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Abstract

A method of operation of a plasma torch and the plasma apparatus to produce a hot gas jet stream directed towards a workpiece to be coated by first injecting a cold high pressure carrier gas containing a powder material into a cold main high pressure gas flow and then directing this combined high pressure gas flow coaxially around a plasma exiting from an operating plasma generator and converging directly into the hot plasma effluent, thereby mixing with the hot plasma effluent to form a gas stream with a net temperature based on the enthalpy of the plasma stream and the temperature and volume of the cold high pressure converging gas, establishing a net temperature of the gas stream at a temperature such that the powdered material will not melt or soften, and projecting the powder particles at high velocity onto a workpiece surface. The improvement resides in mixing a cold high pressure carrier gas with powder material entrained in it, with a cold high pressure gas flow of gas prior to mixing this combined gas flow with the plasma effluent which is utilized to heat the combined gas flow to an elevated temperature limited to not exceeding the softening point or melting point of the powder material. The resulting hot high pressure gas flow is directed through a supersonic nozzle to accelerate this heated gas flow to supersonic velocities, thereby providing sufficient velocity to the particles striking the workpiece to achieve a kinetic energy transformation into elastic deformation of the particles as they impact the onto the workpiece surface and forming a dense, tightly adhering cohesive coating. Preferably the powder material is of metals, alloys, polymers and mixtures thereof or with semiconductors or ceramics and the powder material is preferably of a particle size range exceeding 50 microns. The system also includes a rotating member for coating concave surfaces and internal bores or other such devices which can be better coated using rotation.

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