Issue link: http://www.e-digitaleditions.com/i/901126
A I doubt if wet-sanding will be adequate for preparing the area for recoating. I suspect you'll need a fairly large-grit dry sandpaper. You used the word clear. Do you mean that you will be applying a clear powder over the area in question? If so, I think you may create an appearance problem, among other things. Be prepared to strip the entire part and totally coat it again. Maybe not, but don't be shocked if you have to! —G.T. Powder coating fiberglass and carbon fiber fabrics Q I would appreciate any guid- ance on possible manufactur- ers or producers of the follow- ing: I am investigating powder coating for use in coating fiberglass and carbon fiber fabrics. I would like to coat these materials with a thermoplastic powder at 40 percent coating by weight. The pow- der has a melt temperature of 540°F. Par- ticle size can be controlled through grinding. The end use application is composite part manufacturing. Any info would be helpful. S.R., Anaheim, Calif. A I guess I shouldn't ask as to why you want to powder coat fiber- glass, unless the coating serves another purpose than normal coating. I've coated fiberglass for the purpose of eliminating or reducing outgassing. We had to preheat the fiberglass to get any adhesion. We also applied a material that acted as an enhancement for elec- trostatics. I had my doubts that this ma- terial served much purpose. The preheat was the most beneficial. There have been articles in this maga- zine about coating medium-density fiberboard (MDF), and that process may be of some benefit to you. If you missed them, visit the magazine's Arti- cle Archive and create a free account at www.pcoating.com. You'll be able to access all the articles for free once you're registered. —G.T. Powder coating structural steel Q How many mils of powder do you need on structural steel? J.R., Leesburg, Ohio A It depends on the final product the structural steel is used in, how long you want it to last, and what conditions it will see. Struc- tural steel may be coated just for looks, or it can be coated to resist corrosion or abrasion conditions. The answer to your question lies in what specifications or requirements are de- manded for the end use of the structural steel product you are coating. Decora- tive powder coatings can be applied as low as 1.5 mils and usually lower than 3.0 mils. This coating will provide a good-looking coating with some func- tionality. However, if your structural part requires extended life in severe con- ditions, the coating requires significantly higher functional properties. This may require a zinc-rich epoxy primer and a super-durable TGIC polyester topcoat. This coating may approach 5.0 mils thickness per coating (10.0 mils total). I would start by asking your customer what they expect from the coating and go from there. Communication is extremely important to a good working relationship. —N.L. Post-add gloss killers you add yourself Q I was asked to powder coat some parts with a standard low-temperature-cure pow- der with a 60 percent gloss. This isn't my problem. On the sketch I was quot- ing, it mentioned a gloss killer. Have you ever heard of this? Is it possible to special order it for the powder, or could it be a wet application after the powder coating? T.L., Pittsburgh, Pa. A Some powder coatings manu- facturers have post-add gloss killers available. Make sure the additives, called matting agents, are compatible with the powder coating you're using and follow the manufac- turer's directions thoroughly. —G.T. Mixing different powder chemistries and colors Q We're changing our painting supplier. As far as I know, we can't mix the powders be- cause we can have problems. However, we would like to know what kind of problems or defects we could have, and what kind of defect appears on the pieces. D.T., Monterrey, Mexico A If the powder you intend to mix is all the exact same for- mula (epoxy, polyester, acrylic, so on), and the only difference is color, then the effect of mixing the reclaim ma- terials is color- or appearance-related. The appearance will be speckled, show- ing all the different colors. For instance, white and black powder makes a salt- and-pepper look, not gray. However, if the powders are different formulas (dif- ferent resins, fillers, cross-linkers, and so on), then you'll have a much different look, exhibited as craters, fisheyes, cracks, alligator skin, and more. I don't recommend that you mix different formulation powders. —N.L. PC Editor's note For further reading on the problems discussed in this column, visit Powder Coating magazine's website at www.pcoating.com and search the Article Index by subject category. All articles listed in the archive are available for free download to registered users. George R. Trigg is pres- ident of GRT Engineer- ing, Prospect, Ohio. He has been involved in the powder coating industry for more than 40 years. He holds a BSBA degree from Muskingum Col- lege, New Concord, Ohio. Nick Liberto is presi- dent of Powder Coating Consultants (PCC), a division of Ninan, Inc., 1529 Laurel Ave., Bridgeport, CT 06604. Established in 1988, PCC is an independent engineering firm specializing in the use of powder coating technology. Nick has more than 3 decades of experience in the powder coating industry and is a member of many industry associations, including the Appli- cation Equipment Technical Committee of the Powder Coating Institute. A registered professional engineer in Connecticut, he holds a Bachelor of Science degree in mechanical engineering with a minor in physics. He can be contacted at 203/366- 7244; email pcc@powdercoat.com; website www.powdercc.com. 26 POWDER COATING, November 2017