U.S. patent application number 13/323118 was filed with the patent office on 2012-09-13 for variable-density preforms.
This patent application is currently assigned to FTF, LLC. Invention is credited to Robert G. Coleman, Dallas W. Jolley, JR., Josh E. Loukus, Charles Benjamin Rau, III.
Application Number | 20120227624 13/323118 |
Document ID | / |
Family ID | 39492609 |
Filed Date | 2012-09-13 |
United States Patent
Application |
20120227624 |
Kind Code |
A1 |
Loukus; Josh E. ; et
al. |
September 13, 2012 |
Variable-Density Preforms
Abstract
Provided are novel devices and methods for making a variable
density preform, the methods comprising obtaining a slurry
comprising a reinforcement particle component and a liquid
component; obtaining a die cavity having at least one inlet opening
and at least one exit opening defining at least one die cavity flow
path therebetween directed toward the exit opening, the at least
one exit opening suitably sized or configured to provide for exit
of the at least one liquid component while impeding or blocking
exit of the at least one reinforcement particle component; and
introducing the slurry under pressure, and for a sufficient time
period, through the inlet orifice into the die cavity flow path to
provide for a decreasing pressure gradient along the flow path
direction, to provide for a variable density of the at least one
particle component, the particle density increasing in the at least
one flow path direction.
Inventors: |
Loukus; Josh E.; (Calumet,
MI) ; Coleman; Robert G.; (Augusta, GA) ; Rau,
III; Charles Benjamin; (Gig Harbor, WA) ; Jolley,
JR.; Dallas W.; (University Place, WA) |
Assignee: |
FTF, LLC
Calumet
MI
|
Family ID: |
39492609 |
Appl. No.: |
13/323118 |
Filed: |
December 12, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11949720 |
Dec 3, 2007 |
8075827 |
|
|
13323118 |
|
|
|
|
60868301 |
Dec 1, 2006 |
|
|
|
Current U.S.
Class: |
106/122 ;
106/217.3; 249/105; 264/645 |
Current CPC
Class: |
C04B 35/806 20130101;
B22F 2998/10 20130101; C04B 41/5155 20130101; B22F 2999/00
20130101; B22F 2998/10 20130101; C04B 41/88 20130101; C04B 35/565
20130101; C04B 2111/00405 20130101; F16D 69/026 20130101; C04B
41/009 20130101; C04B 41/5155 20130101; B22F 2003/1054 20130101;
C04B 38/00 20130101; C04B 2111/00362 20130101; B22F 2999/00
20130101; B22F 2201/20 20130101; B22F 3/227 20130101; C04B 35/00
20130101; B22F 3/227 20130101; B22F 3/26 20130101; B22F 3/1025
20130101; C04B 41/009 20130101; C04B 41/009 20130101; B22F 2202/11
20130101; C04B 41/009 20130101; C04B 41/4523 20130101; B22F 3/1025
20130101; C04B 35/806 20130101; C04B 35/565 20130101; B22F 2202/01
20130101; B22F 2202/03 20130101; B22F 3/227 20130101; B22F 2999/00
20130101; C04B 38/00 20130101; C04B 41/009 20130101 |
Class at
Publication: |
106/122 ;
106/217.3; 249/105; 264/645 |
International
Class: |
C04B 35/64 20060101
C04B035/64; B28B 13/04 20060101 B28B013/04; C08L 3/04 20060101
C08L003/04 |
Claims
1. A preform comprising: at least one reinforcement particle
component, wherein the density of the at least one reinforcement
particle component increases in a gradient in at least one flowed
direction through the preform; and wherein the preform is made
using a method comprising: providing a slurry comprising the at
least one reinforcement particle component, and at least one liquid
component; providing a die cavity having at least one inlet opening
or orifice and at least one exit opening or orifice defining at
least one die cavity flow path therebetween directed toward the
exit opening or orifice, the at least one exit opening or orifice
suitably sized or configured to provide for exit of the at least
one liquid component while impeding or blocking exit of the at
least one reinforcement particle component; and introducing the
slurry under pressure, and for a sufficient time period, through
the inlet orifice into the flow path of the die cavity to provide
for a decreasing pressure gradient along the flow path direction,
wherein during said introducing the at least one liquid component
exits through the at least one exit orifice while the at least one
reinforcement particle component is impeded or blocked from exiting
through the at least one exit orifice, to provide a variable
density of the at least one particle component with the particle
density increasing in the gradient in the at least one flow path
direction.
2. An infiltration casting, comprising a preform according to claim
1.
3. A brake rotor or drum comprising a preform according to claim
1.
4. A preform comprising: at least one reinforcement particle
component, wherein the density of the at least one reinforcement
particle component increases in a gradient in at least one flowed
direction through the preform; wherein the preform is porous; and
wherein the preform is made using a method comprising: providing a
slurry comprising the at least one reinforcement particle
component, and at least one liquid component; providing a die
cavity having at least one inlet opening or orifice and at least
one exit opening or orifice defining at least one die cavity flow
path therebetween directed toward the exit opening or orifice, the
at least one exit opening or orifice suitably sized or configured
to provide for exit of the at least one liquid component while
impeding or blocking exit of the at least one reinforcement
particle component; introducing the slurry under pressure, and for
a sufficient time period, through the inlet orifice into the flow
path of the die cavity to provide for a decreasing pressure
gradient along the flow path direction, wherein during said
introducing the at least one liquid component exits through the at
least one exit orifice while the at least one reinforcement
particle component is impeded or blocked from exiting through the
at least one exit orifice, to provide a variable density of the at
least one particle component with the particle density increasing
in the gradient in the at least one flow path direction; drying the
preform to remove residual amounts of the at least one liquid
component; and firing or sintering the dried preform by heating it
to or at a temperature higher than the drying temperature; wherein
the slurry additionally comprises at least one fugitive or organic
binder component, and firing comprises heating the dried preform to
or at a temperature sufficient to effectively remove any residual
amounts of the at least one fugitive or organic binder
component.
5. An infiltration casting, comprising a preform according to claim
4.
6. A brake rotor or drum comprising a preform according to claim
4.
7. A die casting apparatus for casting a preform from a slurry
having at least one reinforcement particle component and at least
one liquid component, comprising: a die cavity having at least one
inlet opening or orifice and at least one exit opening or orifice
defining at least one die cavity flow path therebetween directed
toward the exit opening or orifice, the at least one exit opening
or orifice suitably sized or configured to provide for exit of at
least one liquid component of a slurry while impeding or blocking
exit of at least one reinforcement particle component of the
slurry.
8. The apparatus of claim 7, wherein the die cavity comprises at
least one centrally-positioned inlet orifice and at least one
circumferentially or perimetrically-positioned exit orifice
defining at least one radial flow path and direction.
9. The apparatus of claim 8, wherein the circumference or perimeter
of the die cavity comprises one or more exit openings or orifices
that individually or collectively extend continuously or
discontinuously around the circumference or perimeter of the die
cavity to provide for a concentric radial flow path extending 360
degrees around the at least one centrally positioned inlet orifice,
to provide for production of a variable-density preform with
increasing particle density in the radial direction.
10. The apparatus of claim 7, wherein the at least one exit opening
or orifice is configured to comprise or be in fluid communication
with a filtering element suitably sized or configured to provide
for exit of at least one liquid component of a slurry while
impeding or blocking exit of at least one reinforcement particle
component of the slurry.
11. The apparatus of claim 8, wherein the filtering element
comprises a plurality of effluent flow channels in open or fluid
communication with the filter to provide for variable effluent
flow/psi.
12. The apparatus of claim 9, wherein a plurality of the effluent
flow channels can be individually configured to be in open or fluid
communication with the filer element, and with the slurry flow path
within the die cavity.
Description
CROSS-REFERENCES
[0001] This application is a division of U.S. application Ser. No.
11/949,720, filed Dec. 3, 2007, which claims the benefit of U.S.
Provisional Application No. 60/868,301, filed Dec. 1, 2006, the
content each of which is hereby incorporated by reference in its
entirety.
FIELD
[0002] Certain aspects relate generally to reinforced composites
and reinforced castings, and more particularly to novel "preforms"
comprising a gradient or variable density of reinforcement
particles (e.g., ceramic particles), to novel lightweight
preform-reinforced composites and castings (e.g., brake drums, disk
brake rotors, cylinder liners, clutch parts, etc) comprising matrix
material infiltrated preforms, and to methods for making same.
BACKGROUND
[0003] Traditional materials (e.g., metals, plastics, ceramics,
resins, concrete, etc.) do not always provide components with all
the requisite properties sufficient for adequate performance under
field service conditions. Moreover, despite decades of intensive
research to provide improved methods and materials, substantial
demand still exists in many commercial and industrial applications
for improved technology and low-cost methods to improve final
component performance (e.g., enhanced strength, enhanced mechanical
behavior characteristics, weight reduction, improved wear
resistance, enhanced surface activity/reactivity and/or properties,
enhanced thermal conductivity, low and/or balanced and/or
controlled coefficients of thermal expansion (CTE), reduced
residual stress during the forming process and during thermal
cycling of reinforced components in service, enhanced recycle
potential, reduced fuel consumption, reduced pollutant emissions
and green house gases, etc).
[0004] Reinforcement of Traditional Materials.
[0005] Matrix composites generally refer to traditional materials
(material systems) comprising one or more discrete reinforcement
constituents (the reinforcement material(s)) distributed within a
continuous phase (the matrix material). The distinguishing
characteristics of such matrix composites derive from the
properties of the reinforcement constituent(s), from the
architectural shape and geometry of such constituent(s), and from
the properties of the interfaces between and among different
constituents and the matrix. In particular applications, prior art
forming and manufacturing processes are designed to provide a
uniform distribution of the reinforcement constituent in the
matrix. In alternate applications, the distribution of the
reinforcement constituent is non-uniform. For example, centrifugal
casting applications provide for gradient or layered distributions
of reinforcement constituent(s), but are impractical as discussed
below and are subject to Coriolis effects that preclude uniform
concentric particle density at any given radial position.
Additionally, applications comprising infiltration casting of
matrix materials into porous reinforcement "preforms," while not
providing for continuous gradients, nonetheless provide for
positioning of reinforcement constituent(s) within a defined
portion of a larger casting (i.e., placement of the preform at a
defined position within a casting). In both uniform and non-uniform
applications, it is important that there is an adequate bond formed
between the matrix material and the discrete reinforcing
constituent(s), without substantial degradation of the mechanical
properties of the reinforcing constituent(s). Particle
reinforcement is a preferred reinforcement constituent/material,
and typically comprises non-metallic and commonly ceramic particles
(e.g., SiC, Al.sub.2O.sub.3, etc.), but may comprise a variety of
particles and materials that provide advantages or reinforcement
for one or more properties of the matrix composite. Reinforcement
of matrix material with fibers, continuous-fibers, monofilament,
and/or short-fibers is also known in the art. Generally, different
types of matrix composites require or are preferably associated
with different primary processing routes/methods (e.g., in-situ
reactive processes, diffusion bonding, blending and consolidation,
vapor deposition and consolidation, liquid-state processing, stir
casting/slurry casting, centrifugal casting, and infiltration
processes involving infiltration of matrix material into porous
"preforms").
[0006] Deficiencies of the Art
[0007] Post-manufacture machining of matrix composite materials
comprising durable reinforcement can be time-consuming and
expensive, and near net-shape forming, and selective reinforcement
techniques have therefore been used to help reduce manufacturing
costs. For example, in situ selective reinforcement methods
involving placement and positioning of a pre-cast reinforcement
material member into a near net-shape casting mold, followed by
casting of matrix material around the reinforcement member is known
in the art. However, while the amount and/or density of pre-cast
reinforcement material can be varied as desired, the reinforcement
constituent material of the reinforcement members is not integrated
(not mixed or infiltrated) with the matrix material, except perhaps
in a limited extent at the interfacial boundaries between the
reinforcement member and the unreinforced matrix material.
Therefore, such in situ methods are hindered by abrupt and
problematic differential coefficients of thermal expansion (CTE)
between the matrix and reinforcement member. Such abrupt
transitions in CTE at the matrix:reinforcement interface boundaries
not only give rise to residual stress during the forming process
(e.g., residual stress-concentration), but also manifest in stress
fractures during thermal cycling of the reinforced components in
service.
[0008] Likewise, in another example, there are substantial
deficiencies in in situ selective reinforcement methods involving
infiltration casting of matrix material into porous "preforms"
(comprising reinforcement constituent(s)) positioned in near
net-shape casting molds. While such prior art "preform" methods are
fast, and result in a more integrated, infiltrated reinforcement
"preform" with substantially more contact area between the
reinforcement and matrix materials, they are still substantially
hindered/limited by abrupt transitions in CTE at the
interface/boundaries between the "preform" and the unreinforced
matrix material that results in stress problems as described above.
Additionally, there are practical limits to the amount/density of
reinforcement material in the porous "preforms," because resistance
to infiltration casting substantially increases at high
reinforcement levels (e.g. beyond 15% to 20% material in the
"preform"). Furthermore, while "preforms" are typically positioned
in casting molds that are preheated to facilitate infiltration,
such preheating, for practical reasons, is at a temperature
significantly less than the melting temperature of the molten
matrix material (e.g., aluminum). Therefore, there are practical
limits to the thickness/cross-sectional area of such prior art
preforms, because the matrix material must completely infiltrate
the "preform" prior to significant cooling of the molten matrix
material. Because of this, prior art "preforms" are typically not
thicker than about 0.400 inches, placing a practical limitation on
the extent of reinforcement that can be integrated into the
finished casting.
[0009] In yet another example, there are substantial deficiencies
in selective reinforcement methods involving centrifugal casting
(in near net-shape casting molds) of composite material to
favorably place or distribute reinforcement particles within a
matrix material of differing density (see, e.g., U.S. Pat. No.
