U.S. patent application number 11/806622 was filed with the patent office on 2007-11-08 for airflow masking of carbon-carbon composites for application of antioxidants.
This patent application is currently assigned to HONEYWELL INTERNATIONAL INC.. Invention is credited to David R. Cole, Phillip D. Johnson, Allen H. Simpson, Richard W. Smith, Marcia A. Wright.
Application Number | 20070256634 11/806622 |
Document ID | / |
Family ID | 35845772 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070256634 |
Kind Code |
A1 |
Simpson; Allen H. ; et
al. |
November 8, 2007 |
Airflow masking of carbon-carbon composites for application of
antioxidants
Abstract
Mask (10, 10', 21, 22, 30) for use in coating a carbon-carbon
composite brake disc (25) with anti-oxidant. The mask is composed
of carbon-carbon composite material or nonreactive ceramic
material. The mask is configured with edge ridges (11, 13, 34, 36)
that are aligned with the outer and inner annular diameters of the
carbon-carbon composite brake disc, a gas flow channel (12, 32)
between the ridges, and a gas access port (18, 40) that allows gas
to enter the gas flow channel. The mask may also include a gas exit
port (16) having a valve (17) operatively connected thereto, so
that gas flow may be restricted when pressure within the mask and
carbon-carbon composite brake disc falls below a specified minimum
value. Also, a method of avoiding application of liquid antioxidant
material to a friction surface of a carbon-carbon composite brake
disc, by: covering the friction surface with a mask configured to
deliver compressed gas to the friction surface, and directing
compressed gas across the friction surface and through pores in the
carbon-carbon composite brake disc and/or in the mask while the
masked brake disc is in the presence of the antioxidant material in
a liquid state.
Inventors: |
Simpson; Allen H.;
(Buchanan, MI) ; Smith; Richard W.; (Marcellus,
MI) ; Wright; Marcia A.; (Niles, MI) ;
Johnson; Phillip D.; (Niles, MI) ; Cole; David
R.; (North Liberty, IN) |
Correspondence
Address: |
HONEYWELL INTERNATIONAL INC.;Law Department AB2
P.O. Box 2245
Morristown
NJ
07962-9806
US
|
Assignee: |
HONEYWELL INTERNATIONAL
INC.
|
Family ID: |
35845772 |
Appl. No.: |
11/806622 |
Filed: |
June 1, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10942222 |
Sep 16, 2004 |
7241476 |
|
|
11806622 |
Jun 1, 2007 |
|
|
|
Current U.S.
Class: |
118/406 ;
118/505 |
Current CPC
Class: |
B05D 1/18 20130101; B05D
1/32 20130101; F16D 69/02 20130101; F16D 2250/0038 20130101; B05D
3/042 20130101 |
Class at
Publication: |
118/406 ;
118/505 |
International
Class: |
B05C 3/00 20060101
B05C003/00 |
Claims
1. A mask for coating a carbon-carbon composite brake disc, said
mask being composed of carbon-carbon composite material or
nonreactive ceramic material, said mask being configured with (i)
edge ridges that are aligned with the outer and inner annular
diameters of the carbon-carbon composite brake disc, (ii) a gas
flow channel between said ridges, and (iii) a gas access port that
allows gas to enter said gas flow channel.
2. The mask of claim 1, which further comprises a gas exit port
having a valve operatively connected thereto that allows
restriction of gas flow when pressure within the mask and
carbon-carbon composite brake disc falls below a specified minimum
value.
3. The mask of claim 1, wherein said mask is composed of
carbon-carbon composite material having an open pore structure or
of nonreactive ceramic material having an open pore structure.
4. The mask of claim 1 for coating a carbon-carbon composite brake
disc having an open pore structure, wherein said mask is composed
of carbon-carbon composite material that does not have an open pore
structure or of nonreactive ceramic material that does not have an
open pore structure.
5. The mask of claim 1 wherein at least one of said edge ridges
includes a plurality of channels.
