Hi William
In addition to comments by Len. Unmelted particles are a fact of life. Most good coatings will have some degree of unmelted particles. The reason why, is that the spray process and powders used are not perfect. Powder particles are not perfect in uniformity of size and shape. Larger particles require more heating than smaller particles. Powder feeding and injection is not perfect. The whole process really is a bit chaotic, so we set parameters to cater for the majority and accept a minority of less than perfect. A good coating often displays evidence of a few under-heated particles along with a few over-heated. A poor coating very often will often have a lop-sided relationship between over and under-heated particles.
My use of the word 'perfect' is to mean a system of 100% efficiency or +/- 0 and not an indication that your equipment or powder is less than it should be