U.S. patent application number 10/295939 was filed with the patent office on 2003-04-10 for method and apparatus for manufacturing metallic parts by fine die casting.
This patent application is currently assigned to TAKATA CORPORATION. Invention is credited to Kono, Kaname.
Application Number | 20030066620 10/295939 |
Document ID | / |
Family ID | 26763036 |
Filed Date | 2003-04-10 |
United States Patent
Application |
20030066620 |
Kind Code |
A1 |
Kono, Kaname |
April 10, 2003 |
Method and apparatus for manufacturing metallic parts by fine die
casting
Abstract
An injection molding system includes a feeder in which a metal
is melted and a first chamber into which a desired amount of melted
metal is introduced. A piston in a second chamber first retracts to
create suction, assisting in drawing in the melted metal into the
second chamber from the first chamber and evacuating gas. A ram
then pushes some melted metal remaining in the first chamber into
the second chamber, forcing out gas present in the second chamber.
The piston then injects the melted metal out of the second chamber
into a mold. The melted metal is preferably maintained in a liquid
state throughout the system.
Inventors: |
Kono, Kaname; (Tokyo,
JP) |
Correspondence
Address: |
FOLEY AND LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
TAKATA CORPORATION
|
Family ID: |
26763036 |
Appl. No.: |
10/295939 |
Filed: |
November 18, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10295939 |
Nov 18, 2002 |
|
|
|
09842092 |
Apr 26, 2001 |
|
|
|
09842092 |
Apr 26, 2001 |
|
|
|
09330147 |
Jun 11, 1999 |
|
|
|
6283197 |
|
|
|
|
09330147 |
Jun 11, 1999 |
|
|
|
09160792 |
Sep 25, 1998 |
|
|
|
5983976 |
|
|
|
|
60080078 |
Mar 31, 1998 |
|
|
|
Current U.S.
Class: |
164/113 ;
164/71.1; 164/900 |
Current CPC
Class: |
B22D 17/007 20130101;
Y10S 164/90 20130101; B29C 45/53 20130101; B22D 17/30 20130101 |
Class at
Publication: |
164/113 ;
164/71.1; 164/900 |
International
Class: |
B22D 023/00; B22D
025/00; B22D 027/08 |
Claims
What is claimed is:
1. A method of injecting melted material into a mold, comprising:
introducing the melted material into a first chamber; allowing at
least a portion of the melted material to pass through said first
chamber into a second chamber; pushing at least a portion of the
melted material remaining in the first chamber into said second
chamber; and injecting the melted material from the second chamber
into the mold.
2. The method as claimed in claim 1, comprising creating a suction
in the second chamber to draw the melted material from the first
chamber into the second chamber.
3. The method as claimed in claim 2, wherein the suction in the
second chamber is created before the pushing of the melted material
portion from the first chamber into the second chamber.
4. The method as claimed in claim 2, wherein a piston in the second
chamber retracts to create suction that draws the melted material
into the second chamber.
5. The method as claimed in claim 1, wherein a ram in the first
chamber advances to push the melted material portion from the first
chamber into the second chamber while covering an outlet port of
the first chamber during injection to prevent the melted material
from flowing between the first and the second chambers
6. The method of claim 5, wherein the first chamber includes a
valve that permits melted material to pass only in a direction
toward the second chamber.
7. The method of claim 6, wherein the ram is advanced so that an
end of the ram seals off an outlet port of the first chamber during
injection to prevent melted material from passing between the first
and the second chambers.
8. The method as claimed in claim 5, comprising rotating the ram to
enhance the uniform temperature distribution of the melted material
in the first chamber, and wherein the ram contains supporting
fins.
9. The method as claimed in claim 1, wherein the melted material is
a metal in a liquid state.
10. The method as claimed in claim 9, wherein the melted material
is a melted magnesium alloy.
11. The method as claimed in claim 9, wherein the injected metal
solidifies into a metal part in the mold.
12. The method as claimed in claim 1, wherein the first chamber is
located above the second chamber to allow gravity to assist passage
of the melted material from the first chamber into the second
chamber.
13. The method as claimed in claim 12, wherein the melted material
passing into the second chamber forces out at least a portion of at
least one gas present in the second chamber out of the second
chamber.
14. The method as claimed in claim 1, wherein at least a portion of
at least one gas present in the second chamber escapes the second
chamber through a second material which resists passage the melted
material.
15. The method as claimed in claim 1, comprising introducing solid
material into a feeder; melting the material in the feeder; and
introducing the material into the first chamber from the
feeder.
16. The method as claimed in claim 15, wherein the solid material
is at least one metal ingot.
17. The method as claimed in claim 16, comprising introducing the
at least one metal ingot into a third chamber; and transferring the
at least one metal ingot from the third chamber into the
feeder.
18. The method as claimed in claim 17, wherein at least one of the
third chamber and the feeder contain an inert gas ambient.
19. The method as claimed in claim 18, wherein the inert gas
comprises a at least one of argon, nitrogen, SF.sub.6 and
CO.sub.2.
20. The method as claimed in claim 18, comprising maintaining the
inert gas ambient by at least one of a) at least one door; b) a
vacuum pump; c) at least one inert gas screen.
21. The method as claimed in claim 17, comprising opening a first
door to the third chamber; advancing at least one metal ingot into
the third chamber; closing the first door; opening a second door;
and advancing the at least one metal ingot from the third chamber
into the feeder.
22. The method as claimed in claim 17, comprising introducing the
metal ingots into the third chamber; and passing the metal ingots
down a sloping surface into the feeder.
23. The method as claimed in claim 17, comprising controlling
access to the feeder from the third chamber by movable cover
plate.
24. The method as claimed in claim 23, wherein the movable cover
plate contains an access aperture.
25. The method as claimed in claim 15, comprising controlling
access to the feeder by movable transfer chamber.
26. The method as claimed in claim 25, wherein the movable transfer
chamber comprises a cylinder containing an access aperture.
27. The method as claimed in claim 1, comprising uncovering an
injection nozzle in the second chamber; injecting the melted
material into the mold through the injection nozzle by advancing a
piston; and covering the injection nozzle.
28. The method as claimed in claim 27, wherein the injection nozzle
is covered by a nozzle shut-off plate.
29. The method as claimed in claim 27, comprising partially
advancing the piston, which is surrounded by a seal, to squeeze at
least a portion of at least one gas present in the second chamber
out of the second chamber through at least one of a material which
resists passage of melted material, prior to injecting the melted
material into the mold.
30. The method as claimed in claim 5, comprising advancing a ram in
the first chamber so that the ram seals off an outlet port of the
first chamber during injection to prevent the melted material from
passing between the first and the second chambers; uncovering an
injection nozzle in the second chamber; injecting the melted
material into the mold through the injection nozzle by advancing a
piston; retracting the ram; and retracting an outer portion of the
piston to create a suction in the second chamber to draw the melted
material from the first chamber into the second chamber, while
leaving an inner portion of the piston fully advanced to cover the
injection nozzle.
31. A molded metal part produced by the method of claim 1, having
at least one structure with a thickness less than or equal to 1 mm
that measures approximately 21.0 cm by 29.7 cm.
32. An apparatus for injecting melted material into a mold,
comprising a first chamber which holds melted material, a ram that
moves through said first chamber to force at least a portion of the
melted material from the first chamber through an outlet port
leading into a second chamber, and a piston in the second chamber
that (a) retracts to create suction that assists in drawing into
the second chamber at least a portion of the melted material
through the outlet port from the first chamber; and that (b)
advances to inject the melted material into a mold.
33. The apparatus as claimed in claim 32, wherein the first chamber
includes a valve at one end that permits melted material to pass
only in a direction toward the outlet port.
34. The apparatus as claimed in claim 32, wherein the ram contains
supporting fins.
35. The apparatus as claimed in claim 32, further comprising
heating elements for the first and second chambers to regulate
temperatures therein.
36. The apparatus as claimed in claim 32, further comprising an
open nozzle at one end of the second chamber through which the
melted metal is injected into a mold.
37. The apparatus as claimed in claim 36, further comprising a
nozzle shut-off plate which covers the nozzle and moves
longitudinally to permit the nozzle to engage a mold during
injection.
