U.S. patent application number 09/898198 was filed with the patent office on 2002-01-17 for metal/ceramic composite molding material.
This patent application is currently assigned to AlliedSignal Inc.. Invention is credited to Behi, Mohammad, Burlew, Joan, Duyckinck, Richard Lewis, Zedalis, Michael.
Application Number | 20020006988 09/898198 |
Document ID | / |
Family ID | 22986418 |
Filed Date | 2002-01-17 |
United States Patent
Application |
20020006988 |
Kind Code |
A1 |
Behi, Mohammad ; et
al. |
January 17, 2002 |
Metal/ceramic composite molding material
Abstract
A composite molding compound comprising a combination of metal
and ceramic powders is disclosed. The powders are combined with a
binder, a liquid carrier and other processing additives in a manner
to provide uniform distribution of two phases in a material format
that facilitates the molding of complex parts at relatively low
pressures and temperatures using conventional injection molding
machines. The products formed from these molding compounds may be
designed with tailored physical and mechanical properties such as
thermal conductivity, thermal expansion coefficient, density,
elastic modulus and wear properties.
Inventors: |
Behi, Mohammad; (Lake
Hiawatha, NJ) ; Zedalis, Michael; (Mendham, NJ)
; Duyckinck, Richard Lewis; (Ringoes, NJ) ;
Burlew, Joan; (Rockaway, NJ) |
Correspondence
Address: |
HONEYWELL INTERNATIONAL INC.
101 COLUMBIA ROAD
P O BOX 2245
MORRISTOWN
NJ
07962-2245
US
|
Assignee: |
AlliedSignal Inc.
|
Family ID: |
22986418 |
Appl. No.: |
09/898198 |
Filed: |
July 3, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09898198 |
Jul 3, 2001 |
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09259794 |
Mar 1, 1999 |
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6291560 |
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Current U.S.
Class: |
524/27 ; 264/122;
264/328.2; 264/621; 419/36; 524/405; 524/413 |
Current CPC
Class: |
B22F 1/10 20220101; B22F
3/225 20130101; B22F 2998/00 20130101; C04B 35/636 20130101; B22F
2998/00 20130101; B22F 3/225 20130101; B22F 2998/00 20130101; C22C
1/1084 20130101 |
Class at
Publication: |
524/27 ; 524/405;
524/413; 419/36; 264/122; 264/621; 264/328.2 |
International
Class: |
C04B 035/64; B22F
001/00; B28B 001/24 |
Claims
What is claimed is:
1. A composite molding compound comprising: a) a mixture of a metal
powder and a ceramic powder, b) a gel-forming material selected
from the group of polysaccharides consisting of agaroids, and c) a
gel-forming material solvent, said mixture being formulated in a
blender that provides shearing action thereto and the blender being
heated to raise the temperature of the mixture to about 75 to
100.degree. C.
2. The compound of claim 1, wherein the temperature of the mixture
is raised to between about 80 to 95.degree. C.
3. The compound of claim 1, further including a dispersant, a pH
control substance, a biocide and a carrier.
4. The compound of claim 1, wherein the metal/ceramic powder
mixture is in the form of a slip having a particle size of between
approximately 1 to 60 .mu.m.
5. The compound of claim 1, wherein the ceramic powder is in the
form of oxides, carbides, nitrides, borides, silicides or
combinations thereof, and the metal powder is in the form of
ferrous and/or non-ferrous metals or metal alloys.
6. The compound of claim 1, wherein the composite mixture of metal
powder and ceramic powder form reinforcement particles or a matrix
having a volume fraction in a range from about 0.1 to 99%.
7. The compound of claim 6, wherein the volume fraction is in a
range from about 15 to 75%.
8. The compound of claim 6, wherein the volume fraction is in a
range from about 15 to 40%.
9. The compound of claim 1, further including a gel strength
enhancing agent in the form of a borate compound selected from the
group consisting of magnesium borate, calcium borate, zinc borate,
ammonium borate and boric acid.
10. The compound of claim 1, wherein the weight percent of solid
material in the compound mixture is in the range of approximately
75 to 93 wt %.
