Outgassing Problems

Question:

I am powder coating some small galvanized coated brackets with a white epoxy powder. I think I am getting an outgas reaction from the part as it is full of holes and some places look like their full of dirt. We washed these parts in a three-stage iron phosphate dip system. To be sure these parts were clean, I cleaned them with MEK without a noticeable difference. Normally, we get 90% rejects, but this was reduced to 50% after I preheated some of these parts. Is this outgassing? R.H.

Answer:

Yes, this seems to be an outgassing problem, although it is difficult to tell without actually seeing the parts. The fact that you had a 50% reduction in rejects by preheating the part and that these parts are galvanized leads me to believe that outgassing is the culprit. You may try to preheat these parts at a higher temperature and for a longer time than your normal curing requirements to further reduce rejects caused by this problem. This doesn't always work, but it is the simplest thing to do. You can further reduce this problem by using a powder coating that has been formulated to reduce the effects of outgassing. These powders have extended flow times that allow the gas to escape and flow over the pinhole created by the gas. Be aware that these powder formulas are more prone to sags and can have little effect on galvanized parts that continue to outgas no matter how long you preheat them.