# hollow heat sink source

R

#### [email protected]

Jan 1, 1970
0
Hi all,

I am looking for a source of small quantities of hollow aluminum heat

http://www.mmmetals.com/extrusions/drawings/MM001524.jpg

Has anyone come across anything like this? Basically, a ~3 inch wide
by 1-3 inch high hollow rectangle/square with fins/separators inside.
I need this for a low-budget prototype I am building.

everything I could easily find were open heat sinks. I do need the
closed design.

P

#### PeterD

Jan 1, 1970
0
Hi all,

I am looking for a source of small quantities of hollow aluminum heat

http://www.mmmetals.com/extrusions/drawings/MM001524.jpg

Has anyone come across anything like this? Basically, a ~3 inch wide
by 1-3 inch high hollow rectangle/square with fins/separators inside.
I need this for a low-budget prototype I am building.

everything I could easily find were open heat sinks. I do need the
closed design.

Why not buy from them? They are a good supplier, providing much of our
extrusions at competitive prices... Need only a sample? Contact them,
and they may be willing to send you a small leftover end piece for the
cost of shipping.

R

#### [email protected]

Jan 1, 1970
0
Why not buy from them? They are a good supplier, providing much of our
extrusions at competitive prices... Need only a sample? Contact them,
and they may be willing to send you a small leftover end piece for the
cost of shipping.

Peter - sounds like you know the company. I wrote them for a quote,
and I can't wait to hear back, that's why I was hoping that some
online store sells smth similar.

I am usually disappointed when one can not purchase products from a
company's web site - one has to email for a quote, wait till one hears
back. Plus, no prices were published.

P

#### PeterD

Jan 1, 1970
0
Peter - sounds like you know the company. I wrote them for a quote,
and I can't wait to hear back, that's why I was hoping that some
online store sells smth similar.

I"m not sure where you are, I use their local rep for New England
customers (they are in NH...) The only problem I ever had was when
their sales rep for my area died last year, that was awkward...
I am usually disappointed when one can not purchase products from a
company's web site - one has to email for a quote, wait till one hears
back. Plus, no prices were published.

Prices are very fluid in this stuff, based on the market for aluminum
mostly. They are oriented towards larger sales (they don't sell to end
users for example) the stuff I get comes on a 60ft semi trailer...
<bg>

Unfortunately I don't have anythign like you are looking for.

For anyone else...

We do have end cuttings (typically about 2 to 2.5 inches long of some
other extrusions. They are free for the asking but you must pay
postage (typically about $4.90 or so to US addresses. Right now these just go into the scrap box. R #### [email protected] Jan 1, 1970 0 Unfortunately I don't have anythign like you are looking for. For anyone else... We do have end cuttings (typically about 2 to 2.5 inches long of some other extrusions. They are free for the asking but you must pay postage (typically about$4.90 or so to US addresses. Right now these
just go into the scrap box.

Thanks for letting me know about the end cuttings. Would you happen to
have longer pieces, like, 12 in? I thought more about my, and I should
be able to get away with "open" finned extrusions, since it's so hard
to get exactly what I want.

companies. I am in the Bay Area. Should I drive around and look into
dumpsters in the Silicon Valley?

A

#### [email protected]

Jan 1, 1970
0
Thanks for letting me know about the end cuttings. Would you happen to
have longer pieces, like, 12 in? I thought more about my, and I should
be able to get away with "open" finned extrusions, since it's so hard
to get exactly what I want.

companies. I am in the Bay Area. Should I drive around and look into
dumpsters in the Silicon Valley?

Have you tried a hobby shop? Some of these folks have access to fun
materials like that.
You might be on the bigger end of what hobby extrusions look like but
give it a try.

J

#### John Larkin

Jan 1, 1970
0
I"m not sure where you are, I use their local rep for New England
customers (they are in NH...) The only problem I ever had was when
their sales rep for my area died last year, that was awkward...

Prices are very fluid in this stuff, based on the market for aluminum
mostly. They are oriented towards larger sales (they don't sell to end
users for example) the stuff I get comes on a 60ft semi trailer...
<bg>

Unfortunately I don't have anythign like you are looking for.

For anyone else...

We do have end cuttings (typically about 2 to 2.5 inches long of some
other extrusions. They are free for the asking but you must pay
postage (typically about \$4.90 or so to US addresses. Right now these
just go into the scrap box.