11. A process for forming an article comprising the steps of: a)
formulating a composite mixture of a metal powder and a ceramic
powder, a gel-forming material selected from the group of
polysaccharides consisting of agaroids, and a gel-forming material
solvent, said mixture being formulated in a blender that provides
shearing action thereto and the blender being heated to raise the
temperature of the mixture to about 75 to 100.degree. C.; b)
supplying the mixture at a temperature above the gel point of the
gel-forming material into an injection molding machine; and c)
molding the mixture under conditions of temperature and pressure to
produce a self-supporting article.
12. The compound of claim 11, wherein the temperature of the
mixture is raised to between about 80 to 95.degree. C.
13. The compound of claim 11, further including a dispersant, a pH
control substance, a biocide and a carrier.
14. The compound of claim 11, wherein the metal/ceramic powder
mixture is in the form of a slip having a particle size of between
approximately 1 to 60 .mu.m.
15. The compound of claim 11, wherein the ceramic powder is in the
form of oxides, carbides, nitrides, borides, suicides or
combinations thereof, and the metal powder is in the form of
ferrous and/or non-ferrous metals or metal alloys.
16. The compound of claim 11, wherein the composite mixture of
metal powder and ceramic powder form reinforcement particles or a
matrix having a volume fraction in a range from about 0.1 to
99%.
17. The compound of claim 16, wherein the volume fraction is in a
range from about 15 to 75%.
18. The compound of claim 16, wherein the volume fraction is in a
range from about 15 to 40%.
19. The compound of claim 11, further including a gel strength
enhancing agent in the form of a borate compound selected from the
group consisting of magnesium borate, calcium borate, zinc borate,
ammonium borate and boric acid.
20. The compound of claim 11, wherein the weight percent of solid
material in the compound mixture is in the range of approximately
75 to 93 wt %.
21. The process of claim 11, further including the step of
sintering the composite molded parts at approximately 1300 to
1450.degree. C. for about 2 to 6 hours.
22. A method for producing a homogeneous composite molding compound
comprising the steps of: a) mixing a metal powder with water and a
gel-forming material selected from the group of polysaccharides
consisting of agaroids; b) mixing a ceramic powder with water and a
dispersant, and ball milling the mixture to reduce the particle
size thereof; c) compounding the metal powder mixture and the
ceramic powder mixture; and d) shredding the compound mixture into
a particulate format.
23. The method of claim 22, wherein the ceramic powder is in the
form of oxides, carbides, nitrides, borides and silicides, or
combinations of two or more of these materials, and the metal
powder is in the form of ferrous and/or non-ferrous metals or metal
alloys.
24. The method of claim 23, wherein the composite mixture of
ceramic powder and metal powder is in a range from about 0.1 to
greater than 99 volume %
25. The method of claim 23, wherein the composite mixture is in a
range from about 15 to 75 volume %.
26. The method of claim 23, wherein the composite mixture is in a
range from about 15 to 40 volume %.
27. The method of claim 22, wherein the amount of water in the
composite mixture is between about 5 to 30 weight %.
28. The method of claim 22, wherein the amount of water in the
composite mixture is between about 8 to 20 weight %.
28. The method of claim 22, wherein the temperature of the
composite mixture is raised to between about 70 to 100.degree. C.
during the compounding step.
29. The method of claim 22, wherein the temperature of the
composite mixture is raised to between about 80 to 95.degree. C.
during the compounding step.
30. The method of claim 22, wherein the compound mixture further
includes a dispersant, a pH control substance, a biocide and a
carrier.
31. The method of claim 22, wherein the weight percent of solid
material in the compound mixture is in the range of approximately
75 to 88 weight %.
32. The method of claim 22, wherein the compound mixture is in the
form of a slip having a particle size of between approximately 1 to
60 .mu.m.
