U.S. patent application number 12/982980 was filed with the patent office on 2011-05-05 for method of unidirectional solidification of castings and associated apparatus.
Invention is credited to Men G. Chu, Alvaro Giron, Kenneth Joseph Kallaher, Jeffrey J. Shaw, Ho Yu.
Application Number | 20110100579 12/982980 |
Document ID | / |
Family ID | 37660607 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110100579 |
Kind Code |
A1 |
Chu; Men G. ; et
al. |
May 5, 2011 |
METHOD OF UNIDIRECTIONAL SOLIDIFICATION OF CASTINGS AND ASSOCIATED
APPARATUS
Abstract
Molten metal is injected uniformly into a horizontal mold from a
feed chamber in a horizontal or vertical direction at a controlled
rate, directly on top of the metal already within the mold. A
cooling medium is applied to the bottom surface of the mold, with
the type and flow rate of the cooling medium being varied to
produce a controlled cooling rate throughout the casting process.
The rate of introduction of molten metal and the flow rate of the
cooling medium are both controlled to produce a relatively uniform
solidification rate within the mold, thereby producing a uniform
microstructure throughout the casting, and low stresses throughout
the casting. A multiple layer ingot product is also provided
comprising a base alloy layer and at least a first additional alloy
layer, the two layers having different alloy compositions, where
the first additional alloy layer is bonded directly to the base
alloy layer by applying the first additional alloy in the molten
state to the surface of the base alloy while the surface
temperature of the base alloy is lower than the liquidus
temperature and greater than eutectic temperature of the base alloy
-50 degrees Celsuis.
Inventors: |
Chu; Men G.; (Export,
PA) ; Yu; Ho; (Murrysville, PA) ; Giron;
Alvaro; (Murrysville, PA) ; Kallaher; Kenneth
Joseph; (Trafford, PA) ; Shaw; Jeffrey J.;
(New Kensington, PA) |
Family ID: |
37660607 |
Appl. No.: |
12/982980 |
Filed: |
December 31, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12059620 |
Mar 31, 2008 |
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12982980 |
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11179835 |
Jul 12, 2005 |
7264038 |
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12059620 |
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11179935 |
Jul 12, 2005 |
7320151 |
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11179835 |
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Current U.S.
Class: |
164/94 |
Current CPC
Class: |
B22D 27/045 20130101;
B22D 7/00 20130101 |
Class at
Publication: |
164/94 |
International
Class: |
B22D 19/16 20060101
B22D019/16; B22D 23/00 20060101 B22D023/00 |
Claims
1-38. (canceled)
39. A method of casting metal, comprising: providing a casting
apparatus for casting metal comprising a plurality of sides and a
bottom defining a mold cavity, wherein the bottom has at least two
surfaces, including a first surface and a second surface; at least
one metal feed chamber adjacent to the mold cavity; at least one
control apparatus between the feed chamber and the mold cavity, the
control apparatus being structured to control the flow rates of
molten metal being introduced horizontally into the mold cavity,
wherein the bottom comprises a substrate having (a) sufficient
dimensions, and (b) a plurality of apertures, such that the bottom:
(i) allows one or more cooling mediums to flow through the
apertures and directly contact the metal, wherein a direction of
the flow of the cooling medium is from the first surface of the
bottom into the mold cavity, and (ii) simultaneously resists the
metal initially poured directly onto the second surface of the
bottom from exiting through the apertures to the first surface of
the bottom; introducing a first molten metal into the mold cavity
through an inlet; directing a cooling medium against the first
surface of the bottom of the mold cavity to initiate solidification
of the first molten metal; continuing to introduce the first molten
metal through the inlet until a desired thickness; introducing a
second molten metal through the inlet and continuing to introduce
the second molten metal until a desired thickness; whereby the
molten metal is cooled unidirectionally through its thickness.
40. A method according to claim 39, wherein a rate of introduction
of molten metal into the mold cavity is coordinated with the rate
of cooling.
41. A method according to claim 39 or 40, wherein the cooling rate
is about 0.5.degree. F./sec. to about 3.degree. F./sec.
42. A method according to claim 39, wherein the rate of
introduction of molten metal into the mold cavity slows as the
casting progresses.
43. A method according to claim 42, wherein the cooling rate slows
from about 3.degree. F./sec. to about 0.5.degree. F./sec. as
casting progresses.
44. A method according to claim 39, wherein the rate of
introduction of molten metal into the mold cavity is about 0.5
in./min. to about 4 in./min.
45. A method according to claim 44, wherein the rate of
introduction of molten metal into the mold cavity is slowed as
casting progresses.
46. A method according to claim 45, wherein the rate of
introduction of molten metal into the mold cavity slows from about
4 in./min. to about 0.5 in./min. as casting progresses.
47. A method according to claim 39, wherein a rate of application
of cooling medium is increased as casting progresses.
48. The method according to claim 47, wherein the coolant is
applied by spraying against the bottom of the mold.
