Anodizing temperature

[mudwhump]

Hello,

I received my LCD anodizing kit recently, and of course I'm anxious to set it up and start anodizing parts. In the manual, it states that the ambient temp should be in the 60-75F range when anodizing. What is the affect if the temp is lower? Right now in my area the temp is usually in the 50's during the day and 40's at night. Is it possible to use one of the 110 deg. heaters to heat the anodizing tank, or will the acid destroy the heater? Is the other option to keep the acid tank in the house to warm up until ready to use? Don't know if the wife will tolerate a (even covered) bucket of acid in the house. Thanks for any info you can provide.

Tim

[NeoMoses]

As I understand it, the temperature of the bath affects the dissolution of the anodized layer. As temperature is lowered, the dissolution is slowed. Colder temperatures shouldn't hurt you, they'll just give you a thicker anodized layer.

Here's a good thread to read: General trends in anodizing.

[neilfj]

Actually, the lower temperature for anodization is most likely going to create a thicker anodized coating. Remember, there are 2 process occuring during anodization...the electro-chemical creation of the anodized surface, and the dissolving of the surface by the acid. As long as the surface is created faster than the dissolution, the surface grows.

There are two possible outcomes...or a combination of both...both of which are good.

The lower temperature doesn't affect the creation of the surface, but what it does interfer with is the dissolution of the surface by the acid. The colder the electrolyte, the slower the acid dissolves the surface. All things being equal, the anodized surface should be thicker than if the piece was anodized at a higher temperature or at the very least you may find that the anodization progresses faster since the surface builds quicker without the associated level dissolution.

[Tim Wiltse]

As I understand it the lower temp( much around 65 and lower ) really affects the anodizing process. I know this because of tests I have done. A part done at 65 degrees or less will take much less dye than a part done a 70 for the same time. I am not sure if it's because the size of the pores or the lack of anodizing because of the low temp. Most likely both as higher temps make bigger pores. I'm not sure about the lower temp making a thicker layer... I guess if you left the piece going for long enough it would. I use a 100 watt fish tank heater myself it does ok heating up my anodizing tank( around 4 gallons or so) it does take awhile though.. like a few hours. I turn it on the night before and it is good to go my morning. I have also brought the tank into the house too but have been trying to keep it in the shop.Just my 2 cents.

Later,
Tim

[potsked]

i know tom touched on this, but from what ive heard there's more to be said. an email correspondance from Ron Newman (creator of this site : http://www.focuser.com/atm/anodize/anodize99.html) had this to say about temp.

(NOT MY WORDS CASWELL)

OK I'm going to tell you why I don't think Detecting PAR during anodizing using low current will work well when doing med/large sized parts. I think it is a great way when anodizing very small parts with minimal heat generated into the bath during anodizing. However as soon as larger parts are done the heat generated into the acid bath changes the impedance of the whole system messing up any reading one could make with a meter. How can one detect a very slight impedance change (PAR) if the system as a whole changes due to a few degrees of heat building up in the solution.

Impedance will go down when the temp goes up causing no detection of PAR when it should occur and be detected.

I think LCD can work well if the acid tank is large enough to absorb the energy to the point where it does not raise the acid temp more then a degree duriing the run.

Detecting PAR would be easier with all variables the same.

Again, im not dissing caswell at all, they've done alot of work and research, but there are those that have legitimate points that would disagree.

[Fibergeek]

I had some indirect correspondence with Ron Newman (via Mike) on 10/05/03 regarding LCD and PAR detection. I sent Ron my response, I also invited Ron to direct all LCD/PAR questions to me, more technical the better. I never received a response. This is the gist of it:

1. "Impedance". Ron asserts that rectified AC; as comes from a 25A Caswell rectifier, a battery charger, or any and all of the big stuff (100 Amps+) in commercial use is not actually DC, but rather "half of an AC sine wave". This is technically wrong. By definition; since the waveform (half-sine or otherwise) does not cross zero volts and become the opposite polarity it is DC. This defines a resistance, not an impedance.

2. It doesn't matter if the resistance changes with temperature, it will a little. When dissolution overtakes the anodic layer growth the resistance will go down. We are not looking for a specific value of PAR for detection; we are looking for a change in the direction of PAR, the resistance starts going down instead of up.

3. If you are anodizing a piece large enough to really raise the electrolyte temperature at 6A/sq.ft. , something around 10 sq.ft., you better have some type of cooling system. 10 sq.ft. will dump 15V x 60A = 900W of heat dissipation into the tank. If you were using standard anodizing (12A/sq.ft.) the heat load would be 1.8KW. Again; even in this extreme condition, when dissolution overtakes growth whatever resistance you have will go down.

It's clear that Ron has never tried to detect PAR; if he did he would see that it works, but he has his own commercial axe to grind. It's also clear you haven't either Potsked, but I don't know your reason.

[mcaswell]

Yes, and since LCD is an unconventional method of anodizing, it is sure to bring the contempt of the "anodizing experts". After all, the earth is flat, right!!!

Let us just say this...before Fibergeek imparted his wisdom and we sold the LCD kits, technical support on conventional anodizing was constant due to inconsistent results.

Since selling the LCD system, tech support requests are down 90%. That's proof enough for us that the system works.

BTW - Ron is a good friend of ours, sends us a lot of business which we reward handsomely, despite our difference of opinions on this topic

[potsked]

well, unfortunately my experiences with anodizing have not gone as swimmingly as most others. using caswell's rectifier and LCD i never got a good result, theres a possibility that it has been bad connections all throughout, but before id never had a problem, go figure.

in addition when i did try to run for PAR i never sawi it, just a drop off in current when my volts hit the ceiling

i guess thats why ive been hesitant to completely embrace LCD

[Tim Wiltse]

Potsked,

I never have had a problem with the "old" method. I guess I don't see the reason to change as the LCD doesn't really add any major improvement that I can see. Just seems like alot of hasle to alot of people!

Later,
Tim