Products Finishing magazine is the No. 1 industrial finishing publication in the world. We keep our readers informed about the latest news and trends in plating, painting, powder coating, anodizing, electrocoating, parts cleaning, and pretreatment.
Issue link: https://pf.epubxp.com/i/131829
p aintin gCL IN IC n pfonline.com/experts can we strengthen aBs Parts? Q. My company makes plastic parts for various industries, and one of our customers has complained about cracking of an ABS plastic part. My question is about the structural strength of the coatings. One of our engineers has proposed that we coat the plastic part using a paint of the same color, believing this will increase its strength, prevent cracking and maintain the same appearance. Do you agree with this? K.W. a. You can paint ABS plastic parts the same color as the substrate to maintain their appearance and to prevent minor surface crazing, but no paint will increase the strength of an ABS plastic part to prevent structural cracking. Paints are usually applied at thicknesses of 1 to 3 mils (0.001 to 0.003 inches). If the substrate cracks, the paint will crack as well. n Paint vs. Powder on transformers Q. We are thinking about installing a new painting line at our plant where we produce oil-filled transformer tanks. We have been using a primer, intermediate coat and enamel topcoat with success, but one of our engineers has suggested we look at powder coatings. What are the advantages and disadvantages of powder over liquid painting on the exterior of our products? A.S. a. The answer depends on a number of things, including the size and shape of the tanks. For power transformers, where the tanks are large, I would stick with the liquid paints because powder must be collected to be transfer-effcient, and that becomes more diffcult with large-sized spray booths. For distribution transformers, this is not a problem If the tanks have radiators, corrugations or convolutions, using electrostatically applied liquid paint is better than powder because of the Faraday cage effect. You can shut off the electrostatics and blast the paint into the inside corners. On the other hand, tribocharged pow- der guns can also overcome this problem. Powder coating is said to be less energy-intensive, but that depends on what type of liquid coating you are comparing it with. Low-temperature-curing powders require baking. Even UV-cured powder coatings require heating to fuse the powder before being exposed to UV radiation. On the other hand, fast-curing, two-component liquid paints require no baking. One of the distinct advantages of powder coating is greater flm thickness per coat, which contributes to better corrosion protection. One coat of a powder applied at 3 mils can provide the same corrosion protection as a three-coat liquid paint applied at the same thickness. n colored varnish for marking glass Q. Our factory uses pressure and temperature gages with glass covers to control our processes. I need to mark the safe work zone of the surface of gages so that our operators can easily tell when processes are within parameters. Markings must be made with a clear material that is a bright green color. Permanent markers and transparent stickers do not work because they can be removed by the high-pressure steam we use very often to clean our machines. Can I use some sort of clear lacquer to mark the zones? J.B. a. Yes, you can use a colored clear lacquer for your markings, but a colored clear varnish would be better. Lacquers, in general, use thermoplastic resins as vehicles and may not be able to withstand the highpressure steam cleaning. Varnishes, which have more robust vehicles, should be able to withstand the cleaning process. An epoxy-resin-based varnish colored using a green dye should work for your application. n rePlacing Porcelain enamel with Paint Q. My company produces phone booths, and many of our parts are finished using porcelain enamel because of its durability in environmental exposure and its resistance to vandalism. Applying porcelain to some parts is impractical, however, due to the high firing temperature required, so we are looking for a replacement application. Could you recommend a liquid or powder coating that offers similar vandal-resistant properties such as hardness and scratch resistance? H.J. a. Porcelain has already been replaced by organic coatings in many applications. One example is in the appliance industry where epoxy powder coatings are used on refrigerator and freezer liners. Porcelain also CARL IZZO, Consultant, paintingclinic@pfonline.com 32 JUNE 2013