Quick question on "old" ano method......

[Sid03]

What was the old anodizing bath mixture for high current(12ASF) anodizing? Was it 1:1? I just want to double check. Thanks!

[Moderator Edit: Made Sticky because this thread contains a TON of fantastic information about troubleshooting an anodizing system. ]

[Fibergeek]

By "old" I think you mean pre LCD sold by Caswell. This was I believe a 1:2 battery acid / water mix. If you're anodizing at 12 ASF, it would be a better choice than the LCD ratio. Both mixtures mentioned above are by volume.

BTW, a 1:1 mixture by volume is very close to the traditional 165 grams per liter by weight electrolyte. When you consider this, its evident how much safer and more pleasant to be around the LCD electrolyte is.

[Sid03]

is 1:1 a bad idea when running 12ASF?

Im switching back from LCD for awhile to see if I get better results, and cant remember what I used to run. I know it was either 2:3 or 1:1. Caswells old manual lists both.

[Fibergeek]

A 1:1 Battery acid to water ratio by volume will provide larger pores and a faster dissolution rate than weaker ratios, This alone can create all sorts of new problems if dyeing characteristics are critical. I've never heard of a 2:3 ratio being used. I would use a 1:2 ratio from 6 to 15 ASF, and switch to 1:1 above 15 ASF. I have done Type II anodizing as high as 24 ASF, in order to form "Type II 1/2", this was to grow coatings measuring over 75um (3 mils) thick. This excludes Type III (Hardcoat) where you are back to a weak electrolyte, and low temperatures.

You imply that you aren't getting good results with LCD. Most others who switch from LCD to higher current densities do so to speed up anodizing time. What is going on in your case, what are the symptoms?

BTW; for dyeing, coatings thicker than about 0.7 mils do no good, the dye (any dye) won't penetrate any deeper than that.

[Sid03]

Im switching back because I was getting much better results using the old method. I have since switched to LCD only to get consistently worse results. I truely dont think its building as thick of a layer for me. I know my dyes get no where as deep as they did before. Its simply disturbing seeing my previous results I got when I first set up a small line to try it out as compared to now when I have better equipment and alot more knowledge under my belt.

Basically, im switching back to verify if its me or the something funky going on with the LCD method. If I still get terrible results, ill be back begging for more help from you..........thanks for all the help thus far.

[erogers]

Professional anodizer's use a 15-16% sulphuric concentration. Temperature of bath is really critical to successful operation.

[Fibergeek]

The traditional electrolyte concentration of 165 grams H2SO4 to 1 liter (1 liter = 1000 grams) of water is 165/1000 = 16.5% by weight. This corresponds to a 9.4% concentration by volume. Since no one commonly weighs sulfuric acid, water, or other liquids, its usually measured by volume in practice.

To sum it up:

Concentrated sulfuric acid; 100% by weight and volume.
Commercial battery acid; 35% by weight, and 19.2% by volume.
"Professional" electrolyte; 16.5% by weight, and 9.4% by volume.
Caswell's 1:2 electrolyte; 6.4% by volume.
LCD electrolyte; 4.8% by volume.

Bath temperature is important but I wouldn't call it critical, it effects pore size mostly. If the anodizing is done "open loop" by voltage, temperature becomes much more important, as does the dissolved aluminum content of the electrolyte. This is because both effect the electrical conductance of the electrolyte. Closed Loop anodizing (constant current) automatically compensates for differences in electrolyte conductance.

[Sid03]

I just tried 1:1(battery acid/water) ratio at 12ASF at 45 minutes for a couple batches, and didnt get the best results. Im going to take your advise Fibergeek, and change the ano bath to 1:2(battery acid/water) to try. Would 12ASF be the best, or do you recommend another current? What time frame do think I should let that in for? Thanks alot!!

[Fibergeek]

Since almost everything in anodizing is a matter of degree, there isn't any "best", everything depends on everything else. This is both a blessing and a curse.

Please define "didn't get the best results" in as much detail as you can. As is obvious, we can't see what you are doing or what your results are.

If a large change in both ASF and electrolyte made a small or no change in the results, this problem may have nothing to do with either.