38. The apparatus as claimed in claim 37, further comprising a
heating element in contact with the nozzle shut-off plate.
39. The apparatus as claimed in claim 32, wherein the first chamber
is positioned above the second chamber.
40. The apparatus as claimed in claim 32, wherein the first chamber
is inclined at an angle between 30 and 60 degrees with respect to
the second chamber.
41. The apparatus as claimed in claim 32, wherein the second
chamber comprises at least one gas outlet port.
42. The apparatus as claimed in claim 41, wherein the gas outlet
port comprises at least one of a) a void between the piston and the
walls of the second chamber; b) a seal surrounding the piston; and
c) an opening in the wall of the second chamber connected to a gas
permeable but liquid resistant material.
43. The apparatus as claimed in claim 32, comprising a feeder
connected to the first chamber by a feeder port; and at least one
heating element for the feeder.
44. The apparatus as claimed in claim 43, comprising a third
chamber in communication with the feeder.
45. The apparatus as claimed in claim 44, wherein the third chamber
comprises a push arm to push metal ingots into the third chamber;
and a sloping surface to assist passage of the metal ingots into
the feeder.
46. The apparatus as claimed in claim 44, comprising an inert gas
introduction nozzle in at least one of the feeder and the third
chamber.
47. The apparatus as claimed in claim 44, wherein the third chamber
comprises at least one of a) at least one door; b) a vacuum pump
connected to the third chamber; c) a conveyor belt; d) at least one
heating element; and e) at least one inert gas screen.
48. The apparatus as claimed in claim 44, wherein the third chamber
comprises a movable cover plate.
49. The apparatus as claimed in claim 48, wherein the movable cover
plate comprises an access aperture.
50. The apparatus as claimed in claim 43, comprising a movable
transfer chamber containing an access aperture.
51. The apparatus as claimed in claim 44, comprising an elevator
for delivering metal ingots; and a conveyor for transferring the
metal ingots from the elevator to the third chamber.
52. The apparatus as claimed in claim 51, wherein the elevator
comprises at least one rotatable platform; at least one connector
about which the platform rotates; and a lifting member which lifts
up the platform causing it to rotate about the connector.
53. The apparatus as claimed in claim 43, wherein the, feeder
contains a filter to prevent solid material from entering the first
chamber.
54. The apparatus as claimed in claim 53, wherein the filter
comprises a grate or at least one vertical rod.
55. The apparatus as claimed in claim 32, wherein the piston
comprises an outer portion and an inner portion and wherein the
inner portion is moved independently of the outer portion to
prevent material flow through an injection nozzle into the
mold.
56. The apparatus as claimed in claim 32, wherein the ram comprises
an outer portion and an inner portion and wherein the inner portion
is moved independently of the outer portion.
57. An apparatus for injecting melted material into a mold,
comprising a passing means for passing the melted material; forcing
means for forcing at least a portion of the melted material from
the passing means into an accumulation means for accumulating
melted material; suction means for creating a suction in the
accumulation means to draw at least a portion of the melted
material into the accumulation means; injection means for injecting
the melted material from the accumulation means into the mold.
58. The apparatus as claimed in claim 57, comprising means which
permit passage of the melted material only in a direction toward
the accumulation means.
59. The apparatus as claimed in claim 57, comprising heating means
for heating said passing means and said accumulation means.
60. The apparatus as claimed in claim 57 comprising means to cover
an injection nozzle in the accumulation means.
61. The apparatus as claimed in claim 57 comprising egress means
for removing at least one gas from the accumulation means.
62. The apparatus as claimed in claim 57, comprising melting means
for melting a solid material to form the melted material.
63. The apparatus as claimed in claim 62, comprising filtering
means for preventing entry of the solid material into the passing
means.
64. The apparatus as claimed in claim 62, comprising holding means
for holding the solid material prior to its introduction into the
melting means so as to maintain an inert gas ambient in the melting
means.
65. The apparatus as claimed in claim 64, comprising transfer means
for transferring solid material into the holding means.
66. The apparatus as claimed in claim 65, wherein said transfer
means is synchronized with a door to the holding means to transfer
the solid material into the holding means when the door is
opened.
67. The apparatus as claimed in claim 57, wherein said melted
material is a metal in a liquid state.
Description
RELATED APPLICATION
[0001] This application is related to application Ser. No.
09/______ , filed on the same day as the current application,
titled "Method And Apparatus For Manufacturing Metallic Parts by
Injection Molding From the Semi-Solid State."
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a method and apparatus for
manufacturing metallic parts, more particularly to a method and
apparatus for manufacturing metallic parts by a process involving
injection of a melted metal into a mold, including die casting
methods.
[0004] 2. Description of the Related Art
[0005] One conventional method used to produce molded metallic
parts from melted metal is by die casting. Die casting methods use
liquid metal during casting and, as a consequence, molded metallic
parts produced from this method can have low densities. Molded
metallic parts having low densities are not generally desirable
because of their reduced mechanical strength, higher porosity, and
larger micro shrinkage. It is thus difficult to accurately
dimension conventional molded metallic parts and, once dimensioned,
to maintain their shapes. Moreover, molded metallic parts produced
from conventional die casting have difficulty in reducing the
resilient stresses developed therein.
[0006] Thixotropic methods for producing molded metallic parts
generally improve upon the die casting method by injection molding
a metal from its thixotropic (semi-solid) state rather than from
its liquid state. The result is a molded metallic part which has a
higher density than one produced from the die casting method.
Thixotropic methods are disclosed in U.S. Pat. Nos. 3,902,544 and
3,936,298, both of which are incorporated by reference herein.
[0007] Methods and apparatuses for manufacturing molded metallic
parts from melted metal in its thixotropic state are also disclosed
in U.S. Pat. No. 5,501,226 and Japanese patent publications
5-285626 and 5-285627, which are incorporated by reference herein.
Methods of converting a metal into a thixotropic state by
controlled heating and shearing in an extruder are disclosed in
U.S. Pat. Nos. 5,501,226, 4,694,881 and 4,694,882. The systems
disclosed in these patent documents are essentially in-line
systems, in which the conversion of the metal alloy into a
thixotropic state is assisted by an extruder and the pressurizing
of the same for the purposes of injection molding; all these steps
are carried out within a single cylindrical housing. It is
difficult to accurately control all of the process parameters
within a single cylindrical housing, especially temperature, shot
volume, pressure, time, etc., and as a result, molded metallic
parts of inconsistent characteristics are produced.
[0008] Moreover, some of these systems require that the metal
supplied to the feeder be in pellet form. As a consequence, if a
molded metallic part of undesired characteristics is produced by
its system, recycling of the defective part is not possible unless
the defective part is first recast in pellet form. Furthermore,
metal parts made from metal in the thixotropic state which is
injected into a mold may have an uneven surface. Such metal parts
require further processing before they can be painted.
[0009] The present inventor's co-pending application, Ser. No.
08/873,922, filed on Jun. 12, 1997, which is incorporated by
reference herein, describes a different and improved method for
producing molded metallic parts from melted metal in a thixotropic
state wherein the conversion of melted metal into the thixotropic
state takes place in a physically separate location from the
location where the metal is injected into the mold and under
different conditions.
[0010] An improved system for manufacturing molded metallic parts,
which is capable of accurately producing molded metallic parts of
specified dimensions within a narrow density tolerance that
operates with melted metal in a liquid state, is desired. Further,
a production process for molded metallic parts that can
consistently produce molded metallic parts of desired
characteristics and that can easily accommodate recycling of
defective parts is desired. Further, an improved production process
for molded metallic parts made of lighter metals, like magnesium,
is desired.
SUMMARY OF THE INVENTION
[0011] An object of the invention is to provide a method and
apparatus for producing molded metallic parts through injection of
melted metal into a mold.
[0012] Another object of the invention is to provide an improved
injection molding system for producing molded metallic parts that
is capable of producing molded metallic parts of accurate
dimensions within a narrow density tolerance and operates using
melted metal in a liquid state.
[0013] Still another object of the invention is to provide an
injection molding system for molded metallic parts that is capable
of producing metallic parts of desired characteristics in a
consistent manner.
