Issue link: https://www.e-digitaleditions.com/i/665686
Manually cleaning parts before powder coating Q What is the best cleaner for manually wiping parts clean? One of our sister companies is currently using paint thinner to clean parts prior to powder coating. How- ever, I am looking for a cleaner that not only gets black steel and pregalvanized materials clean, but, more importantly, is safe for the guys applying the cleaner. Thanks. T.B., Monett, MO A Cleaning parts before powder coating is the single most im- portant thing you can do to en- sure proper adhesion. Unfortunately, manual cleaning with solvent is the least efficient and most problematic way to clean any part before applying any paint or powder. Some solvents are more ef- fective than others at removing organic soils (oils, waxes, fingerprints, etc.) and are totally ineffective at removing inor- ganic soils (smut, scale, rust, oxide, etc.). All spirit solvents, by their nature, have an inherent safety problem with fire and some may be health hazards. Carefully reading and following all the guidelines detailed in the Material Safety Data Sheets (MSDS or SDS) will ensure what precautions need to be taken and the conditions that must be maintained when using these materials. Proper per- sonal protection equipment (PPE), room ventilation, and fire precautions are all necessary to ensure you do not have a fire or explosion or subject your personnel to health risks. Now I know that many people do not have spray wand cleaners, dip tank cleaners, inline spray washers, and the like to properly and safely clean their products before powder coating. So for that reason, I will provide some insights on using the solvent wipe methods for cleaning parts. First, ensure your solvent is clean and not reused from another operation so that you do not apply more contaminants than are already on your parts. Second, change your wiping rags frequently to ensure you do not reapply the contaminants. Third, wipe the part surface with a clean rag after sol- vent cleaning to check that all soils have been removed before coating. Finally, make sure the part surface has com- pletely dried and all the solvent has evaporated before applying your pow- der coating. You mentioned that you are cleaning black steel and pregalvanized materials. These materials pose problems with your cleaning method as cleaning sol- vents will not remove the carbon, smut, rust, and oxides often seen on these sub- strates. Furthermore, these inorganic soils can cause adhesion failures on the finished part if not properly removed. You will need to sand, grind, or media blast these soils from the surface before powder coating to ensure proper coat- ing adhesion. This is another reason you should abandon the solvent clean- ing method in your powder coating process if you want a long-lasting coat- ing on your products. —N.L. Recoating parts after burn-off Q We have a high-temperature burn-off oven to burn off items that are to be recoated. The old powder coating is burned right down to the metal. Sometimes, when we recoat these items, the recoat will crack, and the coating separates from the metal and peels off in large chunks. Any idea what causes this? W., Shel- burne, N.S. A I have several questions for you. Are you washing off the ash residue left by the burn-off? What temperature are you operating the burn-off oven at? You could be affecting the tensile strength of the metal, which is causing it to move a bit (surface tension), and the powder isn't ready to be moved, so it pulls away. What temperature are you curing the powder at? Is it to spec? Are you pretreating the metal before re- coating? If you are doing all of these things, then we need to take another ap- proach. But make sure you are doing all of these things first. —G.T. Eliminating bubbles on coated ceramic parts Q We have a problem with bubbles on the surface of powder coated sintered ce- ramic parts. It happens often, but not al- ways. I think it is caused by trapped gas in our ceramic part (porous material), but my company doesn't know how to solve this problem. Our procedure is to powder coat first on one side and then on the other side of the part, separately. The second side always has bubbles. For now, we have solved the problem by coating two times on each side with a lower powder thickness of about 125 microns (usually, the thickness is 250 microns). This is costing extra time and money. We tried preheating the ceramic parts and doing some tests, but nothing has helped. M.B., Ljublijana, Slovenia POWDER COATING, April 2016 33 Questions & Answers George Trigg GRT Engineering Nick Liberto Powder Coating Consultants