[0001] This invention relates to thermal spraying and particularly to a method for combustion
thermal spraying powder at very high velocity.
BACKGROUND OF THE INVENTION
[0002] Thermal spraying, also known as flame spraying, involves the melting or at least
heat softening of a heat fusible material such as metal or ceramic, and propelling
the softened material in particulate form against a surface which is 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 heating and propelling the particles.
In one type of thermal spray gun, the heat fusible material is supplied to the gun
in powder form. Such powders are typically comprised of small particles, e.g., between
100 mesh U.S. Standard screen size (149 microns) and about 2 microns. Heat for powder
spraying is generally from a combustion flame or an arc-generated plasma 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 simply be compressed air.
Quality coatings of certain thermal spray materials have been produced by spraying
at high velocity. Plasma spraying has proven successful with high velocity in many
respects but it can 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.s 2,714,563 and 2,964,420 (both Poorman et al) disclose a detonation
gun for blasting powdered material in a series of detonations to produce coatings
such as metal bonded carbides. High density and tenacity of coatings are achieved
by high impact of the powder particles, and the short dwell time in the heading zone
minimizes oxidation at the high spray temperatures.
[0003] A rocket type of powder spray gun can produce excellent coatings of metals and metal
bonded carbides, particularly tungsten carbide, and is typified in U.S. Patent Nos.
3,741,792 (Peck et al.) and 4,416,421 (Browning). 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.
[0004] Short-nozzle spray devices are disclosed for high velocity spraying in French Patent
No. 1,041,056 and U.S. Patent No. 2,317,173 (Bleakley). Powder is fed axially into
a melting chamber within an annular flow of combustion gas. An annular air flow is
injected coaxially outside of the combustion gas flow, along the wall of the chamber.
The spray stream with the heated powder issues from the open end of the combustion
chamber.
[0005] Since thermal spraying involves melting or at least surface heat softening the spray
material, non-meltable powders such as certain carbides and nitrides cannot be sprayed
into successful coatings without incorporating a binder into the material. 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 as disclosed
in U.S. Patent No. 3,655,425 (Longo and Patel). However, such compositioning has not
been fully sufficient for producing high quality coatings and optimum deposit efficiency
with conventional thermal spray guns, vis. plasma or low velocity combustion.
[0006] Thermoplastic polymer powders such as polyethylene melt easily and many can readily
be thermal sprayed. However, thermoset polymer powders generally do not melt, at least
without first decomposing and/or oxidizing at the high thermal spraying temperature.
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 of the polymer surface of
each particle so as to become surface heat softenable. An example is the poly (paraoxybenzoyl)
ester 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 No. 3,723,165 such 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 gas turbine engine seals and
the like. However, 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 lost. Since this polymer is quite expensive,
there is a need to improve the thermal spraying of the polymer-aluminum blend. There
also has been an on-going need for improvements in abradability and erosion resistance
of the coatings.
[0007] Therefore, objects of the present invention are to provide an improved method for
thermal spraying non-meltable materials, to provide a method for high velocity thermal
spraying particles having a non-meltable component and a heat softenable component,
to provide an improved method of including non-meltable particles in thermal sprayed
coatings at reasonable cost, to provide a method for thermal spraying improved coatings
of certain non-meltable carbides and nitrides, and to provide a method for producing
improved coatings of certain thermoset plastics.
SUMMARY OF THE INVENTION
[0008] 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 chamber therein
with an open end for propelling combustion products into the ambient atmosphere at
supersonic velocity. The method comprises injecting into the chamber a combustible
mixture of combustion gas and oxygen at a pressure in the chamber of at least two
atmospheres 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 stream containing the powder is propelled through the open end, and directing
the spray stream toward a substrate such as to produce a coating thereon.
[0009] In a preferred embodiment the powder particles comprise composite grains of a metal
and a non-meltable mineral, particularly in the form of metal clad mineral. More preferably,
the mineral is selected from the group consisting 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 surface heat softenable by flame modification. Preferably, the polymer grains
comprise poly(paraoxybenzoyl)ester, and the powder further comprises aluminum powder
or aluminum base alloy powder.
