Method and apparatus for ultra high velocity dual stream metal flame spraying

A flame spraying method comprising the steps of:

• establishing an arc column between an internal first electrode within a cylindrical plasma torch body and a constricting bore nozzle of said torch body,
• creating a plasma column annularly separated from the entry bore of an anode element downstream of the exit end of said constricting bore nozzle of said plasma torch body with said arc column passing at least axially part way through the exit bore of the anode element,
• passing a flow of powder or material to be melted into or near the exit of the plasma torch body nozzle bore and along said axial arc column in said primary jet stream,
• igniting a fuel/air mixture in an internal burner combustion chamber to create high pressure, high temperature products of combustion within the confined volume of the combustion chamber,
• causing the products of combustion of said internal burner to exit from said burner through a manifold nozzle closing off one end of the combustion chamber as a converging annular flow of gas from a circular series of closely spaced nozzle orifices or a continuous slot of circumferential ring geometry to form a gaseous accelerating secondary jet stream including a diminished core section defining the inner envlope of said converging annular secondary jet stream into said primary jet stream bearing said melted particles in the same direction of flow as said primary jet stream, and
• controlling combustion within said internal burner to accelerate said molten particles to supersonic velocity and to thereby create an extended length small diameter stream of molten particles downstream of said manifold nozzle of extreme high practice density for rapid, high bonding strength molten particle deposition on a surface to be coated, while maintaining the temperature of said secondary jet stream at a sufficiently high value to prevent solidification of the molten particles over said extended length necessary to reach supersonic velocity prior to impact on said surface.

A supersonic velocity dual stream flame spraying apparatus, said apparatus comprising:

• a cylindrical plasma torch body including a constricting bore nozzle,
• means including said plasma torch body for forming a primary jet stream of melted material particles suspended in a very hot carrier gas and exiting from said constricting bore nozzle of said torch body,
• an internal burner having a combustion chamber,
• means for igniting a fuel/air mixture in said internal burner combustion chamber to create high pressure, high temperature products of combustion within the confined volume of said combustion chamber,
• said internal burner including a manifold nozzle closing off one end of said combustion chamber and having a circular series of closely spaced nozzle orifices or a continuous slot of circumferential ring geometry, said manifold nozzle being positioned downstream and spaced from said constricting bore nozzle of said torch bore body to create an annular gas aspirating passage intermediate of said constricting bore nozzle and said circular series of closely spaced nozzle orifices or said continuous slot of circumferential ring geometry concentrically surrounding the primary jet stream of the melted material particles suspended in the very hot carrier gas exiting from said torch body constricting bore nozzle for creating an accelerating secondary jet stream about said primary jet stream, said said secondary jet stream including a diminished core section defining the inner envelope of said converging annular secondary jet stream with said streams flowing in the same direction, and
• means for controlling combustion within said internal burner to accelerate said molten particles to supersonic velocity and to thereby create an extended length small diameter stream of molten particles downstreams of said manifold nozzle of extremely high density for rapid, high bonding strength molten particle deposition on a surface to be coated, while maintaining the temperature of said secondary jet stream at a sufficiently high value to prevent solidification of said molten particles prior to impact on said surface with said secondary accelerating jet stream aspirating gas flow through said annular passage preventing normal radial expansion of the plasma gas exiting from said plasma torch constricting bore nozzle by causing aspirated gases to converge in the direction of primary and secondary jet streams to squeeze both hot gas streams and the particles entrained therein to focus the stream of molten particles to a constant small diameter over said extended length.