Note: Descriptions are shown in the official language in which they were submitted.
EH-10789(03-550) ~ 02444917 2003-10-15
COLD SPRAYED COPPER FOR ROCKET ENGINE APPLICATIONS
CROSS-REFERENCE TO RELATED APPLICATION S
[0001 ~ The present application claims the benefit of U.S. Provisional Patent
Application No.
(~() 419,~t03, entitled COLD SfRA~'ED COPPER FOR UPPER STAGE ROCKET
I-'\CINES. !il:cl October 1S. 2002.
FIELD OF THE INVENTION
(0002) The present invention relates to a process for applying a copper
deposit onto surfaces
of a substrate, in particular, a manifold to be used in a rocket engine.
[0003) Rocket thmst chamber designs include two manifolds that collect and
distribute the
fuel (typically liquid hydrogen) to the combustion chamber. One of these
manifolds is
usually located immediately adjacent to the injector assembly where the fuel
and oxidizer
(typically liquid oxygen) are mixed and ignited. Both manifolds are made from
a high
strength stainless steel to contain the high pressure cryogenic fuel. The
manifold that is
located near the injector tends to be exposed to very high temperature
combusted gases. As a
result, this manifold requires active cooling on the face that is closest to
the injector.
[0004) Multiple attempts have been made to electroplate pure copper to this
manifold face to
conduct the coolant across the gap to the injector face. However, the manifold
subsequently
receives a high temperature braze cycle which in the past has resulted in
blistered copper.
Deposit thicker than a few mils is very susceptible to blistering when exposed
to heat due to
entrapped solutions/impurities expanding.
(0005) Plating requires the part to be immersed in acids and plating solutions
for long
durations to achieve thick build ups on parts. Significant masking is
required. Acid exposure
is not always pernnitted on a part and could produce fatigue debits. Another
disadvantage is
that thickness build up is measured in days.
(0006] Thermal spray is another technique for applying a con.formal coating to
a part.
Thermal spray requires the part to be exposed to very high temperatures
locally. Parts with
thermal sensitivities and tight dimensional tolerances (distortion from
thermals) are limited to
this exposure. Oxides are typically formed with thermal spray melting and
resolidification in
air atmosphere. Oxides reduce ductility of coatings significantly and are
difficult to remove.
Vacuum systems are possible but very expensive and difficult to control.
(0007) Thus, there is a need for an improved process for applying a copper
deposit to the
surfaces of a manifold used in a rocket engine.
EH-10789(03-550) CA 02444917 2003-10-15
SUMMARY OF THE INVENTION
[0008] Accordingly, it is an object of the present invention to provide a
process for applying
a copper deposit to a substrate which will not blister after receiving a high
temperature braze
cycle.
[0009) The foregoing object is attained by the process of tllc present
inv:a:tio::.
(0010( In accordance with tltc prcscm invention. at process fur applying a
~icposit ;it a
substrate comprises the steps of providing metal powder particles having a
size in the range
of from a size sufficient to avoid getting swept away from the substrate due
to a bow shock
layer to up to 50 microns and forming a deposit layer on at least one surface
of the substrate
by passing the metal powder particles through a spray nozzle at a speed
sufficient to
plastically deform the metal powder particles on the at least one surface.
[0011) The present invention also relates to a rocket engine having a
stainless steel manifold
coated on at least one of an inner surface and/or an outer surface with a
copper alloy coating.
[0012] Other details of the cold sprayed copper for upper stage rocket
engines, as well as
other objects and advantages attendant thereto, are set forth in the following
detailed
description and the accompanying drawing wherein like reference numerals
depict like
elements.
BRIEF DESCRIPTION OF THE DRAWII~TG
[0013] The figure is a schematic representation of a spray nozzle used to coat
the surfaces of
a manifold used in a rocket engine.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS)
[0014] In accordance with the present invention, a process is provided for
forming a deposit
or coating on outer and/or inner surfaces of a substrate 10, such as a
manifold formed from a
metal alloy material, e.g. stainless steel, used in a rocket engine. The
process is a cold gas
dynamic spraying (or "cold spray") process. In this process, .fine metallic
powders are
accelerated to supersonic velocities using compressed gas, for example helium
and
sometimes nitrogen. Helium is a preferred gas in this process due to its low
molecular weight
and produces the highest velocity at the highest gas cost. The powder which is
used to form
the deposit is typically a metal powder having particles with a size in the
range of from 5
microns to 50 microns. Typical thermal spray powders are usually too large for
cold spray.
Smaller particle sizes such as those mentioned above enable the achievement of
higher
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Eli~10789(03-fJ50) ~ 02444917 2003-10-15
particle velocities. Below 5 microns in diameter, the particles of powder get
swept away
from the substrate due to a bow shock layer just above the substrate
(insufficient mass to
propel through the bow shock). The narrower the panicle size distribution, the
better the
velocity is. This is because if one has large and small particles (bi-modal),
the small ones
will hit the slower, larger ones and effectively reduce the velocity of both.
~Q015i Tlle bOtld117g 111eChat11St17 etllplp\'etl by tl7C pl-OCCSS Of the
p1'CSellt 111VCIltlOtl for
11'E117Sf01'lllill~ the metal powder into a deposit is strictly solid state,
lneanin;~ th<It tile yarticics
plastically defonll. Any oxide layer that is formed is broken up and fresh
metal-to-metal
contact is made at very high pressures.
[0016] The powders used to form the deposit are fed using modified thermal
spray feeders.
