Foosh!

[andygates]

How should one light a Solstice bonfire?  This year, I did it with thermite (video has a naughty word 'cos I was startled).  That's about 150 grammes of stoichiometric thermite made with ordinary, off-the-shelf stuff and lit with a sparkler.  The molten iron, at around 2000c, spattered and burned so we didn't retrieve it, but this proof-of-concept firing means I can go ahead with the thermite lost-wax casting I've got in the project file.  Yes, I'm going to be doing mjolnirs.  :)

Comments

[maythen-apple.livejournal.com]

that was fun to see. thank you

[shifty-176.livejournal.com]

I could do with a new hammer...
When I get organised (caveat: this is taking longtime) with the forge and all that jolly stuff, I was thinking of making knives and such, but up to now I never actually considered casting my own hammer. Hmm.

[jarkman.livejournal.com]

I'd guess it would be plain cast iron, and way too soft for hammers. Unless there's some cunning way to control the carbon content of the output. That might be fun.

[andygates.livejournal.com]

Ornamental hammers! Lust for a big chunky mjolnir pendant cast in kaboom is what started this whole gig off...

[jarkman.livejournal.com]

Hurrah for melting!

We had mostly-good results with lost-foam in sand, doing bronze casting. Like lost-wax but without the annoying burnout phase. Not suitable for tiny, tiny work, but I guess with thermite you probably aren't aiming for that anyhow.

[jarkman.livejournal.com]

A few photos of the lost-foam product, by way of illustration:
http://jarkman.co.uk/catalog/fripperies/bronzerobotboy.htm
http://jarkman.co.uk/catalog/fripperies/theclaw.htm
http://jarkman.co.uk/catalog/fripperies/cthulhuspike.htm

Should have some process photos somewhere, too. Wonder where they are ?

[andygates.livejournal.com]

Those robots are lovely fine detail - is that using regular polystyrene foam or something cleverer? (Nice Marvin scuplt, too)

I haven't done any casting since we did lost-foam way back in school, with aluminium. I can't even remember what I cast, though I do remember that a kid called Tony slipped with his metal and took a beautiful negative of his steel-toed boot!

[jarkman.livejournal.com]

It's the stuff builders use - comes in two-inch-thick slabs, a bit denser than ceiling-tile and much more consistent in texture. It goes away like it was never there when the molten metal approaches.

What scale are you thinking for your mjolnirs ? Lost-wax and a plastery investment will give you better resolution, but I think it will be a lot more faff.

[andygates.livejournal.com]

Thermal batt, aye, it's more consistent and less bobbly - I'll give some a try. I was thinking around the 4-6 cm scale (4 across the head, 6 along the shaft) by about one deep, roughly. I like the roughness of sand casting, it pleases me greatly, and a worn piece will patinate really well.

[jarkman.livejournal.com]

I'm liking the sound of this. Do you have some scheme to keep the thermite in till there's a nice puddle of iron ready ?

[andygates.livejournal.com]

Hmm, not yet. I was going to go with a flowerpot full of thermite and a wax plug to keep it in place. I *think* that as it starts at the top, by the time it gets to the bottom it'll be a boiling mass of liquid iron. I'll keep you posted!

[jarkman.livejournal.com]

Very exciting.

You know all about the importance drying your mold and the dangers of metal-splash, I hope ? I've only had one incident along those lines, on a very small scale, and I wouldn't want to have another. We we doing silver casting by the lost-frog process, and we hadn't baked out the frog properly, and got a real silver fountain.

In fact, I'd worry a bit about your wax plug vapourising in a steel-throwing kind of a way. I had a google, and this chap:
http://www.theodoregray.com/PeriodicTable/Elements/026/index.html
reports success using layers of aluminium foil as a plug.

Good luck!

[andygates.livejournal.com]

Top link and duly noted!

"My first large batch, about a pound, burned great for about 3 seconds and then exploded, which is not something thermite is supposed to do. It turns out I should not have used a zinc penny to cover the hole in the bottom of the crucible: The boiling point of zinc is much less than the temperature reached by the reaction, so when the molten iron hit the penny, it exploded into zinc vapor. A copper penny was only slightly less explosive: Turns out you're supposed to use an aluminum disk. Using folded up layers of aluminum foil I have had no more problems with explosions. Which is not to say I'm anywhere closer than 20 feet away whenever I ignite thermite: It would be really quite stupid"

[jarkman.livejournal.com]

:-) Yes. 20 feet doesn't actually seem that far, once you imagine you might have a pound of molten iron flung at you.

[andygates.livejournal.com]

It's about five feet behind the camera... (eek)

[jonnycowbells.livejournal.com]

Can you still send this sort of thing to Harry Hill for a couple of hundred quid? Self-financing thermite is the best.

[andygates.livejournal.com]

Not unless I set fire to my beard or the duck that lives next door...

[andygates.livejournal.com]

...oh, and it's silly cheap. That shot would be about £3 if I hadn't burned all the sparklers while drunk :)

[despaer.livejournal.com]

You can achieve a similar effect by mixing iron filings and powdered sulphur (which I remember getting from a garden centre once upon a time) and lighting with a similar hot source (the pink bit of a match in my case). Give it a go on your next bonfire.

[andygates.livejournal.com]

Flowers of sulphur! Indeedy... though nothing like as violent :)

[despaer.livejournal.com]

Ah, but me and my mate Jez thought it would be much cleverer if we bent a piece of copper pipe over to seal one end, filled it up and lit it. You get a roman candle job about 10 feet high.

[andygates.livejournal.com]

Wheee!