Part not anodizing/Partially anodizing

[taylorm]

I have an LCD anodizing kit and it works occasionally, but the usual problem im having that the parts arent taking dye, which leads me to beliebe that they are not anodizing. Tiny bubbles come off the part when it is in the tank, and when I take the part out it has a grey coating on it (the coating wipes off when i touched it).

Im really confused on calculating all the PAR stuff, so ive just been kinda winging it as far as voltage and times go.

Can somebody explain this for me?

[mcaswell]

You haven't given us much to go on here.

You need to fill in a PRS troubleticket, so we can see exactly what you've done. If you aren't controlling the amps properly, you'll not get good results.

[Fibergeek]

If you just "wing it" you will fail most of the time.

The 720 Rule has been shown to accurately predict anodization time. I recommend that you use this instead of PAR.

720= ASF x minutes / mils.

ASF = Amps per square foot, which is the current density.
Minutes = minutes of anodization time.
Mils = Anodize thickness in mils (1 mil is 0.001 inches)

The anodization temperature must be held to between 70 and 75 deg. F. the 720 Rule will be off if its not, other bad things can happen too.

The Baseline for LCD is 4.5 ASF for 90 minutes. This is intended to produce an anodize layer a little over 0.5 mils thick, which will dye very well.

Some examples:

The surface area is 1 sq.ft., the current density is 4.5 A per sq.ft.

720 / (4.5 / 0.5) = 80 minutes for 0.5 mils thick.

The current you would apply is:

4.5 ASF x 1 sq.ft. = 4.5 Amps.


The surface area is 36 sq.in. (36 / 144 = .25 sq.ft.) the current density is 6 ASF (the high end of the LCD range).

720 / (6 / 0.5) = 60 minutes for 0.5 mils. thick.

The current you would apply is:

6 ASF x 0.25 sq.ft. = 1.5 Amps.

You can form a thicker layer by anodizing longer, but if the temperature in the tank gets higher than 75 deg. F, dissolution effects will enlarge the anodize pore size and trouble starts. Forming a layer much greater than 0.5 mils should not be attempted until you can successfully anodize and dye at 0.5 mils. For dyeing purposes; there is no point going beyond 0.7 mils, this is because the dye (any dye) won't penetrate any deeper than 0.7 mils.

Edited to correct the first equation.

[Sid03]

sadly enough, im kinda lost here. In this example.....

The surface area is 1 sq.ft., the current density is 4.5 A per sq.ft.

720 / (4.5 / 0.5) = 80 minutes for 0.5 mils thick.

The current you would apply is:

4.5 ASF x 1 sq.ft. = 4.5 Amps.

if you worked those numbers out backwards it doesnt work....

720= ASF x minutes x mils
720= 4.5 x 80 x 0.5 <---that isnt correct

What am I missing? I couple more examples of the 720 rule would be appreciated, I would like to try it out this weekend.

[Fibergeek]

Sid,
I arranged the first equation wrong, it should have been

720 = ASF x minutes / thickness in mils

The second equation to solve for anodizing time is correct.

Look at it this way; since coating thickness is proportional to current density (ASF) and time. This means that if you half the time you half the coating thickness.

Good catch, thanks.