Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HIGH VELOCITY PQ~ THERMA1._SP~AY METE~OD
OR SPRAYI~Ç NON MELTAE~LE MATERIALS
This invention relates to thermal spraying and particularly to a
method for combustion thermal spraying powder at very high
velocity.
8ACKGRO~ND OF THE INVENTION
Thermal spraying, also known as flame spraying, involveæ the
melting or at lea~t heat softening o~ a heat fusible material
such as metal or ceramic, and propelling the softened material in
particulate form against a surface which i8 to be coated. The
heated particles strike the surface where they are quenched and
bonded thereto. A thermal spray gun is used for the purpose of
both heatins and propelling the particles. In one type of
thermal spray gun, the heat fusible ~terial is supplied to the
gun in powder form. Such powderæ are typically co~pri~ed of
small particle~, e.g., between 100 me~h U. S. S~andard screen
~ize (149 microns~ and about 2 microns~ Beat for powder spraying
is generally from a combustion flame or an arc-generated plas~a
flame. The carrier gas, which entrains and transports the
powder, may be one of the combustion gases or an inert gas such
as nitrogen, or it may ~imply be compressed alr
Quality coating~ of certain thermal spray material~ have been
produced by spraying at high velocityO Plasma spraying has
proven 6uccessful with high velozity in many re~pect~ but it ~an
suffer from non-uniform heating and~or poor particle entrainment
which must be effected by feeding powder laterally into the high --
velocity plasma stream. U.S. Patent No.~ 2,714,563 and 2,964,420
~both Poorman et al) disclose a detonation gun for blasting
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powdered material in a series of detona~ion6 to produce coatings
such a~ metal bonde~ carbide~. ~igh density and tenacity of
coatings are achieved by high impact of the powder particles, and
the short dwell time in the heating zone minimizes oxidation at
th~ high spray temperatures.
A rocket type of powder spray gun can produce excellen~ coatings
of metals and metal bonded carbides, particularly tungsten
carbide, and is typi~ied in U.S. Pa~ent No~. 3,741,792 (Peck et
al.) and 4,416,421 (~rowning). This type of gun has an internal
combustion chamber with a high pressure combustion effluent
directed through a nozzle chamber. Powder is fed laterally into
the flame or into the nozzle chamber to be heated and propelled
by the combustion effluent.
Short-nozzle spray devices are disclosed foc high velocity
spraying in French Patent No. 1,041,056 and U.S. Pa~ent No.
2,317,173 (Bleakley). Powder is fed ~xially into a melting
chamber wi~hin an annular flow of combu~tion gas. An annular air
flow is injected coaxially outside of the combustion gas flow,
along the wall of the chamber. The spray trea~ with the heated
powder issues from the open end o~ the combustion chamber.
Since thermal spraying involve~ melting or at least surface hea~
softening the spray material, non-meltable powder~ such afi
certain carbides and nitrides cannot be sprayed into ~ucce~sful
coatings without incorporating a binder into the ~aterial~ For
example, powders may be formed by cladding a metal onto a core of
non-meltable material as disclosed in U.S. Patent No. 3,254,970
(Dittrich et al.) or vice versa a~ diæclosed in ~.S. Patent No.
3,655,425 (Longo and Patel). However, such compositioning ha~
not been fully sufficient for producing high quality coatings and
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ME-3889
optimum deposit efficiency with conventional thermal 8pray guns~
vis. plasma or low velocity combu~tion.
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Thermoplastic polymer powders such as polyethylene melt easily
and many can readily be thermal sprayed. However, thermo et
S polymer powders generally do not melt, at least without first
decomposing and/or oxidizing at the high thermal spraying
temperatureO Certain of these thermoset powders~ as disclosed in
U.S. Patent No. 3,723,165 (Longo and Durman) (assigned to the
predecessor in interest of the present assignee) may undergo a
superficial chemical or physical modification o~ the polymer
surface of each particle so as to become surface heat softenable.
An example is the poly (paraoxybenzoyl) e~ter powder described in
U.S. Patent No. 3,784,405 (Economy et al). As further explained
in Example 1 of the aforementioned U.S. Patent ~o. 3,723,165 ~uch
polyester may be utilized in a blend with aluminum alloy powder.