49. A method according to claim 47, wherein at least one material
within the coolant comprises air, water, or a mixture thereof.
50. A method according to claim 39, wherein the casting apparatus
further comprises a coolant manifold disposed under the bottom.
51. A method according to claim 39 wherein the apertures have a
geometry that is equivalent to holes having an equivalent diameter
about of 1/64'' to about 1''.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation-in-part of U.S. application Ser. No.
11/179,935, filed Jul. 12, 2005, the entire disclosure of which is
hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a multiple layer ingot
product formed by casting. More specifically, the present invention
provides an ingot cast by an apparatus and method of
unidirectionally solidifying castings to provide a uniform
solidification rate, thereby providing a casting having a uniform
microstructure and lower internal stresses.
[0004] 2. Description of the Related Art
[0005] Various methods of directional solidification of castings
within a mold have been attempted in an effort to improve the
properties of castings.
[0006] An example of a presently available directional
solidification method includes U.S. Pat. No. 4,210,193, issued to
M. Ruhle on Jul. 1, 1980, disclosing a method of producing an
aluminum silicone casting. The molten material is poured into a
mold having a bottom formed by a tin plate. A stream of water is
applied to the bottom of the tin plate, and a thermocouple inserted
through the tin plate into the casting is used to monitor the
temperature of the casting, and thereby properly control the
cooling stream. Cooling is stopped when the temperature in the
bottom portion of the mold falls from 575.degree. F. to 475.degree.
F., until heat from the surrounding melt increases this region to
540.degree. F. When the aluminum silicone alloy is removed from the
mold, the tin plate has become a part of the casting. The result is
a fine grain structure in the lower portion of the casting. This
method fails to produce a uniform structure with low stresses, and
would likely result in waste due to the necessity of cutting away
the tin plate if it is not to form a part of the final casting.
[0007] U.S. Pat. No. 4,585,047, issued to H. Kawai et al. on Apr.
29, 1986, discloses an apparatus for cooling molten metal within a
mold. The apparatus includes a pipe within the mold through which a
cooling liquid is passed. The pipe is located in a lower portion of
the mold, resulting in directional solidification of the metal from
the bottom of the mold to the top. Once the casting is solidified,
the excess portion of the casting is cut away from the casting, and
then melted away from the pipe so that the pipe can be reused. The
necessity of cutting away the portion of the casting surrounding
the pipe results in added manufacturing steps and waste. The
apparatus further fails to provide for a uniform structure within
the casting or the low stresses within the casting that would
result from a directional solidification.
[0008] U.S. Pat. No. 4,969,502, issued to Eric L. Mawer on Nov. 13,
1990, discloses an apparatus for casting of metals. The apparatus
includes an elongated pouring device structured to pour molten
metal against a vertical plate, thereby dissipating the energy of
the flowing molten metal. Alternatively, a pair of elongated
pouring devices are used to pour molten metal towards each other,
so that the interaction of the two strains of metal flowing towards
each other dissipates the energy of the metal. The result is a
reduced wave action within the mold, so that the cooled casting has
a more uniform thickness. The apparatus fails to provide for a
uniform structure within the casting. It also fails to provide low
stresses within the casting.
[0009] U.S. Pat. No. 5,020,583, issued to M. K. Aghajanian et al.
on Jun. 4, 1991, describes the directional solidification of metal
matrix composites. The method includes placing a metal ingot above
a mass of filler material and then melting the metal so that the
metal infiltrates the filler material. The metal may be alloyed
with infiltration enhancers such as magnesium, and the heating may
be done within a nitrogen gas environment to further facilitate
infiltration. After infiltration, the resulting metal matrix is
cooled by placing it on top of a heat sink, with insulation placed
around the cooling metal matrix, thereby resulting in directional
solidification of the molten alloy. This patent fails to provide
for control of the rate of solidification, for a uniform structure
within the casting, or for low stresses within the casting.
[0010] U.S. Pat. No. 5,074,353, issued to A. Ohno on Dec. 24, 1991,
discloses an apparatus and method for horizontal continuous casting
of metal. The system includes a holding furnace connected to a hot
mold having an open section at its inlet end. Heating elements
around the sides and bottom of the hot mold heat the mold to a
temperature that is at least the solidification temperature of the
casting metal. A cooling spray is applied to the top of the hot
mold. A dummy member secured between upper and lower pinch rollers
is reciprocated into and out of the outlet end of the mold to draw
out the metal as it is solidified. The method of this patent is
likely to result in waste due to the need to separate the casting
from the dummy metal. The apparatus further fails to provide for a
uniform structure within the casting or the low stresses within the
casting that would result from a directional solidification.
[0011] Accordingly, there is a need for an improved apparatus and
method of unidirectional solidifying of casting, providing for a
relatively uniform, controlled cooling rate. Such a method would
result in greater uniformity within the crystal structure of the
casting, with lower stresses within the casting, and a reduced
tendency towards cracking.
