Electro Plasma, Inc.

Sulzer Metco (us) Inc.

Sulzer Metco Ag

Erich Muehlberger

Albert Sickinger

Roland D Kremith

Koichi Takeda

William P Rusch

Tsuyoshi Shinoda

Gary A Hislop

Masamichi Koga

Robert P De La Vega

Don E Bailey

Stephan E Meuhlberger

A cold spraying process for forming a coating of powder particles sprayed in a gas substantially at ambient temperature onto a workpiece is improved by placement in a low ambient pressure environment in which the pressure is substantially less than atmospheric pressure. The low pressure environment acts to substantially accelerate the sprayed powder particles, thereby forming an improved coating of the particles on the workpiece. The low ambient pressure environment is provided by a vacuum tank coupled to a vacuum pump and having both the workpiece and a cold spray gun located therein. The cold spray gun is coupled to a source of pressurized inert gas as well as to a feeder for providing a flow of the powder to be sprayed. A gas compressor downstream of the vacuum pump compresses gas from the vacuum tank for recycling to the source of pressurized gas. The source of pressurized gas is coupled to the cold spray gun where it may be heated by passing through a heating coil coupled to a source of electrical power, before being sprayed from a nozzle onto the workpiece. An arrangement of valves and injection ports enables the powder flow to be introduced at a selected one of a plurality of locations along the heating coil and the nozzle.

Method and apparatus for low pressure cold spraying

A plasma system forms a dense, uniform coating of metallic oxide or other material on a relatively large substrate of metal foil or other composition located a substantial distance from the plasma gun so that the plasma stream covers the entire width of the substrate. A large pressure differential between the pressure inside the plasma gun and the ambient pressure outside of the plasma gun creates a shock pattern within the exiting plasma stream so as to disperse the plasma stream and maintain a high energy level therein, as well as thoroughly mixing a coating material introduced into the plasma stream within the gun. Mixing of the coating material within the plasma stream is further enhanced by introducing the coating material into the plasma stream either in liquid form or in the form of very small particles. In one arrangement, the plasma stream is delivered in a long, narrow configuration across the width of the substrate by a nozzle with a slit-like opening at the lower end of the plasma gun. In still other arrangements, a plasma stream of elongated configuration is provided by a plasma gun of elongated configuration having an elongated cathode assembly disposed within the hollow interior of an elongated anode having a nozzle-forming slot therein. Arc gas introduced into the space between the cathode and adjacent portions of the anode flows out of the slot to form a broad plume plasma stream, in conjunction with spray material introduced in powder form into the spaces between the cathode and the opposite portions of the anode along the length of the plasma gun. The cathode assembly may be of integral construction along the length of the anode, or it may be divided into plural segments disposed in spaced-apart relation along the length of the anode.

Method of forming uniform thin coatings on large substrates

A single cathode plasma gun injects powder therein so that the powder exits along a central axis of an exit barrel of the gun, in order to provide improved coatings of the powder material on a workpiece. The central axis of the single cathode extends from an arc chamber and intersects with the central axis of the exit barrel so as to form an acute angle which is substantially greater than 0.degree. but no greater than 90.degree.. Examples of the acute angle include 45.degree. and 10.degree.. A powder feed passage extends along an axis which may be coincident with the central axis of the exit barrel or may form an angle with the central axis of the exit barrel of as much as 45.degree.. Consequently, the axis of the powder feed passage forms an angle with the central axis of the single cathode which is at least as great as the acute angle between the central axes of the single cathode and the exit barrel. Existing plasma guns can be retrofitted with a new anode attachment to achieve desired angles of plasma flow and powder delivery. Where the central axis of the single cathode forms an acute angle with the central axis of the exit barrel, the resulting bend in the passage extending from the arc chamber below the single cathode is disposed adjacent an entry end of the exit barrel, and the powder feed passage terminates adjacent such bend. Alternatively, the powder can be introduced into the middle of the plasma stream at the entry end of the exit barrel by a powder injector extending into the exit barrel from the wall of the passage. The single cathode can be axially adjusted to move the charged plasma region adjacent the termination of the powder feed passage, for more effective heating of the powder. The angles formed by the central axes of the single cathode and the powder feed passage relative to the central axis of the exit barrel can be adjusted relative to each other so that the injected powder is deflected along the central axis of the exit barrel, again providing for an improved coating of the powder material on a workpiece.

Single cathode plasma gun with powder feed along central axis of exit

A plasma system forms a dense, uniform coating of metallic oxide or other material on a relatively large substrate of metal foil or other composition located a substantial distance from the plasma gun so that the plasma stream covers the entire width of the substrate. A large pressure differential between the pressure inside the plasma gun and the ambient pressure outside of the plasma gun creates a shock pattern within the exiting plasma-stream so as to disperse the plasma stream and maintain a high energy level therein, as well as thoroughly mixing a coating material introduced into the plasma stream within the gun. Mixing of the coating material within the plasma stream is further enhanced by introducing the coating material into the plasma stream in the form of very small particles. In one arrangement, the plasma stream is delivered in a long, narrow configuration across the width of the substrate by a nozzle with a slit-like opening at the lower end of the plasma gun. In still other arrangements, a plasma stream of elongated configuration is provided by a plasma gun of elongated configuration having an elongated cathode assembly disposed within the hollow interior of an elongated anode having a nozzle-forming slot therein.

