U.S. patent application number 09/253235 was filed with the patent office on 2002-06-13 for apparatus and method for integrated semi-solid material production and casting.
Invention is credited to BROWN, STUART B., MENDEZ, PATRICIO F., MYOJIN, SHINYA, RICE, CHRISTOPHER S..
Application Number | 20020069997 09/253235 |
Document ID | / |
Family ID | 24946340 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020069997 |
Kind Code |
A1 |
MENDEZ, PATRICIO F. ; et
al. |
June 13, 2002 |
APPARATUS AND METHOD FOR INTEGRATED SEMI-SOLID MATERIAL PRODUCTION
AND CASTING
Abstract
An apparatus and process is provided for producing semi-solid
material and directly casting the semi-solid material into a
component wherein the semi-solid material is formed from a molten
material and the molten material is introduced into a container.
Semi-solid is produced therefrom by agitating, shearing, and
thermally controlling the molten material. The semi-solid material
is maintained in a substantially isothermal state within the
container by appropriate thermal control and thorough
three-dimensional mixing. Extending from the container is a means
for removing the semi-solid material from the container, including
a temperature control mechanism to control the temperature of the
semi-solid material within the removing means.
Inventors: |
MENDEZ, PATRICIO F.;
(CAMBRIDGE, MA) ; RICE, CHRISTOPHER S.;
(CAMBRIDGE, MA) ; BROWN, STUART B.; (NEEDHAM,
MA) ; MYOJIN, SHINYA; (CAMBRIDGE, MA) |
Correspondence
Address: |
TESTA, HURWITZ & THIBEAULT, LLP
HIGH STREET TOWER
125 HIGH STREET
BOSTON
MA
02110
US
|
Family ID: |
24946340 |
Appl. No.: |
09/253235 |
Filed: |
February 19, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09253235 |
Feb 19, 1999 |
|
|
|
08733125 |
Oct 17, 1996 |
|
|
|
Current U.S.
Class: |
164/71.1 ;
164/133; 164/900 |
Current CPC
Class: |
B22D 17/007
20130101 |
Class at
Publication: |
164/71.1 ;
164/900; 164/133 |
International
Class: |
B22D 027/08; B22D
035/04; B22D 025/00 |
Claims
We claim:
1. An apparatus for directly producing a component from a
semi-solid material comprising: a source of molten material; a
container for receiving said molten material; a thermal control
means for controlling the temperature of said container; an
agitation means for stirring material within said container acting
in conjunction with said thermal control means to produce a
substantially isotropic semi-solid material; a means for removing a
portion of said semi-solid material from said container, said
removing means being thermally controlled; and a casting means
directly connected to said removing means for receiving said
portion of semi-solid material from said removing means and casting
said semi-solid material into a component.
2. The apparatus of claim 1 wherein said agitating means is an
electromagnetic stirring device.
3. The apparatus of claim 1 wherein said agitation means comprises
a mechanical agitating device immersed in said semi-solid
material.
4. The apparatus of claim 3 wherein said mechanical agitating
device comprises a primary stirring component and a secondary
stirring component.
5. The apparatus of claim 4 wherein said primary stirring component
includes an arm having a first portion being substantially parallel
to a side wall of said container.
6. The apparatus of claim 5 wherein said arm of said primary
stirring component includes a second portion being substantially
parallel to a bottom wall of said container.
7. The apparatus of claim 5 wherein said secondary stirring
component is augur-shaped and promotes mixing of said semi-solid
material along an axis of said secondary stirring component.
8. The apparatus of claim 7 wherein said casting means comprises a
die casting device.
9. The apparatus of claim 8 wherein said mechanical agitating
device is a stainless steel coated with a ceramic.
10 The apparatus of claim 1 wherein said semi-solid material
comprises aluminum or an alloy thereof.
11. The apparatus of claim 1 wherein said semi-solid material
comprises steel or an alloy thereof.
12. The apparatus of claim 1 wherein said semi-solid material
comprises magnesium or an alloy thereof.
13. The apparatus of claim 1 wherein said removal means comprises a
transfer tube.
14. The apparatus of claim 13 wherein said transfer tube includes
an inner insulating layer.