[0014] Still another object of the invention is to provide an
injection molding system that minimizes the amount of gas trapped
in liquid metal prior to its injection into the mold.
[0015] Still another object of the invention is to provide molded
metallic parts having exceptionally smooth surfaces.
[0016] Still another object of the invention is to provide molded
metallic parts having reduced porosity compared to parts produced
by known die casting and thixotropic methods.
[0017] Still another object of the invention is to provide molded
metallic parts that do not need to be further processed before they
are painted.
[0018] Still another object of the invention is to provide an
injection molding system for producing molded metallic parts that
accommodates recycling of defective molded metallic parts
easily.
[0019] These and other objects are accomplished by an improved
injection molding method for producing molded metallic parts
comprising the steps of introducing melted metal into a first
chamber through a feeder port, allowing at least a portion of the
melted metal to flow through said first chamber toward an outlet
port, drawing into a second chamber at least a portion of the
melted metal through the outlet port under a suction created in
said second chamber, pushing at least a portion of the melted metal
remaining in the first chamber into said second chamber, and
injecting the melted metal from the second chamber into a mold.
[0020] The improved system comprises a feeder in which the metal is
melted. Melted metal is allowed to flow from the feeder through a
feeder port into a first chamber. At least a portion of the melted
metal is drawn into a second chamber, assisted by suction through
an outlet port leading from the first chamber into the second
chamber. A ram in the first chamber pushes some of the remaining
melted metal from the first chamber through the outlet port leading
into the second chamber, thereby forcing out gas that has
accumulated in the second chamber between the melted metal and a
piston (commonly referred to as the "plunger") that is positioned
inside the second chamber. The pressure from the melted metal being
driven into the second chamber by the ram forces the gas between
the melted metal and the piston to flow past the piston through the
small space between the piston and the wall of the second chamber.
The piston in the second chamber then injects the melted metal,
which is substantially gas-free, into a mold. Before the injection,
the piston in the second chamber is retracted to draw in the melted
metal from the first chamber by creating suction and also to
regulate the volume of melted metal that is held in the second
chamber prior to injection so that it precisely corresponds to the
size of the molded part.
[0021] The above-described process and system provide a very
precise control of the injection volume, to within .+-.0.5% by
weight or less, because the injection volume is determined in
accordance with the position of the piston and any gas that is
present in the melted metal, which can be about 20% by volume, is
forced out by operation the ram advancing, before the melted metal
is injected.
[0022] Further, a fine die-cast method according to the invention
is more advantageous than current thixotropic processes because
conversion of metal into the thixotropic state takes more time.
With the fine die-cast method according to the invention, the
injection cycle time is reduced to about 30 seconds, a 50%
reduction when compared to current thixotropic processes.
[0023] Also, the method of the present invention can be used to
mold parts of a liquid material that are more preferred than parts
molded from current thixotropic processes. They generally require
less post-molding processing, given their more accurate molding
volume and smooth surfaces. This permits a production process that
is stable over many runs.
[0024] In addition, the method of the present invention can provide
molded parts of extremely fine dimensions, having thicknesses less
than 1 mm for a rectangular-shaped part measuring about 21.0 cm by
29.7 cm (which is roughly the size of a DIN size A4 sheet of paper)
and also having more complex structures.
[0025] Additional objects and advantages of the invention will be
set forth in the description which follows. The objects and
advantages of the invention may be realized and obtained by means
of instrumentalities and combinations particularly pointed out in
the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The invention is described in detail herein with reference
to the drawings in which:
[0027] FIG. 1 is a schematic illustration of a side view of the
injection molding system according to one embodiment of the
invention;
[0028] FIG. 2A is a side view showing one embodiment of a valve on
the ram when it is in the position that prevents melted metal from
flowing to positions to the right,of the valve;
[0029] FIG. 2B is a side view showing one embodiment of a valve on
the ram when it is in the position that permits melted metal to
flow from the right of the valve to positions to the left of the
valve;
[0030] FIG. 2C is a front view showing one embodiment of a valve
when it is not fitted onto the ram;
[0031] FIG. 2D is a side view showing one embodiment of a valve
when it is not fitted onto the ram;
[0032] FIG. 3 is a side view of an alternative embodiment of the
feeder tank;
[0033] FIG. 4A is a side view of an embodiment of the nozzle
shut-off plate which includes a die plate that rests flush against
the nozzle;
[0034] FIG. 4B is a side view of an alternative embodiment of the
nozzle shut-off plate which includes a recess in the die assembly
to receive the nozzle; and
[0035] FIG. 4C is a front view of an alternative embodiment of a
die assembly which has a receiving slot to guide the nozzle
shut-off plate;
[0036] FIG. 4D is a side view of the shut-off plate guide and the
drive assembly for the nozzle shut-off plate.
[0037] FIG. 5A is a top view of an embodiment of a loading system
used to load metal ingots into the apparatus of the present
invention;
[0038] FIG. 5B is a side view of another embodiment of a loading
system which includes sealing doors;
[0039] FIG. 5C is a side view of an embodiment of a loading system
which includes a vacuum pump;
[0040] FIG. 5D is a side view of an embodiment of a loading system
which includes inert gas screens;
[0041] FIGS. 5E-H are top views of an alternative embodiment of a
loading system used to load metal ingots into-the apparatus of the
present invention;
[0042] FIG. 5I is a three dimensional view of an alternative
embodiment of a loading system used to load metal ingots into the
apparatus of the present invention;
[0043] FIG. 5J is a side view of an elevator used to deliver the
metal ingots to the conveyor of the loading system;
[0044] FIG. 5K is a side view of an embodiment of a feeder which
utilizes substantially vertical outlet containment rods;
[0045] FIG. 6A is a photomicrograph of a metal sample made by a
prior art method;
[0046] FIG. 6B is a photomicrograph of a metal sample made by a
method of the present invention;
[0047] FIG. 7A is a schematic illustration of a side view of the
injection molding system according to an embodiment of the
invention which contains supporting fins around the ram;
[0048] FIGS. 7B-G are cross sectional and three dimensional views
of specific arrangements of the support fins.
[0049] FIGS. 8A-D are side views of an embodiment of an injection
chamber which includes a two part piston.
[0050] FIG. 9 shows the side view of plug formation in prior art
injection nozzles.
[0051] FIG. 10 is a side view of an embodiment of an injection
chamber with includes an outlet port.
[0052] FIGS. 11A-B are side views of an alternative method of
operating the piston.
[0053] FIGS. 12A-B are side views of an embodiment of a barrel
which includes a two part ram.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0054] In the discussion of the preferred embodiment which follows,
a metal alloy is produced by injection molding from a magnesium
(Mg) alloy ingot or pellets which are melted and processed in a
liquid state. The invention is not limited to processing of Mg and
is equally applicable to other types of materials, metals and metal
alloys.
[0055] The terms "melted metal" and "melted material" as used
herein encompasses metals, metal alloys and other materials which
can be converted to a liquid state and processed in an injection
molding system. A wide range of such metals is potentially useful
in this invention; including aluminum (Al), Al alloys, zinc (Zn),
Zn alloys, and the like.
[0056] Unless otherwise indicated, the terms "a" or "an " refer to
one or more. Unless otherwise indicated, the term "gas" refers to
any gas (including air) that can be present in the injection
chamber at start-up or that is trapped in the injection chamber and
forced out during operation of the invention's system.
[0057] Specific temperature and temperature ranges cited in the
following description of the preferred embodiment are applicable to
the preferred embodiment for processing Mg alloy in a liquid state,
but could readily be modified in accordance with the principles of
the invention by those skilled in the art in order to accommodate
other metals and metal alloys. For example, some Zn alloys become
liquid at temperatures above 450.degree. C., and the temperatures
in the injection molding system of the present invention can be
adjusted for processing of Zn alloys.
[0058] FIG. 1 illustrates an injection molding system 10 according
to a first embodiment of the invention. The system 10 includes
pre-heat tank 19 where Mg alloy pieces or ingots 18 are pre-heated
to approximately 250.degree. C. A conveyor belt 20 transfers the
pre-heated Mg alloy pieces or ingots 18 into a holding tank 12.
