Abstract: An improved plasma arc spray gun performs with higher deposition efficiency and longer lasting anodes and cathodes than prior spray guns. The spray gun of the invention includes a housing made of a glass fiber reinforced TORLON material that remains dimensionally stable under all operating conditions. The anode of a relatively low velocity subsonic spray gun has an interior with five sections, two of which have cylindrical inner surfaces and three of which have frusto-conical surfaces. The cathode tip is carefully located within the anode interior such that the electrical arc between the anode and cathode attaches to the anode at a circular line at a junction of a cylindrical surface and a frusto-conical surface. Relatively high velocity subsonic versions of the plasma arc spray gun utilize anodes with three interior sections and streamlined passages for vortex stabilized flow of the primary gas.

Abstract: A precision powder hopper comprises a canister for storing particulate material and a rotatable carrier wheel that accurately meters small amounts of the material to a powder out port. The carrier wheel has slots therethourgh that receive definite quantities of material, which is tamped into the carrier wheel slots by a tamper assembly. The tamper assembly includes a deflectable leaf spring that mounts to the same shaft that rotates the powder carrier wheel. A cam and spoke arrangement cause the leaf spring to deflect cyclically in response to rotation of the powder carrier wheel. A cupped spring washer cooperates with the leaf spring to absorb some of the deflection thereof, thereby decreasing the bending stress in the leaf spring and increasing its service life. Powder in the carrier wheel slots is wiped by a novel seal that has at least one circular line contact with the carrier wheel.