U.S. patent application number 10/642709 was filed with the patent office on 2005-02-24 for lubricant for improved surface quality of cast aluminum and method.
Invention is credited to Colbert, Raymond J., DeYoung, David H., Giron, Alvaro, Kasun, Thomas J., Kirby, J. Les, Kotow, Nickolas C., Laemmle, Joseph T., Richter, Ray T., Stewart, Patricia A., Wieserman, Larry F..
Application Number | 20050043189 10/642709 |
Document ID | / |
Family ID | 34193691 |
Filed Date | 2005-02-24 |
United States Patent
Application |
20050043189 |
Kind Code |
A1 |
Stewart, Patricia A. ; et
al. |
February 24, 2005 |
Lubricant for improved surface quality of cast aluminum and
method
Abstract
In an oxidation inhibiting lubricant composition suitable for
use in the manufacture of aluminum alloys comprising lubricant base
selected from the group consisting of solid lubricants, liquid
lubricants, grease lubricants, emulsion lubricants, and dispersion
lubricants, the improvement wherein the lubricant composition
further comprises: an effective amount of a fluorine-containing
passivating compound.
Inventors: |
Stewart, Patricia A.;
(Pittsburgh, PA) ; Richter, Ray T.; (Murrysville,
PA) ; Kasun, Thomas J.; (Export, PA) ;
Laemmle, Joseph T.; (Delmont, PA) ; Kotow, Nickolas
C.; (Bethel Park, PA) ; DeYoung, David H.;
(Export, PA) ; Kirby, J. Les; (Delmont, PA)
; Giron, Alvaro; (Murrysville, PA) ; Colbert,
Raymond J.; (Pittsburgh, PA) ; Wieserman, Larry
F.; (Apollo, PA) |
Correspondence
Address: |
ECKERT SEAMANS CHERIN & MELLOTT, LLC
ALCOA TECHNICAL CENTER
100 TECHNICAL DRIVE
ALCOA CENTER
PA
15069-0001
US
|
Family ID: |
34193691 |
Appl. No.: |
10/642709 |
Filed: |
August 18, 2003 |
Current U.S.
Class: |
508/112 ;
164/459; 508/154; 508/155; 508/161; 508/162; 508/165; 508/181;
508/582; 508/590 |
Current CPC
Class: |
C10M 169/04 20130101;
C10M 2213/062 20130101; C10M 2201/081 20130101; C10M 2205/0265
20130101; B22D 11/0668 20130101; C10M 2213/06 20130101; C10M 147/02
20130101; C10M 2201/102 20130101; C10M 2201/082 20130101; B22D
11/07 20130101; C10M 2207/3045 20130101; C10M 2207/2815 20130101;
C10M 147/04 20130101; C10M 2201/087 20130101; C10M 2207/402
20130101; C10N 2030/10 20130101; C10M 2215/20 20130101; C10M
2215/26 20130101; C10M 2201/042 20130101; C10M 2215/18 20130101;
C10M 2211/06 20130101; C10M 2207/2835 20130101; C10M 2205/0206
20130101; C10M 2201/085 20130101; C10M 2213/04 20130101 |
Class at
Publication: |
508/112 ;
508/154; 508/155; 508/161; 508/162; 508/165; 508/181; 508/582;
508/590; 164/459 |
International
Class: |
C10M 125/18; C10M
015/38; C10M 147/00; B22D 011/07 |
Claims
What is claimed is:
1. In an oxidation inhibiting lubricant composition suitable for
use in the manufacture of aluminum alloys comprising lubricant base
selected from the group consisting of solid lubricants, liquid
lubricants, grease lubricants, emulsion lubricants, and dispersion
lubricants, the improvement wherein said lubricant composition
further comprises: an effective amount of a fluorine-containing
passivating compound.
2. The lubricant composition of claim 1 comprising about 0.1% to
about 10% by weight of said fluorine containing passivating
compound.
3. The lubricant composition of claim 1 comprising about 1% to
about 8% by weight of said fluorine containing passivating
compound.
4. The lubricant composition of claim 1 comprising about 3% to
about 5% by weight of said fluorine containing passivating
compound.
5. The lubricant composition of claim 1 wherein said passivating
compound comprises an inorganic fluorine-containing compound.
6. The lubricant composition of claim 1 wherein said passivating
compound comprises an organic fluorine-containing compound.
7. The lubricant composition of claim 1 comprising wherein said
fluorine-containing passivating compound is selected from the group
consisting of: ammonium hexafluozirconate, fluorinated carbon,
sodium bifluoride, potassium bifluoride, magnesium fluoride,
aluminum fluoride, sodium fluoride, calcium fluoride, sodium
hexafluosilicate, sodium hexafluorophosphate, potassium zirconium
fluoride, sodium fluoborate, tetradecafluorohexane, cryolite,
polyhexafluoropropylene oxide, fluorinated ethylene propylene
copolymer, perfluoroalkoxy polymers,
poly(ethylene-co-tetrafluoroethylene), and
polytetrafluoroethylene.
