U.S. patent application number 10/815805 was filed with the patent office on 2005-08-04 for rheoforming apparatus.
This patent application is currently assigned to Chun Pyo HONG. Invention is credited to Hong, Chun Pyo.
Application Number | 20050167073 10/815805 |
Document ID | / |
Family ID | 34420708 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050167073 |
Kind Code |
A1 |
Hong, Chun Pyo |
August 4, 2005 |
Rheoforming apparatus
Abstract
Provided is a rheoforming apparatus that ensures the manufacture
of products with fine, uniform, spherical particles, with
improvements in energy efficiency and mechanical properties of the
products, cost reduction, convenience of forming, and shorter
process duration. The apparatus includes a first sleeve, an end of
which is formed with a slurry outlet port for releasing a slurry, a
second sleeve for retaining a molten metal, an end of which
communicates with the first sleeve, a sealing member for opening or
closing the end of the second sleeve, a stirring unit for applying
an electromagnetic field to the second sleeve, and a plunger, which
is slidably inserted into the other end of the second sleeve to
press the slurry manufactured in the second sleeve.
Inventors: |
Hong, Chun Pyo;
(Eunpyung-gu, KR) |
Correspondence
Address: |
ROTHWELL, FIGG, ERNST & MANBECK, P.C.
1425 K STREET, N.W.
SUITE 800
WASHINGTON
DC
20005
US
|
Assignee: |
Chun Pyo HONG
Eunpyung-gu
KR
Nano Cast Korea Corp.
Incheon-city
KR
|
Family ID: |
34420708 |
Appl. No.: |
10/815805 |
Filed: |
April 2, 2004 |
Current U.S.
Class: |
164/113 ;
164/312; 164/499; 164/900 |
Current CPC
Class: |
B22D 17/007 20130101;
B22D 7/00 20130101; B21C 33/02 20130101 |
Class at
Publication: |
164/113 ;
164/312; 164/900; 164/499 |
International
Class: |
B22D 017/08; B22D
023/00; B22D 025/00; B22D 027/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 4, 2004 |
KR |
2004-7227 |
Claims
What is claimed is:
1. A rheoforming apparatus comprising: a first sleeve, an end of
which is formed with a slurry outlet port for releasing a slurry; a
second sleeve for retaining a molten metal, an end of which
communicates with the first sleeve; a sealing member for opening or
closing the end of the second sleeve; a stirring unit for applying
an electromagnetic field to the second sleeve; and a first plunger,
which is slidably inserted into the other end of the second sleeve
to press the slurry manufactured in the second sleeve.
2. The rheoforming apparatus of claim 1, wherein the sealing member
is a stopper that is removably installed at the end of the second
sleeve communicating with the first sleeve.
3. The rheoforming apparatus of claim 1, further comprising a
forming unit, which is installed outside the slurry outlet port of
the first sleeve to form a predetermined product from the slurry
released from the slurry outlet port.
4. The rheoforming apparatus of claim 3, wherein the forming unit
comprises: a transfer roller for transferring the slurry released
from the slurry outlet port; and a cooler for cooling the slurry
transferred by the transfer roller.
5. The rheoforming apparatus of claim 3, wherein the forming unit
is a press-forming unit comprising a press die that forms a
predetermined product by pressing the slurry released from the
slurry outlet port.
6. The rheoforming apparatus of claim 3, wherein the forming unit
is a forming die comprising a moving die and a fixing die that
define a predetermined forming cavity so that the slurry released
from the slurry outlet port is inserted into the forming
cavity.
7. The rheoforming apparatus of claim 1, further comprising a first
temperature control unit, which is installed around the first
sleeve to adjust the temperature of the slurry pressed toward the
slurry outlet port.
8. The rheoforming apparatus of claim 1, further comprising a
second temperature control unit, which is installed around the
second sleeve to adjust the temperature of the molten metal
retained in the second sleeve.
9. The rheoforming apparatus of claim 1, wherein the second sleeve
is made of a non-magnetic material.
10. The rheoforming apparatus of claim 1, wherein the first sleeve
has a cylindrical shape parallel to the ground, and the second
sleeve is coupled with the first sleeve by moving at a
predetermined angle with respect to the first sleeve.
11. The rheoforming apparatus of claim 10, wherein the stirring
unit moves together with the second sleeve.
12. The rheoforming apparatus of claim 1, wherein the second sleeve
is branched from the first sleeve, and the rheoforming apparatus
further comprises a second plunger slidably inserted into the other
end of the first sleeve to press the slurry in the first sleeve
toward the slurry outlet port.
13. The rheoforming apparatus of claim 1, wherein the second sleeve
is formed in a shape flared from the end intended for the insertion
of the first plunger to the end communicating with the first
sleeve.
14. The rheoforming apparatus of claim 1, further comprising an
electromagnetic field control unit, which is electrically connected
to the stirring unit and controls the stirring unit in such a
manner that an electromagnetic field is applied to the second
sleeve from prior to pouring the molten metal in the second sleeve
and is stopped when crystalline nuclei are formed in the molten
metal.
Description
[0001] This application claims the priority of Korean Patent
Application No. 2004-7227, filed on Feb. 4, 2004, in the Korean
Intellectual Property Office, the disclosure of which is
incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a rheoforming apparatus,
and more particularly, to a rheoforming apparatus for manufacturing
predetermined products from semi-solid metal slurries with a fine,
uniform, spherical particle structure.
[0004] 2. Description of the Related Art
[0005] Metal slurries in a combined solid and liquid phase, i.e.,
semi-molten or semi-solid metal slurries, generally refer to
intermediates manufactured by composite processing of rheoforming
and thixoforming. Semi-solid metal slurries consist of 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 little force due to their thixotropic
properties and can be easily cast like a liquid due to their high
fluidity.
[0006] Rheoforming refers to a process of manufacturing billets or
final products from semi-solid metal slurries having a
predetermined viscosity through forming or forging. Such
rheoforming is closely related to thixoforming and thus is also
expressed as rheoforming/thixoforming. Thixoforming refers to a
process involving reheating billets manufactured through
rheoforming back into semi-molten slurries and forming or forging
the slurries to manufacture final products.
[0007] Such rheoforming/thixoforming has many advantages, compared
to general forming processes using molten metals, such as casting
or squeeze-forming. Because metal slurries used in
rheoforming/thixoforming are fluid at a temperature lower than
molten metals, it is possible to maintain dies contacting with the
slurries at a lower temperature than the molten metals, thereby
extending the lifespan of the dies.
[0008] In addition, when slurries are extruded through a cylinder,
turbulence is less likely to occur, and thus less air is
incorporated during forming. Therefore, the formation of air
pockets in final products is prevented. Besides, the use of
semi-solid metal slurries leads to reduced shrinkage during
solidification, improved working efficiency, mechanical properties,
and anti-corrosion property, and lightweight products. Therefore,
such semi-solid metal slurries can be used as new materials in the
fields of automobiles, airplanes, and electrical, electronic
information communications equipment.
[0009] As described above, semi-solid metal slurries are used both
in rheoforming and thixoforming. In detail, semi-solid slurries
solidified from molten metals by a predetermined method are used in
rheoforming, and semi-molten slurries obtained by reheating solid
billets are used in thixoforming. Throughout the specification of
the present invention, the term "semi-solid metal slurries" means
metal materials in a combined solid and liquid state at a
temperature range between the liquidus temperature and the solidus
temperature of metals, i.e., at a semi-solid temperature range at
which the crystalline particles of metals are partially molten and
are partially solid, or semi-solid slurries which are obtained by
cooling molten metals during rheoforming.
[0010] Meanwhile, conventional rheoforming is largely classified
into a nuclei formation method using crystalline nuclei grown in
molten metals and a stirring method of destroying dendrites grown
in molten metals, according to a slurry manufacturing method.
[0011] In a conventional nuclei formation method, nuclei formation
and growth are slowly performed since the pouring temperature of
molten metals is maintained at a very low level and a cooling rate
is very slow. Therefore, the process duration is excessively
retarded, which renders mass production difficult.
[0012] In a conventional stirring method, molten metals are
generally stirred at a temperature lower than the liquidus
temperature during cooling, to destroy dendrites into spherical
particles suitable for rheoforming, for example, by mechanical
stirring, electromagnetic stirring, gas bubbling, low-frequency,
high-frequency, or electromagnetic wave vibration, electrical shock
agitation, etc.
[0013] For example, U.S. Pat. No. 3,948,650 discloses a method and
an apparatus for manufacturing a liquid-solid mixture. In this
method, a molten metal is vigorously stirred while being cooled for
solidification. A semi-solid metal slurry manufacturing apparatus
disclosed in this patent uses a stirrer to induce flow of the
solid-liquid mixture having a predetermined viscosity to destroy
dendritic structures or disperse destroyed dendritic structures in
the liquid-solid mixture. In this method, dendritic structures
formed during cooling are destroyed and used as crystalline nuclei
for spherical particles. However, because of generation of latent
heat due to formation of solidification layers at an early stage of
cooling, the method causes problems of low cooling rate, long
process duration, uneven temperature distribution in a mixing
vessel, and non-uniform crystalline structure. Mechanical stirring
applied in the semi-solid metal slurry manufacturing apparatus
inherently leads to uneven temperature distribution in the mixing
vessel. In addition, because the mixing vessel is located at a
chamber, it is difficult to continuously perform a subsequent
process.
