U.S. patent application number 09/237267 was filed with the patent office on 2001-11-08 for apparatus for the production of metal ribbons and method therefor.
Invention is credited to GANZA, NIKOLAI ALEKSEYEVICH, HODYREV, BORIS AFANASYEVICH, IIJENKO, EVGENY VLADIMIROVICH, LOSITSKIY, ANATOLY FRANTSEVICH, LYBNIN, VIKTOR ARKADYEVICH, MJASNIKOV, VITALY VASILYEVICH, OVSHINSKY, STANFORD R., RODCHENKOV, NIKOLAI VASILYEVICH, YOUNG, ROSA.
Application Number | 20010037871 09/237267 |
Document ID | / |
Family ID | 20209761 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010037871 |
Kind Code |
A1 |
GANZA, NIKOLAI ALEKSEYEVICH ;
et al. |
November 8, 2001 |
APPARATUS FOR THE PRODUCTION OF METAL RIBBONS AND METHOD
THEREFOR
Abstract
Apparatus and method for continuous melt spin casting of
homogenous materials, including metals, alloys, and non metals. The
material to be cast is provided to a crucible and liquefied. The
melt is filtered prior to casting to provide a melt with a high
degree of purity. The material temperature is maintained throughout
the process to form a solidified product with excellent
homogeneity.
Inventors: |
GANZA, NIKOLAI ALEKSEYEVICH;
(GLAZOV, RU) ; IIJENKO, EVGENY VLADIMIROVICH;
(GLAZOV, RU) ; LOSITSKIY, ANATOLY FRANTSEVICH;
(GLAZOV, RU) ; LYBNIN, VIKTOR ARKADYEVICH;
(GLAZOV, RU) ; MJASNIKOV, VITALY VASILYEVICH;
(MOSCOW, RU) ; RODCHENKOV, NIKOLAI VASILYEVICH;
(GLAZOV, RU) ; HODYREV, BORIS AFANASYEVICH;
(GLAZOV, RU) ; OVSHINSKY, STANFORD R.; (BLOOMFIELD
HILLS, MI) ; YOUNG, ROSA; (TROY, MI) |
Correspondence
Address: |
ENERGY CONVERSION DEVICES INC
1675 WEST MAPLE ROAD
TROY
MI
48084
|
Family ID: |
20209761 |
Appl. No.: |
09/237267 |
Filed: |
January 25, 1999 |
Current U.S.
Class: |
164/452 |
Current CPC
Class: |
B22F 2009/0888 20130101;
B22F 9/10 20130101 |
Class at
Publication: |
164/452 |
International
Class: |
B22D 011/16 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 18, 1998 |
RU |
98115863 |
Claims
What is claimed is:
1. Apparatus for continuous melt spin casting of materials,
comprising: a chamber; a supply crucible and a casting crucible
disposed within said chamber, said supply crucible for supplying
molten material to said casting crucible, said casting crucible for
ejecting at least two streams of molten material for
solidification, each stream being ejected through an orifice in
said casting crucible; monitoring means for determining the level
of molten material in said casting crucible; a selectively actuated
flow control valve for controlling the flow of molten material from
said supply crucible to said casting crucible to maintain the level
of molten material in said casting crucible within a range; valve
control means for actuating said flow control valve as a function
of material level in said casting crucible as sensed by said
monitoring means; means for filtering the molten material prior to
casting; thermal control means for controlling the temperature of
material within said casting crucible; and a chill wheel disposed
within said chamber for the solidification of streams of molten
material ejected through said orifices, each of said orifice being
at an equal distance from a contact point on said wheel, whereby
equal length streams of material at a uniform temperature and flow
rate are rapidly solidified to form homogenous ribbons of
material.
2. Apparatus for continuous melt spin casting of materials
according to claim 1, further comprising a loading vessel to supply
the casting crucible with material.
3. Apparatus for continuous melt spin casting of materials
according to claim 1, wherein said means for filtering is a ceramic
filter element.
4. Apparatus for continuous melt spin casting of materials
according to claim 1, further comprising means for removing
accumulated material from an external surface of said orifices.