8. The lubricant composition of claim 1 sheared in a high speed
mixing operation prior to use in the manufacture of aluminum
alloys.
9. An oxidation inhibiting lubricant composition for use in the
casting of aluminum alloys comprising: casting lubricant base
selected from the group consisting of glycerol trioleate, ethyl
oleate, methyl oleate, butyl ricinoleate, methyl acetyl
ricinoleate, butyl oleate, glycerol triacetyl rincinoleate, butyl
acetyl rincinoleate, polyalphaolefins, poly isobutlyenes, castor
oil, peanut oil, corn oil, canola oil, cotton seed oil, olive oil,
rapseed oil, safflower oil, sesame oil, sunflower oil, soybean oil,
linseed oil, coconut oil, palm kernel oil, neatsfoot oil, and
combinations thereof, the improvement wherein said lubricant
composition further comprises: adding an effective amount of a
fluorine-containing passivating compound.
10. The lubricant composition of claim 9 comprising about 0.1% to
about 10% by weight of said fluorine containing passivating
compound.
11. The lubricant composition of claim 9 comprising about 1% to
about 8% by weight of said fluorine containing passivating
compound.
12. The lubricant composition of claim 9 comprising about 3% to
about 5% by weight of said fluorine containing passivating
compound.
13. The lubricant composition of claim 9 wherein said passivating
compound comprises an inorganic fluorine-containing compound.
14. The lubricant composition of claim 9 wherein said passivating
compound comprises an organic fluorine-containing compound.
15. The lubricant composition of claim 9 wherein said
fluorine-containing passivating compound is selected from the group
consisting of: ammonium hexafluozirconate, fluorinated carbon,
sodium bifluoride, potassium bifluoride, magnesium fluoride,
aluminum fluoride, sodium fluoride, calcium fluoride, sodium
hexafluosilicate, sodium hexafluorophosphate, potassium zirconium
fluoride, sodium fluoborate, tetradecafluorohexane, cryolite,
polyhexafluoropropylene oxide, fluorinated ethylene propylene
copolymer, perfluoroalkoxy polymers,
poly(ethylene-co-tetrafluoroethylene- ), and
polytetrafluoroethylene.
16. The lubricant composition of claim 9 sheared in a high speed
mixing operation prior to use in the casting of aluminum
alloys.
17. An oxidation inhibiting lubricant composition for use in the
casting of aluminum alloys comprising: casting lubricant oil base
selected from the group consisting of glycerol trioleate, ethyl
oleate, methyl oleate, butyl ricinoleate, methyl acetyl
ricinoleate, butyl oleate, glycerol triacetyl rincinoleate, butyl
acetyl rincinoleate, castor oil, peanut oil, corn oil, canola oil,
cotton seed oil, olive oil, rapseed oil, safflower oil, sesame oil,
sunflower oil, soybean oil, linseed oil, coconut oil, palm kernel
oil, neatsfoot oil, and combinations thereof, the improvement
wherein said lubricant composition further comprises: an effective
amount of a fluorine-containing passivating compound.
18. The lubricant composition of claim 17 comprising about 0.1% to
about 10% by weight of said fluorine containing passivating
compound.
19. The lubricant composition of claim 17 comprising about 1% to
about 8% by weight of said fluorine containing passivating
compound.
20. The lubricant composition of claim 17 comprising about 3% to
about 5% by weight of said fluorine containing passivating
compound.
21. The lubricant composition of claim 17 wherein said passivating
compound comprises an inorganic fluorine-containing compound.
22. The lubricant composition of claim 17 wherein said passivating
compound comprises an organic fluorine-containing compound.
23. The lubricant composition of claim 17 wherein said
fluorine-containing passivating compound is selected from the group
consisting of: ammonium hexafluozirconate, fluorinated carbon,
sodium bifluoride, potassium bifluoride, magnesium fluoride,
aluminum fluoride, sodium fluoride, calcium fluoride, sodium
hexafluosilicate, sodium hexafluorophosphate, potassium zirconium
fluoride, sodium fluoborate, tetradecafluorohexane, cryolite,
polyhexafluoropropylene oxide, fluorinated ethylene propylene
copolymer, perfluoroalkoxy polymers,
poly(ethylene-co-tetrafluoroethylene- ), and
polytetrafluoroethylene.
24. The lubricant of claim 17 sheared in a high speed mixing
operation prior to use in the casting of aluminum alloys.
25. An oxidation inhibiting lubricant composition for use in the
casting of aluminum alloys comprising: an existing casting
lubricant oil base selected from the group consisting of glycerol
trioleate, castor oil, and combinations thereof, the improvement
wherein said lubricant composition further comprises: an effective
amount of a fluorine-containing passivating compound.
26. The lubricant composition of claim 25 comprising about 0.1% to
about 10% by weight of said fluorine containing passivating
compound.
27. The lubricant composition of claim 26 comprising about 1% to
about 8% by weight of said fluorine containing passivating
compound.
