Much of the Bay State PlasmaGun® superiority is due to a unique and patented boundary control nozzle design for
use with argon gas. A principal advantage of the boundary layer control is the exceptionally high level of spray
performance. Not only does the gun provide more efficiency, but also nozzle life is extended. The nozzle is
designed with small holes peripherally space around the main exit (1). These holes bleed away the relatively cold
gas next to the nozzle wall, allowing the plasma to completely fill the main exit (2). This permits introducing the
powdered materials into the plasma without traversing the cold boundary layer resulting in greater deposition
efficiency and lower required power levels (3). The nozzle configuration causes the arc emanating from the cathodes
to fan out in an almost complete cone forming multiple arc roots that can be distinguished around the interior periphery of the nozzle (4). The effect produces two desirable conditions:
- Since the arc roots are distributed over the flange that exists between the boundary layer bleed holes and
the main central bore, the nozzle is capable of operating at much higher current levels since erosion seems
to depend on the maximum intensity of the arc column. This is the main reason for the life of the nozzle to be considered not in terms of hours but rather in terms of months.
- A second advantage also results from the fanning out of the arc. Since the arc fans out uniformly over the
interior of the nozzle, almost all the gas that leaves the central bore passes through the arc. Because of this,
the main bore is completely filled with plasma. In designs where only one arc root is developed and the exit
diameter of the nozzle is .300 or greater, the plasma will only partially fill the bore. The high deposition
rates obtainable with the Bay State PlasmaGun® are due to this ability to completely fill the bore with plasma. This feature is unique with Bay State.
The boundary layer bleed holes also allow the PlasmaGun® to spray satisfactorily at lower gas flow rates than have
been commonplace. In some cases these flow rates are as much as 50 to 75% below that used by other gun
designs. Denser coatings result with metals because of the fact that even some of this flow is shunted through the
holes surrounding the main bore. The boundary layer bleed holes allow the Bay State PlasmaGun® to produce superior coatings at lower costs.