5. Apparatus for continuous melt spin casting of materials
according to claim 4, wherein said means for removing material is
said chill wheel.
6. A method for continuous melt spin casting of materials;,
comprising the steps of: providing a chamber; providing a material
supply crucible and a casting crucible disposed within a chamber,
the material supply crucible for receiving molten material to be
supplied to the casting crucible, the casting crucible having at
least two orifices therein; monitoring the level of molten material
in the casting crucible; controllably releasing molten material
from the supply crucible through a flow control valve; filtering
the molten material released from the material supply crucible
prior to crystallizing; maintaining the molten material level in
the casting crucible, whereby the molten material flow rate through
the orifices is controlled by the static pressure of the molten
material in the casting crucible, whereby a constant material flow
rate is achieved; controlling the temperature of the molten
material in the casting crucible to provide material for casting at
a consistent temperature; ejecting at least two streams of molten
material from the casting crucible, each stream ejected through one
of the orifices in the casting crucible, each orifice being
equidistant from an associated contact point on a chill wheel, each
stream having an equal length and diameter; and rapidly solidifying
the molten material by ejecting the streams of molten material upon
the chill wheel, whereby the streams of molten material having a
consistent temperature, flow rate and diameter are quenched to form
materials having homogenous properties.
7. The method according to claim 6, wherein the molten material is
filtered through a ceramic filter element.
8. The method according to claim 6, wherein each orifice in the
casting crucible is in communication with a nozzle.
9. The method according to claim 6, further including the step of
removing accumulated material deposits from the orifices in the
casting crucible.
10. The method according to claim 9, wherein the accumulated
material deposits are removed by the chill wheel.
11. The method according to claim 6, further including the step of
providing a loading vessel to supply the casting crucible with
material.
12. The method according to claim 6, further including the step of
controlling the temperature of the molten material in the supply
crucible.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method and apparatus for
melt spin casting of materials, and more specifically, a
continuous, economical method and apparatus for melt spin casting
of homogenous materials.
BACKGROUND OF THE INVENTION
[0002] A number of techniques are known for the production of
homogeneous materials. In the field of producing powdered
materials, for example those materials used as electrode material
for rechargeable electrochemical cells, property requirements
include size, homogenous chemistry, and homogenous crystalline
structure. In the field of battery production, a hydrogen storage
alloy is commonly formed as a bulk ingot from a melt. One method of
producing a hydrogen storage alloy is disclosed in commonly
assigned U.S. Pat. No. 4,948,423 to Fetcenko, Sumner, and LaRocca
for ALLOY PREPARATION OF HYDROGEN STORAGE MATERIALS, incorporated
herein by reference. However, an inherent concern with
manufacturing materials as an ingot where homogenous material
properties are required is the rate of change of cooling through
the ingot. As the ingot solidifies, the cooling rate of the
interior material is much less than that of the exterior, resulting
in a variation of the material crystalline structure.
[0003] Hydrogen storage negative electrodes utilizing the
aforementioned alloys are of relatively high hardness. Indeed,
these alloys can typically exhibit Rockwell "C" ("Rc") hardness of
45 to 60 or more. Moreover, in order to attain the high surface
areas per unit volume and per unit mass necessary for high capacity
electrochemical performance, the alloy must be in the form of fine
particles. In a preferred exemplification, the hydrogen storage
alloy powder must pass through a 200 U.S. mesh screen, thus being
smaller than 75 microns in size (200 U.S. mesh screen has
interstices of about 75 microns). Therefore, the resulting hydrogen
storage alloy material is comminuted, e.g., crushed, ground, milled
or the like, before the hydrogen storage material is fabricated
into electrode form.
[0004] Comminution of bulk ingots of hydrogen storage alloy
material is made more difficult because the materials described
hereinabove are quite hard, and therefore do not easily fracture
into particles of uniform size and shape. In commonly assigned U.S.
