Method and apparatus for shielding the effluent from plasma spray gun assemblies

Abstract

Method and apparatus for plasma flame-spraying coating material onto a substrate by means of passing a plasma-forming gas through a nozzle electrode, passing an arc-forming current between said nozzle electrode and a rear electrode to form a plasma effluent, introducing spray coating material into the plasma effluent, passing the plasma effluent axially through a wall shroud extending from the exit of said nozzle electrode and forming a hot gas shroud for the plasma effluent at least within the wall shroud. .Iadd.

What is claimed is: 
     
       1. A plasma spray gun assembly for coating substrates comprising, in combination: a nozzle electrode having a nozzle passage therethrough;   a rear electrode;   means for passing plasma-forming gas through the nozzle electrode;   means for passing an arc-forming current between said electrodes to form a plasma effluent;   means for introducing spray coating material into the plasma effluent;   a wall shroud for said plasma effluent extending from the exit of the nozzle electrode; and   means for forming a hot gas shroud for said plasma effluent at least within the wall shroud .Iadd.directed at an angle such that the gas has a component of flow extending in a direction opposite to the direction of flow of the plasma effluent. .Iaddend.   
     
     
       2. A plasma spray gun assembly according to claim 1 wherein said spray coating material is in the form of a powder. 
     
     
       3. A plasma spray gun assembly according to claim 1 wherein said means for forming a hot gas shroud for said plasma effluent at least within the wall shroud comprises means for directing said hot gas shroud at an angle of between about 160° to about 180° with respect to the axis of the plasma effluent. 
     
     
       4. A plasma spray gun assembly according to claim 1 wherein said means for forming a hot gas shroud for said plasma effluent at least within the wall shroud comprises means for directing said hot gas shroud at an angle of about 180° with respect to the axis of the plasma effluent. 
     
     
       5. A plasma spray gun assembly according to claim 4 wherein said means for forming a hot gas shroud for said plasma effluent at least within the wall shroud includes an annular plenum chamber having jet orifice means directed at an angle of about 180° with respect to the axis of the plasma effluent. 
     
     
       6. A plasma spray gun assembly according to claim 1 further comprising means for water cooling said wall shroud. 
     
     
       7. A plasma spray gun assembly according to claim 1 wherein said wall shroud is of cylindrical configuration. 
     
     
       8. A plasma spray gun assembly according to claim 1 wherein said means for introducing spray coating material into the plasma effluent is disposed adjacent the exit of the electrode nozzle. 
     
     
       9. A plasma spray gun assembly according to claim 1 wherein said means for forming a hot gas shroud for said plasma effluent at least within the wall shroud includes an electric heater for preheating the gas for said hot gas shroud. 
     
     
       10. A plasma spray gun assembly according to claim 1 wherein said means for forming a hot gas shroud for said plasma effluent at least within the wall shroud includes a second plasma flame gun assembly for preheating the gas for said hot gas shroud. 
     
     
       11. A plasma spray gun assembly according to claim 1 wherein said means for forming a hot gas shroud for said plasma effluent at least within the wall shroud includes an internal passageway of generally serpentine configuration in said wall shroud for preheating the gas for said hot gas shroud. 
     
     
       12. A plasma spray gun assembly according to claim 1 wherein said means for forming a hot gas shroud for said plasma effluent at least within the wall shroud includes means for preheating the gas for said hot gas shroud to a temperature of from about 500° C. to about 1000° C. 
     
     
       13. A plasma spray gun assembly according to claim 1 wherein said means for forming a hot gas shroud for said plasma effluent at least within the wall shroud includes means for introducing hot gas at a flow rate of between about 1000 cubic feet per hour and about 2000 cubic feet per hour at a temperature of about 500° C. to form said hot gas shroud. 
     
     
       14. A plasma spray gun assembly according to claim 1 wherein said hot gas shroud is formed of an inert gas. 
     
     
       15. A plasma spray gun assembly according to claim 14 wherein said inert gas is selected from the class consisting of nitrogen, argon and helium. 
     
     
       16. A plasma spray gun assembly according to claim 15 wherein said hot gas shroud further comprises a combustible gas. 
     
     
       17. A plasma spray gun assembly according to claim 1 further comprising means for forming an annular curtain effect around the plasma effluent as it leaves the wall shroud and passes towards the substrate. 
     
     
       18. A plasma spray gun assembly according to claim 17 wherein said means for forming an annular curtain effect includes an annular manifold and orifice means mounted adjacent the outer end of said wall shroud. .[.19. A plasma spray gun assembly according to claim 1 wherein said means for forming a hot gas shroud for said plasma effluent at least within the wall shroud comprises means for directing said hot gas at an angle having a component extending parallel to the direction of flow of said plasma effluent..]. .[.20. A plasma spray gun assembly according to claim 1 wherein said means for forming a hot gas shroud for said plasma effluent at least within the wall shroud comprises means for directing said hot gas at an angle having a component extending in a direction opposite to the 
     
     
        direction of flow of said plasma effluent..]. 21. A plasma spray gun assembly according to claim 5 further comprising second jet orifice means directed at an angle of from about zero degrees to about 180° with 
     
     
        respect to the axis of the plasma effluent. 22. A plasma spray gun assembly according to claim 5 further comprising second jet orifice means directed at an angle having a component extending parallel to the 
     