Description
FIELD OF THE INVENTION
[0001] This invention relates to composite molding compounds
comprising a combination of metal and ceramic powders for forming
various complex-shaped parts at relatively low temperatures and
pressures in conventional injection molding equipment. Various
metal/ceramic composite compounds of widely varying compositions
are used to form high quality, net or near-net shape parts, which
exhibit excellent homogeneous distribution of the metal and ceramic
particles in the composition in both the "green" (unfired) and
fired states. The finished parts require little or no machining,
have superior properties and do not experience the cracking,
distortion and shrinkage problems associated with prior art
sintered products.
BACKGROUND OF THE INVENTION
[0002] Metal/ceramic composites are important specialized materials
that are used in a variety of technical applications, e.g., gas
turbine engine valves, pumps and other high-wear components,
electrical and electronic connectors, and heat sinks. In addition
they are used in a multitude of other applications where there is a
need to reduce the weight and cost of a material. These composites
are difficult to produce in a uniformly dispersed, intimately mixed
composition by state-of-the-art processing methods, such as dry
pressing or conventional metal casting, in which the ceramic powder
is added to the molten metal prior to pouring. The problem of
producing uniform composite materials is especially severe at high
loadings of the ceramic component, upwards of about 25 vol %.
[0003] Metal/ceramic composites offer several distinct advantages
to the materials user for certain applications. For example, the
composite can have lower weight and higher elastic modulus than the
metal component, and greater toughness than the ceramic component.
These composites are frequently composed of a continuous metal
phase with a ceramic particulate or fiber or a combination of both
as a reinforcement phase. Obtaining uniform distribution of the
reinforcement phase represents one of the main objectives in
producing these composite materials. Indeed the distribution of the
particulate phase has a great effect on the final properties of the
composite material.
[0004] Various techniques have been employed to produce
metal/ceramic composite materials. Techniques such as liquid metal
pressure casting of ceramic preforms are considered to be
relatively high in cost. In the molten metal mixing process, which
is considered to be a relatively low cost technique, ceramic powder
is mixed with molten metal to produce wrought products or shape
castings. The molten composite has to be stirred continuously prior
to and during the casting process in order to maintain the particle
suspension and minimize the segregation of the ceramic powder in
the mixture. Uniform distribution of ceramic particles is very
difficult to achieve due to large differences in specific gravity
between the metal and ceramic components (e.g., densities of steel
and aluminum oxide powder are approximately 7.8 g/cm.sup.3 and 3.99
g/cm.sup.3, respectively).
[0005] The processing behavior of the molten metal exemplified by
the rheology, sedimentation, reactivity, and fluidity is also
affected by the particulate phase. These factors must be controlled
carefully when a molten metal composite is used for shape casting.
For example, the presence of ceramic particulates in molten
aluminum increases the original viscosity of 10.sup.3 poise
substantially and changes the rheology to non-Newtonian.
[0006] Invariably the viscosity of molten metal increases as the
volume fraction of the reinforcement phase increases and particle
size decreases. This effect causes significant mold design
limitations for casting complex-shaped parts. Sedimentation due to
differences in specific gravity between melt and reinforcement
particles is one of the limitations of the shape casting process.
The settling rate is greatly affected by the shape, size and volume
fraction of the reinforcement particles.
[0007] The dry pressing process for making composite parts also
suffers from distribution problems due to density differences
between ceramic and metal powders. Particle segregation can occur
during the blending, die-filling and pressing steps.
[0008] The present invention provides readily moldable
metal/ceramic composite feedstock compounds suitable for injection
molding complex parts that circumvent the problems associated with
current state-of-the-art shape forming methods. These compounds
overcome the shortcomings of other state-of-the-art shape forming
methods by providing a uniform distribution of the reinforcement
particles. The molding compounds disclosed herein comprise ferrous
and/or nonferrous metal powders and ceramic powders in the form of
oxides, carbides, nitrides, borides, suicides or combinations of
these powders as reinforcement particles. The volume fraction of
the reinforcement particles can vary from 0.1 to 99 vol % depending
on the type of application for the composite. Water is used as the
liquid carrier, and the metal/ceramic composite feedstock compound
can be injection molded at low temperatures (approximately 80 to
90.degree. C.) and low pressures (approximately 500 to 1000 psi) to
produce net or near-net shape articles. The unfired (green) molded
articles can be dried and sintered according to specific sintering
schedules for the composition being used in order to achieve the
final desired properties.
