Anodizing calculations (720 Rule)

[manishnjain]

Ok thanks for that. See i have a 3000 lt anodizing tank capacity so at what propotions should i use...

Distilled Water:-
Sulphuric Acid:-
Oxulic Acid: -

[sreeja]

Thank you for the information.I am new to this field of anodizing.I also don't know about 720 rules.Please tell me deiaily about this.

[mnsherick]

I'm not sure I understand the calulations correct me where I'm wrong.

1) Is the amount of acid bath/ano tank used for calulating time?
2) The Sq Ft. of the part and racking need to be known first?
3) Is 20 ASF the standard for ano, or is 4.75 I recall that number from caswells site somewhere.
4)


From what I understand my part is aprox. 81 Sq. Inches or .57 Sq. Ft.

So to ano 5 mils for 18 min I would need 11.4 amps @ 18.93 Volts.

Or 1 mil thick for 90 mins would be 2.7 amps @ 4.48 volts.

this is the largest part I will be have to ano, so I'm using this as a starting place to get my setup going.

5) Also would there be any noticable changes in using lower voltage/amperage over using higher voltage/amperage, or is it just for times sake?

any help is appreciated.

thanks

-Matt

[sswee]

Originally Posted by mnsherick

I'm not sure I understand the calulations correct me where I'm wrong.

1) Is the amount of acid bath/ano tank used for calulating time?
No. Tank size is only used to mix the proper acid ratio.
2) The Sq Ft. of the part and racking need to be known first?
Yes on the area of the part. Racking very seldom needs to be considered.
3) Is 20 ASF the standard for ano, or is 4.75 I recall that number from caswells site somewhere.
The standard amps per square foot (ASF) for LCD anodizing is 3 to 6 ASF. 4.5 ASF is the most commonly used in learning.
The ASF used is determined by PS capabilities, cooling or agitation and part size.
4)From what I understand my part is aprox. 81 Sq. Inches or .57 Sq. Ft.
So to ano 5 mils for 18 min I would need 11.4 amps @ 18.93 Volts.
Or 1 mil thick for 90 mins would be 2.7 amps @ 4.48 volts.
this is the largest part I will be have to ano, so I'm using this as a starting place to get my setup going.
ASF and desired thickness of coating dictates the time of a run.
a 1 mil coating grown at a 4.5ASF has a run time of 160 minutes.
ASF and size of the part determine the amount of current needed.
A surface area of 81" at 4.5ASF has a current setting of 2.53 amps
ASF and set up circuit resistance controls the needed voltage.
With good electrical connections and a proper LCD acid ratio mix in the tank, a 4.5ASF should have a peak voltage demand of approx. 11.25V.

5) Also would there be any noticable changes in using lower voltage/amperage over using higher voltage/amperage, or is it just for times sake?
The lower the ASF the longer the run time needed to achieve the same thickness of coating.

any help is appreciated.

thanks

-Matt

If this is confusing, just say so and more explanation will be given. No problem.
SS

[mnsherick]

Thanks so much for the quick and detailed reply. A few more things.

1) What is the proper ratio for LCD ano, I'm using 20% Acid to 80% dist. water by volume as of now. Something I found on a site before I stumbled onto caswell.


"ASF and desired thickness of coating dictates the time of a run.
a 1 mil coating grown at a 4.5ASF has a run time of 160 minutes.
ASF and size of the part determine the amount of current needed.
A surface area of 81" at 4.5ASF has a current setting of 2.53 amps
ASF and set up circuit resistance controls the needed voltage.
With good electrical connections and a proper LCD acid ratio mix in the tank, a 4.5ASF should have a peak voltage demand of approx. 11.25V."

2) So I would set it to run at 2.53 amps for current, and 11.25volts max for 160 min according to the formula? = 1 mil

3) Is there any known problems with long runs like this?

4) Would I set the voltage at 11.25? Because I notice you said peak voltage demand or approx. 11.25V. I think this is the only part I don't quite understand at this point.

Also I am looking at this power supply

Amazon.com: MASTECH VARIABLE REGULATED DC POWER SUPPLY 0-30V 0-20A: Home Improvement

Which I assume you can control and monitor voltage and current would this be the correct type?

[sswee]

Originally Posted by mnsherick

Thanks so much for the quick and detailed reply. A few more things.

1) What is the proper ratio for LCD ano, I'm using 20% Acid to 80% dist. water by volume as of now. Something I found on a site before I stumbled onto caswell.
Battery acid is mixed by volume, 1 part acid to 3 parts distilled or RO water. Your 20/80 mix is close enough to work but will have a slightly higher resistance. That will raise the needed voltage a little.

"ASF and desired thickness of coating dictates the time of a run.
a 1 mil coating grown at a 4.5ASF has a run time of 160 minutes.
ASF and size of the part determine the amount of current needed.
A surface area of 81" at 4.5ASF has a current setting of 2.53 amps
ASF and set up circuit resistance controls the needed voltage.
With good electrical connections and a proper LCD acid ratio mix in the tank, a 4.5ASF should have a peak voltage demand of approx. 11.25V."

2) So I would set it to run at 2.53 amps for current, and 11.25volts max for 160 min according to the formula? = 1 mil
Yes, no and yes. If using an adjustable CC/CV PS, with the unit off you would turn the voltage all the way up and the amperage all the way down. Make the connections and turn the PS on. Slowly dial the amperage up to the needed setting (2.53A) and run for 160 minutes. The voltage will take care of itself by delivering whatever is needed to maintain the amperage setting. The voltage reading can tell you how things are going. As the coating grows, the resistance increases and it takes more voltage to maintain the set amperage. If the voltage maxes out you have lost connection in the circuit, most the time the connection to the part.

