WO2004098790A1

WO2004098790A1 - Apparatus for thermal spray processes

Info

Publication number: WO2004098790A1
Application number: PCT/US2004/012810
Authority: WO
Inventors: Viktor Sedov; Richard Thorpe
Original assignee: Praxair S. T. Technology, Inc.
Priority date: 2003-05-02
Filing date: 2004-04-26
Publication date: 2004-11-18
Also published as: EP1638698A4; CN100537051C; JP2006525118A; CN1816398A; EP1638698A1

Abstract

An improved design for a thermal spray gun includes an atomizer (70, 102), a combustion chamber (10, 104), an interconnector (30, 106), and a barrel (50, 108). Also included are methods for thermally spraying a substrate. One method for thermally spraying a substrate includes directing at least one fuel stream and at least one oxidant stream to a thermal spray gun with the improved design to form a thermal spray and directing the thermal spray against the surface to apply the coating.

Description

APPARATUS FOR THERMAL SPRAY PROCESSES

Background Of the Invention

[0001] Thermal spray guns are used in processes for thermal spraying substrates with coatings transported in high energy flow streams. Thermal spraying has also been known as flame spraying, metalizing, high velocity oxy-fuel thermal spraying (H.V.O.F.), and high velocity air-fuel thermal spraying (H.V.A.F.). Coating materials are typically metals, ceramics, or cement-type materials. The high energy flow streams typically include a combustion gas for propelling and transporting the coating material to a substrate target at high velocities. The coating material may travel at what would be the speed of sound in ambient air or higher.

[0002] Coatings applied by thermal spraying are thought to adhere to a substrate primarily by mechanical adhesion resulting from coating particles colliding with the surface of a substrate at high velocities. It is also theorized that bombarding a substrate with high velocity coating particles results in some of the kinetic energy of the coating particles being converted to heat when the coating particles impact with the substrate. This heat from converted kinetic energy is believed to aid in bonding the coating material to the substrate, sometimes referred to as "microbonding."

[0003] A thermal spray combustion gas is typically provided by a high temperature flame-jet resulting from combustion of a fuel and an oxidant, which releases heat and generates a high temperature pressurized gas stream. Thermal spray guns sometimes utilize combustion components, or reactants, such as oxygen and propane, oxygen and hydrogen, oxygen and kerosene, and kerosene and air. A fuel and an oxygen source are injected into a combustion zone where they react in a combustion reaction under pressure and temperature to generate the high temperature pressurized gas stream, which is directed from the combustion zone and into a high velocity flow stream. Coating materials, such as metals, ceramics, or cements, are introduced into the flow stream. The high temperature pressurized gas is directed from the combustion zone and down a flow nozzle to propel the coating material particles into a targeted substrate. Often, several shock diamonds appear in the high velocity flow stream exiting the thermal spray gun to indicate that the high temperature pressurized gas is traveling towards the targeted substrate at several times the speed of sound.

[0004] However, under the high temperature conditions that a thermal spray gun operates, heat loss can be high. Also, the rate of fuel and oxygen consumption can be high, which increases operating expense. Therefore, a need exits for a thermal spray gun that has improved operating efficiency. Summary Of the Invention

[0005] In one embodiment, this invention includes an atomizer for a thermal spray gun, wherein the atomizer includes a plurality of atomization holes arranged about an ignition source .

[0006] In one embodiment, this invention includes a combustion chamber of a thermal spray gun, wherein the combustion chamber comprises a cylinder portion, a narrowing conical zone contiguous with the cylinder portion, and an expanding conical zone. The cylinder portion has a length to diameter ratio in the range of between about 1.3 and about 2 and an exit through which fluids can flow to exit the cylinder portion. The narrowing conical zone has inner walls which taper inward from the exit of the cylinder portion to form a circular nozzle orifice having a diameter in the range of between about 0.2 and about 0.350 inches. The narrowing conical zone includes at least two conical portions, including a first conical portion wherein the inner walls narrow at a conical angle in the range of between about 80° and about 100°, and a second conical portion wherein the inner walls narrow at a conical angle in the range of between about 40° and about 60°. The expanding conical zone is contiguous with the circular nozzle orifice and the inner walls of the expanding conical zone flare outwards at a conical angle in the range of between about 8° and about 17°. [0007] In another embodiment, this invention includes an interconnector for injecting powder into an exhaust stream leaving a combustion chamber in a thermal spray gun. The interconnector comprises a hollow cylinder having at least two contiguous portions, including a first portion and a second portion. The ratio of the diameter of the first portion to the diameter of the second portion is in the range of about 1.1 and about 1.3. The interconnector also includes at least two powder inlet ports opening to the inner walls of the second portion. The powder inlet ports are in a non-opposition arrangement.

[0008] In yet another embodiment, this invention includes a barrel for a thermal spray gun having a hollow central bore through which a thermal spray can flow. The barrel includes a conical entrance portion which converges towards the radial axis of the central bore, a cylindrical portion contiguous with the conical entrance portion, and a conical exit portion which flares away from the radial axis of the central bore. The length of the cylindrical portion is at least half the total length of the barrel .