[0014] U.S. Pat. No. 4,465,118 discloses a method and an apparatus
for manufacturing a semi-solid alloy slurry. A cooling manifold and
a die are sequentially arranged in a coiled electromagnetic field
application unit. A molten metal at an upper position of the die is
continuously poured into the die, and cooling water flows through
the cooling manifold to cool the die. According to the method
disclosed in this patent, a molten metal is poured into the die and
cooled in the cooling manifold, thereby resulting in a
solidification zone. When a magnetic field is applied by the
electromagnetic field application unit, dendritic structures are
destroyed during cooling. Finally, an ingot is formed and then
drawn through a lower portion of the apparatus. However, since the
basic technical idea of this method and apparatus is to destroy
dendrites by vibration after solidification, the above-described
many problems in terms of a manufacturing process and a slurry
structure are involved. In the manufacturing apparatus, since a
molten metal is continuously supplied to form an ingot, it is
difficult to control the state of the molten metal and the overall
process. Moreover, prior to applying an electromagnetic field, the
die is cooled using water, whereby a great temperature difference
exists between the peripheral and core regions of the die.
[0015] Other types of rheoforming/thixoforming known in the art are
described later. However, all of the methods are based on the
technical idea of destroying dendrites after their formation to
form crystalline nuclei of spherical particles. Therefore, problems
as described above arise.
[0016] Japanese Patent Application Laid-open Publication No. Hei.
11-33692 discloses a method of manufacturing a metal slurry for
rheoforming. According to the method disclosed, a molten metal is
poured into a vessel at a temperature near its liquidus temperature
or 50.degree. C. above the liquidus temperature. Next, when at
least a portion of the molten metal reaches a temperature lower
than the liquidus temperature, i.e., at least a portion of the
molten metal starts to pass through the liquidus temperature, the
molten metal is subjected to a force, for example, ultrasonic
vibration, and slowly cooled into the metal slurry containing
spherical particles. This method also uses a physical force, such
as ultrasonic vibration, to destroy the dendrites formed at an
early stage of cooling. Also, if the pouring temperature is higher
than the liquidus temperature, it is difficult to form spherical
particle structures and to rapidly cool the molten metal.
Furthermore, this method leads to non-uniform surface and core
structures.
[0017] Japanese Patent Application Laid-open Publication No. Hei.
10-128516 discloses a method for casting a thixotropic metal. This
method involves pouring a molten metal into a vessel and vibrating
the molten metal using a vibrating bar dipped in the molten metal
to directly transfer a vibrating force to the molten metal. After
forming a semi-solid and semi-liquid molten alloy which contains
crystalline nuclei at a temperature range lower than the 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 for the growth of the nuclei,
thereby resulting in the thixotropic metal. However, this method
provides relatively large crystalline nuclei of about 100 .mu.m,
requires a considerably long process duration, and cannot be
performed in a vessel larger than a predetermined size.
[0018] U.S. Pat. No. 6,432,160 discloses a method for making a
thixotropic metal slurry. This method involves simultaneously
controlling the cooling and the stirring of a molten metal to form
the thixotropic metal slurry. In detail, after pouring a molten
metal 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 metal in the vessel. Next,
the molten metal is rapidly cooled by means of a thermal jacket,
equipped around the mixing vessel, for precise temperature control
of the mixing vessel and the molten metal. During cooling, the
molten metal is continuously stirred in such a manner that when the
solid fraction of the molten metal is low, high-speed stirring is
provided, and when the solid fraction of the molten metal
increases, a greater magnetomotive force is applied.
[0019] Most of the aforementioned conventional
rheoforming/thixoforming methods and apparatuses use a shear force
to destroy dendrites into metal particle structures during cooling.
Since a force such as vibration is applied after at least a portion
of the molten metal is cooled below its liquidus temperature,
latent heat is generated due to formation of solidification layers
at an early stage of the cooling. As a result, there arise many
disadvantages such as reduced cooling rate and increased process
duration. In addition, due to uneven temperature distribution
between the inner wall and the center of a vessel, it is difficult
to form fine, uniform spherical metal particles. Therefore, this
structural non-uniformity of metal particles will worsen if the
pouring temperature of the molten metal into the vessel is not
controlled.
[0020] Meanwhile, in the above-described rheoforming apparatuses,
billets are manufactured by a continuous forming method, which
makes it difficult to directly manufacture products from prepared
slurries by a forming process.
SUMMARY OF THE INVENTION
[0021] The present invention provides a rheoforming apparatus that
ensures the manufacturing of products with fine, uniform, spherical
particles, with improvements in energy efficiency and mechanical
properties, manufacturing cost reduction, convenience of forming,
and shorter process duration.
[0022] The present invention also provides a rheoforming apparatus
for manufacturing products within a short time, with improvement in
durability reduction of constitutional elements of the apparatus
due to pressing and an energy loss.
[0023] In accordance with an aspect of the present invention, there
is provided a rheoforming apparatus comprising: a first sleeve, an
end of which is formed with a slurry outlet port for releasing a
slurry; a second sleeve for retaining a molten metal, an end of
which communicates with the first sleeve; a sealing member for
opening or closing the end of the second sleeve; a stirring unit
for applying an electromagnetic field to the second sleeve; and a
first plunger, which is slidably inserted into the other end of the
second sleeve to press the slurry manufactured in the second
sleeve.
[0024] The sealing member may be a stopper that is removably
installed at the end of the second sleeve communicating with the
first sleeve.
[0025] The rheoforming apparatus may further comprise a forming
unit, which is installed outside the slurry outlet port of the
first sleeve to form a predetermined product from the slurry
released from the slurry outlet port.
[0026] In this case, the forming unit may comprise: a transfer
roller for transferring the slurry released from the slurry outlet
port; and a cooler for cooling the slurry transferred by the
transfer roller.
[0027] The forming unit may be a press-forming unit comprising a
press die that forms a predetermined product by pressing the slurry
released from the slurry outlet port.
[0028] The forming unit may be a forming die comprising a moving
die and a fixing die that define a predetermined forming cavity so
that the slurry released from the slurry outlet port is inserted
into the forming cavity.
[0029] The rheoforming apparatus may further comprise a first
temperature control unit, which is installed around the first
sleeve to adjust the temperature of the slurry pressed toward the
slurry outlet port.
[0030] The rheoforming apparatus may further comprise a second
temperature control unit, which is installed around the second
sleeve to adjust the temperature of the molten metal retained in
the second sleeve.
[0031] The second sleeve may be made of a non-magnetic
material.
[0032] The first sleeve may have a cylindrical shape parallel to
the ground, and the second sleeve may be coupled with the first
sleeve by moving at a predetermined angle with respect to the first
sleeve.
[0033] The stirring unit may move together with the second
sleeve.
[0034] The second sleeve may be branched from the first sleeve, and
the rheoforming apparatus may further comprise a second plunger
slidably inserted into the other end of the first sleeve to press
the slurry in the first sleeve toward the slurry outlet port.
[0035] The second sleeve may be formed in a shape flared from the
end intended for the insertion of the first plunger to the end
communicating with the first sleeve.
[0036] The rheoforming apparatus may further comprise an
electromagnetic field control unit, which is electrically connected
to the stirring unit and controls the stirring unit in such a
manner that an electromagnetic field is applied to the second
sleeve from prior to pouring the molten metal in the second sleeve
and is stopped when crystalline nuclei are formed in the molten
metal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] 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:
[0038] FIG. 1 schematically illustrates a structure of a
rheoforming apparatus according to a first embodiment of the
present invention;
[0039] FIG. 2 is a sectional view of an example of a second sleeve
used in the rheoforming apparatus of FIG. 1;
[0040] FIGS. 3 through 6 illustrate a sequential process for
manufacturing an extrudate using the rheoforming apparatus
according to the first embodiment of the present invention;
[0041] FIG. 7 is a graph of a temperature profile applied to a
rheoforming apparatus according to the present invention;
[0042] FIG. 8 schematically illustrates a structure of a
rheoforming apparatus according to a second embodiment of the
present invention;
[0043] FIGS. 9 through 14 schematically illustrate operational
states of a rheoforming apparatus according to a third embodiment
of the present invention;
[0044] FIGS. 15 through 17 schematically illustrate operational
states of a rheoforming apparatus according to a fourth embodiment
of the present invention;
[0045] FIGS. 18 and 19 schematically illustrate operational states
of a rheoforming apparatus according to a fifth embodiment of the
present invention;
[0046] FIGS. 20 and 21 schematically illustrate operational states
of a rheoforming apparatus according to a sixth embodiment of the
present invention;
[0047] FIG. 22 schematically illustrates a structure of a
rheoforming apparatus according to a seventh embodiment of the
present invention;
[0048] FIG. 23 schematically illustrates a structure of a
rheoforming apparatus according to an eighth embodiment of the
present invention; and
[0049] FIG. 24 schematically illustrates a structure of a
rheoforming apparatus according to a ninth embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0050] The present invention will be described more fully in the
following exemplary embodiments of the invention with reference to
the accompanying drawings.
[0051] A rheoforming apparatus according to the present invention
is used to manufacture products with a predetermined shape using
semi-solid slurries.
[0052] A first embodiment of the present invention will first be
described with reference to FIGS. 1 through 7.
[0053] In a rheoforming process performed using the apparatus of
the first embodiment of the present invention shown in FIGS. 1
through 7, a molten metal M is poured into a second sleeve 22 to
form a semi-solid metal slurry S and then the slurry is extruded at
a low pressure. In this case, the molten metal M is stirred by
applying an electromagnetic field before the molten metal is
completely poured into the second sleeve 22. That is,
electromagnetic stirring is performed before the molten metal is
completely poured into the second sleeve 22 to prevent the
formation of solidification layers and dendrites at an early stage.