5,980,792 to Chamlee). While abrupt transitions in CTE at the
matrix:reinforcement interface boundaries can be reduced in those
centrifugal embodiments where continuous particle gradients are
formed within the matrix material, such methods still suffer from
differential CTE effects in cost-effective embodiments comprising
layered reinforcement particles. Moreover, all centrifugal casting
embodiments (including that of U.S. Pat. No. 5,980,792) are
relatively slow (particularly when used with moderate to high
reinforcement particle densities) compared to other casting methods
(e.g., high pressure die casting, squeeze casting, etc.), and are
thus impractical and too expensive for most commercial
applications. Additionally, in centrifugal methods, the attainable
variations of particle distributions are limited to bands or layers
and/or continuous gradients, and if different reinforcement
particle types having differing densities are simultaneously used,
it may be impossible to get adequate coordinate (co-localized)
particle gradient distributions for the divergent particle types,
or to get the different particle types where they are needed, and
in the desired pattern.
[0010] In further examples, there are substantial deficiencies in
selective reinforcement methods involving deposition or spraying
(e.g., by low or high velocity spray techniques) of reinforcement
particles onto the surface of near net-shape matrix material
castings. A major limitation of such methods for these applications
is that the spray or deposition is superficial, because it is
applied to the surface of solid matrix material castings, and does
not substantially penetrate beyond the surface. Additionally, such
superficial reinforcement coatings must generally be significantly
machined prior to placing the reinforced casting into service.
Moreover, absent resurfacing with more reinforcement, the effective
service life of such castings is over once the superficial
reinforcement layer is worn and/or otherwise degraded. Furthermore,
in such superficial reinforcement applications, bonding and
integration of the sprayed/deposited reinforcement with the matrix
material is limited, even with the most optimal spray/deposition
methods.
[0011] In further examples, there are substantial deficiencies in
making functionally gradient materials having preforms made by
methods such as gelcasting methods (see, e.g., U.S. Pat. No.
6,375,877 to Lauf et al), where gravitational or centrifugal forces
are used to achieve a vertical composition gradient in molded
slurries to form gradient preforms, which may be subsequently
infiltrated. Like centrifugal casting embodiments (including that
of U.S. Pat. No. 5,980,792), such preform gelcasting methods are
relatively slow (particularly when used with high reinforcement
particle densities), and are thus too expensive and impractical for
most commercial applications. Additionally, in such gelcasting
gravitational or centrifugal methods, the attainable variations of
particle distributions are limited to layers and/or continuous
gradients, and if different reinforcement particle types having
differing densities are simultaneously desired/used, it may be
impossible to get adequate coordinate (co-localized) particle
gradient distributions for the divergent particle types, or to get
the different particle types where they are needed, and in the
desired pattern. Additionally, preforms made by such gelcasting
methods are substantially problematic because of excessive warpage
and anisotropic shrinkage occurring during the sintering stage
because of different sintering kinetics for the material
components. This is particularly true of gelcast preforms made from
slurries having less than 60% v. % total solids (see, e.g., U.S.
Pat. No. 6,375,877 to Lauf et al., at Example 1).
[0012] Therefore, there are substantial deficiencies in prior art
selective reinforcement composite material applications, including
but not limited to impracticality and lack of versatility (e.g.,
centrifugation methods), differential CTE problems (e.g., in situ
reinforcement member casting, in situ reinforcement "preform"
castings, layered centrifugation methods), limitations on "preform"
thickness/cross-section, superficiality problems (e.g., surface
spray/deposition methods), and impracticality and
warpage/anisotropric shrinkage problems (gelcasting methods).
Moreover, these deficiencies have substantially limited the scope
of current casting or forming crafts including, but not limited to:
centrifugal casting; high pressure die casting; vacuum die casting;
squeeze casting; high vacuum permanent mold casting; low vacuum
permanent mold casting; vacuum riserless/pressure riserless
casting, surface spray and deposition methods, etc.
[0013] There is, therefore, a pronounced need in the art for novel
and effective methods and compositions to increase the scope of
current selective reinforcement casting or forming crafts by making
the methods and compositions more practical (e.g., faster, more
cost effective, etc.), more versatile (in terms of the amount,
thickness, distribution, pattern and types of reinforcement
constituents that can be applied/used), and less susceptible to
mechanisms (e.g., differential CTE between materials) that give
rise to stress-fracture during formation and/or thermal cycling
during service conditions.
[0014] There is a pronounced need in the art for more effective
methods to produce functional gradient and non-gradient reinforced
composite materials with optimum and/or customized properties
(e.g., enhanced strength, enhanced mechanical behavior
characteristics, weight reduction, improved wear behavior, enhanced
surface reactivities and/or properties (e.g., enhanced reactivity
between a surface of a composite material and a friction material
interacting therewith), enhanced thermal conductivity, low and/or
balanced/controlled coefficients of thermal expansion (CTE),
reduced residual stress during the forming process and during
thermal cycling of reinforced components in service, enhanced
recycle potential, reduced fuel consumption, reduced pollutant
emissions and green house gases, etc).
[0015] There is a pronounced need for cost-effective,
high-throughput methods to make variable density preforms, and for
novel casting apparatus to make preforms and particularly variable
density preforms.
[0016] There is a pronounced need in the art for novel and improved
matrix composites (e.g., lightweight brake drums, disk brake
rotors, cylinder liners, etc.) comprising such preforms.
SUMMARY
[0017] Particular embodiments provide novel methods of making
preforms, and particularly variable density preforms. Certain
embodiments provide a variable density preform, comprising:
obtaining a slurry comprising at least one reinforcement particle
component, and at least one liquid component; obtaining a die
cavity having at least one inlet end or orifice and at least one
exit end or orifice defining at least one die cavity flow path
therebetween and a flow path direction toward the exit end or
orifice, the at least one exit end or orifice suitably sized or
configured to provide for exit of the at least one liquid component
while impeding or blocking exit of the at least one reinforcement
particle component; and introducing the slurry under pressure into
the inlet end or orifice, wherein the at least one exit end or
orifice is operative with the at least one die cavity and flow path
to provide for a decreasing pressure gradient along the flow path
and flow path direction, and wherein the introducing under pressure
is continued for a time sufficient to provide for a
variable-density preform having a variable density of the at least
one particle component, the particle density increasing in the at
least one flow path direction. In particular aspects, the
sufficient amount of time for introducing the slurry under pressure
is determined by measuring the pressure within the die cavity flow
path at at least one position, such as at or near the at least one
inlet end or orifice, at a position at or near the at least one
exit end or orifice, or at both ends or orifices of the flow path.
Certain embodiments comprise agitating or vibrating the die during
the introduction of the mixture. In particular aspects, vibrating
the die comprises broadband excitation of the die, and in certain
embodiments vibrating the die comprises inducing vibrations in the
die suitable to provide for inducing flow of the mixture to
extremities of the die cavity, and/or to increase the apparent
viscosity of rheopectic components of the mixture.
[0018] Specific exemplary aspects provide a method of making a
variable density preform, comprising: obtaining a slurry comprising
at least one reinforcement particle component, and at least one
liquid component; obtaining a die cavity having at least one inlet
opening or orifice and at least one exit opening or orifice
defining at least one die cavity flow path therebetween directed
toward the exit opening or orifice, the at least one exit opening
or orifice suitably sized or configured to provide for exit of the
at least one liquid component while impeding or blocking exit of
the at least one reinforcement particle component; and introducing
the slurry under pressure, and for a sufficient time period,
through the inlet orifice into the flow path of the die cavity to
provide for a decreasing pressure gradient along the flow path
direction, to provide for a variable-density preform having a
variable density of the at least one particle component, the
particle density increasing in the at least one flow path
direction. In certain embodiments, the sufficient amount of time
and the slurry injection pressure are selected to provide for a
linear or substantially linear gradient of a particular slurry.
Particular aspects comprise measuring the slurry injection pressure
at a position at or near the at least one inlet orifice, at a
position at or near the at least one exit orifice, or at both ends
of the flow path. Particular embodiments further comprise agitating
or vibrating the die during the introduction of the mixture. In
certain embodiments, vibrating the die comprises broadband
excitation of the die. In certain aspects, vibrating the die
comprises inducing vibrations in the die suitable to provide for at
least one of inducing flow of the mixture to extremities of the die
cavity, and to increase the apparent viscosity of rheopectic
components of the mixture. In particular embodiments, the die
cavity comprises at least one centrally-positioned inlet orifice
and at least one circumferentially or perimetrically-positioned
exit orifice defining at least one radial flow path and direction,
and vibrating the die comprises vibrating a die plate or die
portion in a manner that imparts broadband concentric vibration
emanating from a position at or near the center of the plate or
portion, and wherein the variable-density of the preform increases
in the at least one radial flow path direction. In certain aspects,
the circumference or perimeter of the die cavity comprises one or
more exit openings or orifices that individually or collectively
extend continuously or discontinuously around the circumference or
perimeter of the die cavity to provide for a concentric radial flow
path extending 360 degrees around the at least one centrally
positioned inlet orifice, and wherein the variable-density of the
preform increases in the radial flow path direction. Certain
embodiment of the method further comprise, during introduction
under pressure of the mixture into the die cavity, application of a
vacuum in fluid communication with the die cavity-distal side of
the at least one exit orifice. Certain aspects, further comprise
drying the preform to remove residual amounts of the at least one
liquid component. In particular embodiments, drying comprises use
of a convection oven and/or infra-red radiation. Certain aspects
further comprise, prior to drying, lowering the temperature of the
preform to a temperature sufficient to induce a phase transition of
the at least one liquid component. In certain aspects, the liquid
component comprises water, and the phase transition comprises
freezing or formation of ice. In particular embodiments, drying
comprises microwave drying. In particular embodiments, microwave
drying comprises microwave drying with convection or air
circulation. In particular embodiments, microwave drying comprises
microwave drying under a vacuum sufficient to reduce the pressure
in the microwave chamber to lower than atmospheric pressure.
Certain aspects further comprise firing or sintering the dried
preform by heating it to or at a temperature higher than the drying
temperature. In particular embodiments, the slurry additionally
comprises at least one fugitive or organic binder component, and
firing comprises heating the dried preform to or at a temperature
sufficient to effectively remove any residual amounts of the at
least one fugitive or organic binder component. In certain aspects,
firing comprises heating to or at about 982.degree. C.
(1,800.degree. F.) or greater. In certain embodiments, the
Reynold's number of the flowing slurry is less than 2,100. In
particular embodiments, the slurry additionally comprises at least
one component selected from the group consisting of a high
temperature or inorganic binder, and a fiber component.
[0019] Additional embodiments provide a preform made by the
disclosed processes, wherein the preform provides for a porous
preform after removal of organic binders or other fugitive
components. In particular embodiment the preform is a porous
preform.
[0020] Further embodiments provide a method of making an
infiltration casting, comprising infiltration of the inventive
preform with a molten matrix material. In particular aspects, the
molten matrix material is a metal or metal alloy. In certain
aspects, the metal and alloy comprise aluminum.
[0021] Yet further embodiments, provide an infiltration casting,
comprising a preform according to the disclosed methods.
[0022] Yet further embodiments, provide a brake rotor or drum
comprising an inventive preform.
[0023] Yet further embodiments, provide a die casting apparatus for
casting a preform from a slurry having at least one reinforcement
particle component and at least one liquid component, comprising: a
die cavity having at least one inlet opening or orifice and at
least one exit opening or orifice defining at least one die cavity
flow path therebetween directed toward the exit opening or orifice,
the at least one exit opening or orifice suitably sized or
configured to provide for exit of at least one liquid component of
a slurry while impeding or blocking exit of at least one
reinforcement particle component of the slurry. In particular
aspects, the die cavity comprises at least one centrally-positioned
inlet orifice and at least one circumferentially or
perimetrically-positioned exit orifice defining at least one radial
flow path and direction. In certain embodiments, the circumference
or perimeter of the die cavity comprises one or more exit openings
or orifices that individually or collectively extend continuously
or discontinuously around the circumference or perimeter of the die
cavity to provide for a concentric radial flow path extending 360
degrees around the at least one centrally positioned inlet orifice,
to provide for production of a variable-density preform with
increasing particle density in the radial direction. In particular
embodiments, the at least one exit opening or orifice is configured
to comprise or be in fluid communication with a filtering element
suitably sized or configured to provide for exit of at least one
liquid component of a slurry while impeding or blocking exit of at
least one reinforcement particle component of the slurry. In
certain aspects, the filtering element comprises a plurality of
effluent flow channels in open or fluid communication with the
filter to provide for variable effluent flow/psi. In particular
implementations, a plurality of the effluent flow channels can be
individually configured to be in open or fluid communication with
the filer element, and with the slurry flow path within the die
cavity.
[0024] Yet additional aspects, provide a method of making a preform
using a die casting apparatus according to the inventive disclosed
methods.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The following drawings illustrate particular embodiments of
the present invention and therefore do not limit the scope of the
invention. The drawings are not to scale (unless so stated) and are
intended for use in conjunction with the explanations in the
following detailed description. Embodiments of the present
invention will hereinafter be described in conjunction with the
appended drawings, wherein like numerals denote like elements.
[0026] FIG. 1 a shows a first effluent filtering die embodiment
showing a split die portion 10 of an exemplary annular die casting
apparatus (approx. 1/2 of the die) for manufacture of an inventive
variable density preform.
[0027] FIG. 1b shows an expanded view of the perimeter 6 of the
split annular die portion 10, showing a plurality of radially
oriented grooves or channels (exit orifices) 4 circumferentially
arranged around the perimeter 6, the grooves or channels suitably
sized and configured to permit exit of a liquid component of a
slurry while selectively or preferentially precluding or retarding
a reinforcement particle component of the slurry.
[0028] FIG. 2 shows, according to particular exemplary aspects of
the present invention, an exemplary die casting apparatus
embodiment for high-production (high-throughput) casting of
inventive preforms.
[0029] FIG. 3 shows, according to particular exemplary aspects of
the present invention, an expanded view of a section of the die
casting apparatus of FIG. 2.
[0030] FIG. 4 shows, according to particular exemplary aspects of
the present invention, a variable density preform made according to
the present inventive method.
[0031] FIG. 5 shows an exemplary preform slurry mixing station
according to aspects of the present invention.
[0032] FIG. 6 shows, in schematic form, the principal of variable
density preform formation according to particular aspects of the
present invention.
[0033] FIG. 7 shows a schematic of a preferred effluent filtering
die design embodiment for the manufacture of the inventive
functionally gradient preforms.
