U.S. patent application number 10/734108 was filed with the patent office on 2005-01-20 for apparatus for manufacturing semi-solid metallic slurry.
This patent application is currently assigned to Hong, Chun Pyo. Invention is credited to Hong, Chun Pyo.
Application Number | 20050011631 10/734108 |
Document ID | / |
Family ID | 33476023 |
Filed Date | 2005-01-20 |
United States Patent
Application |
20050011631 |
Kind Code |
A1 |
Hong, Chun Pyo |
January 20, 2005 |
Apparatus for manufacturing semi-solid metallic slurry
Abstract
Provided is an apparatus for manufacturing a high-quality
semi-solid metallic slurry containing fine, uniform spherical
particles that can be readily and conveniently applied to a
subsequent process, with improvements in energy efficiency and
mechanical properties, cost reduction, convenience of casting,
shorter manufacturing time, and easy discharge. The apparatus
includes: at least one sleeve with two open ends, through one of
which molten metal in liquid state is loaded into the sleeve; a
stirring unit which applies an electromagnetic field to the molten
metal in the sleeve; and a shutter unit which closes the other end
of the sleeve to form a base of the sleeve and opens the base of
the sleeve to discharge a slurry after manufacture from the
sleeve.
Inventors: |
Hong, Chun Pyo; (Seoul,
KR) |
Correspondence
Address: |
ROTHWELL, FIGG, ERNST & MANBECK, P.C.
1425 K STREET, N.W.
SUITE 800
WASHINGTON
DC
20005
US
|
Assignee: |
Hong, Chun Pyo
Nano Cast Korea Corp.
Eunpyung-gu
KR
Incheon-city
KR
|
Family ID: |
33476023 |
Appl. No.: |
10/734108 |
Filed: |
December 15, 2003 |
Current U.S.
Class: |
164/498 ;
164/113; 164/900 |
Current CPC
Class: |
B22D 17/007 20130101;
B22D 27/02 20130101; B22D 1/00 20130101; C22C 1/005 20130101; B22D
7/005 20130101 |
Class at
Publication: |
164/498 ;
164/113; 164/900 |
International
Class: |
B22D 027/02; B22D
023/00; B22D 025/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 15, 2003 |
KR |
2003-0048303 |
Claims
What is claimed is:
1. An apparatus for manufacturing a semi-solid metallic slurry, the
apparatus comprising: at least one sleeve with two open ends,
through one of which molten metal in liquid state is loaded into
the sleeve; a stirring unit which applies an electromagnetic field
to the molten metal in the sleeve; and a shutter unit which closes
the other end of the sleeve to form a base of the sleeve and opens
the base of the sleeve to discharge a slurry after manufacture from
the sleeve.
2. The apparatus of claim 1, wherein the shutter unit is a stopper
fixed to the other end of the sleeve.
3. The apparatus of claim 1, wherein the shutter unit is a plunger
inserted into the other end of the sleeve and moved up and
down.
4. The apparatus of claim 1, further comprising a pressing unit
inserted into the one end of the sleeve to press the slurry in the
sleeve down.
5. The apparatus of claim 1, wherein the molten metal in the sleeve
is cooled until the molten metal has a solid fraction of
0.1-0.7.
6. The apparatus of claim 5, further comprising a temperature
control element to control the temperature of the molten metal
during cooling.
Description
BACKGROUND OF THE INVENTION
[0001] This application claims the priority of Korean Patent
Application No. 2003-48303, filed on Jul. 15, 2003, in the Korean
Intellectual Property Office, the disclosure of which is
incorporated herein in its entirety by reference.
[0002] 1. Field of the Invention
[0003] The present invention relates to an apparatus for
manufacturing a semi-solid metallic slurry, and more particularly,
to an apparatus for manufacturing a semi-solid metallic slurry in a
combined solid and liquid state that contains fine, uniform
spherical particles.
[0004] 2. Description of the Related Art
[0005] Semi-solid metallic slurries refer to metallic materials, in
a combined solid and liquid phase, which are intermediates
manufactured by thixoforming, also expressed as
rheocasting/thixoforming. Semi-solid metallic slurries consist of
spherical solid particles suspended in a liquid phase in an
appropriate ratio at temperature ranges of a semi-solid state, and
thus, they can be transformed even by a small force due to their
thixotropic properties and can be easily cast like a liquid due to
their high fluidity. Rheocasting refers to a process of
manufacturing billets or final products from metallic slurries with
a predetermined viscosity through casting or forging. Thixoforming
refers to a process involving reheating billets, manufactured
through rheocasting, back into semi-molten metallic slurries and
casting or forging the metallic slurries to manufacture final
products.