Do you do custom extrusions, or machining? If so, please post a link
or email me. We need stuff like this from time to time.

jjlarkin atsymbol highlandtecnology alltherest

John

P

#### PeterD

Jan 1, 1970
0
Thanks for letting me know about the end cuttings. Would you happen to
have longer pieces, like, 12 in? I thought more about my, and I should
be able to get away with "open" finned extrusions, since it's so hard
to get exactly what I want.

companies. I am in the Bay Area. Should I drive around and look into
dumpsters in the Silicon Valley?

Our finished product is about five inches, so there would never be a
piece longer than that... <g> The extrusions we get are dimensioned to
do this size, with a bit left over for errors, etc. The suppliers then
add on an half an inch or so so that their pieces are not short.

Dumpster diving is not such a bad idea, as is salvaging 'em from old
equipment too. When I do a one-up project, and nothing I have on hand
is suitable, I usually just trash some old piece of junk... <bg>

P

#### PeterD

Jan 1, 1970
0
Do you do custom extrusions, or machining? If so, please post a link
or email me. We need stuff like this from time to time.

jjlarkin atsymbol highlandtecnology alltherest

John

No custom extrusions, but we cut, drill, tap and sometimes mill them
as needed. Mostly cut, drill, tap, radius the holes, clean the edges,
followed with a washing.

J

#### John Larkin

Jan 1, 1970
0
No custom extrusions, but we cut, drill, tap and sometimes mill them
as needed. Mostly cut, drill, tap, radius the holes, clean the edges,
followed with a washing.

ftp://66.117.156.8/Amp.jpg

The shiny things are solid copper, nickel plated heat spreaders. The
transistors are un-insulated and the whole heatsink is signal-hot,
bolted to the chassis through the delrin blocks at the top of the pic.
17 KW peak power output per axis into an MRI imaging gradient coil.
Since it's imaging, we get to sell three boxes per system.

Some of our users want more output, so we may do a water-cooled
version next. That should be interesting.

John

P

#### Paul Mathews

Jan 1, 1970
0
Allright, I guess I should have looked up Al Oxide, which is 30 W/mK -
only ~7 times better than the adhesive I found.

Please note actual thermal resistance depends on:

1) cross sectional area (inversely proportional)
2) thickness of layer (linearly proportional)

Meaning: with a large cross sectional area and a thin bonding layer,
thermal resistance is low. Get everything very flat, with the Al
pieces in good contact, clamp if necessary. Use fillets of adhesive
instead of a bonding layer. Whatever. Will NOT be a problem.

Also, adhesives filled with high thermal conductivity materials have
higher thermal conductivity than non-filled materials. However, it
won't matter if you follow above.

Paul Mathews

R

#### redbelly

Jan 1, 1970
0
I was thinking to make my own heat sink by bonding plates together.

But I found out that heat conductivity of bonding materials is *much*
poorer compared to solid metal. E.g. this adhesive claims to be 4.5W/
mK, while solid Aluminum is 221 W/mK. That's 50 times worse compared
to a solid heat sink.

As far as adhesives go, 4.5 W/mK is about as good as it gets. Just
clean the parts well with alcohol and clamp them together while the
adhesive is setting. Then heat transfer is through just a thin layer
of adhesive material, and it will barely make a difference for the
overall thermal resistance.

For example, if you had 1/4 square inch of total contact area and
resistance:

(1 m K / 4.5 W) * (0.002/39.37)m / (0.25/39.37^2)m^2
= 0.07 K/W or 0.07 C/W

Regards,

Mark

P

#### Phil Hobbs

Jan 1, 1970
0
redbelly said:
As far as adhesives go, 4.5 W/mK is about as good as it gets. Just
clean the parts well with alcohol and clamp them together while the
adhesive is setting. Then heat transfer is through just a thin layer
of adhesive material, and it will barely make a difference for the
overall thermal resistance.

For example, if you had 1/4 square inch of total contact area and
resistance:

(1 m K / 4.5 W) * (0.002/39.37)m / (0.25/39.37^2)m^2
= 0.07 K/W or 0.07 C/W

Regards,

Mark

Solder is the way to go. You can solder aluminum under oil, or get
special flux.

Cheers,

Phil Hobbs

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