SUMMARY OF THE INVENTION
[0012] A multiple layer cast ingot formed by a method of
unidirectionally solidifying a casting across the thickness of the
casting, at a controlled solidification rate is provide. The method
is particularly useful for casting commercial size ingots of
2.times..times..times. series aluminum alloys cladded with a
1.times..times..times. alloy and a 3.times..times..times. alloy
cladded with a 4.times..times..times. alloy. For purposes of this
description, thickness is defined as the thinnest dimension of the
casting.
[0013] A mold in accordance with the invention is preferably
oriented substantially horizontally, having four sides and a bottom
that may be structured to selectively permit or resist the effects
of a coolant sprayed thereon. One bottom configuration is a
substrate having holes of a size that allow coolants to enter but
resist the exit of molten metal. Such holes are preferably at least
about 1/64 inch in diameter, but not more than about one inch in
diameter. Another bottom configuration is a conveyor having a solid
section and a mesh section. Other bottom configurations include
structures to be removed from the remainder of the mold upon
solidification of the molten metal on the bottom of the mold, with
a mesh, cloth, or other permeable structure remaining to support
the casting.
[0014] A trough for transporting molten metal from the furnace
terminates at one side of the mold, and is structured to transport
metal from the furnace or other receptacle to a molten metal feed
chamber disposed along one side of the mold. In another embodiment,
the molten feed chamber is disposed along the top of one side of
the mold so that it is possible to deliver the molten metal
vertically to the top of the mold cavity in a controlled manner.
The molten metal feed chamber and mold are separated from each
other by one or more gates. A preferred gate is a cylindrical,
rotatably mounted gate, defining a helical slot therein, so that as
the gate rotates, molten metal is released horizontally into the
mold, only at the level of the top of the molten metal within the
mold. Another preferred gate is merely slots at different heights
in the wall separating the mold and feed chamber, so that the rate
at which molten metal is added to the feed chamber determines the
rate and height at which molten metal enters the mold. Another
preferred gate is a flow passage between the molds and the feed
chamber having a vertical slider at each end, so that the vertical
slider resists the flow of molten metal through a slot in both the
mold and the feed chamber, while permitting the flow of molten
metal through the channel. The flow of molten metal is thereby
limited to a desired height within the mold, set by the height of
the channel.
[0015] In some embodiments, a second trough and molten metal feed
chamber may be provided on another side of the mold, thereby
permitting a second alloy to be introduced into the mold during
casting of a first alloy, for example, to apply a cladding to a
cast item. This procedure may be extended to make a multiple layer
ingot product having at least two different alloy layers. The sides
of the mold are preferably insulated. A plurality of cooling jets,
for example, air/water jets, will be located below the mold, and
are structured to spray coolant against the bottom surface of the
mold.
[0016] Molten metal is introduced substantially uniformly through
the gates. At the same time, a cooling medium is applied uniformly
over the bottom area of the mold. The rate at which molten metal
flows into the mold, and the rate at which coolant is applied to
the mold, are both controlled to provide a relatively constant rate
of solidification. The coolant may begin as air, and then gradually
be changed from air to an air-water mist, and then to water. After
the molten metal at the bottom of the mold solidifies, the bottom
of the substrate may be moved so that the solid section underneath
the mold is replaced by a section having openings, thereby
permitting the coolant to directly contact the solidified metal,
and maintain a desired cooling rate. In the case of a perforated
plate substrate, the mold bottom need not be removed.
[0017] Accordingly, it is an object of the present invention to
provide an improved method of directionally solidifying castings
during cooling.
[0018] It is another object of the invention to provide a method of
maintaining a relatively constant solidification rate during the
solidification of the casting.
[0019] It is a further object of the invention to provide a casting
method having minimized waste.
[0020] It is another object of the invention to provide a casting
method resulting in a uniform crystal structure within the
material.
[0021] It is a further object of the invention to provide a casting
method resulting in lower stresses and a reduced probability of
cracking and/or shrinkage voids within the casting.
[0022] It is another object of the invention to provide a casting
having a more uniform structure.
[0023] It is a further object of the invention to provide an
apparatus and method for producing a cladding around the casting,
with the cladding having better adhesion than prior claddings.
[0024] It is a another object of the invention to provide an
apparatus and method for producing a multiple layer ingot product
having at least two layers.
[0025] These and other objects of the invention will become more
apparent through the following description and drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
[0027] FIG. 1 is a top isometric view of a mold according to the
present invention, showing the solid portion of the conveyor below
the mold.
[0028] FIG. 2 is a partially sectional isometric top view of a mold
according to the present invention, taken along the lines 2-2 in
FIG. 1.
[0029] FIG. 3 is an isometric top view of a mold according to the
present invention, showing the mesh portion of the conveyor below
the mold.
[0030] FIG. 4 is a partially sectional isometric top view of a mold
according to the present invention, taken along the lines 4-4 in
FIG. 3.
[0031] FIG. 5 is a top view of a gate according to the present
invention.
[0032] FIG. 6 is a front view of a gate according to the present
invention.