[0034] FIG. 8 is an expanded view of Detail "F" of FIG. 7.
[0035] FIG. 9 shows an expanded view of the effluent filtering die
of FIG. 7, where the die halves are separated.
[0036] FIG. 10 shows an expanded view of the effluent filtering die
of FIG. 7, where the die halves are operatively connected.
[0037] FIG. 11 shows an expanded view (Detail "H") of a section of
FIG. 10. Additionally shown is a preform ejector plate 68, and a
vibrator mounting hole 70.
[0038] FIG. 12 shows a perspective partial assembly view of an
exemplary effluent filtering die set in a press for commercial
production.
[0039] FIG. 13 shows a perspective cross-sectional partial assembly
view of the exemplary effluent filtering die set in a press for
commercial production show in FIG. 12.
[0040] FIG. 14 shows a detailed perspective cross-sectional partial
assembly view of the exemplary effluent filtering die set in a
press for commercial production show in FIGS. 12 and 13.
[0041] FIG. 15 shows shot profile data from an injection cycle
using an embodiment of the inventive preform effluent filtration
die press process and apparatus.
[0042] FIG. 16 shows an infiltration cast motorcycle disk brake
rotor embodiment comprising a particle gradient preform according
to aspects of the present invention. The outer rotor portion is
mounted to an internal carrier by means connecting buttons.
[0043] FIG. 17 shows the particle density variation in an
infiltration cast disk brake rotor embodiment comprising a particle
gradient preform according to aspects of the present invention.
[0044] FIGS. 18A, B and C show electron micrographs of the
inventive preform material at 700, 1,000 and 2,000 times
magnification, respectively.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0045] The following detailed description is exemplary in nature
and is not intended to limit the scope, applicability, or
configuration of the invention in any way. Rather, the following
description provides some practical illustrations for implementing
exemplary embodiments of the present invention. Examples of
constructions, materials, dimensions, and manufacturing processes
are provided for selected elements, and all other elements employ
that which is known to those of ordinary skill in the field of the
invention. Those skilled in the art will recognize that many of the
noted examples have a variety of suitable alternatives.
[0046] Particular aspects of the present invention provide novel
preforms, including variable density preforms, along with novel
methods and apparatus for making same. Aspects of the present
invention solve a long-standing problem in the art by providing,
for the first time, a cost effective, high-throughput method for
manufacturing preforms, including variable density preforms. In
particular embodiments, the variable densities achieved by the
present methods provide for preform applications including but not
limited to disc brake rotors and brake drums, wherein the variable
density aspect provides for enhanced performance of the matrix
composites. For example, disc brake rotors comprising the inventive
variable density preforms (e.g., having, for example, a variable
density of silicon carbide, etc) not only have increased wear
resistance, but also are more resistant to damaging friction and
heat effects (heat cracks, spalling, excessive wear, warping, etc.)
than non-variable density counterparts, particularly at positions
of greater radial distance on the rotor where the surface speed is
faster.
Preform Embodiments
[0047] Particular embodiments provide a method of making a variable
density preform, comprising: obtaining a slurry comprising at least
one reinforcement particle component, and at least one liquid
component; obtaining a die cavity having at least one inlet end or
orifice and at least one exit end or orifice defining at least one
die cavity flow path therebetween and a flow path direction toward
the exit end or orifice, the at least one exit end or orifice
suitably sized or configured to provide for exit of the at least
one liquid component while impeding or blocking exit of the at
least one reinforcement particle component; and introducing the
slurry under pressure into the inlet end or orifice, wherein the at
least one exit end or orifice is operative with the at least one
die cavity and flow path to provide for a decreasing pressure
gradient along the flow path and flow path direction, and wherein
the introducing under pressure is continued for a time sufficient
to provide for a variable-density preform having a variable density
of the at least one particle component, the particle density
increasing (e.g., continuously) in the at least one flow path
direction. In particular aspects, the sufficient amount of time for
introducing the slurry under pressure is determined by measuring
the pressure within the die cavity flow path at at least one
position, such as at or near the at least one inlet end or orifice,
at a position at or near the at least one exit end or orifice, or
at both ends or orifices of the flow path. Certain embodiments
comprise agitating or vibrating the die during the introduction of
the mixture. In particular aspects, vibrating the die comprises
broadband excitation of the die, and in certain embodiments
vibrating the die comprises inducing vibrations in the die suitable
to provide for inducing flow of the mixture to extremities of the
die cavity, and/or to increase the apparent viscosity of rheopectic
components of the mixture. The reinforcement particle density
gradients formed by the inventive methods can assume a variety of
shapes and may extend, for example from about 10% to about 70% or
greater, about 15% to about 65%, about 20% to about 60%, about 25%
to about 55%, about 30% to about 50%, about 35% to about 45%, or
shallower gradients. By stepped introduction of different slurries,
smoothed step gradient preforms can be made that smooths the
particle density transition between "steps" and thereby reducing
differential CTE effects and thermal loading aspects of the
preforms and casting comprising such preforms.
[0048] In particular embodiments, the at least one exit end or
orifice is operative with the at least one die cavity and flow path
to provide for a uniform or substantially uniform pressure along
the flow path and flow path direction, such that a uniform or
substantially uniform preform is obtained having a particle density
higher than that of the input slurry. The inventive process is
distinguished from the art, inter alia, because more process
parameters can be used and controlled to produce different
gradients for different applications (e.g., not just rotational
speed and temperature). For example, variations in the slurry
density, the flock size, the particle size, the particle/fiber
ratio, the vibration intensity, average volume fraction (with
pressure), etc. are used to produce an "engineered" reinforcement
having superior properties and uniformity.
[0049] In certain embodiments of the method, the die cavity
comprises at least one centrally-positioned inlet end or orifice
and at least one circumferentially or perimetrically-positioned
exit end or orifice defining at least one radial flow path and
direction. In certain aspects, vibrating the die comprises
vibrating a die plate or die portion in a manner that imparts
broadband concentric vibration emanating from the center of the
plate or portion, and wherein the variable-density of the preform
increases in the at least one radial flow path direction. In
certain aspects, the circumference or perimeter of the die cavity
comprises one or more exit orifices that individually or
collectively extend continuously or discontinuously around the
circumference or perimeter of the die cavity to provide for a
concentric radial flow path extending 360 degrees around the at
least one centrally positioned inlet end or orifice, and wherein
the variable-density of the preform increases in the radial flow
path direction. Such embodiments can provide variable gradient
disks or tubes (e.g., for use in application such as disk brake
rotors and brake drums).
[0050] In additional embodiments, the method further comprises,
during introduction under pressure of the mixture into the die
cavity, application of a vacuum in fluid communication with the die
cavity-distal side of the at least one exit end or orifice.
[0051] In yet further embodiments, the method further comprises
drying the preform to remove residual amounts of the at least one
liquid component. In certain aspects, drying comprises use of a
convection oven. In particular embodiments, the method further
comprises, prior to drying, lowering the temperature of the preform
to a temperature sufficient to induce a phase transition of the at
least one liquid component (e.g., freezing). In certain aspects,
the liquid component comprises water and the phase transition
comprises freezing or formation of ice (phase transition from
liquid to solid). In certain embodiments, drying comprises
microwave drying, and in particular aspects microwave drying
comprises microwave drying with convection or air circulation
and/or microwave drying under a vacuum sufficient to reduce the
pressure in the microwave chamber to lower than atmospheric
pressure.
[0052] Particular embodiments of the method further comprise firing
or sintering the dried preform by heating it to or at a temperature
higher than the drying temperature. In certain aspects such firing
or sintering comprises heating to or at about 982.degree. C.
(1,800.degree. F.) or greater. In certain embodiments, the slurry
additionally comprises at least one fugitive or organic binder
component, and firing comprises heating the dried preform to or at
a temperature sufficient to effectively remove any residual amounts
of the at least one fugitive or organic binder component to provide
for a porous preform. In particular aspects, the slurry
additionally comprises a high temperature or inorganic binder,
and/or a fiber component.
[0053] In certain aspects of the method, the flow properties of the
slurry within the die cavity are such that the Reynold's number of
the flowing slurry is less than 2100.
[0054] Additional embodiments provide novel preforms, including
porous preforms and porous variable density preforms made by the
inventive methods. Preferably, the preform comprises or consists of
a porous preform or a porous variable density preform.
[0055] Yet further embodiments provide a method of making an
infiltration casting or improved matrix composites (e.g.,
lightweight brake drums, disk brake rotors, cylinder liners, etc.),
comprising infiltration of the inventive porous preforms with a
molten matrix material. In certain aspects, the molten matrix
material is a metal or metal alloy. Preferably, the metal and/or
alloy comprises aluminum.
[0056] Yet additional embodiment provide infiltration castings or
improved matrix composites (e.g., lightweight brake drums, disk
brake rotors, cylinder liners, etc.), comprising an infiltrated
preform according to the present disclosure.
[0057] Yet further embodiments provide a high-throughput preform
die casting apparatus as disclosed and described herein, and
methods for making the inventive preforms with the inventive
preform die casting apparatus.
DEFINITIONS
[0058] The term "slurry" as used herein refers to a fluid mixture
such as a solution, colloidal mixture or colloidal suspension,
comprising at least one particle component (e.g., inorganic
particle component), at least one "fugitive" "(e.g., organic)
binder component, and at least one liquid component, the mixture
having an average particle density. The slurry may optionally
include other components such as fiber components (e.g., ceramic
fibers, CERACHEM.RTM. ceramic fibers) and high temperature binder
components (e.g., inorganic binder components).
[0059] The term "reinforcement particle component" as used herein
refers to essentially any reinforcement particle for which a
variable density distribution is sought, and encompasses
reinforcement particles (e.g., inorganic particles) to provide
strength, durability or some other reinforcement characteristic to
the preform. Such particles include, but are not limited to silicon
carbide (SiC) particles/powders, alumina (Al.sub.2O.sub.3)
particles/powders, mullite (e.g., 3Al..sub.2O.sub.32SiO.sub.2 with
optional additions such as additions of Zr.sub.2O and SiC)
particles/powders, Boron carbide (B.sub.4C) Boron nitride (BN;
c-BN, h-BN), calcined alumina-silica particles/powders (45-55 to
80-20 Alumina-silica ratio), any suitable (e.g., dense, hard, and
stable) ceramic or metal material, silicon metal particles/powders,
etc. Such particles can be of a variety of densities and particle
sizes. In particular aspects particle/powder sizes is about 59 to
about 5 microns, or about 75 to about 45 microns, or about 25 to
about 5 microns in diameter. In particular aspects (e.g., the
slurries) the particles are present at a particular density or
volume fraction or average volume fraction (% reinforcement
material at the material composition selected), or preferably vary
(variable density) across an aspect or direction of the preform.
For example, in the case of a annular composition such as a brake
rotor preform, the particle density variation between the outside
and inside diameter (in terms of volume fraction) may, in certain
aspects, be about 50% V to 25% V, or about 60% V to about 20% V, or
about 30% V to about 10% V.
[0060] The term "fugitive binder" as used herein refers to a binder
characterized as being selectively modifiable, degradable, or
removable from the preform material by virtue of being susceptible
to a respective modifying, degrading, or removing means. For
example, organic binders include those that can be modified,
degraded and/or removed by the application of sufficient heat
(e.g., by firing or sintering).
[0061] The term "inorganic binder" as used herein refers to
inorganic particles that can serve to bind the slurry components,
particularly in the cast preform, and particularly even at high
temperatures (e.g., high temperature binders), where organic binder
fail or are degraded/removed. For example, colloidal silica,
consisting of a dispersion of amorphous silica particles can be
used as an inorganic binder (e.g., comprising silica particle sizes
of the order of less than about 100 nanometers). Other suitable
inorganic binders include, for example, phosphate binders, and
combination binders, such as aluminum/phosphate binders. Such
inorganic binders may serve as surfactants and are used for
flocculating, coagulating, dispersing, stabilizing, etc., even at
high temperatures.
[0062] The term "fiber component" as used herein refers to a
reinforcement fiber, including but not limited to ceramic fibers
(e.g., Al.sub.2O.sub.3--35%; SiO.sub.2--50%; ZrO.sub.2--15% by
weight preferred; optionally 99% Al.sub.2O.sub.3 by weight, or
fibers that are composed of a mixture of at least two components
selected from the group consisting of silica, calcia, magnesia,
iron oxides, sodium oxide, or boron oxide; where a "shot" content
of less than 5% ceramic fiber by weight is preferred, or
alternatively a shot content of 0 to about 60% by weight, with a
shot Size of 100%--44 microns preferred, or a shot size of about
98% 212 microns is possible), glass and polycrystalline fibers,
CERACHEM.RTM. ceramic fibers, KAOWOOL.RTM. alumina-silica fibers,
SUPERWOOL.RTM. soluble vitreous fibers (silica-calcium
oxide-magnesium oxide), SAFFIL.RTM. polycrystalline fibers (mullite
or high alumina chemistry), alumina fibers, basalt fibers, silica
fibers, glass fibers, etc.
[0063] The term "infiltration casting" as used herein refers to
various art recognized methods of introducing liquid matrix
materials (e.g., metals, etc.) into porous matrices of
reinforcement material (e.g., rigid porous "preforms," fabric,
etc.), including as described herein, into the instant preforms and
variable density preforms. The inventive methods encompass any
appropriate means for such introduction of liquid matrix material,
including but not limited to centrifugal casting; high pressure die
casting; vacuum die casting; squeeze casting; high vacuum permanent
mold casting; low vacuum permanent mold casting; vacuum
riserless/pressure riserless casting, surface spray and deposition
methods, etc.
[0064] A "preform," "porous preform," "variable density preform" or
"porous variable density preform" as used herein refers to the
inventive "preforms" suitable for infiltration casting and include,
but are not limited to: porous variable density ceramic preforms
that contain ceramic particles; porous variable density ceramic
hybrid preforms that contain ceramic fibers and particles; ceramic
matrix composites; carbon graphite foam "preforms," pre-cast
Duralcan or other MMC materials formed into a wear liner, etc. In
particular aspects, ceramic variable density "preforms" will
comprise ceramic particles to reinforce, strengthen, and increase
the wear/abrasive resistance of the cast part. Hybrid ceramic
variable density "preforms" may contain both ceramic particle and
fibers, which preferably should not shrink during the firing
process (the sintering process that completes the manufacture of
the preform). Carbon graphite foam-containing variable density
"preforms" may contain silicon carbide particles, and may be
produced so that carbon nanotubes are created during manufacturing
thereof to increase the ultimate strength of the final part.