I know that this is going to require you to do a lot of typing, but it will get your problem solved much faster than having us guess. To get you started, I'll list some assumptions I'm making now about your setup, you correct them:

1. Bath temp. 70-75 deg. F..
2. Al or Pb cathode, at least as large as the work.
3. You are using CC anodizing, or at least really measuring the current.
4. The alloy you are anodizing is 6061 or 6063? We need to know.
5. At 12 ASF and with 1:1 electrolyte, you anodized for 30-45 min., under these conditions, anodizing longer will cause dissolution problems.
6. Exactly what are you using for a rectifier?
7. What is the surface area of the work?
8. What is the connection method to the work? Since you are troubleshooting you should go back to soft Al wire and Al bolts.
9. How are you cleaning and removing native oxide from the work?
10. You have properly measured and mixed anodizing dye; if its red (at least) you did measure and correct the pH.
11. You dyed at 140 deg. F. for at least 20 min. longer doesn't hurt.
12. What is your sealing method?
13. You have sufficient agitation in the anodizing tank.
14. Your electrical connections are good (all of them). I've been a practicing EE for 30 years and I can't tell a good connection from a bad one just by looking at it. Some voltage vs. current measurements would help a lot.

What have I missed?

[Sid03]

I dont think you missed much, other then the approx. time you think it will run at 1:2 ratio with 12ASF.

Im getting the same end result SOMETIMES as I have complained about in the past. I hazey film over the parts. Sometimes you can wipe it off with your fingers or hand buff off with a papertowel, sometimes you cant. Sometimes you get spots on the part that have no haze and are much glossier then the rest of the part, even after you remove all the haze. I get that symptom, OR the parts simply dont dye very deep. I dont think it has a sufficient layer of anodizing on it. Parts are cleaned, desmutted, and pass water break test before ano. Everything is rinsed between each step. Maybe its my connections, maybe it isnt.

1. Bath temp. 70-75 deg. F..

YES

2. Al or Pb cathode, at least as large as the work.

4 8X8 lead/GP plates. My normal large batches are about 140-200 sq. in.

3. You are using CC anodizing, or at least really measuring the current.

Using CC

4. The alloy you are anodizing is 6061 or 6063? We need to know.

6061 and 2011. The 6061 usually turns out better.

5. At 12 ASF and with 1:1 electrolyte, you anodized for 30-45 min., under these conditions, anodizing longer will cause dissolution problems.

I think thats what may have been happening. I think it was hitting PAR at about 30 minutes.

6. Exactly what are you using for a rectifier?

Mastech 20amp/30V CC/CV PS.

7. What is the surface area of the work?

My normal large batches are about 140-200 sq. in.

8. What is the connection method to the work? Since you are troubleshooting you should go back to soft Al wire and Al bolts.

Ti racking now. Used to randomly get same results with Al wire connection too. I simply can not use bolts.....I cant drill holes in the parts being anodized. The Ti almost has to be making a better connection then rigging the Al wire up to the parts.

9. How are you cleaning and removing native oxide from the work?

Caswells stripper. Then parts are polished and cleaned.

10. You have properly measured and mixed anodizing dye; if its red (at least) you did measure and correct the pH.

I measured the Ph when I first mixed it, and it was off from what Caswell said it should be. I got some parts that dyed fine in it, so I become less concerned about the Ph.

11. You dyed at 140 deg. F. for at least 20 min. longer doesn't hurt.

I try to keep dye temp 130-140. Dyed the last batch at 30 minutes just to get a semi-deep red.

12. What is your sealing method?

Caswells sealant(stuff that comes with kit). I can get the same bad results without sealing or with sealing the parts, so I dont think sealing has anything to do with it.

13. You have sufficient agitation in the anodizing tank.

Id like to think so. I have two high output fish tank pumps running into a PVC grid at bottom of tank. It creates a fair amount of agitation.

14. Your electrical connections are good (all of them). I've been a practicing EE for 30 years and I can't tell a good connection from a bad one just by looking at it. Some voltage vs. current measurements would help a lot.

Last batch....143sq.in. ran at 13.5A(12A for the parts and added an extra 1.5A for the Ti racking).

Voltage/ Time:

1 min/ 13.0V
26min/ 10.6V
30min/ 10.1V
40min/ 9.4V
44min/ 9.2V