15. The apparatus of claim 14 wherein said transfer tube includes a
support tube surrounding said insulating layer and an outer layer
surrounding said support tube.
16. The apparatus of claim 15 wherein said transfer tube includes a
heating mechanism for maintaining the temperature of said
semi-solid material passing through said transfer tube.
17. The apparatus of claim 16 wherein said transfer tube includes a
flow control means for regulating a flow of semi-solid material
through said transfer tube.
18. The apparatus of claim 17 wherein said transfer flow control
means regulates said flow of semi-solid material through said
transfer tube such that no more than one tenth of said semi-sold
material is removed per a removal cycle.
19. The apparatus of claim 17 wherein said transfer tube extends
though a cover in said chamber.
20. The apparatus of claim 17 wherein said transfer tube extends
through a side wall in said chamber.
21. The apparatus of claim 1 wherein said casting means includes a
die, a ram, and a shot sleeve disposed therebetween, said shot
sleeve for receiving said portion of said semi-solid and said ram
for forcing said portion into said die to form said component.
22. An apparatus for directly producing a component from a
semi-solid material comprising: a source of semi-solid material; a
container for receiving said semi-solid material; a thermal control
means for controlling the temperature of said semi-solid material;
an agitating means acting with said container for stirring said
semi-solid material in said container; said thermal controller and
said agitating means maintaining said semi-solid material in a
substantially isothermal state; and a die casting device connected
to said container for directly casting said semisolid material into
a component prior to solidification of said semi-solid
material.
23. The apparatus of claim 22 wherein said agitating means is an
electromagnetic stirring device.
24. The apparatus of claim 22 wherein said agitation means
comprises a mechanical agitating device immersed in said semi-solid
material.
25. The apparatus of claim 24 wherein said mechanical agitating
device comprises a primary stirring component and a secondary
stirring component.
26. The apparatus of claim 25 wherein said primary stirring
component includes a portion being substantially parallel to a side
wall of said container.
27. The apparatus of claim 26 wherein said secondary stirring
component is augur-shaped.
28. The apparatus of claim 27 wherein said casting means comprises
a die casting device.
29. The apparatus of claim 28 wherein said mechanical agitating
device is a stainless steel coated with a ceramic.
30. A method of directly producing a component from partially
solidified material semi-solid material comprising: receiving a
molten material in a container; forming said molten material into a
semi-solid material with an agitating means and a thermal
controlling means; maintaining said semi-solid material in a
substantially isothermal state with said agitating means and said
thermal controlling means; transferring a portion of said
semi-solid material directly to a casting apparatus; and casting
said portion of said semi-solid material into a component prior to
complete solidification of said portion.
Description
[0001] This application claims the benefit of copending provisional
application "Apparatus and Method for Integrated Semi-Solid
Material Production and Casting" filed Oct. 4, 1996 (attorney
docket number 0097701-0006, Express Mail Number EH408038515US,
serial number not yet known). A related application titled
"Apparatus and Method for Semi-Solid Material Production" was filed
Oct. 4, 1996 (attorney docket number 0097701-0005, Express Mail
Number EH408038921, serial number not yet known) and is
incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates generally to producing and
delivering a semi-solid material slurry for use in material forming
processes. In particular, the invention relates to an apparatus for
producing a substantially non-dendritic semisolid material slurry
and providing the semi-solid directly to a die casting
apparatus.
BACKGROUND INFORMATION
[0003] Slurry casting or rheocasting is a procedure in which molten
material is subjected to vigorous agitation as it undergoes
solidification. During normal (i.e. non-rheocasting) solidification
processes, dendritic structures form within the material that is
solidifying. In geometric terms, a dendritic structure is a
solidified particle shaped like an elongated stem having transverse
branches. Vigorous agitation of materials, especially metals,
during solidification eliminates at least some dendritic
structures. Such agitation shears the tips of the solidifying
dendritic structures, thereby reducing dendrite formation. The
resulting material slurry is a solid-liquid composition, composed
of solid, relatively fine, non-dendritic particles in a liquid
matrix (hereinafter referred to as a semi-solid material).