Variable density "Preforms" may be created with functional gradient
porosity, which means that during the variable density preform
forming process, or during the drying or sintering process, pores
of varying sizes are created within the structure of the variable
density preforms (or the density of pores may vary to form a
gradient). Such porosity gradients can be either continuous, step,
or combinations and/or gradations therebetween. The purpose of the
functional gradient porosity is to facilitate complete infiltration
of the preform and to reduce the abrupt decrease in CTE at the
intersection of the unreinforced and reinforced area. This is
accomplished, for example in the context of a wear surface
embodiment (e.g., brake drum, disk, cylinder liner, etc), by
forming a variable density preform having pores on the
matrix-proximal side of the variable density preform that are
larger than the pores present in the interior of the variable
density preform or at the wear surface side of the variable density
preform. Alternatively, the pore size could be consistently large
throughout the variable density preform, for example, sufficiently
large to assist in accomplish the softening of the changes in CTE.
Preferably, by design, the variable density "preforms," whether
ceramic, carbon graphite foam-based (or other composite fiber
based) have a porosity (window holes) characteristic.
Significantly, according to particular aspects of the present
invention, the manufacturing procedure for the "preform" material
is altered to provide areas or gradients of higher or lower
quantity or percentage of porosity (window holes). A denser
"preform" typically comprises less porosity (smaller window holes).
According to preferred aspects, the inventive high-pressure
die-cast selectively reinforced composites comprising the inventive
variable density "preforms" equal or exceed the desired physical
strengths normally associated with the traditional forging
techniques. Additionally, and significantly, the inventive
selectively reinforced composites comprise additional improvements
to address coefficient of thermal expansion (CTE) issues, which
could result in residual stress at the interface between an abrupt
edge or end of a variable density reinforcement "preform" and the
un-reinforced aluminum, etc. Therefore, in particularly preferred
embodiments a porosity (window holes) gradient is present in the
variable density "preform," which have larger pores on at least one
outer surface of the variable density "preform" (i.e. the surface
next to an interface with the un-reinforced aluminum. Particular
aspects of the invention thus provide for a gradual, smoothed
transition from more porous, less dense "preform" material (larger
or more numerous window holes) to more dense "preform" material
(smaller or less numerous window holes). This smoothed porosity
gradient is associated with a complementary gradient of infiltrated
aluminum. The materials gradients created, therefore, obviate the
"residual stresses" otherwise encountered at an abrupt interface
between the "preform" and the un-reinforced aluminum (or other
infiltration material). The gradual change in window hole porosity
provides for particularly beneficial CTE properties in high
temperature applications involving substantial heat cycling (e.g.,
truck wheels, brake disks, etc.). The potential of crack formations
from residual stress due to abrupt transitions between materials
having mismatched CTE values is substantially reduced or
eliminated. Additionally, the "preform" porosity gradient provides
for less capillary action resistance during infiltration casting of
the metal or resin that is forced under pressure during casting
procedures. Porosity gradient preforms are described by Rau et al
(WO2007033378, incorporated herein by reference in its
entirety).
[0065] "Selective particle enhancement" or "SPE" as used herein
refers to a preferred process described herein where, prior to
infiltration casting, a porous variable density reinforcement
"preform" (or porosity gradient reinforcement "preform") is
subjected to "selective particle enhancement" (SPE) involving
directed deposition/impingement of selected particles on and/or
penetrating into the porous variable density "preform" material to
provide for selected particle impingement and integration (e.g.,
extending to a desired depth) within the porous variable density
"preform." Either "green" or sintered preforms may be so treated.
Preferably, the type of particle or particles used for SPE are
selected to impart one or more particular characteristics to the
resulting infiltration cast, selectively reinforced composite
product. More than one type of particle may be used, particles may
have differing properties, sizes, shapes, and densities, and
different particle impingement/integration patterns/designs and
combinations are encompassed within the present scope. SPE is
described by Rau et al., supra.
[0066] "Selective particle gradient enhancement" or "SPGE" as used
herein refers to a process described herein where, prior to
infiltration casting, a porous variable density reinforcement
"preform" (or porosity gradient variable density reinforcement
"preforms") is subjected to "selective particle gradient
enhancement" (SPGE) involving directed deposition/impingement of a
gradient of selected particles on and/or penetrating into the
porous variable density "preform" material to provide for particle
gradient integration (e.g., extending to a desired depth) within
the porous "preform." Either "green" or scintered preforms may be
so treated. The direction of such SPGE gradient may be transverse
or at an angle with respect to the variable density gradient
direction. More than one type of particle may be used, particles
may have differing properties, sizes, shapes and densities, and
different particle impingement/integration patterns/designs and
combinations are encompassed within the present scope. Such SPGE
gradients may be continuous gradients, step gradients, or
combination or gradations thereof SGPE is described by Rau et al.,
supra.
[0067] Variable Density Preform Embodiments Optionally Having
Porosity Gradient and/or Specific Particle Enhancement (SPE):
[0068] Particular aspects provide novel selectively reinforced
composite materials and methods for making same involving
infiltration casting of liquid matrix material (e.g., aluminum,
aluminum alloys, etc.) into porous variable density "preforms"
comprising one or more reinforcement constituents (e.g., SiC,
Al.sub.2O.sub.3, etc.). In particular embodiments, the porous
variable density "preforms" comprise at least one porosity
gradient, with either the pore number or pore size, or both
increasing toward at least one "preform" surface.
[0069] In particular embodiments, prior to infiltration casting,
the porous variable density reinforcement "preforms" (with or
without the presence of a porosity gradient) are subjected to
"selective particle enhancement" (SPE) involving directed
deposition/impingement of selected enhancement particles on and/or
penetrating into the porous variable density "preform" material to
provide for selected particle deposition/impingement and
integration extending to a desired depth within the porous variable
density "preform." Essentially any type of particle or particles
is/are used for SPE, and are preferably selected to impart one or
more particular desired properties or characteristics to the
resulting infiltration cast, selectively reinforced composite
product. In particular gradient SPE aspects (i.e., selective
particle gradient enhancement; "SPGE"), such SPGE comprises SPE by
applying a gradient of deposited/impinged particles. This SPGE
particle gradient is distinguished from the variable density
otherwise described herein the in the instant, die-cast variable
density preforms, and from any "porosity gradient" that may
optionally be present within the preform or any variable density.
The inventive methods are broadly applicable to the fabrication of
selectively reinforced composite products including but not limited
to wheels (e.g., cars, trucks, trains, etc), brake drums (e.g.,
cars, trucks, etc.), disk brake rotors, cylinder liners and/or
cylinder blocks, clutch parts (e.g., pressure plate, center plate,
etc), armor (e.g., body armor, field armor), etc. Preferred aspects
encompass fabrication of lightweight reinforced composite products,
and methods for make same.
[0070] Particular exemplary aspects provide novel lightweight
selectively reinforced composite disk brake rotors, and methods for
making same. Preferred aspects provide novel lightweight
selectively reinforced disc brake rotors, having one or more
integrated annular wear plates comprising in each case a variable
density or porous variable density "preform" into which matrix
material has been infiltrated. Preferably, prior to infiltration
casting, the variable density or porous variable density
reinforcement "preforms" (or porosity gradient variable density
reinforcement "preforms") are subjected to SPE as described herein.
Preferably, the type of particle or particles used for SPE are
selected to impart one or more particular characteristics to the
resulting infiltration cast, selectively reinforced composite
product. In particular aspects, such SPE comprises SPGE. In
particular embodiments, the variable density or porous variable
density "preforms" comprise at least one porosity gradient, with
either the pore number or pore size, or both increasing toward at
least one "preform" surface.
[0071] Particular aspects provide novel lightweight selectively
reinforced brake drums and methods for making same. In preferred
aspects the inner tubular members are variable density or porous
variable density preforms as described herein, that are integral to
the drum, having, for example been infiltration cast in casting of
the drum. Particular exemplary aspects provide novel lightweight
selectively reinforced brake drums, having an integrated inner
tubular member (wear liner) comprising a tubular variable density
or porous variable density "preform" into which matrix
material--has been infiltrated, and wherein the "preform optionally
comprises reinforcement wrapping (continuous or discontinuous),
integrated therein or on the exterior surface, to inhibit expansion
of the inner member. Preferably, prior to infiltration casting, the
variable density or porous variable density reinforcement
"preforms" (or porosity gradient variable density reinforcement
"preforms") are subjected to SPE as described herein. Preferably,
the type of particle or particles used for SPE are selected to
impart one or more particular characteristics to the resulting
infiltration cast, selectively reinforced composite product. In
particular aspects, such SPE comprises SPGE. In particular
embodiments, the variable density or porous variable density
"preforms" comprise at least one porosity gradient, with either the
pore number or pore size, or both increasing toward at least one
"preform."
[0072] Yet further embodiments provide for novel lightweight
selectively reinforced composite cylinder liners and/or cylinder
blocks or portions thereof, having integrated cylinder liners, and
methods for making same. Preferred aspects provide novel
lightweight selectively reinforced cylinder liners and/or cylinder
blocks, having one or more integrated cylinder liners comprising in
each case a variable density or porous variable density "preform"
into which molten matrix material has been infiltrated. Preferably,
prior to infiltration casting, the variable density or porous
variable density reinforcement "preforms" (or porosity gradient
variable density reinforcement "preforms") are subjected to SPE as
described herein. Preferably, the type of particle or particles
used for SPE are selected to impart one or more particular
characteristics to the resulting infiltration cast, selectively
reinforced composite product. In particular aspects, such SPE
comprises SPGE. In certain embodiments, the variable density or
porous variable density "preforms" comprise at least one porosity
gradient, with either the pore number or pore size, or both
increasing toward at least one "preform" surface.
[0073] Likewise, selectively reinforced composite clutch disk,
clutch pressure plate, and armor (e.g., field armor and body armor)
embodiments are encompassed within the scope of the present
invention and preferably comprise infiltrated variable density
preforms that have been subjected to SPE or SPGE, as defined
herein, and optional may comprise variable density preforms having
at least one porosity gradient.
[0074] In particular embodiments, disk brake rotor, the brake drum,
cylinder liner, clutch center plate, clutch pressure plate and
armor (e.g., field, body, etc.) embodiments comprise the use of
variable density or porous variable density "preforms" (or porosity
gradient variable density "preforms") comprising carbon graphite
foam, which has high thermal and electrical conductivity.
[0075] Aspects of the present invention provide novel and
substantially improved selectively reinforced matrix composite
castings and products, and methods for making same. Exemplary
embodiments provide novel selectively reinforced matrix composite
products including but not limited to wheels (e.g., cars, trucks,
trains, etc), brake drums (e.g., cars, trucks, etc.), disk brake
rotors, cylinder liners and/or cylinder blocks, clutch parts (e.g.,
pressure plate, center plate, etc), armor (e.g., body armor, field
armor), etc.
[0076] Matrix composites that contain mechanically inhomogeneous
multiphase materials (e.g., matrix composites comprising discrete
constituent reinforcement) are susceptible to stress/strain damage
mechanisms either during the manufacturing forming/solidification
process, and/or during thermal cycling under service. Certain
aspects of the present invention relate generally to novel cost
effective methods of improving fabrication, wear properties, and
the behavior (e.g., mechanical behavior) of, and reducing or
optimizing the coefficient of thermal expansion (CTE) differentials
in matrix composite materials, particularly those behaviors and/or
CTE differentials within, and between the two-face boundary
interface of selectively reinforced matrix composites comprising
infiltrated porous variable "preforms" (e.g., rigid porous
"preforms") utilized in the manufacture of exemplary matrix
composites.
[0077] Particular aspects provide novel selectively reinforced
composite materials and methods for making same involving
infiltration casting of liquid continuous phase matrix material
(e.g., non-ferrous metals such as aluminum, aluminum alloys,
magnesium, magnesium alloys, titanium, titanium alloys, zinc
alloys, copper, or resins/epoxies, polymers, plastics, various
blends of concrete/cement, etc.) into porous variable density
"preforms" (e.g., with defined shapes) comprising one or more
reinforcement constituents (e.g., SiC, Al.sub.2O.sub.3, etc.).
Various art-recognized means can be used to infiltrate the
continuous phase matrix material, in a liquid state, into the
porous pre-forms, and such means include but are not limited to use
of low/high vacuum, low/high pressure, gravity, or induced
centrifugal force (e.g., centrifugal casting, high pressure die
casting, vacuum die casting, squeeze casting, high vacuum permanent
mold casting, low vacuum permanent mold casting, vacuum
riserless/pressure riserless casting, etc.). Exemplary porous rigid
preform materials (reinforcement) include but are not limited to
ceramics, carbon graphite foam, metallic foam, concrete and other
fibrous composites. Typical preferred porous rigid pre-forms
comprise a material system comprised of binders and multiphase
(discrete reinforcement constituent(s)) materials in various volume
fractions. Particular porous rigid variable density "preforms"
contain open-cell porosity (window holes). In preferred porous
variable density "preform" embodiments, at least one porosity
(window hole) gradient (or a series of stepped, functionally
gradient porosity (FGP) layers) is present with either the pore
number or pore size, or both generally increasing toward at least
one variable density "preform" surface, so that there are
significantly larger pores on one or more outer surfaces of the
"preform" (e.g., the surface next to an interface boundaries
between "preform" surface and the un-reinforced continuous phase
matrix material) relative to, for example, the variable density
"preform" interior or the wear surface area (with friction surface
embodiments).