6. The mask of claim 5 wherein said channels are substantially
perpendicular to an edge of said mask.
7. An assembly comprising: at least one carbon-carbon disk having a
first side and a second side and an inner diameter and an outer
diameter; a first annular mask having an inner diameter and an
outer diameter, an inner peripheral ridge and an outer peripheral
ridge, a gas flow channel between said inner and outer peripheral
ridges, and a gas access port communicating with said gas flow
channel; a second annular mask substantially identical to the first
annular mask; said first annular mask being mounted against said
first side of said at least one carbon-carbon disk and said second
annular mask being mounted against said second side of said at
least one carbon-carbon disk.
8. The assembly of claim 7 including support means for holding said
first annular mask and said second annular mask against said at
least one carbon-carbon disk.
9. The assembly of claim 7 wherein said first annular mask inner
diameter is substantially equal to the inner diameter of said at
least one carbon-carbon disk and said first annular mask outer
diameter is substantially equal to said at least one carbon-carbon
disk outer diameter.
10. The assembly of claim 7 wherein said outer peripheral ridge
includes an inner edge and an outer edge and a plurality of
channels connecting said inner edge and said outer edge.
11. The assembly of claim 10 wherein said channels are radially
aligned.
12. The assembly of claim 10 wherein said channels have a width of
from about 0.1 to 1000 micrometers.
13. The assembly of claim 12 wherein said channels are radially
aligned.
14. The assembly of claim 10 wherein said first mask comprises
carbon-carbon composite material.
15. The assembly of claim 10 wherein said first mask comprises a
nonreactive ceramic material.
16. The assembly of claim 10 including at least one support fixture
holding said first and second masks against said at least one
carbon-carbon disk and supporting said first and second masks and
said at least one carbon-carbon disk.
Description
[0001] The present invention is a continuation-in-part of U.S.
application Ser. No. 10/942,222, filed Sep. 16, 2004, and claims
priority from that application under 35 U.S.C. 120.
FIELD OF THE INVENTION
[0002] The present invention is directed to a reliable fixture and
methodology used to apply a liquid coating to a porous material and
to dry that coating in a fast and efficient manner such that it
covers only the desired surfaces of the porous material. This
invention thus provides a simple, low cost and effective method to
prevent application of antioxidant to the friction surfaces of
carbon-carbon composite brake discs. In accordance with the present
invention, a non-reactive mask is created for the brake disc. A
positive airflow is introduced through the mask into the friction
surface. The air flows out at the mask-disc interface and through
the pores of the brake disc. This prevents antioxidant from
reaching friction surfaces where it could modify friction
efficacy.
BACKGROUND OF THE INVENTION
[0003] Certain porous materials need to have liquid coatings
applied. Difficulties arise if the coatings are to be applied only
to part of the porous material, because transport of the liquid
through the porous material will occur. The liquid will then be in
regions where the presence of the liquid or its residue is
undesirable. An example of this is a carbon-carbon composite brake
disc, where liquid anti-oxidant material should be applied only to
the non-friction surfaces and must not contaminate the friction
surfaces.
[0004] Brake discs that operate at high temperatures, such as those
used in commercial and military aircraft, should be manufactured
from materials having high heat resistance and long wear
characteristics. Such brake discs normally operate at temperatures
that exceed 1300.degree. F. and can reach 2000.degree. F. Such
brake discs are commonly made of carbon-carbon composite materials.
However, carbon can oxidize at elevated temperatures, which can
cause disc weakening and can lead to structural damage and/or
reduction of brake disc life.
[0005] Anti-oxidants are usually applied to the carbon surfaces to
protect carbon-carbon composite brake discs from oxidation,
maintain disc strength, and avoid early disc failures.