The stirring process may be performed using ultrasonic waves
instead of the electromagnetic field.
[0054] In detail, after application of an electromagnetic field to
a predetermined portion of the second sleeve 22 surrounded by a
stirring unit 1 is begun, the molten metal is poured into the
second sleeve. At this time, the electromagnetic field has a
sufficient intensity so that solidification layers or dendrites are
not formed in the molten metal at an early stage.
[0055] As shown in FIG. 7, the molten metal is poured into the
second sleeve 22 at a pouring temperature Tp. As described above,
an electromagnetic field may be applied to the second sleeve 22
prior to pouring the molten metal into the second sleeve 22.
However, the present invention is not limited to this, and
electromagnetic stirring may be performed simultaneously with or in
the middle of pouring the molten metal into the second sleeve.
[0056] Due to the electromagnetic stirring performed before the
molten metal is completely poured into the second sleeve 22,
solidification layers are not formed in the molten metal near the
inner wall of the cold second sleeve 22 at an early stage, which
renders formation of dendrites difficult. That is, because the
molten metal is poured into the second sleeve 22 during applying an
electromagnetic field to the second sleeve 22, temperature
differences between the inner wall and the center of the second
sleeve 22 and between the upper portion and the lower portion of
the second sleeve 22 are hardly caused. Therefore, unlike
conventional techniques, solidification near the inner wall of a
vessel at an early stage does not occur. Also, numerous micronuclei
are concurrently generated because the entire molten metal in the
second sleeve 22 is uniformly and rapidly cooled to a temperature
lower than its liquidus temperature.
[0057] By applying an electromagnetic field prior to or
simultaneously with pouring the molten metal into the second sleeve
22, the molten metal is actively stirred in the center and inner
wall regions of the second sleeve 22 and heat is rapidly
transferred throughout the second sleeve 22. Therefore, at an early
stage of cooling, the formation of solidification layers near the
inner wall of the second sleeve 22 is prevented.
[0058] In addition, such active stirring of the molten metal
induces a convection heat transfer between the hot molten metal and
the inner wall of the cold second sleeve 22, thereby rapidly
cooling the molten metal. Due to the electromagnetic stirring,
particles contained in the molten metal scatter simultaneously with
pouring the molten metal into the second sleeve 22 and are
uniformly dispersed in the form of crystalline nuclei throughout
the second sleeve 22. Therefore, a temperature difference
throughout the second sleeve 22 is not caused during cooling.
However, in conventional techniques, when the molten metal contacts
with a low temperature inner vessel wall, solidification layers are
formed at the inner wall of the vessel and then grow into
dendrites.
[0059] The principles of the present invention will become more
apparent when described in connection with solidification latent
heat. That is, the molten metal is not solidified at the inner wall
of the second sleeve 22 at an early stage of cooling, and thus, no
solidification latent heat is generated. Accordingly, discharge of
the amount of heat corresponding to only the specific heat of the
molten metal, which corresponds to about {fraction (1/400)} of the
solidification latent heat, is required to cool the molten
metal.
[0060] Therefore, solidification layers and dendrites which are
frequently generated at the inner wall of a sleeve at an early
stage of cooling like in conventional methods are not formed. The
entire molten metal in the second sleeve 22 can be uniformly and
rapidly cooled within merely about 1 to 10 seconds from the pouring
of the molten metal. As a result, numerous crystalline nuclei are
uniformly dispersed throughout the molten metal in the second
sleeve 22. The increased nuclei density reduces the distance
between the nuclei, which enables formation of spherical particles,
instead of dendrites.
[0061] The same effects can be achieved even when an
electromagnetic field is applied in the middle of pouring the
molten metal into the second sleeve 22. In other words, application
of an electromagnetic field before the pouring of the molten metal
into the second sleeve 22 is completed renders formation of
solidification layers at the inner wall of the second sleeve 22
difficult.
[0062] It is preferable to limit the pouring temperature, Tp, of
the molten metal to a range from its liquidus temperature to
100.degree. C. above the liquidus temperature (melt superheat=0 to
100.degree. C.). Since the entire molten metal contained in the
second sleeve 22 is uniformly cooled, as described above, there is
no need to cool the molten metal to near its liquidus temperature
prior to pouring the molten metal into the second sleeve 22 and the
molten metal may have a high temperature of 100.degree. C. above
the liquidus temperature.
[0063] On the other hand, in a conventional method, after the
pouring of a molten metal into a vessel is completed, an
electromagnetic field is applied to the vessel when a portion of
the molten metal reaches a temperature below its liquidus
temperature. Accordingly, at an early stage of cooling, latent heat
is generated due to the formation of solidification layers near the
inner wall of the vessel. Because the solidification latent heat is
about 400 times greater than the specific heat of the molten metal,
a significant time is required to drop the temperature of the
entire molten metal below the liquidus temperature. Therefore, in
such a conventional method, to shorten a process duration, the
molten metal is generally poured into a vessel after being cooled
to a temperature near the liquidus temperature or a temperature of
50.degree. C. above the liquidus temperature.
[0064] 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 second sleeve 22 reaches a temperature
lower than the liquidus temperature T/, i.e., after crystalline
nuclei of a predetermined amount is formed so that a solid fraction
is about 0.001, as shown in FIG. 7. That is, the electromagnetic
stirring may be stopped when the molten metal in the second sleeve
22 reaches a temperature near its liquidus temperature or when
crystalline nuclei are uniformly formed in the molten metal in the
second sleeve 22.
[0065] With respect to nuclei density in manufacturing the
semi-solid metal slurry from the molten metal, the nucleation in
the molten metal is stopped when the solid fraction of the molten
metal exceeds 0.0001 (10.sup.-4) irrespective of the type of a
metal or alloy material for the molten metal. Meanwhile, it is
difficult to measure the solid fraction of the molten metal to a
level of 0.0001. Therefore, to manufacture a semi-solid metal
slurry commercially available, there is no need to carry out the
nucleation of the molten metal until the solid fraction of the
molten metal is 0.0001. The solid fraction of 0.001 or more is
sufficient. Even with respect to productivity, the solid fraction
of 0.001 or more is preferred.
[0066] Meanwhile, nuclei density in the molten metal can be
sufficiently increased by applying an electromagnetic field only
during formation of crystalline nuclei in the molten metal. Even
though the electromagnetic field is applied to the molten metal for
a longer time, the semi-solid metal slurry can be manufactured.
However, applying the electromagnetic field even when the solid
fraction of the molten metal exceeds 0.1 is not preferable in view
of energy efficiency. Also, the structure of the semi-solid metal
slurry may become coarse and a process duration may become
long.
[0067] The electromagnetic field can be continuously applied to the
molten metal M in the second sleeve 22 until the cooling process of
the molten metal, just before performing a subsequent pressing
process, for example, a forming process. This is because once
crystalline nuclei are uniformly distributed throughout a slurry
manufacturing area of the second sleeve 22, the electromagnetic
stirring at the time of growth of crystalline particles from the
nuclei does not affect properties of the semi-solid metal
slurry.
[0068] Therefore, the electromagnetic stirring may be carried out
at least until the solid fraction of the metal in the second sleeve
22 is 0.001 to 0.7. That is, the electromagnetic stirring may be
stopped when the solid fraction of the metal is 0.001 to 0.7.
However, in view of energy efficiency, it is preferable to carry
out the electromagnetic stirring until the solid fraction of the
metal in the second sleeve is in a range of 0.001 to 0.4, and more
preferably 0.001 to 0.1.
[0069] When uniform crystalline nuclei are formed by the
electromagnetic stirring carried out before the molten metal is
completely poured into the second sleeve 22, the second sleeve 22
is cooled to promote the growth of the nuclei. In this regard, the
cooling process may be performed simultaneously with the pouring of
the molten metal into the second sleeve 22. Also, the
electromagnetic field may be continuously applied during the
cooling process. That is, the cooling process may be carried out
during the application of the electromagnetic field to the second
sleeve 22. Therefore, the semi-solid metal slurry manufactured in
the second sleeve 22 can be directly used in a subsequent process,
i.e., a forming process. Such a cooling process may be carried out
by a separate second temperature control unit 44 or may be
spontaneously carried out by air.
[0070] Such a cooling process may be carried out until just prior
to a subsequent process such as pressing and forming, and
preferably, until the solid fraction of the metal is 0.1 to 0.7,
i.e., up to time t.sub.2 of FIG. 7. In detail, when a product made
from the semi-solid metal slurry S has a thin thickness and a
complicated shape, the cooling is carried out until the solid
fraction of the molten metal is 0.1 (by experiment) so that the
molten metal is approximately in a liquid phase. Also, there is
need to increase a time required for solidification of the
semi-solid metal slurry S in a die so that an insertion rate of the
slurry into the die is promoted. On the other hand, when a product
made from the semi-solid metal slurry S has a thick thickness and a
simple shape, the cooling is carried out until the solid fraction
of the metal is 0.7 so that the molten metal is approximately in a
solid phase. Also, there is need to decrease a time required for
solidification of the slurry S in a die so that an insertion rate
of the slurry into the die is retarded.
[0071] When the solid fraction of the metal used in manufacturing
the slurry is 0.1 to 0.7, irrespective of the type of a metal or
alloy material for the metal, it is possible to manufacture
products of any shape from the slurry made from the molten metal.
