Anodizing calculations (720 Rule)

[GramSlam]

Hello all,

With my past discussions with M_D and Fibergeek, I have learned about the "720 Rule" for anodizing.
I decided to take what I had learned from the dynamic duo, and create an excel format calculator to speed up the calculations.

Here it is. Its very simple. (hopefully M_D and Fibergeek can check it over for me)

(link removed - web page no longer available)

The blue cells are the cells where you plug in your known values. The green ones are the calculated values.

I included a formula to help calculate the surface area of an unknown run. All you need to know is your peak voltage, and the amperage you had your supply set to. This calculation will also account for hanging wires and racks. (I think)

Edited for clarity by CASWELL Inc
Fibergeek's 10 cents worth

The 720 Rule is: 720=ASF x minutes / mils. Where; ASF is Amps per square foot, mils is the desired coating thickness (1 mil = 0.001").

Re-arranging to solve for time: 720 /ASF x mils = minutes

For a current density of 20 ASF, and a thickness of 0.0005" (0.5 mils); 720 / 20 x 0.5 = 18 minutes.

The actual current you would apply is 1.75 sq,ft. x 20 ASF = 35 Amps. The required peak voltage is 0.95 Ohms per sq.ft / 1.75 sq.ft. = .54 Ohms. .54 Ohms x 35 Amps = 18.9 Volts. This assumes no voltage drops due to bad connections, and you haven't increased the actual surface area with racking.

Regarding Amps and Volts. Confusion occurs when the third entity is ignored, which is Ohms. Ohm's Law states that Amps = Volts / Ohms. (I=E/R) An anodizing setup is an electric circuit, as such it obeys Ohm's Law. In all things electrical; current (Amps) does the work, potential (Volts) serves to overcome the resistance (Ohms). Anodic coatings are formed by current, not voltage.

Relating this to anodizing. An electrical resistance exists when the anodic coating is forming, it is caused by the electrolyte being restricted by the porous anodic coating from reaching the base metal. As the coating grows, this resistance increases. his resistance sets the voltage when a given current is flowing. For 20 ASF, 9.4% electrolyte concentration by volume, and 70 deg. F., this resistance is about 0.95 Ohms per square foot. Its value is inversely proportional to surface area (2 sq.ft. = 0.475 Ohms). It varies a little with alloy as well.

Paul Yursis

[GramSlam]

In addition, if anyone feels they can make the calculator work better, feel free to do so. Also, if anyone knows how to program it into a small application of its own, that would be good too.

[Fibergeek]

GrandSlam,

You 720 Rule calculator works good, thanks.

One little point; the Greek letter mu (u) is the abbreviation for micron, not mil. A mil (one thousanth of an inch) doesn't have an abbreviation.


I'm not sure what you are doing with the second calculator, can you explain?

[GramSlam]

Thanks for the feedback.

The second calculator is for calculating the surface area of the parts, hanging wire, racks, ect. In order to perform this calculation, you have to take the known values from a previous run.
This may seem redundant to do after the run is complete, but if you plan to run several batches of the same parts, you will be able to fine tune your surface area measurement of the anode (parts being anodized plus hanging wire or rack).
I think it works. I have tried it several times on the same parts using different current densities to arrive at very similar results.

For the past few months, I have been keeping very detailed logs of each anodizing run I complete. I have noticed that my peak voltages are more predictable since I have been using this formula.
Test it out. I would like to know how it works under different acid concentrations, and different series of Aluminum.

Formula for surface area:

Vmax = Peak Voltage
Ift² = Current Density
Asys = System Current
Sin² = Surface Area

Sin²=(144/Vmax 0.4)Asys
or
Sin²=(144/Ift²)Asys

[destroyer125]

Im kinda confused on how to use this...i dont know if it downloaded wrong or anything.....but wordpad is the only program that will show it...and theres lots of little things i dont understand.....all I can say is my computer does not like it....alot of stuff shows up as weird characters and symbols

[luminous]

It's an .xls file, and it needs to be opened in a spreadsheet program like Excel to use it. If you don't have a spreadsheet program that accepts .xls files and you would like an *excellent* free open source spreadsheet program then I suggest you go here:
http://www.openoffice.org/

[GramSlam]

-------------------------BETA TESTERS NEEDED-------------------------

Over the past eight months I have been developing software based on the “720 Rule calculations” that I learned from M_D and our unforgettable friend Fibergeek.

The purpose of this software is to make any anodizing run highly accurate and precise, without compromising simplicity. The first version of this software will require the operator to populate three data fields (Estimated surface area, Current density, and desired thickness) at the beginning of the run, and update two data fields (Voltage, and Temperature) during the run.

I require three very active anodizers with a very good understanding of anodizing theory, and high quality equipment to allow for accurate measurements.
I will also require two people who are relatively new to anodizing, but are dedicated to following procedures, and learning more about anodizing theory.

To apply for Beta Testing, please send me a PM with:
-Description of your anodizing experience
-Full description of your lab setup
Candidates chosen for the Beta test will be asked to sign a NDA. (Nothing personal)
I would also like to extend an invitation to Caswell and to M_D to join the beta testing.

There will be two versions of the finished product. One will be strictly an application; the other will have full automation capabilities when used with GPIB and/or DAQ. Both will be dedicated to the memory of our friend and mentor, Fibergeek.

Thank you,
Graham

[cameraman]

...if anyone knows how to program it into a small application of its own, that would be good too.

Here you go. I started to write it as a standalone application, but that would limit who could use it and some people might be nervous about viruses and such. So it's written in javascript - anyone with a browser (the vast majority of them execute javascript) can use it, and the source code is out in the open for all to see.

720 Rule Calculator

[GramSlam]

Thanks for the Java Version! Good job.

Well. I know have the .exe version ready for download.
I scaned it with Norton, but if it makes you feel safer, run a scan before you download it.

There will be more versions to follow. The next version that will require the beta testing will have data logging to keep records of all your information. It will also graph out your voltages, time, resistance, and temperature.

You can download it here

link removed - site no longer available

Enjoy, Please post any comments here.

Graham Skjenna
aka. GramSlam

[rayginn_mfg]

I am new to anodizing, and I had no clue what all the terms and electrical settings. So I used your 720 rule program to set my settings. I was amazed at the quality of the anodize after color and sealing. I believe the parts I have done on my first day of using the LCD kit are better than the stuff I just picked up form my local anodize house. I will be posting pictures soon.