[0010] In a preferred method, the thermal spray gun includes a nozzle member with a nozzle
face and a tubular gas cap extending 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. This method comprises injecting an annular flow of
combustible mixture of a combustion gas and oxygen from the nozzle coaxially into
the combustion chamber at a pressure therein of at least two bar above atmospheric
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 comprising particles having heat stable non-meltable cores and heat
softenable surfaces in a carrier gas axially from the nozzle into the combustion chamber,
injecting an annular inner flow of pressurized gas from the nozzle member into the
combustion chamber coaxially between the combustible mixture.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011]
FIG. 1 is an elevation of a thermal spray 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 section of FIG. 2.
FIG. 4 is a section taken at 4-4 of FIG. 1, and a schematic of an associated powder
feeding system.
FIG. 5 is a schematic view of the gun of FIG. 1 producing a supersonic spray stream
according to the present invention.
FIG. 6 is the view of FIG. 5 with a substrate in place.
DETAILED DESCRIPTION OF THE INVENTION
[0012] An example of a preferred thermal spray apparatus for effecting the present invention
is disclosed in copending U.S. Patent Application Serial No. 193,030 filed May 11,
1988, assigned to the assignee of the present invention and detailed herein. The apparatus
is illustrated in FIG. 1, and FIG. 2 shows a horizontal section thereof. A thermal
spray gun
10 has a gas head
12 with a tubular member in the form of a gas cap
14 mounted thereon, a valve portion
16 for supplying fuel, oxygen and air to the gas head, and a handle
17. The valve portion
16 has a hose connection
18 for a fuel gas, a hose connection
19 for oxygen and a hose connection
20 for air. The three connections are connected respectively by hoses from a fuel source
21, oxygen source
22 and air source
24. Orifices
25 in a cylindrical valve
26 control the flow of the respective gases from their connections into the gun. The
valve and associated components are, for example, of the type taught in U.S. Patent
No. 3,530,892, and include a pair of valve levers
27, and sealing means for each gas flow section that include plungers
28, springs
29 and O-rings
30.
[0013] A cylindrical siphon plug
31 is fitted in a corresponding bore in gas head
12, and a plurality of O-rings
32 thereon maintain a gas-tight seal. The siphon plug is 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
36 with a plurality of inter-connecting passages
38 (two shown). With cylinder valve
26 in the open position as shown in FIG. 2, oxygen is passed by means of a hose
40 through its connection
19 and valve
26 into a passage
42 from whence it flows into groove
35 and through passage
38. A similar arrangement is provided to pass fuel gas from source
21 and a hose
46 through connection
18, valve
26 and a passage
48 into groove
36, mix with the oxygen, and pass as a combustible 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
54.
[0014] Referring to FIG. 3 for details, nozzle member
54 is conveniently constructed of a tubular inner portion
55 and a tubular outer portion
56. (As used herein and in the claims, "inner" denotes toward the axis and "outer" denotes
away from the axis. Also "forward" or "forwardly" denotes toward the open end of the
gun; "rear", "rearward" or "rearwardly" denotes the opposite.) Outer portion
56 defines an outer annular orifice means for injecting the annular flow of the combustible
mixture into the combustion chamber. The orifice means preferably includes a forward
annular opening
57 with a radially inward side bounded by an outer wall
58 of the inner portion. The orifice system leading to the annular opening from passages
53 may be a plurality of arcuately spaced orifices, but preferably is an annular orifice
59.
[0015] The combustible mixture flowing 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 holds nozzle
54 and siphon plug
28 on gas head
12. Two further O-rings
61 are seated conventionally between nozzle
54 and siphon plug
31 for gas tight seals. The burner nozzle
54 extends into gas cap
14 which is held in place by means of a retainer ring
64 and extends forwardly from the nozzle.
[0016] Nozzle member
54 is also provided with an axial bore
62, 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 orifices
(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
66 and, therefore, central bore
62, is receptive of powder from a powder feeder
67 entrained in a carrier gas from a pressurized gas source
68 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
gas at high enough pressure to provide powder into the chamber
82 in gun
10.
