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Removing powder coating from aluminum frames Q We manufacture outdoor furniture. The frames are from extruded and drawn aluminum, and we're using polyester powder coating. I need to know how to remove the coating from the furni- ture without a solvent. I saw a method that removes the coating with little parts of glass or sand shot through a gun at high air pressure. Do you know about this method? Can we use this method for our product? A.V., Cortes, Honduras A The method you observed was media blasting. A large variety of media is available for use depending on several factors, not the least of which is the effect the blasting will have on the substrate. Some media choices include soda, sand of varying sizes, metal shot of varying sizes, plastic, and so on. The surest way to find out what will work for your application is to test several types. A harsh blasting media may remove the powder quickly, but it can do damage to the surface of a material like aluminum. You may have to select a media to prevent this damage, but the difference will be the length of time it will take to remove the coating. You might also research chemical stripping. I wouldn't recom- mend any type of burn off for an aluminum substrate. —G.T. Finding powder coatings to keep windows cool Q Are there cool powders? We powder coat aluminum e x t r u s i o n s f o r m a k i n g doors and windows, and we want a powder that will reflect the infrared radiation, and the window will remain cool. Let me know how they work and where I can buy them. L.K., Piraeus, Attica, Greece A All of us in the finishing industry think powder coat- ings are way cool! The phys- ics behind your question are pretty simple: Dark colors absorb light; light colors reflect light. Light absorption will result in heat energy. Therefore, architects for years have selected lighter colors for their buildings in climates where light reflection aids in reducing building energy require- ments. Selecting metallic colors can further improve light reflectance, which is why most energy-efficient buildings have highly reflective colors on their exterior surface. In your application, the best solution is not to apply any color at all but use a clear powder to allow the underly- ing aluminum color to reflect the sunlight. —N.L. Correcting a contamination problem Q We're getting metal expo- sure on our parts. Our parts are being coated with pow- der, but in some areas you can see very good coverage; in other areas, you can see some holes that look like contami- nation of some kind. I used a magni- fier to check what it is, and I can see the metal. I don't know what's hap- pening. Help, and thanks a lot. F.Z., Mexicali, Baja California A If you can see the substrate, then the most likely problem is a contaminant on the metal, probably something that isn't coming off in the cleaning process. And there could be a lot of reasons for this cleaning failure. Get some test panels, or some type of metal panel that you can absolutely guarantee is clean, and run them along with your parts. Don't run the first panel through the washer. Hang it just before the booth entrance. Only after proving that the booth is clean should you move to the washer. There are so many places and ways to contaminate a part that a process of elimination may be in order. However, I really think that you have a problem with some type of mill oil that is set on the parts and will not come off with a standard cleaning method. —G.T. Calculating heat load for a convection oven Q How do I calculate the heat load for a powder curing convection oven? Is there a relation between heat load and the cir- culating fan? If yes, what is the rela- tion? A.H., Bangalore, Karnataka, India 38 POWDER COATING, October 2018 George Trigg GRT Engineering Nick Liberto Powder Coating Consultants Questions & Answers