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An Iron Furnace at Work

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An Iron Furnace at Work An Iron Furnace at Work Bridge House The founder was boss, the charcoal house area technician, and trouble- to the bridge house Tunnel Connecting Shed Head Cooling Shed shooter. He directed and dumped them at the ceaseless round of the tunnel head. Gut- act iv ity at Hopewell termen and moulders Furnace. Raw materials stood ready below to —iron ore, limestone, skim off the slag and and charcoal—were cast the molt en iron supplied by miners, when it was tapped Cast House woodcutters, and col- by the founder. Charcoal House liers and transported by teamsters. Fillers carted materials from An ancient alchemy sustained Hopewell Furnace: transforming mineral into metal. Since 4,000 years ago, when humans learned how to free iron from ore, the basic process has not changed. Iron ox ide is heated in an intense fl ame fed by a carbon fuel. Oxygen in the ore combines with carbon mon oxide re leased from the fuel and is expelled as CO2. What is left is iron. The blast furnace’s height lets the rising gases preheat the ore and gives the iron more distance to descend as it softens—so it absorbs more carbon from the fuel. Because iron’s melting point falls as its carbon content rises, the iron becomes fully molten. A calcium-based “fl ux,” usually limestone, is added. The fl ux combines with the impurities in the ILLUSTRATIONS NPS / L. KENNETH TOWNSEND ore and forms slag. Founder Receiving Box Blowing They tended the furnace, the glowing heart of their community; it yielded iron and a way of life. Tubs Raw Materials of Iron Making The basic ingredients atite, the mag netite American forests were tense heat. The great Iron Ore of iron making—iron used at Hopewell, or Limestone so vast—and bringing Charcoal demand for charcoal ore, limestone, and other iron ores. Most in coal so expensive meant that early fur- Air Duct carbon fuel—are some iron ore was dug in before railroads were naces were sited on of the most common small surface mines. built—that early iron woodlands. One other materials on Earth, but Any substance that plantations like Hop e- ingredient was need - are not found every- contained calcium, like 1 well made their own ed: air. It was dir ected where. Early furnaces sea shells, could be fuel. They slowly into the hearth un der were built where these used as a fl ux, but for burned carefully built pressure by the water- materials were avail- most furnaces, lime- piles of wood to make powered blast ma- 2 able. Iron is usually stone was cheap and char coal, an almost chinery, raising the found in combination abundant. purely carbon fuel fi re in the furnace to Air Blast in the form of hem- that burns with in- smelting temperature. Machinery The Work Force Furnace Operations Historians have styled rural iron making opera- the exacting job of casting the iron. Colliers 1 Chimney: Smelting by- Iron plantation life revolved around the always- of ingredients correct. In temperatures that tions like Hopewell’s, called “iron plantations,” (charcoal makers), miners, and woodcutters prod ucts—CO and CO2 running, roaring furnace. It shut down usually could reach 3,000°F, the molten iron fl owed as feudal. This was a self-suffi cient community provided the raw materials for the furnace. gases and smoke—are once a year—to refurbish its inner walls and down toward the hearth, to be tapped when expelled. of craftsmen and laborers living lives directly or Other workers included team sters, who drove hearth. While it was “in blast,” its cy cles of fi lling the founder judged it ready. At Hopewell he indirectly governed by the furnace. It could be a the wagons carrying raw materials and fi nished 2 Tunnel Head: Limestone, and tapping set life’s rhythm at Hopewell. It de- generally tapped the furnace every 12 hours, diffi cult task master—dirty, noisy, dangerous at products; cleaners, often women and children, iron ore, and charcoal manded close attention. Workers constantly fed at 6 am and 6 pm. After the guttermen drew are dumped into the times, ever needing to be fed and tapped. But a who fi nished the cast products; and teachers. it, watched its fl ame, and listened to the sound off the slag, the iron could be tapped in two furnace. demanding furnace also meant community pros- Women supplemented family incomes by sew- of its blast. For workers around the furnace, it ways: It could fl ow directly into the “pig bed” perity. A silent furnace meant lean times. ing, lodging