Coating processes – Measuring – testing – or indicating
Patent
1997-10-27
1999-05-04
Bareford, Katherine A.
Coating processes
Measuring, testing, or indicating
427446, 219 7616, C23C 412
Patent
active
059002727
ABSTRACT:
An improved segmented anode plasma generator apparatus and method. A combustion mixture of a hydrocarbon and air is injected into the plasma chamber along the direction of the plasma vortex, causing the plasma arc attachment to the anode to be in the diffusion attachment mode, where the plasma arc attaches to the anode surface over a large area, thereby substantially reducing the anode erosion rate. An innovative design of the exit nozzle then reduces the rotational component of the plasma's exit velocity to maximize the axial component of the velocity. By modulating the plasma arc current with very sharp plasma arc current pulses at a frequency related to the dwell time of the spray particles in the plasma, multiple sequential plasma shock waves which disintegrate the spray particles and accelerate them toward the target substrate. The increased velocity of the spray particles combined with their smaller size results in greatly increased cooling rates when they impact the target substrate, thereby resulting in amorphous spray-coatings with improved characteristics, including decreased porosity, higher tensile bond strength, and increased hardness, as well as having a greatly increased deposition rate. The plasma arc current is precisely controlled to assure small time constants in the plasma so that rapid changes in the plasma arc current (approximately 10.sup.8 amperes per second and higher) form plasma shock waves that strongly impact the spray particles.
REFERENCES:
S.L. Chen, et al "Experimental Design and Parameter Optimization for Plasma Spraying of Alumina Coatings" in Thermal Spray: International Advances in Coatings Technology, pp. 51-56, 1992 (no month date).
B. Goodman, "The Influence of Plasma Arc Modulation on the Coating Structure" in Thermal Spray: International Advances in Coatings Technology, pp. 581-585, 1992 (no month date).
Bareford Katherine A.
Friedman Mark M.
Plasma Model Ltd.
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