720 rule vs LCD

[sage]

I hate to open up this whole discussion again, but being of scientific mind I can't help being perplexed by the question "what IS the correct way to achieve a properly anodized chunk of aluminum".
I used to calculate every thing based on amp-minutes per square inch with the knowledge that so many amp-minutes (current x time) would produce a reasonable result. This was based on experience and results. The calculation was simple enough. I used 8 amps-minutes x the square inches of the part and divide by the current of my choice based on power supply abilities tank size and a few other things. The number 8amp minutesscame from test results.
Then I got on this forum and everyone was using the 720 rule and that actually seemed to make more sense since it dictated a particular current density. From a scientific point of view I figured that the actual density of the current or electrons hitting the surface and doing the anodizing would best be controlled accuratly. The 720 rule does this (I think). This was in contradction to my old method which had somewhat variable CD's if you plug the numbers I was unsing into the 720 calculator.
Then along comes the LCD method and the statements posted in this forum:
1amp for 50 sqin for 240 minutes = 1mil
1amp for 25 sqin for 120 minutes = 1mil
These are two completely different current densities and look more like my old method of amp-minutes per square inch calculations.

Now I know that either method works fine but it still begs the question what really is the best / proper method of doing this.

I've standardized on the 720 rule because it seems to be more based on something scientific and I'm getting great results and the calculator is available and it's easier to recalculate if the process changes. But I always used to get good results with my old method too.

Sorry to start this debate all over but my technical mind is not satisfied yet.


Sage

[sswee]

They are basically just different paths to the same place. I don't know the exact origin of the 720 rule but if memory serves Fibergeek tested it to considerable lengths and found it to be correct. Kebo found it to get within +-7% of the target thickness. So scientifically it must be sound. At 1A per square foot current density anodic coating will grow to 1 mil in 720 amp minutes. From this, the only way to effect run time is to vary CD or the thickness of the coating. What needs to be understood also is the effects of different CD's on the coatings growth. ie: pore size. It's my opinion that if you only do a hand full of parts or a part once in a great while you may be able to get by not knowing all the ins and outs but to truly do it right it's almost a necessity to know and understand the process including the calculations. How else can you accurately diagnose a problem if one should arise. The only problems I have had that I did not know how to handle completely have been due to material grade, primarily cast parts. The other problems have been few and far between with little doubt as to their cause.

If you work all the numbers, all the methods are working off current density. The difference is perspective.
These figures were started by MCaswell to try and alleviate newbies confusion with the calculations. To simplify if you will and make the calculations in line with the other plating.
1amp for 50 sqin for 240 minutes = 1mil ( a 2.88 CD )
1amp for 25 sqin for 120 minutes = 1mil ( a 5.76 CD )

Your old method took me a little to sort out but was close in line with the 720 rule. It appeared to me that you were looking more from the perspective of what your PS would do and the time you wanted to do it in while possibly overlooking the basics or not concerned with them as in the CD being run. I mean no insult nor disrespect by what I say just letting you know how it looks from my point of view. You could not be that far off to have gotten the results you have for the time you have been doing anodize. You just had a different approach than I.

SS

[sage]

You are right. The 720 rule is the better way to get consistant results and I realize the variablity in my old way. I think I was restricted to getting good results by the limitation of my power supply - which USED to be an automatic battery charger that luckily seemed to regulate voltage and current to coincidently put almost every batch within the 720 rule calculations. Dumb luck I guess.

BUT - what of the Caswell figures? As you too have calculated these are very different CD's. I believe there was one other set of figures quoted which give yet another CD. If so many CD's are acceptable this tells me that there may be somehing else going on that is the REAL key to proper anodizing.

I understand your point that all the methods are based on the same concepts. I think we all realize it's current and time. But to say that they are all the SAME is not true especially when they cannot be proven by using the numbers from one method in the calculations for another.

So I haven't really been convinced WHY the 720 rule is THE way to do things and that it properly describes what is going on when there are so many contradictory methods that achive good results.

