720 rule vs LCD

[sswee]

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. Sage

No the current density does not have to be fixed to get good results. The 720 rule works and is a useful tool due to the ability to change current densities. Cutting run times are not the only reason for changing current densities. If the part is too large to do at 6 ASF with the power supply available, a drop to any current density down to 3 ASF would render equal results. Some may need to reduce CD due to running a small tank and the part being on the verge of too large for the tank. This sometimes creates to much heat for the tank to dissipate. Dropping to a lower CD will lower the heat being generated and usually make the run possible. The only reasons to go to a higher CD are shorter run times and smaller pore sizes(more to smaller pore size than just a higher CD). There are many more reasons to drop to a lower CD. Whichever is the case, the 720 rule will work. The old saying of, you can have cheap or you can have fast but you cannot have cheap and fast, comes into play. Anodizing is like many other things in that a good job can be done and great results can be had for a reasonable amount of money at the expense of time. If time is a more valuable, you are going to have to pay for it by spending more money on equipment.
SS

[mcaswell]

see:-


ANODIZING FORUM STICKY


The 720 Rule & PAR are DONE!


which confirms the last posting here

[sage]

ANODIZING FORUM STICKY


The 720 Rule & PAR are DONE!


which confirms the last posting here


With all do respect mcaswell the post above is what I'm directly debating (and also the instructions for LCD), because instructions like these although they simplify the process, over simplify it to the point that you are stating that "anodizing SHALL take X minutes" no if's and's or but's.
The manual for LCD says the same thing (last time I looked). Put your parts in the bath adjust the current to x amps per square inch and you SHALL wait 90 minutes.
I can appreciate you need to make it simple for people but I personally don't want to wait around for 90 minutes for a tiny little part to finish anodizing when I don't have to (and my equipment - even the LCD equipment) will do it faster.
I think there is a benefit to point out that the 720 rule is a formula that can be adjusted to suit the equipment capabilities and the patience of the user - and still get good results.

Sage

[mcaswell]

The 720 rule is an equation, therefore it can be altered around to suit what answers you are looking for.
So, you CAN alter the time, AND the surface area, to tell you how long and how thick.

The New LCD Anodizing Power Requirements

1 amp for every 50 sq " for 240 minutes = 0.001"
or
1 amp for every 25 sq" for 120 minutes = 0.001"

Both calculations grow a 1/1000" film

For dying and light service
cut the time by 25%

ie:
1 amp for every 50 sq " for 180 minutes =0.00075"
or
1 amp for every 25 sq" for 90 minutes =0.00075"


There! It's that simple!

I guess the questions a newbie needs to answer first are,
1. surface area
2. Required anodize film thickness

Bear in mind that if color is the main deal, Fibergeek always reckoned it was pretty much a waste of time going any further than 0.00075" as the die does not penetrate any deeper. It is also a good servicable thickness for most applications. Anodizing at this thickness therefore cuts down the time factor considerably, so you can alter the 720 formula to bear this in mind.

Therefore the newbie rules can be altered from

1 amp for every 50 sq " for 180 minutes =0.00075"
or
1 amp for every 25 sq" for 90 minutes =0.00075"

to-
ie:
2 amp for every 50 sq " for 90 minutes =0.00075"
or
2 amp for every 25 sq" for 45 minutes =0.00075"

or

1/2 amp for every 25 sq " for 180 minutes =0.00075"
or
1/2 amp for every 12.5 sq" for 90 minutes =0.00075"

etc etc

It's as clear a crystal to me, but I'm blind in one eye!

Is that what you guys are debating here?

[sage]

Well, it wasn't much of a debate really. I was trying to make a point and seems like everyone so far agrees that the 720 "Rule" is not really a rule but it is a formula that can be altered to suit patience and the equipment at hand.

Having said that - even though you agree (mCaswell) you didn't pick up on my point that (last time I looked) the LCD documentation doesn't stress that it's a formula. It simply states that you SHALL set your current to X amps per square inch and you SHALL wait for Y minutes, PERIOD ! - no mention of the full formula so newbees can get an the idea they can play with it at all.
Even the short list of amps and times you listed in your last post - when you list it that way, seem to dictate "do it this way or this way and that's all there is to it".