Plasma gun apparatus for forming dense, uniform coatings on large

A high velocity, high pressure plasma gun operates in stable fashion and with a relatively constant arc input power using a highly combustible arc gas such as nitrogen. The gun includes an anode having an internal arc chamber and a nozzle extending through the anode from the arc chamber. The gun also includes a cathode disposed within the anode and having a generally cylindrical tip portion with a flat surface facing the arc chamber and formed by a tungsten insert in the tip portion. The arc chamber, which has a wall of varying slope along the length thereof, may comprise successive conical portions of different slope and shape, or it may comprise a bell-shaped configuration. The flat surface of the cathode tip portion and the varying wall slope of the arc chamber combine to prevent the arc produced by nitrogen or other highly combustible arc gases form burning or otherwise damaging the cathode tip and the arc chamber.

High velocity, high pressure plasma gun

Apparatus for delivering heated powder to the plasma gun of the thermal spray plasma system includes a hollow heater tube coupled between a powder feeder and the plasma gun and a power supply coupled between opposite ends of the heater tube. The power supply heats the walls of the heater tube to a temperature below the melting point of the powder particles, to prevent melting and adhesion of the particles thereto. The length of the heater tube is selected to provide an adequate dwell-time of the powder particles therein for a given powder flow rate, so that even relatively large powder particles are heated to a temperature relatively close to that of the heater tube walls upon delivery to the plasma gun. The efficiency of the heater tube is improved by a water cooled reflector tube concentrically disposed about the outside of the heater tube, with oxidation of the tube surfaces being prevented by a flow of inert gas along the space between the heater and reflector rubes. The heated powder delivery apparatus can be used by itself and without the plasma gun to effect thermal spraying in instances where the powder is of the type that can be heated close of the melting point without adhering or clogging. One or more ring-shaped electrodes and associated DC power supplies can be disposed within the plasma stream to provide additional powder particle heating and control within the plasma stream itself.

Plasma systems having improved thermal spraying

A supersonic plasma system in which a vacuum source creates a low static pressure environment within an enclosure containing a plasma gun and a workpiece has plural cathodes of sealed, modular construction in conjunction with a common anode, to provide higher levels of operating power and other advantages which flow from a segmented cathode gun configuration. Inert gas independently introduced into the plural cathodes undergoes swirling motion over the cathode tips. The anode is of modular construction for easy replacement in order to change the configuration of a nozzle, a plurality of arc chambers receiving the plural cathodes or a central mixing chamber between the nozzle and the arc chambers within the anode and coupled to a central powder feed. The powder feed includes a replaceable insert which includes at least one and preferably a plurality of powder feed ports into the various arc chambers. Alternatively, metal which has already been heated to a molten state can be fed directly into the central mixing chamber. The modular cathodes which are independently powered by separate D.C. power sources are also independently cooled by separate cooling water systems as is the common anode. The cooling systems are configured to produce swirling of the cooling water so that cooling action is maximized.

Modular segmented cathode plasma generator

Apparatus for delivering heated powder to the plasma gun of the thermal spray plasma system includes a hollow heater tube coupled between a powder feeder and the plasma gun and a power supply coupled between opposite ends of the heater tube. The power supply heats the walls of the heater tube to a temperature below the melting point of the powder particles, to prevent melting and adhesion of the particles thereto. The length of the heater tube is selected to provide an adequate dwell-time of the powder particles therein for a given powder flow rate, so that even relatively large powder particles are heated to a temperature relatively close to that of the heater tube walls upon delivery to the plasma gun. The efficiency of the heater tube is improved by a water cooled reflector tube concentrically disposed about the outside of the heater tube, with oxidation of the tube surfaces being prevented by a flow of inert gas along the space between the heater and reflector tubes. The heated powder delivery apparatus can be used by itself and without the plasma gun to effect thermal spraying in instances where the powder is of the type that can be heated close to the melting point without adhering or clogging. One or more ring-shaped electrodes and associated DC power supplies can be disposed within the plasma stream to provide additional powder particle heating and control within the plasma stream itself.

Metal particles in powdered form are cleaned of oxides by a method in which the particles are introduced into a plasma stream in the presence of a continuous negative transfer arc. Ionization of a gas within a plasma gun produces a plasma stream into which the metal particles are introduced at a location within the plasma gun. A negative transfer arc power source is continuously coupled between the plasma gun and a cathode downstream of the plasma gun and within the plasma stream to remove oxide coatings from the metal particles as they travel along the plasma stream to either a receptacle located downstream from the cathode or to a substrate which forms the cathode and onto which a relatively oxide-free coating is formed by the metal particles. Such methods of oxide removal are particularly effective with highly oxidizable refractory materials such as titanium, tantalum and aluminum.

