A bit OT: Heat sink hard anodizing company recommendations?

How about DIY...use a bucket of battery acid and a power supply. Keep anodizing till the thickness is right. There are instruments for measuring the anodization thickness. D from BC

We do that a lot. We usually machine them flat, then hard anodize, say

0.5 mil for 50 volt stuff, 1 mil up to 200. You will have to machine off the plain anodize if you buy them that way... hell on cutting tools.

But that small a pin-fin will have a high thermal resistance on its own, so heroic insulating schemes won't help too much.

John

Eek...I was hoping that the clear anodizing on them now (they're not available unplated) could be stripped off by the anodizer.

What kind of volume would you say makes doing it in-house worthwhile? I don't know if 100pc lots every couple of months is worthwhile.

These sinks have a theta-sa of about 0.35-degrees C/W with the recommeded fan...pretty darn good IMHO. I've only found one better,

0.22, and it was a lot more expensive.

Thanks!

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Hmm...interesting idea. Maybe a possibility for the prototypes and some testing but I'm not sure if we can scale it up to 100pc. lots every few weeks.

Do you have any recommended links with how-to's for us to see what's involved. A Google search turns up thousands of them. :-)

Beyond knowing that a power supply and some nasty chemicals are needed, we're pretty ignorant about what's involved with hard anodizing.

Thanks!

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I'm still a newbie at DIY anodizing myself.. My Experiment: I went to the local car battery distributor and got 2 liters of sulfuric acid for $5.00..It was the first time they had somebody come in and just ask for acid.. :)

I had a 12V 4A switchmode power supply to sacrifice and started anodizing in the kitchen.. The power supply got hot and a nearby AM/FM radio got no reception on every channel..

The fumes are a real nose stinger.. :P (I think some H2SO4 mist rides on the O2 and H2 bubbles from electrolysis but my chemistry is crappy..I'm probably wrong..) But I got my parts anodized.. I had to poke a multimeter hard into the aluminum to get conduction.

D from BC

DIY may be OK for a garage shop, but if you're a very big operation at all you'll get caught up in environmental regulations, and if you're going to be paying an employee to do it then you have to conform to safety standards, too. Add in the process knowledge you'll need to make it consistent, and you may just be better off sending it out.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

Maybe hire the local teenage kids to set up shop in Dad's garage :P (yah yah......blinded kids and lawyers sueing.) But you'll be creating an educational and fun summerjob :) D from BC

Maybe so. Ask. But it's still nice to machine the cast, wiggly heat sinks flat, for better heat transfer.

We pay a lot/setup charge of, I think, about $75, plus a fraction of a dollar each, to hard anodize small parts. And you get your choice of colors!

That's good for a small sink like that.

The other thing you could do is make some aluminum plates the same size as the sink, anodize them, and bolt or epoxy them to the sinks. That will improve thermal spreading resistance, too.

John

Hard anodize has more complex chemistry than ordinary anodizing. The regular stuff is more porous and not as good a heat conductor.

Let the pros do it.

John

Good tip! I forgot to mention that the sinks already have a machined surface (before they were clear anodized).

Cool, that's within our budget. Colors? With Type III hardcoat? I thought only black was available (maybe gray). We were going to go with black anyway (usig black-cased fans) but perhaps that decision was a bit hasty. :-)

LOL, brilliant! A while ago we looked for aluminum-oxide insulators for each FET being mounted to the sink but gave up...too expensive. Hmm...probably can't use inexpensive rolled stock, would need to have the surface machined flat. Such a great solution but might end up being harder than having the sinks anodized. Definitely worth exploring though.

Thanks again,

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Yea, I think you're right. The DIY bug hit me and it sounded like alot of fun to try this out. But, we're already working like crazy around here and I must be nuts to think I'd have the time to do this properly in-house. :-)

A little more digging online and I realized that Type III hardcoating takes even more work than the regular Type II that is typically used for DIY anodizing.

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Dark blue is nice for a change. Most elegant.

Alumina is a rotten heat conductor. AlN is excellent. I think I got a quote on reasonable quantities of TO-220 sized AlN insulators for something like $1.50 each.

John

LOL, you're crazy if you think I'd let some teenage kids have all the DIY fun! I'm the one that needs the anodizing learnin'. :-)

We probably won't do it in-house though, too tough to do with Type III.

John

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I agree, my favorite color. :-0

Do you remember the thermal res. of those AlN insulators? We'll need TO-3P/TO-247AC sized ones but I'm pretty sure that they'll be available too. (LOL, famous last words).

John

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You may have read this

Looks like the difficulty with type III is keeping the part at 28degF. D from BC

Just a reminder that this type of passivation makes the material worthless for recycling.

RL

Really? Why so? All they do is melt it and skim the slag off the top...which seems like it wouldn't be terribly sensitive to the coating composition.

Cheers,

Phil Hobbs

On Tue, 05 Jun 2007 11:49:37 GMT, Phil Hobbs wrote: lots. We're in NY, but will be happy to ship anywhere. :-)

You've got me there.

I was told this point blank at a sensitive age and absorbed it like a sponge.. Perhaps what was meant was that the material could only be recycled as scrap, after anodizing. That it could not be reworked or conventionally tooled subsequent to the surface treatment.

Anodizing is actually an environmentally friendly method of surface treatment, when compared to other alternatives, and does not reduce the value of the final scrap material .

Glad you asked.

RL