Powder Coating Frequently Asked Questions
Q) Can I powder coat wood?
A) In special circumstances and with specially formulated low-temperature cure powder. Most of the wood powder coating success has been with medium density fiberboard in the shelving market.
Q) Is blasting sufficient metal preparation for powder coating?
A) Not by itself. Most metal has oil on it unless it has been wiped with solvent or washed with a detergent. Oil can cause many surface defects in powder. Even if the part is oil-free, there is minimal corrosion resistance due to no phosphating/conversion coating of the raw metal.
Phosphating or conversion coating is done with an acid or acrylic additive in the wash water supply. Blasting is great for scale, heavy rust, and weld splatter, but to get a truly superior quality part, chemical pretreatment provides the best results.
Q) Can I liquid coat and powder coat in the same booth?
A) It is never recommended. First, there are safety concerns with a possible spark from the electrostatic powder gun arcing and igniting solvent fumes left in the booth from previous wet paint application. Second, even if the liquid paint is water-base, the booth usually has too strong a fan to effectively powder coat and get a good attraction to the part. The stronger airflow pulls the powder off the part, thereby wasting money. The powder also plugs the filters faster when there is wet paint over spray left.
Q) Do I have to powder coat in air conditioning?
A) No, but a climate controlled environment makes it more likely to achieve good powder coating results. It is important to store your powder in a climate controlled area to maintain shelf-life. It is a good practice to bring a box of powder out of the air conditioning about 2 hours before you use it. This prevents clumping or surging due to condensation in the box from the cold powder hitting the moist hot air.
Q) How do I know if the powder is cured?
A) A simple Methyl Ethyl Keytone rub test will tell you if you are curing your powder sufficiently. Manufacturers usually use a 10% MEK/ 90% Xylene solution and a q-tip to do the MEK rubs. 20 double rubs with light pressure should show if you are breaking through to metal. Don’t worry if some of the powder comes off on the q-tip, that’s normal.
Q) How do I paint successfully in corners?
A) Turn down the kV’s(voltage) till you can’t see metal with a flashlight in the corners.
Q) How can I get a smoother finish?
A) When applying powder, look for a felt-like finish. If it looks more like moss, it will probably orange peel. Turn the powder supply down or turn the air up.
Q) I change colors 8-10 times a day, can I reclaim my powder?
A) Yes, but it takes special application and recovery equipment like a cyclone-system or some of the more elaborate powder paint kitchen systems.
Q) I can’t afford a high-end paint system, how do I make my spray-to-waste system more efficient?
A) Transfer efficiency, also known as the percentage amount of powder that sticks to the part. Many things affect transfer efficiency. Ground, air flow, powder flow, powder particle size, air drafts, and properly working electrostatic manual guns all play a part. Work on one variable at a time and chart your powder usage so you know what change worked. In a properly trained powder job shop, 70% transfer efficiency is a good goal number.
Q) How do I know if I am over baking my parts?
A) If you are using lighter colors it’s fairly obvious, the parts change color by yellowing or darkening. If you are using darker colors, a loss of gloss may be a sign. If you do a cross-hatch adhesion test and the cuts seem to pop off the part, the coating may be over baked because the powder could be warping backwards. The best diagnosis for both over curing and under curing is to run regular Datapaqs or some other oven profiling device to let you see what temperature the metal is achieving. Using an oven profile/recorder to adjust your oven settings to the powder data sheet requirements, is the best way to ensure the proper cure is being achieved.
Powder Coating FAQ provided by Bruce Chirrey of Powder Coating Experts.com