[0006] Such rheocasting/thixoforming is more advantageous than
general forming processes using molten metals, such as casting or
forging. Because semi-solid/semi-molten metallic slurries used in
rheocasting/thixoforming have fluidity at a lower temperature than
molten metals, it is possible to lower the die casting temperature,
thereby ensuring an extended lifespan of the die. In addition, when
semi-solid/semi-molten metallic slurries are extruded through a
cylinder, turbulence is less likely to occur, and thus less air is
incorporated during casting. Therefore, the formation of air
pockets in final products is prevented. Besides, the use of
semi-solid/semi-molten metallic slurries leads to reduced shrinkage
during solidification, improved working efficiency, mechanical
properties, and anti-corrosion, and lightweight products.
Therefore, such semi-solid/semi-molten metallic slurries can be
used as new materials in the fields of automobiles, airplanes, and
electrical, electronic information communications equipment.
[0007] As described above, semi-solid metallic slurries are used
both in rheocasting and thixoforming. In detail, semi-solid
slurries solidified from molten metals by a predetermined method
are used in rheocasting, and semi-molten slurries obtained by
reheating solid billets are used in thixoforming. Throughout the
specification of the present invention, the term "semi-solid
metallic slurries" means metallic slurries in a combined solid and
liquid state at a temperature range between the liquidus
temperature and the solidus temperature of the metals, which can be
manufactured by rheocasting through solidification of molten
metals.
[0008] In conventional rheocasting, molten metals are stirred at a
temperature of lower than the liquidus temperature while cooling,
to break up dendritic structures into spherical particles suitable
for rheocasting, for example, by mechanical stirring,
electromagnetic stirring, gas bubbling, low-frequency,
high-frequency, or electromagnetic wave vibration, electrical shock
agitation, etc.
[0009] By way of example, U.S. Pat. No. 3,948,650 discloses a
method and apparatus for manufacturing a liquid-solid mixture. In
this method, molten metals are vigorously stirred while cooled for
solidification. A semi-solid metallic slurry manufacturing
apparatus disclosed in this patent uses a stirrer to induce flow of
the solid-liquid mixture having a predetermined viscosity to break
up dendritic crystalline structures or disperse broken dendritic
crystalline structures in the liquid-solid mixture. In this method,
dendritic crystalline structures formed during cooling are broken
up and used as nuclei for spherical particles. However, due to
generation of latent heat of solidification at the early stage of
cooling, the method causes problems of low cooling rate,
manufacturing time increase, uneven temperature distribution in a
mixing vessel, and non-uniform crystalline structure. Mechanical
stirring applied in the semi-solid metallic slurry manufacturing
apparatus inherently leads to non-uniform temperature distribution
in the mixing vessel. In addition, because the apparatus is
operated in a chamber, it is difficult to continuously perform a
subsequent process.
[0010] U.S. Pat. No. 4,465,118 discloses a method and apparatus for
manufacturing semi-solid alloy slurries. This apparatus includes a
coiled electromagnetic field application unit, a cooling manifold,
and a die, which are sequentially formed inward, wherein molten
metals are continuously loaded down into the vessel, and cooling
water is flowed through the cooling manifold to cool the outer wall
of the die. In manufacturing semi-solid alloy slurries, molten
metals are injected through a top opening of the die and cooled by
the cooling manifold, thereby resulting in a solidification zone
within the die. When a magnetic field is applied by the
electromagnetic field application unit, cooling is allowed to break
up dendritic crystalline structures formed in the solidification
zone. Finally, ingots are formed from the slurries and then pulled
through the lower end of the apparatus. The basic technical idea of
this method and apparatus is to break up dendritic crystalline
structures after solidification by applying vibration. However,
many problems arise with this method, such as complicated
processing and non-uniform particle structure. In the manufacturing
apparatus, since molten metals are continuously supplied to grow
ingots, it is difficult to control the states of the metal ingots
and the overall process. Moreover, prior to applying an
electromagnetic field, the die is cooled using water, so that a
great temperature difference exists between the peripheral and core
regions of the die.
