Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2001-04-03
2003-10-07
Elve, M. Alexandra (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C427S431000, C118S405000, C118S423000
Reexamination Certificate
active
06629557
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
N/A
BACKGROUND OF THE INVENTION
It is known that materials with superior strength and abrasion-resistance may be developed as composite materials by embedding such reinforcing materials as carbon-based fibers, ceramic-based fibers, or ceramic particles in a metal matrix material such as an aluminum alloy. Such metal matrix composite materials can be manufactured by a die-casting machine
100
such as that shown in
FIGS. 1 and 2
. In a precasting process, a preform
103
is sintered to a desired shape after inorganic fibers or ceramic particles are mixed with water, dehydrated and dried. The preform
103
is placed in a metal mold
101
, while a plunger pump
102
is filled with a molten metal
104
of matrix material. Then a piston
105
forces the metal matrix material to infiltrate into the preform in the metal mold to create a metal matrix composite
106
. The metal matrix composite may find various industrial applications including in airplanes and automobiles as a high-strength, light-weight composite material containing inorganic fibers or ceramic particles ranging from 10 to 50% by volume.
Such a manufacturing method of metal matrix composite materials has two problems. First, because the metal matrix composite is not formed in a hermetic state, chemical reactions such as decomposition, precipitation and metal oxidation occur during infiltration, leading to deterioration in the strength characteristics of the composite. Also, when hollow particles are used as a filling material, gravity (buoyancy)-induced particle separation may occur during metal infiltration, making it difficult to manufacture composite materials with a high content of hollow particles.
Fiber-reinforced composite wires manufactured through the infiltration of metals into inorganic (carbon, ceramics, metals, etc.) fiber bundles may also find many industrial applications. Fiber-reinforced composite wires are known to exhibit superior characteristics in durability and reliability. To this end, a molten metal must infiltrate into the interfiber spacing and increase the overall metal volume percentage. One process for the production of such fiber-reinforced composite wires of the required quality is described in U.S. Pat. No. 5,736,199, the disclosure of which is incorporated by reference herein.
This continuous infiltration process uses a metal infiltration apparatus
200
as shown in
FIGS. 3 and 4
. This apparatus is comprised of a pressure chamber
201
and a bath container
203
for a molten metal
202
, such as aluminum, aluminum alloy, or copper. The bath container is heated by a heater
204
and is equipped with an entering orifice
205
at a bottom surface
201
a
of the pressure chamber and an intermediate orifice
207
for passing inorganic fiber bundles through the bath container for metal infiltration. The entering orifice, connected to a bottom surface
203
a
of the bath container, allows inorganic fiber bundles
210
to enter the bath container. The intermediate orifice extends from a position within the molten metal to a closure member
206
that covers the opening section of the bath container. Furthermore, an exit orifice
208
, provided at an upper surface
201
b
of the pressure chamber, allows the metal-infiltrated inorganic fiber bundles to exit from the pressure chamber.
Referring to
FIG. 4
, functions of the orifices will be described by taking the entering orifice
205
as an example. The orifice is cylindrical in shape, and the exterior surface of the orifice is covered with a cooling jacket
214
. An insertion hole
205
b
is formed along the central axis of an orifice body
205
a
and has an inside diameter slightly greater than the outside diameter of fiber bundles
210
that travel upwardly into the insertion hole. A temperature gradient is provided along the orifice such that the temperature is above the melting temperature of the material in the bath nearest the bath container and below the melting temperature farthest from the bath chamber.
A non-reacting gas, such as argon and nitrogen, is introduced into the pressure chamber
201
from a gas supply source
209
. Thus, the interior spaces of both the pressure chamber and the bath container
203
are respectively maintained at preset pressures when the fiber bundles are infiltrated by metal.
In the infiltration apparatus having such a configuration, inorganic fiber bundles that are fed continuously from a bobbin
211
are introduced into the bath container by way of the entering orifice
205
and are brought into contact with the molten metal
202
. Because the interior spaces of both the pressure chamber and the bath container are pressurized by a gas supplied from the gas supply source
209
, the molten metal infiltrates into the interfiber spacing of the inorganic fiber bundles. The metal-infiltrated fiber bundles then leave the bath container
203
by way of the intermediate orifice
207
.
While the inorganic fiber bundles travel through the inside of the pressure chamber
201
, the molten metal that has adhered to and infiltrated into the inorganic fiber bundles is cooled, so that a part of the metal solidifies within and around the inorganic fiber bundles. Subsequently, a take-up bobbin
213
takes up a fiber-reinforced metal matrix composite wire
212
coming out of the pressure chamber
201
through the exit orifice
208
.
The fiber-reinforced metal matrix composite wire thus produced should be impregnated with the metal in the interior as well as the surface of the bundles. However, for certain metal-fiber combinations with poor wetting characteristics, it is difficult to achieve metal infiltration deep into the interfiber spacing of fiber bundles.
Various efforts have been reported for better metal infiltration through improved wetting characteristics by surface-treating inorganic fiber bundles, including thermal CVD (chemical vapor deposition) reactors and vacuum vapor deposition reactors to deposit metal particles on the surface of fiber bundles. These surface treatments are not effective, however, in depositing metal particles deep within inorganic fiber bundles. Additional requirements of these reactors also increase the manufacturing cost of fiber-reinforced composite wires.
Additionally, when the diameter of a fiber-reinforced metal matrix composite wire produced by the above-described continuous infiltration method is reduced, the through holes of the orifices must become smaller accordingly, making it difficult to pass fiber bundles through holes in this method. Also, the walls of the through holes have been made of carbon-based materials such as graphite, which do not exhibit good durability against wear caused by the friction between the walls and the moving wire. If, on the other hand, the walls are made of materials with high resistance against abrasion, the fiber bundles become more vulnerable to breakage within the orifice.
SUMMARY OF THE INVENTION
In a first embodiment of the present invention, a method is provided of manufacturing high-strength, light-weight composite materials with a high content of hollow particles. In particular, the method provides a composite material comprising hollow particles with a mean particle size ranging from 10 to 100 &mgr;m and a metal as a binding agent. The binding material is placed on top of a layer of hollow particles in a pressurizable container. The binding material is separated from the layer of hollow particles by a heat-resistant filter securely fixed at a position between the two materials. After evacuating the pressurizable container, the binding material is heated until it melts completely. The pressurization of the pressurizable container from above, preferably by injection of an inert gas, forces the binding agent to infiltrate into the spaces between the hollow particles.
Preferably, the hollow particles are either ceramic-based hollow particles, particularly, silas balloons, glass balloons, or alumina balloons, or carbon balloons. Preferably, the binding agent comprises gold, silver,
Blucher Joseph T.
Katsumata Makoto
Elve M. Alexandra
Kerns Kevin P.
Northeastern University
Weingarten Schurgin, Gagnebin & Lebovici LLP
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