Another hopefully useful hint from yours truly....
Powder from coatings is meant to be reclaimed. Theoretical coverages for certain types of polymers are quite staggering due to the fact that there are 100% solids at play here. Just to put it in perspective, a typical pound of polyester powder is good for 25 square feet of coating (I know the book tells you otherwise, but I'm telling real world expectations here) at 1.2 mils. To get that type of coverage from a spray can....you'd have to use 14 common size spray cans at roughly 3.99 each. Do the math. One pound of powder at an average price of say...10 dollars versus 55.86 for the spray cans. Not too shabby a deal if you ask me considering liquid sprays contain VOC's and all sorts of other nasty things. So how do you get the most out of that powder? Well, I'm glad you asked....read on!
First of all, I don't even bother with the stuff that gets caught in the shop-vac (cyclone seperator and canister or bag type filters for all those about to turn "pro"). It's a waste and can be dumped in your garbage. Unless of course...you just want to practice spraying to get a feel for the whole process. If that's the case, be my guest. It's basically a "gimme" at that point for no cost training.
To screen powder of it's impurities you will need (and more than likely Caswell will be offering these to you in the very near future). A set of "filters" to sieve your powder through. These are nothing more than wire mesh screens with grades on them in the following forms. 60/80/100/120/160/200/240. These numbers signify nothing more than the holes per square inch for any screen in particular. 60 has 60 holes per square inch, 80 has 80 crosshatched holes and so on. Each hole getting smaller and smaller as the numbers go higher. Anyways, start with your 60/80 and filter out all the big particles. You'd be amazed at the things you're going to pick out. Lint,hair,wood chips, etc come out at this process. Next is the 100/120 family. Clumps of pigment and most nasty things not deemed sprayable come out at this point. After that we have the 160/200 grouping. This is where you get your "fines" or finely ground particulate back and this will more than likely be your reclaim for pigmented powders. Anything that makes it past the seive at this point is totally sprayable as a coating. Above 200 series screens are really meant for clear and exotic colours. The very finite particles can be found here and give the smoothest flow. All of the powder after the screening process that doesn't filter through is basically worthless in my book and should be tossed in the garbage. I've seen some people actually screen thier powder before they coat with it, which is fine if you need that really smooth home run on an important piece. Some of the industrial guns actually have a 160 sized screen on the pick-up tube before it even hits the gun. However....most powder from the supplier has been through the 160/200 grouping already and can be trusted. Note...when you hear either myself or another coater who's been in the game a while talk about the "grind" on a powder, THIS is the range of which we speak. HB Fuller (the powder that you guys get from Caswell) has a nice grind to it and I've used it industrially for years with no complaints. It sifts well and shelf life is on par with anybody else out there. Remember this though....if you've reclaimed powder from the floor of your booth or elsewhere and you have inexplicable "smut" in it......it's time to sift it. Hope that helps somebody out there wondering what to do with all the excess powder. Take care all......Russ
P.S. - keep looking to the Caswell products for new listings in the very near future for these screens and other helpful coating tools and products coming soon, hopefully.
