DIY Anodizing at home. 720 Rule Calculator for Low Current Anodizing Method.

[ThinWoodsman]

I did a bunch of anodizing a few years back. The .pdf is a print of the project on another site. here's a clip of setting power:

Thanks! Very informative

 

[Sirhc70]

I have just started on the Anodising road after watching a couple of youtube videos showing the basics and neither of them mentioned the 720 rule and because of that it seems to have threw me off the first time I tried.

I have my electronic bench psu 30v 5a and can set in cc mode I also have a decades old (real bench psu with zero electronics inside it that has current or voltage switch on the front that may work as well).
I watched the sodium bisulphate vids on the tube as "battery acid" is hard to come by and dangerous so purchased a small bottle as I am only experimenting on small parts to start with. I have NaOH already from the days of running a hho fule cell in my OLD taxi that failed emmission tests untill the hho was fitted then it passed with flying colours and the tester commented that my readings were the lowest he had ever seen .

I pre clean for 2 mins in NaOH then rinse and give a scrub with a non metalic scouring pad then rinse again and give it a soak for another 2 mins in NaOH so that the whole part is fizzing like an alka seltzer fizzing in a glass of water , then I rinse and connect up to the + Anode of the psu and place it in the etching bath with a (reclaimed/salvaged lead cathode) and set the power and wait. once the time is up I get the part to change to a yellow`ish colour so I take it that I have an active cell structure so I think I am half way, but I am struggling with colour. the clothes dye I bought just does not take even after a 24hr soak in the stuff it just runs off and leaves me with a lightly coloured part to the point if I rinse it the colour washes away.
The price I paid for the dye was minimal and it I will just use it to dye a couple of pairs of white socks and an old t shirt so it`s not wasted.
I have just ordered the correct metal dye for a couple of uk ££ more than the clothes dye so fingers crossed that might take better but all i can do now is read and wait untill it arrives.

Am I doing the anodising steps correctly or should I tweak the first pre wash and etch times longer or shorter or is it dependant on the grade of the aluminium, any advise would be great and more helpfull than general anodising vids on the tube. I have watched the vid by The Recreational Machinist who links to a 720 rule calculator here that is metric compliant to save me converting my math into inches to use the online calculators and it has been the most informative one so far.

thanks Sirhc aka Chris

 

[Joe in Oz]

This is a small java program I made a couple of days ago directed to calculate the anodizing time given the part's surface area, current density (it is directed to users of constant current anodizing rectifiers), and desired oxide layer's depth in mils.

The software was written for a group of users from Spain, so the main screen comes up in spanish but there is a checkbox selection for english speaking users. Surface area can be entered in in2 or cm2.

Hi. Thanks for that Java program! Could you please make to code so the thickness is set in microns in the metric version? I actually had to google what "Mil" means... why isn't "thou" used consistently? Is "Mil" a specific anodizing term?

 

[Sirhc70]

All sorted . I had ZERO luck with clothes dye. I recieved the"real" aluminium colour dye that I bought from a metal finishing company and what a difference. I used exactly the same steps, times etc as with the clothes dye but used the real dye and within mins of soaking it hey presto fully coloured parts and ready for the heat sealing bath. The only problem I have now is that everything Aluminium in my workshop is purple/violet in colour.. I need to buy a different colour. I have attached a picture of the first 3 test parts, the left part was clothes dye & a poor attempt, the right is "real" dye but messed up by following a bad youtube video that said to dry the part after you remove it from the colour bath.. DO NOT DRY IT. leave it wet and get it into boiling water a.s.a.p. the middle part is the 3rd and final good part. glad that I had 3 parts the same to anodise.

 

[JoanTheSpark]

Hi. Thanks for that Java program! Could you please make to code so the thickness is set in microns in the metric version? I actually had to google what "Mil" means... why isn't "thou" used consistently? Is "Mil" a specific anodizing term?

You're aware that this was 8 years ago, yes?

As for changing the code.. I put the .jar file through a decompiler and got the attached source from it.

If my guess is right you'd have to change at least line 301 to resemble what is being done in line 302 till 307 (surface area input being treated differently for metric/imperial, but both get converted into Inch I think) or 315 till 330 (deals with messages in either English or Spanish for to small currents or areas being put into the app).

I 'program' in python mostly, so take with grain of salt.

Good luck?

PS: I wanted the source to find out how the final voltage is being calculated. On finish(dot)com some pro talked about the resistance of the bath+alu and via Ohms law one could calculate the voltage needed to drive the current, if one knows the specific resistance.
The value given there was 0.95 ft^2/Ohm.. just divide by the area and one gets the resistance of the setup.. which then via R=U/I .. U = RxI gives the voltage needed. His example was for some 1.75 ft^2 and 35A, so he wound up with ~19V.. but if you use something like 0.08 ft^2 and 0.5A like The Recreational Machinist does in his video on youtube the final voltage is a ridiculous 10 mV (0.01V).. which just doesn't sound right.
So there is something else here that is not really linear as both this java app or the pro from finish(dot)com assume.
Oh and the app just multiplies the current density with 2.5 to give you the final volts.. hilarious.