Pat. No. 4,893,756 to Fetcenko, Kaatz, Sumner, and LaRocca for
HYDRIDE REACTOR APPARATUS FOR HYDROGEN COMMINUTION OF METAL HYDRIDE
HYDROGEN STORAGE MATERIAL, the disclosure of which is incorporated
herein by reference, a hydride-dehydride cycle comminution process
was disclosed for initial size reduction of bulk ingots of hydrogen
storage alloy material to flakes of about 80-100 mesh size. While
this process is effective for the initial size reduction of
hydrogen storage alloy, it is inadequate for the task of further
comminuting particulate hydrogen storage alloy powder to the
required particle size of 75 microns or less (i.e. 200 mesh or
less). Furthermore, the process begins an ingot which by default,
is subject to the inherent thermal limitations of materials
produced in ingot form as described above. Still another concern
with initiating a powder formation process with material in the
form of an ingot is the size of the ingot with respect to the final
size of the powder material. Initiating a powder formation process
with a large piece of material in order to form a powder is hardly
efficient.
[0005] Any method which can accomplish the objective of providing
economical size reduction of the metal hydride material is a
potential candidate for commercial processing. However, there are
numerous characteristics of the material which require special
handling, instrumentation and other precautions. These
characteristics include: (1) inherent alloy powder hardness, i.e.,
approximately Rockwell "C" ("Rc") 60 hardness. This means that
conventional size reduction processes of shear, abrasion and some
types of impact mechanisms as ball mills, hammer mills, shredders,
fluid energy, and disk attrition, are not very effective for
material in the form of an ingot; (2) sensitivity to oxidation,
such that comminution must be done under an inert environment to
provide a safe environment and maintain acceptable electrochemical
performance; (3) requirement of a specific crystalline structure
necessary for electrochemical activity; i.e., the microstructure of
the material cannot be adversely altered during grinding or
atomization to produce powders directly from a melt; and (4)
requirement of a broad particle size distribution with a maximum
size of 75 microns (200 mesh) which provides optimum packing
density and electrochemical accessibility.
[0006] Early attempts to provide a method for size reduction of
hydrogen storage alloy materials from ingots proved inadequate due
to the extreme hardness of the hydrogen storage alloy materials.
Conventional size reduction processes employing devices such as jaw
crushers, mechanical attritors, ball mills, and fluid energy mills
consistently fail to economically reduce the size of such hydrogen
storage materials. Grinding and crushing processes have also proven
inadequate for initial reduction of ingots of hydrogen storage
alloy material to intermediate sized (i.e. 10-100 mesh)
particulate.
[0007] There are numerous methods for preparing metal powders.
Since the alloys under consideration are at one stage molten, one
might consider ultrasonic agitation or centrifugal atomization of
the liquid stream to prepare powders directly. The cost and the
product yield are the two main concerns with using this approach.
The particle shape is also not optimal. Finally, because it is
difficult to provide a completely inert atmosphere; surface layers,
which are undesirable from an electrochemical perspective, may be
formed on the particulate.
[0008] Attempts to embrittle the hydrogen storage alloy material by
methods such as immersion in liquid nitrogen, so as to facilitate
size reduction are inadequate because: (1) the materials are not
sufficiently embrittled; (2) the methods typically introduce
embrittlement agents in the alloys; which have an undesirable
effect upon the electrochemical properties of the hydrogen storage
alloy material; and (3) as the materials become more brittle, it
becomes increasingly difficult to obtain uniform particle size
distribution. Other methods for embrittling metals are disclosed,
for example, in Canadian patent No. 533,208 to Brown. Brown employs
cathodic charging as a size reduction technique.
[0009] Furthermore, material size reduction by an hydrogenation
processes is not desirable because of the inherent dangers
associated with hydrogen gas. Therefore it is desirous to employ a
technique that minimizes subsequent size reduction processes while
providing homogeneous material properties.
[0010] One alternative for preparing materials for powder formation
is rapid solidification. Rapid solidification refers to a technique
for rapidly quenching material from a liquid, or molten, state into
a solid state at a rate sufficient to freeze the position of atoms.