I guess results and repeatability is what really counts. The 720 rule works for me so I'll stick with it and accept the results.


sage

[sage]

Oh - BTW - one other thing that bothers me about the way the 720 is being presented on this forum is that in almost all cases when someone asks about the 720 rule the following is quoted.

minutes = 720xmls/ASF

This really evaluates to a constant based on what constants one picks for mils and ASF. This only answers the question of HOW LONG.

What we really need to do be poining out to newbees is the other half of the equation which is they need to multiply the ASF x the area of their part and set their current for that. Only then do they have all the information they need to produce results.


Sage

[sswee]

Look at it this way and see if it makes any more sense. When building a motor for a car, all the parts need to be matched to work together to get the maximum benefit as a whole. The CD would be the carburetor. Carbs come in all different sizes rated in CFM. Basically how much air/fuel it will flow for the engine. This needs to be matched with heads, cam, CID, and exhaust flow so they all work together on the same level. The lower CFM carbs are no better or worse than the higher CFM carbs. The size of carb has to be matched to the engine it it used on, the same as a CD needs to be matched to the setup being used. IE: tank size, PS, acid concentration, agitation and cooling that can be achieved.

As for the calculations, there have been numerous posts on how to calculate all the needed information. It has been awhile since I have made or seen one giving them all together. It may just be no one has asked lately.

LCD (Low Current Density) anodizing is considered using current densities between 3 to 6 ASF (amps per square foot). It has been determined that using a CD below 3 ASF does not produce a suitable coating for dyeing or durability.

720 rule
Anodic coating will grow to a 1 mil thickness in 720 amp minutes at a current density of 1 amp per square foot

Anodize time
720 / CD * desired coating thickness from .1 to 1 mil
Ex. 720 / 4.5A CD = 160 minutes 160 * .7 = 112 minutes of anodize time

CD to amp setting on PS
4.5 CD is 4.5 amps per square foot
4.5 / 144" (inches in a square foot) = .03125A per square inch
.03125 * SA of the part in square inches = amp setting on the PS for the run.
Ex. Widget part with 30" of SA
4.5 \ 144 = .03125 .03125A * 30" = .94 amp (rounded off) setting on the PS to anodize a widget. If you have 3 widgets, multiply .94 by 3 to get the amp setting.

SS

[sage]

720 rule
Anodic coating will grow to a 1 mil thickness in 720 amp minutes at a current density of 1 amp per square foot

Anodize time
720 / CD * desired coating thickness from .1 to 1 mil
Ex. 720 / 4.5A CD = 160 minutes 160 * .7 = 112 minutes of anodize time

CD to amp setting on PS
4.5 CD is 4.5 amps per square foot
4.5 / 144" (inches in a square foot) = .03125A per square inch
.03125 * SA of the part in square inches = amp setting on the PS for the run.
Ex. Widget part with 30" of SA
4.5 \ 144 = .03125 .03125A * 30" = .94 amp (rounded off) setting on the PS to anodize a widget. If you have 3 widgets, multiply .94 by 3 to get the amp setting.

Ok, there we have it all in one place.
Thanks for that.
Hopefully that will clarify it for Newbees.

Now, if you stick with me for a minute, let me ask a few questions - not for our benefit - because you and I fully understand what's going on, But, like a FAQ, things can be clarified a bit more.

Q: Using the example above - What happens if I don't want to wait around for almost two hours (112 minutes) to get the job done? If I believe the "720 rule" and the "anodizing time" as stated above then I can half the time required by doubling the current because the rule is based on amp-minutes i.e. instead of 4.5 amps per sqare foot we use 9 and get the same number of electrons over there in half the time. eg.

720 / 9 CD = 80 minutes * .7 = 56 minutes instead of 112 minutes

All things being equal (and please don't confuse the issue with any other factors (temp, bla, bla)

This will produce exactly the same results True? of False?


Sage

[sswee]

Originally Posted by sage

Q: Using the example above - What happens if I don't want to wait around for almost two hours (112 minutes) to get the job done? If I believe the "720 rule" and the "anodizing time" as stated above then I can half the time required by doubling the current because the rule is based on amp-minutes i.e. instead of 4.5 amps per sqare foot we use 9 and get the same number of electrons over there in half the time. eg.

