초록 ▼

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 pr

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.

대표청구항 ▼

What is claimed is: 1. A plasma spray apparatus for applying a coating to an article, the apparatus comprising: a plasma generator which includes a cathode support member, supporting a cathode thereon, a cup shaped plasma nozzle having an inner surface disposed about the cathode and the inner surfa

What is claimed is: 1. A plasma spray apparatus for applying a coating to an article, the apparatus comprising: a plasma generator which includes a cathode support member, supporting a cathode thereon, a cup shaped plasma nozzle having an inner surface disposed about the cathode and the inner surface forming a chamber into which a plasma forming gas is introduced for passage through the cup shaped plasma nozzle, the plasma gas forming a vortex flow around the cathode and exiting the cup shaped nozzle through an orifice, and; an electrical D.C. power source with suitable constant current type operating characteristics providing a negative connection to said cathode and a positive connection to said plasma nozzle of said plasma generator, energizing said plasma generator, which causes a plasma arc to be formed between said cathode and said plasma nozzle causing said plasma gas to be heated and to exit said plasma nozzle in a plasma state, and; a source of main gas which has powder particles entrained, and; A main gas nozzle concentrically surrounding the exterior of said plasma nozzle forming a passage between said main gas nozzle and said plasma nozzle through which said main gas containing powder particles is caused to flow, and; an accelerating nozzle positioned directly at an exit of said plasma nozzle and main gas nozzle, having an entry chamber into which said plasma gas and said main gas with powder particles entrained therein flow and combine to establish a gas mixture having a temperature which is the result of the enthalpy of said plasma gas and said main gas, said gas mixture accelerating through the extended bore of said accelerating nozzle to a sonic or supersonic velocity so that upon impact onto the surface of said article a cohesively bonded coating will form and build-up; and a rotating member having means to commutate said plasma gas flow and said main gas flow with powder particles entrained therein and commutating the electrical power required to function the plasma generator, said rotating member rotating about the central axis of said commutating means, said plasma generator and accelerating nozzle assembly attached to said rotating member and oriented perpendicular to an axis of said commutating means and directed radially towards said axis. 2. Apparatus as in claim 1 wherein the accelerating nozzle has a straight bore. 3. Apparatus as in claim 1 wherein the accelerating nozzle is a de Laval nozzle. 4. Apparatus as in claim 1 wherein the accelerating nozzle has a mixing chamber upstream of the accelerating nozzle. 5. Apparatus as in claim 1 further comprising a powder feeder to inject said powder particles into said main gas flow prior to mixing said main gas with said plasma gas. 6. Apparatus as in claim 1 wherein control means operative to control said main gas pressure, said plasma gas flow, and said plasma generator. 7. A device for coating a concave surface, comprising: An apparatus including a rotating member, said rotating member rotably mounted to rotate about a centerline of said rotating member, a plasma generator and accelerating nozzle mounted on said rotating member; said rotating member for positioning within said concave surface with an axis of rotation generally on an axis of said concave surface; at least one mixing chamber for mixing a flow of powder particles and carrier gas with a main gas; a commutator for commutating said mixture rough a rotating union; a plasma flame for heating said mixture to an elevated temperature, which is controlled to be below the thermal softening temperature of said powder particles; an accelerator for subsequently accelerating the heated mixture of gases and particles into a supersonic jet; said rotating member for rotating about said axis of rotation while directing said high velocity or supersonic jet of gases and particles in a solid state radially against said concave surface and forming a generally even coating of said particles on said concave surface, and; said rotating member for reciprocally moving between a first direction along the axis of said concave surface and a second opposite direction along the axis of said concave surface for coating said concave surface with said particles, forming a cohesive coating. 8. The device as claimed in claim 7 wherein the mixture is mixed with a plasma flame to heat the mixture to a temperature below the thermal softening temperature of the particles. 9. The device as claimed in claim 7, wherein the mixture of gases and particles is mixed with the plasma flame to heat the particles to a temperature above the particles melting point in order to form a coating of adhesively bonded particle splats. 10. The device as claimed in claim 7, wherein the carrier gas and main gas have a pressure between about 200 psig and about 600 psig,. 11. The device as claimed in claim 9, wherein the particles have a particle size of less than 50 microns. 12. The device as claimed in claim 7, wherein the particles have a particle size in excess of 50 microns. 13. The device as claimed in claim 7, wherein the device is made portable by controlling the temperature of the mixture of gases and particles by adjusting the enthalpy of the plasma flame. 14. The device as claimed in claim 7, wherein the powder particles are of at least one first material selected from the group of a metal, alloy, mechanical mixture of metal and an alloy, and a mixture of at least one of a polymer, a ceramic and a semiconductor with at least one of a metal, alloy and a mixture of a metal and an alloy. 15. The device as claimed in claim 7, wherein the particles are accelerated to a velocity of from about 300 to about 1,200 meters/second. 16. The device as claimed in claim 7, wherein the carrier gas and main gas are selected from the group consisting of argon, argon/hydrogen or nitrogen.