U.S. patent application number 13/169202 was filed with the patent office on 2012-12-27 for master alloy production for glassy aluminum-based alloys.
This patent application is currently assigned to UNITED TECHNOLOGIES CORPORATION. Invention is credited to Thomas J. Watson.
Application Number | 20120328470 13/169202 |
Document ID | / |
Family ID | 46049248 |
Filed Date | 2012-12-27 |
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United States Patent
Application |
20120328470 |
Kind Code |
A1 |
Watson; Thomas J. |
December 27, 2012 |
MASTER ALLOY PRODUCTION FOR GLASSY ALUMINUM-BASED ALLOYS
Abstract
Apparatus is provided for forming aluminum alloy ingots in a
sealed chamber having a source of inert gas using a crucible
positioned inside the chamber for melting aluminum alloy powder.
The crucible has a solid top and a source of inert gas therein. An
outlet in the crucible is positioned to draw molten alloy from the
crucible at a point proximate the lowest point in the crucible. A
tundish adapted to control the flow of molten alloy from the
crucible on a path to at least one ingot mold out of the sealed
chamber
Inventors: |
Watson; Thomas J.; (South
Windsor, CT) |
Assignee: |
UNITED TECHNOLOGIES
CORPORATION
Hartford
CT
|
Family ID: |
46049248 |
Appl. No.: |
13/169202 |
Filed: |
June 27, 2011 |
Current U.S.
Class: |
420/528 ;
164/259; 164/68.1 |
Current CPC
Class: |
C22C 21/00 20130101;
F27B 14/04 20130101; C22C 45/08 20130101; B22D 21/04 20130101; F27B
14/10 20130101; B22D 21/007 20130101; B22D 7/005 20130101 |
Class at
Publication: |
420/528 ;
164/259; 164/68.1 |
International
Class: |
C22C 21/00 20060101
C22C021/00; B22D 27/00 20060101 B22D027/00 |
Claims
1. Apparatus for forming aluminum alloy ingots, comprising: a
sealed chamber having a source of inert gas; a crucible positioned
inside the chamber for melting aluminum alloy input stock
including, but not limited to, chips, shot, rod, bar, etc., the
sealed chamber having a solid top and a source of inert gas therein
adapted to drive out other atmosphere; an outlet in the crucible
positioned to draw molten alloy from the crucible at a point
proximate the lowest point in the crucible; and a tundish adapted
to control the flow of molten alloy from the crucible on a path to
at least one ingot mold while maintaining an inert atmosphere
during the flow of alloy to the mold and out of the sealed
chamber.
2. The apparatus of claim 1, wherein the outlet on the crucible is
positioned to flow alloy out the bottom of the crucible.
3. The apparatus of claim 1, wherein the outlet on the crucible is
positioned to flow alloy out of the lower side of the crucible.
4. The apparatus of claim 1, wherein the outlet includes a launder
having, but not limited to, a cylindrical cross section for
transferring the molten alloy from the crucible to the tundish.
5. The apparatus of claim 1, wherein the inert gas is argon.
6. The apparatus of claim 1, wherein the alloy is a devitrified
glass-forming aluminum alloys having a nanometer-sized grain
structure and nanometer-sized intermetallic phase or phases.
7. A method of forming aluminum alloy ingots, comprising the steps
of: melting aluminum alloy feed stock in a crucible having an inert
atmosphere; drawing molten alloy from the crucible at a point below
the inert atmosphere; and maintaining an inert atmosphere during
the flow of alloy from the crucible to a mold.
8. The method of claim 7, wherein the outlet of the crucible means
is proximate the bottom of the crucible.
9. The method of claim 7, wherein the outlet of the crucible is
positioned to flow alloy out of the lower side of the crucible.
10. The method of claim 7, wherein the the molten alloy is
transferred from the crucible to the mold is performed with a
launder having a cylindrical or other cross section.
11. The method of claim 7, wherein the inert gas is argon.
12. The method of claim 7, wherein the alloy is a devitrified
glass-forming aluminum alloys having a nanometer-sized grain
structure and nanometer-sized intermetallic phase or phases.
13. A method of forming aluminum alloy ingots, comprising the steps
of: melting a quantity of aluminum alloy feed stock in a crucible,
the crucible being positioned inside a chamber having an inert
atmosphere at a pressure sufficient to drive out ambient
atmosphere, the crucible melting the feed stock to a molten alloy;
removing molten alloy from the crucible through an outlet at a
point proximate the lowest point of the crucible; controlling the
flow of molten alloy from the crucible to at least one ingot mold
while maintaining an inert atmosphere, the flow being controlled
with a tundish; and removing the at least one ingot mold from an
inert atmosphere.
14. The method of claim 13, wherein the outlet means on the
crucible means is positioned to flow alloy out the bottom of the
crucible.