The manufacture of the slurry with the solid fraction of 0.1 to 0.7
merely occurs within 30 to 60 seconds from the pouring of the
molten metal into the second sleeve 22. Therefore, in order to
manufacture the slurry from the molten metal within 60 seconds, it
is preferable to perform the cooling process until the solid
fraction of the metal is 0.1 to 0.7.
[0072] The molten metal may be cooled at a rate of 0.2 to
5.0.degree. C./sec. The cooling rate may be any value between 0.2
and 2.0.degree. C./sec depending on a desired distribution of
crystalline nuclei and a desired size of particles.
[0073] If the cooling rate of the molten metal is less than
0.2.degree. C./sec, crystalline nuclei may excessively grow in the
molten metal, thereby increasing a time required for slurry
manufacturing. Therefore, productivity and mechanical properties
may be lowered. In this regard, it is necessary to set the cooling
rate of the molten metal to 0.2.degree. C./sec or more. Generally,
it is preferable to increase the cooling rate of the molten metal
because a time required for slurry manufacturing is shortened and
energy efficiency is enhanced. However, if the cooling rate of the
molten metal exceeds 0.5.degree. C./sec, dendrites may be formed in
the molten metal and solidified during cooling.
[0074] Meanwhile, when distances between crystalline nuclei formed
in the molten metal are large, the nuclei can grow into a large
size in the molten metal by cooling the molten metal at a
relatively slow rate of 0.2.degree. C./sec. On the other hand, when
distances between the nuclei formed in the molten metal are small,
it is preferable to perform the cooling at a relatively fast rate
of 0.5.degree. C./sec because there is no need to largely increase
the size of the nuclei in the molten metal.
[0075] When the section area of the second sleeve 2 containing the
molten metal is large, it is preferable to perform the cooling at a
relatively slow rate of 0.2.degree. C./sec. On the other hand, when
the section area of the second sleeve 2 containing the molten metal
is small, even relatively fast cooling rate of 0.5.degree. C./sec
enables sufficient growth of crystalline nuclei in the molten
metal.
[0076] Here, formation of crystalline nuclei in the molten metal
poured in the second sleeve 22 depends on the temperature of the
molten metal when the molten metal is poured in the second sleeve
22, i.e., the pouring temperature. The pouring temperature can be
represented by the degree of heating of the molten metal from the
liquidus temperature, like a temperature of 100.degree. C. above
the liquidus temperature. The degree of heating significantly
affects steps ranging from pouring the molten metal in the second
sleeve 22 to nucleation.
[0077] On the other hand, crystal growth carried out until
solidification of the semi-solid metal slurry in a die after
nucleation in the molten metal is affected by the thickness of a
product made from the molten metal. Therefore, the rate of the
cooling for nuclei growth after completion of nucleation by
electromagnetic field application depends on the degree of heating
of the molten metal for nucleation prior to pouring the molten
metal in the second sleeve 22 and the thickness of a product made
from the slurry. That is, when the degree of heating of the molten
metal is constant and the thickness of a product is given, the
cooling rate of the slurry to be inserted in a die is spontaneously
determined.
[0078] When the degree of heating of the molten metal is high, the
number of crystalline nuclei formed in the molten metal decreases.
In this regard, it is necessary to retard the cooling rate of the
molten metal poured in the second sleeve. On the other hand, when
the degree of heating of the molten metal is low, the number of
crystalline nuclei formed in the molten metal increases. In this
regard, it is necessary to promote the cooling rate of the molten
metal, thereby decreasing the particle size of the slurry.
[0079] Therefore, when the cooling rate of the molten metal is 0.2
to 5.0.degree. C./sec and the molten metal at the time of being
poured in the second sleeve has a temperature ranging from its
liquidus temperature to 100.degree. C. above the liquidus
temperature, the semi-solid metal slurry that can be used in the
casting industry or has a predetermined solid fraction can be
manufactured. The manufactured semi-solid metal slurry can be
directly subjected to press-forming, to form a predetermined
product.
[0080] According to the aforementioned process, the semi-solid
metal slurry can be manufactured within a short time. That is, a
time (t.sub.2) required for manufacturing the slurry with the solid
fraction of 0.1 to 0.7 after the pouring of the molten metal into
the second sleeve 22 is only 30 to 60 seconds. The slurry thus
manufactured can be used in forming a product having a uniform,
dense, spherical, crystalline structure.
[0081] A rheoforming apparatus using the aforementioned semi-solid
slurry manufacture process will now be described with reference to
FIGS. 1 through 6.
[0082] A rheoforming apparatus as shown in FIGS. 1 through 6 is a
vertical type and includes the stirring unit 1 for applying an
electromagnetic field and an elongated cylindrical sleeve. The
sleeve is divided into the first sleeve 21 for injection and the
second sleeve 22 for electromagnetic stirring.
[0083] The second sleeve 22 is in a long, slender cylindrical form
with both ends open. Since the second sleeve 22 has a vertical axis
direction, it is installed to be moved from the vertical axis
direction to a horizontal axis direction. With respect to the
vertical axis direction of the second sleeve 22, an upper end of
the second sleeve 22 is formed with an injection port 25 and a
lower end of the second sleeve 22 opposite to the injection port 25
is formed with a slurry outlet port 26. The second sleeve 22
retains the molten metal M coming from the injection port 25.
[0084] The second sleeve 22 is formed so that the semi-solid metal
slurry made from the molten metal in the second sleeve 22 is
released from the slurry outlet port 26. Also, the second sleeve 22
may be formed in a shape gradually flared from the injection port
25 to the slurry outlet port 26. That is, the inner diameter of the
second sleeve 22 may be gradually increased toward the releasing
direction of the semi-solid metal slurry.
[0085] The stirring unit 1 for applying an electromagnetic field to
the molten metal contained in the second sleeve 22 is installed
around the second sleeve 22. The stirring unit 1 is fixed to the
second sleeve 22 to be moved together with the second sleeve
22.
[0086] A flat stopper 31 as a sealing member 3 is installed at the
slurry outlet port 26 of the second sleeve 22. The stopper 31 is
connected to a driving device (not shown) and may be made of the
same material as that for the second sleeve 22. As shown in FIG. 1,
the stopper 31 seals the slurry outlet port 26 of the second sleeve
22 in a state wherein the injection port 25 of the second sleeve 22
faces upward. In this state, the stopper 31 forms a bottom portion
4 of a slurry manufacturing area T of the second sleeve 22 in which
the molten metal is present, thereby allowing the second sleeve 22
to act as a vessel that retains the molten metal.
[0087] When the stopper 31 is removed in a state wherein the second
sleeve 22 is horizontally positioned, the slurry outlet port 26 of
the second sleeve 22 is opened to release the semi-solid metal
slurry formed in the second sleeve 22 from the slurry outlet port
26. The stopper 31 may have a door shape, an end of which is
hinge-connected to an edge of the slurry outlet port 26 of the
second sleeve 22 to be moved. Alternatively, when the stopper 31 is
comprised of two parts, the two parts may be separated from each
other to render the slurry outlet port 26 open. There are no
limitations on the shape of the stopper 31 provided that the slurry
outlet port 26 of the second sleeve 22 is allowed to be open or
closed.
[0088] The second temperature control unit 44 may be further
installed around the second sleeve 22, as shown in FIG. 2. The
second temperature control unit 44 cools the molten metal contained
in the second sleeve 22 or the semi-solid metal slurry manufactured
in the second sleeve 22. The second temperature control unit 44
includes a water jacket 46 containing a cooling water pipe 45.
[0089] The water jacket 46 is concentrically installed around the
second sleeve 22 to surround the outside of the second sleeve 22.
The cooling water pipe 45 may be buried in the second sleeve 22.
Any coolers capable of cooling the molten metal contained in the
second sleeve 22 may be used.
[0090] The second temperature control unit 44 includes an electric
heating coil 47 as a heater. The electric heating coil 47 may be
spirally installed to surround the outside of the water jacket 46.
Any heaters except the electric heating coil 47 may be used.
[0091] There are no particular limitations on the structure of the
second temperature control unit 44, provided that the second
temperature control unit 44 can adjust the temperature of the
molten metal or the semi-solid metal slurry in the second sleeve
22. The molten metal contained in the second sleeve 22 is cooled at
an appropriate rate using the second temperature control unit 44.
The second temperature control unit 44 may be installed around the
entire second sleeve 22 or around the slurry manufacturing area T
in which the molten metal is present. The molten metal contained in
the second sleeve 22 may be spontaneously cooled without the aid of
the second temperature control unit 44 to manufacture the
semi-solid metal slurry with a desired solid fraction.
[0092] In detail, the second temperature control unit 44 may cool
the molten metal contained in the second sleeve 22 until the solid
fraction of the molten metal is 0.1 to 0.7. The cooling may be
carried out at a rate of 0.2 to 5.0.degree. C./sec, preferably 0.2
to 2.0.degree. C./sec.
[0093] The cooling by the second temperature control unit 44 may be
carried out after the electromagnetic stirring by the stirring unit
1 is completed or irrespective of the electromagnetic stirring,
i.e., during the electromagnetic stirring. In addition, the cooling
may be carried out simultaneously with the pouring of the molten
metal.
[0094] Meanwhile, an electromagnetic field application coil 11 is
disposed in the stirring unit 1 so as to surround a space 12
defined by the stirring unit 1. The space 12 and the
electromagnetic field application coil 11 may be fixed by means of
a separate frame (not shown). The electromagnetic field application
coil 11 is used to apply an electromagnetic field of a
predetermined intensity to the second sleeve 22, which is
accommodated in the space 12. Therefore, the molten metal contained
in the second sleeve 22 is electromagnetically stirred. There are
no particular limitations on the electromagnetic field application
coil 11, provided that the electromagnetic field application coil
11 can be used in a conventional electromagnetic stirring process.
