I have known several folks who have transitioned from brass/bronze to gray iron successfully.
The burner output for iron and brass/bronze is basically the same.
For gray iron, one needs a clay-graphite Morgan "Salamander-Super" crucible, which is ferrous-metal rated, and 2,900 F rated.
The burner needs to be run on the reducing (rich) side, since if you run the burner oxidizing (lean), it will create a lot of slag on top the iron.
And a few sheet metal heat shields in strategic places is very helpful in keeping the gloves from overheating.
Shaded gas welding glasses for the infrared emitted.
And a very slight amount of 75% ferrosilicon added right after the final skim, and just before pouring.
The burner setting must be optimal.
For my furnace interior (13" diameter, 14" tall), 2.7 gal/hr of diesel is what is required, using a variable-speed Toro leaf blower set on its lowest speed.
It generally takes about 1 hour to reach pour temperature with iron.
Use good iron scrap, not window sashes, etc.
I use electrical motor end bells.
Cast iron auto blocks can also be used, or gray iron from any old machine.
Our member "creast" recently successfully poured iron.
Once I figured out the above items, I found that melting and pouring iron for me was actually easier than trying to melt/pour brass or bronze.
With the right setup, and a furnace lining rated for about 3,000 F, iron is not really any more difficult to melt and pour than aluminum, although it is a lot hotter, and requires good leather protection all over, hard hat with face shield and neck shield, and a few sheet metal heat shields, such as on the skimmer handle and on the pouring shank.
The backyard casting section for this forum is located here:
Tons of good casting info here, including how to cast iron.
https://www.homemodelenginemachinist.com/forums/home-foundry-casting-projects.36/
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