[Emc-users] Crucible furnace [Was: A round toit generator]

[Erik C. <dv...@in...>]

On 16.04.14 08:48, Kirk Wallace wrote:
> I think pushing your home-made furnace up the list might be a good idea. 
> Then you know who to call when it doesn't work :). I did this:
> 
> http://www.wallacecompany.com/machine_shop/Furnace/

Very nice crucible handling tools, Kirk. (They put mine to shame.)
It's a shock to realise that it's nearly four decades since I built a
crucible furnace with firebricks (two-brick by half a dozen courses
cavity), using a mix of local clay and sand for fireproof mortar. (As
described in an old steam engineer's handbook) The lid is a firebrick
slab.

The grate was just coarse pebbles on a perforated steel sheet, one
course from the bottom, with a 12v car ventilation fan blowing in under
that, through a piece of rectangular steel downpipe inserted in a gap
left in the first brick course. The PWM speed controller used a 555 and
power transistor to bring things down to a dull roar. OK, there were a
few bangs inside, as a couple of pebbles fragmented during the first
gentle burn, but all was quiet after that.

Fuelled with coke, it melted steel, and on one occasion I made some
aluminium bronze castings, cooking up the bronze from scrap aluminium,
some half inch electrical cable cut up with an axe, and some tiny brads
for the iron content. (Didn't have swarf in those days) The Al-bronze
seemed to be chill cast, because a big angle grinder skated off without
taking much of a bite, when I started fettling.

But mostly it was used for aluminium casting, fuelled with charcoal,
which was to hand, since the furnace stands on the edge of 2 sq km of
hardwood forest. A little bit of Cu and a little Zn made the castings
age hardening.

If I'd had waste oil to burn, then an oil fuelled design would have
appealed, but instead I still have nearly 2 cu m of charcoal for if my
energy levels should again lead to a fit of melting. Better make some
better crucible tools first, though.

Erik

-- 
The northeast coast of Tasmania is a climate-change hotspot. There's been a sea
surface temperature monitor on Maria island for 30 years and in that time the  
sea has warmed 4°C [bringing] the long-spined sea urchin, which was first seen 
around Flinders Island in the late 70s. - Dave Allen, in Weekly Times 02.04.14.