Abstract: A method of coating a surface using a plasma arc torch comprises directing a plasma plume externally from a discharge end of the plasma torch toward the surface, positioning a powder injector proximate the plasma plume to introduce ceramic oxide powder particles at a size less than 20 microns diameter into an outer mantle of the plasma plume so that the powder particles are confined in the outer mantle, directing first and second gas jets at the plasma plume downstream of the powder injector position and on opposite sides of the plasma plume to enhance entrainment of the injected powder particles in the outer mantle, circulating the powder particles in the outer mantle of the plasma plume for a residence time to heat the powder particles to melt them without substantial vaporization, and depositing the melted powder on the surface as a dense coating having closed porosity.

Abstract: A method of coating a surface using a plasma arc torch comprises directing a plasma plume externally from a discharge end of the plasma torch toward the surface, positioning a powder injector proximate the plasma plume to introduce ceramic oxide powder particles at a size less than 20 microns diameter into an outer mantle of the plasma plume so that the powder particles are confined in the outer mantle, directing first and second gas jets at the plasma plume downstream of the powder injector position and on opposite sides of the plasma plume to enhance entrainment of the injected powder particles in the outer mantle, circulating the powder particles in the outer mantle of the plasma plume for a residence time to heat the powder particles to melt them without substantial vaporization, and depositing the melted powder on the surface as a dense coating having closed porosity.

Abstract: An arc plasma generating system includes components for adjusting spacing between the cathode and the anode. A piston affixed to the cathode is slidingly positioned in a cylinder partitioning therein a first chamber and a second chamber. The first chamber is receptive of discharged cooling fluid at reduced pressure. A first valve selectively infuses pressurized control fluid into the second chamber such as to move the piston against the reduced pressure and thereby move the cathode axially in a first direction. A second valve selectively discharges the control fluid from the second chamber such that the reduced pressure in the first chamber moves the piston opposite the first direction. Telescoping tubing affixed between the piston and the end wall of the cylinder is located within the cylinder and conveys cooling fluid to the cathode. A flexible electrical cable connected between the cathode and a source of arc current is located within the cylinder member such as to be cooled by fluid therein.

Abstract: A plasma generating system comprises a plasma gun including a hollow cylindrical anode member, a hollow cylindrical intermediate member electrically isolated from and juxtaposed coaxially with the anode member to form a plasma-forming gas passage through the intermediate member and the anode member, and an axially movable cathode member. The intermediate member comprises tubular segments separated by resilient insulating spacing rings held in compression. Arc radiation is blocked from the spacer rings by meanders in the inter-segment slots and further by ceramic barrier rings. An electric motor or pneumatic piston responsive to a measurement of arc voltage continually adjusts the axial position of the cathode tip relative to the anode nozzle so as to maintain a predetermined arc voltage.