One rapid solidification technique is a spin cast technique where
the molten material into is formed into ribbons. Spin casting is a
method of dispersing molten material on a rotating wheel, also
commonly known as melt spin casting. The rotating wheel, made of a
highly conductive metal, typically copper, is positioned proximal
to a reservoir of molten material. The reservoir typically has an
orifice or nozzle to direct molten material onto the rotating
wheel. The molten material is rapidly solidified because of the
mass of the wheel and the significant difference in temperature
between the wheel and the molten material. The wheel need not be
cooled in order to provide a sufficiently cold moving surface
relative to the molten material, however, the wheel may be cooled
to achieve higher quench rate if so desired. A wheel is typically
between 6" and 10" (15.24 and 25.40 centimeters) in diameter and is
rotated at a rotational velocity of between 1,000 and 5,000 rpm
thereby to obtain a linear velocity, at the point of contact at the
material with the cylindrical periphery of the wheel, of 32.81 to
65.62 feet per second (1,000-2,000 centimeters per second).
[0011] Materials produced by melt spin casting techniques of the
prior art exhibit material property variations due to a number of
factors. Variations such as flow rate, stream diameter and material
temperature, and compositional variations including chemistry and
impurities within the melt stream contribute to inhomogeneity of
the solidified material. Changes in the diameter and flow rate of
the molten material stream result in different cooling rates of the
material. As explained above, different cooling rates will effect
the material's crystalline structure. Inhomogeneity is the main
drawback of the melt spin processes of the prior art. Increased
homogeneity requirements of materials make an improved technique
especially important.
[0012] Melt spin casting is an attractive method for producing
ribbons of material because of the lack of complexity involved.
This technique may be employed to form ribbons of material such as
metals, metal alloys, or thermoplastics. One method of producing
materials by melt spin casting is disclosed in commonly assigned
U.S. Pat. No. 4,637,967 to Keem et al for ELECTRODES MADE WITH
DISORDERED ACTIVE MATERIAL AND METHODS OF MAKING THE SAME, the
disclosure of which is incorporated herein by reference. The '967
patent discloses a heated crucible that is equipped with means for
pressurizing the crucible to extrude molten material through a
nozzle onto the surface of a chill wheel. Although this method is
very good for forming homogeneous materials, the process efficiency
is reduced because the crucible must be pressurized to extrude the
material. The flow rate is also inconsistent as the material level
in the crucible changes, the flow rate of the material changes.
This process is not continuous, therefore an hiatus in the
production of ribbon material is inevitable, resulting in a reduced
capacity.
[0013] Another method and apparatus for spin melt casting of
materials is commonly assigned U.S. Pat. No. 4,339,255 to Ovshinsky
et al for METHOD AND APPARATUS FOR MAKING A MODIFIED AMORPHOUS
GLASS MATERIAL, the disclosure of which is incorporated by
reference. Although the teachings of the '255 patent disclose the
advantages of spin melt casting over thin film processes for making
amorphous materials, the process has inherent limitations. A piston
is provided to cause material within a crucible to be ejected onto
a rotating wheel. However, once all of the material is driven from
the crucible, the process must be halted and the crucible refilled.
This method is also susceptible to temperature and chemistry
variations because he process must be stopped and started.
[0014] In order to improve process efficiency, a hydrostatic system
may be employed to provide the necessary force to extrude the
molten material from the crucible. Such a device is disclosed in
U.S. Pat. No. 4,485,839 to Ward for RAPIDLY CAST ALLOY STRIP HAVING
DISSIMILAR PORTIONS. The '839 patent discloses a planar flow
casting technique for drawing thin ribbons. Although this technique
includes a hydrostatic system for delivering the molten material,
there are shortcomings associated with this invention. The device
disclosed is not capable of providing a true, continuous melt
casting operation. Furthermore, the disclosed operation relies on
heating a crucible to prevent the nozzles from clogging, which is
ineffective since it is commonly known that slags and other
impurities are present within the crucible. Also, because of the
tolerances associated with this device, less than 0.120" (3.05 mm),
the surface of the chill wheel must be constantly maintained.
[0015] Accordingly, there exists a need for an economical, spin
melt casting process for producing homogeneous materials.
