Coal fire foundry advice wanted

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carmytage

carmytage

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Dec 31, 2022
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Hi all,

For starters I've got a 19kg propane tank as a base for a foundry and I'm wanting to fire it using coal as I have an abundance of it through friends who sell it and volunteering at a steam museum.

However I'm struggling to come up with a suitable design that seems like it would work and still be safe. I've seen several videos of people slicing propane tanks vertically in half to make a blacksmiths forge. But I'm concerned if I just lop the top off a bottle, fill it full of coal and crank it up it'll melt the steel bottle if there's no insulation?

All advice welcome, thanks.
 
A forge is used to heat metal to a red state, and then use blacksmithing techinques to shape the metal with a hammer and anvil.

A foundry generally (but not always) uses a crucible contained inside of a furnace, with the furnace being heated by charcoal, coal, propane, natural gas, diesel, kerosene, etc.

A cupola/cupolet melts iron directly using coke, which is coal that has been heated in the absense of oxygen.
The molten iron is tapped and drained into a ladle, and then poured into a mold.

So with any of the above, your steel shell is protected using high temperature refractory, either poured, or in the form of fire-rated bricks, etc.

I have a nephew who melts aluminum in a heavy-walled steel crucible, using charcoal in a metal bucket of some type.
This will work in a pinch, especially for beginner applications.

.
 
I see thank you! so I'm aiming for a coal fired furnace as far as refractory material would you say something like the following is suitable? Castable - C1600 - Kilnlinings

Ideally I'd like to be able to work in iron eventually so I'm trying to plan for something that will be suitable and last longer term.
 
I would say anything in the 2,900 F and above range would work ok for aluminum, brass/bronze, and gray iron.

I used Mizzou, which is 3,000 F rated, and it holds up well to iron temperatures.

Be aware that refractory has a shelf life, so don't purchase more than you need, and keep any unused refractory in a sealed container such as a 5 gallon bucket with gasketed cover.

And refractory mixes with a tiny amount of water, and when you add the water, you would swear that you will never get it mixed in.
If you add excess water, you will not have the hot strength you need.
Follow the instructions religiously on the amount of water added to the mix, and of course wear a good respirator.

I use a mortar mixing tub and a garden hoe to mix refractory.
It takes a while for the water to mix in, but eventually it will become a slighly wet mix that can be rammed into a form.
Pack it in layers of about 4" each in the form, using a 1/2" wood dowel, to get out the air bubbles.

You may want to forgo the coal and just build a diesel burner.
That would save you a LOT of trouble.

You will not melt iron with coal.

I am not aware of any serious foundry person using coal to melt metal.

.
 
Amazing thank you! in that case I'll look at diesel burning instead, whatever works! glad you told me now than after I've faffed around with something that won't work.
 
Some use waste oil for their oil burner, but I am not a fan of waste oil.
It can be contaminated with things like antifreeze, solids that clog the burner, heavy metals, etc.
Handling waste oil is dirty and messy.

Diesel gives a clean consistent burn every time.

.
 
Hi there

The refractory you linked to seems similar to the stuff I used except that mine was 1800 C (steel grade) so it would be great for your furnace lining.

My furnaces were made of old storage heater bricks lined with refractory about 1.5 inches thick.

The smaller one (for aluminium) was fired with a sievert propane torch with a fairly large nozzle.

The big one was fired by coke, DO NOT USE ordinary coal It will make an almighty mess and loads of smoke, It will not reach a high enough temperature,
and worst of all it will eat your crucibles in no time flat !

Best Regards Mark
 
carmytage said:
I see thank you! so I'm aiming for a coal fired furnace as far as refractory material would you say something like the following is suitable? Castable - C1600 - Kilnlinings

Ideally I'd like to be able to work in iron eventually so I'm trying to plan for something that will be suitable and last longer term.
Click to expand...
If you use a used propane tank, make sure you have the propane completly out, if not, you may blow your head off. I have one that I filled with water which was very difficult, then drained it.
 
skyline1 said:
Hi there

The refractory you linked to seems similar to the stuff I used except that mine was 1800 C (steel grade) so it would be great for your furnace lining.