[0017] With reference back to FIGS. 2 and 3, air or other non-combustible gas is passed
from source
24 and a hose
69 through its connection
20, cylinder valve
26, and a passage
70 to a space
71 in the interior of retainer ring
64. Lateral openings
72 in nozzle nut
60 communicate space
71 with a cylindrical combustion 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 through an annular slot
84 between the outer surface of nozzle
54, and an inwardly facing cylindrical wall
86 defining combustion chamber
82 into which slot
84 exits. The flow continues through chamber
82 as an annular outer flow mixing with the inner flows, and out of the open end
88 in gas cap
14. Chamber
82 is bounded at its opposite, rearward end by face
89 of nozzle 54.
[0018] Preferably combustion chamber
82 converges forwardly from the nozzle at an angle with the axis, most preferably between
about 2
o and 10
o, e.g. 5
o. Slot
84 also converges forwardly at an angle with the axis, most preferably between about
12
o and 16
o, e.g. 14.5
o. 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 chamber should converge at a lesser angle than the slot, most preferably
between about 8
o and 12
o, e.g. 10
o less. This configuration provides a converging air flow with respect to the chamber
to minimize powder buildup on the chamber wall.
[0019] The air flow rate should be controlled upstream of slot
84 such as in a rearward narrow orifice
92 or with a separate flow regulator. For example slot length is 8 mm, slot width is
0.38 mm on a 15 mm circle, and air pressure to the gun (source
24) 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/cm² (60 psi) in chamber
82. Also, with valve
26 in a lighting position aligning bleeder holes as described in aforementioned U.S.
Patent No. 3,530,892, an air hole
90 in valve
26 allows air flow for lighting, and the above-indicated angles and dimensions are
important to allow such lighting without backfire. (Bleeder holes in valve
26 for oxygen and fuel for lighting, similar to air hole
90, are not shown.)
[0020] The inner portion
55 of nozzle member
54 has therein a plurality of parallel inner orifices
91 (e.g. 8 orifices 0.89 mm diameter) on a bolt circle (e.g. 2.57 mm diameter) which
provide for an annular inner sheath flow of gas, preferably air, about the central
powder feed issuing from bore
62 of the nozzle. This inner sheath of air contributes significantly to reducing any
tendency of buildup of powder material on wall
86. The sheath air is conveniently tapped from passage
70, via a duct
93 (FIG. 2) to an annular groove
94 around the rear portion of siphon plug
31 and at least one orifice
96 into an annular space
98 adjacent tube
33. Preferably at least three such orifices
96 are equally spaced arcuately to provide sufficient air and to minimize vortex flow
which could detrimentally swirl the powder outwardly to wall
86 of chamber
82. The inner sheath air flow should be between 1% and 10%, preferably about 2% and
5% of the outer sheath flow rate, for example about 3%. The inner sheath may alternatively
be regulated independently of the outer sheath air, for better control.
[0021] 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 shortest distance from nozzle face
89 to open end
88, i.e. from the forwardmost point on the nozzle to the open end. The forwardmost point
on the inner portion should protrude forwardly from the outer portion
56 by a distance between about 10% and 40% of chamber length
102, e.g. 30%.
[0022] A preferred configuration for the inner portion is depicted in FIGS. 2 and 3. Referring
to the outer wall
58 of inner portion
55 of the nozzle, which defines annular opening
57, such wall
58 should extend forwardly from the annular opening with a curvature inward toward the
axis. The curvature should be uniform. For example, as shown, the curvature is such
as to define a generally hemispherical face
89 on inner portion
58. It is believed that the combustion flame is thereby drawn inwardly to maintain the
flows away from chamber wall
86.
[0023] As an example of further details of a thermal spray gun incorporating the present
invention, siphon plug
31 has 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 this gas head central bore
62 is 3.6 mm diameter, and the open end
88 of the gas cap is 0.95 cm from the face of the nozzle (length
102). Thus the combustion chamber
82 that also entrains the powder is relatively short, and generally should be between
about one and two times the diameter of open end
88.