[0011] Other types of rheocasting/thixoforming known in the art are
described later. However, all of the methods are based on the
technical idea of breaking up dendritic crystalline structures
after formation, to generate nuclei of spherical particles.
Therefore, problems arise, such as those described in conjunction
with the above patents.
[0012] U.S. Pat. No. 4,694,881 discloses a method for manufacturing
thixotropic materials. In this method, an alloy is heated to a
temperature at which all metallic components of the alloy are
present in a liquid phase, and the resulting molten metals are
cooled to a temperature between their liquidus and solidus
temperatures. Then, the molten metals are subjected to a shearing
force in an amount sufficient to break up dendritic structures
formed during the cooling of the molten metals to thereby
manufacture the thixotropic materials.
[0013] Japanese Patent Application Laid-open Publication No. Hei.
11-33692 discloses a method for manufacturing metallic slurries for
rheocasting. In this method, molten metals are supplied into a
vessel at a temperature near their liquidus temperature or of
50.degree. C. above their liquidus temperature. Next, when at least
a portion of the molten metals reaches a temperature lower than the
liquidus temperature, i.e., at least a portion of the molten metals
begins with cooling below their liquidus temperature, the molten
metals are subjected to a force, for example, ultrasonic vibration.
Finally, the molten metals are slowly cooled into the metallic
slurries containing spherical particles. This method also uses a
physical force, such as ultrasonic vibration, to break up the
dendrites grown at the early stage of solidification. In this
regard, if the casting temperature is greater than the liquidus
temperature, it is difficult to form spherical particle structures
and to rapidly cool the molten metals. Furthermore, this method
leads to non-uniform surface and core structures.
[0014] Japanese Patent Application Laid-open Publication No. Hei.
10-128516 discloses a casting method of thixotropic metals. This
method involves loading molten metals into a vessel and vibrating
the molten metals using a vibrating bar dipped in the molten metals
to directly transfer its vibrating force to the molten metals.
After forming a semi-solid and semi-liquid molten alloy, which
contains nuclei, at a temperature range lower than its liquidus
temperature, the molten alloy is cooled to a temperature at which
it has a predetermined liquid fraction and then left stand from 30
seconds to 60 minutes to allow the nuclei to grow, thereby
resulting in thixotropic metals. However, this method provides
relatively large particles of about 100 .mu.m and takes a
considerably long processing time, and cannot be performed in a
vessel larger than a predetermined size.
[0015] U.S. Pat. No. 6,432,160 discloses a method for making
thixotropic metal slurries. This method involves simultaneously
controlling the cooling and the stirring of molten metals to form
the thixotropic metal slurries. In detail, after loading molten
metals into a mixing vessel, a stator assembly positioned around
the mixing vessel is operated to generate a magnetomotive force
sufficient to rapidly stir the molten metals in the vessel. Next,
the molten metals are rapidly cooled by means of a thermal jacket,
equipped around the mixing vessel, for precise temperature control
of the mixing vessel and the molten metals. During cooling, the
molten metals are continuously stirred in a manner such that when
the solid fraction of the molten metals is low, a high stirring
rate is provided, and when the solid fraction increases, a greater
magnetomotive force is applied.
[0016] Most of the aforementioned conventional methods and
apparatuses for manufacturing semi-solid metal slurries use shear
force to break dendritic structures into spherical structures
during a cooling process. Since a force such as vibration is
applied after at least a portion of the molten metals is cooled
below their liquidus temperature, latent heat is generated due to
the formation of initial solidification layers. As a result, there
are many disadvantages such as reduced cooling rate and increased
manufacturing time. In addition, due to a non-uniform temperature
between the inner wall and the center of the vessel, it is
difficult to form fine, uniform spherical metal particles.
Therefore, this structural non-uniformity of metal particles will
be greater if the temperature of the molten metals loaded into the
vessel is not controlled.
SUMMARY OF THE INVENTION
[0017] The present invention provides an apparatus for
manufacturing a semi-solid metallic slurry containing fine, uniform
spherical particles, with improvements in energy efficiency and
mechanical properties, cost reduction, convenience of casting, and
shorter manufacturing time.
