Humans are attracted to shiny things. I get it – metallic powder coating is mesmerizing. But before you decide that every metal part you own should glitter, allow us to provide you with a reality check: applying metallic powder coatings is an expensive exercise in frustration, often with unpredictable results.
The short version is that some powders with metallic elements spray well, and others often don’t. More accurately, there are two main types of metallic powder coating on the market:
Non-bonded metallic powder coating
The powder coating (say, black) gets made as it normally would, and the metallic element is added to the powder after the fact (“post-add”), resulting in a heterogeneous mixture of black powder coating combined with silver metallic flake. As you might imagine, the metallic element often settles to the bottom of the box, resulting in a very inconsistent spray. And since the metallic element charges differently than the regular powder coating does, uneven clumps of metallic content are far more likely to appear on the part. It’s a mess. As much as possible, we avoid working with non-bonded metallic powder coating.
Bonded metallic powder coating
If you’re spraying metallic, this is the way to go. The powder coating is extruded as normal, then is run through the extruder again along with the metallic content, so that the metallic element is actually bonded to the powder – the creation process is more expensive, but the spraying experience is much smoother, and you’re far more likely to be pleased with the sparkle distribution on your part.
We’re going to pretend for a moment that non-bonded metallic powder coating doesn’t exist, because it’s not worth our time or your money, and we’ll focus entirely on the challenges of bonded metallic powder coating.
If your film thickness is ANYTHING less than perfectly even, you will likely run into the phenomenon known as “tiger striping” – concentrated metallic stripes interspersed with less-metallic powder coating stripes. It’s not a good look, and the only way to avoid it is to find the spray pattern that works best for the powder you’re using, the gun you have, the way the powder is charged, and the way your part is grounded.
Be careful not to build too much film thickness, either, or you’ll wind up with orange peel texture after the part is cured. Metallic powder coating is typically more prone to orange peel than regular powder. Every single element of this process matters, and could have a dramatic impact the way your coating looks when it’s cured.
I recommend practicing on large test panels to find the spray pattern that works best for your setup. Over years of trial and error, we’ve developed some reliable spray patterns that work pretty well with our equipment and the powder we order, but even at Kaser, our success rate varies part by part, powder by powder. Metallic is tricky.
The trouble doesn’t end when the powder is on the part, either. Often, the metallic content will fall off in clumps, particularly if the parts are traveling through a heavy draft on their way to the oven. This doesn’t typically happen with regular powder coating – metallic elements charge differently, and carry more weight, meaning they’re more likely to fall off the part at the slightest bump. You’re then left with a divot you have to touch up, which is hard to do because you have to match the film thickness of the powder surrounding the divot. Metallic touch-ups will likely be very noticeable when the part is cured.
To summarize, if you’re a powder coating professional dipping your toe into the metallic pool, here’s my advice: test, test, test. Play with your gun settings. Make sure your part is adequately grounded. And above all, establish good spray patterns.
If you’re a customer wanting to glitz up your life, bonded metallic powder coating is equal parts beauty, frustration, and cost. Be patient with your powder coating professionals as they navigate the pitfalls associated with your request.