[0024] A supply of each of the gases to the cylindrical combustion chamber is provided at
a sufficiently high pressure, e.g. at least 30 psi above atmospheric, and is ignited
conventionally such as with a spark device, such that the mixture of combusted gases
and air will issue from the open end as a supersonic flow entraining the powder. The
heat of the combustion will at least heat soften the powder material such as to deposit
a coating onto a substrate. Shock diamonds should be observable. Because of the annular
flow configuration, an expansion type of nozzle exit is not necessary to achieve the
supersonic flow.
[0025] The combustion gas may be propane or hydrogen or the like, but it is preferable that
the combustion gas be propylene gas, or methylacetylene-propadiene gas ("MPS"). These
latter gases allow a relatively high velocity spray stream and excellent coatings
to be achieved without backfire. For example with a propylene or MPS pressure of about
7 kg/cm² gauge (above atmospheric pressure) to the gun, oxygen at 10 kg/cm² and air
at 5.6 kg/cm² at least 8 shock diamonds are readily visible in the spray stream without
powder flow. The appearance of these shock diamonds
108 in spray stream
110 is illustrated in FIG. 5. The position of the substrate
112 on which a coating
114 is sprayed is preferably about where the fifth full diamond would be as shown in
FIG.6, e.g. about 9 cm spray distance.
[0026] According to the method of the present invention certain powders are thermal sprayed
with supersonic combustion spray guns. Although the preferred apparatus is as described
above, the method may alternatively utilize other supersonic guns such as described
in the aforementioned U.S. Patent No. 4,416,421. 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 flame of the thermal spray gun; similarly the term "non-meltable" means that the
referenced component will not substantially melt in the flame. As a test, the non-meltable
component may be fed through a thermal spray gun to be used for the spraying thereof,
collected and inspected microscopically and/or metallographically for decomposing,
oxidizing or melting. For example, normal flattening of the particles on a substrate
will indicate melting. Thus material that merely softens viscously, without a specific
melting point to allow flattening on a substrate, is non-meltable for the purpose
of this invention. Published handbooks on melting points are alternate sources of
meltability information.
[0027] One group of heat-stable non-meltable materials contemplated, for use in the present
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-
meltable nitrides such as silicon nitride, chromium nitride, boron nitride and aluminum
nitride. The mineral need not be naturally occurring. Silicon carbide 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
is virtually unaffected by the thermal spray flame except for surface effects.
[0028] 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, molybdenum, aluminum, copper, or
an alloy of any of these, or may be an oxide such as alumina, titania, zirconia, or
chromia, or a complex oxide.
[0029] 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 as disclosed 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. 3.617,358 (Dittrich).
[0030] A second group of heat-stable non-metallic materials contemplated for the method
herein consists of thermoset polymers. Thermoset is used broadly herein and in the
claims to conventionally cover hydrocarbons (plastics) 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 aforementioned U.S. Patent Nos. 3,723,165 and 3,784,405
fall in this group, as may others such as certain epoxies and polyimides including
those that may be in the form of an incompletely polymerized powder. A feature of
these selected polymers is that only a surface portion is heat softened in the flame.
This surface softening maybe is 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 the presently 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 conventional thermal spray material such as a metal. Quite surprisingly, the
method of supersonic combustion thermal spraying of the above-described powders is
effected with relatively high deposit efficiency, and produces dense, high quality
coatings. The high deposit efficiency is especially surprising because the short dwell
time of particles in the supersonic flame would be expected to cause 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 composition.
[0031] A preferred example is a blend of heat-stable polyester and aluminum alloy, as detailed
in Example 1 below. Conventional plasma spraying, despite high heat, loses a considerable
portion of the polyester relative to the alloy. Conventional, low-velocity combustion
spraying chars the polyester or, with lesser heat, results in poorly cohesive deposits.
Spraying with a supersonic combustion flame provides high deposit efficiency which
allows a lesser proportion of polyester to be in the initial blend to obtain the originally
specified proportions in the coating, and provides excellent coatings.
