U.S. patent application number 10/493006 was filed with the patent office on 2005-02-10 for filtration system for magnesium recycling and purification.
Invention is credited to Choy, Chee Mun, Hu, BangHong, Tong, Kin Kong, Zhang, Su Xia.
Application Number | 20050029718 10/493006 |
Document ID | / |
Family ID | 20430845 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050029718 |
Kind Code |
A1 |
Hu, BangHong ; et
al. |
February 10, 2005 |
Filtration system for magnesium recycling and purification
Abstract
Magnesium alloys are heated to a molten state in preparation for
hot-working thereof, for example, die-casting. The presence of
inclusions within the magnesium alloys results in metallurgical
defects therein and will adversely affect the quality of the
castings produced from the magnesium alloys. An embodiment of the
invention processes the magnesium melt containing impurities
through a non-reactive filter under an environment filled with
protective gas for substantially purifying the magnesium melt and
to reduce the presence of inclusions in castings formed
therefrom.
Inventors: |
Hu, BangHong; (Singapore,
SG) ; Tong, Kin Kong; (Signapore, SG) ; Choy,
Chee Mun; (Singapore, SG) ; Zhang, Su Xia;
(Singapore, SG) |
Correspondence
Address: |
CONLEY ROSE, P.C.
P. O. BOX 3267
HOUSTON
TX
77253-3267
US
|
Family ID: |
20430845 |
Appl. No.: |
10/493006 |
Filed: |
September 27, 2004 |
PCT Filed: |
October 18, 2002 |
PCT NO: |
PCT/SG02/00238 |
Current U.S.
Class: |
266/227 ;
75/600 |
Current CPC
Class: |
C22B 26/22 20130101;
Y02P 10/234 20151101; B22D 17/30 20130101; C22B 9/006 20130101;
Y02P 10/214 20151101; C22B 9/023 20130101; Y02P 10/226 20151101;
B22D 43/004 20130101; Y02P 10/20 20151101 |
Class at
Publication: |
266/227 ;
075/600 |
International
Class: |
C22B 026/22 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 19, 2001 |
SG |
SG 200106275-1 |
Claims
1. A filtration system for magnesium recycling and purification,
the filtration system comprising: a fast chamber for containing
magnesium melt the magnesium melt containing impurities ad the
first chamber enclosing the magnesium melt containing impurities
therein; and a second chamber for receiving purified magnesia melt,
the second chamber enclosing the purified magnesium melt therein
and the first and second chambers respectively separating the
magnesium melt containing impurities and the purified magnesium
melt from the atmosphere, wherein sad first and second chambers
have disposed therebetween a filter, the filter being a
silicon-free medium, and each of the first chamber and the second
chamber for further containing and enclosing protective gases
therein.
2. The filtration system as in claim 1, the second chamber being in
fluid communication with the first chamber and the filter for
substantially removing the impurities from the magnesium melt
flowing from the first chamber into the second chamber.
3. The filtration system as in claim 1, further comprising; a
heating apparatus integrated with the first and second chambers for
maintaining the magnesium melt contained in the first and second
chambers in a molten state.
4. The filtration system as in claim 1, further comprising. a
filter adapter disposed between the first chamber and the second
chamber, the filter being removably coupled to the filter adapter
and the filter adapter for positioning the filter to interface the
first chamber and the second chamber.
5. The filtration system as in claim 1, the filter comprising one
of steel or ceramic material.
6. The filtration system as in claim 5, the filter further
comprises at least one material selected from a group consisting of
Al.sub.2O.sub.3, MgO, AlPO.sub.4 and Mg.sub.3(PO.sub.4).sub.2.
7. The filtration system as m claim 1, the filter comprising an
array of at least one aperture.
8. The filtration system as in claim 7, each of the at least one
aperture being shaped and dimension for preventing passage of a
panicle having a size greater than 5 microns therethrough.
9. The filtration system as in claim 7, each pair adjacent
apertures being spaced apart a distance of 5 to 250 microns.
10. The filtration system as in claim 1, further comprising a
temperature control system for regulating temperature of the
magnesium melt within the first chamber and the second chamber.