28. The lubricant composition of claim 26 comprising about 3% to
about 5% by weight of said fluorine containing passivating
compound.
29. The lubricant composition of claim 26 wherein said passivating
compound comprises an inorganic fluorine-containing compound.
30. The lubricant composition of claim 26 wherein said passivating
compound comprises an organic fluorine-containing compound.
31. The lubricant composition of claim 26 wherein said
fluorine-containing passivating compound is selected from the group
consisting of: ammonium hexafluozirconate, fluorinated carbon,
sodium bifluoride, potassium bifluoride, magnesium fluoride,
aluminum fluoride, sodium fluoride, calcium fluoride, sodium
hexafluosilicate, sodium fluoborate, sodium hexafluorophosphate,
potassium zirconium fluoride, tetradecafluorohexane, cryolite,
polyhexafluoropropylene oxide, fluorinated ethylene propylene
copolymer, perfluoroalkoxy polymers,
poly(ethylene-co-tetrafluoroethylene- ), and
polytetrafluoroethylene.
32. The lubricant of claim 17 sheared in a high speed mixing
operation prior to use in the casting of aluminum alloys.
33. An oxidation inhibiting lubricant composition for use in the
casting of aluminum alloys comprising glycerol trioleate and about
1% to about 5% by weight of a fluorine-containing passivating
compound.
34. The oxidation inhibiting lubricant composition of claim 33
wherein said fluorine containing passivating compound is selected
from the group consisting of: ammonium hexafluozirconate,
fluorinated carbon, sodium bifluoride, potassium bifluoride,
magnesium fluoride, aluminum fluoride, sodium fluoride, calcium
fluoride, sodium hexafluosilicate, sodium hexafluorophosphate,
potassium zirconium fluoride, tetradecafluorohexane, cryolite,
sodium fluoborate, polyhexafluoropropylene oxide, fluorinated
ethylene propylene copolymer, perfluoroalkoxy polymers,
poly(ethylene-co-tetrafluoroethylene), and
polytetrafluoroethylene.
35. The lubricant of claim 34 sheared in a high speed mixing
operation prior to use in the casting of aluminum alloys.
36. A process for the continuous casting of aluminum alloys wherein
molten aluminum alloy is cast into a cooled mold having a
lubricated inner mold wall, said process comprising the steps of:
a) lubricating an inner wall of a cooled, continuous casting mold
with an oxidation inhibiting lubricant composition comprising: i) a
casting lubricant base selected from the group consisting of
glycerol trioleate, ethyl oleate, methyl oleate, butyl ricinoleate,
methyl acetyl ricinoleate, butyl oleate, glycerol triacetyl
rincinoleate, butyl acetyl rincinoleate, polyalphaolefins, poly
isobutlyenes, castor oil, peanut oil, corn oil, canola oil, cotton
seed oil, olive oil, rapseed oil, safflower oil, sesame oil,
sunflower oil, soybean oil, linseed oil, coconut oil, palm kernel
oil, neatsfoot oil, and combinations thereof, and; ii) an effective
amount of a fluorine-containing passivating compound. b) casting a
molten aluminum alloy into said mold, whereby said oxidation
inhibiting lubricant reduces the oxidation of said molten aluminum
base alloy at the meniscus of said lubricated inner mold wall and
said molten aluminum base alloy.
37. The oxidation inhibiting lubricant composition of claim 36
comprising about 0.1% to about 10% by weight of said fluorine
containing passivating compound.
38. The oxidation inhibiting lubricant composition of claim 36
comprising about 1% to about 8% by weight of said fluorine
containing passivating compound.
39. The oxidation inhibiting lubricant composition of claim 36
comprising about 3% to about 5% by weight of said fluorine
containing passivating compound.
40. The oxidation inhibiting lubricant composition of claim 36
wherein said passivating compound comprises an inorganic
fluorine-containing compound.
41. The oxidation inhibiting lubricant composition of claim 36
wherein said passivating compound comprises an organic
fluorine-containing compound.
42. The oxidation inhibiting lubricant composition of claim 36
wherein said fluorine-containing passivating compound is selected
from the group consisting of: ammonium hexafluozirconate,
fluorinated carbon, sodium bifluoride, potassium bifluoride,
magnesium fluoride, aluminum fluoride, sodium fluoride, calcium
fluoride, sodium hexafluosilicate, sodium hexafluorophosphate,
potassium zirconium fluoride, sodium fluoborate,
tetradecafluorohexane, cryolite, polyhexafluoropropylene oxide,
fluorinated ethylene propylene copolymer, perfluoroalkoxy polymers,
poly(ethylene-co-tetrafluoroethylene), and
polytetrafluoroethylene.
43. The lubricant of claim 36 sheared in a high speed mixing
operation prior to use in the casting of aluminum alloys.
Description
FIELD OF THE INVENTION
[0001] The invention relates to coolant and lubricant formulations
for use in the casting of aluminum or aluminum alloy ingots or
bodies. In particular, lubricants and coolants containing a
fluorinated species are used to improve surface quality of cast
ingots or bodies, resulting in enhanced product recovery. A method
for producing aluminum or aluminum alloy ingots with enhanced
surface quality is also disclosed.
