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Particulate material, which may be heat softened or liquified, or which may remain solid, is fed outside of an electrical heating zone for electric arc heating under pressure a continuous flow of heated gas, or outside of a combustion chamber producing high pressure, high temperature products of com

Particulate material, which may be heat softened or liquified, or which may remain solid, is fed outside of an electrical heating zone for electric arc heating under pressure a continuous flow of heated gas, or outside of a combustion chamber producing high pressure, high temperature products of combustion, axially into the converging flow of the heated gas or products of combustion while entering a converging portion of a flow expansion nozzle having a nozzle bore of a length that is at least five times the diameter of the nozzle bore. This restricts the diameter of the column of particles passing through the nozzle bore to prevent build up of particle material on the nozzle bore, if molten or heat softened, while insuring sufficient dwell time within the bore to effect particle heat softening or melting, or if the particles are solid, to prevent abrasion of the nozzle bore wall by the particles while accelerating the particles to supersonic velocity.

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1. In a flame spray method comprising the steps of: electrically arc heating, under pressure, a continuous flow of a gas confined to flow within an essentially closed passage, discharging said heated gas from said passage through a flow expansion nozzle as an extremely hot gas stream, and feedi

1. In a flame spray method comprising the steps of: electrically arc heating, under pressure, a continuous flow of a gas confined to flow within an essentially closed passage, discharging said heated gas from said passage through a flow expansion nozzle as an extremely hot gas stream, and feeding material to said stream for high-temperature heat softening or liquifaction and spraying onto a surface positioned in the path of the stream at the discharge end of the nozzle, the improvement wherein: the step of feeding said material comprises introducing said material in solid form outside of said electrical heating zone and axially into a converging flow of said electrically heated gas after exit from the electrical heating zone, while entering a converging portion of the flow expansion nozzle having a nozzle bore of a length that is at least five times the diameter of the nozzle bore throat to restrict the diameter of the column of particles passing through said nozzle bore and to prevent build-up of particle material on the nozzle bore wall while insuring sufficient dwell time within the bore to effect particle heat softening or melting. 2. The flame spray method as claimed in claim 1, wherein the step of discharging the heated gas from said passage through a flow expansion nozzle as an extremely hot gas stream includes the step of minimizing the whirling velocity component of the gas flow through the flow expansion nozzle bore. 3. The flame spray method as claimed in claim 1, wherein the step of discharging the heated gas from said passage through a flow expansion nozzle as an extremely hot gas stream comprises causing said gas to pass through said nozzle bore over a nozzle bore length of such an extent that the temperature of the hot gas flow is reduced to below the disassociation temperature of the gas flow. 4. The flame spray method as claimed in claim 1, wherein the step of discharging the heated gas from said passage through a flow expansion nozzle as an extremely hot gas stream comprises passing said hot gas stream through a nozzle whose length is such that the particles discharging are still in their molten state. 5. A highly concentrated heat softened or liquified material flame spray apparatus comprising: a spray gun body, passage means defining an essentially closed electric arc heating zone within said body, means for continuously flowing a gas under pressure through said heating zone passage, said body including electrical heating zone discharge passage means at one end thereof, said body further comprising an elongated nozzle downstream of said electrical heating zone discharge passage means, said nozzle including a converging inlet bore portion leading to a throat and having an extended length outlet bore portion, and wherein said bore has a length that is at least five times the diameter of said nozzle bore throat, said electrical heating zone discharge passage means comprising means for conveying a converging flow of the discharging electrically heated gas after exit from the electrical heating zone into the entrance of said nozzle inlet bore portion, and means for introducing material in solid form outside of the electrical heating zone axially into the hot gas for subsequent heat softening or melting and acceleration, with the point of introduction of the solid material being at the entrance to or within the converging inlet portion of the nozzle bore, to prevent build-up of particle material on the nozzle bore wall while insuring sufficient particle dwell time within the gas stream to effect particle heat softening or melting prior to particle impact on a substrate downstream of the discharge end of said nozzle bore. 6. A highly concentrated, hot gas supersonic abrasive blast apparatus comprising: an abrasive blast gun body, a high pressure, essentially closed combustion