pulsing of powder feed and ventillation
08-08-2007, 07:26 AM,
pulsing of powder feed and ventillation
I notice that powder feeder of HVOF system during the spraying time sometimes feed powder not smoothly (powder feed is pulsing). Does it make influence to coating quality, and may someone explain reasons of that.
Also maybe it is possible somewhere to know during the fusing time (main material NiCrBSiWC) what harmful products forms. And what kind of ventillation is the most suitable for that.
Best regards
08-08-2007, 01:24 PM,
RE: pulsing of powder feed and ventillation
Hi Arturas

I think inconsistent or pulsing powder feed will influence your coating quality. It will depend on the severity and frequency of the pulsing. If you can observe the pulsing in the flame, you need to be concerned. Imagine setting up to spray at say 5 kg/hr. With a severe pulse in real time the flame may be seeing 10 maybe 20 kg/hr at one moment in time then zero the next.

The reasons for inconsistent or pulsating feed are varied and complex. It will depend on your powder feeder type and the powder your feeding. The first thing to do is make sure your feeder is in proper working order, check for leaks, vibrator if required, condition of feed hose, condition of pick-up port, condition of powder etc.. Some powders seem naturally resistant to smooth feeding with particular feeder types, and sometimes playing around with changes to feed hose length, hose diameter and reducing bends and kinks, powder pick-up shaft, scrapers, meter wheels (if applicable). Powder condition is very important, make sure it always remains moisture free. Some go the extreme of storing their powder in low temperature ovens and using the powder warm.

I don't think self-fluxing alloys give off any significant noxious fume during fusing and probably the bye-products of combustion (NOx see this thread http://www.gordonengland.co.uk/sef/nox-t-156-2.html) from your fusing torch will be of more of a concern. So a well ventilated area is important not just to remove all the hot air.

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