Other transporting means can be used. A metering device shown as a
threaded screw 21 feeds the Mg alloy pieces or ingots 18 into a
feeder 23. The feeder 23 is provided with at least one heating
element 25 disposed around its outer periphery. The heating element
25 may be of any conventional type and operates to maintain the
feeder 23 at a temperature high enough to keep the metal alloy
supplied through the feeder 23 in a liquid state. For a Mg alloy
ingot, this temperature would be about 600.degree. C. or greater.
Two level detectors 22 detect minimum and maximum levels of melted
metal in the feeder 23. When the upper level detector 22 detects
that the level of melted metal has risen to a maximum point, it
relays a signal to a microprocessor control unit (not shown) which
instructs the screw 21 to stop dispensing. When the lower level
detector 22 detects that the level of melted metal has been
depleted to a minimum point, it relays a signal to the control unit
which activates the screw 21 so that more Mg alloy is dispensed
into the feeder 23.
[0059] Preferably, sufficient metal should be kept in the feeder 23
to supply about 20 times the volume needed for one injection cycle
(or shot) . This is because the amount of time required to melt the
metal necessary for one injection cycle is longer than the
injection cycle time, which in the preferred embodiment is about 30
seconds.
[0060] The feeder 23 further includes a filter 24, which may be in
the form of a grate whose openings are small enough to prevent Mg
alloy pieces 18 from falling through while they are being melted.
This is primarily a concern when the feeder 23 is initially
started. After that, alloy pieces will fall into the molten bath
and be melted, although larger pieces could also be introduced
later on without concern. A mixer (not shown) in feeder 23 may be
included for the purposes of evenly distributing the heat from the
heating element 25 to the metal supplied to the feeder 23.
[0061] The feeder 23, pre-heat tank 19, and all elements
therebetween contain an atmosphere of an inert gas to minimize
oxidizing of the pre-heated and melted metal. A mixture of carbon
dioxide (CO.sub.2) and sulfur fluoride (SF.sub.6) gas is preferred.
However, other gasses, such as CO.sub.2, SF.sub.6, nitrogen or
argon may be used alone or in any combination with each other. The
inert gas may be introduced (e.g. from a pressurized tank) into the
feeder 23 through port 11 to create an inert gas atmosphere above
the bath. The inert gas also travels around the screw and into the
pre-heat tank 19 to also minimize oxidizing there, as well. It is
therefore preferred for the entire feeding system as described to
be maintained under an inert gas environment.
[0062] The melted metal is subsequently supplied into a
temperature-controlled barrel 30 by way of gravity through a feeder
port 27 which may optionally be supplied with a valve serving as a
stopper (not shown) Preferably, no valve is present. A ram 32 is
arranged coaxially with the barrel 30 and extends along the center
axis of the barrel 30. The outer diameter of the ram 32 is smaller
than the inner diameter of the barrel 30 such that melted metal
flows in the space between the ram 32 and the barrel 30. The ram 32
is also controlled by motor 33 for axial movement in both
retracting and advancing directions along the barrel 30 and for
rotation around its own axis if stirring of the melted metal is
desired inside barrel 30.
[0063] A valve 17 is mounted around the outer circumference of the
ram 32 to separate the barrel 30 into upper and lower chambers. The
valve 17 opens and closes to selectively permit and block the flow
of metal between the upper and lower chambers of the barrel 30.
Suitable valves having such a function are known per se to those
skilled in the art, and any of them may be used for purposes of the
present invention. Preferably, the valve 17 is frictionally mounted
on an inner circumference of the barrel 30 and slidably mounted on
the outer circumference of the ram 32 such that, when, for example,
the ram 32 retracts upwardly in the barrel 30, the valve 17 moves
relative to the ram 32 to permit flow of melted metal therethrough,
and when, for example, the ram 32 advances downwardly in the barrel
30, the valve 17 moves relative to the ram 32 to block flow
therethrough.
[0064] FIG. 2A is a side view showing one embodiment of a valve on
the ram when it is in the position that prevents melted metal from
flowing to positions upstream of (to the right of) the valve. FIG.
2B is a side view showing one embodiment of a valve on the ram when
it is in the position that permits melted metal to flow downstream
of the valve (to the left of the valve). FIG. 2C is a front view
showing one embodiment of a valve when it is not fitted onto the
ram. FIG. 2D is a side view showing one embodiment of a valve when
it is not fitted onto the ram.
[0065] In the closed position of FIG. 2A, the rear section 17b of
the valve 17 abuts the body 32b of the ram 32. The blockage of the
flow in this position permits the ram 32 to push the metal in the
lower chamber into an injection chamber 50 through an outlet port
37 (see FIG. 1) without the metal flowing back (as shown in FIG.
2A) into the upper chamber. In the open position of FIG. 2B, the
front section 17a of the valve 17 abuts the head 32a of the ram 32.
The metal is permitted to flow through the valve in this position
because the front section 17a of the valve 17 has gaps formed
between toothed portions and the flow through the valve 17 takes
place through these gaps. As a result, when the valve 17 is in the
open position, the metal in the upper chamber flows into and
collects in the lower chamber.
[0066] The ram 32 as shown in the Figures has a pointed tip, but
any shape may be used, including a blunt end or a rounded end.
Preferably, the end of ram 32 has a shape capable of blocking
outlet port 37 to prevent the flow of melted metal between barrel
30 and injection chamber 50 if ram 32 is fully advanced inside
barrel 30. While injection takes place, ram 32 is preferably fully
advanced inside barrel 30 so that outlet port 37 is closed.
However, the ram 32 need not be fully advanced since valve 17 and
the melted metal that occupies the lower chamber of barrel 30 would
also prevent melted metal from leaving the second chamber during
injection. After injection, the ram 32 is retracted (but may
continue rotating if rotation is being used to stir the melted
metal inside barrel 30), and a piston 45 which is housed in the
injection chamber 50 begins retracting (moved to the right as shown
in FIG. 1) to expand the volume of the injection chamber 50 to a
desired volume according to the dimensions of the molded part being
produced. The piston 45 is stopped when the volume of the injection
chamber 50 becomes equal to the desired injection volume. The
piston 45 may be retracted at the same time that ram 32 is being
retracted or after ram 32 has been retracted to a desired
position.
[0067] After piston 45 is stopped, the ram 32 is advanced downward,
and, as a result, a portion of the metal collected in the lower
chamber of barrel 30 is pushed into the injection chamber 50
through the outlet port 37. The pressure of the metal entering into
injection chamber 50 assists in driving out gas present in the
injection chamber 50 that accumulates between the melted metal and
piston 45. The ram 32 preferably advances through barrel 30 until
its end closes off outlet port 37, and the ram 32 preferably
remains in this position to keep outlet port 37 sealed off until
injection is complete and the next shot is started.
[0068] During each shot, a certain amount of gas accumulates
between the melted metal and the piston 45 as the melted metal
enters injection chamber 50. The volume of this gas can make up as
much as 20% of the volume of the injection chamber 50. Injecting
such a melted metal/gas mix into a mold can result in molded parts
that have uneven surfaces, porosity (caused by gas bubbles trapped
in the metal's surface), or other imperfections including those
that result from an inconsistent volume of melted metal being
injected. Removing as much gas as possible before injection is
desired. In the method of the present invention, that gas
evacuation is primarily accomplished in two ways. First, the piston
45 and injection chamber 50 can evacuate gas like a pharmaceutical
syringe that draws in liquid from a container of liquid.
Specifically, as piston 45 retracts, it creates a suction to draw
in melted metal from the barrel 30 into the injection chamber 50
and it pushes gas out behind it. Secondly, the additional portion
of melted metal driven into the second chamber by ram 32 forces the
gas that accumulates between the melted metal and the piston 45 to
escape around the small space between the piston 45 and the wall of
the second chamber (i.e., the gas is forced out to the right of
piston 45 due to the pressure of the melted metal). Optionally, an
O-ring seal or other implement may be fitted around at least a
portion of piston 45 that allows the gas to pass behind piston 45
and out of the system but not back in. An injection nozzle 57 is
provided with a nozzle shut-off plate 15 which is lowered to
prevent the melted metal from escaping out of the injection chamber
50 when the ram 32 pushes the metal into the injection chamber 50.
