Greenwood Furnace State Park

The ironmaking process was well-known and cold-blast furnaces built in 18th and 19th century America mimicked designs first used 400 years earlier. A thick stone furnace, shaped like a flat-topped pyramid, served as the place of transformation, where minerals became metal.
Fillers dumped alternating layers of charcoal fuel, iron ore and limestone flux into the top of the furnace. As the charcoal burned, air forced into the furnace raised the temperature to 2,600 to 3,000 F creating several byproducts. Carbon gases escaped up the furnace stack, molten iron sank to the bottom, and impurities called slag floated on the liquefied metal. Workers drew off the useless slag and channeled the iron into connected castings called pigs.
Fanning the FireChange did affect some aspects of the ancient ironmaking process. The machinery used to fan the furnace fires evolved from huge leather bellows to more efficient blowing tubs to steam-driven blowing engines.
(Inscriptions under the images in the center-left to right) *Water-powered bellows *Blowing tubs pumped air into the furnace on both the up and down stroke *After 1850, steam engines sometimes powered blast machinery.
Cutaway of a Cold-Blast Furnace:
1. Chimney: Smoke, carbon monoxide and carbon dioxide escape here.
2. Tunnel Head: Limestone, iron ore, and charcoal are dumped into the furnace here.
3. Firebrick: Furnace lining.
4. Insulation: Sand and clay insulate and cushion lining.
5. Air Duct: Machinery forces air through this duct into the furnace.
6. Tuyere (twee-air): This narrow pipe directs air into the furnace and boosts heat.
7. Crucible: Narrowest and hottest part of the furnace where iron melts.
8. Bosh: Melting iron still mixed with impurities (slag).
9. Hearth Stone: Iron and slag settle here.
10. Dam Stone: Holds back iron and slag until tapped.

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