I don't know. I guess all I'm saying is that it's fine to give some exact figures to get someone on the right track, but it's equally important that people are made aware that it's a formula that they can adjust to suit themselves and their equipment.

Simple point - took forever to get it across though

And now that it's here on the board maybe someone will read it and then - Mission accomplished I guess.

Sage

[mcaswell]

Thats what I thought you were trying to say. I wholeheartedly agree with you. It needs to be expanded on. Sometimes we write this stuff and it's pretty obvious to US, but we don't see it from the other perspective.

So, seeing as you caused me all this trouble (joke - joke) how about you rephrase it for me??

[sage]

I'm not the author of the rule so I'll take no credit for it. The sticky "720 rule" lays it all out and also it is re-iterated within the first few posts in this thread. I point everyone those two references

BUT - since you asked for my take on it. I can make it really simple but I warn now that I lost everyone on this a while back and so I'm going to lay it out the best I can but I'm not going to dwell on it.

OK here goes:

For now lets assume 1 mil of desired coating so we can forget it (it's 1 so it doesn't affect the formula)

720 is the really important piece to the 720 rule. It has to stay.
It's the amp-minutes per square FOOT and it's key to what is growing the coating. That's fibregeeks contribution through experimentation - Thanks!

BUT:
Using square feet is really rediculous unless your running a huge operation. You only only end up dividing by 144 to get to square inches in the end anyway so lets do it now.

720/144 = 5

Now the magic number is 5 amp-minutes per square INCH.

So now we know that we need 5 amp-minutes PER sqaure inch to get good results. I think this is where I lose most people because they don't understand the amp-minutes concept, but I'll press on.

Now the simple formula is:

5 * square inches / current = minutes

Example:
Lets say we have 10 square inches to anodize.
Now here is where you need to know what your system is capable of doing in terms of amps etc. Lets say you have no problem putting out 2 amps i.e it doesn't heat up the tank much, doesn't create to many bubbles, etc. etc.

SO
5 * 10 / 2 = 25 minutes

That's it!
Anodize 10 square inches for 25 minutes at 2 amps and you'll get 1mil of coating.

If the 2 amps is causing problems then reduce it to 1 amp.
5 * 10 / 1 = 50 minutes.

If you don't like the time it's going to take then adjust the current (yes - within the limitations of your system). The time adjusts accordingly.

You can even adjust mid stream because you know you need 5 amp-minutes per square inch and if the part has been in the bath for a particular time, you have accumulated so many amp-minutes already. You can adjust the current, calculate the total time again, subract off the time you've already accumulated to get the remaining time required at the new rate.

Ok, I know I've lost every one. But if you get it now you can do it all in your head - no calculators.

Want .7mils, use 3.5 instead of 5 and off you go. (5x.7 instead of 1mil)

Make any sense?

5 x square inches / current = minutes (for 1 mil)
3.5 x square inches / current = minutes (for 0.7 mil)

Any body think it's a completly BAD theory. All I can say is it works for me and if you use the 720 calculator you get exactly the same results. You just have to fiddle with the CD number becasue it's based of Amps per square foot, a somewhat confusing and meaningless parameter. (also the parameter people were adjusting to suit their needs anyway, so that conept is not new)


(boy am I in trouble now)
Sage

[archimedes]

sage,

Job well done . . . .

archi

[sage]

Thankyou

I'm not sure my example was really good because you probably wouldn't want to anodize 10sqin with 2amps (that's a 720 rule CD of around 30) I was picking numbers quickly that calculate easily. But you get the point.
Like I said - somewhere - I'm pretty sure there are boundaries on this dictated by the type of anodizing that grows with excessive (or too low) currents but as long as one keeps things reasonable it's certainly easier to understand and all the parameters are in one calculation usually done in your head.

Nothing new here, just a simple re-organization of the formulas and hard work produced by Fibergeek (I think).


Sage

[blackcote]

sage,

I'm glad you pointed out the current density, becuase that's my next question. While I understand what your saying here... all things being equal the numbers are essentially the same and can be adjusted to suit. But where is the limit... this thread almost gives the impression that you can ignore acid concentration and "let 'er rip". I can't help but wonder... Can your really ignore acid concentration and anodize to say 15 ASF (provided you have control on temps and agitation) and still get good dye absorption? What if any is the limit with the 1:3 concentration? 1:2? etc.