Open porosity

[Mvk]

Hi,

I'm new @ this forum

I am researching to get open porosity with electric arc spray (aluminium wire). Is this possible with electric arc spray or is there an better proces?
I was thinking to spray in an angle with low amperage.
The porosity requirement is >10% with aluminium
Is there any documentation about the parameters to get open porosity?

[LEN WOOD]

So you want to spray an Aluminium coating with 10% porosity?

Depending on the system used I think that you may achieve this with a little 'trial and error' and some 'modifications'.

Send me an email.

[Gordon]

Hi Mvk

to the Surface Engineering Forum.

Experimenting with atomising air pressures, spray distance, spray angle and amps/voltage should enable you to get quite porous coatings. Whether the nature of the porosity/coating is suitable for your particular application is another matter. May I ask what is the application or function of the coating?

Arc spray co-deposition of a pseudo alloy coating for example zinc and aluminium and then acid leaching zinc out of the coating in a post process. This is very dependent on suitability of substrate material and is very limited in flexibility with regard to changing amount of porosity.

Using same principle but with a powder spray process gives much more flexibility as you can tailor the powder mixture to give desired porosity amount, size and distribution. There also more options for the co-deposit material and method of removal. For example plasma or HVOF spraying aluminium polyester blend and then post heat treatment to burn out polyester. Co-spraying with water soluble material and dissolving out in water as a post process is another possibility.

In the distant past I did some work developing coatings for increasing the nucleate boiling effect for heat transfer surfaces exploring some of the above techniques as well as simply detuning process parameters to give what most would call very poor coatings

[Mvk]

Thanks for the reply's, the replies are very useful

We use metal foam for our product (Functionality: Filter).

The metal foam structure:

http://www.bundesregierung.de/Content/EN...poster.jpg

The idea is to create with thermal spray a kind of metal foam structure. The difference with metal foam is the substrate. The reason for electric arc is: low cost.

The idea to spray with HVOF and polyester gives new opportunities and sounds great. Is there documentation about these results?

[Gordon]

Hi Mvk

Quote:The reason for electric arc is: low cost.

Yes, certainly worth exploring, much cheaper and no post processing. Powder spray processes will give more scope in amount, size, shape and distribution of porosity.

Quote:The idea to spray with HVOF and polyester gives new opportunities and sounds great. Is there documentation about these results?

Not aware of documentation related to this subject. Aluminium silicon alloy/polyester blended powders are typically used in aerospace for abradable coatings. With some of these coatings they burn out the polyester prior to service. Off the shelf commercial products like Metco 601 and Diamalloy 4001 and other brands would initially be worth trying (typically around 50% volume polyester retained in coating), but you may find blending your own will give more versatility in fine tuning your coating to give the porosity you need. HVOF is more efficient when spraying these materials and will retain a higher proportion of polyester than plasma spraying (for same powder blend composition).

[Mvk]

Quote:Not aware of documentation related to this subject. Aluminium silicon alloy/polyester blended powders are typically used in aerospace for abradable coatings. With some of these coatings they burn out the polyester prior to service. Off the shelf commercial products like Metco 601 and Diamalloy 4001 and other brands would initially be worth trying (typically around 50% volume polyester retained in coating), but you may find blending your own will give more versatility in fine tuning your coating to give the porosity you need. HVOF is more efficient when spraying these materials and will retain a higher proportion of polyester than plasma spraying (for same powder blend composition).

Ok interesting ! Do you have information about the investment level for HVOF and energy consumption, so i can make an cost calculation to compare it with metal foam.