BACKGROUND OF THE INVENTION
[0002] The casting of alloys may be done by any number of methods
known to those skilled in the art, such as direct chill casting
(DC), electromagnetic casting (EMC), horizontal direct chill
casting (HDC), hot top casting, continuous casting, semi-continuous
casting, die casting, roll casting and sand casting.
[0003] Each of these casting methods mentioned above has a set of
its own inherent problems, but with each technique, surface
imperfections can be an issue. It is well known in the aluminum
alloy casting art that molten metal (or melt for brevity) surface
oxidation can result in various surface imperfections in cast
ingots such as pits, vertical folds, oxide patches and the like,
which can develop into cracks during casting or in later
processing. A crack in an ingot or slab propagates during
subsequent rolling, for example, leading to expensive remedial
rework or scrapping of the cracked material. One mechanical means
of removing surface imperfections from an aluminum alloy ingot is
scalping. Scalping involves the machining off a surface layer along
the sides of an ingot after it has solidified.
[0004] Certain alloys, such as 7050 and other 7xxx alloys as well
as 5182 and 5083 are especially prone to surface defects and
cracking. In the past, beryllium has been added, usually at part
per million (ppm) levels to some of these alloys to control melt
surface defects, and to prevent magnesium loss due to oxidation.
However, beryllium has been banned from aluminum products used for
food and beverage packaging. Further, there have been increased
concerns over the health risks associated with factory workers
using beryllium and products containing beryllium. For these
reasons, suitable replacement strategies to inhibit oxidation
during casting are needed.
[0005] In casting of aluminum alloys it is also well known in the
art to use a mold lubricant, coolant or parting agent. The terms
lubricant, coolant, and parting agent may have slightly different
meanings to those skilled in the art of casting aluminum alloys,
but for the purposes of the instant invention, the three terms are
used interchangeably. Satisfactory ingot surface can only be
obtained using a lubricant that has is effective in keeping
aluminum from sticking to the mold at high temperatures used in
casting aluminum alloys. In early casting practices greases were
commonly employed as mold lubricants. With the advent of modern
casting methods, including continuous casting, continuous
lubrication with free flowing oils has replaced the use of greases
as mold lubricants.
[0006] Continuous casting refers to the uninterrupted formation of
a cast body or ingot. For example, the body or ingot may be cast on
or between belts, as in belt casting; between blocks, as in block
casting; or in a mold or die that is open at both ends, as in
direct chill (DC) casting. Casting may continue indefinitely if the
cast body is subsequently cut into desired lengths. Alternately,
the pouring operation may be started and stopped when an ingot of
desired length is obtained. The latter situation is referred to as
semi-continuous casting.
[0007] Continuous lubrication is required for fully continuous
casting and offers a number of advantages for semi-continuous
casting. These advantages include elimination of flame and smoke,
elimination of dragging and tearing tendencies near the end of the
cast and allowing casting practices that produce better quality and
more uniform surfaces.
[0008] Despite the use of continuous lubrication during casting, a
limitation of current ingot casting practice exists in the
inadequate control of oxide growth at the meniscus of molten metal
at the mold interface. Uncontrolled oxide growth at the meniscus of
the molten metal and mold interface is particularly problematic of
alloying elements that rapidly oxidize in air or in air containing
moisture. Lithium and magnesium are examples of alloying elements
that oxidize rapidly. In both cases, the vapor pressure is higher
than that of aluminum and they diffuse to the surface and react
with oxygen or moisture in the ambient air.
[0009] The use of atmospheres consisting of inert gases to protect
the melt and ingot have been previously employed to limit ingot
surface oxidation. Examples of the use of protective gases during
casting are taught in U.S. Pat. No. 3,087,213, U.S. Pat. No.
4,770,697 and U.S. Pat. No. 6,269,862.
[0010] U.S. Pat. No. 4,092,159 relates to a fluoride-containing
glass flux for metal casting. U.S. Pat. No. 4,766,948 discloses a
process for coating aluminum alloys that uses a halogen-containing
salt mixture on the inner wall of a mold. U.S. Pat. No. 5,415,220
relates to direct chill casting of an aluminum-lithium alloy using
a protective molten salt cover having lithium chloride and at least
one other salt from a group that includes lithium fluoride.
[0011] There remains a need for an effective alternative to
beryllium to prevent surface imperfections, such as vertical folds,
pits, oxide patches and the like from forming during aluminum ingot
casting, and to prevent melt surface oxidation, particularly when
casting aluminum that is alloyed with magnesium an/or lithium. Such
a method would be instrumental in preventing cracks, which can form
during casting or can develop in later processing. Finally, the
method preferably would have no adverse affect on alloy
properties.
[0012] The primary object of the present invention is to provide a
lubricant composition that inhibits oxidation of metal during
casting.