Plasma spraying such a blend has been highly successful for
producing abradable coatings for ga~.turbine engine seals and the
i like. However9 the basic unmeltability of the polymer still
results in poor deposit efficiency, so that even with the high
heat available from a plasma gun, a significant portion of the
polymer constituent is 108t. Since this polymer i8 quite
expenslve, there is a need to improve the thermal spraying of the
polymer-aluminum blend. There also ha~ been an on-going need for
~ improvements in abradability and erosion re~i~tance of the
9j 25 coatings.
Therefore, objects of the present invention are to provide an
improved method for thermal spraying non-meltabl~ materials, to
provide a method for high velocity thermal ~praying particle~
having a non-meltable component and a heat softenable component,
to provide an improved method of including non-meltable particles
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ME-3889
in thermal sprayed coatings at reasonable cost, to provide a
method for thermal sprayin~ improved coatings o~ certain non-
meltable carbides and nitrides, and to provide a method for
producing improved coatings of certain ~hermoset plastics.
S SUMM~R~ OF THE INvENTION
The foregoing and other objects are achieved by a method for
producing a coating with a thermal spray gun having a tubular
member defining a combustion cha~ber therein with an open end for
propelling combustion products into the ambient atmosphere at
supersonic velocity. The method comprise~ injecting ints the
chamber a combustible mixture of combustion ya~ and oxygen at a
~ pressure in the chamber of at lea~t two atmo~pheres above ambient
atmospheric pressure, feeding into the chamber a powder
comprising particles having a heat-stable non-meltable component
and a heat-softenable component, combusting the combustible
mixture in the chamber whereby a supersonic spray ~tream
containing the powder is propelled through the open ~nd, and
directing the cpray stream toward a subrtrate such as to produce
a coating thereon.
In a preferred embodiment ~he powder particles comprise composite
grains of a metal and a non-meltable mineral, particularly in the
form of metal clad mineral. ~ore preferably, the mineral is
selected from the group con~isting of graphite diamonds, non-
meltable carbides and non-meltable nitrides, such as silicon
carbide, silicon nitride, chromium nitride,~boron nitride,
aluminum carbide and aluminum nitride~
Alternatively, the powder particles comprise thermoset polymer
grains characterized by being sur~ace heat softenabl~ by flame
modification. Preferably, the polymer grains comprise
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ME-3889
poly(paraoxybenzoyl)ester~ and the powder further comprises
aluminum powder or aluminum base alloy powder.
In a preferred method, the thermal spray gun include6 a nozzle
member with a nozzle face and a tubular gas cap cxtending from
the nozzle member and having an inwardly facing cylindrical wall
defining a combustion chamber with an open end and an opposite
end bounded by the nozzle face. Thi~ method compri~es injecting
an annular flow of combustible mixture of a combustion gas and
oxygen from the nozzle coaxially into the combu~ion chamber at a
pressure therein of at least two bar above atmo~pheric pressure,
injecting an annular outer flow of pressurized non-combustible
gas adjacent to the cylindrical wall radially outward of the
annular flow of the combustible mixture, feeding a powder
comprisin~ particles having heat stable non-meltable cores and
heat softenable surfaces in a carrier gas axially from ~he nozzle
into the combustion chamber, injecting an annular inner flow of
pressurized gas from the nozzle member into the combu~ion
chamber coaxially be~ween the combu~tible mixture.
BRIEF DESCRIPTION C)F THE DRAWINGS
FIG. 1 is an elevation of a thermal ~pray gun used in the present
invention.
FIG. 2 is a section taken at 2-2 of FIG. 1.
FIG. 3 is an enlargement of the forward end of the sec~ion of
FIG. 2.
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FIG. 4 is a section taken at 4-4 o FIG. 1, and a 6chematic of an
associated powder feeding system.
FIG. 5 is a schematic view of the gun of ~IG. 1 producing a
supersonic spray stream according to the present invention.
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5 FIG. 6 is the view of FIG. 5 with a sub~trate in place.
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DETAILED DESCRIPTION OF THE INVENTION
An example of a preferred thermal spray apparatu6 for effecting
the present invention is disclosed in copending U.S. Patent
Application Serial No. 193,030 iled May 11, 1988, assigned to
10 the assignee of the pre~ent invention and detailed herein. The
apparatus is illus~rated in FIG. 1, and FIG. 2 ~how~ a horizontal
section thereof. A thermal spray gun lO has a ga~ head 12 with a
tubular member in the form of a gas cap 14 mounted ~hereon, a
valve portion 16 for supplyinq fuel, oxygen and ~ir to the gas
15 head, and a handle 17. The valve portion 16 has a hose
r connection 18 for a fuel ga~, a hose connection 1~ for oxygen and
a hose connection 20 for air. The three connec~ion~ are connected
respectively by hoses from a fuel source 21, oxygen ~ource 22 and
air source 24. OrificeR 25 in a cylindrical valYe 26 control the
20 ~low of the respective gases fro~ their connections into the ~un.