[0004] At the molding stage, it is well known that components made
from semisolid material possess great advantages over conventional
molten metal formation processes. These benefits derive, in large
part, from the lowered thermal requirements for semi-solid material
manipulation. A material in a semi-solid state is at a lower
temperature than the same material in a liquid state. Additionally,
the heat content of material in the semi-solid form is much lower.
Thus, less energy is required, less heat needs to be removed, and
casting equipment or molds used to form components from semi-solids
have a longer life. Furthermore and perhaps most importantly, the
casting equipment can process more material in a given amount of
time because the cooling cycle is reduced. Other benefits from the
use of semi-solid materials include more uniform cooling, a more
homogeneous composition, and fewer voids and porosities in the
resultant component.
[0005] The prior art contains many methods and apparatuses used in
the formation of semi-solid materials. For example, there are two
basic methods of effectuating vigorous agitation. One method is
mechanical stirring. This method is exemplified by U.S. Pat. No.
3,951,651 to Mehrabian et al. which discloses rotating blades
within a rotating crucible. The second method of agitation is
accomplished with electromagnetic stirring. An example of this
method is disclosed in U.S. Pat. No. 4,229,210 to Winter et al.,
which is incorporated herein by reference. Winter et al. disclose
using either AC induction or pulsed DC magnetic fields to produce
indirect stirring of the semi-solid.
[0006] Once the semi-solid material is formed, however, virtually
all prior art methods then include a solidifying and reheating
step. This so-called double processing entails solidifying the
semi-solid material into a billet. One of many examples of double
processing is disclosed in U.S. Pat. No. 4,771,818 to Kenney. The
resulting solid billet from double processing is easily stored or
transported for further processing. After solidification, the
billet must be reheated for the material to regain the semi-solid
properties and advantages discussed above. The reheated billet is
then subjected to manipulation such as die casting or molding to
form a component. In addition to modifying the material properties
of the semi-solid, double processing requires additional cooling
and reheating steps. For reasons of efficiency and material
handling costs, it would be quite desirable to eliminate the
solidifying and reheating step that double processing demands.
[0007] U.S. Pat. No. 3,902,544 to Flemings et al., incorporated
herein by reference, discloses a semi-solid forming process
integrated with a casting process. This process does not include a
double processing, solidification step. There are, however,
numerous difficulties with the disclosed process in Flemings et al.
First and most significantly, Flemings et al. require multiple
zones including a molten zone and an agitation zone which are
integrally connected and require extremely precise temperature
control. Additionally, in order to produce the semi-solid material,
there is material flow through the integrally connected zones.
Semi-solid material is produced through a combination of material
flow and temperature gradient in the agitation zone. Thus,
calibrating the required temperature gradient with the (possibly
variably) flowing material is exceedingly difficult. Second, the
Flemings et al. process discloses a single agitation means.
Thorough and complete agitation is necessary to maximize the
semi-solid characteristics described above. Third, the Flemings et
al. process is lacking an effective transfer means and flow
regulation from the agitation zone to a casting apparatus.
Additional difficulties with the Flemings process, and improvements
thereupon, will be apparent from the detailed description
below.
[0008] A primary object of the present invention is to provide an
apparatus and a process for integrating the formation of semi-solid
material with the casting of the semi-solid material while avoiding
a solidification and reheating step.
[0009] An additional object of the present invention is to provide
a more efficient and cost-effective die casting process for use
with semi-solid material formation.
[0010] Another object of the present invention is to provide
semi-solid material formation suitable for casting directly into a
component.
[0011] Still another object of the present invention is to provide
a semi-solid material formation with improved agitation.
[0012] Yet another object of the present invention is to provide a
semi-solid material formation apparatus integrated with a casting
device for casting semi-solid material directly into a
component.
SUMMARY OF THE INVENTION
[0013] The present invention provides a method and apparatus for
producing a component directly from a semi-solid material
comprising a source of molten material, a container for receiving
the molten material, thermal control means mounted to the container
for controlling the temperature of container, an agitation means
for agitating the material, and a casting device directly connected
to the container. The agitation means and the thermal controlling
means act in conjunction to produce a substantially isotropic
semi-solid material in the container. A thermally insulated means
for removing the semi-solid material from the container directly
provides semi-solid material to the casting device which casts the
semi-solid material into a component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic, front sectional view of a semi-solid
production apparatus according to the present invention.
