Notes on Anodizing

[JosephS]

I recently had some parts anodized and came away with some notes. I could be completely wrong as this is what I pieced together from my experience and internet research.

Anodizing is a process that creates a chemically and physically protective coat on aluminum.

There are 3 basic types of anodizing used in RC

• Normal (type 2)

• Hard Anodizing (type 3)

• Hard coated Teflon (type 3 + PTFE)

Normal type 2 anodizing can be any color and was used on the gold pan and black pan team car and rc10t. It's native color is bright silver.

Hard Type 3 was used on the chassis of the World Car and and RC10t2. It is also commonly used on associated team shocks. It is a thicker coating and significantly more abrasion resistant than type2. The thicker coating is also much darker. In native color is a grey. While color can be applied it only can come dark. Typically it can be left as 'hard grey' or dyed black.

Hard Coated Type 3- This is a hard anodize that has a coating of PTFE. It is extremely durable and abrasion resistant. The 'green' non-threaded rc10 team shocks had this coating. The additional thickness of the process makes it unsuited to threaded parts unless they were specifically machined for the coating. So maybe the shock cap threads were specifically cut with the process in mind?

Each metal is different
The processing time for each alloy and temper are different so only like alloy and tempers can be processed together. The World Car and the rc10t2 used a 2000 series aluminum while the other tubs used a 6000 series alloy (6061 I think) that was heat treated to temper 6 (T6) I can believe the A stamp shocks are a different than the chassis, though I don't know what they are.

The basic steps of anodizing are to :

• de-anodize/strip the metal of any contamination

• etch and desmut to remove any reside from the strip

• anodizing

• dying/coloring

• sealing

De-anodyzing /Stripping
The stripping process removes some of the surface of the material and can only be done a limited number of times. As well the metal will need to be resurfaced after this step.

Anodized aluminum is resistant to acid but sensitive to caustic chemicals. Oven cleaner/Lye and de-greasers are common caustics and will strip a chassis. I used greased lightning. Stripped Anodized aluminum will form 'smut' on the metal. Each alloy and temper of aluminum will form a different kind of smut. This is an important detail. A processor should be able to sort the parts by the color of the smut to identify the alloy and tempers.
The Smut will appear as a black or grey coating on the part.

This process is separate from anodizing and has it's own cost.

Etch/Desmut
Think of this like a super cleaning process. Processors use strong chemicals to make sure no contamination gets in their chemical tanks. The Smut can be removed with an acid leaving the base metal. Once this is done then the part need to be refinished. This step will likely happen again after refinishing since any residual contaminants will prevent the anodize from sticking. For home desmutting it has been noted that mild abrasives easialy remove the smut layer.

Refinishing
The smoothness of the surface and cross metal contamination will effect the process. Small bits of metals and scratches can cause defects in the process where patches do not get anodized. For the finished result I couldn't get rid of all my chassis scratches, but the

Bright Dip
The processor I used didn't offer this process, but it has been recommended several times over by users here. It seems to be a chemically surface treatment that leaves a polished like finish. This may be the difference between the finish A stamp v1 gold shocks, vs the extremely polished appearance of v2 gold shocks.

Anodizing
Once the alloys and tempers are separate each batch of parts will be processed together according to the type of processing (2 or 3)

Color
This needs to be done soon after the anodize process. The parts are put in a dye for the color. Each alloy , temper and anodization takes to dye differently so each will be done on it's own batch to get to the proper color match.

Sealing
This step seals the dye in. The sealing process stops the color from fading, but makes the coating weaker to abrasion. There are a few sealing methods and some can lead to long term color fading.

Pricing
Each alloy will incur it's own charge as they need to be run separate. So it cost as the same to process the chassis, nose plate and motor plate (all the same alloy) as it does to do 4 shock bodies.

The prices for the work is done by 'shelf' Basically there is a minimum charge based on a shelf that fits in a processing tank. All of the pieces than can fit on a shelf will go for the same price.

