I pre-heated a couple of aluminum motorcycle rims and then let them cool down to about 100 degrees. I went to spray them with my ew hobby gun and the powder just fell right off. I had the ground wire attached directly to the rim that I was coating. I took the ground wire off the rim and attached it to a smaller piece about 10 inches long and 3/4″ in diameter and sprayed it and it worked fine, then I transfered the ground back to the rim and the powder stuck just fine. I am just wondering why this worked and if there is something I can do to fix it.