[0009] Injection molding is recognized as a premier forming method
for rapidly producing close tolerance net shape, complex parts in
high volume. In Fanelli et al, U.S. Pat. No. 4,734,237, and U.S.
patent application Ser. No. 08/869,053, the disclosures of both of
which are incorporated herein by reference, processes for
successfully molding net shape, complex parts in high volume are
described.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention will be more fully understood and further
advantages will become apparent when reference is made to the
following detailed description and the accompanying drawings in
which:
[0011] FIG. 1 is a schematic representation of the basic steps of
formulating the composite molding compound according to one
embodiment of the invention.
[0012] FIG. 2 is a photograph showing examples of green and fired
composite parts made from composite feedstock material in a
conventional injection molding machine.
[0013] FIG. 3 is a photograph of a SEM micrograph showing uniform
distribution of the ceramic and metal phases.
SUMMARY OF THE INVENTION
[0014] The invention is directed to a composite molding compound
for forming complex-shaped parts comprising a mixture of a metal
powder and a ceramic powder, a gel-forming material selected from
the group of polysaccharides consisting of agaroids, and a
gel-forming material solvent, the mixture being formulated in a
blender that provides shearing action thereto and the blender being
heated to raise the temperature of the mixture to about 75 to
100.degree. C.
[0015] The invention also provides a method for producing a
homogeneous composite molding compound comprising the steps of
mixing a metal powder with water and a gel-forming material
selected from the group of polysaccharides consisting of agaroids,
mixing a ceramic powder with water and a dispersant, and ball
milling the mixture to reduce the particle size thereof,
compounding the metal powder mixture and the ceramic powder
mixture, and shredding the compound mixture into a particulate
format.
[0016] The invention further provides a process for forming an
article from a composite molding compound comprising the steps of
formulating a composite mixture of a metal powder and a ceramic
powder, a gel-forming material selected from the group of
polysaccharides consisting of agaroids, and a gel-forming material
solvent, the mixture being formulated in a blender that provides
shearing action thereto and the blender being heated to raise the
temperature of the mixture to about 75 to 100.degree. C., supplying
the mixture at a temperature above the gel point of the gel-forming
material into an injection molding machine, and molding the mixture
under conditions of temperature and pressure to produce a
self-supporting article. After being allowed to dry, the article is
then fired according to a sintering schedule for the composite
material being used to obtain the desired properties for the
finished article.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present invention provides aqueous, metal/ceramic
composite molding compounds and a method for compounding the
constituent materials into a homogeneous mixture and format that is
useful for manufacturing finished parts by injection molding.
Metal/ceramic molding compounds refer to compositions containing
ferrous and/or nonferrous metal and metal alloy powders in
combination with ceramic powders. The compositions may comprise 0.1
vol % to greater than 99 vol % ceramic powder in the form of
oxides, carbides, nitrides, borides and suicides also used singly
or as a mixture of two or more of these powders in the metal
matrix. The composite molding compounds also contain water, a
binder selected from the agaroid family of polysaccharides, and
minor amounts of other additives that improve the processability of
the composite molding feedstock. Advantageously, the composite
molding compounds disclosed herein contain a mixture of the
essential ingredients for shape-forming parts by injection molding
and will yield homogeneous metal/ceramic composite finished parts
after firing.
[0018] Agaroids act as a binder that allows the fluidized mixture
to set during the injection molding process and then be removed as
a self-supporting structure. An agaroid has been defined as a gum
resembling agar but not meeting all of the characteristics thereof
[See H. H. Selby et al., "Agar", Industrial Gums, Academic Press,
New York, N.Y., 2.sup.nd ed., 1973, Chapter 3, p.29]. As used
herein, however, agaroid not only refers to any gums resembling
agar, but also to agar and derivatives thereof such as agarose.
Agaroids are used in the present invention because they exhibit
rapid gelation within a narrow temperature range, a factor that can
dramatically increase the production rate of injection molded
articles. The preferred gel-forming materials are those which are
water-soluble including agar, agarose or carrageenan, with the most
preferred materials being agar, agarose and mixtures thereof.