chamber within said body, means for continuously flowing an oxy-fuel mixture under high pressure through said combustion chamber for ignition within said chamber, said body including combustion chamber products of combustion discharge passage means at one end thereof, said body further comprising an elongated nozzle downstream of said combustion chamber discharge passage means, said nozzle including a converging inlet bore portion leading to a throat and having an extended length outlet portion leading from said throat, and wherein said bore has a length that is at least five times the diameter of said nozzle bore throat, said combustion chamber discharge passage means comprising means for conveying a converging flow of the discharged hot products of combustion, after exit from the combustion chamber, into the entrance of the nozzle inlet bore portion, and means for introducing solid, particulate, abrasive material outside of said combustion chamber, axially into the hot combustion gases for acceleration thereby with the point of introduction of the particulate abrasive material being at the entrance to or within the converging inlet portion of the bore of said nozzle to restrict the diameter of the column of particles passing through the nozzle bore and prevent contact of the particles with the nozzle bore wall and erosion of the nozzle bore while accelerating the particles to very high velocity prior to particle impact on a workpiece downstream from the discharge end of the nozzle bore. 7. The apparatus as claimed in claim 6, wherein the axis of said nozzle bore and the axis of said combustion chamber are at approximately right angles to each other, said combustion chamber comprises an end wall, said combustion chamber discharge passage means comprise a plurality of circumferentially spaced converging, inclined, small diameter passages within said combustion chamber end wall, said inclined passages being open at one end to the inlet portion of the nozzle bore upstream of the nozzle bore throat and at the other end to said combustion chamber, and wherein said means for introducing solid particulate abrasive material into the hot gases comprises a small diameter particulate material feed passage within said body centered within said circumferentially spaced, inclined passages which converge towards the axis of the bore and with said material feed passage being coaxial with said nozzle bore. 8. The apparatus as claimed in claim 6, wherein said means for introducing solid, particulate, abrasive material axially into the hot combustion gases comprises means for supplying a stream of combustible fluid bearing hard particulate material to said apparatus upstream of said combustion chamber discharge passage means within said body including means defining a confined straight flow path leading to said small diameter material feed passage within said body and centered within said circumferentially spaced, inclined small diameter passages, and means within said confined straight flow path for separating a portion of the combustible fluid radially outward of said confined straight flow path from said hard particulate material and for introducing said particle free fluid into said essentially closed combustion chamber within said body for combustion therein. 9. The apparatus as claimed in claim 7, wherein said means for introducing solid, particulate, abrasive material axially into the hot combustion gases comprises means for supplying a stream of combustible fluid bearing hard particulate material to said apparatus upstream of said combustion chamber discharge passage means within said body including means defining a confined straight flow path leading to said small diameter material feed passage within said body and centered within said circumferentially spaced, inclined, small diameter passages, and means within said confined straight flow path for separating a portion of the combustible fluid radially outward of said confined straight flow path from said hard particulate material and for introducing said particle free fluid into said essentially closed combustion chamber within said body for stabilization of combustion therein. 10. The apparatus as claimed in claim 8, wherein said means for separating combustible fluid free of said hard particulate material from said stream comprises a tubular sand separator positioned within said body axial flow passage, an annular chamber surrounding said tubular sand separator, said tubular sand separator bearing spaced slots, said slots having openings less than the diameter of said solid particulate abrasive material, and wherein said annular chamber surrounding said tubular sand separator is connected by passage means with said combustion chamber to permit the introduction of particle free air from said stream into said combustion chamber. 11. The apparatus as claimed in claim 9, wherein said means for separating combustible fluid free of said hard particulate material from said stream comprises a tubular sand separator positioned within said body axial flow passage, an annular chamber surrounding said cylindrical sand separator, said tubular sand separator bearing spaced slots, said slots having openings less than the diameter of said solid particulate abrasive material, and wherein said annular chamber surrounding said tubular sand separator is connected by passage means with said combustion chamber to permit the introduction of particle free air from said stream into said combustion chamber.