[0018] The present invention also provides an apparatus for
manufacturing a high-quality semi-solid metallic slurry within a
short period of time, which can be readily and conveniently applied
to a subsequent process.
[0019] The present invention also provides an apparatus for
manufacturing and discharging a high-quality semi-solid metallic
slurry in a convenient manner.
[0020] According to an aspect of the present invention, there is
provided an apparatus for manufacturing a semi-solid metallic
slurry, the apparatus comprising: at least one sleeve with two open
ends, through one of which molten metal in liquid state is loaded
into the sleeve; a stirring unit which applies an electromagnetic
field to the molten metal in the sleeve; and a shutter unit which
closes the other end of the sleeve to form a base of the sleeve and
opens the base of the sleeve to discharge a slurry after
manufacture from the sleeve.
[0021] According to specific embodiments of the present invention,
the shutter unit may be a stopper fixed to the other end of the
sleeve. The shutter unit may be a plunger inserted into the other
end of the sleeve and moved up and down. The apparatus may further
include a pressing unit inserted into the one end of the sleeve to
press the slurry in the sleeve down. In the apparatus, the molten
metal in the sleeve may be cooled until the molten metal has a
solid fraction of 0.1-0.7. In this case, the apparatus may further
include a temperature control element to control the temperature of
the molten metal during cooling.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The above and other features and advantages of the present
invention will become more apparent by describing in detail
exemplary embodiments thereof with reference to the attached
drawings in which:
[0023] FIG. 1 is a graph of temperature versus time when a
semi-solid metallic slurry is manufactured with an apparatus
according to the present invention;
[0024] FIG. 2 illustrates the structure of an apparatus for
manufacturing a semi-solid metallic slurry according to an
embodiment of the present invention;
[0025] FIG. 3 is a sectional view of an example of a sleeve used in
a semi-solid metallic slurry manufacturing apparatus according to
the present invention;
[0026] FIG. 4 illustrates discharge of a semi-solid metallic slurry
from the semi-solid metallic slurry manufacturing apparatus of FIG.
2;
[0027] FIG. 5 illustrates the structure of a semi-solid metallic
slurry manufacturing apparatus according to another embodiment of
the present invention that further includes a pressing unit
compared to the apparatus of FIG. 2;
[0028] FIG. 6 illustrates the structure of a semi-solid metallic
slurry manufacturing apparatus according to another embodiment of
the present invention;
[0029] FIG. 7 illustrates discharge of a semi-solid metallic slurry
from the semi-solid metallic slurry manufacturing apparatus of FIG.
6; and
[0030] FIG. 8 illustrates the structure of a semi-solid metallic
slurry manufacturing apparatus according to another embodiment of
the present invention that further includes a pressing unit
compared to the apparatus of FIG. 6.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Embodiments of the present invention will be described in
detail with reference to the appended drawings.
[0032] First, a method of manufacturing a semi-solid metallic
slurry using an apparatus according to the present invention will
be described with reference to FIG. 1.
[0033] Unlike the aforementioned conventional techniques, a method
of manufacturing a semi-solid metallic slurry using the apparatus
of the present invention involves stirring molten metals by
applying an electromagnetic field prior to the completion of
loading the molten metals into a sleeve. In other words,
electromagnetic stirring is performed prior to, simultaneously
with, or in the middle of loading the molten metals into the
sleeve, to prevent the formation of dendritic structures. The
stirring process may be performed using ultrasonic waves instead of
the electromagnetic field.
[0034] First, after an electromagnetic field is applied to at least
one sleeve surrounded by a stirring unit, a molten metal is loaded
into the sleeve. The intensity of the applied electromagnetic field
is strong enough to stir the molten metal.
[0035] As shown in FIG. 1, the molten metal is loaded into the
sleeve at a temperature Tp. As described above, an electromagnetic
field may be applied to the sleeve prior to the loading of molten
metal into the sleeve. However, the present invention is not
limited to this, and electromagnetic stirring may be performed at
the start of in the middle of loading the molten metal into the
sleeve.