[0019] The invention also provides a method for producing
metal/ceramic composite molding compounds. According to a preferred
method, the metal powder is initially mixed with a gel-forming
material and water, which is a solvent for the gel-forming
material. The gel, which is used as a binder in this composite
compound, is from the group of polysaccharides known as agaroids
such as agar, agarose or mixtures thereof. This type of binder is
water-soluble and provides excellent flow characteristics and rapid
gelation within a specific temperature range, important attributes
that can dramatically increase the production rate of articles by
the injection molding process. Ceramic powder is added to the
mixture in the form of oxides, carbides, nitrides, borides and
suicides, or combinations of two or more of these, ranging from
about 0.1 to greater than 99 vol %. A preferred range is from about
15 to 75 vol %, and the most preferred range is from about 15 to 40
vol %. Water is conveniently and advantageously used as a liquid
carrier for the solid constituents in the mixture to facilitate
transport of the feedstock material along the barrel of an
injection molding machine to the mold within the machine. Water is
also a solvent for the gel-forming agaroid binder, and because of
its relatively low boiling point it is easily removed from the
molded part prior to and/or during sintering. The required amount
of water to be added to the molding compound is dependent on the
desired Theological characteristics for optimum behavior of the
composite material during the injection molding process. According
to the present invention, the required amount of water in the
formulation is between about 5 to 30 wt % of the mixture, with
amounts between about 8 to 20 wt % being preferred. Small amounts
of other additives may also be added to the mixture to serve a
number of useful purposes, such as gel-strength enhancing agents
and additives to preserve the functional effectiveness of the
binder and the shelf life of the composite molding compound.
[0020] It should be understood that the metal and ceramic powders
could be initially mixed together with a gel-forming material and
water instead of adding the ceramic powder to the metal powder
mixture, as described above. Substantially similar results are
obtained using this method.
[0021] The ceramic powder is generally processed to reduce the
particle size before being mixed with the metal powder. The ceramic
material can be in the form of a dry powder or slip. Raw ceramic
powders usually require deagglomeration processing before they can
be used in order to prevent cracks, distortions and non-uniform
distribution of the ceramic particles in the composition and to
optimize the average particle size distribution. A number of
different methods can be employed to accomplish the deagglomeration
processing. One such method is ball milling, which is employed in
the present invention to reduce the particle size of the ceramic
powder before it is mixed with the metal powder. The use of
dispersants and pH control agents are well known for improving the
rheology and processability of ceramic suspensions. In the present
case dispersants based on polyacrylates and polymethylmethacrylate
polymer backbones, and tetramethyl-ammonium hydroxide as a pH
control agent are successfully employed to optimize the rheology of
the ceramic powder. The ceramic powder may be added to the batch as
a form of slip comprising about 5 to 25 wt % water based on the
total weight of the ceramic powder, or it may be dried after
processing and added as a dry powder. The amount of dispersant used
for processing the ceramic powder is about 0.1 to 3 wt %, and the
pH is adjusted to a value between approximately 8.8 to 10.
[0022] The invention further provides a method for combining all of
the various con-stituents of the composite molding compounds into a
homogeneous feedstock material for producing homogeneous composite
molded articles that can be fired without cracking. The metal
powder and, optionally, other additives such as biocides to prevent
bacterial growth and metal borates to improve the gel strength of
molded articles are incorporated with the binder/water mixture at
temperatures ranging from about 75 to 95.degree. C. for a period of
about 30 to 120 minutes. The ceramic powder material can be added
to the mixture as a form of slip or dry powder during the last 15
to 45 minutes of the mixing time. Mixing can be done in a number of
different efficient mixers such as sigma or planetary type mixers.
