Powder Coating 101: Interview with Powder Coating Expert, Joe Powder

Hey out there! Let’s talk about Powder Coating and what products Ace-Tex has that can help alleviate this problem for powder coaters. But before we get started, I hope everyone is faring well with the incredible weather we have been having! Some of us love it, some of not so much and some of us just wish the roads would be drivable. Whichever one you are – just be sure to drive carefully.

Being a member of the Powder Coating Institute brings certain perks like a subscription to the association magazine – Powder Coated Tough! I recently sent a few questions into their Powder Coating Expert, Joe Powder. Joe was gracious enough to answer all of my questions and then some. He is definitely the Powder Coating Industry go-to guy!  For those of you not familiar with the industry – check out the PCI website, www.powdercoating.org for some general information.  My questions were a little more pointed, and I wanted to see how our Static-Reducing Wipes fit into the industry.

For those of you out there who have already adopted SRW technology for their powder coating process, you already know what we’re talking about, and for those of you who do not – read on.

What role does static electricity play in powder coating? 
There is static electricity from more than one source when dealing with powder coating application. As you probably already know powder coatings are electrostatically charged typically by a corona mechanism near the tip of the business side (outlet) of the spray gun. This works by very high voltage (80,000 to 100,000 volts) being delivered to the electrode. This high voltage ionizes the air creating a field of electrons or negative charge. (Don’t worry the current is very small, typically micro-amps so the process is relatively safe.) The powder is pneumatically conveyed into this electrostatic field, picks up a charge then heads to the nearest ground. The object of the game is to make your parts the closest ground and then the powder deposits on the surface of said part.
So lots of static electricity is generated by the spray system. It’s important to note that static electricity is generated elsewhere in the finishing system. The mere fact that powder particles are being conveyed into fluidizing hoppers, through powder pumps, hoses and spray guns creates static charges. This extraneous generation of charge affects powder deposition and can influence transfer efficiency.

Does static electricity cause fisheyes, cratering and “bits”?
Very characteristic defects are caused by electrostatics. Excessive charge can build up in a powder coating layer if the powder is applied too thick, too quickly. This phenomenon is known as back ionization. The build-up of charge causes powder particles to microscopically burst away from the substrate. This causes micro defects that resemble volcanoes. These defects cause a rumpled appearance that looks more like localized macro orange peel for lack of a better description. 

Fisheyes are caused by a different mechanism and are more distinct in their appearance. Fisheyes are created by a significant differential in surface tension between a molten powder film and a contaminant. Common contaminants are lubricants and oils. Silicone lubes and penetrating oil (e.g. WD-40) are some of the worst actors. Fisheyes are gross defects characterized as deep circular voids in the coating film that reach the substrate. Craters are ambiguously defined as defects similar to fisheyes but smaller in diameter. Craters often do not reach the surface of the substrate and typically look like dimples.

As for “bits” I imagine you are referring to unmelted protrusions in the finish of the cured powder coating. These are not caused by static electricity. Common sources of “bits” are environmental dirt (oven, spray area, unclean application equipment, etc.), unclean substrate or dirty powder coating. They are typically more prominent at thin films (i.e. < 1.5 mils). If the preponderance of “bits’ decreases with thicker coating films then you can suspect either the powder or a contaminated substrate surface. If film thickness is not a factor then the contaminant is probably environmental and is deposited on the powder after it has been applied.

Regarding repair – fisheyes, craters and “bits” need to be buffed with an abrasive (Scotchbrite or 200 grit sandpaper), the surface wiped (e.g. acetone), dried and recoated. Alternately you can consider using a liquid paint based touch-up if the repair is small and localized. Be careful however as the touch-up may not meet the performance of the original powder coating finish.

Are powder coating companies doing everything to minimize dust and lint?
High quality coating shops are very clean with isolated application areas that use filtered make-up air. Their processes are carefully monitored and controlled. It’s fairly easy to discern their quality level with a visit and tour of their finishing operations. In short, both the powder coating manufacturers and powder applicators need ways to wipe surfaces that do not generate additional static charge. Moreover it is requisite to be lint-free. Lots of powder people realize this, lots do not. Some of us use DuPont products but they are pricey.  

If you are not using SRW®, please contact us via Ace-Tex’s website, www.ace-tex.com.  We can send you a sample of our SRW®, so that you can see what a difference it will make in your repair process. Whatever products you are using, none of them have the Static Reducing ability of Ace-Tex’s SRW®.  Following are the answers to my many questions – than you Joe!  I appreciate your answers and time!

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