Powder coating application issues (1 of 6)

Poor Charge, Low Film Build, and Insufficient Wrap

This trio of issues is like a terrible three-in-one package. All of the above, either alone or together can cause the coating to look bad. Quite often a grainy effect, or tight orange peel, is what you end up with. This can often be caused by low film build, as, simply put, there’s not enough coating on the part to create the nice smooth surface you’re looking for. Plus, if you have a low film build with certain colors, you will see the substrate right through it – yellows and whites are often the culprits.

The Problem

The most common cause of these issues is poor grounding. Now, there is an EFTA standard for what your ground should be, and if that is not met, no matter how you fiddle with your gun settings or gun to surface distance, the powder just will not take a charge; keep this in mind for the rest of the guide, because good ground is going to pop up a lot. Of course, ground is not the only factor in this issue. Your gun settings may actually be the problem. Too much powder flow and incorrect kV levels can affect an application for the worse.

The Fix

Straight away, make sure that you have a good earthen ground. There needs to be some kind of connection from your part – the substrate being coated – to that earthen ground, be it racks or hangers etc. Also, ensure that these connecting parts are clean, because if there is not good metal to metal contact the charge will not pass through as easily. Truthfully, a regular maintenance and cleaning system is a good process to have in place. Powder builds up on racks, electrodes, and hooks, and needs to be cleaned away regularly – i.e.: don’t just paint until you can’t paint anymore and then grind it down.

Now, for the gun settings: check your kV levels and powder flow, especially with consideration to what each individual powder requires. If you do fiddle with the settings frequently and see this application issue crop up, double-check the Technical Data Sheet or call up your supplier for the correct kV and flow settings.

Top Tip: Depending on how old your equipment is, something may have actually broken in the gun itself. Multipliers, cables, pumps, and boards can all go bad, basically. You can physically check the kVs coming out of your gun with a kV Meter. A decent one can be picked up for under $50. You will also want to make sure that no powder is getting into where it shouldn’t, like the controls of your equipment. That is just a whole mess of trouble waiting to happen.

As for flow…if your gun is spraying too much powder it can cause you not to get the proper charge, and will waste a lot of product. Another thing that can cause powder wastage, and improper application, is the humidity in the room. Too much or too little humidity can interfere with the spraying process. You want to try and maintain a constant temperature or relative humidity - both in the storage areas and application rooms. Ideally, the range to keep in is between 50+/- 10 for humidity and 70°+/- 10° for temperature.

Top Tip: Reclaiming powders can cause issues. If the particles are too small, they will not carry a charge as easily. Maintain a proper ratio of virgin to reclaim and you can avoid issues arising due to this particular factor.

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