What Happened?

[mti11988]

I have been anoziding for a couple weeks with success. I have done several parts of different sizes and even multiple parts. I normally use the Titanium Wire and form a spring clip with it. However, I have to anaodize 4 plates that are 20" x 12" x 0.5" and I don't trust the titanium wire to support the part. I want a more 'absolute copnnection'. However, I have run three so far and none of them have anodized. I cannot figure out what is going wrong.
The plates are supported vertically in a cooler. I made two tank bars. Each bar has two 16 ga aluminum wires bolted to it. I bolted two 3.5 inch pieces of aluminum all thread through two holes at either end of the part. The two aluminum wires from each tank bar is also bolted to the all thread studs. Everything is tight and everything is aluminum. The two tank bars are connected together with aluminum wire (bolted). I checked continuity between the supply line and the part before I started each run and continuity is good. The connections seem OK.
I use the resistor method to control current and calculated that I need 15 amps current. Using the 720 rule I calculate I need about 2 hours and 40 minutes immersion.
With everything set up it 'appears' all is well. Normal activity in the solution. Current hums along with normal adjustments. Initial high drops off, settles in and holds fairly steady with minor, periodic adjustments necessary to keep the current level up. About two and a half hours in the current stops declining and starts to increase slightly. At 2 hrs and 45 mins I pull it out.
Part is not anodized at all. Fails continuity test (still conductive). All thread is not anodized. Aluminum nuts are not anodized. Hanging wires are anodized (no way the wires alone can develop 15 amps current).
I am wondering if the all thread or aluminum nuts are causing the problem. I think my next step will be to try it again but add extra jumpers of titanium spring clipped into the holes to make SURE the part is in the circuit. Has anybody had a problem with bolted connections. Is there any certain types of aluminum bolt or nut that might cause this.
Thanks,
Bill

[sswee]

Re: What Happened?

One thing at a time or I'll get confused, I calculate the plates at 512" squared SA. At a 4.5 CD this gives a set amperage of 16A per plate for 112 minutes to get .7 mil coating. I was not clear if your running them one at a time or in multiples.

If your hanging wires anodized and the next part in line did not, that is where you lost connection. The all thread and bolts should not cause the problem other than you may need to scuff up mating surfaces with some sandpaper. I have had trouble with some aluminum wires if I did not hit them with some scotch bright. I went to a sput welder to eliminate electrical connection problems. SS

[acidrain]

Re: What Happened?

You mention the Current rises and falls... are you not controlling the current during ano?
Please describe you power source, how many amps you were running, and what the volts are doing during the run.

[mti11988]

Re: What Happened?

Power Source is a 40 Amp Manual Battery Charger. I use the 0.1 ohm Resistor to control the current as described on page 119 of the Caswell Manual. In this setup a 1.5 volt drop across the resistor equals 15 amps current through the resistor, which was my target.
At initial start I always have to CLOSELY monitor the voltage drop across this resistor as it always starts high and settles in. I adjust the dimmer switch several times in the first few minutes to keep the current at 15 Amps. The the system settles down and runs. I periodically check the system at 15 minutes or so to ensure the current has not dropped too far. Minor adjustments need made thoughout the time cycle. I may check back in 20 minutes and the current has dropped a few thenths of an amp to around 14.8 or 14.7 and I will tweak it back up to 15. There is a point at about 2 hours and 30 minutes into the run that the current has stopped decreasing and actually starts to increase a couple tenths of an amp to 15.1 or 15.2 and I adjust it back down to 15.0 and pull the parts at 2 hrs 45 minutes.
Nothing.
I have had broken connections before and when the connection breaks the current stops. This is not happening now. There are no indications that the connection is broken. Current flows the entire time and exhibits what I think are normal conditions. At least it seems normal when compared to the other parts that I have ran recently.
For some reason, the material is just nor anodizing. The material is 'supposed' to be 6061 T6 Plate. 6061 T6 can be anodized, right?
Thanks for all the help guys.

[mti11988]

Re: What Happened?

One thing at a time or I'll get confused, I calculate the plates at 512" squared SA. At a 4.5 CD this gives a set amperage of 16A per plate for 112 minutes to get .7 mil coating. I was not clear if your running them one at a time or in multiples.

