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Orange peel on second coat applications during powder coat process

We are getting into powder coating a clear coat over a first coat of many colors. We are getting orange peel after the clear is applied. We have used different charge readings on the gun and still have no luck. We use convection curing and have tried different temperatures and cure times and still get the same results. We also have tried to partially cure first coat and then apply clear, still no luck. Any help would be appreciated.

Dustin Wolf
Plant manager - Lebanon, Ohio, United States
March 24, 2008

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First of two simultaneous responses --

Only today did a customer pose almost the same question. He wanted our approval to apply our polyester (TGIC free) transparent onto a hot PC substrate. Of course we had no objections but queried why he wanted to do this as he would possibly use more powder. His reply was that when he applied the clear onto a cold surface it resulted in some orange peel but applying it to a hot surface, he obtained almost perfect flow. As we only coat 6x4 test panels and he refurbishes alloy wheels ù his method is worth a try.

Terry Hickling
Birmingham, United Kingdom
March 25, 2008

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Second of two simultaneous responses --

Two possibilities are paint formulation and coating thickness. TGIC's orange peel, period. Talk to your paint supplier about a smooth finish clear.
Coating thickness takes practice so there isn't any real way to tell you how to do it from here other the clear coat is applied using the same method as a rework to avoid starbursting resulting in a thicker coating, causing the orange peel.
Another theory that I've heard about but haven't experienced is the method of cure. Someone told me once that you can control orange peel curing with IR(even TGIC's) rather than convection but I don't have any personal experience with it. If you have IR capabilities it might be worth experimenting with.

Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina
March 26, 2008