720 / 9 CD = 80 minutes * .7 = 56 minutes instead of 112 minutes

All things being equal (and please don't confuse the issue with any other factors (temp, bla, bla)

This will produce exactly the same results True? of False?
Sage

This is a loaded question that cannot be answered true or false without an explanation. As far as, will these calculations produce good results, true they will. Now for the huge word, IF the setup is sophisticated enough to handle the temp and bla, bla you don't want to consider at this time.
Again with the cars. A high school kid walks in the shop and asks if a Holly 750CFM double pumper is a good carb and will it work on his small block Chevy. I can tell him yes it's a good carb and yes it can run on a small block Chevy but what I can't say is yes it will work on his small block without knowing what all is in the engine and the kind of exhaust. If he has a stock engine, I can tell him to go with a 600 or 650 CFM carb. Back to anodizing. Using a nice setup like Caswell sells they can use the 720 rule and a current density from 3 to 6 ASF(depending on what their power supply will handle) to get the same good results with any of the recommended current densities.
A big carb on a stock engine is only trouble. Using a current density larger than the setup can handle is also trouble.

These are graphs of test results from a man much smarter than I. He went by Fibergeek and helped me to understand the process.

http://forum.caswellplating.com/phot...user/5846/sl/f

http://forum.caswellplating.com/phot...user/5846/sl/f

http://forum.caswellplating.com/phot...user/5846/sl/f

PS: The 720 rule is not in oppostion to LCD anodizing. It is an integral part of CC anodizing.
SS

[sage]

I posted a reply to this a couple of minutes ago. As usual I take too long to get my reply the way I want it and then when I finally submit it, the system makes me log in again. When I do, it compains that an invalid thread was specified and sometimes the message never shows up.

What's up with that - it really annoys me?

I'll look over the graphs you submitted and see if my message shows up. If not I'll start over again.

Later

Sage

[cameraman]

Originally Posted by sage

the system makes me log in again

Put a check in the 'remember me' box.

[sage]

I appreciate and understand your efforts to point out that a lot of things need to be considered in the anodizing process, but I was intentionally trying to avoid the "other" things because I was trying (however poorly) to stress that the 720 rule is a FORMULA as much as it is a RULE ,and to give an example to show it.
I'm not sure the point was made so let me try again.
Say you decide to standardize your process at a CD of 6 and that you will always grow 1mil of ano surface. If you do this then you might as well just say:
"Anodizing takes 120 minutes" and forget about the rule.
Becasue you'll always get 120 minutes as long as you stick with CD of 6 and 1mil using the calculator because it forces you into a particular current to satisfy the 120 minutes and 1mil parameters.
The point I was trying to make (and get someone to confirm my theory on) is that the current does not have to be fixed, and you can, for example, double the current and half the time required because the 720 rule is a FORMULA based on amp-minutes per square foot.
Amp-minutes means you can adjust the amps or the minutes and, as long as you end up with 720 you should get good results. So you don't have to be stuck with 120 minute anodizing jobs on rediculously small items just becasue the calculator says 120 minutes at .03 amps or something ridiculous like that. My theory is that you should be able to double the current to a wopping .06 amps and do the job in 60 minutes or perhaps even 30 or 10 minutes by increasing the current to double or triple what the calculator comes up with (yes - other things considered of course)
You can try this witn the calculator. Increase the "set current", by adjusting the current density number. You'll see that when you have doubled the set current you get half the time. The mils stays the same and obviously the size of the part doesn't change.
Keep in mind I'm not saying this is actually correct in practice. I'm really looking for someone to confirm or deny this theory is true. I'm sure there must be boundary's on this and even other factors like maybe above or below a certain current the anodized layer does not grow properly or something. These are the factors that really need to be considered and pointed out along with the "Rule"
I think it's already been shown that anything from 3-18 A/sqft works to some degree. This is a huge range and if in fact all figures in that range really aren't created equal then I think the pros and cons of anodizing at either end of the range needs to be passes along with the RULE.

I think I've flogged this enough (but I'm still wondering what the answer is)

PS> Thanks for the "remember me box tip"

Sage