When the injection chamber 50 has been filled with the metal and
substantially all gas has been forced out, the nozzle shut-off
plate 15 is pulled up and the nozzle 57 is moved forward (to the
left in FIG. 1) to contact the opening in a die 14. In the
preferred embodiment, the movement of the nozzle 57 is achieved by
mounting the entire apparatus on a slide and moving the entire
apparatus towards the die 14 (to the left in FIG. 1).
[0069] Simultaneously, the piston 45 is pushed to the left,
relative to the injection chamber 50, to force the melted metal in
the injection chamber 50 through the die 14 into a mold 13. After a
pre-set dwell time, the two halves of the die are opened and the
molded metallic part is removed, so that a new cycle can begin.
[0070] The melted metal, while housed in injection chamber 50, is
substantially sealed off from gas that would otherwise enter
injection chamber 50 from outside the machine by virtue of nozzle
shut-off plate 15, seal 41 on piston 45, and the melted metal which
continuously occupies barrel 30 during operation. Although gas is
present in injection chamber 50 prior to start-up, the first run of
shots drives out substantially all gas in injection chamber 50.
Thus, the melted metal that is injected from injection chamber 50
into mold 13 is substantially free of gas. Preferably, the amount
of gas present in injection chamber 50 during injection is less
than 20% , more preferably less than or equal to 1% by volume of
the second chamber.
[0071] As shown in FIG. 1, heating elements 70f-70j are also
provided along the lengths of the injection chamber 50. The
temperature in the feeder differs depending on the material present
in the feeder. For the AZ91 Mg alloy, heating elements 25 are
preferably controlled so that the temperature in the feeder 23 is
about 640.degree. C. near the upper surface of the melted Mg alloy
and about 660.degree. C. near the lower region of feeder 23.
Heating elements referenced and prefixed by the numeral 70 are
preferably resistance heating elements.
[0072] In the barrel 30, the temperature near heating element 70a
is preferably maintained at around 640.degree. C. for the AZ91 Mg
alloy. The temperature near heating element 70b is preferably
maintained at around 650.degree. C. for the AZ91 Mg alloy. The
temperature near heating element 70e is preferably maintained at
around 630.degree. C. for the AZ91 Mg alloy. These temperatures
facilitate the downward flow of metal toward outlet port 37 and
inhibit flow in the opposite direction.
[0073] In the injection chamber 50, the temperature near heating
elements 70h, 70i, and 70j is preferably maintained at around
620.degree. C. for the AZ91 Mg alloy. These temperatures are
sufficiently high to maintain the melted metal entirely in the
liquid state from the time it exits the feeder 23 into the barrel
30 to the time the melted metal is injected into the mold 14 from
the injection chamber 50. The temperature near heating elements 70g
and 70f is preferably maintained at around 570.degree. C. for the
AZ91 Mg alloy. The lower temperature behind the seal 41 helps
prevent the metal from flowing past the seal 41.
[0074] Using the preceding temperatures at these locations permits
molding of the AZ91 Mg alloy in the liquid state. Under these
conditions, one cycle lasts approximately 30 seconds. Molded
metallic parts having extremely smooth surfaces and minimal
porosity can be produced, which allows them to be painted directly
without any further processing. The castings also have extremely
accurate dimensions and consistency, and can be produced with
thicknesses of less than 1 mm when the part roughly has the
dimensions of a DIN size A4 sheet of paper (21.0 cm by 29.7 cm).
Preferably, the range of thickness of molded parts produced
according to the invention is between 0.5 and 1 mm for parts that
have roughly the dimensions of a DIN size A4 sheet of paper. With
known die casting and thixotropic methods, thicknesses no less than
about 1.3 mm can be obtained for parts that have roughly the
dimensions of a DIN size A4 sheet of paper.
[0075] FIGS. 6A shows a photomicrograph of a Mg alloy sample made
by a conventional thixotropic method at a magnification of 350
times. As noted previously, the prior art requires injection
molding of the metal from its thixotropic state in brder to obtain
sufficiently high metal density to improve the mechanical strength
of the cast metal part.
[0076] FIG. 6B shows a photomicrograph of a Mg alloy sample made by
the method of the current invention at a magnification of 350
times. The sample area and thickness are similar to those of the
sample shown in FIG. 6A. The sample in FIG. 6B was made by fine die
casting the metal from its liquid state according to this
invention. The surface of the sample is extremely smooth and has no
visible voids. Such a sample can be painted directly without any
further processing, thus reducing process cost. Furthermore, the
sample made according to the present invention has minimal porosity
and high strength. Thus, it is believed that the method of the
current invention is the first method that allows the achievement
of a low porosity cast metal together with a smooth surface that
requires no further processing, because it is the first process
that uses a uniform liquid metal volume that is substantially free
of trapped gas. The prior art cast metal parts made by liquid state
injection methods suffer from high porosity and low mechanical
strength due to the trapped gas in the liquid metal.
[0077] FIG. 3 shows an alternative embodiment of the invention
having a feeder 23'. Like the feeder 23 of FIG. 1, the feeder 23'
of FIG. 3 includes metering screw 21', level indicators 22', and
heating elements 25'. However, the feeder 23' of FIG. 3 has a lower
region with a bottom surface that is at a lower position than
feeder port 27'. This lower region catches sludge and other
material that is heavier than the melted metal and prevents them
from passing through the feeder port 27', ensuring that pure melted
metal enters barrel 30. Another opening (not shown) may be provided
from this lower region for periodically extracting the heavier
material.
[0078] FIG. 4A shows an alternative embodiment of the invention
having a nozzle shut-off plate 15' that is positioned a
predetermined distance away from a die 14'. In this alternative
embodiment, when the nozzle shut-off plate 15' is pulled up, the
nozzle 57 is pushed to the left to enter a relatively deep recess
that extends partially into support walls 59 and 60. Die 14' is
then positioned to abut support walls 59 and 60. The recess ensures
proper alignment of the nozzle 57' with the opening that leads into
mold 13'. The nozzle shut-off plate may be maintained at a
temperature that minimizes solidification of the liquid metal in
the nozzle. This may be achieved by providing a heating element on
or inside the shut-off plate. However, the plate may also be left
unheated.
[0079] FIG. 4B shows a side view of an alternative embodiment of
the invention having a nozzle shut-off plate 15" that retracts and
advances through a slot just inside the right edge of die 14". In
this alternative embodiment, when the nozzle shut-off plate 15" is
pulled up, the nozzle 57" is pushed to the left to enter a
relatively shallow recess that extends partially into the die 14".
The shallow recess ensures proper alignment of the nozzle 57" with
the opening that leads into mold 13". Support walls 59' and 60'
assist in aligning the nozzle.
[0080] FIG. 4C shows a front view of an alternative embodiment of
the invention having a nozzle shut-off plate 15"' that retracts and
advances through a slot in the face of die 14"'. In this
alternative embodiment, when the nozzle shut-off plate 15"' is
pulled up, a shallow recess, shown as the larger circle around the
smaller circle that is the opening into the die 14"', is exposed.
The shallow recess ensures proper alignment of the nozzle (not
shown) with the opening into die 14"'. In an alternative embodiment
(not shown), the shallow recess may be placed on support walls 59'
and 60' enclosing the nozzle 57, with the shut-off plate moving
within that recess.
[0081] A further embodiment of the present invention shown in FIG.
4D is directed to operation of nozzle shut-off plates 15, 15', 15"
and 15"' shown in FIGS. 1 and 4A-C. In this embodiment, the
shut-off plate 15 moves up and down between the face of the die 14
and support walls 59 and 60 inside the shut-off plate guide 16.
Shut-off plate guide 16 could be a vertical void, which can be
formed between the die face and the support walls as shown in FIG.
1 or inside the die as shown in FIGS. 4A-C. The guide. 16 can also
comprise a void in another direction, such as horizontal. The
shut-off plate 15 is moved through the guide 16 by a cylindrical
motor, an oil cylinder and/or an air cylinder 46. The cylindrical
motor 46 is held upright by a cylinder guide 47.
