hi gordon this is Ravi ,
i have tried spraying tungstun carbide cobolt(metco 71ns) by sulzer metco 9mb gun but i found porosity and the carbide particles were bouncing back. what i need is exact parameters for spraying 71ns.
then do i grind the surface with silicon carbide wheel or diamond wheel. please let me know the procedure as i have lot of work spraing tungstun carbide.
regards
ravi viswanadha

Hi Ravi

to the Surface Engineering Forum.

What parameters are you using?

The recommended parameters from the Metco 71NS technical bulletin or 9MB gun manual should give very good starting point parameters. If these coatings are not as good as you need, then really you should be looking at HVOF/HVAF spraying.

Gordon Wrote:Hi Ravi

to the Surface Engineering Forum.

What parameters are you using?

The recommended parameters from the Metco 71NS technical bulletin or 9MB gun manual should give very good starting point parameters. If these coatings are not as good as you need, then really you should be looking at HVOF/HVAF spraying.

Hi gordon i see some carbide particles bouncing back when i spray with parameters given 71ns technical bulliten.

Hi Ravi

It is possible that this is normal. Depending on which parameter set you are using, deposit efficiency may range from 40 - 75%. The 25 - 60% that goes missing is probably what you are seeing. I would check this out by doing a deposit efficiency test on your powder and spray parameters and see if it is in agreement with the literature.

Hi Ravi,

Sulzer Metco came up with an Technical bulletin years ago to change the 9MB gun parts and 4MP feeder parts to be able to spray 71VF-NS to meet a PWA 257-1 specification. Macro Hardness should be Rc 62-63 and DE's at 60%. However the gun runs hot and the parts might not last that long. If you want better results then Gordon is right about changing to HVOF/HVAF. In the past we have also looked at putting a Praxair SG-100 gun and 1264 feeder onto a Metco console to try and reach the coating requirements easier and have longer lasting gun parts. This PWA spec was originally achieved with the SG-100 gun years ago and I think was done to try and compete with Praxair's D-Gun coatings.

Wouldn't this best be sprayed with a JP5000 gun? I thought the best carbide coating come from HVOF guns and the JP in specific.

Generally, carbide based coatings are best applied by HVOF/HVAF, but there are still many old aerospace specifications that call for specific plasma coatings.

Gordon Wrote:Generally, carbide based coatings are best applied by HVOF/HVAF, but there are still many old aerospace specifications that call for specific plasma coatings.

Have you already found optimized tungsten parameters for 9MB plasma ?

If you need them i can supply them.

regards,

Joris Kraak
Process engineer

Hi Joris

to the surface Engineering forum.

raviswanadha Wrote:hi gordon this is Ravi ,
i have tried spraying tungstun carbide cobolt(metco 71ns) by sulzer metco 9mb gun but i found porosity and the carbide particles were bouncing back. what i need is exact parameters for spraying 71ns.
then do i grind the surface with silicon carbide wheel or diamond wheel. please let me know the procedure as i have lot of work spraying tungsten carbide.
regards
ravi viswanadha

Dear Ravi, you are in a very complicated situation.
First and frankly, plasma praying is not the method for carbides. The jet temperature is too high for optimum coating quality. HVOF/HVAF are the processes to get best coating results. If these methods are not available, then the only solution is to work with (Metco) given parameters.
The bouncing back happens with all materials and spraying methods and is a typical behavior for all materials/processes with bad or normal efficiency factor.
bhe