[0009] In yet another embodiment, this invention includes a barrel for a thermal spray gun having a hollow central bore through which a thermal spray can flow and a total length of two inches or less. The barrel includes a conical entrance portion which converges towards the radial axis of the central bore and a cylindrical portion contiguous with the conical entrance portion.

[0010] In a further embodiment, this invention includes a thermal spray gun. The thermal spray gun of this embodiment includes an atomizer having a plurality of atomization holes arranged about an ignition source. The thermal spray gun of this embodiment also includes a combustion chamber. The combustion chamber includes a cylinder portion having an exit through which fluids can flow to exit the cylinder portion, a narrowing conical zone contiguous with the cylinder portion, and an expanding conical zone contiguous with the circular nozzle orifice. The narrowing conical zone has inner walls which taper inward from the exit of the cylinder portion to form a circular nozzle orifice and wherein the narrowing conical zone includes at least two conical portions having nonequal conical angles. The thermal spray gun of this embodiment also includes an interconnector for injecting powder into an exhaust stream leaving the combustion chamber. The interconnector includes a hollow cylinder having at least two contiguous portions with inner walls having dissimilar diameters and at least two powder inlet ports opening to the inner walls of the second portion. The powder inlet ports are in a non-opposition arrangement. The thermal spray gun of this embodiment further includes a barrel having a hollow central bore through which a thermal spray can flow. The barrel includes a conical entrance portion which converges towards the radial axis of the central bore and a cylindrical portion contiguous with the conical entrance portion.

[0011] In another embodiment, the thermal spray method includes directing at least one fuel stream and at least one oxidant stream to a thermal spray gun to form a thermal spray and directing the thermal spray against the surface to apply the coating. The thermal spray gun of this embodiment includes an atomizer having a plurality of atomization holes arranged about an ignition source, a combustion chamber of a thermal spray gun, an interconnector for injecting powder into an exhaust stream leaving the combustion chamber, and a barrel having a hollow central bore through which a thermal spray can flow. The combustion chamber of this embodiment includes a cylinder portion having an exit through which fluids can flow to exit the cylinder portion; a narrowing conical zone contiguous with the cylinder portion, wherein the narrowing conical zone has inner walls which taper inward from the exit of the cylinder portion to form a circular nozzle orifice and wherein the narrowing conical zone includes at least two conical portions having nonequal conical angles; and an expanding conical zone contiguous with the circular nozzle orifice. The interconnector of this embodiment includes a hollow cylinder having at least two contiguous portions with inner walls having dissimilar diameters and at least two powder inlet ports opening to the inner walls of the second portion, wherein the powder inlet ports are in a non-opposition arrangement. The barrel of this embodiment includes a conical entrance portion which converges towards the radial axis of the central bore and a cylindrical portion contiguous with the conical entrance portion. [0012] The present invention has many advantages. One advantage includes a reduction in the amount of barrel loading over known devices. Barrel loading is a term given to a process of heat powder sticking to the inside of the walls of the barrel. Further, the device allows the application of a coating with a high hardness and strength. Additional advantages include increased powder deposition efficiency and feed rate, reduced fuel and oxygen consumption, and a lower heat transfer to the substrate. In addition, less heat is lost to a coolant system, hence, a smaller and cheaper chiller may be used.

Brief Description Of The Drawings

Figure 1 is a schematic diagram of a cross-sectional side view of an atomizer for an apparatus for thermal spray processes.

[0013] Figure 2 is a schematic diagram of a cross- sectional end view of an atomizer for an apparatus for thermal spray processes.

[0014] Figure 3 is a schematic diagram of a cross- sectional side view of a combustion chamber for an apparatus for thermal spray processes . [0015] Figure 4 is a schematic diagram of a cross- sectional side view of an interconnector for an apparatus for thermal spray processes. [0016] Figure 5 is a schematic diagram of a cross- sectional end view of one embodiment of the interconnector .

[0017] Figure 6 is a schematic diagram of a cross- sectional end view of a second embodiment of the interconnector .

[0018] Figure 7 is a schematic diagram of a cross- sectional side view of a barrel for the apparatus for thermal spray processes .

[0019] Figure 8 is a schematic diagram of a cross- sectional side view of a thermal spray gun for thermal spray processes. Detailed Description Of the Invention [0020] The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. All percentages and parts are by weight unless otherwise noted. [0021] This device generally relates to thermal spraying. More specifically, this device relates to an improved design for a thermal spray gun. This device includes an improved design for a thermal spray gun, including an atomizer, a combustion chamber, an interconnector, and a barrel. Examples of suitable materials of construction for various portions of the thermal spray gun include copper, brass, steel, aluminum, stainless-steel, nickel-based metallic alloys, ceramics, ceramic alloys, and combinations thereof .

[0022] This device includes an atomizer which injects fuels and oxidants into the combustion chamber in such a way that they intimately mix and combust in a stable and continuous manner. Examples of suitable fuels include hydrocarbon gases (e.g., methane, ethane, propane, and butane) , hydrogen, and petroleum-based fuels (e.g., fuel oil and kerosene). In one embodiment, the fuel includes kerosene. Examples of suitable oxidants include air, oxygen, hydrogen peroxide, and nitrous oxide. In another embodiment, the oxidant includes oxygen.

