Pin Holes

[fredmc]

I am doing a test of Columbia Super Clear Coat on polished aluminum.

I polished a piece of thick aluminum and cleaned it with Prep &Clean. I then shot a coat of powder on it, baked it at 375 for 15 minutes(according to directions). The finish is full of pinholes.

So I applied another, heavier coat of powder and baked it again for 15 minutes and its still the same, if not worse.

I am using a HF gun.

What usually causes this?

Thanks
Fred
Fred Mc.

[baz]

Originally Posted by fredmc

I am doing a test of Columbia Super Clear Coat on polished aluminum.

I polished a piece of thick aluminum and cleaned it with Prep &Clean. I then shot a coat of powder on it, baked it at 375 for 15 minutes(according to directions). The finish is full of pinholes.

So I applied another, heavier coat of powder and baked it again for 15 minutes and its still the same, if not worse.

I am using a HF gun.

What usually causes this?

Thanks
Fred
Fred Mc.

could be from outgasing , or from water in your air line.
fix for outgasing problem: before you powder the part . put it in the oven for about 40 minutes at 25 to 50 degrees over the temp tht you will actually cure the part.
fix for water in air line is simply to get a good filtering system

[FigureLLC]

Originally Posted by fredmc

a piece of thick aluminum

1) do you know how the piece of aluminum was formed? outgassing is common with cast parts. tiny air bubbles are formed in the aluminum during the casting process, and when the metal is heated, the metal's pores open up and allow some of the gas to escape, creating pin holes while the powder is curing. solution: outgas prior to shooting per baz's instructions.

2) i'm not sure what the "prep and clean" stuff is, but i think most people use acetone for cleaning because it leaves no residue. some cleaners are either petroleum-based or have some type of corrosion inhibitor, etc. that can mess up powder cure. solution: use acetone to clean.

3) this really should be no. 1... like baz said, clean/dry air will increase finish (and spraying -> reduced clumping) consistency. solution: drain air compressor tank daily (or better yet install an automatic drain, like the $12 one from HF), and in the air line close to point of use install a coalescing filter (removes heavy moisture/oil/particles) followed by dessicant filter (dries air) followed by a regulator/particulate filter (catches the dessicant particles).

[fredmc]

The Prep&Clean stuff is the cleaner recommended by Columbia Coating.

[FigureLLC]

oh, it's probably not that, then. when you cleaned it, did you shoot the spray on it and let it evaporate, or shoot it on and wipe it off? works best to wipe, otherwise oil is disolved into the solvent, the solvent evaporates, then the oil is still on the part.

[Harleydad]

Here's a trouble shooting guide for future reference.
http://www.tiger-coatings.com/filead...guide2_usa.pdf

[FigureLLC]

Originally Posted by Harleydad

Here's a trouble shooting guide for future reference.
http://www.tiger-coatings.com/filead...guide2_usa.pdf

outstanding. thanks!