[Amps] gun drilling liquid cooling holes and making aluminum heat sinks black

[Will Matney]

Mike,

I'll tell you something that will etch it if not faster than sodium hydroxide (household lye). It's the copper etchant that is used to etch PC boards. There's two kinds and neither like aluminum very much. A weak solution of either would work. I'd advise washing it off as soon as it's applied if you want any heatsink left if its not cut. I found this out the hard way when I was a teen. I poured some ferric chloride in an aluminum pie pan, and before I could do anything, it had eat a hole in the bottom and ran out on the bench. If strong enough, it's a pretty violent reaction.

As far as paint, I would not paint the flat surface where the transistors will sit. That needs to be as heat conductive (between the heatsink and transistor) as possible, and I would say that a thin layer of paint would hurt the heat transfer here. I personally dont like anodized heatsinks over this due to the layer of die on the aluminum. The surface has been changed too from the electro-chemical process from the anodizing. I cant see the anodizing or the paint being as heat conductive as the bare aluminum itself.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 7/22/06 at 7:54 AM mike kendall wrote:

>Harold,
>    I will check at the auto hobby shop on base, they may have a bead
>blaster.  In absence of getting my hands on any sodium hydroxide, is there
>any household item that I may use to acid etch it like maybe some kind of
>draino product designed to free clogged drains?  If they don't have a bead
>blaster, I may just use emory cloth by hand on the fins.  Definitely won't
>paint it.
>    I am going to use a combination of this aluminum heat sink and also a
>copper heat spreader that I have coming off ebay and liquid cooling, yes
>this is going to be overkill but I don't see how that is going to hurt
>anything.
>   I am emailing some stateside machine shops about getting some "gun
>drilling" done for the liquid cooling holes (1/4inch across a 5 inch
>width).  I read that commercially, they expand the 1/4inch tubes inside
>the gun drilled holes but that isn't an option because I don't have a clue
>how to "expand" 1/4inch OD copper brake line inside of a gun drilled
>1/4inch hole.  I was thinking to take a drill bit just a little larger in
>diameter after I get the gun drilling done and push the copper brake
>tubing in maybe 1/2" and then solder the tube in place.  I am concerned
>that once I heat up the heat spreader with a torch momentarily to get the
>solder to bond the brake tubing to the gun drilled hole then I will warp
>it.  If I warp it, this will open up a can of worms when trying to get a
>good surface to attach the heatsunk devices and the aluminum heat sink as
>well. Any ideas on how to attach the brake line to the heat spreader?  The
>heat spreader is 3/8" thick and the OD of the
> hole will be approximately 1/4" I've never worked with copper (C110) like
>this and another person even said the copper can get gummy when drilling
>it?
>  Respectfully,
>  Mike Kendall
>  
>
>Harold Mandel <ka1xo at juno.com> wrote:
>  Dear Mike,
>
>When finishing drilling the holes on aluminum heat sinks
>I bring them to a machine shop where they are either
>bead blasted or sand blasted to get rid of the polished surface,
>breaking up the surface RMS (finish).
>
>This enables the wind crossing their surfaces to be disturbed more
>(albeit on a microscopic level) and thereby transferring more surface
>heat to the wind from the aluminum.
>
>The color Flat Black will absorb IR radiation more than shiny metal
>because of the diminishment of reflectivity of wavicle EM radiation,
>but will not emit EM radiation as efficiently.
>
>Remember, the more surface area, even at the microfinish level, then
>more area to transfer heat as a radiator. Finishing the surface thus
>prepared
>with any coating such as varnish or lacquer defeats the purpose entirely.
>The best 
>finish for scuffed aluminum radiators is pickling in caustic soda (Sodium
>Hydroxide).
>
>Respectfully,
>
>Harold Mandel
>W4HBM
>
>-----Original Message-----
>From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
>Behalf Of mike kendall
>Sent: Saturday, July 22, 2006 9:47 AM
>To: amps at contesting.com
>Subject: [Amps] making aluminum heat sinks black
>
>Hello,
>Just recieved a large 1foot long aluminum heat sink off ebay. I read
>that it will work much more efficiently if painted black on one web page.
>Any suggestions on the right kind of paint that will stick and not flake
>off
>and if it is worth making it black instead of leaving it as bare aluminum?
>73,
>Mike Kendall
>
>
>
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