Note: Descriptions are shown in the official language in which they were submitted.
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METHODS FOR RECOVERING MACHINING SCRAP
Cross-Reference to Related Application
[0001] The present application is an international (PCT) patent
application relating to
and claiming the benefit of commonly-owned, copending U.S. Provisional Patent
Application No. 62/588,752, filed November 20, 2017, entitled "METHODS FOR
RECOVERING ALUMINUM-LITHIUM SCRAP," the contents of which are incorporated
herein by reference in their entirety.
io .. Technical Field of the Invention
[0002] The present invention relates to methods for cleaning and
recovering
machining scrap, such aluminum-lithium ("AlLi") alloy scrap, for reuse.
Background of the Prior Art
[0003] When raw metal alloys (e.g., in the form of extrusions or plates)
are to be
machined to produce finished parts, they are coated with water-soluble
lubricant to
facilitate the machining process. In some embodiments, the water-soluble
lubricant
contains one or more organic compounds (i.e., compounds containing carbon)
dissolved in water. The result of the machining process is a finished product
and a
zo quantity of scrap. In some cases, the finished product may use only
about 10% of the
raw material and the remainder of the raw material may become machining scrap,
which remains contaminated with the water-soluble lubricant. The machining
scrap has
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commercial value and is suitable for re-use, but cannot be re-used until the
water-
soluble lubricant has been cleaned therefrom.
Summary of the Invention
[0004] In an embodiment, a method includes providing a quantity of metal,
the
quantity of metal being contaminated by a contaminant including a quantity of
carbon;
configuring a vacuum induction furnace to operate according to a set of
operating
parameters, the set of operating parameters being selected based on
characteristics of
the contaminant, the set of operating parameters including at least one of a
pressure,
an atmosphere composition, a pour temperature, or a hold time; charging the
vacuum
induction furnace with the quantity of metal; and operating the vacuum
induction furnace
to melt the quantity of metal in accordance with the set of operating
parameters,
whereby at least some of the contaminant is removed from the quantity of metal
so as
to provide an output metal having a concentration of carbon that is less than
or equal to
a concentration of carbon in the metal as cast.
[0005] In some embodiments, the quantity of metal includes a quantity of
machining
scrap. In some embodiments, a method also includes the step of prior to
charging the
vacuum induction furnace with the quantity of metal, compacting the quantity
of metal
into a unitary piece of metal.
zo [0006] In some embodiments, the set of operating parameters
includes a hold time,
and the hold time is between 0 minutes and 60 minutes. In some embodiments,
the set
of operating parameters includes a pressure, and the pressure is between 1
micron and
300 microns. In some embodiments, the set of operating parameters includes an
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atmosphere composition. In some embodiments, the atmosphere composition
includes
an inert gas atmosphere. In some embodiments, the set of operating parameters
includes a pour temperature, and the pour temperature is between 700 C and
770 C.
[0007] In some embodiments, the at least one contaminant includes sodium
and a
lubricant. In some embodiments, the set of operating parameters includes a
pressure, a
pour temperature, and a hold time, the pressure is between 1 micron and 300
microns,
the temperature is between 700 C and 755 C, and the hold time is between 30
minutes and 90 minutes.
[0008] In some embodiments, the quantity of metal includes one of a 2000-
series
aluminum alloy, a 5000-series aluminum alloy, a 6000-series aluminum alloy, a
7000-
series aluminum alloy, or an 8000-series aluminum alloy. In some embodiments,
the
quantity of metal includes an aluminum-lithium alloy.
[0009] In some embodiments, the quantity of metal is further
contaminated by a
quantity of sodium. In some embodiments, the operating parameters include a
temperature and a hold time, and the temperature and the hold time are
selected so as
to provide a residual sodium concentration that is less than a target
concentration. In
some embodiments, the target concentration is six parts per million.
[0010] In some embodiments, the contaminant includes a lubricant. In
some
embodiments, the operating parameters include a pour temperature of about 700
C
zo and substantially no hold time. In some embodiments, the operating
parameters
include a pressure of about 300 microns. In some embodiments, the operating
parameters include an argon atmosphere and a pressure of about 1 atmosphere.
