I can't answer all of your questions on this one as that would be speaking out of turn (as for the Caswell powders in blue and such anyways). What I can do is tell you what I see in your pictures and tell you what has helped me in the past. Your coating definately looks "mottled" in parts. That would be the specs that you have circled. Sometimes when the powder gathers around the electrode and finally lets loose it creates a large spec that implants itslef on the part. This effect is also seen when the gun is too close to the part and you get a mock "Farraday" effect but it's localized just to certain pinpoints on a flat surface. One must ask themselves at this point whether or not thier technique is proper. Are you coating form 18"-24" away from the part? Is your ground still sufficient? Too much air forcing the powder onto your part? There's lots of things at play here and all of them give you great trauma when coating clears with tints or metallics. You see..... it's in the "flow" of your powder at that stage in the game. If/when gathered and you've got that voltage swirl from either too high a Kv or standing too close, it will have an effect that looks like a sand swirl from the winds in a desert. I'd also be willing to put money on the fact that the thickness varies by as much as 50% in these areas as well. What's happening there is powder blowout in a sense. Back off and let the powder "dust" it's way onto your part. Another way things could be happening to you is "spitting" of gathered powder particles. All's you need to do on that one is tap the gun lightly every so often to prevent the loose pieces from hitting and sticking onto your part. One of the other things happening to you in this part is almost a true Farraday-Cage effect. That is to say....when you have a part that has charged characteristics, it will negate itself when coating. Think of it this way.... hold a magnet on the non-attracted side and push against the other. It moves away, right? The same thing is happening with your powder. Positivley charged powder will attract to one negatively grounded surface. When such said force is met with two or more negatively ground surfaces, it will "reflect" itself out of there and not coat. One can overcome this with a lot of methods, for you... I suggest hitting the inside corners first and focus on all the tough areas. After you have them coated, back off on the distance and give the entire part a good general once over. BEFORE you bake it....inspect it. If it doesn't look correct, blow it off and keep doing it over until it's correct.
Surface preperation between coats is also paramount. Some people have no problems whatsoever going from one coat to the next. Others, have nothing but grief everytime they attempt it ( yours truly being a prime example) and always have to give some sort of prep between coats. I use a non-destructive solvent and wipe down the part before the clear or tinted coat. Denatured alcohol works the best for me. Just put some lightly on a clean cloth and wipe it all down as you would to clean the part of minor contaminant for a first coat. From time to time I've also been known to take some "0000" steel wool and rub it down lightly as well. Make sure the part is smooth and clean clean clean before the second coat. blow off with a nice strong air gun. I've never had a problem using this method.
I wish you luck and success in your future 2-coat processes. If you can...return to this thread and post new pics of the whole thing once you've beaten the mottle beast to show us how well it came out. I hope something in there helped you....Russ
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09-29-2003, 06:10 PM
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