Friday, August 22, 2008

Preparing your part for Powder Coating

The most important thing to learn as a beginner and starting out with powder coating is a phrase coined from the auto body industry.

"Any monkey can spray a car, but preparing it correctly so the job comes out right is the hard part"

That's never been more true then when it comes to powder coating. Your piece must be meticulous, absolutely spotless, and free of any contamination for the best job possible. As you start working with different objects you will spot problem areas that arise with hobby systems and work around them so that it looks professional. Don't be disheartened if your first one or two jobs have flaws in them, just see what caused it, and fix them. That's really all there is to powder coating!

So lets get started shall we?

Obviously, the first thing you want to do is clean the piece your powder coating up. If it's greasy, oily, grimey, dirty, you name it, it needs to be cleaned. Be careful of using anything too agresive at this point, as leaving an acidic film or something of that nature on the part can leave you with problems during the coating process. I generally spray all my parts off with regular water to remove the big stuff.

At this point, the part may look clean, but you're really not ready for powder coating yet. Many prepping agents are good at removing surface impurities you cannot see with your eye, but in my personal opinion, I prefer sandblasting every piece before coating. Even areas that look spotless, I go over at least once or twice so that I'm 100% positive there are no contaminants on the surface. Sand Blasting is the process of using abrasive sand to basically strip away the top layer of material, much like sand paper would. If you do not have a sand blasting setup, you can either purchase a very cheap setup from a company like harbor freight, or hand sand the piece, but that is quite often difficult as you're not working on flat surfaces.

After that, masking and covering any areas that you do not want powder coated is up. Eastwood sells a very nice system of high temp silicone plugs and caps that you can use on hose barbs, bolt threads, and even bolt holes. They also sell specialized high temperature tape that you can use to mask off gasket areas such as the flange of an intake manifold being powder coated. A major tip that I've learned along the way is not to worry about masking off things like lettering on a valve cover or small raised edges you do not want powder coating applied to. It's extremely easy to come back once it's finished and use an orbital sander or something to remove the powder coat from the raised edges and leave the powder underneath it perfectly fine.

My next part of the process is a burn-off and pre-heating system I've been using all along while powder coating. To further purify the piece, I will place it uncoated in the oven at 450 degrees for about 20 minutes. This will generally burn off all contaminants, and also warms the piece up for the coating process. Care must be taken to slowly raise and lower the temperature of the piece you're working on so that the sudden changes do not effect the metallurgy of the part being powder coated. A inexpensive thermal temperature reader should be used to verify the temperature of the part.

This is where the spraying finally happens! After it's burn-off session, I remove the part from the oven and let it cool down to roughly 150-200 degrees. On the inexpensive hobby systems, no amperage adjustment has given me troubles getting powder to stick evenly and issues with faraday cage effects. I use this slightly higher temperature to help adhesion with the powder and the part that I'm working on. Using this technique while powder coating is commonly referred to as a hot flash, and that is basically stating the temperature isn't high enough for the powder to melt, however it starts to gel just a bit and helps stick to the part. Spray very evenly, in broad strokes and paying attention to the hard to reach spots and doing them first. Once your piece is fully coated, remove the ground strap, and stick it in the oven. Using your infrared temperature probe, wait for the part to reach the powders optimal flowout temp and set your timer.

For the highest gloss, smoothest finishes, when the curing process has completed, turn off the oven and crack the door but not remove the part. Let the part slowly, over 20-30 minutes come back down to room temperature. Cooling down too fast I have found lead to cloudy finishes, or I've also had dust and debris fall into a freshly coated piece leaving the oven. Inside there's little turbulence, and the temperature drops a few degrees every minute, instead of every few seconds.

That's one of your first powder coated pieces step by step right there. Pick up a powder coating kit and give it a try, it really is so easy an idiot like me can do it!


Anonymous said...

I am a powder coater. I believe you are incorrect on the pretreatment process. sandblasting alone will not guarantee good adhesion. In fact the parts sould be phosephated first, run though a clean water rinse. Even a fingerprint on your cleaned part could make the cured powder lift.for the substrate. phosephating, in my opinion is the only way properly pre treat your part.

Anonymous said...

As far as powder coating preheated metal, this could result in the coating to "run" like wet paint. there are proper thickneses, (or Mills)for eack type of powder. said...

Really useful information, thanks so much for the article.

Anonymous said...

Really easy to follow,just what i was searching for, cheers.

albina N muro said...

The most important thing to learn as a beginner and starting out with powder coating is a phrase coined from the auto body industry. cleaning oak

charles said...


Powder coating is the technique of applying dry paint to a part. The final cured coating is the same as a 2-pack wet paint. In normal wet painting such as house paints, the solids are in suspension in a liquid carrier, which must evaporate before the solid paint coating is produced do it with Automatic coating..

Anonymous said...

I am using a sandblaster and he is blasting all my parts. They come out rough and not a smooth finish. So my finish is rough if I were to get a smooth finish will the final piece come out better. And for the pre treat I wash with water only no chemical. Pulling the piece out of oven in to a room tepm is that still a bad thing.

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