View Full Version : Quality differences in "milspec" anodizing.
HansTheHobbit
10-04-16, 13:45
Everybody claims their lower is milspec type III anodized, but most of the cheaper lowers I'm seeing these days feel more like a powder coat of some kind. They also feel soft. I don't really know how to describe it, but if you tap them with something metal the surface just doesn't feel like it's been hardened at all. The sound just isn't right.
I have a Spike's lower I bought about five or six years ago, and I was disappointed when I bought a new one last month that has that powder coat on it. It almost feels like a chalk board. I've bought an Anderson lately as well, and that feels identical to a chalkboard. Same thing with an Aero I picked up.
So what's the deal? Are all lowers really created equal, as so many people claim?
The surface prep is what dictates the texture, not necessarily the type of Ano. If you sandblast the surface with a heavier grit, the texture will reflect that vs someone who uses a finer grit or a glass bead. It's easier to hide imperfections and tooling/machine marks with heavier grit sandblast, while a glass bead finish exposes every little flaw, but results in a much smoother ano finish.
^^^What VIP said^^^ I have a MEGA lower with a BCM upper on it. The upper looks almost grey and the lower looks jet black when together. It's nothing more than the way light is reflected off of different textures.
The milspec def is in reference to the process. The type and how thick the anodizing is. Different base alloys will sound different, the coating can be dyed different colors, and finish can influence feel and appearance.
The black coloring is not the anodizing
HansTheHobbit
10-04-16, 22:40
The black coloring is not the anodizing
From what I understand that's not necessarily true. I don't know about type III, but there are some anodizing processes that produce a black finish naturally. From the limited information I could find, I don't think milspec anodizing has any dyes in it.
From what I understand that's not necessarily true. I don't know about type III, but there are some anodizing processes that produce a black finish naturally. From the limited information I could find, I don't think milspec anodizing has any dyes in it.
It does have a black dye, when you type 3 and with no dye the aluminum has a golden tan hue. 7075 T6 struggles with most colors because of the higher sulfur content vs 6061, so you usually can only successful dye type 3 in blacks, greys, and tans.
Typical MIL-A-8625 anodizing used on AR receivers is Type III Class 2. Class 2 means it's dyed
http://www.arrowcryogenics.com/chemical-processing/hard-coat-aluminum-anodizing
HansTheHobbit
10-05-16, 00:46
Good stuff. So what I'm actually seeing is a difference in machining quality, not a variation in the finish itself. That's interesting about the natural color of type III. I would like to see a picture of an uncolored one just out of curiosity.
From what I understand that's not necessarily true. I don't know about type III, but there are some anodizing processes that produce a black finish naturally. From the limited information I could find, I don't think milspec anodizing has any dyes in it.
There are two classes of Type 3 anodizing :
Class 1 Non-dyed
Class 2 Dyed
All coloring is due to dye applied after the actual anodizing process.
(Actually, all three types of anodizing can be class 1 or class 2.)
Good stuff. So what I'm actually seeing is a difference in machining quality, not a variation in the finish itself. That's interesting about the natural color of type III. I would like to see a picture of an uncolored one just out of curiosity.
Non-dyed anodizing looks like . . . aluminum.
Again, variations in the actual surface, polished, matt, rough-machined will vary the apparent hue from grey to shiny aluminum color.
Oh, and another thing, dyeing aluminum is much like dyeing cloth, exact color matches are not guaranteed, it varies from lot-to-lot and sometimes specimen-to-specimen.
NOTE: The treatment that makes aluminum gold-ish hue is chromate conversion, or alodine, which is altogether different process, done for altogether different reasons.
http://www.finishing.com/143/14352-2.jpg
Non-dyed anodizing looks like . . . aluminum.
Again, variations in the actual surface, polished, matt, rough-machined will vary the apparent hue from grey to shiny aluminum color.
Oh, and another thing, dyeing aluminum is much like dyeing cloth, exact color matches are not guaranteed, it varies from lot-to-lot and sometimes specimen-to-specimen.
Exactly, color matching with Ano is very difficult.
To show the differences in surface treatments here are three uppers in various stages.
Raw
Sandblasted
Glass Beaded
https://c1.staticflickr.com/9/8534/29840368840_cecfbc2bfc_c.jpg (https://flic.kr/p/MsTG2W)
HansTheHobbit
10-05-16, 14:07
There are two classes of Type 3 anodizing :
Class 1 Non-dyed
Class 2 Dyed
All coloring is due to dye applied after the actual anodizing process.
(Actually, all three types of anodizing can be class 1 or class 2.)