[0082] In one embodiment, metal ingots can be loaded into the
apparatus of the present invention instead of metal pellets or
chips. There are several advantages of using ingots instead of
metal pellets and chips. First, the ingots are cheaper than pellets
or chips. Second, the pellets tend to agglomerate into clusters on
the surface of the liquid metal in the feeder. This increases the
time it takes to melt the pellets, because only the pellets on the
bottom of the cluster are in contact with the liquid metal. The
pellets on top of the cluster are only in contact with the solid
pellets below them. On the other hand, the heavier ingots sink to
the bottom of the feeder. Therefore, since the entire ingot is
surrounded by the liquid metal, it melts faster than the pellets. A
loading system configured for loading ingots may also be used to
load recycled molded metallic parts of undesired characteristics
into the feeder without recasting the defective part in pellet
form. Thus, recycled parts may be used instead of ingots according
to another aspect of this embodiment.
[0083] FIG. 5A shows a top view of an alternative loading system to
that shown in FIG. 1 for loading metal ingots 63 into the feeder
23. Ingots may comprise Mg, Zn, Al or alloys thereof or other
metals and alloys. The ingots 63 are transported from a first
conveyor belt 61 onto a second conveyor belt 62. A push arm 64
controlled by a conventional motor 65 pushes the ingots 63 into the
holding chamber 66. The push arm has a size sufficient to
completely cover the opening to the holding chamber. The push arm
can form an air tight seal with the opening into the holding
chamber, if desired. The ingots 63 inside the holding chamber 66
end up on a downward sloping part (e.g. inclined surface) 67, where
a motor controlled piston 68 pushes the ingots 63 into the feeder
23. The holding chamber is preferably maintained under an inert gas
ambient, supplied from a gas port. The gas may be argon, nitrogen
or a sulfur hexafluoride and carbon dioxide mix. The gas pressure
in the holding chamber 66 should preferably be maintained at a
pressure above one atmosphere to prevent outside air, which
contains oxygen, from reaching the feeder 23. The gas pressure
and/or the position of the ingots may be monitored by one or more
sensors. The controlled atmosphere in the holding chamber 66 allows
a decreased amount of air in the feeder and thus decreases a chance
of explosion.
[0084] FIG. 5B shows a side view of another alternative loading
system to that shown in FIGS. 1 and 5A for loading metal ingots 63
into the feeder 23. The ingots 63 are transported on a conveyor 81
to a holding chamber 86, which may have a downward sloping shape.
Access to the holding chamber is controlled by a first door 82.
Egress from the holding chamber is controlled by a second door 84.
The chamber may be heated by heaters 85 to 100-200.degree. C. to
evaporate moisture on the surface of the ingots. The holding
chamber 86 operates as follows. First, door 82 is opened as ingot
63 approaches it. Door 82 can preferably be opened by moving up,
down or sideways through the walls of chamber 86. The ingot 63
enters the chamber 86 and the first door 82 is closed. After the
first door 82 is closed, the second door 84 is opened and the ingot
63 moves out of chamber 86. The conveyor 81 can move continuously
through chamber 86 with doors 82 and 84 opened and closed while the
conveyor is moving. Alternatively, the conveyor 81 moves
intermittently. It stops when an ingot approaches door 82 and when
the ingot is inside the chamber 86. This allows doors to be sealed
hermetically. The conveyor 81 may also end at the sloping part of
chamber 86, such that the ingots slide down under the force of
gravity.
[0085] In another alternative embodiment (not shown), the loading
system shown in FIG. 5A can be used with door 82 of FIG. 5B
positioned between conveyor 62 and chamber 66 and with door 84 of
FIG. 5B positioned between chamber area 67 and the melt tank (e.g.
melt feeder) 23. Door 82 opens synchronously with the movement of
the push arm 64, while door 84 opens synchronously with the
movement of piston 68.
[0086] The holding chamber 86 in FIG. 5B is connected to the melt
tank 23". Melt tank 23" contains a single metal level detector 22".
Alternatively, two level detectors 22, shown in FIG. 1 can be used.
Tank 23" also contains gas port 11". An inert gas, such as at least
one gas selected from a group comprising nitrogen, argon, SF.sub.6
and CO.sub.2, is introduced (e.g. under pressure from a pressurized
tank) into melt chamber 23". The gas pressure of the pumped gas is
preferably above one atmosphere to keep air from entering the melt
tank 23" through holding chamber 86 (the pumped gas flows out
through chamber 86, thus preventing air from flowing into chamber
86).
[0087] The melt chamber shown in FIG. 5B also contains heaters 25",
a filter or screen 24" and a feeder port 27" located above the
bottom of the tank, similar to feeder tank 23' shown in FIG. 3. The
filter may be formed inside port 27" or above port 27", as shown in
FIG. 1.
[0088] Alternatively, a vacuum pump, 87 shown in FIG. 5C can be
attached in chamber 86, between doors 82 and 84. As the ingot 63
enters chamber 86, both doors 82, 84 are closed and the vacuum pump
creates a near vacuum in chamber 86. Door 84 is then opened to
release ingot 63 into melt tank 23" without allowing any air to
enter melt tank 23" because chamber 86 was at vacuum when door 84
is opened.
[0089] As shown in FIG. 5D an inert gas screen 90 can be made to
flow from inert gas source(s) 88 across the back of door 82 and/or
84 and out through optional suction pipes or vents 89. The inert
gas screen 90 keeps air from entering chamber 86 and tank 23". The
inert gas can comprise at least on gas selected from a group
comprising argon, nitrogen, CO.sub.2 and SF.sub.6. The gas screen
of FIG. 5D can be used in combination with vacuum pump of FIG. 5C
to obtain the least air penetration into melt tank 23". The air
control measures, such as melt tank gas port 11", doors 82, 84,
vacuum pump 87 and inert gas screen(s) 90 are all used to prevent
the introduction of air into the melt tank and/or the holding
chamber to reduce the possibility of explosion. FIGS. 5E and 5F
show an alternative loading system to that shown in FIG. 5A. The
holding chamber 66' utilizes a movable aperture plate 72. FIG. 5E
shows a top view of the loading system where the access to the
feeder 23 is closed. The movable aperture plate 72 contains an
aperture 73 which is larger than an ingot. When no more ingots
should be added to the feeder 23, the plate 72 is moved to one side
by a movable arm 74 such that the plate covers the entrance to the
feeder. As shown in FIG. 5F, when additional ingots should be added
into the feeder 23, the plate 72 is moved to the other side, such
that the aperture 73 corresponds to the opening to the feeder 23.
This way, the ingots coming off the conveyor 61' pass through
aperture 73 into the feeder 23. In the embodiment shown in FIGS. 5E
and 5F the aperture plate 72 is utilized instead of a push arm 64
and piston 68 shown in FIG. 5B. However, the aperture cover plate
72 can be utilized in addition to the push arm 64 and piston 68. In
this case, the plate 72 is blocks access to ingots sliding down
sloped surface 67.
[0090] FIGS. 5G and 5H show an alternative loading system to that
shown in FIGS. 5E and 5F. In this embodiment, the holding chamber
66" utilizes a movable cover plate 75 instead of a movable aperture
plate 72. The cover plate 75 has a roughly circular shape which is
sufficient to cover the opening to the feeder 23. FIG. 5G shows a
top view of the loading system where the access to the feeder 23 is
closed. A movable arm 74' moves the cover plate 75 over the opening
to the feeder 23 to block access of ingots coming off conveyor 61".
As shown in FIG. 5H, when additional ingots should be added into
the feeder 23, the cover plate 75 is moved to the other side or
raised up (out of the plane of the drawing), to expose the opening
to the feeder 23. The ingots coming off the conveyor 61" can drop
directly into the feeder 23. In the embodiment shown in FIGS. 5G
and 5H the cover plate 75 is utilized instead of a push arm 64 and
piston 68 shown in FIG. 5A. However, the cover plate 75 can be
utilized in addition to the push arm 64 and piston 68.