[0023] In one embodiment, this device includes an atomizer for a thermal spray gun, wherein the atomizer includes a plurality of atomization holes arranged about an ignition source. One embodiment of the device is shown in Figure 1, which illustrates a schematic diagram of a cross-sectional side view of atomizer 70. Atomizer 70 includes an ignition source in the form of spark plug 72 and mounting assembly 76. Spark plug 72 includes electrode 74. Mounting assembly 76 includes a plurality of atomization holes 78 arranged about electrode 74.

[0024] In one embodiment, the end of the mounting assembly that includes the electrode and the atomization holes is inserted into a combustion chamber. Figure 2 illustrates a cross-section view of the end of atomizer 70 that includes the electrode and the atomization holes. Atomization holes 78 are arranged about electrode 74 in a single circle configuration. The exact configuration of the atomization holes in this device is not limited to a single circle, however. Many configurations of the holes are suitable. In some embodiments, the atomization holes are arranged about the ignition source in several circles, in an oval formation, or any other symmetric pattern.

[0025] In one embodiment, the mounting assembly includes between about 7 and about 12 atomization holes. In another embodiment, the atomization holes each have a diameter in the range of between about 0.51 and about 1.19 millimeters (about 0.02 and 0.047 inches). In yet another embodiment, the atomization holes are positioned to surround the ignition source. [0026] This device also includes a combustion chamber where the atomized mixture is combusted to form combustion gases. The combustion chamber has at least three distinct portions, including a cylinder portion, a narrowing conical zone, and an expanding conical zone .

[0027] One embodiment of the device is shown in Figure 3 which illustrates combustion chamber 10. Combustion chamber 10 includes cylinder portion 2, which is a hollow cylinder region having an entrance at L₀, an exit at Li, and diameter Di. The exit of cylinder portion 2 (at Li) is contiguous with narrowing conical zone 4. In one embodiment, an atomizer (not shown in Figure 3) is connected to the entrance of the cylinder portion. In another embodiment, the inner walls of the cylinder portion have a length-to-diameter ratio (i.e., |L_!-L₀|/Dι) in the range of between about 1.3 and about 2. In yet another embodiment, the length-to-diameter ratio is in the range of between about 1.4 and about 1.7. In yet another embodiment, diameter Di is in the range of between about 38.1 and about 50.8 millimeters (about 1.5 and about 2 inches) . [0028] Cylinder portion 2 is contiguous with narrowing conical zone 4. Narrowing conical zone 4 has inner walls which taper inward from the exit of cylinder portion 2 to form circular nozzle orifice 6. The geometry of the narrowing conical zone is configured to provide a smooth transition of high temperature flow through circular nozzle orifice 6 and reduce the impact of fuel particles onto the inner walls of combustion chamber 2 and circular nozzle orifice 6. Circular nozzle orifice 6 has diameter D₃. Using standard compressible flow formulas, diameter D₃ is selected to control the pressure of combustion chamber 2 as well as the velocity and temperature of the exhausted combustion gases. In one embodiment, diameter D₃ is in the range of between about 5.08 and about 8.89 millimeters (about 0.2 and about 0.35 inches) .

[0029] In one embodiment, the narrowing conical zone includes a plurality of cones. Narrowing conical zone 4 in the embodiment illustrated in Figure 3 has at least two contiguous conical portions, including first conical portion 8 (from Li to L₂) and second conical portion 12 (from L₂ to L₃) . First conical portion 8 tappers at conical angle oca_. until the inner walls of the chamber have diameter D₂. Second conical portion 12 is contiguous with first conical portion 8 and has inner walls that tapper at conical angle α₂ until the inner walls of the chamber form circular nozzle orifice 6 having diameter D₃. In one embodiment, conical angle <Xι is in the range of between about 80° and about 100°. In another embodiment, conical angle c^ is in the range of between about 85° and about 95°. In a further embodiment, conical angle α₂ is in the range of between about 40° and about 60°. In yet another embodiment, conical angle α₂ is in the range of between about 45° and about 55°.

[0030] In one embodiment, the narrowing conical zone is comprised of more than two cones, for example, three, four, or five conical portions with successively decreasing conical angles. In another embodiment, at least two successive conical portions are not contiguous, but are separated by additional cylindrical or nearly cylindrical regions.

[0031] Narrowing conical zone 4 is contiguous with expanding conical zone 14. Expanding conical zone 14 has inner walls that flare outwards at conical angle cc₃ until the inner walls have diameter D₄. In one embodiment, diameter D₄ is in the range of between about 7.62 and about 12.7 millimeters (about 0.3 and about 0.5 inches). In another embodiment, conical angle ct₃ is in the range of between about 8° and about 17°.

[0032] In some embodiments, some or all of the inner walls of the narrowing conical zone and expanding conical zone converge or diverge with a convex or concave curve .

