
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said conduit into said spher~.idization chamber in a manner
.
causing said li~uid to coat the inner portion of the spheroid-
ization chamber wall which is lying in said path, and an exit
port positioned in said collection chamber for removing said
particles from said collection chamber.
The foregoing object and brlef description, as well
as further objects, advantages, and features of the present
invention will become more apparent from the following more
detailed description and appended drawings wherein:
Figure 1 is a generalized schematic diagram of the
two wire process; and
Figure 2 illustrates the internal operation of a
spheroidization column.
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Referring to the general process schematic in Figure
1 the spheroidization column 10 is fitted with an arc spheroid-
i~ation assembly 12 which-includes the metallizing gun. The
spheroidization column and more specifically the metallizing
gun is provided with a sequentially fed wire set 14 including
-a first wire 16 and a second wire 18, each being fed from the
wire supply units ~0 and 22 respectively. The wires may be
fed by an electrical drive or an air pressure drive device.
Other drive devices may obviously be employed. The wires
are fed into the assembly area 12 and then down into the
spheroidization column as will be explained in further detail
below. In accordance with the process, a source of an inert
non-oxidizing gas 26 is fed through line 28 by means of a
high pressure supply or the like, not shown/ into the top
~- portion of the arc spheroidization assembly 24. The wire
elements 16 and 18 are energized by leads 32 and 34 derived
from the power supply indicated generally as 36.
` A washing-recycling system indicated generally as 38
is provided with an inlet conduit 40 providing an internal
wash curtain to the interior walls of the spheroidization
column. The wash effluent exits the spheroidization column
~ia conduit 42 into the supply reservoir 43, and is recycled
back into the column by the recycling pump 41 along line 40.
The supply reservoir 43 may include filtration or like quality
replenishment of the liquid. When metallization occurs
inside the spheroidization column, the resultant product
effluent is recovered, either as particles alone or in the
form of a slurry, via the output conduit 44 from the lower
portion of the spheroidization column. The particles thus
provided are discharged into a drying unit 46, and then to a
screening unit 48 which may serve the function of classifying
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particles in accordance with a desired mesh size, and placing
the desired par-ticles in the receptacles 50 and the undesired
particles in the scrap unit 52.
Referring now to Figure 2, the interior of the
spheroidization column is shown in greater detail. As is
evident, the spheroidization process utilizes arc fusion.
The wiresr illustrated again with reference numerals 16 and 18,
are advanced by a suitable feed mechanism not shown. A set of
wire sleeve guides 53 and 54, which are, for purposes of this
illustration, shown as hollow conductors mounted into the
insulating upper surface 56 of the spheroidization column.
Power in the form of a potential difference is applied to the
wires 16 and 18, by a flow of current supplied from the
electrical leads 3? and 34 to the conductive contacting wire
sleeve guides 53 and 54.
An atomi~ing nozzle 30 is mounted into the insulat-
ing upper portion 56 and provides for an adjustable flow of
a non-oxidizing gaseous stream to the point of intersection
of the two wires 16 and 18. As the wires are advanced by the
feed mechanism, they touch at a common point. Due to the
high density of the current and the contact point resistance,
the extreme heat generated results in an arc at the contact
surface and also results in fusion of the contacting areas of
the metal wires. The melted portion thus forms a globulized
portion 58. The inert, non-oxidizing gaseous s-team is pro-
vided at a momentum sufficient to remove and a-tomize the
globulized portion 58 from the contact area in the form of
droplets which correspond to the particles ultimately formed.
Removal of a globule causes the arc to be briefly in-terrupted.
The resulting space is quickly filled by advancing feed
mechanism, and the process repeats. The proper conditions
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for the regular burning of the arc are created by adjusting
the flow rate and pressure of the gas, the voltage and current,
and by regulating the wire feed rate. By way of example, a
typical current value can range in the order of several
I hundred amperes. The angle at which the two wires are fed
; toward each other can also be adjusted for maximum efficiency
of yield.
The plurality of particles thus formed, indicated
generally as 60, fall away from the arc region of the inter-
secting wires 16 and 18 as droplets and down into the collect-
ing pan 62. As they fall, they are cooled and solidify into
spherical ~orm. The collecting pan area serves to cool as
well as collect particles. From the collecting pan, the
particles are forced out along the output conduit 44, either
in the form of a slurry, by an auger feed, gravity, or other
- -- suitable means for removal~ If the conduit is large enough,
the particles could be collected, dried and discharged through
a cooling auger or other suitable device.
