LCD and various Al alloys + 25 A plating rectifiier

[elton10]

Is it possible to run parts using different alloys in the same LCD anodizing batch? Im going to be doing 7075 and 2024 and would like to run them both togetehr if possible.

Also is Caswell's 25 A rectifier capable of constant current operation?

[Fibergeek]

Yes its possible, but you should avoid it if you can. No two alloys have the same anodizing characteristics. Mixing alloys in the same batch forces some sort of compromise, favoring the one with the most surface area. Try it and see if both alloy samples anodize to your satisfaction.

Caswell's 25A rectifier is not capable of constant current operation.

[mcaswell]

Our 3 amp machine is constant current


Will will have our new 20 amp machine available in about 2-3 weeks.

[elton10]

Originally Posted by caswell

Our 3 amp machine is constant current


Will will have our new 20 amp machine available in about 2-3 weeks.

So with the 25 A it would just be a matter of adjusting voltage to get the 4.5 A figure for 90 mins?

[elton10]

Fiber

Thanks Im planing on trying that. Is it possible to simply allow one or the other to remain in the tank longer(the one with the most surface Im assuming? Which would be the 7075) I noticed that after about 75 min on some of the charts Ive seen in the forum that most of the alloys seem(and I stress SEEM) to have the same characteristics?

[Fibergeek]

If you are operating in constant current mode (or mimicing it) the current density (but not the actual current) will be the same for both the large and small parts.This doesn't address the chemical differences between the different alloys. I don't know what will happen, you have some experimenting to do.

Regarding the 25A Caswell rectifier:
You can make it mimic current mode operation by adjusting it almost constantly for the first 10 -20 minutes; adjusting so that the measured current stays constant, after that the current will settle down and you will only need to adjust it occasionally for the remainder of the anodization.

[elton10]

Fiber

Again, thanks. I figured that was the case re: the recitifier. I'llplan on experimenting a bit with the parts. Im going to start by setting my time/current according to the TOTAL area of all the parts..both alloys.Im guessing thats a good stating point?

Elton

[M_D]

The 2XXX series aluminum can be difficult, it has copper in it which has a larger negative effect on anodizing than about any other aluminum alloying element I am aware of. I think you will find that the 2024 will anodize to the optimum level faster than the 7075, I have found that it is more sensitive to longer anodize times, and should be avoided. The current capacity is different and the voltage-curve will not be the same as other aluminum.

If you do enough of it then you may find the anodizing electrolyte gets contaminated with copper, which may cause some interesting results with other alloys afterward.

I'llplan on experimenting a bit with the parts. Im going to start by setting my time/current according to the TOTAL area of all the parts..both alloys.Im guessing thats a good stating point?

I think it's better to do those two alloys seperately, but that's just my opinion.

If you do try to do both at once, you need to calculate the total area for each alloy seperately. Then, when the 2024 is pulled out earlier (assuming that is what you find is best for your setup and that alloy), you need to adjust the current accordingly.

[elton10]

MD

Thanks for the tip.. That may be what I end up doing... No way to avoid doing the 2024 since one of the parts Im anodizing is made of it. The 7075 parts will be the bulk of the work(surface area wise) and there are 2 of them for each one of the smaller 2024 part. I may just set up separate runs (and perhaps even tanks) for each.

elton