[0013] Another object of the present invention is to provide an
economical and efficient method for minimizing or eliminating
oxidation of aluminum and high vapor pressure alloying elements,
such as but not limited to, magnesium and lithium at the melt/mold
meniscus during continuous casting of aluminum alloys.
[0014] Yet another object of this invention is to provide a casting
lubricant formulation that inhibits oxidation by producing active
fluoride ions that passivate solidifying metal at casting
temperatures in furnaces.
[0015] A still further object of this invention is to provide a
casting lubricant that inhibits oxidation of the cast metal without
requiring the use toxic and corrosive gaseous atmospheres, and thus
eliminating associated emissions and equipment corrosion.
[0016] Still another object of this invention is to provide a
method to inhibit oxide formation on aluminum alloy ingots or
castings that does not require beryllium additions to the
alloy.
[0017] These and other objects and advantages are met or exceeded
by the instant invention, and will become more fully understood and
appreciated with reference to the following description.
SUMMARY OF THE INVENTION
[0018] In the present invention it has been discovered that when
fluorine-containing compounds are added to conventional casting
lubricants, the improved lubricant formulation can protect the
surface of aluminum alloys from oxidation, and in particular from
runaway magnesium or lithium alloying element oxidation, even in
high humidity atmospheres.
[0019] No toxic or corrosive gases are required to practice the
instant invention. Additionally, an inert atmosphere to minimize
oxidation, and associated expensive furnaces and infrastructure
that are required for maintaining the inert atmosphere are not
required for the practice of the instant invention.
[0020] When used in continuous casting operations, effective
fluorine-containing compounds added to the casting lubricant are
able to prevent oxidation from occurring at the meniscus, or where
the melt contacts the mold wall. Existing continuous casting
equipment for aluminum alloys can be used for this invention.
[0021] Fluorine-containing compounds are added to existing
lubricant bases to prepare the oxidation inhibiting lubricant
formulations of this invention. For the purposes of this invention,
the fluorine-containing compounds which are effective at protecting
the aluminum alloy from oxidation are referred to as
fluorine-containing passivating compounds. The fluorine-containing
passivating compound can be an inorganic compound, such as but not
limited to, ammonium hexafluozirconate, fluorinated carbon, sodium
bifluoride, potassium bifluoride, magnesium fluoride, aluminum
fluoride, sodium fluoride, calcium fluoride, sodium
hexafluosilicate, sodium hexafluorophosphate, potassium zirconium
fluoride, sodium fluoborate, and cryolite.
[0022] Alternately, the fluorine-containing passivating compound
can be an organic compound or polymer, such as but not limited to
tetradecafluorohexane, polyhexafluoropropylene oxide, fluorinated
ethylene propylene copolymer, perfluoroalkoxy polymers,
poly(ethylene-co-tetrafluoroethylene), and polytetrafluoroethylene
(Teflon.RTM.--PTFE). For organic compounds, completely fluorinated,
or perfluorinated, compounds are preferred, but it is realized that
partially fluorinated organic compounds, such as for example,
chlorofluorocarbons or hydrofluorocarbons fall within the scope of
this invention.
[0023] Existing lubricant bases that may be used in this invention
include solid lubricants, such as for example molybdenum disulfide
and graphite; liquid lubricants, such as for example mineral oils;
and semi-liquid lubricants, including for example waxes, greases,
emulsions, dispersions, and single phase coolants. Families of
existing lubricants and/or additives that can be used for this
invention include, but are not limited to: mineral oils, synthetic
lubricants, poly (alpha olefins), polyisobutylene, monobasic and
dibasic esters, polyglycols, chlorofluorocarbons, fluorocarbons,
phosphate esters, overbased sulphonates of metals, phosphonic acids
and salts thereof, silicate esters, slianes, siloxanes, polyphenyl
ethers, fluoroesters, neopentyl polyol esters, Teflon.RTM., natural
oils and fats (for example: castor oil, peanut oil, corn oil,
canola oil, cotton seed oil, olive oil, rapseed oil, safflower oil,
sesame oil, sunflower oil, soybean oil, linseed oil, coconut oil,
palm kernel oil, neatsfoot oil), fatty acids, fatty alcohols,
organic metal complexes, ion pairs with amine compounds, soaps,
hydrogenated and semi-hydrogenated oils and fats, organic and
inorganic borates, and lamellar solids.
[0024] The oxidation inhibiting lubricant formulations are mixed in
a high speed mixing operation, such as blending or shearing, or any
other mixing operation known by those skilled in the art to provide
dispersions, emulsions, and/or true solutions. At this stage, the
formulation is ready to use as a oxidation inhibiting casting
lubricant.
[0025] In a preferred embodiment of this invention, glycerol
trioleate is used as the conventional casting lubricant base. About
1% by weight of fluorinated carbon, also known in the art as
fluorinated graphite, is added to the glycerol trioleate base. The
mixture is then sheared in a high speed blender for about 5
minutes. The oxidation inhibiting lubricant so formulated is
applied to a casting mold in any manner that is familiar to those
skilled in the art of casting aluminum alloys.