EXAMPLE 1
[0032] A blend of polyester plastic and aluminum alloy similar to the blend is prepared
as described under Example 1-A of aforementioned U.S. Patent No. 3,723,165, except
the plastic powder is 30% and the alloy is 70% by weight of the blend. The plastic
is a high temperature aromatic poly (paraoxybenzoyl) ester sold under the trade name
of EKONOL
(TM) by the Metaullics Division of the Carboundary Company, Sanborn, N.Y. and has a size
of -88 +44 microns, and the alloy is aluminum 12% silicon with a size of -44 +10 microns.
[0033] The blend is sprayed with the preferred apparatus described above with respect to
FIGS. 1-3, specifically a Metco Type DJ
(TM) Metaullics Division of the Carboundary Compass, Sanford, N.Y. Gun sold by The Perkin-Elmer
Corporation, Westbury, New York, using a #3 insert, #3 injector, "A" shell, #2 siphon
plug and #2 air cap. Oxygen was 10.5 kg/cm² (150 psig) and 212 l/min (450 scfh), 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 [attorney
docket ME-3881] and sold as a Metco Type DJP powder feeder by Perkin-Elmer is used
to feed the powder blend at 23 gm/min (3 lb/hr) in a nitrogen carrier at 8.8 kg/cm²
(125 psig) and 7 l/min (15 scfh). Spray distance is 20 cm and the substrate is grit
blasted nickel alloy.
[0034] Comparisons were made with the 40% powder and spraying thereof of Example 1-A of
the '165 patent, the 40% powder being sold as Metco 601NS by Perkin-Elmer and containing
40% plastic powder, i.e. 1/3 more than the present 30% powder. The Example 1-A 40%
powder was plasma sprayed conventionally with argon-hydrogen plasma gas. The 30% powder
blend sprayed with the supersonic combustion gun yielded a deposit efficiency of 85%,
vs typical 65% deposit efficiency for the 40% powder plasma sprayed. Of more importance
is 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 erosion resistance of the coatings
were also essentially the same. Porosity for the high velocity coating was about 1%
and uniformly dispersed, vs 5% non-uniform porosity for plasma sprayed 40% powder.
Hardness for the high velocity coating was R15y 78 to 83, vs 65 to 75, i.e., again
more uniform.
EXAMPLE 2
[0035] Nickel clad silicon carbide powder is prepared from -44 +5 micron silicon carbide
powder. This is clad with nickel in the known manner by the hydrogen reduction of
an ammoniacal solution of nickel and ammonium sulphate, using anthraquinone as the
coating catalyst. Details 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 is screened to -53 microns.
[0036] The screened powder is sprayed with the apparatus of Example 1 with a #2 insert,
#2 injector, "A" shell, #2 siphon plug and #3 air cap. Oxygen is at 10.5 kg/cm² (150
psig) and 286 l/min (606 scfh), propylene at 7.0 kg/cm² (100 psig) and 79 l/min (168
scfh), and air at 5.3 kg/cm² (75 psig) and 374 l/min (793 scfh). 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 inches) and the substrate is grit blasted mild steel.
[0037] Excellent, dense coatings were effected containing a high retained percentage and
uniform distribution of silicon carbide. No discernable embrittlement was formed metallographically
at nickel/silicon carbide particle interfaces, otherwise found in more conventional
thermal sprayed coatings of such material, apparently due to short dwell time in the
flame.
EXAMPLE 3
[0038] A powder of nickel-chromium-iron alloy core clad with fine particles of aluminum
(3.5%) and boron nitride (5.5%), of the type described in aforementioned U.S. Patent
No. 3,655,425 and sold as Metco 301NS by Perkin-Elmer is sprayed with the same gun
and similar parameters as for Example 2. Dense, uniform coatings having an excellent
combination of abradability and erosion resistance are effected.
EXAMPLE 4
[0039] Composite aluminum-graphite powder sold as Metco 310NS by Perkin-Elmer is produced
by agglomerating fine aluminum -12% silicon -45 +10 microns) and 23% of graphite powder
with 8% of an organic binder by the method used for making the powder of Example 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
resistance are effected.
Example 5
[0040] Example 1 is repeated except that the polyester is replaced with a copolyester of
recurring units of Formula I, III, and IV 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.
