Hard Anodizing

[sswee]

There is benefit to type III anodizing for certain applications if it is a true type III. Type II can be grown with the small pore size and thickness similar to type III and would be hard to tell the difference without going to a lab. The setup cost and difficulty for type II is less than type III (excluding the oxalic which I'm not familiar with). If you like, I could anodize a test piece for you to run through the paces and see if the type II would do the job. If interested just email me.
SS

[pmd34]

Hi, I am new to this whole area of anodising, but I was able to find a good old fashioned book on the subject.

With regards to Oxalic acid anodising the recomended strength is 1-5% with a voltage of 40-60V at 1-2A/dm^2 (strange units but hey!) The colour of the anodising depends on the voltage and temperature of ths solution, becoming progresively more golden in apearence incereasing the voltage to up to 100V.

With regards to temperature, apparetly there are various classes of Oxalic acid anodising. Using the above voltage and currents, at a temperature between 20-30 deg. C a very hard coating can be achieved. Requireing twice the force needed for that of sulphuric acid anodising to scratch the part (actual table of numbers not just me with a knife!) With a temperature above 35C however this reduces the scratch resistance to somewhat less than the sulphuric acid anodised part. (Some patents that can be found suggest even lower temperatures).

There was also a claim that addition of acetic acid to the oxalic gave a coating that was enamelled looking in appearence.

I have tried the regular oxalic acid anodising myself (as oxalic acid can be bought easily from a chemist here in Denmark and sulphuric acid is much hard to get hold of.) The result was a pale gold colour and was excedingly hard to scratch through.

However... I wonder if one of you might help... I did find that after sealing in boiling water for 1hr the surface was very chemicaly clean, so once done greasy finger prints etc left permanent marks on the coating, so I had to "dirty" the whole surface evenly to achieve a suitable coating, any thoughts? Is this normal? Would I be best coating the suface with say silicon oil as a final treatment? A slight chalky film was also observed on the surface, though I wonder if this may be a result of some calcium ions in solution?

Chears,
Dr Phil

[sswee]

pmd34,
I'm not familiar enough on oxalic acid anodizing to be much help. In Type II sulphuric acid anodizing a slightly chalky film on the part would indicate dissolution of the coating. If so it could have a direct connection to the problem after sealing.
SS

[acidrain]

I too can only offer a guess, but it sounds like the part did not get sealed. I'm not sure about type III, but with type II, the nickel acetate sealer offers better chemical and dirt resistance than steam or boiling water sealing. Search further for type III sealing methods?

[recalled]

So, then, are military alloy weapons (M4, M9, and such) "hardcoat" anodized, or type III anodized, or what? This is pretty confusing, on top of being in a specific-knowledge field. I'm glad that some of you folks know this stuff...


- recalled

[Rapt]

Yes US Military weapons systems (M4 M9, M16... etc.) are Type III anodized to the applicable Mil-Spec.

[manishnjain]

Hi,
I have put up with a new plant of hard anodizing.
Please can u guide me in how to get the best results for my anodizing.
I am anodizing utensils but i am getting gray color anodized. I need jet black.
please guide me on the bellow question: -

1. What temperature shoult i anodize.
2. What should be my acid mixture(and how pure should be my acid).
3. What volts and amps should i anodize .
4. What other chemicals can i us.
5. How should i do the sealing.

my tank size is:- length=13ft
Width= 3ft
Hight=3.5ft

please guide me.
thanking you
manish

[Z]

hmmm, I'm pretty sure that hard anodizing isn't going to come out jetblack. Hard anodizing is rarely dyed, usually only for color coding. You wont achieve a deep color like you would with type II anodizing. Also hard coat isn't sealed unless dye, because it softens the coating.

[sumo]

you will need black dye to get the black look you want.