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Brief Description of the Drawings
[0011] FIG. 1 is a flowchart describing the steps of a method according
to an
exemplary embodiment; and
[0012] FIG. 2 is a schematic illustration of a vacuum induction furnace
that may be
used in connection with an exemplary embodiment.
Detailed Description of the Drawings
[0013] The present invention can be further explained with reference to
the included
figures, wherein like structures are referred to by like numerals throughout
the several
io views. The figures constitute a part of this specification and include
illustrative
embodiments of the present disclosure and illustrate various objects and
features
thereof. In addition, any measurements, specifications and the like shown in
the figures
are intended to be illustrative, and not restrictive. Therefore, specific
structural and
functional details disclosed herein are not to be interpreted as limiting, but
merely as a
representative basis for teaching one skilled in the art to variously employ
the present
invention. The figures shown are not necessarily to scale, with emphasis
instead
generally being placed upon illustrating the principles of the present
invention.
Therefore, specific structural and functional details disclosed herein are not
to be
interpreted as limiting, but merely as a representative basis for teaching one
skilled in
zo the art to variously employ the present invention.
[0014] Among those benefits and improvements that have been disclosed,
other
objects and advantages of this invention will become apparent from the
following
description taken in conjunction with the accompanying figures. Detailed
embodiments
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of the present invention are disclosed herein; however, it is to be understood
that the
disclosed embodiments are merely illustrative of the invention that may be
embodied in
various forms. In addition, each of the examples given in connection with the
various
embodiments of the invention is intended to be illustrative, and not
restrictive.
[0015] Throughout the specification and claims, the following terms take
the
meanings explicitly associated herein, unless the context clearly dictates
otherwise.
The phrases in one embodiment" and in some embodiments" as used herein do not
necessarily refer to the same embodiment(s), though they may. Furthermore, the
phrases in another embodiment" and in some other embodiments" as used herein
do
.. not necessarily refer to a different embodiment, although they may. Thus,
as described
below, various embodiments of the invention may be readily combined, without
departing from the scope or spirit of the invention.
[0016] In addition, as used herein, the term "or" is an inclusive "or"
operator, and is
equivalent to the term "and/or," unless the context clearly dictates
otherwise. The term
.. "based on" is not exclusive and allows for being based on additional
factors not
described, unless the context clearly dictates otherwise. In addition,
throughout the
specification, the meaning of "a," "an," and "the" include plural references,
unless the
context clearly dictates otherwise. The meaning of "in" includes "in" and
"on", unless the
context clearly dictates otherwise.
zo [0017] In some embodiments, the exemplary invention relates to a
method for
recovering machining scrap such that it is suitable for re-use. In some
embodiments,
the exemplary invention relates to a method for melting, cleaning, and
purifying
machining scrap such that it is suitable for re-use. FIG. 1 shows a flowchart
of a
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method 100 according to an exemplary embodiment. In step 110, a quantity of
machining scrap is provided. In some embodiments, the machining scrap includes
aluminum. In some embodiments, the machining scrap includes lithium. In some
embodiments, the machining scrap includes aluminum and lithium.
In some
embodiments, the machining scrap includes a 2000-series aluminum alloy (i.e.,
a
copper-based aluminum alloy). In some embodiments, the machining scrap
includes a
7000-series aluminum alloy (i.e., a zinc-based aluminum alloy). In some
embodiments,
the machining scrap includes one or more of the alloys AA2050, AA2055, AA2060,
AA2090, AA2091, AA2094, AA2095, AA2097, AA2098, AA2099, AA2195, AA2196,
io AA2197, AA2198, AA2199, AA2297 and AA2397, as these alloys are by the
Aluminum
Association. In some embodiments, the machining scrap is coated with a
lubricant. In
some embodiments, the lubricant includes sodium.
In some embodiments, the
machining scrap is not coated with a lubricant. In some embodiments, the
machining
scrap includes a non-lithium-containing aluminum alloy. In some embodiments,
the
machining scrap has a bulk density of between 20 and 50 pounds per cubic foot.