11. The filtration system as in claim 10, the temperature control
system, comprising: a controller, the heating apparatus being
electrically connected to the controller; a first thermocouple
being electrically connected to the controller and being disposed
within the first chamber for transducing temperature of the
magnesium melt therein into first temperature signals; and a second
thermocouple being electrically connected to the controller and
being disposed within the second chamber for transducing
temperature of the filtered magnesium melt therein into second
temperature signals, wherein the first temperature signals and the
second temperature signals are transmitted to the controller, the
controller having a control function for controlling the heating
apparatus and thereby maintaining the magnesium melt in a molten
state and preventing overheating of the magnesium melt.
12. The filtration system as in claim 1, further comprising a gas
feed system for introducing a protective gas in to the first and
second chambers.
13. The filtration system as in claim 1, further comprising a step
of: an extractor for extracting the magnesium melt from the second
chamber, the extractor being extending from within the second
chamber to a die-casting assembly, the extractor for providing the
extracted magnesium melt to the die-casting assembly.
14. A filtration method for magnesium recycling and purification,
comprising the steps of: receiving magnesium melt into a first
chamber, the magnesium melt containing impurities within the first
chamber containing impurities and the first chamber enclosing the
magnesium melt containing impurities therein; providing a second
chamber, the second chamber being in fluid communication with the
first chamber, the second chamber enclosing the purified magnesium
melt herein and the first and second chambers respectively
separating the magnesium melt containing impurities and the
purified magnesium melt from the atmosphere; and substantially
removing the impurities from the magnesium melt flowing from the
first chamber into the second chamber using a filter, the filter
being disposed between the first chamber and the second chamber,
each of the first chamber and the second chamber for further
containing and enclosing protective gases therein, and the filter
including a silicon-free medium.
15. The filtration method as in claim 14, ether comprising a step
of: providing a heating apparatus integrated with the first and
second chambers for maintaining the magnesium melt contained in the
first and second chambers in a molten state.
16. The filtration method as in claim 14, the filter comprising one
of steel or ceramic material.
17. The filtration method as in claim 15, further comprising a step
of providing a temperature control system for regulation
temperature of the magnesium melt within the first chamber and the
second chamber.
18. The filtration method as in claim 17, the temperature control
system comprising: a controller, the heating apparatus being
electrically connected to the controller; a first thermocouple
being electrically connected to the controller and being disposed
within the first chamber for transducing temperature of the
magnesium melt therein into first temperature signals; and a second
thermocouple being electrically connected to the controller and
being disposed within the second chamber for transducing
temperature of the filtered magnesium melt therein into second
temperature signals, wherein the first temperature signals and the
second temperature signals are transmitted to the controller, the
controller having a control fraction for controlling the heating
apparatus and thereby maintaining the magnesium melt in a molten
state and preventing overheating of the magnesium melt.
19. The filtration method as in claim 14, further comprising a step
of: extracting the magnesium melt from the second chamber by an
extractor, the extractor extending from within the second chamber
to a die-casting assembly, the extractor for providing the
extracted magnesium melt to the die-casting assembly.
20. A filtration method for magnesium recycling and purification,
comprising the steps of: receiving magnesium into a first chamber,
the magnesium within the first chamber containing impurities, the
first chamber enclosing the magnesium melt containing impurities
therein and the magnesium being one of a magnesium melt or solid
magnesium ingot; providing a second chamber, the second chamber
being in fluid communication with the first chamber, the second
chamber enclosing the purified magnesium melt therein and the fist
and second chambers respectively separating the magnesium melt
containing impurities and the purified magnesium melt from the
atmosphere; heating the magnesium contained in the fist chamber by
a heating apparatus for melting the magnesium and for maintaining
the magnesium melt in a molten state, and the magnesium melt in the
first chamber thereby flowing into the second chamber; and
substantially removing the impurities from the magnesium melt
flowing from the first chamber into the second chamber using a
filter, the filter being disposed between the first chamber and the
second chamber, each of the first chamber and the second chamber
for further containing and enclosing protective gases therein, and
the filter including a silicon-free medium.
Description
FIELD OF INVENTION
[0001] The present invention relates generally to a filtration
system for purifying magnesium. Specifically, the present invention
relates to a filtration system for recycling and purification of
scrap magnesium and magnesium ingots with impurities.
BACKGROUND
[0002] Magnesium alloys are heated to a molten state in preparation
for hot-working thereof. Molten magnesium alloys easily oxidise and
react with impurities, especially when scrap magnesium alloys are
reused. As a result, magnesium alloys are contaminated by
non-metallic and metallic inclusions, for example oxides or
intermetallic compounds, when melted.