Anti-oxidants can affect the friction and wear characteristics of
the disc, and thus extreme care is required to prevent the
anti-oxidant coating from reaching the friction surfaces. Heavy
anti-oxidant coating may be necessary for discs operating at
temperatures exceeding 1000.degree. F., which may require several
repetitions of the coating procedure, thus increasing cost. The
available methods to apply the anti-oxidant to the non-friction
surfaces of a carbon-carbon composite disc include manual or
robotic techniques with possible masking of friction surfaces,
which can be slow, inefficient, and costly. In addition, these
methods are ineffective because the carbon-carbon composite
material may have an open pore structure that will promote
transport of the liquid anti-oxidant materials to the friction
surfaces.
[0006] For instance, U.S. Pat. No. 5,686,144 describes a process in
which a friction face of a brake disc is masked by a plate to
isolate and seal the exterior from liquids. The plate is a
fluid-tight plate. In order to achieve fluid-tightness, the plate
may have annular grooves near its inner and outer circumferences,
with rubber O-rings located in the grooves. See FIG. 5 of the
patent. Alternatively, the faces of the plates that are turned
towards the discs may be provided with elastic beads or edges of
molded rubber. See FIG. 6 of the patent. In another variation, the
plates may be constituted by elastically deformable sheets, for
example of rubber. See FIG. 7 of the patent. The patent teaches
that it is also possible to seal the friction faces by forming a
surface coating that can subsequently be peeled off. The masked
disc is immersed in a bath of impregnating composition containing a
substance that can form a protective layer against oxidation.
Impregnation is effected by establishing a pressure difference
between the pressure at the exterior of the exposed surfaces of the
immersed brake disc and the pressure inside the internal open pore
space of the brake disc. This forces the impregnating composition
to penetrate into the internal open pore space of the disc to form
an internal oxidation protection.
SUMMARY OF THE INVENTION
[0007] The present invention involves protecting the friction
surface of a carbon-carbon composite brake disc with a mask. In
this invention, the mask matches the edges of the friction surface,
but it does not create a seal with the disc. The carbon-carbon
composite disc may be sandwiched between two masks to protect
friction surfaces on both sides of the disc. Both the target
material and the masks are then dipped in a bath of coating. While
immersed and until the coating is dried, compressed air or other
gas is forced into the assembly and out through open pores in the
target material and the gaps at the interface between the target
material and the mask material. This prevents the liquid
anti-oxidant from being transported to the friction surfaces. The
flow of gas is maintained until the coating is dry and thus
immobilized. This approach improves upon current coating techniques
by proving a fast, reliable, and relatively inexpensive method to
apply the coating material to only the non-friction surfaces of a
carbon-carbon composite disc.
[0008] One embodiment of the present invention is a method that
enables the application of a liquid coating material to only
selected surfaces of a solid material. The method involves applying
the liquid coating material to the solid material and subsequently
drying the treated solid material while directing compressed gas
across the surfaces of the solid material that are to be kept free
of the coating material. In use, the gas is normally compressed to
less than 20 psi. The gas is supplied, for instance, at a rate of
0.2-2.0 cubic feet per minute. In this invention, the compressed
gas is directed by means of a mask. Normally, at least one of the
material and the mask is porous. In a particularly preferred
embodiment, the mask is composed of porous carbon-carbon composite
material, the solid material to be coated is a porous carbon-carbon
composite brake disc, and the liquid coating material is an
antioxidant. The gas is supplied at a volume-rate sufficient to
maintain air velocity through the pores and through an interface
between the mask and the solid material during the application and
drying of the liquid coating material. The compressed gas may be
heated, e.g. to a temperature in the range of 100-350.degree. C.,
in order to speed the drying (curing) of the liquid coating
material.
[0009] A preferred embodiment of the invention is method of
avoiding application of liquid antioxidant material to a friction
surface of a carbon-carbon composite brake disc. This method
embodiment includes the steps of covering the friction surface with
a mask configured to cover the friction surface with compressed
gas, and directing compressed gas across the friction surface and
through an interface between the carbon-carbon composite brake disc
and the mask and through pores in the carbon-carbon composite brake
disc and/or in the mask while the masked brake disc is in the
presence of the antioxidant material in a liquid state. The
compressed gas may be heated prior to directing it across the
friction surface and through the disc/mask interface and the pores.