[0018]
In step 120, at least a portion the machining scrap is compressed into a
unitary piece. In some embodiments, the piece is of the type commonly referred
to as a
"puck". In some embodiments, the machining scrap is bailed. In some
embodiments,
the machining scrap includes solids. In some embodiments, the piece has a mass
of
zo about 80 kilograms. In some embodiments, the piece has a weight of about
1,500
pounds. In some embodiments, the piece has a weight of between 3,000 pounds
and
6,000 pounds. In some embodiments, a quantity of the machining scrap (e.g., in
quantities as noted above) is selected for further processing, but is not
compressed into
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a piece. In some embodiments, a puck is broken into smaller pieces before
further
processing occurs. In some embodiments, omitting the step of forming pucks,
or,
alternately, breaking the pucks into smaller pieces, will provide an increased
lubricant-
coated surface area that is exposed during subsequent steps of the method 100.
It will
be apparent to those of skill in the art that this step may be repeated as
necessary
based on the amount of the machining scrap provided in step 110.
[0019]
In step 130, a vacuum induction furnace is provided. In some embodiments,
the vacuum induction furnace is a vacuum induction degassing and pouring
furnace.
FIG. 2 shows an exemplary vacuum induction furnace. In some embodiments, the
vacuum induction furnace includes an enclosed vacuum chamber.
In some
embodiments the vacuum induction furnace includes a vacuum pump that is
configured
to remove gases (e.g., air, argon, vaporized lubricant) from the vacuum
chamber. In
some embodiments, the vacuum pump is configured to provide a configurable
level of
pressure within the vacuum chamber. In some embodiments, the vacuum pump is
configured to provide a level of pressure between 1 micron (i.e., a unit of
pressure that
is equal to 1/1000 of a millimeter of mercury) and 1 atmosphere within the
vacuum
chamber. In some embodiments, the vacuum induction furnace includes a supply
of
argon that is configured to selectively introduce argon into the vacuum
chamber. In
some embodiments, the vacuum induction chamber includes a vent.
In some
zo
embodiments, the vacuum induction furnace includes an induction furnace
within the
vacuum chamber. In some embodiments, the induction furnace is configured to
heat
the contents of a vessel to a selected temperature and for a selected period
of time. In
some embodiments, the vacuum induction furnace includes a mold within the
vacuum
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chamber. In some embodiments, the vacuum induction furnace is configured to be
operable to pour contents of the vessel (e.g., melted machining scrap) into
the mold at a
selected time (e.g., after the contents have been heated for a selected period
of time).
[0020]
Referring back to FIG. 1, in step 140, the vacuum induction furnace is
configured to operate according to a given set of parameters. In some
embodiments,
the parameters are selected so as to clean, melt, and cast aluminum-lithium
machining
scrap while minimizing oxidation losses, maximizing alloy retention
(particularly
maximizing retention of lithium), remove contaminants (e.g., lubricant) if
necessary, and
minimizing cycle time.
In some embodiments, the parameters include a target
temperature. In some embodiments, the parameters include a rate of heating to
arrive
at the target temperature. In some embodiments, heating is performed at a
controlled
rate so as to ensure that no moisture is trapped below the level of the melted
metal. In
some embodiments, the parameters are selected based on the characteristics of
the
machining scrap. In some embodiments, the parameters are selected based on
whether the machining scrap is coated with lubricant. In some embodiments, the
parameters are selected based on whether the machining scrap includes
contaminants
(e.g., sodium, calcium, potassium, etc.). In some embodiments, the vacuum
induction
furnace is configured to provide a vacuum. In some embodiments, the vacuum
induction furnace is configured to provide an argon atmosphere. In some
embodiments
zo in which the vacuum induction furnace is to be configured to melt scrap
having no
lubricant (e.g., scrap resulting from dry machining), the vacuum induction
furnace is
configured to provide an argon atmosphere at or about atmospheric pressure, to
provide a temperature of about 730 C, and to provide no hold time once the
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temperature has been reached. In some embodiments in which the vacuum
induction
furnace is to be configured to melt scrap having lubricant but no
contamination (e.g.,
sodium, calcium, potassium, etc.), the vacuum induction furnace is configured
to
provide either (a) a vacuum of about 300 microns or (b) an argon atmosphere at
or
about atmospheric pressure, to provide a temperature of about 700 C, and to
provide
no hold time once the temperature has been reached. In some embodiments in
which
the vacuum induction furnace is to be configured to melt scrap having
lubricant and
contamination (e.g., sodium, calcium, potassium, etc.), the vacuum induction
furnace is
configured to provide a vacuum of about 300 microns, to provide a temperature
of
io between about 700 C and about 755 C, and to provide a hold time of one
hour. It will
be apparent to those of skill in the art that the above configurations are
only exemplary
and that other optimized configurations may be determined based on the
characteristics
of a specific batch of machining scrap at hand, based on general
characteristics of an
ongoing stream of machining scrap, etc.
