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Backyard Foundry Tips?

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Inducktion

Wed Jun 15 2011, 12:57AM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Today I was kind of bored... So, I rigged up a quick backyard foundry, which consisted of a metal tin with dirt around it, a pipe going into the tin, an air pump from a blow up mattress (mom wasn't too happy about that) and of course, charcoal.

After a while, using a crucible I made myself some years ago in art class, I was melting aluminum. If i had to take a guess, I was in the orange-yellow range for temperature. I had the crucible inside of a steel can, to prevent any "accidents" such as molten aluminum spraying into my face. After a while though, putting more charcoal in, (which I also made myself) I noticed the crucible started to crack, and thus shut it down. After letting it cool off, I had some small bits of aluminum on the bottom of the crucible! So, it was successful, but I need a better crucible. As far as safety goes, I had long sleeves on, leather welding gloves, a face shield, safety glasses, jeans, and work boots on to protect myself if anything bad were to happen.

Any tips or helpful hints on what to do next time? I plan on buying a proper crucible, like this,

And one of these,

In the future, I plan on just being able to melt aluminum and copper, no ferrous metals. Hopefully it'll go even better next time!

Forty

Wed Jun 15 2011, 01:03AM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

won't a cast iron pot work for melting aluminum in? or would there be some chance of a thermite reaction? when melting aluminum (and most other metals) a lid on your vessel might be a good idea to prevent your metal from just oxidizing into powder, and to help prevent any sparks or splatters.

Inducktion

Wed Jun 15 2011, 01:34AM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Steel/iron tends to rust or scale really really quickly, contaminating the metal you're melting, along with weakening the walls over time...so no iron or steel!

magnet18

Wed Jun 15 2011, 06:17AM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

Forty wrote ...

won't a cast iron pot work for melting aluminum in? or would there be some chance of a thermite reaction? when melting aluminum (and most other metals) a lid on your vessel might be a good idea to prevent your metal from just oxidizing into powder, and to help prevent any sparks or splatters.

Thermite requires rust, and lots of it (I have video...)
He might get some sparklies if he poured hot aluminum in, but nothing serious, it isn't auto-catalytic.

klugesmith

Wed Jun 15 2011, 06:29AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Lots of good books for the amateur foundryman from Lindsay Publications:

I discovered them in the 1980's, pre-Internet. Some of their books like Charcoal Foundry by David Gingery were full of practical hints. I had lots of fun making patterns and molds, then casting zinc and aluminum and (a couple of times) brass and copper. Started with charcoal, switched to propane (as do many BBQ enthusiasts). In an early and lucky session, I melted 1/2 gallon of zinc pot metal in a 1 gallon steel paint can using charcoal & a pile of concrete building blocks.

Aside from a crucible & tongs, furnace,
stirring rod (12 inches is pretty short for a furnace & crucible bigger than pint-size),
skimmer

,
and protective wear, it would help to buy or make:
- some molding sand
- some flasks and other molding paraphernalia
- a pyrometer (I got some 10-gauge type-K thermocouple wires at a ceramic supply store, fused one junction with an oxyacetylene torch, connected the other ends to a low resistance meter movement w/ series resistor chosen for calibration. The junction broke after I probed lava in Hawaii (indicated 1800 degrees F) and it crusted over, trapping the probe.

)

I still have a few hundred pounds of surplus molding sand, olivine-based, from a real aluminum foundry. Available for $0.10 per pound + shipping, or pick it up here near San Jose, CA, USA.

[edit]
Other practical hints.

Never let molten metal solidify in a crucible; the thermal expansion on re-heating is likely to break a refractory crucible.

Steel tools are OK for stirring or skimming Al, since they're only in the heat for a few seconds.

Steel pots, as previously mentioned, do grow thick layers of scale on every heat, and can contaminate the melt. But I still have one used many times for zinc. It's made from 4.5-inch steel pipe with a disk welded on one end, a crudely forged pouring spout, and two holes near the rim that engage hooks at the ends of a removable lifting bail made from 3/16" or 1/4" steel rod.
A similar contrivance made from the bottom of a 14-ounce disposable propane cylinder held up for 2 melts of heavy copper wire, and burned through as the third melt was being lifted out of the furnace.

Judging pour temperature by color is impossible for zinc and hard for aluminum, being very sensitive to the ambient light level.

If you care about the mechanical properties of your castings, make a pattern for some test bars. You can inspect them for surface finish and shrinkage, then put them in a vise for a destructive test of ductility and strength.

Ash Small

Wed Jun 15 2011, 10:32AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I found enamelled cooking pots work ok.

Stainless pots are also better than iron or steel.

(iron dissolves in aluminium)

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