[0091] FIG. 5I shows an alternative loading system to that shown in
FIG. 5A. The opening 78 to the feeder 23 is covered by a movable
transfer chamber 76, such as a cylinder. Cylinder 76 has an
aperture 77. Aperture 77 is at the same level as the conveyor 81',
as shown in FIG. 5J. When ever it is desired to add more ingots 63
to the feeder 23, a movable arm 74" moves the cylinder into a
position where the aperture 77 lines up with the end of the
conveyor 81' to allow the ingots to fall from conveyor 81' through
aperture 77 into cylinder 76 and down into the feeder 23 through
opening 78. To close access to the feeder 23, movable arm 74" moves
the cylinder 76 in any direction (e.g. up, to the left or to the
right) such that the end of the conveyor is no longer aligned with
the aperture 77. While transfer chamber 76 has been described as a
cylinder, it may have any other shapes, such as a cube, etc. The
transfer chamber may also be used with a push arm 64 and piston 68
shown in FIG. 5A. In this case, the ingots 63 would slide down the
sloping surface 67 into the transfer chamber instead of dropping
directly into the feeder 23. The transfer chamber 76 may also be
used with the holding chamber 86 FIG. 5B. This is shown in FIG.
5J.
[0092] FIG. 5J shows elevator 100 which delivers the ingots to the
conveyor 81' in the holding chamber 86'. As shown in FIG. 5B, the
holding chamber 86 may have one or two doors (82,84). In FIG. 5J,
only one door 82' is shown for clarity. The ingots are moved up
toward the holding chamber 86' on elevator platforms 101. Each
platform comprises a platform base 102 and a movable platform top
103 connected by at least one connector 104. As each platform
reaches the top of the conveyor 81', a lifting member 105 moves up
pole 106 and pushes up on the back end of the platform top 103. The
back end of the platform top 103 is lifted above platform base 102
by the lifting member 105, which causes the ingot(s) 63 to slide
off the platform top onto the conveyor 81'. The ingots 63 pass from
the conveyor 81' into the feeder. The ingots 63 may optionally pass
through the transfer chamber 76 shown in FIGS. 5I and 5J. After the
ingot(s) are removed from the platform top, the lifting member
moves down the pole 106, placing the platform top 103 onto the
platform base 102. The lifting member 105 then disengages the first
platform 101, the next platform 101 is moved up and the process is
repeated.
[0093] Connector 104 may be a bolt which rotably connects platform
top 103 and base 102. Preferably, the platform top is rotated up
about 20 degrees by the lifting member 105. Alternatively, the
entire platform 101, and not just the platform top may be lifted by
the lifting member. The elevator 100 may also be used with the
holding chamber 66 shown in FIG. 5A and ingots may slide into the
feeder 23 down sloped surface 67.
[0094] Preferably, the movement of the lifting member 105 is
synchronized with the opening of the doors. For example, as the
lifting member 105 moves up on the pole 106, the door 82' is
simultaneously opened to allow the ingot 63 to pass into the
holding chamber 86'. Furthermore, the cover plates 72 or 75 shown
in FIGS. 5E-H or the transfer chamber 76 shown in FIG. 5I may also
be synchronized with the door 82'. Thus, after the door 82' is
closed, the cover plates or the transfer chamber may be moved to
open access to the feeder 23. If back door 84 (shown in FIG. 5B) is
also present, it should be opened after the front door 82' is
closed. Elevator 100 may also be used with conveyor 61 and holding
chamber 66 shown in FIG. 5A.
[0095] FIG. 5K shows another embodiment of a feeder 23 utilizing
substantially vertical outlet containment rods. In FIG. 1 (as well
as FIG. 5B) feeder port 27 was protected by a filter 24 is a shape
of a grate. A grate is required to prevent unmelted metal pieces
from exiting feeder 23 into the barrel 30 through feeder port 27.
However, metal ingots 63 sink to the bottom of the feeder port and
lie flat on the grate. This positioning is not desirable because
the ingots may substantially block liquid metal flow through feeder
port 27"' into the barrel 30. To prevent ingots from blocking the
grate, outlet containment rods 76 should be utilized above the
feeder port 27"' as shown in FIG. 5K. The rods may be of any shape
as long as they prevent the sinking ingots 63 from laying flat
across the feeder port 27"' and blocking it. For example, as shown
in FIG. 5K, the rods in the middle of the feeder port may rise
above the rods near the circumference of the feeder port to force
the ingots 63 to rest on their side toward the edge of the feeder
23"' while melting. Feed tank 23"' may also have a lower region
with a bottom surface that is at a lower position than the feeder
port 27"', as shown in FIG. 3. The sinking ingots which come in
contact with rods 76 will be deflected sideways into the lower
region. The ingots will melt in the lower region without blocking
the feeder port 27"'.
[0096] FIG. 7A shows a side view of an alternative embodiment of
the invention having supporting ribs or fins 34 arranged on ram 32.
FIG. 7A is not to scale and the barrel 30 thickness has been
exaggerated for clarity. The heaters 70 are present but have been
omitted from FIG. 7 for clarity. The fins 34 are preferably
attached to the ram 32 and can slide on the inner circumference of
the barrel 30, both coaxially with the length of the barrel and/or
in a circular motion about the barrel axis 38. The movement
produces a rotation of the fins 34 around the inner circumference
of the barrel 30. Alternatively, the fins 34 may be attached to the
inner circumference of the barrel 30 in such a manner as to allow
the bare ram 32 to slide by. The fins 34 can be made of the same
material as the ram 32 or form a different material that can
withstand the required process temperatures. The purpose of the
fins is two fold. The first purpose is to prevent the ram 32 from
tilting and wobbling away from the barrel axis 38. Since the ram 32
is fairly long, without the fins 34 it has a tendency to tilt. The
unsupported front part of the ram comes closer to the bottom part
of the interior barrel surface than to the top interior barrel
surface under the weight of gravity. Fins 34 prevent ram from
tilting and wobbling by making contact with the inner surface of
the barrel 30, thus keeping the ram 32 centered and aligned with
the axis of the barrel. The second purpose is to enhance the
uniform temperature distribution of the melted metal.
[0097] As shown in FIG. 7A, there are no fins in area 32c of the
ram that moves inside valve 17 so as not to strike the valve. The
cross sectional view across section A-A' in FIG. 7A is shown in
FIG. 7B. As can be seen, the fins 34 do not extend around the
entire circumference of the ram 32 to allow the metal to flow
through the barrel. The fins 34 can be arranged in a number of
different formations around ram 32. For example, as shown in FIG.
7C, two fins can be arranged on opposite sides of the rod at
periodic intervals 36. Each interval can be of the same or
different length. For example, the fins can be spaced closed to
each other on one end of the ram than on another end of the ram, or
the fins can be spaced closer together in one or more sections
nearer to the middle of the ram than one or both ends of the ram.
Alternatively, as shown in FIG. 7D, more than two fins (e.g. three)
can be arranged around the ram at spaced intervals 39. Again, the
intervals along the ram 36, and intervals around the circumference
of the ram 39 can be of the same or different length. Furthermore,
the fins 34 can be tilted at one or more angles other than 90
degrees with respect to the axis of the barrel, as shown in FIG.
7E. Otherwise, some fins 34 may be tilted at 90 degrees while other
fins at an angle other than 90 degrees. As noted above, there can
be more than two tilted fins spaced along the rod at equal or
unequal intervals. Still further, the width and/or thickness of the
fins along the ram and/or around the ram circumference the may
differ, as shown in FIG. 7F. The fins may also be staggered about
the length of the ram, as shown in FIG. 7G. In general any
combination of one of more of the above alternative arrangements
are possible, even if the fins 34 are mounted on the inside of the
barrel 30 rather than on the ram 32. The ram 32 with fins 34 may be
also be used with the embodiments shown in FIGS. 3-5.
[0098] FIGS. 8A-D show side views of another embodiment of the
injection chamber 50'. In this embodiment, the piston 45' is
composed of two parts: an inner part 46 and an outer part 47. The
outer part is substantially a hollow cylinder and the inner part is
substantially a cylinder which slidably fits inside the outer part.
