finishing techniques

[sgunn911]

After I anodize my parts, what is the best way to finish them? Can I use the vibratory tumbler with corncob media without harming the anodize? Also, if this is possible and a good way of finishing or polishing, how long shouls I wait before tumbling and for how long shouls I tumble?

Lot of questions, I know.

Thank you for any help provided.

[neilfj]

Once it is anodized and dyed, it is finished.

If your looking for a particular appearance, you polish, bead/sand blast, sand prior to anodizing. Anodization and dyeing are the final steps in finishing.

[NeoMoses]

the only thing I've found beneficial after anodizing, dyeing, and sealing is to use a little bit of WD-40 or oil to help clean all of the excess dye off the parts. It'll help add a bit of a shine to a glossy finish.

[M_D]

The anodizing is apt to be damaged, especially on edges, if you were to tumble them. The only instance where a tumbler can be of use on anodized part that I know of is in removing smut. I am assuming this is why you are asking about tumbling. If the parts can be gently tumbled for a short time, it can be successful in doing that. You would be more likely to achieve this with small, light parts, rather than larger and heavier parts that will be hard to do without damage.

In general, if the parts are smutty after the cleaning, anodizing, dying, and sealing process is complete, it means something is not quite right in one or more of those steps. Often the smut can be wiped off and the appearance is ok, but it's a lot nicer to give them a simple final rinse and end up with a clean bright part when dried. Here are a few things we have found will help, if not eliminate dirty and unattractive parts:

1) Rinse very well between every step. Don't allow cleaners and other solutions to dry on the part, this takes careful attention with heated solutions like the main degreaser-cleaner and de-smut.

2) Many smut problems stem from the anodizing process. If the acid concentration is too high for the current density, it will leave a less than perfect surface. If the tank temp is too high, smut is often worse. If the parts are anodized for to long, smut can become a problem. Good connections are very important to achieve good and consistent results. Don’t ignore the cathode connections. All of these problems can also cause uneven colors when dyed.

3) If left for to long in the dye tank, smut tends to be worse. Some colors do seem to need more time to dye to reach the desired color depth. Other colors are capable of reaching a dark rich depth in as little as 2 minutes, with 3-6 minutes being common. Agitation of either the part or the dye solution speeds up the dye process and helps to reduce smut. Dye solutions that are mixed too strong (not enough water) will aggravate smut troubles. One would think a strong dye concentration would dye faster and darker and help, but that hasn’t been what we have found. We have rather found that you only want the dye strong enough to reach the desired color in a reasonable time. If the parts are not dying well in 2-40 minutes, suspect the anodizing layer as being inadequate in some form.

4) When sealer is old, or parts are left in the seal bath for too long, smut problems worsen. When using nickel acetate as a sealer additive, don’t mix it too strong.

If it isn’t smut that you are concerned with, but rather the basic texture or appearance of the part, then different preparation prior to anodizing is the only way to correct that. That can mean either mechanical means such as sanding, polishing, or machining to produce a pleasing appearance. Also, the way it is prepped in the cleaning, and etching solution if used, can influence appearance. Usually when done correctly, the part surface qualities should look the same after anodizing as it did when fully prepped and just beginning the anodize process, except for the color change. It can get uglier if something goes wrong, but it won’t get better.

[sgunn911]

I don't think the problem with smut is deriving from the tank or procedure. I am anodizing several items at once, and the same two parts are turning black every time, even with a replacement part. Is some aluminum so bad that you can't use this system, or is there a special technique past the usual polishing, degrease/de-ox steps to help.

The parts are from Japan, but so are some other parts that are coming out perfect. Also, sometimes when I tumblw the finished parts in a untreated corncob media for about a half an hour it will take a little of the matte finish off and shine it up a little. It seems that a lot of pieces come out looking like I painted it instead of anodizing.

I use a rectifier and follow the guidelines (I use the high temp sealer too)

[M_D]

When you say the same two parts turn black every time, do you mean identical parts, or two parts in every load but not necessarily the same type of part? If it is identical parts, then yes it may be the type of aluminum, there are some types of aluminum that are difficult if not impossible to anodize nicely. Cast aluminum is generally in that category, and some types of wrought and extruded aluminum alloys have various undesirable quirks also.

I haven't personally anodized any cast, although I have had it done in the past. From what I am told, a smooth polished cast surface before anodizing may help. I don't know if that is true or not, but it might be worth checking out. I also believe I have read where some of the Japanese aluminum is worse, but again I don't have any personal experience to call on.

On the other hand, too much current can blacken parts, and it's actually called "burning" the parts. So if it was randomly happening to various parts and the alloy didn't seem to be the common denominator, I might suspect the connections or current density might be bad.

[sgunn911]

I have sets of aluminum engine mounts for gasoline Remote Control models. Even brand new out of the package and polished they wont anodize. I can anodize other parts right next to them at the same time with no problem. Also an aluminum exhaust pipe and heat sink, all from O.S. Engines.

[M_D]

It's probably the alloy if the same parts fail to anodize nicely.

[sgunn911]

Any way to treat the parts so they will anodize?

[M_D]

Any way to treat the parts so they will anodize?

If the poor results are because of the alloy, there probably isn't much you can do. Like I mentioned in one of the previous post, I have heard polishing cast can improve the results. Do you know if it is cast aluminum? Do you have any pictures you could post?

[sgunn911]

I'll post some pictures. It does seem to have some properties associated with casting, so it very well may be. If I can't anodize them, I may just powdercaot them.

I will post some pictures a little later.

Thanks for the help so far!