[0033] This device also includes an interconnector in fluid communication with the combustion chamber, wherein the interconnector has at least two powder inlet ports in a non-opposition arrangement. One purpose of the interconnector is to inject powder material into a stream of combustion gases. The powder materials are propelled to the interconnector by a carrier gas. The stream of carrier gas and powder material is directed through the powder inlet ports and into the stream of combustion gases. Examples of suitable powder material include metals, metallic alloys, carbides, metal-coated carbides, ceramics, cement-type materials, and combinations thereof. In one embodiment, the particles of the powder material have an average particle size of less than about 55 μm. In another embodiment, the particles of the powder material have an average particle size in the range of between about 15 μm and about 40 μm for a carbide material and about 22 μm and 53 μm for a metallic material. In a further embodiment, the powder material contains a significant number of particles having a size of less than about 11 μm. In yet another embodiment, the powder material contains a significant number of particles having a size of less than about 5 μm. Examples of suitable carrier gases include inert gases (e.g., helium and argon), nitrogen, air, carbon dioxide, and reactive gases such as hydrogen or hydrocarbon gases (e.g., methane, ethane, propane, propylene, and butane) .

[0034] One embodiment of the interconnector is illustrated in Figure 4 as interconnector 30. Interconnector 30 is a hollow cylinder having at least two contiguous portions including first portion 32, which spans the length from the entrance at L₅ to L₇. The length from L₅ to L₆ of first portion 32 has diameter D₅, which is larger than diameter D₆ of the length from Lβ to L₇. In some embodiments, diameter D₅ is sufficiently wide to allow for the insertion of preceding portions of a thermal spray gun such as, for example, the exit portion of a combustion chamber. In other embodiments, diameter D₆ matches the diameter of the inner walls of the inserted preceding portion so as to provide one continuous flat inner wall throughout the first portion of the interconnector. In yet another embodiment, diameter D₆ is in the range of between about 7.62 and about 12.7 millimeters (about 0.3 and about 0.5 inches). [0035] Interconnector 30 also includes second portion 34, which spans the length from the exit of first portion 32 at L₇ to the exit of interconnector 30 at L₈ and has inner walls with diameter D₇ which is larger than diameter D₆. In some embodiments, the ratio of D₇ to D₆ is in the range of between about 1.1 and about 1.3. Interconnector 30 includes at least two powder inlet ports 36 opening to the inner walls of second portion 34. The larger diameter D₇ provides for the creation of a negative pressure zone at the openings of powder inlet ports 36. This negative pressure zone enhances the injection of powder material into the flow of the combustion gases.

[0036] The transition from diameter D6 to D7, as illustrated in the embodiment of Figure 4, is rather abrupt and at a near-90°. However, in some embodiments, the transition from diameter D6 to D7 in the interconnector is less abrupt. For example, the transition could be at a non-perpendicular angle or a curve, wherein the angle and curve result in an expansion of the diameter of the inner walls so that a negative pressure zone is created at the openings of the powder inlet ports.

[0037] The powder inlet ports of the interconnector are arranged in a non-opposition arrangement around the interior circumference of the second portion so that no two ports are directly 180° apart from each other. This arrangement prevents the direct impact of multiple streams of carrier gas and powder particles in the interior of the second portion. Figure 4 illustrates one embodiment where two powder injection ports 36 are positioned at a right angle to each other around the circumference of the second portion. Figure 6 illustrates another embodiment where three powder injection ports 36 are positioned in two successive 60° angles about the circumference of the second portion.

[0038] In one embodiment the powder inlet ports are positioned at a non-perpendicular angle to the inner wall of the second portion so that the carrier gas/powder material stream is injected into the combustion gas stream at a non-90° angle to the axis of flow. In another embodiment, the powder inlet ports are slanted at about a 10° angle from the perpendicular, so the carrier gas/powder material stream enters the combustion gas stream at either an upstream or downstream angle in the range of between about 80° and about 90° to the axis of flow. In yet another embodiment, the powder inlet ports are slanted for injecting powder into the combustion gas stream at an angle to the axis of flow of between about 10° in the downstream direction and about 1° in the upstream direction, so the carrier gas/powder material stream enters the combustion gas stream at an angle of between 89° in the upstream direction or 80° in the downstream direction. In some embodiments, the powder inlet ports are slanted at an angle that causes the carrier gas/powder material stream to enter the interior of the interconnector along some trajectory other than along the radius or diameter. For example, the angle could cause the carrier gas/powder material streams to follow the trajectory of a chord across the interior of the interconnector .

[0039] This device also includes a barrel for directing the combined streams of combustion gases, carrier gases, and powder material onto a concentrated spot .

[0040] One embodiment of this device is shown in Figure 7 as an illustration of barrel 50. Barrel 50 has a hollow central bore through which a thermal spray can flow, beginning at the entrance at L₉ and ending at the exit at L₁₂ . In some embodiments, the total length of the barrel (i.e., |Lι₂-L₉ |) is in the range of between about 25.4 and about 304.8 millimeters (about 1 and about 12 inches) . In other embodiments, the total length of the barrel is in the range of between about 25.4 and about 203.2 millimeters (about 1 and about 8 inches) .

[0041] Barrel 50 includes conical entrance portion 52 which is a cone shaped portion starting at the entrance to barrel 50 at L₉ and ends at Lι₀. The inner walls of conical entrance portion 52 converge towards the radial axis of the central bore at angle ct₄. In some embodiments, angle cc₄ is in the range of between about 1.5° and about 3°. In other embodiments, angle ₄ is in the range of between about 1.5° and about 2.5°.