[0036] Due to the electromagnetic stirring performed prior to the
completion of loading molten metal into the sleeve, the molten
metal does not grow into dendritic structures near the inner wall
of the low temperature sleeve at the early stage of solidification,
and numerous micronuclei are concurrently generated throughout the
sleeve because the temperature of the entire molten metal is
rapidly dropped to a temperature lower than its liquidus
temperature.
[0037] Applying an electromagnetic field to the sleeve prior to or
simultaneously to loading molten metal into the sleeve leads to
active stirring of the molten metal in the center and the inner
wall regions of the sleeve and rapid heat transfer throughout the
sleeve. Therefore, the formation of solidification layers near the
inner wall of the sleeve at the early stage of cooling is
prevented. In addition, such active stirring of the molten metal
induces smooth convection heat transfer between the higher
temperature molten metal and the lower temperature inner sleeve
wall. Therefore, the molten metals can be rapidly cooled. Due to
the electromagnetic stirring, particles contained in the molten
metals scatter upon loading the molten metal into the sleeve and
are dispersed throughout the sleeve as nuclei, so that only a minor
temperature difference occurs in the sleeve during cooling.
However, in conventional techniques, the temperature of the molten
metal suddenly drops as soon as it contacts the lower temperature
inner vessel wall, so that dendritic crystals grow from
solidification layers formed near the inner wall of the vessel at
the early stage of cooling.
[0038] The principles of the present invention will become more
apparent when described in connection with latent heat of
solidification. Molten metal does not solidify near the inner
sleeve wall at the early stage of cooling, and no latent heat of
solidification is generated. Accordingly, the amount of heat to be
dissipated from the molten metal for cooling is equivalent only to
the specific heat of the molten metal, which corresponds to about
{fraction (1/400)} of the latent heat of solidification. Therefore,
dendrites, which are generated frequently near the inner sleeve
wall at the early stage of cooling when using conventional methods,
are not formed, and the entire molten metal in the sleeve can be
uniformly cooled. It takes merely about 1-10 seconds from the
loading of the molten metal. As a result, numerous nuclei are
created and dispersed uniformly throughout the entire molten metal
in the sleeve. The increased density of nuclei shortens the
distance between the nuclei, and spherical particles instead of
dendritic particles are formed.
[0039] The same effects can even be achieved even when an
electromagnetic field is applied in the middle of loading the
molten metal into the sleeve. In other words, solidification layers
are hardly formed near the inner sleeve wall even when
electromagnetic stirring begins in the middle of loading the molten
metal into the sleeve.
[0040] It is preferable to limit the loading temperature, Tp, of
the molten metal to a range from its liquidus temperature to
100.degree. C. above the liquidus temperature (melt
superheat=0.about.100.degree. C.). According to the present
invention, since the entire sleeve containing the molten metal is
uniformly cooled, there is no need to cool the molten metal to near
their liquidus temperature. Therefore, it is possible to load the
molten metal into the sleeve at a temperature of 100.degree. C.
above its liquidus temperature.
[0041] On the other hand, in conventional methods, an
electromagnetic field is applied to a vessel after the completion
of loading molten metal into the vessel and a portion of the molten
metal reaches below its liquidus temperature. Accordingly, latent
heat is generated due to the formation of solidification layers
near the inner wall of the vessel at the early stage of cooling.
Because the latent heat of solidification is about 400 times
greater than the specific heat of the molten metal, considerable
time is required to drop the temperature of the entire molten metal
below its liquidus temperature. Therefore, in such conventional
methods, the molten metal is loaded into a vessel, in general,
after the molten metal is cooled to a temperature near its liquidus
temperature or to a temperature of 50.degree. C. above its liquidus
temperature.
[0042] According to the present invention, the electromagnetic
stirring may be stopped at any point after at least a portion of
the molten metal in the sleeve reaches a temperature lower than the
liquidus temperature T.sub.l, i.e., after accomplishing nucleation
for a solid fraction of, for example, about 0.001, as illustrated
in FIG. 1. For example, an electromagnetic field may be applied to
the molten metal in the sleeve throughout the cooling process of
the molten metal, but prior to a subsequent molding process such as
die casting or hot forging. This is because, once nuclei are
distributed uniformly throughout the sleeve, even at the time of
growth of crystalline particles from the nuclei, properties of the
metallic slurry are not affected by the electromagnetic stirring.
Therefore, the electromagnetic stirring can be sustained until a
solid fraction of the molten metal reaches at least 0.001-0.7.
