Issue link: http://www.e-digitaleditions.com/i/715656
much coating on the hanger. Make a list of all the things to look for, and then check them out and systematically mark them off of the list until you find the problem. Then fix it. —G.T. Repelling powder from the part when recoating Q When we recoat parts, we get a texture appearance after cure. Can this be due to pow- der repelling from the part? We coat all parts the same way, and the settings are the same in the automatic booths. Also, is there a quick way to discharge a part? G.S., Kent, Wash. A If you're in the coating busi- ness, you should know about orange peel. It's there in the best of powder coatings. You just can't see it in some. Having said that, if you are trying to recoat over a previous coat, you'll emphasize the orange peel effect, and the recoat will show it very clearly. If you're not sanding the first coat, or even light sanding and using the same settings, the application device is at- tempting to apply the same film build as you put on the uncoated piece. You won't get the same film build, but you will get more reclaim because the first coat is insulating. If the application de- vice is close to the part, you could get "starring" from electrostatic rejection. I doubt this is your problem though. Liquid touch-up on rejects is totally ac- ceptable in the industry. It all depends on the size of the defect. Don't re-pow- der coat the entire part for a dime-sized area of rework. (Remember, this is a "for instance." Don't take me literally.) If you want to discharge a part, just ground it to something. However, I fail to understand why you're asking the question. —G.T. Looking for a high-temperature coating that resembles chrome Q Is there a high-temperature powder coating that will re- semble chrome and with- stand the heat from an exhaust pipe? If there is such an animal, is the cure tem- perature the same as that used to cure a TGIC-based polyester powder? H.S., San Diego, Calif. A Some powders have a very close resemblance to a chrome finish, but when you consider that an exhaust pipe or header gets up in the range of 1,000°F or hotter, a material with a cure temperature of 350°F to 450°F won't last very long. Even powder coating applied to engine blocks lasts only about 30,000 to 40,000 miles, but that is considerably longer than the ser- vice life of liquid coatings. You could powder coat the pipes and headers if you wish and not run the engine. It would look great just sitting in the driveway! There are ceramic coatings that can be applied to exhaust systems that have a decent service life, but applying ceram- ics requires some patience, and because ceramics don't take a charge very well, the efficiency of application is low— and you can use up a lot of very expen- sive coating. —G.T. Deciding between liquid or powder coating Q If you had to decide between liquid or powder painting, what would be your decision and why? R.S., Distrito Federal, Mexico A It depends on what you want the coating to do and what your existing painting capabili- ties are. From a pure coatings stand- point, powder will be a better coating. However, other factors influence the choice, some that you can accommo- date and some that you can't or won't. There are several books written on the subject. Check the online Article Index sections at www.pcoating.com. The Powder Coating Institute also offers a text on the subject, visit www.powdercoat ing.org to search for it. You didn't give any other details, so I can't get too far with helping you. To repeat, when it comes to the coating, powder would be my per- sonal choice over liquid. —G.T. Preventing flash fires when recoating Q One of our spray guns had excessive sparking, and a brief flash fire took place. We were recoating parts when this happened. What was the possible cause? R.S., Lin- coln, Nebr. A The flash fire was probably caused by poor ground. The first coat on the part insulates it. As a result, it's highly possible that the hanger didn't have a good grounding surface due to the first coat, and the electrostatics had to do something. You might want to cut the kilovolts a bit on the recoats, but it sounds to me like you had no ground. —G.T. PC Editor's note For further reading on the problems discussed in this column, see Powder Coating magazine's website at www.pcoating.com. Click on Article Index and search by subject category. Have a question? Click on Problem Solving to submit one. George R. Trigg is presi- dent 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 Application Equipment Technical Com- mittee of the Powder Coating Institute. A registered professional engineer in Con- necticut, he holds a bachelor's of science degree in mechanical engineering with a minor in physics. He can be contacted at 203/366-7244; email pcc@powder coat.com; website www.powdercc.com. 26 POWDER COATING, August 2016