Powder Coating, What is it?

We are surrounded by items that are powder coated. For example, patio furniture, garden tools, mail boxes, kitchen appliances, automotive trim, and wire closet shelving are just a few of many! Highway and bridge construction materials must be epoxy powder coated for corrosion protection. Notices the next time you're out for a drive that they many bridges are "lime green" in color.

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What is Powder Coating?

Powder Coating is an advanced yet simple way of spray-painting a very fine, dry plastic powder paint onto a metal surface. As the powder paint cloud gently leaves the front of the spray gun, it is charged with static electricity. The charge attracts the powder paint to the part that requires coating. The part is then placed in an oven, where it bakes at 400 degrees Fahrenheit for 10 minutes. While in the oven, the powder paint melts and flows into a beautiful and durable finish. Primers are not necessary. And there are no unsightly runs or drips, as often results with the use of wet paint. Prior to baking, powder coating is very forgiving of coating mistakes. Because it is powder, the paint can be blown with a low-pressure air nozzle, quickly and easily covering up the mistake.

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Simply put, powder is paint applied by a different method. Most all powder paints start life as a liquid, very similar to spray paint. This is where the resin, various components and pigments are mixed into a homogenous mass. From there they are partially cured, converted into a solid, extruded and ground (cryogenically) to the desired level. Color matches are much more difficult with powder, as once it is made into the powder coating, it is done, versus paint that can have additives used to give desired effects (color tint, gloss, leveling, texture etc.).

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There is a gross misconception out there that powder is some space age material akin to high tech ceramics and carbon fiber. Thats generally not true. Powder is just another method of laying down an organic film, i.e. paint. A powder coating of epoxy will have the same basic properties such as poor UV (sunlight) resistance as a liquid paint. For our purposes, resin types should be limited to Acrylic, Polyester, TGIC Polyester and Urethane resins. These are the systems that have the best UV resistance which equates to gloss retention outdoors.

Most powders have very good chemical and corrosion resistance, but again it is resin specific. Epoxies have excellent chemical resistance. Polyesters and Urethanes are typically used for aesthetic coatings on Cycles and have good resistance. Powders do have an advantage over liquid paint here. If you can, imagine how a liquid coating dries or cures. Solvent has to escape from the film as it "dries down". If you were to look at this under a microscope, you would see a bunch of little pinholes that look like small volcanoes. This is an avenue for moisture and chemicals to penetrate the film more quickly, accelerating corrosion. Powder simply melts down at cure temperature and (usually) isnt prone to pin holing. Castings are the exception here. They should always be coated after pre-heating so that the pores of the casting dont "out gas" during the cure cycle. Typical powder cure cycles are 325-375F @ 12-20 minutes, metal temperature. Actual oven temperature may need to be substantially higher to get the metal to temp in a reasonable amount of time.

Powder coating was introduced to the United States in the late 60s. It started to really take off in the mid 70s and has steadily gained in popularity for a number of reasons.

Powder coating is comparatively environmentally friendly. Powders contain no solvents and thus have very low air emissions when curing. Typical powders have a VOC (Volatile Organic Compound) rating of <1.0 pounds per gallon (there is an EPA test method for this!) versus liquid paints in the range of 2.5-7.0 pounds per gallon. There is very little waste with powder. Powder overspray can be collected and reused, rather than just thrown away as with paint over spray.

Powder coating is easy to do. It is much easier to become "good" at applying powder than it is liquid paint. Clean up is also much easier, you can use an air hose instead of solvent.

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How is it done?

Powder is sprayed (and in some cases dipped) on parts where it clings by static electricity (sort of like dust on your TV or monitor). By the way, that is where the term "electro-statically applied" comes from. Electro-statically applied powder or liquid says nothing about the quality of the workmanship or material. It is just a method. From there, it is baked, where it melts, flows and cures.


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