SUMMARY OF THE INVENTION
[0016] The present invention disclosed herein is an apparatus for
continuous melt spin casting of materials. The apparatus comprises
a supply crucible and a casting crucible disposed a chamber. The
supply crucible provides molten material to the casting crucible
for ejecting at least two streams of molten material upon a chill
wheel for solidification. Each stream is ejected through one of at
least two orifices in the casting crucible. Monitoring means
determine the level of molten material in the casting crucible.
[0017] The apparatus of the present invention includes a
selectively actuated flow control valve for controlling the flow of
molten material from the supply crucible to the casting crucible to
maintain the level of molten material in the casting crucible
within a range. Valve control means actuate the flow control valve
as a function of material level in the casting crucible as; sensed
by the monitoring means. The present invention includes means for
filtering the molten material prior to casting and thermal control
means for controlling the temperature of material within said
casting crucible.
[0018] Each orifice is at an equal distance from a point of contact
on the chill wheel. Equal length streams of material at a uniform
temperature and flow rate are rapidly solidified form homogenous
ribbons by the chill wheel.
[0019] Means for removing accumulated material from an external
surface of said orifices is also disclosed.
[0020] Also disclosed herein is a method for continuous melt spin
casting of materials. The novel method comprises the steps of
providing a material supply crucible and a casting crucible
disposed within a chamber, where the material supply crucible is
provided to receive molten material to be supplied to the casting
crucible; monitoring the level of molten material in the casting
crucible; releasing molten material from the supply crucible
through a flow control valve; filtering the molten material
released from the material supply crucible prior to solidification;
maintaining the molten material level in the casting crucible,
whereby the molten material flow rate through the orifices is
controlled by the static pressure of the molten material in the
casting crucible to provide a constant material flow rate;
maintaining the temperature of the molten material in the casting
crucible to provide material for casting at a consistent
temperature; ejecting at least two streams of molten material from
the casting crucible, each stream ejected through one of at least
two orifices in the casting crucible; and rapidly solidifying the
molten material by ejecting equal length and diameter streams of
molten material upon the chill wheel.
[0021] At least two nozzles may be provided, each nozzle in
communication with one of at least two orifices. accumulated
material deposits are removed from the orifices or nozzles by means
including a shearing device, the chill wheel or a diamond
wheel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a cross sectional view of one embodiment of the
present invention taken through a chamber to reveal the operative
elements therein.
[0023] FIG. 2 is a is a cross sectional view showing one operating
position of one embodiment of a casting crucible in relation to a
chill wheel.
[0024] FIG. 3 is a sectional view of the casting crucible and chill
wheel taken along section A-A of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
[0025] The present invention is directed toward an apparatus and
method for forming ribbons of material by melt spin casting.
Referring now to FIG. 1, the apparatus 10 of the present invention
includes a chamber 20 containing a supply crucible 30 and casting
crucible 40. The supply crucible 30 is provided to receive molten
material and has a selectively actuated flow control valve 70 for
releasing molten material into the casting crucible 40. Referring
now also to FIG. 2, the casting crucible 40 has at least two
orifices 50, each orifice 50 for ejecting a stream of molten
material upon a chill wheel 110 having a horizontal axis of
rotation.
[0026] A loading vessel 130 in communication with the chamber 20
provides material to the supply crucible 30 without exposing the
materials within the chamber 20 to contaminants by incorporating a
flap valve 135. It should be noted that although a flap valve is
used to seal the chamber 20, any suitable means known in the art
may be substituted for a flap valve.
[0027] The apparatus 10 may also include at least two nozzles (not
shown), each nozzle in communication with one of the orifices 50 in
the casting crucible 40. The flow control valve 70 is selectively
actuated by valve control means 80 to provide the molten material
to the casting crucible 40. The valve control means 80 may be
manually operated or automatically controlled by a controller (not
shown). The valve control means 80 are actuated as a function of
the material level in the casting crucible 40.