[0078] Selective Particle Enhancement ("SPE"). According to
particularly preferred aspects, prior to infiltration casting, the
porous reinforcement variable density "preforms" (or porosity
gradient, or porosity layered reinforcement variable density
"preforms") are subjected to "selective particle enhancement" (SPE)
involving directed deposition/impingement of selected particles on
and penetrating into the porous variable density "preform" material
to provide for selected particle impingement and integration
extending to a desired depth within the porous variable density
"preform." Preferably, the type of particle or particles used for
SPE are selected to impart one or more particular characteristics
to the resulting selectively reinforced composite infiltration cast
product. In particular aspects, such SPE comprises SPE with a
gradient of deposited/impinged particles (i.e., selective particle
gradient enhancement; "SPGE"). SPGE involves directed
deposition/impingement of a gradient of selected particles on and
penetrating into the porous "preform" material to provide for
particle gradient integration extending to a desired depth within
the porous "preform." The direction of such a SPGE gradient may be
at an angle or transverse to the direction of the inventive
variable density gradient.
[0079] In particularly preferred embodiments, a controllable
high-velocity deposition/impingement technique (e.g. adjustable
high velocity particle "gun") is used to apply selected particles
(SPE) (with significant characteristics that are similar or
dissimilar) to porous rigid variable density "pre-form" (comprising
reinforcement material with or without functionally gradient
porosity (FGP)) prior to infiltration casting thereof. Preferred
particle application methods for SPE or SPGE are those
art-recognized automated or automatable methods that are precise
and accurate, including but not limited to: cold spray deposition;
combustion power spray; high velocity/low velocity oxygen fuel
(HVOF/LVOF); plasma spray arc; combustion wire spray; chemical
vapor deposition (CVD); physical vapor deposition (PVD), etc.
[0080] Different particle impingement/integration patterns/designs
and combinations are encompassed. Additionally, a very broad range,
and more than one type of particle may be used for SPE and SPGE,
include particles having differing chemical compositions,
properties and densities. Exemplary materials for particles
include, but are not limited to: Silicon Carbide (SiC); Silicon;
Alumina Oxides (Al.sub.2O.sub.3); Mangesium oxide; Tungsten
Carbides; Chromium Carbide; Carbon Diamond; Polycrystalline
Diamond; Nickel; Copper; Zinc; Titanium Boride; fibrous material
(e.g., acrylic fibers, aramid fibers, glass fibers, silica fibers,
carbon fibers, metallic fibers, mineral fibers, carbon graphite
foam, and mixtures thereof); carbonaceous material (e.g., petroleum
coke, metallurgical coke, natural carbon, synthetic carbon and
mixtures thereof); iron powder; inert fillers (e.g., whiting, talc,
barytes, clays and mixtures thereof) and binders (e.g., resinous
binders); metal sulfide-iron powder alloy; metal sulfides,
including but not limited to ZnS, FeS, MoS.sub.2, CuS.sub.2, TiS,
CdS, Sb.sub.2S.sub.3, MnS, CoS, Co.sub.3S.sub.4, CaS, BaS, SrS,
FeS.sub.2, ZrS.sub.2, Cu.sub.2S, Ni.sub.3S.sub.2, NiS,
Ni.sub.3S.sub.4, MnS.sub.2, CoS.sub.2, Co.sub.2S.sub.3, SnS; etc.
For example, according to particular aspects of the present
invention SPE, of "preform" surfaces that represent operational
friction surfaces (e.g., friction surfaces in brake drums and disc
brake rotor embodiments, etc.), using metal sulfides or metal
sulfide-iron powder alloys will provide for enhanced functional
communication between the selectively reinforced matrix composite
friction surface and the friction material of typical brake pads,
resulting in substantially decrease stopping distances that will be
required, for example, to meet upcoming regulatory deadlines for
improved braking in the trucking industry (The National Highway
Transportation Safety Administration is poised to recommend that
heavy duty brakes provide for a 30% reduction in stopping
distances).
[0081] Functional Improvements.
Through the inventive application of infiltration casting of porous
variable density "preforms," functionally gradient porosity (FGP)
variable density "preforms" (or variable density "preforms" with
stepped FGP gradient/layers), and preferably using such "preforms"
in combination with selective particle enhancement (SPE, or SPGE),
long-standing problems with selectively reinforced matrix
composites, such as differential CTE effects, interface debonding,
nucleated inclusions, and phenomena such as constraint/deformation
mechanisms are reduced or effectively eliminated. The effect of
thermal residual stress and growth effects in the base matrix
material are likewise improved. The novel selective particle
enhancement (SPE) utilized in combination with infiltration casting
of porous variable density "preforms" is a substantial improvement
in the overall mechanical behavior and performance of selectively
reinforced matrix composites. Mechanical behavior, coefficients of
thermal expansion (CTE) differentials, concentration of stresses,
and cost-effective methods of manufacture are improved. Likewise,
improvements of weight reduction, wear behavior, and recyclability
provide for effective, efficient products that reduce fuel
consumption, and pollutant emissions including green house
gases.
[0082] In particular, residual stress created during the
manufacturing process of forming and solidification is
substantially reduced, and stress damage due to thermal cycling
during service is substantially reduced. In preferred aspects, SPE,
and particularly SPGE treatment of porous variable density preforms
(having a relatively low CTE value) is used to deposit/impinge a
material (e.g. particle material) having a CTE value that is
intermediate between that of the infiltrated "preform" and the
continuous matrix material. For example, where 356 aluminum alloy
is used for the matrix material, and ceramic variable density
"preforms" (with or without functional gradient porosity (FGP) or
FGF layers) are used, SPGE is used to integrate 390 or 398 aluminum
alloy particles (having an intermediate CTE value), or a gradient
thereof, into the variable density "preform" prior to infiltration
of the variable density "preform" with 356 matrix material. A
gradual smooth CTE value transition is thereby established across
what would otherwise be a two-face boundary interface between the
unreinforced matrix material and the "preform." Generally, any type
of particles that provide intermediate CTE transition/buffering, or
that enhance bonding between the matrix material and the "preform"
are suitable for these inventive aspects. This CTE smoothing and/or
enhanced bonding is particular effective when SPGE is combined with
the use of functional gradient porosity (FGP) variable density
"preforms," or FGF layered variable density "preforms," because
mechanical differential issues are relaxed more efficiently by an
increased presence and microplasticity of the continuous phase
matrix material (because of the larger or more numerous pores at
the interface "preform" surface). According to additional aspects,
relative to non-porosity gradient porous variable density
"preforms," the use of porosity gradient variable density
"preforms" allows for improved SPE penetration/impingement, and
also for improved infiltration casting.
[0083] The properties of the two-face boundary interface become
increasingly important as multiphase materials (discrete
constituent reinforcement), usually ceramic, are introduced in
making matrix composites (e.g., metal matrix composites (MMC) that
can be used at medium and high temperatures). However, when metal
matrix composites (MMC) are fabricated at high temperatures and
subsequently cooled to room temperature, residual stresses are
induced in the composite due to the general mis-match of the
thermal expansion coefficients (CTE) between the continuous phase
matrix material and the reinforcements (discrete constituents)
matrix composite component when exposed to thermal cycling.
Therefore, the inventive methods to relax mechanical differential
issues within the preform area, and at the two-face boundary
interface using SPE or SPGE are particularly beneficial for such
applications.
[0084] In addition, the inventive methods comprising SPE and SPGE
of porous variable density "preforms" allow for, if desired,
coordinate (co-localized) particle gradient distributions for
divergent particle types, or to get various particle types where
needed or desired, and in the desired or optimal pattern and/or
gradient/distribution. Significantly, the present inventive methods
remove a major limitation of prior art methods for these
applications; namely that prior art spray or deposition methods
comprise relatively superficial, non-penetrating particle
applications that not only must generally be machined prior to
placing the reinforced casting into service, but also, absent
resurfacing with more reinforcement, wear out relatively quickly.
By contrast, the present methods provide substantial versatility
selecting different particle combinations, patterns, and extent of
penetration/impingement (integration) into the porous variable
density "preforms." In particularly preferred wear surface
embodiments (e.g., brake drums, disk brake rotors, cylinder liners,
etc.), the inventive methods allow for directed deposition of one
or more particle types, in essentially any desired pattern and/or
gradient, and further provide for particle integration/impingement
to depths that correspond to, for example, the effective wear depth
of the matrix composite part.
[0085] As discussed herein above, suitable infiltration casting
methods include, but are not limited to high pressure vacuum die
casting, squeeze casting, or any other method that can result in
complete infiltration of the variable density preform. In preferred
embodiments, the infiltration casting method comprises indirect
squeeze infiltration of porous rigid preforms on a shot-control
high-pressure die casting machine.
[0086] For example, according to preferred aspects of the present
invention, the production of high quality selectively reinforced
aluminum based metal matrix composite reinforced composite brake
drums, brake rotors, clutch wear plates, cylinder liners,
commercial wheels or other components, where high wear resistance
or high strength are required, can be reproducibly and efficiently
produced via indirect squeeze pressurized liquid metal infiltration
of ceramic or carbon graphite foam variable density "preforms" on a
shot-control commercial die casting machine.
[0087] Preferably, to best accomplish this, the processes of a
shot-control commercial die-casting machine are optimized. Typical
exemplary processing parameters to be optimized are as follows:
preform preheat and melt superheat are preferably adjusted to
preclude premature melt solidification before and during
infiltration; infiltration speed is preferably controlled to avoid
permanent deformation of the ceramic, carbon graphite foam, or
other variable density preforms; the maximum pressure available on
the die caster is preferably deployed to minimize non-infiltration
defects; the gating system is preferably designed to ensure feeding
of the solidification shrinkage in the composite casting, etc.
Vacuum may be employed to reduce or eliminate voids.
[0088] A variable density "preform" with optimized properties is
preferred to provide for complete metal infiltration. For a
finished component where repeated thermal cycling occurs, the
coefficient of thermal expansion differential between the
selectively reinforced area of the component and the unreinforced
area could result in component failure. Therefore, in preferred
embodiments, the forming of a variable density preform with larger
pores at the reinforced and unreinforced interface will assist in
providing for a better transition for gradual decrease in thermal
expansion within the reinforced area, and is preferred for
long-term part integrity. Preferably, such porosity gradient
variable density "preforms" are used in combination with the
disclosed SPE and SPGE aspects to substantially further improve
smoothing of differential CTE values at the interface. Therefore, a
functionally gradient porosity variable density "preform," and in
particular such a preform in combination with SPE and/or SPGE
treatment is a particularly preferred component of such parts as
brake drums, brake rotors, clutch plates, and other parts subject
to large variations in operating temperatures during initial
fabrication and/or service conditions.
[0089] In additional SPE and/or SPGE aspects, an increase in the
quantity of reinforcement particles (e.g., silicon carbide,
alumina, titanium oxide, etc.) towards the wear surface of the part
provides for optimal wear characteristics, because the wear
resistance particles are selectively applied and concentrated
at/deposited in/integrated into (preferable to a depth equal to the
effective service wear depth of the part) the wear surface/working
surface.
Example 1
Novel Variable Density Preforms were Made by an Inventive Preform
Die Casting Process
[0090] This example describes an exemplary method embodiment for
making a novel variable density preform.
[0091] According to particular aspects, a direct injection
technique is used to displace a density of slurry (having a liquid
component and a reinforcement particle component) into an inlet
opening or orifice of an effluent filtering die cavity. FIG. 1A
depicts a first effluent filtering die embodiment showing a split
die portion 10 of an exemplary annular die casting apparatus
(approx. 1/2 of the die) for manufacture of an inventive variable
density preform. The annular die portion 10 shown has a central
inlet 2, and a recessed annular die cavity portion 8. The die
cavity portion 10 has at least one exit opening (e.g., end, opening
or orifice(s)) 4 at a die cavity perimeter 6, defining at least one
flow path between the inlet and exit (e.g., end, opening or
orifice(s)), the exit sized and/or configured to permit exit of a
liquid component of a slurry while selectively or preferentially
precluding or retarding a reinforcement particle component of the
slurry. FIG. 1B shows an expanded view of the perimeter 6 of the
split annular die portion 10, showing a plurality of radially
oriented grooves or channels (exit orifices) 4 circumferentially
arranged around the perimeter 6, the grooves or channels suitably
sized and configured to permit exit of a liquid component of a
slurry while selectively or preferentially precluding or retarding
a reinforcement particle component of the slurry. Also shown is an
outer effluent flow and drain trough or channel 7 in fluid
communication with the die cavity distal portion of the plurality
of radially oriented grooves or channels (exit orifices) 4, and
with a vacuum source (not shown) by means of a vacuum channel 9.
The effluent drain channel directs filtered effluent away from the
die cavity and preform operatively facilitating formation of the
particle gradient preform.
[0092] FIG. 2 shows an exemplary apparatus for making variable
density preforms according to particular embodiments the present
invention. The apparatus comprises an effluent filtering die cavity
8 according to particular aspects. A preform slurry hole plug 11
facilitates control and directing of slurry into the die cavity 8.
A top ejector die portion 12 is shown, along with a top floating
die plate 13. A lower platen 14 and lower die portion 15 are shown.
An injector sleeve-outer wall 16 is depicted, along with a shot
sleeve/injector sleeve seal plate 17, shot sleeve 18 and injector
sleeve inner tube 19. A top fixed plate die portion 20 is shown,
along with a top floating die holding plate 21. A preform shear
ring 22 is shown, along with a preform thickness shim plate 23. An
effluent flow and drain trough or channel 7 is shown.
[0093] FIG. 3 shows an expanded view of Detail A of FIG. 2. The
components cooperatively function to provide for a novel method for
making a variable density preform. For example, the device can be
used in a method of making a variable density preform, comprising:
obtaining a slurry comprising at least one reinforcement particle
component, and at least one liquid component; obtaining a die
cavity 8 having at least one inlet end 2 or orifice and at least
one exit end 4 or orifice defining at least one die cavity flow
path therebetween and a flow path direction toward the exit end or
orifice 4, the at least one exit end or orifice suitably sized or
configured to provide for exit of the at least one liquid component
while impeding or blocking exit of the at least one reinforcement
particle component; and introducing the slurry under pressure into
the inlet end or orifice, wherein the at least one exit end or
orifice is operative with the at least one die cavity and flow path
to provide for a decreasing pressure gradient along the flow path
and flow path direction, and wherein the introducing under pressure
is continued for a time sufficient to provide for a
variable-density preform having a variable density of the at least
one particle component, the particle density increasing (e.g.,
continuously) in the at least one flow path direction.