However, in view of energy efficiency, the electromagnetic stirring
is carried out until a solid fraction of the molten metal reaches
the range of, preferably, 0.001-0.4, and more preferably,
0.001-0.1.
[0043] After the electromagnetic stirring is completed, the
metallic slurry is discharged from the sleeve for a continuous
subsequent process, for example, die casting, hot forging, and
billet formation.
[0044] After an electromagnetic field is applied prior to the
completion of loading the molten metal into the sleeve for uniform
nucleation throughout the sleeve, the sleeve is cooled to
accelerate the growth of the nuclei. This cooling process may be
performed simultaneously to loading the molten metal into the
sleeve.
[0045] As described above, the application of the electromagnetic
field may be sustained throughout the cooling process. In other
words, cooling may be performed while the electromagnetic field is
applied to the sleeve. As a result, a resulting semi-solid metallic
slurry can be immediately used in a subsequent forming process.
[0046] The cooling process may be sustained just prior to a
subsequent forming process, preferably, until the solid fraction of
the molten metals reaches 0.1-0.7, i.e., up to time t.sub.2 of FIG.
1. The molten metal may be cooled at a rate of 0.2-5.0.degree.
C./sec, preferably, 0.2-2.0.degree. C./sec depending on a desired
distribution of nuclei and a desired size of particles.
[0047] A semi-solid metallic slurry containing a predetermined
amount of solid is manufactured through the above-described
processes and readily subjected to billet formation by rapid
cooling, for thixoforming, or die casting, forging, or pressing to
form final products.
[0048] According to the present invention described above, a
semi-solid metallic slurry can be manufactured within a short
period of time, merely in 30-60 seconds from loading the molten
metal into the sleeve for a metallic slurry with a solid fraction
of 0.1-0.7. In addition, the manufactured metallic slurry can be
molded into products having a uniform, dense spherical crystalline
structure.
[0049] The aforementioned method of manufacturing a semi-solid
metallic slurry can be performed using an apparatus according to an
embodiment of the present invention as shown in FIGS. 2 and 3.
[0050] Referring to FIG. 2, a semi-solid metallic slurry
manufacturing apparatus according to an embodiment of the present
invention includes at least one sleeve 2 with two open ends,
through one of which molten metal in liquid state is loaded; a
stirring unit 1 which applies an electromagnetic field to the
molten metal; and at least one shutter) unit 3 which closes the
other end of the sleeve 2 to form a base of the sleeve 2 and opens
the base of the sleeve 2 to discharge a slurry manufactured
therein.
[0051] The stirring unit 1 is mounted on the top of a hollow base
plate 14. The base plate 14 is supported by a support member 15 at
a predetermined height above the ground. A coil 11 for applying an
electromagnetic field is mounted on the base plate 14, while being
supported by a frame 12 having an inner space 13. The coil 11 is
electrically connected to a controller (not shown) and applies a
predetermined intensity of electromagnetic field toward the space
13 to electromagnetically stir the molten metal contained in the
sleeve 2 placed in the space 13. Although not shown in FIG. 2, the
stirring unit 1 may be an ultrasonic stirrer.
[0052] As shown in FIG. 2, the sleeve 2 may be placed inside the
stirring unit 1, i.e., in the space 13. The sleeve 2 may be fixed
on the base plate 14 in contact with the frame 12. The sleeve 2 may
be made of a metallic material or an insulating material. However,
it is preferable to use the sleeve 2 made of a material having a
higher melting point than the molten metal to be loaded thereinto.
The lower end of the sleeve 2 is closed or opened by the shutter
unit 3 and the upper end of the sleeve 2 is open for receiving
molten metal. That is, the sleeve 2 may be a vessel with the
shutter unit 3 at its bottom. However, there are no particular
limitations to the structure of the sleeve 2, provided that its
bottom can be closed or opened with the shutter unit 3. Although
not shown in FIG. 2, a thermocouple may be installed in the sleeve
2 and connected to a controller to provide temperature
information.