An ultrasonic stirrer may also be used.
[0095] The electromagnetic field application coil 11 may be
installed around the second sleeve 22 to be contacted to the
outside of the second sleeve 22. By using the electromagnetic field
application coil 11, the molten metal can be thoroughly stirred
while being poured into the second sleeve 22. When the second
sleeve 22 moves, the stirring unit 1 may move together with the
second sleeve 22, as shown in FIG. 3. Although not shown in the
drawings, it is understood that only the second sleeve 22 can move
in a state wherein the electromagnetic field application coil 11 is
fixed.
[0096] The electromagnetic field application coil 11 is
electrically connected to an electromagnetic field control unit 13
for controlling the electromagnetic field application by the
stirring unit 1, as shown in FIGS. 1 and 3 through 6. The
electromagnetic field control unit 13 may include a control
element. The control element includes a switch (not shown) for
determining the application of electric powder or electromagnetic
field controller (not shown) for controlling an electromagnetic
field by adjusting voltage, frequency, and electromagnetic force.
That is, the electromagnetic field control unit 13 controls the
intensity or duration of an electromagnetic field.
[0097] The electromagnetic field control unit 13 operates the
electromagnetic field application coil 11 in such a manner that
from prior to pouring the molten metal into the second sleeve 22,
the second sleeve 22 is exposed to an electromagnetic field of the
intensity so that solidification layers and/or dendrites are not
formed in the molten metal at an early stage. Also, the
electromagnetic field control unit 13 controls the electromagnetic
field application coil 11 in such a manner that the electromagnetic
field application to the second sleeve 22 is stopped when the
molten metal reaches near its liquidus temperature, i.e., when
crystalline nuclei are formed in the molten metal.
[0098] In this way, the electromagnetic field application of the
electromagnetic field application coil 11 is controlled by the
electromagnetic field control unit 13. As described above, the
application of an electromagnetic field may be sustained until the
prepared semi-solid metal slurry is pressed. However, in view of
energy efficiency, an electromagnetic field may be applied until
the slurry is manufactured, i.e., until the solid fraction of the
slurry is 0.001 to 0.7. Preferably, the application of an
electromagnetic field may be carried out until the solid fraction
of the slurry is 0.001 to 0.4, and more preferably 0.001 to 0.1.
The time required for accomplishing these solid fraction levels can
be determined experimentally by comparing the measured temperature
of the molten metal and the temperature in the phase diagram of a
corresponding metal material.
[0099] Turning to FIG. 1, the first sleeve 21 and the second sleeve
22 have opposed ends that are hinge-connected. The second sleeve 22
can move within a predetermined angle, preferably, less than 90
degrees, with respect to the first sleeve 21. The second sleeve 22
may be installed in the space 12 defined by the stirring unit 1 in
such a way to be concentric with the electromagnetic field
application coil 11.
[0100] The first and second sleeves 21 and 22 may be made of a
metal material or an insulating material such as ceramic.
Preferably, the first and second sleeves 21 and 22 may be made of a
material having a melting point higher than the molten metal M. The
first and second sleeves 21 and 22 may also be made of a
non-magnetic material.
[0101] In particular, the second sleeve 22 may be made of a
non-magnetic metal or an insulating material. Therefore, when an
electromagnetic field is applied to the second sleeve 22, the
second sleeve 22 does not cause induction heating and heat
generation, which is helpful in cooling the molten metal contained
in the second sleeve 22. Also, the cooling of the molten metal may
be initiated simultaneously with pouring the molten metal into the
second sleeve 22. When the second sleeve 22 is made of a
non-magnetic metal material, it is preferable to use a material
having a melting point higher than the temperature of the molten
metal.
[0102] When the temperature of the second sleeve 22 is raised to
that of the molten metal, there is a risk that the second sleeve 22
may be molten. For this reason, the temperature of the second
sleeve 22 cannot be raised to that of the molten metal. In this
regard, when an electromagnetic field is applied to the second
sleeve immediately after pouring the molten metal, dendrites may be
instantly formed at inner wall portions of the second sleeve 22
contacting with the molten metal due to a high temperature
difference between the second sleeve 22 and the molten metal.
[0103] Meanwhile, the first sleeve 21 is in a cylindrical form
parallel to the ground and the second sleeve 22 can move at a
predetermined angle with respect to an end of the first sleeve 21
connected to the second sleeve 22. In such a structure, as will be
described later, the second sleeve 22 corresponds to the slurry
manufacturing area T for retaining the molten metal and
manufacturing the slurry by electromagnetic stirring, and the first
sleeve 21 corresponds to an area for press-forming the manufactured
slurry.
[0104] That is, the second sleeve 22 acts as a slurry manufacturing
vessel for manufacturing the semi-solid slurry using the molten
metal and the first sleeve 21 acts as a forming die for
press-forming the manufactured slurry. Here, both ends of each of
the first and second sleeves 21 and 22 are not necessarily open.
There are no particular limitations on the structures of the first
and second sleeves 21 and 22 provided that the first and second
sleeves are connected to each other, and the semi-solid metal
slurry S manufactured in the second sleeve 22 moves into the first
sleeve 21 and then released from the first sleeve 21.
[0105] In detail, the first sleeve 21 is in a long, slender
cylindrical form with both ends open and is fixedly installed in a
horizontal axis direction. The first sleeve 21 has the same
diameter as that of the second sleeve 22. A blocking member 20 is
installed at an end of the first sleeve 21. A slurry outlet port 23
of a predetermined shape is defined by the blocking member 20. The
semi-solid slurry S is released from the first sleeve 21 via the
slurry outlet port 23. The slurry outlet port 23 is present at the
end opposite to the end of the first sleeve 21 coupled with the
second sleeve 22.
[0106] An extrusion device with an extrusion unit 6 is installed
downstream of the slurry outlet port 23. The extrusion unit 6 is
used as a forming unit to form an extrudate E, which is a product
of a predetermined shape, using the slurry released from the slurry
outlet port 23. The extrusion unit 6 is installed outside the
slurry outlet port 23 of the first sleeve 21.
[0107] The extrusion unit 6 includes a transfer roller 61 for
transferring the extruded slurry. A plurality of spray-type coolers
62 for cooling the slurry released from the slurry outlet port 23
of the first sleeve 21 are installed above a transfer surface 60 of
the transfer roller 61. A cutter 63 is installed outside and above
the slurry outlet port 23 of the first sleeve 21 to be moved in an
upward and a downward direction to cut the semi-solid slurry S
released from the slurry outlet port 23. The cutter 63 is installed
so that the edge of the cutter 63 faces downward. When the slurry
is released to a desired length from the slurry outlet port 23, the
cutter cuts the released slurry by moving in a downward
direction.
[0108] In the extrusion unit 6, the semi-solid metal slurry is
transferred by the transfer roller 61, cooled by the coolers 62,
and cut to a predetermined length by the cutter 63, to form the
extrudate E in the form of a wire or a sheet.
[0109] Since the slurry released from the slurry outlet port 23 is
transferred to the extrusion unit 6, the slurry outlet port 23 of
the first sleeve 21 determines the shape of the slurry S to be
released from the slurry outlet port 23. The shape of the slurry
outlet port 23 may be determined by the shape of the extrudate E to
be formed in the extrusion unit 6 installed downstream of the
slurry outlet port 23. That is, as will be described later, since
the slurry S is released from the slurry outlet port 23 and
transferred to the extrusion unit 6, the shape of the slurry
released is first determined by the slurry outlet port 23. In this
regard, the shape of the slurry outlet port 23 varies depending on
the shape of the extrudate to be formed in the extrusion unit 6. If
the extrudate extruded from the slurry outlet port 23 is of a wire
form, a circular outlet port may be used, while if the extrudate is
of a sheet form, a rectangular outlet port may be used.
[0110] Meanwhile, a slurry inlet port 24 is present at the other
end of the first sleeve 21 opposite to the slurry outlet port 23.
The slurry outlet port 23 and the slurry inlet port 24 communicate
concentrically with each other. The slurry inlet port 24 is formed
to have a shape conforming to that of the slurry outlet port 26 of
the second sleeve 22 so as to communicate concentrically with the
slurry outlet port 26. Therefore, the slurry S manufactured in the
second sleeve 22 is released from the slurry outlet port 23 via the
slurry inlet port 24.
[0111] The first sleeve 21 may be formed in a shape gradually
flared from the slurry inlet port 24 to the slurry outlet port 23.
That is, the inner diameter of the first sleeve 21 may be gradually
increased toward the releasing direction of the slurry, i.e., from
the slurry inlet port 24 to the slurry outlet port 23. Therefore,
the inner diameter of the first sleeve 21 may be equal to or larger
than that of the second sleeve 22.
[0112] A first temperature control unit 41 may be further installed
around the first sleeve 21, as shown in FIGS. 1 and 3 through 6.
The first temperature control unit 41 adjusts the temperature of
the semi-solid slurry S in the first sleeve 21 by adjusting the
temperature of a predetermined area of the first sleeve 21. That
is, the first temperature control unit 41 serves to prevent the
semi-solid slurry S pressed in the first sleeve 21 from rapidly
cooling. In this regard, the first temperature control unit 41 has
a predetermined heat insulating function.