[0003] The magnesium alloys are typically melted for producing
castings. The presence of inclusions within the magnesium alloys
results in metallurgical defects therein and will adversely affect
the quality of the castings produced from the magnesium alloys.
[0004] A known method for removing the impurities is to send the
magnesium alloys to a smelter for smelting. However, smelting is a
costly process. Another known process uses impediment plates
disposed within a furnace for removing top and bottom sludge from
magnesium melts. However, the impediment plates do not remove
inclusions suspended in the magnesium melts.
[0005] Hence, this clearly affirms a need for a filtration system
for purifying magnesium melts.
SUMMARY
[0006] In accordance with a first aspect of the invention, there is
disclosed a filtration system for magnesium recycling and
purification, the filtration system comprising:
[0007] a first chamber for containing magnesium melt, the magnesium
melt containing impurities; and
[0008] a second chamber for receiving purified magnesium melt,
[0009] wherein said first and second chambers have disposed
therebetween a filter, the filter being a silicon-free medium.
[0010] In accordance with a second aspect of the invention, there
is disclosed a filtration method for magnesium recycling and
purification, comprising the steps of:
[0011] receiving magnesium melt into a first chamber, the magnesium
melt containing impurities within the first chamber containing
impurities;
[0012] providing a second chamber, the second chamber being in
fluid communication with the first chamber; and
[0013] substantially removing the impurities from the magnesium
melt flowing from the first chamber into the second chamber using a
filter, the filter being disposed between the first chamber and the
second chamber and the filter including a silicon-free medium.
[0014] In accordance to a third aspect of the invention, there is
disclosed a filtration method for magnesium recycling and
purification, comprising the steps of:
[0015] receiving magnesium into a first chamber, the magnesium
within the first chamber containing impurities and the magnesium
being one of a magnesium melt or solid magnesium ingot;
[0016] providing a second chamber, the second chamber being in
fluid communication with the first chamber;
[0017] heating the magnesium contained in the first chamber by a
heating apparatus for melting the magnesium and for maintaining the
magnesium melt in a molten state, and the magnesium melt in the
first chamber thereby flowing into the second chamber; and
[0018] substantially removing the impurities from the magnesium
melt flowing from the first chamber into the second chamber using a
filter, the filter being disposed between the first chamber and the
second chamber and the filter including a silicon-free medium.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Embodiments of the invention are described hereinafter with
reference to the following drawings, in which:
[0020] FIG. 1 shows a partial front sectional view of a filtration
system according to an embodiment of the invention;
[0021] FIG. 2 shows a partial side sectional view of the filtration
system of FIG. 1;
[0022] FIG. 3 is an illustration of a filter of the filtration
system of FIG. 1;
[0023] FIG. 4 is an illustration of a first chamber and the filter
of FIG. 3;
[0024] FIG. 5a shows a low magnification light optical microscope
(LOM) micrograph of a tensile specimen made from magnesium melt
obtained from the filtration system of FIG. 1;
[0025] FIG. 5b shows the LOM micrograph of FIG. 5a under high
magnification;
[0026] FIG. 6a shows a low magnification light optical microscope
(LOM) micrograph of a mobile phone case specimen made from
magnesium melt obtained from the filtration system of FIG. 1;
[0027] FIG. 6b shows the LOM micrograph of FIG. 6b under high
magnification;
[0028] FIG. 7a shows a graph plotting the tensile strength
(ultimate tensile strength and yield strength) of test samples as a
function of cross-head speed with the test samples being cast from
a magnesium melt purified using the filtration system of FIG. 1;
and
[0029] FIG. 7b shows a graph plotting the percentage elongation of
the test samples of FIG. 7b, as a function of cross-head speed.
DETAILED DESCRIPTION
[0030] An embodiment of the invention, a filtration system 20 is
described with reference to FIG. 1, which shows a partial front
sectional view of the filtration system 20 and FIG. 2 which shows a
partial side sectional view of the filtration system 20. The
filtration system 20 is for use in substantially purifying
magnesium.
[0031] As shown in FIG. 1, the filtration system 20 includes a
crucible 22 being divided into two parts by a filter adapter 24
disposed therein, the two parts of the crucible being namely a
first chamber 26 and a second chamber 28. The first chamber 26 is
in fluid communication with the second chamber 28 through an
opening 30, as shown in FIG. 2, in the filter adapter 24 that forms
a passageway therebetween.