~he valve and associated components are, for exa~ple, of the ~ype
taught in U.S. Patent No. 3,530,892, ~nd include a pair of valve
levers 27, and sealing means for each ga~ flow sec~ion that
include plungers 28, springs 29 and O-rings 30.
25 A cylindrical siphon plug 31 is fit~ed in a corresponding bors in
ga~ head 12, and a plurality of O-ring~ 32 thereon maintaln a
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ME-3889
gas-tight seal. The siphon plug i8 provided with a tube 33
having a central passage 34. The siphon plug further has therein
an annular groove 35 and a further annular groove 3~ with a
plurality of inter-connecting passages 38 (two shown)~ With
cylinder valve 26 in the open position as ~hown in FIG. 2, oxygen
is passed by means of a hose ~0 through its connec~ion 19 and
valve 26 into a passage 42 from whence i~ flows in~o groove 35
and through passage 38. A similar arrdngement i8 provided to
pass fuel gas from source 21 and a hose ~6 through connection 18,
valve 26 and a passage 48 into groove 3C, mix with the oxygen,
and pass as a combus~ible mixture through passages 50 aligned
with passages 38 into an annular groove 52. Annular groove 52
feeds the mixture into a plurality of passages 53 in the rear
section of a nozzle member 5~.
Referring to FIG. 3 for detailæ, nozzle member 5~ i8 conveniently
constructed of a tubular inner portion 55 and a ~ubular outer
portion 56. (As used herein an~ in the claim~t ainner~ denotes
toward the axis and Uouter~ denotes away from the axi~. Al~o
~forward~ or "forwardly~ denote~ toward the open end of the gun;
~rear~, ~rearward~ or ~rearwardlya denote~ the opposite.) Outer
portion 56 defines an outer annular orifice mean~ for injecting
the annular flow of the co~bustible mix~ure into the combustion
chamber. The orifice means preferably includes a forward annular
opening 57 with a radially inward side bounded by an outer wall
~8 of the inner portion. The orifice ~ystem leading to the
annular opening from passages 53 may be a plurality of arcuately
spaced orifices, bu~ preferably i8 an annular orifice 59.
The combustible mixture 10wing from the aligned grooves 52 thus
passes through the orifice (or orifices) 59 to produce an annular
flow which is ignited in annular opening 57. A nozzle nut 60
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holds nozzle 5~ and siphon plug 28 on gas head 12. Two further
o-rings 61 are seated conventionally between nozzle 5~ and ~iphon
plug 31 for gas tight seals. The burner nozzle 5~ extends into
gas cap 1~ which is held in place by mean~ of a retainer ring 64
and extends forwardly from the nozzle.
Nozzle member 5~ is also provided with an axial bore 62t for the
powder in a carrier gas, extending forwardly from tube passage
33. Alternatively the powder may be injected through a small
diameter ring of orifice~ (not shown) proximate the axis 63 of
the gun. With reference to FIG. 4 a diagonal passage 64 extends
rearwardly from tube 33 to a powder connection 65. A carrier
hose ~6 and, therefore, central bore 62~ i8 receptive of powder
from a powder feeder 67 en~rained in a carrier gas from a
pressurized gas source ~8 such as compressed air by way of feed
hose 66. Powder feeder 67 is of the conventional or desired type
but must be capable of delivering the carrier ga~ at hig~ enough
pressure to provide powder into the c~amber 82 in gun 10.
With reference back to FIGS. 2 ànd 3, air or other non-
combustible ~as is passed from source 24 and a hose 69 througb
its connection 20, cylinder valve 26, and a passage 70 to a space
71 in the interior of retainer ring C4. ~ateral openings 72 in
nozzle nut 60 communicate space 71 with a cylindrical combu~tion
chamber 82 in gas cap 14 so that the air may flow as an outer
sheath from space 71 through these lateral openings 72, thence
2S through an annular lot 84 between the outer surface of nozzle
54, and an inwardly facing cylindrical wall 86 defining
combustion chamber 82 into which slot 84 exi~s. The flow
continues through chamber 82 a an annular outer flow mixing with
the inner flows, and ou~ of the open end 88 in ga~ cap 14.
