Issue link: http://www.e-digitaleditions.com/i/799392
Applying a very thin film thickness Q We are looking for a thin coating for an under-the-car application. We need to con- trol the thickness at 0.0005 inch to 0.0008 inch. Can any powder provide a thin, controlled coating? J.W., Elgin, Ill. A You're getting into an area where consistent control of the film build can be difficult. There are thin-film powders available, but a half a mil is pushing it. You need to have a continuous film to get any kind of coverage and protection. At this thin-film range, you would need to con- trol the application carefully. Why do you need such a thin film thickness? You can get thin-film-build materials for 1.0-mil applications that work well. Maybe you should revisit what powder has to offer in performance and see if 1.0 mil would work. Application con- trol would be eased a great deal. Don't make life hard for yourself. —G.T. Sealing seams on powder- coated parts Q I have a customer who is making a formed sheet metal box. He wants the seams sealed shut because of airflow. Do you know of any caulking that can be applied before the coating process that will stick to powder and survive the curing cycle? The seam is very tight, so the caulking thickness has to be very thin (if applied properly and conservatively). Metal repair compounds have been mentioned, but the volume of parts makes them completely impractical. Is our best option to seal the seams after coating? Thanks. R.P., Spokane Valley, Wash. A The preferred practice is to seal the product after powder coat- ing. This allows your customer to select mainstream sealants and caulks that will be unaffected by the cure cycle of the powder coating. Some caulks (sil- icones) present especially dramatic prob- lems with the powder coating process and must be applied after coating to ensure error-free powder coating. —N.L. Letting robotics do all the powder coating Q I am very accustomed to working with robotic spray and dispense applications in manufacturing. However, with powder coating applications, I have only seen manual and vertical reciprocator meth- ods used. Does anyone use robots with powder coating applications, and what are the pros and cons of using a robot? S.J., Des Plaines, Ill. A Powder application has been done with painting robots for many years. In the early '80s, I installed a robot with a standard powder gun to coat the inside of a box. It worked very well. The company did that for quite a few years before the product line was moved elsewhere. Sev- eral of my employer's competitors were doing the same thing. The automotive industry is doing this with a two-headed application gun for certain areas on new car bodies. Several companies have used powder bells mounted on a robot to coat their products. So, there are pow- der applications with robots. Probably the biggest problem with robotic applications is protecting the working parts or the robotic arm so that the powder doesn't get into some very intricate moving section, such as the robotic wrist. The service life of a robotic wrist will be very short if exposed to the powder. The robotics companies make covers for the delicate parts of their products. The big benefit with using robots is that they can coat areas that a person would complain about, and the robots don't have to take breaks. This isn't meant to be a criticism of manual spraying, but product design- ers don't always consider what has to be done to get a part coated. When you require a person to put on a complete suit, with mask and gloves, and tape the sleeves, and then the overspray completely covers the per- son in a matter of minutes, you're asking a bit much. Try doing that 8 hours a day, 5 days a week. This is the kind of job you give to a robot. I won't even get into consistency of finish and operator fatigue! —G.T. Powder coating a wheel in two tones Q I was recently asked how to apply two-tone powder coat- ing to a wheel. Could you please inform me on how to address this issue. I'm kind of baffled. Will the spokes need to be removed? I'll wait to hear back from you. Have a blessed day! L.J., Spring, Tex. A Thanks for the blessing. I can always use an extra one now and then. You have two choices when powder coating a spoked motorcycle wheel in two colors. First, you can disassemble the wheel, coat the parts separately, and reassemble it after- wards (as you state in your question). This is the most bulletproof way of obtaining what you want, at a higher labor cost for the disassembly and reassembly of the wheel. 24 POWDER COATING, March 2017 Questions & Answers George Trigg GRT Engineering Nick Liberto Powder Coating Consultants