[0033] FIG. 7 is a side view of a gate according to the present
invention.
[0034] FIG. 8 is a side isometric, partially cutaway view of
another embodiment of a mold according to the present
invention.
[0035] FIG. 9 is a cutaway side isometric view of another
alternative embodiment of a mold according to the present
invention.
[0036] FIG. 10 is a side isometric view of the mold according to
FIG. 9.
[0037] FIG. 11 is a graph showing temperature of the casting with
respect to time during an example solidification process.
[0038] FIG. 12 is a graph showing cross-sectional stress
distribution across an ingot made according to the present
invention.
[0039] FIG. 13 is a graph showing stress at various locations
within an ingot cast using prior art methods.
[0040] FIG. 14 is a cutaway isometric view of yet another
embodiment of a mold and transfer chamber according to the present
invention.
[0041] FIG. 15 is a cutaway front isometric view of a mold cavity
for a mold according to the present invention.
[0042] FIG. 16 is a top isometric view of a mold according to
another embodiment of the present invention, showing the perforated
portion of the conveyor below the mold.
[0043] FIG. 17 is a partially sectional isometric top view of the
mold shown in FIG. 16, taken along the lines 16-16 in FIG. 16.
[0044] FIG. 18 is a partially sectional isometric top view of the
mold shown in
[0045] FIG. 16, where the mesh portion of the conveyor is below the
mold.
[0046] FIG. 19A is a perspective view of a three layer multiple
ingot for a skin sheet product having a 2024 alloy sandwiched
between two layers of 1050 alloy.
[0047] FIG. 19B is a micrograph of the boxed portion of FIG. 19A
that shows the interface between the 2024 alloy and 1050 alloy.
[0048] FIG. 20A is a perspective view of a three layer multiple
ingot for a brazing sheet product having a 3003 alloy sandwiched
between two layers of 4343 alloy.
[0049] FIG. 20B is a micrograph of the boxed portion of FIG. 20A
that shows the interface between the 3003 alloy and 4343 alloy.
[0050] Like reference characters denote like elements throughout
the drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0051] The present invention provides an apparatus and method of
unidirectionally solidifying a casting, while also providing for a
controlled, uniform solidification rate.
[0052] Referring to FIGS. 1-4, a mold 10 includes four sides 12,
14, 16, 18, respectively, with a mold cavity 19 defined therein.
The sides 12, 14, 16, 18 are preferably insulated. A bottom 20 may
be formed by a conveyor having a solid portion 22 and a mesh
portion 24. The conveyor 20 is continuous, wrapping around the
rollers 26, 28, 30, 32, respectively, so that either of the solid
portion 22 or mesh portion 24 may selectively be placed under the
sides 12, 14, 16, 18. The conveyor may be made from any rigid
material having a high thermal conductivity, with examples
including copper, aluminum, stainless steel, and Inconal. Note that
the mesh portion 24 is a section having openings.
[0053] A molten metal feed chamber 34 defined by sides 36, 38, 40
is defined along the side 12. Likewise, a similar molten metal feed
chamber 42 is defined by the sides 44, 46, 48, along side the sides
16. Some embodiments of the present invention may only have one
molten metal feed chamber, and others may have multiple molten
metal feed chambers. A feed trough 50, 52 extends from a molten
metal furnace (not shown, and well known in the art of casting) to
a location directly above each of the molten metal feed chambers,
34, 42, respectively. A spout 54 extends from the feed trough 50 to
the molten metal feed chamber 34. Likewise, a spout 56 extends from
the feed trough 52 to the molten metal feed chamber 42.
[0054] The side 12 includes one or more gates 58, 60 structured to
control the flow of molten metal from the feed chamber 34 to the
mold cavity 19. Likewise, the side 16 includes gates 62, 64,
structured to control the flow of molten metal from the feed
chamber 42 into the mold cavity 19. The gates 58, 60, 62, 64 are
substantially identical, and are best illustrated in FIGS. 5-7. The
gate 58 includes a pair of walls 66, 68 defining a substantially
cylindrical channel 70 therebetween. The channel 70 includes open
sides 72, 74, on opposing sides of the walls 66, 68. A cylindrical
gate member 76 is disposed within the channel 70. The cylindrical
gate member 76 is substantially solid, and defines a helical slot
78 about its circumference. The channel 70, cylindrical gate member
76, and helical slot 78 are structured so that molten metal is
permitted to flow through a portion of the helical slot 78 that is
directly adjacent to one of the walls 66, 68, and molten metal is
resisted from passing through any other portion of the gate 58. A
drive mechanism 80 is operatively connected to the cylindrical gate
member 76, for controlling the rotation of the cylindrical gate
member 76. Appropriate drive mechanisms 80 are well known to those
skilled in the art, and will therefore not be described in great
detail herein. The drive mechanism 80, may, for example, include an
electrical motor connected through a gearing system to the
cylindrical gate member 76, with the electrical motor being
controlled either through manual switching by an operator observing
the casting process, or by an appropriate microprocessor.