[0042] Barrel 50 also includes cylinder portion 54 which is contiguous with conical entrance portion 52. Cylinder portion 54 is a hollow cylinder, running from Lio to Lii and having diameter D₈. In some embodiments, diameter D₈ is in the range of between about 6.35 and about 15.24 millimeters (about 0.25 and about 0.6 inches) . In other embodiments, the length of the cylinder portion (i.e., | n-Lι₀|) is at least half the total length of the barrel . [0043] Barrel 50 includes conical exit portion 56 which is a cone shaped portion beginning at the exit of cylinder portion 54 at Ln and ends at the exit of barrel 50 at L_i2. The inner walls of conical exit portion 56 flare away from the radial axis of the central bore at angle ₅. In some embodiments, angle o₅ is in the range of between about 0.5° and about 5°. In other embodiments, angle α₅ is in the range of between about 0.5° and about 1.5°.

[0044] In some embodiments, the conical exit portion of the barrel is omitted. In yet other embodiments, the total barrel length is two inches or less and the conical exit portion is omitted. In some embodiments, the inner walls of the conical entrance portion or the conical exit portion converge or diverge with a convex or concave curve .

[0045] One embodiment of the device is shown in Figure 8 which illustrates a cross-sectional side view of thermal spray gun 100. Thermal spray gun 100 includes atomizer 102 (spanning from L_i3 to L_i5) , combustion chamber 104 (spanning from L_i4 to L₂o) _/ interconnector 106 (spanning from L₁₉ to L₂₂) and barrel 108 (spanning from L₂ι to L₂₅) . Atomizer 102 forms one end of combustion chamber 104 and is positioned so that the electrode (not shown in Figure 8) of spark plug 110 and the atomization holes (not shown in Figure 8) are positioned inside of combustion chamber 104. Expanding conical zone 112 of combustion chamber 104 spans from Lι₈ to L₂o with the portion spanning from L₁₉ to L₂o inserted into the first portion of interconnector 106. Barrel 108 is also attached to interconnector 106. [0046] In one embodiment, this device also includes a thermal spray gun, comprising a combustion chamber of a thermal spray gun, an interconnector for injecting powder into an exhaust stream leaving the combustion chamber, and a barrel having a hollow central bore through which a thermal spray can flow. The combustion chamber of this embodiment includes a cylinder portion having an exit through which fluids can flow to exit the cylinder portion; a narrowing conical zone contiguous with the cylinder portion, wherein the narrowing conical zone has inner walls which taper inward from the exit of the cylinder portion to form a circular nozzle orifice and wherein the narrowing conical zone includes at least two conical portions having nonequal conical angles; and an expanding conical zone contiguous with the circular nozzle orifice. The interconnector of this embodiment includes a hollow cylinder having at least two contiguous portions with inner walls having dissimilar diameters and at least two powder inlet ports opening to the inner walls of the second portion, wherein the powder inlet ports are in a non-opposition arrangement. The barrel of this embodiment includes a conical entrance portion which converges towards the radial axis of the central bore and a cylindrical portion contiguous with the conical entrance portion. [0047] This invention also includes a thermal spray method for applying a coating to a surface of a substrate. In one embodiment, the method includes combusting at least one fuel with at least one oxidant to form a combustion gas stream, directing a powder into the combustion gas stream to form a thermal spray, and directing the thermal spray against the surface to apply the coating.

[0048] In one embodiment, the fuel and oxidant are combusted inside of a combustion chamber attached to an atomizer. In another embodiment, the fuel is kerosene and the oxidant is oxygen.

[0049] In one embodiment, the combustion process is initiated by first directing a low flow of oxygen (e.g., about 19.8 scmh (about 700 scfh) ) to the atomizer equipped with a spark plug as an ignition source. The oxygen flows through the atomizer and into the combustion chamber through the plurality of atomization holes. Then a current is sent to the spark plug, and a low flow of fuel is directed to the atomizer (e.g., about 1.9 L/hr or less (about 0.5 gal/hr or less) ) . The fuel flows through the atomizer and into the combustion chamber. The atomized mixture of fuel and oxygen in the combustion chamber is ignited by the electrode of the spark plug as the concentration of the atomized fuel reaches a burnable range. The resulting flame travels outwardly from the electrode throughout the mixture and stabilizes in a low velocity eddy region created by a shear effect of the atomized mixture just outside of the atomization holes arranged about the electrode. This hot recirculating eddy region retains hot gases and serves as the continuous ignition source for the combustion process thereafter. The current to the spark plug is then turned off. The initial ignition process with the spark plug utilizes low flows so that the initial pressure rise upon ignition is low enough so as to not adversely affect the flow of the fuel and oxidant. This low flow also serves to reduce noise produced during the initiation of the combustion process. After the combustion process has been initiated, the flow of oxidant and fuel is increased to normal operating levels. Normal operating levels for oxidant and fuel varies with the type of fuel and oxidant used, as well as the demands of the particular application. In one embodiment, the oxidant flow at normal operating levels is about 34 scmh or less (about 1,200 scfh or less) . In another embodiment, the flow of fuel at normal operating levels is about 15.9 L/hr or less (about 15.9 L/hr or less) . In yet another embodiment, the flow of fuel at normal operating levels is about 20.8 L/hr or less (about 5.5 gal/hr or less) . In one embodiment, the linear velocity of the atomized fuel, atomized oxidant, or atomized mixture of fuel and oxidant from an atomization hole is at least about 225 m/s. In another embodiment, the linear velocity out from an atomization hole is about 330 m/s.

