Shrouded thermal spray gun and method

Abstract

A powder or wire thermal spray gun, useful for spraying a low oxide coating of oxidizable material, comprises a nozzle member with a nozzle face, and a gas cap extending from the nozzle member and having an inwardly facing cylindrical wall defining a combustion chamber with an open end for propelling combustion products into the ambient atmosphere at supersonic velocity and an opposite end bounded by the nozzle face. An annular flow of a combustible mixture is injected from the nozzle member coaxially into the combustion chamber at a pressure therein sufficient to propel combustion products of the mixture from the open end at supersonic velocity. A first annular flow of inert gas is injected adjacent to the cylindrical wall radially outward of the annular flow of the combustible mixture. Heat fusible thermal spray material is fed from the nozzle member into the combustion chamber radially inward of the combustible mixture, whereby a supersonic spray stream containing the heat fusible material in finely divided form is propelled through the open end. A second annular flow of combustion gas is directed adjacently surrounding the spray stream forwardly from the open end. A third annular flow of inert gas is directed adjacently surrounding the second annular flow forwardly of the open end.