To further improve the characteristics of the
~0 spheroid particles thus formed, a wash recycle system 38 is
utilized. Thus, the inlet conduit 40 provides a wash material
curtain mechanism which prevents particulate material 60 from
sticking to the sldes of the spheroidization column. The
inlet 40 provides a stream of wash material, preferably a
liquid, into what is shown as preferably a circular perforated
distributar, ~hich may be formed as a ring 64 mounted high on
the interior portion of the spheroidization column. The ring
64 may include a plurali-ty of ou-tlets 66 which result in
placement of the wash liquid along the interior portion of
the wall of the spheroidization col~n. The ring urlit 64 and
outlets 66 may be positioned or aligned in a manner such tha-t
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the flow o~ liquid emerging from the outlet 66 follc~ws a down-
ward pat-tern about the interior o.~ the wall 6~, flowing down
the inside of the colleeting pan to an exi.t area. The liquid
exits the area by -the exit eondui-t 42 positioned so as to
maintain a desired level of liquid in the eollecting pan 62
and/or spheroidization column 10. As illustrated, the position
of the ring 64 is sueh tnat it assures that a liquid eurtain
e~ists along any portion of the wall which will be, or
possibly may be, struek by particles ejected from the arc
portion of the wire intersection. The general configuration
of the particle discharge from the intersection of the arc
portion will be in the form of an inver-ted cone having slightly
eireular sides. In this manner, the cone portion defines a
perimeter of eontact indicated generally as beginning at the
point 70, the highest point along the interior of the
spheroidization eolumn or collecting pan whieh is possibly
subjeet to being struck by particles 60. sy positioning the
ring 64 above the circumference defined by the perimeter of
eontact, it will be insured that the liquid eurtain will be
on the critical interior wall portion 68 of the spheroidization
eolumn and eolleeting pan 62, thus preventing partieles 60
: from striking and stieking to the interior of the eolumn
wall. The liquid eurtain also serves to reduce -the impaet
forees on partieles striking the interior walls, thereby
improving roundness and thus raising yield.
The liquid may be removed from the chamber in
several ways. For example, an outlet 42 may be provided above
the bottom of the colleeting pan as illustrated in Figure 2.
In this manner, the process may be continuous in the sense
that particles will continue to exit the chamber with some
liquid as a slurry through the outlet 44 and -that the liquid
level seal will be maintained along or above point 45.
As will be evident Erom the descriptions oE Figure 1
and Figure 2, the employment of non-oxidizing environments or
a substantiall~ non-oxidizing environment which forms an
envelope about the particle from the moment of formation of
the particle untilits removal from the collecting pan requires
that the spheroidization column be sealed with a controlled
atmospherej preferably without oxygen. To this end, an
exhaust port, indicated in Figure 1 as element 72, is provided
with a suitable means (not shown) such as a back pressure
valve or the like which will allow release of gases while
maintaining a sufficiently high absolute pressure in the
column resulting from the continuous feeding of the non-
o~idizing gas into the chamber through the nozzle 30. In
this manner, the spheroidization column may continuously be
vented without the fear of backwash resulting in oxidation,
contamination from air or -the like. Further to this end, the
wash recycle system employs a liquid, which is sufficiently
inert and substantially non-oxidizing under the condi.tions of use
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~ithin the spheroidization col~n, such as a pure water, dilute
methanol, alcohol, or other sufficielltly inert liquids. The
~e~p!~rat~re within the collection zone can range from ambient
to as high as the boiling points of the specific li~uids. To
this end, tne port 44 may also include a restxiction valve or
liquid seal such that the differential pressure built up through
the nozzle 30 will prevent backwash of oxidizing atmosphere from
entering the chamber through the port during removal. Alter-
natively, when the removal is discontinuous, the process may be
halted during removal of the particles. - -
The spheroidization column is of sufficient heightand diameter to permit the atomized droplets to assume their
spheroidal shape before striking the collection pan. It has
-been found experimentally that good results are obtained in a
column having a three-foot internal diàmeter and an eight-foot
height. However, it has been found that satisfactory results
- with varying yields may be obtained from a height ranging from
six inches to about twenty feet, and it is estimated that a
- diameter one foot or greater will sufflce.