     
        direction of flow of said plasma effluent. 23. A plasma spray gun assembly according to claim 5 further comprising second jet orifice means directed at an angle having a component extending in a direction opposite to the 
     
     
        direction of flow of said plasma effluent. 24. A plasma spray gun assembly according to claim 1 wherein said wall shroud has a radially-inwardly 
     
     
        directed lip portion disposed towards the exit end thereof. 25. A process for plasma flame-spraying coating material onto a substrate, which comprises the steps of: passing a plasma-forming gas through a nozzle electrode;   passing an arc-forming current between said nozzle electrode and a rear electrode to form a plasma effluent;   introducing coating material into the plasma effluent;   passing the plasma effluent longitudinally through a wall shroud extending from the exit of said nozzle electrode; and   forming a hot gas shroud for said plasma effluent at least within the wall shroud .Iadd.directed at an angle such that the gas has a component of flow extending in a direction opposite to the direction of flow of the   
     
     
        plasma effluent. .Iaddend. 26. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein said coating 
     
     
        material is in a powder form. 27. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein said hot gas shroud is directed at an angle of between about 160° to about 
     
     
        180° with respect to the axis of the plasma effluent. 28. A process for plasma flame-spraying coating material onto a substrate according to claim 27 wherein said hot gas shroud is directed at an angle of about 
     
     
        180° with respect to the axis of the plasma flame. 29. A process for plasma flame-spraying coating material onto a substrate according to claim 25 further comprising the step of passing cooling water through said 
     
     
        wall shroud. 30. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein said coating material is introduced into the plasma effluent adjacent the exit of the electrode 
     
     
        nozzle. 31. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein said step of forming a hot gas shroud for said plasma effluent at least within the wall shroud includes the step of passing the gas for forming said hot gas shroud through an 
     
     
        electric preheater. 32. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein said step of forming a hot gas shroud for said plasma effluent at least within the wall shroud includes the step of using a second plasma flame gun assembly for 
     
     
        preheating the gas for said hot gas shroud. 33. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein said step of forming a hot gas shroud for said plasma effluent at least within the wall shroud includes the step of passing the gas for said hot gas shroud through an internal passageway of generally serpentine 
     
     
        configuration in said wall shroud. 34. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein said step of forming a hot gas shroud for said plasma effluent at least within the wall shroud includes the step of preheating the gas for said gas shroud to 
     
     
        a temperature above about 300° C. 35. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein said step of forming a hot gas shroud for said plasma effluent at least within the wall shroud includes the step of preheating the gas for said gas shroud to a temperature of between about 500° C. and about 
     
     
        1000° C. 36. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein the gas for said hot gas 
     
     
        shroud is a reducing gas. 37. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein the gas in said 
     
     
        hot gas shroud is in a turbulent state. 38. A process for plasma flame-spraying coating material onto a substrate according to claim 25 
     
     
        wherein the gas for said hot gas shroud is an inert gas. 39. A process for plasma flame-spraying coating material onto a substrate according to claim 38 wherein said inert gas is selected from the group consisting of 
     
     
        nitrogen, argon and helium. 40. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein the gas 
     
     
        for forming said hot gas shroud includes a combustible gas. 41. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein the flow rate of said gas in said hot gas shroud is above 
     
     
        about 500 cubic feet per hour. 42. A process for plasma flame-spraying coating material onto a substrate according to claim 41 wherein the flow rate of the gas for forming said hot gas shroud is between about 1000 cubic feet per hour and about 2000 cubic feet per hour at a temperature of 
     
     
        about 500° C. 43. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein said coating 
     
     
        material is a fusible powdered metal. 44. A process for plasma flame-spraying coating material onto a substrate according to claim 25 
     
     
        wherein said coating material is a ceramic material. 45. A process for plasma flame-spraying coating material onto a substrate according to claim 
     
     
        25 wherein said coating material is a carbide. 46. A process for plasma flame-spraying coating material onto a substrate according to claim 25 further comprising the step of forming a fluid annular curtain around the plasma effluent as it leaves the wall shroud passing towards said substrate. .[.47. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein said hot gas shroud is directed at an angle having a component extending parallel to the direction of flow of said plasma effluent..]. .[.48. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein said hot gas shroud is directed at an angle having a component extending in a direction opposite to the direction of flow of said plasma 
     
     
        effluent..]. 49. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein a portion of the gas for forming said hot gas shroud is introduced at an angle of about 180° with respect to the axis of the plasma effluent and a second portion of the gas for forming said hot gas shroud is introduced at an angle of from about zero degrees to about 180° with respect to the axis of the plasma 
     
     
        effluent. 50. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein a portion of the gas for forming said hot gas shroud is introduced at an angle of about 180° with respect to the axis of the plasma effluent and a second portion of the gas for forming said hot gas shroud is introduced at an angle having a component extending parallel to the direction of flow of said plasma 
     
     
        effluent. 51. A process for plasma flame-spraying coating material onto a substrate according to claim 25 wherein a portion of the gas for forming said hot gas shroud is introduced at an angle of about 180° with respect to the axis of the plasma effluent and a second portion of the gas for forming said hot gas shroud is introduced at an angle having a component extending in a direction opposite to the direction of flow of said plasma effluent.