[0026] In another preferred embodiment of this invention,
polyalphaolefin is used as the conventional casting lubricant base.
About 1% by weight of sodium hexafluosilicate is added to the
polyalphaolefin base. A preferred polyalphaolefin base is
ExxonMobil SHF-101 from the ExxonMobil Chemical Company, Houston,
Tex. The mixture is then sheared in a high speed blender for about
5 minutes. The oxidation inhibiting lubricant so formulated is
applied to a casting mold in any manner that is familiar to those
skilled in the art of casting aluminum alloys.
[0027] In a different preferred embodiment of this invention,
glycerol trioleate is used as the conventional casting lubricant
base. About 2% by weight of tetradecafluorohexane, also known in
the art as perfluorinated hexane, is added to the glycerol
trioleate base. The mixture is then sheared in a high speed blender
for about 5 minutes. The oxidation inhibiting lubricant so
formulated is applied to a casting mold in any manner that is
familiar to those skilled in the art of casting aluminum
alloys.
[0028] In yet another preferred embodiment of this invention,
glycerol trioleate is used as the conventional casting lubricant
base. About 1% by weight of sodium hexafluorophosphate is added to
the glycerol trioleate base. The mixture is then sheared in a high
speed blender for about 5 minutes. The oxidation inhibiting
lubricant so formulated is applied to a casting mold in any manner
that is familiar to those skilled in the art of casting aluminum
alloys.
[0029] In still another preferred embodiment of this invention,
glycerol trioleate is used as the conventional casting lubricant
base. About 1% by weight of potassium zirconium fluoride is added
to the glycerol trioleate base. The mixture is then sheared in a
high speed blender for about 5 minutes. The oxidation inhibiting
lubricant so formulated is applied to a casting mold in any manner
that is familiar to those skilled in the art of casting aluminum
alloys.
[0030] In one more preferred embodiment of this invention, an
oxidation inhibiting lubricant formulation of this invention is
supplied to the oil ring of a cooled continuous or semi-continuous
casting mold, which subsequently lubricates the inner wall of the
continuous casting mold. Molten aluminum alloy is cast into the
mold. The oxidation inhibiting lubricant reduces the oxidation of
the molten aluminum base alloy at the meniscus of the lubricated
inner mold wall and the molten aluminum base alloy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a flowchart for preparation of the formulation of
the oxidation inhibiting lubricant of the instant invention.
[0032] FIG. 2 is a schematic characterization of a DC continuous
casting mold used in the method of this invention.
[0033] FIG. 3 is a plot of oxide thickness obtained on the surface
of aluminum alloy 5182 when oxidation inhibiting lubricant
formulations were placed on the alloy surface and heated to
500.degree. C. for 12 hours in air.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] The instant invention provides casting lubricant
formulations and methods for using these formulations that
substantially inhibit the formation of surface oxides during
casting of aluminum alloys. In particular, practice of the instant
invention protects the meniscus of molten aluminum alloy at the
mold interface from uncontrolled oxidation.
[0035] Practice of this invention protects the surface of molten
and solid aluminum alloys from oxidation even in high humidity.
Furthermore, the instant invention is effective in protecting
aluminum alloy surfaces from oxidation, even for aluminum alloys
containing lithium and magnesium.
[0036] Referring now to FIG. 1, a flowchart for preparation of the
oxidation inhibiting lubricant of this investigation is presented.
The invention improves on existing lubricants used in the casting
of aluminum and aluminum base alloy ingots and forms, and in the
general manufacture of aluminum products, using thermomechanical
processes such as, but not limited to, casting, extrusion, hot and
cold rolling, and forging.
[0037] In a preferred embodiment, an existing aluminum alloy
casting lubricant, glycerol trioleate, is used as the lubricant
base. About 1% by weight of fluorinated carbon, also known in the
art as fluorinated graphite, is added to the glycerol trioleate
base. The mixture is then sheared in a high speed blender for about
5 minutes. The oxidation inhibiting lubricant so formulated is
applied to a casting mold in any manner that is familiar to those
skilled in the art of casting aluminum alloys.
[0038] In another preferred embodiment of this invention, glycerol
trioleate is used as the conventional casting lubricant base. About
2% by weight of tetradecafluorohexane, also known in the art as
perfluorinated hexane, is added to the glycerol trioleate base. The
mixture is then sheared in a high speed blender for about 5
minutes. The oxidation inhibiting lubricant so formulated is
applied to a casting mold in any manner that is familiar to those
skilled in the art of casting aluminum alloys.
[0039] In yet another preferred embodiment of this invention,
glycerol trioleate is used as the conventional casting lubricant
base. About 1% by weight of sodium hexafluorophosphate is added to
the glycerol trioleate base. The mixture is then sheared in a high
speed blender for about 5 minutes. The oxidation inhibiting
lubricant so formulated is applied to a casting mold in any manner
that is familiar to those skilled in the art of casting aluminum
alloys.