If your hanging wires anodized and the next part in line did not, that is where you lost connection. The all thread and bolts should not cause the problem other than you may need to scuff up mating surfaces with some sandpaper. I have had trouble with some aluminum wires if I did not hit them with some scotch bright. I went to a sput welder to eliminate electrical connection problems. SS

Well, I didn't count the side surfaces and that is why the difference between 15 and 16 amps. However, I still get 2hrs and 40 minutes for the time.
720/16=45
512/144=3.56
45*3.56=160.2 minutes or 2 hrs and 40 minutes.
Or, am I applying the 720 rule incorrectly. I have a paper written by Ron Newman that says the 720 rule is as follows:
Take 720 and divide by amperage (720/16=45)
Take ACTUAL surface and divide by 1 sq foot or 144 sq in. (512/144=3.56)
Multiply the two numbers to get the total minutes (45*3.56=160 minutes)
This rule has worked for all the smaller stuff I have done but could still be incorrect as far as I know.
Let's see:
720 Amp min per sq foot.
So, if I multiply my amps * my minutes (16*160) I get 2560
If I divide the amp minute (2560) by the sq ft (3.56) I get 719. Mathmatically it appears to me that this is a correct application but I SERIOUSLY don't know for sure. All I know for sure is that my plates aren't plating properly. There is some sort of hard coating on them but they do not pass the continuity test.
Bill

[acidrain]

Re: What Happened?

Hmmm... interesting.
I didn't calc your amperage requirements, but it sounds right.
One thing you didn't describe is your running volts. Monitoring the volts is as important as the amps. It will give all kinds of clues to any problems you may have, and it sounds like you could use some clues.
How do you adjust your power... in-line 110v dimmer type switch?
I used a battery charger quite a bit before going to a CC power source, so I know where you're coming from.
What about the wires... did they ano?
Is it possible you had a partial short circuit between the pos and neg?

[sswee]

Re: What Happened?

You're getting the right numbers. Just a little differently than I was taught and I get the same run time you do if I calculate for a 1 mil coating. An easier way to figure run time is to divide 720 by the CD and multiply the answer by the desired coating thickness if it is different than 1 mil.
IE: 720/4.5 = 160 x .5 = 80 min runtime for a 1/2 mil coating.
I didn't mean to cause any confusion. When you told about the hook up I was not clear if you were running 1 part or 2. I've seen where someone figured the current needed for one part and tried to anodize more than one on the same amount of current.
Most of the parts I do are made of 6061-T6 and it anodizes very nice. Do you know what the voltage is doing on the run? It still sounds like a connection problem. It may have started to anodize the plate causing the hard coating you said it had but lost connection before it got very thick.
It might help show a problem if you'll get a cheap DMM and check what the voltage is doing at the same time. It is most likely something easy to fix if it can just be pin pointed. SS

[mti11988]

Re: What Happened?

Thanks Swee and Acidrain,
I still don't know what went wrong. But, I have anodized a couple of the plates since then. I ran the titanium wire jumpers through some other holes in the part and changed to tank time to reach .7 mil thickness and the new combination worked. I still do not know what the original problem was as I have anodized 20 or so other parts (all 6061 T6) and they looked really good. When I did lose a connection the current just stopped completely so I knew. With this setup the current still flowed but no anodize took place.
At any rate, I use a dimmer switch with a battery charger and monitor the voltage across a resistor to set the current. My resistor burned up on the 2nd try at the plates so I bought ten 1 Ohm Power resistors and hooked them all up in a parallel circuit to get the same 0.1 ohm as before. I have two more plates to run tomorrow after I strip them. I will check the overall voltage each time I check the voltage across the resistor. I did check the overall voltage once on the last plate I did and when the current settled in at the beginning the entire voltage drop across the part and the resistor banks was 9.76 volts. 1.6 volts was dropped across the resistor so the voltage being supplied to the part was 8.16 volts at the beginning of the run.
Bill

[acidrain]

Re: What Happened?