3) Is there any known problems with long runs like this?
No, except boredom or getting busy with something else and forgetting it is going. I've ran parts 3+ hours at the lower ASF.

4) Would I set the voltage at 11.25? Because I notice you said peak voltage demand or approx. 11.25V. I think this is the only part I don't quite understand at this point.
As above you would turn the voltage all the way up. Peak voltage using LCD acid ratio and good electrical connections is approx. 2.5X the ASF used. BUT tank temp, acid and aluminum content of the tank, electrical connections and material grade of the part all affect the circuit resistance. That is why it is approximate. It is also the reason CC anodizing is easier/better, it compensates for all these parameters variances. In CV anodizing, all the parameters must be more controlled.

Also I am looking at this power supply

Amazon.com: MASTECH VARIABLE REGULATED DC POWER SUPPLY 0-30V 0-20A: Home Improvement

Which I assume you can control and monitor voltage and current would this be the correct type?

It will work great. A PS that is CC/CV like that one will have control knobs for amps and volts. I use the same one but under a different brand name. It will do what you want.

[mnsherick]

Thanks for all the help.

BTW I think I mixed my acid 1:3 I was guessing at around %20 now that I think about it, it was 1:3 parts.

[AdrenalineChild]

hey hoping someone who knows their stuff looks here... i have the ps found here.

http://caswellplating.com/kits/rect.htm the third one down the 25 Amp Constant Current Rectifier. just wondering... using the 720 rule calculator.

i input the following;

Surface area: 300 inches2 (or 2.08 ft2)
Thickness: .5 mil
Current Density: 6 (the calculator was preset at 6, dunno what i should put there.)

then it gives me:

Set Current: 12.5 Amps
Time: 60 minutes
Peak Voltage: 15 Vdc

so what do i want to do with these now? sorry for being a nub just wanna do it right, thanx!

[sswee]

Surface area: 300 inches2 (or 2.08 ft2)
Thickness: .5 mil
Current Density: 6 (the calculator was preset at 6, dunno what i should put there.)

then it gives me:

Set Current: 12.5 Amps
Time: 60 minutes
Peak Voltage: 15 Vdc

CD is the amount of current being run through the part per square foot. With that PS I would go to 4.5 or 5 ASF so your voltage available does not max out. Turn your PS to 15V and your amps all the way down. Make the connections and turn the PS on. Slowly adjust the amps up to the 12.5A set current and run for 60 minutes. These numbers will change with different CD's. Don't worry about peak voltage unless it is at or over your PS capabilities.
SS

[dmiom]

Originally Posted by AdrenalineChild

..... i have the ps found here. ....the 25 Amp Constant Current Rectifier. just wondering... using the 720 rule calculator.....
the calculator was preset at 6, dunno what i should put there.......

The 6 in the current density field is 6 amps per square foot (often abbreviated to ASF). Those who use the Caswell LCD ("Low Current Density") process, anodise at current densities typically in the 4.5 to 6 ASF range. 6 ASF is a convenient and relatively safe default, and would suggest you start by using 6 ASF unless you have good need otherwise. One of the main reasons is that, as Acidrain has pointed out before, at 6 ASF a half-thou layer is exactly one hour and a full 1 thou layer is exactly two hours. If you go above 6 ASF without a pumped chiller you risk overheating the tank and getting a poor, chalky surface. The only reason to drop it below 6 is if you are having trouble keeping the tank cool enough. At any particular anodic resistance, the power dissipated is proportional to I squared - so the heat your pumping into the tank at 4.3 ASF is only half the heat you would get at 6 ASF. Lower currents are slower, so keep it at 6 if you can.

Originally Posted by AdrenalineChild

......then it gives me:

Set Current: 12.5 Amps
Time: 60 minutes
Peak Voltage: 15 Vdc

so what do i want to do with these now? ........

First of all, you need to get your head round the idea that what you want in basic LCD process is Constant Current - and that unit looks a good one for that. Most of these modern power supplies allow you set a constant voltage or a constant current. In effect, what you're doing when you set the limit for constant current or constant voltage is saying the the supply 'pump as much as you can into the load (tank) up to the limit(s) I've set'. If you were testing some electronics on the bench, you might set it for 12v and then set a safety limit to the current of 1A. However, when we're doing constant current anodising, we want the power supply to always force the current (12.5 Amps in your case) through the tank. So ... set the current limit at 12.5A and set the voltage control to the maximum - that way it will only be the curent limit that comes into force. If a supply has an actual switch for CC/CV (Constant Current or Constant Voltage) then make sure it is in the CC position.

In terms of the actual procedure, especially as the current gets higher, if you just turned it on and let the current rush in, depending on your racking arrangements, you could get contact-point burns or even blow aluminium wire away - so its always best to

• Power supply off or isolated from the tank
• Set the voltage knob to minimum
• Set the current knob to minimum
• Switch on
• With the current still down at minimum, turn the voltage up to max (or at least, say, 20v if it will go that far)
• SLOWLY turn the current up until you get to your target current (12.5 A in your case)

Slowly is relative - just a few seconds should be enough.

The 60 minutes is the meat of the 720 rule - that is the time from when you get the current on till you turn it back down again (remember though that you shouldn't leave it in the acid after the current is turned off as the ano layer will be eaten away)

The Peak voltage is just an indication. It has absolutely nothing to do with setting your power supply - it is just the peak voltage you might possibly see - its affected by the workpiece itself, temperature, acid and most especially by the type of racking (eg Ti from Servisure) you use.

The peak voltage is also useful because it can help indicate the amount of heat being pumped into the tank by the anodising process. In your case you'll be heating the tank at peak at nearly 200 watts ...... I suspect that unless you've got a big tank, or lots of circulation, you may need to take steps to control the temperature.

cheers / Dave

EDIT ( SS - we crossed because your message was more concise than mine !)