Abstract: 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.

Abstract: A plasma gun assembly for use in high temperature environments couples electrode and cooling water supplying hoses to a plasma gun via an extension arrangement having a conductive cathode extension tube coaxially disposed within a conductive anode extension tube. The cooling water flows through the hollow interior of the cathode extension tube to the plasma gun, then returns from the plasma gun via a passage formed between the outside of the cathode extension tube and the interior wall of the anode extension tube. In this manner the anode and cathode extension tubes are cooled as well as the plasma gun. Powder and plasma gas are supplied to the plasma gun by water-cooled tube arrangements in which such tubes are surrounded by intermediate and outer tubes forming separate passages. Cooling water is coupled via fittings to flow through the passages formed by the intermediate and outer tubes to provide cooling.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: In a plasma gun in which a plasma power source coupled between an anode and a cathode partly disposed within a central plasma chamber within the anode combines with the introduction of inert gas in the region of the cathode to form a plasma arc and a resulting plasma stream flowing from the anode, an improved cooling system is provided for the anode. Cooling fluid in the form of water from a booster pump is introduced generally tangentially into an annular cooling chamber formed between a cylindrical outer surface of the anode and a housing in which the anode is mounted. A helical groove formed by a set of threads in the outer cylindrical surface of the anode provides a spiral flow path for the cooling water within the annular cooling chamber such that the cooling water advances axially along the length of the anode as it flows around the outside of the anode.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.