Keep an eye on the volts. If I understand what you're saying, the volts (between the cathode and the rack) is 9.76 volts (afters settling in). That seems low to me. I usually end up with between 12 and 14 volts (depending on temperature and acid concentration).
What is you tank temp, do you have aggitation, and what acid/water ratio?
Sounds like you're having good results now, so it may be that we'll never know what happened, but it's always nice to get little tid-bits of info that help us down the road.

[destroyer125]

Re: What Happened?

is everything completely clean

[mti11988]

Re: What Happened?

Well, I still have one plate that doesn't want to anodize. I am just about to put it through a 3rd time!! I am thinking I have some bad material or something. It is supposed to be 6061 T6 but I have no certification. When the finished part is placed next to other 6061 T6 parts I have done they look like ****. Like a burnt grey or something. Looks almost like old, corroded aluminum wheels that have been outside too long. They go in clean but come out looking like ****. Although they get harder and harder to clean up each time. Strip, Sand, Scotch Brite this time. The other parts look real nice.
As far as voltage goes it seems like I do have low voltages. Lower than I figured I would have. The voltage has never really been high on any of that parts I have done so far (not that I recall anyway).
Acid ratios are based on the kit I purchased. 1 Gallon of NAPA Battery Acid mixed with 3 gallons of water. I have a total of 3 gallons of battery acid mixed with 9 gallons of water for a total 12 gallon mix.
Baffled.

[sswee]

Re: What Happened?

The burnt Gray sounds like smut. Are you using DeOx/DeSmut? The only parts I have had do just what you describe have been cast. I haven't run into plate or bar stock material that did it yet. What current density are you running?

[mti11988]

Re: What Happened?

OK, you are way over my head on this. Today is made sure and dip the part in the desmut before going to the anodize tank so hopefully that will take care of any desmut issues. The manual says that desmut usually isn't necessary unless you use certain grades and 6061 T6 isn't one of those. But I did use the desmut today.
Current Desnity = ??
I bought the Cawsell Kit and I am following the rules in their manual. I think maybe 4.5 is the answer but I am not sure. I shoot for 4.5 amps per square foot. My voltage is much lower than what you or others are running but I don't see any real control over that with my setup. I must run the current correct I think. Voltage is what it is, right? Currently, I am running 16 amps through my system. The voltage drop from the rack to the cathode is about 5 volts. 2 volts (1.9) are being dropped across the resistor. So Total voltage is still only about 7 volts. This is different from the other day and I really don't know why. Same part, same setup, same everything except desmut.
I will know how this turns out in about an hour and a half.
Bill

[sswee]

Re: What Happened?

The DeOx/DeSmut does more than desmut parts. On 6061-T6 where smut is not a problem, there are still natural oxides that form on the aluminum if it sits around for a time. The desmut removes these. If I have a part that is run and does not anodize, I strip/etch with sodium hydroxide long enough to remove any partial coating and desmut for 2 to 5 minutes. Unless you are after a high shine on the part, it should be ready to reanodize after this process.

Current Density or CD is the current run through the part per square foot to anodize. You use it on the 720 rule. You probably just haven't heard the term.

The voltage is governed by Ohm's law. The low voltage means there is little resistance against the current going through the circuit. It indicates how the circuit is. Low voltage can indicate connection problems, tank or part temp is high, acid concentration is high in electrolyte, or you may not be running the amperage through the part that you think you are.

If you have trouble again on the part. You may try running a higher CD of 6A per square foot one time. If for some reason you are not getting the current you think you are, it should show a potential problem by the changes it produces.

Steve

[mti11988]

Re: What Happened?

Interesting. I found an ammeter with 0.5 amp resolution / accuracy for $90 from a supplier that someone here mentioned. I think I will be purchasing it today as I want to KNOW what current is going through the system.
Also, I just put a very small part in the tank that should require 1 amp at 4.5 CD. Circuit showed about the same 5 volts across the part when I set it up. I cranked it up to where I now indicate 1.5 amps amd the voltage across the part is about 9 volts. Much more activity in the tank. I can tell you this. My voltages do NOT match the voltages in the 720 rule calculator. Something must be wrong.
Oh, I also cleaned the Cathode Plates but it didn't seem to make any measurable difference in the Current / Voltage.