and boarding single workers, and 3 3 Air Duct: Air under pres- was a hot, hard job requiring protective shoes in the cast house fl oor (it looked like a litter of laundering. Some made extra income working sure is brought from air and aprons. Every half-hour fi llers dumped into nursing pigs), where it hardened into pig iron blast machinery. A traditional hierarchy governed the furnace’s as woodcutters and miners. Farmers fed the the tunnel head 400 to 500 pounds of iron ore, ready for market. Or it could be tapped into operations. At the pinnacle was the ironmaster, community, and some worked the furnace for 4 Tuyere: Narrowing pipe 30 to 40 pounds of limestone, and 15 bushels of large la d les, then cast in molds (see Moulder, director of the enterprise and often an owner. part of the year. African Americans also worked directs air blast into the charcoal. With no gauge, the founder used his bot tom center). This crucible, where tempera- furnaces—enslaved at fi rst, later as temporarily Good ironmasters had to be fi nancier, techni- ture is boosted to practiced eye to judge the shape and color of process was repeated cian, bill collector, market analyst, personnel employed runaway slaves and free blacks. 2,600°–3,000°F. the fl ame from the chimney and the color and twice daily as long as director, purchasing agent, and host to prospec- consistency of the molten iron. This told whether the furnace was in 5 Bosh: Iron is becoming tive buyers. His was a volatile job: bad luck or the temperature was right and the proportions blast. molten; with slag, it de- poor judgment usually meant failure. Success Collier Molten Iron scends towards crucible. often brought wealth. A clerk helper kept the and Slag Descend Founder books, or dered supplies, served as paymaster, 6 Crucible: Narrowest and 5 hottest part of furnace, and managed the of fi ce store. The job well per- where iron becomes formed could be a stepping stone to ironmaster. fully molten. 7 Hearth Stone: Molten The quality of the iron was in the founder’s 4 iron and slag settle on 6 Gutterman hands. His job: keep the furnace blowing at this stone. peak effi ciency. He supervised the other furnace 8 8 Dam Stone: Holds mol- workers: keepers helped him mon itor the fur- 7 ten iron and slag in nace and took the night shift; fi llers charged the Slag Iron hearth until the slag is furnace with raw materials; and guttermen di- drawn off and the iron rected molten iron as it fl owed from the fur- is tapped. nace. Moulders, the highest-paid workers, had The Moulder’s Art Finished Products In the “fl ask casting” board,” placing the He then removed the the sand he in serted The fi nal step was to To make the most nails, and horseshoes Hope well. The molten At a fi nery forge, the was oxidized, raising meth od of casting, wooden pattern in- fi rst follow board, a wooden wedge to pour the molten iron money from molten had to be ob tained iron was cast into pig iron was remelted and the melting point. The both sides of a stove side. He then sifted blew away loose sand form a “gate” 4, al- 6 through the gate. iron you would cast through an indi rect iron bars shipped else- much of its carbon iron partially solidifi ed plate were molded. fi ne sand over the from the edges of the lowing the molten After the iron had Moulder fi nished prod ucts at pro cess not in place at where for refi ning. into a pasty lump. The This let the moulder pattern and packed pat tern with a bel- iron to enter. Next he cooled, he separated the furnace. Moulders lump was then beaten pro duce a relatively the rest of the drag lows 3, and “dressed” removed the wedge, the halves of the fl ask cast several items: to drive out the slag light, curved plate. with coarse, damp the edge with a separated drag and and removed the gate plowshares, pots, sash and align the fi bers, The fl ask was two sand 1. After scraping moulder’s spoon. He cope, and carefully from the plate. Oth er and scale weights, produ c ing wrought wooden frames. The away excess sand with at tached the “cope,” removed the pattern workers brushed off cannon, and shot. But iron. More processing moulder laid the bot- the “strike” 2, he the fl ask’s top half, to with a pair of lifters 5. sand and fi led rough as iron stoves grew converted this iron tom half, the “drag,” placed another follow the drag and again He next secured the edg es, readying the more common in into the bars and rods on a piece of wood board on top and added fi ne and coarse two halves of the plate for market.
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