So basic prices I have found in 2021
Strip/etch $60 a shelf
Anodize type 2 and dye $60 a shelf
Anodize hard(type 3) and dye $120 a shelf
Anodize type 3 and Teflon $240 a shelf

It seems that about 3 chassis, nose pieces and motor plates can fit on a shelf.

If people with more experience and knowledge pop in to correct me I will edit this as I can.

[Rep732]

Hey new here first post.

So I've learned how to anodize myself and everything about what you've said is true. It's not simply dipping metal in various baths to get the desired result and its absolutely critical to have the desired surface finish first before anodizing otherwise it's not going to come out the way you want. What I've observed is the way the finish is when it goes into the electrolyte bath is the way the anodized surface will be when finished, it pretty much mirrors the original surface so smooth will be smooth and a sand blasted finish will be the same when pulled out.


I run large scale boats and trucks so I've anodized some stuff on them and I did the engine case for my bonzi boat.

I'd post pics of the stuff I anodized but don't know how to post pics yet.

I'm here as I have a collection of rc10gt's.

[Dadio]

Thanks, that was a really nice explanation of the process.

[Coelacanth]

Smut can be removed with some wet-sanding with fine-grit sandpaper. 800 grit or higher removes it very quickly as the smut is just a thin surface layer.

Here is a topic I shared on this, de-anodizing some Duratrax wheels, it may be helpful to see some pictures of the process:

https://www.rc10talk.com/viewtopic.php?p=327720#p327720

The car parts I've had subsequently re-anodized to colors of my own choosing, I followed the aforementioned process, up to the polishing part. Once the smut was removed/parts polished, they were ready to be shipped to the anodizer. I was told by him that the parts I sent required almost no extra preparation for reanodizing.

[Rep732]

Here's a few things I've anodized. I also found 000 steel wool works excellent and doesn't scratch the anodized parts. Smut is found after the sealing process as well.

[radioactivity]

Good detail and point of reference Joseph.

After doing a few parts myself, another desmut technique that worked for me, is a soft toothbrush and simple green alternated with dish soap.
This removes the smut and wasn't abrasive for my purpose.

From the anodizing process point-of-view dissimilar alloys do anodize differently.
Length of time along with temperature and applied current will make a difference even with the same alloy.

Also attempting basically one-off anodizing is a different ball game vs production scale anodizing.

There is also a form of anodizing known as Bright Dip Anodizing. A process that also includes a phosphoric-nitric acid solution that chemically polishes certain aluminum alloys.
I've seen some anodizing that is almost mirror like and I now wonder if it may have been that process.

Chuck

[JosephS]

Smut can be removed with some wet-sanding with fine-grit sandpaper. 800 grit or higher removes it very quickly as the smut is just a thin surface layer.

Here is a topic I shared on this, de-anodizing some Duratrax wheels, it may be helpful to see some pictures of the process:

https://www.rc10talk.com/viewtopic.php?p=327720#p327720

The car parts I've had subsequently re-anodized to colors of my own choosing, I followed the aforementioned process, up to the polishing part. Once the smut was removed/parts polished, they were ready to be shipped to the anodizer. I was told by him that the parts I sent required almost no extra preparation for reanodizing.

When I desmutted my parts I did use abrasion, 800-2000 grit wet sanding. I think the process would have went better by using a mild acid first, then abrasion, wet to dry sanding with final polishing. I think that that liquid barkeepers friend will be my desmutter of choice if I try this again.

[JosephS]

Smut can be removed with some wet-sanding with fine-grit sandpaper. 800 grit or higher removes it very quickly as the smut is just a thin surface layer.