[0021] Continuing to describe step 140 of the exemplary method 100, the
following
will describe ranges of values for various parameters of the vacuum induction
furnace.
It will be apparent to those of skill in the art that all of the ranges
described herein are
inclusive (i.e., a range of between 100 C and 200 C includes the values of
100 C and
200 C as well as all values therebetween). In some embodiments, the
parameters
zo include an internal atmosphere of the vacuum induction furnace (e.g., an
atmosphere
within the vacuum chamber of the vacuum induction furnace). In some
embodiments,
the internal atmosphere includes a pressure level. In some embodiments, the
pressure
level is represented in microns. In some embodiments, the pressure level is 1
micron.
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In some embodiments, the pressure level is 100 microns. In some embodiments,
the
pressure level is 200 microns. In some embodiments, the pressure level is 300
microns. In some embodiments, the pressure level is between 1 micron and 100
microns. In some embodiments, the vacuum level is between 1 micron and 200
microns. In some embodiments, the pressure level is between 1 micron and 300
microns. In some embodiments, the pressure level is between 100 microns and
200
microns. In some embodiments, the pressure level is between 100 microns and
300
microns. In some embodiments, the pressure level is between 200 microns and
300
microns. In some embodiments, the pressure level is represented in millibars.
In some
embodiments, the pressure level is 0.001 millibars. In some embodiments, the
pressure
level is 0.132 millibars. In some embodiments, the pressure level is 0.263
millibars. In
some embodiments, the pressure level is 0.4 millibars. In some embodiments,
the
pressure level is between 0.001 millibars and 0.132 millibars. In some
embodiments,
the pressure level is between 0.001 millibars and 0.263 millibars.
In some
embodiments, the pressure level is between 0.001 millibars and 0.4 millibars.
In some
embodiments, the pressure level is between 0.132 millibars and 0.263
millibars. In
some embodiments, the pressure level is between 0.132 millibars and 0.4
millibars. In
some embodiments, the pressure level is between 0.263 millibars and 0.4
millibars. In
some embodiments, the pressure level is about 1,000 microns. In some
embodiments,
zo the pressure level is between 900 microns and 1,000 microns. In some
embodiments,
the pressure level is about 1 atmosphere.
In some embodiments, the internal
atmosphere includes an inert gas atmosphere. In some embodiments, the internal
atmosphere includes an argon atmosphere. In some embodiments, the vacuum
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induction furnace is configured to generate a vacuum (e.g., a vacuum of 100
microns)
and then to fill the internal atmosphere with argon. In some embodiments, the
vacuum
induction furnace is configured to generate a vacuum (e.g., a vacuum of 100
microns)
and then to fill the internal atmosphere with argon at a pressure level of
about 1
atmosphere.