[0053] The apparatus according to the present invention may further
include a temperature control element 20 that is installed around
the sleeve 2, as shown in FIG. 3. The temperature control element
20 is comprised of a cooler and/or a heater. In the embodiment of
FIG. 3, a water jacket 22 acts as a cooler and an electric heating
coil 23 acts as a heater. The water jacket 22 is installed around
the sleeve 2 and contains a cooling water pipe 21. The electric
heating coil 23 is installed around the water jacket 22. The
cooling water pipe 21 may be laid in the sleeve 2, and other
heating means, in addition to the electric heating coil 23, may be
used for the heater. There are no particular limitations to the
structure of the temperature control element 20, provided that it
can adjust the temperature of molten metal or slurry. Molten metal
contained in the sleeve 2 can be cooled at an appropriate rate
using the temperature control element 20. It is understood that
such a sleeve 2 can be applied to all of the following embodiments
of a semi-solid metallic slurry manufacturing apparatus according
to the present invention. Cooling means for the molten metal
contained in the sleeve 2 are not limited to the temperature
control element 20, and the molten metal in the sleeve 2 may be
cooled naturally.
[0054] The shutter unit 3 forming the base of the sleeve 2 may have
any structure capable of opening and closing the bottom of the
sleeve 2. In an embodiment of the semi-metallic slurry
manufacturing apparatus according to the present invention, the
shutter unit 3 may be implemented with a stopper 31, as illustrated
in FIG. 2. The stopper 31 can be moved by a driving apparatus (not
shown) to close or open the bottom of the sleeve 2, as shown in
FIGS. 2 and 4. The stopper 31 may be made of the same material as
the sleeve 2. Alternatively, the stopper 31 may be formed as a
hinged door.
[0055] In addition, although not shown in the drawings, the shutter
unit 3 may be removed downward along with a slurry discharged from
the slurry manufacturing apparatus. In other words, when
discharging a slurry after manufacture, the shutter unit 3 is
detached from the sleeve 2 in the downward direction to support the
dropping slurry.
[0056] A loading unit 4 is a means for providing molten metal into
the sleeve 2. As for the loading unit 4, a general ladle, which is
electrically connected to the controller, may be used. In addition,
a furnace where the molten metal is prepared may be directly
connected to the sleeve 4. Any devices for loading molten metal
into the sleeve 2 can be used as the loading unit 4.
[0057] In a semi-solid metallic slurry manufacturing apparatus
according to the present invention having such a structure
described above, as shown in FIG. 2, after the stopper 31 is fitted
to the bottom of the sleeve 2, an electromagnetic field having a
predetermined frequency is applied to the sleeve 2 at a
predetermined intensity by the stirring unit 1. Next, metal M,
which has melted in a separate electric furnace, is loaded via the
loading unit 4 into the sleeve 2 under the electromagnetic field.
Instead of applying the electromagnetic field prior to the loading
of the molten metal into the sleeve, the electromagnetic field can
be applied to the sleeve 2 simultaneously to or in the middle of
loading the molten metal M into the sleeve 2, as described
above.
[0058] After the molten metal is loaded into the sleeve 2, the
molten metal in the sleeve 2 is cooled at a predetermined rate
until the solid fraction of a resultant semi-solid metallic slurry
S reaches the range of 0.1-0.7. The cooling rate may be in a range
of, preferably, 0.2-5.0.degree. C./sec, and more preferably
0.2-2.0.degree. C./sec, as described above. The cooling may be
carried out with the temperature control element 20, without it, or
with some other cooling means. It will be appreciated that the
molten metal contained in the sleeve 2 may be naturally cooled
without the aid of the temperature control element 20.
[0059] Meanwhile, the application of an electromagnetic field may
be sustained until the completion of cooling, i.e., the solid
fraction of the resultant semi-solid metallic slurry reaches the
range of at least 0.001-0.7. In view of energy efficiency, the
application of an electromagnetic field may be sustained after
loading the molten metal into the sleeve 2 until the solid fraction
reaches, preferably, at least 0.001-0.4, and more preferably,
0.001-0.1. The time required for these solid fraction levels can be
previously determined through experiments. It will be appreciated
that cooling can be performed while the electromagnetic field is
applied to the sleeve 2, as described above.