[0055] Referring back to FIGS. 1-4, a coolant manifold 82 is
disposed within the conveyor 20, and is structured to spray a
coolant against the bottom surface 22, 24, of the mold cavity 19. A
preferred coolant manifold 82 is structured to supply air, water,
or a mixture thereof, depending upon the desired rate of
cooling.
[0056] In use, the conveyor 20 will be in the position illustrated
in FIGS. 1-2, with the solid portion 22 directly under the mold
cavity 19. Molten metal will be introduced from the feed trough 50,
through the spout 54, into the feed chamber 34. The gates 58, 60
will have their cylindrical gate members 76 rotated so that the
lowest portion of the helical slot 78 is adjacent to the wall 66 or
the wall 68, thereby permitting molten metal to enter the mold
cavity 19 by flowing substantially horizontally onto the conveyor
surface 22. At the same time, air will be sprayed from the coolant
manifold 82 onto the underside of the surface 22. As the mold
cavity 19 is filled with molten metal, the cylindrical gate members
76 will be rotated so that increasingly elevated portions of the
helical slot 78 are adjacent to either of the walls 66, 68, so
that, as the level of metal within the mold cavity 19 is raised,
the portion of the helical slot 78 through which molten metal is
permitted to pass will be raised a corresponding amount so that the
flow of molten metal from the chamber 34 to the mold cavity 19 is
always horizontal, and always on top of the metal that is already
within the mold cavity 19. The horizontal flow of metal into the
mold cavity 19 will permit the molten metal to properly find its
own level, thereby insuring a substantially even thickness of
molten metal within the mold cavity 19.
[0057] As additional metal is added to the mold cavity 19, the
cooling rate for the metal within the mold cavity 19 will slow. To
maintain a substantially constant cooling rate, the mixture of
coolant from the coolant manifold 82 will be changed from air to an
air-water mist containing increasing quantities of water, and
eventually to all water. Additionally, as the metal at the bottom
portion of the mold cavity 19 solidifies, the conveyor 20 will be
advanced so that the mesh 24 instead of the solid portion 22 forms
the bottom of the mold 10, thereby permitting coolant to directly
contact the solidified metal, as shown in FIGS. 3-4. Additionally,
the rate of metal addition into the mold cavity 19 may be slowed by
controlling either the rotation of the cylindrical gate members 76
of the gates 58, 60, and/or the rate of introduction of metal into
the feed chamber 34 from the feed trough 50. Typically, the cooling
rate will remain between about 0.5.degree. F./sec. to about
3.degree. F./sec., with the cooling rate typically decreasing from
3.degree. F./sec. at the beginning of casting to about 0.5.degree.
F./sec. towards the completion of casting. Likewise, the rate at
which molten metal is introduced into the mold cavity 19 will
typically be slowed from an initial rate of about 4 in./min. to a
final rate of 0.5 in./min. as casting progresses.
[0058] If desired, a second alloy may be introduced into the feed
chamber 42 from the feed trough 52, and through the spout 56. This
second alloy may be used to form a cladding around the first alloy.
For example, the cladding may be a corrosion resistant layer. One
example of a cladding may be formed by first introducing an alloy
from the feed chamber 42, through the gates 62, 64, into the mold
cavity 19 by rotating the cylindrical gate members 76 of the gates
62, 64, so that metal flows from the bottom portion of the helical
channel 78 within these gates into the mold cavity 19, and then
closing the gates 62, 64. The cylindrical gate member 76 of the
gates 58, 60 are then rotated to permit the flow of molten metal
from the feed chamber 34 into the mold cavity 19 at increasingly
elevated portions of the helical slot 78, until the mold cavity 19
is filled almost all of the way to the top, at which point the
gates 58, 60 are closed. The cylindrical gate members 76 of the
gates 62, 64 are then rotated to permit the flow of metal from the
feed chamber 42 into the mold cavity 19 at the highest portion of
the slots 78 within the cylindrical gate members 76 of the gates
62, 64, thereby permitting this molten metal to flow to the top of
the metal already in the mold. The resulting substrate formed from
the alloy within the feed chamber 34 will have a cladding on the
top and bottom made from the alloy within the feed chamber 42.
[0059] To ensure proper bonding at the interface of any of two
successive layer that following procedure must be followed: The
temperature of the surface of the base layer after introduction of
the new subsequent layer that is a different composition from the
base layer must be less than the liquidus temperature (T.sub.liq)
and greater than eutectic temperature (T.sub.eut)-50.degree. C.
where the T.sub.liq is the liquidus temperature of the base layer
and T.sub.eut is the eutectic temperature of the base layer. This
procedure is not limited to just cladding. This procedure enable
the casting a multiple alloys sequentially to create a multiple
layer ingot product.
[0060] Another embodiment of a mold 84 is illustrated in FIG. 8.
