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Foundry Furnace for the Tiny Shop

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vtsteam:
It always seemed confusing to me that wrought iron and cast iron were completely different animals. Wrought iron having less carbon than steel makes sense, "iron" being the element name. But cast "iron" having  more carbon than high carbon steel doesn't. Why call it iron then? Or why steel at all? Just call it all iron, and modify the name by how much carbon it has. Aluminium alloys are always aluminium. I dunno.... there was a time, before I was casting when I thought cast iron was really just pure iron.

Uhhhhhh no.  :wack:

hermetic:
Hi VTsteam, When you put iron ore in a blast furnace with coke and limestone, what you get running out of the bottom, is pure iron, but because it has been smelted with coke, it has picked up a high content of carbon. When the run off is allowed to cool it is known as cast iron. Cast iron is very strong under compression, but also very brittle. The process for producing wrought iron from cast was to remelt the cast iron in a reverbatory furnace (where the iron is heated by indirect heat, so it cannot absorb any more carbon) the furnace, known as a puddlers hearth is also charged with iron oxide, and when the iron melts the carbon reacts with the oxygen in the oxide, and boils out of the iron as carbon dioxide. This reduces the carbon content, and after a process of removing from the furnace and power hammering (and repeating) it becomes almost pure iron with fibres of slag running through it, which can be seen on a piece of fractured wrought iron. Take pure iron, minus the slag, and add to it a small amount of carbon, and you have mild steel, useful, but not hardenable other than case hardening. Add slightly more carbon, and you have a tool steel that can be worked and shaped hot in its soft state, and then hardened through and tempered so it is tough, and will also hold a sharp edge. All these metals are Iron/carbon alloys, and this is a gross simplification of metallurgy as learned in the school metalwork shop and from the excellent Hardening, tempering and heat treating by Tubal Cain, No1 in the workshop practice series. hope this helps,
Phil

vtsteam:
Yup.  I've cast iron. Terry Aspin's books in that same series are some of my favorites.

I'll be tempering the furnace lining today (different kind of tempering) and I hope even casting something, if I can get my old greensand into condition, and the pattern finished.....  :beer:

vtsteam:
Today I made first heat in the Tiny furnace -- working up gradually to drive the moisture out of the lining. I started out with some wood kindling:

vtsteam:
I set a piece of stovepipe on top of the furnace lid for a gentle draw -- a blower would have been too much.

When the wood had burned down, I added a layer of charcoal briquettes, about 2 deep. After half an hour again, I filled the furnace up half way with charcoal, and then let it cook for most of the day.

I also conditioned my greensand, which was dry as the Sahara. All in all a rewarding Spring Saturday, with daffodils in full bloom, and my casting gear coming back into some semblance of working order.  :ddb:

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