[0113] In detail, the first temperature control unit 41 includes a
common water jacket 43 containing a spiral pipe 42. The water
jacket 43 is concentrically installed around the first sleeve 21 to
surround the outside of the first sleeve 21. By appropriately
adjusting the temperature of a medium which flows in the pipe 42,
the temperature of the slurry in the first sleeve 21 can be
adjusted.
[0114] The pipe 42 may also be buried in the first sleeve 21. Any
temperature control units capable of adjusting the temperature of
the slurry contained in the first sleeve 22 may be used. An
electric heater (not shown) may also be used as the first
temperature control unit 41.
[0115] Meanwhile, a first plunger 52 as a first pressing device is
slidably inserted in the injection port 25 of the second sleeve 22.
The first plunger 52 can move reciprocally like a piston in the
first and second sleeves 21 and 22 while being connected to a
separate cylinder unit (not shown), which is in turn connected to a
controller (not shown). Here, a press face 54 which is a front end
of the first plunger 52 may be a flat surface perpendicular to the
moving direction of the first plunger 52.
[0116] When the slurry is manufactured in the second sleeve 22, the
first plunger 52 is inserted into the injection port 25 of the
second sleeve 22 to block the injection port 25 of the second
sleeve 22. The first plunger 52 moves together with the second
sleeve 22 in a state of being inserted into the injection port 25
of the second sleeve 22, thereby preventing the spill out of the
slurry from the injection port 25 of the second sleeve 22. When the
slurry outlet port 26 of the second sleeve 22 communicates with the
slurry inlet port 24 of the first sleeve 21 by removal of the
stopper 31, the first plunger 52 pushes the slurry in the second
sleeve 22 toward the slurry outlet port 23 of the first sleeve 21.
Therefore, the slurry is transferred to the transfer surface 60 of
the transfer roller 61 of the extrusion unit 6 from the slurry
outlet port 23.
[0117] In other words, the first plunger 52 is away from the
injection port 25 of the second sleeve 22 while the second sleeve
22 is exposed to an electromagnetic field and the molten metal in
the second sleeve 22 is cooled, i.e., while the semi-solid slurry
is manufactured from the molten metal in the second sleeve 22, as
shown in FIG. 1. After the slurry is manufactured in the second
sleeve 22, the first plunger 52 is inserted into the injection port
25 and pushes the slurry in the second slurry 22. The first plunger
52 moves together with the second sleeve 22, and pushes the slurry
toward the first sleeve 21.
[0118] A thermocouple (not shown) may be installed in each of the
first sleeve 21 and the second sleeve 22 and connected to a
controller for providing the temperature information of the molten
metal and the slurry to the controller.
[0119] Meanwhile, a pouring unit 51 is used to pour the molten
metal into the second sleeve 22. The pouring unit 51 may be a
common ladle electrically connected to a controller (not shown). In
addition, any pouring units such as a furnace, which melts a metal
material, directly connected to the second sleeve 22, may be used
provided that the molten metal can be poured into the second sleeve
22.
[0120] Hereinafter, operation of the rheoforming apparatus having
the aforementioned structure according to the first embodiment of
the present invention will be described.
[0121] Turning to FIG. 1, first, the second sleeve 22 moves at a
predetermined angle, preferably 90 degrees with respect to the
first sleeve 21 so that the injection port 25 of the second sleeve
22 faces upward. At the same time, the slurry outlet port 24 of the
second sleeve 22 is sealed by the stopper 31 to allow the second
sleeve 22 to act as a vessel for receiving the molten metal.
[0122] Next, the electromagnetic field control unit 13 operates the
electromagnetic field application coil 11 of the stirring unit 1 in
such a manner that the empty second sleeve 22 is exposed to an
electromagnetic field of the intensity so that solidification
layers or dendrites are not formed in the molten metal to be poured
at an early stage.
[0123] At this time, the electromagnetic field application coil 11
may apply an electromagnetic field with an intensity of 500 Gauss
at 250 V and 60 Hz, but is not limited thereto. It is understood
that the intensity of an electromagnetic field may be appropriately
adjusted according to process conditions.
[0124] In this state, the molten metal M that has molten in a
separate furnace is poured via the pouring unit 51 such as a ladle
into the second sleeve 22 under an electromagnetic field. Here, to
promote formation of the molten metal poured in the second sleeve
22 into the semi-solid slurry S and to prevent spill out of the
molten metal through a gap between the slurry outlet port 26 and
the stopper 31 of the second sleeve 22, the solid fraction of the
semi-solid slurry is relatively increased.
[0125] The furnace and the second sleeve 22 may also be directly
connected to each other for directly pouring the molten metal into
the second sleeve 22. As described above, the molten metal may have
a temperature of 100.degree. C. above its liquidus temperature. The
second sleeve 22 may be connected to a separate gas supply tube
(not shown) for supplying an inert gas such as N.sub.2 and Ar,
thereby preventing the oxidation of the molten metal.
[0126] In this way, when the molten metal is poured into the second
sleeve 22 under the electromagnetic stirring, fine crystalline
particles are distributed throughout the second sleeve 22, without
formation of solidification layers at an early stage. The
crystalline particles rapidly grow, thereby preventing the
formation of dendritic structures.
[0127] Application of an electromagnetic field by the
electromagnetic field application coil 11 may be carried out
simultaneously with the pouring of the molten metal into the second
sleeve 22.
[0128] The application of an electromagnetic field may be sustained
until the semi-solid slurry S is pressed by the first plunger 52,
i.e., the solid fraction of the slurry is in a range of 0.001 to
0.7, preferably 0.001 to 0.4, and more preferably 0.001 to 0.1. The
time required for accomplishing these solid fraction levels can be
determined by previous experiments. The application of an
electromagnetic field is carried out during so determined time.
[0129] After completion or in the middle of application of an
electromagnetic field, the molten metal in the second sleeve 22 is
cooled at a predetermined rate until the solid fraction of the
molten metal is in a range of 0.1 to 0.7 to manufacture the
semi-solid slurry.
[0130] In this case, a cooling rate may be adjusted to 0.2 to
5.0.degree. C./sec, preferably 0.2 to 2.0.degree. C./sec, by the
second temperature control unit 44 installed around the second
sleeve 22, as described above. Of course, the cooling may be
spontaneously carried out. The time (t.sub.2) required for reaching
the solid fraction of 0.1 to 0.7 can be determined by previous
experiments.
[0131] The semi-solid metal slurry made from the molten metal in
the second sleeve 22 has the solid fraction to an extent so that
the semi-solid metal slurry is not spilled out from the slurry
outlet port 26 of the second sleeve 22 and the slurry inlet port 24
of the first sleeve 21 while the slurry outlet port 26 is coupled
with the slurry inlet port 24.
[0132] After the semi-solid metal slurry is manufactured in the
second sleeve 22, the first plunger 52 is inserted into the
injection port 25 of the second sleeve 22. In this state, when the
second sleeve 22 moves at an angle of 90 degrees, the slurry outlet
port 26 of the second sleeve 22 is coupled with the slurry inlet
port 24 of the first sleeve 21 via the stopper 31, as shown in FIG.
3. At this time, the first plunger 52 moves together with the
second sleeve 22.
[0133] Then, the stopper 31, which is a sealing member, is removed
so that the slurry outlet port 26 communicates with the slurry
inlet port 24.
[0134] In this state, the first plunger 52 pushes the slurry S in
the second sleeve 22 toward the slurry outlet port 23 of the first
sleeve 21 to force the slurry S into the extrusion unit 6 from the
slurry outlet port 23, as shown in FIG. 4.
[0135] During the pressing in the first sleeve 21, the temperature
of the slurry can be preserved to a predetermined level by the
first temperature control unit 41.
[0136] As shown in FIG. 5, the slurry released from the slurry
outlet port 23 is transferred by the transfer roller 61 while being
rapidly cooled by the coolers 62 of the extrusion unit 6 and cut by
the cutter 63, which is positioned above the slurry outlet port 23,
to form the extrudate E of a predetermined shape.
[0137] The extrudate E is transferred to a collection unit (not
shown) by the transfer roller 61. On the other hand, a biscuit B
left in the first sleeve 21 is removed by a separate ejection unit
(not shown) after returning the first plunger 52 to an original
position and moving back the second sleeve 22 at an angle of 90
degrees to open the slurry inlet port 24 of the first sleeve 21, as
shown in FIG. 6.
[0138] After the biscuit B is removed, the aforementioned process
is repeated by pouring a molten metal into the second sleeve 22, as
shown in FIG. 1. Therefore, the fine and uniform extrudate E can be
obtained.
[0139] As described above, according to the first embodiment of the
present invention, spherical particles can be obtained by
remarkably increasing the density of nuclei at the inner wall of
the second sleeve with stirring at a temperature above the liquidus
temperature of the molten metal within a short time. Therefore, the
semi-solid slurry of fine, uniform, spherical particles can be
manufactured in the second sleeve 22. As a result, the operation
duration can be reduced, thereby minimizing energy loss. Even
though the second sleeve 22 has an unsymmetrical shape instead of a
cylindrical shape, the semi-solid slurry of fine, uniform,
spherical particles can be manufactured.
[0140] Also, since the semi-solid metal slurry in the second sleeve
22 is transferred to the extrusion unit 6 via the first sleeve 21,
the high quality extrudate E can be obtained at a low pressure.
Therefore, power loss can be prevented and the operation duration
can be reduced. At the same time, the reduction of durability of
constitutional elements due to pressing of the slurry can be
prevented and energy loss can be reduced. Therefore, the high
quality extrudate E with fine and uniform structures can be
continuously manufactured within a short time.
