oxide stringers in the bond coat
12-18-2007, 05:19 PM, (This post was last modified: 12-18-2007, 05:35 PM by fhyuan.)
oxide stringers in the bond coat
Hi, everyone.

We sprayed Ni-graphite coating with Ni-Al bond coat. The puzzling problem is we have more oxide stringers (to a unacceptable level) in the bond coat when the Ni-graphite top coat is thinner.
Does anyone have the answer? Thanks.
12-18-2007, 05:50 PM,
RE: oxide stringers in the bond coat
Hi fhyuan

Changes in top coat thickness should not have any significant effect on the microstructure of your bond coat (assuming nothing extreme is happening).
12-19-2007, 04:05 PM,
RE: oxide stringers in the bond coat
The thickness of your top coat won't (or shouldn't, rather) have anything to do with stringers.. the amount of oxides/presences of clustering/stringers is directly related to air setup/flow and gun parameters.

You may need more air or to raise your parameters/spray to the max of each (ie high amps/volts, lower feed rate, etc).
Donald Richards
Product Engineering Technician
Cincinnati Thermal Spray, South
01-08-2008, 02:55 PM,
RE: oxide stringers in the bond coat
If you are still having trouble with this could you please let me know what kind of spray system you are using. One of my operators was having this problem with a 9mb gun. It seems that the powder was not injecting into the flame properly, this created a "flame kick". Once we changed the carrier flow and changed the powder port so that the flame was no longer "kicked" the problems went away. I find that most problems are solved by getting in the booth and studying the flame.

01-08-2008, 03:55 PM,
RE: oxide stringers in the bond coat
Hi Erick

Sign0016 to the Surface Engineering Forum.

Thanks for your input and I certainly agree with your statement:
Quote:I find that most problems are solved by getting in the booth and studying the flame.
03-18-2008, 04:40 PM,
RE: oxide stringers in the bond coat
I agree w/ others that the top coat thickness should not have an effect on oxide stringer.

Try sprying w/ a hydrogen rich parameter set (10-25% more than usual). I have always sprayed some of the dirty coating such as CrC-NiCr this way w/great results.

OK Ok, the nozzle will wear out faster but the result are worth it.

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