Coating Technique
I've had quite a few questions brought to me about "what is or isn't the best technique" in powder coating. There's some general rules to follow here but I've got to say, there's no right or wrong way. Just what works for you. Let's start off with the basics and we'll touch on the advanced stuff in future posts (overcoming Farraday-Cage effect, mottled coatings,and the such). If you have a problem applying....please read on.........
Basic principals of the powder coating process are thus : You take a polymer (your powder) and disperse it mixed with air, force it through a tube that has a charged direct current field and it therefore becomes charged through osmosis( just being within the charged field). It is then exited the spray gun and attracted to a substrate (whatever metal you are coating) which has a ground attached. There is NO difference between this process and say....rubbing a balloon on your head and then sticking it to the wall. Positives and negatives attract, therefore you have adhesion.
Onward and upward.....
I generally start off with my gun a distance of 18-24 inches away from the part. I coat much in the same manner that anybody would with a spray gun or can, the only difference is that I make tiny circles with the tip of the gun while doing this. It helps diffuse the powder that much further and eliminates "spitting" onto the parts. Start in the upper left corner and move to the right. Work "past" the part. Get nice even coverage all over and turn the part around. Same process until the whole thing is evenly coated. At this point I stop and look at what I just did. If any spits or uneven waves in the powder...I can fix it easily using the same process...just blow it off first.
Now...let's just say for example you have a flat piece of sandblasted cold steel. Maybe 12 inches square. What you are looking for is a "dusted" fluffy type of effect. Think of it this way. You've seen your car windshield with a fresh coating of morning dew on it, right? Well...multiply that by two and that's what you should have looks wise on your part. *Just* barely past noticing raw metal under your coating. Don't worry if you can still see metal in the light. The melt and cure of the flowed powder will cover that up just fine. Any excess and you will notice an orange peeled effect to the powder. lumpy bumpy wavy and pock marks mean excess. Too bright a shine from the substrate and it's not heavy enough. Take your time, work slowly and deliberately and the results will be just fine. If you don't like what you see....blow it off and do it again. That's the major advantage that powder has over all other coatings.
Voltages for you guys should be in the 20Kv range for a good solid coating. As for second coats like a clear over a colour, we'll attck that on another post. There's no difference between metallics, clears and pigmented powders! They all spray and coat the same. If your metallic has a wave to it or the metallic flake looks a bit odd, you are too close. Back off and re-spray the part. Same goes with clears. Although a finer powder due to lack of pigment.....you should still have that "morning dew" appearance to it. Again, please note...this is for one-coat process only.
Using this method will usually build a coating of 1 to 1.2 mils which is where you want to be. Until you get a feel for it (and yes, you will) experiment on a bunch of different parts. After all....powder is 100% reclaimable and can be sprayed over and over again, so you have no excuses. Practice makes perfect folks. I hope something in there helped somebody. Take care all......Russ
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