Here is a topic I shared on this, de-anodizing some Duratrax wheels, it may be helpful to see some pictures of the process:

https://www.rc10talk.com/viewtopic.php?p=327720#p327720

The car parts I've had subsequently re-anodized to colors of my own choosing, I followed the aforementioned process, up to the polishing part. Once the smut was removed/parts polished, they were ready to be shipped to the anodizer. I was told by him that the parts I sent required almost no extra preparation for reanodizing.

Did you know the alloy of the material, or did your processor figure it out? I feel like I got into trouble on my last batch with the shocks clearing being different than the chassis, though the motor plates were also ever so slightly different.

[Coelacanth]

Smut can be removed with some wet-sanding with fine-grit sandpaper. 800 grit or higher removes it very quickly as the smut is just a thin surface layer.

Here is a topic I shared on this, de-anodizing some Duratrax wheels, it may be helpful to see some pictures of the process:

https://www.rc10talk.com/viewtopic.php?p=327720#p327720

The car parts I've had subsequently re-anodized to colors of my own choosing, I followed the aforementioned process, up to the polishing part. Once the smut was removed/parts polished, they were ready to be shipped to the anodizer. I was told by him that the parts I sent required almost no extra preparation for reanodizing.

Did you know the alloy of the material, or did your processor figure it out? I feel like I got into trouble on my last batch with the shocks clearing being different than the chassis, though the motor plates were also ever so slightly different.

Unfortunately I have no idea. I've de-anodized Kyosho Gold shocks and most had no smut residue at all after the Easy-Off chemical strip, while a few had the smut. I don't know if that means they were made with different alloys or anodizing processes, but it did seem strange to me at the time that a few had smut while most had none. When ALL of the Duratrax wheels had smut, I just chalked it up to lower-quality aluminum or anodizing.

[radioactivity]

I may have your steps out of sequence but here is what I did...

If the final step before anodizing is de smutting, I would not using any type of abrasive.
Sanding and polishing should leave no traces of smut. The polishing can and will leave wax on the surface.
That I removed with simple green and dish soap then rinsed with distilled water.
This is what worked for me.

Chuck

[Coelacanth]

I may have your steps out of sequence but here is what I did...

If the final step before anodizing is de smutting, I would not using any type of abrasive.
Sanding and polishing should leave no traces of smut. The polishing can and will leave wax on the surface.
That I removed with simple green and dish soap then rinsed with distilled water.
This is what worked for me.

Chuck

That's a good point, Chuck. Most of the time, my aluminum polishing ends up being the final finish, most of those items didn't get sent out to be re-anodized.

[JosephS]

I may have your steps out of sequence but here is what I did...

If the final step before anodizing is de smutting, I would not using any type of abrasive.
Sanding and polishing should leave no traces of smut. The polishing can and will leave wax on the surface.
That I removed with simple green and dish soap then rinsed with distilled water.
This is what worked for me.

Chuck

I had been using a service vs doing it myself. From what I gather desmutting/etching is just always done before they anodize. It was described to me as a very though cleaning to the point of making a surface purely clean.

[Rep732]

Correct me if I'm wrong but isn't smut basically a "flash" oxidation? I've only encountered smut when I'm done sealing my parts

[JosephS]

Correct me if I'm wrong but isn't smut basically a "flash" oxidation? I've only encountered smut when I'm done sealing my parts

I am not sure myself. I am only going on what I have heard and read. I encountered smut when using greased lightning to strip anodizing off my parts.

[radioactivity]

Sealing
This step seals the dye in and as far as i know is optional. The sealing process stops the color from fading, but makes the coating weaker to abrasion. This is why the original world car chassis become purple after a few decades .

As far as I know, the sealing process is the critical last step that finalizes the entire process.
Anodized aluminum that is not sealed will be highly absorbent to all kinds of dirt, grease, oil and stains.
Either boiling in distilled water, or preferably, hot sealed with nickel acetate is very common. There several other sealing techniques as well.
This procedure is used to close the porous aluminum oxide layer after the anodizing step. Consequently it will seal in the dye and form a far superior finish.


Chuck