[0015] FIG. 2 is a schematic, side sectional view of the apparatus
of FIG. 1.
[0016] FIG. 3 is a side sectional view of a removal means according
to the present invention.
[0017] FIG. 4 is a schematic, sectional view of the apparatus of
FIG. 1 integrated with a semi-solid casting apparatus according to
the present invention.
[0018] FIG. 5 is a schematic, side sectional view of the apparatus
of FIG. 1 showing an alternate embodiment of the present
invention.
[0019] FIG. 6 is a schematic, side sectional view of the apparatus
of FIG. 1 showing an alternate embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] In FIG. 1, a semi-solid production apparatus is shown
generally as reference numeral 10. Separated from the apparatus 10
is a source of molten material 11. Generally any material which may
be processed into a semi-solid material 50 is suitable for use with
this apparatus 10. The molten material 11 may be a pure metal such
as aluminum or magnesium, a metal alloy such as steel or aluminum
alloy A356, or a metal-ceramic particle mixture such as aluminum
and silicon carbide.
[0021] The apparatus 10 includes a cylindrical chamber 12, a
primary rotor 14, a secondary rotor 16, and a chamber cover 18. The
chamber 12 has a inner bottom wall 20 and a cylindrical inner side
wall 22 which are both preferably made of a refractory material.
The chamber 12 has an outer support layer 24 preferably made of
steel. The top of the chamber 12 is covered by a chamber cover 18.
The chamber cover 18 similarly has an insulated refractory
layer.
[0022] Thermal control system 30 comprises heating segments 32 and
cooling segments 34. The heating and cooling segments 32, 34 are
mounted to, or embedded within, the outer layer 24 of the chamber
12. The heating and cooling segments 32, 34 may be oriented in many
different ways, but as shown, the heating and cooling segments 32,
34 are interspersed around the circumference of the chamber 12.
Heating and cooling segments 32, 34 are also mounted to the chamber
cover 18. Individual heating and cooling segments 32, 34 may
independently add and/or remove heat, thus enhancing the
controllability of the temperature of the contents of the chamber
12.
[0023] The primary rotor 14 has a rotor end 42 and a shaft 44 which
extends upwards from the rotor end 42. The primary rotor shaft 44
extends through the chamber lid 18. The rotor end 42 is immersed in
and entirely surrounded by the chamber 12. As shown in FIG. 1, the
rotor end 42 has L-shaped blades 43, preferably two such blades
spaced 180 degrees apart, extending from the bottom of the rotor
end 42. The L-shaped blades 43 have two portions, one of which is
parallel to the inner side wall 22 and the other being parallel to
the inner bottom wall 20. The L-shaped blades 43, when rotated,
shear dendrites which tend to form on the inner side wall 22 and
bottom wall 20 of the chamber 12. Additionally, the rotation of the
blades 43 promotes material mixing within horizontal planes. Other
blade 43 geometries (e.g. T-shaped) should be effective so long as
the gap between the chamber inner side wall 22 and the blades 43 is
small. It is desirable that this gap be less than two inches.
Furthermore, to promote additional shearing, the gap between the
chamber bottom 20 and the blades 43 also should be less than two
inches. A typical rotation speed of the shear rotor 14 is
approximately 30 rpm.
[0024] The secondary rotor 16 has a rotor end 48 and a shaft 46
extending from the rotor end 48. The shape of the rotor end 48
should be designed to encourage vertical mixing of the semi-solid
material 50 and enhance the shearing of the semisolid material 50.
The rotor end 48 is preferably auger-shaped or screw-shaped, but
many other shapes, such as blades tilted relative to horizontal
plane, will perform similarly. The shaft 46 extends upwardly from
the auger shaped rotor end 48. Depending on the rotational
direction of the secondary rotor 16, material in chamber 12 is
forced to move in either an upwards or downwards direction. A
typical rotation speed of the secondary rotor 16 is 300 rpm.
[0025] The primary rotor 14 and the secondary rotor 16 are oriented
relative to the chamber 12 and to each other so as to enhance both
the shearing and three dimensional agitation of a semi-solid
material 50. In FIG. 1 it is seen that the primary rotor 14
revolves around the secondary rotor 16. The secondary rotor 16
rotates within the predominantly horizontal mixing action of the
primary rotor 14. This configuration promotes thorough,
three-dimensional mixing of the semi-solid material 50.
