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Painting Over Powder

December 8, 2003
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How can I paint over metal that has been powder coated?

I will assume that the surface to be coated is thoroughly clean. A number of powder coatings can be painted over directly, using the same powder coating, a new powder coating or a solventborne or waterborne paint.

In other instances (and this is more likely to happen), the adhesion is not satisfactory if no additional preparatory steps are taken. When that is observed, one should try a light scuff sanding of the powder coating before repainting. In most cases, this surface abrasion will enable good intercoat adhesion. Should this remedy fail, it will be necessary to try another paint to use for recoating over the existing powder coat.

Found: Olive Drab
I read your column in Industrial Paint & Powder and find it quite helpful. In the April issue you were asked about Olive Drab powder coating. Our primary powder supplier is Prismatic Powders in Oregon (541-826-1422). They have a stock color called Olive Drab that we use frequently.

Thank you so much for the information. I'll immediately pass it along to the original questioner, whom I'm sure will also appreciate your kindness in passing along this olive drab powder source.

ECN/R Anyone?
Norm, I have read a few of your books and that is why I'm calling on you for some help. If a paint company says "sales calls on Fleet and OEM accounts and manufacturing businesses that utilize the ECN/R technologies," what are they talking about? I want to apply for this position, but obviously I need to know what they are talking about. Can you help?

I had not seen the "ECN/R" designation before, and when I tried finding out from a lot of other people in the industrial finishing field what it might mean, they were all mystified as well. So I'll have to guess.

The "EC" part seems to indicate electrocoat, but the part about "Fleet and OEM" suggests truck or auto topcoat painting. If that is correct, then the "N/R" portion may indicate both "new" and "refinish" topcoating.

By the way, the company in question never bothered to respond to my inquiry as to what they mean by "ECN/R." Maybe that tells you something about their operation. I'm not sure how much help I've been. Thanks for asking anyway.

Painting Bulk Quantities of Small Parts
Please give us some guidance on the following application: We do high-volume, small-parts painting; eyelets on shoes, for example. Because of the high volume, we have to use mass production. But for painting, what is the best method, and what kind of paint should we use?

Since the individual pieces being coated are so low in mass, bulk E-coat probably will not be effective, even if they are metallic parts. E-coat will not work on plastics. You mentioned high parts volume, so you may want to check on bulk E-coating, but only if you plan to paint metal parts, and only if you intend to paint in a single color or a few colors. Color changing is slow with E-coat, unless you have a high enough parts volume (and capital budget) to justify multiple E-coat and post-rinse tanks.

Hot barrel painting or dip-spin coating is often used for such small pieces. In the former method, bulk quantities of parts are slowly tumbled in a heated, rotating barrel while fast-drying paint is sprayed onto the parts. With dip-spin painting, the parts are loaded into a perforated barrel that is dipped fully into the paint. The barrel is then lifted out of the paint and the barrel with its contents is allowed to drain briefly. The barrel is then rapidly spun inside an enclosure to remove and capture the excess paint. Parts are slowly dumped onto a belt that carries them through a paint-curing oven. If small void areas are objectionable, the parts can be double coated using either the hot barrel spraying or dip-spin coating.

Acrylic coatings are generally best suited for these kinds of parts due to the finish gloss and hardness, plus their availability in fast-drying formulations. But vinyls, urethanes and epoxies can be (and have been) used as well. The choice of coating application method will largely dictate which types of coatings will be most appropriate for your use, and the equipment suppliers can give you leads on various suitable paints.

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