Aluminum extrusions - may be not much less than that of "poured aluminum",
which has heat conductivity of 161 w/m-k.
Die-cast zinc-aluminum alloy - 127 for "ZA-27", 115 for "ZA-8".
Die-cast zinc "zamak" - 113 w/m-k
Die-cast die-castable aluminum alloy - 96.2 w/m-k
Annealed brass - 61 w/m-k
Extruded copper - 300 w/m-k
Extruded aluminum - 200 w/m-k
6061 aluminum alloy - 166 w/m-k, if I correctly translated from
6061 aluminum alloy - 180 w/m-k
(There are heat-treated versions of 6061 including T4 and T6, which have
mildly increased electrical resistivity, and I suspect also slightly
decreased thermal conductivity.)
If this spacer has to conduct several 10's of watts or more and every
degree matters, I say make it out of copper or silver.
Otherwise, extruded aluminum, poured aluminum and 6061 are close enough
to each other for "best aluminum", and I expect ordinary aluminum plate
and bar stock (to be machined into shape) to be similar.
- Don Klipstein ( email@example.com)
The mating surface should be as flat as possible. Many cheap extrusions fail
this test. Using formed sheet material is very effective.
See Motorola's ( now On Semi's ) AN1040 IIRC for good thermal advice.
We flatten worn oilstones, used for sharpening wood chisels and so on, by
rubbing them with dry sand on a melamine board. Throw some sand on the
board and rub the oilstone on top until all the hollows are gone - noisy
and takes a little time but it does the trick.
Something similar ought to work for heatsinks
On Tue, 05 May 2009 10:34:26 -0700, James Sweet wrote:
The point of the whole exercise was to do it by hand, with a file.
These days, you just upload the program, throw a piece of metal into the
machine, and the finished part comes out the other end. ;-)
Exercise? I thought he wanted to make a heatsink?
For a one-off of a simple operation like milling a surface flat, it's a
lot easier to just stick it in a manual mill. If you want 100 of them,
or you want a complex part, then CNC is the way to go.
Some, perhaps even most, aluminum alloys machine nicely. Pure aluminum,
and just about anything designed to be easy to bend up, is 'gummy', and
hard to get a good finish on.
But 6061 is a treat, and many extrusions seem to be nicely machinable.
Yes, very careful lapping on a piece of glass with finer and finer
grinding paste should produce a suitable finish.
Of course you could try scraping. A friend of mine used to hand scrape
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.