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: 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.