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Aluminium foundry

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Dr. Shark

Tue Jan 23 2007, 04:50PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

I'm not sure if this really fits the "scientific" category, but its definitely not "off topic", so here it goes...
Over christmas I set out to build a litte foundry using aerated concrete bricks for isolation and confinement, coal as fuel, and a petrol engined leaf blower to supply air. The whole setup, which literally took 5 minutes to get ready, worked remarkably well, and I was able to melt about a pound of alu scrap on the first trial. Since I did not have any moulds ready, not expecting liquid alu the first time, I poured it in a tin can, the shape of which the alu took with a near-perfect, smooth surface. I then made some plaster moulds using the lost wax process (first making the desired shape from wax, putting it in plaster and melting it out after hardening), but these did not work so well, since the plaster absorbed quite a lot of the wax which boiled away and destroyed the cast surface with big bubbles. Anyway, cosidering it was only one days effort I was surprised it worked at all.
I also tried melting copper, but due to the higher melting point (1060C compared to 600C for Al) it did not really work. I guess I was blowing too much cold air directly at the crucible in the foundry, but with my quick and dirty setup I could not really improve on this. I managed to produce a considerable quantity of a rather funny Al-Cu alloy however, which was so brittle that it could be ground in a mortar. Probably the most useless alloy ever made

Alex

Tue Jan 23 2007, 08:14PM

Geometrically Frustrated
Registered Member #6 Joined: Thu Feb 02 2006, 04:18AM
Location: Bowdoin, Maine
Posts: 373

Neat, do you have any pictures of your setup or castings? My dad and I made a little foundry out of stove pipe and some special plaster stuff. We used a homemade propane burner (which unfortunately makes it expensive to run), and it worked pretty well. Our sand molds made pretty rough castings, but higher quality sand would probably help that.

Lindsay Publications has quite a few good books on various foundry techniques and projects, you might want to take a look. I reccomend Dave Gingery's books.

Conundrum

Tue Jan 23 2007, 08:25PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Hmm. Have you tested the Al-Cu alloy for any unusual electrical or magnetic properties?

:)
-A

ragnar

Wed Jan 24 2007, 02:25AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Every time I disassemble a hard-drive, find a warped sheet of aluminium, etc, I keep it... I've got a big milkcrate full of scrap aluminium just DYING to be melted into something!

I guess I'd better get my class-E induction heater going.

What's the formation of oxides like with the Aluminium?

Dr. Shark

Wed Jan 24 2007, 11:30AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Sorry, no pictures - I forgot to take my camera home to my parents place where I did the melting.
I used bike parts for the scrap. Cranks are good since the contain a lot of metal with little surface area. Oxidation is maily a problem with small bachtches and when small bits of scrap are used, I that case I think burning away 50% of the metal is a realtistic estimate. Having a lid on the crucible would probably help with that.

I imagine the Al-Cu alloy to be a worse conductor than the constituent metals for the same reason that it is so brittle: It does not have a proper crystal structure, but is just a big mess of crystal defects. An alloy with a proper 1:1 stoichiometry would proabably have very different properties.

ragnar

Wed Jan 24 2007, 01:01PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Hehe, you'll probably find your aluminium-copper mess is a semiconductor, considering the oxidized crap all over it... Well, maybe :D

Have you used flux in your batches?

Marko

Wed Jan 24 2007, 02:08PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Alu foundry.. I also admit I always wanted one.

For smaller amounts, blowtorch actually does it pretty well.

The other, and main problem is, what can it be used for in the end?

I imagine casting out something decent-looking would be impossible with hobby resources.

I would really like to see someone suceed making a good plaster mould...

Industrial production heatsinks and alu parts are done by forcing molten Al into moulds under great pressure,after it cools, it is stretched and then anodized with uniform, invisible oxide layer.

rather funny Al-Cu alloy however, which was so brittle that it could be ground in a mortar.

''Rather funny Al-Cu alloy'' was called duralumin

and after proper age-hardening can be made strong as steel.

I also guess you used much larger percentage of copper wich messed the alloy up.

Anyway it's mostly obsolete today after aluminium-zinc alloys.

Self Defenestrate

Wed Jan 24 2007, 02:45PM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

One of my favorite r-candy sites has a page on aluminum foundrys, and making aluminum rocket engines with the stuff..

Dr. Shark

Wed Jan 24 2007, 03:56PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Whoa, you got me there! That's exactly what I tried to do, make a Laval Nozzle for a toy rocket. Actually I made three plaster moulds: One was a part for a knife, which turned out really well. It hardly required any work other than removing the sprue/git (I had to look that up in the dictionary). The rocket nozzle did not turn out at all, as the sprue/git (still dont know which is correct) was too small and the Al could not enter the mould. The third was a rather phallic sculpure, but this is where the wax left in the form gave a very uneven surface finish. The best surface I got was however the "ingot" which I made by pouring Al in a tin can.

I did not use any flux, since I have no idea what would be suitable to use with Al.

Self Defenestrate

Fri Jan 26 2007, 12:58AM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

I always liked using durhams water putty for my nozzles, but never made a truly reusable motor either. How big of a nozzle are you trying to make?

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