If the word “blooming” evokes happy thoughts of springtime and flowers, congratulations – you’re normal.
If the word “blooming” triggers feelings of frustration and a deep-seated fear of rework, then you (like me) are probably a powder coater.
I would venture to guess that most job shops wrestle with blooming from time to time. Kaser certainly does. For as often as we see it happen, though, I’m a bit fuzzy on its causes. Please drop a comment if you have more information.
Here’s what I know for sure: blooming shows up as a white, chalky, cloud-like haze on powder coated parts coming out of the oven. From a distance, it almost looks like a glare.
It’s not a good look.
In my experience, large, thick, heavy parts are more prone to blooming. I suspect that it’s because they take longer to cure. As the part struggles to heat up, the top of the powder coating begins to cure (or cross link), essentially trapping everything beneath it. Any emissions – from either part or powder – can’t escape through the quickly-curing surface, resulting in blooming.
Though I tend to notice more blooming on higher-gloss powders, we’ve seen blooming on Ag Red, Ag Green, Gloss Black, you name it – the color makes no difference. We’ve also sprayed different manufacturers’ powders with identical results. The one common denominator is large, thick, heavy parts.
Thankfully, blooming is not a death sentence. The haze can usually be removed with a soft cloth. It’s just one more thing for busy job shops to do before the parts go out the door – and if you care about aesthetics (as you should), you won’t want your customers to see it.
Powder coaters and chemists of the world, educate me: what causes blooming, and, most importantly, how do we avoid the headache?