[0094] FIG. 4 shows an inventive particle gradient preform 24 made
by the process and device described above. The reinforcement
particle density gradients (e.g., linear or substantially linear
gradients) formed by the inventive methods can assume a variety of
shapes and may extend, for example from about 10% to about 70% or
greater, about 15% to about 65%, about 20% to about 60%, about 25%
to about 55%, about 30% to about 50%, about 35% to about 45%, or
shallower gradients. By stepped introduction of different slurries,
smoothed step gradient preforms can be made that smooths the
particle density transition between "steps" and thereby reducing
differential CTE effects and thermal loading aspects of the
preforms and casting comprising such preforms.
[0095] The effluent filtering die, or a portion thereof, is
preferably vibrated during the slurry injection, with, for example,
broadband excitation in order to induce annular vibrations in the
die to induce flow to the outer extremities of the cavity and also
to take advantage of the rheopectic (i.e., viscosity increases as a
function of time with broadband excitation) of the slurry in
facilitating gradient formation. Preferably, a vacuum is applied to
the die cavity distal side of the exit orifice (preferably with the
vibration) to drop the vapor pressure to assist in the evacuation
of moisture from the cast preform. The flow path within the die
cavity is of a distance and configuration sufficient to provide for
a pressure drop as a function of length along the flow path to
promote formation of a variable density preform casting.
Preferably, flow characteristics/properties of the slurry and the
configuration of the die cavity flow path are selected to maintain
a laminar flow in the cavity while it is filled to avoid or
preclude significant areas of entrapped air and deleterious void
formation.
[0096] During the injection of the slurry under pressure, and in
the presence of the decreasing pressure gradient along the flow
path toward the exit orifice(s), the liquid component exits the
exit orifice leaving an increasing density of reinforcement
particle component adjacent the exit orifice and extending back
with decreasing density in a direction toward the inlet orifice,
wherein the reinforcement particle density decreases in a direction
toward the inlet orifice (the density increasing in a direction
toward the exit orifice). Preferably, a linear or substantially
linear (e.g., no more than about 2%, 5%, 10% or 20% deviation from
linear) particle gradient is formed.
[0097] After injection (e.g., for a time sufficient to provide for
a variable density preform having a desired density gradient), the
cast preform (die insert) is removed and optionally placed into
cryo-chamber to break the Van der Waals bonds between the colloid
and the liquid (e.g., water) upon phase transformation of the water
(freezing). This allows the water to exit without disturbing the
inorganic binder system. Various heating techniques may be used to
dry the preform. For example, drying may comprise at least one of
the following: microwave drying; microwave drying with convection;
microwave drying with vacuum; continuous pass-through convection
oven, infra-red drying, etc.
[0098] After drying, the dried preform is placed into, for example,
a kiln, furnace, or oven and fired or sintered at or to specific
temperature (e.g., typically significantly greater than the drying
temperature.
[0099] Various exemplary process steps are encompassed by and/or
compatible with the inventive methods and are briefly summarized
below.
[0100] Slurry mixing may, for example, be by mixing the slurry in a
tank with a single shaft and double propeller, where the shaft
makes an angle of ten degrees with the vertical axis of the
tank.
[0101] Vacuum forming may be employed, involving the coagulation of
slurry flocks on a permeable surface in order to allow passage of
water but not the slurry, wherein water passes due to a pressure
gradient established by the low absolute pressure induced by a
vacuum.
[0102] Injection molding may be employed, involving the injection
of the slurry into a die cavity by means of a conventional
injection molding machine. Slurry Extrusion may be employed,
involving the injection of the slurry into a die cavity with the
assistance of a cylindrical impulse generator. Slurry Extrusion
w/vacuum assist may be employed, involving the injection of the
slurry into a die cavity with the assistance of a cylindrical
impulse generator with the cavity previously evacuated.
[0103] Moldable extrusion may be employed, involving the extrusion
of the slurry over a mandrel on order to form a continuous cross
section shape.
[0104] Slurry de-watering techniques may be employed, involving the
design of suitable fluid passages in the die to allow the process
fluid to "bleed-off" during the formation of a preform.
[0105] Die forming-Compression molding of an injected slurry
mixture may be employed, wherein dense slurry and can be the
preform precursor in a mold before filling the voids with high
pressure injected slurry.
[0106] Coriolis segregation techniques may be employed, allowing
for a density gradient of material to form as a function of
Coriolis acceleration of a fluid being provided impetus from slurry
rotation. Acoustical Coriolis particulate segregation may be
employed, wherein the circular vibration patterns of acoustical
emission are used to enhance the effects of the Coriolis
acceleration the particulate undergoes due to their driven
motion.
[0107] Vibrating annulus assisted slurry flow processing may be
employed, involving the vibration excitation of a flat plate in a
manner that imparts broadband concentric vibration emanation from
the center of the plate. Vibration ceramic slurry knitting
processing may be employed, involving the rewetting of the preform
material via the reduced surface tension effects caused by
vibration excitation. Vibration annular membrane assisted slurry
flow may be employed, wherein this process is a larger amplitude
version of due to the fact that a membrane is used instead of a
more rigid plate. Broadband impact excitation for vibration
excitation may be employed, involving imparting of broadband
excitation of dynamic systems by using impact of materials with
inherently high ratios of modulus to density to ensure ultrasonic
resonances of the system are excited.
[0108] Microwave drying may be employed, involving the use of radio
frequency to dry the preform. Microwave firing may be employed,
involving the use of RF to excite the preform to temperature in
excess of the drying temperature in order to drive off the organic
material and set the inorganic material to hold the preform
together during further processing. Microwave vacuum drying may be
employed, and with the optional addition of a vacuum in order to
allow the water to more readily turn to vapor. Microwave vacuum
firing may be employed, and with the addition of a vacuum in order
to allow for constituent oxide reduction due to the firing
process.
[0109] Ionization density control may be employed, involving the
ionization of the process fluid or fluids in order to produce a
repulsive or attractive charge between constituents in order to
organize the preform material.
[0110] Drying using inductive receptive materials may be employed,
involving induction drying using a receptive material and
conduction to dry the preform material.
[0111] Variable annular density lay-up may be employed, involving
the use of bands of varying density preform material in order to
create a functionally graded preform.
[0112] Reaction inclusion infiltration enhancement may be employed,
involving the use of nano fillers in order to control the reaction
kinematics to ensure a net exothermic response from the
infiltration process. Nano-reinforcement may be employed, involving
the use of Nano sized reinforcements and property enhancement to
increase the macro-properties and process mechanisms, such as
reduced viscosity. Nano-dispersive vibration technology or
de-agglomeration technology may be employed, allowing for the fine
scale dispersion of nano sized particles in the preform.
Nano-coating application may be employed, allowing for the preform
to be coated in order to enhance infiltration characteristics.
[0113] Microwave die cavity heating may be employed, use of an RF
wave guide constructed to be attached to the die in order to use
the die cavity as an RF container and preheat the preform and fire
it right in the casting mold as a rapid heat technology. The RF
essentially bounces off the metallic surfaces and only heats the
preform material, and won't allow the preform to take energy from
the liquid melt causing premature freeze off of the infiltration
metal.
[0114] Vibration assisted slurry flow may be employed, allowing for
the "re-knitting" of preform materials in a non-slurry state.
Nano-vibe slurry wetting techniques may be employed.
[0115] Rheopectic visco-elastic shape forming may be employed,
involving exploitation of the non-Newtonian fluid properties of the
slurry and high shear rates in order to press the material
vertically without have the material "squish" laterally.
Split-Hopkinson pressure bar die excitation may be employed,
allowing for precise wave propagation control in the die
excitation. The pulse and wave length can be physically varied from
a square wave or a triangular wave.
[0116] Acoustical selective particle deposition may be employed,
involving the use of standing wave and plane wave patterns in order
to order the particulate/fiber variation in the preform material.
Acoustical excitation for slurry flow processing may be employed,
involving use of acoustical excitation in order to assist the
motion of the material to create the desired functional gradient.
Acoustical multi-node selective density resolution techniques may
be employed, involving creation of nodules of particles at the node
in the slurry in order to spatially segregate preform materials in
a slurry. Acoustical multi-mode excitation technique may be
employed, involving the use of acoustical excitation for the
forming of a preform. Acoustical emission non-destructive
evaluation may be employed, involving the use of acoustical
emission for a cost effective method to determine spatial
resolution.
[0117] Hydrogen assisted vacuum forming may be employed, involving
the burning of hydrogen in the pores of the preform material to
create "local" vacuum to further compact particles therefore
increasing the green strength and density of the preform.
[0118] Hydrolysis drying may be employed, involving applying an
electric current through the preform material in order to convert
the process fluid to its gaseous constituents. Vacuum sublimation
drying may be employed, involving sublimating the water instead of
evaporating the liquid water form the preform.
[0119] Destructive ceramic extreme broadband excitation may be
employed, involving encapsulating the die in ceramic material and
then impacting and breaking the material in contact with the die,
wherein broadband (>20 kHz) mechanical vibrations are
transferred to the die and thereby excites the die cavity and any
fluid and particle in the cavity. Kinematics structure
amplification for vibration excitation may be employed, involving
placing cantilever beams, pendulums, or 1 degree of freedom
linkages on the die cavity and exciting them with a vibrator at
their natural frequencies and thereby transferring more mechanical
energy to the die than from attaching a vibrator directly to the
die.
[0120] Drag-flow induced density gradient techniques may be
employed, involving flowing a fluid, such as hot air or water,
through or over a preform in the die to cause the smaller particles
to migrate to one side of the die in order to create a density
gradient through the section or surface of preform. Flow modified
green strength may be employed, involving flowing a fluid, such as
hot air or water, through or around a preform in a die such that it
will cause the particles to be compacted, thereby changing the
green strength of the preform material prior to drying or
firing.
[0121] Magnetically induced gradient control may be employed,
involving coating the preform fibers/particles with magnetic
materials or adding magnetic particles to the preform mixture and
applying magnetic fields to the structure to disperse the particles
within the preform according to the strength and location of the
magnetic fields, thereby tailoring/customizing preform properties
such as density and green strength.
[0122] Vibration assisted wetting technique may be employed,
involving applying mechanical or acoustic vibration to the fluid
via die vibration, vibration of the particles directly at a
physical interface like a membrane, or acoustic excitation of the
fluid within the preform to help spread out or wet the fluid on the
preform particles evenly and reduce unwanted density variations due
to uncontrolled clumping.
[0123] Super-critical gel density control may be employed,
involving causing the contents of the preform to foam under load
pressure due to the presence of a super-critical fluid. The foam
will cause the density of the gel in the preform to change, thereby
changing the density of the preform. Acoustical super-critical
fluid resonance may be employed, involving applying mechanical or
acoustic vibration at a resonance of the preform die cavity at low
pressure in the presence of a super-critical fluid to help foam and
distribute the particles evenly within the foamed preform.
[0124] Cryo-sublimation drying may be employed, involving freezing
the preform via, for example, liquid nitrogen and then drying it
either under vacuum or heating rapidly using a flame. This helps
hold dimensional tolerances and preform integrity during
drying.
[0125] Structure tuned damping isolation may be employed, involving
controlling the composition and density of the preform selectively,
wherein the entire reinforced part can be tuned with a prescribed
mount of structural damping to help reduce vibration and noise.
[0126] Visco-elastic constituent control may be employed, involving
adding non-viscous fluids like polyolefins to the slurry to help
reduce viscosity during forming and help create a thin boundary
layer around inserts within the preform to provide for ease of
removal from the die and help facilitate bonding between the
particles and fibers within the preform.
[0127] Tailored energy dissipation may be employed, involving
changing the composition of the preform at different selective
locations within the part, wherein the amount of heat and acoustic
energy dissipated from the part can be altered for desired
function. Changes in reinforcement gradient can help pull heat away
from contact areas on a brake and allow for those areas to have
more wear resistance with greater amounts of ceramic
reinforcement.
[0128] Convolution slurry mixing may be employed, involving
selectively placing obstacles within the flow channels to the
preform slurry, wherein a turbulence will be created to help mix
the preform slurry during forming or extrusion. Multivariate
material inclusion optimization may be employed, involving
monitoring the modal or acoustic properties of the preform during
forming at various locations, wherein a multivariate time series
model can be monitored, to help monitor, control, and optimize the
locations of the inclusions within the reinforcements to give the
correlated properties of the preform to the desired functional
properties of the part.
[0129] Upper and lower Darboux sum prognosis may be employed,
wherein the material properties of the preforms can be controlled
precisely according to different geometries within the part. For
instance, a part will have more reinforcement at areas critically
affected by load, characterized by high stress. The material will
have a lower bound for the material properties, where the
reinforcement is the least. By using this information, the part
reliability can be predicted using an upper and lower bound
analysis assuming the range in material properties.
[0130] Supremum variation control may be employed, wherein the
amount of material variation can be controlled by changing the
composition of the preform. The ultimate tensile strength of the
material does not necessarily reflect the strength of the part,
especially in a composite. The supremum variation is defined as the
predicted strength of the part under a prescribed set of torsional,
bending, and axial loads. The reinforcement locations with respect
to the stress concentrations within the part dictate the total
strength of the part. By predicting this strength, the overall
strength variation of the part can be controlled.
[0131] Mobile property control may be employed, involving
selectively placing reinforcements and reinforcement gradients
throughout the part to help tailor/customize the thermal and
physical properties of the part, such as strength, density, CTE,
natural frequency, etc.
[0132] Deleterious effects minimization may be employed, wherein
undesired porosity and impurities can be minimized during forming
by vibrating mechanically or acoustically or electrometrically to
help air and water escape during the forming process, which prevent
cracking and warping during drying.
[0133] Sustainability system control may be employed, wherein the
preform materials are recyclable, which allows for any scraps or
excess materials to be utilized.
