making ahome made crucible.?

[Alistair Hosie]

Has anyone ever made a crucible for a melting furnace. I bought a nice flamefast melting furnace, the small tilting model. It came without lid and crucible. The original lid is made I think from cast iron I could make this from moulding or maybe from a big weight from a barbell set. Also would plate steel say 10 to 12 mm do if I cut it carefully or would it be dangerous also I know the principles of moulding ok and could make a graphite one I fell confident on that. So what , or where, does one get the materials for mixing, or better still a bag of not too expensive ready mix graphite or similar. Buying one in the size I need would I reckon be very expensive, They are not cheap and I would in any case l8ike to make my own I have a lifetime experience in making moulds. I have seen someone on youtube talking about making them from old fire extinguishers or metal tubing how would that hold out surely the heat might make them fall apart? help from the experienced guys here would be great. Kindest regards as always Alistair

[lbender]

Knock yourself out, Alistair

http://www.alloyavenue.com/vb/showth...cible+homemade

[Alistair Hosie]

God bless my old pal ibender your a toff and no mistake matey.LOL Alistair

[macona]

DO NOT MAKE ONE FROM A FIRE EXTINGUISHER. That guy is an idiot. Aluminum will dissolve steel when melted and they guy is lucky he has not severely burned himself.

Real crucibles are not that expensive, they are a consumable. If I remember Silicon Carbide crucibles are cheaper than graphite.

[hojpoj]

DO NOT MAKE ONE FROM A FIRE EXTINGUISHER. That guy is an idiot. Aluminum will dissolve steel when melted and they guy is lucky he has not severely burned himself.

Real crucibles are not that expensive, they are a consumable. If I remember Silicon Carbide crucibles are cheaper than graphite.

SiC crucibles tend to be more expensive than clay graphite, but are a bit more abuse tolerant. A steel crucible is usable, but needs to be fairly heavy walled to avoid Aluminum working through it. It's a tradeoff on the risks you wish to take. If just aluminum melting, you'd be fine with a clay graphite crucible, just read up on the storage and prep requirements.

Oh, and that steel that slowly dissolves in melted aluminum obviously changes the alloy composition, and usually for the worse. Yet another reason to use the right tool for the job.

[J Tiers]

DO NOT MAKE ONE FROM A FIRE EXTINGUISHER. That guy is an idiot. Aluminum will dissolve steel when melted and they guy is lucky he has not severely burned himself.

Real crucibles are not that expensive, they are a consumable. If I remember Silicon Carbide crucibles are cheaper than graphite.

They seem to be used in industry, regardless, for non critical melting. It's not as if they burn right through like water in a sugar cup.

I did see a report once on an accident where the aluminum apparently wore through after some significant usage, and hit a good-sized pocket of rust inside the mild steel crucible bottom.

It was alleged in the report that the combination made a thermite reaction and melted through the thin remaining steel below the pocket suddenly.

[CCWKen]

Anything you make out of fireclay or contains carbide will have a lower limit on what you can melt in it. Typically, ~1800-2000*F max. These are also cheep and you'll spend more buying the raw materials and shipping than what you can buy the crucibles for outright. There's also a safety factor involved. If you don't mix it right or don't cure them, they will explode violently. And don't make material substitutions! They are in there for a reason. I use only graphite crucibles and they aren't that much more expensive. Stay away from steel or iron makeshift crucibles unless all you're melting is lead and/or zinc.

[Mr Fixit]

CCWkKen,

Why not use the steel crucibles for aluminum? It definitely is below the melting point of the steel. I have just started building a propane furnace to do some aluminum 1200*F casting and thought that a schedule 40 pipe welded bottom crucible 2500*F would work fine. Can you help the less knowledgeable and explain the reason for your comments.

TX
Mr fixit for the family
Chris

[J Tiers]

It is done all day in industry, for less than critical uses. The others are being super-fussy.

Steel WILL wear out faster, so make it thick.

[CCWKen]

Yea, aluminum is ok. I just didn't list it. Most of the soft metals except copper. You'll end up with copper ferrite. I used to do a lot of plating so yes, I was fussy about the alloys and contaminants. Less now.

[lynnl]

It's been several years since I've melted aluminum in my (Gingery style) charcoal furnace, but what I used was steel juice cans, specifically the 46 oz size grapefruit and pineapple cans.

After about two or three melts they'd start showing signs of deterioration, from the effects of the hot charcoal surrounding them in the furnace; so I'd just switch to a new can for the next melt.

After awhile I made a heavier duty one from thick steel pipe and welded on bottom. It seemed to deteriorate faster than the thinner cans. I later bought a clay graphite crucible but it is so big there's little room to embed it in the charcoal. Since acquiring it I've not melted any more. Maybe some day I'll resume casting.

(added) If the steel caused any detrimental alloying effects, it certainly was not visible. I cut through, and machined several ingots I cast, and they were all pretty, shiny, solid aluminum, with no voids or bubbles or other blemishes.

[Alistair Hosie]

Charcoal at least has the ability to be moved around. Pease remember I am wanting to use this in conjunction with a Flamefast c m 450 crucible gas powered tilting unit, see here http://www.flamefast.co.uk/cm450-saf...e-furnace.html
all complete in a single unit. Now the crucibles used for or in these seem to be large or larger than normal making one I could do, I feel confident anyway, LOL the idea so far I had in mind was to try the following recipe perhaps mix some clay-add to this-some vermiculite--some--fire cement and concrete powder. Light the blue touch paper and stand clea- eer --orrun away. LOL it will be trial and error aka plenty of trial with lots of built in stupid errors. Apart from vermiculite there's also perlite. anyone like to add a few opinions please feel free. alistair

[hojpoj]

Charcoal at least has the ability to be moved around. Pease remember I am wanting to use this in conjunction with a Flamefast c m 450 crucible gas powered tilting unit, see here http://www.flamefast.co.uk/cm450-saf...e-furnace.html
all complete in a single unit. Now the crucibles used for or in these seem to be large or larger than normal making one I could do, I feel confident anyway, LOL the idea so far I had in mind was to try the following recipe perhaps mix some clay-add to this-some vermiculite--some--fire cement and concrete powder. Light the blue touch paper and stand clea- eer --orrun away. LOL it will be trial and error aka plenty of trial with lots of built in stupid errors. Apart from vermiculite there's also perlite. anyone like to add a few opinions please feel free. alistair

Get some really long tongs, or really thick pants, and maybe some stilts to keep your feet out of the molten metal (because that will be GUARANTEED to fail).

Structurally the additives you named will weaken the structure, and also make it more insulative (which is the opposite of what you want in a crucible). I'm only guessing at how that tilt furnace works, but I'm assuming that the combustion chamber is still below the crucible.

Also, Perlite, Vermiculite, and anything other than proper refractory materials all seem to be fluxes of one type or another, so over time being exposed to the high temperatures will cause the surface to glassify and weaken the crucible.

Only guys I've seen successfully make their own crucibles all used refractory cements (not fire cement or Portland cement). Even then the crucible had to be properly fired like a type of pottery, and didn't last nearly as long as a proper commercially-acquired one.