Coating heat softened particles by projection in a plasma stream of Mach 1 to Mach 3 velocity

Claim 3

A supersonic plasma spray gun for projecting particles of high velocity comprising: means for producing a plasma arc at a pre-selected pressure and electrical power, and including nozzle means for expanding plasma produced in said arc to provide a plasma stream having an exit velocity of greater than Mach 1 and less than Mach 3, means for injecting a stream of particles of a size not greater than 44 microns into said plasma stream to be entrained thereby, and means for controlling time of dwell of said particles within said plasma stream so as to heat the particles to a temperature near to, but below, their melting point and to achieve substantially maximized velocity of said particles, said means for controlling dwell time comprising a plurality of nozzles, each including means for selective and alternative attachment to said spray gun, and each having a bore having a ratio of exit area to throat area sufficient to produce the above-mentioned plasma stream exit velocity, and each of said nozzles having a particle injection conduit providing communication between a source of particles exterior to said nozzles and the bore of said nozzle at a point thereof between said exit and throat for injection of said particles into the plasma stream, a first one of said nozzles for use with particles of low melting points such as bronze, copper and aluminum, having its particle injection conduit extending at a large angle (between 25* and 49*) with respect to a normal to the direction of flow of said plasma stream, and communicating with the bore of said nozzle at a point closely adjacent the nozzle exit to thereby provide a short dwell time that prevents premature melting and plating of the nozzle bore, a second one of said nozzles for use with materials of intermediate melting points (2000*F to 3000*F), such as stainless steel, nickel, chromium, and hard facing alloys having its particle injection conduit extending at an intermediate angle (between 7.5* and 25*) with respect to a normal to the direction of plasma stream flow and communicating with the bore of its associated nozzle at a point substantially midway between the throat and exit, but somewhat closer to the throat whereby the dwell time of such intermediate temperature melting point particles is greater than the dwell time achieved by lower temperature particles in said first-mentioned nozzle, and a third one of said nozzles for use with high temperature melting point particles such as tungsten carbide-cobalt, chromium carbide nickel chromium blends, tungsten and molybdenum, having its particle injection conduit extending at a considerably smaller angle (between -13* and 7.5*) with respect to a normal to the direction of the plasma stream and communicating with the bore of its associated nozzle at a point thereof substantially at its throat whereby dwell time of such high temperature particles is at least sufficient to ensure substantial heat softening of the particles without melting.

Claim 4

A supersonic plasma spray gun for projecting particles of high velocity comprising: means for producing a plasma arc at a pre-selected pressure and electrical power, and including nozzle means for expanding plasma produced in said arc to provide a plasma stream having an exit velocity of greater than Mach 1 and less than Mach 3, means for injecting a stream of particles of a size not greater than 44 microns into said plasma stream to be entrained thereby, and means for controlling time of dwell of said particles within said plasma stream so as to heat the particles to a temperature near to, but below, their melting point and to achieve substantially maximized velocity of said particles, said means for controlling dwell time comprising a plurality of nozzles, each including means for selective and alternative attachment to said spray gun, and each having a bore having a ratio of exit area to throat area sufficient to produce the above-mentioned plasma stream exit velocity, and each of said nozzles having a particle injection conduit providing communication between a source of particles exterior to said nozzles and the bore of said nozzle at a point thereof between said exit and throat for injection of said particles into the plasma stream, a first one of said nozzles for use with particles of low melting points such as bronze, copper and aluminum, having its particle injection conduit extending at a large angle (between 25* and 49*) with respect to a normal to the direction of flow of said plasma stream, and communicating with the bore of said nozzle at a point closely adjacent the nozzle exit to thereby provide a short dwell time that prevents premature melting and plating of the nozzle bore, a second one of said nozzles for use with materials of intermediate melting points (2000*F to 3000*F), such as stainless steel, nickel, chromium, and hard facing alloys having its particle injection conduit extending at an intermediate angle (between 7.5* and 25*) with respect to a normal to the direction of plasma stream flow and communicating with the bore of its associated nozzle at a point substantially midway between the throat and exit, but somewhat closer to the throat whereby the dwell time of such intermediate temperature melting point particles is greater than the dwell time achieved by lower temperature particles in said first-mentioned nozzle, and a third one of said nozzles for use with high temperature melting point particles such as tungsten carbide-cobalt, chromium carbide nickel chromium blends, tungsten and molybdenum, having its particle injection conduit extending at a considerably smaller angle (between -13* and 7.5*) with respect to a normal to the direction of the plasma stream and communicating with the bore of its associated nozzle at a point thereof substantially at its throat whereby dwell time of such high temperature particles is at least sufficient to ensure substantial heat softening of the particles without melting.