[0134] CTE tailoring may be employed, involving adding
reinforcement to the part to reduce CTE, whereby thermal stresses
can be alleviated if the CTE is changed according to the geometry
of the part. For instance, the outer diameter of a homogeneous
brake rotor will grow more than the inner diameter of that same
brake rotor, thereby creating diametrical thermal strains. By
increasing the reinforcement along the exterior of the part and
decreasing the reinforcement along the interior of the part, the
thermal strain can be neutralized and thereby the thermal stress
reduced.
[0135] Heat dissipation in, in-situ forming may be employed,
wherein the preform variation can also aid heat dissipation during
forming and drying. By adding heat dissipation paths of higher
density reinforcements, more heat can be drawn to the surface of
the preform during forming and drying.
[0136] Metronome vibration excitation may be employed, involving
impacting the die with a hammer according to the pulse of a
metronome.
[0137] According to various aspects of the present invention, the
aforementioned process or series of processes are utilized to
create a controlled density preform for multifunctional materials.
The controlled density can be utilized in but are not limited to
braking components, engine components, vehicle suspension
components or any other component that would need tailored
differential densities inside of ceramic reinforcements for metal
matrix composites or insulation. One of the most important aspects
of the variable density preforms is the ability to reduce the
thermal loading of components (e.g., the MMC component). Such
loading can and does cause premature failure in specific
components.
Example 2
Novel Variable Density Preforms were Made by Another Exemplary
Inventive Preform Die Casting Device and Process
[0138] This example describes additional exemplary method and
device embodiments for manufacturing novel variable density
preforms. The process of making an MMC component is delineated in
detail in this Example.
[0139] A porous "preform" is a precursor reinforcement material
that can be infiltrated with matrix material (e.g., aluminum,
aluminum alloys, etc) to make an MMC component (e.g., a reinforced
composite). Basic exemplary steps for making the inventive preforms
are as follows: [0140] 1) measuring of the constituents (e.g.,
weighing); [0141] 2) mixing (e.g., batch mixing) of the
constituents; [0142] 3) formation of "green" preform geometry
(e.g., by using the inventive devices); [0143] 4) drying of the
preform under conditions suitable to support correct preform
geometry; [0144] 5) optional machining of the preform (e.g., to
final net shape); and [0145] 6) "firing" of the preforms (e.g.,
sintering at elevated temperature to eliminate organic binders
and/or other fugitive components of the slurry).
[0146] Mixing Station.
[0147] A mixing station provides a starting point for the ceramic
preform manufacturing process. A suitable blend of ceramic
particles, fiber, binders and water are measured and mixed to
obtain a ceramic slurry suitable for forming in the inventive
preform press to provide variable particle density preforms. The
slurry blend is important for obtaining a MMC component having high
structural integrity and properties tailored, for example, for a
vehicle braking (e.g., disk or drum brake) application. An on-site
mixing station provides for reproducible preform production and
allows for responsive design and property tailoring, based on
mechanical and microstructural analysis of castings made with the
precursor materials. Weighing of the constituents into receptacles
(e.g., one gallon pails) is readily accomplished using, for
example, a calibrated scale. In particular embodiments, individual
constituents may comprise: (1) silicon carbide; (2) silica; (3)
starch; and (4) SAFFIL.RTM. fiber.
[0148] An exemplary mixing station is shown in FIG. 5. The mixing
station 38 comprises one or more water tanks 30, and one or more
mixing tanks 32 equipped with mixing motors 34. In certain aspects,
the mixing is accomplished with a high shear mixing propeller. The
mixing tanks 32 communicate with respective holding or settling
tanks 36. Cycling controls 37, facilitate control of the flow of
liquids and slurries through the system 38. A typical preform batch
mixing procedure may, for example, comprise: (1) filling a mixing
tank with 30 gallon of water; (2) adding 0.5 lb of AZS fiber
(SAFFIL.RTM.) and mixing (e.g., for 5 min. at 1,150 rpm); (3)
adding 8.5 lb. SiC and mixing (e.g., for 5 min. at 1,150 rpm); (4)
adding 1.6875 lb. colloidal silica and mixing (e.g., 1 min. at
1,150 rpm); (5) adding 0.45 lb. starch and mixing (e.g., for 5 min.
at 1,150 rpm); and (6) pumping the mix into a holding tank or
tanks.
[0149] Using the exemplary mixing station of FIG. 5, three separate
slurry batches can be made at one time. The settling tanks hold the
slurry until it is needed in the effluent filtering "preform" die
press (described below). In particular aspects, a mixing tank and a
settling tank comprise one mixing station. In particular aspects,
the holding tank may be the same as the settling tank.
[0150] Inventive Effluent Filtering Preform Die Press.
[0151] After the desired slurry has been properly mixed, it is
ready for forming into a porous preform (e.g., suitable for
infiltration casting with a matrix material). The design of the
effluent filtering preform press is such that preform densities can
be varied through the formed component. Extensive testing, design
and flow analysis has gone into developing a system which is
capable of forming rotor preforms with the desired, tailored and
optimal density variations in the radial direction. In preferred
aspects, the particle gradients are linear or substantially linear,
increasing in the radial direction, and having uniform, or
substantially uniform density around circumferential positions at
any given radius.
[0152] Exemplary specific process steps for making the inventive
variable density preforms include one or more of the following:
[0153] 1. Injecting (e.g., using a direct injection technique) a
slurry into an effluent filtering die cavity (see FIGS. 7-11
illustrating aspects of the exemplary effluent filtering dies used
herein), where in particular aspects injecting the preform slurry
into the die cavity is from a shot cylinder positioned below the
die such that when the slurry reaches the tapered end of the shot
cylinder, the velocity of the slurry is increased thereby
accentuating the density differences of the carrying liquid media
and the ceramic particles/fibers;
[0154] a--vibrating the die with broadband excitation in order to
induce annular vibrations in the die in order to induce flow to the
outer extremities of the cavity and also to take advantage of the
rheopectic (viscosity increases as a function of time with
broadband excitation) of the slurry;
[0155] b--maintaining a sufficient die travel distance to provide
and maintain a pressure drop as a function of length to facilitate
variable density preform formation;
[0156] c--adjusting or providing for flow characteristics to
provide for a substantially laminar flow in the cavity during
filling to preclude entrapped air and formation of deleterious
voids.
[0157] As the slurry enters into the die cavity, there is a
propensity for the liquid media to begin to separate from the
heavier ceramic slurry. Upon hitting the periphery (outer ring) of
the die cavity, the ceramic slurry is stopped, but the liquid media
(effluent) is able to escape or filter out through a path that is
gated or filtered before connecting to the effluent channels (see
FIG. 9). The slurry is continually injected into the die and there
is a continuous separation of effluent and ceramic
particles/fibers. The effluent must travel through the ceramic
material already in the die cavity causing an increased particle
density of the outer regions of the die. With the die completely
filled, pressure is built in the die to promote the release of the
effluent in the die cavity. The hold time and pressure are
important control parameters for controlling the exiting flow and
thereby controlling the density gradient across the final
preform.
[0158] FIG. 6 shows, in schematic form, the principal of variable
density preform formation according to particular aspects of the
present invention. The slurry is ejected in the cavity from the
left side of the figure and as the slurry reaches the right side of
the cavity having effluent filtering means (e.g., suitably sized
openings, channels, mesh, screens, filter particles, etc.) only the
effluent can escape the die cavity, thereby providing for building
up of a functionally graded and ceramic (e.g., porous ceramic
preform).
[0159] 2. Removing the preform from the effluent filtering die and
placing it for drying (e.g., in a infrared convection oven to drive
out the remaining moisture in the preform).
[0160] 3. Placing the preform into a furnace and ramping the
temperature to a sufficient value to burn out the organic binder
and to set the inorganic binder on the ceramic particles and
fibers. This drives out carbon residue from the preform and gives
the preform strength. As will be appreciated in the art, the method
of elimination of binders and/or other fugitive components from the
preform will depend on the nature of the binder or fugitive agent,
and may be other than heat.
[0161] FIG. 7, Section A-A, shows a schematic of a preferred
effluent filtering die design embodiment for the manufacture of the
inventive functionally gradient preforms. An upper die 40 is
connected to an upper platen 42. The upper die 40 comprises a die
cavity 8. The upper die communicates with a lower die 44 connected
to a lower platen 46. There is a plurality of effluent flow
channels 47 and effluent drain channels 48 within the lower die
portion. Slurry is delivered into the die chamber through a shot
nozzle 50 by means of an injection cylinder 52 within a shot sleeve
54. Also shown are slurry cavity 56 and slurry load reservoir
58.
[0162] Detail "F" shows an expanded view of the effluent flow
channels 47 and effluent drain channels 48 within the lower die
portion. Also shown in Detail "F" are a filter cover plate 60, a
filter member 62, discharge cover plate 64 and o-ring grooves 66.
According to preferred aspects the assembly design shown in FIG. 7
and Detail "F" provides for effective making of variable density
preforms using smaller particulate diameters. FIG. 8 is an expanded
view of Detail "F". The slurry initially enters the die and
displaces the initial resident air out through the effluent flow
and drain channels. During filling of the die, the slurry is forced
toward the outside of the die (because the slurry injection gate is
at the center), through the filter under the filter cover plate,
and further through the openings in the discharge cover plate, and
finally out through the effluent flow channels, which are connected
to the effluent drain channels connected to a drain. According to
particular aspects of the present invention, the arrangement of the
covered filter and the plurality of concentrically configured
effluent drain channels provides for additional control the
pressure across the die to facilitate production of a particle
gradient. In particular aspects, a varying number of the
concentrically configured effluent drain channels can be opened
and/or placed in fluid communication with the filter and effluent
flow through the filter, with one or more of the drain channels
optionally closed and/or blocked from fluid communication with the
filter. For example, in the reverse radial direction from the
perimeter, only a subset of the concentrically configured effluent
drain channels can be opened and/or placed in fluid communication
with the filter. In preferred aspects, the outer 2-4 channels are
used to direct and drain the effluent flow from the filter.
Preferably, at least the outer 3 channels are used (e.g., with the
6 inner channels blocked and the three outer channels open). Each
effluent channel is connected to a corresponding effluent drain.
Opening and/or placing increasing numbers of the effluent flow
channels in fluid communication with the filter and effluent flow
enables a higher effluent flow/psi thereby reducing the steepness
of the gradient. It is important that the outer effluent channels
are open and/or in fluid contact with the filter and effluent flow
to establish the correct die chamber flow (see the schematic of
FIG. 6). Provision of a filtering component and a variable effluent
flow path capacity provides a mechanism for effectively filtering
the particulate (including even very fine particulates) out of the
slurry so that the particulate is retained in the die cavity, while
at the same time providing for control and tailoring of the
particle gradient in the final preform.
[0163] In preferred aspects, the effluent filter member comprises a
screen (e.g., with about 50 micron passageways). In certain
aspects, it is made from polypropylene, but any suitable material
will suffice provided that it is proportion appropriately and
displays suitable flow characteristics. Preferably, the filter
material or member (e.g., screen) is durable and wear resistant. A
variety of particle sizes may be used. In particular aspects,
silicon carbide particle sizes of between F200 and F600 grit are
used. In preferred aspects, F500 grit particles (mean particle size
is 17 microns) are used.
[0164] FIG. 9 shows an expanded view of the effluent filtering die
of FIG. 7, where the die halves are separated.
[0165] FIG. 10 shows an expanded view of the effluent filtering die
of FIG. 7, where the die halves are operatively connected.
[0166] FIG. 11 shows an expanded view (Detail "H") of a section of
FIG. 10. Additionally shown is a preform ejector plate 68, and a
vibrator mounting hole 70.
[0167] FIG. 12 shows a perspective partial assembly view of an
exemplary effluent filtering die set in a press for commercial
production.
[0168] FIG. 13 shows a perspective cross-sectional partial assembly
view of the exemplary effluent filtering die set in a press for
commercial production show in FIG. 12.
[0169] FIG. 14 shows a detailed perspective cross-sectional partial
assembly view of the exemplary effluent filtering die set in a
press for commercial production show in FIGS. 12 and 13.
[0170] Preform Press Operation Procedure.
[0171] In particular exemplary aspects, one or more of the
following steps are used for preform press operation: [0172]
Start--Machine in open position--Dies Open, Shot Piston Retracted;
[0173] Open slurry injector door; [0174] Place 0.75 gallons of
slurry in feed tube--Maintain LDT setting to stay between 10-13
inches (on LCD screen at end of shot); [0175] Activate Cycle
Start--Material will be injected into the shot sleeve; [0176] Clean
platen and preform plate free of any excess material; [0177] In
Auto Cycle screen--Press should be in Auto; [0178] Verify that
pressures are set at 1500 psi upper limit and 1200 psi lower limit;
[0179] Verify that timer is set at 7 seconds; [0180] Verify that no
foreign debris/arms/limbs are in the machine clamping area; [0181]
Press Cycle Start; [0182] Prepare additional plate and material for
next shot and batch while injection cycle and hold pressure for set
time; [0183] Cycle complete--Safety gate will raise--Remove plate
with preform from Press; [0184] Cut center excess material out with
tool--Place center material in preform recycle container; [0185]
Remove Tray from Drying Oven and place upside down on preform
plate--Transfer Preform onto Dryer tray and place in oven; and
[0186] End of cycle.
[0187] This die press machine embodiments described herein are able
to form the gradient ceramic shape by injecting the slurry through
an intricately yet robustly designed injection system that fills
the die in a specific manner. The order of operations for the
preform forming press are described herein above. In this process
the variation in density is enhanced by the die design.
[0188] The drying of the preform is a delicate process. Preferably,
this process involves a special drying jig to hold the pieces flat
and at the correct size during drying, and preferably also designed
to be a transfer conveyor to the preform machining area.
[0189] Firing of the preforms is preferably accomplished suing a
batch kiln. In particular aspects, four batch kilns are contained
in a line-up on a preform machining mezzanine. The preforms are
placed on kiln furniture as they are fired. After the firing of the
preform is complete, the preform is ready to be injected (e.g.,
infiltration cast; pressure die cast; squeeze cast, etc.) by the a
molten matrix material (e.g., molten aluminum). Upon entering the
die cast chamber, the preform is heated to 1,093.degree. C.
(2,000.degree. F.) via a pass through kiln. This kiln at this point
is fed manually to Preferably, a robot picks up the heated preform
and automatically places it in a casting die for creation of, for
example, an MMC product.