15. The method of claim 13, wherein the outlet means on the
crucible means is positioned to flow alloy out of the lower side of
the crucible.
16. The method of claim 13, wherein the outlet includes a launder
having a cylindrical or other cross section for transferring the
molten alloy from the crucible to the tundish.
17. The method of claim 13, wherein the inert gas is argon.
18. The method of claim 13, which further includes the step of
maintaining the dew point in the crucible between -35.degree. F.
(-37.2.degree. C.) and -110.degree. F. (-78.9.degree. C.) or
lower.
19. The method of claim 13, wherein the alloy is a devitrified
glass-forming aluminum alloy having a nanometer-sized grain
structure and nanometer-sized intermetallic phase or phases.
20. An aluminum alloy formed by the method of claim 19.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is related to the following co-pending
applications that are filed on even date herewith and are assigned
to the same assignee: DIFFUSION BONDING OF GLASSY ALUMINUM-BASED
ALLOYS, Ser. No. ______, Attorney Docket No. PA0009506U-U73.12-665;
EXTRUSION OF GLASSY ALUMINUM-BASED ALLOYS, Ser. No. ______;
Attorney Docket No. PA0009510U-U73.12-667KL; PRODUCTION OF ATOMIZED
POWDER FOR GLASSY ALUMINUM-BASED ALLOYS, Ser. No. ______, Attorney
Docket No. PA0009512U-U73.12-668KL; and FORGING OF GLASSY
ALUMINUM-BASED ALLOYS, Ser. No. ______; Attorney Docket No.
PA0009508U-U73.12-671KL. All referenced incorporated herein.
BACKGROUND
[0002] Aluminum alloys are important in many industries. Glassy
Al-based alloys and their devitrified derivatives are currently
being considered for applications in the aerospace industry. These
alloys involve the addition of rare earth and transition metal
elements. These alloys have high strength and, when processed
appropriately, have high ductility.
[0003] One of the key requirements for high ductility is control of
the uptake of hydrogen. While all Al-based alloys are sensitive to
hydrogen, alloys containing rare earth elements are particularly
susceptible to the effects of hydrogen during alloy production.
[0004] When Al-based alloys are produced in large quantities, they
are often direct chill cast into molds that drop into well-like
openings in the ground. For reactive materials such as Al--Li--X
alloys, care must be exercised to preclude or prevent reaction of
the Li with any oxidant such as air or water. For more reactive
elements such as Yttrium and other rare earths, even more care is
needed because exposure to water that is used to cool direct chill
molds could result in fire and/or an explosion.
[0005] Al-based alloys such as Al--Y--Ni--Co alloys are devitrified
glass-forming aluminum alloys that derive their strength from a
nanometer-sized grain structure and nanometer-sized intermetallic
phase or phases. The presence of hydrogen destroys the ductility of
these alloys. Consequently, it is necessary to produce master
alloys with hydrogen contents of 1 ppm or less. Examples of such
alloys are disclosed in co-owned U.S. Pat. Nos. 6,974,510 and
7,413,621, the disclosures of which are incorporated herein by
reference in their entirety.
[0006] It is necessary to find an alternative process for
production of these highly reactive Al-based alloys.
SUMMARY
[0007] It has now been discovered that master alloy for devitrified
glass-forming Al-based alloys can be produced in a process that
avoids hydrogen pickup. The molten metal is isolated from the
environment to a substantial degree. The process includes the use
of a bottom-pour or side-pour crucible that is "covered" with an
inert gas such as argon. The gas cover includes a physical cover on
the top of the crucible into which argon or another inert gas such
as nitrogen is bled into the crucible to form a positive pressure.
The heavier argon forces out any air to minimize exposure of the
melt to air.
[0008] The metal is poured out from the side or bottom of the
crucible, rather than tipping to pour out the top. It is poured
into a launder or pipe that is sealed and attached to the crucible,
and is also filled with an inert gas such as argon. The molten
metal flows through a launder or launder/tundish combination and is
deposited directly into molds, which are also filled with inert gas
such as argon.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows one embodiment of a bottom pour furnace with a
vertical feed for producing aluminum alloy ingots while avoiding
hydrogen pickup.
[0010] FIG. 2 shows another embodiment of a bottom pour furnace
with a horizontal feed for producing aluminum alloy ingots while
avoiding hydrogen pickup.
[0011] FIG. 3 is a possible cross section for the horizontal feed
launders of the apparatus of FIG. 2.
[0012] FIG. 4 is a flow diagram illustrating the method of forming
aluminum master alloy ingots.