Chamber 82 is bounded at its oppo~ite, rearward end by face 8~ of
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nozzle 54.
Preferably combustion chamber 82 converge~ forwardly from the
nozzle at an anqle with the axis, most preferably between about
; 2 and 10, e.g. 5O Slot 8~ also converge~ forwardly at ~n
an~le with the axis, most preferably between about 12 and 16,
e.g. 14.5. Slot 84 further should have sufficient length for
the annular air flow to develop, e.g~ comparable to chamber
length 102, but at least greater than half of such length 102.
In addition, the chambe`r should converge at a lesser angle than
the slot, most preferably be~ween about 8 and 12, e.g. 10
less. ~his configuration provides a converging air flow with
respect to the chamber to minimize powder buildup on the chamber
wall.
The air flow rate should be controlled upstream of slo~ 84 such
as in a rearward narrow orifice 92 or with a separate flow
requlator. For example slo~ length ~ 8 mm, slot width is 0.38
mm on a 15 mm circle, and air pressure to the gun (source 2~) is
4.9 kg/cm2 (70 psi) to produce a total air flow of 425 std l/min
(900 scfh) with a pressure of 4.2 kg/cm~ (60 psi) in cha~ber 82.
Also, with valve 26 in a lighting position aligning bleeder holes
as described in aforementioned U.S. Patent No. 3,530,8g2, an air
hole 90 in valve 2C allows air flow for lighting, and the above-
indicated angles and dimensions are important to allow sush
lighting without backfire. (Bleeder hole~ in valve 26 for oxygen
and fuel for lighting, similar ~o air hole 90, are not shown.)
The inner portion 55 of nozzle member 54 has therein a plurality
of parallel inner orifice~ 91 (e.gO 8 orifices 0.89 mm diameter)
on a bolt ciecle (e.g. 2.57 mm diameter) which provide for an
annular inner sheath flow of gas, preferably air, about the
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central powder feed is~uing from bore 62 of the nozzle. Thi~
inner ~heath of air contribute~ 6ignificantly to reducing any
tendency of buildup of powder material on wall 86. ~he ~heath
air is conveniently tapped from paFsage ~0, via a duct 93 (FIG.
2) to an annular groove 9~ around the rear portion of ~iphon plug
31 and at least one orifice 96 into an annular space 98 adjacent
tube 33. Preferably at least three ~uch orifices 9C are equally
spaced arcuately to provide sufficient air and to minimize vorte~
flow which could detrimentally swirl the powder outwardly to wall
86 of chamber 82. The inner sheath air flow 6hould be be~ween 1%
and 10~, preferably about 2% and 5~ of the outer sheath flow
rate, for example about 3%. The inner sheath may alternatively
be requlated independently of ~he outer ~heath air, for better
control.
Chances of powder buildup are further minimized by having the
inner portion 55 of the nozzle member protrude into chamber 82
forwardly of the outer portion 56 as depicted in FIGS. 2 and 3.
A chamber length 102 may be defined as the æhor~e~ distance from
nozzle face 89 to open end 88, i.e. from the forwardmost point on
the nozzle to ~he open end. The forwardmo~ point on the inner
portion should protrude forwardly from the outer portio~ 56 by a
distance between about 10% and 40% of chamber length 102, e.g.
30~.
A preferred configuration for the in~er portion i~ d~picted in
FIGS. 2 and 3. Referring to the outer wall 58 of inner portion
55 of the nozzle, which defines annular spening 5~ such wall 5~
should extend forwardly from the annular opening with a curvature
inward toward the axis. ~he curvature should be uniform. For
example~ as shown, the curvature ic such a~ to define a generally
hemispherical face 89 on inner portion 580 I~ i8 believed that
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the combustion ~lame i~ thereby drawn inwardly to main~ain the
: flow~ away from chamber wall 36
As an example of further detail~ of a thermal Bpray gun
inc~rporating the present invention, siphon plug 31 ha~ 8 oxygen
passages 38 of 1.51 mm each to allow sufficient oxygen flow, and
1.51 mm diameter passages 50 for the gas mixture. In thiz gas
head central bore 62 i~ 3.6 mm diameter, and the open end 88 of
the gas cap is 0.9~ cm from the face of the nozzle (length 102).