[0022] Continuing to describe step 140 of the exemplary method 100, in
some
embodiments, the parameters include a pour temperature. In some embodiments,
the
pour temperature is 700 C. In some embodiments, the pour temperature is 710
C. In
some embodiments, the pour temperature is 720 C. In some embodiments, the
pour
temperature is 730 C. In some embodiments, the pour temperature is 740 C. In
some embodiments, the pour temperature is 750 C. In some embodiments, the
pour
temperature is 755 C. In some embodiments, the pour temperature is 760 C. In
some embodiments, the pour temperature is 768 C. In some embodiments, the
pour
temperature is 770 C. In some embodiments, the pour temperature is between
700 C
and 710 C. In some embodiments, the pour temperature is between 700 C and
720
C. In some embodiments, the pour temperature is between 700 C and 730 C. In
some embodiments, the pour temperature is between 700 C and 740 C. In some
embodiments, the pour temperature is between 700 C and 750 C. In some
embodiments, the pour temperature is between 700 C and 760 C. In some
zo embodiments, the pour temperature is between 700 C and 770 C. In some
embodiments, the pour temperature is between 710 C and 720 C. In some
embodiments, the pour temperature is between 710 C and 730 C. In some
embodiments, the pour temperature is between 710 C and 740 C. In some
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embodiments, the pour temperature is between 710 C and 750 C. In some
embodiments, the pour temperature is between 710 C and 760 C. In some
embodiments, the pour temperature is between 710 C and 770 C. In some
embodiments, the pour temperature is between 720 C and 730 C. In some
embodiments, the pour temperature is between 720 C and 740 C. In some
embodiments, the pour temperature is between 720 C and 750 C. In some
embodiments, the pour temperature is between 720 C and 760 C. In some
embodiments, the pour temperature is between 720 C and 770 C. In some
embodiments, the pour temperature is between 730 C and 740 C. In some
embodiments, the pour temperature is between 730 C and 750 C. In some
embodiments, the pour temperature is between 730 C and 760 C. In some
embodiments, the pour temperature is between 730 C and 770 C. In some
embodiments, the pour temperature is between 740 C and 750 C. In some
embodiments, the pour temperature is between 740 C and 760 C. In some
embodiments, the pour temperature is between 740 C and 770 C. In some
embodiments, the pour temperature is between 750 C and 760 C. In some
embodiments, the pour temperature is between 750 C and 770 C. In some
embodiments, the pour temperature is between 760 C and 770 C.
[0023] Continuing to describe step 140 of the exemplary method 100, in
some
zo embodiments, the parameters include a hold time (i.e., a time period
during which a
charge received in the vacuum induction furnace is held at a target
temperature and
pressure once the target temperature and pressure have been reached). In some
embodiments, the hold time is 0 minutes. In some embodiments, the hold time is
30
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minutes. In some embodiments, the hold time is 60 minutes. In some
embodiments,
the hold time is 90 minutes. In some embodiments, the hold time is between 0
minutes
and 30 minutes. In some embodiments, the hold time is between 30 minutes and
60
minutes. In some embodiments, the hold time is between 60 minutes and 90
minutes.
In some embodiments, the hold time is between 0 minutes and 60 minutes. In
some
embodiments, the hold time is between 30 minutes and 90 minutes. In some
embodiments, the hold time is between 0 minutes and 90 minutes.
[0024]
Continuing to refer to FIG. 1, in step 150, the piece formed from the
machining scrap in step 120 is placed within the vacuum induction furnace. In
step 160,
the vacuum induction furnace is operated to heat the machining scrap. In some
embodiments, heating is performed as configured in step 140. During the
heating
process under the selected conditions, lubricants are removed from the
machining
scrap. In some embodiments, lubricants are vaporized and are carried away from
the
machining scrap in the vacuum stream. In some embodiments, the lubricants are
collected from the vacuum stream for subsequent use and/or disposal. In some
embodiments, small amounts of the lubricants condense on the inside surface of
the
vacuum chamber. In some embodiments, lubricants are vaporized and oxidized.
[0025]
In some embodiments, the heating step includes heating to vaporize
lubricants. In some embodiments, the step of heating to vaporize lubricants
includes
zo
holding the machining scrap at a selected temperature and in a selected
environmental
composition for a time that is sufficient to vaporize the lubricants.
In some
embodiments, the time is about one hour. In some embodiments, the selected
environment is a medium vacuum pressure (e.g., between 0.001 millibars and 30
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millibars) and the temperature is a temperature that is greater than the
boiling point of
the lubricants at the selected pressure, but less than the solidus point of
the machining
scrap (e.g., about 660 C). In some embodiments, the temperature is less than
the
boiling point of the lubricants at standard temperature and pressure (which
is, for
example, 370 C).
[0026] In some embodiments, the environment is an argon environment at
about one
atmosphere and the temperature is a temperature that is greater than the
boiling point
of the lubricants (which is, for example, 370 C at standard temperature and
pressure),
but less than the solidus point of the machining scrap (e.g., about 660 C).
io [0027] In some embodiments, the heating step includes heating to
vaporize and
oxidize lubricants. In some embodiments, the step of heating to vaporize and
oxidize
lubricants includes holding the machining scrap at a selected temperature and
in a
selected environmental composition for a time that is sufficient to vaporize
the
lubricants. In some embodiments, the time is about one hour. In some
embodiments,
the selected environment is a low vacuum pressure (e.g., between 30 millibars
and
1000 millibars) and air environment and the temperature is a temperature that
is greater
than the boiling point of the lubricants at the selected pressure, but less
than the solidus
point of the machining scrap (e.g., about 660 C). In some embodiments, the
temperature is less than the boiling point of the lubricants at standard
temperature and
zo pressure (which is, for example, 370 C).