The two parts have separate drive mechanisms. FIG. 8A shows the
situation when the ram 32 is retracted back in the barrel 30 to
allow metal to flow into injection chamber 50'. The inner part 46
of the piston is fully extended to block the exit 58 from the
injection nozzle 57"' to prevent metal flow into the die 14"". The
outer part 47 of the piston is retracted to expand the volume of
the injection chamber 50' to a desired volume. Likewise, the ram 32
is retracted in the barrel 30. In this configuration, metal flows
into injection chamber 50' from barrel 30' but does not prematurely
flow into the die through injection nozzle aperture 58 because it
is blocked by inner piston part 46. The heating elements 70 are
present but are omitted from the Figure for clarity.
[0099] FIG. 8B shows the next step in the operation of the
injection chamber 50'. Here, ram 32 is fully advanced inside the
barrel 30 to advance the remaining metal from barrel 30 to
injection chamber 50'. The inner piston part 46 is still fully
advanced to block the injection nozzle aperture 58. The outer
piston part 47 is still retracted to allow metal to flow from
barrel 30 into injection chamber 50'. This configuration also
prevents premature flow of the metal into the die.
[0100] FIG. 8C shows the next step in the operation of the
injection chamber 50'. The inner piston part 46 has been retracted
into the outer piston part 47. The injection nozzle is now open.
However, no extra metal flows from barrel 30 into injection chamber
50' because barrel opening is blocked by the advanced ram 32.
[0101] FIG. 8D shows the last step in the operation of the
injection chamber 50'. Both the inner and outer parts 46, 47 of the
piston 45' are pushed to the left to force the melted metal in the
injection chamber 50' into the die 14"" through the injection
nozzle 57"'. As described above, the injection nozzle 57"' may be
moved forward to contact the opening in the die prior to moving the
piston 45' to the left.
[0102] After the step shown in FIG. 8D, the ram 32 and the outer
piston part 47 are retracted, while the inner piston part 46 is
positioned to block the injection nozzle aperture 58, as shown in
FIG. 8A, and the process is repeated as necessary.
[0103] Alternatively, the inner piston part 46 may be retracted
partially into the outer piston part 47; (shown as dashed lines in
FIG. 8C) to allow metal into the die opening, instead of being
retracted all the way in as shown in FIG. 8C. Furthermore, the
inner piston part 46 may move into the injection nozzle 57"' and
further to the left (shown as dashed lines in FIG. 8D) than the
outer piston part 47 instead of moving as far left as the outer
piston part 47, as shown by the solid line in FIG. 8D. Thus, the
nozzle shut-off plate may be replaced by the inner piston part 46,
since both perform the same function. Thus, the apparatus of FIGS.
8A-D is an improvement on the apparatus of FIG. 1 because it
requires only one motor to move the two part piston instead of two
motors required in FIG. 1 (one to operate the piston and the other
to operate the shut-off plate).
[0104] Furthermore, the apparatus shown in FIGS. 8A-D prevents
metal accumulation in the nozzle aperture and allows the inner
piston part 46 to force the melted metal in the injection nozzle
57"' into the die opening. Without the two part piston, the melted
metal may accumulate in the prior art injection nozzle even after
the injection motion by the piston, and solidify as a plug 91, as
shown in FIG. 9. The plug 91 forms in the exit aperture 92 of the
injection nozzle 90 because the tip 93 of the nozzle comes in
contact with the cooler walls of the die (or die support walls) 94.
Therefore, the nozzle tip is at a lower temperature than the rest
of the injection chamber. Such plugs are undesirable because they
block egress from the injection nozzle, thus decreasing the amount
of metal injected into the mold or rendering the apparatus
inoperative.
[0105] However, the inner portion of the piston 46 in FIGS. 8A-D
blocks the injection nozzle aperture from the inside of the nozzle
prior to piston injection movement, thus preventing any metal from
accumulating in the aperture. In addition, the inner piston portion
may be designed to push out any residual metal that may accumulate
in the aperture by including a tapered tip 49 of the inner piston
portion 46 that extends into the aperture, as shown in FIG. 8A.
[0106] FIG. 10 shows another embodiment of the present invention.
In this embodiment, an extra gas outlet port 110 is added. The
extra gas outlet port allows the gas 111 that is trapped between
the melted metal 115 and the piston 45 to escape the injection
chamber. The use of outlet port 110 in addition to the opening
around the piston allows more gas to escape the injection chamber.
Alternatively, the outlet port 110 can comprise the only means for
the trapped gasses to escape. The outlet port 110 is preferably
positioned between the inlet to the injection chamber and the
position of the retracted piston. The outlet port can comprise any
structure which would allow the gasses trapped in the injection
chamber to escape, without letting in the air from outside of the
apparatus into the injection chamber and without letting the melted
metal escape through it during injection into the mold. For
example, the outlet port 110 can contain a semi-permeable material,
such as porous ceramic 112. The porous material allows gas, but not
melted material to pass through it. The outlet port can be
connected to an outlet pipe 113, which contains a one way valve 114
which allows gasses to escape, but which prevents outside air from
entering the injection chamber.
[0107] FIGS. 11A and 11B show an alternative method of operating
the piston. Prior to injecting the melted metal 115 into the mold
14, the piston is partially advanced forward, while the nozzle
shut-off plate 15 blocks metal flow into the mold. The forward
movement of the piston forces the trapped gasses out of the
injection chamber. The gasses exit through the space between the
piston and the injection chamber wall and through the outlet port
110, if present. However, the forward movement of the piston does
not result in the injection of the melted metal into the mold
because the nozzle shut-off plate blocks the nozzle. Once the
trapped gasses are squeezed out of the injection chamber, the
shut-off plate is lifted and the piston is advanced forward to
inject the metal into the mold, as shown in FIG. 11B.
[0108] If the two part piston shown in FIGS. 8A-D is used, then a
similar gas squeeze out method can be used. With the inner portion
of the two part piston blocking the injection nozzle, the outer
portion is partially advanced forward to squeeze the trapped gasses
out of the injection chamber. Then, as the inner portion of the
piston is retracted, the injection nozzle is opened and the piston
is advanced forward to inject the metal into the mold.
[0109] FIG. 12A shows another embodiment of the barrel according to
the present invention. In this embodiment, the ram is composed of
two parts, an inner portion 32d and an outer portion 32e. The outer
portion 32e is slidably mounted on the first portion 32d and can be
advanced and retracted along the axis of the barrel 30. The inner
portion 32d is roughly circular in cross section, whole the outer
portion 32e has a doughnut shape cross section, with an inner
diameter slightly larger than the diameter of the inner portion
32d. The two part ram operates on a principle similar to the two
part piston shown in FIGS. 8A-D. After each injection cycle, the
inner ram portion 32d is partially retracted, while the outer ram
portion 32e is fully retracted. As the melted metal flows from the
feeder 23 through the barrel 30 and into the injection chamber 50,
the inner portion of the ram 32d is extended down the length of the
barrel and rotates about its axis to keep the temperature of the
melted metal uniform. The outer portion 32e is then advanced
forward to push the melted metal in the barrel into the injection
chamber. Prior to the injection of the metal from the injection
chamber to the mold, access to the barrel through the outlet port
37 must be closed. This can be accomplished by blocking the outlet
port 37 with the end of the inner portion of the ram 32b or by
blocking the outlet port 37 with both portions of the ram. The
shape of the outlet port 37 can correspond to the tip of the
composite two part ram such that when both portions of the ram are
fully advanced, they are capable of blocking the outlet port 37, as
shown in FIG. 12B. When the outer portion 32e is fully advanced, it
substantially blocks the inlet to the barrel 30 from the melt
feeder 23, such that substantially no melted metal enter the barrel
30 when the outer ram portion is fully advanced.
[0110] It is important to note that all embodiments shown in FIGS.
1-12 may be used together or separately or in any combination or
permutation without departing from the scope of the current
invention. In other words, any one or more improvements shown in
FIGS. 2-8 may be added to the basic apparatus shown in FIG. 1
without departing from the scope of the current invention.
[0111] This application claims priority of U.S. provisional
application Serial No. 60/080,078 (filed Mar. 31, 1998), the entire
contents of which is incorporated.
[0112] While particular embodiments according to the invention have
been illustrated and described above, it will be clear that the
intention can take a variety of forms and embodiments within the
scope of the appended claims.
* * * * *