Getting stuff Anodized.....

Awl --
Yeah, not doing it myself, but I would like to be better prepared, to appear less of my normally rube-ish self, as I start the procuring process.
I'll be anodizing 1" x 12" rounds w/ tapped ends, and drilled 1/4" plate, anywhere from 8"x36 to 12"x48, with some drilled holes.
Ito of quan, I'd proly be doing any where from 25 rounds/6 plates to mebbe 4 times that, 100 rounds/25 plates or so, at one time.
How finished does "finished" have to be, for "good" anodizing results? For example, is typical alum round bar, extruded, and scotchbrited on a lathe a good enough finish?
Ito "sandpaper grit" finish on plate, how coarse sandpaper is too coarse? 60? 120? 240?
How does their caustic bath act, ito softening sharp edges? Loosening tapped holes? Should these be plugged? I'm assuming these caustic baths will obviate any cleaning/degreasing on my part.
Any stories/experiences? Any sample prices?
So far, my understanding is that regular un-colored anodizing is about 1/3 the cost of colored anodizing. And that the sometimes brilliant finish you see is not anodizing but a kind of clear-coating on top of the anodizing -- extree charge, no doubt. And also extra protection?
And a general Q: How does uncolored anodizing differ from regular aluminum oxidation? Rephrased, why does un-colored anodizing look so good, and oxidized aluminum look so crappy? Isn't it all Al2O3?
And another general Q:
What alternatives are there to anodizing? Paint/laquer? Powder metal coatings? Any "stains" for alum? Any opinions on the relative merits of these, cost or otherwise?
--

Mr. PV'd

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Proctologically Violated wrote:

I guess it depends on what you expect. Scotchbrite or sanded anodizes well. A lot of this depends on what your customer sees. If you want "eye candy" then machined all over is the best in my opinion. For sandpaper I use 120 grit. On parts where looks are important I machine all over and tumble. Sanding to remove and blend tool marks and then tumble also works well.
Not sure what your budget is but I have one of these model 2016:
http://www.abrasivefinishing.com/burrbench/burrbench.htm

120 and 80 grit are what I use if I sand at all.

The etch removes very little material if done properly, so you parts should be deburred completely. Masking is in most cases not needed for type II anodize. Type II is regular anodize, type III is hard anodize and threads need to be masked or tapped oversize, same for other critical dimensions.
My platers charge extra if parts are dirty. I generally wash my parts in Simple Green before they go to plate.

My plater charges $45 for a minimum of clear type II and $5.00 more for colors

No sure what your referring to regarding brilliant finish. Most platers offer a teflon coat for lubricity, which is about all I ever see as far as post plating things on anodize. Like most plating processes the better the finish going in, the better the end result.
Also make sure your anodizer uses a good quality sealer, not just a hot water seal. Nickel acetate is what is generally used IIRC. Sealing is especially critical as it protects colors from fading. Proper sealing is a part of the process and you shouldn't have to pay extra.

Just guessing at this, but it might be because the anodizing is a controlled process?

I would think that if you went with powder coat or paints that threads and close tolerance details would need masking.
Best, Steve
--


Regards,
Steve Saling
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Just a point and it probably doesn't apply here, but I've been told numerous times: "Do not anodize flight critical parts". The fatigue life is reduced by up to 50%. See our website: www.experimentalhelo.com and look for the anodize article. One $100,000 helo bit the dirt because of a little bit of anodizing for looks.
Stu
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For big lots the anodizer we use in Baltimore charges $250 per tankload when we send up large flat plates (18x33"x.16") 30-150 at a time. Their tanks are about 8' long and they can get 8 plates in a load so they charge us $31.25 each. That's for type III hardcoat (also called milspec) which is much thicker and tougher than normal type II commercial anodizing. We negotiated that price based on several hundred plates per year; the type II was about $20 per plate. Another big plater in town quoted us 50% higher, because their tanks were smaller so it would take them more tankloads. For smaller pieces and smaller quantities that wouldn't matter so much but you will probably see a $75-150 minimum lot charge if you only take up a few smaller pieces. The type II has a soft silver color and takes dyes well. The type III looks like a muddy brownish silver, even greenish sometimes, and doesn't look that good dyed. We don't get it dyed, just the natural finish. We used to use type II and have the plates run through a grainer with 220 grit (I think), and the etch step took out all the scratches and left a very smooth surface to the eye and touch. The type III etch is even deeper so we quit graining them, just leave the mill finish, and they come out nice and smooth. The Al2O3 layer is less dense than the aluminum metal so holes actually shrink in diameter about 0.001" or less. We don't have any masking done and the threaded holes come out fine. We have three precision through holes and we just had to tweak the machined diameter slightly so the final size was as desired. I wouldn't leave any big dirt spots on the metal but we just let the coolant drain off and air dry and their wash takes care of it.

It's all Al2O3 but the anodized film is thicker, more uniform, and the sealing step makes it denser and adhere better so it is much more scratch resistant (doesn't flake off). I've cleaned grungy spills with a red scotchbrite pad and didn't leave any scratches.