Prior to this heating step, the pressure of the gas may be reduced
from a pressure of 20-180 psi to a pressure of less than 20
psi.
[0010] Another embodiment of the present invention is mask for
coating a carbon-carbon composite brake disc. This mask may be
composed of carbon-carbon composite material or nonreactive ceramic
material. The mask may but need not have an open pore structure The
mask may be configured with (i) edge ridges that are aligned with
the outer and inner annular diameters of the carbon-carbon
composite brake disc, (ii) a gas flow channel between said ridges,
and (iii) a gas access port that allows gas to enter said gas flow
channel. The mask may have a gas exit port having a valve
operatively connected thereto that allows restriction of gas flow
when pressure within the mask and carbon-carbon composite brake
disc falls below a specified minimum value.
[0011] Yet another embodiment of the invention comprises an
assembly that includes a carbon-carbon disk and first and second
masks masking first and second sides of the disk. The disk has a
first side and a second side and an inner diameter and an outer
diameter, while the masks each have an inner diameter and an outer
diameter, an inner peripheral ridge and an outer peripheral ridge,
a gas flow channel between the inner and outer peripheral ridges,
and a gas access port communicating with the gas flow channel. The
first annular mask is mounted against the first side of the
carbon-carbon disk and the second annular mask is mounted against
the second side of the carbon-carbon disk.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present invention will be more fully understood from the
detailed description given hereinbelow, and from the accompanying
drawings. The drawings, which are in general not to scale, are
provided by way of illustration only, and should not be construed
as limiting the present invention.
[0013] FIGS. 1A, 1B, 1C, and 1D show perspective views of typical
mask pieces of the present invention.
[0014] FIGS. 2A, 2B, and 2C show schematic cross-sectional views of
various combinations of masks and carbon-carbon composite discs of
the present invention.
[0015] FIG. 3A is a schematic cross-sectional view illustrating the
flow of gas in accordance with the present invention. FIG. 3B is a
cross-sectional view schematically illustrating a finished product
of the present invention.
[0016] FIG. 4 is a photograph showing carbon-carbon composite discs
and masks held together by an external fixture in accordance with
the present invention.
[0017] FIG. 5 is a photograph showing immersion of the disc/mask
assembly of FIG. 4 in an anti-oxidant bath in accordance with the
present invention.
[0018] FIG. 6 is a block diagram illustrating overall airflow paths
in accordance with an embodiment of the present invention.
[0019] FIG. 7 shows a perspective view of another embodiment of a
mask according to the present invention.
[0020] FIG. 8 is an enlarged plan view of region VIII of FIG.
7.
DETAILED DESCRIPTION
[0021] The present invention provides a process by which a durable
and effective oxidation protection can be applied to the
non-friction surfaces of a carbon-carbon composite brake disc
without altering the tribological characteristics of the materials
in the friction portions of the disc. The process of this invention
comprising masking each friction face of a brake disc to isolate it
from the exterior from liquids, and immersing the brake disc in a
bath containing an impregnating composition containing at least one
substance which can form a protective layer against oxidation.
[0022] In accordance with the present invention, a carbon-carbon
composite mask may be created for each friction surface of a disc.
The mask is designed to match the edges of the friction surface,
but it is not intended to create a perfect seal with the disc. A
channel may be machined into the mask to permit airflow to nearly
all areas of the friction surface. Air pressure may be applied to
the porous friction surface of the disc through the mating
carbon-carbon composite mask. Once the mask is applied and clamped,
antioxidant liquid may be applied using a brush or spray or by
dipping. As those skilled in the art know, means can be provided to
rotate the disc about a horizontal axis if the antioxidant is being
applied by dipping in a bath. Preferably, several brake discs are
simultaneously immersed and impregnated, each friction face being
masked, the discs being disposed coaxially and assembled in a
clamping apparatus. Two facing friction faces can be masked using a
single plate, which is applied to each of the two friction
faces.
