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-efficient, and that becomes more difficult 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, tribo-charged powder 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 film 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.