Class A Finish

Question:

I saw your article online about the Class A finish. We’re getting parts by our powder coater to a Class B currently, which he says is the most common class. If we want Class A, it's more money per part. He says he developed his own spec, which he shared with us and it has a lot of descriptions of the various defects with powder coating (spitting, orange peel, Faraday cage effect) due to the ISO 9001 certification. We were getting bad service from him and want to use a new powder coater and this guy has no spec (small shop) so we’re using the spec of our old supplier for this new guy (we just put our company name at the top of the document). We want the new supplier to give us Class A service. Are there any pictures available for the various defects that can occur during powder coating? Many of the terms are vague and we do 100% inspection of our parts once they come back from powder coating. With a spec it gives us more leverage in determining whether to reject a part or not. Are there any references that would help me find out more about this issue? R.R.

Answer:

There are several references that can help you. One is the book published by the Powder Coating Institute (www.powdercoating.org) called Powder Coating, The Complete Finisher’s Handbook. Additionally, there is a Terms and Definitions book that is the companion for this manuscript available from the same source. Both of these texts will supply you with written descriptions of these visual defects. There even is a set of standards available from PCI to judge orange peel called the Powder Coating Institute Smoothness Standards.

Since the defects that you describe are considered visual defects, word definitions alone cannot adequately describe what you want your product to look like. Most companies use the definitions provided by PCI and define the total number of these defects they allow per unit area (defects per sq ft). That is how you determine what is Class A for you and your customer. There are no photographic standards of these defects, since each product has different visual standard requirements. Therefore, I recommend that you develop your own photos, or word descriptions, of the surface quality that you require. This situation is best described as “beauty is in the eyes of the beholder.” One company’s class A is another’s class B, for instance. Determine what your quality objectives are and provide enough documentation to your supplier to achieve that quality. In this case, that means you must take your own photographs.