[0040] In still another preferred embodiment of this invention,
glycerol trioleate is used as the conventional casting lubricant
base. About 1% by weight of potassium zirconium fluoride is added
to the glycerol trioleate base. The mixture is then sheared in a
high speed blender for about 5 minutes. The oxidation inhibiting
lubricant so formulated is applied to a casting mold in any manner
that is familiar to those skilled in the art of casting aluminum
alloys.
[0041] The choice of a preferred fluorine-containing passivating
compound can be determined by the intended use of the oxidation
inhibiting lubricant, for example, the use of the lubricant for
casting aluminum alloys at a particular melt temperature. While not
intending to be bound by any particular theory, it is hypothesized
that at or below the operating temperature of the processing step
the fluorine-containing passivating compound in the oxidation
inhibiting lubricant of this invention breaks down to supply a
active fluoride species to the solidifying aluminum alloy surface.
The term "active fluoride" for purposes of this invention, means a
fluorine species that is capable of reacting directly with the
metal to form a metal fluoride, or one that can displace a metal
oxide to form a metal fluoride. Since fluorine is the most
electronegative element on the periodic table of the elements,
active fluorides can displace the oxide on the solidified metal
surface and form metal oxy-fluoride surface compounds. If
sufficient fluoride is present, the entire metal oxide can be
converted to a metal fluoride, thus preventing oxidation of the
metal surface in air or humid air.
[0042] Based on the above hypothesis, it is surprising that certain
fluorine-containing passivating compounds are effective in the
oxidation inhibiting lubricant of this invention. For example,
experiments have shown that 1% magnesium fluoride in glycerol
trioleate is an effective oxidation inhibiting lubricant
formulation for minimizing oxidation of aluminum alloy 5182. The
melting point of magnesium fluoride is 1261.degree. C. ("CRC
Handbook of Chemistry and Physics, 65.sup.th Edition, CRC Press,
Inc., Boca Raton, Fla., 1985), well above the liquidus of most
aluminum alloys. It is speculated that the enough magnesium
fluoride decomposes in the oxidation inhibiting lubricant at the
aluminum alloy casting temperature to provide the 5182 aluminum
alloy surface with sufficient fluoride to prevent oxidation, even
though the temperature during casting is substantially below the
melting point of magnesium fluoride.
[0043] A major benefit of the oxidation inhibiting lubricant of
this invention is realized in preventing oxidation of aluminum and
its alloying elements at the meniscus during DC casting of
aluminum. However, it is recognized by those skilled in the art
that the oxidation inhibiting lubricant of this invention can be
used in any thermomechanical processing of aluminum and its alloys.
These processing steps include, but are not limited to casting, hot
and cold rolling, forging, and extrusion. A fluorine containing
passivating compound can be selected to be effective at the
operating temperature of the thermomechanical process being
considered for use with the oxidation inhibiting lubricant of this
invention.
[0044] Fluorine containing passivating compounds that are effective
for the practice of this invention include, but are not limited to,
ammonium hexafluozirconate, fluorinated carbon, sodium bifluoride,
potassium bifluoride, magnesium fluoride, aluminum fluoride, sodium
fluoride, calcium fluoride, sodium hexafluosilicate, sodium
hexafluorophosphate, potassium zirconium fluoride,
tetradecafluorohexane, cryolite, polyhexafluoropropylene oxide,
fluorinated ethylene propylene copolymer, perfluoroalkoxy polymers,
poly(ethylene-co-tetrafluoroethylene), and
polytetrafluoroethylene.
[0045] Referring now to FIG. 2, a cross-section of a DC casting
mold 10, which can be used to cast aluminum alloy ingots according
to the instant invention, is schematically depicted. The DC casting
mold 10 comprises molten metal 11 from a furnace. The molten metal
is held in a trough 12. A control pin 13 activates and deactivates
the flow of molten metal 11 into a distributor bag 14, which
distributes the molten metal into the cooled mold 15. The molten
metal 11 in the cooled mold 15 may form an oxide skim 16. The inner
wall 17 of the cooled mold 15 is cooled by a water cooling jacket
18 that cools the mold 15 and floods the solidified ingot surface
19 with cooling water 20. The inner wall 17 is also lubricated with
an oxidation inhibiting formulation of the instant invention by
using an oil ring 21 positioned at or near the meniscus of where
the molten metal 11 in the mold 15 contacts the inner wall 17 of
the cooled mold 15. In a preferred embodiment, the oxidation
inhibiting lubricant comprises 1% fluorinated carbon in a glycerol
trioleate base. In another preferred embodiment, the oxidation
inhibiting lubricant comprises 1% fluorinated carbon in a
polyalphaolefin base. Molten metal 11 in the mold 15 solidifies
into a solidified ingot 22. The solidified ingot 22 rests on a
starting block 23. The starting block 23 rests on a starting block
holder 24. The starting block holder 24 is attached to a platen 25.