[0028] Molten material is ejected from the casting crucible 40 onto
the chill wheel 110. The molten material level within the casting
crucible 40 provides hydrostatic pressure at the orifices 50 to
eject molten material upon the chill wheel 110. The material level
in the casting crucible 40 is maintained in order to maintain a
uniform flow rate. The chill wheel 110 is preferably formed of a
material having a high thermal conductivity such as copper. The
temperature of the chill wheel 110 may be controlled by any
suitable cooling means (not shown) known in the art, including a
cooling medium such as a water and ethylene glycol mixture. In the
preferred embodiment, the chill wheel 110 has a passage to allow
the cooling medium to pass through and draw heat away from the
casting wheel 110.
[0029] The supply crucible 30 is heated by thermal control means
100; in the preferred embodiment, the thermal control means is an
induction heater 180. The molten material within the supply
crucible 30 may be mixed by any suitable means known in the art to
maintain homogeneity. The casting crucible 40 is heated by thermal
controls means 105, and in the exemplary embodiment, the thermal
control means is an induction heater 190 as well. Likewise, the
casting crucible 40 may be stirred by any suitable means known in
the art.
[0030] Molten material, raw materials, or ingot material may be
provided to the supply crucible 30 by the loading vessel 130. The
atmosphere in the chamber 20 may consist of an insert gas or may be
pumped down to a vacuum to prevent contamination. Once the supply
crucible has received the materials for casting, heat is provided
by the induction heater 180 to maintain viscosity. The material
within the supply crucible 30 is mixed to maintain homogeneity. By
lowering the frequency of the induction heater 180, the material
may be electrodynamically mixed. In the exemplary embodiment, the
induction heaters 180 and 190 are reduced below 1000 Hz, resulting
in excellent mixing results. It should be noted that other mixing
operations may be substituted for electrodynamic mixing, such as
agitation.
[0031] Referring now also to FIG. 2, the chill wheel 110 is shown
in one of many potential locations. The chill wheel 110 is movable
in the X, Y, and Z-axis, providing many advantages to the present
invention. By adjusting the position of the chill wheel 110 along
the Z-axis, the length of the streams is changed, changing the
exposure time to ambient conditions and ultimately, temperature.
Therefore, fine temperature adjustments of the molten material
prior to contacting the chill wheel 110 may be made by adjusting
the position of the chill wheel 110 along the Z-axis. The form of
the ribbons produced by apparatus 10 of the present invention may
be altered by moving the chill wheel 110 along the X-axis, which
will change the angle of incidence of the material streams on the
chill wheel 110.
[0032] Referring now also to FIG. 3, the chill wheel 110 may be
positioned by any combination of orthogonal coordinate changes and
then translated along the Y-axis to remove material which has
accumulated upon the orifices 50 by shearing the accumulated
material with the chill wheel 110. Furthermore, the orifices 50 or
nozzles (not shown) may be heated to reduce material
accumulation.
[0033] A thermal screen 220 may also be disposed below the supply
crucible 40 to stabilize the flow rate of the molten material
exiting the supply crucible 40. The thermal screen 220 is heated
whereby the material temperature is preserved as the material exits
the supply crucible 40. Means for filtering the molten material
prior to casting are provided. Referring again to FIG. 3, the means
for filtering may be a filter element 230, such as a ceramic filter
capable of high temperature filtering of molten materials for the
removal of slags, oxides or other impurities. A common occurrence
experienced when melting is pieces of the crucible break away due
to thermal cycling, and become inclusions in the melt.
[0034] The temperature of the material within the casting crucible
40 is maintained by the induction heater 190 and stirred to
maintain homogeneity. Monitoring means 60, such as a sight glass
for measuring height or a balance for determining material mass, is
provided to evaluate the material level in the casting crucible 40.
The flow rate of the material from the casting crucible 40 is
governed by hydrostatic pressure. The material level in the casting
crucible 40 will determine the rate material is ejected from the
casting crucible 40. The material level must be maintained within a
range in order to provide a uniform flow rate of the molten
material stream. Once the material stream is ejected from the
casting crucible 40 upon the rotating chill wheel 110, the material
is rapidly solidified and is projected from the chill wheel 110 and
the resulting ribbons of material are captured in a material
collector 210.