[0050] In some embodiments, a portion of the atomization holes only direct oxidant into the combustion chamber, while another portion directs fuel. In other embodiments, the atomization holes direct both oxidant and fuel into the combustion chamber.

[0051] In one embodiment, the combustion process produces combustion gases, which flow from the cylinder portion of the combustion chamber into the narrowing conical region of the combustion chamber. The geometry of the narrowing conical region reduces the impact of uncombusted fuel particles onto the inner wall, thereby reducing the amount of soot and carbon build-up produced during the combustion process. The geometry of the narrowing conical region also provides for a smooth flow of high-temperature, high-velocity combustion gases. The combustion gases pass through the circular nozzle orifice of the narrowing conical region and into the expanding conical zone. [0052] In one embodiment, the combustion gases flow from the expanding conical zone of a combustion chamber into the first portion of an interconnector. The combustion gases then flow into the second portion of the interconnector. In the second portion, two or more flows of a carrier gas through the powder inlet ports deliver powder into the combustion gas stream to form a thermal spray. The amount of powder directed through each inlet ports varies with the demands of the spraying process. In one embodiment, the carrier gas flow rate through each inlet port is in the range of between about 0.57 and about 0.68 scmh (about 20 and about 24 scfh) . In another embodiment, the carrier gas flow rate through each inlet port is in the range of between about 0.28 and about 0.42 scmh (about 10 and about 15 scfh) . In one embodiment, the powder flow rate through each inlet port is less than about 9.1 kg/hr (about 20 lbs/hr) . In yet another embodiment, the powder flow rate through each inlet port is in the range of between about 4.54 and about 6.81 kg/hr (about 10 and about 15 lbs/hr) .

[0053] The increased diameter of the inner walls of the second portion creates a region of negative pressure (e.g., sub-atmospheric pressure), which enhance the flow of powder from the powder inlet ports to the combustion gas stream. The non-opposition arrangement of the powder inlet ports reduces turbulence associated with the introduction of the powder flows to the combustion gas stream. The non- opposition arrangement also reduces the amount of powder that impinges the inner walls of the thermal spray gun, thereby reducing barrel loading.

[0054] In one embodiment, the thermal spray stream flows from the second portion of the interconnector and into the conical entrance portion of a barrel . The convergence of the inner walls in the conical entrance portion results in a higher-temperature, higher- pressure, and lower velocity thermal spray stream. The thermal spray stream then flows through the cylindrical portion of the barrel. If the barrel does not posses a conical exit portion, the thermal spray exits the gun through the cylindrical portion of the barrel and is applied to the substrate being coated.

[0055] If the barrel does posses a conical exit portion, the thermal spray leaves the cylindrical portion the barrel and enters the conical exit portion. The thermal spray expands in the conical exit portion due to the diverging inner walls. This expansion serves to increase the velocity of the thermal spray, and therefore the powder particles being sprayed, while reducing its pressure and temperature. The decreased temperature also reduces barrel loading, barrel erosion, or both. The thermal spray then leaves the gun and is applied to the substrate being coated. The lower temperature produced by the conical exit portion reduces the amount of heat transferred to the substrate being sprayed.

[0056] In some embodiments, heat is removed from some or all portions of the thermal spray gun by a cooling system. In other embodiments, the cooling system uses water as a heat transfer fluid. In yet other embodiments, the water flow rate to the coolant system is less than about 37.9 L/min (about 10 gal/min) . In other embodiments, the water leaves the cooling system at a temperature of less than about 48.9° C (about 120° F) . In still other embodiments, the water leaves the coolant system at a temperature in the range of about to about 15.6° C to about 34.4° C (about 60° F to about 94° F) . In some embodiments, the coolant system uses a chiller to cool the heat transfer fluid.

[0057] In one embodiment, this invention also includes a thermal spray method for applying a coating to a surface . In one embodiment , the thermal spray method includes directing at least one fuel stream and at least one oxidant stream to an atomizer to form an atomized mixture, wherein the atomizer includes a plurality of atomization holes arranged about an ignition source. The atomized mixture is combusted to form a combustion gas stream. A powder is directed into the combustion gas stream to form a thermal spray. The thermal spray is directed against the surface to apply the coating.

[0058] In another embodiment, the thermal spray method includes the combusting at least one fuel and at least one oxidant in a combustion chamber to form a combustion gas stream, wherein the combustion chamber includes a cylinder portion having an exit through which the combustion gas stream can flow to exit the cylinder portion; a narrowing conical zone contiguous with the cylinder portion, wherein the narrowing conical zone has inner walls which taper inward from the exit of the cylinder portion to form a circular nozzle orifice and wherein the narrowing conical zone includes at least two conical portions having nonequal conical angles; and an expanding conical zone contiguous with the circular nozzle orifice. A powder is directed into the combustion gas stream to form a thermal spray. The thermal spray is directed against the surface to apply the coating.