Thus the combustion chamber 82 that also entrains the powder is
: 10 relatively short, and generally should be between about one and
~ two times the diameter of open end 88.
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A supply of each of the gase~ to the cylindrical combustion
chamber is peovided at a sufficiently high pressure, e.g. at
least 30 psi above atmospheric, and i~ ignited conventionally
such as with a spark device, 6ucb that the mixture of combusted
gases and air will is~ue from the open end as a supersonic flow
- entraining the powder. Tbe heat o~ the combustion will at least
heat soften the powder ma~erial 6uch a~ to deposit a coating onto
a substrate. Shock diamonds ~hould be observableO Because of
; 20 the annular flow conf~guration, an expan~ion type of nozzle exit
' i8 not necessary to achieve ~he ~uperæonic flow.
The combustion gas may be propane or hydrogen or the like, but it
i8 preferable that the combustion gas be propylene gas, or
~ methylacetylene-propadiene ga~ PS~). These latter gases allow
;~ 25 a relatively high velocity spray ~tream and exc~llen~ coatings to
be achieved without backfire. For example with a propylene or
MPS pressure of about 7 kg/cm2 gauge (above atmo~pheric pressure)
to the gun, oxygen at 10 kg/cm2 and air at 5L6 kg/cm2 at least 8
shock diamonds are readily visible in the ~pray ~tream withou~
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powder flow. The appearance of these ~hock diamonds 108 in spray
stream 110 is illustrated in FIG~ 5. The position of the
substrate 112 on which a coating 114 is sprayed i~ preferably
about where the fifth ull diamond would be as ~hown in FIG.6,
e~g. about 9 cm spray distance.
~ According to the metnod of the present invention certain powders
are thermal sprayed with supersonic combu~tion spray gun~
Althouqh the preferred apparatus is as described above, the
method may alternatively utilize other supersonic gun~ such as
described in the aforementioned U.S. Patent No. 4,416,~21, The
certain powders are those that contain a heat-stable, non-
meltable component in each powder grain. As used herein and in
the claims the term ~heat-stable~ means that the referenced
component will not substantially decompose or oxidize under the
temperature and time conditions of the ~lame of the ~hermal spray
gun; similarly the term ~non-meltable~ means tbat the referenced
component will not sub~tantially mel~ in the flame. A~ a te~t,
the non-meltable component may be fed through a thermal ~pray gun
; to be used for the spraying thereof, collec~ed and inspected
microscopically and/or metallographacally for decompo~ing,
oxidizing or melting. For example, nor~al flattening of the
parti~le~ on a substrate will indicate melting. ~hus material
that merely softens vi6cou~1y, without a specific ~elting point
to allow flattening on a substrate, i~ non-meltable for the
purpose of this invention. Publi~hed handbooks on melting points
are alternate sources of meltabili~y informationO
One group of heat-stable non-meltable materials contemplated for
use in the pre ent invention are non-meltable minerals. Examples
of such materials are graphite; diamond powder; non-meltable
carbides such as silicon carbide and aluminum carbide; and non-
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meltable nitrides such as ~ilicon nitride, chromium nitride,
boron nitride and aluminum ni~ride. The mineral need no~ be
naturally occurring. Silicon ca`rbide and boron nitride are
particularly preferable as described minerals to incorporate into
coatings. The non-meltable material may be a heat stable
thermoset polymer such as polyimide that i~ vir~ually unaffected
by the thermal spray flame except for surface effects~
The non-meltable minerals, according to the invention, are
composited with a meltable or at least a heat softenable
component. Generally this component is a conventional thermal
spray metal such as an iron-group element, ~olybdenum, aluminum,
copper, or an alloy of any of these, or may be an oxide such as
alumina, titania, zirconia, or chromia, or a co~plex oxide.
The composite powder is produced by the known or desired method.
For example, metal clad mineral may be made by cladding the metal
onto a mineral core as disclosed in the aforementioned U~S.
Patent No. 3,254,970 (e.g. nickel clad diamond), by cladding fine
mineral powder onto a metal core a~ disclo~ed in the
aforementioned U.S. Patent No. 3,655,425 ~e.g. boron nitride clad
nickel alloy), or by agglomerating or spray drying fine powders
of both components as disclosed in U.S. Patent No. 30617,358
(Dittrich).
