Sulfuric Acid Anodizing

Sulphuric Acid Anodizing as per MIL-A-8625 Type II

The sulphuric acid process is the most common method for anodizing. The Sulphuric Acid Anodize process films range from .0001″-.001″ thick. The overall thickness of the coating formed is 67 percent penetration in the substrate and 33 percent growth over the original dimension of the part.

How is Sulphuric Acid Anodizing different from other types of anodizing?

It is particularly suited for applications where hardness and resistance to abrasion is required. However, where parts are subjected to considerable stress, (such as aircraft parts), the possible presence of the corrosive acid residue is undesirable. The porous nature of sulphuric acid films prior to sealing is used to particular advantage in the production of coloured surface finishes on aluminium and its alloys. The porous aluminium oxide absorbs dyes well, and subsequent sealing helps to prevent colour loss in service. Although dyed anodized films are reasonably colourfast, they have a tendency to bleach under prolonged direct sunlight. Some of the colours are: Black, Red, Blue, Green, Urban Grey, Coyote Brown, and Gold. Parts can be treated chemically or mechanically prior to anodizing to achieve a matte (non-reflective) finish.

What are the attributes / characteristics of Sulphuric Acid Anodizing?

  • Less expensive than other types of Anodize with respect to chemicals used heating, power consumption, and length of time to obtain required thickness.
  • More alloys can be finished.
  • MIL-A-8625 Type II
  • Harder than chromic anodize.
  • Clearer finish permits dying with a greater variety of colours.
  • Waste Treatment is easier than chromic anodize, which also helps to reduce cost.

What are the applications of Sulphuric Acid Anodizing?

  • Optical components
  • Hydraulic valve bodies
  • Military weapons
  • Computer and electronic enclosures
  • Mechanical hardware