[0035] The size and the form of the ribbons can be modified by
changing the rotational speed and diameter of the chill wheel 110.
By increasing the speed of the chill wheel, thin ribbons are formed
and the material dwell time is reduced. In the preferred
embodiment, the surface of the casting wheel 40 is polished to
provide sufficient mechanical and thermal contact with the melt
streams.
[0036] By providing multiple orifices 50, process throughput is
increased. The orifices 50 are positioned at a uniform distance
from a contact point of the material stream upon the chill wheel
110. Flow rate, temperature, material purity, and homogeneity must
be simultaneously maintained in order to obtain uniform material
properties such as crystallite size and homogeneity of the
solidified material. The present invention discloses an economical
solution to melt spin casting concerns found in the state of the
art. The present invention has improved throughput without a need
for a mechanical device to provide additional pressure within the
casting crucible 40, such as a piston. Also, an uninterrupted
stream of material with excellent homogeneity and purity for rapid
solidification upon the chill wheel 110 is provided.
EXAMPLE
[0037] In the present example, the chamber 20 is hermetically
sealed and operated in a vacuum to prevent oxidizing of the melt,
thereby achieving higher purity. An ingot of negative electrode
material for a rechargeable electrochemical storage cell is
provided to the supply crucible 30 within chamber 20 by the loading
vessel 130 and heated to 1550.degree. C. After melting, the melt it
is mixed electrodynamically to increase homogeneity.
[0038] Once liquefied, thermal control means 100 sustain the
material temperature until the material is released into casting
crucible 40. The molten material within the supply crucible 30 is
electrodynamically mixed. By lowering the frequency of the
induction heater to below 1000 Hz frequency, more efficient mixing
is achieved.
[0039] The molten material in the supply crucible 30 is released to
the casting crucible 40 by actuating the valve control means 80 to
open the flow control valve 70. The material released by the
control valve 70 passes through the thermal screen 220 where the
material temperature is stabilized to avoid cooling. The material
then passes through the filter element 140 and into the casting
crucible 40. The material temperature in the casting crucible 40 is
stabilized by an induction heater 190. When the level of the
material in the casting crucible 40 rises to about 200 mm, the
valve control means 80 close the supply crucible flow control valve
70.
[0040] The material level in the casting crucible 40 is evaluated
by a sight glass disposed within chamber 20 to assure a material
height of 200 mm is maintained. In the present example, ten streams
of molten material, each stream formed by one of ten calibrated
orifices 50, are ejected onto the rotating chill wheel 110. Each
orifice 50 being uniform in diameter and equidistant from the chill
wheel 110, forms a melt stream that is equal in length and
diameter. In this example, the orifices are disposed about 150 mm
from the contact point on chill wheel 110.
[0041] In the present example, a cooling medium is flowed through a
passage in the chill wheel 110. By cooling the chill wheel 110,
ribbons are formed having a constant width and thickness. The
ribbons produced by this technique exhibit high homogeneity of
properties and uniform crystallite size while increasing the
productivity of the process.
[0042] The temperature of the casting crucible is regulated to
about 1500.degree. C. and the level of the melt bath to about 200
mm. The casting crucible 40 flow rate is between about 0.15 to 0.32
L/min (1 to 2.5 kg/min). The ten streams have an equal length, less
than about 150 mm in the present example, and a diameter between
about 1.0 to 2.5 mm. The chill wheel 110 rotates with a linear
speed of between about 5 to 25 m/sec.
[0043] The apparatus and method of the present can be used to
produce threads, films, ribbons and any variant thereof.
Furthermore, although metallic materials and alloys have been
specifically referenced, it should become apparent to those skilled
in the art that a variety of material, including non metallic
materials, such as plastics, may be formed by employing the
teachings set forth herein.
[0044] While the invention has been described in connection with
preferred embodiments and procedures, it should be understood that
it is not intended to limit the invention to the described
embodiments and procedures. On the contrary, it is intended to
cover all alternatives, modifications and equivalents which may be
included within the spirit and scope of the claims appended
hereto.
* * * * *