[0032] As shown in FIG. 2, the filter adapter 24 is for receiving a
filter 32 therewithin and for removably engaging thereto. FIG. 3 is
an illustration of the filter 32 and FIG. 4 is an illustration of
the first chamber 26 and the filter 32. When the filter 32 is
engaged to the filter adapter 24, the filter 32 blocks the opening
30 of the filter adapter 24, thereby intersecting the passageway
between the first chamber 26 and the second chamber 28, as shown in
FIGS. 1, 2 and 5. The filter adapter 24 is preferably a steel
structure that shaped and dimensioned for holding the filter 32 at
the periphery thereof.
[0033] The filtration system 20 further includes a heating
apparatus coupled to the crucible 22. The heating apparatus is
preferably integrated with the crucible 22 for providing heat to
the crucible 22 and its contents. The heating apparatus is
electrically connected to a controller (all not shown).
[0034] The filtration system 20 is for providing substantially
purified magnesium melts to downstream systems or machineries, for
example, a die-casting machine. For obtaining purified magnesium
melts from the filtration system 20, magnesium ingots or scraps are
provided to the first chamber 26 of the filtration system 20. The
controller activates the heating apparatus to provide heat to the
crucible 22 and the magnesium therein, thereby melting the
magnesium.
[0035] Alternatively, magnesium melt can be provided to the first
chamber 26 of the crucible 22. The heating apparatus provides heat
to the crucible 22 to maintain the magnesium melt in its molten
state and to melt the magnesium scraps and ingots added to the
magnesium melt thereafter.
[0036] The filter 32 of the filtration system 20 is preferably made
of a silicon-free material. Conventional filters, for example a
filter for aluminium alloys, are made of silicon-based materials.
The silicon-based materials readily react with magnesium to cause
contamination therein and are therefore undesirable. The filter 32
is made of one of steels or ceramic material which comprises of one
or more material selected from a group consisting of
Al.sub.2O.sub.3, MgO, AlPO.sub.4 and Mg.sub.3(PO.sub.4).sub.2.
[0037] The filter 32 comprises of an array of apertures (not
shown). Each of the apertures is shaped and dimensioned for
preventing the passage of a particle having a size greater than 5
microns therethrough. Preferably, each pair of adjacent apertures
are spaced apart a distance of 5 to 250 microns. The magnesium melt
38 in the first chamber 26 passes through the filter 32 and into
the second chamber 28 of the crucible 22. Therefore, the impurities
suspended in the magnesium melt 38 contained in the first chamber
26 is substantially removed by the filter 32 before entering the
second chamber 28 as purified magnesium melt 40. The magnesium melt
38 contained in the first chamber 26 contains bottom sludge that
has settled at the bottom of the first chamber 26. In most
situations, top sludge can also be found floating at the surface of
the magnesium melt 38 contained in the first chamber 26. The filter
adapter 24 functions to substantially impede the top sludge and
bottom sludge in the first chamber 26 from entering the second
chamber 28 (all not shown).
[0038] With reference to FIG. 1, the magnesium melt 38 in the first
chamber 26 is drawn into the second chamber 28 by hydrostatic
forces acting on the magnesium melt 38. The magnesium melt 38 in
the first chamber 26 continues to be drawn into the second chamber
until the hydrostatic pressures of magnesium melt 38 in the first
chamber 26 and the purified magnesium melt 40 in the second chamber
28 are in equilibrium.
[0039] Preferably, each of the first chamber 26 and the second
chamber 28 has a thermocouple 42 disposed therewithin. Both the
thermocouples 42 are electrically connected to the controller for
transducing temperature of the magnesium melt 38 in the first
chamber 26 into first temperature signals (not shown) and the
temperature of the purified magnesium melt 40 in the second chamber
40 into second temperature signals (not shown). The first and
second temperature signals are transmitted to the controller. From
the first and second temperature signals, the controller uses a
control function (not shown) to determine and control the heat
output of the heating apparatus, thereby maintaining the magnesium
melt 38 and the purified magnesium melt 40 in a molten state and to
prevent overheating thereof. In the molten state, the viscosities
of both the magnesium melt 38 and the purified magnesium melt 40
are greatly reduced, thereby facilitating flow thereof through the
filter 32.