Difficulty in feeding using standard feeders is due to the fine particle sizes
and high
pressures. One custom designed feeder which may be used is manufactured by
Powder Feed
Dynamics of Cleveland, Ohio. This feeder has an auger type feed mechanism.
Fluidized bed
feeders and barrel roll feeders with an angular slit may also be used.
[0017] In the process of the present invention, the feeders are pressurized
with either nitrogen
or helium. Feeder pressures are usually just above the main gas or head
pressures, which
head pressures usually range from 250 psi to 500 psi, depending on the powder
alloy
composition. The main gas is heated. Gas temperatures are usually 300°F
to 1200°F, but can
go as high as approximately 1250°F depending on the material being
applied to the substrate.
The gas is heated to keep it from rapidly cooling and freezing once it expands
past the throat
of the nozzle. The net effect is a substrate temperature of about 1 I
5°F during deposition
{thus cold spray, not warm spray).
(0018] To form the deposit on the substrate 10, the nozzle 20 of a spray gun
22 must pass
over the surface{s) 24 and 26 of the substrate 10 more than once. The number
of passes
required is a function of the thickness of the deposit to be applied. The
process of the present
invention is capable of forming a deposit 28 having a thickness of 2 - 30 mils
per pass. If
one wants to form a thick layer, the spray gun 22 can be held stationary and
be used to form a
deposit layer which is 2 inches to 3 inches high. When building a deposit
layer, one needs to
limit the thickness per pass in order to avoid a quick build up of residual
stresses and
unwanted debonding between deposit layers. A thickness of S mils per pass
appears to be
optimal.
(0019] It has been found that if one wanted to apply a copper or copper alloy
deposit or
coating 28 to a substrate 10, such as a stainless steel manifold, one can use
copper powder
having particles with a size of up to 50 microns, preferably a particle size
in the range of from
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Eli-10789(03-550) CA 02444917 2003-10-15
microns to 30 microns. The main gas may be passed through the nozzle 20 via
inlet 30
and/or 32 at a flow rate of from 0.001 SCFM to 50 SCFM, preferably in the
range of from 1S
SCFM to 35 SCFM, if helium is used as the main gas. If nitrogen is used by
itself or in
combination with helium as the main 'gas, the nitrogen gas may be passed
through the nozzle
20 at a tow rate of from 0.001 SCFl~t to 30 SC.'FM, preferably from 4.0 SCFM
to 30 SCFM.
ThL main 'gas tcmpcrature may be in the ran'~c of from 600 "F to 1200 "F. The
pressure of the
spray 'gun ?? may be in the rany~c oi~ iiwm 2uu psi to ;ou psi, preferably
from 250 psi to s50
psi. 'I-he copper powder may be fed into the gun via line 34 at a rate in the
range of from 10
grams/min. to 100 gramslmin, preferably from 18 gramshnin. to 50 grams/min.
The copper
powder is preferably fed using a carrier gas, introduced via inlet 30 and/or
32, having a flow
rate of from 0.001 SCFM to 50 SCFM, preferably from 10 SCFM to 35 SCFM, for
helium
and from 0.001 SCFM to 30 SCFM, preferably from 4.0 SC.FM to 10 SCFM, for
nitrogen.
Preferably, the spray nozzle 20 is held at a distance away from the surfaces)
24 or 2G of the
substrate 10 being coated. This distance is known as the spray distance.
Preferably, the
spray distance is in the range of from l0 mm. to 50 mm. The deposit thickness
per pass may
be in the range of 0.001 inch to 0.030 inches.
[0020] While the present invention has been described in the context of
applying copper
powder, the process of the present invention may be used to apply an aluminum
based alloy
or a nickel based alloy deposit. The harder the alloy, the higher the
parameters needed to get
close to the as-sprayed density of softer alloys. The parameter ranges
mentioned above for
forming a copper deposit may also be used to form an aluminum deposit or a
nickel deposit.
For example, an aluminum alloy deposit may be formed using a gun head pressure
of 300 psi,
a gas temperature of 600°F, a powder feed rate of 21 grams/min., a
carrier flow rate of 13
SCFM helium, and a main gas flow rate of 34 SCFM helium.
[0021] The process of the present invention has the advantages of eliminating
long-lead times
and non-environmentally friendly plating processes and can be accomplished in
a much
shorter time than other plating techniques, which techniques often take weeks.
[0022] The process of the present invention has particular utility in applying
a thick copper
deposit, greater than 0.050 inches, to internal and outer surfaces of a
stainless steel manifold
used in rocket engines.
[0023] It has been found that deposits formed on stainless steel substrates in
accordance with
the present invention can undergo heat treatment cycles, such as a
1800°F heat treatment,
without blistering or bond disintegration. Further, the deposits can withstand
cryoshock and
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EH-10789(03-$Sfl~ ~ 02444917 2003-10-15
thernial cycling without bond failure or weakening of coating integrity. Still
further, the
deposits do not blister or de-bond.
[0024] It is apparent that there has been provided in accordance with the
present invention a
cold sprayed copper for upper stage rocket engines which fully satisfies the
objects. means,
and adv,.nta~~es sei forth hereinbefore. While the present invention has been
described in the
ro;~text ol'snecific embociin~ents thereof, other <rlternatives,
modifications, anti variations mill
f~econw ahparcnt to those skilled in the art having read the fore~~oin'~
description.
:accordingly, it is intended to embrace-those alternatives, modifications, and
variations as tall
within the broad scope of the appended claims.