[0141] Also, due to improved energy efficiency, a manufacture cost
can be reduced and the mechanical properties of the extrudate can
be enhanced. In addition, since the extrudate E can be simply
manufactured within a short time, the entire manufacturing process
can be simplified and productivity can be enhanced.
[0142] Meanwhile, a portion of the slurry exposed to air may be
oxidized. According to the present invention, since the second
sleeve 22 for manufacturing the slurry is vertically positioned, an
upper portion of the slurry is oxidized. The oxidized portion of
the slurry is left on the biscuit B without being transferred to
the extrusion unit 6, as shown in FIGS. 5 and 6. Since the biscuit
B is removed, the oxidized portion is also removed together with
the biscuit B. Therefore, the high quality extrudate E can be
obtained.
[0143] In the first embodiment, the molten metal is injected
through the injection port 25 which is an end of the second sleeve
22, and the semi-solid slurry S in the second sleeve 22 is pressed
by the first plunger 52 inserted into the injection port 25.
However, according to a second embodiment of the present invention
as shown in FIG. 8, a separate pouring hole 28 is branched from the
second sleeve 22 and the molten metal is poured into the second
sleeve 22 from the pouring hole 28. In this structure, the first
plunger 52 may be permanently inserted in the injection port 25 of
the second sleeve 22. Such a structure of the second sleeve 22 and
the first plunger 52 may be applied in all embodiments as will be
described later.
[0144] According to a third embodiment of the present invention as
shown in FIGS. 9 through 14, the aforementioned rheoforming
apparatus may be used as a press-forming apparatus provided with a
press-forming unit 7 which is installed outside the slurry outlet
port 23 of the first sleeve 21, instead of the extrusion unit 6
that forms the extrudate E from the slurry released from the slurry
outlet port 23. The press-forming unit 7 includes press dies 71 and
72 and forms a product with a shape conforming to the shape defined
by the press dies 71 and 72 using the slurry released from the
slurry outlet port 23 of the first sleeve 21.
[0145] In the rheoforming apparatus according to the third
embodiment of the present invention, first, the slurry is
manufactured from the molten metal M poured into the second sleeve
22, as shown in FIG. 9. The slurry outlet port 26 of the second
sleeve 22 is then coupled with the slurry inlet port 24 of the
first sleeve 21 by moving the second sleeve 22, as shown in FIG.
10. Then, the slurry outlet port 26 of the second sleeve 22 is
opened by removal of the sealing member 3 so that the slurry outlet
port 26 communicates with the slurry inlet port 24 of the first
sleeve 21.
[0146] In this state, the first plunger 52 pushes the slurry in the
second sleeve 22 toward the slurry outlet port 23 of the first
sleeve 21. At this time, the temperature of the slurry can be
preserved by the first temperature control unit 41 installed around
the first sleeve 21. As shown in FIGS. 12 and 13, the slurry
released from the slurry outlet port 23 of the first sleeve 21 is
formed into a product P with a predetermined shape by pressing
using the press dies 71 and 72 and cut by the cutter 63, which is
positioned above the slurry outlet port 23.
[0147] The biscuit B left in the first sleeve 21 is removed by a
separate ejection unit after returning the first plunger 52 to an
original position and moving back the second sleeve 22 at a
predetermined angle to open the slurry inlet port 24 of the first
sleeve 21, as shown in FIG. 14. After the biscuit B is removed, the
aforementioned process is repeated by pouring a molten metal into
the second sleeve 22, as shown in FIG. 9. Therefore, the product P
with a fine and uniform particle structure can be obtained.
[0148] Like in the first embodiment, according to this embodiment
of the present invention, because the molten metal is subjected to
press-forming in the form of a slurry, the high quality product P
can be manufactured at a low pressure. As a result, the loss of an
electric energy and the operation duration can be reduced.
[0149] Even though an upper portion of the manufactured slurry may
be oxidized, the oxidized portion is removed together with the
biscuit B without being formed. Therefore, a high quality product
can be obtained.
[0150] According to a fourth embodiment of the present invention as
shown in FIGS. 15 and 17, a rheoforming apparatus of the present
invention may be used as a die-casting apparatus having a forming
die 8. That is, the rheoforming apparatus according to the fourth
embodiment of the present invention includes the forming die 8,
which is installed outside the slurry outlet port 23. The forming
die 8 includes a moving die 81 and a fixing die 82. When the moving
die 81 and the fixing die 82 meet with each other, a forming cavity
83 of a predetermined shape is defined by the moving die 81 and the
fixing die 82. The fixing die 82 is formed with a funnel 84 for
directing the slurry into the forming cavity 83. The funnel 84
communicates with the slurry outlet port 23 of the first sleeve 21.
The semi-solid metal slurry S released from the slurry outlet port
23 is directed into the forming cavity 83.
[0151] The moving die 81 and the fixing die 82 are respectively
supported by support plates 85a and 85b which are attached to the
entire equipment (not shown). When the forming is completed, the
moving die 81 is separated from the fixing die 82 and a die cast
formed in the forming cavity 83 is removed.
[0152] In the rheoforming apparatus according to the fourth
embodiment of the present invention, first, the slurry is
manufactured from the molten metal M poured into the second sleeve
22, as shown in FIG. 15. Then, the second sleeve 22 is coupled with
the first sleeve 21, as shown in FIG. 16, and the slurry outlet
port 26 of the second sleeve 22 is opened by removal of the sealing
member 3, as shown in FIG. 17.
[0153] In this state, the first plunger 52 pushes the slurry in the
second sleeve 22 toward the slurry outlet port 23 of the first
sleeve 21. Then, the slurry released from the slurry outlet port 23
of the first sleeve 21 is directed into the forming die 8. At this
time, the slurry S is inserted into the forming cavity 83 via the
funnel 84 of the forming die 8 and rapidly cooled, to form the die
cast corresponding to the shape of the forming cavity 83, as shown
in FIG. 17. When the forming is completed, the moving die 81 is
separated from the fixing die 82. Therefore, the die cast can be
removed from the forming cavity 83.
[0154] Like in the first embodiment, according to this embodiment
of the present invention, because the molten metal is subjected to
die-casting in the form of a slurry, the high quality die cast can
be manufactured at a low pressure. As a result, the loss of an
electric energy and the operation duration can be reduced. Also,
since the slurry with a low temperature is inserted in the forming
die 8 under a low pressure, the reduction of the lifespan of the
forming die 8 is prevented. In addition, since an upper portion of
the manufactured slurry may be oxidized but is not inserted into
the forming die 83, a high quality product can be obtained.
[0155] Meanwhile, the aforementioned rheoforming apparatus may be
modified according to a fifth embodiment of the present invention
as shown in FIGS. 18 and 19. According to the fifth embodiment, the
first sleeve 21 is installed in a vertical direction. The second
sleeve 22 is installed on the first sleeve 21 so that the slurry
inlet port 24 of the first sleeve 21 communicates concentrically
with the slurry outlet port 26 of the second sleeve 22. Therefore,
the first sleeve 21 is connected to the lower end of the second
sleeve 22. The second sleeve 22 is fixedly installed on support
frames 14 and 15.
[0156] Here, the inner peripheral surface of each of the second
sleeve 22 and the first sleeve 21 may be formed in a shape flared
in a downward direction so that the semi-solid metal slurry S
manufactured in the second sleeve 22 can be dropped by its own
gravity. Also, a forming unit such as the forming die 8 is
installed outside the slurry outlet port 23 of the first sleeve 21.
FIG. 18 shows only the forming die 8, but is not limited thereto.
The above-described extrusion unit or press-forming unit may also
be provided.
[0157] In the rheoforming apparatus according to the fifth
embodiment of the present invention, the first sleeve 21 and the
second sleeve 22 are fixedly coupled with each other. The sealing
member 3 as described above is interposed between the first sleeve
21 and the second sleeve 22. The first sleeve 21 and the second
sleeve 22 may also be integrally formed. In this case, the sealing
member 3 may be installed in an inner side of an integrally formed
sleeve.
[0158] First, the slurry is manufactured using the molten metal M
poured into the second sleeve 22 from the injection port 25, as
shown in FIG. 18. Then, the slurry outlet port 26 of the second
sleeve 22 is opened by removal of the sealing member 3 so that the
semi-solid metal slurry S in the second sleeve 22 can be dropped in
the first sleeve 21 by its own gravity. At this time, the slurry S
manufactured in the second sleeve 22 has a solid fraction to an
extent so that the slurry S can be dropped by its own gravity.
Then, the first plunger 52 is inserted into the injection port 25
of the second sleeve 22 and forces the slurry in the first sleeve
21 toward the forming die 8.
[0159] The slurry S is inserted into the forming cavity 83 via the
funnel 84 of the forming die 8 and rapidly cooled, to form the die
cast corresponding to the shape of the forming cavity 83. At this
time, a separate cooler (not shown) may rapidly cool the slurry
inserted in the forming cavity 83. When the forming is completed,
the moving die 81 is separated from the fixing die 82. Therefore,
the die cast can be removed from the forming cavity 83.
[0160] Like in the fourth embodiment, according to this embodiment
of the present invention, because the molten metal is subjected to
die-casting in the form of a slurry, the high quality die cast can
be manufactured at a low pressure. As a result, the loss of an
electric energy and the operation duration can be reduced. Also,
since the slurry with low temperature is inserted in the forming
die 8 under a low pressure, the reduction of the lifespan of the
forming die 8 is prevented. In addition, since the slurry S
manufactured in the second slurry 22 can be dropped in the first
sleeve 21 by its own gravity, the moving of the slurry from the
second sleeve 22 to the first sleeve 21 can be easily
performed.
