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Suitable bath for hard anodising

which is suitable bath for hard anodising.
10% sulfuric or sulfuric& oxalic acid.
what difference in coating properties?
we need 25 micron hard anodising.

Prasad Patwardhan
Shrikrupa ind - Ahamadnagar, INDIA
2007

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Hard coat is typically done at 20% by weight sulfuric acid,with book values of 12 to 22%. 0 Centigrade constant temperature and well mixed solution for temperature uniformity. 25 microns is a bit unusual with engineering hardcoat starting at 50. Other applications go as low as 8.
Some people use an addition of Oxalic acid for "a better coat" but it typically requires a superimposed sine current. There are what some of us refer to as type 2 1/2 anodize which uses an additive that will allow a psuedo hardcoat at higher temperatures.

James Watts
- Navarre, Florida
2007