[0026] Although FIG. 1 depicts a plurality of rotors, a single
rotor that provides the appropriate shearing and mixing properties
may be utilized. Such a single rotor must afford both shearing and
mixing, the mixing being three-dimensional so that the semi-solid
material 50 in the container 12 is maintainable at a substantially
uniform temperature.
[0027] The semi-solid material environment into which the rotors
14, 16 are immersed is quite harsh. The rotors 14, 16 are exposed
to very high temperature, often corrosive conditions, and
considerable physical force. To combat these conditions, the
preferred composition of the rotors 14, 16 is a heat and corrosion
resistant alloy like stainless steel with a high-temperature
MgZrO.sub.3 ceramic coating. Other high-temperature resistant
materials, such as a superalloy coated with Al.sub.2O.sub.3, are
also suitable.
[0028] A frame 56 is mounted to the chamber lid 18. The frame 56
supports a primary drive motor 58 and a secondary drive motor 60.
The respective motors 58, 60 are mechanically coupled to the shafts
44, 46 of the respective rotors 14, 16. As shown in FIG. 1, the
primary motor 58 is coupled to the primary rotor shaft 44 by a pair
of reduction gears 62 and 64. The primary rotor shaft 44 is
supported in the frame 56 by bearing sleeves 66. Similarly, the
secondary rotor shaft 46 is supported in frame 56 by bearing sleeve
68. Both motors 58, 60 may be connected to the rotors through
reduction or step-up gearing to improve power and/or torque
transmission.
[0029] An alternative to the mechanical stirring described above is
electromagnetic stirring. An example of electromagnetic stirring is
found in Winter et al., U.S. Pat. No. 4,229,210. Electromagnetic
agitation can effectuate the desired isotropic, three-dimensional
shearing and mixing properties desired in the present
invention.
[0030] Molten material 11 may be delivered to the chamber 12 in a
number of different fashions. In one embodiment, the molten
material 11 is delivered through an orifice 70 in the chamber cover
18. Alternatively, the molten metal 11 may be delivered through an
orifice in the side wall 22 (not shown) and/or through an orifice
in the bottom wall 20.
[0031] Semi-solid material 50 is formed from the molten material 11
upon agitation by the primary rotor 14 and the secondary rotor 16,
and appropriate cooling from the thermal control system 30. After
an initial start-up cycle, the process is semi-continuous whereby
as semi-solid material 50 is removed from the chamber 12, molten
material 11 is added. However, the rotors 14, 16 and the thermal
control system 30 maintain the semi-solid 50 in a substantially
isothermal state.
[0032] In addition to controlling the temperature of the chamber 12
thereby maintaining the semi-solid material 50 in a substantially
isotropic state, the thermal control system 30 is also instrumental
in starting up and shutting down the apparatus 10. During start-up,
the thermal control system should bring the chamber 12 and its
contents up to the appropriate temperature to receive molten
material 11. The chamber 12 may have a large amount of solidified
semi-solid material or solidified (previously molten) material
remaining in it from a previous operation. The thermal control
system 30 should be capable of delivering enough power to re-melt
the solidified material. Similarly, when shutting down the
apparatus 10, it may be desirable for the thermal control system 30
to heat up the semi-solid material 50 in order to fully drain the
chamber 12. Another shut-down procedure may entail carefully
cooling the semi-solid 50 into the solid state.
[0033] As shown in FIG. 2, removal of semi-solid material 50 formed
in the chamber 12 is preferably via a removal tube 72. A detailed
view of the removal tube 72 is shown in FIG. 3. The removal tube 72
has a cylindrical inner wall 74 which is in contact with the
removed semi-solid material 50. The inner wall 74 is preferably a
refractory material. A support wall 76 is sandwiched between the
inner wall 74 and an outer layer 78. The support wall 76 is made of
a material, such as cast iron, capable of supporting the inner wall
74 and semi-solid material 50 contained therein. The outer layer 78
provides insulation of the removal tube 72 and the semi-solid
material 50. The removal tube 72 also protects the semi-solid
material 50 from being contaminated by the ambient atmosphere.