[0161] In the above structure, the second sleeve 22 may have a
shape flared in a downward direction, as described above. The first
sleeve 21 may also be formed in a shape flared in a downward
direction. That is, the first and second sleeves 21 and 22 may be
formed in a flared shape so that when the slurry manufactured is
dropped in the direction of the forming die 8 by its own gravity or
pressed by the first plunger 52, the cross-sections of the first
sleeve 21 and the second sleeve 22 are increased in the direction
of the forming die 8 to promote the moving of the slurry.
[0162] According to a sixth embodiment of the present invention as
shown in FIGS. 20 and 21, an end of the second sleeve 22 may be
connected to the body of the first sleeve 21. That is, the second
sleeve 22 may be branched from the first sleeve 21. In this
embodiment, the first sleeve 21 is installed so that its axis
direction is parallel to the ground. The second sleeve 22 is
connected to the body of the first sleeve 21 to be positioned above
the first sleeve 21. A second plunger 53 for pressing is slidably
inserted in an opening 30 of the first sleeve 21. Here, a press
face 55 which is a front face of the second plunger 53 is a flat
surface perpendicular to the moving direction of the second plunger
53.
[0163] A forming unit such as the forming die 8 is installed
outside the slurry outlet port 23 of the first sleeve 21. FIG. 20
shows only the forming die 8, but is not limited thereto. The
above-described extrusion unit or press-forming unit may also be
provided.
[0164] The second sleeve 22 is inclined at an angle of about 45
degrees with respect to the first sleeve 21 so that the injection
port 25 of the second sleeve 22 is positioned away from the first
sleeve 21. The slurry outlet port 26 of the second sleeve 22 is
connected to about intermediate portion of the body of the first
sleeve 21. The stopper 31 as the sealing member 3 is removably
installed near the slurry outlet port 26 of the second sleeve 22 to
open or close the slurry outlet port 26. The stirring unit 1 is
installed around the second sleeve 22, as described above.
[0165] The second sleeve 22 may be formed with the separate pouring
hole 28 for pouring the molten metal. The pouring hole 28 is
positioned at a higher position than the stirring unit 1 and is
protruded in an upward direction from the body of the second sleeve
22. The pouring hole 28 communicates with the second sleeve 22. The
molten metal M is poured in the slurry manufacturing area T from
the pouring hole 28 under an electromagnetic field applied by the
stirring unit 1.
[0166] Meanwhile, the second sleeve 22 may be formed in a shape
flared in the direction of the first sleeve 21. By doing so, the
slurry manufactured in the second sleeve 22 can be easily dropped
in the first sleeve 21 by its own gravity or by the first plunger
52.
[0167] As shown in FIG. 20, the molten metal M is poured in the
second sleeve 22 from the pouring hole 28 in a state wherein the
stopper 31 is closed, and is formed into the slurry by an
electromagnetic field applied by the stirring unit. Then, the
slurry outlet port 26 of the second sleeve 22 is opened by upward
removal of the stopper 31 so that the slurry advances toward the
first sleeve 21. At this time, when the first plunger 52 pushes the
slurry toward the first sleeve 21, the moving of the slurry toward
the first sleeve 21 can be promoted.
[0168] When the slurry is inserted in the first sleeve 21, the
second plunger 53 forces the slurry toward the slurry outlet port
23 so that the slurry is inserted into the forming die 8, as shown
in FIG. 21. The slurry is inserted into the forming cavity 83 via
the funnel 84 and rapidly cooled to form the die cast having a
shape corresponding to that of the forming cavity 83. At this time,
a separate cooler (not shown) may rapidly cool the slurry inserted
in the forming cavity 83. When the forming is completed, the moving
die 81 is separated from the fixing die 82. Therefore, the die cast
can be removed from the forming cavity 83.
[0169] Like in the fourth embodiment, according to this embodiment
of the present invention, because the molten metal is subjected to
die-casting in the form of a slurry, the high quality die cast can
be manufactured at a low pressure. As a result, the loss of an
electric energy and the operation duration can be reduced. Also,
since the slurry with low temperature is inserted in the forming
die 8 under a low pressure, the reduction of the lifespan of the
forming die 8 is prevented.
[0170] According to a seventh embodiment of the present invention
as shown in FIG. 22, the first sleeve 21 may be installed
vertically with respect to the ground and the second sleeve 22 may
be branched from the first sleeve 21. Therefore, the slurry
manufactured can easily move in the direction of the forming die 8
by its own gravity, thereby promoting a manufacture process. For
this, both the second sleeve 22 and the first sleeve 21 may be
formed in a shape gradually flared from their own inlet port.
[0171] As described above, in the sixth and seventh embodiments,
since an upper portion of the slurry may be oxidized but is not
inserted in the forming die 8, a high quality product can be
obtained.
[0172] Meanwhile, in the sixth and seventh embodiments, the press
face 54 which is the front face of the first plunger 52 may be
inclined at an angle of about 45 degrees with respect to the moving
direction of the first plunger 52 so that when the first plunger 52
advances toward the first sleeve 21, the press face 54 matches with
the inner peripheral surface of the first sleeve 21.
[0173] In this case, the press face 54 of the first plunger 52 is
formed in the same surface as the inner peripheral surface of the
first sleeve 21 so that when the first plunger 52 pushes the slurry
in the second sleeve 22, the entire slurry can be inserted into the
first sleeve 21. That is, the press face 54 of the first plunger 52
is formed so that the slurry inlet port 24 of the first sleeve 21
is closed along the inner peripheral surface of the first sleeve 21
by the first plunger 52. Therefore, the slope of the press face 54
of the first plunger 52 is the same as the inclined angle of the
second sleeve 22 with respect to the first sleeve 21.
[0174] The press face 54 which is the front face of the first
plunger 52 may also be a flat surface perpendicular to the moving
direction of the first plunger 52, according to an eight embodiment
of the present invention as shown in FIG. 23.
[0175] The same acting effects as in the seventh embodiment can be
achieved even when the forming die 8 is positioned at the upper end
of the first sleeve 21 installed perpendicularly to the ground and
the second plunger 53 is slidably inserted into the lower end of
the first sleeve 21, according to a ninth embodiment of the present
invention as shown in FIG. 24.
[0176] As described above, a rheoforming apparatus according to the
present invention can be widely used for rheoforming various kinds
of metals or alloys, for example, aluminum, magnesium, zinc,
copper, iron, or an alloy thereof.
[0177] That is, in view of solidification theory, the temperature
of a molten metal to be inserted in a sleeve can be discussed with
respect to the specific heat of a metal or alloy material that make
the molten metal.
[0178] The specific heat of aluminum is about 0.25 kcal/g. The
specific heat of other metals except aluminum, for example,
magnesium (about 0.18 kcal/g), zinc (about 0.1 kcal/g), copper
(about 0.1 kcal/g), and iron (about 0.1 kcal/g) is smaller than
that of aluminum. In this regard, other metals except aluminum
require a smaller thermal energy than aluminum. Therefore, even
when molten metals made from these metals are inserted in a sleeve
at a temperature of 100.degree. C. above their liquidus
temperature, latent heat is not generated. As a result, crystalline
nuclei may grow in these molten metals by discharge of only the
specific heat of the molten metals. Therefore, the above-described
advantages can also be obtained from molten metals made from other
metals or alloys except aluminum.
[0179] Theoretically, when the difference between a temperature
(T.sub.I) at which liquid phase is changed to solid phase and a
temperature (T.sub.S) at which solid phase is changed to liquid
phase, i.e., T.sub.I-T.sub.S=.DELTA.T, is zero (0), crystalline
nuclei can be formed in molten metals made from any metals or
alloys by setting the temperature of the molten metals within a
temperature of T.sub.I to T.sub.S.
[0180] Meanwhile, pure aluminum commonly used in the foundry
industry contains about 1% of impurity. Also, pure magnesium, pure
zinc, pure copper, and pure iron commonly used in the foundry
industry also contain about 1% of impurity.
[0181] Therefore, when a magnetic field by electromagnetic field
application is created in molten metals made from magnesium, zinc,
copper, iron, and an alloy thereof in which .DELTA.T is not "0" and
the specific heat is smaller than aluminum, these metals and alloys
can also provide the same results as in aluminum and an alloy
thereof.
[0182] As apparent from the above descriptions, a rheoforming
apparatus according to the present invention provides the following
advantages.
[0183] First, products having a uniform, fine, and spherical
particle structure can be manufactured.
[0184] Second, more nuclei can be formed at an inner wall of a
sleeve within a short time through electromagnetic stirring at a
temperature above the liquidus temperature of molten metals to
thereby obtain spherical particles.
[0185] Third, manufactured products have improved mechanical
properties.
[0186] Fourth, the duration of electromagnetic stirring is greatly
shortened, thereby conserving a stirring energy.
[0187] Fifth, the simplified overall process and the reduced
forming duration improve productivity.
[0188] Sixth, because products are formed from slurries, lower
pressure forming is possible.
[0189] Seventh, because products are formed under a low pressure,
durability of constitutional elements of the apparatus can be
improved, and energy loss and manufacturing duration can be
reduced.
[0190] Eighth, upper portions of slurries manufactured may be
oxidized but the oxidized portions are removed together with
biscuits without being formed. Therefore, high quality products can
be obtained.
[0191] 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.
* * * * *