The mold 84 includes four sides, with three sides 86, 88, 90
illustrated. The sides 86, 88, 90, and the fourth substantially
identical but not shown side may be insulated. The bottom of the
mold 84 is formed by a cloth 92, which may be made of the same
material as the bottom conveyor 20 of the previous embodiment 10. A
bottom substrate 94 is structured to move between an upper position
illustrated in solid lines in FIG. 8, wherein it supports the cloth
92, and a lower position, illustrated in phantom in FIG. 8, wherein
the substrate is removed from the cloth 92 a sufficient distance so
that the spray boxes 96, 98 may be positioned therebetween. The
spray boxes 96, 98 are structured to be moved from a position below
the cloth 92 to a position wherein movement of the substrate 94
between its upper and lower position is permitted. The spray boxes
96, 98 will therefore supply air, water, or a mixture of both, or
possibly other coolants, to either the bottom of the substrate 94
or the bottom of the cloth 92, depending upon whether the substrate
94 is above or below the spray boxes 96, 98.
[0061] In use, the substrate 94 will be in its upper position,
supporting the cloth 92. Molten metal will be introduced into the
mold 84, with air being applied to the bottom of the substrate 94
to provide cooling. As the mold 84 is filled with molten motel, and
the molten metal on the bottom solidifies, the spray boxes 96, 98
will be briefly withdrawn from their position under the substrate
94, thereby permitting the substrate 94 to be removed from its
position under the cloth 92. The spray boxes 96, 98 will then be
placed back underneath the cloth 92, so that they may apply air, an
air/water mixture, or water to the bottom of the cloth 92, with
increasing amounts of water being applied to the bottom of the
cloth 92 as casting progresses.
[0062] FIGS. 9 and 10 illustrate yet another embodiment of a mold
100 that may be used for a method of the present invention. The
mold 100 includes side walls 102, 104, 106, and 108, which may be
insulated. The bottom includes a fixed floor plate 110 defining an
opening below the walls 102, 104, 106, 108, wherein a removable
floorplate 112 may be inserted. The removable floorplate 112 may be
made from a material such as copper. The fixed floorplate 110 may
in some embodiments define a slot 114 structured to receive the
edges of the removable floorplate 112, thereby supporting the
removable floorplate 112. The walls 102, 104, 106, 108, and the
removable floorplate 112, define a mold cavity 116 therein.
[0063] A molten metal feed chamber 118 is defined by the walls 120,
122, and 124 along with the wall 108 and fixed floorplate 110. A
gate 126 is defined within the wall 108, and in the illustrated
examples formed by a pair of slots defined within the wall 108. A
feed trough 128 extends from a molten metal furnace to a location
directly above the molten metal feed chamber 118. A spout 130
extends from the feed trough 128 to the molten metal feed chamber
118.
[0064] A coolant manifold 132 is disposed below the removable
floorplate 112. The coolant manifold 132 is preferably configured
to selectively spray air, water, or a mixture of air and water
against the removable floorplate 112. The illustrated embodiment
further includes a catch basin 134 disposed below the feed chamber
118. The entire mold 100 is supported on the base 136.
[0065] In use, the removable floorplate 112 will be contained
within the slot 114. Molten metal will be introduced from the feed
trough 128 into the feed chamber 118, until the level of molten
metal within the feed chamber 118 reaches the bottom of the slots
126. The slots 126, combined with an appropriately selected feed
rate into the feed chamber 118, will ensure that the feed rate of
molten metal into the mold cavity 116 is controlled. As the level
of molten metal within the mold cavity 116 rises, the feed rate of
molten metal into the feed chamber 118 may be adjusted so that
molten metal is flowing out of the slot 126 directly on top of the
molten metal within the mold cavity 116, thereby ensuring a
substantially horizontal flow of molten metal into the mold cavity
116. Coolant will be sprayed against the removable floorplate 112
through the coolant manifold 132, beginning with air, and then
switching to an air/water mixture, and finally all water. As molten
metal within the bottom of the mold cavity 116 solidifies, the
removable floorplate 112 may be removed, thereby permitting coolant
to directly contact the underside of the ingot within the mold
cavity 116.
[0066] In one example of a casting process according to the present
invention, 7085 aluminum alloy was cast into a
9''.times.13''.times.7'' ingot using a mold 100 as shown in FIGS.
9-10. The initial metal temperature was 1,280.degree. F. The
removable floorplate 112 was made from a 0.5'' thick stainless
steel plate. Thermocouples were placed along the center line of the
ingot at 0.25 inch, 0.75 inch, 2 inches and 4 inches from the
removable floorplate 112. The mold cavity 116 was initially filled
at a rate of 2 inches every 30 seconds, with a fill rate slowing as
casting progressed. The initial water flow rate was 0.25 gallons
per minute, in the form of a combined air/water mixture. The
removable floorplate 112 was removed when a thermocouple located
0.25 inch from the removable floorplate 112 read 1,080.degree. F.
At this point, the flow rate of water was increased to 1 gallon per
minute.
[0067] FIG. 11 shows the cooling rate at each of the four
thermocouples. As can be seen from this figure, the cooling rate
ranged from 1.5 to 2.12.degree. F./sec., a substantially uniform
cooling rate.