[0023] At this point, the airflow through the mask against the
friction surface of the brake disc will prevent the antioxidant
liquid from contacting the friction surface. The rate of airflow
may be adjusted for disc size and material properties to assure
successful masking. Normally, the airflow will be stopped and the
mask removed only after the impregnated antioxidant has dried in
and on the carbon-carbon composite friction material. The gas used
to maintain pressure may be preheated to speed drying. Desirable
gas temperatures may be selected based upon the gas being employed
and the length of time desired to dry the coating. Gas temperatures
as high as 350.degree. C. have been found to be suitable. Even
higher temperatures however may be used.
[0024] Impregnating compositions that may be used in this invention
may comprise solutions or suspensions. Typical impregnating
compositions may comprise, for instance, aqueous solutions of
20-60% P.sub.2O.sub.5, 10-30% ZnO, 10-30% Na.sub.2O, up to 20% of
CuO, CoO, NiO, FeO, MgO, and/or PbO, up to 15% of Li.sub.2O and/or
K.sub.2O, up to 20% of Bi.sub.2O.sub.3, Al.sub.2O.sub.3, and/or
B.sub.2O.sub.3, and up to 5% of V.sub.2O.sub.5 and/or TiO.sub.2.
Other coating materials that may be applied to selected surfaces of
a material such as a carbon-carbon composite brake disc by the
method of this invention include slurries of ceramic precursors,
including (but not limited to) silicon, titanium, or carbon
powders. The ceramic precursors would then be reacted to form
ceramic coatings in subsequent operations.
[0025] A typical mask piece 10 is shown in FIGS. 1A and 1B. FIG. 1A
shows the mating surface of the mask. FIG. 1B shows the outside
surface of the mask. A mask for use in the present invention will
generally be made of a porous carbon-carbon composite having an
open pore structure. It may, however, alternatively be made of a
non-reactive porous ceramic material. When the material being
treated is porous, the mask need not be porous. FIG. 1A is a bottom
perspective view of mask piece 10, in which one can see a channel
12 formed by ridges 11, 13 located at the edges of the annular
mask.
[0026] The mask may have a pre-drilled hole fitted with inserts
that will allow compressed gas to be pumped through it. A gas
access port 18 is also shown in FIG. 1A. FIG. 1B shows a top
perspective view of mask piece 10. In FIG. 1B, the top surface of
the mask is shown as flat. However, it may have any convenient
configuration. A gas nozzle 19 that connects to the gas access port
is shown in FIG. 1B. In some circumstances, for instance when
coating especially large brake discs with antioxidant, it may be
desirable to locate more than one gas entry assembly in the
mask.
[0027] FIGS. 1C and 1D depict an alternative embodiment of the
present invention, in which mask 10' is provided with a gas vent
port 16 and gas vent nozzle 17. The gas vent nozzle 17 may comprise
a valve that is operatively connected to the gas exit port in order
to permit restriction of gas flow when pressure within the mask and
carbon-carbon composite brake disc falls below a specified minimum
value. This gas vent assembly is shown located 180.degree. away
from the gas entry assembly. The use of a gas vent assembly in the
masks of the present invention allows for much faster gas
throughput. It also facilitates recapture of the gas, which may be
desirable when the gas is for instance a relatively expensive gas
such as argon or helium. Optionally, more than one gas vent
assembly may be located in the mask.
[0028] FIGS. 7 and 8 depict a further embodiment of the present
invention in which a mask 30 is shown. Mask 30 is generally similar
to the masks of the previous embodiments of the invention and
includes a channel 32 formed between an inner ridge 34 and an outer
ridge 36. Unlike the other embodiments, in the present embodiment,
at least outer ridge 36 and optionally, inner ridge 34 as well,
have a plurality of micro-channels 38 formed therein having a width
of approximately 0.1 to 1000 micrometers. These micro-channels 38
may be formed, for example, with a grinder. A gas access port 40 is
also illustrated.
