Model SG-100 Plasma Spray Gun
Operator’s Manual
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Issued: 12/11
Page 37
G-7. Powder Tube O-ring
When worn or damaged, the o-ring in the anode powder port can
upset the powder stream and cause pulsing. Pulsing may also result
if the o-ring is left out during gun assembly.
Check o-rings regularly and replace when necessary. Do not apply
o-ring lube on powder tube o-ring.
G-8. Carrier Gas Flow
Insufficient carrier gas flow can cause powder to accumulate in the
powder hose. When build-up is sufficient a surge occurs as the
powder breaks loose.
G-9. Tamper Assembly
Using the tamper assembly with free flowing powders can cause
over-packing of the feed wheel resulting in pulsing.
G-10. Wet Powder
Improperly stored powder can absorb moisture, resulting in erratic
feeding and, in worst cases, severe pulsing.
Store powders properly, preferably in an oven, and use the hopper
heater blanket to help prevent wet powder problems. Typical
blanket temperatures are lower than 125
°
F (52
°
C).
G-11. Improperly Sized Powder
Thermal spraying powder should be monomodal (normally
distributed) and narrowly distributed. Powders that do not exhibit a
normal distribution (having only one bump in the curve, i.e.,
bimodal distributions) cause pulsing and coating problems.
G-12. O-ring Lube
Over application of o-ring lube in hopper metering components
may contaminate and obstruct the powder feed path. Do not
lubricate hopper components that make contact with the powder.
G-13. System Time Constants
Pulsing can occur when the time constants approach equality
throughout the spray system. Hose length and powder velocity in
the powder feed hose create one time constant: the time required
for powder to leave the feeder and reach the gun. A shorter time
constant is found in that portion of the hose in motion at the gun
end.