[0028] In some embodiments, the environment is an argon/air environment.
In some
embodiments, the argon/air environment includes between 0% and 100% argon and
the
balance air. In some embodiments, the temperature is a temperature that is
greater
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than the boiling point of the lubricants (which is, for example, 370 C at
standard
temperature and pressure), but less than the solidus point of the machining
scrap (e.g.,
about 660 C).
[0029] In some embodiments, the environment is an air environment at or
about
atmospheric pressure and the temperature is a temperature that is greater than
the
boiling point of the lubricants (which is, for example, 370 C at standard
temperature
and pressure), but less than the solidus point of the machining scrap (e.g.,
about 660
C).
[0030] Continuing to refer to FIG. 1, in step 170, the vacuum induction
furnace is
operated to melt the machining scrap. In some embodiments, this step includes
maintaining atmospheric conditions (e.g., pressure, atmospheric composition)
that were
used in step 160. In some embodiments, this step includes changing atmospheric
conditions. In some embodiments, this step includes continuing to heat the
machining
scrap (e.g., from a temperature at which lubricant is vaporized and/or
oxidized, as
discussed above with reference to step 160) until the machining scrap reaches
its
solidus point.
[0031] In some embodiments, the melting step includes melting so as to
vaporize
and/or oxidize lubricant during the melting step. In some embodiments, the
step of
melting so as to vaporize and/or oxidize lubricant includes melting at a
predefined
zo environmental composition. In some embodiments, the environment is a low
vacuum
(e.g., between 30 millibars and 1000 millibars) and air environment and the
temperature
is a temperature at or above the solidus point of the machining scrap (e.g.,
about 660
C). In some embodiments, the environment is an argon/air environment at a
pressure
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of at or about atmospheric pressure and the temperature is a temperature at or
above
the solidus point of the machining scrap (e.g., about 660 C). In some
embodiments,
the environment is an air environment at a pressure of at or about atmospheric
pressure
and the temperature is a temperature at or above the solidus point of the
machining
scrap (e.g., about 660 C).
[0032] Continuing to refer to FIG. 1, in step 180, after the machining
scrap is
completely liquid, the temperature is raised to the level selected during step
140, and is
held at this prescribed level for the prescribed hold time. While the melted
scrap is
being held at this temperature, any contaminants (e.g., sodium, calcium,
potassium,
etc.) are vaporized and carried away from the melted scrap in the vacuum
stream. In
some embodiments, the contaminants, if any, are collected from the vacuum
stream for
subsequent use and/or disposal.
[0033] Continuing to refer to FIG. 1, in step 190, the melted machining
scrap is
poured as needed (e.g., cast into a mold, fed into an ingot caster, etc.). It
will be
apparent to those of skill in the art that steps 150 through 190 may be
repeated as
necessary based on the amount of machining scrap at hand. Following step 190,
the
method 100 is complete.
[0034] In some embodiments, the material that is yielded by the
operation of the
vacuum induction furnace as described above has been cleaned of substantially
all
zo lubricant that was originally coated thereon. In some embodiments, the
material that is
yielded by the operation of the vacuum induction furnace as described above
includes
substantially no residual carbon. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace includes 200 parts per million
or less of
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residual carbon. In some embodiments, the material that is yielded by the
operation of
the vacuum induction furnace includes 190 parts per million or less of
residual carbon.
In some embodiments, the material that is yielded by the operation of the
vacuum
induction furnace includes 180 parts per million or less of residual carbon.
In some
.. embodiments, the material that is yielded by the operation of the vacuum
induction
furnace includes 170 parts per million or less of residual carbon. In some
embodiments,
the material that is yielded by the operation of the vacuum induction furnace
includes
160 parts per million or less of residual carbon. In some embodiments, the
material that
is yielded by the operation of the vacuum induction furnace includes 150 parts
per
million or less of residual carbon. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace includes 140 parts per million
or less of
residual carbon. In some embodiments, the material that is yielded by the
operation of
the vacuum induction furnace includes 130 parts per million or less of
residual carbon.
