Aluminum roughness

[sprayloud]

I am combustion wire flame spraying aluminum on steel.
Everything is ok, except i get as sprayed roughness of around Ra20. For my application the goal is Ra40-Ra60. Is it possible to increase roughness to desired values ? The first thing coming to mind is increasing spray distance. Any other ideas ?
I do not have the possibility of using arc spray.

[loriolo]

Hi Sprayloud
As normally people ask for a more smooth surface, in this case is very simple to obtain more roughness, is necessary to increase wire speed or changing parameters, one or two point a time, in order to alter the flame, and reducing a little air pressure.

[Stephen Booth]

Hi Sprayloud, I assume your specification, probably related to semi-conductors, requires a rough as sprayed surface? I imagine it will be trade off between a rough coating and a good coating, but you are on the right track, wire speed, and maybe air pressure and flow.....

interested to hear your results

[KevGarty]

As Stephen mentioned, Air pressure/flow has a big impact on surface roughness. Lowering air pressure reduces particle speed and results in rougher surface.

Dont lower it too much as air still has to drive your gun motor and cool the nozzle etc. You can also look at alternative air caps?

[sprayloud]

Thank you all for the input.
I'll perform some trials in a few days and post the results.