need help finding problem....

[Sid03]

i have no agitation in the dye tank, and didnt know that i should. Is this a big issue?

[whistule]

That's certainly what caused the problems in my case. I just use an airline into the bottom of the dye tank from a aquarium air pump. Another step forward was to heat the dyes - not sure if you do this - and I don't think it'd the cause of your problems but it does help the dyes to be absorbed into the pores.

[Sid03]

yes, i do heat the dye tanks to 140 degrees. Does everybody use agitation of some sort in their dye tanks? Any other input into this?

[M_D]

I haven't noticed any tendency towards a chalky finish in my work, except on parts that were anodized for a very long time. There appears to be some time limit where the anodizing gets very strange. When anodized for a long period the parts soak up dye well, but the anodizing layer is not good. I have seen evidence that one layer builds on top of another one. The parts look good until they dry, and when sealed get worse. I have intentionally over anodized for experimental purposes.

I will keep the thought about the dye tank causing problems filed away, as it may be useful for me to troubleshoot a problem latter.

As with heated dye, I have noticed parts also dye faster with agitation; sometimes just stirring them in the dye by hand accelerates the dying. If the tank is heated, agitation is useful to keep the temperature even, as the upper layer tends to get much warmer than the bottom. If the quality of the anodizing is conducive to rapid dying, and the dye temperature varies too much from top to bottom of the part there can be banding or a gradient effect. If left in the tank long enough, the parts seem to even out, but if you aren’t shooting for a deep color uneven dye temperature could be particularly troublesome.

[Fibergeek]

I concur with M_D.

The chalky stuff is the outermost anodization, undermined by dissolution. Notice how it looks orange under the wiped areas, where the dye hasn't fully penetrated. Excessive dissolution can so weaken the anodize layer that some of it can be rubbed or wiped off, it just crumbles. If you measured the coating thickness you will see that it is noticably thinner than a sample done under similar conditions but was not subject to excessive dissilution.

I also concur that this was probably caused by too long an anodization time for your particular set of anodizing parameters, this is the most likely cause. Other things that can cause this are too high an electrolyte temp., too strong electrolyte concentration, too low an ACTUAL current density (reasonably accurate measurements are important). Agitation in the anodization tank effects how even the coating thickness will be, not dissolution rate. Agitation in the dye tank is certainly helpful.

[Easttex]

I have had this problem on two separate runs. Two of the parts were identical on one run and were run with lots of other misc. parts. The two problem parts were CCM feednecks for paintball guns that were both going into black dye. They looked great until they dried... same chalky appearance that wiped right off. The next time was on a palmer LPR regulator, also for paintball guns, only the problem occurred in blue this time. The conditions were the same in each run.....excellent aeration, 110* dye, run with other parts, all other parts were normal, all other normal LCD parameters. I'm leaning more towards an alloy related problem.......Its the only thing I can figure when the two on the same run both turned out the same, even the other parts that went into the same dye colors were fine. One thing I noticed about the three parts were that they all seemed to be a bit harder feeling than most of the other aluminum parts I've run.
I am equally stumped on this one......Does the info I provided spark any new theories?
Easttex

[M_D]

Originally Posted by Easttex

I have had this problem on two separate runs. Two of the parts were identical on one run and were run with lots of other misc. parts. The two problem parts were CCM feednecks for paintball guns that were both going into black dye. They looked great until they dried... same chalky appearance that wiped right off. The next time was on a palmer LPR regulator, also for paintball guns, only the problem occurred in blue this time. The conditions were the same in each run.....excellent aeration, 110* dye, run with other parts, all other parts were normal, all other normal LCD parameters. I'm leaning more towards an alloy related problem.......Its the only thing I can figure when the two on the same run both turned out the same, even the other parts that went into the same dye colors were fine. One thing I noticed about the three parts were that they all seemed to be a bit harder feeling than most of the other aluminum parts I've run.
I am equally stumped on this one......Does the info I provided spark any new theories?
Easttex

I guess it could be an alloy issue, although if so, a more proper term might be an issue with mixing alloys in the same load. I have found the 2011, 2024 alloys to anodize quicker than 6061 for example. It seems in my work, if 2011 is anodized the same length of time that is optimum for 6061, it is too much. But, that is only my experience. From the information I have, the 2XXX series build a thinner film than 6061, 7065, etc., for the same time. Yet, I haven't had the good success anodizing it for increased amounts of time that I have with 6061 and 6063.

What alloys you are working with may be hard to determine. One thing that has become apparent to me is the 2XXX series get a bronze color in hot (150-180º) SP cleaner well before 6061, and they get a heavier smut in lye stripper or lye etch too. So you might at least acertain if the parts are the same alloy or different alloys by observing this.

One other possiblity is the connections on the sub-par parts went bad. Was there a big size difference between the good and bad parts? A large part requires more current, which taxes the connection more. It's true the connections all need to be good, but what will pass enough current for a small part may not for a larger part. It's just an idea, what the actual problem is I couldn't say for certain.

[Easttex]

The heavy smutting in the stripper sounds familiar. All the parts did have an excessive amount of smut. Is that a characteristic of 6061? If so how can this alloy be identified early on? Is there a recommended current or some special treatments 6061?
Easttex

[Sid03]

I also concluded that it was mainly related to mixing different alloys. I was guessing that some alloys ano faster then others, for whatever reason. I was watching PAR for a batch running 6063 and 2011......when it looked finished the 2011 ended up with a slight hazey film and the 6063 was perfect. I guess that agrees with MD's findings. At this point, im wondering if its even possible to mix alloys in a batch and achieve good results. Also, im wondering if this issue is more relevant to LCD as compared to the old high current method, as I dont remember having this problem with a couple batches I did using high current anodizing. I only have a LCD setup now, so I cant check for myself.

[Fibergeek]

Back when you were using good old fashoned "let it rip" you wern't watching any anodizing parameters (like PAR) were you? Are you sure of what you saw?

According to Wernick, Pinner, and Sheasby; anodic coating growth is slower for 2xxx series alloys compared to 6xxx series. This is because of alloy content. 2xxx contains a fair amount of copper, probably the worst metal from the anodizing perspective.

Keep in mind that any anodizing process is a race between coating growth and dissolution. How the coating turns out depends on who won and by what distance. Fortunately you can rig the race (within limits) so that coating growth wins.

Higher current density accelerates coating growth; but this also raises the temperature which accelerates dissolution, and produces small pores (higher density).

Stronger electrolyte accelerates dissolution; but it also promotes larger pores.

Time increases both coating thickness and the effects of dissolution.

There is no easy answer.

I have been doing quite a bit of work on non-LCD anodizing lately, you couldn't call this "standard" anodizing either, its something different. I'm never satisfied with "good enough", Fibergeeks are like that.

I'm not prepared to talk about this yet, but I will drop a big fat hint, and a warning:

We all know that weak concentration electrolyte (like LCD) makes for smaller pores, and reduces dissolution (its less corrosive). Has anyone thought of testing the limits?

The warning: Watch out for higher power dissipation, if you allow the temperature to rise much this will backfire on you.