[0040] The crucible 22 is preferably enclosed for receiving and
retaining protective gas therein. A gas feed system (not shown) is
connected to the crucible for supplying the protective gas
thereinto. The protective gas prevents both the magnesium melt 38
and the purified magnesium melt 40 from reacting with the
atmosphere by forming a screen therebetween.
[0041] An extractor 44, as shown in FIG. 1, extends from within the
second chamber 28 to a die-casting assembly 46. The extractor 44 is
for extracting the purified magnesium melt 40 from the second
chamber 28 and providing the purified magnesium melt 40 to the
die-casting assembly 46. The extractor 44 shown in FIG. 1 uses a
piston and a goose-neck chamber assembly for extracting the
purified magnesium melt 40.
[0042] Extracting the purified magnesium melt 40 from the second
chamber 28 reduces the level of the purified magnesium melt 40
contained therein. The reduction of the level of the purified
magnesium melt 40 in the second chamber 28 further draws the
magnesium melt 38 from the first chamber 26 and into the second
chamber 28. Magnesium melt and magnesium ingots or scraps can be
further provided to the first chamber 26 for replenishing the
second chamber 28 and thereby the filtration system 20 with
purified magnesium melt 40.
[0043] The purified magnesium melt 40 supplied from the filtration
system 20 to the die-casting assembly 46 provides the die-casting
assembly with a substantially inclusion-free purified magnesium
melt 40 supply for use in a die-casting process.
[0044] Two types of parts, hand-phone case and tensile test
specimens, were cast during tests. The alloy used in the tests was
AZ91 HP having a composition of Al 8-9.5%, Zn 0.3-1.0%,
Mn.gtoreq.0.17%, Si.ltoreq.0.05%, Fe.ltoreq.0.004%,
Cu.ltoreq.0.015%, Ni.ltoreq.0.01%, others .ltoreq.0.01%, others
.ltoreq.0.01%, Mg (remaining). For comparison the tests were
conducted using 100% fresh ingot and ingot including 10% scraps
material.
[0045] After casting, the microstructure and chemical properties of
the specimens were analyzed. The microstructure analysis was
conducted with light optical microscopy (LOM) while mechanical
properties were determined using an Instron tensile testing
machine. The cross-head speed was varied from 0.1 to 20 mm/min
during tensile tests.
[0046] Typical microstructures for the tensile test specimen,
having a diameter of 10 mm-thick walled part and a mobile phone
case, having a wall thickness of 0.6 mm-thin wall part. In both
thick and thin walled parts, the microstructures consist mainly of
.alpha.-Mg, intermetallic-Al.sub.2Mg.sub.17, eutectic composition
and some fine precipitate. However, the thin walled parts showed
much finer structure, as shown in FIGS. 7a and 7b, when compared to
the thick walled parts shown in FIGS. 6a and 6b. The reduced
.alpha.-Mg grain size is due to rapid solidification rate occurred
in the thin walled part.
[0047] Mechanical properties of cast samples were determined after
casting. FIGS. 8a and 8b show the tensile strength, comprising the
ultimate tensile strength (ITS) and yield strength (YS) and
elongation as a function of the cross-head speed. As the cross-head
speed is directly related to the strain rate of the testing, the
results obtained indicated that the strain rate has a very slight
influence on the flow stress and strain of magnesium castings when
tested at room temperature. The UTS and YS are about 142 and 119
MPa respectively with an elongation of about 1%.
[0048] A comparison was made between the mechanical properties of
castings made with filtered magnesium (with about 10% scraps) and
castings made with fresh magnesium (100% new ingot). The strength
of the castings is increased when filtered magnesium is used as
compared to when 100% new magnesium ingot is used. However, the
ductility of the magnesium alloys is reduced. The decreased
ductility is typically due to the presence of more intermetallic
compounds and less magnesium in the alloy having scrap parts
therein although the alloy has already been filtered. Therefore,
the composition of the alloy should be adjusted when using scrap
parts.
[0049] In the foregoing manner, a filtration system is described
according to an embodiment of the invention for addressing the
foregoing disadvantages of conventional filtration devices.
Although only one embodiment of the invention is disclosed, it will
be apparent to one skilled in the art in view of this disclosure
that numerous changes and/or modification can be made without
departing from the scope and spirit of the invention.
* * * * *