A second group of heat-stable non-metallic material~ contemplated
for ~he method herein consists of thermoset poly~er~. Thermoset
is used broadly herein and in the claims to conve~tionally cover
hydrocarbons (plastic~) polymerized by heat, catalyst or reaction
whereby the polymer is not ordinarily softenable by heating, for
example without some chemical modification by the flame. The
poly (paraoxybenzoyl) ester and copolyesters thereof of the
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aforementioned U.s. Paten~ Nos. 3,723,165 and 3,784,405 fall in
this group, as may other~ ~uch as certain epoxie~ and polyimides
including those that may be ~n the form of an incompletely
polymerized powder. A eature of these 6~1ected polymer~ i~ that
S only a surface portion i~ heat softened in the flame. Th$s
surface softening maybe i~ effected by chemical modification
during the short exposure to the hot flame, changing a surface
layer from thermoset to at least partially thermoplastic. Thus,
for the purpose of ~he presen~ly claimed invention, the surface
layer is effectively a heat~softenable component and the core
remains a heat-stable non-meltable component, even though the
initial particle may be homogeneous. Alternatively a non-
meltable thermoset polymer may be clad or otherwise composited
with a meltable polymer such as polyamide, polyethylene or
incompletely polymerized polyester or epoxy, or a copolyester of
the type disclosed in aforementioned U.S. Patent No. 3,784,405~
Characteristic powder according to the invention may be sprayed
neat or blended with a more convent~onal thermal spray material
such as a metal. Qui~e surprisingly9 the method of supersonic
combustion thermal spraying of the above-de~cribed powders i8
effected with relatively high deposit efficiency, and produces
dense, high quality coatings. ~he high deposit efficiency i8
especially surprising because the ~hort dwell time of particles
in the supersonic flame would be expecte~ to cau~e lesser deposit
efficiency, especially with non-meltable components. The
improved deposit efficiency provides not only a cost benefit per
se but allows cost-favorable modification of blends to achieve a
specified coating compositionO
A preferred example is a blend of heat-stable polyester and
aluminum alloy, as detailed in Example 1 belowO Conventional
plasma spraying, despite high heat, loses a considerable portion
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of the polyester relative to the alloy. Conventional, low-
velocity combustion spraying chars the polyester or, with lesser
heat, results in poorly cohesive deposit~. Spraying with a
supersonic combustion flame provides high deposit efficlency
which allows a lesser proportion of polyester to be in the
initial blend to o~tain the originally specified proportions in
the coating, and provides excellent coatings~
EXAMPLE 1
A blend of polyester plastic and aluminum alloy ~imilar to the
blend is prepared as de~cribed under Example l-A of
aforementioned U.S. Patent NoO 3,723,165, except the plastic
powder is 30% and the alloy i~ 70~ by weight of the blend. The
plastic is a high ~emperature aromatic poly (paraoxybenzoyl)
ester sold under the trade name of EKONOL (T~) by the ~etaullics
Division of the Carboundary Company, Sanborn, N.Y. and has a size
of -88 ~44 microns, and the alloy is ?luminum 12~ 8ilicon with a
size of -44 ~lO microns.
The blend is sprayed with the preferred apparatus de~cribed above
with respect to FIGS. 1-3, speci~ically a ~etco Type DJ (~M)
Metaullics Division of the Carboundary Compas~7 S~nford, N.Y. Gun
sold by The Perkin-Elmer Corporation, Westbury, Ne~ York, using a
~3 insert, t3 injector, "A~ shellt ~2 ~iphon plug and ~2 a~r cap.
Oxygen was 10.5 kg/cm2 (150 psig) and 212 l/min ~50 ~cfh),
propylene gas at 7~0 kg/cm2 (100 psig) and 47 l/min (100 scfh),
and air at 5.3 kg/cm2 (75 psig) and 290 l/min (615 scfh). A high
pressure powder feeder of the type disclosed in the present
assignee's copending U.S. Patent Application Serial No. __
filed lattorney docket ME-38813 and ~old as a Metco
Type DJP powder feeder by Perkin-Elmer is used to feed the powder
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blend at 23 gm/min (3 lb/hr) in a nitrogen carrler at 8.8 kg/cm2
(125 psig) and 7 l/min (15 8Cfh). Spray di~tance i8 20 cm and
the substrate i8 grit blasted niskel alloy.
