What's the max crucible size I can fit in a smelter made out of a used 30 lb propane tank ?

maxime.levesque

maxime.levesque

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I want to make a smelting furnace for cast iron, I'm thinking of using a used 30 lb propane thank (12.5" diameter x 24" height) for the outer shell of the furnace.

How thick of an insulation liner does it require ?

I'm thinking this 7" diameter crucible is probably the max you could fit in such a furnace:

https://www.amazon.ca/OTOOLWORLD-Graphite-Crucible-Refining-Aluminum/dp/B07GT5SRDM

It has a 7" diameter, so If I which leaves me 2.5" of space for clearance and insulation liner (12" - 7" / 2), so If I want 0.5" of clearance (between the insulation and the crucible), this leaves me 2" of room for insulation. Is that enough ?

Is that too ambitious of a crucible size ?

Perhaps this one 5.7" diameter crucible is more realistic:

https://www.amazon.ca/Foundry-Graphite-Crucible-Refining-Aluminum/dp/B09LXVY4Z4

?
 
Definitely the smaller. You're probably going to need 2+" thick walls depending on what refractory material you use, and don't forget that you need to be able to get tongs or lifting hooks or something in there as well leave some space for heat / flame.

GsT
 
^^^ This. You need more room. I use an A6 in a similar furnace. My insulation is about 2" of Kastolite.
Just a point about wording. Smelting is the process of making metal from ore. You will be melting.
Let us know your progress and have fun!
 
If you can, may I suggest getting a hold of a used helium tank that was used for blowing up balloons. Much safer when you use a torch on it. Just get rid of the pressure. They are usually painted a red.
 
I've got two casting furnaces. An old soft fire brick lined with an outer shell of hard fire brick held together with a steel frame. Home made propane burner. I can melt copper & aluminum but have never tried Iron. I also have a Vevor cheap combi melt furnace & forge. Two burners so lots of heat but it only holds a relatively small crucible. It is lined with a bit over 1" of Kaowool and I coated it with Satinite after I received it to prevent. breathing the fibers. I don't like working into the horizontal opening forge. The blast coming out is extremely hot. A traditional pan (?) type would be much better. As a melt furnace the Vevor works but the SS shell is pretty thin. Get or make a good lifting tong, & a pouring tong. There are designs online that have latches for better security/safety. For sure you don't want to drop molten metal. I bought boot covers, chaps & gloves made out of fire retardant materials & a full face shield. There is a considerable learning curve to casting. Either work on dry dirt or on a brick surface. If you are casting on a concrete surface, put some clay bricks or a metal riser down. If the surface of the concrete gets hot metal on it it will steam explode. Chips of concrete will fly. Be careful!
Look @ Windyhill foundry. He went from hobby to full time mostly casting iron. Lots of good videos.
 
What are you trying to cast? A quart (liter) of molten metal is a very dangerous thing. Start with the smaller crucible, just to get your feet wet with casting and to learn the techniques required for safe pouring.

Cutting an old propane tank can be dicey. Maybe get yourself an old, discarded water heater for the shell and go from there. A lot of plumbing shops will just give them to you.
 
To be safest when cutting a propane tank, remove the valve assembly and fill with water, then drain it. Other containers to consider are old water heaters and 16 gallon drums. As noted above you can also use insulating firebrick held together with wire or hose clamps and then you could get away without a container.

Here is my propane furnace for an A6 crucible.

1724165756924.jpeg

Before someone comments on the exposed wood, this setup is no longer in use!

To get back to the OPs original post. Cast iron is hard to do well and is very hard or impossible to do with propane fuel. Most home casters use oil to get to iron temps. I can get to bronze with propane if I dial it in just right. If you really want to do CI, go for a duel fuel propane/oil burner. Doing iron will shorten the life of your furnace.
 
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I used a castable refractory for my iron furnace. It showed very little wear after many firings. I built mine in a 15.5gal keg that had been decommissioned.

GsT
 
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