Metallic film forming method using hvof thermal spraying gun and thermal spraying apparatus

Abstract

There are provided a thermal spraying method and a thermal spraying apparatus therefore, in which a gas shroud is disposed in an HVOF thermal spraying gun barrel, the velocity of metallic particles is energized and accelerated with respect to the metallic particle to be thermally sprayed from the gun, and inert gas is supplied into the space defined inside of the shroud through a circumferential slit formed in such a manner as to shield the metallic particles from the atmosphere so as to collide with the surface of a base member, thereby forming a thermally sprayed dense film having a small oxygen content without overheating the base plate by an HVOF method.

1 . A metallic film forming method using a high velocity oxy-fuel (HVOF) thermal spray gun having a cylindrical barrel portion extending in a longitudinal direction towards a base plate, the cylindrical barrel portion having an outlet, the method comprising:
 connecting a gas shroud to the outlet of the cylindrical barrel portion in a coaxial manner, the gas shroud having a substantially cylindrical portion extending in the longitudinal direction with an outlet at one end and an inlet at another end and having a length longer than a diameter of the inlet, the gas shroud being connected to the outlet of the cylindrical barrel portion such that the inlet of the gas shroud and the outlet of the cylindrical barrel portion are in conformity with each other, an inner diameter of the substantially cylindrical portion of the gas shroud being continuously enlarged from the outlet of the cylindrical barrel portion to the outlet of the gas shroud;   spraying metallic particles from the thermal spray gun by a neutral flame or a reducing flame such that the metallic particles collide with the base plate; and   supplying inert gas to a space within the gas shroud through a slit formed at the outlet of the cylindrical barrel portion and in a circumferential manner in the gas shroud, the supplied inert gas suppressing oxidation of the metallic particles by preventing any mixture of the metallic particles with the atmosphere, and the supplied inert gas increasing a velocity of the metallic particles so that the metallic particles collide with the base plate without overheating the base plate, to thereby form a thermally sprayed dense film having a low oxygen content.   
     
     
         2 . The metallic film forming method of  claim 1 , wherein the slit is arranged at an inclination with respect to a spraying direction of the metallic particles such that the inert gas is supplied into the space within the gas shroud along the inclination. 
     
     
         3 . The metallic film forming method of  claim 2 , wherein the inclination is within 70° with respect to a line perpendicular to a center axis of the cylindrical portion of the gas shroud. 
     
     
         4 . The metallic film forming method of  claim 3 , wherein the slit is arranged at a plurality of portions in the longitudinal direction of the gas shroud. 
     
     
         5 . The metallic film forming method of  claim 2 , wherein the slit is arranged at a plurality of portions in the longitudinal direction of the gas shroud. 
     
     
         6 . The metallic film forming method of  claim 1 , wherein the slit is arranged at a plurality of portions in the longitudinal direction of the gas shroud. 
     
     
         7 . The metallic film forming method of  claim 6 , wherein the slit is arranged at least at the inlet of the gas shroud and at the outlet of the gas shroud. 
     
     
         8 . A thermal spraying apparatus comprising:
 a high velocity oxy-fuel (HVOF) thermal spray gun for thermally spraying metallic particles to a base plate, said thermal spray gun having a cylindrical barrel portion extending in a longitudinal direction, said cylindrical barrel portion having an outlet, and said thermal spray gun having a heat source comprising a neutral flame or a reducing flame;   a gas shroud having a substantially cylindrical portion extending in the longitudinal direction with an inlet at one end and an outlet at another end and having a length longer than a diameter of the inlet, said gas shroud being detachably connected in a coaxial manner to said outlet of said cylindrical barrel portion such that said inlet of said gas shroud and said outlet of said cylindrical barrel portion are in conformity with each other, wherein an inner diameter of said substantially cylindrical portion of said gas shroud is continuously enlarged from said outlet of said cylindrical barrel portion to said outlet of said gas shroud; and   said gas shroud having a slit for supplying inert gas into a space within said gas shroud, said slit being formed in said gas shroud at the outlet of the cylindrical barrel portion and in a circumferential manner, wherein said thermal spray gun, said gas shroud and said slit are structured and arranged such that the inert gas supplied through said slit increases a velocity of the metallic particles being sprayed from said thermal spray gun, and suppresses oxidation of the metallic particles by preventing any mixture of the metallic particles with the atmosphere.   
     
     
         9 . The thermal spraying apparatus of  claim 8 , wherein said slit is arranged at an inclination with respect to a spraying direction of the metallic particles such that the inert gas is supplied into said space within said gas shroud along said inclination. 
     
     
         10 . The thermal spraying apparatus of  claim 9 , wherein said inclination is within 70° with respect to a line perpendicular to a center axis of said substantially cylindrical portion of said gas shroud. 
     
     
         11 . The thermal spraying apparatus of  claim 10 , wherein said slit is arranged at a plurality of portions in the longitudinal direction of said gas shroud. 
     
     
         12 . The thermal spraying apparatus of  claim 9 , wherein said slit is arranged at a plurality of portions in the longitudinal direction of said gas shroud. 
     
     
         13 . The thermal spraying apparatus of  claim 8 , wherein said slit is arranged at a plurality of portions in the longitudinal direction of said gas shroud. 
     
     
         14 . The thermal spraying apparatus of  claim 13 , wherein said slit is arranged at least at said inlet of said gas shroud and at said outlet of said gas shroud. 
     
     
         15 . The metallic film forming method of  claim 1 , wherein a porosity of the thermally sprayed dense film is zero. 
     
     
         16 . The metallic film forming method of  claim 15 , wherein the metallic particles include stainless steel powder. 
     
     
         17 . The thermal spraying apparatus of  claim 8 , wherein the metallic particles include stainless steel powder. 
     
     
         18 . The method of  claim 1 , wherein the thermal spray gun further includes a combustion chamber and a divergent nozzle, fuel and oxygen mixing and igniting inside of the combustion chamber to form a combustion flame that passes through the divergent nozzle and passes from the divergent nozzle into the cylindrical barrel portion. 
     
     
         19 . The method of  claim 18 , wherein said spraying metallic particles comprises spraying material powder into the combustion flame at an outlet of the divergent nozzle. 
     
     
         20 . The apparatus of  claim 8 , wherein said thermal spray gun further comprises a combustion chamber and a divergent nozzle such that fuel and oxygen can be mixed and ignited inside of the combustion chamber to form a combustion flame which then passes through said divergent nozzle to said cylindrical barrel portion and wherein said divergent nozzle has an outlet at which material powder can be sprayed into the combustion flame.