5/13/2013
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Q: I have a couple of issues. First, when coating a custom yellow, I get a gritty look to the finish. Second, the finish has a dull look to it regardless of cure time. J.S., Griffin, Ga.
A: I have worked with the custom yellow powder you’re using and haven’t had either of the problems you mention. What that tells me is that you may have a bad box of powder or dirt is getting on the part surface somehow between cleaning and coating. The dull finish? Those two problems seem to be material-related. You need to try a fresh batch of material. Try spraying a sample on a test panel to see if the results are the same. If they are, it will likely confirm my first thought -- bad powder. –G.T.
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5/6/2013
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Q: I have several pieces of copper-plated motorcycle parts. I wiped down the parts with MEK (methyl ethyl ketone), applied a clear coat, and cured them slowly, but the results were a yellowing that looked almost brassy, or golden, not copper at all. I prebaked the fender beforehand to rid it of any hidden buffing compound residue. When the prebake was over, the fender was a bright shiny copper, but the clear coat rid it of all that shine. Any suggestions on what might have happened? J.H., Minneapolis, Minn.
A: What about the cure temperature? Maybe it was a bit too high. Clear coats have a tendency to go to the yellow side of the chart with no assistance from anyone, and a slight elevation in bake temperatures will do it for sure. The MEK should get rid of any buffing compound, especially if you wipe and then rinse and wipe. I don’t believe the prebake is necessary. Actually, it might aggravate the problem. And slow baking might just get the part a bit too hot and contribute to the yellowing problem. Clears are a bit tricky to deal with, and any deviation from a straight-line process could set you up for a part that’s not truly a clear. –G.T.
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4/29/2013
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Q: I have a project that requires anodizing to AMS 2488 type II over thin titanium and painting with Pyromark Series 1200 flat black paint. The part has many areas that are very difficult to paint by conventional means. My question is, can powder coating be done over anodizing? Does powder coating come in a flat finish, and can it withstand temperatures up to 1200°F? E.N., Silver Creek, N.Y.
A: You were doing fine until the last part. Yes, you can powder coat over anodizing, but it has some subtle problems. The problems don’t arise in every case, so talk with your powder supplier and be sure the supplier knows what it is you want to do with the material. You can get powder in a flat-gloss finish. In fact, you can get it in any gloss you desire, from flat to high gloss.
Now the problem: There are powder coatings applied to exhaust manifolds that can withstand 1200°F, but they may present a problem with the anodizing. I’ve never done it, and I don’t personally know anyone who has, so there may or may not be an issue. The temperature requirement may affect the other properties you’re seeking. The magazine’s December Reference & Buyer’s Resource Issue includes powder suppliers who can meet the heat requirements. Go to the home page and click on Online Buyer’s Guide. Certainly one or all of these companies will help you with your specifications. –G.T.
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4/22/2013
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Q: We’re having tremendous powder separation issues. Too much resin is getting on the part before the oven, and it’s causing a brownish, dull gray look to the finished product. We’re trying to get a textured silver. Any info you can provide will be gratefully appreciated. C.J., Webster, S.Dak.
A: Sorry, I fail to understand how too much resin is getting onto your parts. By my definition, the resin base of the powder is only part of the total powder recipe. By my definition, therefore, I’ve never heard of the resin separating from the other powder chemicals and causing a problem. If you mean you’re getting too much powder on the part, then that’s another matter. I suppose too much of the powder formulation you’re using might cause the coloring issue you see, but I don’t know that for sure. If you’re getting too much total powder, the answer is to reduce the film build on your parts. I get the feeling that this isn’t the issue here because the answer is too simple. Maybe a better description of what’s happening would be helpful. –G.T.
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4/15/2013
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Q: I just got into the business. I have been doing parts with just a single coat but recently had a request for multiple coats. I said sure, thinking it would not be a problem for I had read some on applying multiple coats while still hot and other various tips. I used a gloss black with a 350°F oven temperature and 15 minute cure time. So, I sprayed and cured for 10 minutes then resprayed and cured for the full 15 minutes. Once the parts were done, I noticed a spot that wasn't fully coated, not because of improper prep. It was simply missed. When another coat was applied in the general area of the missed spot and cured for 15 minutes, the result was textured only where the new coat was applied. I don't understand why the result was textured. I assumed it would flow out as if it were the first coat. Any information on multiple coats or an answer to this question would be greatly appreciated. R.C., St. Paul, Minn.
A: Should I assume that the original powder is a standard smooth finish, or is it textured by design? In any event, it's one thing to build film by spraying, partially curing, and then applying a full coat over the first versus attempting to spot touch-up. Some companies apply multiple colors in a similar fashion; however, most times there is a mask line between the colors. Spot touch-up has always been an issue with powder coatings. When a spot on a part requires touch-up, there are two ways to fix the problem. The first is to sand the area, and use a good quality liquid touch-up. This is totally accepted in industry. The second is to sand the rework area, and completely respray the entire part. Spot repair with powder leaves a halo ring around the repair area because powder doesn't flow out like a liquid material. This is what you're experiencing. I would be careful about committing to multiple coats. After the second coat, orange peel gets rather mean looking, and the film can become brittle and break off when struck by an alien device. –G.T.
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