My furnaces were made of old storage heater bricks lined with refractory about 1.5 inches thick.

The smaller one (for aluminium) was fired with a sievert propane torch with a fairly large nozzle.

The big one was fired by coke, DO NOT USE ordinary coal It will make an almighty mess and loads of smoke, It will not reach a high enough temperature,
and worst of all it will eat your crucibles in no time flat !

Best Regards Mark
Click to expand...
brilliant thanks! yes I've gone off the idea of coal/coke and moving towards diesel/ waste oil burner. Just going to plan out the structure of it better and then try get the refractory material ordered.
 
Richard Hed said:
If you use a used propane tank, make sure you have the propane completly out, if not, you may blow your head off. I have one that I filled with water which was very difficult, then drained it.
Click to expand...
Yes thank you for the word of warning, I managed to get the valve off yesterday after alot of difficulty and it's currently sat in the garden full of water. I want to get a solid idea of the layout before i start chopping it up and regretting it lol
 
Generally you want to find the maximum size crucible that you want to use, and then design the furnace around that.

I am showing a 40 lb (19 kg) standard propane bottle with dimensions of 29.5" tall and 12.25" diameter.
Typically you would build a form inside of that, or use a waterproofed cardboard sonotube, so as to give between 1" and 1.5" of refractory inside the furnace.

Morgan Salamander-Super crucibles (are iron-rated but can be used for other metals) dimensions are as follows:

Morgan Salamander Super A-shape

Size (Top OD) (Bottom OD) (Height) (Brass Capacity) (CI Capacity) (AL Capacity)
inches inches inches pounds pounds pounds
A0.5 2.625 1.875 3.125 2.2 1.98 0.7
A3 4.125 2.75 5.0 8.2 7.38 2.7
A5 4.875 3.375 6.0 15 13.5 4.9
A6 5.11 3.74 6.49 20 18 6.4
A10 6.29 4.33 7.87 40 36 11 (weight = 5.8 lbs)
A16 7.24 5.11 9.13 51 46 16
A20 7.75 5.70 10.23 66 60 21 (weight = 12.0 lbs)
B20 7.75 5.70 10.5 74 67 24 (weight = 16.6 lbs)
A25 8.26 6.10 11.02 79 71 26
A30 9.13 6.29 11.41 95 86 31
A40 9.12 6.25 12.5 120 108 40 (weight = 20 lbs)

.
 
Last edited:
Here are a few rough sketches, assuming your steel shell diameter is 12.25".

This uses a 1.5" thick refractory hot face, and a 2.5" diameter oil burner tube.

2.5" muffer pipe makes a good oil burner tube.

The crucible should be elevated up on a plinth, which is cast in the same material as your hot face.
Many plastic containers are the approximate size/shape for a plinth, and can be used for a plinth form.


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The lid is typically domed, since all refractory eventually cracks, and a domed lid will be self-supporting even with cracks in it.

Cracks in fractory can easily be patched/filled.
If you have quality refractory rated in the 2,900/3,000 F range, it will crack a bit, but not crumble.

Refractory rated at 2,500 F or less will soon crumble at iron temperatures.

Usually there is a short chimney on top of the lid.

These sketches should give you a rough idea of what your furnace may look like.


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My typical oil burner end cap.

Secured with a wrap of stainless thin sheet.

My burner tube designs have evolved, and this is the latest one I think.

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Here is a slight variation from the one above, and this one has a brake line inside of a standard plumbing pipe.

You can run two pipes inside the burner tube also, which is the more typical way it is done.

Diesel goes in the red valve, and about 15 psi of compressed air goes in the yellow valve.
The compressed air is for atomization.

This burner used muffler pipe, which is somewhat thin, so the welding is a bit sloppy.



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I tried some vanes on the end of the burner tube, but they did not accomplish anything, and so all my burner tubes are just flat on the end now.

This shows you where the spray nozzle should be in relation to the end of the burner tube.

The burner tube should never protrude into the furnace, but stop just short of the interior furnace wall.


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