Hi Jim
Those parameters should give you the desired coating. When you say excessive oxide, is this a judgement from your lab based on comparative photomicrographs or similar? Oxides should be around 1% or less typically for these parameters. Sorry, I always question lab results first, before I start chasing may tail
I assume you are using crossed air jets (crossed @ 4.5" with 40 psi). This may be why you are seeing a split spray stream when the gun is spraying off the job. Are you traversing a rotating work piece or ladder scan? Are the air jets set in a vertical or horizontal plane or should I say in-line or perpendicular to axis of rotating part or in direction of gun movement when ladder scanning?
4.3 NLPM argon carrier gas sounds a bit on the low side to me. Is that what Sulzer recommend? Metco old flow meter readings usually 37 in old money
, which should be roughly 6 - 7 NLPM based on 100 psi. I would check this out.
I would not deviate away from standard parameters unless all other options fail. In this case I would consider increasing argon primary gas flow a little say by 2.5 - 5 nlpm, this should increase the plasma energy a tiny bit (slight rise in voltage) but will in fact have a slight cooling effect on particles because of higher velocity. Be careful though, as oxides may reduce, unmelts may increase. Alternately, you could just reduce secondary hydrogen, but you seem to already be on the lower end of the 60 -70V range, so my preference would be increasing primary gas.