Abstract: A plasma spray method capable of directing plasticized powders against a substrate for deposition of a protective coating thereon is disclosed. Various structural details of the apparatus described enable the attainment of high particle velocities without melting the particles. The technical concepts employed are directed to normalizing the temperature of the plasma stream at a reduced value prior to the injection of coating particles. A general reduction in temperature and substantial elimination of a thermal spike at the core of the stream are achieved. Coating particles are injected into the plasma stream only after the plasma is first cooled and then preferably accelerated. In detailed embodiments, a nozzle extension assembly having a plasma cooling zone, a plasma acceleration zone, a powder injection zone and a plasma/powder discharge zone is affixed to the downstream end of a conventional plasma generator.

Abstract: A thermal spray method capable of directing plasticized powders against a substrate for deposition of a protective coating thereon is disclosed. Various structural details of the apparatus described enable the attainment of high particle velocities without melting the particles. The method is built around the concept of reducing the temperature of a hot plasma stream after the hot plasma stream is generated. Coating particles are injected into the hot plasma stream only after the medium is cooled. In detailed embodiments, a generated plasma is cooled by the addition of a diluent gas or by passing the generated plasma through an elongated heat exchanger upstream of the point at which the powders are to be injected. The plasma is accelerated after the plasma is cooled to recover velocity lost in the cooling step.

Abstract: Thermal spray apparatus capable of directing plasticized powders against a substrate for deposition of a protective coating thereon is disclosed. Various structural details of the apparatus of the present invention enable the attainment of high particle velocities without melting the particles. The apparatus is built around the concept of reducing the temperature of a hot plasma stream after the hot plasma stream is generated. Particles are injectedinto the hot plasma stream only after the medium is cooled. In detailed embodiments, a generated plasma is cooled by the addition of a diluent gas or by passing the generated plasma through an elongated heat exchanger upstream of the point at which the powders are to be injected.