[0060] After the slurry S is manufactured, the stopper 31 is moved
to open the bottom of the sleeve 2 so that the slurry S is
discharged through the bottom of the sleeve 2 due to gravity. An
external transfer unit (not shown) may be installed near the bottom
of the sleeve 2 to transfer the slurry S to a molding apparatus for
subsequent rheocasting. Alternatively, although not illustrated, a
cooler-equipped sleeve may be further installed at the bottom of
the sleeve 2 to immediately mold the discharged slurry S into
billets. A casting die for die-casting and other forming
apparatuses may be further installed at the bottom of the sleeve 2
to process the discharged slurry S into products.
[0061] In addition to the embodiment of the semi-metallic slurry
manufacturing apparatus shown in FIGS. 2 and 4 where the
manufactured slurry S is discharged from the sleeve 2 due to
gravity, the slurry S may be discharged by force applied by a
pressing unit 5, as shown in FIG. 5.
[0062] In an embodiment of the semi-metallic slurry manufacturing
apparatus according to the present invention shown in FIG. 5, the
pressing unit 5, which is connected to a driving unit (not shown),
is inserted into the upper end of the sleeve 2. Any pressing means
capable of pushing the content of the sleeve 2, such as molten
metal or slurry, downward can be used for the pressing unit 5. An
example of a pressing means is a plunger 51. The plunger 51 may be
separated from the sleeve 2 when molten metal is loaded into the
sleeve 3 and inserted into the upper end of the sleeve 2 after the
loading of the molten metal into the sleeve 2. After a
semi-metallic slurry is manufactured and the stopper 31 is removed
from the bottom of the sleeve 2, the semi-metallic slurry is pushed
by the plunger 2 and discharged from the sleeve 1.
[0063] FIGS. 6 through 8 illustrate other embodiments of the
semi-metallic slurry manufacturing apparatus according to the
present invention, in which a plunger 32 is inserted into the lower
end of the sleeve 2 as a shutter unit 3. In particular, the plunger
32 is inserted into the lower end of the sleeve 2 by operating a
separate driving unit (not shown) prior to loading molten metal M
into the sleeve 2. After the manufacture of slurry S, the plunger
32 is removed downward from the sleeve 2 to discharge the slurry S
from the sleeve 2, as shown in FIG. 7. In another embodiment of the
present invention, a transfer unit (not shown), such as a robotic
apparatus, may be further used to stably transfer the discharged
slurry S supported on the plunger 32 for a subsequent process.
[0064] In addition, the pressing unit 5, such as the plunger 51
shown in FIG. 5, may be further inserted into the upper end of the
sleeve 2, as illustrated in FIG. 8, to press the slurry S in the
sleeve 2 downward.
[0065] A large amount of semi-metallic slurry can be manufactured
continuously with one of the semi-solid metallic slurry
manufacturing apparatuses according to the present invention
described above with more convenience when applied to a subsequent
process and enhanced overall processing efficiency. In addition, a
manufactured slurry can be easily discharged from the apparatus
through the bottom of the sleeve.
[0066] The apparatus for manufacturing a semi-solid metallic slurry
according to the present invention is compatible with various kinds
of metals and alloys, for example, aluminum, magnesium, zinc,
copper, iron, and alloys thereof, for rheocasting. A semi-solid
metallic slurry manufactured with the apparatus according to the
present invention contain spherical microparticles of uniform
distribution with an average diameter of 10-60 .mu.m.
[0067] As described above, metallic slurries with improved
mechanical properties that contain uniform, micro, spherical
particles can be manufactured with the apparatus according to the
present invention. According to the present invention, uniform,
spherical particles can be formed within a short time through
electromagnetic stirring initiated at a temperature above the
liquidus temperature of the molten metal to generate more nuclei in
the sleeve.
[0068] When using a semi-solid metallic slurry manufacturing
apparatus according to the present invention, the overall slurry
manufacturing process can be simplified, and the duration of
electromagnetic stirring and molding (casting) time can be greatly
shortened, thereby saving energy for the stirring and costs. The
semi-solid metallic slurry manufacturing apparatus according to the
present invention makes it convenient to perform a subsequent
process and increases the yield of molded products.
[0069] The semi-solid metallic slurry manufacturing apparatus
according to the present invention allows a manufactured slurry to
be discharged easily with a simple structure, so that a large
amount of semi-solid slurry can be rapidly and conveniently
manufactured
[0070] While the present invention has been particularly shown and
described with reference to exemplary embodiments thereof, it will
be understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the following claims.
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