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Determining the flammability of powder coatings Q Are powder coatings flamma- ble? Thanks. R.A., Brandon, Fla. A NFPA classifies powder coat- ings as combustible materials. Combustible materials can ig- nite and support flame in the right con- ditions, while flammable materials can ignite more easily. This does not mean that similar precautions are not neces- sary when using combustible versus flammable materials. In the case of powder coatings, the material must be atomized in air to ignite, a condition that occurs when spraying, fluidizing, or collecting powder coatings. Refer to NFPA 33 guidelines when using and storing powder coatings and you won't have a problem. —N.L. Fine cracking in metallic powder coatings Q I'm having a problem with metallic coatings. I used a gold and silver metallic pow- der with a clear topcoat over it. I did a full cure on both base coats and a full cure on the clear coat. I cured the base coats at around 375°F and 390°F for 15 minutes. I cured the clear coat at 350°F for 15 minutes. Both jobs looked great when picked up. The next day, both jobs started to show fine spiderweb cracks in the base coat. What hap- pened? B.M., Louisville, Ky. A First, is the clear coat compati- ble with the base coat? Your powder supplier should be able to answer this question for you rather quickly. If you're using one supplier's base coat and another supplier's clear coat, you're going to have a problem getting any satisfaction. If this is the case, then contact the base coat supplier and have the supplier fix you up with a clear coat designed to be compatible with the base coat. If the powders are compatible (accord- ing to the supplier), then there may be some surface tension occurring on the base coat, possibly from the second bake. You can verify this by rebaking the base coat without the clear topcoat. My guess is the former. —G.T. Eliminating pinholes when coating steel Q We keep getting small pin- holes in anything we powder coat that is steel, but we have no issues with aluminum. We can spray an aluminum panel and a steel panel side-by-side and the steel looks terrible every time, lots of little pinholes and an overspray look to it. All of our steel items are sandblasted and pressure washed prior to powder coating. We have tried several different combina- tions of oven temperatures, cook times, new powders, and spray gun settings and nothing seems to change at all. Any help you could provide would be much appreciated. Thank you. A.W., Manas- sas, Va. A Your description of your prob- lem does not make it easy to recommend a solution. Not that I don't believe that you didn't try all the things you stated to solve the problem, but I will go over them for the reading audience, just in case they do not understand all the effort you put into solving this problem. First, you isolated the substrate by run- ning aluminum parts and aluminum test panels that did not show the defect. This substrate isolation included using steel panels, different than those you run normally, that still showed the pin- hole problem. Changing the substrate to use known substrates panels pro- vided by reputable sources (ACT or Q- Panel) are a great way to ensure that problem is not related to your parts. Good job! Second, by using precleaned and pre- treated test panels from these known suppliers (ACT or Q-Panel), you iso- lated your media blast and pressure washer as contributing to your prob- lem. Using precleaned and pretreated panels is the best way to eliminate your cleaning and pretreating process as being the cause of the problem. Again, good job! Third, you tried different powder for- mulations from different suppliers and still had the problem. Changing pow- der formulations and suppliers is the best way to eliminate powder formula- tion and production batch as the root cause of your problem. Nothing more can be done with respect to powder for- mulation or batch-to-batch powder consistency. Fourth, because you do not have any is- sues when you run aluminum (only when you run steel), this eliminates all common areas of your process (i.e. compressed air, oven contamination, shop airborne contamination, shop per- 36 POWDER COATING, June 2016 Questions & Answers George Trigg GRT Engineering Nick Liberto Powder Coating Consultants