National Thermospray Inc.
PROJECTS OF INTEREST.
HYDROELECTRIC US ARMY CORPS USACERL REPORT ON HVOF
Theory of Operation:
Plasma Spray is perhaps the most flexible of all of the thermal
spray processes as it can develop sufficient energy to melt any
material. Since it uses powder as the coating feedstock, the
number of coating materials that can be used in the plasma spray
process is almost unlimited. The plasma gun incorporates a
cathode (electrode) and an anode (nozzle) separated by a small
gap forming a chamber between the two. DC power is applied to the
cathode and arcs across to the anode. At the same time, gases are
passed through the chamber. The powerful arc is sufficient to
strip the gases of their electrons and the state of matter known
as plasma is formed. As the unstable plasma recombines back to
the gaseous state thermal energy is released. Because of the
inherent instability of plasma, the ions in the plasma plume
rapidly recombine to the gaseous state and cool. At the point of
recombination, temperatures can be 6,600 ºC to 16,600 ºC
(12,000 ºF to 30,000 ºF), which exceeds surface temperatures of
the sun. By injecting the coating material into the gas plume, it
is melted and propelled towards the target component.
Typical plasma gases are Hydrogen, Nitrogen, Argon and Helium.
Various mixtures of these gases (usually 2 of the 4) are used in
combination with the applied current to the electrode to control
the amount of energy produced by a plasma system. Since the flow
of each of the gases and the applied current can be accurately
regulated, repeatable and predictable coating results can be
obtained. In addition, the point and angle that the material is
injected into the plume as well as the distance of the gun to the
target component can also be controlled. This provides a high
degree of flexibility to develop appropriate spray parameters for
materials with melting temperatures across a very large range.
The distance of the plasma gun from the target components, gun
and component speeds relative to each other and part cooling
(usually with the help of air jets focused on the target
component) keep the part at a comfortable temperature that is
usually in the range of 38 ºC to 260 ºC (100 ºF to 500
ºF). Requirements for a Typical Plasma Spray System:
National Thermospray Inc.
5120 Oak Ave.
Pasadena, Texas 77503-3721
Office: 281-373-0609 or 281-991-1133
Cell: 713-898-6844 (24/7)
Fax: 281-991-9911
Contact: Ken Norris
Sulzer Metco® are regisered trademark of Sulzer Metco
