Troubleshooting Chromate Conversion Coatings

Question:

We are having all kinds of problems with chromate conversion coating. Some of our parts are streaked and others have bare spots. What are we doing wrong? M.C.

Answer:

Your e-mail doesn’t give enough information to do any serious troubleshooting so the best I can do is give you a few suggestions. In general the factors that most affect this type of bath are concentration, immersion time, temperature and pH.

To solve your problems, start out by talking to your chemical vendor and get his suggestions for solving your problems. Most vendors are usually more than willing to help out! Next get yourself a copy of the Metal Finishing Guidebook and Directory, 2000 edition, 914-333-2500. There is an excellent chapter in this publication on chromate conversion coatings. You can also purchase a publication, Chromate Conversion Coatings, from the AESF, 407-281-6441. This publication has a rather complete section on troubleshooting of chromate conversion baths.