Furnace...woot

[Irvine.J]

A while ago I said I put together my old brazier to make a furnace from it, only propblem was we did at some point have a crucible, but lord only knows where it dissapeared to...I'm looking in my uncles direction.

Anyway, I made another crucible, just a smallish one, and will start by melting down a thin aluminium bucket i've cut into small squares, and will use my oven to set shapes made of wood in plaster of paris. I also found a whole packet of assorted SHIM STEEL WOOHOO just in one of my many random boxes lying around...

I got a bunch of heat beads and some charcoal, and will put the heat rocks under the plate, get em fired up, add some charcoal, then just push the crucible down till its sitting on the plate. Then I'll fire up the propane line. These braziers are pretty cool as you can simply open the side "slit" up (with some very thick gloves or pliers) and stick in the propane line. Here, i'm using a primus gas bottle end with the screw attachment drilled to a much bigger hole, its really just to give a bit of extra kick if it needs it, running straight off an unregulated propane tank for lotsa pressure.

Precision made part here we come woohoo! LOL, after alot of practice :-P I'll give it a go tomorrow!

[Zippiot]

I have a temporary oil fired furnace, I say temporary b/c I dropped my refractory one and am using a bunch of garden bricks in a pile now...

If you want some good info on building or running a furnace check out this site:
http://backyardmetalcasting.com/forums/

The main site has a bunch of useful info also!

[Irvine.J]

Do you guys remember ages ago when I had that problem with the dodgey ebay pulsejets!? Remember the sound they made, that wierd girgling near resonation but not quite there?

I was working on my burner when all of a sudden a familiar loudish sound filled the garage at 2:30am this morning waking up one very angry father.

How strange, especially for a straight pipe. Is this a common occurance when making burners?
Perhaps i'm close to getting my burner working, but I still think my burner sucks, and needs alot of refinement, anyway I just thought this was very interesting. I'm using no regulator, with a tiny nozzle, just wish it would work as a burner.

Excuse the 2:30am crazy scientist hair-do :D

[Zippiot]

The venturi looks ok, but maybe drill a few holes near the intake of the pipe to get some extra fresh air in.

[Irvine.J]

Is the burner pipe long enough? My nozzle is very small but I do have 1 thats even smaller. Hard to get it just right thats for sure.

[Zippiot]

You can add a flare to the end of the pipe, should help a bunch to burn completely.

[Irvine.J]

Thanks zippiot, here have a look at this, this is how i'm dremmeling out my casts. Then using baked plaster of paris, which I have already made a small box for. Needs a tiny bit of touch up, but I've been concentrating really hard not to accidently ruin it, and having a break...what you think so far. By the way this is only a little part time project till the metal guys open on monday for my major project.

[Zippiot]

Is the palster just a test or do you plan on using it for a mold?

Also what metal do you wanna melt, I assume its aluminum or zinc (mix the two together and you have an alloy nearly as strong as cast iron!).

[Irvine.J]

Zippiot I'm planning to melt aluminum (pure...that is unless I can find some zinc lying around, I didn't know that about zinc and aluminum!) Maybe thats why this "Zincalum" i'm using as sheet metal is soo good?

Anyway, I'm using the plaster and baking it, then yes will be pouring aluminium into it. I also figured something out... I have some water putty that sets hard, so you can actually use it to keep a negative of the mold later!

First, I make a mix of 90% (or about) vaseline and a touch of kerosene. then paint it all over the wood to be molded, as it prevents sticking. Works EXTREMELY well. I then put the wood in the plaster, let it dry then dug the wood out. (I used balsa cause it soft.) Now, I want to keep a copy of that shape in the mold now, to repair it later or make more if necissary. So I get out my vaseline (no kerosene) and paint the valve plate mold, using the vaseline to fill any holes from air bubles. Then I mix my "Agnews Water Putty since 1891" or some crud, and pour it into the mould, and stick a nail in it with the "Head" imbedded in the putty so I can pull it out later. Now I can make as many copies as I like!

Also CHECK OUT MY RETAINER MOULD!!! Isn't it swell, its simply a large poached egg dish molded with the putty, then used to make a mold in the plaster...it turned out darn smooth indeed. The vaseline was also used in the poaching dish so a couple of sharp taps it pops right out.

[Zippiot]

Well I heard of 2 ways to make the zinc/aluminum. Pennies made after 1982 is a decent source for small batches but larger ones you can buy in bulk zinc bolts/nuts/screws and all).

You can dissolve aluminum foil into molten zinc (well under 1k degrees F) or you can melt the aluminum and drop in a bunch of zinc. The resulting metal looks kinda like dull aluminum but is extremely strong! Cant hold an edge and isnt good for high heat, but anthing that needs to be strong can be heavy and requires a bunch of material can be made from the alloy. Aluminum cans and such are common but alum is hard to find sometimes, so mixing it with cheapo zinc is an easy way to increase the size of the batch.

[Irvine.J]

Well my first cast was going great, melted the aluminium without the propane burner, all was going well then i was ready to cast. I forgot TWO critical parts...
1- To preheat the cast!!! GARRRR!!!
2- Check to see if I'd actually melted enough aluminium! GOSH DARN IT!

Anyway, it wasn't a bad attempt for a first go, I learnt alot, and was quite fun... precision made parts aren't THAT far off...LOL :D The next one will be sweet.

[Dang911]

Did you make sure to add some draft into your molds?

[Irvine.J]

I've tried to do my castings again, this time alot better, but not good enough. i'm using "yellow stone" or a dental casting material as my investment material, it seems to hold up ok, but i'll get some fireclay at some stage. Anyway, I wanted to know, do you drop your cast in water, or let it cool by itself. I've only just discovered after these castings that by dropping it in water it causes the aluminium to crack from the steam generated, and deforms the aluminium. Is this right? Ash, zippiot, should I just let it cool down in the mold?

I've found I usually need to spread it a bit with the bottom of the crucible to make sure it fills all the holes completely, i'm trying to pour it straight on, with the yellow stone hot as by placing it in the fire for about 20 minutes too. Maybe making the moulds from fireclay would solve all my problems?

[Zippiot]

If I want a strong cast as soon as I pour the alum I place it in my ktichen oven (dangerous!!!!!!) preheated to 400 degrees for 2 hours. I gradually turn down the heat and eventually turn it off, adds a decent "temper" to the metal and helps make things more uniform...

Doesnt work with copper castings though, any metal that must get red hot seems to better cool itself down them add a temper.

You can measure how much you need to melt down by pouring rice into your mold them pour the rice filling the mold into a measuring cup.

Preheat the mold too for large or thick castings, smaller things can usually be cast at room temp