# Type III Hard Anodizing



## CoolHands (Sep 15, 2007)

I'm interested in this. How exactly is it created? I always thought something was anodised, (hey - I'm British for spelling :nana or not.



> [FONT=arial, helvetica]The process requires the use of either chromic or sulphuric acid in the
> anodising electrolysis bath.[/FONT]


[FONT=arial, helvetica]

is standard for anodising aluminium.

So how does HA III differ from this, and how does it end up being tougher? (As we probably all know, regular anodising can be scratched fairly easily).

Anyone here tried anodising at home?

Just interested really..

( I enjoyed reading this:
http://homepages.pavilion.co.uk/nickfull/anodise.htm )
[/FONT]


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## Kilovolt (Sep 15, 2007)

I'm afraid this is in American English:

http://en.wikipedia.org/wiki/Anodize

but I find it rather complete. 

Nice reading! 

:wave:


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## TranquillityBase (Sep 15, 2007)

*Type I* is a surface coating, such as chromate conversion, Type II is a surface coating also, same hardness as the *type III*, but not as thick of a coating, and it has no measureable difference post coating (kind of a brittle shell)...*Type III* is not a surface treatment, the process allows the oxide layer to grow into the surface .001", and out .001" 

Yes, you can set-up for anodizing in a home shop, *type II*, but safety must be priority #1...You would need to use, and safely store a bucket/container of battery acid solution, as your anodizing tank.


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## LukeA (Sep 15, 2007)

Kilovolt said:


> I'm afraid this is in American English:
> 
> http://en.wikipedia.org/wiki/Anodize
> 
> ...



Except for procedure.


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## kromeke (Sep 15, 2007)

Short non technical answer:

Type III is the same process as Type II, only it is done with a bath at a reduced temperature (pretty cold anodize bath if I recall, close to freezing). This allows them to form thicker coatings than Type II. There are probably some more specific details, but that is the simple version.

Since dealing with the sulfuric acid is enough of a hassle, having to deal with temperature controlled acid baths are probably even more of a hassle, hence the increased expense. This is probably why you don't see too many people do type III anodize themselves, whereas type II is pretty common DYI procedure.


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## rizky_p (Sep 16, 2007)

Nice i was about to ask the same questions :twothumbs


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## artin51 (Sep 17, 2007)

Hi guys, i've been doing alot of Type 3 hardcoat samples lately and have gained a fair amount of knowledge on the subject (i'd like to think so anyways...). First of all always remember to leave space for build up on your machined parts. Threads/critical dimnensions will need to have compensation in them to allow for the anodizing thickness. Make sure to find out if the anodizer is planning to etch the parts before anodizing, as this will remove a small amount of material (~.0003") form the surface. Try to avoid sharp corners. The oxide layer builds up perpendicular to the surface, to theoretically there is no coating on a perfectly sharp corner. with type 3 you don't have as many color options as with type 2. i think green, gray and black are your only choices. The hardness and scratch resistance will vary also on how they are racked in the bath. 

As you can see there are ALOT of factors involved in getting the anodizing just the way you want it. 

hope this helps!


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## Christexan (Sep 24, 2007)

Most points touched on here (didn't look at the Wiki, maybe a lot more there)... the key process difference is HA-II is done at "room temp" (roughly 68-72F is ideal) and modest current levels (12 amps per square foot I believe is the average standard number, but don't quote me on that). HA-II and HA-III BOTH grow into the surface, however HA-II is roughly a 1/3 to 2/3 ratio (1/3 in, 2/3 out), so it's not as deep as HA-III which is a 1:1 ratio (1/2 in and half out), and also HA-III allows thicker overall layers, although HA-II can get pretty thick as well if done right. 
Related to the above "growth" effects is the pore size, basically either version makes "cells" of aluminum oxide which resemble hollow tubes or a "honeycomb" effect... HA-II has larger pores which allows more colors to be used to color the final product (dyes have different particle dimensions depending on color used, etc). HA-III has smaller pores, which means only the finest particle dyes can be used, which are the green and black basically (there are other types of anodizing where the anodizing process itself makes the material appear either gold, or "shimmering" depending on method, I won't go into that much detail here). 
Now onto HA-III, it is done at a much cooler temperature (sub-50 degrees bath temps), and at a MUCH higher current density (30-70 amps per square foot or something like that, it's been awhile since I researched it). It is also done with a much lower concentration of acid (about half of HA-II I believe, which is around 19-23% by volume, so around 8-12% by volume for HA-III). Basically by reducing the acid concentration and temperature, the newly formed oxide layer is attacked much more slowly by the acid, and in conjunction with the much higher current, can penetrate more deeply into the base material and extend out farther as well. But the high current requirements, and the other stricter requirements (each anodizing shop guards their specifics pretty well as each has their own recipe) make this much harder for "DIY" HA-III. You need a very well controlled current source (hitting an "on" switch would likely burn any connections to the part due to the sudden voltage and current spike and bring a quick halt to any effects), typically this process is ramped up, regulated, and monitored for specific "end of process" effects (voltage changes, current changes, etc). Just not easily replicated at home, you could do it for something very small (an aluminum locket or clasp maybe) if you had a 3-amp power supply, but if you even have a 1/2 sq ft surface area (reasonable for a flashlight for instance), you'd need at least 15-30 amps of current, regulated, and the other requirements. Best to find a shop that can toss it in with their other jobs.