Verizon cut the alt groups so this probably won't get to alt.machines.cnc, sorry.
----- Regards, Carl Ijames
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Carl Ijames wrote:
We used to use type II and have the plates run through a grainer

Graining does give a very nice cosmetic appearance. It's like running plates through a large belt sander where the belt runs horizontal the piece to be grained is on a table and either the belt or the table can be adjusted for thickness. Called brushed finish like you might find on your SST stove top in the kitchen. Expect to pay.
The Al2O3 layer is less dense than the aluminum metal

With my plater on type II I can tell them to maintain size and they can hold things within a .0001 or two.
On type III, hardcoat, milspec, etc. at least around here in Silly Cone Valley you call out a TOTAL buildup, half of the buildup penetrates and half is actual buildup. Assuming we're talking your gym equipment the hard anodize would better resist scratching than type II. Any threaded holes would need to be masked or made over size. If you had any close fits you would need to compensate or mask. Type III dyes black fairly well in my experience, but that's about it for colors.
Be careful who you deal with in platers, there are some real hacks out there that can turn you work into crap in a quick minute!!! Doesn't necessarially mean you have to pay through the nose. When I find a good plater I'm very reluctant to move for chump change. Take a small lot of parts and see how they do. Practice your Spanish. :)

--


Regards,
Steve Saling
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Wow, that's a hefty bill, it rivals the cost of the material PLUS the machining!
Appreciate the reference point, tho, esp. as the geometries are similar.
--

Mr. PV'd

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On Jul 5, 11:33am, "Proctologically Violated"

For a time, I worked Q. C. in a motor home anodizing plant. First tank in was a hot saturated caustic etch solution, any semblance of a polish disappeared rapidly after that. It removed any residual oxide film, plus got rid of bending lube, finger prints and general plant crud. So don't expect a mirror polish to last under your anodizing, not going to happen. There's hundreds of different formulas for anodizing processes, we were using one Alcoa developed for decorative anodizing, which could be dyed. It used sulphuric acid for the electrolyte. Had humongous chillers to keep the solution temp down, too. You can have decorative anodizing, or you can go with the hard stuff, which can't be dyed. Pick your poison. The hard stuff uses chromic acid, EPA hates it. So probably will be limited availability on that. The decorative sort leaves an oxide surface of hexagonal pores, which can be filled with a dye solution and sealed off with a hot nickel acetate solution. The color only lasts as long as the dye, red fades fast, black fades to either blue or brown. The oxide surface is kind of like glass, any extreme bends and the stuff cracks. The decorative sort isn't that abrasion resistant, either, I remember one fellow's Walther PPK was worn down to the metal with just a couple of years of carrying.
Oxidized aluminum just happens, anodizing makes sure that the job is done evenly.
A much more resistant sort of finish is powder coat, we had polyester and epoxy(different colors). Either would outlast anodizing 10 to one in the 1000 hour salt spray test. By the end, the anodized test coupons had vanished, the powder-coated stuff was just a little chewed around the edges.
As far as production cost is concerned, the running cost for powder coating on a production basis is a whole lot less, a lot fewer toxics involved. If done properly, you can recover what little powder escapes the transfer process. We had to have folks spend a lot of time racking and unracking parts on the anodizing side, had to use titanium racks and hardware. Everything had to be bolted up to make electrical contact, lots of hands involved in that. Powder-coating parts were just hung on conveyor hooks that ran through the washer and drying oven, a continuous process.
Stan
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wrote:

For a time, I worked Q. C. in a motor home anodizing plant. First tank in was a hot saturated caustic etch solution, any semblance of a polish disappeared rapidly after that. It removed any residual oxide film, plus got rid of bending lube, finger prints and general plant crud. So don't expect a mirror polish to last under your anodizing, not going to happen. There's hundreds of different formulas for anodizing processes, we were using one Alcoa developed for decorative anodizing, which could be dyed. It used sulphuric acid for the electrolyte. Had humongous chillers to keep the solution temp down, too. You can have decorative anodizing, or you can go with the hard stuff, which can't be dyed. Pick your poison. The hard stuff uses chromic acid, EPA hates it. So probably will be limited availability on that. The decorative sort leaves an oxide surface of hexagonal pores, which can be filled with a dye solution and sealed off with a hot nickel acetate solution. The color only lasts as long as the dye, red fades fast, black fades to either blue or brown. The oxide surface is kind of like glass, any extreme bends and the stuff cracks. The decorative sort isn't that abrasion resistant, either, I remember one fellow's Walther PPK was worn down to the metal with just a couple of years of carrying.
Oxidized aluminum just happens, anodizing makes sure that the job is done evenly.
A much more resistant sort of finish is powder coat, we had polyester and epoxy(different colors). Either would outlast anodizing 10 to one in the 1000 hour salt spray test. By the end, the anodized test coupons had vanished, the powder-coated stuff was just a little chewed around the edges.
As far as production cost is concerned, the running cost for powder coating on a production basis is a whole lot less, a lot fewer toxics involved. If done properly, you can recover what little powder escapes the transfer process. We had to have folks spend a lot of time racking and unracking parts on the anodizing side, had to use titanium racks and hardware. Everything had to be bolted up to make electrical contact, lots of hands involved in that. Powder-coating parts were just hung on conveyor hooks that ran through the washer and drying oven, a continuous process.
==============================================================I thought anodized alum was Da Bomb ito of finishing and durability, but you're saying not so.
So why do people go through the extra expense of anodizing?
What is your opinion on the aesthetic/architectural value of anodized vs. PMC?
I can see the trial and error/decision making on the finishing phase of this part is going to be a long haul.
Also, the little I've read indicates that diy PMC is a lot more practical than diy anodizing. And proly a lot more legal, as well.
--

Mr. PV'd

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Proctologically Violated writes:

Powder coating is just paint, a plastic polymer such as polyester, stuck on the surface. Anodizing is hard and durable metal oxide which is chemically bonded to the elemental metal. Maybe powder coating lasts longer in a salt spray test for a chemically corrosive environment, but it won't stand up to UV exposure outdoors as well as anodizing.
My anodized aluminum screen enclosure has spent 30 years in the Florida sun and rain. The oxide itself is worn but intact. The anodizing dye has started to fade in the more exposed areas. I can't believe paint or powder-coating would have lasted more than 5 or 10 years.
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