[0059] In a further embodiment, the thermal spray method includes directing a combustion gas stream to an interconnector, wherein the interconnector includes a hollow cylinder having at least two contiguous portions including a first portion and a second portion, wherein the ratio of the diameter of the first portion to the diameter of the second portion is in the range of about 1.1 and about 1.3; and at least two powder inlet ports opening to the inner walls of the second portion, wherein the powder inlet ports are in a non-opposition arrangement. A powder is directed into the combustion gas stream to form a thermal spray. The thermal spray is directed against the surface to apply the coating. [0060] In one embodiment, the thermal spray method includes directing a thermal spray through a barrel, wherein the thermal spray includes a combustion gas stream and a powder. The barrel includes a conical entrance portion which converges towards the radial axis of the central bore and a cylindrical portion contiguous with the conical entrance portion. In another embodiment, the length of the cylindrical portion is at least half the total length of the barrel. In yet another embodiment, the barrel includes a conical exit portion which flares away from the radial axis of the central bore. The thermal spray is directed against the surface to apply the coating. [0061] In another embodiment, the thermal spray method includes directing at least one fuel stream and at least one oxidant stream to a thermal spray gun to form a thermal spray and directing the thermal spray against the surface to apply the coating. The thermal spray gun of this embodiment includes an atomizer having a plurality of atomization holes arranged about an ignition source, a combustion chamber of a thermal spray gun, an interconnector for injecting powder into an exhaust stream leaving the combustion chamber, and a barrel having a hollow central bore through which a thermal spray can flow. The combustion chamber of this embodiment includes a cylinder portion having an exit through which fluids can flow to exit the cylinder portion; a narrowing conical zone contiguous with the cylinder portion, wherein the narrowing conical zone has inner walls which taper inward from the exit of the cylinder portion to form a circular nozzle orifice and wherein the narrowing conical zone includes at least two conical portions having nonequal conical angles; and an expanding conical zone contiguous with the circular nozzle orifice. The interconnector of this embodiment includes a hollow cylinder having at least two contiguous portions with inner walls having dissimilar diameters and at least two powder inlet ports opening to the inner walls of the second portion, wherein the powder inlet ports are in a non-opposition arrangement. The barrel of this embodiment includes a conical entrance portion which converges towards the radial axis of the central bore and a cylindrical portion contiguous with the conical entrance portion. [0062] While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A thermal spray gun comprising:

A) an atomizer having a plurality of atomization holes arranged about an ignition source;

B) a combustion chamber of a thermal spray gun, wherein the combustion chamber includes: i) a cylinder portion having an exit through which fluids can flow to exit the cylinder portion; ii) a narrowing conical zone contiguous with the cylinder portion, wherein the narrowing conical zone has inner walls which taper inward from the exit of the cylinder portion to form a circular nozzle orifice and wherein the narrowing conical zone includes at least two conical portions having nonequal conical angles; and iii) an expanding conical zone contiguous with the circular nozzle orifice;

C) an interconnector for injecting powder into an exhaust stream leaving the combustion chamber, wherein the interconnector includes: i) a hollow cylinder having at least two contiguous portions with inner walls having dissimilar diameters; and ii) at least two powder inlet ports opening to the inner walls of the second portion, wherein the powder inlet ports are in a non-opposition arrangement; and D) a barrel having a hollow central bore through which a thermal spray can flow, wherein the barrel includes : i) a conical entrance portion which converges towards the radial axis of the central bore; and ii) a cylindrical portion contiguous with the conical entrance portion.

2. The thermal spray gun of claim 1 wherein the plurality of atomization holes in said atomizer includes between 7 and 12 injector ports, wherein each injector port has a diameter in the range of between about 0.02 and about 0.047 inches, and wherein the ignition source includes at least one spark plug.

3. The thermal spray gun of claim 1 wherein the combustion chamber comprises:

A) a cylinder portion having a length to diameter ratio in the range of between about 1.3 and about 2 and having an exit through which fluids can flow to exit the cylinder portion;

B) a narrowing conical zone contiguous with the cylinder portion, wherein the narrowing conical zone has inner walls which taper inward from the exit of the cylinder portion to form a circular nozzle orifice having a diameter in the range of between about 0.2 and about 0.350 inches and wherein the narrowing conical zone includes at least two conical portions including: i) a first conical portion wherein the inner walls narrow at a conical angle in the range of between about 80° and about 100°; and

ii) a second conical portion wherein the inner walls narrow at a conical angle in the range of between about 40° and about 60°; and C) an expanding conical zone contiguous with the circular nozzle orifice, wherein the inner walls of the expanding conical zone flare outwards at a conical angle in the range of between about 8° and about 17°.

4. The thermal spray gun of claim 3 wherein the cylinder portion has a length to diameter ratio in the range of between about 1.4 and about 1.7, wherein the cylinder portion has a diameter in the range of between about 1.5 and about 2 inches, wherein the first conical portion narrows at a conical angle in the range of between about 85° and about 95°, wherein the second conical portion narrows at a conical angle in the range of between about 45° and about 55°, and wherein the expanding conical zone flares outward to a diameter in the range of between about 0.3 and about 0.5 inches .

