Chemical Film Staining
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.
Many industries that require innovative solutions in cost reduction and weight savings are turning to aluminum as a substitute for stainless steel and other carbon steel alloys for parts and components.
Electropolishing can be a pretreatment for anodizing or a substitute for bright dipping. Either way, it improves the surface of the aluminum...
Types of anodizing, processes, equipment selection and tank construction.