Claim 9

The method of claim 4, wherein said step of injecting particles into said plasma stream comprises injecting said particles into said nozzle in a direction that is inclined rearwardly with respect to the direction of flow of said plasma stream whereby transfer of kinetic energy from said plasma stream to said particles is still further increased.

Claim 10

Particle spraying apparatus for generating and projecting a stream of plasma exiting therefrom at a Mach number exit velocity greater than 1 and less than 3, said apparatus comprising: a gun having front and back electrodes and a vortex chamber extending about said back electrode, means for feeding gas under pressure into said vortex chamber adjacent said back electrode, means for energizing said electrodes to form an arc therebetween to ionize said gas and create a plasma stream flowing to and through said front electrode, said front electrode comprising an exit nozzle communicating with said vortex chamber and having an exit, having a throat spaced downstream of said back electrode, and having a portion diverging from said throat to the exit of said nozzle to provide a ratio of area of said exit to area of said throat sufficient to provide an exit velocity greater than Mach 1 and less than Mach 3, said nozzle having an axis along which said plasma stream flows, said means for feeding gas under pressure including means for effecting a pressure in said vortex chamber in the vicinity of said arc having a relation to ambient pressure sufficient to provide said Mach number exit velocity with said ratio of areas, and means for entraining and heating in said plasma stream a flow of particles having a size of less than 44 microns to be coated upon a substrate against which said plasma stream impinges, said means for entraining and heating causing said particles to be heated to a temperature near but below their melting point, said means for entraining comprising a particle injection conduit intersecting the nozzle at a point adjacent the nozzle throat wherein said plasma stream is of relatively higher density, and means for feeding said particles through said conduit and through the boundary layer of said plasma stream toward the center thereof whereby both transferred kinetic energy and dwell time of the particles in the plasma stream are increased.

Claim 11

Particle spraying apparatus for generating and projecting a stream of plasma exiting therefrom at a Mach number exit velocity greater than 1 and less than 3, said apparatus comprising: a gun having front and back electrodes and a vortex chamber extending about said back electrode, means for feeding gas under pressure into said vortex chamber adjacent said back electrode, means for energizing said electrodes to form an arc therebetween to ionize said gas and create a plasma stream flowing to and through said front electrode, said front electrode comprising an exit nozzle communicating with said vortex chamber and having an exit, having a throat spaced downstream of said back electrode, and having a portion diverging from said throat to the exit of said nozzle to provide a ratio of area of said exit to area of said throat sufficient to provide an exit velocity greater than Mach 1 and less than Mach 3, said nozzle having an axis along which said plasma stream flows, said means for feeding gas under pressure including means for effecting a pressure in said vortex chamber in the vicinity of said arc having a relation to ambient pressure sufficient to provide said Mach number exit velocity with said ratio of areas, and means for entraining and heating in said plasma stream a flow of particles having a size of less than 44 microns to be coated upon a substrate against which said plasma stream impinges, said means for entraining and heating causing said particles to be heated to a temperature near but below their melting point, said means for entraining comprising a particle injection conduit intersecting the nozzle at a point adjacent the nozzle throat wherein said plasma stream is of relatively higher density, and means for feeding said particles through said conduit and through the boundary layer of said plasma stream toward the center thereof whereby both transferred kinetic energy and dwell time of the particles in the plasma stream are increased.