[0041] While the invention has been described above in detail with reference to specific
embodiments, various changes and modifications which fall within the spirit of the
invention and scope of the appended claims will become apparent to those skilled in
this art. The invention is therefore only intended to be limited by the appended claims
or their equivalents.
1. A method for producing a coating containing non-meltable material with a thermal
spray gun having combustion chamber means therein with a combustion chamber and an
open channel for propelling combustion products into the ambient atmosphere at supersonic
velocity, the method comprising feeding through the open channel powder particles
having a heat-stable non-meltable component and a heat-softenable component, injecting
into the chamber and combusting therein a combustible mixture of combustion gas and
oxygen at a pressure in the chamber sufficient to produce a supersonic spray stream
containing the powder issuing through the open channel, and directing the spray stream
toward a substrate such as to produce a coating thereon.
2. A method for producing a coating with a thermal spray gun having a tubular member
defining a combustion chamber therein with an open end for propelling combustion products
into the ambient atmosphere at supersonic velocity, the method comprising injecting
into the chamber a combustible mixture of combustion gas and oxygen at a pressure
in the chamber of at least two atmospheres 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 stream containing the powder is propelled through
the open end, and directing the spray stream toward a substrate such as to produce
a coating thereon.
3. A method according to Claim 2 wherein the combustible mixture is injected at a
sufficient pressure into the combustion chamber to produce at least 8 visible shock
diamonds in the spray stream in the absence of powder-carrier gas feeding.
4. A method according to Claim 3 further comprising selecting the combustion gas from
the group consisting of propylene gas and methylacetylene-propadiene gas.
5. A method according to Claim 2 wherein the powder particles are selected from the
group consisting of the combusting mixture generates a flame and (a) composite grains
comprising a metal and a non-meltable mineral and (b) thermoset polymer grains characterized
by being surface heat softenable by the flame.
6. A method according to Claim 2 wherein the powder particles comprise composite grains
of a metal and a non-meltable mineral.
7. A method according to Claim 6 wherein the mineral is selected from the group consisting
of graphite, diamonds, non-meltable carbides and non-meltable nitrides.
8. A method according to Claim 6 wherein the mineral is selected from the group consisting
of graphite, diamonds, silicon carbide, silicon nitride, chromium nitride, boron nitride,
aluminum carbide and aluminum nitride.
9. A method according to Claim 6 wherein the mineral consists essentially of boron
nitride, and the metal comprises nickel or cobalt or alloys thereof.
10. A method according to Claim 6 wherein the mineral consists essentially of silicon
carbide and the metal comprises nickel or cobalt or alloys thereof.
11. A method according to Claim 2 wherein the combusting mixture generates a flame
and the powder particles comprise thermoset polymer grains characterized by being
surface heat softenable by the flame.
12. A method according to Claim 11 wherein the polymer grains comprise poly(paraoxybenzoyl)ester.
13. A method according to Claim 12 wherein the polymer grains consist essentially
of poly(paraoxybenzoyl)ester.
14. A method according to Claim 12 wherein the polymer grains consist essentially
of a copolyester of poly(paraoxbenzoyl)ester.
15. A method according to Claim 11 wherein the powder further comprises aluminum powder
or aluminum base alloy powder.
16. A method for producing a dense and tenacious coating with a thermal spray gun
including a nozzle member with a nozzle face, and a tubular gas cap extending 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, the method
comprising injecting an annular flow of a combustible mixture of a combustion gas
and oxygen from the nozzle coaxially into the combustion chamber at a pressure therein
of at least two bar above atmospheric 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 comprising particles
having heat stable non-meltable cores and heat softenable surfaces in a carrier gas
axially from the nozzle into the combustion chamber, injecting an annular inner flow
of pressurized gas from the nozzle member into the combustion chamber coaxially between
the combustible mixture and the powder-carrier gas, combusting the combustible mixture,
whereby a supersonic spray stream containing the heat fusible material in finely divided
form is propelled through the open end, and directing the spray stream toward a substrate
such as to produce a coating thereon.