Comparisons were made with the 40% powder and ~praying thereof of
Example l-A of the '165 patent, the 40% powder being sold as
Metco 601NS by Perkin-Elmer and containing 40% pla~tic powder,
i.e. 1/3 more than the present 30~ powder. The Example l-A 40
powder was plasma sprayed conventionally wi~h argon-hydrogen
plasma gas. The ~0% powder blend sprayed with the supersonic
combustion gun yielded a deposit efficiency of 85~, v~ typical
65~ deposit efficiency for the 40% powder plasma sprayed. Of
; more importance i~ the fact that the coatings were of essentially
the same composition as each other, reflecting the better deposit
efficiency of the plastic constituent of the 30% powder with the
supersonic combustion gun. Abradability and ero~ion resi~tance
~f the coatings were also eæ~e~tially th~ same. Poro~ity for the
high velocity coating was about 1% a~ uniformly dispersed, v~ 5~
non-uniform porosity for pla~ma sprayed 40~ powder. ~ardnes~ for
` the high velocity coating was RlSy 78 to 83, V8 65 to 75, i.e.,
20 again more uniform.
EXAMPLE 2
.
Nickel clad silicon carbide powder is prepared from -44 ~5 micron
silicon carbide powder. This i8 clad with nickel in the known
manner by the hydrogen reduction of an ammoniacal ~olution nf
nickel and ammonium sulphate, using anthraquinone as the coating
catalyst. Detail~ of the coating process are taught in
aforementioned U.S. Patent No. 3,254,970. The resulting powder
containing 29~ by weight silicon carbide, balanced nickel i~
screened to -53 micron~.
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~ 16
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2~al2~97
M13-3889
The screened powder iæ sprayed with the appara~u~ of ~xample 1
~ith a ~2 insert, ~2 injector, aA~ shell, ~2 sipbon plug and ~3
air cap. Oxygen i8 at lO,S kg/cm2 (lSO psig) and 286 l/min (606
scfh), propylene at 700 kg~cm2 (100 p8ig) and 79 l/min ~168
S scfh), and air at 5.3 kg/cm2 ~75 p8ig) and 374 l/min (793 ~cfh).
Powder feeder and carrier gas are the same as in Example 1 with a
feed rate of 47 gm/min (6 lb/hr). Spray distance is 15 cm
(6 lnches) and the substrate is qrit blasted mild ~t2el.
Excellent, dense coatings were effected containing a high
retained percentage and uniform distribution of Rilicon carbide~
No discernable embrittlement was formed metallographically at
nickel/silicon carbide particle interfaces, otherwi~e found in
more conventional thermal sprayed coating~ of ~uch material,
apparently due to short dwell time in the flame.
EXAMPLE 3
A powder of nickel-chromium-iron alloy core clad with fine
particlas of aluminum (3.5~) and boron nitride (5.5~1, of the
type described in aforementioned U.S. Patent No. 3,655,425 and
sold as ~etco 301NS by Perkin-Elmer iæ sprayed wi~h the ~ame gun
and similar parameter~ as for Example 2. Den~e, unifor~ coatings
having an excsllent combination of abradability and erosion
resistance are effected.
EXAMPLE 4
Composite aluminum-graphite powder ~old as Metco 310NS by Perkin-
Elmer is produced by agglomerating fine aluminum -12% ~ilicon -45
17
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ME-3889
~10 microns) and 23~ of graphite powder with 8~ of an organic
binder by the method u~ed for making the powder of ~ample 3~
This powder is sprayed with the same gun and similar parameters
as for Example 2. Dense, uniform coatings having an excellent
combination of abradability and erosion re~i6tance are effected.
ExamPle 5
Example 1 is repeated except that the polyester i8 replaced with
a copolyester of recurring units of Formula I, III, and IY as
disclosed in the aforementioned U.S. Patent No. 3,784,405
(incorporated herein by reference) and sold as Xydar(TM) by
Dartco Manufacturing Inc., Augusta Georgia. Similar results are
effected.
While the invention has been d~scribed above in detail with
reference to specific embodiments, various changes and
modifications which fall within the ~pirit of the invention and
scope of the appended claims will become apparent to those
skilled in this art. The invention is therefore only intended ~o
be limited by the appended claims or their equivalents.
18
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