Chemical Film Staining


Facebook Share Icon LinkedIn Share Icon Twitter Share Icon Share by EMail icon Print Icon

Q. What technique is used to avoid staining on aluminum parts when chemical film per Mil-C-5541 is applied? It seems that the bottom few drops dry on the very edge and leave a stain. J.C.

A. Here are some points to think about in this regard when doing the chem film process:

  • Although the bath concentration may vary a small amount depending on its condition, make sure it is not too concentrated. I recommend making up a new chem film bath at 1/2 oz/gal. An older, well-used bath may require 1 oz/gal to perform well.
  • Bath temperature of 70-75°F (21-24°C) is ideal.
  • Rinse thoroughly in a double-counter flow-rinse tank system, followed by a clean deionized (DI) water rinse, then a final warm rinse (150°F, 65°C maximum). That’s four rinses altogether.

The bottom line is, if the bath is too concentrated and/or the parts are not rinsed well enough, the staining is more likely to occur.