Expected Anodize Film Thickness

One of the most common technical questions we receive at Chem Processing is about aluminum anodizing thickness. Engineers and machinists want to know what their final size will be after we anodize or hard coat the part. The calculation is fairly simple, but unlike plated finishes, anodizing penetrates as well as builds. Fortunately, the penetration is consistently around 50% of the total film thickness, which makes it easy to calculate the final dimensional change. If the callout is for MIL-PRF-8625 Type III hardcoat to a standard film thickness of 0.002", then the dimensional change will be 0.001" per surface. This means an ID will shrink by 0.002". For MIL-PRF-8625 Type II anodize, undyed, film thicknesses run around 0.0003" to 0.0004" and the same rule applies: the dimensions will change by 0.0001" to 0.0002". 

MIL-PRF-8625 Type I chromic acid anodize films are very thin (which is the primary reason they don't significantly lower fatigue strength). Dimensional change is typically <0.0001" and difficult to even measure. 

MIL-A-63576 PTFE Impregnation does not add measurably to film buildup.

If you would like to consult regarding your particular anodizing application, contact Chem Processing and talk with our technical team. 

Wally Hanson - Technical Director

Gardiner Rynne - Business Development Manager