I typed in class III type 1, but all the image results were of black parts. If anyone has an image of an undyed type III part I would be curious to see what it looks like. Is the natural color aesthetically pleasing in any way?
Are you sure you're not comparing a receiver that has a Teflon finish to one with plain anodizing? The Teflon finishes are black, smooth, and more shiny versus the anodized which is gray and somewhat rougher.
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I typed in class III type 1, but all the image results were of black parts. If anyone has an image of an undyed type III part I would be curious to see what it looks like. Is the natural color aesthetically pleasing in any way?
See the post above yours. Non-dyed anodizing looks like the bare aluminum.
This is a type 3, class 1 anodized tube:
41764
EDIT:
Are you sure you're not comparing a receiver that has a Teflon finish to one with plain anodizing? The Teflon finishes are black, smooth, and more shiny versus the anodized which is gray and somewhat rougher.
And, anodizing can be quite shiny if you do don't rough the surface up with blasting....
http://g01.a.alicdn.com/kf/HTB1f80aIXXXXXbPXFXXq6xXFXXXE/-3-AN-Male-AN3-Flare-Plug-Fitting-Aluminum-Blue-AD32001-AN-Plug.jpg
I typed in class III type 1, but all the image results were of black parts. If anyone has an image of an undyed type III part I would be curious to see what it looks like. Is the natural color aesthetically pleasing in any way?
Try Type III Class 1. No, the color isn't pleasing. It usually comes out dull and mottled. From the tech article I posted the link to
If the aluminum to be hard coat anodized is not dyed (Class I), the color of the aluminum will change. The color of the aluminum after being hard coat anodized depends on the alloy and the thickness of the coating. On some alloys, the color of the aluminum after hardcoat anodizing will be gray/bronze; on other it will be gray-black
Surface smoothness also depends on whether or not the aluminum was sealed after anodizing
Sealing After Hard Coat Anodizing
After a component has been hard coat anodized, it may or may not be sealed. If the main function of the application is to obtain the maximum degree of abrasion or wear resistance, the coating should not be sealed. If the main function of the application is for corrosion resistance, and reduced abrasion resistance is not an issue, sealing is advised
Link to technical article on sealing- http://aluminumsurface.blogspot.com/2009/04/why-sealing-process-is-so-important.html
Alodine is a chemical conversion performed to prevent corrosion. For non appearance items, the Alodine used will turn the surface of the treated aluminum a bronze-ish to brown color. Alodine used to treat appearance items that will not be painted leaves a colorless conversion coat
Just found out alodine is a chromate conversion coating. You don't want that on your gun.
What's the problem with chromate on a rifle?
HansTheHobbit
10-06-16, 18:44
Just found out alodine is a chromate conversion coating. You don't want that on your gun.
Who uses it? I have no idea what it is, but I've seen enough of your posts to know I should probably just take your word for it.
What's the problem with chromate on a rifle?
It's hexavalent chrome which is carcinogenic and mutigenic.
True. But you don't leave Alodined parts bare. You paint them. Not that I'm advocating Alodining over anodizing
Who uses it? I have no idea what it is, but I've seen enough of your posts to know I should probably just take your word for it.
I doubt it's used on anodized parts like rifles. Chromic acid can be used, but I thint they generally use other methods when possible due to cost.
True. But you don't leave Alodined parts bare. You paint them. Not that I'm advocating Alodining over anodizing
I dont know about alodine specifically, but I've seen a lot of bare chromate parts and tools, just not on firearms (mostly cars). I would bet it could still leach out, but it would definately be corrosion resistant.
We do chromate where I work and it increases the salt spray testing by about 10x.... its rediculous. Completely unnecessary on a rifle, especially an ar.
I see where you're coming from. In aviation, we use Alodine regularly on aluminum parts we fabricate locally or repair locally. After applying Alodine, we supply primer & paint (unless it's an unpainted cosmetic area like polished skin)
Alodine does not make the aluminum surface hard. Type 3 anodizing does.
That' the main reason alodine/paint is not used much in firearms.
Alodine allows to good electrical bonding between parts, anodizing does not, that's why alodine is used extensively in aviation. Also, you have to have a tank large enough to totally immerse a part in to anodize it, hard to do with a large wing panel... And, anodizing alters the fatigue properties of aluminum, the hard surface is more susceptible to crack initiation.
Both are good at corrosion protection.
This is being completely off topic, but-
Alodine converts the surface to aluminum oxide, which is harder than the base aluminum alloy. However, Type III anodizing does a better job and creates a thicker coat than Alodining.