[0068] FIG. 12 is a graph showing residual stresses throughout a
cross-section of the ingot. This data was collected by cutting the
ingot in half in the 9'' direction, and then measuring the
resulting surface deformation as the stresses within the material
relaxed. With the exception of one tensile stress in the lower
left-hand corner of FIG. 12, and one compressive stress in the
lower center portion of FIG. 12, the magnitude of the stresses
throughout the ingot is 0.6 to 3 ksi. The larger compressive stress
at the center of the ingot's bottom is of little concern, because
compressive stress generally does not result in cracking. The high
compressive stresses at this location and high tensile stresses in
the lower left corner are probably the result of molten metal first
impinging on the substrate at these locations, resulting in the
formation of cold shots and possibly other defects. The highest
tensile stress was +6e.sup.+02 PSI.
[0069] Referring to FIG. 13, the residual stresses across the
cross-section of a 4 inch by 13 inch 7085 aluminum alloy DC cast
ingot are illustrated. As the figure shows, the residual stresses
resulting from presently performed DC casting can be as high as 10
ksi. However, the stresses in this ingot were likely even higher,
because the ingot already had a longitudinal crack when the stress
was measured, which would have relaxed these stresses. As used in
the figure, sigma refers to tensile or compressive stress, tau
refers to sheer stress, LT refers to the direction substantially
parallel to the length, and ST refers to a direction substantially
parallel to the thickness.
[0070] The application of coolant to the bottom of the mold, along
with, in some preferred embodiments, the insulation on the sides
12, 14, 16, 18, results in directional solidification of the
casting from the bottom to the top of the mold cavity 19.
Preferably, the rate of introduction of molten metal into the mold
cavity 19, combined with the cooling rate, will be controlled to
maintain about 0.1 inch (2.54 mm.) to about 1 inch (25.4 mm.) of
molten metal within the mold cavity 19 at any given time. In some
embodiments, the mushy zone between the molten metal and solidified
metal may also be kept at a substantially uniform thickness. As a
result of this directional solidification, uniform temperature, and
thin sections of molten metal and mushy zone, macrosegregation is
substantially reduced or eliminated.
[0071] Referring to FIG. 14, another mold assembly 138 is
illustrated. The mold assembly 138 includes 140, 142, 144, and a
fourth side that is not illustrated in the cutaway drawing,
opposite the side 142. All four walls 140, 142, 144, and the
unillustrated wall may be insulated, with a preferred insulating
material being graphite. The mold 138 further includes a bottom
146, which preferably includes a plurality of apertures 148 (best
illustrated in FIG. 15) having a diameter sufficiently large to
permit the passage of typical coolants such as air or water, while
also being sufficiently small to resist the passage of molten metal
there through. A preferred diameter for the apertures 148 is about
1/64 inch to about one inch. The mold's cavity 150 is defined by
the walls 140, 142, 144, the fourth wall, and the bottom 146. Wall
144 defines a slot therein, the edge 152 of the slot visible in
FIG. 14.
[0072] The molten metal feed chamber 154 is defined by the walls
156, 158, 160, a fourth unillustrated wall, and the bottom 162. A
feed trough 164 extends from a molten metal furnace to a location
directly above the molten metal feed chamber 154. A spout 166
extends from the feed trough 164 to the molten metal feed chamber
154.
[0073] A gate 168 is an H shaped structure, having a pair of
vertical slot closure members 170, 172, connected by a horizontal
member 174 defining a channel 176 therethrough. Slot closure member
170 is structured to substantially close a slot in the wall 144 of
the mold cavity 150, while the closure member 172 is structured to
substantially close the slot defined within the wall 156 of the
molten metal feed chamber 154. The gate 168 is structured to slide
between a lower position wherein the channel 176 is located
adjacent to the bottom 146 of the mold cavity 150, and an upper
position corresponding to the top of the mold cavity 150. The slot
closure members 170, 172 are structured to resist the flow of
molten metal through the slots defined in the walls 144, 156 at any
point except through the channel 176, regardless of the position of
the gate 168.
[0074] A coolant manifold 178 is disposed below the bottom 146. The
coolant manifold 178 preferably configured to selectively spray
air, water, or a mixture of air and water against the bottom
146.
[0075] A laser sensor 180 be disposed above the mold cavity 150,
and is preferably structured to monitor the level of molten metal
within the mold cavity 150.
[0076] In use, molten metal will be introduced through the feed
trough 164 into the feed chamber 154. Molten metal may then flow
through the channel 176 into the mold cavity 150. As the level of
molten metal within the mold cavity 150 arises, the gate 168 will
be raised so that molten metal always flows horizontally from the
feed chamber 154 directly on top of the molten metal already in the
mold chamber 150. The feed rate of molten metal into the mold
chamber 150 may be slowed as cooling progresses to control the
cooling rate. Additionally, coolant flowing from the coolant
manifold 178 will change from air to an air/water mixture to all
water as casting progresses to control the cooling rate of the
molten metal within the feed chamber 150. Because coolant may
impinge directly on the metal within the feed chamber 150, it is
unnecessary to remove the bottom 146 during the casting
process.
