Powder Coating

Paint’s shocking competitor

During the three years I lived in Vancouver, Canada, I worked at an office in the back of a large building in an industrial park. Our company didn’t own the building, and as the smallest of several tenants, we didn’t merit a sign on the front. The company that occupied the largest portion of the building, and therefore had its sign in large letters facing the street, was Hudson Powder Coating. I had to explain this to visitors when giving directions, and they were always confused. “What is powder coating anyway?” they usually asked. I had no idea. All I knew was that as I drove through the parking lot, I saw a lot of miscellaneous metal objects sitting in front of the company’s loading area—things like bike racks, lamp stands, car parts, and folding chairs. In the morning, these items were unfinished, and in the evening when I drove by again, they were brightly colored. I inferred from this that “powder coating” must be something like painting, though I didn’t quite see where the powder part came in.

For reasons I cannot fathom, I never actually bothered to find out what powder coating was at any time during the time I worked in the building with the powder coating company. When I finally managed to look it up, it turned out to be much more interesting than I had imagined.

I love tools, building materials, and especially hardware stores—those magical places filled with sacred Things Used To Create Other Things. In particular, I always find myself lingering in the adhesive section, eagerly reading the label of every new epoxy or sealant. I feel the same way about tape. The whole notion of one thing sticking to another has always fascinated me, and that is equally true when it comes to magnets or static electricity. For someone who likes hardware and things that stick, there could hardly be a more exciting topic than powder coating.

The Drip-Free Paint

If you look around at the metal objects in your home or office—filing cabinets, toasters, computer stands, chairs, garbage cans, and whatnot—you’ll probably notice that most of them are painted. Metal things are painted not only to make them prettier, but for the utilitarian reason of protecting them from rust, corrosion, and general dinginess. What may surprise you, however, is that many of those seemingly painted objects have never seen a drop of paint in their lives. More likely than not, the paint-like surface was applied by the wondrous process known as powder coating.

Powder coating starts with, as you might guess, a powder. This powder is somewhat like a finely ground, dried paint—a mixture of resin and pigment. You can also think of it as a powdered plastic. The general idea is to cover an object with this powder, and then heat it briefly in an oven so that the powder melts and flows together, forming a smooth, solid layer. The tricky part, though, is getting the powder to stick, preferably in an extremely even coat. This is done using electrostatic charges—the same phenomenon that makes your hair stick to your comb or dust stick to your computer screen. The powder is applied to the object using a special spray gun that gives the particles a negative electrical charge. Meanwhile, the object being coated is grounded (or, in some cases, given a positive charge). The difference in charge between the particles and the object causes a strong attraction, and presto! The powder sticks to the surface. The object and powder can maintain their attraction for hours, which is much more time than is needed to apply the heat that bakes on the finish.

A Strong Finish

Powder-coated finishes are durable and highly resistant to peeling, chipping, and fading. They can be made in almost any color—or even in wood grain—and with varying degrees of shininess ranging from a high gloss to a dull, flat finish. The process is quick, efficient, and environmentally friendly, producing no pollution or dangerous waste products. There’s also no waiting for paint to dry: as soon as a coated piece comes out of the oven and cools to the touch, it’s ready to be used.

For the most part, powder coating is used for metal objects—appliances, garden tools, engine parts, and so on. But any object that can be given an electrostatic charge is a potential candidate for powder coating. This includes glass, wood, and many kinds of plastic (think of your charged comb). The only problem comes in the curing process—plastic melts at fairly low temperatures, and wood can burn. So special types of resin powder have been created that melt at much lower temperatures; still others can be cured using infrared radiation, with curing times as short as a fraction of a minute.

A Powder Room in Your Home

While the equipment needed for powder coating is considerably more elaborate than a spray can, several companies are now offering kits that make it possible to do this at home. You can buy the special electrostatic spray gun apparatus for less than US$100. In addition, you’ll need, at minimum, an air compressor and a spare electric oven—spare because you really don’t want fumes from melting plastic mixing with your food, and electric because the vapors can ignite in a gas oven. Depending on what kinds of parts you’re coating, you may also need equipment to prepare the surface, such as sandblasting apparatus. Still, a home powder coating workshop is well within the means of many hobbyists, and provides a very professional, high-quality finish that paint often can’t match.

Powder coating is quite similar in concept to the way a photocopier or laser printer works, only in three dimensions. Charge up particles of stuff, make them stick to something else, and apply heat to make the bond permanent. It’s a brilliantly simple idea, yet extremely effective and versatile. And to think, all that magic was going on right around the corner from my office for three years. Sometimes the most interesting things are the ones right under your nose.

Note: This is an updated version of an article that originally appeared on Interesting Thing of the Day on September 10, 2003, and again in a slightly revised form on September 7, 2004.

Image credit: Alexandros T [CC BY-SA 4.0], from Wikimedia Commons