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## yellow (Sep 26, 2007)

not sure on the temp,
but very sure on: WAY higher current
... "only" difference to normal anodizing


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## bobstay (Sep 7, 2008)

So, for hard anodizing at home, how about:

Cooler temperature: put the anodizing bath in a domestic freezer before and during the process, surrounded by ice cubes and run the freezer on boost to keep the temperature down. Pumping 200-400W in there would definitely raise the temperature faster than the freezer could cope with, but with a large thermal mass of pre-frozen ice around your anodizing bath, perhaps it could be kept under 50F for the duration of the run.

Higher current: use a car battery or two. A typical flashlight body 1" in diameter and 10" long comes out at about 63 square inches or under half a square foot, so 15-35A current needed. That's doable with some thick wires and a couple of car batteries - a starter motor takes 100A, and a pair of headlamps 10A.

Reduced acid concentration... easy enough.

Controlled current source: Connect a load of different car bulbs in parallel, each with a swtich in series with it. Put this contraption in series with your anodizing bath. Start by turning on the smallest bulb (sidelight bulb perhaps). Then turn on progressively larger ones (and several of them) to ramp up the current. Measure it with an ammeter; manipulate switches as needed to regulate the current. End up by throwing a switch to short out the whole lot of bulbs and give it full current if needed.

Perhaps I'm being hopelessly naive here, but I don't see any of the hurdles mentioned as a showstopper. Maybe I'll try this sometime if I get bored enough.


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## iconoclast (Sep 8, 2008)

bobstay said:


> So, for hard anodizing at home, how about:
> 
> Cooler temperature: put the anodizing bath in a domestic freezer before and during the process, surrounded by ice cubes and run the freezer on boost to keep the temperature down. Pumping 200-400W in there would definitely raise the temperature faster than the freezer could cope with, but with a large thermal mass of pre-frozen ice around your anodizing bath, perhaps it could be kept under 50F for the duration of the run.



As I understand it, part of the trick to Type III is that the actual anodizing need to be kept cooler. The problem is that the anodizing process produces heat. Often keeping the acid bath cold (such as putting the whole thing in a freezer, etc.) isn't sufficient to keep the anodizing process (where the acid touches the part) cold. To get around this, some form of recirculation is normally used to provide continual cold acid right at the part. (This is likely to be acid solution pumped out of another part of the tank and run through a heat exchanger of some sort.) This is one of the reasons why the level of hassle rises above the typical DIY threshold.
If you search around the web you can find examples of people doing it, but if you look at their setup it's clear that the investment (both time and money) rivals the way some folks around here approach flashlights.


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## bobstay (Sep 10, 2008)

iconoclast said:


> If you search around the web you can find examples of people doing it, but if you look at their setup it's clear that the investment (both time and money) rivals the way some folks around here approach flashlights.



Hmm. I've looked round the web and failed to find any DIYers doing it - do you happen to have any links handy? I'd be interested to read what they do.

As for keeping the part cold - that might actually simplify the setup slightly. Instead of having the whole thing in the freezer, wrap some silicone aquarium tubing round the cold bit (element) inside the freezer (multiple times), have the anodizing bath outside the freezer, and use a car windscreen washer pump to circulate the acid, with the outlet arranged to point right at the part. (Make sure the pump innards & impeller are plastic...)

I guess I'm more into the process of flashlight creation than the outcome!


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## iconoclast (Sep 18, 2008)

bobstay said:


> Hmm. I've looked round the web and failed to find any DIYers doing it - do you happen to have any links handy? I'd be interested to read what they do.



Sorry, I don't have any useful links offhand. 
I stumbled across one roughly 9 months ago, but it didn't have large amounts of detail for Type III. It was actually a page about Type II, with some explanatory comments regarding some of the photos along the lines of "...the thing we're talking about is on the left side of the picture, the one on the right is my Type III setup and different from what I'm writing about..."
Whatever he had connected up in the photo looked very rube goldberg, and if I recall correctly it involved a hacked window-sill type air conditioner unit as part of the cooling apparatus. I'll see if I can't dig up the link again.

Also, one of the "anodizing kit" suppliers claims to have a "studio" size kit that will do Type III. Unfortunately there's not much in the way of details or pictures, and it starts at $500 for the 2.5 gallon kit, not including the chiller. They also mention having USED anodizing chillers available starting at $800. This might be a bit beyond the casual hobby anodizing, but if anyone's interested their info is here: http://www.platingsales.com/anodizingspecialty.html
(I've never dealt with them, and don't know anything about them that isn't on their site.)


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