[0190] Shot Profiles (Pressure, Velocity, and Displacement).
[0191] According to particular aspects, "shot profiles" are
important to monitor for ensuring that a consistent or desired part
characteristic (e.g., particle gradient profile) is produced. Shot
profiles are essential in both the preform casting, and the
subsequent preform infiltration casting processes. In the preform
press, the shot profile tracks how fast the ceramic slurry is
filling the die cavity and at what pressure in order to determine
when the particle gradient preform formation is complete (e.g., to
the desired gradient, density and water content). Likewise, on a
subsequent preform infiltration casting apparatus, the shot profile
allows for control over solidification of metal within the casting
and helps ensure that preforms are infiltrated under the same
conditions for each casting to reduce any porosity that might
otherwise be caused by early solidification.
[0192] FIG. 15 shows shot profile data from an injection cycle
using an embodiment of the inventive preform effluent filtration
die press process and apparatus. The X-axis shows the time in
hundredths of a second (i.e., from 0 to 12 seconds), while the
Y-axis shows pressure (psi) (for the bottom slurry pressure curve)
and shot piston displacement in thousandths of inches (i.e. from 4
to about 9 inches). Pressure is measured from a gauged positioned
in communication with slurry (slurry cavity); in the nozzle portion
of the injection apparatus. As shown in the graph, the shot piston
is activated and pressure builds in the slurry injection cavity
from about 5 to about 7.5 seconds, during which time the pressure
increases to about 600 psi, after which time the piston pressure is
released to provide a pause, before reassertion of the pressure for
a final "ram" of about 1 second at about 800 psi, which helps clear
the device for the next shot cycle. As seen from the upper curve,
during the injection cycle the injection piston rod (fitted with a
liner transducer to measure travel of the piston rod) is displaced
to inject the slurring into the die cavity. In the figure,
displacement is tracked in relation to the slurry pressure stating
at about 4 inches through about 8 inches, followed by a pause
(corresponding to the slurry pressure pause), and then a final
displacement to about 8.5 inches (corresponding to the slurry
pressure "ram" used to clear the device for the next shot cycle).
Typically, for particular motorcycle preform embodiments, the ratio
of slurry volume to cast gradient preform volume in about 3.8:1.
The slurry pressure ramp rate and the final slurry pressure at the
end of the ramp, are important variables with respect to tailoring
preform gradients, and with respect to consistency of manufacturing
of a given configuration.
[0193] As will be apparent to those of ordinary skill in the art,
the slurry pressure ramp rate, the final ramp slurry pressure, the
particle size and flocculation characteristics, and the filtering
geometry/configuration are variable that can be used to effectively
tailor the inventive preforms to encompass a broad range of
particle gradient configurations.
[0194] FIG. 16 shows an infiltration cast motorcycle disk brake
rotor embodiment comprising a particle gradient preform according
to aspects of the present invention. The outer rotor portion is
mounted to an internal carrier by means connecting buttons.
[0195] FIG. 17 shows the particle density variation in an
infiltration cast disk brake rotor embodiment comprising a particle
gradient preform according to aspects of the present invention.
Magnified sections from inner and outer (perimeter) portions of the
composite rotor are shown to illustrate the particle gradient
aspect of the finished infiltration cast preform product. In this
particular embodiment, the particle gradient was engineered to
provide a linear gradient extending from about 33.6% (particulate
volume fraction) to about 44.4% (particular volume fraction).
[0196] FIGS. 18A, B and C show electron micrographs of the
inventive preform material at 700, 1,000 and 2,000 times
magnification, respectively.
Example 3
Novel Discontinuous Variable Density Preforms and Brake Drum
Particle Gradient Preforms
[0197] Additionally, according to particular aspects of the present
invention, the arrangement of the covered filter and the plurality
of concentrically configured effluent drain channels provides not
only for additional control over the pressure across the die to
facilitate production of a particle gradient, but in particular
embodiments can be used to position the gradient within a larger
preform casting. For example, by using a filter cover plate 60
having internal annular openings from die channel to the filter
that communicate with respective internal effluent flow channels,
and by closing off effluent flow channels at the perimeter, and
opening one or more of the internally located effluent flow
channels, the formed particle gradient can be effectively
positioned correspondingly closer to the center of the annular
preform (see, e.g., FIG. 14, illustrating a variant pattern of
operative effluent flow channels). Therefore, opening and/or
placing particular effluent flow channels in fluid communication
with the filter and effluent flow enables tailoring not only of the
gradient shape, but also of the gradient position within the
preform. Moreover, discontinuous gradients, comprising two or more
gradient portions can be produced by opening and/or placing
particular effluent flow channels in fluid communication with the
filter and effluent flow. Furthermore, as will be apparent to those
of ordinary skill in the art, preforms having reversed gradients
can be produced by configuring the apparatus to reverse the shot
flow direction across the die cavity. In particular aspects, for
example, drum brake preforms are produced by increasing the height
of the die chamber (e.g., from about 4 to about 7 inches), while
decreasing the radial distance/thickness. In such drum brake
preform embodiments, the shot flow direction is reversed (i.e.,
toward the center for the annual preform) so that an increased
particle density is established on the inner margin or surface of
the preform, which, in the context of an infiltration cast drum
brake rotor comprising the preform, is in contact with the braking
friction material to provide for enhanced performance and extended
service life of the cast drum brake rotors.
Example 4
Novel Variable Density Preforms were Made by a Novel Preform
Pressing Process
[0198] This example describes another exemplary method embodiment
for making a novel variable density preform, comprising pressing a
tapered preform shape into a non-tapered or reduced taper shape in
to order to increase the reinforcement particle density
proportionate to co-localized with the pressing aspect.
[0199] For example a tapered plate is injection molded while
subjecting the middle/center of the plate to an impact vibration
(e.g., by applying vibration to the annular die by means of impact
loading in the center in order to induce a concentric "ripple wave"
to help mobilize the material to the outside), wherein exit vents
in the die cavity allow water in the slurry to bleed out radially
from the perimeter. Injection and bleeding can be vacuum assisted
or not. The taper shaped preform can then be pressed to the right
density using suitable temperature and pressures. This method is
particularly suitable for casting because multiple die inserts can
be optionally used to make preforms, with subsequent placement of
the preforms into a die holder on a press to cast. This process
allows for production of near net shape of the parts. Drying may be
by pumping hot air through the mold, and the dies may be
additionally heated. A wave guide may be provided to get RF into
the die with the preform in place (i.e., to use the die itself as a
microwave cavity).
Example 5
Inventive Variable Density Preforms were Made by a Novel Preform
Pressing Process
[0200] This example describes another exemplary method embodiment
for making a novel variable density preform:
[0201] Materials:
Preferred solid materials for the slurry include:
[0202] Silicon carbide particles/powders (by weight--83% (Range
25-100%));
[0203] CERACHEM.RTM. ceramic fibers (by weight--17% (Range--0 to
75%));
[0204] Colloidal silica-binder (5% by weight (Range 2.5-10%));
and
[0205] Cationic starch-binder (5% by weight (Range 2.5-10%)).
[0206] In particular aspects, a slurry concentration is determined
that meets processing and volume fraction goals. For example, a
typical concentration of fiber in the slurry is 1% by weight. Water
is added to the forming tank, and any special water treatment may
be applied. The desired weight of fibers is added. The desired
weight of particles is added (for hybrid particle/fiber preforms).
The slurry is mixed at selected mixer speeds to meet proper volume
fraction in formed preform. Desired binder or binder(s) are added
in the order planned for the particular preform. The prepared
slurry is pumped to a forming tank or forming mold depending on the
process flow selected. Fiber or fiber/particulate may be deposited
on the mold porous surface (or exit orifice of an inventive die
chamber) as the water is removed by vacuum and, or pressing to form
the wet preform piece. The "wet" preform is removed from the tool
and transferred to a drying tray as desired and placed in a dryer.
The dried preform is removed from dryer tray and placed in a kiln
for firing if desired. In-process quality checks are optionally but
preferably made at each step to insure that proper volume fraction
and internal integrity is being achieved. Dried or fired preform
blanks are transferred to machining center if that processing route
is selected. Machined preforms are transferred to inspection and
packing area. Dried or fired net-shaped preforms are transferred
directly to the inspection and packing area.
[0207] Additional, Optional Materials Include but are not Limited
to the Following (in Preferred Weight and Ranges as Given
Above):
[0208] Alumina particles/powders;
[0209] Mullite particles/powders
[0210] Boron carbide;
[0211] Boron nitride;
[0212] Ceramic fibers (glass and polycrystalline fibers);
[0213] Calcined alumina-silica particles/powders (45-55 to 80-20
Alumina-silica ratio);
[0214] Any dense, hard, and stable ceramic or metal material;
[0215] Silicon metal particles/powders;
[0216] Colloidal alumina (binder);
[0217] Phosphate (binder); and
[0218] Combination of binders (e.g., aluminum phosphate).
[0219] Material Related Information:
[0220] Volume fraction (% reinforcement material at the material
composition selected) 50-25 preferred outside diameter to inside
diameter. Range could be 60-20 to 30-10.
[0221] Particle/powder size (-59 to +5 u preferred range of
particles). Exemplary options are (-75 to +45 u which is F220 grit)
to (-25 to +5 u which is F500 grit).
[0222] Ceramic Fiber Option Examples:
[0223] KAOWOOL.RTM. alumina-silica fibers;
[0224] SUPERWOOL.RTM. soluble vitreous fibers (silica-calcium
oxide-magnesium oxide);
[0225] SAFFIL.RTM. polycrystalline fibers (mullite or high alumina
chemistry);
[0226] Alumina fibers;
[0227] Basalt fibers;
[0228] Silica fibers; and
[0229] Glass fibers.
[0230] Ceramic Fiber Characteristics:
[0231] Chemistry: Al.sub.2O.sub.3--35%; SiO.sub.2--50%;
ZrO.sub.2--15% by weight preferred; with exemplary options of 99%
Al.sub.2O.sub.3 by weight to fibers that composed of a mixture on
silica, calcia, magnesia, iron oxides, sodium oxide, or boron
oxide).
[0232] Shot content; Less than 5% by weight preferred. 0 to 60%
exemplary shot content.
[0233] Shot Size; 100%--44.mu. preferred. Shot size of 98%--212.mu.
possible.
[0234] Key Process Variables:
[0235] First Stage Slurry mix concentrations (% solids in liquid):
10%; range can be 3 to 30%.
[0236] Slurry forming feed concentrations: 40%; range can be 10 to
70%.
[0237] Pressure differential in forming: measured in chamber
immediately before injection. Production machine will be many
more.
[0238] Quality Test Methods:
[0239] Volume fraction distribution; and
[0240] Particle size distribution.
[0241] Preforms are inspected according to standard quality
procedures. Approved preforms are transferred to the packing and
shipping area, and any "off" specification preforms that can be
re-worked are recycled back to the corresponding step in the
manufacturing process.
Example 6
Exemplary Disk Brake Rotors were Tested Under U.S. Department of
Transportation Testing Standards
[0242] In particular aspects, an exemplary inventive advanced metal
matrix composite (MMC) rotor is currently in commercial production
for motorcycle disc brake rotors. This commercial embodiment (11.5
inches in diameter and 5.5 millimeters thick) has been tested in
accordance with the United States Department of Transportation
(DOT) Federal Motor Vehicle Safety Standard Test 122 (FMVSS 122) by
a certified testing lab (Greening Testing Labs; Detroit, Mich.),
and has not only passed the dynamometer testing requirements, but
has also exceeded the U.S. federal stopping distance and time
requirements. To applicants' knowledge, this is the first composite
disc brake rotor for motorcycles to have completed federal DOT
testing.
Example 7
Exemplary Disk Brake Rotors were Tested on a Test Track Using a
Monitored Test Vehicle and were Found to be Substantially Superior
to Original Equipment Steel Disk Brake Rotors
[0243] To enable sales of motorcycle disc brake rotors in Canada,
Europe, and Japan, rotors must undergo testing on a test track
using a monitored test vehicle. In this regard, the exemplary
inventive advanced metal matrix composite (MMC) rotor (11.5 inches
in diameter and 5.5 millimeters thick) currently in commercial
production was installed on the front axle of a
Harley-Davidson.RTM. SPORTSTER.RTM. to provide a single front disc
brake rotor. The test motorcycle was 256 kg (565 pounds) and the
rider was about 113 kg (250 pounds).
[0244] Without using the rear brake rotor at any time, comparative
on-bike testing was conducted at applicants' test track. As a
comparative benchmark, the original equipment stainless steel rotor
was cycled through multiple 80 mph to 0 stops and within a
15-minute time period, resulting in a warped, grooved and unusable
rotor, and wherein the brake caliper became so hot that the seals
melted and the brake fluid boiled. By contrast, when the inventive
MMC rotor was tested under identical conditions, no warping was
detectable. According to particular preferred aspects, the
inventive rotor runs generally cooler, cooling (e.g., at
400.degree. C.) approximately 5-times faster than a similarly
proportions steel rotor (e.g., at 400.degree. C.). The MMC rotor
face surface was not damaged or grooved, and, as expected, had a
thin gray transfer film from the friction material. Astonishingly,
compared to the stopping distance requirements applicable when
using both a front and rear rotor together, the inventive single
front MMC rotor stopped in about one-half the distance
required.
[0245] Therefore, not only are the exemplary inventive advanced
metal matrix composite (MMC) disk brake rotors (29.2 cm (11.5
inches) in diameter and 5.5 millimeters thick) substantially
lighter than comparable steel rotors, but have demonstrable
performance characteristics that substantially surpass the original
equipment stainless steel rotor under actual on-bike test track
conditions with 365 kg (805 pounds; bike plus rider).
[0246] Thus, embodiments of the invention are disclosed. Although
the present invention has been described in considerable detail
with reference to certain disclosed embodiments, the disclosed
embodiments are presented for purposes of illustration and not
limitation and other embodiments of the invention are possible. One
skilled in the art will appreciate that various changes,
adaptations, and modifications may be made without departing from
the spirit of the invention and the scope of the appended
claims.
* * * * *