[0029] FIG. 8 depicts an enlarged portion of outer ridge 36 in
which micro-channels 38 are visible. It may be desirable to form
these channels at right angles to the edges of the mask 30. The
mask 30 of this embodiment is useful when both the mask and the
material being processed are formed from non-porous materials. When
the mask 30 is applied to an object being treated, micro-channels
38 allow pressurized gas from channel 32 to flow outwardly from
between the mask 30 and the object being processed which reduces or
eliminates wicking of fluid into the gap between the mask and the
object being processed, thereby keeping a processing fluid away
from the surface being protected by mask 30. These micro-channels
are not required when either the mask or the material being
processed is porous because the porous material allows sufficient
airflow between the mask and object being processed to
substantially prevent wicking.
[0030] As shown in FIGS. 2A, 2B, and 2C, various combinations of
masks and carbon-carbon composite discs may be utilized in the
course of implementing the present invention. In FIG. 2A, both the
top and the bottom of carbon-carbon composite disc 25 are masked by
masks 21, 21. In FIG. 2B, two discs 25, 25 are stacked upon one
another, and the top and bottom of the stack are masked by masks
21, 21. In FIG. 2C, two discs 25, 25 are stacked separated by a
mask 22 that has an air channel on both sides. The top and bottom
of the stack are both masked by single-channel masks 21, 21. The
masks in FIGS. 2A-2C, except for the center mask in FIG. 2C,
correspond to a cross-section at line I--I in FIGS. 1A and 1B.
[0031] The gas generally used in the present invention is air,
compressed to less than 20 psi gauge pressure. Lower gauge
pressures, e.g. as low as 1 psi, may be used. However, for economic
reasons, operation is generally in the range 5-15 psi. It is
important that the volume rate of the compressed gas supplied be
sufficient to maintain gas velocity through all pores during
application of the liquid. The volume rate of gas required will
vary considerably based upon the pore size and the pore structure
of the mask and the target materials. Generally, the flow rate used
in this invention is very high, so that the pressure shows as zero
on the gauge regardless of the target pressure at the regulator.
Also, since the gas normally cools as it expands, the actual
temperature as it enter the apparatus is lower than the initial
temperature of the compressed gas used. Air (oxygen) will not
oxidize carbon-carbon composites below 300.degree. C. However, any
gas that is inert under the conditions of use may be employed in
the present invention. Typical inert gases that may be employed
include nitrogen, helium, and argon.
[0032] It is noted that the present invention does not make use of
vacuum and does not involve impregnation of the brake discs being
treated. If vacuum were applied to the discs for even a short time
while they were in the presence of liquid antioxidant coating,
liquid would preferentially reach the friction surfaces.
Accordingly, at all times during immersion and until the liquid is
dry, the internal gas pressure in the brake discs and in the mask
must be higher than ambient pressure. Any impregnation will occur
only as incidental impregnation of closed pores that are unaffected
by the gas flow.
[0033] FIG. 3A illustrates the flow of gas in accordance with the
present invention. FIG. 3A shows the bottom of a porous
carbon-carbon composite disc, the size of the pores being greatly
exaggerated for illustrative purposes. A mask is located on top of
the disc. The mask and disc assembly is immersed in an anti-oxidant
bath. Compressed gas flows down through the access port in the mask
into the channel in the mask. The compressed gas in the channel
flows out through the pores in the carbon-carbon composite disc,
and also flows out through the interface between the ridges of the
mask and the outer edges of the disc. It is this flow of
pressurized gas out through the interface between the mask and the
disc that prevents coating materials from reaching the surface of
the disc covered by the mask. FIG. 3B shows the finished product, a
porous carbon-carbon composite disc having anti-oxidant coating its
outer and inner sides but being free of anti-oxidant on the surface
that was covered with the mask.