You don't need a tank to apply Alodine. A tank is better if you're applying it to a lot of parts. Usually, a tank is too much bother and that includes when Alodining skins and repair doublers
Alodine converts the surface to aluminum oxide, which is harder than the base aluminum alloy.
Well.... bare aluminum forms Al2O3 almost instantly after it becomes bare aluminum.
But, chromate convertion coatings (alodine) convert the surface to mostly to Cr2O3 and CrFe(CN), underneath that a thicker layer of Cr2O3 is formed. At the interface between the coating and aluminum proper is a very thin layer of AlF3, AlOF, and Al2O3. All three layers together are less than a nanometer thick (<0.00004 inch).
Well.... bare aluminum forms Al2O3 almost instantly after it becomes bare aluminum.
But, chromate convertion coatings (alodine) convert the surface to mostly to Cr2O3 and CrFe(CN), underneath that a thicker layer of Cr2O3 is formed. At the interface between the coating and aluminum proper is a very thin layer of AlF3, AlOF, and Al2O3. All three layers together are less than a nanometer thick (<0.00004 inch).
Where does the ferric cyanide and fluorine come from? Maybe part of the alodine? You don't get that with all chomate coatings.
Technically it's aluminum chromate [Al2 (CrO4)3] that is the actual conversion coating, or a mix of hexavalent and trivalent aluminum compounds.
Slight disclaimer, all my experience is with zinc, and I'm assuming it's analogous to aluminum.
Edit to add: you can anodize with chromic acid, but I'm not sure of the mechanism. My guess is that you get a mix of aluminum oxides and chromates, and a thicker coating which, in theory, would be the best of both worlds. Anyone know more about that?
According to the guys I discussed chromate conversion with, fluorine is important to the conversion process. Coating growth is slower in the absence of fluorine. All of this is based on hexavalent chromates, trivalents are slightly different, but the resulting coating is primarily a chromate coating.
Anodizing yields a primarily Al2O3 surface, the overall reaction that takes place during anodization is:
2Al + 3H2O => Al2O3 + 3H2
This is the sum of the separate reactions at each electrode. The reactions at the anode occur at the metal/oxide and oxide/ electrolyte interfaces. The ions that make up the oxide are mobile under the high field conditions.
At the metal/oxide interface the inward moving oxygen anions react with the metal:
2Al + 3O2- => Al2O3 + 6e-
At the oxide/electrolyte interface outward moving aluminum cations react with water:
2Al3+ + 3H2O => Al2O3 + 6H+
(In case of aluminum dissolution into the electrolyte during porous film formation, the anodic reaction is: 2Al => 2Al3+ + 6e-)
The reaction at the cathode is hydrogen gas evolution:
6H+ + 6e- => 3H2
The sealing reaction can be written as:
Al2O3 + 3H2O ==> 2AlOOH*H2Ompound.
The chromium in the bath remains there for the most part, which is why waste treatment of this type of anodizing is important.
I've always wondered why anodizing is so easy to scratch if it is supposed to be so hard.
Lysander, that makes sense. The chromate conversion we do is very light/thin just to "seal" the surface and to augment our main coating. It's a quick, dirty, cude, and minimalistic approach compared to true chromate conversion processes. We just do straight chromate.
I've always wondered why anodizing is so easy to scratch if it is supposed to be so hard.
Easy to scratch compared to what? It's a lot harder than straight aluminum. The base metal is still soft so it won't do much for deforming the surface but is much better for abrasion than aluminum.
Lysander, that makes sense. The chromate conversion we do is very light/thin just to "seal" the surface and to augment our main coating. It's a quick, dirty, cude, and minimalistic approach compared to true chromate conversion processes. We just do straight chromate.
Easy to scratch compared to what? It's a lot harder than straight aluminum.
By things that are lower in hardness value.
By things that are lower in hardness value.
If it's harder than aluminum, it will scratch it pretty easily. The coating helps with abrasion and corrosion resistance. For example, using a steel punch to install a roll pin on a lower: dragging the roll pin on aluminum would scratch bare aluminum, but not an anodized part. But if your pushing on the punch and hit the lower, it will scratch because you went through the coating.
Think of it as thin glass on a piece of plastic. Enough pressure to break through the glass and you'll scratch the plastic, but with something of hardness between that of plastic and glass, you won't wear through the surface if it's rubbing back and forth. Does that make sense?
I've always wondered why anodizing is so easy to scratch if it is supposed to be so hard.
Generally, it is only 0.001" thick.
Imagine a thin sheet of glass glued on a mattress. Great for even pressure and wear, not so good with sharp impacts.
EDIT: I see someone used a similar analogy...
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