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

[Fibergeek]

Sid,

Since you are using CC the electrolyte concentration won't make much difference in the thickness of the anodize. This is not the case with voltage (CV) anodizing. The concentration will effect pore size. I would prefer a 1:2 ratio at 12 ASF, and still use 30-45 min. If everything else is right, this will get you 0.5 to 0.7 mils coating thickness. Recall that dye won't penetrate any deeper than 0.7 mils. regardless of pore size.

The anodizing time is from the "720 rule". I have found; since I can measure the anodize thickness, that it holds up well at any ASF from 3 to 24 ASF.

The measured voltages look OK for 1:1 electrolyte, you should expect to see higher voltages (a little higher) with weaker electrolyte.

As M_D and other Ti racking users will agree here; racking in general is tricky, the two main issues:

1. Connection variance; your spring tension or how and where it makes contact may not be right, or not right most of the time. The sporadic nature of the problem supports this.

2. The parasitic resistance of the rack itself. If the SA of the rack itself is close to or larger than the work, it dominates. Since the Ti won't anodize here this resistance is constant with anodizing time; the resistance won't go up like it does for the work. This can defeat CC; the ASF for the work actually going down, not remaining constant, the power supply can't tell the difference between the rack's resistance, and the work's resistance. A fudge factor added to the ASF will help, I don't know how much extra ASF you will need to compensate.

Just as a test to see if this is the problem; do a test anodization with a piece of 6061, with soft Al wire bolted tightly. I know you can't do this with your real work, this is only to isolate the problem.

By "hazy film that you can sometimes wipe off"; could this be described as "chalky"? If so; it would be a sign of excessive dissolution, and the stronger electrolyte is working against you. Other things that can do this are; too low ASF, too high a temp., too long an anodization time.

[Sid03]

You may be right about the spring tension of the Ti racking, but at this point I wouldnt say thats it. The Ti racking I have seems to put a fair about of pressure on the parts.....more so then what I previously achieved with "rigging" fasteners out of the soft 12 gauge Al ground wire I used. Ill run another batch today at the 1:2 ratio and see how things go. Something tells me that the 2011 alloy has a part to play in this also, since 6000 series Al almost always turns out better!

[Fibergeek]

2xxx series has a very different anodization curve than 6xxx series, the high Cu content of 2xxx doesn't help either. You should avoid anodizing different alloys together, this will complicate things. I'm not sure why this is, but LCD tolerates the traditionally "hard to anodize" 2xxx and 7xxx series better than conventional anodizing.

Try the experiment I suggest above, if we can isolate the problem we can fix it quicker and more effectively. It will be worth the effort.

[Sid03]

could lack of cathode area also give results like a described?

I noticed that the cathode that I directly connect my PS lead to puts off alot more bubbles then the rest. I had the others connected together with some fairly decent test leads.....I think the wire thickness may mostly be insulator now that I look closer at them. I ran some 12gauge Al wire to all the plates and not all the plates seem to be putting off about the same bubbles.

If the cathode plates were only "working" very little before, how would that have effected everything?

[M_D]

We are anodizing 2011 on Ti racking too, and it’s definitely more troublesome for us than 6061 and 6063. At first it gave us fits, now we are quite consistently getting nice results and things seem to go better and better. The commercial anodizer that we have used was especially inconsistent with it (2011), they didn’t like it either. I will say that over 90% of the 2011 we do is dyed black, the balance is fairly evenly divided between clear, red, and blue. The red with 2011 is by far the hardest to get right.

I realized sometime back that the Ti racking makes it difficult if not impossible to calculate the exact amperage that the parts are anodizing at. We started out using 4.5 amps with aluminum hanging wire. Once that was going fairly well, we needed to increase volume and went to Ti racking. We still don’t have a large operation (shopping for a 1,000 amp power supply now), and the most parts per run are 100-200 parts. We started to anodize at “6-8” amps per square foot (1:2.5 electrolyte), to reduce cycle times. The reason I put quotes on the amperages is because that was the calculated amperage for part surface area. Anyway, we were doing ok (not super great) after some experimenting on times and so forth. Then we went to a deeper and larger anodizing tank, and were able to fully submerge our racking (we were only submerging it about 40-50% before that). All of a sudden things got weird. I decided to try more amperage and we are now using 10-12 amps per part square foot (not including racks). It made a huge improvement, the parts are turning out very nice and have very little or no haze that needs wiping off. If we have problems with haze now, it is almost always with 2011. The electrolyte is now the same (1:2.5 electrolyte) as we used with the smaller tank.

It appears to me that anodizing with Ti racking does require compensation in the amperage amount. Too low of amperage causes haze (smut or what ever you call it) and other inconsistencies like black dye being reddish, and etc. Since the Ti racking is altering the electrical calculations, I’m not sure what the actual amperage for parts really is. Like Fibergeek suggested already, I would suggest trying more. I suspect that since you increased the electrolyte concentration so much in addition to the amperage, that you are still low on the actual part amperage and dissolution is occurring now and was before.

You do need to be sure the parts are de-oxidized well, because that positively will cause problems. You might try increasing the soak time, or concentration of the etch solution, if it doesn’t degrade the surface. Are you de-smutting them after the lye etch? I know that very thorough rinsing is needed, and racking multiple parts makes it more difficult than doing a single part that has free access to all sides.

I know none of this information is precise, but is might give you a direction to try. I think with the Ti racking you may need to stick with loads that are fairly consistent, and experiment with the amperage and times until you get good results. If you change the part load, then I believe there will need to be an adjustment on current density. Maybe with time Fibergeek and I will find a formula were it can be calculated before hand.

Added in Edit: I also thing that doing some test pieces with aluminum wire would help. If they turn out good and the results are consistent, and the Ti racked loads don't, it shows the problem is CD related.

I would think a deficiency in the cathodes would cause problems. I have been using aluminum sheet (stays in the tank). I have 2 pieces of 7 square feet each on opposite sides in a 55 gallon tank, connected with a 12 guage wire with solder terminals. The connections are several inches about the solution, but I try to clean them regularly as the acid mist finds it way around.