[0034] FIGS. 4 and 5 show a disc/mask combination of the type
depicted schematically in FIG. 2B. The carbon-carbon composite
discs and masks may be held together by an external fixture, such
as that shown in FIG. 4. The disc/mask assembly is then dipped and
rotated in a bath of anti-oxidant materials as compressed gas is
pumped into the assembly. The compressed gas provides sufficient
propelling force to prevent the liquid anti-oxidant from being
transported to the inside of the assembly and touching or
penetrating the friction surfaces. Immersion of the disc/mask
assembly in an anti-oxidant bath is illustrated in FIG. 5.
[0035] FIG. 6 is a block diagram illustrating overall airflow paths
in accordance with an embodiment of the present invention. While
air is referred to for convenience in this description, those
skilled in the art will appreciate that similar considerations
apply to other gases which can be used in practicing this
invention. Air is supplied to the system at a pressure of 20-180
psi and is regulated to a pressure below 20 psi gauge pressure for
use in the process of the invention. The air passes through a
heater. The heater has a thermostat permitting temperatures of
approximately 0-700.degree. F. (-18 thru 371.degree. C.).
Immediately following the heater a small vent to the atmosphere is
located to ensure that air flows at all time through the heater and
over the thermocouple that controls the heater. This is to ensure
that the heater does not self-destruct. Airflow through the heater
will be at a rate of, for instance, approximately 0.5 cubic feet
per minute. A hose or pipe then passes the hot air into the mask
through a gas inlet port. The hot, compressed air in the port
escapes through the pores of the porous disc and/or porous mask and
also through the interface between the disc and the mask.
Optionally, an exit port may be located in the mask. The exit port
is generally situated in the mask as far from the inlet port as
possible, in order to promote maximum circulation of air within the
mask. A relief valve at the exit port, set to a pressure below 20
psi, prevents air from escaping too rapidly. This speeds the drying
process. Too rapid voiding of the air would allow the pressure
inside the disc/mask assembly to drop, which would lead to
expansion of the air and concomitant cooling thereof. This in turn
would slow the drying process.
[0036] The compressed air or other gas employed in the present
invention may be heated to speed up the drying or curing of the
liquid coating. It has been found with one embodiment of this
invention, for instance, that the drying time is about 25 minutes
with unheated air and less than five minutes using air heated to
about 325.degree. F. (163.degree. C.) prior to its expansion in the
apparatus
[0037] EXAMPLE. Stator discs for aircraft brakes are made of
carbon-carbon composite material having a residual internal pore
space of about 10% by volume. Three discs are assembled coaxially
and the friction faces of the discs are masked using annular end
plates and an intermediate plate, as illustrated in FIG. 2C herein.
The mask plates are formed of carbon-carbon composite having a
residual internal pore space of about 10% by volume. The inner and
outer diameters of the mask plates used in this invention are about
the same as the inner and outer diameters of the stator discs. The
discs mounted in the apparatus are immersed in a bath constituted
by an aqueous solution of phosphate glass precursors: 39%
H.sub.2PO.sub.4, 13% MnPO.sub.4, 3% KOH, 5% NaBO.sub.3, and 40%
water. The discs are immersed in the bath for 5 minutes, during
which time compressed air at 5 psi gauge pressure and ambient
temperature is forced into the mask plates. The coated, masked disc
assembly is then removed from the bath and dried at a temperature
of about 750.degree. C. Subsequently, the coated brake discs are
freed from the apparatus and separated for use in an aircraft
landing system.
[0038] The amount of anti-oxidant deposited on the surfaces of the
porous material may be measured by the weight gain per unit area
before and after application. A typical relative weight gain in
accordance with this invention is less than 2%, depending on the
material used. The present approach matches the results of
conventional methods, but is faster and more reliable.
[0039] The approach of this invention can be used in many different
applications in which a liquid phase material must be applied to
selected areas of a solid porous material, regardless of the
particular solid and liquid materials involved.
* * * * *