DETAILED DESCRIPTION
[0013] FIG. 1 illustrates a bottom pour furnace 10 generally with a
vertical feed. The entire furnace is inside an inert chamber 11,
having a solid top 17, with gas feed 13 introducing argon or
another inert gas such as nitrogen. It is more effective if the
inert gas is heavier than air, as argon is, to more easily push out
any air that is initially present in chamber 11. A top-feed
crucible 15 is located inside chamber 11. Inside crucible 15 is a
quantity of aluminum and various alloy elements in the form of
chips, shot, rod, etc. that is to be made into master alloy ingots.
The aluminum alloy can be any alloy but it has been discovered that
the glassy devitrified alloys such as those disclosed in co-owned
U.S. Pat. Nos. 6,974,510 and 7,413,621, can be formed into low
oxygen and low hydrogen master alloy ingots using the method of
this invention.
[0014] The alloy in crucible 15 is purged with argon or another
inert gas to drive out oxygen and any other reactive gas. Hydrogen
from moisture is also driven out. Crucible 15 may be any low
moisture/low volatiles alumina crucible, such as those produced by
St. Gobain, or a graphite crucible with a spall-free alumina
coating. Typical crucibles are ceramic cylinders that are about two
feet in diameter and about three feet deep.
[0015] The alloy is melted in crucible 15 and exits the bottom of
crucible through launder 19, so that the flow of molten alloy is
controlled by position-control door 21. Launder may not be needed
in some designs of crucible 15. With or without launder 19, the
passage out of crucible 15 is also accomplished in an inert
atmosphere via inert gas feed 23.
[0016] Tundish 25 is a funnel-shaped vessel into which the molten
metal is poured. The purpose of a tundish is to allow the molten
metal to reach a desired height (with a desired head pressure) so
that there is a constant pour rate. It has been discovered that a
slower rate precluded bubbles from forming in the melt. The height
can be adjusted so there is no splashing of the metal into the
molds. Flowing molten alloy 27 pours into waffle ingot molds 29
carried by conveyor belt 31, also in an inert atmosphere.
[0017] Allowing the molten alloy to drain down from the bottom of
crucible 15 eliminates a major problem in prior art furnaces, in
that the dross that accumulates on the top of the molten pool of
alloy remains at the top and does not have to be removed until
crucible 15 is cleaned prior to recharging with more alloy. Also,
the dew point can be monitored, further preventing undesirable gas
from contacting the sensitive elements of the alloy, thus
preserving the low hydrogen/oxygen content of the master alloy.
[0018] For the two embodiments as discussed herein, a hygrometer
with a computer can be used for measuring the amount of moisture,
and therefore hydrogen, in the gases both at the source for 13 and
23, and within chamber 11 as a function of time. Best results are
obtained when the dew point is -110.degree. F. (-78.9.degree. C.)
or lower. A commercially available monitor such as an ALSCAN may be
connected to a computer so that hydrogen readings in the melt may
also be taken in real time. Similar readings in the launder can be
used to monitor hydrogen there as well, which is to be as low as
possible, i.e., less than 1 ppm.
[0019] In an alternative embodiment, a bottom pour furnace 100
generally is shown in FIG. 2. A first inert chamber 111, having a
solid top 117, is maintained in an inert state via inert gas feed
113. Crucible 115 is filled or purged with an inert gas to drive
out all reactive gasses, including hydrogen via the gas from 113. A
launder 119, angled downward, is maintained with an inert
atmosphere by a plurality of inert gas feeds 123 down stream of
metal flow control door 121. Launder 119 has a typical cross
section as shown in FIG. 3, with a steel or other hard casing 141,
a ceramic mold or center passage 143 and the opening 145 through
which the molten alloy flows. Tundish 125 controls the pour rate
and pour height of molten alloy into waffle ingot molds 129 that
are carried by conveyor belt 131. Again inert gas is maintained in
second inert chamber 211 by inert gas feed 213.
[0020] FIG. 4 is a flow diagram of the method of this invention.
Aluminum and the required elements in the form of chips, shot, rod,
etc. (Step 311) are selected and placed in an enclosed crucible
having an inert atmosphere (Step 313) with a positive pressure to
drive out other gasses. The input stock is melted (Step 315) to
form a molten alloy. The molten alloy is transferred (Step 317) to
a mold while maintaining an inert atmosphere at least until the
ingot is solidified. The ingot is then removed (Step 319) and
available for subsequent processing.
[0021] Both bottom and side pouring embodiments have been found to
be effective in producing satisfactory ingots. The advantage of the
system of FIG. 1 is that the system is more compact with the
launder going straight down. However, if the pouring goes too fast
and can't be stopped, the risk of overpouring onto the floor
exists. In the system of FIG. 2, more space is used but there can
be multiple metal flow gates to contain failure at the bottom of
the furnace.
[0022] While the invention has been described with reference to an
exemplary embodiment(s), it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment(s) disclosed, but that the invention will
include all embodiments falling within the scope of the appended
claims.
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