5. The thermal spray gun of claim 1 wherein the interconnector comprises:

A) a hollow cylinder having at least two contiguous portions including a first portion and a second portion, wherein the ratio of the diameter of the first portion to the diameter of the second portion is in the range of about 1.1 and about 1.3; and

B) at least two powder inlet ports opening to the inner walls of the second portion, wherein the powder inlet ports are in a non-opposition arrangement .

6. The interconnector of claim 5 wherein the second portion has two powder inlet ports with at least about 90° of separation about the circumference of the second portion or wherein the second portion has three inlet ports and each part is orientated so as to have at least about 60° of separation from the other two inlet ports about the circumference of the second portion, and wherein at least one of the inlet ports intercepts the inner wall at an angle in the range of about 80° to about 90° or wherein at least one of the inlet ports intercepts the inner wall at an angle of about 90°.

7. The thermal spray gun of claim 1 wherein the barrel comprises:

A) a conical entrance portion which converges towards the radial axis of the central bore;

B) a cylindrical portion contiguous with the conical entrance portion, wherein the length of the cylindrical portion is at least half the total length of the barrel; and

C) a conical exit portion which flares away from the radial axis of the central bore.

8. The thermal spray gun of claim 7 wherein the converging entrance portion has a conical angle in the range of about 1.5° to about 3° or wherein the converging entrance portion has a conical angle in the range of about 1.5° to about 2.5°, wherein the barrel is in the range of about 1 to about 12 inches in length or wherein the barrel is in the range of about 1 to about 8 inches in length, wherein the conical exit portion flares away from the radial axis of the central bore at a conical angle in the range of about 0.5° to about 5° or wherein the conical exit portion flares away from the radial axis of the central bore at a conical angle in the range of about 0.5° to about 1.5°, and wherein the cylinder portion has an inner diameter in the range of about 0.25 to about 0.6 inches or wherein the cylinder portion has an inner diameter in the range of about 0.25 to about 0.5 inches.

9. The thermal spray gun of claim 1 wherein the barrel comprises:

B) a cylindrical portion contiguous with the conical entrance portion.

10. The thermal spray gun of claim 9 wherein the converging entrance portion has a conical angle in the range of about 1.5° to about 3° or wherein the converging entrance portion has a conical angle in the range of about 1.5° to about 2.5°, and wherein the cylinder portion has an inner diameter in the range of about 0.25 to about 0.6 inches or wherein the cylinder portion has an inner diameter in the range of about 0.25 to about 0.5 inches.

11. A thermal spray method for applying a coating to a surface which method comprises:

A) directing at least one fuel stream and at least one oxidant stream to a thermal spray gun to form a thermal spray, wherein the thermal spray gun includes : i) an atomizer having a plurality of atomization holes arranged about an ignition source; ii) a combustion chamber of a thermal spray gun, wherein the combustion chamber includes :

1) a cylinder portion having an exit through which fluids can flow to exit the cylinder portion;

2) a narrowing conical zone contiguous with the cylinder portion, wherein the narrowing conical zone has inner walls which taper inward from the exit of the cylinder portion to form a circular nozzle orifice and wherein the narrowing conical zone includes at least two conical portions having nonequal conical angles; and

3) an expanding conical zone contiguous with the circular nozzle orifice; iii) an interconnector for injecting powder into an exhaust stream leaving the combustion chamber, wherein the interconnector includes :

1) a hollow cylinder having at least two contiguous portions with inner walls having dissimilar diameters; and

2) at least two powder inlet ports opening to the inner walls of the second portion, wherein the powder inlet ports are in a non-opposition arrangement ; and iv) a barrel having a hollow central bore through which a thermal spray can flow, wherein the barrel includes:

1) a conical entrance portion which converges towards the radial axis of the central bore; and

2) a cylindrical portion contiguous with the conical entrance portion; and

B) directing the thermal spray against the surface to apply the coating.

12. A component part of a thermal spray gun selected from:

B) a combustion chamber comprising: i) a cylinder portion having a length to diameter ratio in the range of between about 1.3 and about 2 and having an exit through which fluids can flow to exit the cylinder portion; ii) a narrowing conical zone contiguous with the cylinder portion, wherein the narrowing conical zone has inner walls which taper inward from the exit of the cylinder portion to form a circular nozzle orifice having a diameter in the range of between about 0.2 and about 0.350 inches and wherein the narrowing conical zone includes at least two conical portions including: a) a first conical portion wherein the inner walls narrow at a conical angle in the range of between about 80° and about 100°; and b) a second conical portion wherein the inner walls narrow at a conical angle in the range of between about 40° and about 60°; and iii) an expanding conical zone contiguous with the circular nozzle orifice, wherein the inner walls of the expanding conical zone flare outwards at a conical angle in the range of between about 8° and about 17°; C. an interconnector comprising: i) a hollow cylinder having at least two contiguous portions including a first portion and a second portion, wherein the ratio of the diameter of the first portion to the diameter of the second portion is in the range of about 1.1 and about 1.3; and ii) at least two powder inlet ports opening to the inner walls of the second portion, wherein the powder inlet ports are in a non-opposition arrangement; a barrel comprising: i) a conical entrance portion which converges towards the radial axis of the central bore; ii) a cylindrical portion contiguous with the conical entrance portion, wherein the length of the cylindrical portion is at least half the total length of the barrel ; and iii) a conical exit portion which flares away from the radial axis of the central bore.