In some embodiments, the material that is yielded by the operation of the
vacuum
induction furnace includes 120 parts per million or less of residual carbon.
In some
embodiments, the material that is yielded by the operation of the vacuum
induction
furnace includes 110 parts per million or less of residual carbon. In some
embodiments,
the material that is yielded by the operation of the vacuum induction furnace
includes
100 parts per million or less of residual carbon. In some embodiments, the
material that
zo .. is yielded by the operation of the vacuum induction furnace includes an
amount of
residual carbon that is equal to or less than an amount of residual carbon in
an as-cast
aluminum alloy.
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[0035] In some embodiments, the material that is yielded by the
operation of the
vacuum induction furnace as described above includes substantially no residual
sodium. In some embodiments, the material that is yielded by the operation of
the
vacuum induction furnace as described above includes 25 parts per million or
less of
residual sodium. In some embodiments, the material that is yielded by the
operation of
the vacuum induction furnace as described above includes 24 parts per million
or less
of residual sodium. In some embodiments, the material that is yielded by the
operation
of the vacuum induction furnace as described above includes 23 parts per
million or
less of residual sodium. In some embodiments, the material that is yielded by
the
operation of the vacuum induction furnace as described above includes 22 parts
per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 21
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 20
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 19
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 18
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
zo the operation of the vacuum induction furnace as described above
includes 17 parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 16
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
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the operation of the vacuum induction furnace as described above includes 15
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 14
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 13
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 12
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 11
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 10
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 9
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 8
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 7
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 6
parts per
zo million or less of residual sodium. In some embodiments, the material
that is yielded by
the operation of the vacuum induction furnace as described above includes 5
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 4
parts per
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million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 3
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 2
parts per
million or less of residual sodium. In some embodiments, the material that is
yielded by
the operation of the vacuum induction furnace as described above includes 1
parts per
million or less of residual sodium.
[0036]
In some embodiments, the process described above is performed in the
absence of flux (i.e., is flux-free). In some embodiments, the material that
is yielded by
the operation of the vacuum induction furnace retains substantially all
lithium that was
contained therein. In some embodiments, the material that is yielded by the
operation
of the vacuum induction furnace retains substantially all alloy material that
was
contained therein prior to melting in the vacuum induction furnace.
In some
embodiments, little or no oxidation occurs.
[0037] In some embodiments, the material that is yielded by the operation
of the
vacuum induction furnace includes between 0% and 0.4% lithium.
In some
embodiments, the material that is yielded by the operation of the vacuum
induction
furnace includes between 0.4% and 0.8% lithium. In some embodiments, the
material
that is yielded by the operation of the vacuum induction furnace includes
between 0.8%
zo and 1.2% lithium. In some embodiments, the material that is yielded by
the operation of
the vacuum induction furnace includes between 1.2% and 1.6% lithium. In some
embodiments, the material that is yielded by the operation of the vacuum
induction
furnace includes between 1.6% and 2.0% lithium. In some embodiments, the
material
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that is yielded by the operation of the vacuum induction furnace includes
between 2.0%
lithium and 2.4% lithium. In some embodiments, the material that is yielded by
the
operation of the vacuum induction furnace includes between 2.4% lithium and
2.7%
lithium. In some embodiments, the material that is yielded by the operation of
the
vacuum induction furnace is suitable for repeated commercial use.
[0038] The exemplary embodiments described herein have been described
with
specific reference to techniques for melting and cleaning AlLi machining scrap
that is
contaminated with sodium and/or lubricant. However, it will be apparent to
those of skill
in the art that the principles embodied by the exemplary embodiments are
equally
io applicable to the melting and cleaning of any other metal. It will be
further apparent to
those of skill in the art that the principles embodied by the exemplary
embodiments are
equally applicable to metals contaminated by any other type of high vapor
pressure
contaminant.
[0039] While a number of embodiments of the present invention have been
described, it is understood that these embodiments are illustrative only, and
not
restrictive, and that many modifications may become apparent to those of
ordinary skill
in the art. Further still, unless the context clearly requires otherwise, the
various steps
may be carried out in any desired order, and any applicable steps may be added
and/or
eliminated.
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