It is preferred that the column wall be jacketed
with suitable interwall circulation of coolants or the like
to provide cooling for the wash liquid and to provide further
.insurance against sticking.
The factors generally affecting the process yleld
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include, in order of relative importance, the nature of the
gas, the gas flow rate, gas pressure, current flo~, and wire
intersection angles. As noted above,the gas should preferably
be non-oxidizing or at least substantially non-oxidi~ing and
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should be inert with respect to the materials utilized to ~orm
the particles. It has been found that nitrogen is a suitable
gas ~or this purpose, and is preferred.
In a spherodization process, employing steel wire
souxce material, .094 inches in diameter, it has been ~ound
that acceptable results, providin~ yields significantly
higher than obtainable with prior art processes, are achieved
with a gas ~low rate ranging between 70 and 100 cubic feet
per minute, under a pressure ranging between 80 and 120 pounds
per square inch, with a wire intersection angle ranging between
30 and 60 degrees, and an electrical current f~ow of between
300 and 1000 amperes. The wire feed rate may vary between 30
to 180 pounds per hour. A preferred wash liquid employed is a
5~ solution of methanol in water.
15By way of specific example, the spheroidization
column described in Figure 2 was emplo~ed to produce metallic
~ particles.
- - EXAMPLE I
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- -~ The low carbon steel wire was fed at a rate of 32 lbs/
hour under a current of 350 amps provided by a potential of 43
volts and under a gas pressure of 100 psig. The size yield
was 65~ and ~uality rounds 93%. ~ :
EXAMPLE II
The low carbon steel wire ~as fed at a rate of
25 - 46 lbs/hour under a current o~ 525 amps provided by a potential
of 45 volts under a gas pressure of 90 psig. The size
y~eld was 61% and quality rounds 92~.
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EX~MPLE III
The low carbon steel wire was ~ed at a rate o~ 100
lbs/hour under a current of 750 amps provided by a potential of
40 volts under a gas pressure of ~0 psig. The size yield was
71% and quality rounds 92%.
In the foregoing examples, the size yield indiçates
the desired size range achieved compared to total product
produced. Quality rounds, determined by the vibrating table
- method, indicates the minimum sphere number of acceptable
uni~ormi~y. -
- - The particles produced in all three foregoing examples
were found to have a substantially uniform density indicating
both reliability of the process and a low quantity of voids and
oxide contamination. ~n addition, the yield and roundness
15-~ percentages are significantly higher than heretofore achieved
in-prior art processes.
,
The metal particles formed were then employed in a
; ~ skandard xerographic reproduction apparatus. A developer
composition was formed, utilizing ~he metal particles as a core
material, with a pigmented toner of conventional composition.
-
The resultant reproauctions showed high image density andlow background levels, thereby indicating good to excellent
~erographic response. - - : - - -
The particular configuration of the metallizing gun
ha~ing a separate atomizing nozzle is intended as exemplary
- only and is not intended to be limiting. Thus, for example,
a further embodiment may be employed wherein the atomiæing
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68
nozzle surrounds the wire guide sleeves and a pressure is
supplied about the exterior rather than toward the interior
of the wire guides. Alternatively, it may ~e possible to
provide an atomizing nozzle in each of the wire guides and
inject the inert non-oxidizing gas thereby to the intersection
of the wires metallized.
- In addition, magnetic fields may be employed to
contain or stabilize the arcl as by a magnetic pinch effect.
With regard to the gaseous medium employed, although
the preferred embodiment employs a reservoir tank of nitrogen,
- it is also possible to employ argon, helium, carbon dioxide,
or combinations of these or other inert, non-oxidizing gases.
- Heat sufficient to render the wire contact point
molten may be supplied by means of any suitable electrical
power source ~e.g. motor driven DC generator or constant
voltage rectifier, etc.) that provides the potential to cause
current flow.
. . . :,
he two wire gun illustrated may be replaced by
three,~four or more pluralities o~ wire guns. Various com-
posi~ions of wire may also be employed through each sleeveto produce other metallic or pseudo-alloy core materials.
While the invention has been described with
,
-reference to specific preferred embodiments, it will be
~ - apparent to those skilled in the art that various substitutions,
;~ ~ 25~ alternations and modi~ications may be made therein without
departing from the spirit and scope of the invention.
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