Plasma Sprayed Metco 443 NS microstructure issue
07-21-2022, 04:16 AM, (This post was last modified: 07-21-2022, 04:25 AM by CSiang.)
#1
Plasma Sprayed Metco 443 NS microstructure issue
Hi Guys,

Hope to get your input on this issue.
For the past 1 year, on and off we are seeing some weird big oxides in the Metco 443 coating, which according to our observation, it usually occurred when the batch of powder contained around 3wt% or more of powder at -325mesh size. We feedback to Metco regarding this, which they simply said this issue was mainly due to turbulence and dust. But well, we do not really see this issue happen when the powder contained around 2wt% of -325mesh particle or less....so I am not sure what is the real cause.

We are using Metco 9MB gun, consoles are 9MC or Multicoat (we have 3 systems in total), powder feeder is 9MP.
Below is the parameter we use, unit for airflow is SCFH.

Ar = 90 SCFH, H2 = 28 SCFH, Carrier, N2 = 12 SCFH, current = 550A, Nozzle = GH, SOD = 5.5 inch, surface speed = ~200ft/min, step size = 4 mm.

Microstructure image link below:

https://ibb.co/TrLX2Qs

https://ibb.co/ZmtGK3N



Hope you guys are able to help me on this.


Thanks,
CS
Reply
07-21-2022, 12:47 PM,
#2
RE: Plasma Sprayed Metco 443 NS microstructure issue
Hi CSiang,

Check your powder port and possibly nozzle face for fouling after spraying for a while. More fines in your powder will make this problem worse. Reducing the powder feed rate may help.
Reply
07-22-2022, 02:09 AM,
#3
RE: Plasma Sprayed Metco 443 NS microstructure issue
Hi Gordon,

Thanks for your reply.
While reducing the powder feed rate, do I need to reduce the power by reducing H2 or current to prevent over-melting?
What is the rational behind that reducing powder feed rate may help? Is it to reduce the possibility of powder accumulation at the powder port tip & nozzle face?

At the moment my feed rate is already at 6lb/hr...seems low.


Thanks,
CS
Reply
07-22-2022, 12:51 PM,
#4
RE: Plasma Sprayed Metco 443 NS microstructure issue
Hi CSiang,

I would leave the feed rate alone as that is low to normal for that type of powder. I've seen this problem with very high spray rate parameters.

Check your powder port for build-up, if staying clean then problem lies else where.
Reply
07-25-2022, 10:33 AM,
#5
RE: Plasma Sprayed Metco 443 NS microstructure issue
Noted, thanks Gordon.
Reply




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