[0077] FIG. 16 shows a top isometric view of a mold according to
another embodiment of the present invention, showing the perforated
portion of the conveyor below the mold. All elements in FIG. 16 are
present and identified by the same reference numerals as shown in
FIG. 1. Mold 10 includes four sides 12, 14, 16, 18, respectively,
with a mold cavity 19 defined therein. The sides 12, 14, 16, 18 are
preferably insulated. A bottom 20 may be formed by a conveyor
having a perforated portion 22 and a mesh portion 24. The conveyor
20 is continuous, wrapping around the rollers 26, 28, 30, 32,
respectively, so that either of the perforated portion 22 or mesh
portion 24 may selectively be placed under the sides 12, 14, 16,
18. The conveyor may be made from any rigid material having a high
thermal conductivity, with examples including copper, aluminum,
stainless steel, and Inconal.
[0078] FIG. 17 shows a partially sectional isometric top view of
the mold shown in FIG. 16, taken along the lines 16-16 in FIG.
16.
[0079] FIG. 18 shows a partially sectional isometric top view of
the mold shown in FIG. 16, where the mesh portion of the conveyor
is below the mold.
[0080] FIGS. 16, 17 and 18 are similar to FIGS. 1, 2 and 4. The
main difference between the two sets of Figures is that FIGS. 1, 2
and 4 shows a solid and a mesh portion of the conveyor below the
mold, respectively, whereas FIGS. 16, 17 and 18 shows a perforated
and a mesh portion of the conveyor below the mold,
respectively.
[0081] FIG. 19A shows a three layer multiple layer ingot for a skin
sheet product having a 2024 alloy sandwiched between two layers of
1050 alloy. Here, the 2024 alloy has a liquidus temperature
1180.degree. F. and eutectic temperature of 935.degree. F. and the
1050 alloy has a liquidus temperature 1198.degree. F. and eutectic
temperature of 1189.degree. F. In this example, upon casting a
0.75'' thick layer of the first cladding layer of alloy 1050, a
3.5'' thick layer of the core alloy 2024 was poured at a controlled
rate of 0.7 ipm ensuring that the interface temperature rose to a
value between 1148.degree. F. and 1189.degree. F. After casting the
cores material, a 0.75'' thick second cladding layer of alloy was
poured ensuring that the interface temperature rose to a value
between 885.degree. F. and 1180.degree. F.
[0082] FIG. 19B shows a micrograph showing the interface between
the 2024 alloy and 1050 alloy of the boxed portion of the three
layer multiple layer ingot in FIG. 19A. This shows that the
interface between the 2024 alloy and 1050 alloy is well bonded.
[0083] FIG. 20A shows a three layer multiple layer ingot for a
brazing sheet product having a 3003 alloy sandwiched between two
layers of 4343 alloy. Here, the 3003 alloy has a liquidus
temperature 1211.degree. F. and eutectic temperature of
1173.degree. F. and the 4343 alloy has a liquidus temperature
1133.degree. F. and eutectic temperature of 1068.degree. F. In this
example, upon casting a 0.75'' thick layer of the first cladding
layer of alloy 4343, a 5.5'' thick layer of the core alloy 3003 was
poured at a controlled rate of 0.7 ipm ensuring that the interface
temperature rose to a value between 1018.degree. F. and
1083.degree. F. After casting the cores material, a 0.75'' thick
second cladding layer of alloy was poured ensuring that the
interface temperature rose to a value between 1123.degree. F. and
1211.degree. F.
[0084] FIG. 20B shows a micrograph showing the interface between
the 3003 alloy and 4343 alloy of the boxed portion of the three
layer multiple layer ingot in FIG. 20A. This shows that the
interface between the 3003 alloy and 4343 alloy is well bonded.
[0085] In the present invention, the multiple layer ingot product
is not limited to two or three layers of alloys. The multiple layer
ingot product may have more than three layers of alloys.
[0086] The present invention therefore provides an apparatus and
method for producing directionally solidified ingots, and cooling
these ingots at a controlled, relatively constant cooling rate. The
invention provides the ability to cast crack-free ingots without
the need for stress relief. The method reduces or eliminates
macrosegregation, resulting in a uniform microstructure throughout
the ingot. The method further produces ingots having a
substantially uniform thickness, and which may be thinner than
ingots cast using other methods. The large surface area in contact
with the coolant results in relatively fast cooling, resulting in
higher productivity.
[0087] While specific embodiments of the invention has been
described in detail, it will be appreciated by those skilled in the
art that various modifications and alternatives to those details
could be developed in light of the overall teachings of the
disclosure. Accordingly, the particular arrangements disclosed are
meant to be illustrative only and not limiting as to the scope of
the invention which is to be given the full breadth of the appended
claims and any and all equivalents thereof.
* * * * *