The platen can be lowered or raised by a cylinder ram 26. As molten
metal 11 in the mold 15 solidifies into solidified ingot 22, the
cylinder ram 26 is lowered, which causes the solidified ingot 22 to
also be lowered according to the directional arrows 27 superimposed
onto the schematic cross section of the DC mold 10. As the cylinder
ram 26 and solidified ingot 22 are lowered the control pin 13 is
activated to allow more molten metal 11 in the trough 12 to flow
into the cooled mold 15 via the distributor bag 14, and ingots of
aluminum alloy are cast, the length of such ingots being
constrained only by the movement of the cylinder ram 26. During the
ingot casting operation, the solidified ingot 22 in contact with
the inner wall 17 is continuously lubricated with the oxidation
inhibiting lubricant of this invention via the oil ring 21, thusly
providing a process for minimizing oxidation of the ingot and
undesirable surface defects that were described earlier. During
practice of this invention, there is no requirement for the
undesirable practice of alloying the aluminum with beryllium, nor
is there any reliance on using toxic gases such as ammonium
fluoborate or boron trifluoride to prevent oxidation during
casting.
[0046] To test the efficacy of the oxidation inhibiting lubricant
formulations, several oxidation inhibiting lubricants were
formulated according to the teachings of this invention as
described in the following examples. The oxidation inhibiting
lubricants so formulated were placed onto the surface of a sheet
aluminum alloy 5182, which was then heated in a furnace at
500.degree. C. for 12 hours. The areas of the 5182 sheet that were
covered with the oxidation inhibiting lubricants were analyzed for
oxide thickness as measured by Auger electron spectroscopy (AES)
depth profiling. The results of the AES oxide thickness
measurements are presented graphically in FIG. 3 and in the
Examples found below.
EXAMPLE 1
[0047] About 1% by weight of ammonium fluozirconate was added to a
glycerol trioleate base. The mixture was sheared in a high speed
blender for about 5 minutes. After placing the lubricant on the
5182 sheet and heating as described above, the oxide thickness was
measured as 975 Angstroms (.ANG.).
EXAMPLE 2
[0048] About 1% by weight of fluorinated graphite was added to a
glycerol trioleate base. The mixture was sheared in a high speed
blender for about 5 minutes. After placing the lubricant on the
5182 sheet and heating as described above, the oxide thickness was
measured as 1,050 Angstroms (.ANG.).
EXAMPLE 3
[0049] About 1% by weight of zirconium tetrafluoride was added to a
glycerol trioleate base. The mixture was sheared in a high speed
blender for about 5 minutes. After placing the lubricant on the
5182 sheet and heating as described above, the oxide thickness was
measured as 1,300 Angstroms (.ANG.).
EXAMPLE 4
[0050] About 0.5% by weight of polytetrafluoroethylene (PTFE) was
added to a glycerol trioleate base. The mixture was sheared in a
high speed blender for about 5 minutes. After placing the lubricant
on the 5182 sheet and heating as described above, the oxide
thickness was measured as 1,350 Angstroms (.ANG.).
EXAMPLE 5
[0051] About 1% by weight of sodium fluoborate was added to a
glycerol trioleate base. The mixture was sheared in a high speed
blender for about 5 minutes. After placing the lubricant on the
5182 sheet and heating as described above, the oxide thickness was
measured as 1,300 Angstroms (.ANG.).
EXAMPLE 6
[0052] About 1% by weight of hydrated sodium hexafluosilicate was
added to a glycerol trioleate base. The mixture was sheared in a
high speed blender for about 5 minutes. After placing the lubricant
on the 5182 sheet and heating as described above, the oxide
thickness was measured as 1,400 Angstroms (.ANG.).
EXAMPLE 7
[0053] About 1% by weight of anhydrous sodium hexafluosilicate was
added to a glycerol trioleate base. The mixture was sheared in a
high speed blender for about 5 minutes. After placing the lubricant
on the 5182 sheet and heating as described above, the oxide
thickness was measured as 1,500 Angstroms (.ANG.).
EXAMPLE 8
[0054] About 0.03% by weight of anhydrous sodium hexafluosilicate
was added to a glycerol trioleate base. The mixture was sheared in
a high speed blender for about 5 minutes. After placing the
lubricant on the 5182 sheet and heating as described above, the
oxide thickness was measured as greater than 10,000 Angstroms
(.ANG.). It is speculated that the concentration of the fluorine
containing passivating compound in the lubricant was insufficient
to prevent oxidation of the 5182 sheet as it was heated at
500.degree. C. for about 12 hours.
EXAMPLE 9
[0055] About 1% by weight of potassium iodide was added to a
glycerol trioleate base. The mixture was sheared in a high speed
blender for about 5 minutes. After placing the lubricant on the
5182 sheet and heating as described above, the oxide thickness was
measured as greater than 10,000 Angstroms (.ANG.). Potassium iodide
is not a fluorine containing passivating compound and was not
effective in the formulation of an oxidation inhibiting lubricant
as taught by the instant invention.
[0056] Having described the presently preferred embodiments, it is
to be understood that the invention may be otherwise embodied
within the scope of the appended claims.
* * * * *