Method of oxide removal from metallic powder

A powder feeder for dispensing controlled amounts of powder into a gas stream in a supersonic plasma spraying environment utilizes a stir spindle and a feed impeller mounted on a rotatable first drive shaft at the bottom of a powder cannister to agitate and mix the powder and then dispense the powder in controlled amounts from an aperture in the bottom of the cannister as the first drive shaft is driven by a motor. The controlled amounts of powder dispensed through the aperture in the bottom of the cannister are directed by a conduit through an aperture in the upper end of a housing and into a plurality of slots circumferentially formed about the outer periphery of a feedwheel mounted within the housing to be rotatably driven by a second drive shaft which is also coupled to be driven by the motor. The slots which are uniform in size have bottom surfaces and opposite side surfaces formed by opposite vanes extending upwardly from the upper surface of the feedwheel between a first hollow tube mounted in a fixed location relative to the feedwheel so as to direct a gas flow through the slots and an opposite second hollow tube disposed to receive the gas flow and the powder loaded into the slots. The constant action of the stir spindle, the feed impeller and the feedwheel provides a relatively constant, uniform supply of the powder to the gas stream, even in the face of varying operating conditions.

Powder feeder

A powder feed control system employs an arrangement of conduits and valves for selectively directing a gas flow either through a powder feeder or through a bypass so as to quickly and precisely control the introduction of powder into and the removal of powder from the gas flow in a plasma spraying system. The arrangement of conduits and valves includes a two-way solenoid operated valve for directing the gas flow either into a powder feeder through a main conduit or into a bypass conduit which rejoins the main conduit on the other side of the powder feeder at a powder shutoff valve and a bypass and check valve. The bypass and check valve insures that the gas flow in the bypass conduit flows to the output rather than upstream to the powder shutoff valve. The powder shutoff valve includes a resilient member mounted within the bore of a housing and collapsible upon itself to close off an internal bore therein in response to the introduction of pressurized gas into a space between the housing bore and the resilient member. Air introduced into a cannister in the powder feeder with the loading of powder into the cannister is removed by an arrangement which includes a valve for selectively coupling the inside of the cannister to a vacuum source.

Powder feed control system

In a plasma spraying system in which a main plasma gun electrically coupled to a workpiece or target and equipped with apparatus for introducing a spray powder therein provides a plasma stream to the target at high temperatures and supersonic speeds with an accompanying transfer arc between the main plasma gun and the target in a given polarity relative to the target, apparatus is present for simultaneously providing a second transfer arc at the target which has an opposite polarity relative to the target from the polarity of the transfer arc provided by the main plasma gun. The second transfer arc which is provided by a separate second or clean-up plasma gun electrically coupled to the target acts to reduce oxides at the target during melting of the target, spraying of the target with metallic powders and other plasma operations. The transfer arcs are provided by the main and clean-up plasma guns in conjunction with direct current power supplies coupled between the target and the guns so as to render the target positive with respect to one of the plasma guns and negative with respect to the other plasma gun. Additional direct current power supplies coupled to the main and clean-up plasma guns provide the plasma guns with pilot arcs.

Method of and apparatus providing oxide reduction in a plasma environment

An overspray filter collector unit for a plasma spray system filters fine, relatively small particulate from the overspray upstream of the vacuum pumps. The filter collector unit includes a hollow tank having a pool of oil at the bottom thereof having a top surface onto which the overspray is directed from an inlet conduit. Some of the particulate matter is deposited in the oil and at the same time oil droplets and vapor are entrained in the overspray as it deflects from the oil surface into a tortuous path defined by a plurality of baffles within the tank. The baffle surfaces are wetted by the oil vapor and droplets, and the resulting oil coating entraps the remaining particulate in the overspray before the overspray exits via an outlet conduit to the vacuum pumps. The oil on the surfaces of the baffles with the entrapped particulate therein continuously drains via gravity to the pool of oil at the bottom of the tank and is replaced by oil at the surface of the pool entrained into the continuous flow of overspray. When the accumulation of particulate in the oil is such that the oil rises to a predetermined level, the oil is drained and replaced with fresh oil.

Fine particle filter system having low pressure drop for gaseous flow

Uniform protective coatings are deposited on components with a high strength bond by utilizing a supersonic plasma stream and a transferred arc system of selectively reversible polarity. By maintaining plasma stream velocity at a sufficiently high Mach number, and using stream temperatures and static pressures which establish a shock pattern characteristic that diffuses the arc, the workpiece is made cathodic relative to the plasma gun at predetermined intervals. This creates a sputtering effect in which electrons and atoms are ejected from the workpiece despite the impacting plasma flow and the ambient pressure level. This sputtering action is undertaken to clean the workpiece once it is sufficiently heated and to cause intermingling of molecules of the substrate material with molecules of a deposition powder injected into the plasma flow. This preparatory deposition, together with the clean workpiece surface, enables a subsequent buildup of securely bonded and high uniform material.

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San Clemente, CA, United States of America

Erich Muehlberger