Without such protection, an oxide would form on the outside of the
semi-solid material and intersperse in any components made
therefrom. Provided around the removal tube is a heater 80 to
maintain the semi-solid material 50 at the desired temperature.
[0034] In FIG. 2, the removal port 72 extends from the apparatus 10
through the chamber cover 18. In an alternative preferred
embodiment, the removal port 72 extends from the chamber side wall
22 which has an outlet orifice 112 as shown in FIG. 5.
Alternatively, FIG. 5 also shows a removal port 73 extending from
the bottom wall 20 which has an outlet orifice 113. In either case,
as described above, the removal port includes a heater 80 to
maintain the isotropic state of the semisolid material 50 being
removed.
[0035] Effectuating semi-solid 50 flow through the port 72 may be
achieved by any number of methods. A vacuum could be applied to the
removal port 72, thus sucking the semi-solid out of the chamber 12.
Gravity may be utilized as depicted in FIG. 5 at port 73. Other
transfer methods utilizing mechanical means, such as submerged
pistons, helical rotors, or other positive displacement actuators
which produce a controlled rate of semi-solid material 50 transfer
are also effective.
[0036] To further regulate the flow of semi-solid material 50 out
of the chamber 12 via any of the removal ports described above, a
valve 83 is provided in the port 72. The valve 83 can be a simple
gate valve or other liquid flow regulation device. It may be
desirable to heat the valve 83 so that the semi-solid 50 is
maintained at the desired temperature and clogging is
prevented.
[0037] Flow regulation may also be crudely effectuated by local
solidification. Instead of a valve 83, a heater/cooler (not shown)
can locally solidify the semi-solid 50 in port 72 thus stopping the
flow. Later, the heater/cooler can reheat the material to resume
the flow. This procedure would normally be part of a start-up and
shut-down cycle, and is not necessarily part of the isothermal
semi-solid material production process described above.
[0038] Another manner for transferring semi-solid material 50,
which provides inherent flow control, utilizes a ladle 114 as
depicted in FIG. 6. The ladle 114 removes semi-solid material 50
from the chamber 12 while a heater 82 which is mounted to the ladle
114 maintains the temperature of the semi-solid material 50 being
removed. A ladle cup 115 of the ladle 114 is attached to a ladle
actuator 116. The cup 115 is rotatable to pour out its contents,
and the actuator 116 moves the ladle in the horizontal and vertical
directions.
[0039] To aid in maintaining proper temperature conditions within
the chamber 12, semi-solid material 50 transfer may occur in
successive cycles. During each cycle the above-described flow
regulation allows a discrete amount of semi-solid material 50 to be
removed. The amount of semi-solid material removed during each
cycle should be small relative to the material remaining in the
chamber 12. In this manner, the change in thermal mass within the
chamber 12 during removal cycles is small. In a typical cycle, less
than ten percent of the semi-solid 50 within chamber 12 is
removed.
[0040] Turning now to FIG. 4, a die caster 84 is directly attached
to the removal tube 72 extending from the apparatus 10. The die
caster 84 includes a ram 86, a shot sleeve 88, and a die 90. The
removal tube 72 delivers semi-solid material 50 directly to the
shot sleeve 88 through an opening in the shot sleeve 92. The shot
sleeve 88 has two open ends 94, 96. The shot sleeve is positioned
between, and the open ends 94, 96 face, the die 90 and the ram 86.
The ram 86, is connected to a piston 98 which is pneumatically
actuated by a pneumatic drive 100. When actuated, ram 86 forces the
semi-solid material 50 into the die 90. The semi-solid material 50
enters a die chamber 102 through a die chamber inlet 104 within the
die 90. The die 90 includes two halves 106, 108 which separate to
expose a die cast component 110 which is removed upon cooling.
[0041] The casting device 84 can be any suitable device for forming
a component from the semi-solid material 50. Suitable casting
devices include a mold, a forging die assembly as described in the
specification of U.S. Pat. No. 5,287,719, or other commonly known
die casting mechanisms.
