Companies, who wish to obtain military contracts or want orders from NASA or the National Labs, must conform to certain stringent specifications. By consulting the right documents, fabricators learn what exactly they must do to be able to supply the appropriate metal. When it comes to gold, the standards are provided in MIL-G 45204C. When it comes to anodized aluminum, fabricators look to the specifications supplied in Mil-A-8625.
Military Specifications for Anodizing Aluminum
When anodizing aluminum or any of its alloys, the military specifications are clear. The military requirements look at such things as processing conditions as well as the criteria for their accepting the metal. The military specifications for anodic coatings consider the following:
* Abrasion resistance
* Corrosion resistance
* Dyeing
* General appearance
* Light fastness
* Paint adhesion
* Weight of the coating
Military specs also look at other characteristics including inspection, overall workmanship, quality and process control and, of course, testing.
Mil-A-8625
The military specifications refer to the three different anodizing finishes for aluminum. The directive divides the coatings into separate classes and addresses the requirements for each.
* Type I – Chromic Acid: A non-architectural finish, Type I is less in use than previously because of environmental concerns. Either conventional or low voltage, this type is not as effective and efficient as other classes and types of finishes are.
* Type II – Sulphuric Acid: This type provides outstanding resistance to corrosion as well as high paint adhesion and excellent fatigue resistance. Type II falls into two separate classes 1 and 2.
* Class 1 indicates the material is not dyed
* Class 2: means the anodic coating is dyed
* Type III – Hard Anodic Coatings: This low-temperature process forms an “engineering hardcoat” that is extremely hard, and resistant to abrasion. The result is also porous.
In terms of thickness, MIL-A-8625 states this aspect bears a direct relation to the part drawing and/or the documents of purchase.