Since the molding compound must be in a proper format that is
capable of being fed continuously into an injection molding
machine, the homogeneous composite mixture is allowed to cool below
the gelling point of the binder (<37.degree. C.) and then
removed from the mixer. The mixture is placed in a shredder of a
type commonly used in food processing, having a rotating cutter
blade, and shredded into a particulate format. The moisture content
of the shredded feedstock may be adjusted by exposing the material
to the atmosphere and evaporating any excessive moisture. The
shredded composite feedstock is now capable of being fed directly
into the hopper of an injection molding machine. The useful solids
level (wt % of solid material in mixture) in the molding compounds
is in the range of approximately 75 to 88 wt %. It should be
pointed out that the composite feedstock material could also be
prepared using continuous processing such as a twin-screw
continuous compounder.
[0023] As shown in FIG. 2, the composite molding compounds of the
present invention can be molded to net or near-net shape finished
products. After injection molding, the molded green parts are fired
at approximately 1350 to 1450.degree. C. for a period of about 2 to
4 hours to produce finished parts having the desired
properties.
[0024] The following examples are presented to provide a more
complete understanding of the invention. However, the specific
techniques, conditions, materials, proportions and reported data
set forth to illustrate the principles and practice of the
invention are exemplary and should not be construed as limiting the
scope of the invention.
EXAMPLE 1
[0025] A composite mixture of 33 wt % (51 vol %) aluminum oxide
(Al.sub.2O.sub.3) powder and 66.7 wt % (49 vol %) 316L stainless
steel powder was prepared. Aluminum oxide in the amount of 2800 g
was mixed with 933 g of deionized water containing 1 wt % (solids
basis) ammonium polyacrylate solution and a sufficient amount of
tetramethylammonium hydroxide (TMA) to adjust the pH of the mixture
to 9.85. The powder/water mixture was ball milled for about 5 hours
to reduce the average particle size to approximately 1.1 .mu.m. An
aliquot of 1867 g of the suspension (containing 1400 g powder) was
mixed with 42 g agar, 1.4 g calcium borate, 0.39 g methyl-p-hydroxy
benzoate and 0.29 g propyl-p-hydroxy benzoate in a sigma blender
for about 10 minutes at room temperature. Thereafter, 2800 g of
316L stainless steel powder was added to the blender and mixed at
room temperature for about 15 minutes. The temperature was
increased to 93.degree. C. and mixing continued for about 45
minutes. After the material was allowed to cool to room
temperature, it was removed from the blender and shredded into a
particulate format using a food processor (Kitchen Aid KSM90). The
shredded feedstock was dried to an 87.4 wt % solids level by
exposing a loose bed of the material to the atmosphere. Parts were
molded in the shapes of tensile bars, C-clamps and plates, as shown
in FIG. 2, using a 200 to 900 psi injection pressure at
approximately 80 to 95.degree. C. on Boy 15S and 55 ton Cincinnati
injection molding machines. Following molding, the parts were dried
at ambient conditions and fired at approximately 1350.degree. C. to
1450.degree. C. for about 2 to 4 hours.
EXAMPLE 2
[0026] A composite molding compound was prepared using the
procedures of Example 1, except that this composition contained 50
wt % (about 34 vol %) ceramic powder and 50 wt % (about 66 vol %)
metal powder. The batch was dried to an 89.55 wt % solids level.
Rectangular plates (1.9".times.2.5".times.0.27") were molded using
a 200-300 psi injection pressure at 85.degree. C. on the Boy 15S
injection molding machine.
EXAMPLE 3
[0027] In this example the composite molding compound consisted of
10 wt % (18.3 vol %) aluminum oxide (Al.sub.2O.sub.3) and 90 wt %
(81.7 vol %) 316L stainless steel powders. Deionized water, agar
and the other processing aids described in Example 1 were added to
the sigma blender. The temperature was raised to 93.degree. C. and
the agar was allowed to melt completely. 3780 g of 316L stainless
steel powder was added to the melt and mixed for about 30 minutes.
At this stage 560 g of Al.sub.2O.sub.3 slip (containing 420 g of
Al.sub.2O.sub.3 powder; preparation as in Example 1) was added to
the sigma blender and mixed for an additional approximately 40
minutes. The material was allowed to cool to room temperature,
followed by the same shredding and moisture adjusting procedures as
described in Example 1. Test bars and C-clamps were molded in a Boy
15S injection molding machine from this compound.
* * * * *