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)
Two options (same info) 
1. http://www.flamingpaperbag.com/720ru...calculator.htm
2. http://www.caswellplating.com/720.html
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").
Rearranging 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
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Anodizing calculations (720 Rule)
Last edited by lcaswell; 12032013, 12:44 PM.Tags: None
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Re: Anodizing calculations (720 Rule)
I'm thinking about trying my hand at anodizing I've got a tube 6in long 1.7 dia with 1.1 Id I'd like to test with I'm thinking this would be around 1sq surface ft. not sure about that and need to know if I could do it with a 10a car charger or a 3a 30v psu (it may be 5A I'll have to check).

Re: Anodizing calculations (720 Rule)
The PS is one part that dictates the current density that can be run. Yours at optimum ability can run a 72sq. inch part at 10A ASF. I would run at a 8A current density to give the PS room to compensate for connection and temperature. A 13 sq. inch part would have a set amperage of .72A and run for 90 minutes to get a 1 mil coating.
SS
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Re: Anodizing calculations (720 Rule)
Hi,
My PSU can get 25V and 5 amps.
PSU is not the problem, the problem is the current ratio per square centimeter, or inch. I was doing calculations, and by the calculations stated here, its should go very low amp per square centimeter, or better, decimeter.
I read that it was 2Amps per sq decimeter, and by the calculations here I should go almost 1 amp per sq decimeter.
Thanks,
Marko
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Re: Anodizing calculations (720 Rule)
Originally posted by lopata View PostHello,
I am having difficulty understaing what is true or not.
As I want to anodize ma part without going to mate surface.
My part is 13 sq inches, and calculator says 0.54 per 13 sq inches.
Is this correct?
In the 1st post you said 20 AM per square feet.
Cant figure out which one is true.
Also, I was using 0.023 A (1.92 amps per 13 inches) per square centimeter.
Can you help me out.
Thanks,
Marko
SS
Leave a comment:

Re: Anodizing calculations (720 Rule)
Hello,
I am having difficulty understaing what is true or not.
As I want to anodize ma part without going to mate surface.
My part is 13 sq inches, and calculator says 0.54 per 13 sq inches.
Is this correct?
In the 1st post you said 20 AM per square feet.
Cant figure out which one is true.
Also, I was using 0.023 A (1.92 amps per 13 inches) per square centimeter.
Can you help me out.
Thanks,
Marko
Leave a comment:

Re: Anodizing calculations (720 Rule)
iOS version approved "AnoCalc"
https://itunes.apple.com/us/app/anocalc/id789806232
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Re: Anodizing calculations (720 Rule)
Android version approved.
https://play.google.com/store/apps/d...ulting.anocalc
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Re: Anodizing calculations (720 Rule)
I am working on an iPhone, Android, Windows Mobile app. Its submitted and should be approved in a couple days here. I will keep everyone posted.
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Re: Anodizing calculations (720 Rule)
I know this is a bit old, but I would appreciate if someone could reupload the Excel file. Pretty please?
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Re: Anodizing calculations (720 Rule)
Hi,
I have a question about this 720 rule. Can this rule be applied to all acid concentrations for one preset ASF? I know that high acid concentration makes larger pores at the same ASF than low concentrated acid... and also dilute the oxide layer much quicker. So I presume that for the same ASF the duration of anodizing should be longer because of the dilutation, that fights back the anodiziation process. Therefore for higher concentration the ASF is set higher. Is this correct or maybe I am thinking in the wrong way.
Thanks.
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Re: Anodizing calculations (720 Rule)
Daniel, please carry this to a new post I started for you.
Thanks
SS
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Re: Anodizing calculations (720 Rule)
Originally posted by dmiom View PostFirstly, have a read of this thread
The 720 rule is not about setting the current.
The 720 rule tells you how long to anodise for at a chosen current density.
All of your parts should be racked so that, electrically, they are wired in parallel  i.e. each one connects back to the positive tank bar or however you're racking them  never try daisychaining the parts.
The constant current you set on the supply is based on the total wetted area of all your parts times your chosen current density. A good current density to start from is 6 Amps per square foot. If all your parts add up to, say, 72 square inches (half a quare foot) and you wish to use a CD of 6 ASF, then the constant current limit you should set on your supply would be 3.0 Amps. If your power supply struggles to maintain that constant current, or you are generating more heat than you can take out of the tank, maybe reduce the CD to 4.5 ASF
Dave
My power supply is a 50amps. It should have no issues anodizing the small parts i'm doing. There is a current meter on the front of the power supply, and also an adjustment knob. The current meter's reading seems dependant on the load, so the smaller the parts i am doing, the lower the meter sits. I cannot turn up the current with the adjustment knob, i can only turn it down. Now what i dont understand is what amperage do i go by when calculating the 720 rule... the 50amps my power supply is capable of, or the .5amp load that is on the meter, or neither? I cant set it to 4 or 6asf to my knowledge.
Leave a comment:

Re: Anodizing calculations (720 Rule)
Firstly, have a read of this thread
The 720 rule is not about setting the current.
The 720 rule tells you how long to anodise for at a chosen current density.
All of your parts should be racked so that, electrically, they are wired in parallel  i.e. each one connects back to the positive tank bar or however you're racking them  never try daisychaining the parts.
The constant current you set on the supply is based on the total wetted area of all your parts times your chosen current density. A good current density to start from is 6 Amps per square foot. If all your parts add up to, say, 72 square inches (half a quare foot) and you wish to use a CD of 6 ASF, then the constant current limit you should set on your supply would be 3.0 Amps. If your power supply struggles to maintain that constant current, or you are generating more heat than you can take out of the tank, maybe reduce the CD to 4.5 ASF
Dave
Leave a comment:

Re: Anodizing calculations (720 Rule)
ok i read a bunch but havent found the info i was looking for.... i am anodizing a bunch of small, similarly sized parts. I have a 78 gallon tank, and i am using an Astron vs50m power supply. With one of the parts in there, the amp meter barely moves. Maybe .5A max. With 12 pieces in there, it goes up to approx 5 amps. So what do i use to calculate the 720 rule? It's a 50amp power supply, but it doesnt seem like it'll put out any more amps than the parts will draw.
Also, if i'm anodizing a bunch of different sized parts, and the current goes up because of the larger parts, how to i know what the amperage is for the smaller parts?
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