[0042] The die caster 84 is not limited to a vertical configuration
relative to the apparatus 10 as shown in FIG. 4. The die caster 84
can be positioned relative to the apparatus 10 in any number of
orientations. For example, the die caster 84 can be underneath the
apparatus 10 such that gravity aids the transfer of semi-solid
material 50 through the transfer tube 72 (not shown). Or instead of
a vertical orientation, the die caster 84 may lay horizontally
relative to the apparatus 10 (also not shown).
[0043] In FIGS. 2 and 4, the removal tube 72 extends from the
apparatus 10 through the chamber cover 18. In an alternative
preferred embodiment, the removal tube 72 extends from the chamber
side wall 22 which has an outlet port 112 as shown in FIG. 5.
Alternatively, FIG. 5 also shows a removal tube 73 extending from
the bottom layer 20 which has an outlet port 113. In either case,
as described above, the removal tube 72 connects directly to the
die casting device 84.
[0044] In another preferred embodiment, the chamber side wall 22 is
directly adjacent the die casting device 84 (not shown) eliminating
the need for the transfer tube 72. The outlet port 112 directly
feeds the shot sleeve 88 with semi-solid material 50. The component
110 is formed as described above.
[0045] Although not required, it may be desirable to maintain the
entire apparatus 10 in a controlled environment (not shown). Oxides
readily form on the outer layers of molten materials and semi-solid
materials. Contaminants other than oxides also enter the molten and
semi-solid material. In an inert environment, such as one of
nitrogen or argon, oxide formation would be reduced or eliminated.
The inert environment would also result in fewer contaminants in
the semi-solid material. It may be more economical, however, to
limit the controlled environment to discrete portions of the
apparatus 10 such as the delivery of molten material 11 to the
chamber 12. Another discrete and economical portion for
environmental control may be the removal port 72 (or the ladle
114). At the removal port 72, the semisolid material 50 no longer
undergoes agitation and the material is soon to be cast into a
component. Thus, any oxide skin that forms at this stage will not
be dispersed throughout the material by mixing in the container 12.
Instead, the oxides will be concentrated on the outer layers of the
semi-solid. Therefore, to reduce both oxide formation and to reduce
high-concentration oxide pockets, a controlled nitrogen environment
(or other suitable and economical environment) would be
advantageous at the removal port 72 stage.
[0046] The following is an example of the above described process
and apparatus after the start-up cycle is complete. Molten aluminum
at an approximate temperature of 677 degrees Celsius is poured into
the chamber 12 already containing a large quantity of semi-solid
material. The primary rotor 14 turns at approximately 30 rpm and
stirs and shears the aluminum in a clockwise direction. The
secondary rotor 16 rotates at about 300 rpm and forces the aluminum
upwards and/or downwards while also shearing the aluminum. The
combined effect of the two rotors 14, 16 thoroughly agitates and
shears the aluminum in three dimensions. The thermal control system
30 maintains the temperature of the aluminum at approximately 600
degrees Celsius such that dendritic structures are formed. The
rotors 14, 16 shear the dendritic structures as they are formed.
While the thermal control system maintains the temperature of the
semi-solid aluminum at approximately 600 degrees Celsius, the
rotors 14, 16 continuously mix the semi-solid aluminum keeping the
temperature within the material substantially uniform. The solid
particle size produced by this particular process is typically in
the range of 50 to 200 microns and the percentage by volume of
solids suspended in the semi-solid aluminum is approximately 20
percent.
[0047] The semi-solid aluminum is transferred from the chamber 12
to the shot sleeve 88 of the die caster 84 through the transfer
tube 72. The removal port heater 80 also maintains the semi-solid
aluminum at about 600 degrees Celsius. The ram 86 in the caster 84
is actuated by the pneumatic drive 100 and the semi-solid aluminum
is forced into the die 90 and component 110 is formed. When the
component 110 and die 90 cool to approximately 400 degrees Celsius,
the component is removed.
[0048] While there have been described herein what are considered
to be preferred embodiments of the present invention, other
modifications of the invention will be apparent to those skilled in
the art from the teaching herein. It is therefore desired to be
secured in the appended claims all such modifications as fall
within the true spirit and scope of the invention. Accordingly,
what is desired to be secured by Letters Patent of the United
States is the invention as defined and differentiated in the
following claims.
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