Symptom & Solution

[etyrrany]

Hi,

During the past weekend I was experimenting a bit. I was doing a mirror chrome base and a candy teal top coat and I got a bit of an error. The metal substrate is a section of chromemoly steel pipe that I salvaged from my now defunct bicycle.

The process was to strip the old paint, sandblast with Alum Oxide at 90PSI and clean with IPA and shoot with Mirror Chrome powder. Note, the part was not pre-heated! The part was baked/cured at 375°F for 20 min. Then let air cool for 5min and shoot with Candy Teal which was baked/cured at 350°F for 20min.

This is the result I got:



The areas circled with the red I know what that is. That is the left over lint from the blue shop towels that I used to degrease with IPA. The rest of the little craters I have no idea that it is. Since this is a ferrous metal I am assuming that you do not have to outgas. The little craters do not look like they are they typical outgas problem. I believe that the little craters were evident after the Mirror Chrome was shot but I am not 100% positive. I only noticed them after shooting with the Candy Teal.

I did another sample with the same metal. This included a polished section of pipe that I shot with just Candy Blue and even without preheating it came out flawless.

So my question is what is it and how can it be prevented.

Thanks,

etyrrany

[Fireblade]

You did not preheat the bad part right? Are you sure the IPA (whatever that is) was dryed completely? I did this once before, it was on polished aluminum, and I used acetone trying to clean the surface. I think the acetone was not completely gone before I applied the powder. Same results as you, did you wait longer with the piece that came out good before you spryaed it?

[etyrrany]

Fireblade,

I didn't preheat both parts. I should have mentioned this earlier but the only difference between the bad part and the good part is that the good part was blown off with compressed air to get rid of the lint from the blue towels I was using to degrease.

Also, IPA = IsoPropyl Alcohol.

Thanks,

etyrrany

[Fireblade]

Well, looking at it more, it may be that you were thin with the candy teal as well. Hard to really say, anybody else any ideas?

[tomg552001]

Thats a really funky problem you got there. It's almost like reverse back ionization . I am clueless.

[WAORacing]

well since you said that you blew the part off with compressed air my guess is that it could be moisture and that did not dry before you sprayed the teal. I did a part that ended up having lint in it after i cured it with the chrome. I took a razor blade cut the lint off not digging into or cutting the finish and then i cleared it and cured that. You could still see minor imperfections but not as noticeable as it was to begin with.

[bzer1]

etyrrany,

Doing a 2 stage on chromemoly, you might want to partially cure the first stage then shoot the second stage and do a full curing cycle. In other words bake it till it flows out and just begins to cure, then take it out let it partially cool and shoot it with the candy, then put it back in for a full cure cycle. The double cure time could be causing some sort of seperation of the alloys used to make the bicycle frame. Just a guess on my part but I figure it's worth a try.

[etyrrany]

Thanks alot everybody.

I have lots more of these "sample" pipes available so I will try to solve this in the future.

So far I will try is:

1. Blowing off the blue lint.
2. Pre-heating (even if slightly but enough to evaporate all of my degreaser).
3. Partial Cure on base color.

Too bad I don't have alot of time cause I could attack this in true scinetific style and start isolating each variable till I find the solution. For now as long as I solve it I'll be happy.

Thanks,

etyrrany

[non-stick]

it certainly appears to me like you may have quite a few things going on there all at once and not one singular specific problem. I most definately see "solvent popping" ( where all of the solvent is not completely dry and/or leaves a residue underneath your coating ) and it looks like an unusual amount of airborne particulate stuck on your part.